阅读说明：本技术 可uv固化的喷墨油墨 (UV curable inkjet inks ) 是由 S.德穆特 于 2017-03-20 设计创作，主要内容包括：液体可UV固化的喷墨油墨,其含有一种或更多种光引发剂、有机彩色颜料和含有至少一种单官能可聚合化合物和至少一种多官能可聚合化合物的可聚合组合物,其中基于液体可UV固化的喷墨油墨的总重量计,有机彩色颜料的存在量为6.0～13.0wt％；基于可聚合组合物的总重量计,至少一种多官能可聚合化合物的存在量为至少20.0wt％；且所述可UV固化的喷墨油墨在45℃和10s～(-1)的剪切速率下的粘度为至少16.0mPa.s。(Liquid UV-curable inkjet ink containing one or more photoinitiators, organic colour pigments and a polymerizable composition containing at least one monofunctional polymerizable compound and at least one multifunctional polymerizable compound, wherein the liquid UV-curable inkjet ink is based on liquid UV-curableThe organic color pigment is present in an amount of 6.0 to 13.0 wt% based on the total weight of the inkjet ink; the at least one multifunctional polymerizable compound is present in an amount of at least 20.0 wt%, based on the total weight of the polymerizable composition; and the UV curable inkjet ink is at 45 ℃ and 10s ‑1 Has a viscosity of at least 16.0mpa.s at shear rate.)

1. A liquid UV curable inkjet ink comprising one or more free radical photoinitiators, an organic colour pigment and a polymerizable composition comprising at least one monofunctional polymerizable compound and at least one multifunctional polymerizable compound, characterised in that the organic colour pigment is present in an amount of 6.0 to 13.0 wt% based on the total weight of the liquid UV curable inkjet ink; the at least one multifunctional polymerizable compound is a difunctional acrylate containing two acrylate groups present in an amount of at least 20.0 wt%, based on the total weight of the polymerizable composition; and the UV curable inkjet ink is at 45 ℃ and 10s^-1Has a viscosity of at least 16.0mPa.s at shear rate, and

wherein liquid UV curable inkjet ink means that the UV curable inkjet ink is liquid at 25 ℃.

2. The liquid UV-curable inkjet ink according to claim 1, wherein the at least one multifunctional polymerizable compound is present in an amount of 25.0 to 50.0 wt%, based on the total weight of the polymerizable composition.

3. The liquid UV-curable inkjet ink according to claim 1, wherein at least one of the one or more free-radical photoinitiators is selected from the group consisting of polymeric photoinitiators, polymerizable photoinitiators, and photoinitiators comprising a plurality of photoinitiating groups.

4. The liquid UV-curable inkjet ink according to claim 1, wherein the polymerizable composition is present in an amount of less than 70.0 wt% based on the total weight of the liquid UV-curable inkjet ink.

5. The liquid UV-curable inkjet ink according to claim 1, wherein the liquid UV-curable inkjet ink contains 0 to 10 wt% of an organic solvent based on the total weight of the UV-curable inkjet ink.

6. The liquid UV-curable inkjet ink according to claim 1, wherein said inkjet ink is at 45 ℃ and 10s^-1The viscosity at a shear rate of (A) is 20.0 to 65.0 mPa.s.

7. The liquid UV-curable inkjet ink according to claim 1, wherein the one or more free-radical photoinitiators comprise an acylphosphine oxide photoinitiator and a thioxanthone photoinitiator.

8. A UV curable inkjet ink set for printing different colors comprising at least one liquid UV curable inkjet ink according to claim 1.

9. The UV-curable inkjet ink set according to claim 8, containing at least three liquid UV-curable color inkjet inks each containing one or more different organic color pigments, the pigments being present in an amount of more than 5.0 wt% based on the total weight of the liquid UV-curable color inkjet inks.

10. The UV curable inkjet ink set according to claim 8, further comprising a liquid UV curable white inkjet ink containing titanium dioxide pigment having an average particle size of greater than 180 nm.

11. The UV curable inkjet ink set according to claim 8, further containing a liquid UV curable black ink including a carbon black pigment having an average particle size of less than 200nm and a beta-copper phthalocyanine pigment.

12. A UV curable inkjet printing method comprising the steps of:

a) jetting one or more liquid UV curable inkjet inks according to any one of claims 1-7 onto a substrate with a print head at a jetting temperature of 45 ℃ or higher; and

b) UV curing the jetted liquid UV curable inkjet ink on the substrate.

13. The UV curable inkjet printing method according to claim 12, wherein the substrate is pre-treated by corona, plasma or flame treatment.

14. The UV curable inkjet printing method according to claim 12, wherein the print head is a through-flow piezoelectric drop-on-demand print head.

15. The UV curable inkjet printing method according to claim 12, wherein the one or more liquid UV curable inkjet inks are jetted at a temperature between 45 ℃ and 65 ℃.

Technical Field

The present invention relates to UV curable inkjet inks for use in a multi-colour inkjet printing process.

Background

Industrial inkjet printing systems are increasingly replacing similar printing systems (like offset and flexographic printing) due to their flexibility in use and variable data printing capabilities. UV curable inkjet inks are particularly preferred because high quality color images can be printed on non-absorbing ink receptors (e.g., plastic or metal). For many applications, color images printed on such non-absorbing ink-receivers should exhibit a high degree of scratch resistance. Typically this is achieved by applying a thick, highly cross-linked ink layer. Generally, this works well for metal ink receptors; however, in addition to scratch resistance, sufficient flexibility is often required for plastic substrates.

One approach is to find an optimal balance between monofunctional polymerizable compounds and multifunctional polymerizable compounds, as exemplified by EP 2399965 a (agfa)). Monofunctional monomers generally improve flexibility, while multifunctional monomers increase scratch resistance. However, as shown by fig. 1, there is a direct relationship between the scratch resistance and flexibility of the ink layer, wherein an increase in scratch resistance S results in a decrease in flexibility F, and vice versa. For some applications, the achievable compromise between scratch resistance and flexibility (compromise) is still insufficient.

The second approach is to replace a portion of the monomers in the inkjet ink with one or more specific reactive prepolymers or polymers. For example, US 2004024078(SEIREN) discloses a UV-curable inkjet ink comprising a coloring component, a reactive oligomer and/or a reactive prepolymer, a reactive diluent and a photoinitiator, wherein a polymer of the reactive oligomer and/or the reactive prepolymer and a polymer of the reactive diluent have a glass transition point of 0 ℃ to 70 ℃. Cured films of such inks exhibit good flexibility, scratch resistance, and adhesion. The ink composition has a relatively high viscosity of 60 to 800mPa.s at 25 ℃, and thus requires a high jetting temperature of 60 ℃ or more.

The viscosity of the UV curable color inkjet ink is controlled by selecting suitable low viscosity monomers and oligomers. Since viscosity tends to increase slightly with pigment concentration, commercially available UV-curable color inkjet inks typically contain 1 to 5 wt% of organic color pigments, based on the total weight of the inkjet ink. UV-curable white inkjet inks usually contain much higher concentrations of inorganic pigments (usually at least 15 wt% titanium dioxide) in order to obtain a very opaque white layer. A slightly higher viscosity is tolerable for white inkjet inks because it slows down the settling of the white pigment, which has a greater density and is also present in the inkjet ink at a larger average particle size for good opacity.

An alternative ink jet technology employs so-called hot melt or phase change ink jet inks which are solid at room temperature and, after melting, are jetted at high jetting temperatures of 80 ℃ to 140 ℃ for obtaining a jetting viscosity of about 13 mpa.s. Such UV curable phase change inkjet inks are disclosed, for example, by EP 1456307 a (3 DSYSTEMS)). The disadvantage of jetting at very high temperatures is that the number of suitable ink receptors becomes limited to non-heat sensitive substrates and the energy consumption of the inkjet printing equipment increases dramatically for melting the inkjet ink.

There remains a need for UV curable inkjet inks that exhibit good flexibility and scratch resistance while maintaining high curing speeds and reliability necessary for economical industrial inkjet printing processes.

Disclosure of Invention

To overcome the above problems, a preferred embodiment of the present invention has been realized with a liquid UV curable inkjet ink as defined in claim 1.

Preferred embodiments of the present invention have also been achieved with a UV curable inkjet printing method as defined below.

It has surprisingly been found that a better compromise between scratch resistance and flexibility is obtained by: increasing the viscosity under jetting to 16.0mpa.s or more, increasing the organic pigment concentration in the UV-curable inkjet ink to between 6.5 wt% and 13.0 wt%, and controlling the amount of the polyfunctional polymerizable compound to a certain range. These measures result in thinner ink layers which also have improved feel and feel on, for example, plastics and textiles.

Printing at higher viscosities is always avoided by those skilled in the art of ink jet printing because the print reliability is reduced by increasing the number of satellites (see fig. 3a and 3 b). However, if both the jetting viscosity and the pigment concentration are controlled to values as specified by our invention, the number of satellites unexpectedly decreases even with increasing jetting viscosity (see fig. 4).

Further advantages and preferred embodiments of the invention will become apparent from the description below.

Drawings

Fig. 1 shows the relationship between scratch resistance S and flexibility F of a UV-curable inkjet ink layer. Fig. 2 is a schematic illustration of a print head 1 ejecting ink droplets 2 onto an ink receptor 3. The jetted ink droplet 2 forms a tail 4 of length L before breaking up into a main ink droplet 5 and one or more satellites. Satellites are unwanted ink droplets that are produced behind a main ink droplet, either merging with the main ink droplet (fast satellites 6) or drifting away from the main (ink) drop (slow satellites 7). Upon landing on the ink receptor 3, the primary ink droplets 5 form ink dots 8, while the slow satellites 7 form smaller secondary ink dots 9.

Fig. 3.a shows the general relationship between the tail length L of the jetted droplet and the jetting viscosity V, while fig. 3.b shows the number of satellites # S as a function of the tail length L.

Fig. 4 is a graph depicting the results of example 2 for satellite # S number as a function of viscosity and inkjet inks having different pigment concentrations.

FIG. 5 is a photograph of an apparatus for measuring flexibility.

Detailed Description

Definition of

The term "alkyl" denotes all variants possible for each number of carbon atoms in the alkyl group, i.e. methyl, ethyl; for three carbon atoms: n-propyl and isopropyl; for four carbon atoms: n-butyl, isobutyl, and tert-butyl; for five carbon atoms: n-pentyl, 1-dimethyl-propyl, 2-dimethylpropyl, and 2-methyl-butyl, and the like.

Unless otherwise specified, substituted or unsubstituted alkyl is preferably C₁-C₆-an alkyl group.

Unless otherwise specified, substituted or unsubstituted alkenyl is preferably C₁-C₆-alkenyl.

Unless otherwise specified, substituted or unsubstituted alkynyl is preferably C₁-C₆-alkynyl.

Unless otherwise specified, a substituted or unsubstituted aralkyl group preferably includes one, two, three or more C₁-C₆-phenyl or naphthyl of an alkyl group.

Unless otherwise specified, a substituted or unsubstituted alkaryl group is preferably C comprising phenyl or naphthyl₇-C₂₀-an alkyl group.

Unless otherwise specified, substituted or unsubstituted aryl is preferably phenyl or naphthyl.

Unless otherwise specified, a substituted or unsubstituted heteroaryl group is preferably a five-or six-membered ring substituted with one, two, or three oxygen atoms, nitrogen atoms, sulfur atoms, selenium atoms, or a combination thereof.

The term "substituted" in, for example, substituted alkyl refers to alkyl groups that may be substituted with atoms other than those normally present in such groups (i.e., carbon and hydrogen). For example, a substituted alkyl group may include a halogen atom or a thiol group. Unsubstituted alkyl groups contain only carbon and hydrogen atoms.

Unless otherwise specified, substituted alkyl, substituted alkenyl, substituted alkynyl, substituted aralkyl, substituted alkaryl, substituted aryl and substituted heteroarylThe aryl group is preferably substituted with one or more members selected from the group consisting of: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl and tert-butyl, esters, amides, ethers, thioethers, ketones, aldehydes, sulfoxides, sulfones, sulfonates, sulfonamides, -Cl, -Br, -I, -OH, -SH, -CN and-NO₂。

Inkjet ink

The liquid UV-curable inkjet ink according to a preferred embodiment of the present invention contains one or more photoinitiators, organic color pigments and a polymerizable composition containing at least one monofunctional polymerizable compound and at least one multifunctional polymerizable compound, wherein the organic color pigments are present in an amount of 6.0 to 13.0 wt% based on the total weight of the liquid UV-curable inkjet ink; the at least one multifunctional polymerizable compound is present in an amount of at least 20.0 wt%, based on the total weight of the polymerizable composition; and the UV curable inkjet ink is at 45 ℃ and 10s^-1Has a viscosity of at least 16.0mpa.s at shear rate.

The term "liquid" in a liquid UV curable inkjet ink means that the inkjet ink is liquid at room temperature (25 ℃), thus stating that the liquid UV curable inkjet ink is not a so-called UV curable phase change or hot melt inkjet ink.

The organic color pigment is preferably dispersed in the liquid vehicle of the inkjet ink by a polymeric dispersant. Liquid UV curable inkjet inks may contain dispersion synergists to improve dispersion quality and ink stability. Preferably, at least the magenta ink contains a dispersion synergist. Mixtures of dispersion synergists can be used to further improve dispersion stability.

The liquid UV curable inkjet ink is preferably a so-called 100% solids UV curable inkjet ink. This means that no solvent (i.e., water or organic solvent) is present. However, sometimes a small amount (typically less than 1 wt% or 2 wt%) of water may be present, based on the total weight of the inkjet ink. The water is not intentionally added but enters the inkjet ink as a contaminant via other components (e.g., hydrophilic monomers).

The liquid UV curable inkjet ink is preferably free of organic solvents. It may sometimes be advantageous to incorporate a small amount of organic solvent to improve adhesion to the surface of the substrate after UV-curing. In this case, the solvent added may be in any amount within a range that does not cause problems of solvent resistance and VOC. The liquid UV-curable inkjet ink preferably contains 0 to 10 wt%, more preferably not more than 5.0 wt% of an organic solvent, based on the total weight of the UV-curable inkjet ink.

The liquid UV curable inkjet ink contains one or more photoinitiators for polymerization of the polymerizable composition after UV exposure. In a preferred embodiment of the liquid UV curable inkjet ink, at least one of the one or more photoinitiators is selected from the group consisting of polymeric photoinitiators, polymerizable photoinitiators and photoinitiators comprising a plurality of photoinitiating groups. Preferably, the liquid UV curable inkjet ink is cured by UV leds emitting at a wavelength above 360 nm. To this end, the one or more photoinitiators preferably comprise an acylphosphine oxide photoinitiator and a thioxanthone photoinitiator.

The polymerizable composition contains at least one monofunctional polymerizable compound and at least one multifunctional polymerizable compound. If a polymerizable photoinitiator is present in the inkjet ink, the photoinitiator is also considered part of the polymerizable composition. The at least one multifunctional polymerizable compound is present in at least 20 wt%, based on the total weight of the polymerizable composition.

In a more preferred embodiment of the liquid UV curable inkjet ink, the at least one multifunctional polymerizable compound is present in an amount of from 25.0 to 50.0 wt%, based on the total weight of the polymerizable composition. In the latter case, an optimum compromise is obtained between scratch resistance and flexibility.

In a preferred embodiment of the liquid UV curable inkjet ink, the polymerizable composition is present in an amount of less than 75.0 wt%, more preferably less than 70.0 wt%, and most preferably less than 68.0 wt%, based on the total weight of the liquid UV curable inkjet ink.

UV curable inkjet inks at 45 ℃ and 10s^-1Has a viscosity at shear rate of at least 16.0mpa.s, preferably at least 20.0mpa.s, more preferably 25 mpa.s.0～65.0mPa.s。

UV curable inkjet ink oil in 10s^-1And a viscosity at a temperature of 45 c (more preferably a temperature of 50 c) of at least 16.0 mpa.s.

The viscosity of the liquid UV curable inkjet ink at room temperature (25 ℃) is preferably at least 40.0mpa.s, more preferably at least 50.0mpa.s, and most preferably between 60 and 250 mpa.s. Above 250mpa.s, pumping around UV curable inkjet inks requires more powerful pumps, which represents a financial burden for manufacturing inkjet printers. Above 40.0 to 50.0mpa.s, an enhanced dispersion stability of the organic color pigment in the liquid UV curable inkjet ink is observed.

The surface tension of the liquid UV curable inkjet ink is preferably in the range of 20 to 30mN/m at 25 ℃, more preferably in the range of about 22 to about 25mN/m at 25 ℃.

The liquid UV curable inkjet ink may further contain at least one inhibitor or stabilizer for improving the thermal stability of the ink.

The liquid UV curable inkjet ink may further comprise at least one surfactant for obtaining good spreading characteristics on the substrate.

For printing multi-color images, the liquid UV-curable inkjet ink is part of a UV-curable inkjet ink set. A preferred UV curable inkjet ink set for printing different colors contains at least one liquid UV curable inkjet ink according to the present invention. Simultaneous improvements in scratch resistance and flexibility have been observed with a single liquid UV curable colour inkjet ink according to the present invention, but preferably there are multiple liquid UV curable inkjet inks possessing a composition according to the present invention.

In a particularly preferred embodiment, the UV curable inkjet ink set contains at least three liquid UV curable colour inkjet inks, each containing one or more different organic colour pigments, said pigments being present in an amount of at least 5.0 wt%, more preferably at least 6.0 wt% and most preferably at least 6.5 wt%, based on the total weight of the liquid UV curable colour inkjet ink; with the proviso that at least a liquid UV curable inkjet ink is present having at least 6.0 wt%, and more preferably at least 6.5 wt% (pigment) based on the total weight of the liquid UV curable color inkjet ink.

The UV curable inkjet ink set is preferably a UV curable CMYK or CRYK inkjet ink set. The UV-curable inkjet ink set may also be extended with additional inks, such as red, green, blue, and/or orange, to further expand the color gamut of the image. The UV curable inkjet ink set can also be extended by the combination of full density inkjet inks with low density inkjet inks. The combination of dark and light inks and/or black and gray inks improves image quality through reduced particle size.

The curable inkjet ink set may also include a colorless UV curable inkjet ink, such as a varnish or a primer. Varnishes are used to enhance the gloss of inkjet printed color images. Primers can be used to improve adhesion on different substrates like glass and polypropylene.

The curable inkjet ink set preferably further comprises a liquid UV curable white inkjet ink. The liquid UV curable white inkjet ink preferably contains a titanium dioxide pigment (preferably a rutile pigment) having an average particle size of greater than 180 nm.

White inkjet inks are commonly used in so-called "surface printing" or "reverse printing" to form reflective images on transparent substrates. In surface printing, a white background is formed on a transparent substrate using a white ink, and a color image is further printed thereon, and then the formed final image is seen from the printing side. In so-called back printing, a color image is printed on a transparent substrate using color inks, and then white inks are applied to the color inks, and the color image is observed through the transparent substrate. In a preferred embodiment, the liquid UV curable colour inkjet ink is jetted on an at least partially cured white inkjet ink. Improved wettability of the colour inkjet ink on the white ink layer is observed if the white ink is only partially cured.

The UV curable inkjet ink set is preferably a free radical curable inkjet ink set. It was found that cationically curable inkjet inks cause jetting reliability problems due to UV stray light. UV stray light hitting the nozzle plate of an inkjet print head causes nozzle failure due to clogging of the cured ink in the nozzles. Unlike free radical curable inks, where the free radical species have a much shorter lifetime, cationically curable inks continue to cure once the acid species have been generated by UV light in the nozzle.

Organic colour pigments

The liquid UV-curable inkjet ink contains an organic color pigment in an amount of 6.0 to 13.0 wt% based on the total weight of the liquid UV-curable inkjet ink. The organic color pigment includes a carbon atom, a hydrogen atom, and at least one of a sulfur atom, an oxygen atom, a nitrogen atom, and a selenium atom in its chemical molecular structure. Carbon black and metal oxides (e.g., cobalt oxide and titanium dioxide) are considered inorganic pigments. However, the organic color pigment may include metal atoms or ions, such as copper phthalocyanine pigment.

The organic color pigment may preferably be selected from cyan, magenta, yellow, red, orange, violet, blue, green and brown organic color pigments. The color pigment may be selected from the group consisting of HERBST, Willy et al, Industrial Organic Pigments, Production, Properties, Applications, 3 rd edition, Wiley-VCH, 2004. Those disclosed in ISBN 3527305769.

Suitable organic color pigments are disclosed in paragraphs [0128] to [0138] of WO 2008/074548(AGFA GRAPHICS).

In a preferred embodiment, the liquid UV curable inkjet ink includes organic color pigments having the following numbers described in the color index.

In a preferred embodiment, the liquid UV curable inkjet ink is a liquid UV curable yellow inkjet ink comprising an organic color pigment selected from the group consisting of c.i pigment yellow 120, c.i pigment yellow 150, c.i pigment yellow 151, c.i pigment yellow 155 and c.i pigment yellow 180, more preferably selected from the group consisting of c.i pigment yellow 151 and c.i pigment yellow 155.

A preferred organic color pigment for liquid UV curable cyan inkjet inks is c.i. pigment blue 15: 4.

Preferred organic color pigments for liquid UV curable magenta or red inkjet inks are quinacridone pigments, diketopyrrolopyrrole pigments or mixed crystals thereof.

Mixed crystals are also known as solid solutions. For example, under certain conditions, different quinacridones mix with each other to form solid solutions, which are quite different from the physical mixture of the compounds as well as from the compounds themselves. In solid solution, the component molecules enter the same crystal lattice (usually, but not always, the crystal lattice of one of the components). The x-ray diffraction pattern of the resulting crystalline solid is characteristic of the solid and can be clearly distinguished from the pattern of a physical mixture of the same components in the same proportions. In such physical mixtures, the x-ray pattern of each component can be discerned, and the disappearance of many of these lines is one of the criteria for forming a solid solution. A commercially available example is Cinqasia from Ciba Specialty Chemicals^TMMagenta RT-355-D.

Additionally, mixtures of pigments may also be used in the liquid UV curable inkjet inks.

The pigment particles in the inkjet ink should be small enough to allow the ink to flow freely through the inkjet-printing device (especially at the jetting nozzle). It is also desirable to use small particles for maximum color strength and to slow down sedimentation.

The number average pigment particle size is preferably between 0.050 μm and 1 μm, more preferably between 0.070 μm and 0.300. mu.m, particularly preferably between 0.080 μm and 0.200. mu.m. Most preferably, the number average pigment particle size is no greater than 0.150 μm. Average particle sizes less than 0.050 μm are less desirable due to reduced lightfastness. The determination of the number average particle size is preferably carried out by photon correlation spectroscopy on diluted samples of pigmented inkjet inks at a wavelength of 633nm using a 4mW HeNe laser. A suitable particle size analyzer for use is Malvern available from Goffin-Meyvis^TMnano-S. The sample may be prepared, for example, by: a drop of ink was added to a cuvette containing 1.5mL of ethyl acetate and mixed until a homogeneous sample was obtained. The measured particle size is the average of 3 consecutive measurements consisting of 6 20 second runs.

The organic colour pigment is preferably present in an amount of 6.5 wt% to 13.0 wt%, more preferably 7.0 wt% to 12.0 wt%, and most preferably 8.0 wt% to 11.0 wt%, wherein the weight percentage (wt%) is based on the total weight of the liquid UV curable inkjet ink.

Inorganic colour pigments

The UV curable inkjet ink set for printing different colors containing a plurality of liquid UV curable inkjet inks preferably comprises at least one black or gray UV curable inkjet ink. The liquid UV curable black inkjet ink preferably comprises a carbon black pigment, more preferably further comprising a beta-copper phthalocyanine pigment having an average particle size of less than 200 nm. By including a copper β -phthalocyanine pigment in a black inkjet ink, an image can be printed that has an attractive neutral black or gray color rather than a brown black or gray color.

The UV curable inkjet ink set for printing different colors containing a plurality of liquid UV curable inkjet inks preferably further comprises a liquid UV curable white inkjet ink.

Suitable white pigments are given in table 2 in [0116] of WO 2008/074548(AGFA GRAPHICS). The white pigment is preferably a pigment having a refractive index of greater than 1.60. White pigments may be used alone or in combination. Titanium dioxide is preferably used as a pigment having a refractive index of greater than 1.60. Suitable titanium dioxide pigments are those disclosed in [0117] and [0118] of WO 2008/074548(AGFA GRAPHICS).

The white pigment is preferably present in an amount in the range of 9 to 40 wt%, more preferably in the range of 12 to 35 wt%, and most preferably in the range of 15 to 25 wt%, the weight percent wt% based on the total weight of the inkjet ink. An amount of less than 9% by weight cannot achieve sufficient covering power and often exhibits very poor storage stability and ejection properties.

In a most preferred embodiment, the UV curable white inkjet ink preferably contains titanium dioxide pigment having an average particle size of greater than 180 nm. Titanium dioxide pigments having an average particle size of more than 180nm have a strong light-shielding ability as compared with other inorganic white pigments (e.g., calcium carbonate) having the same average particle size.

The average particle size of the inorganic pigment in the inkjet ink can be determined in the same manner as explained above for the organic color pigment.

Dispersing agent

Typical polymeric dispersants are copolymers of two monomers, but may contain three, four, five or even more monomers. The nature of the polymeric dispersant depends both on the nature of the monomers and on their distribution in the polymer. The copolymer dispersant preferably has the following polymer composition:

□ statistical polymerization of monomers (e.g., monomers A and B polymerized to ABBAABAB);

alternating polymerized monomers (e.g., monomers a and B polymerized to ABABABAB);

gradient (tapered) polymerized monomers (e.g., monomers a and B polymerized to aaabaababbabbb);

block copolymers (e.g., monomers a and B polymerized to AAAAABBBBBB), where the block length of each block (2, 3, 4, 5, or even more) is important for the dispersing ability of the polymeric dispersant;

graft copolymers (a graft copolymer consists of a polymeric backbone and polymeric side chains bound to the backbone); and

mixed forms of these polymers, for example block gradient copolymers.

Suitable polymeric dispersants are listed in the "dispersants" section of EP 1911814A (AGFA) (incorporated herein by specific reference), more specifically in [0064] to [0070] and [0074] to [0077 ].

The number average molecular weight Mn of the polymeric dispersant is preferably between 500 and 30000, more preferably between 1500 and 10000.

The weight average molecular weight Mw of the polymeric dispersant is preferably less than 100,000, more preferably less than 50,000, and most preferably less than 30,000.

The polymeric dispersant has a polydispersity PD preferably less than 2, more preferably less than 1.75, and most preferably less than 1.5.

Commercial examples of polymeric dispersants are as follows:

DISPERBYK available from BYK CHEMIE GMBH^TMA dispersant;

SOLSPERSE available from NOVEON^TMA dispersant;

TEGO from EVONIK^TMDISPERS^TMA dispersant;

fromEDAPAN of CHEMIE^TMA dispersant;

ETHACRYL from LYONDELL^TMA dispersant;

GANEX from ISP^TMA dispersant;

DISPEX from CIBA SPECIALTY CHEMICALS INC^TMAnd EFKA^TMA dispersant;

DISPONER from DEUCHEM^TMA dispersant; and

JONCRYL from JOHNSON POLYMER^TMA dispersant.

Particularly preferred polymeric dispersants include Solsperse from NOVEON^TMDispersant, Efka from CIBA SPECIALTY CHEMICALS INC^TMDispersant and Disperbyk from BYK CHEMIE GMBH^TMA dispersant. A particularly preferred dispersant is Solsperse from NOVEON^TM32000. 35000 and 39000 dispersants.

The polymeric dispersant is preferably used in an amount of 2 to 200 wt%, more preferably 10 to 120 wt%, most preferably 30 to 80 wt%, based on the weight of the pigment.

Photoinitiator

The liquid UV curable inkjet ink contains one or more photoinitiators, preferably one or more free radical photoinitiators. Free radical photoinitiators are compounds that initiate the polymerization of monomers and oligomers by forming free radicals upon exposure to actinic radiation.

Two types of free radical photoinitiators can be identified and used in liquid UV curable inkjet inks. Norrish type I initiators are initiators which cleave after excitation, giving rise to initiating free radicals immediately. Norrish type II initiators are photoinitiators that are activated by actinic radiation and form free radicals by abstracting hydrogen from a second compound that becomes the actual initiating free radical. This second compound is called a polymerization synergist or co-initiator. Both type I and type II photoinitiators can be used in the present invention, either alone or in combination.

To further increase the photosensitivity, the liquid UV curable inkjet ink may additionally contain a co-initiator. Suitable examples of coinitiators can be classified into three groups:

(1) aliphatic tertiary amines such as methyldiethanolamine, dimethylethanolamine, triethanolamine, triethylamine and N-methylmorpholine;

(2) aromatic amines such as amyl-p-dimethylaminobenzoate, 2-n-butoxyethyl-4- (dimethylamino) benzoate, 2- (dimethylamino) ethylbenzoate, ethyl-4- (dimethylamino) benzoate and 2-ethylhexyl-4- (dimethylamino) benzoate; and

(3) (meth) acrylated amines such as dialkylaminoalkyl (meth) acrylates (e.g. diethylaminoethyl acrylate) or N-morpholinoalkyl- (meth) acrylates (e.g. N-morpholinoethyl-acrylate).

Preferred coinitiators are aminobenzoates.

Suitable photoinitiators are disclosed in CRIVELLO, j.v. et al, volume III: photonitiers for Free radial Cationic, second edition, BRADLEY, G. ed, London, UK: John Wiley and Sons Ltd,1998, p.287-294.

Specific examples of photoinitiators may include, but are not limited to, the following compounds or combinations thereof: benzophenone and substituted benzophenones, 1-hydroxycyclohexyl phenyl ketone, thioxanthone (e.g. isopropylthioxanthone), 2-hydroxy-2-methyl-1-phenylpropan-1-one, 2-benzyl-2-dimethylamino- (4-morpholinylphenyl) butan-1-one, benzil dimethyl ketal, bis (2, 6-dimethylbenzoyl) -2,4, 4-trimethylpentylphosphine oxide, 2,4, 6-trimethylbenzoyldiphenylphosphine oxide, 2-methyl-1- [4- (methylthio) phenyl ] -2-morpholinylprop-1-one, 2-dimethoxy-1, 2-diphenylethan-1-one or 5, 7-diiodo-3-butoxy-6-fluorone.

Suitable commercial photoinitiationThe agent comprises Irgacure available from CIBA SPECIALTY CHEMICALS^TM184、Irgacure^TM 500、Irgacure^TM 907、Irgacure^TM 369、Irgacure^TM 1700、Irgacure^TM 651、Irgacure^TM 819、Irgacure^TM 1000、Irgacure^TM 1300、Irgacure^TM 1870、Darocur^TM 1173、Darocur^TM 2959、Darocur^TM4265 and Darocur^TMITX; lucerin available from BASFAG^TMTPO; esacure available from LambertII^TM KT046、Esacure^TM KIP150、Esacure^TMKT37 and Esacure^TMEDB; H-Nu obtainable from SPECTRA GROUP Ltd^TM470 and H-Nu^TM 470X。

In a particularly preferred embodiment of the liquid UV curable inkjet ink, the one or more photoinitiators comprise an acylphosphine oxide photoinitiator and a thioxanthone photoinitiator. Such a combination allows for fast UV curing using UV LEDs emitting above 370 nm.

In a preferred embodiment, at least one of the one or more photoinitiators is selected from the group consisting of polymeric photoinitiators, polymerizable photoinitiators and photoinitiators comprising a plurality of photoinitiating groups, more preferably from the group consisting of polymeric photoinitiators and polymerizable photoinitiators. Such diffusion hindered photoinitiators exhibit much lower mobility in a cured layer of a liquid UV curable inkjet ink than low molecular weight monofunctional photoinitiators (e.g., benzophenone). The inclusion of diffusion hindered photoinitiators and diffusion hindered co-initiators does not only have safety advantages for the operators of ink jet printers, but is also environmentally friendly, as these compounds cannot be leached out by acid rain, for example, from outdoor billboards.

Most preferably, the diffusion hindered photoinitiator is a polymerizable photoinitiator, preferably having at least one acrylate group, more preferably at least two or three acrylate groups. And most preferably, the diffusion hindered co-initiator is a polymerizable co-initiator, preferably having at least one acrylate group.

Suitable diffusion hindered photoinitiators may contain one or more photoinitiating functional groups derived from a norrish type I photoinitiator selected from the group consisting of: benzoin ethers, benzil ketals, α -dialkoxyacetophenones, α -hydroxyalkylphenones, α -aminoalkylphenones, acylphosphine oxides, acylphosphine sulfides, α -haloketones, α -halosulfones, and phenylglyoxylates.

Suitable diffusion hindered photoinitiators may contain one or more photoinitiating functional groups derived from a norrish type II initiator selected from the group consisting of: benzophenones, thioxanthones, 1, 2-diketones and anthraquinones.

Suitable diffusion hindered photoinitiators are also those disclosed in paragraphs [0074] and [0075] of EP 2053101A (AGFA GRAPHICS) for bifunctional and polyfunctional photoinitiators, paragraphs [0077] to [0080] for polymeric photoinitiators and paragraphs [0081] to [0083] for polymerizable photoinitiators.

Other preferred polymerizable photoinitiators are those disclosed in EP 2065362 a (agfa) and EP 2161264 a (agfa) (incorporated herein by reference).

In a particularly preferred embodiment of the liquid UV curable inkjet ink, the one or more photoinitiators comprise an acylphosphine oxide photoinitiator and a polymeric thioxanthone photoinitiator or a polymerizable thioxanthone photoinitiator. Such combinations allow both safety advantages (e.g. food packaging) and fast UV curing using UV LEDs emitting over 370 nm. The acylphosphine oxide photoinitiator may be a bisacylphosphine oxide or a polymeric (bis) acylphosphine oxide photoinitiator or a polymerizable (bis) acylphosphine oxide photoinitiator.

Suitable polymeric acylphosphine oxide photoinitiators and polymerizable acylphosphine oxide photoinitiators are disclosed in US 2015344711 a (fujifilm), WO 2015/031927 a (durst) and US 2015197651 a (fujifilm).

The preferred amount of photoinitiator is from 0 to 50 wt%, more preferably from 0.1 to 20 wt%, and most preferably from 0.3 to 15 wt% of the total weight of the liquid UV-curable inkjet ink. In a most preferred embodiment, the amount of photoinitiator is at least 7.0 wt% or 8.0 wt% of the total weight of the liquid UV curable inkjet ink for obtaining a high curing speed.

Preferred diffusion hindered coinitiators are the polymerizable coinitiators disclosed in paragraphs [0088] and [0097] of EP 2053101A (AGFA GRAPHICS).

Preferred diffusion hindered coinitiators include polymeric coinitiators having a dendritic polymeric structure, more preferably a hyperbranched polymeric structure. Preferred hyperbranched polymeric co-initiators are those disclosed in US 2006014848(AGFA) (incorporated herein by specific reference).

The liquid UV curable inkjet ink preferably comprises a diffusion hindered co-initiator in an amount of 0.1 to 50 wt%, more preferably in an amount of 0.5 to 25 wt%, most preferably in an amount of 1 to 10 wt% based on the total weight of the liquid UV curable inkjet ink.

Monofunctional polymerizable compound

The polymerizable composition of the liquid UV-curable inkjet ink according to a preferred embodiment of the present invention contains at least one monofunctional polymerizable compound. The monofunctional polymerizable compound contains a single polymerizable group, preferably a free-radically polymerizable group, selected from the group consisting of acrylate, methacrylate, acrylamide, methacrylamide, styrene, maleate, fumarate, itaconate, vinyl ether, vinyl ester, allyl ether, and allyl ester.

Any monofunctional polymerizable compound generally known in the art may be used. Combinations of monomers and oligomers may be used. The monofunctional polymerizable compound may be any monomer and/or oligomer found in Polymer Handbook, Vol.1 +2, 4 th edition, edited by J.BRANDRUP et al, Wiley-Interscience, 1999. Oligomers in the context of the present invention are understood to contain from 2 to 8 repeating monomer units.

In a preferred embodiment, the monofunctional polymerizable compound is selected from acrylic acid; methacrylic acid; maleic acid (or salts thereof); maleic anhydride; alkyl (meth) acrylates (straight-chain alkyl, branched-chain alkyl and cycloalkyl), such as methyl (meth) acrylate, n-butyl (meth) acrylate, t-butyl (meth) acrylate, cyclohexyl (meth) acrylate and 2-ethylhexyl (meth) acrylate; aryl (meth) acrylates such as benzyl (meth) acrylate and phenyl (meth) acrylate; hydroxyalkyl (meth) acrylates such as hydroxyethyl (meth) acrylate and hydroxypropyl (meth) acrylate; (meth) acrylates having other types of functional groups (e.g. ethylene oxide, amino, fluorine, polyethylene oxide, phosphate substituted), such as glycidyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, trifluoroethyl acrylate, methoxypolyethylene glycol (meth) acrylate and tripropylene glycol (meth) acrylate phosphate; allyl derivatives such as allyl glycidyl ether; styrenes such as styrene, 4-methylstyrene, 4-hydroxystyrene, 4-acetylstyrene and styrenesulfonic acid; (meth) acrylonitrile; (meth) acrylamides (including N-monosubstituted and N, N-disubstituted), for example N-benzyl (meth) acrylamide; maleimides such as N-phenylmaleimide; vinyl derivatives such as vinyl caprolactam, vinyl pyrrolidone, vinyl imidazole, vinyl naphthalene, and vinyl halides; vinyl ethers such as vinyl methyl ether; vinyl esters of carboxylic acids, such as vinyl acetate, vinyl butyrate and vinyl benzoate. In a more preferred embodiment, the monofunctional polymerizable compound is selected from monoacrylates and vinyllactams, such as N-vinylcaprolactam. Particularly preferred monofunctional polymerizable compounds are selected from the group consisting of isoamyl acrylate, stearyl acrylate, lauryl acrylate, octyl acrylate, decyl acrylate, isoamyl acrylate, isostearyl acrylate, 2-ethylhexyl-diethylene glycol acrylate, 2-hydroxybutyl acrylate, 2-acryloyloxyethyl hexahydrophthalic acid, butoxyethyl acrylate, ethoxydiethylene glycol acrylate, methoxydiethylene glycol acrylate, methoxypolyethylene glycol acrylate, methoxypropylene glycol acrylate, phenoxyethyl acrylate, tetrahydrofurfuryl acrylate, isobornyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, vinyl ether acrylate, 2-acryloyloxyethyl succinate, lauryl acrylate, octyl acrylate, decyl acrylate, isoamyl acrylate, 2-acryloyloxyethyl succinate, 2-acryloyloxyethyl acrylate, 2-acryloyloxyethyl phthalate, 2-hydroxy-2-acryloyloxyethyl phthalate, 2-hydroxyethyl acrylate, 2-acetoxy-phthalate, 2-hydroxyethyl acrylate, 2-acryloyloxyethyl acrylate, and mixtures of the like, 2-acryloxyethyl phthalic acid, 2-acryloxyethyl-2-hydroxyethyl phthalic acid, lactone-modified flexible acrylates, tert-butylcyclohexyl acrylate, caprolactone acrylate, cyclotrimethylolpropane formal acrylate, ethoxylated nonylphenol acrylate, isodecyl acrylate, isooctyl acrylate, octyldecyl acrylate, alkoxylated phenol acrylate, tridecyl acrylate and acryloylmorpholine.

In a more preferred embodiment, the monofunctional polymerizable compound is selected from monoacrylates and vinyllactams, such as N-vinylcaprolactam.

The N-vinyllactam is preferably a compound represented by the formula (I):

wherein n represents an integer of 2 to 6; from the viewpoints of flexibility after curing of the ink composition, adhesion to a substrate, and availability of raw materials, N is preferably an integer of 3 to 5, more preferably 3 or 5, and particularly preferably 5, which is N-vinylcaprolactam. N-vinylcaprolactam is preferable because it is easily available at a relatively low price and provides particularly good ink curability and adhesion of the cured film to a recording medium.

The N-vinyl lactam may have a substituent, such as an alkyl group or an aryl group, on the lactam ring, and may have a saturated or unsaturated ring structure bonded to the lactam ring. The compounds represented by formula (a) may be used alone or in a combination of two or more compounds.

For some applications, it is preferred not to use monofunctional (meth) acrylates. For example, when the substrate is a textile worn directly on human skin, it can cause a skin sensation. In such cases, the monomers and oligomers are preferably selected from the group comprising or consisting of: vinyl, acrylamide, methacrylamide, vinyl carbonate, vinyl ether, vinyl ester, vinyl carbamate, allyl ether, allyl ester, and their corresponding alkyne compounds. Particularly preferred are polymerizable compounds comprising an allyl ether group, a vinyl carbonate group and an alkyne group.

Multifunctional polymerizable compound

The polymerizable composition of the liquid UV-curable inkjet ink according to a preferred embodiment of the present invention contains at least one polyfunctional polymerizable compound. The polyfunctional polymerizable compound contains two, three or more polymerizable groups, preferably free radically polymerizable groups, selected from the group consisting of acrylate, methacrylate, acrylamide, methacrylamide, styrenic groups, maleate, fumarate, itaconate, vinyl ether, vinyl ester, allyl ether and allyl ester.

Any polyfunctional polymerizable compound generally known in the art may be employed. Combinations of monomers and oligomers may be used. The polyfunctional polymerizable compound can be any monomer and/or oligomer found in Polymer Handbook, Vol.1 +2, 4 th edition, edited by J.BRANDRUP et al, Wiley-Interscience, 1999. Oligomers in the context of the present invention are understood to contain from 2 to 8 repeating monomer units.

In a preferred embodiment, the multifunctional polymerizable compound is a difunctional acrylate containing two polymerizable groups (i.e., two acrylate groups).

Preferred multifunctional acrylates include triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, polypropylene glycol diacrylate, 1, 4-butanediol diacrylate, 1, 6-hexanediol diacrylate, 1, 9-nonanediol diacrylate, neopentyl glycol diacrylate, dimethylol-tricyclodecane diacrylate, bisphenol A EO (ethylene oxide) adduct diacrylate, bisphenol A PO (propylene oxide) adduct diacrylate, hydroxypivalate neopentyl glycol diacrylate, propoxylated neopentyl glycol diacrylate, alkoxylated dimethylol tricyclodecane diacrylate and polytetramethylene glycol diacrylate, trimethylolpropane triacrylate, poly (ethylene glycol) acrylate, poly (ethylene glycol) diacrylate, poly (propylene glycol) diacrylate, poly (ethylene glycol) diacrylate, poly (propylene glycol) acrylate, poly (ethylene glycol) acrylate, poly (propylene glycol) acrylate, poly (ethylene glycol) acrylate, poly (propylene glycol) acrylate), poly (propylene glycol) acrylate, poly (ethylene glycol) acrylate, poly (propylene glycol) acrylate, poly (trimethylene glycol) acrylate, and/or combinations thereof, and the like, poly (trimethylene glycol) acrylate), and the like, EO-modified trimethylolpropane triacrylate, caprolactone-modified trimethylolpropane triacrylate, pentaerythritol tetraacrylate, pentaerythritol ethoxytetraacrylate, dipentaerythritol hexaacrylate, ditrimethylolpropane tetraacrylate, glycerol propoxytriacrylate and caprolactam-modified dipentaerythritol hexaacrylate.

Other suitable difunctional acrylates include alkoxylated cyclohexanone dimethanol diacrylate, alkoxylated hexanediol diacrylate, dioxane glycol diacrylate, cyclohexanone dimethanol diacrylate, diethylene glycol diacrylate, and neopentyl glycol diacrylate.

Other multifunctional acrylates include propoxylated and propoxylated glycerol triacrylate, ditrimethylolpropane tetraacrylate, dipentaerythritol pentaacrylate, ethoxylated pentaerythritol tetraacrylate, methoxylated diol acrylate and acrylate.

Preferred multifunctional acrylates include dipropylene glycol diacrylate, tripropylene glycol diacrylate, 1, 6-hexanediol diacrylate, cyclohexanone dimethanol diacrylate, polyethylene glycol 200 diacrylate, 3-methyl 1, 5-pentanediol diacrylate, pentaerythritol tetraacrylate, trimethylolpropane triacrylate, and dipentaerythritol pentaacrylate.

The multifunctional polymerizable compound may have two different polymerizable groups, for example, a vinyl ether group and an acrylate group. Preferred vinyl ether acrylates are those disclosed in US 6310115 (AGFA). A particularly preferred compound is 2- (2-vinyloxyethoxy) ethyl acrylate. Other suitable vinyl ether acrylates are those disclosed in column 3 and column 4 of US 67679890 b (nippon shokubali).

Instead of difunctional or polyfunctional acrylates, it is also possible to use their methacrylate analogues.

For some applications, it is preferred not to use polyfunctional (meth) acrylates. For example, when the substrate is a textile worn directly on human skin, it can cause a skin sensation.

Preferred alternative free radical cure chemistries are the so-called thiol-alkene and thiol-alkyne chemistries. In such chemistry, a combination of at least one polyfunctional thiol compound and at least one polyfunctional polymerizable compound is used. The polyfunctional polymerizable compound is a polyfunctional monomer or oligomer having a plurality of polymerizable groups selected from the group consisting of: vinyl groups, acrylamide groups, methacrylamide groups, vinyl carbonate groups, vinyl ether groups, vinyl ester groups, vinyl carbamate groups, allyl ether groups, allyl ester groups, and alkyne groups. Particularly preferred are polymerizable compounds comprising an allyl ether group, a vinyl carbonate group and an alkyne group.

The synthesis of such monomers is disclosed in the literature, for example, in HURD, Charles D., methylation and the Formation of aldehydes, Journal am. chem. Soc.1956, volume 78, No. 1, page 104-; LOBELL, M.et al, Synthesis of polyhydroxycarboxylic acid vinyl esters, MP Synthesis.1994, Vol.4, p.375-; LEE, T.Y., et al, Synthesis, Initiation, and Polymerization of photosynthetic monomers, Macromolecules, 2005, vol 38, No 18, p 7529-7531; ATTA, A.M., et al, New vinyl ester resins based on rosin for coating applications, React.Funct.Polymer, 2006, vol.66, p.1596-1608; WO 01/00634 a (WRIGHT CHEM CORP); and ROHR, Markus et al, Solvent-free ruthenium-catalyzed vinyl synthesis from phenyl ethylene and ethylene amine in ` super critical ` carbon dioxide, Green Chemistry, 2001, Vol.3, p.123-125.

Preferred polymerizable oligomers and polymers are polyurethanes, polyesters, polyethers, polycarbonates, polyurethanes, polyureas and linear oligomers having the following polymerizable groups: acrylate, methacrylate, vinyl, acrylamide, methacrylamide, vinyl carbonate, vinyl ether, vinyl ester-vinyl carbamate groups, and their corresponding alkyne compounds.

Particularly preferred monomers are selected from difunctional or oligofunctional allyl ethers, difunctional or oligofunctional allyl esters, difunctional or oligofunctional vinyl ethers, difunctional or oligofunctional vinyl esters and difunctional or oligofunctional norbornene derivatives. Typical allyl ethers may be selected from pentaerythritol tetraallyl ether, glycerol triallyl ether, 1, 6-hexanediol diallyl ether, cyclohexane dimethanol diallyl ether, trimethylolpropane triallyl ether, dipentaerythritol hexaallyl ether, and ethoxylated and propoxylated derivatives thereof. Typical vinyl ethers may be selected from pentaerythritol tetravinyl ether, glycerol trivinyl ether, 1, 6-hexanediol divinyl ether, cyclohexanedimethanol divinyl ether, trimethylolpropane trivinyl ether, dipentaerythritol hexavinyl ether, and ethoxylated and propoxylated derivatives thereof. Typical allyl esters can be selected from diallyl adipate, diallyl terephthalate, triallyl trimellitate, tetraallyl pyromellitate, triallyl citrate and diallyl glutarate. Typical vinyl esters may be selected from the group consisting of divinyl adipate, divinyl terephthalate, trivinyl trimellitate, tetraenyl pyromellitate, trivinyl citrate and divinyl glutarate.

Thiol-alkyne chemistry has been described as an extension of thiol-alkene chemistry to design crosslinked networks with higher crosslink density and glass transition temperature compared to thiol-alkene based networks. This Chemistry has recently been reviewed by Lowe et al (Journal of Materials Chemistry,20,4745-4750(2010)) and Hoogenboom R (Angew. chem. int. Ed.49,3415-3417 (2010)).

The optional photochemically induced double addition of the free radicals of the polyfunctional thiol compounds to a di-or polyfunctional alkyne is the basis of thiol-alkyne chemistry. In principle, any di-or multifunctional alkyne (including polymeric alkynes) can be used in combination with any di-or multifunctional thiol compound.

In a preferred embodiment, at least one of the alkyne functional groups in a difunctional or multifunctional alkyne is represented by H-C ≡ C-, wherein represents a covalent bond to the remainder of the difunctional or multifunctional alkyne.

In a more preferred embodiment, all alkyne groups in a di-or polyfunctional alkyne are represented by H-C ≡ C-.

In an even more preferred embodiment, the alkyne functional group in the di-or multifunctional alkyne is selected from the group consisting of propargyl ether, propargyl ester, propargyl carbamate, propargyl urea, propargyl carbonate, propargyl amide, propargyl sulfide, and propargyl amine. In other preferred embodiments, the alkyne group is selected from propargyl ethers, propargyl esters, and propargyl carbamates, with propargyl esters and propargyl carbamates being particularly preferred.

The preferred thiol compounds for conducting thiol-alkene or thiol-alkyne chemistry are thiol molecules comprising at least two thiol groups. Preferred thiol molecules comprise 2 to 6 thiol groups, preferably 3 to 5 thiol groups, and most preferably 4 thiol groups.

The thiol molecule is preferably a compound comprising an aliphatic thiol.

In a preferred embodiment, the thiol molecule is represented by formula (I):

wherein n represents an integer of 1 to 4; m represents an integer of 2 to 6; and R represents an m-valent linking group comprising up to 20 carbon atoms.

In a preferred embodiment, n represents 1 or 2.

In a preferred embodiment, m represents 3 or 4.

In a more preferred embodiment, n represents 1 or 2 and m represents an integer of 2 to 6. In a most preferred embodiment, n represents 1 or 2 and m represents 3 or 4.

In a preferred embodiment, the thiol compound has a molecular weight of less than 1,000 daltons, and more preferably the thiol compound has a molecular weight of less than 500 daltons.

Particularly preferred primary thiol molecules include tetra (ethylene glycol) dithiol (CAS 2781-02-4), ethylene glycol di (3-mercaptopropionate) (CAS 22504-50-3), glycerol dithioglycolate (CAS 63657-12-5), ethylene glycol dimercaptoacetate (CAS 123-81-9), trimethylolpropane trimercaptoacetate (CAS 10193-96-1), pentaerythritol tetramercaptoacetate (CAS 10193-99-4), ethylene glycol di (3-mercaptopropionate) (CAS 22504-50-3), trimethylolpropane tris (3-mercaptopropionate) (CAS 07-83-9), pentaerythritol tetrakis (3-mercaptopropionate) (CAS 7575-23-7), dipentaerythritol hexa (3-mercaptopropionate) (25CAS 359-71-1), Ethoxylated trimethylolpropane tris-3-mercaptopropionate (CAS 345352-19-4) and tris [2- (3-mercaptopropionyloxy) ethyl ] isocyanurate (CAS 36196-44-8).

The above and other thiol molecules are commercially available, for example, as from Bruno Bock Chemische Fabrik GmbH&Thiocure of co^TMA rank.

Suitable thiol molecules include 1,1, 1-trimethylolpropane tris (3-mercaptopropyl) ether, 1,2, 4-tris (2-mercaptoethyl) cyclohexane, tris (3-mercaptopropyl) trimethylolpropane and other thiol molecules disclosed by WO 2011/004255a (kuros biosurgery).

It was found that thiol molecules with secondary thiol groups exhibit less odor than thiol molecules with only primary thiol groups. Thus, the thiol molecules preferably comprise at least 2 secondary thiol groups, more preferably the thiol molecules comprise 2 to 6 secondary thiol groups, preferably 3 to 5 secondary thiol groups, and most preferably 4 secondary thiol groups.

A particularly preferred thiol molecule having a secondary thiol group is pentaerythritol tetrakis (3-mercaptobutyrate). The latter as Omnimer^TMPE1 available from IGM RESINS and as Karenz MT^TMPE1 is available from SHOWA DENKO.

To minimize the odor of the liquid UV curable inkjet ink, especially after UV curing, the molar ratio of thiol molecules having primary thiol groups to thiol compounds having at least one secondary thiol group is preferably 0 to 4, more preferably 0, which means that the thiol molecules in the liquid UV curable inkjet ink consist of thiol molecules having at least one secondary thiol group. To calculate the molar ratio, the thiol molecules having primary thiol groups are considered to have only primary thiol groups, while the thiol molecules containing at least one secondary thiol group may also include primary thiol groups.

In a most preferred embodiment, the thiol molecules consist of thiol molecules containing only secondary thiol groups.

To improve mechanical properties and limited possibilities for water uptake, leaching and degradation, the thiol molecules are preferably ester-free thiol molecules.

Particularly preferred ester-free thiol molecules are silane-based thiol molecules and siloxane-based thiol molecules. Such compounds can be readily synthesized by: thioacetic acid is reacted with a functional olefin to give a thioester derivative which is hydrolysable under basic or acidic conditions.

Suitable silane-based thiol molecules and siloxane-based thiol molecules are disclosed by WO 2011/004255A (KUROS BIOSURGERY), especially those in examples 1-6.

A preferred example of a silane-based thiol molecule for use in liquid UV-curable inkjet inks is tetrakis (3-mercaptopropyl) silane, the synthesis of which is described in example 5 of WO 2011/004255a (kuros biosurgery).

A preferred example of a siloxane based thiol molecule for use in liquid UV curable inkjet inks is 2,4,6, 8-tetrakis (2-mercaptoethyl) -2,4,6, 8-tetramethylcyclotetrasiloxane, the synthesis of which is described in example 4 of WO 2011/004255a (kuros biosurgery).

More preferably, silane-based thiol molecules and siloxane-based thiol molecules comprising secondary thiol groups are used in the liquid UV-curable inkjet ink according to the present invention. Such thiol molecules not only improve mechanical properties but also reduce odor problems.

Preferred examples of the silane-based thiol molecule containing a secondary thiol group are compounds represented by the formula TH-1:

the synthesis of TH-1 may be carried out in a multi-step reaction. In a first step, hydrogen bromide is reacted with tetraallylsilane to give tetrakis (2-bromopropyl) silane. The latter is converted to its isothiuronium salt using thiourea, which is then hydrolyzed with aqueous sodium hydroxide solution to give TH-1.

The thiol compound can also be a so-called thiol pigment. Thiol pigments are inorganic pigments, such as silica pigments or titanium dioxide pigments, whose surface has been functionalized with two or more thiol groups. The main advantage is that liquid UV curable inkjet inks containing thiol pigments exhibit no or less odor prior to UV curing, which is not generally the case with liquid UV curable inkjet inks containing multifunctional thiol molecules. The latter produces an unpleasant odor even with small amounts of evaporated thiol molecules.

Silica nanoparticles are preferred because they are generally small in size, monodisperse and can be easily surface modified. The monodisperse distribution is advantageous for the transparency of the printed colour ink, thereby enlarging the colour gamut.

The introduction of thiol groups onto the surface is preferably carried out using alkoxysilanes which contain thiol groups. Typical examples of the mercaptan-containing siloxanes are 3-mercaptopropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, 4-mercaptobutyltriethoxysilane, 2-mercaptopropyltrimethoxysilane and 3-mercaptobutyltrimethoxysilane. A preferred alkoxysilane containing a thiol group is 3-mercaptopropyltrimethoxysilane (MPTMS).

Examples of suitable synthesis schemes for thiol pigments are as follows: dry phase deposition method is used to make silica particles (e.g., Ludox from GRACE with average particle size of about 22nm^TMTM-50) functionalization. The silica particles were dispersed in absolute ethanol (15 mL of ethanol per gram of silica) and MPTMS (available from ALDRICH) was added so that the ratio of the amount of silica (in g) to the amount of MPTMS (in mL) was 3: 7. Ultra-high purity grade nitrogen gas was bubbled through the mixture to evaporate the ethanol in the fume hood, thereby depositing MPTMS on the surface of the silica. For the silanization reaction, the silica was then placed in an oven at 120 ℃ for 9 hours. The material was allowed to cool and washed twice with 50mL of absolute ethanol to remove any physisorbed MPTMS, again dried in the oven. Analysis Using FTIRSilica to confirm MPTMS deposition on the silica surface.

The number of thiol groups on the surface of the thiol pigment can be easily varied as desired, as long as at least two thiol groups are present. However, there are typically a large number of thiol groups present on the surface of the pigment, preferably more than ten thiol groups, more preferably even more than twenty or fifty thiol groups.

However, the commercially available thiol pigment with a large average particle size of 2.2 μm is Aktisil from HOFMANN MINERAL^TMMM (mercapto modified). The average particle size of the thiol pigment as measured according to ISO 13320-1 is preferably between 10nm and 1 μm, more preferably between 15nm and 250nm, and most preferably between 20nm and 150 nm.

Due to its higher molecular weight per unit, it is not necessary to include secondary thiol groups for odor improvement. Indeed, it is preferred to include primary thiol groups because of their greater reactivity in thiol-alkene and thiol-alkyne click chemistry.

Stabilizer

The liquid UV curable inkjet ink may contain a polymerization inhibitor. Suitable polymerization inhibitors include phenolic antioxidants, hindered amine light stabilizers, phosphor-type antioxidants, hydroquinone monomethyl ether, and hydroquinone, t-butylcatechol, pyrogallol, which are commonly used in (meth) acrylate monomers.

Suitable commercial inhibitors are for example Sumilizer manufactured by Sumitomo Chemical co.ltd^TMGA-80、Sumilizer^TMGM and Sumilizer^TMGS; genorad from Rahn AG^TM 16、Genorad^TM18 and Genorad^TM20; irgastab from Ciba Specialty Chemicals^TMUV10 and Irgastab^TM UV22、Tinuvin^TM460 and CGS 20; floorstab from Kromachem Ltd^TMUV series (UV-1, UV-2, UV-5 and UV-8); additol from Cytec Surface Specialties^TMS series (S100, S110, S120, and S130).

A preferred polymerization inhibitor is Irgastab from BASF^TM UV10。

In a preferred embodiment, the polymerization inhibitor is a mixture of different types of polymerization inhibitors. Preferred polymerization inhibitors are hydrocarbyloxy (oxy) radical based polymerization inhibitors, mixtures of phenol based polymerization inhibitors and amine based polymerization inhibitors. Suitable examples are given in EP 2851402 a (fujifilm).

Since excessive addition of these polymerization inhibitors will reduce the sensitivity of the ink to curing, it is preferable to determine the amount capable of preventing polymerization prior to blending. The amount of polymerization inhibitor is preferably below 2 wt% based on the total weight of the liquid UV curable inkjet ink.

Surface active agent

Surfactants that can be used in liquid UV curable inkjet inks reduce surface tension in order to improve spreading of the inkjet ink. Liquid UV curable inkjet inks must meet stringent performance standards in order to be adequately jettable with high precision, reliability, and over extended periods of time. The surface tension is determined not only by the amount and type of surfactant, but also by the polymerizable compound and other additives in the ink composition.

The one or more surfactants may be anionic, cationic, non-ionic or zwitterionic and are preferably added in a total amount of not more than 2 wt%, preferably less than 1 wt%, based on the total weight of the liquid UV-curable inkjet ink.

Suitable surfactants include fluorinated surfactants, fatty acid salts, ester salts of higher alcohols, alkylbenzene sulfonates, sulfosuccinate and phosphate ester salts of higher alcohols (e.g., sodium dodecylbenzenesulfonate and sodium dioctyl sulfosuccinate), ethylene oxide adducts of higher alcohols, ethylene oxide adducts of alkylphenols, ethylene oxide adducts of polyol fatty acid esters, and acetylene glycol and its ethylene oxide adducts (e.g., polyoxyethylene nonylphenyl ether, and those available from AIR PRODUCTS&CHEMICALS INC SURFYNOL^TM104. 104H, 440, 465 and TG).

Preferred surfactants include fluorosurfactants (e.g., fluorinated hydrocarbons) and silicone surfactants. Silicones are typically siloxanes and can be alkoxylated, polyether modified, polyester modified, polyether modified hydroxy functional, amine modified, epoxy modified and other modifications or combinations thereof. Preferred silicones are polymeric, such as polydimethylsiloxane.

The fluorinated compound or silicone compound used as the surfactant may be a polymerizable surfactant. Suitable polymerizable compounds having a surface-active effect include, for example, polyacrylate copolymers, silicone-modified acrylates, silicone-modified methacrylates, acrylated siloxanes, polyether-modified acrylated siloxanes, fluorinated acrylates and fluorinated methacrylates. These acrylates may be monofunctional, difunctional, trifunctional or higher functional (meth) acrylates.

Depending on the application, surfactants with high, low or moderate dynamic surface tensions may be used. Silicone surfactants are generally known to have low dynamic surface tensions, while fluorinated surfactants are known to have higher dynamic surface tensions.

In the liquid UV curable inkjet ink of the present invention, silicone surfactants, especially reactive silicone surfactants, which are capable of polymerizing with the polymerizable compound during the curing step, are preferred.

Examples of useful commercial silicone surfactants are those supplied by BYK CHEMIE GMBH (including Byk)^TM-302, 307, 310, 331, 333, 341, 345, 346, 347, 348, UV3500, UV3510 and UV 3530); those supplied by TEGO CHEMIE SERVICE (including Tego Rad^TM2100. 2200N, 2250, 2300, 2500, 2600, and 2700); ebecryl from CYTEC INDUSTRIES BV^TM1360 (a silicone hexaacrylate); and Efka from EFKA CHEMICALS b.v^TMSeries-3000 (including Efka)^TM3232 and Efka^TM3883); and those supplied by MOMENTIVE PERFOMANCE MATERIALS, e.g. Coatasil^TM 7500。

Preparation of inkjet inks

The preparation of pigmented UV curable inkjet inks is well known to the person skilled in the art. Preferred preparation processes are disclosed in paragraphs [0076] to [0085] of WO2011/069943 (AGFA).

Ink jet printing method

The UV curable inkjet printing method according to a preferred embodiment of the present invention includes the steps of: a) jetting one or more liquid UV-curable inkjet inks as described above with a print head onto a substrate at a jetting temperature of 45 ℃ or higher; and b) UV curing the liquid UV curable inkjet ink jetted on the substrate.

The one or more liquid UV curable inkjet inks are preferably at a temperature between 45 ℃ and 65 ℃, more preferably not higher than 55 ℃ or 60 ℃. Above 65 ℃, the reliability of liquid UV curable inkjet inks is reduced, as unwanted 'dark' polymerisation can occur, i.e. polymerisation is not caused by UV radiation, but by being held at elevated temperatures for a long time.

The print head is preferably a through-flow piezoelectric drop-on-demand print head. To limit the time that the liquid UV curable inkjet ink is held at the higher temperature, the liquid UV curable inkjet ink may be heated to a jetting temperature just prior to entering the flow-through printhead, while unused ink may cool to 45 ℃ or less upon exiting the flow-through printhead. In this way, the major part of the ink circulation loop supplying ink to the flow-through piezoelectric DOD printhead is maintained at a temperature that prevents unwanted 'dark' polymerisation of the inkjet ink.

The UV curable inkjet printing method preferably employs UV led curing, which is performed between 100ms and 1s (more preferably between 400ms and 600 ms) after jetting the liquid UV curable inkjet ink on the substrate.

In preferred embodiments, the average ink layer thickness to achieve the target density of the UV cured liquid UV curable inkjet ink or inks is less than 8 μm, preferably less than 6 μm and most preferably less than 3 or 4 μm.

Printing equipment

Liquid UV curable inkjet inks are ejected by one or more print heads which eject (ink) droplets in a controlled manner via nozzles onto a substrate which is moving relative to the one or more print heads.

A preferred print head for use in an inkjet printing system is a piezoelectric head. Piezoelectric ink jet printing is based on the movement of a piezoelectric ceramic transducer when a voltage is applied to it. The application of a voltage changes the shape of the piezoelectric ceramic transducer in the printhead, creating a void, which is then filled with an inkjet ink or liquid. When the voltage is removed again, the ceramic expands to its original shape, ejecting a drop of ink from the print head.

The preferred piezoelectric print head is a so-called push-style type of piezoelectric print head having a relatively large piezoelectric element capable of ejecting relatively large or highly viscous droplets of ink-jet ink. Such a print head is available as GEN5 print head from RICOH.

A preferred piezoelectric printhead is a so-called flow-through piezoelectric drop-on-demand printhead. Such a printhead is available as a CF1ou printhead from TOSHIBA TEC.

The inkjet printing method according to the present invention is not limited to piezoelectric inkjet printing, however. Other inkjet print heads may be used and include various types, such as continuous type print heads.

Inkjet print heads typically scan back and forth in a lateral direction across the surface of a moving ink-receiver. Typically the inkjet print head does not print on return. Bi-directional printing is preferred to achieve high area throughput.

Another preferred printing method is by a "single pass" printing process, which can be carried out by using a page wide inkjet print head or multiple staggered inkjet print heads covering the entire width of the ink receptor surface. In a single pass printing process, the inkjet print head is typically held stationary and the ink receptor surface is transported under the inkjet print head.

In a particularly preferred embodiment, the inkjet printing of the liquid UV curable inkjet ink is carried out in a multi-pass (multi-pass) printing mode. Multipass printing is a technique used to reduce banding in inkjet printing. The ink dots tend to flow (run) together while still in liquid form due to surface tension. This is called coalescence. To print a high quality image, it is important to print individual dots. But in order to achieve a fully saturated color, the dots must overlap to completely cover the paper. Coalescence can be largely avoided by printing only a portion of the image data during each print cycle, so as to avoid printing adjacent dots simultaneously. In addition, by avoiding all horizontal abutments, the lateral speed of the printing mechanism can be increased by at most twice the nominal printing speed of the print head. In a preferred embodiment, the number of passes used is 2 to 6, more preferably no more than 4.

The advantage of using a multi-pass printing mode is that the liquid UV curable inkjet ink is cured in successive passes (printing) rather than in a single pass (printing) requiring a curing apparatus with high UV output. The life of the print head for multipass printing is also longer. While in a single pass one side shooter (side shooter) is sufficient to replace the entire print head, in a multi-pass, side shooter and even failure can be tolerated. In addition, the cost of multi-pass presses is generally much lower, especially for wide format substrates.

Curing equipment

The liquid UV curable inkjet ink according to the present invention is cured by ultraviolet radiation.

In inkjet printing, a UV curing device may be arranged in combination with the print head of an inkjet printer, travelling therewith, so that the liquid UV curable inkjet ink is exposed to curing radiation shortly after being jetted.

In such an arrangement, it may be difficult to provide a sufficiently small source of UV radiation connected to and travelling with the print head. Thus, a statically fixed radiation source may be used, such as a curing UV light source connected to the radiation source by a flexible radiation conducting means, such as a fiber optic bundle or an internally reflective flexible tube.

Alternatively, actinic radiation may be supplied to the radiation head from a fixed source by the arrangement of mirrors, including mirrors on the radiation head.

The radiation source, which is arranged to not move with the print head, may also be an elongate radiation source which extends transversely across the surface of the ink-receiver body to be cured and adjacent the transverse path of the print head so that subsequent rows of images formed by the print head pass under the radiation source in steps or continuously.

Any ultraviolet light source may be used as the radiation source, as long as part of the emitted light can be absorbed by the photoinitiator or photoinitiator system, for example, high-or low-pressure mercury lamps, cold-cathode tubes, black light, ultraviolet LEDs, ultraviolet lasers, and flash lamps. Among these, preferred sources are light sources exhibiting relatively long wavelength (dominant wavelength 300-400nm) UV contribution. In particular, UV-a light sources are preferred due to their reduced light scattering leading to more efficient internal curing.

UV radiation is generally classified as UV-A, UV-B and UV-C as follows:

·UV-A：400nm～320nm

·UV-B：320nm～290nm

·UV-C：290nm～100nm。

furthermore, it is possible to cure the image using two light sources of different wavelengths or illumination intensity, either sequentially or simultaneously. For example, the first UV source may be selected to be UV-C rich, especially in the range of 260nm-200 nm. The second UV source may then be rich in UV-a (e.g. gallium doped lamp) or a different lamp with both UV-a and UV-B high. The use of two UV sources has been found to have advantages such as fast cure speed and high degree of cure.

In a particularly preferred embodiment, UV curing is carried out using UVLEDs emitting at wavelengths longer than 370 nm.

To facilitate curing, inkjet printers often include one or more oxygen depleting units. The oxygen depletion unit places a blanket of nitrogen or other relatively inert gas (e.g., CO2) with an adjustable position and an adjustable inert gas concentration to facilitate reducing the oxygen concentration in the curing environment. Residual oxygen levels are typically maintained as low as 200ppm, but are generally in the range of 200ppm to 1200 ppm.

Base material

There is no practical limitation on the type of substrate on which the liquid UV curable inkjet ink of the present invention is inkjet printed. The substrate may have a ceramic, metal, glass, wood, paper or polymer surface for printing. The substrate may also be primed (e.g., by white ink).

The substrate may be porous, such as textile, paper and cardboard substrates; or a substantially non-absorbent substrate such as a plastic substrate having a polyethylene terephthalate surface.

The substrate may also be pretreated, for example by corona, plasma or flame treatment.

Preferred substrates include surfaces of the following materials: polyethylene, polypropylene, polycarbonate, polyvinyl chloride, polyesters like polyethylene terephthalate (PET), polyethylene naphthalate (PEN) and Polylactide (PLA) and polyimides.

The substrate may also be a paper substrate, such as plain paper or resin coated paper, such as polyethylene or polypropylene coated paper. There is no practical limit to the type of paper, and it includes newsprint paper, magazine paper, office paper, wallpaper, and includes higher grammage paper (commonly referred to as board), such as bleached board linerboard, corrugated board, and packaging board.

The substrate may be transparent, translucent or opaque. Preferred opaque substrates include so-called synthetic papers like Synaps from Agfa-Gevaert^TMGrade, which is a density of 1.10g/cm³Or higher opaque polyethylene terephthalate sheets.

There is no limitation on the shape of the substrate. It may be a flat sheet, such as a paper sheet or a polymer film; or it may be a three-dimensional object like, for example, a plastic coffee cup. The three-dimensional object may also be a container, like a bottle or jerry-can, for containing, for example, oils, shampoos, insecticides (insecticides), pesticides (pesticides), solvents, paint thinners or other types of liquids.

In a preferred embodiment of the inkjet printing method, the substrate is selected from the group consisting of textiles, glass, pharmaceutical products and food packaging.

In a preferred embodiment of the ink jet printing method, the substrate is a rigid medium selected from the group consisting of rigid PVC, cardboard, corrugated paper and wood.

In a preferred embodiment of the ink jet printing process, the substrate is a substrate suitable for use in soft signage applications, such as banners, posters, POP/POS displays, interior wall graphics, trade show displays, parasols, banners, outdoor advertising, and backdrop.

The main advantage of the present liquid UV curable inkjet inks in textile inkjet printing is not only that they can be printed on a wide range of textiles, but also that they have improved feel and feel compared to standard UV curable inkjet inks. The reason is that the layer thickness obtained after printing the liquid UV curable inkjet ink of the present invention is much smaller than the layer thickness obtained using standard UV curable inkjet inks.

Suitable textiles can be prepared from a wide variety of materials. These materials come from four major sources: animals (e.g., wool, silk), plants (e.g., cotton, flax, jute), minerals (e.g., asbestos, fiberglass), and synthetics (e.g., nylon, polyester, acrylic). Depending on the type of material, it may be a woven or non-woven textile.

The textile substrate is preferably selected from the group consisting of cotton textiles, silk textiles, linen textiles, jute textiles, hemp textiles, modal textiles, bamboo textiles, pineapple textiles, basalt textiles, ramie textiles, polyester-based textiles, acrylic-based textiles, glass textiles, aramid textiles, polyurethane textiles (e.g. spandex or Lycra textiles)^TM)、Tyvek^TMAnd mixtures thereof.

Suitable polyester textiles include polyethylene terephthalate textiles, cationic dyeable polyester textiles, acetate textiles, diacetate textiles, triacetate textiles, polylactic acid textiles, and the like.

Applications for these textiles include automotive textiles, canvas, banners, flags, upholstery, apparel, hats, shoes, floor mats, door mats, brushes, mattress pads, mattress covers, liners, sacks, stage curtains, fire retardant and protective fabrics, and the like. Polyester fibers, alone or blended with fibers such as cotton, are used in all types of garments. Aramid fibers, such as teflon (Twaron), are used for flame retardant garments, cut protection, and armor. Acrylic is a fiber used to mimic wool.

The liquid UV curable inkjet inks of the present invention are also very suitable for inkjet printing on leather, especially on natural leather.

Examples

Material

Unless otherwise specified, all materials used in the examples are readily available from standard sources, such as Sigma-Aldrich (belgium) and Acros (belgium).

PV19 is a c.i. pigment violet 19 pigment using Ink Jet Magenta E5B02 from CLARIANT.

PR57 is a C.I. pigment Red 57.1 pigment using Symyler from SUN CHEMICAL^TM Brilliant Carmine 6B350SD。

PY150 is a C.I. pigment yellow 150 pigment using Cromophtal from BASF^TMyellow D1085。

SB550 is a carbon Black pigment, and Special Black from EVONIK (DEGUSSA) was used^TM550。

TIO2 is a titanium dioxide pigment available as Sachtleben RDI-S from SACHTLEBEN.

PB15:4 for Hostaperm^TMShort for Blue P-BFS, c.i. pigment Blue 15:4 pigment from CLARIANT.

E7701 is a polyacrylate dispersant which acts as Efka^TM7701 it is obtained from BASF.

DB162 is Disperbyk, a polymeric dispersant for GMBH available from BYK CHEMIE^TM162, from which a solvent mixture of 2-methoxy-1-methylethyl acetate, xylene and n-butyl acetate is removed. The polymeric dispersant is a polyester-polyurethane dispersant based on caprolactone and toluene diisocyanate having an amine value of 13mg KOH/g, an Mn of about 4,425, and an Mw of about 6,270.

S35000 for SOLSPERSE^TM35000 abbreviated as polyethyleneimine-polyester hyperdispersant from LUBRIZOL.

DPGDA is dipropylene glycol diacrylate as Sartomer^TMSR508 may be obtained from ARKEMA.

PEA is 2-phenoxyethyl acrylate, which acts as Sartomer^TMSR339C is available from ARKEMA.

VEEA is 2- (2' -ethyleneoxyethoxy) ethyl acrylate, a difunctional monomer available from NIPPON shokubali (japan).

MPDA is 3-methyl 1, 5-pentanediol diacrylate as Sartomer^TMSR341 is available from ARKEMA.

(EO)3TMPTA is ethoxylated (EO3) trimethylolpropane triacrylate, as Miramer^TMM3130 is available from RAHN.

CN3755 is an acrylated amine synergist, as Sartomer^TMCN3755 is available from ARKEMA.

C704 is an acrylated polyester adhesion promoter as Sartomer^TMThe CN704 may be obtained from ARKEMA.

EBLEO is a multifunctional acrylated photoinitiator which acts as EBECRYL^TMLEO 10101 is available from ALLNEX.

STABI-1 and STABI-2 are polymerization inhibitor forming mixtures having compositions according to Table 1, wherein DPGDA or PEA is used in order to obtain the desired wt% of multifunctional and monofunctional polymerizable compounds.

TABLE 1

wt% of the components	STABI-1	STABI-2
			PEA	82.4	---
DPGDA	---	82.4
			P-methoxyphenol	---	4.0
2, 6-di-tert-butyl-4-methylphenol	---	10.0
			CupferronTM AL	---	3.6

Cupferron^TMAL is N-nitrosophenylhydroxylamine aluminum from WAKO CHEMICALS LTD.

STABI-3 is 4-hydroxy-2, 2,6, 6-tetramethylpiperidinyloxy sebacate as Irgastab^TMUV10 is available from BASF.

TPO-L is ethyl 2,4, 6-trimethylbenzoylphenylphosphinate as Lucirin^TMTPO-L is available from BASF.

BAPO is a bis (2,4, 6-trimethylbenzoyl) -phenylphosphine oxide photoinitiator, which acts as Irgacure^TM819 available from BASF.

DETX is 2, 4-diethylthioxanthone, which acts as Genocure^TMDETX is available from RAHN.

GAB is a polymeric tertiary amine which acts as Genopol^TMAB-1 is available from RAHN.

Tegorad^TM2100 is a free radical crosslinkable silicone acrylate, available from EVONIK. U.S. Pat. No. 5,2011086221 (3M) describes Tegorad^TM2100 is as follows:

wherein n is 10 to 20 and m is 0.5 to 5.

C7500 is a silicone surfactant, which acts as a COATOSIL^TM7500 is available from MOMENTIVE PERFOMANCE MATERIALS.

UV3510 is Byk^TMUV3510, which is a polyether modified polydimethylsiloxane, supplied by BYK Chemie GmbH.

AXANTH is a polymerizable thioxanthone according to formula (AX-1):

the photoinitiator was synthesized as follows:

step 1: omnipol^TMAminolysis of TX

395gOmnipol to be supplied by IGM^TMTX was dissolved in 1850ml of dimethyl sulfoxide. The reaction mixture was heated to 60 ℃ and 363g (3mol) of tris (hydroxymethyl) aminomethane and 415g (3mol) of potassium carbonate were added. The reaction was allowed to continue at 60 ℃ for 2 hours. The reaction mixture was allowed to cool to room temperature. The precipitated salts were removed by filtration and the reaction mixture was added to a mixture of 1500ml water and 250ml acetone. The intermediate thioxanthone precipitated from the medium was isolated by filtration and dried. The crude thioxanthone was treated with 1500ml of acetone, isolated by filtration and dried. 260g of thioxanthone are isolated (TLC-analysis: RP-C18 (Partisil)^TMKC18F, supplied by Whatman), eluent MeOH/0.5M NaCl, R_f0.55). TLC analysis showed the presence of a small amount of isomeric structure (R)_f0.60). The following are providedThe structure is assigned to this isomer:

further use is made of an intermediate which is a mixture of the major and minor isomers.

Step 2: addition to VEEA:

to 227.8g (1.224mol) of VEEA was added 22g (58mmol) of amido-trihydroxy-thioxanthone. 0.13g (86. mu.l, 1.16mmol) of trifluoroacetic acid and 0.25g (1.16mmol) of BHT were added and the mixture was heated to 77 ℃. The reaction was allowed to continue at 77 ℃ for 16 hours. The reaction was allowed to cool to room temperature and 20g of activated Lewatit M600 MB was added. The mixture was stirred at room temperature for 4 hours. The ion exchanger was removed by filtration. AX-1 was used as a solution in VEEA. (TLC-analysis: RP-C18 (Partisil)^TMKC18F, supplied by Whatman), eluent: MeOH/0.5M NaCl 80/20, R_f0.18). Based on¹H-NMR analysis showed that the solution contained 19% by weight of AX-1.

PET100 is a 100 μm unsized (unsubbed) PET substrate with an antiblocking layer having antistatic properties on the back, available as P100C PLAIN/ABAS from AGFA-GEVAERT.

Measuring method

1. Viscosity of the oil

Use of Rotovisco from HAAKE^TMRV1 viscometer at 25 deg.C or 45 deg.C and 10s^-1Or 1,000s^-1The viscosity of the UV curable inkjet ink was measured at a shear rate of (a).

2. Flexibility

Applying a liquid UV curable inkjet ink to Metamark using a bar coater^TMMD5-100 substrate. The coated samples were fully cured using a Fusion DRSE-120 conveyor equipped with Fusion VPS/I600 lamps (D-bulbs) which conveyed the samples on a conveyor belt under a UV-lamp at a speed of 20 m/min.

Flexibility was determined using a custom-made device for stretching a strip having a length of 8cm and a width of 1cm obtained from the coated sample using a cutter. The belt is installed between the first fixed wall and the second fixed wall and can be horizontally moved by rotating the handle.

The tape was elongated from an original length L1 of 5cm to a length L2 at which time the tape broke. The elongation as a percentage is calculated according to formula (III):

elongation (%) (L2-L1/L1) x100 formula (III).

If no break of the tape was observed at 150% elongation, the flexibility was evaluated as "> 150%". Acceptable flexibility means an elongation of at least 40%.

3. Speed of curing

The liquid UV curable inkjet ink was coated on PET100 substrate using a bar coater and a 10 μm wire bar. The coated samples were cured using a Fusion DRSE-120 conveyor equipped with Fusion VPS/I600 lamps (D-bulbs) on which the samples were transported on a conveyor belt under a UV-lamp at a speed of 20 m/min. The maximum output of the lamp is 1.05J/cm²Peak intensity of 5.6W/cm². The percent maximum output of the lamp was used as a measure of cure speed, with lower values giving higher cure speeds. The sample was considered to be fully cured when no visible damage was caused by scratching with a cotton swab. Table 2 shows the W/cm of D-bulbs for different UV regions measured at different lamp output settings for a ribbon speed of 20m/min using UV Power Puck 8651 from EIT Inc (USA)²Maximum Peak Intensity (MPI) and in J/cm²The metered dose.

TABLE 2

The curing speed should be less than 100%, preferably not more than 95%, since the lamp power decreases with aging. A cure speed of more than 100% means that the coated sample has to be transported more than once under the lamp.

4. Scratch resistance

The liquid UV curable inkjet ink was coated on the PET100 substrate using a bar coater. The coated samples were fully cured using a Fusion DRSE-120 conveyor equipped with Fusion VPS/I600 lamps (D-bulbs) that transported the samples on a conveyor belt under a UV-lamp at a speed of 20 m/min.

The scratch resistance of the coated samples of the liquid UV curable inkjet was determined according to ISO 4586-2:2004(E)/ASTM C1624 using a Rockwell indenter using the following parameters: speed 30 mm/sec; loading: 10-200 mN; the length of the test area is 100 mm; and a tip: diamond r15 μm, 90 °.

The test ran a diamond-topped needle across the ink surface while increasing the pressure (applied) to the needle. The test was started with a pressure of 10mN and then increased to 200 mN. The result of the Rockwell indenter scratch test always reveals the pressure value of the first microscopic crack in the pressure trace of the needle. Thus, the location at which the needle begins to penetrate the ink layer marks the maximum force that can be applied to the layer without scratching it. The evaluation of scratch resistance was made using a microscope according to the scale described in table 3.

TABLE 3

Grading	Evaluation of
		+++	No scratching was observed at 120mN
++	Scratching was observed at 70mN to less than 120mN
		+	Scratching was observed at 60mN to less than 70mN
-	Scratching was observed at 50mN to less than 60mN
		--	Scratching was observed at less than 50mN

5. Optical density

Using Macbeth^TMTR924 densitometer (using a visual filter) measures optical density in reflectance.

5. Average particle size

The particle size of the pigment particles in the pigment dispersion was determined by photon correlation spectroscopy at a wavelength of 633nm using a 4mW HeNe laser on a diluted sample of the pigment dispersion. The particle size analyzer used was a Malvern available from Goffin-Meyvis^TM nano-S。

Samples were prepared by: a drop of the pigment dispersion was added to a cuvette containing 1.5mL of ethyl acetate and mixed until a homogeneous sample was obtained. The measured particle size is the average of 3 consecutive measurements consisting of 6 20 second runs.

6. Dynamic viscosity

Dynamic viscosity was determined using a DHR 2-rheometer from TA Instruments equipped with a 60mm1 ° stainless steel cone. For measurements at specific temperatures, the conditioning step was carried out without pre-shearing. The shear rate is logarithmically increased by 1en 1000s^-1With every ten 5 points.

Example 1

This example illustrates the improvement in scratch resistance and flexibility when using UV curable inkjet inks according to the present invention.

Preparation of pigment Dispersion CYAN1

Pigment dispersion CYAN1 was prepared by mixing the components according to table 4 for 30 minutes using a DISPERLUX disperser from DISPERLUX s.a.r.l. (lucenberg). The dispersion was then milled using a Bachofen DYNOMILL ECM mill filled with 0.4mm yttrium stabilized zirconia beads (a "highly abrasion resistant zirconia milling media" from TOSOH corporation). The mixture was circulated through the mill for 2 hours. After milling, the pigment dispersion was discharged into a container through a 1 μm filter.

TABLE 4

The CYAN pigment dispersion CYAN1 had an average particle size of 124 nm.

Preparation of pigment Dispersion CYAN2

Pigment dispersion CYAN2 was prepared in the same manner as dispersion CYAN1, except that the components according to table 5 were used.

TABLE 5

Components	wt％
		PB15:4	15.0
E7701	15.0
		STABI-2	1.0
DPGDA	69.0

The CYAN pigment dispersion CYAN2 had an average particle size of 119 nm.

Preparation of liquid UV curable inkjet inks

Liquid UV-curable inkjet inks C-1 to C-8 and I-1 to I-4 were prepared by mixing the ink components according to tables 6 and 7. The weight percent (wt%) is based on the total weight of the liquid UV curable inkjet ink. The viscosity of each inkjet ink was measured for the conditions shown in the table.

TABLE 6

TABLE 7

Evaluation and results

The scratch resistance, flexibility and curing speed were determined according to the test methods described above using coatings prepared by a bar coater. When printing inkjet inks with higher pigment concentrations, the ink lay-down for obtaining the same optical density can be reduced. Thus, for a fair comparison, an ink layer from a higher concentration of inkjet ink should be applied in a thinner layer thickness than a lower concentration of inkjet ink. The thickness of the layer applied by the bar coater at room temperature is mainly affected by the viscosity and the type of bar used in the bar coater. The best results for fair comparison were obtained according to table 8.

TABLE 8

The results of scratch resistance, flexibility and curing speed are shown by table 9.

TABLE 9

As is clear from Table 9, the use of the ink-jet inks I-1 to I-4 according to the invention has unexpectedly been found to have an improved compromise between scratch resistance and flexibility. Inkjet inks containing only monofunctional polymerizable compounds or, conversely, only multifunctional polymerizable compounds fail in scratch resistance, fail in flexibility, respectively.

The disadvantage is that the curing speed is clearly somewhat reduced, so it is preferred to limit the pigment concentration to 13.0 wt.% to minimize this effect. It is unclear why the cure speed is reduced even in comparison to the presence of slightly higher amounts of photoinitiator for smaller polymerizable compositions in inkjet inks. One hypothesis is that thinner ink layers are more sensitive to oxygen inhibition by free radical polymerization upon UV curing.

Example 2

This example illustrates the effect of pigment concentration and jetting viscosity on the reliability of an inkjet printing process, more particularly on the tail length of the jetted ink droplets and the number of satellites.

Preparation of liquid UV curable inkjet inks

Liquid UV-curable inkjet ink-1 to ink-5 were prepared by mixing the components according to table 10 using a cyan pigment dispersion of PB15:4 in VEEA or DPGDA containing DB162 or S35000 as a polymeric dispersant. The pigment dispersion was prepared in the same manner as described above for pigment dispersion CYAN 1. By selecting different types and amounts of monomers, and polymeric dispersants and monomers, different viscosities of over 16mpa.s at 45 ℃ are achieved for inkjet inks.

Watch 10

wt% of the components	Ink-1	Ink-2	Ink-3	Ink-4	Ink-5
						PB15:4	2.50	2.50	5.00	8.50	8.60
DB162	2.50	2.50	---	---	8.60
						S35000	---	---	2.50	8.50	---
VEEA	11.48	11.48	---	---	43.45
						DPGDA	---	13.55	23.46	35.61	24.00
MPDA	10.00	---	9.50	9.50	---
						(EO)3TMPTA	42.42	9.50	34.35	12.48	---
TegoradTM 2100	---	15.00	---	---	---
						CN3755	---	---	9.52	9.52	---
TPO-L	---	---	4.76	4.76	6.00
						EBLEO10101	30.00	25.00	---	---	---
GAB	---	---	5.56	5.56	5.00
						AXANTH	---	20.00	---	---	---
BAPO	---	---	2.38	2.38	3.00
						STABI-1	1.00	0.17	0.96	1.18	1.25
STABI-3	---	0.20	---	---	---
						C7500	0.10	0.10	2.00	2.00	0.10

Evaluation and results

Different jetting temperatures are used so that at least two different viscosities are obtained with the same inkjet ink. In 10s^-1Shear rate ofThe viscosity was measured at the temperature shown in Table 11.

Jetting was performed using a through-flow piezoelectric DOD printhead CF1ou from TOSHIBA TEC. The jetting voltage was adjusted so that satellite analysis was performed on all inkjet inks at the same drop rate of 6 m/s.

JetXpert analysis tool using drop-in-flight (drop-in-flight) from ImageXpert^TMThe tail length and the number of satellites were determined for a large number of jetted ink droplets. The average is calculated and rounded to the nearest integer. The results are shown in table 11 and fig. 4.

TABLE 11

As can be seen from Table 11, ink-jet ink-1 and ink-2, which contained a state-of-the-art amount (2.5 wt%) of organic color pigment, also exhibited a large amount of satellites at higher jetting viscosities above 16.0 mPa.s. By comparing UV curable inkjet inks ink-1, ink-2 and ink-5 with comparable jetting viscosities at 49 ℃, it should be clear that increased pigment concentration results in less satellites and thus better image quality. The results have been visualized in fig. 4. At a pigment concentration of 5 wt% in the inkjet ink, no change in the number of satellites was observed. It is believed that from a concentration of 6.0 wt% organic color pigment in the inkjet ink, a clear reduction in the number of satellites is observed with increasing jetting viscosity. The preferred range for jetting viscosity is between 45 ℃ and 65 ℃. Below 45 ℃, the number of satellites remains somewhat higher, whereas above 65 ℃, the reliability of the inkjet printing process is reduced, since unwanted free radical polymerization of the inkjet ink can sometimes be observed at higher temperatures.

Example 3

This example illustrates a UV curable CMYKW inkjet ink set.

Preparation of pigment dispersions

Pigment dispersion for ink Y

By using a substance fromDISPERLUX s.a.r.l. (lucenberg) by DISPERLUX^TMThe disperser mixes the components according to table 12 for 30 minutes to prepare the pigment dispersion. The dispersion was then milled using a Bachofen DYNOMILL ECM mill filled with 0.4mm yttrium stabilized zirconia beads (a "highly abrasion resistant zirconia milling media" from TOSOH corporation). The mixture was circulated through the mill for 2 hours. After milling, the pigment dispersion was discharged into a container through a 1 μm filter.

TABLE 12

Components	wt％
		PY150	18.0
E7701	12.0
		STABI-1	1.0
DPGDA	69.0

Pigment dispersions for inks M

Pigment dispersions were prepared in the same manner as ink Y, except that the components according to table 13 were used.

Watch 13

Pigment dispersions for ink C

Pigment dispersions were prepared in the same manner as ink Y, except that the components according to table 14 were used.

TABLE 14

Components	wt％
		PB15:4	15.0
E7701	10.0
		STABI-1	1.0
VEEA	37.5
		DPGDA	36.5

Pigment dispersion for ink K

Pigment dispersions were prepared in the same manner as ink Y, except that the components according to table 15 were used.

Watch 15

Components	wt％
		SB550	9.1
PB15:4	4.2
		PR57	1.7
E7701	7.5
		STABI-1	1.0
VEEA	29.0
		DPGDA	47.5

Pigment dispersion for ink W

Pigment dispersions were prepared in the same manner as ink Y, except that the components according to table 16 were used.

TABLE 16

Preparation of liquid UV curable inkjet inks

Using the pigment dispersions prepared above, UV-curable CMYKW inkjet ink sets were prepared by mixing the components for the respective liquid UV-curable inkjet inks according to table 17.

TABLE 17

wt% of the components	Ink Y	Ink M	Ink C	Ink K	Ink W
						PY150	8.55	---	---	---	---
PB15:4	---	---	8.57	2.08	---
						PV19	---	8.57	---	---	---
PR57	---	---	---	0.86	---
						SB550	---	---	---	4.56	---
TIO2	---	---	---	---	26.10
						E7701	5.70	5.71	5.71	3.75	---
D162	---	---	---	---	2.10
						DPGDA	33.78	29.00	20.86	34.92	24.00
VEEA	27.75	32.50	36.64	23.75	23.60
						CN3755	9.52	9.52	9.52	9.52	---
C704	---	---	---	---	9.00
						TPO-L	4.76	4.76	4.76	6.00	6.00
GAB	5.56	5.56	5.56	5.56	5.00
						BAPO	2.38	2.38	2.38	3.00	3.00
DETX	---	---	4.00	4.00	---
						UV3510	1.00	1.00	1.00	1.00	---
C7500	---	---	---	---	0.10
						STABI-1	1.00	1.00	1.00	1.00	1.10

Evaluation and results

The results of measuring the dynamic viscosity at 25 ℃, 35 ℃ and 45 ℃ of each liquid UV-curable inkjet ink are shown in table 18.

Watch 18

The average particle size was determined after 1 week at 60 ℃. As can be seen from the results in Table 19, the particle size of the organic pigment remained less than 150 nm. The particle size of the white inkjet ink is larger than 200nm, thereby ensuring good opacity.

Watch 19

Inkjet ink	Average particle size
		Ink Y	144nm
Ink M	140nm
		Ink C	116nm
Ink K	140nm
		Ink W	235nm

Good quality multicolor images were printed with a UV-curable CMYKW inkjet ink set on plasma treated polypropylene substrates at a drop speed of 6m/s using a custom inkjet printer using a through-flow piezoelectric DOD printhead CF1ou from TOSHIBA TEC.

List of reference numerals

Watch 20