阅读说明：本技术 近红外(nir)激光加工 (Near Infrared (NIR) laser processing ) 是由 F.拉兹雷格 J.罗库费尔 J.维尼曼 T.德士美 于 2018-11-30 设计创作，主要内容包括：近红外(NIR)激光加工树脂基制品的方法,其包括在所述制品的表面上施加包含特定光热转换剂的组合物和用NIR激光暴露所施加光热转换剂的至少一部分的步骤。所述特定的光热转换对环境具有改善的稳定性并因此使得激光加工方法更可靠。(A method of Near Infrared (NIR) laser processing a resin-based article comprising the steps of applying a composition comprising a specific light to heat converter on the surface of the article and exposing at least a portion of the applied light to heat converter with a NIR laser. The specific photothermal conversion has improved stability to the environment and thus makes the laser processing method more reliable.)

1. A method of Near Infrared (NIR) laser processing a resin based article, the method comprising the steps of:

-applying a composition comprising a light-to-heat converter on the surface of the resin-based article, and

exposing at least a portion of the applied photothermal conversion agent with a NIR laser,

characterized in that the photothermal conversion agent comprises a NIR absorbing compound having a chemical structure according to formula I,

formula I

Wherein:

x is O or S, and X is O or S,

R₁and R₂Represents the necessary atoms to form a substituted or unsubstituted 5-or 6-membered ring,

R₃and R₅Independently selected from unsubstituted alkyl, unsubstituted alkenyl, unsubstituted alkynyl, unsubstituted aralkyl, unsubstituted alkaryl, and substituted or unsubstituted (hetero) aryl,

R₄selected from the group consisting of hydrogen, unsubstituted alkyl, unsubstituted alkenyl, unsubstituted alkynyl, unsubstituted aralkyl, unsubstituted alkaryl, substituted or unsubstituted (hetero) aryl, halogen, unsubstituted alkoxy, substituted or unsubstituted aryloxy, substituted or unsubstituted heteroaryloxy, ester, amine, amide, nitro, thioalkyl, substituted or unsubstituted thioaryl, substituted or unsubstituted thioheteroaryl, carbamate, urea, sulfonamide, sulfoxide, and sulfone,

with the proviso that all of the hydrocarbon groups in formula I are straight chain hydrocarbon groups.

2. The method of NIR laser processing a resin-based article according to claim 1, wherein the composition comprising the photothermal conversion agent is applied image-wise on the surface of the article.

3. The method of NIR laser processing a resin-based article according to claim 2, wherein the composition comprising the photothermal conversion agent is applied image-wise on the surface of the article by a printing method selected from gravure printing, screen printing, flexographic printing, offset printing, inkjet printing, pad printing, valve jet printing and gravure offset printing.

4. The method of near-infrared (NIR) laser processing resin-based articles according to claim 3, wherein the composition comprising the photothermal conversion agent is applied by inkjet printing.

5. The method of NIR laser processing a resin-based article according to any preceding claim, wherein the application step is followed by a fixing step.

6. The method of NIR laser processing resin-based articles according to claim 5, wherein the fixing step is a UV curing step, a heating step, a drying step or a combination thereof.

7. The method of NIR laser processing a resin-based article according to any preceding claim, wherein the composition comprising the photothermal conversion agent is an inkjet ink.

8. The method of NIR laser processing a resin-based article according to claim 7, wherein the inkjet ink is a UV-curable inkjet ink.

9. The method of NIR laser processing a resin-based article according to any preceding claim, wherein the resin-based article is a foil.

10. The method of NIR laser processing a resin-based article according to claim 9, wherein the foil comprises a thermoplastic polymer selected from polyesters, polyamides and polyolefins.

11. The method of NIR laser processing a resin-based article according to claim 9 or 10, wherein the foil-wrapped package.

12. The method of NIR laser processing a resin-based article according to any preceding claim, wherein laser processing is selected from laser cutting, laser perforation and laser welding.

13. The method of NIR laser processing resin-based articles according to any of the preceding claims, wherein the photothermal conversion agent has a chemical structure according to formula II,

formula II

Wherein:

x is O or S, and X is O or S,

R₈and R₁₀Independently selected from unsubstituted alkyl, unsubstituted alkenyl, unsubstituted alkynyl, unsubstituted aralkyl, unsubstituted alkaryl, and substituted or unsubstituted (hetero) aryl,

R₉selected from the group consisting of hydrogen, unsubstituted alkyl, unsubstituted alkenyl, unsubstituted alkynyl, unsubstituted aralkyl, unsubstituted alkaryl, substituted or unsubstituted (hetero) aryl, halogen, unsubstituted alkoxy, substituted or unsubstituted aryloxy, substituted or unsubstituted heteroaryloxy, ester, amine, amide, nitro, thioalkyl, substituted or unsubstituted thioaryl, substituted or unsubstituted thioheteroaryl, carbamate, urea, sulfonamide, sulfoxide, and sulfone.

14. The method of NIR laser processing a resin-based article according to claim 13, wherein R₉Selected from the group consisting of hydrogen, chloro, bromo, methyl, ethyl, methoxy, ethoxy, n-propoxy, and n-butoxy.

15. A package comprising a laser-machined foil obtained according to the method defined in any one of claims 9 to 11.

Technical Field

The present invention relates to Near Infrared (NIR) laser processing of resin-based articles.

Background

High resolution processing or conversion of resin-based articles is a significant challenge, especially for small size or thin resin-based articles.

Machining (e.g., cutting, drilling, or perforating) often results in undesirable damage to the cut or drilled edges. In the case of small-sized or very thin resin-based articles, machining is often even impossible due to the physical properties of the resins used, which may be sensitive to creep or other irreversible deformation during processing, without unacceptably compromising the end result.

Laser machining is an alternative non-contact method that has several advantages over machining.

However, since many resins do not respond to laser radiation by themselves or only to high power long wavelength lasers such as CO₂Laser response, it is very difficult to control the effect of the laser on the polymer-based article, which leads to similar problems as machining. By using these types of lasers, selective welding of e.g. polymer based components is not possible.

Near Infrared (NIR) lasers have the advantage of much better controllable laser power and higher resolution. However, hardly any polymer will respond to NIR laser light by itself.

In order to make the resin-based article responsive to NIR radiation, a coating may be provided on the article to increase its absorption in the NIR region, as disclosed in US 2012244412.

Usually, only a small part of the surface of the resin-based article has to be laser processed, for example those parts of the surface where perforations have to be introduced or those parts of the surface which have to be connected to each other by laser welding. Therefore, designing a resin-based article having an entire surface responsive to NIR laser is generally not an economical solution.

WO2008/102140 discloses a method wherein an energy absorbing material is applied at selected locations of a polymer film using a printing technique, and wherein laser cutting or perforation is subsequently performed at those selected locations.

WO2008/102140 discloses the use of NIR absorbing cyanine dyes as energy absorbing materials. Such NIR absorbing cyanine dyes have an advantage in that they have a narrow absorption peak in the NIR region, resulting in low absorption in the visible region, i.e., low background color.

A disadvantage of typical NIR absorbing cyanine dyes is often their limited stability to, for example, heat, moisture, UV radiation or oxygen. This may result in a lower sensitivity to laser processing and/or an increased background color after storage of the laser-processable article.

Furthermore, the coating compositions or inks used to apply the NIR absorbing dyes have only very limited shelf life stability due to degradation of these components. In an industrial environment, this variation is unacceptable.

Thus, there is a need for laser processable resin based articles containing NIR absorbing compounds, which have low absorption in the visible region and narrow absorption peaks in the IR region and improved stability to the environment.

Disclosure of Invention

It is an object of the present invention to provide a method of NIR laser processing of resin based articles having improved stability to heat, radiation, moisture or oxygen.

This object is achieved by the method defined in claim 1.

It has been found that by using a specific cyanine compound as a photothermal conversion agent, a more stable laser-processable resin-based article can be obtained.

Other objects of the present invention will become apparent from the following description.

Detailed Description

Definition of

Unless otherwise indicated, the term "alkyl" refers to all possible variations of 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-dimethyl-propyl, and 2-methyl-butyl, and the like.

Unless otherwise specified, substituted or unsubstituted alkyl is preferably C₁To C₆An alkyl group.

Unless otherwise specified, substituted or unsubstituted alkenyl is preferably C₂To C₆An alkenyl group.

Unless otherwise indicated, substituted or unsubstitutedAlkynyl of (C) is preferably C₂To C₆Alkynyl.

Unless otherwise specified, a substituted or unsubstituted aralkyl group preferably contains one, two, three or more C₁To C₆Alkyl phenyl or naphthyl.

Unless otherwise specified, a substituted or unsubstituted alkaryl group is preferably a C comprising a phenyl or naphthyl group₇To C₂₀An 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.

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

Unless otherwise indicated, substituted alkyl, substituted alkenyl, substituted alkynyl, substituted aralkyl, substituted alkaryl, substituted aryl and substituted heteroaryl groups are preferably substituted with one or more substituents selected from: 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。

Method of Near Infrared (NIR) laser processing resin-based articles

A method of NIR processing of a resin-based article comprises the steps of:

-applying on the surface of the article a composition comprising a light-to-heat converter as described below, and

-exposing at least a portion of the applied photothermal conversion agent with a NIR laser.

As used herein, laser processing of a resin-based article refers to any laser-induced process that results in a physical or chemical change in the resin of the resin-based article.

Examples of laser processing are laser welding, laser hybrid welding, laser drilling, laser perforation, laser cutting, laser riveting, laser cladding, laser alloying, laser engraving, laser ablation, laser cleaning, laser induced surface modification, laser sintering. The laser processing is preferably laser welding, laser perforation and laser cutting, and more preferably laser perforation.

As used herein, Near Infrared (NIR) radiation refers to infrared radiation having a wavelength between 780 and 2000 nm.

According to one embodiment, the photothermal conversion agent is applied over the entire surface of the resin-based article. In this case, the photothermal conversion agent may be applied to the resin-based article by any conventional coating technique such as dip coating, blade coating, extrusion coating, spin coating, spray coating, slide hopper coating, and curtain coating.

However, in a preferred embodiment, the method of laser processing a resin-based article comprises the steps of: (a) imagewise applying a light-to-heat converting agent on a surface of a resin-based article, and (b) exposing at least a portion of the applied light-to-heat converting agent to a NIR laser.

The photothermal conversion agent may be applied imagewise on the surface of the resin-based article by any printing method (e.g., gravure printing, screen printing, flexographic printing, offset printing, ink jet printing, pad printing, valve jet printing, gravure offset printing, etc.).

In a preferred embodiment, ink jet printing is used.

Optionally, after the photothermal conversion agent is applied on the surface of the resin-based article, a fixing step may be applied. Such a fixing step may include a heating step, a UV curing step, or a combination thereof.

The heating step is preferably carried out at a temperature between 40 ℃ and 200 ℃, more preferably between 50 ℃ and 150 ℃. The heating step may also be carried out at a temperature below 100 ℃.

The fixing step may also be accomplished by drying, for example, by directing a gas stream over the applied photothermal conversion agent. Such drying may be carried out at ambient temperature, for example below 40 ℃, more preferably below 30 ℃.

The pattern obtained by imagewise applying the photothermal conversion agent may comprise a continuous line, a series of dots, or a combination thereof.

The emission wavelength of the NIR laser is between 780 and 2000 nm, preferably between 930 and 1150 nm. A particularly preferred NIR laser is an NdYAG laser emitting at about 1064 nm.

Photothermal conversion agent

As used herein, a photothermal conversion agent refers to a compound or particle capable of absorbing radiation, preferably in the range of 780 to 2000 nm, and converting it into heat.

The photothermal conversion agent includes a NIR absorbing compound having a chemical structure according to formula I,

formula I

Wherein:

x is O or S, and X is O or S,

R₁and R₂Represents the necessary atoms to form a substituted or unsubstituted 5-or 6-membered ring,

R₃and R₅Independently selected from unsubstituted alkyl, unsubstituted alkenyl, unsubstituted alkynyl, unsubstituted aralkyl, unsubstituted alkaryl, and substituted or unsubstituted (hetero) aryl,

R₄selected from the group consisting of hydrogen, unsubstituted alkyl, unsubstituted alkenyl, unsubstituted alkynyl, unsubstituted aralkyl, unsubstituted alkaryl, substituted or unsubstituted (hetero) aryl, halogen, unsubstituted alkoxy, substituted or unsubstituted aryloxy, substituted or unsubstituted heteroaryloxy, ester, amine, amide, nitro, thioalkyl, substituted or unsubstituted thioaryl, substituted or unsubstituted thioheteroaryl, carbamate, urea, sulfonamide, sulfoxide, and sulfone,

with the proviso that all of the hydrocarbon groups in formula I are straight chain hydrocarbon groups.

As used herein, linear hydrocarbyl refers to linear hydrocarbyl groups that are not further functionalized with hydrocarbon substituents.

As used herein, hydrocarbyl refers to a functional group consisting of only carbon atoms in the backbone or ring.

The hydrocarbyl group is preferably selected from alkyl, alkenyl, alkynyl and aralkyl groups.

In a preferred embodiment, R₃And R₅Independently selected from unsubstituted alkyl, unsubstituted alkaryl and unsubstituted (hetero) aryl.

In a more preferred embodiment, R₃And R₅Independently selected from the group consisting of unsubstituted lower alkyl groups containing no more than six carbon atoms and unsubstituted alkaryl groups.

In a particularly preferred embodiment, R₃And R₅Independently selected from methyl, ethyl, n-propyl, n-butyl, benzyl and aryl.

In all of the above embodiments, R₄Preferably selected from the group consisting of hydrogen, halogen, linear unsubstituted alkyl and linear unsubstituted alkoxy.

In all of these embodiments, R₄More preferably selected from hydrogen, chlorine, bromine, methyl, ethyl, methoxy, ethoxy, n-propoxy and n-butoxy.

The NIR absorbing compound preferably has a chemical structure according to formula II,

formula II

Wherein:

x is O or S, and X is O or S,

R₈and R₁₀Independently selected from unsubstituted alkyl, unsubstituted alkenyl, unsubstituted alkynyl, unsubstituted aralkyl, unsubstituted alkaryl, and substituted or unsubstituted (hetero) aryl,

R₉selected from the group consisting of hydrogen, unsubstituted alkyl, unsubstituted alkenyl, unsubstituted alkynyl, unsubstituted aralkyl, unsubstituted alkaryl, substituted or unsubstituted (hetero) aryl, halogen, unsubstitutedSubstituted or unsubstituted aryloxy, substituted or unsubstituted heteroaryloxy, ester, amine, amide, nitro, thioalkyl, substituted or unsubstituted thioaryl, substituted or unsubstituted thioheteroaryl, carbamate, urea, sulfonamide, sulfoxide, and sulfone.

In a particularly preferred embodiment, R₉Selected from the group consisting of hydrogen, chloro, bromo, methyl, ethyl, methoxy, ethoxy, n-propoxy, and n-butoxy.

Specific examples of NIR absorbing compounds according to the present invention are given in table 1, but not limited thereto.

TABLE 1

Other photothermal conversion compounds may be used in combination with the above-mentioned NIR absorbing compounds, such as infrared absorbing pigments or dyes as disclosed in WO2016/184881(Agfa Gevaert) paragraphs [042] to [058 ].

The amount of the photothermal conversion agent is preferably at least 10^-10g/m²More preferably from 0.0001 to 0.5 g/m²Between 0.001 and 0.2 g/m, most preferably²In the meantime.

Resin-based article

A resin-based article is defined as an article having a continuous phase of synthetic, semi-synthetic or natural polymeric material.

Any resin-based article may be used. The resin-based article is preferably a (film) or foil. The film or foil may be opaque or transparent.

The thickness of the foil is preferably less than 500 μm, more preferably less than 250 μm, most preferably less than 100 μm.

Synthetic resins are defined as resins that require at least one polymerization step in the manufacture of the resin. Typical examples are poly (olefins) (e.g. high density Polyethylene (PE), low density PE, polypropylene (PP)), polyesters, poly (amides), poly (urethanes), poly (acetals), poly (ethers) or combinations thereof.

Semi-synthetic resins are defined as resins made from natural polymers such as cellulose which are converted to the final resin by at least one synthetic chemical modification step such as esterification or alkylation. Typical examples are Cellulose Acetate Butyrate (CAB), cellulose triacetate, nitrocellulose, carboxymethylcellulose or phthaloyl gelatin.

Natural resins are defined as resins that are extracted from natural resources and are not further modified by synthetic chemical steps. Typical examples are dextran, pullulan and the like.

Particularly preferred are synthetic resins and semi-synthetic resins, and most preferred are synthetic resins. Poly (esters), poly (amides), and poly (olefins) are particularly preferred, with poly (olefins) being most preferred.

Preferably, the resin-based article is a thermoplastic polymer film or foil.

Examples of thermoplastic polymers include polyolefins such as Polyethylene (PE), polypropylene (PP), polyesters such as polyethylene terephthalate (PET), polyethylene 2, 5-difuranate (PEF) and polyethylene naphthalate (PEN), polylactic acid (P L A), Polyacrylonitrile (PAN), Polyamides (PA), Polyurethanes (PU), polyacetals such as polyvinyl butyral, polymethyl methacrylate (PMMA), Polyimides (PI), Polystyrene (PS), Polycarbonate (PC), acrylonitrile-butadiene-styrene (ABS), polyvinyl chloride (PVC), and copolymers thereof.

Preferred thermoplastic polymers are Polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET) and polyethylene-2, 5-furandicarboxylate (PEF).

Since bio-based furan dicarboxylic acid (FDCA) can be used to produce PEF, the carbon footprint of its manufacturing process is much smaller compared to the production of, for example, PET. Furthermore, it is, for example, directed to O₂And CO₂May be better.

Laser cutting-perforating

Laser cutting is commonly applied to different kinds of materials, where complex profiles require precise, fast and force-free machining.

The laser can produce a narrow cut and thus can achieve a high precision cut. Laser cutting does not generally show any deformation and in many cases, post-treatment is not necessary since the component is subjected to only little heat input and can be virtually slagless.

Laser cutting has been cost effective for small volume production compared to alternative techniques such as die cutting. The great benefit of laser cutting is that the localized laser energy input provides a small focal diameter, small kerf width, high feed rate, and minimal heat input.

The laser is particularly suitable for perforating paper or plastic foil. Typically, the web material is processed at high speeds of up to 700m/min at the winder system.

Using a laser, a perforation aperture in the range of 50-400 microns can be achieved. High precision laser systems can achieve perforation speeds of up to 420,000 holes per second.

In a preferred embodiment, the photothermal conversion agent is applied on a cut or perforated line of a resin-based article (e.g., a polymeric film or foil).

The cutting or perforation is then performed by exposing at least a portion of the applied photothermal conversion agent with a NIR laser.

Laser perforation may be used for packaging films. For example, in food packaging films to extend the freshness and quality of perishable food products. Micro-perforation will increase the shelf life of vegetables etc. by exchanging oxygen through micro-pores in the range of 60-100 μm.

Perforations in the polymeric foil of the wrap-around package may facilitate removal of the wrapped foil. It may be advantageous to introduce perforations in the foil when the foil has wrapped the package. In this case it is important that the laser perforation does not damage the package, e.g. a cardboard package.

The use of a photothermal conversion agent to improve the NIR response of the polymeric foil makes it possible to use a low power NIR laser to perforate the foil and thus increase the yield.

It may also be advantageous to apply the photothermal conversion agent on the wrapped polymer foil, preferably by inkjet. This will allow the perforation line to be adjusted later in the packaging process.

Laser welding

Laser beam welding (L BW) is a welding technique used to join portions of material by using a laser.

Laser beam welding is commonly used to join components that need to be joined at high welding speeds, thin and small welds, and low thermal distortion. The high welding speed, excellent automation and the possibility of controlling the quality on-line during the process make laser welding a common joining method in modern industrial production.

Laser welding of plastics involves bonding thermoplastics under heat and pressure. The bonded surfaces must be in a thermoplastic state.

Laser welding of plastics is only available for fusible polymers; in general, all amorphous and semi-crystalline thermoplastics and thermoplastic elastomers can be used. On the other hand, elastomers and thermosets are not suitable for laser welding. The temperature at which the resin is exposed must be above the melting temperature of the material, but below the degradation temperature. Therefore, local heat generation in the weld is desired to avoid degradation (carbonization).

The melting temperature regions of the plastic parts to be bonded should overlap and the melts should be compatible with one another.

During the laser welding process of two plastic materials, the spacing between the two (bridging gap) is typically less than 100 μm. One plastic material is typically a laser transparent thermoplastic selected according to the laser wavelength, which material heats up little, if any, as the laser beam passes through it.

For the weld seam to be produced, another plastic material must absorb the laser radiation, for example by applying photothermal conversion on the surface. When this plastic material absorbs enough energy, it will start to melt and transfer its energy to another plastic material. In order that energy may actually be transmitted to each other, the separation between the two is typically less than 100 μm. During the laser welding process, the two materials are pressed together; otherwise, a strong bond (welding) cannot be guaranteed despite the application of energy. The pressure required to join the plastic parts should be applied as close to the weld as possible; only then does the externally applied compaction pressure blend the melt and weld the plastic parts to each other.

Composition comprising photothermal conversion agent

The composition comprising the photothermal conversion agent may be optimized for the application method.

In embodiments where the entire surface of the resin-based article is applied with the light-to-heat converter, the composition may be considered a coating solution, which may be optimized for the coating technique used.

In other embodiments where the photothermal conversion agent is applied imagewise, the composition may be considered an ink, which may be optimized for the printing technique used.

The photothermal conversion agent is preferably applied as an ink to the polymer-based article. The ink is preferably an inkjet ink. The ink may contain a binder, a surfactant, a solvent, and the like in addition to the photothermal conversion agent.

The inks may be solvent borne, water borne or UV curable. The ink is preferably a UV curable inkjet ink. UV curable inkjet inks can be used on non-absorbing resins. In addition, the application (printing and curing) of UV-curable inks on resins can be carried out at high speeds.

It has been observed that the absorption properties of the photothermal conversion agent according to the present invention do not substantially change during UV curing of the applied ink, contrary to the absorption properties of conventional NIR absorbing compounds, resulting in more stable laser processing results.

UV-curable inks typically comprise at least one photoinitiator and at least one polymerizable compound. The UV-curable ink may further comprise a polymeric dispersant, a polymerization inhibitor, or a surfactant.

To obtain reliable industrial inkjet printing, the viscosity of the UV curable inkjet ink is preferably not more than 20 mpa.s at 45 ℃, more preferably between 1 and 18 mpa.s at 45 ℃, and most preferably between 4 and 14 mpa.s at 45 ℃.

In order to obtain good image quality and adhesion, the surface tension of the radiation curable inkjet ink is preferably in the range of 18 to 70 mN/m at 25 ℃, more preferably in the range of 20 to 40 mN/m at 25 ℃.