阅读说明：本技术 改善以平顶网点为特征的柔性版印刷板光稳定性的方法 (Method for improving light stability of flexible plate printing plate using flat top lattice point as characteristic ) 是由 乔艾布·布卡夫塔内 埃里克·李 于 2018-04-02 设计创作，主要内容包括：本发明提供了一种可光致固化的凸纹图像印刷坯料,包括：(a)支撑层；(b)设置在支撑层上的一个或多个可光致固化的层,其中一个或多个可光致固化的层包括：i)粘结剂；ii)一个或多个单体；iii)α-氨基酮光引发剂；以及任选地,iv)添加剂,该添加剂选自由以下项构成的组：亚磷酸盐、膦、硫醚胺化合物,以及上述物质中的一者或多者的组合；(c)设置在一个或多个可光致固化的层上的可激光烧蚀的掩模层,该可激光烧蚀的掩模层包括辐射不可透过的材料；以及(d)任选地,可移除的覆盖片材。在曝光和显影后,如果将所得凸纹图像印刷元件保持在环境光下一段较长的时间,其不会降解。(A photocurable relief image printing blank is provided comprising (a) a support layer, (b) one or more photocurable layers disposed on the support layer, wherein the one or more photocurable layers comprise i) a binder, ii) one or more monomers, iii) α -aminoketone photoinitiator, and optionally, iv) an additive selected from the group consisting of phosphites, phosphines, thioether amine compounds, and combinations of one or more of the foregoing, (c) a laser-ablatable mask layer disposed on the one or more photocurable layers, the laser-ablatable mask layer comprising a radiation-opaque material, and (d) optionally, a removable cover sheet that, after exposure and development, does not degrade if the resulting relief image printing element is maintained in ambient light for an extended period of time.)

1. A photocurable printing blank comprising:

a) a support layer;

b) one or more photocurable layers disposed on the support layer, wherein the one or more photocurable layers comprise:

i) a binder;

ii) one or more monomers;

iii) α -aminoketone photoinitiator, and optionally

iv) an additive selected from the group consisting of: phosphites, phosphines, thioether amine compounds, and combinations of one or more of the foregoing;

c) a laser ablatable mask layer disposed on the one or more photocurable layers, the laser ablatable mask layer comprising a radiopaque material; and

d) optionally, a removable cover sheet.

2. The photocurable printing blank of claim 1, wherein the photocurable layer comprises an additive comprising tris (nonylphenyl) phosphite.

3. The photocurable printing blank of claim 1, wherein the photocurable layer comprises an additive comprising a thioether amine compound selected from the group consisting of: 2, 6-di-tert-butyl-4- (4, 6-bis (octylsulfanyl) -1,3, 5-triazin-2-ylamino) phenol, 4- [ [4, 6-bis (nonylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-bis (octadecylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-octylsulfanyl ] -1,3, 5-triazin-2-yl ] amino ] -2, 6-bis (2-methylnonyl-2-yl) phenol, 4- [ [4, 6-bis (hexylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-bis (heptylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-bis (octylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2-tert-butyl-6-m-ethylphenol, 4- [ [4, 6-bis (ethylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-bis (2,4, 4-trimethylpentan-2-ylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-bis (2-octylsulfanylethylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-bis (octylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-dibutylphenol, 4- [ [4, 6-bis (octylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-dimethylphenol, 2, 6-di-tert-butyl-4- [ [4- (3, 5-di-tert-butyl-4-hydroxyanilino) -6] -octylsulfonyl-1, 3, 5-triazin-2-yl ] amino ] phenol, 4- [ [4, 6-bis (pentylsulfanyl) -1,3, 5-triazin-2-yl ] amino-2, 6-dimethylphenol, 4- [ [4, 6-bis (hexylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2-tert-butylphenol, 2, 6-di-tert-butyl-4- [ (4-octylsulfanyl-1, 3, 5-triazin-2-yl) amino ] phenol, 4- [ [4, 6-bis (ethylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-dimethylphenol, 4- [ [4, 6-bis (octylsulfanyl) -1,3, 5-triazin-2-yl ] -butylamino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-bis (octylsulfanyl) -1,3, 5-triazin-2-yl ] -cyclohexylamino ] -2, 6-di-tert-butylphenol, 2- [ [4, 6-bis (octylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -6-tert-butylphenol, 2-tert-butyl-6-methyl-4- [ [ 4-octylsulfanyl-6- [ (2,2,6, 6-tetramethylpiperidin-4-yl) amino ] -1,3, 5-triazin-2-yl ] amino ] phenol, 4- [ [4, 6-bis (octylsulfanylmethyl) -1,3, 5-triazin-2-yl) amino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-bis (octylsulfanyl) -1,3, 5-triazin-2-yl) methylamino ] -2, 6-di-tert-butylphenol, 4- [ (4-amino-6-chloro-1, 3, 5-triazin-2-yl) amino ] -2, 6-di-tert-butylphenol and 4- [ (4-cyclohexyl-6-cyclohexylsulfanyl-1, 3, 5-triazin-2-yl) amino ] -2, 6-di (propan-2-yl) phenol.

4. The photocurable printing blank of claim 3, wherein the additive comprises 2, 6-di-tert-butyl-4- (4, 6-bis (octylthio) -1,3, 5-triazin-2-ylamino) phenol.

5. The photocurable printing blank of claim 1, wherein the photocurable layer comprises an additive comprising a phosphine selected from the group consisting of: triphenylphosphine, tri-p-tolylphosphine, benzhydrylphosphine, phenethylphosphine, diphenylpropylphosphine, dimethylphenylphosphine, diethylphenylphosphine, dipropylphenylphosphine, divinylphenylphosphine, divinyl-p-methoxyphenyl phosphine, divinyl-p-bromophenylphosphine, divinyl-p-tolylphosphine, diallylphenylphosphine, divinyl-p-bromophenylphosphine, diallyl-p-tolylphosphine, and combinations of one or more of the foregoing.

6. The photocurable printing blank of claim 1, comprising a material selected from the group consisting of: a photoinitiator containing an amine moiety, an amine acrylate, an amine reaction promoter, and a combination of one or more of the foregoing.

7. The photocurable printing blank of claim 6, comprising an aminoacetophenone initiator.

8. The photocurable printing blank of claim 7, wherein the aminoacetophenone photoinitiator is dimethylamine-2- (4-methyl-benzyl) -1- (4-morpholin-4-yl-phenyl) -butan-1-one.

9. The photocurable printing blank of claim 6, wherein the material is present in the at least one photocurable layer in an amount between about 0.1% and about 10% by weight based on the total weight of the photocurable composition.

10. The photocurable printing blank of claim 1, wherein the at least one photocurable layer further comprises one or more compounds selected from the group consisting of: plasticizers, antiozonants, fillers, reinforcing agents, ultraviolet absorbers, and combinations of one or more of the foregoing.

11. The photocurable printing blank according to claim 1, wherein the at least one photocurable layer does not comprise butylated hydroxytoluene, 2, 4-bis (octylthio) -6- (4-hydroxy-3, 5-di-tert-butylanilino) -1,3, 5-triazine, or 1,3, 5-trimethyl-2, 4, 6-tris (3, 5-di-tert-butyl-4-hydroxybenzyl) benzene.

12. The photocurable printing blank of claim 10, wherein the one or more compounds comprise a plasticizer.

13. A method of producing a relief pattern printing element from a photocurable printing blank, the method comprising the steps of:

a) providing a photocurable printing blank, the photocurable printing blank comprising:

i) a backing or support layer;

ii) one or more photocurable layers disposed on the backing or support layer,

wherein the one or more photocurable layers comprise:

1) a binder;

2) one or more monomers;

3) α -aminoketone photoinitiator, and optionally

4) An additive selected from the group consisting of: phosphites, phosphines, thioether amine compounds, and combinations of one or more of the foregoing; and

iii) a laser ablatable mask layer disposed on the at least one photocurable layer, the laser ablatable mask layer comprising a radiopaque material;

b) selectively ablating the laser ablatable mask laser to produce an in situ negative of a desired image in the laser ablatable mask layer;

c) exposing the at least one photocurable layer to actinic radiation to selectively crosslink and cure portions of the at least one photocurable layer through the in situ negative; and

d) developing the exposed at least one photocurable layer of the photocurable printing blank to reveal the relief pattern therein, the relief pattern comprising a plurality of relief printing dots.

14. The method of claim 13, wherein the photocurable layer comprises an additive comprising tris (nonylphenyl) phosphite.

15. The method of claim 13, wherein the photocurable layer comprises an additive comprising a thioether amine compound selected from the group consisting of: 2, 6-di-tert-butyl-4- (4, 6-bis (octylsulfanyl) -1,3, 5-triazin-2-ylamino) phenol, 4- [ [4, 6-bis (nonylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-bis (octadecylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-octylsulfanyl ] -1,3, 5-triazin-2-yl ] amino ] -2, 6-bis (2-methylnonyl-2-yl) phenol, 4- [ [4, 6-bis (hexylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-bis (heptylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-bis (octylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2-tert-butyl-6-m-ethylphenol, 4- [ [4, 6-bis (ethylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-bis (2,4, 4-trimethylpentan-2-ylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-bis (2-octylsulfanylethylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-bis (octylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-dibutylphenol, 4- [ [4, 6-bis (octylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-dimethylphenol, 2, 6-di-tert-butyl-4- [ [4- (3, 5-di-tert-butyl-4-hydroxyanilino) -6] -octylsulfonyl-1, 3, 5-triazin-2-yl ] amino ] phenol, 4- [ [4, 6-bis (pentylsulfanyl) -1,3, 5-triazin-2-yl ] amino-2, 6-dimethylphenol, 4- [ [4, 6-bis (hexylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2-tert-butylphenol, 2, 6-di-tert-butyl-4- [ (4-octylsulfanyl-1, 3, 5-triazin-2-yl) amino ] phenol, 4- [ [4, 6-bis (ethylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-dimethylphenol, 4- [ [4, 6-bis (octylsulfanyl) -1,3, 5-triazin-2-yl ] -butylamino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-bis (octylsulfanyl) -1,3, 5-triazin-2-yl ] -cyclohexylamino ] -2, 6-di-tert-butylphenol, 2- [ [4, 6-bis (octylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -6-tert-butylphenol, 2-tert-butyl-6-methyl-4- [ [ 4-octylsulfanyl-6- [ (2,2,6, 6-tetramethylpiperidin-4-yl) amino ] -1,3, 5-triazin-2-yl ] amino ] phenol, 4- [ [4, 6-bis (octylsulfanylmethyl) -1,3, 5-triazin-2-yl) amino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-bis (octylsulfanyl) -1,3, 5-triazin-2-yl) methylamino ] -2, 6-di-tert-butylphenol, 4- [ (4-amino-6-chloro-1, 3, 5-triazin-2-yl) amino ] -2, 6-di-tert-butylphenol and 4- [ (4-cyclohexyl-6-cyclohexylsulfanyl-1, 3, 5-triazin-2-yl) amino ] -2, 6-di (propan-2-yl) phenol.

16. The method of claim 15, wherein the additive comprises 2, 6-di-tert-butyl-4- (4, 6-bis (octylthio) -1,3, 5-triazin-2-ylamino) phenol.

17. The method of claim 13, wherein the photocurable layer comprises an additive comprising a phosphine selected from the group consisting of: triphenylphosphine, tri-p-tolylphosphine, benzhydrylphosphine, phenethylphosphine, diphenylpropylphosphine, dimethylphenylphosphine, diethylphenylphosphine, dipropylphenylphosphine, divinylphenylphosphine, divinyl-p-methoxyphenyl phosphine, divinyl-p-bromophenylphosphine, divinyl-p-tolylphosphine, diallylphenylphosphine, divinyl-p-bromophenylphosphine, diallyl-p-tolylphosphine, and combinations of one or more of the foregoing.

18. The method of claim 13, the photocurable printing blank comprising a material selected from the group consisting of: a photoinitiator containing an amine moiety, an amine acrylate, an amine reaction promoter, and a combination of one or more of the foregoing.

19. The process of claim 18 comprising an aminoacetophenone initiator.

20. The process of claim 19 wherein the aminoacetophenone initiator is dimethylamine-2- (4-methyl-benzyl) -1- (4-morpholin-4-yl-phenyl) -butan-1-one.

21. The method of claim 18, wherein the material is present in the at least one photocurable layer in an amount between about 0.1% and about 10% by weight based on the total weight of the photocurable composition.

22. The method of claim 13, wherein the at least one photocurable layer further comprises one or more compounds selected from the group consisting of: plasticizers, antiozonants, fillers, reinforcing agents, ultraviolet absorbers, and combinations of one or more of the foregoing.

23. The method of claim 13, wherein the at least one photocurable layer does not comprise butylated hydroxytoluene, 2, 4-bis (octylthio) -6- (4-hydroxy-3, 5-di-tert-butylanilino) -1,3, 5-triazine, or 1,3, 5-trimethyl-2, 4, 6-tris (3, 5-di-tert-butyl-4-hydroxybenzyl) benzene.

Technical Field

The present invention generally relates to digital relief image printing elements having improved storage stability and lightfastness.

Background

Flexography is a printing process that is commonly used for high volume runs. Flexographic printing is employed to print on a variety of substrates such as paper, paperboard stock, corrugated board, films, foils, and laminates. Newspapers and grocery bags are prominent examples. Rough surfaces and stretch films can only be economically printed by flexographic printing.

Flexographic printing plates are relief plates with image elements raised above the open areas. Generally, the plate is somewhat flexible and flexible enough to wrap around the print cylinder and durable enough to be able to print over a million parts. Such plates offer a number of advantages to the printer, primarily based on their durability and their ease of fabrication. A typical flexographic printing plate delivered by its manufacturer is a multilayer article made from, in order: a backing or support layer; one or more unexposed photocurable layers; optionally a protective layer or slip film; and is typically a protective cover sheet.

The support (or backing) layer provides support for the panel. The support layer may be formed of a transparent or opaque material such as paper, cellulose film, plastic, or metal. Preferred materials include sheets made from synthetic polymeric materials such as polyesters, polystyrenes, polyolefins, polyamides, and the like. One widely used support layer is a flexible film of polyethylene terephthalate.

The photocurable layer may include any known polymers, monomers, initiators, reactive and/or non-reactive diluents, fillers, and dyes. As used herein, the term "photocurable" refers to a composition that undergoes polymerization, cross-linking, or any other curing or hardening reaction in response to actinic radiation with the result that the unexposed portions of the material can be selectively separated and removed from the exposed (cured) portions to form a three-dimensional relief pattern of cured material. Exemplary photocurable materials are disclosed in european patent application nos. 0456336 a2 and 0640878 a1 to Goss et al, british patent No. 1,366,769, U.S. patent No. 5,223,375 to Berrier et al, U.S. patent No. 3,867,153 to MacLahan, U.S. patent No. 4,264,705 to Allen, U.S. patent nos. 4,323,636, 4,323,637, 4,369,246 and 4,423,135 to Chen et al, U.S. patent No. 3,265,765 to Holden et al, U.S. patent No. 4,320,188 to Heinz et al, U.S. patent No. 4,427,759 to Gruetzmacher et al, U.S. patent No. 4,622,088 to Min, and U.S. patent No. 5,135,827 to Bohm et al, the subject matter of each of which is incorporated herein by reference in its entirety. More than one photocurable layer may also be used.

Photocurable materials typically crosslink (cure) and harden by free radical polymerization in at least some actinic wavelength region. As used herein, "actinic radiation" refers to radiation capable of polymerizing, crosslinking, or curing the photocurable layer. Actinic radiation includes, for example, amplified (e.g., laser) and non-amplified light, particularly in the Ultraviolet (UV) and violet wavelength ranges.

The slip film is a thin layer that protects the photopolymer from dust and makes it easier to handle. In a conventional ("analog") sheet making process, the slip film is transparent to ultraviolet light, and the printer peels the cover sheet off the printing plate blank and places a negative on top of the slip film layer. The plate and negative are then subjected to a blanket exposure of ultraviolet light through the negative. The areas exposed to light cure or harden and the unexposed areas are removed (developed) to produce the relief image on the printing plate.

In the "digital" or "direct to plate" approach, a laser is guided by an image stored in an electronic data file and is used to create an in situ negative in a digital (i.e., laser ablatable) masking layer, which is typically a slip film that has been modified to include a radiation opaque material. Portions of the laser ablatable layer are then ablated by exposing the mask layer to laser radiation at a selected wavelength and power of the laser. Examples of laser ablatable layers are disclosed, for example, in U.S. Pat. Nos. 5,925,500 to Yang et al, and 5,262,275 and 6,238,837 to Fan, the subject matter of each of which is incorporated herein by reference in its entirety.

The processing steps used to form the relief image printing element typically include the steps of:

1) image generation, which can be mask ablation of digital "computer to plate" printing plates or negative production of conventional analog plates;

2) back-exposing to form a floor layer in the photocurable layer and to establish a relief depth;

3) front side exposure through a mask (or negative) to selectively cross-link and cure portions of the photocurable layer not covered by the mask, thereby creating a relief pattern,

4) development to remove unexposed photopolymer by solvent (including water) or thermal development;

and

5) post-exposure and detackification are carried out if necessary.

A removable cover sheet is also preferably provided to protect the photocurable printing element from damage during shipping and handling. Prior to processing the printing element, the cover sheet is removed and the photosensitive surface is imagewise exposed to actinic radiation. Upon imagewise exposure to actinic radiation, polymerization occurs in the exposed areas, whereby the insolubility of the photopolymerizable layer occurs. Treatment with a suitable developer solvent (or alternatively, thermal development) removes the unexposed areas of the photopolymerizable layer, leaving a printing relief that can be used for flexographic printing.

As used herein, "back exposure" refers to exposure of the photopolymerizable layer to a blanket of actinic radiation on the side opposite the side that does or ultimately will bear the relief. This step is typically accomplished by a transparent support layer and is used to form a shallow layer of photocurable material, i.e., a "floor," on the support side of the photocurable layer. The purpose of the cliche is generally to sensitize the photocurable layer and determine the relief depth.

After a brief back exposure step (i.e., brief as compared to the subsequent imagewise exposure step), imagewise exposure is carried out using a digitally imaged mask or photographic negative mask which is in contact with the photocurable layer and through which the actinic radiation is directed.

The type of radiation used depends on the type of photoinitiator in the photopolymerizable layer. The digitally imaged mask or photographic negative prevents the underlying material from being exposed to actinic radiation so that those areas covered by the mask do not polymerize, while areas not covered by the mask are exposed to actinic radiation and polymerize. Any conventional source of actinic radiation can be used for this exposure step, including, for example, carbon arcs, mercury vapor arcs, fluorescent lamps, electron flash units, electron beam units, LEDs, and photographic flood lamps.

After imaging, the photosensitive printing element is developed to remove unpolymerized portions of the layer of photocurable material and to display a crosslinked relief image in the cured photosensitive printing element. Typical development methods include washing with various solvents or water, usually with a brush. Other development possibilities include the use of an air knife or thermal development, which typically uses heat plus a blotting material. The resulting surface has a relief pattern that typically includes a plurality of dots that reproduce the image to be printed. After the relief image is formed, the resulting relief pattern printing element may be mounted on a press and printing may begin. Further, if desired, after the development step, the relief pattern printing element may be post-exposed and/or de-pasted, as is generally known in the art.

The shape of the dots and the depth of the relief affect, among other factors, the quality of the printed image. It is also very difficult to print small graphic elements such as fine dots, lines, and even text using flexographic printing plates while keeping the inverted text and shadows open. In the brightest areas of the image, commonly referred to as highlights, the density of the image is represented by the total area of dots in a halftone screen representation of a continuous tone image. For Amplitude Modulation (AM) screening, this involves shrinking a number of halftone dots located on a fixed periodic grid to a very small size, the density of the highlight being represented by the area of the dots. For Frequency Modulation (FM) screening, the size of the halftone dots is typically maintained at some fixed value, and the number of randomly or pseudo-randomly placed dots represents the density of the image. In both cases, very small dot sizes must be printed to adequately represent the highlighted area.

Round vertices (RTDs) of bullet shape are generated in conventional digital boards and are due to oxygen inhibition that occurs on the surface layer during imaging. Flat Top Dots (FTD) have been shown to be superior to RTD in printing performance. However, in order to obtain FTD, oxygen inhibition in the surface layer must be suppressed.

Furthermore, due to the nature of the platemaking process, it can be very difficult to maintain small dots on a flexographic printing plate. In a digital platemaking process using a UV opaque mask layer, the combination of the mask and the ultraviolet light exposure produces relief dots having a generally conical shape. The smallest of these dots is easily removed during processing, which means that ink is not transferred to these areas during printing (i.e., the dots do not "stay" on the plate and/or press). Alternatively, if the dots remain after processing, they are susceptible to damage by the press. For example, small dots may fold and/or partially break during printing, resulting in either excessive or no transfer of ink.

As described in U.S. patent No. 8,158,331 to rechhia and U.S. patent No. 2011/0079158 to rechhia et al, the subject matter of each of which is incorporated herein by reference in its entirety, a particular set of geometric characteristics can define the shape of the bending point that produces excellent printing performance, including but not limited to (1) the planarity of the point surface; (2) a shoulder angle of the point; (3) the depth of the relief between points; and (4) the sharpness of the edge where the top of the point transitions to the shoulder of the point.

To improve surface curing, it has also generally been found beneficial to perform additional processes and/or use additional equipment, including: (1) laminating the film to a surface of a photopolymer; (2) purging oxygen from the photopolymer using an inert gas; and/or (3) imaging the photopolymer with a high intensity UV source.

Purging oxygen from the photopolymer using an inert gas typically involves placing the photocurable resin plate in an inert gas such as carbon dioxide gas or nitrogen gas prior to exposure in order to displace ambient oxygen. One notable disadvantage of this approach is that it is inconvenient and cumbersome, and requires a large space for the equipment.

Another method involves subjecting the plate to a preliminary exposure to actinic radiation (i.e., "bump exposure"). During bump exposure, a low intensity "pre-exposure" dose of actinic radiation sensitizes the resin before the plate is subjected to a main exposure dose of higher intensity actinic radiation. Bump exposures are typically applied to the entire plate area and are short, low dose exposures of the plate that reduce the concentration of oxygen, which inhibits photopolymerization of the plate (or other printing element) and helps maintain fine features (i.e., highlight dots, fine lines, isolated dots, etc.) on the finished plate. However, the pre-sensitization step may also result in shadow tone filling, thereby reducing the tone range of the halftone in the image. In an alternative approach, selective preliminary exposure has also been proposed, as discussed, for example, in U.S. patent publication No. 2009/0043138 to Roberts et al, the subject matter of which is incorporated herein by reference in its entirety.

Other efforts to reduce the effects of oxygen on photopolymerization processes have involved the use of special plate formulations alone or in combination with bump exposure. For example, flexographic printing plates have been developed to inherently exhibit FTD without the above-described methods. These intrinsic FTD plates greatly simplify the plate making process and save the cost required to support the additional equipment and techniques described, for example, in U.S. patent No. 8,808,968 to Choi et al, the subject matter of which is incorporated herein by reference in its entirety. These photocurable relief image printing elements include: an additive selected from the group consisting of: phosphites, phosphines, thioether amine compounds, and combinations of one or more of the foregoing in the photocurable layer.

However, fully processed intrinsic FTD plates, such as those described in U.S. patent No. 8,808,968, tend to have slight instability due to the unique nature of their photoresist chemistry. Thus, even in climate controlled environments, if these FTD photoresists are left in ambient UV light (0.4 μ W/cm)²) Lower lengthTime (i.e., more than 2 weeks), they have a tendency to degrade. The degraded photoresist becomes brittle and loses elasticity, which greatly includes printing performance. If degradation continues, cracks develop in the bulk photoresist under stress, as shown in FIG. 1. Therefore, it is desirable to maintain these intrinsic FTD panels covered or stored in a dark environment to prevent degradation of the panels by ambient UV light.

Accordingly, it would be desirable to provide an improved photocurable composition for use as a fully processed intrinsic FTD board, and which exhibits good photostability and does not degrade even after prolonged storage.

Disclosure of Invention

It is an object of the present invention to provide a relief image printing element having improved surface cure.

It is another object of the present invention to provide a method of tailoring or modifying the shape of the relief printing dots in a relief pattern printing element for optimal printing on a variety of substrates and/or under a variety of conditions.

It is another object of the present invention to provide an improved method of producing a relief image printing element comprising dots having a desired geometric characteristic.

It is another object of the present invention to simplify the workflow of the digital platemaking process.

It is another object of the present invention to provide an improved method of producing a relief pattern printing element having customized relief dots in terms of edge definition, shoulder angle, and/or printing surface.

It is another object of the present invention to provide photocurable compositions for use as fully processed intrinsic FTD boards.

It is another object of the present invention to provide photocurable compositions that exhibit good ambient light stability.

It is another object of the present invention to provide a photocurable composition which does not degrade even after long-term storage.

To this end, in one embodiment, the present invention is generally directed to a photocurable relief image printing element comprising:

a) a support layer;

b) one or more photocurable layers disposed on the support layer, wherein the one or more photocurable layers comprise:

i) a binder;

ii) one or more monomers;

iii) α -aminoketone photoinitiator, and optionally

iv) an additive selected from the group consisting of: phosphites, phosphines, thioether amine compounds, and combinations of one or more of the foregoing.

c) A laser-ablatable mask layer disposed on the one or more photocurable layers, the laser-ablatable mask layer comprising a radiopaque material; and

d) optionally, a removable cover sheet.

Detailed description of the preferred embodiments

The present invention relates to improved photocurable compositions that improve the ambient light stability of fully processed intrinsic FTD photoresists without the use of conventional antioxidants that tend to impair the imaging characteristics. The improved photocurable compositions of the present invention have the benefit that the board handling and storage characteristics of the intrinsic FTD boards are comparable to those of conventional board formulations without compromising the technical advantages of the intrinsic FTD photoresist.

The present inventors have discovered that the use of α -aminoketone photoinitiators in photocurable compositions can improve the photostability of the plates without deteriorating the imaging characteristics of the intrinsic FTD photoresists.

As described herein, it is an object of the present invention to improve the ambient light stability of fully processed intrinsic FTD plates without the use of conventional antioxidants that tend to impair the different imaging characteristics of the intrinsic FTD resin, such as 1:1 replication (dot size on plates ≈ dot size on plates in the document) and well-defined flat-top dots the present invention relates generally to improved photopolymer compositions comprising α aminoketone photoinitiators.

In one embodiment, the present invention is generally directed to a photocurable relief image printing element comprising:

a) a support layer;

b) one or more photocurable layers disposed on the support layer, wherein the one or more photocurable layers comprise:

i) a binder;

ii) one or more monomers;

iii) α -aminoketone photoinitiator, and optionally

iv) an additive selected from the group consisting of: phosphites, phosphines, thioether amine compounds, and combinations of one or more of the foregoing;

c) a laser-ablatable mask layer disposed on the one or more photocurable layers, the laser-ablatable mask layer comprising a radiopaque material; and

d) optionally, a removable cover sheet.

Photopolymerizable compositions generally include one or more binders, monomers, and plasticizers in combination with one or more photoinitiators and the above-described additives.

The type of binder is not critical to the photopolymer composition and most, if not all, of the styrene copolymer rubber can be used in the composition of the present invention. Suitable binders include natural or synthetic polymers of conjugated dienes including 1, 2-polybutadiene, 1, 4-polybutadiene, butadiene/acrylonitrile, butadiene/styrene, thermoplastic elastomeric block copolymers such as styrene-butadiene-styrene block copolymers, styrene-isoprene-styrene block copolymers, and the like, as well as copolymers of binders. It is generally preferred that the binder be present in an amount of at least 60% by weight of the photosensitive layer. As used herein, the term binder also encompasses core shell microgels or blends of microgels and preformed macromolecular polymers.

Non-limiting examples of binders that can be used in the compositions of the present invention include Styrene Isoprene Styrene (SIS), a commercial product of which may be available under the trade name styreneD1161 was purchased from Kraton Polymers, LLC; styrene Isoprene Butadiene Styrene (SIBS), a commercial product of which may be sold under the trade name

π, D1171 was purchased from Kraton polymers, LLC; and Styrene Butadiene Styrene (SBS), which is commercially available from Kraton Polymers LLC under the trade designation DX 405.

Monomers suitable for use in the present invention are addition polymerizable ethylenically unsaturated compounds. The photocurable composition may comprise a single monomer or a mixture of monomers that form a compatible mixture with the binder to produce a clear (i.e., non-cloudy) photosensitive layer. The monomers are generally reactive monomers, in particular acrylates and methacrylates. Such reactive monomers include, but are not limited to, trimethylolpropane triacrylate, hexanediol diacrylate, 1, 3-butanediol diacrylate, diethylene glycol diacrylate, 1, 6-hexanediol diacrylate, neopentyl glycol diacrylate, polyethylene glycol (200) diacrylate, tetraethylene glycol diacrylate, triethylene glycol diacrylate, pentaerythritol tetraacrylate, tripropylene glycol diacrylate, ethoxylated bisphenol A diacrylate, trimethylolpropane triacrylate, dimethylolpropane diacrylate, triacrylate of tris (hydroxyethyl) isocyanurate, dipentaerythritol hydroxypentaacrylate, pentaerythritol triacrylate, ethoxylated trimethylolpropane triacrylate, triethylene glycol dimethacrylate, ethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, and mixtures thereof, Polyethylene glycol (200) dimethacrylate, 1, 6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate, polyethylene glycol (600) dimethacrylate, 1, 3-butanediol dimethacrylate, ethoxylated bisphenol A dimethacrylate, trimethylolpropane trimethacrylate, diethylene glycol dimethacrylate. 1, 4-butanediol diacrylate, diethylene glycol dimethacrylate, pentaerythritol tetramethacrylate, glycerol dimethacrylate, trimethylolpropane dimethacrylate, pentaerythritol trimethacrylate, pentaerythritol dimethacrylate, pentaerythritol diacrylate, urethane methacrylate or acrylate oligomers, and the like, which may be added to the photopolymerizable composition to modify the cured product. Monoacrylates including, for example, cyclohexyl acrylate, isobornyl acrylate, lauryl acrylate, and tetrahydrofurfuryl acrylate, as well as the corresponding methacrylates, can also be used in the practice of the present invention. Particularly preferred acrylate monomers include hexanediol diacrylate (HDDA) and trimethylolpropane triacrylate (TMPTA). Particularly preferred methacrylate monomers include hexanediol dimethacrylate (HDDMA) and trimethylolpropane triacrylate (TMPTA). It is generally preferred that the one or more monomers are present in an amount of at least 5 wt% of the photosensitive layer.

The photopolymer layer also optionally but preferably includes a compatible plasticizer that serves to lower the glass transition temperature of the binder and facilitate selective development. Suitable plasticizers include, but are not limited to, dialkyl phthalates, alkyl phosphates, polyethylene glycols, polyethylene glycol esters, polyethylene glycol ethers, polybutadiene styrene copolymers, hydrogenated heavy naphthenic oils, hydrogenated heavy paraffin oils, and polyisoprene. Other useful plasticizers include oleic acid, lauric acid, and the like, if used, the plasticizer is present in an amount of at least 10% by weight based on the weight of the total solids of the photopolymer composition. Commercially available plasticizers that may be used in the compositions of the present invention include 1, 2-polybutadiene, available from Nippon Soda Co., Inc. under the trade designation Nisso PB B-1000; ricon 183, a polybutadiene styrene copolymer available from Cray Valley; nyflex 222B, a hydrogenated heavy naphthenic oil, available from Nynas AB company; ParaLux 2401, a hydrogenated heavy paraffin wax available from Chevron u.s.a., inc; and Isolene 40-S, which is polyisoprene, available from Royal Elastomers.

Photoinitiators for photocurable compositions include α -aminoketone photoinitiators, such as Genocure PMP, Genocure BDMM (available from RAHN company) and TR-KS-001 (available from TRONLY company) the inventors have found that these α -aminoketone photoinitiators produce printing plates that produce printed dots having preferred printing characteristics as described herein and are resistant to degradation when exposed to ambient light the photocurable layers may also include other photoinitiators, such as benzoin alkyl ethers, such as benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether and benzoin isobutyl ether, dialkoxyacetophenones, such as 2, 2-dimethoxy-2-phenylacetophenone and 2, 2-diethoxy-2-phenylacetophenone, aldehyde and ketone carbonyl compounds having at least one aromatic nucleus directly attached to the carboxyl group, including benzophenone, benzene, o-methoxybenzophenone, acenaphthenequinone, methyl ethyl ketone, pentaphenone, hexabenzophenone, α -phenylketoneketone, p-phenylacetophenone, p-acetylbenzophenone, 4-acetylbenzophenone, such as benzophenone, 4-acetyl-4-benzophenone, such as benzophenone, p-acetyl-4-acetylbenzophenone, such as benzophenone, p-acetyl-4-acetyl-4-acetylbenzophenone, p-5-acetylbenzophenone, p-4-acetylbenzophenone, p-3-acetylbenzophenone, p-4-5, p-4-acetylbenzophenone, p-4-acetylbenzophenone, p-5, p-acetylbenzophenone, p-4-benzophenone, p-benzoylbenzophenone, p-4-5, p-acetylbenzophenone, p-4-5, p-4-.

As described herein, the additive may include a phosphite having the general structure P (OR)₃Or P (OAr)₃Phosphine of the general structure PR₃PAr₃A thioether amine compound, or a combination of one or more of the foregoing. Additives may be used in the photopolymer composition in an amount of about 0.1 to about 10 weight percent, more preferably about 0.05 to about 2 weight percent.

Suitable phosphites include, but are not limited to, tris (nonylphenyl) phosphite (TNPP) (CAS number 26523-78-4), triphenyl phosphite, diphenyl phosphite, tridecyl phosphite, triisodecyl phosphite, tris (tridecyl) phosphite, trilauryl phosphite, distearyl pentaerythritol diphosphite, diisodecyl phenyl phosphite, diphenylisodecyl phosphite, diphenyloctyl phosphite, diphenylisooctyl phosphite, diphenyltriisodecyl monophenyl dipropylene glycol diphosphite, alkyl bisphenol a phosphite, tetraphenyl dipropylene glycol diphosphite, poly dipropylene glycol phenyl phosphite, tris (dipropylene glycol) phosphite, and dioleyl hydrogen phosphate. In one embodiment, the phosphite comprises TNPP.

Suitable phosphines include, but are not limited to, triphenylphosphine, tri-p-tolylphosphine, benzhydrylphosphine, phenethylphosphine, diphenylpropylphosphine, dimethylphenylphosphine, diethylphenylphosphine, dipropylphosphine, divinylphenylphosphine, divinylp-methoxyphenyl phosphine, divinylp-bromophenylphosphine, divinylp-tolylphosphine, diallylphosphine, divinylp-bromophenylphosphine, and diallylphosphine.

Suitable thioether amine compounds include, but are not limited to, 2, 6-di-tert-butyl-4- (4, 6-bis (octylsulfanyl) -1,3, 5-triazin-2-ylamino) phenol (CAS number 991-84-4), 4- [ [4, 6-bis (nonylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-bis (octadecylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-octylsulfanyl ] -1,3, 5-triazin-2-yl ] amino ] -2, 6-bis (2-methylnonyl-2-yl) phenol, 4- [ [4, 6-bis (hexylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-bis (heptylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-bis (octylsulfanyl) -1,3, 5-triazin-2-y ] amino ] -2-tert-butyl-6-methylphenol, 4- [ [4, 6-bis (ethylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-bis (2,4, 4-trimethylpentan-2-ylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-bis (2-octylsulfanylethyl-sulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-bis (octylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-dibutylphenol, 4- [ [4, 6-bis (octylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-dimethylphenol, 2, 6-di-tert-butyl-4- [ [4- (3, 5-di-tert-butyl-4-hydroxyanilino) -6-octylsulfonyl-1, 3, 5-triazin-2-yl ] amino ] phenol, 4- [ [4, 6-bis (pentylsulfanyl) -1,3, 5-triazin-2-yl ] amino-2, 6-dimethylphenol, 4- [ [4, 6-bis (hexylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2-tert-butylphenol, 2, 6-di-tert-butyl-4- [ (4-octylsulfanyl-1, 3, 5-triazin-2-yl) amino ] phenol, 2, 6-di-tert-butyl-4- [ (3-octylsulfanyl-1, 3, 5-triazin-2-yl) amino ] phenol, and, 4- [ [4, 6-bis (ethylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -2, 6-dimethylphenol, 4- [ [4, 6-bis (octylsulfanyl) -1,3, 5-triazin-2-yl ] -butylamino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-bis (octylsulfanyl) -1,3, 5-triazin-2-yl ] -cyclohexylamino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-bis (octylsulfanyl) -1,3, 5-triazin-2-yl ] amino ] -6-tert-butylphenol, 2-tert-butyl-6-methyl-4- [ [ 4-octyl-sulfanyl ] amino ] -2-tert-butyl-6 -6- [ (2,2,6,6, -tetramethylpiperidin-4-yl) amino ] -1,3, 5-triazin-2-yl ] amino ] phenol, 4- [ [4, 6-bis (octylsulfanylmethyl) -1,3, 5-triazin-2-y ] amino ] -2, 6-di-tert-butylphenol, 4- [ [4, 6-bis (octyl-sulfanyl) -1,3, 5-triazin-2-yl) methylamino ] -2, 6-di-tert-butylphenol, 4- [ (4-amino-6-chloro-1, 3, 5-triazin-2-yl) amino ] -2, 6-di-tert-butylphenol and 4- [ (4-cyclohexyl-6-cyclohexylsulfanyl-1, 3, 5-triazin-2-yl) amino ] -2,6-d-i (propan-2-yl) phenol. In one embodiment, the thioether amine compound comprises 2, 6-di-tert-butyl-4- (4, 6-bis (octylthio) -1,3, 5-triazin-2-ylamino) phenol (also known as phenol, 4- [ [4, 6-bis (octylthio) -1,3, 5-triazin-2-yl ] amino ] -2, 6-bis (1, 1-dimethylethyl).

Various dyes and/or colorants can also optionally be used in the practice of the present invention, but the inclusion of a dye and/or colorant is not necessary to achieve the benefits of the present invention. Suitable colorants are designated as "window dyes" which do not absorb actinic radiation in the spectral region activatable by the initiator present in the composition. Colorants include, for example, CI 109 red dye, methylene violet (CI basic Violet 5), "Luxol". Fast blue MBSN (CI solvent blue 38), "pontoyl", wool blue BL (CI acid blue 59 or CI 50315), "pontoyl", wool blue GL (CI acid blue 102 or CI 50320), Victoria pure blue BO (CI basic blue 7 or CI 42595), rhodamine 3GO (CI basic Red 4), rhodamine 6GDN (CI basic Red I or CI 45160), 1,1 '-diethyl-2, 2' -iodine cyanide, magenta dye (CI 42510), acid Green S (CI 44090), anthraquinone blue 2GA (CI acid blue 58), Solvaperm Red BB (solvent Red 195), and the like. The dye and/or colorant must not interfere with the imagewise exposure. The dye and/or colorant must not interfere with the imagewise exposure.

Other additives may also be included in the photopolymerizable composition, depending on the desired final properties, including antiozonants, fillers or reinforcing agents, thermal polymerization inhibitors, ultraviolet light absorbers, and the like. Such additives are generally well known in the art. However, care must be taken to ensure that the use of these other additives does not compromise the imaging properties of the photopolymerizable composition.

Suitable fillers and/or reinforcing agents include immiscible, polymeric or non-polymeric organic or inorganic fillers or reinforcing agents that are substantially transparent and do not scatter actinic radiation at the wavelengths used to expose the photopolymer material, such as polystyrene, silicones, bentonites, silica, powdered glass, colloidal carbon, and various types of dyes and pigments. The amount of such materials used will vary depending on the desired characteristics of the elastomeric composition. Fillers may be used to improve the strength of the elastomeric layer, reduce tack, and may also be used as colorants. Agents such as silicone monomers may also be added to modify the surface energy.

Suitable amine acrylates include, for example, n-hexane-1, 6-dialkyldiprop-2-enoate-2-aminoethanol (CAS #:67906-98-3), which is commercially available from IGMResins under the trade names Photomer 4771 and Photomer 4775; and the reaction product of 2-propanoic acid, (1-methyl-1, 2-ethanediyl) bis (methyl-2, 1-ethanediyl) ester with diethylamine (CAS #:111497-86-0), a commercial product available from IGM Resins under the trade name Photomer 4967.

Suitable amine reaction promoters include primary, secondary and tertiary aliphatic, aromatic, aliphatic or heterocyclic amines. Examples of such amines include butylamine, dibutylamine, tributylamine, cyclohexylamine, benzyldiethylamine, dicyclohexylamine, triethanolamine, N-methyldiethanolamine, phenyldiethanolamine, piperidine, piperazine, morpholine, pyridine, quinoline, ethyl p-dimethylaminobenzoate, butyl p-dimethylaminobenzoate, 4 '-bis (dimethylamino) -benzophenone (michelson) and 4,4' -bis (diethylamino) -benzophenone. Particularly preferred amine reaction promoters include dibutylamine and triethanolamine.

In another embodiment, the present invention is generally directed to a method of making a relief pattern printing element from a photocurable printing blank, the method comprising the steps of:

a) providing a photocurable printing blank, the photocurable printing blank comprising:

i) a backing or support layer;

ii) one or more photocurable layers disposed on the backing or support layer, wherein the one or more photocurable layers comprise:

1) a binder;

2) one or more monomers;

3) α -aminoketone photoinitiator;

4) an additive selected from the group consisting of: phosphites, phosphines, thioether amine compounds, and combinations of one or more of the foregoing;

iii) a laser ablatable mask layer disposed on the at least one photocurable layer, the laser ablatable mask layer comprising a radiopaque material;

b) selectively ablating the laser ablatable mask laser to produce an in situ negative of the desired image in the laser ablatable mask layer;

c) exposing the at least one photocurable layer to actinic radiation to selectively crosslink and cure portions of the at least one photocurable layer through the in situ negative; and

d) developing the exposed at least one photocurable layer of the photocurable printing blank to reveal a relief pattern therein, the relief pattern comprising a plurality of relief printing dots.

The photocurable composition can be developed using a solvent to dissolve away the uncured and uncrosslinked portions of the photocurable composition or using thermal development, wherein the uncured and uncrosslinked portions are softened and/or dissolved and then wicked away. Other methods of developing the photocurable composition are also known to those skilled in the art.

The resulting photocurable relief pattern printing element preferably has a shore a hardness of between about 45 and about 70, more preferably between about 50 and about 65.

As described in U.S. patent No. 8,808,968, improved surface cure in relief image printing elements can be manifested by the shape of the dots, and it is desirable that the shape of the dots exhibit a flat top.

The planarity of the top of a point can be measured as the radius of curvature r across the top surface of the point_e. It should be noted that rounded dot surfaces are undesirable from a printing point of view, since the size of the contact surface between the printing surface and the dots varies exponentially with the embossing force. Thus, the top of the dots preferably has planarity with a radius of curvature of the top of the dots that is greater than the thickness of the photopolymer layer, more preferably twice the thickness of the photopolymer layer, and most preferably more than three times the total thickness of the photopolymer layer.

Edge sharpness relates to the presence of a well-defined boundary between the top of a planar point and the shoulder, and it is generally preferred that the point edge be sharp and defined. These well-defined dot edges better separate the "printed" portion of the dot from the "support" portion, allowing for a more consistent contact area between the dot and the substrate during printing,

edge sharpness may be defined as the radius of curvature r (at the intersection of the shoulder and the top of the point)_eThe ratio to the width p of the top of the dot or the printing surface. For truly rounded tips, it is difficult to define an accurate printing surface because there is no real edge in the commonly understood sense, and r_eThe ratio of p may approach 50%, in contrast to the point of sharp edge which will have very little r_eA value of and r_eP will approach zero. In practice, r of less than 5% is preferred_eP, wherein r is most preferably less than 2%_e:p。

Finally, it is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.