Flexographic printing plate precursor

Abstract

To provide a relief printing form that can meet the increasing demands for print quality to improve the transfer of ink to printed substrate and to print, particularly solid areas, with uniform, dense coverage of ink.SOLUTION: A printing form precursor comprises (a) a photopolymerizable layer comprising a first binder, a monomer, and a photoinitiator, supported by a support layer, (b) an infrared ablation layer that is ablatable by infrared radiation and opaque to non-infrared actinic radiation, the infrared ablation layer comprising (i) at least one infrared absorbing material, (ii) a radiation opaque material, and (iii) at least one second binder, wherein the infrared ablation layer comprises an overcoat / barrier layer which is thermally embossable on the side facing the photopolymerizable layer and is embossed with a microcell pattern, and (c) a cover sheet.SELECTED DRAWING: None

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority under 35 U.S.C. § 119 from U.S. Provisional Application No. 62 / 778,007, filed December 11, 2018. [Background technology]

[0002] FIELD OF THEINVENTION This invention relates to photosensitive elements, and more particularly to photosensitive elements that are printing plate precursors useful for forming printing plates suitable for letterpress printing.

[0003] Flexographic printing plates are widely used for printing packaging materials ranging from corrugated boxes to cardboard boxes and continuous webs of plastic film. Flexographic printing plates are useful in letterpress printing where ink is carried from a raised image surface and transferred to a substrate. Flexographic printing plates can be made from photopolymerizable compositions such as those described in U.S. Pat. Nos. 4,323,637 and 4,427,759. Photosensitive elements usually have a solid layer of photopolymerizable composition sandwiched between a support and a cover sheet or multilayer cover element. Photopolymerizable elements are characterized by their ability to crosslink or harden when exposed to actinic radiation.

[0004] The photopolymerizable element is converted into a flexographic relief printing plate through a multi-step process. The photopolymerizable element is imagewise exposed to actinic radiation through an image-bearing design (such as a photographic negative film, a positive film, or a phototool (e.g., a silver halide film)) for so-called analog workflow, or through an in-situ mask with radiation-opaque areas already formed above the photopolymerizable layer for so-called digital workflow. Exposure to actinic radiation is typically carried out using ultraviolet (UV) radiation. Actinic radiation enters the photosensitive element through the transparent areas and is prevented from entering the black or opaque areas of the positive film or in-situ mask. Areas of the photopolymerizable layer that were exposed to actinic radiation crosslink and harden; areas of the photopolymerizable layer that were not exposed, i.e., areas that were under the opaque areas of the positive film or in-situ mask at the time of exposure, do not crosslink or harden and are removed by treatment with a wash solution or heat, leaving a relief image suitable for printing. After all required processing steps, the printing plate is then mounted on a cylinder and used for printing.

[0005] Analog workflows include creating an intermediate, i.e., a photographic negative, positive, or phototool. Creating a phototool, such as from silver halide film, is a complex, costly, and time-consuming process that may require separate processing equipment and chemical developers. Alternatively, phototools can be created from thermally developed film or by inkjet processes. Also, the use of phototools may cause quality issues since the dimensions of the phototool may change slightly due to changes in temperature and humidity, and all surfaces of the phototool and photopolymerizable plate must be cleaned and free of dust and dirt. The presence of such foreign matter may cause image artifacts as well as poor adhesion between the phototool and the plate.

[0006] An alternative to analog workflow is called digital workflow, which does not require the creation of a separate phototool.Photosensitive elements suitable for use as masters and processes capable of forming in-situ masks in digital workflow are described in U.S. Pat. No. 5,262,275; U.S. Pat. No. 5,719,009; U.S. Pat. No. 5,607,814; U.S. Pat. No. 6,238,837; U.S. Pat. No. 6,558,876; U.S. Pat. No. 6,929,898; U.S. Pat. No. 6,673,509; U.S. Pat. No. 6,037,102; and U.S. Pat. No. 6,284,431.Masters or assemblages using masters include a layer that is sensitive to laser light, typically infrared laser light, and opaque to actinic radiation. The infrared-sensitive layer is imagewise exposed to the laser light of a digital imaging unit, whereby the infrared-sensitive material is removed from the overlying film of the assemblage or transferred onto / from it to form an in-situ mask with radiation-opaque and transparent areas adjacent to the photopolymerizable layer. Conventionally, the master is exposed to actinic radiation through the in-situ mask in the presence of atmospheric oxygen (as no vacuum is required). Due in part to the presence of atmospheric oxygen during imagewise exposure, the flexographic printing plate has a relief structure (based on the same size mask openings in both workflows) that differs from the relief structure formed in the analog workflow. The digital workflow forms raised elements (i.e., dots or lines) in the relief structure that have a surface area on its top surface (i.e., printing surface) that is significantly smaller than the openings in the in-situ mask that correspond to the relief structure, depending on the specific chemistry of the master and the actinic radiation exposure. Digital workflows produce relief images with different structures of raised elements (i.e. raised surface elements) that print small dots, which are typically smaller and have rounded tops and curved sidewall shapes, often referred to as a dot sharpening effect. Dots produced by analog workflows are typically cone-shaped and have flat tops.The relief structure created by the digital workflow results in beneficial print characteristics such as finer printed highlight dots that fade to white, an expanded printable tonal range, and sharper linework. Therefore, the digital workflow is widely accepted as a desirable method for producing flexographic printing plates due to its ease of use and desirable printing performance. However, this dot sharpening effect is not considered beneficial in all end use applications.

[0007] It is known to those skilled in the art that in free radical photopolymerization processes, the presence of oxygen (O2) during exposure results in a primary reaction between reactive monomer molecules while a side reaction occurs in which free radical molecules react with oxygen. This side reaction is known as inhibition (i.e., oxygen inhibition) since it retards polymerization or crosslinked molecule formation. Many prior disclosures recognize that photopolymerization exposure to actinic radiation is desirably performed in air (as in digital workflows), under vacuum (as in analog workflows), or in an inert environment. As disclosed in U.S. Pat. No. 8,241,835, a conventional digital workflow is modified in which the imagewise exposure of the master is performed in an environment having an inert gas and an oxygen concentration less than atmospheric oxygen but greater than a complete inert gas environment (i.e., an oxygen concentration between 190,000 parts per million (ppm) and 100 ppm). The modified digital workflow provides the ease of use of a digital workflow while avoiding the dot sharpening effect of relief features associated with conventional digital workflows to produce relief features with an analog-like appearance.

[0008] In addition, it is often desirable to have a flexographic letterpress printing plate for printing images, especially solid areas with a uniformly dense coverage of ink, the so-called solid ink density. Poor transfer or spreading of the ink from the printing plate to the substrate, especially over large areas, results in printing defects such as mottle and graininess. Particularly unsatisfactory printing results are obtained with solvent-based printing inks and UV-curable printing inks.

[0009] There are many ways to try and improve the ink density of solid areas of an image printed by a flexographic letterpress printing plate. One way to improve solid ink density is to increase the physical pressure between the printing plate and the substrate. While this increases the solid ink density, the increased pressure tends to deform the smaller plate elements, resulting in increased dot gain and loss of resolution. Another way to improve solid ink density involves increasing the surface area of ​​the letterpress printing plate, since a letterpress printing plate with a rough surface can hold more ink than a smooth surface, thereby transferring more ink to the substrate and creating a more uniform appearance. However, the surface roughness needs to be enough to increase the ink transfer, but not so much as to create discreet features for direct printing, since this can create undesirable artifacts in the final print. Printing plates having a matte layer and produced by an analog workflow typically retain the rough surface well, although in some cases some of the microstructure of the rough surface may be lost due to dot sharpening effects when produced by a conventional digital workflow.

[0010] Solid screening is a well-known process for improving solid ink density in flexographic printing. Solid screening consists of forming a pattern in the solid printing area of ​​a letterpress printing plate that is small enough that the pattern is not reproduced (i.e., printed image) in the printing process, and large enough that the pattern is substantially different from the normal or unscreened printing surface. The pattern of small features used for solid screening is often called the plate cell pattern or microcell pattern.

[0011] GB 2241352A discloses a process for producing a photopolymer plate having a plurality of well-like depressions by exposing the photopolymer layer to actinic radiation through a photographic mask containing optically transparent and optically opaque areas and a screen having a plurality of opaque separation dots or other geometric features on the photopolymer plate, and developing the plate to form a plurality of depressions in the flat surface of the relief in the exposed portions of the photopolymer layer.

[0012] Samworth in U.S. Patent No. 6,492,095 discloses a flexographic printing plate having a solid image area covered by a plurality of very small shallow cells. The cells are formed by a screened halftone negative of the film, an intermediate photomask, or by a top layer on the plate used as a mask.

[0013] Currently, various microcell patterns are widely used to improve the ability of letterpress printing plates for solid printing with uniform dense coverage of ink, i.e. solid ink density. Microcell patterns can be used not only in solid areas for improved printed ink density, but also for text, line art, halftones, i.e. any kind of image element where improved ink transfer properties are realized. In a digital workflow, the microcell pattern is processed into a digital file that is used by a digital imaging unit to incorporate the microcell pattern by forming an in situ mask using laser light, usually infrared laser light.

[0014] That is, the microcell pattern is formed from the infrared-sensitive layer forming an in-situ mask. The microcell pattern is effectively superimposed in the digital file onto the image areas (often solid) where improved solid ink density is desired. Examples of patterns are small "negative" (actinic radiation blocking) features, such as 96% halftone dots at 400 lines per inch (representing an array of actinic radiation blocking dots about 14 micrometers in diameter spaced about 64 micrometers apart); and small "positive" (actinic radiation transparent) features that are much closer together, such as 12% halftone dots at 1400 lines per inch (representing an array of actinic radiation transparent dots about 7 micrometers in diameter spaced about 18 micrometers apart). In the latter example of small "positive" features, oxygen effects (dot sharpness) associated with conventional digital workflows can affect the ability of the letterpress printing plate to retain the microcell pattern in the solid printing areas. Typically, the finer the microcell pattern formed, i.e., the smaller the size of each cell and the closer the spacing between cells, the better the results. One problem with this method is that the additional cells increase the time required for the photosensitive element to be laser imaged by the laser imaging unit. To obtain finer microcell patterns, companies that manufacture digital imaging units have had to not only improve the optical resolution of the imaging device, but also improve the imaging software. Both aspects substantially increase the cost of the imaging device and the time required to image the photosensitive element.

[0015] In US 2010 / 0143841, Stolt et al. disclose a method for improving the printing capability of solid ink density of a relief printing plate by digital patterning of the image area of ​​the master. Stolt et al. disclose patterning a masking layer and then laminating it to a photopolymer layer. After UV exposure and development, the pattern, which is smaller than the actual printable halftone image, resulted in an increase in the density of the printed solid ink. However, the customer needs to invest in a laminator. To some extent, the yield may be compromised. Imaging needs to be done at a higher resolution than usual, which takes more time.

[0016] Samworth et al., in U.S. Patent No. 7,580,154, disclose a printing plate that contains ink cells in both the sale and halftone areas. It is possible to laser image Samworth's digital flexo plates. However, this method requires higher resolution imaging, which adds significant cost. The higher resolution imaging process takes significantly longer to complete.

[0017] Blomquist et al., in US Patent Application Publication No. 2016 / 0355004, disclose a pre-printed layer on a masking layer to provide a microcell pattern that is integrated into the plate itself. Although it is easy to significantly improve the solid ink density using this method, it is very difficult to print a pattern at the desired resolution that can maximize the solid ink density.

[0018] Fronczkiewicz et al., in U.S. Patent Application Publication No. 2016 / 0154308, disclose a process for making flexographic printing plates having an additional embossing step in which the surface of the developed printing plate is textured by embossing to improve the print quality of the printing plate. Summary of the Invention [Problem to be solved by the invention]

[0019] There is a need for a letterpress printing plate that can meet the increasing demands for print quality, for improving the transfer of ink to the printed substrate and for printing solid areas in particular with uniformly dense coverage of ink. It is also desirable that the printing plate has a relief structure that allows printing of a full tonal range, including printing of fine print elements and highlight dots, thereby providing improved print quality. There is also a need for a method that can provide a printing plate with a relief structure that improves the transfer of ink to the substrate without adversely affecting dot gain and / or image resolution, while being simple and relatively fast, when making a letterpress printing plate from a photosensitive printing plate precursor. It is desirable because of its ease and simplicity that the method utilizes a digital-like workflow that produces a printing plate with a relief structure that has the features required for high-quality printing, without additional costs for upgrading or purchasing new digital imaging equipment and software, and without loss of productivity, e.g., additional imaging time, for high-resolution imaging to form microcell patterns. [Means for solving the problem]

[0020] One embodiment provides a printing form precursor, the printing form precursor comprising: (a) a photopolymerizable layer comprising a first binder, a monomer, and a photoinitiator, the photopolymerizable layer being supported by a support layer; (b) an infrared ablative layer that is ablatable by infrared radiation and opaque to non-infrared actinic radiation; (i) at least one infrared absorbing material; (ii) a radiation opaque material, where (i) and (ii) can be the same or different; and (iii) at least one second binder; an infrared ablative layer that is embossed with a microcell pattern on a surface facing the photopolymerizable layer; (c) a cover sheet.

[0021] Another embodiment provides that the infrared ablative layer is embossed with a microcell pattern and applied by lamination to the surface of the photopolymerizable layer opposite the support layer.

[0022] Another embodiment provides that the infrared ablative layer has a transmission optical density greater than 2.0.

[0023] Another embodiment provides that the microcell pattern comprises a plurality of features, each feature having an area between 5 and 750 square micrometers.

[0024] Another embodiment provides that the first binder is different from the second binder.

[0025] Another embodiment provides a printing plate precursor, the printing plate precursor comprising: (a) a photopolymerizable layer comprising a first binder, a monomer, and a photoinitiator, the photopolymerizable layer being supported by a support layer; (b) an infrared ablative layer that is ablatable by infrared radiation and opaque to non-infrared actinic radiation; (i) at least one infrared absorbing material; (ii) a radiopaque material, where (i) and (ii) can be the same or different; and (iii) at least one second binder; The infrared ablative layer includes an overcoat / barrier layer that is thermally embossable on a surface facing the photopolymerizable layer and that is embossed with a microcell pattern; (c) a cover sheet; and Equipped with.

[0026] Another embodiment provides a printing plate precursor, the printing plate precursor comprising: (a) a cover sheet; (b) a release layer that is embossed with a microcell pattern on a surface opposite the cover sheet; (c) a photopolymerizable layer comprising a binder, a monomer, and a photoinitiator, the photopolymerizable layer being between the release layer and the support layer; and Equipped with.

[0027] Another embodiment provides a method for making a printing plate precursor, the method comprising: a) providing a transparent thermopolymer cover sheet; b) providing an infrared ablative composition on the cover sheet that forms an infrared ablative layer, the infrared ablative composition comprising: (i) at least one infrared absorbing material; (ii) a radiopaque material, where (i) and (ii) can be the same or different; and (iii) at least one second binder; c) embossing the infrared ablative layer with a microcell pattern on the surface opposite the cover sheet; d) applying a photopolymerizable composition between the infrared ablation layer and the support layer to form a photopolymerizable layer, the photopolymerizable composition including a first binder, a monomer, and a photoinitiator; Includes.

[0028] Another embodiment provides a method for making a printing plate precursor, the method comprising: a) providing a transparent thermopolymer cover sheet; b) applying an infrared ablative composition onto the cover sheet to form an infrared ablative layer, said infrared ablative composition comprising: (i) at least one infrared absorbing material; (ii) a radiopaque material, where (i) and (ii) can be the same or different; and (iii) at least one second binder; c) applying a thermal embossable overcoat / barrier layer onto the infrared ablative layer; d) embossing the overcoat / barrier layer with a microcell pattern on the side opposite the cover sheet; e) applying a photopolymerizable composition between the overcoat / barrier layer and the support layer to form a photopolymerizable layer, the photopolymerizable composition comprising a first binder, a monomer, and a photoinitiator; Includes.

[0029] Another embodiment provides a method for making a printing plate precursor, the method comprising: a) providing a transparent thermopolymer cover sheet; b) applying a hot embossable release layer; c) embossing the release layer with a microcell pattern on the side opposite the cover sheet; d) applying a photopolymerizable composition between the release layer and the support layer to form a photopolymerizable layer, the photopolymerizable composition including a binder, a monomer, and a photoinitiator; Includes.

[0030] Yet another embodiment provides a method for making a printing plate precursor, the method comprising: a) providing a transparent thermopolymer cover sheet; b) applying a hot embossable release layer; c) embossing the release layer with a microcell pattern on the side opposite the cover sheet; d) applying a photopolymerizable composition between the release layer and the support layer to form a photopolymerizable layer, the photopolymerizable composition including a binder, a monomer, and a photoinitiator. e) removing the cover sheet; f) providing a mask over the release layer; Includes.

[0031] These and other features and advantages of the present invention will be readily understood by those of ordinary skill in the art upon reading the following detailed description. Certain features of the invention that are, for clarity, described above or below as separate embodiments may also be provided in combination in a single embodiment. Conversely, various features of the invention that are described in the context of a single embodiment may also be provided separately or in any subcombination. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] Throughout the following detailed description, like reference numerals refer to like elements in all figures of the drawings.

[0033] Unless otherwise stated, the following terms used herein have the meanings as defined below.

[0034] "Actinic radiation" refers to radiation capable of initiating a reaction or reactions to change the physical or chemical characteristics of the photosensitive composition.

[0035] "Lines per inch" (LPI) refers to a measure of printing resolution in systems that use halftone screens. It is a measure of how close the lines are to each other in a halftone grid. Higher LPI generally indicates greater image detail and sharpness.

[0036] "Halftone" is used to reproduce continuous-tone images by a screening process that converts an image into dots of various sizes spaced equally on their centers. Halftone screens allow the creation of light and dark (or gray) areas in a printed image by the transfer (or non-transfer) of a printing medium such as ink.

[0037] "Continuous tone" refers to an image having a virtually unlimited range of color or gray shades, including unscreened, unbroken gradient tones.

[0038] "Dots per inch" (DPI) is the frequency of dot structures in a tone image and is a measure of spatial print dot density, specifically the number of individual dots that can be placed within one linear inch (2.54 cm). DPI values ​​tend to correlate with image resolution. Typical DPI ranges for graphics applications are 75 to 150, but can reach 300.

[0039] "Line screen resolution", sometimes called "screen ruling", is the number of lines or dots per inch on a halftone screen.

[0040] "Optical density" or simply "density" is the measure of darkness (light absorption or opacity) of an image and can be determined from the following relationship: concentration=log 10 {1 / reflectance} The reflectance in the formula is {reflected light intensity / incident light intensity}. Density is usually calculated according to ISO 5 / 3:2009 International Standard for Photographic and Graphic Techniques - Densitometry - Part 3: Spectral Conditions.

[0041] "Solid ink density" is a measure of the density of a printed area that is intended to show the maximum amount of printed color.

[0042] "Graininess" refers to the variation in density of a printed area. The ISO-13660 international print quality standard defines it as "non-periodic variations in density with a spatial frequency greater than 0.4 cycles per millimeter in all directions." The measure of graininess in ISO-13660 is the standard deviation of density in a number of small areas that are 42um square.

[0043] "Embossed microcell pattern" refers to a composite of features that together form a pattern for incorporation at some stage in the manufacture of the photosensitive element of the present invention. Embossed microcell patterns that incorporate a plurality of features into a photosensitive element are distinct from microcell patterns that are conventionally formed in a digital layer of a photosensitive element using infrared laser light by a digital imaging device.

[0044] "Microcell" refers to image elements or microcells that modify the printing surface, which may appear as small depressions and / or very small inversions, each smaller in at least one dimension than the spacing between the smallest periodic structures on a printing plate derived from the photosensitive element of the present invention. Microcells are irregularities on the printing surface of a relief printing plate designed to improve the uniformity and apparent density of the ink printed by the relief printing plate on a substrate. In some embodiments, the microcells of the relief printing plate can correspond to features of a printed microcell pattern integrated into the photosensitive element of the present invention.

[0045] "Microcell pattern" refers to a combination of imaging elements or microcells that together form a pattern that modifies the printing surface of a relief printing plate derived from the photosensitive element of the present invention.

[0046] The term "pattern" refers to the arrangement of individual features relative to one another, including but not limited to with respect to "microcell patterns" and "printed microcell patterns", as a composite of individual feature patterns that are random, pseudorandom, or regular in one or two directions.

[0047] "Visible radiation or visible light" refers to the range of electromagnetic radiation detectable by the human eye, with radiation wavelengths ranging from about 390 to about 770 nm.

[0048] "Infrared or infrared light" is approximately 770 to 10 6 Refers to the emission wavelength in nm.

[0049] "Ultraviolet radiation or ultraviolet light" refers to radiation wavelengths between about 10 and 390 nm.

[0050] It should be noted that the wavelength ranges given for infrared, visible, and ultraviolet are general guidelines, and that there may be some overlap in radiation wavelengths between what is generally considered ultraviolet and what is generally considered visible light, and between what is generally considered visible light and what is generally considered infrared.

[0051] "White light" refers to light that contains all visible wavelengths of light at roughly equal intensities, such as sunlight.

[0052] "Room light" refers to light that provides normal illumination in a room. Room light may or may not include all wavelengths of visible light.

[0053] The term "photosensitive" encompasses any system capable of reacting with actinic radiation to cause the photosensitive composition to initiate a reaction or reactions, particularly photochemical reactions. Exposure to actinic radiation induces chain growth polymerization of monomers and / or oligomers, either by condensation mechanisms or free radical addition polymerization. While all photopolymerization mechanisms are contemplated, the compositions and processes of the present invention are described with respect to free radical initiated addition polymerization of monomers and / or oligomers having one or more terminal ethylenically unsaturated groups. In this regard, a photoinitiator system can function as the source of free radicals necessary to initiate polymerization of the monomers and / or oligomers upon exposure to actinic radiation. The monomers may have non-terminal ethylenically unsaturated groups, and / or the composition may contain one or more other components, such as binders or oligomers that promote crosslinking. Thus, the term "photopolymerizable" is intended to encompass photopolymerizable, photocrosslinkable, or both systems. As used herein, photopolymerization may also be referred to as curing. The photosensitive element is sometimes referred to herein as a photosensitive master, a photosensitive printing master, a printing master, and a master.

[0054] As used herein, the term "solid" refers to the physical state of a photosensitive layer that has a definite volume or shape and resists forces that tend to change its volume or shape. A layer of a photopolymerizable composition is solid at room temperature (a temperature of about 5°C to about 30°C). A solid layer of a photopolymerizable composition may be polymerized (photocured), unpolymerized, or both.

[0055] The term "digital layer" includes layers that are responsive or ablatable by laser light, particularly infrared laser light, and more particularly layers that are ablatable by infrared laser light. Digital layers are also opaque to non-infrared actinic radiation. Digital layers may also be referred to herein as infrared sensitive layers, infrared sensitive ablatable layers, laser ablatable layers, or actinic radiation opaque layers.

[0056] Unless otherwise indicated, the terms "photosensitive element," "printing plate precursor," "printing blank," and "printing plate" include elements or structures of any form suitable as a printing blank, including, but not limited to, flat-sheets, plates, seamless continuous plates, cylinders, plates-on-sleeves, and plates-on-carriers.

[0057] photosensitive element The photosensitive element is a photopolymerizable printing plate precursor. The photosensitive element includes a layer of a composition sensitive to actinic radiation (in most embodiments, a photopolymerizable composition). The photosensitive element includes a layer of a photosensitive composition and a digital layer adjacent to the photosensitive layer. The digital layer is used in digital direct-to-plate imaging techniques in which laser light, typically infrared laser light, is used to form a mask of an image for the photosensitive element (instead of a conventional positive image or phototool). The digital layer includes an infrared ablative layer that is ablatable by infrared radiation and opaque to non-infrared actinic radiation. The infrared ablative layer includes (i) at least one infrared absorbing material and (ii) a radiation opaque material, where (i) and (ii) can be the same or different. In one embodiment, the infrared ablative layer is embossed with a microcell pattern on the surface facing the photopolymerizable layer. In another embodiment where the infrared ablative layer comprises an overcoat / barrier layer, the overcoat / barrier layer is embossed with a microcell pattern on the side facing the photopolymerizable layer. In yet another embodiment for an analog process, the photosensitive element comprises a cover sheet and a release layer between the cover sheet and the photopolymerizable layer. The release layer is embossed with a microcell pattern on the side opposite the cover sheet. The cover sheet is removed and a mask is applied over the release layer before exposing the photosensitive element to UV radiation.

[0058] The microcell pattern includes a plurality of features, each feature having an area of ​​5 to 750 square micrometers. The microcell pattern is introduced by a hot embossing process.

[0059] Hot embossing is a common graphic arts technique used to impart a raised surface to a substrate. This technique is commonly used for embossing paper, foil, and plastic films. This technique is capable of sub-micrometer resolution and is commonly used for reproducing surface holograms.

[0060] Hot embossing begins with the use of a master image with a raised pattern that matches the desired pattern of the final product. The master can be either flat or circular, with circular being used in high speed roll-to-roll applications. These masters can be anything with a raised surface. One common method of making the master involves either mechanical or laser etching methods. These masters can also be made by photolithographic processes, as is commonly done for holograms.

[0061] The advantages of the photosensitive element of the present invention having an embossed microcell pattern layer integrated therein include that it can save end users time and increase productivity in preparing printing plates from the photosensitive element. The presence of the embossed microcell pattern allows the mask to be formed in the digital layer by a low-resolution digital imaging device operating at high speed, thus avoiding the need for end users to form the microcell pattern in the digital layer using a digital imaging device, thus increasing productivity in making printing plates. Since the microcell pattern is pre-embossed at the time of manufacture, end users can avoid the need for expensive high-resolution digital imaging devices with the associated significant increase in imaging time to create the plate cell pattern and mask from the digital layer. Furthermore, the relief printing plate obtained from the photosensitive master of the present invention advantageously meets the increasing demand for print quality to improve the transfer of ink to the printed substrate and to enable printing of a full tonal range, including printing of fine print elements and highlight dots, especially for printing solid areas with uniform dense coverage of ink.

[0062] In some embodiments, the photosensitive element initially includes a digital layer disposed above and covering or substantially covering the entire surface of the photopolymerizable layer. In some embodiments, the infrared laser light imagewise removes (i.e. ablates or vaporizes) the digital layer to form an in-situ mask. Suitable materials and structures for this actinic radiation opaque layer are disclosed by Fan in U.S. Pat. No. 5,262,275; Fan in U.S. Pat. No. 5,719,009; Fan in U.S. Pat. No. 6,558,876; Fan in European Patent Publication No. 0741330A1; and Van Zoeren in U.S. Pat. Nos. 5,506,086 and 5,705,310. As disclosed by Van Zoeren in U.S. Pat. No. 5,705,310, a material capture sheet adjacent to the digital layer may be present during laser exposure to capture the material of the digital layer, since the material of the digital layer is removed from the photosensitive element. Only those portions of the digital layer that are not removed from the photosensitive element remain on the element forming the in situ mask.

[0063] The materials that make up the digital layer and the structure in which it is incorporated are not particularly limited, so long as the digital layer can be imagewise exposed to form an in-situ mask on or adjacent to the photopolymerizable layer of the photosensitive element. The digital layer may substantially cover the surface of the photopolymerizable layer, or may cover only the imageable portion. The digital layer may be used with or without a barrier layer. When used with a barrier layer, the barrier layer is disposed between the photopolymerizable layer and the digital layer to minimize the migration of materials between the photopolymerizable layer and the digital layer. The monomers and plasticizers, if compatible with the materials of the adjacent layers, may migrate over time, which may change the laser light sensitivity of the digital layer, or may cause staining and sticking of the digital layer after imaging. The digital layer also has sensitivity to laser light that allows the digital layer to be selectively removed or transferred.

[0064] In some embodiments, the digital layer comprises a radiation opaque material, an infrared absorbing material, and an optional binder. Dark inorganic pigments such as carbon black and graphite, mixtures of pigments, metals, and metal alloys usually function as both infrared sensitive materials and radiation opaque materials. The optional binder is a polymeric material, including, but not limited to, self-oxidizing polymers, non-self-oxidizing polymers, thermochemically decomposable polymers, polymers and copolymers of butadiene and isoprene with styrene and / or olefins, thermally decomposable polymers, amphoteric interpolymers, polyethylene wax, materials conventionally used as release layers as described above, and combinations thereof. The thickness of the digital layer should be in a range that optimizes both sensitivity and opacity, which is usually about 20 angstroms to about 50 micrometers. The digital layer needs to have a transmission optical density greater than 2.0 to effectively block actinic radiation and polymerize the underlying photopolymerizable layer.

[0065] The digital layer comprises (i) at least one infrared absorbing material, (ii) a radiopaque material, where (i) and (ii) can be the same or different, and at least one binder. The following materials are suitable as binders for the digital layer: polyamide, polyethylene oxide, polypropylene oxide, ethyl cellulose, hydroxyethyl cellulose, cellulose acetate butyrate, ethylene-propylene-diene terpolymer, copolymers of ethylene and vinyl acetate, copolymers of vinyl acetate and vinyl alcohol, copolymers of vinyl acetate and pyrrolidone, polyvinyl acetate, polyethylene wax, polyacetal, polybutyral, polyalkylene, polycarbonate, polyester elastomers, copolymers of vinyl chloride and vinyl acetate, copolymers of styrene and butadiene, copolymers of styrene and isoprene, styrene and isoprene, styrene and isopropyl alcohol ... Examples of suitable block copolymers include, but are not limited to, thermoplastic block copolymers of styrene and butadiene, thermoplastic block copolymers of styrene and isoprene, polyisobutylene, polybutadiene, polychloroprene, butyl rubber, nitrile rubber, thermoplastic polyurethane elastomers, cyclic rubbers, copolymers of vinyl acetate and (meth)acrylates, acrylonitrile-butadiene-styrene terpolymers, methacrylate-butadiene-styrene terpolymers, polymers or copolymers of alkyl methacrylates, copolymers of styrene and maleic anhydride, copolymers of styrene and maleic anhydride partially esterified with an alcohol, and combinations thereof.Preferred binders include polyamides, polyethylene oxide, polypropylene oxide, ethyl cellulose, hydroxyethyl cellulose, cellulose acetate butyrate, ethylene-propylene-diene terpolymers, copolymers of ethylene and vinyl acetate, copolymers of vinyl acetate and vinyl alcohol, copolymers of vinyl acetate and pyrrolidone, polyvinyl acetate, polyethylene waxes, polyacetals, polybutyrals, polyalkylenes, polycarbonates, cyclic rubbers, copolymers of styrene and maleic anhydride, copolymers of styrene and maleic anhydride partially esterified with alcohols, polyester elastomers, and combinations thereof.

[0066] Suitable materials for use as radiopaque and infrared absorbing materials include, but are not limited to, metals, metal alloys, pigments, carbon black, graphite, and combinations thereof. A mixture of pigments may be used with a binder, with each pigment functioning as either an infrared absorbing material or a radiopaque material (or both). Dyes are also suitable as infrared absorbing agents. Examples of suitable dyes include poly(substituted)phthalocyanine compounds; cyanine dyes; squarylium dyes; chalcogenopyrroarylidene dyes; bis(chalcogenopyrrolo)-polymethine dyes; oxidolizine dyes; bis(aminoaryl)-polymethine dyes; merocyanine dyes; croconium dyes; metal thiolate dyes; and quinoid dyes. Preferred materials that function as both infrared absorbing and radiopaque materials are carbon black, graphite, metals, and metal alloys. The radiopaque and infrared absorbing materials may be in a dispersion to facilitate handling and uniform distribution of the materials.

[0067] The photopolymerizable layer is a solid layer formed from a composition comprising a binder, at least one ethylenically unsaturated compound, and a photoinitiator. The photoinitiator is sensitive to actinic radiation. Throughout this specification, actinic radiation includes ultraviolet and / or visible light. The solid layer of the photopolymerizable composition is treated with one or more solutions and / or heated to form a relief suitable for letterpress printing. As used herein, the term "solid" refers to the physical state of a layer that has a definite volume or shape and resists forces that tend to change its volume or shape. The solid layer of the photopolymerizable composition may be polymerized (photohardened), unpolymerized, or both. In some embodiments, the layer of the photopolymerizable composition is elastomeric. In some embodiments, the photosensitive element comprises a layer of a photopolymerizable composition that is composed of at least a binder, at least one ethylenically unsaturated compound, and a photoinitiator. In another embodiment, the layer of the photopolymerizable composition comprises an elastomeric binder, at least one ethylenically unsaturated compound, and a photoinitiator. In some embodiments, the relief printing plate is an elastomeric printing plate (ie, the photopolymerizable layer is an elastomeric layer).

[0068] The binder may be a single polymer or a mixture of polymers. In some embodiments, the binder is an elastomeric binder. In other embodiments, the layer of the photopolymerizable composition is an elastomer. Binders include natural or synthetic polymers of conjugated diolefin hydrocarbons, such as polyisoprene, 1,2-polybutadiene, 1,4-polybutadiene, butadiene / acrylonitrile, and diene / styrene thermoplastic-elastomeric block copolymers. Preferably, the elastomeric block copolymers are ABA type block copolymers, where A is a non-elastomeric block, preferably a vinyl polymer, most preferably polystyrene, and B is an elastomeric block, preferably polybutadiene or polyisoprene. In some embodiments, the elastomeric ABA block copolymer binder may be a poly(styrene / isoprene / styrene) block copolymer, a poly(styrene / butadiene / styrene) block copolymer, and combinations thereof. The binder is present in an amount of about 10% to 90% by weight of the photosensitive composition, hi some embodiments, the binder is present in an amount of about 40% to 85% by weight of the photosensitive composition.

[0069] Other suitable binders include acrylics; polyvinyl alcohols; polyvinyl cinnamates; polyamides; epoxies; polyimides; styrene block copolymers; nitrile rubbers; nitrile elastomers; non-crosslinked polybutadienes; non-crosslinked polyisoprenes; polyisobutylene and other butyl elastomers; polyalkylene oxides; polyphosphazenes; elastomeric polymers and copolymers of acrylates and methacrylates; elastomeric polyurethanes and polyesters; elastomeric polymers and copolymers of olefins such as ethylene-propylene copolymers and non-crosslinked EPDM; elastomeric copolymers of vinyl acetate and its partially hydrogenated derivatives.

[0070] The photopolymerizable composition may contain at least one compound capable of addition polymerization that is compatible with the binder, so long as a clear, non-cloudy photosensitive layer is produced. The at least one compound capable of addition polymerization may also be referred to as a monomer, and may be a single monomer or a mixture of monomers. Monomers that can be used in the photopolymerizable composition are well known in the art and include, but are not limited to, addition-polymerizable ethylenically unsaturated compounds having at least one terminal ethylene group. The monomer can be appropriately selected by one skilled in the art to impart elastomeric properties to the photopolymerizable composition. The at least one compound capable of addition polymerization (i.e., monomer) is present in an amount of at least 5% by weight, typically 10% to 20% by weight, of the photopolymerizable composition.

[0071] The photoinitiator may be any single compound or combination of compounds that are sensitive to actinic radiation and generate free radicals that initiate the polymerization of the monomer or monomers without excessive termination. Any known class of photoinitiators may be used, particularly free radical photoinitiators. Alternatively, the photoinitiator may be a mixture of compounds where one of the compounds provides the free radicals upon generation of the free radicals by a sensitizer activated by radiation. In most embodiments, the photoinitiator for the main exposure (as well as post-exposure and backflash) is sensitive to visible or ultraviolet radiation between 310 and 400 nm, preferably between 345 and 365 nm. The photoinitiator is typically present in an amount of 0.001% to 10.0% by weight of the photopolymerizable composition.

[0072] The photopolymerizable composition may contain other additives depending on the final properties required. Additional additives to the photopolymerizable composition include sensitizers, plasticizers, rheology modifiers, thermal polymerization inhibitors, colorants, processing aids, antioxidants, antiozonants, dyes, and fillers.

[0073] The thickness of the photopolymerizable layer may vary over a wide range, for example, from about 0.005 inches to about 0.250 inches or more (about 0.013 cm to about 0.64 cm or more), depending on the type of printing plate required. In some embodiments, the photopolymerizable layer has a thickness of about 0.005 inches to about 0.0450 inches (0.013 cm to about 0.114 cm). In some other embodiments, the photopolymerizable layer has a thickness of about 0.020 inches to about 0.112 inches (about 0.05 cm to about 0.28 cm). In other embodiments, the photopolymerizable layer has a thickness of about 0.112 inches to about 0.250 inches or more (0.28 cm to about 0.64 cm or more). As is conventional in the art, manufacturers typically identify a printing master by comparing it to the total thickness of the printing plate on the press, which includes the thickness of the support and the photopolymerizable layer. The thickness of the photopolymerizable layer of the printing plate is typically less than the thickness designed by the manufacturer, since it does not include the thickness of the support.

[0074] The photosensitive element may include one or more additional layers on or adjacent to the photosensitive layer. In most embodiments, the one or more additional layers are on the side of the photosensitive layer opposite the support. Examples of additional layers include, but are not limited to, protective layers, capping layers, elastomeric layers, barrier layers, and combinations thereof. The one or more additional layers may be removable in whole or in part during one of the steps of converting the element into a printing plate, such as processing.

[0075] Optionally, the photosensitive element may include an elastomeric capping layer on at least one photopolymerizable layer. The elastomeric capping layer is typically part of a multilayer cover element that becomes part of the photosensitive printing element upon calendering of the photopolymerizable layer. Multilayer cover elements and suitable compositions for the elastomeric capping layer are disclosed in U.S. Pat. Nos. 4,427,759 and 4,460,675 to Gruetzmacher et al. In some embodiments, the composition of the elastomeric capping layer includes an elastomeric binder, optional monomers and photoinitiators and other additives, all of which may be the same or different from those used in the bulk photopolymerizable layer. Although the elastomeric capping layer does not necessarily contain a photoreactive component, the layer will eventually become photosensitive when in contact with the underlying bulk photopolymerizable layer. Thus, upon imagewise exposure to actinic radiation, the elastomeric capping layer has cured portions that have polymerized or crosslinked and uncured portions that remain unpolymerized or uncrosslinked. Upon treatment, the unpolymerized portions of the elastomeric capping layer are removed along with the photopolymerizable layer to form a relief surface. The elastomeric capping layer exposed to actinic radiation remains on top of the polymerized areas of the photopolymerizable layer and becomes the actual printing surface of the printing plate. In embodiments of the photosensitive element that includes an elastomeric capping layer, the cell pattern layer is disposed between the elastomeric capping layer and the digital layer.

[0076] For some embodiments of photosensitive elements useful as relief printing plates, the surface of the photopolymerizable layer may be tacky, or a release layer having a substantially non-tacky surface may be provided on the surface of the photopolymerizable layer. Such a release layer can protect the surface of the photopolymerizable layer from damage during removal of an optional temporary cover sheet or other digital mask element, and can ensure that the photopolymerizable layer does not stick to the cover sheet or other digital mask element. During image exposure, the release layer can prevent the digital element with the mask from bonding with the photopolymerizable layer. The release layer is not sensitive to actinic radiation. The release layer is also suitable as a first embodiment of the barrier layer that is optionally interposed between the photopolymerizable layer and the digital layer. An elastomeric capping layer can also function as a second embodiment of the barrier layer. Examples of materials suitable for the release layer are well known in the art and include polyamides, polyvinyl alcohols, hydroxyalkyl celluloses, copolymers of ethylene and vinyl acetate, amphoteric interpolymers, and combinations thereof.

[0077] The photosensitive printing element may also include a temporary cover sheet on the top layer of the element, which can be removed before making a printing plate.One purpose of the cover sheet is to protect the top layer of the photosensitive printing element during storage and handling.Examples of materials suitable for the cover sheet include thin films of polystyrene, polyethylene, polypropylene, polycarbonate, fluoropolymers, polyamides, or polyesters, which may be subbed with a release layer.The cover sheet is preferably made of polyester, such as Mylar® polyethylene terephthalate film.

[0078] Process for preparing the photosensitive element The process of making the photosensitive element includes forming a microcell pattern by embossing the microcell pattern on a layer of the photosensitive element or on a layer or film of a separate element that forms an assembly with the photopolymerizable layer to form the photosensitive element. The microcell pattern is integrated into the photosensitive element during manufacture. In most embodiments, the microcell pattern is embossed and incorporated as part of the digital layer and faces the photopolymerizable layer of the photosensitive element. In some embodiments, the microcell pattern is embossed into an overcoat / barrier layer adjacent to the digital layer. The overcoat / barrier is heat embossable and is embossed on the side that faces the photopolymerizable layer. In some other embodiments, the microcell pattern is embossed on a release layer between the cover sheet and the photopolymerizable layer, with the microcell pattern being on the side opposite the cover sheet.

[0079] It is well within the skill of the art to make or produce a photosensitive element printing plate precursor comprising a layer of a photopolymerizable composition formed by mixing a binder, a monomer, a photoinitiator, and other optional additives. In most embodiments, the cell pattern layer is provided by printing on the surface of the digital layer that will be adjacent to the photopolymerizable layer, so the cell pattern layer must be able to withstand the high temperatures typically used for the manufacture of photopolymerizable printing plate precursors without being disturbed or destroyed. In most embodiments, the photopolymerizable mixture is formed into a hot melt at a temperature above room temperature to a desired thickness between two sheets, such as a support and a temporary cover sheet with a digital layer, or between a flat sheet and a release roll, extruded, and calendered. Alternatively, the photopolymerizable material may be extruded and / or calendered to form a layer on a temporary support, and then laminated to a desired final support or digital cover sheet. The printing plate precursor can also be made by mixing the ingredients in a suitable mixing device and then compressing the material into a desired shape in a suitable mold. The material is usually compressed between the support and a cover sheet. The molding process may involve pressure and / or heat.

[0080] The photosensitive element comprises at least one photopolymerizable layer, which may be a bilayer or multilayer structure.The photosensitive element may further comprise an elastomeric capping layer on the at least one photopolymerizable layer.Multilayer cover elements and compositions suitable for the elastomeric capping layer are disclosed in U.S. Patent No. 4,427,759 and U.S. Patent No. 4,460,675 to Gruetzmacher et al.

[0081] Cylindrical shaped photopolymerizable elements can be made by any suitable method. In one embodiment, cylindrical shaped elements can be made from a photopolymerizable printing plate rolled onto a carrier or cylindrical support or sleeve and the ends of the plate mated to form a cylindrical shape. Cylindrical shaped photopolymerizable elements can also be made by circular extrusion and calendering according to the method and apparatus disclosed in U.S. Patent No. 5,798,019 to Cushner et al.

[0082] The photosensitive element can be manufactured in several ways, and in one embodiment, it can be sold as a printing plate precursor with all the necessary layers, i.e., a photopolymerizable layer and a digital layer with an embossed microcell pattern, or a photopolymerizable layer, a digital layer, and an overcoat / barrier layer between the digital layer and the photopolymerizable layer and embossed with a microcell pattern on the surface facing the photopolymerizable layer. Alternatively, the photosensitive element can be sold as separate components, such as a cover sheet, a release layer embossed with a microcell pattern on the surface opposite the cover sheet, and a photopolymerizable between the release layer and the support. These separate components are processed separately, but are assembled to form the photosensitive element prior to imagewise exposure of the photopolymerizable layer.

[0083] 1. In an embodiment, a digital composition is coated on a web of a polymer film, such as a polyester film, to form a digital layer on the film. A microcell pattern is continuously embossed on the side of the digital layer opposite the film to form a digital cover sheet. The features of the microcell pattern are continuously embossed, so that the embossed microcell pattern does not include seams, interruptions, or divisions of the pattern on the digital layer web. The photopolymerizable composition is extruded to form a photopolymerizable layer between a base support, such as a polyester film, and a digital cover sheet, and the side of the digital cover sheet with the microcell pattern layer contacts the photopolymerizable layer opposite the support. A printing plate precursor including a base support, a photopolymerizable layer, a digital layer with an embossed microcell pattern, and an optional polymer film as a cover sheet can be cut to any finished dimensions and sold to end users.

[0084] 2. In another embodiment, the digital composition is coated on a web of polymer film, such as polyester film, to form a digital layer on the film, which is then cut into a specific size of sheet. A microcell pattern is embossed on the sheet on the side of the digital layer opposite the film to form a digital cover sheet. The digital cover sheet can be laminated to a photopolymerizable layer, and the embossed microcell pattern contacts the photopolymerizable layer to form a printing plate precursor.

[0085] 3. In one other embodiment, a polymeric film, such as a polyester film, is embossed with a microcell pattern to form a microcell pattern on the film, and a layer of a thermally imageable composition is provided on the film on the side opposite the microcell pattern to construct a digital cover sheet. The digital cover sheet is laminated onto the surface of the photopolymerizable layer, with the embossed microcell pattern in contact with the photopolymerizable layer to form a printing plate precursor.

[0086] 4. In yet another embodiment, the photopolymerizable layer is disposed on a support that is a polymeric film, such as a polyester film. A release layer is embossed with a microcell pattern and is disposed on the photopolymerizable layer with the side having the microcell pattern in contact with the photopolymerizable layer. A cover sheet is placed on top of the release layer to form a printing plate precursor. The cover sheet can be removed and replaced with a mask on top of the release layer when the printing plate precursor is converted to a letterpress printing plate.

[0087] Those skilled in the art, having the benefit of the teachings of the invention as set forth above, may affect various modifications thereto, which modifications are to be construed as falling within the scope of the invention as set forth in the appended claims. EXAMPLES

[0088] In the following examples, all percentages are by weight unless otherwise specified. CYREL® photopolymerizable printing plates, CYREL® exposure units, and CYREL® processing equipment are all available from The DuPont Company (Wilmington, Del.).

[0089] In the following examples, a commercially available DPR® digital plate by DuPont™ was used to make a printing plate. The cover sheet film of the digital plate may have a special coating on PET, as further described in the following examples. The original unembossed cover sheet film was used as is to serve as a control. The embossing of the cover sheet film was performed using a random pattern obtained from a sheet of 3M 261X wrapping film with a surface of 5 micrometers. The embossing was performed on a Professional Laminating Systems PL238WF system at 300°F and a speed of 6.5 inches per minute. The embossing was performed by contacting the rough surface of the wrapping film with the coated surface of the PET cover sheet. The wrapping film was removed and discarded immediately after lamination. A flexographic printing plate master was made by laminating this cover sheet to a photopolymer using the same lamination system at the same temperature, but at a speed of 55 inches per minute. The laminated plate was then left overnight at 60°C.

[0090] The printing plate master was converted to a letterpress printing plate according to the Cyrel® Instructions for Use manual. The analog plate was imaged using a transparency negative to create large solid areas. The digital plate was imaged on an Esko CDI Spark2530 using an image that created large solid areas suitable for measuring solid ink density. The letterpress printing plate was tested for solid printing on a substrate. A Mark Andy 830 press and Aquaverse Pro Cyan ink from Sun Chemical were used. The ink density of the solid printed areas was measured using a Techkon SpectroJet scanning spectrophotometer-densitometer from Techkon USA, Danvers, MA, USA.

[0091] Example 1 In this example, the cover sheet film of the DPR® digital plate was used directly without any additional coating to make a standard digital flexographic printing plate. The cover sheet consisted of a 2.5 micrometer thick ablatable layer coated on a PET film. One sample of this cover sheet film was used as a control as is. Another sample was embossed as described above. Flexographic printing plates incorporating these cover sheet films were made and tested in printing. The solid ink density of the unembossed sample was 1.12, while the solid ink density of the embossed sample was 1.23. This resulted in a significant visible improvement in the printed samples.

[0092] Example 2 In this example, the cover sheet film of a DPR® digital plate was coated with a 10 micrometer thick oxygen barrier. The barrier layer was composed of a polyamide resin. One sample of the modified cover sheet film was used as a control as is to create a digital flexographic plate with a barrier layer to prevent oxygen migration to the plate during curing. The barrier layer helps to create a flexographic plate with flat-top dots, which may be preferred when printing. Another sample of the modified cover sheet film was embossed as described above. Flexographic printing plates incorporating these cover sheet films were made and tested in printing. The solid ink density of the unembossed sample was 1.12, while the solid ink density of the embossed sample was 1.25. This resulted in a significant visible improvement in the printed samples.

[0093] Example 3 In this example, a standard analog flexographic printing plate was made using a commercially available flexographic plate, HORB® Digital Plate by DuPont™. The cover sheet film of the flexographic plate has a release layer of 4.0 micrometers coated on a PET film. One sample of this cover sheet film was used as a control as is. Another sample of the cover sheet film was embossed on its release layer as described above. Flexographic printing plates incorporating these cover sheet films were made and tested in printing. The solid ink density of the non-embossed sample was 1.08, while the solid ink density of the embossed sample was 1.20. This resulted in a significant visible improvement in the printed samples.

[0094] Significant improvements in solid ink density were obtained by embossing the coating onto the cover sheet prior to preparing the flexographic printing plate, as shown in Examples 1-3. Further improvements in solid ink density can be achieved by optimizing the pattern used for embossing.

Claims

1. (a) a photopolymerizable layer comprising a first binder, a monomer, and a photoinitiator, the photopolymerizable layer being supported by a support layer; (b) an infrared ablative layer that is ablatable by infrared radiation and opaque to non-infrared actinic radiation; (i) at least one infrared absorbing material; (ii) a radiopaque material, where (i) and (ii) can be the same or different; and (iii) at least one second binder; an infrared ablative layer comprising an overcoat / barrier layer that is thermally embossable on a surface facing the photopolymerizable layer and that is embossed with a microcell pattern; (c) a cover sheet; and A printing plate precursor comprising:

2. (a) a cover sheet; (b) a release layer, the release layer being embossed with a microcell pattern on a surface opposite the cover sheet; (c) a photopolymerizable layer comprising a binder, a monomer, and a photoinitiator, the photopolymerizable layer being between the release layer and the support layer; and A printing plate precursor comprising: