Method and system for thermal treatment of flexographic printing elements - Patents.com

Abstract

The present disclosure relates to a system and method configured to cure unreactive photopolymer collected by an absorbent blotting material during thermal processing of a flexographic printing element. The uncured, unreacted portions of the photopolymer are removed by contacting one or more layers of photopolymer with a web of absorbent blotting material at elevated temperature to soften or liquefy the uncured, unreacted portions of the one or more layers of photopolymer and absorbing the softened or liquefied uncured, unreacted portions into the absorbent web of absorbent blotting material. The web of absorbent blotter material, including the absorbed, softened or liquefied, unreacted portions of the photopolymer, is exposed to actinic radiation from one or more UV light sources to crosslink and cure the softened or liquefied unreacted portions of the photopolymer.

Description

[Technical field]

[0001] SUMMARY The present disclosure generally relates to systems and methods configured to cure non-reactive photopolymer collected by an absorbent blotting material during thermal processing of a flexographic printing element. [Background technology]

[0002] Flexography is a printing method commonly used for high volume production. Flexography is employed to print on a variety of substrates, such as paper, paperboard stock, corrugated board, films, foils, and laminates. Flexographic printing elements are relief plates that have image elements raised above the open areas. Such plates offer several advantages to printers, based primarily on the durability of the plates and the ease with which they can be made.

[0003] A typical flexographic printing element is a multilayer article made up of, in order, a backing or support layer, one or more unexposed photohardenable layers, a protective layer or slip film, and a cover sheet. The photohardenable printing element can be in the form of a continuous (seamless) sleeve or can be a flat planar plate mounted on a carrier. The relief image in the flexographic printing element is produced by imaging and exposing one or more unexposed photohardenable layers. This is generally accomplished by selectively exposing one or more photohardenable materials to actinic radiation, which acts to cure or crosslink the one or more photohardenable materials in the irradiated areas.

[0004] The one or more photohardenable layers are generally formed from photopolymerizable materials that include one or more binders, one or more reactive monomers, one or more photoinitiators, and other performance additives. Photopolymerizable compositions include those described in U.S. Patent Application Publication No. 2004 / 0146806, the teachings of which are incorporated herein by reference in their entirety. Various photopolymerizable compositions can be used as binders, including those based on polystyrene-isoprene-styrene, polystyrene-butadiene-styrene, polyurethanes, and / or thiolene. Preferred binders include, for example, polystyrene-isoprene-styrene, and polystyrene-butadiene-styrene, especially block copolymers thereof.

[0005] A printing element can be selectively exposed to actinic radiation in a variety of ways. In one alternative, a photographic negative with transparent and substantially opaque areas is used to selectively block the transmission of actinic radiation to the printing plate element. In another alternative, a photopolymer layer is coated with an actinic radiation (substantially) opaque layer that is sensitive to laser ablation. A laser is then used to ablate selected areas of the actinic radiation opaque layer to create a negative in situ. This technique is well known in the art and is described, for example, in U.S. Pat. Nos. 5,262,275 and 6,238,837 to Fan and U.S. Pat. No. 5,925,500 to Yang et al., the subject matter of each of which is incorporated herein by reference in its entirety. In yet another alternative, a focused beam of actinic radiation is used to selectively expose the photopolymer. Any of these methods are acceptable based on their ability to selectively expose the photopolymer to actinic radiation, thereby selectively hardening portions of the photopolymer.

[0006] The photopolymer layer of the printing element is then developed to remove the uncured (i.e., non-crosslinked) portions without disturbing the cured portions to reveal the relief image. The development step can be accomplished in a variety of ways, including water washing, solvent washing, and thermal development (or processing).

[0007] During thermal processing, the melting temperature difference between the cured and uncured photopolymer is used to develop the latent image.The basic parameters of this process are known, as described in U.S. Pat. Nos. 7,122,295, 6,773,859, 5,279,697, 5,175,072 and 3,264,103, WO 01 / 88615, WO 01 / 18604 and EP 1239329, the subject matter of each of which is incorporated herein by reference in its entirety.These processes allow for the elimination of developing solvents and the long plate drying times required to remove the solvents.The speed and efficiency of these processes allow for their use in the manufacture of flexographic printing elements for printing newspapers and other publications, where fast turnaround times and high productivity are important.

[0008] For the printing element to be thermally developable, the composition of the photopolymer must be such that there is a substantial difference in melting temperature between the cured and uncured polymer. It is exactly this difference that makes it possible to create an image in the photopolymer when heated. The uncured photopolymer (i.e., the portion of the photopolymer that is not in contact with actinic radiation) melts and / or substantially softens, while the cured photopolymer remains solid and intact at the selected temperature. The difference in melting temperature allows the selective removal of the uncured photopolymer, thereby creating the desired image.

[0009] During thermal development, the printing element is heated to a temperature of at least about 140° C. The exact temperature will depend on the characteristics of the particular photopolymer used. However, two main factors should be considered in determining the development temperature: (1) The development temperature is preferably set between the melting temperature of the uncured photopolymer at the bottom and the melting temperature of the cured photopolymer at the top, allowing the photopolymer to be selectively removed to create an image. (2) The temperature should be sufficient to melt or substantially soften the uncured photopolymer and thereby remove it; the higher the development temperature, the faster the process time; however, the development temperature should not be so high as to exceed the melting temperature of the cured photopolymer or to degrade the cured photopolymer.

[0010] The uncured photopolymer can then be softened and / or melted and removed.

[0011] In one type of thermal processor, the heated printing element is contacted with an absorbent material that absorbs or otherwise removes the softened and / or melted uncured photopolymer, this removal process is commonly referred to as "blotting."

[0012] Once the blotting process is complete, the printing plate element can be post-exposed to additional actinic radiation and / or subjected to detackification, if desired, cooled, and then ready for use.

[0013] The uncured photopolymer (i.e., non-reactive plate material) is absorbed into a web of absorbent blotter material and then rewound onto a roller for subsequent disposal. This non-reactive plate material can be classified as hazardous depending on local environmental regulations because it can be harmful to the environment and difficult to dispose of. Furthermore, a common method of disposal of the web or absorbent blotter material containing unreacted plate material is incineration, which can release volatile materials into the air.

[0014] Based thereon, it would be desirable to provide an improved method of disposing of webs of absorbent blotter material containing unreacted material that makes disposal of the material easier and is better for the environment. Summary of the Invention

[0015] SUMMARY OF THE PRESENT EMBODIMENT It is an object of the present invention to provide an improved method for treating non-reactive materials absorbed into a web of absorbent blotter material during heat treatment.

[0016] Another object of the present invention is to provide an improved means for disposing of used webs of absorbent blotter material containing absorbed non-reactive materials.

[0017] It is yet another object of the present invention to provide a method for reacting non-reactive components to crosslink the non-reactive components contained in a web of absorbent blotter material.

[0018] Another object of the present invention is to provide a method for disposing of used webs of absorbent blotter material that is safer for the environment.

[0019] It is yet another object of the present invention to provide a method for disposing of used blotter material webs which reduces disposal costs.

[0020] To that end, in one embodiment, the present invention generally relates to a method of curing unreacted photopolymer absorbed in a web of absorbent blotter material during thermal processing of a flexographic printing element in a thermal development assembly, where the thermal development assembly receives an imaged and exposed flexographic printing element, the imaged and exposed flexographic printing element comprising one or more photopolymer layers, the one or more layers of photopolymer including crosslinked cured portions of the photopolymer that form a cured relief image and uncured unreacted portions of the photopolymer that are removed during thermal processing to expose the cured relief image.

[0021] the uncured, unreacted portions of the photopolymer are removed by contacting the one or more layers of photopolymer with a web of absorbent blotting material at an elevated temperature to soften or liquefy the uncured, unreacted portions of the one or more layers of photopolymer and absorbing the softened or liquefied uncured, unreacted portions into the absorbent web of absorbent blotting material; This method is a) positioning one or more UV light sources within a thermal processor adjacent a width of an absorbent web of blotter material containing absorbed, softened or liquefied, unreacted portions of photopolymer, wherein the absorbent web of blotter material containing absorbed, softened or liquefied, unreacted portions of photopolymer moves relative to the one or more UV light sources; b) exposing the web of absorbent blotter material to actinic radiation from one or more UV light sources to crosslink and harden the softened or liquefied unreacted portions of the photopolymer as the absorbent web of blotter material moves relative to the one or more UV light sources.

[0022] The present disclosure provides an improved method for handling and disposing of non-reactive materials absorbed into a web of absorbent blotter material during thermal processing, and an improved means for disposing of a web of absorbent blotter material containing absorbed non-reactive materials.

[0023] The system includes one or more UV light sources positioned proximate to at least a portion of the web of absorbent material.

[0024] Any combination or permutation of the features, functions, and / or embodiments disclosed herein is contemplated. Additional advantageous features, functions, and applications of the disclosed systems and methods of the present disclosure will become apparent from the following description, particularly when read in conjunction with the accompanying drawings. [Brief description of the drawings]

[0025] Features and aspects of the embodiments are described below with reference to the accompanying drawings, in which elements are not necessarily drawn to scale and in certain figures, parts may be exaggerated or removed for clarity.

[0026] Exemplary embodiments of the present disclosure are further described with reference to the accompanying drawings, in which it is noted that the various features, steps, and combinations of features / steps described below and illustrated in the figures can be arranged and organized differently to result in embodiments that are still within the scope of the present disclosure.

[0027] The invention will now be described with reference to the following drawings: [Figure 1] 1 illustrates a cross-sectional view of an exemplary thermal-based development system according to the present disclosure.

[0028] Also, although not every element may be labeled in every figure, all elements having the same reference numbers indicate similar or identical parts. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] The present disclosure provides systems and methods configured to cure non-reactive photopolymer collected by an absorbent blotting material during thermal processing of a flexographic printing element.

[0030] However, it should be understood that the disclosed embodiments are merely illustrative of the present disclosure, which may be embodied in various forms, and thus the details disclosed herein with reference to exemplary assembly / manufacturing methods and associated processes / techniques of assembly and use should not be construed as limiting, but merely as a basis for teaching those skilled in the art how to make and use the advantageous assemblies / systems described herein.

[0031] As used herein, "a," "an," and "the" refer to both the singular and the plural, unless the context clearly dictates otherwise.

[0032] As used herein, the term "about" refers to a measurable value of a parameter, amount, duration, etc., and is meant to include no more than + / -15% variation, preferably no more than + / -10% variation, more preferably no more than + / -5% variation, even more preferably no more than + / -1% variation, and even more preferably no more than + / -0.1% variation of and from the specifically recited value, so long as such variations are appropriate to practice the invention described herein. It is further to be understood that the values ​​referred to by the modifier "about" are themselves specifically disclosed herein.

[0033] As used herein, spatially relative terms such as "beneath," "below," "lower," "above," "upper," "front," and "back" are used for ease of explanation to describe the relationship of one element or feature to another element or feature. It is further understood that the terms "front" and "back" are not intended to be limiting and are intended to be interchangeable where appropriate.

[0034] As used herein, the terms "comprise(s)" and / or "comprising" specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0035] As used throughout, the absorbent material may also be referred to as a "blotter," "blotting material," "absorbent web," or "web of absorbent blotter material" without departing from the spirit / scope of this disclosure.

[0036] The present invention uses a UV light source to expose and crosslink uncured, unreacted photopolymer absorbed into the web of absorbent blotter material during thermal processing. The exposed and crosslinked material is cured and hardened, and the web or absorbent blotter material is then wound onto a rewind roller for easy and safe disposal.

[0037] In one embodiment, the invention generally relates to a method of curing unreacted photopolymer absorbed in a web of absorbent blotter material during thermal processing of a flexographic printing element in a thermal development assembly, wherein the thermal development assembly receives an imaged and exposed flexographic printing element, the imaged and exposed flexographic printing element comprising one or more photopolymer layers, the one or more layers of photopolymer comprising crosslinked cured portions of the photopolymer that form a cured relief image and uncured unreacted portions of the photopolymer that are removed during thermal processing to form the cured relief image. the uncured, unreacted portions of the photopolymer are removed by contacting the one or more layers of photopolymer with a web of absorbent blotting material at an elevated temperature to soften or liquefy the uncured, unreacted portions of the one or more layers of photopolymer and absorbing the softened or liquefied uncured, unreacted portions into the absorbent web of absorbent blotting material; This method is a) positioning one or more UV light sources within a thermal processor adjacent to and spaced apart from a width of an absorbent web of blotter material containing the absorbed, softened or liquefied, unreacted portions of photopolymer, wherein the absorbent web of blotter material containing the absorbed, softened or liquefied, unreacted portions of photopolymer moves relative to the one or more UV light sources; b) exposing the web of absorbent blotter material to actinic radiation from one or more UV light sources to crosslink and harden the softened or liquefied unreacted portions of the photopolymer as the absorbent web of blotter material moves relative to the one or more UV light sources.

[0038] Thereafter, the web of cured, crosslinked, and absorbent blotter material, including the cured unreacted portions, can be wound onto an unwind roller.

[0039] A preferred UV light source operates at a wavelength within the range of about 365-405 nm. A variety of UV light sources can be used, including, for example, LED, fluorescent, or other similar light sources.

[0040] In one embodiment, the UV light source operates at a wavelength of 365 nm. The UV light source can operate at higher wavelengths, such as 390 nm, but exposure times may be longer.

[0041] The intensity of the UV light source is typically around 11-16 mW / cm 2 , more preferably about 13 to 15 mW / cm 2 This intensity varies as the power and amount of light source is changed, and as the distance of the UV light source from the surface of the web of absorbent blotter material is changed. In one embodiment, the intensity of the UV light source is between 13 and 15 mW / cm when the UV light source is positioned at a distance of about 0.5 inches from the surface of the web of absorbent blotter material. 2 It is.

[0042] An important parameter for UV light sources is the dose, which is defined as: Dose = Intensity (of the light source) x Dwell (time of exposure).

[0043] The dose varies depending on the type of light, the exposure time, and the photopolymer itself.

[0044] In one aspect of the invention, the UV light source includes one or more UV-LEDs, preferably multiple UV-LEDs arranged across the width of the blotter material. In one embodiment, multiple UV-LEDs are arranged in a row across the width of the blotter material, at least approximately equidistant from each other. In one embodiment, additional rows of UV-LEDs are used to increase the cure or dose. The use of higher intensity UV-LEDs also requires less time to obtain the same dose.

[0045] It is desirable for the web of absorbent blotter material to be uniformly exposed to actinic radiation from the UV light source so that all of the uncured unreacted material contained in the web of absorbent blotter material is crosslinked and cured. In one embodiment, the UV-LEDs are placed close to each other so that the overlap of light (i.e., UV radiation) is uniform. In one aspect, the UV-LEDs are placed close to each other to increase the intensity, obtain the required dose, and crosslink the photopolymer faster. The number of UV-LEDs depends in part on the intensity of each individual UV-LED, the distance of the UV-LEDs from the web of absorbent blotter material, and the width of the web of absorbent blotter material.

[0046] For example, the UV-LEDs may be approximately equally spaced about 12.5 mm (0.5 inches) from one another along the width of the web of absorbent blotter material. This spacing is just one example of UV-LED spacing, and the spacing can be varied as different arrangements or configurations of UV-LEDs are tested.

[0047] In one embodiment, a source of UV light, such as UV LEDs, is fixably mounted within the thermal processor housing and the blotter material is continuously passed under or relative to the fixably mounted UV LEDs. In one embodiment, the speed of the web of absorbent blotter material relative to the fixably mounted UV light source is within the range of about 1 to about 10 feet / minute, more preferably about 5 feet / minute (1 inch / second).

[0048] To calculate the required dose, data from a typical exposure unit used to expose through the bottom of the plate to give a "floor" across the plate was analyzed.

[0049] From this standard UV exposure source, 30mW / cm 2 It was determined that the dose required to cure 0.002 inches of photopolymer in a fixed system using a light source with an intensity of 30 mW / cm2 was 5 seconds. 2 ×5 seconds=150mJ / cm2 In addition, we can calculate that on average, about 0.002 inches of photopolymer (uncured, unreacted photopolymer) is removed per pass of the blotter material in the thermal processor during thermal treatment (0.024 inches / 12 passes of plate relief=0.002 inches of polymer per pass). As described herein, during thermal treatment, the web of absorbent blotter material is contacted with the flexographic relief image printing element at elevated temperatures that soften or liquefy the uncured, unreacted portions of the photopolymer, which are absorbed into the web of absorbent blotter material.

[0050] In one embodiment, the dose is at least 130 mJ / cm 2 , preferably at least 140 mJ / cm 2 , more preferably at least 150 mJ / cm 2 , more preferably at least 160 mJ / cm 2 The present inventors have found that a dose within this range is capable of fully curing the uncured, unreacted photopolymer absorbed into the web of absorbent blotter material for subsequent disposal.

[0051] However, this high dose can be difficult to achieve depending on the particular UV source.

[0052] For example, most common UV-LEDs emit only about 13-14mW / cm 2 1000 nm. Thus, a larger number of UV-LEDs would be required to achieve the desired dose. For example, using 3 rows of LEDs with 1 inch distance between LEDs and a web speed of 5 ft / min would require a dwell time (dose / intensity) of 9-10 seconds, which would also require a larger number of UV LEDs. Thus, to reduce the exposure / dwell time and the number of rows of LEDs, the intensity of the LEDs themselves would need to be increased or the LEDs would need to be packed closer together.

[0053] On the other hand, lower web processing speeds may be more suitable for UV-LEDs. Shorter process times of about 2-3 ft / min, more preferably 2.5-2.7 ft / min, and 13-14 mW / cm 2 At this intensity, the number of UV-LEDs and / or the number of UV-LED rows can be reduced by 50%.

[0054] To cover higher production rates (i.e., 5 ft / min or greater), fluorescent UV exposure tubes can be used, with an intensity of about 30 mW / cm 2 and the same dose (30 mJ / cm 2 Only a 5 second exposure is required to achieve a 300 x 300 nm (300 x 5 seconds). Each standard UV tube is approximately 1 inch in diameter, so the exposure could be done with 5 UV fluorescent tubes. While this may seem like a better option, UV fluorescent tubes are fragile and can easily break if mishandled. Also, the one or more UV light sources include one or more fluorescent UV exposure tubes, and the intensity of each of the one or more fluorescent UV exposure tubes is at least 20 mW / cm 2 It is.

[0055] The speed of the blotter is constant before and after the array of lights in the thermal system. Typically, the processing speed of the blotter remains the same throughout the process. Extra rows of LEDs or UV lamps can be easily added and / or switched on / off as the machine process speed increases. Thus, in one embodiment, the system includes enough light sources to cover all situations including blotter speed, specific photopolymer, etc., along with control mechanisms to adjust the web speed and the number / position of light sources used.

[0056] Due to the difficulty of monitoring reactivity on the fly, the dose requirements are chosen to be higher than necessary with a safety factor, however, one of ordinary skill in the art can determine dose requirements for special types of photopolymers and / or higher intensity light sources, etc., by the processes described herein.

[0057] Temperature has a negative effect on UV output, with higher temperatures reducing UV output. In one embodiment, part of the system's design includes a heat sink to remove / dissipate heat from the UV-LEDs. In addition, the temperature of the resin in the blotter generally has a positive effect. The resin is heated during the thermal process, which increases the reactivity of the photopolymer and reduces the required dose. Therefore, optionally, the system can also include a heater to help cure the resin in the blotter. In one embodiment, if a heater is used to help cure the resin in the blotter, the required dose is reduced by either using lower intensity / fewer light sources and / or reducing the dwell time.

[0058] The systems described herein can be used with photopolymers that use photoinitiators operating in the range of about 365-405 nm. Additionally, photopolymers that contain various elements that can polymerize more quickly reduce the cost of the unit by reducing the dose required to cure the plate (i.e., reduced light intensity and / or reduced dwell time).

[0059] 1, the present invention generally relates to a thermal development assembly comprising a system 10 used to process a relief image printing element 14. The photosensitive printing element 14 typically includes a flexible substrate and at least one layer of photosensitive material deposited on the flexible substrate.

[0060] The system 10 includes a housing 12, a conveyor 16 including a continuous loop 17 on which a photosensitive printing element 14 is positionable, at least one heatable roller 24 mounted within the housing 12, and an absorbent material 32 covering at least a portion of the at least one heatable roller 24, the absorbent material 32 being capable of absorbing liquefied or softened uncured photosensitive material from the photosensitive printing element 14 when the photosensitive printing element 14 contacts the absorbent material 32 on the portion of the at least one heatable roller 24.

[0061] The system 10 for processing a photosensitive printing element 14 includes an enclosure 12 for housing at least the components of the heat-based development system 10 .

[0062] The thermal-based development system 10 described herein accepts a preformed, imagewise actinic radiation exposed flexible photosensitive printing element 14 having a base layer, an adjacent layer of radiation curable elastomeric material (curable layer), and optionally an infrared-sensitive layer that is used to form an in-situ mask on the curable layer using laser radiation, such as by laser ablation, prior to exposure to actinic radiation. Examples of photosensitive printing elements processable in the thermal-based development system of the present invention are described in U.S. Patent No. 5,175,072 to Martens, U.S. Patent Nos. 5,262,275 and 6,238,837 to Fan, and U.S. Patent Nos. 5,925,500 and 6,605,410 to Yang et al., the subject matter of each of which is incorporated herein by reference in its entirety.

[0063] In one embodiment, and prior to processing in the thermal development assembly described herein, a portion of the radiation curable layer is preferably cured by actinic radiation through the underside of the base to form a hardened "floor layer." The film is then imagewise exposed from the opposite surface to harden the desired portions of the plate, either through a photographic negative or an in situ negative created by laser ablation of the mask layer. The remaining portion of the radiation curable layer after curing consists of cured and uncured portions. The photosensitive printing element is then transferred to the thermal development assembly to remove the uncured portions of the radiation curable layer to form a relief image therein, the relief image consisting of crosslinked and cured portions of the radiation curable layer of the photosensitive printing element.

[0064] 1, a conveyor 16 attached to a drive motor (not shown) is typically used to transport the photosensitive printing element 14 through the thermal plate processing system. The conveyor 16 may be mounted in a fixed position within the housing 12 and includes a continuous loop 17 supported by at least a first roller 18 and a second roller 20. Optionally, one or more additional rollers (not shown) may be used to provide additional support to the conveyor 16 and prevent the continuous loop 17 from sagging under the weight of the photosensitive printing element 14. In one embodiment, the continuous loop 17 comprises a wire mesh.

[0065] The leading edge of the photosensitive printing element 14 may be held in place against the continuous loop 17 of the conveyor 16 by a suitable fastening means (not shown), such as a clamp and / or a vacuum. In one embodiment, a vacuum is provided to at least one of the first roller 18 and second roller 20 of the conveyor 16 and used alone or in combination with the fastening means to hold the photosensitive printing element 14 in place on the continuous loop 17 of the conveyor 16.

[0066] During operation, the conveyor 16 with the photosensitive printing element 14 mounted thereon moves in a first direction 22 toward the heatable roller 24 such that the photosensitive printing element 14 passes through a gap 26 between the conveyor 16 and the heatable roller 24 as the continuous loop 17 of the conveyor 16 rotates over and around the second roller 20. In one embodiment, the heatable roller 24 rotates in an opposite direction 28 from the conveyor 16. The heatable roller 24 can be urged toward the photosensitive printing element 14 positioned on the conveyor 16 as the conveyor moves in the first direction 22 and the heatable roller 24 moves in the opposite direction 28. Preferably, the heatable roller 24 is fixably mounted on a pivot (not shown) to allow it to be urged toward the conveyor 16.

[0067] In some embodiments, the heatable roller 24 is urged toward the photosensitive printing element 14 on the conveyor 16 using suitable means, such as one or more pneumatic cylinders (not shown). The pneumatic cylinders position the heatable roller 24 a preset distance from the outer surface of the second roller 20 of the conveyor 16 to create a gap 26 through which the photosensitive printing element 14 passes as it moves on the continuous loop 17 of the conveyor 16 around the second roller 20.

[0068] The web of absorbent material 32 is directed over at least a portion of an outer surface 30 of the heatable roller 28. The web of absorbent material 32 can absorb (e.g., remove) liquefied or softened uncured material from the photosensitive printing element 14 as the heatable roller 24 rotates and becomes heated, causing the web of absorbent material 32 to contact at least a portion of the photosensitive printing element 14. The heatable roller 24 rotates in a direction 28 that is opposite the direction 22 of the conveyor 16, so that the photosensitive printing element 14 and the web of absorbent material 32 can contact one another and then be separated.

[0069] Heat may be provided to the heatable roller 24 by a core heater capable of maintaining a surface temperature of the heatable roller 24 sufficient to soften or liquefy at least a portion of the photosensitive material. The temperature to which the heatable roller 24 is heated is selected based on the composition of the photosensitive material and the melting temperatures of the monomers and polymers contained within the photosensitive material. In one embodiment, the heatable roller 24 is heated to and operates at a temperature of about 150° C. to about 250° C. The upper limit may be determined in large part by the melting temperature of the web of absorbent material 32. That is, the temperature of the heatable roller 24 must be low enough so that the absorbent material 32 does not melt when the web of absorbent material 32 is not moving and the portion of the web of absorbent material 32 in contact with the heatable roller 24 is stationary. The heatable roller 24 preferably includes an electric core heater to provide the desired surface temperature, although the use of steam, oil, hot air, and various other heating sources may also provide the desired skin temperature.

[0070] A web of absorbent material 32 is supplied to at least a portion of the outer surface 30 of the heatable roller 24 from a supply roll 34 of the web of absorbent material 32. The selection of the absorbent material 32 may depend in part on the thickness of the photosensitive printing element 14 being processed, the melting temperature of the web of absorbent material 32, and the heat transfer characteristics of both the photosensitive printing element 14 and the web of absorbent material 32. The web of absorbent material 32 may be nonwoven or woven, and any suitable absorbent material that would be known to one of ordinary skill in the art may be used in the present invention.

[0071] After being contacted with the flexographic printing element at an elevated temperature that softens or liquefies the uncured, unreacted portions of one or more photopolymer layers of the flexographic printing element, the web of absorbent material 32 accumulates or absorbs the softened or liquefied photopolymer that has been removed (i.e., absorbed) from the photosensitive printing element 14.

[0072] As described herein, the system 10 includes a UV light source 48. The UV light source (e.g., UV LED, UV fluorescent) 50 may be positioned proximate to the absorbent blotter material web 32. For example, the UV light source may be positioned at a distance of about 0.25 to about 2 inches, more preferably about 0.50 to about 1.0 inches, from the web of absorbent blotter material 32. The UV light source 48 cures the liquefied or softened material absorbed by the web of absorbent material 32. In a non-limiting example, the wavelength of the UV light source may be from about 365 nm to about 405 nm.

[0073] The desired intensity of the UV light source may be related at least in part to at least one of the following, including, but not limited to, the speed of the web of absorbent blotter material, the proximity of the UV light source to the web of absorbent blotter material, the wavelength of the UV light source, operating parameters of the UV light source (e.g., the number of LEDs in an LED array), and combinations thereof.

[0074] In some embodiments, the system 10 can include a second UV light source (not shown) positioned proximate to the first UV light source. For example, this second UV light source can be positioned opposite the first UV light source such that the second UV light source crosslinks and cures the softened or liquefied unreacted photopolymer on the opposite side of the absorbing material 32. In a non-limiting example, the wavelength of the second UV light source can be about 365 nm to about 405 nm. In another non-limiting example, the desired intensity of the second UV light source can be at least partially associated with the elements of the first UV light source 50, as defined above. The wavelengths and / or intensities of the UV light source 50 and the second UV light source can be similar to each other or different from each other. Additionally, the second UV light source can be positioned the same distance from the web of absorbent blotter material as the first UV light source. In one embodiment, both the first UV light source and the second UV light source are positioned 0.5 to 1.0 inches from the web of absorbent blotter material.

[0075] The absorbent material 32 containing the cured non-reactive product can then be wound onto a take-up roller for subsequent removal and / or disposal.

[0076] The take-up roller 38 is belt-driven independently by a motor (not shown), preferably a variable speed motor. The take-up roller 38 collects the "used" web of absorbent material 32 after it has contacted the photosensitive printing element 14 and removed any liquefied or softened portions of photosensitive material. The speed of the motor is adjusted so as not to interfere with the selected web tension. If the motor interferes with the web tension, the resulting flexographic printing plate may vary in height in the relief portions or may be distorted and commercially unacceptable.

[0077] In another embodiment, the system 10 may include a secondary heating source (not shown) that may be positioned adjacent the point where the absorbent material 32 contacts the at least one layer of photosensitive material on the conveyor 16. The secondary heating source may provide a supplemental heat source to further soften and liquefy portions of the at least one layer of photosensitive material on the conveyor 16.

[0078] It will be apparent to one skilled in the art that the conveyor 16, including the first and second rollers 18 and 20, and the heatable roller 24, are driven by suitable means, i.e., a motor. Additionally, a controller, such as a microprocessor, may be used in the system of the present invention to control the operation of each element within the plate processor 10. Such controllers are well known in the art. One example of a controller used to control the various elements within a plate processor is described in U.S. Patent No. 5,279,697 to Peterson et al., the subject matter of which is incorporated herein by reference in its entirety.

[0079] The method of the present invention comprises the following steps. The method includes the steps of (1) positioning a photosensitive printing element 14 on a conveyor 16, the conveyor 16 including a continuous loop 17 supported by at least a first roller 18 and a second roller 20, the photosensitive printing element 14 being supported on the continuous loop 17; (2) providing an absorbent material 32 on at least a portion of an exterior surface 30 of a heatable roller 24 mounted for rotation within the housing 12, the absorbent material 32 being capable of absorbing uncured, unreacted portions of another photopolymer layer of the photosensitive printing element 14 when the heatable roller 24 is heated and rotated and the absorbent material 32 contacts at least a portion of the photosensitive printing element 14; (3) heating the heatable roller 24 to a temperature sufficient to soften or liquefy at least a portion of the at least one layer of photosensitive material when the absorbent material 32 contacts the at least one layer of photosensitive material; (4) contacting a surface of at least one photosensitive layer with absorbent material 32 at a point between conveyor 16 and heatable roller 24 such that at least a portion of the liquefied or softened material is absorbed by absorbent material 32; (5) positioning one or more UV light sources 48 within the thermal processor adjacent a width of the absorbent web of blotter material 32 containing the absorbed, softened or liquefied, unreacted portions of photopolymer, wherein the absorbent web of blotter material 32 containing the absorbed, softened or liquefied, unreacted portions of photopolymer moves relative to the one or more UV light sources 48; (6) exposing the web of absorbent blotter material 48 to actinic radiation from one or more UV light sources 32 to crosslink and harden the softened or liquefied unreacted portions of the photopolymer as the absorbent web of blotter material 32 moves relative to the one or more UV light sources 48.

[0080] Preferably, the photosensitive printing element is processed through multiple process steps so that most, if not all, of the uncured photosensitive material can be removed from the surface of the photosensitive printing element to obtain a relief image. The number of passes depends in part on the thickness of the plate relief, the type of photopolymer, the temperature of the thermal processor, etc. For example, a 0.024 inch plate relief would remove an average of 0.002 inches of photopolymer (uncured, unreacted photopolymer) per pass of blotter material, requiring the photosensitive printing element to pass through the thermal processor 12 times.

[0081] Any suitable means for maintaining uniform tension in the web of absorbent material throughout the system may be used, including, for example, one or more idler rollers 36. Other means for maintaining tension in the web may also be provided and will be known to those skilled in the art.

[0082] In some embodiments, one or more idler rollers 36 may be positioned in direct or indirect contact with the web of absorbent material 32. The one or more idler rollers 36 may facilitate changes in direction of the web of absorbent material 32 and / or provide tension to the web of absorbent material 32 to maintain a uniform and desired tension. In some cases, two or more idler rollers 36 may be positioned in close proximity to one another. For example, two or more idler rollers 36 may be positioned in close proximity to one another such that the web of absorbent material 32 is tightly wrapped (i.e., turns sharply) to maintain at least partial contact with an outer surface of each of the two or more idler rollers 36.

[0083] In some embodiments, the linear speeds of the heatable roller 24, the web of absorbent material 32, and the photosensitive printing element 14 can be substantially the same to avoid shear stresses on the photosensitive printing element 14 that can result in non-uniformity in the relief portion plate thickness.

[0084] Although the present disclosure has been described with reference to exemplary implementations, the present disclosure is not limited by or to such exemplary implementations, but rather, various modifications, improvements, and / or alternative implementations may be employed without departing from the spirit or scope of the present disclosure.

Claims

1. 1. A method of curing unreacted photopolymer absorbed in a web of absorbent blotter material during thermal processing of a flexographic printing element in a thermal development assembly, the thermal development assembly receiving an imaged and exposed flexographic printing element, the imaged and exposed flexographic printing element comprising one or more photopolymer layers, the one or more photopolymer layers comprising crosslinked cured portions of photopolymer that form a cured relief image and uncured unreacted portions of photopolymer that are removed during thermal processing to expose the cured relief image; an uncured, unreacted portion of the photopolymer is removed by contacting the one or more photopolymer layers with the web of absorbent blotter material at an elevated temperature to soften or liquefy the uncured, unreacted portion of the one or more photopolymer layers and allowing the softened or liquefied uncured, unreacted portion to be absorbed into the web of absorbent blotter material; The method further comprising: a) positioning one or more UV light sources within the thermal development assembly at a distance from a width of the web of absorbent blotter material containing the absorbed, softened or liquefied, unreacted portions of the photopolymer, wherein the web of absorbent blotter material containing the absorbed, softened or liquefied, unreacted portions of the photopolymer moves relative to the one or more UV light sources; b) exposing the web of absorbent blotter material to actinic radiation from the one or more UV light sources to crosslink and harden the softened or liquefied unreacted portions of the photopolymer as the web of absorbent blotter material moves relative to the one or more UV light sources.

2. The method of claim 1 further comprising winding the web of absorbent blotter material including the crosslinked and cured unreacted portions onto an unwind roller.

3. The method of claim 1 , wherein the one or more UV light sources include one or more UV-LEDs, one or more fluorescent UV exposure tubes, or a combination thereof.

4. 2. The method of claim 1, wherein the one or more UV light sources include a plurality of UV light sources positioned approximately equidistant from one another across the width of the web of absorbent blotter material, such that the width of the web of absorbent blotter material is uniformly exposed to actinic radiation from the one or more UV light sources.

5. The method of claim 1 , wherein the one or more UV light sources operate at wavelengths in the range of 365 to 405 nm.

6. The one or more UV light sources include a plurality of UV-LEDs, and the intensity of each of the one or more UV-LEDs is at least 10 mW / cm ２ The method according to claim 3, wherein

7. The intensity of each of the one or more UV-LEDs is at least 13 mW / cm ２ The method according to claim 6, wherein

8. The intensity of each of the one or more UV light sources is between 13 and 15 mW / cm when the one or more UV light sources are positioned at a distance of about 0.5 inches from the surface of the web of absorbent blotter material. ２ The method of claim 1, wherein

9. The one or more UV light sources include one or more fluorescent UV exposure tubes, and the intensity of each of the one or more fluorescent UV exposure tubes is at least 20 mW / cm ２ The method according to claim 3, wherein

10. The one or more UV light sources include one or more fluorescent UV exposure tubes, and the intensity of each of the one or more fluorescent UV exposure tubes is at least 30 mW / cm ２ The method according to claim 8, wherein

11. The dose of the one or more UV light sources (defined as the intensity of the light source times the residence time of exposure) is at least 130 mJ / cm ２ The method of claim 1, wherein

12. The dosage of the one or more UV light sources is at least 150 mJ / cm ２ The method of claim 10, wherein

13. The dosage of the one or more UV light sources is at least 160 mJ / cm ２ The method of claim 11, wherein

14. 10. The method of claim 1, further comprising one or more heaters that can be positioned either before or after the one or more UV light sources, the one or more heaters assisting in curing uncured unreacted portions of the photopolymer within the web of absorbent blotter material.

15. 2. The method of claim 1, wherein the dose of the one or more UV light sources, defined as the product of light source intensity and exposure residence time, is reduced by using a lower intensity UV light source, fewer UV light sources, or a reduced exposure residence time.

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