Method and system for thermal treatment of flexographic printing elements

Abstract

The present disclosure relates to a system and method configured for curing non-reactive photopolymers collected by an absorbent blotter during heat treatment of a flexographic printing element. Uncured non-reactive portions of the photopolymers are removed by contacting one or more layers of the photopolymers with a web of the absorbent blotter at an elevated temperature to soften or liquefy the uncured non-reactive portions of the one or more layers of the photopolymers and absorbing the softened or liquefied uncured non-reactive portions into the absorbent web of the absorbent blotter. The web of the absorbent blotter material containing the absorbed softened or liquefied non-reactive portions of the photopolymers is exposed to actinic radiation from one or more UV light sources to crosslink and cure the softened or liquefied non-reactive portions of the photopolymers.

Description

Technical Field

[0001] The present disclosure generally relates to a system and method configured for curing non-reactive photopolymers collected by an absorbent ink-receiving material during thermal processing of a flexographic printing element. Background Art

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

[0003] Typical flexographic printing elements are multilayer products, which are sequentially made of a backing or support layer, one or more unexposed photocurable layers, a protective layer or slip film, and a cover sheet. The photocurable printing element can be in the form of a continuous (seamless) sleeve or as a flat printing plate mounted on a carrier. The relief image in the flexographic printing element is produced by imaging and exposing one or more unexposed photocurable layers. This is usually achieved by selectively exposing one or more photocurable layers to actinic radiation, which is used to harden or crosslink one or more photocurable layers in the irradiated area.

[0004] One or more photocurable layers are formed by photopolymerizable materials, which generally include one or more binding agents, one or more reactive monomers, one or more photoinitiators and other performance additives. Examples of photopolymerizable compositions include those described in U.S. Patent Application Publication No. 2004 / 0146806, the teaching of which is incorporated herein by reference in its entirety. Various photopolymerizable compositions include those that can be used as binding agents based on polystyrene-isoprene-styrene, polystyrene-butadiene-styrene, polyurethane and / or thiols (thiolenes). Preferred binding agents include, for example, polystyrene-isoprene-styrene and polystyrene-butadiene-styrene, especially block copolymers of the aforementioned materials.

[0005] Printing elements can be selectively exposed to actinic radiation in various ways. In one alternative, a photographic negative having transparent areas and substantially opaque areas is used to selectively block actinic radiation from being transmitted 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, thereby producing an in-situ negative. This technology is well known in the art, and is described, for example, in U.S. Patents 5,262,275 and 6,238,837 to Fan and 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 is acceptable based on the ability to selectively expose the photopolymer to actinic radiation to selectively cure a portion of the photopolymer.

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

[0007] During the thermal treatment, the different melting temperatures between the cured light and the uncured photopolymer are used to develop the latent image. The basic parameters of this process are known, as described in U.S. Patent No. 7,122,295, U.S. Patent No. 6,773,859, U.S. Patent No. 5,279,697, U.S. Patent No. 5,175,072 and U.S. Patent No. 3,264,103 and WO01 / 88615, WO01 / 18604 and EP1239329, the subject matter of each of which is incorporated herein by reference in its entirety. These processes allow the elimination of the developer solvent and the lengthy plate drying time required to remove the solvent. The speed and efficiency of these processes allow them to be used in the manufacture of flexographic printing elements for printing newspapers and other publications, where fast turnaround times and high productivity are important.

[0008] In order for the printing element to be heat developable, the composition of the photopolymer must be such that there is a significant difference in melting temperature between the cured and uncured polymers. It is this difference that allows an image to be created in the photopolymer upon heating. At the selected temperature, the uncured photopolymer (i.e., the portion of the photopolymer that has not come into contact with the actinic radiation) melts and / or substantially softens, while the cured photopolymer remains solid and intact. The difference in melting temperature allows the uncured photopolymer to be selectively removed, 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 depends on the properties of the particular photopolymer used. However, two main factors should be considered in determining the development temperature:

[0010] (1) the development temperature is preferably set between the melting temperature of the uncured photopolymer at the lower end and the melting temperature of the cured photopolymer at the upper end to allow selective removal of the photopolymer to produce an image; and

[0011] (2) The temperature should be sufficient to melt or substantially soften the uncured photopolymer, thereby allowing it to be removed, and the higher the development temperature, the faster the processing time will be. However, the development temperature should not be so high as to exceed the melting temperature of the cured photopolymer, nor should it be so high as to degrade the cured photopolymer.

[0012] Thereafter, the uncured photopolymer may be softened and / or melted and removed.

[0013] In one type of thermal processor, the heated printing element is contacted with a web of absorbent blotter material, which absorbs or otherwise removes softened and / or melted uncured photopolymer. This removal process is often referred to as "blotting."

[0014] After complete ink absorption, the printing plate element can be post-exposed to further actinic radiation if desired and / or subjected to detackification, cooled, and then ready for use.

[0015] The uncured photopolymer (i.e., non-reactive plate material) is absorbed into a web of absorbent blotter material, which is then rewound onto a roll for subsequent disposal. Depending on the environmental regulations of a region, the non-reactive plate material may be classified as hazardous because it may be harmful to the environment and difficult to dispose of. In addition, a common method of disposing of a web containing non-reactive plate material or absorbent blotter material is incineration, which may release volatile materials into the air.

[0016] In view of the above, it would be desirable to provide an improved method of disposing of a web of absorbent blotter material containing non-reactive material which makes disposal of the material easier and better for the environment. Summary of the invention

[0017] It is an object of the present invention to provide an improved method for handling non-reactive materials which are absorbed into a web of absorbent blotter material during heat treatment.

[0018] It is another object of the present invention to provide an improved method of treating a used web of absorbent blotter material having non-reactive material absorbed therein.

[0019] Still another object of the present invention is to provide a method of reacting a non-reactive component to cross-link the non-reactive component contained in a web of absorbent blotter material.

[0020] It is a further object of the present invention to provide a method for disposing of used webs of absorbent blotter material which is safer for the environment.

[0021] Still another object of the present invention is to provide a method for disposing of used webs of blotter paper material which reduces disposal costs.

[0022] To this end, in one embodiment, the present invention is generally directed to a method of curing a non-reactive photopolymer absorbed into a web of absorbent blotter material during thermal treatment of a flexographic printing element in a thermal developing assembly, wherein the thermal developing assembly receives an imaged and exposed flexographic printing element, the imaged and exposed flexographic printing element comprising one or more layers of photopolymer, the one or more layers of photopolymer comprising cross-linked cured portions of the photopolymer that form a cured relief image and uncured, non-reactive portions of the photopolymer that are removed during thermal treatment to reveal the cured relief image,

[0023] wherein the uncured, non-reactive portions of the photosensitive polymer are removed by contacting the one or more layers of photosensitive polymer with a web of absorbent ink blotting material at an elevated temperature to soften or liquefy the uncured, non-reactive portions of the one or more layers of photosensitive polymer and absorbing the softened or liquefied uncured, non-reactive portions into the absorbent web of absorbent ink blotting material, the method comprising the steps of:

[0024] a) arranging one or more UV light sources in a thermal processor adjacent to a width of an absorbent blotter material containing absorbed softened or liquefied non-reactive portions of a photopolymer, wherein the absorbent web of blotter material containing absorbed softened or liquefied non-reactive portions of a photopolymer is moved relative to the one or more UV light sources; and

[0025] b) exposing the web of absorbent blotter material to actinic radiation from one or more UV light sources as the absorbent web of blotter material moves relative to the one or more UV light sources to crosslink and cure the softened or liquefied non-reactive portions of the photopolymer.

[0026] The present invention provides an improved method of handling and disposing of non-reactive material absorbed into a web of absorbent blotter material during heat treatment, and an improved apparatus for disposing of a web of absorbent blotter material having non-reactive material absorbed therein.

[0027] The system includes one or more UV light sources disposed in close proximity to at least a portion of a web of absorbent material.

[0028] Any combination or arrangement of features, functions and / or embodiments disclosed herein is foreseeable. Additional advantageous features, functions and applications of the disclosed systems and methods of the present disclosure will be apparent from the following description, particularly when read in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Features and aspects of the embodiments are described below with reference to the drawings, where elements are not necessarily drawn to scale and where components may be exaggerated or removed in some views for clarity.

[0030] Exemplary embodiments of the present disclosure are further described with reference to the accompanying drawings. It should be noted that various features, steps and combinations of features / steps described below and shown in the drawings can be arranged and organized in different ways to produce embodiments that are still within the scope of the present disclosure.

[0031] The present invention will now be described with reference to the following drawings, in which:

[0032] Figure 1 schematically depicts a cross-sectional view of an exemplary thermal-based development system according to the present disclosure;

[0033] Additionally, although not all elements may be labeled in every drawing, all elements having the same reference number indicate similar or identical parts. DETAILED DESCRIPTION

[0034] The present disclosure provides a system and method configured for curing non-reactive photopolymer collected by an absorbent ink blotting material during thermal processing of a flexographic printing element.

[0035] However, it should be understood that the disclosed embodiments are merely illustrative of the present disclosure, which can be implemented in various forms. Therefore, the details disclosed herein with reference to exemplary components / manufacturing methods and associated components and processes / techniques used should not be interpreted as limiting, but only as a basis for teaching those skilled in the art how to make and use the advantageous components / systems described herein.

[0036] As used herein, "a," "an," and "the" refer to both the singular and the plural, unless the context clearly indicates otherwise.

[0037] As used herein, the term "about" refers to a measurable value, such as a parameter, amount, duration, etc., and is intended to include variations of + / -15% or less, preferably + / -10% or less, more preferably + / -5% or less, even more preferably + / -1% or less, and still more preferably + / -0.1% or less relative to the specifically stated value, as long as such variations are suitable for performing in the invention described herein. In addition, it should also be understood that the value to which the modifier "about" refers is itself specifically disclosed herein.

[0038] As used herein, for ease of description, spatially relative terms such as "below", "beneath", "lower", "above", "upper", "front", "rear", etc. are used to describe the relationship of one element or feature structure to another or more elements or features. It should also be understood that the terms "front" and "rear" are not intended to be limiting and are intended to be interchangeable under appropriate circumstances.

[0039] As used herein, the terms “include” and / or “comprises” 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.

[0040] As used herein, absorbent material may also be referred to as a "blotter," "blotter material," "absorbent web," or "web of absorbent blotter material" without departing from the spirit / scope of the present disclosure.

[0041] The present invention uses a UV light source to expose and crosslink uncured non-reactive photopolymers which are absorbed into a web of absorbent blotter material during heat treatment. The exposed and crosslinked material is cured and hardened and the web or absorbent blotter material is then wound on a rewind roll for easy and safe disposal.

[0042] In one embodiment, the present invention is generally directed to a method of curing a non-reactive photopolymer absorbed into a web of absorbent blotter material during thermal treatment of a flexographic printing element in a thermal developing assembly, wherein the thermal developing assembly receives an imaged and exposed flexographic printing element, the imaged and exposed flexographic printing element comprising one or more layers of photopolymer, the one or more layers of photopolymer comprising cross-linked, cured portions of the photopolymer that form a cured relief image and uncured, unreacted portions of the photopolymer that are removed during thermal treatment to reveal the cured relief image,

[0043] wherein the uncured, non-reactive portions of the photosensitive polymer are removed by contacting the one or more layers of photosensitive polymer with a web of absorbent ink blotting material at an elevated temperature to soften or liquefy the uncured, non-reactive portions of the one or more layers of photosensitive polymer and absorbing the softened or liquefied uncured, non-reactive portions into the absorbent web of absorbent ink blotting material, the method comprising the steps of:

[0044] a) arranging one or more UV light sources in a thermal processor adjacent to and at a distance from a width of an absorbent blotter material containing absorbed softened or liquefied non-reactive portions of a photopolymer, wherein the absorbent web of blotter material containing absorbed softened or liquefied non-reactive portions of a photopolymer is moved relative to the one or more UV light sources; and

[0045] b) exposing the web of absorbent blotter material to actinic radiation from one or more UV light sources as the absorbent web of blotter material moves relative to the one or more UV light sources to crosslink and cure the softened or liquefied non-reactive portions of the photopolymer.

[0046] Thereafter, the web of absorbent blotter material, now containing the hardened, cross-linked and cured non-reactive portions, may be wound onto a rewinding roll.

[0047] Preferred UV light sources operate at wavelengths in the range of about 365 nm to 405 nm. Various UV light sources may be used including, for example, LED, fluorescent or other similar sources.

[0048] 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 it can take longer to expose.

[0049] The intensity of UV light source is usually about 11mW / cm 2 Up to 16mW / cm 2 In the range of about 13 mW / cm 2 Up to 15mW / cm 2 The intensity varies with the power and number of light sources and with the distance of the UV light sources from the surface of the web of absorbent blotter material. In one embodiment, when the UV light source is arranged at a distance of about 0.5 inches from the surface of the web of absorbent blotter material, the intensity of the UV light source is 13 mW / cm 2 Up to 15mW / cm 2 .

[0050] An important parameter of UV light source is dosage, which is defined as:

[0051] Dosage = (light source) intensity × dwell time (exposure time)

[0052] The amount used varies with the type of light, exposure time, and the photopolymer itself.

[0053] In one aspect of the invention, the UV light source comprises one or more UV-LEDs, preferably a plurality of UV-LEDs arranged across the width of the blotter material. In one embodiment, the plurality of UV-LEDs are arranged in a row at least approximately equidistant from one another across the width of the blotter material. In one embodiment, additional rows of UV-LEDs are used to increase curing or dosage. Using higher intensity UV-LEDs also requires less time to obtain the same dosage.

[0054] Ideally, the web of absorbent blotter material is uniformly exposed to actinic radiation from the UV light source so that all uncured, non-reactive material contained in the web of absorbent blotter material is crosslinked and cured. In one embodiment, the UV-LEDs are arranged in close proximity to each other so that the light (i.e., UV radiation) overlap is uniform. In one aspect, the UV-LEDs are arranged closely together to increase intensity and obtain the desired dosage, and crosslink the photopolymer more quickly. The number of UV-LEDs will depend in part on the intensity of each individual UV-LED, the distance of the UV-LED from the web of absorbent blotter material, and the width of the web of absorbent blotter material.

[0055] For example, the UV-LEDs may be spaced approximately equidistantly from one another by about 12.5 mm (0.5 in) along the width of the web of absorbent blotter material. This spacing is only one example of spacing of the UV-LEDs, and the spacing may vary with different arrangements or configurations of the UV-LEDs being tested.

[0056] In one embodiment, a UV light source, such as a UV-LED, is fixedly mounted in a housing of the thermal processor and the blotter material is continuously passed under or relative to the fixedly mounted UV-LED. In one embodiment, the velocity of the web of absorbent blotter material relative to the fixedly mounted UV light source is in the range of about 1 ft / min to about 10 ft / min, more preferably about 5 ft / min (1 inch / second).

[0057] To calculate the required dosage, data from a typical exposure unit used to expose through the bottom of a plate to give a "bottom" across the entire plate is analyzed.

[0058] According to this standard UV exposure light source, it is determined that the light source used has a power of 30mW / cm 2The intensity of the light source required to cure 0.002 inches of photopolymer in a static system is 5 seconds. This gives 30mW / cm 2 × 5 seconds = 150 mJ / cm 2 In addition, we can calculate that an average of about 0.002 inches of photopolymer (uncured, unreacted photopolymer) is removed per pass of the blotter material in the thermal processor during the thermal treatment (0.024 inches of plate relief / 12 passes = 0.002 inches of polymer per pass). As described herein, during the thermal treatment, the web of absorbent blotter material is contacted with the flexographic relief image printing element at an elevated temperature that softens or liquefies the uncured, non-reactive portions of the photopolymer, and the uncured, non-reactive portions are absorbed into the web of absorbent blotter material.

[0059] In one embodiment, the dosage is at least 130 mJ / cm 2 , preferably at least 140 mJ / cm 2 , more preferably at least 150 mJ / cm 2 , and more preferably at least 160 mJ / cm 2 The inventors of the present invention have found that an amount within this range is capable of completely curing the uncured, unreacted photopolymer absorbed in the web of absorbent blotter material for subsequent disposal.

[0060] However, depending on the particular UV light source, such high dosages may be difficult to achieve.

[0061] For example, many common UV-LEDs have a power of only about 13 mW / cm 2 Up to 14mW / cm 2 Intensity. Therefore, a larger number of UV-LEDs will be needed to achieve the desired dosage. For example, using 3 rows of LEDs with one inch distance between them and a web speed of 5 ft / min will require a dwell time (dosage / intensity) of 9 to 10 seconds, and will also require a large number of UV LEDs. In order to reduce the exposure / dwell time and the number of rows of LEDs, it is therefore necessary to increase the intensity of the LEDs themselves or pack them closer together.

[0062] On the other hand, lower web processing speeds may be better suited for UV-LEDs. Using a lower processing time of about 2 ft / min to 3 ft / min, more preferably 2.5 ft / min to 2.7 ft / min, and using 13 mW / cm 2 Up to 14mW / cm 2 The intensity, the number of UV-LEDs and / or the number of UV-LED rows can be reduced by 50%.

[0063] To cover higher production speeds (i.e., 5 ft / min or higher), fluorescent UV exposure tubes can also be used. With fluorescent UV exposure tubes, the intensity is about 30 mW / cm 2 , and in order to achieve the same dosage (30mJ / cm 2 × 5 seconds), only 5 seconds of exposure will be needed. Each standard UV tube is about 1 inch in diameter, and 5 UV fluorescent tubes can be used for exposure. Although this seems to be a better choice, UV fluorescent tubes are fragile and may break easily if not handled properly.

[0064] The speed of the blotter paper is constant in the thermal system before and after the lamp array. Typically, the processing speed of the blotter paper remains constant throughout the process. Additional LED or UV lamp rows can be easily added and / or switched on / off as the machine processing speed increases. Therefore, in one embodiment, the system includes enough light sources to cover all situations, including blotter paper speed, specific photopolymers, etc., and control mechanisms to adjust the speed of the web and the number / position of light sources used.

[0065] Since it is difficult to monitor reactivity in real time, the dosage requirements are chosen to be higher than necessary with a safety margin. However, one skilled in the art can determine the dosage requirements for a particular type of photopolymer and / or a higher intensity light source, etc., using the processes described herein.

[0066] Temperature has a negative impact on UV output, and higher temperatures reduce UV output. In one embodiment, part of the system design includes a heat sink for removing / dissipating heat from the UV-LEDs. In addition to this, the temperature of the resin in the blotter paper generally has a positive impact. The resin is heated during thermal treatment, which will increase the reactivity of the photopolymer and result in a reduction in the required dosage. Therefore, optionally, the system may also include a heater for helping to cure the resin in the blotter paper. In one embodiment, if a heater is used to help cure the resin in the blotter paper, the required dosage is reduced by using a lower intensity / smaller amount of light source and / or reducing the residence time.

[0067] The system described herein can be used with photopolymers using photoinitiators operating in the range of about 365 nm to 405 nm. Among other things, photopolymers (including various elements that can polymerize more quickly) will reduce the cost of the unit by reducing the amount required to cure the printing plate (i.e., reducing light intensity and / or reducing dwell time).

[0068] In one embodiment and as Figure 1As shown, the present invention is generally directed to a thermal development assembly including a system 10 for processing a relief image printing element 14. The photosensitive printing element 14 generally includes a flexible substrate and at least one layer of photosensitive material deposited on the flexible substrate.

[0069] The system 10 includes a housing 12, a conveyor 16 including a continuous loop 17 (wherein a photosensitive printing element 14 can be positioned on the continuous loop 17 of the conveyor 16), at least one heatable roller 24 mounted in the housing 12, and an absorbent blotter material 32 covering at least a portion of the at least one heatable roller 24 (wherein the absorbent material 32 can absorb liquefied or softened uncured photosensitive material from the photosensitive printing element 14 when the photosensitive printing element 14 contacts the absorbent material 32 on a portion of the at least one heatable roller 24).

[0070] The system 10 for processing a photosensitive printing element 14 includes a housing 12 for housing at least the elements of the thermal-based development system 10 .

[0071] The thermal-based development system 10 described herein contains a preformed, image-wise exposed to actinic radiation, flexible photosensitive printing element 14 having a base layer, an adjacent layer of radiation-hardenable elastomeric material (curable layer), and an optional infrared-sensitive layer for forming 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 that can be processed in the thermal-based development system of the present invention are described in U.S. Pat. Nos. 5,175,072 to Martens, 5,262,275 and 6,238,837 to Fan, and 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.

[0072] In one embodiment, and prior to processing in a thermal development assembly as described herein, a portion of the radiation-curable layer is cured, preferably by actinic radiation passing through the lower surface of the substrate to produce a cured "bottom layer". The film is then imagewise exposed from the opposite surface, either through a photographic negative or an in-situ negative produced by laser ablation of a mask layer, to cure the desired portion of the plate. The remaining portion of the radiation-curable layer after curing consists of a cured portion and an uncured portion. The photosensitive printing element is then transferred to a thermal development assembly to remove the uncured portion of the radiation-curable layer and expose a relief image therein, wherein the relief image consists of the crosslinked and cured portions of the radiation-curable layer of the photosensitive printing element.

[0073] like Figure 1As described, a conveyor 16 attached to a drive motor (not shown) is typically used to transport and convey the photosensitive printing element 14 into and through the thermal plate processing system. The conveyor 16 can be mounted in a fixed position in 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) can be used to provide additional support to the conveyor 16 and prevent the continuous loop 17 from sagging due to the weight of the photosensitive printing element 14. In one embodiment, the continuous loop 17 includes a wire mesh.

[0074] The leading edge of the photosensitive printing element 14 may be held in place against the continuous loop 17 of the conveyor 16 by suitable fastening means (not shown), such as clamps and / or vacuum. In one embodiment, vacuum is provided to at least one of the first roller 18 and the second roller 20 of the conveyor 16 and is 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.

[0075] During operation, the conveyor 16 with the photosensitive printing element 14 mounted thereon moves in a first direction 22 toward a 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 a direction 28 opposite to 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 fixedly mounted on a pivot (not shown), which allows the heatable roller to be urged toward the conveyor 16.

[0076] In some embodiments, a suitable device, such as one or more pneumatic cylinders (not shown), is used to push the heatable roller 24 toward the photosensitive printing element 14 on the conveyor 16. The pneumatic cylinder positions the heatable roller 24 at 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 travels on the continuous loop 17 of the conveyor 16 around the second roller 20.

[0077] A web of absorbent material 32 is guided over at least a portion of an outer surface 30 of heatable roller 28. When heatable roller 24 rotates and is heated and the web of absorbent material 32 contacts at least a portion of photosensitive printing element 14, the web of absorbent material 32 is able to absorb (e.g., remove) liquefied or softened uncured material from photosensitive printing element 14. Heatable roller 24 rotates in direction 28 opposite direction 22 of conveyor 16 so that photosensitive printing element 14 and the web of absorbent material 32 can contact each other and then separate.

[0078] Heat can be provided to the heatable roller 24 by a core heater, which can maintain 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 in the photosensitive material. In one embodiment, the heatable roller 24 is heated to a temperature between about 150°C and about 250°C and operates at this temperature. This upper limit is largely determined by the melting temperature of the web of the 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 the absorbent material 32 does not move and the portion of the web of the absorbent material 32 that contacts the heatable roller 24 is stationary. Although the heatable roller 24 preferably includes an electric core heater to provide the desired surface temperature, the desired surface temperature can also be provided using steam, oil, hot air and various other heating sources.

[0079] 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 absorbent material 32 may depend in part on the thickness of the photosensitive printing element 14 to be 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 suitable absorbent materials will be known to those skilled in the art and may be used in the present invention.

[0080] The web of absorbent material 32 has deposited therein or absorbed therein the softened or liquefied photopolymer removed (i.e., absorbed) from the photosensitive printing element 14 after contact with the flexographic printing element at an elevated temperature that softens or liquefies uncured, non-reactive portions of one or more photopolymer layers of the flexographic printing element.

[0081] As described herein, the system 10 includes a UV light source 48. A UV light source (e.g., UV LED, UV fluorescent) 50 can be positioned in close proximity to the web of absorbent blotter material 32. For example, the UV light source can be positioned at a distance of about 0.25 inches to about 2 inches from the web of absorbent blotter material 32, and more preferably at a distance of about 0.50 inches to about 1.0 inches from the web of absorbent blotter material. The UV light source 48 cures the liquefied or softened material that has been absorbed by the web of absorbent material 32. In a non-limiting example, the wavelength of the UV light source can be between about 365 nm and about 405 nm.

[0082] The desired intensity of the UV light source can be at least partially associated with 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, the operating parameters of the UV light source (e.g., the number of LEDs in the LED array), and combinations of the foregoing.

[0083] In some embodiments, the system 10 may include a second UV light source (not shown) arranged in close proximity to the first UV light source. For example, the second UV light source may be positioned opposite the first UV light source so that the second UV light source crosslinks and cures the softened or liquefied non-reactive photosensitive polymer on the opposite side of the absorbent material 32. In a non-limiting example, the wavelength of the second UV light source may be between about 365nm and about 405nm. In another non-limiting example, the desired intensity of the second UV light source may be at least partially related to the elements of the first UV light source, as defined above. The wavelengths and / or intensities of the UV light source and the second UV light source may be similar to each other or may be different from each other. In addition, the second UV light source may be arranged at 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 arranged at a distance of 0.5 inches to 1.0 inches from the web of absorbent blotter material.

[0084] The absorbent material 32 containing the solidified and non-reactive products may then be wound onto a take-up roll for subsequent removal and / or disposal.

[0085] Take-up roll 38 is independently driven by a motor (not shown), which is preferably a variable speed motor. Take-up roll 38 collects the "spent" web of absorbent material 32 after it has contacted photosensitive printing element 14 and the removed portion of the liquefied or softened 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 have variable heights in the relief portions, or may warp and be commercially unacceptable.

[0086] In another embodiment, the system 10 may include a second heating source (not shown) that may be positioned adjacent to the point where the absorbent material 32 contacts the at least one layer of photosensitive material on the conveyor 16. The second heating source may provide an auxiliary heating source to further soften and liquefy portions of the at least one layer of photosensitive material on the conveyor 16.

[0087] It will be apparent to those skilled in the art that the conveyor 16 including the first roller 18 and the second roller 20 and the heatable roller 24 are driven by suitable means (i.e., motors). In addition, a controller (such as a microprocessor) may be used in the system of the present invention to control the operation of each of the elements in the plate processor 10. Such controllers are well known in the art. An example of a controller for controlling various elements in a plate processor is described in U.S. Pat. No. 5,279,697 to Peterson et al., the subject matter of which is incorporated herein by reference in its entirety.

[0088] The method of the present invention comprises the following steps:

[0089] (1) positioning a photosensitive printing element 14 on a conveyor 16, the conveyor 16 comprising a continuous loop 17 supported by at least a first roller 18 and a second roller 20, wherein the photosensitive printing element 14 is supported on the continuous loop 17;

[0090] (2) supplying an absorbent material 32 to at least a portion of an outer surface 30 of a heatable roller 24 mounted for rotation within housing 12, wherein the absorbent material 32 is capable of absorbing uncured, non-reactive portions of one or more photopolymer layers of photosensitive printing element 14 when heatable roller 24 is heated and rotated and the absorbent material 32 contacts at least a portion of photosensitive printing element 14;

[0091] (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;

[0092] (4) contacting the surface of the at least one layer of photosensitive material and the absorbent material 32 at a point between the conveyor 16 and the heatable roller 24 so that at least a portion of the liquefied or softened material is absorbed by the absorbent material 32; and

[0093] (5) arranging one or more UV light sources 48 in the thermal processor adjacent to a width of the absorbent blotter material 32 containing the absorbed softened or liquefied non-reactive portions of the photopolymer, wherein the absorbent web of blotter material 32 containing the absorbed softened or liquefied non-reactive portions of the photopolymer is moved relative to the one or more UV light sources 48; and

[0094] (6) Exposing the web of absorbent blotter material 32 to actinic radiation from one or more UV light sources 48 as the absorbent web of blotter material 32 moves relative to one or more UV light sources 48 to crosslink and cure the softened or liquefied non-reactive portions of the photopolymer.

[0095] Preferably, the photosensitive printing element is processed through the steps of the process a number of times so that most, if not all, of the uncured photosensitive material is removed from the surface of the photosensitive printing element to obtain the relief image. The number of passes will depend in part on the thickness of the plate relief, the type of photopolymer, the temperature of the thermal processor, etc. For example, for a 0.024 inch plate relief, where the blotter material removes an average of 0.002 inches of photopolymer (uncured, unreacted photopolymer) per pass, 12 passes of the photosensitive printing element through the thermal processor would be required.

[0096] 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 are known to those skilled in the art.

[0097] In some embodiments, one or more idler rollers 36 may be positioned in direct or indirect contact with the web of absorbent material 32. One or more idler rollers 36 may facilitate changing the direction of the web of absorbent material 32 and / or may 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 each other. For example, two or more idler rollers 36 may be positioned in close proximity to each other so that the web of absorbent material 32 is tightly wound (i.e., makes a sharp turn) so as to maintain at least partial contact with the outer surface of each of the two or more idler rollers 36.

[0098] In some embodiments, the line speeds of heatable roller 24, web of absorbent material 32, and photosensitive printing element 14 may be substantially the same to avoid any shear stress on photosensitive printing element 14. Shear stress as disclosed may result in non-uniform relief portion plate thickness.

[0099] Although the present disclosure has been described with reference to exemplary embodiments, the present disclosure is not limited to such exemplary embodiments. Instead, various modifications, improvements and / or alternative embodiments may be adopted without departing from the spirit or scope of the present disclosure.

Claims

1. A method of curing a non-reactive photopolymer absorbed into a web of absorbent blotter material during heat treatment of a flexographic printing element in a thermal developing assembly, wherein the thermal developing assembly receives an imaged and exposed flexographic printing element, the imaged and exposed flexographic printing element comprising one or more layers of photopolymer, the one or more layers of photopolymer comprising cross-linked cured portions of the photopolymer forming a cured relief image and uncured, non-reactive portions of the photopolymer that are removed during heat treatment to reveal the cured relief image, wherein the uncured, non-reactive portions of the photopolymer are removed by contacting the one or more layers of photopolymer with the web of absorbent blotter material at an elevated temperature to soften or liquefy the uncured, non-reactive portions of the one or more layers of photopolymer and absorbing the softened or liquefied uncured, non-reactive portions into the web of absorbent blotter material, The method comprises the following steps: a) arranging one or more UV light sources in a thermal processor, said one or more UV light sources being at a distance from a surface of the web of absorbent blotter material containing the absorbed softened or liquefied non-reactive portions of said photopolymer, wherein the web of absorbent blotter material containing the absorbed softened or liquefied non-reactive portions of said photopolymer is moved relative to said one or more UV light sources; and b) exposing the web of absorbent blotter material to actinic radiation from the one or more UV light sources as the web of absorbent blotter material moves relative to the one or more UV light sources to crosslink and cure the softened or liquefied non-reactive portions of the photopolymer.

2. The method of claim 1 further comprising the step of winding the web of absorbent blotter material containing the cross-linked and cured non-reactive portions onto a rewind roll.

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

4. The method of claim 1 , wherein the one or more UV light sources are a plurality of UV light sources arranged equidistant from one another on the surface of the web of absorbent blotter material, wherein the surface of the web of absorbent blotter material is uniformly exposed to actinic radiation from the plurality of UV light sources arranged equidistant from one another.

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

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

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

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

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

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

11. The method of claim 1, wherein the one or more UV light sources have a dosage of at least 130 mJ / cm 2 , the dosage is defined as the intensity of the light source multiplied by the dwell time of exposure.

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

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

14. The method of claim 1, further comprising one or more heaters positionable before or after the one or more UV light sources, wherein the one or more heaters assist in curing the uncured, unreacted photopolymer in the web of absorbent blotter material.

15. The method of claim 1, wherein the dosage of the one or more UV light sources is reduced by using a lower intensity UV light source, fewer UV light sources, or a reduced exposure dwell time, the dosage being defined as the intensity of the light source multiplied by the exposure dwell time.

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