Apparatus for Thermal Processing of Flexographic Printing Elements

Abstract

An apparatus for thermally processing a relief image printing element and a method of using the same. The relief image printing element comprises at least one photopolymer layer, and is selectively exposed to actinic radiation to crosslink portions of the at least one photopolymer layer, while portions of the at least one photopolymer layer are not exposed to actinic radiation, and are not crosslinked. The apparatus comprises: a) a means for supporting the relief image printing element; b) heating means for melting or softening non-crosslinked portions of the at least one photopolymer layer; c) at least one rotatable roll that is capable of bringing a blotting material into contact with the at least one photopolymer layer to remove the melted or softened non-crosslinked portions of the at least one photopolymer layer; and d) a rotatable cleaning roll arranged adjacent to the at least one rotatable roll, for removing non-crosslinked photopolymer remaining on a surface of the at least one rotatable roll after step c).

Claims

1. An apparatus for thermally processing a relief image printing element, wherein the relief image printing element comprises at least one photopolymer layer, and wherein the relief image printing element is selectively exposed to actinic radiation to crosslink portions of the at least one photopolymer layer, while portions of the at least one photopolymer layer are not exposed to actinic radiation, and are not crosslinked, the apparatus comprising: a) means for supporting the relief image printing element; b) heating means for melting or softening non-crosslinked portions of the at least one photopolymer layer; c) at least one rotatable roll that is capable of bringing a moving web of blotting material into contact with the at least one photopolymer layer to remove the melted or softened non-crosslinked portions of the at least one photopolymer layer, wherein a nip is formed between the means for supporting the relief image printing element and the at least one rotatable roll, wherein as the at least one rotatable roll rotates against the relief image printing element, melted or softened non-crosslinked portions of the at least one photopolymer layer are transferred from the printing element to the moving web of blotting material; d) a rotatable cleaning roll arranged adjacent to the at least one rotatable roll, for removing non-crosslinked photopolymer remaining on a surface of the at least one rotatable roll after step c), wherein the rotatable cleaning roll comprises a cleaning belt, wherein the cleaning belt is supported by the rotatable cleaning roll and a second roll spaced apart from the rotatable cleaning roll; wherein the rotatable cleaning belt rotates against the surface of the at least one rotatable roll after the moving web of blotting material has removed substantially all of the non-crosslinked photopolymer remaining on the surface of the at least one roll to transfer non-crosslinked photopolymer from the surface of the at least one rotatable roll to a surface of the cleaning belt.

2. (canceled)

3. The apparatus according to claim 1, wherein the rotatable cleaning roll rotates at a speed that is sufficient to remove substantially all of the residual photopolymer remaining on the at least one rotatable roll.

4. The apparatus according to claim 3, wherein the rotatable cleaning roll rotates at a speed that is slower than the rotational speed of the at least one rotatable roll.

5. The apparatus according to claim 3, wherein the rotatable cleaning roll rotates at substantially the same speed as the at least one rotatable roll.

6. The apparatus according to claim 1, wherein the rotatable cleaning roller is substantially smaller than the at least one rotatable roll.

7. The apparatus according to claim 6, wherein the rotatable cleaning roller has a diameter that is less than about 75% of the diameter of the at least one rotatable roll.

8. The apparatus according to claim 7, wherein the rotatable cleaning roller has a diameter that is less than about 50% of the diameter of the at least one rotatable roll.

9. (canceled)

10. The apparatus according to claim 1, wherein the cleaning belt is a continuous belt.

11. The apparatus according to claim 1, wherein the cleaning belt comprises a material selected from the group consisting of polyurethane resins, ethylene-propylene-diene rubbers, silicone rubbers and combinations of one or more of the foregoing.

12. The apparatus according to claim 1, comprising a scraping means positioned adjacent to the second roll, when the scraping means scrapes collected residual photopolymer from the surface of the cleaning belt.

13. (canceled)

14. A method of thermally processing a relief image printing element, wherein the relief image printing element comprises a backing layer and at least one photopolymer layer disposed on the backing layer, wherein the relief image printing element is selectively exposed to actinic radiation to crosslink portions of the at least one photopolymer layer, wherein portions of the at least one photopolymer layer are not exposed to actinic radiation and are not crosslinked, the method comprising the steps of: a) melting or softening non-crosslinked portions of the at least one photopolymer layer; b) causing contact between the surface of the relief image printing element and a moving web of blotting material arranged on a portion of the at least one rotatable roll, wherein when the at least one rotatable roll rotates, the moving web of blotting material contacts at least a portion of a surface of the at least one photopolymer layer and melted or softened non-crosslinked portions of the at least one photopolymer layer are transferred to the moving web of blotting material; and c) causing contact between the at least one rotatable roll and a rotatable cleaning roll after the moving web of blotting material contacts the at least the portion of the surface of the at least one photopolymer layer, wherein the rotatable cleaning roll comprises a cleaning belt, wherein the cleaning belt is supported by the rotatable cleaning roll and a second roll spaced apart from the rotatable cleaning roll; wherein the cleaning belt rotates against the surface of the at least one rotatable roll after the moving web of blotting material has removed substantially all of the non-crosslinked photopolymer remaining on the surface of the at least one roll to transfer non-crosslinked photopolymer from the surface of the at least one rotatable roll to a surface of the cleaning belt.

15. (canceled)

16. (canceled)

17. The method according to claim 14, wherein the cleaning belt is a continuous belt.

18. The method according to claim 14, further comprising the step of scraping collected residual photopolymer from the surface of the cleaning belt.

19. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] For a fuller understanding of the invention, reference is had to the following description taken in connection with the accompanying figures, in which:

[0037] FIG. 1 depicts an apparatus for thermally processing a relief image printing element in accordance with one embodiment of the present invention.

[0038] FIG. 2 depicts an apparatus for thermally processing a relief image printing element in accordance with another embodiment of the present invention.

[0039] Also, while not all elements may be labeled in each figure, all elements with the same reference number indicate similar or identical parts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0040] In one embodiment, the present invention relates generally to an apparatus for thermally processing a relief image printing element, wherein the relief image printing element comprises at least one photopolymer layer, and wherein the relief image printing element is selectively exposed to actinic radiation to crosslink portions of the at least one photopolymer layer, while portions of the at least one photopolymer layer are not exposed to actinic radiation, and are not crosslinked, the apparatus comprising: [0041] a) means for supporting the relief image printing element; [0042] b) heating means for melting or softening non-crosslinked portions of the at least one photopolymer layer; [0043] c) at least one rotatable roll that is capable of bringing a blotting material into contact with the at least one photopolymer layer to remove the melted or softened non-crosslinked portions of the at least one photopolymer layer, wherein a nip is formed between the means for supporting the relief image printing element and the at least one rotatable roll, wherein as the at least one rotatable roll rotates against the relief image printing element, melted or softened non-crosslinked portions of the at least one photopolymer layer are transferred from the printing element to the blotting material; [0044] d) a rotatable cleaning roll arranged adjacent to the at least one rotatable roll, for removing non-crosslinked photopolymer remaining on a surface of the at least one rotatable roll after step c).

[0045] As described herein, the rotatable cleaning roll is used to remove residual photopolymer remaining on a surface of the at least one rotatable roll after thermal processing.

[0046] The rotatable cleaning roll is situated at a point after the used blotting material detaches from the at least one rotatable roll, but before the point where the clean non-woven blotter initially contacts the at least one rotatable roll. Thus, in one embodiment, and as seen in FIG. 1, the rotatable cleaning roll 40 is situated at a point that is approximately 180 from the nip 28 formed between the means for supporting the relief image printing element 20 and the at least one rotatable roll 24. Thus, the rotatable cleaning roll 40 is situated at a point that is approximately directly opposite that of the nip 28.

[0047] The rotatable cleaning roll 40 rotates against a surface of the at least one rotatable roll 24 to remove any non-crosslinked photopolymer remaining on the surface of the at least one rotatable roll 24 after the blotting material 26 has removed substantially all of the non-crosslinked photopolymer from the surface of the printing element 20.

[0048] The rotatable cleaning roll 40 rotates at a speed that is sufficient to remove substantially all of the residual photopolymer remaining on the at least one rotatable roll 24. By substantially what is meant is that there is no visible residual photopolymer remaining on the surface of the at least one rotatable roll.

[0049] In one embodiment, the at least one rotatable roll 24 rotates at a first speed and the rotatable cleaning roll 40 rotates at a second slower speed. In another embodiment, the at least one rotatable roll 24 and the rotatable cleaning roll 40 rotate at substantially the same speed.

[0050] As also seen in FIG. 1, the rotatable cleaning roll 40 is substantially smaller than the at least one rotatable roll 24 so that the rotatable cleaning roll 40 does not interfere in any way with the operation of the at least one rotatable roll 24 in removing non-crosslinked photopolymer from the surface of the relief image printing element 20. Thus, in one embodiment the rotatable cleaning roll 40 has a diameter that is less than about 75% of the diameter of the at least one rotatable roll 24, and more preferable has a diameter that is less than about 50% of the diameter of the at least one rotatable roll 24.

[0051] In one embodiment, the rotatable cleaning roll 40 comprises a cleaning belt 42. The cleaning belt 42 is a continuous belt that is supported by the rotatable cleaning roll 40 and a second larger roll 44 spaced apart from the rotatable cleaning roll 24 to maintain tension on the cleaning belt 42 wrapped around the rotatable cleaning roll 40 and the second roll 44. Thus, in this embodiment the cleaning belt itself picks up the residual non-crosslinked photopolymer remaining on the at least one rotatable roll 24. In addition, if desired, the cleaning belt 42 may further comprise a scraping means 50 positioned adjacent to the second larger roll 44 to scrape collected photopolymer from the surface of the cleaning belt 42. The scraping means 50 can be a doctor blade or another similar device shaped to fit against the surface of the second larger roll 44. The scraping means 50 may be coupled to a blade holder so that the scraping means 50 can be adjusted and/or replaced as needed.

[0052] In another embodiment, the rotatable cleaning roll 40 comprises a blotting material 48 that is brought into contact with a surface of the at least one rotatable roll 40 at a point substantially opposite the nip 28 so that the blotting material 48 on the rotatable cleaning roll 40 can remove residual non-crosslinked photopolymer remaining on the surface of the at least one rotatable roll 24. In this embodiment, the blotting material 48 of the rotatable cleaning roll 40 is separate from the blotting material 26 of the at least one rotatable roll 24 and the two blotting materials each have a separate feed roll and take up roll as seen in FIG. 2. Thus, the primary blotting material 26 for removing non-crosslinked photopolymer from the surface of the relief image printing element 20 is supplied from a supply roller 30 and is rewound onto take-up roller 32, while the secondary blotting material 48 for removing residual non-crosslinked photopolymer is supplied from secondary supply roller 52 and is rewound onto secondary take-up roller 54. In addition, while the particular blotting material used for both the at least one rotatable roll 24 and the rotatable cleaning roll 40 may comprise the same material, the feed sources for each source of blotting material are different.

[0053] One advantage of the cleaning roll described herein is that the cleaning roll functions continuously during operation of the thermal processor, thereby reducing the amount of time that that the photopolymer residue remains on the hot surface of the at least one rotatable roll. This reduces the tendency of the photopolymer residue to degrade and become intractable to cleaning.

[0054] The thermal processor 10 of the invention comprising a means for supporting the relief image printing element 20. As depicted in FIG. 1, one means for supporting the relief image printing element 20 comprises a conveyor 12 comprising a continuous loop 14 arranged around a plurality of rolls 16 and 18. Optionally, one or more additional rollers (not shown) may be used to provide additional support to the conveyor 12 to prevent the continuous loop 14 from sagging from the weight of the relief image printing element 20. In one embodiment, the continuous loop 14 comprises wire mesh. The relief image printing element 20 may be held on the conveyor 12 by various means, including a clamp, vacuum or friction. In an alternate embodiment, the relief image printing element may be in the form of a continuous in-the-round (CITR) photopolymer sleeve and the means for supporting the CITR photopolymer sleeve comprising a printing cylinder. Other means for supporting the relief image printing element 20 would also be known to those skilled in the art.

[0055] The heating means for melting or softening non-crosslinked photopolymer may comprise a supplemental heater 22 arranged in a preheating zone prior to and/or adjacent to the at least one rotatable roll 24 to improve the efficiency of the softening/melting of the non-crosslinked photopolymer and to further soften and liquefy portions of the at least one layer of photopolymer material. Although various types of heaters may be used, preferably the supplemental heater is an infrared heater.

[0056] In addition, the at least one rotatable roll 24 is preferably heated to and maintained at a temperature of between about 120 and about 200 C. while the relief image printing element 20 is in contact with the at least one rotatable roll 24 through the blotting material 26. This allows the at least one rotatable roll 24 to melt and/or soften the non-crosslinked photopolymer and allows for the melted or softened photopolymer to be removed from the surface of the relief image printing element 20.

[0057] The at least one rotatable roll 24 is capable of bringing a blotting material 26 into contact with the at least one photopolymer layer of the relief image printing element 20 to remove the melted or softened non-crosslinked portions of the at least one photopolymer layer, wherein a nip 28 is formed between the means for supporting the relief image printing element 20 and the at least one rotatable roll 24, wherein as the at least one rotatable roll 24 rotates against the relief image printing element 20, melted or softened non-crosslinked portions of the at least one photopolymer layer are transferred from the printing element 20 to the blotting material 26.

[0058] The blotting material 26 is supplied to the at least one rotatable roll 24 from a supply roll 30 of the blotting material 26, wherein the blotting material 26 is fed from the supply roll 30 and around an outer surface of the at least one rotatable roll 24, wherein the blotting material 26 initially contacts the at least one rotatable roll 24 at a point prior to the nip 28 and separates from the at least one rotatable roll 24 at a point after the nip 28. The blotting material 26 is looped under and around at least the portion of the at least one rotatable roll 24 that contacts the imaged surface of the relief image printing element 20. Fresh blotting material 26 is continuously supplied to the surface of the at least one rotatable roll 24 from the supply roll 30 of the web of blotting material 26.

[0059] The apparatus described herein also comprises a take-up roll 32, wherein the blotting material 26 containing melted or softened non-crosslinked portions of the at least one photopolymer layer is rewound for disposal. The take-up roll 32 may be independently belt driven by a motor (not shown), such as a variable speed motor. The take-up roll 32 collects the web of blotting material 26 after it has contacted the relief image printing element 20 and removed portions of the photopolymer layer that were liquefied or softened. An auto-slicing device (not shown), may be used to change over the supply roll 30 of blotting material 26 to a fresh roll of blotting material 26.

[0060] The blotting materials 26 and 48 may be selected from the group consisting of screen mesh, woven fabric, non-woven fabric, paper and other similar materials that can withstand the operating temperatures of the thermal processor and absorb and remove non-crosslinked photopolymer. Either woven or non-woven fabric is used and the fabric can be polymer based or paper, so long as the fabric can withstand the operating temperatures involved. The selection of the blotting material depends in part upon the thickness of the photosensitive printing element to be processed, the melting temperature of the blotting material, and the heat transfer characteristics of both the photosensitive printing element and the blotting material. In one embodiment, the blotting material 26 is a non-woven blotting material, such as a non-woven fabric.

[0061] The cleaning belt 42 may comprise a material that is suitable for taking up and removing non-crosslinked photopolymer remaining on the surface of the at least one rotatable roll 24. The material of the cleaning belt must be sufficient tough and durable for long term use at the temperature of the thermal processor and be flexible to be wrapped around the rotatable cleaning roll 40. For example, the cleaning belt may comprise polyurethane resins, ethylene-propylene-diene rubbers, silicone rubbers, among others.

[0062] The apparatus described herein also preferably comprises a means for maintaining contact between the at least one roll 24 and the relief image printing element 20. The means for maintaining contact may comprise an air cylinder or a hydraulic cylinder that acts to force the at least one roll 24 against the imaged surface of the relief image printing element 20. Other means for maintaining contact between the at least one roll 24 and the relief image printing element 20 would also be known to those skilled in the art.

[0063] The present invention also relates generally to a method of thermally processing a relief image printing element using the apparatus described herein. As described above, the relief image printing element comprises a backing layer and at least one photopolymer layer disposed on the backing layer, wherein the relief image printing element is selectively exposed to actinic radiation to crosslink portions of the at least one photopolymer layer, wherein portions of the at least one photopolymer layer are not exposed to actinic radiation and are not crosslinked. The method generally comprises the steps of: [0064] a) melting or softening non-crosslinked portions of the at least one photopolymer layer; [0065] b) causing contact between the surface of the relief image printing element and a blotting material arranged on a portion of the at least one rotatable roll, wherein when the at least one rotatable roll rotates, the blotting material contacts at least a portion of a surface of the at least one photopolymer layer and melted or softened non-crosslinked portions of the at least one photopolymer layer are transferred to the blotting material; and [0066] c) causing contact between the at least one rotatable roll and a rotatable cleaning roll after the blotting material contacts the at least the portion of the surface of the at least one photopolymer layer.

[0067] As described herein the step of causing contact between the at least one rotatable roll 24 and a rotatable cleaning roll 40 after the blotting material 26 contacts the at least the portion of the surface of the at least one photopolymer layer comprises positioning the rotatable cleaning roll 40 adjacent to the at least one rotatable roll 24 at a point that is approximately opposite the nip 28 formed between the means for supporting the relief image printing element 20 and the at least one rotatable roll 24. Thus, when the at least one rotatable roll 24 rotates against at least a portion of the relief image printing element 20 and non-crosslinked photopolymer is removed from the surface of the at least the portion of the relief image printing element 20 by the blotting material 26, any residual non-crosslinked photopolymer remaining on the surface of the at least one rotatable roll after the blotting step can be removed by the at least one rotatable cleaning roll 40.

[0068] The thermal nip 28 is used to transfer non-crosslinked photopolymer from the imaged relief image printing element 20 to the surface of at least one rotatable roll 24 which is preferably heated to a temperature of between about 120 and about 200 C. Thereafter, the at least one rotatable roll with the cleaning belt 42 or the secondary blotting material 48 positioned thereon, is used to remove the residual non-crosslinked photopolymer.

[0069] The use of the at least one rotatable cleaning roll 40 described herein improves the function of the thermal processing device; while at the same time drastically reduces the complexity of the thermal processing device.