CN1981241A - Method of making a photopolymer sleeve blank for flexographic printing - Google Patents

Abstract

A method of making a photopolymer sleeve blank is provided which includes providing a base sleeve, applying a cushion layer over the base sleeve, and applying a first photopolymer layer over the cushion layer. The exteriorfacing surface of the first photopolymer layer is exposed to a curing source, followed by the application of a second, uncured photopolymer layer over the first photopolymer layer. The first photopolymer layer is preferably ground to a predetermined thickness either before or after exposure to the curing source to provide a preferred floor dimension. The resulting photopolymer sleeve blank has a uniform floor which can be readily imaged and processed by conventional equipment used in the flexographic printing industry.

Description

Method for making photopolymer sleeve blanks for offset printing

technical field

The present invention relates to a method of making a photopolymer sleeve blank, and more particularly to an improved method of making a photopolymer sleeve blank for use in offset printing applications, the photopolymer sleeve The blanks can be used for imaging by an end user.

Background technique

In printing applications, the use of offset printing plates formed from photopolymerizable composite materials is well known. Such photopolymerizable composite materials typically include at least an elastomeric binder, a monomer, and a photoinitiator. Polymerization of the photopolymerizable layer occurs when the photopolymer sheet is exposed to actinic radiation from behind. This step is often referred to as the initial "back exposure" step, in which a polymerized portion of the printing plate profile, also referred to as the "floor", is formed. The bottom layer provides the basis for creating a relief image on the plate. After the desired image of the printing plate has been formed on the bottom layer, it is usually washed with a solvent to remove the unexposed areas of the plate and form the relief of the printing. However, when the printing cylinder or the printing sleeve is individually wrapped with the associated sheet, seams or gaps interrupt the image, causing cracks or distortions in the printed image transferred to the underside.

In more recent years, "seamless" hollow cylindrical sleeves have been developed which include a photopolymer layer as a support for various types of printing. For example, in one existing printing process and product (commercially available from OEC Graphics, Inc. under the designation SEAMEX(R) ), a metal or plastic sleeve is wrapped with a photopolymerizable material in the form of a flat paper, which is then heated. , to melt the end and bond the photopolymerizable material to the sleeve. Before wrapping the sleeve, the photopolymerizable material is subjected to back exposure in order to obtain the sublayer required to support the relief image details. However, it is often desirable to make a seamless photopolymer surface that includes an underlying backing layer, such as foam for the backing. While the process described above can include such a backing layer, this is very time consuming and limits throughput.

In order to obtain high yields of seamless photopolymer sleeves, it is not possible to have a bottom layer because, during fusion, the bottom layer does not have the same melting conditions as the unexposed photopolymer on the bottom layer, causing disturbances in the seam.

Ideally, a photopolymer sleeve that includes an unexposed photopolymer layer on a backing layer can be manufactured in high throughput and is readily exposed to radiation to form the desired sublayer. It would also be desirable to produce blank photopolymer sleeves that can be immediately imaged by the end user to improve print quality.

Accordingly, there is a need in the art for an improved method of making photopolymer sleeve blanks for use in offset printing operations.

Contents of the invention

The present invention addresses this need by providing an improved seamless photopolymer sleeve blank formed by providing first and second photopolymer layers, The first of these is exposed to radiation in the exposure state, typically to the bottom layer of the back exposure plate, and the second of these remains uncured, or "green". The resulting photopolymer sleeve blank has a uniform "bottom layer" and can be immediately imaged and processed using conventional equipment used in the offset printing industry.

According to one aspect of the present invention, there is provided a method of making a photopolymer sleeve blank, the method comprising: providing a base sleeve having an inner surface and an outer surface; applying a liner layer to the outer surface of the base sleeve; coating the backing layer with a first photopolymer layer; exposing the outwardly facing surface of the first photopolymer layer with a radiation source; and coating a second photopolymer layer over the first photopolymer layer.

Preferably, the base sleeve comprises a fiber reinforced polymer resin. The wall thickness of the base sleeve is preferably between about 0.01 and about 6.35 mm, more preferably between about 0.60 and about 0.80 mm.

The backing layer preferably comprises a polymeric material selected from the group consisting of closed cell foam, open cell foam, or volume displaceable material. The thickness of the backing layer is preferably between about 0.25 and about 3.25 mm, more preferably between about 1.00 and about 1.50 mm. The backing layer is preferably applied to the base sleeve by coating on the surface of the base sleeve. Alternatively, the backing layer can be applied to the base sleeve as a pre-cured layer around the sleeve.

Preferably, after coating the backing layer, the surface of the backing layer is ground to a predetermined thickness. An optional sealant or adhesive promoter may be applied to the backing layer surface prior to application of the first photopolymer layer. Then, preferably, a first photopolymer layer is laminated to the surface of the backing layer. In one embodiment, the first photopolymer layer is fused to the surface of the backing layer by heating.

The first and second photopolymer layers preferably comprise a styrenic block copolymer-based material. The curing source used to expose the first photopolymer layer preferably includes radiation. A preferred radiation curing source is a UV light source located on the outside of the substrate sleeve. Preferably, the first photopolymer layer is abraded to obtain a predetermined thickness either before or after exposing the first photopolymer layer to a curing source, more preferably after exposure to radiation. This predetermined thickness provides the desired bottom layer dimensions. The first photopolymer layer preferably comprises about 40% to 80% of the total sleeve thickness.

A second photopolymer layer is then coated on, and preferably laminated to, the first photopolymer layer. In one embodiment, the second photopolymer layer is fused to the first photopolymer layer by heating. After lamination, the second photopolymer layer is preferably ground to a predetermined thickness. The second photopolymer layer preferably comprises about 20% to 60% of the total sleeve thickness.

Preferably, the method of the invention includes coating the second photopolymer layer with an ablatable coating. The ablatable coating serves to protect the second photopolymer layer from UV light, thereby preventing the layer from curing prior to use. The resulting sleeve blank, comprising the second (uncured) photopolymer layer, can be imaged and processed using conventional equipment used in the art.

Accordingly, it is a feature of the present invention to provide a photopolymer sleeve blank utilizing first and second photopolymer layers for use in offset printing applications. Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, and from the appended claims.

Description of drawings

1 is a cross-sectional view of a photopolymer sleeve blank according to an embodiment of the present invention; and

FIG. 2 is a flowchart illustrating a method of making a photopolymer sleeve blank according to an embodiment of the present invention.

Detailed ways

As a method implemented in an embodiment of the present invention that provides several advantages over prior art methods, the method of the present invention uses a "back exposure" step to the photopolymer printing plate prior to assembly on the liner layer. By grinding the first photopolymer layer to the desired substratum dimensions and exposing it to radiation from a location outside the substrate sleeve, also known as the "front side" exposure step, a more uniform substratum is created for imaging. Additionally, providing a sleeve blank with a uniform underlayer for use by the end user results in higher print quality due to a more consistent relief depth. The method implemented also enables improved control of the depth dimension of the relief. Embodiments of the invention are also more economical to implement than prior art methods because the product is manufactured directly on the sleeve as opposed to manufacturing the product and then mounting it on the sleeve, which results in a seam on the product.

FIG. 1 depicts an embodiment of a photopolymer sleeve blank 10 with a seamless surface comprising a base sleeve 12, a backing layer 14, and first and second photopolymer sleeve blanks 10. 16 and 18. The base sleeve 12 is preferably formed of a thin walled hollow cylindrical sleeve comprising a fiber reinforced polymer resin having an arm thickness between about 0.01 and 6.35 mm, more preferably about 0.60 to 0.80 mm between. An example of a base sleeve configuration that may be used in the present invention is described in commonly assigned U.S. Patent No. 6,703,095. The cylindrical base is expandable upon application of fluid pressure and provides a fluid-tight seal when the sleeve is mounted over a cylinder, rod, or the like.

As shown in FIG. 1 , a backing layer 14 is coated on the base sleeve 12 . Preferably, the thickness of the backing layer is between about 0.25 and 3.25 mm, more preferably between about 1.00 and 1.50 mm. The backing layer can take many forms, including open or closed cell polymeric foams with uniform distribution of microspheres or chemical spray holes, or volume displaceable materials with low Shore hardness. The backing layer preferably comprises polyurethane, styrene-butadiene block copolymer, styrene-isoprene block copolymer ), polysiloxane (polysiloxane), and other elastic polymers with a glass transition temperature below about -1°C. The backing layer can be applied as an uncured tacky coat and then cured, or it can be applied as a pre-cured layer around the sleeve. Recommended processes for making the liner include extrusion, spin coating, spin casting, doctor blade, or spray coating.

As shown in FIG. 1, a first polymer layer 16 is coated on the liner layer 14 to form an integral sleeve. The first polymer layer preferably comprises a styrenic blockcopolymer-based material such as Dupont Cyrel(R) HORB or MacDermid SP6.0. The thickness of the first polymer layer 16 is preferably equal to or greater than the desired thickness of the base layer, and is preferably about 40% to about 80% of the total sleeve thickness. The thickness is preferably between about 0.020 inches and 0.120 inches (about 0.05 and 0.30 cm), more preferably about 0.035 inches (about 0.09 cm).

A second photopolymer layer 18 is coated on the first photopolymer layer 16 . The second photopolymer layer is uncured and may comprise a styrenic block copolymer as described above. It should be noted that while in one embodiment the first and second photopolymer layers comprise the same material, they may also comprise different materials. The thickness of the second photopolymer layer is preferably about 20% to 60% of the total sleeve thickness. The thickness is preferably between about 0.020 inches and 0.075 inches (about 0.05 to 0.19 cm), more preferably about 0.025 inches (about 0.06 cm).

Figure 2 is a flow chart showing a general representation of the stages in the manufacture of a photopolymer sleeve blank in accordance with a preferred embodiment of the present invention. A base sleeve (20) is provided, and a backing layer is applied to the base sleeve (22). The liner layer is preferably applied to the base sleeve by methods well known in the art, such as, for example, liquid spin casting. Alternatively, the liner can be preformed and then slipped on in uncured, semi-cured, or cured form. After coating, the backing layer is ground to the desired thickness (24) using methods well known in the art such as, for example, grinding with a grinding wheel.

A first photopolymer layer (26) is then coated on the backing layer. Preferably, the first photopolymer layer is laminated to the backing layer by applying a thin layer of sealant and/or adhesion promoter to the surface of the backing layer. Such sealants or adhesion promoters are well known in the art. It should be noted that no sealant or bond promoter may be required if the liner surface is sufficiently smooth after grinding. However, it is critical to maintain the integrity of the bond between the liner layer and the first photopolymer layer. After lamination, the first photopolymer layer is fused to the backing layer surface, preferably by heating in a manner sufficient to locally melt the polymer so that any seams flow together and are eventually eliminated. Preferably, the first photopolymer layer is fused to the backing layer by infrared heating.

The first photopolymer layer is then exposed (28) to radiation. The radiation source is preferably a UV light source located on the outside of the substrate sleeve to provide "front side" exposure. The photopolymer surface is preferably ground to the desired wall thickness (30) to precisely build up the sublayer either before or after exposure to radiation. Preferably, the layer is ground by conventional methods such as grinding with an abrasive wheel.

Then, a second photopolymer layer (32) is applied over the first photopolymer layer, followed by grinding (34) to the final desired thickness and polymer surface finish. Preferably, before grinding, infrared heating is also used to fuse the second photopolymer to the surface of the first photopolymer. An optional adhesion promoter can be applied to the first photopolymer layer prior to the application of the second photopolymer layer.

After grinding, the sleeve is preferably cleaned and coated with a thin layer of ablative coating, such as a LAMS coating. The coating blocks UV light from reaching the second photopolymer layer, preventing the layer from polymerizing prior to use.

The resulting sleeve, comprising a ready-to-image, seamless, unitary sleeve blank, can be imaged and processed in a cylindrical fashion using conventional equipment. As is well known in the art, the outer surface of the second photopolymer layer of the sleeve can be imaged to provide a raised relief surface or depressions of the flexographic printing plate. For example, the second photopolymer layer can be imaged by actinic radiation, by mechanical abrasion, or by laser ablation to form an imaged relief surface. The resulting sleeve gives a high print quality.

Although the invention has been described in detail with reference to the preferred embodiment, it should be noted that modifications and variations are possible without departing from the scope of the invention.

Claims (27)

1. method of making photopolymer sleeve blank comprises:

Provide the base sleeve of inside surface and outside surface;

On the described outside surface of described base sleeve, the coated gaskets layer;

On described laying, apply first photopolymer layer;

Make the outside face exposure of described first photopolymer layer with curing source; With

On described first photopolymer layer, apply second photopolymer layer.

2. according to the process of claim 1 wherein that described base sleeve comprises fiber-reinforced polymeric resin.

3. according to the process of claim 1 wherein the wall thickness of described base sleeve, between 0.01 to about 6.35mm.

4. according to the process of claim 1 wherein the wall thickness of described base sleeve, between 0.60 to about 0.80mm.

5. according to the process of claim 1 wherein described first photopolymer layer, comprise styrenic block copolymer-based material.

6. according to the process of claim 1 wherein described second photopolymer layer, comprise styrenic block copolymer-based material.

7. according to the process of claim 1 wherein described laying, but be from comprise closed-cell foam, open celled foam or volume displacement material one group, to select.

8. according to the process of claim 1 wherein the thickness of described laying, about 0.25mm between about 3.25mm.

9. according to the process of claim 1 wherein the thickness of described laying, between 1.00 to about 1.50mm.

10. according to the process of claim 1 wherein described laying, be, be coated on the described base sleeve as the lip-deep coating of described base sleeve.

11., be, be enclosed within on the described base sleeve as the pre-hardening thickness of the described sleeve of parcel according to the process of claim 1 wherein described laying.

12. according to the method for claim 1, be included in after the described laying coating, grind described laying surface, to reach preset thickness.

13., be included in before described first photopolymer layer of coating, to the promoter of described laying surface-coated sealant or cementing agent according to the method for claim 1.

14. according to the method for claim 13, comprise, be layered in the described surface of described laying described first photopolymer layer.

15. according to the method for claim 13, comprise, the described surface of described first photopolymer layer and described laying merged by heating.

16. according to the method for claim 1, be included in described curing source and make before the exposure of described first photopolymer layer, grind the described first photopolymer laminar surface, to reach preset thickness.

17. according to the method for claim 1, be included in described curing source and make after the exposure of described first photopolymer layer, grind the described first photopolymer laminar surface, to reach preset thickness.

18. according to the process of claim 1 wherein that described first photopolymer accounts for about 40% to about 80% of total sleeve thickness.

19., be laminated on described first photopolymer layer according to the process of claim 1 wherein described second photopolymer layer.

20. according to the method for claim 19, comprise, described second photopolymer layer and described first photopolymer layer merged by heating.

21., comprise and grind the described second photopolymer laminar surface, to reach preset thickness according to the method for claim 20.

22. according to the process of claim 1 wherein that described second photopolymer layer accounts for about 20% to about 60% of total sleeve thickness.

23. according to the process of claim 1 wherein that described curing source comprises radiation.

24. according to the method for claim 21, wherein said radiation curing source comprises the UV light source that is positioned at described base sleeve outside.

25. according to the method for claim 1, but comprise, apply described second photopolymer layer with ablative coating.

26., be included in and form picture on the described sleeve blank according to the method for claim 1.

27. a photopolymer sleeve blank that has or not joint surface, this no joint surface is formed by the method for claim 1.

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