JPH0374380B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flexographic printing plate, a method for making the same, and a laminate for use in making the same.

For the production of photopolymer flexographic printing plates,
There are two common methods. In the first method,
A plate comprising a solid layer of photopolymerizable elastomer in the backing layer is imagewise exposed to crosslink the desired portions of the solid layer. The uncrosslinked portions of the layer are removed by washing with a solvent that dissolves the uncrosslinked material but not the crosslinked material. This leaves a board with embossed areas. The board is processed in the usual manner to give a smooth surface in the relief areas.

Boards handled in this manner are commercially available with a thin layer of non-tacky material on the surface of the solid layer remote from the backing layer. This may then be covered with a protective sheet to facilitate storage. The backing layer may include more than one layer, often comprising a relatively thin support layer in contact with the solid layer and a softer, flexible layer on the surface of the support layer remote from the solid layer. Plates of this type are described, for example, in British Patents Nos. 1,489,193 and 1,525,965. Such boards can be used simply by removing the protective layer.

Since such plates are manufactured in a factory, their production can be closely controlled. Therefore, the plate can be made highly durable and each layer has a uniform thickness, ie it can be ensured that the exposed and developed plate has a uniform thickness in all its relief areas. However, this type of board is expensive since its price includes the material and manufacturing costs of many layers. Moreover, materials comprising solid layers of photopolymerizable substances tend to be expensive and must contain various components to prevent them from crosslinking during storage.

A second method of manufacturing photopolymer flexographic printing plates uses a liquid photopolymerizable material to produce the exposed plate in situ. In a typical method, the negative is placed on a glass plate and covered with a thin layer of material. A quantity of liquid photopolymerizable elastomer material is evenly spread over a thin layer and covered with a backing layer. Generally, the backing layer and liquid material are applied at the same time. The laminate thus produced is imagewise exposed to crosslink and thereby solidify the desired areas of the liquid material and bond it to the backing layer.
Wash out the non-crosslinked liquid material with a suitable solvent,
The laminate is processed in a conventional manner to produce the final flexographic printing plate.

This above method is possible because the liquid material is formulated to have a high viscosity. It therefore remains a separate layer for a period long enough to perform imagewise exposure and crosslinking.

Unless the process conditions and machine maintenance are carefully controlled, flexographic printing plates produced by this second method are not necessarily of good quality. The thickness of the photopolymerized material layer is not uniform, so the board is inked unevenly and the print quality is poor.

Non-uniform thickness can be caused by one or a combination of the following factors: The platen on which the negative is placed is
Due to poor retention, the area may be uneven due to uneven heating by the light used to expose the plate. This will distort the board. The equipment used to apply the backing layer and the layer of liquid material in a thin layer may not be sufficient to provide a layer of uniform thickness. Even if it is sufficient, poor retention can result in a loss of ability to produce a uniform layer. The viscosity of the liquid material may change due to changing atmospheric conditions or due to uneven heating of the platen.

It has therefore proven difficult to produce high quality flexographic printing plates by this method.

According to the invention, a layer of abradable elastomer having a thickness of up to 1000 microns is clamped to a layer of photopolymerized elastomer material produced by actinic radiation of a photopolymerizable liquid. A flexographic printing plate is provided, characterized in that the layer of abradable elastomer has a uniform thickness due to being abraded.

Optionally, a support layer, typically having a thickness of 75-150 microns, may be interposed between and rigidly bonded to the layers of abradable elastomer and photopolymerizable elastomer material.

Elastic bodies that can be polished include commonly available rubber,
For example, it may be polybutadiene, butadiene-acrylonitrile, butadiene-styrene, isoprene-styrene, silicone, or polysulfide rubber. Preferably, the elastic body is natural rubber, polychloroprene rubber or polyurethane rubber. The elastomer may contain conventional fillers to make it easier to abrade. The elastic body is at least
30, but should have a shore A hardness not exceeding 80. Preferably, the hardness is between 40 and 60 Shore A.

The abradable elastomer may contain a reinforcing and stabilizing matrix or web, such as a woven or nonwoven fabric, which is particularly desirable when no support layer is present.

If the liquid material cannot polymerize rapidly, the elastomer should be transparent so that the liquid material can be exposed from both sides. However, the elastomer may be opaque if the liquid material rapidly polymerizes upon exposure.

Preferably, the elastomer has a thickness of 100 to 500 microns, most preferably a thickness of about 400 microns.

The support layer, if present, may be any one commonly used in the art. For example, a sheet of aluminum or other metal foil,
It may be a sheet of plastic material or a layer of cross-linked surface coating. The support layer can also be reinforced, for example with glass or woven fibers.

Preferably, the support layer comprises a film of polyester plastic material about 100 microns thick.

The support layer should provide a sufficiently hard surface without compromising the flexibility of the final board, the thickness of the support layer should be determined with these criteria in mind, and for a given material may be outside the range of typical values mentioned above.

Preferably, the liquid material producing the layer of photopolymerized elastomer material has a molecular weight of about 500 to 500,000 at 23°C.
More preferably, it has a viscosity of 5,000 to 50,000 cP.

A suitable material for use in the manufacture of this layer is a methacrylate terminated polyurethane polyether. This is around 5000-50000, typically around 25000
may have an average molecular weight of

Other suitable liquids that are photopolymerized to form solid elastomers and have suitable viscosities are known in the art.

Generally, the liquid material will contain a photoinitiator such as benzoin or an ether formed from benzoin and methanol or isopropanol, and also a photosensitizer such as benzophenone. The liquid may also contain chain transfer agents and molecular weight modifiers. In the case of the methacrylate-terminated polymers mentioned above, a portion of acrylate or methacrylate monomers may be included.

The liquid material may also contain other conventional additives, such as thermal polymerization inhibitors (eg p-methoxyphenol, hydroquinone or N-nitrosocyclohexyl-hydroxylamine), antioxidants, and plasticizers.

Once the liquid material is crosslinked by imagewise exposure to actinic radiation, it will become a solid with a raised surface and uncrosslinked material surrounding the surface. The uncrosslinked material is removed in a conventional manner, leaving a raised surface on the remainder of the board. The description of the thickness of the elastic material layer is to be considered as relating to the thickness of the relief area, unless otherwise stated.

In some cases it may be necessary to provide an anchor layer between the abradable elastomer and the photopolymerized material. If the support layer is present, that layer and one of the other layers surrounding it.
or both. Such pinning layers are provided to promote bonding between adjacent layers.

The anchoring layer can be a coating on the support layer and/or on the abradable elastomer, or it contains a layer of adhesive applied to the support layer and/or the abradable elastomer. It may be.
Obviously the nature of the anchoring layer or its necessity will depend on the nature of the layers to be bonded. However, one skilled in the art will facilitate the selection of an appropriate adhesive or coating for a particular application.

Preferably, if a support layer is present, the anchoring layer is a coating applied to both sides of the support layer.
If the support layer is polyester, the fixing layer may be a coating of a mixture of polyvinyl chloride and polyvinyl acetate.

In manufacturing the flexographic printing plates of the present invention, a layer of liquid photopolymerizable material is first applied to a support layer that is or may include a layer of abrasive elastomer. applying the liquid, imagewise exposing the liquid to actinic radiation to photopolymerize the liquid material in the image areas, treating the exposed material to provide areas of relief in the photopolymerized layer, and forming a support layer. If it does not include a layer of abradable elastomer, it is attached to a support layer.

The support layer comprising the layer of abradable elastomer as described above may include a layer of abradable elastomer having a thickness of up to 1000 microns, typically a support layer having a thickness of 75 to 150 microns. A laminate formed by tightly bonding is preferred.

In the past, flexographic printing plates have been subjected to conventional processing after exposure in order to provide a flat surface to the embossed areas of the plate. However, such a plate would still have the disadvantage that the layer of elastomer material would have a non-uniform thickness. This drawback can be overcome by removing part of the layer of the abrasive elastic material, so that the abrasive plate has a uniform thickness in the relief area.

Therefore, in the method of the present invention, a flexographic printing plate of uniform thickness is produced by polishing the abradable elastomer to remove a portion thereof following the above steps.

The conventional methods described above may include contact or non-contact exposure. Both methods are commonly used in the printing industry for the production of embossed printing plates. Non-contact exposure is often used in newspaper printing.

Sanding can be carried out on a conventional sanding machine and should preferably provide a tolerance of no more than ±40 microns.

By using the flexographic printing plates of the invention, it is possible to use liquid methods to produce printing plates of uniform thickness, which allows the production of high-quality printed products.

The invention will now be described, by way of example only, with reference to the accompanying drawings, in which: FIG. This drawing shows a cross-sectional side view of a flexographic printing plate according to the invention in outline only.

Referring to the drawing, the flexographic printing plate is
It comprises a layer 1 of filled natural rubber having a Shore A hardness of 50. It is firmly bonded to layer 3 by a layer of rubber adhesive 2. Layer 3 consists of a polyester sheet with a surface coating 4 to increase adhesion with layer 5. This surface-coated polyester sheet 3 is the product name
It is commercially available under the name Bexford LP40 (Bexford
is a subsidiary of ICI).

As can be seen from the drawing, layer 5 has a region 6 surrounded by a region 7 of lesser thickness. Layer 5 comprises a photopolymerized elastomer material produced by photopolymerizing a methacrylate terminated polyurethane polyether. In this example, WRGrace (Park Royal, London)
A commercially available liquid material sold under the name Flexopolymer Type 40 was used. The relief areas 6 are those that can be photopolymerized during imagewise exposure, while the other areas 7 are washed out of non-crosslinked material. The part of layer 5 closest to support layer 3 was photopolymerized by back exposure with actinic radiation, so that zone 7 had some thickness.

Layer 1 was 400 microns thick, layer 3 was 100 microns thick, and layer 5 was about 6 mm thick and non-uniform.

Flexographic printing plates are manufactured using conventional machines, e.g.
It was manufactured by the following method using an ALF type machine manufactured by Asahi Chemical Industry.

The negatives were placed on the machine's glass platen and covered with a non-tacky, tear-resistant transparent polypropylene film. Apply an amount of Flexopolymer 40 type to polypropylene film and at the same time
A sheet of polyester film covered with Bexford LP40 was applied over the Flexopolymer 40 mold. Then both sides of this laminate are exposed to actinic radiation,
At least some of the Flexopolymer type 40 was crosslinked and solidified. The solidified material was also bonded to a polyester film.

The exposed plate was then processed in a conventional manner to remove uncrosslinked material and prepare the surface of the relief areas for printing. After normal processing, the boards were laminated to sheets of natural rubber filled using a common rubber adhesive.

In other experiments, filled natural rubber was
The same procedure was followed except that it was laminated to a polyester support before use in an ALF type machine.

Flexographic printing plates, as shown in the drawings and produced by any of the methods described above, were polished to a uniform thickness on a Vandercook rubber sander. These polished plates were used in a flexographic printing process, which gave prints with uniform ink distribution and good quality. In contrast, when the above-described flexographic printing plates were used without polishing, the ink spread unevenly over the embossed surface, resulting in uneven or poor quality prints.

From the above description, it will be appreciated that the present invention enables the use of liquid-based flexographic printing plates that can be used to produce high quality prints. Until now this has generally been possible using expensive solid-based printing plates.

[Brief explanation of drawings]

The drawing shows a cross-sectional side view in outline only of a flexographic printing plate according to the invention.

Claims (1)

Claims: 1. A layer of photopolymerized elastomer material produced by exposure of a photopolymerizable liquid to actinic radiation, producing a layer of abradable elastomer having a thickness of up to 1000 microns. , in a firm bond with or without a support layer, and the layer of the abradable elastic material has a uniform thickness due to being abraded. Flexographic printing plate. 2. The flexographic printing plate of claim 1, wherein the photopolymerizable liquid is a methacrylate-terminated polyurethane polyether having a molecular weight of about 25,000. 3. Claim 1, wherein the abrasive elastic body is natural polypropylene or polyurethane rubber.
Flexographic printing plate as described in section. 4. Flexographic printing plate according to any one of claims 1 to 3, wherein the abradable elastic body contains a filler. 5. A flexographic printing plate according to any one of claims 1 to 4, wherein the abradable elastic body has a Shore A hardness of 30 to 80. 6. A flexographic printing plate according to claim 5, wherein the abrasive elastomer has a Shore A hardness of 40 to 60. 7. Flexographic printing plate according to any one of claims 1 to 6, wherein the layer of abrasive elastomer has a thickness of 100 to 500 microns. 8. A flexographic printing plate according to any one of claims 1 to 7, comprising an anchoring layer between the abradable elastomer and the photopolymerized material to promote adhesion between these layers. 9. A flexographic printing plate according to claim 1, wherein the support layer has a thickness of 75 to 150 microns. 10. The flexographic printing plate of claim 1, wherein the support layer has a thickness of about 100 microns. 11. Flexographic printing plate according to any one of claims 1 to 10, wherein the support layer comprises a metal foil, a sheet of plastic material or a layer of a crosslinked surface coating. 12. Flexographic printing plate according to claim 11, wherein the support layer is reinforced with glass or textile fibers. 13. A flexographic printing plate according to any one of claims 1 to 11, wherein the support layer comprises a sheet of polyester material. 14. The flexo according to any one of claims 1 to 13, wherein the support layer is provided on one or both sides with a fixing layer for promoting adhesion between it and each adjacent layer. Graph printing board. 15 A layer of abradable elastomer having a thickness of up to 1000 microns is applied to a layer of photopolymerized elastomer material produced by exposure of a photopolymerizable liquid to actinic radiation, with a support layer. for producing a flexographic printing plate having a uniform thickness by being polished, the layer of abradable elastomer comprising:
A laminate characterized in that it comprises a layer of abradable elastomer having a thickness of up to 1000 microns firmly bonded to a support layer. 16 A layer of abradable elastomer having a thickness of up to 1000 microns is applied to a layer of photopolymerized elastomer material produced by exposure of a photopolymerizable liquid to actinic radiation, with a support layer. A method for manufacturing a flexographic printing plate, comprising a layer of an abradable elastic material in combination with a clamp, with or without an intermediary, and having a uniform thickness due to the abradable elastomer layer being abraded. a layer of liquid photopolymerizable material is applied to a layer of abradable elastomer or a support layer which may include a layer of abradable elastomer, and the liquid is imaged by actinic radiation. exposure to light to photopolymerize the liquid material in the image area, and processing the exposed material to provide areas of relief in the photopolymerized layer, the support layer not comprising a layer of abradable elastomer. A method characterized in that the layer of elastic material, optionally attached to a support layer, is polished to produce a printing plate having a uniform thickness. 17. The fixing layer is between the layer of liquid photopolymerizable material and the layer of abrasive elastomer, between the layer of liquid photopolymerizable material and the support layer, or the layer of abrasionable material. 17. The method of claim 16, including the step of providing between layers of elastic material. 18. The method of any one of claims 16 to 17, which uses a contact exposure method to expose the liquid to actinic radiation. 19 To expose a liquid to actinic radiation,
Claims 16 to 1 using a non-contact exposure method
Any one method described in item 7.