WO1981001474A1

WO1981001474A1 - Method and apparatus for manufacturing continuous design rollers

Info

Publication number: WO1981001474A1
Application number: PCT/EP1980/000126
Authority: WO
Inventors: L Anselrode
Original assignee: Stork Screens Bv; L Anselrode
Priority date: 1979-11-14
Filing date: 1980-11-04
Publication date: 1981-05-28
Also published as: EP0047737A1; DK311381A; IT1133787B; NL7908327A; IT8025877A0; NO812396L; JPS56501542A

Abstract

Method for manufacturing seamless design rollers, which method is carried out on the outer surface of a vertically positioned cylindrical core (1), -which core comprises an outside covering of elastomeric material and, if desired, an adhesion promoting layer-; the method comprises the uniform coating of said surface with a layer of liquid photopolymer said layer being simultaneously evenly exposed by a source (8) of UV-radiation, so effecting a partial curing of the freshly deposited layer, which prevents a sagging of the photopolymer, during which coating process the cylindrical core and the UV-exposure source (8) perform a relative rotation. Subsequently a second step of UV-curing is carried out by means of a patternwise exposure of the respective layer, with a mask being the negative of the desired pattern, whereupon the exposed layer is developed and dried, so that a relief image of the desired shape is left.

Description

METHOD AND APPARATUS FOR MANUFACTURING CONTINUOUS DESIGN

ROLLERS.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention concerns a method for manufacturing continuos design rollers, consisting of α cylindrical core with an outside covering of elastomeric material in which method the cylindrical core, which may have an adhesion promotion layer on its surface, is coated with a layer of liquid photopolymer material , which material is cured by UV-radiation in such a way, that after development and drying a relief image of the desired shape is left.

In the field of this invention liquid photopolymer material is used which has the property of being crosslinkable by exposυre to UV-radiation, whereupon the liquid State transforms into the solid State.

Elasticity and hardness of the end product are related to the chemical composition and can vary from rubber-like to relatively hard.

The very elastic products find their υse in the flexography, whereas hard products are cpplied in bookprinting.

In said field use is made of the property that the solubility of such photopolymers in certain solvents is reduced as a result of UV exposure. Substances which, for example, in non-exposed condition are water developable, loose this property when the polymerization has proceeded so for, that the product is transformed from the liquid into the more or less solid State.

The product is then still soluble in certαin solvente so αs chlorinated hydrocarbons or other organic solvents.

2. Description of the Prior Art.

So far, liquid photopolymer substances were coated in the desired thickness onto horizontally rotating cylindrical cores.

During said coating the thickness of the layer is controlled by means of a glass plate, on the surface of which a film is applied containing the negative pattern in UV-impermeable parts. The film is covered with a very thin, UV-radiation transmitting foil, on which the photopolymer substance does not adhere.

Imagewise exposure of the photopolymer through the film is carried out during the coating process,

Obviously this process requires very much accuracy of the respective apparatus.

Furthermore, the control of the layer thickness is very critical.

A known method for application of a liquid coating to a cylinder is described in British Patent 1 455 289, in which method the thickness of the liquid layer is very easily controlled.

Said Application start a method in which a vertical cylindrical member is coated with liquid material by the use of an annular reservoir, being positioned around the cylinder and fitting to the outer surface of the cylinder in such a way that a thin liquid coating is left on the surface, when the reservoir is moved in a controlled way along the cylinder from top to bottom. By control of the vertical movement the layer thickness on the cylinder surface is governed.

SUMMARY OF THE INVENTION

It is a principal object of the present invention to provide a method which is less critical with regard to accuracy in the coating stage, whereas the coating thickness is very easily controlled.

According to the invention this is attained in that the cured photopolymeric covering in pattern form is applied to the outside of a cylindrical core in such a way that UV-curing of the liquid photopolymeric material is carried out in at least two steps, comprising a first step in which a homogeneous exposure with UV-radiation is carried out during the process of applying a homogeneous coating of liquid photopolymer in a known manner to the outer surface of a vertically positioned cylindrical core, the exposive being such that a partial curing, preventing flow of the photopolymer is achieved, and a second step in which a pattern-wise exposure to UV-radiation is carried out, using a film, which is the negative of the desired pattern, as a mask, after which the exposed layer is developed and dried in a known way.

The first step of the UV-curing process is a homogeneous exposure to UV-light, due to which a viscosity increase of the photopolymer is realized which is such, that flow of the layer after application is prevented.

The second step of the UV-curing process can be carried out either in a separate exposure machine or in the coating apparatus itself. In both cases a film having a pattern which is the negative of the desired pattern is wrapped around the coated cylinder after which exposure is carried out in a known way.

Preferably there is provided a relative rotary movement between the cylindrical core and the UV-source during the first exposure step, so as to ensure a perfectly homogeneous exposure of the total cylinder surface.

It has appeared to be very beneficial to apply a homogeneous post exposure with UV-radiation to the developed and dried printing cylinder in order to ensure a total curing of the exposed portions.

The present invention is not restricted to the use of thick-walled printing cylinder cores as are usual in printing industries.

Thin-walled, seamless cylinders can also be used, consisting for instance of nickel, which cylinders can be mounted in a known way on cylindrical rigid cores, by means of pneumatical processes.

The present invention is also embodied in an apparatus for carrying out the aforedescribed method. This apparatus comprises means for mounting a cylindrical core with its central axis in a vertical position, an annular reservoir being positioned around the cylinder, fitting in a sealing way to the cylinder surface which reservoir can be moved along the cylinder in a controlled way.

This known apparatus comprises for the purpose of the present invention an annular UV-radiation source which exposes an area directly above the reservoir while the vertical movement of the source is identical to that of the reservoir, a UV-shield between reservoir and source and means providing a relative rotary movement of the soυrce with respect to the cylinder.

It has αppeared to be benificial to give α rotation to the cylinder to be coated, while the source is being kept stationary.

DESCRIPTION OF THE DRAWING

The drawing is a vertical cross-section of the present apparatus.

DESCRIPTION OF A PREFERRED EMBODIMENT

The apparatus consists of a cylindrical core 1 with a vertical upright axis 2.

Moυnting means 3 and 4 of the core 1 are rotatably installed in bearings in frame part 5. Around cylinder 1 an annular reservoir is situated, said reservoir consisting of a wall 6 and a sealing ring 7, co-operating with the outer surface of core 1.

Above reservoir 6, 7, an annular UV-soυrce 8 is moumed in fixed relationship to the reservoir and close to the reservoir.

Between source 8 and reservoir 6, 7 a UV-impermeable shield 9 is situated.

The reservoir 6, 7 with source 8 and shield 9 are supported on bearings 10 on Single spindles 11. The spindles are interconnected in the top by means of an

12 endless chain or the like, to give the same rotational direction while one of the two spindles 11 is connected to a drive motor 13.

The lower end 4 of the core 1 is, via mounting means, 14, connected with a gear box and the drive motor 16.

By energizing motor 13, the reservoir 6, 7 can be driven together with shield 9 with uniform speed along the outer surface of core 1. Motor 16 is suited to rotate core 1 slowly during the vertical movement of the reservoir.

The method according to the present invention is carried out as follows:

By means of motor 13 reservoir 6, 7 is placed in the upper position whereupon said reservoir is filled with liquid photopolymer.

Motor 13 is then started for the downward movement of reservoir 6, 7 while source 8 is put on.

It is beneficial to also energize motor 16 so as to rotate core 1 slowly around its vertical axis, although this is not essential for the envisaged method.

During the downward movement of reservoir 6, 7 a coating layer of photopolymer adheres to the outer surface of core 1.

UV-radiation of source 8 can only radiate that part of coating, which is situated above shield 9, by which exposure the substance is thυs partially hardened so that no streaming will occur.

When the reservoir has reached the bottom end 4 motors 13 and 16 are stopped, after which core 1 is removed from the machine, for instance by removing the upper part of frame 5.

Subsequently, the negative film is wrapped tightly around the coating, whereupon the second exposure is carried out.

Those parts of the coating which correspond to the pattern to be printed will be further hardened by this treatment.

After this second exposure the only pre-exposed parts of the coating will be removed by washing with a suitable solvent.

If necessary a uniform post-exposure step can be carried out to harden remaining quantities of not exposed photopolymer or insufficiently hardened photopolymer.

As an example of photopolymerizable substances every type of UV-curing mix whether or not mixed with additives may be chosen, e.g.

1) unsatuated epoxy resins;

2) unsaturated polyester resins;

3) unsatuated alkyd resins;

4) υnsatυrated acrylic resins;

5) unsaturated urethane resins;

6) polybutadiene resins.

Mixtures of unsaturated polymers and UV-ring mixtures of unsaturated polymers with monomeric compounds can also be used.

Furthermore, if necessary, photoinitiators or mixtures of different photoinitiators can be added in quantities of 0.05-10% by weight with respect to the weight of resin.

Claims

What is claimed is:

1. Method for manufacturing continuous design rollers consisting of α cylindrical core with an outside covering of elastomeric material in which method the cylindrical core, which may have an adhesion promotion layer on its surface, is coated with a layer of liquid photopolymer material which material is cured by UV-radiation in such a way, that after development and drying a relief image of the desired shape is left, characterized in that, UV-curing of the liquid photopolymeric material is carried out in at least two steps comprising a first step in which a homogeneous exposure with UV-radiation is carried out during the process of applying a homogeneous coating of liquid photopolymer to the outer surface of a vertically positioned cylindrical core (1), the exposure being such that a partial curing preventing a flow of the photopolymer is achieved, and a second step in which a patternwise exposure to UV-radiation is carried out using a film, which is the negative of the desired patte rn, as a mask, after which the exposed layer is developed and dried.

2. Method according to claim 1, characterized in that, during the coating process the cylindrical core (1) and the UV-exposυre source (8) are rotated relatively with respect to each other.

3. Method according to claims 1 and 2, characterized in that, after developing and drying, the photopolymer layer is subjected to a homogeneous post-exposure with UV-radiation.

4. Method according to Claims 1-3, characterized in that, the photopolymeric covering is applied to a cylin dric core (1) made of thin-walled seamless material.

5. Method according to claim 4, characterized in that, the photopolymer coating is applied to a thin nickel sleeve (1).

6. Apparatus for carrying out the method as described in any one or more of the foregoing Claims comprising mounting means for a cylindrical core, its central axis being in a vertical position and an annular reservoir being positioned around the cylinder and fitting in a sealing way to the cylinder surface, which reservoir can be moved along the cylinder in a controlled way, the apparatus being characterized in that, it comprises an annular UV-radiation source (8) which exposes an area directly above the reservoir (6, 7), while the vertical movement of the source is identical to that of the reservoir, a UV-impermeable shield (9) being present between reservoir and source, and means (13, 16) to provide for a relative rotary movement of the soυrce (8) with respect to the cylinder (1).