WO2000029223A1

WO2000029223A1 - Method and device for removing the coating from printing screens

Info

Publication number: WO2000029223A1
Application number: PCT/IB1998/001802
Authority: WO
Inventors: Hanspeter Iten
Original assignee: Iten Galvanik Ag
Priority date: 1998-11-13
Filing date: 1998-11-13
Publication date: 2000-05-25
Also published as: AU9641598A

Abstract

The invention relates to a method and a device for removing the coating from printing screens. The inventive method comprises a step according to which the photosensitive resist adhering to the printing screen is weakened in an emollient bath and is somewhat removed from the printing screen. Said printing screen with the softened and partially removed photosensitive resist is rinsed with water so that the softened photosensitive resist hardens but is not re-fixated to the screen. In a final step, the hardened but partially removed photosensitive resist is removed from the screen by applying a high-pressure water jet while the surface of the screen is not damaged. The invention also relates to an arrangement for removing the coating from cylindrical printing screens (rotary machine printing screens).

Description

METHOD AND DEVICE FOR COATING PRINTING STENCILS

TECHNICAL AREA

The present invention relates to a method and an apparatus for decoating printing stencils.

BACKGROUND OF THE INVENTION

Stencil or screen printing, especially for printing on textiles, is a commercial branch that has been working under increasing cost pressure in recent years. For the implementation of screen printing processes, stencils (planographic or rotary printing stencils) made of nickel are mainly used, which are extremely expensive. These are in turn coated with a suitable photoresist, which has a corresponding pattern with regard to the desired print. The photoresist coating on the screen-like template thus defines the printing form to a certain extent. After variable but finite throughput times, the stencils have to be replaced because they are no longer able to work in the desired quality (eg high resolution) due to wear. As a result of the extremely high purchase costs for a printing stencil, in the past few years it has been decided not to simply discard the used but expensive stencil (ie to dispose of it), but to recycle it for reuse. According to the prior art, this takes place in the context of a complex process in the course of which the photoresist is removed with the aid of a suitable solvent and any other mechanical means. It should be noted that the sensitive printing stencil to be recycled will be returned without the slightest damage. In accordance with the prior art, the photoresist layer is thus chemically dissolved with solvent and the stencil is sprayed and rinsed with further organic solvent until the stencil is actually in its native state, ie completely freed from the photoresist.

Although this method is quite suitable for bringing the used printing stencils coated with photoresist back to their original state, they are completely unsatisfactory in terms of their ecological balance. Not only do comparatively large amounts of used solvent - containing the dissolved photoresist - accumulate, which in turn has to be disposed of at great expense, the process is also cumbersome in terms of process technology, in that it has to work with a permanent inflow of new solvent, which in its unused state Chemically dissolves the photoresist layer. This means that a closed circuit is hardly possible, but usually only a flow-through method. Ultimately, a process that does not include a closed cycle is also financially unsatisfactory because new solvents have to be procured and disposed of permanently.

PRESENTATION OF THE INVENTION

It was therefore an object of the present invention to provide a stripping process which at least partially avoids the disadvantages and problems mentioned above.

Another object of the present invention was to provide an apparatus for performing an ecological stripping process.

These tasks are solved according to the preamble of independent claims 1 and 14. Further preferred embodiments are the subject of the dependent claims. Instead of, as in the prior art, completely dissolving the photoresist layer on the printing stencil to be recycled with a solvent, in the method according to the invention said photoresist layer is merely “softened”. The term “softened” means that the photoresist layer to be removed means of a suitable solvent is not chemically dissolved and thus goes into solution, but is weakened according to the invention only to the extent and as long as a partial or substantially extensive loosening takes place between said photoresist and the stencil substrate, ie the stencil surface.

The photoresist layer, which is rather slightly adherent in a slimy, softened form, is then mechanically removed from the stencil base using a high-pressure water jet. In order to make the removal of the photoresist layer even easier and to maintain the detached photoresist in an easily disposable form, the softened photoresist layer is rinsed with water beforehand. On the one hand, the photoresist layer is hardened or cured again and can be removed and conveniently filtered off using the high-pressure water jet. On the other hand, the hardening or the re-hardening is not associated with a reconnection of the photoresist to the stencil substrate.

The advantage of the method according to the invention is, in particular, that on the one hand it can be carried out in a tank filled with a softening agent, which does not have to be constantly replaced. Rather, the method is carried out in an essentially closed circuit, so that no extensive and permanent disposal effort with regard to the solvent has to be carried out, as in the prior art. Instead, the softening agent can be used again and again. On the other hand, it can flake off in solid form with the high-pressure water jet Photoresist film can be separated using a filter in the solvent tank and can be disposed of relatively easily.

BRIEF DESCRIPTION OF THE DRAWINGS Further advantages and applications of the invention result from the following description with reference to the figures.

Figure 1 shows a side view of a softening system. This includes a double wall system (upper inner tub (6) and insulated lower tub (5)) as well as a heater (4) in the lower part of the system (5), a pump device (2) in the middle part of the system, level monitoring (3), a support tube (9) on which the template to be decoated is placed and a suction device (1) for the heatable softening liquid in the upper part of the system.

Figure 2 shows the front view of a softening system, with a drive motor (7), an overflow (8), a filter basket (10), an adjustable cylinder support (11) and a template (12) which is to be stripped.

Figure 3 shows a side view of a high-pressure system, comprising a system housing (1 '), a water tank (2') / a filter housing (3 '), a slide guide (4') and a rotatable support (5 ') above a tub for loading with a cylindrical printing template.

FIG. 4 again shows the front view of a high-pressure system, comprising a drive motor (7 '), an adjustable water jet nozzle (8'), a high-pressure pump device (6 '), a rotatable support (5') above a trough for fitting with a cylindrical one Printing template (12). FIG. 5 shows a schematic side view of a high-pressure system, focused in relation to the nozzle setting of the high-pressure water jet (10 ') to the rotating printing stencil (12). The template (12) rests on a carrier tube (5 ') and the nozzle (8') is adjusted in such a way that the water jet strikes the pressure template (12) below the tube center axis.

FIG. 6 shows a schematic plan view of a high-pressure system in relation to the nozzle setting of the high-pressure water jet (10 ') for the printing stencil (12) lying thereon. Appropriate adjustment of the nozzle (8 ') to the stencil surface axially prevents the stencil (12) from moving forward.

WAYS OF IMPLEMENTING THE INVENTION The process according to the invention for decoating printing stencils comprises or consists of a) a softening step, the photoresist adhering to the printing stencil being weakened in a softening bath, i.e. its binding power to the printing stencil is loosened, and b) a hardening step, the printing stencil with the softened or partially detached photoresist located thereon being rinsed with water, so that the softened photoresist is hardened again but not reattached to the stencil, and finally c) a removal step, wherein the cured but essentially loosened photoresist is removed from the stencil by a high pressure water jet without the stencil surface being damaged.

In principle, according to the invention, any chemical solvent or solvent mixture which softens the photoresist layer does not dissolve chemically, but only softens. An aqueous environment is preferably used, in particular because this meets the strict fire protection regulations in a simple manner. An acidic softening bath is very particularly preferably used to carry out the process according to the invention, the pH preferably being between 1 and 4, very particularly preferably around 3 and being able to be brought about by both organic and inorganic acids. However, an HC1 solution is preferably used and the hydrocarbons preferably comprise a mixture of glycols in water. The softening bath very particularly preferably contains a mixture of about 50-75% by weight of butylglycol, methylglycol and ethylenglycolmonoethylether (ethylglycol), about 2 to 20, preferably of about 5% by weight of HCl, and 10-25% by weight. -% Water

An optimal softening agent for carrying out the method according to the invention is a mixture with the brand name "Easy Stripp LP 237" from Prelit in CH-5608 Stetten.

In a preferred embodiment, the softening bath containing a suitable softening agent has a temperature of between 40-100 ° C., preferably of 60-80 ° C., and very particularly preferably of about 70 ° C. Step a), i.e. the softening process is preferably carried out for about 5 to 40 minutes, preferably between 10 and 20 minutes.

The printing stencil can remain static during the softening step, or else it can be kept in motion, for example in the case of rotating stencils in a rotational movement, so that the softening takes place uniformly.

When curing step c) is carried out, water is preferably used at a temperature of 20 to 40 ° C. After a single rinse, the photoresist layer hardened to such an extent that it can be removed by a high pressure water jet and the solid paint parts can be separated off by a suitable filter. However, the originally firm bond between said photoresist layer and the stencil substrate underneath is irreversibly weakened by the softening process a) and consequently is not brought back to the original state from before step a) by the curing step b).

In the subsequent removal step c), a mechanical and ecological means, i.e. remove the unwanted photoresist layer with a water jet. The water jet pressure is preferably between 100-220 bar, preferably about 190 bar. The water used for the removal step c) can be used again and again for the implementation of step c), which results in a closed cycle. The circuit should have a pH of between about 8 to 12. A pH of about 10 is preferably set in order to achieve a degreasing effect or to reduce the surface tension to a minimum. The purpose of the alkaline environment is the optimal degreasing of the printing stencil in order to achieve optimal conditions for the re-application of a new photoresist on the stencil treated according to the invention. The preferred pH of about 9-10 is achieved, for example, by adding sodium hydroxide (NaOH) to the tank filling containing 150 liters of water.

If necessary, the native printing template obtained can then be rinsed again with water and dried over a warm air blower.

The method according to the invention can in principle be carried out for all types of printing stencils. These include in particular the flat stencils and the rotary stencils, which have a cylindrical shape. In a very particularly preferred embodiment the inventive method for stripping cylindrical stencils, ie rotary stencils.

When stripping rotary templates, the cylindrical template (12) preferably lies on a concentric, rotatable tube (5 '), for example made of rough PVC. In order to prevent the high-pressure water jet from bending or otherwise damaging the impact point (see FIG. 5) of the high-pressure water jet (10 ') (from the high-pressure nozzle (8')) onto the template surface (12) below (preferably about 10 mm) of the pipe center axis, on which the template rests. This ensures that the high-pressure water jet does not bounce off the stencil surface and does not form a water film on the pipe surface, but undermines and definitely detaches the photoresist layer.

In addition, a uniform removal of the photoresist layer is sought, so that in a preferred embodiment, on the one hand, the tube on which the rotary template rests rotates, preferably rotates at a speed of about 10 to 50, more preferably between 20 and 30 revolutions per minute, and on the other hand the water jet axis (3) (to the normal) is inclined about 3% sideways (see Figure 6) in order to prevent the stencil to be cleaned from moving forward.

Another object of the present invention is an arrangement for stripping cylindrical printing stencils (rotary printing stencils), which a) a system for softening the photoresist layer, comprising an insulated double wall system (upper inner tub (6) and insulated lower tub (5)) equipped with a heater ( 4) in the lower part of the plant, as well as an inner tub in the upper part of the plant (6), a pump device (2) and a suction device (1) for the heated solvent liquid, the treatment template (12) resting on a tube (9), and b) a high-pressure system comprising an exposed, rotatable tube (5 '), preferably a PVC carrier tube with a rough surface , above a tub, for equipping with a cylindrical pressure stencil (12), an adjustable water jet nozzle (8 '), a high-pressure pump device (3') with a filter screen and a filter mat, a slide (4 ') and optionally a counter .

In the following, the present invention will be illustrated using an example, which should not be interpreted as limiting the scope of the application.

example

Process for decoating a rotary printing stencil

a) In a softening system according to Figures 1 and 2, a common rotation template (12) with a worn but still firmly bonded photoresist is introduced. In the lower part of this softening system there is a tank (5) which is filled with approximately 200 l of a softening agent. The said softening bath has a temperature of approximately 70 ° C. and contains a mixture of approximately 35% by weight butyl glycol, 20% by weight methyl glycol, 15% by weight ethylene glycol monoethyl ether, and 5% by weight HC1 and 25 % By weight of water.

The rotary template (12) is put on a plastic tube (9), dips into the bath (6) on one side and is softened by slow but permanent rotation in the bath for about 20 minutes. b) The template with the softened photoresist layer is then removed from the softening system and by rinsing once with water (25 ° C) cleaned so that the soft photoresist layer hardens again. c) In the third step, the pretreated rotary template is placed in a high-pressure system according to FIGS. 3 and 4, again on a rotating plastic tube (5 ') and, depending on the length of the template, for about 20 minutes with a high-pressure water jet (of approximately 25 ° C) sprayed. The high pressure rinse water has a pH of 10. The photoresist layer on the stencil flakes off in this way and is removed in the course of this method step c). In order to prevent the high-pressure water jet (10 ') from bending or otherwise damaging the template (12), the impact point (see FIG. 5) of the high-pressure water jet (10') (from the nozzle (8 ')) on the template surface (12) preferably about 10 mm below the pipe center axis on which the template rests. This ensures that the high-pressure water jet does not bounce off the stencil surface and does not form a water film on the pipe surface, but undermines and definitely detaches the photoresist layer. The photoresist layer is rinsed in the form of fragments of lacquer into the pouring basin of the high-pressure system, where it is filtered out in the lower part. After about 20 minutes, the high-pressure removal step is complete and the completely clean template can be removed from the plastic tube.

The template thus obtained is thus in its native state, i.e. preserved completely intact and freed from the photoresist layer. It can now be reused by applying a new photoresist for a new run in a printing process.

While preferred embodiments of the invention are described in the present application, it should be clearly pointed out that the invention is not limited to these is limited and can be carried out in other ways within the scope of the following claims.

Claims

EXPECTATIONS

1. A process for decoating printing stencils, comprising or consisting of a) a softening step, wherein the photoresist adhering to the printing stencil is weakened with a softening bath and the bond to the printing stencil is loosened, and wherein the softening agent essentially does not chemically dissolve the photoresist layer, but only its Binding to the stencil surface weakens, and b) a hardening step, the printing stencil with the soaked and partially detached photoresist on it being rinsed with water, so that the softened photoresist is hardened again but not reattached to the stencil, and c) a removal step , whereby the hardened but partially detached photoresist is removed from the stencil by a high pressure water jet without the stencil surface being damaged.

2. The method according to claim 1, characterized in that the softening bath comprises or consists of an aqueous, acidic solution containing a mixture of hydrocarbons.

3. The method according to claim 2, characterized in that the softening bath comprises a solution of glycols and organic or inorganic acids, preferably HCl, in water.

4. The method according to any one of claims 2 or 3, characterized in that the softening bath is a mixture of about 50-75 wt .-% butylene glycol, methyl glycol and ethylene glycol monoethyl ether, about 2 to 20, preferably about 5 wt .-% HCl, in Contains 10-25 wt .-% water.

5. The method according to any one of claims 1 to

4, characterized in that the softening bath has a temperature of between 40-100 ° C, preferably 60-80 ° C, and very particularly preferably of about 70 ° C.

6. The method according to any one of claims 1 to

5, characterized in that the softening step is carried out for about 5 to 40 minutes, preferably between 10-20 minutes.

7. The method according to any one of claims 1 to

6, characterized in that the printing stencil is held by a rotary movement during the softening step, so that the detachment takes place evenly.

8. The method according to any one of claims 1 to

7, characterized in that the removal step c) is carried out with a water jet pressure of between 100-220 bar, preferably of 190 bar.

9. The method according to any one of claims 1 to

8, characterized in that the process for the stripping of flat stencils is carried out.

10. The method according to any one of claims 1 to 8, characterized in that the method for stripping cylindrical stencils is carried out.

11. The method according to claim 10, characterized in that the cylindrical template (12) rests on a rotatable tube (5 ') and the point of impact of the high-pressure water jet (10') on the template surface is below the central axis of the tube (5 ') ), and thus does not bounce off the stencil surface and does not form a water film on the pipe surface.

12. The method according to any one of claims 10 or 11, characterized in that the water jet direction is inclined sideways by about 3% to the normal and thus prevents a forward movement of the stencil to be cleaned.

13. A method for stripping rotary printing stencils according to one of the preceding claims, comprising or consisting of a) a softening step, wherein the binding of the photoresist on the printing stencil with a softening bath containing a mixture of about 50-75 wt .-% butylglycol, methylglycol , Ethylene glycol monoethyl ether, about 2 to 20% by weight, preferably about 5% by weight of HCl and 10-25% by weight of water, and b) a curing step, the rotary printing stencil having the softened and partially detached photoresist is rinsed with water, so that the softened photoresist is hardened again but not reattached to the template, and c) a removal step, the cylindrical template resting on a concentric, rotatable tube and the point of impact of the high-pressure water jet the template surface below the pipe center axis, on which the template egt lies and thus neither bounces off the surface of the stencil nor forms a water film on the surface of the tube and the hardened but partially detached photoresist is removed from the stencil by a high pressure water jet.

14. Arrangement for stripping cylindrical printing stencils, in particular according to one of claims 1 to 13, characterized in that they a) a softening system, comprising an insulated double wall system equipped with a heater (4) in the lower part of the system (5), and an inner tub (6 ) at the top Plant part, a pump device (2), a level monitor (3), a support tube (9) on which the template (12) to be stripped is placed and a suction device (1) for the heated solvent liquid, and b) a high-pressure system, comprising a system housing (1 '), a water tank (2'), a filter housing (3 '), a slide guide (4'), a rotatable support (5 ') above a trough for fitting with a cylindrical pressure template (12), a drive motor (7 '), an adjustable water jet nozzle (8') and a high pressure pump device (6 ').