Process for the removal of patterning material from a screen printing stencil and a device for use of the process

Abstract

 Process and apparatus for the removal of patterning material selectively applied to a screen printing stencil according to a pattern, in which a medium is sprayed at high pressure locally against the stencil and the stencil is moved in such a way relative to the spraying point that the entire part of the stencil coated by patterning material is covered. The medium can be water of which the pressure lies in a range between 150 and 300 bar. Preferably the spraying is always carried out oppositely from both sides of the stencil. Further the spraying may take place in a pulsating manner and prior to spraying the stencil may be treated with a weakening medium which weakens the bond between the patterning material and the stencil, while essentially maintaining the bond.

Description

[0001] The invention relates to a process for the removal of patterning material selectively applied to a screen printing stencil according to a pattern.

[0002] A process of this type is known in practice. In the known process the patterning material is completely dissolved and removed from the surface and from the apertures of the stencil by means of chemicals of, for example, a mixture essentially comprising formic acid and dichloromethate. If the stencil is shaped like a cylinder whose edges are bonded to edges of fixing rings, in the known process the rings are generally first removed from the stencil by means of a suitable solvent, before the patterning material is removed.

[0003] The disadvantage of the known process is that it is labour-intensive and takes a fairly long time. Besides, the solvents are contaminated by the adhesive and/or the patterning material, which is generally a suitable lacquer, as a result of which these agents are less effective and after some time cannot be used any more for solvent action, thus giving rise to the problem of disposal of contaminated chemicals, which is currently serious as regards the environment. Another disadvantage is that the chemicals used are often volatile, with the result that special measures have to be taken as regards the safety of the personnel and as regards pollution of the environment.

[0004] The object of the invention is to eliminate the advantages of the known process.

[0005] This object is achieved according to the invention for the process of the type mentioned in the preamble by spraying a medium at high pressure locally against the stencil and by moving the stencil in such a way relative to the spraying point that the entire part of the stencil coated by patterning material is covered. It has been found that in this way an environmentally friendly process for good removal of the patterning material from the stencil is obtained.

[0006] The environmentally friendly aspect is enhanced through the fact that the removal medium can be water at a pressure preferably between 150 and 300 bar. The particles of the patterning material carried along by the water can easily be collected, for example, through settling.

[0007] It is always preferable to spray against the stencil from positions lying opposite each other on either side of the stencil, so that the stencil is subjected to essentially the same mechanical stress on either side, thereby avoiding damage to it.

[0008] The stencil is preferably held in a slanting position during the spraying, so that the surface to be sprayed is kept free from loosened particles of the patterning material.

[0009] The effect of the spraying can be increased by spraying in a pulsating manner.

[0010] The stencil is preferably treated prior to spraying, for example through immersion, with a weakening medium which does weaken the bond between the patterning material and the stencil, but essentially does not break it. This weakening medium is then essentially kept free of particles of the patterning material, so that the weakening medium remains usable for a long time, while, during the subsequent spraying with the removal medium, the stencil can be cleaned more quickly and with relatively little mechanical stress. Such a weakening medium can be a liquid based on formic acid, or a lye.

[0011] The invention also relates to a device according to Claims 12 to 15 for use of the process.

[0012] The invention is explained with reference to the drawing, which shows an embodiment of a device which is suitable for use of the process according to the invention.

[0013] The device comprises a partially open housing 1 with a slanting bottom 2 into which arms running parallel to the bottom 2, such as the arm 3, project with rollers, such as the roller 4, by means of which a stencil 5 with coupling rings 6 is supported at an angle in the housing 1. The supporting arms 3 are driven by a motor 10 by means of a gear wheel 7, a chain or toothed belt 8, and a gear wheel 9, in order to make the stencil rotate about a longitudinal axis of the stencil 5.

[0014] A motor 11 is connected, by means of a gear wheel 12, a chain or toothed belt 13 and a gear wheel 14, to a screw 15 running parallel to the stencil 5. The screw 15 projects through a threaded bore 16 of a bracket 17 which is moved up or down when the screw 15 is driven by the motor. Fixed to the bracket 17 is an arm 18 which projects through a side wall of the housing 1 and into the stencil 5, and which at the end inside the stencil 5 has a spray nozzle 19 with a spray aperture directed towards the stencil. Fixed to the bracket 17 is another arm 20 which projects through an aperture in the housing 1 and in a position outside the stencil 5 opposite the spray nozzle 19 of the arm 18 has a spray nozzle 21 with a spray aperture directed towards the stencil 5.

[0015] The arms 18 and 20 are hollow for the conveyance to the spray nozzles 19 and 21 of a medium, in particular water, which is pumped to the other end of the arms 18 and 20 through a hose 22 by a high-­pressure pump 23 driven by a motor 24.

[0016] The housing 1 has means (not shown) for discharging the medium sprayed inside the housing 1 and containing released patterning material particles from a stencil 5.

[0017] Before a stencil 5 is placed in the device, it is preferably immersed in a weakening medium, which can be a liquid based on formic acid, or a lye, for weakening the bond of the patterning material to the stencil 5, but the bond is essentially not broken.

[0018] The stencil 5 is subsequently placed in the device. During the operation of the device, the stencil 5 is turned and the spray nozzles 19 and 21 are moved to and fro axially over the length of the stencil 5, so that the spray nozzles 19 and 21 cover the whole surface of the stencil 5 during spraying. This operation is repeated for a number of revolutions of the stencil 5, if necessary.

[0019] The pump 23 is preferably capable of generating a pulsating pressure of the medium to the spray nozzles 19 and 21.

[0020] It is pointed out that the device shown and explained is given only as an example, and the process according to the invention can also be achieved in another manner and can be used for various types of stencils, including flat ones.

Claims

1. Process for the removal of patterning material selectively applied to a screen printing stencil according to a pattern, characterized by spraying a medium at high pressure locally against the stencil and by moving the stencil in such a way relative to the spraying point that the entire part of the stencil coated by patterning material is covered.

2. Process according to Claim 1, characterized in that the medium is water.

3. Process according to Claim 1, characterized in that the pressure lies in a range between 150 and 300 bar.

4. Process according to Claim 1, characterized in that spraying is always carried out oppositely from both sides of the stencil.

5. Process according to Claim 1, characterized in that the stencil is held in a slanting position during the spraying.

6. Process according to Claim 1, in which the stencil is shaped like a cylinder, characterized in that the stencil is rotated about a longitudinal axis thereof during spraying.

7. Process according to Claim 1, characterized in that spraying takes place in a pulsating manner.

8. Process according to Claim 1, characterized in that, prior to spraying, the stencil is treated with a weakening medium which weakens the bond between the patterning material and the stencil, while essentially maintaining the bond.

9. Process according to Claim 8, characterized in that the treatment involves immersion in the weakening medium.

10. Process according to Claim 8, characterized in that the weakening medium is a liquid based on formic acid.

11. Process according to Claim 8, characterized in that the weakening medium is a liquid based on a lye.

12. Device for the removal of patterning material selectively applied to a screen printing stencil according to a pattern, characterized by means for locating the stencil, spray means with a first spray nozzle which is fixed on a first arm and receives a medium under pressure from a supply source, said means spraying the medium against the stencil, and conveyance means which move the spray nozzle at a distance over the surface of the stencil covered with patterning material.

13. Device according to Claim 12, characterized in that the spray means have a second nozzle fixed on a second arm and having an aperture opposing an aperture of the first nozzle, while provision is made between the arms and nozzles for a suitable space for allowing through a part of the stencil to be sprayed, and the conveyance means move the nozzles equally.

14. Device according to Claim 12 or 13, in which the stencil is a cylindrical shape, characterized in that the conveyance means comprise a stationary feed screw placed at an angle on the central axis of the stencil, with a bracket having a threaded passage for allowing through the screw, while an arm of a nozzle is fixed to the bracket and the screw is turned by drive means, and in that rotation means are present for turning the stencil about a longitudinal axis of the stencil.

15. Device according to Claim 12 or 13, characterized in that an arm is a pipe for conveying the medium to the nozzle fixed on the arm.

Drawing