GB2048515A

GB2048515A - Stencil washing apparatus and method

Info

Publication number: GB2048515A
Application number: GB8013198A
Authority: GB
Original assignee: Svecia Silkscreen Maskiner AB
Current assignee: Svecia Silkscreen Maskiner AB
Priority date: 1979-04-24
Filing date: 1980-04-22
Publication date: 1980-12-10
Also published as: FR2454913A1; JPS55150397A; DE3015160A1; IT1127450B; IT8048501A0

Abstract

A stencil washing apparatus includes a high-pressure system capable of supplying liquid to a surface of the stencil 3 at a pressure of at least 50 kg/cm<2>. Conveniently the high pressure system includes a pair of spray devices (12b,13b) movable horizontally relative to the screen and providing at least one and preferably several pairs of nozzles (12b',13b') capable of supplying liquid to the front and rear surfaces of the screen. The nozzles of each pair lie generally in the same horizontal plane but offset laterally (longitudinally to the screen) with respect to one another so that as the spray devices are moved horizontally relative to the screen, the screen is carried to bend under the liquid pressure. In a method of washing ink from the stencil, washing liquid is supplied to the surface of the screen at a pressure of at least 50 kg/cm<2>. Preferably, an ink dissolving agent is first sprinkled onto the screen at low pressure e.g. by sprays 12a, 13a, and, after allowing a sufficient period of time for the ink to be dissolved, the high pressure washing liquid is supplied to remove the dissolving agent and ink dissolved therein. <IMAGE>

Description

SPECIFICATION Stencil washing apparatus and method The present invention relates to an arrangement for washing a stencil and more particularly a stencil intended for use in a silkscreen printing machine.

In principle, there are two different methods by which a stencil which is intended for a silkscreen printing machine can be produced - the first method is called "indirect stencil method" and the second method is called "direct stencil method".

The indirect stencil method utilizes a film, a so-called stencil film, which consists of a base and a light-sensitive material or emulsion which is applied to the base. This film is subjected to light from high-efficiency lamps shining through a negative with the intended pattern, this light treatment resulting in the intended pattern being transfered to the film. This is followed by the film being hung up and being subjected to a water treatment. In this water treatment the pattern is washed and rinsed off and the product obtained is called "stencil". After that the stencil is taken and placed (rolled out) on a cloth which is already held in a frame, with the emulsion facing the cloth, on which the stencil dries to some extent so that the base can then be removed. The emulsion itself adheres to the cloth and dries.

A stencil produced in the above-mentioned manner can be used for inks based on a petroleum base, that is to say on thinner and the like.

An indirect stencil produced in this way can be washed clean of emulsion by being sprayed with water and the cloth held on the frame can be re-used for other patterns.

As far as the direct stencil method is concerned, a cloth is utilized which is already held in a frame and which is covered with a light-sensitive emulsion, normally of a different type than the type mentioned above. This light-sensitive emulsion is illuminated, through 3 pattern, with high-efficiency lamps and a hardening of the emulsion occurs. Normally, a positive film is used and its pattern is transferred to the cloth and the emulsion covering it. This is followed by a water treatment in order to wash and rinse the pattern, followed by drying.

A stencil which is produced according to the direct stencil method can be used not onlyfor petroleumbased inks but also for water-based inks.

This means that the emulsion used in the production of direct stencils can be removed only with difficulty and that it cannot be removed simply by spraying it with water.

In order to be able to remove the emulsion applied to a direct stencil, it is necessary that the stencil is first sprayed with a special detergent solution, normally containing sodium hypochlorite. After the stencil has been sprayed with the said solution the stencil stands and "matures" so that the solution can have a loosening effect on the emulsion. Only then will the emulsion come away from the cloth when using a water spray.

The indirect stencil method has proved superior to the direct stencil method for printing in which great emphasis is placed on line sharpness and correct reproduction of fine screens. In addition it can be said that the indirect stencil method is particularly Used-in the production offour-colourscreen print ing. The direct stencil method is used particularly where water-based inks are to be used.

It is extremely desirable that, within this technical field, an arrangement can be used which is provided with elements and means which make it possible to remove effectively the emulsion applied in accord ance with the direct stencil method to a frame holding a cloth. Effective cleaning by means only of a water spray is also a problem with stencils produced according to the indirect method.

It is the object of the present invention to provide an arrangement which eliminates the abovementioned disadvantages. Essentially, this is done by the invention specifying partly a low-pressure system and partly a high-pressure system. The arrangement uses the following sequence: a) The low-pressure system is connected and sprinkles an agent, which is suitable for dissolving ink, on the stencil.

b) The agent intended and suitable for dissolving ink is allowed to work on the stencil for a certain time.

c) The high-pressure system is connected and sprinkles an agent, which is intended for washing out the ink-solvent and the ink dissolved in the latter, on the stencil, normally water and preferably warm water. The nozzles of the high-pressure system are mounted in an organ which makes it possible to allow the part under treatment to be displaced over the stencil (so-called scanning). The high-pressure system is to be fed with a pressure in excess of 50 kp/cm2.

With watersoluble stencils, the treatment under "c" removes even the stencil material and leaves only the stencil cloth washed clean.

With non-watersoluble stencils, besides the abovementioned process for removing ink from stencils the following is required: d) The low-pressure system is connected and sprinkles an agent, which is intended for dissolving the stencil material, on the stencil. This can most suitably be done simultaneously over the whole height of the stencil.

e) The agent intended and suitable for dissolving the stencil material is allowed to work on the stencil for a certain time.

f) The high-pressure system is connected and sprinkles on the stencil according to "c" above.

Advantages of the invention: It has been shown that it is possible, with a method and arrangement according to the present invention, to wash clean stencils in a most effective manner in a shorter time than with the earlier processes.

Brief description of the attached drawings: An embodiment proposed for the present and provided with the features which are characteristic of the present invention will be explained in greater detail with reference to the attached drawings, in which: Figure 1 shows a perspective view, with certain parts cut away, of an arrangement for producing and washing a stencil, Figure 2 shows a section through the arrangement according to Figure 1, Figure 3 shows a side view of a part of the high-pressure system according to the present invention, Figure 4 shows the orientation of the nozzles in the high-pressure system, and Figure 5shows a proposed scanning cycle.

Arrangement 1 provides a complete combined arrangement equipped with all functions, that is to say, development of an indirect stencil, development of a direct stencil, washing off of the ink, washing off of the emulsion with water and washing off of the emulsion with a detergent (stripper), and consists of a stationary frame 1, the lower part of which works in conjunction with a discharge trough 2 which is provided to take away the solvent or liquid which is sprayed against a stencil 3 placed into a frame 3a.

The stencil 3 is covered with an emulsion in accordance with the direct or indirect stencil method. On each side of the discharge trough 2 two rails 4 and 5 are located. The rails 4 and 5 support and work in conjunction with the frame parts 1 a, 1 b and ic. These parts form a gable with a truncated right-angled triangle shape. The frame part 1 d is also associated with the truncated right-angled triangle shape. In the same way, the opposite gable is provided with frame parts 1 e, if, 1g and lh. Between the gables parallel frame parts 1k extend and these frame parts are intended to support the stencils 3 held in the frame 3a. The frame parts 1k are also provided with a number of holding elements 1 m for the frame 3a of the stencil 3.

Inside the stationary outer frame construction 1 an inner frame construction 10 is located which can be displaced along the outer frame construction. The shape of this frame construction 10 corresponds to a truncated right-angled triangle and serves as a holder for a plurality of parts belonging to the arrangement and intended for the treatment of the stencils.

Thus the inner frame construction 10 supports a hydraulically-driven pump with the reference designation 6. This pump is provided to pump water from a water trough 11 to the front and rear rinsing arms 12 and 13 which enter into the low-pressure system.

This is done by means of lines 14 and couplings, not shown in greater detail in the drawing, between the pump 6 and the arms 12 and 13. It must be noted here that the rinsing arms 13 are located behind the horizontal braces lkwhilstthe rinsing arms 12 are located in front. There is also an hydraulically-driven pump 14which is connected to a container 14a containing a detergent, a socalled "stripper", and this pump 14 is intended to pump the detergent to the rinsing arms 12' and 13' through pipes not shown in greater detail in the drawing. The rinsing arms 12 are located directly next to the arms 12' and the rinsing arms 13 are located directly next to the arms 13'.In the upper part of the stationary frame construction there is also a hose guide 15 which is designed to feed hydraulic pressure to the energyconsuming devices contained in the displaceable frame construction.

Finally, the frame construction 10 supports an hydraulic drive motor 16 which is connected, preferably via a change-over device 17, to one or several drive wheels which are provided so that the holder 10 can be displaced along the rail 4 and 5. In the drawing three drive wheels are shown of which one or two can be used doubly as drive wheels.

All of these four pipes are provided with a number of nozzles 12a, 13a. It is essential that the nozzles 12a face toward the nozzles 1 3a and that the pipes for the water and the pipes for the detergent are preferably arranged in parallel.

As far as the nozzles 1 2a, 13a are concerned, these are of metal and provide an adequate and even flow and output of liquid with overlapping spray patterns.

In order to prevent a different effect on the upper and lower part of the cloth or stencil, the spray arms or pipes can be advantageously provided with a number of reduction valves so that the pressure of the spray can be adjusted to stay equal in the vertical direction.

Afilm,with a base and an exposed emulsion, applied thereto, or a frame, holding a cloth which is covered with a light-sensitive emulsion and which is exposed to highly-efficient lamps, having the reference designation 3, is applied in the arrangement in such a manner that it rests against one or several support bars 1 k. If a film is used the film is hung up in pegs but here a frame 3a holding a cloth 3 is used and special fastening elements 1 m for the frame are available which can be applied to any support bars. It should be said here, perhaps, that in the production of indirect stencil films a special plate, preferably of aluminium or plastic, must be applied against and in front of the bars before the stencil is fastened to the pegs applied to the plate.

It is certainly also possible to hang up a frame holding a cloth and allow this cloth to serve as a support for the film. The inner frame construction, to which, among others, pipes 12, 13 are firmly attached, can be advantageously located in its one end position or side position when the film or cloth 3 is placed into its desired position. After that the drive motor 16 contained in the lower part of the frame construction is allowed to displace the frame laterally along the film or cloth 3. The power is transferred from the motor 16 via a changeover device 17 to a rubber wheel which rests against and drives against the rail 4. This arrangement provides a soft and quiet run and gives an in built skid protection with overload. Certainly, the wheel does not need to be separate and of rubber. It is also possible to drive with the aid of one or two of the supporting wheels.

Such an arrangement also gives an inbuilt skid protection with overload.

In the drawing a sliding magnetic limit position element 18 is also shown with which only the desired length of travel is set, that is to say the movement forward and back of the inner frame. The hydraulic control which is based on the setting of the magnetic limit position element is not shown in the attached drawing and does not constitute any part of the present invention.

The water treatment takes place via the lowpressure system from both sides of the cloth or film by virtue of two pipes 12, 13, provided with nozzles 12a, 13a which face one another, being placed on each side of the cloth or film 3. These pipes work in conjunction with the inner frame which is arranged to be displaceable along the cloth or film so that the stencil is formed after the treatment. Certain pipes are consequently placed on the rear of the bars 1 k whilst other pipes are placed in front of the bars.

It must be noted here that a plate 19, which covers the pipes, serves to keep liquid, and particularly from the nozzles 12a, 13a,from passing outside and limits space.

Two pairs of pipes with nozzles are arranged on the inner frame on each side of the stencil 3 and the one pair of pipes having nozzles facing one another is intended for spraying water on the cloth or film and the second pair of pipes is intended for spraying detergent which can remove the emulsion applied to a cloth in accordance with the direct stencil method.

In the drawing seven support parts or bars 1k are shown to run parallel and horizontal between pairs of pipes and between gables and to support the cloth or film. In the mean time, there is nothing to prevent these support bars from being fewer or more in number or to let them be attached to the gable parts in a removable manner.

According to the invention, the pressure applied to each pipe can be different and the pressure for the front pipe is preferably higher than the pressure for the back pipe. It is here required to obtain a larger amount of liquid at the front of the stencil than at the rear of the stencil. For this feature the nozzles can be different for the two pipes so that in this way a larger amount of liquid is obtained at the front of the cloth or film than at the rear. In another case the pipe at the rear can be provided with a restriction.

The developing of indirect stencils requires first a hardening process with, for example, hydrogen peroxide. Such arrangements can be built in smaller format and must posses a recirculation system for the hardener. The spray system can here be constructed in such a mannerthat it only sprays from the front.

According to the present invention, the arrangement also comprises two spray elements 12b, 13b for the high-pressure system. The one spray element 1 2b can be displaced synchronously with the second spray element 13b and up and down along a support 20, 21 which can also be displaced with the carriage 10. This is not shown in Figure 1 since it is concealed by the plate 19. The support 20, 21 is fixed to the carriage 10.

This makes it possible to wash the stencil in accordance with the following process: a) The low-pressure system 12, 13 is connected and sprinkles an agent, which is suitable for dissolving ink, on the stencil. This can most suitably be done simultaneously over the whole height of the stencil.

b) The agent suitable and intended for dissolving ink is allowed to work on the stencil for a certain time.

c) The high-pressure system is connected and sprinkles an agent, which is intended for washing out the ink-solvent and the ink dissolved in the latter, on the stencil, normally water and preferably warm water. The nozzles of the high pressure system 12b, 13b are mounted in an organ which makes it possible to allow the part under treatment to be displaced over the stencil (so-called scanning). The high-pressure system is to be fed with a pressure in excess of 50 kp/cm2.

With water soluble stencils, the treatment under "c" removes also the stencil material and leaves only the stencil cloth washed clean.

With non-water soluble stencils, besides the abovementioned process for removing ink from stencils the following is required: d) The low-pressure system is connected and sprinkles an agent, which is intended for dissolving the stencil material, on the stencil.

The water pressure in the high-pressure system should be higher than 50 kp/cm2. Variations in the range of 75-150 kp/cm2 appear to be suitable. The pressure should preferably be 90-130 kp/cm2 or about 120 kp/cm2. It is also possible to let the pressure be variable.

The spray elements 1 2b, 1 3b provide at least one, and preferably several, pairs of nozzles 12b' and 13b' which are preferably of a hard metal type and cover only a part of the total surface of the stencil.

However, the spray elements 1 2b and 1 3b may be controlled in such a way that they assume one height position at one displacement of the frame 10, shift to another adjoining height position with a return displacement of the frame 10 and so forth.

In this manner the whole stencil can be "scanned".

The high-pressure pump has in Figure 3 been given the reference designation 22 and it can be controlled by a control element 23, in such a manner that when the spray element 1 2b and 1 3b approaches the edge of the stencil the displacement of the frame 10 is connected and the spray element changes its height position.

The control is here of a conventional type.

In Figure 4 the spray nozzle 12b' and 13b' is shown to have their spray cones laterally offset so that the stencil under treatment forms a wave which moves due to the displacement of the frame 10.

The high-pressure system should be fed with warm water with a temperature of 70-80 C.

Figure 5 shows a proposed scanning cycle beginning in the upper left-hand corner of the stencil 3 and ending in the bottom right-hand corner of the stencil.

The reference designation 3 b indicates the portion under treatment which follows the scanning line 3c.

The invention is certainly not limited to the embodiments mentioned above as examples.

Claims

1. An arrangementforwashing a stencil, intended for use in a silkscreen printing machine, in which arrangement the cloth or film undergoes a water treatment for washing off the pattern and/or ink, normally the ink dissolved in a solvent, characterised in that one water treatment takes places by means of a high-pressure system, at a pressure in excess of 50 kp/cm2.

2. An arrangement according to Claim 1, characterised in that nozzles (12b', 13b') are arranged on both sides of the cloth (3) and have spray areas which are offset with respect to one another.

3. An arrangement according to Claim 1, characterised in that a number of nozzles are attached to a spray element which is displaceably arranged on a support (20, 21).

4. An arrangement according to Claim 1, char acterised in that the displacement of the spray element is carried out in such a manner that the stencil is scanned.

5. An arrangement according to Claim 1, char acterised in that the high-pressure system has a pressure in the range of 75-150 kp/cm2, and prefer ably in the range of 90-130 kp/cm2 and advan tageously about 120 kp/cm2.

6. An arrangement according to Claim 1, char acterised in that the following are used for washing a stencil, a) a low-pressure system which is connected and sprinkles an agent, which is suitable for dissolving ink, on the stencil (3), b) an agent, intended and suitable for dissolving ink, which is allowed to work on the stencil for a certain time, c) a high-pressure system which is connected and sprinkles an agent, which is intended for washing out the ink-solvent and the ink dissolved in the latter, on the stencil, normally water and preferably warm water, the high-pressure system nozzles being mounted in elements which make it possible to allow the portion under treatment to be displaced over the stencil (so-called scanning).

7. An arrangement according to Claim 6, char acterised in that for non-watersoluble stencils also the following is required: d) the low-pressure system is connected and sprinkles an agent, which is intended for dissolving the stencil material, on the stencil, e) the agent intended and suitable for dissolving the stencil material is allowed to work on the stencil for a certain time, and f) the high-pressure system is connected and sprinkles on the stencil according to "c".

8. An arrangement according to Claim 6 or 7, characterised in that the low-pressure system is allowed to act over the whole width of the stencil.

9. An apparatus for supplying liquid to a screen during washing of a stencil, which apparatus in cludes a high pressure system capable of supplying liquid at a pressure of at least 50 kp/cm2 to a surface of the screen.

10. An apparatus according to claim 9, wherein the high pressure system includes a pair of spray devices providing at least one pair of nozzles capable of supplying liquid to the front and rear surfaces of the screen respectively, the nozzles of the or each pair thereof lying generally in the same horizontal plane as one another but being offset with respect to one another, the apparatus additionally including means for displacing horizontally one of (a) the stencil and (b) the said pair of spray devices relative to the other during the supply of liquid to the screen so that on said displacement the screen is caused to bend under the liquid pressure from the offset nozzles.

11. An apparatus for supplying liquid to a screen which apparatus is substantially as herein described and illustrated with reference to the accompanying drawings.

12. A method of washing a stencil screen which includes the step of supplying a washing liquid to a surface of the screen at a pressure of at least 50 kg/cm2.

13. A method according to claim 12, which includes the preliminary step of supplying an inkdissolving agent to the surface of the screen at a low pressure and allowing a period of time for the ink to dissolve in the said agent, the dissolved ink and agent thereafter being removed from the screen by the said step of supplying the washing liquid to the surface of the screen.

14. A method of washing a screen substantially as herein described and illustrated with reference to the accompanying drawings.