DE3508920A1 - Metallic printing plate for tampon printing, and process for making a block for tampon printing - Google Patents

Abstract

A metallic printing plate for making blocks for tampon printing, having an engraving depth of at least 20 mu m, is characterised in that the printing plate has at least two metal layers, of which the first metal layer is situated on the printing upper side, and that the at least one metal layer adjoining the first metal layer can be etched down to a depth of at least 35 mu m by a single etchant which essentially does not attack the first metal layer. This printing plate can be reproduced and processed into blocks in a simple manner.

Description

Representative;
Patent attorneys
Kohler Schwindling Späth
Hohentwielstrasse 41
7,000 Stuttgart 1

Metallic printing plate for pad printing and method for producing a cliché for pad printing

The invention initially relates to a metallic printing plate for the production of clichés for pad printing with an engraving depth of at least 20 μm.

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In pad printing, an engraved cliché, which can also be engraved by etching, is coated with printing ink colored, then wiped off and then the in The printing ink left behind in the indentations of the engraving is caused by a pad pressed onto the cliché, which is also known as Pressure pad could be referred to and generally consists of silicone rubber, taken over from this to the transferring the object to be printed. In order for this latter color transfer to be effective, the material is des Tampons, namely the silicone rubber, chosen so that the printing ink only weakly adheres to it. Hence the cliché must be depending on the material of the object to be printed one Have an engraving depth that goes up to 35 or 40 μΐΕ, so taking into account the due to the low liability on Tampon in the engraving remaining color from this engraving nevertheless enough color is taken to the desired one To achieve color coverage. With pad printing, the objects to be printed are often complicated molded technical parts, for example typewriter keys made of plastic, which can be attached to two Sides are to be printed. When printing these technical objects, a very high edge definition of the Put emphasis on pressure.

To produce the printing ink-receiving depressions in the cliché, the metallic printing plate is either engraved using suitable tools, i.e. metal is removed mechanically. This way of making the Engraving is only suitable for line engraving. The line engraving can also be made by etching. The etching is also suitable for making a grid engraving. The grid engraving offers the advantage over the line engraving,

that even in the area of large-area etchings always up to the original surface of the printing plate reaching webs or mountain-like projections are present that the squeegee in support essentially over their entire length, so that the squeegee does not, even if only to a very small extent, can bend and penetrate into the depressions.

The following are those that already contain an engraving and are therefore immediately suitable for use in the pad printing machine plates that can be used are referred to as clichés, and the plates that are not yet engraved and that are used for the production of the Serving clichés are referred to as a printing plate or simply a plate. The expression "plate" says how the embodiment is clear, nothing about the thickness and rigidity of such a plate, rather a plate according to the invention can also be so flexible that it can be bent by hand without difficulty, if they, for example, only a total thickness of 200 μm having. However, the known metal printing plates are so thick that visible deformation is not possible.

For the production of a cliché using a known printing plate made of metal by etching, a person skilled in the art is namely a chemistry designer who has the extensive specialist knowledge required to etch a flawless one Clichés are required. The etching takes place with the help of an etching mask, which is photographic is applied to the plate. For this purpose, the plate can already be supplied with a light-sensitive Coating be provided, or it will be provided with such a coating shortly before the production of the cliché Mistake. When making the cliché it is important to consider

that the required etching depth for the production of a perfectly usable cliché in pad printing is not always can be predicted with absolute certainty. For safety reasons, when in doubt, one initially becomes less deep etch than presumably necessary because an etch that is too shallow can be deepened with less effort, as if an etching has gotten too deep and then cannot be filled in again. Such corrections to the Etching is definitely considered because it serves as the starting material for the production of a cliché Metal printing plate is often expensive because of the complex manufacturing process. If after a first Etching process has shown that the etching is too shallow in whole or in some areas of the motif, so will Replace the not yet usable cliché from the chemigraph on the printing surface with a light-sensitive one Coating, and then the same film that was used for the first exposure is applied exposed again, because the parts of the plate surface that remained in the first etching process were also exposed during the second etching process must not be attacked. The photographic film must therefore be mounted extremely precisely, especially with raster engraving, so that the second exposure takes place exactly at the same point as the first Exposure has taken place. The areas of the surface of the printing plate not removed during the first etching process are thus again provided by the second exposure process with a cover that is resistant to the etchant provided and thus protected. In the remaining areas the photosensitive material is washed out, and there can now be tried by another etching process,

Ref .: P 35 08 920.2 Stuttgart, March 22nd, 1985

Note: Wilfried Philipp ^ j. P 4644 R / Ho

to increase the depth of the engraving made by etching. The work described can only be done by one person experienced and trained chemists can be carried out successfully.

The invention has for its object to provide a printing plate of the type described above, in which to Production of a cliché for pad printing requires considerably less knowledge and skills than in the production of the metal clichés described above.

This object is achieved according to the invention in that the printing plate has at least two metal layers, of which the first metal layer lies on the upper side to be printed, and that which adjoins the first metal layer at least one metal layer can be etched by a single etchant to a depth of at least 35 μm is that does not substantially attack the first metal layer.

Preferably, at least the side adjoining the first metal layer is the further metal layer or further Metal layers chosen so that they are substantially of an etchant suitable for etching the first metal layer is not attacked.

There are known metallic printing plates of the type mentioned, which are made of copper. According to embodiments

According to the invention, a printing plate according to the invention can be provided which, in terms of the service life of the finished cliché, does not differ, or only slightly, from clichés made from the known copper plates. In this package, the plates according to the invention are a full ¹ "substitute for the known copper plates in terms of service life, but they can be processed into clichés much more easily influenced.

In principle, the first metal layer, the surface of which forms the surface of the finished cliché, is numerous Metals can be used. Purely the availability is important that a first etchant can be found which etches this first metal layer, this first etchant preferably the layer lying below the first metal layer does not attack or only slightly attacks, and that a Second etchant can be found, which is the metal layer lying below the first metal layer or the one below first metal layer lying etched metal layers, it is necessary here that this second etchant first metal layer does not attack or only insignificantly.

Chromium, which will be discussed in detail below, is preferably used as the metal for the first metal layer. However, niobium, tungsten, cobalt, nickel and titanium in particular are also considered for the first metal layer drawn. All of these metals, including chromium, are metals that have the property of

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Show passivity. This also includes aluminum, which is not to be excluded from the invention, in general however, it is too soft, in particular it is also softer than copper.

Although all of the metals just mentioned are particularly considered for the invention, they are likely to follow current opinion not all in the same way for use on a large scale, especially when taken into account the manufacturing costs and ease of use by unskilled workers. So become etching of titanium, hydrofluoric acid or other hot acids, which are less easy to handle than in the exemplary embodiment, are required hydrochloric acid / sulfuric acid mixture used at room temperature. The material costs for niobium are considerable higher than, for example, for chromium or nickel, and this may be a reason that niobium is used in practice is less of a consideration. As far as is known here, there are no cheap methods available for tungsten to achieve this Applying tungsten in a thin layer to another metal layer. In particular, there seems to be no experience of that Apply by electroplating to be present. In contrast, tungsten can be deposited on other metals by vapor deposition. For this, however, vacuum systems are required, which are at least not currently available in the sizes available stand that the areas of printing plates required for the pad printing industry can be generated efficiently.

Niobium has a Vickers hardness HV of approximately 84, titanium a Brinell hardness HB of approximately 200 to 240, and tungsten one Brinell hardness HB from about 200 to 400 and according to other sources a Mohs hardness of 4.5 in the pure state to 8 for one Content of carbon. These last-mentioned metals are therefore in principle able to create a printing plate,

the surface hardness of which is similar to that of the well-known copper plates (copper has a Mohs hardness of around 2.5 to 3> according to other sources a Brinell hardness HB depending on Variety from 50 to 100).

Nickel has a Mohs hardness of 3.8 and can be etched with hydrochloric or sulfuric acid. If a brass plate from
For example, 200 μm thick with a nickel layer of about 6 μm thick, similar etchants can be used as in the exemplary embodiment, whereby the first etchant (hydrochloric acid and / or sulfuric acid) does not attack the brass and the second etchant (ferric chloride solution) does not attack the nickel attacks.

Cobalt has a Mohs hardness of 5.5 and is therefore significant
harder than copper. It is also with hydrochloric acid or
Sulfuric acid can be etched. A printing plate with cobalt as the first metal layer and a brass layer below the cobalt layer that is sufficient for the required engraving depth
therefore has a greater abrasion resistance and service life than the known copper plates.

If the number of prints to be produced is significantly higher than about 40,000, the known clichés made of plastic, copper or glass can no longer be used
steel plates are then used in the prior art. This is made from printing plates, which are made of alloyed cross-rolled hardened tool steel in the form of a generally rectangular plate, and the later printing surface is precisely ground and lapped and therefore has only a very small surface
Roughness of a maximum of 1 to 2 μπι. The surface hardness

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such steel plates is about 64 "to 65 HRC (Rockwell hardness C). Such clichés are useful for a number of over 100,000 prints. Because of the complex production Such steel pressure plates are expensive.

In one embodiment of the invention it is provided that the first metal layer on its surface has a Rockwell hardness of at least 64 HRC. This record is therefore at least as hard as steel.

One embodiment of the invention makes it possible, in a simple manner, to produce equivalent pressure plates made of steel to create printing plates according to the invention, which in particular also achieve the high hardness mentioned, and at which have a low surface roughness comparable to that of steel plates in a simple manner, especially without the costly one Lapping process, can be achieved. A small surface roughness is therefore necessary in pad printing so that the The surface of the cliché does not already have depressions of such depth from the manufacture of the plate has that it can remain in this color after doctoring. This color would be on the tampon transferred object to be printed and would disturb the print image.

This embodiment, which is qualitatively comparable to the printing plates made of steel, has a first metal layer Layer which essentially contains the chromium already mentioned above. The Mohs hardness of chrome is greater than 7 what with a Rockwell hardness HRC of 70 is comparable. The chrome layer can be easily combined with that in the exemplary embodiment Etch hydrochloric acid / sulfuric acid mixture described, it is particularly important for pad printing that the Etching is very fine, so that there are clean contours of the

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Engraving result. The etching in the first metal layer, im Example of the chrome layer, namely for the edge sharpness responsible for the pressure.

The first metal layer, which is essentially formed by chromium, depending on the manufacturing process Additives can be added, is designed so that their top is smooth and flat with a surface roughness of at most the value just mentioned of 2μπι is formed. Such a chrome layer can be produced simply as a so-called hard chrome layer, in particular by electroplating. The hardness of such a chrome layer is around HRC and is therefore no lower than that of the steel plates mentioned at the beginning. The material used in the electroplating bath, in particular copper or brass sheet, should have a maximum surface roughness of 2 to 5μπι.

The advantages of the invention will now be discussed, with the invention using a cliché for simplicity is discussed, which has a chromium layer as the first metal layer, as is also the case in the exemplary embodiment is provided.

A worker assigned to make clichés in the printing shop who has no specialist training in the production of the Clichés required, as with the known clichés, either exposed one on top of the chrome layer at the manufacturer or subsequently applied light-sensitive Layer that hardens in the exposed areas, possibly after a development process. To the The light-sensitive layer is removed from unexposed areas by suitable measures, in particular by washing off with Water, removed. Now the printing plate is placed in a tub that contains a first etchant, the chrome

etches sufficiently fine. The etchant described later is at room temperature and that in the embodiment described layer thickness of the chromium layer requires an etching time of about 30 minutes. The worker can Observe the cliché during the etching and, for example, determine whether the etching process is being carried out on the basis of the development of gas is still in progress. If, according to a preferred embodiment of the invention, that metal layer on which the Chrome layer is applied, has a color different from the chrome layer, so the worker can work particularly easily recognize at which points on the printing plate the chrome layer has already been etched through and can in this way observe the completion of the etching process particularly closely. It happens when, as in the exemplary embodiment, a relatively mild etching agent is used, does not imply that a certain etching time is adhered to to the second, but also if the etching time is exceeded by, for example, one minute or two minutes, the Chromium layer is underetched to a disruptive extent. If the first etchant is the one below the chromium layer Metal is not attacked or only slightly attacked, recognizing the end of the etching process is facilitated by that the gas formation ceases or becomes less, whereby then a different color of the lying under the chrome layer Metal layer can be recognized particularly easily. However, it would affect the quality of the cliché produced In most cases, this does not do any harm if the chrome etchant also noticeably attacks the layer below the chrome, provided that this layer, which lies beneath the chromium layer, is not carried out at a considerably greater speed is etched away as the chrome itself.

If the chromium layer is etched through in the manner described in accordance with the exposed pattern, then rinse the worker removes the partially etched plate under running water to remove the chrome etchant because of it could possibly affect the puncture ability of the later used second etchant if it is in this is entered. The etching mask produced by exposure is expediently not yet removed so that it becomes one forms mechanical protection for the surface of the plate. For further etching, the one produced by exposure would be Etching mask no longer necessary.

Then the partially etched cliché is placed in a tub in which there is a second etchant, which etches the metal below the chromium, but does not attack the chromium itself, or only attacks it to an insignificant extent. at During this second etching process, the remaining surface of the printing plate is not attacked (even if the etching mask produced by exposure has already been removed), and also the contours of the chrome layer introduced etching are not (or not to a somehow disruptive extent) changed or impaired. The etching process only takes place below the level of the chrome layer. The chrome layer, or more generally the first metal layer, acts as an etching mask. If in this etching process in the area of the boundary between the chromium layer and the last-mentioned layer should be somewhat undercut of the underlying metal layer, so bothers In general, as experiments have shown, not. The etching process is now ready (i.e. taking into account the ambient temperature for such a long time) until the etching depth required for printing is possible reached, but not yet exceeded. The worker now takes the cliché out of the tub and rinses it

to remove the second etchant completely, dries it, for example, with the help of a stream of warm air and uses it in the pad printing machine to make test prints to assess whether the desired color saturation of the printed object is achieved at all points of the etching is available. Before making the test prints, the etching mask produced by exposure, if it is still present is removed, if necessary with the aid of a solvent.

If the cliché has not yet been etched deep enough in whole or in some parts, it is necessary to deepen the Etching only required that the worker a suitable covering, for example asphalt paint, by means of a Brush on those parts of the cliché that have already been etched deep enough. There where bigger Areas of the chrome layer are still present, this covering agent does not need to be applied. Then will the cliché, which is partially covered in the manner described, is again placed in the second etchant and etched again, in order to deepen the etching in the areas that have already been etched and free of the cover. The renewed etching can be referred to as correction etching. After a while, the worker takes the stereotype again from the second Etching agent out, rinsing it off, removing the masking varnish with suitable means, for example with alcohol, if there is was about asphalt paint and is repeating his test prints. There is therefore no need to deepen the etching repeated exposure process required, rather the already etched chrome layer acts as a Etching mask that is not attacked during the etching process described last.

For the easy execution of the second etching process, it is only necessary that this second etching process with Can be performed using a single etchant. However, it is not theoretically necessary that the Chromium layer adjoining metal layer is overall uniform in itself, although this is for the sake of simplicity Production "is preferred. It would at least be conceivable that an extremely thin copper or Brass layer is arranged to ensure the color contrast with the chrome layer, this copper or Brass layer is considerably thinner than the maximum required engraving depth, and that is below this Copper or brass layer is followed by another metal layer, which may be white in color and thus a chrome-like color. For example, given the current state of knowledge, it is believed possible that beneath an extremely thin layer of copper or brass, an engraving depth that enables the necessary engraving depth Layer made of a copper-nickel alloy with a high copper content is, as is known, such alloys with with a nickel content of only about 20 to 25 $ already white or are silver colored. Since it appears technically possible, the metal layer arranged below the chrome layer in the To build up the described manner from several chemically different layers, the invention is expressly not intended be limited to the presence of only two metal layers.

In one embodiment of the invention, the at least one metal layer adjoining the first metal layer has at least on their facing the first metal layer

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A different color from its color. Through this the worker can particularly easily recognize when the first metal layer has been etched through. The said deviating Color can in particular be caused by a copper content. It can be pure copper or a red to yellow copper alloy, especially brass.

In one embodiment of the invention, the metal layer adjoining the first metal layer consists at least up to a depth of 40 μm made of copper. It is about here thus a uniform second metal layer with the thickness mentioned. Said thickness is provided because in pad printing generally with etching depths of up to 40 μπι is to be expected. Instead of the second metal layer made of copper, a second metal layer made of brass can be provided. This can be mechanically more stable than a copper layer.

The printing plate preferably has a total thickness of approximately 100 μm to 5 mm, preferably a thickness of approximately 200 μm up to 500 μπι. With a thickness of about 200 μm there is a risk mechanical damage to the printing plate due to clumsy handling is no longer too great, and a printing plate of 5 mm is not too heavy, even with a larger area, so that it is also easy to handle and can be transported. A thickness of approximately 200 μm to 500 μm is particularly preferred because the printing plate is here already has a noticeable stability, although it can still be bent by hand. With the thinner printing plates Brass is preferred as the metal located below the first metal layer, provided it is copper-containing Metal layer acts. This is preferably cross-rolled brass Ms 63 »which has a copper component

between 62 and 65 # (remainder zinc) and that due to its good suspension properties "exposed to no risk of mechanical damage during normal handling is. In particular, such a plate cannot persist in an undesirable manner with normal handling bend and lose their overall flat shape.

In one embodiment of the invention, the first metal layer is preferably produced by electroplating. By Many metals, especially chromium, can be electroplated in the desired thickness as a uniform thickness Produce a layer with a very smooth surface that has the desired low surface roughness. With the galvanic The chrome layer applied is a so-called hard chrome layer, which predominantly contains chrome and may also contain additives. Electroplating is, as is known per se to the electroplating technician, for production a hard chrome layer a sufficiently high amperage is necessary. The hardness of such a galvanically produced The hard chrome layer is around 70 HRC.

In embodiments of the invention, the thickness of the first metal layer is preferably 3 μm to 8 μm, where in this case, in turn, a thickness of about 6 to 8 μm is preferred will. Such first metal layers can be etched through with the desired high contour definition, and the etched The first metal layer is also sufficiently stable in the edge area of the etchings, even if the underlying metal layer should have been slightly underetched in the edge area of the etchings of the first metal layer. It can therefore be at the Doctoring off the entire surface of the first metal layer

be wiped cleanly. Such metal layers with a thickness of 6 to 8 μm are also sufficiently wear-resistant.

As stated above, in embodiments of the invention contains the one lying below the first metal layer Layer of copper (consists for example of brass) or consists of copper. One advantage here is that in Form of ferric chloride solution an easily available and relatively harmless and thus suitable for handling particularly suitable etchant is available through unskilled workers. Another suitable etchant is Nitric acid. Both etchants do not attack the etching mask made of polyvinyl alcohol, which is still present as mechanical protection at.

Clichés with a thickness of about 0.2 to 0.5 mm can be used particularly easily on a pad printing machine which has a rubber-coated vacuum plate on which the cliché is placed and by means of a suction pump is firmly pressed. Such a vacuum plate is known from German Offenlegungsschrift 3,048,498 and described in this. Because the cliché has the said small thickness and because the rubber coating the vacuum plate is somewhat compliant, that which is used to strip off the paint is essentially achieved as a rigid doctor blade made of steel, which is, however, mounted somewhat resiliently, thickness tolerances to a certain extent of the cliché, because the squeegee can compensate for the cliché where it is thicker and thus further down at the top than in other areas of the cliché, the cliché presses something into the rubber pad and / or the squeegee evades a little. This is possible because

the cliché is sufficiently flexible with the described low thickness. With such a thin cliché are therefore not as high demands on the evenness as with a conventional steel cliché that consists of a for example 10 mm thick steel plate is made. Instead of using the vacuum plate mentioned above, that could described thin cliché also with the help of a pressure-sensitive Glue on a rubber pad in the printing machine be glued on, provided that an adhesive is used that allows the cliché to be stuck on without damage can be solved again. If the adhesive is applied in a noticeable layer thickness, so that it is resilient itself Has properties, the cliché could also be glued to a rigid base with the help of such an adhesive and it would still be possible to compensate for the thickness to a certain extent during doctoring in the manner described above. If necessary, the cliché can also be glued to a steel foil, with the help of which the cliché becomes magnetic can be recorded in the printing press.

In one embodiment of the invention, the first layer is metal the printing plate provided with a photosensitive plastic layer which has a thickness of at least 15 μπι has. The advantage is that with a photosensitive plastic layer with such a thickness retouching work before etching can be dispensed with, because the photosensitive layer is insensitive to fine Uncleanliness, for example dust, and pilm cut edges. It can therefore be used to expose one of several sections existing and bonded film can be used, and it is not necessary to use this bonded film prior to exposure by a primary copying process on a

transferring one-piece film. The exposure process can therefore be carried out without difficulty by a skilled worker be made. On the other hand, great care would have to be taken with a considerably thinner photosensitive layer Avoidance of dust on the layer to be exposed and, in the case of assemblies, a copying process is necessary, and this work can only be done by a qualified chemigrapher be made.

In one embodiment of the invention, the printing plate has a photosensitive layer on the first metal layer Plastic layer with a thickness between 20 μm and 60 μm on. The advantage here is that this plastic layer is either light-sensitive like the one described above Plastic layer alone can be used to produce an etching mask, or that optionally after exposure and washing out and, if necessary, after a hardening process, which anyway for increasing the resistance to the First etching agent is necessary, this plate with a first metal layer that has not yet been etched as a cliché for pad printing can be used, the color after inking and doctoring only in the plastic layer formed wells sits. These depressions always extend to the surface of the first metal layer. This embodiment of the invention gives the printer the option of after the etching mask has been produced to quickly make a few test prints without etching. Provided that these proofs show that also with the completely etched The cliché the desired printing results can be expected to be achieved is etched. However, it shows based on

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the test prints that a satisfactory print result cannot be expected, the etching process can be omitted, and then necessary changes, for example to the layout, can be made and a new one Printing plate are exposed.

Polyvinyl alcohol, which is favorable in terms of sufficient resistance to doctoring, is beneficial can also easily be developed into an etching mask. The hardening process to make the polyvinyl alcohol resistant to the Making etchants used is carried out using chromium trioxide.

The just described use of the exposed and washed-out plastic layer for printing is also considered an invention viewed.

The invention also relates to a method for producing a cliché for pad printing. This procedure is in the claims and explained in the description of the embodiment and is already in the above Executions described.

Further features and advantages of the invention emerge from the following description of an exemplary embodiment of the invention based on the drawing, the essential to the invention Shows details and from the claims. The individual characteristics can be used individually or in groups be realized in any combination in one embodiment of the invention. Show it:

Pig. 1 shows a schematic cross section through an inventive Pressure plate, which consists of a brass foil with a chrome layer "applied to it,"

Fig. 2 aborted one of the pig. 1 corresponding representation, in which there is a light-sensitive coating on the chromium layer for manufacture an etching mask is on photographic means,

Pig. 3 shows a schematic cross section through the plate after Pig. 2, in which the etching mask was produced by photographic means,

Pig. 4 one of the pig. 3 corresponding cross-section through the printing plate after the chrome layer has been etched through,

Pig. 5 one of the pig. 4 corresponding representation after the second etching process, in which the brass layer was etched,

Pig. 6 is a schematic representation of a plan view of the Pig plate. 5 in which the etched Pattern is indicated and it is also indicated that part of the etching by a masking lacquer has been covered to put in the uncovered already etched parts of the brass layer to deepen another etching process.

In the drawing are the thicknesses of the individual layers not to scale and shown greatly exaggerated for the sake of better recognizability.

In Fig. 1, the printing plate 1 consists of a first metal layer 2 made of chrome, which is applied to a second metal layer 4 made of brass Ms 63 by electroplating. In the The chrome layer is a hard chrome layer with a Rockwell hardness HRC of about 70. The printing plate 1 carries no photosensitive coating. Such a coating can be applied in the printing company if necessary or the manufacturer of the printing plates has already provided the printing plate 1 with a light-sensitive one Coating, so that such a modified printing plate 6 then has the cross section shown in FIG. It is here again the first metal layer 2 and the second metal layer 4 as provided in FIG. 1. On the first Metal layer 2 is applied a photosensitive coating 7, which in the example consists of a polyvinyl alcohol Diazo sensitizers is made up. Such a photosensitive one Layer is described in German patent specification 29 06 902 and US patent application 06/688 212. Through the Reference is made to the content of all other applications and publications mentioned in the present application Content of the present application made. Instead, another photosensitive coating could be used be upset. The layer 7 is covered by an opaque, easily removable protective layer 8 made of paper, to protect the layer 7 from undesired exposure.

Although it is assumed that the printing plate according to the invention mainly by photographic means with an etching mask

is provided. However, it is entirely possible that the steps shown in FIG. 1 To provide printing plate 1 shown with an etching mask that, for example, a pattern by hand by means of a Indian ink or ink resistant to the first etchant is applied. In this pail that would be the The image produced by pad printing corresponds to the negative of the image applied with the ink. It would also be possible first of all to cover the entire surface of the first metal layer 2 with said ink and after drying the ink by means of a suitable tool, for example an engraving needle, which, however, removes the chrome layer 2 does not attack, remove again. Then, with pad printing, the result is a positive that is engraved in the layer of ink Pattern.

Pig. 3 shows the printing plate 6 according to Pig. 2 after making the etching mask. This is done after removing the paper layer 8, an image has been exposed onto the photosensitive layer, the exposure using a negative the desired pressure. The first metal layer 2 must be there where there should be no color in the finished print remain, and there the photosensitive layer 7 is exposed so that it hardens as a result of the exposure. The exposed layer 7 is then washed out with a water jet, the unexposed areas, which are not hardened are washed off, whereas the exposed areas remain.

After washing out, the remainder of the layer 7 that has remained on the metal layer 2, if necessary, by means of a Dried with hot air. The remaining parts of the layer 7 form an etching mask for the first etchant

which the chromium layer 2 is etched through. For this it is necessary that the etchant attacks the chromium, but not the exposed parts of the layer 7. After washing out and drying, the exposed parts of the layer 7 hardened parts of the photosensitive plastic layer in immersed a solution of 20 g of chromium trioxide (that is, chromic anhydride) in 80 cnr of water for 30 to 60 seconds and thereby made the plastic layer sufficiently resistant to the first etchant used in In one embodiment, the mixture of hydrochloric acid and sulfuric acid with glycerine, which will be given later, is formed and wherein the photosensitive layer 7 is made of the above material (polyvinyl alcohol).

Instead of the polyvinyl alcohol, a so-called dry resist, which is used for the production of printed circuits, can also be used used and ironed on.

The first etchant is at room temperature (approximately 20 ° Celsius) and must be 6 μm thick from the first Metal layer 2 act for about 30 minutes until the first Metal layer 2 is etched through. During this time, there is no need to monitor the etching process.

The cross-section through the partially etched cliché in which the first metal layer 2 (chrome layer) is etched through is shown in FIG. The one in Pig. 4 is also the partially etched cliché shown by the Photosensitive layer 7 formed etching mask, which is still present in Fig. 3, has been removed.

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That in Pig. 4 shown partially etched cliché, which is provided with the reference numeral 11, is now in a trough inserted, in which a 50 $ ferric chloride solution turns out to be second etchant is located. The worker leaves the partially etched cliché 11 in this second etchant for so long lie until the required etching depth has definitely not yet been exceeded, as already explained above became. The cliché etched in the second etchant is shown in FIG. There are 4 etchings 14 in the brass foil available. In the right part of Fig. 5 it is indicated that the brass layer below the remaining parts of the first metal layer 2 can be slightly underetched. This point is provided with the reference number 16.

If the cliché shown in Fig. 5 after it has been extracted from the second etchant has been removed, cleaned and inserted into the printing machine, good printing results delivers, the production process for the cliché is complete. Unless some places in the brass layer 4 have not yet been etched deep enough, the areas of the top of the that have already been etched deep enough will be Clichés covered with a covering means, in the example asphalt paint, as the top view of FIG. 6 shows schematically. Of the motif, which is symbolically represented by the capital letters A and B, the one with the solid lines should be visible Area still through a second Ätzvoxgang in the second Etchants are deepened. For this purpose, the surface of the cliché 18 according to FIG. 5 has been covered with asphalt paint 20, a point 22 where the engraving is to be deepened is free of asphalt paint. Where there are bigger ones There are areas of the first metal layer 2 free of an engraving, the asphalt paint 20 does not necessarily have to be applied as shown in FIG.

iff

In the exemplary embodiment, the first etchant with the the first metal layer 2 made of chromium is etched through, the following mixture is used:

25 ml hydrochloric acid with a density of 1.19 15 ml nitric acid with a density of 1.40 45 ml of glycerine.

The glycerine serves as an anhydrous diluent for the relatively strongly concentrated acids. This and also the glycerine does not attack the polyvinyl alcohol layer. Etchants without nitric acid are also possible. nitric acid alone is not suitable for etching.

Another example of the first etchant is as follows:

15 ml zinc chloride solution, 20% 25 ml hydrochloric acid, density 1.19
45 ml of glycerine

This also does not attack the polyvinyl alcohol layer. The zinc chloride also protects the etching mask.

So far only the purely chemical etching has been spoken of, which means that no electrochemical processes are used will. The printing plate 6 provided with an etching mask can, however, also be etched electrochemically, with the following first etchant is used:

95 ml ethyl alcohol $ 96
5 ml hydrochloric acid with a density of 1.19

The pressure plate is connected as the anode, and it becomes a V2A steel cathode used. A DC voltage in the range of 5 Ms 10 volts is applied. In the described Exemplary embodiments, a thickness of approximately 2 to 8 μm is sufficient for the etching mask arranged on the chrome layer the end.

In the exemplary embodiments, a thickness of approximately 2 to 8 μm is sufficient for the etching mask arranged on the chrome layer, preferably about 6 μm. The thickness is advantageous but about 15 μm or larger, so no retouching work are necessary.

Another advantage of the invention is that the printing plate, when the etching mask is exposed and washed out and, if necessary, has been produced by a hardening treatment, in particular using chromium trioxide, this intermediate product, which is suitable for the first etching process, can already be used as a cliché for pad printing can if for the photosensitive coating 7 a Material is used that is sufficiently resistant to doctoring. The printer can therefore After completing the etching mask, insert this not yet finished cliché into the printing machine and some to produce a few or several hundred pad prints, for example to present them to the client for assessment to be sent. If these test prints turn out to be satisfactory, the first etching process is started. To also at Use of the etching mask as the topmost cliché layer

In order to achieve sufficient color saturation in the test prints, it may be useful to use the light-sensitive Layer to be dimensioned sufficiently thick, in particular a thickness range between 20 and 60 μπι, depending on the motif in different thicknesses can be kept in stock. Such thick layers are inherently more resistant than if only a thin layer of, for example, 6 μm thickness is provided for the plastic coating would; however, this last-mentioned relatively thin layer is completely sufficient mechanically for the etching mask if it is not intended to loll on the plastic layer. In one embodiment, the light sensitive Layer of polyvinyl alcohol 20 μm thick, with another Example 60 μπι. Otherwise, these last-mentioned are correct Examples correspond to the printing plate described with reference to FIGS. 1 and 2. As mentioned, the plastic layer is hardened after exposure, washing out and drying with chromium trioxide solution.

In the description of the exemplary embodiment, it was assumed that the etching mask produced by exposure was removed from polyvinyl alcohol before the second etching process because it is not required for the second etching process will. However, as already mentioned above, the etching mask produced by exposure can be advantageous as long as possible on the printing plate, i.e. until the end of the second etching process, in order to do this to obtain mechanical protection for the etched chrome layer.

The advantage of the relatively thick photosensitive layers (Photo layers) consists in the fact that no retouching work is required after exposure and washing out of the photo layer are. If the printing plates are already supplied by the manufacturer with a polyvinyl alcohol layer with diazo sensitizers delivered, in which the photo layer can be stored for about one year, the following advantages result from the Use: Since the photo layer has already been applied, there is no need for specialist knowledge to apply it a photo layer that is as uniform as possible. The exposed photo layer is made of water with no additional chemical Means can be developed, and therefore in particular no unpleasant or even unhealthy odors arise. If the photo layer has a thickness of at least 20 μm, so the plate can be used immediately after the production of the photomask for the production of test prints. As above already mentioned several times, there is no need for retouching work before etching if the photo layer has a DJ.oke of at least about 15 μιη has. The polyvinyl alcohol photo layer with diazo sensitizers Compared to other photo layers, it is relatively weakly sensitive to light and can therefore also be used in one only a slightly darkened room or at a greater distance from the window of a room are processed into a photo mask; it is so no darkroom required.

In the exemplary embodiment, it was said that the second etching process was carried out using ferric chloride solution in a tub he follows. However, this is not necessary. Rather, the worker can use a suitable tool, preferably Using a flat brush, apply the ferric chloride solution to the one that has already been etched for the first time and then washed off and apply the dried plate. The proportionate

A small amount of ferric chloride solution is sufficient to etch the second metal layer sufficiently deep. The advantage is that always fresh iron chloride solution with a predetermined concentration, for example a 50 ^ ige Solution, is used and that therefore always the same etching results achieved when a certain etching time is adhered to will. In contrast, if the ferric chloride solution is in a tub, the possibility that the solution is not changed frequently enough so that its concentration changes in a disturbing manner and therefore the etching time must be increased.

Claims (18)

Claims 1. Metallic printing plate for making clichés for pad printing with an engraving depth of at least 20 μΐη, characterized in that the Printing plate (1) has at least two metal layers (2,4), of which the first metal layer on the printing upper side lies, and that the at least one metal layer adjoining the first metal layer (4) can be etched to a depth of at least 35 μm by a single etchant, which is the first Metal layer essentially does not attack. 2. Printing plate according to claim 1, characterized in that T ~ that the at least one metal layer (4) adjoining the first metal layer (2) has a color different from its color at least on its side facing the first metal layer. 3. Printing plate according to claim 2, characterized in that the subsequent to the first metal layer (2) Metal layer (4) has copper at least on its side facing the first metal layer. 4. Printing plate according to claim 3, characterized in that that the metal layer adjoining the first metal layer at least to a depth of 35 μm is made of copper. 5 · printing plate according to claim 3> characterized in that subsequent to the first metal layer (2) metal layer (4) at least up to z \ x a depth of 35μπι consists of brass. 6. Printing plate according to one of the preceding claims, characterized in that the pressure plate (1) has a Total thickness of about 100 μm to 5 mm, preferably of has about 200 μm to 500 μm. 7 · Printing plate according to one of the preceding claims, characterized in that the first metal layer (2) is produced by electroplating. 8. Printing plate according to one of the preceding claims, characterized in that its surface is a Rockwell hardness of at least 64 HRC and a maximum peak-to-valley height of 2 μm. 9 · Printing plate according to claim 8, characterized in that the first metal layer (2) consists essentially of Chromium is made. 10. Printing plate according to one of the preceding claims, characterized in that the first metal layer (2) a thickness of 3 to 8 μm, in particular from 6 to 8 μιη has. 11. Printing plate according to one of the preceding claims, characterized in that the first metal layer is provided with a photosensitive plastic layer which has a thickness of at least 15 μm. 12. Printing plate according to one of the preceding claims, characterized in that the first metal layer is provided with a photosensitive plastic layer is, which has a thickness between 20 μm and 60 μm, and after the exposure and development of the etching mask, possibly after an additional hardening treatment, brakel against the etchant for the first metal layer and against mechanical stresses from A ″ is resilient. 13 · Printing plate according to claim 12, characterized in that the plastic layer is polyvinyl alcohol with sensitizers contains. 14 · Process for producing a cliché for pad printing with an engraving depth of if necessary at least 20 μm, characterized in that a printing plate (1) according to one of the preceding claims on the surface of the first metal layer (2) with an etching mask, in particular on a photographic one Ways is provided that the first metal layer is etched through with a first etchant that then - optionally after a previous rinsing process to remove the first etchant, and optionally after removing the etching mask applied to the first metal layer - with a second etchant is etched, which does not attack the first metal layer substantially, but the attacks the layer lying under the first metal layer. 15. The method according to claim 14, characterized in that an etchant is used to etch the first metal layer is used which contains hydrochloric acid, optionally with an additive which weakens the corrosive effect. 16. The method according to claim 15, characterized in that the additive is an alcohol or an alcohol mixture is. 17. The method according to claim 16, characterized in that the additive contains glycerine. 18. The method according to any one of claims 14 to 17, characterized characterized in that the second etchant contains iron chloride or nitric acid as an active substance. 19 · Use of a printing plate according to claim 12 or after the production of the etching mask and, if necessary, after one additional hardening process for the etching mask as a cliché for pad printing.