HK1020616B - Process for producing a screen printing form and screen printing fabric of a coated screen web - Google Patents

Description

The invention relates to a method for producing a screen printing form from a screen, for example from plastic filaments, by coating it with an emulsion, particularly a light-sensitive one.

The method of silk-screen printing -- centuries after its first use in China -- has been known in Europe since about the 19th century; a fine mesh of textile or wire is stretched in a silk-screen frame and covered with a color-transparent template in the image-free areas. In addition to hand-cut templates -- for example, for labels -- today, photographically-produced direct or indirect templates are preferred; the choice of type of template -- for direct templates such as those with emulsion, with direct film and emulsion or with direct film and water -- is left to the printer.

The process of creating a silk-screen usually involves several steps: first, a silk-screen is stretched over a print frame made of light metal, wood, etc., and glued to the print frame in its tension position; then the fabric is coated with a light-sensitive emulsion - for example, by using a coating line manually or by machine with a coating machine. Since the coating cannot be produced exactly to the inside of the frame, the remaining surface must be subsequently sealed with a silk filler.

The low solid content of the emulsion, usually less than 50%, causes the layer to sink into the mesh openings of the fabric during the subsequent drying process, which can result in a certain surface roughness.

If a number of small frames are to be tensioned, for example for the production of small printed images, a so-called mother frame is used and the screen is stretched on it, held on the mother frame, for example, by clamps described in the applicant's EP 0 650 832 A1.

A method for the manufacture of photochemically coated material for screen printing cylinders is given in DE 34 41 593 A. A chrome wire mesh of suitable mesh size is coated with nickel by electrolysis, chemical or vacuum evaporation to ensure that the intersection points of the wire are secured without displacement; the solidified material is then coated with at least one layer of a light-sensitive emulsion by applying this emulsion to a flat surface and embedding the fabric in the back of the emulsion layer and connecting them by applying a further layer of emulsion coating to remove a copy layer on the back side of the surface of the sheet.

US 3 834 348 A describes a flexible frame with a woven field fixed in it by means of woven elements, over which a groove for a viscous fluid or emulsion is allowed to flow, which flows from adjacent slits in the groove wall onto the woven field to form a coating on it, which is then dried or hardened on the woven field.

JP 5 216 239 A reveals a container with a tensioned frame in which a fabric is coated with a photosensitive film. The fluid is introduced into the container until a desired layer thickness has been adjusted on the fabric.

In view of these circumstances, the inventor set out to improve a process of the type described at the outset and, in particular, to enable the production of limited coating fields to be connected to a clamping frame by an adhesive process without difficulty.

The theory of independent claims is a solution to this problem; the subclaims indicate favourable designs.

According to the invention, a sieve is partially covered with coating fields consisting of the emulsion within a given contour, the emulsion being preferably applied to the sieve in a linear or even point-wise manner.

The coating fields can be produced in different ways. Firstly, they can be applied directly to the sieve, at low demands, on a rough surface, and then dried. It is also possible to cover these coating fields directly on the sieve with a protective film and then bring them to the drying station, especially at high demands and good roughness value in the Z-axis.

It is within the scope of the invention that a midline of the resulting coating field, preferably defined by its four outline lines, includes an inclination angle with a longitudinal edge of the sieve rail; the outline lines are rotated around the centre of the coating field at that angle, preferably less than 45°.

The application of the coating fields at an angle of inclination to the screen allows, according to the invention, a curved stretching of the coated sections of fabric on a printed frame.

The manufacturing process is simplified by composing the coating field with parallel adjacent coating lines, each produced by a nozzle or by a tool, whose longitudinal edges intersect so that no contour strips remain through the coating field.

According to another feature of the invention, each narrow edge of the striped coating track is each assigned to one of the contours of the coating field angled to the axis of the mother frame.

The invention consists in placing in the centre of the contour of the coating field the centre line of a tension frame attached to the coating field, which is placed at a distance from the contour lines and then glued with the sieve in its tensioned state outside the coating field.

In special cases, the coating fields can also be produced by another method: the sieve is coated on a surface with a continuous emulsion layer, from which the areas which do not belong to a given pattern are removed from the coating fields.

It's particularly beneficial to suck out these redundant areas of the coating immediately after they're commissioned -- so in the wet state of the emulsion.

Further advantages, features and details of the invention defined by the claims are given in the following description of the preferred embodiments and in the illustration, which is given in: Fig. 1:the view of a device for the tensioning of a coated sieve band with groups of span devices;Fig. 2:a sketched side view of a sieve coating system;Fig. 3, 4:Drain views of a sieve with coating fields;Fig. 5, 6:other views of the sieve, which is reduced compared to Fig. 3, 4;Fig. 7:an enlarged sieve compared to Fig. 3 to 6 with several coated areas for the associated span frames;Fig. 8:a coated area compared to Fig. 7 enlarged curve;Fig. 9:a drain view of the representation of the corresponding other system;Fig. 10:the view of the drainage scheme on Fig. 9.

A device 10 for opening a rectangular piece of equipment or a sieve 12 made of a material of a gaseous type, preferably used in the sieve printing process, has several clamping elements or clamping devices 16 along the four sides of a frame 14 which, each with a clamping mouthpiece 18, grab a section of the sieve 12 in its peripheral area and then tighten the sieve 12 attached to it by positioning a draw cylinder 19 in the direction of pull in each case x. The sieve 12, whose surface is equipped with coating fields 20, is located on its mother 14 and is drawn from the outside edge to the clamping mouthpiece 18 in its closing position at an unclosed angle of about 6°.

22 indicates a control unit fed from a line 24 with a maximum of 10 bar of compressed air, from which three control lines 25,25a,25b for the span devices 16 originate.

According to Fig. 2, a rail-like support material 28 is fed to sieve 12 and coated in a coating station 30 in a process to be described with areas of light-sensitive emulsion, not shown in the drawing for reasons of clarity; these areas correspond, for example, in their dimensions and spacing to the coating areas 20 on sieve 12 in Fig. 3.

After the transit station 34, the coating fields 20 are located in the configuration previously present on the support material 28 on the sieve 12, which can now be separated from the support material 28 or with it as a temporary protective coating.

A procedure diagram is not shown for coating fields applied directly to sieve 12 without the film-like support material 28; the sieve is either fed immediately to the drying or flowing station 34 after the coating station 30 or provided with a protective film before the latter, which can be removed after the drying process.

In Fig. 3 a screen 12 of track width b is shown with coating fields 20 parallel to its longitudinal axis A; six of these are provided within a so-called report 36 of length z. One of these labelling fields 20 is highlighted by a grid scraper for better overview.

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Figures 4 to 6 also indicate the smaller coating fields 20a corresponding to Figure 3 in inclined positions with respect to the longitudinal axis A or the parallel longitudinal edges of track 13 (Fig. 4) and larger coating fields 20, 20a, of which only one or two are present per report 36.

Figure 7 shows a frame 36 of a screen 12 of free track length a of about 1400 mm and free track width b of 900 mm with clamping elements 16 attached to a frame 14 of width a1 or b1 respectively.

On the free surface of the screen or screen 12 there are -- to the left of the longitudinal axis A1 of the mother frame 40 -- three of the square coating fields 20 bounded by a contour with four contour lines 42 of light-sensitive emulsion -- preferably of the type mentioned at the beginning -- represented as a photosensitive coating of width e of 180 mm, which in the loose state of the screen 12 are arranged at intervals i of 380 mm -- and i1 of 394 mm in the dry state -- to each other. The distance f to the longitudinal axis A1 of the system The cross-sectional lines of these three coating fields 20 are also parallel to the quadrants -- the midline of a series of those second right-angle fields Q1 and Q20 correspond to the two voltage fields 20 and 20 in the loose state of each screen, respectively, and are located in the middle of the perimeter of the screen.

Each of the coating fields 20 shall be arranged within the contour of a small, sheet-frame 38 - which is suspended on the supporting plate 41 and under the screen 12 - so that it can be easily glued to an uncoated zone of the screen outside the coating field 20; in order to apply the adhesive to the screen 12 without affecting the coating field 20, the latter shall be a coating-free woven strip 44 of minimum width h - and in glued condition a free edge of width h1 - should remain.

To illustrate the connection process described, Fig. 7 shows examples of coating fields 20 of printing templates for direct printing on compact discs, on the right side the coating fields 20 are outlined within their spanning frame 38 where the lower frame 38a and its central axis B are rotated at an angle of inclination w of 22.5° from the median line M around the centre point Z of the coating field 20 so that the corners 43 of the coating field 20 are placed at a slight but continuous distance from the sides of the frame; the inner lengths of the spanning frame are here 38.38a 260 mm at an outer length of 310 mm.

The minimum width h of the said fabric 44 is half the difference between the outer length n and the field width e. Their half the difference to the inner length m gives the free edge width h1.

The coating fields 20 are to be arranged with their contours within their frame 38.38a so that they are at a distance h1 from the frame 38.38a, which may be problematic, for example, in the case of inclined arrangements as described in frame 38a. For this reason, a coating field 20a of any position of the frame axis B, as shown in Figure 8, with an exemplary angle of inclination w of 22.5°, is produced by the resulting emulsion through unmarked workpieces running parallel to the rail A axis, on which the support material 28 described in Figure 2 is laid in integral coating strips 46 disc widths t. The different L of the different parallel strips 46 and 42a are not perpendicular to each other.

In this context, a design in which the emulsion is applied in a point-like manner within the boundaries of 42a is not shown, and a liquid-impermeable layer surrounding the coating field 20, 20a and covering the coating-free fabric 44 is also omitted.

Figures 9, 10 show an alternative to the above procedure, whereby the carrier film 28 is coated in the coating station 30 with a layer 52 of width c of that emulsion, in full or in broad bands, and immediately afterwards passed through a suction station 54, where individual coating fields 20b are formed by suctioning out the unwanted layer areas in respect of a pre-selectable pattern of the coating fields 20b.

Claims (16)

1. Process for the production of a screen printing forme from a screen web, e.g. of plastic filaments, by coating with an emulsion, in particular a light-sensitive emulsion, which is dried, characterised in that the screen web (12, 12_a) is partially provided with at least one coating panel (20, 20_a) composed of a plurality of coating regions applied separately, the emulsion being applied in parallel adjacent coating webs (46).
2. Process for the production of a screen printing forme from a screen web, e.g. of plastic filaments, by coating with an emulsion, in particular a light-sensitive emulsion, which is dried, characterised in that the screen web (12, 12_a) is provided with a layer (52) of the emulsion and a plurality of coating panels (20_b) are produced by the subsequent removal of parts of the layer.
3. Process for the production of a screen printing forme from a screen web, e.g. of plastic filaments, by coating with an emulsion, in particular a light-sensitive emulsion, which is dried, characterised in that a substrate web (28) is provided with a layer (52) of the emulsion and a plurality of coating panels (20_b) are produced by the subsequent removal of parts of the layer, after which the coating panels of the substrate are transferred to the screen web (12) and the latter is dried.
4. Process according to claim 2 or claim 3, characterised in that the layer (52) of damp emulsion (52) is divided into coating panels (20b) by partial suction.
5. Process according to claim 1 or claim 2, characterised in that the emulsion is sprayed on substantially in points.
6. Process according to one of claims 1 to 5, characterised in that the emulsion is applied by means of at least one nozzle, the nozzle, in particular a slot nozzle, possibly being guided parallel to a longitudinal edge (13) of the screen web (12, 12_a).
7. Process according to claim 6, characterised in that the coating panels (20, 20_a, 20_b) are applied to a substrate web (28) and are transferred from there to the screen web (12, 12_a), after which the latter is dried, the substrate web (28) then possibly being removed from the screen web (12, 12_a) bearing the coating panels (20, 20_a, 20_b) or the substrate (28) being joined to the screen web (12, 12_a) as a protective film.
8. Process according to one of claims 1 to 7, characterised in that the centre line (B) of the coating panel (20_a, 20_b) is aligned at an angle of inclination (w) relative to the longitudinal axis (A) of the web, an angle of inclination (w, w₁) of less than 50°, preferably less than 30°, possibly being selected.
9. Process according to claim 1, characterised in that the coating webs (46) include an angle of inclination (w₁) with the centre line (B) of the coating panel (20_a) or its contour/s, an angle of inclination (w, w₁) of less than 50°, preferably less than 30°, possibly being selected and/or each narrow edge (46) of the coating strip (46) being associated with a respective contour (42_a) of the coating panel (20_a).
10. Process according to claim 1 or claim 9, characterised in that the length (q) of each coating web (46) is adapted to the position of the contour (42_a) determined by the angle of inclination (w).
11. Process according to at least one of claims 1 to 10, characterised in that the centre line of a stretching frame (38, 38_a) associated with the coating panel and arranged a distance (h₁) from the contours (42_a) is disposed along the centre line (B) of the contour of the coating panel (20_a, 20_b), the stretching frame (38, 38_a) possibly being glued on to the screen web (12, 12_a) in its taut state outside the coating panel (20_a, 20_b) and/or an impermeable layer surrounding the coating panel (20, 20_a, 20_b) being applied to the screen web (12, 12_a) within the stretching frame (38, 38_a).
12. Screen printing forme of a screen web, e.g. of plastic filaments, coated with an emulsion, preferably a light-sensitive emulsion, produced, in particular, according to at least one of the preceding claims 1, 3, 7 to 11, characterised in that the screen web (12) is provided with coating panels (20_a) composed of a plurality of coating regions, the coating panels (20_a) possibly being produced on a substrate film and transferred to the screen web (12), the substrate forming a protective film.
13. Screen printing forme according to claim 12, characterised in that the coating panels (20_a) are formed by coating webs (46) and/or that the coating webs (46) include an angle of inclination (w₁) with the centre line (B) of the coating panel (20_a) or its contour/s (42_a).
14. Screen printing forme with an associated stretching frame according to claim 12 or claim 13, characterised in that the coating webs (46) extend at an angle of inclination (w₁) relative to the centre axis (B) of a stretching frame (38) receiving them.
15. Screen printing forme according to claim 12 or claim 13, characterised in that the screen web (12) is provided with a liquid-impermeable layer of a fabric edge (44) surrounding the coating panel (20, 20_a).
16. Screen printing forme according to one of claims 12 to 14, characterised in that the coating webs (46) extend approximately parallel to the longitudinal axis (A) of the screen web (12).