PRECISION CUT PRINTING SCREEN

Abstract

Disclosed is a precision cut printing screen in which the features of a printing pattern are defined on a sheet material by a plurality of apertures within a target printing boundary. Also disclosed is a method of making the printing screen.

Claims

1. A printing screen comprising a sheet material, for screen printing a printing pattern comprising at least one continuous printed feature on a substrate; the printing screen comprising a printing screen pattern comprising plurality of apertures within a printing screen pattern boundary representing a target boundary around a periphery of at least one feature to be printed on a substrate; the at least one feature being defined on the sheet material by a plurality of apertures through the thickness of the sheet material, within the printing screen pattern boundary; wherein the printing screen pattern boundary corresponds to the target pattern boundary when the printing screen is placed on a substrate in use.

2. The printing screen of claim 1, wherein the printing screen pattern boundary of the at least one feature to be printed has a predetermined spatial relationship to an array of the said apertures adjacent to the printing screen pattern boundary.

3. The printing screen of claim 2, wherein the predetermined spatial relationship comprises a minimum distance, or range of minimum distances, between an aperture in the array and the closest part of the printing screen pattern boundary, wherein the minimum distance or range is shared between a series of or all of the apertures in the array.

4. The printing screen of claim 3, wherein the predetermined spatial relationship comprises a minimum distance, or acceptable range of minimum distances, between a series of adjacent apertures or each adjacent aperture in the array.

5. The printing screen of claim 1, wherein the sheet material comprises a metal sheet material.

6. The printing screen of claim 1, wherein the apertures are provided by laser cutting.

7. The printing screen of claim 1, wherein the or each feature to be printed has surface area in the range of 1-500 mm.sup.2, and/or wherein the apertures have a diameter or width between around 1 μm and 500 μm.

8. (canceled)

9. The printing screen of claim 1, wherein at least one said feature includes apertures of multiple sizes and the apertures increase in size with distance from the printing screen pattern boundary; and/or wherein the number density of apertures decreases with distance from the printing screen pattern boundary of the at least one said feature.

10. (canceled)

11. The printing screen of claim 1, comprising a frame, wherein the sheet material is mounted to the frame in tension.

12. The printing screen of claim 11, wherein the sheet material is welded to the frame.

13. A method of making a printing screen, comprising: providing a sheet material; and precision cutting a printing pattern comprising a plurality of apertures through the thickness of the sheet material, within a printing screen pattern boundary representing a target boundary around a periphery of at least one feature of a printing pattern to be printed on a substrate, so as to define the at least one feature on the sheet material by the plurality of apertures.

14. The method of claim 13, comprising laser cutting the apertures.

15. The method of claim 13, comprising tensioning the sheet material prior to precision cutting.

16. The method of claim 13, comprising mounting the sheet material to a frame.

17. The method of claim 13, comprising tensioning the sheet material and mounting the sheet material to the frame in tension.

18. The method of claim 13, comprising precision cutting an array of the said apertures in a predetermined spatial relationship with respect to the printing screen pattern boundary.

19. The method of claim 18, comprising precision cutting a said array around a part, or substantially all of the periphery of the or each feature defined on the sheet material.

20. A method of printing a pattern on a substrate, the method comprising: providing a printing screen according to claim 1; placing the printing screen on a substrate so as to place a first side of the printing screen against the substrate; applying a printing medium to a second side of the printing screen; and flowing the printing medium through the apertures through the thickness of the sheet material to the substrate.

21. The method of claim 20, comprising passing a wiper across the printing screen, to distribute the printing medium.

22. The method of claim 21, comprising removing the printing screen from the substrate.

23. (canceled)

Description

DESCRIPTION OF THE DRAWINGS

[0067] Example embodiments will now be described with reference to the following figures in which:

[0068] FIG. 1 shows a target printing boundary of a printing pattern superimposed on a mesh;

[0069] FIG. 2(a) shows a circular printing screen pattern boundary of a feature a printing pattern on a mesh printing screen, and FIG. 2(b) shows the same circular feature on a sheet material; and

[0070] FIGS. 3(a) to 3(d) schematically illustrate the steps of a method of making an embodiment of a printing screen.

DETAILED DESCRIPTION

[0071] FIG. 1 shows the outline of two features A and B to be printed, of a printing pattern projected on to a conventional printing screen mesh M. To create an emulsion printing screen, a polymeric material would be created over the region P, leaving the features A and B of the mesh bare.

[0072] Feature A has target printing boundaries. These are represented on the mesh printing screen by printing screen pattern boundaries 1 and 2. Edge 1 has a filament 3 that runs along the edge 1, such that the boundary of the feature A is bounded by the edges of the apertures 4 in the mesh. Another printing screen pattern boundary 2, however, runs part way along a row of apertures 5. As a consequence, ink will inevitably flow into the apertures 5, beyond the boundary 2 of the printed feature A, when printing the feature A onto a substrate. Similarly, the relationship between the printing screen pattern boundaries 6, 7, and 8 of feature B are all different from one another in relation to the positions of the mesh filaments and apertures.

[0073] FIG. 2(a) is a diagram which shows the outline (i.e. the printing screen pattern boundary, and thus when placed on a substrate, the target printing boundary) of a circular feature 10 of a printing pattern represented on an emulsion screen 12 made from a metal mesh. The emulsion screen has a masked area 14, and a bare area 16. The feature 10 to be printed is represented on the emulsion screen 12 by apertures 20 between woven wire filaments. The filaments themselves are omitted for clarity, however example paths of the filaments (as viewed from perpendicular to the screen) are shown by the dotted lines 18, 19. It will also be understood that each of the filaments alternately pass over and under other filaments across the printing screen and therefore curve in and out of the plane of the screen, leading to differences between the configuration of each apertures 16 in relation to a planar substrate, in three dimensions.

[0074] The apertures 16 are necessarily arranged in rows and columns and so in use, the distance between the target boundary of the feature 10 and the nearest aperture 16 within its boundary varies significantly around the periphery of the feature 10. This severely limits the extent to which the circular shape of the feature 10 can be reflected in the final printed pattern on a substrate.

[0075] FIG. 2(b) shows an embodiment of a printing screen 112 as disclosed herein, comprising a sheet material 114 (stainless steel in the embodiment shown). The circular feature 10 is defined on the sheet material by a plurality of apertures 120 which have been laser cut through the thickness of the sheet material 114, within a printing screen pattern boundary 10a.

[0076] The array 122 of apertures 120 adjacent to the boundary of the feature 10a extends around the printing screen pattern boundary 10a (in this case the circumference) of the feature 10. The apertures in the array 122 have a predetermined spatial relationship to one another and in this embodiment are equidistant from the boundary 10a, and to one another; thus providing a more accurate representation of the feature 10 (i.e. with a boundary more closely related to the target printing boundary) when, printed on a substrate.

[0077] While the apertures in the array 122 in the embodiment shown are evenly spaced from the boundary 10a and each other, in other embodiments, for example in relation to more complex or convoluted printing boundaries, these distances, or indeed the shape of the apertures, may be required to vary. For example, whilst a series (more than two in a row) of apertures may have the same spatial relationship to the printing screen pattern boundary as each other along one part of a boundary, the relationship may differ in other parts, for example more tightly curved regions, corners etc. In other parts of the printing screen pattern boundary, therefore, the size, shape and or spatial relationships may differ.

[0078] Referring again to FIG. 2(b), both the size and the number density of the apertures 120 differs with distance from the printing screen pattern boundary 10a of the feature 10. The aperture size generally increases towards the middle of the feature, and the number density generally decreases. However the sizes of the apertures do increase and then decrease with distance from the boundary in the embodiment shown, in order to allow the apertures to “tesselate” somewhat and reduce the minimum distance between apertures.

[0079] FIG. 3 is a schematic showing a method of making an embodiment of a printing screen. Referring now to FIG. 3(a), a sheet 214 of steel is provided. The sheet 214 is then tensioned, in the example shown biaxially (i.e. by mechanically gripping the edges of the sheet and applying outward forces in the plane of the sheet), illustrated by the arrows T. Means for tensioning metal sheets are well known in the art.

[0080] Whilst under tension, the sheet is mounted to a metal box section frame 230, and spot welded around its periphery 232, as shown in FIG. 3(b), such that the sheet 214 is maintained in tension in the resulting “blank” screen 200b.

[0081] The blank screen 200b is then placed under a precision laser machining head 300, such as that of a Tannlin T-series of ventilated stencil laser systems (Tannlin is a trade mark). This is illustrated in the schematic cross sectional side view of FIG. 3(c), showing the blank screen 200b supported over a ventilated well 302. A laser beam 304 cuts a plurality of apertures 120 through the thickness of the material 214, within a printing screen pattern boundary representing a target boundary of at least one feature to be printed on a substrate. Thus, the at least one feature is represented on the sheet material (in “pixelated” form) by the plurality of apertures; as disclosed herein. The CNC control over laser machining processes, and the features of the associated apparatus are known to those skilled in the art.

[0082] The resulting printing screen 200 is shown in FIG. 3(d). The screen 200 can then be used in screen printing processes in a generally conventional manner, by placing the screen 200 on a substrate with the sheet 214 face down on the substrate. Ink or another desired printing medium is placed on the upper side of the sheet 214 and spread over the sheet by a wiper (not shown) such that the printing medium flows through the apertures 120 and on to the substrate, thereby creating the printing pattern.

[0083] Whilst exemplary embodiments have been described herein, these should not be construed as limiting to the modifications and variations possible within the scope of the invention as disclosed herein and recited in the appended claims.