Screen printing

Abstract

A method for screen printing using a screen, preferably a metal screen made by electroforming, having a pattern of openings separated by bridges and crossing points, and having a flat surface on the squeegee side, wherein on the printing side of the screen the screen has a 3-D structure comprising peaks (P) and valleys (V) formed by a difference in thickness between the bridges and crossing points. The use of the method in the production of RFID tags, solar panels, electronic printing boards. A 3-D printing screen, with an attached stencil with or without the negative of an image to be printed. A printing machine comprising: one or more 3-D printing screens, in combination with one or more reservoirs for ink and/or in combination with a roller or squeegee.

Claims

1. A method for high resolution screen printing an image on a substrate, using a screen having a pattern of openings separated by bridges and crossing points, the screen having a squeegee side and an opposite printing side, and having a flat surface on the squeegee side, wherein on the printing side of the screen the screen has a 3-D structure comprising peaks and valleys formed by a difference in thickness between the bridges and crossing points, and at the printing side of the screen a stencil facing the substrate, which stencil is a negative of the image to be printed, the method comprising depositing ink on the substrate through the openings of the screen and stencil, thereby forming an image having a resolution below 100 micrometer.

2. The method of claim 1, wherein the screen is made of metal and made by electroforming.

3. The method of claim 1, wherein the crossing points form the peaks, with a higher thickness than the bridges forming the valleys.

4. The method of claim 1, wherein the difference in thickness between the bridges and the crossing points is from 5 to 100 micrometer.

5. The method of claim 1, wherein a flat-bed, cylinder or rotary screen is used.

6. The method as claimed in claim 5, wherein a seamless rotary screen is used.

7. The method as claimed in claim 5, wherein the screen is a metal screen material with a mesh number of 150-1000 mesh.

8. The method as claimed in claim 7, wherein the screen is a metal screen material with a mesh number of 190-800 mesh, preferably 300-650 mesh.

9. The method of claim 1, wherein the screen has a thickness of from 20 to 200 micrometer, preferably from 35 to 160 micrometer and/or a hole diameter of the opening of from 5 to 130 micrometer, preferably from 15 to 105 micrometer.

10. The method of claim 1, wherein the printed image forms a part of an RFID tag, a solar panel, or an electronic printing board.

11. A method for screen printing raised images and/or solid areas on a substrate, using a screen having a pattern of openings separated by bridges and crossing points, the screen having a squeegee side and an opposite printing side, and having a flat surface on the squeegee side, wherein on the printing side of the screen the screen has a 3-D structure comprising peaks and valleys formed by a difference in thickness between the bridges and crossing points and at the printing side of the screen a stencil facing the substrate, which stencil is a negative of the image to be printed, the method comprising depositing ink on the substrate through the openings of the screen and stencil with an amount of wet ink deposition expressed as the theoretical wet ink deposit (estimated using theoretical wet ink volume which is the volume of ink in mesh openings per unit of area of substrate, calculated as: % open areamesh thickness) that is greater than 6 micrometer.

12. The method as claimed in claim 11, wherein the amount of wet ink deposition expressed as the theoretical wet ink deposit (estimated using theoretical wet ink volume which is the volume of ink in mesh openings per unit of area of substrate, calculated as: % open areamesh thickness) is greater than 10 micrometer.

13. The method of claim 11, wherein an opening is delimited by opposite walls and wherein the screen has a mesh of from 35 to 500, preferably of from 75 to 450, and/or a thickness of from 35 to 200 micrometer, preferably of from 60 to 150 micrometer, and/or a smallest distance between the two opposite walls of the opening (hole diameter of the opening) of from 10 to 650 micrometer, preferably of from 15 to 400 micrometer.

14. The method of claim 11, wherein the screen is made of metal and made by electroforming.

15. The method of claim 11, wherein the crossing points form the peaks, with a higher thickness than the bridges forming the valleys.

16. The method of claim 11, wherein the difference in thickness between the bridges and the crossing points is from 5 to 100 micrometer.

17. The method of claim 11, wherein the printed image forms a part of an RFID tag, a solar panel, or an electronic printing board.

18. A 3-D printing screen, having a pattern of openings separated by bridges and crossing points, the screen having a squeegee side and an opposite printing side, and having a flat surface on the squeegee side, wherein the screen comprises peaks and valleys formed by a difference in thickness between the bridges and crossing points on the printing side of the screen, with an attached stencil with or without the negative of an image to be printed.

19. The 3-D printing screen as claimed in claim , made by electroforming.

20. A printing machine comprising: one or more 3-D printing screens according to claim 18, in combination with one or more reservoirs for ink and/or in combination with a roller or squeegee.

Description

BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS

(1) The first figure is a schematic representation of the rotary screen printing principle. A is the screen. B is the squeegee. C is the impression roller. D is the substrate. E is the stencil. F is the printed image.

(2) In the second figure schematic representations of screens according to a preferred embodiment of the invention since manufactured by electroforming may be found. These are therefore non-woven screens. Shown is a hexagonal structure of the screen opening (honeycomb hole formation), with so-called bridges connecting crossing points. Electroforming may also be used in the manufacture of screens with other structures; e.g., that are rectangular. Shown here (from top left to bottom right, labelled a)-g)) is the indication of the a) Mesh/linear inch; b) Thickness; c) Open area; d) Hole diameter; e) Theoretical wet ink deposit; f) Maximum particle size and g) Resolution. Mesh/linear inch is the number of openings per linear inch of a screen. Thickness is the screen thickness. Open area is the percentage of all openings in relation to the total screen area. Hole diameter is the smallest distance between the two opposite walls of the opening. Theoretical wet ink deposit is estimated using theoretical ink volume which is the volume of ink in mesh openings per unit area of substrate, calculated as: % open areamesh thickness. It is typically reported in micrometers, or as the equivalent cm.sup.3/m.sup.2. Maximum particle size is of the hole diameter for the best ink passage.

(3) The third figure is a schematic representation of a photo made by optical microscope, showing the top view of the print side of rectangular screen material according to invention with a 3-D structure, wherein the hole diameter is roughly 40 micrometer. This screen (S) has rectangular hole formation (H). Also a close-up is shown. Ovals indicate the valleys (V) formed by the bridges. Circles indicate the peaks (P) formed by the crossing points.

DETAILED DESCRIPTION OF THE INVENTION

(4) An electroforming method for making metal products having a pattern of openings separated by bridges using a mandrel in an electroplating bath is known from e.g., WO 9740213.

(5) In the patent application WO 2004043659 a metal screen material with a 3-D surface structure is specifically proposed for use as a perforating stencil in perforating plastic films, etc, similar to the method and device known from, for example, U.S. Pat. No. 6,024,553. The 3-D surface structure is formed on just one side of the screen by the difference in thickness between the bridges and the crossing points. No teaching is provided in WO 2004043659 about the use of the claimed screen material for screen printing.

(6) It has now been found that for printing of solid areas and raised images the new 3-D screens provide for greater ink deposition and sharper deposition.

(7) Moreover, it has now been found that for very high resolution screen printing the new 3-D screens, with a mesh number of 150-1000 mesh, preferably 190 to 800 mesh having a flat squeegee side, and a network of peaks and valleys on the print side of the screen material, are ideal. These screens allow the printing of much finer lines when compared to a screen material without such a 3-D surface structure.

(8) The achieved print quality is surprisingly better than that obtained with a screen with a much higher open area and smaller bridges. It is hypothesised that the 3-D surface structure, with peaks and valleys on the print side, enhances the transfer of ink through the screen and allow for the deposition of a greater amount of ink on the substrate due to the peaks, whereas the valleys allow for the sharp deposition of the ink. This is an advantage both when depositing ink to produce solids with an even print on the substrate and/or raised images, but also when producing continuous fine lines with sharp edges. Moreover, these advantages are achieved without any major loss of screen strength, stability and durability.

(9) The method for making the screen material is not part of this invention. Indeed, the methods known from U.S. Pat. No. 4,383,896 or U.S. Pat. No. 4,496,434 may be used to prepare a flat screen, whereas by way of forced flow conditions a 3-D structure on the print side of the screen material may be created, similar to the method disclosed in the aforementioned WO 2004043659. In addition, a metal screen material with a 3-D surface structure may be made with different techniques and with different materials. Thus, the 3-D structure may also be made by laser engraving, etching or ECM (electrochemical machining). Also within the scope of the invention is the preparation of such a screen by embossing on a polymer, or coating a mesh by CVD (chemical vapour deposition), PVD (physical vapour deposition), plasma spraying or other coating techniques. The 3-D surface structure may also be produced with a separate layer of lacquer on a screen.

(10) The new 3-D screen may be used in flat-bed and cylinder screen-printing, and in rotary screen-printing.

(11) For printing solid areas and raised images, a screen with a high amount of wet ink deposition (greater than 6 microns, preferably greater than 10 microns) is preferred. Herein the amount of wet ink deposition is expressed in terms of the theoretical wet ink deposition as defined previously in the present specification. Suitable screens have a mesh of 35 to 500, preferably 75 to 450. The thickness may vary from 35 to 200 micrometer, preferably from 60 to 150 micrometer. The hole diameter may vary from 10 to 650 micrometer, preferably from 15 to 400 micrometer.

(12) For producing high resolution prints, with a resolution below 100 micrometer, a screen with a mesh number of 150-1000 mesh, preferably 190 to 800 mesh is preferred. The thickness may vary from 20 to 200 micrometer, preferably from 35 to 160 micrometer. The hole diameter may vary from 5 to 130 micrometer, preferably from 15 to 105 micrometer.

(13) Preferably, the screen is a rotary screen.

(14) In addition, the invention claims a printing screen comprising the 3-D structure, with an attached stencil with or without the negative of an image to be printed. This combination of 3-D screen and stencil is novel and has the inherent advantages of improved printing as set out above.

(15) In addition the invention claims a printing machine comprising one or more 3-D printing screens according to the current invention in combination with one or more reservoirs for ink and/or in combination with a roller or squeegee.