Printing screen

Abstract

A printing screen includes a screen-shaped fabric layer with fabric threads being angled relative to one another to form a carrier layer. An imaged stencil layer is connected to the fabric layer and provided with passages. A respective passage forms a continuous channel and has an opening that is smaller on a printing material side of the printing screen than on a squeegee side of the printing screen. Such a printing screen has sufficient stability and advantageously allows the finest lines and dots to be printed. A method for imaging such a printing screen is also provided.

Claims

1. A printing screen, comprising: a printing material side and a squeegee side of the printing screen; a screen-shaped fabric layer acting as a carrier structure, said screen-shaped fabric layer including fabric threads each having a fabric thread diameter; and an imaged stencil layer connected to said fabric layer and provided with passages, each respective passage forming a continuous channel and having an opening on said printing material side and an opening on said squeegee side; said opening on said printing material side being smaller than said opening on said squeegee side; said opening on said squeegee side having a width being greater than said fabric thread diameter; and said opening on said printing material side having a width being at most equal to said fabric thread diameter.

2. The printing screen according to claim 1, wherein said fabric threads are disposed at an angle relative to one another.

3. The printing screen according to claim 1, wherein each respective passage forms a line-shaped or dot-shaped ink channel.

4. The printing screen according to claim 1, wherein each respective passage has at least one channel wall with at least one of an angled or stepped or convex or concave shape.

5. The printing screen according to claim 1, wherein said fabric layer is a steel fabric layer.

6. The printing screen according to claim 1, wherein said fabric layer is a stainless steel fabric layer.

7. The printing screen according to claim 1, wherein said fabric layer is provided with a metal coating.

8. The printing screen according to claim 1, wherein said fabric layer is provided with a metal coating containing nickel.

9. The printing screen according to claim 1, wherein said stencil layer is formed of a polymer.

10. The printing screen according to claim 1, wherein said stencil layer is formed of a photopolymer.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is a fragmentary, diagrammatic cross-sectional view of a printing screen of the invention;

(2) FIG. 2 is a fragmentary, diagrammatic cross-sectional view of a prior art printing screen;

(3) FIGS. 3A-3F are fragmentary, diagrammatic cross-sectional views of different embodiments of the printing screen of the invention;

(4) FIG. 4 is a top-plan view of an ink channel;

(5) FIGS. 5A and 5B are top-plan views from both sides of a printing screen with a dot-shaped passage;

(6) FIG. 6 is a perspective view of a printing screen; and

(7) FIG. 7 is a perspective view illustrating the use of the printing screen as a screen in a rotary printing operation.

DETAILED DESCRIPTION OF THE INVENTION

(8) Referring now in detail to the figures of the drawings, in which mutually corresponding elements and components have the same reference symbol and in which the figures are not drawn to scale, and first, particularly, to FIG. 6 thereof, there is seen a flat screen material 10 having a fabric layer 1 in accordance with the prior art. On one side, the screen material 10 has a photopolymer coating 2 (direct stencil). In a non-illustrated alternative embodiment, a film that has already been imaged may be applied to the screen structure 10 (indirect stencil). The nickel-plated flat screen material 10 is built up from the fabric 1. Different forms of fabric, which are also referred to as types of fabric, are possible.

(9) Screen materials 10 of that kind and printing screens 10 of the invention are used in rotary screen printing. To that end, FIG. 7 indicates a screen 100 including a flat screen material 10 formed to create a cylindrical sleeve for rotary screen printing. The screen material 10 is held in its cylindrical shape by end pieces that are not illustrated in any detail. A non-illustrated squeegee or blade of a screen printing unit is provided in the interior of the screen 100 to press ink through the screen material 10. The squeegee may be oriented to be parallel to the axis of rotation of the screen 100. A double arrow indicates the circumferential direction U of the screen 100 in which the screen rotates during a printing operation.

(10) FIG. 1 is a cross-sectional view of a portion of a printing screen 10 of the invention. The printing screen 10 is formed of a fabric layer 1, which is at least partly embedded in a stencil layer 2. The fabric layer 1 is calendered. Alternatively, non-calendered or more strongly calendered fabric layers 1 may be used in accordance with the invention. The stencil layer 2 may be a photopolymer layer. The fabric layer 1 is formed of a plurality of interwoven fabric threads 6. FIG. 1 illustrates three fabric threads 6 in a cross-sectional view as well as two fabric threads 6 running at right angles relative thereto.

(11) The printing screen 10 has a printing material side 4 and a squeegee side 5. The squeegee side 5 is the side of the ink supply, which is applied to the squeegee side 5 of the printing screen 10 by using a non-illustrated squeegee. Passages 3, which form ink channels, allow ink 30 to travel to the printing material side 4 of the printing screen 10, where the ink comes into contact with a printing material 20. In order to be able to print ink 30 onto a printing material 20 at high quality, a smooth flow F of ink through the passages 3 of the printing screen 10 is required. In order to be able to print very fine dots and ink lines 30 onto a printing material 20, i.e. to be able to print lines of a very small line width a, an opening 9 of the printing screen 10 needs to have a small width at the printing material side 4.

(12) For this purpose, the passages 3 of the printing screen 10 are constructed as follows: the opening 9 has a width I on the squeegee side 5 that is greater than the width d of the opening 9 on the printing material side 4, i.e. d<I. The width I of the squeegee side opening 9 is also greater than the diameter D of a coated fabric thread 6 having a metal coating 7. In contrast, the width d of the printing material side opening is smaller than the diameter D of a coated fabric thread, i.e. I>D>d. This construction ensures a smooth, reliable, and continuous flow of ink 30 between passage walls 8 flowing past the fabric thread 6 from the squeegee side 5 to the printing material side 4.

(13) In order to point out the differences between a printing screen 10 of the invention as shown in FIG. 1 and a printing screen of the prior art, FIG. 2 illustrates a printing screen 10 in accordance with the prior art. In such known printing screens, the ink channels are rather wide passages 3 having a constant width over their entire length. Although these passages ensure a smooth flow of ink F, the line width a that can be printed is limited, only allowing comparatively wide ink lines 30 to be printed onto a printing material 20. The printable line width a is a function of the printing material side width d of the opening 9 of the passage 3, which approximately corresponds to the width I of the squeegee side opening 9, i.e. dI. The width I of the squeegee side opening 9 is a multiple of the diameter D of a coated thread of fabric, i.e. I>>D.

(14) In the exemplary embodiment of the printing screen 10 shown in FIG. 1, the channel walls 8 of the passage 3 have an angled orientation. FIGS. 3A to 3F illustrate alternative geometric shapes of the channel walls 8, which are likewise considered to be advantageous. For instance, in the embodiment of FIG. 3A the channel walls 8 have a concave shape. In the embodiment shown in FIG. 3B, the channel walls have a convex shape. In the embodiment shown in FIG. 3C, similar to the embodiment of FIG. 1, the channel walls 8 are substantially angled, but, in the printing material side end region of the passage 3, they are shaped to be perpendicular to the surface of the printing screen 10. In the embodiment of FIG. 3D, the channel walls 8 have a stepped/step-shaped geometry. The channel walls 8 may have more than the one step shown in FIG. 3. As shown in FIG. 3E, the channel walls may have a free shape, i.e. they may have an arbitrary geometry. As shown in FIG. 3F, a combination of different channel wall constructions for the two channel walls 8 is conceivable. In particular, the geometries shown in FIGS. 1 and 3A to 3E may be combined.

(15) FIG. 4 is a top view of a passage 3 from the squeegee side 5. The passage is embodied as a line-shaped ink channel 3 for printing a line. In contrast, FIGS. 5A and 5B are top views of a printing screen 10 with a dot-shaped passage 3 viewed from both sides of the printing screen, i.e. from the printing material side 4 in FIG. 5A and from the squeegee side 5 in FIG. 5B. Due to the dot-shaped passages 3 having a printing material side diameter d, fine dots of a diameter a may be printed.