EP3107735B1 - Screen printing stencil and method for imaging it - Google Patents

Description

The invention relates to a screen printing stencil with the preamble features of claim 1.

State of the art

The industrial application of fabrics and fabrics is known from various fields.
When used in the field of filtration, the square mesh is the usual embodiment. For the printing application, this mesh has been adopted. With the available photo layers and the well-known application methods, a reasonable image resolution can only be achieved with a large number of "supports". Therefore, increasingly high mesh fabrics are being used.

When electronic printing as thin as possible sieves or fabrics are used with the thinnest possible wire to ensure a good flow of pastes and to allow the finest of fine images.
In solar cell coating, ie solar cell metallization, a high paste application and a precise and fine image resolution are required. For example, for the application of printed conductors as a current finger with the lowest possible coverage of the solar cells, so as to ensure a high efficiency of the solar cells.
The screens or fabrics used for electronic printing are very expensive and sensitive to processing, so that they are hardly suitable for the production of screen printing plates for rotary screen printing. The lack of suitability is also due to the fact that the screen fabric in the rotary screen can be stretched in one direction only, namely the cylinder longitudinal axis, in flat screen printing, however, in two dimensions.

In rotary screen printing, the color is transported through the screen by the hydrodynamic pressure generated by the rotation of the screen and by the squeegee in front of the squeegee. By design, only open or semi-open squeegee systems can be used, so that the dynamic pressure is influenced by many factors such as viscosity, filling quantity and rotational speed. By increasing the speed of rotation or the amount of ink, the hydrodynamic pressure can be easily increased.
Such a rotary screen printing unit is for example in the WO 99/19146 A1 described.

As basic structures for screen materials, prior art stainless steel cloths are often used with linen weave. The ratio of sieve opening, contact area and fabric thickness has proven to be suitable. The thickness of the structure, ie the fabric thickness (initial dimension before calendering) corresponds approximately to twice the wire thickness. The basic structure is processed in a further step in a calendering process and brought to the desired raw fabric thickness. Also, a higher smoothness of the screen and thus a lower screen and blade wear is achieved. In the subsequent Vernickelungsvorgang the fabric is reinforced for the purpose of a higher mechanical stability and wear resistance and increases the support points in the region of the crossing points.

A method for producing such screen materials is for example in EP 0 182 195 A2 described.

As an alternative to the woven screen materials, electroformed templates are used.
The use of metal fleeces, plastic fabrics, perforated sheets, metal foils, even in combination with each other is possible.

In order to ensure that color dots and color lines are printed accurately, it must be ensured when imaging the screen materials that line or punctiform forms are formed from the squeegee side of the screen materials to the printing material side of the screen materials Pass through passages, so-called color channels. The color channels must not be interrupted or blocked by the tissue strands. Therefore, the color channels according to the prior art are made with a width which corresponds to a multiple of the diameter of the tissue strands (at least 2 to 2.5 times). Such a sieve material is in the DE 10 2011 016 453 A1 described.

However, if fine lines (about 10 to 100 micrometers) and dots are to be printed, as shown e.g. is required for electronics and solar cells, the color channels may have only a small width.

Nevertheless, in order to ensure a color flow from the squeegee to the printing material side of the screen materials, fabrics with a very fine weave structure are used. These are often woven from strands of less than 30 microns in diameter, so that a mesh size of 300 mesh (number of stitches per 25.4 mm) and more can be realized. Such fine screen materials are expensive to manufacture and have poor stability.
In the case of electroformed templates, the holes in the known hexagonal, square and round hole geometry are made particularly fine.

task

Object of the present invention is to provide a screen printing stencil which has sufficient stability and allows the printing of fine lines or points. Another object is to describe a method of how such a screen printing stencil can be imaged.

This object is achieved by the screen printing stencil with the features of claim 1 and by a method according to claim 7.

The screen printing stencil according to the invention has at least one sieve-like fabric layer, in particular with tissue strands arranged at an angle to one another as support structure, wherein the fabric strands are arranged in particular at right angles to one another, and one illustrated stencil layer. Electro-formed templates, for example made of nickel, and perforated plates or perforated films, such as stainless steel films are considered in this context as a sieve-like fabric layers. The stencil layer and the fabric layer are connected to each other, wherein the fabric layer is at least partially embedded in the stencil layer. The stencil layer is provided with passages in order to allow a color flow from a doctor side of the screen printing stencil on a printing material side of the screen printing stencil. According to the invention, a respective passage on the printing material side of the screen printing stencil has a smaller opening, ie an opening of smaller width, than on the squeegee side of the screen printing stencil and thus forms a passage extending from the squeegee side to the printing material side as a passage for ink. According to the invention, the opening of the passage on the doctor side is greater than the diameter of a possibly coated fabric strand. The opening of the passage on the substrate side corresponds at most to the diameter of a possibly coated fabric strand. This makes it possible to print very fine structures. The opening of the passage on the printing material side can also be significantly smaller than the diameter of a possibly coated fabric strand. A respective passage may be linear with a certain extent or punctiform in order to print either color lines or only individual points. Depending on the image to be printed, the passages are then offset in parallel, positionally equal to or at an oblique angle to the tissue strands to lie.

Such a screen printing stencil makes it possible in an advantageous manner to be able to print particularly fine lines and dots. The small opening on the substrate side allows for particularly fine line widths, while the larger squeegee side opening ensures a continuous flow of color, so that lines and dots of continuous ink coverage, i. constant line height, can be printed.

A respective passage configured in this way can also be referred to as a color channel.

In an advantageous embodiment of the screen printing stencil according to the invention, a respective passage may have differently configured channel walls. So be oblique and / or stepped and / or convex and / or concave channel walls considered advantageous.
In a particularly advantageous and therefore preferred embodiment, the fabric layer of the screen printing stencil is designed as a woven steel fabric, in particular made of stainless steel. Alternatively, polyester fabrics can be used. It is also advantageous if the fabric layer is provided with a stabilizing metal coating, the metal coating in particular containing nickel. The fabric layer may possibly be calendered. Also a very strong calendering up to max. The simple wire thickness can be advantageous. Advantageously, the stencil layer is formed by a polymer, in particular by a photopolymer, ie a light-sensitive polymer, which allows a particularly simple imaging.
The invention also relates to a method for imaging a screen-printing stencil having at least one sieve-like fabric layer as the support structure and an imageable stencil layer, wherein the stencil layer is provided with apertures during imaging, which can be referred to as color channels to a color flow from a doctor blade side on a printing material side of the screen printing stencil to enable. According to the invention, a respective passage is formed such that it has a smaller opening on the printing material side than on the doctor side of the screen printing stencil. According to the invention, the width 1 of the opening on the doctor blade side is greater than the diameter (D) of a fabric strand (1> D) and the width d of the opening on the printing material side corresponds at most to the diameter (D) of a woven strand (d ≦ D). This results in the advantages described above.
In an advantageous embodiment of the method according to the invention, the stencil layer is imaged by means of laser. The laser is driven in such a way that it has different penetration depths, that is, it acts differently far below the surface of the stencil layer. By laser imaging involves the two alternatives curing by polymerization and Webrennen the photo layer (similar to laser cutting). Alternatively, the template layer can be imaged in classical exposure by using multiple film masks with adjusted exposure time and intensity. In an alternative method variant, the stencil layer is imaged with different light spectra, ie with light in different wavelength ranges. For this, the stencil layer can consist of several Be constructed emulsion layers of different sensitivity. The stencil layer can also be imaged with specially designed masks, for example a film mask with locally different light transmission.

The described invention and the described advantageous developments of the invention, namely the differently designed channel walls, are also in combination with each other advantageous developments of the invention.
Also for the filtration extremely fine passages are needed. Thus, for polymeric membranes advantageously as described above Siebschablonen be used. Their use facilitates cleaning and contributes to less sticking during backwashing.
With regard to further advantages and constructive and functional advantageous embodiments of the invention, reference is made to the dependent claims and the description of exemplary embodiments with reference to the accompanying figures.

embodiment

The invention will be explained in more detail with reference to attached figures. Corresponding elements and components are provided in the figures with the same reference numerals. In favor of a better clarity of the figures was waived a true to scale representation.

Figur 1:

eine erfindungsgemäße Siebdruckschablone in einer Schnittdarstellung

Figur 2:

eine Siebdruckschablone in einer Schnittdarstellung gemäß dem Stand der Technik

Figur 3a-f:

verschiedene Ausführungen von erfindungsgemäßen Siebdruckschablonen

Figur 4:

eine Draufsicht auf einen Farbkanal

Figur 5a, b:

Draufsichten von beiden Seiten auf eine Siebdruckschablone mit punktförmigem Durchlass

Figur 6:

eine Siebdruckschablone in einer Ansicht als Übersichtsdarstellung

Figur 7:

die Anwendung der Siebdruckschablone als Rotationssiebdrucksieb

It show in a schematic representation

FIG. 1:

a screen printing stencil according to the invention in a sectional view

FIG. 2:

a screen printing stencil in a sectional view according to the prior art

FIGS. 3a-f:

various embodiments of screen printing stencils according to the invention

FIG. 4:

a plan view of a color channel

FIG. 5a, b:

Top views from both sides on a screen printing stencil with point-shaped passage

FIG. 6:

a screen printing stencil in a view as an overview

FIG. 7:

the application of the screen printing stencil as a rotary screen

FIG. 6 shows a flat screen material 10 with a fabric layer 1 according to the prior art, which is provided on one side with a photo-polymer coating 2 (direct template). In an alternative embodiment, not shown, an already imaged film can be applied to the screen structure 10 (indirect template). The nickel-plated planar sieve material 10 is constructed from a fabric 1. Different tissue forms are possible, which are also referred to as tissue type.

Such screen materials 10 as well as the screen printing stencils 10 according to the invention are used in rotary screen printing: In FIG. 7 is a sieve 100 with a flat screen material 10 in cylindrical sleeve shape for the rotary screen printing indicated. The screen material 10 is held by unspecified tails in its cylindrical shape. Inside the screen 100 is an invisible squeegee of a screen printing unit to press paint through the screen material 10. The orientation of the doctor blade may be parallel to the axis of rotation of the wire 100. The circumferential direction U of the screen 100, in which this is rotated during printing, is indicated by a double arrow.

In FIG. 1 a section of a screen printing stencil 10 according to the invention is shown in a cross section. The screen printing stencil 10 consists of a fabric layer 1, which is at least partially embedded in a stencil layer 2. The fabric layer 1 is calendered. Likewise, uncalendered or more calendered fabric layers 1 can be used according to the invention. The stencil layer 2 may be a photopolymer. The fabric layer 1 is formed by a multiplicity of interwoven fabric strands 6 FIG. 1 There are three fabric strands 6 in the Cross-section to recognize as well as two perpendicular thereto extending tissue strands 6 in a view.

The screen printing stencil 10 has a printing material side 4 and a squeegee side 5. On the doctor side 5 is an ink supply, which is applied by means of a doctor, not shown, on the doctor side 5 of the screen printing stencil 10. Through passages 3, which form color channels, ink 30 reaches the printing material side 4 of the screen printing stencil 10 and comes there into contact with a printing substrate 20. To print a substrate 20 in high quality with color 30, a good color flow F through the passages 3 of the screen printing stencil 10 required. In order to be able to print particularly fine dots and color lines 30 on a printing substrate 20, that is, in order to realize a particularly small printable line width a, the printing material-side 4 opening 9 of the screen printing stencil 10 must have a narrow width.

For this purpose, the passages 3 of the screen printing stencil 10 have the configuration described below: The opening 9 is larger on the doctor blade side 5 with a width 1 than on the printing material side 4, where the opening has a width d. The width 1 of the squeegee-side opening 9 is therefore also greater than the diameter D of a coated fabric strand 6. The width d of the printing material-side opening, however, is smaller than the diameter D of a coated fabric strand. So there is 1> D> d. On account of this embodiment, it is ensured that the color flow of ink 30 from the doctor blade side 5 onto the printing material side 4 between the channel walls 8 and the fabric strand 6 can take place particularly reliably and continuously.

To illustrate the differences between a screen printing stencil 10 according to the invention, as in FIG FIG. 1 shown, and a screen stencil according to the prior art, is by FIG. 2 illustrates a screen printing stencil 10 according to the prior art. Such known screen printing stencils have quite wide passages 3, which are constant over their extent, as a color channel. This ensures that a good color flow F is present. However, the printable line width a is limited, so that only relatively wide color lines 30 can be printed on a substrate 20. The printable line width a results from the substrate-side width d of the opening 9 of the passage 3, which corresponds approximately to the width 1 of the squeegee-side opening 9. It therefore applies d ≈ 1. The width 1 of the squeegee-side opening 9 is a multiple of the diameter D of a coated fabric strand. So 1 >> D.

While in the embodiment of the screen printing stencil 10 according to FIG. 1 the channel walls 8 of the passage 3 have an oblique configuration are in the FIGS. 3a to 3f shown alternative geometry shapes of the channel walls 8, which are also considered advantageous. Thus, the channel walls 8 in the embodiment according to FIG. 3a concave. In the embodiment according to FIG. 3b the channel walls 8 are convex. In the variant according to Figure 3c are the channel walls 8, as well as in the embodiment according to FIG. 1 , configured substantially obliquely, but have in the printing material side end portion of the passage 3 a perpendicular to the surface of the screen printing stencil 10 extending shape. The channel walls 8 in the embodiment according to 3d figure have a stepped or stepped geometry. Also, the channel walls 8 more than the only one in FIG. 3 have shown stage. As in FIG. 3e shown, the channel walls 8 may also have the shape of a free forming line, ie a fairly random geometry. As in FIG. 3f illustrated, however, the combination of different channel wall configurations for the two channel walls 8 is conceivable. In particular, those in the FIGS. 1 and 3a to 3e Geometry variants are combined with each other.

FIG. 4 shows a plan view of a passage 3 from the doctor side 5. The passage is designed as a linear color channel 3, for printing a line.
In FIG. 5 on the other hand, plan views of a screen printing stencil 10 with a punctiform passage 3 from both sides of the screen printing stencil are shown: in Fig. 5a the printing material side 4 view and in Fig. 5b the rakelseitige 5 view. Thanks to punctiform passages 3 with printing-material-side diameter d, fine dots having a diameter a can be printed.

LIST OF REFERENCE NUMBERS

1

fabric layer

2

stencil layer

3

Passage as a color channel

4

Bedruckstoffseite

5

squeegee side

6

tissue strand

7

coating

8th

channel wall

9

Opening in stencil layer

10

screen printing stencil

20

substrate

30

Color (color line, color point)

100

Rotationssiebdrucksieb

a

Printable line width (color line width or color point diameter)

d

Width of the printing material side opening

1

Width of the squeegee-side opening

D

Diameter tissue strand

U

circumferentially

F

color flow

Claims (8)

1. Printing screen (10) comprising at least a screen-like fabric layer (1) as a carrier structure, in particular including threads of fabric (6) arranged at an angle relative to one another, and an imaged stencil layer (2) connected to the fabric layer (1) and provided with passages (3),
   a respective passage (3) having a smaller opening (9) on the printing material side (4) of the printing screen (10) than on the squeegee side (5) of the printing screen (10) and forming a continuous channel,
   wherein the width 1 of the opening (9) on the squeegee side (5) is greater than the diameter (D) of a thread of fabric (6) (1>D) and wherein the width d of the opening (9) on the printing material side (4) at the maximum corresponds to the diameter (D) of a thread of fabric (6) (d ≤ D).
2. Printing screen according to claim 1,
   characterized in
   that a respective passage (3) forms a line-shaped or dot-shaped ink channel.
3. Printing screen according to any one of the preceding claims,
   characterized in
   that a respective passage (3) has at least one channel wall (8) that is angled and/or stepped and/or convex and/or concave.
4. Printing screen according to any one of the preceding claims,
   characterized in
   that the fabric layer (1) is embodied as a steel fabric, in particular a stainless steel fabric.
5. Printing screen according to any one of the preceding claims,
   characterized in
   that the fabric layer is provided with a metal coating (7), the metal coating in particular containing nickel.
6. Printing screen according to any one of the preceding claims,
   characterized in
   that the stencil layer (2) is formed by a polymer, in particular a photopolymer.
7. Method for imaging a printing screen (10) to manufacture a printing screen according to claim 1, the printing screen (10) comprising at least a screen-like fabric layer (1) as a carrier structure and an imageable stencil layer (2), the stencil layer (2) and the fabric layer (1) connected to one another and the stencil layer (2) provided with passages (3) in an imaging process to provide an ink flow (F) from a squeegee side (5) to a printing material side (4) of the printing screen (10), wherein a respective passage (3) is formed to have a smaller opening (9) on the printing material side (4) than on the squeegee side (5) of the printing screen (10), causing the width 1 of the opening (9) on the squeegee side (5) to be greater than the diameter (D) of a thread of fabric (6) (1 > D) and the width d of the opening (9) on the printing material side (4) at the maximum corresponds to the diameter (D) of a fabric thread (6) (d ≤ D).
8. Method for imaging a printing screen according to claim 7,
   characterized in
   that the stencil layer (2) is imaged directly using a laser or by exposure to different spectrums of light or by means of a number of different photographic screens with an adapted exposure or by means of a specifically embodied photographic screen.

Images