Method for making tensioned printing screen and tensioned printing screen

Abstract

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

Description

[Technical field]

[0001] The present invention relates to a high precision screen printing method and apparatus. [Background technology]

[0002] Certain technology applications use screen printing methods that require a high degree of dimensional accuracy and precise definition of printed features, for example, printing electronic features such as those required for modern batteries or printed electronics, and sensor features, which must have consistently defined edge features and often consistent ink levels across the printed features.

[0003] Conventional precision screen printing is performed with emulsion screens. A mesh material (usually woven net or titanium mesh) with an appropriate mesh size is selected, and a printing screen is constructed in which the mesh is held under tension in a rigid frame. A layer of a photosensitive polymer precursor solution or suspension is applied to the mesh. The photosensitive polymer is selectively cured (e.g., with a UV laser or with a pre-cut sheet or mask) to create a negative of the required printing pattern, and the uncured precursor is washed away to leave the desired printing pattern defined on the screen by the bare areas of the mesh that are surrounded by the mask. The resulting emulsion screens suffer from some inherent limitations.

[0004] One limitation of emulsion screens is that the location of the mesh openings relative to the printed feature boundaries can vary, both within a given printed feature and between different features of the printed pattern, as shown in Figure 1 and discussed in further detail below.

[0005] Mesh printing screens must be tensioned to keep the mesh as flat as possible once the print media or ink has been applied to avoid pooling when the screen is removed. Another limitation of emulsion screens is that due to different tensions on different parts of the screen, the aspect ratio of the mesh that is then tensioned can vary across the printing screen. Again, this can lead to inconsistencies in print thickness and accuracy.

[0006] A further limitation is that the mesh forming the emulsion screen has three dimensional features that result in the mesh filaments being woven above and below each other relative to the plane of the printing screen, again causing inconsistent flow.

[0007] The aforementioned drawbacks are especially evident at low ink viscosities, and although some of the drawbacks may be mitigated by selecting a smaller mesh size, there is a tradeoff with the speed or amount of ink that can penetrate the mesh. The minimum mesh size is also limited to about 100 microns between mesh filaments, and mesh filaments with diameters of about 30-50 microns. Thus, there remains a need for improvements in high precision screen printing. Summary of the Invention

[0008] According to a first aspect of the present invention there is provided a printing screen for screen printing a print pattern having at least one continuous print feature on a substrate, the printing screen comprising a sheet material, the printing screen has a printing screen pattern having a plurality of openings within a printing screen pattern boundary representing a target boundary around at least one feature to be printed on the substrate; at least one feature is defined on the sheet material by a plurality of openings through a thickness of the sheet material within a printing screen pattern boundary; When the printing screen is placed over a substrate in use, the printing screen pattern boundary corresponds to the target pattern boundary.

[0009] A "feature" printed on a substrate is a contiguous area of ​​print medium (e.g., ink) that has a boundary around at least a portion of its perimeter. The target print boundary is the ideal desired boundary or edge where the feature will be printed on the substrate. The feature to be printed is represented by the printing screen pattern on the sheet material as a plurality of openings through the sheet material within the printing screen pattern boundary, such that the feature to be printed effectively appears in a "pixelated" form on the printing screen. In use, when the printing screen is placed over the substrate, the printing pattern boundary corresponds to the target pattern boundary, such that the print medium flows through the plurality of openings and merges within the target print boundary to print a contiguous feature on the substrate.

[0010] The relationship between the openings through the sheet material and the printing screen pattern boundary can be precisely selected, and therefore, for example, to correspond to the rheological properties of the printing medium and be better optimized to provide a printing feature or plurality of printing features on a substrate, where the boundary around the printing feature or each printing feature most closely matches the target printing boundary and therefore the desired printing pattern in use.

[0011] The printing screen pattern boundary of at least one feature to be printed may have a predetermined spatial relationship to the array of multiple openings adjacent to the printing screen pattern boundary, and thus, when the printing screen is disposed on a substrate in use, the target printing boundary of at least one feature to be printed may have a predetermined spatial relationship to the array of multiple openings adjacent to the target printing boundary.

[0012] Thus, the printing screen may have one or more features defined by a plurality of apertures, with each feature having an array around some or substantially all of its perimeter.

[0013] The predetermined spatial relationship between the printing screen pattern boundary and the array of multiple openings may include a minimum distance (in the plane of the sheet material) between an opening in the array and the nearest portion of the printing screen pattern boundary (and thus the printing boundary of the target in use), which minimum distance is shared between a series of multiple openings or all of the multiple openings in the array.

[0014] The predetermined spatial relationship between the target printing screen pattern boundary and the array of multiple openings may include an allowable range of minimum distances between the multiple openings in the array and the nearest portion of the printing screen pattern boundary.

[0015] That is, along some or all of the printing screen pattern boundary of a feature, the closest opening (i.e., member of the array) to the printing screen pattern boundary may be a uniform minimum distance from the printing screen pattern boundary or may be within an acceptable range of the minimum distance from the boundary.

[0016] The predetermined spatial relationship may comprise a minimum distance, or an acceptable range of minimum distances, between a series of adjacent openings or between each adjacent opening in the array.

[0017] By minimum distance we refer to the closest distance in the plane of the sheet material from the edge of the sheet material that defines each opening and the location of the printing screen pattern boundary relative to the sheet material or, as the case may be, the closest edge that defines an adjacent opening.

[0018] It should be understood that, inevitably, the shape of the features to be printed may vary in distance for some members of the array, e.g., near corners, curves, vertices, etc. In such circumstances, the optimal location of an opening adjacent to a printing screen pattern boundary and / or adjacent opening may be defined in part by the required distance to adjacent openings in the array and / or adjacent openings within a printing feature that is away from the printing screen pattern boundary.

[0019] By sheet material is meant a sheet material, for example a plastic or, more commonly, a metal sheet material such as stainless steel. Exceptionally, the sheet material may comprise a fabric or film material, and the dimensions of any holes or openings in the material may be impermeable to the ink or print medium to be applied.

[0020] The sheet material can generally be tensioned higher than a comparable fabric or mesh material, and therefore is more resistant to sagging during use.

[0021] The sheet material also provides a smoother flat surface on which to apply to the substrate than a mesh material (which must necessarily contain filaments that pass over and under each other outside the plane of the mesh applied to the substrate).

[0022] The openings may be cut by any suitable form of precision cutting including, for example, laser cutting, but also photochemical machining or electrical discharge machining.

[0023] The dimensions of the apertures may be at least one order of magnitude, and in some embodiments, two or more orders of magnitude smaller than the major dimension of at least one feature to be printed, such that an array of apertures along or around the printing screen pattern boundary is 10 to 15 cm in size. 1 ~10 3 The optical fiber may have at least on the order of apertures or more.

[0024] A feature to be printed may have a shape or configuration, such as a major dimension, such as a length or perimeter, that is greater than a minor dimension across all or a portion of its width or thickness. For example, a printed feature may have a length (whether it is straight, curved or spiral) on the order of mm or cm, but a width on the order of mm or microns.

[0025] For example, in some embodiments, the features to be printed are between 1 and 500 mm 2 , or 5 to 100 mm 2 , or about 10 to 50 mm 2 The major dimension of the printed feature (e.g., across, along, or around) may be, for example, between about 1-500 mm, 1-250 mm, or between about 1-100 mm. The minor dimension (e.g., the thickness of the printed feature) may be between about 0.05-5 mm, or 0.1-5 mm, or between about 0.2-3 mm.

[0026] The aperture may be any shape, but for convenience is roughly circular. A circular aperture may be created with a single shot of a laser (or other precision machined head).

[0027] In some embodiments, roughly circular features (same or different) created with a single shot (eg, of a laser) may overlap to some extent to create more complex aperture configurations.

[0028] The printing screen, or each of its features, may have openings of a single size. Alternatively, at least one feature may include openings of multiple sizes. For example, the openings may increase in size with distance from the printing screen pattern boundary. The openings may be of any suitable size as required for a particular printing medium.

[0029] The openings may range in size from about 1 μm to about 500 μm, between about 1-300 μm, or between about 5-300 μm in diameter (or width). A given printing screen may include openings, for example, about 10 μm in size, disposed around the periphery of its feature or features, and larger openings away from the periphery of the or each feature (and thus the printing screen pattern boundary) up to, for example, 300 μm in size.

[0030] Precision cutting, particularly laser cutting, may be used to create smaller openings than would otherwise be available from mesh printing screens, 10 microns or less in size for some screen materials. In contrast, more appropriately, the best available mesh screens (about 375 filaments per inch) have spacing of about 75-100 microns between filaments, i.e., filaments of about 30 microns diameter. Thus, the best openings between strands are in the 50 micron diameter region, with potential variations in the openings through the mesh and optimal location of the target print boundary at 10 microns. 1 It is on the order of microns (i.e., the thickness of the filament).

[0031] One skilled in the art will appreciate that the aperture size may be selected based on the viscosity of the print medium (e.g., ink). For example, larger apertures may be required to print higher viscosity media. Higher viscosity media may have a dynamic viscosity in the range of about 100-2000 Pa.s, or about 200-1800 Pa.s, or about 300-1600 Pa.s. Conversely, lower viscosity media may have a viscosity in the range of about 0.01-100 Pa.s, or about 0.04-100 Pa.s, and may require the use of smaller apertures positioned at least adjacent to the print screen pattern boundary and the print boundary of the target in use.

[0032] The printing screen, or each feature thereof, may comprise a constant number density of apertures (i.e., the number of apertures per unit area of ​​the feature to be printed). Alternatively, the number density of apertures may vary across at least one feature. For example, the number density of apertures may increase or decrease with distance from the printing screen pattern boundary.

[0033] In some embodiments, both the number density and size of the openings may be varied across the representation of the feature on the printing screen, for example, a higher number density of small openings may be required around the printing screen pattern boundary of at least one feature to most accurately define the boundary of the resulting feature printed on the substrate (i.e., to most closely match the target printing boundary), and a lower number density of larger openings may be used elsewhere in the representation of the feature to be printed.

[0034] A given printed pattern may include a representation of a number of features to be printed, each having a different required level of printing precision. For example, in some embodiments, the printed pattern may include a representation of one or more high precision features, such as battery terminals or sensors, extending to lower precision features, such as conductive tracks.

[0035] Precision cutting of the sheet material provides complete control over the pixilation of each feature of the printed pattern to be printed.

[0036] The printing screen may include a frame, and the sheet material is attached to the frame. The invention is not limited to any particular type of frame, which may be, for example, a metal or plastic material, or any suitable rigid material. In some embodiments, a metal (box or L-section) frame may be used. The sheet material may be attached to the frame under tension.

[0037] The sheet material may be attached to the frame by any suitable means. For example, the plastic or metal sheet material may be welded to the frame. The sheet material may be glued to the frame or secured by fixtures (such as screws or rivets).

[0038] According to a second aspect of the present invention there is provided a method of making a printing screen comprising the steps of: Providing a sheet material; precision cutting a printing pattern having a plurality of openings through a thickness of the sheet material within a printing screen pattern boundary representing a target boundary around at least one feature of the printing pattern to be printed on the substrate, the plurality of openings defining at least one feature on the sheet material. Equipped with.

[0039] The method may comprise laser cutting the openings (although other precision cutting methods may also be employed).

[0040] In some embodiments, the method may include tensioning the sheet material (typically biaxially) prior to the precision cutting step.

[0041] The method may comprise attaching the sheet material to a frame. The sheet material may be under tension and attached to the frame in a tensioned state.

[0042] The method may include precision cutting an array of apertures in a predetermined spatial relationship to a printing screen pattern boundary.

[0043] The method may comprise precision cutting the array around part, or substantially all, of the periphery of the features or each feature defined on the sheet material.

[0044] The invention extends in a third aspect to a method of printing a pattern having at least one print feature on a substrate, the method comprising: Providing a printing screen according to a first embodiment; placing the printing screen over the substrate such that a first side of the printing screen is positioned relative to the substrate; applying a print medium to a second side of the printing screen; flowing the print medium through a plurality of openings through the thickness of the sheet material onto the substrate; Equipped with.

[0045] The method of printing may include passing a wiper across the printing screen to distribute the print medium. The wiper may pass over the printing screen one or more times, or may pass over the printing screen in more than one direction or orientation.

[0046] The method may include removing excess print medium from a second side of the print screen.

[0047] The method may comprise removing the printing screen from the substrate and further such steps as are known in the art of screen printing. The substrate may be planar. The substrate may be substantially oriented laterally. The printing screen may be tensioned such that, in use, it is substantially planar. The printing screen may be provided by the method of the second aspect.

[0048] The present invention is not limited to any particular form of substrate or print media. The substrate may be, for example, a plastic or metal substrate. The substrate may comprise a composite material, such as a fiberglass or carbon fiber composite. The substrate may be a fabric material or a film-like material. In some embodiments, the substrate may be a circuit board for a printed circuit board.

[0049] The print medium may be a solution, ink, solder paste, or suspension (e.g., metal colloid or polymeric suspension). The print medium may include photoactive materials or environmentally responsive materials such as biological materials.

[0050] The optional features of each aspect of the invention correspond to the optional features of any other aspect of the invention. In particular, a method disclosed herein may include any such steps disclosed for the function or use of an apparatus disclosed herein. Furthermore, an apparatus may comprise any such features necessary to carry out a method disclosed herein. [Brief description of the drawings]

[0051] Exemplary embodiments will now be described with reference to the following figures. [Figure 1] 1 shows the print boundary of a target for a print pattern that is overlaid on a mesh. [Figure 2(a)] 1 shows a circular printing screen pattern boundary of a feature of a printing pattern on a mesh printing screen. [Figure 2(b)] 3 shows the same circular feature on a sheet of material. [Figure 3(a)] 1 illustrates diagrammatically steps in a method for making an embodiment of a printing screen; [Figure 3(b)] 1 illustrates diagrammatically steps in a method for making an embodiment of a printing screen; [Figure 3(c)] 1 illustrates diagrammatically steps in a method for making an embodiment of a printing screen; [Figure 3(d)] 1 illustrates diagrammatically steps in a method for making an embodiment of a printing screen; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0052] Figure 1 shows an outline of two features to be printed, A and B, of a printing pattern projected onto a conventional printing screen mesh M. To create an emulsion printing screen, a polymer material is created above area P, leaving mesh features A and B exposed.

[0053] Feature A has a target printing boundary. These are represented on the mesh printing screen by printing screen pattern boundaries 1 and 2. Edge 1 has filament 3 extending along it, so that the boundary of feature A is bounded by the edge of opening 4 in the mesh. However, another printing screen pattern boundary 2 extends partway along the row of openings 5. As a result, when printing feature A on the substrate, ink will necessarily flow beyond printing feature A's boundary 2 into opening 5. Similarly, the relationship between feature B's printing screen pattern boundaries 6, 7, and 8 are all different from each other relative to the mesh filament and opening locations.

[0054] FIG. 2(a) illustrates the contours of circular features 10 of a print pattern (i.e., the print screen pattern boundary, and therefore the target print boundary when placed on a substrate) as represented on an emulsion screen 12 made from a metal mesh. The emulsion screen has masked areas 14 and bare areas 16. The features 10 to be printed are represented on the emulsion screen 12 by openings 20 between the metal mesh filaments. The filaments themselves have been omitted for clarity, however, exemplary paths of the filaments (as viewed perpendicular to the screen) are shown by dotted lines 18, 19. It will also be appreciated that each of the filaments passes alternately above and below the other filaments across the print screen, thus curving in and out of the plane of the screen, leading to differences between the configuration of each opening 16 relative to the planar substrate in three dimensions.

[0055] Because the apertures 16 are necessarily arranged in rows and columns, in use the distance between the target boundary of a feature 10 and the nearest aperture 16 within that boundary will vary 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 the substrate.

[0056] 2(b) illustrates one embodiment of a printing screen 112 as disclosed herein having a sheet material 114 (stainless steel in the embodiment shown). Circular features 10 are defined in the sheet material by a plurality of openings 120 that are laser cut through the thickness of the sheet material 114 within the printing screen pattern boundary 10a.

[0057] The array 122 of openings 120 adjacent the boundary of the feature 10a extends around (in this case, around) the printed screen pattern boundary 10a of the feature 10. The openings in the array 122 have a predetermined spatial relationship to one another and, in this embodiment, are equidistant from one another from the boundary 10a, thus providing a more accurate representation of the feature 10 when printed on a substrate (i.e., having boundaries that more closely relate to the target printing boundary).

[0058] While the apertures in the array 122 in the embodiment shown are equally spaced from one another from the boundary 10a, in other embodiments, such as for more compound or complex print boundaries, these distances, or indeed the shapes of the apertures, may need to vary. For example, a series of (more than two consecutive) apertures may have the same spatial relationship to one another in relation to the printed screen pattern boundary along a portion of the boundary, while the relationship may be different in other portions, such as more tightly curved regions, corners, etc. Thus, in other portions of the printed screen pattern boundary, the size, shape and / or spatial relationship may be different.

[0059] Referring again to Figure 2(b), both the size and number density of the openings 120 vary with distance from the printing screen pattern boundary 10a of the feature 10. The opening size generally increases and the number density generally decreases towards the center of the feature. However, the size of the openings increases and decreases with distance from the boundary in the embodiment shown, allowing the openings to "tessellate" somewhat and reducing the minimum distance between openings. Figure 3 shows a schematic of a method of making one embodiment of a printing screen.

[0060] 3(a), a sheet of steel 214 is provided. The sheet 214 is then tensioned (i.e., by mechanically gripping the edges of the sheet and applying a force toward the outside of the plane of the sheet) in the illustrated example in two axes indicated by arrows T. Means for tensioning metal sheets are well known in the art.

[0061] As shown in FIG. 3(b), while under tension, the sheet is attached to a metal box section frame 230 and spot welded around its perimeter 232 so that the sheet 214 is maintained in tension in the resulting "blank" screen 200b.

[0062] The blank screen 200b is then placed under a precision laser machining head 300, such as a Tannlin T-series precision laser machining head of a ventilated stencil laser system (Tannlin is a trademark). This is shown in the schematic cross-sectional side view of FIG. 3(c), showing the blank screen 200b supported above a ventilated well 302. The laser beam 304 cuts a plurality of apertures 120 through the thickness of the material 214 within the printed screen pattern boundary that represents the target boundary of at least one feature to be printed on the substrate. Thus, at least one feature is represented on the sheet material by the plurality of apertures (in a "pixellated" form), as disclosed herein. CNC control and associated apparatus features for laser machining processes are known to those skilled in the art.

[0063] The resulting printing screen 200 is shown in Figure 3(d). The screen 200 can then be used in a screen printing process in a generally conventional manner by placing the screen 200 on a substrate with the sheet 214 face down against the substrate. Ink or another desired print medium is placed on the top side of the sheet 214 and spread across the sheet by a wiper (not shown) so that the print medium flows through the apertures 120 and onto the substrate, thereby creating a printed pattern.

[0064] Although exemplary embodiments have been described herein, these should not be construed as limiting the modifications and variations possible within the scope of the invention as disclosed herein and recited in the appended claims.

Claims

1. A method for making a tensioned printing screen, comprising the steps of: Providing a sheet material; applying tension to the sheet material; attaching the sheet material under tension to a frame; thereafter, precision cutting a printing pattern having a plurality of apertures through a thickness of the sheet material within a printing screen pattern boundary representing a target boundary around at least one feature of the printing pattern to be printed on the substrate, the plurality of apertures defining the at least one feature on the sheet material; A method comprising:

2. The method of claim 1 comprising laser cutting the plurality of openings.

3. 3. The method of claim 1 or 2, comprising precision cutting the array of apertures in a predetermined spatial relationship to the printing screen pattern boundary.

4. The method of claim 3 , comprising precision cutting the array around a portion of, or substantially all of, the periphery of the or each feature defined on the sheet material.

5. 1. A method of printing a pattern on a substrate, the method comprising: Providing a tensioned printing screen made by the method of claim 1 or 2; placing the printing screen over the substrate such that a first side of the printing screen is positioned relative to the substrate; applying a print medium to a second side of the printing screen; flowing the print medium through the plurality of openings through a thickness of the sheet material onto the substrate; A method comprising:

6. The method of claim 5 , comprising passing a wiper across the printing screen to distribute the print medium.

7. The method of claim 6 comprising removing the printing screen from the substrate.

8. A tensioned printing screen obtainable by the method of claim 1 or 2 for screen printing a printing pattern having at least one continuous printing feature on a substrate, comprising: the printing screen comprises a sheet of material attached under tension to a frame; the printing screen has a printing screen pattern having a plurality of openings within a printing screen pattern boundary representing a target boundary around at least one feature to be printed on a substrate; the at least one feature is defined on the sheet material by a plurality of openings through a thickness of the sheet material within the printing screen pattern boundary; A printing screen, wherein when the printing screen is placed over a substrate in use, the printing screen pattern boundary corresponds to the target boundary.

9. A tensioned printing screen as described in claim 8, wherein the printing screen pattern boundary of at least one feature to be printed has a predetermined spatial relationship to the array of the plurality of openings adjacent the printing screen pattern boundary.

10. A tensioned printing screen as described in claim 9, wherein the predetermined spatial relationship comprises a minimum distance or range of minimum distances between an opening in the array and a nearest portion of the printing screen pattern boundary, the minimum distance or range being shared between a series of the plurality of openings in the array or between all of the plurality of openings.

11. A tensioned printing screen as described in claim 10, wherein the predetermined spatial relationship comprises a minimum distance between a series of adjacent openings or between each adjacent opening in the array, or an acceptable range of minimum distances.

12. The tensioned printing screen of claim 8, wherein the sheet material comprises a metallic sheet material such as stainless steel.

13. The tensioned printing screen of claim 8, wherein the plurality of openings are formed by laser cutting.

14. A tensioned printing screen as described in claim 8, wherein the or each feature to be printed has a surface area in the range of 1 to 500 mm2 and / or the plurality of apertures have a diameter or width of between about 1 μm and 500 μm.

15. The tensioned printing screen of claim 8, wherein some or all of the plurality of openings are circular.

16. A tensioned printing screen as described in claim 8, wherein at least one of the features includes openings of multiple sizes, the openings increasing in size with distance from the printing screen pattern boundary.

17. A tensioned printing screen as described in claim 16, wherein the number density of the plurality of openings decreases with the distance of the at least one feature from the printing screen pattern boundary.

18. The tensioned printing screen of claim 8, wherein the sheet material is welded to the frame.

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