WO2008067099A1

WO2008067099A1 - Method of making lattice barrier partitions and articles

Info

Publication number: WO2008067099A1
Application number: PCT/US2007/082925
Authority: WO
Inventors: Hiroshi Kikuchi; Akira Yoda
Original assignee: 3M Innovative Properties Company
Priority date: 2006-11-29
Filing date: 2007-10-30
Publication date: 2008-06-05
Also published as: TW200832496A

Abstract

The invention relates to (e.g. plasma) display panels having display cells and sub-cells, methods of molding lattice barrier partitions on a substrate, flexible molds suitable for use in the method of molding lattice barrier partitions, and methods of making flexible mold.

Description

METHOD OF MAKING LATTICE BARRIER PARTITIONS AND ARTICLES

Background A plasma display panel (PDP) generally contains a large number of fine discharge display cells. Each discharge display cell is encompassed and defined by a pair of glass substrates spaced apart from each other with barrier ribs (also called "barrier partitions") between the glass substrates. The barrier ribs are generally a fine structure comprised of ceramic material. When a single set of parallel barrier ribs are employed, the barrier partitions form a striped pattern. In such embodiment, the discharge display cells are the recesses between the barrier ribs.

Alternatively, the barrier ribs may have a lattice pattern wherein each cell such as described US 2003/0090443, US2003/0178938, WO 2005/013308, US 2006/0093202, JP 8-273537, JP 8-273538, JP 9-283017, and JP 10-134705. U.S. Patent No. 6,703,782 describes a plasma display panel display discharge cells and addressing discharge cells adjacent the display discharge cells.

In comparison to the stripe pattern, the lattice barrier pattern typically exhibits improved vertical resolution and improved light emission efficiency. However, lattice barrier patterns are also recognized by those skilled in the art as being more difficult to manufacture.

Summary of the Invention

Presently described are (e.g.) display panels, methods of molding lattice barrier partitions on a substrate, flexible molds suitable for use in the method of molding lattice barrier partitions, and methods of making a flexible mold.

In one embodiment, a display panel component is described consisting of a plurality of intersecting cell walls comprised of a glass or ceramic material wherein the cell walls have coplanar top surfaces and at least a portion of adjacent rows of cells are separated by sub-cells. In another embodiment, a flexible mold is described comprising a polymeric microstructured surface comprising intersecting groove recesses suitable to form rows of cell structures wherein at least a portion of adjacent rows of cells are separated by sub-cell forming structures.

In another embodiment, a method of molding barrier partitions for a display panel is described comprising providing a curable (e.g. glass or ceramic paste) material between a (e.g. electrode patterned) substrate and the microstructured surface of a flexible mold

(e.g. as just described), curing the curable material, and removing the mold.

In another embodiment, a method of making a flexible mold is described comprising providing a microstructured (e.g. silicone) transfer or (e.g. metal) master mold comprising a plurality of intersecting cell walls wherein at least a portion of adjacent rows of cells are separated by sub-cells, providing a polymerizable resin composition on the microstructured surface of the mold, contacting the surface of polymerizable resin composition (opposite the microstructured surface of the mold) with a (e.g. polymeric film) support, curing the polymerizable resin composition, and removing the cured polymerizable resin composition together with the support, thereby forming a flexible mold.

In some aspects, each adjacent row of cells is separated by sub-cells. In other aspects, every other row of cells is separated by sub-cells. Depending on the purpose of the sub-cells, other arrangements of sub-cells may also be employed. In each of these embodiments, the cells and sub-cells typically have a common width (i.e. in a direction parallel to a row). The sub-cells typically have a length that ranges from one-tenth to one- half the (e.g. average) length of the adjacent cells. The cell walls preferably have a base that consists of the same glass or ceramic material as the cell walls. In order to facilitate removal of the mold without breakage of the molded (e.g. glass or ceramic) microstructures, the cell wall intersections preferably form obtuse angles or form curved peripheral boundaries particularly at the corners of the cells. The cell walls also preferably intersect with a base surface of the cell forming obtuse angles or curved peripheral boundaries. Further, each cell wall preferably has curved peripheral boundaries extending the coplanar top surface.

Brief Description of the Drawings

Fig. 1 is a sectional view schematically showing an illustrative plasma display panel cell. Fig. 2a is a plane view showing a portion of an embodied back panel having cells separated by sub cells.

Fig. 2b is a side view of Fig. 2a depicting the pitch ("p") of the cells and the length of a sub-cells (L_sc).

Fig. 2c is a side view of Fig. 2a depicting the width ("w") of the cells and sub- cells.

Fig. 3 is a plane view showing another embodied back panel having cells separated by sub-cells. Fig. 4 is a sectional view of the cells and lattice pattern barrier partitions taken through curved corner portions of a row of cells.

Detailed Description of the Preferred Embodiments

The invention relates to display panels, methods of molding lattice barrier partitions on a substrate, flexible molds suitable for use in the method of molding lattice barrier partitions, and methods of making flexible mold. In the description that follows, embodiments of the invention will be explained in detail with respect to the production of lattice pattern barrier partitions suitable for a (e.g. plasma) display panel as an exemplary fine structure. However, the invention is surmised useful for other microstructured articles.

A (e.g. plasma) display panel contains a large number of discharge display cells. For example, the number of discharge cells typically ranges from about two to about eighteen million for 42-inch displays. As schematically shown in Fig. 1, each discharge display cell 56 is encompassed and defined by a pair of substrates, 51 and 61, spaced apart from each other in combination with barrier structures 54 arranged between the substrates that separate areas in which red (R), green (G), and blue (B) phosphors are deposited. A transparent substrate 61 (e.g. glass) is provided on the front (i.e. viewing) surface and a back (i.e. non- viewing) substrate 51, is also commonly glass.

The front surface glass substrate 61 is equipped thereon with a transparent display electrode 63 consisting of a scanning electrode and a retaining electrode, a transparent dielectric layer 62 and a transparent protective layer 64. The back surface glass substrate 51 is equipped thereon with an address electrode 53 and a dielectric layer 52. Each discharge display cell 56 has on its inner wall a phosphor layer 55, contains a rare gas (Ne- Xe gas, for example) sealed therein, and can cause spontaneous light emission display due to plasma discharge between the electrodes described above.

With reference to the plane views of Fig. 2-3, an embodied back panel comprises a first row of cells including individual cells 211-216 and a second adjacent row of cells including individual cells 221-226 separated by a row of sub-cells including individual sub-cells 281-286. The sub-cells can serve various purposes. For example, the sub-cells may serve as addressing discharge cells as described in U.S. 6,703,782. When the sub- cells are intended for use as addressing discharge cells, each and every row of cells is typically separated by a row of sub-cells. Alternatively, every other row of cells can be separated by sub-cells such as shown in Fig. 3. This design also provides a sub-cell adjacent each cell. The sub-cells could further be divided into a pair of sub-cells. When the sub-cells are present for other purposes, the sub-cells may be provided in various other arrangements. With reference to Fig. 4, a sectional view of the cells and lattice pattern barrier partitions taken near the corner portion of a row of cells, the height ("h") of the barrier partitions and thus the height of the discharge cell walls are generally at least about 50 μm and typically no greater than about 500 μm. Preferably, the height is at least about 100 μm and no greater than about 300 μm. The top surfaces of the cell walls are generally coplanar, i.e. top surface 548a and 548b lie within the same plane. Accordingly, the cells walls throughout the array have the same height. The array is free of cell walls having a lower height or higher height.

The pitch ("p") of the barrier partitions (i.e. distance from the center of a first barrier partition to the center of a second adjacent parallel barrier partition) is generally at least about 60 μm and typically no greater than about 1 ,000 μm. Preferably, the pitch is at least about 150 μm and no greater than about 800 μm. The pitch corresponds to the cell length.

The width ("Wb") of the barrier partitions is generally at least about 10 μm and typically no greater than about 100 μm. Preferably, the width is at least about 30 μm and no greater than about 80 μm. The width of the barrier partitions may be different at the upper surface than at the lower surface. Typically it is preferred that the barrier partitions are slightly larger at the bottom surface gradually tapering toward the upper surface. In at least some embodiments, it is preferred that the width of the barrier partitions is smaller in width at the upper surface in comparison to the bottom surface such that the included angle to a plane orthogonal to the substrate is no more than 20°. Tapered barrier partitions tend to facilitate removal of the mold in methods of manufacture that involve molding a ceramic paste material.

The cells of the back panel array may have different dimensions (e.g. arranged in a repeating pattern). The cells of the array may have substantially the same dimensions as shown in Fig. 2. The cells and (e.g. adjacent) sub-cell(s) typically have a common width (w), the width being parallel to the direction of a row. The average length of the sub- cell(s) (Lsc) is typically smaller that the average length of the (e.g. adjacent) cells (p). In some embodiments, the average length of the sub-cells is 1/10* to one/half the average length of the cells.

The cells depicted in Figs 2 and 3 are substantially quadrilateral in shape (e.g. square or rectangular). In order to facilitate removal of the mold without breakage of the molded (e.g. glass or ceramic) microstructures, peripheral boundaries of the cells preferably form obtuse angles or form curved peripheral boundaries (e.g. rather than 90° angles or less) as described in U.S. Published Application No. 2007/0071948.

When the cell walls intersect at obtuse angles, i.e. greater than 90°, the cells in plane view are polygons having more than four sides in plane view. The number of sides may range for example from 5 (i.e. pentagons) to 12 for example. Preferably, the obtuse angle is at least 100°, more preferably at least 120°, and more preferably at least 140°.

In some embodiments, it is useful to define the curved surface by a radius of curvature R. The radius of curvature R and the curvature K, are inversely proportional to each other and can be represented by the equation: R= 1/κ

As the radius of curvature R increases, the curvature K, decreases. The radius of curvature R for a curved surface can be described relative to other dimensions of the microstructure, for example, the barrier portion height "h", the barrier portion width "Wb", or the land portion thickness "t" (as depicted in Figure 4), or the cell wall length "p" i.e. distance between opposing (e.g. parallel) barrier partitions.

With reference to Fig. 4, the cell wall intersections preferably form obtuse angles or form curved peripheral boundaries 547 particularly at the corners of the cells. The curved surfaces of the cell wall intersections typically have a radius of curvature of at least 5% of the cell wall length, preferably at least 10%, and more preferably at least 12%. Further, the radius of curvature is typically no greater than 80% of the cell wall length. In at least some embodiments, the preferred radius of curvature is less than about 50% of the barrier partition height and more preferably about 25% or less. When the curvature of the intersecting cell walls spans to the top surface, the cells may be circular or elliptical in plan view.

The cell walls also preferably intersect with the base surface of the cell forming obtuse angles or curved peripheral boundaries. This radius of curvature is in the range of 5% to 80% of the barrier rib height, in the range of 10% to 50% of the barrier rib height, or in the range of 12% to 25% of the barrier rib height.

In addition, each cell wall preferably has curved peripheral boundaries 549 extending from both sides of the coplanar top surfaces 548a and 548b. The radius of curvature is typically at least 3% of the barrier rib width, preferably at least 5%, and more preferably at least 10%. Further, to ensure that the top surfaces 548a and 548b remains coplanar, the radius of curvature is typically no more than 80% of the barrier rib width. In at least some embodiments, the preferred radius of curvature is less than about 75% of the barrier rib width and more preferably about 70% or less.

In some embodiments, the base of the cells may be a different material than the barrier partitions such as when the base of the cell is the electrode patterned glass substrate. In other embodiments, the base of the cells and the cell walls are comprised of the same (e.g. ceramic) material. A continuous layer of curable ceramic material is thus disposed between the substrate of the display and the base of the cells.

In other embodiments, the invention relates to flexible molds having microstructures suitable for molding the lattice barrier partitions comprising sub-cells as just described. In general, the flexible mold has the inverse pattern of the barrier partitions to be made. In some aspects the flexible mold is prepared from a transfer mold (having the same pattern as the barrier partitions), which in turn is prepared from a master mold (having the inverse pattern). Suitable transfer molds are described in JP Application 2004- 001108 filed January 6, 2004. Alternatively, the flexible mold can be prepared directly from a master mold having the same pattern as the barrier partitions such as described in WO 2005/013308. The flexible mold can be produced in accordance with various known methods. The method comprises providing a microstructured mold comprising a plurality of intersecting cells walls that form rows of cells wherein at least a portion of adjacent rows of cells are separated by sub-cells; providing a polymerizable resin composition on the microstructured surface of the mold; contacting the surface of polymerizable resin composition, opposite the microstructured surface of the mold, with a support; curing the polymerizable resin composition; and removing the cured polymerizable resin composition together with the support, thereby forming a flexible mold.

The flexible support film may be comprised of a variety of polymeric materials such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), stretched polypropylene, and polycarbonate and triacetate, etc. For embodiments wherein the curable molding material is photocured, it is preferred that the flexible film has sufficient transparency to transmit the ultraviolet rays irradiated through the flexible film layer. The thickness of the flexible film is generally at least about 50 μm and more typically at least about 100 μm. Further, the flexible film typically has a thickness of less than 500 μm and more typically less than about 400 μm. The flexible film may be surface treated to improve adhesion of the molding material. The flexible film may be preconditioned in a humidity and temperature controlled environment as previously described.

A variety of curable compositions are suitable for use as the molding material. For example, a UV-curable composition containing an acryl monomer and/or oligomer as its main component can advantageously be used. Suitable acryl monomers include urethane acrylate, polyether acrylate, polyester acrylate, acrylamide, acrylonitrile, acrylic acid, acrylic acid ester, etc. Suitable acryl oligomers include urethane acrylate oligomer, polyether acrylate oligomer, polyester acrylate oligomer, epoxy acrylate oligomer, etc. UV-curable compositions typically comprise a photoinitiator and other additives (e.g. antistatic agent) as desired. Preferred compositions are described in U.S. Published Application No. 2006/0231728.

The lattice barrier rib structures described herein are preferably prepared by known methods of molding a curable material (e.g. ceramic paste) with a (e.g. flexible polymeric) mold having a microstructured surface, curing the curable material, and removing the mold. The flexible mold is positioned such that the electrodes will be aligned between the barrier partitions. A transparent mold is advantageous for such positioning since it is possible to locate the electrodes through the mold. The positioning may be conducted manually with eyesight or by use of a sensor such as a charge coupled device camera. Aligning the microstructures of the mold with the (e.g. electrode) patterned substrate may be accomplished by adjusting the humidity and or temperature as described in WO 01/52299 or by means of stretching the mold as described in U.S. Patent No. 6,616,887. A barrier partition precursor composition, such as a curable ceramic paste can be provided between the substrate and the shape-imparting layer of the flexible mold in a variety of ways. The curable material can be placed directly in the pattern of the mold followed by placing the mold and material on the substrate, the material can be placed on the substrate followed by pressing the mold against the material on the substrate, or the material can be introduced into a gap between the mold and the substrate as the mold and substrate are brought together by mechanical or other means. Further, the precursor may be (e.g. uniformly) coated onto the entire surface of the flat glass sheet such as described in WO03/032353.

A (e.g. rubber) roller, typically driven by a motor may be employed to engage the flexible mold with the barrier precursor. The roller is typically placed at one of the end of the mold with the remainder of the mold being unconstrained. As the roller advances, pressure is applied to the mold due to the weight of the roller spreading the precursor between the flat glass sheet and the mold filling the (e.g. groove) recess portions. The air, formerly filling the recesses, is discharged towards the periphery and then outside the mold.

After forming the precursor into lattice patterned barrier partitions with the mold, the precursor is cured. The precursor is preferably cured by exposure to (e.g. UV) light rays through the transparent substrate and/or through the mold resulting in cured barrier partitions bonded to the electrode patterned substrate.

The barrier partitions (e.g. together with the flat glass sheet having preapplied electrodes) are sintered or fired. Firing temperatures may vary widely from about 400⁰C to 1600⁰C, but typical firing temperatures for PDPs manufactured onto soda lime glass substrates range from about 400⁰C to about 600⁰C, depending on the softening temperature of the ceramic powder in the slurry. The front substrate preferably has the same or about the same coefficient of thermal expansion as that of the back substrate.

The curable rib precursor (also referred to as "slurry" or "paste") typically comprises at least three components. The first component is a glass- or ceramic- forming particulate material (e.g. powder). The powder will ultimately be fused or sintered by firing to form microstructures. The second component is a curable organic binder capable of being shaped and subsequently hardened by curing, heating or cooling. The binder allows the slurry to be shaped into rigid or semi-rigid "green state" microstructures. The binder typically volatilizes during debinding and firing and thus may also be referred to as a "fugitive binder". The third component is a diluent. The diluent typically promotes release from the mold after hardening of the binder material. Alternatively or in additional thereto, the diluent may promote fast and substantially complete burn out of the binder during debinding before firing the ceramic material of the microstructures. The diluent preferably remains a liquid after the binder is hardened so that the diluent phase-separates from the binder material during hardening. The rib precursor preferably has a viscosity of less than 20,000 cps and more preferably less than 5,000 cps to uniformly fill all the microstructured groove portions of the flexible mold without entrapping air.

Photocurable rib precursor compositions further comprise one or more photoinitiators at a concentrations ranging from 0.01 wt-% to 1.0 wt-% of the polymerizable resin composition. Suitable photointitiators include for example, 2- hydroxy-2 -methyl- 1 -phenylpropane- 1 -one; 1 -[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2- methyl- 1 -propane- 1 -one; 2,2-dimethoxy- 1 ,2-diphenylethane- 1 -one; 2-methyl- 1 -[4- (methylthio)phenyl]-2-morpholino-l-propanone; and mixtures thereof.

The rib precursor may optionally comprise various additives including but not limited to surfactants, catalysts, etc. as known in the art. For example, the rib precursor may comprise 0.1 to 1 parts by weight of a phosphorus-based compound alone or in combination with 0.1 to 1 parts by weight of a sulfonates based compounds. Such compounds are described in PCT Publication No. WO2005/019934. Further, the rib precursor may comprise an adhesion promoter such as a silane coupling agent to promote adhesion to the substrate (e.g. glass panel of PDP).

The amount of curable organic binder in the rib precursor composition is typically at least 2 wt-%, more typically at least 5 wt-%, and more typically at least 10 wt-%. The amount of diluent in the rib precursor composition is typically at least 2 wt-%, more typically at least 5 wt-%, and more typically at least 10 wt-%. The totality of the organic components is typically at least 10 wt-%, at least 15 wt-%, or at least 20 wt-%. Further, the totality of the organic compounds is typically no greater than 50 wt-%. The amount of inorganic particulate material is typically at least 40 wt-%, at least 50 wt-%, or at least 60 wt-%. The amount of inorganic particulate material is no greater than 95 wt-%. The amount of additive is generally less than 10 wt-%.

A preferred ceramic paste composition is described in Published U.S. Application No. 2006/0235107. The flexible mold and replications thereof are surmised suitable for the manufacture of other fine structure patterns such as (e.g. disposable) microfluidic articles that are useful in detecting and enumerating microorganisms. Microfluidic articles may be formed from a plurality of microcompartments in a culture device as well as a biological or chemical assay device. For example, the fine structured pattern can be advantageously used in the form of articles disclosed in U.S. Patent No. 6,696,286.

Examples

Example 1 A lattice patterned master tool was prepared as described in WO2005/013308 and depicted in Fig. 1. The vertical partition (i.e. cell wall parallel to a column) had a top width of 0.04 mm (40 microns), a bottom width of 0.10 mm (100 microns), and a height of 0.11 mm (110 microns). The lateral partition (i.e. cell wall parallel to a row) had a top width of 0.03 mm (30 microns), a bottom width of 0.16mm (160) microns, and a height of 0.11 mm (110 microns). The lateral partitions intersected the vertical partitions forming substantially rectangular shaped cells having a radius of curvature of 90 microns at the partition intersections.

A flexible mold was prepared from the master tool using a UV curable resin prepared from 80 parts by weight (pbw) of Ebecryl 270 acrylated urethane oligomer, 20 pbw phenoxyethylacrylate monomer, and 1 wt-% of 2-hydroxyl-2-methyl-l-phenyl-propane-l- on photinitiator manufactured by Ciba-Gigy under the trade designation "Darocure 1173"). The acrylate was filled between the master tool and PET film, cured by exposure of 300-400 nm wavelength light for 30 sec and released together with the PET film from the master tool to obtain a flexible plastic mold.

A photocurable ceramic paste was made as follows. 21.0 g of dimethacrylate of bisphenol A diglycidyl ether (Kyoeisha Chemical Co., Ltd.), 9.0 g of triethylene glycol dimethacrylate (Wako Pure Chemical Industries, Ltd.), 30.0 g of 1,3-butandiol (Wako Pure Chemical Industries, Ltd.), 0.3 g of bis(2,4,6-trimethylbensoil)- phenylphosphyneoxide photointiator (Ciba-Gigy under the trade designation "Irgacure 819"), 3.0 g of POCA (phosphateed polyoxyalkyl polyol) 180.0 g of a mixture of glass frit and ceramic particles (RFW-030, made byAsahi Glass Co) were mixed to obtain the photocurable glass paste.

The paste was coated on a glass substrate at a thickness of 0.08-0.10 mm (80 -100 microns) using a blade coater, and then the flexible mold was laminated on the paste by rubber roller. The lamination direction is parallel to vertical grooves. After the lammination, 400-500 nm wavelength light was exposed for 30 seconds to cure the paste and then the flexible mold was released from the substrate to obtain lattice- pattern partition. The de-molding was done in parallel to vertical partition with 90 deg peel angle.

No rib defects were found.

Claims

What is claimed is:

1. A display panel component consisting of intersecting cell walls comprised of a glass or ceramic material wherein the cells walls have coplanar top surfaces and at least a portion of adjacent rows of cells are separated by sub-cells.

2. The display panel of claim 1 wherein the cells and sub-cells have a common width.

3. The display panel of claim 1 wherein the cells adjacent a sub-cell have an average length and the sub-cell has a length that ranges from one-tenth to one-half the average length of the adjacent cells.

4. The display panel of claim 1 wherein the cell walls have a base that consists of the same glass or ceramic material as the cell walls.

5. The display panel of claim 1 wherein the cell wall intersections form obtuse angles or form curved peripheral boundaries.

6. The display panel of claim 1 wherein the cell walls intersect with a base surface of the cells forming obtuse angles or curved peripheral boundaries.

7. The display panel of claim 1 wherein the cell walls have curved peripheral boundaries extending from the coplanar top surfaces.

8. The display panel of claim 1 wherein each adjacent row of cells is separated by sub- cells.

9. The display panel of claim 1 wherein every other row of cells is separated by sub-cells

10. A flexible mold comprising a polymeric microstructured surface comprising intersecting groove recesses suitable to form rows of cells wherein at least a portion of adjacent rows of cells are separated by sub-cells.

11. The flexible mold of claim 10 wherein the microstructured surface is disposed on a polymeric film support.

12. A method of molding barrier partitions for a display panel comprising: providing a flexible microstructured mold according to claim 10; providing a curable material between the microstructured surface and a substrate such that the groove recesses are filled with the curable material; curing the curable material; and removing the mold.

13. The method of claim 12 wherein the recesses form cell walls from the curable material.

14. The method of claim 13 wherein the cell walls have coplanar top surfaces.

15. The method of claim 12 wherein the groove recesses are filled with the curable material by laminating the mold to the substrate in a lamination direction.

16. The method of claim 13 wherein the groove recesses are continuous in a direction parallel to a column and the lamination direction is parallel to the column.

17. The method of claim 16 wherein the groove recesses are continuous in a direction parallel to a row.

18. The method of claim 12 wherein the mold is transparent.

19. The method of claim 18 wherein the curing comprises photocuring through the mold, through the glass panel, or a combination thereof.

20. A method of making a flexible mold comprising providing a microstructured mold comprising a plurality of intersecting cells walls that form rows of cells wherein at least a portion of adjacent rows of cells are separated by sub- cells; providing a polymerizable resin composition on the microstructured surface of the mold; contacting the surface of polymerizable resin composition, opposite the microstructured surface of the mold, with a support; curing the polymerizable resin composition; and removing the cured polymerizable resin composition together with the support, thereby forming a flexible mold.