WO2008073719A1

WO2008073719A1 - Method of molding barrier ribs with hygroscopic polymeric molds

Info

Publication number: WO2008073719A1
Application number: PCT/US2007/085997
Authority: WO
Inventors: Akira Yoda; Hiroshi Kikuchi
Original assignee: 3M Innovative Properties Company
Priority date: 2006-12-07
Filing date: 2007-11-30
Publication date: 2008-06-19
Also published as: TW200903570A

Abstract

The present invention relates to a method of making a flexible mold with a hygroscopic support, the flexible mold, and methods of using the mold to make microstructures.

Description

Method of Molding Barrier Ribs With Hygroscopic Polymeric Molds

Background Advancements in display technology, including the development of plasma display panels (PDPs) and plasma addressed liquid crystal (PALC) displays, have led to an interest in forming electrically-insulating barrier ribs on glass substrates. The barrier ribs separate cells in which an inert gas can be excited by an electric field applied between opposing electrodes. The gas discharge emits ultraviolet (UV) radiation within the cell. In the case of PDPs, the interior of the cell is coated with a phosphor that gives off red, green, or blue visible light when excited by UV radiation. The size of the cells determines the size of the picture elements (pixels) in the display. PDPs and PALC displays can be used, for example, as the displays for high definition televisions (HDTV) or other digital electronic display devices. One way in which barrier ribs can be formed on glass substrates is by direct molding. This has involved laminating a mold onto a substrate with a glass- or ceramic- forming composition disposed therebetween. Suitable compositions are described for example in U.S. Patent No. 6,352,763. The glass- or ceramic- forming composition is then solidified and the mold is removed. Finally, the barrier ribs are fused or sintered by firing at a temperature of about 550⁰C to about 1600⁰C. The glass- or ceramic-forming composition has micrometer-sized particles of glass frit dispersed in an organic binder. The use of an organic binder allows barrier ribs to be solidified in a green state so that firing fuses the glass particles in position on the substrate. See for example WO 2004/010452, WO 2004/043664, and JP Application No. 2004-108999. The mold for producing the barrier ribs may be a flexible mold. The flexible mold may comprise a support and a shape-imparting layer comprising the reaction product of at least one (meth)acryl oligomer and at least one (meth)acryl monomer as described in WO2006/113412. The flexible mold may be produced from a transfer mold having substantially the same microstructured pattern as the eventual barrier ribs. US2005/0212182 describes a flexible mold comprising a support containing a moisture to saturation at a temperature and a relative humidity at the time of use by a moisture absorption treatment applied in advanced. As described in paragraph 0031 when the PET film is allowed to sufficiently absorb moisture to stabilize its dimension and is then used to manufacture the mold, dimensional changes of the mold after manufacture can be suppressed.

Brief Description of the Drawings

Fig. 1 is a perspective view of an illustrative flexible mold suitable for making barrier ribs.

Fig. 2 is a perspective view of an illustrative transfer mold suitable for making the flexible mold of Fig. 1 Fig. 3A-3C is a sectional view, in sequence, showing an illustrative method of making a flexible mold from a transfer mold.

Fig. 4A-4C is a section view, in sequence of an illustrative method of making a fine structure (e.g. barrier ribs) by use of a flexible mold.

Detailed Description of the Preferred Embodiments The present invention relates to a method of making a flexible mold, the flexible mold, and methods of using the mold to make microstructures. Hereinafter, the embodiments of the invention will be explained with reference to a flexible mold suitable for making microstructures such as barrier ribs. The polymerizable resin and flexible mold can be utilized with other (e.g. microstructured) devices and articles such as for example, electrophoresis plates with capillary channels and lighting applications.

The recitation of numerical ranges by endpoints includes all numbers subsumed within the range (e.g. the range 1 to 10 includes 1, 1.5, 3.33, and 10).

Unless otherwise indicated, all numbers expressing quantities of ingredients, measurements of properties, and so like as used in the specification and claims are to be understood to be modified in all instances by the term "about."

("Meth)acryl" refers to functional groups including acrylates, methacrylates, acrylamide, and methacrylamide.

"(Meth)acrylate" refers to both acrylate and methacrylate compounds. Fig. 1 is a partial perspective view showing an illustrative (e.g. flexible) mold 100. The flexible mold 100 generally has a two-layered structure having a planar support layer 110 and a microstructured surface, referred to herein as a shape-imparting layer 120 provided on the support. The flexible mold 100 of Fig. 1 is suitable for producing a grid- like rib pattern (also referred to as a lattice pattern) of barrier ribs on a (e.g. electrode patterned) back panel of a plasma display panel. Another common barrier ribs pattern (not shown) comprises plurality of (non-intersecting) ribs arranged in parallel with each other, also referred to as a linear pattern. The flexible mold will be suitable sized depending on the size of the finished article (e.g. display panel). For example, the flexible mold may be rectangular in shape (700 mm X 400 mm).

The depth, pitch, and width of the microstructures of the shape-imparting layer can vary depending on the desired finished article. The depth of the microstructured (e.g. groove) pattern 125 (corresponding to the barrier rib height) is generally at least 100 μm and typically at least 150 μm. Further, the depth is typically no greater than 500 μm and typically less than 300 μm. The pitch of the microstructured (e.g. groove) pattern may be different in the longitudinal direction in comparison to the transverse direction. The pitch is generally at least 100 μm and typically at least 200 μm. The pitch is typically no greater than 600 μm and preferably less than 400 μm. The width of the microstructured (e.g. groove) pattern 4 may be different between the upper surface and the lower surface, particularly when the barrier ribs thus formed are tapered. The width is generally at least 10 μm, and typically at least 50 μm. Further, the width is typically no greater than 100 μm and typically less than 80 μm.

The thickness of a representative shape-imparting layer is at least 5 μm, typically at least 10 μm, and more typically at least 50 μm. Further, the thickness of the shape- imparting layer is no greater than 1,000 μm, typically less than 800 μm and more typically less than 700 μm. When the thickness of the shape-imparting layer is below 5 μm, the desired rib height typically cannot be obtained. When the thickness of the shape- imparting layer is greater than 1,000 μm, warp and reduction of dimensional accuracy of the mold can result due to excessive shrinkage. The thickness of the polymeric support film is typically at least 0.025 millimeters, and typically at least 0.075 millimeters. Further the thickness of the polymeric support film is generally less than 0.5 millimeters and typically less than 0.300 millimeters. The tensile strength of the polymeric support film is generally at least about 5 kg/mm² and typically at least about 10 kg/mm². The polymeric support film typically has a glass transition temperature (Tg) of about 60⁰C to about 200⁰C.

The flexible mold is typically prepared from a transfer mold or master mold, having a corresponding inverse microstructured surface pattern as the flexible mold. For example, a perspective view of an illustrative transfer or master mold 200 suitable for making the flexible mold of Fig. 1 is depicted in Fig. 2. A sectional view of transfer mold 200 of Fig. 2 taken along line IV-IV is depicted in Fig. 3 A. The transfer mold may have a microstructured surface comprised of a cured (e.g. silicone rubber) polymeric material, such as described in Published U.S. Application No. 205/0206034. Alternatively, a master mold (e.g. having a metal support layer) can be prepared as described in WO 2005/013308.

In an embodied method of manufacture as depicted in Fig. 3A-3C of the flexible mold (e.g. of Fig. 1) with a transfer mold (e.g. of Fig. 2), a polymerizable resin composition 350 is provided at least in the recesses of the microstructured surface of the polymeric transfer or master mold 200. This can be accomplished with known customary coating means such as a knife coater or a bar coater. A support 380 comprising a flexible polymeric film is stacked onto the polymerizable resin filled mold such that the resin contacts the support. While stacked in this manner, the polymerizable resin composition is cured. Photocuring is typically preferred. For this embodiment, it is preferred that the support as well as the polymerizable composition are sufficiently optically transparent such that rays of light irradiated for curing can pass through the support. Typically, the flexible mold has a haze (as measured according to the test method described in the examples) of less than 15%, typically less than 10% and more typically no greater than 5%. Once cured, the flexible mold 100, having support film 380 integrally bonded to the shape-imparting layer formed from the cured polymerizable resin, is separated from the transfer mold 200.

In the method of making the mold of the present invention, a hygroscopic polymeric support is conditioned and the mold is prepared in a suitable environment having a first temperature and relative humidity. The (i.e. first) temperature and/or relative humidity utilized during the method of making the mold is different than the (i.e. second) temperature and/or relative humidity the mold is subjected to during the method of making the ceramic microstructures. In doing so, the dimensions (e.g. pitch) of the microstructures of the mold can be adjusted during the mold making process. This aspect is particularly useful when the master mold or transfer mold from which the flexible mold is formed has dimensions (e.g. pitch) that are greater than or less than a target dimension, the target dimension being the dimension of the (e.g. ceramic barrier rib) microstructures that are subsequently formed from the flexible mold. If the flexible mold were used to mold a ceramic paste at the same conditions (i.e. temperature and relative humidity) as utilized during the mold making operation, then the microstructure dimensions (e.g. pitch) of the mold are the same at the time it was made in comparison to the time the mold is used to mold the ceramic paste.

In some aspects, the first and second temperature are substantially the same (i.e. the difference is not such that the mold dimensions can be adjusted. Accordingly, the first relative humidity differs from the second relative humidity. When for example the pitch of the master or transfer mold is greater than the target, the (i.e. first) relative humidity of the mold making environment is typically greater than the (i.e. second) temperature and/or relative humidity employed during the method of using the mold to make ceramic microstructures. Accordingly, the microstructures swells such that the pitch of the mold can be reduced to the target dimension during the method of making the mold. Conversely, when the pitch of the master or transfer mold is less than the target, the temperature and/or relative humidity of the mold making environment is typically lower to shrink the microstructures thereby increasing the pitch to the target dimensions. The difference in relative humidity between the first and second relative humidity can vary from about 1%RH to as much as about 40%RH. Typically, the environment in which the mold is prepared has a (i.e. first temperature and relative humidity) that is the same or relatively close to the temperature and relative humidity employed to precondition the hygroscopic support. For example, the difference is typically no greater than about 10%RH (e.g. 9%RH, 8%RH, 7%RH, 6%RH, 5%RH, 4%RH) and may be as little as 1%RH, 2%RH, or 3%RH. The first temperature and relative humidity is also relatively close but not equal to the second temperature and relative humidity. In doing so, the adjustment of the microstructures during the method of making the mold is typically on the order of magnitude of up to about 5 ppm per percent relative humidity.

Various hygroscopic plastic film materials can be used for the support of the flexible mold such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), stretched polypropylene, polycarbonate, and cellulose triacetate. These plastic films may be used either as a single-layered film or as a composite or laminate film of two or more kinds in combination. The surface of the support may be treated to promote adhesion to the polymerizable resin composition. Examples of suitable polyester based materials include photograde polyethylene terephthalate and polyethylene terephthalate (PET) having a surface that is formed according to the method described in U.S. Pat. No. 4,340,276.

The preconditioning of the hygroscopic support may include applying moisture to the plastic film before being used to make the mold. Suitable means for applying moisture include spraying or immersing the film into (e.g. hot) water, or by passing the film through a high-temperature high-humidity atmosphere such as steam. Typically, the plastic film is conditioned in a temperature and humidity controlled chamber to obtain the desired first humidity.

Flexible mold 100, can be used to produce (e.g. barrier rib) microstructures on a substrate such as a (e.g. plasma) display panel. Prior to use in the method, the transfer mold and support film are typically conditioned in a humidity and temperature controlled chamber (e.g. 22°C/55% relative humidity) to minimize any dimensional changes thereof. In view of the dimensional adjustments of the microstructures that are accomplished by use of the different (i.e. first) relative humidity employed during the making of the flexible mold, the mold typically has the target dimensions and thus requires no further adjustment such as described in WO 2004/043664.

With reference to Fig. 4A-4C, a flat transparent (e.g. glass) substrate 41, having an (e.g. striped) electrode pattern is provided. The flexible mold 100 of the invention is positioned for example by use of a sensor such as a charge coupled device camera, such that the barrier pattern of the mold is aligned with the electrode pattern of the substrate. A barrier rib precursor 45 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. As depicted in Fig. 4A, a (e.g. rubber) roller 43 may be employed to engage the flexible mold 100 with the barrier rib precursor. The rib precursor 45 spreads between the glass substrate 41 and the shape-imparting surface of the mold 100 filling the groove portions of the mold. In other words, the rib precursor 45 sequentially replaces air of the groove portions. Subsequently, the rib precursor is cured. The rib precursor is preferably cured by radiation exposure to (e.g. UV) light rays through the transparent substrate 41 and/or through the mold 100 as depicted on Fig. 4B. As shown in Fig. 4C, the flexible mold 100 is removed while the resulting cured ribs 45 remain bonded to the substrate 41.

Although the mold may comprise other (e.g. cured) polymeric materials, at least the (e.g. microstructured surface) molding surface of the mold comprises the photopolymerized reaction product of a polymerizable composition generally comprising at least one ethylenically unsaturated oligomer and at least one ethylenically unsaturated diluent. The ethylenically unsaturated diluent is copolymerizable with the ethylenically unsaturated oligomer. The oligomer generally has a weight average molecular weight (Mw) as determined by Gel Permeation Chromatography (described in greater detail in the example) of at least 1,000 g/mole and typically less than 50,000 g/mole. The ethylenically unsaturated diluent generally has a Mw of less than 1,000 g/mole and more typically less than 800 g/mole.

The oligomer and monomer have functionality that react (e.g. crosslink) upon exposure to light. Representative examples of photopolymerzable groups include epoxy groups, (meth)acrylate groups, olefmic carbon-carbon double bonds, allyloxy groups, alpha-methyl styrene groups, (meth)acrylamide groups, cyanate ester groups, vinyl ethers groups, combinations of these, and the like. Free radically polymerizable groups are preferred. Of these, (meth)acryl functionality is typical and (meth)acrylate functionality more typical. Typically at least one of the ingredients of the polymerizable composition, and most typically the oligomer, comprises at least two (meth)acryl groups. Various known oligomers having (meth)acryl functional groups can be employed. Suitable oligomers include (meth)acrylated urethanes (i.e., urethane (meth)acrylates), (meth)acrylated epoxies (i.e., epoxy (meth)acrylates), (meth)acrylated polyesters (i.e., polyester (meth)acrylates), (meth)acrylated (meth)acrylics, (meth)acrylated polyethers (i.e., polyether (meth)acrylates) and (meth)acrylated polyolefins. The oligomer(s) and monomer(s) preferably have a glass transition temperature (Tg) of about -80⁰C to about 60⁰C, respectively, meaning that the homopolymers thereof have such glass transition temperatures.

The oligomer is generally combined with the monomer in amounts of 5 wt-% to 90 wt-% of the total polymerizable composition of the mold. Typically, the amount of oligomer is at least 20 wt-%, more typically at least 30 wt-%, and more typically at least 40 wt-%. In at least some preferred embodiments, the amount of oligomer is at least 50 wt-%, 60 wt-%, 70 wt-%, or 80 wt-%.

In some embodiments, the polymerizable composition of the flexible mold may comprise one or more urethane (meth)acrylate oligomers such as commercially available from Daicel-UCB Co., Ltd. under the trade designation "EB 270" and "EB 8402". In other embodiments, the polymerizable composition of the flexible mold may comprise one or more polyolefm (meth)acrylate oligomers such as commercially available from Osaka Organic Chemical Industry Ltd., under the trade designation "SPDBA". Other suitable flexible mold compositions are known.

Various (meth)acryl monomers are known including for example aromatic (meth)acrylates including phenoxyethylacrylate, phenoxyethyl polyethylene glycol acrylate, nonylphenoxy polyethylene glycol, 3-hydroxyl-3-phenoxypropyl acrylate and (meth)acrylates of ethylene oxide modified bisphenol; hydroxyalkyl (meth)acrylates such as 4-hydroxybutylacrylate; alkylene glycol (meth)acrylates and alkoxy alkylene glycol

(meth)acrylates such as methoxy polyethylene glycol monoacrylate and polypropylene glycol diacrylate; polycaprolactone (meth)acrylates; alkyl carbitol (meth)acrylates such as ethylcarbitol acrylate and 2-ethylhexylcarbitol acrylate; as well as various multifunctional (meth)acryl monomers including 2-butyl-2-ethyl-l,3-propanediol diacrylate and trimethylolpropane tri(meth)acrylate.

Preferred polymerizable compositions for use in making the flexible mold are described in published U.S. Patent Application No. 2006/0231728. The photocurable rib precursor (also referred to as "slurry" or "paste") comprises at least three components in addition to the photoinitiator just described. 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 semirigid "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 composition preferably has a viscosity of less than 20,000 cps and more preferably less than 10,000 cps to uniformly fill all the microstructured groove portions of the flexible mold without entrapping air. The rib precursor composition preferably has a viscosity of between about 20 to 600 Pa-S at a shear rate of 0.1/sec and between 1 to 20 Pa-S at a shear rate of 100/sec.

Various curable organic binders can be employed. The curable organic binder is curable for example by exposure to radiation or heat. The binder may comprise monomers and oligomers in any combination, so long as the mixture with inorganic particulate material has a suitable viscosity. It is typically preferred that the binder is radiation curable under isothermal conditions (i.e. no change in temperature). This reduces the risk of shifting or expansion due to differential thermal expansion characteristics of the mold and the substrate, so that precise placement and alignment of the mold can be maintained as the rib precursor is hardened.

The diluent is not simply a solvent compound for the resin. The diluent is preferably soluble enough to be incorporated into the resin mixture in the uncured state. Upon curing of the binder of the slurry, the diluent should phase separate from the monomers and/or oligomers participating in the cross-linking process. Preferably, the diluent phase separates to form discrete pockets of liquid material in a continuous matrix of cured resin, with the cured resin binding the particles of the glass frit or ceramic powder of the slurry. In this way, the physical integrity of the cured green state microstructures is not greatly compromised even when appreciably high levels of diluent are used (i.e., greater than about a 1 :3 diluent to resin ratio). This provides two advantages. First, by remaining a liquid when the binder is hardened, the diluent reduces the risk of the cured binder material adhering to the mold. Second, by remaining a liquid when the binder is hardened, the diluent phase separates from the binder material, thereby forming an interpenetrating network of small pockets, or droplets, of diluent dispersed throughout the cured binder matrix which facilitates the debinding process.

Optionally, the photocurable rib precursor compositions may comprise a dispersant and/or a thixotropic agent. Each of these additives may be employed in amounts from about 0.05 to 2.0 wt-% of the total rib precursor composition. Typically, the amount of each of these additives is no greater than about 0.5 wt-%. 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 rib precursor may also optionally comprise various additives including but not limited to surfactants, catalysts, etc. as known in the art.

In general, inorganic thixotropes may comprise clays (e.g. bentonite), silica, mica, smectite and others, having particles sizes of less than 0.1 μm. In general, organic thixotropes may comprise fatty acids, fatty acid amines, hydrogenated castor oil, casin, glue, gelatin, gluten, soybean protein, ammonium alginate, potassium alginate, sodium alginate, gum arabic, guar gum, soybean lecithin, pectin acid, starch, agar, polyacrylic acid ammonium, sodium polyacrylate, ammonium polymethacrylate, potassium salt, (e.g. modified acrylic polymers and copolymers, polyhydroxycarboxylic acid amines and amides (such as available from BYK-Chemie Co. under the trade designation "BYK 405"), polyvinyl alcohol, vinyl polymer (vinyl methyl ether/maleic anhydride), vinyl pyrrolidone copolymer, polyacrylamide, fatty acid amide or other aliphatic amide compound, carboxylated methylcellulose, hydroxymethycellulose, hydroxyethylcellulose, xanthic acid cellulose, carboxylated starch, urea urethane, oleic acid, and sodium silicate. In some aspects, the dispersant is a basic polymer, i.e. a homopolymer, oligomer, or copolymer of at least one moderately to strongly polar Lewis base-functional copolymerizable monomer. Polarity (e.g. hydrogen or ionic bonding ability) is frequently described by the use of terms such as "strongly", "moderately" and, "poorly". References describing these and other solubility terms include "Solvents paint testing manual", 3rd ea., G. G. Seward, Ed., American Society for Testing and Materials, Philadelphia, Pennsylvania, and "A three-dimensional approach to solubility", Journal of Paint Technology, Vol. 38, No. 496, pp. 269-280. Various basic polymer dispersants are known such as an anionic polyamide based polymeric dispersant commercially available from

Ajinomoto-Fine-Techno Co. under the trade designation "Ajisper PB 821".

In other embodiments, an acidic polymer may be employed as a dispersant. For example, the rib precursor may comprise 0.1 to 1 parts by weight of a phosphorus-based compound having at least one phosphorus-acid group alone or in combination with 0.1 to 1 parts by weight of a sulfonates based compound. Such compounds are described in

WO2005/019934. Other acidic polymer for use as dispersants are commercially available such as from Noveon under the trade designation "SolPlus D520".

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-%.

The paste can be prepared by conventional mixing techniques. For example, the glass- or ceramic- forming particulate material (e.g. powder) can be combined with diluent and dispersant at a ratio of about 10 to 15 parts by weight of diluent; followed by the addition of the remainder of the paste ingredients. The paste is typically filtered to 5 microns.

In preferred embodiments, the flexible mold can be reused. The number of times the flexible mold can be reused relates to the rib precursor composition employed in the method for making the microstructures. By proper selection of the rib precursor composition as described herein, the flexible mold can be reused any number of times ranging from at least one reuse to at least 5 reuses. In preferred embodiments the polymeric transfer mold can be reused at least 10 times, at least 15 times, at least 20 times, or at least 30 times. The transfer mold can be reused when the extent of swelling of the microstructured surface of the flexible mold is less than 10% and more typically less than 5%, as can be determined by visual inspection with a microscope.

For embodiments wherein the rib precursor is cured through the flexible mold, the flexible mold is suitable for reuse when the flexible mold is sufficiently transparent. A sufficiently transparent flexible mold typically has a haze (as measured according to the test method described in the examples) of less than 15%, preferably of less than 10% and more preferably no greater than 5% after a single use. Even more preferably, the flexible mold has the haze criteria just described after being reused at least 5 times. In preferred embodiments, the rib precursor comprises a diluent having a solubility parameter that is less than the curable organic binder.

The solubility parameter of various monomers, δ(delta), can conveniently be calculated using the expression: δ = (ΔEv / V)^1/2, where ΔEv is the energy of vaporization at a given temperature and V is the corresponding molar volume. According to Fedors' method, the SP can be calculated with the chemical structure (R.F.Fedors, Polym. Eng. ScL, 14(2), p.147, 1974, Polymer Handbook 4^th Edition "Solubility Parameter Values" edited by J.Brandrup, E.H.Immergut and E.A.Grulke). The difference between the solubility parameter of the curable binder and the diluent is at least 1 [MJ/m³]^1/2 and typically at least 2 [MJ/m³]^1/2. The difference between the solubility parameter of the curable binder and the diluent is preferably at least 3 [MJ/m³]^1/2, 4 [MJ/m³]^1/2, or 5 [MJ/m³]^1/2. The difference between the solubility parameter of the curable binder and the diluent is more preferably at least 6 [MJ/m³]^1/2, 7 [MJ/m³]^1/2, or 8 [MJ/m³]^1/2. Various organic diluents can be employed depending on the choice of curable organic binder. In general suitable diluents include various alcohols and glycols such as alkylene glycol (e.g. ethylene glycol, propylene glycol, tripropylene glycol), alkyl diol (e.g. 1, 3 butanediol,), and alkoxy alcohol (e.g. 2-hexyloxyethanol, 2-(2-hexyloxy)ethanol, 2-ethylhexyloxyethanol); ethers such as dialkylene glycol alkyl ethers (e.g. diethylene glycol monoethyl ether, dipropylene glycol monopropyl ether, tripropylene glycol monomethyl ether); esters such as lactates and acetates and in particular dialkyl glycol alkyl ether acetates (e.g. diethylene glycol monoethyl ether acetate); alkyl succinate (e.g. diethyl succinate), alkyl glutarate (e.g. diethyle glutarate), and alkyl adipate (e.g. diethyl adipate).

The glass- or ceramic- forming particulate material (e.g. powder) is chosen based on the end application of the microstructures and the properties of the substrate to which the microstructures will be adhered. One consideration is the coefficient of thermal expansion (CTE) of the substrate material (e.g. glass panel of PDP). Preferably, the CTE of the glass- or ceramic- forming material of the slurry of the present invention differs from the CTE of the substrate material (e.g. electrode patterned glass panel of a PDP) by no more than 10%. When the substrate material has a CTE which is much less than or much greater than the CTE of the ceramic material of the microstructures, the microstructures can warp, crack, fracture, shift position, or completely break off from the substrate during processing. Further, the substrate can warp due to a high difference in CTE between the substrate and the fired microstructures. Inorganic particulate materials suitable for use in the slurry of the present invention preferably have coefficients of thermal expansion of about 5 X 10^"6/°C to 13 X 10^"6/°C .

Glass and/or ceramic materials suitable for use in the slurry of the present invention typically have softening temperatures below about 600⁰C, and usually above 400⁰C. The softening temperature of the ceramic powder indicates a temperature that must be attained to fuse or sinter the material of the powder. The substrate generally has a softening temperature that is higher than that of the ceramic material of the rib precursor. Choosing a glass and/or ceramic powder having a low softening temperature allows the use of a substrate also having a relatively low softening temperature.

Suitable composition include for example i) ZnO and B2O3; ii) BaO and B2O3; iii) ZnO, BaO, and B2O3; iv) La₂θ3 and B2O3; and v) AI2O3, ZnO, and P2O5. Lower softening temperature ceramic materials can be obtained by incorporating certain amounts of lead, bismuth, or phosporous into the material. Other low softening temperature ceramic materials are known in the art. Other fully soluble, insoluble, or partially soluble components can be incorporated into the ceramic material of the slurry to attain or modify various properties. The preferred size of the particulate glass- or ceramic- forming material of the rib precursor depends on the size of the microstructures to be formed and aligned on the patterned substrate. The average size, or diameter, of the particles is typically no larger than about 10% to 15% the size of the smallest characteristic dimension of interest of the microstructures to be formed and aligned. For example, the average particle size for PDP barrier ribs is typically no larger than about 2 or 3 microns.

The photocurable polymerizable compositions for use in making the mold or for use as a binder in making the ceramic microstructures preferably comprises one or more photoinitiators at a concentrations ranging from 0.05 wt-% to 5 wt-% of the polymerizable resin composition. Suitable photoinitiators include for example, 2-hydroxy-2-methyl-l- phenylpropane- 1 -one; 1 -[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy -2 -methyl- 1 -propane- 1 - one; 2,2-dimethoxy-l ,2-diphenylethane- 1 -one; 2-methyl- 1 -[4-(methylthio)phenyl]-2- morpholino-1-propanone; and mixtures thereof. Suitable photoinitiator combinations are described in U.S. Patent No. 6843952 and pending U.S. Patent Application Serial No.

11/538933, filed October 5, 2006.

Various other aspects that may be utilized in the invention described herein are known in the art including, but not limited to each of the following patents: U.S. Patent No. 6,247,986; U.S. Patent No. 6,537,645; U.S. Patent No. 6,352,763; U.S. 6,843,952,

U.S. 6,306,948; WO 99/60446; WO 2004/062870; WO 2004/007166; WO 03/032354;

WO 03/032353; WO 2004/010452; WO 2004/064104; U.S. Patent No. 6,761,607; U.S.

Patent No. 6,821,178; WO 2004/043664; WO 2004/062870; WO2005/042427;

WO2005/019934; WO2005/021260; and WO2005/013308.

The present invention is illustrated by the following non-limiting examples.

Examples:

Hygroscopic Polymeric Support Preconditioning

As a hygroscopic polymeric support for use in the manufacture of the mold, 4 different samples of 250 micron thick polyester film (trade name: Tetron film HS250, manufactured by Teijin Dupont Film ) were each preconditioned for 24 hours using 3 different preconditioning environments.

Support Preconditioning A: 22 degree C / 55% RH Support Preconditioning B: 22 degree C / 58% RH

Support Preconditioning C: 22 degree C / 61% RH

Preparation of Master Tool

A master tool having lattice type PDP barrier rib pattern in was prepared. A rectangular transfer mold was made from a metal master tool, using silicone material and a stainless steel substrate, as described in WO2005/013308 and published U.S. Patent Application No. U.S. 2005/0206034-A1. The cell pitch was 0.270 mm in the direction of the longer side and 0.808 mm in the direction of the shorter side.

Preparation of Flexible Mold

A photocurable resin for use as the shape-imparting layer of the mold was prepared as follows:

Aliphatic urethane acrylate oligomer 80 parts

(Ebecryl (EB) 8402 manufactured by Daicel UCB)

Lactone modified acrylate monomer 20 parts

(FA2D manufactured by Daicel UCB) photoinitiator 1 part

(Irgacure 2959 manufactured by Chiba-Geigy)

The viscosity of the resin was 10,000 cps (Brookfield viscometer with No.5 spindle at 20 rpm rotation speed).

In four separate experiments, this resin was coated onto the microstructured surface of the tool such that the recesses of the microstructured surface were filled.

Each of the preconditioned polyester films were laminated to the photocurable resin filled tool surface in an environment having the same temperature and relative humidity as used to precondition the PET support film. By use of a low pressure mercury lamp (Chemical lamp, the irradiation wave length: 300-400nm, manufactured by Mitsubishi Osram), the resin was photocured with 3,000 mJ/cm² of UV irradiated through the preconditioned polyester film support. Then the mold was removed from the tool.

The results show that the pitch can be adjusted by about 5 ppm per degree relative humidity.

Claims

What is claimed is:

1. A method of producing a microstructured article comprising the steps of: providing a mold comprising a hygroscopic support wherein the mold was prepared at a first temperature and relative humidity; providing a curable ceramic paste material between a substrate and the microstructured surface of the mold at a second temperature and relative humidity that is different in temperature, humidity, or a combination thereof than the first temperature and humidity; curing the material forming micro structures integrally bonded with the substrate; and removing the mold from the microstructured article.

2. The method of claim 1 where preparing the mold comprises providing a polymeric transfer mold or master mold having a microstructured surface; providing a polymerizable resin composition in at least recesses of the microstructured surface of the microstructured surface of the mold; stacking the preconditioned support onto the microstructured surface of the mold; curing the polymerizable resin composition; and removing the cured polymerizable resin composition together with the support from the mold, thereby forming a flexible mold.

3. The method of claim 2 wherein the microstructured surface of the transfer mold or master mold comprises microstructures disposed at a pitch and the first temperature or relative humidity adjusts the pitch of the microstructures.

4. The method of claim 2 wherein the microstructured surface of the transfer mold or master mold has microstructures with a pitch greater than a target pitch.

5. The method of claim 4 wherein the first relative humidity is 1% to 40% higher than the second relative humidity.

6. The method of claim 4 wherein the first relative humidity is 1% to 10% higher than the second relative humidity.

7. The method of claim 4 wherein the first relative humidity is 1% to 5% higher than the second relative humidity.

8. The method of claim 2 wherein the transfer mold or master mold has microstructures with a pitch less than a target pitch.

9. The method of claim 8 wherein the first relative humidity is 1% to 40% lower than the second relative humidity.

10. The method of claim 8 wherein the first relative humidity is 1% to 10% lower than the second relative humidity.

11. The method of claim 8 wherein the first relative humidity is 1% to 5% lower than the second relative humidity.

12. The method of claim 2 wherein the polymerizable composition comprises the reaction product of at least one ethylenically unsaturated oligomer and at least one ethylenically unsaturated monomer.

13. The method of claim 12 wherein the oligomer comprises a urethane (meth)acrylate oligomer.

14. The method of claim 1 wherein the curing comprises photocuring through the mold, through the substrate, or a combination thereof.

15. The method of claim 1 wherein the substrate is a component of a display panel and the microstructures are barrier ribs.

16. The method of claim 1 wherein the first temperature and second temperature are the same.