WO2005083520A1

WO2005083520A1 - Inorganic paste composition, method for preparing inorganic paste composition, and sheet-shaped unbaked body for producing display panel

Info

Publication number: WO2005083520A1
Application number: PCT/JP2005/001648
Authority: WO
Inventors: Hiroyuki Obiya; Kiminori Oshio; Tomoyuki Inoue; Shigeru Suzuki
Original assignee: Tokyo Ohka Kogyo Co., Ltd.
Priority date: 2004-02-27
Filing date: 2005-01-28
Publication date: 2005-09-09
Also published as: CN1926473B; JP2005239952A; CN1926473A; JP3938919B2; KR20060114015A; KR100849976B1; TW200602416A; TWI279415B

Abstract

An inorganic paste composition containing inorganic powders, a binder resin having a hydroxyl group in a side chain thereof, and an organic solvent having no hydroxyl group, and contains an organic solvent having a hydroxyl group in an amount equal to or less than 5% by weight. The composition gives a film having a uniform dispersion of the inorganic powders therein and uniform thickness. The resulting film does not cause much shrinkage.

Description

DESCRIPTION

INORGANIC PASTE COMPOSITION, METHOD FOR PREPARING INORGANIC PASTE COMPOSITION, AND SHEET-SHAPED UNBAKED ^" BODY FOR PRODUCING DISPLAY PANEL

TECHNICAL FIELD The present invention relates to an inorganic paste composition, a method for preparing the same, and a sheet-shaped unbaked body for producing a display panel using the inorganic paste composition.

BACKGROUND ART A plasma display, which forms an image by causing a number of fine cells to emit light by themselves utilizing a discharge phenomenon, has excellent features such that it can achieve a large image and is thin, lightweight, and flat, which features cannot be realized by conventional displays, and its prevalence has been designed. Conventional plasma displays mainly use cells having a straight structure in which ribs are formed only in the longitudinal direction. However, recently, for efficiently introducing light to the front of the plasma display, cells having a waffle structure in which ribs are formed not only in the vertical direction but also in the horizontal direction have been developed. In the cells having a waffle structure, leakage of light from the adjacent cells is prevented, enabling introduction of light to the front with extremely high efficiency. The plasma display having waffle structure type cells is a display device which comprises a front plate comprising combined electrodes formed in parallel to one another wherein each combined electrode is comprised of a transparent electrode and a bus electrode, and a back plate comprising address electrodes formed in parallel to one another in the cross direction with respect to the combined electrodes, wherein the front plate and the back plate are disposed so as to face each other and integrated. The front plate has a transparent glass substrate as a display plane, and the combined electrodes are disposed on the inner side of the glass substrate, namely, on the side thereof facing the back plate. A dielectric layer is formed so as to cover the combined electrodes, and a patterned spacer layer is provided on the dielectric layer, and a protective film comprised of, for example, MgO is formed on the surface of the dielectric layer and spacer layer. On the other hand, the address electrodes are disposed on a substrate of the back plate on the side facing the front plate, and a dielectric layer is formed so as to cover the address electrodes, and the light emitting portions described below are formed on the dielectric layer. The light emitting portions consist of a number of cells each of which is located in a space where the combined electrode crosses the address electrodes . The cells are comprised of ribs formed on the dielectric layer in the vertical and horizontal directions, and a fluorescence layer is provided so as to cover the sidewall of the rib and the surface of the dielectric layer in the rib, that is, the inner wall and bottom of each cell. In the plasma display, a predetermined voltage from an alternating power source is applied to the combined electrodes of the front plate to form an electric field between the electrodes, so that discharge occurs in the cells. The discharge results in generation of ultraviolet light, which further causes light emission from the fluorescence layer. In the waffle structure type plasma display, a number of spacer layers are provided on the dielectric layer so that they are arranged in a form of equally spaced lines. In the front plate, the spacer layer is in contact with the rib, and therefore a gap is formed at the upper portion of each cell surrounded by the rib, and rare gas can be introduced to each cell through the gap. As a process for producing such a plasma display front plate, a process using a photolithography method is mainly used. The production process using a photolithography method will be described below. First, a dielectric layer comprised of a non-photosensitive glass paste film and a spacer layer comprised of a photosensitive glass paste film are formed on a glass substrate, and the spacer layer is irradiated with, for example, ultraviolet light through a photomask. Then, the layer is developed so that a resist pattern appears, followed by baking at 500 to 700 °C, thus forming a dielectric layer and a spacer layer simultaneously. In the production process using a photolithography method, the dielectric layer and the spacer layer can be baked at the same time in a single baking operation, and therefore the cost for production can be advantageously lowered, as compared to the cost for production required in a process using a screen printing method.

DISCLOSURE OF THE INVENTION The glass paste composition for forming the dielectric layer and spacer layer may be prepared by dispersing glass frit in a binder component which has been obtained by dissolving a binder resin in an appropriate organic solvent. As the binder resin, a hydroxyl group-containing resin has conventionally been used from the viewpoint of achieving adhesion to a glass substrate. As an organic solvent which dissolves therein the hydroxyl group-containing resin, from the viewpoint of obtaining solubility of the hydroxyl group-containing resin in the solvent and securing the environmental safety, an alcohol solvent is mainly used in the industrial production scale. However, when glass frit is added to the binder component comprised of a combination of the hydroxyl group-containing resin and the alcohol solvent, a problem occurs in that the glass frit is not uniformly dispersed and frequently forms aggregation. For forming a uniform film from the glass paste composition, it is very important that glass frit is uniformly dispersed in the binder component. When the glass frit is not uniformly dispersed in the binder component, that is, when there are thick and thin portions in the dispersion of the glass frit in the binder component, a mass of the glass paste, which is the thick portion in the dispersion, causes a streak on the surface of a film when forming the film by applying the glass paste composition onto a removable support film, leading to a lowering of the quality. There is a close relationship between the dispersibility of glass frit and the hydroxyl group content, of the binder resin, and the dispersibility of glass frit in the binder resin can be improved by increasing the hydroxyl group content of the binder resin. However, when using the binder resin having a large amount of hydroxyl group, the dielectric layer suffers shrinkage in the baking step, and strain is caused between the substrate and the dielectric layer, so that another problem disadvantageously arises that crazing is caused in the dielectric layer. Thus, it is difficult for the conventional glass paste composition to improve the dispersibility of glass frit and the flatness of the dielectric layer simultaneously. The present invention has been accomplished in view of the above problems, and an object of the present invention is to provide an inorganic paste composition which is advantageous not only in that the dispersibility of glass frit in the composition is excellent, but also in that a film having a uniform thickness can be formed from the composition, and a method for preparing the inorganic paste composition. Further, another object is to provide a sheet-shaped unbaked body for producing a display panel, which has a uniform thickness and can suppress the shrinkage during the baking. The present inventors have conducted intensive studies for solving the above-mentioned problems. As a result, they have found that, for improving the dispersibility of glass frit, it is important that hydrogen bonding is formed between a hydroxyl group derived from moisture adsorbed on the surface of the glass frit and a hydroxyl group derived from the binder resin. Further, they have found that, when an organic solvent having no hydroxyl group is used and the content of an organic solvent having a hydroxyl group is limited to equal to or less than 5% by weight, hydrogen bonding between the glass frit and the binder resin can be formed preferentially and efficiently. When an organic solvent having no hydroxyl group is used and the amount of an organic solvent having a hydroxyl group contained in the composition is limited to a predetermined range, it is possible to inhibit the binder resin and the organic solvent from forming together hydrogen bonding, thus improving the dispersibility of the glass frit in the binder resin. Specifically, the inorganic paste composition of the present invention is a composition which comprises inorganic powders, a binder resin having a hydroxyl group in its side chain, and an organic solvent having no hydroxyl group, wherein the inorganic paste composition contains an organic solvent having a hydroxyl group in an amount equal to or less than 5% by weight. As the organic solvent having no hydroxyl group, it is preferred to use at least one organic solvent selected from the group consisting of an ether, a ketone, and an ester. As the binder resin having a hydroxyl group in its side chain, it is preferred to use an acrylic resin having a hydroxyl group. It is preferred that the content of the hydroxyl group in the side chain of the binder resin is equal to or less than 0.3 per one monomer unit, in terms of an average number of the hydroxyl group contained in the side chain per monomer unit of the binder resin. The method for preparing an inorganic paste composition of the present invention is to prepare an inorganic paste composition which comprises inorganic powders, a binder resin having a hydroxyl group in its side chain, and an organic solvent having no hydroxyl group, wherein the method comprises a step of mixing together at least the three components and kneading the resultant mixture, wherein the mixture contains an organic solvent having a hydroxyl group in an amount equal to or less than 5% by weight. The sheet-shaped unbaked body for producing a display panel of the present invention is a sheet-shaped material which comprises a removable support film and an inorganic paste film formed on the removable support film wherein the inorganic paste film is comprised of at least the inorganic paste composition of the present invention. In the present specification, the term "sheet-shaped unbaked body for producing a display panel" means a sheet-shaped material used in the production of a display panel, in which the layer formed on a removable support film is peeled off from the removable support film and stacked on a glass substrate. In the inorganic paste composition of the present invention, by using an organic solvent having no hydroxyl group and using an organic solvent having a hydroxyl group in an amount equal to or less than 5% by weight, the dispersibility of the inorganic powders in the binder resin is considerably improved, so that occurrence of streaks during the application of the composition can be prevented. Further, by using an organic solvent having no hydroxyl group and using an organic solvent having a hydroxyl group in an amount equal to or less than 5% by weight, even when the hydroxyl group content of the binder resin is relatively low, satisfactory dispersibility of glass frit in the composition can be maintained, and therefore the content of the hydroxyl group in the binder resin can be set to be equal to or less than 0.3 per one monomer unit, in terms of an average number of the hydroxyl group contained in the side chain per monomer unit of the binder resin. Conventionally, for uniformly dispersing inorganic powders in a binder resin, the hydroxyl group content of the binder resin has been inevitably adjusted to a certain high level, which has caused shrinkage during the baking. When the hydroxyl group content of the binder resin is equal to or less than 0.3 per one monomer unit, in terms of an average number of the hydroxyl group contained in the side chain per monomer unit of the binder resin, such a problem can be solved. That is, in the inorganic paste composition of the present invention, the uniform dispersibility of the inorganic powders in the binder resin and the film properties including flatness of a film can be improved simultaneously. In the inorganic paste composition of the present invention, by using an acrylic resin having a hydroxyl group as the binder resin, adhesion to a glass substrate can be improved. In addition, by using at least one organic solvent selected from the group consisting of an ether, a ketone, and an ester as the organic solvent having no hydroxyl group, the dispersibility of the inorganic powders can be further improved. In the method for preparing an inorganic paste composition of the present invention, ingredients are mixed together using an organic solvent having no hydroxyl group, and therefore hydrogen bonding between a hydroxyl group derived from moisture adsorbed on the surface of the inorganic powders and a hydroxyl group derived from the binder resin can be formed at a high rate (preferentially and efficiently), so that an inorganic paste composition having excellent dispersibility and excellent film properties can be prepared. The sheet-shaped unbaked body for producing a display panel of the present invention is used as a material for forming a dielectric material and a spacer material layer in various displays, such as a plasma display, a plasma address liquid-crystal display, and a field emission display, and can be advantageously used for forming a dielectric layer and a spacer material layer especially in a plasma display front plate required to have high precision. BEST MODE FOR CARRYING OUT THE INVENTION Exemplary embodiments of the present invention will be explained below.

(A) Inorganic paste composition The inorganic paste composition of the present invention comprises at least inorganic powders, a binder resin having a hydroxyl group in its side chain, and an organic solvent having no hydroxyl group, wherein the inorganic paste composition contains an organic solvent having a hydroxyl group in an amount equal to or less than 5% by weight. The inorganic paste composition of the present invention is a paste comprising inorganic powders dispersed in a binder component which has been obtained by dissolving a binder resin having a hydroxyl group in its side chain, in an organic solvent having no hydroxyl group. In the inorganic paste composition of the present invention, as the binder resin, a hydroxyl group-containing resin having a hydroxyl group at a terminal of its side chain is used from the viewpoint of achieving excellent adhesion to a glass substrate. The hydroxyl group-containing resin is easily dissolved in an organic solvent having a hydroxyl group and therefore, conventionally, a hydroxyl group-containing solvent, such as alcohol, has generally been used. In contrast, the inorganic paste composition of the present invention is characterized in that an organic solvent having no hydroxyl group is used as a solvent. When using the organic solvent having no hydroxyl group, no hydrogen bonding is formed between the binder resin and the organic solvent, and therefore the solvent does not inhibit the inorganic powders and the binder resin from forming together hydrogen bonding. For this reason, the amount of hydrogen bonding between the inorganic powders and the binder resin is increased, thus making it possible to improve the dispersibility of the inorganic powders in the binder resin.

(a) Organic solvent With respect to the organic solvent used in the present invention, there is no particular limitation as long as it is an organic solvent which is capable of easily dissolving the binder resin, and which has no hydroxyl group in its molecule. As the organic solvent, it is preferred to use at least one organic solvent selected from the group consisting of an ether, a ketone, and an ester. Specific examples of organic solvents for use in the present invention may include ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate, ethylene glycol diacetate, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, ethylene glycol dimethyl ether, ethylene glycol monophenyl ether acetate, ethylene glycol monohexyl ether acetate, glycerol triacetate, glycerol trilaurate, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, diethylene glycol diacetate, diethylene glycol dimethyl ether acetate, diethylene glycol diethyl ether acetate, diethylene glycol dibutyl ether acetate, diethylene glycol dibenzoate, triethylene glycol dimethyl ether, triethylene glycol monomethyl ether acetate, propylene glycol diacetate, propylene glycol dimethyl ether, propylene glycol diethyl ether, propylene glycol dibutyl ether, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monobutyl ether acetate, dipropylene glycol diacetate, dipropylene glycol dimethyl ether, dipropylene glycol diethyl ether, dipropylene glycol dibutyl ether, dipropylene glycol monomethyl ether acetate, dipropylene glycol monoethyl ether acetate, dipropylene glycol monobutyl ether acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, acetylacetone, acetophenone, isophorone, ethyl n-butyl ketone, diacetoηe alcohol (4-hydroxy-4-methyl-2-pentanone), diisobutyl ketone, diisopropyl ketone, diethyl ketone, cyclohexanone, di-n-propyl ketone, methyl n-amyl ketone (amyl methyl ketone), methylcyclohexanone, methyl n-butyl ketone, methyl n-propyl ketone, methyl n-hexyl ketone, methyl n-heptyl ketone, diethyl adipate, trimethyl acetylcitrate, triethyl acetylcitrate, tributyl acetylcitrate, methyl acetoacetate, ethyl acetoacetate, butyl acetoacetate, isoamyl benzoate, methyl benzoate, ethyl benzoate, butyl benzoate, propyl benzoate, benzyl benzoate, isoamyl formate, isobutyl formate, ethyl formate, butyl formate, propyl formate, hexyl formate, benzyl formate, methyl formate, triethyl citrate, tributyl citrate, amyl acetate, allyl acetate, isoamyl acetate, methylisoamyl acetate, methoxybutyl acetate, isobutyl acetate, isopropyl acetate, ethyl acetate, methyl acetate, secondary-hexyl acetate, 2-ethylhexyl acetate, 2-ethylbutyl acetate, cyclohexyl acetate, methylcyclohexyl acetate, n-butyl acetate, secondary-butyl acetate, isopropyl acetate, benzyl acetate, methylcyclohexyl acetate, diamyl oxalate, diethyl oxalate, diethyl oxalate, dibutyl oxalate, diethyl tartarate, dibutyl tartarate, amyl stearate, methyl stearate, ethyl stearate, butyl stearate, amyl lactate, methyl lactate, ethyl lactate, butyl lactate, phthalic esters, γ-butyrolactone, isoamyl propionate, methyl propionate, ethyl propionate, butyl propionate, benzyl propionate, diisopropyl malonate, dimethyl malonate, diethyl malonate, dibutyl malonate, isoamyl butyrate, isopropyl butyrate, methyl butyrate, ethyl butyrate, butyl butyrate, alkanes, toluene, hexanes, cyclohexane, cyclohexene, cyclopentane, hydrocarbon halides, and nitrogen-containing compounds. Among these, preferred are organic solvents having a boiling point of

250 °C or lower, and especially preferred are organic solvents having a boiling point of 100 to 200 °C, specifically, preferred are dichloroethyl ether (boiling point: 178.6 °C), n-butyl ether (boiling point: 140.9 °C), diisoamyl ether (boiling point: 173.2 °C), methyl phenyl ether (boiling point: 153.9 °C), ethyl phenyl ether (boiling point: 170.1 °C), cresyl methyl ether (boiling point: 171.8 to 176.7 °C), ethyl benzyl ether (boiling point: 185 °C), epichlorohydrin (boiling point: 117 °C), diglycidyl ether (boiling point: 103 °C), 1 ,4-dioxane (boiling point: 101.4 °C), trioxane (boiling point: 114.5 °C), furfural (boiling point: 162 °C), cineole (boiling point: 176 to 177 °C), diethylacetal (boiling point: 104.2 °C), methyl n-propyl ketone (boiling point: 102.4 °C), methyl n-butyl ketone (boiling point: 127.2 °C), methyl isobutyl ketone (boiling point: 116.7 °C), methyl n-amyl ketone (boiling point: 150.2 °C), methyl n-hexyl ketone (boiling point: 174 °C), diethyl ketone (boiling point: 101.7 °C), ethyl n-butyl ketone (boiling point: 147.4 °C), di-n-propyl ketone (boiling point: 144.2 °C), diisobutyl ketone (boiling point: 168.2 °C), acetonylacetone (boiling point: 191.4 °C), diacetone alcohol (boiling point: 163 to 167.9 °C), mesityl oxide (boiling point: 131.4 °C), phorone (boiling point: 198.2 °C), cyclohexanone (boiling point: 156 °C), o-methylcyclohexanone (boiling point: 165 °C), n-butyl formate (boiling point: 106.8 °C), amyl formate (boiling point: 130.4 °C), n-propyl acetate (boiling point: 101.6 °C), n-butyl acetate (boiling point: 126.3 °C), isobutyl acetate (boiling point: 118 °C), secondary-butyl acetate (boiling point: 112.2 °C), n-amyl acetate (boiling point: 149.0 °C), isoamyl acetate (boiling point: 142 °C), methylisoamyl acetate (boiling point: 146.3 °C), methoxybutyl acetate (boiling point: 173 °C), secondary-hexyl acetate (boiling point: 146.3 °C), 2-ethylbutyl acetate (boiling point: 162 to 163 °C), 2-ethylhexyl acetate (boiling point: 197.5 to 198 °C), cyclohexyl acetate (boiling point: 175 to 176 °C), methylcyclohexyl acetate (boiling point: 181.5 to 186.5 °C), n-butyl propionate (boiling point: 146.8 °C), isoamyl propionate (boiling point: 160.3 °C), methyl butyrate (boiling point: 102.3 °C), ethyl butyrate (boiling point: 121.3 °C), n-butyl butyrate (boiling point: 164.8 °C), isoamyl butyrate (boiling point: 179 °C), ethyl oxyisobutyrate (boiling point: 147.5 to 149 °C), methyl acetoacetate (boiling point: 171.7 °C), ethyl acetoacetate (boiling point: 180.4 °C), isoamyl isovalerate (boiling point: 192.7 °C), methyl lactate (boiling point: 143.8 °C), ethyl lactate (boiling point: 154.1 °C), n-butyl lactate (boiling point: 188 °C), methyl benzoate (boiling point: 199.5 °C), diethyl oxalate (boiling point: 183.5 °C), and diethyl malonate (boiling point: 198.9 °C). The solvents may be used individually or in combination. When a plurality of solvents are used in combination, the azeotropic temperature of the solvents may preferably be 250 °C or lower, especially preferably 100 to 200 °C.

(b) Inorganic powders It is preferred that the inorganic powders used in the present invention is glass frit which is baked to form glass, and examples thereof may include PbO-SiO₂, PbO-B₂O₃-SiO₂, ZnO-SiO₂, ZnO-B₂O₃-SiO₂, BiO-SiO₂, BiO-B₂O₃-SiO₂, PbO-B₂O₃-SiO₂-AI₂O₃, and PbO-ZnO-B₂O₃-SiO₂ glass frit. In addition to glass frit, inorganic powders comprised of ceramic (e.g., cordierite) or a metal may be used. Specific examples of such inorganic powders may include cobalt oxide, iron oxide, chromium oxide, nickel oxide, copper oxide, manganese oxide, neodymium oxide, vanadium oxide, cerium tipaque yellow oxide, cadmium oxide, ruthenium oxide, and oxides of Na, K, Mg, Ca, Ba, Ti, Zr, or Al, such as silica, magnesia, and spinel. With respect to the particle size of the inorganic powders, inorganic powders having an average particle size of 0.1 to 10 μm is preferably used, more preferably 0.5 to 8 μm is used. When using inorganic powders having an average particle size of more than 10 μm, the surface of a film may disadvantageously be roughened upon forming a pattern with high precision, and, when using inorganic powders having an average particle size of less than 0.1 μm, fine pores may disadvantageously be formed in the film during the baking to cause insulation failure. Examples of forms of the inorganic powders may include a spherical form, a block form, a flake form, and a dendrite form, and they may be used individually or in combination. Alternatively, the inorganic powders may be a mixture of fine particles having different physical property values. Especially when using glass frit and ceramic powders having a heat softening point different from that of the glass frit, the shrinkage during the baking may be suppressed. The inorganic powders are preferably prepared by changing the combination of the forms and the physical property values depending on the use of the inorganic paste composition.

(c) Binder resin In the inorganic paste composition of the present invention, a resin having a hydroxyl group in its side chain is used as the binder resin. The binder resin may include those obtained by polymerizing or copolymerizing the monomers given below which are capable of introducing a hydroxyl group into the resultant resin. The monomer capable of introducing a hydroxyl group may preferably be a (meth)acrylic acid ester, an ethylenically unsaturated carbonic acid, or another copolymerizable monomer, and examples thereof may include benzyl acrylate, benzyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, phenoxyethyl acrylate, phenoxyethyl methacrylate, phenoxy polyethylene glycol acrylate, phenoxy polyethylene glycol methacrylate, styrene, nonylphenoxy polyethylene glycol monoacrylate, nonylphenoxy polyethylene glycol monomethacrylate, nonylphenoxy polypropylene monoacrylate, nonylphenoxy polypropylene monomethacrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-acryloyloxyethyl phthalate, 2-acryloyloxyethyl-2-hydroxyethyl phthalate, 2-methacryloyloxyethyl-2-hydroxypropyl phthalate, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, i-propyl acrylate, i-propyl methacrylate, n-butyl acrylate, n-butyl methacrylate, i-butyl acrylate, i-butyl methacrylate, sec-butyl acrylate, sec-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate,

2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 2-hydroxybutyl acrylate, 2-hydroxybutyl methacrylate, 3-hydroxybutyl acrylate, 3-hydroxybutyl methacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, 3-ethylhexyl acrylate, ethylene glycol monoacrylate, ethylene glycol monomethacrylate, glycerol acrylate, glycerol methacrylate, dipentaerythritol monoacrylate, dipentaerythritol monomethacrylate, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, tetrahydrofurfuryl acrylate, tetrahydrofurfuryl methacrylate, acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, itaconic anhydride, citraconic acid, and citraconic anhydride. Among these, acrylic acid and methacrylic acid are preferably used. Examples of other copolymerizable monomers may include compounds having the same structures as those of the above-mentioned specific examples of (meth)acrylates except that (meth)acrylate is replaced by fumarate, maleate, crotonate, or itaconate, α-methylstyrene, o-vinyltoluene, m-vinyltoluene, p-vinyltoluene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, o-methoxystyrene, m-methoxystyrene, p-methoxystyrene, vinyl acetate, vinyl butyrate, vinyl propionate, acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, isoprene, chloroprene, and 3-butadiene. The content of the hydroxyl group in the side chain of the binder resin used in the present invention is preferably equal to or less than 0.3, more preferably 0.1 to 0.3, especially preferably 0.15 to 0.25 per one monomer unit, in terms of an average number of the hydroxyl group contained in the side chain per monomer unit of the binder resin. When the hydroxyl group content of the molecule exceeds 0.3 per one monomer unit, shrinkage may disadvantageously occur during the baking, causing crazing in the dielectric layer. The binder resin having a hydroxyl group in its side chain may be used together with another binder resin. Examples of such other binder resins for use may include a cellulose derivative, such as cellulose, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose, carboxyethyl cellulose, or carboxyethylm ethyl cellulose, or a copolymer of the cellulose derivative and an ethylenically unsaturated carboxylic acid or a (meth)acrylate compound.

Examples of binder resins may also include polyvinyl alcohols, such as polybutyral resins which are reaction products of polyvinyl alcohol and butylaldehyde; polyesters obtained by ring-opening polymerization of a lactone, such as δ-valerolactone, ε-caprolactone, β-propiolactone, α-methyl-β-propiolactone, β-methyl-β-propiolactone, α-methyl-β-propiolactone, β-methyl-β-propiolactone, α,α-dimethyl-β-propiolactone, or β,β-dimethyl-β-propiolactone; polyesters obtained by a condensation reaction of diols that may be one or more of alkylene glycols such as ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, dipropylene glycol, or neopentyl glycol, and a dicarboxylic acid, such as maleic acid, fumaric acid, glutaric acid, or adipic acid; polyethers, such as polyethylene glycol, polypropylene glycol, polytetram ethylene glycol, and polypentamethylene glycol; and polycarbonates which are reaction products of a diol, such as bisphenol A, hydroquinone, or dihydroxycyclohexane, and a carbonyl compound, such as diphenyl carbonate, phosgene, or succinic anhydride. The binder resins may be used individually or in the form of a mixture of two or more types of binder resins. In this case, based on 100 parts by weight of the total amount of the binder resin having a hydroxyl group in its side chain and another binder resin, the amount of the binder resin having a hydroxyl group in its side chain may be 30 parts by weight or more and the amount of the another binder resin may be 70 parts by weight or less. It is preferred that the amount of the binder resin having a hydroxyl group in its side chain is 50 parts by weight or more and the amount of the another binder resin is 50 parts by weight or less, and it is more preferred that the amount of the binder resin having a hydroxyl group in its side chain is 70 parts by weight or more and the amount of the another binder resin is 30 parts by weight or less. When the amount of another binder resin is increased, the dispersibility of the inorganic powders in the composition may disadvantageously become poor.

(d) Other components The inorganic paste composition of the present invention comprises the above-described (a) organic solvent having no hydroxyl group, (b) inorganic powders, and (c) binder resin having a hydroxyl group in its side chain as essential components, and may further comprise other components depending on the use thereof. For example, when the inorganic paste composition of the present invention is used for producing a spacer layer in a plasma display front plate, the paste composition containing the three essential components may further contain a photopolymerizable monomer and a photopolymerization initiator as components for imparting photosensitivity to the composition. Examples of the photopolymerizable monomers may include monomers shown above in connection with the (c) binder resin having a hydroxyl group in its side chain, and preferred are monomers having two or more polymerizable ethylenically unsaturated bonds (hereinafter referred to as "multifunctional monomers"). Examples of multifunctional monomers may include diacrylates or dimethacrylates of an alkylene glycol, such as ethylene glycol or propylene glycol; diacrylates or dimethacrylates of polyalkylene glycol, such as polyethylene glycol or polypropylene glycol; and polyacrylates or polymethacrylates of polyhydric alcohol, such as glycerol, trimethylolpropane, pentaerythritol, or dipentaerythritol; as well as dicarboxylic acid modified products thereof. Among these monomers, specific examples may include ethylene glycol diacrylate, ethylene glycol dimethacrylate, triethylene glycol diacrylate, triethylene glycol dimethacrylate, tetraethylene glycol diacrylate, tetraethylene glycol dimethacrylate, propylene glycol diacrylate, propylene glycol dimethacrylate, polypropylene glycol diacrylate, polypropylene glycol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, tetramethylolpropane tetraacrylate, tetramethylolpropane tetramethacrylate, pentaerythritol triacrylate, pentaerythritol trimethacrylate, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, dipentaerythritol pentamethacrylate, dipentaerythritol hexaacrylate, and dipentaerythritol hexamethacrylate. Examples of photopolymerization initiators may include

1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-1 ,2-diphenylethan-1-one, 2-methyl-1 -[4-(methylthio)phenyl]-2-morpholinopropan-1 -one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one, 2-hydroxy-2-m ethyl- 1 -phenylpropan-1 -one, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 1 -[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1 -propan-1 -one, 2,4-diethylthioxanthone, 2-chlorothioxanthone, 2,4-dimethylthioxanthone, 3,3-dimethyl-4-methoxybenzophenone, benzophenone, 1 -chloro-4-propoxythioxanthone, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 1 -(4-dodecylphenyl)-2-hydroxy-2-methylpropan-1 -one, 4-benzoyl-4'-methyldimethyl sulfide, 4-dimethylaminobenzoic acid, methyl 4-dimethylaminobenzoate, ethyl 4-dimethylaminobenzoate, butyl 4-dimethylaminobenzoate, 2-ethylhexyl 4-dimethylaminobenzoate, 2-isoamyl 4-dimethylaminobenzoate, 2,2-diethoxyacetophenone,

2,2-dimethoxy-2-phenylacetophenone, benzyldimethyl ketal, benzyl-β-methoxyethylacetal, 1-phenyl-1 ,2-propanedione 2-(o-ethoxycarbonyl)oxime, methyl o-benzoylbenzoate, bis(4-dimethylaminophenyl) ketone, 4,4'-bisdiethylaminobenzophenone, 4,4'-dichlorobenzophenone, benzil, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin n-butyl ether, benzoin isobutyl ether, p-dimethylaminoacetophenone, p-tert-butyltrichloroacetophenone, p-tert-butyldichloroacetophenone, thioxanthone, 2-methylthioxanthone, 2-isopropylthioxanthone, dibenzosuberone, α,α-dichloro-4-phenoxyacetophenone, pentyl 4-dimethylaminobenzoate, 9-phenylacridine, 1 ,7-bis-(9-acridinyl)heptane, 1 ,5-bis-(9-acridinyl)pentane, and 1 ,3-bis-(9-acridinyl)propane. These photopolymerization initiators may be used individually or in combination. When the inorganic paste composition of the present invention is used for producing a dielectric layer in a plasma display front plate, the dielectric layer may contain a light absorber capable of absorbing light having such a wavelength that it sensitizes the spacer layer, namely, optically activates a photopolymerization initiator contained in the spacer layer. As such a light absorber, one which absorbs light having a wavelength of 300 to 450 nm is preferably used, and examples may include azo dyes, aminoketone dyes, xanthene dyes, quinoline dyes, benzophenone dyes, triazine dyes, benzotriazole dyes, and anthraquinone dyes. When the dielectric layer contains a light absorber capable of absorbing light having such a wavelength that it optically activates a photopolymerization initiator contained in the spacer layer, in the patterning into a predetermined form by exposure of the spacer layer in a state in which the dielectric layer and the spacer layer are stacked on one another, incident light on the first layer may be prevented from being scattered due to the inorganic powders in the dielectric' layer. In other words, when the dielectric layer contains no light absorber, light may be scattered due to particles of the inorganic powders in the dielectric layer, so that the spacer layer may be exposed to light entering in an indefinite direction from the dielectric layer, making it difficult to form a pattern with high accuracy in accordance with the mask. For preventing this, the spacer layer may have to be formed and exposed and then baked after baking the dielectric layer so as to be in a transparent glass state, that is, two individual steps of baking may be required. In contrast, when the dielectric layer contains a light absorber, baking for the dielectric layer and the spacer layer may be made at the same time to form a desired pattern. For imparting plasticiticy to a film, a plasticizer may be added to the composition. As a plasticizer, one conventionally known may be used, and preferred are plasticizers which have a boiling point of 200 °C or higher and which are in a liquid state at room temperature and excellent in transparency. Examples of plasticizers may include phthalic acid compounds, such as dimethyl phthalate, diethyl phthalate, dibutyl phthalate, diheptyl phthalate, di-2-ethylhexyl phthalate, diisononyl phthalate, diisodecyl phthalate, dibutylbenzyl phthalate, dioctyl phthalate, and butyl phthalylbutyl glycolate; adipic acid compounds, such as diisobutyl adipate, diisononyl adipate, diisodecyl adipate, and dibutoxyethyl adipate; sebacic acid compounds, such as dibutyl sebacate and di-2-ethylhexyl sebacate; phosphoric acid compounds, such as triethyl phosphate, triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, and cresyl phenyl phosphate; fatty acid compounds, such as dioctyl sebacate and methylacetyl ricinoleate; epoxy compounds, such as diisodecyl 4,5-epoxytetrahydrophthalate; trimellitic acid compounds, such as tributyl trimellitate, tri-2-ethylhexyl trimellitate, tri-n-octyl trimellitate, and triisodecyl trimellitate; and butyl oleate, chlorinated paraffin, polybutene, and polyisobutylene. These may be used individually or two or more types of them may be mixed if necessary.

(e) Composition ratio The inorganic paste composition of the present invention is characterized in that it contains an organic solvent having a hydroxyl group in an amount equal to or less than 5% by weight. Examples of the organic solvents having a hydroxyl group may include organic solvents for dilution, such as alcohol, added in an amount such that the effect aimed at by the present invention to improve the dispersibility of the inorganic powders is not impaired. Examples of the organic solvents having a hydroxyl group may also include a hydroxyl group-containing organic solvent inherently contained in any of the additives. Specific examples of such organic solvents having a hydroxyl group may include alcohols, such as methanol, ethanol, ethylene glycol, diethylene glycol, propylene glycol, and 3-methoxy-3-methylbutanol; and alkyl ethers of polyhydric alcohol, such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether. When the content of the organic solvent having a hydroxyl group in the inorganic paste composition exceeds 5% by weight, hydrogen bonding may disadvantageously be formed between the organic solvent having a hydroxyl group and the binder resin to inhibit the binder resin and the inorganic powders from forming together hydrogen bonding. The content of the organic solvent having a hydroxyl group in the inorganic paste composition of the present invention is preferably equal to or less than 1 % by weight, more preferably equal to or less than 0.1 % by weight. Ratio of ingredients in the inorganic paste composition of the present invention may be appropriately adjusted in accordance with use of the composition as long as the content of the organic solvent having a hydroxyl group in the inorganic paste composition is equal to or less than 5% by weight. Ratio of ingredients will be described below in detail with respect to especially (1) composition used for forming a dielectric layer in a plasma display front plate and (2) composition used for forming a spacer layer in a plasma display front plate. Composition (1) When the inorganic paste composition of the present invention is used for forming a dielectric layer, the organic solvent having no hydroxyl group may advantageously be incorporated in an amount of 30 to 500 parts by weight, preferably 50 to 300 parts by weight, more preferably 100 to 250 parts by weight, per 100 parts by weight of the binder resin having a hydroxyl group in its side chain. It is preferred that the inorganic powders are incorporated in an amount of 100 to 1 ,000 parts by weight, per 100 parts by weight of the total amount of all the organic components (including the organic solvent, the binder resin, and others). A plasticizer may advantageously be incorporated in an amount of 200 parts by weight or more, preferably 5 to 100 parts by weight, more preferably 10 to 80 parts by weight, per 100 parts by weight of the binder resin having a hydroxyl group in its side chain. It is preferred that a light absorber is mixed in an amount of 30 parts by weight or more, per 100 parts by weight of the total amount of the inorganic powders, the binder resin, and the light absorber. When the amount of the light absorber exceeds 30 parts by weight, the resulting composition may absorb too much light, so that the spacer layer near the interface may not be satisfactorily exposed, which may cause problems such as that the film is peeled off or a pattern cannot be formed.

Composition (2) When the inorganic paste composition of the present invention is used for forming a spacer layer, the organic solvent having no hydroxyl group may advantageously be incorporated in an amount of 30 to 700 parts by weight, preferably 50 to 500 parts by weight, more preferably 100 to 300 parts by weight, per 100 parts by weight of the binder resin having a hydroxyl group in its side chain. It is preferred that the inorganic powders are incorporated in an amount of 100 to 1 ,000 parts by weight, per 100 parts by weight of the total amount of all the organic components (including the organic solvent, the binder resin, the photopolymerizable monomer, the photopolymerization initiator, and others). The photopolymerizable monomer may advantageously be used in an amount of 10 to 500 parts by weight, preferably 30 to 300 parts by weight, further preferably in the range of 50 to 200 parts by weight, per 100 parts by weight of the binder resin having a hydroxyl group in its side chain. The photopolymerization initiator is preferably used in an amount in the range of 0.01 to 50 parts by weight, more preferably in the range of 0.1 to 20 parts by weight, per 100 parts by weight of the binder resin having a hydroxyl group in its side chain. When the amount of the photopolymerization initiator is less than 0.01 part by weight, the curing property of the composition becomes poor. On the other hand, when the amount of the photopolymerization initiator exceeds 50 parts by weight, curing failure at the bottom due to absorption of the initiator may be observed.

(B) Method for preparing inorganic paste composition The method for preparing an inorganic paste composition of the present invention is characterized in that the method comprises a step of mixing together three components comprising inorganic powders, a binder resin having a hydroxyl group in its side chain, and an organic solvent having no hydroxyl group and kneading the resultant mixture, wherein the mixture in the kneading step contains an organic solvent having a hydroxyl group in an amount equal to or less than 5% by weight. In the present invention, with respect to the order of mixing the binder resin, the organic solvent, and the inorganic powders, there is no particular limitation. For example, three components comprising the binder resin, the organic solvent, and the inorganic powders may be mixed together at the same time, or the inorganic powders may be added and mixed into a binder component which is preliminarily prepared by dissolving the binder resin in the organic solvent. Taking the latter method as an example, the method for preparing an inorganic paste composition of the present invention will be described below, but the order of mixing the components is not limited to this example. First, the organic solvent having no hydroxyl group and the binder resin are mixed together by means of a stirrer to dissolve the binder resin in the solvent, for preparing a binder component. In this step, a photopolymerizable monomer, a photopolymerization initiator, and an additive, such as a plasticizer, a dispersant, a tackifier, a surface tension adjuster, a stabilizer, or a defoamer, may be added. After the binder component is prepared, inorganic powders are added to the binder component to prepare a mixture, and the mixture is kneaded to disperse the inorganic powders. When the inorganic powders are stored under normal conditions, it adsorbs moisture in air and hence has a hydroxyl group derived from the moisture adsorbed on the surface of the inorganic powders. Therefore, there is no need to subject the inorganic powders to any special treatment for introducing a hydroxyl group into the surface of the inorganic powders. However, when the inorganic powders are stored under dry conditions for a long time, it is preferred that the inorganic powders are optionally allowed to absorb moisture before being used and then added to the binder component. In the present invention, the mixture in the kneading step preferably contains the organic solvent having a hydroxyl group in an amount as small as possible. Specifically, it is necessary that the content of the organic solvent having a hydroxyl group in the mixture is limited to 5% by weight or less. An organic solvent having a hydroxyl group may be contained in the mixture as an additive or impurity. In such a case, when the content of the organic solvent having a hydroxyl group in the mixture is too high, hydrogen bonding may unpreferably be formed between the organic solvent having a hydroxyl group and the binder resin to inhibit the binder resin and the inorganic powders from forming together hydrogen bonding. In the kneading step, the content of the organic solvent having a hydroxyl group in the mixture is preferably equal to or less than 5% by weight, more preferably equal to or less than 1% by weight, further preferably equal to or less than 0.1 % by weight. In the present invention, an organic solvent having a hydroxyl group, such as alcohol, may be added before or after dispersing the inorganic powders as long as the effect aimed at by the present invention to improve the dispersibility of the inorganic powders is not impaired. When a hydroxyl group-containing solvent is added to the mixture before dispersing the inorganic powders, namely, before hydrogen bonding is formed between the inorganic powders and the binder resin, the binder resin and the hydroxyl group-containing solvent may disadvantageously form together hydrogen bonding, causing the dispersibility of the inorganic powders to lower. However, when the total amount of the organic solvents having a hydroxyl group contained in the mixture is equal to or less than 5% by weight, there is no problem even when the mixture contains a certain amount of a hydroxyl group-containing solvent. The mixture obtained by dispersing the inorganic powders through the kneading step may be used as such as the inorganic paste composition of the present invention. An additional component may further be added to the mixture obtained by dispersing the inorganic powders, and the resultant mixture may be used as the inorganic paste composition. For example, after the inorganic powders are dispersed to form hydrogen bonding between the inorganic powders and the binder resin, the hydrogen bonding between the inorganic powders and the binder resin is kept relatively stable. Therefore, in this case, even when an organic solvent having a hydroxyl group, such as alcohol, is added to the mixture, the hydrogen bonding between the inorganic powders and the binder resin is not adversely affected. Therefore, after the kneading step, an organic solvent having a hydroxyl group, such as alcohol, may optionally be added to control the concentration of the inorganic paste composition.

(C) Sheet-shaped unbaked body for producing display panel The sheet-shaped unbaked body of the present invention comprises a removable support film and an inorganic paste film which is formed by applying the inorganic paste composition of the present invention to the removable support film and drying the resultant film. For example, a sheet-shaped unbaked body using a non-photosensitive inorganic paste composition may be used as a material for forming a dielectric layer in a plasma display front plate, and a sheet-shaped unbaked body using a photosensitive inorganic paste composition may be used as a material for forming a spacer layer in the plasma display front plate. The sheet-shaped unbaked body of the present invention may have the surface of the inorganic paste film protected by a removable film which may be easily peeled off, and hence it is easy to store, transport, and handle. The sheet-shaped unbaked body of the present invention is formed using the inorganic paste composition of the present invention in which the inorganic powders are uniformly dispersed, and hence has excellent flatness. In addition, the shrinkage during the baking may be suppressed, and therefore a dielectric layer or spacer layer having a uniform thickness free from crazing may be obtained, thus enabling production of a high-quality display panel. Further, the sheet-shaped unbaked body of the present invention has a feature such that it may be preliminarily produced and stored for a predetermined term, which is a limited term although, and therefore it may be immediately used for producing a display panel, making it possible to improve the efficiency of production of the display panel. It is preferred that the sheet-shaped unbaked body of the present invention is provided in the form of an inorganic paste film having both surfaces protected by removable films which may be easily peeled off. Specifically, a dielectric layer, which is formed on a removable support film, is covered with a protective film as a protective layer. With respect to the support film used for producing the sheet-shaped unbaked body of the present invention, there is no particular limitation as long as the support film is a removable film such that the layer formed on the support film may be easily peeled off the support film and transferred to a glass substrate, and examples thereof may include flexible films having a thickness of 15 to 125 μm comprised of a synthetic resin film, such as polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, or polyvinyl chloride. It is preferred that the support film is treated so as to be removable if necessary for facilitating transfer. In the formation of the inorganic paste film on the support film, the inorganic paste composition of the present invention is prepared, and the inorganic paste composition is applied to the support film using, e.g., an applicator, a bar coater, a wired bar coater, a roll coater, or a curtain flow coater. The roll coater is especially preferred since it may efficiently form a film having excellent uniformity in thickness and having a satisfactorily large thickness. After drying the film, it is preferred that the surface of the inorganic paste film is covered with a protective film for stably protecting the inorganic paste film before use. As the protective film, preferred is a polyethylene terephthalate film, polypropylene film, or polyethylene film having silicone coated or baked and having a thickness of about 15 to 125 μm. In the production of a display panel, the protective film may be peeled off the sheet-shaped unbaked body of the present invention, and the resultant unbaked body may be placed on a glass substrate so that the exposed inorganic paste film is in contact with the surface of the glass substrate on which electrodes are formed, and a heat roller may be moved over the support film to hot-press the inorganic paste film on the surface of the substrate. The hot press is preferably conducted under conditions such that the substrate is heated so that the surface temperature becomes 80 to 140 °C, the roll pressure is in the range of 1 to 5 kg/cm², and the moving speed is in the range of 0.1 to 10.0 m/min. The glass substrate may be preheated, and the preheating temperature may be selected, for example, in the range of 40 to 100 °C. The protective film peeled off the inorganic paste film may be successively taken up by a take-up roller and stored in the form of a roll, which may be reused. The inorganic paste film may be heat-bonded to the surface of the substrate in this way, and then the support film may be peeled off the inorganic paste film to expose the surface of the inorganic paste film on the substrate. The support film peeled off the inorganic paste film on the substrate may also be successively taken up by a take-up roller and stored in the form of a roll, which may be reused. The inorganic paste film thus formed on the surface of the glass substrate may be baked at 500 to 700 °C to sinter the glass frit contained in the inorganic paste film, forming any one of a dielectric layer and/or a spacer layer. In the baking step, the organic substance contained in the inorganic paste film may volatilize and decompose, so that substantially no organic component remains in the dielectric layer or spacer layer. Thus, the display panel in the present invention is obtained. After the display panel is produced in this way, it is preferred that the exposed dielectric layer is covered with a protective film comprised of, e.g., MgO.

Examples The present invention will be explained in more details with reference to the examples below. Note that the invention is not limited by the examples.

Examples 1 to 7 and Comparative Example 1 (1) Preparation of glass paste composition In accordance with the composition ratio (unit: part(s) by weight) shown in Table 1 below, a binder resin, a solvent, and other components were mixed by means of a stirrer for 3 hours to prepare an organic component, and then 40 parts by weight of this organic component (solids content: 50%) and 80 parts by weight of (PbO-SiO₂) glass frit were mixed and kneaded to prepare a glass paste composition.

(2) Production of sheet-shaped unbaked body The glass paste composition obtained was applied to a support film comprised of polyethylene terephthalate using a lip coater, and the resultant film was dried at 100 °C for 6 minutes to completely remove the solvent, thus forming a glass paste film having a thickness of 60 μm on the support film. Then, a polyethylene film having a thickness of 25 μm was stacked on the glass paste film, to produce a sheet-shaped unbaked body. (3) Formation of dielectric film layer While peeling off the polyethylene film in the sheet-shaped unbaked body obtained in (2) above, the glass paste film was laminated on a glass substrate having bus electrodes formed thereon which had been preheated to 80 °C, at 105 °C by means of a hot roll laminator. The air pressure was 3 kg/cm², and the lamination speed was 1.0 m/min.

(4) Evaluation of glass paste film For evaluating the performance of each of the glass paste films in Examples 1 to 7 and Comparative Example 1 , examinations were conducted as to the below-mentioned evaluations. The results are shown in Table 1 below.

(Observation of appearance after peeling support film) After peeling off the polyethylene terephthalate as the support film in the dielectric layer obtained in (3) above, appearance of the glass paste film was observed.

G: No defect, such as a streak or crater, was found.

NG: A defect, such as a streak or crater, was found.

(Surface roughness Rmax before baking) Surface roughness of the glass paste film was measured by means of a stylus surface roughness tester.

(Surface roughness Rmax after baking) For evaluating the properties of the glass paste film after baking, the film was subjected to baking treatment in which the temperature was elevated at the rate of 1.0°C/min and then maintained at 580 °C for 30 minutes, and then surface roughness of the resultant film was measured by means of a stylus surface roughness tester.

(Withstanding voltage) After baking, withstanding voltage was measured. G: The withstanding voltages measured are even in the surface. NG: The withstanding voltages measured are uneven in the surface.

Table 1

Note: (A-1): Binder resin having hydroxyl group in side chain Isobutyl methacrylate/hydroxyethyl acrylate = 90/10 (% by weight) copolymer (Mw: 70,000)

(A-2): Binder resin having hydroxyl group in side chain Styrene/hydroxyethyl methacrylate = 55/45 (% by weight) copolymer

(Mw: 40,000) (A-3): Binder resin having hydroxyl group in side chain Hydroxypropyl cellulose (B-1): Solvent Ethyl acetate (B-2): Solvent Butyl acetate

(B-3): Solvent 3-Methoxybutyl acetate (B-4): Solvent Ethyl n-butyl ketone

(B-5): Solvent Ethyl acetate/ethyl n-butyl ketone = 50/50 (% by weight) (B-6): Solvent 3-Methoxy-3-methylbutanol (C-1 ): Monomer 2-Methacryloyloxyethyl-2-hydroxypropyl phthalate

(C-2): Photopolymerization initiator 2,2-Dimethoxy-2-phenylacetophenone (C-3): Light absorber Azo dye (trade name: Dye SS; manufactured by Daito Chemix Corporation) (for preventing halation) (C-4): Plasticizer Dibutyl phthalate

In Examples 1 to 5 and 7, an organic solvent having no hydroxyl group was used as the organic solvent, resulting in extremely excellent dispersibility of the glass frit, precisely flat glass paste film as seen from the results of evaluation shown in Table 1 with respect to the surface roughness Rmax before the baking and the surface roughness Rmax after the baking, and uniform withstanding voltage. Further, in Example 6, an organic solvent having a hydroxyl group (3-methoxy-3-methylbutanol) constitutes part of the organic solvent, but the content of that solvent is as very small as 0.1 % by weight, based on the total weight of the organic solvents (0.0167% by weight, based on the weight of the glass paste composition), and hence the dispersibility was extremely excellent like in Examples 1 to 5 and 7, and a glass paste film having excellent flatness was formed, and the measurements of withstanding voltage were uniform. By contrast, in Comparative Example 1 , the dispersibility of glass frit was unsatisfactory, as compared to the dispersibility in Examples 1 to 7. The reason for this resides in that an organic solvent having a hydroxyl group (3-methoxy-3-methylbutanol) is used as the organic solvent in Comparative Example 1 and the content of the organic solvent is 16.7% by weight, based on the weight of the glass paste composition, which is higher than the requisite value (5% by weight) defined in the present invention. As seen from the results of evaluation shown in Table 1 with respect to the surface roughness Rmax before the baking and the surface roughness Rmax after the baking, the film flatness was poor, as compared to the flatness in Examples 1 to 7, and the measurements of withstanding voltage were uneven in the surface.

Example 8

(1) Production of sheet-shaped unbaked body A sheet-shaped unbaked body 1 was produced in the same manner as in Example 1 except that 0.5 part by weight of an azo dye (trade name: Dye SS; manufactured by Daito Chemix Corporation) was added as a light absorber. Then, a sheet-shaped unbaked body 2 was produced in the same manner as in Example 7 except that the thickness of the glass paste film was 40 μm.

(2) Formation of sheet-shaped unbaked laminate While peeling off the polyethylene film of the sheet-shaped unbaked body 1 , the unbaked body 1 was laminated on a glass substrate having bus electrodes formed thereon, which had been preheated to 80 °C, at 105 °C by means of a hot roll laminator. The air pressure was 3 kg/cm², and the lamination speed was 1.0 m/min. Then, the polyethylene terephthalate as a support film was peeled off. Then, while peeling off the polyethylene film in the sheet-shaped unbaked body 2, the unbaked body 2 was laminated at room temperature by means of a roll laminator on the surface of the sheet-shaped unbaked body 1 on the glass substrate preheated to 80 °C. The air pressure was 3 kg/cm², and the lamination speed was 1.0 m/min. Thus, a sheet-shaped unbaked laminate comprising the sheet-shaped unbaked body 1 and the sheet-shaped unbaked body 2 on the glass substrate was formed. In this stage, the surface of the laminate was covered with the support film.

(3) Evaluation of sheet-shaped unbaked laminate and production of dielectrics The sheet-shaped unbaked laminate was exposed to ultraviolet light at irradiation energy of 300 mJ/cm² by means of an ultra-high pressure mercury lamp through a test pattern mask having a predetermined pattern formed therein. Subsequently, the polyethylene terephthalate as the support film was peeled off. Then, the resultant laminate was subjected to spray development using water at a temperature of 30 °C through a nozzle at a jet pressure of 3 kg/cm² for 30 seconds to remove the unexposed portion of the photosensitive film capable of being developed by the use of water, thus forming a pattern. The pattern obtained was evaluated with respect to the pattern form. As a result, the minimum line width was 60 μm among the lines formed. Then, the pattern was subjected to baking treatment in which the temperature was elevated at the elevation rate of 10°C/min and then maintained at 580 °C for 30 minutes. As a result, an excellent dielectric pattern was obtained.

INDUSTRIAL APPLICABILITY As described above, the inorganic paste composition of the present invention is advantageous not only in that the dispersibility of the inorganic powders in the composition is excellent, but also in that a film having a uniform thickness can be formed from the composition. Further, the shrinkage after the baking can be suppressed, and therefore the inorganic paste composition is very useful as a material for forming a dielectric layer and a spacer layer in a multilayer circuit and various displays, such as a plasma display, a plasma address liquid-crystal display, and a field emission display, especially in a plasma display front plate required to have high precision.

Claims

1. An inorganic paste composition comprising inorganic powders, a binder resin having a hydroxyl group in a side chain thereof, and an organic solvent having no hydroxyl group, wherein the inorganic paste composition contains an organic solvent having a hydroxyl group in an amount equal to or less than 5% by weight.

2. The inorganic paste composition according to claim 1 , wherein the organic solvent having no hydroxyl group is at least one organic solvent selected from the group consisting of an ether, a ketone, and an ester.

3. The inorganic paste composition according to claim 1 , wherein the binder resin having a hydroxyl group in its side chain is an acrylic resin having a hydroxyl group.

4. The inorganic paste composition according to claim 3, wherein the content of the hydroxyl group in the side chain of the binder resin is equal to or less than 0.3 per one monomer unit, in terms of an average number of the hydroxyl group contained in the side chain per monomer unit of the binder resin.

5. The inorganic paste composition according to claim 1 , further comprising a photopolymerizable monomer and a photopolymerization initiator.

6. A method for preparing an inorganic paste composition which comprises inorganic powders, a binder resin having a hydroxyl group in its side chain, and an organic solvent having no hydroxyl group, the method comprising a step of mixing together three components comprising the inorganic powders, the binder resin having a hydroxyl group in its side chain, and the organic solvent having no hydroxyl group and kneading the resultant mixture, wherein the mixture in the kneading step contains an organic solvent having a hydroxyl group in an amount equal to or less than 5% by weight.

7. A sheet-shaped unbaked body for producing a display panel which comprises a substrate and a dielectric layer formed on the substrate, the sheet-shaped unbaked body being used for producing the dielectric layer in the display panel, wherein the sheet-shaped unbaked body comprises a removable support film and an inorganic paste film formed on the removable support film, the inorganic paste film being comprised of at least the inorganic paste composition according to claim 1.

8. A sheet-shaped unbaked body for producing a display panel which comprises a substrate and a dielectric layer formed on the substrate, the sheet-shaped unbaked body being used for producing the dielectric layer in the display panel, wherein the sheet-shaped unbaked body comprises a removable support film and an inorganic paste film formed on the removable support film, the inorganic paste film being comprised of at least the inorganic paste composition according to claim 2.

9. A sheet-shaped unbaked body for producing a display panel which comprises a substrate and a dielectric layer formed on the substrate, the sheet-shaped unbaked body being used for producing the dielectric layer in the display panel, wherein the sheet-shaped unbaked body comprises a removable support film and an inorganic paste film formed on the removable support film, the inorganic paste film being comprised of at least the inorganic paste composition according to claim 3.

10. A sheet-shaped unbaked body for producing a display panel which comprises a substrate and a dielectric layer formed on the substrate, the sheet-shaped unbaked body being used for producing the dielectric layer in the display panel, wherein the sheet-shaped unbaked body comprises a removable support film and an inorganic paste film formed on the removable support film, the inorganic paste film being comprised of at least the inorganic paste composition according to claim 4.

11. A sheet-shaped unbaked body for producing a display panel which comprises a substrate, a dielectric layer formed on the substrate, and a plurality of spacer layers each having a uniform thickness formed on the dielectric layer, the sheet-shaped unbaked body being used for producing the spacer layers in the display panel, wherein the sheet-shaped unbaked body comprises a removable support film and an inorganic paste film formed on the removable support film, the inorganic paste film being comprised of at least the inorganic paste composition according to claim 5.