BINDER FOR PRODUCTION OF INORGANIC SINTERED BODY

Abstract

The present invention provides a binder for producing an inorganic sintered body having excellent thermal decomposability and capable of providing, especially when used as a binder for a ceramic green sheet, a ceramic green sheet that has sufficient mechanical strength and flexibility, is less likely to absorb moisture, and can maintain its excellent sheet properties over a long period of time. The present invention also provides a paste for producing an inorganic sintered body and a ceramic green molded article each obtained using the binder for producing an inorganic sintered body. The present invention relates to a binder for producing an inorganic sintered body containing a graft copolymer, the graft copolymer having a unit including polyvinyl butyral and a unit including a poly(meth)acrylic compound, the polyvinyl butyral having a degree of polymerization of 800 to 5,000, a hydroxy group content of 20 to 40 mol %, and a degree of butyralization of 60 to 80 mol %, the unit including a poly(meth)acrylic compound having a glass transition temperature of 65 C. or higher and lower than 0 C.

Claims

1. A binder for producing an inorganic sintered body comprising a graft copolymer, the graft copolymer having a unit including polyvinyl butyral and a unit including a poly(meth)acrylic compound, the polyvinyl butyral having a degree of polymerization of 800 to 5,000, a hydroxy group content of 20 to 40 mol %, and a degree of butyralization of 60 to 80 mol %, the unit including a poly(meth)acrylic compound having a glass transition temperature of 65 C. or higher and lower than 0 C.

2. The binder for producing an inorganic sintered body according to claim 1, wherein the graft copolymer having a unit including polyvinyl butyral and a unit including a poly(meth)acrylic compound has an average glass transition temperature obtained using the formula (2) of 30 C. to 50 C.:
Average glass transition temperature={(Glass transition temperature of the unit including polyvinyl butyral)(Content rate of the unit including polyvinyl butyral in the graft copolymer)}+{(Glass transition temperature of the unit including a poly(meth)acrylic compound)(Content rate of the unit including a poly(meth)acrylic compound in the graft copolymer)}(2).

3. The binder for producing an inorganic sintered body according to claim 1, wherein the graft copolymer having a unit including polyvinyl butyral and a unit including a poly(meth)acrylic compound contains 10 to 90% by weight of the unit including polyvinyl butyral and 10 to 90% by weight of the unit including a poly(meth)acrylic compound.

4. The binder for producing an inorganic sintered body according to claim 1, wherein the poly(meth)acrylic compound includes a (meth)acrylic compound containing 90% by weight or more of a methacrylic compound.

5. The binder for producing an inorganic sintered body according to claim 1, wherein the poly(meth)acrylic compound includes a (meth)acrylic compound containing 3 to 50% by weight of a (meth)acrylic compound having a carboxyl group, a hydroxy group, an epoxy group, or an ether group in a molecule.

6. A paste for producing an inorganic sintered body comprising: the binder for producing an inorganic sintered body according to claim 1; an organic solvent; and inorganic fine particles.

7. The paste for producing an inorganic sintered body according to claim 6 further comprising a pore-forming agent for achieving porosity.

8. A ceramic green molded article produced using the paste for producing an inorganic sintered body according to claim 6.

Description

DESCRIPTION OF EMBODIMENTS

[0098] Embodiments of the present invention are specifically described with reference to examples, but are not limited only to these examples.

EXAMPLE 1

(1) Preparation of a Graft Copolymer

[0099] A reaction vessel equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a condenser tube was charged with 25 parts by weight of polyvinyl butyral (degree of polymerization: 1,100, degree of butyralization:

[0100] 68.0 mol %, hydroxy group content: 31.2 mol %, acetyl group content: 0.8 mol %), 23 parts by weight of 2-ethylhexyl methacrylate, 2 parts by weight of 2-hydroxyethyl methacrylate, and 100 parts by weight of ethyl acetate. The contents were stirred so that polyvinyl butyral was dissolved. Next, nitrogen gas was blown into the reaction vessel for 30 minutes so that the air inside was substituted with nitrogen, and the contents in the reaction vessel were heated to 75 C. with stirring. Thirty minutes later, a polymerization initiator solution prepared by diluting 0.5 parts by weight of t-hexyl peroxypivalate as a polymerization initiator with 16 parts by weight of ethyl acetate was added dropwise to the reaction vessel over 5 hours. Then, the reaction was allowed to proceed at 75 C. for 3 hours.

[0101] Next, the reaction solution was cooled to give a graft copolymer solution (solid content of 30% by weight) containing a graft copolymer.

[0102] The weight average molecular weight in terms of polystyrene of the obtained graft copolymer was measured by the GPC method using a 2690 Separations Model (available from Waters) as a column, and was 230,000.

[0103] The graft efficiency was 69% and the graft ratio was 69%.

[0104] The poly(meth)acrylic compound unit had a glass transition temperature of 6 C. The obtained graft copolymer had an average glass transition temperature of 31 C.

(2) Production of a Ceramic Green Sheet

[0105] The obtained graft copolymer solution was diluted with a diluting solvent (mixed solvent of ethanol and toluene, weight ratio (ethanol:toluene) of 1:1) to give a solution having a solid content of 10% by weight. Next, 20 parts by weight of the solution was blended with 20 parts by weight of barium titanate powder (BT-03, average particle size of 0.3 m, available from Sakai Chemical Industry Co., Ltd.) as ceramic powder, and mixed using a ball mill for 48 hours to give slurry for a ceramic green sheet.

[0106] The obtained slurry for a ceramic green sheet was applied to a PET film preliminarily subjected to mold release treatment, using a coater to a dry thickness of 3 m. The applied slurry was air-dried at normal temperature for one hour, and dried at 80 C. for one hour and then at 120 C. for one hour by a hot air dryer, thereby providing a ceramic green sheet.

EXAMPLE 2

[0107] A graft copolymer solution (solid content of 30% by weight) containing a graft copolymer was prepared in the same manner as in Example 1, except that, in (1) Preparation of a graft copolymer of Example 1, polyvinyl butyral (degree of polymerization: 1,700, degree of butyralization: 68.0 mol %, hydroxy group content: 31.2 mol %, acetyl group content: 0.8 mol %) was used and that 5 parts by weight of 2-ethylhexyl methacrylate, 18 parts by weight of isodecyl methacrylate, and 2 parts by weight of 2-hydroxyethyl methacrylate were used instead of 23 parts by weight of 2-ethylhexyl methacrylate and 2 parts by weight of 2-hydroxyethyl methacrylate.

[0108] The weight average molecular weight in terms of polystyrene of the obtained graft copolymer was measured by the GPC method using a 2690 Separations Model (available from Waters) as a column, and was 260,000.

[0109] The graft efficiency was 61% and the graft ratio was 61%.

[0110] The poly(meth)acrylic compound unit of the obtained graft copolymer had a glass transition temperature of 29 C. The obtained graft copolymer had an average glass transition temperature of 19 C.

[0111] A ceramic green sheet was obtained in the same manner as in (2) Production of a ceramic green sheet in Example 1, except that the obtained graft copolymer solution was used.

EXAMPLE 3

[0112] A graft copolymer solution (solid content of 30% by weight) containing a graft copolymer was prepared in the same manner as in Example 2, except that, in (1) Preparation of a graft copolymer of Example 2, 5 parts by weight of isodecyl methacrylate, 18 parts by weight of n-lauryl methacrylate, and 2 parts by weight of 2-hydroxyethyl methacrylate were used instead of 5 parts by weight of 2-ethylhexyl methacrylate, 18 parts by weight of isodecyl methacrylate, and 2 parts by weight of 2-hydroxyethyl methacrylate.

[0113] The weight average molecular weight in terms of polystyrene of the obtained graft copolymer was measured by the GPC method using a 2690 Separations Model (available from Waters) as a column, and was 270,000.

[0114] The graft efficiency was 59% and the graft ratio was 59%.

[0115] The (meth)acrylic compound unit of the obtained graft copolymer had a glass transition temperature of 54 C. The obtained graft copolymer had an average glass transition temperature of 7 C.

[0116] A ceramic green sheet was obtained in the same manner as in (2) Production of a ceramic green sheet in Example 1, except that the obtained graft copolymer solution was used.

EXAMPLE 4

[0117] A graft copolymer solution (solid content of 40% by weight) containing a graft copolymer was prepared in the same manner as in Example 1, except that, in (1) Preparation of a graft copolymer of Example 1, polyvinyl butyral (degree of polymerization: 4,000, degree of butyralization: 67.9 mol %, hydroxy group content: 30.7 mol %, acetyl group content: 1.4 mol %) was used and that 50 parts by weight of n-lauryl methacrylate and 2 parts by weight of 2-hydroxyethyl methacrylate were used instead of 23 parts by weight of 2-ethylhexyl methacrylate and 2 parts by weight of 2-hydroxyethyl methacrylate.

[0118] The weight average molecular weight in terms of polystyrene of the obtained graft copolymer was measured by the GPC method using a 2690 Separations Model (available from Waters) as a column, and was 500,000.

[0119] The graft efficiency was 72% and the graft ratio was 150%.

[0120] The (meth)acrylic compound unit of the obtained graft copolymer had a glass transition temperature of 62 C. The obtained graft copolymer had an average glass transition temperature of 20 C.

[0121] A ceramic green sheet was obtained in the same manner as in (2) Production of a ceramic green sheet in Example 1, except that the obtained graft copolymer solution was used.

EXAMPLE 5

[0122] A graft copolymer solution (solid content of 34% by weight) containing a graft copolymer was prepared in the same manner as in Example 1, except that, in (1) Preparation of a graft copolymer of Example 1, polyvinyl butyral (degree of polymerization: 800, degree of butyralization: 70.0 mol %, hydroxy group content: 29.0 mol %, acetyl group content: 1.0 mol %) was used and that 10 parts by weight of n-butyl methacrylate, 25 parts by weight of 2-ethylhexyl methacrylate, and 1 part by weight of 2-hydroxyethyl methacrylate were used instead of 23 parts by weight of 2-ethylhexyl methacrylate and 2 parts by weight of 2-hydroxyethyl methacrylate.

[0123] The weight average molecular weight in terms of polystyrene of the obtained graft copolymer was measured by the GPC method using a 2690 Separations Model (available from Waters) as a column, and was 220,000.

[0124] The graft efficiency was 69% and the graft ratio was 100%.

[0125] The (meth)acrylic compound of the obtained graft copolymer had a glass transition temperature of 1 C. The obtained graft copolymer had an average glass transition temperature of 26 C.

[0126] A ceramic green sheet was obtained in the same manner as in (2) Production of a ceramic green sheet in Example 1, except that the obtained graft copolymer solution was used.

EXAMPLE 6

[0127] A graft copolymer solution (solid content of 30% by weight) containing a graft copolymer was prepared in the same manner as in Example 1, except that, in (1) Preparation of a graft copolymer of Example 1, polyvinyl butyral (degree of polymerization: 1,100, degree of butyralization: 67.9 mol %, hydroxy group content: 30.7 mol %, acetyl group content: 1.4 mol %) was used and that 23.5 parts by weight of 2-ethylhexyl methacrylate, 0.5 parts by weight of glycidyl methacrylate, and 1 part by weight of methacrylic acid were used instead of 23 parts by weight of 2-ethylhexyl methacrylate and 2 parts by weight of 2-hydroxyethyl methacrylate.

[0128] The weight average molecular weight in terms of polystyrene of the obtained graft copolymer was measured by the GPC method using a 2690 Separations Model (available from Waters) as a column, and was 230,000.

[0129] The graft efficiency was 72% and the graft ratio was 72%.

[0130] The (meth)acrylic compound unit of the obtained graft copolymer had a glass transition temperature of 4 C. The obtained graft copolymer had an average glass transition temperature of 31 C.

[0131] A ceramic green sheet was obtained in the same manner as in (2) Production of a ceramic green sheet in Example 1, except that the obtained graft copolymer solution was used.

EXAMPLE 7

[0132] A graft copolymer solution (solid content of 42% by weight) containing a graft copolymer was prepared in the same manner as in Example 1, except that, in (1) Preparation of a graft copolymer of Example 1, polyvinyl butyral (degree of polymerization: 1,700, degree of butyralization: 66.1 mol %, hydroxy group content: 32.9 mol %, acetyl group content: 1.0 mol %) was used and that 50 parts by weight of 2-ethylhexyl methacrylate, 5 parts by weight of isodecyl methacrylate, 3 parts by weight of 2-hydroxyethyl methacrylate, 0.5 parts by weight of glycidyl methacrylate, and 1 part by weight of methacrylic acid were used instead of 23 parts by weight of 2-ethylhexyl methacrylate and 2 parts by weight of 2-hydroxyethyl methacrylate.

[0133] The weight average molecular weight in terms of polystyrene of the obtained graft copolymer was measured by the GPC method using a 2690 Separations Model (available from Waters) as a column, and was 360,000.

[0134] The graft efficiency was 85% and the graft ratio was 203%.

[0135] The (meth)acrylic compound unit of the obtained graft copolymer had a glass transition temperature of 8 C. The obtained graft copolymer had an average glass transition temperature of 15 C.

[0136] A ceramic green sheet was obtained in the same manner as in (2) Production of a ceramic green sheet in Example 1, except that the obtained graft copolymer solution was used.

EXAMPLE 8

[0137] A graft copolymer solution (solid content of 22% by weight) containing a graft copolymer was prepared in the same manner as in Example 1, except that, in (1) Preparation of a graft copolymer of Example 1, polyvinyl butyral (degree of polymerization: 1,700, degree of butyralization: 66.5 mol %, hydroxy group content: 32.2 mol %, acetyl group content: 1.3 mol %) was used and that 3 parts by weight of 2-ethylhexyl methacrylate, 3 parts by weight of isodecyl methacrylate, and 2 parts by weight of n-lauryl methacrylate were used instead of 23 parts by weight of 2-ethylhexyl methacrylate and 2 parts by weight of 2-hydroxyethyl methacrylate.

[0138] The weight average molecular weight in terms of polystyrene of the obtained graft copolymer was measured by the GPC method using a 2690 Separations Model (available from Waters) as a column, and was 290,000.

[0139] The graft efficiency was 55% and the graft ratio was 18%.

[0140] The (meth)acrylic compound unit of the obtained graft copolymer had a glass transition temperature of 37 C. The obtained graft copolymer had an average glass transition temperature of 43 C.

[0141] A ceramic green sheet was obtained in the same manner as in (2) Production of a ceramic green sheet in Example 1, except that the obtained graft copolymer solution was used and dibutyl phthalate was used as a plasticizer.

EXAMPLE 9

[0142] A graft copolymer solution (solid content of 23% by weight) containing a graft copolymer was prepared in the same manner as in Example 1, except that, in (1) Preparation of a graft copolymer of Example 1, polyvinyl butyral (degree of polymerization: 1,700, degree of butyralization: 66.1 mol %, hydroxy group content: 32.9 mol %, acetyl group content: 1.0 mol %) was used and that 2 parts by weight of n-butyl methacrylate, 8 parts by weight of 2-ethylhexyl methacrylate, and 0.5 parts by weight of 2-hydroxyethyl methacrylate were used instead of 23 parts by weight of 2-ethylhexyl methacrylate and 2 parts by weight of 2-hydroxyethyl methacrylate.

[0143] The weight average molecular weight in terms of polystyrene of the obtained graft copolymer was measured by the GPC method using a 2690 Separations Model (available from Waters) as a column, and was 280,000.

[0144] The graft efficiency was 44% and the graft ratio was 1.8%.

[0145] The (meth)acrylic compound unit of the obtained graft copolymer had a glass transition temperature of 2 C. The obtained graft copolymer had an average glass transition temperature of 48 C.

[0146] A ceramic green sheet was obtained in the same manner as in (2) Production of a ceramic green sheet in Example 1, except that the obtained graft copolymer solution was used.

EXAMPLE 10

[0147] A graft copolymer solution (solid content of 22% by weight) containing a graft copolymer was prepared in the same manner as in Example 1, except that, in (1) Preparation of a graft copolymer of Example 1, polyvinyl butyral (degree of polymerization: 1,700, degree of butyralization: 66.1 mol %, hydroxy group content: 32.9 mol %, acetyl group content: 1.0 mol %) was used and that 1 part by weight of n-butyl methacrylate and 7 parts by weight of 2-ethylhexyl methacrylate were used instead of 23 parts by weight of 2-ethylhexyl methacrylate and 2 parts by weight of 2-hydroxyethyl methacrylate.

[0148] The weight average molecular weight in terms of polystyrene of the obtained graft copolymer was measured by the GPC method using a 2690 Separations Model (available from Waters) as a column, and was 260,000.

[0149] The graft efficiency was 31% and the graft ratio was 10%.

[0150] The (meth)acrylic compound unit of the obtained graft copolymer had a glass transition temperature of 7 C. The obtained graft copolymer had an average glass transition temperature of 51 C.

[0151] A ceramic green sheet was obtained in the same manner as in (2) Production of a ceramic green sheet in Example 1, except that the obtained graft copolymer solution was used.

EXAMPLE 11

[0152] A graft copolymer solution (solid content of 45% by weight) containing a graft copolymer was prepared in the same manner as in Example 1, except that, in (1) Preparation of a graft copolymer of Example 1, polyvinyl butyral (degree of polymerization: 800, degree of butyralization: 70.0 mol %, hydroxy group content: 29.0 mol %, acetyl group content: 1.0 mol %) was used and that 2 parts by weight of 2-ethylhexyl methacrylate, 65 parts by weight of n-lauryl methacrylate, and 1 part by weight of 2-hydroxyethyl methacrylate were used instead of 23 parts by weight of 2-ethylhexyl methacrylate and 2 parts by weight of 2-hydroxyethyl methacrylate.

[0153] The weight average molecular weight in terms of polystyrene of the obtained graft copolymer was measured by the GPC method using a 2690 Separations Model (available from Waters) as a column, and was 270,000.

[0154] The graft efficiency was 77% and the graft ratio was 210%.

[0155] The (meth)acrylic compound unit of the obtained graft copolymer had a glass transition temperature of 63 C. The obtained graft copolymer had an average glass transition temperature of 28 C.

[0156] A ceramic green sheet was obtained in the same manner as in (2) Production of a ceramic green sheet in Example 1, except that the obtained graft copolymer solution was used.

EXAMPLE 12

[0157] A graft copolymer solution (solid content of 46% by weight) containing a graft copolymer was prepared in the same manner as in Example 1, except that, in (1) Preparation of a graft copolymer of Example 1, polyvinyl butyral (degree of polymerization: 800, degree of butyralization: 70.0 mol %, hydroxy group content: 29.0 mol %, acetyl group content: 1.0 mol %) was used and that 2 parts by weight of 2-ethylhexyl methacrylate and 73 parts by weight of n-lauryl methacrylate were used instead of 23 parts by weight of 2-ethylhexyl methacrylate and 2 parts by weight of 2-hydroxyethyl methacrylate.

[0158] The weight average molecular weight in terms of polystyrene of the obtained graft copolymer was measured by the GPC method using a 2690 Separations Model (available from Waters) as a column, and was 280,000.

[0159] The graft efficiency was 78% and the graft ratio was 233%.

[0160] The (meth)acrylic compound unit of the obtained graft copolymer had a glass transition temperature of 64 C. The obtained graft copolymer had an average glass transition temperature of 32 C.

[0161] A ceramic green sheet was obtained in the same manner as in (2) Production of a ceramic green sheet in Example 1, except that the obtained graft copolymer solution was used.

EXAMPLE 13

[0162] A graft copolymer solution (solid content of 37% by weight) containing a graft copolymer was prepared in the same manner as in Example 1, except that, in (1) Preparation of a graft copolymer of Example 1, polyvinyl butyral (degree of polymerization: 1,700, degree of butyralization: 66.1 mol %, hydroxy group content: 32.9 mol %, acetyl group content: 1.0 mol %) was used and that 40 parts by weight of n-lauryl methacrylate and 2 parts by weight of 2-hydroxyethyl methacrylate were used instead of 23 parts by weight of 2-ethylhexyl methacrylate and 2 parts by weight of 2-hydroxyethyl methacrylate.

[0163] The weight average molecular weight in terms of polystyrene of the obtained graft copolymer was measured by the GPC method using a 2690 Separations Model (available from Waters) as a column, and was 320,000.

[0164] The graft efficiency was 73% and the graft ratio was 123%.

[0165] The (meth)acrylic compound unit of the obtained graft copolymer had a glass transition temperature of 61 C. The obtained graft copolymer had an average glass transition temperature of 14 C.

[0166] A ceramic green sheet was obtained in the same manner as in (2) Production of a ceramic green sheet in Example 1, except that the obtained graft copolymer solution was used.

EXAMPLE 14

[0167] A graft copolymer solution (solid content of 24% by weight) containing a graft copolymer was prepared in the same manner as in Example 1, except that, in (1) Preparation of a graft copolymer of Example 1, polyvinyl butyral (degree of polymerization: 800, degree of butyralization: 70.0 mol %, hydroxy group content: 29.0 mol %, acetyl group content: 1.0 mol %) was used and that 10 parts by weight of 2-ethylhexyl methacrylate and 2 parts by weight of i-butyl acrylate were used instead of 23 parts by weight of 2-ethylhexyl methacrylate and 2 parts by weight of 2-hydroxyethyl methacrylate.

[0168] The weight average molecular weight in terms of polystyrene of the obtained graft copolymer was measured by the GPC method using a 2690 Separations Model (available from Waters) as a column, and was 200,000.

[0169] The graft efficiency was 49% and the graft ratio was 23%.

[0170] The (meth)acrylic compound unit of the obtained graft copolymer had a glass transition temperature of 12 C. The obtained graft copolymer had an average glass transition temperature of 39 C.

[0171] A ceramic green sheet was obtained in the same manner as in (2) Production of a ceramic green sheet in Example 1, except that the obtained graft copolymer solution was used.

COMPARATIVE EXAMPLE 1

[0172] An amount of 25 parts by weight of polyvinyl butyral (degree of polymerization: 1,100, degree of butyralization: 68.0 mol %, hydroxy group content: 31.2 mol %, acetyl group content: 0.8 mol %) was dissolved in a mixed solvent of ethanol and toluene (ethanol:toluene=1:1) to a solid content of 10% by weight, thereby preparing a polyvinyl butyral resin solution.

[0173] The weight average molecular weight in terms of polystyrene of the obtained polyvinyl butyral was measured by the GPC method using a 2690 Separations Model (available from Waters) as a column, and was 230,000.

[0174] A ceramic green sheet was obtained in the same manner as in (2) Production of a ceramic green sheet in Example 1, except that the obtained polyvinyl butyral resin solution was used instead of the graft copolymer solution and 0.4 parts by weight of dioctylphthalate was added as a plasticizer.

COMPARATIVE EXAMPLE 2

[0175] An amount of 25 parts by weight of polyvinyl butyral (degree of polymerization: 1,100, degree of butyralization: 68.0 mol %, hydroxy group content: 31.2 mol %, acetyl group content: 0.8 mol %) was dissolved in a mixed solvent of ethanol and toluene (ethanol:toluene=1:1) to a solid content of 10% by weight, thereby preparing a polyvinyl butyral resin solution. The weight average molecular weight in terms of polystyrene of the obtained polyvinyl butyral was measured by the GPC method using a 2690 Separations Model (available from Waters) as a column, and was 230,000.

[0176] A ceramic green sheet was obtained in the same manner as in (2) Production of a ceramic green sheet in Example 1, except that the obtained polyvinyl butyral resin solution was used instead of the graft copolymer solution.

COMPARATIVE EXAMPLE 3

[0177] An amount of 25 parts by weight of poly(2-ethylhexyl methacrylate) (weight average molecular weight: 280,000) was dissolved in a mixed solvent of ethanol and toluene (ethanol:toluene=1:1) to a solid content of 10% by weight, thereby preparing a poly(2-ethylhexyl methacrylate) solution.

[0178] A ceramic green sheet was obtained in the same manner as in (2) Production of a ceramic green sheet in Example 1, except that the obtained poly(2-ethylhexyl methacrylate) solution was used instead of the graft copolymer solution.

[0179] The poly(2-ethylhexyl methacrylate) had a glass transition temperature of 10 C.

COMPARATIVE EXAMPLE 4

[0180] A mixture (weight ratio of 1:1) of 25 parts by weight of polyvinyl butyral (degree of polymerization: 1,100, degree of butyralization: 68.0 mol %, hydroxy group content: 31.2 mol %, acetyl group content: 0.8 mol %) and 25 parts by weight of poly(2-ethylhexyl methacrylate) (weight average molecular weight: 280,000) was dissolved in a mixed solvent of ethanol and toluene (ethanol:toluene=1:1) to a solid content of 10% by weight, thereby preparing a mixed resin solution.

[0181] A ceramic green sheet was obtained in the same manner as in (2) Production of a ceramic green sheet in Example 1, except that the obtained mixed resin solution was used instead of the graft copolymer solution and 0.4 parts by weight of dioctylphthalate was added as a plasticizer.

COMPARATIVE EXAMPLE 5

[0182] A reaction vessel equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a condenser tube was charged with 25 parts by weight of polyvinyl butyral having a mercapto group at an end (degree of polymerization: 1,100, degree of butyralization: 68.0 mol %, hydroxy group content: 31.2 mol %, acetyl group content: 0.8 mol %), 2 parts by weight of n-butyl methacrylate, 6 parts by weight of 2-ethylhexyl methacrylate, and 100 parts by weight of ethyl acetate. The contents were stirred so that polyvinyl butyral was dissolved.

[0183] Next, nitrogen gas was blown into the reaction vessel for 30 minutes so that the air inside was substituted with nitrogen, and the contents in the reaction vessel were heated to 75 C. with stirring.

[0184] Thirty minutes later, a polymerization initiator solution obtained by diluting 0.5 parts by weight of AIBN as a polymerization initiator with 16 parts by weight of ethyl acetate was dropwise added to the reaction vessel over five hours.

[0185] Then, the reaction was allowed to proceed at 75 C. for three hours.

[0186] Next, the reaction solution was cooled to give a block copolymer solution (solid content of 20% by weight) containing a block copolymer.

[0187] The weight average molecular weight in terms of polystyrene of the obtained block copolymer was measured by GPC method using a 2690 Separations Model (available from Waters) as a column, and was 350,000.

[0188] A ceramic green sheet was obtained in the same manner as in (2) Production of a ceramic green sheet in Example 1, except that the obtained block copolymer solution was used and 0.15 parts by weight of dioctylphthalate was further added as a plasticizer.

COMPARATIVE EXAMPLE 6

[0189] A graft copolymer solution (solid content of 30% by weight) containing a graft copolymer was prepared in the same manner as in Example 1, except that, in (1) Preparation of a graft copolymer of Example 1, polyvinyl butyral (degree of polymerization: 1,700, degree of butyralization: 68.0 mol %, hydroxy group content: 30.8 mol %, acetyl group content: 1.2 mol %) was used and that 25 parts by weight of isobornyl methacrylate was used instead of 23 parts by weight of 2-ethylhexyl methacrylate and 2 parts by weight of 2-hydroxyethyl methacrylate.

[0190] The weight average molecular weight in terms of polystyrene of the obtained graft copolymer was measured by the GPC method using a 2690 Separations Model (available from Waters) as a column, and was 250,000.

[0191] The graft efficiency was 66% and the graft ratio was 66%.

[0192] The poly(meth)acrylic compound unit of the obtained graft copolymer had a glass transition temperature of 180 C. The obtained graft copolymer had an average glass transition temperature of 123 C.

[0193] A ceramic green sheet was obtained in the same manner as in (2) Production of a ceramic green sheet in Example 1, except that the obtained graft copolymer solution was used.

COMPARATIVE EXAMPLE 7

[0194] A graft copolymer solution (solid content of 30% by weight) containing a graft copolymer was prepared in the same manner as in Example 1, except that, in (1) Preparation of a graft copolymer of Example 1, polyvinyl butyral (degree of polymerization: 800, degree of butyralization: 67.0 mol %, hydroxy group content: 32.0 mol %, acetyl group content: 1.0 mol %) was used and that 25 parts by weight of methacrylic acid was used instead of 23 parts by weight of 2-ethylhexyl methacrylate and 2 parts by weight of 2-hydroxyethyl methacrylate.

[0195] The weight average molecular weight in terms of polystyrene of the obtained graft copolymer was measured by the GPC method using a 2690 Separations Model (available from Waters) as a column, and was 210,000.

[0196] The graft efficiency was 69% and the graft ratio was 69%.

[0197] The poly(meth)acrylic compound unit of the obtained graft copolymer had a glass transition temperature of 228 C. The obtained graft copolymer had an average glass transition temperature of 148 C.

[0198] A ceramic green sheet was obtained in the same manner as in (2) Production of a ceramic green sheet in Example 1, except that the obtained graft copolymer solution was used.

COMPARATIVE EXAMPLE 8

[0199] A graft copolymer solution (solid content of 30% by weight) containing a graft copolymer was prepared in the same manner as in Example 1, except that, in (1) Preparation of a graft copolymer of Example 1, polyvinyl butyral (degree of polymerization: 600, degree of butyralization: 80.0 mol %, hydroxy group content: 18.0 mol %, acetyl group content: 2.0 mol %) was used and that 12.5 parts by weight of n-butyl methacrylate and 12.5 parts by weight of 2-ethylhexyl methacrylate were used instead of 23 parts by weight of 2-ethylhexyl methacrylate and 2 parts by weight of 2-hydroxyethyl methacrylate.

[0200] The weight average molecular weight in terms of polystyrene of the obtained graft copolymer was measured by the GPC method using a 2690 Separations Model (available from Waters) as a column, and was 170,000.

[0201] The graft efficiency was 69% and the graft ratio was 69%.

[0202] The poly(meth)acrylic compound unit of the obtained graft copolymer had a glass transition temperature of 4 C. The obtained graft copolymer had an average glass transition temperature of 32 C.

[0203] A ceramic green sheet was obtained in the same manner as in (2) Production of a ceramic green sheet in Example 1, except that the obtained graft copolymer solution was used.

COMPARATIVE EXAMPLE 9

[0204] A graft copolymer solution (solid content of 30% by weight) containing a graft copolymer was prepared in the same manner as in Example 1, except that, in (1) Preparation of a graft copolymer of Example 1, polyvinyl butyral (degree of polymerization: 5,300, degree of butyralization: 55.0 mol %, hydroxy group content: 44.0 mol %, acetyl group content: 1.0 mol %) was used and that 25 parts by weight of n-lauryl methacrylate was used instead of 23 parts by weight of 2-ethylhexyl methacrylate and 2 parts by weight of 2-hydroxyethyl methacrylate.

[0205] The weight average molecular weight in terms of polystyrene of the obtained graft copolymer was measured by the GPC method using a 2690 Separations Model (available from Waters) as a column, and was 500,000.

[0206] The graft efficiency was 72% and the graft ratio was 72%.

[0207] The poly(meth)acrylic compound unit of the obtained graft copolymer had a glass transition temperature of 66 C. The obtained graft copolymer had an average glass transition temperature of 3 C.

[0208] A ceramic green sheet was obtained in the same manner as in (2) Production of a ceramic green sheet in Example 1, except that the obtained graft copolymer solution was used.

(Evaluation Method)

[0209] Properties of the obtained resin solutions and ceramic green sheets were evaluated by the following methods. Table 1 shows the results.

(Glass Transition Temperature of poly(meth)acrylic Compound Unit)

[0210] Each obtained resin solution was dried at 110 C. for one hour and then dissolved in xylene. An insoluble matter and a soluble matter thereof were separated. Here, the soluble matter was determined to be a homopolymer of a (meth)acrylic compound and the insoluble matter was determined to be a graft copolymer thereof.

[0211] The obtained graft copolymer was subjected to differential scanning calorimetry using a DSC6200 (available from SII) at a rate of temperature rise of 10 C./rain.

[0212] Out of two measured glass transition temperatures, the glass transition temperature not derived from a polyvinyl acetal unit within a range of 50 C. to 70 C. was determined to be the glass transition temperature of the poly(meth)acrylic compound unit.

(Evaluation of Thermal Decomposability)

[0213] A film of a binder resin having a thickness of 100 m was prepared using each obtained resin solution. The film was heated to 600 C. and observed whether or not it was completely decomposed. The thermal decomposability was evaluated based on the following criteria. [0214] (Excellent): Completely decomposed with no residues. [0215] (Good): Almost completely decomposed with few residues. [0216] (Poor): Residues were obviously left.

(Evaluation of Strength/Peeling Property)

[0217] Each obtained ceramic green sheet was peeled from the polyester film, and the condition thereof was visually observed. The strength/peeling property thereof was evaluated based on the following criteria. The evaluation test was carried out immediately after the preparation of the ceramic green sheet. [0218] (Excellent): Each ceramic green sheet was finely peeled from the polyester film, and the tested ceramic green sheet had no cuts or breaks. [0219] (Good): Each ceramic green sheet was finely peeled from the polyester film, and a few of the tested ceramic green sheets had slight cuts. [0220] (Average): Each ceramic green sheet was finely peeled from the polyester film, and nearly half of the tested ceramic green sheets had slight cuts. [0221] (poor): Each ceramic green sheet could not be peeled from the polyester film, or most of the tested ceramic green sheets had cuts or breaks.

(Flexibility)

[0222] The central portion of the green sheet was pressed by a glass core rod having a diameter of 2 mm. A 180 bending test was performed in which the green sheet was bended from the pressed central portion. The flexibility of the sheet was evaluated based on the following criteria. The evaluation test was carried out immediately after the preparation of the ceramic green sheet. [0223] (Good): No crack was observed. [0224] (Average): Slight cracks were observed. [0225] (Poor): Remarkable cracks were observed.

(Sheet Stability)

[0226] Each obtained green sheet was left to stand for 10 days, and the strength/peeling property and the flexibility were evaluated as described above. The stability was evaluated based on the following criteria. [0227] (Excellent): The evaluation results of the strength/peeling property and the flexibility were both or . [0228] (Good): One of the evaluation results of the strength/peeling property and the flexibility was . [0229] (Average): One of the evaluation results of the strength/peeling property and the flexibility was . [0230] (Poor): The evaluation results of the strength/peeling property and the flexibility were both .

TABLE-US-00001 TABLE 1 Example 1 2 3 4 5 6 7 8 9 10 11 12 Binder Polyvinyl Polyvinyl butyral Amount (parts by weight) 25 25 25 25 25 25 25 25 25 25 25 25 resin butyral Degree of polymerization 1100 1700 1700 4000 800 1100 1700 1700 1700 1700 800 800 unit Degree of butyralization (mol %) 68 68 68 67.9 70 67.9 66.1 66.5 66.1 66.1 70 70 Hydroxyl group content (mol %) 31.2 31.2 31.2 30.7 29 30.7 32.9 32.2 32.9 32.9 29 29 Glass transition temperature ( C.) 67 67 67 66 64 66 68 68 68 68 64 64 Poly(meth) n-Butyl metyacrylate Amount (parts by weight) 0 0 0 0 10 0 0 0 2 1 0 0 acrylic 2-Ethylhexyl methacrylate Amount (parts by weight) 23 5 0 0 25 23.5 50 3 8 7 2 2 compound Isodecyl methacrylate Amount (parts by weight) 0 18 5 0 0 0 5 3 0 0 0 0 unit n-Lauryl methacrylate Amount (parts by weight) 0 0 18 50 0 0 0 2 0 0 65 73 2-Hydroxyethyl methacrylate Amount (parts by weight) 2 2 2 2 1 0 3 0 0.5 0 1 0 Glycidyl methacrylate Amount (parts by weight) 0 0 0 0 0 0.5 0.5 0 0 0 0 0 Methacrylic acid Amount (parts by weight) 0 0 0 0 0 1 1 0 0 0 0 0 Isobornyl methacrylate Amount (parts by weight) 0 0 0 0 0 0 0 0 0 0 0 0 i-Butyl acylate Amount (parts by weight) 0 0 0 0 0 0 0 0 0 0 0 0 Glass transition temperature ( C.) 6 29 54 62 1 4 8 37 2 7 63 64 Average glass transition temperature ( C.) 31 19 7 20 26 31 15 43 48 51 28 32 Evaluation of resin solution Weight fraction of polyvinyl 59 62 63 40 50 58 33 85 85 91 32 30 butyral unit (%) Weight fraction of 41 38 37 60 50 42 67 15 15 9 68 70 poly(meth)acrylic compound unit (%) Thermal decomposability evaluation Evaluation of green sheet Strength/peeling property evaluation Flexibility Sheet stability Moisture absorbability (%) 0.22 0.21 0.21 0.16 0.25 0.2 0.15 0.38 0.35 0.45 0.15 0.15 Example Comparative Example 13 14 1 2 3 4.sup.*1 5.sup.*2 6 7 8 9 Binder Polyvinyl Polyvinyl butyral Amount (parts by weight) 25 25 25 25 0 25 25 25 25 25 25 resin butyral Degree of polymerization 1700 800 1100 1100 1100 1100 1700 800 600 5300 unit Degree of butyralization (mol %) 66.1 70 68 68 68 68 68 67 80 55 Hydroxyl group content (mol %) 32.9 29 31.2 31.2 31.2 31.2 30.8 32 18 44 Glass transition temperature ( C.) 68 64 20 67 20 50 66 68 59 71 Poly(meth) n-Butyl metyacrylate Amount (parts by weight) 0 0 0 0 0 0 2 0 0 12.5 0 acrylic 2-Ethylhexyl methacrylate Amount (parts by weight) 0 10 0 0 25 25 6 0 0 12.5 0 compound Isodecyl methacrylate Amount (parts by weight) 0 0 0 0 0 0 0 0 0 0 0 unit n-Lauryl methacrylate Amount (parts by weight) 40 0 0 0 0 0 0 0 0 0 25 2-Hydroxyethyl methacrylate Amount (parts by weight) 2 0 0 0 0 0 0 0 0 0 0 Glycidyl methacrylate Amount (parts by weight) 0 0 0 0 0 0 0 0 0 0 0 Methacrylic acid Amount (parts by weight) 0 0 0 0 0 0 0 0 25 0 0 Isobornyl methacrylate Amount (parts by weight) 0 0 0 0 0 0 0 25 0 0 0 i-Butyl acylate Amount (parts by weight) 0 2 0 0 0 0 0 0 0 0 0 Glass transition temperature ( C.) 61 12 10 180 228 4 66 Average glass transition temperature ( C.) 14 39 123 148 32 3 Evaluation of resin solution Weight fraction of polyvinyl 45 81 60 59 59 58 butyral unit (%) Weight fraction of 55 19 40 41 41 42 poly(meth)acrylic compound unit (%) Thermal decomposability x x x evaluation Evaluation of green sheet Strength/peeling property x x x x x x x evaluation Flexibility x x x x x Sheet stability x x x x x x Moisture absorbability (%) 0.24 0.36 0.61 0.72 0.11 0.3 0.46 0.26 6.5 0.36 0.27 .sup.*1Resin mixture .sup.*2Block copolymer Note: A plasticizer is contained in Comparative Examples 1, 4, and 5

(Moisture Absorbability)

[0231] Each obtained green sheet was dried at 110 C. for three hours, and allowed to stand still in a constant-temperature and constant-humidity condition at 30 C. and 95%RH for three days. Then, the green sheet was taken out and the weight thereof before and after the standing in a constant-temperature and constant-humidity condition was measured to obtain the moisture absorption rate. The moisture absorption rate was calculated using the following equation (5).

Moisture absorption rate (%)={[(Sheet weight before standing in a constant-temperature and constant-humidity condition)(sheet weight after standing in a constant-temperature and constant-humidity condition)]/(Sheet weight before standing in a constant-temperature and constant-humidity condition)}100

INDUSTRIAL APPLICABILITY

[0232] The present invention can provide a binder for producing an inorganic sintered body having excellent thermal decomposability and capable of providing, especially when used as a binder for a ceramic green sheet, a ceramic green sheet that has sufficient mechanical strength and flexibility, is less likely to absorb moisture, and can maintain its excellent sheet properties over a long period of time. The present invention can also provide a paste for producing an inorganic sintered body and a ceramic green molded article each obtained using the binder for producing an inorganic sintered body.

[0233] The binder for producing an inorganic sintered body of the present invention can be also suitably used as a binder for a ceramic green sheet to be used in a fuel cell.