ELECTROCONDUCTIVE PASTE

Abstract

The present invention provides a conductive paste which leaves less fine undissolved matter when dissolved in an organic solvent and thus can be easily filtrated, which has excellent printability, and which can exhibit excellent surface smoothness after printing. Provided is a conductive paste used for forming an electrode of a multilayer ceramic capacitor, the conductive paste containing: a polyvinyl acetal resin; an organic solvent; and a conductive powder, the polyvinyl acetal resin having a wave number A (cm.sup.−1) of a peak within a range of 3,100 to 3,700 cm.sup.−1 in an IR absorption spectrum measured using an infrared spectrophotometer; and a hydroxy group content (mol %), the wavenumber A of the peak and the hydroxy group content satisfying relations of the following formulas (1) and (2):

[(3,470−A)/Hydroxy group content]≤5.0  (1)

(3,470−A)≤150  (2)

wherein A is a wavenumber which is lower than 3,470 cm.sup.−1 and at which a transmittance a (%) satisfying [100−(100−X)/2] is exhibited, where X (%) is s minimum transmittance of the peak within the wavenumber range of 3,100 to 3,700 cm.sup.−1.

Claims

1. A conductive paste used for forming an electrode of a multilayer ceramic capacitor, the conductive paste comprising: a polyvinyl acetal resin; an organic solvent; and a conductive powder, the polyvinyl acetal resin having: a wavenumber A (cm.sup.−1) of a peak within a range of 3,100 to 3,700 cm.sup.−1 in an IR absorption spectrum measured using an infrared spectrophotometer; and a hydroxy group content (mol %), the wavenumber A of the peak and the hydroxy group content satisfying relations of the following formulas (1) and (2):
[(3,470−A)/Hydroxy group content]≤5.0  (1)
(3,470−A)≤150  (2) wherein A is a wavenumber which is lower than 3,470 cm.sup.−1 and at which a transmittance a (%) satisfying [100−(100−X)/2] is exhibited, where X (%) is a minimum transmittance of the peak within the wavenumber range of 3,100 to 3,700 cm.sup.−1.

2. The conductive paste according to claim 1, wherein the polyvinyl acetal resin has a wavenumber B (cm.sup.1) of the peak within the wavenumber of 3,100 to 3,700 cm.sup.1 in the IR absorption spectrum measured using the infrared spectrophotometer; and the wavenumber A of the peak and the wavenumber B of the peak satisfy a relation of the following formula (3):
(3,470−A)/(B−3,470)≤1.4  (3) wherein B is a wavenumber which is higher than 3,470 cm.sup.−1 and at which the transmittance a (%) satisfying [100−(100−X)/2] is exhibited, where X (%) is the minimum transmittance of the peak within the wavenumber range of 3,100 to 3,700 cm.sup.−1.

3. The conductive paste according claim 1, wherein the polyvinyl acetal resin has a hydroxy group content of 16 to 25 mol %, an acetyl group content of 0.1 to 12 mol %, and an acetoacetal group content of 27 mol % or less.

4. The conductive paste according to claim 1, wherein the polyvinyl acetal resin contains a carboxy group-containing constitutional unit in an amount of 0.01 to 1.0 mol %.

5. The conductive paste according claim 2, wherein the polyvinyl acetal resin has a hydroxy group content of 16 to 25 mol %, an acetyl group content of 0.1 to 12 mol %, and an acetoacetal group content of 27 mol % or less.

6. The conductive paste according to claim 2, wherein the polyvinyl acetal resin contains a carboxy group-containing constitutional unit in an amount of 0.01 to 1.0 mol %.

7. The conductive paste according to claim 3, wherein the polyvinyl acetal resin contains a carboxy group-containing constitutional unit in an amount of 0.01 to 1.0 mol %.

8. The conductive paste according to claim 5, wherein the polyvinyl acetal resin contains a carboxy group-containing constitutional unit in an amount of 0.01 to 1.0 mol %.

Description

DESCRIPTION OF EMBODIMENTS

[0181] The present invention is more specifically described in the following with reference to, but not limited to, examples.

EXAMPLE 1

(Preparation of Polyvinyl Acetal Resin)

[0182] An amount of 100 g of a polyvinyl alcohol resin A (average degree of polymerization 1,750, degree of saponification 88 mol %, crystallinity 16%) was added to 1,000 g of pure water, and stirred at a temperature of 90° C. for two hours for dissolution. This solution was cooled to 40° C. To the solution were added 90 g of hydrochloric acid (concentration 35% by weight), 30 g of acetaldehyde, and 40 g of n-butyraldehyde. The solution temperature was decreased to 10° C., and this temperature was maintained while acetalization reaction was performed. After the reaction was completed, neutralization, washing with water, and drying were performed, whereby white powder of a polyvinyl acetal resin was obtained.

[0183] The crystallinity of the polyvinyl alcohol resin was measured by the following method.

[0184] Specifically, the polyvinyl alcohol resin was subjected to differential scanning calorimetry using a thermal analyzer (produced by Hitachi High-Tech Science Corporation, “DSC6200R”) under the following conditions. The heat of fusion in the second heating was measured to measure the crystallinity.

<Measure Conditions>

[0185] 0° C. (holding for five minutes).fwdarw.(first heating at heating rate of 10° C./min).fwdarw.270° C..fwdarw.(cooling at cooling rate of 10° C./min).fwdarw.0° C. (holding for five minutes).fwdarw.(second heating at heating rate of 10° C./min).fwdarw.270° C.

[0186] The heat of fusion was calculated from the area of a peak appearing between 100° C. and 270° C. in the second heating. The area of the peak was, as shown in FIG. 3, determined as the area of the region surrounded by the straight line connecting the points A and B and the DSC curve. The point A was the point at which a straight line drawn along the linear approximation portion of the DSC curve from 170° C. toward the higher temperature side leaves the DSC curve. The point B was the point on the DSC curve that shows the end-of-melt temperature. The crystallinity was calculated assuming that the heat of fusion of a polyvinyl alcohol resin having a crystallinity of 100% was 156 J/g.

(Preparation of Conductive Paste)

[0187] The obtained polyvinyl acetal resin (10 parts by weight) was dissolved in 90 parts by weight of dihydroterpineol to prepare a resin solution. Then, 180 parts by weight of nickel powder as a conductive powder and 20 parts by weight of barium titanate were mixed with 50 parts by weight of dihydroterpineol, and then mixed with the obtained resin solution, followed by dispersion in a triple roll mill. A conductive paste was thus obtained.

EXAMPLE 2

[0188] White powder of a polyvinyl acetal resin was obtained as in Example 1, except that 100 g of a carboxylic acid-modified polyvinyl alcohol resin B was used instead of 100 g of the polyvinyl alcohol resin A.

[0189] The carboxylic acid-modified polyvinyl alcohol resin B contained a carboxy group-containing constitutional unit represented by the formula (7-1) (in the formula (7-1), R.sup.2 is a single bond, R.sup.3 is CH.sub.2, X.sup.1 and X.sup.2 are hydrogen atoms), had an average degree of polymerization of 1,750, a degree of saponification of 89.2 mol %, a carboxy group content of 0.8 mol %, and a crystallinity of 19%.

[0190] A conductive paste was obtained as in Example 1 using the obtained polyvinyl acetal resin.

EXAMPLE 3

[0191] White powder of a polyvinyl acetal resin was obtained as in Example 1, except that a polyvinyl alcohol resin C (average degree of polymerization 1,750, degree of saponification 99 mol %, crystallinity 29%) was used instead of 100 g of the polyvinyl alcohol resin A and that the aldehydes used for reaction were changed to 25 g of acetaldehyde and 57 g of n-butyraldehyde.

[0192] A conductive paste was obtained as in Example 1 using the obtained polyvinyl acetal resin.

EXAMPLE 4

[0193] White powder of a polyvinyl acetal resin was obtained as in Example 1, except that 100 g of a polyvinyl alcohol resin D (average degree of polymerization 1,750, degree of saponification 96 mol %, crystallinity 22%) was used instead of 100 g of the polyvinyl alcohol resin A and that the aldehydes used for reaction were changed to 90 g of n-butyraldehyde.

[0194] A conductive paste was obtained as in Example 1 using the obtained polyvinyl acetal resin.

EXAMPLE 5

[0195] White powder of a polyvinyl acetal resin was obtained as in Example 1, except that 100 g of a carboxylic acid-modified polyvinyl alcohol resin E was used instead of 100 g of the polyvinyl alcohol resin A and that the aldehydes used for reaction were changed to 90 g of n-butyraldehyde.

[0196] The carboxylic acid-modified polyvinyl alcohol resin E contained a carboxy group-containing constitutional unit represented by the formula (7-1) (in the formula (7-1), R.sup.2 is a single bond, R.sup.3 is CH.sub.2, and X.sup.1 and X.sup.2 are hydrogen atoms) and had an average degree of polymerization of 1,750, a degree of saponification of 97.9 mol %, a carboxy group content of 0.1 mol %, and a crystallinity of 22%.

[0197] A conductive paste was obtained as in Example 1 using the obtained polyvinyl acetal resin.

EXAMPLE 6

[0198] White powder of a polyvinyl acetal resin was obtained as in Example 1, except that 100 g of a polyvinyl alcohol resin F (average degree of polymerization 1,750, degree of saponification 98 mol %, crystallinity 26%) was used instead of 109 g of the polyvinyl alcohol resin A and that the aldehydes used for reaction were changed to 95 g of n-butyraldehyde.

[0199] A conductive paste was obtained as in Example 1 using the obtained polyvinyl acetal resin.

EXAMPLE 7

[0200] White powder of a polyvinyl acetal resin was obtained as in Example 1, except that 100 g of a polyvinyl alcohol resin G (average degree of polymerization 900, degree of saponification 96 mol %, crystallinity 32%) was used instead of 100 g of the polyvinyl alcohol resin A and that the aldehydes used for reaction were changed to 85 g of n-butyraldehyde.

[0201] A conductive paste was obtained as in Example 1 using the obtained polyvinyl acetal resin.

EXAMPLE 8

[0202] White powder of a polyvinyl acetal resin was obtained as in Example 1, except that 100 g of a polyvinyl alcohol resin B (average degree of polymerization 900, degree of saponification 90 mol %, crystallinity 29%) was used instead of 100 g of the polyvinyl alcohol resin A and that the aldehydes used for reaction were changed to 15 g of acetaldehyde and 70 g of n-butyraldehyde.

[0203] A conductive paste was obtained as in Example 1 using the obtained polyvinyl acetal resin.

EXAMPLE 9

[0204] White powder of a polyvinyl acetal resin was obtained as in Example 1, except that 100 g of a polyvinyl alcohol resin J (average degree of polymerization 600, degree of saponification 98 mol %, crystallinity 381) was used instead of 100 g of the polyvinyl alcohol resin A and that the aldehydes used for reaction were changed to 30 g of acetaldehyde and 70 g of n-butyraldehyde.

[0205] A conductive paste was obtained as in Example 1 using the obtained polyvinyl acetal resin.

EXAMPLE 10

[0206] White powder of a polyvinyl acetal resin was obtained as in Example 1, except that 100 g of a polyvinyl alcohol resin K (average degree of polymerization 600, degree of saponification 99 mol %, crystallinity 38%) was used instead of 100 g of the polyvinyl alcohol resin A and that the aldehydes used for reaction were changed to 90 g of n-butyraldehyde.

[0207] A conductive paste was obtained as in Example 1 using the obtained polyvinyl acetal resin.

EXAMPLE 11

[0208] White powder of a polyvinyl acetal resin was obtained as in Example 1, except that 100 g of a polyvinyl alcohol resin L (average degree of polymerization 600, degree of saponification 96 mol %, crystallinity 3.5%) was used instead of 100 g of the polyvinyl alcohol resin A and that, the aldehydes used for reaction were changed to 20 g of acetaldehyde and 70 g of n-butyraldehyde.

[0209] A conductive paste was obtained as in Example 1 using the obtained polyvinyl acetal resin.

EXAMPLE 12

[0210] White powder of a polyvinyl acetal resin, was obtained as in Example 1, except that 100 g of a polyvinyl alcohol resin M (average degree of polymerization 400, degree of saponification 98 mol %, crystallinity 42%) was used instead of 100 g of the polyvinyl alcohol resin A and that the aldehydes used for reaction were changed to 25 g of acetaldehyde and 70 g of n-butyraldehyde.

[0211] A conductive paste was obtained as in Example 1 using the obtained polyvinyl acetal resin.

EXAMPLE 13

[0212] White powder of a polyvinyl acetal. resin was obtained as in Example 1, except that 100 g of a polyvinyl alcohol resin N (average degree of polymerization 400, degree of saponification 96 mol %, crystallinity 38%) was used instead of 100 g of the polyvinyl alcohol resin A and that the aldehydes used for reaction were changed to 30 g of acetaldehyde and 55 g of n-butyraldehyde.

[0213] A conductive paste was obtained as in Example 1 using the obtained polyvinyl acetal resin.

EXAMPLE 14

[0214] White powder of a polyvinyl acetal resin was obtained as in Example 1, except that 100 g of a polyvinyl alcohol resin P (average degree of polymerization 250, degree of saponification 88 mol %, crystallinity 32%) was used instead of 100 g of the polyvinyl alcohol resin A and that the aldehydes used for reaction were changed to 30 g of acetaldehyde and 45 g of n-butyraldehyde.

[0215] A conductive paste was obtained as in Example 1 using the obtained polyvinyl acetal resin.

EXAMPLE 15

[0216] White powder of a polyvinyl acetal resin was obtained as in Example 1, except that 100 g of a carboxylic acid-modified polyvinyl alcohol resin Q was used instead of 100 g of the polyvinyl alcohol resin A and that the aldehydes used for reaction were changed to 15 g of acetaldehyde and 70 g of n-butyraldehyde.

[0217] The carboxylic acid-modified polyvinyl alcohol resin Q contained a carboxy group-containing constitutional unit represented by the formula (7-2) (in the formula (7-2), R.sup.4 is CH.sub.3, R.sup.5 and R.sup.6 are hydrogen atoms, R.sup.7 is a single bond, and X.sup.3 is a hydrogen atom) and had an average degree of polymerization of 250, a degree of saponification of 87 mol %, a carboxy group content of 1 mol %, and a crystallinity of 29%.

[0218] A conductive paste was obtained as in Example 1 using the obtained polyvinyl acetal resin.

EXAMPLE 16

[0219] White powder of a polyvinyl acetal resin was obtained as in Example 1, except that 100 g of a polyvinyl alcohol resin R (average degree of polymerization 250, degree of saponification 90 mol %, crystallinity 32%) was used instead of 100 g of the polyvinyl alcohol resin A and that the aldehydes used for reaction were changed to 30 g of acetaldehyde and 60 g of n-butyraldehyde.

[0220] A conductive paste was obtained as in Example 1 using the obtained polyvinyl acetal resin.

EXAMPLE 17

[0221] White powder of a polyvinyl acetal resin was obtained as in Example 1, except that 100 g of a carboxylic acid-modified polyvinyl alcohol resin S was used instead of 100 g of the polyvinyl alcohol resin A and that the aldehydes used for reaction were changed to 95 g of n-butyraldehyde.

[0222] The carboxylic acid-modified polyvinyl alcohol resin S contained a carboxy group-containing constitutional unit represented by the formula (7-1) (in the formula (7-1), R.sup.2 is a single bond, R.sup.3 is CH.sub.2, and X.sup.1 and X.sup.2 are hydrogen atoms) and had an average degree of polymerization of 250, a degree of saponification of 98.99 mol %, a carboxy group content of 0.01 mol %, and a crystallinity of 45%.

[0223] A conductive paste was obtained as in Example 1 using the obtained polyvinyl acetal resin.

EXAMPLE 18

[0224] White powder of a polyvinyl acetal resin was obtained as in Example 1, except that 100 g of a polyvinyl alcohol resin T (average degree of polymerization 250, degree of saponification 99 mol %, crystallinity 45%) was used instead of 100 g of the polyvinyl alcohol resin A and that the aldehydes used for reaction were changed to 95 g of n-butyraldehyde.

[0225] A conductive paste was obtained as in Example 1 using the obtained polyvinyl acetal resin.

EXAMPLE 19

[0226] White powder of a polyvinyl acetal resin was obtained as in Example 1, except that 100 g of a carboxylic acid-modified polyvinyl alcohol resin 2 was used instead of 100 g of the polyvinyl alcohol resin A and that the aldehydes used for reaction were changed to 15 g of acetaldehyde and 80 g of n-butyraldehyde.

[0227] The carboxylic acid-modified polyvinyl alcohol resin Z contained a carboxy group-containing constitutional unit represented by the formula (7-1) (in the formula (7-1), is a single bond, R.sup.3 is CH.sub.2, and X.sup.1 and X.sup.2 are hydrogen atoms) and had an average degree of polymerization of 600, a degree of saponification of 96 mol %, a carboxy group content of 0.1 mol %, and a crystallinity of 20%.

[0228] A conductive paste was obtained as in Example 1 using the obtained polyvinyl acetal resin.

EXAMPLE 20

[0229] White powder of a polyvinyl acetal resin was obtained as in Example 1, except that 100 g of a polyvinyl alcohol resin a (average degree of polymerization 1,750, degree of saponification 93 mol %, ethylene content 5 mol %, crystallinity 25%) was used instead of 100 g of the polyvinyl alcohol resin A and that the aldehydes used for reaction were changed to 95 g of n-butyraldehyde. A conductive paste was obtained as in Example 1 using the obtained polyvinyl acetal resin.

EXAMPLE 21

[0230] White powder of a polyvinyl acetal resin was obtained as in Example 1, except that 100 g of a polyvinyl alcohol resin β (average degree of polymerization 400, degree of saponification 96 mol %, ethylene content 10 mol %, crystallinity 25%) was used instead of 100 g of the polyvinyl alcohol resin A and that the aldehydes used for reaction were changed to 30 g of acetaldehyde and 55 g of n-butyraldehyde.

[0231] A conductive paste was obtained as in Example 2 using the obtained polyvinyl acetal resin.

EXAMPLE 22

[0232] White powder of a polyvinyl acetal resin was obtained as in Example 1, except that 50 g of a carboxylic acid-modified polyvinyl alcohol resin Z and 50 g of the polyvinyl alcohol resin β were used instead of 100 g of the polyvinyl alcohol resin A and that the aldehydes used for reaction were changed to 10 g of acetaldehyde and 85 g of n-butyraldehyde.

[0233] A conductive paste was obtained as in Example 1 using the obtained polyvinyl acetal resin.

COMPARATIVE EXAMPLE 1

[0234] White powder of a polyvinyl acetal resin, was obtained as in Example 1, except that 100 g of a polyvinyl alcohol resin U (average degree of polymerization 2,000, degree of saponification 88 mol %, crystallinity 35%) was used instead of 100 g of the polyvinyl alcohol resin A and that the aldehydes used in reaction were changed to 15 g of acetaldehyde and 75 g of n-butyraldehyde.

[0235] A conductive paste was obtained as in Example 1 using the obtained polyvinyl acetal resin.

COMPARATIVE EXAMPLE 2

[0236] White powder of a polyvinyl acetal resin was obtained as in Example 1, except that 100 g of a polyvinyl alcohol resin V (average degree of polymerization 2,000, degree of saponification 99 mol %, crystallinity 38%) was used instead of 100 g of the polyvinyl alcohol resin A and that the aldehydes used in reaction were changed to 40 g of acetaldehyde and 45 g of n-butyraldehyde.

[0237] Preparation of a conductive paste using the obtained polyvinyl acetal resin was attempted as in Example 1. However, the resin was not dissolved in dihydroterpineol, so that no conductive paste was obtained.

[0238] Here, “resin is dissolved” means that 10% by weight or more of precipitate is not formed relative to the weight of the added resin, whereas “resin is not dissolved” means that 10% by weight or snore of precipitate is formed relative to the weight of the added resin.

COMPARATIVE EXAMPLE 3

[0239] White powder of a polyvinyl acetal resin was obtained as in Example 1, except that 100 g of a polyvinyl alcohol resin W (average degree of polymerization 1,750, degree of saponification 85 mol %, crystallinity 13%) was used instead of 100 g of the polyvinyl alcohol resin A and that the aldehydes used in reaction were changed to 40 g of acetaldehyde and 25 g of n-butyraldehyde.

[0240] Preparation of a conductive paste using the obtained polyvinyl acetal resin was attempted as in Example 1. However, the resin was not dissolved in dihydroterpineol, so that no conductive paste was obtained.

COMPARATIVE EXAMPLE 4

[0241] White powder of a polyvinyl acetal resin was obtained as in Example 1, except that 100 g of a polyvinyl alcohol resin X (average degree of polymerization 500, degree of saponification 85 mol %, crystallinity 26%) was used instead of 100 g of the polyvinyl alcohol resin A and that, the aldehydes used in reaction were changed to 40 g of acetaldehyde and 25 g of n-butyraldehyde.

[0242] Preparation of a conductive paste using the obtained polyvinyl acetal resin was attempted as in Example 1. However, the resin was not dissolved in dihydroterpineol, so that no conductive paste was obtained.

COMPARATIVE EXAMPLE 5

[0243] White powder of a polyvinyl acetal resin was obtained as in Example 1, except that 100 g of a polyvinyl alcohol resin Y (average degree of polymerization 1,750, degree of saponification 99.9 mol %, crystallinity 38%) was used instead of 100 g of the polyvinyl alcohol resin A and that the aldehydes used in reaction were changed to 95 g of n-butyraldehyde.

[0244] A conductive paste was obtained as in Example 1 using the obtained polyvinyl acetal resin.

COMPARATIVE EXAMPLE 5

[0245] White powder of a polyvinyl acetal resin was obtained as in Example 1, except that 100 g of a polyvinyl alcohol resin Y (average degree of polymerization 500, degree of saponification 99.9 mol %, crystallinity 71%) was used instead of 100 q of the polyvinyl alcohol resin A and that the aldehydes used in reaction were changed to 95 g of n-butyraldehyde.

[0246] A conductive paste was obtained as in Example 1 using the obtained polyvinyl acetal resin.

COMPARATIVE EXAMPLE 7

[0247] White powder of a polyvinyl acetal resin was obtained as in Example 1, except that 100 g of a polyvinyl alcohol resin γ (average degree of polymerization 1,750, degree of saponification 99.2 mol %, crystallinity 35%) was used instead of 100 g of the polyvinyl alcohol resin A and that the aldehydes used in reaction were changed to 70 g of n-butyraldehyde.

[0248] Preparation of a conductive paste using the obtained polyvinyl acetal resin was attempted as in Example 1. However, the resin was not dissolved in dihydroterpineol, so that no conductive paste was obtained.

(Evaluation)

[0249] Polyvinyl acetal resins or conductive pastes obtained in Examples 1 to 22 and Comparative Examples 1 to 7 were evaluated as follows. The results are shown in Table 1 and Table 2.

(1) Evaluation of Polyvinyl Acetal Resin

[0250] (1-1) Acetal Group Content, Hydroxy Group content, and Acetyl Group content

[0251] The obtained polyvinyl acetal resin was dissolved in DMSO-D.sub.6 at a concentration of 10% by weight. The solution was subjected to .sup.13C-NMR to measure the acetal group content, hydroxy group content, and acetyl group content.

(1-2) Number Average Molecular Weight (Mn), Weight Average Molecular Weight (Kw), and Mw/Hn

[0252] The obtained polyvinyl acetal resin was dissolved in tetrahydrofuran at a concentration of 0.05% by weight and subjected to measurement using a GPC device HLC-8220 (produced by Tosoh Corporation). From the measurement results, the number average molecular weight Mn, the weight average molecular weight Mw, and the Mw/Mn were calculated using a molecular weight calibration curve obtained from monodispersed polystyrene standards. The column used was the Shedex LF-804 column (produced by Showa Denko K.K.).

(1-3) IR Absorption Spectrum

[0253] The obtained polyvinyl acetal resin was dissolved in a 1:1 weight ratio mixture solution of ethanol and toluene. The solution was then applied to a PET film. The thickness of the measurement sample was adjusted such that the peak appearing near 2,980 cm.sup.−1 derived from the stretching vibrations of the C—H bond would have a minimum transmittance of 22%. A polyvinyl acetal resin sheet was thus obtained. An IR absorption spectrum was measured for the obtained polyvinyl acetal resin sheet at 20° C. using an infrared spectrophotometer (produced by HORIBA, FT-720). In the measurement results, a baseline was drawn for the peak appearing within the waver-umber range of 3,100 to 3,700 cm.sup.−1 and correction was performed to adjust the transmittance of both ends of the peak to 100%. The corrected data was subjected to peak analysis to measure the minimum transmittance X, the transmittance a, and the wavenumbers A and B of the peak.

(1-4) Number and Percentage (% By Volume) of Particles Having a Diameter of 0.5 to 1.0 μm

[0254] The obtained polyvinyl acetal resin was dissolved to 0.2% by weight in dihydroterpinyl acetate. The particle size distribution of the obtained solution (10 ml) was measured using a particle counter (produced by Rion Co., Ltd., KS-42C) to measure the number of particles having a diameter of 0.5 to 1.0 μm per 10 ml. The volume of the particles having a diameter of 0.5 to 1.0 μm was calculated assuming that they were true spheres having a diameter of 0.75 μm. Based on the obtained measurement results, the percentage (% by volume) of the particles having a diameter of 0.5 to 1.0 μm was calculated.

(2) Evaluation of Conductive Paste

(2-1) Paste Filterability

[0255] The obtained conductive paste (2 ml) was put in a 2.5-ml syringe. To the end of the syringe was attached an injection needle having an outer diameter of 0.81 mm, an inner diameter of 0.51 mm, and a length of 33 mm. A force of 5 kgf was applied, and the time needed to eject ail the paste from the tip of the injection needle was measured.

(2-2) Printability

[0256] The conductive paste was printed in an environment at. a temperature of 23° C. and a humidity of 50% using a screen printing machine, a screen printing plate, and a printing glass substrate. The solvent was dried in a fan oven at 100° C. for 30 minutes. The screen printing machine, the screen printing plate, and the printing glass substrate used were as follows.

[0257] Screen printing machine (MT-320TV, produced by Microtec Co., Ltd.)

[0258] Screen printing plate (produced by Tokyo Process Service Co., Ltd., 3T500, emulsion 2 μm, 2012 pattern, screen frame 320 mm×320 mm)

[0259] Printing glass substrate (soda glass, 150 mm×150 mm, thickness 1.5 mm)

[0260] The printed pattern was observed visually or using a magnifying microscope to examine the shape of the edges of the print surface. Printability was evaluated in accordance with the following criteria.

∘ (Good): The paste was printed according to the printing pattern, and no string-like disturbance was observed at any portion of the edges of the print.
Δ (Fair): The paste was printed according to the printing pattern, and string-like disturbances were observed in one portion of the edges of the print.
× (Poor): The paste was not printed according to the printing pattern (e.g., blurred or faint printing), or string-like disturbances were observed in two or more portions of the edges of the print.

(2-3) Surface Roughness

[0261] The printed pattern of the conductive paste obtained in “(2-2) Printability” was used to measure the surface roughness at 10 sites using a surface roughness meter (SURFCOM, produced by Tokyo Seimitsu Co., Ltd.). The surface roughness was evaluated in accordance with the following criteria.

∘ (Good) The average surface roughness Ra of the 10 sites was smaller than 0.100 μm.
Δ (Fair): The average surface roughness Ra of the 10 sites was 0.100 μm or greater and smaller than 0.150 μm.
× (Poor) The average surface roughness Ra of the 10 sites was 0.150 μm or greater.

TABLE-US-00001 TABLE 1 Polyvinyl acetal resin Carboxy group-containing Average Butyral Acetyl Hydroxy constitutional degree of group group group group Ethylene unit polymer- content content content content content Amount ization (mol %) (mol %) (mol %) (mol %) (mol %) Structure (mol %) Example 1 1750 27.0 38.0 12.0 22.0 0 — 0 2 1750 27.0 38.2 10.0 24.0 0 (7-1) 0.8 3 1750 20.0 54.0 1.0 25.0 0 — 0 4 1750 0 74.0 4.0 22.0 0 — 0 5 1750 0 75.9 2.0 22.0 0 (7-1) 0.1 6 1750 0 80.0 2.0 18.0 0 — 0 7 900 0 73.0 4.0 23.0 0 — 0 8 900 10.0 58.0 10.0 22.0 0 — 0 9 600 25.0 53.0 2.0 20.0 0 — 0 10 600 0 78.0 1.0 21.0 0 — 0 11 800 15.0 56.0 4.0 25.0 0 — 0 12 400 20.0 56.0 2.0 22.0 0 — 0 13 400 27.0 47.0 4.0 22.0 0 — 0 14 250 27.0 36.0 12.0 25.0 0 — 0 15 250 10.0 55.0 12.0 22.0 0 (7-2) 1.0 16 250 27.0 45.0 10.0 18.0 0 — 0 17 250 0 73.99 1.0 25.0 0 (7-1) 0.01 18 250 0 74.0 1.0 25.0 0 — 0 19 600 10.0 63.9 4.0 22.0 0 (7-1) 0.1 20 1750 0 70.0 2.0 23.0 5.0 — 0 21 400 25.0 38.0 4.0 23.0 10.0 — 0 22 500 5.0 64.95 4.0 21.0 5.0 (7-1) 0.05 Comparative 1 2000 10.0 60.0 12.0 18.0 0 — 0 Example 2 2000 37.0 37.0 1.0 25.0 0 — 0 3 1750 37.0 18.0 15.0 30.0 0 — 0 4 500 37.0 18.0 15.0 30.0 0 — 0 5 1750 0 79.9 0.1 20.0 0 — 0 6 500 0 79.9 0.1 20.0 0 — 0 7 1750 0 66.7 0.8 32.5 0 — 0 Polyvinyl acetal resin Acetyl Carboxy group group group Ethylene content/ content/ content/ content/ butyral butyral acetyl hydroxy group group group group content content content content Mn Mw Mw/Mn Example 1 0.69 0.308 0 0 109000 295000 2.7 2 0.71 0.262 0.08 0 110000 331000 3.0 3 0.37 0.019 0 0 109000 341000 3.1 4 0 0.054 0 0 115000 299000 2.6 5 0 0.026 0.05 0 115000 321000 2.8 6 0 0.025 0 0 116000 328000 2.8 7 0 0.055 0 0 58900 159000 2.7 8 0.17 0.172 0 0 58700 170000 2.9 9 0.47 0.038 0 0 37500 97000 2.6 10 0 0.013 0 0 39300 98400 2.5 11 0.27 0.071 0 0 37700 101800 2.7 12 0.38 0.036 0 0 25000 65100 2.8 13 0.57 0.035 0 0 24800 62000 2.5 14 0.75 0.333 0 0 15600 39000 2.5 15 0.18 0.218 0.083 0 16500 38000 2.3 16 0.6 0.222 0 0 16500 38000 2.4 17 0 0.014 0.01 0 16100 35000 2.2 18 0 0.014 0 0 16100 37000 2.3 19 0.18 0.063 0.025 0 38700 98000 2.5 20 0.00 0.029 0.000 0.2 115000 400000 3.5 21 0.66 0.000 0.4 25100 56700 2.3 22 0.08 0.062 0.013 0.2 31600 74800 2.4 Comparative 1 0.17 0.200 0 0 133000 426000 3.2 Example 2 1 0.027 0 0 119000 391000 3.3 3 2.06 0.833 0 0 105000 284000 2.7 4 2.06 0.833 0 0 30000 72000 2.4 5 0 0.001 0 0 115000 322000 2.8 6 0 0.001 0 0 32900 72200 2.2 7 0 0.012 0 0 116000 310000 2.7 indicates data missing or illegible when filed

TABLE-US-00002 TABLE 2 Polyvinyl acetal resin Percentage of particles  of having particles particle Conductive paste evaluation Hydroxy having size of Paste Minimum group particle filter- Surface content size of (% by ability roughness (%) (%) volume) ( ) Printability (μm) Example 1 74 67 3390 3570 80 0.80 3.84 9000 4 0 portion ∘ 0.092 ∘ 2 71.5 65.75 3370 3570 100 1.00 4.17 9500 4 0 portion ∘ 0.096 ∘ 3 70.5 65.25 3350 3570 120 1.20 4.80 11000 4 0 portion ∘ 0.095 ∘ 4 75 3400 3570 70 0.70 3.18 9000 3.5 0 portion ∘ 0.067 ∘ 5 74.5 67.25 3380 3580 80 1.00 4.08 9500 3.5 0 portion ∘ 0.069 ∘ 6 82 91 3400 3580 70 0.78 3.88 9500 3.5 0 portion ∘ 0.091 ∘ 7 73 86.5 3380 3570 80 0.90 3.91 8000 2 0 portion ∘ 0.064 ∘ 8 75 87.5 3400 3580 70 0.78 3.18 8500 2.5 0 portion ∘ 0.068 ∘ 9 78 89 3390 3570 80 0.80 4.00 8500 2 0 portion ∘ 0.062 ∘ 10 78 89 3380 3580 90 1.00 4.28 8000 1.5 0 portion ∘ 0.079 ∘ 11 71 85.5 3360 3580 110 1.00 4.40 8000 2 0 portion ∘ 0.078 ∘ 12 74 87 3380 3570 90 0.90 4.08 7500 1.5 0 portion ∘ 0.075 ∘ 13 73 86.5 3390 3570 80 0.80 3.84 7000 1.5 0 portion ∘ 0.071 ∘ 14 70 85 3380 3580 110 1.00 4.40 6000 1.5 0 portion ∘ 0.069 ∘ 15 74 87 3380 3570 90 0.90 4.09 6000 1.5 0 portion ∘ 0.072 ∘ 16 81 90.5 3390 3580 80 0.89 4.44 6000 1 0 portion ∘ 0.065 ∘ 17 70 85 3380 3570 110 1.10 4.40 6500 1 0 portion ∘ 0.062 ∘ 18 71 85.5 3380 3570 110 1.10 4.40 6500 1 0 portion ∘ 0.063 ∘ 19 78 89 3390 3570 80 0.80 3.84 7000 1.5 0 portion ∘ 0.070 ∘ 20 76 88 3360 3570 110 1.10 4.78 10000 3.5 0 portion ∘ 0.090 ∘ 21 73 86.5 3380 3570 80 0.90 3.81 8000 1.5 0 portion ∘ 0.074 ∘ 22 76 88 3370 3570 100 1.00 4.70 8000 1.5 0 portion ∘ 0.086 ∘ Comparative 1 60 90 3360 3560 110 1.22 6.11 20000 6 .sup. 3 portions x 0.325 x Example 2 68 84.5 3320 3570 150 1.50 6.00 Not — — — — — — dissolved in solvent 3 66 83 3310 3560 160 1.78 5.33 Not — — — — — — dissolved in solvent 4 65 82.5 3310 3560 160 1.78 5.33 Not — — — — — — dissolved in solvent 5 78 88 3360 3560 110 1.22 5.50 25000 6 .sup. 2 portions x 0.257 x 6 78 89.5 3360 3560 110 1.22 5.50 23000 5.5 1 portion Δ 0.11  Δ 7 52 81 3310 3560 160 1.78 4.82 Not — — — — — — dissolved in solvent indicates data missing or illegible when filed

INDUSTRIAL APPLICABILITY

[0262] The present invention can provide a conductive paste which leaves less fine undissolved matter when dissolved in an organic solvent and thus can be easily filtrated, which has excellent printability, and which can exhibit excellent surface smoothness after printing.