JP2001146483A - Method for producing slurry for laminated ceramic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a slurry for laminated ceramic capacitor, capable of producing a thin green sheet maintaining a strength, having excellent coating properties. SOLUTION: Ceramic raw material powder is dispersed and blended by using a binder composed of a polymer composition having 120-1,600 degree of polymerization. Then the mixture is blended and kneaded with a binder composed of a polymer composition having 600-900 degree of polymerization.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a slurry for a multilayer ceramic capacitor, and more specifically, to obtain a green sheet capable of reducing the thickness of a green sheet and maintaining strength. And a method for producing a slurry for a multilayer ceramic capacitor.

[0002]

2. Description of the Related Art In general, a multilayer ceramic capacitor is
A ceramic raw material powder such as barium titanate, a binder comprising a polymer composition such as polyvinyl butyral (hereinafter referred to as PVB), dibutyl phthalate (hereinafter referred to as DBP)
A slurry formed by kneading a plasticizer such as ethanol, a solvent such as ethanol, and an additive such as a surfactant using a stirring means such as a ball mill on a PET film, and forming a sheet ( This is formed by laminating printed materials of the internal electrode paste on a green sheet) and firing and the like.

[0003] Further, the above slurry is prepared by adding a minimum amount of a binder and a solvent to the ceramic raw material powder, dispersing and mixing to prepare an emulsion (mill base) for the purpose of dispersing the ceramic raw material powder. In order to obtain the green sheet characteristics (strength, adhesiveness, etc.), the mixture is kneaded (let down) while adding a binder, a solvent, a plasticizer, and the like necessary for the green sheet. Then, this slurry is coated and peeled by a coating method such as a doctor blade method,
The green sheet is formed.

[0004]

In recent years, there has been an increasing demand for higher capacitance of multilayer ceramic capacitors, and in order to satisfy this demand, it is necessary to make the ceramic layer thinner. Further, in order to reduce the thickness of the ceramic layer, it is necessary to reduce the thickness of the green sheet, and a green sheet of 6 μm or less has been required. However, when the green sheet is thinned to this level, there is a problem that the strength of the green sheet is reduced and handling becomes difficult.

The present invention has been proposed to solve the above-mentioned problems of the prior art, and an object of the present invention is to reduce the thickness of the green sheet and maintain the strength of the green sheet. An object of the present invention is to provide a method for producing a slurry for a multilayer ceramic capacitor capable of obtaining a sheet.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have completed the present invention. As described above, when the thickness of the green sheet is reduced in order to increase the capacity of the multilayer ceramic capacitor, the strength of the green sheet decreases. Therefore, first, it was examined whether or not the strength of the green sheet could be maintained using a binder made of a polymer composition having a higher degree of polymerization. However, when a binder having a high degree of polymerization is added, the viscosity of the slurry increases, and the coatability (moldability of the green sheet) decreases,
A good green sheet could not be obtained.

In general, in a slurry, a binder is dispersed in a solvent in a state where the binder is adsorbed on the ceramic raw material powder or in a state where the ceramic raw material powder is used alone. Here, a surfactant is usually added in order to disperse these ceramic raw material powders in a solvent. Therefore, by adding a surfactant,
An investigation was made as to whether the viscosity of the increased slurry could be reduced due to the addition of the binder having a high polymerization degree. As a result, it was found that the addition of the surfactant did not reduce the viscosity of the slurry.

The reason was presumed to be as follows. That is, by adding a surfactant, the ceramic raw material powder in a single state can be dispersed, but this surfactant also acts on the binder adsorbed on the ceramic raw material powder. In the slurry using a binder having a high degree of polymerization, the added surfactant largely acts on the binder having a high degree of polymerization adsorbed on the ceramic raw material powder, and the binder is desorbed from the ceramic raw material powder, and the ceramic is removed. It is considered that aggregation of the raw material powder occurs, and as a result, the viscosity of the slurry does not decrease. The results also suggest that the contribution of the binder to the ceramic raw material powder is greater in the adsorbability of the binder to the ceramic raw material powder than in the dispersibility of the surfactant.

Therefore, various studies have been conducted to optimize the binder used in the mill base and let down without adding a surfactant, thereby increasing the dispersibility of the ceramic raw material powder and lowering the viscosity of the slurry. went. As a result, the viscosity of the slurry can be reduced by using a binder composed of a polymer composition having a high degree of polymerization on a mill base and using a binder composed of a polymer composition having a low degree of polymerization on a letdown basis. It was found that the sex could be maintained. And it turned out that a green sheet which is thin and maintains strength can be obtained by using this slurry.

As described above, the viscosity of the slurry can be reduced by using a binder composed of a polymer composition having a high degree of polymerization on a mill base and using a binder composed of a polymer composition having a low degree of polymerization in a letdown manner. The possible reasons are considered as follows. That is, the binder having a high degree of polymerization used in the mill base is adsorbed on the ceramic raw material powder during dispersion and mixing. Then, the binder having a low degree of polymerization added by red-down thereafter adsorbs to some extent the ceramic raw material powder, but the binder not adsorbed floats in the slurry. Since the suspended binder has a low degree of polymerization and a low viscosity, the viscosity of the entire slurry becomes low. It is considered that a low-viscosity slurry can be obtained in the above-described situation.

Here, as the polymer composition used for the binder, those generally used as a binder for a slurry for a multilayer ceramic capacitor may be used.
B, PMMA (polymethyl methacrylate) or the like can be used and is not particularly limited. Further, the degree of polymerization of the polymer composition having a high degree of polymerization is preferably from 1200 to 1600, and the degree of polymerization of the polymer composition having a low degree of polymerization is preferably from 600 to 900.

Further, according to this method, a good slurry can be obtained without using a surfactant. Therefore, as described above, the disadvantage that the binder is desorbed from the ceramic raw material powder by the addition of the surfactant can be prevented, so that the ceramic raw material powder is not aggregated and the dispersibility is not reduced, and as a result, Thus, a dense ceramic sintered body can be obtained.

Further, by changing the polymerization degree and the weight ratio of the binder used in the mill base and the let down,
Since the viscosity of the slurry can be changed over a wide range, it is possible to obtain a slurry that can be used for various coating methods having different appropriate viscosities, such as a doctor blade, a gravure, and a die.

[0014]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. In Examples, a binder having a high degree of polymerization was used on a mill basis, and in Comparative Examples, a binder having a low degree of polymerization was used on a mill basis.

(Example) For 100 parts by weight of barium titanate having an average particle diameter of 0.5 μm, 40 parts by weight of a mixture of ethanol and toluene in a ratio of 4: 6 as a solvent, and a binder having a polymerization degree of 1600 as a binder. 1.6 parts by weight of PVB was added and mixed with a ball mill to prepare a mill base, and the viscosity was measured using a rotary viscometer. Then, a degree of polymerization of 80 was added to the mill base as a binder.
6.0 parts by weight of PVB with a polymerization degree of 1600
Was added, and a slurry was prepared by kneading while adding 45 parts by weight of a mixture of ethanol and toluene in a ratio of 4: 6 as a solvent and 2.4 parts by weight of DBP as a plasticizer. The viscosity was measured using a rotary viscometer.

(Comparative Example) For 100 parts by weight of barium titanate having an average particle size of 0.5 μm, 40 parts by weight of a mixture of ethanol and toluene in a ratio of 4: 6 as a solvent, and a binder having a polymerization degree of 800 as a binder were used. 2.0 parts by weight of PVB was added and mixed with a ball mill to prepare a mill base, and the viscosity was measured using a rotary viscometer. Then, a degree of polymerization of 80 was added to the mill base as a binder.
Of PVB having a polymerization degree of 1600 and 4.0 parts by weight of PVB having a polymerization degree of 1600
Was added, and kneaded while adding 45 parts by weight of a mixed solution of ethanol and toluene in a ratio of 4: 6 as a solvent and 2.4 parts by weight of DBP as a plasticizer to prepare a slurry. The viscosity was measured using a rotary viscometer.

[Table 1]

As is clear from Table 1, in the example using a binder having a high polymerization degree on a mill base, the viscosity of the mill base is as high as "405 cps", but the viscosity of the final slurry is as low as "280 cps". ing.
On the other hand, in a comparative example using a binder having a low polymerization degree in a mill base, the viscosity of the mill base is "140c".
ps ", but the final slurry has a viscosity of" 455 cps ", although the total amount of each of the high and low polymerization binders in the final slurry is the same. It is about 1.6 times.

As described above, in the examples, the viscosity of the final slurry is low and the viscosity is such that the slurry can be applied.
Also, it was found that a slurry having a coatable viscosity can be obtained without using a surfactant.

[0019]

As described above, according to the present invention,
While reducing the thickness of the green sheet,
It is possible to provide a method for producing a slurry for a multilayer ceramic capacitor capable of obtaining a green sheet maintaining strength.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yohachi Yamashita 70, Yanagicho, Yukicho, Kawasaki-shi, Kanagawa Prefecture Inside the Toshiba Yanagimachi Plant (72) Inventor Hideyuki Kanai 70, Yanagicho, Yukicho, Kawasaki-shi, Kanagawa Prefecture F-term in the factory (reference) 4G030 AA10 AA16 BA09 GA09 GA14 GA17 GA20 PA22 5E001 AB03 AE00 AE02 AE03 AH00 AJ02

Claims (1)

[Claims] 1. A ceramic raw material powder having a degree of polymerization of 120.
A multilayer ceramic capacitor characterized by dispersing and mixing using a binder made of a polymer composition having a polymer composition of 0 to 1600, and then adding and kneading a binder made of a polymer composition having a polymerization degree of 600 to 900; Manufacturing method of slurry for use.