JPH07112953B2 - Slurry composition for ceramic green sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a slurry composition used as a raw material for producing a ceramic green sheet by, for example, a doctor blade method.

Conventional technology Ceramic thin plates used for ceramic multilayer capacitors, multilayer ICs, etc. are manufactured by the doctor blade method, roll molding method, or extrusion molding method.In the doctor blade method, binder and solvent are added to ceramic powder. In addition, the mixed ceramic slurry is used as a raw material. The doctor blade method is to pour the raw material slurry onto a belt, spread it thinly with a blade called a doctor blade, cut or punch the obtained green sheet, and sinter it to obtain a desired product. Although this is a method for obtaining a shaped sintered body, the quality of the obtained thin plate is greatly influenced by the properties of the raw material slurry. For example, when the amount of the solvent is small and the viscosity is high, the kneading property deteriorates, which causes inconveniences such as density unevenness and generation of cracks, and when the amount of the solvent is increased and the viscosity is lowered, molding is performed.・ Inconvenience such as cracking during drying occurs.

As described above, the slurry for a green sheet is required to have contradictory characteristics during kneading and during molding. Therefore, efforts have hitherto been made in selecting a solvent and adjusting the amount of the solvent.

For example, in a low boiling point solvent, since the drying rate is faster than the shrinkage rate of the ceramic molded body and cracks easily occur, a high boiling point solvent is used in a relatively large amount. Since it takes time, the viscosity is adjusted by adjusting the temperature together with the pressure reduction. Further, in the method described in JP-A-59-195573, the amount of the binder and the plasticizer is reduced during the mixing, and the binder and the plasticizer are added during the molding, whereby the kneading is performed. Viscosity is made different at the time of molding and at the time of molding so as to obtain a viscosity suitable for each.

Problems to be Solved by the Invention However, when a high boiling point solvent is used, in the method of adjusting the viscosity by temperature, the viscosity decreases as the temperature rises, but the correlation between temperature and viscosity is not accurately determined. Besides, it is difficult to set the temperature accurately, and in the end,
It is difficult to adjust the viscosity accurately.

In addition, it may be possible to adjust the viscosity as expected by a method in which the amount of the binder or plasticizer is different during kneading and during molding, but the binder or plasticizer added after kneading Is not sufficiently mixed and dispersed, there is a possibility that product quality may vary.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a slurry composition for a ceramic green sheet, the viscosity of which can be easily adjusted and which does not cause a crack when a molded sheet is dried. .

Means for Solving the Problems The present invention, in order to achieve the above-mentioned object, uses a high-boiling point solvent having a boiling point of 110 ° C. or higher and a low-boiling point solvent of 90 ° C. or lower. When the amount of the slurry is adjusted only with the high boiling point solvent, the viscosity is 8000 centipoise (cp
s), and when the amount of the low boiling point solvent is adjusted to a slurry together with the high boiling point solvent, the viscosity is 3000 cp.
It is characterized by setting the amount to be less than s.

That is, the present invention has been made as a result of various experiments and studies as described below with respect to the relationship between the viscosity of the slurry and the kneading properties and the degree of occurrence of cracks, and the ease of adjusting the viscosity.

Al ₂ O ₃ powder was used as the ceramic powder, and polyvinyl butyral (PVB) was added as the binder, and n-hexyl alcohol (boiling point 158 ° C.) was added and kneaded as the solvent to prepare the slurry, and the slurry was prepared. The kneadability of the above and the occurrence of cracks in the formed sheet during drying were examined. The mixing ratio is 1 kg of Al ₂ O ₃ powder and 50 g of PVB.
Was added, and n-hexyl alcohol was added to this to 300-1000 m
It is assumed that the blending ratio is changed stepwise in the range of l, the viscosity, the kneading property, the presence or absence of coarse particles in the sheet formed by the doctor blade method, and the dried sheet The presence or absence of cracks was examined. The results are shown in Table 1.

First, the kneadability is examined. When the amount of the solvent is 500 ml or less and the viscosity is 3000 cps or more (Sample No. 4, 5, 6,
In 7), for example, when kneading with a ball mill, the slurry adheres between the cobblestone and the pot due to the adhesive force of the binder and the cobblestone does not rotate, resulting in insufficient kneading and Al ₂ O ₃ powder. Are not evenly distributed. Therefore, in such a case, coarse particles are mixed in the dry sheet, and a smooth sheet cannot be obtained. From this result, the viscosity when kneading is 30
It is necessary to adjust the value to less than 00 cps, and the amount of the solvent needs to be adjusted accordingly.

On the other hand, when examining the occurrence of cracks during drying, if the viscosity is 8000 cps or less (Sample No. 1,2,3,4,5), the solvent amount is large and the powder particle spacing is wide, and as a result, Due to the high shrinkage, cracks occur during drying.

Therefore, from the above two points, the viscosity of the slurry needs to be less than 3000 cps during kneading and more than 8000 cps during molding.

In the present invention, such adjustment of the viscosity is performed by using a low boiling point solvent and a high boiling point solvent in combination and adjusting the amount of the solvent.

That is, when a method of reducing pressure, which has been conventionally used as a viscosity adjusting means, was carried out at a pressure of −600 mmHg after kneading the slurry of sample No. 3 in Table 1, the viscosity was 10000 cp.
It took a long time of 2 days to adjust to s. We also considered removing the solvent by heating, but since the viscosity of the slurry fluctuates greatly depending on the temperature, it is not possible
It was extremely difficult to adjust the viscosity to the intended value at (° C) and was not practical.

Further, the above n-hexyl alcohol which is a high boiling point solvent was replaced with trichloroethylene which is a low boiling point solvent, and the amount of the solvent was adjusted so that the viscosity of the slurry was 2000 cps, and kneading was performed. Was adjusted to 10000 cps. Although the time required for adjusting the viscosity was 15 minutes, which was an extremely short time, cracks occurred when the sheet was formed and then dried. This is because the drying time of the sheet is fast due to the small amount of solvent and the drying shrinkage of the sheet is accordingly premature.

There is also a method of appropriately adjusting the viscosity of the slurry by changing the amount of the binder or the plasticizer during kneading and during molding. However, in this method, the binder and the like are not uniformly dispersed as described above. There is a risk of variations in quality.

In this way, neither the method of adjusting the viscosity by decompression / heating, the method of using a low boiling point solvent, nor the method of changing the amount of additives other than the solvent such as the binder gives satisfactory results. In the invention, the high boiling point solvent and the low boiling point solvent are used in combination, and the amount of each solvent is set to the above-mentioned amount.

The high boiling point solvent that can be used in the present invention has a boiling point of 110.
C. or higher, for example, n-hexyl alcohol (boiling point 158 ° C.), n-butyl alcohol (boiling point 117 ° C.),
Cyclohexane (boiling point 156.5 ° C), etc., and low-boiling point solvents having a boiling point of 90 ° C or less, such as trichloroethylene (boiling point 87 ° C), ethyl alcohol (boiling point)
78 ° C), acetone (boiling point 56.5 ° C), etc. Further, the binder that can be used in the present invention is not limited to PVB, but PVA, nitrocellulose, polyethylene, ethyl cellulose, polymethacrylate, etc. can be used.

Action In the slurry composition of the present invention, the high boiling point solvent and the low boiling point solvent are added to the ceramic powder so that the viscosity is adjusted to be less than 3000 cps, so that the kneading property of the slurry is good, and thus a homogeneous slurry is obtained. be able to. The slurry is formed into a sheet by reducing the amount of the solvent by a method such as decompression after kneading, but when the amount of the solvent is reduced, the low boiling point solvent is mainly removed, and the low boiling point solvent and the high boiling point solvent are azeotroped. If it is a mixture, some high-boiling solvent is also removed,
In any case, since the solvent to be removed is a low boiling point solvent, the amount of the solvent is reduced in a short time and the viscosity is adjusted. And in the slurry composition of the present invention, the viscosity when adjusted with only the high boiling point solvent is set to exceed 8000 cps, so the solvent becomes sufficiently small and the viscosity becomes high during molding and drying. Therefore, even if the sheet molded body is dried, there is no possibility that cracks will occur.

Examples Examples of the present invention will be described below.

Trichlorethylene (boiling point 87 ° C) as low boiling point solvent, n-hexyl alcohol (boiling point 158 ° C) as high boiling point solvent
50 g of these solvents in 1 kg of Al ₂ O ₃ powder.
To prepare a slurry. The amount of n-hexyl alcohol which is the high boiling point solvent is 400 ml with reference to the sample No. 6 in Table 1, and the amount of trichlorethylene which is the low boiling point solvent is referred to the sample No. 3 in Table 1. Then, the total amount of solvent was set to 200 ml so as to be 600 ml.

The resulting slurry had good kneading properties and a viscosity of 18
It was 00 cps.

When the viscosity of the slurry was adjusted to 10000 cps by the pressure reduction method (pressure: -600 mmHg), the adjustment time required was 14 minutes, and the viscosity could be adjusted in an extremely short time.
The evaporation amount of the solvent at this time was about 200 ml, and it is considered that trichlorethylene corresponding to the evaporation amount was evaporated mainly.

When the slurry after the viscosity adjustment was formed into a sheet and dried, no cracks were found at all.

Effects of the Invention As is apparent from the above description, according to the slurry composition for a ceramic green sheet of the present invention, a high boiling point solvent and a low boiling point solvent are used in combination as a solvent, and the amount of the high boiling point solvent is set to the high boiling point solvent. The viscosity when adjusting the slurry with only
The viscosity is 30 when the slurry is adjusted together with the high boiling point solvent by setting the amount of the low boiling point solvent above 8000 cps.
Since the amount is set to less than 00 cps, the viscosity at the time of kneading is sufficiently low and a slurry with good kneading property can be obtained, and the low boiling point solvent is rapidly removed during viscosity adjustment by the commonly used decompression method. Therefore, the viscosity of the slurry can be adjusted in a short time, and the high-boiling solvent is difficult to be removed by decompression for a short time, and the viscosity of the slurry is mainly determined by the high-boiling solvent. It is possible to prevent a large deviation from the desired value. Further, in the slurry of the present invention, the amount of the solvent at the time of molding / drying can be reduced to obtain the desired viscosity, and thus the molded sheet can be dried without causing cracks.

Claims (1)

[Claims] 1. A slurry composition obtained by adding at least a binder and a solvent to ceramic powder, wherein the solvent comprises a high boiling solvent having a boiling point of 110 ° C. or higher and a low boiling solvent having a boiling point of 90 ° C. or lower. The viscosity of the high-boiling solvent when the slurry is adjusted only by the high-boiling solvent is set to an amount exceeding 8000 centipoise, and the amount of the low-boiling solvent is adjusted when the slurry is adjusted together with the high-boiling solvent. A slurry composition for ceramic green sheets, characterized in that the viscosity is set to less than 3000 centipoise.