JPH0696993A - Green sheet and production thereof - Google Patents

Abstract

PURPOSE:To enhance tensile strength by preventing deposition and gelation of binder composed of an acrylic acid polymer in slurry thereby flattening the surface of green sheet to be obtained. CONSTITUTION:A slurry is prepared containing a dielectric material powder which contains an alkaline earth metal, and a chelating agent forming a complex with alkaline earth metal ion. The slurry is then admixed with a binder composed of an acrylic acid polymer and the slurry is shaped into a sheet which is subsequently dried to produce a green sheet. Alkaline earth metal ions eluted into the slurry react on the chelating agent preferentially to the acrylic acid polymer of the binder and masked thus blocking deposition and gelation of binder in the slurry and enhancing flatness and tensile strength on the surface of the green sheet. Since a thin green sheet can be used, a small and highly reliable multilayer ceramic capacitor can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a green sheet for forming a dielectric layer of a laminated ceramic capacitor and a green sheet manufactured by this method.

[0002]

2. Description of the Related Art Generally, a laminated porcelain capacitor is formed by printing a large number of internal electrode patterns on a green sheet containing a dielectric material powder as a main component, laminating a plurality of these patterns, cutting them into chips, and heating them at 1000 ° C. It is manufactured by firing at high temperature.

A green sheet is a sheet of dielectric material powder bound with a binder. As the binder, high molecular polymers such as polyvinyl alcohol, polyacrylic acid resin, polyacrylic acid ester, polyvinyl butyrate and ethyl cellulose are used.

Acrylic acid polymers such as polyacrylic acid resins and polyacrylic acid esters have a dispersing effect by themselves and are easy to form a dielectric material powder into a sheet, and therefore are widely used as a binder and a dispersant. There is.

[0005]

The acrylic acid polymer has a structure as shown in Chemical formula 1 and has a carboxylic acid group. The carboxylic acid group can be esterified, and various binders are commercially available depending on the proportion of acrylic acid group, the degree of polymerization, the esterification rate, the type of ester group, and the like. However, when it is used as a water-soluble resin, it must have a free carboxylic acid group.

[0006]

[Chemical 1]

However, the anionic acrylic acid polymer having a free carboxylic acid group is likely to combine with the ions of the alkaline earth metal constituting the dielectric material powder to form an insoluble binder, which roughens the surface of the green sheet. As a result, its tensile strength is reduced.

By the way, at present, a laminated ceramic capacitor is required to have a large capacity. For this reason, improvements have been made to make the green sheet as thin as possible. However, when the surface of the green sheet becomes rough, the dielectric layer However, there is a problem that an excessively thin portion is formed and the reliability of the laminated ceramic capacitor is lowered.

According to the present invention, the surface of the obtained green sheet is smoothed and the tensile strength of the green sheet is enhanced by preventing the precipitation and gelation of the binder made of an acrylic acid polymer in the slurry. It is an object to provide a manufacturing method and such a green sheet.

[0010]

A method for producing a green sheet according to the present invention comprises a slurry containing a dielectric material powder containing an alkaline earth metal and a chelating agent which forms a complex with an alkaline earth metal ion. And a step of mixing a binder made of an acrylic acid polymer into the slurry, a step of forming the slurry into a sheet, and a step of drying the sheet-formed slurry to form a green sheet. is there.

The ability of chelating agents to form complexes with alkaline earth metal ions is generally low in the acidic to neutral range,
Since the pH is high in the alkaline region, the pH of the slurry needs to be on the alkaline side from the beginning to the end of the reaction. Since the hydroxide of alkaline earth metal is eluted from the dielectric material powder containing alkaline earth metal, the more ions in the eluate, the more alkaline the slurry system is. It is preferably alkaline.

Therefore, in the present invention, in the step of forming a slurry, a slurry containing a dielectric material powder containing an alkaline earth metal as a main component is formed in advance, and an alkali is added to this slurry to adjust the pH to 9 or more. It is preferable to adjust it to enhance its complex-forming ability, and then add and mix a chelating agent to this slurry.

Although barium titanate can be used as a dielectric material containing an alkaline earth metal, it goes without saying that the present invention can be applied to compounds of other dielectric materials. Examples of the alkaline earth metal include Mg, Ca, Sr, and Ba.

Examples of the chelating agent include ethylenediaminetetraacetic acid (EDTA), diethyleneaminepentaacetic acid (DTPA) and nitrilotriacetic acid (NT).
A), ammonium salt, sodium salt, or potassium salt of triethylenetetrahexaacetic acid (TTHA) can be mentioned, but it goes without saying that other salts can also be used.

As the acrylic acid polymer, a polyacrylic acid resin or a polyacrylic acid ester can be exemplified, and these further include a ratio of acrylic acid group,
There are various materials having different degrees of polymerization, esterification rates, kinds of ester groups, etc., and it goes without saying that these materials can also be used.

The green sheet according to the present invention contains a compound powder containing an alkaline earth metal, a chelating agent forming a complex with an alkaline earth metal ion, and a binder made of an acrylic acid polymer. Is.
Here, the contents of the alkaline earth metal, the chelating agent, and the acrylic acid polymer are the same as those described in the method for manufacturing the green sheet described above.

[0017]

In the present invention, the alkaline earth metal ions eluted in the slurry are preferentially reacted with the chelating agent before being masked by reacting with the chelating agent before reacting with the acrylic acid polymer as the binder, so that precipitation of the binder or gel in the slurry occurs. And the like are prevented.

[0018]

【Example】

Example 1 150 g of barium titanate powder having an average particle size of 2 μm, water 8
0 g, 10% EDTA-NH ₄ (ethylenediamine 4
(Ammonium acetate salt) aqueous solution (5 g) was put into a 1-liter pot mill together with a large number of urethane balls (3φcm), the pot mill was rotated at 100 rpm for 0.5 hours to stir and mix them, and then 10% ammonia water was added. In addition, the pH was adjusted to 9, and the pot mill was further rotated at 100 rpm for 0.5 hours to stir and mix them.

Thereafter, 50 g of acrylic acid binder (TB01, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., solid content: 35%) was added to the mixture in the pot mill, and the pot mill was rotated at a rotation number of 10
These were rotated at 0 rpm for 2 hours and sufficiently stirred and mixed to obtain a slurry.

Next, this slurry was placed in a vacuum defoaming machine to be defoamed, and applied uniformly on a PET film by a doctor blade method, and this was dried at 70 ° C. for 0.1 hour and dried green. Sheets were formed on PET film.

Next, the green sheet was peeled from the PET film, and its thickness (μm), surface roughness (μm) and tensile strength (g / mm ² ) were measured. The surface roughness was measured by measuring the center line roughness (Ra) and the maximum height (R _max ), and the tensile strength was measured for a sample of 2 cm × 10 cm.

The thickness of the green sheet is 20 μm,
Table 1 shows the surface roughness (μm) and tensile strength (g / mm ² ).
It was as shown in. That is, regarding the surface roughness in this example, the center line roughness (Ra) is 0.5 μm and the maximum height (R) is
_max ) is 1.5 μm and the tensile strength is 2000 g /
It was mm ² .

Example 2 Example 1 except that DTPA-NH ₄ (diethyleneamine pentaacetic acid ammonium salt) was used as the chelating agent.
A green sheet was obtained in the same manner as in, and the thickness (μm), surface roughness (μm) and tensile strength (g / mm ² ) of the green sheet were obtained in the same manner as in Example 1. The thickness of the green sheet was 20 μm, and the surface roughness (μm) and the tensile strength (g / mm ² ) were as shown in Table 1. That is, regarding the surface roughness in this example, the center line roughness (Ra) is 0.7 μm, and the maximum height (R _max ) is 1.3 μm.
The tensile strength was 2300 g / mm ² .

Comparative Example 1 A green sheet was obtained in the same manner as in Example 1 except that the chelating agent was not used, and the thickness (μm), surface roughness (μm) and thickness of the green sheet were obtained in the same manner as in Example 1. The tensile strength (g / mm ² ) was determined. The thickness of the green sheet is 2
0 μm, surface roughness (μm) and tensile strength (g /
mm ² ) was as shown in Table 1. That is, the surface roughness in this example has a center line roughness (Ra) of 5.7 μm.
m, the maximum height (R _max ) was 7.0 μm, and the tensile strength was 500 g / mm ² .

[0025]

[Table 1]

From the results of Examples 1 and 2 and Comparative Example 1 described above, when the chelating agent is not used as in Comparative Example 1, the surface of the green sheet is very rough and the tensile strength is weak. It can be seen that the tensile strength of the green sheet is significantly improved when the chelating agent is used to mask Ba ²⁺ ions in the slurry as in Nos. 1 and 2. By the way, it is considered that the tensile strength of the green sheet used for the laminated ceramic capacitor is required to be 1000 g / mm ² or more.

[0027]

EFFECTS OF THE INVENTION According to the present invention, since precipitation and gelation of the acrylic acid binder in the slurry are prevented, the surface of the obtained green sheet becomes smooth and the tensile strength becomes strong, and a thin green sheet is obtained. Therefore, it is possible to obtain a small and highly reliable laminated ceramic capacitor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shoichi Tosaka 6-16-20 Ueno, Taito-ku, Tokyo Taiyo Induction Co., Ltd.

Claims (9)

[Claims] 1. A step of forming a slurry containing a dielectric material powder containing an alkaline earth metal and a chelating agent which forms a complex with an alkaline earth metal ion, and a binder made of an acrylic acid polymer in the slurry. And a step of forming the slurry into a sheet, and a step of drying the sheet-formed slurry to form a green sheet. 2. The method for producing a green sheet according to claim 1, wherein the pH of the slurry is adjusted to 9 or more by adding an alkali before mixing the binder made of an acrylic acid polymer. 3. The dielectric material containing an alkaline earth metal is barium titanate, according to claim 1 or 2.
The manufacturing method of the described green sheet. 4. The chelating agent is ethylenediaminetetraacetic acid (EDTA), diethyleneaminepentaacetic acid (DT).
PA), nitrilotriacetic acid (NTA), ammonium salt, sodium salt, or potassium salt of triethylenetetrahexaacetic acid (TTHA), The manufacturing method of the green sheet of Claims 1-3 characterized by the above-mentioned. 5. The method for producing a green sheet according to claim 1, wherein the acrylic acid polymer is a polyacrylic acid resin or a polyacrylic acid ester. 6. A green containing a powder of a dielectric material containing an alkaline earth metal, a chelating agent forming a complex with an alkaline earth metal ion, and a binder made of an acrylic acid polymer. Sheet. 7. The green sheet according to claim 6, wherein the dielectric material containing an alkaline earth metal is barium titanate. 8. The chelating agent is ethylenediaminetetraacetic acid (EDTA), diethyleneaminepentaacetic acid (DT).
PA), nitrilotriacetic acid (NTA), ammonium salt, sodium salt, potassium salt of triethylenetetrahexaacetic acid (TTHA), The green sheet according to claim 6 or 7. 9. The green sheet according to claim 6, wherein the acrylic acid polymer is a polyacrylic acid resin or a polyacrylic acid ester.