JPS63265857A - Production of low expansion substrate - Google Patents

Abstract

PURPOSE:To enable production of a thick sheet and broadening of a calcination temp. range by adding org. fibers to a slurry consisting of cordierite, ceramics raw materials and inorg. fibers to prepare the specific compsn. at the time of producing a sheet-like material from the above-mentioned slurry. CONSTITUTION:The ceramics raw materials such as clay, feldspar, talc and kaolin are added at 5-35wt.% ratio to raw material powder of a cordierite compsn. and 3-40pts.wt. inorg. fibers and 0.2-5wt.% org. fibers are mixed therewith to prepare the aq. slurry. This slurry is aggregated and sheeted to obtain a green ceramics sheet which is then calcined at 1,300-1,400 deg.C to obtain a dense substrate having a low coefft. of thermal expansion. Since the green sheet having high flexibility is obtd. by this method, even the sheet having >=2mm thickness is easily produced; in addition, the density of the sheet is increased in the wide calcination temp. range as mentioned above.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a method for manufacturing a dense substrate with a low coefficient of thermal expansion.

<Technical background of the invention and its problems> Cordierite has been known as a ceramic with a small coefficient of thermal expansion, and is used for substrates of planar heating elements, etc.

However, since cordierite has a narrow sintering temperature range, it is difficult to sinter it as a single body using normal means, and a porosity of less than 1.0% cannot be obtained. Therefore, an appropriate sintering aid such as zircon is added, but even in this case, the firing temperature is as high as 1400°C, the sintering temperature range is narrow at around 50°C, and the cost of raw materials is high. There is a drawback.

Furthermore, when forming such an unfired sheet-like product, methods such as press forming and doctor blade method are used, but in the case of the former, at least 7.00 kg/c+a
It requires a higher press pressure and is not suitable for mass production. In addition, the latter method uses an organic binder, a solvent, etc., and therefore has problems in the working environment, and has the disadvantage that the binder removal step during sheet firing is extremely complicated and difficult.

As a method for eliminating the above-mentioned drawbacks and producing a dense, low-expansion substrate, the present inventors have filed an application for a method for producing an unfired sheet-like material by a papermaking method using inorganic Ili fibers. That is, ceramic raw materials such as clay, feldspar, talc, and kaolin are added to raw powder having a cordierite composition at a ratio of 5 to 35% by weight, and inorganic fibers such as asbestos and alumina are mixed with this to form an aqueous slurry. This is a method for producing a sheet-like product made of the above-mentioned raw material powder, ceramic raw material, and inorganic fiber by performing , aggregation, and paper-making.

However, when inorganic fibers are used alone as the fibrous material, the plasticity of the unfired sheet produced is poor and cracks are likely to occur in the sheet. Therefore, there was a drawback that it was difficult to produce a sheet with a thickness of two or more layers.

<Objective of the Invention> The present invention provides a method for manufacturing a ceramic substrate that is dense, has a small coefficient of thermal expansion, and can be manufactured at low cost by eliminating the above-mentioned drawbacks.

<Summary of the Invention> That is, the present invention provides a raw material powder having a cordierite composition,
5 to 35 ceramic raw materials such as clay, feldspar, talc, kaolin, etc.
% by weight, and 3 to 40 parts by weight of non-molecular fibers such as albest and alumina, and 0.2 to 5 parts by weight of organic fibers such as wood pulp are mixed to form an aqueous slurry and coagulate. , a sheet-like product made of the raw material powder, ceramic raw materials, inorganic fibers, and organic fibers is obtained by paper-making, and the sheet-like product is fired at 1,300 to 1,400°C, which is dense and has a low coefficient of thermal expansion. This is a method for manufacturing a substrate.

<Detailed Description of the Invention> That is, in the present invention, ceramic raw materials such as clay, feldspar, talc, and kaolin are added to cordierite, which is a low expansion material, and
Ceramic green sheets are obtained by mixing inorganic fibers such as asbestos, alumina fibers, and organic fibers such as wood pulp into an aqueous slurry, coagulating, and papermaking. The present invention provides a method for densifying cordierite materials, which could only be sintered in a very narrow range, over a wide firing temperature range of 1300°C to 1400'C.

To explain this point specifically, ceramic raw materials such as clay, feldspar, talc, and kaolin improve the plasticity of the aqueous ceramic green sheet obtained by the papermaking method, and further promote the sintering of the raw material cordierite. 5 for purpose
~35% heavy weight. At this time, if the amount of ceramic raw materials added is less than 5% by weight, the green sheet obtained by papermaking will have poor plasticity and will be difficult to handle.
On the other hand, if more than 35% by weight is added, the composition will deviate greatly from the cordierite composition, and the sintered body will not have a low coefficient of thermal expansion.

Note that the paper-making method used here refers to the process of adding organic fibers such as wood pulp and inorganic fibers such as asbestos to the powder of general ceramic materials such as clay, feldspar, pottery stone, talc, and kaolin. An aqueous slurry containing 2 to 40% by weight is prepared, and a coagulant is added to adsorb and aggregate the solid content onto the fibers.The aggregate is poured onto a filter plate or screen to a uniform thickness, and then naturally This is a method of obtaining a sheet-like material by performing filtration using a method such as filtration or vacuum filtration. In the present invention using this papermaking method, inorganic fibers such as asbestos, alumina fibers, ceramic fibers, and rock wool act as carriers that hold particles, literally playing the role of fibers in paper. Furthermore, by sufficiently stirring the aqueous slurry at the stage of making the aqueous slurry, the raw material powder, ceramic raw materials, and inorganic fibers are mixed homogeneously, so that the sheet-like material produced is in a homogeneous state that is suitable for sintering. This is the result.

The inorganic fibers are added in an amount of 3 to 40% by weight, preferably 5 to 20% by weight, based on the raw material powder.

If the amount of inorganic fiber added is less than 3% by weight based on the raw material powder, it will be difficult to form a sheet by the papermaking method, and conversely, if it is more than 40% by weight, it will be difficult to obtain a dense sintered body.

The role of the i1M fiber is not only to serve as a carrier for the powder, but also to serve as a carrier for the powder.
In addition, it is itself a component of a sintered low expansion substrate. That is, the inorganic fibers remain in the sintered product as fibers or in a partially dissolved form, contributing to the creation of a dense substrate.

On the other hand, organic fibers such as wood pulp are added to improve the plasticity of the green sheet and to obtain a sheet that is relatively thick in terms of papermaking properties. Organic fibers have superior plasticity compared to inorganic fibers, and also have superior ability to support sinterable inorganic powder, so they can prevent cracks in raw sheets and produce raw sheets with a body thickness of 3 mm to 5 mm. can. However, when adding organic fibers, one must be careful about the amount of organic fibers added. That is, the organic fibers are burned away during firing, leaving voids where the fibers were, making it difficult to form a dense sintered body.

Therefore, in order to avoid leaving pores in the sintered body, the amount of organic fiber added is 0.2 to 5 parts by weight, preferably 1 part by weight, based on the raw material powder.
-2 parts by weight.

Furthermore, in addition to inorganic fibers, clay, feldspar, talc,
Additives such as kaolin form a liquid phase near the firing temperature and promote sintering of the substrate at relatively low temperatures and over a wide range (1300-1400'C).

In other words, the present invention facilitates molding and sintering of cordierite in an aqueous system, which has been difficult in the past, and provides a dense, low-expansion substrate with a much simpler process than when using a solvent system. It is.

The present invention will be explained below based on specific examples. In addition, all compositions are weight ratios.

<Example 1> Preparation of FAI sample (B) Flocculant 120 parts of 0.2% aqueous solution of di-flocculant First, 2.5 parts of alumina fiber was placed in a pulper (defibration machine).
30 to 6 parts, add 0.5 parts of wood pulp and an appropriate amount of water.
The fibers are defibrated for 0 minutes. 27.5 parts of cordierite, which was crushed and mixed in advance with this, and 10.0 parts of raw frog's eye clay.
1 part of talc, and 50 parts of water are added to the raw material slurry.

After adding the raw material slurry, an appropriate amount of water is further added to prepare an aqueous slurry having a solid content concentration of 3 to 10%.

A pre-prepared sulfuric acid band aqueous solution is added to this aqueous slurry and stirred to adjust the pH of the solution to 2-6, preferably 3-6.
After adjusting to 4, add the aqueous solution of polyacrylamide polymer flocculant, which was also prepared in advance,
Add 100% to 100% and flocculate. The thus aggregated sample is made into paper using a paper machine to form a sheet having a thickness of 1.5 to 3 am.

The material processed into an appropriate shape is placed in an electric furnace and fired at 1380°C for 1 hour in an oxidizing atmosphere to sinter the ceramic.

When the thermal expansion coefficient of the thus obtained ceramic sheet was examined, it was found to be 23 x 10-7 (1/'c), porosity 0.2%, and bending strength 800 kg/cIa.

<Example 2> (A) Preparation of sample (B) Flocculant Using the above compositions (A) and (B) in the same manner as in Example 1, baking at 1350°C for 4 hours resulted in a low The expansion board is ready. The thermal expansion coefficient at this time is 18 x 1
0-' (1/°C), porosity was 0.3%, and bending strength was 800 kg/crA.

<Effects of the Invention> According to the present invention, the porosity of cordierite, which is difficult to sinter, is reduced to 1% by adding feldspar, kaolin, talc, frog's eye clay, asbestos, alumina fiber, hemp, etc.
With the following, densification can be easily performed, and the coefficient of thermal expansion is 2.
It can be as low as 5xlO-'(1/'C) or less.

Moreover, since the present invention uses paper-making technology using fibers to form the sheet for firing, it is thin, has good workability, can be formed into any shape, is lightweight, strong, and resistant to thermal shock. It is a ceramic substrate with the following advantages.

In addition, compared to conventional methods, the process is simpler and the firing temperature is lower, so it is useful for energy saving and can be supplied at low cost.

The low expansion substrate with excellent thermal shock resistance obtained in this way is
It is suitable for use as a heat-resistant substrate in planar heater substrates, household heat-resistant plates, barbecue plates, and industrial fields such as medical, food, and chemical fields.

Claims (2)

[Claims] (1) Clay, feldspar,
Ceramic raw materials such as talc and kaolin are added in a proportion of 5 to 35% by weight, and to this is added 3 to 40 parts by weight of inorganic fibers and 0.5% by weight.
2 to 5% by weight of organic fibers are mixed to form an aqueous slurry,
By agglomerating and paper-making, a sheet-like material made of the above-mentioned raw material powder, ceramic raw materials, inorganic fibers, and organic fibers is obtained, and the sheet-like material is fired at 1300 to 1400°C. Substrate manufacturing method. (2) The method for producing a dense substrate with a low coefficient of thermal expansion according to claim 1, wherein the thickness of the obtained unfired sheet is 1 to 5 mm.