JPH0393671A - Sintering method for ceramic form - Google Patents

Abstract

PURPOSE:To obtain in high efficiency a uniform sintered compact free from crack or warpage etc., by putting, when a ceramic form is to be sintered, a ceramic sheet with the surface uneven and the thickness not greater than a specified value beneath the ceramic form to also provide the back surface of the ceramic form with vent holes for the gas to be generated. CONSTITUTION:Firstly, a ceramic sheet 1 (e.g. alumina sheet) <=2mm thick with its surface uneven is prepared. It is preferable that the uneven pattern be of plain weave form, represent repetition of fine unit and be free from sharp edges. Second, this ceramic sheet 1 is laid on a shelf board 2 and a form 3 consisting of a ceramic raw material (e.g. lead zirconate titanate) is put on the sheet 1. Thence, the resulting system is heated to elevated temperatures and sintered, thus obtaining the objective sintered compact free from deformation and from the adherence of foreign matter. The above ceramic sheet can be use repeatedly.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a firing method for producing ceramic materials used in electronic materials, refractory materials, biomaterials, industrial materials, optical materials, etc. It is. (Conventional technology) When a molded body made of ceramic raw materials is fired, it has traditionally been fired by placing it on a refractory material called a shelf. However, the molded body sometimes shrinks during firing, causes friction with the shelf board, and becomes deformed.

Therefore, in order to reduce frictional resistance, a ceramic powder called kafunko was spread on the shelf board, and then the large-sized body was placed on top of the shelf board and fired. However, this method
Not only was it time-consuming to spread the bedding powder, but it was also uneconomical because it was disposable. Even more problematically, this bedding powder sometimes adhered to the molded body and caused contamination. This was fatal in the field of fine ceramics, including electronic materials, where precision and purity are required. Therefore, a sheet for baking has been introduced that eliminates the need for laying powder and allows it to be spread over shelf boards with high precision. Some of these sheets were made of organic materials and others were made of inorganic fibers, but neither of them could completely solve the above-mentioned problems.

In other words, organic material sheets are disposable once only.
Economic problems still remained, and the problem of ceramic powder contained in organic substances adhering to ceramic molded bodies was gradually resolved.

On the other hand, sheets made of inorganic fibers also have almost the same problems as organic sheets.

(Purpose) The present invention solves these conventional problems, and furthermore,
When the ceramic contains a large amount of combustible material called a binder, a vent for the gas generated during firing can also be formed on the bottom of the molded body, resulting in a uniform ceramic without cracks or warping. We can provide fired products.

(Means for Solving the Problems) In the present invention, when firing a molded body made of raw ceramic material, a ceramic sheet having an uneven surface shape and a wall thickness of 20 mm or less is placed on the bottom surface of the molded body. This is achieved by laying the ceramic sheet and firing it, preferably by making the unevenness pattern of the ceramic sheet into a plain weave shape.

The present invention will be explained in detail below.

The material of the ceramic sheet in the present invention can be selected depending on the NWA of the molded body using the ceramic raw material to be fired thereon. The selection criterion is to use a ceramic material that does not react within the firing temperature range of the molded body. For example, high-purity alumina is used for piezoelectric ceramics based on lead zirconate titanate, and zirconia is used for barium titanate. Further, the thickness of the sheet must be 2 llm or less. If it is 2 mm or more, the following problems will occur.

■Thermal capacity increases and thermal conductivity deteriorates.

This delays the firing schedule of the furnace, which runs counter to one of the objectives of the present invention, which is to save labor in the firing process. ■Thermal shock resistance deteriorates as the thickness increases.

The sheet used in the present invention must have an uneven pattern formed on its surface. It is desirable that this pattern of protrusions and recesses does not have sharp corners, for example, as shown in FIGS. 2 and 3, which have a plain weave shape, and that it has repeating fine units. This is because the friction generated between the fired product and the fired product when it contracts is to be minimized. Further, if the texture of the unevenness is coarse, there is a risk that marks of the texture may be left due to the load of the fired product. The scale of this uneven pattern is 30 to 80 pieces of ridges per square centimeter, and the area of ridges to the total area is 10 to 70 pieces.
% is desirable. By firing a ceramic molded body using the sheet of the present invention, the ceramic molded body will not be deformed during the firing process, and the bottom surface will not stick to the shelf board after firing. The molded body can be easily taken out. Also, since the sheet was not damaged,
It becomes possible to use it repeatedly.

The method of the present invention will be explained in detail in Examples below. Example 1 A ceramic molded body was prepared by press-molding a powder of lead zirconate titanate containing 10% of an organic binder into a disk shape of φ100 mm and height of 5-1 mm. Also, the purity is 99.
A green sheet was prepared using a doctor blade method using 9% alumina, and then the sheet was pressed with an embossing roller to form an uneven pattern on the surface of the sheet. Next, try this sheet! It was fired at 600°C and made into a ceramic sheet. Next, spread the ceramic sheet l on the shelf board 2, place the ceramic molded body 3 on top of it, and heat it to 1250°C.
This ceramic molded body 3 was fired for 18 hours, kept at that temperature for 2 hours, and then cooled to room temperature.
The fired product was taken out.

Although the fired product had a linear shrinkage rate of 20%, it could be easily taken out without any deformation or adhesion of foreign matter. We also conducted a similar test using the same sheet for 50
I repeated it several times, and in each case there were no problems as with the first time. Example 2 Barium titanate powder containing 23% organic binder was formed into a sheet with a thickness of 1 mm by the doctor blade method, and a sheet of 5 ms square was punched out.
This was made into a ceramic molded body.

In addition, zirconia containing 7 moles of yttria was made to form an uneven pattern on its surface in the same manner as in Example 1.
Ceramic sheets were made by firing at 0°C. Next, the ceramic sheet was spread on a shelf board, the ceramic molded body was placed on top of it, and the temperature was raised to 1350°C for 24 hours.
The ceramic molded body was fired for a long time, kept at that temperature for 3 hours, cooled to room temperature, and the fired ceramic molded product was taken out. Observations similar to those in Example 1 were made, and good results were obtained in all cases.

Comparative example l A ceramic molded body similar to that in Example 1 was used.

However, the same test as in Example 1 was carried out by placing sheets of alumina fibers obtained by paper-making using polyvinyl alcohol as a binder on the shelves. After firing, I tried to take it out of the furnace, but the sheet Ichiro was stuck to the fired product. Further, the binder of the fibers constituting the sheet was burned out, and the sheet became extremely brittle and could not be used again.

Comparative example 2 A ceramic molded body similar to that in Example 1 was used.

The same test as in Example 1 was conducted using a sheet in which Yamabe's tanro had minute cylindrical protrusions that were not curved to simulate the unevenness of the sheet in Example i. When the fired product was taken out of the furnace after firing and observed, it was found that there were streaks on the bottom surface of the fired product that appeared to have occurred during shrinkage.

(Effects of the Invention) Using the method of the present invention not only greatly saves labor in the furnace firing process for ceramic molded bodies, but also improves yield and quality. It is possible to obtain a fired ceramic body with high heat resistance.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a state in which a ceramic sheet according to the present invention is placed on a shelf board, and a ceramic molded body is further placed on top of the ceramic sheet. FIG. 2 is a partially enlarged plan view of the ceramic sheet used in Example 1 of the present invention.
FIG. 3 is a sectional view taken along line A-A of the ceramic sheet shown in FIG. l... Ceramic sheet, 2.
...II1.3... Ceramic molded body

Claims (2)

[Claims] (1) When firing a molded body made of ceramic raw materials, a ceramic sheet having an uneven surface shape and a wall thickness of 2 mm or less is laid on the bottom surface of the molded body, and then fired. How to burn the body. (2) The method for firing a ceramic molded body according to claim 1, wherein the pattern of unevenness of the ceramic sheet is a plain weave shape.