JPH0222172A - Production of ceramic moldings - Google Patents

Abstract

PURPOSE:To obtain ceramic moldings capable of efficiently generating heat by sending an electric current and suitable as an heating element having electric resistance by blending an organosilicon polymer with titanium, molding the blend, calcining the obtained moldings under inert atmosphere and transforming the calcined moldings into ceramic. CONSTITUTION:An organosilicon polymer (e.g., polycarboxystyrene copolymer or polycarbosilane) is blended with a titanium powder and preferably further silicon carbide powder, sizing material (e.g., carboxymethylcellulose), liquid medium (e.g., water), etc. Then the blend is molded into a prescribed shape such as sheet. Then the obtained moldings are calcined under inert atmosphere (e.g., in nitrogen) and transformed into ceramic to provide the ceramic moldings.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for manufacturing a ceramic molded body useful as an electrical resistance heating element. More specifically, the present invention relates to a method for industrially manufacturing a ceramic molded body in the form of a thin sheet (flat plate) or other shape that generates heat when energized and is suitable as an electrical resistance heating element.

[Background Art] In recent years, household cooking utensils and commercial cooking utensils that utilize electric heat have been widely used. Examples include microwave ovens, toasters, ovens, frying pans, etc. These devices either self-heat the food to be cooked using a magnetron or the like, or are equipped with an electric heater using a nichrome wire or the like. Although these are convenient cooking utensils, they cannot be called perfect cooking utensils as consumers have become more gourmet-oriented today. For example, meat in the microwave.

Although it is possible to heat and cook fish, it is not possible to make it burnt and give off an aromatic aroma. For this reason, there are some methods that have been designed to reheat food using a nichrome wire heater, etc., but the heating is not sufficient and it has not been possible to satisfy the recent gourmet-oriented consumers. The reason for this is the lack of heat resistance of such metal heaters, and it can be pointed out that the heater temperature is insufficient. Another problem is that most heaters are rod-shaped and cannot heat the food evenly.

Therefore, one solution would be to replace these metal heaters with heat-resistant ceramic heaters, and it would be even more preferable to use a planar heating element instead.

It is well known that for uniform heating, it is preferable that the heat source has an area. However, in the case of a flat metal, there is a problem in that the electrical resistance is too low to connect terminals at both ends and connect it to a household 100 volt or 200 volt power source.

On the other hand, although ceramic electrical resistors are known, none that meet this purpose have been put into practical use. For example, silicon carbide-based resistance heating elements are known, but these have low electrical conductivity and cannot be used as they are in cooking appliances and the like.

Resistors using carbon alone or with a ceramic filler are also known, but these are mainly components of communication equipment and cannot be used for heating purposes.

When ceramics are used for heating elements, there is also the problem of strength in order to make them smaller, particularly in the form of thinner sheets. for example,
If the sheet is made thin and thin, it will break easily due to the characteristics of ceramics. In particular, it is not easy to handle the molded material before firing, a so-called green sheet. There is a method of increasing the amount of glue added to the green sheet in order to improve the handling properties of the green sheet, but this method often causes problems in the subsequent firing. That is,
Usually, only sheets that break during firing or are easily brittle even if they do not break are obtained.

For these reasons, it is actually extremely difficult to provide a ceramic molded body that is thin, has a large heat dissipation portion, and is useful as a sheet-like heating element that can uniformly heat the ceramic body during cooking or the like. Therefore, at present, such a sheet-like heating element has not yet been manufactured industrially.

As a solution to this problem, the present inventors previously proposed a method in which a mixture of a polycarbosilastyrene copolymer and carbon is fired to form a sheet (Japanese Patent Application No. 38740/1982).

In addition, sheet-like ceramic molded products using polycarbosilane are disclosed in JP-A-60-235765 and JP-A-5.
A method has also been proposed in which the material described in No. 9-174575 is used, and this material and a thermoplastic resin are simultaneously extruded and fired as two layers. However, the ceramics obtained by these methods tend to contain free carbon, and when fired, the yield is poor due to large shrinkage due to the loss of organic matter, and the sheet-shaped ceramic heating elements obtained do not change when energized. It also has disadvantages such as being easy to use. Furthermore, there is a problem in that the electrical resistance gradually increases when energization (heat generation) is repeated, and many problems remain to be improved when used as a heat generating element.

[Problems to be Solved by the Invention] The present invention solves the various problems observed when using the conventional sheet-shaped ceramic molded body as an electrical resistance heating element, and provides a thin sheet-shaped ( The purpose of the present invention is to provide an industrially advantageous method for manufacturing ceramic molded bodies of any shape, including flat plate shapes.

[Means for solving the problem] These problems can be solved by using polycarbosilastyrene copolymer,
A method in which a mixture containing organosilicon polymers such as polycarbosilane and fine titanium metal powder is molded into a sheet or any other arbitrary shape, and the resulting molded body is fired in an inert atmosphere to form a ceramic. achieved.

The organosilicon polymer used in the method of the present invention includes polycarbosilane, polysilane, polysilastyrene, polycarbosilastyrene copolymer, and the like.

Among these, polycarbosilastyrene copolymer is the most preferred because it has a good yield during firing and the ceramic molded product after firing has excellent physical properties and electrical properties.

The polycarbosilastyrene copolymer here refers to the polycarbosilastyrene copolymer proposed by the present inventors, in which the main chain of the molecule contains carbosilane bonds (published by FSi CHZ) and silastyrene bonds in a ratio of 70/30 to 30/70. The coexisting high-molecular organosilicon polymer having a molecular weight of 1,000 to 50,000 is described in detail in European Patent Publication No. 0212485 regarding its production method and properties.

However, in the method of the present invention, for example, polycarbosilane made from dimethyldichlorosilane can also be effectively used.

On the other hand, titanium (Ti) used in combination with the organosilicon polymer
), titanium powder is usually used.

When manufacturing a thin sheet with a thickness of 3s or less, especially a thickness of 2jw or less, the titanium powder is preferably finer, and the average particle size is 10μm or less, particularly 0.5 in the case of a thin sheet.
It is preferably less than μm.

The main feature of the method of the present invention is that it uses a mixture of n-silicon polymer and titanium as a raw material to be formed into a sheet, and the amount of titanium added to the organosilicon polymer is It is influenced by the required physical properties and the type and base of the paste, sintering aid, etc. added as necessary. In the case of using only an organosilicon polymer and titanium, it is often preferable that titanium is about 0.1 to 1.0 (weight ratio) to the polymer. When a sizing agent and a sintering aid are added, it is preferable that the ratio of titanium to the polymer is even higher.

It may be preferable to add polysilane or a low melting point organosilicon polymer to the organosilicon polymer. That is, these are thought to play the role of melt adhesion during sintering.

In the method of the present invention, in addition to the organosilicon polymer and titanium, silicon carbide (St C) and silicon <Sr> may also be added depending on the properties required of the ceramic molded body obtained. In some cases, it is preferable. These SiC and 3i are also usually used in the form of powder, and the nominal diameter of these powders is preferably 10 μm or less, and particularly preferably 0.5 μm or less when forming a thin sheet.

The particle size of titanium and silicon carbide poses a problem, particularly in terms of formability when forming into a sheet to form a green sheet.

When carrying out the method of the invention, if necessary, further sizing agents and sintering aids can be added to the mixture. for example,
When the mixture is made into a paste, which is molded and fired, it is preferable to add a paste. The glue used in this case is CM, which is commonly used when forming raw materials for ceramics.
C (carboxymethyl cellulose), PVA (polyvinyl alcohol), PEG (polyethylene glycol, polyvinyl butyral), etc. are used. In addition, higher fatty acids (such as stearic acid, valmitic acid, oleic acid, etc.),
Higher fatty acid esters (for example, butyl stearate), animal and vegetable oil waxes, etc. may also be used.

Furthermore, in making a paste, a dispersion medium such as water or a liquid medium such as an organic solvent may be used. Water is the most economical dispersion medium, but dense molded products can be obtained by using an organic solvent that can dissolve the organosilicon polymer.

Further, powder of alumina or other metal may be mixed for the purpose of adjusting electrical and mechanical properties.

In the method of the present invention, these raw materials are pulverized and mixed to create a sheet-like or other shaped molded product (in the case of a sheet-like product, it is called a green sheet).

Below, we will explain the case of making a sheet as an example. When making a paste into a sheet using a wet method, organic silicon polymer, titanium powder, if necessary, a paste, silicon carbide, a baking aid, etc. are mixed, water etc. Add a dispersion medium and knead to make a paste. Next, this paste is formed into a sheet by extrusion molding, press molding, or the like. In the case of extrusion molding, etc., it is preferable to reprocess with a calendar.

On the other hand, when forming a sheet by melt molding, an organosilicon polymer and titanium powder are mixed and melt extrusion molded through a slit die. At this time, silicon carbide,
Of course, the process may be carried out by adding a sizing agent, a sintering aid, etc.

In the case of powder molding, the mixture can be formed into a sheet by uniformly pouring the mixture into a press, or by uniformly scattering the powder onto a base material, heating and pressing.

The green sheet thus obtained is fired in an inert atmosphere such as nitrogen or argon. If necessary, infusibility treatment is performed prior to this firing. Various reports have already been made regarding the infusibility treatment of organosilicon polymers (for example, JP-A-58-215426), and heat treatment, radiation treatment, ultraviolet treatment, and others are known. When infusibility is required in the method of the present invention, any of these methods can be employed. However, if the amount of powder such as titanium or silicon carbide is large, the powder layer absorbs the molten organosilicon polymer, so the infusibility treatment is not necessary, and it may be preferable not to perform it. When performing infusibility treatment, it may be desirable to perform it before forming into a sheet.

In either case, these sheets are fired in an inert atmosphere to form a ceramic, and the firing temperature is between 1000°C and 2.0°C.
000°C, particularly preferably 1200°C to 1800°C. Industrially, at temperatures below this range, the decomposition of the organosilicon polymer and the reaction between the resulting product and titanium are insufficient, and the effects of the present invention are not as desired. At temperatures higher than this, other reactions such as the generation of titanium dioxide due to the reaction with oxygen contained in nitrogen or argon and the generation of titanium nitride due to the reaction with nitrogen cannot be ignored. Since all of these products are electrically insulating, they reduce the electrical conductivity of the resulting ceramic sheet.

According to the research conducted by the present inventors, when polycarbosilastyrene copolymer is fired to make ceramics, 1300℃
When fired at a certain temperature, the shrinkage during firing is close to 20%. Even with the products described in JP-A-60-235765 and JP-A-59-17457, the dimensional shrinkage was 2. ~4%, and the weight reduction reaches as much as 10%. However, according to the method of the present invention, the weight reduction can be reduced to 1%, depending on the selection of raw material composition.

The resulting ceramic sheet is electrically conductive, for example, more conductive than if the organosilicon polymer was fired without the addition of titanium.
The loss on firing is low, the electrical conductivity is increased, and the properties as a heating element sheet can be improved. This reaction is different from when titanium is not added, and titanium reacts with the substance generated when the organosilicon polymer decomposes during firing to form a ceramic (SiC), forming a ceramic component (TiC). It is presumed that this is because the Since this TiC has good electrical conductivity, it is thought that the electrical conductivity of the sheet produced by the method of the present invention is also improved.

Although the method of the present invention has mainly been described above for producing ceramic sheets, the method of the present invention is also effective in producing molded bodies of other shapes.

[Effects of the Invention] As described above, by the method of the present invention, a ceramic molded body suitable for use as a thin (thickness 3 am or less) sheet-like (flat plate) or other arbitrary shape electric waste heat body can be produced in good yield. Furthermore, this molded product shows little change when repeatedly energized, and has very good stability when used as an electric heating element.

The conductivity of the ceramic molded body obtained in this way can be improved by adjusting the composition of the raw material mixture, and it can also be designed with a resistance value that allows it to be connected directly to a household power source as a heating element in any shape such as a sheet. It is extremely useful as a surface heating element for ceramic heaters.

[Example] Next, Examples and Comparative Examples of the present invention will be given, but the present invention is not limited thereto. Note that unless otherwise specified, "parts" in each example are parts by weight.

Example 1 Polysilastyrene was obtained by polymerizing equimolar amounts of dichlorodimethylsilane and dichloromethylphenylsilane in toluene with the addition of metallic sodium. This polysilastyrene was treated at 390° C. for 50 minutes in a nitrogen atmosphere and the pressure was reduced to obtain a polycarbosilastyrene copolymer (PC3S). The softening point of this copolymer is 222°C.

10 parts of polycarbosilastyrene copolymer (PC3S),
5 parts of crushed titanium of 320 mesh or less;
80 parts of commercially available silicon carbide with a nominal diameter of 0.27 μm, industrial stearin! 15 parts of paraffin and 5 parts of paraffin were mixed, cooled and pulverized to obtain a fine powder.

This was put into a mold, leveled uniformly, pressed at a pressure of 1.5 t/d, formed into a sheet at 220°C, cooled and taken out, and a sheet with a thickness of 0.8#I was made. Obtained.

This sheet was fired in a stream of high purity nitrogen. During firing, the temperature should be raised to the indicated temperature of the furnace, 1300°C, at a heating rate of 50°C/hr; however, the temperature detection end and the sample are not in close contact with each other).

After being held at 1300°C for 1 hour, it was cooled and taken out.

The obtained ceramic sheet had a volume resistivity of 2.00 mm, and the weight reduction rate from raw material to product was 7%.

Examples 2 to 4 and Comparative Example 1 Ceramic sheets were produced in the same manner as in Example 1, except for the amount of titanium powder added as shown in the table. The respective implementation results are as shown in the numerical table (the data of the above-mentioned Example 1 is also shown).

It shows the results.

A comparative sample was prepared in exactly the same manner except that one part of Aρ203 was used in place of the titanium in Example 1 (Comparative Example 2).
. The specific resistance value of this sample was 4×100Ωα.

A repeated energization test was conducted on a sample prepared in the same manner as in Example 1 and on a sample of Comparative Example 2. The results are shown in the numerical table. Note that the temperature of the sample rose to 1000° C. when electricity was applied.

This result shows that the components that were scattered during firing when titanium was not added (Comparative Example 1) were turned into ceramic when titanium was added (Examples 1 to 4). They also show that the resistivity of ceramics can be changed by adding titanium.

Example 5 and Comparative Example 2 In this Example and Comparative Example, small "cracks" were observed in the sample of Comparative Example 2 after the repeated energization test was completed. Furthermore, it was observed that the sample of Comparative Example 2 had changed color after being energized compared to immediately after trial production, and the black color had changed to gray. The sample of Example 5 also had some discoloration, but the degree of discoloration was much less.

Reference Example 1 A polycarbosilane styrene copolymer having a melting point of 220°C was melt-extruded to form a film, and the resulting film was slowly heated to 230°C in air. It took 10 hours to raise the temperature from room temperature to 230°C. After making the polycarbosilastyrene copolymer film infusible in this way, it was heated to 1400°C at a rate of 50'C/hr in nitrogen.
The temperature was raised to 100.degree. C. and fired to obtain a ceramic film mainly composed of SiC. The weight loss during firing was 13%, and the volume resistivity of the film was 1. OX 100Ω was 0.

Example 6 Same polycarbosilastyrene copolymer 100 as Reference Example 1
4 parts of titanium powder was mixed with 4 parts of titanium powder and fired in the same manner as in Reference Example 3 to obtain a ceramic film mainly composed of SiC. The weight loss during firing was 10%. Further, the volume resistivity was 0.5×100Ωα, and it was confirmed that both were improved over Reference Example 1.

Example 7 Adding sodium to dimethyldichlorosilane and polymerizing it,
Polysilane was obtained. This polysilane was heated at 430°C under pressure.
The temperature was raised to 90°C to rearrange into polycarbosilane.

A similar operation was performed using this carbosilane instead of the polycarbosilane styrene copolymer of Example 1 to obtain a ceramic sheet. The volume resistivity of the obtained ceramic sheet was 4×100ΩCIR. Furthermore, the weight loss rate during firing was 9%.

Example 8 Ethyl cellulose was dissolved in ethanol to form a solution, which was applied to a chrome-plated brass plate and dried.

50 parts of polycarbosilane styrene copolymer powder, 50 parts of titanium powder, and 50 parts of silicon carbide powder were mixed, re-pulverized, and uniformly and thinly spread on the chrome-plated plate coated with the above-mentioned ethyl cellulose.・Heating (1100N/c
m, 230°C), and then the obtained sheet (green sheet) was removed from the root soil.

The obtained green sheet was fired at 1500° C. in a nitrogen stream to obtain a ceramic sheet with a thickness of 1 am.

The specific resistance value of this ceramic sheet is 2. OX100
It was Ωα.

14'.

Claims (5)

[Claims] (1) A method for producing a ceramic molded body, which comprises molding a mixture containing an organosilicon polymer and titanium into a predetermined shape, and firing the resulting molded product in an inert atmosphere to form a ceramic. (2) Ceramic molded body with a thickness of 3 mm or less, preferably 2
The manufacturing method according to claim (1), wherein the sheet is made into a sheet having a size of 1 mm or less. (3) The method according to claim 1 or 2, wherein the organosilicon polymer is a polycarbosilastyrene copolymer or a polycarbosilane. (4) A claim in which the mixture to be molded is a paste-like mixture consisting essentially of organosilicon polymer, titanium powder, silicon carbide powder, glue, and liquid medium (
1), (2) or (3). (5) Claim (2), wherein a mixture substantially consisting of organosilicon polymer, titanium powder, and silicon carbide powder is uniformly spread on a substrate, and the sheet-like product formed by heating and pressing is fired in an inert atmosphere. Or the manufacturing method described in (3).