JPH01298067A - Production of ceramic sheet - Google Patents

Abstract

PURPOSE:To industrially and advantageously obtain the title thin, small-sized, and sheet-shaped ceramic formed body useful as a heating element by calcining the sheet-shaped formed body of a mixture contg. an organosilicic polymer and silicon in an inert atmosphere. CONSTITUTION:The mixture of an organosilicic polymer and silicon is formed into a sheet, the obtained formed body is calcined in an inert atmosphere to convert the body into a ceramic, and the desired sheet is obtained. Copolymers such as polycarbosilane, polycarboborosilane, polysilastyrene, and polycarbosilastyrene are exemplified as the organosilicic polymer to be used. Silicon powder is usually used as the silicon. When a thin sheet having <=3mm, especially <=1mm, thickness is to be produced, finer silicon powder having <=10mu mean particle diameter is preferably used. When a thinner sheet is to be produced, the average particle diameter is preferably controlled to <=0.5mu.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application 1 The present invention relates to a method for producing a ceramic sheet useful as an electrical resistance heating element. More specifically, the present invention relates to a method for industrially manufacturing a thin sheet-like (flat plate-like) ceramic molded body 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. For example, microwave oven, 1~-star, oven, frying pan, etc. these are,
This is due to the self-heating of the food being cooked using a magnetron or the like, or leakage from 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, although there are some methods of reheating with a nichrome wire heater, etc., sufficient heating is not achieved, and this has not been able 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 evenly heat the food to be cooked.

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 are industrial rod-shaped or vibrator-shaped products, and these industrial heating elements cannot be used as they are in cooking appliances or the like.

Resistors using carbon alone or in combination with a ceramic base material 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 remove the molded material before firing, a so-called green sheet. In order to improve the absorbency of the green sheet, there is a method of increasing the amount of glue added to the green sheet, but this method often causes problems in the subsequent firing. That is,
In the process of firing, only a sheet that is easily destroyed or not destroyed during firing can be 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 first proposed a method in which a mixture of a polycarbosilastyrene copolymer and carbon is fired to form a sheet (Japanese Patent Application No. 53-38740).

In addition, as a sheet-like ceramic molded product using polycarbosilane, there are
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.

[Problem to be Solved by the Invention 1] The present invention solves the various problems observed when using the conventional sheet-like ceramic molded body as described in (a) above as an electric resistance heating element, and provides a thin and useful heating element. The object of the present invention is to provide an industrially advantageous method for manufacturing small-sized sheet-like (flat plate-like) ceramic molded bodies.

[Means for solving the problem] These problems can be solved by using polycarbosilastyrene copolymer,
Achieved by a method in which a mixture containing organosilicon polymers such as polycarbosilane and silicon is formed into a so-called green sheet, and the obtained sheet 1 is fired in an inert atmosphere to form a ceramic. be done.

In the method of the present invention, polycarbosilane, polycarboborosilane, polysilastyrene, polycarbosilastyrene copolymer, etc. are used as the silicon-containing polymer.

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 herein refers to the polycarbosilane bond +5i-CH2-1□ and the silastyrene bond -(-8i-8i-+-6H5) in the main chain of the molecule, as proposed by the present inventors. 1fi70/30~30/70) Ratio T: Coexistence 5
It is a high-molecular silicon polymer having an f-number of m1,000 to 50,000, and its manufacturing method and properties are described in detail in European Patent Publication No. 0212485.

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

On the other hand, silicon powder is usually used as the silicon (Sl) used in the silicon fluoride polymer.

When making a thin sheet with a thickness of 3 mm or less, especially 1M or less, it is preferable that the silicon powder is fine, and the average particle size is 10 μm or less, and in the case of a particularly thin sheet, the silicon powder is fine.
m or less is preferable.

The main feature of the method of the present invention is that it uses a wired silicon polymer mixed with silicon as a raw material to be formed into a sheet. It is influenced by the required physical properties and the type and amount of glue, sintering aid, etc. added as necessary. In the case of using only an organosilicon polymer and silicon, it is often preferable that the amount of silicon is about 0.1 to 1.0 (by weight) based on 1 part of the polymer. When a sizing agent and a sintering aid are added, it is preferable that the ratio of silicon to the polymer is even higher.

It may be preferable to add polysilane or a low melting point organosilicon polymer to the organosilicon polymer. In other words, these are thought to play the role of melt bonding during sintering.

In the method of the present invention, silicon carbide may be added in addition to the organosilicon polymer and silicon, and it may be preferable to actively add silicon carbide depending on the properties required of the ceramic sheet. This silicon carbide is also usually used in powder form, and preferably has a nominal diameter of 10 μm or less,
In particular, when forming a thin sheet, the thickness is preferably 0.5 μm or less. The size of silicon and silicon carbide particles poses a problem, particularly in terms of formability when forming into a sheet and forming 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 and this is made into a paste and fired, it is preferable to add a paste. The glue used in this case is CMC (carboxymethyl cellulose), PVA (polyvinyl alcohol), PEG (polyethylene glycol), etc., which are commonly used in the molding of ceramic raw materials. Further, higher fatty acids, higher fatty acid esters such as stearic acid, balmitic acid, oleic acid, higher fatty acid esters such as butyl stearate, 8
Okemono fat wax or the like may also be used.

Furthermore, in making a paste, a dispersion medium such as water or a liquid medium such as a Uiso 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, for the purpose of adjusting electrical and mechanical properties, powder of alumina and its squid metal may be mixed.

In the method of the present invention, these raw materials are pulverized and mixed to form seams 1 to 1.
A shaped molded product (so-called green sheet) is created.

When making a paste into a wet sheet, mix silicon polymer, silicon powder, and if necessary, paste, silicon carbide, baking aid, etc., add a dispersion medium such as water, and knead to make a paste. . This base is then extruded,
Form into a sheet by press molding, etc. 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, the silicone polymer and silicon powder are mixed and melt extruded from 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 thus prepared green sheet is fired in an inert atmosphere such as nitrogen or argon. If necessary, an infusible treatment is performed prior to this firing. Regarding the infusible treatment of organosilicon polymers. There have already been various reports (for example, Japanese Patent Application Laid-Open No. 58-215426), 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 silicon or silicon carbide is large, the infusibility treatment is not necessary because these layers absorb the molten □ silicon polymer, and it may be preferable not to perform the infusibility treatment. 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 1200°C.
~2000°C, particularly preferably 1300°C ~1800°C
It is ℃. Industrially, if the temperature is lower than this, the decomposition of the organosilicon polymer and the reaction of the resulting product with silicon will not be sufficient, and the effects of the present invention will not be as desired. At temperatures higher than this, other reactions such as the generation of silicon dioxide due to the reaction with oxygen contained in nitrogen or argon and the generation of silicon 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 research conducted by the present inventors, when polycarbosilane is fired to form ceramics, the shrinkage during firing is close to 20% when fired at about 1300°C.

Even with the products described in JP-A-60-235765 and JP-A-5917457, the dimensional shrinkage was 2 to 4%, and the weight loss was 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, and is more conductive than, for example, when an organosilicon polymer is fired without the addition of silicon.
The loss on firing is low and the desired physical properties are 14 times easier. This is because the reaction is different from when no silicon is added, and silicon reacts with the substance generated when the organosilicon polymer decomposes during firing to form a ceramic <SiC>, forming a ceramic component. Presumed.

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

The conductivity of the ceramic sheet obtained in this way can be adjusted by adjusting the composition of the raw material mixture, and the resistance value can be designed so that it can be directly connected to a household power source as a sheet heating element. Extremely useful as a heating element.

[Example] Next, Examples and Comparative Examples of the present invention will be given, but the present invention is not limited thereto. In addition, unless otherwise specified, "1 part" in each example is a heavy ω part.

Example 1 Equimolar moles of dichlorodimethylsilane and dichloromethylphenylsilane were mixed in toluene with the addition of metallic sodium to give 1 q of polysilastyrene. This polysilastyrene was treated at 390°C in a nitrogen atmosphere for 30 minutes,
Reduce the pressure and add polycarbosilastyrene copolymer (PC8S
) was obtained. The softening point of this copolymer is 220°C.

10 parts of polycarbosilastyrene copolymer (PC8S),
10 parts of pulverized silicon having 250 mesh or less, 80 parts of commercially available silicon carbide with a nominal diameter of 0.27 μm, 5 parts of industrial stearic acid, and 5 parts of paraffin were mixed, cooled and pulverized to obtain a fine filA powder.

Put this into a mold, level it evenly, and make 1.5 t/ci.
The mixture was pressed at a pressure of 220° C., formed into a sheet at 220° C., cooled and taken out to obtain a sheet with a thickness of 0.1 m.

This sheet was fired in a stream of high purity nitrogen. During firing, the temperature was raised to the indicated temperature of 1300°C in the furnace at a heating rate of 50°C/hr (note that the temperature detection end and the sample were not in close contact).

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

The obtained ceramic sheet had a volume resistivity of 4 Ωcm, and the reduction rate from raw material to product was 7%.

Examples 2 to 4 and Comparative Example 1 Ceramic sheets were manufactured in the same manner as in Example 1, except that the amount of silicon powder added was changed as shown in the following table. The results of each experiment are shown in the following table (the data of Example 1 mentioned above is also shown).

This result shows that the components that were scattered during firing when silicon was not added (Comparative Example 1) were turned into ceramic when silicon was added (Examples 1 to 4). It has also been shown that the hardness resistance of ceramics can be changed by adding silicon.

Example 5 and Comparative Example 2 This Example and Comparative Example show the results of a repeated energization test.

A comparative sample was prepared in exactly the same manner except that one part of AJJz03 was used in place of the silicon in Example 1. <Comparative Example 2
〉. The specific resistance hB of this sample was 4×100 Ωcm.

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

At the end of the experiment, small "cracks" were observed in the sample of Comparative Example 2.Also, the sample of Comparative Example 2 was discolored after being energized compared to immediately after the prototype, and the black color changed to gray. The sample of Example 5 was also slightly discolored, but the degree of discoloration was quite small.

Comparative Example 3 A polycarbosilane styrene copolymer having a melting point of 220°C was melt-extruded into 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 infusibleizing the polycarbosilastyrene copolymer film in this way, it was heated to 1400 ml at a rate of 50'C/hr in nitrogen
The film was fired by stomach warming to ℃ 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 was 100Ωcm.

Example 6 Polylupocylasdyrene copolymer 100 same as Comparative Example 3
4 parts of silicon powder was mixed with 4 parts of silicon powder and fired in the same manner as in Comparative Example 3 to obtain a ceramic film mainly composed of SiC. The weight loss during firing was 10%. Further, the volume resistivity was 0.7×100 Ωcm, and rJfi was recognized to be improved over Comparative Example 3 in both cases.

Example 7 Adding sodium to dimethyldichlorosilane and polymerizing it,
Polysilane was obtained. This polysilane was heated to 350°C to transform it 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 Sea 1~ was 50 cm.

Further, the weight reduction rate during firing was 8%.

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

$5) 50 parts of polycarbosilane styrene copolymer,
50 parts of silicon powder and 50 parts of silicon carbide powder were mixed, re-pulverized and evenly and thinly sprinkled on a chrome plated plate coated with the above ethyl cellulose, and then heated under pressure (100 kg).
/cm, 230°C), and then the obtained sheet (green sheet) was removed from the plate.

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

The specific resistance value of this ceramic sheet was 3Ωcrr+.

Patent applicant Teijin Kaisha Ltd.

Claims (5)

[Claims] (1) A method for producing a ceramic sheet, which comprises molding a mixture containing an organosilicon polymer and silicon into a sheet, and firing the molded product in an inert atmosphere to form a ceramic. (2) The manufacturing method according to claim (1), wherein the thickness of the ceramic sheet is 3 mm or less, preferably 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 pasty mixture consisting essentially of an organosilicon polymer, silicon powder, silicon carbide powder, paste, and liquid medium (
The manufacturing method described in 1), (2) or (3). (5) Claim (1), wherein a mixture of substantially organosilicon polymer, silicon powder, and silicon carbide powder is uniformly dispersed on a substrate, and the sheet-like product formed by heating and pressurizing is fired in an inert atmosphere. The manufacturing method described in (2) or (3).