JPH0157056B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing crystallized glass having low expansion and high mechanical strength.

SiO ₂ ―Al ₂ O ₃ ―Li ₂ O-based crystallized glass has a low coefficient of thermal expansion, generally less than 30 × 10 ^-7 /℃ (30 to 380℃), so it is difficult to cook because it is resistant to thermal shock. It is widely used as a constituent material for vessels, etc. In recent years, crystallized glass, which has excellent thermal shock resistance, has been used as the material for the top plate of electric or gas cooking appliances that are provided with a top plate that does not expose the heating source directly to the surface. The top plate is required not only to have excellent thermal shock resistance, but also to have high mechanical strength, particularly high impact strength, since it is sometimes subjected to sharp impacts. For example, Underwriters Laboratories (U.S.)
According to Standard 858 (Laboratories), it is required that a 535g steel ball not be broken in the center of the top plate even if it is dropped from a height of 54.1cm. In order to meet this standard, it is considered that the bending strength of crystallized glass needs to have a value of at least 2500 Kg/cm ² or more. However, the bending strength of SiO ₂ -Al ₂ O ₃ -Li ₂ O-based low-expansion crystallized glass is usually only 1000
It remains at ^around 1400Kg/cm2. Several methods have been proposed to increase the bending strength of crystallized glass. However, for example,
The method of incorporating F, which has the effect of improving strength, in the glass composition, as in 4870, poses a problem in terms of pollution control, as F evaporates during glass melting. The method of strengthening crystallized glass by ion exchange treatment and creating compressive stress in the surface layer requires a special process of bringing the object to be treated into contact with a molten salt solution after the crystallization heat treatment, and is not practical. There is a problem above.

Therefore, as a result of various studies in order to improve the mechanical strength of low-expansion crystallized glass, the inventors of the present invention have developed a crystalline glass having a SiO ₂ -Al ₂ O ₃ -Li ₂ O system composition. In a method for producing crystallized glass by heat treating a possible glass molded product,
A low-expansion, high-strength crystallized glass can be obtained by coating the surface of the crystalline glass molded article with a coating material containing γ-alumina and a surfactant and heat-treating it to promote crystallization of the surface layer. The present invention is proposed as the present invention.

As is well known, crystallized glass is produced by melting and shaping glass raw materials containing crystallizable components, and then heat-treating and crystallizing the glass molded product. Some crystallized glasses have high expansion coefficients of 50 to 130 x 10 ^-7 /°C and high strength, but they are vulnerable to thermal shock. The production method of the present invention targets low-expansion SiO ₂ - which is resistant to thermal shock and has a coefficient of thermal expansion of 30×10 ^-7 /°C or less.
It is an Al ₂ O ₃ -Li ₂ O based crystallized glass, and the present invention intends to provide this crystallized glass with high mechanical strength. In carrying out the present invention, as the crystallized glass of this system, SiO ₂ 55
~75, Al ₂ O ₃ 15 ~ 30, Li ₂ O 2 ~ 6, MgO 0 ~ 5,
_{P2O5 0} ~5, ZrO2 ₀ ~5, _TiO2 1~15, _Na2O0 ~
5, K ₂ O 0 to 5, and other trace amounts of AS ₂ O ₃ and Sb ₂ O ₃ as fining agents, with β- as the main crystal phase.
Those that generate spodium (Li ₂ O.Al _{2 O} 3.4SiO ₂ ) are preferred and suitable. In the production of such crystallized glass, the present invention covers the surface of the crystalline glass before heat treatment with a coating material containing γ-alumina powder and a surfactant, and during the next heat treatment period, the crystalline glass The surface of the γ-alumina should be in contact with the γ-alumina. By the way, γ-alumina is an oxidation product obtained by heating and dehydrating bauxite, hydrated aluminum oxide, etc. at about 500 to 700°C, and has a spinel-type structure with lattice defects. In addition to γ-alumina, the present inventor has discovered various reagents such as silica, zirconia, mullite,
Water-resistant materials such as cordierite were applied to the surface of crystalline glass and subjected to crystallization heat treatment to investigate the effect of increasing strength, but almost no effect was observed. γ-
Although alumina had the effect of slightly increasing strength, it is inferior to γ-alumina and is not preferred for practical use.

The present inventor observed the surface layer of crystallized glass coated with γ-alumina powder and heat-treated, and found that
Compared to the surface layer of crystallized glass without coating with γ-alumina, crystallization was promoted and it was observed that mullite (3Al ₂ O ₃ .2SiO ₂ ) and other crystal phases were precipitated. The reason why crystallization is promoted in the surface layer is not fully clear, but it is thought to be due to the special chemical properties of this component, ie, the high activity due to the presence of structural defects. According to the method of the present invention, the crystallization of the surface layer is promoted, the glassiness is reduced or disappears, and the surface gloss of the obtained crystallized glass becomes poor. However, in the case of a top plate for a cooker to which the present invention is particularly applicable, there is no problem because the method of the present invention is carried out on only one side, and that one side is used as the back side of the top plate. The coating material used in the method of the present invention contains γ-alumina powder and a surfactant. If the particle size of the γ-alumina powder is very fine, such as 5 μ or less, it tends to adhere to the surface of the crystallized glass after heat treatment and become matte, which is undesirable. Since there is no close contact, sufficient strength may not be obtained, and therefore 10~
A particle size of about 70μ is preferable. The type of surfactant is not particularly limited, but anionic higher alcohol surfactants such as alkyl sulfate ester soda salt, sulfated castor oil ester soda salt, and polyoxyethylene octyl phenyl ether sulfate ester soda salt are preferred. , an aqueous solution with a concentration of about 15 to 70% of that is mixed with γ-alumina powder.
It is appropriate to mix at a ratio of 30% by weight. The inclusion of this surfactant improves the dispersion of the γ-alumina powder and enables homogeneous adhesion to the glass surface.
Therefore, it is possible to obtain a product with stable and high strength compared to the case of using only γ-alumina powder.

A coating material containing such γ-alumina and a surfactant is coated on the surface of crystalline glass before heat treatment. In the case of this coating, there is a method of directly sprinkling the coating material in powder form, but it is also possible to prepare a paste using water or polyvinyl alcohol and apply it by spraying, screen printing, etc.
It is better to coat by dipping method, spatula coating method, etc.
It is preferable because it adheres well to the glass surface. Furthermore, it is effective to add a binder such as carboxyl methyl cellulose to impart appropriate tackiness to the paste and facilitate coating operations.

The crystalline glass coated with the coating material in this manner is placed in a heat treatment furnace and subjected to crystallization treatment at a predetermined temperature schedule. Generally, this heat treatment for crystallization involves heating to a temperature that generates crystal nuclei in the glass, holding it for a certain period of time, and then increasing the temperature further and holding it at a temperature that sufficiently crystallizes the amorphous glass. . After crystallization is completed, the crystallized glass is taken out from the heat treatment furnace, and the γ-alumina powder adhering to the surface is removed with a brush or the like to obtain a product with a clean surface.

Next, examples of the present invention will be described.

Example 1 In weight %, SiO ₂ 66.4, Al ₂ O ₃ 22.0, Li ₂ O 4.2,
MgO0.5, P ₂ O ₅ 1.4, ZrO ₂ 2.3, TiO ₂ 1.9,
Samples of crystalline glass rods (outer diameter 5 mm, length 60 mm) and plates (300 x 400 x 4 mm) were made with the compositions of Na ₂ O 0.5, K ₂ O 0.3, and As ₂ O ₃ 0.5. . The standard heat treatment schedule for this crystalline glass is to heat it at 750°C for 2 hours to generate crystal nuclei.
Next, it is heated to 1140°C at a heating rate of 60°C/hour and held at that temperature for 1 hour to complete crystallization. The obtained crystallized glass has a thermal expansion coefficient of 11×10 ⁻⁷ /° C. and produces β-spodium as a crystalline phase.

Weight ratio of γ-alumina (average particle size 40μ) 50:12
Aqueous solution containing % polyvinyl alcohol 45:40%
A paste consisting of an alkyl sulfate ester sodium salt having a concentration of 5 was prepared and applied to the surface of the crystalline glass bar to form a coating layer with a thickness of 1 mm. This was heat-treated according to the above schedule to obtain crystallized glass. In order to measure the bending strength, this bar of crystallized glass was supported by two support blades placed in parallel at a 50 mm interval, and a load was applied from above to the center of the bar.
It showed 3300Kg/ ^cm2 . On the other hand, a bar sample of crystalline glass having the above composition without coating with γ-alumina was heat-treated for crystallization under the same conditions as above, and its bending strength was measured to be 1100 Kg/cm ² .

The same paste containing γ-alumina as before was coated on one side of a crystalline glass plate having the above composition to a thickness of about 1 mm using the stainless steel screen method.
This was crystallized using the temperature schedule described above. As a result of performing a drop impact test on the obtained crystallized glass plate with a 535g steel plate, the average height at which the plate broke was
It was 120cm. On the other hand, crystallized glass plates without γ-alumina cracked at an average height of 50 cm.

Example 2 In weight%, SiO ₂ 67.7, Al ₂ O 199, Li ₂ O 3.3,
MgO1.7, ZnO1.5, _TiO2 5.0, _Na2O0.4 , _K2O0.1 ,
Bars and samples of crystalline glass having a composition of AS ₂ O ₃ 0.4 (dimensions identical to those of the previous example) were made. For this crystalline glass,
After heating at 740℃ for 2 hours, heating at a rate of 60℃/hour,
A heat treatment was performed at 1140°C for 1 hour to obtain a crystallized glass having an expansion coefficient of 10×10 ^-7 /°C and a main crystal phase of β-spodium.

Weight ratio of γ-alumina (average particle size 50μ) 43:3
% carboxymethyl cellulose aqueous solution 53:40%
A paste prepared at a concentration of 4 parts alkyl sulfate sodium salt was coated on the surface of the crystalline glass bar and plate material to a thickness of about 1 mm. This was heat-treated according to the above schedule to obtain crystallized glass. The bending strength of the obtained solid bar of crystallized glass was measured under the same conditions as in the previous example, and it was found to be 3500 Kg/cm ² . On the other hand, crystallized glass without γ-alumina paste has a weight of 1300Kg/cm ²
It was hot.

Furthermore, when the obtained crystallized glass plate was subjected to a steel ball drop impact test of 535 g, the average height at which the plate broke was 140 cm. On the other hand, crystallized glass plates without γ-alumina cracked at an average height of 50 cm.

As explained above, according to the present invention, the surface of crystalline glass is coated with a coating material containing γ-alumina powder and a surfactant, and then this is heat-treated to convert it into low-expansion crystalline glass. It can impart properties of strength. The crystallized glass produced by the method of the present invention is expected to be used not only as a material for top plates but also in a wide variety of other applications.

Claims (1)

[Claims] 1. A method for producing crystallized glass having a coefficient of thermal expansion of 30×10 ^-7 /°C or less by heat-treating a SiO ₂ -Al ₂ O ₃ -Li ₂ O-based crystalline glass molded product , the surface of the crystalline glass molded product is coated with a coating material containing γ-alumina powder and a surfactant, and heat treated;
A method for producing a low-expansion, high-strength crystallized glass characterized by promoting crystallization of a surface layer. 2. The method for producing a low-expansion, high-strength crystallized glass according to claim 1, wherein the surfactant is an anionic higher alcohol-based activator. 3. A method for producing low-expansion, high-strength crystallized glass according to claim 1, wherein one side of crystallized glass is coated with a coating material and heat-treated. 4 SiO ₂ -Al ₂ O ₃ -Li ₂ O-based crystalline glass contains SiO ₂ 55 to 75, Al ₂ O ₃ 15 to 30, Li _{2 O} 2 to 6, by weight%.
MgO0~ ₅ , _P2O50 ~5, ZrO20 _~ 5, TiO21 _~
15, Na ₂ O 0 to 5, and K ₂ O 0 to 5. 5. The method for producing a low-expansion, high-strength crystallized glass according to claim 1 or 4, wherein the main crystalline phase of the crystallized glass is β-spodumene.