JPS6140610B2 - - 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℃), and is highly resistant to thermal shock, so it is used in cooking utensils, etc. It is widely used as a constituent material. 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 impact resistance, since it is sometimes subjected to large 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 at most 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, into the glass composition, as in 4870, poses a problem in terms of pollution control, as F generates heat during glass melting, and it also prevents crystallization, as in Japanese Patent Publication No. 47-492999. The method of subjecting glass to ion exchange treatment to create compressive stress on the surface layer to strengthen it requires a special process in which the object to be treated comes into contact with molten salt after crystallization heat treatment, which poses practical problems. . Therefore, as a result of various studies 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, that is, In the process of heat-treating and crystallizing a crystallizable glass molded product, the surface of the crystallizable glass molded product is heat-treated while contacting a compound containing Na and/or S to promote crystallization of the surface layer. It has been found that a low-expansion and high-strength crystallized glass can be obtained by this method, and the present invention is proposed here. As is well known, crystallized glass is produced by melting a glass raw material, shaping it, and then heat-treating the glass molded product to crystallize it. 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 manufacturing method of the present invention targets low-expansion SiO ₂ -Al ₂ O ₃ -Li ₂ O-based crystallized glass that is resistant to thermal shock and has a thermal expansion coefficient of 30 × 10 ^-7 /°C or less. The present invention intends to provide this crystallized glass with high mechanical strength. In carrying out the present invention, the crystallized glass of this system contains SiO ₂ 55-75, Al ₂ O ₃ 15-30, Li ₂ O2 in weight%.
~6, MgO0~5, ZnO0~5, P ₂ O ₅ 0~5,
ZrO2 ₀ ~5, TiO2 ₁ ~15, _Na2O0 ~5, _K2O0 ~
5. It is preferable that the composition contains trace amounts of clarifiers such as AS ₂ O ₃ and Sb ₂ O ₃ and produces β-spodium (Li ₂ O・Al ₂ O ₃・4SiO ₂ ) as the main crystal phase. It is. In the production of such crystallized glass, the present invention coats the surface of the crystallized glass with a compound containing Na and/or S (hereinafter referred to as a strengthening agent) before heat treatment, and then performs the next heat treatment step. During the heating process, the surface of the crystalline glass and the strengthening treatment agent should be in contact with each other. The present inventor observed the surface layer of crystallized glass that had been heat-treated by contacting with a strengthening treatment agent, and found that the crystallization of the surface portion was less than that of crystallized glass that had been heat-treated without such treatment. 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. In the present invention, the strengthening treatment agent brought into contact with the crystallized glass contains alkali ions that may ion-exchange with other ions in the crystallized glass, such as Na ⁺ , Zn ⁺⁺ , Mg ⁺⁺ , etc. The distribution of these ions in the surface layer of the crystallized glass of the present invention was measured using EPMA (Electron probe micro
It was confirmed that these ions were not diffused into the crystallized glass at all. Therefore, the strengthening mechanism of the present invention is different from the strengthening mechanism by ion exchange, which generates compressive stress in the surface layer by exchanging alkali ions in crystallized glass with larger alkali ions. different. According to the method of the present invention, the crystallization of the surface layer is promoted and the glassiness is reduced, so that the surface gloss of the obtained crystallized glass tends to deteriorate. but,
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. In the present invention, the following methods can be used to coat the surface of crystalline glass with the strengthening treatment agent. (1) A solution of a strengthening treatment agent dissolved in water, alcohol, etc. is coated on crystalline glass by a spray method. (2) Mix the strengthening treatment agent and diluent, add water etc. to make a slurry, dip into crystalline glass,
Cover by screen printing, etc. As the diluent, powders of refractory substances such as alumina, mullite, and zirconia are preferred. In order to give the slurry appropriate viscosity and make coating work easier,
It is effective to add a binder such as carboxyl or methyl cellulose. (3) Sprinkle a mixture of a strengthening treatment agent and a diluent on crystalline glass in the form of a dry powder. When heat treatment is performed with the strengthening agent and diluent present between two stacked crystalline glass plates, the amount of sprinkling is extremely small and the amount of sprinkling is uneven in some areas. It was found that the entire board was strengthened evenly. The reason for this is that the gas (possibly containing Na and/or S) generated by the decomposition or volatilization of the strengthening agent is trapped between the two plates, and this gas comes into contact with the crystalline glass. In particular, it is thought that a strengthening effect similar to that obtained when the strengthening treatment agent comes into contact with crystalline glass in a solid state can be obtained. In this manner, the crystalline glass coated with the strengthening treatment agent is placed in a heat treatment furnace and subjected to crystallization treatment at a predetermined temperature schedule. Generally, this crystallization heat treatment involves heating to a temperature that generates crystal nuclei in the glass, holding it for a certain period of time, and then raising the temperature further and holding it at a temperature that sufficiently crystallizes the amorphous glass. taken. After crystallization is completed, the crystallized glass is taken out from the heat treatment furnace, and the strengthening treatment agent adhering to the surface is then removed with a brush or the like to obtain a product with a clean surface. Next, examples of the present invention will be described. Examples 1 to 9

【table】

[Table] The simplest way to implement the invention is to
Alternatively, an aqueous solution of a compound containing S may be coated on crystalline glass before crystallization, and heat treatment may be performed after drying.
SiO ₂ 66.4, Al ₂ O ₃ 22.0, Li ₂ O 4.2, in weight%
MgO0.5, P ₂ O ₅ 1.4, ZrO ₂ 2.3, TiO ₂ 1.9,
A bar of crystalline glass (outer diameter 5 mm, length 60 mm) having a composition of Na ₂ O 0.5, K ₂ O 0.3, and AS ₂ O ₃ 0.5 was made, and Examples 1 to 1 in Table 1 above were prepared. After applying the strengthening treatment agent solution shown in No. 9, heat treatment was performed. Heat treatment is
After heating at 750℃ for 2 hours, heat to 1140℃ at a rate of 60℃/hour.
This was carried out by raising the temperature to 1140°C and holding it for 1 hour. The thermal expansion coefficient of the crystallized glass obtained by this heat treatment is 11×10 ^-7 /℃, and the crystalline phase is β-
Generated by Spodiumen. In order to increase the adhesion strength after drying, 2% microcrystalline wax was added to the strengthening treatment agent solution. In the case of heat treatment (Comparative Example 1), the bending strength of crystallized glass was 1300 Kg/cm ² , whereas the examples of the method of the present invention showed an average value of 2500 Kg/cm ² or more. Examples 10-13

[Table] Although an increase in strength was achieved in Examples 1 to 9, the surface of the crystallized glass reacted with the coating substance and tended to become matte with a loss of surface gloss. In order to improve this point, Examples 10 to 13 in Table 2 use a diluent mixed with the strengthening treatment agent. Aqueous solution and diluent of strengthening treatment agent (average particle size 40μ)
were mixed in the proportions shown in Table 2 and made into a paste, which was applied to crystalline glass and heat-treated. The crystalline glass used had SiO ₂ 68.2% by weight,
Al ₂ O ₃ 18.8, Li ₂ O2.7, MgC2.6, ZnO1.2,
It is a solid rod (outer diameter 5 mm, length 60 mm) having a composition of TiO ₂ 4.9, Na ₂ O 0.5, K ₂ O 0.1, and AS ₂ O ₃ 1.0.
The heat treatment was carried out by heating at 740°C for 2 hours, then heating at a rate of 60°C/hour to 1050°C, and maintaining this temperature for 5 hours. The number of samples thus obtained was 2600.
It had an average bending strength of more than Kg/cm ² and had almost no loss of surface gloss. In addition, diluent (α-
The bending strength of the sample (Comparative Example 2) coated only with alumina and heat treated was a low value of 1400 Kg/cm ² . Example 14 When a plate-shaped crystallized glass is strengthened according to the present invention, a mixture of a strengthening treatment agent and a diluent is sprinkled in powder form on the surface of a crystallized glass plate, and then another crystallized glass plate is strengthened. The effect of increasing the strength can be obtained by heat-treating the layer while stacking it on top of it. A crystalline glass plate (size: 300 x 400 x 4 mm) having the same composition as that used in Examples 1 to 9 was prepared. The powder for sprinkling was prepared by drying a paste prepared by mixing a 10% Na ₂ SO ₄ aqueous solution and α-alumina in Example 10 into a powder state. In this case, it is not essential to mix Na ₂ SO ₄ with the diluent in the form of an aqueous solution, but mixing it with the diluent in the form of an aqueous solution is more effective in obtaining a uniform mixed state. After sprinkling the above powder thinly on a plate of crystalline glass, another sheet of crystalline glass was placed on top of it, heated to 740℃ for 2 hours, and then raised to 1050℃ at a rate of 60℃/hour. It was held for 2 hours. In order to examine the impact strength of the plate, a 535g steel ball was dropped onto the center of the plate. In this case, the impact test was conducted so that the side on which the sprinkling was applied was the back side.
The boards that were sprinkled were broken at an average length of 140 cm. On the other hand, the boards that were not subjected to the sprinkling process cracked at an average length of 50 cm.

Claims (1)

[Claims] 1. In 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 crystalline glass molded product is 1. A method for producing low-expansion highly crystallized glass, characterized in that the surface of the product is heat-treated while being brought into contact with a compound containing Na and/or S to promote crystallization of the surface layer.