JPS5935032A - Preparation of crystallized glass having low expansibility and high strength - Google Patents

Abstract

PURPOSE:To obtain the titled glass, having improved flexural strength, by heat- treating a molded SiO2-Al2O3-Li2O type crystalline glass article while bringing the surface thereof into contact with a compound containing Na and (or) S to promote the crystallization of the surface layer. CONSTITUTION:A molded SiO2-Al2O3-Li2O type crystalline glass article is prepared by incorporating SiO2, Al2O3 and Li2O as main raw materials with if necessary a raw material, e.g. MgO, ZnO, P2O5, ZrO2, TiO2, Na2O or K2O. The resultant crystalline glass is then coated with an aqueous solution containing Na and (or) S, e.g. Na2SO4 or Na2S2O7, dried and heat-treated. Thus, the resultant glass has <=30X10<-7>/ deg.C coefficient of thermal expansion, deposited crystalline phase of mullite (3Al2O3.2SiO2) and others and improved flexural strength with the promoted crystallization of the surface part thereof.

Description

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

SiO2-Al2O3-Li2O-based crystallized glass generally has a coefficient of thermal expansion of 30 x 10-7/°C (30 to 380
It is widely used as a component material for cooking utensils because of its low thermal expansion resistance (lower than ℃) and its resistance to thermal expansion. In recent years, crystallized glass with excellent thermal shock resistance has been used as a material for the top plate of electric or gas cooking appliances that are provided with a top plate without exposing the heating source directly to the surface. As a top plate, in addition to excellent thermal shock resistance, it is required to have high mechanical strength and impact resistance because it is sometimes subjected to large impacts. For example, U.S. Underwriters Laboratories (Underwriters L.
According to Standard 858, the center of the top plate is required to not break even if a 535 g steel ball is dropped from a height of 54.1 cm. To meet this standard, the bending strength of crystallized glass must be at least 2
It is considered necessary to have a value of 500 kg/cm2 or more. However, usually SiO2-Al2O2-Li2O
The bending strength of low expansion crystallized glass is at most 1000 ~
It remains at around 1400 kg/cm2. Several methods have been provided to increase the bending strength of crystallized glass. However, the example is Tokushu 45-4870
F, which has the effect of improving strength in the glass composition, such as
The method of incorporating F evaporates during glass melting, which poses a problem in terms of pollution control.Also, as in Japanese Patent Publication No. 47-49299, crystallized glass is subjected to ion exchange treatment to generate compressive stress in the surface layer. The method of strengthening by heating requires a special step of bringing the object to be treated into contact with the molten salt after the crystallization heat treatment, which poses a practical problem.

Therefore, as a result of various studies to improve the mechanical strength of low-expansion crystallized glass, the inventors of the present invention discovered that SiO2-
Crystalline glass having an Al2O3-Li2O system structure,
That is, in the process of heat-treating and crystallizing a crystallizable glass molded product, Na is added to the surface of the crystallizable glass molded product.
It has been discovered that a low expansion and high strength crystallized glass can be obtained by heat treatment while contacting a compound containing S and/or S to promote crystallization of the surface layer, and the present invention is proposed herein.

As is well known, crystallized glass is manufactured by melting glass raw materials, forming them, and then heat-treating and crystallizing the glass molded product.Crystallized glass has a thermal expansion coefficient of 50 to 130 x 10. Some have high expansion and strength of -7/°C, but they are vulnerable to thermal shock. The production method of the present invention targets low-expansion SiO2-Al2 that is resistant to thermal shock and has a thermal expansion coefficient of 30X10-7/℃ or less.
It is an O3-Li2O-based crystallized glass, and 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 55 to 75% by weight of SiO2, Al2O3
15-30, Li2O 2-6, MgO0-5, Zn
O 0-5, P2O5 0-5, ZrO2 0-5, T
iO2 1-15, Na2O 0-5, K2O 0-5
, and other small amounts of fining agents such as AS2O3 and Sb2O3, and β-spodumene (L) as the main crystal phase.
It is preferable and suitable to use one that generates i2O.Al2O3.4SiO2).

In the present invention, in producing such crystallized glass, a compound containing Na and/or S (hereinafter referred to as a strengthening agent) is coated on the surface of the crystallized glass before heat treatment, and During the process, the surface of the crystalline glass and the strengthening agent are kept in contact.

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. mullite (3Al2O3.
2SiO2) It was observed that 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 undergo ion exchange with other ions in the crystallized glass, such as Na+, Zn++, and Mg++. The distribution of these ions in the surface layer of chemically heated glass was analyzed using
ron probe micro analyzer)
As a result of the investigation, 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 ion-exchange strengthening mechanism, which generates compressive stress in the surface layer by exchanging alkali ions in the crystallized glass with larger alkali ions.

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. However, in the case of a top plate for a cooker to which the present invention is particularly applied, 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, so there is no problem.

In the present invention, the following methods can be used to coat the surface of crystalline glass with the strengthening treatment agent. (1) Strengthening treatment agent,
A solution dissolved in water, alcohol, etc. is coated on crystalline glass by a spray method. (2) A strengthening treatment agent and a diluent are mixed, water is added to form a slurry, and the slurry is coated on crystalline glass by dipping, screen printing, etc. As the diluent, powders of refractory substances such as alumina, mullite, and zirconia are preferred. It is effective to add a binder such as carboxyl or methylcellulose to give the slurry appropriate tackiness to facilitate coating operations. (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. It was also found that the entire board was strengthened uniformly. The reason for this is that the gas (possibly containing Na and/or S) generated by the decomposition or volatilization of the strengthening treatment agent is trapped between the two plates.
It is believed that the contact of this gas with the crystalline glass provides a strengthening effect similar to that obtained when the strengthening treatment agent contacts the crystalline glass in a solid state.

The crystalline glass coated with the strengthening treatment agent in this manner 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 then the strengthening treatment agent 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.

Examples 1 to 9 The simplest method of implementing the present invention is to coat crystalline glass before crystallization with an aqueous solution of a compound containing Na and/or S, and heat-treat the coated glass after drying. SiO2 6 in weight%
6.4, Al2O3 22.0, Li2O 4.2, M
gO 0.5, P2O5 1.4, ZrO2 2.3,
TiO2 1.9, Na2O 0.5, K2O 0.3
, AS2O3 A solid glass rod (outer diameter 5 mm, length 60 mm) having a structure of 0.5 was made, and the strengthening treatment solution shown in Examples 1 to 9 in Table 1 above was applied to it, followed by heat treatment. did. Heat treatment is heated at 750℃ for 2 hours and then heated to 60℃
The temperature was raised to 1.140°C at a rate of 1.140°C and maintained at 1.140°C for 1 hour. The thermal expansion coefficient of the crystallized glass obtained by this heat treatment is 11X10-7/
℃, β-spodumene was formed as a crystalline phase. 2% microcrystalline wax was added to the strengthening treatment agent solution in order to increase the adhesion strength after drying.

In the case of no treatment (comparative example 1), the bending strength of crystallized glass is 1
．． 300 Kg/cm2, whereas the examples of the method of the present invention showed an average value of 2.500 Kg/cm2 or more.

Examples 10 to 13 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 used a strengthening treatment agent mixed with a diluent.

Aqueous solution of strengthening treatment agent and diluent (average particle size 40μ) were added to the second
They were mixed in the proportions shown in the table and made into a paste, which was applied to crystalline glass and heat-treated. The crystalline glass used is
In weight%, SiO2 68.2, Al2O3 18.8
, Li2O 2.7, MgO 2.6, ZnO 1.2
, TiO2 4.9, Na2O0.5, K2O 0.1
, AS2O3 1.0 (outer diameter 5
mm, length 60 mm). Heat treatment was performed at 740℃ for 2
After heating for an hour, the mixture was heated to 1.050°C at a rate of 60°C/hour and maintained at this temperature for 5 hours. The sample thus obtained had an average bending strength of 2.600 kg/cm2 or more, and the surface had almost no loss of gloss. The bending strength of the sample (Comparative Example 2) that was heat-treated after applying only the diluent (α-alumina) was 1.400 kg.
The value was as low as /cm2.

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 another crystallized glass plate is strengthened. The effect of increasing the strength can be obtained by heat-treating it while stacking it on top of it. A crystalline glass plate (size 300x400x
4 mm) was prepared, and the powder for sprinkling was the N of Example 10.
A paste made by mixing a 10% a2SO4 aqueous solution and α-alumina is dried and made into a powder. In this case N
Although it is not essential to mix a2SO4 with the diluent in the form of an aqueous solution, it is more effective to mix the a2SO4 with the diluent in the form of an aqueous solution in order to obtain 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 heated to 60℃/
The temperature was raised to 1.050° C. over an hour and maintained at this temperature for 2 hours.

In order to examine the impact strength of the plate, a 535 g 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 broke at an average length of 140 cm. On the other hand, the plates that were not subjected to the sprinkling treatment were broken at an average length of 50 cm.

patent applicant Nippon Electric Glass Co., Ltd. Representative Nagasaki ■

Claims (1)

[Claims] In a method for producing crystallized glass having a coefficient of thermal expansion of 30×10-7/°C or less by heat-treating a SiO1-Al2O3-Li2O-based crystalline glass molded product, Na and/or Na and/or A method for producing low-expansion, high-strength crystallized glass, characterized in that heat treatment is performed while contacting with a compound containing S to promote crystallization of a surface layer.