JPS58145642A - Strengthening of glass - Google Patents

Abstract

PURPOSE:To manufacture strengthened glass, by coating SiO2 to the surface of a glass plate containing Na and Li, and carrying out the ion exchange treatment of the glass, thereby eliminating the influence of the surface microcracks of the glass on the strength. CONSTITUTION:A soda-lime silicate glass 3 is immersed in a solution of SiO2 in e.g. ethyl acetate, taken out of the solution, and heated in an oven to expel the organic solution 4 and form an SiO2 film 1. The microcracks 2 on the surface of the glass 3 are completely covered with the film 1 by this procedure. The coated glass is immersed in molten KNO3 in an electric furnace to effect the ion exchange and introduce the compressive stress to the surface of the glass. Since the film 1 has a network structure, the alkali ions in the glass 3 are diffused in the film 1 during the above process. In the figure, the numbers 5 and 6 represent K<+> ion and Na<+> ion, respectively. The treated glass is taken out of the furnace slowly, cooled to room temperature, and washed with water to remove the KNO3.

Description

[Detailed description of the invention] This invention relates to a method for strengthening glass.

Conventionally, there are two types of strengthening of glass used for glass substrates for electronic components: chemical strengthening and physical strengthening. Glass originally has very fine cracks called Griffith's flats, which are unique to the structure of the glass. Even if the surface layer of the glass containing the second flaw is removed, new microcracks will occur on the glass surface due to processing damage.

Therefore, by introducing permanent compressive stress into the surface layer where these microcracks exist, it is possible to increase the strength of the glass.

Chemical strengthening and physical strengthening are methods for introducing compressive stress hair onto the surface of the crow.

Chemical strengthening involves low-temperature ion exchange, in which compressive stress is introduced to the surface of the glass by first exchanging the alkali ions in the glass with larger ions and easily available alkali ions below the glass's transition temperature. In addition, ion exchange is performed at a temperature above the transition temperature of the blade lath, thereby forming a layer with a small expansion coefficient on the glass surface layer, and when this layer is cooled to room temperature, due to the difference in expansion coefficient between the surface layer and the inside, There is a high-temperature ion exchange that produces compressive stress on the surface and tensile stress on the inside. Still another method involves coating a different type of glass at high temperature with a smaller coefficient of expansion than the underlying glass, and then compressing the covering glass when it cools.

Next, physical strengthening involves heating the sheet glass to near its softening point.
Next, air is blown onto the glass surface to rapidly cool it, making use of the thermal stress caused by the temperature difference between the inside and outside of the glass to create compressive stress on the surface. This is liquid-cooling strengthening in which compressive stress is created on the surface by bringing it into contact with a liquid.

With these conventional methods, even if permanent compressive stress was introduced to the surface, the presence of micro-cracks on the glass surface caused stress concentration on the cracks, which led to fracture and reduced strength. .

The glass strengthening method of the second invention was made in order to eliminate the above-mentioned conventional drawbacks, and was intended to eliminate the influence on the strength of the glass of the microcrank.

That is, using glass containing sodium and/or lithium, S
This method is characterized by applying iO2 and then performing ion exchange treatment on the applied glass.

The second invention will be explained below based on one embodiment.

First, in a container containing 5i02 dissolved in ethyl acetate, add soda, lime, and silicate glass (Si02:
7 011101% + N a 2 0
:15 mo1%, CaO: ]5 mo1%),
size 23.2x+OOx], 6 mm, was then taken out and heated in an oven at 450°C for 1 hour. The film thickness of 5i02 was 100OA. Then, the second glass was immersed in potassium nitrate in an electric furnace maintained at 43F) to 450C and subjected to ion exchange treatment for 4 hours. Then, it was slowly taken out of the oven over a period of 30 minutes, cooled to room temperature, and then potassium nitrate was washed off with water.

The amount of strain in this glass and the depth of the strained layer were measured using the waveguide method. Figure 1 shows 5i02/5i02 on the underlying glass J.
It is coated with 8102, and 8102/2 is fully penetrated into the micro cracks. In Figure 2, this was heated to 450°C to drive out the organic solvent and to cause mutual diffusion between the glass 3 and the coated 3-8i02/. The mark indicates an organic solvent that is evaporating.

The microcracks are completely encapsulated through the following process. Next, compressive stress was introduced into the glass surface by low-temperature ion exchange treatment (in KNO3 maintained at 450°C) (see Figure 3). 2-5
5i02 coated with a network structure of i02/
/Alkaline ions diffuse inside. 6 indicates a + ion, and O indicates a Na+ ion. From the experimental results, the amount of strain on the glass surface was up to 49% for the uncoated glass (comparative example) that was ion-exchanged without Si○2 coating.
, 56kg/mm2, minimum 38, 92kg/+um2
, the average is 44.80 kg/mm2, σn=3.30, and the maximum weight is 52.08 for the one coated with SiO2.
kg/mm2. The minimum is 33°32 kg/av+", the average is 44.48 kg/mm", and σn6°23. In addition, the depth of the strained layer is maximum 1 for uncoated glass.
4.7μm, minimum 14.5i1 rrl, average 14.6
μm, ono, 10, and those coated with Si4-〇2 had a maximum of 14.6 μm, a minimum of 14.2 μn1, an average of 14.4 μm, and σno, I2, which were almost the same. This indicates that sufficient ion exchange was achieved even if 5i02 was coated. This is shown in Table-1.

Table 1 * is dimensionless. In the above example, glass containing sodium was explained by low temperature ion exchange, but glass containing lithium was immersed in an alkali salt (e.g. sulfate, nitrate),
Lithium ions in the glass may be replaced with sodium or potassium ions, and the same effects as in the above embodiments can be obtained.

Although the coated 5i02 was heated to 450° C., this may be omitted since the glass is preheated during ion exchange.

Next, as shown in FIG. 4, the bending strength was measured using an autograph. In the figure, 7 indicates the glass, 8 indicates the span, 7 indicates the thickness of the glass, and 10 indicates the load. The bending strength S was determined using the following formula.

2d" ω (kg/man") As described above, since the glass strengthening method of the second invention encapsulates microcracks, the measurement results of the bending strength after 5i02 coating are Smax=17, 90kg/n+n
+”, Sm1n=7, 16kg/mm2, S
=11.87kg/mm2. an=3.67, and the bending strength increased by about 22% compared to untreated glass (no ion exchange treatment or St○2 coating). Also, after ion exchange treatment, Smax = 49.05kg/mm
2.8m1n=20.91kg/nun2, S:
=3 7. 0 3kg/mm”, (7n=9
．． 58, and the bending strength is approximately 3°8 compared to untreated glass.
The bending strength was increased by about 31.6% compared to the non-coated glass. This is shown in Table-2.

Table-2 *Dimensionless (Note) Reference example 1 only has Si○2 coating, Reference example 2
is untreated glass.

7-

[Brief explanation of drawings]

Figures 1 to 3 are side views showing the state of glass at each step in the glass strengthening method of the present invention, and Figure 1 is 5102.
When the coating is applied, FIG. 2 shows the state when heated at 450° C., and FIG. 3 shows the state during ion exchange treatment. FIG. 4 is a schematic side view showing a method for measuring bending strength. /5i02,. 2 Micro crack 3 Glass DA Organic solvent, 5 + ions O Na + ions 7 Glass
8 Span? Glass thickness 10 Load 8-

Claims (1)

[Claims] 1. A glass strengthening method using glass containing sodium and/or lithium, which is characterized by applying 5 in 2 on the surface of the glass, and then subjecting the applied glass to ion exchange treatment. . 2. The glass strengthening method according to claim 1, wherein the ion exchange treatment is a low-temperature ion exchange treatment.