JPS6360128A - Method for chemically tempering glass - Google Patents

Abstract

PURPOSE:To reduce the generation of warpage in the chemical tempering of float glass by dipping the float glass in the molten salt contg. Na<+> or Li<+> and a specified sodium salt or bringing into contact with the salt for the pretreatment, and then chemically treating the glass. CONSTITUTION:From 0.001-5wt% 1 or >=2 kinds selected from sodium nitrite, sodium sulfite, and sodium phosphite are incorporated in the molten salt contg. an Na ion or an Li ion. Glass, especially float glass, is dipped in the molten salt or brought into contact with the salt for the pretreatment, and then chemically tempered by a low-temp. ion-exchange process, etc. The sodium salts are used as the compds. to be incorporated into the molten salt, because the introduction of an Na ion into the glass surface is further enhanced when the Na ions on the bottom and top surfaces of the glass are balanced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to the use of glass, especially glass manufactured by the float method, particularly soda-lime float glass, as a substrate for electronic materials, particularly a glass substrate for optical disks. Concerning chemical strengthening methods applied as such.

The present invention is applicable not only to scales used in display and disk substrates, but also to thin, large-area architectural and vehicle window glasses, various molded products using float glass, cooking glass products, and various electronic and electrical equipment. board, etc.
Widely used.

(Prior art) Float glass has superior surface smoothness, flatness, thickness uniformity, etc. compared to so-called ordinary plate glass, so it is used not only in fields such as architecture and vehicles, but also in the field of electronic materials, such as displays such as liquid crystals and plasma. It is becoming widely used.

Furthermore, as a recent trend, thin sheet glass of 4 ml or less is being used, and the thinner the thickness, the higher the strength is desired.

It is well known that a chemical tempering method using alkali ion replacement is applied to effectively strengthen thin glass. However, if a chemical tempering method is applied to float glass as is, the glass will warp (for example, if the glass is 1 fi thick). 0.4 to 1.3
m/300M-diameter), which impairs the flatness required for optical disk substrates (for example,
．． 2"11/300 mm diameter or less).The cause of the warping is presumed to be due to the influence of molten metal, typically Sn, penetrating into the contact glass surface during glass float molding. , no MXJI method has been found to deal with this warping. For example, it has been proposed to grind and polish the Sn-infiltrated surface of the glass and then perform an alkali ion replacement treatment. The Sn diffusion layer is 10 to 20 μm thick, and this layer requires grinding and polishing at most. This method not only requires complicated steps, but also causes problems with the grinding and polishing itself, which can cause cracks and defects in the glass. However, it is also expensive in terms of cost.

Therefore, in the above-mentioned method, float glass was not used for optical disk substrates and the like.

In addition, there is, for example, Japanese Patent Publication No. Sho 5i-i77ss as a pre-treatment during chemical strengthening, and in the examples of this publication, NaN0. and K
A method is described in which conventional chemical strengthening is carried out by performing a preliminary treatment in a mixed salt bath consisting of NO, and a method for increasing the strength of glass articles is disclosed.

[Problem that the invention seeks to solve]

As mentioned above, when chemically strengthening glass, especially float glass, the molten metal contact surface is ground and polished.
Unless the Sn diffusion layer is removed,
The pre-treatment described in Japanese Patent Application No. 17765 cannot prevent the float glass from warping. etc., but
Furthermore, it is possible to use the above treatment conditions stably over a long period of time with a shorter treatment time and lower treatment temperature, and it is possible to further prevent the clouding phenomenon that tends to occur on the glass surface, making it particularly suitable for mass-produced products. I was in a situation where a method was desired.

[Means for solving problems]

The present invention has been made in view of such drawbacks of the conventional art, and when chemically strengthening glass, especially float glass, the float glass is brought into contact with the molten metal contact surface (bottom surface) in its original state and the molten metal is strengthened. When performing pretreatment to balance Na ions with the non-contact surface (top surface), a specific amount of a specific compound is added to the pretreatment molten salt, used as a mixed molten salt, and then chemically strengthened. The purpose of the present invention is to provide an improved chemical strengthening method that can solve the problem of warpage caused by treatment.

That is, the present invention provides glass, particularly float glass,
After immersion or contact pretreatment in a molten salt containing Na ions or Li ions, at least 5% by weight of o, ooi, or 144 of sodium nitrate, sodium sulfite and sodium phosphite
Alternatively, it provides a method for chemically strengthening glass characterized by containing two or more kinds.

Here, examples of the molten salt containing Na ions or Li ions include sodium nitrate, sodium sulfate, sodium phosphate, mixed salts thereof, or mixed salts of lithium nitrate, lithium sulfate, and lithium phosphate.

Furthermore, the compound to be contained at least in the molten salt is one or more of thorium suboxide, sodium sulfite, and sodium phosphite, for example, on the bottom surface and top surface of the float glass. Na with
This is because it has been found that this contributes to further increasing the introduction of R1Na ions, which balance the ions, into the glass surface layer. However, although the reason for this has not been fully elucidated, it is presumed that its presence lowers the surface roughness of the glass and makes the introduction of Na ions into the surface layer of the glass more effective.

Furthermore, i); the amount of lfi or two or more of sodium nitrite, sodium sulfite, and sodium phosphite contained at least in the molten salt in 1. is 0.001 to 5% by weight percentage; is o, ooi%
If it is less than 0.001%, it will not be possible to achieve a shorter processing time or lower processing temperature, making it impossible to achieve the desired more efficient production, and if it exceeds 5%, clouding will occur on the glass surface. By keeping it at ~5%, it becomes stable over a long period of time and can be adapted to mass production. Preferably, the content is 0.101 to 3%, which eliminates variations in the introduction of Na ions into the glass-friendly surface layer, thereby eliminating variations in the amount of sheet warpage and making it stable.

In addition, when carrying out the above-mentioned immersion or contact pretreatment, it becomes even more effective if the glass is preheated (7), and then slow cooling such as step cooling is performed after the immersion or contact pretreatment, followed by washing.

Furthermore, for the chemical strengthening treatment, commonly used known treatment methods can be used.

[Effect]

As mentioned above, the chemical strengthening method of the glass of the present invention, especially float glass, requires a unique pre-processing process, including the problem that as the glass becomes thinner from about 4n, sufficient strengthening cannot be achieved using the air-cooling strengthening method. By doing this, the warping of float glass can be reduced to a value close to that of raw glass (without surface treatment), and therefore properties such as surface roughness, plane parallelism, and smoothness can be improved without the need for grinding or polishing. In addition to being able to chemically strengthen by taking advantage of the process, it is also possible to improve efficiency with shorter processing times and lower processing temperatures, and by specifying a mixed molten salt for pre-treatment, it is possible to control board warpage more stably over the long term. This made it possible to reduce the variation, making it suitable for mass-produced products.Furthermore, float glass, which was thinner, had a relatively large area, and was strong, was used for many purposes. In addition, as the need for countermeasures against warping increases, we have found a solution.
It is capable of improving the precision of the shape of molded products, etc., and satisfies the specifications for not only displays, but also disks such as warpage of 0.2 m/300 mm diameter or less, and has the characteristics of greatly improving yield etc. It is.

〔Example〕

The present invention will be explained in detail below.

u''11~6 As the glass substrate, a float glass with a thickness of about 1.0 fl and a diameter of about 300 mm was used, sodium nitrate was used as the molten salt containing Na ions, and sodium nitrite was used as the compound to be mixed with the molten salt. Each sample was subjected to a pre-immersion treatment under the conditions of temperature and time shown in Table 1, and was also subjected to ordinary chemical strengthening treatment using potassium nitrate by a low-temperature ion exchange method to prepare a sample.

Regarding these samples, the amount of warpage was determined by DEKTAKII.
Table 1 shows the amount of warpage of the chemically strengthened dust (surface compressive stress value) measured using a surface stress measuring needle (a shape measuring instrument manufactured by 5LOAN Inc. (USA)) and a surface stress measuring needle.

Examples 7 to 11 Using the same float glass as Examples 1 to 6 and using sodium nitrate and sodium sulfite as the mixed molten salt, Table 1
Samples were prepared by pre-immersion treatment under the temperature and time conditions shown in Figure 2, and chemically strengthened by low-temperature ion exchange using potassium nitrate.

The amount of warpage and the surface compressive stress value were measured using the same equipment as in Examples 1-6. Table 1 shows the amount of warpage.

Example 121 Sodium nitrate and sodium phosphite were used as the pressure mixed molten salt, the rest was the same as in the previous example, and pre-immersion treatment was carried out under the conditions of temperature and time shown in Table 1, as well as the same chemical strengthening treatment. was conducted and used as a sample.

Measurements were made in the same manner as in the above examples, and the amount of warpage is shown in Table 1.

Comparative Examples 1 to 2 The same float glass as in the example was pretreated with only sodium nitrate as a molten salt containing Na ions, and the same chemical strengthening treatment as in the example was performed to prepare a sample. The processing conditions are as shown in Table 1, and the amount of warpage is shown in Table 1.

Comparative Examples 3 to 7 Under the same conditions as Examples 1 to 6, pretreatment was performed only for the content of sodium nitrite as shown in Table 1 outside the scope of the present invention, and the amount of warpage was measured. It is shown in Table 1.

Comparative Example 8 A sample was prepared by using the same float glass as in Example, which was chemically strengthened without being treated with a molten salt containing Na ions, but otherwise under the same conditions.

The amount of warpage and the surface compressive stress value were measured using the same equipment as in the examples.

Table 1 shows the amount of warpage.

The amount of warpage was measured using the same equipment as in the example using the same float glass as in Example 1 (current η1) as a sample (green plate).

The results are shown in Table 1.

Note that the amount of warpage in Table 1 is the measured value of five samples, and a negative value indicates that the bottom surface side is warped in a convex manner.

Table 1 [Effects of the invention] As is clear from Table 1, which compares the above-mentioned embodiments of the present invention and comparative examples including conventional methods, it has become more efficient and suitable for mass production, and the quality has also improved. More stable, especially l!
It is made of an L-plate float glass substrate, etc., and has a fire-shaped surface with high strength and a small amount of warping.

Furthermore, since the breaking strength of glasses other than float glass can be increased and transparency can be maintained, they can be used in a wider range of fields than before.

Claims (1)

[Claims] Glass, especially float glass, is treated with Na ions or Li.
After immersion or contact pretreatment in molten salt that also contains ions, chemical strengthening using low-temperature ion exchange methods, etc.
At least 0.001 to 5% by weight in the molten salt
%, sodium nitrite, sodium sulfite, and sodium phosphite.