JPH0768051B2 - Method of chemically strengthening float glass - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention applies glass manufactured by a float method, particularly soda lime-based float glass, as a substrate for electronic materials, particularly as a glass substrate for optical discs, and the like. Regarding the chemical strengthening method.

INDUSTRIAL APPLICABILITY The present invention can be applied not only to a display and a disk substrate, but also to a thin plate having a large area such as a window glass for construction and vehicles, and various molded products using a float glass plate, and a glass for cooking. It is widely used as a chemically strengthened float glass in the form of processed plates such as substrates for products and various electronic and electrical devices.

[Conventional technology]

Float glass has excellent surface smoothness, flatness, thickness uniformity, etc. compared to so-called ordinary flat glass, so it is widely used not only in the fields of construction, vehicles, etc., but also in the field of electronic materials, such as liquid crystal and plasma displays. is there.

Further, as a recent trend, thin glass with a thickness of 4 mm or less has been favored, and it is desired to improve the strength as the thickness decreases.

It is well known to apply the chemical strengthening method by alkali ion substitution to effectively strengthen thin glass, but when the chemical strengthening method is used for float glass as it is, warpage occurs in the glass (for example, 1 mm thick 0.4-1.3mm / 300mm
However, the flatness required for optical disk substrates and the like (for example, 0.2 mm / 300 mm diameter or less at a thickness of 1 mm) cannot be obtained. The cause of the warpage is presumed to be due to the influence of molten metal, usually Sn, infiltrating the contact glass surface during glass float molding, but no epoch-making countermeasure against this warpage has been found. For example, it has been practiced to grind and polish the Sn infiltrated surface of glass, and then to carry out alkali ion substitution treatment.
Since the Sn diffusion layer on the Sn contact glass surface is 10 to 20 μm, grinding and polishing of this layer are required at the maximum, and this method not only complicates the process but also causes cracks and defects in the glass. However, the polishing itself has a problem, and the cost is high.

Therefore, in the above-mentioned method, the float glass is not used for the optical disk substrate or the like.

Incidentally, there is, for example, Japanese Patent Publication No. 54-17765 as an attempt to perform the pre-treatment at the time of chemical strengthening, and in the examples of the publication, in a mixed salt bath consisting of NaNO ₃ and KNO ₃ kept at a constant temperature. Describes a method of performing a conventional chemical strengthening by performing a pre-treatment, and discloses a method of increasing the strength of a glass article.

[Problems to be solved by the invention]

As described above, when chemically strengthening the float glass, its molten metal contact surface is ground, polished, unless the Sn diffusion layer is removed, and also in the pretreatment described in JP-B-54-17765, It is impossible to prevent the warp of the float glass.

[Means for solving problems]

The present invention has been made in view of such drawbacks of the prior art, in chemically strengthening the float glass, the alkali concentration of the molten metal contact surface and the molten metal non-contact surface of the float glass as it is A new method that can solve the problem of warpage by reducing the difference and performing chemical strengthening after processing to make the amount of warpage after chemical strength within 0.2 mm / 300 mm diameter. It is provided.

That is, the present invention, the float glass in the holding temperature range of 350 ~ 600 ℃, in a molten salt containing only Na ions as alkali ions, after immersion treatment for 0.5 to 100 hours, to perform chemical strengthening by a conventional method It is characterized by having done.

Here, when the temperature of the molten salt is less than 350 ° C., it does not act on both the molten metal contact and non-contact surfaces of the float glass, and the influence of Na ions or the like in the surface layer portion of the both surfaces hardly changes,
The difference in alkali concentration between both surfaces is not reduced, and there is no effect in preventing warpage during chemical strengthening, preferably 450 ° C or higher. In addition, especially when the strain point exceeds about 600 ℃, it is likely to deform because it is close to the softening temperature of the glass itself, and when it is immersed for a long time, the glass surface becomes clouded. Although it shrinks, it causes a drawback. The stable and reliable temperature of the molten salt is 600 ° C or lower.

On the other hand, in the above-mentioned immersion treatment, as shown in FIG. 1 showing the relationship between the molten salt temperature, the immersion time and the amount of warpage, the amount of warpage varies depending on the treatment time even at a constant treatment temperature. It can be arbitrarily selected within the processing time. 0.5 hours, preferably 1 hour or more, the treatment temperature is 600
The reason why the temperature is not higher than 100 ° C. and the time is not longer than 100 hours, preferably not longer than 80 hours is to prevent the change of the glass surface from progressing excessively in addition to the economical aspect.

It is more effective to preheat the glass before the dipping treatment, and after the dipping treatment, perform slow cooling such as step cooling and wash.

As the molten salt containing Na ions, for example, sodium nitrate, sodium nitrite, sodium sulfate, sodium phosphate, a mixed salt thereof, or the like is used.

Further, for the chemical strengthening, a known chemical strengthening method which is usually used, that is, at a temperature not higher than the strain point, alkali ions in the float glass surface layer after the treatment are treated with an alkali having a larger ionic radius. The chemical strengthening method of substituting with ions can be applied.

[Action]

As described above, according to the chemical strengthening method of the float glass of the present invention, the peculiar pre-stage treatment is performed, including the problem that the plate thickness of about 4 mm is thinned but the wind cooling strengthening method cannot sufficiently strengthen. By doing so, the warpage in float glass was reduced to a value close to that of a raw plate (without surface treatment), and therefore surface roughness, surface parallelism, smoothness, etc. without the need for grinding and polishing. Since it can be chemically strengthened by making full use of the characteristics of, the float glass, which is thinner and has a relatively large area and strength, will be used for multiple purposes, and the thinner the thickness and the larger the area, the greater the need for warpage countermeasures. Among them, we have found a solution to this problem and can improve the accuracy of the shape of molded products, etc.
It is characterized by satisfying the disk specifications such as m / 300 mm diameter or less and greatly improving the yield.

〔Example〕

 Examples of the present invention will be described below.

Examples 1 to 6 Float glass having a plate thickness of about 1.0 mm and a diameter of about 300 mm was used as a glass substrate, and sodium nitrate was used as a molten salt containing Na ions. The temperature and time shown in Table 1 were used for immersion. The sample was processed and subjected to ordinary chemical strengthening using potassium nitrate.

For these samples, the amount of warpage is DEKTAK II (SLOAN
Using a (US) shape measuring instrument), the degree of chemical strengthening (surface compressive stress value) was measured using a surface stress measuring instrument.

The amount of warpage is shown in Table 1.

Comparative Example 1 The same float glass as in the example was not chemically treated with a molten salt containing Na ions, but was chemically strengthened under the same conditions as other samples.

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

The amount of warpage is shown in Table 1.

Comparative Example 2 The same float glass as in Example was used as it was (raw plate) as a sample, and the amount of warpage was measured with the same equipment as in Example.

The results are shown in Table 1.

Comparative Examples 3 and 4 The same glass and molten salt as in the examples were used, only the dipping treatment conditions were performed at the temperature and time shown in Table 1, and the other conditions were the same as those in the Examples, and the warpage amounts are shown in Table 1.

However, the amount of warp is a measured value of five samples, and a minus sign indicates that the side in contact with the molten metal surface is convex.

〔The invention's effect〕

As is clear from Table 1 showing the comparison of the above-described examples of the present invention and comparative examples including conventional examples, conventional chemical strengthening only or chemistry after immersion treatment in which the immersion treatment temperature is less than the lower limit of the present invention. If it is reinforced, the warp amount is several times to several tens of times that of the green plate, and in the present invention, the warp amount is close to that of the green plate, and the effect is remarkable.

Further, with respect to the degree of chemical strengthening, even when the present invention is carried out, the surface compressive stress value is 2500 to 35 with almost no difference on both the molten metal contact surface and the non-contact surface of the float glass plate.
It is 00 kg / cm ² , and the bending fracture strength is 4500 to 6000 kg / cm ² , which is about the same as the degree of strengthening by the conventional method.
Further, the compressive stress layer from the surface is 20 to 30 μm, which sufficiently satisfies the specifications in the field of electronic materials.

FIG. 1 summarizes the examples of the present invention and shows the immersion treatment temperature,
It is a graph showing the relationship between the immersion treatment time and the amount of warp, and as is clear from the figure, it goes without saying that a shorter immersion treatment time is sufficient if the immersion treatment temperature is high within the scope of the present invention. The amount can also be arbitrarily selected according to the specifications.Furthermore, if you want to make the depth from the surface of the compressive stress layer deeper and keep the amount of warpage within 0.2 mm / 300 mm diameter, you can freely set from this relationship. Can be selected and achieved.

As described above, the present invention, in the chemical strengthening of the float glass, by solving the warp that has not been solved in the past,
It has an excellent effect that thin float glass can be used in a wide range of fields such as electronic materials, particularly optical disc substrates and construction.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the immersion treatment conditions and the warp amount of the present invention.

Claims (1)

[Claims] 1. When chemically strengthening soda lime type float glass, 0.5 to 1 is added to a molten salt having a holding temperature in the range of 350 to 600 ° C. and containing only Na ions as alkali ions.
After the immersion treatment of the glass for 00 hours, the alkali ion in the treated glass surface layer is subjected to a chemical strengthening treatment for substituting the alkali ion having a larger ionic radius at a temperature below the strain point. Method of chemically strengthening float glass.