JPH0768052B2 - 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 disk play 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, for cooking. Widely used as chemically strengthened float glass such as glass plates and substrates for various electronic and electrical devices, such as processed plates.

[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 warp is molten metal during float forming of glass, usually Sn
It is presumed that this is due to the effect of the invasion of the contact glass surface, but no epoch-making countermeasure against this warp 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, as an attempt to pre-stage process during chemical strengthening, for example, there is Japanese Patent Publication 54-17765 discloses, in the embodiment of this publication, a mixture salt bath consisting of NaNO ₃ and KNO _3, which is 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 performing treatment so that the amount of warpage after chemical strengthening is within 0.2 mm / 300 mm diameter. It is provided.

That is, the present invention, in a molten salt containing Li ions or a mixed molten salt of two or more kinds containing Li ions and Na ions, in which the float glass has a holding temperature range of 350 to 600 ° C.,
After the dipping treatment for 06 to 50 hours, the alkali ions in the treated glass surface layer are chemically strengthened by substituting the alkali ions with a larger ionic radius at a temperature below the strain point,
The feature is that the warp amount is ± 0.2 mm / 300 mm diameter or less.

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, there is almost no diffusion of Li ions or the like in the surface layer portions of the both surfaces, and the difference in alkali concentration on both surfaces. Does not shrink and has no effect on preventing warpage during chemical strengthening, preferably at 400 ° C or higher.
Moreover, especially when the strain point exceeds about 650 ° C, the glass tends to be deformed because it is close to the softening temperature of the glass itself, and if it is immersed for a long period of time, a turbid phenomenon occurs on the glass surface. It causes other drawbacks of shrinkage, and the stable and reliable treatment temperature of molten salt is 600 ° C or lower.

On the other hand, in the above-mentioned dipping treatment, the amount of warpage changes depending on the temperature of the molten salt and the dipping time, and the dipping treatment can be arbitrarily selected from the treatment time of 0.06 to 50 hours depending on the treatment temperature. 0.06 hours, preferably 0.1 hours or more, the treatment temperature is 600
The reason why the temperature is not higher than 50 ° C. and the time is not longer than 50 hours, preferably not longer than 40 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 Li ions, for example, lithium sulfate, lithium nitrite, lithium sulfate, lithium phosphate, or a mixed molten salt thereof is used, and in addition, two or more kinds containing Li ion and Na ion are used. Other additives may be supplementarily used in the mixed molten salt of.

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.

[Work]

As described above, according to the method for chemically strengthening the float glass of the present invention, the peculiar pre-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 it. 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 has strength, will be used for multiple purposes. 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.

Furthermore, when two or more kinds of mixed solution salts containing Li ions and Na ions are used, the stability of the molten salt itself increases, which is preferable in terms of cost.

〔Example〕

 Examples of the present invention will be described below.

Examples 2 to 9 A glass substrate having a thickness of about 1.0 mm and a size of about 300 mm × 300 mm
The float glass of No. 1 and lithium sulfate as a molten salt containing Li ions are subjected to immersion treatment under the conditions of temperature and time as shown in Table 1 and normal chemical strengthening using potassium sulfate to obtain a sample. And

For these samples, the amount of warpage is DEKTAK II (SLO
An AN (US) shape measuring instrument) was used, and 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 treated with a molten salt containing Li ions, but was chemically strengthened under the same conditions as the 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 to 6 The same glass and molten salt as in the examples were used, only the dipping treatment conditions were carried out at the temperature and time shown in Table 1, and the others were carried out in the same way as the Examples, and the warpage amounts thereof 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 between the above-described examples of the present invention and the comparative examples including the conventional method, the conventional chemical strengthening only or the chemical treatment after the immersion treatment in which the immersion treatment temperature is less than the lower limit of the present invention is performed. If it is reinforced, the warp amount is several times to several tens of times that of the raw plate, and if it is the present invention, the warp amount becomes a value close to that of the raw plate, and in some cases, it may be less than the raw plate. It is possible and its effect is remarkable.

Regarding the degree of chemical strengthening, even when the present invention is carried out,
The surface compression stress value of the float glass plate is 2500 to 3500 kg on both the contact surface and the non-contact surface of the molten metal.
/ cm ² and bending fracture strength of 4500-6000 kg / cm ² ,
It is possible to obtain the same degree of strengthening as in the conventional method. Further, the compressive stress layer from the surface is also about 20 to 30 μm, which sufficiently satisfies the specifications in the field of electronic materials.

Furthermore, it goes without saying that a short immersion treatment time is sufficient if the immersion treatment temperature is high within the scope of the present invention,
The amount of warp can 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 warp within ± 0.2 mm / 300 mm diameter, you can freely select it. It is possible and attainable.

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.

Claims (1)

[Claims] 1. When chemically strengthening float glass, in a molten salt containing Li ions or a mixed molten salt of two or more kinds containing Li ions and Na ions, the holding temperature of which is in the range of 350 to 600 ° C., After the immersion treatment of the glass for 0.06 to 50 hours, alkali ions in the glass surface layer, at a temperature below the strain point, to perform chemical strengthening to replace the alkali ions with a larger ionic radius Method of chemically strengthening float glass.