JPH0768053B2 - Method of chemically strengthening float glass - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is applicable to 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. Method of chemical strengthening.

INDUSTRIAL APPLICABILITY The present invention can be applied not only to display and disk substrates, but also to thin and large-area building and vehicle window glass, and also various molded products using float glass, glass products for cooking, and various electronic and electrical devices. Substrate, etc.
Widely used.

[Conventional technology]

Float glass has excellent surface smoothness, flatness, and uniformity of thickness compared to so-called ordinary flat glass, so it is widely used not only in fields such as construction and vehicles but also in 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 that the chemical strengthening method by alkali ion substitution is applied to effectively strengthen the thin glass, but when the chemical strengthening method is directly used for the float glass, the glass warps (for example, about 1 mm. 0.4-1.3m in thickness
m / 300mm diameter) Flatness is impaired, especially the flatness required for optical disk substrates, etc. (eg 0.2mm / 300 at a thickness of about 1mm)
mm diameter or less) could not 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 float forming of glass, but no epoch-making countermeasure against this warpage has been found. For example, the Sn infiltrated surface of the glass is ground and polished, and then alkali ion substitution treatment is carried out.However, the Sn diffusion layer on the contact glass surface of the Sn is
10 to 20 μm, which requires grinding and polishing of this layer at maximum.
In this method, not only is the process complicated, but there is also a problem in the grinding and polishing itself, which causes cracks and defects in the glass, 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.

On the other hand, as an example of coating on a glass surface for chemical strengthening, for example, in JP-A-56-125244, an aqueous solution containing specific weight% of K and Na ions is coated on soda-lime glass and coated. To maintain the temperature below the annealing point for a sufficient time for the ion exchange to occur, and then to cool it to room temperature to efficiently exchange ions and obtain a glass of high strength. What is known is.

[Problems to be solved by the invention]

As described above, when chemically strengthening the float glass, unless the Sn diffusion layer is removed by grinding and polishing the molten metal contact surface, as described in JP-A-56-125244, a small amount of Even if a treatment of applying an aqueous solution of potassium ions to which sodium ions are added, it is impossible to prevent the warp of the float glass.

[Means for solving problems]

The present invention has been made by paying attention to such a drawback of the prior art, and in chemically strengthening the float glass, only the molten metal contact surface of the float glass which is in a state not surface-treated is treated. After reducing the difference in the alkali concentration between the molten metal contact surface and the molten metal non-contact surface so that the amount of warpage after chemical strengthening is within 0.2 mm / 300 mm diameter, and then chemically strengthening It is intended to provide a new method capable of solving the problem of remaining warp.

That is, according to the present invention, an inorganic salt containing Li ions or a mixed inorganic salt of two or more kinds containing Li ions and Na ions is applied onto the molten metal contact surface of the float glass, and the temperature is 380 to 650 ° C.
After heat treatment in the ambient temperature range of 0.01 to 30 hours, the alkali ions in the treated glass surface layer are chemically strengthened by substituting alkali ions having a larger ionic radius at a temperature of the strain point or less, ± 0.2. The present invention provides a chemical strengthening method for float glass, which is characterized in that the warp amount is equal to or less than a diameter of mm / 300 mm.

Here, when the atmosphere temperature is lower than 380 ° C., the molten metal contact surface of the float glass is hardly acted on by an inorganic salt containing Li ions or the like, and diffusion or the like to the surface layer of Li ions or the like does not occur on the contact surface. In addition, the difference in alkali concentration between the molten metal contact surface and the non-contact surface is not reduced, and there is no effect for preventing warpage after chemical strengthening.

It is preferably 400 ° C. or higher. Further, the ambient temperature is 6
If it exceeds 50 ° C., it is too close to the softening temperature of the glass itself, and in some cases, deformation is likely to occur, a white turbidity phenomenon is likely to occur on the glass surface, smoothness tends to be lost, and unevenness is likely to occur. Although the influence difference such as "1" can be reduced, it causes the above-mentioned drawbacks. Preferably 600 ° C
It is the following.

On the other hand, the heating time has a close relationship with the ambient temperature, but 0.01 hours or more, preferably 0.08 hours or more, if less than 0.01 hours, the temperature must be 650 ℃ or more, Even if it can improve the warp, with the above-mentioned defects, it is not preferable, and within 30 hours, preferably 25 hours, in addition to the economical aspect over 30 hours, the change of the glass surface Is too advanced.

In addition, in applying the inorganic salt coating heat treatment, the glass is preheated, and after the treatment, slow cooling such as step cooling is performed, and the inorganic salt adhering to the glass is removed to perform a chemical strengthening treatment. If done, it will be more effective in eliminating the warp.

Moreover, as the inorganic salt containing Li ions, for example, lithium nitrate, lithium nitrite, lithium sulfate, lithium phosphate, or a mixed salt thereof or the like is used.

Further, regarding the chemical strengthening, a known chemical strengthening method that is usually used, that is, a temperature of not higher than the strain point is used to remove alkali ions in the surface layer of the float glass after the treatment, which has a larger ionic radius. The chemical strengthening method of substituting with alkali ions can be applied.

[Work]

As described above, according to the method for chemically strengthening the float glass of the present invention, the plate thickness of about 4 mm or less, that is, including the problem that it can not be sufficiently strengthened by the air-cooling strengthening method, but a unique pre-treatment As a result, the warp in the float glass is reduced to a value close to that of a green plate (unprocessed surface), and it is therefore possible to solve the problems of surface roughness, surface parallelism, and surface roughness without grinding and grinding. Float glass, which is thinner and has a relatively large area and has strength, is used for multiple purposes because it can be chemically strengthened by making the most of its smoothness and other characteristics. As the need increases, we have found a solution to this problem, and it is possible to improve the shape accuracy of molded products, etc., as well as display, warpage is 0.2 mm / 300 mm or less Also satisfy the disk specifications such as say, those having a characteristic that also greatly improved yield, and the like.

〔Example〕

 Examples of the present invention will be described below.

Examples 1 to 9 Float glass having a thickness of about 1.0 mm and about 300 mm × 300 mm was used as a glass substrate, and lithium nitrate was used as an inorganic salt containing Li ions. The lithium nitrate was maintained at about 390 ° C. Immediately after immersing the glass substrate in the molten bath, when the glass substrate is cooled and the coated lithium nitrate is solidified, the lithium nitrate coated on the non-contact side of the molten metal is treated with water or water. Spray with mist to remove, wash, and dry. Incidentally, it goes without saying that other methods such as applying a mask to the non-contact surface of the molten metal and subjecting it to dipping may be used for the coating. After that, heat treatment was performed in a heating furnace under the conditions of temperature and time as shown in Table 1, and thereafter, ordinary chemical strengthening was performed using potassium nitrate to obtain a sample.

For these samples, the DEKTAK II (shape measurement device made by SLOAN) was used as the amount of warp, and the chemical strength (surface compressive stress value)
Was measured using a surface stress measuring instrument.

Comparative Example 1 The same float glass as in Example was chemically treated under the same conditions without being treated with an inorganic salt containing Li ions, and used as a sample.

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 inorganic salt as in the examples were used, only the heat treatment condition was performed at the temperature and time shown in Table 1, the other conditions were the same as those of the examples, and the amount of warpage is shown in table 1.

However, the warp amount is a measured value of each of the 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 comparison between the above-mentioned examples of the present invention and comparative examples including conventional methods, conventional chemical strengthening only or post-treatment chemicals in which heat treatment conditions deviate from the upper limit or 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. In the present invention, the warp amount is reduced to a value close to that of the green plate, and the effect is remarkable.

Regarding chemical strengthening, even when the present invention is carried out,
Float glass has almost no difference between the contact surface and non-contact surface of molten metal, and the surface compressive stress value is 2500 to 3500 kg.
/ cm ² , and the bending fracture strength is 4500-6000 kg / cm ² ,
The degree of strengthening obtained by the conventional method is comparable to that of the conventional method. Furthermore, regarding the compressive stress layer from the surface,
A thickness of up to 30 μm is obtained, which sufficiently satisfies the specifications in the field of electronic materials.

Further, within the scope of the present invention, the conditions can be arbitrarily selected and the specification of the amount of warpage can be satisfied, as well as the depth from the surface of the compressive stress layer, and the amount of warpage is, for example, ± 0.2 mm / 30
It can be freely accommodated within a diameter of 0 mm. Further, the warp amount varies depending on the plate thickness and size, but this can be sufficiently dealt with.

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,
The thin and high-strength float glass can be adopted in a wide range of fields such as electronic materials, especially optical disc substrates and construction, and the like.

Claims (1)

[Claims] 1. When chemically strengthening a plate-shaped glass produced by the float process and processed, an inorganic salt containing Li ions or a mixed inorganic salt of two or more kinds containing Li ions and Na ions is added to the above-mentioned inorganic salt. Apply it to the surface of the glass that is in contact with the molten metal surface, and apply 0.01 to 30
After heat treatment for a period of time, alkali ions in the treated glass surface layer are chemically strengthened by substituting alkali ions having a larger ionic radius at a temperature of a strain point or lower. Chemical strengthening method.