JPH0651580B2 - Method of chemically strengthening float glass - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is applied to the field of electronic materials such as soda-lime float glass, especially optical disks, which are used for various moldings such as thin and large-area construction, vehicle glass, furniture and the like. The present invention relates to a method for chemically strengthening float glass used.

[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 fields such as construction and vehicles, but also in electronic materials fields such as liquid crystal and plasma displays. is there.

Furthermore, as a recent trend, thin glass with a thickness of 4 mm or less has been favored, and the thinner the thickness, the higher the strength is desired.

It is well known that the chemical strengthening method by alkali ion substitution is applied to effectively strengthen thin glass, but when the chemical strengthening method is directly used for float glass, the glass warps (for example, at a thickness of 1 mm. 0.45 to 1.25
mm / 300 mmφ) flatness was impaired, and in particular, the flatness required for an optical disk substrate or the like (for example, 0.2 mm or less / 300 mmφ at a thickness of 1 mm) could not be obtained.

It is speculated that the cause of the warp is 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 warp has been found. For example, the Sn infiltrated surface of glass is ground and polished, and then alkali ion substitution treatment is carried out, but this method not only complicates the process but also easily causes cracks and surface defects, and the cost is high. There was a problem of becoming. A prior art that is similar to the structure of the present invention is, for example, JP-A-54-142227. It is presumed that this is a combination of alkali ion substitution and dealkalization treatment over the entire surface of soda-lime glass and has the characteristics of improving the mechanical strength and chemical durability of the glass, but the object of the present invention is to And of float glass
It is completely different from the one that suppresses the warpage that occurs during the alkali ion substitution due to the difference in the Sn contact surface.

[Problems to be solved by the invention]

As described above, in the prior art, the process is complicated and costly even if it is polished to suppress the warpage that occurs when the float glass is subjected to ion substitution, or even simple dealkalization is effective. There is a problem that the warp cannot be suppressed.

The present invention provides a novel method for suppressing the occurrence of warpage when strengthening float glass by alkali ion substitution.

[Means for solving problems]

The present invention is a method for chemically strengthening soda lime-based float glass, wherein the glass is first subjected to a temperature condition of 500 ° C. to 650 ° C., and the non-contact surface with the molten metal during the float forming does not contain a metal component. It is characterized in that an oxidizing gas or an acidic liquid is brought into contact with the soda ion reducing treatment, and then the soda ions on the entire surface of the glass are replaced by alkali ions having a larger ionic radius than that to form a surface compression layer. It is a thing.

At the time of float molding, molten glass is molten metal (usually S
n) extends along the surface to form a smooth surface (hereinafter referred to as the bottom surface), while its upper surface contacts the atmosphere to form a smooth free surface (hereinafter referred to as the top surface). The Sn
On the bottom surface in contact with Sn, Sn penetrates into the glass to a depth of 10 to 20 μm. It is presumed that other components such as soda ions in the glass are relatively reduced due to the infiltration of Sn into the bottom surface.

By the way, it is clear that when the float glass is reinforced by alkali ion substitution as it is, a warp occurs in which the top surface side expands and the top surface is convex, but this is the alkali ion on the bottom surface as described above. It is presumed that this is probably because the substitution is suppressed, while the substitution of alkali ions on the top surface side is not suppressed, and the radius of the substituted alkali ions is large.

The present invention has been made in view of this point, and the radius of the top surface is increased by performing the above-mentioned treatment to reduce the soda ion concentration on the top surface prior to the alkali ion substitution. It is intended to limit the substitution with alkali ions and eliminate the warpage at the time of alkali ion substitution.

As an example of the treatment method for reducing the soda ion concentration, CCl ₃ F, CCl ₂ F ₂ , C ₂ Cl ₄ F ₂ , CBr ₃ F, or other chlorofluorocarbon gas, H
Float glass preheated to a temperature range of about 500 ° C to 650 ° C in which an oxidizing gas such as F gas or SO ₂ is appropriately used, for example, air is used as a carrier and the glass is efficiently subjected to chemical treatment without deformation. 1 minute to a few on the top surface of
A method of spraying for 0 minutes is suitable. The soda on the glass surface reacts with these gases and evaporates in the form of Na ₂ F, for example.

To heat the glass, use an electric furnace to suspend or stand or place the glass horizontally (in these cases, it is good to install an arbitrary blocking member so that the gas does not reach the bottom surface). Is provided with a gas introduction pipe having a gas introduction hole and a nozzle at the tip so that the gas effectively acts on the top surface of the glass, and a gas for discharging the gas above the heating furnace. Provide a discharge hole.

In addition, in order to continuously process the glass, a method of blowing the gas while moving the glass in a heating furnace of a tunnel furnace type can be appropriately adopted.

In other methods, a dealkalizing solution such as an acidic solution containing sulfuric acid, hydrochloric acid, or a salt thereof is applied to the top surface of the glass by any means such as spraying, heating, alkali leaching, and the glass is washed, and then the alkali is removed. You may make it perform an ion substitution process. Also in this case, the effect of preventing warpage can be exhibited by setting the temperature in the range of 500 ° C. to 650 ° C. and the treatment time of several minutes to several tens of minutes.

It is to be noted that the top surface of the glass is applied with another metal capable of replacing soda (for example, Sn, Ti, etc.) in the form of a compound such as SnCl ₄ , Ti (OC ₃ H ₇ ) _{4 in} the form of gas, liquid or slurry. Although some methods can be considered, they are partially replaced with soda in the glass, but they have a large effect of depositing on the glass surface to coat the glass, and it is difficult to suppress it, so it is not a good idea. .

Preferably, a desired amount of the liquid or slurry of the compound is applied to the top surface of the glass and heat-treated at 500 ° C. or higher for several minutes to several tens minutes.

After the treatment for reducing the soda concentration on the top surface of the float glass is performed as described above, the whole surface of the float glass is subjected to ion substitution with alkali ions having a large ionic radius, usually potassium, to form a surface compression layer on the glass.

For this processing, a conventionally known method can be adopted. That is, in a bath of potassium-containing salt such as potassium nitrate or potassium sulfate, float glass is immersed in the temperature range of strain point or slow cooling point of glass for 30 minutes to several hours, or the whole surface of float glass contains potassium. By coating with salt, spraying, coating, etc. and heating to a temperature below the annealing point.
˜50 μm potassium substitution layer is formed.

After these operations, the glass is cooled and washed. As a result, it is possible to obtain glass that is suppressed in warpage and chemically strengthened.

〔Example〕

 A specific example of the embodiment will be described below.

Example 1 Five pieces of float glass having a size of 300 mmφ and a thickness of 1 mm were prepared.

A resistance heating type electric furnace is used as the heating furnace, and a plurality of gas nozzles pierced through the gas introduction pipe for guiding gas from the outside of the furnace at one place on the side wall of the furnace and glass branched from the gas introduction pipe are installed inside the furnace. It is arranged so as to face the top surface when it is arranged in the furnace.

Heat the inside of the heating furnace to 550 ° C in advance, then guide the glass standing on the steel frame to the inside of the furnace, and then mix the mixed gas containing 10VOl% CBrF ₃ gas into the air preheated to 100 ° C.
The top surface of the glass was sprayed at a rate of 43 / min for 3 minutes.

After that, the glass was taken out, allowed to cool, washed with water, and subjected to alkali ion substitution treatment.

Alkali ion substitution treatment is performed according to a conventionally known method.
The glass suspended on a steel support was immersed in a potassium nitrate bath heated to 0 ° C., and after holding for 150 minutes, the glass was taken out, allowed to cool, and washed with water.

The following tests were performed on the obtained glass.

Warpage: The displacement of the surface shape was measured using a shape measuring instrument (DEKTAKII manufactured by SLOAN).

Bending fracture strength: Load ring diameter of 40 mmφ, support ring diameter of 100 mmφ, load speed of 2 mm according to the concentric load bending method
The breaking strength was measured under the condition of / min.

The results are shown in Table 1, Example 1.

Example 2 Five float glass sheets similar to those in Example 1 were changed in soda reduction treatment conditions only, and the same treatments as in Example 1 were carried out and subjected to the test.

In the soda reduction treatment, a mixture of 5 vol% HF gas in air preheated to 100 ° C. was sprayed at a rate of 52 / min for 3 minutes on the top surface of glass preheated to 500 ° C.

The results are shown in Table 1, Example 2.

Example 3 Five float glass sheets similar to those in Example 1 were coated with about 12 cc of a 10 wt% NH ₄ Cl aqueous solution on the top surfaces thereof, dried, and heated to 550 ° C. in the same heating furnace as in Example 1 ( However, the gas was not sprayed) and held for 10 minutes. After that, the glass was taken out, allowed to cool, washed with water, and then subjected to alkali ion substitution treatment under the same conditions as in Example 1 and subjected to the test.

The results are shown in Table 1, Example 3.

Reference Example 1 Five pieces of float glass similar to those in Example 1 were subjected to alkali ion substitution treatment under the same conditions as in Example 1 without being subjected to soda reduction treatment, and then subjected to the test.

The results are shown in Table 1, Reference Example 1.

Reference Example 2 Five pieces of float glass similar to those in Example 1 were directly subjected to the test without any treatment.

The results are shown in Table 1, Reference Example 2.

When Examples 1 to 3 are compared with Reference Examples 1 and 2, all of Examples 1 to 3 are float green glass (Reference Example 2).
It can be seen that the warpage is small, and the bending fracture strength is almost comparable to that of the glass not subjected to the soda reduction treatment (Reference Example 1).

(Effect of the invention) As described above, according to the present invention, a warp of 0.45 to 1.25 mm / 300 mmφ occurs when the conventional float glass is simply chemically strengthened, whereas a low cost and easy operation of 0.06 to 0.15 mm
/ 300mmφ, flatness comparable to that of float green sheet glass is obtained, and its strength is comparable to that of the conventional method, and it can be widely used in the electronic material field such as various substrates such as day spray and disc. Is played.

Claims (1)

[Claims] 1. A method of chemically strengthening a soda-lime float glass, wherein the glass is first subjected to a temperature condition of 500 ° C. to 650 ° C., and a metal component is added to a non-contact surface with the molten metal during the float forming. It is characterized by contacting with an oxidizing gas or acidic liquid that does not contain soda ion reduction treatment, then replacing the soda ions on the entire surface of the glass with alkali ions having a larger ionic radius than that to form a surface compression layer. Method of chemically strengthening float glass.