WO2014045979A1

WO2014045979A1 - Production method of chemically toughened glass

Info

Publication number: WO2014045979A1
Application number: PCT/JP2013/074584
Authority: WO
Inventors: 拓山田; 敏史仁平; 和良倉嶋; 渡邉　邦夫
Original assignee: 旭硝子株式会社
Priority date: 2012-09-18
Filing date: 2013-09-11
Publication date: 2014-03-27
Also published as: TW201418184A

Abstract

This production method of chemically toughened glass involves immersing sodium-containing glass in a first tank provided with potassium nitrate-containing molten salt to form a compressive stress layer on the surface of the glass, and includes a step for transferring a part of the molten salt in the first tank to a second tank, a step for adding potassium phosphate to the transferred molten salt in the second tank, a step in which the sodium compound precipitated in the molten salt in the second tank after adding the potassium phosphate is separated from the molten salt, and a step for transferring to the first tank the molten salt after separation of the sodium compound.

Description

Method for producing chemically strengthened glass

The present invention relates to a method for producing chemically tempered glass by ion exchange, and more particularly to a method for producing chemically tempered glass having a stable quality by regenerating and reusing molten salt used for chemically strengthening the glass.

Glass that has been chemically strengthened by ion exchange or the like (hereinafter also referred to as “chemically strengthened glass”) is used for a cover glass of a display device such as a digital camera, a mobile phone, and a PDA (Personal Digital Assistants) and a glass substrate of the display. It has been. Although glass has a high theoretical strength, the strength is greatly reduced by scratching. Chemically tempered glass has a higher mechanical strength than unstrengthened glass and prevents the glass surface from being scratched.

The chemical strengthening treatment of the glass by ion exchange is performed by substituting a metal ion (for example, Na ion) having a small ionic radius and a metal ion (for example, K ion) having a larger ionic radius contained in the glass. In this process, a compressive stress layer is formed to improve the strength of the glass.

When Na ₂ O is contained in the glass composition, the glass is immersed in a molten salt (inorganic potassium salt) containing K ions, and Na ions in the glass and K ions in the molten salt are ion-exchanged. As the molten salt, an inorganic potassium salt that is in a molten state at the strengthening treatment temperature is used, and potassium nitrate is often used among them.

As one of evaluation methods for chemically strengthened glass, surface compressive stress (CS) can be cited. The maximum CS value can be given to glass after chemical strengthening treatment only when using a molten salt (new molten salt) that has not been subjected to ion exchange. Thus, the obtained CS value gradually decreases. It is known that the factor that CS decreases is due to the fact that potassium nitrate molten salt is diluted with Na ions eluted from the glass by ion exchange, and there is a correlation between Na ion concentration and CS decrease.

In order to continue to obtain the desired CS value, in Patent Document 1, the temperature of the molten salt subjected to the chemical strengthening treatment is lowered and dissolved in water to precipitate the salt, and after solid-liquid separation, the salt is brought to a temperature higher than the melting point. A method for remelting the molten salt by remelting is disclosed.
Patent Document 2 discloses a method of dividing the chemical strengthening process into two stages and increasing the DOL by coarse strengthening in the first stage and securing the CS value of the surface in the second stage.
In Patent Document 3, in order to suppress large variability in compressive stress and continuous periodic variation of chemically strengthened glass, all or part of the molten salt is discarded and replaced with a new molten salt that has not been subjected to ion exchange. A method is disclosed.

Japanese Unexamined Patent Publication No. 58-194761 Japan Special Table 2011-529438 Japanese Unexamined Patent Publication No. 2003-146705

However, in the regeneration method described in Patent Document 1, a large amount of waste is generated because the molten salt is dissolved in water. In addition, when regenerating molten salt, many series of steps of dissolution in water, precipitation, separation, and remelting are required, so the load on facilities and costs is large, and energy loss is also large. Therefore, there is room for improvement in terms of reducing the amount of waste, reducing manufacturing energy, and improving throughput.

In addition, in the method described in Patent Document 2, although it can be said that the life (lifetime) of the molten salt is long because the Na deterioration rate in the molten salt is slow, replacement and dilution of the molten salt are essential. A large amount of waste is generated. In addition, in order to perform the chemical strengthening process in two stages, it is necessary to repeat the pretreatment process such as preheating and cooling, and the posttreatment process twice, which may reduce the throughput. In addition, since two strengthening tanks of the same size are required for each process, spatial constraints may arise along with initial investment and maintenance problems.

Furthermore, in Patent Document 3, since all or part of the molten salt is discarded, the amount of waste is very large and costly. Therefore, it is realistic to actually perform chemical strengthening treatment of glass using the method. There was room for improvement.

Therefore, in the present invention, a method for producing chemically strengthened glass while regenerating the molten salt so that a desired CS value can be obtained continuously (stably), which reduces the amount of waste generated and improves the throughput. An object of the present invention is to provide a method for producing chemically strengthened glass at low cost.

The inventors transferred a part of the molten salt deteriorated by the chemical strengthening of the glass to a separate tank (second tank) independent of the chemical strengthening tank (first tank). The present invention found that a stable CS value can be imparted to glass while realizing a reduction in the amount of waste and low cost by carrying out a regeneration treatment of the molten salt in the process, and transferring the regenerated molten salt to a strengthening tank. It came to be completed.

That is, the present invention is as follows.
<1> A method for producing chemically strengthened glass in which a glass containing sodium is immersed in a first tank including a molten salt containing potassium nitrate, and a compressive stress layer is formed on the surface of the glass,
Transferring a part of the molten salt in the first tank to the second tank;
Adding potassium phosphate to the molten salt in the transferred second tank,
Separating the sodium compound precipitated in the molten salt in the second tank after the addition of the potassium phosphate from the molten salt; and transferring the molten salt after the sodium compound separation to the first tank;
A method for producing chemically strengthened glass, comprising:
<2> The chemically strengthened glass according to <1>, wherein the temperature T ₁ of the molten salt in the first tank and the temperature T ₂ of the molten salt in the second tank satisfy a relationship of T ₁ ≧ T ₂ . Production method.
<3> The method for producing chemically tempered glass according to <1> or <2>, wherein the molten salt in the first tank further contains potassium carbonate.
<4> The method for producing chemically tempered glass according to any one of <1> to <3>, wherein the potassium phosphate is potassium orthophosphate.

According to the method for producing chemically strengthened glass according to the present invention, chemically strengthened glass having a stable quality (CS value) can be continuously produced by one-step strengthening while regenerating and reusing the molten salt. As a result, the throughput can be improved, and the amount of molten salt raw material used for chemical strengthening can be reduced at the same time as the amount of waste is greatly reduced, thereby reducing the cost.

FIG. 1 is a schematic view showing an example of the entire apparatus for producing chemically strengthened glass. FIG. 2 is a graph showing the relationship between the glass treatment area per molten salt weight and the Na concentration in the strengthening tank in the production methods of Example 1 and Comparative Example 1. FIG. 3 is a graph showing the relationship between the glass treatment area per molten salt weight and the CS value in the production methods of Example 1 and Comparative Example 1. FIG. 4 is a graph showing the relationship between the glass treatment area per molten salt weight and the amount of waste in the production methods of Example 1 and Comparative Example 2. FIG. 5 is a graph showing the relationship between the glass treatment area per weight of molten salt and the waste reduction rate in the production method of Example 1.

Hereinafter, the present invention will be described in detail.
In the present specification, “mass%” and “wt%” are synonymous. Further, “mass ppm” and “weight ppm” are synonymous.
In the present invention, the chemically strengthened glass is obtained by immersing a glass plate containing Na in a first tank (also referred to as a chemical strengthening tank or simply a strengthening tank) provided with a molten salt containing potassium nitrate, on the surface of the glass. It is obtained by forming a compressive stress layer. Here, a part of the molten salt in the first tank (chemical strengthening tank) is extracted and transferred to the second tank (also referred to as a regeneration tank or a sedimentation tank), and phosphoric acid is added to the molten salt in the transferred second tank. Add potassium. By the addition of the potassium phosphate, a Na-containing compound is precipitated in the molten salt, so that the Na ion concentration in the molten salt is reduced and the molten salt is regenerated. The molten salt from which the Na-containing precipitate has been separated is transferred again to the first tank (chemical strengthening tank), so that the glass is chemically strengthened to produce chemically strengthened glass having a stable CS value. be able to.

The method for producing chemically strengthened glass according to the present invention can be applied, for example, to a chemical strengthening apparatus as shown in FIG. .
<Aspect A: Batch regeneration process>
Step 1: Preparation of molten salt Step 2: Chemical strengthening of glass Step 3: Judgment of molten salt deterioration Step 4: Extraction of molten salt from tempering tank (part of molten salt in tempering tank is extracted into regeneration tank)
Step 4 ′: Adjusting the temperature of the regeneration tank to a predetermined temperature Step 5: Molten salt regeneration step (adding potassium phosphate, stirring, standing)
Step 6: Extraction of regenerated molten salt Step 7: Removal of Na-containing precipitates 7 ′: Preheating the regenerated molten salt from which the Na has been removed to the strengthening temperature Step 8: Returning the regenerated molten salt from which the Na has been removed to the strengthening tank 9: Step 10 for confirming Na concentration in tempering tank: Chemical strengthening process in which steps 2 to 9 are repeated

<Aspect B: Continuous regeneration process>
Step 1: Preparation of molten salt Step 2: Chemical strengthening of glass Step 4: Extraction of molten salt from tempering tank (part of molten salt in tempering tank is extracted into regeneration tank)
Step 4 ′: Adjusting the temperature of the regeneration tank to a predetermined temperature Step 5: Molten salt regeneration step (adding potassium phosphate, stirring, standing)
Step 6: Extraction of regenerated molten salt Step 7: Removal of Na-containing precipitates 7 ': Preheating the regenerated molten salt from which the Na has been removed to the strengthening temperature Step 8: Returning the regenerated molten salt from which the Na has been removed to the strengthening tank 10: Chemical strengthening process that repeats steps 2 to 8 above

In the batch regeneration process of Aspect A, a part of the molten salt is intermittently extracted from the chemical strengthening tank, and after the regeneration treatment in the regeneration tank, the molten salt after the regeneration treatment is returned to the chemical strengthening tank. Go through a circular process.
In the continuous regeneration process of aspect B, a part of the molten salt is continuously extracted from the chemical strengthening tank and regenerated in the regeneration tank, and then the molten salt after the regeneration is returned to the chemical strengthening tank. Go through a circular process.
That is, the difference between Aspect B and Aspect B is whether the operation of extracting the molten salt to be subjected to the regeneration process from the chemical strengthening tank is performed intermittently or continuously. Step 3 and step 9 for confirming the Na concentration in the strengthening tank are not included.

Hereinafter, each step will be described with reference to FIG.
(Process 1)
In Step 1, an inorganic potassium salt is charged into the preparation tank 3, and the molten salt is prepared by heating and melting to a temperature equal to or higher than the melting point of the inorganic potassium salt. This is put into a chemical strengthening tank (strengthening tank, first tank) 1.

The inorganic potassium salt is preferably one that is in a molten state below the strain point (usually 500 to 600 ° C.) of the glass to be chemically strengthened. In the present invention, it contains potassium nitrate (melting point 330 ° C.). Further, it is preferable that potassium nitrate is a main component because it is in a molten state below the strain point of the glass and is easy to handle in a general temperature range when a chemical strengthening treatment is performed. Here, the main component means 50% by mass or more in the molten salt.

The molten salt may contain other inorganic potassium salts in addition to potassium nitrate, and examples thereof include combinations with one or more selected from alkali sulfates such as potassium sulfate and potassium chloride, alkali chlorides and potassium carbonate, and the like. .
Among them, the mixed molten salt of potassium nitrate and potassium carbonate has a lower rate of decrease in ion exchange capacity due to an increase in Na concentration and a longer life of the molten salt compared to a molten salt consisting only of potassium nitrate, so the frequency of regeneration is reduced. From the viewpoint of cost reduction due to the above.
The addition amount of potassium carbonate needs to be not more than the saturation solubility at the set temperature of the chemical strengthening tank 1 and the regeneration tank (sedimentation tank, second tank) 2 and is preferably 15% by mass or less with respect to potassium nitrate. In addition, 15 mass% is equivalent to the saturated dissolution amount of potassium carbonate with respect to potassium nitrate at 470 ° C.

In the preparation tank 3, the inorganic potassium salt is melted. Since potassium nitrate has a melting point of 330 ° C. and a boiling point of 500 ° C., it is preferably carried out within that temperature range. In particular, it is more preferable that the melting temperature be 350 ° C. or more and 500 ° C. or less from the viewpoint of the balance between the CS value that can be imparted to the glass and the stress depth (DOL) and the strengthening time.

When there are two or more kinds of inorganic potassium salts constituting the molten salt, they are mixed so that the whole becomes uniform by a stirring blade or the like at the time of melting. In this case, the order of addition of potassium nitrate and other inorganic potassium salts is not limited, and either may be added first or simultaneously.
The stirring time in the case of stirring for mixing is not particularly limited, but is preferably 1 minute to 10 hours, and more preferably 10 minutes to 2 hours.
When the inorganic potassium salt to be added exceeds the saturation solubility for potassium nitrate, K ₂ CO ₃ , K ₃ PO ₄ , NaHCO ₃ , NaK ₂ PO _4, etc. may be precipitated. It is allowed to stand until it settles or a solid-liquid separation operation is performed, and only the liquid is transferred to the chemical strengthening tank 1.

Materials such as metal, quartz and ceramics can be used for the preparation tank 3 for melting the inorganic potassium salt. Among these, a metal material is preferable from the viewpoint of durability, and a stainless steel (SUS) material is preferable from the viewpoint of corrosion resistance.

(Process 2)
In step 2, the glass is chemically strengthened. The molten salt prepared in step 1 is transferred from the preparation tank 3, and the chemical strengthening tank 1 including the molten salt containing potassium nitrate is defined as the first tank. The temperature of the molten salt in the chemical strengthening tank 1 is adjusted to a temperature at which chemical strengthening is performed. As glass to be tempered, glass containing Na is preheated.
The glass will be described in detail later. After the pre-heated Na-containing glass is immersed in the molten salt in the chemical strengthening tank 1 for a predetermined time, the glass is pulled out of the molten salt and allowed to cool for chemical strengthening. Processing (formation of a compressive stress layer on the surface of the glass) is performed. In addition, it is preferable to perform shape processing according to a use, for example, mechanical processing, such as a cutting | disconnection, an end surface processing, and a boring process, before performing chemical strengthening processing to glass.

The chemical strengthening treatment is performed by immersing the glass in a molten salt and ion-exchanging the metal ions in the glass with ions in the molten salt having an ionic radius larger than that of the metal ions. The ion exchange changes the composition of the glass surface, and compressive stress is generated in the glass surface layer, thereby strengthening the glass.

The glass preheating temperature depends on the temperature at which the chemical strengthening treatment is performed (temperature of the salt bath), but is generally preferably 100 ° C. or higher.

The chemical tempering temperature of the glass is preferably not more than the strain point (usually 500 to 600 ° C.) of the glass to be tempered, and preferably 350 ° C. or more in order to obtain a higher depth of compressive stress (Depth of Layer: DOL).

The immersion time of the glass in the molten salt is preferably 10 minutes to 12 hours, more preferably 30 minutes to 10 hours. If it exists in this range, the chemically strengthened glass excellent in the balance of an intensity | strength and the depth of a compressive-stress layer can be obtained.

The chemical strengthening tank 1 that performs the chemical strengthening treatment can use metal, quartz, ceramics, or the like. Among these, a metal material is preferable from the viewpoint of durability, and a stainless steel (SUS) material is preferable from the viewpoint of corrosion resistance.

(Process 3)
If the chemical strengthening treatment of the glass is continued in Step 2, a desired ion exchange amount cannot be obtained according to the glass treatment area, and the CS value imparted to the glass is lowered. Therefore, in step 3, the degree of deterioration of the molten salt is determined.
As the chemical treatment continues, Na ions are dissolved from the glass in the molten salt, and as the area of the treated glass increases, the Na ion concentration in the molten salt increases and the ion exchange capacity between K ions and Na ions decreases. To do. The ion exchange amount decreases due to a decrease in ion exchange capacity, leading to a decrease in the CS value imparted to the glass.
Therefore, the deterioration state of the molten salt is investigated by measuring the Na ion concentration in the molten salt or the CS value of the glass after chemical strengthening, and the molten salt can be used continuously, or after step 4 described later. It is determined whether or not the molten salt needs to be regenerated.
The Na concentration in the molten salt can be measured by ICP emission spectrometry or atomic absorption spectrometry, and the CS value of the glass after chemical strengthening treatment can be measured by a surface stress meter (Orihara Seisakusho FSM-6000LE).

In the present invention, the control value of CS required by the type of glass or the Na concentration in the molten salt corresponding to the control value of CS is defined each time. Perform the playback process.
However, when performing the chemical strengthening treatment of the glass and the regeneration treatment of the molten salt using the “continuous regeneration process” represented by the aspect B, the molten salt is continuously regenerated regardless of the Na ion concentration in the molten salt. Therefore, it is not necessary to perform this step 3.

(Process 4)
In step 4, in order to perform the regeneration treatment of the molten salt subjected to the glass chemical strengthening treatment, a part of the molten salt is transferred from the first tank (chemical strengthening tank 1) to the second tank (regeneration tank (sedimentation tank) 2). The molten salt is transferred by the molten salt transfer means 4. A known method such as a pump, pumping, pumping out, or siphoning can be used for feeding the molten salt.
The size of the regeneration tank 2 that is the destination of the molten salt may be determined according to the size of the chemical strengthening tank 1 and the Na ion concentration range to be controlled, and is not particularly limited. Among these, from the viewpoint of continuous strengthening treatment in the strengthening tank 1 and equipment costs, the size of the regeneration tank 2 is preferably ½ or less of the volume of the chemical strengthening tank 1.

An example of the case where the size of the regeneration tank 2 is determined based on the Na ion concentration range to be controlled is shown below.
When the concentration management of the Na ion concentration in the chemical strengthening tank 1 is in the range of 1800 to 2000 ppm, the Na ion concentration in the strengthening tank 1 is 2000 ppm and the management range of the Na ion concentration is 200 ppm. Therefore, the size of the regeneration tank 2 in this case is 200/2000 = 1/10, and 1/10 of the chemical strengthening tank 1 is required.

In the case of the batch regeneration process represented by the aspect A, the frequency of regenerating the molten salt can be arbitrarily determined according to the Na ion concentration control range in the strengthening tank 1.
The regeneration tank 2 is preferably preheated to 330 ° C. or higher in advance so that the transferred molten salt does not solidify.

The regeneration tank 2 that performs the molten salt regeneration process can use metal, quartz, ceramics, or the like. Among these, a metal material is preferable from the viewpoint of durability, and a stainless steel (SUS) material is preferable from the viewpoint of corrosion resistance.

(Process 4 ')
The temperature of the regeneration tank 2 can be arbitrarily selected depending on how much the Na ion concentration of the transferred molten salt is reduced. As the regeneration temperature is lower, the Na ion concentration can be lowered even if the amount of potassium phosphate added in Step 5 is reduced, and the Na removal efficiency is increased. This is due to the fact that the lower the temperature, the lower the saturation solubility of the Na salt, and the greater the amount of precipitation.
Since the improvement of Na removal efficiency leads to a reduction in the amount of potassium phosphate added, a cost reduction effect can be obtained.
The regeneration temperature T ₂ is preferably in the range of 350 to 500 ° C., and from the viewpoint of temperature dependence of solubility, T ₂ should be such that the inequality T ₁ ≧ T ₂ with respect to the chemical strengthening temperature T ₁ . Is preferred. Further, the temperature difference between T ₁ and T ₂ is preferably 0 to 150 ° C. from the viewpoint of the temperature dependence of the solubility of the Na-containing precipitate.
As described above, in step 4 ', the temperature T ₂ of the regeneration tank 2 is adjusted so as to satisfy the above requirements.

(Process 5)
In step 5, the molten salt is regenerated.
By adding potassium phosphate to the molten salt transferred to the regeneration tank 2, the molten salt can be regenerated so that a desired CS value can be given again. In the molten salt regeneration treatment step, Na ions in the molten salt increased by chemical strengthening treatment and K ions of potassium phosphate were ion-exchanged to precipitate Na and solidify and separate the supernatant. It can be reused as a molten salt (regenerated molten salt).

The temperature T ₂ of the regeneration tank 2 can be arbitrarily selected depending on how much the Na ion concentration of the transferred molten salt is lowered as described in the step 4 ′. The lower the regeneration temperature, the lower the Na ion concentration even if the amount of potassium phosphate added is reduced. This is due to the fact that the lower the temperature, the lower the saturation solubility of the Na salt, and the greater the amount of precipitation.
Since the improvement of Na removal efficiency leads to a reduction in the amount of potassium phosphate added, a cost reduction effect can be obtained.
Play temperature _{T 2} is preferably in the range of 350 ~ 500 ° C., from the viewpoint of the temperature dependence of the solubility, _{T 2} for chemical strengthening temperature _{T 1,} it is preferable that the _{_T 1} ≧ _T _2.

Examples of potassium phosphate added to the molten salt include potassium orthophosphate (K ₃ PO ₄ ), potassium pyrophosphate (K ₄ P ₂ O ₇ ), and potassium metaphosphate ((KPO ₃ ) _n ). You may use together in combination. Of these, potassium orthophosphate is preferable from the viewpoint of Na removal efficiency during melting.
The amount of potassium phosphate added is determined in consideration of the temperature of the regeneration treatment, the concentration of Na ions in the transferred molten salt, and the amount of molten salt to be regenerated. For example, the upper limit of the added amount of potassium orthophosphate when the regeneration temperature is 470 ° C. and the liquid phase recovery rate is 50% is preferably 22% by mass or less.

When potassium orthophosphate is added as potassium phosphate, the potassium orthophosphate may be hydrated or dehydrated. The content of potassium orthophosphate added to the molten salt is preferably 0.1% by mass to 25% by mass with respect to the molten salt. If it is this range, it is preferable from a viewpoint of making a liquid recovery rate more than a desired ratio.

When potassium pyrophosphate is added as potassium phosphate, potassium pyrophosphate may be hydrated or dehydrated. The content of potassium pyrophosphate added to the molten salt is preferably 0.1% by mass to 25% by mass with respect to the molten salt. If it is this range, it is preferable from a viewpoint of making a liquid recovery rate more than a desired ratio.

When potassium metaphosphate is added as potassium phosphate, the potassium metaphosphate may be hydrated or dehydrated. The content of potassium metaphosphate added to the molten salt is preferably 0.1% by mass to 25% by mass with respect to the molten salt. If it is this range, it is preferable from a viewpoint of making a liquid recovery rate more than a desired ratio.

After adding potassium phosphate to the molten salt, the precipitated Na-containing compound (hereinafter also referred to as “Na-containing precipitate”) and the liquid phase (regenerated molten salt) are separated. For example, the molten salt in the regeneration tank 2 can be separated into a liquid phase and a sediment containing precipitates by standing after stirring for a certain time.
The sediment contains KNO ₃ , K ₂ NaPO ₄ , KNaCO ₃ , K ₂ O and the like. The liquid phase contains KNO ₃ , K ₂ CO _{3 and the} like.

The stirring conditions after the addition of potassium phosphate are not particularly limited as long as the molten salt and potassium phosphate are mixed without a shortage. Moreover, it does not specifically limit about the stationary conditions after stirring, What is necessary is just to stand still until Na containing precipitate precipitates completely. The time required for the precipitate to settle completely depends on the particle size of the precipitate, and the smaller the particle size, the longer the time is required, but 30 minutes to 10 hours are preferable.
However, in the case where a solid-liquid separation device such as a filter or a centrifugal separator is used, the standing step is not necessary.

(Step 6)
In step 6, the regenerated molten salt (supernatant liquid, supernatant) after separating the Na-containing precipitate in step 5 is extracted. The extraction method can be arbitrarily selected, and examples thereof include pumping and pumping.

(Step 7)
In step 7, the Na-containing precipitate that has precipitated in the lower portion of the regeneration tank 2 in step 5 is removed out of the system. The removal method can be arbitrarily selected, and examples thereof include pumping and pumping.
Note that either step 6 or step 7 may be performed first.

(Step 7 ')
Step 7 ′ is a step of preheating the molten salt from which Na has been removed (regeneration treatment) to the strengthening temperature.
Compared with the molten salt extracted from the strengthening tank 1 in the step 4, the regenerated molten salt extracted in the step 6 after finishing the regenerating process is reduced by removing the precipitate generated in the regenerating process in the step 7.
Therefore, when returning the molten salt (recycled molten salt) that has been regenerated to the strengthening tank 1, a new molten salt that has not been subjected to the chemical strengthening process so as to have the same amount as the amount of the molten salt extracted in step 4. Add The molten salt composition to be added is the same as the composition charged into the strengthening tank 1 in step 1.
Before transferring the regenerated molten salt after removal of Na to the strengthening tank 1, preheating is performed to the same temperature as the strengthening tank 1. By this heating, the regenerated molten salt can be introduced into the strengthening tank 1 without reducing the throughput in the chemical strengthening treatment.

(Process 8)
In Step 8, the regenerated molten salt preheated in Step 7 is returned to the chemical strengthening tank 1, but the transfer means is not particularly limited. Specific examples include pumping and pressure feeding using a siphon.

(Step 9)
In the case of the batch regeneration process represented by the aspect A, in Step 9, after returning the regenerated molten salt to the chemical strengthening tank 1 in Step 8, the Na ion concentration in the chemical strengthening tank 1 is measured. If the Na ion concentration has not decreased to the desired value (the desired CS value cannot be obtained by the chemical strengthening process), Steps 4 to 8 are repeated again.
Similarly to step 3, the Na ion concentration can be measured by ICP emission analysis or atomic absorption analysis, and the CS value can be measured by a surface stress meter (Orihara Seisakusho FSM-6000LE).
When the chemical strengthening treatment of glass and the regeneration treatment of molten salt are performed using the “continuous regeneration process” represented by the aspect B, this step 9 is not necessary.

(Process 10)
In the case of the batch regeneration process of aspect A, if it can be confirmed in step 9 that the Na ion concentration in the chemical strengthening tank 1 has decreased to a desired value, the process returns to the chemical strengthening treatment step for glass in step 2 as step 10; The process up to step 9 is repeated.
In the case of the continuous regeneration process of the aspect B, unlike the aspect A, the molten salt is extracted from the strengthening tank 1 while being subjected to the chemical strengthening treatment of the glass regardless of the Na ion concentration in the strengthening tank 1, and then to the regeneration tank 2. A series of steps of transferring the molten salt, regenerating the molten salt, and transferring the regenerated molten salt to the strengthening tank 1 are performed. Therefore, in the process 10 in the aspect B, when the regenerated molten salt is returned to the strengthening tank 1 in the process 8, the process from the chemical strengthening treatment process of the glass in the process 2 to the process 8 is repeated.

As described above, by performing steps 1 to 10, a chemically strengthened glass is manufactured while processing a molten salt so as to obtain a desired CS value continuously (stably) for a molten salt containing potassium nitrate. Can do.
In the present invention, a tank for performing chemical strengthening treatment (strengthening tank 1) and a tank for performing molten salt regeneration treatment (regeneration tank 2) are separately performed to reinforce the molten salt regeneration. Since it is not necessary to interrupt the treatment and the chemical strengthening treatment of the glass can be performed continuously, the throughput can be improved.
Moreover, since the molten salt is circulated continuously or intermittently for recycling and reuse, the amount of waste generated is reduced. For the same reason, since the amount of the molten salt raw material that needs to be newly added is small, the molten salt cost can be reduced.

<Glass>
The glass used in the present invention only needs to contain sodium, and glass having various compositions can be used as long as it has a composition that can be strengthened by molding and chemical strengthening treatment. Specific examples include soda lime glass, aluminosilicate glass, borosilicate glass, lead glass, alkali barium glass, and aluminoborosilicate glass.

The method for producing the glass is not particularly limited, and a desired glass raw material is charged into a continuous melting furnace, and the glass raw material is heated and melted preferably at 1500 to 1600 ° C., clarified, and then supplied to a molding apparatus. It can be manufactured by forming into a plate shape and slowly cooling.

It should be noted that various methods can be employed for forming the glass. For example, various forming methods such as a down draw method (for example, an overflow down draw method, a slot down method and a redraw method), a float method, a roll-out method, and a press method can be employed.

The thickness of the glass is not particularly limited, but is usually preferably 5 mm or less and more preferably 3 mm or less in order to effectively perform the chemical strengthening treatment.

Although it does not specifically limit as a composition of the glass for chemical strengthening of this invention, For example, the following glass compositions are mentioned.
(I) a composition that is displayed in mol%, the SiO ₂ 50 ~ 80%, the _{_{Al 2 O 3 2 ~ 25%}} , the Li ₂ O 0 ~ 10%, a _{_{Na 2 O 0 ~ 18%,}} K 2 O Is represented by a glass (ii) mol% containing 0-10%, MgO 0-15%, CaO 0-5% and ZrO ₂ 0-5%, SiO ₂ 50-74%, Al ₂ O ₃ 1-10%, Na ₂ O 6-14%, K ₂ O 3-11%, MgO 2-15%, CaO 0-6% and ZrO ₂ 0-5% The total content of SiO ₂ and Al ₂ O ₃ is 75% or less, the total content of Na ₂ O and K ₂ O is 12 to 25%, and the total content of MgO and CaO is 7 to 15%. a composition which is displayed at a certain glass (iii) mol%, a SiO ₂ 68 ~ 80%, the _{_{Al 2 O 3 4 ~ 10%}} , The a ₂ O 5 ~ 15%, the _{K 2} O 0 to 1%, the MgO 4 ~ 15% and ZrO ₂ is composition displaying a glass (iv) mole% containing 0 to 1%, a SiO ₂ 67 -75%, Al ₂ O ₃ 0-4%, Na ₂ O 7-15%, K ₂ O 1-9%, MgO 6-14% and ZrO ₂ 0-1.5% The total content of SiO ₂ and Al ₂ O ₃ is 71 to 75%, the total content of Na ₂ O and K ₂ O is 12 to 20%, and when CaO is contained, the content is 1% Glass that is less than

Glass may be polished before chemical strengthening treatment as necessary. Examples of the polishing method include a method of polishing with a polishing pad while supplying a polishing slurry. As the polishing slurry, a polishing slurry containing an abrasive and water can be used. As the abrasive, cerium oxide (ceria) and silica are preferable.

If the glass is polished, the polished glass is cleaned with a cleaning solution. The washing liquid is preferably a neutral detergent and water, and more preferably washed with water after washing with a neutral detergent. A commercially available neutral detergent can be used.

The glass substrate cleaned by the cleaning process is finally cleaned with a cleaning solution. Examples of the cleaning liquid include water, ethanol, and isopropanol. Of these, water is preferred.

After the final cleaning, the glass is dried. The drying conditions may be selected in consideration of the cleaning solution used in the cleaning process, the characteristics of the glass, and the like.

Examples of the present invention will be specifically described below, but the present invention is not limited to these.

(Glass composition)
Aluminosilicate glass was used as the chemically strengthened glass. The composition of the glass is as follows.
Aluminosilicate glass (mol%): SiO ₂ 64.4%, Al ₂ O ₃ 8.0%, Na ₂ O ₃ 12.5%, K ₂ O 4.0%, MgO 10.5%, CaO 0. 1%, SrO 0.1%, BaO 0.1%, ZrO ₂ 2.5%

(Evaluation of glass (determination of molten salt deterioration))
Glass was evaluated by measuring surface compressive stress (CS) and compressive stress layer depth (DOL). CS and DOL were determined by measuring the difference in refractive index between the glass surface and the inside using a surface stress meter (FSM-6000LE manufactured by Orihara Seisakusho).

(Measurement of Na ion concentration)
The concentration of Na ions in the chemical strengthening tank was measured with an atomic absorption photometer (Hitachi High-Tech Z-2310) by dissolving the recovered molten salt in an aqueous nitric acid solution and adding cesium chloride to suppress ion interference. Quantified by

(Determining the amount of waste)
After the molten salt regeneration process, the molten salt and precipitates that could not be recovered for transferring the recycled molten salt to the strengthening tank are defined as waste, and the total amount of the waste is defined as the amount of waste. For Examples 1-1 to 1-6 and Comparative Examples 2-1 to 2-5, the amount of waste was measured. The amount of waste was determined by calculating the difference between the recycle container weight after recovering the regenerated molten salt solution and the recycle container empty weight.
In addition, the amount of waste in Examples 1-2 to 1-6 and Comparative Examples 2-2 to 2-5 includes the amount of waste discharged up to the previous process of the Example or Comparative Example, and the cumulative amount thereof. Is expressed as the amount of waste.
In Examples 2-1 to 2-6, the waste reduction rate is W1 when the molten salt extracted from the strengthening tank is recycled / reused, and when the entire amount of molten salt extracted from the strengthening tank is discarded. Assuming that the amount of waste of W2 is W2, it was calculated by (W2-W1) / W2 × 100.

Example 1:
[Example 1-1]
(Preparation of molten salt and chemical strengthening treatment)
To a SUS preparation tank / strengthening tank, 2816 g of potassium nitrate, 162 g of potassium carbonate and 22 g of sodium nitrate were added and heated to 430 ° C. with a mantle heater to prepare a deteriorated molten salt. Here, the deterioration represents a state in which a part of K in the molten salt is replaced with Na and the CS value obtained by the chemical strengthening treatment becomes low. The Na ion concentration in the molten salt was 2037 ppm.
Next, an aluminosilicate glass having a total surface area of 0.14 m ² was preheated to 100 ° C. and immersed in the prepared molten salt (430 ° C.) for 8 hours to perform chemical strengthening treatment. Thereafter, the glass was washed with ion exchange water at 100 ° C. and dried at 60 ° C. for 2 hours. When the surface compressive stress (CS value) and the compressive stress layer depth (DOL) of the glass after the chemical strengthening treatment were measured, the CS value was 810 MPa and the DOL was 57 μm.
Further, the Na concentration in the molten salt after the chemical strengthening treatment increased from 2037 ppm to 2126 ppm.

(Melting salt extraction and regeneration process)
301 g (10% by mass of the whole) of the molten salt was extracted from the strengthening tank subjected to the chemical strengthening treatment and transferred to a SUS regeneration tank. The temperature of the regeneration tank was adjusted to 380 ° C., and 7.3 g of potassium orthophosphate trihydrate (K ₃ PO ₄ .3H ₂ O) (2.0 mass of K ₃ PO ₄ with respect to the molten salt subjected to the regeneration treatment) %) Was added, and the mixture was stirred for 2 hours using a stirring motor and four propeller blades, and then allowed to stand for 2 hours or more to precipitate the precipitate, and the molten salt was regenerated.
Thereafter, 263 g of the liquid phase was recovered from the regeneration tank (regeneration tank liquid phase recovery rate 87%), preheated to 430 ° C., and then transferred again to the strengthening tank as a regeneration liquid.
Also, the difference between the amount extracted from the strengthening tank to the regeneration tank and the amount reused as the regeneration solution and sampled for analysis is 56 g of new molten salt (potassium nitrate containing 4 mol% of potassium carbonate) and 3 g of potassium carbonate. The tank was added and replenished to keep the amount of molten salt in the strengthening tank constant.
The Na concentration in the strengthening tank after the regeneration liquid transfer decreased from 2126 ppm to 1970 ppm through the regeneration process. Note that the amount of waste during the regeneration treatment was 38 g, which was 0.013 kg in terms of the amount of waste per kg of molten salt.

[Example 1-2]
An aluminosilicate glass having a total surface area of 0.14 m ² was preheated to 100 ° C. and immersed in the molten salt after finishing Example 1-1 for 8 hours to perform chemical strengthening treatment. Thereafter, the glass was washed with ion exchange water at 100 ° C. and dried at 60 ° C. for 2 hours. The CS value and DOL of the glass after chemical strengthening treatment were 812 MPa and 57 μm, respectively, and the CS value and DOL equivalent to those of Example 1-1 were obtained.
Further, the Na concentration in the molten salt after the chemical strengthening treatment increased from 1970 ppm to 2206 ppm.
The molten salt is extracted and regenerated in the following steps: the amount of molten salt extracted from the strengthening tank is 328 g (11% by mass of the total), and the amount of K ₃ PO ₄ .3H ₂ O to be added is 8.5 g (molten salt to be regenerated). However, it was carried out under the same conditions as in Example 1-1 except that K ₃ PO ₄ was 2.0% by mass.
As for the liquid transfer to the strengthening tank, the liquid was transferred again into the strengthening tank under the same conditions as in Example 1-1 except that the regenerated liquid to be transferred was 245 g (regeneration tank liquid phase recovery rate 75%). Thereafter, 89 g of potassium nitrate and 5 g of potassium carbonate were added to the strengthening tank for replenishment, and the amount of molten salt in the strengthening tank was kept constant.
The Na concentration in the strengthening tank after the regeneration liquid transfer decreased from 2206 ppm to 1998 ppm through the regeneration process. Note that the amount of waste during the regeneration treatment was (39 g + 83 g) = 122 g, which was 0.041 kg when converted to the amount of waste per kg of molten salt.

[Example 1-3]
An aluminosilicate glass having a total surface area of 0.14 m ² was preheated to 100 ° C. and immersed in the molten salt after finishing Example 1-2 for 8 hours to perform chemical strengthening treatment. Thereafter, the glass was washed with ion exchange water at 100 ° C. and dried at 60 ° C. for 2 hours. The CS value and DOL of the glass after chemical strengthening treatment were 813 MPa and 57 μm, respectively, and the CS value and DOL equivalent to those of Example 1-1 were obtained.
Further, the Na concentration in the molten salt after the chemical strengthening treatment increased from 1998 ppm to 2146 ppm.
The molten salt is extracted and regenerated in the following steps: 320 g (11% by mass of the total amount) of molten salt extracted from the strengthening tank, and 8.2 g of the amount of K ₃ PO ₄ · 3H ₂ O to be added (molten salt to be regenerated) However, it was carried out under the same conditions as in Example 1-1 except that K ₃ PO ₄ was 2.0% by mass.
As for the liquid transfer to the strengthening tank, the liquid was transferred again into the strengthening tank under the same conditions as in Example 1-1 except that the regenerated liquid to be transferred was 290 g (recovery tank liquid phase recovery rate 91%). Thereafter, 61 g of potassium nitrate and 3 g of potassium carbonate were added to the strengthening tank for replenishment, and the amount of molten salt in the strengthening tank was kept constant.
The Na concentration in the strengthening tank after the regeneration liquid transfer decreased from 2146 ppm to 1966 ppm through the regeneration process. Note that the amount of waste during the regeneration treatment was (122 g + 30 g) = 152 g, which was 0.050 kg when converted to the amount of waste per kg of molten salt.

[Example 1-4]
An aluminosilicate glass having a total surface area of 0.14 m ² was preheated to 100 ° C. and immersed in the molten salt after completion of Example 1-3 for 8 hours for chemical strengthening treatment. Thereafter, the glass was washed with ion exchange water at 100 ° C. and dried at 60 ° C. for 2 hours. The CS value and DOL of the glass after chemical strengthening treatment were 811 MPa and 56 μm, respectively, and the CS value and DOL equivalent to those of Example 1-1 were obtained.
Further, the Na concentration in the molten salt after the chemical strengthening treatment increased from 1966 ppm to 2123 ppm.
In the extraction and regeneration process of the molten salt, the amount of the molten salt extracted from the strengthening tank was 315 g (11% by mass of the whole), and the amount of K ₃ PO ₄ · 3H ₂ O added was 8.1 g (the molten salt subjected to the regeneration treatment). However, it was carried out under the same conditions as in Example 1-1 except that K ₃ PO ₄ was 2.0% by mass.
As for the liquid transfer to the strengthening tank, the liquid was transferred again into the strengthening tank under the same conditions as in Example 1-1, except that the regenerated liquid to be transferred was 287 g (regeneration tank liquid phase recovery rate 91%). Thereafter, 57 g of potassium nitrate and 3 g of potassium carbonate were added to the strengthening tank and supplemented to keep the amount of molten salt in the strengthening tank constant.
The Na concentration in the strengthening tank after the regeneration liquid transfer decreased from 2123 ppm to 1978 ppm through the regeneration process. Note that the amount of waste during the regeneration treatment was (152 g + 28 g) = 180 g, which was 0.06 kg in terms of the amount of waste per kg of molten salt.

[Example 1-5]
An aluminosilicate glass having a total surface area of 0.14 m ² was preheated to 100 ° C. and immersed in the molten salt after finishing Example 1-4 for 8 hours to perform chemical strengthening treatment. Thereafter, the glass was washed with ion exchange water at 100 ° C. and dried at 60 ° C. for 2 hours. The CS value and DOL of the glass after chemical strengthening treatment were 808 MPa and 56 μm, respectively, and the CS value and DOL equivalent to those of Example 1-1 were obtained.
Moreover, the Na concentration in the molten salt after the chemical strengthening treatment increased from 1978 ppm to 2158 ppm.
The molten salt is extracted and regenerated in the amount of 311 g (10% by mass of the total amount) of molten salt extracted from the strengthening tank and 8.0 g (molten salt to be regenerated) of K ₃ PO ₄ .3H ₂ O to be added. However, it was carried out under the same conditions as in Example 1-1 except that K ₃ PO ₄ was 2.0% by mass.
As for the liquid transfer to the strengthening tank, the liquid was transferred again into the strengthening tank under the same conditions as in Example 1-1 except that the regenerated liquid to be transferred was changed to 282 g (regeneration tank liquid phase recovery rate 91%). Thereafter, 48 g of potassium nitrate and 3 g of potassium carbonate were added to the strengthening tank for replenishment, and the amount of molten salt in the strengthening tank was kept constant.
The Na concentration in the strengthening tank after the regeneration liquid transfer decreased from 2158 ppm to 1989 ppm through the regeneration process. Note that the amount of waste during the regeneration treatment was (180 g + 28 g) = 208 g, which was 0.07 kg in terms of the amount of waste per kg of molten salt.

[Example 1-6]
Aluminosilicate glass having a total surface area of 0.14 m ² was preheated to 100 ° C. and immersed in the molten salt after finishing Example 1-5 for 8 hours to perform chemical strengthening treatment. Thereafter, the glass was washed with ion exchange water at 100 ° C. and dried at 60 ° C. for 2 hours. The CS value and DOL of the glass after the chemical strengthening treatment were 814 MPa and 55 μm, respectively, and the CS value and DOL equivalent to those of Example 1-1 were obtained.
Further, the Na concentration in the molten salt after the chemical strengthening treatment increased from 1989 ppm to 2151 ppm.
The molten salt is extracted and regenerated in the following steps: 312 g of molten salt extracted from the strengthening tank (11% by mass of the total), and 8.2 g of molten K ₃ PO ₄ .3H ₂ O to be added (molten salt to be regenerated) However, it was carried out under the same conditions as in Example 1-1 except that K ₃ PO ₄ was 2.0% by mass.
As for the liquid transfer to the strengthening tank, the liquid was transferred again into the strengthening tank under the same conditions as in Example 1-1 except that the regenerated liquid to be transferred was 284 g (regeneration tank liquid phase recovery rate 91%). Thereafter, 43 g of potassium nitrate and 2 g of potassium carbonate were added to the strengthening tank for replenishment, and the amount of molten salt in the strengthening tank was kept constant.
The Na concentration in the strengthening tank after the regeneration liquid transfer decreased from 2151 ppm to 1961 ppm through the regeneration process. The amount of waste during the regeneration treatment was (208 g + 28 g) = 236 g, which was 0.08 kg in terms of the amount of waste per kg of molten salt.

Comparative Example 1:
[Comparative Example 1-1]
An aluminosilicate glass having a total surface area of 0.14 m ² is preheated to 100 ° C., the chemical strengthening treatment in Example 1-1 is finished, and immersed in a molten salt (Na concentration: 2126 ppm) that has not been regenerated for 8 hours. Chemical strengthening treatment was performed. Thereafter, the glass was washed with ion exchange water at 100 ° C. and dried at 60 ° C. for 2 hours.
Further, the Na concentration in the molten salt after the chemical strengthening treatment increased from 2123 ppm to 2354 ppm.

[Comparative Example 1-2]
An aluminosilicate glass having a total surface area of 0.14 m ² was preheated to 100 ° C. and immersed in the molten salt after completion of Comparative Example 1-1 for 8 hours for chemical strengthening treatment. Thereafter, the glass was washed with ion exchange water at 100 ° C. and dried at 60 ° C. for 2 hours. The CS value and DOL of the glass after the chemical strengthening treatment were 797 MPa and 62 μm, respectively.
Further, the Na concentration in the molten salt after the chemical strengthening treatment increased from 2354 ppm to 2497 ppm.

[Comparative Example 1-3]
An aluminosilicate glass having a total surface area of 0.14 m ² was preheated to 100 ° C. and immersed in the molten salt after completion of Comparative Example 1-2 for 8 hours to perform chemical strengthening treatment. Thereafter, the glass was washed with ion exchange water at 100 ° C. and dried at 60 ° C. for 2 hours.
Further, the Na concentration in the molten salt after the chemical strengthening treatment increased from 2497 ppm to 2661 ppm.

[Comparative Example 1-4]
An aluminosilicate glass having a total surface area of 0.14 m ² was preheated to 100 ° C. and immersed in the molten salt after completion of Comparative Example 1-3 for 8 hours to perform chemical strengthening treatment. Thereafter, the glass was washed with ion exchange water at 100 ° C. and dried at 60 ° C. for 2 hours.
Further, the Na concentration in the molten salt after the chemical strengthening treatment increased from 2661 ppm to 2842 ppm.

[Comparative Example 1-5]
The aluminosilicate glass having a total surface area of 0.14 m ² was preheated to 100 ° C. and immersed in the molten salt after the completion of Comparative Example 1-4 for 8 hours for chemical strengthening treatment. Thereafter, the glass was washed with ion exchange water at 100 ° C. and dried at 60 ° C. for 2 hours. The CS value and DOL of the glass after the chemical strengthening treatment were 789 MPa and 61 μm, respectively.
Further, the Na concentration in the molten salt after the chemical strengthening treatment increased from 2842 ppm to 2999 ppm.

Comparative Example 2:
[Comparative Example 2-1]
After chemical strengthening treatment, 301 g of molten salt is extracted from the strengthening tank, and the entire amount (301 g) of the molten salt is discarded without regenerating, and 301 g of new molten salt (potassium nitrate containing 4 mol% of potassium carbonate) is used in the strengthening tank. Except for the addition, the glass was chemically strengthened and the molten salt in the strengthening tank was exchanged under the same conditions as in Example 1-1.
Here, since no regeneration treatment was performed, the amount of waste was 301 g because it corresponds to the total amount of molten salt extracted from the strengthening tank, and was 0.100 kg when converted to the amount of waste per kg of molten salt. .

[Comparative Example 2-2]
Aluminosilicate glass having a total surface area of 0.14 m ² was preheated to 100 ° C. and immersed in the molten salt for 8 hours after the completion of Comparative Example 2-1, for chemical strengthening treatment. Thereafter, the glass was washed with ion exchange water at 100 ° C. and dried at 60 ° C. for 2 hours.
After the chemical strengthening treatment, 328 g of the molten salt was extracted from the strengthening tank, the entire amount was discarded, and 328 g of new molten salt (potassium nitrate containing 4 mol% of potassium carbonate) was put into the strengthening tank. The amount of waste at this time was (301 g + 328 g) = 629 g, which was 0.210 kg when converted to the amount of waste per kg of molten salt.

[Comparative Example 2-3]
Aluminosilicate glass having a total surface area of 0.14 m ² was preheated to 100 ° C. and immersed in the molten salt after completion of Comparative Example 2-2 for 8 hours to perform chemical strengthening treatment. Thereafter, the glass was washed with ion exchange water at 100 ° C. and dried at 60 ° C. for 2 hours.
After the chemical strengthening treatment, 320 g of molten salt was extracted from the strengthening tank, the entire amount was discarded, and 320 g of new molten salt (potassium nitrate containing 4 mol% of potassium carbonate) was charged into the strengthening tank. The amount of waste at this time was (629 g + 320 g) = 949 g, which was 0.316 kg in terms of the amount of waste per kg of molten salt.

[Comparative Example 2-4]
Aluminosilicate glass having a total surface area of 0.14 m ² was preheated to 100 ° C. and immersed in the molten salt after completion of Comparative Example 2-3 for 8 hours to perform chemical strengthening treatment. Thereafter, the glass was washed with ion exchange water at 100 ° C. and dried at 60 ° C. for 2 hours.
After the chemical strengthening treatment, 315 g of the molten salt was extracted from the strengthening tank, the entire amount was discarded, and 315 g of a new molten salt (potassium nitrate containing 4 mol% of potassium carbonate) was put into the strengthening tank. The amount of waste at this time was (949 g + 315 g) = 1264 g, which was 0.421 kg in terms of the amount of waste per kg of molten salt.

[Comparative Example 2-5]
Aluminosilicate glass having a total surface area of 0.14 m ² was preheated to 100 ° C. and immersed in the molten salt after completion of Comparative Example 2-4 for 8 hours for chemical strengthening treatment. Thereafter, the glass was washed with ion exchange water at 100 ° C. and dried at 60 ° C. for 2 hours.
After the chemical strengthening treatment, 311 g of the molten salt was extracted from the strengthening tank, the entire amount was discarded, and 311 g of new molten salt (potassium nitrate containing 4 mol% of potassium carbonate) was charged into the strengthening tank. The amount of waste at this time was (1264 g + 311 g) = 1575 g, which was 0.525 kg in terms of the amount of waste per kg of molten salt.

[Comparative Example 2-6]
An aluminosilicate glass having a total surface area of 0.14 m ² was preheated to 100 ° C. and immersed in the molten salt after completion of Comparative Example 2-5 for 8 hours for chemical strengthening treatment. Thereafter, the glass was washed with ion exchange water at 100 ° C. and dried at 60 ° C. for 2 hours.
After the chemical strengthening treatment, 313 g of the molten salt was extracted from the strengthening tank, the entire amount was discarded, and 313 g of new molten salt (potassium nitrate containing 4 mol% of potassium carbonate) was put into the strengthening tank. The amount of waste at this time was (1575 g + 313 g) = 1888 g, which was 0.629 kg in terms of the amount of waste per kg of molten salt.

Na concentration in molten salt, regeneration conditions, CS value and DOL in Example 1 (1-1 to 1-6), and Na concentration in molten salt in Comparative Example 1 (1-1 to 1-5) Table 1 shows the reproduction condition, CS value, and DOL. Furthermore, the graph showing the relationship between the glass processing area per molten salt weight of these Example 1 and Comparative Example 1 and the Na density | concentration of a reinforcement | strengthening tank in FIG. 2, The glass processing area per molten salt weight, CS value, and FIG. A graph showing the relationship is shown in FIG.

Table 2 shows the amount of waste in Example 1 (1-1 to 1-6) and the amount of waste in Comparative Example 2 (2-1 to 2-6). Further, when the entire amount of the molten salt extracted from the strengthening tank without being regenerated is discarded (Comparative Examples 2-1 to 2-6), when the regenerating process is performed (Examples 1-1 to 1-6) ) Is the waste reduction rate (%) and is also shown in Table 2. Furthermore, the graph showing the relationship between the glass processing area per molten salt weight and the amount of waste in these Example 1 and Comparative Example 2 is shown in FIG. 4, with the glass processing area per molten salt weight and the waste reduction rate. A graph showing the relationship is shown in FIG.

From Table 1, about 10% of the molten salt in the strengthening tank subjected to the chemical strengthening treatment is extracted, subjected to a regeneration treatment, and returned to the strengthening tank again, so that the Na concentration in the molten salt is changed to that before the chemical strengthening treatment. It was able to reduce to the same level as. That is, it was found that by performing the regeneration treatment, a high CS value can be stably given over a long period in the chemical strengthening treatment of glass.

Although a part of the molten salt subjected to the chemical strengthening treatment is extracted and the entire amount is discarded without replacement and replaced with a new molten salt, a high CS value can be imparted to the glass. The amount of waste is very large. On the other hand, when adopting the method for producing chemically strengthened glass with a regeneration treatment step according to the present invention, in addition to stably obtaining a CS value as high as the conventional method of discarding the entire amount, from Table 2, The amount of waste can be reduced to 20% or less than the conventional amount.

Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on a Japanese patent application filed on September 18, 2012 (Japanese Patent Application No. 2012-205040), the contents of which are incorporated herein by reference.

In the method for producing chemically tempered glass according to the present invention, a part of the molten salt is taken out from the tempering tank and subjected to a regeneration treatment, and the recycled molten salt is reused to be subjected to the chemical strengthening treatment of the glass. By adopting this production method, chemically tempered glass with stable quality (CS value) can be continuously produced with one-step tempering, as well as improving throughput, drastically reducing waste amount, and chemical strengthening. It is also possible to reduce the amount of molten salt raw material.

1 Chemical strengthening tank (strengthening tank, first tank)
2 Regeneration tank (settlement tank, second tank)
3 Preparation tank 4 Molten salt transfer means

Claims

A method for producing chemically strengthened glass, comprising immersing glass containing sodium in a first tank comprising a molten salt containing potassium nitrate, and forming a compressive stress layer on the surface of the glass,
Transferring a part of the molten salt in the first tank to the second tank;
Adding potassium phosphate to the molten salt in the transferred second tank,
Separating the sodium compound precipitated in the molten salt in the second tank after the addition of the potassium phosphate from the molten salt; and transferring the molten salt after the sodium compound separation to the first tank;
A method for producing chemically strengthened glass, comprising:
The first temperature T 2 of the molten salt temperature T 1 and the second tank of the molten salt in the tank satisfy the relation of T 1 ≧ T 2, the manufacturing method of chemically strengthened glass according to claim 1.
The method for producing chemically strengthened glass according to claim 1 or 2, wherein the molten salt in the first tank further contains potassium carbonate.
The method for producing chemically strengthened glass according to any one of claims 1 to 3, wherein the potassium phosphate is potassium orthophosphate.