JP6241309B2 - Method for producing regenerated salt for chemically strengthening glass and method for producing chemically strengthened glass - Google Patents

Description

  The present invention relates to a method for producing a regenerated salt for glass chemical strengthening obtained by regenerating a molten salt used for chemical strengthening treatment and a method for producing chemically strengthened glass.

  Glass that has been chemically strengthened by ion exchange or the like (hereinafter sometimes simply referred to as “chemically tempered glass”) is used for cover glasses and display glass substrates of display devices such as mobile phones, smartphones, and tablet terminals. ing.

  Chemical strengthening treatment by ion exchange compresses the glass surface by substituting metal ions with a small ionic radius (for example, Na ions) and metal ions with a larger ionic radius (for example, K ions) contained in the glass. This is a process for generating a stress layer and improving the strength of the glass.

  In the case of producing chemically strengthened glass by ion exchange of Na in glass and K in molten salt in molten salt containing potassium nitrate (potassium nitrate molten salt), Na ions in the glass are molten salt by chemical strengthening treatment. The Na concentration in the molten salt is increased by melting into the molten salt. Since the surface compressive stress (hereinafter also referred to as CS), which is one of the characteristics of chemical strengthening, decreases as the Na concentration in the potassium nitrate molten salt increases, if the CS of the resulting chemically strengthened glass falls below the standard value, the melting It is necessary to discard the salt and use new molten salt.

  The deteriorated molten salt in which the desired CS cannot be obtained by the chemical strengthening treatment is usually allowed to cool and solidify, and then crushed into small blocks and discarded. However, the treatment method has a problem that a deteriorated molten salt (hereinafter also referred to as a deteriorated salt) cannot be used again, and a large amount of new salt has to be added.

  Therefore, in Patent Document 1, it is assumed that Li or Cs in the glass component is mixed as an impurity in the molten salt, and that the ion exchange ability of the molten salt is reduced, and the salt in a high temperature molten state is added to the water in the tank. A method of obtaining a regenerated salt by allowing it to fall into a shower and dissolving, cooling and separating the molten salt in the water is disclosed.

JP 58-194761 A

  By the way, nitrates such as potassium nitrate have a property of generating oxygen when heated, and it is known that there is a risk of explosion especially when the nitrate is in a powder form. For this reason, careful handling of powdered nitrate is required. In addition to this, in Japan, for example, the Fire Service Act (Act No. 186 of 1948), the Cabinet Order on the Regulation of Dangerous Goods (Cabinet Order No. 306 of 1944), and the Dangerous Goods Testing and According to the dangerous goods judgment test stipulated in the ministerial ordinance on properties (February 17, 1989, Ministry of Autonomy Ordinance No. 1), 160 times per minute while rotating a mesh sieve with a mesh of 2 mm If the screen is shaken and the mesh sieve passes through the mesh screen for 30 minutes, it is judged as the first class of dangerous materials (oxidizing solids) under the Fire Service Act. In some cases, there may be significant legal restrictions on transportation and storage.

  The method described in Patent Document 1 is useful in that the deteriorated salt can be used again, but no consideration has been given to the problem of handling the regenerated salt.

  Therefore, an object of the present invention is to provide a method for producing a regenerated salt for glass chemical strengthening and a method for producing chemically strengthened glass, which suppresses the disposal of deteriorated salts and the increase in waste water costs, and is excellent in handleability.

  As a result of earnest study, the present inventors dissolved the deteriorated salt after being used in the chemical strengthening treatment in water, and cooled the aqueous solution to precipitate the regenerated salt so as not to exceed a predetermined cooling rate. It has been found that the powder rate of the regenerated salt can be lowered by cooling to a low temperature, and the present invention has been completed.

That is, the present invention relates to the following (1) to (4).
(1) A method for producing a regenerated salt for strengthening glass chemistry,
A dissolution step of dissolving the salt after glass chemical strengthening treatment in water;
A precipitation step of cooling the aqueous solution obtained in the dissolution step to precipitate a regenerated salt,
A method for producing a regenerated salt for strengthening glass chemistry, wherein the aqueous solution is cooled at a cooling rate not exceeding 8.5 ° C./h during all periods of the precipitation step.
(2) The method for producing a regenerated salt for glass chemical strengthening according to (1), further comprising a dehydration step of dehydrating the regenerated salt by centrifugation or filtration after the precipitation step.
(3) The method for producing a regenerated salt for glass chemical strengthening according to (1) or (2), wherein the regenerated salt for glass chemical strengthening contains potassium nitrate as a main component.
(4) A method for producing chemically strengthened glass, comprising subjecting glass to a chemical strengthening treatment using the regenerated salt obtained by the method for producing a regenerated salt for glass chemical strengthening according to (1) to (3) above.

  According to the method for producing a regenerated salt for glass chemical strengthening according to the present invention, the degraded salt after the chemical strengthening treatment that has been conventionally discarded can be used again for the chemical strengthening treatment, which is economically useful. In addition, since the amount of discarded deteriorated salt can be reduced, it is possible to reduce the risk and cost associated with transporting the deteriorated salt to be discarded, and to reduce the environmental load. Furthermore, by cooling the aqueous solution at a cooling rate not exceeding 8.5 ° C./h during the entire precipitation step, the powder rate of the regenerated salt is lowered, and the handleability and safety of the regenerated salt are improved.

  In addition, according to the method for producing chemically strengthened glass according to the present invention, the surface compressive stress, the surface compressive stress depth (hereinafter also referred to as DOL) equivalent to the chemically strengthened glass chemically strengthened using a new salt, mechanical Chemically tempered glass having strength and transmittance can be produced.

FIG. 1 is a solubility curve showing a measured value of solubility of a salt that can be contained in a molten salt after glass chemical strengthening treatment with respect to 100 g of water. In (a), the regenerated salt obtained by cooling the aqueous solution from about 100 ° C. to room temperature (about 25 ° C.) over 16 hours at a cooling rate not exceeding 8.5 ° C./h is dehydrated and dried. It is a figure which shows the photograph crushed to some extent, (b) is a figure which shows the photograph which expanded (a). (A) is a photograph in which a regenerated salt obtained by cooling an aqueous solution from about 100 ° C. to room temperature (about 25 ° C.) over 2 hours at a cooling rate of 8.5 ° C./h or more is dehydrated and dried. (B) is a figure which shows the photograph which expanded (a). It is a graph which shows the relationship between a cooling rate and a powder rate. It is a graph which shows the temperature history explaining the calculation method of a cooling rate. It is a table | surface which shows the impurity analysis result contained in degradation potassium nitrate and reproduction | regeneration potassium nitrate. (A) is a graph which shows surface compressive stress (CS), (b) is a graph which shows surface compressive stress depth (DOL). It is a graph which shows the Weibull plot based on the fracture strength by a ring-on-ring test. It is a graph which shows the transmittance | permeability of the wavelength range of 400-1200 nm by the transmittance | permeability measurement.

  Hereinafter, the present invention will be described in detail, but the present invention is not limited to the following embodiments, and can be arbitrarily modified without departing from the gist of the present invention. In this specification, “Na concentration” means a concentration as Na.

<Regeneration of molten salt>
The present invention is a method for producing a regenerated salt for glass chemical strengthening, wherein a molten salt after glass chemical strengthening treatment is dissolved in water, and an aqueous solution obtained in the dissolving step is cooled to precipitate the regenerated salt. And a precipitation step, wherein the aqueous solution is cooled at a cooling rate not exceeding 8.5 ° C./h during the entire period of the precipitation step.

  In the chemical strengthening treatment of glass, Na ions in the glass are ion-exchanged with K ions in the molten salt by immersing the glass as a raw material in a molten salt for glass strengthening (hereinafter also simply referred to as a molten salt). In this process, a compressive stress layer is formed on the glass surface.

  The molten salt in the present invention contains an inorganic potassium salt. As the inorganic potassium salt, those having a melting point below the strain point (usually 500 to 600 ° C.) of the glass to be chemically strengthened are preferable. In the present invention, a molten salt containing potassium nitrate (melting point 330 ° C.) as a main component is preferable. If potassium nitrate is the main component, it is preferable because it is in a molten state below the strain point of glass and is easy to handle in the operating temperature range. Here, the main component means that the content in the molten salt is 50% by mass or more.

The molten salt is further selected from the group consisting of K ₂ CO ₃ , Na ₂ CO ₃ , KHCO ₃ , NaHCO ₃ , K ₃ PO ₄ , Na ₃ PO ₄ , K ₂ SO ₄ , Na ₂ SO ₄ , KOH and NaOH. It may contain at least one salt.

For example, when K ₂ CO ₃ is added to a molten salt containing potassium nitrate as a main component and glass is chemically strengthened, the content of K ₂ CO ₃ in the molten salt is 0.1% by mass or more, and chemical strengthening is performed. When the treatment temperature is 350 to 500 ° C., the chemical strengthening treatment time is preferably 1 minute to 10 hours, more preferably 5 minutes to 8 hours, and further preferably 10 minutes to 4 hours.

  Furthermore, the molten salt used for the chemical strengthening treatment in the present invention may contain other chemical species as long as the effects of the present invention are not impaired, for example, sodium chloride, potassium chloride, sodium borate, boric acid. Examples include alkali chlorides such as potassium and alkali borates. These may be added alone or in combination of two or more.

  The molten salt used for the chemical strengthening treatment of the glass can be produced by a known method, and the chemical strengthening treatment of the glass can be performed by a known method using the molten salt.

The deteriorated molten salt is solidified by cooling or cooling the deteriorated molten salt, which is no longer capable of producing the desired CS in the glass, to a temperature below the melting point of the deteriorated molten salt by the chemical strengthening treatment. When a molten salt containing potassium nitrate is used as the molten salt, the deteriorated salt includes potassium nitrate and sodium nitrate. Depending on the type of salt added to the molten salt, the deteriorated salt includes the potassium salt and sodium salt of the added salt. That is, for example, when potassium carbonate (K ₂ CO ₃ ) is added, the deteriorated salt includes potassium carbonate and sodium carbonate.
The Na concentration in the deteriorated salt is generally 3000 to 20000 mass ppm although it depends on the CS to be generated in the glass.

  In the deteriorated salt, Na is present at a higher concentration than in the molten salt before chemical strengthening treatment. The solid state deteriorated salt having a high Na concentration is taken out and dissolved in water (dissolution step).

The water for dissolving the deteriorated salt is not particularly limited as long as it does not contain excessive impurities, and pure water, distilled water, industrial water, and the like can be used.
The temperature of the aqueous solution after dissolving the deteriorated salt is a temperature lower than the melting point of the salt, preferably 60 to 120 ° C, more preferably 80 to 120 ° C. The temperature of the aqueous solution can be appropriately adjusted by a known method such as a water bath, an oil bath, or a thermostat.
In addition, the density | concentration of the deterioration salt in aqueous solution is so preferable that it is preferable, it is more preferable to melt | dissolve to the saturation solubility in 60 degreeC, and it is further more preferable to melt | dissolve to the saturation solubility at the time of reaching the boiling point of aqueous solution.

  When dissolving the deteriorated salt, it is preferable to dissolve the aqueous solution while stirring since the concentration distribution of the aqueous solution can be made uniform. The stirring speed is usually preferably 50 to 2000 rpm, more preferably 100 to 1000 rpm.

  When the deteriorated salt is completely dissolved in water, the aqueous solution is cooled (precipitation step). In addition, when the desired salt contained in the deteriorated salt is dissolved to saturation solubility, depending on the type of salt and the proportion contained in the deteriorated salt, other salts may not be completely dissolved and remain in the aqueous solution as a solid. There is. In that case, the salt which has not melt | dissolved by filtration etc. is removed, and a filtrate is cooled by the said method.

  Precipitates are formed in the aqueous solution after cooling due to the difference between the maximum salt solubility in the dissolution step and the saturated salt solubility at the temperature when cooled (crystallization). When a molten salt containing potassium nitrate is used, the deteriorated salt and the precipitate include potassium nitrate and sodium nitrate. Further, depending on the type of salt added to the molten salt, the precipitate contains a potassium salt or a sodium salt corresponding to the added salt.

  FIG. 1 is a solubility curve (g / 100 g of water) of measured values showing the temperature dependence of solubility in water for potassium nitrate, sodium nitrate, potassium carbonate and sodium carbonate.

  For example, when a degraded salt containing potassium nitrate as the main component and other three salts of sodium nitrate, potassium carbonate and sodium carbonate is dissolved in an aqueous solution heated to the boiling point, the maximum solubility of each chemical species in the dissolution process And the salt of the difference between the saturated solubility of each chemical species at the temperature when cooled is precipitated as a solid. When the salt to be used as the regenerated salt is potassium nitrate, the potassium nitrate which is the main component of the deteriorated salt is precipitated as a solid in an amount corresponding to the difference. On the other hand, since other chemical species are contained in the deteriorated salt in a smaller amount than the main component potassium nitrate, the respective solubility in the dissolution process is small, and the saturation of each chemical species at the temperature when cooled is achieved. Usually does not exceed solubility. That is, other chemical species hardly precipitate as a solid. Therefore, the precipitate contains potassium nitrate in a higher ratio than the original deteriorated salt, can be used again as a molten salt for glass chemical strengthening treatment, and can be called “regenerated salt”.

  Here, when cooling the aqueous solution in which the deteriorated salt is dissolved, the aqueous solution is cooled (slowly cooled) at a cooling rate not exceeding 8.5 ° C./h. For cooling, a known method such as natural cooling (cooling), air cooling, water cooling, or ice cooling can be used. Cooling is preferably performed from the vicinity of the boiling point to, for example, a temperature of 20 ° C. or lower and a freezing point or higher, and it is more preferable to cool to a temperature of 10 ° C. or lower and a freezing point or higher. The cooling rate can be obtained from the temperature history of the aqueous solution during cooling, and the temperature history can be obtained by arranging a temperature sensor such as a thermocouple in the aqueous solution in which the deteriorated salt is dissolved. It is preferable to use a plurality of temperature sensors. In this case, the temperature history is obtained from an average value of the plurality of temperature sensors.

  Thus, by cooling the aqueous solution at a cooling rate not exceeding 8.5 ° C./h, compared with the case of cooling (rapid cooling) at a cooling rate of 8.5 ° C./h or more, When a sieve having a mesh size of 2 mm is rotated and subjected to vibration 160 times per minute, the ratio of those passing through the mesh sieve in 30 minutes can be reduced. The powder ratio is preferably less than 10% from the viewpoint of handleability and safety.

  In the present invention, the cooling rate refers to an average cooling rate in one hour from an arbitrary time point. For example, the cooling rate at the start of cooling is the slope of an approximate straight line obtained by using the least square method for the temperature history obtained from the temperature measured in one hour from the start of cooling. Thereby, the cooling rate at the arbitrary time in a precipitation process can be determined uniquely.

  The lower limit of the cooling rate is not particularly limited, but the cooling rate is preferably 1.0 ° C./h or more in terms of productivity, and more preferably 3.0 ° C./h or more. preferable.

  FIG. 2 (a) shows a dehydrated salt obtained by slowly cooling an aqueous solution from about 100 ° C. to room temperature (about 25 ° C.) over 16 hours at a cooling rate not exceeding 8.5 ° C./h. It is a figure which shows the photograph which dried and was crushed to some extent, FIG.2 (b) is a figure which shows the photograph which expanded FIG.2 (a). FIG. 3 (a) shows dehydration of the regenerated salt obtained by rapidly cooling the aqueous solution from about 100 ° C. to room temperature (about 25 ° C.) over 2 hours at a cooling rate of 8.5 ° C./h or more. It is a figure which shows the dried photograph, FIG.3 (b) is a figure which shows the photograph which expanded FIG.3 (a).

  Comparing FIGS. 2 (a) and 2 (b) with FIGS. 3 (a) and 3 (b), the aqueous solution was cooled (slowly cooled) at a cooling rate not exceeding 8.5 ° C./h, which resulted in rapid cooling. It can be seen that the regenerated salt is present in a lump and each crystal grows larger than that. On the other hand, it can be seen that the rapidly cooled one contains the regenerated salt in the form of powder and many small crystals (the large crystals cannot be seen). Actually, when the powder ratio was measured, the powder ratio of the slowly cooled one was 8.7%, whereas the powder ratio of the rapidly cooled one was 24.7%.

  This is because, when cooled slowly, nuclei are generated from the portion contacting the bottom or side surface of the container containing the aqueous solution in which the deteriorated salt is dissolved, and each nucleus forms large crystals by rapid growth, whereas rapid cooling is performed. In this case, it is assumed that new nuclei are generated one after another faster than the growth of the nuclei and the crystal does not grow greatly.

  As described above, in the present invention, a low Na concentration salt that can easily handle a deteriorated salt having a high Na concentration by a recrystallization method using a difference in saturation solubility of potassium nitrate between a high temperature region and a low temperature region. Can be played.

  Since the obtained regenerated salt is precipitated in the aqueous solution, solid-liquid separation is performed in order to use it again for the chemical strengthening treatment of glass. For the solid-liquid separation, known methods such as filtration and centrifugation can be used.

  After recovering the regenerated salt by solid-liquid separation, it is preferable to perform a dehydration treatment by a method such as centrifugation or filtration before being reused for the chemical strengthening treatment (dehydration step). By dehydrating, the amount of water in the regenerated salt can be reduced.

  Further, the regenerated salt may be dried by a drying process following a dehydration process such as centrifugation or filtration. A drying temperature should just be 40-200 degreeC normally, and 80-200 degreeC is more preferable. The drying time is usually 10 minutes to 12 hours, and more preferably 1 to 4 hours. Moreover, you may reduce pressure simultaneously with a heating at the time of drying. For the drying, a known method such as a hot plate or heating vacuum drying can be used.

  The regenerated salt that has undergone the dehydration step can be used as a molten salt for glass chemical strengthening treatment by heating to a temperature at which the glass is chemically strengthened.

  In addition, as long as the glass provided to the chemical strengthening process in this invention has a composition which can be strengthened by shaping | molding and a chemical strengthening process, the thing of a various composition can be used. Specific examples include aluminosilicate glass, soda lime glass, borosilicate glass, lead glass, alkali barium glass, and aluminoborosilicate glass. Especially, since aluminosilicate glass has much Na content in glass, the amount of Na substitution in chemical strengthening processing also increases, and deterioration of molten salt is severe. For this reason, it is preferable because the effect of the molten salt regeneration method according to the present invention can be remarkably obtained.

  There are no particular limitations on the method for producing and molding the glass subjected to the chemical strengthening treatment, and the glass can be produced and molded based on known methods. Moreover, the thickness of the glass used for the chemical strengthening treatment and the presence or absence of polishing are also arbitrary.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these.
[Powder rate measurement]
Dissolving potassium nitrate deteriorated salt (hereinafter also simply referred to as “degraded salt”), which can no longer obtain the desired CS by chemical strengthening treatment, in pure water, the cooling capacity of the cooling device from about 85-100 ° C. to room temperature (25 ° C.) By cooling while changing, a regenerated salt of potassium nitrate (hereinafter also simply referred to as regenerated salt) was obtained. The temperature sensors for measuring the cooling rate are arranged at three different locations in the aqueous solution in which the deteriorated salt is dissolved, and temperature histories are created from the temperatures obtained from the three temperature sensors. As shown in FIG. From the slope of the approximate straight line of the temperature history for 1 hour, the cooling rate at the start of cooling was calculated (only examples 3 and 4 described later are displayed). The regeneration of the deteriorated salt by this recrystallization method was performed 6 times in Examples 1 to 6 while changing the cooling capacity so that the cooling rate was different. In any of the examples, the cooling rate at the start of cooling was the highest among the cooling rates in all periods of the precipitation step. Hereinafter, in this embodiment, when simply referred to as a cooling rate, it refers to the cooling rate at the start of cooling.

  The percentage of powder that passes through the mesh sieve in 30 minutes when the obtained regenerated salt is taken out of the aqueous solution and shaken 160 times per minute while rotating the mesh sieve with a mesh opening of 2 mm. Was measured. Table 1 shows the cooling rate and powder ratio obtained.

FIG. 4 is a graph in which the cooling rate obtained in Table 1 is plotted on the horizontal axis and the powder rate is plotted on the vertical axis.
As is clear from FIG. 4, a relationship was observed between the cooling rate and the powder rate that increased as the cooling rate increased. From this, it was found that the powder rate can be kept low by limiting the cooling rate. From FIG. 4, it was demonstrated that the cooling rate should be less than 8.5 ° C./h in order to realize a powder rate of less than 10%, which is a guideline for excellent handling and safety of nitrate. Therefore, in Table 1, Examples 1 to 4 correspond to examples of the present invention, and Examples 5 and 6 correspond to comparative examples.

[Impurity analysis]
Impurities contained in the deteriorated salt (deteriorated KNO ₃ ) in which the desired CS could not be obtained by chemical strengthening treatment and the amount thereof were measured. The measurement was performed by an inductively coupled plasma (ICP) emission spectrometry using an ICP emission analyzer (SPS5520 manufactured by Hitachi High-Tech).
Further, the deteriorated salt is dissolved in pure water, the obtained aqueous solution is gradually cooled at a cooling rate not exceeding 8.5 ° C./h, and impurities contained in the obtained regenerated salt (regenerated KNO ₃ ) and the amount thereof. Was measured in the same manner as the analysis of deteriorated salt. The results are shown in FIG. FIG. 6 also shows the results of analysis of impurities contained in new potassium nitrate (new KNO ₃ , hereinafter also simply referred to as new salt) for comparison.

From FIG. 6, it can be seen that in the regenerated salt obtained by the recrystallization method, the concentrations of Na, Cr and NO ₂ ⁻ in potassium nitrate were greatly reduced. Thus, although it was inferior to a new salt, the refinement | purification of potassium nitrate was realizable by the recrystallization method.

[Chemical tempered glass evaluation]
Subsequently, three types of glasses having different compositions (samples 1 to 3) are cut into a predetermined size, and chemically strengthened under the conditions described below using regenerated salt and new salt, CS of chemically strengthened glass, DOL, ring-on-ring strength, and transmittance were measured.

A CS and DOL
-Chemical strengthening conditions-
Glass material: Samples 1-3
Shape: 50mm x 50mm
Thickness: 0.7mm
Strengthening temperature: 450 ° C
Strengthening time: 1 hour

-Measurement conditions-
The CS and DOL of the glass after chemical strengthening treatment were measured with a surface stress measuring device (FSM-6000 manufactured by Orihara Seisakusho).

  FIG. 7A is a graph showing CS, and FIG. 7B is a graph showing DOL. In the figure, the same shape marks (squares, diamonds, triangles) represent glass having the same composition, the black marks are regenerated salt, and the white marks are chemically strengthened using new salt. Comparing FIG. 7 (a) and FIG. 7 (b), regardless of the difference in the glass composition, the chemical strengthening treatment using the new salt or the chemical strengthening treatment using the regenerated salt is equivalent. CS and DOL were obtained. As shown in FIG. 7A and FIG. 7B, the same result was obtained when the chemical strengthening treatment was performed a plurality of times using the same molten salt. That is, in CS and DOL, there was almost no adverse effect on the chemically strengthened glass due to the regenerated salt.

B Ring-on-ring strength-Conditions for chemical strengthening-
Glass material: Sample 1
Shape: 50mm x 50mm
Thickness: 0.56mm
Strengthening temperature: 450 ° C
Strengthening time: 1 hour

-Ring-on-ring test conditions-
The breaking load of the glass after chemical strengthening treatment was measured in a ring-on-ring test with an upper ring diameter of 10 mm, a lower ring diameter of 30 mm, and a crosshead speed of 1.0 mm / min. UTA-5kN manufactured by Orientec Corp. was used as a destructive testing machine.

  FIG. 8 shows a Weibull plot based on the breaking strength by the ring-on-ring test. The vertical axis represents the fracture probability (Cracability), and the horizontal axis represents the fracture strength (RoR strength). From FIG. 8, it was confirmed that the obtained chemically strengthened glass had the same breaking strength whether it was chemically strengthened using new salt or chemically strengthened using regenerated salt. That is, even in the breaking strength, there was hardly any adverse effect on the chemically strengthened glass due to the regenerated salt.

C Transmittance-Chemical Strengthening Conditions-
Glass material: Sample 1
Shape: 50mm x 50mm
Thickness: 0.7mm
Strengthening temperature: 450 ° C
Strengthening time: 1 hour

-Transmittance measurement-
The transmittance of the glass after the chemical strengthening treatment was measured using a spectrophotometer (UV3100PC, manufactured by Shimadzu Corporation).

  FIG. 9 shows the transmittance in the wavelength region of 400 to 1200 nm. From FIG. 9, the transmittance of the chemically strengthened glass at the first time (after 1 Batch) was slightly decreased by less than 0.1% when using regenerated salt as compared to when using new salt. The transmittance of the chemically tempered glass at the 32nd time (after 32 Batch) was the same as that in the case of using the new salt even when the recycled salt was used. Therefore, in the transmittance, there was almost no adverse effect on the chemically strengthened glass due to the regenerated salt.

  Thus, chemically strengthened glass chemically treated with recycled salt has the same characteristics as chemically strengthened glass chemically treated with new salt in any measurement, and is similar to new salt. In addition, it was demonstrated that chemical strengthening treatment can be performed using regenerated salt.

  According to the present invention, a regenerated salt having the same performance as that of a new salt can be obtained by subjecting the used deteriorated salt provided to the chemically strengthened glass to a regeneration treatment. By this regeneration treatment, the amount of used deteriorated salt discarded can be reduced, and the production of chemically tempered glass can be performed at low cost while reducing the environmental load, and high productivity can be realized.

Claims (4)

A method for producing a regenerated salt for strengthening glass chemistry,
A dissolution step of dissolving the salt after glass chemical strengthening treatment in water;
A precipitation step of cooling the aqueous solution obtained in the dissolution step to precipitate a regenerated salt,
Cooling the aqueous solution at a cooling rate of 4.1 ° C./h or more at the start of the precipitation step; and
A method for producing a regenerated salt for strengthening glass chemistry, wherein the aqueous solution is cooled at a cooling rate not exceeding 8.5 ° C./h during all periods of the precipitation step.   The method for producing a regenerated salt for glass chemical strengthening according to claim 1, further comprising a dehydration step of dehydrating the regenerated salt by centrifugation or filtration after the precipitation step.   The method for producing a regenerated salt for glass chemical strengthening according to claim 1 or 2, wherein the regenerated salt for glass chemical strengthening contains potassium nitrate as a main component.   The manufacturing method of the chemically strengthened glass characterized by carrying out the chemical strengthening process of the glass using the regenerated salt obtained by the manufacturing method of the regenerated salt for glass chemical strengthening of any one of Claims 1-3.