JP2019006615A - Manufacturing method of chemically strengthened glass - Google Patents

Abstract

To provide a method for manufacturing a chemically strengthened glass having strength and appearance quality.SOLUTION: There is related a manufacturing method of a chemically strengthened glass including a chemically strengthening process for ion exchanging Na in a glass and K in an inorganic salt by contacting the glass containing sodium and the inorganic salt containing a specific salt, an acid treatment process for acid treating the glass after the chemically strengthening process, and an alkali treatment process for alkali treating the glass after the acid treatment process. A first embodiment has frequency and sound pressure in ultrasonic cleaning as specific conditions. In a second embodiment, a series of process from the acid treatment process to the alkali treatment process is conducted under a wet environment.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing chemically strengthened glass.

  In a flat panel display device such as a digital camera, a mobile phone, or a personal digital assistant (PDA), a thin plate-like cover glass that has a wider area than the image display portion in order to enhance the protection and aesthetics of the display. Is placed in front of the display. Although glass has a high theoretical strength, the strength is greatly reduced due to scratches. Therefore, a chemically strengthened glass with a compressive stress layer formed on the glass surface by ion exchange or the like is used for the cover glass that requires strength. Yes.

  With the demand for weight reduction and thinning of the flat panel display device, it is required to make the cover glass itself thin. Accordingly, the cover glass is required to have further strength on the surface in order to satisfy its purpose.

  As one of the techniques for improving the strength of glass, Patent Document 1 discloses a method for producing chemically strengthened glass in which an acid treatment step and an alkali treatment step are performed after a chemical strengthening step with an inorganic salt containing a specific salt. . According to the manufacturing method described in Patent Document 1, the surface strength is significantly higher than that of chemically strengthened glass obtained by conventional chemical strengthening without performing polishing or etching treatment using hydrofluoric acid after chemical strengthening. High chemical tempered glass can be obtained.

  On the other hand, in the mass production process of chemically strengthened glass, ultrasonic cleaning is performed between the processes. In ultrasonic cleaning, glass is immersed in a cleaning liquid and ultrasonic vibration is applied to the cleaning liquid. At this time, particles such as water molecules in the cleaning liquid vibrate at high speed and water is rapidly vaporized to generate bubbles, and the bubbles are repeatedly condensed and disappeared repeatedly. It becomes a state. This phenomenon is called cavitation. Contaminants are peeled from the glass by cavitation and easily dispersed in the cleaning liquid, so that the glass can be cleaned effectively. In particular, ultrasonic cleaning is an effective technique when glass having a shape that is difficult to physically clean, such as brush cleaning.

  Patent Document 2 discloses a method of manufacturing a glass substrate for magnetic disk including a cleaning step of ultrasonically cleaning the glass substrate for magnetic disk, and when the size of foreign matter to be removed is mainly 1.0 μm or less. A manufacturing method is disclosed in which the frequency of ultrasonic waves is 80 kHz to 120 kHz, and the sound pressure of ultrasonic waves is 1.5 mV to 2.5 mV.

  Further, Patent Document 3 discloses a method of cleaning white burns of glass products by ultrasonic cleaning using a cleaning agent and removing white burns from glass products, with a frequency of 20 to 400 kHz and a sound of 10 to 150 mV. Disclosed is a method for cleaning white burns of glass products by ultrasonic cleaning of pressure.

International Publication No. 2015/008763 JP 2010-238298 A JP 2007-253065 A

  As shown in FIG. 1A, a method for producing chemically tempered glass described in Patent Document 1 including a chemical strengthening step with an inorganic salt containing a specific salt (hereinafter also abbreviated as a manufacturing method including a chemical strengthening step with an inorganic salt containing a specific salt). In order to increase the cleanliness of the glass, it is usually preferable to perform a washing step after the chemical strengthening treatment, a water rinse in the acid treatment step, a water rinse in the alkali treatment step, and a washing step after the alkali treatment step. These cleaning processes may be ultrasonic cleaning performed by applying ultrasonic waves.

  In addition, as shown in FIG. 1B, in a method for producing chemically tempered glass including a conventional chemical strengthening step using an inorganic salt that does not contain a specific salt (hereinafter, also abbreviated as a production method including a conventional chemical strengthening step), A cleaning step is performed after the strengthening step.

  The inventors of the present invention drastically improve the surface strength of the chemically strengthened glass obtained by the manufacturing method including the chemical strengthening step using the inorganic salt containing the specific salt as compared with the manufacturing method including the conventional chemical strengthening step. However, when ultrasonic cleaning is performed under normal conditions to ensure the appearance quality of chemically strengthened glass, the glass is damaged, and the chemical strength obtained by the manufacturing method including the conventional chemical strengthening process is achieved. It has been found that there is a problem of lowering to the same level as tempered glass.

  Such a problem is manifested because a manufacturing method including a chemical strengthening step using an inorganic salt containing a specific salt can achieve a significantly higher surface strength than a conventional manufacturing method including a chemical strengthening step. is there.

  Accordingly, an object of the present invention is to provide a method for producing a chemically strengthened glass having both strength and appearance quality.

  In the method for producing chemically strengthened glass in which an acid treatment step and an alkali treatment step are performed after a chemical strengthening step with an inorganic salt containing a specific salt, the present inventors have made ultrasonic cleaning a condition in a specific range or an acid treatment. By performing a series of processes from the process to the alkali treatment process in a wet environment, it is possible to suppress the strength of chemically strengthened glass from being reduced by ultrasonic cleaning, and when ultrasonic cleaning is performed multiple times. Discovered that chemically tempered glass having both strength and appearance quality can be obtained by performing the process between ultrasonic cleaning and ultrasonic cleaning in a wet environment, and completed the present invention.

That is, the present invention is as follows.
1. A glass containing sodium is selected from the group consisting of potassium nitrate and 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. A chemical strengthening step for ion-exchange of Na in the glass and K in the inorganic salt by contacting with an inorganic salt containing at least one selected salt, and the glass is acid-treated after the chemical strengthening step. An acid treatment step, a method for producing chemically strengthened glass comprising an alkali treatment step of alkali-treating the glass after the acid treatment step,
The manufacturing method of chemically strengthened glass further including at least 1 washing process chosen from following (1)-(4).
(1) Cleaning treatment with ultrasonic waves having a frequency of 25 kHz to 80 kHz and a sound pressure of 80 mV or less during the acid treatment step (2) A frequency of 25 kHz to 80 kHz after the acid treatment step and before the alkali treatment step, Cleaning treatment with ultrasonic waves with a sound pressure of 80 mV or less (3) Cleaning treatment with ultrasonic waves with a frequency of 25 kHz to 80 kHz and sound pressures of 80 mV or less during the alkali treatment step (4) After the alkali treatment step, a frequency of 25 kHz or more 1. Cleaning treatment with ultrasonic waves of 80 kHz or less and sound pressure of 80 mV or less 2. The method for producing chemically tempered glass as described in 1 above, wherein when performing at least one cleaning treatment selected from (1) to (4) a plurality of times, a step between the cleaning treatments is performed in a wet environment.
3. 3. The method for producing chemically tempered glass according to 1 or 2, wherein a drying step is included after the alkali treatment step, and the process from the acid treatment step to before the drying step is performed in a wet environment.
4). The method for producing chemically tempered glass according to any one of 1 to 3, wherein the chemically tempered glass is a cover glass.
5. A glass containing sodium is selected from the group consisting of potassium nitrate and 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. A chemical strengthening step for ion-exchange of Na in the glass and K in the inorganic salt by contacting with an inorganic salt containing at least one selected salt, and the glass is acid-treated after the chemical strengthening step. An acid treatment step, a method for producing chemically strengthened glass comprising an alkali treatment step of alkali-treating the glass after the acid treatment step,
A method for producing chemically strengthened glass, wherein a series of steps from the acid treatment step to the alkali treatment step is performed in a wet environment.

  The manufacturing method of the chemically strengthened glass of this invention is a manufacturing method which performs an acid treatment process and an alkali treatment process after the chemical strengthening process by the inorganic salt containing a specific salt. According to the first embodiment of the present invention, by including an ultrasonic cleaning process in which the frequency and sound pressure are in a specific range, the occurrence of submicron-order damage due to ultrasonic cleaning is prevented, and the surface is greatly improved. It is possible to produce chemically strengthened glass that suppresses strength reduction and has both strength and appearance quality.

  In addition, according to the second embodiment of the present invention, by performing a series of steps from the acid treatment step to the alkali treatment step in a wet environment, appearance quality can be ensured without performing ultrasonic cleaning. It is possible to produce a chemically strengthened glass having both strength and appearance quality.

FIG. 1A is a schematic diagram for explaining a process of a method for producing chemically strengthened glass including a chemical strengthening process using an inorganic salt containing a specific salt. Moreover, FIG. 1B is the schematic for demonstrating the process of the manufacturing method of the conventional chemically strengthened glass including the chemical strengthening process by the inorganic salt which does not contain a specific salt. FIG. 2 is a schematic diagram for explaining a method of measuring sound pressure in ultrasonic cleaning. 3 (a) to 3 (d) are schematic views showing a process for producing chemically strengthened glass according to the present invention. FIG. 4 is a schematic diagram for explaining a ball-on-ring test method. FIG. 5 shows the results of evaluating the surface strength of the chemically strengthened glass (composition: glass A) obtained in the examples or comparative examples. FIG. 6 shows the results of evaluating the surface strength of the chemically strengthened glass (composition: glass B) obtained in the examples or comparative examples. FIG. 7 shows the results of evaluating the surface strength of the chemically strengthened glass (composition: glass C) obtained in the examples or comparative examples. FIG. 8 shows the results of evaluating the surface strength of the chemically strengthened glass (composition: glass D) obtained in the examples or comparative examples.

  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. Here, in the present specification, “mass%” and “weight%”, “mass ppm” and “weight ppm” have the same meaning. In addition, when “ppm” is simply described, it indicates “weight ppm”.

The method for producing chemically tempered glass of the present invention (hereinafter, also referred to as the production method of the present invention) is obtained by converting a glass containing sodium into potassium nitrate and K ₂ CO ₃ , Na ₂ CO ₃ , KHCO ₃ , NaHCO ₃ , K ₃ PO ₄ , By contacting with an inorganic salt containing at least one salt selected from the group consisting of Na ₃ PO ₄ , K ₂ SO ₄ , Na ₂ SO ₄ , KOH and NaOH, Na in the glass and the inorganic salt A chemical strengthening step for ion exchange with K, an acid treatment step for acid-treating the glass after the chemical strengthening step, and an alkali treatment step for alkali-treating the glass after the acid treatment step.

〔Ultrasonic cleaning〕
1st embodiment of this invention is characterized by including the at least 1 washing process chosen from following (1)-(4).
(1) Cleaning treatment with ultrasonic waves having a frequency of 25 kHz to 80 kHz and a sound pressure of 80 mV or less during the acid treatment step (2) A frequency of 25 kHz to 80 kHz after the acid treatment step and before the alkali treatment step, Cleaning treatment with ultrasonic waves with a sound pressure of 80 mV or less (3) Cleaning treatment with ultrasonic waves with a frequency of 25 kHz to 80 kHz and sound pressures of 80 mV or less during the alkali treatment step (4) After the alkali treatment step, a frequency of 25 kHz or more Cleaning process using ultrasonic waves of 80 kHz or less and sound pressure of 80 mV or less The cleaning processes (1) to (4) will be described below.

  About (1), by performing ultrasonic cleaning during the acid treatment step, the inorganic salt used in the chemical strengthening step and the deposits such as the glass elution generated during the acid treatment step are efficiently removed from the glass surface. The effect of acid treatment can be enhanced to improve the strength and cleanliness of the glass. The sound pressure of ultrasonic cleaning during the acid treatment step is 80 mV or less, preferably 60 mV or less, more preferably 40 mV or less. By setting the sound pressure to 80 mV or less, it is possible to suppress a decrease in surface strength due to ultrasonic cleaning.

  About (2), by performing ultrasonic cleaning after the acid treatment step and before the alkali treatment step, the deposits such as acid and glass eluate used in the acid treatment step are efficiently removed from the glass surface. The effect of the treatment can be enhanced to improve the strength and cleanliness of the glass. The sound pressure of ultrasonic cleaning performed after the acid treatment step and before the alkali treatment step is 80 mV or less, preferably 60 mV or less, more preferably 40 mV or less. By setting the sound pressure to 80 mV or less, it is possible to suppress a decrease in surface strength due to ultrasonic cleaning.

  About (3), by performing ultrasonic cleaning during the alkali treatment step, the acid used in the acid treatment step, and the deposits such as the glass eluate generated during the alkali treatment step are efficiently removed from the glass surface, The effect of the alkali treatment can be enhanced to improve the strength and cleanliness of the glass. The sound pressure of the ultrasonic cleaning is 80 mV or less, preferably 60 mV or less, more preferably 40 mV or less. By setting the sound pressure to 80 mV or less, it is possible to suppress a decrease in surface strength due to ultrasonic cleaning.

  About said (4), by performing ultrasonic cleaning after an alkali treatment process, the deposits, such as the alkali used for the alkali treatment process, and a glass elution thing, are removed efficiently from the glass surface, and the intensity | strength and cleanliness of glass Can be improved. The sound pressure of the ultrasonic cleaning is 80 mV or less, preferably 60 mV or less, more preferably 40 mV or less. By setting the sound pressure to 80 mV or less, it is possible to suppress a decrease in surface strength due to ultrasonic cleaning.

  Regarding the above (1) to (4), the lower limit of the output of the ultrasonic wave is not particularly limited, but the sound pressure is usually preferably 10 mV or more from the viewpoint of ensuring the appearance quality.

  The sound pressure of ultrasonic cleaning can be measured using a commercially available ultrasonic sound pressure meter (for example, 19001D type main body 11003 type sensor manufactured by Kaijo Corporation). Depending on the position of the ultrasonic transducer and the configuration in the cleaning tank, sound pressure distribution may occur in the cleaning tank. Therefore, the sensor part is manually swept at the upper, middle, and lower parts in the cleaning tank to maximize the sound pressure. Measure.

  FIG. 2 shows a schematic diagram for explaining a sound pressure measuring method. As shown in FIG. 2, the sensor portion 12 of the ultrasonic sound pressure gauge 11 is manually swept in the direction of the arrow in each of the upper glass plate 14, the middle glass plate 15, and the lower glass plate 16 in the cleaning tank 13. Measure the maximum sound pressure.

  About said (1)-(4), the frequency of an ultrasonic wave is 25 kHz or more, Preferably it is 38 kHz or more. Moreover, it is 80 kHz or less, Preferably it is 78 kHz or less. By setting the frequency of the ultrasonic wave to 25 kHz or more and 80 kHz or less, an effective cleaning effect can be obtained for foreign matters or the like attached in the cover glass process. Generally, the smaller the frequency value, the easier it is to generate cavitation and the higher the cleaning effect. On the other hand, as the frequency value is larger, the degree of influence on the surface strength by ultrasonic cleaning can be reduced.

  Regarding the above (1) to (4), the cleaning liquid for ultrasonic cleaning is not particularly limited, and examples thereof include aqueous alkali using a surfactant, neutral detergent, pure water, ion-exchanged water, and the like. . The cleaning liquid for ultrasonic cleaning during the acid treatment step (1) and ultrasonic cleaning during the alkali treatment step (3) is pure water or ion exchange from the viewpoint of not inhibiting the acid treatment and alkali treatment. Water is preferred. Examples of the alkali or neutral cleaning agent include caustic soda, a cleaning agent containing a small amount of caustic potash, and a glycol-based cleaning agent.

  Regarding the above (1) to (4), the ultrasonic cleaning temperature is usually preferably 5 ° C. or higher, more preferably 10 ° C. or higher, and usually preferably 100 ° C. or lower, more preferably 90 ° C. or lower. is there.

  As for the above (1) to (4), the shorter the ultrasonic cleaning time is, the more the surface strength can be prevented from lowering due to ultrasonic cleaning. The ultrasonic cleaning time is not particularly limited and can be set as appropriate. Usually, it is preferably 1 to 100 minutes, more preferably 3 to 60 minutes.

[Wet environment]
In 1st embodiment of this invention, when performing at least 1 washing process chosen from said (1)-(4) in multiple times, it is preferable to perform the process between these washing processes in a wet environment.
Thereby, strength and appearance quality can be improved.

  In the first embodiment of the present invention, the appearance quality can be further improved by preferably performing a series of steps from an acid treatment step to an alkali treatment step in a wet environment. For example, when a drying process is further included after the alkali treatment process in the first embodiment, it is preferable that the process is performed in a wet environment from the acid treatment process to before the drying process.

  The second embodiment of the present invention is characterized in that a series of steps from an acid treatment step to an alkali treatment step is performed in a wet environment. By performing a series of steps from an acid treatment step to an alkali treatment step in a wet environment, appearance quality can be ensured without performing ultrasonic cleaning.

  In this specification, “performing a series of steps in a wet environment” means, for example, maintaining a state in which the glass is immersed in water between each step, or while spraying water on the glass. Means to keep it dry.

  Hereafter, each process in the manufacturing method of this invention is demonstrated.

[Chemical strengthening process]
In the chemical strengthening process, glass containing sodium is mixed with potassium nitrate and 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 An ion-exchanged compressive stress layer is obtained by ion-exchange of Na in the glass and K in the inorganic salt by contacting with an inorganic salt containing at least one salt selected from the group consisting of NaOH. It is a process of forming on the glass surface.

  By the ion exchange, the surface of the glass is ion exchanged to form a surface layer in which compressive stress remains. Specifically, alkali metal ions (typically Li ions, Na ions) having a small ion radius on the surface of the glass plate by ion exchange at a temperature below the glass transition point are converted to alkali ions (typically Is substituted for Na ions or K ions for Li ions and K ions for Na ions. Thereby, compressive stress remains on the surface of the glass, and the strength of the glass is improved.

  The glass used in the production method of 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 aluminosilicate glass, soda lime 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 preferably heated and melted 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.

  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. Further, from the viewpoint of particularly improving the surface strength by the acid treatment described later, the thickness of the glass is more preferably 1 m or less, and particularly preferably 0.7 mm or less. On the other hand, if the glass is too thin, the strength of the glass may not be sufficiently secured, so 0.4 mm or more is preferable.

  Moreover, the shape of glass is not specifically limited. For example, various shapes of glass such as a flat plate shape having a uniform plate thickness, a shape having a curved surface on at least one of the front surface and the back surface, and a three-dimensional shape having a bent portion can be employed.

Although it does not specifically limit as a composition of glass, For example, the following compositions are mentioned.
(I) a composition that is displayed in mole percent on the oxide basis, of SiO ₂ 50 to 80%, the _{Al 2 O 3 2~25%, 0~10} % of Li ₂ O, the Na ₂ O 0 to 18% , A composition containing 0 to 10% of K ₂ O, 0 to 15% of MgO, 0 to 5% of CaO and 0 to 5% of ZrO ₂ , expressed in terms of mol% based on oxide (ii), SiO 2 ₂ 50 to 74%, the _{Al 2 O 3 1~10%, 6~14} % of Na ₂ O, the _{K 2} O 3 to 11% of MgO 2 to 15% Less than six% and ZrO of CaO ₂ to 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%, the content of MgO and CaO in the composition the sum of is displayed in mole% of the glass (iii) oxide basis is 7 to 15%, SiO ₂ 68 80%, the _{Al 2 O 3 4~10%, Na} 2 O 5-15% of _{K 2} O 0 to 1% MgO 4-15% and glass containing ZrO ₂ 0~1% (iv ) the composition viewed in mole percent on the oxide basis, of SiO ₂ 67 to 75%, the _{Al 2 O 3 0~4%, 7~15} % of Na ₂ O, 1 to 9% of _{K 2} O, MgO 6-14% and ZrO ₂ 0-1.5%, the total content of SiO ₂ and Al ₂ O ₃ is 71-75%, the total content of Na ₂ O and K ₂ O is 12 It was 20%, a composition in which the content is displayed in mole percent of glass (v) oxide basis is less than 1% when containing CaO, the _{SiO 2 55.5~80%, Al 2 O} 3 8-20% 8-25% of Na ₂ O, 0 to 3% of _{K 2} O, the TiO ₂ 0 to 1% 0 to the ZrO ₂ %, The composition (the RO that MgO + CaO + SrO + a BaO) alkaline earth metal RO displayed in mole percent of glass (vi) oxide basis, containing at least 1%, the SiO ₂ from 56 to 72%, the _Al 2 _{O 3} 8 to _20% B 2 _{O 3} 3-20% of _{Na 2 O 8~25%, K 2} O 0 to 5 percent, MgO 0 to 15 percent, CaO 0 to 15% and the TiO ₂ 0 ˜1% glass (vii) composition expressed in terms of mol% based on oxide, 5 to 76.5% of SiO ₂ , 5 to 20% of Al ₂ O ₃ , 8 to 25 of Na ₂ O %, K ₂ O 0 to 5%, P ₂ O ₅ 0.1% or more, and an alkaline earth metal RO (RO is MgO + CaO + SrO + BaO) 1% or more mol percentage based on glass (viii) oxide in the display, the SiO ₂ 64~71%, a ₂ O ₃ of 2.1 to 4.6%, from 12 to 18% of Na ₂ O, 6 to 9% of CaO, MgO containing 5-8% of the total content of Na ₂ O and _{K 2} O Is expressed in terms of a mole percentage based on glass (ix) oxide, which is 12 to 19%, SiO ₂ is 67 to 74%, Al ₂ O ₃ is 0.9 to ₂ %, Na ₂ O is 10 to 14%, CaO 7-10%, MgO 5-8%, the total content of Na ₂ O and K ₂ O is 10-15%

In the production method of the present invention, chemical strengthening is performed by bringing a glass into contact with an inorganic salt containing potassium nitrate (KNO ₃ ). As a result, Na ions on the glass surface and K ions in the inorganic salt are ion-exchanged to form a high-density compressive stress layer. Examples of the method of bringing the glass into contact with the inorganic salt include a method of applying a paste-like salt to the glass, a method of spraying an aqueous salt solution onto the glass, and a method of immersing the glass in a salt bath of a molten salt heated to a melting point or higher. Although possible, in these, the method of immersing in molten salt is preferable.

  As the inorganic 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, the inorganic salt contains potassium nitrate (melting point 330 ° C.). By containing potassium nitrate, 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. The content of potassium nitrate in the inorganic salt is preferably 50% by mass or more.

The inorganic 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. Contains at least one salt. Among these, it is preferable to contain at least one salt selected from the group consisting of K ₂ CO ₃ , Na ₂ CO ₃ , KHCO ₃ and NaHCO ₃ .

  The salt (hereinafter also referred to as “flux”) has a property of cutting a glass network represented by Si—O—Si bonds. Since the temperature at which the chemical strengthening treatment is performed is as high as several hundred degrees Celsius, the covalent bond between Si-O of the glass is appropriately broken at that temperature, and the density reduction treatment described later easily proceeds.

  The degree of breaking the covalent bond varies depending on the chemical composition treatment conditions such as the glass composition, the type of salt (flux) used, the temperature and time for the chemical strengthening treatment, but the four covalent bonds extending from Si. Of these, it is considered preferable to select conditions that are sufficient to break one or two bonds.

For example, when K ₂ CO ₃ is used as a flux, if the content of the flux in the inorganic salt is 0.1 mol% or more and the chemical strengthening treatment temperature is 350 to 500 ° C., the chemical strengthening treatment time is 1 minute to 10 hours is preferable, 5 minutes to 8 hours is more preferable, and 10 minutes to 4 hours is more preferable.

The amount of the flux added is preferably 0.1 mol% or more, more preferably 1 mol% or more, and particularly preferably 2 mol% or more from the viewpoint of controlling the surface hydrogen concentration. Further, from the viewpoint of productivity, the saturation solubility or less of each salt is preferable. In addition, excessive addition of flux may lead to corrosion of the glass. For example, when K ₂ CO ₃ is used as the flux, it is preferably 24 mol% or less, more preferably 12 mol% or less, and particularly preferably 8 mol% or less.

  In addition to potassium nitrate and a flux, the inorganic salt may contain other chemical species as long as the effects of the present invention are not impaired. For example, alkali salts such as sodium chloride, potassium chloride, sodium borate, potassium borate, etc. Examples include chlorides and alkali borates. These may be added alone or in combination of two or more.

  Hereinafter, the chemical strengthening step will be described by taking an example in which chemical strengthening is performed by a method of immersing glass in a molten salt.

(Manufacture of molten salt 1)
The molten salt can be produced by the steps shown below.
Step 1a: Preparation of potassium nitrate molten salt Step 2a: Addition of flux to potassium nitrate molten salt

(Step 1a-Preparation of molten potassium nitrate salt)
In step 1a, potassium nitrate is put into a container and heated to a temperature equal to or higher than the melting point to melt, thereby preparing a molten salt. Melting is performed at a temperature within the range of the melting point (330 ° C.) and boiling point (500 ° C.) of potassium nitrate. In particular, the melting temperature is preferably 350 to 470 ° C. from the viewpoint of the balance between the surface compressive stress (CS) and the compressive stress layer depth (DOL) that can be applied to the glass, and the strengthening time.

  As the container for melting potassium nitrate, metal, quartz, ceramics, or the like can be used. 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.

(Step 2a-Addition of flux to potassium nitrate molten salt-)
In Step 2a, the above-mentioned flux is added to the potassium nitrate molten salt prepared in Step 1a, and the whole is mixed uniformly with a stirring blade while keeping the temperature within a certain range. When using a plurality of fluxes in combination, the order of addition is not limited, and they may be added simultaneously.

  The temperature is preferably equal to or higher than the melting point of potassium nitrate, that is, 330 ° C. or higher, and more preferably 350 to 500 ° C. The stirring time is preferably 1 minute to 10 hours, and more preferably 10 minutes to 2 hours.

(Manufacture of molten salt 2)
In the above-described molten salt production 1, the method of adding a flux after preparation of the molten salt of potassium nitrate was exemplified, but the molten salt can also be produced by the steps shown below.
Step 1b: Mixing of potassium nitrate and flux Step 2b: Melting of mixed salt of potassium nitrate and flux

(Step 1b-Mixing of potassium nitrate and flux-)
In step 1b, potassium nitrate and a flux are put into a container and mixed with a stirring blade or the like. When using a plurality of fluxes in combination, the order of addition is not limited, and they may be added simultaneously. The same container as that used in the above step 1a can be used.

(Step 2b-Melting of mixed salt of potassium nitrate and flux-)
In step 2b, the mixed salt obtained in step 1b is heated and melted. Melting is performed at a temperature within the range of the melting point (330 ° C.) and boiling point (500 ° C.) of potassium nitrate. In particular, the melting temperature is preferably 350 to 470 ° C. from the viewpoint of the balance between the surface compressive stress (CS) and the compressive stress layer depth (DOL) that can be applied to the glass, and the strengthening time. The stirring time is preferably 1 minute to 10 hours, and more preferably 10 minutes to 2 hours.

  In the molten salt obtained through the above step 1a and step 2a or step 1b and step 2b, in the case where precipitates are generated by the addition of a flux, before the chemical strengthening treatment of the glass, the precipitates are Let stand until it settles to the bottom. This precipitate includes a flux exceeding the saturation solubility and a salt in which the cations of the flux are exchanged in the molten salt.

  The molten salt preferably has a Na concentration of 500 ppm by weight or more, more preferably 1000 ppm by weight or more. It is preferable that the Na concentration in the molten salt is 500 ppm by weight or more because the low-density layer is easily deepened by the acid treatment step described later. There is no restriction | limiting in particular as an upper limit of Na density | concentration, It is permissible until a desired surface compressive stress (CS) is obtained.

  In addition, the molten salt which performed the chemical strengthening process once or more contains the sodium eluted from glass. Therefore, if the Na concentration is already within the above range, glass-derived sodium may be used as it is as the Na source. If the Na concentration is not sufficient, or if a molten salt not used for chemical strengthening is used, nitric acid is used. It can adjust by adding inorganic sodium salts, such as sodium.

  As described above, the molten salt can be prepared by the steps 1a and 2a or the steps 1b and 2b.

  Next, chemical strengthening treatment is performed using the prepared molten salt. The chemical strengthening treatment is performed by immersing glass in a molten salt and replacing metal ions (Na ions) in the glass with metal ions (K ions) having a large ionic radius in the molten salt. By this ion exchange, the composition of the glass surface can be changed to form the compressive stress layer 20 in which the glass surface is densified [FIGS. 3A to 3B]. Since compressive stress is generated by increasing the density of the glass surface, the glass can be strengthened.

  Actually, the density of the chemically strengthened glass gradually increases from the outer edge of the intermediate layer 30 (bulk) existing in the center of the glass toward the surface of the compressive stress layer. There is no clear boundary between the density changes. Here, the intermediate layer is a layer present in the center of the glass and sandwiched between the compressive stress layers. Unlike the compressive stress layer, this intermediate layer is a layer that is not ion-exchanged.

Specifically, the chemical strengthening treatment can be performed by the following step 3.
Process 3: Chemical strengthening treatment of glass

(Process 3-Chemical strengthening treatment of glass)
In step 3, the glass is preheated, and the molten salt prepared in steps 1a and 2a or steps 1b and 2b is adjusted to a temperature at which chemical strengthening is performed. Next, the preheated glass is immersed in the molten salt for a predetermined time, and then the glass is pulled up from the molten salt and allowed to cool. 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 drilling process, before a chemical strengthening process to glass.

  The preheating temperature of the glass depends on the temperature at which it is immersed in the molten salt, but is generally preferably 100 ° C. or higher.

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

  The immersion time of the glass in the molten salt is preferably 1 minute to 10 hours, more preferably 5 minutes to 8 hours, and even more preferably 10 minutes to 4 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.

  From the viewpoint of ensuring strength and appearance quality, it is preferable to wash the glass using industrial water, ion-exchanged water or the like between the chemical strengthening step and the acid treatment step. The washing conditions vary depending on the washing solution used, but when ion-exchanged water is used, washing at 0 to 100 ° C. is preferable from the viewpoint of completely removing the attached salt. Ultrasonic waves may be applied at the time of cleaning. Specifically, the conditions are preferably that the frequency is preferably 25 kHz or more and 80 kHz or less, and the sound pressure is preferably 80 mV or less.

[Acid treatment process]
The acid treatment step is a step of acid-treating the glass after the chemical strengthening step. The acid treatment of the glass is performed by immersing the chemically strengthened glass in an acidic solution, whereby Na and / or K on the surface of the chemically strengthened glass can be replaced with H.

  The solution is not particularly limited as long as it is acidic, and may be less than pH 7. The acid used may be a weak acid or a strong acid. Specifically, acids such as hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, acetic acid, oxalic acid, carbonic acid and citric acid are preferred. These acids may be used alone or in combination.

  The temperature at which the acid treatment is performed varies depending on the type, concentration, and time of the acid used, but is preferably 100 ° C. or less. Although the time for performing the acid treatment varies depending on the type, concentration and temperature of the acid used, 10 seconds to 5 hours is preferable from the viewpoint of productivity, and 1 minute to 2 hours is more preferable.

  The concentration of the solution for acid treatment varies depending on the type, time, and temperature of the acid to be used, but is preferably a concentration at which there is little concern about container corrosion, and specifically 0.1% by mass to 20% by mass.

  From the viewpoint of ensuring strength and appearance quality, ultrasonic waves may be applied in the acid treatment step. When applying ultrasonic waves in the acid treatment step, specific conditions are, for example, that the frequency is preferably 25 kHz or more and 80 kHz or less, and the sound pressure is preferably 80 mV or less, more preferably 60 mV or less.

  Further, ultrasonic cleaning may be performed during the acid treatment step, and in that case, it is preferable to perform ultrasonic cleaning under the conditions described above for (1) in [Ultrasonic cleaning].

  By passing through the acid treatment step, the surface of the glass layer further has a low-density layer 10 in which the surface layer of the compressive stress layer 20 has been modified, specifically, a low-density layer [FIG. c)]. The low density layer is formed by Na (leaching) from the outermost surface of the compressive stress layer (leaching) and H entering (replacement) instead.

  Since the low density layer is removed by an alkali treatment described later, the glass surface is more easily removed as the low density layer is thicker. Therefore, the thickness of the low density layer is preferably 5 nm or more, and more preferably 20 nm or more from the viewpoint of the glass surface removal amount. The thickness of the low density layer can be controlled by the flux concentration, sodium concentration, temperature, time, etc. in the chemical strengthening step.

  The density of the low density layer is preferably lower than the density of the region (bulk) deeper than the ion-exchanged compressive stress layer from the viewpoint of glass surface removability.

  The thickness of the low-density layer can be obtained from the period (Δθ) measured by the X-ray reflectivity method (X-ray-Reflectometry: XRR). The density of the low density layer can be determined from the critical angle (θc) measured by XRR. In addition, it is also possible to confirm the formation of the low density layer and the thickness of the layer by simply observing a cross section of the glass with a scanning electron microscope (SEM).

  From the viewpoint of ensuring strength and appearance quality, it is preferable to wash the glass using industrial water, ion-exchanged water or the like between the acid treatment step and the alkali treatment step. When applying ultrasonic waves during cleaning, it is preferable to perform ultrasonic cleaning under the conditions described above for (2) in [Ultrasonic cleaning].

[Alkali treatment process]
The alkali treatment step is a step of alkali-treating the glass after the acid treatment step. A part or all of the low density layer 10 formed up to the acid treatment step can be removed by the alkali treatment step [FIGS. 3C to 3D].

  The alkali treatment is performed by immersing the chemically strengthened glass in a basic solution, whereby a part or all of the low density layer can be removed. The solution is not particularly limited as long as it is basic, and may have a pH exceeding 7, and a weak base or a strong base may be used. Specifically, a base such as sodium hydroxide, potassium hydroxide, potassium carbonate or sodium carbonate is preferred. These bases may be used alone or in combination.

  Although the temperature which performs an alkali treatment changes also with the kind of base used, a density | concentration, and time, 0-100 degreeC is preferable, 10-80 degreeC is more preferable, and 20-60 degreeC is especially preferable. If it is this temperature range, there is no possibility that glass will corrode and it is preferable.

  Although the time for performing the alkali treatment varies depending on the type, concentration and temperature of the base used, it is preferably 10 seconds to 5 hours from the viewpoint of productivity, and more preferably 1 minute to 2 hours. Although the density | concentration of the solution which performs an alkali treatment changes with kinds, time, and temperature of a base to be used, 0.1 mass%-20 mass% are preferable from a viewpoint of glass surface removability.

  From the viewpoint of ensuring strength and appearance quality, ultrasonic waves may be applied in the alkali treatment step. When applying ultrasonic waves in the alkali treatment step, specific conditions are, for example, that the frequency is preferably 25 kHz to 80 kHz, and the sound pressure is preferably 80 mV or less, more preferably 60 mV or less.

  Further, ultrasonic cleaning may be performed during the alkali treatment step. In that case, it is preferable to perform ultrasonic cleaning under the conditions described above for (3) in [Ultrasonic cleaning].

  By the alkali treatment, part or all of the low density layer into which H has penetrated is removed, and chemically strengthened glass having improved surface strength can be obtained. Further, since the scratches existing on the glass surface are also removed at the same time by removing the low density layer, this point is also considered to contribute to the strength improvement.

  Note that the amount of the low density layer to be removed depends on the conditions of the alkali treatment. FIG. 3D shows a mode in which the low density layer 10 is completely removed, but a part of the low density layer 10 may be removed and a part may remain. From the viewpoint of improving the strength, the effect can be obtained without removing all of the low density layer, but it is preferable to remove all of the low density layer from the viewpoint of stably securing the transmittance of the glass.

  From the viewpoint of ensuring the appearance quality, it is preferable to wash the glass using industrial water, ion-exchanged water or the like after the alkali treatment step. When applying ultrasonic waves during cleaning, it is preferable to perform ultrasonic cleaning under the conditions described above for (4) in [Ultrasonic cleaning].

  According to the production method of the present invention, it is possible to obtain chemically tempered glass having significantly improved surface strength and excellent appearance quality safely and efficiently. The production method of the present invention is preferable as a production method of a cover glass that requires excellent surface strength and appearance quality, and 2.5D glass or 3D glass suitable for ultrasonic cleaning as a washing method.

  The strength (surface strength) of the chemically strengthened glass obtained by the production method of the present invention can be evaluated by the BoR strength measured by a ball on ring (BoR) test. The test method and conditions for the BoR test are specifically as follows.

  A state in which a glass plate having a thickness of t (mm) is arranged on a ring made of stainless steel having a diameter of 30 mm and a contact portion having a radius of curvature of 2.5 mm, and a sphere made of steel having a diameter of 10 mm is in contact with the glass plate. The BoR strength F (N) measured by a BoR test in which the sphere is loaded at the center of the ring under a static load condition is evaluated.

  FIG. 4 shows a schematic diagram for explaining the BoR test used in the present invention. In the BoR test, with the glass plate 1 placed horizontally, the glass plate 1 is pressed using a pressing jig 2 made of SUS304 (hardened steel, diameter 10 mm, mirror finish) to increase the strength of the glass plate 1. taking measurement.

  In FIG. 4, a glass plate 1 serving as a sample is horizontally installed on a receiving jig 3 made of SUS304 (diameter 30 mm, contact portion curvature R2.5 mm, contact portion is hardened steel, mirror finish). Above the glass plate 1, a pressurizing jig 2 for pressurizing the glass plate 1 is installed.

The central region of the glass plate 1 is pressurized from above the glass plate 1. The test conditions are as follows.
Lowering speed of the pressure jig 2: 1.0 (mm / min)
At this time, the breaking load (unit N) when the glass is broken is defined as the BoR strength, and the average value of 20 measurements is defined as the BoR average strength. However, if the glass plate fracture starting point is 2 mm or more away from the ball pressing position, it is excluded from the data for calculating the average value.

The chemically strengthened glass obtained by the production method of the present invention preferably satisfies F ≧ 1300 × t ² , and more preferably F ≧ 1500 × t ² [where F is the BoR strength measured by the BoR test ( N), and t is the thickness (mm) of the glass substrate. ]. When the BoR strength F (N) is within the above range, excellent strength is exhibited even when the plate is thinned.

  In the present specification, “appearance quality is ensured” means a state in which there is no foreign matter such as dirt in the glass surface, and when the glass surface is visually observed under the condition of illuminance of 1500 lux, there are defects. It means no state.

  The chemically strengthened glass obtained by the production method of the present invention preferably has no polishing scratches on the surface. Here, the term “polishing” in the present invention refers to smoothing by polishing the glass surface using abrasive grains. The presence or absence of polishing flaws can be determined by surface observation with an AFM (Atomic Force Microscope), and there are two or more scratches having a length of 5 μm or more and a width of 0.1 μm or more in a 10 μm × 5 μm region. If not, it can be said that there is no polishing flaw on the surface.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these.

<Evaluation method>
(Area strength)
The glass surface strength was measured according to the test method and conditions of the ball-on-ring test described above. The plate thickness of the glass for BoR strength evaluation was 0.7 mm, and the top surface (T surface) which is a surface not touching the molten metal in the float bath or the bottom surface (B surface) opposed to the top surface was evaluated. .

Regarding the measured BoR intensity F (N), the case where F ≧ 2000 × t ² is “、”, the case where F ≧ 1500 × t ² is “◯”, and the case where F ≧ 1300 × t ² is “Δ” ".

(Surface stress)
The compressive stress value of the compressive stress layer and the depth of the compressive stress layer of the chemically strengthened glass of the present invention can be measured using a surface stress meter (for example, FSM-6000 manufactured by Orihara Seisakusho). Further, the depth of the compressive stress layer can be substituted by an ion exchange depth measured using an EPMA (Electron Probe Micro Analyzer) or the like. In the examples, the surface compressive stress value (CS, unit is MPa) and the depth (DOL, unit is μm) of the compressive stress layer were measured using a surface stress meter (FSM-6000) manufactured by Orihara Seisakusho.

(Removal amount)
The glass removal amount thickness was determined by measuring the weight before and after the chemical treatment with an analytical electronic balance (HR-202i; manufactured by AND) and converting the thickness using the following formula.
(Removed thickness per side) = [(weight before treatment) − (weight after treatment)] / (glass specific gravity) / treated area / 2
At this time, the glass specific gravity was calculated as 2.48 (g / cm ³ ).

(Appearance quality)
The surface of the glass was visually observed under conditions of an illuminance of 1500 lux, and the case where there were no defects such as dirt and foreign matter was marked as ◯, and the case where there were defects such as dirt and foreign matter was marked as x.

<Manufacture of chemically strengthened glass>
[Examples 1 to 16 and Comparative Examples 1 to 7, 10 to 13, 16 to 19, and 21 to 26]
(Chemical strengthening process)
To a SUS cup, 5100 g of potassium nitrate, 637 g of potassium carbonate, and 220 g of sodium nitrate were added, and the mixture was heated to 450 ° C. with a mantle heater to prepare a molten salt mainly composed of potassium nitrate containing 8 mol% of potassium carbonate and 10,000 ppm by weight of sodium. Prepare glass of the composition shown in Table 1 of 50 mm x 50 mm x 0.7 mm, preheat each to 200-400 ° C, immerse in molten salt at 450 ° C for 120 minutes, perform ion exchange treatment, then cool to near room temperature The chemical strengthening process was performed. The obtained chemically strengthened glass was washed with water and subjected to the next step.

The composition of glass A to D (expressed as mol% based on oxide) is shown below.
Glass _{A: SiO 2 64.2%, Al} 2 O 3 8.0%, Na 2 O 12.5%, K 2 O 4.0%, 10.5% MgO, CaO 0.1%, SrO 0. 1%, BaO 0.1%, ZrO ₂ 0.5%
Glass B: SiO ₂ 68.0%, Al ₂ O ₃ 10.0%, Na ₂ O 14.0, MgO 8.0%
Glass C: SiO ₂ 67%, B ₂ O ₃ 4%, Al ₂ O ₃ 13%, Na ₂ O 14%, K ₂ O <1%, MgO 2%, CaO <1%
Glass D: SiO ₂ 68.7%, Al ₂ O ₃ 3.0%, Na ₂ O 14.2%, K ₂ O 0.2%, MgO 6.2%, CaO 7.8%

(Acid treatment process)
6.0% by weight of nitric acid hydrochloride (HNO ₃ ; manufactured by Kanto Chemical Co., Inc.) was prepared in a beaker, and the temperature was adjusted to 40 ° C. using a water bath. Each glass obtained in the chemical strengthening step was immersed in adjusted nitric acid for 120 seconds, acid-treated, and then washed several times with pure water. Glass D was immersed in nitric acid adjusted to 60 ° C. for 600 seconds in the same procedure.

(Alkali treatment process)
A 4.0 wt% aqueous sodium hydroxide solution was prepared in a beaker, and the temperature was adjusted to 40 ° C. using a water bath. Each glass obtained in the acid treatment step was immersed in an adjusted aqueous sodium hydroxide solution for 120 seconds, subjected to an alkali treatment, and then washed several times with pure water. Glass D was immersed in nitric acid adjusted to 60 ° C. for 600 seconds in the same procedure.

(Ultrasonic cleaning)
The glass was ultrasonically cleaned under the conditions shown in Table 1 using an ultrasonic cleaner having the following ultrasonic vibrator.
Frequency 26 kHz: Kaijo 26 kHz, 600 W ultrasonic vibrator Frequency 40 kHz: Branson 40 kHz, 600 W ultrasonic vibrator Alkaline detergent: Lion TL-110 diluted 30 times with pure water

  The sound pressure in ultrasonic cleaning was manually swept at the upper, middle, and lower parts in the cleaning tank using the 19001D main body 11003 sensor manufactured by Kaijo Co., Ltd. according to the method described in [Ultrasonic Cleaning]. The maximum sound pressure was measured.

[Comparative Examples 8, 14, 20, and 27]
(Chemical strengthening process)
The plate-shaped glass having a glass composition of 50 mm × 50 mm × 0.7 mm and having the glass composition shown in Table 1 is preheated to 350 to 400 ° C. in a laboratory, and then contains potassium nitrate containing 2000 mass ppm of sodium at 450 ° C. as a main component. After being immersed in the molten salt for 120 minutes and subjected to an ion exchange treatment, a chemical strengthening treatment was performed by cooling to near room temperature.

[Comparative Examples 9, 15 and 28]
Except for ultrasonic cleaning under the conditions shown in Table 1 after the chemical strengthening step, the same procedure as in Comparative Examples 8, 14 and 27 was performed.

  Various evaluations were performed on the chemically strengthened glass thus obtained. The processing conditions and evaluation results for glass are shown in Table 1 and FIGS. In Table 1, “in the wet environment” of “◯” indicates that a series of steps from the acid treatment step to the alkali treatment step was performed in the wet environment.

  As shown in Table 1 and FIGS. 5 to 8, the chemically strengthened glass obtained by the production method of the present invention has high surface strength and secured appearance quality as compared with the chemically strengthened glass of the comparative example. It was.

  The chemically strengthened glass obtained by the production method of the present invention has significantly higher surface strength and appearance compared to the chemically strengthened glasses of Comparative Examples 9, 15 and 28, which were subjected to ultrasonic cleaning after the conventional chemical strengthening step. Had quality. Moreover, it turned out that the effect by 1st embodiment of this invention improves more by performing a series of processes from an acid treatment process to an alkali treatment process in a wet environment.

  In addition, the chemically strengthened glass of Example 1 in which the ultrasonic cleaning is not performed after chemically strengthening with a molten salt containing a specific salt and the series of steps from the acid treatment step to the alkali treatment step is performed in a wet environment. Appearance quality was guaranteed. On the other hand, the chemically strengthened glass of Comparative Example 7 in which ultrasonic cleaning was not performed after chemical strengthening with a molten salt containing a specific salt and a series of steps from an acid treatment step to an alkali treatment step was not performed in a wet environment. The appearance quality was not guaranteed.

  Further, Example 2 in which a series of steps from an acid treatment step to an alkali treatment step was performed in a wet environment and ultrasonic cleaning was performed during the acid treatment, and a series of steps from the acid treatment step to the alkali treatment step were wet. The chemically strengthened glass of Example 3, which was performed in an environment and subjected to ultrasonic cleaning both during acid treatment and alkali treatment, both had high surface strength and ensured appearance quality.

  The chemically tempered glasses of Examples 7 and 16 and Comparative Examples 6 and 26 using an alkaline detergent as the cleaning liquid were treated in the same conditions as in Examples 6 and 15 and Comparative Examples 5 and 25 except that pure water was used. The surface strength was higher than that of the chemically strengthened glass. This is presumably because the alkaline detergent generally has a low surface tension, which inhibits the generation of cavitation.

  Further, as shown in FIGS. 5 and 6, the surface strength is dramatically increased by performing the acid treatment step and the alkali treatment step after the chemical strengthening treatment step, but the surface strength increases as the ultrasonic output increases. Was found to decrease. This is considered to be because the glass surface is damaged by ultrasonic cleaning.

  From these results, the ultrasonic cleaning process in which the frequency and sound pressure defined in (1) to (4) in the first embodiment of the present invention are in a specific range is included, or in the second embodiment of the present invention. By performing a series of steps from an acid treatment step to an alkali treatment step in a wet environment as specified, it is remarkable by performing an acid treatment step and an alkali treatment step after chemical strengthening using an inorganic salt containing a specific salt In addition, it was found that high surface strength can be suppressed by ultrasonic treatment and appearance quality can be ensured.

  According to the method for producing chemically strengthened glass of the present invention, it is possible to obtain chemically strengthened glass having extremely high surface strength and excellent appearance quality without performing etching treatment using polishing or hydrofluoric acid after chemical strengthening. it can. That is, it is possible to obtain a chemically strengthened glass excellent in surface strength and appearance quality free from appearance defects due to expansion of latent scratches due to etching treatment with hydrofluoric acid or the like and polishing scratches associated with polishing.

  For this reason, it can be applied to any glass regardless of the presence or degree of surface scratches and latent scratches on the glass before chemical strengthening treatment, and is highly versatile. And since a process can be advanced by immersion in a solution, it is efficient at the point of being easy to respond | correspond to various glass shapes and large area glass. Further, the safety is high and the cost is low as compared with etching using hydrofluoric acid or the like.

DESCRIPTION OF SYMBOLS 11 Ultrasonic sound pressure meter 12 Sensor part 13 Cleaning tank 14,15,16 Glass plate 1 Glass plate 2 Pressing jig 3 Receiving jig 10 Low density layer 20 Compressive stress layer 30 Intermediate layer

Claims (5)

A glass containing sodium is selected from the group consisting of potassium nitrate and 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. A chemical strengthening step for ion-exchange of Na in the glass and K in the inorganic salt by contacting with an inorganic salt containing at least one selected salt, and the glass is acid-treated after the chemical strengthening step. An acid treatment step, a method for producing chemically strengthened glass comprising an alkali treatment step of alkali-treating the glass after the acid treatment step,
The manufacturing method of chemically strengthened glass further including at least 1 washing process chosen from following (1)-(4).
(1) Cleaning treatment with ultrasonic waves having a frequency of 25 kHz to 80 kHz and a sound pressure of 80 mV or less during the acid treatment step (2) A frequency of 25 kHz to 80 kHz after the acid treatment step and before the alkali treatment step, Cleaning treatment with ultrasonic waves with a sound pressure of 80 mV or less (3) Cleaning treatment with ultrasonic waves with a frequency of 25 kHz to 80 kHz and sound pressures of 80 mV or less during the alkali treatment step (4) After the alkali treatment step, a frequency of 25 kHz or more Cleaning treatment with ultrasonic waves of 80 kHz or less and sound pressure of 80 mV or less   The method for producing chemically strengthened glass according to claim 1, wherein when at least one cleaning treatment selected from (1) to (4) is performed a plurality of times, the steps between the cleaning treatments are performed in a wet environment.   The manufacturing method of the chemically strengthened glass of Claim 1 or 2 including a drying process after the said alkali treatment process, and performing from the said acid treatment process to before the said drying process in a wet environment.   The method for producing chemically strengthened glass according to claim 1, wherein the chemically strengthened glass is a cover glass. A glass containing sodium is selected from the group consisting of potassium nitrate and 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. A chemical strengthening step for ion-exchange of Na in the glass and K in the inorganic salt by contacting with an inorganic salt containing at least one selected salt, and the glass is acid-treated after the chemical strengthening step. An acid treatment step, a method for producing chemically strengthened glass comprising an alkali treatment step of alkali-treating the glass after the acid treatment step,
A method for producing chemically strengthened glass, wherein a series of steps from the acid treatment step to the alkali treatment step is performed in a wet environment.

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