JPWO2008004480A1 - Method for producing alkali-free glass substrate - Google Patents

Abstract

The present invention efficiently produces a protective film that can be easily removed in a cleaning process, and produces an alkali-free glass substrate that suppresses the occurrence of scratches on the back surface of the glass substrate while reducing the amount of sulfurous acid used. It is an object of the present invention to provide a method and a non-alkali glass substrate obtained by the production method. The present invention is a method for producing an alkali-free glass substrate for producing an alkali-free glass substrate by a float process, a molding step for molding molten glass on a molten tin on a glass substrate, and the glass molded by the molding step A slow cooling step of slowly cooling the substrate, a first supply step of spraying an inorganic substance containing an alkali metal on the surface of the glass substrate in contact with the molten tin, and after the first supply step, The present invention relates to a method for producing an alkali-free glass substrate, comprising: a second supply step of blowing SO2 gas onto the surface of the glass substrate that contacts the molten tin.

Description

  The present invention relates to a method for producing an alkali-free glass substrate.

Many glass substrates including glass substrates for displays are manufactured by the float process or the fusion process. Unlike the fusion method, the float method is an excellent method in that a large-area glass substrate can be efficiently produced.
This float method generally includes a molding step of molding molten glass onto a glass substrate on molten tin in a molten tin bath, and a slow cooling step of slowly cooling the glass substrate molded by the molding step. It is.
However, since the glass substrate molded by this molding process is transported by the roller after leaving the molten tin bath, the back surface of the glass substrate (the surface that hits the roller) is scratched during transport, and the quality of the glass substrate There was a problem of lowering.

Therefore, in order to prevent scratches on the back surface of the glass substrate that are generated during the transportation, sulfurous acid gas (SO ₂ gas) is sprayed on the back surface of the glass substrate, and reacted with an alkali metal (for example, sodium) existing in the glass. A method is known in which scratches are prevented by forming sodium sulfate on the back surface of a substrate and using it as a protective film (see, for example, Patent Document 1 and Non-Patent Document 1).

International Publication No. 2002/051767 Pamphlet U. Senturk etc, J. et al. Non-Cryst. Solids, Vol. 222, p. 160 (1997)

  However, in order to realize the high scratch prevention ability required for high-quality displays in recent years, it is necessary to increase the thickness of the protective film, and for that purpose, it is necessary to use a large amount of sulfurous acid gas, There was a problem of deterioration of environmental load and work environment. Further, since sulfurous acid gas is a highly corrosive gas, there is a problem that the furnace material is corroded and the life of the furnace material is shortened.

In particular, in the case of producing a glass substrate composed of glass that does not substantially contain an alkali metal (hereinafter, also referred to as “non-alkali glass”), sodium sulfate is not generated depending on the method of blowing sulfurous acid gas, Salts such as calcium sulfate and strontium sulfate, which are reaction products with alkaline earth metals, are formed on the glass substrate. Although these salts derived from alkaline earth metals act as protective coatings to prevent scratches on the glass substrate, their production efficiency is significantly lower than that of sodium sulfate, so their action may not be sufficient. . Moreover, since it is a hardly water-soluble salt even if produced | generated, there existed a problem that it was very difficult to remove in a subsequent washing | cleaning process.
Moreover, although these salts can be removed by polishing, in order to obtain a glass substrate with high smoothness, a considerable thickness must be polished, which increases manufacturing time and manufacturing cost. was there.
Furthermore, non-alkali glass is required to have a high-quality surface such as a flat panel display, and if there is a scratch on the glass substrate, it causes problems such as disconnection failure. .

  Therefore, the present invention is a method for producing a glass substrate made of alkali-free glass used in a liquid crystal display (hereinafter also referred to as “alkali-free glass substrate”), and can be easily removed in a cleaning process. Method for producing an alkali-free glass substrate capable of efficiently producing a protective coating and suppressing the occurrence of scratches on the back surface of the glass substrate while reducing the amount of sulfurous acid used, and the alkali-free obtained by the production method An object is to provide a glass substrate.

As a result of diligent study to achieve the above object, the present inventor sprayed an inorganic substance containing an alkali metal onto the surface of the glass substrate that was in contact with the molten tin in the manufacturing process by the float process. Then, by blowing SO ₂ gas onto the surface, a protective coating that can be easily removed in the cleaning process is efficiently generated, and the amount of sulfurous acid gas used is reduced while reducing the amount of sulfurous acid used. The present inventors have found that the generation of scratches can be suppressed and completed the present invention.

That is, the present invention provides the following (1) to (14).
(1) A method for producing an alkali-free glass substrate by producing an alkali-free glass substrate by a float method,
Comprising a molding step of molding molten glass on a molten tin on a glass substrate, and a slow cooling step of slowly cooling the glass substrate molded by the molding step,
A first supply step of spraying an inorganic substance containing an alkali metal on the surface of the glass substrate in contact with the molten tin; and a surface of the glass substrate in contact with the molten tin after the first supply step. And a second supply step of spraying SO ₂ gas on the substrate.

(2) The method for producing an alkali-free glass substrate according to (1), wherein the first supply step is performed between the molding step and the slow cooling step.
(3) The method for producing an alkali-free glass substrate according to (1), wherein the first supply step is performed at a temperature in the range of the glass transition point ± 100 ° C. of the glass substrate.
(4) The method for producing an alkali-free glass substrate according to (1), wherein the first supply step is performed at 600 to 800 ° C.
(5) The method for producing an alkali-free glass substrate according to any one of (1) to (4), wherein the second supply step is performed between the molding step and the slow cooling step.
(6) The method for producing an alkali-free glass substrate according to any one of (1) to (4), wherein the second supply step is performed at a temperature in the range of the glass transition point ± 100 ° C. of the glass substrate.
(7) The method for producing an alkali-free glass substrate according to any one of (1) to (4), wherein the second supply step is performed at 600 to 800 ° C.

(8) A method for producing an alkali-free glass substrate for producing an alkali-free glass substrate by a float method,
Comprising a molding step of forming molten glass on a molten tin on a glass substrate;
A first supply step of spraying an inorganic substance containing an alkali metal on the surface of the glass substrate that contacts the molten tin at 600 to 800 ° C., and the glass substrate at 600 to 800 ° C. after the first supply step. And a second supply step of spraying SO ₂ gas on the surface in contact with the molten tin.

(9) The method for producing an alkali-free glass substrate according to any one of (1) to (8), further comprising a cleaning step for removing the protective film.
(10) The method for producing an alkali-free glass substrate according to any one of (1) to (9), wherein the inorganic substance containing an alkali metal contains sodium and boron.
(11) The method for producing an alkali-free glass substrate according to (10), wherein the inorganic substance containing the alkali metal is sodium tetraborate.

  (12) An alkali-free glass substrate produced by the production method described in (10) or (11) above.

(13) An alkali-free glass substrate produced by the production method according to (10) or (11) above,
The glass substrate is a mass percentage display based on oxide,
SiO _2: 30~85%,
Al ₂ O ₃ : 0 to 35%,
B ₂ O ₃ : 0 to 35%,
MgO: 0 to 35%,
CaO: 0 to 35%,
SrO: 0 to 35%,
BaO: 0 to 35%,
Alkali metal component: 0.5% or less
An alkali-free glass substrate in which the average boron concentration on the surface of the glass substrate that has been in contact with the molten tin is 4 to 10 atomic%, and the diffusion depth of boron into the glass substrate is 5 nm or more.

(14) Oxide-based mass percentage display,
SiO _2: 30~85%,
Al ₂ O ₃ : 0 to 35%,
B ₂ O ₃ : 0 to 35%,
MgO: 0 to 35%,
CaO: 0 to 35%,
SrO: 0 to 35%,
BaO: 0 to 35%,
Alkali metal component: 0.5% or less
An alkali-free glass substrate having an average boron concentration of at least one surface of 4 to 10 atomic% and a boron diffusion depth from the surface to the inside of 5 nm or more.

  As shown below, according to the present invention, a protective coating that can be easily removed in the cleaning process is efficiently generated, and the occurrence of scratches on the back surface of the glass substrate while reducing the amount of sulfurous acid gas used. The manufacturing method of the alkali free glass substrate which suppresses, and the alkali free glass substrate obtained by this manufacturing method can be provided.

FIG. 1 is a conceptual diagram showing an example of a glass production line by a float process. FIG. 2 is a cross-sectional view of the large tubular furnace used in the examples. FIG. 3 is an explanatory view showing a portion (wear portion) hit by a wear ring of a Taber experimental machine used for evaluation of scratch resistance and a number measurement portion (measurement portion) of scratches.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Molten tin 2 Molten tin bath 3 Molten kiln 4 Molten glass 5 Draw roll 6 Slow cooling furnace 11 Large tubular furnace 12 Quartz tube 13 Alkali glass substrate 14 Alumina boat 15 Reagent 16, 17 Arrow 18 Specimen 19 Wear part 20 Measurement part

The present invention is described in detail below.
The method for producing an alkali-free glass substrate according to the first aspect of the present invention (hereinafter also referred to as “the production method of the present invention”) is a method for producing an alkali-free glass substrate by producing an alkali-free glass substrate by a float process. There,
Comprising a molding step of molding molten glass on a molten tin on a glass substrate, and a slow cooling step of slowly cooling the glass substrate molded by the molding step,
First, an inorganic substance containing an alkali metal (hereinafter also referred to as “alkali metal-containing inorganic substance”) is sprayed on the surface (hereinafter also referred to as “bottom surface”) of the glass substrate in contact with the molten tin. And a second supply step of spraying SO ₂ gas on the surface of the glass substrate in contact with the molten tin, that is, the bottom surface sprayed with the inorganic substance after the first supply step. This is a method for producing an alkali-free glass substrate.
Moreover, it is preferable that the manufacturing method of this invention comprises the washing | cleaning process which removes the said protective film further.
Next, the molding step, the slow cooling step, the first supply step and the second supply step, and the cleaning step provided as desired in the production method of the present invention will be described in detail.

[Molding process]
The forming step is a step of forming molten glass on a glass substrate on molten tin in a molten tin bath, and is a conventionally known step in a general float method.

FIG. 1 is a conceptual diagram showing an example of a glass production line by a float process.
As shown in FIG. 1, in the float process, first, molten glass 4 is continuously flowed from a melting furnace 3 onto a bath surface of a molten tin bath 2 filled with molten tin 1 to form a glass ribbon. . Next, the glass ribbon is advanced along the bath surface of the molten tin bath 2 while being floated, so that the glass ribbon is formed into a plate shape as the temperature decreases. Thereafter, the glass substrate thus produced is drawn out by the drawing roll 5 and is conveyed to the slow cooling furnace 6 in a state of being continuous in the longitudinal direction.

Here, in FIG. 1, the said formation process is a process until it shape | molds the molten glass 4 in plate shape through a glass ribbon.
In the present invention, similar to the general float method, the molten tin bath 2 is composed of a tin bath furnace and a ceiling lined with a special refractory inside the metal case, and has a sealed structure to prevent oxidation of tin. Use one. As the atmospheric gas in the molten tin bath, a mixed gas composed of hydrogen and nitrogen (hydrogen content is 2 to 10% by volume) can be used.
Moreover, the temperature conditions in the molten tin bath in the molding step are 600 to 1050 ° C., that is, the temperature of the molten glass flowing into the molten tin bath is 900 to 1050 ° C. on the upstream side, as in the general float process. The temperature can be 600 to 800 ° C. on the downstream side. In addition, although this temperature is normally maintained with the calorie | heat amount of a molten glass, you may use a heater and a cooler for temperature control.

In the production method of the present invention, an alkali-free glass substrate is formed on the molten tin by the forming step.
Here, the non-crisp glass is glass that does not substantially contain an alkali metal as described above. Specifically, the alkali-free glass is an oxide-based mass percentage display in the present invention,
SiO _2: 30~85%,
Al ₂ O ₃ : 0 to 35%,
B ₂ O ₃ : 0 to 35%,
MgO: 0 to 35%,
CaO: 0 to 35%,
SrO: 0 to 35%,
BaO: 0 to 35%,
Alkali metal component: 0.5% or less. The “alkali metal component” refers to an alkali metal component inevitably contained regardless of the first supply step described later.

[Slow cooling process]
The slow cooling step is a step of slowly cooling the glass substrate formed by the forming step.

Here, in FIG. 1, the said slow cooling process is a process until it draws the plate-formed glass substrate with the drawing roll 5, and is carried to the slow cooling furnace 6 in the continuous state in a longitudinal direction until it cools slowly.
In the present invention, the slow cooling furnace may be the same as that used in a general float method, and a heater or the like may be provided for temperature control.
Further, the slow cooling conditions in the slow cooling furnace in the slow cooling step can be set to temperatures of 550 to 750 ° C. at the inlet of the slow cooling furnace and 200 to 300 ° C. at the outlet, as in the general float method. The descent speed can be 90 ° C. ± 10 ° C./m.

[First supply process]
The first supply step is a step of supplying an alkali metal to the bottom surface by spraying an alkali metal-containing inorganic substance onto the bottom surface of the glass substrate.
Here, as described above, the alkali metal-containing inorganic substance refers to an inorganic substance containing an alkali metal, and includes, for example, lithium (Li), sodium (Na), potassium (K), cesium (Cs), and the like. This applies to inorganic substances.
By using such an alkali metal-containing inorganic substance to supply an alkali metal to the bottom surface of the glass substrate and then spraying SO ₂ gas, a protective film made of an alkali sulfate salt can be efficiently produced. Moreover, this protective film can be easily removed by a cleaning process. Furthermore, since the same protective effect can be obtained even if the amount of SO ₂ gas is reduced, it is possible to suppress the occurrence of scratches on the back surface of the glass substrate while reducing the amount of sulfurous acid gas used.
This is because the SO ₂ gas sprayed in the second supply step described later reacts preferentially with the alkali metal supplied to the bottom surface, and the hardly water-soluble alkaline earth metal (Ca, Sr) that exists even in the alkali-free glass. This is thought to be because the reaction with the Also, by spraying an alkali metal source called an alkali metal-containing inorganic substance from the outside, it was used to obtain a reactive organism (calcium sulfate, strontium sulfate, etc.) of SO ₂ gas and alkaline earth metal as a protective coating. The same protective effect can be obtained with a smaller amount of SO ₂ gas than the amount of SO ₂ gas.

Specific examples of the inorganic substance containing Na include, for example, NaOH, Na ₂ S, NaCl, NaF, NaBr, NaI, soda ash, NaNH ₂ , sodium benzyl oxide, NaBH ₄ , NaCN, NaNO ₃ , Na _2. B ₄ O ₇ -10H ₂ O (sodium tetraborate decahydrate), Na ₂ B ₄ O ₇ , (C ₂ H ₅ ) ₄ BNa and the like may be used, and these may be used alone. Two or more kinds may be used in combination.

Specific examples of the inorganic substance containing K include, for example, KOH, KCl, KF, KBr, KI, KCN, K ₂ CO ₃ , potassium gluconate, KHF ₂ , KNO ₃ , K ₂ B ₄ O ₇ − Examples thereof include 4H ₂ O (potassium tetraborate tetrahydrate), K ₂ B ₄ O ₇ , KBF _{4 and the} like, and these may be used alone or in combination of two or more.

Specific examples of the inorganic substance containing Cs include CsOH, CsCl, CsF, CsBr, CsI, cesium acetylacetonate, HCO ₂ Cs, and CsNO ₃ , and these can be used alone. Or two or more of them may be used in combination.

  It is preferable that the alkali metal-containing inorganic substance is an inorganic substance containing Na, because the production efficiency of the protective film (sodium sulfate) formed in the second supply step described later is further improved and the washing and removal are facilitated. .

Among them, the alkali metal-containing inorganic substance is an inorganic substance containing Na and boron, and the non-alkali glass substrate obtained by the production method of the present invention further has wear resistance even after the cleaning step described later. Therefore, it is more preferable. Specifically, Na ₂ B ₄ O ₇ -10H ₂ O and Na ₂ B ₄ O ₇ are preferable, and Na ₂ B ₄ O ₇ -10H ₂ O is more preferable.
As a result of supplying not only Na but also boron by spraying an inorganic substance containing Na and boron, boron diffuses from the bottom surface into the glass substrate, and the strength of the glass substrate itself is improved.
Therefore, in addition to non-alkali glass substrates, for example, DNA diffusion glass substrates, microchip / biochip glass substrates, etc. should be used to satisfy a high level of scratch resistance by utilizing this boron diffusion. Can do.

  In the first supply step, the alkali metal is supplied to the bottom surface by spraying such an alkali metal-containing inorganic substance onto the bottom surface of the glass substrate. As for, the following embodiments are preferably exemplified.

The timing of spraying the alkali metal-containing inorganic substance is not particularly limited as long as it is before the second supply step described later. Specifically, even if it is simultaneous with the molding step, it is simultaneous with the slow cooling step described later. However, it is preferable to be between the molding step and the slow cooling step because the occurrence of scratches on the back surface of the glass substrate can be further suppressed.
Here, “simultaneously with the molding process” means a stage immediately after forming the glass substrate in the molding process and included in the molding process, for example, a forming furnace, a molten tin bath (float bath) and the entire furnace. In the case where an exit portion (shield rare) is provided, this means that the spray portion may be sprayed. Further, “simultaneously with the slow cooling step” means that the spraying may be performed near the inlet of the slow cooling furnace or upstream of the slow cooling furnace. Furthermore, “between the molding step and the slow cooling step” means that the glass substrate may be sprayed between the forming furnace and the slow cooling furnace.

On the other hand, the method of spraying the alkali metal-containing inorganic substance includes, for example, a method of heating and vaporizing the alkali metal-containing inorganic substance, and spraying the vaporized substance on the bottom surface of the glass substrate using a nozzle; A method of heating and vaporizing the alkali metal-containing inorganic substance by lamp heating, laser heating or the like is preferable.
The vaporizing substance is preferably sprayed at a temperature in the range of ± 100 ° C. of the glass transition point of the glass substrate. In particular, the glass transition point of the glass substrate is preferably in the range of −30 ° C. to glass transition point + 100 ° C. This is because if the spraying is performed within this temperature range, the glass becomes soft at the glass transition point, and therefore, scratching can be more effectively prevented by forming a film in that region.
Specifically, it is preferably performed at 600 to 800 ° C. in that the vaporized material is efficiently vaporized and the substrate temperature does not rapidly decrease when sprayed onto the glass substrate surface.
Furthermore, spraying of vapors is preferably from 0.2~10L / m ^2, more preferably from 0.2~3L / m ^2, and even a 0.2~1L / m ² Particularly preferred. If the amount sprayed is in this range, while suppressing the spraying amount of SO ₂ gas, the supply amount of the alkali metal to be supplied to the bottom surface of the glass substrate becomes sufficient, SO ₂ is blown in the second feed step described below gas The production efficiency of the protective film formed by reacting with is further improved.

  When sodium tetraborate decahydrate is used as the alkali metal-containing inorganic substance, the temperature is about 850 ° C. in a furnace other than the glass substrate forming furnace and the slow cooling furnace (for example, the large tube furnace used in the examples). After vaporizing sodium tetraborate with a nozzle, a method of spraying the vaporized substance onto a bottom surface of a glass substrate transported between a forming furnace or a slow cooling furnace having a temperature of about 700 ° C. using these nozzles, etc. It is mentioned as a preferred embodiment.

  By spraying the alkali metal-containing inorganic substance by such a method, the alkali metal is supplied to the bottom surface of the glass substrate. The presence of the alkali metal on the bottom surface of the glass substrate can be confirmed by X-ray photoelectron spectroscopy (XPS) or fluorescent X-ray analysis of the bottom surface of the glass substrate.

[Second supply step]
The second supply step is a step of forming a protective film on the bottom surface by spraying SO ₂ gas on the bottom surface of the glass substrate supplied with the alkali metal after the first supply step.
This second supply step is different from a conventionally known step in a general float method in that a protective film is formed on the bottom surface of the glass substrate supplied with the alkali metal.
That is, in the second supply step, the alkali metal and the SO ₂ gas are reacted by blowing SO ₂ gas onto the bottom surface of the glass substrate to which the alkali metal has been supplied in the first supply step, so that the glass substrate This is a step of forming a protective film made of an alkali sulfate salt (for example, sodium sulfate) on the bottom surface.

As for the timing (timing) of blowing the SO ₂ gas and the blowing method in the second supply step, the following modes are preferably exemplified.

The timing of blowing the SO ₂ gas is not particularly limited as long as it is after the first supply step, but from the viewpoint of preventing scratches on the surface of the glass substrate being transferred, it is preferably immediately after the first supply step. More preferably, it is between the molding step and the slow cooling step. Note that it is not preferable to spray each gas at the same time because each gas reacts and it becomes difficult to form a film.

On the other hand, the method of spraying SO ₂ gas can be performed by a method similar to a conventionally known method in a general float method. Specifically, for example, it can be carried out by a method of spraying from a nozzle installed below the glass substrate in the width direction of the glass substrate (for example, the method described in claim 12 of Patent Document 1).
However, in the present invention, as compared with the conventional example using an alkaline earth metal-derived sulfate (for example, calcium sulfate) as a protective coating on the alkali-free glass substrate, the SO ₂ gas is secured while ensuring an equivalent protective effect. The amount of spraying can be reduced. This is because, as described above, the SO ₂ gas sprayed in the second supply step reacts preferentially with the alkali metal supplied to the bottom surface, and the alkaline earth metal (low-reactivity) existing even in the alkali-free glass ( This is considered to be because the reaction with Ca, Sr, etc.) is suppressed. Specifically, in the present invention, spraying amount of SO ₂ gas can be reduced with 0.05~2.5L / m ^2, in particular 0.05~0.3L / m ^2.
The SO ₂ gas is preferably sprayed at a temperature in the range of ± 100 ° C. of the glass transition point of the glass substrate. This is because the glass becomes soft at the glass transition point, so that a scratch can be more effectively prevented by forming a protective film in that region. Specifically, it is more preferable that the SO ₂ gas is sprayed at 600 to 800 ° C. When spraying is performed at this temperature, a protective coating made of sulfate that can be easily removed in the cleaning process can be generated more efficiently, and the occurrence of scratches on the back surface of the glass substrate can be further suppressed. It is.

[Washing process]
The cleaning step performed as desired is a step of cleaning and removing the protective film formed in the second supply step, and is a conventionally known step in a general float method.

  About the time (timing) of the said washing | cleaning process and the washing | cleaning method, the aspect shown below is illustrated suitably.

  The timing of the cleaning step is not particularly limited as long as it is after the second supply step, but the protective coating is made against a scratch on the surface (bottom surface) of the glass substrate that occurs during roller conveyance. Therefore, it is preferable that the final stage of the slow cooling process or immediately after the slow cooling process.

On the other hand, the cleaning method in the above-described cleaning step can be removed by an easy method because a protective film made of an alkali metal sulfate (for example, a water-soluble salt such as sodium sulfate) is formed in the present invention. For example, it can be removed by washing with water. Note that without performing the first feed step, if sprayed with SO ₂ gas, the protective film formed on the bottom surface of the glass substrate sulfates derived from alkaline earth metals (e.g., poorly water-soluble, such as calcium sulfate Salt), which makes it difficult to wash easily.

In the production method of the present invention, to improve the smoothness of the obtained alkali-free glass substrate, to reduce the distortion, undulation, microcorrugation and scratches and foreign matter defects of the glass substrate, and to obtain a highly uniform surface quality A polishing step may be provided as necessary after the cleaning step.
This polishing step is a conventionally known step in a general float method, and specifically, as a polishing method, a method of polishing a glass substrate placed on foamed urethane using a cerium oxide-based abrasive. Is mentioned.

The method for producing an alkali-free glass substrate according to the second aspect of the present invention is a method for producing an alkali-free glass substrate for producing an alkali-free glass substrate by a float method,
Comprising a molding step of forming molten glass on a molten tin on a glass substrate;
A first supply step of spraying an inorganic substance containing an alkali metal on the surface of the glass substrate that contacts the molten tin at 600 to 800 ° C., and the glass substrate at 600 to 800 ° C. after the first supply step. And a second supply step of blowing SO ₂ gas onto the surface on the side in contact with the molten tin.

  Here, the molding step in the second aspect of the present invention is the same as that described in the first aspect of the present invention, and the temperature is set to 600 to 800 ° C. in the first supply step and the second supply step. Except as specified, this is the same as that described in the first aspect of the present invention. Also in the second aspect of the present invention, it is preferable that the cleaning step is provided, and further the polishing step may be provided.

In the case where an inorganic substance containing Na and boron is used in the production method of the present invention (including the second aspect, the same applies hereinafter), the alkali-free glass substrate obtained by the production method of the present invention. It is also what provides.
Specifically, an alkali-free glass substrate is provided by spraying an inorganic substance containing Na and boron on the bottom surface of the glass substrate in the first supply step and then performing the cleaning step as necessary. Can do.

The alkali-free glass substrate of the present invention preferably has the following composition.
That is, in the alkali-free glass substrate of the present invention, the glass substrate is represented by a mass percentage based on oxide,
SiO _2: 30~85%,
Al ₂ O ₃ : 0 to 35%,
B ₂ O ₃ : 0 to 35%,
MgO: 0 to 35%,
CaO: 0 to 35%,
SrO: 0 to 35%,
BaO: 0 to 35%,
An alkali metal component: 0.5% or less, and
The average boron concentration of the bottom surface of the glass substrate is 4 to 10 atomic%, and the diffusion depth of boron into the glass substrate is 5 nm or more.

Here, the content of SiO ₂ (expressed in terms of mass percentage based on oxide) is preferably 50 to 80%, more preferably 50 to 70%, and still more preferably 56 to 66%. 58-60% is particularly preferable.
Further, the content of Al ₂ O ₃ (expressed in terms of mass percentage based on oxide) is preferably 0 to 30%, more preferably 3 to 22%, and further preferably 3 to 20%. It is preferably 15 to 20%, most preferably 15 to 19%.
The content of B ₂ O ₃ (oxide basis of mass percentage) is preferably from 0-30%, more preferably from 0 to 15%, more in the range of 5 to 12% preferable.
Further, the content of MgO (expressed in terms of mass percentage based on oxide) is preferably 0 to 20%, more preferably 0 to 8%, and still more preferably 0 to 6%.
The CaO content (expressed in terms of mass percentage based on oxide) is preferably 0 to 20%, more preferably 0 to 9%, and still more preferably 0 to 8%.
Further, the content of SrO (mass percentage based on oxide) is preferably 0 to 20%, more preferably 0 to 12.5%, and more preferably 3 to 12.5%. Further preferred.
Further, the BaO content (expressed in terms of mass percentage based on oxide) is preferably 0 to 20%, and more preferably 0% or more and less than 2%.
Further, the content of alkali metal component (expressed in terms of mass percentage based on oxide) is preferably 0.5% or less, more preferably 0.2% or less, and 0.1% or less. Is more preferable.

Here, the content of SiO ₂ , Al ₂ O ₃ , B ₂ O ₃ , MgO, CaO, SrO, BaO and the alkali metal component of the glass substrate is the alkali-free used for the alkali-free glass substrate as described above. The glass composition is within the range.

  In the present invention, the average boron concentration of the bottom surface of the glass substrate can be obtained as an average value when arbitrarily measuring five points by X-ray photoelectron spectroscopy. In the X-ray photoelectron spectroscopy, an XPS spectrometer (5500, manufactured by PHI) was used, and an X-ray AlKα ray monochromatized with a monochromator was used as an X-ray source. Further, the detection angle of X-ray photoelectrons was 75 °, and measurement was performed by irradiating an electron shower for charge correction.

In the present invention, the diffusion depth of boron into the glass substrate can be estimated from the depth at which the secondary ion intensity reaches the same level as the background by secondary ion mass spectrometry (SIMS). .
Specifically, the diffusion depth was measured at five points on each of the five points on the glass substrate with a secondary ion mass spectrometer (ADEPT 1010, manufactured by ULVAC-PHI), and the average value was obtained.
Here, the conversion of the splatter time to the splatter depth was performed in terms of SiO ₂ (4 nm = 1 min). The primary ions were measured under the conditions of an oxygen ion beam, an acceleration voltage of 5 keV, a beam current of 400 nA, an incident angle of primary ions of 45 degrees with respect to the normal of the sample surface, and a beam scanning range of 400 × 400 μm ² .

  The alkali-free glass substrate of the present invention has an average boron concentration of 4 to 10 atomic% on the bottom surface of the glass substrate, and a boron diffusion depth into the glass substrate of 5 nm to 80 nm, preferably 50 nm. Therefore, the strength of the glass substrate itself is improved, the wear resistance is excellent, and the scratch resistance is also excellent in transportation and processing steps after the protective coating is removed. The reason why boron is diffused from the bottom surface into the glass substrate and remains on the surface of the glass substrate to improve wear resistance and scratch resistance is that the network structure of the glass is strengthened. .

The alkali-free glass substrate of the present invention is not only before the cleaning step, but also after the cleaning step, if necessary, because boron remains on the surface of the glass substrate. This is preferable because generation of scratches can be continuously suppressed.
In the alkali-free glass substrate of the present invention, boron remains on the surface layer of the glass substrate. According to the first supply step, boron easily enters the glass substrate and remains on the surface layer of the glass substrate. I guess it is because it is easy to do.

Therefore, the present invention is expressed in mass percentage on an oxide basis,
SiO _2: 30~85%,
Al ₂ O ₃ : 0 to 35%,
B ₂ O ₃ : 0 to 35%,
MgO: 0 to 35%,
CaO: 0 to 35%,
SrO: 0 to 35%,
BaO: 0 to 35%,
Alkali metal component: 0.5% or less
It is also possible to provide an alkali-free glass substrate in which the average boron concentration on at least one surface is 4 to 10 atomic% and the diffusion depth of boron from the surface to the inside is 5 nm or more.

  Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto.

(Example 1)
The experimental apparatus shown in FIG. 2 was used. FIG. 2 is a cross-sectional view of the large tubular furnace used in the examples.
Specifically, a quartz tube 12 is installed in a large tubular furnace 11 whose temperature can be adjusted, a non-alkali glass substrate 13 (10 cm square) having a thickness of 0.7 mm is placed in the quartz tube 12, and the large tubular furnace 11 is installed. Heated to 700 ° C. Here, the “non-alkali glass substrate” is expressed in terms of mass percentage based on oxide, and is 68% ≦ SiO ₂ ≦ 80%, 0% ≦ Al ₂ O ₃ <12%, 0% <B ₂ O ₃ <7. %, 0% ≦ MgO ≦ 12%, 0% ≦ CaO ≦ 15%, 0% ≦ SrO ≦ 4%, 0% ≦ BaO ≦ 1%, and the content of the alkali component is 0.05% by mass or less. Non-alkali glass was used. In addition, the glass transition point of the said glass was 700 degreeC.
Next, the sodium tetraborate decahydrate reagent 15 placed in the alumina boat 14 is locally heated to about 850 ° C. to vaporize it, and the vaporized material is blown from the end of the quartz tube in the direction indicated by the arrow 16. By attaching, sodium which is an alkali metal was supplied to the surface of the alkali-free glass substrate 13. The spray amount of sodium tetraborate decahydrate at this time was 0.4 L / m ² , and the temperature of the alkali-free glass substrate 13 was 700 ° C.
Next, SO ₂ gas is sprayed from the direction indicated by the arrow 17 to form a protective film so that the amount of spray on the surface of the alkali-free glass substrate 13 is 0.1 L / m ^2, and the alkali-free glass with protective film is formed. A substrate was manufactured. The temperature of the alkali-free glass substrate 13 at this time was 700 ° C.
Note that this embodiment, spraying an alkali metal-containing inorganic material between the molding step and the annealing step, the same conditions as blowing SO ₂ gas immediately.

(Example 2)
A non-alkali glass substrate with a protective coating was produced in the same manner as in Example 1 except that the amount of SO ₂ gas sprayed was 0.4 L / m ² .

(Example 3)
A non-alkali glass substrate with a protective coating was produced in the same manner as in Example 1 except that the amount of SO ₂ gas sprayed was 1.0 L / m ² .

(Comparative Example 1)
A non-alkali glass substrate with a protective coating was produced in the same manner as in Example 1 except that sodium tetraborate was not used and only SO ₂ gas was sprayed.

(Comparative Example 2)
A non-alkali glass substrate with a protective coating was produced in the same manner as in Example 2 except that sodium tetraborate was not used and only SO ₂ gas was sprayed.

(Comparative Example 3)
A non-alkali glass substrate with a protective coating was produced in the same manner as in Example 3 except that sodium tetraborate was not used and only SO ₂ gas was sprayed.

(Comparative Example 4)
A non-alkali glass substrate was produced in the same manner as in Example 1 except that sodium tetraborate was not used, SO ₂ gas was not blown, and heating was simply performed at 700 ° C. for 15 minutes.

(Comparative Example 5)
An alkali-free glass substrate was produced in the same manner as in Example 1 except that sodium tetraborate was not used and SO ₂ gas was not sprayed.

About each alkali-free glass substrate with a protective coating obtained in Examples 1 to 3 and Comparative Examples 1 to 3, the amount of protective coating, scratch resistance, average boron concentration / diffusion depth, and wear resistance are shown below. It was measured and evaluated by the method. The results are shown in Table 1 below.
As for the glass substrate for the flat panel glass obtained in Comparative Example 4 and 5 is not blowing SO ₂ gas, since no form a protective coating were measured by the following methods abrasion resistance only. The results are shown in Table 1 below.

<Amount of protective coating>
The obtained protective coating of each non-alkali glass substrate with a protective coating was dissolved in pure water, sulfur was quantified using ICP emission spectrometry, and sodium was quantified using atomic absorption spectrometry.
From these quantitative values, the amount of sodium sulfate adhering was calculated as the amount of protective coating attached. In addition, this adhesion amount was calculated | required as an average value computed from ten sheets of the obtained non-alkali glass substrate.

<Scratch resistance>
The scratch resistance was evaluated by a Taber test according to JIS R3221 (1990). The Taber test was carried out using a Taber tester (Tdedyne Taber Model 503) with the wear wheel fixed to CS-10F, the load set to 250 g, and the number of wears fixed to 3 times.
Then, in order to remove the protective coating of each alkali-free glass substrate with a protective coating used as a test specimen, the substrate was washed with a shower for 30 seconds under flowing pure water (3 liters / minute) at 20 ° C.
The surface of the glass substrate obtained by removing the protective film was observed with a microscope, and the number of scratches (number of scratches) having a length in the major axis direction of 0.2 mm or more existing in a 1 cm × 1 cm square was measured. . The measurement part was the central part of the part subjected to the Taber test (see FIG. 3). In FIG. 3, a wear part 19 by a wear ring is formed on a test body (non-alkali glass substrate) 18, but the measurement part 20 is a central part of the wear part 19.
In addition, the measurement of the number of scratches was carried out for any 10 points for each glass substrate, and the average value was obtained. Furthermore, the number of scratches was determined as an average value calculated from 10 of the obtained glass substrates.

<Average boron concentration / diffusion depth>
(1) Each obtained non-alkali glass substrate with a protective coating was washed with water in a place where pure water (flow rate: 3 liters / minute) at 20 ° C. flows down to remove the protective coating. Thereafter, the average boron concentration on the surface of the glass substrate after washing was determined as an average value when five points were measured by X-ray photoelectron spectroscopy. In the X-ray photoelectron spectroscopy, an XPS spectrometer (5500, manufactured by PHI) was used, and an X-ray AlKα ray monochromatized with a monochromator was used as an X-ray source. Further, the detection angle of X-ray photoelectrons was 75 °, and measurement was performed by irradiating an electron shower for charge correction.

(2) The diffusion depth of boron into the glass substrate was estimated from the depth at which the secondary ion intensity reached the same level as the background by secondary ion mass spectrometry (SIMS).
Specifically, the diffusion depth was measured at five points on each of the five points on the glass substrate after washing with a secondary ion mass spectrometer (ADEPT 1010, manufactured by ULVAC-PHI), and the average value was obtained. Here, the conversion of the splatter time to the splatter depth was performed in terms of SiO ₂ (4 nm = 1 min).
The primary ions were measured under the conditions of an oxygen ion beam, an acceleration voltage of 5 keV, a beam current of 400 nA, an incident angle of primary ions of 45 degrees with respect to the normal of the sample surface, and a beam scanning range of 400 × 400 μm ² .
In Table 1 below, the diffusion depth column of Comparative Examples 1 to 3 is “−”, which indicates that diffusion could not be confirmed.

<Abrasion resistance>
Abrasion resistance was determined by examining the rate of change in the haze rate before and after the Taber test (rate of change in haze).
First, the haze ratio of each obtained alkali-free glass substrate was measured with a haze meter.
Subsequently, the obtained alkali-free glass substrate was subjected to a Taber test according to JIS R3221 (1990). The Taber test was conducted using a Taber tester (Tdedyne Taber Model 503), the wear wheel was fixed to CS-10F, and the load was fixed to 500 g.
Subsequently, the haze rate after 1000 times Taber abrasion was measured with a haze meter, and the rate of change was determined from the haze rate before the Taber test.
Here, the haze value is defined by the following formula using scattered light (Td) and transmitted light (Tt).
Haze rate = (Td / Tt) × 100%
Further, the change rate (ΔH) of the haze rate (H) is represented by the following formula.
ΔH = Haze ratio H after 1000 wear times−Haze ratio H before Taber test

From the results shown in Table 1, the alkali-free glass substrates of Examples 1 to 3 obtained using sodium tetraborate had an equivalent or lower SO ₂ gas spraying amount as compared with Comparative Examples 1 to 3. It was also found that the protective coating was formed efficiently. It was also found that the boron concentration was increased and the scratch resistance was remarkably improved.
In Comparative Examples 1 to 3, although the amount of sodium sulfate was the same, the reason why the scratch count decreased with the increase in the amount of SO ₂ gas sprayed was that the sulfate (derived from alkaline earth metal) This is because calcium sulfate, strontium sulfate, etc.) are generated and function as a protective coating.
Moreover, the non-alkali glass substrate of Examples 1-3 confirmed that the protective film formed on the surface of the glass substrate was removed after the normal water washing, and the clean surface appeared. On the other hand, in the non-alkali glass substrates of Comparative Examples 1 to 3, the protective film formed on the surface of the glass substrate could not be removed even if ordinary water washing was performed, and remained. Further, when the components of the remaining film were measured, they were calcium sulfate and strontium sulfate.
Furthermore, the alkali-free glass substrates of Examples 1 to 3 have a reduced haze change rate and improved wear resistance compared to the alkali-free glass substrates of Comparative Examples 1 to 5 due to the diffusion of boron. I understood.

Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
This application is based on a Japanese patent application filed on July 7, 2006 (Japanese Patent Application No. 2006-187727), the contents of which are incorporated herein by reference.

  According to the present invention, a non-alkali glass substrate that efficiently generates a protective film that can be easily removed in a cleaning process and suppresses the occurrence of scratches on the back surface of the glass substrate while reducing the amount of sulfurous acid gas used. And a non-alkali glass substrate obtained by the production method. The alkali-free glass substrate of the present invention can be suitably used for high quality displays.

Claims (14)

A method for producing an alkali-free glass substrate for producing an alkali-free glass substrate by a float process,
Comprising a forming step of forming molten glass on a molten tin on a glass substrate, and a slow cooling step of gradually cooling the glass substrate formed by the forming step,
A first supply step of spraying an inorganic substance containing an alkali metal to a surface of the glass substrate in contact with the molten tin; and a surface of the glass substrate in contact with the molten tin after the first supply step. And a second supply step of spraying SO ₂ gas on the substrate.   The method for producing an alkali-free glass substrate according to claim 1, wherein the first supply step is performed between the forming step and the slow cooling step.   The method for producing an alkali-free glass substrate according to claim 1, wherein the first supply step is performed at a temperature in a range of a glass transition point of ± 100 ° C. of the glass substrate.   The manufacturing method of the alkali free glass substrate of Claim 1 with which a said 1st supply process is performed at 600-800 degreeC.   The method for producing an alkali-free glass substrate according to any one of claims 1 to 4, wherein the second supply step is performed between the molding step and the slow cooling step.   The method for producing an alkali-free glass substrate according to any one of claims 1 to 4, wherein the second supply step is performed at a temperature in a range of a glass transition point ± 100 ° C of the glass substrate.   The manufacturing method of the alkali free glass substrate in any one of Claims 1-4 with which the said 2nd supply process is performed at 600-800 degreeC. A method for producing an alkali-free glass substrate for producing an alkali-free glass substrate by a float process,
Comprising a molding step of forming molten glass on a molten tin on a glass substrate;
A first supply step of spraying an inorganic substance containing an alkali metal on the surface of the glass substrate that contacts the molten tin at 600 to 800 ° C., and the glass substrate at 600 to 800 ° C. after the first supply step. And a second supply step of spraying SO ₂ gas on the surface in contact with the molten tin. A method for producing an alkali-free glass substrate.   Furthermore, the manufacturing method of the alkali free glass substrate in any one of Claims 1-8 which comprises the washing | cleaning process which removes the said protective film.   The method for producing an alkali-free glass substrate according to any one of claims 1 to 9, wherein the inorganic substance containing an alkali metal contains sodium and boron.   The method for producing an alkali-free glass substrate according to claim 10, wherein the inorganic substance containing an alkali metal is sodium tetraborate.   An alkali-free glass substrate produced by the production method according to claim 10. An alkali-free glass substrate produced by the production method according to claim 10 or 11,
The glass substrate is a mass percentage display based on oxide,
SiO _2: 30~85%,
Al ₂ O ₃ : 0 to 35%,
B ₂ O ₃ : 0 to 35%,
MgO: 0 to 35%,
CaO: 0 to 35%,
SrO: 0 to 35%,
BaO: 0 to 35%,
Alkali metal component: 0.5% or less
An alkali-free glass substrate in which an average boron concentration on the surface of the glass substrate that has been in contact with the molten tin is 4 to 10 atomic%, and a boron diffusion depth into the glass substrate is 5 nm or more. In mass percentage display based on oxide,
SiO _2: 30~85%,
Al ₂ O ₃ : 0 to 35%,
B ₂ O ₃ : 0 to 35%,
MgO: 0 to 35%,
CaO: 0 to 35%,
SrO: 0 to 35%,
BaO: 0 to 35%,
Alkali metal component: 0.5% or less
An alkali-free glass substrate having an average boron concentration of at least one surface of 4 to 10 atomic% and a boron diffusion depth from the surface to the inside of 5 nm or more.

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