JP2011020864A - Method for producing glass substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a glass substrate where the glass substrate having a small thermal shrinkage factor is produced directly by a down-draw method. <P>SOLUTION: The method for producing the glass substrate comprises a shaping step to shape molten glass to a glass ribbon by the down-draw method, an annealing step to anneal the glass ribbon and a cutting step to cut the glass ribbon and obtain the glass substrate after the annealing step. In the annealing step, the glass ribbon is cooled so that the average cooling rate of the glass ribbon in a temperature range from the annealing point of the glass ribbon to the annealing point of the glass ribbon minus 50°C is satisfied with a following equation denoted as log<SB>10</SB>R≤0.00018361Ta<SP>2</SP>-0.23414Ta+75.29 (wherein, R is the average cooling rate of the glass ribbon (°C/min); and Ta is the annealing point of the glass ribbon (°C)). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a glass substrate, and more particularly to a method for manufacturing a glass substrate suitable for a display including a thin film transistor (TFT) having a low-temperature polysilicon film.

  In recent years, flat panel displays such as liquid crystal displays have been rapidly spreading. In a flat panel display, a glass substrate is generally used as a support substrate. On the surface of the glass substrate, an electric circuit pattern such as a thin film transistor (TFT) is formed. For this reason, the glass substrate is exposed to a high temperature atmosphere in an electric circuit pattern forming process such as a thin film forming process or a thin film patterning process. When the glass substrate is exposed to a high temperature atmosphere, the structural relaxation of the glass proceeds, so that the volume of the glass substrate shrinks (hereinafter, the shrinkage of the glass is referred to as “thermal shrinkage”). If thermal shrinkage occurs in the glass substrate during the electrical circuit pattern formation process, the shape and dimensions of the electrical circuit pattern formed on the glass substrate will deviate from the design values, and a flat panel display having the desired electrical performance is obtained. It will be difficult.

  For this reason, a glass substrate on which a thin film pattern such as an electric circuit pattern is formed on the surface, such as a glass substrate for a flat panel display, is desired to have a small thermal shrinkage rate. In particular, a glass substrate for a high-definition display including a TFT having a low-temperature polysilicon film is exposed to a very high temperature atmosphere of, for example, 450 ° C. to 600 ° C. when the low-temperature polysilicon film is formed. Since heat shrinkage tends to occur and the electrical circuit pattern has a high definition, even if small heat shrinkage occurs, it tends to be difficult to obtain the desired electrical performance. It is rare.

  Conventionally, as a glass substrate forming method used for a flat panel display or the like, a float method, a down draw method represented by an overflow down draw method described in Patent Document 1, for example, and the like are known.

  In the float method, molten glass is flown out onto a float bath filled with molten tin, and stretched in the horizontal direction to form a glass ribbon. Then, the glass ribbon is gradually cooled in a slow cooling furnace provided downstream of the float bath. This is a method for forming a glass substrate. In the float process, since the conveying direction of the glass ribbon is the horizontal direction, it is easy to lengthen the slow cooling furnace. For this reason, it is easy to make the cooling rate of the glass ribbon in a slow cooling furnace low enough. Therefore, the float method has an advantage that it is easy to obtain a glass substrate having a small heat shrinkage rate.

  However, with the float method, it is difficult to mold a thin glass substrate, and after molding, the surface of the glass substrate must be polished to remove tin adhering to the surface of the glass substrate. There are disadvantages.

  On the other hand, the downdraw method is a method in which molten glass is drawn downward to form a plate shape. In the overflow downdraw method, which is a kind of downdraw method, a glass ribbon is formed by stretching downward the molten glass overflowed from both sides of a forming body having a substantially wedge-shaped cross section. In the overflow down draw method, the molten glass overflowing from both sides of the molded body flows down along both side surfaces of the molded body and joins below the molded body. Therefore, in the overflow down draw method, the surface of the glass ribbon does not come into contact with anything other than air, and is formed by surface tension. A flat glass substrate can be obtained. Further, the overflow downdraw method has an advantage that a thin glass substrate can be easily formed.

WO2007 / 080924 A1

  In the downdraw method, the molten glass flows downward from the molded body. Therefore, in order to dispose a long slow cooling furnace under the molded body, the molded body must be disposed at a high place. However, in practice, there is a restriction on the height at which the molded body can be disposed due to the height restriction of the ceiling of the factory. For this reason, in the downdraw method, the length dimension of the slow cooling furnace is limited, and it may be difficult to arrange a sufficiently long slow cooling furnace. When the length of the slow cooling furnace is short, the cooling rate of the glass ribbon becomes high, so that it becomes difficult to form a glass substrate having a small heat shrinkage rate.

  For this reason, in general, when a glass substrate having a low thermal shrinkage rate is manufactured using the downdraw method, a heat treatment (off-line annealing) for reducing the thermal shrinkage rate has been performed after molding. Therefore, there are problems that the manufacturing process is complicated and a long time is required for the manufacturing. Therefore, a method capable of directly manufacturing a glass substrate having a small heat shrinkage rate using the downdraw method is desired.

  This invention is made | formed in view of this point, The objective is to provide the manufacturing method of the glass substrate which can manufacture directly a glass substrate with a small heat shrinkage rate by a downdraw method.

  Regarding the heat shrinkage rate, for example, in the above-mentioned Patent Document 1, the cooling rate in the temperature range from (annealing point + 50 ° C.) to (annealing point−100 ° C.) is greatly involved in the heat shrinkage rate. It is described. Japanese Patent Application Laid-Open No. H10-260260 describes that variation in the heat shrinkage rate in the width direction can be reduced by increasing the cooling rate in the above temperature range. Specifically, the average cooling rate of the glass ribbon in the temperature range from the annealing point to (annealing point−100 ° C.) is 200 ° C./min or more, preferably 300 ° C./min or more, more preferably 350 ° C./min. As described above, it is described that the variation in the thermal shrinkage rate in the width direction can be reduced by setting the temperature to 400 ° C./min or more, particularly preferably 500 ° C./min or more. However, the thermal shrinkage rate in the central portion in the width direction of the glass substrate formed in this case is 40 ppm or more, and it is difficult to directly manufacture a glass substrate having a sufficiently small thermal shrinkage rate by the method described in Patent Document 1. It is.

  As a result of intensive studies, the present inventors have found the following items (1) to (3), and as a result, have reached the present invention.

(1) The thermal shrinkage rate of the glass substrate is mainly determined by the cooling rate of the glass ribbon in the temperature range from the annealing point to a temperature lower by 50 ° C. than the annealing point. (2) The glass ribbon in the temperature range. (3) The cooling rate of the glass ribbon in the above temperature range is determined by changing the cooling rate of the glass ribbon and the thermal shrinkage rate of the glass substrate. A glass substrate having a small thermal shrinkage rate can be obtained even when the cooling rate of the glass ribbon in the temperature range other than the above temperature range is increased by making it within a predetermined speed range correlated with Ta).

  That is, the method for producing a glass substrate according to the present invention comprises a forming step of forming molten glass into a ribbon-like glass ribbon by a down draw method such as an overflow down draw method or a slot (slit) down draw method, and a glass ribbon gradually. A method for producing a glass substrate comprising a slow cooling step for cooling, and a cutting step for cutting the glass ribbon to obtain a glass substrate after the slow cooling step, wherein the glass from the annealing point of the glass ribbon in the slow cooling step The glass ribbon is cooled so that the average cooling rate of the glass ribbon in the temperature range up to a temperature lower by 50 ° C. than the annealing point of the ribbon satisfies the following formula (1).

log ₁₀ R ≦ 0.00018361Ta ² −0.23414Ta + 75.29 (1)
However,
R: Average cooling rate of glass ribbon (° C / min),
Ta: annealing point of glass ribbon (° C),
It is.

In the present invention, the “slow cooling point” is a temperature at which the glass exhibits a viscosity of 10 ¹³ dPa · s, and is a temperature measured by a method prescribed in ASTM C336-71.

  The “average cooling rate” is calculated by calculating the time required for the central portion of the glass ribbon in the width direction to pass through a predetermined temperature region, and dividing the temperature difference within the predetermined temperature region by the time required for passing. This is the speed obtained.

In the present invention, the glass in the temperature range between the annealing point of the glass ribbon and the temperature lower by 50 ° C. than the annealing point of the glass ribbon, which is the temperature range that most greatly affects the magnitude of the thermal shrinkage rate of the glass substrate. The average cooling rate of the ribbon is set to a low range that satisfies the above formula (1). For this reason, a glass substrate with a small thermal contraction rate can be manufactured. Specifically, a glass substrate having a heat shrinkage rate of 30 ppm or less can be produced. In the slow cooling step, the average cooling rate of the glass ribbon in the temperature range from the slow cooling point of the glass ribbon to a temperature lower by 50 ° C. than the slow cooling point of the glass ribbon satisfies the following formula (1), and glass The ribbon's annealing point (Ta) is higher than the extreme value (638 ° C.) of the quadratic function (log ₁₀ R = 0.00018361Ta ² −0.23414Ta + 75.29) representing the criticality of the above formula (1). preferable.

  From the viewpoint of manufacturing a glass substrate having a smaller thermal shrinkage rate, the average cooling rate of the glass ribbon in the temperature range from the annealing point of the glass ribbon to a temperature lower by 50 ° C. than the annealing point of the glass ribbon is even lower. It is preferable.

  Specifically, the glass ribbon has an average cooling rate in the temperature range from the annealing point of the glass ribbon to a temperature lower by 50 ° C. than the annealing point of the glass ribbon so as to satisfy the following formula (2). It is preferable to perform slow cooling. By doing so, a glass substrate having a thermal shrinkage rate of 23 ppm or less can be produced.

log ₁₀ R ≦ 0.00013786Ta ² −0.17422Ta + 55.53 (2)

In the slow cooling step, the average cooling rate of the glass ribbon in the temperature range from the slow cooling point of the glass ribbon to a temperature lower by 50 ° C. than the slow cooling point of the glass ribbon satisfies the following formula (2), and glass The ribbon's annealing point (Ta) is higher than the extreme value (632 ° C.) of the quadratic function (log ₁₀ R = 0.00013786Ta ² −0.17422Ta + 55.53) representing the criticality of the above formula (1). More preferred.

  Further, the glass ribbon is gradually cooled so that the average cooling rate of the glass ribbon in the temperature range from the annealing point of the glass ribbon to a temperature lower by 50 ° C. than the annealing point of the glass ribbon satisfies the following formula (3). It is preferable to carry out. By doing so, a glass substrate having a thermal shrinkage rate of 20 ppm or less can be produced.

log ₁₀ R ≦ 0.00011821Ta ² −0.14847Ta + 47.03 (3)

In the slow cooling step, the average cooling rate of the glass ribbon in the temperature range from the slow cooling point of the glass ribbon to a temperature lower by 50 ° C. than the slow cooling point of the glass ribbon satisfies the following formula (3), and glass The annealing point (Ta) of the ribbon is higher than the extreme value (628 ° C.) of the quadratic function (log ₁₀ R = 0.00011821 Ta ² −0.14847 Ta + 47.03) representing the criticality of the above formula (1). More preferred.

  Further, the glass ribbon is gradually cooled so that the average cooling rate of the glass ribbon in the temperature range from the annealing point of the glass ribbon to a temperature lower by 50 ° C. than the annealing point of the glass ribbon satisfies the following formula (4). It is preferable to carry out. By doing so, a glass substrate having a thermal shrinkage rate of 10 ppm or less can be produced.

log ₁₀ R ≦ 0.000054326Ta ² −0.064985Ta + 19.56 (4)

In the slow cooling step, the average cooling rate of the glass ribbon in the temperature range from the slow cooling point of the glass ribbon to a temperature lower by 50 ° C. than the slow cooling point of the glass ribbon satisfies the following formula (3), and glass The ribbon's annealing point (Ta) is higher than the extreme value (598 ° C.) of the quadratic function (log ₁₀ R = 0.000054326Ta ² −0.064985Ta + 19.56) representing the criticality of the above formula (1). More preferred.

Further, from the viewpoint of more reliably obtaining a glass substrate having a small thermal shrinkage rate, the maximum cooling rate of the glass ribbon in the temperature range between the annealing point of the glass ribbon and the temperature 50 ° C. lower than the annealing point of the glass ribbon. (Log ₁₀ R _MAX ) preferably satisfies the following formula (5), more preferably satisfies the following formula (6), and more preferably satisfies the following formula (7). It is still more preferable that the following formula (8) is satisfied.

At the same time, it is preferable that the annealing point of the glass ribbon is higher than the extreme value of the quadratic function indicating the criticality of the formulas (5) to (8) that define the range of log ₁₀ R _MAX .

log ₁₀ R _MAX ≦ 0.00018361Ta ² −0.23414Ta + 75.29 (5)
log ₁₀ R _MAX ≦ 0.00013786Ta ² −0.17422Ta + 55.53 (6)
log ₁₀ R _MAX ≦ 0.00011821Ta ² −0.14847Ta + 47.03 (7)
log ₁₀ R _MAX ≦ 0.000054326Ta ² −0.064985Ta + 19.56 (8)

  As described above, the magnitude of the heat shrinkage rate of the glass substrate obtained depends on the cooling rate of the glass ribbon in the temperature range between the annealing point of the glass ribbon and the temperature 50 ° C. lower than the annealing point of the glass ribbon. It is greatly influenced. On the other hand, the cooling rate of the glass ribbon in the temperature range other than the temperature range between the annealing point of the glass ribbon and the temperature lower by 50 ° C. than the annealing point of the glass ribbon is the magnitude of the thermal contraction rate of the glass substrate. Does not affect so much. Therefore, in the present invention, the cooling rate of the glass ribbon in the temperature range other than the temperature range between the annealing point of the glass ribbon and the temperature lower by 50 ° C. than the annealing point of the glass ribbon is the length of the installable annealing furnace. It can be set appropriately according to the above.

  For example, in the slow cooling step, the average cooling rate of the glass ribbon in a temperature range higher than the slow cooling point of the glass ribbon, and the average cooling rate of the glass ribbon in a temperature range lower than 50 ° C. lower than the slow cooling point of the glass ribbon Each of the glass ribbon is cooled so as to be higher than the average cooling rate of the glass ribbon in a temperature range between the annealing point of the glass ribbon and a temperature lower by 50 ° C. than the annealing point of the glass ribbon. it can. Even in this case, a glass substrate having a small heat shrinkage rate can be manufactured.

  That is, according to the present invention, the average cooling rate of the glass ribbon in the temperature range from the annealing point of the glass ribbon to a temperature lower by 50 ° C. than the annealing point of the glass ribbon is defined as a function of the annealing point of the glass ribbon. The average cooling rate of the glass ribbon in the temperature range other than the temperature range between the annealing point of the glass ribbon and the temperature lower by 50 ° C. than the annealing point of the glass ribbon is increased by setting the speed to be equal to or lower than the predetermined rate. It becomes possible. Therefore, according to the present invention, it is possible to directly manufacture a glass substrate having a small thermal shrinkage rate by a downdraw method using a glass manufacturing apparatus having a short annealing furnace.

  As described above, the cooling rate of the glass ribbon in the temperature range other than the temperature range between the annealing point of the glass ribbon and the temperature lower by 50 ° C. than the annealing point of the glass ribbon is from the annealing point of the glass ribbon to the glass. The cooling rate of the glass ribbon in the temperature range up to 50 ° C. lower than the annealing point of the ribbon does not significantly affect the magnitude of the heat shrinkage rate of the glass substrate. However, in a temperature range other than the temperature range between the annealing point of the glass ribbon and the temperature lower than the annealing point of the glass ribbon by 50 ° C., the glass ribbon starts from a temperature that is 50 ° C. lower than the annealing temperature of the glass ribbon. The cooling rate of the glass ribbon in the temperature range lower by 200 ° C. than the annealing point of the glass ribbon is the cooling rate of the glass ribbon in the temperature range lower than the temperature lower by 200 ° C. than the annealing temperature of the glass ribbon, or the annealing temperature of the glass ribbon The influence on the magnitude of the thermal contraction rate of the glass substrate obtained is larger than the cooling rate of the glass ribbon in a higher temperature range. In particular, the heat shrinkage of the glass substrate to be obtained as the cooling rate of the glass ribbon in the temperature range on the high temperature side within the temperature range from 50 ° C. lower than the annealing point of the glass ribbon to 200 ° C. lower than the annealing point of the glass ribbon. The effect on the rate is large. Therefore, the average cooling rate of the glass ribbon in the temperature range on the high temperature side within the temperature range from the temperature 50 ° C. lower than the annealing point of the glass ribbon to the temperature 200 ° C. lower than the annealing point of the glass ribbon is also expressed by the above formula ( 1) is preferably satisfied, the above formula (2) is more preferably satisfied, the above formula (3) is more preferably satisfied, and the above formula (4) is more preferably satisfied. In addition, the average cooling rate of the glass ribbon in the entire temperature range from the temperature lower by 50 ° C. than the annealing point of the glass ribbon to the temperature lower by 200 ° C. than the annealing point of the glass ribbon satisfies the above formula (1). Preferably, the above formula (2) is more preferably satisfied, the above formula (3) is particularly preferably satisfied, and the above formula (4) is more preferably satisfied.

That is, in the slow cooling step, when Tx is set to a temperature that is lower than the temperature lower by 50 ° C. than the slow cooling point of the glass ribbon and 200 ° C. lower than the slow cooling point of the glass ribbon, the glass ribbon is slowly cooled. It is preferable to cool the glass ribbon so that the average cooling rate of the glass ribbon in the temperature range from the point to Tx satisfies the above formula (1), and it is more preferable to cool the glass ribbon so as to satisfy the formula (2). More preferably, the glass ribbon is cooled so as to satisfy the formula (3), and more preferably, the glass ribbon is cooled so as to satisfy the formula (4). By doing so, a glass substrate with a smaller heat shrinkage rate can be manufactured. Furthermore, it is preferable to cool the glass ribbon so that the maximum cooling rate (R _MAX ) of the glass ribbon in the temperature range from the annealing point of the glass ribbon to Tx satisfies the above formula (5), and the above formula (6) More preferably, the glass ribbon is cooled so as to satisfy the above condition, more preferably, the glass ribbon is cooled so as to satisfy the above formula (7), and the glass ribbon is preferably cooled so as to satisfy the above formula (8). preferable.

At the same time, it is preferable that the annealing point of the glass ribbon is higher than the extreme value of the quadratic function indicating the criticality of the formulas (1) to (8) that define the range of log ₁₀ R.

  In addition, the lower limit of the average cooling rate of the glass ribbon in the temperature range from the annealing point of the glass ribbon to a temperature lower by 50 ° C. than the annealing point of the glass ribbon is not particularly limited, but there is a restriction on the height dimension of the glass manufacturing apparatus. When considered, the average cooling rate of the glass ribbon in the temperature range from the annealing point of the glass ribbon to a temperature lower by 50 ° C. than the annealing point of the glass ribbon is preferably 0.34 ° C./min or more. / Min or more, more preferably 2 ° C./min or more, still more preferably 5 ° C./min or more. Similarly, the average cooling rate of the glass ribbon in the temperature range from a temperature 50 ° C. lower than the annealing point of the glass ribbon to Tx is also preferably 0.34 ° C./min or more, and preferably 1 ° C./min or more. More preferably, it is 2 ° C./min or more, more preferably 5 ° C./min or more.

  The cooling rate of the glass ribbon in each of the temperature range having a small influence on the magnitude of the thermal shrinkage rate of the glass substrate obtained, that is, the temperature range higher than the annealing point of the glass ribbon and the temperature range lower than Tx is high. Is preferred. This is because by increasing the cooling rate of the glass ribbon in these temperature ranges, the time required for slow cooling of the glass ribbon can be shortened, so that the length of the slow cooling furnace can be shortened. Specifically, the average cooling rate of the glass ribbon in the temperature range lower than Tx is preferably 50 ° C./min or more. Moreover, it is preferable that the average cooling rate of the glass ribbon in a temperature range higher than a slow cooling point is 30 degree-C / min or more.

  In the present invention, the method of forming the glass ribbon in the forming step is not particularly limited as long as it is a downdraw method, but it is preferable to form the glass ribbon by the overflow downdraw method among the downdraw methods. This is because by forming the glass ribbon by the overflow down draw method, it is possible to directly manufacture a glass substrate having high surface smoothness and no foreign matter attached to the surface.

  In the present invention, the width of the glass ribbon formed in the forming step is preferably 500 mm or more, more preferably 600 mm or more, further preferably 700 mm or more, and still more preferably 800 mm or more. More preferably, it is 900 mm or more, and particularly preferably 1000 mm or more. In this case, the effect of the present invention can be obtained more remarkably. Specifically, the larger the width of the glass ribbon, the more difficult it is to polish the surface of the glass substrate. However, when the glass substrate is produced according to the present invention, it is not necessary to polish the surface. Can be manufactured. In addition, as the width of the glass ribbon increases, the glass substrate is more likely to warp or distort. However, by manufacturing the glass substrate according to the present invention, it is possible to effectively generate warpage and distortion even with a large glass substrate. Can be suppressed.

In the present invention, the viscosity (liquid phase viscosity) of the molten glass at the liquidus temperature is preferably 10 ^4.5 dPa · s or higher, more preferably 10 ^5.0 dPa · s or higher, more preferably 10 ^5. More preferably, it is more than ^1.5 dPa · s, and still more preferably more than 10 ^6.0 dPa · s. According to this configuration, even when the temperature of the molten glass is lowered to a temperature suitable for forming a glass ribbon by the overflow downdraw method, the molten glass is not devitrified. That is, the temperature of the molten glass can be lowered until the molten glass has a viscosity suitable for the overflow downdraw method. For this reason, a glass ribbon can be suitably shape | molded by the overflow downdraw method.

  In addition, a liquid phase viscosity can be calculated | required with the following procedures. First, glass is pulverized, and glass powder that passes through a standard sieve 30 mesh (50 μm) and does not pass 50 mesh (300 μm) is prepared. The glass powder is put on a platinum board and held at a predetermined temperature for 24 hours, and then the presence or absence of crystals is visually confirmed. This is performed for a plurality of temperatures, and the highest temperature (liquid phase temperature) at which crystals precipitate is obtained. Moreover, the viscosity of the molten glass at each temperature is measured by a platinum ball pulling method, and a viscosity curve is created. From this viscosity curve and the liquidus temperature, the viscosity of the molten glass at the liquidus temperature (liquidus viscosity) is calculated.

  Moreover, in this invention, it is preferable that the annealing point (Ta) of a glass ribbon is 600 degreeC or more. The annealing point (Ta) of the glass ribbon correlates with the thermal shrinkage rate of the glass substrate. Specifically, the higher the annealing point (Ta), the smaller the thermal shrinkage rate of the glass substrate. Therefore, by setting the annealing point (Ta) of the glass ribbon to 600 ° C. or higher, a glass substrate having a smaller heat shrinkage rate can be produced. From the viewpoint of obtaining a glass substrate having a smaller thermal shrinkage rate, the annealing point (Ta) of the glass ribbon is more preferably 630 ° C. or higher, and further preferably 650 ° C. or higher. The upper limit of the annealing point (Ta) of the glass ribbon is preferably 1000 ° C., for example, and more preferably 900 ° C.

As a molten glass that can obtain a glass ribbon having a low liquidus temperature, a high liquidus viscosity, and a high strain point, for example, in terms of mass percentage, SiO ₂ : 50 to 70%, Al ₂ O ₃ : 10 _{25%, B 2 O 3:} 3~15%, MgO: 0~10%, CaO: 0~10%, SrO: 0~15%, BaO: 0~15% and _Na 2 O: the 0-5% The molten glass to contain is mentioned. In addition, by using such molten glass, for example, a glass substrate excellent in characteristics required for a glass substrate for flat panel displays, for example, chemical resistance, specific Young's modulus, chemical durability, etc. Can be manufactured.

  The production method according to the present invention can be suitably used for general production of glass substrates that are required to have a low thermal shrinkage rate, such as a glass substrate on which an electric circuit pattern is formed. Specifically, the manufacturing method according to the present invention includes, for example, a glass substrate for a flat panel display such as a liquid crystal display, an electroluminescence display, and a plasma display, a charge coupled device (CCD) and a complementary metal oxide film. It can be suitably used for a glass substrate for an imaging element such as a semiconductor (CMOS: Complementary Metal-Oxide Semiconductor device). Among these, the manufacturing method according to the present invention is suitable for manufacturing a glass substrate for flat panel displays in which a high-definition electric circuit pattern is formed and the area of the glass substrate is large. The present invention is particularly suitable for manufacturing a glass substrate of a flat panel display including a glass substrate having a thin film transistor formed thereon.

  In the present invention, the glass in the temperature range between the annealing point of the glass ribbon and the temperature lower by 50 ° C. than the annealing point of the glass ribbon, which is the temperature range that most greatly affects the magnitude of the thermal shrinkage rate of the glass substrate. Since the average cooling rate of the ribbon is set so as to satisfy the above formula (1), a glass substrate having a small thermal contraction rate can be directly manufactured by the downdraw method.

It is a typical block diagram showing a part of glass manufacturing apparatus. It is a graph showing the temperature change of the glass ribbon in a slow cooling process. Logarithm of the cooling speed (R) and _{(log 10} R), is a graph showing the relationship between the thermal shrinkage. It is a graph showing the relationship between the logarithm (log ₁₀ R) of the cooling rate (R) when the heat shrinkage rate is 30 ppm, and the annealing point (Ta). It is a graph showing the relationship between the logarithm (log ₁₀ R) of the cooling rate (R) when the thermal shrinkage rate is 23 ppm, and the annealing point (Ta). It is a graph showing the relationship between the logarithm (log ₁₀ R) of the cooling rate (R) when the thermal shrinkage rate is 20 ppm, and the annealing point (Ta). It is a graph showing the relationship between the logarithm (log ₁₀ R) of the cooling rate (R) when the thermal shrinkage rate is 10 ppm, and the annealing point (Ta). It is a schematic diagram for demonstrating the measuring method of a thermal contraction rate.

  Hereinafter, in this embodiment, an example of the preferable form which implemented this invention is demonstrated in detail.

  FIG. 1 is a schematic configuration diagram showing a part of a glass manufacturing apparatus in the present embodiment. A glass manufacturing apparatus 1 shown in FIG. 1 is an apparatus for manufacturing a glass substrate by an overflow down draw method. As shown in FIG. 1, the glass manufacturing apparatus 1 includes a forming furnace 10. Inside the molding furnace 10, a forming body 11 having a substantially wedge-shaped cross section is arranged. The molded body 11 is supplied with molten glass 12 melted in a glass melting furnace (not shown). The supplied molten glass 12 overflows from both sides of the molded body 11 and merges below the lower end portion of the molded body 11. As a result, the glass ribbon 13 is formed. A roller pair 14 is disposed below the molded body 11. By passing the glass ribbon 13 between the roller pair 14, the shape of the glass ribbon 13 is adjusted.

  Although the glass material used in this embodiment is not specifically limited, It is preferable that the annealing point (Ta) of the glass ribbon 13 is 600 degreeC or more. The annealing point (Ta) correlates with the thermal shrinkage rate of the glass substrate 25. Specifically, the higher the annealing point (Ta), the smaller the thermal shrinkage rate of the glass substrate 25. Therefore, by setting the annealing point (Ta) of the glass ribbon 13 to 600 ° C. or higher, the glass substrate 25 having a smaller heat shrinkage rate can be manufactured. From the viewpoint of obtaining a glass substrate 25 having a smaller thermal shrinkage rate, the annealing point (Ta) of the glass ribbon 13 is more preferably 630 ° C. or higher, and further preferably 650 ° C. or higher. The upper limit of the annealing point of the glass ribbon 13 is preferably 1000 ° C, and more preferably 900 ° C.

Further, the viscosity (liquid phase viscosity) at the liquidus temperature of the molten glass 12 is preferably 10 ^4.5 dPa · s or more, more preferably 10 ^5.0 dPa · s or more, and 10 ^5.5. It is more preferably dPa · s or more, and still more preferably 10 ^6.0 dPa · s or more. In this case, even when the temperature of the molten glass is lowered to a temperature suitable for forming the glass ribbon 13 by the overflow down draw method, the molten glass 12 is not devitrified. That is, the temperature of the molten glass 12 can be lowered until the molten glass 12 has a viscosity suitable for the overflow downdraw method. Therefore, the glass ribbon 13 can be suitably formed by the overflow down draw method.

As the molten glass 12 that can obtain the glass ribbon 13 having a low liquidus temperature, a high liquidus viscosity, and a high strain point, for example, in terms of mass percentage, SiO ₂ : 50 to 70%, Al ₂ O ₃ : _{10~25%, B 2 O 3:} 3~15%, MgO: 0~10%, CaO: 0~15%, SrO: 0~15%, BaO: 0~10% and _Na 2 O: 0 to 5 % Containing molten glass. Further, by using such a molten glass, for example, a glass substrate 25 excellent in characteristics required for a glass substrate for a flat panel display, for example, characteristics such as chemical resistance, specific Young's modulus, and chemical durability. Can be manufactured.

  In addition, the detail of the preferable reason of the range of each said composition is as follows.

SiO ₂ is a component that becomes a network former of glass. When the content of SiO ₂ is too large, there is a tendency that the viscosity of the molten glass 12 becomes too high and tends to molten glass 12 tends to be devitrified. On the other hand, if the content of SiO ₂ is too small, the chemical durability of the glass substrate 25 tends to decrease.

Al ₂ O ₃ is a component for increasing the strain point and annealing point of the glass substrate 25. When the content of Al ₂ O ₃ is too large, the molten glass 12 is devitrified, also tends to chemical durability against buffered hydrofluoric acid of the glass substrate 25 is reduced. On the other hand, when the content of Al ₂ O ₃ is too small, strain point and annealing point of the glass substrate 25 is lowered, there is a tendency that thermal shrinkage is increased.

B ₂ O ₃ is a component that acts as a flux and improves the meltability of the glass. B strain point and annealing point of the content is too large glass substrate 25 of the ₂ O ₃ is low, there is a tendency that thermal shrinkage is increased. Further, the chemical resistance of the glass substrate 25 to hydrochloric acid tends to be reduced. On the other hand, when the content of B ₂ O ₃ is too small, the higher the viscosity of the molten glass 12, there is a tendency that the meltability decreases. The more preferable content of B ₂ O ₃ is 5 to 15% by weight.

  MgO, CaO, SrO, and BaO are optional components that lower the viscosity of the molten glass 12 and improve the meltability of the glass. SrO and BaO are also components that improve the chemical durability of the glass substrate 25. When there is too much content of MgO, CaO, SrO, BaO, it will become easy to devitrify the molten glass 12, and it exists in the tendency for the chemical durability with respect to the buffer food hydrofluoric acid of the glass substrate 25 to also fall. Moreover, when there is too much content of BaO, it exists in the tendency for the density of the glass substrate 25 to become high too much. A more preferable content of MgO is 0 to 5% by weight. A more preferable content of CaO is 0 to 12% by weight. A more preferable content of SrO is 0 to 10% by weight. A more preferable content of BaO is 0 to 5% by weight.

Na ₂ O is a component that reduces the viscosity of the molten glass 12 and improves the meltability of the glass. When the content of Na 2 _O is too large, the strain point of the glass substrate 25 is lowered, there is a tendency that the thermal shrinkage rate is low. Further, elution of Na component from the glass substrate 25 may be a problem.

  In addition to the above components, various components such as a clarifying agent may be included in the molten glass 12 as necessary.

  In the present embodiment, the glass melting step is not particularly limited. For example, a glass raw material or glass cullet mixed at a desired ratio is charged into, for example, a Pt crucible or a refractory crucible and heated to a predetermined temperature of, for example, about 1500 ° C. to 1650 ° C. The molten glass 12 can be obtained by stirring and clarifying.

  In the present embodiment, the width of the glass ribbon 13 formed in the forming step is preferably 500 mm or more, more preferably 600 mm or more, further preferably 700 mm or more, and preferably 800 mm or more. More preferably, it is 900 mm or more, and particularly preferably 1000 mm or more. Thus, when the width of the glass ribbon 13 is large, the effect of the overflow downdraw method appears more remarkably. Specifically, the larger the width of the glass ribbon 13, the more difficult it is to polish the surface of the glass substrate 25, but when the glass substrate 25 is manufactured by the glass substrate manufacturing method of the present embodiment, Since it is not necessary to polish the surface, the glass substrate 25 can be manufactured easily and inexpensively. Further, as the width of the glass ribbon 13 increases, the glass substrate 25 is more likely to be warped or distorted. However, when the glass substrate 25 is manufactured by the method for manufacturing a glass substrate of the present embodiment, the glass substrate 25 having a large width is used. However, the occurrence of warpage and distortion can be effectively suppressed.

  Further, the thickness of the glass ribbon 13 is not particularly limited, and can be appropriately set according to the use of the glass substrate 25 and the like. For example, when manufacturing the glass substrate 25 used for a mobile display, the thickness of the glass ribbon 13 can be set so that the thickness of the glass substrate 25 is about 0.1 to 0.5 mm. Moreover, when manufacturing the glass substrate 25 for flat panel displays, such as a monitor and television, the thickness of the glass ribbon 13 can be set so that the thickness of the glass substrate 25 may be about 0.3-1.1 mm. it can.

  The formed glass ribbon 13 is guided to a slow cooling furnace 20 disposed below the forming furnace 10. In this slow cooling furnace 20, the slow cooling process which cools the glass ribbon 13 slowly to predetermined | prescribed temperature is performed. Specifically, the slow cooling furnace 20 is provided with a plurality of heaters 21. The temperature in the slow cooling furnace 20 is controlled by the plurality of heaters 21. Specifically, the heater 21 arranged on the upstream side is set to a higher temperature, and the heater 21 arranged on the downstream side is set to a lower temperature. Then, by gradually lowering the set temperature of the heater 21 from the upstream side toward the downstream side, a temperature gradient is formed in the slow cooling furnace 20, and desired cooling conditions for the glass ribbon 13 to be described later are realized. Yes.

  The slow cooling furnace 20 is provided with a plurality of tension roller pairs 22, and the glass ribbon 13 is pulled by the plurality of tension roller pairs 22. Thereby, the glass ribbon 13 is suppressed from contracting in the width direction of the glass ribbon 13. The length (height) of the slow cooling furnace 20 is not particularly limited, but the length (height) of the slow cooling furnace 20 is set to about 200 to 3000 cm, for example.

  A cooling chamber 23 is disposed below the slow cooling furnace 20. The glass ribbon 13 that has been gradually cooled in the slow cooling furnace 20 is cooled by natural cooling in the cooling chamber 23 to near room temperature. Although the length (height) of the cooling chamber 23 is not particularly limited, the length (height) of the cooling chamber 23 can be set to, for example, about 200 to 1000 cm.

  A cutting chamber 24 is disposed below the cooling chamber 23. By cutting the glass ribbon 13 into a predetermined dimension in the cutting chamber 24, the glass substrate 25 is completed. In addition, the cutting method of the glass ribbon 13 is not specifically limited, The glass ribbon 13 can be cut | disconnected by a known cutting method.

(Slow cooling process)
FIG. 2 is a graph showing the temperature change of the glass ribbon in the slow cooling process. In FIG. 2, the horizontal axis is the elapsed time after the glass ribbon 13 enters the slow cooling furnace 20, and the vertical axis is the temperature of the glass ribbon 13. In FIG. 2, a solid line represents the slow cooling process in this embodiment, and a one-dot broken line represents the slow cooling process when the glass ribbon is slowly cooled at a constant speed.

  Next, details of the slow cooling step will be described mainly with reference to FIGS. 1 and 2. In the present embodiment, as shown in FIG. 1, the first slow cooling zone 20 a, the second slow cooling zone 20 b, and the third slow cooling inside the slow cooling furnace 20 from the upstream side toward the downstream side. Zone 20c is provided.

  In the first slow cooling zone 20a arranged on the most upstream side, the first slow cooling step A1 is performed. As shown in FIG. 2, the first slow cooling step A <b> 1 is a step of gradually cooling the glass ribbon 13 until the temperature of the glass ribbon 13 reaches the slow cooling point (Ta) of the glass ribbon 13.

  As shown in FIG. 1, the second slow cooling step A2 is performed in the second slow cooling zone 20b disposed on the downstream side of the first slow cooling zone 20a. As shown in FIG. 2, the second slow cooling step A <b> 2 is a step of gradually cooling the glass ribbon 13 until the temperature of the glass ribbon 13 reaches Tx from the slow cooling point (Ta) of the glass ribbon 13. Here, Tx is equal to or lower than the temperature that is 50 ° C. lower than the annealing point (Ta) of the glass ribbon 13 and is equal to or higher than the temperature that is 200 ° C. lower than the annealing point (Ta) of the glass ribbon 13.

  As shown in FIG. 1, in the 3rd slow cooling zone 20c arrange | positioned in the downstream of the 2nd slow cooling zone 20b, the 3rd slow cooling process A3 is performed. As shown in FIG. 2, the third slow cooling step A3 is a step of gradually cooling the glass ribbon 13 from Tx to a temperature lower than Tx. The number of times the glass ribbon 13 is cooled in the third slow cooling step A3 can be set as appropriate according to the characteristics of the glass ribbon 13 and the length restriction of the slow cooling furnace 20. The slow cooling step A3 is preferably performed until the temperature of the glass ribbon 13 reaches a temperature that is 250 ° C. lower than Tx. The glass ribbon 13 that has undergone the third slow cooling step A3 is transported to the cooling chamber 23 shown in FIG. 1 and is naturally cooled in the cooling chamber 23.

  In the present embodiment, the average cooling rate of the glass ribbon 13 in the second slow cooling step A2 satisfies the following formula (1).

log ₁₀ R ≦ 0.00018361Ta ² −0.23414Ta + 75.29 (1)
However,
R: Average cooling rate of the glass ribbon 13 Ta: An annealing point (° C.) of the glass ribbon 13,
It is.

  In contrast, in the first slow cooling step A1 and the third slow cooling step A3 other than the second slow cooling step A2, the average cooling rate is higher than the average cooling rate of the glass ribbon 13 in the second slow cooling step A2. Is also set high.

  Thus, the average cooling rate of the glass ribbon 13 in the second annealing step A2 that greatly affects the thermal shrinkage rate of the glass substrate 25 is determined from a predetermined cooling rate derived from the annealing point (Ta) of the glass ribbon 13. The cooling rate of the glass ribbon 13 is increased by increasing the average cooling rate of the glass ribbon 13 in the first and third gradual cooling steps A1 and A3 that do not significantly affect the thermal contraction rate of the other glass substrate 25. The glass substrate 25 with a small thermal shrinkage rate can be manufactured while shortening the time required. Specifically, by setting the average cooling rate of the glass ribbon 13 in the second slow cooling step A2 so as to satisfy the above formula (1), regardless of the glass composition of the glass substrate 25, the glass substrate 25 The heat shrinkage rate can be 30 ppm or less.

  From the viewpoint of reducing the thermal contraction rate of the glass substrate 25, it is preferable to lower the average cooling rate of the glass ribbon 13 in the second slow cooling step A2. Specifically, by setting the average cooling rate of the glass ribbon 13 in the second slow cooling step A2 so as to satisfy the following formula (2), the thermal contraction rate of the glass substrate 25 is set to 23 ppm or less. Can do. Moreover, the thermal contraction rate of the glass substrate 25 can be 20 ppm or less by setting the average cooling rate of the glass ribbon 13 in 2nd slow cooling process A2 so that following formula (3) may be satisfy | filled. Furthermore, the thermal contraction rate of the glass substrate 25 can be 10 ppm or less by setting the average cooling rate of the glass ribbon 13 in 2nd slow cooling process A2 so that following formula (4) may be satisfy | filled.

log ₁₀ R ≦ 0.00013786Ta ² −0.17422Ta + 55.53 (2)
log ₁₀ R ≦ 0.00011821Ta ² −0.14847Ta + 47.03 (3)
log ₁₀ R ≦ 0.000054326Ta ² −0.064985Ta + 19.56 (4)

  In order to reduce the thermal shrinkage rate of the glass substrate 25 more reliably, it is preferable that the maximum cooling rate of the glass ribbon 13 in the second slow cooling step A2 satisfies the following formula (5). It is more preferable to satisfy the formula (6), it is more preferable to satisfy the following formula (7), and it is still more preferable to satisfy the following formula (8).

log ₁₀ R _MAX ≦ 0.00018361Ta ² −0.23414Ta + 75.29 (5)
log ₁₀ R _MAX ≦ 0.00013786Ta ² −0.17422Ta + 55.53 (6)
log ₁₀ R _MAX ≦ 0.00011821Ta ² −0.14847Ta + 47.03 (7)
log ₁₀ R _MAX ≦ 0.000054326Ta ² −0.064985Ta + 19.56 (8)
However,
R _MAX : Maximum cooling rate of glass ribbon (° C / min),
Ta: annealing point of glass ribbon (° C),
It is.

  In addition, while setting the average cooling rate of the glass ribbon 13 in 2nd slow cooling process A2 so that Formula (1)-(8) may be satisfy | filled, it is a quadratic function which shows the criticality of Formula (1)-(8). It is preferable that the annealing point of the glass ribbon is higher than the extreme value. Specifically, when the average cooling rate of the glass ribbon 13 in the second slow cooling step A2 is set so as to satisfy the expressions (1) and (5), the annealing point of the glass ribbon 13 is set to 638 ° C. or higher. It is preferable to do. When setting the average cooling rate of the glass ribbon 13 in 2nd slow cooling process A2 so that Formula (2) and (6) may be satisfy | filled, it is preferable that the annealing point of the glass ribbon 13 shall be 632 degreeC or more. When setting the average cooling rate of the glass ribbon 13 in 2nd slow cooling process A2 so that Formula (3) and (7) may be satisfy | filled, it is preferable that the annealing point of the glass ribbon 13 shall be 628 degreeC or more. When setting the average cooling rate of the glass ribbon 13 in 2nd slow cooling process A2 so that Formula (4) and (8) may be satisfy | filled, it is preferable that the annealing point of the glass ribbon 13 shall be 598 degreeC or more.

  In the present embodiment, when the second annealing step A2 is the longest, the temperature of the glass ribbon 13 is 200 from the annealing point (Ta) of the glass ribbon 13 to 200 ° C. than the annealing point (Ta) of the glass ribbon 13. Although it will be performed until it becomes a low temperature of ° C., the glass ribbon 13 has glass annealing temperature (Ta) to 200 ° C. lower than the annealing temperature (Ta) of the glass ribbon 13. The temperature range from the annealing point (Ta) of the ribbon 13 to a temperature 50 ° C. lower than the annealing point (Ta) of the glass ribbon 13 has the greatest influence on the thermal shrinkage rate of the glass substrate 25. The temperature range from a temperature 50 ° C. lower than the annealing point (Ta) of the glass ribbon 13 to a temperature 200 ° C. lower than the annealing point (Ta) of the glass ribbon 13 is the annealing point (Ta) of the glass ribbon 13. From the temperature range up to 50 ° C. lower than the annealing point (Ta) of the glass ribbon 13, the influence on the thermal contraction rate of the glass substrate 25 is small. Therefore, it is not always necessary to perform the second slow cooling step A2 until the temperature of the glass ribbon 13 becomes 200 ° C. lower than the annealing point (Ta) of the glass ribbon 13, and at least the temperature of the glass ribbon 13 is glass. If the second slow cooling step A2 is performed until the temperature becomes 50 ° C. lower than the annealing point (Ta) of the ribbon 13, a glass substrate 25 having a small thermal shrinkage rate can be obtained.

  When it is desired to further reduce the thermal contraction rate of the glass substrate 25, the second slow cooling is performed until the temperature of the glass ribbon 13 becomes lower than the temperature lower by 50 ° C. than the slow cooling point (Ta) of the glass ribbon 13. It is preferable to perform step A2. However, since the cooling rate of the glass ribbon 13 in the temperature range lower than the temperature lower by 200 ° C. than the annealing point (Ta) of the glass ribbon 13 hardly affects the thermal shrinkage rate of the glass substrate 25, the second It is sufficient that the slow cooling step A2 is performed up to a temperature 200 ° C. lower than the slow cooling point (Ta) of the glass ribbon 13.

  For example, as shown by a dashed line in FIG. 2, in all of the first to third slow cooling steps A1 to A3, the average cooling rate of the glass ribbon 13 may be set to a rate that satisfies the above formula (1). It is done. Even in such a case, the glass substrate 25 having a small heat shrinkage rate can be manufactured. However, as apparent from FIG. 2, in this case, it takes a long time to cool the glass ribbon 13. For this reason, it is necessary to make the length (height) of the slow cooling furnace 20 very large. Therefore, the height dimension of the glass manufacturing apparatus 1 becomes very large, and the construction of the glass manufacturing apparatus 1 becomes practically extremely difficult. Therefore, when manufacturing a glass substrate by the overflow downdraw method, the average cooling rate of the glass ribbon 13 is set to a rate satisfying the above-described formula (1) in all of the first to third slow cooling steps A1 to A3. This is extremely difficult in practice.

  In addition, although the minimum of the average cooling rate of the glass ribbon 13 in 2nd slow cooling process A2 is not specifically limited, when the restrictions of the height dimension of the glass manufacturing apparatus 1, etc. are considered, the glass ribbon in 2nd slow cooling process A2 The average cooling rate of 13 is preferably 0.34 ° C./min or more, more preferably 1 ° C./min or more, still more preferably 2 ° C./min or more, and 5 ° C./min or more. It is still preferred that there be.

  In the present embodiment, the average cooling rate of the glass ribbon 13 in the first slow cooling step A1 is not particularly limited as long as it is higher than the average cooling rate of the glass ribbon 13 in the second slow cooling step A2. The average cooling rate of the glass ribbon 13 in the slow cooling step A1 is preferably higher by 5 ° C./min or higher than the average cooling rate of the glass ribbon 13 in the second slow cooling step A2, more preferably higher by 10 ° C./min or higher. Preferably, it is more preferably at least 15 ° C./min, more preferably at least 20 ° C./min, particularly preferably at least 25 ° C./min.

  Specifically, the average cooling rate of the glass ribbon 13 in the first slow cooling step A1 is, for example, preferably 30 ° C./min or more, more preferably 35 ° C./min or more, and 40 ° C. / More preferably, it is at least minutes. According to this, the time required for the first slow cooling step A1 can be further shortened. In addition, if the average cooling rate of the glass ribbon 13 in the first gradual cooling step A1 is too low, the shape of the molten glass is not determined quickly, so that the shape of the glass ribbon 13 is difficult to control. As a result, the glass ribbon 13 tends to be warped or distorted.

  The average cooling rate of the glass ribbon 13 in the first slow cooling step A1 is, for example, preferably 300 ° C./min or less, and more preferably 150 ° C./min or less. If the average cooling rate of the glass ribbon 13 in the first slow cooling step A <b> 1 is too high, the glass ribbon 13 cannot be uniformly cooled, and cooling unevenness is likely to occur in the width direction of the glass ribbon 13. Therefore, control of the thickness of the glass ribbon 13 tends to be difficult, and the glass ribbon 13 tends to be distorted and warped.

  In the present embodiment, the average cooling rate of the glass ribbon 13 in the third slow cooling step A3 is not particularly limited as long as it is higher than the average cooling rate of the glass ribbon 13 in the second slow cooling step A2. The average cooling rate of the glass ribbon 13 in the third slow cooling step A3 is preferably higher by 20 ° C./min or higher than the average cooling rate of the glass ribbon 13 in the second slow cooling step A2, and higher by 25 ° C./min or higher. Preferably higher than 30 ° C / min, more preferably higher than 35 ° C / min, preferably higher than 40 ° C / min, preferably higher than 45 ° C / min, more than 50 ° C / min It is still preferably high, more preferably 55 ° C / min or higher, still more preferably 60 ° C / min or higher, still more preferably 65 ° C / min or higher. Preferably, even more preferably more that higher 70 ° C. / min or more, and particularly preferably greater 75 ° C. / min or more. Specifically, the average cooling rate of the glass ribbon 13 in the third slow cooling step A3 is, for example, preferably 50 ° C./min or more, more preferably 70 ° C./min or more, and 90 ° C./min. More preferably, it is at least minutes. According to this, the time required for the third slow cooling step A3 can be further shortened. However, if the average cooling rate of the glass ribbon 13 in the third slow cooling step A3 is too high, cracks and cracks are likely to occur in the glass ribbon 13, so that the average of the glass ribbon 13 in the third slow cooling step A3 The cooling rate is preferably 1000 ° C./min or less, and more preferably 500 ° C./min or less.

  The glass substrate manufacturing method of the present embodiment can be suitably used for general glass substrate manufacturing that requires a low thermal shrinkage rate, such as a glass substrate on which an electric circuit pattern or the like is formed. Specifically, the glass substrate manufacturing method of the present embodiment includes, for example, a glass substrate for a flat panel display such as a liquid crystal display, an electroluminescence display, and a plasma display, a charge coupled device (CCD: Charge Coupled Device), and a complementary type. It can be suitably used for a glass substrate for an image sensor such as a metal oxide semiconductor (CMOS). In particular, the method for manufacturing a glass substrate according to the present embodiment is suitable for manufacturing a glass substrate for a flat panel display in which a high-definition electric circuit pattern is formed and the area of the glass substrate is large. It is particularly suitable for manufacturing a glass substrate of a flat panel display including a glass substrate on which a thin film transistor having a silicon film is formed.

  In the above embodiment, the example in which the glass ribbon 13 is cooled at a constant speed in each of the first to third slow cooling steps A1 to A3 has been described. However, the first to third slow cooling steps A1 to A3 are described. In each of the above, the cooling rate of the glass ribbon 13 may not be constant.

  For example, in the second slow cooling step A2, the cooling rate of the glass ribbon 13 in the temperature range from the slow cooling point of the glass ribbon 13 to a temperature lower than the slow cooling point of the glass ribbon 13 by 50 ° C. The cooling rate of the glass ribbon 13 in the temperature range from a temperature 50 ° C. lower than the cold spot to Tx may be varied. Specifically, in the second slow cooling step A2, the cooling rate of the glass ribbon 13 in the temperature range from the slow cooling point of the glass ribbon 13 to a temperature lower by 50 ° C. than the slow cooling point of the glass ribbon 13 is determined by the glass ribbon. You may make it lower than the cooling rate of the glass ribbon 13 in the temperature range from the temperature 50 degreeC lower than the annealing point of 13 to Tx.

  In the above embodiment, an example of manufacturing a glass substrate by the overflow downdraw method has been described. However, in the present invention, for example, a downdraw method other than the overflow downdraw method such as the slot downdraw method may be used. .

(Experimental example 1)
In Experimental Example 1, an experiment was performed to determine the relationship between the annealing point and the cooling rate when the thermal shrinkage rate was 30 ppm, 20 ppm, and 10 ppm using a molded glass substrate.

  As samples 1 to 4, glass substrates (30 mm × 160 mm × 0.7 mm) having the composition, strain point, and annealing point shown in Table 1 below and optically polished on both surfaces were prepared. Then, each sample was covered with a refractory, heated to a temperature 100 ° C. higher than the annealing point of each sample, and held at that temperature for 1 hour. Next, heat treatment was performed by gradually cooling to a temperature lower by 50 ° C. than the annealing point at a cooling rate of 8 ° C./min, 16 ° C./min, 30 ° C./min, or 300 ° C./min, and then naturally cooling.

  The sample cooled at a cooling rate of 8 ° C./min was cooled as follows. First, the sample maintained at a temperature 100 ° C. higher than the annealing point was transferred into an annealing furnace maintained at the annealing temperature of the sample while being covered with the refractory. Next, the temperature was lowered to 50 ° C. below the annealing point while controlling the temperature of the annealing furnace so that the cooling rate was 8 ° C./min. Thereafter, the sample covered with the refractory was removed from the annealing furnace, the refractory was removed, and the sample was placed on an aluminum plate and allowed to cool naturally.

  On the other hand, each sample cooled at a cooling rate of 16 ° C./min, 30 ° C./min, and 300 ° C./min was cooled as follows. First, each sample maintained at a temperature 100 ° C. higher than the annealing point was taken out of the heat treatment furnace and cooled in the air covered with a refractory. Next, when the temperature of each sample reached 50 ° C. lower than the annealing point, the refractory was removed, and each sample was placed on an aluminum plate and allowed to cool naturally.

  The cooling rate (16 ° C./min, 30 ° C./min or 300 ° C./min) of the sample cooled in the air without being put in the annealing furnace was adjusted by the amount of the refractory. Specifically, the sample to which the thermocouple is attached is cooled in advance by changing the amount of the refractory, and the relationship between the amount of the refractory and the cooling rate of the sample is confirmed. The amount of the refractory was adjusted so that the cooling rate of the sample became a predetermined cooling rate.

  Next, the thermal contraction rate (Ta) of each sample was measured in the following manner. First, as shown in FIG. 8 (a), two linear marks M1, M2 are entered at predetermined intervals in a predetermined portion of the glass substrate 25, and then, as shown in FIG. By dividing the substrate 25 in a direction perpendicular to the mark M, a glass plate piece 25a and a glass plate piece 25b were obtained. Then, only the glass plate piece 25a was heated from normal temperature to 450 ° C. at a rate of 10 ° C./min, held at 450 ° C. for 10 hours, and then cooled to normal temperature at a rate of 10 ° C./min. Thereafter, as shown in FIG. 8C, the glass plate piece 25a subjected to the heat treatment and the glass plate piece 25b not subjected to the heat treatment are arranged side by side and fixed with the adhesive tape T. , M2 and the marks M1 and M2 of the glass plate piece 25b were measured, and the thermal contraction rate was calculated based on the following formula (9).

(Thermal shrinkage (ppm)) = (Δl ₁ (μm) + Δl ₂ (μm)) / l ₀ (m) (9)
However,
l ₀ : distance between the marks M on the glass substrate 25,
l ₁ : distance between the mark M1 of the glass plate piece 25a and the mark M1 of the glass plate piece 25b,
l ₂ : distance between the mark M2 of the glass plate piece 25a and the mark M2 of the glass plate piece 25b,
It is.

  The results are shown in Table 2 below and FIG. A straight line L1 in FIG. 3 is an approximate straight line (primary approximate curve) of the data of the sample 1. The straight line L2 is an approximate straight line of the data of the sample 2. The straight line L3 is an approximate straight line of the data of the sample 3. The straight line L4 is an approximate straight line of the data of the sample 4. The straight lines L1 to L4 are represented by the following approximate expressions (10) to (13).

Approximate straight line L1: (heat shrinkage rate) = 27.617 (log ₁₀ R) -10.849 (10)
Approximate straight line L2: (heat shrinkage rate) = 19.388 (log ₁₀ R) −8.725 (11)
Approximate straight line L3: (heat shrinkage rate) = 15.884 (log ₁₀ R) −8.8894 (12)
Approximate straight line L4: (thermal contraction rate) = 8.99062 (log ₁₀ R) −6.0868 (13)

As shown in FIG. 3, the thermal contraction rate of each sample 1 to 4 tends to increase as the logarithm (log ₁₀ (R (° C./min))) of the cooling rate (R (° C./min)) increases. I understand that there is. Specifically, it can be seen that the heat shrinkage rate and the logarithm of the cooling rate are almost linearly correlated, and the relationship between the heat shrinkage rate and the logarithm of the cooling rate can be suitably approximated by a linear function.

  Next, based on the above approximate expressions (10) to (13), a cooling rate at which the thermal shrinkage rate of the glass substrate was 30 ppm was calculated. The results are shown in Table 3 below and FIG.

  As shown in FIG. 4, it can be seen that the logarithm of the cooling rate at which the thermal shrinkage rate of the glass substrate becomes 30 ppm tends to increase as the annealing point increases. As a result of fitting an approximate curve to the logarithm of the cooling rate at which the thermal shrinkage rate of the glass substrate becomes 30 ppm and the annealing point, in the case shown in FIG. When the quadratic curve was fitted, the correlation coefficient was higher. Moreover, the correlation coefficient when fitting a cubic curve was equivalent to the correlation coefficient when fitting a quadratic curve (0.995 or more). Specifically, the correlation coefficient when fitting a quadratic curve is 1.000, the correlation coefficient when fitting a straight line is 0.990, and the correlation coefficient when fitting a cubic curve Was 1.000. Since the fitting can be performed with a sufficiently high correlation coefficient by the quadratic curve, the approximate curve C1 represented by the following quadratic function (14) is adopted in the case shown in FIG.

Approximate curve C1: log ₁₀ R = 0.00018361Ta ² −0.23414Ta + 75.29 (14)

  From the above results, it is understood that the glass ribbon may be cooled so as to satisfy the following formula (1) in the slow cooling step in order to make the thermal shrinkage of the obtained glass substrate 30 ppm or less.

log ₁₀ R ≦ 0.00018361Ta ² −0.23414Ta + 75.29 (1)
However,
R: Average cooling rate of glass ribbon (° C / min),
Ta: annealing point of glass ribbon (° C),
It is.

  Next, a cooling rate at which the thermal shrinkage rate of the glass substrate was 23 ppm was calculated based on the above approximate expressions (10) to (13). The results are shown in Table 4 below and FIG.

  As shown in FIG. 5, it can be seen that the logarithm of the cooling rate at which the thermal shrinkage rate of the glass substrate becomes 23 ppm tends to increase as the annealing point increases. As a result of fitting an approximate curve to the logarithm of the cooling rate at which the thermal shrinkage rate of the glass substrate becomes 23 ppm and the annealing point, the case shown in FIG. 5 is the same as the case shown in FIG. When a quadratic curve was fitted, a sufficiently high correlation coefficient was obtained. For this reason, in the case shown in FIG. 5, the approximate curve C2 represented by the following quadratic function (15) was adopted. When the approximate curve C2 was adopted, the correlation coefficient was 1.000.

Approximate curve C2: log ₁₀ R = 0.00013786Ta ² −0.17422Ta + 55.53 (15)

  From the above results, it can be seen that the glass ribbon may be cooled so as to satisfy the following formula (2) in the slow cooling step in order to reduce the thermal shrinkage of the obtained glass substrate to 23 ppm or less.

log ₁₀ R ≦ 0.00013786Ta ² −0.17422Ta + 55.53 (2)

  Next, a cooling rate at which the thermal shrinkage rate of the glass substrate was 20 ppm was calculated based on the above approximate expressions (10) to (13). The results are shown in Table 5 below and FIG.

  As shown in FIG. 6, it can be seen that the logarithm of the cooling rate at which the thermal shrinkage rate of the glass substrate becomes 20 ppm tends to increase as the annealing point increases. As a result of fitting the approximate curve to the logarithm of the cooling rate at which the thermal shrinkage rate of the glass substrate becomes 20 ppm and the annealing point, the case shown in FIG. 4 and FIG. Similarly, when a quadratic curve was fitted, a sufficiently high correlation coefficient was obtained. For this reason, in the case shown in FIG. 6, the approximate curve C3 represented by the following quadratic function (16) was adopted. When the approximate curve C3 was employed, the correlation coefficient was 1.000.

Approximate curve C3: log ₁₀ R = 0.00011821Ta ² −0.14847Ta + 47.03 (16)

  From the above results, it can be seen that in order to make the thermal shrinkage of the obtained glass substrate 20 ppm or less, the glass ribbon may be cooled so as to satisfy the following formula (3) in the slow cooling step.

log ₁₀ R ≦ 0.00011821Ta ² −0.14847Ta + 47.03 (3)

  Next, the cooling rate at which the thermal shrinkage rate of the glass substrate was 10 ppm was calculated based on the above approximate expressions (10) to (13). The results are shown in Table 6 below and FIG.

  As shown in FIG. 7, it can be seen that the logarithm of the cooling rate at which the thermal shrinkage rate of the glass substrate becomes 10 ppm tends to increase as the annealing point increases. As a result of fitting an approximate curve to the data of the logarithm of the cooling rate at which the thermal shrinkage rate of the glass substrate becomes 10 ppm and the annealing point, FIG. 7, FIG. 5, FIG. Similarly to the case shown in Fig. 5, the correlation coefficient when the quadratic curve was fitted was the highest. For this reason, in the case shown in FIG. 7, the approximate curve C4 represented by the following quadratic function (17) was adopted. When the approximate curve C4 was employed, the correlation coefficient was 0.998.

Approximate curve C4: log ₁₀ R = 0.000054326Ta ² −0.064985Ta + 19.56 (17)

  From the above results, it is understood that the glass ribbon may be cooled so as to satisfy the following formula (4) in the slow cooling step in order to make the thermal shrinkage of the obtained glass substrate 10 ppm or less.

log ₁₀ R ≦ 0.000054326Ta ² −0.064985Ta + 19.56 (4)

(Experimental example 2)
In Experimental Example 2, an experiment was conducted to confirm that the conditional expression (1) calculated in Experimental Example 1 can be applied to slow cooling of a glass ribbon formed by the downdraw method. Specifically, molten glass was supplied to the molded body 11 of the glass manufacturing apparatus 1 shown in FIG. 1, and a glass ribbon was formed using the roller pairs 14 and 22. The glass ribbon had a width of 1500 mm and a thickness of 0.7 mm. And it annealed by the slow cooling conditions shown in following Table 7 and Table 8 with the slow cooling furnace of length L, and after natural cooling in the cooling chamber 23, it cut | disconnected and produced the glass substrate. Thereafter, the thermal shrinkage rate, fictive temperature, average surface roughness (Ra), strain value, and warpage value of the glass substrate were measured. The measurement results are shown in Table 7 and Table 8 below.

  In addition, the thermal contraction rate of the glass substrate was computed in the same procedure as the said Experimental example 1.

  The fictive temperature of the glass substrate was measured as follows. The glass substrate was put into an electric furnace heated to 700 ° C. and held for 1 hour. Thereafter, the glass substrate was rapidly cooled on an aluminum plate, and then the thermal shrinkage rate was measured. The same heat treatment was performed at 720 ° C., 740 ° C., and 760 ° C., and the heat shrinkage rate was measured in the same manner. Then, the data of the heat treatment temperature and the heat shrinkage rate are approximated by a first order approximate curve, the heat treatment temperature at which the heat shrinkage rate becomes 0 ppm is obtained from the first order approximate curve, and the heat treatment temperature is set as a virtual temperature.

  The average surface roughness (Ra) of the glass substrate was measured according to SEMI D7-94 “Measurement method of surface roughness of FPD glass substrate”.

  The strain value of the glass substrate was measured by an optical heterodyne method using a strain meter manufactured by UNIOPT.

  The warpage value of the glass substrate was measured with a glass substrate warpage measuring machine manufactured by Toshiba Corp. with a sample having a size of 550 mm × 650 mm cut out from the center of the glass substrate.

  The drawing speed shown in Tables 7 and 8 below means the peripheral speed of the tension roller.

  When the annealing point (Ta) is 705 ° C., from the above formula (1), it is necessary to set the cooling rate in the annealing step to 30 ° C./min or less in order to make the heat shrinkage rate 30 ppm or less. It becomes. For this reason, if the conditional expression (1) calculated in Experimental Example 1 is applicable to the slow cooling of the glass ribbon formed by the downdraw method, Experimental Example 2 having a cooling rate higher than 30 ° C./min. -1 and Experimental Example 2-2 have a heat shrinkage rate of more than 30 ppm, and the cooling rate is 30 ° C./min or less. Should be. Here, when the results shown in Table 7 and Table 8 are seen, it can be seen that also in Experimental Example 2 in which an actual glass substrate was formed, a result consistent with the above formula (1) was obtained. From this result, it is understood that the conditional expression (1) calculated in Experimental Example 1 can be applied to the slow cooling of the glass ribbon formed by the downdraw method.

Furthermore, as shown in Table 7 and Table 8, the heat calculated from the approximate straight line L1 calculated in Experimental Example 1 ((heat shrinkage rate) = 27.617 (log ₁₀ R) -10.849 (10)). The shrinkage rate and the actually measured thermal shrinkage rate almost coincided. Also from this result, it is understood that the conditional expression (1) calculated in Experimental Example 1 can be applied to the slow cooling of the glass ribbon formed by the downdraw method.

  Moreover, it turns out from the comparison with Experimental example 2-5 and Experimental example 2-6 that the cooling rate in a 1st slow cooling process has not influenced the thermal contraction rate largely.

  Further, from comparison between Experimental Example 2-4 and Experimental Example 2-7, it can be seen that lowering Tx can reduce the thermal shrinkage rate.

DESCRIPTION OF SYMBOLS 1 ... Glass manufacturing apparatus 10 ... Molding furnace 11 ... Molded body 12 ... Molten glass 13 ... Glass ribbon 14 ... Roller pair 20 ... Slow cooling furnace 20a ... 1st slow cooling zone 20b ... 2nd slow cooling zone 20c ... 3rd slow Cold zone 21 ... Heater 22 ... Tension roller pair 23 ... Cooling chamber 24 ... Cutting chamber 25 ... Glass substrates 25a, 25b ... Glass plate pieces

Claims (20)

A forming step of forming molten glass into a ribbon-like glass ribbon by a downdraw method;
A slow cooling step of slowly cooling the glass ribbon;
After the slow cooling step, a glass substrate manufacturing method comprising a cutting step of cutting the glass ribbon to obtain a glass substrate,
In the slow cooling step, the average cooling rate of the glass ribbon in the temperature range from the slow cooling point of the glass ribbon to a temperature lower by 50 ° C. than the slow cooling point of the glass ribbon satisfies the following formula (1): A method for producing a glass substrate, wherein the glass ribbon is cooled.
log ₁₀ R ≦ 0.00018361Ta ² −0.23414Ta + 75.29 (1)
However,
R: Average cooling rate of glass ribbon (° C / min),
Ta: annealing point of glass ribbon (° C),
It is. In the slow cooling step, the average cooling rate of the glass ribbon in the temperature range from the slow cooling point of the glass ribbon to a temperature lower by 50 ° C. than the slow cooling point of the glass ribbon satisfies the following formula (2): The method for producing a glass substrate according to claim 1, wherein the glass ribbon is cooled.
log ₁₀ R ≦ 0.00013786Ta ² −0.17422Ta + 55.53 (2) In the slow cooling step, the average cooling rate of the glass ribbon in the temperature range from the slow cooling point of the glass ribbon to a temperature lower by 50 ° C. than the slow cooling point of the glass ribbon satisfies the following formula (3): The method for producing a glass substrate according to claim 2, wherein the glass ribbon is cooled.
log ₁₀ R ≦ 0.00011821Ta ² −0.14847Ta + 47.03 (3) In the slow cooling step, the average cooling rate of the glass ribbon in the temperature range from the slow cooling point of the glass ribbon to a temperature lower by 50 ° C. than the slow cooling point of the glass ribbon satisfies the following formula (4): The method for producing a glass substrate according to claim 3, wherein the glass ribbon is cooled.
log ₁₀ R ≦ 0.000054326Ta ² −0.064985Ta + 19.56 (4) In the slow cooling step, the maximum cooling rate of the glass ribbon in the temperature range from the slow cooling point of the glass ribbon to a temperature lower by 50 ° C. than the slow cooling point of the glass ribbon satisfies the following formula (5): The manufacturing method of the glass substrate as described in any one of Claims 1-4 which cools the said glass ribbon.
log ₁₀ R _MAX ≦ 0.00018361Ta ² −0.23414Ta + 75.29 (5)
However,
R _MAX : Maximum cooling rate of glass ribbon (° C / min),
Ta: annealing point of glass ribbon (° C),
It is.   The manufacturing method of the glass substrate as described in any one of Claims 1-5 whose annealing point (Ta) of the said glass ribbon is 600 to 1000 degreeC.   In the slow cooling step, the average cooling rate of the glass ribbon in a temperature range higher than the slow cooling point of the glass ribbon, and the glass ribbon in a temperature range lower than a temperature lower by 50 ° C. than the slow cooling point of the glass ribbon. Each of the average cooling rate is higher than the average cooling rate of the glass ribbon in a temperature range from the annealing point of the glass ribbon to a temperature lower by 50 ° C. than the annealing point of the glass ribbon. The manufacturing method of the glass substrate as described in any one of Claims 1-6 which cools a glass ribbon.   In the slow cooling step, when Tx is set to a temperature that is lower than the temperature lower by 50 ° C. than the slow cooling point of the glass ribbon and is equal to or higher than 200 ° C. lower than the slow cooling point of the glass ribbon, The manufacturing of the glass substrate as described in any one of Claims 1-7 which cools the said glass ribbon so that the average cooling rate of the glass ribbon in the temperature range from an annealing point to the said Tx may satisfy | fill said Formula (1). Method. 9. The glass according to claim 8, wherein in the slow cooling step, the glass ribbon is cooled such that an average cooling rate of the glass ribbon in a temperature range from the slow cooling point of the glass ribbon to the Tx satisfies the following formula (2). A method for manufacturing a substrate.
log ₁₀ R ≦ 0.00013786Ta ² −0.17422Ta + 55.53 (2) The glass of Claim 9 which cools the said glass ribbon so that the average cooling rate of the glass ribbon in the temperature range from the slow cooling point of the said glass ribbon to the said Tx may satisfy | fill following formula (3) in the said slow cooling process. A method for manufacturing a substrate.
log ₁₀ R ≦ 0.00011821Ta ² −0.14847Ta + 47.03 (3) The glass of Claim 10 which cools the said glass ribbon so that the average cooling rate of the glass ribbon in the temperature range from the slow cooling point of the said glass ribbon to the said Tx may satisfy | fill following formula (4) in the said slow cooling process. A method for manufacturing a substrate.
log ₁₀ R ≦ 0.000054326Ta ² −0.064985Ta + 19.56 (4)   The manufacturing method of the glass substrate as described in any one of Claims 8-11 whose average cooling rate of the said glass ribbon in the temperature range lower than said Tx is 50 degrees C / min or more.   The manufacturing method of the glass substrate as described in any one of Claims 1-12 whose average cooling rate of the said glass ribbon in the temperature range higher than the annealing point of the said glass ribbon is 30 degrees C / min or more.   The manufacturing method of the glass substrate as described in any one of Claims 1-13 which forms the said glass ribbon whose width is 500 mm or more in the said formation process.   The manufacturing method of the glass substrate as described in any one of Claims 1-14 which forms the said glass ribbon by the overflow down draw method in the said formation process. Process for producing a glass substrate according to any one of claims 1 to 15 viscosity of 10 ^{4.5 dPa} · s or more at the liquidus temperature of the molten glass.   The strain point of the said glass ribbon is 600 degreeC or more, The manufacturing method of the glass substrate as described in any one of Claims 1-16. The molten glass, by mass _{percentage, SiO 2: 50~70%, Al} 2 O 3: 10~25%, B 2 O 3: 3~15%, MgO: 0~10%, CaO: 0~10% , SrO: 0~15%, BaO: 0~15% and _Na 2 O: glass substrate manufacturing method according to any one of claims 1 to 17 containing 0-5%.   It is a method for manufacturing the glass substrate for flat panel displays, The manufacturing method of the glass substrate as described in any one of Claims 1-18.   The method for producing a glass substrate according to any one of claims 1 to 19, which is a method for producing the glass substrate of a flat panel display comprising a glass substrate on which a thin film transistor having a low-temperature polysilicon film is formed. Method.

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