JP5365970B2 - Glass substrate for display - Google Patents

Description

  The present invention relates to a glass substrate for display, and more particularly to a glass substrate used for a liquid crystal display.

  As shown in FIG. 1, the liquid crystal display has a structure in which a liquid crystal cell 1 is sandwiched between two glass substrates, that is, a rear glass substrate 2 (array glass substrate) and a front glass substrate 3 (color filter glass substrate). It has become.

  In the glass substrate 2 for the array, a thin film transistor 4 (TFT), a transparent pixel electrode 5 and an alignment film 6 are formed on the substrate surface in contact with the liquid crystal cell 1, and a polarizing plate 7 is formed on the opposite surface. It is pasted.

  The glass substrate 3 for the color filter has a transparent counter electrode 8, a red, blue and green color filter 9 and an alignment film 10 formed on the substrate surface in contact with the liquid crystal cell 1, and the surface on the opposite side. Is attached with a polarizing plate 11. In addition, the polarization direction of the polarizing plate 7 stuck on the glass substrate 2 for arrays and the polarizing direction of the polarizing plate 11 stuck on the glass substrate 3 for color filters are mutually orthogonal.

  A backlight 12 is installed behind the array glass substrate 2. In a liquid crystal display used for a notebook personal computer or the like, the backlight 12 has a structure that guides light from several small-diameter cold cathode tubes to a liquid crystal cell through a diffusion plate (not shown), for example.

  The outline of the display principle of the liquid crystal display is as follows. By applying a voltage controlled by the thin film transistor 4 between the pixel electrode 5 and the counter electrode 8, the liquid crystal molecules 13 in the liquid crystal cell 1 are aligned in a straight line, and the polarizing plate attached to the glass substrate 2 for the array The direction of vibration of the light from the backlight 12 polarized in 7 does not rotate (rotate) in the liquid crystal cell 1, so the light is blocked by the polarizing plate 11 attached to the color filter glass substrate 3 to display black. To do. Conversely, when no voltage is applied between the electrodes, the liquid crystal molecules 13 in the liquid crystal cell 1 are maintained in a twisted state, and therefore the backlight 12 polarized by the polarizing plate 7 attached to the array glass substrate 2. The direction of vibration of light from the light rotates (rotates) in the liquid crystal cell 1 and passes through the polarizing plate 11 attached to the glass substrate 3 for color filter, and displays red, blue or green. In this way, by controlling the alignment of the liquid crystal molecules in the liquid crystal cell, the vibration direction of the light from the backlight is controlled, and light is transmitted or blocked by the polarizing plate attached to the glass substrate for the color filter. The image is displayed.

  By the way, as a glass substrate, a glass melt melted in a glass melting furnace is formed into a certain thickness by a float method, a slot down draw method, an overflow down draw method, a redraw method, etc., and cut into a predetermined size. Things are used.

  Usually, distortion remains in the glass substrate manufactured by the above method, retardation occurs in the glass substrate, and the polarization state of transmitted light changes. For this reason, when a glass substrate in which distortion remains is used for a liquid crystal display, there is a problem in that light leakage occurs at a place where light is originally blocked and luminance unevenness occurs on the entire screen or a part thereof. In order to solve this problem, it is conceivable to anneal the glass substrate cut to a predetermined size to reduce the amount of strain remaining on the glass substrate, but there is a problem that processing time and cost are increased.

Therefore, in order to prevent the occurrence of luminance unevenness, Patent Document 1 proposes to use a glass substrate in which the product of the thickness of the glass substrate and the photoelastic constant is limited to a predetermined value or less. Patent Document 2 proposes to use a glass substrate in which the product of the thermal expansion coefficient, Young's modulus, and photoelastic constant of glass is limited to a predetermined value or less.
JP 2001-255517 A JP 2001-172041 A

  In recent years, the display has been increased in size, and the size of the glass substrate has been increased accordingly.

  However, as the glass substrate becomes larger, the amount of residual strain tends to increase, and even when the glass substrate disclosed in Patent Documents 1 and 2 is used, uneven brightness may occur on the entire screen. .

  The objective of this invention is providing the glass substrate for liquid crystal displays which can suppress generation | occurrence | production of the brightness nonuniformity of a liquid crystal display even with a big screen.

As a result of various studies, the inventor formed a glass substrate having a predetermined glass composition by a downdraw method, and the retardation in the glass substrate surface was Δ (nm) by light orthogonal to the glass substrate surface, and the glass of the retardation When the azimuth angle with respect to the side direction of the substrate is θ (°), unevenness of the value obtained by {sin (2θ)} ² × {sin (180 ° · Δ / 550)} ² is reduced in the glass substrate surface. That is, when the rate of change of the value obtained by {sin (2θ)} ² × {sin (180 ° · Δ / 550)} ² in the glass substrate surface is suppressed to a certain value or less, a liquid crystal display is obtained. In addition, the inventors have found that it is possible to suppress the occurrence of uneven brightness and have proposed the present invention.

That is, the glass substrate for a display of the present invention is a glass substrate formed by a downdraw method, and the glass composition has a mass percentage of SiO ₂ 40 to 70%, Al ₂ O ₃ 2 to 25%, B ₂ O ₃ 0-20%, MgO 0-10%, CaO 0-15%, SrO 0-10%, BaO 0-15%, ZnO 0-10%, R ₂ O (R is Li, Na, K) Represents 0 to 0.1%, ZrO ₂ 0 to 10%, and the retardation measured at 50 mm intervals in the glass substrate surface by light orthogonal to the glass substrate surface is Δ (nm), and the retardation of the glass substrate of the retardation An azimuth angle with respect to the side direction is θ (°), and a value obtained by {sin (2θ)} ² × {sin (180 ° · Δ / 550)} ² at an arbitrary measurement point a is adjacent to A and the measurement point a. {Si at the matching measurement point a ′ ^{(2θ)} 2 × {sin} ' when used as a measurement point adjacent a, a' values calculated in (180 ° · Δ / 550) } 2 A value of A, the rate of change of A '((A- A ′) / 50) is 4.0 × 10 ⁻⁷ or less.

The glass substrate of the present invention is adjacent in the glass substrate surface when the retardation in the glass substrate surface is Δ by light orthogonal to the glass substrate surface and the azimuth angle of the retardation with respect to the side direction of the glass substrate is θ. Since the rate of change of the value obtained by {sin (2θ)} ² × {sin (180 ° · Δ / 550)} ² at the measurement point is reduced, the occurrence of uneven brightness is suppressed when a liquid crystal display is used. can do. Therefore, it is suitable as a glass substrate for display used in a liquid crystal display.

  The occurrence of luminance unevenness in the display is affected not only by the magnitude of the retardation of the glass substrate, but also by the azimuth angle of the retardation with respect to the side direction of the glass substrate and the distribution state thereof.

Therefore, as described above, the display glass substrate of the present invention has a rate of change of the value obtained by {sin (2θ)} ² × {sin (180 ° · Δ / 550)} ² at the adjacent measurement points of 4 Since it is set to be as small as 0.0 × 10 ⁻⁷ or less, occurrence of luminance unevenness can be suppressed when a liquid crystal display is used. When the rate of change of the value obtained by {sin (2θ)} ² × {sin (180 ° · Δ / 550)} ² at adjacent measurement points is larger than 4.0 × 10 ⁻⁷ , a liquid crystal display is formed. In this case, uneven brightness tends to occur on the entire screen. A preferable range of this value is 3.8 × 10 ⁻⁷ or less, and more preferably 3.6 × 10 ⁻⁷ or less.

In order to more reliably suppress the occurrence of luminance unevenness, in addition to the above, the value obtained by {sin (2θ)} ² × {sin (180 ° · Δ / 550)} ² at each measurement point is set to 3. 5 × 10 ⁻⁵ or less is desirable.

  In order to obtain the glass substrate as described above, for example, when a glass melt melted in a glass melting furnace is formed into a plate-like glass (glass ribbon) in a forming furnace (molded body), the end of the glass ribbon is When the glass ribbon is molded so that the thickness is almost the same as the thickness of the center of the glass ribbon, or when the molded glass ribbon is slowly cooled (cooled) in a slow cooling furnace, the temperature distribution in the width direction of the glass ribbon should be as small as possible Just cool it down.

  In the molding process, the thickness of the end of the glass ribbon is approximately the same as the thickness of the center of the glass ribbon because the thickness of the end of the glass ribbon is the same as the thickness of the center of the glass ribbon. If it is different, the cooling rate is different between the end portion and the center portion of the glass ribbon in the cooling step after molding, and as a result, the retardation in the glass substrate surface and the azimuth angle are likely to vary. To form the glass ribbon so that the thickness of the end of the glass ribbon is the same as the thickness of the center of the glass ribbon, adjust the rotational speed of the forming roll etc. to stretch the glass melt into the glass ribbon. It can be carried out.

Moreover, in the cooling process in the slow cooling furnace, in order to make the temperature distribution in the width direction of the glass ribbon as small as possible, it can be performed as follows.
(1) The number of heaters is increased so that the glass ribbon is uniformly heated.
(2) A soaking plate is installed between the heater and the glass ribbon so that the heat from the heater is uniformly transmitted to the glass ribbon.
(3) An enclosure is installed at the end of the glass ribbon or a large number of heaters are arranged at the end so that the difference in the cooling rate between the center and the end of the glass ribbon is reduced.
(4) Lower (slow) the glass drawing speed.

  In addition, after forming the glass melt into a glass ribbon in a molding furnace, the glass substrate is drawn in the vertical direction (downward), cooled (slow cooling) in a slow cooling furnace, and then cut to obtain a glass substrate. Unlike the float method in which the glass melt is drawn horizontally, slowly cooled, and cut to obtain a glass substrate, the slit down draw method is different from the low temperature atmosphere cutting step to the high temperature atmosphere annealing furnace and molding furnace direction. In addition, a low-temperature air flow always rises along the surface of the glass ribbon, and after the heated low-temperature air flow is heated inside a slow cooling furnace or the like, a part of it leaks to the external atmosphere through the gap in the peripheral wall. The atmospheric temperature of the slow cooling furnace and the molding furnace is likely to fluctuate. As a result, a glass substrate formed by the overflow downdraw method or the slit downdraw method is likely to vary in the size of the retardation in the glass substrate surface and its azimuth angle.

  Therefore, when forming a glass substrate by the overflow downdraw method or the slit downdraw method, in addition to making the thickness of the end portion and the center portion of the glass ribbon substantially the same thickness, reducing the temperature distribution, It is necessary to suppress an increase in the low-temperature air flow in the molding furnace.

  In order to suppress the rise in the low-temperature air flow in the slow cooling furnace or the forming furnace, a convection prevention plate is provided in the slow cooling furnace, or the air pressure in the external atmosphere of the forming furnace or the slow cooling furnace is adjusted using a blower or the like. Then, it is only necessary to make it difficult for the air in the molding furnace and the slow cooling furnace to leak into the external atmosphere.

In addition to the above methods, the content of SiO ₂ , Al ₂ O ₃ and B ₂ O ₃ in the glass is increased to reduce the thermal expansion coefficient of the glass, or the content of alkaline earth metal oxide To increase the photoelastic constant of the glass.

  The display glass substrate of the present invention is particularly suitable as a large glass substrate in which distortion is likely to remain and luminance unevenness is likely to appear, specifically, a glass substrate having a short side length of 1000 mm or more. is there.

The specific composition of the glass substrate for display of the present invention is determined in consideration of chemical resistance, heat shrinkability, meltability, moldability, thermal expansion coefficient, and the like . The glass composition range according to the present invention is in percentage by mass, SiO ₂ 40 to 70%, Al ₂ O ₃ 2 to 25%, B ₂ O ₃ 0 to 20%, MgO 0 to 10%, CaO 0 to 15%, SrO 0~10%, BaO 0~15%, 0~10% ZnO, R 2 O (R represents Li, Na, and K) 0~ _0.1%, a ZrO 2 0%.

  The reason for limiting the glass composition as described above in the present invention is as follows.

SiO ₂ is a component that becomes a glass network former, reduces the thermal expansion coefficient of the glass, suppresses variations in the retardation Δ of the glass substrate and the azimuth angle θ of the retardation with respect to the side direction of the glass substrate, and is adjacent. This component reduces the rate of change of the value obtained by {sin (2θ)} ² × {sin (180 ° · Δ / 550)} ² at the measurement point. Moreover, it is also a component which improves the acid resistance of glass or raises the strain point of glass and makes the thermal contraction of a glass substrate small. Its content is 40-70%. When the content of SiO ₂ is increased, the high-temperature viscosity of the glass is increased, the meltability is deteriorated, and devitrification blisters of cristobalite tend to precipitate. On the other hand, when the content decreases, the thermal expansion coefficient of the glass tends to increase, and the variation of the retardation Δ of the glass substrate and the azimuth angle θ of the retardation tends to increase, and {sin (2θ)} at adjacent measurement points. ² × {sin (180 ° · Δ / 550)} ² tends to increase the rate of change of the value obtained. Further, the acid resistance and strain point of the glass tend to decrease. A more preferable range of SiO ₂ is 50 to 67%, and a further preferable range is 57 to 64%.

Al ₂ O ₃ reduces the thermal expansion coefficient of the glass, suppresses variations in the retardation Δ of the glass substrate and the azimuth angle θ of the retardation with respect to the side direction of the glass substrate, and {sin (2θ)} at adjacent measurement points. ² × {sin (180 ° · Δ / 550)} ² is a component for reducing the rate of change of the value obtained by ² . It also has the effect of raising the strain point of the glass and suppressing the devitrification of cristobalite. Its content is 2 to 25%. When the content of Al ₂ O ₃ increases, the buffered hydrofluoric acid resistance of the glass deteriorates or the liquidus temperature tends to increase, making it difficult to form. On the other hand, when the content decreases, the thermal expansion coefficient of the glass tends to increase, and the variation of the retardation Δ of the glass substrate and the azimuth angle θ of the retardation tends to increase, and {sin (2θ)} at adjacent measurement points. ² × {sin (180 ° · Δ / 550)} ² tends to increase the rate of change of the value obtained. Moreover, it exists in the tendency for the strain point of glass to fall. A more preferable range of Al ₂ O ₃ is 10 to 20%, and a more preferable range is 14 to 17%.

B ₂ O ₃ is a component that acts as a flux, lowers the viscosity of the glass, and improves the meltability. In addition, the thermal expansion coefficient of the glass is decreased to suppress the retardation Δ of the glass substrate and the variation of the azimuth angle θ of the retardation with respect to the side direction of the glass substrate, and {sin (2θ)} ² × {sin (180 ° · Δ / 550)} ² is also a component that reduces the rate of change of the value obtained by ² . Its content is 0-20%. When the content of B ₂ O ₃ increases, the strain point of the glass tends to decrease or the acid resistance tends to deteriorate. On the other hand, when the content decreases, the thermal expansion coefficient of the glass tends to increase, and the variation of the retardation Δ of the glass substrate and the azimuth angle θ of the retardation tends to increase, and {sin (2θ)} at adjacent measurement points. ² × {sin (180 ° · Δ / 550)} ² tends to increase the rate of change of the value obtained. Moreover, it does not act sufficiently as a flux and tends to lower the meltability. A more preferable range of B ₂ O ₃ is 5 to 15%, and a more preferable range is 7.5 to 12%.

  MgO is a component that improves the meltability of glass by lowering only the high temperature viscosity without lowering the strain point of the glass. It is also a component that lowers the photoelastic constant of glass. Its content is 0-10%. When the content of MgO is increased, devitrification is likely to precipitate. In addition, the buffered hydrofluoric acid resistance decreases, the glass substrate surface is eroded, the reaction product adheres to the glass substrate surface, and the glass substrate is likely to become cloudy. A more preferable range of MgO is 0 to 5%, and a more preferable range is 0 to 3.5%.

  CaO is a component that remarkably improves the meltability of the glass by reducing only the high temperature viscosity without reducing the strain point of the glass. It is also a component that lowers the photoelastic constant of glass. Its content is 0-15%. When the content of CaO increases, the resistance to buffered hydrofluoric acid tends to deteriorate. A more preferable range of CaO is 0 to 12%, and a more preferable range is 3.5 to 9%.

SrO is a component that improves the chemical resistance and devitrification resistance of glass. It is also a component that lowers the photoelastic constant of glass. Its content is 0-10%. When the SrO content increases, the thermal expansion coefficient of the glass tends to increase, the thermal expansion coefficient of the glass tends to increase, and the variation of the retardation Δ of the glass substrate and the azimuth angle θ of the retardation tends to increase. The rate of change of the value obtained by {sin (2θ)} ² × {sin (180 ° · Δ / 550)} ² at the matching measurement point tends to increase. A more preferable range of SrO is 0 to 8%, and a more preferable range is more than 0.5 to 8%.

  BaO, like SrO, is a component that improves the chemical resistance and devitrification resistance of glass. It is also a component that lowers the photoelastic constant of glass. Its content is 0-15%. When the content of BaO increases, the density and thermal expansion coefficient of the glass increase, and the meltability tends to deteriorate significantly. A more preferable range of BaO is 0 to 10%, and a more preferable range is 0 to 8%.

  ZnO is a component that improves the buffered hydrofluoric acid resistance and meltability of glass. Its content is 0-10%. When the content of ZnO increases, the devitrification resistance and strain point of the glass tend to decrease. A more preferable range of ZnO is 0 to 5%, and a more preferable range is 0 to 1%.

R ₂ O (R represents Li, Na, K) is a component that reduces the viscosity of the glass and improves the meltability. Its content is from 0 0.1%. When the content of R ₂ O increases, the strain point of the glass tends to decrease .

In addition, when using the glass substrate for a display of this invention for a liquid crystal display use, the glass to be used should be an alkali free glass. The reason is that when an alkali metal oxide is contained in the glass, the alkali component in the glass may deteriorate the characteristics of various films and TFT elements formed on the glass substrate. In addition, alkali free means that R ₂ O is 0.1% or less.

ZrO ₂ is a component that increases the strain point of glass, and its content is 0 to 10%. When the ZrO ₂ content is increased, the density of the glass is remarkably increased, and devitrified materials due to ZrO ₂ tend to precipitate. A more preferable range of ZrO ₂ is 0 to 7%, and a more preferable range is 0 to 5%.

In the present invention, in addition to the above components, for example, Y ₂ O ₃ , La ₂ O ₃ , Nb ₂ O ₃ , and P ₂ O ₅ are added to each of 3 in order to improve the moldability by lowering the liquidus temperature. As ₂ O ₃ , As ₂ O ₃ , Sb ₂ O ₃ , SnO ₂ , SO ₃ , F, Cl, etc. can be added up to 2% in total. _{However, As 2 O 3, Sb 2} O 3 is because the Ru environmental pollutants der should be avoided introduced.

  Next, a method for producing the glass substrate for display of the present invention will be described.

First, a glass raw material is prepared so that it may become said glass composition range. Subsequently, the prepared glass raw material is put into a continuous melting furnace, heated and melted, defoamed, and then the glass melt is supplied to the molding apparatus so that the thickness of the end portion and the thickness of the central portion are substantially the same. In the cooling process in the slow cooling furnace, the temperature distribution in the width direction of the glass ribbon is made as small as possible, so that {sin (2θ)} ² × {sin (180 ° · Δ / 550)} A glass substrate having a small change rate of the value obtained in ² can be obtained.

As the molding method for a glass substrate, da Undoro method, in particular, it is preferably molded into a plate shape by an overflow down draw method. The reason is that in the overflow downdraw method, it is relatively easy to obtain a large glass substrate, and unlike other molding methods, the surface of the glass substrate does not come into contact with the molded body. A glass substrate with no glass surface can be obtained. For this reason, polishing of the glass substrate surface becomes unnecessary, and the manufacturing cost can be suppressed. Moreover, generation | occurrence | production of the fine damage | wound by grinding | polishing can also be eliminated. However, when the glass substrate is formed by the overflow down draw method, the end portion and the center portion of the glass ribbon are made to have substantially the same thickness, and the temperature distribution is reduced, and in addition, the temperature is reduced in a slow cooling furnace or a forming furnace. It is necessary to suppress the rise in airflow.

  Hereinafter, the glass substrate for display of this invention is demonstrated in detail based on an Example.

  Table 1 shows Examples (Sample Nos. 1 and 2) and Comparative Examples (Sample No. 3) of the present invention, respectively.

  Each sample in the table was prepared as follows.

First, in _{mass%, SiO 2 59%, Al} 2 O 3 15%, B 2 O 3 10%, CaO 6%, SrO 7%, BaO 2%, formulating the glass raw material so that the ZnO 1% of the composition And melted in a continuous melting furnace.

  Subsequently, using an overflow downdraw facility as shown in FIG. 2, the molten glass A is supplied to the top of the molded body 21 provided in the molding furnace 20, and the molten glass A overflows from the top of the molded body 21. The glass ribbon B is formed by drawing out and fusing both ends of the fused glass A at a lower end portion of the molded body 21, and sandwiching and drawing between a pair of forming rolls (edge rolls) 22 provided in the vicinity of the lower end portion of the molded body 21. Was molded.

  Next, the glass ribbon B is pulled in the width direction with a plurality of pulling rolls (annealing rolls) 24 installed in the vertical direction in the slow cooling furnace 23 so that the formed glass ribbon B does not shrink in the width direction due to surface tension or the like. The temperature difference between the center and the edge of the glass ribbon B when the temperature of the center of the glass ribbon B is 700 ° C., the maximum temperature in the width direction of the glass ribbon when the temperature of the center of the glass ribbon B is 680 ° C. By pulling downward while cooling so that the difference in the minimum temperature and the plate drawing speed are the values shown in Table 1, a glass ribbon B having a thickness of about 0.7 mm at the center and at the end is obtained.

  Next, the glass ribbon B solidified by a plurality of pairs of support rolls 26 disposed in the cooling chamber 25 provided below the slow cooling furnace 23 is cooled down to room temperature while being pulled downward, and the glass ribbon B is cut in the cutting chamber 27. By doing this, the glass substrate C was obtained and this was made into sample glass.

  In order to suppress an increase in the low-temperature air flow in the molding furnace 20 and the slow cooling furnace 23, the blower 29 disposed in the molding chamber 28 is operated, and the molding chamber is installed from the outside of the equipment through the filter 31 attached to the peripheral wall portion 30. The glass substrate was produced by introducing air into 28 to pressurize the external atmosphere of the forming furnace 20 and the slow cooling furnace 23. The slow cooling furnace refers to an apparatus equipped with a heater or a cooler and capable of controlling the temperature in a range including the range of the slow cooling point to the strain point of glass. ) Indicates the length of this slow cooling device. Sample No. 1 and no. For sample No. 3, the sample No. Sample 2 was cut into a size of 1050 mm × 1250 mm to obtain a sample glass.

When the thermal expansion coefficient, photoelastic constant, annealing point and strain point of the obtained glass were measured, the thermal expansion coefficient of each sample was 37 × 10 ⁻⁷ / ° C., and the photoelastic constant was 33 (nm / cm ) / MPa, the annealing point was 705 ° C., and the strain point was 650 ° C.

For each sample thus obtained, the retardation Δ in the glass substrate and the azimuth angle θ of the retardation with respect to the side direction of the glass substrate are measured at intervals of 50 mm, and {sin (2θ)} ² × at adjacent measurement points. The rate of change of the value obtained by {sin (180 ° · Δ / 550)} ² was obtained. In addition, a display device was produced using the produced glass substrate, and the state of occurrence of luminance unevenness was evaluated. These results are shown in Table 1.

As is clear from Table 1, sample No. 1 is that the maximum value of the rate of change of the value obtained by {sin (2θ)} ² × {sin (180 ° · Δ / 550)} ² at adjacent measurement points in the glass substrate plane is 1.0 × 10. ^-7 and Sample No. 2 was as small as 3.5 × 10 ⁻⁷ . In addition, the state of occurrence of luminance unevenness when the display device was manufactured and turned on was not recognized or weak at all.

On the other hand, sample No. which is a comparative example. 3, the maximum value of the rate of change of the value obtained by {sin (2θ)} ² × {sin (180 ° · Δ / 550)} ² at adjacent measurement points is as large as 7.0 × 10 ⁻⁷ , Brightness unevenness also occurred when the device was manufactured and turned on.

In addition, about the rate of change of the value calculated | required by {sin (2 (theta))} ² * {sin (180 (degree) * (DELTA) / 550)} ² in an adjacent measurement point, it is an optical heterodyne method using the strain gauge made from Uniopt, The retardation Δ and the azimuth angle θ of the retardation with respect to the side direction of the glass substrate are measured in the glass substrate plane at intervals of 50 mm, and {sin (2θ)} ² × {sin (180 ° · Δ / 550)} ² at the measurement point a. And the value A ′ obtained by {sin (2θ)} ² × {sin (180 ° · Δ / 550)} ² at the measurement point a ′ adjacent to the measurement point a and the value A obtained in step (a). A ′) / 50). 3 to 5, the center of each circle is the measurement point, the diameter of the circle is the size of the retardation Δ, and the direction of the line drawn as the diameter of the circle indicates the azimuth angle θ of the retardation with respect to the side direction of the glass substrate. ing.

  As for the occurrence of uneven brightness, the uneven brightness on the screen when the display device is turned on is visually observed, and “◎” indicates that the uneven brightness is not recognized at all. The case where “○” was given and the case where the luminance unevenness was strong was made “X”.

  Regarding the thermal expansion coefficient, each sample was remelted at 1400 ° C. using a platinum crucible to produce a glass lump, and the obtained glass lump was processed into a cylindrical sample having a diameter of 5.0 mm and a length of 20 mm, The average coefficient of thermal expansion at 30 to 380 ° C. was measured with a dilatometer.

  The photoelastic constant was obtained by preparing a sample with a diameter of 30 mm × 5 mm and using a disk compression method.

  The annealing point and strain point were measured based on the method of ASTM C336-71.

  The glass substrate for display of the present invention is not limited to the liquid crystal display application, and can be used as a glass substrate for applications such as a plasma display, a field emission display, and an electroluminescence display.

It is the schematic which shows the structure of a liquid crystal display. It is a schematic front view which shows the manufacturing equipment of the glass substrate by the overflow downdraw method. Sample No. It is a figure which shows the result of having measured the retardation of the glass substrate in 1, and its azimuth. Sample No. It is a figure which shows the result of having measured the retardation of the glass substrate in 2, and its azimuth. Sample No. 3 is a diagram showing the results of measuring the retardation of a glass substrate and the azimuth angle thereof in FIG.

Explanation of symbols

1 Liquid crystal cell 2 Back glass substrate (glass substrate for array)
3 Front glass substrate (glass substrate for color filter)
4 Thin film transistor (TFT)
5 Pixel electrode 6 Alignment film (for back side)
7 Polarizing plate (for the back)
8 Counter electrode 9 Color filter 10 Alignment film (for front)
11 Polarizing plate (for front)
12 Backlight 13 Liquid Crystal Molecule 20 Molding Furnace 20a Molding Furnace Wall 21 Molded Body 22 Molding Roll 23 Slow Cooling Furnace 23a Slow Cooling Furnace Furnace Wall 24 Pulling Roll 25 Cooling Chamber 26 Supporting Roll 27 Cutting Chamber 28 Molding Chamber 29 Blower 30 Peripheral Wall 31 Filter A Molten glass B Glass ribbon C Glass substrate

Claims (5)

A glass substrate formed by a downdraw method,
As a glass composition, in weight _{percent, SiO 2 40~70%, Al 2} O 3 2~25%, B 2 O 3 0~20%, 0~10% MgO, CaO 0~15%, SrO 0~10% BaO 0-15%, ZnO 0-10%, R ₂ O (R represents Li, Na, K) 0-0.1%, ZrO ₂ 0-10%,
Retardation measured in the glass substrate surface at intervals of 50 mm by light orthogonal to the glass substrate surface is Δ (nm), the azimuth angle of the retardation with respect to the side direction of the glass substrate is θ (°), and { sin (2θ)} ² × {sin (180 ° · Δ / 550)} ² is A, and {sin (2θ)} ² × {sin (180 °) at the measurement point a ′ adjacent to the measurement point a. Δ / 550)} When the value obtained in ² is A ′,
A glass substrate for a display, wherein a rate of change ((AA ′) / 50) of values A and A ′ at adjacent measurement points a and a ′ is 4.0 × 10 ⁻⁷ or less.   The glass substrate for a display according to claim 1, wherein the length of the short side of the glass substrate is 1000 mm or more. A glass substrate for a display according to claim 1 or 2, wherein the content of Al ₂ O ₃ in the glass composition is 10 to 20 mass%.   The glass substrate for display according to any one of claims 1 to 3, which is formed by an overflow downdraw molding method.   It is used as a glass substrate of a liquid crystal display, The glass substrate for a display in any one of Claims 1-4 characterized by the above-mentioned.