JP2000169177A - Float glass for display substrate - Google Patents

Abstract

(57) [Summary] [0005] Deterioration of liquid crystal characteristics such as defects such as disconnection of electrode lines formed on the surface, insufficient capacity of pixel liquid crystal, and reduced adhesion of oxide layer is unlikely to occur, and the strain point is 580 ° C. The above-mentioned float glass for a display substrate is obtained. A float glass having a strain point of 580 ° C. or more, wherein the content of SO _{3 in} a mother glass is 1 ppm.
The float glass for a display substrate having a content of less than 30 ppm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a float glass used for a display substrate such as a liquid crystal display substrate and a plasma display substrate.

[0002]

2. Description of the Related Art As a glass for a liquid crystal display (hereinafter referred to as LCD) substrate, a glass which does not contain alkali or has a small amount of alkali even if containing alkali, and has a high strain point and a small thermal expansion coefficient is required. Conventionally, aluminosilicate glass has been used as an alkali-free or low-alkali glass satisfying the above characteristics. The viscosity of such a glass in a molten state is higher than that of soda-lime silica glass widely used for window glass, for example, and it is difficult to remove bubbles, that is, to clarify. As a fining agent, arsenous acid, antimony oxide, a halogen element (F, Cl, Br, I), a sulfate, or the like is generally used.
Arsenous acid and antimony oxide are most effective.

[0003] On the other hand, most sheet glass represented by window glass is manufactured by a float method which can obtain a sheet glass having high flatness and smoothness at low cost. In the float method, molten glass is poured onto molten tin having a higher specific gravity than glass, and is formed while being spread on the molten tin in a plate shape. The float bath containing molten tin is kept in a reducing atmosphere to prevent oxidation of the molten tin.
Therefore, if a component that is easily reduced, such as arsenous acid or antimony oxide, is present in the glass, there is a possibility that metal deposition and accompanying coloring may occur.

[0004] Therefore, the fining agents that can be used for float-molded glass are limited, and it is generally difficult to use arsenous acid or antimony oxide. On the other hand, the above-mentioned problems do not occur with sulfates.

[0005] In view of the above, the LC to be float-molded
In alkali-free or low-alkali aluminosilicate glass for D substrate (hereinafter referred to as float glass for LCD substrate), sulfate is often used as a fining agent. As the sulfate, an alkali metal sulfate or an alkaline earth metal sulfate is usually used.

The steps of manufacturing a TFT-LCD using the float glass for an LCD substrate manufactured as described above are as follows. That is, the float glass is cut into a predetermined size to form a glass substrate. After washing the glass substrate, the glass substrate is put into a TFT-LCD manufacturing process. A gate electrode line (hereinafter simply referred to as an electrode line) and an oxide layer for gate insulation (hereinafter simply referred to as an oxide layer) are formed on one surface of a glass substrate, and a pixel electrode and the like are formed on the surface of the oxide layer. To form an array substrate. An RGB color filter and a counter electrode are formed on one surface of another glass substrate to form a color filter substrate. Next, a liquid crystal material is sandwiched and sealed between the array substrate and the color filter substrate to manufacture a TFT-LCD. Note that a general TFT-
On the LCD substrate, the line width of the electrode line is about 5 to 10 μm, and the electrode line interval corresponding to the pixel pitch is 100 to 200 μm.
The cell gap of the liquid crystal is about 5 μm.

Conventionally, irrespective of the cleanliness of the above-mentioned washing process and TFT-LCD manufacturing process, defects such as disconnection of electrode lines, deterioration of liquid crystal characteristics such as insufficient capacity of pixel liquid crystal, deterioration of adhesion of oxide layer, etc. In some cases, these have been the causes of lower LCD manufacturing yields.

[0008]

SUMMARY OF THE INVENTION The present invention has a distortion point of 58.
An object of the present invention is to provide a float glass having a temperature of 0 ° C. or higher and which is unlikely to cause the above-described poor quality.

[0009]

According to the present invention, a distortion point is 580.
The present invention provides a float glass for a display substrate, which has a SO ₃ content of 1 ppm or more and less than 30 ppm with respect to a mother glass, which is a float glass having a temperature of at least 0 ° C.

[0010] The present inventor: 1) When manufacturing a TFT-LCD using a float glass, defects such as disconnection of an electrode line and a pixel, which are generated irrespective of the cleanliness of a cleaning process or a TFT-LCD manufacturing process. The causes of poor quality such as a decrease in liquid crystal characteristics such as insufficient capacity of the liquid crystal, a decrease in adhesion of the oxide layer, and the like are caused by deposits or dents present on the surface of the float glass. 2) The surface of the float glass not in contact with the molten tin That is, the generation of deposits present on the top surface, or the formation of depressions on the surface of the float glass, and the S of the float glass
The inventors have found that there is a correlation with the O ₃ content, and have reached the present invention. Here, the deposit is mainly composed of metallic tin or a tin compound.

That is, when the aluminosilicate glass containing SO ₃ is formed by the float method, the mechanism by which metal tin or a tin compound adheres to the top surface is as follows.
It was found that it was as shown below. here,
SO ₃ is supplied from, for example, sulfate used as a fining agent.

The SO ₃ contained in the glass is eluted from the surface where the glass is in contact with the molten tin, ie, the bottom surface, to form tin sulfide. Tin sulfide exists in a gaseous state at the temperature and atmosphere of a normal float bath, has a high vapor pressure, and immediately escapes from molten tin to vaporize.
The vaporized tin sulfide diffuses into the float bath atmosphere, and is promptly reduced by hydrogen in the atmosphere to form metal tin particles. When the particles grow and grow and fall on the top surface of the ribbon-shaped glass (glass ribbon) in the float bath, they become metal tin deposits. Further, the tin compound deposit is oxidized after the metal tin deposit has left the float bath.

The depression present on the top surface is a shell of the deposit of the metallic tin or tin compound. That is,
Immediately after the glass ribbon comes out of the float bath, metallic tin or tin compound deposits are blown off from the top surface by the airflow flowing just above the top surface. Although the formation mechanism of the dents present on the bottom surface is unknown, it has been found that the occurrence frequency increases with the SO ₃ content in the glass.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The float glass for a display substrate in the present invention is a sheet glass produced by a float method, and is a sheet glass before a surface treatment such as formation of an electrode wire or an oxide layer is performed on the surface thereof. And includes, for example, those that have been cleaned and / or polished before the surface treatment is performed.

The display substrate in the present invention is a plate glass cut to a predetermined size, that is, a substrate glass having an electrode wire or an oxide layer formed on the surface thereof.
For example, an LCD substrate, a plasma display panel (hereinafter, referred to as PDP) substrate, and the like.

The strain point of the float glass for a display substrate of the present invention is 580 ° C. or higher. LC below 580 ° C
In the heat treatment process for manufacturing D, PDP, etc., there is a possibility that a problem of thermal deformation or a dimensional change of an LCD substrate, a PDP substrate, etc. may occur. In the following, a case used for manufacturing a TFT-LCD will be described.

The deposits present on the surface of the float glass referred to in the present invention mainly consist essentially of metallic tin or a tin compound. If the size is less than 20 μm, the thickness of the attached matter is negligible, the disconnection of the electrode wire is rare, and the capacity of the pixel liquid crystal is insufficient. However, when an electrode line is formed on an attachment having a size of 20 μm or more, the electrode line is more likely to be disconnected. In addition, when a pixel area is formed on the attachment, a pixel liquid crystal is formed. In this case, there is a high possibility that the liquid crystal characteristics may be deteriorated due to insufficient capacity of the liquid crystal, and in any case, the LCD manufacturing yield may be reduced. Those having a size of 300 μm or more have a small adhesive force to glass and can be removed by a general washing step, and there is little possibility of causing a problem. Hereinafter, among the deposits of metal tin or tin compound existing on the float glass surface, those having a size of 20 to 300 μm are referred to as deposit defect.

The depth existing on the float glass surface is 1 μm.
Depressions of m or more (hereinafter referred to as depression defects) cause disconnection of the electrode wires formed on the surface of the glass substrate or decrease in adhesion of the oxide layer formed on the surface of the glass substrate to the glass substrate. Lower the retention.

The case where the present invention is used in the manufacture of a TFT-LCD has been described above, but the present invention is not limited to this. Float glass for an STN-LCD substrate, float glass for a PDP substrate, etc. Oxide layer,
The present invention is applied to a float glass on which a thin film layer is formed.

The SO ₃ content of the float glass for a display substrate of the present invention is 1 ppm or more and less than 30 ppm with respect to the base glass. When the content is 30 ppm or more, the frequency of occurrence of the deposit defect and the dent defect increases, and it becomes difficult to use the glass as a display substrate glass. Preferably it is 20 ppm or less, more preferably 10 ppm or less. If it is less than 1 ppm, the fining effect is small. Here, “with respect to the base glass” means that the content is expressed in an external number.

The alkali oxide of the float glass for a display substrate of the present invention is not an essential component, but may be contained up to 2.0% by weight based on the mother glass. 2.0% by weight
If it is too large, it may be difficult to use it as a glass for a display substrate, particularly as a glass for an LCD substrate.

[0022]

EXAMPLES The composition of the mother glass (aluminosilicate glass) expressed in% by weight is as follows: SiO ₂ : 60, Al ₂ O ₃ : 17,
Regarding four types of float glass for LCD substrate having a thickness of 0.7 mm, which are B ₂ O ₃ : 7, MgO: 4, CaO: 5, and SrO: 7, the SO ₃ content (unit: p
pm) and the total (unit: number) of the number of adherent defects and the number of hollow defects per 6.0 m ^{2 of} the top surface are shown in Table 1. This float glass is made of Na ₂ O,
K ₂ O and BaO are contained in 0.05% by weight, 0.01% by weight and 0.2% by weight, respectively, and their strain points are 665 ° C. It is preferable that the total of the number of the deposit defects and the number of the concave defects is 90 or less.

Regarding the deposit defect and the hollow defect,
By a so-called edge light inspection for inspecting the main surface of the glass plate irradiated with light from the side surface of the glass plate in a dark room, deposits having a size of 20 to 300 μm and dents were examined. The inspection was performed on 50 300 mm × 400 mm glass plates. The total area of the inspected glass plate surface is 6.
0 m ² .

The depth of the dent present on the top surface was measured by using a laser microscope, and the one having a depth of 1 μm or more was regarded as a dent defect.

The SO ₃ content (unit: ppm) was measured by the method described below. First, as a pretreatment, a glass sample was decomposed with hydrofluoric acid and hydrochloric acid. At this time, hydrogen peroxide was added as an oxidizing agent in order to prevent some of the sulfur from being reduced or volatilized.

Next, a 4% aqueous solution of sodium hydroxide 0.5
An oxidation trap containing 5 ml of hydrogen peroxide, 5 ml of hydrogen peroxide and 5 ml of ion-exchanged water is prepared. The three-necked flask containing the pretreated sample and the oxidation trap are set in a measuring vessel, and after purging the inside of the measuring vessel with nitrogen, about 8 ml of a reducing agent is added to the three-necked flask. The reducing agent is hypophosphorous acid 5 ml,
20 ml of hydroiodic acid and 3.5 g of sodium iodide were weighed out and heated at 200 ° C. for 3 to 4 hours while bubbling with nitrogen.

The three-necked flask is heated to 180 to 200 ° C. in a sand bath while gently flowing nitrogen gas, and gently boiled. By this operation, all the sulfur in the sample is S ^2-
And released as H ₂ S gas. This H ₂ S gas is introduced into the oxidation trap together with the nitrogen stream, and is collected in the form of SO ₄ ²⁻ . The sulfur in the oxidation trap was analyzed by an ICP emission spectrometer (SPS400, manufactured by Seiko Instruments Inc.).
Quantification using 0) gave the SO ₃ content.

[0028]

[Table 1]

[0029]

According to the present invention, there is provided a float glass having a strain point of 580 ° C. or more, a defect such as a disconnection of an electrode wire formed on the surface thereof, a decrease in liquid crystal characteristics such as a lack of capacity of a pixel liquid crystal, A float glass for a display substrate, in which the adhesiveness of the oxide layer is unlikely to be reduced and the like, is obtained, and the production yield of LCDs, PDPs and the like is improved.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takashi Mukai 1-1, Suehirocho, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture Inside Asahi Glass Co., Ltd. F term (reference) 2H090 JB02 JC06 JD08 JD17 LA04 4G062 AA04 BB01 CC04 DA06 DB04 DC03 EA01 EA02 EA03 EB01 EB02 EB03 EC01 EC02 EC03 ED03 EE03 EF03 FA10 GB01 GB02 HH20 JJ10 KK10 MM27NN01

Claims (2)

[Claims] 1. A float glass having a strain point of 580 ° C. or higher, wherein the content of SO ₃ with respect to the mother glass is 1 ppm.
The float glass for a display substrate having a content of less than 30 ppm. 2. The float glass for a display substrate according to claim 1, wherein the content of the alkali oxide with respect to the mother glass is 2.0% by weight or less.