JP2001261355A - Method of improving strength of end face of glass substrate and glass substrate for flat panel display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of improving the strength of the end faces of a glass substrate, and a glass substrate for flat panel display. SOLUTION: The method of improving the strength of the end faces of a glass substrate comprises the following steps: a solution containing one or more kinds of compounds selected from among lithium salts, sodium salts, potassium salts, boric acid and phosphoric acid is applied on the end faces of a glass substrate; the substrate is dried; and subsequently, it is heat-treated at a temperature of the strain point of the glass ±100 deg.C. The glass substrate for flat panel display is also provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for improving the strength of an end face of a glass substrate, and a glass substrate for a flat panel display whose strength is improved by the method.

[0002]

2. Description of the Related Art Liquid crystal displays (hereinafter referred to as "LCD"), plasma displays (hereinafter referred to as "PDP"), inorganic and organic electroluminescent displays, field emission displays (hereinafter referred to as "PDP").
Conventionally, glass substrates of various compositions have been used as glass substrates for flat panel displays such as “FED”.

A glass substrate for a flat panel display is manufactured, for example, through the following steps. First, melt the raw materials prepared to have a composition suitable for the application,
A glass base plate is manufactured by a float method, a fusion method, a downdraw method, or the like. Next, cutting the glass blank to dimensions used in flat panel displays,
The end face is chamfered and finished using a grindstone or the like.

When it is necessary to improve the flatness of a glass substrate, at least one of the main surfaces of the glass substrate
The surface on which a film is formed in a flat panel display manufacturing process is polished. Here, the main surface refers to the front and back surfaces of the plate-shaped glass substrate, and excludes the end surfaces.

In recent years, flat panel displays, particularly LCDs and PDPs, have become larger and thinner, making it more difficult to handle in the manufacturing process. In particular, since a large substrate is often subjected to a large bending stress by its own weight, the presence of a slight flaw leads to a substrate crack in a manufacturing process.

One of the factors governing the mechanical strength of a glass substrate for a flat panel display is a flaw existing on the end face of the glass substrate. However, in a glass substrate for a flat panel display, the end surface generally has a coarser surface roughness than the main surface of the glass substrate that requires high flatness. The reason is that the end face is a cut surface cut out from a glass base plate, so that the surface quality (surface roughness, etc.) before chamfering and finishing is not originally good, and high finishing accuracy is not required because it is not involved in image display. And so on.

[0007]

In order to further improve the mechanical strength of the glass substrate, the end face is finished with abrasive grains (grinding wheels made of fixed abrasive grains) having a particle size smaller than the conventional 500 mesh. It has also been attempted to reduce the depth of the flaw, but there is still a rather deep flaw on the end face. Furthermore, in order to improve the finish of the end face, it is necessary to perform multi-step processing using abrasive grains of which the grain size is changed stepwise (processing with a grinding wheel using abrasive grains of coarse grain size, and then grinding with fine grain size). Multi-step processing, such as processing with a grinding wheel using grains, is required to gradually change from coarse grains to fine grains in a step-wise manner. However, there is a problem that productivity is lowered and cost is remarkably increased.

As a method of improving the strength of a glass substrate, which is different from the improvement of the finished state of the end surface, a glass substrate is immersed in a bath of a molten salt of sodium nitrate, a molten salt of potassium nitrate, or a molten salt of a mixture thereof to remove Li ions near the glass surface. An ion exchange strengthening method for ion exchange between Na ions in sodium nitrate molten salt, Na ions in the vicinity of glass surface and K ions in potassium nitrate molten salt to form a compressive stress layer on the glass surface to improve the strength of the glass substrate; There is a method of increasing the strength by a so-called chemical strengthening method.

However, the effect of improving the strength by the chemical strengthening method is effective only for glass containing a predetermined ratio of an alkali metal such as Li or Na. When constructing a flat panel display, an amorphous silicon TFT (a-SiTFT) and a polysilicon TFT (p-SiTFT) are used.
In the case of forming a thin film of a semiconductor such as SiTFT) or an oxide on a glass substrate, for example, in a TFT-LCD, when a large amount of alkali metal is present in the glass substrate, alkali metal ions diffuse into the thin film to form a film. In order to deteriorate the characteristics, a glass substrate containing substantially no alkali metal ions is used. In this case, application of the chemical strengthening method is difficult.

Further, in the flat panel display manufacturing process such as a thin film forming process, a high-temperature heat treatment process is often employed. In this case, the stress layer on the glass surface formed by the chemical strengthening method is relaxed by the heat treatment. In many cases, a sufficient strengthening effect cannot be obtained.

On the other hand, glass has a phenomenon in which the average strength is improved by heat treatment at a temperature near and above the strain point. Hereinafter, this phenomenon will be described.

When a flaw or crack present in the glass is subjected to tensile stress in a direction perpendicular to the crack, stress concentration occurs and the stress is maximum at the crack tip. As shown in FIG. 3, when a tensile stress σ acts on a crack 3 having a semi-elliptic cross section at a depth C existing on the surface 2 of the object 1 in the vertical direction, the stress σ _m at the crack tip becomes Given by

Σ _m = 2σ (C / ρ) ^1/2 (1) where ρ is the radius of curvature of the crack tip. According to Equation 1, when the depth C of the crack becomes small, or when the radius of curvature ρ of the crack tip becomes large, stress concentration on the crack tip becomes difficult to occur, and as a result, even if the same stress acts, the fracture occurs. It becomes difficult.

Although the radius of curvature ρ of a normal crack tip is sufficiently small, that is, often sharp, such a crack is a state in which a chemical bond is broken and the energy is high. Therefore, if the glass is subjected to heat treatment at a temperature near or above its strain point, the radius of curvature ρ of the crack tip becomes large due to mass transfer such as diffusion, and in extreme cases, crack healing due to recombination of the crack may occur. There is. This phenomenon is generally caused by crack healing.
calling. When such a phenomenon occurs, stress concentration on the crack tip is unlikely to occur as described above, and even when the same stress acts, destruction is unlikely to occur.

However, when a flaw of a predetermined size or more is present on the glass, as in a conventional glass substrate having a processed end face, a crack-healing phenomenon is unlikely to occur, so that a remarkable strength-improving effect is obtained. Hateful. In this case, the effect of improving the strength can be obtained by increasing the heat treatment temperature so that mass transfer easily occurs. However, since flatness is required for glass substrates for flat panel displays, heat treatment at an excessively high temperature, particularly at a temperature higher than the annealing point, causes thermal deformation of the glass substrate and deteriorates the flatness of the glass substrate. Is not preferred.

An object of the present invention is to provide a method for improving the end face strength of a glass substrate which solves the above-mentioned problems, and to provide a glass substrate for a flat panel display using the same.

[0017]

According to the present invention, a lithium salt, a sodium salt, a potassium salt,
A solution containing at least one compound selected from boric acid and phosphoric acid (hereinafter, referred to as "specific compound") is applied, dried, and then heat-treated within a temperature range of the strain point of the glass ± 100 ° C. To provide a method for improving the strength of an end face of a glass substrate. By adopting such a method, it is possible to relatively easily improve the end face strength of the glass substrate without causing thermal deformation of the glass substrate. Also, the solution containing the specific compound,
This is because the material can be easily obtained, and can be safely and simply prepared, and is suitable as a method for improving the end face strength of the glass substrate. Further, the present invention provides a glass substrate for a flat panel display obtained by improving the end face strength by the above method.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION A flat panel display according to the present invention refers to a display having a flat screen such as an LCD, a PDP, an inorganic and organic electroluminescent display, and an FED.

The glass substrate in the present invention is a glass substrate (for example, a glass ribbon formed by a down-draw method such as a float method or a fusion method) cut into a predetermined size. The shape usually used as a glass substrate for a flat panel display of the present invention is a rectangle,
The dimensions are expressed in mm and the long side 650, short side 550, plate thickness 0.7, or long side 1050, short side 650, plate thickness 2.
8, etc. As described above, the main surface of the glass substrate in the present invention refers to the front and back surfaces of the plate-shaped glass substrate, and excludes the end surface of the substrate.

Generally, SiO ₂ —Al ₂ O ₃ —RO glass is used for a glass substrate for a flat panel display. In the present invention, by treating local portions of these glasses, as a result of searching for a component that apparently significantly reduces the strain point of the local portions, lithium salt, sodium salt, potassium salt, boric acid, and phosphoric acid are removed. Found to be effective.

In the present invention, a solution containing at least one specific compound is applied to the end face of the glass substrate, dried, and then heat-treated within a temperature range of ± 100 ° C. of the strain point of the glass. As a result, the strain point of the glass near the end face decreases, so that even when heat treatment is performed at a relatively low temperature, the crack healing effect is easily obtained, and the strength of the glass is improved without impairing the flatness of the glass.

As the specific compound, Li ₂ C is used because the material is easily available and the compound can be safely and simply prepared.
O ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , B ₂ O ₃ .nH ₂ O (for example, H ₃ BO ₃ ), P ₂ O ₅ .nH ₂ O (for example, H ₃ PO ₄ )
Etc. are preferred, but not limited thereto. The solvent of the solution is preferably an organic solvent such as water or alcohol, but any solvent that dissolves the specific compound used can be used.
It is not limited to these.

The heat treatment temperature of the glass substrate is set within a range of ± 100 ° C. of the strain point of the glass. Here, the heat treatment temperature refers to the maximum temperature of the treatment atmosphere during the heat treatment step (the details of the heat treatment conditions for the glass substrate are shown in FIG. 1 described later). The holding time at the highest temperature may be 5 minutes or more. When higher flatness is required for the glass substrate, the heat treatment temperature is preferably within the range of ± 50 ° C. of the strain point of the glass,
C) to within the range of the strain point.

Incidentally, the glass substrate for a flat panel display may be pre-heat-treated at a temperature near the strain point in advance in order to suppress heat shrinkage during the heat treatment or the like during the manufacturing process. Therefore, if the above-mentioned solution is applied to the end face portion of the substrate and dried, and then the heat treatment shown in FIG. 1 described later is performed, the heat shrinkage suppressing effect and the end face strength improving effect can be simultaneously obtained. In this case, since it is not necessary to newly perform a heat treatment for improving the strength, the process can be omitted.

[0025]

EXAMPLES In terms of mass%, SiO ₂ : 58%, Al ₂ O ₃ : 7
%, MgO: 2%, CaO: 5%, SrO: 7%, Ba
O: 7.5%, ZrO ₂ : 3%, Na ₂ O: 4%, K
₂ O: glass having a composition of 6.5% (strain point: 570)
° C), length 50-55 mm, width 4 mm, thickness 2.8 m
The test sample was fabricated by processing into a size of m and rubbing the surface for evaluating the strength with a 320-mesh GC abrasive (green silicon carbide abrasive) to damage the surface. 10 test samples
0 pieces were prepared, and 20 to 30 pieces were divided into four groups, and the following processes were respectively performed.

Process 1: unprocessed (comparative example) Process 2: Only the heat treatment shown in FIG. 1 was performed in a muffle furnace (comparative example). Treatment 3: After immersing in a 4% by mass aqueous solution of H ₃ BO ₃ for 2 seconds,
After air drying at room temperature, the heat treatment shown in FIG. 1 was performed in a muffle furnace. Treatment 4: After immersing in a 4% by mass aqueous solution of Na ₂ CO ₃ for 2 seconds, air-drying is performed at room temperature, and after drying, the heat treatment shown in FIG. 1 is performed in a muffle furnace.

The four-point bending strength test (J
IS R1601, lower span 30mm, upper span 10m
m, crosshead speed 0.5 mm / min) and the strength was compared. In addition, the sample whose fracture origin is not a damaged surface was excluded from the following data. FIG. 2 shows the obtained Weibull plot, and Table 1 shows the measurement results.

[0028]

[Table 1]

Comparing the results of processing 1 and processing 2,
It can be seen that the average breaking strength is improved by the heat treatment.
However, the Weibull coefficient in Process 2 was smaller than that in Process 1, and no significant improvement was seen when compared with 0.1% probability of fracture stress. The reason is presumed to be that the crack healing phenomenon did not occur in the large wound. In the actual flat panel display manufacturing process,
Since cracking with a fracture probability of about 0.1% becomes a problem, it cannot be said that the strength was sufficiently improved in the treatment 2.

On the other hand, it can be seen that the average fracture strength is improved in the treatments 3 and 4, and the Weibull coefficient is higher than that in the treatment 1, so that the 0.1% fracture probability stress is also increased. The reason for this is presumed to be that the strain point of the glass is locally reduced by the application of H ₃ BO ₃ and Na ₂ CO ₃ and the heat treatment, and the crack healing phenomenon occurs even with a large flaw. From this result, it is considered that the probability of destruction in practical use is greatly reduced. Thus, according to the present invention,
The breaking strength of glass, especially the probability of breaking stress, which is a practical problem, can be increased, and the breaking of glass can be prevented.

[0031]

According to the present invention, the strength of the end face of the glass substrate, which does not necessarily require chemical strengthening and greatly affects the mechanical strength of the glass substrate, can be improved. In particular, it is possible to increase the probability of fracture stress at a low probability, which is a practical problem. Thereby, a high-strength glass substrate for a flat panel display can be provided.

[Brief description of the drawings]

FIG. 1 is a graph showing a heat treatment pattern of a sample in an example of the present invention.

FIG. 2 is a Weibull plot of a result of a four-point bending strength test in an example of the present invention.

FIG. 3 is a schematic cross-sectional view illustrating a crack existing on the surface of a glass substrate.

[Explanation of symbols]

 1: Object 2: Surface of object 3: Crack C: Depth of crack

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H090 JA11 JB02 JC06 JD13 LA04 4G015 DA05 5C094 AA36 BA21 BA27 BA31 BA43 EB02 GB10

Claims (2)

[Claims] 1. A solution containing at least one compound selected from a lithium salt, a sodium salt, a potassium salt, boric acid and phosphoric acid is applied to an end surface of a glass substrate, dried, and then subjected to a strain point ± 100 of the glass. A method for improving the strength of an end face of a glass substrate, wherein the heat treatment is performed within a temperature range of ° C. 2. A glass substrate for a flat panel display, wherein the end face strength is improved by the method according to claim 1.