JPH06247730A - Method for slowly cooling sheet glass - Google Patents

Abstract

PURPOSE:To improve the thermal dimensional stability by placing paper between sheet glasses, heating the laminate close to the slow-cooling points of the sheet glasses, keeping the laminate at that temp. for a specified time and then slowly cooling the laminate. CONSTITUTION:A highly heat-conductive SiC board 2 having about 5mm thickness is placed on a heat-insulating chamotte brick 1 having >=10mm thickness, an interleaving paper 3 is placed thereon, and a sheet glass 4 previously cut to the same size as the interleaving paper 3 is successively and alternately laminated thereon. An SiC board 2 is placed on the interleaving paper 3 and a chamotte brick 1 further thereon, and a weight 5 of stainless steel, etc., is placed at the uppermost part to constitute an aggregate 6. The aggregate 6 is put in a stainless-steel box, gaseous N2 is sealed into the box to control the oxygen concn. in the box to <=0.3%, the sheet glass 4 is heated close to the slow-cooling point in a heat-treating furnace, kept at that temp. for a specified time and then slowly cooled, and the sheet glass 4 having high thermal dimensional stability and high flatness is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gradual cooling method for sheet glass, and more particularly to a gradual cooling method for obtaining a high quality sheet glass having high thermal dimensional stability and flatness.

[0002]

2. Description of the Related Art Conventionally, plate glass has been precision processed and surface-polished for elements such as photomasks, hard disks, optical disks, and liquid crystal displays to satisfy required dimensions and flatness accuracy before being used as a glass substrate. Was there. In the technical field of these elements, the glass substrate is required to have high thermal stability and high flatness and high quality, as compared with flat glass for construction, and strict standards are set.

Usually, a glass plate obtained by a manufacturing method such as a down-draw method or a float method is processed into a predetermined size and then surface-polished to obtain a glass substrate satisfying strict dimensional accuracy and flatness. . These glass substrates are subjected to various heat treatments in order to add performance in the process of forming the element, but after the heat treatment, shrinkage of dimensions and deterioration of flatness occur, which causes a problem of deviating from the standard.

The occurrence of these heat shrinkage and the deterioration of flatness are caused by the distortion of the plate glass. That is, the distortion of the sheet glass is mainly caused by the density distribution of the glass caused by the difference in the cooling rate between the glass surface and the inside which is generated in the cooling step in which the sheet glass is molded from the molten state in the manufacturing process and then gradually cooled and cooled. It is said.

In order to solve this problem, prior to the step of forming the element, heat treatment was performed in a heating furnace for a required time to make the stress distribution uniform, and then gradually cooled to room temperature. Since the flatness is deteriorated due to thermal deformation due to slow cooling and rough surface irregularities are generated on the glass surface, the polishing amount for surface polishing after slow cooling is at least 80-100.
μm (one side) was required. This has been an obstacle to lowering the cost of the glass substrate.

Further, when it is used as a disk substrate, it is generally necessary to perform vacuum suction on a table of a processing machine when performing circular processing or the like, but at that time, if the surface of the plate glass is rough,
The attraction force to the processing machine table becomes weak, which causes a reduction in processing yield.

[0007]

The conventional precision processing / polishing plate glass has the following problems with respect to thermal dimensional stability and flatness. (1) When heat treatment is performed near the annealing point of the plate glass in order to improve the stability of the plate glass in the thermal dimension, the stability of the plate glass in the thermal dimension improves but the flatness deteriorates by 2 to 4 times. (When the glass is placed vertically and annealed). (2) If the flatness of the plate glass is poor, the amount of polishing increases and the polishing cost increases. (3) When flattening the flat glass, the glasses are placed horizontally and heat treated near the annealing point, rather the flatness deteriorates.If the heat treatment temperature is higher than the annealing point of the glass, the fusion of glass The phenomenon occurs. (4) In Japanese Patent Application No. 4-163981 of the related art, the annealing temperature is set to be not less than the annealing point and less than the softening point and the graphite plate is sandwiched between the plate glasses, but this method suppresses the above-mentioned fusion phenomenon. However, the surface of the plate glass becomes rough. The present invention seeks to solve the above problems.

[0008]

The present invention has been made to solve the above-mentioned problems, and provides a slow cooling method for flat glass in which a sheet is sandwiched between flat glasses and the flat glass is gradually cooled in a nitrogen atmosphere. To do.

Further, according to the present invention, a high thermal conductor having a high flatness is placed on a heat insulating material, and a plurality of papers and plate glasses are alternately laminated on the high thermal conductor, and the high thermal conductor is laminated thereon. On top of it, and then heat insulation on top of it, and then heat the assembly with the weight of the metal block on top to a temperature near the annealing point of the sheet glass in a nitrogen atmosphere. Then, the plate glass is gradually cooled after being kept at the temperature for a predetermined period of time, and then provided.

As the heat insulating material, for example, a clay brick can be used, and in this case, a material having a thickness of 10 mm or more is preferable. As the high thermal conductor, for example, a SiC plate or a graphite plate can be used. As the temperature near the annealing point of the plate glass, a temperature lower by about 10 ° C. than the annealing point can be selected.

As the above-mentioned paper, one that meets the object of the present invention can be selected from Japanese paper and foreign paper. For example, when stacking two or more sheet glasses in the sheet glass industry, paper called interleaving paper, which is usually sandwiched between sheet glasses, is preferably used.

In the present invention, by adopting a method of sandwiching the above-mentioned interleaving paper as a paper between plate glass and gradually cooling the whole assembly in a nitrogen atmosphere, a glass substrate having good thermal stability and flatness. It was confirmed that could be obtained with high productivity. The plate glass annealed by the annealing method of the present invention has less surface roughness. Therefore, when trying to obtain the substrate glass by polishing the plate glass, since the surface of the plate glass before polishing is less rough, sufficient quality can be obtained with a polishing amount of about 40 μm on one side, which has been impossible until now. It was confirmed.

The present invention will be described below with reference to examples. As shown in FIG. 1, a high flatness (10 μm or less) with a thermal conductivity of 40 kcal / m · h · ° C. or higher on a clay brick 1 having a thickness of 65 mm and dimensions of 115 mm × 115 mm for the purpose of vertical heat insulation. With a thickness of 5 mm and dimensions of 115 m
One m × 115 mm SiC plate 2 is placed, and a slip sheet 3 cut to a thickness of 0.05 mm and a size of 115 mm × 115 mm is placed on it, and a plate glass 4 cut in advance to the same size as the slip sheet is placed. Twenty sheets are laminated alternately in sequence. The SiC plate 2 is placed on the laminated interleaving paper in the same manner as above, the clay brick is placed thereon, and the weight 5 made of stainless steel of 5 kg is placed on the uppermost part to form the aggregate 6. According to the size of the heat treatment furnace, this assembly is charged with a required number of assemblies in the stainless box 7 shown in FIG. Nitrogen gas was sealed in the stainless box by pipe 8 to prevent carbonization of the interleaving paper by about 0.5 Nm ³ / hr, and heat treatment was performed while keeping the oxygen concentration in the box at 0.3% or less, preferably 0.1% or less. I do. The heat treatment furnace used is an electric furnace whose temperature pattern can be controlled, and heat treatment is performed by a batch type or continuous type electric furnace. The heat treatment is performed by raising the temperature, maintaining the temperature, gradually cooling, and cooling in a temperature pattern as shown in FIG.

[0014]

In the present invention, by using clay bricks on the upper and lower sides, sandwiching interleaving paper between plate glass, and raising the temperature to a temperature near the annealing point of the plate glass and gradually cooling, the following effects There is.

(1) By placing a clay brick having a high heat insulating property and a plate having a high heat conductivity such as SiC on the upper and lower sides, the temperature difference between the upper surface and the lower surface near the strain point of the laminated glass sheets is reduced to 0. It can be suppressed to 0.02 ° C. or less, and the warp due to the temperature difference between the upper surface and the lower surface can be 0.4 μm or less. (2) The interleaf paper is sandwiched between plate glass and gradually cooled in a nitrogen atmosphere, the interleaf paper is carbonized, and carbonized interleaf paper is created between the plate glass, so the flatness is originally poor. In addition, the plate glass that is warped during the temperature rising process freely slides, and by the synergistic effect of the effect of the weight, the warp is corrected and the flatness of the plate glass can be reduced to 10 μm or less per 100 mm diameter. (3) Since the heating temperature is raised only up to near the annealing point of the plate glass, the microscopic surface of the plate glass can maintain a surface state almost the same as that before the annealing. (4) After the plate glass annealed by this method is processed and surface-polished, the heat treatment for adding performance shows that the heat shrinkage of the plate glass is 100 ppm before and after the heat treatment.
Was smaller than the conventional product of 175 ppm. It was also confirmed that the change in flatness before and after the heat treatment was hardly seen.

By these actions, the stability of the thermal dimension is improved, at the same time the flatness of the plate glass is good, the surface is not roughened, and one-side polishing is possible, and a high flatness glass substrate is manufactured at low cost. I was able to.

[0017]

[Example] As shown in FIG. 1, an aluminosilicate glass (annealing point 571 ° C.) having a thickness of 0.72 mm or 0.53 mm and dimensions of 115 mm × 115 mm is sandwiched between plate glass and 20 layers. After forming the following aggregate and setting it in a stainless steel box, it was gradually cooled in a nitrogen atmosphere in a nitrogen atmosphere in the temperature pattern shown in FIG. 10 degrees
95% or more at 10 μm or less per 0 mm diameter, 470 ° C. ×
Thermal shrinkage is 100ppm even after further heat treatment for 8 hours
Is smaller than the conventional product, and the flatness after heat treatment is hardly deteriorated. As for the amount of polishing, since the surface of the plate glass after the slow cooling was good, polishing of 40 μm on one side could be achieved. Such a glass substrate is a glass substrate suitable as a glass substrate for a hard disk.

[0018]

[Table 1]

[0019]

The plate glass annealed by the annealing method of the present invention has the following characteristics. (1) The dimensional change before and after heat treatment is extremely small. (2) The flatness of 10 μm or less can be increased to 95% or more. (3) Since the flatness is high, the polishing amount can be reduced and the polishing cost can be reduced. (4) Since the surface condition is good, the amount of polishing can be further reduced, which is effective in reducing the polishing cost, that is, the effect that one-side polishing is possible is remarkable. (5) The carbon coating formed on the glass surface can be easily washed and removed, but this coating helps prevent the glass from being burnt and stains. (6) Since the graphite setter is not used, the number of sheets to be put in one batch can be increased and the cost of the setter can be reduced.
Cost reduction is possible. Therefore, the plate glass annealed by the annealed cooling method of the present invention can be suitably used as a glass substrate for the photomask, hard disk, or the like.

[Brief description of drawings]

FIG. 1 is a perspective view of a laminated assembly according to an embodiment of the present invention.

FIG. 2 is a perspective view of a box into which a stacked assembly is loaded according to an embodiment of the present invention.

FIG. 3 is a graph of a slow cooling temperature pattern in an example of the present invention.

[Explanation of symbols]

 1: Clay brick 2: SiC plate 3: Interleaf paper 4: Sheet glass 5: Weight 6: Laminated assembly

Claims (4)

[Claims] 1. A method of gradually cooling a plate glass, in which a sheet of paper is sandwiched between the plate glasses and the plate glass is gradually cooled in a nitrogen atmosphere. 2. A high thermal conductor having high flatness is placed on a heat insulating material, a plurality of papers and plate glasses are alternately laminated on the high thermal conductor, and the high thermal conductor is placed on it. Then, after further placing a heat insulating material on it, the aggregate formed by placing the weight of the metal block on the top is heated to a temperature near the annealing point of the plate glass in a nitrogen atmosphere, A gradual cooling method for plate glass, which comprises holding at a temperature for a predetermined time and then gradually cooling. 3. The method for gradually cooling plate glass according to claim 2, wherein the heat insulating material is a clay brick. 4. The method for gradually cooling plate glass according to claim 2, wherein the high thermal conductor is made of SiC or graphite.