KR20150053745A - Method for polishing glass substrate - Google Patents

Abstract

A first polishing step of polishing the glass substrate using a first polishing grindstone and a second polishing step of polishing the glass substrate using a second polishing grindstone having an average particle diameter smaller than that of the first polishing grindstone, 2 abrasive grinding stone comprises abrasive grains comprising abrasive grains comprising cerium oxide abrasive grains having a grain size of 0.5 to 10 占 퐉 and diamond abrasive grains having a grain size of 0.5 to 10 占 퐉 and a bond comprising a polyimide resin having a modulus of elasticity of 2.5 to 3 GPa A method of polishing a substrate.

Description

[0001] METHOD FOR POLISHING GLASS SUBSTRATE [0002]

The present invention relates to a polishing method for a glass substrate.

In recent years, with the high-density recording of magnetic disks, required characteristics for a glass substrate for a magnetic recording medium have become strict. Particularly, in the case of polishing a main surface or an end surface of a disc-shaped glass substrate for a magnetic recording medium having a circular hole in the central portion, the required accuracy with respect to the quality of the end surface shape and dimensions of the glass substrate and the required strength of the glass substrate are It is getting higher.

In addition, there is a growing demand for a display glass including a cover glass for protecting a display in a mobile phone such as a smart phone or a portable device such as a PDA. Particularly, techniques for thinning and lightening portable devices have been demanded, and weight reduction and thinning of display glass have been progressing. In general, when the glass plate is thin, the strength is lowered, and therefore, a display glass having a higher strength than the conventional one is required.

In order to secure the strength of the glass substrate or the glass for display, for example, as in Patent Document 1, a polishing method combining polishing using a chamfer and brush polishing is employed.

Further, grindstones exemplified in Patent Document 2, Patent Document 3, and Patent Document 4 are disclosed as grinding wheels used for glass polishing.

Japanese Patent Application Laid-Open No. 2010-131679 Japanese Patent Application Laid-Open No. 62-130179 Japanese Patent Application Laid-Open No. 2008-274293 Japanese Patent Application Laid-Open No. 2010-131679

However, in the method of Patent Document 1, since a plurality of processes are combined, the process is complicated and the cost is increased.

Therefore, the present embodiment provides a polishing method of a glass substrate, which can simplify the processing steps and have sufficient strength to the glass substrate.

A first polishing step of polishing the glass substrate using a first polishing grindstone;

And a second polishing step of polishing the glass substrate by using a second polishing stone having an average particle diameter smaller than that of the first polishing stone,

The second abrasive wheel comprises abrasive abrasive comprising abrasive abrasive grains having a diameter of 0.5 to 10 占 퐉 and abrasive abrasive grains having a diameter of 0.5 to 10 占 퐉 and a polyimide resin having a modulus of elasticity of 2.5 to 3 GPa , A polishing method of a glass substrate is provided.

According to the present embodiment, it is possible to provide a polishing method for a glass substrate, which can simplify the processing steps and can provide sufficient strength to the glass substrate.

1 is a schematic view showing a thickness direction distribution of a residual stress S of a glass plate after chemical strengthening.
Fig. 2 is a schematic diagram after cutting the glass plate after chemical strengthening. Fig.
3 is a schematic view of an example of a polishing unit of the polishing apparatus of the present embodiment.
4 is a schematic view for explaining the polishing method of the present embodiment.

Hereinafter, the present embodiment will be described in more detail with reference to the drawings.

(Glass substrate)

The glass substrate to which the polishing method of the present embodiment can be applied is not particularly limited, and examples thereof include a substrate for a TFT (Thin Film Transistor), a glass substrate for a PDP (Plasma Display Panel), a field emission display (FED) A glass substrate for a magnetic recording medium, a cover glass, and the like.

In addition, the glass-unfired substrate of the glass substrate to which the polishing method of the glass substrate of the present embodiment can be applied is produced by a method such as a float method, a fusion method, a reedrow method, a press molding method, Is not limited in this respect.

The polishing method of the glass substrate of the present embodiment can also be applied to chemically tempered glass in which the glass substrate is chemically strengthened. In this case, it may be applied to chemically tempered glass which is chemically reinforced with a glass-unavoidable plate and cut to a predetermined dimension for a desired use, or may be cut into a predetermined size for a desired use, It may be applied to chemically tempered glass. The method of chemically reinforcing the glass-unoccupied sintered plate and then cutting the glass-unoccupied sintered plate to a predetermined size for a desired application is generally higher than the method of chemical-strengthening after cutting the glass-unoccupied sintered plate to a predetermined dimension for a desired use, It has a feature that cutting is technically difficult.

In the present specification, as an example, an example of chemically tempered glass obtained by chemically reinforcing a glass-unperturbed plate and then cutting it into a predetermined dimension for a desired use will be described.

The chemical tempered glass is a glass in which the surface of the glass is ion-exchanged to form a surface layer in which a compressive stress remains. Specifically, ions of a small ionic radius (for example, Li ion and Na ion) contained in the glass are replaced with ions of a large ionic radius (for example, K ion) by ion-exchanging the surface of the glass. As a result, compressive stress remains on the surface of the glass, and the strength of the glass is improved.

Fig. 1 is a schematic view showing the thickness direction distribution of the residual stress S of the glass plate after chemical strengthening. S1 is the maximum residual compressive stress of one surface layer (referred to as a surface layer) of the glass sheet, S2 is the maximum residual compressive stress (usually S1 = S2) of the other surface layer D is the thickness of the backside layer, D is the thickness of the glass plate, and T is the average residual tensile stress of the intermediate layer present between the surface layer and the backside layer. The horizontal axis in Fig. 1 indicates the distance in the plate thickness direction when the surface layer is set as a reference point (= 0).

As shown in Fig. 1, the compressive stress remaining in the surface layer or the backside layer tends to gradually decrease from the front surface and back surface toward the inside. On the other hand, as a reaction for forming a surface layer and a back layer on which compressive stress remains, an intermediate layer in which tensile stress remains remains between the surface layer and the back layer. At this time, the tensile stress remaining in the intermediate layer is almost constant.

Fig. 2 is a schematic view for explaining a glass plate after chemical strengthening. More specifically, Fig. 2 (a) is a schematic view before cutting the glass plate after chemical strengthening, and Fig. 2 (b) is a schematic view after cutting the glass plate after chemical strengthening.

As apparent from the description of FIG. 1 and FIG. 2 (a), the glass plate after chemical strengthening has a surface layer and a back layer as compression stress layers and an intermediate layer existing between the surface layer and the back layer as a tensile stress layer .

As is clear from the schematic diagram after cutting the glass plate after chemical strengthening shown in FIG. 2 (b), when the glass plate after chemical strengthening is cut, the tensile stress layer is exposed on the surface of the cut surface. When stress acts on the tensile stress layer of the glass sheet after cutting, it may be broken even by a force smaller than usual. Therefore, in the case of the embodiment in which the glass plate after chemical strengthening is cut, it is preferable that the polishing is carried out by the polishing method of the glass substrate of this embodiment, which will be described later, to have sufficient strength.

(First polishing step)

The abrasive grinding stone usually has abrasive grains and a bond for fixing the abrasive grains. In the first polishing step, the abrasive grains having abrasive grains larger in average particle diameter than the abrasive grains of the abrasive grains used in the second polishing step to be described later are polished. Normally, the average grain size of the abrasive grains used in the first polishing step is 5 to 10 占 퐉 (# 2000 in the number of grinding wheels).

The kind of abrasive grains that can be used in the first polishing step is not particularly limited, and for example, cerium oxide, silicon oxide, diamond, chromium oxide, aluminum oxide, zirconium, silicon carbide and the like can be used.

The kind of the bond that can be used in the first polishing step is not particularly limited, and for example, a non-tripide bond, a metal bond, a resin bond, and an electrodeposited grindstone formed by fixing abrasive grains can be used.

In the first polishing step, a standard size grinding process in which the above-described first grinding stone is polished while changing the force of pressing the first grinding stone according to the shape of the main surface or the end surface (the outer peripheral side surface portion, the outer peripheral chamfer portion, etc.) desirable. By accurately grinding the dimensions of the glass by the standard size grinding in the first grinding step using the grinding stone having the abrasive grains larger in average particle diameter than the abrasive grains of the abrasive grinding stone used in the second grinding step which will be described later, It is not necessary to perform precise dimensional control in the subsequent polishing of the second polishing step. Here, the outer circumferential side surface portion and the outer circumferential chamfer portion refer to all the surfaces on the outer circumferential side of the glass plate which are not parallel to the main surface of the glass plate, and the shape thereof may be a curved surface. The chamfering and polishing may be performed simultaneously in the first polishing step.

(Second polishing step)

Following the first polishing step, a second polishing step is performed as a finishing step.

Examples of abrasive grains that can be used in the second polishing step include abrasive grains mixed with abrasive grains obtained by mixing cerium oxide abrasive grains having an average grain diameter of 0.5 to 10 탆 and diamond abrasive grains having an average grain diameter of 0.5 to 10 탆 . The average particle diameter of the abrasive grains can be measured by using, for example, a laser diffraction particle size measuring apparatus or the like. By setting the average grain size of the abrasive grains in the above range, it is possible to remove the scratches on the chamfered portions and the end faces of the glass substrate in the first polishing step and polish them to have sufficient strength.

The bond that can be used in the second polishing step is a polyimide resin having a modulus of elasticity of 2.5 to 3 GPa at 20 캜. The elastic modulus of the bond can be measured by using, for example, a dynamic viscoelasticity measurement device or the like.

Conventionally, after the chamfering step or the rough polishing step of the first step, a method of further polishing using brush polishing or a grinding stone has been employed in order to further improve the strength. However, there has been a problem in that, in brush drawing, conveyance of the glass substrate is troublesome. On the other hand, a method of further grinding using a grinding stone can be carried out only by exchanging the grinding stone after the first grinding process, but has a problem that the treatment time becomes long and is not practical. Further, if the second polishing step is performed on the glass on which the first polishing step is not performed, the lifetime of the grinding stone is extremely shortened, which is not preferable.

The inventors of the present invention have found that the strength of a glass substrate is improved in a short period of time in a polishing method using a grinding stone by using a polishing grindstone using a polyimide resin having a modulus of elasticity of 2.5 to 3 GPa as a bond. Concretely, the glass substrate having the bending strength of 500 MPa or more can be finished by polishing using the abrasive wheel described above. If the elastic modulus is larger than the above-mentioned range, the treatment time becomes long. If the elastic modulus is smaller than the above-mentioned range, the life of the abrasive wheel is shortened, which is not practical. Further, there is a possibility that a glass substrate having sufficient strength after polishing may not be obtained.

The content (V1) of the diamond abrasive grains in the bond is preferably 10 vol% to 20 vol%, and the content (V2) of the cerium oxide abrasive grains in the bond is preferably 5 vol% to 30 vol%. When V1 is less than 10 vol% or when V2 is less than 5 vol%, a sufficient amount of polishing may not be ensured. Therefore, cerium oxide abrasive to be polished by chemical reaction and diamond abrasive to mechanically polish are referred to as By weight. Further, when the sum of V1 and V2 exceeds 30 vol%, the polishing performance as a polishing grinding stone may be lowered, and therefore, it is more preferable to set V1 + V2 to 30%.

In the second polishing step, there may be a standard size polishing step in which the above-described second polishing stone is polished while changing the pressing force according to the shape of the main surface or the end surface of the glass substrate, and the above- Or may be a static pressure polishing step in which the main surface or the end surface of the glass substrate is pressed to perform polishing.

In the second polishing step, it is preferable to carry out the polishing until the surface roughness Ra of the main surface or end face of the glass substrate becomes 8 nm or less, depending on the type of the glass substrate to be used.

(Polishing unit)

Next, an example of a polishing unit capable of carrying out the polishing method of the present embodiment will be described. However, in the present embodiment, the first polishing step of polishing the glass substrate with the first polishing grindstone, the second polishing step of polishing the glass substrate by using the second polishing grindstone having an average particle diameter smaller than that of the first polishing grindstone, Wherein the second abrasive grains have abrasive grains including cerium oxide abrasive grains having an average grain diameter of 0.5 to 10 占 퐉 and diamond abrasive grains having an average grain diameter of 0.5 to 10 占 퐉 and abrasive grains having a modulus of elasticity of 2.5 to 3 GPa The present invention is not limited to the polishing unit having the following constitution.

Alternatively, the first polishing step and the second polishing step may be performed by using a different polishing apparatus. After the first polishing step, the first polishing stone is changed to the second polishing stone, and polishing is performed by the same polishing apparatus .

Fig. 3 shows a schematic view of an example of a polishing unit of the polishing apparatus of the present embodiment. The polishing unit 100 is provided on the shaft 1 through a horizontal rotating arm or the like (not shown) of a polishing apparatus body (not shown). The shaft (1) is rotationally driven by the servo motor (2).

In the housing 3 of the polishing unit 100, a bearing 4 is arranged in the vertical direction and the spindle 5 is pivotally supported.

A grindstone 6 is provided at the front end of the spindle 5 and at the rear end thereof is coupled to the shaft of a drive motor 7 provided outside the housing via pulleys 8a and 8b and a belt 9.

The bearing (4) is installed in the housing (3) so as to be slidable in the horizontal direction through the slide guide (10). The bearing 4 may be configured to be displaceable in the horizontal direction by expansion or contraction of a pneumatic cylinder (not shown). On the side surface of the belt 9, a tensioner 11 for pressing the side surface is provided. With the displacement of the bearing 4, the tensioner 11 absorbs a variation in the length of the belt 9 to be crossed.

(Examples 1 to 8)

Next, embodiments in which the peripheral chamfered portion of the glass plate is polished will be described with reference to examples. In this embodiment, a method of polishing the peripheral chamfered portion of the glass plate will be described, but the present embodiment is not limited in this respect. For example, the polishing method of this embodiment can be applied to a method of polishing a main surface or an outer peripheral side surface of a glass substrate or the like.

Table 1 shows the conditions of the polishing grindstone used in the second polishing process in Examples 1 to 8. Example 1 in Table 1 is a condition of the polishing method of the present embodiment, and Examples 2 to 7 are conditions of a polishing method of the reference example. The # 3000 has an average particle diameter of 4 to 8 占 퐉, the # 2000 has an average particle diameter of 5 to 10 占 퐉, the # 1000 has an average particle diameter of 14 to 22 占 퐉, the elastic modulus of the bond is 21 占 폚 .

In Table 1, the grindstones of Examples 1 to 3 have a content of abrasive grains 1 of 20 wt%, a content of abrasive grains 2 of 5 wt%, grits of Examples 4 to 8 have a content of abrasive grains 1 of 25 wt% %.

Fig. 4 is a schematic view for explaining the polishing method of the present embodiment. More specifically, Fig. 4 is a schematic view of the periphery of the abrasive wheel 6 of Fig. 3 for explaining a method of polishing the outer chamfered portion of the glass plate 20 which is an untreated plate.

An annular grinding groove 32 extending in the peripheral direction is formed on the outer peripheral surface 31 of the abrasive grindstone 6. The wall surface portion of the grinding groove 32 corresponds to the abrasive portion.

In this embodiment, first, as the abrasive wheel 6 used in the first abrasion step, the abrasive wheel 6 having abrasive abrasive grains larger in average particle diameter than the abrasive abrasive grains used in the subsequent second abrasive step And the peripheral chamfered portion of the glass plate 20 was polished. Specifically, in Examples 1 to 8, the abrasive grains of diamond having an average particle diameter of 14 to 22 占 퐉 and the abrasive grindstone having a polyimide and metal bond were mounted, and the peripheral chamfered portion of the glass plate 20 was polished .

The abrasive grindstone 6 is relatively moved along the outer edge of the glass plate 20 while being rotated around the center line of the abrasive grindstone 6 so that the peripheral chamfered portion of the glass plate 20 is polished from the wall surface of the grinding groove 32 do. At this time, it is preferable that the polishing is proceeded by the standard size polishing in which the polishing grindstone 6 is polished while changing the pressing force according to the shape of the glass substrate. In polishing, a coolant such as water may be used.

Thereafter, the grinding wheel 6 was changed to the second grinding wheel 6 including the abrasive grains shown in Table 1 and the bond.

The abrasive grinding wheel 6 is relatively moved along the outer edge of the glass plate 20 while being rotated around the center line of the abrasive grinding wheel 6 so that the outer peripheral chamfered portion of the glass plate 20 is grinded 32). At this time, the polishing may be advanced by a standard size grinding in which the grinding stone 6 is polished while varying the force of pressing the grinding stone 6 according to the shape of the glass substrate. The second grinding stone is pressed to the glass substrate by a constant force, Polishing may be performed by static pressure polishing. Also in the second polishing step, a coolant such as water may be used at the time of polishing.

In the second polishing step, the polishing is continued until the surface roughness Ra of the glass substrate is preferably 8 nm or less, and the polishing is terminated.

(evaluation)

ㆍ Bending strength

In the present embodiment, the bending strength was measured by a four-point bending test. Specifically, a chevron-shaped notch was formed at the center of a test piece having a thickness of 0.7 mm, a width of 50 mm, and a length of 100 mm. A bending test was carried out at a crosshead speed of 1 mm / min so that stable fracture occurred from the tip of the notch of a test piece supported with a span of 30 mm using a tensile-type strength tester. The upper span in the four-point bending test was 10 mm.

Arithmetic mean surface roughness Ra

The surface roughness of the glass substrate was measured using a contact type surface roughness meter (Multimode V SPM-Nanoscope V controller manufactured by Veeco). In addition, the measurement values were measured by measuring the surface roughness of any six points from the glass plate and representing the average value thereof.

Table 1 also shows the evaluation results of the glass substrates obtained in Examples 1 to 8 by the evaluation method described above.

As is clear from Table 1, a glass substrate having sufficient bending strength at a short processing time (polishing time) was obtained by the polishing method (Example 1) of the present embodiment.

On the other hand, in the polishing methods of the reference examples of Examples 2 to 5, it is found that the treatment time (polishing time) necessary for obtaining a sufficient bending strength is long, which is not practical. Further, the glass substrates obtained by the polishing methods of Examples 6 to 8 are rough in surface roughness and lack bending strength.

As described above, according to the present embodiment, the first polishing step of polishing the glass substrate with the first polishing grindstone, the second polishing grindstone having the smaller average particle diameter than the first polishing grindstone, Wherein the second abrasive grains have abrasive grains including cerium oxide abrasive grains having an average grain diameter of 0.5 to 10 占 퐉 and diamond abrasive grains having an average grain diameter of 0.5 to 10 占 퐉 and abrasive grains having a modulus of elasticity of 2.5 to 3 GPa By polishing the glass substrate by the polishing method including the bond including the resin, the glass substrate can have sufficient strength by a simple processing step.

The present application claims priority based on Japanese Patent Application No. 2012-197742 filed on September 7, 2012, and the entire contents of Japanese Patent Application No. 2012-197742 are hereby incorporated by reference into the present application.

1: Axis
2: Servo motor
3: Housing
4: Bearings
5: Spindle
6: Grinding wheel
7: Driving motor
8: Pulley
9: Belt
10: Slide guides
11: Tensioner
20: Glass plate
100: polishing unit

Claims (6)

A first polishing step of polishing the glass substrate using a first polishing grindstone,
And a second polishing step of polishing the glass substrate by using a second polishing stone having an average particle diameter smaller than that of the first polishing stone,
Wherein the second abrasive wheel comprises abrasive grains comprising abrasive grains comprising cerium oxide abrasive grains having an average particle diameter of 0.5 to 10 占 퐉 and diamond abrasive grains having an average grain diameter of 0.5 to 10 占 퐉 and a polyimide resin having a modulus of elasticity of 2.5 to 3 GPa ≪ / RTI > The glass substrate polishing method according to claim 1, wherein the content of the diamond abrasive grains in the bond is 10 vol% to 20 vol%, and the content of the cerium oxide abrasive grains is 5 vol% to 30 vol%. The glass substrate polishing method according to claim 2, wherein the sum of the content of the diamond abrasive grains and the content of the cerium oxide abrasive grains in the bond is 30 vol% or less. The method according to any one of claims 1 to 3, wherein the first polishing step is a standard size polishing step of performing polishing while changing a force for pressing the first grinding stone according to the shape of the glass substrate,
Wherein the second polishing step is a hydrostatic polishing step of pressing the second abrasive wheel with the constant force to the glass substrate to perform polishing. The method according to any one of claims 1 to 3, wherein the first polishing step is a standard size polishing step of performing polishing while changing a force for pressing the first grinding stone according to the shape of the glass substrate,
Wherein the second polishing step is a standard size polishing step of performing polishing while changing the force for pressing the second grinding stone according to the shape of the glass substrate. The method for polishing a glass substrate according to any one of claims 1 to 5, wherein the surface roughness Ra of the glass substrate is set to 8 nm or less by the second polishing step.

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