JP2014083647A - Magnetic fluid for glass substrate polishing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic fluid for glass substrate polishing, which enables smooth processing of an end surface of a glass substrate and which can make processing time shorter than ever.SOLUTION: A polishing wheel 12b includes: a rotating shaft 1; a magnetic field forming portion 2 that comprises first and second disc-like members 2a and 2b rotating with the rotating shaft 1; and a magnetic fluid 3. A concentration of magnetic abrasive grain in the magnetic fluid 3 is 70 wt% or more, and a shape can be retained to some extent even in a state with no restraint caused by a magnetic field.

Description

  The present invention relates to a magnetic fluid for polishing a glass substrate.

  The manufacturing process of the glass substrate for flat panel displays, such as a liquid crystal display and a plasma display, includes the process of cut | disconnecting a glass substrate. When the glass substrate is cut, a scribe line is formed on the glass substrate, and the tensile stress is concentrated on the scribe line to cleave the glass substrate. The scribe line is generally formed by a method of mechanically forming using a diamond cutter or a method of causing an initial crack to proceed by heating and rapid cooling using a laser.

  When the scribe line is formed mechanically, fine cracks inevitably exist around the scribe line. When a scribe line is formed using a laser, a very sharp edge is formed at a corner between the end surface and the front and back surfaces of the divided glass substrate. Therefore, the end surface of the glass substrate after cutting is ground by the diamond wheel, and cracks and sharp edges are removed, and the shape is adjusted so that, for example, the cross section has an R shape. Thereafter, the end surface of the glass substrate is finished into a mirror surface by polishing using a flexible polishing wheel made of, for example, foamed resin.

  Patent Documents 1 to 3 disclose a technique using a magnetic fluid for polishing an end face of a glass substrate. In the polishing process using a magnetic fluid, a magnetic fluid containing magnetic abrasive grains is held between a pair of magnets, and the end surface of the glass substrate and the magnetic fluid are brought into contact with the magnetic fluid. By relatively moving, the end face of the glass substrate is polished. In the polishing process using a magnetic fluid, the magnetic abrasive grains can be polished while following the shape of the workpiece, and damage to the workpiece is relatively small. Therefore, when a magnetic fluid is used for polishing the end face of the glass substrate, a smoother end face can be obtained as compared with a polishing process using a conventional polishing wheel.

International Publication No. 2012/066757 International Publication No. 2012/006504 International Publication No. 2011/163450

  However, a polishing process using a magnetic fluid requires a very long processing time compared to a polishing process using a conventional polishing wheel. For example, as described in Patent Document 1, when a magnetic fluid in which magnetic abrasive grains of 20 vol% to 40 vol% are dispersed in water is used, it is very long to remove a desired amount of glass. Since processing time is required, it is not suitable for mass production of glass substrates.

  Therefore, the present invention provides a magnetic fluid for polishing a glass substrate, which can process the end surface of the glass substrate smoothly and can reduce the processing time as compared with the prior art.

One aspect of the present invention is a magnetic fluid for polishing a glass substrate that contains magnetic abrasive grains and is held by a magnetic field to polish the end surface of the glass substrate. This magnetic fluid is characterized in that the concentration of the magnetic abrasive grains in the magnetic fluid is 70 wt% or more.
In the magnetic fluid for polishing a glass substrate of the above aspect, the concentration of the magnetic abrasive grains may be 85 wt% or more.
In the magnetic fluid for polishing a glass substrate according to the above aspect, the magnetic abrasive grains may have a maximum magnetic flux density of 1 T or more and a maximum permeability of 3.0 H / m or more.
In the magnetic fluid for polishing a glass substrate of the above aspect, the magnetic abrasive grains may be irregularly shaped particles having corner portions. In this case, the magnetic abrasive grains may have an average particle size of 15 μm or less.
In the magnetic fluid for polishing a glass substrate according to the above aspect, the magnetic abrasive grains may be spherical particles having no corners. In this case, the magnetic abrasive grains may have an average particle diameter of 6 μm or more and 20 μm or less.

  According to the magnetic fluid for polishing a glass substrate of the present invention, the end surface of the glass substrate can be processed smoothly, and the processing time can be shortened as compared with the prior art.

It is a top view which shows the outline of the grinding | polishing wheel of this embodiment. It is sectional drawing which follows the II-II line of FIG. It is process drawing explaining the process of the manufacturing method of the glass substrate of this embodiment. It is a figure which shows typically the apparatus which performs from a melt | dissolution process to a cutting process. It is a figure which shows the flow of the end surface processing of the glass substrate of this embodiment. It is a perspective view which shows a 1st grinding wheel and a 2nd grinding wheel. It is sectional drawing which shows the measurement location of the surface roughness of the glass substrate in an Example.

  Hereinafter, embodiments of the magnetic fluid for polishing a glass substrate of the present invention will be described with reference to the drawings. FIG. 1 is a plan view showing an outline of polishing using the magnetic fluid according to the present embodiment. 2 is a cross-sectional view taken along the line II-II in FIG. In this embodiment, the end surface of the glass substrate which is cut into a predetermined size and whose cross-sectional shape is ground into an arc shape or an R shape by a diamond wheel is polished.

As shown in FIGS. 1 and 2, the polishing wheel 12 b includes a rotating shaft 1, a magnetic field forming unit 2, and a magnetic fluid 3.
The rotation shaft 1 is connected to a rotation drive unit (not shown) and is provided to rotate around a shaft at a desired rotation speed. Moreover, the rotating shaft 1 is provided so that it may approach and leave | separate with respect to the glass substrate G by the moving mechanism not shown.
The magnetic field forming unit 2 includes a disk-shaped first member 2 a and a second member 2 b that are fixed to the rotating shaft 1 and rotate together with the rotating shaft 1. The first member 2 a and the second member 2 b are arranged at a predetermined interval suitable for polishing the glass substrate G in the axial direction of the rotation shaft 1. The first member 2a and the second member 2b are composed of magnets such as permanent magnets and electromagnets, for example, and are provided so as to form a magnetic field having a desired strength between the first member 2a and the second member 2b. .

The magnetic fluid 3 is composed of magnetic abrasive grains and a liquid, and is held by a magnetic field formed between the first member 2a and the second member 2b of the magnetic field forming unit 2.
The magnetic abrasive grains are abrasive grains for polishing a brittle material such as the glass substrate G, and are composed of magnetic particles such as iron oxide and ferrite. By using ferrite as the magnetic abrasive grains, it is possible to suppress the deterioration of the magnetic abrasive grains over time while eliminating or eliminating the additive for preventing oxidation.

  As the liquid mixed with the magnetic abrasive grains, for example, water, hydrocarbons, esters, ethers, hydrogen fluoride and the like can be used. Alternatively, a liquid containing water as a main component and added with hydrocarbons, esters, ethers, hydrogen fluoride, or the like may be used. Furthermore, in order to prevent aggregation of magnetic abrasive grains, a surfactant may be added to the magnetic fluid at 0.5 wt% or less. Examples of the surfactant include fatty acid esters. Moreover, in order to relieve the composition change, propylene glycol having a boiling point higher than that of water may be added to the magnetic fluid at less than 3%.

In the present embodiment, the magnetic abrasive grains and water are mixed so that the concentration of the magnetic abrasive grains in the magnetic fluid 3 is 70 wt% or more. The concentration of the magnetic abrasive grains is preferably 80 wt% or more, more preferably 85 wt% or more, from the viewpoint of the glass removal ability.
When the concentration of the magnetic abrasive grains in the magnetic fluid 3 is 70 wt% or more, the magnetic fluid 3 becomes a paste. That is, even when the magnetic fluid 3 is not restrained by the magnetic field, the magnetic fluid 3 can be maintained in a certain shape between the first member 2a and the second member 2b.

  The shape of the magnetic abrasive grains contained in the magnetic fluid 3 is a spherical shape or an indefinite shape having corners. Here, the spherical shape includes not only a circular cross-sectional shape but also a rounded shape with no corners such as an elliptical shape or an oval cross-sectional shape. Further, the indefinite shape having a corner includes a three-dimensional non-uniform shape having one or a plurality of sharp corners. Also, having a corner means that the particle is thinning toward the edge, that the cross-sectional outline of the particle forms one or more acute or obtuse angles, and that the edge of the particle is sharp. including.

The average particle diameter of the magnetic abrasive grains may be, for example, 2 μm or less. The average particle diameter of the magnetic abrasive grains may be 2 μm or more and 6 μm or less. Further, the average particle diameter of the magnetic abrasive grains may be 6 μm or more and 15 μm or less, or may be larger than 15 μm.
Here, the average particle diameter of the magnetic abrasive grains can be obtained, for example, by image analysis of particles. Specifically, the average particle diameter of the irregularly shaped magnetic abrasive grains can be obtained by taking an image of the particle and using the diameter of the circular particle equal to the projected area of the particle as the particle diameter. .

  In the case where the shape of the magnetic abrasive grains is an indefinite shape having corners, the average particle size of the magnetic abrasive grains is compatible from the viewpoint of achieving both the ability to remove glass as the material to be polished and the smoothness of the surface to be polished. The diameter is preferably 15 μm or less. That is, when the shape of the magnetic abrasive grains is an indefinite shape having corners, the ability to grind the glass is higher than that of spherical magnetic abrasive grains having the same diameter. When the diameter exceeds 15 μm, it becomes difficult to improve the smoothness of the end face of the glass substrate G to be polished.

  When the shape of the magnetic abrasive grains is spherical, the average particle diameter of the magnetic abrasive grains is 2 μm or more from the viewpoint of achieving both the ability to remove the glass as the material to be polished and the smoothness of the surface to be polished. It is preferable that it is 20 micrometers or less. That is, when the shape of the magnetic abrasive grains is spherical, the ability to grind the glass is lower than that of an irregularly shaped magnetic abrasive grain having the same diameter corner, so the average grain size of the magnetic abrasive grains When the diameter is less than 2 μm, the processing time required for polishing becomes too long to be suitable for mass production of the glass substrate G. Moreover, when the shape of the magnetic abrasive grains is spherical and the average particle diameter of the magnetic abrasive grains exceeds 20 μm, it becomes difficult to improve the smoothness of the end face of the glass substrate G to be polished.

  The magnetic abrasive grains preferably have a maximum magnetic flux density of 1.0 T or more and a maximum permeability of 3.0 H / m or more. Further, when the concentration of the magnetic abrasive grains in the magnetic fluid 3 is less than 85%, the maximum magnetic flux density is 1.3 T or more or 1.6 T or more, and the maximum magnetic permeability is 3.3 H / m or more. Is more preferable. When the concentration of the magnetic abrasive grains in the magnetic fluid 3 is less than 85%, the higher the maximum magnetic flux density and the maximum magnetic permeability, the greater the binding force of the magnetic field on the magnetic abrasive grains. This is because the removal capability, that is, the polishing capability is improved.

Hereinafter, the manufacturing method of the glass of this embodiment using the above-mentioned grinding wheel 12b is demonstrated. FIG. 3 is a process diagram for explaining the process of the glass substrate manufacturing method of the present embodiment.
The glass substrate manufacturing method includes a melting step (ST1), a clarification step (ST2), a homogenization step (ST3), a supply step (ST4), a molding step (ST5), and a slow cooling step (ST6). The cutting process (ST7), the grinding process (ST8), the polishing process (ST9), and the cleaning process (ST10) are mainly included. In addition, a plurality of glass substrates that have an inspection process, a packing process, and the like and are stacked in the packing process are transported to a supplier.

  FIG. 4 is a view schematically showing an apparatus for performing the melting step (ST1) to the cutting step (ST7). As shown in FIG. 4, the apparatus mainly includes a melting apparatus 200, a molding apparatus 300, and a cutting apparatus 400. The dissolution apparatus 200 mainly has a dissolution tank 201, a clarification tank 202, a stirring tank 203, a first pipe 204, and a second pipe 205.

In the melting step (ST1), the glass raw material supplied into the melting tank 201 is heated and melted with a flame generated from a burner (not shown), thereby producing a molten glass MG. Thereafter, the molten glass MG is energized and heated using an electrode (not shown).
The clarification step (ST2) is performed in the clarification tank 202. When the molten glass MG in the clarification tank 202 is heated, bubbles such as O ₂ contained in the molten glass MG grow by absorbing oxygen generated by the reductive reaction of the clarifier and float on the liquid surface. And released. Or gas components, such as oxygen in a bubble, are absorbed in molten glass for the oxidation reaction of a clarifying agent, and a bubble disappears.
In the homogenizing step (ST3), the molten glass MG in the stirring vessel 203 supplied through the first pipe 204 is stirred using a stirrer, so that the glass components are homogenized.
In the supplying step (ST4), the molten glass MG is supplied to the molding apparatus 300 through the second pipe 205.

In the molding apparatus 300, a molding process (ST5) and a slow cooling process (ST6) are performed.
In the forming step (ST5), the molten glass MG is formed into a sheet glass, and a flow of the sheet glass is created. In this embodiment, an overflow downdraw method is used. In the slow cooling step (ST6), the sheet-like glass that is formed and flowed is cooled to have a desired thickness, so that internal distortion does not occur and the thermal shrinkage rate does not increase.
In the cutting step (ST7), the cutting device 400 cuts the sheet-like glass supplied from the forming device 300 into a predetermined length, thereby obtaining a glass substrate. The cut glass substrate is further cut into a predetermined size to produce a glass substrate of a target size.

  When cutting the glass substrate G, a scribe line is formed on the glass substrate G, and tensile stress is concentrated on the scribe line to cleave the glass substrate G. The scribe line is generally formed by a method of mechanically forming using a diamond cutter or a method of causing an initial crack to proceed by heating and rapid cooling using a laser. When the scribe line is formed mechanically, fine cracks inevitably exist around the scribe line. When a scribe line is formed using a laser, a very sharp edge is formed at the corner between the end surface and the front and back surfaces of the divided glass substrate G. Therefore, the glass substrate G cut in the cutting step (ST7) removes cracks and sharp edges generated around the scribe line, and improves the breaking strength at the end face, so that the grinding step (ST8) and the polishing step (ST9). ) Is carried to the end face processing line.

  FIG. 5 is a diagram showing a flow of end face processing of the glass substrate of the present embodiment. The glass substrate end face processing line 10 is provided with a first chamfering machine 12, a second chamfering machine 14, and a reversing machine 18. The 1st chamfering machine 12, the reversing machine 18, and the 2nd chamfering machine 14 are arrange | positioned in order from the upstream of a conveyance path | route. FIG. 6 is a perspective view showing the first grinding wheel and the second grinding wheel in the first chamfering machine 12 and the second chamfering machine 14.

In the grinding step (ST8), as shown in FIG. 5, the first chamfering machine 12 was provided on both sides of the conveyance path with respect to the short side end surface of the rectangular glass substrate G while conveying the glass substrate G. Grinding is performed using the diamond wheel 12a for grinding. As shown in FIG. 6, the diamond wheel 12a in the direction of the rotation axis Z, and is configured in the first grinding wheel 12a ₁ and second 2-stage grinding wheel 12a _2.

The first grinding wheel 12a ₁ is a grinding wheel in which diamond abrasive grains are hardened with a metallic binder containing iron. As the binder for the first grinding wheel, a binder having higher hardness and rigidity than the binder for the _second grinding wheel 12a ₂ is used. Here, hardness is Shore hardness, and rigidity is Young's modulus. If the binder of the first grinding wheel 12a ₁ is a metal, other metal binders such as cobalt and bronze may be used. Further, the higher hardness and rigidity than the binder of the second grinding wheel, the binder of the ceramic membrane may be used as the first binding agent of the grinding wheel 12a _1. First grinding wheel 12a ₁ is, for example, may be used diamond abrasive grains of grain size of about ♯400 from ♯300 defined by JIS R6001-1987. In the present embodiment, the first grinding wheel 12a ₁ uses a diamond abrasive grains of grain size of # 400. The abrasive grains are not limited to diamond but may be CBN (borazone).
First granularity of the grinding wheel 12a ₁ may be the second grinding wheel 12a whether or rougher than equal the diamond abrasive particle size _2.

The second grinding wheel 12a ₂ is a grinding wheel in which diamond abrasive grains are hardened with a resin-based binder containing epoxy. The second binding agent of the grinding wheel 12a ₂ is intended hardness and rigidity is lower than the first binding agent of the grinding wheel 12a ₁ is used. The second binding agent of the grinding wheel 12a ₂ is the lower the hardness and synthetic than the first binding agent of the grinding wheel 12a _1, may be used a binder of the ceramic electrolyte. As long as it is resin-based, for example, a polyimide-based material may be used. The abrasive grains are not limited to diamond but may be CBN. In the present embodiment, the second grinding wheel 12a ₂ uses diamond abrasive grains having a grain size of # 400 defined by JIS R6001-1987.
The first abrasive grain size of the grinding wheel 12a ₁ is preferable in that the second and or coarser than equal abrasive grain of the grinding wheel 12a ₂ performs efficiently grinding.

The grinding step (ST8) of the present embodiment includes a first grinding step and a second grinding step. In the first grinding step, in the first chamfering machine 12, the glass substrate G is transported in the transport direction indicated by the arrow in FIG. 5, and the grinding groove W indicated by the dotted line in FIG. 6 of the _first grinding wheel 12a1. Thus, the end surface of the glass substrate G is ground. The first grinding wheel 12a ₁ grinds the end surface of the glass substrate G by a predetermined grinding amount. Thereby, the end surface of the glass substrate G retreats to the center side of the glass substrate from the original end surface, and the cross-sectional shape of the end surface has a curvature corresponding to the cross-sectional shape of the grinding groove W of the _first grinding wheel 12a1. It is ground into a convex shape, an arc shape or an R shape. Here, the grinding amount is the distance from the original end face before grinding to the apex of the convex end face after grinding which has been ground and retreated. That is, the amount of the end surface of the glass substrate G ground in the direction of the main surface of the glass substrate G. Grinding amount of the first glass substrate G by the grinding wheels 12a ₁ is, for example, in the range from 40μm to 60 [mu] m. It is preferable that the conveyance speed of the glass substrate G in a 1st grinding process is 10 m / min or more from a viewpoint of ensuring productivity. In this embodiment, the conveyance speed of the glass substrate G is 10 m / min.

  In the first grinding step, the glass substrate is such that the maximum height Rmax defined by JIS B 0601-1982 of the end surface of the glass substrate G is at least 10 μm and 18 μm, more preferably 13 μm and 14 μm. The end face of G is ground. Moreover, the arithmetic average roughness Ra prescribed | regulated by JISB0601-1994 of the end surface of the glass substrate G will be about 0.5 micrometer, for example.

Thereafter, as shown in FIG. 6, the diamond wheel 12 a moves in the direction of the rotation axis Z so that the grinding groove W of the second grinding wheel 12 a ₂ corresponds to the position of the end face of the glass substrate G. In the second grinding step, the glass substrate G is transported in the direction opposite to the arrow in FIG. 5, and the end surface is ground by the grinding groove W of the _second grinding wheel 12a ₂ during the transport. Thereby, the cross-sectional shape of the end surface of the glass substrate G is ground into a convex shape, a circular arc shape, or an R shape with a curvature corresponding to the cross-sectional shape of the grinding groove W of the _second grinding wheel 12a2.

The amount of grinding of the glass substrate G by the second grinding wheel 12a ₂ is in the range from 10 μm to 30 μm, for example. The conveyance speed of the glass substrate G in the second grinding step is preferably 10 m / min or more, and more preferably 15 m / min or more from the viewpoint of ensuring productivity. In this embodiment, the conveyance speed of the glass substrate G is 15 m / min. It is preferable that the conveyance speed of the glass substrate G in a 2nd grinding process is larger than the conveyance speed of the glass substrate G in a 1st grinding process.

  In the second grinding step, the end surface of the glass substrate G is set so that the maximum height Rmax defined by JIS B 0601-1982 of the end surface of the glass substrate G is at least 4 μm and 8 μm or less, more preferably about 6 μm. Grind. Further, the arithmetic average roughness Ra of the end face of the glass substrate G is, for example, about 0.1 μm to 0.2 μm.

  In addition, about the rotation direction of the grinding wheel 12a, the movement direction of the outer peripheral surface of the grinding wheel 12a in the point which contacts the glass substrate G may be set so that it may become the same as the conveyance direction of the glass substrate G, and vice versa. May be set in the direction. In the present embodiment, the movement direction of the outer peripheral surface of the grinding wheel 12a at the point of contact with the glass substrate G in the first grinding step is opposite to the conveying direction of the glass substrate G, and the glass in the second grinding step. The grinding wheel 12a is rotated in one direction so as to be in the same direction as the transport direction of the substrate G.

  In the grinding step (ST8), the cross-sectional shape of the end surface of the glass substrate G is ground into a convex shape with a curvature, an arc shape, or an R shape as described above, and the arithmetic average roughness Ra of the end surface of the glass substrate G is as described above. Is ground to be, for example, about 0.1 μm to 0.2 μm. However, a layer containing micro cracks called micro cracks or hair cracks is formed on the end surface of the glass substrate G ground by the grinding wheel 12a which is a diamond wheel. This layer is called a work-affected layer or a fragile fracture layer, and exists in a thickness of about 1 μm to 3 μm, for example. The presence of such a layer reduces the breaking strength at the end face of the glass substrate G. In order to remove such a layer and improve the breaking strength at the end face of the glass substrate G, a polishing step (ST9) is performed.

  In the polishing step (ST9), the work-affected layer or the brittle fracture layer on the end surface of the glass substrate G is removed, and the polishing wheel 12b is set so that the arithmetic average roughness Ra of the end surface of the glass substrate G is less than 0.01 μm, for example. Thus, the end surface of the glass substrate G is polished. As shown in FIG. 5, the glass substrate G that has finished the grinding of the end surface by the grinding wheel 12a is transported to a position where the polishing by the polishing wheel 12b is performed. Thereafter, as shown in FIG. 2, the polishing wheel 12 b is rotated about the rotating shaft 1. The end of the glass substrate G bites into the magnetic fluid 3, and the polishing wheel 12b rotates while the end surface of the glass substrate G is in contact with the magnetic fluid 3, so that the end surfaces of the magnetic fluid 3 and the glass substrate G are Move relatively. As a result, the end surface of the glass substrate G is polished by the magnetic abrasive grains in the magnetic fluid 3 constrained by the magnetic field formed by the magnetic field forming unit 2.

  In the present embodiment, the end surface is ground and polished without moving the diamond wheel 12a and the polishing wheel 12b in the conveyance direction of the glass substrate G. However, while the glass substrate G is stationary or the glass substrate G is conveyed, The end face of the glass substrate G may be ground and polished by moving the diamond wheel 12a and / or the polishing wheel 12b.

After the polishing, as shown in FIG. 5, the reversing machine 18 rotates the direction of the glass substrate G by 90 degrees and conveys the glass plate G to the second chamfering machine 14 along the conveyance path. The second chamfering machine 14 includes a diamond wheel 14 a similar to the diamond wheel 12 a of the first chamfering machine 12. As shown in FIG. 6, the diamond wheel 14 a is similar to the first grinding wheel 12 a ₁ and the second grinding wheel 12 a _{2 of} the first chamfering machine 12, and the first grinding wheel 14 a ₁ and the second grinding wheel 14 a _2. And.

In the second chamfering machine 14, the rectangular glass substrate G to the end face of the long side, the first grinding wheel 14a ₁ of the diamond wheel 14a provided on both sides of the conveyance path similar to the first chamfering machine 12 A first grinding step is performed. Then, the end face of the long sides of the rectangular glass substrate G, a second grinding step similar to the first chamfering machine 12 is performed by the second grinding wheel 14a _2.

  Thereafter, in the polishing step, polishing of the end face of the glass substrate G that has been ground using the polishing wheels 14b provided on both sides of the transport path is performed. The grinding wheel 14 b is configured in the same manner as the grinding wheel 12 b of the first chamfering machine 12. Thereafter, the glass substrate G is transferred to the cleaning step (ST10).

The cleaning step (ST10) includes an end surface cleaning step for removing the magnetic abrasive grains attached to the end surface of the glass substrate G in the polishing step (ST9). Specifically, the end surface of the glass substrate G is cleaned by acid cleaning. Further, the end surface of the glass substrate G may be cleaned by alkali cleaning. After the end surface cleaning step, the front and back surfaces and the end surface of the glass substrate G are cleaned with a normal cleaning liquid.
Thereafter, the glass substrate is inspected for abnormal defects such as bubbles and striae in the inspection process, and the glass substrate that has passed the inspection is packed in the packing process and shipped as a product.

  As described above, in this embodiment, the magnetic abrasive grains and water are mixed so that the concentration of the magnetic abrasive grains in the magnetic fluid 3 is 70 wt% or more. Therefore, compared with the case where the density | concentration of a magnetic body abrasive grain is less than 70 wt%, the grinding | polishing capability which removes the work-affected layer or the weak fracture layer of the end surface of the glass substrate G improves, and time required for grinding | polishing processing is shortened. Can do. Furthermore, the end surface of the glass substrate G can be polished smoothly, and the surface roughness of the end surface of the glass substrate G can be, for example, less than 0.01 μm in terms of arithmetic average roughness Ra.

Further, when the concentration of the magnetic abrasive grains in the magnetic fluid 3 is 85 wt% or more, the glass substrate is further improved while improving the polishing ability to remove the work-affected layer or the brittle fracture layer on the end face of the glass substrate G. The surface roughness of the end face of G can be smoothly polished so that, for example, the arithmetic average roughness Ra is less than 0.01 μm.
By smoothly polishing the end surface of the glass substrate G in this way, dust generation over time from the end surface of the glass substrate G is suppressed, and the amount of particles adhering to the front and back surfaces of the glass substrate G compared to the conventional case. Can be significantly reduced. Therefore, even when a Cu alloy wiring such as a Cu-Mn alloy that is relatively easy to peel off is formed on the surface of the glass substrate G for the purpose of reducing the resistance of the wiring such as a TFT, the peeling of the wiring is effectively performed. And the yield of the flat panel display can be improved.

  In the present embodiment, the magnetic abrasive grains in the magnetic fluid 3 have a maximum magnetic flux density of 1.0 T or more and a maximum permeability of 3.0 H / m or more. Thereby, the binding force by the magnetic field formed by the magnetic field forming unit 2 sufficiently acts on the magnetic abrasive grains, and the magnetic abrasive grains and the glass substrate when the magnetic abrasive grains polish the end surface of the glass substrate G. The contact force with G can be sufficiently increased. Thereby, the grinding | polishing capability of the glass substrate G by the magnetic fluid 3 improves, and the time which grinding | polishing processing requires can be shortened.

When the magnetic abrasive grains are irregularly shaped particles having corners, the ability of the magnetic fluid 3 to polish the glass substrate G is improved as compared with the case where the magnetic abrasive grains are spherical particles. In this case, the magnetic abrasive grains can improve the smoothness of the end face of the glass substrate G while ensuring the polishing ability of the glass substrate G by setting the average particle diameter to 2 μm or more and 15 μm or less. .
When the magnetic abrasive grains are spherical particles having no corners, damage to the glass substrate G can be suppressed as compared to the irregularly shaped particles having the corners. In this case, the magnetic abrasive grains can improve the smoothness of the end surface of the glass substrate G while ensuring the polishing ability of the glass substrate G by setting the average particle diameter to 6 μm or more and 20 μm or less. .

Further, in the present embodiment, after the polishing process (ST9) of the glass substrate G, an end face cleaning process for removing the composition of the magnetic fluid 3 such as magnetic abrasive grains adhering to the end face is provided. Therefore, the composition of the magnetic fluid 3 such as magnetic abrasive grains is not brought into the subsequent process.
Further, the end surface of the glass substrate G is polished smoothly by the polishing step (ST9), and the work-affected layer or the brittle fracture layer is removed. Therefore, even if acid cleaning or alkali cleaning is performed on the end face of the glass substrate G, micro cracks such as microcracks and hair cracks do not exist on the end face, and cracks do not grow. Therefore, even if acid cleaning or alkali cleaning is performed, the breaking strength at the end face of the glass substrate G does not decrease. Further, it is possible to effectively remove magnetic abrasive grains made of iron oxide or ferrite particles adhering to the end face of the glass substrate G by acid cleaning or alkali cleaning.

As mentioned above, although the embodiment of the manufacturing method of the magnetic fluid and the glass substrate of the present embodiment has been described in detail, the present invention is not limited to the above-described embodiment, and various improvements and modifications can be made without departing from the gist of the present invention. You may make changes.
For example, the apparatus using the magnetic fluid for polishing a glass substrate of the present invention is not limited to the apparatus described in the above embodiment. For example, the magnetic fluid of this embodiment can be used in the apparatus disclosed in Japanese Patent No. 4412783. In this case, after forming a groove on the peripheral surface, polishing may be performed along the end surface of the glass substrate. Moreover, the magnetic fluid of this embodiment can be used for the apparatus disclosed in International Publication No. 2012/0667587.

Examples of the present invention will be described in detail below.
First, it is a ferrite-based magnetic body, the shape of the particles is an indefinite shape having corners, the average particle diameter is 2 μm or more and 6 μm or less, the maximum magnetic flux density is 1.3 T, and the maximum permeability is 3 A magnetic abrasive grain of 0.0 H / m was prepared. Next, the magnetic fluid was produced by mixing the prepared magnetic abrasive grains and water. At this time, the magnetic abrasive grains and water are mixed so that the concentration of the magnetic abrasive grains in the magnetic fluid is 40% to 95%, so that Comparative Examples 1 to 3 and Example 1 shown in Table 1 are mixed. To 5 magnetic fluids were obtained. The magnetic fluids of Comparative Examples 1 to 3 were almost liquid, but the magnetic fluids of Examples 1 to 5 were pasty.

In the comparative examples and examples described above, the concentration of the magnetic fluid was controlled using wt% in consideration of ease of management and mass production applicability, but the concentration of the magnetic fluid was controlled by vol. % Can also be used. The conversion between wt% and vol% can be calculated based on the bulk specific gravity of the magnetic abrasive grains and the density of water 1 g / cm ³ . For example, the concentration of 80 wt% of the magnetic abrasive grains in the magnetic fluid of Example 2 can be converted to 71 vol% to 72 vol%. In the above comparative examples and examples, in consideration of evaporation of water from the magnetic fluid during polishing, the evaporated water is replenished to the magnetic fluid.

  Next, the magnetic fluids of Comparative Examples 1 to 3 and Examples 1 to 4 are used as the magnetic fluid 3 of the polishing wheel 12b described in FIGS. 1 and 2 of the above-described embodiment, and the end face of the glass substrate is polished. Processing was performed. The glass substrate to be polished is one that has been subjected to the cutting step (ST7) and the grinding step (ST8) described in the above embodiment, and the entire length of one side of the glass substrate is not polished, and about 1/3 is polished. did. The polishing was carried out while carrying the glass substrate in the carrying direction and then carrying out the glass substrate in the opposite direction to the carrying direction, so that the polishing was performed once or twice with respect to 1/3 of the end surface of the glass substrate. . The diameter of the polishing wheel 12b was φ30 mm, the rotation speed was 2000 rpm, and the relative movement speed between the glass substrate and the polishing wheel 12b was 10 mm / min. Thereafter, the magnetic abrasive grains adhering to the end face of the glass substrate are removed by washing with water, and then the polished area and the unpolished area of the end face of the glass substrate are compared to determine the polishing amount, that is, the glass removal amount. Was measured. Further, the surface roughness was measured in the polished region of the end face of the glass substrate.

  The measurement of arithmetic average roughness Ra which is the removal amount of glass and surface roughness is using the surfcom A1400 by Tokyo Seimitsu Co., Ltd., and the vertex A of the end surface of the glass substrate G shown in FIG. Was performed at points B and C in the vicinity of. The measurement of the glass removal amount was performed with the measurement mode being the cross-section measurement mode, the measurement speed being 0.6 mm / s, the inclination correction being the first half correction, and the measurement distance being 20 mm. Further, the surface roughness was measured by measuring the roughness in the measurement mode, measuring the measurement speed by 0.3 mm / s, and measuring the method by JIS 1994. The arithmetic average roughness Ra is measured with a cutoff of 0.08 and a measurement length of 0.4 mm when Ra <0.02, and a cutoff of 0.25 when 0.02 <Ra <0.2. The measurement length was 1.25 mm, and when 0.1 <Ra <2, the cut-off was 0.8 and the measurement length was 4 mm. The obtained results are shown in Table 2.

As shown in Table 2, regarding the glass removal amount by polishing, when the glass was removed to such an extent that the work-affected layer or the brittle fracture layer could be removed, the glass removal amount was “achieved” and the work-affected layer or When the glass could not be removed to such an extent that the brittle fracture layer could be removed, the glass removal amount was deemed “insufficient”. Here, the thickness of the work-affected layer or the brittle fracture layer was 2 μm.
As a result, in the polishing using the magnetic fluid of Comparative Examples 1 to 3, the glass removal amount was insufficient, whereas in the polishing using the magnetic fluid of Examples 1 to 5, the glass was removed. The amount could be achieved.

  Moreover, as shown in Table 2, regarding the end face state of the polished glass substrate, the case where the arithmetic average roughness Ra at points A, B, and C shown in FIG. 7 is less than 0.05 μm is “good”. It was. In addition, the case where the arithmetic average roughness Ra of both the points A and B was 0.05 μm or more and less than 0.1 μm was defined as “slightly good”. A case where the arithmetic average roughness Ra of at least one of the points A and B is 0.1 μm or more is defined as “bad”.

  As a result, in the polishing using the magnetic fluids of Comparative Examples 1 to 3, the end face state of the polished substrate was poor. Further, in the polishing using the magnetic fluids of Examples 1, 2, and 5, the end face state of the polished substrate was slightly good. Further, in the polishing using the magnetic fluid of Example 3 and Example 4, the end face state of the polished substrate was good. In addition, the arithmetic average roughness Ra of the end face of the glass substrate was smaller in the polishing with the magnetic fluid in Example 4 than in the polishing with the magnetic fluid in Example 3. In the polishing with the magnetic fluid of Example 4, the arithmetic average roughness Ra of the end surface of the glass substrate was less than 0.01 μm. From the above, it was found that the concentration of the magnetic abrasive grains in the magnetic fluid is preferably 85 wt% or more and less than 95 wt%.

  In the polishing using the magnetic fluid of Example 5, burns occurred on part of the end surface of the polished glass substrate. Discoloration of the end face of the glass substrate could not be improved by controlling the concentration of the magnetic abrasive grains of the magnetic fluid in Example 5, but could be suppressed by shortening the processing time. That is, in the polishing using the magnetic fluid of Example 5, by controlling the distance and time that the magnetic fluid contacts the end face of the glass substrate, the temperature rise of the descending magnetic fluid is suppressed, Occurrence could be suppressed.

  Next, there are six types of magnetic abrasives that are ferrite-based magnetic bodies, have a maximum magnetic flux density of 1.3 T, a maximum magnetic permeability of 3.0 H / m, and have different particle shapes and average particle diameters. Prepared grains. Magnetic abrasive grains having a spherical shape and an indefinite shape having corners, each having an average particle size of less than 2 μm, an average particle size of 6 μm or more and 15 μm or less, and An average particle size of greater than 15 μm and 20 μm or less was prepared. Next, by mixing the prepared magnetic abrasive grains and water so that the concentration of the magnetic abrasive grains in each magnetic fluid is 85%, the magnetic flows of Comparative Examples 4 and 5 shown in Table 3 are used. And magnetic fluids of Examples 6 to 9 were obtained.

  Next, similarly to the polishing using the magnetic fluids of Examples 1 to 5, the magnetic fluids of Comparative Examples 4 and 5 and the magnetic fluids of Examples 6 to 9 were polished as described in the above embodiment. Using the magnetic fluid 3 of the wheel 12b, the end surface of the glass substrate was polished. Thereafter, similarly to the glass substrate polished with the magnetic fluid of Examples 1 to 5, the magnetic fluid of Comparative Examples 4 and 5, and the glass removal amount of the glass substrate polished with the magnetic fluid of Examples 6 to 9, The end face state was measured. Table 4 shows the obtained results.

  As shown in Table 4, with respect to the glass removal amount and end face state of the glass substrates polished using the magnetic fluids of Comparative Examples 4 and 5 and the magnetic fluids of Examples 6 to 9, the magnetic properties of Examples 1 to 5 were used. Evaluation was performed in the same manner as the glass substrate polished with the fluid. In the polishing using the magnetic fluid of Comparative Example 4, the glass removal amount was insufficient and the end face state was also poor. On the other hand, in the polishing using the magnetic fluid of Example 6, the glass removal amount could be achieved and the end face condition was also good. This is because the irregularly shaped magnetic abrasive grains having the corners used in the magnetic fluid of Example 6 have a higher polishing ability than the spherical magnetic abrasive grains used in the magnetic fluid of Comparative Example 4. It is high.

  As shown in Table 4, in the polishing using the magnetic fluids of Examples 7 and 8, the target glass removal amount was achieved and the end face state was also good. From this, it was found that even when spherical magnetic abrasive grains are used for the magnetic fluid, the necessary polishing ability can be obtained by setting the average particle diameter to 2 μm or more.

  Further, in the polishing using the magnetic fluid of Example 9, the target glass removal amount was achieved, and the end face state was also good. On the other hand, in the polishing using the magnetic fluid of Comparative Example 5, although the target glass removal amount was achieved, Ra increased from that before polishing and the end face state became poor. From this, it was found that when the particle shape of the magnetic abrasive grains is an indefinite shape having corners, the average particle diameter of the magnetic abrasive grains is preferably 15 μm or less.

In addition, magnetic abrasive grains having a spherical particle shape and an average particle diameter of 25 μm or more and 30 μm or less were prepared, and a magnetic fluid was prepared and the glass substrate was polished in the same manner as in Example 9. The condition became bad. This is presumably because the particle diameter of the magnetic abrasive grains becomes too large, causing unevenness in the contact of the magnetic abrasive grains with the end face of the glass substrate, resulting in a reduction in polishing ability. From this, it was found that when the shape of the magnetic abrasive grains is spherical, if the average particle diameter is 20 μm or less, the achievement of the glass removal amount and a good end face state can both be achieved.
For the magnetic fluids of Comparative Examples 4 and 5 and Examples 6 to 9, the glass substrate was similarly polished by changing the concentration of the magnetic abrasive grains between 70% and 95%. Similar results were obtained with polishing using the magnetic fluids of Examples 4 and 5 and Examples 6-9.

  Next, under the same conditions as in Examples 1 to 4, except that the maximum magnetic flux density of the magnetic abrasive grains is 1.6 T and the maximum permeability is 3.3 H / m, the magnetic properties of Examples 10 to 13 are respectively set. A fluid was made. Table 5 shows the conditions of the magnetic fluids of Examples 10 to 13 produced. Furthermore, the end surfaces of the glass substrates were polished using the magnetic fluids of Examples 10 to 13 in the same manner as the polishing with the magnetic fluids of Examples 1 to 4. Furthermore, the glass removal amount at the end face of the glass substrate polished with each magnetic fluid of Examples 10 to 13 was measured and compared with Examples 1 to 4, respectively. Table 6 shows the result of comparison.

  As shown in Table 6, by increasing the maximum magnetic flux density and the maximum magnetic permeability of the magnetic abrasive grains, in the polishing with the magnetic fluid of Example 10 and Example 11, the polishing of Example 1 and Example 2 was performed. The amount of glass removal increased compared to polishing with a magnetic fluid. On the other hand, in the polishing with the magnetic fluid of Example 12 and Example 13, the glass removal amount did not increase even when the maximum magnetic flux density and the maximum magnetic permeability of the magnetic abrasive grains were increased.

That is, it was found that when the concentration of the magnetic abrasive grains in the magnetic fluid is less than 85%, the polishing ability is improved by increasing the maximum magnetic flux density and the maximum magnetic permeability of the magnetic abrasive grains. This is considered to be due to the apparent viscosity being increased by restraining the magnetic abrasive grains in the magnetic fluid by the magnetic field, and polishing the glass substrate in this state.
The viscosity of the magnetic fluids of Example 2 and Example 11 before the magnetic abrasive grains were restricted by the magnetic field was about 15 Pa · s to 20 Pa · s. However, the magnetic abrasive grains of the magnetic fluid of Example 11 have better magnetization characteristics than the magnetic abrasive grains of the magnetic fluid of Example 2. Therefore, when the magnetic abrasive grains in the magnetic fluid pair were constrained by the magnetic field, the apparent viscosity of the magnetic fluid of Example 11 was higher than the apparent viscosity of the magnetic fluid of Example 2. Similarly, in the magnetic fluids of Example 1 and Example 10, the apparent viscosity of the magnetic fluid of Example 10 was higher than the apparent viscosity of the magnetic fluid of Example 1.
Thus, it is considered that the apparent viscosity of the magnetic fluid increases, so that the contact force of the magnetic abrasive grains to the end surface of the glass substrate increases and the polishing ability is improved.

On the other hand, when the concentration of the magnetic abrasive grains in the magnetic fluid was 85% or more, no improvement in polishing ability was observed even when the maximum magnetic flux density and the maximum magnetic permeability of the magnetic abrasive grains were increased. This is presumably because the concentration of the magnetic abrasive grains in the magnetic fluid is relatively high and the viscosity of the magnetic fluid before being restrained by the magnetic field is relatively high. In other words, when the concentration of the magnetic abrasive grains in the magnetic fluid is 85% or more, the magnetic fluid is restrained by the magnetic field even if the magnetization characteristics of the magnetic abrasive grains are relatively low. This is probably because an apparent viscosity sufficient for polishing is obtained. That is, when the concentration of the magnetic abrasive grains in the magnetic fluid is 85% or more, it is possible to polish the end face of the glass substrate while reducing the influence of the magnetization characteristics.
When the magnetic properties of the magnetic abrasive grains are low, it is necessary to manage the concentration of the magnetic abrasive grains in the magnetic fluid relatively accurately. However, when the magnetic properties of the magnetic abrasive grains are high, there is an advantage that the concentration of the magnetic abrasive grains in the magnetic fluid can be managed relatively slowly.

Next, magnetic abrasive grains similar to those in Examples 1 to 5 are prepared, and the magnetic abrasive grains and water are added so that the concentration of the magnetic abrasive grains in the magnetic fluid is 87% or more and 89% or less. By mixing, the magnetic fluid of Example 14 shown in Table 7 was obtained.

  Next, the obtained magnetic fluid of Example 14 was used as the magnetic fluid 3 of the polishing wheel 12b described with reference to FIGS. 1 and 2 of the above-described embodiment, and the end surface of the glass substrate was polished. The glass substrate to be polished was a glass substrate that had undergone the grinding step (ST8) of the above-described embodiment, and the arithmetic average surface roughness Ra of the end face was 0.17 μm. Polishing was performed under three different conditions. In the first condition, 1/3 of the end face of the glass substrate was polished only once while the glass substrate was conveyed at a speed of 5 mm / min. The second condition is that the glass substrate is polished while being transported at a speed of 10 mm / min in the transport direction, and then polished while transporting the glass substrate at the same speed in the direction opposite to the transport direction. 1/3 was polished once or twice. The third condition is that the glass substrate is polished while being transported at a speed of 20 mm / min in the transport direction, and then polished while being transported at the same speed in the direction opposite to the transport direction. Polishing was performed two reciprocations, that is, four times with respect to 1/3. The diameter of the grinding wheel 12b was 30 mm, and the rotation speed was 2000 rpm. Thereafter, in the same manner as in Examples 1 to 5, the magnetic abrasive grains adhering to the end face of the glass substrate were removed by washing with water, and then the surface roughness was measured in the polished region of the end face of the glass substrate. The arithmetic average roughness Ra at points A, B, and C of the glass substrate shown in FIG. 7 is less than 0.01 μm in all of the first condition to the third condition, and more specifically 0. The range was from 006 μm to 0.008 μm. Further, when a plurality of glass substrates were polished under similar conditions, the arithmetic average roughness Ra at points A, B, and C of the glass substrate shown in FIG. It was less than 0.01 μm.

G Glass substrate 3 Magnetic fluid

Claims (7)

A magnetic fluid that contains magnetic abrasive grains and that is held by a magnetic field to polish the end face of a glass substrate,
The concentration of the magnetic abrasive grains in the magnetic fluid is 70 wt% or more,
Magnetic fluid for polishing glass substrates. The concentration of the magnetic abrasive grains is 85 wt% or more.
The magnetic fluid for glass substrate polishing according to claim 1. The magnetic abrasive grains have a maximum magnetic flux density of 1.0 T or more and a maximum permeability of 3.0 H / m or more.
The magnetic fluid for glass substrate polishing according to claim 1 or 2. The magnetic abrasive grains are irregularly shaped particles having corners,
The magnetic fluid for glass substrate polishing according to any one of claims 1 to 3. The magnetic abrasive grains have an average particle diameter of 15 μm or less.
The magnetic fluid for glass substrate polishing according to claim 4. The magnetic abrasive grains are spherical particles having no corners,
The magnetic fluid for glass substrate polishing according to any one of claims 1 to 3. The magnetic fluid for polishing a glass substrate according to claim 6, wherein the magnetic abrasive grains have an average particle diameter of 2 μm or more and 20 μm or less.

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