JP2010094805A - Polishing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polishing method wherein a polished workpiece can be kept flat and the flatness of the polished workpiece can be maintained during polishing. <P>SOLUTION: When a polished workpiece is polished, a back pad 1 is sticked on the undersurface of a surface pressure plate 71 using a double-faced tape. A template 76 has an opening part exposing a skin layer of the back pad 1 to which the polished workpiece 78 is stuck and inserted, and the polished workpiece 78 is abutted to a buildup area of the approximately center of the skin layer by soaking the skin layer with a moderate amount of water. After that the polished workpiece 78 is forcibly pressed approximately-uniformly toward the surface pressure plate 71 and held by the back pad 1. The pressure surface plate 71 applies pressure downward to the polished workpiece 78 and polishes the undersurface of the polished workpiece 78 with a polishing cloth 75 by rotating a rotating surface plate 72. Air caught between the skin layer and the polished workpiece 78 is taken into foam through multiple pores, thereby the polished workpiece 78 is maintained approximately flat by back pad 1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polishing method, and in particular, has a skin layer disposed on one surface side, and a foam layer disposed on the inner side of the skin layer and continuously foamed, and the other surface side is a first fixed surface. The present invention relates to a polishing method for polishing an object to be polished using a soft plastic sheet for holding the object to be polished on a first surface plate by contacting the object to be polished on one surface.

  Conventionally, optical materials such as lenses, plane-parallel plates and reflecting mirrors, hard disk substrates, silicon wafers, glass substrates for liquid crystal displays and the like (objects to be polished) require high-precision flatness. Polishing processing using is performed. Usually, in the polishing process, a double-side polishing machine that simultaneously polishes both surfaces of an object to be polished or a single-side polishing machine that polishes one surface at a time. In the double-side polishing machine, the polishing process is performed while supplying the polishing liquid containing the abrasive particles and the like by bringing both surfaces of the object to be polished into contact with the polishing cloth adhered to the upper and lower surface plates having a flat surface. On the other hand, in a single-side polishing machine, one surface of the object to be polished is held on a pressure surface plate with a flat surface, and the other surface (processed surface) of the object to be polished is attached to a polishing cloth adhered to a rotating surface plate with a flat surface. The polishing process is carried out while supplying the polishing liquid with the contact.

  In polishing using a single-side polishing machine, a holding pad such as a soft cloth is usually interposed between the object to be polished and the pressure platen in order to hold the object to be pressed on the pressure platen. Since the pad retainability of the object to be polished is insufficient, the object to be polished moves during the polishing process, and the flatness of the processed surface is impaired. In order to prevent movement of the object to be polished, polishing is performed by inserting the object to be polished into a mold (template) or the like. In this case, the object to be polished is removed from the mold after the polishing process, but the object to be polished, particularly a glass substrate for a liquid crystal display, is increased in size, for example, a plate thickness of 1 mm, an outer dimension of 1.5 × 1. Since a large glass substrate of 8 m is polished, a large holding pad that can hold an object to be polished without using a mold is required.

  Generally, a soft plastic sheet having a skin layer and a foamed layer in which foaming is continuously formed is used for the holding pad. This soft plastic sheet is obtained by applying a resin solution in which a soft plastic is dissolved in a water-miscible organic solvent to a sheet-like film formation substrate and then coagulating and regenerating the resin in an aqueous coagulation liquid (wet film formation method) Manufactured by. With the solidification regeneration, a dense skin layer is formed on the surface of the soft plastic sheet, and a foam layer is formed inside the skin layer. Since the surface of the dense skin layer is excellent in flatness and contact with the object to be polished, the object to be polished can be held. Usually, in order to hold an object to be polished on a pressure platen, the object to be polished is brought into contact with a skin layer of a soft plastic sheet in which the opposite surface side of the skin layer is fixed to the pressure platen through a small amount of water. . Thus, the object to be polished is held on the pressure platen using the surface tension of water.

  However, when holding the object to be polished, air may be caught between the surface of the skin layer and the object to be polished. Since the skin layer surface is dense, and the water intervening between the skin layer surface and the object to be polished is obstructed from moving to the soft plastic sheet side, the air is between the skin layer surface and the object to be polished. Store. If polishing is performed while air is stored, the pressure applied to the object to be polished increases in the air storage part, so that the processing surface of the part is greatly polished (the air storage part is transferred to the object to be polished) and flat. It will damage the sex. In order to reduce the biting of air between the skin layer surface and the object to be polished, a technique for laminating an adhesive resin layer on the surface of a soft plastic sheet and forming irregularities on the surface of the adhesive resin layer is disclosed ( For example, see Patent Document 1).

JP 2002-355755 A

  However, in the technique of Patent Document 1, although air entrained between the soft plastic sheet and the object to be polished can be dispersed using the unevenness formed on the surface of the adhesive resin layer, the amount of air entrainment When becomes larger, it becomes difficult to remove air from between the soft plastic sheet and the object to be polished. For this reason, since the processing surface side of the object to be polished becomes convex due to the amount of air stored between the soft plastic sheet and the object to be polished, the portion of the object to be polished corresponding to the convex part during polishing is excessive. There is a risk of being flattened due to polishing. In particular, since the amount of air biting tends to be large in the above-described large object to be polished, air is stored and the object to be polished is not held flat on the surface plate. It becomes difficult to ensure.

  In view of the above-described problem, an object of the present invention is to provide a polishing method that can hold the object to be polished flat and ensure the flatness of the object to be polished held during the polishing process.

  In order to solve the above problems, the present invention includes a skin layer disposed on one side and a foam layer disposed on the inner side of the skin layer and continuously formed with foam, and the other side is first. A polishing process for polishing the object to be polished using a soft plastic sheet that is fixed to the surface plate and abuts the object to be polished on one side and holds the object to be polished on the first surface plate. In the method, a pore that allows air entrained between the object to be polished is formed on the surface of the skin layer by a pore forming agent added to the soft plastic solution for producing the soft plastic sheet. A mounting step of mounting the soft plastic sheet having the pores formed in the foam layer in communication with the foam on the first surface plate on the foam layer side, and a soft plastic sheet mounted in the mounting step. Above A holding step for bringing one surface side of the object to be polished into contact with the kin layer side through water and pressing the object to be pressed against the first surface plate side; and the object to be polished held in the holding step A polishing step of polishing the other surface side of the object while applying pressure with a polishing pad mounted on a second surface plate disposed opposite to the first surface plate.

  In the present invention, a hole that allows air entrained between the object to be polished is formed on the surface of the skin layer of the soft plastic sheet by the pore forming agent added to the soft plastic solution for producing the soft plastic sheet. The porous layer communicates with the foam formed continuously in the foam layer, so that the skin layer and the surface to be polished are brought into contact with the skin layer side through water in the holding step. Even if air is caught between the objects to be polished, the object to be polished is substantially flat on the skin layer because the air is accommodated in the foam through the pores by pressing the object to be polished to the first surface plate side. Is held on the first surface plate, the flatness of the object to be polished can be ensured by polishing while applying pressure in the polishing step.

  In this case, in the holding step, it is preferable to press the object to be polished so that the air bitten between the skin layer and the object to be polished is accommodated in the foam formed in the foam layer. In the mounting step, the foamed layer side of the soft plastic sheet can be adhered to the first surface plate via the double-sided adhesive tape. The foamed layer side of such a soft plastic sheet may be buffed so that the thickness of the soft plastic sheet is substantially uniform. Moreover, it is preferable that the pore-forming agent is soluble in a soft plastic solution and hardly soluble or insoluble in water. In such a polishing method, a glass substrate for a liquid crystal display can be used as an object to be polished.

  According to the present invention, the surface of the skin layer of the soft plastic sheet is formed by the pore forming agent added to the soft plastic solution for producing the soft plastic sheet, which allows the air entrained between the object to be polished. When the one surface side of the object to be polished is brought into contact with the skin layer side through the water in the holding step, the skin is communicated with the foam formed continuously in the foam layer. Even if air is caught between the layer and the object to be polished, the object to be polished becomes a skin layer because air is accommodated in the foam through the pores by pressing the object to be polished to the first surface plate side. Since it is held substantially flat and held on the first surface plate, it is possible to obtain the effect that the flatness of the object to be polished can be ensured by polishing while applying pressure in the polishing step.

It is sectional drawing which shows the back pad of embodiment to which this invention is applied. It is process drawing which shows the manufacturing process of a back pad. It is a front view which shows schematic structure of the film-forming apparatus used for manufacture of the polyurethane sheet of a back pad. It is sectional drawing which shows the change of the polyurethane sheet in a back surface buffing process, (A) is a polyurethane sheet solidified and regenerated on the film-forming substrate, (B) is a polyurethane sheet when pressed against a pressure roller, (C) is The polyurethane sheets after the buffing are respectively shown. It is sectional drawing which shows the part holding the to-be-polished object of the single-side polish machine which fixed the back pad. It is explanatory drawing which shows typically the positional relationship of a back pad and a to-be-polished object when evaluating air storage between a back pad and to-be-polished object, (A) is a top view, (B) is sectional drawing. It is the electron micrograph of the back pad surface, (A) is the back pad surface of Example 1 which added 0.2 part of cellulose derivatives, (B) is the back of Example 2 which added 2.0 parts of cellulose derivatives. Pad surface (C) shows the back pad surface of Comparative Example 1 to which no cellulose derivative was added. It is explanatory drawing which shows typically the mode of the air storage when a glass plate is put on a back pad and a load is applied with a weight, (A) is a state in the back pad using the polyurethane sheet which added the cellulose derivative, ( B) shows a state of the back pad using a polyurethane sheet to which no cellulose derivative is added.

  Hereinafter, an embodiment in which the present invention is applied to polishing of an object to be polished held on a surface plate with a back pad will be described with reference to the drawings.

(Back pad)
As shown in FIG. 1, the back pad 1 includes a polyurethane sheet 4 as a soft plastic sheet formed of a polyurethane resin. The polyurethane sheet 4 has a skin layer 4a in which dense micropores (not shown) are formed on the holding surface P side in contact with the object to be polished, and on the side (inside) opposite to the holding surface P of the skin layer 4a. Has a nap layer 4b (foamed layer). In the nap layer 4b, the foam 3 having a substantially triangular cross section rounded along the thickness direction of the polyurethane sheet 4 is continuously formed. The space volume of the foam 3 is larger than the micropore (not shown) formed in the skin layer 4a, and the size on the holding surface P side is smaller than the opposite surface side of the holding surface P. The foam 3 communicates in a three-dimensional mesh shape with a communication hole (not shown) smaller than the average diameter of the space volume of the foam 3. The polyurethane sheet 4 is buffed on the opposite side of the holding surface P so that the thickness of the polyurethane sheet 4 (length in the vertical direction in FIG. 1) is substantially uniform (details will be described later). For this reason, a part of foam 3 is opened on the surface on the opposite surface side.

  On the holding surface P of the polyurethane sheet 4 (surface of the skin layer 4a), a porous 2 communicating with the foam 3 formed on the nap layer 4b is formed. The pore diameter of the pore 2 is larger than the micropore formed in the skin layer 4 a and smaller than the foam 3. The pore diameter of the communication hole that communicates the pore 2 and the foam 3 is formed larger than the pore diameter of the skin layer 4a. The pores 2 are formed by a pore forming agent added to the polyurethane resin solution when the polyurethane sheet 4 described later is formed. The hole diameter on the surface of the porous skin layer 4a is set to 0.05 mm or less.

  Further, the back pad 1 has a support layer 6 that supports the polyurethane sheet 4 on the opposite surface side (buffed surface side) of the holding surface P. For the support layer 6, at least one selected from a flexible film such as a polyethylene terephthalate (hereinafter abbreviated as PET) film, a nonwoven fabric, or a woven fabric is used. On the lower surface side of the support layer 6, a double-sided tape 7 (double-sided pressure-sensitive adhesive tape) having a release paper 8 on the other surface side (lowermost surface side) for fixing the back pad 1 to the polishing machine is bonded.

(Manufacture of back pads)
The back pad 1 is manufactured through each process shown in FIG. First, in the preparation step, polyurethane resin, N, N-dimethylformamide (hereinafter abbreviated as DMF), a water-miscible organic solvent capable of dissolving polyurethane resin, an additive and a pore-forming agent are mixed to form polyurethane resin. Dissolve. For the polyurethane resin, a polyester resin, a polyether resin, a polycarbonate resin or the like having a 100% modulus of 20 MPa or less is selected and used, for example, dissolved in DMF so that the polyurethane resin becomes 30%. As the additive, a pigment such as carbon black, a hydrophilic activator that promotes foaming, and a hydrophobic activator that stabilizes the coagulation regeneration of the polyurethane resin are used to control the size and amount (number) of foam 3. be able to.

  As the pore-forming agent, a predetermined amount of a cellulose derivative that is soluble in DMF for dissolving polyurethane resin and hardly soluble or insoluble in water is added. As the cellulose derivative, at least one selected from ester derivatives, ether derivatives, ether ester derivatives, and aromatic-containing derivatives can be used. Examples of ester derivatives include cellulose acetate, cellulose propionate, cellulose butyrate, cellulose valerate, and cellulose acetate butyrate. Examples of ether derivatives include ethyl cellulose and hydroxypropyl cellulose. Examples of ether ester derivatives include acetylethyl cellulose and acetoxypropyl cellulose. The addition amount of the cellulose derivative is set so that the pore diameter of the porous 2 on the surface of the skin layer 4a is 0.05 mm or less. The obtained solution is filtered to remove aggregates and the like, and then defoamed under vacuum to obtain a polyurethane resin solution.

  In the coating process, coagulation regeneration process, and washing / drying process, the polyurethane resin solution obtained in the preparation process is continuously applied to the film-forming substrate and immersed in an aqueous coagulation liquid to coagulate and regenerate the polyurethane resin, followed by washing. After drying, the polyurethane sheet 4 is obtained. The coating process, the coagulation regeneration process, and the cleaning / drying process are continuously executed by the film forming apparatus shown in FIG.

  As shown in FIG. 3, the film forming apparatus 60 is filled with a pretreatment liquid 15 such as water or a DMF aqueous solution (mixed liquid of DMF and water) that pretreats a nonwoven fabric or a woven cloth of a film forming substrate. Pretreatment tank 10, coagulation tank 20 filled with coagulation liquid 25 mainly composed of water which is a poor solvent for polyurethane resin for coagulating and regenerating polyurethane resin, water for washing polyurethane resin after coagulation and regeneration A cleaning tank 30 filled with a cleaning liquid 35 such as the above and a cylinder dryer 50 for drying the polyurethane resin are continuously provided.

  On the upstream side of the pretreatment tank 10, a substrate supply roller 41 that supplies a film forming substrate 43 is disposed. The pretreatment tank 10 has a pair of guide rollers 13 at the lower part inside the substantially central part in the same longitudinal direction as the transport direction of the film forming substrate 43. Above the pretreatment tank 10, guide rollers 11 and 12 are disposed on the substrate supply roller 41 side, and an excessive pretreatment liquid contained in the pretreated film forming substrate 43 is disposed on the coagulation tank 20 side. A mangle roller 18 for removing 15 is disposed. On the downstream side of the mangle roller 18, a knife coater 46 for applying the polyurethane resin solution 45 to the film forming substrate 43 substantially uniformly is disposed. A guide roller 21 is disposed on the downstream side of the knife coater 46 and above the coagulation tank 20.

  In the coagulation tank 20, a guide roller 23 is disposed at the inner lower part on the cleaning tank 30 side. A mangle roller 28 is disposed on the washing tank 30 side above the coagulation tank 20 for dehydrating the polyurethane resin after coagulation regeneration. A guide roller 31 is disposed on the downstream side of the mangle roller 28 and above the cleaning tank 30. In the cleaning tank 30, four guide rollers 33 at the upper part and five guide rollers 33 at the lower part are arranged alternately in the vertical direction in the same longitudinal direction as the transport direction of the film forming substrate 43. A mangle roller 38 for dehydrating the washed polyurethane resin is disposed on the cylinder dryer 50 side above the cleaning tank 30. In the cylinder dryer 50, four cylinders having heat sources inside are arranged in four stages. On the downstream side of the cylinder dryer 50, a take-up roller 42 that winds up the dried polyurethane resin (together with the film forming substrate 43) is disposed. The mangle rollers 18, 28, 38, the cylinder dryer 50 and the take-up roller 42 are connected to a rotation drive motor (not shown), and the film formation substrate 43 is made to be a substrate supply roller by these rotation drive forces. It is conveyed from 41 to the winding roller 42.

  When a non-woven fabric or a woven fabric is used as the film forming substrate 43, the film forming substrate 43 is pulled out from the substrate supply roller 41 and continuously introduced into the pretreatment liquid 15 through the guide rollers 11 and 12. . When the polyurethane resin solution 45 is applied by passing the film-forming substrate 43 between the pair of guide rollers 13 in the pretreatment liquid 15 and performing the pretreatment (sealing), the film-forming substrate 43 is brought into the film forming substrate 43. Of the polyurethane resin solution 45 is suppressed. After the film forming substrate 43 is pulled up from the pretreatment liquid 15, it is pressurized by the mangle roller 18 and the excess pretreatment liquid 15 is squeezed out. The pre-processed film-forming substrate 43 is conveyed in the direction of the coagulation tank 20. In the case where a flexible film made of PET or the like is used as the film forming substrate 43, pretreatment is not necessary, so that the film is directly fed from the guide roller 12 to the mangle roller 18 or in the pretreatment tank 10. The pretreatment liquid 15 may not be added. Hereinafter, in this example, the film forming substrate 43 is described as a PET film.

  As shown in FIG. 2, in the application process, the polyurethane resin solution 45 prepared in the preparation process is applied almost uniformly to the film forming substrate 43 by the knife coater 46 at room temperature. At this time, the application thickness (application amount) of the polyurethane resin solution 45 is adjusted by adjusting the gap (clearance) between the knife coater 46 and the upper surface of the film forming substrate 43.

  In the coagulation regeneration process, the film forming substrate 43 coated with the polyurethane resin solution 45 by the knife coater 46 is introduced into the coagulation liquid 25 from the guide roller 21 toward the guide roller 23. In the coagulating liquid 25, first, substitution of DMF of the polyurethane resin solution 45 and the coagulating liquid 25 proceeds on the surface of the applied polyurethane resin solution 45 to form dense micropores. The micropores are formed to a thickness of about several μm and constitute the skin layer 4a. Thereafter, the polyurethane resin is coagulated and regenerated on one surface of the film forming substrate 43 by the progress of substitution of the DMF in the polyurethane resin solution 45 and the coagulating liquid 25 between the skin layer 4 a and the film forming substrate 43. Along with the replacement of the coagulating liquid 25 by the removal of DMF, the foam 3 and the communication holes that connect the foam 3 in a three-dimensional mesh shape are formed inside the skin layer 4a to constitute the nap layer 4b. Further, at the time of solvent removal, the pore 2 is formed by the cellulose derivative added to the polyurethane resin solution 45, and a communication hole that connects the pore 2 and the foam 3 is formed. Foam 3 does not allow water to permeate the film-forming substrate 43 of the PET film, so that solvent removal occurs on the surface side (skin layer 4a side) of the polyurethane resin solution 45, and the film-forming substrate 43 side is formed larger than the surface side. Is done.

  Here, the formation of the porous 2 will be described. In the polyurethane resin solution 45, since the cellulose derivative and the polyurethane resin are poorly compatible, it is considered that the two phases are separated. In addition, when the polyurethane resin is coagulated and regenerated, the coagulation characteristics of the cellulose derivative and the polyurethane resin in the coagulation liquid 25 are different, so that there is a difference in shrinkage, and the compatibility between the cellulose derivative and the polyurethane resin is poor. Since the interfacial bonding force is reduced and a desorption phenomenon occurs, it is considered that the porous 2 is formed. For this reason, the pore 2 is larger than the micropore of the skin layer 4a and smaller than the foam 3 of the nap layer 4b, and the pore diameter of the communication hole connecting the pore 2 and the foam 3 is larger than the pore diameter of the micropore.

  The solidification regeneration of the polyurethane resin is completed while the film-forming substrate 43 coated with the polyurethane resin solution 45 enters the coagulating liquid 25 and reaches the guide roller 23. The coagulated and regenerated polyurethane resin is pulled up from the coagulating liquid 25, and after the excess coagulating liquid 25 is squeezed out by the mangle roller 28, the polyurethane resin is conveyed to the cleaning tank 30 via the guide roller 31 and introduced into the cleaning liquid 35.

  In the cleaning / drying step, the polyurethane resin introduced into the cleaning liquid 35 is passed through the guide roller 33 alternately up and down to clean the polyurethane resin. After the cleaning, the polyurethane resin is pulled up from the cleaning liquid 35 and the excess cleaning liquid 35 is squeezed out by the mangle roller 38. Thereafter, the polyurethane resin is dried by passing along the circumferential surface of the cylinder alternately between the four cylinders of the cylinder dryer 50 (in the direction of the arrow in FIG. 3). The dried polyurethane resin (polyurethane sheet 4) is taken up by the take-up roller 42 together with the film forming substrate 43.

  In the back surface buffing process, buffing is performed on the side opposite to the holding surface P of the polyurethane sheet 4 after drying. As shown in FIG. 4A, the polyurethane sheet 4 taken up by the take-up roller 42 is formed on a PET film of the film forming substrate 43. Since the thickness of the polyurethane sheet 4 varies during film formation, the holding surface P is uneven. After the film-forming substrate 43 is peeled off, as shown in FIG. 4B, the holding surface P becomes flat by holding the surface of the pressing roller 65 with the flat surface against the holding surface P, thereby holding the holding surface P flat. Unevenness appears on the surface Q side opposite to the surface P. Unevenness appearing on the opposite surface Q side is removed by buffing. In this example, since the continuously manufactured polyurethane sheet 4 is in a band shape, the opposite surface Q side is continuously buffed while the pressing roller 65 is pressed against the holding surface P. As a result, as shown in FIG. 4C, the thickness variation of the polyurethane sheet 4 on which the opposite surface Q side is buffed to form the substantially flat opposite surface Q 'is eliminated. In FIG. 4 (C), the holding surface P and the opposite surface Q ′ are shown flat for easy understanding. However, when the polyurethane sheet 4 is a single body, the thickness of the polyurethane sheet 4 is uniform on both surfaces. The holding surface P becomes substantially flat when the support layer 6 is bonded or attached to a polishing machine.

  As shown in FIG. 2, in the laminating process, a PET film support layer 6 is bonded to the opposite surface Q ′ side of the buffed polyurethane sheet 4. On the back side of the support layer 6, a double-sided tape 7 having a release paper 8 attached to the other side is bonded. After cutting into a desired shape such as a circle in the cutting step, the back pad 1 is completed by performing an inspection such as confirming that there is no adhesion of dirt or foreign matter.

  When polishing an object to be polished, the back pad 1 is fixed to a pressure surface plate of a single-side polishing machine, and the object to be polished is brought into contact with and held on the back pad 1. As shown in FIG. 5, the single-side polishing machine 70 has a pressurizing surface plate 71 that presses an object to be polished during polishing, and a rotatable surface plate 72 on the lower side. Both the lower surface of the pressure surface plate 71 and the upper surface of the rotating surface plate 72 are formed flat. A polishing cloth 75 for polishing an object to be polished is attached to the upper surface of the rotating surface plate 72. When the workpiece 78 is attached to the pressure platen 71, first, the back pad 1 is attached to the lower surface of the pressure platen 71 via the double-sided tape 7. In order to prevent displacement of the object to be polished 78, a template 76 in which the surface of the back pad 1 (holding surface P) is made of glass epoxy, made of bakelite or the like and has an opening into which the object to be polished 78 can be inserted is formed at a substantially central portion. Adhere. An appropriate amount of water is contained in the skin layer 4a of the back pad 1 exposed at the opening of the template 76, and the object to be polished 78 is brought into contact therewith. Thereafter, the workpiece 78 is pressed substantially uniformly in the direction of the pressure platen 71. As a result, the air bitten between the skin layer 4a and the workpiece 78 is accommodated in the foam 3 through the perforations 2 communicating with the foam 3 of the nap layer 4b. The object to be polished 78 is held substantially flat on the back pad 1 by the surface tension of water and the adhesiveness of the polyurethane resin of the polyurethane sheet 4 without air being stored between the skin layer 4a and the object to be polished 78. The lower surface (processed surface) of the workpiece 78 is polished with the polishing cloth 75 by rotating the rotating platen 72 while pressing the workpiece 78 downward with the pressurizing platen 71.

(Function)
Next, the effect | action etc. of the grinding process using the back pad 1 of this embodiment are demonstrated.

  In the back pad 1 of the present embodiment, the perforation 2 communicating with the foam 3 of the nap layer 4 b is formed on the holding surface P of the polyurethane sheet 4. For this reason, when water is contained in the skin layer 4a of the back pad 1 fixed to the single-side polishing machine 70 and the object to be polished 78 is pressed, the elastic polyurethane sheet 4 is deformed and the foam 3 of the nap layer 4b is deformed. To do. Thus, even if air is caught between the skin layer 4a and the workpiece 78, air is accommodated in the foam 3 through the porous 2 communicating with the foam 3, so that the skin layer 4a and the workpiece 78 are sandwiched. It is possible to prevent the air from being stored. At this time, since water intervenes between the skin layer 4a and the object to be polished 78, air cannot enter the fine pores of the skin layer 4a. Can get in. Accordingly, since the object 78 can be held substantially flat on the pressure platen 71 without air being stored between the skin layer 4a and the object 78, the object 78 is substantially evenly distributed during polishing. Since the processed surface of the workpiece 78 is polished almost uniformly by the polishing cloth 75, the flatness of the processed surface can be improved.

  Moreover, in the back pad 1 of this embodiment, since the space volume of the foam 3 formed in the nap layer 4b is larger than the porosity 2, the air bitten between the skin layer 4a and the workpiece 78 is reliably accommodated. be able to. Moreover, since the hole diameter of the communication hole which connects the porous 2 and the foam 3 is larger than the microporous hole diameter of the skin layer 4a, air can be accommodated smoothly. Further, since the foam 3 is communicated in a three-dimensional mesh shape through the communication holes, the entire foam 3 formed in the nap layer 4b can be accommodated even if the air biting amount is large.

  Further, if the pore diameter of the pore 2 exceeds 0.05 mm, the contact area between the surface of the skin layer 4a (the holding surface P) and the workpiece 78 is reduced, and the holding property of the polishing object is lowered. In the back pad 1 of the present embodiment, the pore diameter of the porous 2 is set to 0.05 mm or less. For this reason, the contact area (contact property) of the to-be-polished object 78 surface and the skin layer 4a surface is securable. Therefore, the workpiece 78 can be reliably held.

  Furthermore, in the present embodiment, when the polyurethane sheet 4 is manufactured, a cellulose derivative that is DMF soluble and hardly soluble or insoluble in water is added to the polyurethane resin solution 45. For this reason, when the polyurethane resin is coagulated and regenerated, the porous 2 is formed with the cellulose derivative as the DMF is removed. Thereby, the porous 2 can be easily formed in the back pad 1 without complicating the manufacturing process.

  Furthermore, in the back pad 1 of the present embodiment, the polyurethane sheet 4 is buffed on the opposite surface Q side of the holding surface P. For this reason, the thickness accuracy of the polyurethane sheet 4 can be improved (thickness variation generated during film formation can be reduced) without reducing the skin layer 4a having a flat surface. By sticking the back pad 1 to the flat pressure platen 71 of the single-side polishing machine 70, the holding surface P, that is, the entire surface of the skin layer 4a becomes substantially flat. Therefore, since the object to be polished 78 is held substantially flat on the back pad 1, the flatness of the object to be polished 78 can be improved during the polishing process.

  In the back pad 1 of the present embodiment, a PET film support layer 6 is bonded to the buffed opposite surface Q ′ side. For this reason, since the flexible polyurethane sheet 4 is supported by the support layer 6, it is possible to easily handle the back pad 1 when it is transported or attached to the single-side polishing machine 70.

  In the conventional back pad, the object to be polished is held in contact with the skin layer on the surface formed at the initial stage of the solidification regeneration of the polyurethane resin, but when the skin layer is in contact with the object to be polished, air is bitten. Since this air is stored between the skin layer and the object to be polished, the object to be polished cannot be held flat, and the processed surface of the object to be polished has a convex shape in the portion where the air is stored. The portion of the object to be polished corresponding to the convex portion is excessively polished and the flatness is impaired. Air can be dispersed by laminating adhesive resin on the surface of the back pad and forming irregularities on the adhesive resin surface, but the manufacturing process becomes complicated, and when the amount of air bite increases, air becomes skinned. Store between the layer and the work piece. In addition, the skin layer has a dense micropore, and the skin layer and the nap layer are connected, but water is used to hold the object to be polished. As a result, air remains stored. The present embodiment is a back pad that can solve these problems.

  In addition, in the back pad 1 of this embodiment, although the cellulose derivative was illustrated as a pore formation agent which forms the porosity 2, this invention is not limited to this, It is soluble in the organic solvent used for melt | dissolution of a polyurethane resin It is sufficient if it is hardly soluble or insoluble in water used for the coagulation liquid. In addition to cellulose derivatives, such pore formers include, for example, polyacrylonitrile (PAN), polyvinyl chloride, polyvinyl acetate, vinylidene chloride / vinyl chloride copolymer, polycaprolactone (PCL), polystyrene (PS), poly A polymer compound such as methyl methacrylate (PMMA) can be used. Moreover, you may use it, mixing 2 or more types of these high molecular compounds and the cellulose derivative mentioned above.

  In the present embodiment, the example in which the template 76 is used when the workpiece 78 is mounted on the single-side polishing machine 70 is shown, but the present invention is not limited to this. By adjusting the pore diameter of the porous 2 so as to be suitable for the size of the object to be polished 78, even a large object to be polished can be held without using the template 76. The pore diameter of the porous 2 can be adjusted by changing the amount of cellulose derivative added to the polyurethane resin solution 45.

  Furthermore, in the present embodiment, the back pad 1 is attached to the pressure surface plate 71 on the upper side of the single-side polishing machine 70, and the skin layer 4a is in contact with the upper surface of the workpiece 78. However, the back pad 1 may be attached to the lower surface plate and abutted against the lower surface of the workpiece 78. In this way, the object to be polished 78 is sucked by the surface tension of the water contained in the skin layer 4a of the back pad 1, and therefore the weight of the object to be polished (normally without pressing the object 78 with external force) The workpiece 78 can be held on the surface plate by the pressure.

  Furthermore, in the back pad 1 of this embodiment, although the PET film was illustrated for the support layer 6, this invention is not limited to this, For example, you may use a nonwoven fabric, a woven fabric, etc. Alternatively, the polyurethane sheet 4 may be attached to the pressure platen 71 alone without attaching the support layer 6 such as a PET film. Furthermore, in the back pad 1, although the example which has the double-sided tape 7 on the opposite surface side of the holding surface P was shown, you may bond together when sticking the back pad 1 on a surface plate. Further, in the back pad 1 of the present embodiment, the example in which the foam 3 is opened on the buffed surface (opposite surface Q ′) side of the polyurethane sheet 4 is shown, but the thickness variation at the time of film formation is small. If so, the thickness removed by the buffing process can be reduced, so the foam 3 does not necessarily open.

  Furthermore, in the back pad 1 of the present embodiment, an example has been shown in which the opposite surface Q side is continuously buffed while the pressure roller 65 is pressed against the holding surface P in the back surface buffing process. It is not limited. For example, after the polyurethane sheet 4 is cut to a desired size, a flat plate having a flat surface may be pressed against the holding surface P and the opposite surface Q side may be buffed.

  Moreover, in this embodiment, although the polyurethane resin whose 100% modulus is 20 Mpa or less was illustrated as a material of the polyurethane sheet 4, this invention is not limited to this. For example, a polyester resin or the like may be used. If the 100% modulus of the resin is 20 MPa or less, the wet-formed resin sheet closely adheres to the shape of the object to be polished. Can be achieved. In the present embodiment, an example in which the polyurethane resin is dissolved in DMF so as to be 30% is shown, but the present invention is not limited to this, and the viscosity of the polyurethane resin solution 45 and the thickness of the polyurethane sheet 4 are not limited thereto. It may be appropriately changed depending on the situation.

  Hereinafter, examples of the back pad 1 manufactured according to the present embodiment will be described. In addition, it describes together about the back pad of the comparative example manufactured for the comparison.

Example 1
In Example 1, a polyester MDI (diphenylmethane diisocyanate) polyurethane resin having a 100% modulus of 10 MPa was used as the polyurethane resin. 0.2 parts of cellulose acetate butyrate as a cellulose derivative was added to 100 parts of a DMF solution containing 30% polyurethane resin. Further, 50 parts of DMF for viscosity adjustment and 20 parts of a DMF dispersion containing 30% of pigment carbon black were mixed to prepare a polyurethane resin solution 45. At this time, since cellulose acetate butyrate is a solid (solid), it was dissolved in a small amount of DMF for viscosity adjustment and added in advance in order to mix uniformly. When applying the polyurethane resin solution 45, the clearance of the coating device was set to 1 mm. In order to enhance the washing effect in the washing step, washing after coagulation regeneration was performed with warm water. The back pad 1 of Example 1 was manufactured by buffing the polyurethane sheet 4 using a sandpaper of buff count # 180 with a buff treatment amount of 0.25 mm.

(Example 2)
Example 2 was the same as Example 1 except that the amount of cellulose acetate butyrate added was 2.0 parts with respect to 100 parts of the DMF solution of polyurethane resin.

(Comparative Example 1)
In Comparative Example 1, the back pad of Comparative Example 1 was produced in the same manner as in Example 1 except that the cellulose derivative was not added.

(Evaluation)
Next, for the back pads of Examples and Comparative Examples, the pore diameter of the porous 2 was measured by observation with an electron microscope on the surface of the skin layer 4a, and the average pore diameter was calculated. The presence or absence of air storage was measured by the following method. As shown in FIGS. 6A and 6B, the back pad 1 cut to a diameter of 660 mm is attached to a surface plate 81 having a substantially flat surface, and water is sprayed on the surface (holding surface P) of the back pad 1. After spraying with, lightly remove the surface water with a wiper. Next, a glass plate 82 having a length of 370 mm, a width of 470 mm, and a thickness of 0.7 mm is placed on the back pad 1, and a weight 83 is placed on the glass plate 82 so that a load of 80 g / cm ² is applied. The weight 83 was removed 1 minute and 5 minutes after the weight 83 was placed, and the presence or absence of air retention was visually determined. The measurement results of the average pore diameter and the presence or absence of air storage are shown in Table 1 below.

  As shown in Table 1, in the back pad of Comparative Example 1 to which cellulose acetate butyrate was not added, no porosity was observed on the skin layer surface, and air was retained between the skin layer and the glass plate 82. For this reason, if the glass plate 82 held on the back pad of Comparative Example 1 is polished, the polishing process proceeds excessively in the air storage portion, and therefore high flatness after the polishing process cannot be expected. On the other hand, in the back pads 1 of Example 1 and Example 2 to which cellulose acetate butyrate was added, pores 2 having pore diameters of 0.5 to 2 μm and 1 to 10 μm were formed on the surface of the skin layer 4a, respectively. The average pore diameter of the porous 2 was 0.9 μm in Example 1 and 4.2 μm in Example 2. In addition, no air retention was observed between the skin layer 4a and the glass plate 82 either after 1 minute or after 5 minutes. Furthermore, it was confirmed that the air accommodated in the foam 3 of the nap layer 4b did not return between the skin layer 4a and the glass plate 82 over time. In addition, it was confirmed that the polished article retention of the back pad 1 of Example 1 and Example 2 was equivalent to the back pad of Comparative Example 1.

  As shown in FIGS. 7A and 7B, it can be seen from the electron micrographs of the surfaces of the back pads 1 of Example 1 and Example 2 that the pores 2 are formed. In addition, it can be seen that the back pad 1 of Example 2 in which the amount of cellulose acetate butyrate added is larger than that of the back pad 1 of Example 1, and the number of the pores 2 is larger. On the other hand, as shown in FIG. 7C, in the back pad of Comparative Example 1, the porous 2 was not recognized and a substantially uniform skin layer surface was observed.

  When the state of air storage after 5 minutes when the glass plate 82 was placed on the back pad of Example 1 and Comparative Example 1 and a load was applied with the weight 83, as shown in FIG. In the back pad 1, no air retention was observed. On the other hand, as shown in FIG. 8 (B), in the back pad of Comparative Example 1, air storage 85 was observed.

  Therefore, in the back pad 1 in which the pores 2 are formed on the surface of the skin layer 4a of the polyurethane sheet 4 by adding a cellulose derivative to the polyurethane resin solution 45, the skin layer 4a and the glass plate 82 are secured while securing the glass plate 82. It has been found that air accumulation can be prevented. For this reason, since the glass plate 82 can be held substantially flat, it can be expected that the processed surface of the workpiece 78 is flattened with high accuracy during the polishing process.

  The present invention provides a polishing method capable of holding the object to be polished flat and ensuring the flatness of the object to be polished held during the polishing process. Since it contributes to the manufacture and sale of pads, it has industrial applicability.

P Holding surface 1 Back pad 2 Porous 3 Foamed 4 Polyurethane sheet (soft plastic sheet)
4a Skin layer 4b Nap layer (foamed layer)
71 Pressurized surface plate (first surface plate)
72 Rotating surface plate (second surface plate)
78 Workpiece

Claims (6)

It has a skin layer disposed on one surface side and a foam layer that is disposed on the inner side of the skin layer and in which foaming is continuously formed. The other surface side is fixed to the first surface plate and is polished on the one surface side. A polishing method for polishing the object to be polished using a soft plastic sheet for contacting the object and holding the object to be polished on the first surface plate,
A porosity allowing air entrained between the object to be polished is formed on the surface of the skin layer by a pore forming agent added to the soft plastic solution for producing the soft plastic sheet, and the porosity is A mounting step of mounting a soft plastic sheet in communication with foam formed in the foam layer on the first surface plate on the foam layer side;
Holding the soft plastic sheet mounted in the mounting step with one side of the object to be polished being brought into contact with the skin layer side through water and pressing and holding the object to be polished on the first surface plate side Steps,
A polishing process step of polishing the other surface side of the object held in the holding step while applying pressure by a polishing pad mounted on a second surface plate disposed opposite to the first surface plate; ,
A polishing method comprising the steps of:   The said holding | maintenance step presses the said to-be-polished object so that the air bitten between the said skin layer and the to-be-polished object is accommodated in the foam formed in the said foaming layer. 2. The polishing method according to 1.   2. The polishing method according to claim 1, wherein, in the mounting step, the foamed layer side of the soft plastic sheet is adhered to the first surface plate via a double-sided adhesive tape.   The polishing method according to claim 3, wherein the soft plastic sheet is buffed on the foam layer side so that the thickness of the soft plastic sheet is substantially uniform.   The polishing method according to claim 1, wherein the hole forming agent is soluble in the soft plastic solution and hardly soluble or insoluble in water.   The polishing method according to claim 1, wherein the object to be polished is a glass substrate for a liquid crystal display.

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