JP5091417B2 - Polishing cloth - Google Patents

Description

  The present invention relates to an abrasive cloth, and more particularly to an abrasive cloth having a polishing surface for polishing an object to be polished.

  Conventionally, optical materials such as lenses, parallel flat plates, reflecting mirrors, silicon wafers (bare silicon), materials such as glass substrates for liquid crystal displays, and hard disk substrates (objects to be polished) require high-precision flatness. Therefore, polishing using a polishing cloth is performed. Normally, during polishing, a polishing liquid (slurry) containing abrasive particles and the like is supplied between the object to be polished and the polishing cloth with the polishing cloth facing both surfaces or one side of the object to be polished.

  In general, a resin-impregnated nonwoven fabric, a hard plastic sheet, a soft plastic sheet, or the like is used as a polishing cloth used for polishing according to the polishing characteristics of an object to be polished. This soft plastic sheet is obtained by applying a resin solution obtained by dissolving a soft plastic in a water-miscible organic solvent to a sheet-like substrate and then coagulating and regenerating the resin in an aqueous coagulation liquid (wet film-forming method) Manufactured and used in many ways. Along with the coagulation regeneration, the micro-pores constituting the surface layer (skin layer) are densely formed on the surface of the soft plastic sheet with a thickness of about several μm, and many foams constituting the foam layer are formed inside the surface layer. It is formed continuously. Usually, foaming of the foamed layer is formed in a conical shape (substantially triangular shape in cross section) that has an average pore size larger than the fine pores of the skin layer and decreases as it approaches the skin layer.

  Since the surface of the skin layer of such a soft plastic sheet has smoothness as well as flatness, depending on the type of polishing liquid supplied at the time of polishing, the abrasive particles in the polishing liquid are held between the object to be polished and the polishing cloth. Difficult to do. In order to avoid this, by removing the skin layer by buffing or the like, foaming of the foamed layer is opened on the surface of the soft plastic sheet. Since the polishing liquid enters the foam through the opening, the polishing liquid can be supplied between the polishing cloth and the object to be polished while being stored in the foam.

  However, when the soft plastic sheet is worn as the polishing process proceeds, the foaming is conical, and the opening diameter on the surface becomes large, and the flatness of the surface of the soft plastic sheet is impaired. As a result, the object to be polished is not evenly polished and it is difficult to achieve highly accurate flatness. In addition, in the production of soft plastic sheets by wet film formation, the thickness of the resin solution is likely to vary when applied to the substrate due to the viscosity of the resin solution. Foam formation during solidification regeneration (replacement of organic solvent and aqueous coagulant) However, thickness variations tend to occur. For this reason, since the soft plastic sheet itself has a greatly wavy surface, it becomes difficult to improve the flatness of the object to be polished during polishing. In order to solve this, a polishing cloth is disclosed in which a high-hardness film or the like is bonded to a soft plastic sheet having a foam structure by a wet film forming method (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 10-249709

  However, in the polishing cloth of Patent Document 1, since the soft plastic sheet is pressed almost uniformly with a high-hardness film, the flatness of the object to be polished can be improved by polishing, but the polishing supplied at the time of polishing is performed. The elasticity of the soft plastic sheet may decrease due to contact with the liquid. When the elasticity is lowered, the soft plastic sheet is hardened and the followability to the object to be polished is lowered, so that the flatness of the object to be polished is lowered. In order to avoid this, it is desirable to replace the soft plastic sheet before it becomes hard, but this will reduce the life of the polishing pad. Further, when the soft plastic sheet becomes hard, scratches or the like are likely to occur on the processed surface of the object to be polished due to polishing debris generated during the polishing process.

  In view of the above-described case, an object of the present invention is to provide a polishing cloth that can ensure followability to an object to be polished and improve flatness.

In order to solve the above-described problems, the present invention provides a first soft plastic sheet having a polishing surface for polishing an object to be polished and having foam formed in a three-dimensional network inside, and pores in the inside. And a second soft plastic sheet formed substantially evenly. The first soft plastic sheet has the second soft plastic sheet bonded to the opposite side of the polishing surface, and the polishing surface The foam is formed in the first flexible plastic sheet while the side is buffed so that the entire thickness of the first and second flexible plastic sheets is uniform and the foam is opened . Has a length in the thickness direction of the first soft plastic sheet and is reduced in diameter on the polishing surface side, and the first soft plastic sheet extends inward from the polishing surface. The average pore diameter by more than at least 15% of the thickness is equal to or is 25μm or less.

In the present invention, the first soft plastic sheet is buffed so that the entire thickness of the first and second soft plastic sheets is uniform on the polishing surface side, and the foam is opened. The second soft plastic joined to the opposite side of the polishing surface of the first soft plastic sheet, while the elasticity gradually decreases and hardens due to the penetration of the polishing liquid into the foam during the polishing process Since the pores formed inside the sheet do not communicate with the foam of the first flexible plastic sheet and the elasticity is maintained, the flattened polished surface is obtained by making the entire thickness uniform. because it is pressed against the workpiece at a substantially uniform pressure by the elasticity of the soft plastic sheet, suppress scratching ensuring traceability for the first flexible plastic sheet workpiece even harder during polishing In addition, the foam formed inside the first soft plastic sheet has a length in the thickness direction of the first soft plastic sheet and is reduced in diameter on the polishing surface side. Since the average pore diameter is 25 μm or less until it exceeds at least 15% of the thickness of the first flexible plastic sheet in the direction, even if the flexible plastic sheet is worn as the polishing process proceeds, the opening diameter on the surface is excessively increased. Therefore, the flatness of the object to be polished can be improved over a long period .

In this case, the second soft plastic sheet may be more elastic than the first soft plastic sheet. At this time, the average pore diameter of the pores formed inside the second soft plastic sheet may be made larger than the foam formed inside the first soft plastic sheet . The second soft plastic sheet may have a surface layer in which micropores having an average pore diameter smaller than that of the foam of the first soft plastic sheet are formed on the opposite surface side joined to the first soft plastic sheet. . Also, both the first and second soft plastic sheets may be made of polyurethane resin. At this time, the first and second soft plastic sheets can be joined with a polyurethane resin. Moreover, the single side | surface of the double-sided tape for mounting | wearing with a surface plate may further be bonded to the other surface side where the 1st soft plastic sheet of the 2nd soft plastic sheet was joined. At this time, at least one kind of substrate selected from a flexible film, a nonwoven fabric, and a woven fabric may be further bonded between the second soft plastic sheet and the double-sided tape.

According to the present invention, the first soft plastic sheet is buffed on the polishing surface side so that the entire thickness of the first and second soft plastic sheets is uniform, and the foam is opened. It is formed inside the second soft plastic sheet joined to the opposite side of the polishing surface of the first soft plastic sheet, whereas the elasticity gradually decreases and hardens due to the penetration of the polishing liquid during processing. Since the pores do not communicate with the foaming of the first soft plastic sheet and the elasticity is maintained, the flattened polishing surface is pressed against the object to be polished with substantially equal pressure by the elasticity of the second soft plastic sheet. is therefore, suppresses the scratching ensuring traceability for the first flexible plastic sheet workpiece even harder during polishing, the first flexible plastic sheet The foam formed in the portion has a length in the thickness direction of the first soft plastic sheet and is reduced in diameter on the polishing surface side, and the thickness of the first soft plastic sheet from the polishing surface toward the inside. Since the average pore diameter is 25 μm or less until it exceeds at least 15% of the thickness, an excessive increase in the opening diameter on the surface is suppressed even if the soft plastic sheet is worn as the polishing process proceeds. The effect that the flatness of the polished product can be improved can be obtained.

  Hereinafter, an embodiment of a polishing cloth according to the present invention will be described with reference to the drawings.

(Polishing pad)
As shown in FIG. 1, a polishing cloth (generally referred to as a polishing pad, hereinafter referred to as a polishing pad) 1 has a polishing surface P that is formed of a polyurethane resin and has a polishing surface P for polishing an object to be polished. A polyurethane sheet 2 as a first soft plastic sheet, and a polyurethane sheet 5 as a second soft plastic sheet bonded to the opposite side of the polishing surface P of the polyurethane sheet 2 and formed with a polyurethane resin.

  In the polyurethane sheet 2, foam 3 having a length in the thickness direction of the polyurethane sheet 2 (longitudinal direction in FIG. 1) is formed substantially uniformly. The foam 3 includes a foam 3a having a length over almost the entire thickness of the polyurethane sheet 2, and a foam 3b formed at a position biased toward the polishing surface P between the foams 3a and having a smaller length than the foam 3a. The length of the polyurethane sheet 2 varies in the thickness direction. The average pore diameter of the foam 3 is formed such that the size on the polishing surface P side is smaller than the opposite surface side of the polishing surface P. That is, the diameter of the foam 3 is reduced on the polishing surface P side. In the polyurethane resin between the foams 3, fine foams having an average pore diameter smaller than that of the foams 3 and not shown are formed. The micro-foaming and foaming 3 not shown are communicated in a three-dimensional mesh shape with communication holes (not shown) having a smaller hole diameter than the micro-foaming not shown. Further, the foams 3 a and 3 b are maintained at an average pore diameter of 25 μm or less until at least 15% of the thickness of the polyurethane sheet 2 extends from the polishing surface P to the inside of the polyurethane sheet 2.

  On the other hand, the polyurethane sheet 5 has a skin layer 5a in which micropores (not shown) having an average pore diameter smaller than that of the foam 3 formed on the polyurethane sheet 2 are densely formed on the opposite side to which the polyurethane sheet 2 is bonded. doing. On the inner side (polyurethane sheet 2 side) of the skin layer 5a of the polyurethane sheet 5, pores 6 having an average pore diameter larger than the foam 3 formed in the polyurethane sheet 2 are formed substantially evenly. The pores 6 are formed in a substantially triangular shape having a rounded length along the thickness direction with a length almost covering the entire thickness of the polyurethane sheet 5. The pores 6 are formed such that the average pore diameter on the polyurethane sheet 2 side is larger than that on the skin layer 5a side. In the polyurethane resin between the pores 6, minute pores (not shown) having an average pore diameter larger than the micropores formed in the skin layer 5 a and smaller than the pores 6 are formed. The fine pores (not shown), the pores 6 and the fine pores (not shown) of the skin layer 5a communicate with each other in a three-dimensional mesh shape through communication holes not shown.

  Since the average pore diameter of the pores 6 formed inside the polyurethane sheet 5 is larger than the average pore diameter of the foam 3 formed inside the polyurethane sheet 2, when the polyurethane sheets 2 and 5 are respectively pressurized, the polyurethane sheet 5 Therefore, the elasticity of the polyurethane sheet 5 is greater than that of the polyurethane sheet 2. The polyurethane sheet 2 and the polyurethane sheet 5 are joined with a polyurethane resin. The opposite surface side of the polyurethane sheet 2 to which the polyurethane sheet 5 is bonded, that is, the polishing surface P side, is buffed so that the entire thickness of the polyurethane sheet 2 and the polyurethane sheet 5 is uniform (details will be described later). . For this reason, the foam 3 of the polyurethane sheet 2 opens at the polishing surface P to form an opening 4.

  The polishing pad 1 has a base material 11 that supports the polyurethane sheets 2 and 5 bonded to the skin layer 5 a side of the polyurethane sheet 5. As the base material 11, at least one kind selected from a flexible film such as a film made of polyethylene terephthalate (hereinafter abbreviated as PET), a nonwoven fabric or a woven fabric is used. In addition to the double-sided tape 12 for mounting the polishing pad 1 on the surface plate of the polishing machine having the release paper 13 on one side (the lowermost side) on the lower surface side (the side opposite to the polyurethane sheet 5) of the substrate 11 The face side is pasted.

(Manufacture of polishing pad)
The polishing pad 1 is manufactured through the steps shown in FIG. 2, and the polyurethane sheets 2 and 5 formed in the preparation step to the cleaning / drying step are joined in the joining step. The production of the polyurethane sheet 2 and the production of the polyurethane sheet 5 will be described in this order.

  In the preparation step, polyurethane resin, N, N-dimethylformamide (hereinafter abbreviated as DMF) which is a water-miscible organic solvent capable of dissolving polyurethane resin, and a hydrophilic additive for forming foam 3 are mixed. To dissolve the polyurethane resin. As the polyurethane resin, a polyester resin, a polyether resin, a polycarbonate resin, or the like is selected and used. For example, the polyurethane resin is dissolved in DMF so as to be 30%. Further, when the polyurethane resin is dissolved, a pigment such as carbon black, a hydrophobic active agent that stabilizes the coagulation regeneration of the polyurethane resin, and the like can be appropriately added as other additives.

  As the hydrophilic additive, for example, an anionic surfactant such as carboxylate, sulfonate, sulfate ester salt, phosphate ester salt or the like is used. The amount of the hydrophilic additive added to the polyurethane resin is set according to the pore diameter and number on the polishing surface P side of the foam 3. The obtained mixed solution is filtered to remove aggregates and the like, and then defoamed under vacuum to obtain a polyurethane resin solution 45.

  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. Thereafter, the polyurethane sheet 2 is obtained by drying. 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 includes a coagulation tank 20 filled with a coagulation liquid 25 for coagulating and regenerating the polyurethane resin, the main component being water which is a poor solvent for the polyurethane resin. A washing tank 30 filled with a washing liquid 35 such as water for washing the polyurethane resin and a cylinder dryer 50 for drying the polyurethane resin are continuously provided.

  On the upstream side of the coagulation tank 20, a substrate supply roller 41 that supplies a film forming substrate 43 is disposed. A guide roller 48 is disposed on the downstream side of the substrate supply roller 41, and a knife coater 46 for applying the polyurethane resin solution 45 to the film forming substrate 43 substantially uniformly is disposed on the downstream side of the guide roller 48. . A guide roller 21 is disposed on the downstream side of the knife coater 46 and above the coagulation tank 20. For the film forming substrate 43, a flexible film made of PET or the like that does not allow the coagulation liquid 25 to permeate is used.

  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 28 and 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 moved from the substrate supply roller 41 by these rotation drive forces. It is conveyed to the winding roller 42.

  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 coagulation liquid 25, first, micropores constituting a skin layer are formed on the surface of the applied polyurethane resin solution 45 over a thickness of several μm. Thereafter, the polyurethane resin coagulates and regenerates on one surface of the film forming substrate 43 as the substitution of the DMF in the polyurethane resin solution 45 and the coagulating liquid 25 proceeds. This coagulation regeneration is completed while the film-forming substrate 43 coated with the polyurethane resin solution 45 enters the coagulation liquid 25 and reaches the guide roller 23. When DMF removes the solvent from the polyurethane resin solution 45, foam 3 is formed in the polyurethane resin. 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.

  Here, the formation of the foam 3 will be described. When the polyurethane resin coagulates and regenerates at the interface of the polyurethane resin solution 45 with the coagulating liquid 25, the solvent is removed by the action of the hydrophilic additive added to the polyurethane resin solution 45. Since the number of occurrences of the penetration of the liquid 25 increases, the number of micropores increases, the water permeability to the resin solution layer is improved, and the substitution rate of DMF is increased. Since subsequent desolvation occurs through the microporosity of the skin layer, the desolvation proceeds rapidly by increasing the number of micropores formed in the skin layer, so that the number of foams 3 increases and the pore size decreases, An elongated foam is formed. For this reason, the average diameter of the foam 3 is 25 μm or less from the skin layer until it exceeds at least 15% of the thickness of the polyurethane sheet 2. Further, since the film formation substrate 43 of the PET film does not permeate water, desolvation occurs only on the skin layer side. Therefore, the foam 3 is formed larger on the film formation substrate 43 side than the skin layer side. The diameter of the communicating hole that communicates is larger than the diameter of the microporous hole.

  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 the four cylinders of the cylinder dryer 50 alternately (in the direction of the arrow in FIG. 3) along the peripheral surface of the cylinder. The dried polyurethane resin (polyurethane sheet 2) is taken up by the take-up roller 42 together with the film-forming substrate 43.

  Next, production of the polyurethane sheet 5 will be described, but the description of the same steps, conditions, and film forming apparatus as those of the polyurethane sheet 2 described above will be omitted, and only different steps will be described.

  In the preparation step, a polyurethane resin, DMF and additives are blended. That is, the hydrophilic additive used in the preparation of the polyurethane sheet 2 is not added. After the polyurethane resin, DMF, and additives are mixed to dissolve the polyurethane resin, the resulting mixed solution is filtered to remove aggregates and the like, and then defoamed under vacuum to obtain a resin emulsion 49.

  In the coagulation regeneration process, the film forming substrate 43 coated with the resin emulsion 49 is introduced into the coagulation liquid 25 to coagulate and regenerate the polyurethane resin. In the coagulation liquid 25, first, a skin layer 5 a is formed on the surface of the resin emulsion 49, and pores 6 having an average pore diameter larger than that of the foam 3 formed on the polyurethane sheet 2 are formed substantially uniformly inside the skin layer 5 a. Is done.

  Here, formation of the pores 6 of the polyurethane sheet 5 will be described. DMF used for dissolving the polyurethane resin is a solvent generally used for dissolving the polyurethane resin, and can be mixed in an arbitrary ratio with respect to water. For this reason, in the production of the polyurethane sheet 5, when the resin emulsion 49 is immersed in the coagulation liquid 25, first, substitution of DMF with the coagulation liquid 25 (coagulation regeneration of the polyurethane resin) occurs on the surface of the resin emulsion 49, and the skin layer 5a is finely formed. A porosity is formed. Thereafter, since the coagulating liquid 25 enters the resin emulsion 49 from the part where the skin layer 5a easily enters, a part where the substitution of the DMF and the coagulating liquid 25 proceeds rapidly and a part where the replacement is delayed are generated. Is formed. Since a film made of PET that does not allow the coagulation liquid to permeate the film-forming substrate 43 is used, DMF elutes only from the surface side of the resin emulsion 49 (skin layer 5a side). It becomes a rounded triangular pyramid shape. Further, since the pores 6 are formed along with the removal of DMF, the pores 6 are communicated in a three-dimensional mesh shape with communication holes smaller than the average pore diameter of the pores 6.

  In the bonding step, the dried polyurethane sheets 2 and 5 are peeled off from the film forming base material 43, and the opposite surface side of the skin layer 5a of the polyurethane sheet 5 is bonded to the opposite surface side of the polishing surface of the polyurethane sheet 2. For joining, a joining solution in which a small amount of polyurethane resin is dissolved in DMF is used. The same polyurethane resin as the polyurethane sheets 2 and 5 is used for this polyurethane resin. The amount of the polyurethane resin dissolved is only required to be able to join the polyurethane sheets 2 and 5, and may be, for example, about 1 to 5%. The polyurethane sheets 2 and 5 are brought into contact with each other through the bonding solution and heated while being pressurized. By evaporating DMF, the polyurethane sheets 2 and 5 are joined via the polyurethane resin.

  In the buffing process, buffing is performed on the polishing surface P side of the polyurethane sheet 2. As shown in FIG. 4A, the polyurethane sheets 2 and 5 wound around the winding roller 42 are respectively formed on a PET film of the film forming substrate 43. Since the thickness of each of the polyurethane sheets 2 and 5 varies at the time of film formation, the surface of the polyurethane sheets 2 and 5 formed on the substantially flat film formation base material 43 (on the side opposite to the film formation base material 43). ) Is uneven. After joining the polyurethane sheets 2 and 5 from which the film-forming substrate 43 has been peeled off, the surface of the pressure roller 65 having a flat surface is pressed against the skin layer 5a side of the polyurethane sheet 5 as shown in FIG. By doing so, the surface of the skin layer 5a becomes flat, and irregularities appear on the opposite surface P1 side of the polyurethane sheet 2 to which the polyurethane sheet 5 is bonded. Unevenness appearing on the opposite surface P1 side is removed by buffing. In this example, since the continuously manufactured polyurethane sheets 2 and 5 are belt-like, the opposite surface P1 side is continuously buffed while pressing the pressing roller 65 to the skin layer 5a side. As a result, as shown in FIG. 4C, the opposite surface P1 side is buffed, so that the variation in the overall thickness of the joined polyurethane sheets 2 and 5 is eliminated, and a flat polished surface P is formed. The In FIG. 4A, the foam 3 and the pores 6 formed on the polyurethane sheets 2 and 5 are shown separately. Further, in FIG. 4C, the polishing surface P and the surface of the skin layer 5a are shown flat for easy understanding, but the bonded polyurethane sheets 2 and 5 are the entire polyurethane sheets 2 and 5 on both sides. The polishing surface P becomes substantially flat when the substrate 11 is bonded or attached to a polishing machine.

  As shown in FIG. 2, in the laminating process, the base material 11 is bonded to the skin layer 5 a side of the polyurethane sheet 5. The other surface side of the double-sided tape 12 having the release paper 13 attached to one surface is bonded to the surface of the base 11 opposite to the polyurethane sheet 5. Then, after cutting into a desired shape such as a circle, an inspection such as confirming that there is no adhesion of dirt or foreign matter is performed to complete the polishing pad 1.

  When polishing the object to be polished with the obtained polishing pad 1, for example, the polishing pad 1 is attached to the upper surface plate and the lower surface plate of the double-side polishing machine. In the double-side polishing machine, an object to be polished is sandwiched between two polishing pads 1 attached to an upper surface plate and a lower surface plate, and both surfaces are simultaneously polished. The surface to which the polishing pad 1 is applied, that is, the lower surface of the upper surface plate and the upper surface of the lower surface plate are both formed flat. For this reason, the polishing pad 1 affixed to the upper surface plate and the lower surface plate both forms a flat polishing surface P.

(Function)
Next, the operation and the like of the polishing pad 1 of the present embodiment will be described.

  In the conventional wet film formation method used for manufacturing a polishing pad, it is obtained by variation in coating thickness generated when a polyurethane resin solution having a viscosity is applied to a film formation base material or variation in solvent removal generated during solidification regeneration of the polyurethane resin. The thickness of the polyurethane sheet varies. In order to reduce thickness variation, a buffing process is performed on the polishing surface side of the polishing pad. For this reason, since the foam formed inside opens at the polishing surface, the polishing liquid is stored in the foam during the polishing process so that the supply of the polishing liquid to the object to be polished is equalized and the flatness of the object to be polished is improved. Can be improved. However, when the polishing liquid penetrates into the foamed polyurethane sheet, there is a problem that the elasticity of the polyurethane sheet gradually decreases and the polyurethane sheet itself becomes hard. When the polyurethane sheet is hard, the followability to the object to be polished is lowered and the object to be polished cannot be pressed uniformly, resulting in a loss of flatness of the object to be polished. In addition, the presence of polishing scraps between the polishing pad and the object to be polished causes scratches or the like on the surface of the object to be polished. By exchanging the polishing pad before the polyurethane sheet becomes hard, flatness can be ensured, but the life of the polishing pad is reduced. On the other hand, in the foam formed inside the polyurethane sheet produced by the wet film forming method, the average pore diameter greatly increases as the distance from the polished surface increases. When the polyurethane sheet is worn as the polishing process proceeds, the opening diameter of the foam is greatly increased, so that the surface state becomes uneven and the flatness of the object to be polished is lowered. For this reason, in the conventional polyurethane sheet, the average pore diameter range of 25 μm or less effective for polishing is only a range of less than 10% of the thickness of the polyurethane sheet. In order to improve the flatness of the object to be polished, since the polishing cloth needs to be replaced before the hole diameter becomes large, the life of the polishing cloth is inferior. The present embodiment is a polishing pad that can solve these problems.

  In the polishing pad 1 of the present embodiment, the polyurethane sheet 5 is bonded to the opposite side of the polishing surface P of the polyurethane sheet 2. Since the average pore diameter of the pores 6 formed in the polyurethane sheet 5 is larger than the foam 3 formed in the polyurethane sheet 2, the elasticity of the polyurethane sheet 5 is larger than that of the polyurethane sheet 2. The foam 3 of the polyurethane sheet 2 and the pores 6 of the polyurethane sheet 5 communicate with each other inside the polyurethane sheets 2 and 5, respectively, but the foam 3 and the pores 6 do not communicate with each other at the joint portion of the polyurethane sheets 2 and 5. For this reason, since the polishing liquid supplied at the time of the polishing process enters the foam 3 and the polyurethane sheet 2 becomes hard, the polishing liquid does not enter the polyurethane sheet 5. Is maintained. Thereby, even if the polyurethane sheet 2 becomes hard, the polishing surface P is pressed against the object to be polished with substantially equal pressure by the polyurethane sheet 5 performing a cushion function, so that it is possible to ensure followability to the object to be polished. It is possible to suppress a decrease in flatness of the object to be polished. Further, by ensuring the followability to the object to be polished, the polishing process can be continued and the life of the polishing pad 1 can be prevented from being reduced.

  Moreover, in the polishing pad 1 of this embodiment, the foam 3 formed on the polyurethane sheet 2 is maintained at an average pore diameter of 25 μm or less until it exceeds at least 15% of the thickness from the polishing surface P to the inside of the polyurethane sheet 2. ing. For this reason, the foam 3 has an elongated shape in the thickness direction of the polyurethane sheet 2 and can be used for polishing until at least 15% of the thickness is worn. Accordingly, the object to be polished is polished on the polishing surface P having an opening diameter of 25 μm or less and a substantially uniform surface state. Therefore, the object to be polished can be polished flatly for a long period of time. Lifespan can be improved.

  Furthermore, in the polishing pad 1 of the present embodiment, a hydrophilic additive is added to the polyurethane resin solution 45 when the polyurethane sheet 2 is manufactured. For this reason, the point at which desolvation of DMF occurs during solidification regeneration of the polyurethane resin increases. Thereby, the elongated foam 3 can be easily formed in the polyurethane sheet 2 without complicating the manufacturing process.

  Furthermore, in the polishing pad 1 of the present embodiment, both the polyurethane sheets 2 and 5 are formed of a polyurethane resin. When the two polyurethane sheets 2 and 5 are joined, a joining solution in which the same polyurethane resin is dissolved is used. Since the polyurethane sheets 2 and 5 are joined with the same material polyurethane resin, the affinity at the joining surface is superior to the joining of different materials, so that the polyurethane sheets 2 and 5 can be joined easily and reliably.

  Furthermore, in the polishing pad 1 of this embodiment, the polishing surface P side of the polyurethane sheet 2 is buffed after the polyurethane sheets 2 and 5 are joined. For this reason, even if the polyurethane sheets 2 and 5 have thickness variations, the overall thickness accuracy can be improved and the flatness of the polished surface P can be improved.

  Moreover, in the polishing pad 1 of this embodiment, the base material 11 of the PET film is bonded to the skin layer 5 a side of the polyurethane sheet 5. For this reason, since the polyurethane sheets 2 and 5 are supported by the base material 11, the handling at the time of conveyance of the polishing pad 1 or attachment to a polishing machine can be facilitated.

  In the polishing pad 1 of the present embodiment, the example in which the polyurethane sheets 2 and 5 are made of the same polyurethane resin is shown, but the present invention is not limited to this. For example, a sheet in which pores are formed inside a resin such as polyethylene may be used in place of the polyurethane sheet 5 as long as elasticity can be maintained during polishing. For example, instead of the polyurethane sheet 2, a sheet in which a three-dimensional mesh-like foam is formed inside a polyethylene resin or the like may be used. Moreover, in the polishing pad 1 of this embodiment, although the example which produces the polyurethane sheets 2 and 5 with the wet film-forming method was shown, you may make it produce with the dry method.

  Further, in the polishing pad 1 of the present embodiment, the average pore diameter of the pores 6 formed in the polyurethane sheet 5 is made larger than that of the foam 3 formed in the polyurethane sheet 2, and the elasticity of the polyurethane sheet 5 is made larger than that of the polyurethane sheet 2. Although an example is shown, the present invention is not limited to this. For example, the average pore diameter of the pores 6 and the foam 3 may be the same, and the elasticity of the polyurethane sheets 2 and 5 may be the same. Even if it does in this way, even if the polyurethane sheet 2 becomes hard at the time of a grinding | polishing process, since the elasticity of the polyurethane sheet 5 is maintained, the effect mentioned above can be acquired. Of course, two identical polyurethane sheets 5 may be joined. Furthermore, in this embodiment, although the elasticity of the polyurethane sheets 2 and 5 differed by the difference in the average hole diameter of the foam 3 and the air_hole | stoma 6, this invention is not limited to this, For example, foam 3 Alternatively, the elasticity may be changed by adjusting the number of pores 6. Further, the elasticity of the polyurethane sheet 5 may be made different by using a polyurethane resin softer than the polyurethane resin of the polyurethane sheet 2 (for example, having a smaller modulus of 100%). Further, instead of comparing the elasticity, the comparison may be performed using, for example, a compression ratio, which is an index for evaluating the elasticity.

  Furthermore, in the polishing pad 1 of the present embodiment, an example in which an anionic surfactant is added as a hydrophilic additive during the production of the polyurethane sheet 2 in order to make the foam 3 into an elongated shape has been shown. The material is not limited, and any material that is soluble and hydrophilic in the organic solvent used for dissolving the polyurethane resin may be used. Examples of such hydrophilic additives include hydrophilic ester-based, ether-based, ester-ether-based, amide-based nonionic surfactants, and the like. Two or more of these hydrophilic additives may be mixed and used.

  Furthermore, the addition amount of the hydrophilic additive added to the polyurethane resin solution 45 may be set according to the hole diameter and number on the polishing surface P side of the foam 3 and is not particularly limited. By increasing the amount of hydrophilic additive added, the number of micropores in the skin layer can be increased. As the number of micropores increases, the number of points where desolvation occurs increases, so the pore diameter of the foam 3 decreases and the number increases. Although the addition amount of a hydrophilic additive changes with kinds of additive and the kind of resin, for example, it adds between 0.2-5 parts with respect to 100 parts of resin solutions. If the addition amount of the hydrophilic additive is small, the foamed shape does not change, and if it is too much, the film formability is hindered.

  Furthermore, in this embodiment, an example in which a joining solution in which a small amount of polyurethane resin is dissolved in DMF is used for joining the polyurethane sheets 2 and 5 is shown, but the present invention is not limited to this. For example, even when only DMF is used, the polyurethane on the joining surfaces of the polyurethane sheets 2 and 5 is softened by DMF, and therefore can be sufficiently joined by applying pressure. Further, the joining surfaces of the polyurethane sheets 2 and 5 may be softened by heating to be joined. Of course, it is also possible to use an adhesive or the like.

  Moreover, in this embodiment, although the example which affixes the base material 11 of a PET film on the skin layer 5a side of the polyurethane sheet 5 was shown, this invention is not limited to this, For example, a nonwoven fabric and a woven fabric Or the like may be used as the base material 11. The double-sided tape 12 may be bonded directly without bonding the base material 11. Further, the bonded polyurethane sheets 2 and 5 can be used for polishing without bonding the base material 11 and the double-sided tape 12 together. In this case, an adhesive or a double-sided tape may be used when the polishing pad is mounted on the surface plate of the polishing machine.

  Furthermore, in the present embodiment, the knife coater 46 is exemplified for the application of the polyurethane resin solution 45 and the resin emulsion 49. However, for example, a reverse coater, a roll coater, or the like may be used. The coating is not particularly limited as long as it can be applied. Moreover, in this embodiment, although the cylinder dryer 50 was illustrated for drying of a polyurethane resin, this invention is not limited to this, For example, you may use a hot air dryer etc.

  Furthermore, in this embodiment, the polyurethane sheet 2 to which the polyurethane sheet 5 is bonded is buffed on the polishing surface P side by a buffing machine or the like, but the buffing amount is the maximum of the entire thickness of the polyurethane sheets 2 and 5. It is desirable that the difference be greater than or equal to the minimum value. Various materials such as sandpaper and diamond buffol are used in the buffing, but any can be used as long as uniform processing (grinding removal) is possible. At this time, the higher the buff count (number indicating the roughness of the abrasive grains), the more fine the abrasive grains can be ground and the uniform buffing process can be performed. Furthermore, the thickness accuracy is improved by buffing with a low buff count (rough abrasive grains) at the first time, and buffing with a buff count higher than the first time with a lower buff count. It can also be raised.

  Hereinafter, examples of the polishing pad 1 manufactured according to the present embodiment will be described. A comparative polishing pad manufactured for comparison is also shown.

Example 1
In Example 1, polyester MDI (diphenylmethane diisocyanate) polyurethane resin was used as the polyurethane resin for the production of the polyurethane sheets 2 and 5. In preparation of polyurethane sheet 2, 1 part of hydrophilic additive sodium lauryl sulfate (SLS) is added to 100 parts of 30% polyurethane resin solution, and 45 parts of DMF for viscosity adjustment, carbon black of pigment are added. A polyurethane resin solution 45 was prepared by adding 40 parts of a 30% DMF dispersion and 2 parts of a hydrophobic stabilizer of a film forming stabilizer and mixing them. On the other hand, in the production of the polyurethane sheet 5, a resin emulsion 49 was prepared in the same manner as the preparation of the polyurethane resin solution 45 except that no hydrophilic additive was added. Further, in order to enhance the cleaning effect in the cleaning process, cleaning after coagulation regeneration was performed with warm water. The opposite surface side of the skin layer 5 a of the polyurethane sheet 5 was joined to the opposite surface side of the polishing surface P of the polyurethane sheet 2. The polishing surface P side of the polyurethane sheet 2 was buffed using a sandpaper of buff count # 180 with a buff treatment amount of 0.05 mm, and the polishing pad 1 of Example 1 was manufactured.

(Comparative Example 1)
In Comparative Example 1, only the polyurethane sheet 2 produced in Example 1 was used, the polishing surface P side was buffed with a buff treatment amount of 0.05 mm, the base material 11 and the double-sided tape 12 on the opposite surface side of the polishing surface P Were bonded together to produce a polishing pad of Comparative Example 1.

(Evaluation of the physical properties)
Next, the thickness of the polyurethane sheet 2, the polyurethane sheet 5 and the polyurethane sheet 2 prepared in each of the examples and comparative examples were joined to the polyurethane sheet 5 and bonded to the base material 11 (hereinafter referred to as a pre-sheet). Each physical property value of bulk density, compression rate, compression modulus and A hardness was measured. The thickness was measured using a dial gauge (minimum scale 0.01 mm) and applying a load of 100 g / cm ² . Each sheet of 1 m in length and 1 m in width was read up to 1/10 (0.001 mm) of the minimum scale at a pitch of 10 cm in length and width, and the average value of thickness and standard deviation σ were obtained. The bulk density was calculated by measuring the weight per unit area and using the measurement result of the thickness. The compressibility and the compressive elastic modulus were determined using a shopper type thickness measuring instrument (pressure surface: circular shape with a diameter of 1 cm) in accordance with Japanese Industrial Standard (JIS L 1021). Specifically, the thickness t ₀ after pressing for 30 seconds with an initial load was measured, and then the thickness t ₁ after standing for 5 minutes under the final pressure was measured. All the loads were removed, and after standing for 5 minutes, the thickness t ₀ ′ after pressing for 30 seconds with the initial load again was measured. The compression rate is calculated as compression rate (%) = (t ₀ −t ₁ ) / t ₀ × 100, and the compression modulus is calculated as compression modulus (%) = (t ₀ ′ −t ₁ ) / (t ₀ -T ₁ ) × 100. At this time, the initial load was 100 g / cm ² and the final pressure was 1120 g / cm ² . The A hardness was determined from the indentation depth of the push needle pressed against the surface of the test piece via a spring according to Japanese Industrial Standard (JIS K 6253). The measurement results of thickness, bulk density, compression rate, compression modulus and A hardness are shown in Table 1 below. In Table 1, the measured values of the PET film used for the substrate 11 are also shown.

As shown in Table 1, the standard deviation σ of the thickness was 0.006 mm and 0.008 mm for the polyurethane sheet 2 and the polyurethane sheet 5, respectively. This is considered that the standard deviation σ is increased due to variations in the application of the resin solution and variations during regeneration coagulation. The bulk density is 0.20 g / cm ³ in the polyurethane sheet 2 in which the foam 3 is formed, and 0.22 g / cm ³ in the polyurethane sheet 5 in which the pores 6 are formed. From this, it can be seen that the space volume of the pores 6 occupying the polyurethane sheet 5 is smaller than the space volume of the foam 3 occupying the polyurethane sheet 2. However, the compression ratio of the polyurethane sheet 2 is 5.2%, and that of the polyurethane sheet 5 is 8.4%. From this, it can be seen that the polyurethane sheet 5 is more elastic than the polyurethane sheet 2. As for the compression elastic modulus, the polyurethane sheet 5 is more elastic than the polyurethane sheet 2. Accordingly, it is conceivable that the pores 6 of the polyurethane sheet 5 are smaller in number than the foam 3 of the polyurethane sheet 2 but have a large average pore diameter.

  On the other hand, since the pre-sheet in which the polyurethane sheets 2 and 5 are joined is buffed, the standard deviation σ of the thickness is 0.005 mm, which is smaller than the respective sheets. Furthermore, in this pre-sheet, since the polyurethane sheets 2 and 5 are bonded with a DMF solution of 5% polyurethane resin, the compressibility is higher than that of the respective sheets. Moreover, since the compression elastic modulus shows 90.0%, it turns out that the elasticity remains even if the polyurethane sheet 5 is joined to the polyurethane sheet 2. By polishing with the polishing pad 1 of Example 1, it can be expected that the surface of the object to be polished is flattened with high accuracy.

(Pore diameter evaluation)
With respect to the polyurethane sheet 2 and the polyurethane sheet 5, the average pore diameters of the foam 3 and the pores 6 were measured as follows. Moreover, the opening diameter and opening rate in a grinding | polishing surface were measured about the pre-sheet. Foam formed at 5%, 10%, 15%, 20%, and 30% of the thickness of each sheet from the skin layer side from cross-sectional photographs (scanning electron microscope) of the formed polyurethane sheets 2 and 5 The average pore diameter of 3 or pores 6 was measured. For the pre-sheet, the opening diameter was measured from the photograph of the polished surface, and the ratio of the opening area per unit area was calculated. The measurement results of the average pore diameter are shown in Table 2 below.

  As shown in Table 2, in the polyurethane sheet 5 produced without adding a hydrophilic additive, the average pore diameter is 25.5 μm at a position of 10% of the thickness, and the average pore diameter increases as the thickness ratio increases. It shows that it will grow. For this reason, even if the polyurethane sheet 5 is used as a polishing pad, the pore diameter of the pores 6 increases as the polyurethane sheet wears during polishing. Therefore, the polishing pad has a life before it reaches 10% of the thickness of the polyurethane sheet 5, and if the polishing process is continued as it is, the flatness of the object to be polished will be lowered. On the other hand, the polyurethane sheet 2 produced by adding a hydrophilic additive exhibits an average pore diameter of 25 μm or less until it exceeds 20% of the thickness, and the foam 3 of the polyurethane sheet 2 has pores 6 of the polyurethane sheet 5. It is formed longer and longer. Therefore, the polishing pad 1 of Example 1 in which the polyurethane sheet 5 is bonded to the polyurethane sheet 2 can be used for polishing until it exceeds 20% of the thickness of the polyurethane sheet 2. Further, since the opening diameter of the pre-sheet was 12.6 μm and the opening ratio was 12%, it is considered that the polishing liquid can be supplied substantially uniformly to the object to be polished while storing the polishing liquid in the foam 3 at the time of polishing.

(Polishing performance evaluation)
Next, using the polishing pads of each of the examples and comparative examples, the polishing process of the aluminum substrate was repeated 10 times under the following polishing conditions, and the polishing performance was determined by the polishing amount, polishing rate, and swell in the 11th polishing process. Evaluated. The amount of polishing was determined by measuring the weight reduction of the aluminum substrate before and after polishing. The polishing rate is the amount of polishing per minute expressed by thickness, and was calculated from the measured value of the polishing amount, the polishing area of the aluminum substrate, and the specific gravity. The waviness is one of the measurement items for evaluating the surface accuracy (flatness). The waviness (Wa) of the surface image per unit area observed with an optical non-contact surface roughness meter is Expressed in angstroms (Å). A surface roughness measuring machine (manufactured by Zygo, model number New View 5022) was used for the measurement of waviness. Table 3 shows the measurement results of the polishing amount, polishing rate, and swell.
(Polishing conditions)
Polishing machine used: Speedfam, 9B-5P polishing machine Polishing speed (rotation speed): 30 rpm
Processing pressure: 100 g / cm ²
Polishing time: 330 seconds Slurry: Alumina slurry Slurry supply amount: 100 cc / min
Workpiece: Aluminum substrate for hard disk (outer diameter 95mmφ, inner diameter 25mm, thickness 1.27mm)

  As shown in Table 3, the polishing pad of Comparative Example 1 using only the polyurethane sheet 2 had a polishing rate of 0.233 μm / min and a swell of 8.5 mm. On the other hand, the polishing pad 1 of Example 1 in which the polyurethane sheets 2 and 5 were joined and used had a polishing rate of 0.258 μm / min, which was larger than that of Comparative Example 1. Moreover, the undulation showed 7.0 mm, and it was found that excellent flatness could be secured. Therefore, by joining the polyurethane sheet 5 to the polyurethane sheet 2, the elasticity of the polyurethane sheet 5 makes the contact pressure of the polishing pad 1 to the object to be polished uniform and improves the followability to the aluminum substrate. It was found that the flatness of the substrate can be improved. In addition to the polyurethane sheet 2 having the polishing surface P, the polishing pad 1 includes the polyurethane sheet 5 that is not easily exposed to an environment that causes wear and deterioration and can maintain elasticity. Therefore, the wear of the polishing pad 1 is reduced and the life can be extended (improvement of life).

  The present invention contributes to the manufacture and sale of abrasive cloths in order to provide an abrasive cloth that can ensure followability to the object to be polished and improve the flatness, and thus has industrial applicability.

It is sectional drawing which shows the polishing pad which concerns on this invention. It is process drawing which shows the manufacturing process of the polishing pad of embodiment. It is a front view which shows schematic structure of the film-forming apparatus used for manufacture of the polyurethane sheet of a polishing pad. It is sectional drawing which shows the state change of the polyurethane sheet in a buff processing process, (A) is a state when formed in the film-forming base material, (B) is a polishing surface after joining two polyurethane sheets. The state when pressed against the pressure roller, (C) shows the state when the pressure roller is removed after buffing.

Explanation of symbols

P Polishing surface 1 Polishing pad (polishing cloth)
2 Polyurethane sheet (first soft plastic sheet)
3 Foam 4 Opening 5 Polyurethane sheet (second soft plastic sheet)
6 pores

Claims (8)

A first soft plastic sheet in which a polishing surface for polishing an object to be polished is formed and foam is formed in a three-dimensional network, and a second soft plastic in which pores are substantially uniformly formed. A first soft plastic sheet, the second soft plastic sheet being joined to the opposite side of the polishing surface, the polishing surface side of the first and second soft plastic sheets The foam is opened by buffing so that the entire thickness is uniform, and the foam formed inside the first soft plastic sheet is the thickness of the first soft plastic sheet. A length in a direction that is reduced in diameter on the polishing surface side, and at least 15% of the thickness of the first flexible plastic sheet in an internal direction from the polishing surface Polishing cloth Hitoshiana径is characterized in that it is 25μm or less.   The polishing cloth according to claim 1, wherein the second soft plastic sheet has elasticity greater than that of the first soft plastic sheet.   The second soft plastic sheet is characterized in that the pores formed inside the second soft plastic sheet have a larger average pore diameter than the foam formed inside the first soft plastic sheet. The abrasive cloth according to claim 2.   The second soft plastic sheet has a surface layer in which micropores having an average pore diameter smaller than that of the foam of the first soft plastic sheet are formed on the opposite surface side joined to the first soft plastic sheet. The polishing cloth according to claim 1, wherein   2. The polishing cloth according to claim 1, wherein each of the first and second soft plastic sheets is made of a polyurethane resin. 6. The polishing cloth according to claim 5 , wherein the first and second soft plastic sheets are joined with a polyurethane resin. The one side of the double-sided tape for mounting to a surface plate is further affixed on the opposite side to which the said 1st soft plastic sheet of the said 2nd soft plastic sheet was joined. The polishing cloth according to claim 6 . 8. The substrate according to claim 7 , wherein at least one kind of substrate selected from a flexible film, a nonwoven fabric, and a woven fabric is further bonded between the second soft plastic sheet and the double-sided tape. The polishing cloth as described.

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