JP2018167389A - Holding pad - Google Patents

Abstract

To provide a holding pad wherein, the cushioning property of the holding pad is secured while the durability of a polyurethane foam sheet is improved, so that the pad usable time is increased.SOLUTION: A holding pad has a polyurethane foam sheet that has a holding face for holding a polishing object, and has foam formed inside the holding face, the foam to communicate with the holding face. The polyurethane foam sheet contains fine fibers of 0.1-10 mass% relative to the total mass.SELECTED DRAWING: None

Description

  The present invention relates to a holding pad, and in particular, a holding pad having a polyurethane foam sheet having a holding surface for holding an object to be polished and having foam formed on the inner side of the holding surface and communicating with the holding surface. About.

  In materials (objects to be polished) such as semiconductor wafers, glass substrates, and magnetic disks, high-precision flatness is required, and therefore polishing using a polishing pad is performed. Usually, for polishing of these objects to be polished, a double-side polishing machine for simultaneously polishing both surfaces of the object to be polished and a single-side polishing machine for polishing one surface of the object to be polished are used.

  In polishing processing using a single-side polishing machine, the parallelism between the holding surface plate that holds the object to be polished and the polishing pad and the offset load that occurs during the polishing process are absorbed, and the object to be polished is approximately held by the holding surface plate. A holding pad is attached to the holding surface plate for the purpose of holding it flat. As the holding pad, a polyurethane resin foam sheet formed by a wet film forming method is used. In the wet film-forming method, a resin solution in which a polyurethane resin is dissolved in a water-miscible organic solvent is applied to a film-forming substrate, and then immersed in an aqueous coagulating liquid, whereby the resin is coagulated and regenerated into a sheet. The foamed sheet thus obtained has a dense skin layer at the interface with the coagulation liquid, is vertically long in the thickness direction inside the skin layer, and spreads on the side opposite to the skin layer (hereinafter referred to as the back side). It has a continuous foamed structure in which a plurality of foams to be diameterd and a large number of micropores having an average diameter smaller than the average diameter of the foam are continuously formed. Since the holding pad has such a foam structure, cushioning properties are exhibited during the polishing process, and the object to be polished can be held substantially flat. The holding surface is flat and excellent in contact with the object to be polished, and the object to be polished can be reliably held by fixing the object to be polished by water-filled adsorption. That is, the surface of the holding sheet becomes a holding surface for holding the object to be polished.

  Since the holding pad is continuously used while exchanging an object to be polished, durability is required. However, in the case of the holding pad formed by the wet film formation method, the object to be polished sinks into the holding pad during the polishing process. Therefore, if the polishing process is continued, the holding surface in contact with the outer edge of the object to be polished is easily damaged and damaged. The holding power of the object to be polished may be reduced. In addition, the larger the foam size, the more cushioning properties of the holding pad, while the lower the resin density, the more repeatedly the compression and recovery, the plastic part between the adjacent foam and foam is plastically deformed, and the cushioning properties are improved. Loss and flatness may deteriorate.

  Therefore, in Patent Document 1, in order to increase the strength of the holding pad and make it difficult to break, there is a technique in which both surfaces of the foam under wet coagulation are sandwiched between smooth members and heated and pressed to make the foam on both surfaces dense. It is shown.

  On the other hand, Patent Document 2 proposes that durability is enhanced by a holding pad made of fibers having a number average diameter of 1 nm to 5 μm, having a fine holding surface derived from ultrafine fibers, and fibers made of polyester. Has been.

JP 2011-156633 A JP 2009-88456

  However, in the holding pad described in Patent Document 1, since both surfaces of the polyurethane foam sheet are heated and pressurized, the porosity of the foam is reduced and the cushioning property is lowered, and the polyurethane resin is deteriorated and hardened by heating. By doing so, the cushioning properties are further reduced.

  In addition, the holding pad described in Patent Document 2 does not include a porous film or foamed foam, and the ultrafine fibers are arranged on the fiber base material. It is difficult to improve the waviness of polished objects. In addition, the ultrafine fibers fixed to the nonwoven fabric or the woven fabric may fall off and cause a polishing scratch.

  An object of the present invention is to improve the durability of a polyurethane foam sheet and improve the usable time of the pad while securing cushioning properties by the holding pad.

  The invention according to claim 1 is a holding pad comprising a polyurethane foam sheet having a holding surface for holding an object to be polished and having foam formed on the inner side of the holding surface and communicating with the holding surface. The polyurethane foam sheet contains 0.1 to 10% by mass of microfibers with respect to the total mass.

  The invention according to claim 2 is the invention according to claim 1, wherein the microfibers have a fiber diameter of 1 to 1000 nm and an aspect ratio of 10 to 10,000.

  The invention according to claim 3 is the invention according to claim 1 or 2, wherein the microfiber is a microfiber obtained from a polysaccharide.

  ADVANTAGE OF THE INVENTION According to this invention, durability of a polyurethane foam sheet can be improved and pad usable time can be improved, ensuring the cushioning property by a holding pad in a holding pad.

1. Configuration of Holding Pad The holding pad of the present invention includes a polyurethane foam sheet having a holding surface for holding an object to be polished, and having foam formed in communication with the holding surface on the inner side of the holding surface. The polyurethane foam sheet is obtained by wet-forming a polyurethane resin solution containing 0.1 to 10% by mass of microfibers with respect to the total mass.

  That is, in the holding pad, the above-mentioned polyurethane foam sheet is made of a polyethylene terephthalate (PET) having a thickness in the range of 0.1 to 0.5 mm, for example, and arranged on a flexible substrate. .

  (a) A wet-formed polyurethane foam sheet has a holding surface for holding an object to be polished, is vertically long in the thickness direction inside the holding surface, and is opposite to the holding surface (back surface) It has a plurality of substantially tear-shaped foams that are expanded in diameter on the side, and has a continuous foam structure in which a large number of micropores having an average diameter smaller than the average diameter of the tear-shaped foams are continuously formed, Since the compressive modulus elastic modulus is large and it is formed in a porous structure, it becomes soft, ensures elastic recovery during polishing, and can hold the object to be polished substantially flat.

  The holding pad preferably has a compression modulus of 70 to 100%, more preferably 80 to 100%, and most preferably 90 to 100%. By making the compression elastic modulus within the above range, while maintaining the elastic recoverability of the object to be polished and the flatness of the holding pad, the recoverability under repeated use is good, the followability to the object to be held and Achieved flatness (rise) is good.

  The holding pad preferably has a polyurethane foam sheet thickness of 0.3 to 2.0 mm, more preferably 0.5 to 2.0 mm, and most preferably 0.7 to 2.mm. 0 mm. By setting the thickness within the above range, the cushion performance for the object to be polished is sufficiently exhibited, and the waviness of the object to be polished can be reduced.

  (b) The wet-formed polyurethane foam sheet is in a denser state when the microfibers dispersed around the foamed foam are pushed and moved along with the growth of the foam when the tear-shaped foam grows. Disperse in the resin during foaming to structurally strengthen the resin. In addition, since the microfibers dispersed in the resin of the polyurethane foam sheet interact with the polyurethane resin to form a network, the structural strength deficiency due to the occurrence of tear-shaped foam is improved. This increases the structural strength of the holding pad having a skin layer on the holding surface, improves durability, and holds the object to be polished by holding it in contact with the outer edge of the object to be polished. Since surface damage is suppressed, and damage to the skin layer is suppressed, it is possible to prevent the slurry from infiltrating into the holding pad and reducing the holding power of the object to be polished. Further, when the foamed portion of the holding pad repeats compression / recovery, it is possible to suppress the sag (plastic deformation) between the adjacent foams and foam and maintain the cushioning property. That is, the wear resistance can be improved and the pad usable time can be improved.

  In the present embodiment, an example is shown in which the back side of the holding sheet having the skin layer is buffed for the purpose of uniformizing the thickness of the polyurethane foam sheet, but the present invention is not limited to this. In the grinding process, other than buffing, any method may be used as long as the thickness is uniformized and flattened. For example, it may be flattened by hot pressing to such an extent that the cushioning property is not impaired, or may be flattened by slicing using a slicing machine. In the present invention, mild sanding (dressing treatment) may be performed on the holding surface side so that the skin layer is not removed. Further, the skin layer side can be ground and flattened. Further, the holding surface may be buffed or sliced to remove the skin layer and flatten it. When dressing or buffing is performed on the holding surface, the holding force is reduced, but the work of removing the object to be polished from the holding pad after polishing is facilitated.

  Furthermore, in order to suppress the lateral displacement of the object to be polished, holding by attaching a frame material having one or more holding holes for holding the object to be polished on the holding surface of the holding pad so as to surround the outer periphery of the object to be polished. The holding pad of the present invention can be used as a tool. In such a holder, the object to be polished can be accommodated in the holding hole of the frame member, the object to be polished can be held by the holding pad, and polishing can be performed in that state.

  The addition amount of the microfiber with respect to the total mass of the polyurethane foam sheet is preferably 0.1 to 10% by mass. When 0.1% by mass or more, the effect of improving wear resistance is obtained, and when 10% by mass or less, an increase in viscosity of the resin solution is suppressed when added to and mixed with the polyurethane resin solution, Microfibers are preferred because they can flow and disperse in the resin and do not interfere with film formation.

  (c) The fine fibers used in the present invention preferably have a fiber diameter of 1 to 1000 nm and an aspect ratio of 10 to 10,000, more preferably a fiber diameter of 5 to 800 nm and an aspect ratio of 10 to 5000. When the size of the microfiber is within the above range, the microfiber is dispersed in the polyurethane resin and the strength of the holding pad is improved.

  The microfibers are dispersed in a polyurethane resin solvent (DMF) and mixed with the polyurethane resin solution.

  The raw materials for the microfibers are, for example, chitin, chitosan, collagen, pullulan, cellulose, hyaluronic acid, alginic acid, silk protein and other natural polymer systems, carbon fiber and other inorganic polymer systems, nylon, vinylon, polyester, acrylic, polyolefin And synthetic polymer systems such as polyvinyl alcohol, polyvinyl pyrrolidone, polyurethane, polyether sulfone, and polyamide.

  Microfiber production methods include electrospinning, melt spinning, meltblowing, centrifugal spinning, flash spinning, etc., and physical and chemical defibration of fibers and fiber bundles (for example, pulp). Is mentioned.

2. Specific embodiment of microfiber
(a) Preferred microfibers From the viewpoint of increasing the rigidity of the polishing pad and improving the durability, the raw materials for the microfibers are more preferably those obtained from polysaccharides that can form hydrogen bonds. In the present application, the term “polysaccharide” means a polymer which is linked together by a glycosidic bond and is repeatedly polymerized. Among the polysaccharides, cellulose, chitin, and chitosan that can obtain high-strength microfibers are preferable. Examples of the form of microfibers obtained from the polysaccharide include microfibrillar cellulose, chitin, chitosan, cellulose, chitin, chitosan microcrystals, microfibrous lignocellulose, and bacterial cellulose. In the present invention, any of these microfibers can be used. However, among these, microfibrous cellulose is more preferable.

  By adding microfibrous cellulose, the rigidity of the resin portion can be increased. Thereby, durability of a holding pad can be improved and a lifetime can be improved.

(b) Production method of microfibrous cellulose The production method of microfibrous cellulose includes high-pressure homogenizer method, underwater counter collision method, grinder method, ball mill method, biaxial kneading method, etc. What was obtained by well-known methods, such as the method of performing the chemical treatment by a TEMPO catalyst as pretreatment of textiles, can be used.

  The fiber diameter of the microfibrous cellulose is preferably 3 to 1000 nm and the fiber length is 100 to 100,000 nm. Within this range, the fine fibrous cellulose can be uniformly dispersed in the polyurethane resin. The aspect ratio is preferably 10 to 10,000. If it is this range, the uniformly disperse | distributed microfiber will contact moderately and the intensity | strength of a polyurethane foam sheet can be improved based on the bond strength of a hydroxyl group and a polyurethane resin.

(c) Characteristics of microfibrous cellulose Natural cellulose fibers have a structure composed of cellulose microfibril bundles and lignin and hemicellulose filling them. That is, it is presumed that hemicellulose covers a cellulose microfibril and / or cellulose microfibril bundle, and further has a structure in which this is covered with lignin. Cellulose microfibrils and / or cellulose microfibril bundles are firmly bonded by lignin to form plant fibers. Therefore, it is preferable that lignin in the plant fiber is removed in advance from the viewpoint that aggregation of the cellulose fiber in the plant fiber can be prevented. Specifically, the lignin content in the plant fiber-containing material is usually about 40% by mass or less, preferably about 10% by mass or less. Further, the lower limit of the lignin removal rate is not particularly limited, and it is preferably as close to 0% by mass. On the other hand, a microfibrous lignocellulose treated in a state dispersible in an organic solvent by chemical treatment in a state containing lignin can also be used.

Most of the microfibrous cellulose is used as a bundle of a plurality of cellulose microfibrils, for example, several tens of cellulose cellulose, which is the smallest unit of cellulose fibers. The fiber diameter of the preferred microfibrous cellulose (the dimension in the direction perpendicular to the length direction, corresponding to the diameter in the case of one and the diameter of the bundle in the case of multiple bundles) is 3 to 1000 nm (multiple Including the width when bundled). In particular, considering the availability of the microfibrous cellulose, a more preferable width of the microfibrous cellulose can be 3 to 300 nm, further 3 to 150 nm, and particularly 3 to 100 nm. . In addition, a normal cellulose fiber has a diameter of about 10 to 50 μm (micrometer order), and has an order difference of 10 ³ level from the microfibrous cellulose used in the present invention. The aspect ratio (fiber length / fiber diameter) of the microfibrous cellulose used in the present invention can be an average value of 10 to 10,000, more preferably 10 to 1000, and particularly 100 to 500. Can be. In addition, the average value of the fiber diameter and fiber length of a microfibrous cellulose is an arithmetic average value measured about at least 50 or more microfibrous cellulose within the visual field of an electron microscope.

  Since microfibrous cellulose is on the order of nanometers, it can be dispersed in a polyurethane resin even when added in a small amount and the number of fibers per unit volume of the resin can be improved. Abrasion can be improved. If the amount added is increased, further improvement in wear resistance can be expected. However, the addition of microfibrous cellulose increases the viscosity of the raw material, so when added in a large amount, it may cause a dispersion failure and consequently the foaming balance may be lost. Therefore, the preferable addition amount of the microfibrous cellulose is 0.1 to 10% by mass, more preferably 0.15 to 5% by mass with respect to the total mass of the polyurethane foam sheet. Furthermore, the wet coagulation method in which a large amount of the resin solvent is added can lower the viscosity of the raw material mixture liquid, while facilitating the addition of cellulose microfibers and improving the dispersion of the microfibrous cellulose in the raw material mixture liquid. Can do. Furthermore, since the dispersed microfibrous cellulose forms a network with the urethane resin by hydrogen bonding in the drying step after the coagulation regeneration, the polyurethane foam sheet of the present invention is remarkably improved by the wet coagulation method. Those produced are preferred. In a sheet in which a polyurethane resin is impregnated with a nonwoven fabric, woven fabric or knitted fabric obtained by entanglement of fine fibers or ultrafine fibers and tightly entwining the fibers to each other, the microfibers flow uniformly in the polyurethane resin. It is not preferable because it cannot be dispersed in the water.

3. Manufacturing method of holding pad The holding pad of the present invention is a process for preparing a polyurethane resin solution in which a polyurethane resin, N, N-dimethylformamide (DMF), an additive, and fine fibers are mixed and dispersed, for example, a wet film formation method. And a step of applying a polyurethane resin solution to a substrate and a coagulation regeneration step of a polyurethane resin in which the substrate coated with the polyurethane resin solution is immersed in a coagulation liquid.

(1) Step of preparing polyurethane resin solution i. The concentration of the urethane resin in the polyurethane resin solution is, for example, 10 to 50% by mass, preferably 20 to 40% by mass. Within this concentration range, the sheet density is adjusted to an appropriate range, and a desired foam structure can be formed.

  ii. DMF, which is a good solvent for polyurethane resin, can be mixed at an arbitrary ratio with respect to water, so the replacement speed with the coagulation liquid (water) is fast, and the lower layer (base material side) of the polyurethane resin solution A part of the resin moves to the upper layer (surface layer) side, and relatively large foaming (foaming vertically long in the sheet thickness direction) is easily formed on the lower layer side.

  iii. The fine fibrous cellulose added to the holding pad of the present invention is dispersed in DMF, which is a solvent for the polyurethane resin, and then mixed with the polyurethane resin. In order to enhance the dispersibility in DMF, a dispersant may be added even if it is chemically modified. In the present invention, in order to add the microfibrous cellulose to the polyurethane resin, it is preferable to chemically modify the hydroxyl groups of the microfibrous cellulose with a modifying group to reduce the number of hydroxyl groups. It can be easily dispersed in the polyurethane resin by preventing strong adhesion due to hydrogen bonding between the microfibrous cellulose. Examples of the modifying compound include functional groups such as an alkyl group, an acyl group, an acylamino group, a cyano group, an alkoxy group, an aryl group, an amino group, an aryloxy group, a silyl group, and a carboxyl group. A fine fibrous modified cellulose can be obtained by chemically bonding a functional group.

  iv. The polyurethane resin solution may further contain an additive as necessary. The additive is not particularly limited, but in the process of solidifying and regenerating the polyurethane resin, the solidification rate of the polyurethane resin is adjusted to form a desired foamed shape, so that a pigment such as carbon black, a hydrophobic active agent, a hydrophilic property An activator is preferred. These additives can be used alone or in combination of two or more. The compounding amount of the additive is not particularly limited, and is, for example, 20 parts by mass or less, preferably 0.1 to 15 parts by mass with respect to 100 parts by mass of the urethane resin-containing solution.

(2) Polyurethane resin solution coating process The substrate used in the polyurethane resin solution coating process may be a flexible material, such as a plastic film (polyester film, polyolefin film, etc.), a nonwoven fabric, or the like. . The method of applying the polyurethane resin-containing solution to the substrate is not particularly limited, and examples thereof include a method of applying using a conventional coater (knife coater, reverse coater, roll coater, etc.). The coating thickness is, for example, 0.3 to 2.5 mm, preferably 0.5 to 2.0 mm, and more preferably 0.8 to 1.5 mm from the viewpoint of forming a predetermined foam structure.

(3) Polyurethane resin coagulation regeneration step In the polyurethane resin coagulation regeneration step, the coagulation liquid for immersing the base material coated with the polyurethane resin solution contains a poor solvent (such as water) for the polyurethane resin as a main component. As the coagulation liquid, for example, water alone may be used, or a mixed solution of water and a polar solvent (for example, DMF, DMAc, THF, DMSO, NMP, acetone, etc.) may be used. The concentration of the polar solvent in the mixed solution is preferably 0.1 to 30% by mass.

  A polyurethane foam sheet solidified on the substrate can be obtained by the solidification regeneration process of the polyurethane resin. The manufacturing method of the holding pad of the present invention may further include a step of washing and drying the polyurethane foam sheet obtained by coagulation on the substrate, if necessary after peeling from the substrate.

(4) Washing and drying process of polyurethane resin By washing and drying, the solvent (DMF) remaining in the polyurethane resin and the coagulating liquid (water) are removed. Water is usually used as the cleaning liquid used for cleaning. Drying is performed at 80 to 150 ° C. for about 5 to 60 minutes, for example.

4). Foam structure of the holding pad As described above, the wet film forming method applied to the manufacturing of the holding pad according to the present invention involves dissolving the polyurethane resin to be formed in an organic solvent and applying the resin solution to a sheet-like substrate. The organic solvent is dissolved but the resin is not dissolved, soaking in a coagulating liquid to replace the organic solvent, coagulating, washing, and drying to form a foamed layer. Normally, when a polyurethane foam sheet is produced by a wet film forming method, the foam layer is formed into a porous structure. The mechanism is that when the polyurethane resin solidifies through the coagulating liquid, the solvent in the polyurethane resin is When the coagulated liquid that falls into the coagulated liquid enters the resin layer and undergoes substitutional solidification, the cavity formed in the polyurethane resin foams the holding sheet. At this time, a macro foam having a substantially tear shape (hereinafter referred to as a tear foam) and a fine foam which is smaller than the tear foam and allows water or gas to pass therethrough are formed in the entire polyurethane foam sheet.

  Tear-shaped foam is formed by the process of coagulating and regenerating polyurethane resin and is anisotropic, meaning that the foam diameter gradually increases from the polishing layer surface to the bottom of the polishing pad. This means a shape with a tapered side. Teardrop foam has a much larger cross-sectional area or volume than microfoam. Therefore, it is easy to distinguish between tear-shaped foam and fine foam. When this tear-shaped foam grows, the microfibrous cellulose where foaming has occurred is pushed along with the growth of the foam, and the resin between the tear-shaped foamed cells is thinned and structurally weakened by the growth of foam. Disperses in a denser state. The resin part between the foamed cells is reinforced by the fine fibrous cellulose dispersed more densely.

  After the tear-shaped foam is formed in the coagulation regeneration process, after the washing process, the moisture in the coagulation bath is removed from the polyurethane foam sheet in the drying process, the fine fibrous cellulose uniformly and densely dispersed in the polyurethane resin becomes hydrogen. A strong network is formed with the urethane resin by bonding, and this microfibrous cellulose network improves structural strength deficiency due to tear foaming, improves the durability of the holding pad, and increases the rigidity of the polyurethane foam sheet The wear resistance when used as a holding pad is improved, and the pad usable time can be improved.

5. Specific implementation results 5-1. The holding pads of Examples 1 to 4 and Comparative Examples 1 to 3 were manufactured.

Example 1
30 parts of DMF in which 1% by mass of carbon microfibers having a fiber diameter of about 40 nm and an aspect ratio of about 200 are dispersed as microfibers, and a 100% modulus 6.0 MPa polyester-based polyurethane resin-containing DMF solution (solid content concentration: 30% by mass) 100 A polyurethane resin solution was obtained by mixing the parts. The obtained polyurethane resin solution was coated on a polyester film (thickness: 188 μm). When applying the resin solution on the film-forming substrate, the clearance of the coating apparatus was set to 1.4 mm. Thereafter, the polyester film casted with the resin-containing solution is immersed in a coagulation bath (coagulation liquid is water) at 18 ° C. for 60 minutes to solidify the resin-containing solution, and then washed and dried. The polyurethane foam sheet having a thickness of 0.9 mm was peeled off.

  The side opposite to the skin layer formed on the surface of the obtained polyurethane foam sheet was ground (amount of grinding: 100 μm). Thereafter, a PET base material was bonded to the ground surface of the polyurethane foam sheet via an adhesive, and the PET base material and double-sided tape were bonded together to obtain a holding pad having a thickness of 1.25 mm.

(Example 2)
A holding pad was prepared in the same manner as in Example 1 except that microfibrous chitosan (fiber diameter: about 300 nm, aspect ratio: about 400) was used as the microfiber.

(Example 3)
A holding pad was prepared in the same manner as in Example 1 except that microfibrous cellulose (fiber diameter: about 100 nm, aspect ratio: about 300) was used as the microfiber.

Example 4
A holding pad was produced in the same manner as in Example 1 except that the addition amount of the microfibrous cellulose in Example 3 was 3% by mass.

(Comparative Example 1)
A holding pad was prepared in the same manner as in Example 1 except that no microfiber was added.

(Comparative Example 2)
A holding pad was prepared in the same manner as in Example 3 except that the addition amount of microfibrous cellulose was 15% by mass.

(Comparative Example 3)
A holding pad was prepared in the same manner as in Example 3 except that microfibrillar cellulose having a fiber diameter of 3 nm and an aspect ratio of 5 was used as the cellulose microfiber.

  5-2. About the holding pad of each Example and a comparative example, the abrasion loss, the compression elastic modulus, the breaking strength, the breaking elongation, and the tearing strength in the friction test of the polyurethane foam sheet were investigated, and the results shown in Table 1 were obtained.

(Abrasion test)
About each polyurethane foam sheet of each Example and a comparative example, the friction wear test was done on the following test conditions according to Japanese Industrial Standard (JIS K6902), and the amount of wear was compared. That is, the amount of wear after 500 revolutions on the polishing surface was measured when the polishing surface was brought into contact with a wear ring having abrasive paper adhered to the outer surface and rotated on the outer periphery. That is, the wear tester has a rotating disk on which a test sample is attached and which is pivotally supported so as to be able to rotate. Above the turntable, a pair of cylindrical wear wheels are arranged with their end faces facing each other. The outer peripheral surface of the wear wheel is disposed so as to be in contact with the test sample attached to the rotating disk. The wear wheels are arranged on both sides in the radial direction of the rotating disk so as to be equidistant from the rotation axis of the rotating disk. When measuring the amount of wear, a test sample cut into the same shape as the turntable is attached to the turntable. The wear ring with the abrasive paper is brought into contact with the upper surface of the test sample and pressed while applying a load. By rotating the turntable, a pair of wear wheels whose outer peripheral surfaces are in contact with the test sample rotate in opposite directions. Thereby, the test sample surface is worn. In this example, the change in weight of the test sample before and after rotating the turntable 500 times was defined as the amount of wear. The measurement results are shown with the wear amount of Comparative Example 1 being 1, and the wear amounts of other samples being expressed as a ratio value with respect to the wear amount of Comparative Example 1. That is, the smaller the value, the smaller the amount of wear and the better the wear resistance. The results are shown in Table 1.

Test conditions Taber abrasion tester: Mize tester No.502 Taber ablation tester Polishing speed (rotation speed): 70rpm
Weight: 250g
Wear wheel: inner diameter 15.88mm x outer diameter 50.0mm x thickness 13.0mm
Abrasive paper: # 1000 sandpaper

(Compressive modulus)
The compression elastic modulus is determined by using a shopper type thickness measuring instrument (product name No. 517 thickness measuring instrument digital (manufactured by Miz Tester Co., Ltd.); pressure surface: circular with a diameter of 1 cm), and Japanese Industrial Standard (JIS L 1021) Measured according to In this case, the thickness t0 after pressing for 30 seconds at the initial pressure was measured, and then the thickness t1 after standing for 5 minutes under the final pressure was measured. Except for all the loads, after being left for 5 minutes, the thickness t0 ′ after pressing for 30 seconds with the initial load again is measured. At this time, the initial pressure is 100 g / cm ² and the final pressure is 1120 g / cm ² . The compression elastic modulus is calculated by the following formula.

  Formula: Compression modulus (%) = (t0'-t1) / (t0-t1) * 100

(Breaking strength)
A polyurethane foam sheet is punched into a dumbbell shape (length: 90 mm, end width: 20 mm, sample width: 10 mm). The value at which the measured value reached the peak (cut) was obtained as the strength (maximum load). The number of n is 2, and the breaking strength is calculated from the breaking strength (kgf / mm ² ) = strong (maximum load) kgf / (thickness (mm) x sample width (10 mm)), and the breaking strength is calculated from the average value. did. The sample thickness was measured using a thickness meter when the measurement sample was mounted on a chuck, and calculated using a dimension table.

(Elongation at break)
The elongation of the polyurethane foam sheet is the elongation at break in the tensile measurement. The breaking strength and elongation at the time of tension were measured by a method according to Japanese Industrial Standard (JIS K 6550) with A & D Corporation, Tensilon Universal Testing Machine RTC.

(Tear strength)
A 70 mm cut is made from the end of the polyurethane foam sheet sample piece (100 mm × 25 mm) in the longitudinal direction, and two places at 25 mm along the cut from the end of the cut in the sample piece are clamped and fixed. The two specimens are pulled with the universal material testing machine Tensilon (A & D Tensilon type universal testing machine RTC-1210 Co., Ltd.) in the opposite direction along the notch (direction in which one of the two places is rotated 180 degrees with respect to the other). The measurement was performed until it broke, and the strength (maximum load) kgf at which the measured value reached its peak was determined. The tear strength was determined from tear strength (kgf / mm) = strong (maximum load) kgf / thickness (mm).

(Holding pad life measurement)
A holding pad was attached to a predetermined position of a polishing machine (trade name “SP-1200” manufactured by Speed Fem Co., Ltd.). Next, after spraying an appropriate amount of water onto the holding surface of the resin sheet provided in the holding pad and draining it appropriately, the glass substrate for liquid crystal display (470 mm x 370 mm x 0.5 mm) to be polished is adsorbed to the holding pad. I let you. Polishing was performed under the following conditions using Polypass FX-7M (trade name, manufactured by Fujibow Atago Co., Ltd.) as a polishing pad. Polishing is performed until the polishing is no longer possible when the object to be polished is detached from the holding pad or damaged, or when the surface of the holding pad is damaged, depending on the number of objects to be polished. Lifespan was evaluated. The maximum number of objects to be polished was 50.

Used polishing machine: Oscar polishing machine SP-1200 (trade name made by Speed Fem Co., Ltd.)
Polishing speed (rotation speed): 61rpm
Processing pressure: 76 gf / cm ²
Slurry: Show Rocks A-10 (trade name, manufactured by Showa Denko KK) 10% slurry Polishing time: 10 minutes / sheet

  As a result of the abrasion test, the abrasion resistance was improved in the examples as compared with the comparative example in which the fine fibers were not added. For this reason, in the example product, damage to the holding surface can be suppressed.

  As a result of investigating the compression elastic modulus, breaking strength, breaking elongation, and tearing strength, the strength was improved while maintaining the compression modulus and breaking elongation in the examples as compared with the comparative example in which no microfiber was added. From this, it is possible to prevent the resin part between adjacent foams from being plastically deformed and to lose cushioning properties by repeating compression / recovery in the example products, and to improve the flatness of the object to be polished. Can contribute.

  As a result of the life evaluation of the holding pad, in Comparative Examples 1 and 3, the holding surface was shaved at the edge of the object to be polished, and the object to be polished was displaced in the in-plane direction of the holding pad. Can no longer be used. On the other hand, in Examples 1 to 4, since the strength was improved, it was still usable without problems even after polishing 50 objects to be polished.

ADVANTAGE OF THE INVENTION According to this invention, durability of a polyurethane foam sheet can be improved and pad usable time can be improved, ensuring the cushioning property by a holding pad in a holding pad.

Claims (3)

A holding pad having a polyurethane foam sheet having a holding surface for holding an object to be polished and having foam formed on the inner side of the holding surface and communicating with the holding surface;
A holding pad, wherein the polyurethane foam sheet contains 0.1 to 10% by mass of microfibers based on the total mass of the polyurethane foam sheet.   The holding pad according to claim 1, wherein the microfiber has a fiber diameter of 1 to 1000 nm and an aspect ratio of 10 to 10,000.   The holding pad according to claim 1, wherein the microfiber is a microfiber obtained from a polysaccharide.