WO2014125797A1

WO2014125797A1 - Rigid sheet and process for manufacturing rigid sheet

Info

Publication number: WO2014125797A1
Application number: PCT/JP2014/000616
Authority: WO
Inventors: 目黒　将司; 励永山; 高岡　信夫; 林　浩一
Original assignee: 株式会社クラレ
Priority date: 2013-02-12
Filing date: 2014-02-05
Publication date: 2014-08-21
Also published as: TW201440956A; JP6220378B2; EP2957672B1; KR102136441B1; CN105008614B; TWI607832B; JPWO2014125797A1; EP2957672A1; EP2957672A4; KR20150116876A; CN105008614A; US20160002835A1

Abstract

A rigid sheet which comprises both a nonwoven fabric made of ultrafine fibers and a polymeric elastomer applied to the nonwoven fabric, exhibiting a JIS-D hardness of 45 or more, an R% of 0 to 20%, and a total content of ions causing a change in the pH of water of 400μg/cm³ or less. The R% is calculated from six D hardness values according to the formula: R(%) = (maximum D hardness value - minimum D hardness value)/average D hardness value × 100. The six D hardness values are determined by: dividing the thicknesswise cross section of the sheet equally into three layers; taking the layers as a first surface layer, an intermediate layer and a second surface layer respectively from one surface side of the sheet; and measuring JIS-D hardness at three arbitrary points in each of the first surface and intermediate layers.

Description

Hard sheet and method for manufacturing hard sheet

The present invention relates to a polishing pad, and more particularly to a hard sheet preferably used as a polishing layer of a polishing pad for polishing a semiconductor wafer, a semiconductor device, a silicon wafer, a hard disk, a glass substrate, an optical product, or various metals.

An integrated circuit formed on a semiconductor wafer is highly integrated and multi-layered. Such a semiconductor wafer is required to have high flatness.

Chemical mechanical polishing (CMP) is known as a polishing method for polishing a semiconductor wafer. CMP is a method of polishing a surface of a substrate to be polished with a polishing pad while dropping a polishing slurry containing abrasive grains (hereinafter also simply referred to as slurry).

The following Patent Documents 1 to 4 disclose a polishing pad made of a polymer foam having an independent foam structure used for CMP. The polymer foam is produced by casting and foaming a two-component curable polyurethane. A polishing pad manufactured from a polymer foam has higher rigidity than a non-woven fabric type polishing pad described later. Therefore, it is preferably used for polishing a semiconductor wafer that requires high flatness.

Polishing pad made of polymer foam has high rigidity. Therefore, a load is selectively applied to the convex portion of the substrate to be polished. As a result, a relatively high polishing rate can be obtained. However, when agglomerated abrasive grains are present on the polishing surface, a load is selectively applied to the agglomerated abrasive grains. Therefore, scratches were likely to occur on the polished surface. In particular, when polishing a substrate having copper wiring or a low dielectric constant material having weak interface adhesion, scratches and interface peeling are likely to occur (see, for example, Non-Patent Document 1). In cast foam molding, the polymer elastic body tends to foam inhomogeneously, so that the flatness of the substrate to be polished and the polishing rate at the time of polishing tend to be inhomogeneous. Further, the abrasive rate gradually decreases due to the clogging of abrasive grains and polishing scraps in the independent holes of the polymer foam.

The following Patent Documents 5 to 14 disclose a nonwoven fabric type polishing pad obtained by impregnating a nonwoven fabric with wet-coagulated porous polyurethane. Since the nonwoven fabric type polishing pad is excellent in flexibility, the polishing pad is easily deformed. For this reason, since it is difficult for the load to be selectively applied to the abrasive grains agglomerated on the polished surface, scratches are hardly generated. However, since the non-woven polishing pad is flexible, the polishing rate is low. Moreover, since the nonwoven fabric type polishing pad deforms following the surface shape of the substrate to be polished, the flattening performance, which is a property of flattening the substrate to be polished, was low.

Further, Patent Documents 15 to 18 below disclose polishing pads having a high leveling performance including a nonwoven fabric of ultrafine fibers. For example, Patent Document 15 discloses a polishing pad made of a sheet-like material obtained by impregnating a non-woven fabric obtained by entanglement of polyester microfiber bundles having an average fineness of 0.0001 to 0.01 dtex with a polymer elastic body mainly composed of polyurethane. Is disclosed. This document discloses that such a polishing pad achieves a polishing process with higher accuracy than before.

For a polishing pad using a general ultrafine fiber nonwoven fabric, a nonwoven fabric obtained by needle punching a short ultrafine fiber has been widely used. Such a nonwoven fabric has a low apparent density and a high porosity, and thus has a low rigidity. For this reason, the flattening performance is low because of deformation following the surface shape of the polished surface.

Patent Document 19 includes a fiber entangled body formed from a fiber bundle of ultrafine single fibers and a polymer elastic body, and a part of the polymer elastic body exists inside the fiber bundle, Disclosed is a polishing pad that is focused and has a volume fraction in the range of 55-95% excluding voids.

Patent Document 20 discloses that a polishing pad having a polishing layer and an underlayer includes an intermediate layer having a water absorption of 1% or less between the polishing layer and the underlayer. A polishing pad having a D hardness difference of 20 or less is disclosed.

JP 2000-178374 A Japanese Patent Laid-Open No. 2000-248034 JP 2001-89548 A Japanese Patent Laid-Open No. 11-322878 JP 2002-9026 A Japanese Patent Laid-Open No. 11-99479 Japanese Patent Laid-Open No. 2005-212055 JP-A-3-234475 JP-A-10-128674 JP 2004-311731 A JP-A-10-225864 JP 2005-518286 JP 2003-201676 A JP 2005-334997 A JP 2007-54910 A JP 2003-170347 A JP 2004-130395 A JP 2002-172555 A JP 2008-207323 A JP 2011-200904 A

A polishing pad having a high polishing rate and having a polishing rate that hardly changes over time is provided.

One aspect of the present invention is a hard sheet including a non-woven fabric of ultrafine fibers having a fineness of 0.0001 to 0.5 dtex, and a polymer elastic body imparted to the non-woven fabric, and has a JIS-D hardness of 45 or more. Yes, in the cross section in the thickness direction, when each layer is equally divided into three, the first surface layer, the middle layer, and the second surface layer in order from either surface side, the JIS-D hardness of the first surface layer and the middle layer Are measured at three arbitrary points at a total of 6 points, and using the D hardness of 6 points in total, the following formula:
R% calculated from R (%) = (D hardness maximum value−D hardness minimum value) / D hardness average value × 100, and R% is 0 to 20%, and the total number of ions causing pH change of water It is a hard sheet having a content of 400 μg / cm ³ or less.

Further, another aspect of the present invention is a polishing pad comprising the hard sheet as a polishing layer.

In addition, another aspect of the present invention is (1) an ultrafine fiber generation type capable of forming a non-woven fabric having an apparent density of 0.35 g / cm ³ or more of ultrafine fibers having a fineness of 0.5 dtex or less by ultrafine fiberization treatment. A step of preparing a fiber entangled sheet of long fibers of fiber, and (2) impregnating the fiber entangled sheet with a first emulsion containing a gelling agent containing an ion that causes a pH change of water and a polymer elastic body. Then, the first emulsion is gelled, and the polymer elastic body is solidified by heating and drying, and (3) the ultrafine fiber-generating fiber is treated with ultrafine fiber to increase the non-woven fabric. A step of forming a first complex containing a molecular elastic body; and (4) impregnating the first complex with a second emulsion containing a gelling agent and a polymer elastic body, and further drying by heating. High polymer elasticity When the respective layers when uniformly divided into three in the thickness direction are the first surface layer, the middle layer and the second surface layer in order from any one of the surface sides, the porosity of the first surface layer and the middle layer A step of forming a second composite having a difference of 5% or less; and (5) a hard sheet is obtained by washing the second composite with water so that the total ion content is 400 μg / cm ³ or less. And (6) a step of hot pressing at least one selected from the first composite, the second composite, and the hard sheet in order to set the surface hardness of the hard sheet to JIS-D hardness 45 or more. .

A hard sheet for obtaining a polishing pad having a high polishing rate and the polishing rate hardly changing with time can be obtained.

FIG. 1 is a schematic cross-sectional view of an embodiment of a hard sheet.

An embodiment of the hard sheet according to the present invention will be described in detail below. FIG. 1 is a schematic cross-sectional view of a hard sheet 10 of the present embodiment. FIG. 1 also shows an enlarged schematic view of a part of the region surrounded by a circle.

As shown in FIG. 1, the hard sheet 10 is a hard sheet that includes a nonwoven fabric 1 that is an entangled body of ultrafine fibers 1 a and a polymer elastic body 2 that is imparted to the nonwoven fabric 1. The hard sheet 10 has a JIS-D hardness of 45 or more, and when each layer is divided into three equally in the thickness direction, the first surface layer 3, the middle layer 4 and the second surface layer 5 are sequentially formed from the surface side. (1) JIS-D hardness of the surface layer 3 and the middle layer 4 is measured at three points each at arbitrary points for a total of 6 points, and the following formula is used by using the D hardness of 6 points in total:
R% calculated from R (%) = (D hardness maximum value in 6 points−D hardness value in 6 points) / 6 D hardness average value of 6 points × 100 is 0 to 20%. Preferably, the JIS-D hardness of the second surface layer 5 and the middle layer 4 is measured at three arbitrary points at a total of 6 points, and the R% calculated from the above formula using the total 6 points of D hardness is also given. 0 to 20%. And it is a hard sheet | seat whose total content of the ion which causes the pH change of water is 400 microgram / cm < ³ > or less.

In the hard sheet 10, the ultrafine fibers 1a forming the nonwoven fabric 1 form a fiber bundle 1b in which a plurality of ultrafine fibers 1a are bundled. Further, the plurality of fiber bundles 1 b are bound by a polymer elastic body 2. Preferably, more than half of the plurality of fiber bundles 1 b are bound by the polymer elastic body 2. Further, the ultrafine fibers 1 a forming the fiber bundle 1 b are also bound by the polymer elastic body 2. Preferably, more than half of the ultrafine fibers 1 a are bound by the polymer elastic body 2. A composite of a nonwoven fabric and a polymer elastic body including such a nonwoven fabric 1 and a polymer elastic body 2 is a dense hard sheet 10 having a small amount of voids and a high hardness. Such a hard sheet 10 has high rigidity because of the reinforcing effect of the fiber bundle 1b and the high filling rate (that is, low porosity) of the hard sheet.

The hard sheet 10 contains a nonwoven fabric 1 of ultrafine fibers forming a fiber bundle. The fiber bundle in the non-woven fabric existing on the surface is split or fibrillated during polishing. As a result, ultrafine fibers having a high fiber density are exposed on the polished surface. The exposed ultrafine fibers are in contact with the substrate to be polished over a large area and can hold a large amount of slurry. Further, the exposed ultrafine fibers suppress a load from being selectively applied to the aggregate of abrasive grains in order to make the surface of the polishing pad soft. As a result, the occurrence of scratches is suppressed.

Further, the hard sheet 10 has a JIS-D hardness of 45 or more, and the JIS-D hardness of the first surface layer 3 and the middle layer 2 is measured at a total of 6 points, respectively, for a total of 6 points. Following formula:
R (%) = (D hardness maximum value−D hardness minimum value) / D hardness average value × 100, adjusted so that the R% calculated from R is 0 to 20% and is uniform in the thickness direction. ing. Preferably, the JIS-D hardness of each of the second surface layer 5 and the middle layer 2 is measured at a total of 6 points for a total of 6 points, and the calculated R% is also 0 to 20% using the total D hardness of 6 points. Thus, it is preferable to adjust so that it may become uniform in the thickness direction. Thus, by adjusting the hardness to be uniform, uniform polishing becomes possible.

The hard sheet 10 is adjusted so that the total content of ions that cause the pH change of water is 400 μg / cm ³ or less. Generally, a gelling agent is used in order to uniformly apply the polymer elastic body in the thickness direction as described above. The ions contained in the hard sheet may change the pH of the slurry during polishing. When the pH of the slurry changes, the polishing rate is lowered or the abrasive grains are easily aggregated. In such a case, the reduction of the polishing rate caused by the change in pH of the slurry can be suppressed by reducing the ionic compound contained in the hard sheet by washing with water or the like. The ions that cause the pH change of water are all ions that change the pH when dissolved in water.

As will be described in detail later, the hard sheet of the present embodiment is produced by impregnating a dense nonwoven fabric of ultrafine fibers with a polymer elastic body at a high content uniformly in the thickness direction. In the production of such a hard sheet, it is preferable to use an emulsion of a polymer elastic body containing a gelling agent in order to impregnate the nonwoven fabric with a high content of the polymer elastic body. And in the manufacturing process of a hard sheet, it can manufacture by washing with water so that the total content of the ion which causes the pH change of the water contained in a gelatinizer may be 400 microgram / cm < ³ > or less.

Hereinafter, each element of the hard sheet of the present embodiment will be described in more detail.

The nonwoven fabric in the present embodiment is formed from ultrafine fibers, and the ultrafine fibers preferably form a fiber bundle.

The ultrafine fiber has a fineness of 0.0001 to 0.5 dtex, preferably 0.001 to 0.01 dtex. When the fineness of the ultrafine fibers is less than 0.0001 dtex, the ultrafine fibers in the vicinity of the surface are hardly sufficiently separated during polishing, and as a result, the slurry holding amount decreases. When the fineness of the ultrafine fiber exceeds 0.5 dtex, the polishing rate is lowered due to the surface becoming too rough, and the abrasive grains easily aggregate on the surface of the ultrafine fiber.

It is preferable that the ultrafine fiber is a long fiber (filament), specifically, the average fiber length is 100 mm or more, and more preferably 200 mm or more. The upper limit of the average fiber length is not particularly limited, but may include, for example, fibers having a length of several meters, several hundreds of meters, several kilometers, or more as long as it is not cut in the entanglement step described later. The ultrafine fiber long fibers increase the rigidity of the hard sheet by increasing the fiber density. Further, long fibers are difficult to fall off during polishing. In addition, the short fiber of an ultrafine fiber is hard to raise fiber density, and a rigid sheet with high rigidity cannot be obtained. Moreover, short fibers are easy to fall off during polishing.

The ultrafine fibers forming the nonwoven fabric are preferably a bundle of a plurality of ultrafine fibers forming a fiber bundle. The average cross-sectional area of the fiber bundles present in the cross section in the thickness direction is preferably 80 μm ² or more, more preferably 100 μm ² or more, and particularly preferably 120 μm ² or more from the viewpoint of obtaining a hard sheet having particularly high rigidity.

Moreover, it is preferable that the fiber bundle which exists in the cross section of the thickness direction is 25% or more of fiber bundles which have a cross-sectional area of 40 μm ² or more with respect to the total number of fiber bundles of the cross section in the predetermined thickness direction. When used for polishing pads for silicon wafers, semiconductor wafers, and semiconductor devices that require particularly high flatness, fiber bundles having a cross-sectional area of 40 μm ² or more are 40% or more, and further 50% or more. In particular, 100% is preferable. When the proportion of fiber bundles of 40 μm ² or more is too low, the polishing rate tends to decrease or the planarization performance tends to be low.

In the hard sheet of the present embodiment, the bundle density of the fiber bundle per unit area of the cross section in the thickness direction is 600 bundles / mm ² or more, further 1000 bundles / mm ² or more, and 4000 bundles / mm ² or less. Furthermore, it is preferably 3000 bundles / mm ² or less. In the case of such a bundle density, the fiber bundle on the surface is split or fibrillated at the time of polishing to form many ultrafine fibers and improve the amount of slurry retained. Further, when the fiber bundle is split or fibrillated, the surface of the polished surface becomes soft and the generation of scratches is suppressed. When the bundle density is too low, the fiber density of the ultrafine fibers formed on the surface tends to be low, and the polishing rate tends to decrease or the flattening performance tends to decrease. In addition, when the density of the fiber bundle is too high, the amount of slurry retained and the polishing rate tend to decrease due to the surface becoming too dense. In addition, in the hard sheet | seat of this embodiment, it is preferable from the point from which polishing stability becomes high that there are few density spots of a fiber bundle in a thickness direction and a surface direction.

The ultrafine fibers are preferably formed from a thermoplastic resin having a glass transition temperature (T _g ) of 50 ° C. or higher, more preferably 60 ° C. or higher. If the T _g of the thermoplastic resin is too low, the time of polishing, rigid planarization performance is reduced insufficient, also, over time the rigidity is lowered polishing stability and polishing uniformity decreases Tend. The upper limit of T _g is not particularly limited, but is preferably 300 ° C., and more preferably 150 ° C. for industrial production. Incidentally, since the the water state in the polishing process, T _g is that after processing the of 50 ° C. Hot water, T _g, as measured in the wet state is 50 ° C. or higher, more preferably. The water absorption of the thermoplastic resin is preferably 4% by mass or less, and more preferably 2% by mass or less. When the water absorption rate exceeds 4% by mass, the rigidity decreases with time by gradually absorbing the water in the slurry during polishing. In such a case, the planarization performance is likely to deteriorate with time, and the polishing rate and polishing uniformity are likely to fluctuate. The water absorption is preferably 0 to 2% by mass.

Specific examples of the thermoplastic resin include, for example, polyethylene terephthalate (PET, T _g 77 ° C., water absorption 1% by mass), isophthalic acid-modified polyethylene terephthalate (T _g 67-77 ° C., water absorption 1% by mass), sulfoisophthalate. acid-modified polyethylene terephthalate (T _g 67 ~ 77 ℃, water absorption 1 to 4 mass%), polybutylene naphthalate (T _g 85 ° C., water absorption 1 wt%), polyethylene naphthalate (T _g 124 ° C., water absorption 1 They include terephthalic acid, nonanediol and methyl octanediol copolymer nylon (T _g 125 ~ 140 ℃, water absorption 1-4 wt%) semi-aromatic polyamide resins such as is; mass%) aromatic polyester resin such as It is done. These may be used alone or in combination of two or more. Among these, polyethylene terephthalate (PET), isophthalic acid-modified polyethylene terephthalate, polybutylene naphthalate, and polyethylene naphthalate are preferable because they can sufficiently maintain rigidity, water resistance, and abrasion resistance. In particular, modified PET, such as PET and isophthalic acid-modified PET, has a dense and high-density fiber entanglement in order to greatly crimp in a wet heat treatment process for forming ultrafine fibers from a web-entangled sheet of sea-island type composite fibers described later. It is preferable from the viewpoints of being able to form a coalescence, easily increasing the rigidity of the hard sheet, and being less likely to change with time due to moisture during polishing.

In addition, as long as the effects of the present invention are not impaired, ultrafine fibers made of other thermoplastic resins may be included as necessary. Examples of such thermoplastic resins include polylactic acid, polybutylene terephthalate, polyhexamethylene terephthalate, polyethylene succinate, polybutylene succinate, polybutylene succinate adipate, and polyhydroxybutyrate-polyhydroxyvalylate copolymer. Aromatic polyesters and aliphatic polyesters and copolymers thereof; aliphatic nylons such as nylon 6, nylon 66, nylon 10, nylon 11 and nylon 12, and copolymers thereof; polyolefins such as polyethylene and polypropylene; 25 ethylene units Modified polyvinyl alcohol containing 70 mol%; elastomers such as polyurethane elastomers, nylon elastomers, polyester elastomers, etc. may be used in combination.

The hard sheet contains a polymer elastic body applied to a nonwoven fabric of ultrafine fibers.

Specific examples of the polymer elastic body include, for example, polyurethane, polyamide-based elastic body, (meth) acrylic ester-based elastic body, (meth) acrylic ester-styrene-based elastic body, (meth) acrylic ester-acrylonitrile-based Elastic body, (meth) acrylic ester-olefin elastic body, (meth) acrylic ester- (hydrogenated) isoprene elastic body, (meth) acrylic ester-butadiene elastic body, styrene-butadiene elastic body Styrene-hydrogenated isoprene elastic body, acrylonitrile-butadiene elastic body, acrylonitrile-butadiene-styrene elastic body, vinyl acetate elastic body, (meth) acrylate ester-vinyl acetate elastic body, ethylene-vinyl acetate system Elastic bodies, ethylene-olefin elastic bodies, silicone elastic bodies, System elastic body, and, a polyester-based elastic material or the like.

The polymer elastic body is preferably non-porous. In addition, the non-porous form means that it does not substantially have voids (closed cells) that a porous or sponge-like polymer elastic body has. For example, it means that it is not a polymer elastic body having many closed cells, which is obtained by coagulating solvent-based polyurethane.

When the polymer elastic body is non-porous, high polishing stability is obtained, it is difficult to wear, and slurry waste and pad waste are less likely to remain in the voids. Therefore, a high polishing rate can be maintained for a long time. Moreover, since the adhesiveness to the ultrafine fibers is high, the fibers are less likely to come off. Furthermore, since high rigidity is obtained, the planarization performance is excellent.

The water absorption of the polymer elastic body is preferably 0.5 to 8% by mass, more preferably 1 to 6% by mass. When the water absorption rate of the polymer elastic body is too low, the wettability with respect to the slurry is lowered. As a result, the polishing rate, polishing uniformity, and polishing stability tend to decrease, and the abrasive grains tend to aggregate. When the water absorption of the polymer elastic body is too high, the rigidity of the hard sheet decreases with time during polishing, and the planarization performance decreases. Also, the polishing rate and polishing uniformity are likely to fluctuate. The water absorption rate of the polymer elastic body is the water absorption rate when the dried polymer elastic body film is immersed in water at room temperature and saturated and swollen. In addition, when it contains two or more kinds of polymer elastic bodies, it is theoretically calculated as the sum of values obtained by multiplying the water absorption of each polymer elastic body by the mass fraction.

The water absorption of the polymer elastic body can be adjusted by introducing a hydrophilic functional group or adjusting the degree of crosslinking. Examples of the hydrophilic functional group include a carboxyl group, a sulfonic acid group, and a polyalkylene glycol group having 3 or less carbon atoms. The hydrophilic group can be introduced by copolymerizing a monomer having a hydrophilic group. The copolymerization ratio of the monomer unit having a hydrophilic group is preferably 0.1 to 20% by mass, and more preferably 0.5 to 10% by mass.

The polymer elastic body preferably has a storage elastic modulus [E ′ (150 ° C., dry)] at 150 ° C. of 0.1 to 100 MPa, more preferably 1 to 80 MPa. The storage elastic modulus of the polymer elastic body can be adjusted by adjusting the degree of crosslinking. When two or more kinds of polymer elastic bodies are contained, it is theoretically calculated as the sum of the values obtained by multiplying [E ′ (150 ° C., dry)] of each polymer elastic body by the mass fraction. .

The polymer elastic body may be used alone or in combination of two or more. Among these, polyurethane is preferable from the viewpoint of excellent binding properties to ultrafine fibers.

The ultrafine fibers forming the fiber bundle are preferably bundled with a polymer elastic body, and more than half of the ultrafine fibers are preferably bundled with a polymer elastic body.
In addition, a plurality of fiber bundles are bound by a polymer elastic body existing outside the fiber bundle, and more than half of the fiber bundles are bound by a polymer elastic body to form a bulk shape. It is preferable that it exists in. By binding the fiber bundles, the form stability of the hard sheet is improved and the polishing stability is improved. A hard sheet having a uniform high hardness can be obtained by bundling ultrafine fibers with a polymer elastic body or binding fiber bundles together.

When the ultrafine fibers forming the fiber bundle are not converged, the ultrafine fibers are flexible, so that it is difficult to obtain high planarization performance. In addition, the ultrafine fibers are easily removed during polishing, and the abrasive grains are aggregated on the removed fibers to easily generate scratches. The fact that the ultrafine fibers are focused by the polymer elastic body means that the ultrafine fibers existing inside the fiber bundle are bonded and restrained by the polymer elastic body existing inside the fiber bundle.

The ratio of the nonwoven fabric to the polymer elastic body (nonwoven fabric / polymer elastic body) in the hard sheet is preferably 90/10 to 55/45, more preferably 85/15 to 65/35, in mass ratio. When the ratio of the nonwoven fabric to the polymer elastic body is within the above range, the rigidity of the hard sheet can be easily increased. Moreover, the density of the ultrafine fibers exposed on the surface of the hard sheet can be sufficiently increased. As a result, polishing stability, polishing rate, and planarization performance can be sufficiently enhanced.

The apparent density of the hard sheet is preferably 0.5 to 1.2 g / cm ³ , and more preferably 0.6 to 1.2 g / cm ³ from the viewpoint of maintaining high rigidity.

The hard sheet of the present embodiment has a JIS-D hardness of 45 or more, and in the cross section in the thickness direction, each layer is divided into three equal parts, and the first surface layer, middle layer, In the case of the surface layer, the JIS-D hardness of the first surface layer and the middle layer was measured at three points each at arbitrary points for a total of 6 points, and the following formula: R (%) = (D R% calculated from (hardness maximum value−D hardness minimum value) / 6 average value of D hardness at 6 points × 100 is 0 to 20%. Preferably, the JIS-D hardness of the second surface layer and the middle layer is measured at three arbitrary points at a total of 6 points, and the R% calculated from the above formula using the total 6 points of D hardness is also 0 to 20%.

The JIS-D hardness of the hard sheet is 45 or more, preferably 45 to 75, more preferably 50 to 70. By adjusting the hardness of the first surface layer to 45 or more in JIS-D hardness, high planarization performance can be obtained. If the JIS-D hardness is too high, scratches are likely to occur. Note that the hard sheet of the present embodiment has a soft surface despite being hard in order to expose ultrafine fibers with a high fiber density on the surface. Therefore, it is difficult for scratches to occur.

The JIS-D hardness of the first surface layer and the middle layer of the hard sheet is measured at 6 points in total at 6 points in total, and the R% calculated from the above formula using the 6 points of D hardness is 0 to 20%, preferably 0 to 15%. When the R% of the first surface layer and the intermediate layer is in such a range, when used as a polishing pad, the change in the polishing rate in the first surface layer and the intermediate layer is reduced, and stable polishing performance is obtained. When R% exceeds 20%, a change in the polishing rate becomes large during polishing, and stable polishing performance cannot be obtained. In addition, the arbitrary point for measuring JIS-D hardness is arbitrary at which point of the layer, and R% is 0 to 20% regardless of where it is measured. Means. In such a case, since there is no deviation in hardness not only in the thickness direction but also in the width direction, the polishing rate is uniform in the planar direction, and thus stable polishing performance can be obtained. Similarly, the JIS-D hardness of the second surface layer and the middle layer of the hard sheet is measured at three arbitrary points at a total of 6 points, and using the total 6 points of D hardness, R% calculated from the above formula is It is preferably 0 to 20%, more preferably 0 to 15%.

In the hard sheet of this embodiment, the total content of ions that cause the pH change of water is 400 μg / cm ³ or less. As will be described later, the hard sheet of the present embodiment is obtained by, for example, impregnating a nonwoven fabric with an emulsion of a polymer elastic body, and then heating and drying the polymer elastic body to solidify the polymer elastic body in the nonwoven fabric. Is manufactured. In such a process, moisture in the emulsion impregnated in the nonwoven fabric is dried from the surface. For this reason, as the water evaporates, the emulsion in the nonwoven fabric undergoes migration that moves to the surface layer. When migration occurs, the polymer elastic body is unevenly distributed in the vicinity of the surface layer of the nonwoven fabric, the polymer elastic body in the vicinity of the middle layer is reduced, and voids are likely to remain in the vicinity of the middle layer. Such migration is suppressed by adding a gelling agent to the emulsion and gelling the emulsion before drying. The inventors of the present invention are to reduce the polishing rate during polishing when a predetermined amount or more of ions that cause pH change of water contained in the obtained gelling agent remain in the hard sheet. I found it.

The total content of ions that cause a change in the pH of water contained in the hard sheet is 400 μg / cm ³ or less, preferably 350 μg / cm ³ , more preferably 100 μg / cm ³ or less. The total content of ions is preferably a 0 Pg / cm ^3, from an industrial washing efficiency, 1 ~ 100μg / cm ^3, more is preferably about 10 ~ 50μg / cm ^3. When the total content of ions that cause the pH change of water contained in the hard sheet exceeds 400 μg / cm ³ , the slurry undergoes a pH change, the polishing rate decreases, and the abrasive grains tend to aggregate. Become.

The ions that cause the pH change of water are all ions that change the pH when dissolved in water. Specifically, for example, sulfate ions contained in a general gelling agent, Nitrate ions, carbonate ions, ammonium ions, sodium ions, calcium ions, potassium ions, and the like.

[Production method of polishing pad]
Next, an example of a manufacturing method of a hard sheet will be described in detail. A hard sheet | seat can be manufactured through the following processes, for example.

(1) Step of preparing a fiber entangled sheet of long fibers of ultrafine fiber generating fibers In this step, a fiber entangled sheet of long fibers of ultrafine fiber generating fibers is prepared. The fiber entangled sheet of ultrafine fiber-generating fibers can be produced, for example, as follows.

First, a long fiber web made of sea-island composite fibers having a water-soluble thermoplastic resin as a sea component and a water-insoluble thermoplastic resin as an island component is manufactured. The sea-island type composite fiber is an ultra-fine fiber generating fiber that generates an ultra-fine fiber made of an island component resin by dissolving a sea component. In this embodiment, an example of using a sea-island composite fiber as an ultra-fine fiber generating fiber will be described. However, a known ultra-fine fiber generating fiber such as a multilayer laminated cross-section fiber is used instead of a sea-island composite fiber. Also good.

The water-soluble thermoplastic resin is a thermoplastic resin that can be dissolved or removed by water, an alkaline aqueous solution, an acidic aqueous solution, or the like, and a resin that can be melt-spun. Specific examples of the water-soluble thermoplastic resin include, for example, PVA resins such as polyvinyl alcohol (PVA) and PVA copolymer; modified polyester containing polyethylene glycol and / or alkali metal sulfonate as a copolymer component; Examples thereof include ethylene oxide. Of these, PVA resins are preferably used.

When the PVA-based resin is dissolved from the sea-island type composite fiber containing the PVA-based resin as the sea component, the ultrafine fiber that is the island component is greatly crimped. As a result, a nonwoven fabric with a high fiber density is obtained. In addition, when PVA resin is dissolved from sea-island type composite fiber containing PVA resin, physical properties of ultrafine fiber and polymer elastic body are deteriorated because ultrafine fiber and polymer elastic body that are island components do not decompose or dissolve. Is unlikely to occur.

As the PVA-based resin, ethylene-modified PVA containing 4 to 15 mol%, more preferably 6 to 13 mol% of ethylene units is preferably used from the viewpoint of improving the physical properties of the sea-island composite fibers.

The viscosity average degree of polymerization of the PVA resin is preferably in the range of 200 to 500, more preferably 230 to 470, and particularly preferably 250 to 450. The melting point of the PVA resin is 160 to 250 ° C., more preferably 175 to 224 ° C., particularly 180 to 220 ° C., and excellent mechanical properties and thermal stability, and melt spinnability. From the point which is excellent in it.

As the water-insoluble thermoplastic resin that forms the island component, a thermoplastic resin that is not dissolved or removed by water, an alkaline aqueous solution, an acidic aqueous solution, or the like and that can be melt-spun is used. Specific examples of the water-insoluble thermoplastic resin include the above-described various resins that form ultrafine fibers, preferably the thermoplastic resin having a Tg of 50 ° C. or more and a water absorption of 4% by mass or less.

Non-water-soluble thermoplastic resins include, for example, catalysts, anti-coloring agents, heat-resistant agents, flame retardants, lubricants, antifouling agents, fluorescent whitening agents, matting agents, coloring agents, gloss improvers, antistatic agents, You may contain additives, such as a fragrance | flavor, a deodorant, an antibacterial agent, an acaricide, and inorganic fine particles.

Sea-island type composite fibers can be produced by using a composite spinning method in which a water-soluble thermoplastic resin and a water-insoluble thermoplastic resin having low compatibility with the water-soluble thermoplastic resin are melt-spun and then combined. The sea-island type composite fiber is preferably formed into a web as a long fiber.

A long-fiber web of sea-island type composite fibers can be obtained, for example, by melt-spinning a water-soluble thermoplastic resin and a water-insoluble thermoplastic resin by a spunbond method, then compounding, and stretching and depositing. It is done. In addition, a long fiber is a continuous fiber manufactured without passing through a cutting process like manufacturing a short fiber. An example of a method for producing a long-fiber web of sea-island type composite fibers will be described in detail below.

First, a water-soluble thermoplastic resin and a water-insoluble thermoplastic resin are melt-kneaded with separate extruders, and molten resin strands are simultaneously discharged from different spinnerets. Then, after the discharged strands are combined with the composite nozzle, the sea-island type composite fibers are formed by discharging from the nozzle holes of the spinning head.

The mass ratio of the water-soluble thermoplastic resin to the water-insoluble thermoplastic resin in the sea-island composite fiber is not particularly limited, but is 5/95 to 50/50, more preferably 10/90 to 40/60. preferable. When the mass ratio between the water-soluble thermoplastic resin and the water-insoluble thermoplastic resin is within such a range, a high-density nonwoven fabric is obtained, which is preferable from the viewpoint of excellent formability of ultrafine fibers. In the melt composite spinning, the number of islands in the sea-island type composite fiber is preferably 4 to 4000 islands / fiber, more preferably 10 to 1000 islands / fiber. The fineness of the sea-island type composite fiber is not particularly limited, but is preferably about 0.5 to 3 dtex from the viewpoint of industrial properties.

After the sea-island type composite fiber is cooled by a cooling device, it is drawn by a high-speed air flow at a speed corresponding to a take-up speed of 1000 to 6000 m / min so as to obtain a desired fineness using a suction device such as an air jet nozzle. . Thereafter, a stretched composite fiber is deposited on a movable collection surface to form a long fiber web. At this time, the deposited long fiber web may be partially crimped as necessary.

Next, several webs are stacked and intertwined. The web entanglement process can be performed using a needle punch or a high-pressure water flow process. As a representative example, the entanglement process by the needle punch will be described in detail.

First, a silicone-based oil agent or a mineral oil-based oil agent such as a needle breakage preventing oil agent, an antistatic oil agent, or an entanglement improving oil agent is applied to the web. And a web is entangled with a needle punch. The basis weight of the entangled web is preferably in the range of 100 to 1500 g / m ² from the viewpoint of excellent handleability.

Next, the fiber density is increased by shrinking the entangled long fiber web. By contracting the long-fiber web, the web can be greatly contracted as compared with the case of contracting the short-fiber web. The shrinkage treatment is preferably performed by wet heat shrinkage treatment such as steam heating. Examples of the steam heating conditions include conditions in which the heat treatment is performed for 60 to 600 seconds at an ambient temperature of 60 to 130 ° C. and a relative humidity of 75% or more, and further a relative humidity of 90% or more.

In the wet heat shrinkage treatment, it is preferable to shrink the entangled long fiber web so that the area shrinkage rate is 35% or more, and further 40% or more. By shrinking at such a high shrinkage rate, the fiber density becomes extremely high. The upper limit of the area shrinkage rate is preferably about 80% or less from the viewpoint of shrinkage limit and processing efficiency. The area shrinkage rate (%) is calculated by the following formula.
(Area of entangled web before shrinking process−area of entangled web after shrinking process) / area of entangled web before shrinking process × 100

In this way, the entangled web that has been subjected to the wet heat shrinkage treatment may be further increased in fiber density by heating rolls or hot pressing. As a change in the basis weight of the entangled web before and after the wet heat shrinkage treatment, the basis weight after the shrinkage treatment is 1.2 times (mass ratio) or more compared to the basis weight before the shrinkage treatment. It is preferably 5 times or more, 4 times or less, and more preferably 3 times or less. In this way, a long fiber web of sea-island type composite fibers (hereinafter referred to as a fiber entangled sheet) is obtained.

Such a fiber entangled sheet is converted into a non-woven fabric having an apparent density of 0.35 to 0.90 g / cm ³ by making the sea-island type composite fiber ultrafine.

The entangled web containing long fibers shrinks greatly by wet heat due to the formation of ultrafine fibers compared to the entangled web containing short fibers. Therefore, the fiber density of the ultrafine fibers becomes denser. And the nonwoven fabric containing the fiber bundle of an ultrafine fiber is formed by selectively removing the water-soluble thermoplastic resin of a sea-island type composite fiber. At this time, voids are formed in the portion where the water-soluble thermoplastic resin is dissolved and extracted. By imparting high polymer elasticity to the voids so as to have a high content, the ultrafine fibers constituting the fiber bundle are focused and the fiber bundles are bound together. In this way, a hard sheet having high fiber density, low porosity, and high rigidity can be obtained.

(2) The fiber entangled sheet is impregnated with a first emulsion containing a gelling agent containing an ion that causes a pH change of water and a polymer elastic body, and then the first emulsion is gelled. The process of solidifying the polymer elastic body by heating and drying

In this step, the fiber entangled sheet is uniformly filled with a polymer elastic body in the thickness direction. The polymer elastic emulsion has a high concentration, a low viscosity, and an excellent impregnation permeability. Further, by including a gelling agent in the emulsion of the polymer elastic body, migration in which the emulsion is unevenly distributed in the thickness direction at the time of drying can be suppressed.

Unlike the case of using a polymer elastic body solution that has been generally used conventionally, when a polymer elastic body emulsion is used, a non-porous polymer elastic body can be formed.

The polymer elastic body is preferably a hydrogen-bonding polymer elastic body from the viewpoint of high adhesion to fibers. The hydrogen-bonding polymer elastic body is an elastic body made of a polymer that crystallizes or aggregates by hydrogen bonding, such as polyurethane, polyamide-based elastic body, and polyvinyl alcohol-based elastic body.

Hereinafter, the case where polyurethane is used as the polymer elastic body will be described in detail as a representative example.

Examples of the polyurethane include various polyurethanes obtained by reacting a polymer polyol having an average molecular weight of 200 to 6000, an organic polyisocyanate, and a chain extender in a predetermined molar ratio.

Specific examples of the polymer polyol include, for example, polyether polyols such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol, poly (methyltetramethylene glycol), and copolymers thereof; polybutylene adipate diol, polybutylene sebacate Polyester polyols such as diol, polyhexamethylene adipate diol, poly (3-methyl-1,5-pentylene adipate) diol, poly (3-methyl-1,5-pentylene sebacate) diol, polycaprolactone diol, and the like Copolymers; polyhexamethylene carbonate diol, poly (3-methyl-1,5-pentylene carbonate) diol, polypentamethylene carbonate diol, polytetramethylene carbonate Polycarbonate polyols and copolymers thereof, such as borate sulfonate diol; polyester carbonate polyols and the like. If necessary, a trifunctional alcohol such as trimethylolpropane, a polyfunctional alcohol such as a tetrafunctional alcohol such as pentaerythritol, or ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol. Etc. You may use together short chain alcohols, such as. These may be used alone or in combination of two or more. In particular, the use of amorphous polycarbonate polyols, alicyclic polycarbonate polyols, linear polycarbonate polyols, and mixtures of these polycarbonate polyols with polyether polyols or polyester polyols are resistant to water. This is preferable because a hard sheet having excellent durability such as decomposability and oxidation resistance can be obtained. A polyurethane containing a polyalkylene glycol group having 5 or less carbon atoms, particularly 3 or less carbon atoms is preferred from the viewpoint of particularly good wettability with water.

Specific examples of the organic polyisocyanate include, for example, non-yellowing diisocyanates such as aliphatic or alicyclic diisocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, norbornene diisocyanate, 4,4′-dicyclohexylmethane diisocyanate; 2,4-tri Examples thereof include aromatic diisocyanates such as diisocyanate, 2,6-tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, and xylylene diisocyanate polyurethane. Moreover, you may use together polyfunctional isocyanates, such as trifunctional isocyanate and tetrafunctional isocyanate, as needed. These may be used alone or in combination of two or more. Among these, 4,4′-dicyclohexylmethane diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4′-diphenylmethane diisocyanate, and xylylene diisocyanate have high adhesion to fibers, Moreover, it is preferable from the point from which the hard sheet | seat with high hardness is obtained.

Specific examples of the chain extender include, for example, diamines such as hydrazine, ethylenediamine, propylenediamine, hexamethylenediamine, nonamethylenediamine, xylylenediamine, isophoronediamine, piperazine and derivatives thereof, adipic acid dihydrazide, and isophthalic acid dihydrazide; Triamines such as diethylenetriamine; tetramines such as triethylenetetramine; ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,4-bis (β-hydroxyethoxy) benzene, 1,4 -Diols such as cyclohexanediol; Triols such as trimethylolpropane; Pentaols such as pentaerythritol; Aminoethyl alcohol, Aminopropyl alcohol It includes amino alcohols such as and the like. These may be used alone or in combination of two or more. Among these, it is preferable to use a combination of two or more of hydrazine, piperazine, hexamethylenediamine, isophoronediamine and derivatives thereof, and triamines such as ethylenetriamine from the viewpoint of completing the curing reaction in a short time. In addition, during the chain extension reaction, together with the chain extender, monoamines such as ethylamine, propylamine and butylamine; carboxyl group-containing monoamine compounds such as 4-aminobutanoic acid and 6-aminohexanoic acid; methanol, ethanol, propanol, butanol, etc. Monools may be used in combination.

In addition, a polyurethane containing a carboxyl group-containing diol such as 2,2-bis (hydroxymethyl) propionic acid, 2,2-bis (hydroxymethyl) butanoic acid, 2,2-bis (hydroxymethyl) valeric acid, etc. By introducing an ionic group such as a carboxyl group into the skeleton, water wettability can be further improved.

Moreover, in order to control the water absorption rate and storage elastic modulus of polyurethane, a crosslinking agent containing two or more functional groups capable of reacting with the functional group of the monomer unit forming the polyurethane, a polyisocyanate compound, It is preferable to form a crosslinked structure by adding a self-crosslinking compound such as a polyfunctional blocked isocyanate compound.

The combination of the functional group of the monomer unit and the functional group of the crosslinking agent includes a carboxyl group and an oxazoline group, a carboxyl group and a carbodiimide group, a carboxyl group and an epoxy group, a carboxyl group and a cyclocarbonate group, a carboxyl group and an aziridine group, and a carbonyl group. And hydrazine derivatives and hydrazide derivatives. Among these, a monomer unit having a carboxyl group and a crosslinking agent having an oxazoline group, a carbodiimide group or an epoxy group, a combination of a monomer unit having a hydroxyl group or an amino group and a crosslinking agent having a blocked isocyanate group, and a carbonyl group A combination of a monomer unit having a hydrazine derivative or a hydrazide derivative is particularly preferred from the viewpoint of easy crosslinking and excellent rigidity and wear resistance of the hard sheet. The cross-linked structure is preferably formed in the heat treatment step after applying polyurethane to the fiber entangled sheet from the viewpoint of maintaining the stability of the polymer elastic body emulsion. Among these, a carbodiimide group and / or an oxazoline group are particularly preferable because they are excellent in crosslinking performance and pot life of the emulsion, and have no problem in safety. Examples of the crosslinking agent having a carbodiimide group include water-dispersed carbodiimide compounds such as “Carbodilite E-01”, “Carbodilite E-02”, and “Carbodilite V-02” manufactured by Nisshinbo Industries, Ltd. Examples of the crosslinking agent having an oxazoline group include water-dispersed oxazoline compounds such as “Epocross K-2010E”, “Epocross K-2020E”, and “Epocross WS-500” manufactured by Nippon Shokubai Co., Ltd. The blending amount of the crosslinking agent is preferably 1 to 20% by mass, more preferably 1.5 to 1% by mass, and more preferably 2 to 10% by mass of the active ingredient of the crosslinking agent with respect to the polyurethane. More preferably it is.

In addition, from the viewpoint of enhancing the adhesiveness to the ultrafine fibers and increasing the rigidity of the fiber bundle, the content of the polymer polyol component in the polyurethane is preferably 65% by mass or less, and more preferably 60% by mass or less. . Moreover, it is preferable from the point which can suppress generation | occurrence | production of a scratch by providing moderate elasticity that it is 40 mass% or more, and also 45 mass% or more.

The method for preparing the polyurethane emulsion is not particularly limited, and a known method can be used. Specifically, for example, by using a monomer having a hydrophilic group such as a carboxyl group, a sulfonic acid group, and a hydroxyl group as a copolymerization component, a method of imparting self-emulsifying property to water to a polyurethane, or a polyurethane A method of emulsifying by adding a surfactant is mentioned. Since the polymer elastic body containing a monomer unit having a hydrophilic group as a copolymerization component is excellent in water wettability, it can hold a large amount of slurry.

Specific examples of the surfactant used for emulsification include, for example, sodium lauryl sulfate, ammonium lauryl sulfate, polyoxyethylene tridecyl ether sodium acetate, sodium dodecylbenzene sulfonate, alkyl diphenyl ether sodium disulfonate, sodium dioctyl sulfosuccinate and the like. Anionic surfactants; nonionic surfactants such as polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, polyoxyethylene-polyoxypropylene block copolymer Etc. Moreover, you may use what is called reactive surfactant which has reactivity. Moreover, heat-sensitive gelation property can also be provided to an emulsion by selecting suitably the cloud point of surfactant.

The solid content concentration of the emulsion is preferably 15 to 40% by mass, and more preferably 25 to 35% by mass, from the viewpoint that the polymer entangled sheet can be uniformly filled with a polymer elastic body in the thickness direction. The particle size of the emulsion is preferably 0.01 to 1 μm, more preferably 0.03 to 0.5 μm.

The first emulsion contains a gelling agent containing ions that cause a pH change of water. The gelling agent is used to gel emulsion particles by heating by changing the pH of the emulsion. The moisture in the emulsion impregnated in the nonwoven fabric dries from the surface. Therefore, it is easy to cause migration in which the emulsion in the nonwoven fabric moves to the surface layer as the evaporation of moisture proceeds. When the emulsion in the nonwoven fabric migrates, the polymer elastic body is unevenly distributed in the vicinity of the surface layer of the nonwoven fabric, the polymer elastic body in the vicinity of the middle layer is reduced, and voids are likely to remain in the vicinity of the middle layer. When voids remain in the vicinity of the middle layer, the hardness in the middle layer decreases and the hardness becomes inhomogeneous. Such migration is suppressed by adding a gelling agent to the emulsion and allowing the emulsion to gel before drying.

The gelling agent is not particularly limited as long as it is a water-soluble salt that changes the pH of the emulsion to such an extent that the emulsion particles are gelled by heating. Specific examples thereof are monovalent or divalent inorganic salts such as sodium sulfate, ammonium sulfate, sodium carbonate, calcium chloride, calcium sulfate, calcium nitrate, zinc oxide, zinc chloride, magnesium chloride, potassium chloride, potassium carbonate. Sodium nitrate, lead nitrate and the like.

The content ratio of the gelling agent in the first emulsion is 0.5 to 5 parts by mass, more preferably 0.6 to 4 parts by mass with respect to 100 parts by mass of the elastic polymer. It is preferable from the viewpoint that it can be imparted moderately.

The first emulsion is a penetrant, an antifoaming agent, a lubricant, a water repellent, an oil repellent, a thickener, a bulking agent, a curing accelerator, an antioxidant, an ultraviolet absorber, a fluorescent agent, an antifungal agent, and a foaming agent. Water-soluble polymer compounds such as polyvinyl alcohol and carboxymethyl cellulose, dyes, pigments, inorganic fine particles and the like may be further contained.

The method of impregnating the fiber emulsion sheet with the first emulsion is not particularly limited, and for example, a method such as dip nip, knife coating, bar coating, or roll coating may be used.

Then, after the fiber entangled sheet is impregnated with the first emulsion, the first emulsion gels in the fiber entangled sheet by heating. As such a heating condition for gelation, for example, a condition of holding at 40 to 90 ° C., further 50 to 80 ° C. for about 0.5 to 5 minutes, is preferably used. Moreover, it is preferable to heat with the steam from the point which can also heat an inner layer uniformly, suppressing the migration of the emulsion by rapid evaporation of a water | moisture content from a surface layer.

Then, after the first emulsion is gelled, the polymer elastic body is solidified by heating and drying.

Examples of heat drying include a method of heat drying in a drying apparatus such as a hot air dryer, a method of heat drying in a dryer after infrared heating, and the like. Examples of the heating and drying conditions include conditions in which heating is performed for 2 to 10 minutes so that the maximum temperature is 130 to 160 ° C., further 135 to 150 ° C. By heating and drying, the water in the first emulsion is evaporated and the polymer elastic body is uniformly agglomerated, whereby the polymer elastic body can be uniformly applied in the thickness direction in the fiber entangled sheet.

(3) The process of forming the 1st composite_body | complex containing the nonwoven fabric and polymer elastic body of an ultrafine fiber by carrying out the ultrafine fiber process of an ultrafine fiber generation type | mold fiber

The sea-island type composite fiber contained in the fiber entangled sheet impregnated with the polymer elastic body is subjected to ultrafine fiber treatment to form a first composite containing a nonwoven fabric of ultrafine fibers and a polymer elastic body. The

In this step, ultrafine fibers are formed from a sea-island composite fiber containing a water-soluble thermoplastic resin that is an island component and a water-insoluble thermoplastic resin that is a sea component, by ultrafine fiber removal treatment that removes the water-soluble thermoplastic resin. It is a process.

The ultra-fine fiber treatment is performed by dissolving and removing the water-soluble thermoplastic resin forming the sea component by subjecting the fiber entangled sheet containing the sea-island type composite fiber to hydrothermal heating treatment with water, an alkaline aqueous solution, an acidic aqueous solution, or the like. This is a process of disassembling and removing.

As a specific example of the hot water heat treatment, for example, the fiber entangled sheet is immersed in hot water of 65 to 90 ° C. for 5 to 300 seconds as the first step, and then further 85 to 100 ° C. as the second step. A method of treating in hot water for 100 to 600 seconds is preferably used. Moreover, in order to improve dissolution efficiency, you may perform the nip process by a roll, a high pressure water flow process, an ultrasonic process, a shower process, a stirring process, a stagnation process, etc. as needed.

By subjecting the fiber entangled sheet to hot water heating treatment, the water-soluble thermoplastic resin is dissolved from the sea-island composite fiber to form ultrafine fibers. Note that when the ultrafine fibers are formed, the ultrafine fibers are greatly crimped. By this crimping, the fiber density of the ultrafine fibers becomes dense. Further, by removing the water-soluble thermoplastic resin from the sea-island type composite fiber, a void is formed in the portion where the water-soluble thermoplastic resin was present. This void is filled with a polymer elastic body in a later step. Moreover, the gelling agent contained in the fiber entangled sheet is dissolved and removed in the hot water by subjecting the fiber entangled sheet to hot water heating treatment. In this way, the first complex is formed.

(4) After impregnating the first composite with the second emulsion containing the gelling agent and the polymer elastic body, the second emulsion is gelled and further heated and dried to obtain the polymer elastic body. Solidifying to form a second composite

As described above, in the first composite formed by removing the water-soluble thermoplastic resin from the sea-island composite fiber, voids are formed in the portion where the water-soluble thermoplastic resin was present. In order to obtain a hard sheet having a high hardness uniformly in this embodiment, the voids in the first composite are filled with a polymer elastic body to restrain the ultrafine fibers.

∙ By filling the gap formed by removing the water-soluble thermoplastic resin with the polymer elastic body, the fine fibers can be focused and the porosity of the hard sheet can be reduced. When the ultrafine fibers form a fiber bundle, the emulsion is easily impregnated by capillary action.

As the second emulsion, the same emulsion as the first emulsion is used. Note that the second emulsion and the first emulsion may have the same composition or different compositions.

In this step, when the second composite formed is equally divided into three in the thickness direction, each layer, in order from any one of the surface sides, becomes the first surface layer, the middle layer, and the second surface layer, It is preferable that the second emulsion is applied for gelation so that the difference in porosity between the surface layer and the middle layer is 5% or less, further 3% or less. By adjusting in this way, a hard sheet with high hardness is obtained uniformly.

The difference in porosity between the first surface layer and the middle layer is calculated from the following formula.
Difference in porosity between first surface layer and middle layer (%) = absolute value (middle layer porosity (%) − first surface layer porosity (%))

The porosity of each layer is obtained as follows. A cross section in the thickness direction of the second composite is photographed with a scanning electron microscope at a magnification of 30 times. Then, using the image analysis software Popimaging (manufactured by Digital being kids. Co), the obtained photograph is binarized by a dynamic threshold method to identify the void. Then, an inscribed circle is drawn in each void portion, and the total area of the inscribed circle is defined as the total layer void amount. And the part which divided | segmented 1/3 in the thickness direction from one surface of the thickness direction of the 2nd composite using the photograph to the 1st surface layer, and the part divided | segmented into 1/3 in the thickness direction from the other surface With the second surface layer and the remaining layers as the middle layer, the total area of the inscribed circle was determined for each layer, and the amount of voids in each layer was obtained. And the porosity of each layer,
The porosity of each layer = the amount of voids of each layer / the amount of voids of all layers × 100 (%).

The method of impregnating the first emulsion into the first composite, the method of gelation, and the method of heat drying are the same as the method of impregnation of the first emulsion, the method of gelation, and the method of heat drying. A method may be used. In this way, a second complex is formed.

(5) A step of washing the second complex with water so that the total content of ions causing a pH change is 400 μg / cm ³ or less.

As described above, the hard sheet of the present embodiment uses an emulsion containing a gelling agent in order to suppress migration of the emulsion to the surface layer when a polymer elastic body is applied to the nonwoven fabric. The present inventors have found that when a large amount of ions contained in the gelling agent remains in the obtained hard sheet, the polishing rate is reduced during polishing. And it discovered that the fall of a grinding | polishing rate can be suppressed by making the residual amount of ion into 400 microgram / cm < ³ > or less by washing with water.

The step of washing with water is carried out so that the total content of ions causing the pH change of the water contained in the hard sheet is 400 μg / cm ³ or less, preferably 350 μg / cm ³ , more preferably 100 μg / cm ³ or less. It is a process to do. As the water washing method, for example, a heated water washing treatment is preferable from the viewpoint of high water washing efficiency. As specific conditions, for example, the second composite is immersed in hot water of 80 ° C. or higher. Specifically, for example, as a first step, after being immersed in hot water at 65 to 90 ° C. for 5 to 300 seconds, and further as a second step, treatment is performed in hot water at 85 to 100 ° C. for 100 to 600 seconds. Conditions. Moreover, in order to improve the washing efficiency, you may perform the nip process by a roll, a high pressure water flow process, an ultrasonic process, a shower process, a stirring process, a stagnation process, etc. as needed.

(6) A step of hot pressing at least one selected from the first composite, the second composite, and the hard sheet so that the surface hardness of the hard sheet is JIS-D hardness 45 or more.

The void existing inside the hard sheet reduces the hardness and hardness uniformity. In this step, the voids are reduced by hot pressing the first composite, the second composite, and / or the hard sheet. By reducing the voids in this way, the apparent density of the hard sheet is increased, and the hardness and the homogeneity and rigidity of the hardness are increased. The hot press treatment conditions are preferably such that the ultrafine fibers and the polymer elastic body are pressed at a linear pressure of 30 to 100 kg / cm with a metal roll heated to 160 to 180 ° C., for example.

Through the above-described steps, the hard sheet of this embodiment is obtained. The hard sheet of this embodiment is preferably used as a polishing layer of a polishing pad. Specifically, the polishing layer can be formed by performing desired processing on the hard sheet as necessary. For example, brushing with sandpaper or needle cloth, diamond, reverse brushing, hot pressing or embossing is performed. In addition, grooves, holes such as lattices, concentric circles, and spirals may be formed on the surface of the hard sheet.

If necessary, an elastic body layer such as a knitted fabric, a woven fabric, a nonwoven fabric, an elastic resin film, or an elastic sponge body may be laminated with the hard sheet as a polishing layer. As elastic films and elastic sponge bodies, non-woven fabrics impregnated with polyurethane currently used for general purposes (for example, “Suba400” (manufactured by Nitta Haas Co., Ltd.)), natural rubber, nitrile rubber, polybutadiene rubber, Examples thereof include rubbers such as silicone rubbers; thermoplastic elastomers such as polyester-based thermoplastic elastomers, polyamide-based thermoplastic elastomers, and fluorine-based thermoplastic elastomers; foamed plastics; polyurethanes and the like. By laminating the elastic layer in this manner, the local flatness of the surface to be polished (local flatness of the wafer) can also be improved. In addition, the polishing pad is one in which the polishing layer and the elastic body layer are directly bonded by fusion bonding or the like, in which both layers are bonded by an adhesive or a double-sided adhesive tape, or between the two layers. In addition, those having another layer are also included.

The polishing pad using the hard sheet of the present embodiment is a chemical mechanical polishing (CMP) in which a known CMP apparatus is used and the surface to be polished and the polishing pad are brought into contact with each other at a constant speed under a pressure through a slurry. ) Can be used. The slurry contains components such as a liquid medium such as water and oil; an abrasive such as silica, aluminum oxide, cerium oxide, zirconium oxide, and silicon carbide; a base, an acid, and a surfactant. Moreover, when performing CMP, you may use lubricating oil, a coolant, etc. together with a slurry as needed.

The article to be polished is not particularly limited, and examples thereof include crystal, silicon, glass, an optical substrate, an electronic circuit substrate, a multilayer wiring substrate, and a hard disk. In particular, the object to be polished is preferably a silicon wafer or a semiconductor wafer. Specific examples of semiconductor wafers include, for example, insulating films such as silicon oxide, silicon oxyfluoride, and organic polymers, wiring metal films such as copper, aluminum, and tungsten, and barrier metals such as tantalum, titanium, tantalum nitride, and titanium nitride. Examples thereof include those having a film or the like on the surface.

Hereinafter, the present invention will be specifically described with reference to examples. In addition, this invention is not limited at all by the Example.

First, the evaluation method used in this example will be described below.

[Apparent density of hard sheet]
The apparent density (g / cm ³ ) was obtained by dividing the mass (g / cm ² ) per unit area of the hard sheet by the thickness (cm). Then, the apparent density was measured at any ten locations on the hard sheet, and the value obtained by arithmetic averaging was defined as the apparent density. The thickness was measured at a load of 240 gf / cm ² according to JISL1096.

[Measurement of JIS-D hardness of hard sheet surface, first surface layer and middle layer, and calculation of R%]
The D hardness of the surface of the hard sheet, the first surface layer and the middle layer was measured according to JIS K 7311. Specifically, the D hardness of the surface of the hard sheet is obtained by stacking eight hard sheets having a thickness of about 1.25 mm, measuring the hardness at three points evenly in the width direction, and calculating the average of the D hardness of the surface of the hard sheet. Hardness.
The D hardness of the first surface layer was obtained by grinding a hard sheet having a thickness of about 1.25 mm from the second surface layer side to obtain a sheet of the first surface layer having a thickness of 0.40 mm. Then, 25 sheets of the obtained first surface layer were stacked, and the hardness at three points was measured uniformly in the width direction, and the average was defined as the JIS-D hardness of the first surface layer. Furthermore, the D hardness of the middle layer was obtained by uniformly grinding the hard sheet from the first surface layer side and the second surface layer side to obtain a middle layer sheet having a thickness of 0.40 mm. And 25 sheets of the obtained middle layer were piled up, the hardness of 3 points | pieces was measured equally in the width direction, and the average was made into the hardness of the middle layer. Then, using the obtained JIS-D hardness values of 6 points in total, that is, 3 points of D hardness of the first surface layer and 3 points of D hardness of the middle layer, the following formula:
R (%) was obtained from R (%) = (D hardness maximum value−D hardness minimum value) / D hardness average value × 100.

[Total ion content causing water pH change]
A piece of a hard sheet cut into a strip shape and 10 mL of water were cut and placed in a screw test tube. And the water-soluble substance in a hard sheet was hot-water-extracted by heating a screw opening test tube with a block heater at 90 degreeC for 2 hours. Then, ion components in the extract were detected using an ion chromatograph (ICS-1600). In this, the total amount of sulfate ions and ammonium ions, which are ions that cause the pH change of water, was measured and converted to the amount of ions contained in the hard sheet per unit volume.

[Polishing rate]
The hard sheet was cut into a circular shape having a diameter of 51 cm, and grooves having a width of 1.0 mm and a depth of 0.5 mm were formed on the surface in a lattice pattern at intervals of 15.0 mm to prepare a polishing pad. Then, after sticking an adhesive tape on the back surface of the polishing pad, it was mounted on a CMP polishing apparatus (“PP0-60S” manufactured by Nomura Seisakusho Co., Ltd.). Next, slurry (SHOROXA-31 manufactured by Showa Denko KK) was supplied at a rate of 100 ml / min under the conditions of a platen rotation rate of 70 rpm, a head rotation rate of 69 rpm, and a polishing pressure of 40 g / cm ^2. Then, synthetic quartz having a diameter of 4 inches was polished for 3 hours. And the thickness of arbitrary 25 points | pieces in the surface of the synthetic quartz after grinding | polishing was measured, and the grinding | polishing rate (nm / min) was calculated | required by remove | dividing the average of the grind | polished thickness in each point by grinding | polishing time.
In addition, the polishing rate of the 0.70 mm-thick hard sheet which exposed the 1st surface layer of the hard sheet about 1.25 mm thick and the middle layer was measured, respectively.

[Example 1]
Water-soluble PVA was used as the sea component, and isophthalic acid-modified PET having a modification degree of 6 mol% was used as the island component. Water-soluble PVA and isophthalic acid-modified PET were discharged from a melt compound spinning die (number of islands: 25 islands / fiber) at 260 ° C. so as to be 25/75 (mass ratio). Then, the ejector pressure was adjusted so that the spinning speed was 3700 m / min, and long fibers having a fineness of 3 dtex were collected on a net to obtain a web having a basis weight of 35 g / m ² .

Sixteen webs were overlapped by cross-wrapping to produce an overlapped web having a total basis weight of 480 g / m ² . Then, the needle breakage preventing oil was sprayed on the overlapping web. Then, using a needle needle with a needle count of 42 with one barb and a needle needle with a needle number of 42 with six barbs, the overlapping web is entangled by needle punching at 3150 punch / cm ^2. Got the web. The basis weight of the entangled web was 770 g / m ² and the delamination force was 9.6 kg / 2.5 cm. Moreover, the area shrinkage rate by the needle punch process was 25.8%.

Next, the entangled web was steamed for 70 seconds at 110 ° C. and 23.5% RH. The area shrinkage rate at this time was 44%. Then, after drying in an oven at 90 to 110 ° C., and further hot pressing at 115 ° C., a fiber entangled sheet having a basis weight of 1312 g / m ² , an apparent density of 0.544 g / cm ³ , and a thickness of 2.41 mm Got.

Next, the fiber entangled sheet was impregnated with a polyurethane emulsion as the first emulsion. Polyurethane is a mixture of polycarbonate polyol and polyalkylene glycol having 2 to 3 carbon atoms in a ratio of 99.8: 0.2 (molar ratio) as a polyol component, and 1.5% by mass of a carboxyl group-containing monomer. It is a non-yellowing polyurethane contained. Polyurethane is a non-porous polyurethane that forms a crosslinked structure by heat treatment. The first emulsion contains 4.6 parts by mass of a carbodiimide-based crosslinking agent and 1.8 parts by mass of ammonium sulfate as a gelling agent with respect to 100 parts by mass of polyurethane, and is adjusted so that the solid content of polyurethane is 20%. It is.

The fiber entangled sheet impregnated with the first emulsion was heated at 90 ° C. in a 30% RH atmosphere to gel the first emulsion, and further dried at 150 ° C. Further, by hot pressing at 140 ° C., the basis weight was adjusted to 1403 g / m ² , the apparent density 0.716 g / cm ³ , and the thickness 1.96 mm.

Next, by using a nip treatment and a high-pressure water treatment, the fiber-entangled sheet provided with polyurethane is immersed in hot water at 95 ° C. for 10 minutes to dissolve and remove the water-soluble PVA, and have a fineness of 0.09 dtex. It was converted to ultrafine fibers and further dried. In this way, a first composite having a basis weight of 1009 g / m ² , an apparent density of 0.538 g / cm ³ , and a thickness of 1.87 mm was obtained.

Next, the first composite was impregnated with a polyurethane emulsion (solid content 30% by mass) as the second emulsion. The polyurethane is the same as the previously impregnated polyurethane. The second emulsion contains 4.6 parts by mass of a carbodiimide-based crosslinking agent and 1.0 part by mass of ammonium sulfate with respect to 100 parts by mass of polyurethane, and is adjusted so that the solid content of polyurethane is 30%.

The first composite impregnated with the second emulsion was heated at 90 ° C. in a 60% RH atmosphere to gel the second emulsion, and further dried at 150 ° C. In this way, a ^second composite having a basis weight of 1245 g / m ² , an apparent density of 0.748 g / cm ³ and a thickness of 1.66 mm was obtained. The difference in porosity between the first surface layer and the middle layer of the second composite was 1.8%.

Then, the second composite was washed with water by immersing it in hot water at 95 ° C. for 10 minutes using nip treatment and high-pressure water flow treatment. And it dried at 180 degreeC. And the intermediate body of the hard sheet | seat which is 1212 g / m < ² > of fabric weights, the apparent density of 0.795 g / cm < ³ >, and the thickness of 1.53 mm was obtained by carrying out the hot press process on linear pressure of 100 kg / cm and 160 degreeC conditions.

The surface layers on both sides of the intermediate of the hard sheet are ground by 0.15 mm each using # 100 paper to obtain a hard sheet having a basis weight of 994 g / m ² , an apparent density of 0.788 g / cm ³ and a thickness of 1.26 mm. Finished. The JIS-D hardness of the hard sheet was 52, and R% of the JIS-D hardness was 11.3%. The total amount of sulfate ions and ammonium ions, which are ions that cause pH change, contained in the hard sheet was 26.9 μg / cm ³ .

Evaluation results are shown in Table 1.

[Example 2]
A hard sheet was produced and evaluated in the same manner as in Example 1 except that the first composite before applying the second emulsion was subjected to hot press treatment under the conditions of a linear pressure of 100 kg / cm and a temperature of 160 ° C. The obtained hard sheet had a basis weight of 996 g / m ² , an apparent density of 0.808 g / cm ³ , and a thickness of 1.23 mm. The results are shown in Table 1.

[Example 3]
In Example 1, a hard sheet was produced and evaluated in the same manner as in Example 1 except that the water washing degree of the second composite was lowered. The total amount of sulfate ions and ammonium ions, which are ions that cause pH change, contained in the hard sheet was 300 μg / cm ³ . The results are shown in Table 1.

[Comparative Example 1]
In Example 1, instead of washing the second composite by immersing it in 95 ° C. hot water for 10 minutes, it was the same as in Example 1 except that the second composite was not washed with water. Were manufactured and evaluated. The results are shown in Table 1.

[Comparative Example 2]
In Example 1, the first composite was further hot-pressed under the conditions of a linear pressure of 100 kg / cm and a temperature of 160 ° C. Then, instead of impregnating the second emulsion containing the gelling agent, a hard sheet was produced and evaluated in the same manner as in Example 1 except that the emulsion having the same composition not containing the gelling agent was impregnated. The obtained hard sheet had a basis weight of 969 g / m ² , an apparent density of 0.817 g / cm ³ , and a thickness of 1.19 mm. The results are shown in Table 1.

[Comparative Example 3]
In Example 1, a hard sheet was produced and evaluated in the same manner as in Example 1 except that the water washing degree of the second composite was lowered. The total amount of sulfate ions and ammonium ions, which are ions that cause pH change, contained in the hard sheet was 404 μg / cm ³ . The results are shown in Table 1.

[Comparative Example 4]
In Example 1, a hard sheet was produced and evaluated in the same manner as in Example 1 except that the water washing degree of the second composite was lowered. The total amount of sulfate ions and ammonium ions, which are ions that cause pH change, contained in the hard sheet was 504 μg / cm ³ . The results are shown in Table 1.

From the results of Table 1, when the JIS-D hardness according to the present invention is 45 or more, R% is 0 to 20%, and the total content of ions causing pH change of water is 400 μg / cm ³ or less. All of the polishing pads using the hard sheets obtained in Examples 1 to 3 had a polishing rate of the first surface layer, that is, an initial polishing rate of 120 nm / min, and an initial polishing averaged after 5 hours. Maintained over 90% of the rate. On the other hand, the polishing pad using the hard sheet of Comparative Example 1 in which the gelling agent was blended into the second emulsion and was not sufficiently washed with water, had a remarkably low polishing rate of 93 nm / min for the first surface layer. Further, the hard sheet of Comparative Example 2 is obtained by homogenizing the hard sheet by hot pressing instead of blending the second emulsion with a gelling agent and uniformly filling the polymer elastic body. The polishing pad of Comparative Example 2 had a small total content of ions, but was inhomogeneous with an R% of 30.2%. As a result, only 89% of the initial polishing rate was maintained on average after 5 hours. Further, the total content of ions Comparative Example 4 Comparative Example 3, and 504μg / cm ³ of 404μg / cm ³ were not only able to maintain about 84% of the initial polishing rate either an average of up to 5 hours .

DESCRIPTION OF SYMBOLS 1 Nonwoven fabric 1a Extra fine fiber 1b Fiber bundle 2 Polymer elastic body 3 First surface layer 4 Middle layer 5 Second surface layer

Claims

A hard sheet comprising a nonwoven fabric of ultrafine fibers having a fineness of 0.0001 to 0.5 dtex, and a polymer elastic body imparted to the nonwoven fabric,
JIS-D hardness is 45 or more,
In the cross section in the thickness direction, when each layer is equally divided into three, in order from any one of the surface side, the first surface layer, the middle layer and the second surface layer,
The JIS-D hardness of the first surface layer and the middle layer was measured at three arbitrary points at a total of 6 points, and a total of 6 points of D hardness was used.
R (%) = (D hardness maximum value−D hardness minimum value) / D hardness average value × 100
R% calculated from 0 to 20%,
And the hard sheet | seat characterized by the total content of the ion which causes the pH change of water being 400 microgram / cm < 3 > or less.
The hard sheet according to claim 1, wherein the total content of the ions is 1 to 100 µg / cm 3 .
The hard sheet according to claim 1, wherein the ultrafine fibers are long fibers and form a fiber bundle.
The hard sheet according to claim 3 , wherein the apparent density of the nonwoven fabric is 0.35 to 0.90 g / cm 3 .
The hard sheet according to claim 3, wherein at least a part of the ultrafine fibers forming the fiber bundle are bundled by the polymer elastic body in a cross section in the thickness direction.
The hard sheet according to claim 5, wherein at least a part of the fiber bundles are bound to each other by the polymer elastic body in a cross section in the thickness direction.
The rigid sheet according to claim 3, wherein in the cross section in the thickness direction, more than half of the ultrafine fibers forming the fiber bundle are converged by the polymer elastic body.
The hard sheet according to claim 7, wherein more than half of the fiber bundles are bound to each other by the polymer elastic body in a cross section in the thickness direction.
The hard sheet according to claim 1, wherein the polymer elastic body is a non-porous polymer elastic body.
2. The hard sheet according to claim 1, wherein a mass ratio (nonwoven fabric / polymer elastic body) between the nonwoven fabric and the polymer elastic body is 90/10 to 55/45.
The hard sheet according to claim 10, wherein the apparent density is 0.50 to 1.2 g / cm 3 .
The JIS-D hardness of the second surface layer is 45 or more,
The JIS-D hardness of the second surface layer and the middle layer was measured at arbitrary points, 3 points each, for a total of 6 points, and using the 6 points of D hardness, the following formula:
2. The hard sheet according to claim 1, wherein R% calculated from R (%) = (D hardness maximum value−D hardness minimum value) / D hardness average value × 100 is 0 to 20%.
A polishing pad comprising the hard sheet according to any one of claims 1 to 12 as a polishing layer.
(1) Prepare a fiber-entangled sheet of ultrafine fiber-generating fibers that can form a nonwoven fabric with an apparent density of 0.35 g / cm 3 or more of ultrafine fibers having a fineness of 0.5 dtex or less by ultrafine fiber treatment. And a process of
(2) After impregnating the fiber entangled sheet with a first emulsion containing a gelling agent containing an ion that causes a pH change of water and a polymer elastic body, the first emulsion is gelled, A step of solidifying the polymer elastic body by heating and drying;
(3) forming the first composite containing the nonwoven fabric and the polymer elastic body by subjecting the ultrafine fiber-generating fiber to an ultrafine fiber treatment;
(4) The first composite is impregnated with the second emulsion containing the gelling agent and the polymer elastic body, and further heat-dried to solidify the polymer elastic body in the thickness direction. When each layer when equally divided into three is the first surface layer, the middle layer and the second surface layer in order from any one of the surface sides, the difference in porosity between the first surface layer and the middle layer is 5% or less. Forming a second complex,
(5) A step of obtaining a hard sheet by washing the second complex with water so that the total content of ions is 400 μg / cm 3 or less;
(6) a step of hot pressing at least one selected from the first composite, the second composite, and the hard sheet so that the surface hardness of the hard sheet is JIS-D hardness 45 or more. And a method for producing a hard sheet.
The method for producing a hard sheet according to claim 14, wherein a total content of the ions is 1 to 100 µg / cm 3 .
The ultrafine fiber-generating fiber is a sea-island composite fiber containing a water-soluble thermoplastic polyvinyl alcohol-based resin as a sea component and a water-insoluble thermoplastic resin as an island component,
The method for producing a hard sheet according to claim 14, wherein the ultrafine fiberizing treatment in the step (3) is a step of selectively removing the water-soluble thermoplastic polyvinyl alcohol resin by dissolving it in warm water.