Abstract: There is disclosed a powder magnetic core in which a permeability does not easily drop even when an applied magnetic field intensifies, comprising: a bulk body containing a main component of a powder of an Fe-base alloy having a soft magnetic property, and the balance substantially including a heat-treated insulation binder and a void, wherein an aspect ratio of the powder is in a range of 1 to 1.5, and a volume ratio of the powder in the bulk body is in a range of 40 to 60 volume %, and an initial permeability (?0) has a value which satisfies 6??0?20, and a relation of ?/?0?0.5 is established between K and A, when the permeability is ? with an applied magnetic field of 24 kA/m.

Abstract: A braze preform and a method for making the braze preform are disclosed. The braze preform includes a filler metal that has been sintered to produce a liquid phase of at least a portion of the filler metal.

Abstract: High theoretical density, metal-based materials containing graphite or hexagonal boron nitride have low coefficients of friction and wear rates are useful for bearings, bushings and other articles subject to bearing loads.

Abstract: A method of forming a powder metal material includes molding a compact from a powder mix comprising an iron-containing powder and glass, and subsequently sintering the compact. Also disclosed is a sintered powder metal material including iron and glass.

Abstract: A sintered material and a method for the production thereof is described. The material comprises an alloy selected from one of the groups having a composition comprising in weight %: either Cr 5-30/Mo 0-15/Ni 0-25/W 0-15/C 0-5/Si 0-5/Fe 0-5/Mn 0-5/others 10max/Co balance, or Cr 10-20/Mo 0-15/Co 0-20/W 0-5/Fe 0-20/Al 0-5/Ti 0-5/others 15max/Ni balance; said alloy having incorporated therein from 3-15 weight % of Sn; and optionally from 1-6 weight % of a solid lubricant material.

Abstract: An iron-based sintered alloy, which consists of from 0.5 to 5% of Ni, from 0.5 to 4% of Cr, from 0.5 to 2% of C, the balance being Fe and unavoidable impurities, and which has a micro-structure comprising an iron-based matrix containing Ni and a part of Cr as solutes and carbides containing the other part of Cr and dispersed in the matrix. The iron-based sintered alloy is appropriate for use as a valve seat of an internal combustion engine. Wear resistance is maintained at a moderate level while the additive amount of alloying elements is decreased to attain low cost.

Abstract: A method of forming a powder metal material or article includes the steps of molding a compact from a metallurgical powder, and then sintering the compact. The metallurgical powder may include at least one of a stainless steel powder and a low-chromium steel-base powder, and about 0.5 to about 15 weight percent of glass powder. Alternatively, the metallurgical powder may include at least one of a stainless steel powder and a low-chromium steel-base powder, about 3 to about 15 weight percent molybdenum, and about 1 to about 15 weight percent of nickel-base alloy powder. The present invention also is directed to metallurgical powders useful in and materials and articles made by the methods of the present invention. Such articles include, but are not limited to, valve guides for internal combustion engine EGR systems, valve seats, exhaust system components, combustion chambers, other combustion engine parts subjected to high temperature, and chemical industry valve and corrosion parts.

Abstract: Ag particles produced by chemical reduction and having a mean particle size of 5 &mgr;m are added by 0.05-3 wt % and Zn are added by 2-10 wt % to a Pb-less brush body containing graphite, Cu and a metal sulfide solid lubricant of a metal-graphite brush.

Abstract: The invention concerns a powder composition including an iron or iron based powder and a lubricating amount of an alkylalkoxy or polyetheralkoxy silane, wherein the alkyl or polyether group has between 8 and 30 carbon atoms and the alkoxi group includes 1-3 carbon atoms.

Abstract: A brush body 4 of a metal-graphite brush 2 is composed of a Pb-less commutator side portion 6 which contains graphite, copper and a metal sulfide solid lubricant, and a lead side portion 8 which contains graphite, copper, the metal sulfide solid lubricant and Pb.

Abstract: A sintered alloy that enables the reducing of coefficient of friction and the sealing of pores on a surface thereof and a method of manufacturing the same. A sintered alloy body includes a resin film layer and pores. The pores define a porosity ranging from 2 to 35 volume %, each having an inlet portion and an inside portion, defining a pore inlet diameter and a pore inside diameter respectively. The pore inlet diameter ranges from 10 to 200 &mgr;m, and an average ratio of the pore inlet diameter to the pore inside diameter is at least. Solid lubricant is dispersed in the resin film layer. After forming the layer 3, it is pressed against the sintered alloy body. Thus, the layer enters into the pores to closely contact them, thereby sealing the pores, reducing the coefficient of friction due to the solid lubricant.

Abstract: A ferrous sintered valve seat material is made of mixed powders comprising a sinter-hardenable phase and a finely dispersed carbide phase. The powder mixture comprises a sinter-hardening prealloyed powder forming 75 to 90 wt. % of the mixture and a tool steel powder with finely dispersed carbides forming 5 to 25% of the mixture. Machinability additives of MnS, CaF2 or MoS2 types are added in an amount of 1 to 5 wt. %. Improved thermal conductivity is obtained by infiltrating the compact with Cu up to 25 wt. %.

Abstract: A powder metal engine component particularly suited for use as a valve seat insert in both light and heavy duty internal combustion engine applications. The powder metal engine component contains an intermetallic phase such as a Laves phase for both the cobalt or iron based alloy.

Abstract: An iron-based sintered alloy, which consists of from 0.5 to 5% of Ni, from 0.5 to 4% of Cr, from 0.5 to 2% of C, the balance being Fe and unavoidable impurities, and which has a micro-structure comprising an iron-based matrix containing Ni and a part of Cr as solutes and carbides containing the other part of Cr and dispersed in the matrix. The iron-based sintered alloy is appropriate for use as a valve seat of an internal combustion engine. Wear resistance is maintained at a moderate level while the additive amount of alloying elements is decreased to attain low cost.

Abstract: A valve seat is provided in which wear resistance can be ensured by optimizing the matrix structure without dispersing of expensive hard particles, and therefore the machinability can be improved and the holding down of cost can be achieved. The valve seat exhibits a metallographic structure consisting of only bainite single phase or only a mixed phase of bainite and martensite, has an area ratio of bainite and martensite in cross section of 100:0 to 50:50, and has a matrix hardness of 250 to 850 Hv.

Abstract: In a copper-based sintering sliding material, to reduce attacking power to the counter material by expressing an ability to scrape a local adhered object on the sliding surface, improve abrasion resistance of the material, and suppress the abrasive heat generation due to the hard phase, thereby improving the seizure limit, heat shock resistant ceramics comprising two or more selected from SiO2 and/or SiO2, Al2O3, LiO2, TiO2 and MgO are dispersed in an amount of 0.05 to 0.5% by weight or less, as nonmetallic particles comprising one or more kind(s) selected from finely grinded oxides, carbides and nitrides.

Abstract: An iron-based sintered powder metal mixture for valve guides, valve seat inserts and other high temperature, high wear applications requiring excellent net-shape stability during sintering comprises a powder metal mixture consisting essentially of 0.5-2.0 wt. % of fine, soluble graphite which goes into solution in the elemental iron matrix, 0.5-2.5 wt. % stable graphite which remains as free graphite in the sintered structure, 0.5-3.0 MoS2, which reacts with 1.0-5.0 wt. % copper to drive a sintering reaction at relatively low sintering temperatures of between 1030—1150° C. The resulting sintered particles have good mechanical strength and wear resistance and possess excellent machineability and dimensional stability.

Abstract: A self-grown monopoly compact grit and high pressure, high temperature process for preparing the same. The high pressure, high temperature sintered/synthesized monopoly compact grit is used in various industrial tools such as saw blades, grinding wheels, cutting tools and drill bits. Further, the monopoly compact grit of the present invention is produced from a seed of a mono-crystal of diamond or cubic boron nitride surrounded by either a self-grown crystal layer or an integrally bonded poly-crystalline sintered compact layer. The self-grown crystal layer is a new grown crystal structure where the seed crystal grows into a new phase through a normal diamond or cubic boron nitride synthesis process in the presence of a catalyst metal solvent.

Abstract: Disclosed is a sintered alloy material for valve guides, containing: 1.5% to 4% by mass of carbon; 1% to 20% by mass of copper; 0.1% to 2% by mass of tin; 0.01% or more than 0.01% and less than 0.1% by mass of phosphorus; and an iron base. The metallographic structure of the sintered alloy material has a matrix phase composed mainly of pearlite, and a free carbon phase being dispersed in the matrix phase.

Abstract: A powder metal blend for making a powder metal part especially a valve guide 14 for an internal combustion engine particularly suited for operation where there is little or no engine oil lubricant at the valve stem 30 and valve guide 14 interface. The powder metal blend having a chemical composition on a weight percent basis of about 2 to about 10 percent copper; about 0.5 to about 5.0 percent solid lubricant; about 1.0 to about 3.0 percent graphite; about 1.0 to about 8.0 percent bronze; about 0.2 to about 1.5 percent copper-and/or iron phosphorus; about 0.3 to about 1.0 percent fugitive lubricant; and the balance being a low alloy steel powder containing about 0.3 to about 1.0 percent manganese.

Abstract: In the invention, a stainless steel powder of the desired composition is either directly mixed with a h-BN powder, compressed and sintered or the stainless steel powder is compressed, impregnated with a solution containing h-BN and then sintered or compressed, sintered and then impregnated with a solution containing h-BN. The sintered bodies in all the aforementioned cases may be resin impregnated. Steel body formation may be done by traditional press compacting or, alternatively, by injection molding steel powder in molds (metal injection molding, MIM).

Abstract: With the objectives of alleviating the property of attacking on the mating member by scratching-off of local agglutinates on the sliding contact surface, achieving improved wear resistance, and achieving improved seizure resistance through restraint of frictional heat generation by a hard phase, a copper based sintered contact material contains shock-resistant ceramics in an amount of 0.05 to less than 0.5 wt % as non-metallic particles composed of one or more substances selected from pulverized oxides, carbides and nitrides. The shock-resistant ceramics are comprised of SiO2 and/or two or more substances selected from SiO2, Al2O3, LiO2, TiO2 and MgO.

Abstract: A brush body 4 of a metal-graphite brush 2 is composed of a Pb-less commutator side portion 6 which contains graphite, copper and a metal sulfide solid lubricant, and a lead side portion 8 which contains graphite, copper, the metal sulfide solid lubricant and Pb.

Abstract: Multiphase polymeric binders for binder assisted forming of sinterable powder bodies are formulated to demonstrate improved rheological properties in the form of newtonion or near newtonion flow behavior thereby reducing dependence of binder viscosity on shear by tailoring the molecular weight and molecular weight distribution of the polymeric binder phases and the resulting polymer admixtures of the invention demonstrate shear rate independent behavior. Reduction of interfacial tension between binder phases by introduction of at least one macromolecule with separate segments selected to be compatible with the individual phases of the binder further increases processing performance as does use of polymer macromolecules having attributes that allow them to act as surface active materials at the interface of the sinterable powder and the multiphase binder composition. Predispersion of the surface active materials in the powder is facilitated by emulsification thereof in water prior to admixture with the powder.

Abstract: A coated body that has a substrate of tungsten, carbon, and cobalt, and wherein the substrate presents a surface. Eta phase is present at the surface of the substrate. Fibrous tungsten carbide grains are present at the surface of the substrate. The surface of the substrate has a surface roughness, Ra, of greater than about 12 microinches. A coating layer is on the surface of the substrate. A process for making a coated body comprising the steps of: providing a substrate comprising tungsten, carbide and cobalt, and the substrate having at least one surface with eta phase thereon; subjecting the substrate with eta phase on the surface thereof to a conversion treatment at a temperature between about 1250° C. and about 2000° C.

Abstract: The invention concerns new lubricants comprising a combination of a polyethylene oxide and an oligomer amide and an improved metallurgical powder composition comprising a major amount of an iron-based powder and a minor amount of this new lubricant. Furthermore, the invention concerns a method requiring low ejection force and low ejection energy for producing green products having high green strength. The method comprises the steps of mixing an iron-based powder and optional additives with the new lubricant and compacting the obtained powder composition.

Abstract: A contact material which provides improved wear resistance as well as reduced adhesion utilizing the features of an intermetallic compound having an ordered phase, with the intention of (i) improving the seizure resistance and/or wear resistance of an implement bearing which slides under low-speed, high-surface-pressure conditions and is susceptible to lubricant starvation; (ii) preventing abnormal noises; and (iii) achieving prolonged greasing intervals. The contact material contains 10% by volume or more a metallic alloy phase having such a composition range that causes an order-disorder transition. The metallic alloy phase is a Fe base alloy phase containing one or more elements selected from the group consisting of Al, Si, Co and Ni.

Abstract: A composite structural metal use, for example, in drill bit bodies is disclosed. The metal includes powdered tungsten carbide, and binder metal consisting of a composition by weight of manganese in a range of about zero to 25 percent, nickel in a range of about zero to 15 percent, zinc in a range of about 3 to 20 percent, tin in a range of more than 1 percent to about 10 percent, and copper making up about 24 to 96 percent by weight of the composition. In one embodiment, the composition includes about 6 to 7 percent tin therein. In another embodiment, the composition includes about 0-6 percent by weight of cobalt.

Abstract: An unbalanced magnetron sputter ion plating system has a first magnetron with a first target of metal sulphide (e.g. MoS2) and a second magnetron with a second target of metal (e.g. Titanium). In order to recover water and sulphur impurities from the surfaces of the coating chamber the metal target is energised in a pre-coating ion cleaning operation. The Titanium target remains energised during the deposition of the molybdenum-sulphur coating to produce a MoxTiySz coating where x+y≈1 and Z≈2. Best results are achieved if the Titanium content is about 18% or less by weight of the total coating content.

Abstract: A mixture for a powder metallurgy product, including iron powder, graphite powder and copper (Cu) of about 3.0 to about 5.0 weight percent. Iron powder includes iron grains which contain MnS therein. The mixture contains the MnS of about 0.65 to about 1.40 weight percent. The graphite powder is contained in the mixture such that an amount of carbon (C) in the powder metallurgy product is about 0.3 to about 0.7 weight percent. An amount (wt % C) of the carbon and an amount (wt % Cu) of the copper is determined to obtain a target fatigue strength FS (MPa) and a target hardness HR (HRB) based on a relation FS=66.63×(wt % C)+22.61×(wt % Cu)+280.84 HR=22.96×(wt % C)+2.99×(wt % Cu)+78.91.

Abstract: The method of producing an R—Fe—B magnet of the present invention is characterized in that R—Fe—B alloy fine powder is molded in a magnetic field and sintered using a lubricant for molding magnets containing specific components, individually or as a mixture, of specific amounts of methyl caproate and/or methyl caprylate, which provide high crystal orientation, and lubricant comprising depolymerized polymer for improving molded article strength, or a lubricant for molding magnets wherein Ti coupling agent that improves crystal orientation is added to this lubricant for molding magnets. Each particle of the fine powder has a high degree of crystal orientation in the direction of the magnetic field, and molded article strength is markedly improved, leading to improved mass-productivity and yield. Moreover, the above-mentioned lubricants do not react with this magnet powder during sintering and are emitted as a gas.

Abstract: A process for producing a high-density iron-based green compact is provided that can form a green compact with a high density. Also provided is a process for producing a sintered compact from the green compact. A specified combination lubricant is applied to the surface of a die for compacting by electrical charging, wherein the combination lubricant includes a first lubricant having a melting point that is higher than a preset compacting temperature, and a second lubricant having a melting point that is lower than a compacting temperature. A heated iron-based powder mixture is filled into the die, followed by compacting, whereby a green compact is formed. The green compact can be sintered to provide a sintered compact.

Abstract: Disclosed is a sintered alloy material for valve guides, containing: 1.5% to 4% by mass of carbon; 1% to 20% by mass of copper; 0.1% to 2% by mass of tin; 0.01% or more than 0.01% and less than 0.1% by mass of phosphorus; and an iron base. The metallographic structure of the sintered alloy material has a matrix phase composed mainly of pearlite, and a free carbon phase being dispersed in the matrix phase.

Abstract: A swash plate for a swash plate compressor, wherein aluminum alloy containing 12 to 60% of Si and, as required, 0.1 to 30% of Sn is sprayed onto the iron or aluminum base plate of the swash plate compressor to form a seizure-resisting and abrasion-resisting surface layer dispersed with granulated Si.

Abstract: The invention relates to an iron-based high-temperature wear-resistant sintered alloy. This alloy contains 3.74-13.36 wt % W, 0.39-5.58 wt % V, 0.2-5.78 wt % Cr, 0.1-0.6 wt % Si, 0.39-1.99 wt % Mn, 0.21-1.18 wt % S, and up to 2.16 wt % C. This alloy includes 20-80 wt % of a first phase and 80-20 wt % of a second phase, each distributed therein, in the form of spots. The first phase contains 3-7 wt % W, up to 1 wt % Cr, 0.1-0.6 wt % Si, 0.2-1 wt % Mn, 0.1-0.6 wt % S, and up to 2.2 wt % C. The first phase may contain 0.5-1.5 wt % V, and in this case the vanadium content of the alloy becomes 0.79-5.88 wt %. The second phase contains 7-15 wt % W, 2-7 wt % V, 1-7 wt % Cr, 0.1-0.6 wt % Si, 0.2-1 wt % Mn, 0.1-0.6 wt % S, and up to 2.2 wt % of C. Each phase contains 0.3-1.6 wt % MnS and a carbide of at least tungsten, which are dispersed therein. The second phase further contains 10-20 areal % tungsten carbide (particle diameter: ≧1 &mgr;m) dispersed therein. The alloy further contains 0.

Abstract: The seizure resistance of an Al-based flame-sprayed layer formed on the swash plate of a swash-plate type comressor is increased to such a level comparable to that of a flame-sprayed bronze layer. The Al-based flame-sprayed layer of the present invention contains: from 12 to 60% of Si and granular Si particles dispersed in the matrix thereof, and at least one dispersing phase of graphite carbon, amorphous carbon and carbon, the crystallizing degree of which is between the graphite carbon and amorphous carbon, and MoS2.

Abstract: A lead-free plain bearing is formed by dispersing an alloy powder formed from 7-13 mass percent of Sn, 0.1-5 mass percent of Ag, and Cu on a backing, such as a steel plate, and sintering. The alloy powder may further include one or more of 0.05-0.5 mass percent of molybdenum disulfide powder and 0.1-2 mass percent of graphite powder. The bearing surface may be rough finished by machining to a roughness of 0.3-1 &mgr;m Ra and then fine finished by polishing to a roughness of at most 0.1 &mgr;Ra.

Abstract: There is provided a copper-based sliding alloy excellent in wear resistance and anti-seizure property. A phase of 2 to 30 wt. % lead is dispersed in the copper alloy. This lead phase contains 0.1 to 6 vol. % hard particles such as SiC, SiO2, Si3N4, Al2O3, TiC, WC and TiN having an average particle size of 5 to 25 &mgr;m. Because hard particles are included in the lead phase, wear resistance is excellent and anti-seizure property is improved. The lead phase, which is soft, serves as a cushion and the attack on a mating member by hard particles is reduced. Further, the falling-off of lead is minimized because the lead phase also includes the hard particles.

Abstract: The present invention provides a sintered material having high mechanical strength and superior wear resistance, and to a process of manufacture therefor. A sintered alloy having superior wear resistance has an overall composition consisting of, in percent by weight, Ni in an amount of 6.0 to 25.0%, Cr in an amount of 0.6 to 8.75%, C in an amount of 0.54 to 2.24%, and balance consisting of Fe, the sintered alloy exhibiting a metallographic structure in which the following hard phase is dispersed in a mixed structure of martensite and austenite, the hard phase comprising a core consisting of Cr carbide and a ferrite phase diffused Cr, or a mixed phase of ferrite and austenite diffused Cr, surrounding the core, and an area ratio of austenite in the mixed structure in the metallographic structure ranging from 5 to 30%.

Abstract: The present invention relates to a sinter and a casting comprising a high-hardness glassy alloy containing at least Fe and at least a metalloid element and having a temperature interval &Dgr;Tx of a supercooled liquid as expressed by &Dgr;Tx=Tx−Tg (where, Tx is a crystallization temperature and Tg is a glass transition temperature) of at least 20° C., which permit easy achievement of a complicated concave/convex shape.

Abstract: A powder metallurgy product which is made from constituent including iron powder. The iron powder includes iron grains which contain machinability improving element in the iron grains. The machinability improving element is configured to improve machinability of the powder metallurgy product and has a pinning effect. An amount (Q) of the machinability improving element is adjusted such that an absolute value of a differential coefficient (dS/dQ) is at least a predetermined value, where (S) is a grain size of iron in the powder metallurgy product.

Abstract: A sintered alloy having superb wear resistance comprising: composite phases dispersed in a matrix of the sintered alloy; the composite phase consisting of; a particle group in which Cr carbide particles and Cr sulfide particles exist in a mixed condition; and a ferrite phase or a mixture phase of ferrite and austenite surrounding the particle group as a core.

Abstract: Machinability is drastically improved while maintaining some degree of hardness in an Fe-based sintered alloy. A good machinability Fe-based sintered alloy has an overall composition of, in percent by weight, at least one element selected from the group consisting of P in an amount of 0.1 to 1.0% and Si in an amount of 2.0 to 3.0%, B in an amount of 0.003 to 0.31%, 0 in an amount of 0.007 to 0.69%, C in an amount of 0.1 to 2.0%, and the balance consisting of Fe and unavoidable impurities, has a matrix hardness ranging from Hv 150 to 250, and has free graphite dispersed therein.

Abstract: A powdered metal blend mixture for making a powdered metal part especially a valve seat insert. The mixture includes 15 to 30 wt. % of a valve steel powder, 0 to 10 wt. % nickel, 0 to 5 wt. % copper, 5 to 15 wt. % of a ferro-alloy powder, 0 to 15 wt. % of a tool steel powder, 0.5 to 5 wt. % of a solid lubricant, 0.5 to 2 wt. % graphite, 0.3 to 1.0% of a temporary lubricant, and the balance being substantially a low alloy steel powder containing 0.6 to 2.0 wt. % molybdenum, 0 to 5 wt. % nickel, and 0 to 3.0 wt. % copper. The present invention provides improved high temperature wear and corrosion resistance over prior art materials as well as improved machinability. The blend of the present invention provides a relatively high density material that allows for a single press and sinter technique.

Abstract: The present invention provides for nanostructured metal compacts exhibiting a preferred grain orientation formed from nanosize metal particles, preferably having anisometric morphology. The compact may comprise a single-phase metal powder, that is, a metal powder comprised of a single element, or may be an alloy, or the metal powder may be admixed with another component thereby resulting in a compact exhibiting heterogenous properties. The metal particles are fabricated or compacted, as by a powder metallurgical process, utlizing a relatively high pressure sufficient to form a compact, object, body, article, product or the like, with desired integrity and desity. The particles tend to become oriented with their largest dimension perpendicular to the direction of the applied force. Compaction occurs at about ambient temperature, but may be at subambient or elevated temperatures provided this temperature variation is not deleterious to the grain structure of the compact.

Abstract: An iron-based powder which is a mixture comprising a major proportion of a first alloy powder, a minor proportion of a second alloy powder and a proportion of a solid lubricant. The first alloy powder consists of, in weight percentages, 14 to 30 chromium, 1 to 5 molybdenum, 0 to 5 vanadium, 0 to 6 tungsten, the total of molybdenum, vanadium and tungsten being at least 3, a total of 0 to 5 of other strong carbide forming elements, 0 to 1.5 silicon, carbon with a minimum level sufficient to form carbides with substantially all of the molybdenum, vanadium, tungsten, and any other strong carbide forming elements present, and a balance which is iron and incidental impurities. The second alloy powder is an austenitic stainless steel.

Abstract: The invention relates to bullets having increased frangibility (or which can be easily fragmented) and to materials and processes for the manufacture of such bullets. The bullets of the present invention are typically made from copper or copper alloy powders (including brass, bronze and dispersion strengthened copper) which are pressed and then sintered under conditions so as to obtain bullets with the desired level of frangibility. In preferred embodiments of the invention, the bullets also contain several additives that increase or decrease their frangibility.

Abstract: The present invention is related to a family of materials that may act as a replacement for lead in applications where the high density of lead is important, but where the toxicity of lead is undesirable. The present invention more particularly provides a high density material comprising tungsten, fiber and binder. Methods and compositions of such materials and applications thereof are disclosed herein.

Abstract: Metallurgical powder compositions are provided that contain a metal powder that is associated with a polymeric material in admixture with a solid, particulate polyether lubricant. The incorporation of the polyether lubricant enhances the green strength properties of compacted parts made from the powder compositions, and generally reduces the ejection forces required to remove the compacted part from the die cavity.

Abstract: An iron-based powder mixture for powder metallurgy, comprising: an iron-based powder, and from 0.05 to 0.50% by weight of a thermoplastic resin powder which comprises 50% or more by weight of units of at least one monomer selected from the group consisting of acrylic esters, methacrylic esters, and aromatic vinyl compounds, and whose average primary particle size is from 0.03 to 5 .mu.m, whose average agglomeration particle size is from 5 to 50 .mu.m, and whose average molecular weight measured by the specific viscosity of a solution is from 30000 to 5000000.