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fully saponified or a partially saponified poly(vinyl alcohol› ethylene) copolymer), cellulose derivatives (such as car› boxymethyl cellulose, hydroxyalkyl cellulose (hydroxyethyl cellulose, hydroxypropyl cellulose, ethylhydroxyethyl cel› lulose), methyl cellulose, ethyl cellulose, carboxymethyl- ethyl cellulose, carboxymethyl cellulose, carboxymethyl cellulose sodium, cellulose ester, etc.), polyalkylene glycol, sucrose fatty acid ester, poly (oxyethylene alkyl phenyl ether), poly (oxyalkyl ether), polyvinyl pyrrolidone, water› soluble nylon, polyacrylic acid, and polymethacrylic acid. More preferably they are polyvinyl alcohol groups (such as a fully saponified or a partially saponified poly(vinyl alco› hol), orpoly(vinyl alcohol-ethylene) copolymer groups such as a fully saponified or a partially saponified poly(vinyl alcohol-ethylene) copolymer), cellulose derivatives (such as carboxymethyl cellulose, hydroxyalkyl cellulose (hydroxy› ethyl cellulose, hydroxypropyl cellulose, ethylhydroxyethyl cellulose), methyl cellulose, ethyl cellulose, carboxymethy› lethyl cellulose, carboxymethyl cellulose, carboxymethyl cellulose sodium, cellulose ester, etc.), polyalkylene glycol, polyvinyl pyrrolidone, water-soluble nylon, and polyacrylic acid. Particularly preferably they are polyvinyl alcohol groups such as a fully saponified or a partially saponified poly(vinyl alcohol), hydroxyalkyl cellulose such as hydroxyethyl cellulose, hydroxypropyl cellulose, etc., poly› alkylene glycol, polyvinyl pyrrolidone, water-soluble nylon, and polyacrylic acid. 

As the polymer Bother than polyamide 1010 resin in the present invention, remarkably preferably polyvinyl alcohol groups are used. In more detail, the polyvinyl alcohol group means a polymer having a structure represented the follow› ing general formula (1) in its molecule. 

Although it may be a poly(vinyl alcohol) (a fully saponi› fied or a partially saponified poly(vinyl alcohol). There is also a case where it is called merely as a polyvinyl alcohol.) and a poly(vinyl alcohol-ethylene) (a fully saponified or a partially saponified poly(vinyl alcohol-ethylene)), a polyvi› nyl alcohol is preferred from the viewpoint of solubility. 

The molecular weight of the polymer B other than poly› amide 1010 resin is preferably 1,000 to 100,000,000 as weight average molecular weight, more preferably 1,000 to 10,000,000, further preferably 5,000 to 1,000,000, particu› larly preferably 10,000 to 500,000, and most preferably 10,000 to 100,000. 

The weight average molecular weight referred to here is the weight average molecular weight value measured by gel permeation chromatography (GPC) using water as solvent and converted in terms of polyethylene glycol. 

Dimethyl formamide is used if water does not serve for the measurement, and tetrahydrofuran is used if measure› ment is still impossible. If it is still further impossible to make measurements, then hexafluoroisopropanol is used. 

With respect to the polyvinyl alcohol group, it is general to produce polyvinyl alcohol by polymerizing vinyl acetate as a raw material and thereafter hydrolyzing it under an alkali condition, and therein usually sodium acetate partially remains as impurities, which is contained around 0.2 mass% even in a product on the market. 

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We found that the above-described sodium acetate con› tained in the polyvinyl alcohol influences to some extent, and when an emulsion is formed by dissolving and mixing it into polyamide 1010 resin and an organic solvent, if the temperature is 100° C. or higher, the microparticles are colored, or the recycling property deteriorates by deteriora- tion of the polyvinyl alcohol. 

Namely, to stabilize the polyvinyl alcohol group which is polymer B other than polyamide 1010 resin even under a condition for producing microparticles at 100° C. or higher, it is preferred to reduce the amount of sodium acetate existed in the system for forming an emulsion. As a method therefor, it is preferred to use polyvinyl alcohol with a small content of sodium acetate as the polyvinyl alcohol group. 

In this case, the amount of sodium acetate in the used polyvinyl alcohol relative to 100 parts by mass of polyvinyl alcohol is 0.1 part by mass or less, preferably 0.05 part by mass or less, more preferably 0.01 part by mass or less. 

By controlling it in this range, even if polyamide 1010 resin is made into microparticles under a high-temperature condition, it can be suppressed that the polyvinyl alcohol group is modified originating from decomposition or cross› linking, and making it into microparticles under a high› temperature condition can be stabilized. Further, a prefer- able lower limit thereof is 0 part by mass. 

To obtain polyvinyl alcohol group in little content of sodium acetate, for example, exemplified are a method for washing it by an organic solvent such as methanol or ethanol, a reprecipitation method for producing it by pre› cipitating it in a poor solvent for polyvinyl alcohol group after dissolving it in water and the like, a ultrafiltration method, a method for removing the sodium acetate by ion exchange resin, ion exchange carrier and the like. 

Further, as another method of suppressing the influence due to sodium acetate when an emulsion is formed, a method for adding an acid compound to the system of forming the emulsion can be exemplified. By this, a condition where sodium acetate substantially is not contained can be realized. 

As the acid compounds, exemplified are aliphatic carbox- ylic acids such as formic acid, acetic acid, valeric acid, butyric acid, hexanoic acid, heptanoic acid, octanoic acid, acrylic acid, methacrylic acid, crotonic acid, oxalic acid, malonic acid, fumaric acid, maleic acid, glutaric acid, adipic acid, sebacic acid, pyruvic acid, succinic acid and poly- acrylic acid, carboxylic acids having a hydroxyl group such as lactic acid, glycolic acid, L-ascorbic acid, erythorbic acid, malic acid, shikimic acid, citric acid, hydrosuccinic acid and tartaric acid, aromatic carboxylic acids such as benzoic acid, 2-fluorobenzoic acid and regioisomers thereof, 2-chloroben- zoic acid and regioisomers thereof, 2-bromobenzoic acid and regioisomers thereof, 2-nitro benzoic acid and regioi› somers thereof, 2-toluic acid and regioisomers thereof, phe› noxyacetic acid, cinnamic acid, phenyl malonic acid, phthalic acid, terephthalic acid and salicylic acid, amino acids such as glycine, alanine, valine, leucine, isoleucine, serine, threonine, praline, lysin, aspartic acid, glutaminic acid, cysteine, methionine, phenylalanine, tyrosine, histi› dine, asparagine, glutamine, arginine, tryptophan, omithine and sarcosine, organic sulfonic acids such as methane sul- fonic acid, benzene sulfonic acid, p-toluene sulfonic acid and regioisomers thereof, p-hydroxybenzene sulfonic acid and regioisomers thereof, organic phosphorus acids such as phenyl phosphonic acid, diphenyl phosphinic acid, diphenyl phosphate and 1-naphthyl phosphate, salts consisting of a strong acid and a weak base such as magnesium sulfate, magnesium chloride, ammonium chloride and anm10nium sulfate, and inorganic acids such as hydrochloric acid, 

