A resin powder for solid freeform fabrication, having a ratio (Mv/Mn) of 2.00 or less, where Mv represents a volume average particle diameter and Mn represents a number average particle diameter and a ratio of melt mass-flow rate B to melt mass-flow rate A of greater than 0.80 to 1.20, wherein the melt mass-flow rate A and the melt mass-flow rate B are respectively measured at 15 degrees C. higher than the melting point under a load of 2.16 kg according to JIS K7210 format before and after the resin powder is maintained at a temperature 15 degrees C. lower than the melting point under a pressure of 0.1 kPa for four hours.

To provide a polyacetal resin composition and a molded article thereof, which are less likely to crack even if stressed in contact with any hydrochloric acid-containing liquid. The polyacetal resin composition contains, per 100 parts by mass of a polyacetal resin: 0.01 to 10 parts by mass of at least one fatty acid metal salt selected from 1) to 3) below; and 0.1 to 5 parts by mass of a stress relaxant having a melting point of 67.5° C. to 200° C. when measured by using a differential scanning calorimeter at a flow rate of nitrogen of 20 cm.sup.3/min and at a heating rate of 10° C./min. 1) metal salt formed of long chain fatty acid having 10 to 34 carbon atoms and calcium; 2) metal salt formed of long chain fatty acid having 10 to 34 carbon atoms and zinc; and, 3) metal salt formed of long chain fatty acid having 10 to 34 carbon atoms and magnesium

To provide a polyacetal resin composition and a molded article thereof, which are less likely to crack even if stressed in contact with any hydrochloric acid-containing liquid. The polyacetal resin composition contains, per 100 parts by mass of a polyacetal resin: 0.01 to 10 parts by mass of at least one fatty acid metal salt selected from 1) to 3) below; and 0.1 to 5 parts by mass of a stress relaxant having a melting point of 67.5° C. to 200° C. when measured by using a differential scanning calorimeter at a flow rate of nitrogen of 20 cm.sup.3/min and at a heating rate of 10° C./min. 1) metal salt formed of long chain fatty acid having 10 to 34 carbon atoms and calcium; 2) metal salt formed of long chain fatty acid having 10 to 34 carbon atoms and zinc; and, 3) metal salt formed of long chain fatty acid having 10 to 34 carbon atoms and magnesium

To provide a polyacetal resin composition and a molded article thereof, which are less likely to crack even if stressed in contact with any hydrochloric acid-containing liquid. The polyacetal resin composition contains, per 100 parts by mass of a polyacetal resin: 0.01 to 10 parts by mass of at least one fatty acid metal salt selected from 1) to 3) below; and 0.1 to 5 parts by mass of a stress relaxant having a melting point of 67.5° C. to 200° C. when measured by using a differential scanning calorimeter at a flow rate of nitrogen of 20 cm.sup.3/min and at a heating rate of 10° C./min. 1) metal salt formed of long chain fatty acid having 10 to 34 carbon atoms and calcium; 2) metal salt formed of long chain fatty acid having 10 to 34 carbon atoms and zinc; and, 3) metal salt formed of long chain fatty acid having 10 to 34 carbon atoms and magnesium

A gear is provided that has excellent continuous moldability for practical use, and both high slidability and high durability. The provided gear is a molded resin constructed of a resin composition comprising a thermoplastic resin (A) and cellulose nanofibers (B) with an average fiber diameter of 1000 nm or smaller, and having a number average molecular weight of the thermoplastic resin (A) in the range of 10,000 to 150,000, wherein a sliding surface of the gear with another gear teeth has an arithmetic mean surface roughness Sa of 3.0 μm or lower.

A gear is provided that has excellent continuous moldability for practical use, and both high slidability and high durability. The provided gear is a molded resin constructed of a resin composition comprising a thermoplastic resin (A) and cellulose nanofibers (B) with an average fiber diameter of 1000 nm or smaller, and having a number average molecular weight of the thermoplastic resin (A) in the range of 10,000 to 150,000, wherein a sliding surface of the gear with another gear teeth has an arithmetic mean surface roughness Sa of 3.0 μm or lower.

Provided is a resin composition having high conductivity, having a reduced variation in conductivity among pellets, and being excellent in surface appearance when injection-molded. The resin composition includes: a polyacetal; conductive carbon black; and graphite, wherein the conductive carbon black has a dibutyl phthalate oil absorption of 320 mL/100 g or less, wherein the content of the polyacetal in the resin composition is 50 mass % or more, wherein the content of the conductive carbon black in the resin composition is 11 mass % or more and 18 mass % or less, and wherein the conductive carbon black has a packed bulk density specified in JIS K 5101-12-2 of 0.14 g/mL or more and 0.25 g/mL or less.

Provided is a resin composition having high conductivity, having a reduced variation in conductivity among pellets, and being excellent in surface appearance when injection-molded. The resin composition includes: a polyacetal; conductive carbon black; and graphite, wherein the conductive carbon black has a dibutyl phthalate oil absorption of 320 mL/100 g or less, wherein the content of the polyacetal in the resin composition is 50 mass % or more, wherein the content of the conductive carbon black in the resin composition is 11 mass % or more and 18 mass % or less, and wherein the conductive carbon black has a packed bulk density specified in JIS K 5101-12-2 of 0.14 g/mL or more and 0.25 g/mL or less.

To provide a resin composition, a pellet, a composite molded article, a method for manufacturing a composite molded article and a tank, all capable of enabling tight joining and integration of the polyacetal resin molded article and the polyethylene resin molded article, and of suppressing formaldehyde emission and occurrence of mold deposit. The resin composition contains a resin ingredient and melamine, the resin ingredient containing a polyacetal resin and a maleic anhydride-modified polyethylene resin, the polyacetal resin and the maleic anhydride-modified polyethylene resin following a mass proportion of (20 to 49):(80 to 51), and molar concentration of the maleic anhydride group capable of reacting with amino group of melamine contained in the resin composition being 5 to 25 μmol/g.

To provide a resin composition, a pellet, a composite molded article, a method for manufacturing a composite molded article and a tank, all capable of enabling tight joining and integration of the polyacetal resin molded article and the polyethylene resin molded article, and of suppressing formaldehyde emission and occurrence of mold deposit. The resin composition contains a resin ingredient and melamine, the resin ingredient containing a polyacetal resin and a maleic anhydride-modified polyethylene resin, the polyacetal resin and the maleic anhydride-modified polyethylene resin following a mass proportion of (20 to 49):(80 to 51), and molar concentration of the maleic anhydride group capable of reacting with amino group of melamine contained in the resin composition being 5 to 25 μmol/g.