Objects of the present invention are to provide a phosphoric acid-esterified fine cellulose fiber of which slurry shows superior transparency, and to provide a method for producing a phosphorylated fine cellulose fiber showing superior transparency with good efficiency and high yield. According to the present invention, there is provided a phosphoric acid-esterified fine cellulose fiber, of which 0.2 mass % aqueous dispersion shows a solution haze of 15% or lower.

Objects of the present invention are to provide a phosphoric acid-esterified fine cellulose fiber of which slurry shows superior transparency, and to provide a method for producing a phosphorylated fine cellulose fiber showing superior transparency with good efficiency and high yield. According to the present invention, there is provided a phosphoric acid-esterified fine cellulose fiber, of which 0.2 mass % aqueous dispersion shows a solution haze of 15% or lower.

A fine cellulose fiber-containing substance that has excellent dispersibility in water and can be manufactured easily. A method is for manufacturing the fine cellulose fiber-containing substance, and a method is for manufacturing a fine cellulose fiber dispersion. A fine cellulose fiber-containing substance contains fine cellulose fibers into which a phosphite containing a cation of an inorganic substance is introduced. The ratio of the cation of the inorganic substance with respect to 1 g of the fine cellulose fibers is 0.14 mmol or more. In manufacturing the fine cellulose fiber-containing substance, a phosphite is introduced into cellulose fibers, and then the cellulose fibers are defibrated to obtain a dispersion containing fine cellulose fibers, during which an alkali metal ion-containing substance is added to the cellulose fibers, and the dispersion is concentrated. In manufacturing a fine cellulose fiber dispersion, the fine cellulose fiber-containing substance is mixed with water.

An object of the present invention is to provide ultrafine fibrous cellulose capable of exhibiting excellent coating suitability when added to paint. The present invention relates to fibrous cellulose having a fiber width of 1,000 nm or less, in which, when the fibrous cellulose is dispersed in water to form a dispersion liquid having a viscosity of 2,500 mPa.Math.s at 23° C., and the dispersion liquid is stirred under predetermined stirring conditions, a viscosity change rate falls within ±50%, calculated by the following formula: viscosity change rate (%)=(viscosity after stirring−viscosity before stirring)/viscosity before stirring×100

An object of the present invention is to provide ultrafine fibrous cellulose capable of exhibiting excellent coating suitability when added to paint. The present invention relates to fibrous cellulose having a fiber width of 1,000 nm or less, in which, when the fibrous cellulose is dispersed in water to form a dispersion liquid having a viscosity of 2,500 mPa.Math.s at 23° C., and the dispersion liquid is stirred under predetermined stirring conditions, a viscosity change rate falls within ±50%, calculated by the following formula: viscosity change rate (%)=(viscosity after stirring−viscosity before stirring)/viscosity before stirring×100

Composite particles that are biodegradable and easy to handle while maintaining the characteristics of cellulose nanofibers, a method of producing composite particles, a dry powder containing the composite particles, and a skin application composition and a method of producing the skin application composition. A composite particle contains at least one type of particle and fine cellulose with which at least part of a surface of the particle is coated, wherein the particle and the fine cellulose are inseparable.

Fine cellulose fiber has a dispersion with a very high transparency and viscosity. A method is for producing the fine cellulose fiber. In the cellulose fiber, a part of hydroxy groups of cellulose fiber is substituted with a predetermined functional group to introduce an ester of phosphorus-oxo acid, and substituted with a carbamate group to introduce a carbamate. The method for producing fine cellulose fiber includes adding an additive (A) and an additive (B) including at least one of urea and a urea derivative to cellulose fiber, heating the mixture at 100 to 210° C., washing the mixture, and then fibrillating the mixture, the additive (B) being added in an amount of 0.01 to 100 mol based on 1 mol of the additive (A).

The present invention is intended to enhance the transparency of a composition obtained using ultrafine cellulose fibers having phosphorous acid groups, while suppressing the yellowing of the ultrafine cellulose fibers. The present invention relates to cellulose fibers having a fiber width of 1000 nm or less and having a phosphorus oxoacid group or a phosphorus oxoacid group-derived substituent, wherein when a first amount of dissociated acid in the cellulose fibers is set to be A1 and a total amount of dissociated acid in the cellulose fibers is set to be A2, A1 is 1.35 mmol/g or more, and the value of A1/A2 is 0.51 or more, and when a sheet is formed under a predetermined condition, the YI value of the sheet is 6.0 or less.

The present invention is intended to provide ultrafine cellulose fibers capable of enhancing the transparency of an ultrafine cellulose fiber-dispersed solution having phosphorous acid groups. The present invention relates to a method for producing cellulose fibers, comprising: mixing a compound having a phosphorous acid group and/or a salt thereof and urea and/or a urea derivative into a cellulose raw material to obtain a phosphorous acid esterified cellulose raw material, and performing a fibrillation treatment on the phosphorous acid esterified cellulose raw material to obtain cellulose fibers having a fiber width of 1000 nm or less and having a phosphorous acid group, wherein, in obtaining the phosphorous acid esterified cellulose raw material, the decomposition percentage of the urea and/or the urea derivative is set to be 90% or less.

The present invention is intended to provide ultrafine cellulose fibers capable of enhancing the transparency of an ultrafine cellulose fiber-dispersed solution having phosphorous acid groups. The present invention relates to a method for producing cellulose fibers, comprising: mixing a compound having a phosphorous acid group and/or a salt thereof and urea and/or a urea derivative into a cellulose raw material to obtain a phosphorous acid esterified cellulose raw material, and performing a fibrillation treatment on the phosphorous acid esterified cellulose raw material to obtain cellulose fibers having a fiber width of 1000 nm or less and having a phosphorous acid group, wherein, in obtaining the phosphorous acid esterified cellulose raw material, the decomposition percentage of the urea and/or the urea derivative is set to be 90% or less.