This isocyanate production method, for continuously producing an isocyanate while suppressing side reactions, is a method for producing an isocyanate through the thermal decomposition of carbamate, and comprises: a thermal decomposition step in which a mixed solution containing carbamate and a compound (A) having a specific structure is continuously put into a pyrolysis reactor and carry out a pyrolysis reaction of carbamate; a low-boiling-point decomposition product recovery step in which a low-boiling-point decomposition product having a lower standard boiling point than the compound (A) is continuously extracted in a gaseous form from the pyrolysis reactor, and a high-boiling-point component recovery step in which a liquid phase component, which is not recovered in a gaseous form in the low-boiling-point decomposition product recovery step, is continuously extracted as a high-boiling-point component from the pyrolysis reactor.

This isocyanate production method, for continuously producing an isocyanate while suppressing side reactions, is a method for producing an isocyanate through the thermal decomposition of carbamate, and comprises: a thermal decomposition step in which a mixed solution containing carbamate and a compound (A) having a specific structure is continuously put into a pyrolysis reactor and carry out a pyrolysis reaction of carbamate; a low-boiling-point decomposition product recovery step in which a low-boiling-point decomposition product having a lower standard boiling point than the compound (A) is continuously extracted in a gaseous form from the pyrolysis reactor, and a high-boiling-point component recovery step in which a liquid phase component, which is not recovered in a gaseous form in the low-boiling-point decomposition product recovery step, is continuously extracted as a high-boiling-point component from the pyrolysis reactor.

According to an embodiment, the pH of a diisocyanate composition and a diamine hydrochloride composition used in the preparation of an optical lens is adjusted to a specific range, whereby it is possible to enhance not only the yield and purity of the diisocyanate composition but also the optical characteristics of the final optical lens by suppressing the striae and cloudiness. Specifically, according to the process of the embodiment, the amount of an aqueous hydrochloric acid solution introduced to the reaction may be adjusted to control the pH of the diisocyanate composition to a desired range, thereby enhancing the yield and purity. Accordingly, the process for preparing a diisocyanate composition according to the embodiment can be applied to the preparation of a plastic optical lens of high quality.

According to an embodiment, the pH of a diisocyanate composition and a diamine hydrochloride composition used in the preparation of an optical lens is adjusted to a specific range, whereby it is possible to enhance not only the yield and purity of the diisocyanate composition but also the optical characteristics of the final optical lens by suppressing the striae and cloudiness. Specifically, according to the process of the embodiment, the amount of an aqueous hydrochloric acid solution introduced to the reaction may be adjusted to control the pH of the diisocyanate composition to a desired range, thereby enhancing the yield and purity. Accordingly, the process for preparing a diisocyanate composition according to the embodiment can be applied to the preparation of a plastic optical lens of high quality.

According to an embodiment, the pH of a diisocyanate composition and a diamine hydrochloride composition used in the preparation of an optical lens is adjusted to a specific range, whereby it is possible to enhance not only the yield and purity of the diisocyanate composition but also the optical characteristics of the final optical lens by suppressing the striae and cloudiness. Specifically, according to the process of the embodiment, the amount of an aqueous hydrochloric acid solution introduced to the reaction may be adjusted to control the pH of the diisocyanate composition to a desired range, thereby enhancing the yield and purity. Accordingly, the process for preparing a diisocyanate composition according to the embodiment can be applied to the preparation of a plastic optical lens of high quality.

The present invention relates to a method for operating a plant for continuous production of an isocyanate by converting a primary amine A with phosgene P whilst maintaining, based on the amino groups of the primary amine, a stoichiometric excess of phosgene in the presence of a solvent L in the liquid phase, using a first, adiabatically operated reaction chamber and a second, isothermally operated reaction chamber. The method is characterised in that a combination of measures, in particular the maintenance of a sufficiently high starting pressure and a sufficiently high starting temperature, is applied in order to bring the plant back into the target state, standard operation, starting from a state of interruption to production.

The present invention relates to a method for operating a plant for continuous production of an isocyanate by converting a primary amine A with phosgene P whilst maintaining, based on the amino groups of the primary amine, a stoichiometric excess of phosgene in the presence of a solvent L in the liquid phase, using a first, adiabatically operated reaction chamber and a second, isothermally operated reaction chamber. The method is characterised in that a combination of measures, in particular the maintenance of a sufficiently high starting pressure and a sufficiently high starting temperature, is applied in order to bring the plant back into the target state, standard operation, starting from a state of interruption to production.

An isocyanate composition according to the present invention contains: a difunctional or more-functional isocyanate compound; and 1.0 ppm by mass to 1.0×10.sup.4 ppm by mass, based on the isocyanate compound, of a compound having at least one unsaturated bond excluding unsaturated bonds constituting an aromatic ring, the compound being different from the isocyanate.

An isocyanate composition according to the present invention contains: a difunctional or more-functional isocyanate compound; and 1.0 ppm by mass to 1.0×10.sup.4 ppm by mass, based on the isocyanate compound, of a compound having at least one unsaturated bond excluding unsaturated bonds constituting an aromatic ring, the compound being different from the isocyanate.

An object of the present invention is to provide a sizing agent composition that gives a carbon fiber from which a carbon fiber-reinforced composite material having excellent adhesion between a resin and the carbon fiber and having excellent mechanical properties can be formed. The sizing agent composition of the invention is a sizing agent composition comprising (A) a blocked isocyanate, and (B) a compound containing at least one polar group and at least one unsaturated group per molecule. In the invention, the mixing ratio (mass ratio) of the blocked isocyanate (A) and the compound (B) containing at least one polar group and at least one unsaturated group per molecule (A/B) is preferably 95/5 to 5/95. In the invention, the blocked isocyanate (A) is preferably a compound having an aliphatic skeleton.