Sizing agent, sizing agent-adhered carbon fibers and method for producing same, aqueous dispersion of sizing agent, prepreg and method for producing same, and method for producing carbon fiber-reinforced composite material

Sizing agent-adhered carbon fibers, comprising:

• a sizing agent adhered to carbon fibers, wherein
• the sizing agent comprises 5 to 25% by mass a surfactant, based on a total mass of the sizing agent,
• a heat weight loss B-2 is 65% or more, as determined by a measurement method defined below with respect to an extract extracted from the sizing agent-adhered carbon fibers by an extraction operation defined below,
• wherein the extraction operation comprises:
• immersing 100 parts by mass of the sizing agent-adhered carbon fibers in 2000 parts by mass of methyl ethyl ketone, followed by performing ultrasonic cleaning at 30° C. for 30 minutes;
• separating the carbon fibers from an extraction liquid obtained by ultrasonic cleaning by a filtration operation;
• repeating operations of the immersing and separating three times with respect to the separated carbon fibers;
• and mixing the extraction liquids obtained in respective filtration operations and depressurized to distill off the methyl ethyl ketone to obtain an extract,
• wherein the measurement method for the heat weight loss B-2 comprises:
• taking W20 (mg) of the extract in a range of 10±2 mg;
• heating the extract from 100° C. at a rate of 5° C./min in a nitrogen stream of 200 mL (in terms of a volume at 1 atm and 25° C.)/min, using a thermogravimetric analyzer;
• reading the mass of the extract having reached 350° C. as W22 (mg);
• and calculating the heat weight loss B-2 by formula (iv):
• heat weight loss B-2(%)={(W20−W22)/W20}×100 (iv), and
• the surfactant has a heat weight loss B-4 of 10% or more, as determined by a measurement method defined below,
• wherein the measurement method for the heat weight loss B-4 comprises:
• taking W40 (mg) of the surfactant in a range of 10±2 mg;
• heating the surfactant from 100° C. at a rate of 5° C./min in a nitrogen stream of 200 mL (in terms of a volume at 1 atm and 25° C.)/min, using a thermogravimetric analyzer:
• reading the mass of the surfactant having reached 350° C. as W42 (mg);
• and calculating the heat weight loss B-4 by formula (iii):
• heat weight loss B-4(%)={(W40−W42)/W40}×100 (iii).

A sizing agent aqueous dispersion, comprising:

• a sizing agent comprising 5 to 25% by mass a surfactant, based on a total mass of the sizing agent;
• and
• water, wherein
• the sizing agent aqueous dispersion has a heat weight loss B-3 of 65% or more as determined by a measurement method defined below,
• wherein the measurement method for the heat weight loss B-3 comprises:
• weighting 1 g of the sizing agent aqueous dispersion, followed by heating at 110° C. for 1 hour to remove water to recover the sizing agent;
• taking W30 (mg) of the sizing agent in a range of 10±2 mg;
• heating the sizing agent from 100° C. at a rate of 5° C./min in a nitrogen stream of 200 mL (in terms of a volume at 1 atm and 25° C.)/min, using a thermogravimetric analyzer;
• reading the mass of the sizing agent having reached 350° C. as W32 (mg);
• and calculating the heat weight loss B-3 by formula (vi):
• heat weight loss B-3(%)={(W30−W32)/W30}×100 (vi), and
• the surfactant has a heat weight loss B-4 of 10% or more, as determined by a measurement method defined below,
• wherein the measurement method for the heat weight loss B-4 comprises:
• taking W40 (mg) of the surfactant in a range of 10±2 mg;
• heating the surfactant from 100° C. at a rate of 5° C./min in a nitrogen stream of 200 mL (in terms of a volume at 1 atm and 25° C.)/min, using a thermogravimetric analyzer:
• reading the mass of the surfactant having reached 350° C. as W42 (mg);
• and calculating the heat weight loss B-4 by formula (iii):
• heat weight loss B-4(%)={(W40−W42)/W40}×100 (iii).

A sizing agent, having a heat weight loss B-1 of 65% or more as determined by a measurement method defined below,

• wherein the sizing agent comprises a compound (1) of formula (1):
• X1 being a direct bond or a binding group of formula (1′),
• R1 and R2 independently being H or a substituent comprising 1 to 7 carbon atoms, and R3, R4, R5 and R6 independently being H or a hydrocarbon group comprising 1 to 3 carbon atoms,
• Y1 and Y2 independently being H or a hydrocarbon group comprising 1 to 3 carbon atoms, and each wavy line indicating a bonding site with an adjacent group, and
• the measurement method for the heat weight loss B-1 comprises:
• taking W10 (mg) of the sizing agent in a range of 10±2 mg;
• heating the sizing agent from 100° C. at a rate of 5° C./min in a nitrogen stream of 200 mL (in terms of a volume at 1 atm and 25° C.)/min, using a thermogravimetric analyzer;
• reading a mass of the sizing agent having reached 350° C. as W12 (mg);
• and calculating the heat weight loss B-1 by formula (i):
• heat weight loss B-1(%)={(W10−W12)/W10}×100 (i).

Sizing agent-adhered carbon fibers, comprising:

• a sizing agent adhered to carbon fibers,
• wherein the sizing agent comprises a compound (1) of formula (1):
• X1 being a direct bond or a binding group of formula (1′),
• R1 and R2 independently being H or a substituent comprising 1 to 7 carbon atoms, and R3, R4, R5 and R6 independently being H or a hydrocarbon group comprising 1 to 3 carbon atoms,
• Y1 and Y2 independently being H or a hydrocarbon group comprising 1 to 3 carbon atoms, and each wavy line indicating a bonding site with an adjacent group, and
• a heat weight loss B-2 is 65% or more as determined by a measurement method defined below with respect to an extract extracted from the sizing agent-adhered carbon fibers by an extraction operation defined below,
• wherein the extraction operation comprises:
• immersing 100 parts by mass of the sizing agent-adhered carbon fibers in 2000 parts by mass of methyl ethyl ketone, followed by performing ultrasonic cleaning at 30° C. for 30 minutes;
• separating the carbon fibers from an extraction liquid obtained by ultrasonic cleaning by a filtration operation;
• repeating operations of the immersing and separating three times with respect to the separated carbon fibers;
• and mixing the extraction liquids obtained in respective filtration operations and depressurized to distill off the methyl ethyl ketone to obtain an extract,
• wherein the measurement method for the heat weight loss B-2 comprises:
• taking W20 (mg) of the extract in a range of 10 f 2 mg;
• heating the extract from 100° C. at a rate of 5° C./min in a nitrogen stream of 200 mL (in terms of a volume at 1 atm and 25° C.)/min, using a thermogravimetric analyzer;
• reading the mass of the extract having reached 350° C. as W22 (mg);
• and calculating the heat weight loss B-2 by formula (iv):
• heat weight loss B-2(%)={(W20−W22)/W20}×100 (iv).