JP7206618B2 - Prepreg manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a resin-coated reinforcing fiber base material, a method for producing the same, a method for producing a prepreg, and a method for producing a fiber-reinforced molded product.

Fiber-reinforced molded articles are used in a wide range of applications such as vehicles (automobiles, railroad vehicles, etc.), transportation equipment such as aircraft, construction members, and electronic devices, due to their high strength and light weight. A prepreg in which a reinforcing fiber base material is impregnated with a matrix resin is used for manufacturing a fiber-reinforced molded article. Thermosetting resins and thermoplastic resins have been conventionally used as matrix resins. It has also been proposed to use a fluororesin as the matrix resin.

Patent Document 1 discloses a prepreg in which a reinforcing fiber base material is impregnated with a matrix resin obtained by adding fluororesin powder to a thermosetting resin.
Patent Document 2 discloses a prepreg in which a reinforcing fiber base material is impregnated with a matrix resin obtained by dry-blending a thermoplastic resin and a fluororesin.
Patent Document 3 discloses a prepreg in which a reinforcing fiber base material is impregnated with a matrix resin consisting of a fluororesin alone or a matrix resin consisting of a mixed resin with a thermoplastic resin containing a fluororesin as a main component.

WO2017/122743 WO2017/122735 WO2017/122740

However, the mechanical strength of fiber-reinforced molded articles obtained using prepregs such as those disclosed in Patent Documents 1 to 3 is still insufficient, and further improvement in mechanical strength is required.

The present invention aims to provide a resin-coated reinforcing fiber base material, a method for producing a resin-coated reinforcing fiber base material, a method for producing a prepreg, and a method for producing a fiber-reinforced molded product, which can produce a fiber-reinforced molded product with high mechanical strength. aim.

The present invention has the following configurations.
[1] A powder containing a fluororesin having a D50 of 0.5 to 100 μm is added to a reinforcing fiber base material, and the ratio of the volume of the reinforcing fiber base material to the total volume of the reinforcing fiber base material and the powder is 0.5. A method for producing a resin-coated reinforcing fiber base material, in which the coating is applied so as to be 70 to 0.99.
[2] The method for producing a resin-coated reinforcing fiber base material according to [1], wherein the reinforcing fiber base material coated with the powder is heated at a temperature equal to or higher than the melting point of the fluororesin.
[3] The fluororesin has at least one functional group selected from the group consisting of a carbonyl group-containing group, a hydroxy group, an epoxy group and an isocyanate group, and has a melting point of 100 to 325° C. [ 1] or [2] method for producing a reinforcing fiber base material with resin.
[4] The method for producing a resin-coated reinforcing fiber base material according to [3], wherein the fluororesin has a melting point of 150°C or higher and lower than 260°C.
[5] The method for producing a resin-coated reinforcing fiber base material according to [3], wherein the fluororesin has a melting point of 260°C or higher and 325°C or lower.
[6] The resin according to any one of [1] to [5], wherein the reinforcing fiber base material is any one of a reinforcing fiber fabric, a reinforcing fiber sheet in which reinforcing fibers are aligned in one direction, or a reinforcing fiber nonwoven fabric. A method for producing a reinforcing fiber base material with.
[7] The method for producing a resin-coated reinforcing fiber base material according to any one of [1] to [6], wherein the reinforcing fiber contained in the reinforcing fiber base material is carbon fiber, glass fiber, or aramid fiber. .
[8] A reinforcing fiber base material with resin is produced by the method for producing a reinforcing fiber base material with resin according to any one of [1] to [7], and a non-fluororesin is added to the reinforcing fiber base material with resin. Impregnated so that the ratio of the volume of the reinforcing fiber base material to the total volume of the fiber base material, the resin component derived from the resin of the resin-attached reinforcing fiber base material, and the non-fluororesin is 0.40 to 0.60. A method for manufacturing a prepreg.
[9] The method for producing a prepreg according to [8], wherein the non-fluororesin is a thermoplastic resin or a thermosetting resin.
[10] The method for producing a prepreg according to [8] or [9], wherein the resin-coated reinforcing fiber base material is surface-treated before being impregnated with the non-fluororesin.
[11] A reinforcing fiber base material and a powder containing a fluororesin having a D50 of 0.5 to 100 μm, wherein the ratio of the volume of the reinforcing fiber base material to the total volume of the reinforcing fiber base material and the powder is 0.70 to 0.99 resin-coated reinforcing fiber base material.
[12] A method for producing a fiber-reinforced molded product, comprising producing a prepreg by the method for producing a prepreg according to any one of [8] to [10], and molding the prepreg to obtain a fiber-reinforced molded product.
[13] Laminating the resin-coated reinforcing fiber base materials obtained by any of the production methods of [1] to [7] to produce a laminate composed of a plurality of resin-coated reinforcing fiber base materials, and heating the laminate. A method for producing a fiber-reinforced molded product, comprising impregnating with a plastic resin or thermosetting resin and then molding.
[14] After laminating the resin-coated reinforcing fiber base material obtained by the production method of any one of [1] to [7] and a film made of a thermoplastic resin in a mold, the melting point of the thermoplastic resin A method for producing a fiber-reinforced molded product, which is formed by hot-pressing at the above temperature.

According to the present invention, it is possible to provide a resin-coated reinforcing fiber base material, a method for producing a resin-coated reinforcing fiber base material, a method for producing a prepreg, and a method for producing a fiber-reinforced molded product, which can produce a fiber-reinforced molded product with high mechanical strength. .

The following terms have the following meanings.
"D50" of the powder is the volume-based cumulative 50% diameter determined by the laser diffraction/scattering method. That is, the particle size distribution is measured by a laser diffraction/scattering method, and the cumulative curve is obtained with the total volume of the group of particles being 100%.
"Melting point" means the temperature corresponding to the maximum melting peak measured by differential scanning calorimetry (DSC).
By "melt moldable" is meant exhibiting melt flowability.
“Exhibiting melt fluidity” means that there exists a temperature at which the melt flow rate is 0.01 to 1000 g/10 minutes at a temperature 20° C. or more higher than the melting point of the resin under a load of 49 N. .
"Melt flow rate" means melt mass flow rate (MFR) defined in JIS K 7210:1999 (ISO 1133:1997).
"A unit based on a monomer" is a general term for an atomic group directly formed by polymerization of one molecule of a monomer and an atomic group obtained by chemically converting a part of the atomic group. In this specification, units based on monomers are also simply referred to as monomer units.
A "monomer" is a compound having a polymerizable unsaturated bond such as a polymerizable double bond.
"Acid anhydride group" means a group represented by -C(=O)-OC(=O)-.
A "carbonyl group-containing group" is a group having a carbonyl group (-C(=O)-) in its structure.
An “etheric oxygen atom” is an oxygen atom (—C—O—C—) present between carbon atoms.
A “perfluoroalkyl group” is a group in which all hydrogen atoms of an alkyl group are substituted with fluorine atoms. A “perfluoroalkylene group” is a group in which all hydrogen atoms of an alkylene group are substituted with fluorine atoms.
"~" indicating a numerical range means that the numerical values before and after it are included as lower and upper limits.
A copolymer having units based on ethylene and units based on tetrafluoroethylene is referred to as an "ethylene/tetrafluoroethylene copolymer". Other copolymers are similarly described.

[Reinforcing fiber base material with resin]
The resin-coated reinforcing fiber base material of the present invention includes a reinforcing fiber base material and powder containing a fluororesin having a D50 of 0.5 to 100 μm (hereinafter referred to as “powder A”).

(Reinforcing fiber base material)
Inorganic fibers, metal fibers, and organic fibers can be exemplified as the reinforcing fibers used in the reinforcing fiber base material.
Examples of inorganic fibers include carbon fibers, graphite fibers, glass fibers, silicon carbide fibers, silicon nitride fibers, alumina fibers, silicon carbide fibers, and boron fibers.
Examples of metal fibers include aluminum fibers, brass fibers, and stainless steel fibers.
Examples of organic fibers include aromatic polyamide fibers, polyaramid fibers, polyparaphenylenebenzoxazole (PBO) fibers, polyphenylene sulfide fibers, polyester fibers, acrylic fibers, nylon fibers, and polyethylene fibers.
As the reinforcing fiber, carbon fiber, glass fiber, or aramid fiber is preferable from the viewpoint of availability.

The reinforcing fibers may or may not be opened. The reinforcing fibers may be surface-treated. Reinforcing fibers may be used singly or in combination of two or more.
As the reinforcing fibers, continuous filaments having a length of 10 mm or more are preferable. The reinforcing fibers do not need to be continuous over the entire lengthwise length or the widthwise width of the reinforcing fiber substrate, and may be divided in the middle.

The form of the reinforcing fiber substrate is not particularly limited, and includes a reinforcing fiber bundle composed of a plurality of reinforcing fibers, a reinforcing fiber fabric obtained by weaving reinforcing fibers, a reinforcing fiber sheet in which reinforcing fibers are aligned in one direction, and reinforcing fibers. A nonwoven fabric and a combination of these can be exemplified. As the reinforcing fiber substrate, a reinforcing fiber fabric, a reinforcing fiber sheet in which reinforcing fibers are aligned in one direction, and a reinforcing fiber nonwoven fabric are preferable from the viewpoint of the strength properties of the resulting fiber-reinforced molded article.

The thickness of the reinforcing fiber base material is preferably 10-500 μm, more preferably 20-300 μm. When the thickness of the reinforcing fiber base material is at least the lower limit value of the above range, the handling properties of the reinforcing fiber base material are excellent. When the thickness of the reinforcing fiber base material is equal to or less than the upper limit value of the above range, the impregnating properties are excellent when producing a fiber-reinforced molded article.
The surface of the carbon fiber is coated (also called sizing) to facilitate handling of the fiber, but in the present invention, both coated carbon fiber and carbon fiber from which the coating agent has been removed can be used. can.

(Powder A)
The powder A preferably contains a fluororesin as a main component. If the fluororesin is the main component, the dielectric constant and dielectric loss tangent of the fiber-reinforced molded article can be made lower. Moreover, the powder A having a high bulk density is easily obtained. The higher the bulk density of the powder A, the better the handleability. The powder A containing a fluororesin as a main component means that the proportion of the fluororesin in the powder A is 80% by mass or more. The proportion of the fluororesin in the powder A is preferably 85% by mass or more, more preferably 90% by mass or more, and particularly preferably 100% by mass.

The fluororesin forming the powder A is preferably melt-moldable. The melting point of the fluororesin is preferably 100 to 325°C, more preferably 150 to 325°C, even more preferably 170 to 325°C. If the melting point of the fluororesin is equal to or higher than the lower limit of the above range, the fiber-reinforced molded product will have excellent heat resistance. If the melting point of the fluororesin is equal to or lower than the upper limit of the above range, a general-purpose apparatus can be used in producing the fiber-reinforced molded product, and the adhesion between members (interlayers) in the fiber-reinforced molded product is excellent.

When a fluororesin having a relatively low melting point is used, the adhesiveness between members (interlayers) in the fiber-reinforced molded article is excellent even if the prepreg is molded at a low temperature. In this respect, the melting point of the fluororesin is preferably 150°C or higher and lower than 260°C, more preferably 170 to 250°C.
It is preferable to use a fluororesin having a relatively high melting point because a fiber-reinforced molded article having high heat resistance can be obtained. From this point of view, the melting point of the fluororesin is preferably 260 to 325°C, more preferably 280 to 325°C.
Note that the melting point of the fluororesin can be adjusted by the type and content of units constituting the fluororesin, the molecular weight, and the like. For example, the melting point tends to be higher as the proportion of the unit u1, which will be described later, increases.

The melt flow rate of the fluororesin is preferably 0.1 to 1000 g/10 minutes, more preferably 0.5 to 100 g/10 minutes, still more preferably 1 to 30 g/10 minutes, and particularly preferably 3 to 25 g/10 minutes. . When the melt flow rate is at least the lower limit of the above range, the fluororesin has excellent moldability. If the melt flow rate is equal to or lower than the upper limit of the above range, the mechanical strength of the fiber-reinforced molded product will be high.

As the fluororesin, polychlorotrifluoroethylene (PCTFE), ethylene/tetrafluoroethylene (hereinafter also referred to as "TFE") copolymer (ETFE), ethylene/chlorotrifluoroethylene (hereinafter also referred to as "CTFE" .) Copolymer (ECTFE), CTFE / TFE copolymer, TFE / hexafluoropropylene (hereinafter also referred to as "HFP".) Copolymer (FEP), TFE / perfluoro (alkyl vinyl ether) (hereinafter, "PAVE ), copolymers (PFA), polyvinylidene fluoride (PVdF), modified polytetrafluoroethylene, and the like. Polytetrafluoroethylene may also be used as long as it exhibits melt fluidity.

Modified polytetrafluoroethylene includes (i) a product obtained by copolymerizing TFE with a very small amount of CH ₂ =CH(CF ₂ ) ₄ F or CF ₂ =CFOCF ₃ , (iii) a copolymer of TFE and a very small amount of an adhesive functional group-containing monomer; (iv) plasma treatment of polytetrafluoroethylene, etc. (v) those obtained by introducing adhesive functional groups into (i) by plasma treatment or the like. Examples of the adhesive functional group include a carbonyl group-containing group, a hydroxy group, an epoxy group, and an isocyanate group.

As the fluororesin, a fluororesin having at least one functional group (hereinafter referred to as "functional group f") selected from the group consisting of a carbonyl group-containing group, a hydroxy group, an epoxy group and an isocyanate group (hereinafter referred to as " Fluororesin F") is preferred. The preferred range of the melting point of the fluororesin F is as described above.
Note that the fluororesin may be a fluororesin that does not have the functional group f.

The functional group f possessed by the fluororesin F may be of one type or two or more types. The functional group f preferably has a carbonyl group-containing group from the viewpoint of adhesiveness between members (interlayers) in the fiber-reinforced molded product.
The carbonyl group-containing group includes, for example, a group having a carbonyl group between carbon atoms of a hydrocarbon group, a carbonate group, a carboxy group, a haloformyl group, an alkoxycarbonyl group, an acid anhydride group, and the like.

Examples of the hydrocarbon group in the group having a carbonyl group between carbon atoms of the hydrocarbon group include an alkylene group having 2 to 8 carbon atoms. The number of carbon atoms in the alkylene group is the number of carbon atoms not including the carbon atoms in the carbonyl group. The alkylene group may be linear or branched.
A haloformyl group is represented by -C(=O)-X (where X is a halogen atom). The halogen atom in the haloformyl group includes a fluorine atom, a chlorine atom and the like, and a fluorine atom is preferred. That is, the haloformyl group is preferably a fluoroformyl group (also referred to as a carbonyl fluoride group).
The alkoxy group in the alkoxycarbonyl group may be linear or branched, preferably an alkoxy group having 1 to 8 carbon atoms, particularly preferably a methoxy group or an ethoxy group.

The content of the functional group f in the fluororesin F is preferably 10 to 60,000, more preferably 100 to 50,000, and even more preferably 100 to 10,000 per 1×10 ⁶ main chain carbon atoms of the fluororesin F. , 300 to 5000 are particularly preferred. When the content of the functional group f is at least the lower limit of the above range, the adhesiveness between members (interlayers) in the fiber-reinforced molded article is further excellent. If the content of the functional group f is equal to or less than the upper limit of the above range, the adhesiveness between members (interlayers) in the fiber-reinforced molded product is excellent even if the prepreg is molded at a low temperature.

The content of the functional group f can be measured by methods such as nuclear magnetic resonance (NMR) analysis and infrared absorption spectroscopy. For example, using a method such as infrared absorption spectrum analysis as described in JP-A-2007-314720, the ratio (mol%) of units having a functional group f in all units constituting the fluororesin F is determined. , the content of the functional group f can be calculated from the ratio.

Examples of the fluororesin F include a unit having a functional group f and a fluoropolymer having a terminal group having a functional group f. Specifically, fluororesins obtained by introducing a functional group f into PCTFE, ETFE, ECTFE, CTFE/TFE copolymers, FEP, PFA, PVdF and the like can be exemplified.

As the fluororesin F, the following fluoropolymer X is preferable from the viewpoint of excellent adhesiveness between members (interlayers) in the fiber-reinforced molded article.
Fluorine-containing polymer X: a unit based on TFE or CTFE (hereinafter also referred to as "unit u1") and a cyclic hydrocarbon monomer having an acid anhydride group (hereinafter also referred to as "acid anhydride-based monomer" ) (hereinafter also referred to as “unit u2”) and a unit based on a fluorine-containing monomer (excluding TFE and CTFE) (hereinafter also referred to as “unit u3”). polymer.

As the monomer constituting the unit u1, TFE is preferable because of its excellent heat resistance.

Acid anhydride monomers include itaconic anhydride (hereinafter also referred to as "IAH"), citraconic anhydride (hereinafter also referred to as "CAH"), 5-norbornene-2,3-dicarboxylic anhydride. (hereinafter also referred to as "NAH"), maleic anhydride, and the like. The acid anhydride-based monomers may be used singly or in combination of two or more.
Preferred acid anhydride monomers are IAH, CAH and NAH. When any one of IAH, CAH and NAH is used, a fluorine-containing compound having an acid anhydride group can be obtained without using a special polymerization method (see JP-A-11-193312) that is required when maleic anhydride is used. Polymer X can be easily produced.
As the acid anhydride-based monomer, IAH and NAH are preferable from the viewpoint of further excellent adhesiveness between members (interlayers) in the fiber-reinforced molded product.

In the fluorine-containing polymer X, a part of the acid anhydride group in the unit u2 is hydrolyzed, and as a result, a dicarboxylic acid corresponding to the acid anhydride-based monomer (itaconic acid, citraconic acid, 5-norbornene-2 , 3-dicarboxylic acid, maleic acid, etc.) may be included. When a unit derived from the dicarboxylic acid is included, the content of the unit is included in the content of the unit u2.

The fluorine-containing monomer constituting the unit u3 is preferably a fluorine-containing compound having one polymerizable carbon-carbon double bond, such as a fluoroolefin (vinyl fluoride, vinylidene fluoride, TFE, HFP, hexafluoro isobutylene, etc., excluding TFE), PAVE, CF ₂ =CFOR ^f2 SO ₂ X ¹ (wherein R ^f2 is a perfluoroalkylene group having 1 to 10 carbon atoms which may contain an etheric oxygen atom between carbon atoms; and X ¹ is a halogen atom or a hydroxyl group), CF ₂ ═CFOR ^f3 CO ₂ X ² (wherein R ^f3 is a perfluoroalkylene group having 1 to 10 carbon atoms and optionally containing an etheric oxygen atom between carbon atoms and X ² is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.), CF ₂ =CF(CF ₂ ) _p OCF=CF ₂ (where p is 1 or 2), CH ₂ =CX ³ (CF ₂ ) _q X ⁴ (where X ³ is a hydrogen atom or a fluorine atom, q is an integer of 2 to 10, and X ⁴ is a hydrogen atom or a fluorine atom) (hereinafter referred to as " FAE”), fluorine-containing monomers having a ring structure (perfluoro(2,2-dimethyl-1,3-dioxole), 2,2,4-trifluoro-5-trifluoromethoxy-1,3 -dioxole, perfluoro (2-methylene-4-methyl-1,3-dioxolane), etc.).
Examples of PAVE include CF ₂ ═CFOR ^f1 (where R ^f1 is a perfluoroalkyl group having 1 to 10 carbon atoms which may contain an etheric oxygen atom between carbon atoms) and the like.

As the fluoromonomer constituting the unit u3, at least one selected from the group consisting of HFP, PAVE and FAE is preferable, and PAVE is particularly preferable, from the viewpoint of excellent moldability of the fluoropolymer X.
As PAVE, CF2 _{= CFOCF2CF3} , CF2 _{= CFOCF2CF2CF3 (} hereinafter also referred to as "PPVE"), _{CF2 = CFOCF2CF2CF2CF3 , CF2 = CFO (} CF ₂ ) ₈ F, etc., and PPVE is preferred.

As FAE, _CH2 =CF(CF2) _2F , _CH2 =CF(CF2) _3F , _CH2 =CF _{( CF2} )4F, _{CH2 =} CF _{( CF2} ) _5F , _CH2 =CF(CF2)8F, _CH2 =CF ₍ CF2) _2H , _CH2 =CF( _CF2 ) _3H , _{CH2 =} CF( _CF2 ) _4H , _{CH2 =} CF ₍ CF2) _5H , _{CH2 =} CF ₍ CF2)8H, _{CH2 =} CH ₍ CF2) _2F , _CH2 =CH(CF2) _3F , _CH2 =CH( _CF2 )4F, _{CH2 =} CH ₍ CF2)5F, _CH2 =CH(CF2)6F, _CH2 =CH( _CF2 ) _8F , _{CH2 =} CH _{( CF2} ) _2H , _{CH2 =} CH( _CF2 ) ₃ H, _{CH2 =} CH ₍ CF2)4H, _CH2 =CH _{( CF2} ) _5H , _CH2 =CH( _CF2 )8H and the like.
FAE is preferably CH ₂ ═CH(CF ₂ ) _q1 X ⁴ (q1 is 2 to 6, preferably 2 to 4), CH ₂ ═CH(CF ₂ ) ₂ F, CH ₂ =CH(CF2) _3F , _CH2 =CH(CF2)4F, _CH2 =CF ₍ CF2) _3H , _more preferably _{CH2 =} CF( _CF2 ) _4H , _{CH2 =} CH( CF ₂ ) ₄ F (hereinafter also referred to as “PFBE”) and CH ₂ =CH(CF ₂ ) ₂ F (hereinafter also referred to as “PFEE”) are particularly preferred.

The preferred ratio of each unit to the total amount of units u1, u2 and u3 in the fluoropolymer X is as follows.
The proportion of the unit u1 is preferably 90 to 99.89 mol%, more preferably 95 to 99.47 mol%, even more preferably 96 to 98.95 mol%.
The proportion of the unit u2 is preferably 0.01 to 3 mol%, more preferably 0.03 to 2 mol%, even more preferably 0.05 to 1 mol%.
The proportion of the unit u3 is preferably 0.1 to 9.99 mol%, more preferably 0.5 to 9.97 mol%, even more preferably 1 to 9.95 mol%.

In the fluoropolymer X, if the ratio of each unit is within the above range, the adhesiveness between members (interlayers) in the fiber-reinforced molded article is further excellent.
If the ratio of the units u2 is within the above range, the amount of acid anhydride groups in the fluoropolymer X will be appropriate, and the adhesiveness between members (interlayers) in the fiber-reinforced molded article will be further excellent.
If the ratio of the units u3 is within the above range, the moldability of the fluoropolymer X is further excellent.
The ratio of each unit can be calculated by melt NMR analysis, fluorine content analysis, infrared absorption spectrum analysis, etc. of the fluoropolymer X.

In addition to the units u1 to u3, the fluoropolymer X has units (hereinafter also referred to as "unit u4") based on non-fluorinated monomers (excluding acid anhydride monomers). You may have
The non-fluorine-based monomer is preferably a non-fluorine compound having one polymerizable carbon-carbon double bond, such as olefins (ethylene, propylene, 1-butene, etc.), vinyl esters (vinyl acetate, etc.), and the like. mentioned. The non-fluorine-based monomers may be used singly or in combination of two or more.
As the non-fluorinated monomer, ethylene, propylene and 1-butene are preferable, and ethylene is particularly preferable, from the viewpoint of excellent mechanical strength of the fluororesin film.

When the fluoropolymer X consists of units u1, units u2, units u3, and units u4, and unit u4 is an ethylene unit, the ratio of each unit to the total amount of units u1, units u2, units u3, and units u4 Preferred ratios are as follows.
The proportion of the unit u1 is preferably 25 to 80 mol%, more preferably 40 to 65 mol%, even more preferably 45 to 63 mol%.
The proportion of the unit u2 is preferably 0.01 to 5 mol%, more preferably 0.03 to 3 mol%, even more preferably 0.05 to 1 mol%.
The proportion of the unit u3 is preferably 0.2 to 20 mol%, more preferably 0.5 to 15 mol%, even more preferably 1 to 12 mol%.
The proportion of ethylene units is preferably 20 to 75 mol %, more preferably 35 to 50 mol %, even more preferably 37 to 55 mol %.

Specific examples of the fluoropolymer X include TFE/NAH/PPVE copolymer, TFE/IAH/PPVE copolymer, TFE/CAH/PPVE copolymer, TFE/IAH/HFP copolymer, TFE/CAH /HFP copolymer, TFE/IAH/PFBE/ethylene copolymer, TFE/CAH/PFBE/ethylene copolymer, TFE/IAH/PFEE/ethylene copolymer, TFE/CAH/PFEE/ethylene copolymer, TFE/IAH/HFP/PFBE/ethylene copolymer and the like.
As the fluorine-containing polymer X, PFA having a functional group f is preferable, and TFE/NAH/PPVE copolymer, TFE/IAH/PPVE copolymer, and TFE/CAH/PPVE copolymer are more preferable.

A fluoropolymer having a functional group f such as the fluoropolymer X can be produced by a conventional method. When a fluoropolymer is produced by polymerizing a monomer, a polymerization method using a radical polymerization initiator is preferred as the polymerization method.
As the polymerization method, a bulk polymerization method, a solution polymerization method using an organic solvent (fluorocarbon, chlorinated hydrocarbon, fluorochlorinated hydrocarbon, alcohol, hydrocarbon, etc.), an aqueous medium and, if necessary, a suitable organic solvent and an emulsion polymerization method using an aqueous medium and an emulsifier, and a solution polymerization method is preferred.

As the radical polymerization initiator, an initiator having a half-life of 10 hours at a temperature of 0 to 100°C is preferable, and an initiator having a temperature of 20 to 90°C is more preferable.
Radical polymerization initiators include azo compounds (azobisisobutyronitrile, etc.), non-fluorinated diacyl peroxides (isobutyryl peroxide, octanoyl peroxide, benzoyl peroxide, lauroyl peroxide, etc.), peroxydicarbonates (diisopropyl peroxide, carbonate, etc.), peroxyesters (tert-butyl peroxypivalate, tert-butyl peroxyisobutyrate, tert-butyl peroxyacetate, etc.), fluorine-containing diacyl peroxides ((Z(CF ₂ ) _r COO) ₂ (where Z is a hydrogen atom, a fluorine atom or a chlorine atom, and r is an integer of 1 to 10.), inorganic peroxides (potassium persulfate, sodium persulfate, ammonium persulfate, etc.), etc. be done.

A chain transfer agent may be used to control the melt viscosity of the fluoropolymer X during the polymerization. Chain transfer agents include alcohols (methanol, ethanol, etc.), chlorofluorohydrocarbons (1,3-dichloro-1,1,2,2,3-pentafluoropropane, 1,1-dichloro-1-fluoroethane, etc. ), and hydrocarbons (pentane, hexane, cyclohexane, etc.).

Organic solvents used in the solution polymerization method include perfluorocarbons (perfluorocyclobutane, etc.), hydrofluorocarbons (1-hydroperfluorohexane, etc.), chlorohydrofluorocarbons (1,3-dichloro-1,1,2,2,3-pentane fluoropropane, etc.), hydrofluoroethers (methylperfluorobutyl ether, etc.), and the like. The number of carbon atoms in these is preferably 4-12.

As the fluororesin F, a fluoropolymer having a functional group f as a main chain terminal group may be used. A fluoropolymer having a functional group f as a main chain terminal group is produced by a method of polymerizing a monomer using a chain transfer agent or a polymerization initiator that provides the functional group f during polymerization of the monomer. can.

A chain transfer agent having a carboxy group, an ester bond, a hydroxy group, or the like is preferable as the chain transfer agent that provides the functional group f. Specific examples include acetic acid, acetic anhydride, methyl acetate, ethylene glycol, propylene glycol and the like.
As the polymerization initiator that provides the functional group f, peroxide-based polymerization initiators such as peroxycarbonate, diacylperoxide and peroxyester are preferred. Specific examples include di-n-propylperoxydicarbonate, diisopropylperoxydicarbonate, tert-butylperoxyisopropylcarbonate, bis(4-tert-butylcyclohexyl)peroxydicarbonate, di-2-ethylhexylperoxydicarbonate and the like. .

The powder A may further contain a component other than the fluororesin, if necessary, as long as the effects of the present invention are not impaired. Components other than the fluororesin include resins other than the fluororesin, inorganic fillers, rubbers, and the like. Examples of resins other than fluororesins include aromatic polyesters, polyamideimides, thermoplastic polyimides, polyphenylene ethers, polyphenylene oxides, and the like.

D50 of powder A is 0.5 to 100 μm, preferably 1 to 90 μm, more preferably 3 to 80 μm, even more preferably 5 to 60 μm. If the D50 of the powder A is equal to or higher than the lower limit of the above range, the application to the reinforcing fiber substrate is excellent. If the D50 of the powder A is equal to or less than the upper limit of the above range, the adhesion to the reinforcing fiber substrate is excellent.

For example, powder A having D50 in the above range can be obtained by pulverizing powder material containing fluororesin obtained by polymerization or commercially available fluororesin and then classifying (sieving, etc.) if necessary. When the fluororesin is produced by solution polymerization, suspension polymerization, or emulsion polymerization, the organic solvent or aqueous medium used in the polymerization is removed to recover the granular fluororesin, followed by pulverization and classification (sieving, etc.). . When D50 of the granular fluororesin after polymerization is within the desired range, the fluororesin can be used as the powder A as it is. As the method for pulverizing and classifying the powder material, the methods described in [0065] to [0069] of WO 2016/017801 can be adopted.
In addition, as powder A, you may use a commercial item.

In the reinforcing fiber base material with resin of the present invention, the ratio of the volume of the reinforcing fiber base material to the total volume of the reinforcing fiber base material and the powder A (hereinafter also referred to as “ratio Q _A ”) is 0.70 to 0.99, preferably 0.75 to 0.95, more preferably 0.80 to 0.90. When the ratio _QA is equal to or higher than the lower limit of the above range, the strength characteristics of the reinforcing fiber molded article are excellent. If the ratio _QA is equal to or less than the upper limit value of the above range, the impact resistance of the reinforcing fiber molded product will be excellent.
The ratio _QA can be calculated from the charged amount at the time of manufacturing the reinforcing fiber base material with resin and the specific gravity of the material.

(Method for producing resin-coated reinforcing fiber base material)
As a method for producing a reinforcing fiber base material with resin of the present invention, the powder A is added to the reinforcing fiber base material, and the ratio Q _A of the volume of the reinforcing fiber base material to the total volume of the reinforcing fiber base material and the powder A is 0. For example, a method of coating such that it becomes 0.70 to 0.99 can be exemplified.

The method of applying the powder A is not particularly limited, and electrostatic coating, thermal spraying, and a method of immersing the reinforcing fiber base material in a dispersion of the powder A can be exemplified.
The liquid medium used for the dispersion is not particularly limited, and water; alcohols such as methanol and ethanol; nitrogen-containing compounds such as N,N-dimethylformamide, N,N-dimethylacetamide and N-methyl-2-pyrrolidone; Sulfur-containing compounds such as dimethyl sulfoxide; Ethers such as diethyl ether and dioxane; Esters such as ethyl lactate and ethyl acetate; Ketones such as methyl ethyl ketone and methyl isopropyl ketone; Glycol ethers such as ethylene glycol monoisopropyl ether; , ethyl cellosolve, and the like. As the liquid medium, one type may be used alone, or two or more types may be used in combination.
The solid content concentration of the dispersion is preferably 5 to 60% by mass, more preferably 10 to 50% by mass.

In the present invention, the reinforcing fiber base material coated with the powder A may be heated at a temperature equal to or higher than the melting point of the fluororesin forming the powder A. By melting at least part of the powder A by heating after applying the powder A, the fluororesin can be more efficiently present between the reinforcing fiber base material and the non-fluororesin described below in the prepreg. This makes it easier to obtain a fiber-reinforced molded product with high mechanical strength.

[Prepreg manufacturing method]
In the method for producing a prepreg of the present invention, a reinforcing fiber base material with resin is produced by the above-described method for producing a reinforcing fiber base material with resin, and the reinforcing fiber base material with resin is impregnated with a non-fluororesin at a specific ratio. .
Examples of non-fluororesins include thermoplastic resins and thermosetting resins.

Examples of thermoplastic resins include crystalline resins, amorphous resins, and thermoplastic elastomers.
Crystalline resins include polyester resins (polyethylene terephthalate, polybutylene terephthalate, polytrimethylene terephthalate, polyethylene naphthalate, liquid crystal polyester, etc.), polyolefin resins (polyethylene, polypropylene, polybutylene, acid-modified polyethylene, acid-modified polypropylene, acid-modified modified polybutylene, etc.), polyoxymethylene, polyamide, polyarylene sulfide resin (polyphenylene sulfide, etc.), polyketone, polyetherketone, polyetheretherketone, polyetherketoneketone, polyethernitrile, and liquid crystal polymer.

Examples of amorphous resins include styrene resins (polystyrene, acrylonitrile styrene resin, acrylonitrile butadiene styrene resin, etc.), polycarbonate, polymethyl methacrylate, polyvinyl chloride, unmodified or modified polyphenylene ether, thermoplastic polyimide, polyamideimide, Examples include polyetherimide, polysulfone, polyethersulfone, and polyarylate.

Examples of thermoplastic elastomers include polystyrene-based elastomers, polyolefin-based elastomers, polyurethane-based elastomers, polyester-based elastomers, polyamide-based elastomers, polybutadiene-based elastomers, polyisoprene-based elastomers, acrylonitrile-based elastomers, and the like.

As the thermoplastic resin, from the viewpoint of improving the heat resistance of the prepreg, polyamide, polyarylene sulfide resin (polyphenylene sulfide, etc.), polyketone, polyetherketone, polyetheretherketone, polyetherketoneketone, polyethernitrile, modified Polyphenylene ethers, thermoplastic polyimides, polyamideimides, polyetherimides, polysulfones, polyethersulfones and polyarylates are preferred.
The thermoplastic resin may be used alone or in combination of two or more.

Examples of thermosetting resins include epoxy resins, cyanate ester resins, unsaturated polyester resins, vinyl ester resins, phenol resins, urea-melamine resins, polyimides, and bismaleimide resins.
As the thermosetting resin, epoxy resins and anate ester resins are preferred, and epoxy resins are more preferred, from the viewpoint of the mechanical properties of the fiber-reinforced molded article.

Examples of epoxy resins include glycidyl ether epoxy resins (bisphenol epoxy resins, (poly)alkylene glycol epoxy resins, phenol novolac epoxy resins, orthocresol novolak epoxy resins, etc.), glycidyl ester epoxy resins, glycidyl amine epoxy resins. Resin (N,N,N',N'-tetraglycidyldiaminodiphenylmethane, triglycidyl-p-aminophenol, triglycidyl isocyanurate, etc.), alicyclic epoxy resin (dicyclopentadiene type, etc.), sulfur atom in main chain can be exemplified by epoxy resins, urethane-modified epoxy resins, and rubber-modified epoxy resins.
Thermosetting resins may be used alone or in combination of two or more.

When a thermosetting resin is used as the non-fluororesin, a curing agent may be added to the thermosetting resin. The curing agent can be appropriately selected according to the type of thermosetting resin.
When the thermosetting resin is an epoxy resin, examples of curing agents include 4,4'-diaminodiphenylsulfone, dicyandiamide, diaminodiphenylmethane, diaminodiphenyl ether, bisaniline, and benzyldimethylaniline.
When the thermosetting resin is a cyanate ester resin, the curing agent is preferably a diepoxy compound from the viewpoint of improving the toughness of the fiber-reinforced molded product.
Curing agents may be used alone or in combination of two or more.

Additives such as inorganic fillers, organic fillers, organic pigments, metallic soaps, surfactants, ultraviolet absorbers, lubricants, silane coupling agents, etc., to the non-fluororesin, if necessary, as long as the effects of the present invention are not impaired. may be blended.

In the present invention, the ratio of the volume of the reinforcing fiber base material to the total volume of the reinforcing fiber base material, the resin component derived from powder A, and the non-fluororesin (hereinafter also referred to as “ratio Q _B ”) is 0.40 to 0. The resin-coated reinforcing fiber base material is impregnated with a non-fluororesin so as to have a density of 0.60.
The ratio Q _B is 0.40 to 0.60, preferably 0.42 to 0.60, more preferably 0.45 to 0.60. If the ratio QB is at least the lower limit of the above range, the strength characteristics of the fiber _- reinforced molded product will be excellent. If the ratio QB is equal to or less than the upper limit of the above range, the fiber _- reinforced molded product will have excellent impact resistance.
The ratio QB can be calculated from the amount charged during manufacturing of the resin _- attached reinforcing fiber base material, the amount charged during manufacturing of the prepreg, and the specific gravity of the material.

The method for impregnating the resin-coated reinforcing fiber base material with the non-fluororesin is not particularly limited. For example, a non-fluororesin film and a resin-coated reinforcing fiber substrate are superimposed and hot-pressed to impregnate the resin-coated reinforcing fiber substrate with the non-fluororesin.

In the present invention, the resin-coated reinforcing fiber substrate may be surface-treated before being impregnated with the non-fluororesin. Plasma treatment is preferred as the surface treatment.
The plasma irradiation apparatus used for plasma treatment is not particularly limited, and may be a high-frequency induction system, a capacitively coupled electrode system, a corona discharge electrode-plasma jet system, a parallel plate system, a remote plasma system, an atmospheric pressure plasma system, or an ICP high-density plasma system. An apparatus employing a mold or the like can be exemplified.
The gas used for plasma treatment is not particularly limited, and oxygen, nitrogen, rare gas (argon), hydrogen, and ammonia can be exemplified.

[Method for producing fiber-reinforced molded product]
The method for producing a fiber-reinforced molded article of the present invention is a method of producing a prepreg by the method for producing a prepreg of the present invention, and producing a fiber-reinforced molded article by molding using the prepreg.
The fiber-reinforced molded product may be manufactured using only the prepreg manufactured by the manufacturing method of the present invention, and the prepreg manufactured by the manufacturing method of the present invention and other prepregs other than the prepreg manufactured by the manufacturing method of the present invention. and may be manufactured using A fiber-reinforced molded article may be produced using the prepreg produced by the production method of the present invention and members other than the prepreg.

Other prepregs include prepregs in which the matrix resin contains a thermoplastic resin and does not contain a fluororesin.
Examples of members other than prepreg include metal foils and resin films made of metals such as iron, stainless steel, aluminum, copper, brass, nickel, and zinc.

A fiber-reinforced molded product is obtained, for example, by hot-pressing a laminated material obtained by laminating a plurality of prepregs including the prepreg of the present invention. When an uncured thermosetting resin is used as the non-fluororesin, the resulting fiber-reinforced molded article contains a cured thermosetting resin.
The molding method includes a press molding method using a mold, a method using an autoclave, and the like.

When using a prepreg containing a thermoplastic resin or an uncured thermosetting resin, the temperature for hot pressing the laminated material containing the prepreg should be the melting point of the thermoplastic resin or higher, or the curing temperature of the thermosetting resin or higher. is preferred.

The fiber-reinforced molded article of the present invention can also be molded by a method that does not use the prepreg of the present invention. For example, the reinforcing fiber base material with resin of the present invention is produced, a laminate obtained by stacking the reinforcing fiber base material with resin is placed in a mold, and a thermosetting resin is injected into the mold for impregnation. and hardening. Such a molding method is generally called resin transfer molding (RTM), and the method of vacuuming the mold when impregnated with thermosetting resin is called vacuum assisted resin transfer molding (VaRTM).
Alternatively, the resin-coated reinforcing fiber base material of the present invention is produced, a film made of the resin-coated reinforcing fiber base material and a thermoplastic resin is laminated in a mold, and then hot-pressed at a temperature equal to or higher than the melting point of the thermoplastic resin. The fiber-reinforced molded article of the present invention can also be obtained by When the resin-coated reinforcing substrate is A and the thermoplastic resin film is B, the above lamination may be alternately laminated with ABABAB, or may be laminated in an irregular order such as AABAABB.

Applications of the fiber-reinforced molded article are not particularly limited. Printed circuit boards, housings for electronic devices, internal members (trays, chassis, etc.), building materials (panels, etc.), vehicles such as automobiles, motorcycles, railroad cars, parts related to transportation equipment such as aircraft, sporting goods such as rackets and bats , industrial machinery, robots, and parts of medical equipment.

As described above, in the present invention, a prepreg is obtained by impregnating a resin-coated reinforcing fiber base material obtained by applying powder A to a reinforcing fiber base material at a specific ratio with a non-fluororesin at a specific ratio. By using such a prepreg, a fiber-reinforced molded product with high mechanical strength can be produced. It is considered that the reason why the above effect is obtained by the present invention is that the flexible fluororesin enters between the reinforcing fiber and the non-fluororesin.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited by the following description.
[Measuring method]
Various measurement methods for fluororesin and powder are shown below.
(1) Copolymerization composition The copolymerization composition of the fluororesin was determined by melt NMR analysis and fluorine content analysis.

(2) Melting point (°C)
Using a differential scanning calorimeter (DSC device) manufactured by Seiko Electronics Co., Ltd., the melting peak is recorded when the temperature of the fluororesin is increased at a rate of 10 ° C./min, and the temperature (° C.) corresponding to the maximum value is taken as the melting point (Tm ).

(3) MFR (g/10 minutes)
Using a melt indexer manufactured by Technoseven Co., Ltd., the mass (g) of the fluororesin flowing out from a nozzle with a diameter of 2 mm and a length of 8 mm for 10 minutes (unit time) was measured under the following temperature and load to obtain the MFR. .

(4) D50 of powder
Using a laser diffraction/scattering particle size distribution analyzer (LA-920 measuring instrument) manufactured by Horiba, Ltd., the powder was dispersed in water, the particle size distribution was measured, and D50 (μm) was calculated.

(5) Bending strength The bending strength of the molded product was measured using a tensile compression tester "Strograph R-2" manufactured by Toyo Seiki Co., Ltd. under the conditions of a load cell rating of 1000 kg, a speed of 5 mm/min, and a distance between fulcrums of 8 cm.

[Resin material]
The resin materials used in this example are shown below.
(Fluororesin F)
Fluororesin F-1: In the same manner as in Example 5 of International Publication No. 2016/006644, the copolymer composition is TFE units/ethylene units/CH ₂ =CH (CF ₂ ) ₂ F units/IAH units (molar ratio) = A 54.7/42.8/2.1/0.4 fluororesin was produced. The melting point was 240° C., the MFR (297° C., load 49 N) was 20.6 g/10 minutes, and the specific gravity was 1.76.

(Polyamide resin B)
Polyamide resin B-1: Polyamide 6 (UBE nylon 1022B manufactured by Ube Industries, specific gravity: 1.14).

[Example 1]
The fluororesin F-1 was pulverized with a frozen pulverizer TPH-01 manufactured by AS ONE to obtain a fluororesin powder A-1 having a D50 of 50 μm.
Non-spread carbon cloth (plain weave CF3000, manufactured by Sunlight Co., Ltd., thickness: 0.25 mm, specific gravity: 1.80) was cut into a size of 10 cm long by 10 cm wide to obtain a reinforcing fiber substrate. By electrostatic coating, the powder A-1 was applied to the reinforcing fiber base material so that the ratio Q _A of the volume of the reinforcing fiber base material to the total volume of the reinforcing fiber base material and the powder A-1 was 0.90. applied. Then, it was heat-exposed at 260° C. for 3 minutes in a hot air circulating dryer to obtain a resin-coated reinforcing fiber base material C-1.

Using a single-screw extruder (manufactured by Tanabe Plastics Machinery Co., Ltd., VS-30) and a 400 mm width T die, a set resin temperature of 260 ° C., a rotation speed of 50 rpm, and a line speed of 2.0 m / min Polyamide resin B-1. A polyamide film having a thickness of 50 μm was obtained by extrusion molding. Two films of 10 cm long × 10 cm wide are cut out from the polyamide film, laminated on both sides of the reinforcing fiber base material C-1 with resin, and using a melt heat press machine (manufactured by Tester Sangyo Co., Ltd.) at a temperature of 240 ° C. and a pressure of 1 MPa. , press-molded under conditions of a press time of 3 minutes to obtain a prepreg P-1. In the prepreg P-1, the ratio QB of the volume of the reinforcing fiber base material to the total volume of the reinforcing fiber base material, the fluororesin F-1 and the polyamide resin _B -1 was 0.50.

Ten sheets of prepreg P-1 were laminated, and a melt heat press (manufactured by Tester Sangyo Co., Ltd.) was used at a temperature of 280 ° C., a pressure of 10 MPa, a press time of 15 minutes (preheating process: 12 minutes (no pressure), compression process: 3 minutes) to obtain a fiber-reinforced molded article having a thickness of 2.3 mm.

[Comparative Example 1]
Powder A-1 was applied to the reinforcing fiber base material in the same manner as in Example 1 except that the ratio Q _A was 0.50 to obtain a resin-coated reinforcing fiber base material C-2.
10 sheets of reinforcing fiber base material C-2 with resin are laminated, and using a melt heat press (manufactured by Tester Sangyo Co., Ltd.), the temperature is 280 ° C., the pressure is 10 MPa, and the pressing time is 15 minutes (preheating process: 12 minutes (no pressure ), compression step: 3 minutes) to obtain a fiber-reinforced molded product with a thickness of 2.2 mm.

[Comparative Example 2]
Polyamide resin B-1 and fluororesin A-1 are dry blended so that the volume ratio of polyamide resin B-1: fluororesin A-1 = 90: 10, and a twin-screw extruder (manufactured by Technobell, KZW15TW- 45 MG), and melt-kneaded under the conditions of a resin discharge rate of 2.0 kg/hour, a screw rotation speed of 200 rpm, and a set resin temperature of 240° C. to obtain a resin composition.
Using a single screw extruder (manufactured by Tanabe Plastics Machinery Co., Ltd., VS-30) and a 400 mm width T die, the resin composition is extruded at a set resin temperature of 260 ° C., a rotation speed of 50 rpm, and a line speed of 2.0 m / min. A blend film having a thickness of 50 μm was obtained. Two films each having a length of 10 cm and a width of 10 cm were cut out from the blend film. These two films were laminated on both sides of a reinforcing fiber base material of 10 cm long x 10 cm wide cut out from unspread carbon cloth (manufactured by Sunlight, plain weave CF3000, thickness 0.25 mm, specific gravity: 1.80). Then, using a melt heat press (manufactured by Tester Sangyo Co., Ltd.), press molding was performed under the conditions of a temperature of 240° C., a pressure of 1 MPa, and a pressing time of 3 minutes to obtain a prepreg P-2. In the prepreg P-2, the ratio QB of the volume of the reinforcing fiber base material to the total volume of the reinforcing fiber base material, the fluororesin F-1 and the polyamide resin _B -1 was 0.50.
11 sheets of prepreg P-2 were laminated, and using a melt heat press (manufactured by Tester Sangyo Co., Ltd.), the temperature was 280 ° C., the pressure was 10 MPa, the pressing time was 15 minutes (preheating process: 12 minutes (no pressure), compression process: 3 minutes) to obtain a fiber-reinforced molded article having a thickness of 2.2 mm.

Table 1 shows the results of measuring the flexural strength of the fiber-reinforced molding obtained in each example.

As shown in Table 1, the fiber-reinforced molded article of Example 1 using the prepreg produced by the production method of the present invention is a comparative example in which a reinforcing fiber base material with a resin having a _QA ratio of 0.50 is used as a prepreg. 1 and the fiber-reinforced molded article of Comparative Example 2 using a prepreg obtained by impregnating a reinforcing fiber base material with a blend of fluororesin and polyamide resin, the bending strength was higher.

Claims (8)

A powder containing a fluororesin having a D50 of 0.5 to 100 μm is added to a reinforcing fiber base material, and the ratio of the volume of the reinforcing fiber base material to the total volume of the reinforcing fiber base material and the powder is 0.70 to 0. .99 to produce a resin-coated reinforcing fiber base material, a polyamide resin is added to the resin-coated reinforcing fiber base material, and a resin derived from the resin of the reinforcing fiber base material and the resin-coated reinforcing fiber base material. A method for producing a prepreg, wherein the impregnation is performed so that the ratio of the volume of the reinforcing fiber base material to the total volume of the components and the polyamide resin is 0.40 to 0.60. The method for producing a prepreg according to claim 1, wherein the reinforcing fiber base material coated with the powder is heated at a temperature equal to or higher than the melting point of the fluororesin to produce the resin-coated reinforcing fiber base material. Claim 1 or wherein the fluororesin is a fluororesin having at least one functional group selected from the group consisting of a carbonyl group-containing group, a hydroxy group, an epoxy group and an isocyanate group, and having a melting point of 100 to 325°C. 3. The method for producing a prepreg according to 2. The method for producing a prepreg according to claim 3, wherein the fluororesin has a melting point of 150°C or higher and lower than 260°C. The method for producing a prepreg according to claim 3, wherein the fluororesin has a melting point of 260°C or higher and 325°C or lower. The prepreg according to any one of claims 1 to 5, wherein the reinforcing fiber base material is a reinforcing fiber fabric, a reinforcing fiber sheet in which reinforcing fibers are aligned in one direction, or a reinforcing fiber nonwoven fabric. Production method. The method for producing a prepreg according to any one of claims 1 to 6, wherein the reinforcing fibers contained in the reinforcing fiber base material are carbon fibers, glass fibers, or aramid fibers. The method for producing a prepreg according to any one of claims 1 to 7 , wherein the resin-coated reinforcing fiber base material is surface-treated before being impregnated with the polyamide resin.