Patent Description:
Sheet molding compound (hereinafter, also described as "SMC") is a material impregnated with a resin composition containing a thermosetting resin into a sheet-like reinforcing fiber group, in which short cut reinforcing fibers are piled up. A cured and molded article formed of SMC has excellent appearance, mechanical characteristics, water resistance, corrosion resistance, and the like. Therefore, the product is widely used in the field of household appliances, automobiles, electric instruments, and the like.

The length of the reinforcing fiber in SMC is short. Therefore, although the mechanical characteristics of the molded article formed of SMC are poorer than those of prepreg containing continuous fiber, SMC is appropriate for producing a molded article having differential thickness or a molded article of a complicated shape having fine irregularities, each of which is difficult to mold with prepreg.

Although a cured and molded article formed of SMC is usually produced by press-molding SMC, in a case where SMC is cured by press-molding, due to the cure shrinkage that occurs during curing, the heating resulting from a curing reaction, thermal contraction resulting from cooling after the curing reaction, and the like, distortion frequently occurs in the interior of the molded article. In the case of a molded article having a thick portion, serious interior distortion occurs in the thick portion, and a shaping failure such as an internal crack, a sink mark, deformation, or the like easily occurs.

As a method for inhibiting a sink mark that occurs on the surface of a molded article due to the volumetric shrinkage in a case where a thermosetting resin is cast-molded, the following method is suggested although this is not a technique relating to the press-molding of SMC.

As molded articles formed of SMC in which the occurrence of an internal crack, a sink mark, and deformation in a thick portion is inhibited, the following molded articles are suggested.

(<NUM>) Molded article including a thick portion constituted with an inner layer which is formed of a cured material of a glass fiber-containing bulk molding compound and a surface layer which is formed of a cured material of glass fiber-containing SMC (hereinafter, also described as "GF-SMC") surrounding the inner layer (Patent Literature <NUM>).

(<NUM>) Molded article including a thick portion constituted with an inner layer which is formed of a cured material of GF-SMC with a high glass fiber content rate and a surface layer which is formed of a cured material of GF-SMC with a low glass fiber content rate that surrounds the inner layer (Patent Literature <NUM>).

In recent years, as reinforcing fiber, carbon fiber has drawn attention because this has a high specific strength and a high specific elastic modulus and makes it possible to greatly lighten a molded article. For the reinforcing fiber contained in SMC, glass fiber is increasingly replaced with carbon fiber. (Patent Literature <NUM> and <NUM>).

However, molding a thick portion by using SMC containing carbon fiber (hereinafter, also described as "CF-SMC") as reinforcing fiber is more difficult than molding a thick portion by using GF-SMC.

Compared to GF-SMC, CF-SMC conducts heat better and is stiffer. Furthermore, in a case where the CF-SMC is press-molded to produce a molded article having a thick portion, distortion and cracks easily occur in the interior of the molded article. In addition, compared to GF-SMC, CF-SMC has a larger fiber tow width and a lower specific gravity.

As effective means for improving the thick portion-molding properties of GF-SMC, there is a method of adding a large amount of a thermoplastic resin-type shrinkage reducing agent or an inorganic filler such as calcium carbonate. However, applying this method to CF-SMC is not preferable, because impregnation properties or uniformity tends to be impaired, and the specific gravity increases.

For these reasons, it is difficult to improve the internal cracks that occur during the molding of a thick product without impairing the excellent characteristics of CF-SMC.

Even though the methods (<NUM>) and (<NUM>) relating to cast molding and the techniques (<NUM>) and (<NUM>) using GF-SMC are applied to the press-molding of CF-SMC, the thick portion-molding properties of CF-SMC are not sufficiently improved. Particularly, in a case where the techniques of (<NUM>) and (<NUM>) are applied to improve the thick portion-molding properties of CF-SMC, CF-SMC tends to be affected by the difference in thermal expansion and thermal contraction between materials having different characteristics, and internal cracks easily occur at the interface.

Furthermore, in molding a thick portion by using CF-SMC, it is also important to ensure die release properties such that the molded article is released from a die.

An object of the present invention is to provide a sheet molding compound (CF-SMC) having excellent thick portion-molding properties that can inhibit the occurrence of internal cracks even during the molding of a thick portion and enables a carbon fiber composite material molded article to be excellently released from a die. Another object of the present invention is to provide a carbon fiber composite material molded article.

The present invention has the constitutions as in the appended claims.

In a case where SMC of the present invention is used, the occurrence of internal cracks can be inhibited even during the molding of a thick portion, and a carbon fiber composite material molded article excellently released from a die is obtained.

<FIG> is a schematic constitution view showing an example of an SMC producing apparatus.

The following definitions of terms are applied to the present specification and claims.

"Sheet molding compound (SMC)" means a sheet-like uncured composite material containing reinforcing fiber which is short fiber and a thermosetting resin.

"Epoxy resin" is a generic term for thermosetting compounds having two or more reactive epoxy groups in a molecule.

"Vinyl ester resin" is a resin obtained by addition reaction of a vinyl group-containing monobasic acid (carboxylic acid or the like) with an epoxy resin.

"Volumetric molding shrinkage rate of a thermosetting resin composition" is a cure shrinkage rate calculated by the following equation by using a difference between specific gravities that are measured before and after the curing of a thermosetting resin composition according to a density measurement method (JIS K-<NUM><NUM>-<NUM>). <MAT> (In the above equation, r represents a volumetric molding shrinkage rate (%); dl represents a specific gravity of a liquid thermosetting resin composition that is measured using a specific gravity bottle method before the composition is cured; and ds represents a specific gravity of a cured material of the thermosetting resin composition that is measured by a specific gravity measurement method for solids (weighing in a liquid)).

"Average fiber length of carbon fiber" is the average length of <NUM> carbon fiber filaments randomly selected from the fiber substrate (A).

"(Meth)acrylic acid" means an acrylic acid or a methacrylic acid.

"(Meth)acrylate" means acrylate or methacrylate.

The sheet molding compound (SMC) of the present invention is CF-SMC containing a fiber substrate (A) containing carbon fiber and a thermosetting resin composition (B). SMC of the present invention can be suitably used as SMC for molding a carbon fiber composite material molded article (hereinafter, also simply referred to as "molded article") with a thick portion having a thickness of <NUM> or more.

The fiber substrate (A) is a substrate containing carbon fiber.

The form of the fiber substrate (A) is not particularly limited, and examples thereof include a substrate in which short fiber tows, which are prepared by cutting carbon fiber tows constituted with continuous carbon fiber aligned in one direction in a specific length, are arranged in the form of a mat.

Examples of the carbon fiber include polyacrylonitrile (PAN)-based carbon fiber, rayon-based carbon fiber, pitch-based carbon fiber, and the like. As the carbon fiber, PAN-based carbon fiber is preferable because this fiber improves the compression strength of the molded article. It is preferable that the carbon fiber is in the form of a short fiber tow, because then the molding properties of SMC and the mechanical characteristics of the molded article are balanced well.

The average fiber length of the carbon fiber contained in the fiber substrate (A) is <NUM> or more, preferably <NUM> or more, and more preferably <NUM> or more. In a case where the average fiber length of the carbon fiber is the lower limit of the above range ore more, the mechanical characteristics of the molded article are excellent.

The average fiber length of the carbon fiber is preferably <NUM> or less, more preferably <NUM> or less, and even more preferably <NUM> or less. In a case where the average fiber length of the carbon fiber is the upper limit of the above range or less, the molding properties of SMC are excellent.

The average fiber length of the carbon fiber is, for example, preferably <NUM> or more and <NUM> or less, more preferably <NUM> or more and <NUM> or less, and even more preferably <NUM> or more and <NUM> or less.

In view of the molding properties of SMC, the mechanical characteristics and weight lightening of a molded article, the content rate of the carbon fiber contained in SMC (100mass%) of the present invention is preferably 30mass% or more and 70mass% or less, and more preferably 40mass% or more and 60mass% or less. In a case where the content rate of the carbon fiber contained in SMC is the lower limit of the above range or more, the strength or stiffness of the molded article is sufficiently improved. Therefore, the thickness of the molded article does not need to be increased, and the molded article can be lightened. In addition, the content rate of a resin is reduced, and it is more difficult for internal cracks to occur. In a case where the content rate of the carbon fiber contained in SMC is the upper limit of the above range or less, the molding properties of SMC are further improved, and a molded article having a more complicated shape can be produced.

Unless the effects of the present invention are impaired, the fiber substrate (A) may contain other reinforcing fiber in addition to the carbon fiber. Examples of those other reinforcing fiber include glass fiber and the like.

The content rate of the carbon fiber contained in the fiber substrate (A) with respect to the total number (mass) of reinforcing fiber in the fiber substrate (A) is preferably <NUM>% or more, more preferably <NUM>% or more, even more preferably <NUM>% or more, and particularly preferably <NUM>%.

In a case where carbon fiber and glass fiber are used as the fiber substrate (A), the content rate of the carbon fiber contained in the fiber substrate (A) with respect to the total number (total number of strands) of reinforcing fiber in the fiber substrate (A) is preferably <NUM>% or more, more preferably <NUM>% or more, and even more preferably <NUM>% or more.

The thermosetting resin composition (B) is a resin composition that contains a thermosetting resin and has a volumetric molding shrinkage rate <NUM>% or more and <NUM>% or less.

The volumetric molding shrinkage rate of the thermosetting resin composition (B) is <NUM>% or less, preferably <NUM>% or less, more preferably <NUM>% or less, and even more preferably <NUM>% or less. In a case where the volumetric molding shrinkage rate of the thermosetting resin composition (B) is the upper limit of the above range or more, the internal distortion that occurs during the molding of a thick portion is reduced, and internal cracks hardly occur.

The volumetric molding shrinkage rate of the thermosetting resin composition (B) is <NUM>% or more, preferably <NUM>% or more, and more preferably <NUM>% or more. In a case where the volumetric molding shrinkage rate of the thermosetting resin composition (B) is the lower limit of the above range or more, the molded article is excellently released from a die during the molding of a thick portion.

The volumetric molding shrinkage rate of the thermosetting resin composition (B) is <NUM>% or more and <NUM>% or less. For example, the volumetric molding shrinkage rate is preferably <NUM>% or more and <NUM>% or less, more preferably <NUM>% or more and <NUM>% or less, and even more preferably <NUM>% or more and <NUM>% or less.

The thermosetting resin is not particularly limited, and examples thereof include an unsaturated polyester resin, an epoxy resin, a phenol resin, a silicone resin, a vinyl ester resin, and the like.

Among these resins, in view of versatility, mechanical characteristics, molding properties, and cure shrinkage, an unsaturated polyester resin, an epoxy resin, and a vinyl ester resin are preferable. Among these, a vinyl ester resin is more preferable in view of release properties and fluidity during molding, and an epoxy resin is more preferable because this resin has particularly excellent mechanical characteristics and less causes cure shrinkage.

The thermosetting resin composition (B) may contain one kind of thermosetting resin or two or more kinds of thermosetting resins.

As the unsaturated polyester resin, unsaturated polyester resins used in CF-SMC can be used without limitation. Examples of the unsaturated polyester resin include a resin obtained by causing a condensation reaction between a dicarboxylic acid including an unsaturated dicarboxylic acid and a divalent glycol.

Examples of the epoxy resin include a bisphenol A epoxy resin, a cyclic aliphatic epoxy resin, a novolac epoxy resin, a heat-resistant epoxy resin, and the like.

In a case where the epoxy resin is used, an epoxy equivalent of this resin (number of grams of the resin containing <NUM> gram equivalent of epoxy groups (g/eq)) is preferably in a range of <NUM> to <NUM>. In a case where the epoxy equivalent is <NUM> or more, SMC that less undergoes cure shrinkage tends to be obtained. The epoxy equivalent is more preferably <NUM> or more, and even more preferably <NUM> or more. Furthermore, in a case where the epoxy equivalent is <NUM> or less, the fiber substrate tends to be excellently impregnated with the resin composition during the production of SMC. The epoxy equivalent is more preferably <NUM> or less, and even more preferably <NUM> or less.

As the vinyl ester resin, vinyl ester resins used in CF-SMC can be used without limitation. Examples of the vinyl ester resin include an epoxy (meth)acrylate resin obtained by addition reaction of a (meth)acrylic acid with an epoxy resin, and the like.

The thermosetting resin composition (B) may contain other components in addition to the thermosetting resin.

It is preferable that the thermosetting resin composition (B) further contains a curing agent, because then a tough cured material that is not dissolved or melted can be formed.

The thermosetting resin composition (B) may contain one kind of curing agent or two or more kinds of curing agents.

In a case where a vinyl ester resin is used, examples of the curing agent include an organic peroxide and the like.

Examples of an organic peroxide include peroxyketal, peroxycarbonate, ketone peroxide, diacyl peroxide, dialkyl peroxide, alkyl perester, and the like.

In a case where the epoxy resin is used, examples of the curing agent include aliphatic polyamine, polyamide, aromatic diamine, an acid anhydride, tertiary amine, and the like.

It is preferable that the thermosetting resin composition (B) further contains a polyisocyanate compound as a thickener and a reactive diluent, because then the mechanical characteristics of the molded article and the molding properties are improved. Particularly, in a case where the thermosetting resin composition (B) contains an unsaturated polyester resin as a thermosetting resin, it is more preferable that the thermosetting resin composition (B) further contains a polyisocyanate compound and a reactive diluent.

Examples of the polyisocyanate compound include diphenylmethane diisocyanate, hexamethylene diisocyanate, tolyene diisocyanate, xylene diisocyanate, <NUM>,<NUM>'-methylenebis(cyclohexylisocyanate), isophorone diisocyanate, trimethylhexamethylene diisocyanate, and the like.

The thermosetting resin composition (B) may contain one kind of polyisocyanate compound or two or more kinds of polyisocyanate compounds.

Examples of the reactive diluent include a vinyl monomer, a monofunctional (meth)acrylate, and the like. The thermosetting resin composition (B) may contain one kind of reactive diluent or two or more kinds of reactive diluents.

Examples of the vinyl monomer include styrene, α-methylstyrene, α-ethylstyrene, vinyl toluene, and the like.

Examples of the monofunctional (meth)acrylate include methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, isobutyl (meth)acrylate, <NUM>-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, alkyl (meth)acrylate (having <NUM> or <NUM> carbon atoms), tridecyl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate, isobornyl (meth)acrylate, glycidyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, allyl (meth)acrylate, <NUM>-hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, <NUM>-methoxyethyl (meth)acrylate, <NUM>-ethoxyethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, dimethylaminoethyl methyl (meth)acrylate, dimethylaminoethyl benzyl (meth)acrylate, diethylaminoethyl (meth)acrylate, trifluoroethyl (meth)acrylate, heptadecafluorodecyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, dicyclopentanyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, and the like.

Particularly, in a case where the thermosetting resin composition (B) contains a vinyl ester resin as a thermosetting resin, it is preferable that the composition (B) further contains a shrinkage reducing agent.

In this case, it is more preferable to use a shrinkage reducing agent that stays in liquid state at room temperature, because then the fiber substrate (A) tends to be excellently impregnated with the resin composition during the production of SMC.

Examples of the shrinkage reducing agent include polyfunctional (meth)acrylate and the like.

The thermosetting resin composition (B) may contain one kind of shrinkage reducing agent or two or more kinds of shrinkage reducing agents.

Examples of the polyfunctional (meth)acrylate include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate (n = <NUM> to <NUM>), propylene glycol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate (n = <NUM> to <NUM>), <NUM>-butyl-<NUM>-ethyl-<NUM>,<NUM>-propanediol di(meth)acrylate, <NUM>-hydroxy-<NUM>,<NUM>-propanediol di(meth)acrylate, butanediol di(meth)acrylate, <NUM>,<NUM>-butylene glycol di(meth)acrylate, polybutylene glycol di(meth)acrylate (n = <NUM> or <NUM>), neopentyl glycol di(meth)acrylate, pentanediol di(meth)acrylate, <NUM>,<NUM>-hexanediol di(meth)acrylate, trimethylolethane tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, tetramethylolmethane tetra(meth)acrylate, pentaerythritol di(meth)acrylate, dipentaerythritol di(meth)acrylate, sorbitol di(meth)acrylate, trishydroxyethyl isocyanurate, nonanediol di(meth)acrylate, tris(<NUM>-(meth)acryloyloxyethyl)isocyanurate, <NUM>,<NUM>-bis[<NUM>-((meth)acryloxyethoxy)phenyl]propane, <NUM>,<NUM>-bis[<NUM>-((meth)acryloxydiethoxy)phenyl]propane, <NUM>,<NUM>-bis[<NUM>-((meth)acryloxypolyethoxy)phenyl]propane (n = <NUM> to <NUM>), <NUM>-hydroxy-<NUM>-acryloxy-<NUM>-methacryloxypropane, and the like.

Examples of other components used in addition to the curing agent, the polyisocyanate compound, the reactive diluent, and the shrinkage reducing agent include resins other than the thermosetting resin, a filler other than the reinforcing fiber, an internal release agent, a defoaming agent, a flame retardant, a weather fastness enhancer, an antioxidant, a heat stabilizer, an ultraviolet absorber, a plasticizer, a lubricant, a colorant, a compatibilizer, a thickener other than the polyisocyanate compound, a polymerization inhibitor, a rubber reinforcing agent, a surface coating agent, and the like.

The method for producing SMC of the present invention is not particularly limited. For example, SMC is produced by a method of impregnating the fiber substrate (A) with the thermosetting resin composition (B) and keeping the fiber substrate (A) as it is for a certain period of time such that the thermosetting resin composition (B) is thickened.

Hereinafter, as an example of the method for producing SMC of the present invention, a method using an SMC producing apparatus <NUM> illustrated in <FIG> will be described.

For the convenience of description, the dimensional ratio in <FIG> is different from the actual dimensional ratio.

The SMC producing apparatus <NUM> includes a first supply roll <NUM>, a second supply roll <NUM>, a first doctor blade <NUM>, a second doctor blade <NUM>, a chopper <NUM>, a plurality of impregnation roll pairs <NUM>, and a winding roll <NUM>.

The first supply roll <NUM> supplies a first carrier film <NUM>. The second supply roll <NUM> supplies a second carrier film <NUM>.

By the first doctor blade <NUM>, the surface of the first carrier film <NUM> supplied from the first supply roll <NUM> is coated with a thermosetting resin composition (B) <NUM>. By the second doctor blade <NUM>, the surface of the second carrier film <NUM> supplied from the second supply roll <NUM> is coated with a thermosetting resin composition (B) <NUM>.

The chopper <NUM> cuts a carbon fiber tow <NUM>, scatters cut short fiber tows <NUM> onto the thermosetting resin composition (B) <NUM> on the surface of the first carrier film <NUM> such that a fiber substrate (A) <NUM> is formed.

In the SMC producing apparatus <NUM>, the first carrier film <NUM> that is coated with the thermosetting resin composition (B) <NUM> and includes the fiber substrate (A) <NUM> formed on the composition (B) <NUM> and the second carrier film <NUM> that is coated with the thermosetting resin composition (B) <NUM> are stacked such that the fiber substrate (A) <NUM> and the thermosetting resin composition (B) <NUM> contact each other. In this way, a laminated sheet <NUM> is prepared.

Each of the impregnation roll pairs <NUM> is constituted such that the laminated sheet <NUM> passes between the rolls.

The winding roll <NUM> winds up the laminated sheet <NUM> that has passed through the impregnation roll pairs <NUM>.

SMC is produced as below by using the SMC producing apparatus <NUM>.

The surface of the first carrier film <NUM> supplied from the first supply roll <NUM> is uniformly coated with the thermosetting resin composition (B) <NUM> at a predetermined thickness by using the first doctor blade <NUM>.

A plurality of carbon fiber tows <NUM> supplied from a plurality of bobbins are cut by the chopper <NUM> such that the average fiber length thereof becomes <NUM> or more. In addition, short fiber tows <NUM> generated by the cutting are scattered and deposited in the form of a sheet on the thermosetting resin composition (B) <NUM> on the surface of the first carrier film <NUM>. In this case, the fiber substrate (A) <NUM> is formed.

The surface of the second carrier film <NUM> supplied from the second supply roll <NUM> is uniformly coated with the thermosetting resin composition (B) <NUM> at a predetermined thickness by using the second doctor blade <NUM>.

The first carrier film <NUM> that is coated with the thermosetting resin composition (B) <NUM> and includes the fiber substrate (A) <NUM> formed of the short fiber tows <NUM> deposited on the composition (B) <NUM> so as to be two-dimensionally and randomly aligned and the second carrier film <NUM> that is coated with the thermosetting resin composition (B) <NUM> are stacked such that the fiber substrate (A) <NUM> and the thermosetting resin composition (B) <NUM> contact each other. In this way, the laminated sheet <NUM> is prepared.

The laminated sheet <NUM> is caused to sequentially pass through the plurality of impregnation roll pairs <NUM> such that the sheet-like fiber substrate (A) <NUM> is impregnated with the thermosetting resin composition (B) from the upper and lower surface thereof.

The laminated sheet <NUM> having passed through the impregnation roll pairs <NUM> is wound up around the winding roll <NUM>, then left to age for several days at a temperature <NUM> or more and <NUM> or less such that the thermosetting resin composition (B) is thickened, thereby obtaining SMC.

It is preferable that the thermosetting resin composition (B) has viscosity at which the fiber substrate (A) can be impregnated with the composition (B) but the resin composition does not drip from the side of the carrier film. Furthermore, it is preferable that the viscosity of the aged thermosetting resin composition (B) is increased to such a degree that the carrier film can be easily exfoliated.

The molded article of the present invention includes a thick portion that is formed of a cured material of SMC of the present invention and has a thickness of <NUM> or more. The molded article of the present invention may be a molded article that is totally constituted with a thick portion having a thickness of <NUM> or more, or a molded article that includes a thick portion having a thickness of <NUM> or more and a thin portion having a thickness less than <NUM>.

The thickness of the thick portion can be appropriately set as long as it is <NUM> or more. For example, the thickness of the thick portion can be <NUM> or more and <NUM> or less.

The specific gravity of the molded article of the present invention is preferably <NUM> or less, more preferably <NUM> or less, even more preferably <NUM> or less, and particularly preferably <NUM> or less. In a case where the specific gravity of the molded article is the upper limit of the above range or less, the molded article is useful as a lightweight molded article.

The lower limit of the specific gravity of the molded article of the present invention is not particularly limited. The specific gravity of the molded article is generally <NUM> or more.

As the method for producing the molded article of the present invention, for example, known press-molding methods is adopted without particular limitation.

An appropriate amount of SMC of the present invention is put into a die (constituted with a lower die and an upper die) for molding a thick portion that is mounted on a press machine. By using the press machine, the die controlled (heated) to a predetermined temperature is clamped. While being heated, SMC is compressed by the upper die and the lower die. In this way, SMC is shaped in the form of the die. In the clamped die, SMC is cured by being kept as it is for a predetermined period of time. The die is cooled, and then the molded article is taken out of the die.

As described above, in the present invention, SMC is used which contains the fiber substrate (A) containing carbon fiber having an average fiber length <NUM> or more and thermosetting resin composition (B) having a volumetric molding shrinkage rate <NUM>% or more and <NUM>% or less. The use of the fiber substrate (A) makes it possible to obtain a molded article having excellent mechanical characteristics. Furthermore, because the volumetric molding shrinkage rate of the thermosetting resin composition (B) is controlled within the above range, the occurrence of internal distortion is inhibited even during the molding of a thick portion. Therefore, internal cracks hardly occur, and the molded article has excellent die release properties.

Hereinafter, the present invention will be specifically described using examples, but the present invention is not limited to the following description.

The volumetric molding shrinkage rate (%) of a thermosetting resin composition was calculated by the following equation by using a difference between specific gravities that were measured before and after curing according to a density measurement method (JIS K-<NUM><NUM>-<NUM>). <MAT> (In the above equation, r represents a volumetric molding shrinkage rate (%); dl represents a specific gravity of a liquid thermosetting resin composition that is measured before the composition is cured; and ds represents a specific gravity of a cured material of the thermosetting resin composition.

The specific gravity dl was measured for a liquid thermosetting resin composition by a specific gravity bottle method before the composition is cured.

The specific gravity ds was measured by the following method. A die was charged with the thermosetting resin composition, and the composition was cured by being heated and pressed for <NUM> minutes under the conditions of a die temperature of <NUM> and a pressure of <NUM> MPa, thereby obtaining a flat plate-like thermosetting resin molded article having a size of <NUM> × <NUM> × <NUM> (thickness). By using the obtained thermosetting resin molded article, the specific gravity ds was measured by a specific gravity measurement method for solids (weighing in a liquid).

The specific gravity of the carbon fiber composite material molded article produced in each example was measured by a specific gravity measurement method for solids (weighing in a liquid).

For the carbon fiber composite material molded article (a thick molded article) produced in each example, how well the molded articles are released from the die was evaluated. An example in which the molded article was smoothly released from the die was marked with "Excellent (○)". An example in which the molded article stuck to the die when released was marked with "Poor (X)".

Three carbon fiber composite material molded articles (thick molded articles) produced in each example were cut, and the way the internal cracks occur in the cut portions was visually checked. An example in which internal cracks occurred in none of the three molded articles was marked with "○". An example in which internal cracks occurred in one molded article or two molded articles was marked with "Δ". An example in which internal cracks occurred in all of the three molded articles was marked with "X".

The raw materials used in the present example are as follows.

Thermosetting resin (a-<NUM>): a vinyl ester resin (manufactured by Japan U-Pica Company Ltd. , NEOPOL (registered trademark) <NUM>, containing an epoxy (meth)acrylate resin, an unsaturated polyester resin, and styrene).

Thermosetting resin (a-<NUM>): a mixture of <NUM> parts by mass of a liquid bisphenol A epoxy resin (manufactured by Mitsubishi Chemical Corporation, jER (registered trademark) <NUM>) and <NUM> parts by mass of N,N,N',N'-tetraglycidyl-m-xylylenediamine (manufactured by MITSUBISHI GAS CHEMICAL COMPANY, INC. , TETRAD-X).

Thermosetting resin (a-<NUM>): a liquid bisphenol A epoxy resin (manufactured by Mitsubishi Chemical Corporation, jER (registered trademark) <NUM>).

Reactive diluent (b-<NUM>): a mixture of <NUM> parts by mass of <NUM>-ethylhexyl glycidyl ether (manufactured by Mitsubishi Chemical Corporation, YED188) and <NUM> parts by mass of <NUM>,<NUM>-hexanediol diglycidyl ether (manufactured by Mitsubishi Chemical Corporation, YED216M).

Shrinkage reducing agent (c-<NUM>): polyfunctional (meth)acrylate (manufactured by Mitsubishi Chemical Corporation, ACRYESTER PBOM, polybutylene glycol di(meth)acrylate (n=<NUM>, <NUM>)).

Thickener (d-<NUM>): modified diphenylmethane diisocyanate (manufactured by Mitsui Chemicals, Inc. , COSMONATE (registered trademark) LL).

Thickener (d-<NUM>): <NUM>-methyl-<NUM>,<NUM>,<NUM>,<NUM>-tetrahydrophthalic anhydride and <NUM>-methyl-<NUM>,<NUM>,<NUM>,<NUM>-tetrahydrophthalic anhydride (manufactured by Hitachi Chemical Co. , HN-<NUM>).

Thickener (d-<NUM>): <NUM>,<NUM>'-dimethyl-<NUM>,<NUM>'-diaminodicyclohexylmethane (manufactured by Mitsubishi Chemical Corporation, jER CURE (registered trademark) <NUM>).

Curing agent (e-<NUM>): <NUM> part by mass of a <NUM>% solution of <NUM>,<NUM>-di(t-butylperoxy)cyclohexane (manufactured by NOF CORPORATION, PERHEXA (registered trademark) C-<NUM> (EB)) and <NUM> parts by mass of a <NUM>% solution of t-butylperoxyisopropyl carbonate (manufactured by Kayaku Akzo Corporation, KAYACARBONE (registered trademark) BIC-<NUM>).

Curing agent (e-<NUM>): <NUM> part by mass of dicyandiamide (manufactured by Air Products and Chemicals, Inc. , DICYANEX 1400F) and <NUM> parts by mass of <NUM>,<NUM>-diamino-<NUM>-[<NUM>'-methylimidazolyl-(<NUM>')]-ethyl-s-triazine (manufactured by SHIKOKU CHEMICALS CORPORATION. ,2MZA-PW) (<NUM> parts by mass in total).

Curing agent (e-<NUM>): <NUM> parts by mass of dicyandiamide (manufactured by Air Products and Chemicals, Inc. , DICYANEX 1400F) and <NUM> parts by mass of <NUM>,<NUM>-diamino-<NUM>-[<NUM>'-methylimidazolyl-(<NUM>')]-ethyl-s-triazine (manufactured by SHIKOKU CHEMICALS CORPORATION. ,2MZA-PW) (<NUM> parts by mass in total).

Internal release agent (f-<NUM>):a phosphoric acid ester-based derivative composition (manufactured by AXEL Plastics Research Laboratories, Inc. , MOLD WIZINT-EQ-<NUM>).

Stabilizer (g-<NUM>): <NUM>,<NUM>-benzoquinone.

The thermosetting resin (a-<NUM>) (<NUM> parts by mass), <NUM> parts by mass of the shrinkage reducing agent (c-<NUM>), <NUM> part by mass of the curing agent (e-<NUM>), <NUM> parts by mass of the internal release agent (f-<NUM>), <NUM> parts by mass of the thickener (d-<NUM>), and <NUM> parts by mass of the stabilizer (g-<NUM>) were thoroughly mixed and stirred together, thereby obtaining a thermosetting resin composition (B- <NUM>) in a paste state. The volumetric molding shrinkage rate of the thermosetting resin composition (B-<NUM>) was <NUM>%.

The thermosetting resin (a-<NUM>) (<NUM> parts by mass) and <NUM> parts by mass of the curing agent (e-<NUM>) were mixed in advance and kneaded with a triple roll. The obtained mixture was mixed with <NUM> parts by mass of the thickener (d-<NUM>), thereby obtaining a thermosetting resin composition (B-<NUM>) in a paste state. The volumetric molding shrinkage rate of the thermosetting resin composition (B-<NUM>) was <NUM>%.

The liquid bisphenol A epoxy resin (manufactured by Mitsubishi Chemical Corporation, jER (registered trademark) <NUM>) (<NUM> parts by mass) and <NUM> parts by mass of the curing agent (e-<NUM>) were mixed together in advance and kneaded with a triple roll. The obtained mixture was mixed with <NUM> parts by mass of the reactive diluent (b-<NUM>) and <NUM> parts by mass of the thickener (d-<NUM>), thereby obtaining a thermosetting resin composition (B-<NUM>) in a paste state. The volumetric molding shrinkage rate of the thermosetting resin composition (B-<NUM>) was <NUM>%.

A thermosetting resin composition (X-<NUM>) in a paste state was obtained in the same manner as in Production Example <NUM>, except that the shrinkage reducing agent (c-<NUM>) was not used. The volumetric molding shrinkage rate of the thermosetting resin composition (X-<NUM>) was <NUM>%.

A thermosetting resin composition (X-<NUM>) in a paste state was obtained in the same manner as in Production Example <NUM>, except that the amount of the shrinkage reducing agent (c-<NUM>) used was changed to <NUM> parts by mass. The volumetric molding shrinkage rate of the thermosetting resin composition (X-<NUM>) was <NUM>%.

By using a doctor blade, a carrier film made of polyethylene was coated with the thermosetting resin composition (B-<NUM>) obtained in Production Example <NUM> such that the thickness of the composition became <NUM>. On the applied thermosetting resin composition (B-<NUM>), chopped carbon fiber tows, which were obtained by cutting a carbon fiber tow constituted with <NUM>,<NUM> filaments (manufactured by Mitsubishi Chemical Corporation, TR50S <NUM>) in an average fiber length of <NUM>, were scattered such that the basis weight of the carbon fiber became substantially uniform and the fiber in the carbon fiber tows was aligned in random directions. In this way, a fiber substrate (A-<NUM>) was formed.

By using a doctor blade, another carrier film made of polyethylene was coated with the thermosetting resin composition (B-<NUM>) such that the thickness of the composition became <NUM>.

The fiber substrate (A-<NUM>) was interposed between the two sheets of carrier films such that the side of the thermosetting resin composition (B-<NUM>) became inside. The obtained laminate was pressed between the impregnation roll pairs such that the fiber substrate (A-<NUM>) was thoroughly impregnated with the thermosetting resin composition (B-<NUM>), thereby obtaining a sheet-like SMC precursor. The SMC precursor was left to stand for <NUM> hours at room temperature (<NUM>) such that the thermosetting resin composition (B-<NUM>) in the SMC precursor was fully thickened, thereby obtaining CF-SMC (C-<NUM>). The content rate of carbon fiber in CF-SMC (C-<NUM>) was 50mass%.

A die was charged with a charge material, which was prepared by cutting CF-SMC (C-<NUM>) in a size of <NUM> × <NUM> and laminating the cut pieces, at a charge ratio (a ratio of the area of the charge material to the area of the die) of <NUM>%. The resin composition in the charge material was cured by being heated and pressed under the conditions of a die temperature of <NUM> and a pressure of <NUM> MPa, thereby obtaining a flat plate-like carbon fiber composite material molded article having a size of <NUM> × <NUM> × <NUM> (thickness). In addition, carbon fiber composite material molded articles were produced in the same manner as in Example <NUM>, except that the thickness was changed to <NUM>, <NUM>, <NUM>, <NUM>, and <NUM>. In each example, three carbon fiber composite material molded articles having different thicknesses were produced.

The pressing time in the die was set such that a carbon fiber composite material molded article of interest was pressed for <NUM> minute per thickness of <NUM> of the material. For example, in a case where a carbon fiber composite material molded article of interest is <NUM> thick, the pressing time is <NUM> minutes, and in a case where a carbon fiber composite material molded article of interest is <NUM> thick, the pressing time is <NUM> minutes.

CF-SMC (C-<NUM>) and (C-<NUM>) were prepared in the same manner as in Example <NUM>, except that the thermosetting resin composition (B-<NUM>) was changed to the thermosetting resin compositions (B-<NUM>) and (B-<NUM>) as shown in Table <NUM>.

Carbon fiber composite material molded articles were produced in the same manner as in Example <NUM>, except that CF-SMC (C-<NUM>) and (C-<NUM>) were used instead of CF-SMC (C-<NUM>).

CF-SMC (C-<NUM>) was prepared in the same manner as in Example <NUM>, except that the thermosetting resin composition (B-<NUM>) was changed to the thermosetting resin compositions (X-<NUM>) and (X-<NUM>) as shown in Table <NUM>.

A carbon fiber composite material molded article was produced in the same manner as in Example <NUM>, except that CF-SMC (C-<NUM>) was used instead of CF-SMC (C-<NUM>).

Table <NUM> shows the measurement results of physical properties of the thermosetting resin compositions in examples and comparative examples and the evaluation results of specific gravity, internal cracks, and die release properties of the carbon fiber composite material molded articles in examples and comparative examples.

Claim 1:
A sheet molding compound comprising:
a fiber substrate (A) comprising carbon fiber; and
a thermosetting resin composition (B),
wherein an average fiber length of the carbon fiber is <NUM> or more, and
a volumetric molding shrinkage rate (as measured according to the description) of the thermosetting resin composition (B) is <NUM>% or more and <NUM>% or less.