JP5532549B2 - Method for forming prepreg and fiber-reinforced composite material - Google Patents

Description

  The present invention relates to a method for molding a prepreg and a fiber-reinforced composite material.

Fiber reinforced composite materials are widely used from sports / leisure applications to industrial applications such as automobiles and aircrafts, taking advantage of their light weight, high strength and high rigidity. In recent years, in particular, fiber reinforced composite materials that are lighter and have higher strength and rigidity are often used in aircraft and other industrial fields.
A fiber reinforced composite material is a material that has reinforced fibers and a matrix resin as essential components. The strength and elastic modulus in the fiber axis direction of the reinforced fibers are both extremely high, but the direction perpendicular to them is low. Material.

In the production of fiber reinforced composite materials, a method of laminating a sheet-like precursor called a prepreg, in which reinforcing fibers are impregnated with an uncured thermosetting resin, molding, and curing is widely used.
When obtaining a fiber reinforced composite material from a prepreg, a method using a prepreg made of reinforced fibers in a woven fabric, or a method of laminating prepregs composed of reinforced fibers arranged in one direction in different directions are laminated. Control of physical properties in each direction of a fiber reinforced composite material which is an isotropic material is performed.

  However, when the prepregs are laminated in this way, the interlaminar fracture is dominant in the post-impact compression strength of the fiber reinforced composite material in any laminate configuration, so the strength of the reinforced fiber is improved. Is not known to lead to drastic improvements. Here, the interlayer of the fiber reinforced composite material means the vicinity of the surface corresponding to the interface between the prepregs when the prepregs are laminated. In this region, since the fraction of the reinforcing fibers is small and the orientation of the reinforcing fibers on the both sides is different, the stress tends to concentrate. In particular, when a thermosetting resin is used as a matrix resin, it has various advantages such as cost, productivity, and heat resistance, but also has a disadvantage of poor toughness, so that the fiber-reinforced composite material has insufficient compressive strength after impact. It will be a thing.

Various methods have been proposed as methods for improving the post-impact compressive strength of fiber reinforced composite materials. Among them, many methods have been proposed in which a material different from the matrix resin is disposed between the layers of the fiber reinforced composite material to absorb the breaking energy.
For example, in Patent Document 1, the compression strength after impact is improved by arranging fine particles made of resin between layers.
Patent Documents 2 and 3 disclose techniques for improving compression strength after impact while maintaining interlayer shear strength and heat resistance using particles having relatively high rigidity.
Japanese Unexamined Patent Publication No. 63-162732 JP 2001-114915 A JP 2005-105151 A

However, in the method described in Patent Document 1, when fine particles having a high effect of improving compressive strength after impact are used, other physical properties such as interlaminar shear strength and heat resistance may be deteriorated. A fiber reinforced composite material obtained by laminating a plurality of prepregs is required to have high interlayer shear strength.
Further, the techniques described in Patent Documents 2 and 3 do not necessarily satisfy the recent demand for higher post-impact compressive strength.

  This invention is made | formed in view of the said situation, and it aims at providing the shaping | molding method of the prepreg and fiber reinforced composite material which can shape | mold the fiber reinforced composite material which is excellent in the compressive strength after impact, and interlayer shear strength.

The prepreg of the present invention is a prepreg including the following components (A), (B), and (C), and the component (C) is distributed at a higher concentration near the surface than the inside of the prepreg. It is characterized by that.
(A): Reinforcing fiber.
(B): Epoxy resin.
(C): Fine particles of polyamide 12 having a melting point of 180 to 190 ° C.

The component (C) is preferably polyamide 12 fine particles obtained by a reprecipitation method or polyamide 12 fine particles obtained by further freeze-pulverizing fine particles obtained by a reprecipitation method.
Furthermore, the method for molding a fiber-reinforced composite material of the present invention is characterized in that the prepreg is used and cured at a curing temperature of 180 ° C. or lower.

  According to the prepreg of the present invention, a fiber-reinforced composite material excellent in compressive strength after impact and interlaminar shear strength can be obtained.

Hereinafter, the present invention will be described in detail.
[Prepreg]
The prepreg of the present invention comprises: component (A): reinforcing fiber; component (B): base resin mainly composed of thermosetting resin; component (C): fine particles of polyamide 12 having a melting point of 180 to 190 ° C. including.

<Component (A)>
The component (A) used for this invention is a reinforced fiber, and various things can be used according to the intended purpose of a fiber reinforced composite material. Specific examples of the reinforcing fibers used in the present invention include reinforcing fibers used for ordinary fiber-reinforced composite materials such as carbon fibers, graphite fibers, aramid fibers, boron fibers, and glass fibers. The reinforcing fibers may be used alone or in combination of two or more.
Among these reinforcing fibers, carbon fibers and graphite fibers having high specific strength and specific elastic modulus and having a great effect on weight reduction are suitable for the present invention. Any type of carbon fiber or graphite fiber can be used as the carbon fiber or graphite fiber depending on the application.

  The shape and arrangement of the reinforcing fibers are not limited. For example, reinforcing fibers having a shape such as milled, chop, or long fiber can be used. In addition, reinforcing fibers having an arrangement such as a single direction, a random direction, a sheet shape, a mat shape, a fabric shape, and a braided shape can be used. Furthermore, particularly when a fiber-reinforced composite material is required to have a high specific strength and high inelastic modulus, an array in which reinforcing fibers are aligned in a single direction is most suitable. An array of shapes is also suitable for the present invention.

<Component (B)>
The component (B) used in the present invention is a base resin containing a thermosetting resin as a main component, and is generally used in combination with a curing agent or a curing aid. In the present invention, “main component” means that 70% by mass or more is contained in 100% by mass of the base resin. However, the content of the thermosetting resin is a value including the curing agent and the curing aid.
The content of the thermosetting resin including the curing agent and the curing aid is preferably 80% by mass or more in 100% by mass of the base resin.

  Examples of the thermosetting resin include epoxy resins, phenol resins, unsaturated polyester resins, vinyl ester resins, urethane resins, urea resins, melamine resins, maleimide resins and the like. Among these, an epoxy resin is preferable because it is low-cost and a fiber-reinforced composite material excellent in heat resistance and mechanical properties can be easily obtained.

As the epoxy resin, an amine, a phenol, or a compound having a carbon-carbon double bond as a precursor is preferable. Specific examples of the epoxy resin having amines as a precursor include various isomers of tetraglucidyldiaminodiphenylmethane, triglycidyl-p-aminophenol, triglycidyl-m-aminophenol, and triglycidylaminocresol.
Examples of the epoxy resin having a phenol as a precursor include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, phenol novolac type epoxy resin, and cresol novolac type epoxy resin.
An alicyclic epoxy resin etc. are mentioned as an epoxy resin which uses the compound which has a carbon carbon double bond as a precursor.
The epoxy resin is not limited to these. Moreover, the brominated epoxy resin which brominated the epoxy resin mentioned above can also be used. Among these, an epoxy resin having an aromatic amine represented by tetraglycidyldiaminodiphenylmethane as a precursor is particularly preferable because a fiber-reinforced composite material having excellent heat resistance can be easily obtained.

  The epoxy resin is preferably used in combination with an epoxy curing agent. As the epoxy curing agent, a compound having an active group capable of reacting with an epoxy group or a compound improving the reactivity between epoxy groups is preferable. For example, aromatic amine such as diaminodiphenylmethane, diaminodiphenylsulfone, aliphatic amine, imidazole derivative, dicyandiamide, tetramethylguanidine, thiourea addition amine, methylhexahydrophthalic anhydride, carboxylic acid amide, polyphenol compound, novolac resin, Examples include, but are not limited to, polymercaptons and Lewis acid complexes such as boron trifluoride monoethylamine complex. Preferably, a compound having an amino group, an acid anhydride group, or an azide group is suitable. Specifically, dicyandiamide, various isomers of diaminodiphenylsulfone, various derivatives of diaminodiphenylmethane, and aminobenzoic acid esters are suitable. Specifically, dicyandiamide is preferably used because it has excellent prepreg storage stability. Further, various isomers of diaminodiphenylsulfone are most suitable for the present invention because they give a cured product having good heat resistance.

  These epoxy curing agents can be combined with an appropriate curing aid in order to increase the curing activity. Preferred examples include dicyandiamide, 3-phenyl-1,1-dimethylurea, 3- (3,4-dichlorophenyl) -1,1-dimethylurea (DCMU), 3- (3-chloro-4-methylphenyl). ) Examples of combining urea derivatives such as 1,1-dimethylurea and 2,4-bis (3,3-dimethylureido) toluene as curing aids; Curing aids with tertiary amines on carboxylic anhydrides and novolak resins Examples in which diaminodiphenylsulfone is combined with an urea complex such as imidazole compound and phenyldimethylurea (PDMU), an amine complex such as boron trifluoride monoethylamine, and an amine trichloride complex as a curing aid.

  In addition to thermosetting resins, the base resin contains various additives such as reactive diluents, thermoplastic resins, elastomers and other modifiers, fillers, stabilizers, flame retardants, and pigments. Also good.

A mixture of a thermosetting resin and a thermoplastic resin gives even better results than when the thermosetting resin is used alone. In other words, the brittleness of the thermosetting resin is compensated by the toughness of the thermoplastic resin, and further, tackiness is improved, and the thermosetting resin compensates for the molding difficulty of the thermoplastic resin. Become.
In particular, as the thermoplastic resin, it is preferable that at least one resin selected from polysulfone, polyethersulfone, polyetherimide, and polyimide is mixed and dissolved in the base resin. Furthermore, the thermoplastic resin which has the functional group which can react with a thermosetting resin in the terminal or molecular chain is further more preferable.

  It is also preferable to add an inorganic filler such as finely divided silica to the base resin in order to improve the mechanical properties such as rheological property control, rigidity, and toughness.

<Component (C)>
The component (C) used in the present invention is a fine particle of polyamide 12 having a melting point of 180 ° C. or higher. If the melting point of the polyamide 12 fine particles is 180 ° C. or higher, it will have a melting point of a curing temperature (177 ° C., 180 ° C.) or higher that is general for aircraft use.
In the present invention, the reason for using the fine particles of polyamide 12 having a melting point of 180 ° C. or higher is as follows.

When the surface area of the polyamide 12 fine particles decreases due to the polyamide 12 fine particles being dissolved in the base resin, the volume of the polyamide 12 fine particles is reduced, or the polyamide 12 fine particles are fused by melting. The energy absorption capacity of the is reduced. On the other hand, when the fine particles of polyamide 12 are dissolved in the base resin, the rigidity of the base resin is lowered, so that the interlaminar shear strength is easily lowered.
Therefore, in order to express the compressive strength after impact and the interlaminar shear strength, it is important that most of the fine particles of polyamide 12 are not dissolved in the base resin during the curing process and the shape of the particles is maintained.
When the melting point of the polyamide 12 fine particles is 180 ° C. or higher, the particle shape can be maintained in the base resin without completely melting the polyamide 12 fine particles during curing.
On the other hand, when the melting point of the polyamide 12 fine particles is too higher than necessary, the polyamide 12 fine particles are not melted at all at the curing temperature, and the adhesion at the interface between the polyamide 12 fine particles and the base resin is weakened. Therefore, there is a possibility that the compressive strength after impact is reduced. Accordingly, the melting point of the polyamide 12 fine particles is preferably 180 to 190 ° C, more preferably 180 to 185 ° C.
The “melting point” in the present invention is a temperature at which the heat of fusion reaches a peak when measured with a differential scanning calorimeter at a rate of temperature increase of 10 ° C./min.

  The polyamide 12 fine particles having a melting point of 180 ° C. or higher can be easily obtained by reprecipitation or by further freeze-pulverizing fine particles obtained by the reprecipitation method. As the reprecipitation method and the freeze pulverization method, known methods can be employed.

In the present invention, “fine particles” mean particles having an average particle diameter of 2 to 90 μm.
If the average particle diameter of the polyamide 12 is 2 μm or more, the particles (polyamide 12) can be localized between the layers of the reinforcing fibers and can be localized between the layers of the prepreg laminate, and the presence effect of the particles can be sufficiently exerted and impact Post compression strength can be further improved. On the other hand, if the average particle diameter is 90 μm or less, the arrangement of the reinforcing fibers is disturbed, or the layers of the fiber reinforced composite material obtained by lamination are thickened more than necessary, and thus adverse effects such as lowering the physical properties. Can be reduced. The average particle size of the polyamide 12 is particularly preferably 5 to 40 μm, and most preferably 5 to 25 μm.
An average particle diameter is calculated | required from the photograph of the particle | grains expanded 200-500 times with the scanning electron microscope (SEM). In the present invention, it is sufficient to measure 100 arbitrarily selected particles. The length (particle diameter) is measured for each particle, and the average value is taken as the average particle diameter.

  Examples of the fine particles of polyamide 12 having a melting point of 180 ° C. or higher include VESTOSINT1111, VESTOSINT2070, VESTOSINT2157, VESTOSINT2158, and VESTOSINT2159 (manufactured by Daicel-Evonik Co., Ltd.). These fine particles are generally commercially available and are excellent in availability and cost, but are not limited to the fine particles listed here.

The outer shape, surface or internal form of the polyamide 12 fine particles may be either spherical or non-spherical particles.
Spherical particles are preferred in that they do not reduce the flow characteristics of the base resin described above, but the purpose of using polyamide 12 microparticles having a specific particle size is to localize these microparticles between the layers of the laminate. Therefore, the outer shape, surface or internal form of the polyamide 12 fine particles is not particularly limited.

The fine particles of polyamide 12 are distributed at a higher concentration near the surface than inside the prepreg. The surface on which the fine particles of the polyamide 12 are distributed at a high concentration may be one side of the prepreg or both sides. Since the polyamide 12 fine particles are distributed at a high concentration in the vicinity of the surface, the polyamide 12 fine particles are localized between the layers when a plurality of prepregs are laminated. As a result, the fine particles of polyamide 12 absorb the breaking energy, so that the compressive strength after impact of the fiber-reinforced composite material is improved.
The addition amount of the polyamide 12 fine particles in the vicinity of the surface of the prepreg is preferably 1 to 20 g / m ^{2 and} more preferably 7.5 to 15 g / m ² per unit area of the prepreg.
In the present invention, “near the surface” refers to a region within a range of 0 to 30% from the surface with respect to a thickness of 100% of the prepreg. In the present invention, it is assumed that 90% by mass or more of polyamide 12 fine particles are localized in this region.

The degree of localization of the fine particles of polyamide 12 in the prepreg can be confirmed as follows.
First, the prepreg is closely adhered between two smooth support plates, and is cured by gradually raising the temperature over a long period of time. What is important at this time is to make the gel as low as possible. If the temperature is raised before gelation, the resin in the prepreg flows and the fine particles of the polyamide 12 move, making it difficult to accurately evaluate the particle distribution in the original prepreg.
After gelation, the prepreg is cured by gradually applying temperature over time. Using the cured prepreg, the cross section is magnified 200 times or more with a microscope and a photograph of 200 mm × 200 mm or more is taken.
First, an average prepreg thickness is obtained using the obtained cross-sectional photograph. The average thickness of one prepreg layer is measured at at least five points arbitrarily selected on the photograph, and the average is taken.
Next, a line is drawn in parallel to both directions of the prepreg at a position 30% of the thickness of the prepreg from the surface in contact with both support plates. The cross-sectional area of the polyamide 12 fine particles existing between the surface in contact with the support plate and 30% parallel lines is quantified on both sides of the prepreg, and the cross-sectional area of the polyamide 12 fine particles existing over the entire width of the prepreg is calculated. By quantifying and taking the ratio, the amount of particles existing within 30% of the thickness of the prepreg is calculated from the prepreg surface.

The quantification of the particle cross-sectional area may be performed by an image analyzer, or may be performed by cutting out all the particle portions existing in a predetermined region from the cross-sectional photograph and weighing the mass. In order to eliminate the influence of the dispersion of the partial distribution of polyamide 12 fine particles, this evaluation is performed over the entire width of the obtained photograph, and the same evaluation is performed for five or more arbitrarily selected photographs. It is necessary to take the average.
When it is difficult to distinguish between the polyamide 12 fine particles and the base resin, one of them may be selectively dyed and observed.
As the microscope, an optical microscope or a scanning electron microscope may be used, and it may be properly used depending on the size of the polyamide 12 fine particles and the staining method.

<Other components>
The prepreg of the present invention may contain other components in addition to the components (A), (B), and (C) described above as long as the effects of the present invention are not impaired.
Examples of other components include thermoplastic resins and organic / inorganic fillers. These may be in any shape such as particles, milled, chop, whisker.

<Method for producing prepreg>
The prepreg in which the component (C) is distributed at a high concentration in the vicinity of one or both surfaces of the prepreg can be produced by, for example, the following method, but is not limited thereto.
The first method is to impregnate the component (B) from both sides or one side of the sheet-shaped component (A) using a film (F1) in which the component (B) is coated on a release paper or the like. The primary prepreg is prepared and the component (C) is dispersed on both sides or one side.

As a method for impregnating the constituent element (A) with the constituent element (B), a known method can be adopted, and examples thereof include a method of pressurizing with a hot press roll.
Moreover, what is necessary is just to set suitably the thickness of a prepreg, fiber fabric weight, base resin content rate, etc. according to the use of a prepreg. The base resin content can be adjusted, for example, by adjusting the resin basis weight of the film (F1) and the fiber basis weight of the component (A).

The second method is a film (F2) produced by coating the component (B) on a release paper and the like, and further dispersing the component (C) on the component (B). Using the primary prepreg produced in the same manner as above, the film (F2) is placed on both sides or one side of the primary prepreg so that the component (C) side of the film (F2) and the component (B) of the primary prepreg are in contact with each other. It is a method of sticking.
The component (B) of the primary prepreg and the component (B) of the film (F2) may have the same composition or different compositions.

In the third method, a film (F3) produced by coating the component (B) kneaded with the component (C) on a release paper or the like, and a primary prepreg produced in the same manner as in the first method, It is a method of using and sticking a film (F3) to both sides or one side of a primary prepreg.
The component (B) of the primary prepreg and the component (B) of the film (F3) may have the same composition or different compositions.

  The fourth method uses a film (F4) in which a component (B) kneaded with the component (C) is coated on a release paper or the like, from both sides or one side of the component (A) formed into a sheet. In this method, the component (B) is impregnated and filtered by the component (A) to leave the component (C) near the surface.

  When other components are included in the prepreg, the other components may be used together with the component (B), and are dispersed together with the component (C) or kneaded into the component (B). May be.

  The prepreg of the present invention thus obtained contains specific components (A), (B) and (C), and the component (C) is distributed at a higher concentration near the surface than inside the prepreg. Therefore, a fiber-reinforced composite material excellent in compressive strength after impact and interlaminar shear strength can be formed, and it is suitable as a precursor of a fiber-reinforced composite material that requires high post-impact compressive strength.

[Fiber-reinforced composite materials]
The fiber-reinforced composite material of the present invention is molded by curing at a curing temperature of 180 ° C. or less using the prepreg of the present invention. The curing time depends on the curing temperature and the molding method and cannot be determined unconditionally. For example, 1 to 4 hours is preferable.
Examples of the molding method include autoclave molding, oven molding, and press molding.
In the present invention, by setting the curing temperature to 180 ° C. or lower, it is possible to use general equipment as the equipment and auxiliary materials used for molding, which is advantageous in terms of cost.

  The fiber reinforced composite material thus obtained is excellent in compressive strength after impact and interlaminar shear strength because the prepreg of the present invention is used as a precursor. Such a fiber reinforced composite material is particularly suitably used in the field of aircraft and the like.

EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited at all by these.
In the examples and comparative examples, various tests were performed according to the following.

(1) Measurement of compressive strength after impact (CAI) 12 laminates obtained by superposing 3 sets of 4 prepregs laminated in the direction of [+ 45 ° / 0 ° / −45 ° / 90 °], and [ 90 laminates of 4 laminates in the direction of 90 ° / -45 ° / 0 ° / + 45 °] are stacked so that the 90 ° direction is aligned with each other, and a total of 24 laminates. Was put in a bag and heated in an autoclave at 180 ° C. for 2 hours and cured to produce a molded plate (fiber reinforced composite material). During this time, the inside of the autoclave was pressurized to 0.7 MPa, and the inside of the bag was kept in vacuum.
A test piece was cut out from the resulting molded plate, and a falling weight impact of 25 J was applied to the center of the test piece, and then the post-impact compression strength of the test piece was measured according to Airbus Industries Test Method AITM 1.0010.
In this test, since the influence of Vf (fiber volume content) of the test piece is small, the measured value was calculated as an actually measured value not converted to Vf.

(2) Measurement of interlaminar shear strength (ILSS) In order to obtain a molded plate having a thickness of about 2 mm, 12 prepregs were laminated in a single direction and placed in a bag, which was placed in an autoclave at 180 ° C. for 2 hours. A molded plate was prepared by heating and curing. During this time, the inside of the autoclave was pressurized to 0.7 MPa, and the inside of the bag was kept in vacuum.
A test piece was cut out from the resulting molded plate, and the interlaminar shear strength of the test piece was measured at ambient temperatures of 23 ° C. and 70 ° C. in accordance with AECMA EN2563.

(3) Measurement of melting point (Tm) About 5 mg of the fine particles used as component (C) were collected, put in an aluminum pan, and a differential scanning calorimeter (TA Instruments, “Q-1000”). Measurement was carried out at a heating rate of 10 ° C./min. The peak top temperature in melting of the obtained endothermic curve was taken as the melting point.

(4) Measurement of average particle diameter The average particle diameter of the fine particles used as the component (C) was measured with a scanning electron microscope ("JSM-6390" manufactured by JEOL Ltd.). Specifically, fine particles were affixed to a carbon tape and sputter coated with platinum using an auto fine coater (manufactured by JEOL Ltd., “JFC-1600”) to prepare a sample. The sample processed above was magnified 200 to 500 times with a scanning electron microscope, and a photograph was taken. The length of at least 100 particles arbitrarily selected in the photograph was measured, and the average was taken as the average particle size of the fine particles. When the particles are not spherical, the major axis length and minor axis length of the arbitrarily selected particles are measured, and the major axis length and minor axis length are measured in at least 100 locations. The average particle size was taken.

(5) Measurement of the degree of localization of the fine particles of polyamide 12 The prepreg was put in close contact between two smooth support plates, and was cured by gradually raising the temperature over a long period of time. After gelation, the prepreg was cured by gradually applying temperature over a period of time. A cross section of the cured prepreg was magnified 200 times with an optical microscope, and a photograph of 200 mm × 200 mm was taken.
First, an average prepreg thickness was determined using the obtained cross-sectional photograph. The average thickness of one prepreg layer was measured at at least 5 points arbitrarily selected on the photograph, and the average was taken.
Next, a line parallel to both directions of the prepreg is drawn from the surface in contact with both support plates to a position of 30% of the thickness of the prepreg, and the polyamide existing between the surface in contact with the support plate and 30% parallel lines The cross-sectional area of 12 fine particles was quantified on both sides of the prepreg. Similarly, the cross-sectional area of the polyamide 12 fine particles existing over the entire width of the prepreg was quantified, and the ratio was calculated to calculate the amount of particles existing within 30% of the prepreg thickness from the prepreg surface.
The particle cross-sectional area was quantified by cutting out all the particle portions existing in a predetermined region from the cross-sectional photograph and weighing the mass. In order to eliminate the influence of the dispersion of the partial distribution of the polyamide 12 fine particles, this evaluation is performed over the entire width of the obtained photograph, and the same evaluation is performed for five arbitrarily selected photographs. Performed and averaged.

[Example 1]
Two films were prepared by coating an epoxy resin (“# 1054X resin” manufactured by Mitsubishi Rayon Co., Ltd.) as a base resin (component (B)) on a release paper with a basis weight of 50.5 g / m ² . Two films are arranged so that the coating surfaces face each other, and carbon fiber (manufactured by Mitsubishi Rayon Co., Ltd., “MR60H”) is placed as a reinforcing fiber (component (A)) between the two films, and heated press A unidirectional primary prepreg was produced by pressurizing with a roll and impregnating carbon fiber with an epoxy resin. This primary prepreg had a carbon fiber basis weight of 196 g / m ² and a base resin content of 34.0% by mass.
A fine particle of polyamide 12 (manufactured by Daicel-Evonik Co., Ltd., “VESTOINT 2159”) as a component (C) was sprayed on one side of the primary prepreg to obtain a prepreg. The amount of fine particles added per unit area was 11 g / m ² . It was also confirmed that fine particles were distributed at a high concentration near the surface of the prepreg.
Using the obtained prepreg, the compression strength after impact and the interlaminar shear strength were measured. The obtained results are shown in Table 1. In addition, when the cross section of the thickness direction of the obtained molded plate was confirmed with an optical microscope, some of the fine particles of polyamide 12 were observed to be fused to each other, but most of them were in the shape of particles. It was confirmed that
Further, the melting point and the particle diameter of the fine particles used as the component (C) were measured. The results are shown in Table 1.

[Examples 2-3]
A prepreg was produced in the same manner as in Example 1 except that the fine particles shown in Table 1 were used as the component (C). The amount of fine particles added per unit area was 11 g / m ² . It was also confirmed that fine particles were distributed at a high concentration near the surface of the prepreg.
Using the obtained prepreg, the compression strength after impact and the interlaminar shear strength were measured. The obtained results are shown in Table 1. In addition, when the cross section of the thickness direction of the obtained molding board was confirmed with the optical microscope, the fine particle of the polyamide 12 was observed in the state that several fine particles were fused, but most maintained the particle shape. It was confirmed that
Further, the melting point and the particle diameter of the fine particles used as the component (C) were measured. The results are shown in Table 1.

[Comparative Example 1]
A prepreg was produced in the same manner as in Example 1 except that the fine particles shown in Table 1 were used as the component (C). The amount of fine particles added per unit area was 11 g / m ² . It was also confirmed that fine particles were distributed at a high concentration near the surface of the prepreg.
Using the obtained prepreg, the compression strength after impact and the interlaminar shear strength were measured. The obtained results are shown in Table 1. In addition, when the cross section of the thickness direction of the obtained molded plate was confirmed with an optical microscope, the fine particles of polyamide 12 were fused with each other, and in a form like a film shape that was widely continuous in the lamination direction. I confirmed that there was.
Further, the melting point and the particle diameter of the fine particles used as the component (C) were measured. The results are shown in Table 1.

The fine particles in Table 1 are as follows.
VESTOSINT 2159: Polyamide 12, manufactured by Daicel Evonik,
VESTOSINT 2158: Polyamide 12, manufactured by Daicel Evonik,
VESTOSINT 1111: Polyamide 12, manufactured by Daicel Evonik,
Orgasol 2002D NAT1: Polyamide 12, manufactured by Arkema Co., Ltd.

  As is clear from Table 1, the fiber-reinforced composite materials obtained from the prepregs of each example have better post-impact compressive strength and interlaminar shear strength than the comparative examples, and the post-impact compressive strength and interlaminar shear strength are higher. We were able to achieve both.

  The prepreg of the present invention can form a fiber-reinforced composite material excellent in compressive strength after impact and interlaminar shear strength. The fiber-reinforced composite material thus obtained can meet the recent demand for higher compressive strength after impact and can maintain the interlaminar shear strength. Therefore, the applicable range of application can be greatly expanded.

Claims (3)

A prepreg comprising the following components (A), (B) and (C),
The prepreg characterized in that the component (C) is distributed in a higher concentration near the surface than in the prepreg.
(A): Reinforcing fiber.
(B): Epoxy resin.
(C): Fine particles of polyamide 12 having a melting point of 180 to 190 ° C.   The component (C) is a polyamide 12 microparticles obtained by further freeze-pulverizing polyamide 12 microparticles obtained by a reprecipitation method or microparticles obtained by a reprecipitation method. Prepreg.   A method for molding a fiber-reinforced composite material, wherein the prepreg according to claim 1 or 2 is used and cured at a curing temperature of 180 ° C or lower.