JP2020045481A - Prepreg, prepreg with release sheet, and fiber-reinforced composite material - Google Patents

Abstract

To provide a prepreg suitable for producing a fiber-reinforced composite material in a short time without using an autoclave, which can obtain a fiber-reinforced composite material that suppresses occurrence of voids and exhibits excellent impact resistance, and is excellent in handling property, and a fiber-reinforced composite material using the same.SOLUTION: A prepreg in which a reinforcement fiber [A] that is arranged in a layer form is partially impregnated with an epoxy resin composition containing an epoxy resin [B] and a curing agent [C] has an impregnation ratio φ of 30-95%, a thermoplastic resin [D] insoluble in the epoxy resin [B] is unevenly distributed on the surface on both sides of the prepreg, in the layer of the reinforcement fiber [A], a non-impregnation part of the epoxy resin composition is localized in the vicinity of the surface on both of the sides of the prepreg, and a localization parameter σ specifying a degree of localization is in a range of 0.10<σ<0.45.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a prepreg, a prepreg with a release sheet, and a fiber-reinforced composite material.

  Fiber reinforced composite materials consisting of matrix fibers and reinforced fibers such as carbon fibers and glass fibers are lightweight, yet have excellent mechanical properties such as strength and rigidity, heat resistance, and corrosion resistance. It has been applied to many fields such as automobiles, railway vehicles, ships, civil engineering and sporting goods. Above all, members for aircraft such as general passenger aircraft and regional jets and members for spacecraft such as artificial satellites, rockets and space shuttles require particularly excellent mechanical properties and heat resistance. Therefore, in such applications, a lightweight and highly rigid carbon fiber is often used as the reinforcing fiber, and a thermosetting resin such as an epoxy resin having excellent heat resistance, elastic modulus and chemical resistance is used as the matrix resin. Is often done.

  The main cause of the deterioration of the mechanical properties of the fiber-reinforced composite material is the existence of voids interposed inside the fiber-reinforced composite material. When a mechanical load is applied to the fiber-reinforced composite material containing voids, damages such as cracks and peeling are likely to occur, which lowers the mechanical strength and rigidity. For this reason, many studies have been made on materials / forming techniques for suppressing such voids since ancient times.

  Among the methods for producing fiber-reinforced composite materials, there is an autoclave molding method as a molding method capable of particularly suppressing generation of voids. In this molding method, the resin can be cured by heating while applying pressure, so that the size of the void can be reduced. In addition, since the evaporation of volatile components contained in the matrix resin can be suppressed, the amount of voids can be significantly suppressed. However, in the autoclave molding method, a large initial investment is required to introduce a pressure vessel (autoclave) that can withstand high pressure, and this is a major factor that makes the technology of aeronautical and aerospace parts with a small number of production expensive. Met.

  Therefore, a deautoclave molding method using only a vacuum pump and an oven without using expensive pressurizing equipment such as an autoclave has been proposed. However, in the conventional de-autoclave molding method, since volatile components in the epoxy resin are easily vaporized during heating, it is necessary to place in a preheated state (for example, 60 to 120 ° C.) for a long time under vacuum in order to remove the volatile components. there were. Therefore, compared with the conventional autoclave molding method, there is a problem that the molding time is longer, voids are apt to remain, and the defective product ratio is high.

  As means for solving such a problem, Patent Document 1 discloses that when impregnating a matrix resin into a reinforcing fiber layer, the impregnation of the resin is suppressed and an unimpregnated portion is interposed inside the prepreg, so that the volatile content of the prepreg and There has been proposed a partially impregnated prepreg provided with a void for exhausting trapped air. Using this method, using only a vacuum pump and an oven, even in the case of molding under an atmospheric pressure environment without using an autoclave, the volatile components and air entrapment that are the cause of voids are generated through the voids. The fiber reinforced composite material having few voids can be manufactured in a short time.

  Further, Patent Document 2 discloses that as a fiber-reinforced composite material for an aircraft / spacecraft, a high-toughness thermoplastic resin is localized between fiber layers, thereby dramatically improving the impact resistance. Technology has been proposed. In actual operation of aircraft and spacecraft, impact damage such as collision with birds and hail is a problem, but by using the above-mentioned interlayer toughening technology, the impact strength of fiber reinforced composite material is dramatically increased. Can be enhanced.

U.S. Pat. No. 6,139,942 JP-A-10-231372

  However, even when the partially impregnated prepreg described in Patent Literature 1 is used, in order to efficiently remove volatile components and reduce the frequency of occurrence of voids, the unimpregnated portion is made large, and a void portion is formed. It was necessary to ensure continuity. However, if the unimpregnated portion is too large, the prepreg may be cut or fuzzed from the cut surface when the prepreg is cut, or the prepreg may be broken in an out-of-plane direction. Had led to a decline in gender. That is, there is a trade-off relationship between the reduction of the risk of generating voids and the handling property of the prepreg, and no means has been proposed to solve them at the same time.

  Further, the thermoplastic resin disposed between the layers described in Patent Document 2 is generally in a solid or high-viscosity state at a molding temperature. For this reason, movement of the matrix resin (hereinafter, referred to as a flow) during molding is less likely to occur, and the resin is easily cured without impregnating the voids contained in the prepreg laminate with the resin. I was

  In view of the background art, an object of the present invention is a prepreg suitable for producing a fiber-reinforced composite material without using an autoclave and in a short time, in which generation of voids is suppressed, and excellent immunity is obtained. An object of the present invention is to provide a prepreg which can obtain a fiber-reinforced composite material exhibiting impact properties and has excellent handling properties, and to provide a fiber-reinforced composite material using the same.

  The inventors of the present invention have conducted intensive studies in order to solve such a problem, and by localizing the non-impregnated portion of the prepreg reinforcing fiber layer near both sides of the prepreg, the continuation of this unimpregnated portion has been achieved. It has been found that it is possible to dramatically improve the properties and to efficiently remove air trapped during lamination and volatile components contained in the matrix resin to the outside of the prepreg laminate. Thus, it has been found that even with a prepreg having a small unimpregnated portion, a fiber-reinforced composite material having a small amount of voids and excellent in impact resistance can be formed in a short time.

  Based on such knowledge, the present invention employs the following means. That is, the prepreg of the present invention is a prepreg obtained by partially impregnating an epoxy resin composition containing an epoxy resin [B] and a curing agent [C] into a reinforcing fiber [A] arranged in a layered manner, The impregnation ratio φ is 30 to 95%, the thermoplastic resin [D] insoluble in the epoxy resin [B] is unevenly distributed on both surfaces of the prepreg, and the epoxy resin in the layer of the reinforcing fiber [A] The unimpregnated portion of the resin composition is localized near both surfaces of the prepreg, and the localization parameter σ that defines the degree of localization is in the range of 0.10 <σ <0.45. It is characterized by the following.

  Further, the prepreg with a release sheet of the present invention has a release sheet attached to both surfaces of the prepreg.

  Further, the fiber-reinforced composite material of the present invention is obtained by curing a laminate of the prepreg.

  The prepreg of the present invention is a prepreg suitable for producing a fiber-reinforced composite material in a short time without using an autoclave, in which the generation of voids is suppressed, and a fiber exhibiting excellent impact resistance. It is a prepreg that can obtain a reinforced composite material and has excellent handling properties.

  Further, the prepreg with a release sheet of the present invention is a prepreg excellent in maintaining continuity of the resin-unimpregnated portion of the reinforcing fiber layer and maintaining tackiness of the surface.

  Further, the fiber reinforced composite material of the present invention is a fiber reinforced composite material that suppresses generation of voids and exhibits excellent impact resistance.

It is an outline sectional view showing the conventional prepreg for vacuum pressure molding. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic sectional drawing which shows the prepreg for vacuum pressure molding of this invention. FIG. 4 is a schematic cross-sectional view of a prepreg showing a method for calculating a localization parameter σ. It is the schematic which shows the structure which measures the penetration coefficient K of the in-plane direction of a prepreg.

  The prepreg of the present invention is a prepreg obtained by partially impregnating a layered reinforcing fiber [A] with an epoxy resin composition containing an epoxy resin [B] and a curing agent [C]. Rate is 30 to 95%, the thermoplastic resin [D] insoluble in the epoxy resin [B] is unevenly distributed on both surfaces of the prepreg, and the epoxy resin in the reinforcing fiber [A] layer A prepreg in which the unimpregnated portion of the composition is localized in the vicinity of both surfaces of the prepreg, and the localization parameter σ defining the degree of the localization is in the range of 0.1 <σ <0.45. It is.

  The reinforcing fiber [A] used in the present invention may be any fiber such as glass fiber, Kevlar fiber, carbon fiber, graphite fiber, and boron fiber. Among them, carbon fibers having excellent specific strength and specific elastic modulus are preferable in order to obtain a particularly high weight saving effect.

  In one preferred embodiment of the prepreg of the present invention, the reinforcing fibers [A] are continuous fibers arranged in one direction. By using continuous fibers, it is possible to exhibit higher mechanical strength than fibers cut short. Further, by arranging the fibers in one direction, a fiber reinforced composite material having a high fiber content and excellent strength and rigidity can be obtained. In the present invention, “arranged in one direction” means that the surface of the prepreg is observed with an optical microscope, the orientation angle of each fiber is θ, and the average value is Θ−10 ° <θ < It means a state where fibers satisfying Θ + 10 ° exist in 90% or more of the whole. In calculating the average value, a 0.5 mm visual field was observed with an optical microscope, and out of the fibers included in the range, any 30 fibers were selected, and the average value of the orientation angles was used. I do. Further, the “continuous fiber” in the present invention is a reinforcing fiber having a length capable of exhibiting high strength, and specifically means a reinforcing fiber having a length of 10 cm or more.

  In another preferred embodiment, in the prepreg of the present invention, the reinforcing fiber [A] is in a woven form. By using a woven base material, the base material itself is easily deformed in the in-plane direction, and the base material is easily formed into a shape having three-dimensional irregularities. Examples of the woven form include a bidirectional woven fabric, a multiaxial woven fabric, a knit, and a braid. In these woven fabric substrates, the contact surface between the bundles of carbon fibers having different orientations is often located at the center in the thickness direction of the substrate. In this case, as compared with a configuration in which a non-impregnated portion is provided at the central portion as in the case of the conventional partially impregnated prepreg, the base material is prevented from cracking by shifting the non-impregnated portion from the center in the thickness direction as in the present invention. Becomes possible. This makes it possible to obtain a prepreg excellent not only in air permeability but also in handling properties.

  In still another preferred embodiment of the prepreg of the present invention, the reinforcing fiber [A] is a sheet-like short fiber base. The short fiber base material is more easily stretched than the woven base material, and the base material is easily formed into a more complicated three-dimensional shape. Examples of the short fiber base include a nonwoven fabric, a mat, and a sheet molding compound material. The fiber length of the reinforcing fibers included in this embodiment is preferably 12 mm or more, and more preferably 25 mm or more, when giving priority to mechanical strength. This is because a higher mechanical strength can be easily exhibited as compared with a reinforcing fiber of less than 12 mm. When giving priority to the extensibility of the base material, the thickness is preferably 25 mm or less, more preferably 12 mm or less. Further, these preferred embodiments can be appropriately selected depending on the application and the use environment.

  The epoxy resin [B] included in the present invention may be any epoxy resin as long as it has one or more glycidyl groups, but preferably has two or more glycidyl groups in one molecule. In the case of an epoxy resin having two or more glycidyl groups in one molecule, the glass transition temperature of a cured product obtained by heat-curing a mixture with a curing agent described below (hereinafter referred to as an epoxy resin composition) has a glycidyl group. Higher than a cured product of an epoxy resin having one.

  Examples of the epoxy resin that can be used in the present invention include bisphenol A epoxy resins, bisphenol F epoxy resins, bisphenol AD epoxy resins, bisphenol S epoxy resins, and other bisphenol epoxy resins, and tetrabromobisphenol A diglycidyl ether. Novolak epoxy resins such as brominated epoxy resins, epoxy resins having a biphenyl skeleton, epoxy resins having a naphthalene skeleton, epoxy resins having a dicyclopentadiene skeleton, phenol novolak epoxy resins, cresol novolak epoxy resins, and diaminodiphenylmethane Epoxy resin, diaminodiphenyl sulfone epoxy resin, aminophenol epoxy resin, meta-xylene diamine epoxy resin, 1, - bisaminomethylcyclohexane type epoxy resins, glycidyl amine epoxy resins such as isocyanurate type epoxy resins. Among them, an epoxy resin having three or more glycidyl groups in one molecule is preferable because it can exhibit a higher glass transition temperature and a higher elastic modulus.

  These epoxy resins may be used alone or as a mixture of a plurality of epoxy resins. When using a mixture of a plurality of epoxy resins, for example, at an arbitrary temperature equal to or lower than the curing start temperature of the epoxy resin composition, mixing an epoxy resin having fluidity and an epoxy resin having no fluidity, It is effective for controlling the fluidity of the matrix resin during prepreg molding. If the fluidity is not controlled, for example, during prepreg molding, if the fluidity shown before the matrix resin gels is large, the orientation of the reinforcing fibers may be disturbed, or the matrix resin may be removed from the reinforcing fiber layer. By flowing out, the fiber mass content becomes excessively high, and the mechanical properties of the resulting fiber-reinforced composite material may be reduced. Combining a plurality of types of epoxy resins exhibiting various viscoelastic behaviors at an arbitrary temperature is also effective for making tack (adhesion) and drape properties of the obtained prepreg appropriate.

  In the present invention, it is also effective to mix a thermoplastic resin compatible with the epoxy resin in the epoxy resin [B]. In particular, mixing a thermoplastic resin compatible with the epoxy resin [B] makes it possible to optimize the tack of the obtained prepreg, control the fluidity of the matrix resin at the time of prepreg heating and curing, and obtain the fiber-reinforced composite material. Effective for improving toughness. As such a thermoplastic resin, a thermoplastic resin composed of a polyarylether skeleton is preferable, and examples thereof include polysulfone, polyphenylsulfone, polyethersulfone, polyetherimide, polyphenylene ether, polyetheretherketone, and polyetherethersulfone. Is a candidate. The thermoplastic resins composed of these polyaryl ether skeletons may be used alone or in combination as appropriate. Among them, polyethersulfone and polyetherimide can be preferably used because they can impart toughness without lowering the heat resistance and mechanical properties of the obtained fiber-reinforced composite material.

  Further, in the thermoplastic resin composed of a polyarylether skeleton, it is effective to appropriately select the type of the terminal functional group in order to control the affinity and the reactivity with the epoxy resin. For example, examples of the selectable terminal functional groups include primary amines, secondary amines, hydroxyl groups, carboxyl groups, thiol groups, acid anhydrides and halogen groups (chlorine and bromine). When a halogen group is used as a terminal functional group, a prepreg excellent in storage stability can be obtained because of low reactivity with an epoxy resin. On the other hand, when it is desired to increase the reactivity with the epoxy resin and shorten the curing time of the epoxy resin composition, a primary amine, a secondary amine, a hydroxyl group, a carboxyl group, a thiol group, an acid It is effective to select a functional group such as an anhydride.

  The curing agent [C] included in the present invention may be any compound having an active group capable of cross-linking with a glycidyl group. For example, a compound having an amino group, an acid anhydride group or an azide group is suitable as the curing agent [C]. Specific examples of the curing agent [C] include dicyandiamide, diaminodiphenylmethane, various isomers of diaminodiphenylsulfone, aminobenzoic acid esters, various acid anhydrides, phenol novolak resins, cresol novolak resins, polyphenol compounds, and imidazole derivatives , Aliphatic amines, tetramethylguanidine, thiourea-added amines, methylhexahydrophthalic anhydride, other carboxylic anhydrides, carboxylic hydrazides, carboxylic amides, polymercaptans, boron trifluoride ethylamine complexes and other Lewis Acid complexes and the like. These curing agents can also be used alone or in combination.

  Above all, by using an aromatic diamine as the curing agent [C], a cured resin having good heat resistance can be obtained. In particular, various isomers of diaminodiphenyl sulfone are most preferable because a cured resin having good heat resistance can be obtained. The amount of the aromatic diamine curing agent to be added is preferably such that the active hydrogen in the aromatic amine compound is in the range of 0.7 to 1.3 per glycidyl group in the epoxy resin composition. And more preferably 0.8 to 1.2. Here, active hydrogen refers to a hydrogen atom bonded to nitrogen, oxygen, and sulfur of an amino group, a hydroxyl group, and a thiol group in an organic compound. When the ratio of the epoxy group to the active hydrogen is within the above-mentioned predetermined range, a cured resin excellent in heat resistance and elastic modulus can be obtained.

Further, in the prepreg of the present invention, a curing aid may be included in the curing agent [C] in order to exhibit high heat resistance and water resistance while curing at a relatively low temperature. Here, the curing aid is one that directly reacts with the glycidyl group of the epoxy resin [B] and does not form a crosslinked structure, but promotes a crosslinking reaction between the epoxy resin [B] and the curing agent [C] as a catalyst. It is. Examples of the curing aid include 3-phenol-1,1-dimethylurea, 3- (3-chlorophenyl) -1,1-dimethylurea, 3- (3,4-dichlorophenyl) -1,1-dimethylurea Urea compounds such as 2,4-toluenebisdimethylurea and 2,6-toluenebisdimethylurea).
If the viscosity of the epoxy resin composition (which may contain a curing aid) composed of these epoxy resin and the curing agent is low and a problem occurs in the handling property of the prepreg, the epoxy resin composition is pre-reacted. It is also effective to increase the viscosity. With the increase in viscosity, it is possible to impart appropriate tackiness to the prepreg, thereby improving the handling property or the storage stability of the prepreg.

  The thermoplastic resin [D] included in the present invention is insoluble in the epoxy resin [B] and is disposed on the surface of the prepreg. In a prepreg laminate obtained by stacking a plurality of prepregs and a cured product thereof, the thermoplastic resin [D] is unevenly distributed between the fiber layers. In general, when an impact load is applied to the fiber reinforced composite material from an out-of-plane direction, delamination progresses, but in a fiber reinforced composite material containing a thermoplastic resin between layers, a highly tough thermoplastic resin is localized between the layers. Therefore, excellent impact resistance can be realized. The thermoplastic resin may be in any form as long as it can be arranged in layers, and may be in any form such as particles, short fiber mats, non-woven fabrics, or films.

  The thermoplastic resin [D] used in the present invention may or may not have crystallinity. Examples of specific thermoplastic resins include polyamide, polycarbonate, polyacetal, polyphenylene oxide, polyphenylene sulfide, polyarylate, polyester, polyamideimide, polyimide, polyetherimide, polyimide having a phenyltrimethylindane structure, polysulfone, and polyethersulfone. , Polyetherketone, polyetheretherketone, polyaramid, polyethernitrile, polybenzimidazole and the like. Among them, polyamide is most preferable because it greatly improves impact resistance due to excellent toughness. Among the polyamides, a semi-IPN (polymer interpenetrating network structure) is formed with a polyamide 12, a polyamide 6, a polyamide 11, a polyamide 6/12 copolymer or an epoxy compound described in Example 1 of JP-A-1-104624. Polyamide fine particles (semi-IPN polyamide) have particularly good adhesive strength to an epoxy resin. Therefore, it is preferable because the delamination strength of the fiber-reinforced composite material at the time of falling weight impact increases and the impact resistance improves.

  When particles are used as the thermoplastic resin [D], the particles may be spherical, non-spherical, porous, whisker-shaped, or flake-shaped. However, it is most preferable to use spherical particles in order to ensure impregnation of the reinforcing fibers of the epoxy resin and to reduce the effect of stress concentration induced by the difference in rigidity between the thermoplastic resin and the matrix resin. . In order to keep these particles between layers when a fiber-reinforced composite material is formed, it is preferable to increase the size of the particles so that they do not enter the gap between the reinforcing fibers adjacent to each other. On the other hand, by reducing the size of the particles, the thickness of the resin layer between layers can be reduced, and the fiber volume content can be increased. As a particle size for satisfying both, the average particle diameter is preferably in the range of 3 μm to 40 μm, and more preferably in the range of 5 μm to 30 μm.

  On the other hand, when a fiber is used as the thermoplastic resin [D], the shape may be a short fiber or a long fiber. In the case of short fibers, as described in JP-A-2-69566, a method of using fibers in the same manner as particles or a method of processing into a mat is possible. In the case of long fibers, a method of arranging long fibers in parallel to the surface of a prepreg as shown in JP-A-4-292634, or a method of randomly arranging fibers as shown in WO 94/016003 Can be used. Further, the fiber may be processed and used as a sheet-type base material such as a woven fabric as disclosed in JP-A-2-32843 or a nonwoven fabric material or a knitted fabric as disclosed in WO 94/016003. it can. Also, a method of spinning short fiber chips, chopped strands, milled fibers and short fibers into yarns and then arranging them in parallel or randomly to form a woven or knitted fabric can be used.

  Here, being insoluble in the epoxy resin means that the thermoplastic resin [D] is not substantially dissolved in the epoxy resin when the epoxy resin in which the thermoplastic resin [D] is dispersed is heated and cured. . More specifically, for example, using a transmission electron microscope, the thermoplastic resin [D] and the matrix resin can be used without substantially reducing the thermoplastic resin [D] from its original size in the cured epoxy resin. Point can be observed with a clear interface.

  The prepreg of the present invention is characterized in that the thermoplastic resin [D] insoluble in the epoxy resin [B] is unevenly distributed on both surfaces of the prepreg.

  The resin mass content in the prepreg of the present invention is preferably in the range of 25 to 45%. Here, the resin mass content means that the resin components excluding the reinforcing fiber [A] (the sum of the epoxy resin [B], the curing agent [C], and the thermoplastic resin [D] and other additives) are included in the prepreg. It refers to the mass ratio occupied. By setting the resin mass content to 25% or more, the matrix resin in the prepreg flows sufficiently, and when the prepreg is cured, the unimpregnated portion of the reinforcing fiber layer can be easily filled with the matrix resin. Voids are less likely to occur in the material. By setting the resin mass content to 45% or less, the advantage of the fiber-reinforced composite material, that is, excellent in specific strength and specific elastic modulus, is easily obtained. In view of these, a more preferable range of the resin mass content is 30 to 36%.

  The prepreg of the present invention is a prepreg in which the reinforcing fibers are partially impregnated with the epoxy resin composition. Here, the prepreg partially impregnated means a state in which the layer of the reinforcing fiber of the prepreg includes a region not impregnated with the resin (unimpregnated portion).

In the present invention, the impregnation ratio φ of the epoxy resin composition in the prepreg is 30 to 95%, preferably 50 to 95%, and more preferably 60 to 90%. If the impregnation rate φ of the epoxy resin composition in the prepreg is high, the frequency of occurrence of cracks in the prepreg starting from the non-impregnated portion can be reduced, for example, when cutting or laminating the prepreg. Specifically, by setting the impregnation rate to 30% or more, preferably 50% or more, more preferably 60% or more, a prepreg excellent in handling properties can be obtained. On the other hand, by lowering the impregnation ratio φ of the epoxy resin composition in the prepreg, continuity of the non-impregnated portion for removing volatile components can be easily secured, and volatile components can be removed efficiently. As a result, the generation of voids in the fiber-reinforced composite material can be suppressed. However, by setting the impregnation rate to 95% or less, preferably 90% or less, a prepreg in which voids are unlikely to be generated can be obtained. Here, the impregnation rate φ of the epoxy resin composition in the prepreg is
(Number of reinforcing fibers present per unit width to which the epoxy resin composition does not adhere) / (Total number of reinforcing fibers present per unit width)
Is calculated as As a method of counting the number of reinforcing fibers, a prepreg is cut with a knife, and the fracture surface is observed with a SEM. At this time, the cutting direction of the prepreg is a plane where the number of reinforcing fibers included in the cut plane is the largest. For example, in the case of a prepreg in which reinforcing fibers are arranged in one direction, the cross section is taken in the direction perpendicular to the fibers. When it is difficult to specify a surface where the number of reinforcing fibers included in the cut surface, such as a short fiber base material, is large, four sections of the prepreg at 45 ° intervals (0 ° direction, 45 ° direction, 90 ° direction, (135-degree direction) Observation is performed, and a cross section in which the number of carbon fibers included in each cross section is the largest is adopted. At this time, the observation magnification of the SEM is set to 500 times, an image whose photographing regions do not overlap each other is acquired for a width of 1 mm, the impregnation rate φ of the prepreg is measured for each image, and the average value is calculated.

  In the prepreg of the present invention, the thermoplastic resin [D] insoluble in the epoxy resin [B] is unevenly distributed on both surfaces of the prepreg, and the non-impregnated portion of the epoxy resin composition in the reinforcing fiber [A] layer. Are localized near both surfaces of the prepreg.

  In order to explain the present invention more specifically, FIGS. 1 (a) and 1 (b) are cross-sectional schematic views of a conventional prepreg for vacuum pressure molding, and FIG. 2 is a cross-sectional schematic view of a prepreg of the present invention. Shown respectively. Hereinafter, description will be made with reference to these drawings.

  In a conventional prepreg for vacuum pressure molding, as shown in FIG. 1A, an interlayer forming layer 3 containing an epoxy resin composition 1 and a thermoplastic resin 2 insoluble in an epoxy resin is formed on both surfaces of the prepreg. In the center of the reinforcing fiber layer 6 in which the reinforcing fibers 5 are arranged in a layered manner, there is an aggregate of reinforcing fibers to which the epoxy resin composition does not adhere, that is, an unimpregnated layer 7. Since the non-impregnated layer 7 functions as a flow path for removing volatile components and trapped air, a fiber-reinforced composite material having few voids can be obtained. However, in the conventional prepreg, when the impregnation ratio φ is increased, the impregnation distance of the resin (from the surface of the reinforcing fiber layer to the Distance to the impregnation tip). Here, when the epoxy resin composition is impregnated from both surfaces of the prepreg, if the portions having large impregnation distances are stochastically overlapped, as shown in FIG. The objects are connected and the continuity of the unimpregnated layer 7 is lost. For this reason, the function as a flow path for removing the volatile component of the non-impregnated layer is lost, which is a factor of generating voids.

  On the other hand, in the prepreg of the present invention, as shown in FIG. 2, there are two aggregates of reinforcing fibers to which the epoxy resin composition does not adhere, that is, two unimpregnated layers 7. In the vicinity of the interlayer forming layer 3. In the prepreg of the present invention, the interlayer forming layer 3 suppresses the impregnation of the epoxy resin composition into the reinforcing fiber layer and makes the tip of the resin impregnated portion smooth. Therefore, the resin surface of the impregnated portion on the side of the interlayer forming layer 3 becomes relatively smooth, and even if the thickness of the central impregnated layer 4 is uneven at every location, the continuity of the unimpregnated layer for removing volatile components is maintained. Can be secured.

  A plurality of methods can be considered as means for suppressing the impregnation of the epoxy resin composition into the reinforcing fiber layer in the vicinity of the upper and lower interlayer forming layers 3. For example, it is effective to set the viscosity of the epoxy resin composition on the interlayer forming layer 3 side higher than the viscosity of the epoxy resin composition of the central impregnation layer 4. Alternatively, the sheet-like reinforcing fibers are almost completely impregnated with the epoxy resin composition, and then sheet-like carbon fibers containing no resin are arranged on the upper and lower sides. It is also effective to arrange the prepreg on both outer sides with high viscosity.

  Here, in order to quantitatively express that the two unimpregnated layers 7 are localized near the interlayer forming layer on both surfaces of the prepreg, a localization parameter σ is defined by the following procedure. Here, a method of calculating the localization parameter σ will be described with reference to the schematic diagrams of the prepreg cross sections of FIGS. 3A and 3B.

  First, as shown in FIG. 3A, a region corresponding to a width of 1 mm of the prepreg cross-sectional image is extracted, and a line perpendicular to the reinforcing fiber sheet and dividing the region into 11 equal parts in the width direction ( Draw 10 equal lines 8). Next, the y-coordinate of the end of the lower reinforcing fiber layer 6 in the figure is calculated on the dividing line, and this is set as the lower end y-coordinate of the reinforcing fiber layer. In the same procedure, the lower end y-coordinate of the figure is calculated for ten equal lines 8, and the average value is set to −T / 2 on the y-coordinate axis. Next, the average value of the y-coordinate at the upper end in FIG. 3 is obtained by the same procedure, and this y-coordinate is set to T / 2. At this time, T corresponds to the thickness of the reinforcing fiber layer 6, and the origin of the y coordinate axis coincides with the center of the reinforcing fiber layer 6. In addition, the y-coordinate h3U of the upper end of the reinforcing fiber and the y-coordinate h3L of the lower end of the reinforcing fiber in the upper non-impregnated layer 7 are acquired from the equidistant line 8, and their average values are H3U and H3L, respectively. And Similarly, in the equidistant line 8, the y coordinate h4U of the upper end of the reinforcing fiber in the lower unimpregnated layer 7 and the y coordinate h4L of the lower end are obtained, and their average values are H4U and H4U, respectively. H4L. However, in the calculation of H3U, H3L, H4U, and H4L, if two unimpregnated layers are not included on the dividing line 8, the dividing line 8 is excluded from the calculation of the average value calculation. That is, when there is one equal line 8 in which two layers of unimpregnated fibers cannot be confirmed, H3U, H3L, H4U, and H4L are calculated from the coordinates of the remaining nine unimpregnated fibers.

At this time, if the center coordinates of the upper unimpregnated layer are H3 and the center coordinates of the lower unimpregnated layer are H4,
H3 = (H3U + H3L) / 2
H4 = (H4U + H4L) / 2
Can be expressed as
Further, here, the localization parameter σ is given by σ = (| H3 | + | H4 |) / 2T
Is defined.

  In this parameter, as shown in FIG. 3 (c), H3 which is the average value of the y-coordinate of the inner end of the reinforcing fiber in the non-impregnated layer on the contour line 8, and the unimpregnated layer on the contour line 8 In the case where H4, which is the average value of the y-coordinate of the outer end portion of the reinforcing fiber in the above, matches, and the epoxy resin composition substantially completely impregnates the reinforcing fiber near the interlayer forming layer 3, H3 = T / 2, H4 = −T / 2, and the localization parameter σ is 0.5. When the center coordinates of the reinforcing fiber layer substantially coincide with the center coordinates of the unimpregnated layer as shown in FIG. 3D, H3 = H4 = 0 and the localization parameter σ becomes zero. Note that, in the present invention, the condition of being within the range of 0.05 <σ <0.50 is defined as “localized near the interlayer forming layer”. In the prepreg of the present invention, the localization parameter σ is in the range of 0.10 <σ <0.45, preferably in the range of 0.20 <σ <0.45. By setting the localization parameter within this range, continuity in the in-plane direction of the unimpregnated portion inside the prepreg laminate is easily ensured, and volatile components can be efficiently removed. As a result, voids generated in the fiber-reinforced composite material can be suppressed.

The prepreg of the present invention preferably has a reinforcing fiber amount per unit area of 30 to 600 g / m ² . When the amount of the reinforcing fibers is 30 g / m ² or more, it is not necessary to increase the number of laminations to obtain a predetermined thickness when molding the fiber reinforced composite material, and the work load is easily reduced. Further, when the amount of the reinforcing fibers is 600 g / m ² or less, the drapability of the prepreg is easily improved. Alternatively, when preparing the prepreg or when heating and curing the prepreg, the epoxy resin composition may be easily impregnated into the voids of the reinforcing fiber layer, and voids may be less likely to be generated. Furthermore, in order to achieve a continuous ventilation path while expressing a high impregnation ratio φ, it is better to have a small basis weight in order to shorten the impregnation distance. More preferably, it is in the range of 300 g / m ² .

In addition, the prepreg of the present invention can more efficiently remove volatile components in the prepreg by ensuring continuity from the vacuum suction section to the unimpregnated section of the prepreg. For that purpose, it is preferable that continuity of the non-impregnated portion in the prepreg is ensured and the prepreg has air permeability. Here, the simplest method for securing the continuity of the non-impregnated portion is to decrease the impregnation degree φ and increase the non-impregnated portion. However, in order to eliminate voids in the fiber-reinforced composite material by eliminating voids by resin flow after removing volatile components, or to suppress out-of-plane cracking of the prepreg during prepreg lamination, It is preferable to keep φ high. In order to realize these, in the prepreg of the present invention, the in-plane permeability coefficient K is 1.1 × (1-φ / 100) × 10 ⁻¹³ [m ² ] or more (φ = impregnation rate (%) ), And more preferably 1.5 × (1-φ / 100) × 10 ⁻¹³ [m ² ] or more.

Here, the measurement for calculating the in-plane permeation coefficient K in the present invention is performed by using a ventilation measurement method schematically shown in FIG. The details of the measurement method are described below. First, in a prepreg laminate 9 in which ten layers of strip-shaped prepregs (fiber orientation direction 100 mm, fiber vertical direction 50 mm) are laminated, a sealant 10 is used in a prepreg thickness direction in a state where only both ends in the fiber orientation direction of the prepreg are opened. , And block the ventilation of the sides. The prepreg laminate 9 and the sealant 10 are sealed with a cover film 11 and a metal plate 12. An air flow path is secured along the glass tape 13 at the end of the prepreg laminate 9. The vent 15 is opened to the atmospheric pressure (the pressure of the pressure gauge 16 on the side of the vent 15 is set to Pa (unit: Pa)), and the opposite side is operated by the vacuum pump 17 in a vacuum pressure environment (the pressure Is Pv (unit: Pa). At this time, a pressure difference occurs on both sides of the prepreg, and the in-plane permeability coefficient K (unit: m ² ) of the prepreg is defined by the following equation (1).

Here, μ is the air viscosity (unit: Pa · s), L is the prepreg length (unit: m), Ap is the prepreg sectional area (unit: m ² ), and Qa is the air flow rate measured by the air flow meter 14. (Unit: m ³ / s).

  In the present invention, the orientation direction means a cross section in the Θ direction when the surface of the prepreg is observed with an optical microscope, the orientation angle of each fiber is θ, and the average value is Θ. In calculating the average value Θ, an arbitrary 30 fibers are selected from the fibers observed by the optical microscope, and the average value of the orientation angles is used. In the prepreg of the present invention, the thermoplastic resin [D] insoluble in the epoxy resin [B] may be unevenly distributed on both surfaces of the prepreg, and the amount of the thermoplastic resin [D] is contained in the same amount on both sides of the prepreg. Or different amounts may be contained. However, when the amount of the thermoplastic resin [D] is different on both sides of the prepreg, the amount of the thermoplastic resin [D] may change between layers when the prepreg is laminated without distinguishing the front and back sides. In this case, the mechanical properties of the obtained fiber-reinforced composite material may vary, or the quality of the laminate may be degraded. Therefore, in the present invention, it is preferable that the content of the thermoplastic resin [D] is the same on both sides of the prepreg. Thereby, even if the prepreg is laminated without distinguishing between the front and back sides, there is an advantage that the same amount of the thermoplastic resin [D] can be secured between any layers of the prepreg laminate. Here, "the content of the thermoplastic resin [D] is the same on both sides of the prepreg" means that the difference in the content of the thermoplastic resin [D] on both sides of the prepreg is the same as the content of the thermoplastic resin [D] contained in the prepreg. ] In the range of 10% by mass or less of the total amount.

  A plurality of methods can be considered as a method for producing the prepreg of the present invention.

The simplest method for producing the prepreg of the present invention is a hot melt method in which an epoxy resin film is overlaid on the surface of a reinforcing fiber arranged in a sheet shape and impregnated with pressure / heat. For example, it can be obtained through the following steps (a) and (b).
(A) The epoxy resin film forming the interlayer forming layer 3 is sandwiched from one side and the epoxy resin film is sandwiched from the other side on the surface of the reinforcing fiber sheet arranged in a sheet shape, and the epoxy resin film is passed through a heating impregnation roll, thereby forming the interlayer forming layer. A primary prepreg in which the non-impregnated layer is localized near one of the interlayer forming layers is prepared.
(B) Two primary prepregs are prepared and laminated so that the interlayer forming layers are arranged outside each other.

As another prepreg manufacturing method, for example, (c) a reinforcing fiber arranged in a sheet shape, which can be obtained through the following steps (c) and (d), is almost completely impregnated with the epoxy resin composition. Thereafter, reinforcing fibers arranged in a sheet shape are arranged on both outer sides thereof.
(D) Further, a film of an epoxy resin composition containing a thermoplastic resin is disposed on both outer sides thereof.

  In order to maintain the continuity of the unimpregnated portion of the prepreg of the present invention and to maintain the tackiness of the prepreg surface, it is effective to stick and store a release sheet on the surface of the prepreg. By adhering the release sheet to the surface of the prepreg, it is possible to suppress the progress of impregnation of the surface resin into the reinforcing fiber sheet, and to maintain the efficiency of removing volatile components and trapped air through the non-impregnated portion. Can be. At this time, sticking the release sheet not only on one surface of the prepreg but also on both surfaces is particularly effective for maintaining the impregnation degree φ of the prepreg and the permeability coefficient K in the in-plane direction. It is effective to maintain the effect of prepreg.

  Examples of the release sheet here include release paper and plastic films such as a polyethylene film, a polypropylene film, and a polytetrafluoroethylene film, but are not limited thereto.

The release sheet desirably has no pores or has only minute pores, and more preferably has a smooth surface. For example, when a release sheet having many holes, such as a nonwoven fabric or a foam sheet having large pores, is attached to the prepreg, the resin in the pore portions of the nonwoven fabric or the foam sheet out of the surface resin of the prepreg may be changed over time. At the same time, the impregnation proceeds into the inside of the prepreg, the nonwoven fabric or the foam sheet. Further, when a release sheet having a rough surface is attached to the prepreg, the surface resin of the prepreg cannot contact the release sheet at the valleys of the release sheet, and the effect of suppressing impregnation is reduced. Therefore, a preferable release sheet has an air permeability coefficient of less than 10 ⁻⁶ cm ² / cmHg, and has a surface roughness whose surface irregularities are smaller than the reinforcing fiber diameter of the prepreg.

  In the production of prepreg, release paper may be used to support the epoxy resin film to be transferred to the reinforcing fiber sheet.However, it is not possible to leave the release paper as it is on the prepreg after transferring the epoxy resin film. It is valid. In particular, by supporting a thin prepreg with a relatively rigid sheet such as release paper, it becomes difficult to bend under its own weight, and handling properties are improved. For example, release paper having a thickness of 100 μm is preferable. On the other hand, when laminating the prepreg, it is necessary to peel off these release sheets, but at this time, cracks starting from the non-impregnated portion tend to occur. In order to suppress such cracking, it is desirable to attach a thin plastic film or the like that can be peeled off with a small force as a release sheet. For example, a polyethylene film having a thickness of 20 μm is preferable. From such a background, it is important to select an effective release sheet according to the thickness of the prepreg and the ratio of the unimpregnated portion. For example, in the case of a prepreg having a large prepreg thickness and being hard to bend under its own weight, it is possible to prevent cracks starting from an unimpregnated portion by attaching both sides with a thin plastic film. On the other hand, when the thickness of the prepreg is thin, a release sheet such as a relatively rigid release paper is attached and supported on one surface, and a release sheet such as a thin plastic film is attached on the opposite surface. Is preferred. In this case, when laminating the prepreg, it is necessary to peel off only the thin plastic film and laminate, and then peel off the release sheet such as release paper, but the thickness of the laminate is increased compared to one prepreg Therefore, the bending stiffness is improved, and cracks starting from the unimpregnated portion are less likely to occur even when the release paper is peeled off.

  The fiber-reinforced composite material of the present invention is obtained by laminating and curing the above-described prepreg of the present invention. That is, the fiber-reinforced composite material of the present invention can be produced by heating and curing the prepreg of the present invention or a laminate thereof. The prepreg of the present invention is suitable for vacuum pressure molding, but can also be used as a prepreg in which voids are unlikely to occur in autoclave molding and press molding.

  When the prepreg of the present invention is cured by heating in an oven, for example, a fiber-reinforced composite material having few voids can be obtained by using the following molding method. A prepreg laminate obtained by laminating a single-layer prepreg or a plurality of prepregs is wrapped in a bag having an internal pressure of 11 kPa or less, and is kept at a temperature of 20 to 70 ° C. to remove volatile components, and the pressure is reduced to 11 kPa or less. While maintaining the temperature, the temperature is raised to the curing temperature. Here, the removal of volatile components is preferably performed under a condition of a pressure of 0.1 kPa to 11 kPa, and more preferably under a condition of a pressure of 0.1 kPa to 7 kPa. The higher the degree of vacuum, that is, the lower the internal pressure, the shorter the volatile component can be removed. By setting the internal pressure to 11 kPa or less, it becomes easy to sufficiently remove volatile components in the prepreg, and it is difficult to generate voids in the obtained fiber-reinforced composite material.

  Further, at the time of molding, it is necessary to fill the resin into the non-impregnated portion. For that purpose, it is effective to reduce the viscosity of the resin. For example, the resin is kept at a temperature (40 ° C. to 130 ° C.) lower than the curing start temperature of the resin for a long time while being in a heated state, and is filled with the resin in the unimpregnated portion. (200 ° C.), and the resin is preferably cured.

  Hereinafter, the present invention will be described in detail with reference to examples. However, the scope of the present invention is not limited to these examples. The unit “parts” of the composition ratio means parts by mass unless otherwise specified. The measurement of various characteristics was performed in an environment at a temperature of 23 ° C. and a relative humidity of 50%, unless otherwise specified.

<Materials used in Examples and Comparative Examples of the present invention>
(1) Component [A]: Reinforcing fiber [Carbon fiber]
-Carbon fiber (product name: "Treca (registered trademark)" T800S-24K-10E, number of filaments 24,000, tensile strength 5.9 GPa, tensile modulus 290 GPa, tensile elongation 2.0%, manufactured by Toray Industries, Inc.) .

(2) Component [B]: Epoxy resin [Epoxy resin]
-Bisphenol A type epoxy resin (product name: "jER (registered trademark)" 825, manufactured by Mitsubishi Chemical Corporation)
-Tetraglycidyldiaminodiphenylmethane (product name: "Araldite (registered trademark)" MY721, manufactured by Huntsman Advanced Materials)
-Bisphenol F type epoxy (product name: "Epiclon (registered trademark)" 830, manufactured by DIC Corporation).

(3) Component [C]: Curing agent [Aromatic amine curing agent]
-4,4'-diaminodiphenyl sulfone (product name: "Seika Cure S", manufactured by Wakayama Seika Kogyo Co., Ltd.).

(4) Constituent element [D]: thermoplastic resin insoluble in epoxy resin [B] [thermoplastic resin]
-Polyamide fine particles obtained by the following production method (average particle diameter: 13 µm)
90 parts of a transparent polyamide ("Grillamide (registered trademark)" TR55, manufactured by Ms. Chemie Japan KK), 7.5 parts of an epoxy resin ("jER (registered trademark)" 828, manufactured by Mitsubishi Chemical Corporation) and a curing agent 2.5 parts of "Tomide (registered trademark) # 296, manufactured by T & K Toka Co., Ltd." were added to a mixed solvent of 300 parts of chloroform and 100 parts of methanol to obtain a homogeneous solution. Next, using a spray gun for coating, the obtained uniform solution was sprayed in the form of a mist toward the liquid surface of the stirring 3000 parts of n-hexane to precipitate a solute. The precipitated solid was separated by filtration, washed well with n-hexane, and vacuum-dried at 100 ° C. for 24 hours to obtain spherical epoxy-modified polyamide particles having a semi-IPN structure.

(5) Other components: thermoplastic resin / polyether sulfone soluble in epoxy resin [B] (product name: "Sumika Excel (registered trademark)" PES5003P, manufactured by Sumitomo Chemical Co., Ltd.).

<Evaluation method>
The epoxy resin composition and prepreg of each example were measured using the following measurement methods.

(1) Measurement of impregnation rate φ of epoxy resin composition of prepreg The prepreg was cut with a knife, and the fracture surface was observed by SEM (“VHX (registered trademark)” D510, manufactured by KEYENCE CORPORATION). The ratio φ = (the number of carbon fibers to which the epoxy resin composition does not adhere) / (the total number of carbon fibers existing per unit width).

(2) Measurement of localization parameter σ The prepreg is cut with a knife, and the fracture surface is observed with a SEM (“VHX (registered trademark)” D510, manufactured by Keyence Corporation) to obtain the coordinates of the center point of each carbon fiber. Then, the localization parameter σ was calculated according to the above method.

(3) Permeability coefficient K in the in-plane direction
Eight layers of strip-shaped prepregs having a fiber orientation direction of 100 mm and a fiber vertical direction of 50 mm were laminated according to the above-mentioned method, and the amount of air flowing in the fiber direction of the prepreg laminate and the pressures Pa and Pv at both ends of the prepreg were measured. In addition, the in-plane permeation coefficient K was evaluated according to Equation 1.

(4) Handling property of prepreg When the prepreg is cut with a knife in an environment of 23 ° C, fluff generated at the end thereof, peeling of the prepreg in an out-of-plane direction at the time of lamination, and correction by lamination at the time of lamination. Ease was confirmed, and the superiority was judged based on the following criteria.
A: Good B: Lamination is possible, but some fluff is generated from the end C: Lamination is possible, but fuzz is generated from the end, and it is necessary to devise correction of bonding D: Poor.

(5) Measurement of void ratio of fiber reinforced composite material Eight prepregs having a length of 300 mm and a width of 150 mm are laminated in one direction to form a prepreg laminate, and a PTFE film having a thickness of 100 μm is arranged on both surfaces of the prepreg laminate. And placed on a 10 mm thick aluminum plate and covered with a nylon film. Further, in a 25 ° C. environment, the degree of vacuum around the prepreg laminate was set to 3 kPa, and the mixture was left for 3 hours to remove volatile components. Thereafter, while maintaining the degree of vacuum at 3 kPa, the temperature is raised to a temperature of 120 ° C. at a rate of 1.5 ° C./min and maintained for 180 minutes. After holding for 120 minutes to cure the resin, a fiber-reinforced composite material was obtained. Three sample pieces of 10 mm length x 10 mm width were cut out from this fiber reinforced composite material, and after polishing the cross section, observed with an optical microscope using a 50x lens so that the upper and lower surfaces of the fiber reinforced composite material were within the field of view. And then I got the image. The void ratio of each image was calculated by calculating the ratio of the void area to the total cross-sectional area from the acquired image. The same operation was performed at three places for each sample, that is, nine places in total, and the average value was defined as the void ratio of each evaluation level.

<Example 1>
60 parts by mass of "Araldite (registered trademark)" MY721 and 40 parts by mass of "jER (registered trademark)" 825 are added to a kneader, and further 12 parts by mass of "Sumika Excel (registered trademark)" PES5003P are added and heated. Then, 46 parts by mass of Seika Cure S as a curing agent was kneaded to prepare an epoxy resin composition (for the first film) containing no thermoplastic resin insoluble in the epoxy resin. Similarly, 60 parts by mass of "Araldite (registered trademark)" MY721 and 40 parts by mass of "jER (registered trademark)" 825 are added to a kneader, and further 12 parts by mass of "Sumika Excel (registered trademark)" PES5003P are added. In addition, the mixture is heated and melted, and 45 parts by mass of polyamide fine particles, which are thermoplastic resin particles, are kneaded. Then, 46 parts by mass of "Seika Cure S" is kneaded as a curing agent, and an epoxy resin composition containing a thermoplastic resin insoluble in an epoxy resin. A product (for the second film) was produced.

Each of the two prepared epoxy resin compositions was applied to release paper with a knife coater so as to be 52 g / m ² to obtain a resin film containing no thermoplastic resin particles and a resin film containing thermoplastic resin particles. . Here, a resin film containing no thermoplastic resin particles is referred to as a first film, and a resin film containing a thermoplastic resin is referred to as a second film. Next, carbon fibers are arranged in one direction at 190 g / m ² to form a carbon fiber sheet. Then, a first film is stuck on one side and impregnated with resin while pressing a roller having a surface temperature of 100 ° C. Was. Subsequently, the back surface of the carbon fiber sheet was impregnated with a second film containing polyamide fine particles while pressing a roller having a surface temperature of 100 ° C. Thus, a primary prepreg having a resin mass fraction of 35% was produced.
Furthermore, two primary prepregs were prepared and laminated so that the resin films containing the thermoplastic resin particles were on the outside of each other, and a prepreg with a carbon fiber weight of 380 g / m ² having thermoplastic particles disposed on both surfaces was prepared. did.

<Examples 2 and 3: Influence of impregnation degree on air permeability, handleability, and void ratio>
A prepreg was prepared in the same manner as in Example 1 except that the roller surface temperature when transferring the first film was 120 ° C. in Example 2 and 140 ° C. in Example 3 to obtain a fiber-reinforced composite material. .

<Comparative Example 1: When the position of the unimpregnated portion is near the center>
60 parts by mass of "Araldite (registered trademark)" MY721 and 40 parts by mass of "jER (registered trademark)" 825 are added to a kneader, and further 12 parts by mass of "Sumika Excel (registered trademark)" PES5003P are added and heated. Dissolve and knead 23 parts by mass of polyamide fine particles which are thermoplastic resin particles, and then knead 46 parts by mass of "Seika Cure S" as a curing agent to prepare an epoxy resin composition containing a thermoplastic resin insoluble in epoxy resin. did.

Next, each of the prepared epoxy resin compositions was applied to release paper at 104 g / m ^{2 by a} knife coater to obtain a resin film containing thermoplastic resin particles. Next, after arranging carbon fibers in one direction so as to be 380 g / m ^2, and forming a carbon fiber sheet, the resin film is attached to both surfaces and impregnated with the resin while pressing a roller having a surface temperature of 140 ° C. Was. Thus, a prepreg having a resin mass fraction of 35% was produced.

  Comparative Example 1 has the same degree of impregnation as that of Example 2, but the unimpregnated portion is not localized on the prepreg surface, the localization parameter is small, the in-plane direction has a small permeability coefficient, and the number of voids is large. Was.

<Comparative Examples 2, 3: Impregnation degree, handleability, and void>
The content of "SUMIKAEXCEL (registered trademark)" PES5003P of the epoxy resin composition for the first film and the epoxy resin composition for the second film was 12 parts by mass and 18 parts by mass in Comparative Example 2, respectively, and in Comparative Example 3, respectively. The roller surface temperature when transferring the first film was 70 ° C. in Comparative Example 2, 130 ° C. in Comparative Example 3, and the roller surface temperature when transferring the second film was Comparative Example 2. Then, a prepreg was prepared in the same manner as in Example 1 except that the temperature was set to 70 ° C. and the temperature was set to 120 ° C. in Comparative Example 3 to obtain a fiber-reinforced composite material.

  As compared with Examples 1 to 3, Comparative Example 2 having a low impregnation degree φ had difficulty in handling the prepreg, and Comparative Example 3 having a high impregnation degree generated many voids.

1: epoxy resin composition 2: thermoplastic resin insoluble in epoxy resin 3: interlayer forming layer 4: central impregnated layer 5: reinforcing fiber 6: reinforcing fiber layer 7: unimpregnated layer 8: equidistant line 9: prepreg lamination Body 10: Sealant 11: Cover film 12: Metal plate 13: Glass tape 14: Air flow meter 15: Vent 16: Pressure gauge 17: Vacuum pump

Claims (8)

  A prepreg in which an epoxy resin composition containing an epoxy resin [B] and a curing agent [C] is partially impregnated in a reinforcing fiber [A] arranged in a layered manner, and the impregnation rate φ is 30 to 95. %, The thermoplastic resin [D] insoluble in the epoxy resin [B] is unevenly distributed on both surfaces of the prepreg, and the unimpregnated portion of the epoxy resin composition in the layer of the reinforcing fiber [A] A prepreg that is localized near both surfaces of the prepreg and has a localization parameter σ defining the degree of localization in the range of 0.10 <σ <0.45. ^2. The prepreg according to claim 1, wherein the in-plane direction has a permeability coefficient K of 1.1 × (1−φ / 100) × 10 ⁻¹³ [m ² ] or more.   The prepreg according to claim 1 or 2, wherein the reinforcing fibers [A] are continuous fibers arranged in one direction.   The prepreg according to claim 1 or 2, wherein the reinforcing fiber [A] is in a woven form.   The prepreg according to any one of claims 1 to 4, wherein the content of the thermoplastic resin [D] is the same on both sides of the prepreg.   A prepreg with a release sheet comprising a release sheet attached to both surfaces of the prepreg according to any one of claims 1 to 5.   The prepreg with a release sheet according to claim 6, wherein, of the release sheets on both surfaces of the prepreg, one side is release paper and the other side is a plastic film.   A fiber-reinforced composite material obtained by curing the prepreg according to claim 1.

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