JP2023147223A - Prepreg with release sheet, and fiber-reinforced composite material - Google Patents

Abstract

To provide a reinforcement fiber prepreg which is excellent in peelability of a release sheet while keeping high tackiness, even if it has a low percentage content of a matrix resin, and a fiber-reinforced composite material.SOLUTION: A prepreg with a release sheet has a release sheet arranged on at least one surface of a prepreg in which a reinforcement fiber is impregnated with a matrix resin, and satisfies the following conditions (I), (II) and (III). (I) A matrix resin coverage rate x1 on the outermost surface facing the release sheet in the prepreg and peeling strength y1 when the release sheet is peeled from the prepreg satisfy a specific relation expression. (II) As for the prepreg from which the release sheet is peeled, a water absorption rate x2 and drape property y2 calculated from a water absorption test satisfy a specific relation expression. (III) x1 is 40% or more and less than 100%, and x2 is 0.0% or more and 20.0% or less.SELECTED DRAWING: Figure 2

Description

The present invention relates to a fiber-reinforced composite material obtained from prepreg with a release sheet and reinforcing fiber prepreg, which is suitably used to obtain a lightweight and high-performance fiber-reinforced composite material, and which has excellent handling properties.

Fiber-reinforced composite materials made of reinforcing fibers such as glass fibers, carbon fibers, and aramid fibers and matrix resins are lightweight but have excellent mechanical properties such as strength, rigidity, impact resistance, and fatigue resistance. Fiber-reinforced composite materials using thermosetting resins such as unsaturated polyester resins, vinyl ester resins, epoxy resins, phenol resins, cyanate resins, and bismaleimide resins have excellent heat resistance and corrosion resistance, so they are used in aircraft. It has been applied in many fields such as spacecraft, automobiles, railway vehicles, ships, civil engineering and construction, sporting goods, and general industrial goods.

In the production of such fiber-reinforced composite materials, a widely used method is to create reinforced fiber prepreg, which is an intermediate consisting of reinforcing fibers and matrix resin, to laminate a predetermined number of the resulting reinforced fiber prepregs, and then heat-cure them. I've been exposed to it.

Examples of reinforced fiber prepreg include unidirectional prepreg, which is a sheet-like material made of reinforcing fibers aligned in one direction and impregnated with matrix resin, and woven prepreg, which is a fabric made of reinforcing fibers impregnated with matrix resin. For demanding applications, unidirectional prepregs have been preferably used.

Many reinforced fiber prepregs have a release sheet placed on at least one side of the reinforced fiber prepreg during the manufacturing process, and when manufacturing fiber reinforced composite materials as described above, reinforcing fiber prepregs are It is necessary to peel off the release sheet from the fiber prepreg. In recent years, there has been an increasing demand for lightweight fiber-reinforced composite materials, and there has been an increasing demand for reinforced fiber prepregs in which the proportion of matrix resin in the prepregs is small. When peeling off a release sheet from such a reinforcing fiber prepreg, if the stiffness of the reinforcing fiber prepreg is low, problems occur such as the ends of the prepreg being torn and the release sheet being difficult to peel off.

On the other hand, as a means to increase the rigidity of reinforced fiber prepreg, there is a method of increasing the degree of impregnation of matrix resin into reinforcing fibers during the production of reinforced fiber prepreg, but if the degree of impregnation of matrix resin is increased too much, The amount of matrix resin present on the surface of the prepreg becomes extremely small, and the tackiness of the reinforcing fiber prepreg becomes insufficient.

Patent Document 1 discloses a sheet-like prepreg with good quality, which has a low amount of resin, has the necessary tackiness on both sides of the prepreg when wrapped around a mandrel, and has controlled peeling resistance of the release paper on the surface. Disclosed.

Furthermore, Patent Document 2 discloses that a thermosetting resin is appropriately impregnated using a heated metal roll to obtain an appropriate surface resin coverage, without using methods such as modifying the resin or adhering powder to the surface. As a scope, an invention is disclosed for obtaining a prepreg that is easy to handle when wound around a mandrel.

Japanese Patent Application Publication No. 2011-132389 Japanese Patent Application Publication No. 2003-138041

The prepreg according to Patent Document 1 controls the tack value of both surfaces and the peeling resistance between the prepreg and the release sheet, but does not take into account the rigidity of the prepreg, and when peeling the release sheet from the prepreg, the prepreg It could not be said that the ability to trim the edges was sufficient.

The prepreg according to Patent Document 2 improves tackiness by controlling the matrix resin coverage on the surface of the prepreg, but does not take into account the releasability from the release sheet, and when peeling the release sheet from the prepreg. However, it was not enough to prevent it from becoming difficult to peel.

Therefore, the object of the present invention is to provide a reinforced fiber prepreg that maintains high tackiness and has excellent releasability of a release sheet even if the reinforced fiber prepreg has a low matrix resin content, and to provide a fiber reinforced prepreg using the same. Our goal is to provide composite materials.

The prepreg with release sheet of the present invention is represented by configurations 1 to 9 below.
1. A release sheet is disposed on at least one side of a prepreg in which reinforcing fibers are impregnated with a matrix resin, and the following conditions (I), (II), and (III) are satisfied.
(I) When the matrix resin coverage on the outermost surface of the release sheet surface of the prepreg with a release sheet is x ₁ and the peel strength when peeling the release sheet from the prepreg with a release sheet is y ₁ , the following Formula (1) is satisfied.

(II) When the water absorption rate calculated by the water absorption test of the prepreg with the release sheet removed from the prepreg with the release sheet is x ₂ and the drapeability of the prepreg is y ₂ , the following formula (2) is satisfied. .

(III) x ₁ is 40% or more and less than 100%, and x ₂ is 0.0% or more and 20.0% or less.

Here, RAW is the matrix resin mass per unit area of the prepreg [g/m ² ], FAW is the reinforcing fiber mass per unit area of the prepreg [g/m ² ],
G'' is the loss modulus [MPa] in the dynamic viscoelasticity measurement of the matrix resin, and G' is the storage modulus [KPa] in the measurement.
2. The FAW is 100 g/m ² or more and 300 g/m ² or less,
The prepreg with a release sheet according to 1 above, wherein the mass content of reinforcing fibers in the prepreg obtained by peeling off the release sheet from the prepreg with a release sheet is 70% by mass or more and 90% by mass or less.
3. 3. The prepreg with a release sheet according to 1 or 2 above, wherein the reinforcing fibers are carbon fibers.
4. 4. The prepreg with a release sheet according to any one of 1 to 3 above, wherein the matrix resin has a complex viscosity of 10,000 Pa·s or more and less than 100,000 Pa·s at a temperature of 25°C.
5. 5. The prepreg with a release sheet according to any one of 1 to 4 above, wherein the matrix resin is a composition containing a thermosetting resin as a main component.
6. 5. The prepreg with a release sheet as described in 5 above, wherein the matrix resin is an epoxy resin.
7. After applying the adhesive tape (adhesive strength with SUS304: 6.9 to 7.3 N/cm) to the release sheet, the peel strength when peeling off is 0.5 N/cm or more and 7.5 N/cm or less, The prepreg with a release sheet according to any one of 1 to 6 above.
8. 8. The release sheet prepreg according to any one of 1 to 7 above, wherein the tack coefficient on the surface of the prepreg from which the release sheet is peeled is 0.4 kgf or more and 1.5 kgf or less.
9. 9. The prepreg with a release sheet according to any one of 1 to 8 above, which has a peel strength of 0.01 N/25 mm or more and 0.40 N/25 mm or less when the release sheet is peeled off from the prepreg.

Moreover, the fiber reinforced composite material in the present invention is obtained by curing the prepreg from which the release sheet has been peeled off from the prepreg with the release sheet.

The prepreg with a release sheet of the present invention maintains high tackiness and has excellent peelability of the release sheet, so when it is used in the production of fiber-reinforced composite materials, when the release sheet is peeled off from the reinforced fiber prepreg, There are no problems such as the ends of the prepreg being cut or the release sheet being difficult to peel off, and it is easy to handle. Therefore, fiber-reinforced composite materials can be efficiently produced.

FIG. 2 is a schematic diagram of a support used for peel strength measurement according to the present invention. FIG. 3 is a schematic diagram showing a state in which peel strength is measured in the present invention. It is a schematic diagram showing the state where drapability is being measured in the present invention.

The present invention will be explained in more detail below.

The prepreg with a release sheet of the present invention has a release sheet disposed on at least one side of a prepreg in which reinforcing fibers are impregnated with a matrix resin.

As such reinforcing fibers, carbon fibers, glass fibers, aramid fibers, metal fibers, etc., or combinations thereof are used, but in order to obtain lightweight and high-performance composite materials, it is necessary to use materials with excellent specific strength and specific modulus. Carbon fiber is particularly preferably used. Such carbon fibers are not particularly limited, and known carbon fibers such as acrylic, pitch, and rayon fibers can be used, and multiple types of these fibers may be used in combination, but in particular Acrylic carbon fibers are preferably used because a composite material with excellent tensile strength can be obtained.

Such reinforcing fibers preferably have a tensile modulus of elasticity of 200 to 900 GPa, more preferably 200 to 400 GPa, as determined by JIS R 7608 (2007). By setting the tensile modulus to 200 GPa or more, it becomes easier to improve the mechanical properties such as the bending modulus of fishing rods. Further, by setting the pressure to 900 GPa or less, crushing deformation can be easily suppressed, especially when prepregs are laminated in the circumferential direction of a fishing rod with a large diameter and thin wall.

The mass of the reinforcing fibers per unit area of the prepreg with release sheet of the present invention is preferably 100 g/m ² or more, preferably 150 g/m ² or less, and more preferably 300 g/m 2 or less. ^m2 or less. By setting the mass to 100 g/m ² or more, the thickness and rigidity of the prepreg can be ensured, and deformation of the prepreg can be suppressed when peeling from the release sheet, during prepreg production, storage, and transportation. In addition, by reducing the mass to 300 g/ ^m2 or less, the impregnation properties of the resulting fiber-reinforced composite material are improved, and tearing between the fiber layers when peeled off from the release sheet can be suppressed, resulting in increased strength and light weight. A fiber-reinforced composite material with excellent properties can be obtained.

The matrix resin used in the prepreg with release sheet of the present invention is not particularly limited, but it is preferable that the main component is a thermosetting resin. Examples of such thermosetting resins include epoxy resins, unsaturated polyester resins, vinyl ester resins, benzoxazine resins, phenol resins, urea resins, melamine resins, and thermosetting polyimide resins, and modified products and A mixture of multiple types can also be used. Further, these thermosetting resins may be ones that self-cure by heating, or may be ones that are cured by adding a curing agent, a curing accelerator, or the like.

Epoxy resins are not particularly limited, and include bisphenol-type epoxy resins, amine-type epoxy resins, phenol novolac-type epoxy resins, cresol novolac-type epoxy resins, resorcinol-type epoxy resins, phenol aralkyl-type epoxy resins, and naphthol-type epoxy resins. , a dicyclopentadiene type epoxy resin, an epoxy resin having a biphenyl skeleton, an isocyanate-modified epoxy resin, a tetraphenylethane type epoxy resin, a triphenylmethane type epoxy resin, and the like.

Here, bisphenol type epoxy resin is a bisphenol compound in which two phenolic hydroxyl groups are glycidylated, and bisphenol A type, bisphenol F type, bisphenol AD type, bisphenol S type, or halogen or alkyl of these bisphenols. Examples include substituted products and hydrogenated products. Moreover, not only monomers but also polymers having a plurality of repeating units can be suitably used.

Commercially available bisphenol A epoxy resins include "jER (registered trademark)" 825, 828, 834, 1001, 1002, 1003, 1003F, 1004, 1004AF, 1005F, 1006FS, 1007, 1009, 1010 (all of which are manufactured by Mitsubishi Chemical). Co., Ltd.). Examples of the brominated bisphenol A epoxy resin include "jER (registered trademark)" 505, 5050, 5051, 5054, and 5057 (all manufactured by Mitsubishi Chemical Corporation). Commercially available hydrogenated bisphenol A epoxy resins include ST5080, ST4000D, ST4100D, and ST5100 (all manufactured by Nippon Steel Chemical & Materials Co., Ltd.).

Commercially available bisphenol F-type epoxy resins include "Epiclon (registered trademark)" 830 (manufactured by DIC Corporation), "jER (registered trademark)" 806, 807, 4002P, 4004P, 4007P, 4009P, 4010P (the above, (manufactured by Mitsubishi Chemical Corporation), "Epotote (registered trademark)" YDF2001, YDF2004 (manufactured by Nippon Steel Chemical & Materials Corporation), and the like. Examples of the tetramethylbisphenol F-type epoxy resin include YSLV-80XY (manufactured by Nippon Steel Chemical & Materials Co., Ltd.).

Examples of the bisphenol S-type epoxy resin include "Epiclon (registered trademark)" EXA-1514 (manufactured by DIC Corporation).

Among these, bisphenol A epoxy resin, bisphenol F epoxy resin, and bisphenol S epoxy resin are preferred because they have a good balance of elastic modulus, toughness, and heat resistance.

Examples of the amine type epoxy resin include tetraglycidyldiaminodiphenylmethane, triglycidylaminophenol, triglycidylaminocresol, tetraglycidylxylylene diamine, and halogen- and alkynol-substituted products and hydrogenated products thereof.

Commercial products of tetraglycidyldiaminodiphenylmethane include "Sumi Epoxy (registered trademark)" ELM434 (manufactured by Sumitomo Chemical Co., Ltd.), YH434L (manufactured by Nippon Steel Chemical & Materials Co., Ltd.), and "jER (registered trademark)" 604 (Mitsubishi Chemical Co., Ltd.). Chemical Co., Ltd.), "Araldide (registered trademark)" MY720, MY721 (manufactured by Huntsman Japan Co., Ltd.), and the like. Commercial products of triglycidylaminophenol or triglycidylaminocresol include "Sumiepoxy (registered trademark)" ELM100 (manufactured by Sumitomo Chemical Co., Ltd.), "Araldide (registered trademark)" MY0500, MY0510, MY0600 (manufactured by Huntsman)・JER (registered trademark) 630 (manufactured by Mitsubishi Chemical Corporation), etc. Commercially available products of tetraglycidylxylylene diamine and hydrogenated products thereof include TETRAD-X and TETRAD-C (manufactured by Mitsubishi Gas Chemical Co., Ltd.).

Commercial products of phenol novolac type epoxy resin include "jER (registered trademark)" 152, 154 (manufactured by Mitsubishi Chemical Corporation), "Epicron (registered trademark)" N-740, N-770, N-775 (all manufactured by Mitsubishi Chemical Corporation). The above examples include those manufactured by DIC Corporation.

Among these thermosetting resins, those containing epoxy resins are preferred because they have an excellent balance of heat resistance, mechanical properties, and adhesion to carbon fibers, and those containing epoxy resins and curing agents and/or curing accelerators are preferable. A matrix resin composed of the following is preferably used.

Such curing agents include, but are not limited to, amine compounds such as aliphatic amines, aromatic amines, and alicyclic amines, phenolic resins, dicyandiamide or its derivatives, acid anhydrides, polyaminoamides, and organic acid hydrazides. , isocyanate may also be used.

Examples of aromatic amines include xylene diamine, diaminodiphenylmethane, phenylenediamine, diaminodiphenylsulfone, and the like.

Among these, it is preferable to use at least one selected from aromatic amines and phenolic resins because of their excellent heat resistance, and more preferably diaminodiphenyl because of its excellent balance of heat resistance, storage stability, and mechanical properties. The solution is to use sulfone.

Further, the total amount of the curing agent preferably includes an amount of active hydrogen groups in the range of 0.6 to 2.0 equivalents, more preferably 0.7 to 1 equivalent of epoxy groups in all epoxy resin components. to 1.5 equivalents. Here, the active hydrogen group means a functional group that can react with the epoxy group of the curing agent component, and by setting the active hydrogen group to 0.6 equivalent or more, the reaction rate, heat resistance, elastic modulus, plasticity It is easy to obtain a cured resin product with excellent deformability, and it is also easy to obtain a fiber-reinforced composite material with excellent glass transition temperature, strength, and impact resistance. In addition, by controlling the active hydrogen group to 2.0 equivalents or less, a cured resin product with excellent reaction rate, heat resistance, and elastic modulus can be easily obtained, and a fiber-reinforced composite material with excellent glass transition temperature and strength can be obtained. It's easy to get caught.

Examples of the above-mentioned curing accelerator include urea compounds, tertiary amines and their salts, imidazole and its salts, triphenylphosphine or its derivatives, carboxylic acid metal salts, Lewis acids, Bronsted acids and their salts, etc. . Among these, urea compounds are preferably used because of their balance between storage stability and catalytic ability.

Examples of urea compounds include N,N-dimethyl-N'-(3,4-dichlorophenyl)urea, toluenebis(dimethylurea), 4,4'-methylenebis(phenyldimethylurea), 3-phenyl-1, 1-dimethylurea and the like can be used. Commercially available products of such urea compounds include DCMU99 (manufactured by Hodogaya Chemical Co., Ltd.), "Omicure (registered trademark)" 24, 52, 94 (all manufactured by Emerald Performance Materials, LLC), and the like.

The blending amount of the urea compound is preferably 1 to 6 parts by weight based on 100 parts by weight of the total epoxy resin component. By setting the amount of the urea compound to 1 part by mass or more, the reaction can proceed sufficiently and a cured resin product with excellent elastic modulus and heat resistance can be easily obtained. Furthermore, by controlling the amount of the urea compound to be 6 parts by mass or less, the reaction between the epoxy resin and the curing agent can proceed more easily, making it easier to obtain a cured resin product with excellent toughness and elastic modulus.

When a thermosetting resin is used as the matrix resin, a thermoplastic resin may be blended in order to adjust toughness and fluidity within a range that does not impair the effects of the present invention. When using an epoxy resin as the thermosetting resin, the thermoplastic resin includes a thermoplastic resin that is soluble in the epoxy resin, and organic particles such as rubber particles and thermoplastic resin particles that are partially soluble or insoluble in the epoxy resin. can be blended.

As the thermoplastic resin soluble in the epoxy resin, a thermoplastic resin having a hydrogen-bonding functional group that can be expected to improve the adhesion between the matrix resin and the carbon fibers is preferably used. Examples of hydrogen-bonding functional groups include alcoholic hydroxyl groups, amide bonds, sulfonyl groups, and carboxyl groups.

Examples of thermoplastic resins having alcoholic hydroxyl groups include polyvinyl acetal resins such as polyvinyl formal and polyvinyl butyral, polyvinyl alcohol, and phenoxy resins.

Examples of the thermoplastic resin having an amide bond include polyamide, polyimide, polyamideimide, and polyvinylpyrrolidone.

Examples of the thermoplastic resin having a sulfonyl group include polysulfone and polyethersulfone.

Examples of the thermoplastic resin having a carboxyl group include polyester, polyamide, polyamideimide, and the like. The carboxyl group may be present in either the main chain or the terminal, or both.

Among the above, polyamide, polyimide, and polysulfone may have a functional group such as an ether bond or a carbonyl group in the main chain. Moreover, the polyamide may have a substituent on the nitrogen atom of the amide group.

Commercially available thermoplastic resins that are soluble in epoxy resins and have hydrogen-bonding functional groups include "Mowital (registered trademark)" (manufactured by Kuraray Co., Ltd.) and "Vinylec (registered trademark)" (manufactured by Kuraray Co., Ltd.) as polyvinyl acetal resins. (manufactured by JNC Co., Ltd.).

Further, as a thermoplastic resin that is soluble in epoxy resin and has a hydrogen-bonding functional group, acrylic resin has high compatibility with epoxy resin and is suitably used for fluidity adjustment such as thickening.

As the rubber particles that are partially soluble or insoluble in the epoxy resin, crosslinked rubber particles and core-shell rubber particles in which a different polymer is graft-polymerized on the surface of the crosslinked rubber particles are preferably used from the viewpoint of ease of handling.

As the thermoplastic resin particles that are partially soluble or insoluble in the epoxy resin, polyamide particles and polyimide particles are preferably used.

In the present invention, inorganic particles such as silica, carbon, alumina, smectite, and synthetic mica may be blended with the matrix resin to adjust fluidity within a range that does not impair the effects of the present invention.

In the prepreg with a release sheet of the present invention, the matrix resin preferably has a complex viscosity at 25° C. of 10,000 Pa·s or more and 100,000 Pa·s or less. By setting the viscosity to 10,000 Pa・s or more, the adhesion between the prepreg and the release sheet will be sufficient, so the adhesion will be sufficient, and the rigidity of the prepreg will be sufficient, so the reinforced fiber prepreg The shape retention property of the film becomes sufficient, and deformation when peeled from the release sheet can be suppressed, so that the peelability becomes sufficient. On the other hand, from the viewpoint of ensuring tackiness, it is preferably 100,000 Pa·s or less. More preferably, the lower limit is 20,000 Pa·s or more, the upper limit is 90,000 Pa·s or less, and even more preferably the upper limit is 80,000 Pa·s or less, and within this range, the reinforcing fiber Since shape retention and tackiness of the prepregs can be achieved at the same time, workability when bonding the prepregs together and peeling off the release sheet is improved.

Here, the complex viscosity of the matrix resin is measured using a dynamic viscoelasticity measuring device (for example, ARES-G2: manufactured by TA Instruments) using a parallel plate, maintaining the temperature at 25°C, and measuring 0 strain. It refers to the complex viscosity η* measured at a frequency of 0.1%, a frequency of 0.5 Hz, and a plate spacing of 1 mm.

In the prepreg with a release sheet of the present invention, a release sheet is arranged on at least one side of the prepreg in order to maintain the shape of the prepreg, store it, or transport it. When the release sheet is placed only on one side of the prepreg, work efficiency is good because the prepregs can be bonded together without peeling off the release sheet, but the adhesiveness of the surface of the prepreg without the release sheet tends to change over time. Tend. On the other hand, when release sheets are placed on both sides of the prepreg, the adhesiveness of the prepreg surface is less likely to change over time because the release sheets are in close contact with both sides. must be peeled off, which increases the amount of work. Therefore, it is preferable to select the necessary form depending on the purpose of use. Such a release sheet is not particularly limited, but a thermoplastic resin sheet, silicone-coated processing paper for prepreg, etc. can be used. Among these, silicone-coated processing paper for prepreg is preferably used from the viewpoints of shape stability, strength, and cost.

When using silicone-coated processing paper for prepreg as a release sheet, it is possible to adjust the composition of the silicone used as a release agent, the amount of application, drying after coating, heat treatment, etc. to prevent release from the prepreg of the present invention. You can adjust the intensity.

The release sheet preferably has a peel strength of 0.5 N/cm or more, more preferably 1.5 N/cm or more when peeled off from the adhesive tape. Further, it is preferably 7.5 N/cm or less, more preferably 6.0 N/cm or less. By setting the peel strength when peeling off from the adhesive tape to 0.5 N/cm or more and 7.5 N/cm or less, the adhesion between the reinforcing fiber prepreg of the present invention and the release sheet is sufficient, so it is possible to It is possible to prevent the prepreg from peeling off from the release sheet during storage and transportation. The adhesive tape used here has an adhesive force with SUS304 of 6.9 N/cm or more and 7.3 N/cm or less, and is determined by the adhesive force when attached to a SUS304 stainless steel plate according to JIS Z0237 (2009). As a commercially available adhesive tape having an adhesive force of 6.9 N/cm or more and 7.3 N/cm or less, "Scotch Tape (registered trademark)" No. 250, No. 8916, No. 8898 (manufactured by 3M Japan Ltd.), "Thuriontech (registered trademark)" No. 8063, No. 9241 (manufactured by Maxell Corporation), “DAITAC (registered trademark)” PF-050H, PF-075H, E-2100LC, 52050LA (manufactured by DIC Corporation), “Colalian Tape (registered trademark)” #550 (manufactured by Denka Co., Ltd.), line tape No. 154 (manufactured by Daikyo Giken Kogyo Co., Ltd.).

The prepreg with a release sheet of the present invention is produced by producing a release paper sheet with a resin film (hereinafter sometimes referred to as "resin film") in which a release sheet is coated with a matrix resin using a so-called hot melt method. Next, a resin film is placed on the reinforcing fiber side from both sides or one side of the reinforcing fiber, and the reinforcing fiber is impregnated with the matrix resin by heating and pressurizing the reinforcing fiber. More specifically, for example, the so-called one-stage impregnation hot melt method involves impregnating the reinforcing fibers with the matrix resin in a single step by heating and pressing a resin film made of the matrix resin from both sides or one side of the reinforcing fibers. This is a multi-stage impregnation hot-melt method in which the reinforcing fibers are impregnated with a resin film from both sides or one side by heating and pressing in multiple stages. In the present invention, a multi-stage impregnation hot-melt method in which reinforcing fibers are first impregnated with a low-viscosity matrix resin and then further impregnated with a high-viscosity matrix resin is used to create a prepreg with good release sheet releasability. It is preferred because it is easy to obtain.

The temperature at which the reinforcing fibers are impregnated with the matrix resin is preferably adjusted within the range of 50°C to 150°C. By adjusting the temperature within this range, the viscosity of the matrix resin can be adjusted, so the degree of impregnation of the matrix resin between the fiber layers can be adjusted, making it possible to create prepregs that have both high tackiness and good release properties of the release sheet. Easy to obtain. Regarding the pressure when impregnating the matrix resin, it is preferable to adjust the linear pressure in the range of 1 N/m to 100 N/m. When impregnating the matrix resin, when feeding the reinforcing fibers and resin with a roller, the rotation speed It is preferable to adjust the speed within a range of 2 m/min to 30 m/min. By adjusting the pressure and speed within the above ranges, the flow of the matrix resin can be adjusted, making it easy to obtain a prepreg that has both high tackiness and good releasability of the release sheet.

In the prepreg with a release sheet of the present invention, the mass content of reinforcing fibers in the prepreg removed by peeling off the release sheet is preferably 70% by mass or more, more preferably 75% by mass or more. be. Further, it is preferably 90% by mass or less, more preferably 85% by mass or less. The mass content of such reinforcing fibers may be confirmed using a prepreg without a release sheet, even if it is unclear whether or not the release sheet has been peeled off. By setting the mass content of the reinforcing fibers to 70% by mass or more, it is possible to achieve lightweight products using prepreg, and by setting the mass content to 90% by mass or less, the impregnability of the resulting fiber-reinforced composite material can be improved. It is possible to easily suppress the phenomenon of tearing between the fiber layers when peeled off from the release sheet, and to obtain a fiber reinforced composite material with excellent strength and lightness.

In the prepreg with a release sheet of the present invention, the matrix resin coverage of the outermost surface facing the release sheet in the prepreg is x ₁ [%], and the peel strength when peeling the release sheet from the prepreg is y ₁ [N/ 25 mm], it is necessary to satisfy condition (I) expressed by equation (1).

Here, RAW [g/m ² ] in the first term on the right side of equation (1) refers to the matrix resin mass per unit area of the prepreg, and G'' [MPa] in the second term refers to the matrix resin mass per unit area of the prepreg. is the loss modulus measured using the above-mentioned dynamic viscoelasticity measuring device using parallel plates at a temperature of 25° C., a strain of 0.1%, a frequency of 100 Hz, and a plate spacing of 1 mm.

To explain from the second term first, the loss modulus G'' of the matrix resin at a frequency of 100 Hz is an index representing the viscosity of the matrix resin, and if G'' is less than a certain value, the is not desirable. However, the rigidity of the prepreg is increasing. Therefore, when G'' is lower than a specific value, the matrix resin coverage x ₁ increases, and as the contact area with the release sheet increases, the peel strength y ₁ also increases, but on the other hand, if y ₁ is high, However, the acceptable value for good peelability is high, and the range is defined by the second term.

On the other hand, if G'' exceeds the above-mentioned certain value and becomes larger, the matrix resin becomes more easily deformed and the adhesion between the prepreg and the release sheet increases, so the ends of the prepreg may be cut when the release sheet is peeled off from the prepreg. It is necessary to reduce the peel strength so as to suppress this.In other words, as the rigidity of the prepreg decreases, _x1 increases, and as the contact area with the release sheet increases, the peel strength _y1 also increases. At the same time, the allowable value for _y1 is low, making it difficult to peel off the release sheet.Therefore, the range in which RAW and _x1 can be designed is limited within the range that satisfies formula (1). , in other words, these design ranges are defined by equation (1). In the present invention, as a result of study, we have found that the constant value of G" is 2.7 [MPa], and have arrived at the above equation. As shown in the example, even if G" exceeds 2.7 [MPa], by designing _RAW , We are getting prepreg.

Here, x ₁ is 40% or more and less than 100%, preferably 45% or more, and more preferably more than 50%. Further, it is preferably less than 80%, more preferably less than 70%, and still more preferably 65% or less. If _x1 is 40% or more, the tackiness required when winding the prepreg around a core material such as a mandrel can be ensured.

Further, y ₁ is preferably 0.05 N/25 mm or more, more preferably 0.10 N/25 mm or more. Further, it is preferably less than 1.00N/25m, more preferably less than 0.80N/25mm, even more preferably less than 0.50N/25mm. If _y1 is 0.05N/25mm or more, the release sheet is in close contact with the prepreg without peeling off naturally, and if it is less than 1.00N/25m, when the release sheet is peeled off from the prepreg, It can be easily peeled off by hand without disturbing the fiber direction of the prepreg or cutting the ends of the prepreg.

Next, to explain the first term, the peel strength _y1 affects not only the matrix resin coverage x1 _and the loss modulus G'' but also the matrix resin mass RAW per unit area of the prepreg in the first term. When RAW is made smaller, the peel strength _y1 is also reduced, but since parts of the fiber layer in the prepreg that are not impregnated with the matrix resin tend to occur, the prepreg is In order to suppress the edges from being cut, _y1 must be smaller than a specific value that varies depending on the RAW, and the RAW should be designed to satisfy equation ( ₁ ) according to y1. This is shown by the first term.The range of RAW is not specified as long as formula (1) is satisfied, but as mentioned above, if the mass content of reinforcing fibers in the prepreg is 70% by mass or more, It is preferably at least 75% by mass, more preferably at least 75% by mass. It is also preferably at most 90% by mass, more preferably at most 85% by mass, and is preferably designed within this range. Note that when the loss elastic modulus G'' is the constant value, the influence of the second term disappears, so the influence of RAW on the first term increases.

Furthermore, as mentioned above, the design according to equation (1) is possible even if G'' is 2.7 MPa or more or less than 2.7 MPa, but it is preferably 2.7 MPa or more, and 2. When it is larger than 7 MPa, a prepreg with excellent tackiness is easily obtained.

The prepreg with a release sheet of the present invention has a water absorption rate calculated by a water absorption test called the water pickup method (WPU method) as x ₂ [%], and a drape property of the prepreg from which the release sheet has been peeled off as y ₂ [°]. , it is necessary to satisfy equation (2).

Here, FAW [g/m ² ] in the first term on the right side of equation (2) refers to the reinforcing fiber mass per unit area of the prepreg mentioned above, and G' [KPa] in the second term is: It refers to the storage elastic modulus of the matrix resin measured using the above-mentioned dynamic viscoelasticity measuring device using parallel plates, maintaining the temperature at 25° C., strain 0.1%, frequency 0.01 Hz, and plate spacing 1 mm.

The prepreg according to the present invention needs to have a water absorption rate _x2 of 0.0% or more and 20.0% or less, preferably 0.1% or more, and more preferably 1. It is 0% or more. Moreover, it is preferably 10.0% or less, more preferably 7.0% or less. If the water absorption rate is 20.0% or less, the impregnation of the matrix resin between the fiber layers is sufficient, and tearing between the fiber layers when peeled from the release sheet can be suppressed. This water absorption rate can be determined by increasing the temperature and/or pressure when impregnating the matrix resin between the fiber layers, by decreasing the impregnation rate, and by increasing the complex viscosity in the temperature range during impregnation. It can also be lowered by selecting a matrix resin with a small value.

Further, drapeability _y2 is preferably 10° or more, preferably less than 50°, and more preferably less than 30°. If _y2 is 10° or more, the shapeability required when wrapping the prepreg around a core material such as a mandrel can be ensured, and if it is less than 50°, the ends of the prepreg can be secured when the release sheet is peeled off from the prepreg. It is possible to prevent the department from making judgments.

Regarding the first term on the right side of equation (2), when FAW is increased, parts of the prepreg where the matrix resin is not impregnated are likely to occur between the fiber layers, and the ends of the prepreg will be cut when the release sheet starts to be peeled off from the prepreg. This shows that it is highly important to reduce the drape property _y2 in order to suppress this. As mentioned above, the FAW is preferably 100 g/m ² or more, preferably 300 g/m ² or less, and more preferably 150 g/m ² or less.

Regarding the second term, the storage modulus G' at a frequency of 0.01 Hz is an index representing the rigidity of the matrix resin, and if G' is decreased, the rigidity of the prepreg itself may tend to decrease. Since it becomes difficult to peel off, in order to suppress a decrease in the rigidity of the prepreg, it is necessary to design the drape property _y2 to be smaller, and specifically, means to select appropriate reinforcing fibers can be mentioned. In other words, if G' is less than a certain value, from the viewpoint of the rigidity of the prepreg, it will be difficult to peel off from the release paper, but as the water absorption _rate The prepreg ends are less likely to break when the release sheet is peeled off, and the allowable value for _y2 becomes higher. When G' exceeds a certain value, the rigidity of the prepreg becomes high, so when _x2 becomes large, it is a direction in which it is easy to peel off from the release paper. Therefore, since there are many portions in the fiber layer that are not sufficiently filled with resin, the allowable value for _y2 increases, although the possibility of cracking in the fiber layer increases. In the present invention, as a result of studies, it has been found that the constant value of G' is 3.0 [KPa]. Note that when the storage elastic modulus G' is the above-mentioned constant value, the influence of the second term disappears, so the influence of FAW becomes large.

Note that the water absorption rate x ₂ and drapeability y ₂ may be confirmed using a prepreg without a release sheet, even if it is unclear whether the release sheet is removed or not.

The prepreg with a release sheet of the present invention preferably has a tack coefficient of 0.4 kgf or more on the release sheet side immediately after peeling off the release sheet in a 25°C environment, and preferably 1.5 kgf or less. It is preferably 0.5 kgf or more, and the upper limit is more preferably 1.1 kgf or less, still more preferably 0.9 kgf or less. Regarding the tack coefficient, an example of a measuring method will be described later in Examples. If the tack coefficient is 0.4 kgf or more, the prepreg can be wound without peeling or lifting between the core material such as a mandrel and the prepreg, or between the prepregs.

The fiber-reinforced composite material according to the present invention is obtained by peeling off the release sheet from the prepreg described above and curing it under predetermined conditions, using known curing conditions.

The upper and lower limits of the numerical ranges described above can be arbitrarily combined.

Hereinafter, the present invention will be described in detail with reference to Examples. Note that the present invention is not limited to the following examples. The matrix resins, reinforcing fibers, and various measurement methods used in the Examples and Comparative Examples are as follows.
<Epoxy resin>
・Bisphenol A type liquid epoxy resin (“jER (registered trademark)” 828, manufactured by Mitsubishi Chemical Corporation)
・Bisphenol A type solid epoxy resin (“jER (registered trademark)” 1001, manufactured by Mitsubishi Chemical Corporation)
・Bisphenol F type solid epoxy resin (“Epicron (registered trademark)” 830, manufactured by DIC Corporation)
・Bisphenol F type solid epoxy resin (“jER (registered trademark)” 4007P, manufactured by Mitsubishi Chemical Corporation)
・Phenol novolac type epoxy resin (“Epicron (registered trademark)” N-740, manufactured by DIC Corporation)
・Triglycidylaminophenol (“Araldide (registered trademark)” MY0600, manufactured by Huntsman Advanced Materials Co., Ltd.)
<Thermoplastic resin>
・Polyvinyl formal (“Vinylec (registered trademark)” K, manufactured by jNC Co., Ltd.)
<Curing agent>
・Dicyandiamide (DICY7, manufactured by Mitsubishi Chemical Corporation)
<Curing accelerator>
・Urea compound (DCMU99, manufactured by Hodogaya Chemical Industry Co., Ltd.)
<Reinforced fiber>
・Carbon fiber (“Torayca (registered trademark)” T1100GC-12K, manufactured by Toray Industries, Inc., tensile modulus: 324 GPa, tensile strength: 7000 MPa)
(1) Method for measuring dynamic viscoelasticity of matrix resin A matrix resin composition was measured using a dynamic viscoelasticity measuring device (ARES-G2: manufactured by TA Instrument) using parallel plates with a diameter of 8 mm. The thickness of the resin composition was 1.0 mm, the measurement temperature was 25 ° C., the strain was 0.1%, and the storage modulus (G') was measured at a frequency of 0.01 Hz while changing the frequency from 0.01 Hz to 100 Hz. [KPa], complex viscosity [Pa·s] at a frequency of 0.5 Hz, and loss modulus (G”) [MPa] at a frequency of 100 Hz.
(2) Method for measuring peel strength (y ₁ ) between prepreg and release sheet The prepreg with release sheet was cut into strips with a width of 25 mm and a length of 300 mm with the axial direction of the fibers as the length direction. was created. Next, as shown in FIG. 1, the test piece 1 is folded using double-sided adhesive tape 3 (Sony Chemical double-sided tape T4000, width 50 mm) that is large enough to cover the entire surface of the test piece. It was attached to a stainless steel support 2 with an angle θ of 165° with the release sheet facing outside. Next, as shown in FIG. 2, the test piece support 6 is attached to the lower chuck 8 of the tensile testing machine, the release sheet 4b is peeled off by 10 mm from the prepreg 4a, and the peeled end of the release sheet 4b is clipped. 9. It was attached to the upper chuck 11 via the metal wire 10. Next, the release sheet 4b was peeled off from the prepreg 4a in an atmosphere with a temperature of 25±2°C and a humidity of 50±5% RH at a pulling speed of 10 m/min, and the load was measured until the release sheet was completely peeled off. . From the measurement results obtained, excluding the 1 second at the beginning of peeling and 1 second at the end of peeling, read 5 points from the top of the peak of the load and 5 points from the bottom of the load from the bottom, and calculate these 10 points. A simple average value of the loads was calculated. The same measurement was performed at least 5 times at any location on the prepreg, and the simple average value of the 5 measurements was determined to determine the peel strength [N/25 mm].
(3) Method for measuring peel strength of adhesive tape and release sheet Scotch Tape No. manufactured by 3M Japan Ltd. was used as an adhesive tape. 250 (adhesive strength with SUS304: 7.06 N/cm), was pressed to the release sheet at 0.1 MPa for 5 minutes, and the measurement was performed in the same manner as in (1), except that the prepreg was replaced with the above adhesive tape. The adhesive force was defined as [N/cm].
(4) Matrix resin coverage on the outermost surface of the prepreg release sheet surface (x ₁ )
The release sheet is peeled off from the prepreg with a release sheet, and the prepreg immediately after peeling is viewed from the plane direction using a microscope (VHX-5000: manufactured by KEYENCE), and the prepreg surface in a unit area of 10 mm x 10 mm square. Image processing was performed on the part where the resin material existed (covered) based on the optically captured image, and the percentage was calculated by a binarization method. Such measurements were performed at five or more arbitrary locations on the prepreg, and the simple average value of those five points was determined to be the matrix resin coverage [%].
(5) Water Absorption Test The water absorption rate (x ₂ ) measured by the water pickup method (WPU method) is an index indicating the degree of resin impregnation in the prepreg. A test piece with a square size of 100 mm x 100 mm (length in the fiber longitudinal direction x width direction (direction orthogonal to the fiber direction)) was cut from the prepreg with a release sheet, and a release sheet or cover was pasted on the surface of the prepreg. Peel off the film. When the width of the prepreg is less than 100 mm, the length of the test piece in the width direction may be 100 mm or less, but the length in the fiber direction is 100 mm. Next, after measuring the mass W1 of the obtained test piece, one side of the test piece is arranged so that the fiber direction of the test piece is perpendicular to the water surface, and a range of 5 mm from the end of the test piece ( That is, 100 mm x 5 mm) is immersed in water for 5 minutes. After immersing the test piece for 5 minutes, take it out of the water, wipe off the water adhering to the surface of the test piece with a cloth or the like, being careful not to touch the immersed surface, and then measure the mass W2 of the test piece. The percentage was calculated by dividing the mass of water absorbed by the test piece (W2-W1) by W1. The measurement was performed at least 5 times at any arbitrary location on the prepreg, and the simple average value of the 5 points was determined to determine the water absorption rate [%].
(6) Drapability (y ₂ )
The prepreg with a release sheet was cut into strips with a width of 25 mm and a length of 300 mm with the axial direction of the fibers as the length direction, a test piece was prepared, and the release sheet and cover film affixed to the surface of the prepreg were peeled off. do. Next, as shown in Figure 3, a 100 mm portion from the longitudinal direction of the test piece was fixed to the edge of the work table, and the remaining 200 mm portion was placed so as to protrude from the work table. The horizontal length a and the vertical length b were measured, and θ calculated by the formula θ=tan ⁻¹ (b/a) was taken as drapability [°].
(7) Tack coefficient Peel the release sheet from the prepreg with a release sheet, and immediately after peeling, test it using a tack tester (for example, EMX-1000N: Stock A cover glass of 18 mm x 18 mm square was crimped from directly above onto the horizontally placed prepreg for 1 second under a load of 0.5 kgf (4.9 N), and the cover glass was pressed at a speed of 30 m/min. The film was peeled off directly above, and the resistance to peeling was measured. Such measurements were performed at least 5 times at arbitrary locations on the prepreg, and the simple average value of these 5 measurements was determined to be the tack coefficient [kgf].
(8) Workability evaluation method A prepreg with a release sheet cut into 1000 mm x 1000 mm squares was prepared with a release sheet attached to one side and no release sheet attached to the other side, and released from the mold. The surfaces with no sheets attached were laminated and bonded together so that the fibers were perpendicular to each other, pressed together with nip rolls, and then cut into strips with a width of 100 mm and a length of 1000 mm along the fiber direction. Next, the release sheet supported on the upper prepreg was peeled off by hand with the surface in which the axial direction of the fibers was the longitudinal direction facing upward, and the workability was evaluated. "A" indicates that the adhesion between the prepregs is good, and the release sheet can be peeled off while retaining the shape of the prepreg; "A" indicates that the adhesion between the prepregs is good, but the edges of the prepreg can be torn when the release sheet is peeled off. "B" was used when the prepregs were not in close contact with each other, "C" was given when the prepregs were not in close contact with each other, and "D" was given when the release sheet and the prepreg were not in close contact with each other before work and were floating.

Tables 1 and 2 summarize the results of measuring the characteristics of the matrix resin and the prepreg with release sheet for each Example and Comparative Example using the above method.
<Example 1>
A matrix resin was prepared by mixing the components shown in Table 1. As a result of measuring the viscosity of the obtained matrix resin, the complex viscosity at 25°C was 40,000 Pa·s at a frequency of 0.5 Hz, the storage modulus was 2.95 KPa at a frequency of 0.01 Hz, and the loss The elastic modulus G" was 2.8 MPa at 100 Hz. The obtained matrix resin composition was applied onto a release sheet using a coater to produce a resin film. The release sheet contained the following: A tape with an adhesive strength of 4.8 N/cm was used.Next, carbon fiber "Torayka (registered trademark)" T1100GC-12K was used with a carbon fiber mass per unit area (FAW) of 150 g/m2 ^. After stacking the above resin films one above the other by aligning them in one direction so that A unidirectional carbon fiber prepreg with a release sheet was produced.The obtained prepreg had a matrix resin coverage x ₁ of 52%, a water absorption rate of 6.0%, and a peel strength y ₁ from the release sheet of 0.33N. /25 mm, drapeability was 18°, satisfying formulas (1) and (2).Furthermore, the tack coefficient was 0.5 kgf, and the workability rating was "A".
<Examples 2 to 6>
Using the same matrix resin composition and carbon fibers as in Example 1, in the step of impregnating the carbon fibers with a resin film under heat and pressure, comparisons with Example 1, Examples 2 and 4 were made so that the properties listed in the table could be obtained. In Example 3, the pressure was increased while keeping the temperature constant, and in Examples 5 and 6, the temperature was decreased and the pressure was increased to produce a unidirectional carbon fiber prepreg with a release sheet. The evaluation results are shown in Table 1. All Examples satisfied formula (1) and formula (2), and were evaluated as "A" in workability.
<Examples 7 and 8>
A unidirectional carbon fiber prepreg with a release sheet was produced in the same manner as in Example 1, except that the carbon fiber mass FAW per unit area was 125 g/m ² and 100 g/m ² , respectively. The evaluation results are shown in Table 1. All Examples satisfied formula (1) and formula (2), and were evaluated as "A" in workability.
<Examples 9 and 10>
A unidirectional carbon fiber prepreg with a release sheet was produced in the same manner as in Example 1, except that the components shown in Table 1 were mixed to prepare a matrix resin composition. The evaluation results are shown in Table 1. All Examples satisfied formula (1) and formula (2), and were evaluated as "A" in workability.
<Examples 11 to 14>
Carbon fibers "Torayka (registered trademark)" T1100GC-12K were aligned in one direction so that the carbon fiber mass FAW per unit area was 100 g/ ^m2 , and the same matrix resin composition as in Example 1 was used. After stacking the resin films on top of each other, the resin films were impregnated with heat and pressure using a multi-stage impregnation hot melt method to produce a unidirectional carbon fiber prepreg with a release sheet so that the carbon fiber mass content was 82%. did. In the process of impregnating carbon fibers with a resin film under heat and pressure, in order to obtain the properties listed in the table, in comparison with Example 8, Examples 11 and 12 have a weight of the resin composition per unit area of the reinforcing fiber prepreg. In Examples 13 and 14, in addition to lowering the mass of the resin composition, a unidirectional carbon fiber prepreg with a release sheet was produced by passing the heating and pressurizing impregnation process twice by the multi-stage impregnation hot melt method. . The evaluation results are shown in Table 1. All Examples satisfied formula (1) and formula (2), and were evaluated as "A" in workability.
<Examples 15 to 17>
A unidirectional carbon fiber prepreg with a release sheet was produced in the same manner as in Example 1, except that the carbon fiber mass FAW per unit area was 125 g/m ² . In comparison with Example 7, Examples 15 and 16 lowered the mass of the resin composition per unit area of the reinforcing fiber prepreg, and Example 17 lowered the mass of the resin composition, and also used a multi-stage impregnation hot melt method. A unidirectional carbon fiber prepreg with a release sheet was produced by passing through the heating and pressurizing impregnation process twice. The evaluation results are shown in Table 1. All Examples satisfied formula (1) and formula (2), and were evaluated as "A" in workability.
<Comparative example 1>
Using the same matrix resin composition and carbon fiber as in Example 1, in the step of impregnating the carbon fiber with a resin film under heat and pressure, both the temperature and pressure were lowered compared to Example 1 so that the properties listed in the table could be obtained. A unidirectional carbon fiber prepreg with a release sheet was produced. The evaluation results are shown in Table 1. The obtained prepreg had a matrix resin coverage x ₁ of 75%, a water absorption rate x ₂ of 16.0%, a peel strength y ₂ from the release sheet of 0.52 N/25 mm, and a drape property y ₂ of 32°. Yes, neither formula (1) nor formula (2) was satisfied. Further, the tack coefficient was 1.1 kgf, and the end of the prepreg was torn when the release sheet was peeled off, so the workability rating was "B".

In the prepreg of Comparative Example 1, the matrix resin coverage x ₁ was higher than that of the example, the peel strength y ₁ with the release sheet was not at a level that would allow the matrix resin coverage x ₁ , and the water absorption rate x ₂ was higher than that of the example. Since the drapeability _y2 was higher than that of the example and the water absorption rate _x2 was not at an acceptable level, it is thought that the impregnation of the matrix resin into the fiber layer was poor, leading to the prepreg edges being torn.
<Comparative Examples 2 to 5>
Using the same matrix resin composition and carbon fiber as in Example 1, in the process of impregnating the carbon fiber with a resin film under heat and pressure, in comparison to Comparative Example 1, pressure was applied at a constant temperature to obtain the properties listed in the table. Then, a unidirectional carbon fiber prepreg with a release sheet was produced. The evaluation results are shown in Table 1. These comparative examples did not satisfy either or both of formula (1) and formula (2), and were rated "B" or "C" for workability.

It is considered that the prepregs of Comparative Examples 2, 3, and 5 had poor impregnation of the matrix resin into the fiber layer, which led to the ends of the prepregs being cut, as in Comparative Example 1. Although the prepreg of Comparative Example 4 had no problem in impregnation, the matrix resin coverage x ₁ was lower than that of the example, which is thought to have led to a decrease in the tackiness of the prepreg.
<Comparative Examples 6 and 7>
A unidirectional carbon fiber prepreg with a release sheet was produced in the same manner as in Example 1, except that the carbon fiber mass content was 95%. The evaluation results are shown in Table 1. These comparative examples did not satisfy either or both of formula (1) and formula (2), and were rated "B" or "C" for workability.

Since the prepregs of Comparative Examples 6 and 7 had a higher carbon fiber mass content than the examples, the amount of resin in the prepregs was too small, the impregnation of the matrix resin into the fiber layer was poor, and the ends of the prepregs were cut. I believe that this may have led to a decrease in the tackiness of the prepreg due to a lower resin coverage.
<Comparative Examples 8 to 11>
A unidirectional carbon fiber prepreg with a release sheet was produced in the same manner as in Example 1, except that the components shown in Table 1 were mixed to prepare a matrix resin composition. The evaluation results are shown in Table 1. These comparative examples did not satisfy either or both of formula (1) and formula (2), and were rated "B" or "C" for workability.

The matrix resins used in Comparative Examples 8 to 11 have a larger loss modulus G'' than the resin used in the examples, so the matrix resins are more easily deformed and the adhesion between the prepreg and the release sheet tends to increase. As a result, the rigidity of the prepreg is reduced, and the prepreg is in strong contact with the release sheet, which is thought to have led to the release sheet becoming difficult to peel off, even though the peel strength y1 is not high.
<Comparative Examples 12 and 13>
A unidirectional carbon fiber prepreg with a release sheet was produced in the same manner as in Example 1, except that the release sheet had an adhesive force of 0.8 N/cm with the adhesive tape. The evaluation results are shown in Table 1. These comparative examples did not satisfy formula (1) and were rated "D" in terms of workability.

The release sheets used in Comparative Examples 12 and 13 had lower adhesion to the adhesive tape than in the examples, so the adhesion between the prepreg and the release sheet deteriorated, causing the release sheet to float. think.

1: Test piece (prepreg with release sheet)
2: Stainless steel support 3: Double-sided adhesive tape θ: Bent angle 4a: Unidirectional prepreg 4b: Release sheet 5: Test piece (prepreg with release sheet)
6: Stainless steel support 7: Double-sided adhesive tape 8: Lower chuck 9: Clip 10: Metal wire 11: Upper chuck 12: Test piece (prepreg with release sheet)
13: Workbench

The prepreg with a release sheet of the present invention has both tackiness and peelability of the release paper, and is excellent in handling, so it can be used as a lightweight, high-strength, and high-rigidity fiber-reinforced composite material for fishing rods, golf shafts, etc. In addition to sports and leisure applications, it is preferably used in a wide range of fields such as industrial applications such as automobiles and aircraft.

Claims (10)

A prepreg with a release sheet, which has a release sheet disposed on at least one side of a prepreg in which reinforcing fibers are impregnated with a matrix resin, and satisfies the following conditions (I), (II), and (III).
(I) When the matrix resin coverage of the outermost surface facing the release sheet in the prepreg is x ₁ and the peel strength when peeling the release sheet from the prepreg is y ₁ , the following formula (1) is satisfied. ,

(II) The prepreg from which the release sheet has been removed satisfies the following formula (2), where _x2 is the water absorption rate calculated by the water absorption test, and _y2 is the drape property.

(III) x ₁ is 40% or more and less than 100%, and x ₂ is 0.0% or more and 20.0% or less.

Here, RAW is the matrix resin mass per unit area of the prepreg [g/m ² ], FAW is the reinforcing fiber mass per unit area of the prepreg [g/m ² ],
G'' is the loss modulus [MPa] in the dynamic viscoelasticity measurement of the matrix resin, and G' is the storage modulus [KPa] in the measurement. The FAW is 100 g/m ² or more and 300 g/m ² or less,
The prepreg with a release sheet according to claim 1, wherein the mass content of reinforcing fibers in the prepreg obtained by peeling off the release sheet from the prepreg with a release sheet is 70% by mass or more and 90% by mass or less. The prepreg with a release sheet according to claim 1 or 2, wherein the reinforcing fibers are carbon fibers. The prepreg with a release sheet according to claim 1, wherein the matrix resin has a complex viscosity of 10,000 Pa·s or more and less than 100,000 Pa·s at a temperature of 25°C. The prepreg with a release sheet according to claim 1 or 4, wherein the matrix resin is a composition containing a thermosetting resin as a main component. The prepreg with a release sheet according to claim 5, wherein the thermosetting resin is an epoxy resin. After applying the adhesive tape (adhesive strength with SUS304: 6.9 to 7.3 N/cm) to the release sheet, the peel strength when peeling off is 0.5 N/cm or more and 7.5 N/cm or less, The prepreg with a release sheet according to claim 1. The release sheet prepreg according to claim 1 or 7, wherein the tack coefficient on the surface of the prepreg from which the release sheet is peeled is 0.4 kgf or more and 1.5 kgf or less. The prepreg with a mold release sheet according to claim 1 or 7, wherein the peel strength when peeling the mold release sheet from the prepreg is 0.01 N/25 mm or more and 0.40 N/25 mm or less. A fiber-reinforced composite material obtained by curing the prepreg in the prepreg with a release sheet according to claim 1.

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