JP2014151448A - Method for producing release film and fiber-reinforced plastic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a release film which is excellent in releasability and heat resistance and is capable of producing a fiber-reinforced plastic with high productivity and handleability even if a prepreg is pressure molded at a high temperature in a state of being interposed between the prepreg and a press surface.SOLUTION: A release layer of a release film is formed by a Calkylated melamine-formaldehyde resin and the centerline average roughness Ra of the surface is adjusted to be 0.012 to 2 μm. The release film further contains a base material layer and the release layer may be formed on at least one surface of the base material layer. The release layer has an average thickness of 0.2 to 5 μm and the base material layer may have an average thickness of 12 to 75 μm. The release film may be a release film for molding a fiber-reinforced plastic by hot-pressing a prepreg in a state of being interposed between the prepreg and a press surface.

Description

  The present invention relates to a release film, in particular, a release film useful for producing a fiber reinforced plastic (FRP) by molding a prepreg, and a method for producing a fiber reinforced plastic using the release film.

  Fiber reinforced plastic (fiber reinforced resin composite material) made by impregnating and curing an uncured matrix resin such as epoxy resin on a reinforced fiber base material such as glass cloth, carbon fiber, and aramid fiber is formable, thin, lightweight, high It is excellent in rigidity, productivity, and economy, and is frequently used for electrical / electronic parts and casings such as electrical / electronic equipment parts, automobile equipment parts, home appliances.

  As a typical method for producing fiber reinforced plastic (FRP), a method in which continuous reinforcing fibers are laminated with fiber reinforced prepregs impregnated with uncured resin and cured by heating press (compression or pressure molding). It has been known. In this method, a release film interposed between the press surface and the FRP is used in order to improve the releasability between the press surface (molding die) and the FRP at the time of hot pressing. In particular, in the molding of carbon fiber reinforced plastic (CFRP), a prepreg impregnated with carbon fiber as a base material and impregnated with an uncured matrix resin such as an epoxy resin is molded by heating and pressing. Is preferably a material having high heat resistance.

  Examples of the release film used for these applications include a fluorine-based film, a silicone-coated polyethylene terephthalate film, a polymethylpentene film, and a polypropylene film. However, a fluorine-based film that has been widely used as a release film has been excellent in heat resistance and release properties, but is expensive and difficult to burn in waste incineration after use. It is easy to generate poisonous gas. In addition, the silicone-coated polyethylene terephthalate film has a risk of deteriorating mold stains and prepreg quality due to migration of the silicone component. Furthermore, the polymethylpentene film is excellent in releasability, but the film is easily wrinkled during molding. Furthermore, the polypropylene film has low heat resistance and insufficient releasability.

  JP-A-2006-257399 (Patent Document 1) discloses a release film made of a cyclic polyolefin resin as a release film having excellent heat resistance, release properties, and non-staining properties. Further, this document also describes that an appropriate embossed pattern is provided on at least one surface for the purpose of air removal during hot press molding. However, even with this release film, heat resistance is not sufficient, and usable matrix resins are limited. Moreover, although the film which has an embossed pattern can improve handling property, embossing is required and productivity is low.

  A release film formed of a melamine-formaldehyde resin (melamine resin), which is a thermosetting resin, has also been proposed. Japanese Patent No. 44453080 (Patent Document 2) discloses ultra-smoothness, peelability, and oligomer. As a release film excellent in the effect of preventing precipitation, a melamine resin film having a critical surface tension (unit: mN / m) of 25 to 40 on at least one surface of a plastic film having a surface centerline average roughness Ra of 7 nm or less A release film for casting molding of an acrylic resin sheet for protecting a Blu-ray disc recording film is disclosed. In this document, ultra-smoothness is imparted to the surface of the release film in order to realize a release film with less surface defects on the protective sheet of the optical disk recording film. Further, this document describes that the plastic film has a thickness of 12 to 188 μm, and in the examples, a biaxially stretched polyester film having a thickness of 125 μm is used. Furthermore, in this document, after the polymethyl methacrylate paint is applied to the release surface of the release film with an applicator and dried, the resulting acrylic sheet is peeled off.

  However, this document does not describe either FRP or pressure molding (hot press). Also, there is no description about heating in the application and drying of the polymethyl methacrylate paint. Furthermore, the present inventors applied this release film having high smoothness to the molding of FRP, because the handling property is low and wrinkles are easily generated, and it is difficult for air to escape in hot press molding. It was confirmed that wrinkles were likely to occur.

  Japanese Patent No. 4762177 (Patent Document 3) discloses a release sheet in which a melamine resin film containing an alkylated melamine-formaldehyde resin having an alkyl group having 6 to 18 carbon atoms is formed on at least one surface of a base sheet. Is disclosed. This document describes that the release sheet is used for casting an adhesive resin applied to a printed wiring board or the like, and a polyimide-based adhesive is described as the adhesive resin. The polyimide adhesive is applied to the surface of the melamine resin coating with an applicator and dried at 100 ° C., and then the obtained semi-cured adhesive resin layer is peeled off. Furthermore, in this document, in order to form a smooth surface of the adhesive resin layer, it is described that the surface of the melamine resin film preferably has a centerline average surface roughness (Ra) of 50 nm or less (particularly 30 nm or less). In the examples, a release sheet of Ra 23 to 25 nm is manufactured.

  However, neither FRP nor hot press is described in this document.

JP 2006-257399 A (Claim 1, paragraph [0035]) Japanese Patent No. 44453080 (Claim 1, paragraphs [0016] and [0019], Examples) Japanese Patent No. 4762177 (Claim 1, paragraphs [0005] [0018] [0026], Example)

  Accordingly, an object of the present invention is to release-mold a film having excellent release properties and heat resistance, in particular, press-molding (hot pressing) the prepreg at a high temperature in a state of being interposed between the prepreg and the press surface. Another object of the present invention is to provide a release film capable of producing a fiber reinforced plastic (molded product) with high productivity and handleability (stability) and a method for producing a fiber reinforced plastic using the release film.

  Another object of the present invention is to provide a release film capable of producing a fiber-reinforced plastic in which wrinkles are suppressed by press molding a prepreg at a high temperature even if it is thin, and a fiber-reinforced plastic using the release film. It is in providing the method of manufacturing.

As a result of intensive studies to achieve the above-mentioned problems, the present inventors have formed a release layer of a release film with a C _1-4 alkylated melamine-formaldehyde resin, and adjusted the surface roughness to thereby release the release layer. Excellent in moldability and heat resistance, fiber reinforced plastic with high productivity and handleability (stability) even if the prepreg is press-molded at high temperature (hot pressing) in a state of being interposed between the prepreg and the press surface The present inventors have found that a (molded product) can be produced and completed the present invention.

That is, the release film of the present invention includes a release layer formed of a C _1-4 alkylated melamine-formaldehyde resin, and the center line average roughness Ra of the release layer surface is 0.012 to 2 μm. is there. The release film of the present invention may further include a base material layer, and the release layer may be formed on at least one surface of the base material layer. The release layer may have an average thickness of 0.2 to 5 μm, and the base layer may have an average thickness of 12 to 75 μm. The release layer may contain fine particles having an average particle diameter of 0.01 to 20 μm. The base material layer may be at least one selected from polyester, polyamide, polyimide, polycarbonate, polyethersulfone, and a cellulose derivative. The release layer may be a layer formed by coating. The release film of the present invention may be a release film for molding a fiber reinforced plastic by hot pressing the prepreg in a state of being interposed between the prepreg and the press surface.

  In the present invention, heat for molding a fiber reinforced plastic by hot pressing the prepreg at a temperature of 120 to 220 ° C. and a pressure of 0.1 to 20 MPa with the release film interposed between the prepreg and the press surface. A method for producing a fiber reinforced plastic including a pressing step is also included. The fiber reinforced plastic may contain carbon fiber and epoxy resin. The hot pressing step may be hot pressing in a vacuum.

  In addition, in this specification, a melamine-formaldehyde resin and a melamine resin are synonymous.

In the present invention, the release film includes a release layer formed of a C _1-4 alkylated melamine-formaldehyde resin, and the center line average roughness Ra of the release layer surface is 0.015 to 2 μm. Therefore, it is excellent in releasability and heat resistance. Therefore, even if the prepreg is press-molded at a high temperature while being interposed between the prepreg and the press surface, the fiber-reinforced plastic can be produced with high productivity and handleability. In particular, if the release film is thin, the release film easily deforms and air tends to accumulate, or the fiber reinforced plastic is likely to wrinkle.In the present invention, the prepreg is used even if the release film is thin. By pressure molding at a high temperature, it is possible to mold a fiber reinforced plastic in which wrinkles are suppressed.

[Release film]
Release film of the present invention, C _1-4 alkylated melamine - formed by formaldehyde resin (C _1-4 alkylated melamine resin), and includes a release layer having a predetermined surface roughness.

(Release layer)
The C _1-4 alkylated melamine-formaldehyde resin forming the release layer is a resin obtained by curing a resin precursor in which at least a part of methylol melamine groups is alkyl etherified with C _1-4 alcohol. In the present invention, by using an alkyl etherified resin precursor, the productivity of the release layer can be improved and a release layer having an appropriate surface roughness can be easily formed.

Examples of the C _1-4 alcohol include linear or branched alcohols such as methanol, ethanol, propanol, butanol, and isobutanol. These alcohols can be used alone or in combination of two or more. Of these alcohols, methanol, ethanol, (iso) butanol and the like are widely used.

  In the resin precursor, the ratio of methylolation (average added mole number of formaldehyde with respect to melamine) can be selected from the range of about 1 to 6 moles with respect to 1 mole of melamine, for example, 1 to 5 moles, preferably 1.5. It is about -4.5 mol, More preferably, it is about 2-4 mol (especially about 3 mol). That is, mono to hexamethylol melamine can be selected depending on the degree of methylolation, and it is preferable to include di to tetramethylol melamine. If the degree of methylolation is too low, the crosslink density is lowered, so that the mechanical properties of the release layer are lowered.

  Further, the ratio of the alkyl etherized methylol group (alkoxymethyl group) may be, for example, 50% or more, preferably 80% or more, more preferably 90% or more (particularly substantially omitted) with respect to the total number of methylol groups. 100%). If the ratio of alkyl etherification is too small, the productivity of the release layer cannot be improved.

Examples of C _1-4 alkylated melamine-formaldehyde resins include methylated melamine-formaldehyde resins (such as trimethylol trimethoxymethyl melamine), ethylated melamine-formaldehyde resins, propylated melamine-formaldehyde resins, butylated melamine-formaldehyde. Examples thereof include resins (such as trimethylol tributoxymethyl melamine) and isobutylated melamine-formaldehyde resins. In addition, _C1-4 alkylated melamine-formaldehyde resin may contain oligomers, such as a dimer and a trimer.

The resin precursor may contain a conventional curing agent (curing catalyst). Examples of the curing agent include aromatic sulfonic acids (paratoluenesulfonic acid, paratoluenesulfonic acid ester, paratoluenesulfonic acid amide, etc.), inorganic acids (hydrochloric acid, etc.), salts (ammonium chloride, ammonium phosphate ammonium hydrochloride, etc.) ), Carboxylic acids (such as dimethyl oxalate, phthalic anhydride), organic halides, urea salicylic acid adducts, and the like. These curing agents can be used alone or in combination of two or more. Of these, aromatic sulfonic acids such as p-toluenesulfonic acid ester are preferred. The ratio of the curing agent is, for example, 0.01 to 20 parts by weight, preferably 0.1 to 15 parts by weight, and more preferably 0.5 to 10 parts by weight with respect to 100 parts by weight of the C _1-4 alkylated melamine resin. Part (particularly 1 to 8 parts by weight).

  The release layer may contain fine particles (anti-blocking agent or filler) in order to adjust the surface roughness. The fine particles include organic particles and inorganic particles.

  Examples of the organic particles include cross-linked styrene resin particles, cross-linked acrylic resin particles, cross-linked polyethylene particles, fluororesin particles, and melamine resin particles. Examples of inorganic particles include carbonaceous materials (carbon black, graphite, etc.), synthetic ceramics (metal oxides such as zinc oxide, magnesium oxide, titanium oxide, and aluminum oxide), and metal silicates such as calcium silicate and aluminum silicate. Salts, metal carbides such as silicon carbide and tungsten carbide, metal nitrides such as titanium nitride, aluminum nitride and boron nitride, metal carbonates such as magnesium carbonate and calcium carbonate, metal sulfates such as calcium sulfate and barium sulfate), Examples include mineral materials (zeolite, diatomaceous earth, calcined siliceous clay, activated clay, alumina, silica, talc, mica, kaolin, clay, etc.). These fine particles can be used alone or in combination of two or more. Among these, inorganic particles such as zeolite particles are preferable because they have high peelability and little influence on FRP.

  The average particle size of the fine particles is, for example, about 0.01 to 20 μm, preferably about 0.1 to 15 μm, and more preferably about 0.5 to 10 μm. If the particle size of the fine particles is too large, the surface roughness of the release layer becomes too large, and if the particle size is too small, it becomes difficult to adjust the surface roughness with the fine particles.

The proportion of the fine particles is, for example, 0.01 to 20 parts by weight, preferably 0.05 to 10 parts by weight, more preferably 0.1 to 5 parts by weight with respect to 100 parts by weight of the C _1-4 alkylated melamine resin. Degree. If the proportion of the fine particles is too large, the mechanical strength of the release layer is lowered, and if the proportion is too small, it is difficult to adjust the surface roughness with the fine particles.

  The release layer may further contain a conventional additive. Conventional additives include, for example, lubricants (waxes, fatty acid esters, fatty acid amides, etc.), antistatic agents, stabilizers (antioxidants, heat stabilizers, light stabilizers, etc.), flame retardants, viscosity modifiers, A sticky agent, an antifoaming agent, etc. may be contained. From the viewpoint of improving releasability, it is preferable to include organic or inorganic particles (especially anti-blocking agents such as zeolite).

  In particular, in the present invention, it is preferable that the releasability can be improved without containing a low molecular weight release agent such as a silicone compound that easily contaminates FRP, and it is preferable that the silicone compound is not substantially contained.

  The center line average roughness Ra of the release layer surface is 0.015 to 2 μm. In the present invention, since the centerline average roughness Ra of the release layer surface is in this range, an appropriate gap is formed between the surface of the prepreg and the release layer, so that air can escape, Fiber with excellent heat resistance, high productivity even if the prepreg is press-molded at a high temperature in a state of being interposed between the prepreg and the press surface, and even if the release film is thin, the fiber with suppressed wrinkles Reinforced plastic can be molded. The center line average roughness Ra may be 0.012 to 2 μm, for example, 0.013 to 1.8 μm, preferably 0.015 to 1.5 μm, more preferably 0.02 to 1.0 μm, ( Particularly, it is about 0.025 to 0.5 μm), and may be about 0.03 to 0.5 μm (particularly 0.06 to 0.3 μm), for example, depending on the application.

  In the present specification, the center line average roughness Ra can be measured by a method based on JIS B0601.

  The average thickness of the release layer can be selected from the range of about 0.2 to 5 μm, for example, 0.25 to 4 μm, preferably 0.28 to 3 μm, more preferably 0.3 to 3 μm (particularly 0.3 to 2). .About.5 μm). If the thickness of the release layer is too thick, the economic efficiency is lowered. On the other hand, if the thickness of the release layer is too thin, the release layer is easily peeled off.

  In the present specification, the average thickness of the release layer can be calculated by dividing the coating amount of the release layer by the density (coating amount / density).

(Base material layer)
Since the release layer is formed by coating, the release film of the present invention further includes a substrate layer, and the release layer is formed on at least one surface (usually one surface) of the substrate layer. May be. The base material layer is formed of a material having high heat resistance and high dimensional stability, and is usually formed of a synthetic resin from the viewpoint of excellent productivity.

As the synthetic resin, for example, various thermoplastic resins and thermosetting resins can be used, but a thermoplastic resin is preferable from the viewpoint of flexibility that allows a release film to be produced by a roll-to-roll method. Examples of the thermoplastic resin include polypropylene resin, cyclic polyolefin, polyvinyl alcohol polymer, polyester, polyamide, polyimide, polycarbonate, polyethersulfone, polyphenylene ether, polyphenylene sulfide, and cellulose derivatives. These thermoplastic resins can be used alone or in combination of two or more. Of these thermoplastic resins, at least one selected from polyesters, polyamides, polyimides, polycarbonates, polyethersulfones and cellulose derivatives is preferable, and polyesters are particularly preferable from the viewpoint of excellent balance between heat resistance and flexibility. Furthermore, as the polyester, poly C _2-4 alkylene arylate resins such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) can be preferably used.

  Since the release layer is thin and the uneven shape on the surface of the base material layer is easily followed by the release layer, the surface roughness of the release layer may be controlled by the surface shape of the base material layer. It is preferable that the surface of the material layer also has an appropriate surface roughness. The centerline average roughness Ra of the release layer surface may be 0.012 to 2 μm, for example, 0.013 to 1.8 μm, preferably 0.015 to 1.5 μm, and more preferably 0.02 to 0.02 μm. It is about 1.0 μm (particularly 0.025 to 0.5 μm), and may be about 0.03 to 0.5 μm (particularly 0.06 to 0.3 μm), for example. If Ra is too small, the surface of the release layer also becomes smooth, wrinkles and the like are easily generated, and handling properties are deteriorated. On the other hand, if Ra is too large, the releasability is lowered.

  The base material layer may be formed of a stretched film from the viewpoint of improving the film strength and controlling the surface shape. The stretching may be uniaxial stretching, but biaxial stretching is preferred from the viewpoint that the film strength can be improved. Further, the biaxial stretching may be sequential biaxial stretching, but simultaneous biaxial stretching is preferable from the viewpoint of excellent surface roughness uniformity. In sequential biaxial stretching, scratches are easily caused by contact with a roll during longitudinal stretching, and the surface roughness tends to be non-uniform. . The stretching ratio may be, for example, 1.5 times or more (for example, 1.5 to 6 times), preferably 2 to 5 times, more preferably about 3 to 4 times, in the longitudinal and transverse directions, respectively. It is. If the draw ratio is too low, the film strength tends to be insufficient.

  In the present invention, air retention due to hot pressing can be suppressed by the surface shape of the release layer, so that the base material layer can be thinned. A release film can be produced by a roll-to-roll method by thinning the base material layer. The average thickness of a base material layer is 12-75 micrometers, for example, Preferably it is 25-75 micrometers, More preferably, it is about 30-70 micrometers (especially 40-60 micrometers). When the thickness of the base material layer is too large, production by a roll-to-roll method becomes difficult and economical efficiency is also lowered. When it is too thin, dimensional stability is lowered.

  The average thickness ratio of the substrate layer and the release layer is, for example, substrate layer / release layer = 100 / 0.1 to 100/10, preferably 100 / 0.3 to 100/8, more preferably 100. /0.4 to 100/5 (particularly 100 / 0.5 to 100/3).

  The surface of the base material layer may be subjected to a surface treatment in order to improve the adhesion with the release layer. Examples of the surface treatment include conventional surface treatments such as corona discharge treatment, flame treatment, plasma treatment, ozone and ultraviolet irradiation treatment. Of these, corona discharge treatment is preferred.

  The release film of the present invention is suitable as a release film used in the production process of fiber-reinforced plastics. Specifically, in a state where the release film is interposed between the prepreg and the press surface, the prepreg is hot-pressed to produce fibers. It may be a release film for molding reinforced plastic.

(Manufacturing method of release film)
The release film can be produced by coating (or casting) a solution containing an uncured _C1-4 alkylated melamine-formaldehyde resin on the base material layer and then drying.

  As the coating method, conventional methods such as roll coater, air knife coater, blade coater, rod coater, reverse coater, bar coater, comma coater, die coater, gravure coater, screen coater method, spray method, spinner method and the like can be mentioned. It is done. Of these methods, the bar coater method is widely used.

  Solvents include water, alcohols (methanol, ethanol, isopropanol, butanol, cyclohexanol, etc.), hydrocarbons (aliphatic hydrocarbons such as hexane, aromatic hydrocarbons such as toluene, xylene, etc.), halogenated Carbons (dichloromethane, dichloroethane, etc.), esters (methyl acetate, ethyl acetate, etc.), ketones (acetone, methyl ethyl ketone, etc.), ethers (dioxane, tetrahydrofuran, etc.), cellosolves (methyl cellosolve, ethyl cellosolve, etc.), cellosolve Acetates, carbitols (such as methyl carbitol), aqueous ammonia, aliphatic amines (trialkylamines such as trimethylamine and triethylamine, triethanolamine, dimethylaminoethanol, etc.) Etc. Kanoruamin acids), amides (dimethylformamide, dimethylacetamide, etc.), and others. These solvents can be used alone or as a mixed solvent.

  Of these solvents, alcohols such as methanol and butanol are preferred from the viewpoint of excellent solubility of the alkylated melamine resin. Furthermore, you may combine basic solvents, such as aqueous ammonia and aliphatic amines, with respect to the said alcohol from the point which adjusts pH and adjusts hardening reaction. The proportion of the basic solvent is about 0.1 to 5% by weight, preferably about 0.2 to 3% by weight, and more preferably about 0.3 to 1% by weight, based on the entire solution.

  The solid content concentration in the solution is, for example, about 10 to 80% by weight, preferably about 20 to 70% by weight, and more preferably about 30 to 60% by weight.

  Drying may be natural drying, or the solvent may be evaporated by heating and drying. 50 degreeC or more may be sufficient as drying temperature, for example, 50-200 degreeC, Preferably it is 80-180 degreeC, More preferably, it is about 100-160 degreeC. When drying by heating, it is necessary to adjust the drying time so that the curing reaction does not proceed. For example, it may be 10 to 60 seconds, preferably about 20 to 50 seconds.

[Production method of fiber reinforced plastic]
The method for producing a fiber reinforced plastic (FRP) of the present invention is a method of hot pressing a prepreg at a temperature of 120 to 220 ° C. and a pressure of 0.1 to 2 MPa with the release film interposed between the prepreg and a press surface. And a hot press step of molding the fiber reinforced plastic.

  The prepreg includes uncured thermosetting resin and fibers. Examples of the thermosetting resin include unsaturated polyester, epoxy resin, diallyl phthalate resin, phenol resin, melamine resin, and silicone resin. These thermosetting resins can be used alone or in combination of two or more. Among these, an epoxy resin is preferable because it has little cure shrinkage and is excellent in adhesion to fibers.

  Examples of the epoxy resin include conventional epoxy resins such as glycidyl ether type epoxy resins, glycidyl ester type epoxy resins, alicyclic epoxy resins, glycidyl amine type epoxy resins, and long chain aliphatic epoxy resins. Of these, glycidyl ether type epoxy resins are widely used because they are excellent in adhesiveness and dimensional stability.

Examples of glycidyl ether type epoxy resins include bisphenol type epoxy resins [for example, epoxy resins having a bis (hydroxyphenyl) C _1-10 alkane skeleton such as bisphenol A type, bisphenol F type, and bisphenol AD type epoxy resins, and bisphenol S type epoxy. Resin etc.], novolac type epoxy resin (eg phenol novolak type, cresol novolak type epoxy resin etc.), aliphatic type epoxy resin (eg hydrogenated bisphenol A type epoxy resin, propylene glycol mono to diglycidyl ether, pentaerythritol mono To tetraglycidyl ether), monocyclic epoxy resin (for example, resorcing ricidyl ether), heterocyclic epoxy resin (for example, triglycidyl isocyanurate). And hydantoin type epoxy resin), tetrakis (glycidyloxyphenyl) ethane and the like.

  Examples of the curing agent include amine-based curing agents [for example, aliphatic polyamines (ethylenediamine, diethylenetriamine, triethylenediamine, tetraethylenepentamine, diethylaminopropylamine, hexamethylenediamine, etc.), alicyclic polyamines (isophoronediamine, etc.), Aromatic polyamines (such as xylenediamine)], polyaminoamide-based curing agents (for example, polycondensates of polyethylene polyamines and fatty acids), acid and acid anhydride-based curing agents [for example, aliphatic carboxylic acid anhydrides (dodecenyl anhydride) Succinic acid and the like), alicyclic carboxylic acid anhydrides (such as methyltetrahydrophthalic anhydride), aromatic carboxylic acid anhydrides (such as phthalic anhydride), and the like. These curing agents can be used alone or in combination of two or more. Among these curing agents, amine-based curing agents such as the above-mentioned amine-based curing agents or modified products thereof (epoxy addition products, acrylonitrile addition products, ethylene oxide addition products, Mannich reaction products, Michael reaction products, thiourea reaction products, etc.) Particularly preferred is a modified product of an aliphatic amine-based curing agent.

  The proportion of the curing agent can be selected from the range of about 1 to 100 parts by weight with respect to 100 parts by weight of the epoxy resin, for example, 10 to 90 parts by weight, preferably 20 to 80 parts by weight, more preferably 30 to 70 parts by weight. (Particularly 40 to 60 parts by weight).

  Examples of the fiber include glass fiber, asbestos fiber, carbon fiber, silica fiber, silica / alumina fiber, alumina fiber, zirconia fiber, potassium titanate fiber, Tyranno fiber (Si-Ti-CO-based fiber), silicon carbide Examples thereof include fibers and metal fibers [amorphous metal fibers, stainless fibers, superelastic NT (nickel / titanium) alloy wires, titanium wires, etc.]. Examples of the organic fiber include high-strength polyethylene fiber, polyacetal fiber, aliphatic or aromatic polyamide fiber, polyarylate fiber, fluorine fiber, boron fiber, polyacrylonitrile fiber, aramid fiber, PBO (poly-p-phenylenebenzobisoxazole). ) Fiber and the like. These fibers can be used alone or in combination of two or more.

  Of these fibers, inorganic fibers, particularly carbon fibers, are preferable from the viewpoints of heat resistance and mechanical strength. Carbon fibers can be classified into synthetic polymer-derived carbon fibers (polyacrylonitrile-based, polyvinyl alcohol-based, rayon-based carbon fibers, etc.) and mineral-derived carbon fibers (such as pitch-based carbon fibers), depending on the origin of the raw materials. . Of these, polyacrylonitrile-based carbon fibers and pitch-based carbon fibers are preferable.

  The average diameter of the fibers is, for example, about 0.1 to 100 μm, preferably 0.5 to 50 μm, more preferably about 1 to 30 μm (particularly 1 to 10 μm).

  The fiber may be a long fiber continuously fed from a bobbin using a roving fiber. For example, the average length is 1 to 500 mm, preferably 3 to 200 mm, more preferably 5 to 100 mm (particularly 5 to 50 mm). ) Degree of short fibers.

  In the prepreg (FRP), the ratio of the thermosetting resin is, for example, 1 to 500 parts by weight, preferably 3 to 300 parts by weight, more preferably 5 to 100 parts by weight (particularly 10 to 100 parts by weight) with respect to 100 parts by weight of the fiber. 50 parts by weight).

  As the hot pressing process, a conventional method used in the production of FRP can be used. The heating temperature should just be a temperature which can cure a thermosetting resin, for example, 120-220 degreeC, Preferably it is 130-200 degreeC, More preferably, it is about 150-180 degreeC. In this invention, since the heat resistance of a release film is high, even if it heats at such high temperature, it is excellent in the peelability of a release film and FRP.

  The pressure of the hot press can be selected from the range of, for example, about 0.1 to 10 MPa, for example, 0.1 to 2 MPa, preferably 0.15 to 1.5 MPa, and more preferably 0.2 to 1 MPa (particularly 0.1. 25 to 0.5 MPa). In this invention, since the release property of a release film is high, even if it pressurizes with such a pressure, it is excellent in the peelability of a release film and FRP.

  Furthermore, the hot pressing step may be hot pressed under vacuum, and when the release film of the present invention is used, generation of wrinkles in FRP can be suppressed even when hot pressing is performed under vacuum.

  In the hot pressing step, the prepreg may be used as a single layer or may be used by laminating a plurality of layers.

  The peel strength between the release layer of the release film and the cured prepreg (FRP) is, for example, 0.5 to 10 mN / mm, preferably 0.6 to 5 mN / mm, and more preferably 0.6 to 3 mN / mm. It is about mm. If the peeling strength is too high, the peeling operation becomes difficult, and if it is too low, the workability in the hot press process is lowered.

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. The peelability of the release films obtained in Examples and Comparative Examples was evaluated by the following method.

[Center line average roughness Ra]
In accordance with JIS B0601 (2001), the roughness of the release layer surface of the film was measured using a non-contact surface shape measurement system (“Vert Scan 2.0” manufactured by Ryoka System Co., Ltd.), and the number of measurements n = 5 The average value of was used.

[Peelability]
In the laminate of the release film and CFRP obtained in the examples and comparative examples, the state when the CFRP from the release film was peeled was confirmed and evaluated according to the following criteria.

A: Easily peels off O: The whole is in close contact, but peels off X: The whole is in close contact, and is difficult to peel off.

[Peel strength]
The cured adhesives obtained in the examples and comparative examples were cut to a width of 15 mm, and left at 23 ° C. and 50 RH% for 1 hour or longer, and then the release film side was peeled 180 ° under the conditions of 300 mm / min. .

[Average thickness]
The average thickness of the release layer was calculated from the release layer, the coating amount, and the density.

[Preparation Example of Coating Liquid A]
Methyl paratoluenesulfonate (Wako Pure Chemical Industries, Ltd.) is used as a curing accelerator for 100 parts by weight of a methylated melamine resin (“Super Becamine L-105-60” manufactured by DIC Corporation, solid content 60% by weight). )) 20 parts by weight of a solution prepared by dissolving 7 parts by weight in a mixed solvent of 2.5 parts by weight of methanol and 0.5 parts by weight of triethylamine, and 345 parts by weight of xylene, 160 parts by weight of methanol, and 115 parts by weight of butanol as solvents. Addition and mixing were performed to prepare coating solution A.

[Preparation example of coating liquid B]
To coating solution A, 0.4 parts by weight of silica particles (“EXP3600” manufactured by Evonik Degussa Japan Co., Ltd., particle size 5 μm) was further added and ultrasonically dispersed to prepare coating solution B.

[Example of preparation of coating liquid C]
2 parts by weight of silica particles (EXP3600) was further added to the coating liquid A, and ultrasonic dispersion was performed to prepare a coating liquid C.

[Example of preparation of coating liquid D]
7 parts by weight of methyl paratoluenesulfonate as a curing accelerator, 2 parts by weight of methanol / triethylamine 1 per 100 parts by weight of a butylated melamine resin (“Uban 20SE60” manufactured by Mitsui Chemicals, Inc., solid content 50% by weight) 25 parts by weight of a solution dissolved in parts by weight of a mixed solvent was added, and 220 parts by weight of xylene and 330 parts by weight of butanol were added and mixed as solvents to prepare a coating solution D.

[Example of preparation of coating liquid E]
A cyclic olefin-based resin (“TOPAS 6013S” manufactured by Polyplastics Co., Ltd.) was stirred and dissolved in toluene to prepare a coating liquid E having a solid content concentration of 15%.

[Production Example 1 of Release Film]
A biaxially stretched polyethylene terephthalate film ("Embret S50" manufactured by Unitika Ltd., thickness 50 μm) is used as the base layer of the release film, and coating liquid A is coated on one side of this film by the Mayer bar coating method. Then, it was dried at a temperature of 150 ° C. for 30 seconds to form a release layer having a thickness of 0.3 μm, whereby a release film 1 was obtained.

[Production Example 2 of Release Film]
Except that a polyethylene naphthalate film (manufactured by Teijin DuPont Films Co., Ltd., thickness 50 μm) was used as the base layer of the release film, the release film 2 was prepared in the same manner as in Release Film Production Example 1. Obtained.

[Production Example 3 of Release Film]
A release film 3 was obtained in the same manner as in Release Film Production Example 1 except that the coating liquid B was used and the thickness at the time of coating was 12 μm.

[Production Example 4 of Release Film]
A release film 4 was obtained in the same manner as in Release Film Production Example 1 except that the coating liquid C was used and the thickness at the time of coating was 12 μm.

[Production Example 5 of Release Film]
A release film 5 was obtained in the same manner as in Release Film Production Example 1 except that the coating liquid D was used and the coating liquid was coated so that the thickness of the release layer was 2.5 μm. .

[Production Example 6 of Release Film]
A release film 6 was obtained in the same manner as in Release Film Production Example 2 except that the coating liquid E was used and dried at a temperature of 100 ° C. for 1 minute.

  The properties of the obtained release film are shown in Table 1.

Example 1
A release film 1 and an easy-adhesive biaxially stretched polyester film (manufactured by Toyobo Co., Ltd., Cosmo Shine A4100) were prepared and each cut into 10 cm × 20 cm. Pitch-based CFRP prepreg (manufactured by Nippon Steel Materials Co., Ltd., pitch-based unidirectional carbon fiber reinforced resin, epoxy resin impregnation, curing temperature 130 ° C.) is cut into 7.5 cm × 7.5 cm, and the release layer of the release film The both sides of the prepreg were sandwiched between the side and the easy-adhesion layer side of the polyester film, and hot-pressed at 130 ° C. under a pressure of 0.5 MPa for 2 hours to cure and bond the prepreg to the release layer, and then cooled.

Example 2
Using the release film 2, a polyacrylonitrile (PAN) CFRP prepreg (manufactured by Toray Industries, Inc., epoxy resin impregnation, curing temperature 180 ° C.) is used as a CFRP prepreg at 180 ° C. under a pressure of 1.0 MPa. The prepreg was cured and bonded to the release film in the same manner as in Example 1 except that it was hot-pressed for a period of time.

Examples 3-5
The prepreg was cured and bonded to the release film in the same manner as in Example 1 except that the release films 3 to 5 were used.

Comparative Example 1
The prepreg was cured and bonded to the release film in the same manner as in Example 1 except that the release film 6 was used.

Comparative Examples 2-3
Example except that an olefin film (Unitika Ltd., Unipeel TR1-38, thickness 38 μm) or a polyester release film (Toyobo Co., Ltd., TN100, thickness 38 μm) was used as the release film. In the same manner as in No. 1, the prepreg was cured and bonded to the release film.

  The results of evaluating the peelability of the obtained CFRP are shown in Table 2.

  As is clear from the results in Table 1, the release films of the examples had excellent peelability, whereas the release films of the comparative examples had low peelability.

  The release film of the present invention is used for producing a fiber reinforced plastic (particularly a carbon fiber reinforced epoxy resin).

Claims (10)

A release film comprising a release layer formed of a C _1-4 alkylated melamine-formaldehyde resin and having a center line average roughness Ra of 0.012 to 2 μm on the surface of the release layer.   The release film according to claim 1, further comprising a base material layer, wherein a release layer is formed on at least one surface of the base material layer.   The release film according to claim 2, wherein the release layer has an average thickness of 0.2 to 5 μm and the base layer has an average thickness of 12 to 75 μm.   The release film according to claim 1, wherein the release layer contains fine particles having an average particle diameter of 0.01 to 20 μm.   The release film according to any one of claims 1 to 4, wherein the base material layer is at least one selected from polyester, polyamide, polyimide, polycarbonate, polyethersulfone and cellulose derivatives.   The release film according to any one of claims 1 to 5, wherein the release layer is a layer formed by coating.   The release film according to any one of claims 1 to 6, which is a release film for molding a fiber-reinforced plastic by hot pressing the prepreg in a state of being interposed between the prepreg and the press surface.   Fiber reinforced by hot pressing the prepreg at a temperature of 120 to 220 ° C. and a pressure of 0.1 to 2 MPa with the release film according to claim 1 interposed between the prepreg and the press surface. A method for producing a fiber reinforced plastic including a hot pressing process for molding plastic.   The manufacturing method according to claim 8, wherein the fiber reinforced plastic contains carbon fiber and an epoxy resin.   The manufacturing method according to claim 8 or 9, wherein in the hot pressing step, the hot pressing is performed in a vacuum.