Curable composition, prepreg, fiber-reinforced resin molded article, and method for producing prepreg

Abstract

This invention provides a technology for obtaining a fiber-reinforced resin molded article that is flame-retardant and has excellent strength. [Solution] The curable composition is a curable composition for prepregs containing a thermosetting resin and an amine-based curing accelerator, wherein the thermosetting resin contains an aralkyl cyanate resin and a phenolic resin in a mass ratio of 100:0 to 60:40.

Description

[Technical Field]

[0001] This disclosure relates to a curable composition, a prepreg, a fiber-reinforced resin molded article, and a method for producing a prepreg. [Background technology]

[0002] Fiber-reinforced polymers (CFRP), which use carbon fibers as a reinforcement, are lightweight materials with excellent mechanical properties, making them suitable for parts in automobiles, ships, railways, manned aircraft, unmanned aircraft, and other transportation equipment. Their importance has been increasing in recent years.

[0003] Thermosetting resins are used as the matrix resin in fiber-reinforced resins. One such thermosetting resin is cyanate resin. Cyanate resins crosslink by forming triazine rings through a trimerization reaction of cyanate groups. When fiber-reinforced resins are used in applications such as electronic and electrical equipment, aircraft and railway structures, and building materials, flame retardancy is required because ignition due to heat generation could cause fires.

[0004] A known method for imparting flame retardancy to fiber-reinforced resins involves adding a flame retardant to the matrix resin composition (see Patent Document 1). Furthermore, a method for imparting flame retardancy to fiber-reinforced resins involves making the matrix resin itself flame-retardant (see Patent Document 2). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2009-1768 [Patent Document 2] Japanese Patent Application Publication No. 11-269285 [Overview of the project] [Problems that the invention aims to solve]

[0006] The technology disclosed in Patent Document 1 uses a large amount of ammonium polyphosphate as an inorganic flame retardant, raising concerns about a decrease in the physical properties of the fiber-reinforced resin. Furthermore, the technology disclosed in Patent Document 2 uses a phenolic resin, raising concerns about a decrease in physical properties such as rigidity of the fiber-reinforced resin.

[0007] This disclosure has been made in view of the above circumstances and provides a technology for obtaining a fiber-reinforced resin molded article that is flame-retardant and has excellent strength. This disclosure can be implemented in the following forms: [Means for solving the problem]

[0008] A curable composition for prepregs containing a thermosetting resin and an amine-based curing accelerator, The aforementioned thermosetting resin is A curable composition containing aralkyl cyanate resin and phenolic resin in a mass ratio of 100:0 to 60:40. [Effects of the Invention]

[0009] This disclosure provides a technology for obtaining a fiber-reinforced resin molded article that is flame-retardant and has excellent strength. [Brief explanation of the drawing]

[0010] [Figure 1] This figure schematically shows the prepreg according to this embodiment. [Figure 2] This is a diagram illustrating an example of a prepreg manufacturing method. [Figure 3] This figure schematically shows a fiber-reinforced resin molded product according to this embodiment. [Modes for carrying out the invention]

[0011] Herein lies a preferred example of this disclosure. [1] A curable composition for prepregs containing a thermosetting resin and an amine-based curing accelerator, The aforementioned thermosetting resin is A curable composition containing an aralkyl type cyanate resin and a phenol resin in a mass ratio of 100:0 to 60:40. [2] The curable composition according to [1], wherein the amine-based curing accelerator contains a tertiary amine and a salt of a Bronsted acid. [3] The curable composition according to [1] or [2], wherein the mass ratio of the aralkyl type cyanate resin to the phenol resin is 90:10 to 70:30. [4] A prepreg containing a cured product of the curable composition according to any one of [1] to [3] and a fiber substrate. [5] A fiber reinforced resin molded body containing a cured product of the curable composition according to any one of [1] to [and a fiber substrate. [6] A method for producing a prepreg by heating a fiber substrate together with a thermosetting resin and an amine-based curing accelerator, wherein the thermosetting resin is in a powder state before heating, and contains an aralkyl type cyanate resin and a phenol resin in a mass ratio of 100:0 to 60:40, and the amine-based curing accelerator is in a powder state before heating.

[0012] Hereinafter, the present disclosure will be described in detail. In this specification, for a description using "~" for a numerical range, unless otherwise specified, it includes the lower limit value and the upper limit value. For example, in the description "10~20", both the lower limit value "10" and the upper limit value " are included. That is, "10~20" has the same meaning as "10 or more and 20 or less". Also, in this specification, the upper limit value and the lower limit value of each numerical range can be arbitrarily combined. ​​​​​​​​​​The thermosetting resin contains aralkyl cyanate resin and phenolic resin in a mass ratio of 100:0 to 60:40. The thermosetting resin may contain only aralkyl cyanate resin, or only aralkyl cyanate resin and phenolic resin. Furthermore, the thermosetting resin may further contain thermosetting resins other than aralkyl cyanate resin and phenolic resin (hereinafter also referred to as other thermosetting resins). When other thermosetting resins are included, it is desirable that they are resins that can ensure the flame retardancy of the fiber-reinforced resin molded article. Examples of other thermosetting resins include aralkyl epoxy resin.

[0015] Aralkyl cyanate resins are cyanate resins having an aralkyl skeleton. Cyanate resins are thermosetting resins having cyanate groups (cyanato groups), and are also called cyanate monomers. Before curing, it is preferable that the cyanate resin has an aromatic ring and multiple cyanate groups in one molecule.

[0016] Besides aralkyl cyanate resins, other known cyanate resins include bisphenol A type cyanate resins, novolac type cyanate resins, and resol type cyanate resins. This disclosure was developed based on the new finding that the flame retardancy of fiber-reinforced resin molded articles can be improved by using aralkyl cyanate resins as the cyanate resin. The reason why the flame retardancy can be improved by using aralkyl cyanate resins is not clear, but it is presumed that the presence of an aralkyl skeleton forms a carbonized foam layer on the flame contact surface, and flame retardancy is exhibited due to the foaming heat insulation effect. This disclosure is not intended to be limited to this presumed reason.

[0017] The aralkyl-type cyanate resin is not particularly limited. Preferably, the aralkyl-type cyanate resin is one or more selected from the group consisting of, for example, cyanate resins having a naphtholphenylaralkyl skeleton, cyanate resins having a binaphtholphenylaralkyl skeleton, cyanate resins having a phenolbiphenylaralkyl skeleton, and cyanate resins having a phenolphenylaralkyl skeleton. The aralkyl-type cyanate resin may be one type or two or more types.

[0018] An example of a cyanate resin having a naphthol phenylaralkyl skeleton is the cyanate resin represented by the following formula (1). [ka] (In formula (1), R 1 Each of these independently represents either a hydrogen atom or a methyl group, and n represents an integer of 1 or more.

[0019] In the above equation (1), R 1 Each of these independently represents either a hydrogen atom or a methyl group, with hydrogen atoms being preferred. In formula (1) above, n represents an integer of 1 or more, and the upper limit of n is usually 10, preferably 7, and more preferably 6.

[0020] An example of a cyanate resin having a binaphthol phenylaralkyl skeleton is the cyanate resin represented by the following formula (2). [ka] (In formula (2), R 2 Each of these independently represents either a hydrogen atom or a methyl group, and n represents an integer of 1 or more.

[0021] In equation (2) above, R 2 Each of these independently represents either a hydrogen atom or a methyl group, with hydrogen atoms being preferred. In formula (2) above, n is an integer of 1 or more, and the upper limit of n is usually 10, preferably 7, and more preferably 6.

[0022] A cyanate resin having a phenol biphenyl aralkyl skeleton is, for example, a cyanate resin represented by the following formula (3). [ka] (In formula (3), R 3 Each of these independently represents either a hydrogen atom or a methyl group, and n represents an integer of 1 or more.

[0023] In equation (3) above, R 3 Each of these independently represents either a hydrogen atom or a methyl group, with hydrogen atoms being preferred. In formula (3) above, n is an integer of 1 or more, and the upper limit of n is usually 10, preferably 7.

[0024] A cyanate resin having a phenolphenylaralkyl skeleton is, for example, a cyanate resin represented by the following formula (4). [ka] (In formula (4), R 4 Each of these independently represents either a hydrogen atom or a methyl group, and n represents an integer of 1 or more.

[0025] In the above equation (4), R 4 Each of these independently represents either a hydrogen atom or a methyl group, with hydrogen atoms being preferred. In formula (4) above, n represents an integer of 1 or more, and the upper limit of n is usually 10, preferably 7.

[0026] The physical properties of the aralkyl cyanate resin are not particularly limited. The melting point of the aralkyl cyanate resin is preferably 70°C to 110°C, more preferably 75°C to 105°C, and even more preferably 80°C to 100°C.

[0027] Thermosetting products of aralkyl cyanate resins generally have higher rigidity than thermosetting products of phenolic resins, etc. By appropriately adding phenolic resin to the curable composition, the rigidity of fiber-reinforced resin molded articles can be adjusted according to the application. Phenolic resin is said to be flame-retardant, although it is not self-extinguishing. By blending phenolic resin with aralkyl cyanate resin, flame retardancy can be achieved while maintaining a certain level of rigidity. Furthermore, the use of phenolic resin is advantageous in terms of cost.

[0028] The phenolic resin is not particularly limited. Phenolic resins include, for example, novolac type and resol type, with the novolac type being preferable. Furthermore, novolac type powdered phenolic resin is preferred. The physical properties of the phenolic resin are not particularly limited. The melting point of the phenolic resin is preferably 80°C to 100°C.

[0029] The mass ratio of aralkyl-type cyanate resin to phenolic resin is 100:0 to 60:40, preferably 97:3 to 60:40, more preferably 95:5 to 65:45, and even more preferably 90:10 to 70:30.

[0030] The total amount of aralkyl cyanate resin and phenolic resin is preferably 60 parts by mass or more, more preferably 70 parts by mass or more, even more preferably 80 parts by mass or more, and particularly preferably 90 parts by mass or more, when the total amount of thermosetting resin is 100 parts by mass. The upper limit of the total amount of aralkyl cyanate resin and phenolic resin is, for example, 100 parts by mass.

[0031] The state of the thermosetting resin is not particularly limited. From the viewpoint of storage stability, the thermosetting resin is preferably solid at 25°C and 1 atm. The thermosetting resin is preferably in powder form. When the thermosetting resin is in powder form, the median diameter (particle size relative to 50% of the cumulative distribution) of the thermosetting resin is preferably 10 μm to 1000 μm, more preferably 100 μm to 800 μm, and even more preferably 400 μm to 600 μm, from the viewpoint of workability and ease of melting during prepreg preparation.

[0032] (2) Amine-based curing accelerators The amine-based curing accelerator is not particularly limited, and for example, one or more compounds selected from the group consisting of amine compounds having primary to tertiary amines and quaternary ammonium compounds can be used as appropriate. The amine-based curing accelerator may be just one type or two or more types.

[0033] The amine-based curing accelerator preferably contains a salt of a tertiary amine and a Brønsted acid. By including the tertiary amine as a neutralized salt of the Brønsted acid, the curing-promoting activity of the tertiary amine can be suitably controlled. For example, it may exhibit so-called latent properties, such as having low activity at room temperature (usually 20°C-35°C) and accelerating the curing of thermosetting resins only when heated.

[0034] The tertiary amine is not particularly limited. Examples of the tertiary amine include the amine represented by Chemical Formula (11) {1,8-diazabicyclo[5,4,0]-undecene-7 (DBU; "DBU" is a registered trademark of San Apro Limited)}, the amine represented by Chemical Formula (12) {1,5-diazabicyclo[4,3,0]-nonene-5 (DBN)}, the amine represented by Chemical Formula (13) {for example, cyclic amines such as 1-azabicyclo[2.2.2]octane, 3-hydroxy-1-azabicyclo[2.2.2]octane, and 1,4-diazabicyclo[2.2.2]octane, and trialkylamines (such as tributylamine, trioctylamine, octyldimethylamine, and diisopropylethylamine), trialkenylamines (such as triallylamine), and triarylamines (such as triphenylamine, tri-p-tolylamine, and diphenyl-p-tolylamine)}, and the amine represented by Chemical Formula (14) {for example, 1-methylimidazole, 1,2-dimethylimidazole, 1-methyl-2-ethylimidazole, etc.}. Among these, the tertiary amine is preferably a heterocyclic tertiary amine. More preferably, it is the amine represented by Chemical Formula (11) (l,8-diazabicyclo[5,4,0]-undecene-7).

[0035]

Chem.

[0036] The Brønsted acid is not particularly limited, as long as it forms a salt with the tertiary amine described above. Preferably, the Brønsted acid is one or more selected from the group consisting of, for example, phenol novolac resin, trimellitic acid, phenol resin, phenol, 2-ethylhexanoic acid, formic acid, o-phthalic acid, and p-toluenesulfonic acid. Among these, the Brønsted acid is more preferably a phenol novolac resin.

[0037] The amine-based curing accelerator may be, for example, a thermobase generator. Examples of commercially available thermobase generators include U-CAT SA-1, U-CAT SA-102, U-CAT SA-506, U-CAT SA-603, U-CAT SA-810, U-CAT SA-841, U-CAT SA-851, and U-CAT SA-838A, all manufactured by Sunapro Co., Ltd.

[0038] The activity temperature of the amine-based curing accelerator is not particularly limited. The activity temperature of the amine-based curing accelerator is preferably above the melting start temperature of the thermosetting resin and below the curing reaction start temperature of the thermosetting resin. From the viewpoint of storage stability, the activity temperature of the amine-based curing accelerator is preferably 100°C or higher, more preferably 110°C or higher, and even more preferably 120°C or higher. From the viewpoint of reactivity during molding, the activity temperature of the amine-based curing accelerator is preferably 160°C or lower, more preferably 150°C or lower, and even more preferably 140°C or lower. From these viewpoints, the activity temperature of the amine-based curing accelerator is preferably 100°C to 160°C, more preferably 110°C to 150°C, and even more preferably 120°C to 140°C.

[0039] The amount of amine-based curing accelerator is not particularly limited. From the viewpoint of reactivity during molding, the amount of amine-based curing accelerator is preferably 0.1 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 0.8 parts by mass or more, per 100 parts by mass of thermosetting resin. From the viewpoint of optimizing the reaction rate, the physical properties of the matrix resin, and cost, the amount of amine-based curing accelerator is preferably 8 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less. From these viewpoints, the amount of amine-based curing accelerator is preferably 0.1 parts by mass or more and 8 parts by mass or less, more preferably 0.5 parts by mass or more and 5 parts by mass or less, and even more preferably 0.8 parts by mass or more and 3 parts by mass or less.

[0040] The state of the amine-based curing accelerator is not particularly limited. From the viewpoint of workability during prepreg preparation, the amine-based curing accelerator is preferably solid at 25°C and 1 atm. The amine-based curing accelerator is preferably in powder form.

[0041] (3) Other ingredients Various additives such as flame retardants, pigments, antibacterial agents, and ultraviolet absorbers may be added to the curable composition, as long as they do not affect its physical properties. Since flame retardancy is ensured by the thermosetting resin, the curable composition does not need to contain a flame retardant, and even if it does contain one, the amount added can be reduced.

[0042] For example, non-halogen flame retardants and halogen flame retardants can be used as appropriate. Because they have low toxicity to the environment and human health and excellent flame retardancy, phosphorus-based flame retardants are preferred. Examples of phosphorus-based flame retardants include polyphosphates, phosphate ester compounds, condensed phosphate ester compounds, and red phosphorus compounds. From the viewpoint of ensuring various physical properties, the amount of flame retardant added is preferably 12 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 5 parts by mass or less, per 100 parts by mass of thermosetting resin. The lower limit of the amount of flame retardant added may be 0 parts by mass or 1 part by mass or more.

[0043] 2. Prepreg (1) Prepreg composition The prepreg of this embodiment includes the curable composition described in section "1. Curable Composition" and a fibrous substrate. The prepreg can be obtained by impregnating the fibrous substrate with the curable composition. The prepreg is used as an intermediate material (precursor) for the manufacture of fiber-reinforced resin molded articles. An example of a prepreg is shown in Figure 1. The prepreg 10 shown in Figure 1 is formed by heating and compressing a fibrous substrate 11 together with a curable composition 15, so that the curable composition 15 is impregnated into the fibrous substrate 11. The curable composition 15 impregnated into the fibrous substrate 11 is in a solid state before the curing reaction of the thermosetting resin begins. Note that the curable composition 15 does not necessarily need to be uniformly impregnated into the interior of the fibrous substrate 11; for example, it may be fixed to the surface of the fibrous substrate 11.

[0044] In the prepreg 10 shown in Figure 1, the fiber base material 11 consists of one layer, but the prepreg may be composed of multiple layers. The fiber base material 11 is not particularly limited. Examples of fiber base material 11 include woven fabrics and nonwoven fabrics made of glass fibers, aramid fibers, basalt fibers, carbon fibers, etc. Carbon fiber woven fabrics are preferred because they are lightweight and have excellent rigidity. Suitable carbon fiber woven fabrics include plain weave, twill weave, satin weave, and triaxial weave, which are composed of warp and weft threads. Furthermore, in terms of impregnation of the curable composition and the rigidity of the fiber-reinforced resin molded body, the fiber weight of the carbon fiber woven fabric should be 50 g / m². 2 ~600g / m 2 Those that are preferable.

[0045] The shape of the curable composition 15 is not particularly limited. Preferably, the shape of the curable composition 15 is a solid powder before heating in the production of the prepreg 10. Examples of specific powder shapes include spherical, needle-shaped, and flake-shaped.

[0046] (2) Method for manufacturing prepregs The method for producing the prepreg according to this embodiment is, for example, a method for producing a prepreg in which a fibrous substrate is heated together with a thermosetting resin and an amine-based curing accelerator. The thermosetting resin is preferably in powder form before heating and contains aralkyl cyanate resin and phenol resin in a mass ratio of 100:0 to 60:40. The amine-based curing accelerator is preferably in powder form before heating.

[0047] An example of a prepreg manufacturing method will be described with reference to Figure 2. In the manufacturing method of the prepreg 10, a fiber base material 11 and a curable composition 15 placed in contact with the fiber base material 11 are sandwiched between release plastic films 17, 17, and then heated and compressed by sandwiching them between the upper mold 51 and lower mold 52 of a heated mold 50. At this time, the curable composition 15 is placed on one or both of the upper and lower surfaces of the fiber base material 11.

[0048] The amount of curable composition is preferably adjusted so that the VF value (%) of the fiber-reinforced resin molded article obtained from the prepreg is between 40% and 75%. The VF value (%) is calculated as (total weight of the fiber substrate / density of the fibers) / (volume of the fiber-reinforced resin molded article) × 100.

[0049] The heating temperature during prepreg production is above the melting start temperature of the curable composition and below the curing reaction start temperature. More preferably, the heating temperature is above the melting start temperature of the thermosetting resin + 5°C and below the curing reaction start temperature - 5°C. More specifically, the heating temperature during prepreg production can be, for example, 80°C to 120°C or 90°C to 110°C. The above heating temperature can be controlled, for example, by adjusting the temperature of the mold 50. The mold 50 is heated by a heating means such as an electric heater.

[0050] During prepreg manufacturing, the curable composition 15 may be pressurized (compressed) after melting to ensure good impregnation of the fibrous substrate 11. The pressure during prepreg manufacturing can be, for example, 0.5 MPa to 2 MPa. However, pressurization (compression) during prepreg manufacturing is not required. The curable composition 15 melts upon heating and compression, impregnates the fibrous substrate 11, and solidifies upon cooling in the state before the curing reaction begins. In this solidified state, the thermosetting resin has not undergone the curing reaction and is uncured. The method for manufacturing the prepreg is not limited to the method using the mold described above, but may also be other methods such as the hot roller method, which heats and compresses with a hot roller, the double belt method, which heats and compresses between upper and lower belts, or the method using a conveyor oven. In the method using a conveyor oven, for example, a solid powder-like curable composition 15 is sprinkled onto a fibrous base material 11 such as a carbon fiber fabric, and the curable composition 15 is melted and impregnated by passing it through a conveyor oven with hot air at a predetermined temperature (e.g., 90°C or higher) for a predetermined time (e.g., 60 seconds to 300 seconds).

[0051] 3. Fiber-reinforced resin molded body (1) Structure of fiber-reinforced resin molded body The fiber-reinforced resin molded article of this disclosure includes a cured product of the curable composition described in section "1. Curable Composition" and a fiber substrate. The fiber substrate 11 is integrated with the thermosetting resin of the curable composition 15. The curable composition and the fiber base material 11 are described as follows in "1. Curable Composition" and "2. Prepreg". The fiber base material 11 may be a single layer or multiple layers, and the number of layers is determined according to the application of the fiber-reinforced resin molded article.

[0052] (2) Physical properties of fiber-reinforced resin molded articles (2.1) Flame retardant When the fiber-reinforced resin molded article is subjected to the following combustion test, it is preferable that the vertical combustion evaluation is "A" or "B", and more preferably "A". Furthermore, when the fiber-reinforced resin molded article is subjected to the following combustion test, it is preferable that the cotton does not ignite due to dripping caused by combustion. [Combustion test] The combustion test was conducted using the UL-94 V method as a reference. A strip-shaped test specimen, 15 mm wide and 100 mm long, was held vertically by securing one end of the specimen with a clip. A flame was then applied to the specimen from the other end at the bottom for 10 seconds, after which the flame was removed and the combustion behavior was observed. The number of tests (n) was 5. In the vertical combustion evaluation, an "A" was given if all five test pieces showed self-extinguishing properties, a "B" was given if the flame reached the clipped end face of 1 to 4 of the five test pieces, and a "C" was given if the flame reached the clipped end face of all five test pieces. The drip evaluation involved placing cotton at the bottom of the test specimen and checking whether the cotton ignited due to the drip caused by combustion.

[0053] (2.2) Bending strength The flexural strength (JIS K7074 Method A) of a fiber-reinforced resin molded article is not particularly limited. From the viewpoint of achieving high strength, the flexural strength of a fiber-reinforced resin molded article is preferably 700 MPa or higher, more preferably 800 MPa or higher, and even more preferably 900 MPa or higher at a measurement ambient temperature of 23°C. While a higher flexural strength is desirable, it is usually 1500 MPa or lower.

[0054] (2.3) Storage stability with respect to bending strength When the following storage performance evaluation test is performed on the fiber-reinforced resin molded article, it is preferable that the rate of change in flexural strength is less than 10%, and more preferably less than 5%. [Storage performance evaluation test] After allowing the prepreg to stand for 3 months at 23°C and 50% humidity, a fiber-reinforced resin molded article is prepared, and the flexural strength σ1 of the fiber-reinforced resin molded article is measured in accordance with JIS K7074 Method A. Immediately after preparing the prepreg, i.e., without allowing it to stand, a fiber-reinforced resin molded article is prepared, and the flexural strength σ0 of the fiber-reinforced resin molded article is measured in accordance with JIS K7074 Method A. The rate of change (%) of the flexural strength is calculated based on the following formula. Change in bending strength (%) = (|σ1-σ0| / σ0) × 100

[0055] (2.4) Flexural modulus The flexural modulus (JIS K7074 Method A) of a fiber-reinforced resin molded article is not particularly limited. From the viewpoint of achieving high rigidity, the flexural modulus of a fiber-reinforced resin molded article is preferably 50 GPa or higher, and more preferably 55 GPa or higher, at a measurement ambient temperature of 23°C. A higher flexural modulus is desirable, but it is usually 100 GPa or lower.

[0056] (2.5) Storage stability with respect to flexural modulus When the following storage performance evaluation test is performed on the fiber-reinforced resin molded article, it is preferable that the rate of change in the flexural modulus is less than 10%, and more preferably less than 5%. [Storage performance evaluation test] After allowing the prepreg to stand for 3 months at 23°C and 50% humidity, a fiber-reinforced resin molded article is prepared, and the flexural modulus E1 of the fiber-reinforced resin molded article is measured in accordance with JIS K7074 Method A. Immediately after preparing the prepreg, i.e., without allowing it to stand, a fiber-reinforced resin molded article is prepared, and the flexural modulus E0 of the fiber-reinforced resin molded article is measured in accordance with JIS K7074 Method A. The rate of change (%) of the flexural modulus is calculated based on the following formula. Change in flexural modulus (%) = (|E1 - E0| / E0) × 100

[0057] (3) Method for manufacturing fiber-reinforced resin molded articles The method for manufacturing the fiber-reinforced resin molded article of this embodiment involves, for example, heating the prepreg obtained by the method described in "(2) Method for manufacturing prepreg" in the "2. Prepreg" section at a predetermined temperature to cure the thermosetting resin. A fiber-reinforced resin molded body can also be manufactured, for example, by heating and compressing a curable composition 15 in contact with a fiber substrate 11 using a mold, thereby impregnating the fiber substrate 11 with a thermosetting resin and allowing it to harden.

[0058] The heating temperature during the production of the fiber-reinforced resin molded article is equal to or higher than the curing reaction initiation temperature of the curable composition 15. More preferably, the heating temperature is 5°C or higher than the curing reaction initiation temperature of the curable composition 15. The upper limit of the heating temperature is not particularly limited and may be 200°C or lower, 190°C or lower, 180°C or lower, 170°C or lower, or 160°C or lower. More specifically, the heating temperature during the production of the fiber-reinforced resin molded article may be, for example, 120°C or higher and 200°C or lower, or 140°C or higher and 200°C or lower. The above heating temperature can be controlled, for example, by adjusting the temperature of the mold. The mold is heated by a heating means such as an electric heater.

[0059] 4. Effects of this embodiment This embodiment provides a technology for obtaining a fiber-reinforced resin molded article that is flame-retardant and has excellent strength. For example, a curable composition using a bisphenol A type cyanate resin as the thermosetting resin may result in a fiber-reinforced molded article that is easily flammable. Furthermore, if the amount of flame retardant in the curable composition is excessively increased to enhance the flame retardancy of the fiber-reinforced resin molded article, a problem may arise in which the strength of the fiber-reinforced resin molded article decreases. On the other hand, this embodiment uses an aralkyl type cyanate resin and a phenol resin in a predetermined mass ratio as the thermosetting resin, and also uses an amine-based curing accelerator, thereby enhancing flame retardancy and suppressing deterioration of various physical properties caused by the addition of flame retardants. Furthermore, this embodiment offers excellent storage stability for the prepreg, thus suppressing deterioration of various physical properties in the fiber-reinforced resin molded article obtained by heat-curing the prepreg after long-term storage. [Examples]

[0060] 1.Curable composition (1) Preparation of curable composition Curable compositions for Examples 1 to 3 and Comparative Examples 1 to 6 were prepared by blending thermosetting resins and amine-based curing accelerators in the proportions shown in Table 1. Details of the raw materials are as follows. • Cyanate resin A (manufactured by Mitsubishi Gas Chemical Company, Inc., Cytester TA): Bisphenol A type cyanate resin, flake-type solid with a melting point of 80°C. • Cyanate resin B (manufactured by Mitsubishi Gas Chemical Company, Inc., Cytester N-CN): Aralkyl type cyanate resin, massive solid with a melting point of 90°C. • Epoxy resin (manufactured by Mitsubishi Chemical Corporation, jER1001): Bisphenol A type epoxy resin, molecular weight 900, epoxy equivalent 475 g / eq., softening point 65°C, flake-like solid. • Phenolic resin A (manufactured by Sumitomo Bakelite Co., Ltd., Sumilite Resin PR-50235D): Novolac-type phenolic resin, flake-type solid • Phenolic resin B (manufactured by Sumitomo Bakelite Co., Ltd., Sumilite Resin PR-55791B): Resol-type phenolic resin, ethanol-diluted liquid with a solid content concentration of 60 wt%. • Flame retardant (EXOLIT AP 462, manufactured by Clariant Japan Co., Ltd.): Ammonium polyphosphate with a melamine-coated surface, phosphorus content 30%, nitrogen content 16% • Amine-based curing accelerator (manufactured by Sunapro Co., Ltd., U-CAT SA-841): 1,8-diazabicyclo[5.4.0]-7-undecene phenol novolac resin salt Furthermore, amine-based curing accelerators include "salts of tertiary amines and Brønsted acids."

[0061] 2. Preparation of prepregs and fiber-reinforced resin molded articles (1) Examples 1-3, Comparative Examples 1-5 A thermosetting resin, which had been pulverized to have a median diameter of approximately 500 μm, and a reaction accelerator were weighed and mixed in the ratios shown in Table 1 to obtain a mixed powder.

[0062] As a fiber base material, carbon fiber fabric (manufactured by Teijin Limited, Tenax W-3161 3K twill weave, basis weight 200g / m) 2A carbon fiber fabric (0.25 mm thick) was prepared. The resulting mixed powder was evenly sprinkled onto a carbon fiber fabric cut to 250 mm x 200 mm, and another carbon fiber fabric was placed on top. After hot pressing under the conditions shown in Table 1, it was removed from the hot press and allowed to cool naturally to obtain an intermediate prepreg (two carbon fiber fabrics laminated in the thickness direction). Note that the coating amounts shown in the table represent the values ​​per carbon fiber fabric. In other words, in the case of a prepreg using two carbon fiber fabrics, the entire prepreg is coated with twice the coating amount shown in the table.

[0063] Two prepregs were laminated together and hot-pressed under the conditions shown in the table to obtain a fiber-reinforced resin molded body (with four layers of carbon fiber fabric laminated in the thickness direction). After the fiber-reinforced resin molded body cooled to room temperature, strip-shaped test pieces measuring 15 mm wide x 100 mm long were cut out.

[0064] (2) Comparative Example 6 As a fiber base material, carbon fiber fabric (manufactured by Teijin Limited, Tenax W-3161 3K twill weave, basis weight 200g / m) 2 A carbon fiber fabric (0.25 mm thick) was prepared. The carbon fiber fabric, cut to 250 mm x 200 mm, was immersed in phenolic resin B, and after removal, it was air-dried at 25°C for 2 hours to obtain resin-impregnated carbon fiber fabric.

[0065] A thermosetting resin foam sheet (manufactured by Inoac Corporation, Malt Filter MF-50, 0.4 mm thick) was laminated to this to create a prepreg.

[0066] The prepared prepregs were laminated and hot-pressed under the conditions shown in Table 1 to obtain a fiber-reinforced resin molded body (with four layers of carbon fiber fabric laminated in the thickness direction). After the fiber-reinforced resin molded body was cooled to room temperature, strip-shaped test pieces measuring 15 mm in width and 100 mm in length were cut out.

[0067] 3. Evaluation of fiber-reinforced resin molded products (1) Bending strength, bending modulus In accordance with JIS K 7074, a three-point bending test was performed on a strip-shaped test specimen measuring 15 mm in width and 100 mm in length, with a crosshead speed of 5 mm / min and a support distance of 30 mm. Bending strength was categorized as follows: "A" for measured values ​​of 900 MPa or higher, "B" for values ​​between 700 MPa and 900 MPa, and "C" for values ​​below 700 MPa. The bending modulus was categorized as follows: "A" for measured values ​​of 55 GPa or higher, "B" for values ​​between 50 GPa and 55 GPa, and "C" for values ​​below 50 GPa. The prepreg was left to stand for 3 months at 23°C and 50% humidity, then thermoset. The bending strength and bending modulus were measured, and the rate of change was calculated based on the measured values ​​without standing. For storage performance evaluations related to bending strength and bending modulus, a change rate of less than 5.0% was classified as "A," a change rate of 5.0% or more but less than 10.0% was classified as "B," and a change rate of 10.0% or more was classified as "C."

[0068] (2) Combustion test Following the UL-94 V method, a strip-shaped test specimen measuring 15 mm in width and 100 mm in length is held vertically by fixing one end face of the specimen with a clip, and the other end face of the lower part of the specimen... After exposing the test specimen to the flame for 10 seconds, the flame was removed from the specimen and the combustion behavior was observed. The number of tests (n) was set to 5. In the vertical combustion evaluation, an "A" was given if all five test pieces showed self-extinguishing properties, a "B" was given if the flame reached the clipped end face of 1 to 4 of the five test pieces, and a "C" was given if the flame reached the clipped end face of all five test pieces. The drip evaluation involved placing cotton at the bottom of the test specimen and checking whether the cotton ignited due to the drip caused by combustion.

[0069] [Table 1]

[0070] 5.Results The results of each evaluation are listed in Table 1. Examples 1 to 3 satisfy the following requirements (a) and (b). In contrast, Comparative Examples 1 to 5 do not satisfy requirement (b). Comparative Example 6 does not satisfy requirements (a) and (b). • Requirement (a): A curable composition for prepregs containing a thermosetting resin and an amine-based curing accelerator. • Requirement (b): The thermosetting resin contains aralkyl cyanate resin and phenolic resin in a mass ratio of 100:0 to 60:40.

[0071] Examples 1 to 3, which satisfy requirements (a) and (b), had a vertical combustion evaluation of "A" and no drip during combustion. In addition, Examples 1 to 3 had a bending strength evaluation of "A" and a bending modulus evaluation of "A".

[0072] Furthermore, Examples 1 to 3 received a storage performance evaluation of "A" or "B" for both flexural strength and flexural modulus. Examples 1 to 3 were able to obtain prepregs with excellent storage stability, and the decrease in strength of the fiber-reinforced resin molded article obtained by thermosetting the prepreg after long-term storage was suppressed.

[0073] Comparative Examples 1 to 4 are examples in which bisphenol A type cyanate resin was used instead of aralkyl type cyanate resin. Although Comparative Examples 1 to 4 showed "no" drip during combustion, their vertical combustion evaluation was "C". Comparative Examples 1 to 4 did not possess sufficient flame retardancy.

[0074] Comparative Example 5 is an example of using a bisphenol A type cyanate resin in combination with a flame retardant. Comparative Example 5 received a vertical combustion evaluation of "B" and showed "no" drip during combustion, but its flexural strength evaluation was "C" and its flexural modulus evaluation was "C". Comparative Example 5 did not have sufficient strength.

[0075] Comparative Example 6 is an example in which only phenolic resin was used as the thermosetting resin. Comparative Example 6 received an "A" rating for vertical combustion and showed "no" drip during combustion, but its flexural strength was rated "B" and its flexural modulus was rated "C". Comparative Example 6 did not possess sufficient strength. Furthermore, Comparative Example 6 received a "C" rating for storage performance in terms of flexural strength and a "C" rating for storage performance in terms of flexural modulus. Comparative Example 6 also had inferior storage stability.

[0076] 6. Effects of the Examples Examples 1 to 3 demonstrated that we were able to obtain fiber-reinforced resin molded articles that were flame-retardant and had excellent strength.

[0077] This disclosure is not limited to the embodiments detailed above, and various modifications or alterations are possible. [Explanation of Symbols]

[0078] 10…Prepreg 11… Fiber base material 15...Curable composition 17…Release plastic film 20…Fiber-reinforced resin molded body 50…Mold 51…Upper mold 52…Lower mold

Claims

1. A curable composition for prepregs containing a thermosetting resin and an amine-based curing accelerator, The aforementioned thermosetting resin is A curable composition containing aralkyl cyanate resin and phenolic resin in a mass ratio of 100:0 to 60:

40.

2. The curable composition according to claim 1, wherein the amine-based curing accelerator comprises a salt of a tertiary amine and a Brønsted acid.

3. The curable composition according to claim 1 or claim 2, wherein the mass ratio of the aralkyl-type cyanate resin to the phenolic resin is 90:10 to 70:

30.

4. A prepreg comprising the curable composition according to claim 1 or claim 2, and a fibrous substrate.

5. A fiber-reinforced resin molded article comprising a cured product of the curable composition according to claim 1 or claim 2, and a fiber substrate.

6. A method for producing a prepreg, comprising heating a fibrous substrate together with a thermosetting resin and an amine-based curing accelerator, The thermosetting resin is in powder form before heating and contains aralkyl cyanate resin and phenol resin in a mass ratio of 100:0 to 60:

40. The amine-based curing accelerator is in powder form before heating, and this is a method for producing a prepreg.

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