Epoxy resin composition and method for producing prepreg

Abstract

To provide an epoxy resin composition suitable for a matrix resin of a prepreg, particularly a matrix resin of a sheet molding compound.SOLUTION: An epoxy resin composition contains an epoxy resin component, a diisocyanate component, a polycarbonate diol component and an epoxy resin curing agent component, with its room-temperature viscosity being, for example, 0.1 Pa s or more and 50 Pa s or less. When held at 23°C, the epoxy resin composition reaches a viscous state, preferably, in one day or longer and 30 days or shorter. In the viscous state, its viscosity is, for example, 1000 Pa s or more and less than 100000 Pa s.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention primarily relates to an epoxy resin composition and a method for producing a prepreg. [Background technology]

[0002] One method for manufacturing fiber-reinforced plastic articles is to use prepregs such as sheet molding compounds (SMCs), which are intermediate materials made by pre-impregnating fiber reinforcement with a matrix resin. Epoxy resin compositions for use as matrix resins in sheet molding compounds are known, which contain polyols and polyisocyanates to thicken the resin after impregnation with fiber reinforcement materials (Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Unexamined Patent Publication No. 58-191723 [Patent Document 2] Japanese Patent Application Publication No. 4-88011 Summary of the Invention [Problem to be solved by the invention]

[0004] The main object of the present invention is to provide an epoxy resin composition suitable as a matrix resin for prepregs, particularly for sheet molding compounds, and to provide a method for producing prepregs containing sheet molding compounds using the epoxy resin composition. [Means for solving the problem]

[0005] Embodiments of the present invention include the following. [1] An epoxy resin composition containing an epoxy resin component, a diisocyanate component, a polycarbonate diol component, and an epoxy resin curing agent component. [2] The epoxy resin composition according to [1], which has a room temperature viscosity of 50 Pa·s or less. [3] The epoxy resin composition according to [2], which has a room temperature viscosity of 0.1 Pa·s or more. [4] The epoxy resin composition according to any one of [1] to [3], which reaches a thickened state in 1 day or more and 30 days or less when kept at 23°C. [5] The epoxy resin composition according to any one of [1] to [3], wherein the room temperature viscosity in a thickened state is 1,000 Pa·s or more and less than 2,000 Pa·s, 2,000 Pa·s or more and less than 3,000 Pa·s, 3,000 Pa·s or more and less than 4,000 Pa·s, 4,000 Pa·s or more and less than 5,000 Pa·s, 5,000 Pa·s or more and less than 6,000 Pa·s, 6,000 Pa·s or more and less than 8,000 Pa·s, 8,000 Pa·s or more and less than 10,000 Pa·s, 10,000 Pa·s or more and less than 15,000 Pa·s, 15,000 Pa·s or more and less than 20,000 Pa·s, 20,000 Pa·s or more and less than 50,000 Pa·s, or 50,000 Pa·s or more and less than 100,000 Pa·s. [6] The epoxy resin composition according to any one of [1] to [5], wherein the amount of the epoxy resin component blended is 50 wt % or more of the total amount of the epoxy resin composition. [7] The epoxy resin composition according to any one of [1] to [6], wherein the amount of the diisocyanate component is 8 parts by weight or more per 100 parts by weight of the epoxy resin component. [8] The epoxy resin composition according to any one of [1] to [7], wherein the ratio of the number of moles of the polycarbonate diol component to the number of moles of the diisocyanate component is 0.1 or more. [9] The epoxy resin composition according to [8], wherein the ratio of the number of moles of the polycarbonate diol component to the number of moles of the diisocyanate component is 1 or less.

[10] The epoxy resin composition according to any one of [1] to [9], wherein the number average molecular weight of the polycarbonate diol component is 500 or more and 5,000 or less.

[11] The epoxy resin composition according to any one of [1] to

[10] , wherein bis(4-isocyanatophenyl)methane is blended as the diisocyanate component.

[12] The epoxy resin composition according to any one of [1] to

[11] , wherein toluene diisocyanate is blended as the diisocyanate component.

[13] The epoxy resin composition according to any one of [1] to

[12] , wherein the polycarbonate diol component is a polycarbonate diol having a 1,4-butanediol residue, a 1,5-pentanediol residue, a 3-methyl-1,5-pentanediol residue, or a 1,6-hexanediol residue.

[14] The epoxy resin composition according to any one of [1] to

[13] , wherein the polycarbonate diol component is a polycarbonate diol having an isosorbide residue, a neopentyl glycol residue, a cyclohexanediol residue, or a cyclohexanedimethanol residue.

[15] The epoxy resin composition according to any one of [1] to

[14] , wherein a bisphenol-type epoxy resin is blended as the epoxy resin component.

[16] The epoxy resin composition according to any one of [1] to

[15] , wherein the epoxy resin curing agent component is one or more epoxy resin curing agents selected from imidazoles and dicyandiamide.

[17] The epoxy resin composition according to any one of [1] to

[16] , wherein either one or both of an organophosphorus flame retardant and a nitrogen-based flame retardant are blended.

[18] A method for producing a prepreg, comprising impregnating a fiber reinforcement material with the epoxy resin composition according to any one of [1] to

[16] .

[19] The method according to

[18] , wherein the temperature of the epoxy resin composition during the impregnation is 80°C or lower.

[20] The method according to

[18] or

[19] , wherein the impregnation is carried out indoors at an air temperature of 17°C or higher and 28°C or lower without heating the epoxy resin composition.

[21] The method according to any one of

[18] to

[20] , wherein the epoxy resin composition is thickened after the impregnation.

[22] The manufacturing method according to any one of

[18] to

[21] , wherein the prepreg is a sheet molding compound. [Effects of the Invention]

[0006] According to a preferred embodiment of the present invention, there is provided an epoxy resin composition suitable as a matrix resin for prepregs, particularly as a matrix resin for sheet molding compounds. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram showing a sheet molding compound manufacturing apparatus. [Figure 2] FIG. 2 is a graph showing the relationship between the amount of diisocyanate in an epoxy resin composition and the viscosity at room temperature after the composition has reached a thickened state. [Figure 3] FIG. 3 is a graph in which the ratio of the room temperature viscosity 5 days after preparation (before the thickened state was reached) to the room temperature viscosity 14 days after preparation (after the thickened state was reached) is plotted against the molar ratio of polycarbonate diol and diisocyanate blended in the epoxy resin composition. DETAILED DESCRIPTION OF THE INVENTION

[0008] 1. Epoxy resin composition One embodiment of the present invention relates to an epoxy resin composition. The epoxy resin composition according to the embodiment contains an epoxy resin component, a diisocyanate component, a polycarbonate diol component, and an epoxy resin curing agent component. In one example, the diisocyanate component and the polycarbonate diol component may act as a thickener, i.e., the epoxy resin composition according to the embodiment may reach a thickened state (defined below) as the reaction between the diisocyanate component and the polycarbonate diol component progresses over time.

[0009] The epoxy resin composition according to the embodiment may be a liquid or a low-viscosity paste at room temperature, and in this case, the viscosity at room temperature may be 50 Pa·s or less, 40 Pa·s or less, 30 Pa·s or less, 25 Pa·s or less, 20 Pa·s or less, 15 Pa·s or less, etc. In this application, the room temperature viscosity refers to the viscosity at 25°C. When the epoxy resin composition according to the embodiment is a liquid or a low-viscosity paste at room temperature, its viscosity at room temperature may be 0.1 Pa·s or more, 0.5 Pa·s or more, 1 Pa·s or more, 5 Pa·s or more, 10 Pa·s or more, etc.

[0010] The "thickened state" is defined as follows: an epoxy resin composition is considered to have reached a thickened state when, at a certain point in time, its room-temperature viscosity exceeds 10 times its initial value and, even after being kept at 23°C for a further 7 days from that point, the room-temperature viscosity does not increase by 1.3 times or more. Here, the initial value refers to the room-temperature viscosity of a freshly prepared epoxy resin composition after being kept at 23°C for 30 minutes. Therefore, for example, if an epoxy resin composition with an initial room temperature viscosity of 30 Pa s is kept at 23°C for 10 days after preparation and has a room temperature viscosity of 2000 Pa s, and if it is kept at 23°C for 17 days after preparation and has a room temperature viscosity of 2600 Pa s, this epoxy resin composition is considered to have already reached an increased viscosity state 3 days after preparation.

[0011] The time required for the epoxy resin composition according to the embodiment to reach a viscous state is preferably 1 day or more and 30 days or less when the holding temperature is 23° C. This time can be extended by lowering the holding temperature, and can be shortened by raising the holding temperature. The room temperature viscosity of the epoxy resin composition according to the embodiment in a thickened state may be 1,000 Pa·s or more and less than 2,000 Pa·s, 2,000 Pa·s or more and less than 3,000 Pa·s, 3,000 Pa·s or more and less than 4,000 Pa·s, 4,000 Pa·s or more and less than 5,000 Pa·s, 5,000 Pa·s or more and less than 6,000 Pa·s, 6,000 Pa·s or more and less than 8,000 Pa·s, 8,000 Pa·s or more and less than 10,000 Pa·s, 10,000 Pa·s or more and less than 15,000 Pa·s, 15,000 Pa·s or more and less than 20,000 Pa·s, 20,000 Pa·s or more and less than 50,000 Pa·s, or 50,000 Pa·s or more and less than 100,000 Pa·s, etc.

[0012] In the epoxy resin composition according to the embodiment, the blending amount of the epoxy resin component may be, for example, 50 wt % or more of the entire epoxy resin composition, 60 wt % or more, 65 wt % or more, 70 wt % or more, 75 wt % or more, etc. There are no particular limitations on the epoxy resin that is blended as an epoxy resin component in the epoxy resin composition according to the embodiment. Any epoxy resin, such as a bisphenol-type epoxy resin such as a bisphenol A-type epoxy resin or a bisphenol F-type epoxy resin, a novolac-type epoxy resin, or a glycidylamine-type epoxy resin, can be blended as an epoxy resin component in the epoxy resin composition according to the embodiment.

[0013] In a preferred embodiment, at least a portion of the epoxy resin blended in the epoxy resin composition according to the embodiment is a bisphenol-type epoxy resin, particularly a bisphenol A-type epoxy resin. As is well known, bisphenol A epoxy resin is a mixture whose main component is bisphenol A diglycidyl ether, a compound where n = 0 in the following formula (a), and which also contains small amounts of components where n = 1. The average n of commercially available bisphenol A epoxy resins that are liquid at room temperature is approximately 0.1 to 0.2.

[0014] [ka]

[0015] In the epoxy resin composition according to the embodiment, the amount of the diisocyanate component is preferably 8 parts by weight or more, and may be 9 parts by weight or more, 10 parts by weight or more, per 100 parts by weight of the epoxy resin component. There are no particular limitations on the diisocyanate that is blended as a diisocyanate component in the epoxy resin composition according to the embodiment. Suitable examples include diisocyanates having an aromatic ring in the molecular structure, such as bis(4-isocyanatophenyl)methane and toluene diisocyanate, but the diisocyanate is not limited to these, and one or more arbitrary diisocyanates may be blended as a diisocyanate component in the epoxy resin composition according to the embodiment.

[0016] The molar ratio R of the polycarbonate diol component and the diisocyanate component blended in the epoxy resin composition according to the embodiment M That is, the ratio of the number of moles of the polycarbonate diol component to the number of moles of the diisocyanate component is preferably 0.1 or more, and can be 0.1 or more and less than 0.15, 0.15 or more and less than 0.2, 0.2 or more and less than 0.25, 0.25 or more and less than 0.3, 0.3 or more and less than 0.35, 0.35 or more and less than 0.4, 0.4 or more and less than 0.45, 0.45 or more and less than 0.5, 0.5 or more and less than 1, etc. According to the inventors' findings from experiments, the molar ratio R M When is less than 1, the molar ratio R M As the value approaches 1, the time required for the epoxy resin composition to reach a thickened state tends to become shorter.

[0017] In the epoxy resin composition according to the embodiment, the number average molecular weight of the polycarbonate diol component is not limited, but may be, for example, 500 or more and 800 or less, 800 or more and 1000 or less, 1000 or more and 2000 or less, 2000 or more and 2500 or less, or 2500 or more and 5000 or less. According to experiments conducted by the present inventors, when the number of moles of the polycarbonate diol component to be blended is the same, the viscosity of the epoxy resin composition in a thickened state tends to increase as the number average molecular weight increases.

[0018] There is no particular limitation on the polycarbonate diol to be blended in the epoxy resin composition according to the embodiment. One or more arbitrary polycarbonate diols may be blended in the epoxy resin composition according to the embodiment as the polycarbonate diol component. Suitable examples of polycarbonate diols include polycarbonate diols having an isosorbide residue, a neopentyl glycol residue, a cyclohexanediol residue, or a cyclohexanedimethanol residue, and polycarbonate diols having a 1,4-butanediol residue, a 1,5-pentanediol residue, a 3-methyl-1,5-pentanediol residue, or a 1,6-hexanediol residue. The polycarbonate diol having the above-mentioned isosorbide residue, neopentyl glycol residue, cyclohexanediol residue or cyclohexanedimethanol residue may have a 1,4-butanediol residue, 1,5-pentanediol residue, 3-methyl-1,5-pentanediol residue or 1,6-hexanediol residue in addition to a diol residue selected from these four diol residues.

[0019] At least a part of the polycarbonate diol component blended in the epoxy resin composition according to the embodiment may be a polycarbonate diol having one or more types of first repeating units and one or more types of second repeating units defined below introduced into its structure by a transesterification reaction. The first repeating unit and the second repeating unit are represented by the following general formulas (A) and (B), respectively.

[0020] [ka]

[0021] The diol residue -O-R1-O- in the first repeating unit is derived from an aliphatic diol HO-R1-OH that does not contain an alicyclic structure. The diol residue -O-R2-O- in the second repeating unit is derived from an aliphatic diol HO-R2-OH containing an alicyclic structure. Examples of aliphatic diols HO-R1-OH that do not contain an alicyclic structure include 1,3-propanediol, 2-methyl-1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 2-methyl-1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,14-tetradecanediol, 1,16-hexadecanediol, 1,18-octadecanediol, and 1,20-eicosanediol. Examples of aliphatic diols HO-R2-OH containing an alicyclic structure include 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, tricyclodecane dimethanol, pentacyclopentadecanedimethanol, 2,6-decalindimethanol, 1,5-decalindimethanol, 2,3-decalindimethanol, 2,3-norbornane dimethanol, 2,5-norbornane dimethanol, 1,3-adamantanedimethanol, isosorbide These are 3,9-bis(1,1-dimethyl-2-hydroxyethyl)-2,4,8,10-tetraoxaspiro(5.5)undecane (common name: spiroglycol), 3,9-bis(1,1-diethyl-2-hydroxyethyl)-2,4,8,10-tetraoxaspiro(5.5)undecane, 3,9-bis(1,1-dipropyl-2-hydroxyethyl)-2,4,8,10-tetraoxaspiro(5.5)undecane, and dioxane glycol.

[0022] There are no particular limitations on the epoxy resin curing agent that can be blended into the epoxy resin composition according to the embodiment. Suitable examples include latent curing agents that initiate curing of the epoxy resin component using heat as a trigger, but the present invention is not limited thereto. One or more known epoxy resin curing agents can be blended into the epoxy resin composition according to the embodiment as the epoxy resin curing agent component. The above-mentioned latent curing agents that initiate curing of an epoxy resin using heat as a trigger are solids that have low solubility in the epoxy resin component at room temperature, and only when heated to melt or dissolve in the epoxy resin component do they exhibit sufficient function as a curing agent.

[0023] Some imidazoles and dicyandiamide are typical examples of latent curing agents that initiate the curing of epoxy resins using heat as a trigger. Imidazoles are compounds having an imidazole ring, and include substituted imidazoles in which the hydrogen atoms of imidazole are substituted with substituents, as well as imidazolium salts and imidazole complexes. Examples of imidazoles that function as latent curing agents include, but are not limited to, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2-phenyl-4-methylimidazole, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2-phenyl-4-benzyl-5-hydroxymethylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-paratoluyl-4-methyl-5-hydroxymethylimidazole, 2-paratoluyl-4,5-dihydroxymethylimidazole, 2-metatoluyl-4-methyl-5-hydroxymethylimidazole, 2-metatoluyl-4,5-dihydroxymethylimidazole, 1-cyanoethyl-2-phenylimidazole, and 1-cyanoethyl-2-phenylimidazolium trimellitate.

[0024] The epoxy resin composition according to the embodiment may contain optional components in addition to the epoxy resin component, diisocyanate component, polycarbonate diol component, and epoxy resin curing agent component. Examples of optional components include, but are not limited to, antioxidants, internal mold release agents, low-profile agents, colorants, flame retardants, and modifiers made of rubber, elastomers, or thermoplastic resins.

[0025] The flame retardant that can be blended into the epoxy resin composition according to the embodiment is not particularly limited, but suitable examples include non-halogen flame retardants. Examples of non-halogenated flame retardants include, but are not limited to, inorganic phosphorus flame retardants such as red phosphorus, organic phosphorus flame retardants such as phosphate esters, organic phosphates, phosphonates, and phosphinates, nitrogen-based flame retardants such as triazine compounds, cyanuric acid compounds, and isocyanuric acid compounds, silicone-based flame retardants, inorganic flame retardants such as metal hydroxides and metal oxides, and organic metal salt-based flame retardants such as ferrocene and acetylacetone metal complexes. In a preferred example, the epoxy resin composition according to the embodiment may contain either or both of an organic phosphorus-based flame retardant and a nitrogen-based flame retardant.

[0026] 2. Prepreg manufacturing method The epoxy resin composition according to the embodiment can be preferably used for producing a prepreg. In the prepreg obtained by impregnating a fiber reinforcement material with the epoxy resin composition according to the embodiment, the reaction product between the diisocyanate component and the polycarbonate diol component acts to suppress a decrease in viscosity during heating, and therefore, it is expected that the amount of flash generated will be reduced when the prepreg is used in compression molding.

[0027] A prepreg using the epoxy resin composition according to the embodiment can be produced, for example, by a production method comprising the following steps 1 and 2. (Step 1) A plurality of components including at least an epoxy resin component, a diisocyanate component, a polycarbonate diol component, and an epoxy resin curing agent component are mixed to prepare an epoxy resin composition according to the embodiment. (Step 2) A fiber reinforcement material prepared in advance is impregnated with the epoxy resin composition prepared in Step 1 to form a composite.

[0028] For example, when the room temperature viscosity of the epoxy resin composition prepared in step 1 is 30 Pa s or less, step 2 can be carried out without heating the epoxy resin composition in a room with a suitable temperature of 17°C to 28°C. In this case, when the room temperature viscosity of the epoxy resin composition is 25 Pa s or less, further 20 Pa s or less, or even 15 Pa s or less, the impregnation of the fiber reinforcing material in step 2 can be carried out more reliably in a shorter time.

[0029] In step 2, in order to ensure that the fiber reinforcing material is impregnated in a short time, the epoxy resin composition prepared in step 1 may be heated to reduce its viscosity. The heating is carried out so that the temperature of the epoxy resin composition does not exceed 80°C, preferably does not exceed 70°C, more preferably does not exceed 50°C, and even more preferably does not exceed 40°C. The reason for this is to prevent the initiation of a curing reaction of the epoxy resin component due to the action of the epoxy resin curing agent component.

[0030] The material of the fiber reinforcing material to be impregnated with the epoxy resin composition in step 2 is not particularly limited, but suitable examples include carbon fiber, glass fiber, and aramid fiber. Of these, carbon fiber is most preferred because of its low specific gravity and high strength. The form of the fiber reinforcement material is not particularly limited, but typical examples include woven fabric, nonwoven fabric, and non-crimp fabric. The fiber reinforcement may be a fiber mat that is deposited by scattering chopped fiber tows on a carrier film, and a prepreg using such a fiber mat as the fiber reinforcement is called a sheet molding compound.

[0031] Step 2 may be followed, optionally, by Step 3, in which the epoxy resin composition in the composite formed in Step 2 is thickened. This step is preferably carried out by, but not limited to, maintaining the composite at a predetermined thickening temperature. The viscosity increasing temperature can be selected, for example, from room temperature to about 80° C. The higher the viscosity increasing temperature, the shorter the time it takes for the epoxy resin composition to reach a viscosity increasing state.

[0032] 3. Manufacturing method of sheet molding compound The following is a specific description of the case where a sheet molding compound is produced as a prepreg. For producing the sheet molding compound, for example, a sheet molding compound production apparatus shown in FIG. 1 can be used.

[0033] Referring to FIG. 1, a continuous fiber bundle 10, which is the raw material for the fiber reinforcement material, is drawn from a fiber package P and fed to a rotary cutter 1. The continuous fiber bundle 10 may be a carbon fiber bundle made up of, for example, 3,000 to 100,000 carbon fiber filaments.

[0034] The continuous fiber bundle 10 is cut by a rotary cutter 1 into chopped fiber bundles 20 . The fiber length of the chopped fiber bundle 20 is, for example, within a range of 5 mm to 100 mm, and can be 1 cm or more and less than 2 cm, 2 cm or more and less than 3 cm, 3 cm or more and less than 4 cm, or 4 cm or more and less than 6 cm. The chopped fiber bundles 20 fall onto the surface of the first carrier film 51 traveling below the rotary cutter 1 to form a fiber mat 30 .

[0035] Before the fiber mat 30 is deposited, a first resin paste layer 41L made of the epoxy resin composition according to the embodiment is applied to the surface of the first carrier film 51 by a first coater 2a equipped with a doctor blade. The first carrier film 51 is a synthetic resin film that is resistant to the components of the first resin paste 41 . The material of the first carrier film 51 can be appropriately selected from polyolefins such as polyethylene and polypropylene, polyvinylidene chloride, vinyl chloride resins, polyamides, and the like. The first carrier film 51 may be a multi-layer film.

[0036] When the room temperature viscosity of the first resin paste 41 is 0.1 Pa·s or more, or even 0.5 Pa·s or more and 30 Pa·s or less, a first resin paste layer 41L can be easily formed with a uniform thickness on the first carrier film 51 in a room with an air temperature of 17°C or more and 28°C or less without heating the first resin paste 41. The basis weight of the fiber mat 30, the thickness of the first resin paste layer 41L, and the thickness of the second resin paste layer 42L described below are set in consideration of the fiber content and basis weight of the sheet molding compound to be produced.

[0037] The fiber content of a sheet molding compound in which the fiber reinforcement is carbon fiber can be, for example, 40 wt% or more but less than 45 wt%, 45 wt% or more but less than 55 wt%, 55 wt% or more but less than 65 wt%, 65 wt% or more but less than 80 wt%, etc. The basis weight of the sheet molding compound is, for example, 500 g / m 2 More than 1500g / m 2 Below 1500g / m 2 More than 2500g / m 2 Below 2500g / m 2 More than 3500g / m 2 Below 3500g / m 2 More than 5000g / m 2 It could be the following:

[0038] Following the formation of the fiber mat 30, the first carrier film 51 and the second carrier film 52 are bonded together with the fiber mat 30 sandwiched therebetween, thereby forming the laminate 60. Before lamination, a second resin paste layer 42L made of an epoxy resin composition having the same composition as the first resin paste 41 is applied to one surface of the second carrier film 52 by a second coater 2b equipped with a doctor blade.

[0039] The laminate 60 is formed so that the surface of the first carrier film 51 on which the first resin paste layer 41L is applied faces the surface of the second carrier film 52 on which the second resin paste layer 42L is applied. The second carrier film 52 is a synthetic resin film that is resistant to the components of the second resin paste 42 , and its material and structure may be the same as those of the first carrier film 51 .

[0040] The laminate 60 is pressed in the impregnation machine 3 to impregnate the fiber mat 30 with the first resin paste 41 and the second resin paste 42 . After passing through the impregnation machine 3, the laminate 60 is wound up on a bobbin. The steps up to this point are carried out using the sheet molding compound manufacturing apparatus shown in FIG.

[0041] The laminate 60 on the bobbin is maintained at a predetermined temperature for a certain period of time to thicken the epoxy resin composition that has permeated the fiber mat 30, thereby completing the sheet molding compound. If the viscosity of the matrix resin increases by no more than 1.3 times per week when stored at 23°C, the tack and drape properties of the sheet molding compound will not change so significantly during storage that they become difficult to handle.

[0042] The room temperature viscosity of the epoxy resin composition in a thickened state may be 1,000 Pa·s or more and less than 2,000 Pa·s, 2,000 Pa·s or more and less than 3,000 Pa·s, 3,000 Pa·s or more and less than 4,000 Pa·s, 4,000 Pa·s or more and less than 5,000 Pa·s, 5,000 Pa·s or more and less than 6,000 Pa·s, 6,000 Pa·s or more and less than 8,000 Pa·s, 8,000 Pa·s or more and less than 10,000 Pa·s, 10,000 Pa·s or more and less than 15,000 Pa·s, 15,000 Pa·s or more and less than 20,000 Pa·s, 20,000 Pa·s or more and less than 50,000 Pa·s, or 50,000 Pa·s or more and less than 100,000 Pa·s, etc.

[0043] 4. Experimental Results The results of the experiments conducted by the present inventors are described below. The materials used in the experiment are shown in Table 1 below.

[0044] [Table 1]

[0045] The epoxy resin used was jER (registered trademark) 827 from Mitsubishi Chemical Corporation, a bisphenol A type epoxy resin with a viscosity of about 10 Pa·s at 25°C. Amicure (registered trademark) PN-23J from Ajinomoto Fine-Techno Co., Ltd., used as curing agent A, is a latent curing agent for amine adduct epoxy resins. Curesol 2MZA-PW from Shikoku Chemicals Corporation, used as curing agent B, is an epoxy resin curing agent made of an imidazole compound with a triazine skeleton introduced therein. Cosmonate (registered trademark) LL from Mitsui Fine Chemicals, Inc., which was used as the diisocyanate, is a mixture in which bis(4-isocyanatophenyl)methane is partially modified, and contains bis(4-isocyanatophenyl)methane.

[0046] The material used as diol A was a polycarbonate diol with a number average molecular weight of about 800, synthesized by reacting isosorbide, 1,6-hexanediol, and a carbonate diester in the presence of a transesterification catalyst. For details of the synthesis method, see, for example, International Publication WO2011 / 129377. The material used as diol B is a polycarbonate diol with a number average molecular weight of about 1000, synthesized by reacting neopentyl glycol (2,2-dimethyl-1,3-propanediol), 1,4-butanediol, and a carbonate diester in the presence of a transesterification catalyst. For details of the synthesis method, see, for example, International Publication WO2011 / 129377. The material used as diol C was a polycarbonate diol having a number average molecular weight of about 2,000, which was synthesized in the same manner as diol B. Diol A, Diol B and Diol C were all waxy solids at room temperature.

[0047] The room temperature viscosity of the epoxy resin composition was measured by the parallel plate method using a Thermo Scientific HAAKE MARS 40 rheometer from Thermo Fisher Scientific Inc. The diameter of the parallel plates was 25 mm, the plate gap was 500 μm, and the measurement conditions were a frequency of 1.59 Hz, a stress of 300 Pa, and a temperature of 25°C.

[0048] In the following description of the experimental results, the term "initial room temperature viscosity" refers to the viscosity at room temperature measured after placing a freshly prepared epoxy resin composition in a sealed container and leaving it at 23°C for 30 minutes. In the following descriptions of experimental results, the term "viscosity N days after preparation" or "viscosity N days after preparation" refers to the room temperature viscosity measured after placing a freshly prepared epoxy resin composition in a sealed container and leaving it at 23°C for N days. In the following description of experimental results, the amounts of components other than the epoxy resin blended into the epoxy resin composition may be expressed in the unit [phr]. "phr" is an abbreviation for per hundred resin and is a unit commonly used in the industry. When the amount of component Y blended in epoxy resin composition X is said to be Z phr, this means that Z parts by weight of component Y are blended into epoxy resin composition X per 100 parts by weight of the epoxy resin.

[0049] Experiment 1 An epoxy resin composition containing neither diisocyanate nor polycarbonate diol, and epoxy resin compositions containing different amounts of diisocyanate and polycarbonate diol with a fixed molar ratio of polycarbonate diol to diisocyanate of 1 were prepared and their thickening properties were investigated. Table 2 shows the formulations of the five epoxy resin compositions prepared, as well as the initial room temperature viscosity and room temperature viscosity measured for each epoxy resin composition after a certain number of days had passed since preparation.

[0050] [Table 2]

[0051] Sample 1, which did not contain diisocyanate or polycarbonate diol, did not show an increase in viscosity even after 8 days had passed since preparation, whereas Samples 2 to 5, which contained diisocyanate and polycarbonate diol, all showed an increase in room temperature viscosity after preparation. The room temperature viscosities of Samples 2 to 5 were substantially the same 3 days, 6 days, and 19 days after preparation. In other words, the epoxy resin compositions of Samples 2 to 5 all reached an increased viscosity state 3 days after preparation.

[0052] The room temperature viscosity in the thickened state increased monotonically with increasing amount of diisocyanate. Figure 2 is a graph showing the relationship between the amount of diisocyanate and the room temperature viscosity 6 days after preparation for Samples 2 to 5. After preparing Sample 1, it was immediately cured at 140°C for 30 minutes to obtain a cured epoxy resin having a flexural modulus of 3.2 GPa and a flexural strength of 94 MPa. The cured epoxy resins obtained by curing Samples 2 to 5 under the same conditions all had a flexural modulus of elasticity exceeding 3.2 GPa and a flexural strength exceeding 140 MPa.

[0053] Experiment 2 Epoxy resin compositions were prepared by varying the molar ratio of polycarbonate diol to diisocyanate, with the diisocyanate content fixed at 9 phr, and the thickening properties were investigated. Table 3 shows the formulations of the four epoxy resin compositions prepared, as well as the initial room temperature viscosity and room temperature viscosity measured for each epoxy resin composition after a certain number of days had passed since preparation.

[0054] [Table 3]

[0055] In all of Samples 6 to 9, the room temperature viscosity was one to two orders of magnitude larger than the initial value 5 days after preparation, and the room temperature viscosity 14 days after preparation was even higher than that 5 days after preparation, but the room temperature viscosities 14, 20, and 27 days after preparation were substantially the same. In other words, the epoxy resin compositions of Samples 6 to 9 had all already reached an increased viscosity 14 days after preparation. A graph in which the ratio of the room temperature viscosity 5 days after preparation to the room temperature viscosity 14 days after preparation is plotted against the molar ratio of polycarbonate diol to diisocyanate blended into the epoxy resin composition is shown in Figure 3. The graph shows that the rate of increase in the room temperature viscosity of the epoxy resin composition at the stage before it reaches a thickened state tends to increase monotonically as the molar ratio of polycarbonate diol to diisocyanate increases.

[0056] The room temperature viscosities in the thickened state were substantially the same among Samples 7 to 9, but Sample 6, which had the smallest molar ratio of diol A to diisocyanate, had a slightly lower room temperature viscosity in the thickened state than Samples 7 to 9. After preparing Samples 6 to 9, they were immediately cured at 140°C for 30 minutes to obtain cured epoxy resins. All of the cured epoxy resins had a flexural modulus of more than 3.2 GPa and a flexural strength of more than 140 MPa.

[0057] Experiment 3 Epoxy resin compositions were prepared by varying the type of polycarbonate diol used, with the diisocyanate content fixed at 10 phr and the molar ratio of polycarbonate diol to diisocyanate fixed at 0.34, and the thickening properties were investigated. Table 4 shows the formulations of the three epoxy resin compositions prepared, as well as the initial room temperature viscosity and room temperature viscosity measured for each epoxy resin composition after a certain number of days had passed since preparation.

[0058] [Table 4]

[0059] Diol B and diol C were polycarbonate diols containing diol residues different from those of diol A. It was confirmed that the room temperature viscosity of Samples 11 and 12, which contained Diol B and Diol C, respectively, increased after preparation and reached a thickened state. The room temperature viscosity in the thickened state was similar for Sample 10, which used diol A with a number-average molecular weight of approximately 800, and Sample 11, which used diol B with a number-average molecular weight of approximately 1000, while Sample 12, which used diol C with a number-average molecular weight of approximately 2000, had a higher viscosity than Samples 10 and 11. After preparing Samples 10 to 12, they were immediately cured at 140°C for 30 minutes to obtain cured epoxy resins. All of the cured epoxy resins had a flexural modulus of more than 3.2 GPa and a flexural strength of more than 140 MPa. [Explanation of symbols]

[0060] 1 rotary cutter 2a First coating machine 2b Second coating machine 3 Impregnation machine 10 Continuous fiber bundle 20 chopped fiber bundles 30 Fiber Mat 41 Daiichi Resin Paste 41L First resin paste layer 42 Second resin paste 42L Second resin paste layer 51 Daiichi Carrier Film 52 Secondary Carrier Film 60 laminate

Claims

1. An epoxy resin composition comprising an epoxy resin component, a diisocyanate component, a polycarbonate diol component, and an epoxy resin curing agent component, As the polycarbonate diol component, a polycarbonate diol having an isosorbide residue is blended, the amount of the epoxy resin component is 50 wt % or more of the total epoxy resin composition; the blending amount of the diisocyanate component is 8 parts by weight or more per 100 parts by weight of the epoxy resin component, an epoxy resin composition, wherein the ratio of the number of moles of the polycarbonate diol component to the number of moles of the diisocyanate component is 0.1 or more and 1 or less.

2. 2. The epoxy resin composition according to claim 1, which has a room temperature viscosity of 50 Pa·s or less.

3. 3. The epoxy resin composition according to claim 2, which has a room temperature viscosity of 0.1 Pa·s or more.

4. 4. The epoxy resin composition according to claim 1, which reaches a thickened state in 1 day or more and 30 days or less when kept at 23°C.

5. 4. The epoxy resin composition according to claim 1, wherein the viscosity at room temperature in a thickened state is 1,000 Pa·s or more but less than 100,000 Pa·s.

6. The epoxy resin composition according to any one of claims 1 to 5, wherein the number average molecular weight of the polycarbonate diol component is 500 or more and 5,000 or less.

7. 7. The epoxy resin composition according to claim 1, wherein bis(4-isocyanatophenyl)methane is blended as the diisocyanate component.

8. The epoxy resin composition according to any one of claims 1 to 7, wherein toluene diisocyanate is blended as the diisocyanate component.

9. The epoxy resin composition according to any one of claims 1 to 8, wherein a polycarbonate diol having a 1,4-butanediol residue, a 1,5-pentanediol residue, a 3-methyl-1,5-pentanediol residue, or a 1,6-hexanediol residue is blended as the polycarbonate diol component.

10. The epoxy resin composition according to any one of claims 1 to 9, wherein a bisphenol-type epoxy resin is blended as the epoxy resin component.

11. 11. The epoxy resin composition according to claim 1, wherein the epoxy resin curing agent component is one or more epoxy resin curing agents selected from imidazoles and dicyandiamide.

12. 12. The epoxy resin composition according to claim 1, wherein either one or both of an organic phosphorus-based flame retardant and a nitrogen-based flame retardant are blended.

13. A method for producing a prepreg, comprising impregnating a fiber reinforcement material with the epoxy resin composition according to any one of claims 1 to 12.

14. The method according to claim 13, wherein the temperature of the epoxy resin composition during the impregnation is 80°C or less.

15. The method according to claim 13 or 14, wherein the impregnation is carried out in a room at an air temperature of 17°C or higher and 28°C or lower without heating the epoxy resin composition.

16. The method according to any one of claims 13 to 15, wherein the epoxy resin composition is thickened after the impregnation.

17. The manufacturing method according to any one of claims 13 to 16, wherein the prepreg is a sheet molding compound.

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