Polyurethane-modified epoxy resin composition and cured product

Abstract

To provide a new polyurethane-modified epoxy resin composition which has a high glass transition temperature, has low viscosity and excellent fiber impregnation property, and has high attenuation property of resin itself, in an urethane-modified epoxy resin used in a casting material, a composite material and a structural adhesive, and a cured product of the same.SOLUTION: There are provided: a polyurethane-modified epoxy resin composition that contains a polyurethane non-modified epoxy resin (A), a polyurethane-modified epoxy resin (B) having a structure derived from polyether polyol and such a structure that a terminal isocyanate group of a molecular chain is reacted with a secondary hydroxyl group of a bisphenol type epoxy resin, and a curing agent (C) as essential components, contains 20-70 wt.% of the polyurethane-modified epoxy resin (B) with respect to the total amount (solid content) of the epoxy resin composition, in which the component (A) and the component (B) are compatible with each other, wherein as a cured product after curing reaction, the component (A) and the component (B) form a phase separation structure, and a loss coefficient (tanδ) measured using a dynamic viscoelasticity apparatus under conditions of a frequency of 10 Hz and a rate of temperature rise of 2°C / min is higher than 0.03 in a temperature range of -40°C to 40°C; and a cured product using the same.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an epoxy resin composition having excellent properties such as excellent impregnation ability into fiber substrates, heat resistance, and damping properties, and to a cured product using the same. [Background technology]

[0002] Epoxy resins are easy to process and have a variety of cured product properties, including high heat resistance, high insulation reliability, high rigidity, high adhesion, and high corrosion resistance, so they are used in large quantities for a variety of applications, including electrical insulating materials (casting, impregnation, laminates, and sealing materials), matrix resins for composite materials such as CFRP, structural adhesives, and heavy-duty corrosion-resistant paints.

[0003] On the other hand, epoxy resin cured products have low elongation at break, low fracture toughness, and low peel strength. Therefore, in applications where these properties are required, such as matrix resins for composite materials and structural adhesives, the above properties have been improved by various modifications such as rubber modification and polyurethane modification.

[0004] Regarding polyurethane modification, for example, Patent Documents 1 and 2 disclose an epoxy resin / polyurethane mixture (B) containing a diglycidyl ether of a bisphenol A-alkylene oxide adduct (A), an epoxy resin, and a polyurethane dispersed in the epoxy resin, wherein the polyurethane is a polyurethane obtained by reacting, in the epoxy resin, a polyisocyanate compound with a curing agent capable of reacting with the polyisocyanate compound. Patent Document 3 discloses a resin composition containing a compound having an epoxy group and a polyurethane containing a structural unit represented by general formula (II) in the molecule. Patent Document 4 discloses a polyurethane-modified epoxy resin obtained by modifying a bisphenol-based epoxy resin (a) with a medium- to high-molecular-weight polyol compound (b), a polyisocyanate compound (c), and a low-molecular-weight polyol compound (d) as a chain extender, using a predetermined amount of epoxy resin (a) and reacting the medium- to high-molecular-weight polyol compound (b) and the polyisocyanate compound (c) in predetermined amounts, and then adding a predetermined amount of the low-molecular-weight polyol compound (d). Patent Document 5 discloses a polycarbonate-modified epoxy resin in which a hydroxyl group-containing epoxy resin (A), a polyisocyanate compound (B), and a polycarbonate polyol (C) are essential reaction raw materials, and the polycarbonate polyol (C) is used in a predetermined amount. Patent Document 6 discloses an epoxy resin composition for fiber-reinforced composite materials obtained by blending an epoxy resin (A), a urethane prepolymer (B) having a structure derived from a polyether polyol and having an isocyanate group or a hydroxyl group at both ends of the molecular chain, and a curing agent (C), in which (A) and (B) are compatible with each other before the curing reaction, and after the curing reaction, (A) forms a sea structure and (B) forms island structures, and the resulting cured product of the epoxy resin composition has a sea-island phase-separated structure.

[0005] As other techniques, Patent Documents 7 to 9 disclose epoxy resin compositions containing an epoxy resin, a thermoplastic resin such as a polyethersulfone resin, and a curing agent. Patent Document 10 discloses that impact properties are improved by forming a resin layer containing a thermoplastic resin having a polyaryl ether skeleton and particles made of a thermoplastic resin and a thermosetting resin.

[0006] However, even these patent documents still do not always fully satisfy the required properties. The present invention proposes a polyurethane-modified epoxy resin that satisfies the required physical properties for various applications and has excellent damping properties. It is expected that the resin itself having damping properties will prevent the deterioration of the mechanical properties, thermal properties, chemical resistance, etc. of the cured product caused by the addition of an elastomer that has poor heat resistance and solvent resistance, and will also eliminate the need to form a stress relaxation layer (adhesive layer). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-284467 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-284474 [Patent Document 3] Japanese Patent Application Laid-Open No. 2007-224144 [Patent Document 4] Japanese Patent Application Laid-Open No. 2016-11409 [Patent Document 5] Japanese Patent Application Publication No. 2017-226717 [Patent Document 6] Japanese Patent Application Laid-Open No. 2017-82128 [Patent Document 7] Japanese Patent Application Laid-Open No. 2005-105151 [Patent Document 8] Japanese Patent Application Laid-Open No. 2007-284545 [Patent Document 9] Japanese Patent Application Laid-Open No. 2008-144110 [Patent Document 10] WO2019 / 098243 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention aims to provide a novel polyurethane-modified epoxy resin composition and a cured product thereof, which has a high glass transition temperature, low viscosity, excellent fiber impregnation ability, and high damping properties, and is used in casting materials, composite materials, structural adhesives, etc. as a urethane-modified epoxy resin. [Means for solving the problem]

[0009] The present invention provides a polyurethane-modified epoxy resin composition comprising, as essential components, an unmodified polyurethane resin (A), a polyurethane-modified epoxy resin (B) having a structure derived from a polyether polyol and having a structure in which a terminal isocyanate group in the molecular chain has reacted with a secondary hydroxyl group of a bisphenol epoxy resin, and a curing agent (C), wherein the polyurethane-modified epoxy resin (B) accounts for 20 to 70% by weight of the total weight (solid content) of the epoxy resin composition, and components (A) and (B) are compatible with each other. The polyurethane-modified epoxy resin composition is characterized in that, after the curing reaction, components (A) and (B) form a phase-separated structure in the cured product, and the loss factor (tan δ) measured using a dynamic viscoelasticity apparatus under conditions of a frequency of 10 Hz and a heating rate of 2°C / min is higher than 0.03 in the temperature range of -40°C to 40°C.

[0010] In the polyurethane-modified epoxy resin composition of the present invention, it is desirable that 30 mol % or more of the structures derived from polyol compounds in the polyurethane-modified epoxy resin (B) are derived from polytetramethylene ether glycol (PTMG). It is preferable that the polyurethane-modified epoxy resin (B) has a weight-average molecular weight of 10,000 or more, and the amount of the polyol compound and isocyanate compound in component (B) is 12% by weight or more relative to the total amount of components (A) and (B).

[0011] The polyurethane-modified epoxy resin (B) is represented by the following formula (1), and is a liquid bisphenol-based epoxy resin (a) having an epoxy equivalent of 150 to 300 g / eq and a hydroxyl equivalent of 800 to 3600 g / eq, which is mixed with polytetramethylene ether glycol (PTMG) (b-1), a polyol compound (b-2) other than PTMG having a number average molecular weight of 500 or more, a polyisocyanate compound (c), and a number average molecular weight of 100 or more as a chain extender. Desirably, the epoxy resin (a) is modified with a low-molecular-weight polyol compound (d) having an Mn of less than 500, and is obtained by reacting the epoxy resin (a) with the components (b-1), (b-2), and (c) in such a manner that the epoxy resin (a) is used in an amount of 50 to 85% by weight based on the total amount of the components (a), (b-1), (b-2), (c), and (d), and the component (b-1) is used in an amount of 30 to 100% by weight based on the total amount of the components (b-1), (b-2), and (d). [ka] [Effects of the Invention]

[0012] The polyurethane-modified epoxy resin composition of the present invention has low viscosity, excellent fiber impregnation ability, inhibits a decrease in glass transition temperature, and forms an optimally phase-separated state in the cured product, and has a high loss factor (tan δ). Therefore, the composition is suitable as a matrix resin for composite materials and a compounding resin for adhesives for industrial, sports and leisure, civil engineering and construction applications that require damping properties. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a stereomicroscope image showing the phase structure of a cured product (Example 1). [Figure 2] 1 is a stereomicroscope image showing the phase structure of a cured product (Example 7). [Figure 3] 1 is a stereomicroscope image showing the phase structure of a cured product (Example 9). [Figure 4] 1 shows a stereomicroscope image and an AFM image showing the phase structure of a cured product (Comparative Example 1). DETAILED DESCRIPTION OF THE INVENTION

[0014] The polyurethane-modified epoxy resin composition of the present invention is characterized in that it contains, as essential components, a polyurethane-unmodified epoxy resin (A) as a polyurethane concentration adjuster, and a curing agent (C) in a polyurethane-modified epoxy resin (B), and contains 20 to 70% by weight of the polyurethane-modified epoxy resin (B) relative to the total weight (solid content) of the epoxy resin composition. The resin composition of the present invention may contain, as required, a curing accelerator (D) and inorganic fillers such as calcium carbonate, talc, and titanium dioxide as extenders and reinforcing materials.

[0015] The polyurethane-modified epoxy resin (B) used in the present invention contains as essential components a liquid bisphenol-based epoxy resin (a), polytetramethylene ether glycol (PTMG) (b-1), and a polyisocyanate compound (c). From the perspectives of optimizing physical properties and viscosity, fine-tuning compatibility, and molecular weight control, a polyol compound (b-2) other than PTMG with a number-average molecular weight of 500 or more and a low-molecular-weight polyol compound (d) with a number-average molecular weight of less than 500 as a chain extender may also be used. Each component of the polyurethane-modified epoxy resin (B) will be described below.

[0016] The epoxy resin (a) is liquid at room temperature, and from this viewpoint, it preferably has an epoxy equivalent of 300 g / eq or less, and more preferably has an epoxy equivalent of 150 to 300 g / eq and a hydroxyl equivalent of 800 to 3600 g / eq. Specifically, a secondary hydroxyl group-containing bisphenol-based epoxy resin represented by the following general formula (1) and having an epoxy equivalent of 150 to 200 g / eq and a hydroxyl group equivalent of 2000 to 3000 g / eq is suitable. [ka] In the formula, R1's are each independently H or an alkyl group, and a is a number of 0 to 10. When it is an alkyl group, it preferably has 1 to 3 carbon atoms, and more preferably has 1 carbon atom.

[0017] Particularly preferred epoxy resins (a) are bisphenol A type epoxy resins represented by formula (1a) or bisphenol F type epoxy resins represented by formula (1b). [ka] In the formula, a1 and a2 are numbers from 0 to 10. In formula (1), formula (1a), and formula (1b), the average value (number average) of the repeating number a, a1, or a2 is in the range of 1-5, and preferably in the range of 1-3.

[0018] Polytetramethylene ether glycol (PTMG) (b-1) is a linear polyether glycol having primary hydroxy groups at both ends, as represented by the following formula (2a), and its number average molecular weight ranges from about 200 to over 4000. [ka] In the present invention, the number average molecular weight is preferably about 500 to 4000, and in consideration of compatibility with resins and damping properties, it is preferably 2000 to 4000.

[0019] Examples of polyol compounds (b-2) other than PTMG and having a number average molecular weight of 500 or more include compounds represented by the following formulas (2b) to (2d), such as polyethylene glycol (PEG), polypropylene glycol (PPG), polyethylene propylene glycol (PEPG), and copolymers of two or more alkylene oxides (e.g., ethylene oxide-propylene oxide copolymers). Furthermore, polyol compounds such as lactone-modified polyols, polyester polyols, and polycarbonate polyols can also be used, provided that the object of the present invention is not impaired. These compounds can be used alone or in combination. [ka] Here, R2 is H or a methyl group, b1, b2, and b3 are independently numbers from 1 to 50, and c is a number of 0 or 1. [ka] Here, q1, q2, q3, and q4 are independently numbers from 1 to 20. [ka] Here, r, s, and t are independently numbers from 1 to 20, and n is a number from 1 to 50.

[0020] The polyisocyanate compound (c) may have two or more NCO groups, but preferably has two. It is preferably represented by general formula (3), in which R4 is a divalent group selected from formulas (i) to (vi). Among these, those having excellent compatibility with the epoxy resin (a) are preferably selected. Specific examples include toluene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), hydrogenated xylylene diisocyanate (HXDI), isophorone diisocyanate (IPDI), and naphthalene diisocyanate. [ka] Here, R4 is a divalent group selected from formulae i to vi. [ka] In particular, 4,4'-diphenylmethane diisocyanate (MDI) represented by formula (3a) is preferred from the viewpoints of low molecular weight, no thickening, low cost, safety, etc. [ka]

[0021] The low-molecular-weight polyol compound (d) is a polyol compound having a number-average molecular weight of less than 500, preferably less than 200. It is used as a chain extender. Preferably, it is a diol compound represented by formula (4) having two primary hydroxyl groups. [ka] Here, R5 is an alkylene group represented by formula vii, and g is a number from 1 to 10.

[0022] Specific examples of the low-molecular-weight polyol compound (d) include polyhydric alcohols such as 1,4-butanediol and 1,6-pentanediol. In particular, 1,4-butanediol is more preferred in terms of availability and a good balance between price and properties.

[0023] Next, polyurethane-modified epoxy resins using components (a), (b-1), (b-2), (c), and (d) will be explained, along with their reaction mechanisms. Each component can be used alone or in combination of two or more.

[0024] The OH groups in the epoxy resin (a) are primarily secondary OH groups. On the other hand, the OH groups in the polytetramethylene ether glycol (PTMG) (b-1) and the polyol compound (b-2) other than PTMG and having a number average molecular weight of 500 or more are primarily primary OH groups. Therefore, when the epoxy resin (a), the polytetramethylene ether glycol (PTMG) (b-1), the polyol compound (b-2) other than PTMG and having a number average molecular weight of 500 or more, and the polyisocyanate compound (c) are charged and reacted, the primary OH groups in the polytetramethylene ether glycol (PTMG) (b-1) and the polyol compound (b-2) other than PTMG and having a number average molecular weight of 500 or more react preferentially with the NCO groups in the polyisocyanate compound (c).

[0025] Typically, the primary OH groups in polytetramethylene ether glycol (PTMG) (b-1) and the polyol compound (b-2) other than PTMG with a number average molecular weight of 500 or more react with the NCO groups in the polyisocyanate compound (c) to produce an NCO-terminated urethane prepolymer (P1). The secondary OH groups in the epoxy resin (a) then react with some of the terminal NCO groups of the urethane prepolymer (P1) to form urethane bonds, forming a urethane prepolymer (P2) in which the epoxy resin (a) is attached to both or one of the terminals of the urethane prepolymer.

[0026] In other words, the urethane prepolymer (P) is thought to be a mixture of an NCO-terminated urethane prepolymer (P1) and a urethane prepolymer (P2) in which epoxy resin (a) has been added to one or both ends of P1; however, because the molar ratio of NCO groups is high and a large excess of epoxy resin is used, it is thought that the urethane prepolymer (P2) in which epoxy resin has been added to both ends is mainly produced.

[0027] The epoxy resin (a) is preferably used in an amount of 50 to 85% by weight based on the total amount of the components (a), (b-1), (b-2), (c), and (d). As the charging ratio of epoxy resin (a) increases, both ends or one end is capped with epoxy resin (a), the terminal NCO groups are consumed, the amount of urethane prepolymer (P2) that does not react with the chain extender low-molecular-weight polyol compound (d) increases, the proportion of the original urethane prepolymer (P1) that has NCO groups at its ends decreases, and the amount of polyurethane produced by the reaction between the terminal NCO groups of P1 and the OH groups of the chain extender low-molecular-weight polyol compound (d) decreases, and the molecular weight distribution of the polyurethane-modified epoxy resin also shifts to the lower molecular weight side.

[0028] Conversely, if the ratio of epoxy resin (a) charged is reduced, the amount of urethane prepolymer (P2) with both or one end capped with epoxy resin (a) decreases, and the ratio of the original urethane prepolymer (P1) with NCO groups at the ends increases. As a result, the amount of polyurethane produced by the reaction between the terminal NCO groups of P1 and the OH groups of the low-molecular-weight polyol compound (d), which acts as a chain extender, increases, and the molecular weight distribution of the polyurethane-modified epoxy resin also shifts to a higher molecular weight side.

[0029] Epoxy resin (a) is often a mixture of a monomer with a repeat number a of 0 and a polymer with a repeat number a of 1 or more. In the case of the polymer, the epoxy group has a secondary OH group generated by ring-opening. This OH group is reactive with the NCO group of the polyisocyanate compound (c) or the terminal NCO group of the urethane prepolymer (P), so the a=1 or greater units in the epoxy resin (a) react. However, the a=0 units, which do not have an OH group, do not participate in this reaction.

[0030] The polyurethane-modified epoxy resin composition of the present invention exhibits damping properties due to phase separation of the polyurethane-modified epoxy resin portion within the epoxy resin composition. While phase separation is often reported to result in the formation of a sea-island structure, the present invention does not refer to a sea-island structure in which the islands are spherical, but rather to a structure in which the islands begin to connect to each other. Such a phase-separated structure is also known as an interpenetrating structure or an interconnected structure, and the present invention preferably employs a phase-separated structure that at least partially has an interpenetrating structure or an interconnected structure. When a polyurethane-modified epoxy resin is used in which 30% or more of the polyol compound having a polyether polyol-derived structure is polytetramethylene ether glycol (PTMG), the phase-separated island portion (polyurethane-modified epoxy resin portion) exhibits a gentle peak in the island Tg range from −40°C to 40°C, and the island portion is almost incompatible with the sea portion (epoxy resin portion) and phase-separates, forming a structure in which the island portions begin to connect to each other, thereby enabling the composition to exhibit a high loss factor (tan δ) in the −40°C to 40°C temperature range and thereabouts. Therefore, to achieve the phase-separated structure of the present invention, it is necessary to control the size and number of the islands, their compatibility with the sea, and other factors. Figures 1 to 4 show stereomicroscope and AFM images of the phase-separated state. When a complete sea-island structure is formed, with the islands each presenting individually at a size of several nanometers to several tens of nanometers, tan δ is low. However, as the islands aggregate to a size of several hundred nanometers to several micrometers and begin to show shading in the sea-island structure, tan δ increases. Furthermore, as phase separation progresses, a phase-separated structure is formed in which the islands are connected to a size of several tens to several hundred micrometers, resulting in a more suitable tan δ. However, if the phase-separated size is too large, mechanical properties deteriorate. To achieve the phase-separated structure of the present invention, the island size of the phase separation is preferably 10 nm to 200 μm, and particularly preferably 100 nm to 100 μm.

[0031] The size of the phase-separated islands is determined not only by the molecular weight of the polyurethane-modified epoxy resin, but also by its compatibility with the sea region. High compatibility leads to miscibility of the islands with the sea region during curing of the epoxy resin composition, preventing phase separation and preventing the formation of the desired phase-separated structure. Therefore, to achieve the desired size and number of islands, the polyurethane-modified epoxy resin for the islands must have a certain molecular weight and be incompatible with the unmodified epoxy resin for the sea region. Furthermore, over time, incompatible islands gradually link together to form larger domains during phase separation, resulting in a deterioration of mechanical properties. Therefore, the optimal molecular weight and composition of the polyurethane-modified epoxy resin must be selected based on the viscosity of the resin composition and the curing conditions (curing temperature, curing time, and heating rate) appropriate for the application. Since it is preferable that the island portions are incompatible with the sea portion, it is preferable to avoid the use of polyols that impart compatibility to the island portions as much as possible.

[0032] In the polyurethane-modified epoxy resin (B), since the Tg of the phase-separated island portion has a gentle peak in the range of -40°C to 40°C, it is preferable that 30 mol% or more of the structure derived from the polyol compound is a structure derived from polytetramethylene ether glycol (PTMG). More preferably, it is 50 mol% or more, and even more preferably, it is 75 mol% or more, and it is recommended to use 100%. As used here, "mol" is defined as the weight of each component divided by the number average molecular weight.

[0033] Because the phase-separated island portions are not compatible with the sea portion, it is preferable that the polyurethane-modified epoxy resin (B) has a weight-average molecular weight of 10,000 or more, and that the blending amount of the polyol compound and polyisocyanate compound in component (B) is 12% or more relative to the total amount of components (A) and (B). The weight-average molecular weight is more preferably 12,000 or more and 45,000 or less, and even more preferably 12,000 or more and 35,000 or less. Furthermore, in order to form a desirable phase-separated structure, it is preferable that the blending amount of the polyol compound and polyisocyanate compound in component (B) is more preferably 14% or more and 18% or less, and even more preferably 15% or more and 18% or less, relative to the total amount of components (A) and (B).

[0034] In one example of a method for producing the polyurethane-modified epoxy resin used in the present invention, 50 to 85% by weight of epoxy resin (a) is used relative to the total weight of polytetramethylene ether glycol (PTMG) (b-1), a polyol compound (b-2) other than PTMG with a number-average molecular weight of 500 or greater, a polyisocyanate compound (c), and a low-molecular-weight polyol compound (d) acting as a chain extender, and polytetramethylene ether glycol (PTMG) (b-1), a polyol compound (b-2) other than PTMG with a number-average molecular weight of 500 or greater, and a polyisocyanate compound (c) are reacted in the presence of epoxy resin (a) (Reaction 1). In this Reaction 1, the reaction of polytetramethylene ether glycol (PTMG) (b-1), a polyol compound (b-2) other than PTMG with a number-average molecular weight of 500 or greater, and a polyisocyanate compound (c) occurs preferentially, producing a urethane prepolymer (P1). Thereafter, a reaction occurs between a portion of the urethane prepolymer (P1) and the epoxy resin (a), producing primarily a urethane prepolymer (P2) in which both ends are epoxidized, and it is desirable that this be a mixture of a small amount of a urethane prepolymer (P3) in which one end is epoxidized and a urethane prepolymer (P1) in which both ends remain NCO.

[0035] The reaction between the urethane prepolymer (P1) and the epoxy resin (a) is preferably carried out at a temperature in the range of 80 to 150°C for a period of 1 to 5 hours, since it is necessary to react the low-reactivity secondary OH groups in the epoxy resin (a) with the NCO groups to form urethane bonds.

[0036] Thereafter, if necessary, a low molecular weight polyol compound (d) is added so that the molar ratio (P):(d) of the NCO groups in the urethane prepolymer (P) to the OH groups in the low molecular weight polyol compound (d) is in the range of 0.9:1.0 to 1.0:0.9, and a polyurethane reaction is carried out (Reaction 2). Note that the epoxy groups of the epoxy resin and the OH groups of the polyol compound (d) are alcoholic OH groups and therefore do not react with each other.

[0037] The reaction temperature for Reaction 2 is preferably in the range of 80 to 150°C, and the reaction time is preferably in the range of 1 to 5 hours. However, since Reaction 2 is a reaction between the NCO group and the OH group in the low-molecular-weight polyol compound (d), milder conditions than Reaction 1 may be used.

[0038] A catalyst can be used as needed in the above reactions (Reactions 1 and 2). The catalyst is used to ensure that the formation of urethane bonds is completed sufficiently, and examples of the catalyst include amine compounds such as ethylenediamine, tin compounds, and zinc compounds.

[0039] In reaction 2, the small amount of urethane prepolymer (P1) having NCO at both or one end reacts with the low-molecular-weight polyol compound (d) to extend the chain length and form polyurethane, while the urethane prepolymer (P2) having epoxy resin (a) at both ends remains unreacted. That is, the polyurethane-modified epoxy resin used in the present invention is a mixture of a resin component in which epoxy resin (a) is attached to both ends of a urethane prepolymer (P), a minor component in which epoxy resin (a) is attached to one end of a urethane prepolymer (P) and the other end is an NCO group, and a resin component in which both ends of a urethane prepolymer (P) are NCO groups, and epoxy resin (a), and preferably has an epoxy equivalent in the range of 180 to 1000 g / eq and a viscosity at 120°C in the range of 0.1 to 30 Pa s.

[0040] The polyurethane concentration in the polyurethane-modified epoxy resin composition can be increased or decreased by increasing or decreasing the amount of polyurethane-unmodified epoxy resin (A). The polyurethane concentration in the epoxy resin composition is calculated using the following formula: Polyurethane concentration = {(b-1) + (b-2) + (c) + (d)} x 100 / {(A) + (B) + (C)} Here, (a) to (d), (A), (B), and (C) are the weights of the corresponding components used. When other components, such as a curing accelerator (E), are added, the amount of these other components is added to the denominator. In the present invention, the concentration of polyurethane in the epoxy resin composition is preferably 5 to 30% by weight, more preferably 10 to 20% by weight, and even more preferably 10 to 15% by weight. In the polyurethane-modified epoxy resin (B), the urethane component concentration is preferably 20 to 40% by weight, more preferably 20 to 35% by weight, where the urethane component concentration is {(b-1) + (b-2) + (c) + (d)} / {(a) + (b-1) + (b-2) + (c) + (d)}.

[0041] The epoxy resin (a) described above, which is used as a raw material for the polyurethane-modified epoxy resin (B), can be preferably used as the polyurethane-unmodified epoxy resin (A) used in the polyurethane-modified epoxy resin composition of the present invention. That is, an epoxy resin that is not polyurethane-modified and is liquid at 30°C is preferred. Among these, bisphenol A epoxy resin or bisphenol F epoxy resin is preferred from the viewpoints of availability and a good balance between price and properties.

[0042] In the polyurethane-modified epoxy resin composition of the present invention, a trifunctional or higher polyfunctional epoxy resin can be used as the polyurethane-unmodified epoxy resin (A) to adjust viscosity or increase Tg. The use of a polyfunctional epoxy resin increases crosslink density, alters phase separation, and reduces fracture toughness, so it is preferable to use 0.1 to 10 wt% of the total composition. Examples of trifunctional or higher polyfunctional epoxy resins include phenol novolac epoxy resins, cresol novolac epoxy resins, glycidylamine epoxy resins such as tetraglycidyldiaminodiphenylmethane, glycidylphenyl ether epoxy resins such as tetrakis(glycidyloxyphenyl)ethane and tris(glycidyloxyphenyl)methane, and glycidylamine and glycidylphenyl ether epoxy resins such as triglycidylaminophenol. Furthermore, epoxy resins modified with these epoxy resins and brominated epoxy resins obtained by brominating these epoxy resins are also included.

[0043] In this case, it is preferable to use an epoxy resin with a viscosity of 5000 mPa·s or less at 25°C. This reduces the viscosity of the composition, improving its ability to impregnate carbon fibers and enabling its application to tow prepregs and pultrusion molding. Examples include glycidyl ether epoxy resins, glycidyl ester epoxy resins, glycidyl amine epoxy resins, and alicyclic epoxy resins. These epoxy resins can be used alone or in combination of two or more types.

[0044] Examples of glycidyl ether type epoxy resins include glycerol glycidyl ether type epoxy resins, butyl glycidyl ether type epoxy resins, phenyl glycidyl ether type epoxy resins, (poly)ethylene glycol diglycidyl ether type epoxy resins, (poly)propylene glycol diglycidyl ether type epoxy resins, neopentyl glycol diglycidyl ether type epoxy resins, 1,4-butanediol diglycidyl ether type epoxy resins, 1,6-hexanediol diglycidyl ether type epoxy resins, trimethylolpropane polyglycidyl ether type epoxy resins, diglycerol polyglycidyl ether type epoxy resins, allyl glycidyl ether type epoxy resins, 2-ethylhexyl glycidyl ether type epoxy resins, p-(tert-butyl)phenyl glycidyl ether type epoxy resins, dodecyl glycidyl ether type epoxy resins, tridecyl glycidyl ether type epoxy resins, etc. These glycidyl ether type epoxy resins can be used alone or in combination of two or more.

[0045] Examples of glycidyl ester type epoxy resins include hexahydrophthalic anhydride diglycidyl ester type epoxy resins, tetrahydrophthalic anhydride diglycidyl ester type epoxy resins, tertiary fatty acid monoglycidyl ester type epoxy resins, o-phthalic acid diglycidyl ester type epoxy resins, dimer acid glycidyl ester type epoxy resins, etc. These glycidyl ester type epoxy resins can be used alone or in combination of two or more.

[0046] Examples of glycidylamine type epoxy resins include m-(glycidoxyphenyl)diglycidylamine type epoxy resins, N,N-diglycidylaminobenzene type epoxy resins, o-(N,N-diglycidylamino)toluene type epoxy resins, etc. These glycidylamine type epoxy resins can be used alone or in combination of two or more.

[0047] Examples of alicyclic epoxy resins include alicyclic diepoxy adipate type epoxy resins, 3,4-epoxycyclohexylmethylcarboxylate type epoxy resins, vinylcyclohexene dioxide type epoxy resins, and hydrogenated bisphenol A diglycidyl ether type epoxy resins.

[0048] As the curing agent (C), dicyandiamide (DICY) or its derivatives are preferably used, since they can be made into a one-component composition with excellent storage stability and are readily available.

[0049] When the curing agent (C) is DICY, the ratio of the number of moles of epoxy groups in the total epoxy resin, including the polyurethane-modified epoxy resin (B) and the polyurethane-unmodified epoxy resin (A), to the number of moles of active hydrogen groups in DICY is preferably set in the range of 1:0.3 to 1:1.2, and more preferably 1:0.9 to 1:1.1, from the viewpoint of the properties of the cured product.

[0050] The urethane-modified epoxy resin composition of the present invention can further contain a curing accelerator (D). As the curing accelerator (ED), an imidazole-based curing aid is preferably used to impregnate the reinforcing fibers during mixing, suppress viscosity increase, and satisfy heat resistance during curing. Preferred imidazole-based curing aids include 2-methylimidazole, 1,2-dimethylimidazole, 2-ethyl-4-methylimidazole, 1-benzyl-2-methylimidazole, 2-undecylimidazole, 2-heptadecylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2-phenyl-4',5'-dihydroxymethylimidazole, and 1-cyanoethyl-2-ethyl-4-methylimidazole. Furthermore, imidazole compounds containing a triazine ring are preferred, and examples of such compounds include 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine, 2,4-diamino-6-[2'-ethyl-4'-methylimidazolyl-(1')]-ethyl-s-triazine, and 2,4-diamino-6-[2'-undecylimidazolyl-(1')]-ethyl-s-triazine. Among these, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine is more preferred because it can be cured in a short time. The imidazole compounds containing a triazine ring may be used alone or in combination of two or more. On the other hand, depending on the application or construction method, there may be cases where the short curing time mentioned above is not necessary. In such cases, crystalline imidazole compounds such as 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid addition salt (2MA-OK) or urea compounds such as 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) can be used. The amount of curing accelerator (D) is preferably in the range of 0.1 to 5 wt% based on the total amount of epoxy resin (including polyurethane-modified epoxy resin (B) and polyurethane-unmodified epoxy resin (A)) and curing agent (C).

[0051] The epoxy resin composition of the present invention can contain a release agent (E) as needed depending on the application and processing method. Release agents include liquid and solid (powder) release agents. Liquid release agents are sufficient as long as they are liquid at room temperature (10 to 30°C) so that they can be uniformly mixed into low-viscosity compositions. Furthermore, incorporating a release agent into the resin improves pultrusion moldability. This improves the orientation of fibers in the molded product, improving mechanical properties such as compressive strength, and also improves adhesion to adhesives due to the smooth surface.

[0052] The amount of release agent added is preferably 0.1 to 6 parts by mass relative to 100 parts by mass of the total epoxy resin. More preferably, it is 0.1 to 4 parts by mass. If the amount is less than 0.1 part by mass, sufficient release properties may not be obtained. If the amount is more than 6 parts by mass, the strength of the molded product may decrease, or the adhesion and bonding properties may decrease. The release agents may be used alone or in combination of two or more.

[0053] Such liquid release agents are not particularly limited as long as they do not phase separate from the epoxy resin composition and do not evaporate or decompose at the temperature of the mold. Specific examples of such liquid release agents include MOLDWIZ INT-1324, 1324B, 1836, 1846, 1850, 1854, and 1882 manufactured by Tomoe Engineering Co., Ltd., which are produced by polycondensation of organic acids and glycerides.

[0054] Furthermore, examples of solid (powder) release agents include animal waxes such as shellac wax, beeswax, and spermaceti; vegetable waxes such as carnauba wax and spermaceti; mineral waxes such as paraffin wax and microcrystalline wax; and synthetic waxes such as Fischer-Tropsch wax, polyethylene wax, and polypropylene wax. It is desirable for these agents to be in powder form so that they can be uniformly dispersed in the epoxy resin composition, and also to have properties that allow them to melt and dissolve at the temperatures during molding and curing.

[0055] The cured product of the present invention is obtained by subjecting the epoxy resin composition to a curing reaction. The method for obtaining the cured product may conform to a general method for curing curable resin compositions. For example, the heating temperature conditions may be appropriately selected depending on the type of curing agent to be combined, the intended use, and the like. For example, a method may be used in which the epoxy resin composition is heated in a temperature range of about room temperature to 250°C. General methods for curable resin compositions may also be used for molding.

[0056] The cured product of the present invention has excellent heat resistance and excellent damping properties, and therefore the cured product preferably has a glass transition temperature (Tg) of 120°C or higher and a loss factor (tan δ) of 0.03 or higher in the temperature range of -40°C to 40°C.

[0057] The fiber-reinforced composite material of the present invention can be obtained by impregnating reinforcing fibers with the epoxy resin composition of the present invention to obtain a fiber-reinforced composite material composition, which is then molded and cured. The reinforcing fibers may be twisted, untwisted, or non-twisted. Untwisted or non-twisted fibers are preferred due to their excellent moldability in fiber-reinforced composite materials. Furthermore, the reinforcing fibers may be unidirectionally aligned or woven. Fabrics such as plain weave and satin weave can be freely selected depending on the location and application. Specific examples of reinforcing fibers include carbon fiber, glass fiber, aramid fiber, boron fiber, alumina fiber, and silicon carbide fiber, which have excellent mechanical strength and durability. These fibers can be used alone or in combination. Of these, carbon fiber is particularly preferred due to the excellent strength of the molded product. Various carbon fibers, such as polyacrylonitrile, pitch, and rayon, can be used.

[0058] The method for obtaining a fiber-reinforced composite material from the epoxy resin composition of the present invention is not particularly limited, and examples include a method in which the components constituting the epoxy resin composition are uniformly mixed to produce a varnish, and the varnish is used to form a prepreg, for example, a material in which continuous carbon fibers are arranged in one direction to form a sheet or a carbon fiber fabric is impregnated with the resin, a carbon fiber substrate in which a resin layer is disposed on at least one surface of the carbon fiber substrate, and another fiber layer is disposed on the surface of the resin, a method in which unidirectional reinforcing fibers in which reinforcing fibers are aligned in one direction are immersed in the varnish obtained above (a state before curing in the pultrusion method or filament winding method, a tow prepreg), a method in which reinforcing fiber sheets or fabrics are stacked and set in a mold, and then a resin is injected into the mold and impregnated by applying pressure or by reducing the internal pressure (a state before curing in the RTM method), and the like.

[0059] In the fiber-reinforced composite material of the present invention, the volume content of the reinforcing fibers relative to the total volume of the molded product is preferably 40% to 85%, and from the viewpoint of strength, it is more preferably in the range of 50 to 75%. If the volume content is less than 40%, the content of the epoxy resin composition may be too high, resulting in an insufficient modulus of elasticity or strength of the resulting cured product, or inability to satisfy the required properties. If the volume content exceeds 85%, the resin in the reinforcing fibers may be insufficient, leading to insufficient adhesion and the occurrence of voids, resulting in an insufficient modulus of elasticity or strength of the cured product, or reduced interfacial adhesion. [Example]

[0060] The present invention will now be described in detail with reference to examples. The present invention is not limited to these examples, and various modifications and variations are possible without departing from the spirit and scope of the present invention.

[0061] The physical properties were evaluated as follows. (1) Determination of the presence or absence of residual NCO groups by IR: 0.05 g of the obtained polyurethane-modified epoxy resin was dissolved in 10 ml of tetrahydrofuran, and then applied to a KBr plate using a MicroSpatel flat plate. The sample was dried at room temperature for 15 minutes to evaporate the tetrahydrofuran, and a sample for IR measurement was prepared. This was set in a PerkinElmer FT-IR Spectrum-One device, and the characteristic absorption band of the NCO group, 2270 cm -1 When the stretching vibration absorption spectrum of the compound disappeared, it was determined that there were no remaining NCO groups. (2) Epoxy equivalent: Quantified according to JIS K 7236. (3) Hydroxyl Equivalent: 25 ml of dimethylformamide was placed in a 200 ml Erlenmeyer flask with a glass stopper. A weighed sample containing 11 mg / equivalent or less of hydroxyl groups was added and dissolved. 20 ml of 1 mol / L-phenyl isocyanate toluene solution and 1 ml of dibutyltin maleate catalyst solution were added using a pipette, mixed thoroughly, and the flask was sealed and allowed to react for 30 to 60 minutes. After the reaction was complete, 20 ml of 2 mol / L-dibutylamine toluene solution was added, mixed thoroughly, and allowed to stand for 15 minutes to react with the excess phenyl isocyanate. Next, 30 ml of methyl cellosolve and 0.5 ml of bromocresol green indicator were added, and the excess amine was titrated with a standardized methyl cellosolve perchlorate solution. The indicator changed color from blue to green and then to yellow. The point at which the indicator first turned yellow was designated as the endpoint, and the hydroxyl equivalent was calculated using the following equations (i) and (ii). Hydroxyl group equivalent (g / eq)=(1000×W) / C(SB) (i) C: Concentration of methyl perchlorate cellosolve solution mol / L W: Sample size (g) S: Titration volume of methyl perchlorate cellosolve solution (ml) B: Titration volume (ml) of methyl perchlorate cellosolve solution required for blank test during titration C=(1000×W) / {121×(sb)}···(ii) w: Amount of tris-(hydroxymethyl)-aminomethane weighed for standardization (g) s: Volume (ml) of methyl perchlorate cellosolve solution required for titration of tris-(hydroxymethyl)-aminomethane b: Titration volume (ml) of methyl perchlorate cellosolve solution required for blank test during standardization

[0062] (4) Glass transition temperature (Tg): The glass transition temperature (Tg) was calculated by measuring the intersection of the tangent line at the baseline and the inflection point using a differential scanning calorimeter (DSC) at a heating rate of 10°C / min. (5) Tensile test: Test pieces were prepared by molding the cured material into the shape specified in JIS K 7161 using a mold. Tensile tests were carried out at room temperature of 23°C using a universal testing machine to measure the tensile strength, tensile elongation, and tensile modulus of elasticity. (6) Weight average molecular weight (Mw): Measured by gel permeation chromatography (GPC) under the following conditions. Measuring device: Tosoh Corporation HLC-8420GPC Column: TSKgel SuperMultiporeHZ-M x 2 Measurement conditions: temperature 40℃, eluent THF, flow rate 0.35mL / min Sample: Polystyrene SRM706a (7) Loss factor (tan δ): The cured resin or molded product was cast into a mold to a shape of 50 mmL x 10 mmW x 2 mmT, and the loss factor (tan δ) of the processed test specimen was measured using a dynamic viscoelasticity device at a frequency of 10 Hz and a heating rate of 2°C / min, and the value was calculated in the temperature range of -40°C to 40°C. (8) Evaluation method for the phase separation structure of the cured product: The resin compositions obtained in the examples and comparative examples were vacuum degassed and, using a casting plate with a 4 mm thick spacer sandwiched between metal plates, cured products were obtained at 120°C for 1 hour and then at 150°C for 1 hour in the case of non-rapid-curing systems such as those using 2MAOK as the curing accelerator (D). In the case of fast-curing systems such as those using 2MZA-PW as the curing accelerator (D), cured products were obtained at 130°C for 15 minutes. The cured products were then cut out and trimmed with a microtome, and the surfaces were observed with a stereomicroscope or an atomic force microscope (AFM). Stereo microscope: Equipment: Leica stereo microscope M205C Lighting: Coaxial lighting Atomic Force Microscopy (AFM): Equipment: Dimension Icon AFM (manufactured by Bruker-AXS) Probe: NCHV (manufactured by Bruker-AXS) Tip curvature radius 10nm Spring constant 42N / m (nominal value) Mode: Tapping Mode The criteria for judgment are as follows: ×: Sea-island structure. Spherical island structure, island size is on the order of several tens of nm, and tan δ is low (0.01 to 0.02 level). △: Phase separation structure. Island aggregation occurs, island size is on the order of several μm, and tan δ is about 0.03. ○: Phase separation structure. Island aggregation expands to form a salami-like structure, with island sizes ranging from several tens to hundreds of μm. Tan δ is 0.04 or higher.

[0063] The raw materials used were as follows: Ingredient A Nippon Steel Chemical & Material Co., Ltd. Epotohto YD-128, bisphenol A epoxy resin, epoxy equivalent weight 187g / eq, liquid Nippon Steel Chemical & Material Co., Ltd. Epotohto YH-300, glycidyl polyether of trimethylolpropane, epoxy equivalent weight 142g / eq, liquid YD-014, manufactured by Nippon Steel Chemical & Material, bisphenol A type bifunctional epoxy resin, epoxy equivalent weight 950g / eq, solid Component B Epoxy resin (a): Nippon Steel Chemical & Material Co., Ltd. Epotohto YDF-170, bisphenol F epoxy resin, epoxy equivalent 170g / eq, hydroxyl equivalent 2600g / eq, liquid Polytetramethylene ether glycol (b-1): Mitsubishi Chemical PTMG1000, number average molecular weight 1000, hydroxyl equivalent weight 500g / eq, Mitsubishi Chemical PTMG2000, number average molecular weight 2000, hydroxyl equivalent 1000g / eq, Mitsubishi Chemical PTMG3000, number average molecular weight 3000, hydroxyl equivalent weight 1500g / eq, Mitsubishi Chemical PTMG4000, number average molecular weight 4000, hydroxyl equivalent weight 2000g / eq, [ka] Polyol compound (b-2): ADEKA ADEKA Polyether P-2000, polypropylene glycol, number average molecular weight 2000, hydroxyl equivalent 1020g / eq [ka] Polyisocyanate compound (c): Cosmonate PH, 4,4'-diphenylmethane diisocyanate, manufactured by Mitsui Chemicals [ka] Mitsui Chemicals Cosmonate T-80, tolylene diisocyanate (a mixture of 2,4- and 2,6-isomers of the following formula) [ka] Low molecular weight polyol compound (d): 1,4-Butanediol (reagent), molecular weight 90 [ka] Component C: EVONIK DICYANEX1400F, dicyandiamide Component D: Crystalline imidazole, Curezol 2MZA-PW, and 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine manufactured by Shikoku Chemical Industries, Ltd. Crystalline imidazole manufactured by Shikoku Chemical Industry Co., Ltd., Curezol 2MA-OK, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine isocyanuric acid adduct

[0064] Synthesis Example 1 The epoxy resin (a) used was Epotohto YDF-170, the polytetramethylene ether glycol used was Mitsubishi Chemical PTMG2000, and the polyisocyanate (c) used was Cosmonate PH. The amounts used are shown in Table 1. Epotohto YDF-170 and PTMG2000 were placed in a 1000 ml four-neck separable flask equipped with a nitrogen inlet tube, a stirrer, and a temperature controller, and the mixture was heated to 120°C and stirred for 120 minutes. Cosmonate PH was then added, and the mixture was allowed to react at 120°C for 2 hours to obtain a polyurethane-modified bisphenol F epoxy resin (Synthesis Example 1). The completion of the reaction was confirmed by IR measurement, whereby the absorption spectrum of the NCO group disappeared. The resulting polyurethane-modified bisphenol F-type epoxy resin (Synthesis Example 1) had an epoxy equivalent of 218 g / eq and a weight-average molecular weight (Mw) of 14,000.

[0065] Synthesis Examples 2-12 A polyurethane-modified bisphenol F epoxy resin was obtained by carrying out the reaction in the same manner as in Synthesis Example 1, except that the raw material charging composition was as shown in Table 1.

[0066] Next, examples of epoxy resin compositions and cured epoxy resin products using the polyurethane-modified epoxy resins obtained in the above Synthesis Examples 1 to 12 will be shown. The results are summarized in Tables 2 and 3.

[0067] Example 1 The polyurethane-modified bisphenol F epoxy resin obtained in Synthesis Example 1 as polyurethane-modified epoxy resin (B), Epotohto YD-128 as polyurethane-unmodified epoxy resin (A), dicyandiamide as curing agent (C), and 2MZA-PW as curing accelerator (D) were each placed in a 200 ml dedicated disposable cup in the formulations shown in Table 2, and the mixture was stirred and mixed while vacuum degassing using a rotation-revolution laboratory vacuum planetary mixer for 5 minutes to obtain a liquid resin composition. The molar ratio of epoxy groups to dicyandiamide was 1.0:0.5, and 140 g of polyurethane-modified bisphenol F epoxy resin composition was prepared. Next, this liquid resin composition was poured into a mold with a groove shape corresponding to the test specimen dimensions specified in JIS K7161. The tensile test specimen and fracture toughness test specimen dimensions were dumbbell-shaped, and the DMA test specimen dimensions were 100 mm L x 10 mm W x 1 mm T. The liquid was poured into a mold or silicone frame and cut to the appropriate size for measurement. The pourability was sufficient for casting. The mold containing the resin was then placed in a hot air oven and heated to 130°C for 15 minutes for curing, yielding a cured epoxy resin test specimen. The test results using these test specimens are shown in Table 2.

[0068] Examples 2 to 10, Comparative Examples 1 to 5 Resin compositions and cured products were obtained by carrying out the reaction in the same manner as in Example 1, except that the amounts of raw materials charged were as shown in Tables 2 and 3. The test results using these test pieces are shown in Tables 2 and 3. 1 to 4 show images of typical phase-separated morphologies observed with a stereomicroscope for Examples 1, 7, and 9 and Comparative Example 1. Note that for Comparative Example 1, an AFM image is also shown. In order to achieve an excellent loss factor in the present invention, it is important to form an optimal phase-separated state (interconnected structure) of the polyurethane-modified epoxy resin portion relative to the surrounding other epoxy resin portions. Therefore, the function may or may not be achieved depending on the combination of conditions such as the amount of polyurethane-modified epoxy resin portion added, molecular weight, and curing time until phase separation after curing. Therefore, even with the same resin composition, depending on the curing conditions for a fast-curing system, curing may proceed before phase separation, resulting in a low loss factor. In all of Examples 1 to 10, the polyurethane-modified epoxy resin portion (B) forms an optimal phase-separated structure relative to the surrounding epoxy resin portion (A), whereas in Comparative Examples 1 to 5, an optimal phase-separated structure is not formed. In Comparative Examples 1, 2, 3, and 5, the amount of urethane component added was low, so a sufficient loss factor was not achieved. Generally, the higher the molecular weight, the easier it is to cause phase separation, and the higher the molecular weight of the polyether polyol, the easier it is to cause phase separation from the epoxy moiety, so the amount added that produces the effect varies. In Comparative Example 4, a different polyol is used, so the peak itself decreases when phase separation occurs, and a high loss factor cannot be obtained in the room temperature range.

[0069] Example 11 The polyurethane-modified bisphenol F epoxy resin obtained in Synthesis Example 6 as polyurethane-modified epoxy resin (B), Epotohto YD-128 as polyurethane-unmodified epoxy resin (A), dicyandiamide as curing agent (C), and 2MAOK as curing accelerator (D) were each placed in a 200 ml dedicated disposable cup in the formulations shown in Table 4, and the mixture was stirred and mixed using a rotation-revolution laboratory vacuum planetary mixer while vacuum degassing for 5 minutes to obtain a liquid resin composition. The molar ratio of epoxy groups to dicyandiamide was 1.0:0.5, and 140 g of polyurethane-modified bisphenol F epoxy resin composition was prepared. Next, this liquid resin composition was poured into a mold with a groove shape corresponding to the test specimen dimensions specified in JIS K7161. The tensile test specimen and fracture toughness test specimen dimensions were dumbbell-shaped, and the DMA test specimen dimensions were 100 mm L x 10 mm W x 1 mm T. The liquid was poured into a mold or silicone frame and cut to the appropriate size for measurement. The pourability was sufficient for casting. Next, the mold containing the resin was placed in a hot air oven and heated and cured at 120°C for 60 minutes, followed by 150°C for 60 minutes, to prepare cured epoxy resin test specimens. The test results using these test specimens are shown in Table 4.

[0070] Examples 12 and 13, Comparative Examples 6 to 8 The reaction was carried out in the same manner as in Example 11, except that the amounts of raw materials charged were as shown in Table 4, to obtain a resin composition and a cured product. When using a solid epoxy resin to adjust the viscosity, it was mixed with a liquid epoxy resin at 100-150°C beforehand. The test results using these test pieces are shown in Table 4. In both Examples 12 and 13, the polyurethane-modified epoxy resin portion (B) forms an optimal phase-separated structure relative to the surrounding epoxy resin portion (A), whereas in Comparative Examples 6 to 8, the optimal phase-separated structure is not formed. In Comparative Example 6, a different polyol is used, so the peak itself decreases upon phase separation, and therefore a high loss factor cannot be obtained in the room temperature region. In Comparative Example 7, a large amount of a low-molecular-weight polyol compound with a number-average molecular weight of less than 500 is added, which increases the compatibility of the polyurethane-modified epoxy resin with the epoxy resin moiety, reducing the size and number of island moieties that phase separate, and thus failing to obtain a sufficient loss factor. In Comparative Example 8, the molecular weight of the polyether polyol is low, and the molecular weight of the polyurethane-modified epoxy resin is also small, so the size and number of island moieties that phase separate are reduced, and similarly failing to obtain a sufficient loss factor.

[0071] The cured products of the compositions containing the specified amounts of Examples 1 to 13 had Tg of 120°C or higher and tan δ of 0.03 or higher over a wide temperature range from -40°C to 40°C, compared to Comparative Examples 1 to 8.

[0072] Carbon fiber was passed through a resin bath containing the composition of Example 2 heated to 50°C, and then pultrusion molding was performed through a mold heated to 150°C to obtain a carbon fiber reinforced composite material. The carbon fiber used was a medium-elasticity PAN-based carbon fiber (T-700SC, manufactured by Toray Industries, Inc., tensile elasticity 230 GPa). The produced sample had a Vf of 70% and a tan δ of 0.03 or greater over a wide temperature range from -40°C to 40°C (CFRP1).

[0073] On the other hand, carbon fiber was passed through a resin bath containing the composition of Comparative Example 4 heated to 50°C, and then pultrusion molding was performed through a mold heated to 150°C to obtain a carbon fiber reinforced composite material. The carbon fiber used was a medium-elasticity PAN-based carbon fiber (T-700SC, manufactured by Toray Industries, Inc., tensile elasticity 230 GPa). The produced sample had a Vf of 69% and a tan δ of 0.03 or less in the temperature range of 0°C to 40°C (CFRP2).

[0074] [Table 1]

[0075] [Table 2]

[0076] [Table 3]

[0077] [Table 4] [Industrial Applicability]

[0078] The polyurethane-modified epoxy resin composition of the present invention has low viscosity, excellent fiber impregnation ability, and inhibits a decrease in glass transition temperature. The cured product forms an optimal phase-separated structure and has a high loss factor (tan δ). Therefore, it is useful as a matrix resin for composite materials and a compounding resin for adhesives for industrial, sports and leisure, civil engineering and construction applications that require damping properties.

Claims

1. 1. A polyurethane-modified epoxy resin composition comprising, as essential components, an unmodified polyurethane epoxy resin (A), a polyurethane-modified epoxy resin (B) having a structure derived from a polyether polyol and having a structure in which a terminal isocyanate group of the molecular chain has reacted with a secondary hydroxyl group of a bisphenol epoxy resin, and a curing agent (C), wherein the unmodified polyurethane epoxy resin (A) is a bisphenol A epoxy resin or a bisphenol F epoxy resin, and the polyurethane-modified epoxy resin (B) accounts for 20 to 70 wt % of the total weight (solid content) of the epoxy resin composition, and components (A) and (B) are compatible with each other.

2. A polyurethane-modified epoxy resin composition comprising, as essential components, an unmodified polyurethane epoxy resin (A), a polyurethane-modified epoxy resin (B) having a structure derived from a polyether polyol and having a terminal isocyanate group of the molecular chain reacted with a secondary hydroxyl group of a bisphenol epoxy resin, and a curing agent (C), wherein the unmodified polyurethane epoxy resin (A) is a bisphenol A epoxy resin or a bisphenol F epoxy resin, and the polyurethane-modified epoxy resin (B) accounts for 20 to 70 wt % of the total weight (solid content) of the epoxy resin composition, and components (A) and (B) are compatible with each other.

3. A cured product obtained after a curing reaction has a phase-separated structure in which components (A) and (B) form a loss factor (tan δ) of greater than 0.03 in the temperature range of -40°C to 40°C, as measured using a dynamic viscoelasticity apparatus under conditions of a frequency of 10 Hz and a heating rate of 2°C / min.

2. 2. The polyurethane-modified epoxy resin composition according to claim 1, wherein in the polyurethane-modified epoxy resin (B), 30 mol % or more of the structures derived from the polyol compound are derived from polytetramethylene ether glycol.

3. 2. The polyurethane-modified epoxy resin composition according to claim 1, wherein the polyurethane-modified epoxy resin (B) has a weight-average molecular weight of 10,000 or more, and the blending amount of the polyol compound and the polyisocyanate compound in component (B) is 12% by weight or more based on the total amount of component (A) and component (B).

4. The polyurethane-modified epoxy resin (B) is a liquid bisphenol-based epoxy resin (a) represented by the following formula (1), having an epoxy equivalent of 150 to 300 g / eq and a hydroxyl equivalent of 800 to 3600 g / eq, which is mixed with polytetramethylene ether glycol (PTMG) (b-1), a polyol compound (b-2) other than PTMG having a number average molecular weight of 500 or more, a polyisocyanate compound (c), and a low-molecular-weight polyisocyanate having a number average molecular weight of less than 500 as a chain extender.

2. The polyurethane-modified epoxy resin composition according to claim 1, which is modified with a polyol compound (d) and is obtained by reacting epoxy resin (a) with components (b-1), (b-2), and (c) in such a manner that epoxy resin (a) is used in an amount of 50 to 85% by weight, based on the total amount of components (a), (b-1), (b-2), (c), and (d), and component (b-1) is used in an amount of 30 to 100% by weight, based on the total amount of components (b-1), (b-2), and (d). 【Chemistry 1】 In the formula, each R 1 is independently H or an alkyl group, and a is a number from 0 to 10.

5. 3. The polyurethane-modified epoxy resin composition according to claim 2, wherein in the polyurethane-modified epoxy resin (B), the polytetramethylene ether glycol has a number average molecular weight of 2,000 or more.

6. A cured product obtained by curing the polyurethane-modified epoxy resin composition according to any one of claims 1 to 5.

7. A resin composition for fiber-reinforced composite materials, characterized in that the polyurethane-modified epoxy resin composition according to any one of claims 1 to 5 is impregnated into reinforcing fibers.

8. A fiber-reinforced composite material obtained from the resin composition for a fiber-reinforced composite material according to claim 7.

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