JP2024059456A - Polyurethane-modified epoxy resin, polyurethane-modified epoxy resin composition as well as cured product with composition, resin composition for fiber-reinforced composite material and fiber-reinforced composite material - Google Patents

Abstract

To provide a composition that uses a novel polyurethane-modified epoxy resin that is used in such as injection molding materials, composite materials, and structural adhesives, has a high glass transition temperature, is excellent in fiber permeability at low viscosity, and has high tensile elasticity and tensile strength of the resin itself, and a cured product thereof.SOLUTION: Provided is an epoxy resin composition characterized in that the resin composition comprises, as essential components: a polyurethane-modified epoxy resin (A) that has a structure derived from polyol and a structure derived from polyisocyanate, and, a structure in which a structure having an isocyanate group at the end of a molecular chain reacts with a hydroxyl group of an epoxy resin having an average of two or more epoxy groups in a molecule, wherein the polyol-derived structure contains 55 mol% or more of a polycarbonate diol-derived structure having a structural unit containing a cyclic ether structure and a carbonate group in the molecule, and 1/3 or more of moles of the epoxy resin having an average of 2 or more in the molecule is an aliphatic epoxy resin, and a urethane component concentration is 15 to 60 wt.%; a polyurethane-unmodified epoxy resin (B); and a curing agent (C), the epoxy resin composition containing 20 to 70 wt.% of component (A), 30.0 to 80.0 wt.% of component (B), and 0.1 to 20.0 wt.% of component (C) based on the entire composition. A cured product therewith is also provided.SELECTED DRAWING: None

Description

The present invention relates to an epoxy resin composition that has excellent performance in terms of impregnation into fiber substrates, heat resistance, and mechanical properties, and to a cured product using the same.

In recent years, fiber-reinforced composite materials, which use carbon fiber, glass fiber, aramid fiber, or other structural fibers as reinforcing fibers, have been used in structural materials for boats and automobiles, sporting goods such as tennis rackets, golf clubs, and fishing rods, and in general industrial applications, taking advantage of their excellent specific strength and specific elastic modulus.

Methods for manufacturing fiber-reinforced composite materials include a method in which uncured matrix resin is injected into reinforcing fibers to form a sheet-like prepreg intermediate, which is then cured, and a transfer molding method in which liquid resin is poured into reinforcing fibers set in a mold to create an intermediate, which is then cured. Epoxy resin is commonly used as the resin for these molding methods, as it has excellent heat resistance, adhesiveness, and mechanical strength. In recent years, as the application of fiber-reinforced composite materials to structural members has expanded, there has been an increasing demand for further weight reduction in the members, and there has been a demand for higher performance for the epoxy resin used in the prepreg. Specifically, it is possible to design lightweight, high-performance fiber-reinforced composite materials by increasing the elastic modulus and stress strength in tensile tests and bending tests of cured epoxy resins.

Patent Document 1 discloses a technique for achieving both a high bending modulus and a high breaking strength in a cured epoxy resin by using a polyfunctional bisphenol-type epoxy resin and an amine-type epoxy resin in combination.
Patent Document 2 discloses a technique for increasing the elastic modulus of a cured epoxy resin by using a tri- or higher functional amine-type epoxy resin and a high molecular weight bisphenol F-type epoxy resin.
Furthermore, Patent Document 3 discloses a technique for increasing the elastic modulus of a cured epoxy resin by curing an aminophenol type epoxy resin with an aromatic amine compound.

Meanwhile, with the recent expansion of applications for carbon fiber, molding methods are also spreading. Among these, the filament winding method is a method that is preferably used for manufacturing hollow containers and cylinders such as pressure vessels. From the viewpoints of productivity and quality, in addition to the conventional wet method, a method that uses a narrow intermediate substrate called a tow prepreg, yarn prepreg, or strand prepreg, in which a reinforcing fiber bundle is pre-impregnated with a thermosetting resin, is attracting attention. Another method that is attracting attention from the viewpoint of productivity is the pultrusion molding method, in which the reinforcing fiber bundle is passed through a resin bath containing a liquid matrix resin to impregnate the matrix resin, and then the reinforcing fiber bundle is passed through a squeeze die and a heated mold, and is continuously pulled out by a pulling machine while hardening.

In applications such as pressure vessels for which tow prepregs are suitable, there is an increasing demand for further weight reduction of components, and there is a demand for resins with high elasticity and strength, and adhesion at the fiber interface. If a resin or elastomer having a highly crosslinked structure is used to increase the elasticity and strength of the resin, the viscosity of the resin composition increases, causing a problem of insufficient impregnation into the fiber. In addition, if a large amount of rubber components or core-shell rubber particles is added to improve adhesion at the fiber interface, the viscosity of the resin composition also increases, which may result in insufficient impregnation into the fiber.
Similarly, in the pultrusion molding method, low viscosity and fast curing are required from the standpoint of resin impregnation and die extraction, which has the problem of limiting the use of high-viscosity resins, elastomer components, rubber components, and core-shell rubber particles.

Regarding polyurethane-modified epoxy resins, for example, Patent Documents 4 and 5 disclose an epoxy resin/polyurethane mixture (B) which contains a diglycidyl ether of a bisphenol A-alkylene oxide adduct (A), an epoxy resin, and a polyurethane dispersed in the epoxy resin, and 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 6 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 7 discloses a polyurethane-modified epoxy resin obtained by modifying a bisphenol-type 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), 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 8 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 contained in a predetermined amount.
Patent Document 9 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 an island structure, and the obtained cured product of the epoxy resin composition has a sea-island phase-separated structure.

Patent Document 10 proposes a polyurethane elastomer having improved mechanical strength, low compression set, low rebound resilience, water resistance, and the like, by using diphenylmethane diisocyanate as a polyisocyanate compound, a polycarbonate diol as a polyol, and using three components having specific molecular weight ranges, i.e., a diol, a polyether polyol, and a propylene oxide adduct of glycerin, as a curing agent.
Furthermore, Patent Document 11 proposes a polyurethane elastomer having improved flexibility, strength, and water resistance, which uses a base material obtained by reacting a polycarbonate diol, a polyether polyol, and a polyisocyanate compound, and a curing agent such as 1,4-butanediol.
Patent Document 12 proposes a polycarbonate diol comprising a combination of a linear diol and a branched or cyclic diol having an isosorbide structure.
Furthermore, Patent Document 13 proposes a polycarbonate resin composition containing a polycarbonate resin including a structure derived from an isosorbide compound and a structure derived from an alicyclic dihydroxy compound, and a soft styrene-based resin.
Furthermore, Patent Document 14 proposes a polyurethane-modified epoxy resin having a polycarbonate structure and a composition using the same.

However, in Patent Documents 4 to 6, urethane is introduced into the epoxy structure to make it compatible with the epoxy, thereby improving toughness, and increasing wettability and interfacial adhesion with fibers and additives. In addition, in the urethane-modified epoxy resins such as those in Patent Documents 7 to 11, a polyol with a specific structure is used to improve elongation and toughness, and the values achieved are still not satisfactory. Patent Documents 12 and 13 propose polycarbonate zeal and its resin composition having a structure derived from an isosorbide compound, but only the possibility of use as a urethane or a polycarbonate resin is presented, and no application as a urethane-modified epoxy resin is presented. Patent Document 14 shows that the impact resistance and fracture toughness are improved by phase separation, but the flexural strength and flexural modulus still do not fully meet the required properties in some cases, and the viscosity of the composition itself is high, making it impossible to apply to the filament winding method or the pultrusion molding method.

JP 2017-226745 A JP 2012-197413 A JP 2010-275493 A JP 2007-284467 A JP 2007-284474 A JP 2007-224144 A Patent No. 6547999 JP 2017-226717 A Patent Publication No. 6593636 JP 2013-163778 A Patent No. 6341405 Patent 6465132 Patent 6519611 WO2021/060226

The present invention proposes a polyurethane-modified epoxy resin and a composition thereof that exhibits high elasticity and high strength at a relatively gentle curing temperature of about 120-160°C while having low viscosity and fast curing properties suitable for the filament winding method and pultrusion molding method.

In other words, the present invention aims to provide a new polyurethane-modified epoxy resin composition and its cured product, which has a high glass transition temperature, low viscosity, excellent fiber impregnation, and excellent tensile elasticity and tensile strength suitable for filament winding (FW) molding and pultrusion molding, and is used in urethane-modified epoxy resins for casting materials, composite materials, structural adhesives, etc.

The present invention relates to a composition comprising the following components (A) to (C);
(A) a polyol-derived structure and a polyisocyanate-derived structure, the structure having an isocyanate group at a molecular chain end being reacted with a hydroxyl group of an epoxy resin having two or more epoxy groups on average in the molecule;
The polyol-derived structure contains 55 mol % or more of a structure derived from a polycarbonate diol having a structural unit containing a cyclic ether structure and a carbonate group in the molecule,
one-third or more of the number of moles of the epoxy resin having two or more epoxy groups in an average molecule is an aliphatic epoxy resin,
A polyurethane-modified epoxy resin having a urethane component concentration of 15 to 60% by weight.
The polyurethane-modified epoxy resin composition comprises (B) a polyurethane unmodified epoxy resin, and (C) a curing agent, and is characterized in that it contains 20 to 70% by weight of component (A), 30.0 to 80.0% by weight of component (B), and 0.1 to 20.0% by weight of component (C) based on the total weight of the composition.

（ここで、Ｒは、酸素を含んでいてもよい２官能アルコールに由来する構造を含む炭素数１～１５の２価の基であり、少なくとも一部に一般式（６）で表される化合物由来の構造を含む。ｍは１～５０の数である。）

The polyurethane-modified epoxy resin composition of the present invention is characterized in that, in component (A), the polycarbonate diol forming the structure derived from the polycarbonate diol contains a structure represented by general formula (5).

(Here, R is a divalent group having 1 to 15 carbon atoms containing a structure derived from a difunctional alcohol which may contain oxygen, and at least a portion of the structure is derived from a compound represented by general formula (6). m is a number from 1 to 50.)

In addition, in the polyurethane-modified epoxy resin (A), it is desirable that at least half of the moles of the epoxy resin having, on average, two or more epoxy groups in the molecule are aliphatic epoxy resins.

In addition, it is preferable that the polyurethane-modified epoxy resin (A) has a weight average molecular weight of 3000 or more.

In addition, in the polyurethane-modified epoxy resin (A), the aliphatic epoxy resin is preferably a polyglycidyl ether of trimethylolpropane.

The present invention also relates to a cured product obtained by curing the polyurethane-modified epoxy resin composition, a resin composition for fiber-reinforced composite materials obtained by impregnating reinforcing fibers with the composition, and a fiber-reinforced composite material obtained from the composition.

Further, the present invention provides a polyol-derived structure and a polyisocyanate-derived structure, the structure having an isocyanate group at a molecular chain end being reacted with a hydroxyl group of an epoxy resin having two or more epoxy groups on average in the molecule,
The polyol-derived structure contains 55 mol % or more of a structure derived from a polycarbonate diol having a structural unit containing a cyclic ether structure and a carbonate group in the molecule,
one-third or more of the number of moles of the epoxy resin having two or more epoxy groups in an average molecule is an aliphatic epoxy resin,
The polyurethane-modified epoxy resin has a urethane component concentration of 15 to 60% by weight.

The polyurethane-modified epoxy resin composition of the present invention has a low viscosity of preferably 50 Pa·s or less at 25°C, excellent fiber impregnation, inhibits a decrease in glass transition temperature, and forms an optimal phase-separated state in the cured product. It also has excellent tensile elasticity and tensile strength, making it suitable as a matrix resin for composite materials and compounded resins for adhesives in industrial, sports and leisure, civil engineering and construction applications that require mechanical properties and interfacial strength.

The polyurethane-modified epoxy resin composition of the present invention contains, as essential components, polyurethane-modified epoxy resin (A), polyurethane-unmodified epoxy resin (B) as a polyurethane concentration adjuster, and curing agent (C), and is characterized in that it contains 20 to 70% by weight of polyurethane-modified epoxy resin (A), 30.0 to 80.0% by weight of polyurethane-unmodified epoxy resin (B), and 0.1 to 20.0% by weight of curing agent (C) relative to the total amount (solid content) of the epoxy resin composition.

The resin composition of the present invention can be blended with a curing accelerator (D), inorganic fillers such as calcium carbonate, talc, and titanium dioxide, and a release agent, if necessary.

The polyurethane-modified epoxy resin (A) used in the present invention uses, as essential components, an epoxy resin having two or more epoxy groups on average in the molecule, such as a liquid bisphenol-type epoxy resin (a-1) or an aliphatic-type epoxy resin (a-2) [hereinafter, these may be collectively referred to as (a)], a polyol compound such as a polycarbonate diol (b-1) having a structural unit containing a cyclic ether structure and a carbonate group in the molecule, and a polyisocyanate compound (c). In addition to the polycarbonate diol, a polyol compound (b-2) having a number average molecular weight of 500 or more and a low molecular weight polyol compound (d) having a number average molecular weight of less than 500 as a chain extender may be appropriately used from the viewpoints of optimizing physical properties and viscosity, fine-tuning compatibility, and molecular weight control. The number average molecular weight described here is a value converted from the hydroxyl value, and the hydroxyl value is usually a value measured by a measurement method according to JIS K1557. The same applies below.
Each component of the polyurethane-modified epoxy resin (A) will be described below.

As the epoxy resin (a) having two or more epoxy groups on average in the molecule, it is preferable to use the above-mentioned (a-1) or (a-2). By having two or more epoxy groups on average in the molecule, it is advantageous in that various physical properties are expressed by the subsequent reaction with a curing agent.

Here, the epoxy resin (a-1) is a component suitable for expressing heat resistance and mechanical properties, and is liquid at room temperature. From this viewpoint, it is preferable that the epoxy equivalent is 300 g/eq or less. More preferably, it is an epoxy resin having 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 type epoxy resin represented by the following general formula (1), having an epoxy equivalent of 150 to 200 g/eq and a hydroxyl equivalent of 2000 to 3000 g/eq, is suitable.

式中、Ｒ_１はそれぞれ独立に、Ｈ又はアルキル基であり、ａは０～１０の数である。Ｒ_１がアルキル基である場合、好ましくは炭素数１～３の範囲であり、より好ましくは炭素数１である。

In the formula, each R ₁ is independently H or an alkyl group, and a is a number from 0 to 10. When R ₁ is an alkyl group, it preferably has 1 to 3 carbon atoms, and more preferably has 1 carbon atom.

Particularly preferred epoxy resins (a-1) are bisphenol A type epoxy resins represented by formula (1a) and/or bisphenol F type epoxy resins represented by formula (1b).

式中、ａ１、ａ２は０～１０の数である。
式（１）、式（１ａ）、式（１ｂ）において、繰り返し数ａ、ａ１又はａ２の平均値（数平均）は１～５の範囲であり、好ましくは１～３の範囲である。

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 number of repetitions a, a1, or a2 is in the range of 1 to 5, and preferably in the range of 1 to 3.

Epoxy resin (a-2) is also a suitable component for reducing the viscosity of polyurethane-modified epoxy resins and compositions using the same, and the viscosity at 25°C is preferably 100 mPa·s or more and 5000 mPa·s or less. Any epoxy resin containing hydroxyl groups in the structure may be used, and either a primary hydroxyl group or a secondary hydroxyl group may be used in the reaction. Hydroxyl groups of epoxy resins in which terminal glycidylation is not completed may be used. From the viewpoint of reducing the viscosity of polyurethane-modified epoxy resins and compositions using the same, the aliphatic epoxy resin (a-2) is used in an amount of 1/3 or more of the total number of moles of epoxy resin (a) reacting with the above-mentioned epoxy resin (a). It is preferable to use 1/2 or more. More preferably, it is 2/3 or more of the number of moles. In addition, for the "number of moles" referred to here, it is preferable to use the value obtained by dividing the amount (mass) of each epoxy resin used by the hydroxyl group equivalent and converting it to a unit functional group. In the present invention, it is assumed that one of the secondary hydroxyl groups of the polymer of epoxy resins (a-1) and (a-2) (for example, when a=1 or more in the above formula (1)) reacts with an isocyanate group to form a urethane prepolymer in such a way that the end of the urethane structure is capped. However, when a=2 or more, it is assumed that the end of the urethane structure is not capped and that it tends to contribute to the extension of the molecular chain, and that the increase in molecular weight may lead to gelation. Therefore, since most of the a=1 forms are other than the a=0 form, it is assumed that the value divided by the hydroxyl group equivalent indicates approximately the number of n1 forms. Therefore, this number is expressed as the number of moles, and the ratio of the numbers is expressed as the molar ratio.

As the aliphatic epoxy resin, polyglycidyl ether of divalent or higher aliphatic alcohol is preferred, which may have an alicyclic skeleton. Examples of divalent aliphatic alcohols include 1,4-butanediol, 3-methyl-1,5-pentanediol, diethylene glycol, neopentyl glycol, 1,6-hexanediol, 1,9-nonanediol, cyclohexanedimethanol, and propylene glycol. Examples of trivalent or higher aliphatic alcohols include glycerin, trimethylolpropane, trimethylolethane, tetramethylolpropane, sorbitol, and pentaerythritol. Among these, polyglycidyl ether of trimethylolpropane is preferred from the viewpoints of viscosity, compatibility, mechanical properties, and the like.

The polycarbonate diol (b-1) is a polycarbonate diol having a structural unit containing a carbonate group as exemplified by the following general formula (5), and the polycarbonate diol has a structural unit derived from a dihydroxy (bifunctional alcohol) compound having a cyclic ether structure as exemplified by the following general formula (6). Specifically, the structural unit derived from such a dihydroxy (bifunctional alcohol) compound may be a structural unit derived from at least one selected from the group consisting of isosorbide, isomannide, and isoidite.

In formula (5), R is a divalent group having 1 to 15 carbon atoms that contains a structure derived from a dihydroxy (difunctional alcohol) compound that may contain oxygen. At least a portion of the structure contains a structural unit derived from a compound represented by general formula (6). m is a number from 1 to 50.) The structure derived from a dihydroxy (difunctional alcohol) compound refers to the remaining structure of a dihydroxy (difunctional alcohol) compound excluding at least one hydroxyl group (which may include a portion) at the molecular end.

The polycarbonate diol may have a structural unit other than that derived from a dihydroxy (difunctional alcohol) compound having a cyclic ether structure represented by formula (6) as a part of its structure, and may have a repeating structure of a divalent hydrocarbon group having 2 to 20 carbon atoms. For example, the divalent hydrocarbon group having 2 to 20 carbon atoms may have a structure derived from an alkylene ether glycol. Specifically, the structure is derived from at least one selected from the group consisting of polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol, copolymerized polytetramethylene ether glycol of 3-methyltetrahydrofuran and tetrahydrofuran, copolymerized polyether polyol of neopentyl glycol and tetrahydrofuran, copolymerized polyether polyol of ethylene oxide and tetrahydrofuran, and copolymerized polyether glycol of propylene oxide and tetrahydrofuran.
Furthermore, the structural unit having a divalent hydrocarbon group having 4 to 12 carbon atoms is derived from at least one selected from the group consisting of neopentyl glycol, 3-methyl-1,5-pentanediol, 2-methyl-1,3-propanediol, and 2-methyl-1,4-butanediol.

The dihydroxy compound having a cyclic ether structure represented by formula (2) as part of the structure of the polycarbonate diol is preferably 10 to 90 mol %, and more preferably 20 to 80 mol %, of the structural units.

Commercially available polycarbonate diols (including those containing a structure derived from a dihydroxy compound having a cyclic ether structure represented by formula (6) in part of their structure) include Benebiol HS0840H (trade name, manufactured by Mitsubishi Chemical Corporation).

In the component (A), the structure derived from the polycarbonate diol (b-1) is 55 mol% or more of the structures derived from all polyol compounds including the polyol compound (b-2) described below. In other words, by using the structure derived from the polycarbonate diol (b-1) in such an amount range among (b-1) and (b-2), it is possible to develop high elasticity and high strength when the cured product is formed, which is preferable. More preferably, 75 mol% or more, and even more preferably, 100 mol% is used. The mole used here refers to the value obtained by dividing the weight of each component by the number average molecular weight. However, the polyol compounds other than the polycarbonate diol (b-1) mentioned here do not include the low molecular weight polyol compound (d) having a number average molecular weight of less than 500 as a chain extender described below.

The polyol compound (b-2) other than the polycarbonate diol (b-1) is a compound represented by the following formulas (2b) to (2d), and examples thereof include polyethylene glycol (PEG), polypropylene glycol (PPG), polytetramethylene ether glycol (PTMG), polyethylene propylene glycol (PEPG), and two or more alkylene oxide copolymers (for example, ethylene oxide-propylene oxide copolymers). In addition, polyol compounds such as lactone-modified polyols, polyester polyols, and polycarbonate polyols can be used as long as they do not impede the object of the present invention, and these can be used alone or in a mixture of two or more. It is preferable that these (b-2) components also have the same number average molecular weight as (b-1).

ここで、Ｒ_２はＨ又はメチル基であり、ｂ１、ｂ２、ｂ３は独立に１～５０の数で、ｃは０又は１の数である。

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.

ここで、ｑ１、ｑ２、ｑ３、ｑ４は独立に１～２０の数である。

Here, q1, q2, q3, and q4 are independently numbers from 1 to 20.

ここで、ｒ，ｓ，ｔは独立に１～２０の数であり、ｎは１～５０の数である。

Here, r, s, and t are independently numbers from 1 to 20, and n is a number from 1 to 50.

The polyisocyanate compound (c) may have 2 or more NCO groups, but preferably has 2. It is preferably represented by general formula (3), in which _R4 is a divalent group selected from formulas (i) to (vi). Among these, it is preferable to select one having excellent compatibility with the epoxy resin (a).

Specific examples include toluene diisocyanate (TDI), 4,4'-diphenylmethane diisocyanate (MDI), xylylene diisocyanate (XDI), hydrogenated xylylene diisocyanate (HXDI), isophorone diisocyanate (IPDI), and naphthalene diisocyanate.

Here, _R4 is preferably a divalent group selected from the formulae i to vi.

In particular, 4,4'-diphenylmethane diisocyanate (MDI) represented by formula (3a) is more preferred from the viewpoints of low molecular weight, no thickening, low cost, safety, and the like.

ここで、Ｒ_５は式viiで表されるアルキレン基であり、ｇは１～１０の数である。 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. It is preferably a diol compound represented by formula (4) having two primary hydroxyl groups.

Here, R ₅ is an alkylene group represented by formula vii, and g is a number from 1 to 10.

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 ease of availability and the good balance between price and properties.

Next, we will explain polyurethane-modified epoxy resins using any or all of the above-listed components (a-1), (a-2), (b-1), (b-2), (c) and (d), including the reaction mechanism. Each component can be used alone or in a mixture of two or more types.

The OH groups in the epoxy resin (a) (e.g., (a-1), (a-2)) are mainly secondary OH groups. On the other hand, the OH groups in the polycarbonate diol (b-1) and the polyol compound (b-2) other than the polycarbonate diol are mainly primary OH groups. Therefore, when the epoxy resin (a), the polycarbonate diol (b-1) and/or the polyol compound (b-2) other than the polycarbonate diol, and the polyisocyanate compound (c) are charged and reacted, the primary OH groups in (b-1) and (b-2) react preferentially with the NCO group in the polyisocyanate compound (c).

Typically, the primary OH groups in (b-1) and (b-2) react with the NCO groups in (c) to produce a urethane prepolymer (P1) with NCO groups at the end. That is, the urethane prepolymer (P1) is formed by combining a structure derived from a polyol derived from (b-1) and (b-2) with a structure derived from a polyisocyanate compound. Here, the polyol-derived structure refers to the remaining structure of the polyol compound excluding at least one hydroxyl group (which may include a portion) at the molecular end. Also, the polyisocyanate compound-derived structure refers to the remaining structure of the polyisocyanate compound excluding at least one isocyanate group (which may include a portion) at the molecular end. It is preferable that the urethane prepolymer (P1) having NCO groups at both ends after the reaction is produced. It is believed that the OH groups (preferably secondary OH groups) in the epoxy resin (a) then react with the terminal NCO groups of the urethane prepolymer (P1) to form urethane bonds, resulting in a urethane prepolymer (P2) in which the epoxy resin (a) is added to both ends or one end of the urethane prepolymer (P1).

In other words, the urethane prepolymer (P) is considered to be a mixture of an NCO-terminated urethane prepolymer (P1) and a urethane prepolymer (P2) in which an epoxy resin (a) [a structure derived from an epoxy resin (a)] is added to both ends or one end of P1. However, because the molar ratio of NCO groups is large and the epoxy resin is used in large excess, it is considered that a urethane prepolymer (P2) in which an epoxy resin is added to both ends of P1 is mainly produced. Here, the structure derived from an epoxy resin refers to the remaining structure excluding at least one hydroxyl group (which may include a portion) of the epoxy resin.

The epoxy resin (a) is preferably used at a ratio of 50 to 90% by weight based on the total amount of components (a), (b-1), (b-2), (c), and (d). As the ratio of epoxy resin (a) is increased, both ends or one end of the urethane prepolymer (P1) are blocked with the epoxy resin (a), the terminal NCO groups are consumed, the amount of urethane prepolymer (P2) that does not react with the low molecular weight polyol compound (d) as a chain extender increases, the ratio of the original urethane prepolymer (P1) with NCO groups at the end decreases, and 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) as a chain extender decreases, so that the molecular weight distribution of the polyurethane-modified epoxy resin also shifts to the low molecular weight side.

Conversely, if the proportion of epoxy resin (a) is reduced, the amount of urethane prepolymer (P2) with both or one end blocked with epoxy resin (a) decreases, and the proportion 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 serves as a chain extender, increases, and the molecular weight distribution of the polyurethane-modified epoxy resin also shifts to the higher molecular weight side.

Regarding epoxy resin (a), for example, (a-1) and (a-2) are 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, but in the case of a polymer, it has a secondary OH group generated by ring-opening of the epoxy group. This secondary OH group is reactive with the NCO group of the polyisocyanate compound (c) or the NCO group at the end of the urethane prepolymer (P), so if the epoxy resin (a-1) or (a-2) has a secondary OH group (for example, a = 1 or more in formula (1)), it will react. Note that if the epoxy resin (a) does not have an OH group (for example, a = 0 in formula (1)), it will not be involved in this reaction. In this way, the polyurethane-modified epoxy resin (A) of the present invention has a complex structure formed by reacting any or all of the above-listed components (a-1), (a-2), (b-1), (b-2), (c), and (d), and is in the form of a mixture that contains the aforementioned epoxy resin (a) that does not have OH groups in a state that is difficult to completely distinguish or eliminate, although it is not thought to be directly involved in the reaction or expression of function. Therefore, there are some circumstances in which it is impossible or impractical to directly identify the (A) component by its structure or properties (so-called impossible or impractical circumstances).

The polyurethane-modified epoxy resin composition of the present invention exhibits high elasticity and high strength because the polyurethane-modified epoxy resin portion undergoes phase separation within the epoxy resin composition.

Since the phase-separated island portion is not compatible with the sea portion, it is preferable that the polyurethane-modified epoxy resin (A) has a weight average molecular weight of 3000 or more, and the amount of the urethane component described later in component (A), i.e., the amount of the polyol compound and the polyisocyanate compound, is 6% by weight or more relative to the total amount of the entire composition. The weight molecular weight is more preferably 3500 or more, and even more preferably 5000 or more. It is also preferable that it is 15000 or less. In order to form a desirable phase-separated structure, the amount of the urethane component described later in component (A), i.e., the amount of the polyol compound and the polyisocyanate compound, is 6.0% by weight or more and 15% by weight or less relative to the total amount of the entire composition, and more preferably 8.0% by weight or more and 12% by weight or less.

The method for producing the polyurethane-modified epoxy resin (A) used in the present invention is, for example, to use (a-1), (a-2), etc. as the epoxy resin (a) in an amount of 50 to 90% by weight based on the total amount of the polycarbonate diol (b-1) as the polyether polyol compound, the polyol compound (b-2) other than the polycarbonate diol, the polyisocyanate compound (c), and the low molecular weight polyol compound (d) having a number average molecular weight of less than 500 as the chain extender, and to react (b-1), (b-2), and the polyisocyanate compound (c) in the presence of the epoxy resin (a) (reaction 1). In this reaction 1, the reaction between (b-1) and (b-2) and the polyisocyanate compound (c) occurs preferentially, and a urethane prepolymer (P1) is produced. Thereafter, the urethane prepolymer (P1) reacts with the epoxy resin (a), and a urethane prepolymer (P2) in which both ends of P1 are mainly epoxidized is produced.

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

After that, 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 (P1) 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) do not react with each other because they are alcoholic OH groups.

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, but because this is a reaction between the NCO groups and the OH groups in the low molecular weight polyol compound (d), milder conditions than those for reaction 1 may be used.

In the above reactions (Reactions 1 and 2), a catalyst can be used as necessary. This catalyst is used for the purpose of fully completing the formation of urethane bonds, and examples of the catalyst include amine compounds such as ethylenediamine, tin compounds, and zinc compounds.

In reaction 2, the remaining urethane prepolymer (P1) having NCO at both or one end reacts with the low-molecular-weight polyol compound (d) to elongate its chain and form a polyurethane, while the urethane prepolymer (P2) having both ends as an adduct of epoxy resin (a) remains unreacted with component (d).
When the low molecular weight polyol compound (d) is not used, when the polyisocyanate compound (c) is added, the terminal NCO reacts with each hydroxyl group to form a urethane prepolymer (P2).
The polyurethane-modified epoxy resin used in the present invention 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.

The polyurethane concentration in the polyurethane-modified epoxy resin composition can be increased or decreased by increasing or decreasing the amount of the polyurethane-unmodified epoxy resin (B). Here, the polyurethane concentration in the epoxy resin composition is calculated by the following formula when the above-mentioned components are used, but the types of each component are not limited thereto.
Polyurethane concentration={(b−1)+(b−2)+(c)+(d)}×100/{(A)+(B)+(C)}
In this case, (A) = (a-1) + (a-2) + (b-1) + (b-2) + (c) + (d).
Here, (a-1), (a-2), (b-1), (b-2), (c), (d), (A), (B), and (C) are the weights of the corresponding components used. When other components, such as a curing accelerator (D), 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 6 to 20% by weight.

In the polyurethane-modified epoxy resin (A) of the present invention, in the above-mentioned example, the urethane component concentration is {(b-1) + (b-2) + (c) + (d)} / {(a-1) + (a-2) + (b-1) + (b-2) + (c) + (d)}. In the present invention, the urethane component concentration is 15 to 60% by weight, and preferably 18 to 45% by weight. If the urethane component concentration is less than 15% by weight, the molecular weight of the urethane decreases, the compatibility of the islands during phase separation increases, and it becomes difficult to form sufficient island sizes, and the required physical properties may not be expressed. Conversely, if it exceeds 60% by weight, the molecular weight of the urethane increases more than necessary, and the viscosity of the polyurethane-modified epoxy resin and its composition increases, which may reduce the impregnation of carbon fibers, etc.

As the polyurethane-unmodified epoxy resin (B) used in the polyurethane-modified epoxy resin composition of the present invention, the above-mentioned epoxy resin (a) (a-1), (a-2), etc. used as the raw material for the polyurethane-modified epoxy resin (A) can be preferably used. That is, epoxy resins that are not polyurethane-modified and are liquid at 30°C are preferred. Among them, bisphenol A type epoxy resins and/or bisphenol F type epoxy resins are preferred from the viewpoints of ease of availability and good balance between price and properties. As (a-2), polyglycidyl ether of trimethylolpropane is preferred from the viewpoints of viscosity, compatibility, mechanical properties, etc.

In the polyurethane-modified epoxy resin composition of the present invention, a polyfunctional epoxy resin having three or more functionalities can be used as the polyurethane-unmodified epoxy resin (B) to adjust the viscosity or increase the Tg. When a polyfunctional epoxy resin is used, the crosslink density increases, the phase separation state changes, and the fracture toughness is lost, so it is preferable to use 0.1 to 10% by weight based on the total composition weight. Examples of polyfunctional epoxy resins having three or more functionalities include phenol novolac type epoxy resins, cresol novolac type epoxy resins, glycidylamine type epoxy resins such as tetraglycidyldiaminodiphenylmethane, glycidylphenyl ether type epoxy resins such as tetrakis(glycidyloxyphenyl)ethane and tris(glycidyloxyphenyl)methane, and glycidylamine type and glycidylphenyl ether type epoxy resins such as triglycidylaminophenol. Furthermore, epoxy resins modified from these epoxy resins, brominated epoxy resins obtained by brominating these epoxy resins, and the like can be used.

In this case, it is preferable to use an epoxy resin with a viscosity of 10,000 mPa·s or less at 25°C. This reduces the viscosity of the composition, improves the impregnation of carbon fibers, and enables application to tow prepregs and pultrusion molding. Examples include glycidyl ether type epoxy resins, glycidyl ester type epoxy resins, glycidyl amine type epoxy resins, and alicyclic epoxy resins. These epoxy resins can be used alone or in combination of two or more types.

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.

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 types.

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 types.

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.

As the hardener (C), it is recommended to use dicyandiamide (DICY) or its derivatives, since it can be made into a one-component with excellent storage stability and is easily available. Examples of derivatives include guanidine, dicyandiamide, diguanide, and melamine.

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 (A) and the polyurethane-unmodified epoxy resin (B) 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.

In the urethane-modified epoxy resin composition of the present invention, the (A) component is preferably 20 to 70% by weight. The (B) component is preferably 30.0 to 80.0% by weight. Furthermore, the (C) component is preferably 0.1 to 20.0% by weight, and more preferably 1 to 10% by weight.

The urethane-modified epoxy resin composition of the present invention can further contain a curing accelerator (D). As the curing accelerator (D), an imidazole-based curing assistant is preferably used to impregnate the reinforcing fibers during mixing, suppress the increase in viscosity, and satisfy the heat resistance during curing. As the imidazole-based curing assistant, it is preferable to use 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, 1-cyanoethyl-2-ethyl-4-methylimidazole, etc. 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 preferably used from the viewpoint of being able to cure in a short time. The imidazole compounds containing a triazine ring may be used alone or in combination of two or more kinds.

On the other hand, depending on the application or construction method, there may be cases where it is not necessary to cure in such a short time as described above. 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 the curing accelerator (D) is preferably in the range of 0.1 to 5 wt % based on the total amount of the epoxy resin including the polyurethane-modified epoxy resin (A) and the polyurethane-unmodified epoxy resin (B) and the curing agent (C).

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

The amount of release agent to be 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, and the adhesion and bonding properties may decrease. The release agents may be used alone or in combination of two or more types.

There are no particular limitations on such liquid release agents, so 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.

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

The epoxy resin composition of the present invention can contain a rubber component (F) as necessary depending on the application and construction method. A copolymer made from acrylonitrile and butadiene is preferably used as the rubber component because it has excellent solubility in epoxy resin, but since the viscosity of the resin composition is likely to increase, particles containing a rubber component insoluble in epoxy resin are preferred. Crosslinked rubber particles themselves can also be used, but rubber particles having a core-shell structure in which the surface of epoxy resin-insoluble rubber particles is coated with a non-rubber component are particularly preferred. In this case, the coating component may be one that dissolves or swells in epoxy resin, such as polymethyl methacrylate, and is preferred because it improves the dispersion of the particles in the epoxy resin.

The rubber component preferably has a volume average particle size of 1 to 500 nm, more preferably 3 to 300 nm. The amount of rubber component (F) in the composition is preferably 1 to 15% by weight, more preferably 3 to 12% by weight. The addition of the rubber component makes it easier to obtain the fracture toughness required for the molded fiber-reinforced composite material.

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 a curable resin composition, and for example, the heating temperature conditions may be appropriately selected depending on the type of curing agent to be combined and the intended use. For example, the epoxy resin composition may be heated in a temperature range of room temperature to about 250°C. For molding, a general method for curable resin compositions may also be used.

The cured product of the present invention has excellent heat resistance, tensile elasticity, and tensile strength, so the glass transition temperature (Tg) of the cured product is preferably 105°C or higher, the tensile modulus is preferably 3.2 GPa or higher, and the tensile strength is preferably 80 MPa or higher.

The fiber-reinforced composite material of the present invention can be obtained by impregnating the epoxy resin composition of the present invention into reinforcing fibers to obtain a fiber-reinforced composite material composition, which is then molded and cured. The reinforcing fibers may be any of twisted, untwisted, or non-twisted yarns, but untwisted or non-twisted yarns are preferred because they have excellent moldability in fiber-reinforced composite materials. Furthermore, the form of the reinforcing fibers may be one in which the fibers are aligned in one direction, or a woven fabric. For woven fabrics, plain weave, satin weave, and other fabrics may be freely selected depending on the part to be used and the application. Specifically, carbon fiber, glass fiber, aramid fiber, boron fiber, alumina fiber, silicon carbide fiber, and the like are excellent in mechanical strength and durability, and these may be used alone or in combination of two or more types. Among these, carbon fiber is particularly preferred because it provides good strength to the molded product, and various types of carbon fiber such as polyacrylonitrile, pitch, and rayon can be used.

The method for obtaining a fiber-reinforced composite material from the epoxy resin composition of the present invention is not particularly limited, but examples include a method in which each component constituting the epoxy resin composition is uniformly mixed to produce a varnish, and a prepreg is produced by impregnating a material such as a sheet in which continuous carbon fibers are arranged in one direction or a carbon fiber fabric with resin, a carbon fiber substrate with a resin layer on at least one surface, and a fiber layer is further arranged on the surface, a method in which unidirectional reinforcing fibers in which reinforcing fibers are aligned in one direction are immersed in the varnish obtained above (state before curing in the pultrusion method or filament winding method, tow prepreg), a method in which sheets or fabrics of reinforcing fibers are stacked and set in a mold, and then resin is injected into the mold and impregnated by applying pressure or by reducing the pressure inside (state before curing in the RTM method), etc.

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 preferable that it is in the range of 50 to 75%. If the volume content is less than 40%, the content of the epoxy resin composition is too high, and the resulting cured product may have insufficient elastic modulus or strength, or may not be able 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, and the cured product may have insufficient elastic modulus or strength, or may have reduced interfacial adhesion.

Next, the present invention will be specifically described based on examples. The present invention is not limited to these specific examples, and any modifications or changes are possible without departing from the gist of the present invention.

The physical properties were evaluated as follows.
(1) Judgment 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 Micro Spatula flat plate, and dried at room temperature for 15 minutes to evaporate the tetrahydrofuran to prepare a sample for IR measurement. This was set in a PerkinElmer FT-IR device Spectrum-One, and it was judged that there were no residual NCO groups when the stretching vibration absorption spectrum at 2270 cm ^-1 , which is the characteristic absorption band of the NCO group, disappeared.
(2) Epoxy equivalent: Quantified according to JIS K 7236.
(3) Hydroxyl equivalent: 25 ml of dimethylformamide is placed in a 200 ml glass-stoppered Erlenmeyer flask, and a sample containing 11 mg/equivalent or less of hydroxyl is precisely weighed and added to dissolve. 20 ml of 1 mol/L-phenylisocyanate toluene solution and 1 ml of dibutyltin maleate catalyst solution are added with a pipette, shaken well to mix, and then sealed to react for 30 to 60 minutes. After the reaction is complete, 20 ml of 2 mol/L-dibutylamine toluene solution is added, shaken well to mix, and left to stand for 15 minutes to react with the excess phenylisocyanate. Next, 30 ml of methyl cellosolve and 0.5 ml of bromocresol green indicator are added, and the excess amine is titrated with a standardized methyl cellosolve perchlorate solution. The indicator changes from blue to green and then to yellow, so the first point at which it turns yellow is taken as the end point, and the hydroxyl equivalent is calculated using the following formulas I and II.
Hydroxyl equivalent (g/eq)=(1000×W)/C(S−B) (i)
C: Concentration of methyl perchlorate cellosolve solution mol/L
W: sample amount (g)
S: Titration volume of methyl perchlorate cellosolve solution (ml)
B: Amount of methyl perchlorate cellosolve solution required for blank test during titration (ml)
C = (1000 × w) / {121 × (s-b)} ... (ii)
w: Amount of tris-(hydroxymethyl)-aminomethane weighed for standardization (g)
s: Amount of methyl perchlorate cellosolve solution required for titration of tris-(hydroxymethyl)-aminomethane (ml)
b: Titration volume of methyl perchlorate cellosolve solution required for blank test during standardization (ml)
(4) Hydroxyl value: Measured by a method based on JIS K1557.
(5) Viscosity: The viscosity value at 25° C. was measured using a cone-plate type E-type viscometer. The epoxy resin composition of the present invention was prepared, and 0.8 mL of the composition was used for measurement. The value 60 seconds after the start of measurement was recorded as the viscosity value.

(6) Glass transition temperature (Tg): The glass transition temperature (Tg) was determined by measuring the intersection of the tangent line at the base line and the inflection point with a differential scanning calorimeter (DSC) at a heating rate of 10° C./min.
(7) Tensile test: Test pieces were prepared by molding the cured products into the shape specified in JIS K 7161 using a mold, and a tensile test was carried out at room temperature of 23° C. using a universal testing machine to measure the tensile strength, tensile elongation, and tensile modulus.
(8) 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°C, eluent THF, flow rate 0.35 mL/min
Sample: Polystyrene SRM706a
(9) Fracture toughness: Test pieces were prepared from cured products molded by casting into a mold in the shape specified in JIS K 6911, and tested using a universal testing machine at a room temperature of 23° C. and a crosshead speed of 0.5 mm/min. Before testing, notches (indentations) were made in the test pieces by applying a razor blade to the test pieces and impacting the razor blade with a hammer.

The raw materials used were as follows:
Component A
Epoxy resin (a-1):
Epotohto YDF-170 manufactured by Nippon Steel Chemical & Material, bisphenol F type epoxy resin, epoxy equivalent 170 g/eq, hydroxyl equivalent 2600 g/eq, liquid epoxy resin (a-2):
Nippon Steel Chemical & Material Co., Ltd. Epotohto YH-300, polyglycidyl ether of trimethylolpropane, epoxy equivalent 142g/eq, hydroxyl equivalent 837g/eq, liquid

Polycarbonate diol (b-1):
Benebiol HS0840H manufactured by Mitsubishi Chemical, number average molecular weight 800, hydroxyl equivalent 400g/eq

Polyol compound (b-2):
ADEKA ADEKA POLYETHER P-2000, polypropylene glycol, number average molecular weight 2000, hydroxyl equivalent 1000g/eq

Polyisocyanate compound (c):
Cosmonate PH, 4,4'-diphenylmethane diisocyanate (MDI) manufactured by Mitsui Chemicals

Component B
Nippon Steel Chemical & Material Co., Ltd. Epotohto YD-128, bisphenol A type epoxy resin, epoxy equivalent 187g/eq, liquid Nippon Steel Chemical & Material Co., Ltd. Epotohto YDF-170, bisphenol F type epoxy resin, epoxy equivalent 170g/eq, liquid Nippon Steel Chemical & Material Co., Ltd. Epotohto YH-300, polyglycidyl ether of trimethylolpropane, epoxy equivalent 142g/eq, liquid

Component C:
EVONIK DICYANEX1400F, dicyandiamide

Component D:
Crystalline imidazole, Curesol 2MZA-PW, 2,4-diamino-6-[2'-methylimidazolyl-(1')]-ethyl-s-triazine manufactured by Shikoku Chemical Industry Co., Ltd. Component F:
Kaneka MX-154, core-shell rubber content 40 wt%, BPA type epoxy resin content 60 wt%, average particle size 150-200 nm

Example 1
The epoxy resin (a-1) used was Epotohto YDF-170, the epoxy resin (a-2) used was Epotohto YH-300, the polycarbonate diol used was Mitsubishi Chemical HS0840H, and the polyisocyanate (c) used was Cosmonate PH (MDI). The amounts used (unit: parts by weight) are shown in Table 1.
Epotohto YDF-170, Epotohto YH-300, and HS0840H were charged into 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 and mixed for 120 minutes. Cosmonate PH was then added, and the mixture was reacted at 120° C. for 2 hours to obtain a polyurethane-modified epoxy resin (UE1).
The completion of the reaction was confirmed by the disappearance of the absorption spectrum of the NCO group by IR measurement. The epoxy equivalent of the obtained polyurethane-modified epoxy resin was 195 g/eq and the weight average molecular weight was 5,800.

Examples 2 to 5, Comparative Examples 1 to 5
The reaction was carried out in the same manner as in Example 1, except that the raw material charging compositions were as shown in Table 1, to obtain polyurethane-modified epoxy resins (UE2 to UE10). The epoxy equivalents were 222 g/eq for UE2, 213 g/eq for UE3, 179 g/eq for UE4, 202 g/eq for UE5, 215 g/eq for UE6, 209 g/eq for UE7, 242 g/eq for UE8, 253 g/eq for UE9, and 206 g/eq for UE10.

Next, examples of epoxy resin compositions and cured epoxy resin products using the polyurethane-modified epoxy resins obtained in Examples 1 to 5 and Comparative Examples 1 to 5 are shown. The results are summarized in Table 2.

Example 6
The polyurethane-modified epoxy resin UE1 obtained in Example 1 as the polyurethane-modified epoxy resin (A), Epotohto YD-128, Epotohto YDF-170, and Epotohto YH-300 as the polyurethane-unmodified epoxy resin (B), dicyandiamide as the curing agent (C), and 2MZA-PW as the curing accelerator (D) were charged in a 200 ml dedicated disposable cup in the formulations shown in Table 2, and the mixture was stirred and mixed while vacuum degassing for 5 minutes using a vacuum planetary mixer for rotation and revolution laboratory to obtain a liquid resin composition. Here, the molar ratio of epoxy groups to dicyandiamide was 1.0:0.5, and 140 g of a polyurethane-modified epoxy resin composition was prepared.
Next, this liquid resin composition was poured into a mold having a groove shape of the test piece dimensions of JIS K7161. The test piece dimensions for the tensile test were dumbbell-shaped, the fracture toughness test piece dimensions were 100 mmL x 10 mmW x 4 mmt, and the DMA test piece dimensions were 100 mmL x 10 mmW x 2 mmt. The liquid resin composition was poured into a mold or silicon frame, and cut to a size suitable for the measurement. The pourability at this time was at a level that allowed for sufficient pouring with a margin. Next, the resin composition was poured into a mold that had been preheated at 130°C, and then placed in a hot air oven and heated and cured at 130°C for 10 minutes to prepare an epoxy resin cured product test piece. The test results using this test piece are shown in Table 2.

Examples 7 to 16, Comparative Examples 6 to 11
A resin composition and a cured product 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 Table 2. The test results using these test pieces are shown in Table 2.
By using the polyurethane-modified epoxy resin part of the present invention, curing can be completed within a short curing condition of 130°C for 10 minutes, and a resin composition can be obtained that has low viscosity, excellent impregnation properties, sufficient heat resistance, and excellent tensile elasticity and tensile strength.

The polyurethane-modified epoxy resin composition of the present invention has low viscosity, excellent fiber impregnation, and excellent tensile modulus and tensile strength while suppressing the decrease in glass transition temperature, making it useful as a matrix resin for composite materials for industrial, sports and leisure, civil engineering and construction, etc., and as a compounding resin for adhesives.

Claims (9)

The following components (A) to (C):
(A) a polyol-derived structure and a polyisocyanate-derived structure, in which a structure having an isocyanate group at a molecular chain end has reacted with a hydroxyl group of an epoxy resin having two or more epoxy groups on average in the molecule;
The polyol-derived structure contains 55 mol % or more of a structure derived from a polycarbonate diol having a structural unit containing a cyclic ether structure and a carbonate group in the molecule,
one-third or more of the number of moles of the epoxy resin having two or more epoxy groups in an average molecule is an aliphatic epoxy resin,
A polyurethane-modified epoxy resin having a urethane component concentration of 15 to 60% by weight.
A polyurethane-modified epoxy resin composition comprising (B) a polyurethane unmodified epoxy resin, and (C) a curing agent, the polyurethane-modified epoxy resin composition containing 20 to 70% by weight of component (A), 30.0 to 80.0% by weight of component (B), and 0.1 to 20.0% by weight of component (C) based on the total weight of the composition. The polyurethane-modified epoxy resin composition according to claim 1, characterized in that, in the polyurethane-modified epoxy resin (A), the polycarbonate diol forming the structure derived from the polycarbonate diol contains a structure represented by general formula (5).

(Here, R is a divalent group having 1 to 15 carbon atoms containing a structure derived from a difunctional alcohol which may contain oxygen, and at least a portion of the structure is derived from a compound represented by general formula (6). m is a number from 1 to 50.)

The polyurethane-modified epoxy resin composition according to claim 1, characterized in that in the polyurethane-modified epoxy resin (A), at least half of the number of moles of the epoxy resin having, on average, two or more epoxy groups in the molecule is an aliphatic epoxy resin. The polyurethane-modified epoxy resin composition according to claim 1, characterized in that the polyurethane-modified epoxy resin (A) has a weight average molecular weight of 3,000 or more. The polyurethane-modified epoxy resin composition according to claim 1, characterized in that in the polyurethane-modified epoxy resin (A), the aliphatic epoxy resin is a polyglycidyl ether of trimethylolpropane. A cured product obtained by curing the polyurethane-modified epoxy resin composition according to any one of claims 1 to 5. 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. A fiber-reinforced composite material obtained from the resin composition for fiber-reinforced composite materials described in claim 7. a polyol-derived structure and a polyisocyanate-derived structure, and a structure having an isocyanate group at a molecular chain end, the structure being reacted with a hydroxyl group of an epoxy resin having two or more epoxy groups on average in the molecule;
The polyol-derived structure contains 55 mol % or more of a structure derived from a polycarbonate diol having a structural unit containing a cyclic ether structure and a carbonate group in the molecule,
one-third or more of the number of moles of the epoxy resin having two or more epoxy groups in an average molecule is an aliphatic epoxy resin,
A polyurethane-modified epoxy resin having a urethane component concentration of 15 to 60% by weight.