Abstract: A styrenic thermoplastic resin composition of the present invention comprises about 100 parts by weight of base resin comprising (A) about 10 to about 99 parts by weight of styrenic resin containing an epoxy group and (B) about 1 to about 90 parts by weight of polyester resin; and (C) about 0.1 to about 97 parts by weight of amorphous modified polyester resin, based on the total weight of the base resin. A molded article produced from the styrenic thermoplastic resin composition of the present invention can have excellent impact resistance and paintability.

Abstract: Disclosed herein is a thermoplastic resin composition with good heat stability, light stability and impact strength. In an exemplary embodiment, the thermoplastic resin composition comprises (A) about 10 to about 99 parts by weight of an epoxy group-containing styrenic resin; (B) about 1 to about 90 parts by weight of a polyester resin; (C) about 0.1 to about 10 parts by weight of a thermoplastic polyester resin comprising a cycloaliphatic diol such as cyclohexane dimethanol, per about 100 parts by weight of a base resin comprising (A)+(B); (D) about 0.05 to about 2 parts by weight of a hindered phenolic compound, per about 100 parts by weight of a base resin comprising (A)+(B); (E) about 0.05 to about 4 parts by weight of a phosphite compound, per about 100 parts by weight of a base resin comprising (A)+(B); and (F) about 0.

Abstract: The present invention relates to cationically curable compositions for curing on a surface comprising a cationically curable component, an accelerator species comprising at least one vinyl ether functional group and an initiator component capable of initiating cure of the cationically curable component. The initiator comprises at least one metal salt, which is chosen so that it is reduced at the surface, and where the standard reduction potential of the initiator component is greater than the standard reduction potential of the surface, and where when the composition is placed in contact with the surface, the metal salt of the initiator component of the composition is reduced at the surface, thereby initiating cure of the cationically curable component of the composition. The accelerator species comprising at least one vinyl ether functional group greatly enhances the rate of cure. No catalytic component is required in the composition for efficient cure.

Abstract: The present invention relates to compounds suitable to use as curing agents for epoxy systems which can be obtained by reacting an amine-functional compound with an ?-? unsaturated acid and/or ester and a mono-functional epoxy compound. The invention further relates to coating compositions comprising these curing agents.

Abstract: An active-hydrogen-containing (carboxyl or hydroxyl) phosphorus compound is provided. An epoxy resin semi-thermoset formed by bonding the phosphorus compound to an epoxy group is also provided. A flame-retardant epoxy resin thermoset is formed after reacting the epoxy resin semi-thermoset with a curing agent. The epoxy resin thermoset possesses excellent flame retardancy, heat stability, and high glass transition temperature (Tg), does not produce toxic and corrosive fumes during combustion, and thus is an environmentally friendly flame-retardant material.

Abstract: Curative fibre components comprise one or more fibres for filaments of curative suitable to cure curable resins such as thermoset resin. In curative fibre components comprising a plurality of fibres of curative, the fibres can be commingled, such as twisting, to form a thread or yarn. Curative fibre components can be used to form a material in the form of a sheet, fabric, layer, textile or mat of woven or non-woven curative fibres. Curative fibre components can be used to produce composite materials such as fibre reinforced resinous composite materials. The curative fibre components can be commingled, including interwoven, stitched and layered with other fibres or fibrous materials, such as fibrous reinforcement, fibrous curable resin, fibrous thermoplastic, other non-reinforcing fibres to form composite materials, prepregs, preforms and articles.

Abstract: The present invention relates to an epoxy resin composition for optical-semiconductor element encapsulation, including the following ingredients (A), (B) and (C): (A) an epoxy resin; (B) a curing agent including a phenol resin (b1) represented by the following general formula (1), and an acid anhydride (b2) in which R represents -phenyl- or -biphenyl-, and n is 0 or a positive integer; and (C) a curing accelerator, in which a ratio between the number of hydroxyl groups of the ingredient (b1) and the number of hydroxyl groups of the ingredient (b2), in the ingredient (B) is 99.99/0.01 to 50/50 in terms of b1/b2.

Abstract: Modified epoxy resins comprising the reaction product of rosin and a linking molecule, further reacted with an epoxy resin, are disclosed. Aqueous dispersions and coatings comprising these resins are also disclosed.

Abstract: Compositions comprising surface-modified nanocalcite particles dispersed in a curable resin, and to coatings and fibrous composites incorporating such compositions are described. The surface-modifying agents include a binding group ionically associated with the calcite and a compatiblizing segment, compatible with the curable resin. The surface-modifying agent may also include a reactive group capable of reacting with the curable resin. Methods of preparing nanocalcite composites and coating a fibrous composites prepared from such nanocalcite composites are also described.

Abstract: Oligomers and polymers containing epoxide groups and silane groups and preparable by reacting (A) at least one low molecular mass, oligomeric or polymeric compound containing at least two epoxide groups (a1) with (B) at least one silane containing (b1) at least one at least divalent organic radical which per se is not hydrolyzable, (b2) at least one cyclic dicarboxylic anhydride group and (b3) at least one silane group containing at least one hydrolyzable group (b31), the cyclic dicarboxylic anhydride groups (b2) being attached to the silane groups (b3) via the radicals (b1), the equivalent ratio of epoxide groups (a1) to dicarboxylic anhydride groups (b2) being 0.7 to 100; processes for preparing them, and their use for preparing anhydrous curable compositions.

Abstract: Provided are: an adamantane derivative represented by the following general formula (I) giving a cured product excellent in optical characteristics such as transparency and light resistance, durabilities such as heat resistance, and electrical characteristics such as dielectric constant; a method of producing the adamantane derivative; a resin composition containing the adamantane derivative and an epoxy resin curing agent; and a sealing agent for an optical semiconductor using the resin composition: where: Y represents a group selected from a hydrocarbon group, a hydroxyl group, a carboxyl group, and an ?O group formed by two Y's being combined together; Z represents a cyclic ether group; n represents an integer of 0 or more; and p represents an integer of 2 to 4 and q represents an integer of 0 to 14, while satisfying 2?p+q?16.

Abstract: The disclosure pertains to amphiphilic block copolymers comprising an aliphatic polycarbonate chain coupled to a hydrophilic polymer. Such amphiphilic polymers may have the formula A-L-B, where A- is a polycarbonate or polyethercarbonate chain having from about 3 to about 500 repeating units, L is a linker moiety and —B is a hydrophilic oligomer having from about 4 to about 200 repeating units. Provided copolymers are useful as surfactants capable of emulsifying aqueous solutions and supercritical carbon dioxide. Provided copolymers also have utility as additives for use in enhanced oil recovery methods.

Abstract: The present invention is directed to a passivating material suitable for passivating a metal surface. The passivating material comprises a polymer which comprises (a) at least one nitro group, and/or pyridine group, and/or phenolic hydroxyl group; and (b) at least one group selected from a phosphorous-containing group and/or a carboxylic acid group, wherein the at least one phosphorous-containing group is selected from a phosphate, a phosphite, or a non-nitrogen substituted phosphonate.

Abstract: A process for preparing a diaminoacetonitrile which includes reacting by contacting an amine comprising two primary amine groups with a cyanohydrin. The diaminoacetonitrile produced may subsequently be used in the production of polymers and/or as a curing agent for epoxy resins.

Abstract: A heat-conductive dielectric polymer material having an inter-penetrating-network (IPN) structure includes a polymer component, a curing agent, and a heat-conductive filler uniformly dispersed in the polymer component. The polymer component includes a thermoplastic plastic and a thermosetting epoxy resin. The curing agent is used to cure the thermosetting epoxy resin at a curing temperature. The heat conductivity of the heat-conductive dielectric polymer material is larger than 0.5 W/mK. A heat dissipation substrate including the heat-conductive dielectric polymer material in the present invention has a thickness of less than 0.5 mm and bears a voltage of over 1000 volts.

Abstract: An embodiment of the present invention is a technique to form a resin. A mixture is formed by a curing agent dissolved in the epoxy resin. The epoxy resin contains a first rigid rod mesogen. The curing agent contains a second rigid rod mesogen and one of a hydroxyl, amine, and anhydride.

Abstract: Polymers having polyolefin segments as the side chain, with a structural unit represented by the following Formula (1): wherein A is an olefin polymer having a weight average molecular weight of 400 to 500,000; R is H, an alkyl group, or an aralkyl group; W and Z are each O, HN, or S; and x and y are each 0 or 1, with the proviso that at least one of them is 1. The polymer can be applied as an antistatic agent, a cosmetic additive, a releasing agent for toner, a pigment dispersant, a lubricant for vinyl chloride resins, a coating material, an emulsion composition and the like.

Abstract: Improved mechanical properties of carbon nanotube (CNT)-reinforced polymer matrix nanocomposites are obtained by functionalizing the CNTs with a compound that bonds well to an epoxy matrix before dispersing the solution using a microfluidic process. Well-dispersed particles are obtained that sufficiently improve mechanical properties of the nanocomposites, such as flexural strength and modulus. The resulting composite material is used for coatings on marine vessels.

Abstract: The present invention inhibits the occurrence of the foreign matters attributable to an adhesive for bonding an injection needle to a needle-base member so as to enhance the yield of a syringe when producing the same. A front-assembly (3) additionally provided at a leading end of an injection cylinder (2) comprises an injection needle (4), a needle-base member (5), a connection hub (6) and a protector cap (7). The injection needle (4) and the needle-base member (5) are fixed to each other with an epoxy adhesive (19). This adhesive (19) contains denatured aliphatic epoxy resin in the amount set to about 10 to about 25 wt % and its viscosity is set to about 20000 to about 40000 mPa·s. This adhesive (19) is heated at a temperature of at least 130 degrees C. for about 20 minutes to cure it. After the front-assembly (3) and the injection cylinder (2) have been sterilized with vapor, the connection hub (6) has a connection portion (17) external fitted and secured to the leading end of the injection cylinder (2).

Abstract: Disclosure is provided for imidazole derivative compounds that prevent, remove and/or inhibit the formation of biofilms, compositions comprising these compounds, devices comprising these compounds, and methods of using the same.

Abstract: An adamantane derivative of formula (I), a compound of formula (VII) or (VIII), compositions containing them, and optical electronic members using the resin compositions. In the formulas, W represents, for example, a hydrogen atom, X is bonded to a bridge-head adamantane carbon and represents, for example, a group of represented by the general formula (II), Y represents a group of formula (V) or (VI), R1 represents a methyl group or an ethyl group, R2 represents a C1 to C10 hydrocarbon group which may contain O or S, m is an integer of 2 to 4, k is an integer of 0 to (16?m) and p and q are each an integer of 1 to 5.

Abstract: A composition for preparing a resin is provided. The composition includes a brominated epoxy resin, a urethane-modified copolyester, a curing agent and a solvent. A prepreg is also provided. The prepreg includes a glass fabric and a resin layer on the glass fabric. The resin layer is made from the foregoing resin.

Abstract: Compounds having the formula (I) wherein L is a linking group, at least one of R1 to R10 comprises the group C?N, at least one of R1 to R5 and at least one of R6 to R10 comprise the group NH2 for use as curing agents in an epoxy resin, together with a process for their synthesis and composites comprising the curing agents.

Abstract: Provided are an epoxy composition, an adhesive film, a dicing die bonding film and a semiconductor device using the same. Specifically, the epoxy composition and a use thereof are provided, wherein the epoxy composition has a gel content of 5˜20%, measured under certain conditions. The epoxy composition according to the present invention, as an adhesive agent, shows excellent elastic properties, when prepared to have a low glass transition temperature, exhibiting good adhesion at high temperature and having minimal occurrence of buns during processing. According to the present invention, it is therefore possible to prevent defects owing to die cut shift, during a wire bonding or molding process at high temperature, and obtain a highly reliable semiconductor device owing to the excellent adhesiveness and workability of the adhesive agent.

Abstract: A prepreg composite material that includes a fiber layer and a resin comprising a thermoset resin component, a curing agent and a fibrous micropulp. The micropulp component is an aramid fiber having a volume average length of from 0.01 to 100 micrometers. The prepreg is useful in composite panel construction for minimizing fluid permeation into the cured structure. This prepreg is particularly suitable for making honeycomb sandwich panels. Film adhesives, liquid and paste resins containing aramid fiber micropulp are also disclosed.

Abstract: The invention describes amphiphilic polymer compounds which are prepared by a) reacting a di-, tri- or tetraglycidyl compound (A) with an optionally unsaturated reactive component (B) consisting of C8-C28-fatty acid, a C8-C28-alcohol or a secondary C8-C28-amine, and allowing b1) the reaction product from stage a) to react further first with b1?) an aliphatic or aromatic polyisocyanate compound (C) b1?) and optionally then with a polyalkylene oxide compound (D), and b1?) reacting the reaction product from stage b1?) or optionally b1?) with a component (E) which is reactive towards isocyanates and has at least one OH, NH2, NH or SH group, or b2) allowing the reaction product from stage a) to react to completion with the reaction product of component (C) with component (E) and optionally (D) and (C), or b3) allowing the reaction product from stage a) to react to completion with the reaction product from component (C) and component (D) and optionally (C) and optionally the reaction product of component (C) and

Abstract: A heat-curing epoxy resin composition that includes an epoxy resin, a curing agent, an accelerator, and an optional toughener. The epoxy resin compositions are suitable in particular for use as bodyshell adhesives and for preparation of structural foams. An accelerator of formula (I) results in increased impact strength the of heat-curing epoxy resin compositions.

Abstract: An epoxy resin curable composition for a prepreg, comprising the following components (A) to (E): (A) a polyamide compound having a structure derived from an aromatic diamine including a phenolic hydroxyl group, the aromatic diamine having the phenolic hydroxyl group in a position adjacent to an amino group; (B) an epoxy resin; (C) an epoxy resin curing agent; (D) a filler; and (E) a solvent.

Abstract: Processes for enzymatic synthesis comprising: (a) providing an aliphatic poly(oxyalkylene)amine; and (b) reacting the aliphatic poly(oxyalkylene)amine with a reactant selected from the group consisting of acrylic acid compounds and alkyl esters thereof, in the presence of a hydrolase in bulk or in a liquid reaction medium comprising an organic solvent to for a poly(oxyalkylene)acrylamide.

Abstract: Use of a resin system for making a composite material in a liquid moulding process. The resin system comprises an epoxy component and at least one curing agent, and at least 35 wt. % of the epoxy component is one or more naphthalene based epoxy resin. There is also provided a cured composite material, and a method of making the cured composite material in a liquid moulding process which comprises placing fibre reinforcement and the resin system in a mould and curing. The resin system and the methods of making a cured composite material are particularly applicable to liquid moulding processed such as resin trans moulding (RTM), vacuum assisted resin transfer moulding (VARTM), Seeman composite resin infusion moulding (SCRIMP), resin infusion under flexible tooling (RIFT), and liquid resin infusion (LRI).

Abstract: A protective crosslinkable coating composition comprising modified epoxy resin and crosslinker the modified epoxy resin being the reaction product, by weight, of i) from 80 to 99.9 parts of di-epoxy resin of epoxy equivalent weight from 500 to 5000 and formed from the reaction of bis phenol A diglycidyl ether and bis phenol A and ii) from 0.1 to 20 parts of reactive material characterised in that a) the di-epoxy resin contains minor amounts of resin components of molecular weight less than 1000 Daltons, and the reactive material comprises b) mono-functional organic material of molecular weight at: least 100 Daltons having one moiety capable of reacting with the epoxy moieties of the di-epoxy resin and c) dicarboxylic acid of molecular weight less than 300 Daltons having two moieties capable of reacting with the epoxy moieties of the di-epoxy resin.

Abstract: The present application discloses a method of modifying a macromolecule, the method comprising the steps of (i) providing the macromolecule; (ii) providing a compound of the general formula (I): wherein N is a primary amino group protected with the protecting group P, wherein the protecting group involves both free valences of the primary amino group; m is an integer of 1-12 and n is an integer of 1-2000; R1 and R2 are independently selected from the group consisting of hydrogen and C1-4-alkyl; and X is a reactive group; and (iii) allowing the compound of the general formula (I) to react with the macromolecule so as to form grafts on the macromolecule. Compounds of the general formula (i) and a method for the preparation thereof are also disclosed.

Abstract: The epoxy resin molding material of the invention comprises (A) an epoxy resin and (B) a curing agent, wherein the (B) curing agent contains a polyvalent carboxylic acid condensate. The thermosetting resin composition of the invention comprises (A) an epoxy resin and (B) a curing agent, wherein the viscosity of the (B) curing agent is 1.0-1000 mPa·s at 150° C., as measured with an ICI cone-plate Brookfield viscometer.

Abstract: An adduct comprises at least one reaction product of (i) an epoxy resin material (A) and (ii) a reactive compound (B). The epoxy resin material (A) comprises a cis, trans-1,3- and -1,4-cyclohexanedimethylether moiety and the reactive compound (B) comprises a compound having two or more reactive hydrogen atoms per molecule, wherein the reactive hydrogen atoms are reactive with epoxide groups. A curable epoxy resin composition comprises the adduct described above. A cured epoxy resin is prepared by a process of curing the curable epoxy resin composition.

Abstract: A thermally conductive adhesive composition includes a powder of a high melting point metal or metal alloy, a powder of a low melting point metal or metal alloy, and a polymerizable fluxing polymer matrix composition having a polyepoxide polymer resin and a low-melting solid or liquid acid-anhydride and a polymer diluent or diluents with carbon carbon double bonds and/or functional hydroxyl groups. The ratio by weight of the low melting point powder to high melting point powder ranges from about 0.50 to about 0.80, and may range from about 0.64 to about 0.75, and may be 0.665. Heretofore unpredicted substantially higher thermal conductivity improvements in performance have been found using these ratios of low melting point powder to high melting point powder.

Abstract: The epoxy resin molding material of the invention comprises (A) an epoxy resin and (B) a curing agent, wherein the (B) curing agent contains a polyvalent carboxylic acid condensate. The thermosetting resin composition of the invention comprises (A) an epoxy resin and (B) a curing agent, wherein the viscosity of the (B) curing agent is 1.0-1000 mPa·s at 150° C., as measured with an ICI cone-plate Brookfield viscometer.

Abstract: A prepreg is provided capable of being a composite material having suitable high heat resistance, impact resistance, and mechanical properties under high temperature and high humidity conditions. As the matrix resin, a composition including a specific epoxy resin component (A), a specific bifunctional epoxy resin (B), a specific tetrafunctional epoxy resin (C), and a specific aromatic amine compound (D) at specific proportions are used. Particularly, as the epoxy resin component (A), one obtained by mixing and heating a bifunctional epoxy resin (a1), a trifunctional epoxy resin (a2), a phenol compound (a3), and a specific polyamide resin (a4) is used so as to be able to solve the above-described problems.

Abstract: To provide an epoxy resin giving a cured object having high heat resistance, which is improved in impact resistance and moisture resistance as compared with conventional high-heat-resistance epoxy resins. The epoxy resin is obtained by glycidylating one or more phenol compounds comprising 95% or more 1,1,2,2-tetrakis (hydroxyphenyl)ethane, and is characterized in that in an examination by gel permeation chromatography, the epoxy resin has a tetranucleus-form content of 50 to 90% by area and an octanucleus-form content of at least 5% by area and has a total chlorine content of 5,000 ppm or smaller.

Abstract: A recyclable epoxy resin composition using a plant biomass in a resin skeleton and a cured material of the epoxy resin composition, and various types of products using them are provided. The epoxy resin composition comprises an epoxy resin; and a curing agent, wherein the curing agent is a biomass-derived acid anhydride having an acid anhydride bonded via an ester linkage to a biomass with a weight-average molecular weight of 300 to 5000.

Abstract: A circuit-connecting material for interposing between circuit electrodes facing each other and electrically connecting the electrodes, after curing by heat and pressure, either by direct contact or via conductive particles present in the material. The circuit-connecting material features the following essential components: (1) a curing agent capable of generating free radicals upon heating, (2) a phenoxy resin having a weight average molecular weight of 10,000 or more, and that is chemically modified by a carboxyl-group-containing elastomer, and (3) a radical-polymerizable substance.

Abstract: The present invention relates to a method for preparing macromolecular species with a modified surface, comprising a step (e) in which macromolecular species (M), initially carrying —OH and/or —SH functions, are brought into contact with: a catalyst (C) carrying at least one conjugated guanidine function; and reactive species (E), comprising reactive groups including: (i) at least one group including an a,b-unsaturated carbonyl group C?C—C?O and/or an a,b-unsaturated thiocarbonyl group C?C—C?S; and/or (ii) at least one heterocyclic group comprising from 3 to 5 ring members, said group being selected from cyclic ethers, cyclic thioethers and aziridine rings; and/or (iii) at least one group selected from isocyanate —N?C?O or thioisocyanate —N?C?S groups, and trivalent groups of formula >C?CZ—, where Z is an electron-withdrawing group. The invention also relates to the macromolecular species with a modified surface that are obtained in this context.

Abstract: Aqueous dispersions and coatings comprising modified epoxy resins comprising the reaction product of rosin and a dienophile, further reacted with an epoxy resin, are disclosed.

Abstract: An adhesive film composition includes a polyester-based thermoplastic resin, an elastomer resin containing at least one of a hydroxyl group, a carboxyl group, or an epoxy group, an epoxy resin, a phenol curing agent, one or more of a latent catalytic curing agent or a curing catalyst, a silane coupling agent, and a filler.

Abstract: A powder primer composition comprising as essential components (A) a carboxyl group-containing thermosetting polyester resin, (B1) a bisphenol A-type epoxy resin with an epoxy equivalent of 400-2000 g/eq or (B2) a bisphenol-type epoxy resin with an epoxy equivalent of 400-2000 g/eq and (C1) a bisphenol F-type epoxy resin with an epoxy equivalent of 400-2000 g/eq or (C2) a modified epoxy resin containing phenolic hydroxyl groups, obtained by reacting (a) a bifunctional epoxy resin with (b) an excess of a bifunctional phenol. Coating films obtained using the powder primer composition have excellent finished appearance and corrosion resistance.

Abstract: A process for purification of water soluble polymers is provided. A polymer of interest can be separated from a mixture of polymers, provided the polymer of interest differs from other polymers in the mixture in the number of reactive terminal groups. The process involves derivatizing polymers at the reactive terminal groups with a derivatizing molecule, bearing either (i) two or three cationic or anionic ionizable groups, and a group capable of covalent bonding to the reactive terminal groups or (ii) three or four ionizable groups, at least one of which is capable of covalent bonding to the reactive terminal groups; followed by ion exchange. The process allows removal of PEG from MPEG, and can be used for polymers having an average size greater than 9,000 Da Derivatization may be reversible in order to allow re-use of recovered contaminant polymers.

Abstract: The present invention relates to heat-curing epoxy resin compositions, which are used in particular as body shell adhesives for vehicle construction, in that they have improved wash-out resistance, especially also at temperatures around 60° C., and the viscosity of which at room temperature enables an application at room temperature.

Abstract: A thermoset resin, including the reaction product of: an epoxy resin mixture including at least one cycloaliphatic epoxy resins; a cycloaliphatic anhydride hardener; and a catalyst; wherein the reaction product has a glass transition temperature greater than or equal to 210° C. Also disclosed is a process for forming a thermoset resin, including: admixing two or more epoxy resins and a cycloaliphatic anhydride hardener to form a curable composition, wherein the epoxy resins include at least one cycloaliphatic epoxy resin; thermally curing the curable composition at a temperature of at least 150° C. to result in a thermoset resin having a glass transition temperature of at least 210° C. Such curable compositions may include: 35 to 65 weight percent of an epoxy resin mixture having at least one cycloaliphatic epoxy resins; 35 to 65 weight percent of a cycloaliphatic anhydride hardener; and from greater than 0 to 10 weight percent of a catalyst.

Abstract: A thermosetting resin composition comprising (A) a thermoplastic resin having a structure represented by the following general formula (a) and/or a structure represented by the following general formula (b) in which 5 to 99 mol % of hydroxyl groups of polyhydroxyether are esterified, and (B) a thermosetting resin: wherein R1 represents C1-18 aliphatic or aromatic-ring-containing alkylene group or —SO2—, 5 to 99 mol % of R2 represent a straight chain or cyclic carbonyl group or aromatic carbonyl group having 1 to 20 carbon atoms, the residue 95 to 1 mol % represent a hydrogen atom, and R3 represents a hydrogen atom or a methyl group, with a proviso that a plurality of R3's may be the same or different.

Abstract: The present invention relates to heat-curing epoxy resin compositions, which are characterized by high impact strength, good storage stability, and a low curing temperature. The epoxy resin compositions are suitable for use as a construction shell adhesive and for producing structural foams. They can already be cured in so-called bottom-baking conditions. Furthermore, it has been found that the use of an accelerator of the formula (Ia) or (Ib) results in an increase of the impact strength of heat-curing epoxy resin compositions.

Abstract: It is an object of the present invention to provide an epoxy resin curing agent which has a favorable pot life and good storage stability as a curing agent for epoxy resins and from which an epoxy resin cured product having good water resistance and hardness is obtained through curing. The present invention is an epoxy resin curing agent containing a secondary or tertiary branched thiol compound having a substituent on a carbon atom at the ?-position to a thiol group, and is also an epoxy resin composition comprising a polyvalent epoxy compound and the epoxy resin curing agent.