The present invention provides an epoxy resin including a reaction product of 1,2,4-trihydroxybenzene and an epihalohydrin, the epoxy resin containing a cyclic compound that has a cyclic structure containing, as constitutional atoms, oxygen atoms at 1-position and 2-position derived from 1,2,4-trihydroxybenzene, the cyclic compound being contained in an amount of 0.003 to 0.070 mol based on 100 g of the epoxy resin. The epoxy resin is liquid and is excellent in pyrolysis resistance.

Provided is an encapsulating resin composition for a power device including an epoxy resin, an inorganic filler, a curing agent, and a curing accelerator. This composition is molded under a condition of 175° C. for 2 minutes and then subjected to after-curing under a condition of 175° C. for 4 hours to obtain a test piece having a diameter of 100 mm and a thickness of 2 mm, and a half width of a current-time curve obtained by measuring the test piece with a thermally stimulated depolarization current method according to an order of (i) to (v) below is equal to or less than 800 seconds, (i) increase a temperature of the test piece to 150° C. at a rate of 5° C./min without applying a voltage, (ii) applying a constant voltage of 500 V for 30 minutes while maintaining the temperature of the test piece at 150° C., (iii) lower the temperature of the test piece to 45° C. at a rate of 5° C./min while applying the constant voltage of 500 V, (iv) stop applying the voltage while maintaining the temperature of the test piece at 45° C. and leave the test piece to stand for 5 minutes, and (v) increase the temperature of the test piece at a rate of 3.5° C./min without applying a voltage to the test piece, and measure a value of a current flowing during the increase in the temperature to obtain a current-time curve.

Embodiments of this invention are directed to bio-based epoxy compositions, and method of their preparation and use. Other embodiments are directed to cured bio-based epoxies, and manufactured articles having bio-based epoxy coatings, adhesives, or composites.

Phenolic-terminated and phenolic pendent curable polyimides with very good dielectric properties have been prepared. These materials in combination with epoxy resins and other co-curable resins are ideal for being transformed into flexible films that are ready to be laminated for example between copper foils for applications such as copper-clad laminates for a variety of electronics applications.

The present invention provides an epoxy resin composition containing an epoxy resin (A) having a viscosity at 25° C. of 1000 mPa.Math.s or less, an epoxy resin (B) having at least two epoxy groups that is other than the epoxy resin (A), a core-shell rubber particle (C), and an amine curing agent (D). The content of the epoxy resin (A) is in the range of 0.5 to 15 mass % relative to the total mass of (A), (B), (C), and (D), and the content of the core-shell rubber particle (C) is in the range of 1 to 10 mass % relative to the total mass of (A), (B), (C), and (D). This epoxy resin composition has low viscosity and good impregnation property into fibers and is capable of forming into a cured product having high heat resistance, high mechanical properties, and high water absorption resistance.

The present invention aims to provide an epoxy resin composition that is high in both fast curability and storage stability, a prepreg prepared by using the epoxy resin composition, and a fiber reinforced composite material prepared by curing the prepreg. The epoxy resin composition contains the following components [A], [B], [C], and [D] and meets the following requirements [a], [b], and [c]: [A]: epoxy resin, [B]: dicyandiamide, [C]: aromatic urea, [D]: borate ester, [a]: 0.014≤(content of component [D]/content of component [C])≤0.045, [b]: 0.9≤(number of moles of active groups in component [A]/number of moles of active hydrogen in component [B])≤1.2, and [c]: 14≤(content of component [A]/content of component [C])≤25.

A prepreg contains: a reinforcing fiber material; and a resin composition with which the reinforcing fiber material is impregnated. The resin composition contains an epoxy resin, an amine curing agent, and an imidazole curing agent. An amount of the amine curing agent is less than or equal to 3.8 parts by mass, relative to 100 parts by mass of the epoxy resin, and a sum of the amount of the amine curing agent and an amount of the imidazole curing agent is less than or equal to 10 parts by mass, relative to 100 parts by mass of the epoxy resin. The fiber-reinforced composite material is a cured product of the prepreg.

A curable composition comprising: i) a glycidyl ether of a novolac, comprising or consisting of moieties having the formula (I), wherein —R.sub.a is either always hydrogen or always methyl; —B is either always *—CH2-** or always formula (A); —a fraction of 0.8 to 0.99 of the Y moieties are essentially —O-glycidyl, this fraction being designated as x, and the remainder of the Y moieties, this fraction being designated as (1-x), are divalent bridging spacers of the structure *—O—CH.sub.2—CH(OH)—CH.sub.2—O—** connecting two moieties according to above formula (I); and—n is a number in the range of 0.1 to 3.0; and wherein said novolac glycidyl ether has an epoxy equivalent weight FEW in the range of 160 to 270 g/eq. and the average number of epoxy groups per molecule of novolac glycidyl ether (I), designated as f, is in the range of 2.1 to 5.0; ii) dicyandiamide; and iii) an urea derivative of the formula (II). This composition is stable upon storage at room temperature and fire-retardant. It can be used for preparation of prepregs and in core filling, particularly in the aerospace field.

A resin composition for a fiber-reinforced composite material that makes it possible to improve productivity by suppressing deformation at the time of removal from a mold, in particular, in the PCM method, while achieving both rapid curing and storage stability. The resin composition for a fiber-reinforced composite material includes an epoxy resin (A) including a phenol novolac epoxy resin and a bisphenol A epoxy resin; a phenoxy resin (B); dicyandiamide (C); an imidazole-based curing aid (D); and a phenol-based curing accelerator (E) as essential components, wherein the phenol novolac epoxy resin of the epoxy resin (A) constitutes 40 parts by mass to 75 parts by mass, the bisphenol A epoxy resin constitutes 10 parts by mass to 35 parts by mass, and the phenoxy resin (B) constitutes 5 parts by mass to 15 parts by mass in the total of 100 parts by mass of the components (A) to (E).

A resin composition is comprised of an epoxy resin comprised of a solid epoxy resin and a liquid polyurethane toughener that is dissolved in the epoxy resin and, upon curing of the liquid epoxy resin, the liquid polyurethane toughener phase separates into particles having a particle size of 50 nm to 2 micrometers, an epoxy hardener; and an epoxy soluble latent catalyst. The resin composition provides a more homogeneous infusion of the resin into a fibrous material for forming a prepreg and ultimately an epoxy fiber reinforced composition with improved toughness without sacrificing speed of impregnation or uniformity of the epoxy matrix within the composite.