The present invention provides a polyfunctional phenolic resin and a polyfunctional epoxy resin having low viscosity and having excellent mechanical properties and heat resistance of a cured product to be obtained, a curable resin composition containing these, and a cured product thereof. Specifically, provided are a polyfunctional phenolic resin formed with a naphthol structure optionally having a substituent on an aromatic ring and a catechol structure optionally having a methyl group as a substituent on an aromatic ring bonded together via a methylene group optionally having a substituent, a polyfunctional epoxy resin obtained by epoxidizing the polyfunctional phenolic resin, a curable resin composition containing any of these, and a cured product thereof.

A novolak resin including a partial structure represented by —C(CF.sub.3)H—. In addition, there are provided a photosensitive resin composition containing the above-described novolak resin and a photosensitizing agent. In addition, there is provided an epoxy resin having a partial structure represented by —C(CF.sub.3)H—. In addition, there is provided a curable resin composition containing the novolak resin or the epoxy resin. In addition, there is provided a cured substance obtained by curing the composition. In addition, there is provided a production method for a novolak resin, including reacting an aromatic compound with fluoral in a presence of an acid catalyst to produce a novolak resin having a partial structure represented by —C(CF.sub.3)H—. Further, there is provided a production method for an epoxy resin, including an epoxidation step of reacting a novolak resin having a partial structure represented by —C(CF.sub.3)H— with epihalohydrin in a presence of a base.

A polyhydric phenol resin is provided. The polyhydric phenol resin comprises a polyhydric phenol resin component and a first component. When the polyhydric phenol resin is characterized in a high-performance liquid chromatography (HPLC), the first component is eluted at a retention time ranging from 27.1 minutes to 28.0 minutes, and based on the total area of the chromatographic peaks of the polyhydric phenol resin, the area percentage of the chromatographic peak of the first component at the corresponding retention time in the spectrum ranges from 1.0% to 20%.

A composition of epoxide-functionalized resins comprises at least a first epoxide-functionalized novolac resin, a second epoxide-functionalized novolac resin, and a curing agent selected from phenolic or amine-type curing agents, the average molar mass of the group consisting of the entirety of the epoxidized novolac resins in the said composition being between 550 and 650 g/mol, the average epoxide functionality of the said group being between 3 and 3.5 eq epoxide/mol, and the said composition having a glass transition temperature Tg of at least 160° C.

A composition of epoxide-functionalized resins comprises at least a first epoxide-functionalized novolac resin, a second epoxide-functionalized novolac resin, and a curing agent selected from phenolic or amine-type curing agents, the average molar mass of the group consisting of the entirety of the epoxidized novolac resins in the said composition being between 550 and 650 g/mol, the average epoxide functionality of the said group being between 3 and 3.5 eq epoxide/mol, and the said composition having a glass transition temperature Tg of at least 160° C.

Polyphenolic condensates and epoxidized products prepared from said condensates are prepared by a reaction utilizing multi catalysts to control the weight average molecular weight (Mw) and the number average molecular weight (Mn). Improved color and ultraviolet absorbance are possessed by the condensates described herein.

Polyphenolic condensates and epoxidized products prepared from said condensates are prepared by a reaction utilizing multi catalysts to control the weight average molecular weight (Mw) and the number average molecular weight (Mn). Improved color and ultraviolet absorbance are possessed by the condensates described herein.

Provided are an epoxy resin composition, which exhibits excellent low dielectric properties, and imparts excellent copper foil peel strength and interlayer cohesive strength when used in printed circuit plate applications; and a phenolic resin or an epoxy resin, which are for forming the epoxy resin composition. The phenolic resin is represented by General Formula (1) below.

##STR00001##

In the formula, R.sup.1's each represent a hydrocarbon group having 1 to 10 carbon atoms; R.sup.2's each represent a hydrogen atom, Formula (1a), or Formula (1b), where at least one of R.sup.2's is Formula (1a) or Formula (1b); and n represents the number of repetitions of 0 to 5.

Provided are a curable resin composition capable of providing excellent heat resistance and toughness for a cured product, in which these physical properties are less deteriorated even in a case of being exposed to humidity and heat conditions, and a cured product, a fiber reinforced composite material, and a molded article thereof. The curable resin composition includes an epoxy resin and a curing agent, in which the epoxy resin is an epoxy resin obtained by the polyglycidyl-etherification of a phenol novolac resin. The phenol novolac resin contains bisphenol F having different binding sites, and in the bisphenol F components, the content of the [o, p′[ conjugate is in a range of 30% to 45% relative to the total of the [o, p′[ conjugate+the [o, o′] conjugate+the [p, p′[ conjugate in terms of the area ratio according to a liquid chromatography measurement.

An epoxy resin exhibits a small change in volume after thermal history, is excellent in low thermal expansion and low moisture absorption, and has high heat resistance, in terms of a cured product obtained therefrom; a curable resin composition; a cured product which has all the above properties; a semiconductor encapsulating material; a semiconductor device; a prepreg; a circuit board; a buildup film; a buildup substrate; a fiber-reinforced composite material; and a molded article. The present invention is characterized by an epoxy resin, characterized by including as essential components, a cresol-naphthol co-condensed novolac type epoxy resin (A), a naphthol glycidyl ether compound (B), and one or more xanthene compounds (C) selected from the group of compounds represented by the following structural formulae (1) to (3), wherein the content of the xanthene compound(s) (C) is from 0.1% to 5.5% in terms of area ratio in a GPC measurement.

##STR00001##