A photocurable composition is provided. A cured product formed by curing the photocurable composition has reworkability and excellent heat resistance while having flexibility. The photocurable composition includes a telechelic acrylic polymer having an acryloyl group at both ends; a polyfunctional acrylic polymer having acryloyl groups; a monofunctional acrylic monomer; and a fumed silica including at least one of a hydrophilic fumed silica or a fumed silica having a polar group. The photocurable composition has a Martens hardness of 0.07 to 0.75 N/mm.sup.2, where the Martens hardness is a hardness after the photocurable composition is cured.

A seal material for a semiconductor manufacturing device is made of a rubber composition containing fluororubber and phenol resin powder. The content of the phenol resin powder is 1 part by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the fluororubber. The average particle size of the phenol resin powder is 1 μm or more and 20 μm or less.

a fluororubber composition includes (a) a peroxide-crosslinkable fluorine-containing elastomer; (b) a spherical particle of a silica/cured melamine resin composite; (c) carbon black; (d) an organic peroxide as a crosslinking agent; and (e) a co-crosslinking agent.

Polysulfide compositions having a polyether synergist are disclosed. Polysulfide compositions that contain polyether synergists exhibit a rapid onset of cure and have acceptable final properties. The polysulfide compositions can be used as sealants.

The invention relates to a composition that is liquid at room temperature, can be fixed by radiation and cured by heat, comprising the following components: (A) an at least bifunctional epoxy-containing compound; (B) an at least bifunctional thiol; (C) a radiation-curable compound; (D) a photoinitiator; (E) a stabilizer blend that contains at least one sulfonyl isocyanate and at least one acid; and (F) a nitrogen compound as an accelerator. The compositions are processable at room temperature over a period of at least 24 h and can be completely cured even at low temperatures.

A photocurable composition is provided. A cured product formed by curing the photocurable composition has reworkability and excellent heat resistance while having flexibility. The photocurable composition includes a telechelic acrylic polymer having an acryloyl group at both ends; a polyfunctional acrylic polymer having acryloyl groups; a monofunctional acrylic monomer; and a fumed silica including at least one of a hydrophilic fumed silica or a fumed silica having a polar group. The photocurable composition has a Martens hardness of 0.07 to 0.75 N/mm.sup.2, where the Martens hardness is a hardness after the photocurable composition is cured.

A gasket includes an elastic part containing a rubber having a dynamic-to-static ratio, Kd/Kst, of 2.5 or lower, wherein the dynamic-to-static ratio, Kd/Kst, is a ratio between a dynamic spring constant, Kd, and a static spring constant, Kst. The dynamic spring constant, Kd, represents a constant as measured under conditions of 23±2° C., 100 Hz, and a strain amplitude of 0.1% according to JIS K6394:2007, and the static spring constant, Kst, represents a constant as measured under conditions of 23±2° C. and a strain amplitude of 0.1% according to JIS K6394:2007.

A gasket includes an elastic part containing a rubber having a dynamic spring constant of 1.5 g/μm or lower as measured under conditions of 23±2° C., 100 Hz, and a strain amplitude of 0.1% according to JIS K6394:2007.

An ultra-white granular silica-based filler comprises at least 99.5 wt. % silica, wherein the crystal structure of the silica is such that the silica-based filler comprises 40 to 80 wt. % cristobalite, 1 to 25 wt. % tridymite, 2-60 wt. % quartz and <5 wt. % amorphous silica, wherein the temperature of the ultra-white granular silica-based filler is no higher than 50° C. and further wherein the ultra-white granular silica-based filler exhibits an L* value in the CIELAB color space of 95-98. In addition, an ultra-white powder filler is obtained by milling, grinding or comminuting the ultra-white granular silica-based filler. The ultra-white powder filler exhibits an L* value in the CIELAB color space of 95-98.5.

A seal rubber composition contains a carboxyl group-containing acrylic rubber, silica, and two or more inorganic fibers, an amount of the silica per 100 parts by weight of the carboxyl group-containing acrylic rubber is 25 to 100 parts by weight, and a total amount of the inorganic fibers per 100 parts by weight of the carboxyl group-containing acrylic rubber is 35 to 100 parts by weight. A sealing member includes a sliding portion composed of a vulcanized product of the seal rubber composition.