A crosslinked polyolefin foam that is a crosslinked foam of a polyolefin resin composition, the composition comprising a polyolefin resin (A) and a rubber (B) having a Mooney viscosity (ML.sub.1+4, 100° C.) of 15 to 85. The rubber (B) is contained in an amount of 10 to 150 parts by mass relative to 100 parts by mass of the polyolefin resin (A). The foam has a thickness of 1.5 mm or more, a 25% compressive hardness of 60 kPa or less, and a crosslinking degree of at least one of surface layers at both surfaces with a depth of 500 μm from the surface that is at least 5% higher than the crosslinking degree of the middle layer excluding the both surface layers.

This foam has a 25% compressive strength at 23° C. of 90 kPa or lower and an elongation at break at 160° C., measured in accordance with JIS K6251, of 200% or higher. The present invention makes it possible to provide a foam with which it is possible to obtain a molded article having an exceptional appearance even in secondary processing into a complex shape, without harming the flexibility.

The present invention provides an electret sheet that retains high piezoelectricity under high-temperature condition. The electret sheet of the invention is characterized by including a charged porous sheet, in which the electret sheet has a volume resistivity of 1.0×10.sup.15 Ω.Math.cm or more at 25° C. and a dielectric breakdown voltage of 7 kV or more at 25° C. The electret sheet preferably having a volume resistivity of 1.0×10.sup.14 Ω.Math.cm or more at 37° C. and a dielectric breakdown voltage of 7 kV or more at 37° C. retains excellent piezoelectricity even after being left under a high-temperature atmosphere over a long period.

One object of the present invention is to provide a polyolefin resin foam which does not have a difference between the front side and the back side on the top and bottom surfaces which sandwich in the thickness direction the foam which is excellent in flexibility, buffer property, and heat insulation property despite its thinness, and which can be used suitably in the fields of architecture, electricity, electronics, vehicles, and the like as a variety of heat-resistant sealing materials. The surface hardness of the foam measured by a micro rubber hardness tester is 30° or more and 70° or less, and the centerline average roughness Ra75 of a first surface portion on one side of the foam in the thickness direction and of a second surface portion on the other side of the foam in the thickness direction is 5 μm or more and 20 μm or less.

The present disclosure provides a process. In an embodiment, the process includes providing a foamable composition. The foamable composition includes an ethylene-based elastomer, a blowing agent, and a peroxide. The process includes heating the foamable composition to form a pliable formulation. The pliable formulation has (i) a viscosity (0.1 rad/s at 180 C.) from greater than 70,000 Pa.Math.s to 2,000,000 Pa.Math.s, (ii) a tan delta (0.1 rad/s at 180 C.) from 0.2 to less than 2, (iii) a strain hardening index greater than 2.5 to 6, and (iv) an extensional viscosity (1 s.sup.1 at 180 C.) from greater than 400,000 Pa-s to 7,000,000 Pa-s. The process includes introducing the pliable formulation into a mold having an expandable mold cavity and unidirectionally expanding the expandable mold to form a crosslinked foam article. The process includes cooling, in the expanded mold, the crosslinked foam article; and removing the crosslinked foam article from the expandable mold.

A thermally expandable composition includes at least one polymer P cross-linkable by peroxide, and at least one acrylate, and at least one peroxide, azodicarbonamide and a zinc compound. The thermally expandable composition leads to low odor formation and low ammonia emission during and after the foaming process. The thermally expandable composition further shows excellent properties in terms of expansion stability.

A polymer composition may include an ethylene vinyl acetate (EVA) polymer at an amount ranging from 10 to 90 phr; an elastomeric EVA composition at an amount ranging from 10 to 90 phr; a plasticizer at an amount ranging from 5 to 40 phr; a blowing agent in an amount ranging from 2 to 10 phr; and a peroxide in an amount ranging from 0.3 to 4 phr.

A polyolefin foam having improved light-transmittance comprises an average cell size of about 70 microns to about 500 microns; a total cell wall thickness to gauge ratio of between about 0.15 to about 0.55; a basis weight of about 0.00005 lb/in.sup.2 to about 0.00050 lb/in.sup.2; an L color solid value of about 95 to about 45; and a light transmittance of about 10% to about 50% according to JIS K 7361-1.

A process for producing a polyolefin foam having improved light-transmittance comprises extruding a foamable sheet at a pressure from about 1 psi to about 55 psi, and foaming the foamable sheet with a foaming agent having an average diameter of about 10 to about 25 microns to produce a foam having a light transmittance of about 10% to about 50% according to JIS K 7361-1.

An elastomer alloy includes a base polymer including hydrogenated nitrile butadiene rubber (HNBR) and at least one secondary polymer, which is at least one of paraffin wax, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), and a plastomer. The base polymer and the at least one secondary polymer are blended into a polymer matrix. The elastomer alloy also includes a plurality of smart fillers dispersed within the polymer matrix, at least one chemical foaming agent, and a curing activator.

A method for producing a millable silicone rubber sponge is a method for producing a millable silicone rubber sponge with an open cell ratio of not lower than 20%, comprising: performing a heat treatment on a silicone rubber composition at 200 C. or higher, the silicone rubber composition containing: (A) an organopolysiloxane having at least two alkenyl groups in one molecule and a polymerization degree of not lower than 3,000; (B) a reinforcing silica; (C) thermally expandable microcapsules exhibiting an expansion starting temperature of 90 to 150 C., and contracting from a maximum expansion volume by 20% or more when heated at 200 C. for 5 min; (D) a curing agent; and (E) an open cell-forming agent which is a solid high temperature decomposition-type organic foaming agent having a decomposition starting temperature of not lower than. 180 C., and starting to decompose after the component (A) is cured.