Foam and process for producing same

Claim 1

A foam composed of closed cells having a specific tensile strength of 150 kg/cm 2 or more, a compression recovery of 80% or more and a heat shrinkage of 50% or less, a variation in thickness of foam of less than 50%, a corrugation value of less than 100% and a surface smoothness of less than 2 mm, an average cell diameter of 0.05-3 mm, said foam having a foam density of 0.007-0.10 g/cm 3 , a variation in thickness of cell wall film of ±30% or less and a variation of cell diameter of 70% or less, obtained by foaming a composition consisting essentially of 100 parts by weight of a substantially non-crosslinked crystalline polyethylene having a density of 0.935 g/cm 3 or more and a melting point of 117° C. or more, 0.05-10 parts by weight of a foaming decelerant having the capability of prolonging the foaming time by at least one second as compared with the absence of the foaming decelerant, as measured by a glass tube blowing test method, wherein said foaming decelerant is a compound represented by a formula selected from at least one of the general formula: (H).sub.x --N[(R.sub.1 -O).sub.n A].sub.3-x I. wherein R 1 is an alkylene group having 1-5 carbon atoms, A is a hydrogen atom or an acyl group, n is an integer of 1-10, and x is 0 or an integer of 1-2; HO(R.sub.2 O).sub.m H II. wherein R 2 's may be identical with or different from one another and represent divalent hydrocarbon groups having 1-6 carbon atoms and m is an integer of 1 or more; and ##STR11## wherein R 5 is hydrogen or a substituent represented by ##STR12## wherein R 9 and R 10 represent hydrogen or hydrocarbon groups having 1-23 carbon atoms; R 11 is a hydrocarbon group having 1-6 carbon atoms, and l is 0 or an integer of 1-6, R 6 and R 7 are hydrogen or hydrocarbon groups having 1-23 carbon atoms; and R 8 is hydrogen or a hydrocarbon group having 1-6 carbon atoms, and 0.001-5 parts by weight of a nucleating agent.