Laminates comprising a foamed polyimide layer

Claim 1

A laminate comprising at least one polyimide foam layer and at least one reinforcing layer bonded thereto, said polyimide foam layer being prepared by foaming an unfoamed polymer containing a blowing agent compatible with said polymer and present therein in an amount sufficient to foam the polymer on heating the polymer at a temperature from 170° C. to 250° C., said unfoamed polymer being obtained by free-radically polymerizing a member selected from the group consisting of (I) a mixture of (a) 20-99.99 percent by weight of acrylic acid or methacrylic acid, (b) 0.01-5 percent by weight of a metal salt of acrylic acid or methacrylic acid, (c) 0-79.99 percent by weight of a further ethylenically unsaturated comonomer copolymerizable with (a) and (b), and (d) a blowing agent comprising a compound having an amide structure which cleaves ammonia on heating, and (II) a mixture of (a) acrylonitrile or methacrylonitrile with acrylic acid or methacrylic acid in a mole ratio from 2:3 to 3:2, (b) 0-20 percent by weight of (a) of a further ethylenically unsaturated comonomer copolymerizable therewith, and (c) 1-15 percent by weight of the sum of (a) and (b) of a monovalent aliphatic alcohol having 3-8 carbon atoms as said blowing agent.

Claim 10

The method of making a laminate which comprises pressure bonding at least one reinforcing layer to at least one polyimide foam layer with a heat-hardenable duroplast resin at a temperature of at least 100° C. and under such limitation on temperature, pressure, and time that at least two of the following three conditions are met: (i) the hardening temperature is at least 140° C., (ii) the compressive pressure is at least 1.0 N/mm 2 , (iii) the hardening time is at least 30 minutes, said polyimide foam layer being prepared by foaming an unfoamed polymer containing a blowing agent compatible with said polymer and present therein in an amount sufficient to foam the polymer on heating the polymer at a temperature from 170° C. to 250° C., said unfoamed polymer being obtained by free-radically polymerizing a member selected from the group consisting of (I) a mixture of (a) 20-99.99 percent by weight of acrylic acid or methacrylic acid, (b) 0.01-5 percent by weight of a metal salt of acrylic acid or methacrylic acid, (c) 0-79.99 percent by weight of a further ethylenically unsaturated comonomer copolymerizable with (a) and (b), and (d) a blowing agent comprising a compound having an amide structure which cleaves ammonia on heating, and (II) a mixture of (a) acrylonitrile or methacrylonitrile with acrylic acid or methacrylic acid in a mole ratio from 2:3 to 3:2, (b) 0-20 percent by weight of (a) of a further ethylenically unsaturated comonomer copolymerizable therewith, and (c) 1-15 percent by weight of the sum of (a) and (b) of a monovalent aliphatic alcohol having 3-8 carbon atoms as said blowing agent.

Claim 11

The method of making a laminate which comprises pressure bonding at least one reinforcing layer to at least one polyimide foam layer with a heat-hardenable duroplast resin at a temperature of at least 100° C. and under such limitation on temperature, pressure, and time that at least two of the following three conditions are met: (i) the hardening temperature is at least 140° C., (ii) the compressive pressure is at least 1.0 N/mm 2 , (iii) the hardening time is at least 30 minutes, said polyimide foam layer being prepared by foaming an unfoamed polymer containing a blowing agent compatible with said polymer and present therein in an amount sufficient to foam the polymer on heating the polymer at a temperature from 170° C. to 250° C., said unfoamed polymer being obtained by free-radically polymerizing a member selected from the group consisting of (I) a mixture of (a) 20-99.99 percent by weight of acrylic acid or methacrylic acid, (b) 0.01-5 percent by weight of a metal salt of acrylic acid or methacrylic acid, (c) 0-79.99 percent by weight of a further ethylenically unsaturated comonomer copolymerizable with (a) and (b), and (d) a blowing agent comprising a compound having an amide structure which cleaves ammonia on heating, and (II) a mixture of (a) acrylonitrile or methacrylonitrile with acrylic acid or methacrylic acid in a mole ratio from 2:3 to 3:2, (b) 0-20 percent by weight of (a) of a further ethylenically unsaturated comonomer copolymerizable therewith, and (c) 1-15 percent by weight of the sum of (a) and (b) of a monovalent aliphatic alcohol having 3-8 carbon atoms as said blowing agent.