Process for making glass-reinforced multi-layer sheets from olefin polymer materials

A process for making a multi-layer sheet comprising:

• (1) extruding a sheet comprising a propylene polymer material selected from the group consisting of:
• (a) a propylene polymer selected from (i) a propylene homopolymer, (ii) a copolymer of propylene and ethylene, and (iii) a copolymer of propylene and a 4-8 C alpha-olefin, wherein the polymerized ethylene or polymerized alpha-olefin content of the copolymer is not greater than 20%, and, optionally about 0.15% to about 0.70% of a nucleating agent,
• (b) a graft copolymer comprising a backbone of a propylene polymer material, having graft polymerized thereto polymerized monomers selected from the group consisting of (i) at least one acrylic monomer, (ii) at least one styrenic monomer, and (iii) mixtures of (i) and (ii), and, optionally, about 0.5% to about 1.5% of a nucleating agent, and
• (c) an olefin polymer composition comprising:
• (i) about 10 parts to about 60 parts by weight of a crystalline propylene homopolymer having an isotactic index greater than 80, or a crystalline copolymer from monomers selected from the group consisting of (1) propylene and ethylene, (2) propylene, ethylene and a C4-C8 α-olefin, and (3) propylene and a C4-C8 α-olefin, the copolymer having a polymerized propylene content of more than 85% by weight and an isotactic index greater than 85;
• (ii) about 5 parts to about 25 parts by weight of a copolymer of ethylene and propylene or a C4-C8 α-olefin that is insoluble in xylene at ambient temperature;
• and
• (iii) about 30 parts to about 70 parts by weight of an elastomeric copolymer from monomers selected from the group consisting of (1) ethylene and propylene, (2) ethylene, propylene, and a C4-C8 α-olefin, and (3) ethylene and a C4-C8 α-olefin, the copolymer optionally containing about 0.5% to about 10% by weight of a polymerized diene, and containing less than 70% by weight of polymerized ethylene and being soluble in xylene at ambient temperature and having an intrinsic viscosity measured in decahydro-naphthalene at 135° C. of about 1.5 to about 4.0 dl/g;
• the total of (ii) and (iii), based on the total olefin polymer composition being from about 50% to about 90%, and the weight ratio of (ii)/(iii) being less than 0.4, wherein the composition is prepared by polymerization in at least two stages and has a flexural modulus of less than 150 MPa;
• the sheet of propylene polymer material having a thickness of about 0.001 inch to about 0.25 inch,
• (2) forming a sheet by laying-up alternate layers of (a) a sheet of a propylene polymer material selected from the group consisting of (i) a propylene homopolymer, (ii) a copolymer of propylene and ethylene, and (iii) a copolymer of propylene and a 4-8 C alpha-olefin, wherein the polymerized ethylene or polymerized alpha-olefin content of the copolymer is not greater than 20%, the melt flow rate of the propylene polymer material in layer (2) is higher than the melt flow rate of the propylene polymer material in layer (1), and the sheet has a thickness of about 0.01 to about 0.1 inch, arid (b) glass fiber mats having a weight per unit area of about 0.5 to about 4.5 oz/ft2, that have been preheated to a temperature of about 140° to about 200° C., with the sheet of propylene polymer material as the top and bottom layers, compressing the layers at a pressure of at least 300 psi, and then cooling while maintaining this pressure, and
• (3) joining the sheets produced in steps (1) and (2) by applying heat to both sheets at a temperature sufficient to soften the surfaces to be joined, while simultaneously applying pressure to the sheet produced in step (1).