METHOD FOR MOLDING FRPS

Abstract: A FRP part is made by compression molding under heat and pressure a glass fiber reinforced thermosetting resin composition at an initial high pressure for a short period of time and then substantially reducing the pressure for a longer period of time to form an almost cured FRP part at which time there is applied to the exterior or outer surface of the FRP part an in-mold coating composition and heat and pressure are continued to cure the in-mold coating composition and to complete the cure of the FRP part. During the molding process the temperature gradient across, or the temperature non-uniformities of, the molding or working surfaces of the mold halves is less than about 5 C.

Description: This invention relates to a method or process for molding a glass fiber reinforced thermosetting resin composition to form an FRP (fiberglass reinforced plastic) part and for in-mold coating (IMC) said part. Apparatus, composition and methods for making and using SMCs, BMCs, HMCs, IMCs and FRPs are known. In this connection please see "Modern Plastics Encyclopedia," 1975-1976, October, 1975, Vol. 52, No. 10A, McGraw-Hill, Inc., New York, pages 61, 62 and 105 to 107; "Modern Plastics Encyclopedia," 1979-1980, October, 1979, Volume 56, Number 10A, pages 55, 56, 58, 147 and 148 and "Modern Plastics Encyclopedia," 1980-81, October, 1980, Volume 57, Number 10A, pages 59, 60 and 151 to 153, McGraw-Hill, Inc., New York, N.Y. Please see, also, "Proceedings Reinforced Plastics/Composites Institute," 31st Annual Conference, The Society of the Plastics Industry, Inc., February, 1976, Todd, Section 18-B, pages 1-5; "Modern Plastics," June, 1976, pages 54-56; "Proceedings of the Thirty-second Annual Conference Reinforced Plastics/Composites Institute," SPI, Washington, February, 1977, Griffith et al, Section 2-C, pages 1-3; "33rd Annual Technical Conference, 1978 Reinforced Plastics/Composites Institute The Society of the Plastics Industry, Inc.," SPI, Ongena, Section 14-B, pages 1-7 and "Reinforced Plastics/Composites Institute," 38th Annual Conference, The Society of the Plastics Industry, Inc., February, 1983, McClusky et al, Section 1-A, pages 1-6. See, also, U.S. Patent Nos. 4,076,780; 4,076,788; 4,081,578; 4,082,486; 4,187,274; 4,189,517; 4,222,929; 4,235,833; 4,239,808; 4,245,006; 4,245,976; 4,329,134; 4,331,735; 4,367,192; 4,374,238; 4,414,173; 4,438,062; 4,508,785; 4,515,710 and 4,534,888. In particular US-A-4 081 578 (van Essen et al.) describes an in-mould coating process in which an FRP part is formed and cured in a mould at about 6900 kPa (1000 psi); an isocyanate-based coating compound is applied to the cured part and cured onto it under heat and a pressure of from 2000-7000 kPa (300-1000 psi). US-A-4 076 788 upon which the preamble of claim 1 is base described an in-mould coating process in which an FRP part is formed and at least 90% cured at 150°C under about 5500 kPa (800 psi), for about 90 s. Mould pressure is then released and coating composition injected to separate the mould halves slightly. The coating is cured under the same conditions as for the FRP. The present invention seeks to provide a new method for making an in-mould coated FRP part, in particular seeking to reduce problems with porosity, sink marks and surface waviness. Accordingly the invention provides a method of forming a coated FRP part, comprising: placing a curable glass fibre reinforced thermosetting resin composition on a heated mould half; closing the mould so that the composition adopts the configuration defined by the mould halves; effecting at least 90% cure of the composition under pressure, the temperature being from about 147°C to 151°C, to form an FRP part; applying a thermosetting in-mould coating composition to the surface of the FRP part, and applying further heat and pressure to cure the coating composition onto the FRP surface and ensure complete curing of the FRP part, characterised in that temperature non-uniformities across the mould surfaces do not exceed about 5°C during the moulding and in-mould coating steps, and in that after closing the mould the composition is subjected to a mould pressure of from about 5650 kPa to about 8300 kPa (about 820 to about 1200 psi) for from about 5 to 12 seconds, after which the pressure is reduced, to from about 550 kPa to about 2300 kPa (80 to 330 psi), for from about 30 to 100 seconds. Preferably the in-mould coating composition is applied to the FRP surface at a pressure of from about 550 kPa to about 2800 kPa (about 80 to 400 psi), at a temperature of from about 143°C to 154°C, for a period of 0.5 to 180 seconds. Glass fiber reinforced thermoset plastics (FRPs) are made from a cured resin containing glass fibers. The resin can be an unsaturated polyester resin or a vinyl ester resin crosslinked with an unsaturated monomer like styrene using a free radical initiator, e.g., a peroxide. Fillers, maturation agents and low-profile or low-shrink additives and so forth can be added to the curable, moldable compound. They can be a sheet molding compound (SMC) or a bulk molding compound (BMC), or other thermosetting material as well as a high strength molding compound (HMC) or a thick molding compound. The compound can have from about 10 to 75% by weight of glass fibers. Preferably, the SMC compound contains from about 25 to 30% by weight of glass fibers while the HMC compound may contain from about 55 to 60% by weight of glass fibers. The glass fiber reinforced thermoset plastic (FRP) can be rigid or semirigid (may contain a flexibilizing moiety such as an adipate group in the polyester). It, also, may contain other flexibilizing polymers, the elastomers and plastomers, such as the styrene-butadiene block copolymers. In-mold coatings (IMC) which are thermosetting are now well known. They can be prepared from isocyanate or polyurethane based materials containing unsaturated compounds and also containing the usual low-shrink additives, fillers and conductive carbon black where the coating is later to be electrostatically painted. A preferred IMC composition is based on a polymerizable epoxy based oligomer having at least two acrylate groups with other unsaturated materials and additives. The processes and products of the present invention can be used in the manufacture of automobile parts such as grille and headlamp assemblies, deck hoods, fenders, door panels and roofs as well as in the manufacture of food trays, appliance and electrical components, furniture, machine covers and guards, bathroom components, structural panels and so forth. EXAMPLE The SMC (for making the FRP part) used in this Example was a conventional composition of unsaturated polyester, styrene, polyvinyl acetate in styrene, calcium carbonate, zinc stearate, magnesium oxide, peroxide catalyst and glass fibers. The IMC composition comprised a diacrylate terminated epoxy based oligomer, a polyoxyethylene glycol dimethacrylate, polyvinylacetate, styrene, hydroxypropyl methacrylate, inhibitor, zinc stearate, cobalt octoate, conductive carbon black, talc and tertiary butyl perbenzoate. A 43 × 56 cm (17 × 22 inch) compression mold with a ribbed insert was used in a 244 tonne (240-ton) press. The temperature gradient across the working mold surfaces (male and female) was maintained within a range of not over 5°C. The molding data obtained on making the FRP part and in-mold coating the same are shown in Tables 1 and 2, below: The surface waviness of the in-mold coated FRP parts of Run Nos. 11 to 16 was improved as compared to Runs 1 to 7. A is best.

Claims: 1. A method of forming a coated FRP part, comprising: placing a curable glass fibre reinforced thermosetting resin composition on a heated mould half; closing the mould so that the composition adopts the configuration defined by the mould halves; effecting at least 90% cure of the composition under pressure, the temperature being from about 147°C to 151°C, to form an FRP part; applying a thermosetting in-mould coating composition to the surface of the FRP part, and applying further heat and pressure to cure the coating composition onto the FRP surface and ensure complete curing of the FRP part, characterised in that temperature non-uniformities across the mould surfaces do not exceed about 5°C during the moulding and in-mould coating steps, and in that after closing the mould the composition is subjected to a mould pressure of from about 5650 kPa to about 8300 kPa (about 820 to about 1200 psi) for from about 5 to 12 seconds, after which the pressure is reduced, to from about 550 kPa to about 2300 kPa (80 to 330 psi), for from about 30 to 100 seconds. 2. A method according to claim 1 in which the in-mould coating composition is applied to the FRP surface at a pressure of from about 550 kPa to about 2800 kPa (about 80 to 400 psi), at a temperature of from about 143°C to 154°C, for a period of 0.5 to 180 seconds. 3. A method according to claim 1 or claim 2, further comprising removing the coated FRP part from the mould. 4. A method according to any one of claims 1 to 3 in which the coating composition is isocyanate or polyurethane based.

Inventors: CASTRO, JOSE' M., SHANOSKI, HENRY, STRAUS, ELLIOTT J.
Applicants: GENCORP INC.
Application year: 1988
Main classification: B29C43
IPC codes: B29C43, B29C70, B29K105, B29C37, B29K101