Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Shaping against forming surface
Patent
1996-12-26
1999-10-26
Short, Patricia A.
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Shaping against forming surface
264320, 2643282, 26433118, 523522, 523523, 523526, 525 64, 525168, 525170, C08L 6706, C08J 324, C08J 524
Patent
active
059722720
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a novel unsaturated polyester resin composition and a process for molding the composition. More particularly, the present invention relates to an unsaturated polyester resin composition which shows a low shrinkage, can be made into a sheet molding compound (hereinafter, referred to as SMC) or a bulk molding compound (hereinafter, referred to an BMC) by thickening in a short time, provides a compound which shows suppressed increase in the viscosity afer the viscosity has been increased to a value sufficient for preparation of an SMC or a BMC, i.e. a compound having an excellent storage stability, enables molding of the compound at a low temperature under a low pressure, and provides a molded product having a large strength and a low modulus.
BACKGROUND ART
In recent years, the demand for SMC and BMC prepared by using unsaturated polyester resins as the base material have steadily been increasing in the processing industry of reinforced plastics as novel industrial materials for machine molding satisfying the requirements of labor saving, mass production, and improvements in thw working environment.
SMC stands generally for a sheet material prepared as follows: an oxide or a hydroxide of an alkaline earth metal used as a thickening agent (an agent for preparation of a sheet) is added to a fluid dispersion obtained by mixing an unsaturated polyester resin, a liquid polymerizable monomer, a curing agent, an inorganic filler, a mold release agent, a flame retardant, a pigment, and the like; a fluid composition is prepared by adding a reinforcing material, such as glass fiber, to the obtained fluid dispersion in an amount of 20 to 50 parts by weight per 100 parts by weight of the fluid dispersion in order to provide the fluid composition with toughness; the prepared fluid composition is sandwiched between release films; thickening of the fluid composition is allowed to take place by reaction for several days; and the resultant fluid composition is formed into a sheet.
The sheet prepared in the above is transferred to the place for molding and molded by heating in a mold to obtain a molded product having a finished shape. The molding is generally conducted by pressing the sheet under a condition of a high temperature and a high pressure, such as a temperature of 100 to 180.degree. C. and a pressure of 30 to 100 kgf/cm.sup.2 (gauge).
Because shrinkage of about 7 to 10% by volume takes place with the molded product obtained by the pressing of the sheet, addition of a thermoplastic resin as a low shrinkage agent is generally conducted for improving the shrinkage (Japanese Patent Publication Showa 46(1971)-14541, Japanese Patent Application Laid-Open No. Heisei 6(1994)-32809, and like others).
Although the technology for molding has been improved by the above process, and unsaturated polyester resins have increasingly been used, unsaturated polyester resins have not widely been used for articles produced in small numbers because molds which are durable under a high pressure are expensive, and other facilities for high temperatures and high pressures are necessary.
Thus, development of an unsaturated polyester resin composition for SMC which is easily processed in molding at a low temperature (40 to 100.degree. C.) and/or under a low pressure (0.1 to 10 kgf/cm.sup.2), even under a vacuum, has been desired.
In particular, when the molding is conducted at a low temperature, a curing agent of a low temperature decomposition type must be adopted. When the molding is conducted under a low pressure, the molding must be conducted while the viscosity of SMC during heating is decreased by adjusting the formulation of the compound, for example, by decreasing the added amount of a metal oxide or an inorganic hydroxide which is mixed as a filler or as a flame retardant or by decreasing the mixed amount of glass fiber which is used as a reinforcing material.
However, when the SMC described above which can be molded at a low temperature is prepared, it is necessary that a curing
REFERENCES:
patent: 4230813 (1980-10-01), Cooke
patent: 5362804 (1994-11-01), Oshima
Ching-Chih Lee et al., "Simulation of Compression Molding for Fiber-Reinforced Thermosetting Polymers" Transactions of the ASME Journal of Engineering for Industry, vol. 1106, May 1984, pp. 114,-125, XP-002081728.
Kobayashi Takeo
Nagase Toshio
Tsukamoto Atsushi
Nippon Zeon Co. Ltd.
Short Patricia A.
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