JPH0252617B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing foam reinforced plastic molded articles. Reinforced plastic (hereinafter referred to as FRP) is
Due to its excellent performance and workability, it is widely used in the construction field, such as bathtubs, septic tanks, and water tanks, as well as in the fields of ships, automobiles, and electrical machinery. In particular, thermosetting resins such as unsaturated polyester resins and vinyl ester resins are blended with thermoplastic resins, fillers, curing catalysts, colorants, mold release agents, reinforcing fibers, etc., and then this is processed into sheet, lump, or rod shapes. , pelletized molding materials are so-called SMC,
It has been used in large quantities in recent years due to its ease of handling and excellent moldability, such as BMC. These molding materials are molded using methods such as compression molding, transfer molding, and injection molding using heated molds. In this case, the specific gravity of the molded product obtained is
It depends on the type and amount of filler or reinforcing fiber used, but the value is usually 1.7 to 2.1.
Many of them are in the range of . One of the major features of FRP is that it is lightweight compared to metal. However, recently there has been a demand for lighter weight FRP. A conventional measure to meet these demands is to lower the specific gravity of FRP molded products by using hollow fillers such as glass balloons, saran microspheres, and glass balloons. However, with this method, the range of specific gravity adjustment is narrow. When a large shearing force is applied during mixing or molding, the hollow body may be destroyed, and the reproducibility of the specific gravity of the resulting molded product is poor. In addition, attempts have been made for a long time to obtain lightweight molded products by adding a foaming agent to the molding material and foaming it during molding. However, even if various organic and inorganic blowing agents are used, SMC and BMC
Normal molding pressure of 30 to 100 kg/cm ² is usually insufficient for foaming and foaming does not occur. Therefore, a method has been proposed in which a heating mold is filled with a molding material containing a foaming agent, and then the mold is opened a predetermined amount to foam and harden the molding material until the molding material gels. With this method, molded products with a constant expansion ratio can be molded with good reproducibility, but because the mold is semi-strongly separated from the surface of the fluidized molding material, it is difficult to form a skin layer on the surface of the molded product, resulting in molded products with beautiful surfaces. There is a drawback that it cannot be obtained. The inventors of the present invention have completed the present invention as a result of intensive research aimed at improving the above-mentioned drawbacks. That is, the present invention involves manufacturing a resin molded product by molding an unsaturated polyester resin compound blended with a blowing agent using a mold consisting of multiple pieces.
This method of producing a foam reinforced plastic molded article is characterized in that at least one piece of the mold is moved until it reaches a predetermined thickness within a range that does not exceed the expansion rate of the compound surface, and then thermal curing is completed. The molding material used in the method of the present invention is so-called
A foaming agent is added to the unsaturated polyester resin compound conventionally used as SMC, BMC, etc., and includes hardening agents, mold release agents, fillers, colorants, thickeners, polymerization inhibitors, and reinforcing agents. All materials used in normal SMC and BMC manufacturing can be used. Foaming agents to be blended include azo compounds such as azobisisobutyronitrile, azodicarbonamide, 2-t-butylazo-2-methoxy-4-methylpentane,
Hydrazine compounds such as paratoluenesulfonylhydrazide and 4,4'-oxybis(benzenesulfonylhydrazide), nitroso compounds such as dinitrosopentamethylenetetramine, and inorganic compounds such as sodium bicarbonate are used alone or in appropriate combinations. I can do it. The amount of blowing agent to be used can be selected arbitrarily depending on the type of blowing agent and the desired expansion ratio, but it is usually 0.5~
Preferably, 5% by weight is used. Also foaming aid,
The combined use of a foam stabilizer is also effective. To carry out the method of the present invention, first, a compound material mixed with a blowing agent is fed into a mold having a predetermined shape as in the conventional method, then the mold is closed, and the compound is compressed under heat. Fill the entire surface of the mold, and then move on to the operation of moving the mold. The mold may be made of any material that can withstand heat and pressure, and a metal mold is usually used. This mold usually consists of multiple pieces, most commonly an upper and a lower piece, depending on the shape of the molded product. All you have to do is move it within the range. In such a method, for example, the upper mold piece is hung from a movable press platen, a compound containing a foaming agent is supplied, the mold is closed, and a single pressure is applied to fill the compound into the cavity. , the press movable platen is pulled up a predetermined distance. Then, only the weight of the upper mold piece is applied to the compound in the mold, and the upper mold piece is lifted and moved by the foaming pressure of the compound, and when the upper mold piece contacts the press movable platen, the upper mold piece is Movement stops. When the mold cannot be moved by foaming pressure alone, a method such as applying an auxiliary force from the outside using a lift cylinder or the like may be used. According to the present invention, the specific gravity of conventional FRP molded products is 1.7~
~2.1 can be reduced to 1.2 or lower. Moreover, the occurrence of pinholes on the surface of the resulting FRP molded product is extremely low, and the reproducibility of thickness, specific gravity, etc. is also extremely excellent. The FRP molded product manufactured according to the present invention can be used as a building material,
It is widely used in automobile parts, but in addition to reducing weight,
It also has the effect of reducing sink marks on the back of the ribs, making it extremely useful in practice. The present invention will be explained below with reference to Examples, but these are only examples of how to carry out the present invention, and the present invention is not limited by these in any way. Example: 980 g of maleic anhydride, 1480 g of phthalic anhydride,
1670g of propylene glycol in a nitrogen gas stream
65 parts of unsaturated polyester with an acid value of 25 obtained by heating and dehydration condensation at 200°C was dissolved in 35 parts of styrene, and the viscosity was 8.
Poise unsaturated polyester resin was obtained. 100 parts of calcium carbonate to 100 parts of this unsaturated polyester resin
parts, 1 part of t-butyl peroxybenzoate, p
-0.04 parts of benzoquinone, 3 parts of zinc stearate,
5 parts of cream coloring agent, plus 5 parts of dinitrosopentamethylenetetramine as a blowing agent, 0.5 part of paratoluenesulfonyl hydrazide, and 4,4'-oxybis(benzenesulfonylhydrazide).
0.5 parts and 2 parts of a urea foaming aid were added and kneaded to prepare a resin paste. Add 2 parts of magnesium oxide as a thickener to this resin paste and use an SMC impregnation machine to make 1 inch glass chopped strands of 25%
Impregnated with SMC. This SMC was aged at 40°C for 2 days to obtain an SMC molding material. A mold capable of forming a flat plate of 500 x 400 x 2 mm was attached to a forming press that can precisely push up the movable platen with a lift cylinder. The lower mold was fixed to the fixed press plate in the usual way, but the upper mold was installed so that it was suspended approximately 10 mm below the movable press plate. 140 molds
℃, charge 800g of SMC, operate the press, pressurize at 100Kg/cm ² After 10 seconds, activate the lift cylinder, lift the press movable platen by a predetermined amount, and the upper mold is lifted and movable by the foaming pressure. I made it stop when it hits the board. After 3 minutes had passed in that state, the mold was opened and the molded product was taken out, the surface condition was observed, and the specific gravity was measured. The results are shown in the table below. 【table】

Claims (1)

[Claims] 1. When manufacturing a resin molded product by molding an unsaturated polyester resin compound blended with a blowing agent using a mold consisting of multiple pieces, at least one piece of the mold is heated at a specified rate within a range that does not exceed the expansion rate of the compound surface. A method for producing a foamed reinforced plastic molded product, which is characterized by moving it until it reaches a certain thickness and then completing thermosetting.