JPS6226893B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for molding a polyvinyl chloride foam molded product, in which the final molded product has a foamed interior, an unfoamed surface, and a grained pattern to provide a good appearance. Foamed thermoplastics, typified by polyvinyl chloride, are used in large quantities for a variety of purposes, taking advantage of their characteristics such as heat insulation, cushioning, soundproofing, vibrationproofing, light weight, and low cost. Molding methods for these foams include extrusion molding, injection molding, cast molding, and blow molding. Further, foaming methods include impregnating the resin with a volatile liquid, mixing a gas into the molten resin or emulsion, and kneading a chemical blowing agent. The present inventor has arrived at the present invention as a result of intensive studies to obtain a foamed molded product using polyvinyl chloride with a good appearance with a non-foamed surface and a clear grain pattern. . The present invention involves forming a polyvinyl chloride resin composition containing a chemical foaming agent into a foam molded product by injection molding, and then molding the molded product into a molded product having a cavity of the same shape.
A textured pattern is formed on the inner surface of this cavity, and the molded product is placed directly or indirectly into a mold that has a coating of 2 mm or less of non-foamed thermoplastic resin that will become the skin layer of the final molded product. The coating layer on the inner surface of the cavity and the foam are integrated by reheating and melting by heating to a temperature of It is a molding method for making products. A common method for efficiently mass-producing foamed products of arbitrary shapes is to foam a vinyl chloride resin composition containing a chemical blowing agent by injection molding, but this method has major drawbacks. That is, foam molded products produced by injection molding have a pattern called shark skin on the surface of the molded product, making it impossible to obtain a smooth surface. The skin layer on the surface of the molded product is also extremely thin, and damaged foam cells remain on the surface, making it impossible to create a clear grain pattern. Various methods have been attempted to overcome these drawbacks, one of which is a two-color injection molding technique called Sanderch molding. This is a technology that uses a molding machine with two injection cylinders to obtain a molded product made of resin with a non-foamed surface layer and a foamed inner layer. However, this method requires a special molding machine and two types of resin, foamed and non-foamed, which leads to increased costs, and because non-foamed resin is used for the surface layer, it is difficult to produce molded products with low specific gravity. . It is also conceivable to paint the surface of the foam, but this has the drawbacks of not being able to create a textured pattern and of being expensive. In the present invention, the blowing agent contained in the vinyl chloride resin composition includes azo, hydrazo, and nitroso organic compounds, and any blowing agent used in general thermoplastic resins may be used. Further, the plasticizer is not limited in any way as long as it is used for vinyl chloride resin. Fillers such as calcium carbonate, acrylic polymers that improve the retention of foam cells, oligomers, coloring pigments, ultraviolet absorbers, antioxidants,
It is not limited to the addition of polyurethane, EVA-based, olefin-based polymer modifiers, etc. Furthermore, there are no limitations as long as the resin is typified by PVC-based EVA graft, ethylene copolymer, and vinyl acetate copolymer. Furthermore, there is no problem in adding hollow bodies typified by glass, shirasu phenol, carbon, and the like. On the other hand, the non-foamed thermoplastic resin that forms the skin layer of the final foamed molded product according to the present invention is not limited to the present invention as long as it is a thermoplastic resin that can be thermally welded to the vinyl chloride resin of the inner layer foam. Further, the form of this thermoplastic resin may be, for example, a powder, sol or sheet of soft vinyl chloride resin, or may be a polyurethane paint, which does not interfere with the present invention in any way. Of these, sol-like products tend to have uneven thickness, sheet-like products tend to have burrs on the mating surfaces, and paints have disadvantages such as difficulty in obtaining large thicknesses, but these are also disadvantageous. It does not impede invention. The first step of the present invention is the step of molding a vinyl chloride resin composition containing a foaming agent into a foam molded article by injection molding. Since this process determines the weight of the molded product, it is necessary to carefully examine the amount of foaming agent added, molding conditions, mold gate shape during molding, etc. In the second step of the present invention, the foam molded product obtained in the first step is provided with a cavity 4 having the same shape as that of the foam molded product, a desired grain pattern 5 on the inner surface of the cavity, and a foam and heat applied to the grain surface. This is a step in which the foam is placed in a mold having a skin layer made of a fusible thermoplastic resin, and the foam and the thermoplastic resin that will become the skin are directly or indirectly integrated by heating and fusing. Through this step, the skin layer of the molded product and the foam are fused together, and a non-foamed foamed molded product with a textured pattern and good appearance can be obtained. As an example, Fig. 1 is a cross-sectional view of a handle, in which an inner layer 2 of foam is formed on an iron core 1, and then a non-foamed skin layer 3 is provided, and Fig. 2 is a sectional view of a handle in which a non-foamed skin layer 3 is provided on an iron mold 6. It has a cavity 4 with holes 7 for cooling.
It is equipped with the following. In order to fuse and integrate the foam obtained in the first step with the skin layer, there are methods of heating the mold electrically, heating in a heat-resistant oven, heating with steam, heating with a heating medium, There is an indirect heating method using high-frequency induction, and a direct method using high-frequency dielectric heating. Table 1 shows the features of each method. That is, the indirect method is a method in which a mold is heated to heat-fuse the thermoplastic resin that has been applied in advance on the textured surface to form the skin and the foamed molded product by heat conduction. In addition, the direct method involves placing the skin and foam in a mold with a low electrical permittivity, such as Teflon.
A foamed molded product with a good appearance is obtained by fusion bonding and integration using dielectric heating using microwaves from the outside. These methods should be selected taking into account equipment costs, molding cycles, work environment, etc. The purpose of the present invention is to increase the surface temperature of the foam obtained in the first step to 100°C or higher, 400°C or higher. The prerequisite for obtaining good results is to maintain the temperature below ℃ and to integrate it with the resin of the skin layer. In particular, it has been experimentally confirmed that the optimum temperature range is between 140°C and 220°C. Below 140°C, the gelation of the surface is insufficient, and above 200°C, gloss becomes noticeable, and vinyl chloride resin is easily thermally decomposed, making time control extremely difficult. Next, the present invention will be explained according to examples. Polyvinyl chloride manufactured by Sumitomo Chemical Co., Ltd. SX-115=
1100) 100 parts by weight DOP 60 Calcium carbonate (Shiraishi Kogyo Co., Ltd.)
CCR) 10 parts by weight Epoxidized soybean oil (Dainippon Ink Co., Ltd. Hidec W-100) 3 Calcium stearate 1 Zinc stearate 1 Foaming agent (ADCA) (Eiwa Kasei Co., Ltd. Vinifol)
AC#1) 2 is made into pellets with a diameter of approximately 3 mm using a φ50 extruder. An automobile steering wheel with an iron core was molded using a 35-ounce injection molding machine. The resulting foam has a specific gravity of 0.6
Although the resin basis weight was 280 g, phenomena such as shark skin had occurred on the surface. Molded articles were obtained from this foamed article using each heating method. Example 1 Using an S45C iron mold, apply polyurethane paint to the grained surface, put the foam described above, hold it in a heat press at a temperature of 210°C for 5 minutes, and then press the entire mold.
The molded product was cooled in water for 10 minutes and then taken out. The obtained molded product is a good foamed molded product with a non-foamed layer of about 60 microns, a specific gravity of 0.6, and a textured surface. Example 2 A 100μ film made of soft vinyl chloride resin containing 50 parts by weight of a phthalate ester plasticizer was applied to the textured surface inside the cavity using a Teflon mold, the above foam was placed therein, and microwaves were applied at 6000 volts and 46MHz. Apply from the outside of the mold for 90 seconds, then remove the mold from the
After cooling in water for a minute, the molded product was taken out. The obtained molded product had a specific gravity of approximately 0.6, and had a non-foamed surface with a textured pattern and a good appearance. As described above, the present invention is an excellent molding method for producing molded products with good appearance regardless of the appearance after injection molding. 【table】

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a handle that is one of the embodiments of the present invention. Figure 2 is a cross section of a mold with iron grains inside the cavity.

Claims (1)

[Claims] 1. After molding a vinyl chloride resin composition containing a foaming agent into a foam by an injection molding method, the molded product has a cavity of the same shape, and a textured pattern is provided on the inner surface of the cavity, The molded product is placed in a mold in which a skin layer of a non-foamed thermoplastic resin coating of 2 mm or less is formed on the surface of the cavity, and the molded product is melted and integrated by heating directly or indirectly. A method for molding a polyvinyl chloride foam, which is characterized by being non-foamed and comprising a skin layer with a textured pattern and an inner layer of the foam. 2. A patent claim in which the indirect heating method is a method using electric heat, an air tank in a heat-resistant oven, steam, a heat medium, high-frequency induction heating, etc., and the surface of the molded product is heated to 100 to 400°C. The molding method according to scope 1. 3. The molding method according to claim 1, wherein the surface of the molded article in the mold made of a material with a dielectric constant of 4 or less is directly heated to 100 to 400°C by high-frequency dielectric heating.