JPS6092814A - Manufacture of molded item with expanding layer - Google Patents

Abstract

PURPOSE:To manufacture the titled molded item with high productivity at low cost by a method wherein a highly expanding sheet made of polyolefin is set in advance onto the inner surface of a mold and polyolefin is injection-molded in said mold. CONSTITUTION:A highly expanding polyolefin sheet 4, preferably with high heat- resisting temperature such as polypropylene foam or the like, is set onto the inner surface of a mold 1 and, after the mold is being closed, polyolefin 5 such as polypropylene or the like is injection-molded in the mold in order to obtain an intended molded item. USE:The titled manufacturing method is applied to parts, which concern to automobile and with which heat insulating property, cushioning property, sound absorbing quality and the like are equipped.

Description

Detailed Description of the Invention At present, various polyolefin molded products, typically polypropylene, are widely used in various fields, and injection molded products, in particular, can produce products with three-dimensional shapes and complex shapes in a single process. In order to improve the home performance, cushioning properties, sound absorption properties, etc., as well as industrial applications such as road vehicles and electric ia-related vehicles, foamed resin sheets are pasted on the surface, and foaming agents are used. Attempts have also been made to produce molded articles that are entirely or partially foamed. However, the method of gluing one foam sheet together requires more steps, and there is no good adhesive for polyolefins, resulting in high costs. In addition, it is particularly difficult to obtain injection molded products of polyolefin with a high foaming rate, and even if they are obtained, it is difficult to achieve uniform foaming.
The appearance also becomes non-uniform with flow patterns, etc., and the cooling time during molding becomes longer, resulting in a significant decrease in production speed. Furthermore, if only the foam is used, the rigidity and strength will be insufficient unless the wall thickness is increased too much.

An object of the present invention is to provide a new method for injection molding polyolefins that solves the above-mentioned problems of traditional molding. That is, the present invention is characterized in that a highly foamed sheet of polyolefin is set or temporarily pasted on the inner surface of a mold in advance, and the polyolefin is injection molded thereon.The highly foamed layer portion is formed on the entire or part of the surface. This is a method for manufacturing polyolefin molded products.

The method for manufacturing the molded article of the present invention will be explained in more detail below. First, the highly foamed polyolefin sheet used in the present invention means one with a foaming rate of about 5 to 50 times, and is currently commercially available. There is a crab that is 30 times more foamed, and such a crab is suitable. Since this foam comes into contact with the molten resin in the mold, it is preferable that it has a high heat resistance, and if the heat resistance is too low, the bubbles will collapse. Therefore, it must be able to withstand melting temperatures even for a limited short period of time.

However, since the mold side of the foam is cooled by the mold, a cross-linked highly foamed material that flows well is relatively heat resistant and is suitable for use in this method.

The highly foamed sheet may be not only a flat sheet, but also a sheet formed three-dimensionally by nitrogen molding or the like, or a sheet formed by bending a flat sheet three-dimensionally.

First, such a highly foamed sheet is sectioned into a predetermined location on the inner surface of a mold (FIG. 1). In this case, depending on the purpose of the product, by setting foam in both molds, a molded product having foam layers on both sides can be obtained. But in any case, the gate part must be avoided. Depending on the shape, the sheet may be set by fitting it into a mold, but if the sheet is flat, it may be attached using a weak adhesive or double-sided adhesive tape. When using a vertical injection molding machine, it can be placed on the lower mold.

After setting the highly foamed notebook as described above, close the mold and then injection mold the polyolefin as usual to obtain an injection molded product with a high-visibility sheet layer on the surface (Figures 2 and 3). figure).

The polyolefin used in the present invention refers to those suitable for injection molding, such as polypropylene and high-density polyethylene, and includes not only homopolymers thereof but also copolymers with other olefins and other polyolefins. It also includes mixtures with diystomers, and those to which inorganic fillers are added.However, in any case, the molding conditions used in the method of the present invention should be kept as low as possible in relation to the highly foamed material. Since it is often desirable to use a low pressure, it is desirable to use a resin that flows well.

Hereinafter, the method of the present invention will be explained in more detail with reference to Examples and drawings.

Example (1) The following 211, a commercially available polypropylene, was used as the polyolefin (both are Chisso ■ products).

7775 for Nisso Polypropylene (melt flow rate
75 f/10 min) Nisso Polyprooleform TV (Melt Flowray)
9F/10 minutes, 20 pieces of inorganic filler) (11) Torebe 7PF30040 (Al2O
) (Toshi ■ Product 9, foam magnification approximately 30 times, thickness 2 m) was used.

610 molding machine: Toshiba S-200B injection molding machine (manufactured by Toshiba Machine) 4ψ metal mold box mold (230MX115cm x 115cm (height).

Wall thickness (t) = 3111, 120 with flange, bottom direct gate) Using the above raw material RiIL, first cut the highly foamed sheet 4 so that the inner surface of the cavity side 1 of the box mold is exposed, and fit it with double-sided tape. Attach the sticker (Figure 1). When injection molding was carried out under the conditions shown in Table 1, a box-shaped product with a good feel was obtained, with the outside of the box covered with a foam layer of about 1 to 1.2 mm, regardless of the resin used. (Figures 2 and 3).

The overall wall thickness in Table 1 was 3.6 to 4.01111 mm, of which the thickness of the foam layer was 1.1 to 1.21111 mm. Foaming 1-
The adhesive force between the peeling layers was strong, and when I tried to peel it off, the foam 114 was more likely to break. In addition, in order to compare the insulation properties of the molded product obtained in this way with that of a normal molded product, we filled a box with 22°C water, covered it with styrofoam, and placed it in a constant temperature bath at -20°C. When we measured the time it took for the water temperature inside to reach 2°C, it took 1 hour and 45 minutes for the molded products obtained in this example, but it took 1 hour and 45 minutes for the molded products obtained using the same mold without a foam layer. For normal molded products, it takes 1 hour and 15 minutes to
It has become ℃.

[Brief explanation of the drawing]

FIGS. 1 to 3 are diagrams schematically showing the method of the present invention, and each is a longitudinal sectional view of a mold. l... Mold (cavity side) 2... Mold (core side) 3... Gate 4... Highly foamed sheet 5...・Polyolefin resin 1st 72 Showai 3rd cycle

Claims (2)

[Claims] (1) A highly foamed sheet of polyolefin is set or temporarily affixed to the inner surface of a mold in advance, and the polyolefin is injection molded thereon.The surface has a highly foamed layer portion in whole or in part. Method for manufacturing polyolefin molded products. (2) The highly foamed sheet is made of polypropylene foam,
The method for producing a molded article according to claim 1, wherein the polyolefin is polypropylene.