JPS6260180B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Technical Field> The present invention relates to a method for manufacturing a foam blow-molded article for full molding, the outer surface of which is covered with a thin non-foamed resin layer.

<Background and conventional technology> Conventionally, foamed molded products of thermoplastic resin such as polystyrene or polymethyl methacrylate are embedded in casting sand as fugitive molds, and molten metal is injected into this.
The manufacturing method of burning the above-mentioned fugitive foam molded product and manufacturing a cast product having the same shape as the foam molded product is well known as the full mold method. In order to obtain the foam molded product used in this full mold method, pre-foamed expandable resin particles are filled into the cavity of a mold, and the resin particles are heated and expanded using a heating medium such as steam. They were then heat-sealed together and molded. However, the foam molded product obtained in this way is formed by the resin particles expanding in the mold cavity and being fused together, so the surface of the foam molded product has traces of fusion of the resin particles. remain. Therefore, according to the full molding method using this foam molded product, the fusion traces (particle structure) of resin particles clearly appear on the surface of the cast product, making it possible to obtain a cast product with a smooth surface. was difficult.

In addition, since the surface of the foam molded product is soft, when filling with sand, the sand may dig into the surface of the foam molded product.
There was a drawback that these bite marks appeared on the surface of the cast iron product.

Therefore, in order to cast a cast product with a smooth surface, it is necessary to use a foam molded product with a smooth surface as a fugitive mold. In addition to bonding a foamable thin film with an adhesive, wax is applied to the inner surface of the cavity of a mold, the cavity is filled with primary foamed resin particles, and then steam is blown into the cavity. There are foam molded products with a wax surface that are made by secondary foaming of resin particles while melting wax.In the former case, which uses thin film adhesion, the adhesive used dissolves the layer of the foam molded product and causes bubble collapse. However, it is difficult to select an adhesive, and wrinkles are likely to occur during bonding, resulting in poor workability. On the other hand, the latter method requires a lot of work to attach the wax to the inner surface of the mold cavity.
The wax used has a low melting point, so if the mold is not cooled below the melting point of the wax after foam molding,
Even if wax was attached to the mold cavity, it would melt, and like the former, the workability for molding was poor.

<Purpose> The purpose of the present invention is to obtain a foam blow-molded product for a full mold with a skin that can eliminate the drawbacks and inconveniences of the conventional foam molding for a full mold. The foamed resin part that is to become the inner surface of the extruded molded product can be molded without reducing the foaming ratio or decreasing the strength due to the pressure during blowing.

<Structure> The structure of the first invention for achieving the above object is that on the outside of the foamed resin containing a foaming agent,
A parison laminated with non-foamed resin is extruded from a blow molding machine, this parison is placed in a cooled blow molding mold, the mold is clamped, air is blown into the parison to form it hollow, and the outside of the molded product is molded. After the thin non-foamed resin layer on the surface has hardened, a vacuum is applied to the inner surface of the molded product made of the foamed resin layer, and the inner surface of the molded product is foamed under reduced pressure. It is characterized by obtaining a foam blow-molded product that is integrated with.

Furthermore, a configuration of a second invention for achieving the above object is that instead of blowing air into the parison in the first invention, a vacuum is applied to the parison from the inner surface of the mold to draw the parison into the inner surface of the mold. It is characterized by making it hollow to obtain a foam blow-molded product.

<Example> Next, examples of the present invention will be illustrated below with reference to the drawings.

Polystyrene resin 5' containing 3.5% blowing agent
and a polystyrene resin 50' that does not contain a foaming agent on the outside thereof are extruded by a blow molding machine 1, and then extruded from a soybean 2 [20 mmφ, 3 mmt] at the tip of the extruder. Blow molding mold 3 [H=250mm, 120mmφ]
and then tighten the mold. Next, air is blown from a nozzle 40 that passes through the solenoid valve 4 and projects into the parison p in the mold (6 kg/cm ² pressure, blowing time 1.0 seconds).
The parison p is formed into a hollow shape along the blow mold 3. Since the blow molding die 3 is being cooled at this time, the non-foamed resin layer 50 forming the outer surface of the hollow blow molded product A is hardened. After the non-foamed resin layer 50 has hardened, a vacuum is applied from the inner surface of the molded product before the foamed resin has completely cooled down. The inner surface of the molded product is foamed by reducing the pressure (100 mmHg) inside the blow molded product through 60 connected to a vacuum pump. In this way, it was possible to obtain a foamed blow-molded product A in which the foamed resin layer 5 and the smooth, thin skin formed by the non-foamed resin layer 50 were integrated on the outer surface. In this case, the molded product had a skin of non-foamed resin layer 50 formed on the outer surface with a thickness of 0.4 mm, a foamed resin layer 5 on the inner surface of the molded product with a thickness of 2.5 mm, and a foaming ratio of about 8 times.

Further, using the apparatus exemplified above, a parison p similar to the above is placed in a blow molding mold 3 and the mold is clamped. Then, the solenoid valve 7 controls the blow molding mold 3.
600-650mmHg from the hole 70 that can be drilled on the inner surface of
Suction is applied for 0.5 seconds to make the parison P hollow along the inner surface of the blow mold 3. This solenoid valve 8 is kept open. The non-foamed resin layer 50, which comes into contact with the cooled blow mold 3 and forms the outer surface of the molded product, is hardened. After curing, a vacuum is applied to the blow molded product A from the inner surface while the foamed resin layer 5 has not completely cooled down. Specifically, the solenoid valve 8 is closed and the solenoid valve 6 is connected to a vacuum pump to apply a vacuum. By reducing the pressure inside the blow molded product A (300 mmHg), the foamed resin layer 5 forming the inner surface of the molded product is foamed. In this way, it was possible to obtain a foamed blow-molded product in which a smooth and thin skin of the non-foamed resin layer 50 was formed on the outer surface of the molded product. In this case, the molded product has a non-foamed resin layer 5 formed on the outer surface.
A product was obtained in which the skin was 0.3 mm thick, the foamed resin layer 5 on the inner surface of the molded product was 2.7 mm thick, and the foaming ratio was 11 times.

In addition, 9 in the figure indicates a cooling pipe, and 10 indicates a control panel for controlling the process.

In the above examples, polystyrene resin particles were used as the expandable thermoplastic resin particles, but in addition to polystyrene, polymethyl methacrylate, polyethylene, or other expandable thermoplastic resin particles that can be foamed and blow molded can be used. As the material, propane, butane, pentane, hexane and other materials known for use in foam molding can be used. In addition, it is preferable to use the same type of non-foamed resin as the resin to be foamed in order to integrate the whole body.

As described above, according to the present invention, both the method of blowing air into the parison placed in the mold to make it hollow, and the method of making the parison placed in the mold hollow by vacuum suction from the inner surface of the mold can be used. By applying a vacuum from the inner surface of the molded product after the foamed resin layer that forms the outer surface of the molded product is cured, the inner surface of the molded product can be reliably foamed after the non-foamed resin layer has been cured.

In this way, a skin of a non-foamed resin layer can be formed on the outer surface of the foam blow-molded product, and the drawbacks of ordinary foam blow molding can be overcome as a whole. That is, it was possible to overcome the disadvantage that foaming was suppressed by blowing pressure, resulting in a decrease in expansion ratio and strength, and it was possible to increase the strength and expansion ratio of the foam blow-molded product. Moreover, since the molded product obtained by this invention is hollow, it is possible to save material by that much compared to the conventional solid-shaped molded product, and the molded product for full molding can be manufactured at low cost.

<Effects> As described above, the foam blow-molded product provided by the present invention is hollow with a thin and smooth skin formed by a non-foamed resin layer on the outer surface, and the overall foaming ratio can be increased. Therefore, the outer surface becomes a kind of film skin, which is hard, smooth and beautiful, and is cheaper than conventional solid-shaped products.Moreover, even though it is a lightweight hollow product, it is resistant to external pressure. It is also strong, making it the best product for full molds.

In other words, when used as a foam molded product for full molding, there is much less combustion material when pouring molten metal than in a full foam molded product, and when sand is put into the surface of the molded product and compacted, The surface of the non-foamed resin layer prevents sand from digging into the molded product, resulting in a clean surface of the full molded product.
Furthermore, troubles such as deformation can be reduced, and it is possible to provide an excellent foam blow-molded product with extremely high utility value for full mold use.

[Brief explanation of the drawing]

The figures illustrate embodiments of the present invention, and Figure 1 is a schematic diagram during manufacturing, Figure 2 is an enlarged cross-sectional view when a parison is inserted into a mold, and Figure 3 is a manufactured foam blow-molded product. FIG. 2 is a partially enlarged cross-sectional view. DESCRIPTION OF SYMBOLS 1... Blow molding machine, 2... Soybeans, 3... Blow molding mold, 4... Solenoid valve, 40... Nozzle, A... Blow molded product, 5... Foamed resin layer, 50... Skin with non-foamed resin layer, 6, 7... Solenoid valve, 70... Suction hole, 8...
Solenoid valve, p...parison.

Claims (1)

[Claims] 1. A parison in which a non-foamed resin is laminated on the outside of a foamed resin containing a foaming agent is extruded from a blow molding machine, and this parison is placed in a cooled blow molding mold and the mold is clamped. None, air is blown into the parison to form it hollow, and after the thin non-foamed resin layer on the outer surface of the molded product has hardened, a vacuum is applied from the inner surface of the molded product due to the foamed resin layer to foam the inner surface of the molded product under reduced pressure. A method for producing a foam blow-molded product for full molding with a skin, the method comprising: obtaining a foam blow-molded product in which a skin made of a non-foamed resin layer on the outer surface and a foamed resin layer on the inner surface are integrated. 2 A parison in which a non-foamed resin is layered on the outside of a foamed resin containing a foaming agent is extruded from a blow molding machine, this parison is placed in a cooled blow molding mold, the mold is closed, and a vacuum is applied from the inside of the mold. The parison is drawn into the inner surface of the mold to form a hollow shape, and after the thin non-foamed resin layer on the outer surface of the molded product has hardened, a vacuum is applied to the inner surface of the molded product from the foamed resin layer. A method for producing a foam blow-molded product for full molding with a skin, characterized by obtaining a foam blow-molded product in which a skin made of a non-foamed resin layer on the outer surface and a foamed resin layer on the inner surface are integrated by performing vacuum foaming.