JPS6342532B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Technical Field> The present invention relates to a foam blow-molded product for full molding.

<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.
A casting method in which the above-mentioned foamed molded product, which becomes an extinguishable molded product, is burned to produce a cast product having the same shape as the foamed product is well known as the full molding method. The foam molded product used in this full mold method is produced by filling pre-foamed expandable resin particles into the cavity of a mold, and heating and expanding the resin particles with a heating medium such as steam. They were formed by heat-sealing them together. 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 mold method using this foam molded product, traces of fusion of resin particles (particle structure) are clearly visible on the surface of the cast product, making it difficult to obtain a cast product with a smooth surface. It was hot.

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 the foamed thin film bonded to the surface with adhesive, wax is applied to the inner surface of the cavity of the 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. The disadvantages are that it is difficult to select an adhesive because it is easy to bond, and wrinkles are likely to occur during bonding, resulting in poor workability. On the other hand, in the case of the latter type with wax, it is time-consuming to attach the wax to the inner surface of the mold cavity, and the wax used has a low melting point, so the mold is not cooled below the melting point of the wax after foam molding. However, even if wax was applied inside the mold cavity, it would melt away, and as with the former, the molding process was also poor.

<Objective> The object of the present invention is to obtain a foam blow-molded product that can eliminate the drawbacks and inconveniences of the conventional foam-molded products for full molding.

<Structure> The structure of the present invention for achieving the above object is a hollow foam blow-molded product formed from a parison made of a synthetic resin containing a foaming agent and extruded by a blow molding machine. It is characterized by a smooth skin formed on the surface of the same material as the molded product but with a different expansion ratio.

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

5 is a foam blow-molded product made of foamed polystyrene resin, and a smooth skin 50 made of the same material as the molded product but with a different expansion ratio is formed on the surface. To specifically explain the production of this foam blow-molded product 5, first, a blowing agent of 3.5
% polystyrene resin is extruded by blow molding extruder 1, and soybean 2 at the tip of the extruder is extruded.
The parison P extruded from [20mmφ, 3mmt] is put into the blow molding mold 3 [H=250mm, 120mmφ] and tightened. Next, air is blown from a nozzle 40 that passes through the solenoid valve 4 and protrudes into the parison p in the mold (6 kg/cm ² pressure, blowing time 1.0 seconds).
is formed into a hollow shape along the blow molding die 3.
Since the blow molding die 3 is being cooled at this time, the surface of the hollow blow molding die 5 is hardened. After the surface hardens, a vacuum is applied from the inside of the molded product before the foamed resin has completely cooled down.
Specifically, the parison p is formed hollow and has a diameter of approximately 2.5 mm.
After seconds have elapsed, the inside of the blow molded product is depressurized (100mm
Hg) to foam the inner surface of the molded product. As a result, a foam blow-molded product 5 with a smooth skin 50 formed on the surface could be obtained. In this case, the molded product has a smooth skin 50 with a thickness of 0.4 mm and a foaming ratio of about 2 times, and the rest has a thickness of 2.5 mm and a foaming ratio of about 8.
I got twice as much.

Further, to explain the manufacture of another foam blow-molded product 5 using the above-mentioned apparatus, a parison p similar to the above-mentioned one is placed in a blow-molding mold 3 and the mold is clamped. Then, suction is applied for 0.5 seconds at 600 to 650 mmHg from a hole 70 made in the inner surface of the blow mold 3 by the electromagnetic valve 7 to make the parison p hollow along the inner surface of the blow mold 3. At this time, the solenoid valve 8 is kept open. Then, the surface of the molded product is hardened by contacting the blow molding die 3 which is being cooled. After curing, a vacuum is applied to the blow molded product 5 from its inner surface while the foamed resin has not completely cooled down. Specifically, solenoid valve 8
is closed and the solenoid valve 6 is connected to a vacuum pump to apply a vacuum to reduce the pressure (300 mmHg) inside the blow molded product 5, thereby foaming the inner surface of the molded product. In this way, a foam blow-molded product with a smooth skin 50 formed on the surface could be obtained. In this case, the molded product has a surface skin 50 with a thickness of 0.3 mm and an expansion ratio of 3.5.
A foam with a thickness of 2.7 mm and a foaming ratio of 11 times was obtained. In addition, 9 in the figure indicates a cooling pipe, and 10 indicates a control panel that controls 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 this way, it is possible to obtain a foam blow-molded product having a smooth skin on the surface, and also to overcome the drawbacks of ordinary foam blow-molded products as a whole. In other words, it was possible to overcome the drawback that the foaming of the molded product was suppressed by blowing pressure, resulting in a lower expansion ratio and lower strength, and it was possible to obtain a foamed blow-molded product with strong strength and increased expansion ratio. .

Moreover, since the molded product is hollow, it is possible to save material by that much compared to conventional solid-shaped molded products, making it a cheaper full-mold molded product.

<Effects> As described above, the foam blow-molded product of the present invention is a hollow product with a smooth skin formed on the surface of the same material as the molded product but with a different foaming ratio, and which increases the overall foaming ratio. Because of the obtained product, the surface is hard, smooth and beautiful, and it is cheaper than conventional solid-shaped products, and the whole product is strong against external pressure despite being a lightweight hollow product. This product is ideal for full mold use.

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 smooth surface of the sand prevents it from digging into the molded product, resulting in a clean surface of the full molded product. Furthermore, troubles such as deformation can be reduced, resulting in an excellent foam blow-molded product with extremely high utility value for full mold applications.

[Brief explanation of drawings]

The figure illustrates an embodiment of the invention,
FIG. 1 is a schematic diagram during manufacture, and FIG. 2 is a partially enlarged sectional view of the foam blow-molded product. 1... Extruder, 2... Soybeans, 3... Blow molding mold, 4... Solenoid valve, 40... Nozzle, 5... Blow molded product, 50... Surface skin, 6, 7... Solenoid valve , 70... Suction hole, 8... Solenoid valve, p...
Parison.

Claims (1)

[Claims] 1 A hollow foam blow-molded product made from a parison made of synthetic resin containing a foaming agent and extruded by a blow molding machine, with a surface made of the same material as the molded product but with a different expansion ratio. A foam blow-molded product for full mold with a skin, which is characterized by forming a smooth skin.