JPS61216836A - Production of expanded blow molding for full mold having skin - Google Patents

Abstract

PURPOSE:To obtain a smooth surface having different expanding ratios by blowing air into the parison obtd. by extruding a synthetic resin contg. a foaming agent from a blow molding machine to make hollow the parison and applying a vacuum from the inside surface to expand the parison under the reduced pressure after hardening of the surface. CONSTITUTION:The polystyrene resin contg. the foaming agent is extruded from the blow molding machine 1 and the parison P extruded from a die 2 is put into blow molds 3 and the molds are clamped. The air is then blown from a nozzle 40 into the parison to hollow the parison P along a blow molding die 3. Since the molds 3 are kept cooled, the surface of a blow molding 5 is hardened. The inside of the molding 5 is evacuated through a pipe 60 connected to a vacuum pump by a solenoid valve 6 so that the inside surface of the molding is expanded before the molding is not thoroughly cooled after the surface hardening. The expanded blow molding 5 formed with the smooth film on the surface is obtd. in the above-mentioned manner.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a method for manufacturing a full-mold foam blow-molded product with a skin.

<Background and prior art> Conventionally, foamed molded products of thermoplastic resin such as polystyrene or polymethyl methacrylate are embedded as fugitive molds in castings, molten metal is injected into them, and the foamed molded products that become fugitive molded products are combusted. The casting method for manufacturing a cast product having the same shape as this 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 there are fusion marks of the resin particles on the surface of the foam molded product. 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.

Furthermore, since the surface of the foamed molded product is soft, there is a drawback that when sand is filled in, the sand digs into the surface of the foamed molded product, leaving traces of this digging on the surface of the cast 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. After bonding the foamable 1 film 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. This method has disadvantages in that it is easy to bond, making it difficult to select an adhesive, and that 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, and the wax used has a low melting point.
If the mold is not cooled below the melting point of the wax after foam molding, even if the wax adheres to the mold cavity, it will melt, and like the former, the workability for molding will be poor. Ta.

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

The structure of the first invention to achieve the above object is to place a parison extruded from a blow molding machine into a synthetic resin containing a foaming agent into a cooled blow mold and clamp the mold. , air is blown into the parison to form it hollow, and after the surface of the molded product has hardened, a vacuum is applied from the inside of the molded product to cause the inside surface of the molded product to foam under reduced pressure, so that the surface is made of the same material as the molded product. It is characterized by obtaining smooth foam blow-molded products with different magnifications.

Furthermore, a second aspect of the invention to achieve the above object is that, in the first invention, instead of blowing air into the parison, 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, an example of the present invention will be illustrated below the station with reference to the drawings.

A polystyrene resin containing 3.5x of a blowing agent is extruded using a blow molding machine (1), and a die (2) at the tip of the extruder is used.
) [20mmφ, 3mn+t] Extruded parison (
El) into a blow molding mold (3) [H-250mm,
120+nmφ] and clamp the mold. Next, air is blown from the nozzle (40) that passes through the solenoid valve (4) and protrudes into the parison (p) inside the mold (6 to 94 pressure for 1 hour and 1.0 seconds) to blow the parison (El). It is formed into a hollow shape along the mold (3). At this time, the blow molding mold (3) is cooled, so the surface of the hollow blow molded product (5) is hardened. After the surface hardens, the foamed resin is molded before it has completely cooled. A vacuum is applied from the inside of the product. Specifically, after approximately 2.5 seconds have passed since the parison (D) is formed into a hollow material, the vacuum is applied through a pipe (60) connected to a vacuum pump using a solenoid valve (6). The inner surface of the molded product was foamed by reducing the pressure (100 mmt19) inside the blow molded product (5). In this way, a foamed blow molded product (5) with a smooth skin (50) formed on the surface was obtained. In this case, the molded product had a surface skin (50) with a thickness of 0.4 mm and a foaming ratio of about 2 times, and the rest had 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, 600 to 650 mm HCl
Apply suction for 0.5 seconds to make the parison (p) hollow along the inner surface of the blow mold (3). This solenoid valve (8
) is left open. The surface of the molded product is then hardened by contacting the cooled blow molding die (3).

After curing, the blow molded product (5
) from its inner surface. Specifically, the solenoid valve (8) is closed, and the solenoid valve (6) connects with the vacuum pump to apply a vacuum to the inside of the blow molded product (5) (300 m
mHg), the inner surface of the molded product is foamed. 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 had a surface skin (50) having a thickness of 0.3 mm and a foaming ratio of 3.5 times, and the remaining skin having a thickness of 2.7 mm and a foaming ratio of 11 times.

Note that (9) in the figure indicates the cooling pipe, and □□□ indicates the control panel that controls the process. In the above example, polystyrene resin particles were used as the expandable thermoplastic resin particles, but polystyrene resin particles were used as the expandable thermoplastic resin particles. Additionally, polymethyl methacrylate, polyethylene or other foam blow moldable expandable thermoplastic particles can be used;
As the foaming agent, propane, butane, pentane, hexane, and other known foaming agents can be used.

As described above, according to the present invention, molding can be performed by both the method of blowing air into the parison placed in a mold to make it hollow, and the method of making it hollow by sucking the parison placed in the mold with a vacuum from the inner surface of the mold. The inner surface of the molded product after surface hardening can be foamed by applying a vacuum from the inner surface of the molded product to reduce the pressure on the inner surface of the molded product.

In this way, a skin can be formed on the 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 skin formed on the surface, and the overall foaming ratio can be increased, so the surface is hard, smooth and beautiful. Therefore, in terms of cost, it is cheaper than conventional solid-shaped products, and even though it is a lightweight hollow product, it is strong against external pressure, so it is the optimal amount for full molding.

In other words, when used as a foam molded product for full mold,
When molten metal for foundry is poured, there is much less combustion material compared to solid foam molded products, and when sand is placed on the surface of the molded product and compacted, the sand does not dig into the molded product due to the skin on the surface. The surface of full-molded products becomes clean. Moreover, 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 drawings]

The drawings illustrate an embodiment of the present invention, and FIG. 1 is a schematic view during manufacturing, and FIG. 2 is a partially enlarged sectional view of the manufactured foam blow-molded product.

Claims (1)

[Claims] 1. Blow-forming synthetic resin containing a foaming agent The parison extruded from the shaping machine is cooled. Place it in a blow molding mold and tighten the mold. Then blow air into the parison to make it hollow. After the surface of the molded product has hardened, the A vacuum is applied to the inner surface of the molded product. By foaming under reduced pressure, Shaped products are flat products made of the same material but with different foaming ratios. Obtain a foam blow molded product with a smooth skin. A full mold with skin that is characterized by A method for manufacturing foam blow molded products. 2. Blow molding of synthetic resin containing a foaming agent The parison extruded from the shaping machine is cooled. Place it in a blow molding mold and tighten the mold. Then, apply a vacuum from the inside of the mold to make the parison. Formed hollow by suction to the inner surface of the mold After the surface of the molded product has hardened, Apply vacuum from the inside surface to reduce the inside surface of the molded product. Molded products on the surface by pressure foaming is a smooth material with the same material but different foaming ratio. Obtaining a foam blow-molded product with a skin formed A full-mold product with skin featuring A method for producing foam blow molded products.