JPS5919017B2 - Method for manufacturing hollow articles - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing a synthetic resin hollow article.

As a method for molding hollow articles using synthetic resin, the method using extruded parylin has been mainly used, or
The objective was achieved by joining multiple molded parts together using adhesives or the like.

These methods have limitations depending on the shape of the molded product.
In addition, since the molding cost is also high, a better method for molding hollow parts is required. In order to solve the above-mentioned problem, the present applicant previously proposed in Patent Application No. 120318 of 1971 a method of molding a hollow article by pressurizing gas. According to this method, after the plasticized synthetic resin is injected into the mold cavity, the hollow part of the molded body is filled by press-fitting the gas, or by press-fitting the gas while injecting the molten synthetic resin. Form. However, in this method, the fluidity of the molten synthetic resin and the gas inside the mold cavity is quite different, so there are restrictions on the shape of the molded product in order to produce a uniform hollow body. For example, it is suitable for forming columnar objects, but has many problems when forming flat objects. That is, the gas body tends to run forward in the molten synthetic resin, and tends to form a non-uniform hollow body. An object of the present invention is to provide a manufacturing method that can easily and inexpensively mold a hollow article with a complicated shape. The method of manufacturing a hollow article invented by Wood is
The method is characterized in that a plasticized synthetic resin is injected into a mold cavity, and a liquid is pressurized into the injected resin during or after the injection to form a hollow portion of the synthetic resin molded body.

The present invention will be explained in more detail using a thermoplastic resin.

When heat-plasticized synthetic resin is injected into a mold cavity formed by a cooled mold, during or immediately after injection, the surface layer of the synthetic resin in contact with the mold wall cools and solidifies. However, the inner core of the injected synthetic resin is in a thermoplastic state. In this state, when liquid is pressurized into the synthetic resin inner core from the same injection port (gate) etc. to the mold cavity, the liquid pushes out the synthetic resin in the inner core, which is still in a plasticized state, and enters the inner core, causing the surface layer to Forms a hollow body whose inner core is made of synthetic resin and liquid. The injected liquid is injected into the synthetic resin without breaking the surface layer of the cooled and solidified synthetic resin, forming a good hollow body.
In the present invention, any commonly used thermoplastic resin can be used as the synthetic resin, and if necessary, a thermosetting resin can also be used.

Various additives such as dyes and pigments, extenders, and glass fibers may be added to the resin. In the present invention, liquid means a substance that is liquid at room temperature, such as water, glycerin, liquid paraffin,
This includes hydraulic oil and the like, with water being particularly preferred.

It is preferable that the liquid be heated to around the molding temperature of the injected resin at the time of press-fitting. If water is used, the liquid should be heated to a sufficient pressure to maintain the liquid phase in the heated state, that is, as a high-temperature, high-pressure liquid. It is preferable to press fit into the inside. The manufacturing method of the present invention will be explained below with reference to the accompanying drawings.

In FIG. 1, plasticized resin 9 is stored in an injection cylinder 1 by a screw 2 having a known structure for plasticizing and injecting the resin, and fills a mold cavity 13 made of molds 11 and 12. After injecting an insufficient amount of plasticized resin 9 into the mold cavity 13, liquid is subsequently pressurized into the plasticized resin in the mold cavity 13 from the liquid injection tube 4 provided in the nozzle portion 8.

The liquid injection tube 4 is fixed to a support member 3 installed at the center of the nozzle section. The injected liquid enters the plasticized resin and forms an inner wall surface constituting the hollow portion. Due to the advance of the piston 6 of the separately provided liquid press-fitting piston-cylinder device 5, the liquid supplied into the cylinder front part 10 from the pipe 7A through the valve 7 is sent through the injection pipe 4. FIG. 2 shows another example of a device 3 for implementing the method of the invention, showing only the inventive part of the mold.

The plasticized resin passes through sprues 17, runners 18, and gates 19 formed in the molds 14 and 15, and is injected into a mold cavity 20 constituted by the molds 15 and 16. A valve 21 for pressurizing liquid into the plasticized resin is provided in the middle 5 of the runner 18, and this valve 21 is connected to the cylinder chamber 2 of the cylinder device 23, which is divided by the piston 23A.
It is driven by supplying and withdrawing pressurized fluid from ports 24 and 25 to 3B and 23C. Type key 4 Yabitei 2
After injecting an insufficient amount of plasticizing resin into the mold cavity 20 to fill the mold cavity 20, the mold cavity 20 is filled with the plasticizing resin and the liquid by pressing down the valve 21 and pressurizing the liquid from the passage 26, A molded article having a resin surface layer and a liquid inner core can be obtained. After injecting the liquid through the passage 26, the switching valve 27 is subsequently switched from the liquid inlet 28 to the gas inlet 29, the gas is injected into the mold cavity 20 through the passage 26, and the inner core of the molded body is discharged from the outlet 22. The constituting liquid is drained to obtain a hollow part. In the embodiments described so far, the liquid is injected after the plasticizing resin is injected, but the liquid can also be injected at the same time as the plasticizing resin is being injected.

After most of the plasticized resin has been injected, it is particularly preferred to simultaneously inject the remaining plasticized resin and press in the liquid. Depending on the shape of the article to be molded, the liquid may break the surface resin layer, resulting in poor mold surface reproducibility and difficulty in molding.In such cases, apply gas pressure to the mold cavity. It is best to perform the formation in a state where the

If the article to be molded is thick, the surface resin layer may become too thick. In such cases, the movable mold shown at 12 in Figure 1 can be moved back during liquid injection to enlarge the mold cavity. Favorable results can be obtained. Furthermore, if this is applied when the cavity during resin injection is thin,
Hollow bodies with extremely uniform and thin surface layers can be obtained. Figure 3 shows the process of forming the hollow body. In FIG. 3, a conduit 33 is inserted into a mold cavity 32 formed by molds 30 and 31.
, pressurized gas is injected from the groove 34 surrounding the mold cavity 32 to maintain the mold cavity in a pressurized state (3A). An O-ring 35 is installed on the mold dividing surface to keep the mold cavity under pressure. Plasticized synthetic resin 37 is injected into the pressurized mold cavity 32 through the injection port 36 in an amount insufficient to fill the mold cavity (3B), and then heated liquid is injected into the mold cavity through the same injection port 36. The mixture is poured into a plasticized resin to form a hollow body (3C). Next, examples will be shown.

Example 1 Using the apparatus shown in Fig. 1, a diameter of 1501 fr! Ft,
A disk-shaped molded product with a thickness of 7 Trft was molded.

Polyethylene “Stylon 470” as thermoplastic resin
(registered trademark, Asahi Tau Co., Ltd. product) as a liquid.
Water heated to 00°C was used. The mold cavity was made 5m thick and filled with molten resin, then heated water was added at 150kg/C.
The mold cavity was expanded to a thickness of 7 wrm by gradually retracting the movable mold 12 with the water injection pressure.
After cooling the resin in the mold, a hollow disk-shaped mold was obtained. Example
2 Using the device shown in Figure 2, the diameter is 20rm and the length is 30mm.
A cylindrical mold of 0 rvn was molded.

ABS resin “Starlac◆100” is used as a thermoplastic resin.
” (registered trademark, manufactured by Asahi Tau Co., Ltd.) and water heated to 200°C as the liquid. 70% of the amount of plasticized resin to fill the mold cavity is injected, then heated water is injected from the passage 26 through the valve 21 at 150 Kf/Cd, the mold cavity is filled with water injection pressure, and the resin is cooled in the mold. A hollow cylindrical mold was obtained.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an example of a molding apparatus suitable for carrying out the present invention, FIG. 2 is a cross-sectional view showing another example suitable for carrying out the present invention, and FIG. In Figure 1, which is a schematic diagram showing the process of forming a hollow body by the method,
1... Injection cylinder, 2... Injection screw, 3.
...Support member, 4...Liquid injection pipe, 5...Piston cylinder device, 6...Piston, 7...Valve, 8...
・Nozzle part, 9... Plasticized resin, 10... Cylinder front part, 11, 12... Mold, 13... Mold cavity,
In Fig. 2, 14, 15, 16...mold, 17...
...Sprue, 18...Runner, 19...Gate, 20...Type cavity, 21...Valve, 22...
Mold cavity inlet, 23... Cylinder device, 23A.
...Piston, 23B, 23C...Cylinder chamber, 24
, 25... Pressurized fluid, 26... Gutter passage, 27... Switching valve, 28... Liquid inlet, 29... Gas body inlet,
In Fig. 3, 30, 31... type, 32... type cavity, 33... conduit, 34... groove, 35...
0-ring, 36... Inlet, 37... Plasticized synthetic resin.

Claims (1)

[Claims] 1. A hollow article characterized in that a plasticized synthetic resin is injected into a mold cavity and a liquid is pressurized into the injected resin during or after the injection to form a hollow part of a synthetic resin molded body. Production method.