JP7428880B2 - Manufacturing method of resin pipe - Google Patents

Description

The present invention relates to a method for manufacturing a resin pipe, and more specifically, a method for manufacturing a resin pipe that allows thin-walled resin pipes to be more stably manufactured by resin injection molding using an assist material such as a gas-assisted molding method. It is related to.

As a method for manufacturing resin pipes, a gas-assisted molding method is known in which molten resin is injected into a cavity formed in a mold, and then high-pressure gas such as nitrogen gas is injected into the cavity (for example, see Patent Document 1). ). Instead of high-pressure gas, water, metal balls, or resin balls are sometimes injected into the mold at high pressure as assisting materials.

In resin injection molding using an assist material, the moment the injected molten resin contacts the surface of the cavity, it is cooled and begins to harden. That is, the molten resin has already begun to harden near the surface of the cavity before the assist material is injected. Since the hardened resin cannot be discharged from the cavity by the injected assist material, it is difficult to manufacture thin-walled resin pipes. Therefore, there is room for improvement in stably manufacturing thin-walled resin pipes by resin injection molding using assist materials.

Japanese Patent Application Publication No. 2003-181868

An object of the present invention is to provide a method for manufacturing a resin pipe that can more stably manufacture a thin-walled resin pipe by resin injection molding using an assist material.

In order to achieve the above object, the method for manufacturing a resin pipe of the present invention includes injecting molten resin into a cavity formed in a mold, and then injecting an assisting material into the cavity in the direction in which the cavity extends. By discharging the molten resin from the cavity and hardening the molten resin remaining in the cavity, a thin resin pipe with a peripheral wall thickness of 0.5 mm to 1.5 mm is formed in the cavity. The method of manufacturing a resin pipe is characterized in that the surface of the cavity is formed into a heat insulating layer having a lower thermal conductivity than the material of the base of the mold.

According to the present invention, the surface of the cavity is formed into a heat insulating layer having a thermal conductivity lower than that of the material of the base material of the mold, so that the molten resin injected into the cavity is transferred to the heat insulating layer without coming into contact with the base material of the mold. come into contact with. Therefore, it is advantageous to avoid rapid cooling of the molten resin by the mold. Accordingly, since the amount of molten resin that hardens before the assist material is injected into the cavity is suppressed, it becomes possible to more stably manufacture a thin-walled resin pipe.

A resin pipe manufactured according to the present invention is illustrated, and FIG. 1(A) is a longitudinal cross-sectional view, and FIG. 1(B) is a cross-sectional view. FIG. 2 is an explanatory diagram illustrating a molding apparatus for manufacturing a resin pipe. The mold of FIG. 2 is illustrated, with FIG. 3(A) being a longitudinal cross-sectional view and FIG. 3(B) being a cross-sectional view. FIG. 4 is an explanatory diagram illustrating a state in which molten resin is injected into the cavity of FIG. 3 in a vertical cross-sectional view. FIG. 5 is an explanatory diagram illustrating a state in which an assist material is injected into the cavity in FIG. 4 in a longitudinal cross-sectional view. 6 is an explanatory diagram illustrating a resin pipe molded in the cavity of FIG. 5. FIG.

EMBODIMENT OF THE INVENTION Hereinafter, the manufacturing method of the resin pipe of this invention is demonstrated based on embodiment shown in the figure.

As illustrated in FIG. 1, the resin tube 7 manufactured according to the present invention is a cylindrical body made of resin and has an outer diameter D2 and a pipe line 8 having an inner diameter D1. As the resin forming the resin tube 7, various known resins such as polypropylene, ABS resin, and nylon resin are used. A dashed-dotted line CL in the figure indicates a center line passing through the center of the cross section of the conduit 8. The resin pipe 7 is not limited to a straight shape, but may have a curved shape.

In this embodiment, the resin tube 7 is made of a single material, but it may also have a multilayer structure in which a plurality of layers are laminated coaxially. The type (specification) of the resin used for the resin pipe 7 is determined based on the performance required of the resin pipe 7. For example, a resin is used that has excellent durability against fluid flowing through the pipe 8, external impact, abrasion, ultraviolet rays, and the like. These resins may also be mixed with reinforcing fibers (eg, glass fibers or carbon fibers) in a predetermined ratio.

This resin pipe 7 is manufactured using the molding apparatus 1 illustrated in FIG. 2. The molding apparatus 1 includes a cylinder 1a that injects molten resin 5 into a mold 2 (2a, 2b), and an assist material injection section 1b that injects an assist material 6 into the mold 2.

The assist material 6 may be of any known type, and an appropriate material is selected from among gases such as nitrogen gas, liquids such as water, and solids such as metal balls, resin balls, bullet-shaped metal lumps, and resin lumps. For the assist material injection part 1b, a known appropriate mechanism is adopted depending on the type of the assist material 6.

As illustrated in FIG. 3, the mold 2 is of a so-called two-part type, and is composed of one mold 2a and the other mold 2b to be assembled. The molds 2a and 2b are joined and separated using the parting line PL as a boundary.

The inside of each mold 2a, 2b is formed into a predetermined shape, and the assembled mold 2 has a cavity 3 formed therein. This cavity 3 has the same outer shape as the resin pipe 7 to be manufactured, and in this embodiment, it has a cylindrical shape with an outer diameter D2.

The surface 3a of the cavity 3 is a heat insulating layer 4 having a lower thermal conductivity than the base material of the mold 2. That is, the entire surface 3a of the cavity 3 is covered with the heat insulating layer 4. Note that this thermal conductivity is a value at room temperature.

The heat insulating layer 4 is produced, for example, by attaching ceramic to the surface of a base formed in a predetermined shape inside the mold 2 with a binder or the like and then firing the ceramic. Thereby, this ceramic heat insulating layer 4 is integrally joined to the base of the mold 2 and formed on the surface 3a of the cavity 3.

Since the mold 2 is used repeatedly, the injected molten resin 5 comes into contact with the heat insulating layer 4 repeatedly. Therefore, the heat insulating layer 4 is required to have a low thermal conductivity and have excellent heat resistance and durability. Therefore, it is preferable to use various ceramics for the heat insulating layer 4.

The thermal conductivity of general ceramics is 0.60 to 0.62 W/m/K. The thermal conductivity of carbon steel used as the base material of mold 2 is 46 to 50 W/m/K, so if the ceramic heat insulating layer 4 is used, the thermal conductivity will be 1/100 of the base material of mold 2. It will be about.

The cavity 3 is connected to an injection nozzle of the molding device 1 via a runner or the like formed in the mold 2. The mold 2 is also provided with a discharge section for discharging an excess amount of molten resin 5 from the cavity 3 and a discharge section for discharging the assist material 6 injected into the cavity 3.

Next, an example of a procedure for manufacturing the resin pipe 7 illustrated in FIG. 1 will be described.

First, as illustrated in FIG. 3, the molds 2a and 2b are assembled together and closed. In this state, the molten resin 5 is sequentially injected into the cavity 3, and the assist material 6 is injected into the cavity 3. The injection conditions for the molten resin 5 and the injection conditions for the assist material 6 are tested in advance to understand the appropriate range in which a resin pipe 7 of good quality can be manufactured. Then, the injection of the molten resin 5 and the injection of the assist material 6 are performed under conditions within the appropriate range determined in advance.

More specifically, the molten resin 5 is injected into the cavity 3 by injecting it from the cylinder 1a in the direction in which the cavity 3 extends. By injecting the molten resin 5, the cavity 3 is filled with the molten resin 5, as illustrated in FIG. In the cavity 3, the injected molten resin 5 contacts the heat insulating layer 4, but does not contact the base of the mold 2. That is, the heat insulating layer 4 is interposed between the molten resin 5 and the base of the mold 3.

Immediately after the cavity 3 is filled with the molten resin 5, the assist material 6 is injected into the mold 2 from the assist material injection part 1b at a predetermined high pressure, as illustrated in FIG. The injected assist material 6 passes through the cavity 3 filled with the molten resin 5 along the extending direction of the cavity 3 under high pressure. As the assist material 6 passes, an excess amount of the molten resin 5 that has not yet been completely cured is discharged to the outside of the cavity 3. As a result, the molten resin 5 is molded into a cylindrical shape inside the cavity 3, and a conduit 8 is formed.

Thereafter, the molten resin 5 remaining in the cavity 3 is completely cured. Thereby, as illustrated in FIG. 6, a resin pipe 7 having a desired shape along the cavity 3 is manufactured inside the cavity 3.

When manufacturing the resin pipe 7, the temperature of the molten resin 5 is, for example, about 200°C to 250°C, and the temperature of the base of the mold 3 is, for example, about 80°C. The temperature is very low compared to the average temperature. Therefore, without the heat insulating layer 4, the portion of the molten resin 5 injected into the cavity 3 that contacts the surface 3a is rapidly cooled by the mold 3 and begins to harden. Since there is a slight time lag between when the molten resin 5 is injected into the cavity 3 and when the assist material 6 is injected, a thin layer of hardened molten resin 5 forms near the surface 3a of the cavity 3 during this time lag. It is formed.

However, in the present invention, since the heat insulating layer 4 is present, the heat of the molten resin 5 injected into the cavity 3 is suppressed from being rapidly transmitted to the base of the mold 2 due to the heat insulating effect of the heat insulating layer 4. That is, the molten resin 5 is prevented from being rapidly cooled by the mold 3. Therefore, even if there is a time lag between when the molten resin 5 is injected into the cavity 3 and when the assist material 6 is injected, it becomes difficult for the molten resin 5 to form a hardened layer near the surface 3a during this time lag. . As a result, it is advantageous to manufacture a resin tube 7 with a thinner peripheral wall thickness ((outer diameter D2 - inner diameter D1)/2).

That is, even though the assist material 6 is used for resin injection molding, it is possible to stably manufacture the thin resin pipe 7. For example, a thin resin tube 7 having a circumferential wall thickness of about 0.5 mm to 1.5 mm can be stably manufactured.

In order to obtain a sufficient heat insulating effect by the heat insulating layer 4, the thermal conductivity of the heat insulating layer 4 is preferably set to 1/10 or less of the thermal conductivity of the base material of the mold 2, and is set to 1/50 or less. It is more preferable to do so.

The thickness of the heat insulating layer 4 is set to, for example, 0.3 mm or more and 2 mm or less, more preferably 1 mm or more. If the thickness of the heat insulating layer 4 is less than 0.3 mm, it is difficult to obtain a sufficient heat insulating effect to retard the curing of the molten resin 5. Moreover, even if the layer thickness of the heat insulating layer 4 exceeds 2 mm, a commensurate improvement in the heat insulating effect cannot be expected. Furthermore, as the thickness of the heat insulating layer 4 increases, the cost increases. Therefore, the thickness of the heat insulating layer 4 is appropriately within the above range.

To make the peripheral wall of the resin pipe 7 more stably and uniformly thin, when using gas as the assist material 6, stop the flow of the gas injected into the cavity 3 until the molten resin 5 is completely cured. It is preferable to continue applying internal pressure by the injected gas to the inner circumferential surface of the molten resin 5. Alternatively, it is also effective to increase the injection speed of the molten resin 5. Alternatively, it is also effective to inject the assist material 6 into the cavity 3 before the injection of the molten resin 5 into the cavity 3 is completed.

1 Molding device 1a Cylinder 1b Assist material injection part 2 (2a, 2b) Mold 3 Cavity 3a Surface 4 Heat insulating layer 5 Molten resin 6 Assist material 7 Resin pipe 8 Pipe line

Claims (4)

After injecting the molten resin into the cavity formed in the mold, an assist material is injected into the cavity in the direction in which the cavity extends, and the excess molten resin is discharged from the cavity so that it remains in the cavity. A method for manufacturing a resin pipe, wherein a thin resin pipe with a peripheral wall thickness of 0.5 mm to 1.5 mm is formed in the cavity by curing the molten resin, the method comprising:
A method for manufacturing a resin pipe, characterized in that the surface of the cavity is formed into a heat insulating layer having a lower thermal conductivity than the base material of the mold. The method for manufacturing a resin pipe according to claim 1, wherein the thermal conductivity of the heat insulating layer is set to 1/50 or less of the thermal conductivity of the material of the base material. The method for manufacturing a resin pipe according to claim 1, wherein the thickness of the heat insulating layer is set to 0.3 mm or more and 2 mm or less. 4. The method for manufacturing a resin pipe according to claim 1, wherein the assist material is injected into the cavity before injection of the molten resin into the cavity is completed .

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