JP3027753B1 - Manufacturing method of synthetic resin hollow molded article - Google Patents

Abstract

Abstract: PROBLEM TO BE SOLVED: To blow-mold a heated raw tube 6 by pressurized air blown into a mold 1, both ends of which are fixed to the mold 1 and expanded by a pressurized air. When the original tube 6 is externally fitted to the outer tube 5 in a free state, and the original tube 6 is indirectly blow-formed, the original tube 6 is perturbed. SOLUTION: When a center portion of a rubber tube 5 is thinned and both end portions are thickened and a center portion is expanded first and then both end portions are expanded, the original tube 6 does not move.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a synthetic resin hollow molded article by providing a rubber-like elastic skin in a split mold.

[0002]

2. Description of the Related Art The main molding methods of synthetic resin molded articles include injection molding, extrusion molding, vacuum molding, and hollow molding, among which the hollow molding method is a method of molding synthetic resin in a molten state. At the same time, insert the nozzle for pressurized air into the cylindrical molten synthetic resin from the bottom, cover the outside with the mold at the same time, then inject pressurized air through the pressurized air welding nozzle to melt. In general, a synthetic resin is molded in close contact with an outer mold (called a hot parison method).

[0003] In the hollow molding method, besides a method of suspending the molten synthetic resin in a cylindrical shape, a material which is primarily molded into a cylindrical shape, for example, an original tube or an original plate is heated and softened and inserted into a molding die. Then, pressurized air is flowed into the heat-softened material to form, or an elastic skin is inserted into the heat-softened material, and pressurized air is flowed into the elastic skin. ,
There is a method of molding by expanding (referred to as a cold parison method, for example, see Japanese Patent No. 2850217).

The cold parison method, in which the primary molding material is heated and softened and pressurized air is introduced into the inside to form the material, has a lower heating temperature than the hot parison method and is easier to press-mold. Has the advantage that it can be greatly simplified.

In the cold parison method, a method in which pressurized air is directly introduced into a material softened by heating is generally used. However, in a molding method using an elastic skin (the above-mentioned patent method), Has the following features.

[0006] 1) When pressurized air is allowed to flow directly into the heat-softening material, it is required to prevent leakage of pressurized fluid from the gap between the material to be inserted and the mold every time molding is performed. If a body is used, the pressurized fluid is sealed within the elastic skin and does not leak. Therefore, the fabrication of the mold is facilitated and economical.

2) For the same reason, there is no need to insert the heat-softened material in the mold (referred to as clamping or chucking), so that the size of the material can be shortened and the loss of the material is reduced, which is economical.

[0008] 3) The expansion of the elastic skin due to the inflow of the pressurized fluid causes the heat-softened material to be pressed against the mold, so that the material can be uniformly spread, and the partial thickness variation is small.

[0009]

However, in the method of expanding the heat-softening material through the elastic skin, a method for injecting the pressurized fluid when the elastic skin is expanded by the flow of the pressurized fluid, Due to various factors such as the method of installing the heat-softening material and the method of attaching the elastic skin, the expansion start point of the elastic skin is different, and as a result, the heat-softening material is pushed in the expansion delay direction from the expansion point of the elastic skin. As a result, there is a problem that a molded article having a uniform shape may not be obtained.

As a solution to this problem, there is a method in which an end of the heat-softening material is sandwiched between a core having a mold and an elastic body attached thereto in order to prevent the heat-softening material from moving. In this method, since the chucking loss cannot be eliminated, the effect of using the elastic skin is reduced.

Further, when the heat-softening material is shifted, the elastic skin is caught in the heat-softening material, which damages the elastic skin, resulting in a short life.

Accordingly, a main object of the present invention is to solve the above-mentioned problem and obtain a greater effect.

[0013]

In order to achieve the above object, the gist of the present invention is as follows. 1) An elastic skin which expands and expands with a pressurized fluid is installed inside a mold forming a cavity inside, A synthetic resin molded body in a heated and softened state is inserted in a free state into a space formed between a molding die and the elastic skin, and a pressurized fluid flows into the elastic skin to expand it. In the method for manufacturing a synthetic resin hollow molded article in which the heat-softened synthetic resin molded article is molded along a cavity, the cross-sectional area of the elastic skin is partially changed, and the above-mentioned elastic cross-section is expanded and stretched under pressure. A method of manufacturing a synthetic resin hollow molded article characterized by providing a time difference of expansion and extension by a partial change, and 2) a raw pipe made of thermoplastic resin such as polyvinyl chloride which is heated and softened. Set in a mold and blow compressed air into the original tube Bro - per the molding is clamped to both ends in the mold, protect state in which the heating,
In addition, the original tube is shortened from the elastic tube and fitted around the elastic tube in a free state, and the compressed tube is blown into the elastic tube. In a method of manufacturing a large-diameter synthetic resin hollow molded article by preventing the inner surface of a tube from being quenched by blown air, a center portion of the elastic tube which expands in a relatively free state is made thin, A method for producing a synthetic resin hollow molded product, characterized in that the clamp side is made thick to provide a time difference during pressure expansion and extension.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to embodiments shown in the accompanying drawings. 1 to 3 are sectional views of an embodiment of the present invention.

In the first embodiment shown in FIG. 1, the cross-sectional shape of the elastic body 2 is substantially cylindrical as a whole, and both ends fixed in the axial direction are made thick, so that the elastic skin 2 is relatively free at the time of expansion and extension. The central part of the negative state is made thin and the thickness between the two parts is gradually changed, and those shown in FIG. 2 and FIG.
This is a third embodiment.

The details will be described below with reference to FIG. FIG.
1, 1a is a molding die made of metal (mild steel or an aluminum alloy or the like) which is divided into upper and lower parts or plural parts (for example, divided into upper and lower parts), and has a cavity (molded product outer surface forming surface) 7 on the inner surface. are doing.

The upper and lower mold halves 1
And 1a are air holes (or air vent grooves) 1b during molding.
Are deployed as needed. Inside the molding dies 1 and 1a, an elastic skin 2 and cores 3 and 3a for holding the elastic skin 2 are provided so as to penetrate therethrough.

A pressurized fluid (air or oil) inlet 4 is bored in the left and right cores 3 and 3a, and these cores 3 and 3a are integrated by a plurality of core connecting rods 3b. Have been. The elastic skin 2 is fixed at its both ends to the cores 3 and 3a by fixtures 5.

The outer tube of the elastic skin 2 has an inner diameter larger than the outer diameter of the elastic skin 2 (including the inner diameter in a heated state), and the original tube heated in advance to a softening temperature specific to the synthetic resin or more. The heat softening material 6 is fitted outside in a free state.

The heat-softening material 6 as the original tube is shorter than the entire length of the substantially cylindrical elastic skin 2, and is formed by the molding dies 1 and 1a.
Has a length that can be accommodated in the cavity 7 formed.

In the above construction, the elastic skin 2 is formed by clamping the molding dies 1 and 1a and allowing the pressurized fluid to flow from the pressurized fluid inlet 4 of the cores 3 and 3a. Expands, comes into contact with the heat-softened material 6, expands the heat-softened material 6 together, and presses the heat-softened material 6 against the inner surfaces of the molding dies 1 and 1a to complete the expansion and obtain a desired molded product. Can be.

When the material of the heat-softening material 6 is a hard vinyl chloride resin, the heating surface temperature of the heat-softening material 6 is as follows:
Approximately 100 to 120 ° C., and the pressurized fluid is air at room temperature and the inflow pressure is 0.6 to 1 MPa (6.1 to 10.2 kg).
f / cm ² ), it is appropriate that the diameter expansion ratio (the outer peripheral length of the molded article / the outer peripheral length of the material × 100) is 150 to 170%. Since the increase in the diameter expansion rate directly affects the raw material cost, the diameter expansion rate may be set to 200% or more to reduce the raw material cost.

By increasing the diameter expansion rate of the heat-softened material 6, the cost of raw materials can be reduced. On the other hand, the increase in the diameter expansion rate is caused by poor appearance such as whitening and cracks and the elastic skin 2
Due to the partial deviation of the expansion speed (time), the heat-softened material 6 is pushed to one side, and it is easy to induce molding failure.

Therefore, in order to improve these molding defects in particular, in the present embodiment, the fixed end portions of the elastic skin 2 are made thick, and the vicinity of the center portion which expands relatively free is made thin. In this state, the thickness between the two portions is gradually changed so that the elastic skin 2 expands from the central portion when the pressurized fluid flows.

Therefore, when the elastic skin 2 expands from the center and the heat-softening material 6 expands from the center, the expansion force generated in the left-right direction is canceled out, so that the one side of the molding dies 1 and 1a. And the molding failure can be prevented.

According to this method, the molding dies 1 and 1
It is not necessary to sandwich both ends of the heat-softening material 6 between the a and the fixture 5 to prevent the heat-softening material 6 from moving at the time of expanding the diameter, and no chucking loss of the material occurs.

When the phenomenon that the elastic skin 2 expands from the center and the heat-softening material 6 is pushed to one side can be eliminated,
The elastic skin 2 is also prevented from being caught in the heat-softening material 6, and the elastic skin 2 can be prevented from being damaged, so that the life (durable time) can be improved.

As an example of the material of the elastic skin 2, the elongation is as high as 100 to 1000% and the maximum operating temperature is 130.
Chloroprene rubber, which has heat resistance to ℃, is suitable.

Although the variation of the thickness is sufficient even with a slight difference, it is preferable that the thin portion is about 85 to 50% of the thick portion. The portion is 5 mm, the thin portion is 3 mm, and the thin portion is 60% of the thick portion.

Therefore, according to this molding method, when a synthetic resin manhole is molded using a raw tube of, for example, PVC or ABS, an inspection cylinder diameter of 650 mmφ to 700 m
A large diameter of mφ can be manufactured.

In particular, the height of the rising connection portion for connecting the inspection tube can be made large, and it is made of a thick wall to maintain the strength, and it is not necessary to reinforce the overlay such as FRP. Benefits are obtained.

FIG. 2 shows a bag-like heat-softening material 6a having one end opened and the other end closed, using an elastic skin 2a having a closed end and a thinner end than the open end. FIG. 3 shows an embodiment in which the bag-like heat-softening material 6a is intentionally expanded from the tip end thereof. FIG. Structure 2
At least two holes 2d are provided at the center of one layer 2c of the elastic skins 2b and 2c.
14 is another embodiment in which the cross-sectional area of c is partially changed.

In addition, as the material of the elastic skin 2, besides the above-mentioned chloroprene rubber, silicon rubber excellent in heat resistance or an elastic synthetic resin film may be used.

The method of changing the wall thickness does not necessarily need to be changed gradually as in the embodiment shown in FIG. 1, and the same effect can be obtained even when the thickness is changed in one or more steps.

The material of the heat-softening material 6 may be other thermoplastic resin such as acrylic resin, high-density polyethylene resin, ABS resin and polypropylene resin, in addition to the hard vinyl chloride resin of the embodiment.

[0036]

According to the present invention, by the pressure of the pressurized fluid, the elastic skin expands from a portion having a small cross-sectional area and comes into contact with the heat-softened material. Since the heat-softening material is prevented from moving in one direction by closely adhering to the mold or symmetrically generating an expansion force, a molded article having a stable shape can be obtained, and no chucking loss occurs.

Further, since the life of the elastic body can be prevented from being shortened due to the offset of the molded product, material costs and equipment costs can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first main embodiment of the present invention.

FIG. 2 is a sectional view showing a second embodiment of the present invention.

FIG. 3 is a sectional view showing a third embodiment of the present invention.

[Explanation of symbols]

1, 1a: Mold for molding, 2, 2a, 2b, 2c: Elastic skin, 2d: Hole for meat, 3, 3a: Core, 3b: Core connecting rod, 4: Pressure fluid inlet, 5 … Fixture, 6,6a… Heat softening material

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-11-48318 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B29C 49/00-49/80

Claims (2)

(57) [Claims] 1. An elastic skin that expands and expands with a pressurized fluid is installed inside a mold that forms a cavity inside, and a heat softened state is formed in a space formed between the mold and the elastic skin. Insert the synthetic resin molded body of
In a method of manufacturing a synthetic resin hollow molded article in which a pressurized fluid flows into and expands the elastic skin, and the heat-softened synthetic resin molded body is molded along a cavity, the elastic skin is cut off. A method for producing a synthetic resin hollow molded article, characterized in that the area is partially changed, and a time difference in expansion and extension is provided by the partial change during pressure expansion and extension. 2. A raw tube made of a thermoplastic resin such as polyvinyl chloride or the like in a softened state is set in a split mold, and pressurized air is blown into the raw tube to perform blow molding. The original tube is shortened from the elastic tube and fitted around the elastic tube in a free state while being clamped to protect the heated state and expand by the pressurized air. A method of manufacturing a large-diameter synthetic resin hollow molded article by blowing compressed air into a tube so that the inner surface of the original tube is not rapidly cooled by the blown air. A method for producing a synthetic resin hollow molded product, characterized in that a central portion which expands in a smooth state is made thinner and a clamp side is made thicker so as to provide a time difference during pressure expansion and extension.