JPH0359821B2 - - Google Patents

Description

Detailed Description of the Invention The present invention provides a bellows hollow body that is flexible, has excellent elasticity, and has excellent mechanical strength such as tensile strength and abrasion resistance, and is used as a duct, hose, tube, boot, seal, or cover. This relates to a manufacturing method.

Conventionally, thermoplastic plastic is melt-kneaded in an extruder and extruded as a parison 11 from an extrusion die 21 as shown in FIG. Introducing pressure fluid to mold cavity surface 2
A blow-molded bellows hollow body having alternating peaks and valleys as shown in FIG. Since the troughs 18 are formed, the wall thickness of the peaks 17, which have a particularly high expansion ratio, is extremely small, resulting in poor mechanical strength such as tensile strength and abrasion resistance.

Therefore, if blow molding is performed using a material with excellent mechanical strength, the above problems can be solved to some extent, but
The uneven wall thickness between the peaks 17 and the valleys 18 cannot be resolved, and since materials with excellent mechanical strength are generally hard and have poor flexibility, the resulting bellows hollow body The bellows main body had poor elasticity.

In the present invention, when blow molding a multilayer parison consisting of a main layer and a covering layer, the inner surfaces of the peaks are welded and integrated, and moreover, the tips of the peaks are occupied by a coating layer with excellent mechanical strength. Thus, the present invention provides a method for manufacturing a bellows hollow body that is flexible, has excellent elasticity, and has excellent mechanical strength such as abrasion resistance by moving the cavity surface in the axial direction.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is a partially cutaway front view of a bellows hollow body 1 obtained by the manufacturing method of the present invention, in which 2 is a bellows portion that can be bent and expanded, and 3 is a mouth portion that connects with other members. . The bellows hollow body 1 is composed of three layers by coextrusion blow molding, 4 is a main layer made of a flexible material, 5 is an outer covering layer made of a material with excellent mechanical strength, and 6 is an inner layer. This is a coating layer made of a material with excellent mechanical strength.
Also, 7 and 8 are the peaks and valleys of the bellows part,
The crest 7 is formed by welding the inner surfaces together, and since the coating layer 5 is narrowed during manufacturing, it is formed thicker than other parts, and the tip of the ridge 7 is occupied by the coating layer 5. It is configured like this.

Next, to explain the manufacturing method of the present invention, first, a flexible material and a material with excellent mechanical strength are melt-kneaded in separate extruders, and the respective materials are joined in a coextrusion die. A three-layer parison 1a is extruded from a coextrusion die, with a main layer 4 made of a flexible material and covering layers 5 and 6 made of materials with excellent mechanical strength on both sides of the main layer 4. After the extruded parison 1a is placed between the split molds 9 (only one mold 9 side is shown in FIGS. 2 to 4) and closed, a pressurized fluid such as compressed air is introduced into the parison 1a. The parison 1a is then expanded into the shape of the cavity surface 10 of the mold 9, as shown in FIG. Next, as shown in FIG. 3, the mold unit 9A engaged with each peak 7a of the expanded and shaped bellows portion is moved in the axial direction, and the mold unit 9A is brought into contact with the peak 7a of each mold unit 9A. The peak portion 7a is narrowed at the cavity surface 10A, and the inner surfaces are welded together to form a peak portion 7b. Furthermore, as shown in FIG. 4, the inner surfaces are welded together and the peak portion 7b filled with material is narrowed, so that the coating layer 5 in contact with the cavity surface 10A is cooled and hardened. In comparison, since the main layer 4 inside is in a softened state, the main layer 4 moves inward with the covering layer 5 almost remaining at the tip, and the tip part becomes a mountain occupied by the covering layer 5. A section 7 is formed. After cooling the molded product, the mold 8 is opened to obtain a bellows hollow body 1 as shown in FIG.
In addition, in the above embodiments of the present invention, a coextrusion die,
Although the overall arrangement of the split-type mold and parison is not shown in the drawings, the main difference is that the split-type mold is engaged with each mold unit in the present invention and is movable in the axial direction. It is basically the same as the conventional device shown in FIG.

In the present invention, the flexible material constituting the main layer is a thermoplastic or elastomer having a Shore A hardness (ASTM, D-2240) of 93 or less, preferably 86 or less, such as soft polyvinyl chloride,
Preferred are ethylene-vinyl acetate copolymers, styrene elastomers, olefin elastomers, and the like. In addition, the material with excellent mechanical strength constituting the coating layer is a thermoplastic plastic or elastomer with a tensile strength (JIS, K6301) of 150 Kg/Km ² or more, preferably 200 Kg/cm ² or more, such as polyester elastomer, polyurethane elastomer,
Polyamide elastomers and the like are preferred.

In addition, in the bellows hollow body obtained by the manufacturing method of the present invention, all the peaks can be welded together on the inner surfaces, and only the peaks in necessary locations can be welded together, and the third It is also possible to obtain a bellows hollow body by completing the molding with the shape of the peaks as shown in the figure. Furthermore, the outer surface shape of the ridge may not only have a flat tip, but may also have an acute angle, or may have a rounded bulge 12 as shown in FIG. In addition, although a bellows hollow body with a three-layer structure was shown in the example,
The structure may be two layers or four or more layers consisting of an outer surface coating layer and a main layer.

[Brief explanation of drawings]

Figure 1 is a front view of a bellows hollow body obtained by the manufacturing method of the present invention, Figures 2, 3, and 4.
The figure is a schematic cross-sectional view of the main parts of the entire mold in the blow molding process, Fig. 5 is a cross-sectional view of the main parts showing another example of the bellows hollow body obtained by the manufacturing method of the present invention, and Fig. 6 is a conventional bellows hollow body. FIG. 7 is a front view of a mold showing the blow molding process, and FIG. 7 is a sectional view of a main part of a bellows hollow body obtained by a conventional blow molding method. 1... Bellows hollow body, 2... Bellows part, 3
... Mouth part, 4 ... Main layer, 5, 6 ... Covering layer, 7
...Yamabe, 8...Tanibe.

Claims (1)

[Claims] 1 A multilayer parison having a main layer made of a flexible material and a covering layer made of a material with excellent mechanical strength is placed between molds, and a pressure fluid is introduced into the parison to form a bellows-shaped cavity surface. A method for producing a hollow bellows body, which comprises expanding the parison into a shape, then moving the cavity surface in contact with the peaks of the bellows in the axial direction, and welding and integrating the inner surfaces of the peaks.