JPH09187859A - Production of hollow molded form - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the break rate of a closed-end parison at time for blowing blow gas and to enhance the nondefective rate of a product. SOLUTION: In a method for producing a hollow molded form by blowing blow gas into an injection-molded closed-end parison to perform injection blow molding, in the case of injection-molding the closed-end parison, a bag-shaped expandable film body having an opening in the bottom is internally inserted into the cavity 13 of an injection molding die 10 so as to fix the opening to a gate 14. Furthermore, the closed-end parison is molded by injecting a molten resin into the bag-shaped film body 16 and preliminary heated and blow gas is blown through the molding die. The molten resin has temperature more lower than the temperature lower than either the temperature higher than melting temperature of the bag-shaped film body 16 by 30 deg.C or the thermal decomposition temperature thereof.

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 hollow molded body by injection blow molding by blowing blow gas into an injection-molded bottomed parison.

[0002]

2. Description of the Related Art Conventionally, as described in Japanese Patent Application Laid-Open No. 4-27520, a hollow molded body manufactured by injection blow molding is manufactured by using a hollow mold with a bottomed parison preheated to a temperature capable of expansion and deformation. And blow gas is blown into it.

[0003]

However, in the conventional method as described in JP-A-4-27520, the blow gas is blown due to the variation in the heating temperature generated by the preheating of the bottomed parison. At this time, the bottomed parison is likely to be broken from the high temperature portion of the resin temperature, and there is a problem in productivity such that the non-defective product rate decreases.

The present invention has been made in view of the above-mentioned problems, and an object thereof is to solve these problems and to break the bottomed parison at the time of blowing the blow gas. It is intended to provide a method for producing a hollow molded article, which is capable of reducing the production cost and improving the yield rate of products.

[0005]

In the method for producing a hollow molded article of the present invention, blow gas is blown into an injection-molded bottomed parison, and in the method for producing a hollow molded article by injection blow molding, the bottomed parison is injected. At the time of molding, a bag-shaped film body having expandability in the cavity of the injection molding die and having an opening at the bottom is internally mounted so that the opening is fixed to the gate. The bottomed parison is molded by injecting a molten resin having a temperature higher than the melting temperature by 30 ° C. or a thermal decomposition temperature, whichever is lower, into the bag-shaped film body to form a bottomed parison. Is preheated, and blown gas is blown by a molding die.

The bottomed parison injection-molded as described above varies depending on the type of resin used, but is not less than the deformable glass transition temperature of the expansive bag-shaped membrane and the bottomed parison molding resin. After preheating to a temperature equal to or lower than the melting point, it is sealed in a cavity of a die for hollow molding, and blow gas is blown therein.

The expansive bag-shaped film used in the present invention is a material having a malleability or a material softened by heating, for example, a thermoplastic resin film, a rubber film, or a multi-layered material thereof. What is formed from the film in the same shape as the bottomed parison is preferably used. The expandable bag-shaped film body as used herein refers to a film that is stretchable by elasticity or tensile yielding, and that can withstand stretching due to blowing of blow gas and that can stretch by 100% or more. preferable.

Examples of the resin material for forming the bag-shaped film body made of the thermoplastic resin include fluorine resin, polyvinyl chloride resin, polyurethane resin, acrylic resin, polyester, ethylene-vinyl acetate copolymer, polypropylene,
Examples include polyethylene and thermoplastic elastomers.

Further, as a rubber material for forming a rubber bag-shaped film body, natural rubber, styrene-butadiene rubber, acrylonitrile-butadiene rubber, isoprene rubber, butadiene rubber, chloroprene rubber, urethane rubber, silicone rubber and fluorine are used. Rubber, acrylic rubber, etc. can be raised.

It is also possible to use a mixture of the above-mentioned thermoplastic resin and rubber.

The wall thickness of the bag-shaped film having expandability is determined by the degree of stretching by blowing blow gas and the degree of unevenness of the molded product, and is preferably 100 μm to 2 mm, but in terms of moldability and cost. From 200 μm to 1
The range of mm is more preferable.

Examples of the molding resin for the bottomed parison in the present invention include polyethylene, polyethylene, polybutene, polycarbonate, polystyrene, polyethylene ionomer, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, vinyl chloride-based resin. Resins, chlorinated vinyl chloride resins, vinylidene fluoride resins, polytetrafluoroethylene, polyphenylene sulfides, polyamides, polyether ether ketones, polyether sulfones, polysulfones, acrylonitrile butadiene styrene copolymers, etc. can be used. Mixtures and, if necessary, reinforcing fibers such as glass fiber, carbon fiber and polyimide fiber, fillers such as talc, calcium carbonate and mica, colorants such as carbon black and titanium oxide, dioctane Rufutareto, plasticizers may be included, such as stearic acid.

The resin temperature in the injection molding of the bottomed parison is 30 ° C. higher than the melting temperature of the bag-shaped film having expandability, or the temperature at which the bag-shaped film having expandability causes a decomposition reaction. It is necessary to be lower than either lower temperature. If this condition is satisfied, the expansive bag-shaped film body can be melted by heat transfer and injection and filling can be completed before it is destroyed, and decomposition is prevented.

Further, in the case of an amorphous thermoplastic resin, it does not show a definite melting point, but a temperature higher by 20 ° C. than the softening temperature can be used as a measure of the melting temperature.

Generally, an inert gas such as nitrogen gas or carbon dioxide gas is suitable as the blow gas, but dry air,
In addition, any gas that has poor reactivity and does not deteriorate under molding temperature conditions can be used.

[0016]

In the method of manufacturing a hollow molded article of the present invention, when a bottomed parison is injection-molded, an expansive bag-like film body is provided in the cavity of an injection molding die. To fix it to the gate,
A molten resin having a temperature 30 ° C. higher than the melting temperature of the bag-shaped film body or a temperature lower than the lower temperature of the thermal decomposition temperature is injected into the bag-shaped film body to form a bottomed parison. Then, the bottomed parison is preheated, and blown gas is blown by the molding die, so that the bottomed parison is supported by the tension of the bag-shaped film body having expandability, so that the blown gas breaks through the bottomed parison. It is possible to prevent leaks and form with a high yield rate.
Further, it is possible to obtain a hollow molded body having an appearance surface excellent in texture and the like.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments will be described below with reference to the drawings. 1 to 4 are cross-sectional views showing an example of the method for producing a hollow molded body of the present invention. FIG. 1 shows an injection mold 10 for injection-molding a bottomed parison. The injection mold 10 is composed of a fixed mold 11 and a movable mold 12, and has a cavity 13 for molding the bottomed parison. Has been formed. The fixed mold 11 is provided with a sprue 15 for injecting a molten resin and a gate 14.

In the cavity 13, an expansive bag-like film body 16 is attached by fixing the opening 17 at the tip thereof to the gate 14 so that the fixed mold 11 and the movable mold 12 are closed. . Subsequently, the molten resin is injected into the cavity 13 through the gate 14 to fill the cavity 13 and form the bottomed parison 18 as shown in FIG.

Next, the bottomed parison 18 taken out from the injection molding die 10 is preheated by a preheating device as shown in FIG. 3, and heated up to a resin temperature range where it can be stretched by blowing a blow gas. .

Subsequently, the preheated bottomed parison 18 is moved and set in the molding die 30 shown in FIG. 4, and blown gas is blown into the bottomed parison 18 to expand the film 16 having expandability. While simultaneously stretching, the bottomed parison 18 is simultaneously stretched to form the molding die 30 into a container shape, and then cooled to obtain a hollow molding 18A.

At this time, the bag-shaped film body 16 having expandability
Since the bottomed parison 18 is held by the tension of, the blow gas is prevented from breaking through the bottomed parison 18 and leaking, and the conventional defectiveness at the time of molding is prevented.

The temperature of the injection molding die 10 varies depending on the resin used and the material of the bag-shaped film body, but it is preferable to heat at a temperature lower than the softening temperature of the filling resin.

Example 1 Using the injection molding die shown in FIG. 1, an expansive film made of silicon rubber (polysiloxane) having a thickness of 1 mm was used, and this film was injection-molded at a temperature adjusted to 25 ° C. Installed in the cavity of the mold, polypropylene (Showa Denko KK product name HM6649) was used at a resin temperature of 20.
Injection was performed under the condition of 0 ° C. to mold a bottomed parison. In this example, in order to shorten the molding cycle, the mold temperature was set to 30 ° C., which is lower than the softening temperature 60 ° C. of polypropylene used for filling.

The bottomed parison has a surface temperature of 12
After cooling to 0 ° C. and releasing, the bottomed parison was heated to 160 ° C. by a preheating device, the preheated bottomed parison was set in a molding die, and blown gas was blown to mold it. Cooled to obtain a hollow molded body.

(Comparative Example 1) A hollow molded article was obtained under the same conditions as in the above Example except that a film having expandability was not used during injection molding of a bottomed parison.

The results are shown in Table 1, and it was confirmed that the non-defective product rate was improved from 90% to 99% by the method for producing a hollow molded article using the bottomed parison of the present invention.

[0027]

[Table 1]

Example 2 Using the injection molding die shown in FIG. 1, a 500 μm thick thermoplastic resin (tetrafluoroethylene resin) expansive bag-shaped membrane was used. Installed in a cavity of an injection mold whose temperature was adjusted to 25 ° C, and made of polypropylene (trade name HM66 manufactured by Showa Denko KK).
49) was injected at a resin temperature of 220 ° C. to form a bottomed parison. In this example, in order to shorten the molding cycle, the mold temperature was set to 30 ° C., which is lower than the softening temperature 60 ° C. of polypropylene used for filling.

The bottomed parison has a surface temperature of 14
After cooling to 0 ° C. and releasing, the bottomed parison is heated to 180 ° C. by a preheating device, the preheated bottomed parison is set in a molding die, and blown gas is blown to mold it. Cooled to obtain a hollow molded body.

The hollow molded article was evaluated by an acid resistance test according to ASTM D543. As a result, the outer surface of the hollow molded article was not corroded.

COMPARATIVE EXAMPLE 2 Except that an expansive bag-shaped membrane was not used during injection molding of a bottomed parison.
Hollow molded bodies were obtained under the same conditions as in the above-mentioned examples.
The hollow molded body was evaluated by performing an acid resistance test in the same manner as in Example 2 above. As a result, the outer surface of the hollow molded body was corroded.

[0032]

In the method for producing a hollow molded article of the present invention, when the bottomed parison is injection-molded, an expansive bag-shaped film body is provided in the lower part of the cavity of the injection mold. The opening is fixed to the gate so that the inside of the bag is filled with molten resin having a temperature higher than the melting temperature of the bag-shaped film body by 30 ° C. or a thermal decomposition temperature, whichever is lower. The bottomed parison is formed by injecting into a film-shaped film body, pre-heating this bottomed parison, and blowing a blow gas with a molding die, whereby the bottomed parison is pulled by the tension of the expansive bag-shaped film body. Since it is supported, blow gas is prevented from breaking through the bottomed parison and leaking, molding can be performed with a high yield rate, and a hollow molded article having an excellent appearance such as texture can be obtained. . Therefore, it is preferably used as a method for producing a hollow molded body.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of an injection molding die used in the method for producing a hollow molded body of the present invention.

FIG. 2 is a sectional view showing an example of an injection molding die used in the method for producing a hollow molded body of the present invention.

FIG. 3 is a sectional view of a preheating device used in the method for producing a hollow molded body of the present invention.

FIG. 4 is a cross-sectional view of a molding die used in the method for producing a hollow molded body of the present invention.

[Explanation of symbols]

 10 Injection Mold 11 Fixed Mold 12 Movable 13 Cavity 14 Gate 15 Sprue 16 Bag-shaped Membrane 17 Opening 18 and 18A Bottomed Parison 20 Preheating Device 30 Mold

Claims (1)

[Claims] 1. In a method for producing a hollow molded article by injection blow molding, in which blow gas is blown into an injection-molded bottomed parison, when the bottomed parison is injection molded,
A bag-shaped film body having expandability in the cavity of the injection-molding die and having an opening at the bottom is internally mounted so that the opening is fixed to the gate, and the temperature is higher than the melting temperature of the bag-shaped film body. Three
The bottomed parison is molded by injecting a molten resin having a temperature higher by 0 ° C. or a lower thermal decomposition temperature, whichever is lower, into the bag-shaped film body, and preheated the bottomed parison. A method for producing a hollow molded article, which comprises blowing a blow gas with a molding die.