JPS61206623A - Manufacture of multilayer container - Google Patents

Abstract

PURPOSE:To obtain a multilayer container, which is excellent not only in gas barrier property but also in visual luster, by a structure wherein the surface of a thermoplastic resin parison is covered with heat-shrinkable film manufactured by inflation method. CONSTITUTION:The surface of a parison made of thermoplastic resin such as saturated polyester resin or polypropylene is covered with cyclic heat shrinkable film, the major component of which is acrylonitrile directly manufactured in advance by inflation method so as to tightly adhere to the parison by being shrunk with heat. Because the titled multilayer container is obtained by biaxially stretching blow molding, strong adherence is given to the parison main body and covering film by being pushed to a mold during the shaping with blowing air. The property of the covering film is also improved because of being biaxially stretched. When a film with gas barrier property is employed, the gas barrier property is also improved through the blow molding.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a novel method for manufacturing a multilayer container. More specifically, the present invention relates to a method for producing a multilayer container in which the surface of the parison is coated with a heat-shrinkable film and then biaxially stretched and blow-molded.

[Conventional technology]

BACKGROUND OF THE INVENTION In recent years, blow-molded plastic containers have come into widespread use as containers for drinks, carbonated drinks, beer, and the like. The properties required for this plastic container are transparency, impact strength, and rigidity.

Although it is lightweight, these properties can be improved by biaxial stretch blow molding using polyethylene terephthalate (hereinafter abbreviated as PET) or polypropylene (hereinafter abbreviated as PP). It has started to show its characteristics and has been accepted by consumers.

However, the shelf life of the contents is still not sufficient.
In the case of contents containing pressurized carbon dioxide gas, such as carbonated drinks and beer, the carbon dioxide gas may pass through the container wall and dissipate, or conversely,
When oxygen enters from the outside through the container wall, the taste changes, resulting in a product with low commercial value. With regard to juices that do not contain carbon dioxide gas, the same problem arises, such as the contents being oxidized by oxygen entering from the outside through the container wall, resulting in loss of flavor.

Conventionally, in order to solve these problems, attempts have been made to mold multilayer containers made of resins with excellent gas barrier properties such as carbon dioxide and oxygen, and PET, PP, and the like. For example, JP-A-56-77143, JP-A-57-140129,
JP-A-57-138923 discloses a technique in which a high gas barrier resin is laminated on a saturated polyester resin by insert molding, and then biaxially stretched and blown. Also.

JP-A No. 59-1352 discloses a stretch-blown container in which a multilayer heat-shrinkable film with excellent carbon dioxide gas barrier properties is adhered to the entire circumference of the body of the container or the entire circumference of the body from the top of the shoulder to the bottom by heat shrinkage. is disclosed.

[Problem that the invention seeks to solve]

However, the method of molding a multilayer container by insert forming requires multiple injection molding machines and injection molds because the multilayer parison is molded by injection molding.
When an adhesive layer is provided between the resin forming the container body and the insert molding resin, the mechanism becomes even more complicated and requires expensive equipment.

On the other hand, in the method of covering a pre-stretch blow-molded container with a heat-shrinkable film and fixing it by heat-shrinking in the Sealink tunnel, the stretched container itself tends to heat-shrink and cannot be heated at high temperatures for long periods of time. It is difficult to select conditions that will sufficiently shrink the film, and especially in the case of containers with complicated shapes, adhesion to the stretched container becomes a problem.

Furthermore, when covering with a heat-shrinkable film, the heat-shrinkable film is usually sealed using heat or an adhesive, which may leave seams in the film and cause problems with the appearance of the container.

The present invention solves these problems and provides a method for manufacturing a multilayer container that does not require complicated equipment, is inexpensive, and has excellent adhesion between one main body resin layer and a coating resin layer.

[Means to solve the problem]

The present invention relates to a method for manufacturing a multilayer container, which is biaxially stretched and blow molded using a multilayer parison made of a thermoplastic resin parison whose surface is coated with a heat shrink film.The heat shrink film is a blown film. This is a method for manufacturing a multilayer container.

That is, one means of multilayering in the present invention is to apply a ring-shaped heat-shrinkable film directly to the surface of the thermoplastic resin parison by an inflation method, and then shrink the film by heat to tightly adhere it to the parison. A multilayer container is obtained by biaxially stretching blow molding using this multilayered parison, so when it is shaped by the parison main body, coating film, and cuff flow air, it is pressed against the mold and gives strong adhesion. be done. Since the covering film is also biaxially stretched, the performance is improved, and when a gas barrier film is used, the gas barrier property is further improved, and even a thin film can provide a container with excellent gas barrier properties.

In the present invention, the resin used for the thermoplastic resin parison may be any resin that can be biaxially stretched and blow molded, but resins with good transparency are particularly suitable considering the intended use. saturated polyester resin,
Examples include PP, polyvinyl chloride, polystyrene, polycarbonate, polymethylmethacrylate-1, polymethylpentene, polyethylene, and the like. Among them, PE'T and PP are optimal. PP is propylene homopolymer IJ
Random copolymers of 7- and propylene- and mono-olefins are suitable, and may contain small amounts of other components such as polyethylene and rubber.

Further, the thermoplastic resin parison in the present invention may be made by either injection molding or extrusion molding.

In the present invention, it is preferable to use a heat-shrinkable film made of a resin having excellent gas barrier properties against carbon dioxide, oxygen, etc. as the heat-shrinkable film, since a container with excellent gas barrier properties can be obtained. As resins having excellent gas barrier properties, for example, acrylonitrile resins containing acrylonitrile as a main component (hereinafter abbreviated as AN resins), saponified ethylene-vinyl acetate copolymers, polyamide resins, and the like are used.

A, N-based resin means 50% by weight or more of acrylonitrile.
- A copolymer containing, as other components, an acrylic ester and a methacrylic ester.

Refers to substances containing one or more of butadiene, styrene, etc.

The heat-shrinkable film used is one manufactured by an inflation method. The method for manufacturing heat-shrinkable film using the inflation method is a known method.1 For example, a thermoplastic resin is extruded at a temperature lower than the normal film forming temperature, and then blown 1.1 to 4 times in the transverse direction. can get.

Further, in order to improve the adhesion between the parison main body and the heat-shrinkable film, the surface of the parison may be coated with an adhesive, or subjected to corona discharge treatment or frame treatment, as necessary. As the adhesive, for example, a two-component polyurethane adhesive or a silicone adhesive can be used.

In the present invention, the surface of the thermoplastic resin parison is coated with a heat-shrinkable film by, for example, the following method.

In the so-called hot parison molding method of injection stretch blow molding, injection molding → preheating → biaxial stretch blowing is performed in a continuous process, but the cylindrical heat shrink film is attached to the injection molded hot parison. , the parison is thermally contracted by the heat held by the parison to cover the surface of the parison. This multilayer parison is then proceeded to the next step, where it is preheated and then biaxially stretched and blown to obtain a multilayer container. The parison may be coated with the heat-shrinkable film in another step before biaxial stretching and blowing.

In addition, in the so-called cold parison injection stretch blow molding, the injection molded parison is cooled once, and in the next step it is reheated to a temperature suitable for stretching and then stretch blow molded. Attaching the heat shrink film can be done as long as it is a step before stretch blow molding.There are two methods: attaching the film before reheating and using the reheating temperature to heat shrink the film, and attaching it to the reheated parison and forming the parison. Any method may be used, such as a method in which the material is shrunk by the heat it possesses, or a method in which a separate film is attached and heat-shrinked before the reheating process.

In this way, the parison can be used in any of the above cases.

The entire surface of the parison is covered with a heat-shrinkable film from just below the mouth to the entire circumference of the body and part of the bottom.

A multilayer container obtained by biaxially stretching and blow molding this multilayer parison has a single mouth and a portion of the bottom which are not covered with the coating film. Both parts are thicker than the body and do not pose any practical problems. For example, gas barrier
As for the properties, this part is thick and has low gas permeability.
If the body is covered with a gas barrier film, the gas barrier properties of the entire container will be significantly improved.

〔Example〕

Examples of the present invention are shown below.

Example 1 ASB manufactured by Nissin ASB Machinery, an injection molding blow molding machine
A parison made of PET was injection molded using a -50 machine. The PET used is manufactured by Mitsui Pet Resin Co., Ltd., product name is Mitsui P.
ET Ji35. The injection molding conditions are shown below.

Injection temperature: 280°C Injection time: 5.0 seconds Cooling time: 4.8 seconds Mold cooling temperature: +5°C This parison is covered with a gas barrier external heat-shrinkable film made of AN-based resin that is slightly thicker than the outside diameter of the parison. The film was then attached to the parison, and the heat contained in the parison caused the film to roughly shrink and adhere tightly to the parison, creating a multilayer parison.

Next, this multilayer parison was preheated to adjust the temperature to a stretch blow molding temperature, and then biaxially stretch blow molded to obtain a round bottle with an outer diameter of 70 M and a volume of 540 cc.

The preheating and biaxial stretch blow molding conditions were as follows.

Preheating temperature 90 to 130°C Time 14 seconds Stretching ratio Longitudinal ] 77 times 2.7 times Blow air pressure IQ kg/cJ Blow time 4.0 seconds The AN resin heat shrink film is A, N resin Balenox. 210 (trademark, manufactured by Sohio Chemical Co.) by an inflation method, and was formed at a resin temperature of 180° C. and a blow-up ratio of 1.5. The thickness of the obtained film is approximately 120μ
ya, 02 and C02 permeation velocity are 2.1 m each
t/rd・24Hr-atm.

4.6 ml/d·24I (r-atm). When immersed in an oil bath at 100° C. for 10 seconds, 30% shrinkage in the lateral direction was observed.

The resulting bottle was a multi-layered bottle in which the entire surface of the bottle, except for a portion of the bottom, was covered with A, N-based resin from just below the bottle opening, and had an excellent appearance.

In addition, the thickness of the PET layer in the center of the body is approximately 3
The thickness of the AN resin layer was approximately 30 μm. When we measured the gas permeation rate of this bottle, we found that
02 transmission rate is 0.12,,t/24 I-Jr
・Aim, CO2 permeation rate is 0.27ml/24I-
It was Ir-aim.

Comparative Example 1 In Example 1, a bottle was molded only from PET without using the gas barrier shrink film.

The 02 permeation rate of the obtained bottle was 0.26 mt/2
41 (r・atm, Co2 permeation speed is 0.88 m//
24I-Jr-atm.

Example 2 In Example 1, PET was replaced with polypropylene resin (Mitsui Toatsu Chemical Co., Ltd.), Mitsui Noblen MJS-
G) was used to mold a stretched bottle in the same manner except that the injection molding conditions and blow molding conditions were changed as shown below.

Injection temperature 220°C Injection time 60 seconds Cooling time 7.0 seconds Mold cooling temperature 15°C Preheating temperature 100-120°C Preheating time 14 seconds Blow air pressure 10 kg/ctK blow 1 hour 4.0 seconds Obtained multilayer bottle The 02 transmission speed of is 0.13mz/2
411r-aim, CO2 permeation rate is 0.33,
It was t/24Hr-atm.

〔Effect of the invention〕

Since the parison normally used in biaxial stretch blow molding has a cylindrical shape or a very simple shape similar to that, it is easy and reliable to shrink the heat-shrinkable film to the parison and bring it into close contact with the parison.

A container with excellent appearance can be obtained.

Further, since the gas barrier heat-shrinkable film coated on the parison is also biaxially stretched at the same time as the container is formed, the film's physical properties such as gas barrier properties, transparency, and surface gloss are improved.

In addition, since the heat shrink film used is manufactured by the inflation method, it is originally cylindrical and has no seams, which eliminates the sealing process, and the resulting multilayer container also has a good appearance with no seal marks. Becomes a container.

Therefore, the multilayer container obtained according to the present invention not only has excellent gas barrier properties but also has an excellent glossy appearance.
Suitable as containers for juice, carbonated drinks, beer, etc.

Claims (3)

[Claims] (1) A method for producing a multilayer container in which the surface of a thermoplastic resin parison is coated with a heat-shrinkable film and then biaxially stretched blow-molded, wherein the heat-shrinkable film is an annular inflation film. Method. (2) The method for manufacturing a multilayer container according to claim 1, wherein the heat-shrinkable film is a heat-shrinkable film made of a resin whose main component is acrylonitrile. (3) The method for manufacturing a multilayer container according to claim 1, wherein the thermoplastic resin is a saturated polyester resin or polypropylene.