JPH0473696B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a polyester bottle, in which a panel-shaped recess for absorbing internal pressure of the container is formed in the body.

(Prior art) Biaxially stretched blow-molded containers made of thermoplastic polyester such as polyethylene terephthalate have excellent transparency and surface gloss, as well as impact resistance, rigidity, and gas barrier properties necessary for bottles.
It is used as a container for bottling various liquids.

In addition, stretched polyester bottles are significantly superior to other plastic bottles in terms of transparency, gas barrier properties, and pressure resistance against gas-filled beverages, but the stretching and forming temperature is relatively low (80 to 110°C). In addition, since it has non-stretched parts or low-stretched parts, it has no heat resistance, so when hot-packing, it cannot be put to practical use unless the filling temperature is 65°C or lower, and it has the disadvantage of losing its shape retention.

In order to eliminate this drawback, it has been proposed to heat-set the unstretched parts (for example, the neck and neck) and the stretched parts (for example, the body) of the polyester bottle.

Heat setting of biaxially oriented polyester has the effect of preventing thermal deformation at temperatures up to about 65° C. in the case of containers with smooth walls.

However, in the production of bottled products by hot filling into biaxially oriented polyester bottles, there is a fairly large volume change between the volume of the contents when heated and the volume when cooled, and it is necessary to deal with this volume change. This creates a significant pressure difference between the inside and outside of the container.

In order to prevent this, panel-shaped recesses with relatively small diameters are arranged at regular intervals in the container body, and these panel-shaped recesses expand in the radial direction of the body in response to pressure changes inside the container. And, it is being made to have the function of being able to contract.

(Problems with the Prior Art) The polyester bottle having the panel portion described above is manufactured by stretch blow molding using a split mold having a cavity surface corresponding to such a panel-shaped recess.

However, in the polyester bottle obtained by such a manufacturing method, the wall thickness of the panel-shaped recess is substantially equal to the wall thickness of the other column parts, and the panel-shaped recess has a structure in which it is particularly easy to deform. I'm not used to it.

Therefore, when hot filling the bottle with the contents,
Since deformation also occurs in the body other than the panel-shaped recess due to changes in bottle internal pressure, there is a problem in that the appearance of the container is significantly impaired.

Such a problem also occurs when a bottle is filled with contents and then heat sterilized.

(Purpose of the Invention) Therefore, the technical object of the present invention is to solve the above-mentioned problems, and the panel-shaped recess formed in the bottle body is made to move more easily than other parts according to changes in the internal pressure of the bottle. It is an object of the present invention to provide a method for manufacturing a biaxially oriented polyester bottle having a structure that can be deformed very easily.

(Means for Solving the Problems) According to the present invention, a bottomed preform made of thermoplastic polyester and having a neck corresponding to the neck of a container is biaxially stretched blow-molded in a blow mold, An intermediate molded product having a shape in which convex portions with a relatively large diameter are formed on the body at predetermined intervals is manufactured, and then the convex portions formed on the body of this intermediate molded product are inverted to form panel-shaped concave portions. Provided is a method for producing a biaxially oriented polyester bottle, characterized in that the bottle is shaped into a final container shape.

(Function) In the present invention, an intermediate molded product in which a convex portion with a relatively large diameter is formed on the body portion is manufactured by biaxial stretch blow molding, and then this convex portion is reversed to form a panel-like concave portion. This is a notable feature.

That is, when a convex portion is formed on the body by blow molding, the degree of expansion of this portion is greater than that of the other body portions. As a result, the wall thickness of this convex portion becomes thinner than that of other portions.

According to the present invention, since such a convex portion is inverted to form a panel-like recess, the panel-like recess in the final container has a thin wall and has a structure that is easily deformed according to changes in the internal pressure of the container. The container shape is well maintained during filling and heat sterilization.

(Preferred Embodiments of the Invention) The present invention will be described below based on specific examples shown in the accompanying drawings.

First, FIG. 1 shows the shape of a bottle to be manufactured by the manufacturing method of the present invention.

This bottle (represented as 1 as a whole) has panel-shaped recesses 3 formed at regular intervals in a body 2, and pillars 4 are formed between the panel-like recesses 3.

That is, in the bottle 1, the panel-shaped recess 3 absorbs the bottle internal pressure, deforms appropriately according to the internal pressure, and becomes the bottle 1.
The appearance of the product is maintained well.

Container Material In the present invention, the thermoplastic polyester is a thermoplastic polyester mainly containing ethylene tereftate units, such as PET, a glycol component containing a small amount of other glycols such as hexahydroxylylene glycol, or a dibasic acid component. As such, so-called modified PET containing a small amount of other dibasic acid components such as isophthalic acid and hexahydroterephthalic acid is used. These polyesters can be used alone or in the form of blends with other resins such as nylons, polycarbonates, or polyarylates. The polyester used should, of course, have a sufficient molecular weight to form a film.

Bottomed Preform The bottomed preform used in stretch blow molding is manufactured by any method known per se, such as injection molding method, pipe extrusion molding method, etc. In the former method, molten polyester is injected to produce a bottomed preform in an amorphous state with a neck and neck corresponding to the final container. The latter method is advantageous for producing a bottomed preform with a gas barrier intermediate resin layer such as ethylene-vinyl alcohol copolymer, and involves cutting an extruded amorphous pipe,
While forming a mouth and neck part by compression molding on one end,
The other end is closed to form a bottomed preform. In order to maintain good engagement with the lid and sealing under high temperatures, only the portion that will become the mouth and neck of the container can be thermally crystallized in advance. Of course, this thermal crystallization can also be performed at any subsequent step.

Biaxial stretch blow molding In the manufacturing method of the present invention, the above-mentioned bottomed preform is biaxially stretch blow molded using a split mold 10 having a cavity surface as shown in FIGS. 2-A and 2-B. An intermediate molded product 30 having a convex portion 20 having a relatively large diameter on its body is formed.

In this intermediate molded product 30, since the degree of expansion of the convex portion 20 is greater than that of other portions, its wall thickness is formed to be thinner than that of other portions, for example, the column portions 21.

Biaxial stretch blow molding of the preform in the mold shown in FIG.
This is done by stretching a preform preheated to a stretching temperature of 120° C. in the axial direction using a stretching rod, and expanding and stretching it in the circumferential direction by blowing fluid.

In this biaxial stretch blow molding, the split mold 10 is heated to a heat-setting temperature, and the biaxial stretch blow molding is performed in this state, and the formed intermediate molded product 30 has fluid pressure inside. The applied state is then held in the split mold shown in FIGS. 2-A and 2-B, and heat-setting is performed.

Generally, the body-compatible surface 1 of this intermediate molded product 30
0a is a heat setting temperature lower than the melting point of the thermoplastic polyester, for example 120 to 230°C, especially 150 to 230°C.
The temperature is preferably maintained at 200° C., while the shoulder-compatible surface 10b and the bottom-compatible surface 10c have a lower degree of molecular orientation in the shoulder and bottom regions than in the torso. It is preferable to maintain the temperature at a temperature lower than the temperature of the mold surface 10a, lower than the whitening temperature, and as high as possible. The specific heating temperature is 70 to 140°C for the shoulder compatible surface 10b;
In particular, the temperature range is preferably from 100 to 130°C, and the temperature at the bottom corresponding surface 10c is preferably from 70 to 140°C, particularly from 80 to 120°C.

The time required for heat setting in the mold varies depending on the mold surface temperature, but generally it is 1 to 30 seconds.
In particular, a time of about 3 to 15 seconds is sufficient.

Reversal of Convex Portions The heat-set intermediate molded product 30 is then taken out from the split mold, cooled, and the convex portions 20 formed on the body of the molded product 30 are reversed.

That is, by inverting the convex portion 20,
A recess corresponding to the panel-shaped recess of the final container is formed.

Such reversal of the convex portions 20 can be carried out by, for example, pressing appropriate rods 40 corresponding to the convex portions 20 with the heat-set intermediate molded product 30 fixed in position, as shown in FIG. This can be easily done by recessing the convex portion.

A panel-like recess is thus formed, and the recess has a thinner wall than other parts.

Cooling is performed to prevent excessive deformation of the molded product taken out from the mold, but from the standpoint of stability of shape and dimensions, it is preferable to perform cooling before the above-mentioned inversion operation.

The degree of cooling is preferably such that the temperature of the body of the molded article is generally 3 to 40°C lower, particularly 5 to 30°C lower than the temperature of the surface of the mold corresponding to the body. This cooling is performed either by exposing the molded product to an air atmosphere at room temperature and allowing it to cool when transferring the molded product from the blow molding mold to the above-mentioned reversal operation area or the secondary blow molding area described below, or by cooling the molded product by exposing it to an air atmosphere at room temperature, or by removing it from the blow mold. This can be done by actively blowing cold air onto the molded product. Alternatively, it can be placed in a cooling mold and subjected to expansion. When using a cooling mold, the following secondary blow molding is not necessary.

Secondary Blow Molding The molded product, which has been cooled and has the predetermined panel-like recesses formed therein, is then held in a secondary mold and molded into the final container shape under fluid blowing.

During this secondary blow molding (final blow molding), it is sufficient to perform molding or shape retention to maintain the final container shape, and the degree of stretching of any part of the molded product is kept as low as possible. It is better to do so. The inner surface temperature of the secondary mold is naturally lower than that of the primary mold, and generally a temperature of 10 to 70°C is appropriate.

The stretched polyester bottle thus obtained is
It is useful as a sealed storage container for hot filling the contents at a temperature of 70 to 98°C, or for heating sterilization at a temperature of 70 to 95°C after filling.

The manufacturing method of the present invention has been described above using an example in which the manufacturing method of the present invention is applied to the manufacture of a heat-set stretched polyester bottle by the so-called two-mold method, but the present invention is not limited to this. For example, stretch blow molding The fact that it can also be applied to the so-called one-mold method, in which a mold for carrying out the process is maintained at a high temperature for heat treatment, heat treatment is performed in this mold following stretch blow molding, and then the mold is cooled in the mold and taken out. It will be easily understood by those skilled in the art.

(Effects of the Invention) According to the manufacturing method of the present invention, the wall thickness of the panel-shaped recess formed in the body of the bottle can be made thinner than other parts, and as a result, the panel-shaped recess is Since the container easily deforms in response to changes in the internal pressure of the container, it is effectively possible to prevent the container from becoming unsightly and deformed due to hot filling or heat sterilization, thereby impairing its appearance characteristics.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a bottle obtained by the manufacturing method of the present invention, FIG. 2-A, and FIG. 2-B.
The figure shows the state of a convex part in the body of a molded structure obtained by stretch blow molding in the manufacturing method of the present invention, and FIG. 3 shows the means for inverting the convex part to form a concave part. It is a figure showing an example. 3...Panel-shaped recessed part, 4...Column part, 10...Mold, 20...Protrusion part.

Claims (1)

[Claims] 1. A bottomed preform made of thermoplastic polyester and having a neck corresponding to the neck of a container is biaxially stretched and blow-molded in a blow mold to form a convex portion with a relatively large diameter. It is characterized by manufacturing an intermediate molded product having a shape formed on the body at predetermined intervals, and then inverting the protrusions formed on the body of this intermediate molded product to form panel-like recesses to form the final container shape. A method for manufacturing biaxially oriented polyester bottles. 2. The manufacturing method according to claim 1, wherein during biaxial stretch blow molding in a blow mold, the blow mold is heated to a heat setting temperature and heat set is performed within the mold.