JPS63202425A - Manufacture of biaxially stretched polyester bottle - Google Patents

Abstract

PURPOSE:To make it possible to retain the favorable shape of a container even at hot filling and sterilization by heating by a method wherein an intermediate molded item, on the body part of which projected parts relatively large in diameter are formed, is once manufactured by biaxially stretching blow molding and, after that, said projected parts are reversed to be formed into panel-like recessed parts. CONSTITUTION:With split molds 10 having cavity surfaces, the biaxially stretching blow molding of a bottomed preform is performed so as to form an intermediate molded item 30, on the body part of which projected parts relatively large in diameter are formed. In this case, said split molds 10 are heated up to a thermosetting temperature so as to thermoset the formed intermediate molded item by successively holding in the split molds under the state that fluid pressure is applied in the interior of the molded item. Proper corresponding rods 40 are pressed against the projected parts 20 of the thermoset intermediate molded item 30, under the condition that the position of which is fixed, so as to dent the projected parts in order to reverse the projected parts 20. Thus, panel-like recessed parts, the wall of each of which is thinner than that of the remaining part, are formed.

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 bottle recognition container for 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 there is a non-stretched portion or a low-stretched portion, there is no heat resistance, so when hot-backing, the filling temperature must be 65° C. or lower to be used for practical purposes.There is a drawback that the shape retention property is lost.

In order to eliminate this drawback, it has been proposed to heat-treat (heat set) the non-stretched 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 stretched polyester bottles, there is a fairly large volume change between the volume of the contents when heated and the volume when cooled, and this volume change Correspondingly, a considerable pressure difference occurs 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
It is manufactured by stretch blow molding using a split mold having a cavity surface corresponding to such a panel-shaped recess.

However, in a 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. It is not.

Therefore, when the bottle is hot-filled with contents, the body other than the panel-shaped recess is also deformed due to changes in the internal pressure of the bottle, resulting in 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.

(Objective 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 be more stable than other parts in response 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 extremely easily deformed.

(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 and 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 a panel shape. A method for manufacturing a biaxially oriented polyester bottle is provided, characterized in that the final container shape is defined as a recess.

(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,
This portion has a greater degree of expansion than 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 internal pressure of the bottle, deforms appropriately according to the internal pressure, and maintains the appearance of the bottle 1 well.

In the present invention, the thermoplastic polyester is a thermoplastic polyester mainly composed of ethylene terephthalate units, such as PET, a glycol component containing a small amount of other glycols such as hexahydroxylylene glycol, or a dibasic acid. So-called modified PET containing a small amount of other dibasic acid components such as isophthalic acid and hexahydroterephthalic acid is used as a component. 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, vibrator extrusion, and the like. In the former method, molten polyester is injected to produce a bottomed preform in an amorphous state with a mouth and neck corresponding to the final container. The latter method is advantageous for manufacturing bottomed preforms with a gas barrier intermediate resin layer such as ethylene-vinyl alcohol copolymer, and involves cutting the extruded amorphous pipe and compressing it at one end. The mouth and neck are formed by molding, and 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.

In the manufacturing method of the present invention, Fig. 2-A and Fig. 2-B
Biaxial stretch blow molding of the above-mentioned bottomed preform is performed using a split mold 10 having a cavity surface as shown in the figure, and an intermediate molded product 30 having a convex portion 20 with a relatively large diameter on the body thereof to form.

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. The reforming is carried out by stretching in the axial direction using a stretching rod and expanding and stretching in the circumferential direction by blowing fluid.

In addition, in this biaxial stretch blow molding, the split mold 10
is heated to a heat-setting temperature, and biaxial stretch blow molding is performed in this state, and the formed intermediate molded product 30 continues as shown in FIGS. 2-A and 2 with fluid pressure applied inside. - It is held in the split mold shown in Figure B and heat set.

Generally, the body-compatible surface 10a of this intermediate molded product 30 is
It is preferred to maintain a heat-setting temperature below the melting point of the thermoplastic polyester, for example at a temperature of 120-230°C, especially 150-200°C, while shoulder-compatible surface iob and bottom-compatible surface 10c are Since the degree of molecular orientation at the bottom is smaller than that at the body, it is preferable to maintain the temperature at a temperature that is lower than the temperature of the body-compatible surface 10a, lower than the whitening temperature, and as high as possible. . The specific heating temperature is 70 to 140 for the shoulder compatible surface tab.
℃, especially in the range of 100 to 130℃, and 70 to 140℃, especially 80 to 12℃ for the bottom compatible surface 10c.
A range of 0°C is preferable.

The time required for heat setting in the mold varies depending on the mold surface temperature, but generally 1 to 30 seconds, especially 3 to 1 second.
A time of about 5 seconds is sufficient.

The intermediate molded product 3.0 that has been subjected to direct heat fixation is then taken out from the split mold and cooled, and the convex portion 20 formed on the body of the molded product 30 is reversed. It is done.

That is, by inverting the convex portion 20, a concave portion corresponding to the panel-like concave portion of the final container is formed.

Such an inversion of the convex portion 20 is, for example, as shown in FIG.
This can be easily done by pressing appropriate rods 40 corresponding to the convex portions 20 of the heat-fixed intermediate molded product 30 in a fixed position to recess the convex portions.

In this way, a panel-shaped recess is 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 generally such that the temperature of the body of the molded product is 3 to 40°C lower than the temperature of the mold surface corresponding to the body, particularly 5 to 30°C.
It is preferable to cool the molded product to a temperature as low as ℃.This cooling is performed when the molded product is exposed to an air atmosphere at room temperature when the molded product is transferred from the blow molding mold to the inversion operation described above or to the secondary blow molding area described below. This can be carried out by leaving it to cool, or by actively blowing cold air onto the molded product taken out from the blow mold. 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.

The molded product, which has been varnished and cooled in an L-shape and has a predetermined panel-like recess formed therein, is then held in a secondary mold and molded into the final container shape under fluid injection.

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

Although the manufacturing method of the present invention has been explained above by taking as an example the case where it is applied to the manufacturing of heat-set and stretched polyester bottles by the so-called two-mold method, the present invention is not limited to this, and for example, stretch blow molding may be performed. Those skilled in the art will appreciate that it can also be applied to the so-called one-mold method in which a mold is maintained at a high temperature for heat treatment, heat treatment is performed in the mold following stretch blow molding, and the mold is further cooled and removed. If so, it would be easily understood.

(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, and FIG. 2-A and FIG. 2-B are diagrams showing a molded structure obtained by stretch blow molding in the manufacturing method of the present invention. FIG. 3, which is a diagram showing the state of the convex part in the body, is a diagram showing an example of means for inverting the convex part to form a concave part. 3...Panel-shaped recess, 4...Column part,
10...Mold, 20...Protrusion. Patent applicant: Toyo Seikan Co., Ltd. Figure 1 Figure 2-A Figure 0a 0a Figure 2-8 Figure 3

Claims (2)

[Claims] (1) A preform with a bottom made of thermoplastic polyester and having a neck corresponding to the neck of the container is biaxially stretched and blow molded in a blow mold, and convex parts with relatively large diameters are formed at predetermined intervals. A second method characterized in that an intermediate molded product having the shape formed on the body is manufactured, and then the protrusion formed on the body of this intermediate molded product is inverted to form a panel-like recess to form the final container shape. Method for manufacturing axially stretched 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-setting is performed within the mold.