JPH0443498B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for manufacturing a heat-set stretch-molded container made of thermoplastic polyester.

(Prior Art) Biaxially stretched blow-molded containers made of thermoplastic polyester such as polyethylene terephthalate (PET) 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.

However, polyester containers have the disadvantage of poor heat resistance, and when used for hot-filling with contents, polyester containers suffer from thermal deformation and shrinkage deformation in volume.・Many proposals have already been made to

As shown in Japanese Patent Publication No. 60-56606, the heat setting method involves taking out the molded product obtained by stretch blow molding from the blow mold, and then holding it in a heat setting mold to heat set it. How to do it
As seen in Japanese Patent No. 6216, a method is known in which heat setting is carried out simultaneously with stretch blow molding in a blow mold. Also, in Japanese Patent Application Laid-Open No. 57-53326,
Heat treatment is performed simultaneously with stretch blow molding in the primary mold, without taking out the molded product and cooling it.
A method of blow molding in a secondary processing mold is described.

(Problems to be Solved by the Invention) However, the method using the stretch-blow type and heat-setting type described above requires heating again for heat-setting, which is uneconomical in terms of thermal energy. The drawback is that the heat-setting mold occupies a long time and productivity is low.

In addition, the method of heat setting at the same time as stretch blow molding in a blow mold has a problem in taking out the molded product after heat setting, and as seen in Japanese Patent Publication No. 59-6216, heating for heat setting is difficult. The method of subsequently cooling the mold for removal is still not fully satisfactory in terms of thermal efficiency, mold occupation time, and productivity.

Furthermore, in the method disclosed in JP-A-57-53326, unstretched or lightly stretched bottoms and shoulders tend to thermally crystallize and turn white during heat setting, and There are defects such as irregular deformation of the molded product during transfer to the mold, making final blow molding difficult.

Therefore, the technical problem of the present invention is to create a biaxially stretched blow-molded container made of thermoplastic polyester that does not whiten the bottom or shoulders of the final container and is stably heat-set as a whole, with excellent thermal efficiency and productivity. The purpose of the present invention is to provide a method for manufacturing the same.

(Means for Solving the Problems) The method of the present invention is to produce a bottomed preform made of thermoplastic polyester and having a neck portion corresponding to the neck portion of the container, in which the mold surface corresponding to the body portion is heated to a high temperature. The mold surface corresponding to the bottom and the mold surface corresponding to the shoulder are biaxially stretch blow molded in a mold heated to a temperature at which the crystallization rate of the polyester is low, and the molded product is placed in the mold. The heat-set molded product is removed from the mold, the molded product is cooled and allowed to shrink, and then the molded product is held in a secondary mold. It is characterized in that it is molded into the final container shape under fluid injection.

(Function) According to the present invention, for the body part whose molecules are highly oriented in biaxial directions, by heating the mold surface corresponding to the body part of the blow mold to a high temperature, the molecules can be highly oriented. By heating the corresponding mold surface under conditions that do not reach the crystallization temperature or higher, even for the bottom and shoulders where the degree of molecular orientation is small, it is possible to prevent these from becoming white. The degree of crystallization can be improved. Therefore, according to the present invention, a high degree of heat fixation can be stably performed while maintaining the appearance of the final container in a good condition so as not to make it unsightly due to whitening of the shoulders and bottom. In addition, since the preform is preheated to the drawing temperature and the entire inner surface of the blow mold is heated, the time for heat setting is short, and therefore the time occupied by the blow mold can be shortened. It turns out.

Next, the molded product that has been heat-set is immediately taken out from the blow mold, and the molded product is cooled and self-shrinked. Placing the molded product under unrestrained conditions and allowing it to self-shrink is intended to relieve the stress remaining in the molded product after the stretch blow molding-heat setting stage and stabilize its dimensions. At this time, cooling the molded product taken out suppresses irregular and unnecessary deformation of the molded product transferred to the secondary mold, and also reduces the temperature of the molded product during molding in the secondary mold. It acts to bring the temperature to the appropriate temperature. In particular, by this cooling, the high-temperature and thin-walled body part is cooled more rapidly than other parts, and reaches a temperature suitable for molding in the secondary mold.

Finally, the cooled molded article is held in a secondary mold and molded into the final container shape under fluid injection.
In the present invention, since the molded product is preliminarily cooled prior to secondary molding, the time occupied by the molded product in the secondary mold is shortened, and the molded product can be heat-set with high overall thermal efficiency and productivity. It becomes possible to manufacture a biaxially stretched blow container.

(Description of Preferred Embodiments) In the present invention, the thermoplastic polyester is a thermoplastic polyester mainly containing ethylene terephthalate units, such as PET, containing a small amount of other glycols such as hexahydroxylylene glycol as a glycol component, or So-called modified PET, which contains a small amount of other dibasic acid components such as isophthalic acid and hexahydroterephthalic acid, is used as the dibasic acid 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.

The preform used in stretch blow molding is manufactured by any method known per se, such as injection molding, pipe extrusion molding, and the like. In the former method, molten polyester is injected to produce an amorphous preform with a neck and neck corresponding to the final container. The latter method is an advantageous method for producing a preform with a gas barrier intermediate resin layer such as an ethylene-vinyl alcohol copolymer, and involves cutting the 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 carried out at any subsequent step.

In the present invention, in FIGS. 1 and 2 for explaining the mold used for stretch blow molding and heat setting, this mold is roughly divided into cavity mold 1.
It consists of a core mold 2 and a base mold 3. The core mold 2 is for gripping the mouth and neck of the preform, and the cavity mold 1 is a split mold with a cavity 1a inside, and defines the shape of the container body and shoulder to be molded. be. The base mold 3 defines the bottom shape of the container,
It may be fixed integrally with the cavity mold 1, or it may be movable in the axial direction of the cavity mold to provide further stretching to the bottom.

The cavity mold 1 consists of an inner cylinder part 4 and an outer cylinder part 5, and a heat insulating material 6 is provided between the inner cylinder part 4 and the outer cylinder part 5. Further, a doughnut-shaped heat insulating material 7 is also provided between the core mold 2 and the cavity mold inner cylindrical portion 4. It will thus be understood that the cavity mold inner cylindrical portion 4 is insulated from both the outer cylindrical portion 5 and the core mold 2.

In order to heat the inner surface of the cavity, a plurality of cartridge heaters 8 extending in the axial direction of the cavity are arranged in a circumferential manner in the cavity mold inner cylindrical part 4. Similarly, a heater 9 is provided inside the base mold 3 to heat the surface thereof. Further, the core mold 2 is provided with a cooling medium passage 10 for cooling the preform mouth and neck portion held by the mold.

The cavity mold inner cylindrical part 4 is provided with insulation,
Moreover, since the heater 8 is provided inside, the torso-compatible surface 11 is heated to a high temperature, while the shoulder-compatible surface 12 is forcedly cooled due to the long heat transfer distance from the heater 8. By being connected to the core mold 2, the core mold 2 is heated to a temperature lower than that of the body corresponding mold surface 11, but not higher than the whitening temperature. In addition, the bottom compatible surface 1
3 is maintained at a temperature within the same range as above by a heater 9.

The biaxial stretch blow molding of the preform in the mold shown in FIG.
The preform, which has been preheated to a temperature of 120° C., is pulled and stretched in the axial direction by a stretching rod, and expanded and stretched in the circumferential direction by blowing fluid. The axial stretching ratio is 1.5 to 3.5 times,
In particular, the stretching ratio in the circumferential direction is preferably 2 to 5 times, particularly 3 to 4.5 times in the body.

The molded article formed by stretch blow molding is continuously held in the mold shown in FIG. 1 while fluid pressure is applied to the inside, and heat setting is performed.

Typically, the torso-compatible surface 11 will have a heat setting temperature below the melting point of the thermoplastic polyester, e.g.
It is preferable to maintain a temperature between 120 and 230°C, especially between 150 and 200°C, while the shoulder-compatible surface 12 and the bottom-compatible surface 13 are arranged so that the degree of dispersion of the shoulder and bottom portions is that of the torso. Since it is relatively small, it is preferable to maintain the temperature at a temperature lower than the temperature of the torso-compatible surface 11 and lower than the whitening temperature, but as high as possible. The specific heating temperature is shoulder compatible surface 1.
2 preferably in the range of 70 to 140°C, especially 100 to 130°C, and bottom-compatible surface 13 preferably in the range of 70 to 140°C, especially 80 to 120°C.

In the present invention, since the entire surface of the mold is heated, an advantage is that the time required for heat setting within the mold is relatively short, and this time varies depending on the mold surface temperature. However, generally a time of 1 to 30 seconds, particularly 3 to 15 seconds, is sufficient.

Open the mold and take out the heat-set molded product.
The molded product is cooled and allowed to shrink. This level removes the stress remaining in the molded product after stretching and heat setting, and stabilizes its form and dimensions. However, by cooling the molded product after heat setting in this process, This prevents excessive deformation of the molded product taken out from the mold, and quickly brings the molded product to a temperature suitable for molding in the secondary mold. The degree to which the molded product is cooled at this stage after being taken out is such that the temperature of the molded product body is 3 to 40°C lower than the temperature of the surface of the mold corresponding to the body, particularly 5 to 30°C lower. It is better. This cooling can be done by exposing the molded product to an air atmosphere at room temperature while it is being transferred from the blow molding mold to the secondary mold, or by actively blowing cold air onto the molded product after it has been taken out. This can be done by spraying.

The cooled and shrunken molded article is then held in a secondary mold and formed into the final container shape under fluid injection. In this final blow molding, it is sufficient to carry out molding or shape retention to maintain the final container shape, and it is preferable to keep the degree of stretching as low as possible in any part of the molded product. in general,
This molding is desirably carried out so that the volumetric expansion rate is 30% or less, particularly 20% or less, based on the molded product after cooling and shrinkage. That is, if the volumetric expansion coefficient exceeds the above range, thermal shrinkage or thermal deformation of the final container will occur due to stretching strain during secondary forming.
It is desirable that this volumetric expansion coefficient be as small as possible from the viewpoint of the heat resistance of the container, but if it is set too low, it will be difficult to hold the molded product in the secondary mold. It is desirable that the volumetric expansion rate be 30% or less, particularly 20% or less.

Naturally, the mold inner temperature of the secondary mold is
The temperature is lower than the inner surface temperature of the primary mold, and generally a temperature of 10 to 70°C is appropriate.

According to the present invention, the volumetric shrinkage rate at a temperature of 85° C. is suppressed to 1% or less, and thermal deformation at this temperature is also effectively prevented.

(Operations and Effects of the Invention) According to the present invention, there is provided an excellent biaxially stretched blow-molded container made of thermoplastic polyester, which does not whiten at the bottom or shoulders of the final container and is stably heat-set throughout. The advantage is that it is manufactured with thermal efficiency and productivity.

(Example) Example 1 A bottomed preform with a height of 162 mm, a body diameter of 26 mm, an average body thickness of 4 mm, and a neck thickness of 1.5 mm was formed by injection molding polyethylene terephthalate with an intrinsic viscosity of 1.0. It was crystallized by heat treatment using hot air (240°C).

This preform is heated to a stretching temperature of 95°C to 100°C, and the heated preform has a cavity surface temperature of 180°C at the body, 110°C at the shoulder, and 100°C at the bottom.
An intermediate molded product is formed by biaxial stretching blowing in a blow mold (primary mold) having a cavity with an internal volume of 1150 c.c., which is heated to After heat setting, the intermediate molded product is taken out from the blow mold, and the intermediate molded product is allowed to cool to about 30℃ by natural cooling.
%, the cavity surface was maintained at 60°C, and the final shape of the container was blow-molded in a secondary mold with a smaller internal volume than the primary mold to obtain a container with an internal volume of 1000 c.c. The molding cycle in this case was 6 seconds/piece.

This container had a good appearance with no cloudiness on the bottom or shoulders.

Even when this container was filled with liquid at 85°C, no shrinkage or deformation occurred. Furthermore, no shrinkage or deformation occurred even after heat treatment at 120°C.

Example 2 Multilayer copolymer in which the inner and outer layers are polyethylene terephthalate with an intrinsic viscosity of 1.0, the intermediate layer is an ethylene-vinyl alcohol copolymer containing 70 mol% of vinyl alcohol, and the adhesive layer interposed between the inner and outer layers and the intermediate layer is a copolyamide. Injection molded, height 162mm, body diameter 26mm,
A bottomed preform with an average body thickness of 4 mm and a neck thickness of 1.5 mm was molded, and only the mouth part was heat-treated with hot air (240°C) to crystallize it.

This preform is heated to a stretching temperature of 95°C to 100°C, and the heated preform is biaxially stretched in a primary mold heated to a cavity surface temperature of 180°C at the body, 110°C at the shoulder, and 100°C at the bottom. An intermediate molded product is formed by blowing, and after being held in the primary mold for 4 seconds to perform heat setting, the intermediate molded product is taken out from the blow mold, and the intermediate molded product is left to cool naturally. Cool it to about 30℃, shrink it by about 20%, and blow mold it into a final shape container in a secondary mold with a cavity surface maintained at 60℃ and an internal volume smaller than the primary mold, with an internal volume of 1000 c.c. Got the container. The molding cycle in this case was 7 seconds/piece.

This container had a good appearance with no cloudiness on the bottom or shoulders.

Even when this container was filled with liquid at 93°C, no shrinkage or deformation occurred. Furthermore, no shrinkage or deformation occurred even after heat treatment at 120°C.

Comparative Example 1 The preform used in Example 1 was stretched at a temperature of 95
The preform is heated to ~100°C, and the heated preform is biaxially stretched and blown using a heated fluid in a primary mold whose cavity surface temperature is approximately 120°C to form a container and placed inside the primary mold. After heat setting by holding for 12 seconds, the heating fluid in the primary mold was changed to a cooling fluid to obtain a container with an internal volume of 1000 c.c. The molding cycle in this case was 16 seconds/piece.

In this container, cloudiness occurred in the center of the bottom and above the shoulder due to thermal crystallization. Furthermore, even when this container was filled with liquid at 85℃, there was almost no shrinkage or deformation.
When heat treated at 120°C, the container contracted and was significantly deformed.

Comparative Example 2 The preform used in Example 1 was stretched at a temperature of 95
The heated preform is heated to ~100°C, and the heated preform is biaxially stretched and blown using a heated fluid in a primary mold whose cavity surface temperature is approximately 180°C to form an intermediate molded product. After heat setting by holding for 3 seconds,
As stated in Publication No. 53326, when transferring the intermediate molded product from the primary mold to the secondary mold without cooling it, the intermediate molded product cannot be transferred from the primary mold to the secondary mold properly, resulting in unsatisfactory results. A container in its final shape was not obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a primary mold used in the present invention, and FIG. 2 is a sectional view taken along line AA in FIG. 1...Cavity mold, 2...Core mold, 3...
...Base mold, 6,7...Insulation material, 8,9...Heater.

Claims (1)

[Scope of Claims] 1. A preform with a bottom made of thermoplastic polyester and having a neck portion corresponding to the neck portion of the container is heated to a primary mold surface corresponding to the body portion and a mold surface corresponding to the bottom portion. Stretch blow molding is carried out in biaxial directions in a mold in which the mold surface corresponding to the shoulders is heated to a temperature at which the crystallization rate is low, and the molded product is held in the mold for heat fixing, followed by blow molding. The heat-set molded article is removed from the mold, the molded article is cooled and allowed to shrink, and then the molded article is held in a secondary mold to form the final container shape under fluid injection. 1. A method for producing a heat-set stretched container characterized by forming the container into a shape. 2. During stretch blow molding and heat setting, the surface of the mold corresponding to the body was heated to a temperature of 160 to 230℃, and the surface of the mold corresponding to the bottom was heated to a temperature of 160 to 230℃.
Temperatures from 70 to 140°C, shoulder-compatible surfaces from 70 to 140°C
2. A method according to claim 1, wherein the temperature is respectively maintained at .degree. 3. The method according to claim 1, wherein heat setting is carried out by holding the molded product in a mold for 1 to 30 seconds. 4 The temperature of the body of the molded product is 3 below the temperature of the surface of the mold corresponding to the body.
The method according to claim 1, wherein the method is cooled to a temperature that is 40 to 40°C lower. 5. The method according to claim 1, wherein the molding in the secondary mold is performed such that the volumetric expansion rate is 30% or less.