JPS62238730A - Manufacture of thermally fixed oriented container - Google Patents

Abstract

PURPOSE:To obtain a biaxially oriented blow molded container of thermoplastic polyester to the whole of which thermal fixation has been applied stably without whitening the bottom and a shoulder part of the container, by a method wherein blow molding and thermal fixation are applied to a preform within a mold whose mold surface corresponding to a shell part and that corresponding to the bottom and shoulder part are heated respectively at a high temperature and low temperature, a molded product is cooled and shrunk by unloading the same, held within a secondary mold and molded under blowing-in of a fluid. CONSTITUTION:An inner cylindrical part 4 of a cavity mold is provided by applying heat insulation to the same and the inside of the same is provided with a heater 8. A mold surface 11 corresponding to a shell part is heated at a high temperature and, on the one hand, mold surfaces 12, 13 corresponding to a shoulder part and the bottom are heated at the temperature which is lower than that of the mold surface 11 corresponding to the shell part and does not become more than the whitening temperature. Biaxially oriented blow molding is applied to a preform in the mold, a formed molded product is held within the mold in a state that fluid pressure is applied to the inside and thermal fixation is applied to the same. The molded product is cooled by unloading the same by breaking the mold and shrinkage is allowed. The cooled and shrunk molded product is held within a secondary mold and molded into the final container form under blowing-in of a fluid.

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 (CPET) have excellent transparency and surface gloss, as well as the impact resistance and
It also has rigidity and gas barrier properties, and is used as a bottle filler for various liquids.

However, polyester containers have the disadvantage of poor heat resistance, and are not suitable for hot filling applications.
Many proposals have already been made to heat-set biaxially stretched blown containers after molding to avoid thermal deformation and volume shrinkage deformation.

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. There are known methods for carrying out heat setting at the same time as stretch blow molding in a blow mold, as shown in Japanese Patent Publication No. 59-6218. In addition, JP-A-57
Japanese Patent No. 53326 describes a method in which heat treatment is carried out simultaneously with stretch blow molding in a sinking mold, and blow molding is carried out in a secondary treatment mold without taking out the molded product and cooling it.

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

In addition, the method of heat setting in a blow mold at the same time as stretch blow molding has problems in taking out the molded product after heat setting, and as seen in Japanese Patent Publication No. 59-6216, 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 whiten 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 this invention is to provide a method that can be manufactured using the following methods.

(Means for Solving the Problems) The method of the present invention uses a bottomed preform made of thermoplastic polyester and having a mouth neck corresponding to the container mouth neck, when the mold surface corresponding to the body is heated to a high temperature. Stretch blow molding is carried out in biaxial directions in a mold in which the mold surface corresponding to the bottom and the mold surface corresponding to the shoulder are heated to a temperature at which the crystallization rate of the polyester is low. The molded product is held and heat-set, the heat-set molded product is taken out of the mold, the molded product is cooled and allowed to shrink, and then the molded product is placed in a secondary mold. It is characterized by being held and molded into the final container shape under fluid injection.

(Function) According to the present invention, by heating the body-corresponding mold surface of the blow mold to a high temperature, the cavities in which molecules are highly oriented in biaxial directions 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 achieve oriented crystallization within a range that does not cause whitening. It is possible to improve the degree of crystallization. Therefore, according to the present invention, a high degree of heat setting 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 stretching 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, 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. , to cool the molded product taken out at this time,
It functions to suppress irregular and unnecessary deformation of the molded product transferred to the secondary mold, and to bring the temperature of the molded product to a temperature suitable for molding in the secondary mold. 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 in the secondary mold for m-shaped products is shortened, resulting in high thermal efficiency and productivity as a whole. 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, or containing a small amount of other glycols such as hexahydroxylylene glycol as a glycol component; 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 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 mouth and neck corresponding to the final container. The latter method is advantageous for producing a bottomed preform having a gas barrier intermediate resin layer such as ethylene-vinyl alcohol copolymer, and involves cutting an extruded amorphous pipe.

A mouth and neck part is formed at one end by compression molding.

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 molds used for stretch blow molding and heat setting, these molds are roughly divided into a cavity mold, a core mold 2, and a base (bottom) mold. Consists of 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 la inside, which defines the shape of the container body and shoulder to be molded. The pace mold 3 defines the bottom shape of the container, and may be fixed integrally with the cavity mold 1, or may be movable in the axial direction of the cavity mold. It may be something that you can now get your hands on.

The cavity mold l 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. Thus,
It will be appreciated that the cavity mold inner tube 4 is insulated from both the outer tube 5 and the core mold 2.

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 in order to heat the inner surface of the cavity. 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 neck of the preform rotor held by the mold.

Since the cavity mold inner cylindrical part 4 is provided with heat insulation and a heater 8 is provided inside thereof, the body part corresponding mold surface 11 is heated to a high temperature, while the shoulder part corresponding surface treatment 2 is heated to a high temperature.
Due to the long heat transfer distance from the heater 8 and the connection with the forcedly cooled core mold 2, the temperature is lower than that of the body corresponding mold surface j1 and does not exceed the whitening temperature. heated. In addition, the bottom compatible surface 1
3 is maintained at a temperature within the same range as above by a heater 9.

The two-body stretch blow molding of the preform in the mold shown in FIG. 1 is carried out under conditions known per se, such as the stretching temperature,
Generally, the preform is preheated to a temperature of 90 to 130°C, particularly 100 to 120°C, and the preform is stretched in the axial direction with a stretching rod, and circumferentially [1111!] by blowing fluid. Stretched. The stretching ratio in the axial direction is 1.5 to 3.5 times, especially 2 to 3 times,
The stretching ratio in the circumferential direction is 2 to 5 times, especially 3 to 4 times, in the body.
It is better to increase it by 5 times.

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 is heated at a heat setting temperature below the melting point of the thermoplastic polyester, e.g.
℃, especially between 150 and 200 degrees Celsius, while the shoulder-compatible surface 12 and the bottom-compatible surface 13 have a lower degree of molecular orientation in the shoulder and bottom regions than in the torso. Therefore, it is preferable to maintain the temperature at a temperature lower than the temperature of the torso corresponding surface 11 and lower than the whitening temperature, but as high as possible. A temperature range of 140°C to 140°C, particularly 100°C to 130°C is preferable, and a temperature of 70°C to 140°C is preferable for the bottom-compatible surface 13.
℃, particularly preferably in the range of 80 to 120℃.

In the present invention, since the entire surface of the mold is heated,
Another advantage is that the time required for heat setting in the mold is relatively short, and although this time varies depending on the mold surface temperature, it is generally 1 to 30 seconds, particularly 3 to 15 seconds. It is enough.

The mold is opened, the heat-set molded product is taken out, and the molded product is cooled and allowed to shrink. This process removes the stress remaining in the molded product after stretching and heat setting, and stabilizes its shape and dimensions.
By cooling the molded product after heat setting in this process, excessive deformation of the molded product taken out from the mold is prevented, and
The molded article is quickly brought to a temperature suitable for molding within 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 cavity is 3 to 40°C lower than the temperature of the mold surface corresponding to the body, particularly 5 to 30°C lower. This cooling should 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. During this final blow molding, it is sufficient to perform molding or shape retention to maintain the final container shape, and it is best to keep the degree of stretching as low as possible in any part of the molded product. This molding is preferably carried out so that the volumetric expansion rate is 30% or less, especially 20% or less, based on the molded product after cooling and shrinking.In other words, if the volumetric expansion rate exceeds the above range, , thermal shrinkage and thermal deformation of the final container occur due to stretching strain during secondary molding. 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.

The mold inner surface temperature of the secondary mold is, of course, lower than the mold inner surface temperature of the -forming mold, and is generally 10 to 7
A temperature of 0°C is suitable.

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, a 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, has excellent thermal efficiency. The advantage is that it can be manufactured with high productivity.

(Example) Example 1 Polyethylene terephthalate with an intrinsic viscosity of 1.0 is injection molded to form a bottomed preform with a height of 162 mm, a body diameter of 26 mm, an average body thickness of 4+w+a, and a neck thickness of 1.5 IIm. Then, only the mouth part was heat-treated with hot air (240°C) to crystallize it.

This preform was heated to a stretching temperature of 95°C to 100°C, and the heated preform was heated to a cavity surface temperature of 180°C at the body, 110°C at the shoulder, and 100°C at the bottom. After molding the intermediate molded product by biaxial stretching blowing in a blow mold (-forming mold) having a 150 cc cavity, and holding it in the 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 for about 30 minutes.
℃ and shrink by about 20% until the cavity surface reaches 60℃.
The final shape of the container is blow molded in a secondary mold that is maintained at ℃ and has an internal volume smaller than the primary mold, with an internal volume of 1.0OOcc.
I got a container of. 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 The inner and outer layers were made of polyethylene terephthalate with an intrinsic viscosity of 1.0, the middle layer was made of ethylene-vinyl alcohol copolymer containing 70 mol% of vinyl alcohol, and the adhesive layer interposed between the inner and outer layers and the middle layer was made of copolyamide. Multi-layer co-injection molding,
Height 162mm, body diameter 28+s■, body average thickness 41
A bottomed preform with a neck wall thickness of 1.5 rats was molded, and only the mouth portion 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 placed in a primary mold whose cavity surface temperature is 180°C at the body, 110°C at the shoulder, and 100°C at the bottom. An intermediate molded product is formed by two-wheel stretch blowing, and after being held in the mold for 4 seconds to perform heat setting, the intermediate molded product is taken out from the blow mold and this intermediate molded product is The cavity surface is maintained at 60°C, and the container is blow-molded into the final shape in a secondary mold, which has a smaller internal volume than the primary mold. A container of 0OOcc was obtained. 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 l The preform used in Example 1 was stretched at a temperature of 95 to 10
The heated preform is heated to 0°C and biaxially stretched and blown using a heated fluid in a primary mold whose cavity surface temperature is approximately 120°C to form a container.
After heat setting by holding in the mold for 12 seconds,
The heating fluid in the mold was changed to a cooling fluid to obtain a container with an internal volume of 1.000 cc. 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. Further, even when this container was filled with a liquid at 85° C., there was almost no shrinkage or deformation, but when heat treated at 120° C., the container contracted significantly and deformed.

Comparative Example 2 The preform used in Example 1 was stretched at a temperature of 95 to 10
The heated preform is heated to 0°C and 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. When the intermediate molded product is transferred from the primary mold to the secondary mold without cooling as described in JP-A No. 57-53326, the intermediate molded product is The transfer from the primary mold to the secondary mold was not successful, and a container with the final shape of N14 could not be obtained.

[Brief explanation of drawings]

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. l...Cavity mold 2.Old...Core mold 3...Base mold 6,7...Insulation material 8.9...Heater

Claims (5)

[Claims] (1) A preform with a bottom made of thermoplastic polyester and having a neck part corresponding to the mouth neck part of the container is heated to a high temperature and the primary mold surface corresponding to the body part is heated to a high temperature, and the mold surface corresponding to the bottom part and the shoulder part are heated to a high temperature. Stretch blow molding is carried out in biaxial directions in a mold in which the corresponding mold surface is heated to a temperature at which the crystallization rate is low, and the molded product is held in the mold and heat set to perform blow heat setting. Removing the molded article from the mold, allowing the molded article to cool and shrink, and then retaining the molded article in a secondary mold and forming it into the final container shape under fluid injection. A method for producing a heat-set stretched container characterized by: (2) During stretch blow molding and heat setting, the temperature of the mold surface corresponding to the body is 160 to 230 °C, and the surface of the mold corresponding to the bottom is 70 °C.
Temperatures from 140°C to 70°C 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 method according to claim 1, wherein the body of the molded product is cooled to a temperature 3 to 40° C. lower than the temperature of the surface of the mold corresponding to the body. (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.