JPH0747591A - Heat-resistant and pressure-resistant self-supporting container - Google Patents

Abstract

PURPOSE:To manufacture a heat-resistant and pressure-resistant container of a saturated polyester self-supporting container which is biaxially stretching blow molded and of superior resistance to impact and resistance to chemicals. CONSTITUTION:A saturated polyester container with self-supporting bottom structure is biaxially stretching blow molded, and a low stretched areas formed in a central section 3 and/or a central section periphery 4 of the container bottom 2 of the above-said heat-resistant and pressure-resistant self-supporting container 1 and so semicrystallized as to obtain the density of 1.337g/cm<3>-1.360g/ cm<3>.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially stretch blow-molded saturated polyester self-standing container suitable for filling carbonated drinks, soft drinks, etc., and more particularly,
The present invention relates to a self-standing container that has improved heat resistance and pressure resistance during heat sterilization of contents and has excellent impact resistance.

[0002]

2. Description of the Related Art Conventionally, as a heat-resistant and pressure-resistant container, in order to enhance the pressure resistance of the container body, the bottom portion is bulged and molded into a hemispherical shell shape, and a base cup molded in a bottomed cylindrical shape is attached to this. The mainstream container is a container with an independent function. However, the use of the base cup requires that the base cup be separately molded and mounted and fixed, the weight of the container becomes large and the shape also becomes large, and hot water is sufficiently supplied to the bottom of the container during the heat sterilization process. There were various problems such that the heat sterilization of the contents could not be smoothly carried out because it did not reach, and that at this time, water was accumulated in the base cup and it was difficult to drain it quickly.

Further, it is desired to effectively reuse a used empty container from the viewpoint of resource saving and environmental problems.
In a container equipped with a base cup, the container body and base are usually used.
Since the materials of the scup and the adhesive are different, they must be separated when they are reused, and there is a problem that the process cost becomes high.

Due to these problems, a heat-resistant and pressure-resistant container that does not require a base cup is desired. Several proposals have been made for a pressure-resistant container that does not require a base cup, and generally, a plurality of leg pieces are radially bulged around the center of the bottom and valleys are formed between these leg pieces. It has either a line wall structure or a champagne type structure. These are, for example, JP-B-48-570.
No. 8, No. 59-40693, No. 61-9170, No. 63-202424, and No. 3-43342.
It is described in Japanese Patent Publication No.

[0005]

However, although the container described in each of these items can obtain satisfactory performance as a pressure resistant container, when used as a heat resistant and pressure resistant container for performing a heat sterilization step. Can't get enough performance. That is, the container described in each of the above items has a bottom center part and a low stretch region existing around the center part, and the temperature of the contents is 50 ° C. during heat sterilization.
When the temperature rises to about 70 ° C., the internal pressure increases, and the container material itself also easily undergoes creep deformation, so that the center part of the bottom part protrudes, and the container loses its self-sustaining stability.

As a method for solving this problem, for example,
It is conceivable to use the container described in JP-A-5-85535. Since this container is a container in which the center of the bottom is crystallized and the periphery of the center is sufficiently stretched, it is considered to have sufficient pressure resistance against an increase in internal pressure during heat sterilization. However, when a part of the bottom is crystallized with high density like this container, the crystallized part becomes brittle and the impact resistance when a drop impact is given to the container is extremely poor, and it loses practicality. The problem arises.

The present invention has solved these problems, and (A) the central portion of the bottom of the container and / or (B).
The low stretching region existing around the center has a density of 1.337 g / c.
By semi-crystallizing so that m ^{3 to} 1.360 g / cm ³ ,
Provided is a heat-resistant and pressure-resistant self-supporting container which does not lose its self-sustaining stability due to creep deformation of the bottom during heat sterilization of the container and which is also excellent in impact resistance and chemical resistance.

[0008]

That is, the present invention relates to a biaxially stretched blow molded saturated polyester container having a self-supporting bottom structure, which comprises (A) a center part of the container bottom and / or (B) A heat-resistant and pressure-resistant freestanding container characterized by semi-crystallizing a low-stretch region existing around the central part so that the density becomes 1.337 g / cm ^{3 to} 1.360 g / cm ^3. To do.

As the saturated polyester resin used in the present invention, polyethylene terephthalate resin is suitable from the viewpoint of strength, transparency and gas barrier property.

The container bottom structure in the present invention includes a structure in which a plurality of leg pieces are radially bulged around the center of the bottom and a champagne type structure.

In the present invention, the density of the (A) center of the bottom of the container and / or (B) the low-stretched region around the center is set to 1.337 g / cm ^{3 to} 1.360 g / cm ^3. The semi-crystallized region is preferably semi-crystallized, but it is preferable that the semi-crystallized region occupies 50% or more of each of the respective parts. Further, in the valley line portion, the low stretch region adjacent to the periphery of the central portion may be partially semi-crystallized. The low stretch of the present invention means that the stretch ratio is less than 1.5 times. Biaxial stretching means a stretching ratio of 1.5 times or more, preferably 2 to 6 times.

In the present invention, (A) the bottom portion of the container and / or (B) the low-stretching region existing around the center portion is semi-crystallized by biaxially stretching a reheated preform. When blow molding, the bottom is 100 ℃
Or heat setting at ~ 150 ° C for 3 to 15 seconds, or
There is a method of heating the bottom of the container after the biaxial stretch blow molding with hot air or an infrared heater. These two methods make it easier to control the semi-crystalline state compared to the method in which the preform bottom is semi-crystallized in advance and then the biaxially stretch blow molding is performed. It can be crystallized.

The density of the semi-transparent semi-crystallized low-stretched polyethylene terephthalate resin at the bottom of the container is 1.
337 g / cm ^{3 to} 1.360 g / cm ³ , preferably 1.340 g / cm ^{3 to} 1.35
A range of 0 g / cm ³ is good.

When the density of the low-stretching region is 1.337 g / cm ³ or less, the bottom of the container easily undergoes creep deformation during heat sterilization, and the container loses its self-sustaining stability. Also, 1.360g / c
When it is m ³ or more, the impact resistance is lowered, and the portion is easily broken when a drop impact is given to the container.

By semi-crystallizing the low-stretched portion, the chemical resistance to the lubricant on the conveyor line of the filling factory can be improved, and the occurrence of stress cracks can be suppressed.

[0016]

EXAMPLES The present invention will be described in more detail below. A preform obtained by injection molding of polyethylene terephthalate resin is reheated and then placed in a blow mold, stretched in the axial direction by a stretch rod while being stretched in the circumferential direction by air blow, and biaxial stretch blow molding. I went.
At this time, while the bottom of the mold was heated to 120 ° C., heat fixing was performed for 5 seconds, and then air at room temperature was circulated in the blow mold to cool the molded body, and then the molded body was taken out to obtain a volume of 1.
A 5-liter container 1 was obtained (Fig. 1). As shown in FIG. 2, in the bottom portion 2 of the container 1, five leg pieces 5 are radially bulged around the center portion at equal intervals, and valley line portions 6 are formed between the leg pieces 5. It has a self-standing structure, and the low-stretched regions existing in the central portion 3, the central peripheral portion 4 and the valley portion 6 are semi-crystallized. This container 1 was filled with 2.5 gas volume of carbonated water up to the permeation line of 43 mm at 5 ° C., capped, followed by a hot water shower at 70 ° C. for 30 minutes, and then naturally cooled to room temperature. However, the bottom of the container never lost its self-sustaining stability. Next, as a result of dropping the filled container from a height of 1.5 meters in an upright state, there was no breakage in the bottom of the container. The density of the semi-crystallized portion at the bottom of the container was measured by the density gradient tube method and found to be 1.340 g / cm ^{3 to} 1.347 g / cm ³ .

[0017]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, it is possible to provide a heat-resistant and pressure-resistant self-supporting container which prevents bottom projection during heat sterilization and has excellent impact resistance and chemical resistance. Further, since the container according to the present invention does not require a base cup, hot water at the time of heat sterilization reaches the bottom of the container sufficiently, and heat sterilization of the contents can be smoothly performed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a self-supporting container of the present invention.

FIG. 2 is a bottom view of the self-supporting container of the present invention.

FIG. 3 is a cross-sectional view of the bottom of the self-supporting container of the present invention.

[Explanation of symbols]

 1. Freestanding container 2. Bottom 3. Central part 4. Around the center 5. Leg piece 6. Valley line

Claims (1)

[Claims] 1. A biaxially stretched blow molded saturated polyester container having a self-supporting bottom structure comprising:
The density of the low-stretched region (A) in the center of the bottom of the container and / or (B) around the center is 1.337 g / cm ³ to 1.
A heat-resistant and pressure-resistant freestanding container characterized by being semi-crystallized to give 360 g / cm ³ .