JPH06166094A - Manufacture of biaxially oriented blow vessel - Google Patents

Abstract

PURPOSE:To constitute the manufacturing method so that a vessel is molded so as to eliminate irregularity of shrinkage factor by controlling shrinkage at the time of heat treatment of the primary molded product. CONSTITUTION:A preform 1 is formed into the primary molded product 2 having a form of a vessel by an orientation blow molding and after the primary molded product 2 is shrinked by heat treatment, the same is blot-molded into the vessel 4. In the heat treatment, a mouth part of the primary molded product 2 is sealed up and shrinkage following heating of the primary molded product is performed while raising inner pressure of the primary molded product.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method which can be used for producing a biaxially stretched blow container having excellent heat resistance and the like.

[0002]

2. Description of the Related Art Generally, a synthetic resin thin-walled packaging container, which is called a biaxially stretched blow container, stretches an injection- or extrusion-molded preform in the mold in the axial direction, and at the same time blows the blown gas. It is manufactured by expanding laterally by pressure.

In such a molding method, since the preform is designed according to the size and shape of the container to be molded, the preform is necessarily designed to be thick. The problems with this thick preform are that it takes time to cool during injection molding and that it takes time to adjust the temperature of the preform before stretch-blowing, which makes it difficult to shorten the molding cycle time. That is.

Therefore, the biaxial stretch blow molding after preform temperature control is made into three steps of primary molding-heat treatment (heat shrinkage) -final molding, and the primary molded article is molded larger than the final molded article, and the primary molding is performed. A preform was designed for products, and a molding method was developed by which the wall thickness of the preform could be reduced.

[0005]

However, in this molding method, since there is no means for controlling the heat shrinkage of the primary molded product, there is a large variation in shrinkage, which causes uneven thickness during re-blow molding. However, there are problems such as unevenness in heat resistance, and further improvement is required for practical use.

When the material of the container is polyethylene terephthalate, acetaldehyde which is a decomposition product of polyethylene terephthalate is generated during molding.

Since this acetaldehyde is an organic substance having a peculiar fragrance, as a container for cola beverages, mineral water, edible oil, etc., the acetaldehyde is removed as much as possible so that the taste and aroma of the contents do not change. Is desired.

Therefore, in the past, during the molding of the preform, the screw rotation speed of the injection device was lowered or the injection speed was slowed so that the polyethylene terephthalate was not decomposed, so that acetaldehyde was generated due to the decomposition of the resin. I have suppressed it, but it is still not enough,
Depending on the contents, we are aware of the high cost of the container and use highly refined materials.

The present invention is intended to solve the problems in the above-mentioned biaxial stretching blow including such problems, and its purpose is to control shrinkage during heat treatment of a primary molded article, Another object of the present invention is to provide a new molding method capable of molding a container having a uniform shrinkage rate and reduced acetaldehyde by heat treatment.

[0010]

According to a first aspect of the present invention, a preform is formed by stretch blow molding into a primary molded product having a container shape, the primary molded product is contracted by heat treatment, and then blow molded into a container. In doing so, the heat treatment step is characterized in that the mouth of the primary molded product is sealed and the shrinkage accompanying the heating of the primary molded product is performed while increasing the internal pressure of the primary molded product.

According to the second aspect of the present invention, the stretch blow of the preform using polyethylene terephthalate is 1.2 to 3.0 times the volume of the container to be the final product.
It is characterized in that the primary molded article is shrunk by heat treatment at a temperature of 280 ° C. or lower for 20 to 120 seconds to reduce the generation of acetaldehyde from polyethylene terephthalate.

[0012]

According to the first aspect of the invention, the increase in the pressure of the gas in the primary molded product limits the shrinkage of the primary molded product due to heating, and the shrinkage caused by the shrinkage is evenly distributed, resulting in a uniform wall thickness distribution even during reblowing. Heat resistance is improved.

According to the second aspect of the invention, the generation of acetaldehyde can be reduced.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The drawings show the molding steps in sequence, 1 is a bottomed preform by injection molding, 2 is a primary molded product, 3 is a heat-treated molded product, and 4 is a final molded product.

The length and wall thickness of the preform 1 are as follows.
It is designed for the primary molded product 2. Since this primary molded product 2 is blow molded about 1.5 times larger than the container 4, the preform 1 can be made longer and the wall thickness is also larger than in the case of normal molding in view of the blow ratio. Can be thinned.

The injection-molded preform 1 is adjusted to a temperature suitable for stretch blow molding as usual, and then housed in a cavity of a primary blow mold 5 to be stretch blow molded into a primary molded product 2.

After molding, the primary molded product 2 is sent to a heat treatment device 6 such as an oven. At this time, since the cap member 7 shown in FIG. 2 is airtightly covered on the mouth portion of the primary molded product 2, the internal pressure thereof increases as the primary molded product 3 contracts.

That is, the cap member 7 has a high-pressure blow air passage 8 and a relief valve 9 for adjusting the internal pressure.
And are connected. Then, the primary molded product 3 whose mouth is sealed by the cap member 7 is heated at a predetermined temperature. The heated primary molded product 3 contracts, and the entire molded product shrinks, leaving the mouth.

This reduction is performed until it becomes smaller than the cavity of the product blow mold 10 for molding the container 4 against the internal pressure. At this time, the wall of the molded product 3 is strained due to the increase in the internal pressure of the primary molded product 3 due to the contraction. For this reason, partial shrinkage is unlikely to occur, and as a result of heat shrinkage in the molded product 3 in balance with the internal pressure, shrinkage unevenness is extremely reduced.

The molded product 3 which has been heat-shrinked as described above is
Directly transferred to the product blow mold 10 set in the range of room temperature to 120 ° C., and blow molded into the container 4.

Further, the preform 1 is stretch blown to 1.2 to 3.0 times the volume ratio of the container 4 to form a primary molded product 2, which is 20 to 12 in a temperature range of 100 to 280 ° C.
When the container 4 is blow-molded after being kept at 0 ° C., preferably at 130 ° C. or higher for 30 seconds or longer, the generation of acetaldehyde is extremely reduced.

[0022]

As described above, according to the present invention, the preform is molded into a primary molded product having a higher draw ratio than that of the container as the final product, and the heat treatment of the primary molded product is performed while applying an internal pressure. At that time, a high degree of crystallinity is already obtained, and since shrinkage and shrinkage due to heating are performed evenly, the thickness distribution is adjusted during heat treatment, so the thickness of the container that will be the final molded product is uniform, and Since the container is molded with the residual stress removed by the heat treatment of, the residual stress is smaller than in the conventional method,
Not only the change over time due to residual stress but also the shrinkage rate of the container during heating and filling does not vary significantly. Therefore, a container having excellent impact resistance, reduced pressure strength, heat resistance, etc. can be obtained.

Further, since the generation of acetaldehyde is reduced by the heat treatment and the amount thereof is extremely small, it is suitable as a container for cola drink, mineral water, edible oil, etc., from injection molding of preforms to blow molding of containers. The molding cycle is also shortened as compared with the case where the heat treatment is performed by the blow mold, and the molding efficiency is further improved.

[Brief description of drawings]

FIG. 1 is a schematic process explanatory view of a method for manufacturing a biaxially stretched blow container according to the present invention.

FIG. 2 is a cross-sectional view of a cap member.

[Explanation of symbols]

 1 Preform 2 Primary molded product 3 Heat treated molded product 4 Container

Claims (2)

[Claims] 1. A preformed product is formed by stretch blow molding into a primary molded product having the form of a container, and the primary molded product is contracted by heat treatment and then blow molded into a container. The method for producing a biaxially stretched blow container, characterized in that the mouth of the primary molded product is sealed and the shrinkage of the primary molded product due to heating is performed while increasing the internal pressure of the primary molded product. 2. The stretch blow of the preform with polyethylene terephthalate is 1.2 to 3.0 times the volume ratio of the container as the final product, and the shrinkage due to the heat treatment of the primary molded product is performed at a temperature of 280 ° C. or less. The method for producing a biaxially stretched blow container according to claim 1, wherein generation of acetaldehyde from polyethylene terephthalate is reduced by maintaining it for 20 to 120 seconds.