JPS6230019A - Biaxially oriented blow molding process - Google Patents

Abstract

PURPOSE:To mold a bottle having an extremely high heat resistance against heat contraction by producing primary intermediate molding product out of the preform formed as desired by means of the biaxially oriented blow molding under the specified temperature, heat treating under specified temperature into the secondary intermediate molding product by means of heat transformation, and blow molding the said secondary intermediate molding product into a bottle. CONSTITUTION:The process of molding the preform 1 into the primary molding product 4 by means of the biaxially oriented blow molding is carried out under a temperature heated up to 90 deg.C-130 deg.C in which elongation effect including temperature value 120 deg.C just before heat crystalization of PET can be achieved. The process of molding the secondary intermediate molding product 5 into the bottle 6 is carried out by blow molding the secondary intermediate molding product 5, heated up to 170 deg.C-255 deg.C and heat contracted into the bottle 6, with the secondary blow mold heated up to 120 deg.C-150 deg.C, higher by several degrees than the maximum atmospheric temperature in which the bottle 6 to be molded is actually used. The bottle 6, heat set with the secondary blow mold heated up to high temperature, is free from inner residual stress and of high heat resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for biaxial stretch blow molding of polyethylene terephthalate resin.
The present invention relates to a method for forming a biaxially stretched blow-molded bottle made of polyethylene terephthalate resin that has high heat shrinkage resistance while maintaining high transparency.

[Conventional technology]

Polyethylene terephthalate resin (hereinafter simply referred to as PET) is used in large quantities in various fields as a biaxially stretched blow-molded bottle due to its stable physical properties, non-polluting properties, excellent transparency, and high mechanical strength. It is widely used, and is particularly useful as food bottles.

In this way, PET bottles effectively exhibit a number of excellent properties, but PET bottles without heat treatment
The biaxially stretched blow molded bottle made by ET is weak against heat.
It deforms significantly at high temperatures of 70°C or higher.

For this reason, it cannot be used as a storage container for retort foods that are heat-treated by leaving them for 30 minutes at 120°C, or for foods that are geothermally treated. Currently, there is a strong desire for this.

Conventionally, methods for providing heat resistance against shrinkage of PET bottles include (1) raising the temperature of the blow mold during blow molding to a temperature higher than the target heat-resistant temperature in order to raise the size of the PET9 bottle; (2) A method of heating and blow molding, (2) making an intermediate molded product which is a primary blow molding product, and reheating it (1)
There is a method to make a finished product by blow molding again after cooling the molded product (about 10°C).

[Problem that the invention seeks to solve]

Among these methods, method (1) deteriorates as the mold temperature rises, and its heat resistance against heat shrinkage is limited to about 85℃ filling. It has not been possible to use it at all for foods that are heat-treated.

In addition, method (2) of the method for imparting heat resistance to bottle shrinkage to the PETl bottle described above was out of the question since it could not provide better heat resistance to heat shrinkage than the method shown in method (1).

The present invention was devised to solve the problems and dissatisfied points in the conventional examples described above, and to satisfy the conventional demands. By molding into an intermediate molded product, heat treating this primary intermediate molded product to cause heat shrinkage and deformation to form a secondary intermediate molded product, and blow molding this secondary intermediate molded product into a finished product, a bottle. The purpose of this invention is to obtain a bottle that exhibits extremely high heat shrinkage resistance.

[Means and operations for solving the problems] The present invention will be explained below with reference to the drawings showing one embodiment of the present invention.

The present invention is a method for axial stretch blow molding of a PET bottle, in which a main body portion 2 to be biaxially stretch blow molded of a preform 1 previously formed into a desired shape is heated to a temperature just before PET thermal crystallization. The primary intermediate molded product 4 is heated to 90°C to 130°C, which is the temperature range that allows blow molding to produce a stretching effect, including 120°C, using a primary blow mold, and this 2 The primary intermediate molded product 4 subjected to axial stretch blow molding is heated to a temperature of 170° C. to 255° C., which is higher than the mold temperature of the primary blow mold, and the mold temperature of the secondary blow mold is adjusted to a temperature higher than that of the molded bottle. 120°C to 150°C, which is several degrees higher than the maximum temperature of the atmosphere in which the body 6 is used.
The bottle 6 is blow-molded while heated to .degree.

This biaxial stretch blow molding method according to the present invention.

To explain more specifically, the blow molding method according to the present invention includes a first step of molding a preform 1 into a desired shape using injection molding or the like, and a first step of forming the preform 1 into a desired shape without stretching or deforming it. A second step is to thermally crystallize the final molded product, that is, the mouth portion forming a part of the bottle 6, in its shape at the time of molding so as not to be thermally deformed, and a blow molding operation which is the gist of the method of the present invention. It consists of a third step.

The first step, that is, the molding operation of the preform 1, is often achieved by ordinary injection molding, but the shape of the preform J-1 to be molded is not specified; As shown in the solid line in the figure, it may have a JII+ shape, or it may have an elongated cylindrical shape with a bottom.

This preform 1 is composed of a mouth part 3 which is a part to be assembled into a mold, and a main body part 2 which is a body part including a bottom part of a bottle 6 to be stretch-molded.

According to the results of experiments, the appropriate amount of stretching for the main body part 2 to be formed into the primary intermediate molded product 4 without whitening despite the high mold temperature of the primary blow mold is If the stretching area magnification is 5 to 13 times or less, the primary intermediate molded product 4 will be heated and the secondary intermediate molded product 5 will become white due to heating during forced heat shrinkage molding. On the other hand, if the stretching area magnification is 13 or more, voids will occur and stretch molding can be performed, but the film will become cloudy and the formability will deteriorate.

The main body portion 2 of the preform 1 is stretched at a stretching area magnification of about 5 to 13 times, as described above, to prevent thermal crystallization, that is, whitening, when the primary intermediate molded product 4 is heated, thereby making the primary intermediate molded product 4 oriented. Crystal with a density of approximately], 350 1:g
/cnOu.

In addition, the peripheral end portion and the central portion of the main body portion 2, which are the connecting portions with the mouth portion 3, are more difficult to receive stretching action than other portions of the main body portion 2, and are easily whitened. It is preferable that the portion is relatively thinner than the other portions so that it can be easily stretched.

In this way, the preform 1 molded into the desired shape is subjected to whitening treatment of the mouth part 3 by a thermal crystallization operation, prior to the biaxial stretching blow molding operation to the primary intermediate molded product 4. I do.

The whitening of the mouth part 3 can be achieved by slowly cooling the mouth part 3 from a sufficiently heated state.

However, when performing the whitening treatment on the single portion 3, care must be taken to ensure that the mouth portion 3 is not deformed into an undesirable shape due to the whitening treatment.

In particular, the deterioration of the roundness of the mouth portion 3 due to deformation is due to
Since the function of the bottle 6, which is a molded product, as a container will be significantly reduced, it is necessary to prevent it extremely strictly.

Once the mouth 3 of the preform 1 has been whitened in this manner, the preform 1 is molded into a bottle 6 in the third step of blow molding.
This blow molding process includes a step of biaxial stretch blow molding the preform 1 into a primary intermediate molded product 4, and a step of heating and heat-shrinking the primary intermediate molded product 4 to form a secondary intermediate molded product 5. , and finally blow-molding the secondary intermediate molded product 5 into a bottle 6.

The primary biaxial stretch blow molding step is to biaxially stretch blow mold the preform 1 into the primary intermediate molded product 4.

This preform 1, more precisely, the main body part 2 of the preform 1, can be blow-molded within a temperature range that can produce a stretching effect, including a temperature value of 120°C, which is just before the thermal crystallization of the molded synthetic resin + PET, which is the A material. This is achieved by heating the temperature to 90°C to 130°C.

In this primary biaxial stretch blow molding step. As described above, as a specific means for performing stretch molding without thermal crystallization due to heating during secondary blow molding, the body portion including the bottom portion of the primary intermediate molded product 4, that is, the main body portion 2 Needless to say, the stretch-blow-molded part has oriented crystals, and its density is 1.350.
(g/cffl) or more, preform 1
The stretching ratio from the to the primary intermediate molded product 4 is 5 to 2 area ratio.
It is best to set it to 13 times.

Next, the step of heating the primary intermediate molded product 4 to absorb heat and forming it into the secondary intermediate molded product 5 is for forcibly eliminating internal residual stress generated within the biaxially stretched blow molded product. , each stretch-molded part of the primary intermediate molded product 4 is freed according to the internal residual stress generated in each stretch-molded part of the primary intermediate molded product 4 biaxially stretch-blow-molded using the primary blow mold. In this way, the internal residual stress described above is forcibly eliminated.

Deformation according to the internal residual stress occurring in each stretch-molded part of this primary intermediate molded product 4 naturally results in shrinkage deformation, but the secondary intermediate molded product 5 formed by this shrinkage deformation Stretch molding part.

That is, as shown in FIG. 2, the main body part 2, which is the body part including the bottom part, has a size that is approximately the same or slightly smaller than the body part including the bottom part, which is the stretch-molded part of the medium 6, which is the object to be molded. The magnification of the stretch molding from the preform 1 to the primary intermediate molded product 4 and the dimensions of the primary intermediate molded product 4 are set so that

The step of blow molding the secondary intermediate molded product 5 onto the culture medium 6 is the step described above, and the second intermediate molded product 5 is heated to a temperature of 170° C. to 255° C., which is higher than the mold temperature of the primary blow mold, and is then heat-shrinked. Next, the intermediate molded product 5 is heated to a temperature several degrees higher than the maximum temperature of the atmosphere in which the culture medium 6, which is the molding object, is used.
The medium 6 is blow-molded using a secondary blow mold heated to 20°C to 150°C.

In the step of blow molding the medium 6 of the secondary intermediate molded product 5, as described above, the main body portion 2, which is the body portion including the bottom portion which is the blow molded portion of the secondary intermediate molded product 5, and the medium 6 The length of the secondary intermediate molded product 5 is approximately equal to or only slightly smaller than the body including the corresponding bottom, so the amount of stretching during stretching from the secondary intermediate molded product 5 to the culture medium 6 is extremely small. By stretching the molded article 5 into the culture medium 6, the formed culture medium 6 is in the stretch-formed portion.

Almost no internal residual stress is generated due to stretch forming.

In addition, since the culture medium 6 is blow-molded by a secondary blow mold whose temperature is higher than the maximum temperature of the atmosphere in which it is used, it is heat set by this secondary blow mold, resulting in internal residual stress. Therefore, it is possible to obtain a culture medium 6 that is free from heat shrinkage and has high heat resistance.

In this way, the biaxial stretch blow molding method according to the present invention is
Although it is possible to mold the culture medium 6 which has extremely excellent heat shrinkage resistance, it is possible to more accurately control the degree of shrinkage of the secondary intermediate molded product 5 that is heat-shrink molded from the primary intermediate molded product 4. In order to obtain a medium 6 with less internal residual stress, high dimensional accuracy, and appropriate wall thickness distribution, the mold temperature of the primary blow mold can be controlled to control the amount of heat shrinkage of the primary intermediate molded product 4 to be molded. It is preferable to set the temperature between 110°C and 230°C.

The mold temperature of this primary blow mold should be set according to the stretching area magnification of the primary intermediate molded product 4 to be stretch-molded, and it is preferable to set the temperature value higher as the stretching area magnification increases.

〔Example〕

One specific example of the molding method according to the present invention will be described below.

The heating temperature of the preform 1 is 115°C, the mold temperature of the primary blow mold is 180°C, the blowing pressure is 25 kg/cm, and the blowing time is 1.4 seconds to form the primary intermediate molded product 4 from the preform 1.
Primary biaxial stretch blow molding was carried out to 9. Next, the heating temperature for the primary intermediate molded product 4 was 225°C. 1. The mold temperature of the secondary blow mold was 140°C, and the blow pressure was 30 kg/an! Then, in a blowing time of 4.4 seconds, the -ash intermediate molded product 4 was heat-shrinked and deformed into a secondary intermediate molded product 5, and at the same time, this secondary intermediate molded product 5 was molded into a tank body 6.

The tank body 6 formed in this way is placed in the storage tank at 120
The tank body 6 was heated by immersing it in glycerin heated to ℃ for 30 minutes without a cap, and the tank body 6 was taken out from the glycerin and cooled with water to determine the change from before heating. The volume change rate of body 6 is 0.33%
From this, it has become clear that it is possible to mold a PET bottle that is sufficiently resistant to heat shrinkage.

When the above-mentioned tank is filled with the content liquid at 80°C and capped, and subjected to retort sterilization treatment, there is no change at the retort sterilization temperature of 120°C and F value of 6 to 10, and the capacity change rate is 0.5%. It was below.

In addition, the PET material for forming the tank body 6 does not contain any additives, exhibits extremely excellent transparency, and has a density of 1.3853 to 1.3.
918 (g/cn?), and the crystallinity of this type of tank without conventional heat treatment is about 16%, and the crystallinity of the tank with conventional heat setting is about 33%. On the other hand, the crystallinity of the tank body 6 molded according to the present invention described above was about 49%.

In this way, it was possible to obtain a sufficiently high density and high moldability, and therefore mechanical strength such as vacuum strength was also significantly improved.

Furthermore, when we measured the internal residual stress inside the bottle 6, we found that internal residual stress began to appear for the first time when the heating salinity exceeded 110°C, and its value gradually increased as the heating temperature increased. When heated to 150°C, the maximum value of the internal residual stress developed was 0.22 [g/v
It was an extremely small value.

When the tank body 6 in each of the above-mentioned Examples was observed, a slight cloudiness was observed near the center of the bottom of the bottle 6, but this was more pronounced in the center of the bottom of the bottle 6 than in other parts. This seems to be because the stretching cannot always be applied sufficiently.

〔Effect of the invention〕

As is clear from the above description, the method for forming a PET bottle according to the present invention can form a tank that has no internal residual stress and has extremely high heat shrinkage resistance, and also has sufficient density in each part of the bottle. Since it can be made large, it can be molded into a tank with high mechanical strength such as vacuum strength, and furthermore, it can be carried out by appropriately combining conventional heating means and blow molding means. It is easy to implement and exhibits many excellent effects such as being able to maintain high transparency.

[Brief explanation of drawings]

The drawings are for explaining the method of the present invention, and FIG. 1 is a longitudinal sectional view showing the primary blow molding operation state, and FIG. 2 is a longitudinal sectional view showing the secondary blow molding operation state. Explanation of symbols 1: Preform, 2: Main body, 3: Mouth. 4: Primary intermediate molded product, 5: Secondary intermediate molded product. 6; Tank body.

Claims (8)

[Claims] (1) A biaxial stretch blow molding method for polyethylene terephthalate resin bottles, in which a preform previously formed into a desired shape is blow molded to produce a stretching effect at a temperature of 120°C, which is on the verge of thermal crystallization. The primary intermediate molded product is subjected to primary biaxial stretch blow molding using a primary blow mold while heated to a possible temperature range of 90°C to 130°C, and the biaxially stretch blow molded primary intermediate molded product is It is heated to a temperature of 170°C to 255°C, which is higher than the mold temperature of the mold, and the mold temperature of the secondary blow mold is set to a temperature several degrees higher than the maximum temperature of the atmosphere in which the molded bottle is used.
A biaxial stretch blow molding method in which a bottle is blow molded while being heated to 0°C to 150°C. (2) A biaxial stretch blow molding method for polyethylene terephthalate resin bottles, in which a preform previously formed into a desired shape is blow molded to produce a stretching effect at a temperature of 120°C, which is on the verge of thermal crystallization. While heated to a possible temperature range of 90°C to 130°C, a primary blow mold with a stretching area magnification of 5 to 13 times the stretching area of the stretch-molded part of the preform is used to form a primary intermediate molded product. Axial stretch blow molding is performed, and the biaxial stretch blow molded primary intermediate molded product is heated to a temperature of 170°C to 255°C, which is higher than the mold temperature of the primary blow mold, and the mold of the secondary blow mold is heated. A biaxial stretch blow molding method in which the bottle is heated to 120°C to 150°C, which is several degrees higher than the maximum temperature of the atmosphere in which the bottle is used. (3) A biaxial stretch blow molding method for a polyethylene terephthalate resin bottle, in which a preform previously formed into a desired shape is blow molded to produce a stretching effect at a temperature of 120°C, which is on the verge of thermal crystallization. The primary intermediate molded product is subjected to primary biaxial stretch blow molding using a primary blow mold while heated to a possible temperature range of 90°C to 130°C, and the biaxially stretch blow molded primary intermediate molded product is It is heated to a temperature of 170°C to 255°C, which is higher than the mold temperature of the mold, and the mold temperature of the secondary blow mold is set to a temperature several degrees higher than the maximum temperature of the atmosphere in which the molded bottle is used.
Blow molded into a bottle while heated to 0°C to 150°C,
Furthermore, the dimensions of each stretch-molded part of the primary intermediate molded product are calculated based on the dimensions of the corresponding parts of the bottle when the primary intermediate molded product is reheated to 170°C to 255°C and shrinks into a secondary intermediate molded product. A biaxial stretch blow molding method that is set to a value that is equal to or slightly smaller than the dimensions. (4) A biaxial stretch blow molding method for polyethylene terephthalate resin bottles, in which a preform previously formed into a desired shape is blow molded to produce a stretching effect at a temperature of 120°C, which is on the verge of thermal crystallization. While heated to a possible temperature range of 90°C to 130°C, a primary blow mold with a stretching area magnification of 5 to 13 times the stretching area of the stretch-molded part of the preform is used to form a primary intermediate molded product. Axial stretch blow molding is performed, and the biaxial stretch blow molded primary intermediate molded product is heated to a temperature of 170°C to 255°C, which is higher than the mold temperature of the primary blow mold, and the mold of the secondary blow mold is heated. The bottle is blow-molded at a temperature of 120°C to 150°C, which is several degrees higher than the maximum temperature of the atmosphere in which the molded bottle is used, and each stretch-molded part of the primary intermediate molded product is The dimensions of the primary intermediate molded product are 17
A biaxial stretch blow molding method in which the size is set to be equal to or slightly smaller than the dimensions of the corresponding parts of the bottle when it is reheated to 0°C to 255°C and shrunk into a secondary intermediate molded product. (5) A biaxial stretch blow molding method for polyethylene terephthalate resin bottles, in which a preform formed in advance into a desired shape is blow molded to produce a stretching effect including a temperature value of 120°C, which is on the verge of thermal crystallization. In addition to heating to a possible temperature range of 90°C to 130°C, the mold temperature of the primary blow mold is set to 110°C to 230°C so that stretch molding can be performed without thermal crystallization due to heating during secondary blow molding. The primary intermediate molded product is subjected to primary biaxial stretch blow molding in a state heated to
The bottle is heated to 5℃ and the mold temperature of the secondary blow mold is heated to 120℃ to 150℃, which is several degrees higher than the maximum temperature of the atmosphere in which the molded bottle will be used. Biaxial stretch blow molding method. (6) A biaxial stretch blow molding method for a polyethylene terephthalate resin bottle, in which a preform formed in advance into a desired shape is blow molded to produce a stretching effect including a temperature value of 120°C on the verge of thermal crystallization. The mold temperature of the primary blow mold is heated to a possible temperature range of 90°C to 130°C, and the stretching area magnification of the stretch-molded portion of the preform is set to 5 to 13 times. The primary intermediate molded product is subjected to primary biaxial stretch blow molding in a state heated to 110°C to 230°C so that stretch molding can be performed without thermal crystallization due to heating, and the primary intermediate molded product subjected to the biaxial stretch blow molding is The product is heated to a temperature of 170°C to 255°C, which is higher than the mold temperature of the primary blow mold, and the mold temperature of the secondary blow mold is several degrees higher than the maximum temperature of the atmosphere in which the molded bottle is used. A biaxial stretch blow molding method in which a bottle is blow molded while being heated to a temperature of 120°C to 150°C. (7) A biaxial stretch blow molding method for polyethylene terephthalate resin bottles, in which a preform previously formed into a desired shape is blow molded to produce a stretching effect including a temperature value of 120°C, which is on the verge of thermal crystallization. In addition to heating to a possible temperature range of 90°C to 130°C, the mold temperature of the primary blow mold is set to 110°C to 230°C so that stretch molding can be performed without thermal crystallization due to heating during secondary blow molding. The primary intermediate molded product is subjected to primary biaxial stretch blow molding in a state heated to
The bottle is heated to 5°C and the mold temperature of the secondary blow mold is heated to 120°C to 150°C, which is several degrees higher than the maximum temperature of the atmosphere in which the molded bottle is used, and blow molded into the bottle. Furthermore, the dimensions of each stretch-molded part of the primary intermediate molded product are determined to be the same as those of the bottle when the primary intermediate molded product is reheated to 170°C to 255°C and shrunk into a secondary intermediate molded product. A biaxial stretch blow molding method in which values are set to be equal to or slightly smaller than the dimensions of each part. (8) A biaxial stretch blow molding method for polyethylene terephthalate resin bottles, in which a preform previously formed into a desired shape is blow molded to produce a stretching effect including a temperature value of 120°C, which is on the verge of thermal crystallization. The mold temperature of the primary blow mold is heated to a possible temperature range of 90°C to 130°C, and the stretching area magnification of the stretch-molded portion of the preform is set to 5 to 13 times. After performing primary biaxial stretch blow molding on the primary intermediate molded product in a state heated to 110°C to 230°C so that stretch molding can be performed without thermal crystallization due to heating, the biaxially stretch blow molded primary intermediate The molded product is heated to a temperature of 170°C to 255°C, which is higher than the mold temperature of the primary blow mold, and the mold temperature of the secondary blow mold is set several degrees higher than the maximum temperature of the atmosphere in which the molded bottle is used. Blow molding is performed into a bottle while heated to a high temperature of 120°C to 150°C, and the dimensions of each stretch-molded part of the primary intermediate molded product are re-heated to 170°C to 255°C. A biaxial stretch blow molding method in which the size is set to be equal to or slightly smaller than the dimensions of the corresponding parts of the bottle when it is heated and shrunk into a secondary intermediate molded product.