JPH09314650A - Biaxially stretching blow molding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a bottle, which shows extremely high heat resistance against heat shrinkage by a method wherein a secondary intermediate molded article, which is obtained by heat-shrinking a biaxially stretching blow-molded primary intermediate molded article at a higher temperature, is secondarily blow-molded at a temperature, which is higher than a maximum usable temperature by several degrees. SOLUTION: Primarily biaxially stretching blow-molding is applied to a primarily intermediate molded article 4 with a primarily blowing mold under the state that a main body part, which is obtained by biaxially stretching blow-molding a perform formed in advance in desired form, is heated up to the blow-moldable temperature range of 90-130 deg.C, which includes the temperature value of 120 deg.C or the temperature just before the heat crystallization temperature of PET and can produce stretching effect. By heating the resultant primarily intermediate molded article 4, which has been biaxially stretching blow-molded, up to the temperature higher than the temperature of a primarily blow mold or 170-255 deg.C and the secondarily blow mold up to the temperature higher than the highest temperature of the atmosphere, under which a molded bottle 6 is used, by 5-10 deg.C, blow molding is applied to the primarily intermediate molded article 4 so as to obtain the bottle 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxial stretch blow molding method made of polyethylene terephthalate resin, and more specifically, it is made of polyethylene terephthalate resin having high heat resistance against heat shrinkage while maintaining high transparency. The present invention relates to a method for forming a biaxially stretch blow molded bottle body.

[0002]

2. Description of the Related Art Polyethylene terephthalate resin (hereinafter simply referred to as PET resin) has stable physical properties, no pollution, excellent transparency, and high mechanical strength. It is used in a large amount in various fields as a container for the body and the like, and is extremely useful as a bottle for foods.

As described above, the PET resin bottle effectively exhibits a number of excellent characteristics. However, the PET biaxially stretch-blow molded bottle which has not been appropriately heat-treated is It is weak against, and is significantly deformed by heating and filling at a high temperature of 70 ° C or higher. Therefore, PET cannot be used as a container for retort foods that are left to heat for 30 minutes at 120 ° C, or as a container for fruit drinks and other foods that are heat-treated, and PET has high heat resistance against heat shrinkage. At present, the appearance of resin bottles is strongly desired.

As a method of imparting heat resistance to heat shrinkage to such a bottle made of PET resin, there is a conventional method (1) P
To increase the density of ET resin bottles, blow molding is performed by heating the mold temperature of the blow mold during blow molding to a temperature higher than the target heat-resistant temperature. (2) Intermediate blow molding that is a primary blow molding product There is a method of making a finished product, reheating it (about 110 ° C) and then blow-molding it again to make a finished product.

[0005]

SUMMARY OF THE INVENTION Among these methods,
In the method of (1), as the mold temperature rises, the moldability deteriorates, and conventionally, the heat resistance to heat shrinkage of about 85 ° C. is the limit, so as used now, It could not be used for foods that are heat-treated at a temperature much higher than 95 ° C. Further, the above method (2) of imparting heat resistance to heat shrinkage to the PET resin bottle was out of the problem because heat resistance to heat shrinkage higher than the method shown in (1) cannot be expected.

The present invention was devised to solve the above-mentioned problems and dissatisfactions in the conventional example, and to meet the conventional demands. Biaxial stretch blow molding of a preform formed in a desired shape in advance. Then, it is molded into a primary intermediate molded product, and this primary intermediate molded product is subjected to heat treatment to forcibly undergo heat shrinkage deformation to be molded into a secondary intermediate molded product, and this secondary intermediate molded product is a finished bottle The purpose is to obtain a bottle that exhibits extremely high heat resistance against heat shrinkage by blow molding.

[0007]

DISCLOSURE OF THE INVENTION The present invention is a method for biaxially stretch blow molding a bottle made of PET, wherein a preform 1 molded in a desired shape in advance has a main body 2 which is biaxially stretch blow molded. A temperature range of 120 ° C. on the verge of thermal crystallization of PET, which is a temperature range in which blow molding can be performed in which the stretching effect can be exhibited 90
C. to 130.degree. C., primary biaxial stretch blow molding is performed on the primary intermediate molded product 4 by the primary blow mold, and the biaxially stretch blow molded primary intermediate molded product 4 is heated to the mold temperature of the primary blow mold. It is heated to a higher temperature of 170 ℃ ~ 255 ℃, and the mold temperature of the secondary blow mold is changed to the molded bottle body 6.
A few degrees higher than the maximum temperature of the atmosphere used (5
The bottle 6 is blow-molded while being heated to about 10 ° C. 120 ℃ ~ 150 ℃

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The biaxial stretch blow molding method of the present invention will be specifically described below with reference to the drawings showing one embodiment of the present invention. The blow molding method according to the present invention includes a first step of molding the preform 1 into a desired shape in advance by using injection molding or the like, and a final molded article having the shape at the time of the first step molding without stretching deformation. That is, it comprises a second step of thermally crystallizing the mouth part forming a part of the bottle body 6 so as not to be thermally deformed, and a third step of the blow molding operation which is the gist of the method of the present invention. There is.

The first step, that is, the molding operation of the preform 1 is often accomplished by ordinary injection molding, but the shape of the preform 1 to be molded is not specified. As shown by the solid line in FIG.
It may have a dish shape, or may have an elongated tubular shape with a bottom. Such a preform 1 is
It comprises a mouth part 3 which is an assembly part to a blow molding die, and a main body part 2 which is a body part including a bottom part of a bottle body 6 to be stretch-molded. Despite the mold temperature, the appropriate stretching amount for molding into the primary intermediate molded product 4 without whitening is that the area magnification (main part of the preform 1 is surface area S ₁ of 2, is approximately 5 to 13 times is represented by S ₂ / S ₁₎ when the surface area S ₂ of the primary intermediate product 4.

If the stretched area ratio is 5 times or less, the primary intermediate molded product 4 may be heated and the secondary intermediate molded product 5 may be whitened by the heating temperature during the forced heat shrink molding.
On the other hand, when the stretching area ratio is 13 or more, voids are generated and the stretch molding can be performed, but it becomes cloudy and the shapeability is deteriorated. Therefore, the main body portion 2 of the preform 1 in the embodiment
In order to prevent thermal crystallization, that is, whitening, during heating of the primary intermediate molded product 4, the stretched area ratio (S ₂ / S ₁ ) of the primary intermediate molded product 4 is set to about 5 to 13 times as described above. When molded, it has an oriented crystallization density of about 1.350 [g / cm
³ ] It has a dish shape so that the above can be done.

Further, the peripheral end portion and the central portion of the preform 1 which are the connecting portions with the mouth portion 3 of the main body portion 2 are less subject to the stretching action than the other portions of the main body portion 2 and are easily whitened. Therefore, it is preferable that the thickness of these portions is made relatively thin as compared with the other portions so that they can be easily stretched. As described above, the preform 1 molded into a desired shape is subjected to the whitening treatment of the mouth portion 3 by the thermal crystallization operation of the mouth portion 3 prior to the biaxial stretch blow molding operation for the primary intermediate molded product 4. To do.

To whiten the mouth 3 as described above, it is sufficient to cool the mouth 3 from a sufficiently heated state. However, what should be noted in the whitening treatment of the mouth 3 is the whitening treatment. This is to prevent the mouth portion 3 from being deformed into an inconvenient form. In particular, the deformation of the roundness of the mouth portion 3 due to the deformation significantly deteriorates the function of the bottle body 6 which is a molded product as a container, and therefore must be strictly prevented.

In this way, the mouth portion 3 of the preform 1
If whitening is achieved, this preform 1
The bottle body 6 is molded by the blow molding process, which is a process of the first step, and the blow molding process includes a step of performing the primary biaxial stretch blow molding of the preform 1 into the primary intermediate molded product 4 and the primary intermediate molded product. 4 is heated to forcibly heat-shrink to form a secondary intermediate molded product 5, and finally, this secondary intermediate molded product 5 is subjected to secondary blow molding into a bottle body 6. . In the primary biaxial stretch blow molding step of biaxially stretch blow molding the preform 1 into the primary intermediate molded product 4, the preform 1, to be precise, the main body portion 2 of the preform 1 is formed of PET which is a synthetic resin material. It is achieved in a state where the resin is heated to a temperature range of 90 ° C to 130 ° C, which is a temperature range in which blow molding can be performed, in which a stretching effect including a temperature value of 120 ° C just before thermal crystallization is exhibited.

In the above-mentioned primary biaxial stretch blow molding step, as a concrete means for enabling the stretch molding to be performed in the state where it is not thermally crystallized by the heating at the time of the secondary blow molding, as described above, the primary intermediate It goes without saying that the body including the bottom of the molded product 4, that is, the portion where the main body 2 is stretch-blow-molded has oriented crystals, but its density is
In order to obtain 1.350 [g / cm ³ ] or more, it is preferable to set the stretch ratio from the preform 1 to the primary intermediate molded product 4 to 5 to 13 times in area ratio.

Next, the step of heating the primary intermediate molded product 4 to forcibly heat-shrink it to mold it into the secondary intermediate molded product 5 includes 2 steps.
The purpose is to forcibly and quickly eliminate the internal residual stress generated in the axial stretch blow-molded product, and in each stretch-molded part of the primary intermediate-molded product 4 biaxially stretch-blow molded using the primary blow mold. According to the generated internal residual stress, each stretch-molded portion of the primary intermediate molded product 4 is freely deformed, so that the internal residual stress described above is forcibly eliminated.

The deformation according to the internal residual stress generated in each stretch-molded portion of the primary intermediate molded product 4 as described above naturally becomes the contractive deformation, but the secondary molded by this contractive deformation. As shown in FIG. 2, the stretch-molded portion of the intermediate molded product 5, that is, the body portion 2 which is the body portion including the bottom portion, includes the bottom portion which is the stretch-molded portion of the bottle body 6 as the molding target. The draw ratio of the stretch molding from the preform 1 to the primary intermediate molded product 4 and the size of the primary intermediate product 4 are set so that the size is slightly smaller than the body part.

The step of blow molding the secondary intermediate molded product 5 into the bottle body 6 is carried out by heating to 170 ° C. to 255 ° C. which is a temperature higher than the mold temperature of the primary blow mold in the above-mentioned step. The contracted secondary intermediate molded product 5 is heated by a secondary blow mold heated to 120 ° C. to 150 ° C., which is a temperature several degrees higher than the maximum temperature of the atmosphere in which the bottle body 6 which is the molding target is used. The body 6 is blow-molded. In the blow molding process of the secondary intermediate molded product 5 into the bottle 6, as described above, the main body 2 which is the body including the bottom which is the blow molded portion of the secondary intermediate molded product 5 is Since it is almost equal to or slightly smaller than the body including the corresponding bottom, the amount of stretching during the stretch forming from the secondary intermediate molded product 5 to the bottle body 6 is extremely small, and therefore, the secondary intermediate By the stretch molding from the molded product 5 to the bottle 6, almost no internal residual stress due to the stretch molding is generated in the stretch-molded portion of the molded bottle 6.

Further, since the bottle body 6 is blow-molded by the secondary blow mold whose temperature is higher than the maximum temperature of the atmosphere in which it is used, it is heat set by the secondary blow mold. Therefore, it is possible to obtain the bottle body 6 having no internal residual stress and having high heat resistance against heat shrinkage. As described above, the biaxial stretch blow molding method according to the present invention can mold the bottle 6 having extremely excellent heat resistance against heat shrinkage. Intermediate molded product 5
In order to obtain a bottle body 6 with more accurate control of the degree of shrinkage, less internal residual stress, high dimensional accuracy, and proper wall thickness distribution, the primary intermediate molding in which the mold temperature of the primary blow mold is molded To be able to control the amount of heat shrinkage of item 4
It is better to set it to 110-230 ℃. The mold temperature of the primary blow mold is the same as that of the primary intermediate molded product 4 to be stretch-molded.
It should be set according to the stretching area ratio, and the temperature value should be set larger as the stretching area ratio increases.

[0019]

EXAMPLES Next, examples of the molding method of the present invention will be described below. Preform 1 preformed by injection molding
At a heating temperature of 115 ° C., a mold temperature of the primary blow mold of 180 ° C., a blow pressure of 25 kg / cm ² , and a blow time of 1.4 seconds, the primary biaxial stretch blow molding was performed from the preform 1 to the primary intermediate molded product 4. . Next, the mold is opened, and the primary intermediate molded product 4 is subjected to heat shrinkage deformation from the primary intermediate molded product 4 to the secondary intermediate molded product 5 at a heating temperature of 225 ° C. The secondary intermediate molded product 5 was molded into a bottle body 6 at a mold temperature of 140 ° C., a blow pressure of 30 kg / cm ² , and a blow time of 4.4 seconds.

The bottle body 6 thus formed is immersed in glycerin heated to 120 ° C. in a storage tank for 30 minutes without being capped and heated to heat the bottle body 6 to the above-mentioned glycerin. The volume change rate of this bottle 6 was 0.33% when it was taken out from the inside, cooled with water and the change from before heating was obtained.
From this, it became clear that a PET bottle having sufficiently high heat resistance against heat shrinkage can be molded. When the bottle body molded as described above is filled with the content liquid at 80 ° C and capped and subjected to retort sterilization treatment, the retort sterilization treatment temperature is 120 ° C and the F value (sterilization time value).
There was no change in 6 to 10 (minutes), and the rate of change in capacity was 0.5% or less.

Further, no additives were mixed in the PET resin material for molding the bottle 6, and it was possible to exhibit extremely excellent transparency.
Its crystallized density is 1.3853 to 1.3918 [g / cm ³ ] (where this is the surface area S ₃ of the secondary intermediate molded product 5 and the surface area S _{4 of the} bottle body 6, the stretching area ratio S ₄ / S ₃ is 1.5. Although the crystallinity of this type of bottle without conventional heat treatment is about 16%, the crystallinity of the bottle with conventional heat setting is about 33%. On the other hand, the crystallinity of the bottle body 6 molded according to the present invention was about 49%.

As described above, according to the present invention, a sufficiently high density can be obtained and a high moldability can be obtained, so that the mechanical strength such as the reduced pressure strength can be greatly improved. Furthermore, when the internal residual stress of the bottle 6 was measured, the internal residual stress began to appear when the heating temperature exceeded 110 ° C, and gradually increased as the heating temperature increased, but up to 150 ° C. Upon heating, the maximum value of the internal residual stress developed was 0.22 [kg / mm ² ] which was a very small value. Therefore, it becomes possible to mold a bottle that can withstand hot filling at a temperature of about 95 ° C as the atmosphere in which the bottle is used, and the secondary blow mold is performed at a mold temperature of 100 ° C to 105 ° C. I'm fine. As a result of observing the bottle 6 in each of the above-mentioned examples, a slight white turbidity was observed in the vicinity of the center of the bottom of the bottle 6, but this was compared with the other parts, which was the center of the bottom of the bottle 6 described above. It seems that the stretching cannot always be performed sufficiently.

[0023]

As is apparent from the above description, the method for forming a PET bottle according to the present invention can form a bottle having no internal residual stress and having a high heat resistance against heat shrinkage. Since the density of each part can be made sufficiently large, it can be molded into a bottle having high mechanical strength such as decompression strength, and a heating means such as a far infrared heating device conventionally used for heating a preform. Since it can be carried out by appropriately combining the blow molding means and the blow molding means,
It is easy to carry out, and exhibits many excellent effects such as maintaining high transparency.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a preform primary blow molding operation state.

FIG. 2 is a vertical cross-sectional view showing forced heat shrinkage deformation of a primary intermediate molded product.

FIG. 3 is a vertical cross-sectional view of a secondary blow molding operation state of a secondary intermediate molded product.

[Explanation of symbols]

 1 Preform 2 Body part 3 Mouth part 4 Primary intermediate molded product 5 Secondary intermediate molded product 6 Bottle

Claims (7)

[Claims] 1. A preform formed of a polyethylene terephthalate resin which has been molded in a desired shape in advance is capable of effective biaxial stretch blow molding including a temperature value of 120 ° C. immediately before thermal crystallization, which is a temperature range of 90 ° C. In a state of being heated to 130 ° C., primary biaxial stretch blow molding was performed on a primary intermediate molded product using a primary blow molding die in which a stretching area ratio of a stretched portion of the preform was set to 5 to 13 times, and then the primary The blow molding die is opened, and the biaxially stretch blow molded primary intermediate molded article is heated to a temperature higher than the mold temperature of the primary blow molding die to be heat-shrinked to form a secondary intermediate molded article.
The secondary intermediate molded product is secondarily blow molded into a bottle by a secondary blow molding die which is heated to a temperature several degrees higher than the maximum temperature of the atmosphere in which the bottle as a product is used. A biaxial stretch blow molding method characterized by fixing. 2. A preform formed of a polyethylene terephthalate resin which has been molded into a desired shape in advance is capable of effective biaxial stretch blow molding including a temperature value of 120 ° C. immediately before thermal crystallization, which is a temperature range of 90 ° C. In a state of being heated to 130 ° C., primary biaxial stretch blow molding was performed on a primary intermediate molded product using a primary blow molding die in which a stretching area ratio of a stretched portion of the preform was set to 5 to 13 times, and then the primary The blow molding die is opened, and the biaxially stretch blow molded primary intermediate molded article is heated to a temperature higher than the mold temperature of the primary blow molding die to be heat-shrinked to form a secondary intermediate molded article.
A twin-screw for secondary blow molding of a bottle into a bottle by a secondary blow molding die obtained by heating the secondary intermediate molded product to a temperature that is several degrees higher than the maximum temperature of the atmosphere in which the bottle that is the product is used. In the stretch blow molding method, the primary intermediate molded product is 170
When reheated to ℃ ~ 255 ℃ to shrink to the secondary intermediate molded product, the size of each part where the primary intermediate molded product is stretch blow molded is equal to or less than the size of each corresponding part of the bottle. Is set to a value that is smaller than 2
Axial stretch blow molding method. 3. A temperature range of 90 ° C., which is a temperature range of 120 ° C. on the verge of thermal crystallization, in which a preform made of a polyethylene terephthalate resin molded in a desired shape can be effectively biaxially stretch blow molded. While being heated to 130 ° C, the primary blow molding die in which the stretching area ratio of the stretched portion of the preform is set to 5 to 13 times can be stretch-molded without being thermally crystallized by heating during the secondary blow molding. After performing primary biaxial stretch blow molding on the primary intermediate molded product while heating it to 110 ° C to 230 ° C as much as possible, open the primary blow molding die to obtain the biaxial stretch blow molded primary intermediate molded product. , The primary blow molding die is heated to a temperature higher than that of the mold to be heat-shrinked to form a secondary intermediate molded product, and the secondary intermediate molded product is the highest in the atmosphere in which the bottle body is used. A few degrees higher than the temperature Biaxial stretch blow molding method, characterized in that the secondary blow molded bottle body by heating the secondary blow molding mold comprising. 4. A temperature range of 90.degree. C., which is a temperature range of 120.degree. C. on the verge of thermal crystallization, in which a preform made of a polyethylene terephthalate resin molded in a desired shape can be effectively biaxially stretch blow molded. A state in which the mold temperature of the primary blow molding die, which is heated to 130 ° C. and the stretching area ratio of the stretched portion of the preform is set to 5 to 13 times, is not thermally crystallized by the heating during the secondary blow molding. After the primary biaxial stretch blow molding is performed on the primary intermediate molded product in a state of being heated to 110 ° C to 230 ° C so that the primary biaxial stretch blow molding is performed, the primary blow molding die is opened. The intermediate molded product is heated at a temperature higher than the mold temperature of the primary blow molding die to be heat-shrinked to form a secondary intermediate molded product, and the secondary intermediate molded product is used as a product bottle. A few degrees higher than the maximum temperature of the atmosphere 2 to the secondary blow molding the bottle body by There secondary blow molding mold comprising heating to a temperature
In the axial stretch blow molding method, when the primary intermediate molded product is reheated to a temperature higher than the mold temperature of the primary blow molding die to shrink into the secondary intermediate molded product, the primary intermediate molded product is stretched. A biaxial stretch blow molding method, characterized in that the dimensions of each part to be blow molded are set to values equal to or slightly smaller than the dimensions of the corresponding parts of the bottle. 5. The biaxial stretch blow molding method according to any one of claims 1 to 4, wherein the secondary intermediate molded product is the highest in the atmosphere in which the bottle is used. A biaxially stretch blow-molding method, characterized in that the bottle is subjected to secondary blow-molding by a secondary blow-molding die which is heated to 100 ° C to 150 ° C which is several degrees higher than the temperature. 6. The biaxial stretch blow molding method according to any one of claims 1 to 4, wherein the primary intermediate molded product is heated to a temperature higher than the mold temperature of the primary blow molding die. In order to form a secondary intermediate molded product by heat-shrinking, the mold is opened and the primary intermediate molded product is heated at a heating temperature of 170 ° C to 255 ° C to shrink the secondary intermediate molded product.
Axial stretch blow molding method. 7. The method according to claim 4, wherein
In the axial stretch blow molding method, the primary intermediate molded product is heated to a temperature higher than the mold temperature of the primary blow molding mold at 170 ° C to 25 ° C.
Biaxial stretch blow molding, characterized in that the secondary intermediate molded product that has been reheated to 5 ° C and contracted is subjected to secondary stretch blow molding so that the stretched area ratio is 1.0 to 1.5 times, and molded into a bottle. Method.