JP4525922B2 - Polyester resin container and molding method thereof - Google Patents

Description

  The present invention relates to a polyester resin container used for applications requiring retort treatment and a molding method thereof.

  In recent years, containers made of polyester resin such as polyethylene terephthalate (hereinafter referred to as PET) resin that has been biaxially stretch blow molded have come to be used for food applications that require retort treatment. .

However, in a conventional biaxial stretch blow molded polyester container, when the retort processing temperature reaches a high temperature of about 120 ° C., the container shrinks due to residual strain due to stretching deformation, and the appearance is impaired and cannot be used as a product. Met.
Since then, various developments have been carried out in order to increase the heat resistance of the PET resin container, and one of them has been developed by the present applicant (see Patent Document 1) and is called “Dulblow Molding Method”. This technique is an effective method and is used as a method for forming a container that is retorted at about 120 ° C. for about 30 minutes.

This double blow molding method includes a primary blow molding process in which a preform previously molded into a desired shape is biaxially stretch blow molded into a primary intermediate molded product, and the primary intermediate molded product is heated and thermally contracted to form a secondary. It consists of a process to form an intermediate molded product and finally a secondary blow molding process to blow mold this secondary intermediate molded product into the final product container, and heat-shrink the primary intermediate molded product Thus, it is possible to eliminate the residual strain generated in the primary intermediate molded product without lowering the crystallization that has progressed by stretching, thereby obtaining a highly heat-resistant casing.
Japanese Patent Publication No. 7-67732

On the other hand, as the use of PET resin containers for retort processing advances, the low cost, convenience, and merchantability of PET resin containers are widely recognized in the field of retort foods. There is a growing demand for the application of contents that require processing.
For example, soups require processing conditions of about 60 minutes at 120 ° C. If the processing temperature can be further increased, the processing time can be greatly reduced, and if processing can be performed at a high temperature in a short time. Since the deterioration of the contents due to heat can be reduced, a container having higher heat resistance is demanded from both the productivity and quality aspects.

  The problem to be solved by the present invention is the development of a container made of a polyester resin that can be sufficiently used for retort processing at temperatures exceeding 120 ° C. up to about 130 ° C., and improving the productivity or quality of the retort food. It is an object of the present invention to provide a polyester resin container that can be used and a method for producing the same.

Hereinafter, the invention according to claim 1, claim 2, and claim 3 relates to a double blow molding method of a polyester resin container,
Among them, the method according to the first aspect of the present invention is such that the preform is heated to a temperature range of 70 ° C. to 130 ° C., and the mold temperature is set to 50 ° C. to 230 ° C. to perform primary biaxial stretching. A primary blow molding step for forming a molded product, a step of heating the primary intermediate molded product in a temperature range of 110 ° C. to 250 ° C. for shrink molding into a secondary intermediate molded product, and blow molding the secondary intermediate molded product. In a double blow molding method comprising a secondary blow molding process for molding into a container, the mold temperature in the secondary blow molding is set to a temperature exceeding 210 ° C.

The inventors of the present application are required as a product in a retort process at a high temperature exceeding 120 ° C. to about 130 ° C. when the mold temperature of the secondary blow molding is 210 ° C. or less for a polyester resin container subjected to double blow molding. In order to further exert the heat setting effect of increasing the mold temperature of the secondary blow molding, the mold is brought to around 250 ° C. at which the secondary intermediate molded product made of PET resin starts to melt. A test was conducted in which the container was molded at an elevated temperature.
Among them, at least at a mold temperature of 230 ° C., there is no problem with moldability, and the haze associated with whitening of the container after molding is not particularly large, and in a temperature range of about 120 to 130 ° C. The present inventors have found that shrinkage deformation after retort treatment is suppressed in a range where the appearance is not impaired, and that it can be used as a product, and has been achieved.

  That is, by the above-mentioned method according to claim 1, by setting the mold temperature in the secondary blow molding to a temperature exceeding 210 ° C. in the double blow molding method, the temperature exceeds 120 ° C. and 130 ° C. without particularly impairing the moldability. To provide a polyester resin container that does not impair the appearance by suppressing shrinkage deformation to a sufficiently small degree even in retort processing up to a degree, and that does not impair the transparency in a container having transparency such as a PET resin container. Can do.

  In the present invention, a polyester resin that can be biaxially stretch blow molded and crystallized can be used as the polyester resin, and a resin such as a PET resin, a polybutylene terephthalate resin, or a polyethylene naphthalate (PEN) resin is used. can do. Further, blends of these polyester resins, and resins obtained by blending these polyester resins as a main component with polyolefin resins, polycarbonate resins, arylate resins, nylon resins and the like can also be used.

In addition, the polyester resin container of the present invention may be made of, for example, a PET resin / nylon resin / PET resin to improve gas barrier properties, or heat resistance and moldability, as long as the essence of the polyester resin container is not impaired. In order to adjust the balance, the entire wall or a part of the wall can be made into a laminated structure, such as PET resin / PEN resin / PET resin.
Moreover, in order to improve gas barrier properties, a carbon thin film or a silicon oxide thin film can be formed on the inner wall surface by plasma CVD.

  The method of the invention described in claim 2 is that, in the invention of claim 2, the mold temperature in the secondary blow molding is set to a temperature of 215 ° C. or higher.

According to the method of claim 2, the mold temperature in the secondary blow molding is more preferably 215 ° C. or more, whereby the volumetric shrinkage after the retort treatment can be suppressed sufficiently low, and the product yield is 100. % Can be close.

  According to a third aspect of the present invention, in the first or second aspect of the invention, the polyester resin is a PET resin.

  According to the above-described configuration, it is preferable to use a PET-based resin having a low raw material cost and excellent biaxial stretch blow moldability among polyester resins.

  As the PET-based resin used in the present invention, PET is mainly used. As long as the essence of the PET resin is not impaired, a copolymer polyester containing other polyester units can be used mainly with ethylene terephthalate units, For example, in order to improve heat resistance, resins such as nylon resins and polyethylene naphthalate resins can be blended and used. Examples of the component for forming the copolyester include dicarboxylic acid components such as isophthalic acid, naphthalene 2,6 dicarboxylic acid, and adipic acid, propylene glycol, 1,4 butanediol, tetramethylene glycol, neopentyl glycol, cyclohexanedimethanol, Mention may be made of glycol components such as diethylene glycol.

  Next, claim 4 and claim 5 relate to a polyester resin container, in which the means of the invention of claim 4 is based on a retort treatment at 124 ° C. for 42 minutes in a polyester resin container. The volume shrinkage rate is 0.75% or less.

  The inventors of the present invention have made the volume shrinkage of the container extremely high even in a retort treatment at 120 to 130 ° C. due to a heat setting effect in which the mold temperature of the secondary blow molding is increased, particularly for the polyester resin container subjected to double blow molding. As a result, the present invention has been found. And by making the volumetric shrinkage ratio by retorting at 124 ° C. for 42 minutes 0.75% or less, retorting at a temperature exceeding 120 ° C. and reaching about 130 ° C. without damaging the appearance due to local deformation. The container which can be used for can be provided. Here, the retort condition at 124 ° C. for 42 minutes is a condition having a bactericidal effect corresponding to a treatment at 120 ° C. for about 60 minutes in soups.

  Here, when the volumetric shrinkage rate exceeds 0.75%, the appearance after the retort treatment is frequently impaired, and when it exceeds 2%, the appearance is almost 100% damaged and cannot be handled as a product. It becomes.

  The means of the invention described in claim 5 is that, in the invention described in claim 4, the polyester resin is a PET resin.

  According to the above configuration of the fifth aspect, it is preferable to use a PET resin having a low raw material cost and excellent biaxial stretch blow moldability among polyester resins.

The present invention has the above-described configuration, and has the following effects.
In the invention according to claim 1, by setting the mold temperature in the secondary blow molding to a temperature exceeding 210 ° C. in the double blow molding method, the temperature exceeds 120 ° C. and about 130 ° C. without impairing the moldability. Provides a polyester resin container that does not impair the appearance by suppressing shrinkage deformation to a sufficiently small degree even in retort processing at temperatures up to, and that does not impair the transparency of containers with transparency such as PET resin containers can do.

  In the invention described in claim 2, by setting the mold temperature in the secondary blow molding to 215 ° C. or higher, the volume shrinkage after the retort treatment can be suppressed sufficiently low, and the yield of products can be improved. it can.

  In the invention described in claim 3, it is preferable to use a PET resin having a low raw material cost and excellent biaxial stretch blow moldability among polyester resins.

  In the invention according to claim 4, the volume shrinkage rate by retort treatment at 124 ° C. for 42 minutes is set to 0.75% or less, and at a temperature exceeding 120 ° C. to about 130 ° C., It is possible to provide a container that can be used for retorting without deteriorating the appearance due to deformation.

  In the invention described in claim 5, it is preferable to use a PET resin having a low raw material cost and excellent biaxial stretch blow moldability among polyester resins.

Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these descriptions.
FIG. 1 shows a front view of a casing 1 which is an embodiment of the polyester container of the present invention. This casing 1 is made of PET resin and formed by a double blow molding method to be described later. A round bottle having a mouth tube part 2, a shoulder part 3, a cylindrical body part 4 and a bottom part 5 and having a height of 130 mm and a body diameter of 66 mm. Further, the mouth tube portion 2 is in a state of being whitened by the thermal crystallization process, and further, a concave portion 5a is formed in the bottom portion 5 in a depressed shape.

The body portion 4 is formed with six decompression absorption panels 6 arranged in parallel with the wall surface gently recessed into a concave shape leaving the upper end portion and the lower end portion. And the vertical rib-shaped pillar part 7 is formed in the state left without being depressed between adjacent decompression absorption panels 6, and this is also depressed in the upper end part and lower end part of the trunk | drum 4. A short cylindrical annular portion 8 is formed in a state where it is left without.
The rigidity of the entire casing 1 is ensured mainly by the pillar portion 7 and the annular portion 8, and when the decompression absorption panel 6 of the trunk portion 4 is inflated and deformed in an inverted state at a high temperature during the retort process. The upper and lower annular portions 8 exhibit a function as a restraint portion of the expansion and deformation, and exhibit a function of accommodating the expansion and deformation of the housing 1 in a certain mode.

Next, a double blow molding method for molding the casing 1 of the above embodiment will be described with reference to FIG. FIG. 2 is an explanatory view showing a front view of a molded product by each step of the double blow molding method.
The double blow molding method basically includes a primary blow molding process in which the preform 11 (FIG. 2A) is biaxially stretch blow molded to form a primary intermediate molded product 21, and the primary intermediate molded product 21 is heated. Then, the molding method includes a heat shrinking process for forcibly shrink-molding the secondary intermediate molded product 31 and a secondary blow molding process for blow molding the secondary intermediate molded product 31 into the container 1.

More specifically about each process,
1) Primary blow molding process test The preform 1 injection-molded into a tubular shape is heated from a temperature of 70 ° C. at which a stretching effect is obtained to a temperature just before thermal crystallization of the PET resin to 130 ° C., preferably 90 ° C. to 120 ° C. The primary intermediate molded product 21 (FIG. 2B) is molded by a biaxial stretch blow molding method at a mold temperature of 50 ° C. to 230 ° C., preferably 70 ° C. to 180 ° C.
2) Heat shrinking step The temperature range of the primary intermediate molded product 21 from 110 ° C., which is close to the crystallization temperature of the PET resin, to 250 ° C. where the degree of softening of the PET resin is large and it is difficult to maintain the shape, desirably Heating to 130 ° C. to 200 ° C. causes the secondary intermediate molded product 31 to undergo heat shrinkage deformation (see FIG. 2C). Here, the residual stress due to the biaxial stretch blow molding in the primary blow molding process is alleviated.
3) Secondary blow molding Considering the maximum use temperature such as the retort processing temperature of the casing 1 which is the final molded product, the secondary intermediate molded product 31 has a large softening degree of PET resin and maintains its shape. The casing 1 (see FIG. 2 (d)) is molded by a blow molding method with appropriate setting in a temperature range up to 250 ° C. where it is difficult to perform.

Example The case 1 of FIG. 1 was shape | molded by the double blow molding method on the following conditions using PET resin, and the case 1 of Examples 1-4 and the comparative examples 1 and 2 was obtained. The preform 11, the primary intermediate molded product 21, the secondary intermediate molded product 31, and the housing 1 have the shapes shown in FIGS. 2 (a), (b), (c), and (d), respectively.
(1) Primary blowing step Preform heating temperature 115 ° C, mold temperature 170 ° C, longitudinal draw ratio 2.5 times, transverse draw ratio 3.0 times (2) Heat shrinkage step Heating temperature 200 ° C (molded product surface temperature) , Heating time 50 seconds (3) secondary blow molding process mold temperature 170-230 ° C., holding time 2.8 seconds, air circulation 0.4 seconds As shown in Table 1, Example 1 to Example 4 Each of the bodies has secondary blow molding mold temperatures of 215 ° C, 220 ° C, 225 ° C, and 230 ° C.
The casings of Comparative Examples 1 and 2 have mold temperatures of 170 ° C. and 210 ° C., respectively.

Each of the examples and comparative examples molded by the double blow molding method under the molding conditions as described above were filled with water at 90 ° C. at high temperature and sealed with a cap. A retort treatment was performed for a minute.
For each housing, volume shrinkage measurement, appearance evaluation, and haze measurement were performed, and the results are shown in Table 1. (Measured values of volumetric shrinkage and haze are average values (n = 10).)
The volume shrinkage rate (%) is obtained by the formula ((volume before treatment−volume after treatment) / volume before treatment) × 100.
In addition, the appearance was evaluated by checking the presence or absence of partial concave deformation, etc., and evaluating whether it could be used as a product. Here, for example, 10/10 OK indicates that 10 out of 10 products can be used as products, and 2 / 10NG indicates that 2 out of 10 products are unusable due to the appearance being damaged.

From the results in Table 1, it was found that the appearance after retorting was all OK in the casings of Examples 1 to 4 in which the mold temperature in the secondary blow molding process was 215 ° C. or higher.
On the other hand, the result of the comparative example shows that all of the 10 samples in the comparative example 1 at 170 ° C. are NG, and in the comparative example 2 at 210 ° C., the two are NG, which is unsatisfactory when considering the product yield. It was found that a housing having a temperature of 210 ° C. or lower cannot be used for retort treatment exceeding 120 ° C. Here, the main cause of the appearance NG was a bent depression in the trunk wall.

  In Table 1, it can be seen from the volume shrinkage rate that the shrinkage rate decreases as the mold temperature increases. And by adapting the volume change rate to 0.75% or less from the correspondence with the appearance, the appearance is not impaired even after retorting at a temperature exceeding 120 ° C. and reaching about 130 ° C., and it can be used as a product. It turned out to be.

  The haze was measured to evaluate the transparency of the casing, but the correlation with the mold temperature of the secondary blow molding was not clear and was about 20% at most, and the change before and after the retort treatment There were few, and there was no problem as a product.

  The polyester container according to the present invention is an unprecedented polyester container having high heat resistance that can be used for retort processing even at temperatures exceeding 120 ° C. up to about 130 ° C., and improves productivity by increasing the temperature of retort processing. At the same time, quality can be improved and retort food can be expected to be used in a wide range of applications.

It is a whole front view which shows one Example of the container of this invention. It is explanatory drawing which arranged and showed the front view of the molded article by each process in the shaping | molding method of this invention.

Explanation of symbols

1; Housing (container)
2; Mouth tube portion 3; Shoulder portion 4; Body portion 5; Bottom portion 5 a; Recessed portion 6; Depressurized absorption panel 7; Column portion 8; Ring portion 11; Preform 21: Primary intermediate molded product 31;

Claims (5)

Primary blow molding in which the preform (11) is heated to a temperature range of 70 ° C to 130 ° C, and the mold temperature is 50 ° C to 230 ° C and biaxial stretch blow molding is performed to form a primary intermediate molded product (21). A step of forcibly shrink-molding the primary intermediate molded article (21) into a secondary intermediate molded article (31) by heating in a temperature range of 110 ° C. to 250 ° C. , and the secondary intermediate molded article (31 In a double blow molding method comprising a secondary blow molding process in which a mold temperature in the secondary blow molding is set to a temperature exceeding 210 ° C. Molding method.
The method for molding a polyester resin container according to claim 1, wherein the mold temperature in the secondary blow molding is 215 ° C. or higher. The method for molding a polyester resin container according to claim 1 or 2, wherein the polyester resin is a polyethylene terephthalate resin. A polyester resin container having a volume shrinkage of 0.75% or less by retorting at 124 ° C. for 42 minutes. The polyester resin container according to claim 4, wherein the polyester resin is a polyethylene terephthalate resin.

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