JP4811700B2 - Retort-compatible polyester container and method for producing the same - Google Patents

Description

  The present invention relates to a retort-compatible polyester container and a method for producing the same. More specifically, the present invention relates to a retort-compatible polyester container that is used as a storage container for foods, beverages, etc. The present invention relates to a method for producing the container by axial stretch two-stage blow molding.

Plastic containers are superior in light weight, economy, ease of molding, impact resistance, transparency and reusability, and recently surpassed conventional metal and glass containers, It is widely used for daily necessities and industrial use. Among plastic containers, polyester containers represented by so-called PET bottles (polyethylene terephthalate containers) have excellent mechanical strength, cleanliness, high gas shielding properties, and non-polluting properties. Demand has been highest since it was approved. In particular, recently, small PET bottles have been heavily used by consumers as portable beverage small containers, and such demand is expected to increase more and more significantly in the future.
Furthermore, until recently, PET bottles were insufficient in heat resistance and pressure resistance and could not be used for high-temperature beverages or beverages requiring high-temperature sterilization. With the development of molding methods and the like, the polyethylene terephthalate preform has been sufficiently stretched and crystallized, and the heat resistance and pressure resistance of the PET bottle have been significantly improved (see, for example, Patent Document 1). It is now possible to meet the strong demands of consumers for portable hot drinks for winter.

The demand for long-term storage performance and hygiene safety in food and beverages has increased due to the extremely high demand for container-packed foods and beverages due to the diversification of consumer lifestyles in recent society and the safety orientation of these products. There is a growing tendency to be regarded as important. Therefore, it is necessary to ensure long-term storage performance and safety from spoilage or alteration in plastic containers for food and beverages. For example, beverages such as green tea and milk coffee, and foods and beverages such as processed foods and infant foods are stored. There is an increasing need for high temperature sterilization treatment of such containers.
For high-temperature sterilization treatment of containers containing food and drink, high-temperature and long-time treatment, that is, treatment of sterilization for about 20 to 50 minutes in a high-temperature atmosphere of 100 to 125 ° C. is desirable. For this purpose, for example, high-temperature steam is injected. So-called retort treatment with a heating kettle is heavily used and highly convenient, but with conventional polyester containers, even if the heat resistance and pressure resistance are remarkably improved by the development of the two-stage blow molding method, it is a short time of about 90 ° C. It can withstand only the heat treatment of, and under severe conditions of high temperature and long time such as retort treatment, expansion of the container due to high heat during sterilization, deformation of the container due to temperature reduction and decompression after sterilization, or significant deterioration of the container itself In some cases, the container may be damaged without being able to withstand the internal pressure load caused by the beverage in the container at high temperatures and the external pressure load caused by internal shrinkage when the temperature is lowered. Fear Re even, it can not be put into practical use as a product of the food and drink of the retort processing.

Therefore, in the use of a polyester container such as a PET bottle that cannot be sterilized by retort after food or drink storage, the shelf life of the food or drink itself is improved (for example, refer to Patent Document 2) or the retort treatment is endured. Many improvements have been proposed, such as modifying the properties of the polyester resin or modifying the layer structure of the plastic container to a special laminated structure (see, for example, Patent Document 3).
Such a situation reveals the technical circumstances of trying to replace lack of retort suitability by means of improvement from other viewpoints even if the retort suitability is not provided in the polyester container as a food and drink storage container, such as PET Except for the retort performance, the polyester container is particularly excellent in various functions as a container for foods and drinks, and is nothing but a very high necessity as a container for foods and drinks.

This technical situation reveals that polyester containers such as PET are strongly demanded and expected to have excellent retort performance, and in order to meet such demands and needs, polyester containers are excellent. Improvement research has been started to add retort function.
However, only a few techniques have been disclosed in polyester containers under severe processing conditions such as retort treatment that do not cause expansion of the container due to high heat during sterilization or deformation of the container due to temperature reduction after sterilization. Absent.
The applicant of this application performs retort sterilization by forming a polyester container by biaxial stretching and two-stage blow molding, causing the container to undergo heat shrinkage and heat setting, and identifying the bottom of the container by the endothermic peak of the DSC curve. However, a polyester container which does not cause deformation or whitening due to heat shrinkage at the bottom of the container is disclosed (see Patent Document 4), and the polyester container is formed by biaxial stretching and two-stage blow molding to heat shrink and heat set the container. The polyester container which does not produce a deformation | transformation in the trunk | drum of a container is disclosed even if it performs a retort sterilization process by specifying the shrinkage | contraction rate by TMA measurement of the trunk | drum of a container (refer patent document 5).
Under the conditions of severe retort treatment at a higher temperature and longer time than these improved methods, the container does not expand as a result of the high heat during sterilization, the container deforms due to the temperature drop after sterilization, or the container itself shrinks as much as possible. This is a situation where improved methods are desired.

Japanese Patent Laid-Open No. 5-200839 (Claims and paragraph 0006) JP 11-169113 A (summary) JP 2001-55216 A (summary) JP 2001-150522 A (abstract and claims) JP 2003-291205 A (abstract and claims)

As described above in paragraphs 0003 to 0005, against the background of the extremely high demand for container-contained foods and drinks due to diversification of consumers' lives and the orientation of safety to them, storage performance and rot or Since it is inevitable to ensure safety from alteration, and polyester containers are strongly demanded and expected to have excellent retort performance, the present invention provides a retort function at the bottom and body of the container at the same time. A problem to be solved by the invention is to develop a polyester container and a method for producing the same that can be applied and that does not cause deformation and shrinkage of the container as much as possible even under severe retort processing conditions at high temperatures and for a long time. It is what.
In other words, the present invention considers the improvement proposal recently disclosed for imparting the retort function, and provides the polyester container with a more excellent retort function economically by simple means. Is a problem to be solved.

  With the aim of solving the above-mentioned problems of the invention, the present inventors have economically advanced by a simple means, based on the improvement proposal mainly composed of the biaxially stretched two-stage blow molding disclosed above. In order to provide the polyester container with a retort function superior to the technology, the molding conditions in the biaxially stretched two-stage blow molding, the structure of the mold, the heat treatment method of the molded product, the material of the preform, and the heat of the primary molded product Regarding shrinkage processing and heat-set processing after secondary blow, etc., we continued to search for improvement means through diversified thoughts, repeated trial search and experimental examination, and retort by each example and comparative example described later As a result of the verification test by performance test, as a result, in the prior art by the present applicant, the conditions of heat shrinkage and heat setting are selectively specified, and the surface property of the blow molding die, etc. If devised, prior art from the superior retort function to polyester containers such as PET bottles, which resulted in the creation of the present invention by finding recognized that can easily and economically by including.

  This prior art performs retort sterilization by forming a polyester container by biaxial stretching and two-stage blow molding, heat-shrinking and heat-setting the container, and specifying the shrinkage rate by TMA measurement of the body of the container. Discloses a polyester container that does not deform the body of the container. Specifically, in order to withstand a retort treatment at 120 ° C. for 20 to 50 minutes, the shrinkage ratio in the body by TMA measurement is 0. The temperature when it becomes 66% is 120 ° C., biaxially stretched blow-molded so that the thickness reduction rate of the body portion becomes 5% or more with a secondary mold heated to 150 to 210 ° C., and heat set. A method for producing a polyester container in which a primary molded product is heated and shrunk at a surface temperature of 100 to 250 ° C. (see claims and paragraph 0013 in Patent Document 5 above).

The inventors have selectively improved the prior art to produce a polyester container that does not deform or shrink at the body and bottom of the container even after 1 to 50 minutes of retort sterilization at 125 ° C. Therefore, when the polyester container is molded by biaxial stretching two-stage blow molding and the container is subjected to heat shrinkage and heat setting, the first-stage blow molded article is subjected to heat shrinkage treatment to form a secondary molded article. The biaxially stretched blow molding of the second stage blow is performed with the secondary mold whose surface is treated, and then the blow molded article is heat set in the mold at a specific surface temperature exceeding 210 ° C. and below 250 ° C. A process for producing a retort-compatible polyester container is developed, and the shrinkage capacity of the container treated with an autoclave at 125 ° C. for 30 minutes is 1% or less, and at a higher temperature such as 1 to 50 minutes at 125 ° C., One was able to realize a polyester container to accommodate long retort.
The first-stage blow-molded product is subjected to heat shrinkage treatment at a specific region temperature of 190 to 220 ° C., and then the blow-molded product is heat-set at a temperature exceeding 210 ° C. and not more than 250 ° C. Polyester containers that do not deform or shrink on the body and bottom of the container even after retort sterilization for 1 to 50 minutes can be easily produced, and a surface-treated secondary mold coated with fluororesin is used. By doing so, even if second-stage blow molding is performed at a high temperature of 210 to 250 ° C., the suitability of the retort treatment can be improved without causing wrinkles, surface roughness, or uneven thickness on the surface of the molding container.

  Furthermore, in the present invention, as an additional feature, biaxial stretch blow molding is performed so that the thickness reduction rate of the body of the container is 5 to 30%, and shrinkage starts in the circumferential direction of the container in TMA (thermomechanical analysis) measurement. It is also a retort-compatible polyester container having a temperature of 120 ° C. or higher.

As described above, in the present invention, a polyester container that does not cause deformation and shrinkage as much as possible in the body and bottom of the container even if retort sterilization is performed at 125 ° C. for 1 to 50 minutes by a specific manufacturing method. Can be easily manufactured, and can fully meet the strong demand and expectation of providing excellent retort performance in polyester containers in the field of food and drink storage containers.
In addition, the present invention is such that the first-stage blow-molded product is subjected to heat shrinkage treatment, and then the blow-molded product is heat-set at a temperature of more than 210 ° C. and not more than 250 ° C. A polyester container that does not deform or shrink at the body and bottom of the container even when the retort sterilization treatment is performed can be easily produced, and furthermore, a fluororesin coating treatment, preferably PFA (tetrafluoroethylene perfluoroalkyl) is performed. By using a secondary mold coated with a vinyl ether copolymer) fluororesin or PTFE (polytetrafluoroethylene) fluororesin, even if second-stage blow molding is performed at a high temperature of 210 to 250 ° C., Increases retort processing suitability without causing wrinkles, surface roughness, or uneven thickness on the surface of the molded container Since those which can bets, the present invention is distinctly different, the invention is the above prior art, it can be said that from this prior art is an excellent invention that is not suggested.

  In the above, since the present invention has been described in overview with respect to the background of the creation of the present invention and the basic components of the present invention, the present invention will be described as follows. The invention is composed of unit groups, and the invention of [1] is a basic invention, and the inventions below it embody the basic invention or form an embodiment. (The invention group as a whole is collectively referred to as “the present invention”.)

[1] A preform formed from a polyester resin is biaxially stretched and blow molded with a primary mold to form a primary molded product, and the primary molded product is heated to shrink to form a secondary molded product, and the secondary molded product is surface-treated. The retort is characterized in that the biaxially stretched blow molding is performed with the formed secondary mold, and the surface temperature of the blow molded product is heat set in the secondary mold at a temperature exceeding 210 ° C and not more than 250 ° C. The manufacturing method of the corresponding polyester container.
[2] The method for producing a retort-compatible polyester container according to [1], wherein the surface-treated secondary mold is a mold coated with a fluororesin.
[3] The method for producing a retort-compatible polyester container according to [2], wherein the fluororesin is tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA) or polytetrafluoroethylene (PTFE).
[4] In the biaxial stretch blow molding in the secondary mold, the thickness reduction rate of the body part of the container is molded to be 5 to 30%, [1] to [3] The manufacturing method of the polyester container corresponding to retort in any.
[5] A retort-compatible polyester container produced by the production method according to any one of [1] to [4], wherein the shrinkage capacity of the container treated with an autoclave at 125 ° C. for 30 minutes is 1% or less. Retort compatible polyester container.
[6] The retort-compatible polyester container according to [5], wherein in the thermomechanical analysis (TMA) measurement, the shrinkage start temperature is 120 ° C. or more in the circumferential direction of the container.
[7] The retort-compatible polyester container according to [5] or [6], wherein retort sterilization is possible at 125 ° C. for 1 to 50 minutes.
[8] A container-stored beverage in which a beverage is stored in the retort-compatible polyester container according to [7].

  The polyester container of the present invention and the production method thereof can provide a retort function to the polyester container at the same time on the bottom and body of the container by a simple and economical method, and a retort treatment at 125 ° C. for 1 to 50 minutes. Even under high-temperature and long-time severe retort processing conditions, the container is not deformed or shrunk as much as possible, and has an excellent effect that it is highly practical and suitable as a retort container for food and drink. It is what you play.

  The present invention has been described in accordance with the basic configuration of the present invention as a means for solving the problems, but in the following, embodiments of the invention of the present invention group described above will be described with reference to the drawings. The details will be described in detail.

1. Manufacturing method of polyester container (1) Biaxially stretched two-stage blow molding The process diagram of the biaxially stretched two-stage blow molding of the present invention is schematically shown in FIG. In (b), the formed preform is charged into a primary mold and biaxially stretched and blow molded to form a primary molded product having a shape larger than the final product container shown in (d). In c), the primary molded product is heated and shrunk at a surface temperature of 190 to 220 ° C., preferably 200 ° C., preferably about 60 to 90% by heating with a hot air oven or an infrared heater, and (d ), A secondary molded product having a shape smaller than the final product container shown in FIG. 2B. In (d), the secondary molded product is biaxially stretch blow-molded with a surface-treated secondary mold, and the secondary mold is molded. Then blow molding in The product is composed of each step of heat-setting the product at a surface temperature exceeding 210 ° C. and not more than 250 ° C., preferably for about 1 to 5 seconds.

(2) Blow molding conditions The preform is preferably preheated to a temperature of, for example, about 90 to 120 ° C above its glass transition temperature (Tg). The mold temperature in the primary blow molding is preferably performed at a temperature of about 70 to 250 ° C., and if it is less than 70 ° C., the container is excessively shrunk due to heat shrinkage in the subsequent step (c), and the secondary metal in the step (d). Since the amount of processed containers in the mold blow becomes too large, it becomes a container with poor molding or inferior heat resistance of the knitted meat or meat reservoir, and when it exceeds 250 ° C, the primary molded product is fused to the mold, Damage may occur. When the primary blow mold temperature is 210 ° C. to 250 ° C., the above problem is solved by coating the mold surface with a fluororesin.
In the present invention, the blow molding in the secondary mold is performed by heat setting the blow molded product at a surface temperature of more than 210 ° C. and not more than 250 ° C. after blow molding in the secondary mold. It is efficient to set the secondary mold temperature to 210 ° C to 250 ° C.
The pressure fluid for blowing is preferably air or heated air for convenience. Blowing air pressure is normal 2-4MPa Degree.
The draw ratio in the biaxial stretch blow molding is preferably about 2 to 5 times in length and width in the primary blow, and about 1.1 to 2.0 times in length and width in the two-stage blow. In particular, the transverse stretch ratio of the primary blow is preferably 3 to 5 times, and the longitudinal stretch ratio is preferably 2 to 4 times.
In general, the mouth portion of the container (not shown in particular) is not stretched due to the structure of the mold. Therefore, prior to the primary blow molding, for example, as disclosed in Japanese Patent Application Laid-Open No. 2002-145238 (see abstract). Crystallization by heating improves strength and heat resistance. Further, a reinforcing structure such as a bead or a rib for reinforcement can be formed on the container at the time of molding.

(3) Preform The preform is formed by an ordinary means such as an injection molding machine, an extrusion molding machine, or a compression molding machine, and is preferably made of thermoplastic polyethylene terephthalate (commonly known as PET), but other polyesters may also be used. Can be used. In addition, a laminated preform can be used as appropriate. For example, when laminated with polyamide or eval, the oxygen shielding property is improved. In addition, an oxygen absorption layer may be provided in the intermediate layer to improve oxygen absorption.

(4) Specific process In the present invention, in the above-mentioned process, the primary molded product is heated to shrink freely to be highly crystallized to remove molding distortion, thereby forming a secondary molded product, and blow molding in the secondary mold. The product is characterized by heat-setting the crystal state by heat setting at a surface temperature exceeding 210 ° C. and below 250 ° C. In such blow molding, heat shrinkage and heat setting are performed at a very high temperature. Therefore, it is considered that a high retort characteristic can be obtained as shown in Examples described later.

(5) Surface-treated secondary mold In the present invention, the secondary molded product is also characterized by biaxial stretch blow molding using a surface-treated secondary mold, thereby exceeding 210 ° C to 250 ° C. Even if second-stage blow molding is performed at the following high temperature, the suitability of the retort treatment can be improved without causing wrinkles, surface roughness, or uneven thickness on the surface of the molding container. When blow molding is performed at a high temperature using a secondary mold that is not surface-treated, a part of the polyester resin, its oligomer, or additive is deposited on the mold surface, causing minute wrinkles and rough skin on the surface of the molded product, and blowing. During molding, the flow of the molding material becomes worse on the surface of the mold, resulting in a thin thickness, which deteriorates the retort suitability of the molding container.

  The surface treatment is performed by coating a fluororesin or a silicone resin. As the fluororesin, it is preferable to use tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA) or polytetrafluoroethylene (PTFE) from the viewpoint of heat resistance, peeling resistance, and scratch resistance of the coating resin.

(6) Thickness reduction rate The present invention is characterized in that biaxially stretched blow molding is performed by the surface-treated secondary mold so that the thickness reduction rate of the body portion of the container is 5 to 30%. .
The thickness reduction rate is the thickness reduction rate, where t _{1 is} the thickness of the barrel in the secondary molded product after heat shrinkage, and t ₂ is the thickness of the barrel of the heat-set container after the second blow molding. = {(T ₁ −t ₂ ) / t ₂ } × 100 (%).
If it is less than 5%, minute wrinkles are likely to occur on the surface of the container, and if it is 5 to 30%, the heat resistance of the container will be good.

2. Polyester container (1) Retort function The polyester container produced by the method for producing a container of the present invention described in detail above has high heat resistance and particularly excellent retort suitability, and is 1 to 50 minutes at 125 ° C. The container is not deformed or shrunk as much as possible even under high temperature and long time severe retort treatment conditions such as the retort treatment, and it is highly practical and suitable as a retort container for food and drink.
Specifically, the retort-compatible polyester container of the present invention exhibits the characteristics of a container suitable for retort that the shrinkage capacity of the container treated with an autoclave at 125 ° C. for 30 minutes is 1% or less.
The retort condition is illustrated as a simplified graph in FIG. The retort conditions (hot water shower, isobaric control 2.45 kgf / cm ² ) in FIG. 5 are such that the retort starts from the liquid temperature 20 ° C., the liquid temperature 125 ° C. and the retort kettle internal pressure 2.45 kgf / cm ² in 20 minutes. Control (time proportional control), and after retorting for 30 minutes, the liquid temperature is controlled to 20 ° C. and the pressure in the retort kettle to atmospheric pressure in 20 minutes.

(2) TMA measurement characteristics The retort-compatible polyester container of the present invention is characterized by having a shrinkage start temperature of 120 ° C. or more in the circumferential direction of the container in TMA measurement, and exhibits excellent heat resistance. TMA no-shrink temperature characteristics are also presented in Table 1 in each example.
This is illustrated in the graph of FIG. 2, where the horizontal axis represents the temperature rise (° C.) and the vertical axis represents the length variation (μm) of the sample piece. Once the temperature rises (extends) and exceeds the maximum point, it starts to fall (shrink). The container of the present invention has a temperature at the maximum point of 120 ° C. or higher.
The TMA measurement conditions in FIG. 2 are: test piece cut-out size 5 × 40 mm, distance between test piece gauge points 20 mm, load 0 [N], heating at heating rate 5 ° C./min, measurement start point (reference The point) is the length of the sample piece at a temperature of 75 ° C.
The sample piece sampling position and test piece of the TMA measurement of the container are illustrated in the schematic diagram of FIG.

3. Molding Material for Polyester Container (1) Polyester Material As a material constituting the polyester container of the present invention, thermoplastic polyethylene terephthalate (PET) is most preferable from the viewpoints of performance and price.
Further, as the ethylene terephthalate thermoplastic polyester, a thermoplastic polyester resin in which most of the ester repeating units, generally 70 mol% or more, particularly 80 mol% or more are occupied by ethylene terephthalate units is suitable.
In addition, any polyester resin that can be biaxially stretch blow molded and crystallized can be used. Polyester such as polybutylene terephthalate or polyethylene naphthalate, or these polyesters and polycarbonate or acrylate resin, etc. Mixtures can also be used.

(2) Laminate Material Polyethylene terephthalate and other resins can be laminated and used. Moreover, the polyester container of this invention is good also as a multilayer structure which provided the oxygen shielding layer and the oxygen absorption layer in the intermediate | middle layer of the polyester resin layer which comprises an inner and outer layer. Oxygen shielding and oxygen absorption enhance the resistance of stored food and drink to microbial decay and chemical alteration.
Examples of the thermoplastic resin constituting the oxygen shielding layer include an ethylene-vinyl alcohol copolymer and polyamide.
As the oxygen absorbing layer, for example, a layer in which an oxygen absorbent is blended in a resin is used, and examples of the oxygen absorbent include metal powder having reducibility.

(3) Additives Various known additives can also be used. If necessary, a filler, a colorant, a heat stabilizer, a weather stabilizer, an antioxidant, an anti-aging agent, a light stabilizer, an ultraviolet absorber, an antistatic agent, a lubricant and the like may be blended.

Next, the present invention will be described by way of examples by way of examples and comparative examples for comparison, but these show preferred embodiments of the present invention, which make the present invention clearer and more flexible in its scope. It will manifest more widely.
[Explanation of embodiments with drawings]
Each process of (a)-(d) in the manufacturing method of the retort correspondence container by the two-stage blow molding method of this invention is typically shown as a schematic diagram in FIG. Specific details are described in paragraph 0017 above.

[Example 1-1]
A retort-compatible PET bottle by the biaxially stretched two-stage blow molding method of the present invention was produced along the steps (a) to (d) schematically shown in FIG.
(1) Primary blow molding After preliminarily crystallizing (whitening) the mouth of a preform made of polyethylene terephthalate resin by heating means, the preform is heated to 110 ° C. above the glass transition point, and the mold temperature is Biaxial stretch blow molding with a stretch ratio of 3 times in length and 4.5 times in width was performed by a primary mold at 160 ° C. to obtain a primary molded product.
(2) Heat Shrinkage Next, the obtained primary molded product was heated and shrunk in a heating oven so that the surface temperature was 200 ° C. to obtain a secondary molded product.
(3) Secondary blow molding Next, the secondary molded product subjected to heat shrinkage is a secondary mold in which the mold temperature is 245 ° C. and the PFA fluororesin coating treatment is performed. .06-fold biaxial stretch blow molding was performed.
(4) Heat set
The body and bottom, excluding the mouth, were heat-set at 245 ° C for 5 seconds, the full volume was about 333.5 ml, the cross-sectional shape was almost circular except for the body panel, and the body panel was surrounded by a vacuum absorbing panel. Since it has six sides in the direction (the three sides of the panel are visible from the front in FIG. 3), it is a substantially regular hexagonal polyester container.

[Example 1-2 to Example 2 and Comparative Example 1-1 to Comparative Example 2-2]
Blow molding was performed under the conditions described in Table 1 based on the biaxially stretched two-stage blow molding in Example 1-1.
The molding conditions and results of each Example and each Comparative Example are summarized in Table 1. The measurement position of the wall thickness is shown in FIG. An empty bottle before filling and a bottle after retorting in Example 1-1, a bottle after filling and retorting in Example 1-3, and a bottle after filling and retorting in Comparative Example 1-2, respectively. 6 and 7 are illustrated as photographic diagrams. The bottles after filling and retorting in Examples 1-1 and 1-3 have no change in the shape of the container, but in the bottle after filling and retorting in Comparative Example 1-2, the neck is deformed and thinned. Yes.

[Consideration of results of Examples and Comparative Examples]
By comparing each example and each comparative example, the polyester container of the present invention and the method for producing the same can impart a retort function to the polyester container at the same time by a simple and economical method. Can be used as a retort container for foods and beverages without causing deformation or shrinkage of the container as much as possible even under high temperature of 1-50 minutes of retort treatment at 125 ° C. It has been made clear.
Specifically, in contrast to each example and each comparative example, in Example 1-1 to Example 1-3, a secondary blow mold having a PFA fluororesin coating treatment applied to the molding surface of the mold, By using at 215 to 245 ° C, the heat setting temperature of the PET bottle increased, but the releasability of the PET bottle from the mold was good, and there were abnormalities in the appearance and knitted meat of the mold and the PET bottle. Moreover, the retort resistance of the container was also improved. (See Figure 6)
In Example 2, a secondary blow mold having a PTFE (polytetrafluoroethylene) fluororesin coating treatment applied to the molding surface of the mold was used, but no abnormality was observed in both the PET bottle and the beverage storage product.
In contrast, Comparative Example 1-1 has a secondary blow mold temperature (heat set temperature) that is too high, and Comparative Example 1-2 has a secondary blow mold temperature (heat set temperature) that is too low. Since the requirements of the invention were not satisfied, the retort resistance was poor. (See Figure 7)
In Comparative Examples 2-1 and 2, the temperature of the secondary blow mold (heat set temperature) satisfies the requirements of the present invention, but the secondary mold is mirror-finished on the mold product surface as usual. Since it was applied or moderately damaged with a file, the mold release was poor.

It is the schematic which shows typically each process of the manufacturing method of the retort corresponding | compatible container by the biaxial stretching two-stage blow molding method in this invention. It is a graph showing the TMA measurement characteristic in this invention. It is the schematic showing the sample piece sampling position and test piece of TMA measurement of a container. It is the schematic showing the position which measured the thickness of PET bottle. It is a graph which shows retort conditions. It is a photograph figure showing the PET bottle before filling and the PET bottle after retorting. It is a photograph figure showing the PET bottle after retorting in comparative example 1-2.

Claims (3)

A preform formed from a polyester resin is biaxially stretched and blow molded with a primary mold to form a primary molded product. The primary molded product is heated to shrink to form a secondary molded product, and the secondary molded product is coated with a fluororesin. The biaxially stretched blow molding is performed with the secondary mold surface-treated by the above, and the surface temperature of the blow molded article is heat-set at a temperature exceeding 210 ° C and not more than 250 ° C in the secondary mold as it is. A method for producing a retort-compatible polyester container. The method for producing a retort-compatible polyester container according to claim 1, wherein the fluororesin is tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA) or polytetrafluoroethylene (PTFE). The biaxially-stretched blow molding in the secondary mold is formed so that the thickness reduction rate of the container body is 5 to 30%. A method for producing a retort-compatible polyester container.

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