JP4550700B2 - Method for producing heat-resistant polyester container - Google Patents

Description

  The present invention relates to a method for producing a heat-resistant polyester container. More specifically, the present invention relates to a method for producing a heat-resistant polyethylene terephthalate bottle container.

  A stretch blow molded container (PET bottle) made of polyethylene terephthalate has extremely excellent transparency, excellent gas barrier properties and moisture impermeability, and has excellent content resistance and storage stability. It is used in large quantities for many applications including

  However, ordinary PET bottles have the disadvantage of being inferior in heat resistance such as causing heat shrinkage deformation. For this reason, for applications in which a heat-sterilized beverage or the like is filled at a high temperature, thermal deformation or shrinkage deformation of the volume (hereinafter simply referred to as “thermal deformation or the like”) occurs. Therefore, for such applications, heat-resistant PET bottles (heat-resistant polyester containers) in which stretched blow-molded bodies are crystallized by heat setting (heat set) after molding to increase heat resistance are used. .

As a method for producing such a heat-resistant PET bottle, the molded body after heat setting is cooled to some extent, taken out from the mold at a relatively high temperature, and then the taken-out molded body is annealed (removed) in an air-cooled atmosphere. There has been proposed a method of obtaining a heat-resistant PET bottle by shrinking the volume of the formed body (free shrinkage) by removing distortion by cooling (see, for example, Patent Documents 1 and 2).
JP 58-162321 A JP-A 63-185620

  In these conventional manufacturing methods, it is necessary to cool and harden the entire molded body to some extent so that a desired shape can be maintained (maintained) even after taking out from the mold after heat setting. Therefore, it has been proposed to cool the cooling fluid such as cooling air by circulating it from the bottom to the inside of the molded body before taking it out of the mold.

  However, the cooling fluid sprayed on the bottom of the molded body is heated until it circulates and reaches the top. Therefore, it is necessary to circulate a large amount of cooling fluid in order to sufficiently cool the upper part of the molded body so that a desired shape can be maintained even when taken out from the mold. As a result, the energy efficiency in the production process of the heat resistant polyester container becomes very poor.

  Furthermore, in a molded body manufactured by a conventional manufacturing method in which a cooling fluid is circulated and cooled, if it is cooled to the upper part of the molded body and almost completely cured before annealing, free shrinkage occurs at that time. The overall shape (particularly the upper shape) may be greatly distorted, resulting in a problem that a large number of defective products are generated.

  Then, this invention makes it a subject to provide the manufacturing method of the heat resistant polyester container which is energy efficient in a production process, and is hard to be distorted at the time of annealing in view of this situation.

  In order to solve the above problems, in the method for producing a polyester container according to the present invention, a polyester preform heated to 80 ° C. or more and 130 ° C. or less is stretch blow molded in a mold, and then a high temperature of 130 ° C. or more and 180 ° C. or less. The inner surface of the molded body thus obtained was cooled by spraying a cooling fluid from a plurality of blowing holes provided along the longitudinal direction of the drawing rod, and the molded body was taken out of the mold and allowed to cool. Annealing is performed in an atmosphere so that the shrinkage rate of the outer volume of the molded body with respect to the inner volume of the mold is freely shrunk so as to be larger than 3.0% and not more than 6.0%.

  According to the above manufacturing method, the molded body that is heat-set after being stretch-blow-molded in the mold has the cooling fluid blown out almost simultaneously from the plurality of blow-out holes provided along the longitudinal direction of the stretch rod. By spraying on the inner surface, the entire inner surface of the molded body is cooled and cured in a well-balanced manner.

  Then, even if the outer surface portion of the molded body is not sufficiently cooled and is not sufficiently cured, the inner surface portion of the cooled and cured molded body supports another portion (the outer surface portion of the molded body). As a result, the shape of the molded body can be maintained (maintained), so that the molded body can be taken out from the mold even when the entire molded body is at a higher temperature than the conventional manufacturing method.

  Accordingly, since it is not necessary to cool the entire molded body more than necessary, the amount of cooling fluid required for cooling is less than when cooling the cooling fluid by circulating it from the bottom of the molded body. Energy efficiency is improved in the process.

  Furthermore, when the molded body is taken out from the mold at a high temperature and annealed in a cooling atmosphere, the shape is greatly distorted by free shrinkage unless the whole is cooled and cured to some extent if it is a conventional manufacturing method. . However, since the inner surface portion of the molded body is cured by being cooled in a well-balanced manner (that is, it is difficult to expand and contract), even if other portions are freely contracted by annealing, a large distortion is caused. Occurrence can be suppressed.

  That is, the inner surface portion of the molded body is cooled and cured in a well-balanced manner, so that the molded body is removed from the mold at a high temperature and sufficiently annealed (excluded) in order to increase resistance to future thermal deformation. Even if it is free-shrinked by removing distortion due to cooling, a molded body having a desired shape can be obtained without the entire shape being greatly distorted.

  Furthermore, by making the shrinkage rate larger than 3%, the molded body is more resistant to thermal deformation of the molded body due to heat at the time of filling the contents. For example, a molded body (polyester container) is sealed with a lid after filling a content such as a high-temperature sterilized beverage at the time of use. Thereafter, the product is cooled and returned to room temperature before being shipped, but the resistance to deformation of the molded body due to the high temperature of the contents at that time becomes strong (that is, it becomes difficult to deform). As a result, troubles such as clogging caused by the deformation in the production line, the packing work line, and the like when sticking the label to the molded body can be prevented, for example.

  Further, in the present invention, since the inner surface portion of the molded body is cured in a well-balanced manner, the heat resistance against thermal deformation and the like is enhanced as long as the shrinkage is larger than 3% and 6% or less. At the same time, the large distortion of the molded body during annealing can be sufficiently suppressed.

In addition, according to the cooling, the cooling fluid is sprayed so as to form a columnar shape-retaining portion and concentrated cooling is performed, and a plurality of blowing holes are provided along the longitudinal direction of the extending rod as described above. Therefore, the entire inner surface portion of the molded body is cooled and cured in a well-balanced manner. In addition, a part of the obtained molded body is centrally cooled in a columnar shape by a cooling fluid, thereby forming a columnar shape-retaining portion that cools and cures faster than other portions.

  Therefore, when taking out from a metal mold | die, it becomes easier to maintain a shape, even if the temperature of the whole molded object is high. Furthermore, since it is easier to maintain the shape when annealing in a cooling atmosphere, it is possible to suppress the occurrence of large strains even when sufficiently contracted freely. Accordingly, it is possible to obtain a polyester container having a higher heat resistance than a small amount of thermal deformation.

  Moreover, it is preferable to cool so that a plurality of the columnar shape retaining portions are formed on the peripheral side portion of the molded body.

  According to the above manufacturing method, since a plurality of columnar shape retaining portions are formed on the peripheral side portion of the molded body, the suppression of distortion in the length direction of the molded body becomes stronger, and thus a straight molded body is obtained. It becomes easy.

  As mentioned above, according to the manufacturing method of the polyester container of this invention, the energy efficiency in the production process of a container (molded object) can be improved. Furthermore, it is possible to provide a method for producing a polyester container which is resistant to future thermal deformation and the like, and can keep the shape of the container in a desired shape against free shrinkage during annealing.

  Hereinafter, although the manufacturing method of the polyester container (henceforth a "container") 1 which concerns on one Embodiment of this invention is demonstrated based on an accompanying drawing, this invention is limited only to these embodiment. Instead, various modifications can be made without changing the gist of the present invention.

  First, the basic configuration of the container 1 manufactured by the manufacturing method according to the present embodiment will be described.

  As shown in FIGS. 1A and 1B, the container 1 includes a mouth portion 2, a shoulder portion 3, a trunk portion 4, and a bottom portion 5 in order from the top.

  The mouth 2 has a thread 6 and a support ring 7 that can be fitted to a cap (lid), and has a substantially circular cross section.

  The body portion 4 is formed in a substantially quadrangular shape with a transverse section having a corner portion 8 as a short hypotenuse. The four side edges 9 form a reduced pressure absorption panel 10 provided on the periphery of the trunk portion. The reduced pressure absorption panel 10 is a part for absorbing thermal expansion and contraction of the contents by deformation.

  Further, the corner portion 8 forms a column portion 11 provided on the circumferential side portion of the trunk portion. This column part 11 is a site | part for maintaining the shape of the container 1 with respect to external force.

  Moreover, in this embodiment, although the cross section of the trunk | drum 4 of the container 1 is substantially square shape, it is not necessary to limit to this shape and polygons, such as a hexagon, may be sufficient. Also in that case, it is preferable that the corners 8, 8,. The cross section may be circular.

  In the case of the present embodiment, as will be described later, since the part to be concentrated and cooled after the heat fixation at the time of manufacture is the same part as the pillar part 11, the columnar shape retaining part 11 that is less likely to expand and contract than other parts during annealing. 'Is formed in the same part as the column part 11, but the columnar shape retaining part 11 ′ and the column part 11 may be formed in different parts.

  The shoulder portion 3 is a portion connecting the body portion 4 having a substantially square cross section and the mouth portion 2 having a substantially circular shape, and the cross section gradually changes from a substantially square shape to a substantially circular shape from the lower end toward the upper end. It is formed to do.

  Next, as shown in FIGS. 2 (a) and 2 (b), the basic structure of a mold part 20 of a biaxial stretch blow molding apparatus (hereinafter simply referred to as "molding apparatus") for molding the container 1 is used. A simple configuration will be described.

  The mold part 20 of the molding apparatus includes a blow mold 21, a bottom mold 22, and a stretching rod 23.

  The stretching rod 23 functions as a stretching rod and also serves as a cooling air supply pipe that blows cooling air A onto the inner surface of the molded body (container) 1, so that a cooling air supply path 24 is provided in the axial direction of the stretching rod 23. Is formed.

  As shown in FIGS. 2A and 2B, the extending rod 23 is provided with a plurality of air blowing portions for blowing out the cooling air A along the length direction. This air blowing portion is blown out into a portion that radiates from the axial center of the extending rod 23 and divides the periphery at equal intervals so that a plurality of columnar shape retaining portions 11 ′ are formed by blowing the cooling air A. A plurality of air blowing portions having four 25 are provided along the longitudinal direction.

  When the columnar shape retaining portion 11 ′ is formed by blowing the cooling air A from the air blowing portion, the cooling air is almost simultaneously emitted from the plurality of air blowing portions provided along the longitudinal direction of the extending rod 23. A is blown out toward the inner surface of the molded body 1. As will be described later, by this blowing, a columnar shape retaining portion 11 ′ is formed, and the entire inner surface portion of the molded body (container) 1 is cooled in a well-balanced manner.

  Next, the preform (parison) 30 used for biaxial stretch blow molding will be described.

  As shown in FIG. 3, the preform 30 is formed in a test tube having a mouth portion 31.

  The preform 30 is formed by injecting and filling polyethylene terephthalate melted by an injection molding machine into a mold by applying pressure, cooling and taking out. At that time, the bottomed preform 30 provided with the mouth portion 31 corresponding to the final container 1 is formed in an amorphous state.

  The preform 30 is formed of a thermoplastic resin made of polyethylene terephthalate. However, the thermoplastic resin may be a polyester in which a small amount of a copolymerization component is copolymerized. An appropriate amount of an additive such as an inhibitor, a thermal degradation inhibitor, an ultraviolet degradation inhibitor, an antistatic agent, an antibacterial agent, or the like may be added.

  Next, the manufacturing method of the polyester container which concerns on this embodiment is demonstrated, referring FIG. 2 (A) and (B).

  First, the preform (parison) 30 is heated to a stretching temperature of 80 ° C. or higher and 130 ° C. or lower before stretch blow in a preform heating section of a stretch blow molding machine. The temperature is the temperature of the mold surface, and in the present embodiment, it is preferably 100 ° C. or higher and 120 ° C. or lower.

  Next, the preform 30 is supplied into the space formed by the mold 21 and the bottom mold 22, and the stretching rod 23 is inserted into the preform 30, and the bottom thereof is stretched in the axial direction by the stretching rod 23.

  In addition, almost simultaneously with the stretching of the preform 30 in the axial direction, the preform 30 is stretched in the radial direction by blow air to perform biaxial stretching blow molding to a predetermined shape. Heat to below ℃ and heat fix. The temperature is the temperature of the mold surface, and in the present embodiment, it is preferably 140 ° C. or higher and 160 ° C. or lower.

  Thereafter, cooling air A is blown onto the inner surface of the molded body 1 through the extending rod 23, and columnar shape-retaining portions (that is, columnar portions that are less likely to shrink during annealing than other portions due to cooling) on the corners 8. Concentrated cooling is performed so that 11 'is formed.

  In the present embodiment, the cooling air A is used as a cooling fluid for cooling the molded body 1, but other cooling fluid may be used.

  Next, the molded body 1 is taken out from the mold 21. At this time, in the present embodiment, the outer surface temperature of the shape-retaining portion 11 ′ after about 0.5 seconds is about 130 ° C. to 132 ° C.

  In this way, by cooling the inner surface portion of the molded body 1, the shape retaining portion 11 ′ is formed, so that the outer surface temperature at other parts other than the shape retaining portion 11 ′ of the molded body 1 is about 130. The shape of the molded body 1 can be maintained even when the temperature is higher than ℃ to 132 ° C., and the molded body 1 can be taken out from the mold 21.

  In the conventional manufacturing method, the cooling air A is blown out to the bottom of the molded body 1 and circulated to cool the shoulder. Therefore, even if the bottom is cooled to such an extent that the shape can be maintained, the shoulder is not sufficiently cooled to maintain the shape, and the molded body 1 can maintain the overall shape even when taken out from the mold. There wasn't. Therefore, the shape of the molded body cannot be maintained unless it is taken out from the mold after being cooled and cured until the temperature of the entire molded body becomes 120 ° C. or lower.

  In contrast, in the present embodiment, as described above, the columnar shape retaining portion 11 of the molded body 1 is cooled by cooling so that a plurality of columnar shape retaining portions 11 ′ are formed on the peripheral side portion of the molded body 1. Even if the outer surface temperature other than 'is high (higher than about 130 ° C to 132 ° C), the entire shape can be maintained. As a result, the molded body 1 can be taken out from the mold 21 at a higher temperature.

  Therefore, when the same temperature of cooling air is used, the amount of cooling air A used in this embodiment is reduced compared to the amount of cooling air used for cooling the entire container by circulating from the bottom to the shoulder.

  Thereafter, the molded body 1 taken out from the mold 21 is annealed in a room temperature atmosphere, and the molded body 1 is freely shrunk so that the shrinkage rate is greater than 3% and 6% or less. By the free shrinkage of the molded body 1 due to the annealing, the residual strain (residual stress) in the peripheral side wall of the molded body 1 is relaxed, and the dimensional stability, the deflection temperature under load, the mechanical properties, etc. of the molded body 1 are improved. As a result, the asymmetrical deformation (partial deformation) of the vessel wall is suppressed during filling of the contents at high temperature and heat sterilization of the molded body 1.

  Further, in the present embodiment, after forming a plurality of columnar shape retaining portions 11 ′ on the peripheral side portion of the molded body 1, the shrinkage rate is more than 3% and not more than 6% by annealing because it is taken out from the mold. Even if free contraction is performed, it is possible to suppress the overall shape from being greatly distorted.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples.

<Example>
(1) Preform molding by injection molding machine Using polyethylene terephthalate, a bottomed preform having a test tube shape was injection molded by an injection molding machine.

(2) Blow molding and heat setting with a biaxial stretch blow molding machine The preform obtained in (1) above was molded with a stretch blow molding machine. Specifically, using a biaxial stretch blow molding machine, the preform is heated until the surface temperature becomes 100 to 120 ° C., and the pressure of 38 kg / cm ² is increased with the rise of the longitudinal stretching rod in the mold. Biaxial stretch blow molding was performed to obtain a molded body (blow container) 1.

  Next, the mold 21 and the bottom mold 22 were heated until the surface temperature (heat setting temperature) reached 140 to 160 ° C., and held in that state, and the molded body 1 was heat set. It is assumed that the surface temperature of the bottom mold 22 is lower than the surface temperature of the mold 21.

(3) Cooling and annealing of the molded body The molded body 1 obtained in the above (2) is centrally cooled from the inside by the cooling air A blown out from the stretching rod 23 to centrally cool the columnar shape-retaining part 11 ′. Formed. Then, it took out from the metal mold | die 21 in the range whose outer surface temperature of the column part 11 of the molded object 1 is about 130 to 132 degreeC, and annealed in indoor atmosphere.

  The outer surface temperature of the column 11 is fixed in a stretch blow molding machine with a measuring device (radiation temperature sensor FTH30 manufactured by Keyence Corporation) so that the sensor faces the molded body 1 taken out of the mold. The outer surface temperature of the molded body 1 0.5 seconds after taking out from the mold is measured.

  At this time, the cooling time with cooling air A is adjusted, the shrinkage rate of free shrinkage during annealing is changed, the amount of cooling air A used due to the change in shrinkage rate, and the occurrence rate of defective products are measured, and the results are shown. It was shown in 1.

<Comparative example>
A molded body was produced in the same manner as in the example except that the shrinkage ratio during annealing was 3.0% or less or greater than 6.0%. As in the example, the amount of cooling air A used and the rate of occurrence of defective products were measured, and the results are shown in Table 1.

上記表１において、冷却エアーの使用量は、実施例１での使用量を１とした場合の使用量である。

In Table 1 above, the amount of cooling air used is the amount used when the amount used in Example 1 is 1.

  As a result, when the shrinkage rate is larger than 3.0%, it can be evaluated that the energy efficiency is improved by reducing the amount of cooling air A used. When the shrinkage rate is 6.0% or less, the defective product generation rate due to distortion is in the manufacturing stage. It was possible to evaluate that it was within the permissible range. Further, as a result of examining both values of energy efficiency and defective product occurrence rate, in this example, it is preferable that the shrinkage rate is 3.2% or more.

(A) is a front view of the polyester container manufactured by the manufacturing method which concerns on this embodiment, (b) shows (alpha)-(alpha) sectional drawing in a front view. (B) is a schematic diagram of a longitudinal section of a mold part of a biaxial stretch blow molding machine used in the manufacturing method according to the embodiment, Show. The front view of the preform used for the manufacturing method which concerns on the embodiment is shown.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Heat-resistant polyester container (Polyethylene terephthalate bottle container, heat-resistant PET bottle, or molded object), 11 '... Shape retention part, 20 ... Mold part of a biaxial stretch blow molding machine, 21 ... Mold, 22 ... Bottom Mold, 23 ... Extension rod, 24 ... Cooling air supply path, 25 ... Cooling air blowout hole, 30 ... Preform (parison), A ... Cooling air

Claims (2)

A polyester preform heated to 80 ° C or higher and 130 ° C or lower is stretch blow molded in a mold, and then heat-set at a high temperature of 130 ° C or higher and 180 ° C or lower. Cooling fluid is sprayed from a plurality of blowout holes provided along the longitudinal direction of the drawing rod so that a columnar shape-retaining portion is formed on the molded body to perform intensive cooling, and the molded body is taken out from the mold and released. Production of a heat-resistant polyester container characterized by annealing in a cold atmosphere and free shrinking so that the shrinkage ratio of the outer volume of the molded body with respect to the inner volume of the mold is greater than 3.0% and not more than 6.0% Method. The columnar shape retention portion The method for producing a heat-resistant polyester container of claim 1, wherein the cooling to be more formed on the peripheral side portion of the molded body.

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