JPS6220012B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for molding a biaxially stretched blow container made of thermoplastic polyester. Conventionally, the so-called injection oriented blow molding method or biaxial stretch blow molding method has been used as a molding method for thermoplastic polyester containers. The manner in which this molding method is carried out is as follows, as shown in FIGS. 1 to 5. First, a polyester resin 1 is injected from an injection molding machine 2 into a mold 6 consisting of a male mold 3, a lip mold 4, and a female mold 5 to obtain a bottomed parison 7 (first
figure). Next, while holding the threaded part 8 of the bottomed parison 7 in the lip mold 4, the parison is placed in the heating pot 9.
, and place the inner and outer surfaces of the bottomed parison 7 on the heating core 1.
0 and the heaters 11 and 12 of the heating pot 9 (Fig. 2). The heated parison 7 is transferred to a stretching blow mold 13 and stretched in the axial direction by a stretching rod 14 (FIG. 3). Next, pressurized air 15 is blown into the bottomed parison 7 to stretch it in the lateral direction, thereby performing blow molding (FIG. 4). The stretch blow mold 13 is removed from the stretched bottomed parison 7, that is, the molded product 7', and the lip mold 4 is divided and removed from the molded product 7' (FIG. 5). The polyester molded article, ie, the container, obtained by the above method is a high-quality container with excellent mechanical strength, barrier properties against water, oxygen, odors, etc., protection of contents, and aesthetic appearance. However, even when the container is left at room temperature as well as at high temperatures, there is a problem in that the stretched and oriented wall surface shrinks and the internal volume changes. When the internal volume changes, the liquid level of the contents filled into the container changes when the contents are injected into the container. Especially when controlling the process based on the liquid level, for example, the liquid level height changes. This has an undesirable effect on the method of quantifying the contents of the container by weighing the amount. Also, depending on the type of content, heat filling, heat sterilization, heat sterilization, etc. at high temperatures of 70 to 80 degrees Celsius may be necessary, but if heat filling is performed at a temperature of 70 degrees Celsius or higher, the internal volume will increase. There are serious restrictions in terms of use, such as changes due to shrinkage or unsightly deformation, making it unusable, and the development of high-temperature heat-resistant containers is desired. As a countermeasure to this problem, there is a method of carrying out blow molding while maintaining the blow mold temperature at a temperature lower than the glass transition temperature of polyethylene terephthalate and at least 10°C lower than the glass transition temperature, as shown in Japanese Patent Application Laid-Open No. 53-74570. Proposed. However, although the polyester containers obtained by this method have improved heat shrinkage resistance to some extent than containers obtained by the normal stretch-blowing method, when the containers are filled with heat at 70°C or higher, the inner volume decreases due to shrinkage. It has the disadvantage of changing or deforming,
It is not necessarily practical as a heat-resistant container. The present inventors have an object to provide a biaxially oriented polyethylene terephthalate container that is free from such drawbacks and retains the mechanical strength, gas barrier properties, chemical resistance, aesthetic appearance, etc. inherent to polyethylene terephthalate. As a result of intensive studies aimed at this purpose, it was discovered that the above object can be achieved by controlling the temperature of the blowing mold and the temperature of the blown gas within a certain range, and the present invention was achieved. That is, when molding a biaxially stretched blow container made of thermoplastic polyester, the present invention maintains the temperature of the blow mold within a temperature range that satisfies the following formula () and stretches the heated bottomed parison in the axial direction. , provides a method for molding a thermoplastic polyester container, characterized in that the parison is expanded and stretched in the transverse direction by blowing pressurized gas heated to a temperature range satisfying the following formula () into the parison. (Tg−15)<MT<Tg......() 140<(AT+MT)<190...() In the formula, Tg is the glass transition temperature of thermoplastic polyester (℃), and MT is the blowing mold temperature (℃)
and AT indicates the heated and pressurized gas temperature (°C). More preferably, after stretching in the transverse direction, a method of quenching the stretched molded container by blowing gas at room temperature or lower temperature therein is used in combination to more effectively achieve the above object of the present invention. Specifically, the method of the present invention will be explained in detail with reference to the drawings. FIG. 6 is an enlarged view of one apparatus for specifically carrying out the stretching operation and blow molding operation shown in FIGS. 3 and 4, in which the bottomed parison 7 is attached to the lip mold 4. Stretch blow mold 13
There is no difference from the conventional apparatus in that these are placed on top and the drawing rod 14 is present inside the bottomed parison 7. In addition, an eccentricity prevention rod 1 is attached to the bottom of the mold 13.
5 (this is indicated by a chain line) is attached, and the lower end of the stretching rod 14 has a hemispherical tip 1
4', and the rod 14 passes through the hollow body 17 via an air passage 16. The rod 14 can be moved up and down by a hydraulic device 18, and in FIG. 6, the state when it moves up is shown by a solid line, and the state when it moves down is shown by a chain line. It is shown. An air introduction pipe 20 from a pressurized air tank 19 communicates with the air passage 16 . A valve 21 is installed in the middle of the pipe 20. The above summary is also necessary for the conventional device, but in the device used in the method of the present invention, a heated air tank 22 is provided outside the tank 19 and communicates with the pipe 20. ing. Of course, as long as the heated air tank 22 is capable of introducing air from the pressurized air tank 19 through the air introduction pipe 23, heating it and introducing it into the introduction pipe 20 or the air passage 16, Any means may be adopted. Therefore, for example, a pipe structure in which the introduction pipe 20 is branched into two parts and then merged,
For example, a structure in which a heater can be inserted into one tube to form a heated air flow and an unheated air flow may be used. The method of the present invention using the apparatus having the above structure is carried out by the following operations. After performing the operations up to the steps shown in FIG. 2, the bottomed parison 7 and the lip mold 4 are moved to the stretch blow molding process.
(solid line diagram in Figure 6). Next, the hydraulic system 18 is operated to release the rod 14.
(Figure 6, chain line diagram). Then, the bottomed parison 7 is stretched. Simultaneously with the stretching, or subsequently, heated air is pumped into the air passage 16 from the heating tank 22. However, since the rod tip 14' has already started or is descending, heated air is forced into the interior 7'' of the bottomed parison 7 from between it and the hollow body 17, and resists the pressure. The bottomed parison 7 is
It expands to the inner surface 13' of the mold 13. Stretch blow molding therefore takes place and a molded article 7' (indicated by a dashed line in FIG. 6) is obtained. In the present invention, the temperature MT of the stretch blow mold 13 during the above operation is set between the glass transition temperature (Tg) of the thermoplastic polyester and (the glass transition temperature -15
℃), and the stretching blow mold temperature MT as heated air i.e. heated pressurized gas temperature AT
It is important to adopt a temperature range in which the sum of If the temperature MT of the stretch blow mold is higher than the glass transition temperature, the molded container will not be sufficiently cooled and will be easily deformed, the transparency will decrease, and furthermore, a whitening phenomenon will occur due to crystallization, which is undesirable. In addition, the mold temperature MT is (glass transition temperature - 15
℃) is not preferable because a container with excellent heat shrinkage resistance, which is the object of the present invention, cannot be obtained. Furthermore, if the sum of the heated and pressurized gas temperature AT and the stretch blow mold temperature MT is below 140°C, the shrinkability of the molded container, which is the object of the present invention, cannot be improved, and if it exceeds 190°C, This is undesirable because the stretching effect is lowered and the strength of the molded container is likely to decrease, and a whitening phenomenon due to crystallization occurs. Thus, after stretch blow molding, the heated air within the molded article 7' is then evacuated therefrom. The degassing method may be to blow cooled air and use it to replace the gas in the molded product 7', or to actively degas it by passing the gas inside the molded product 7' to a vacuum source. It's okay to worry about it. Although such equipment is not shown in FIG. 6, known equipment may be used. When the heated air is exhausted from the molded product 7', cooling air is supplied from the pressurized air blowing tank 19 to the molded product 7'.
The molded article 7' is cooled to about room temperature. This cooling can prevent the molded product 7' from becoming cloudy. A polyester having ethylene terephthalate as a main repeating unit, which is a preferable thermoplastic polyester for forming the molded article or container of the present invention, is one in which 80 mol% or more of the repeating units constituting the polyester is composed of ethylene terephthalate.
As starting materials, in addition to terephthalic acid or its alkylene ester derivative and ethylene glycol, isophthalic acid and p-
(β-oxyethoxy)benzoic acid, naphthalene 2,6-dicarboxylic acid, diphenoxyethane-
Dicarboxylic acid components such as 4,4'-dicarboxylic acid, 5-sodium sulfoisophthalic acid, adipic acid, sebacic acid or their alkyl ester derivatives, propylene glycol, 1,4-butanediol, neopentyl glycol, 1,6- hexylene glycol, cyclohexane dimenol,
It may also contain a glycol component such as an ethylene oxide adduct of bisphenol A. These thermoplastic polyesters can be obtained by either direct esterification followed by polycondensation or transesterification followed by polycondensation. The thermoplastic polyester obtained by the above melt polymerization method may be subjected to solid phase polymerization at a temperature of 180 to 250°C under reduced pressure or in an inert gas. Furthermore, the thermoplastic polyester in the present invention may contain additives such as colorants, ultraviolet absorbers, antistatic agents, and heat stabilizers in appropriate proportions, if necessary. The average degree of polymerization of the thermoplastic polyester of the present invention is determined by taking into consideration moldability, impact resistance of the container, etc.
- The intrinsic viscosity of the chlorophenol solution at 25° C. is preferably 0.54 to 1.40, preferably 0.60 or more and 1.20 or less. The thermoplastic polyester container produced by the method of the present invention has both transparency and heat shrinkage resistance, and can withstand heat treatments such as heat filling and heat sterilization at temperatures above 70°C, which conventional polyethylene terephthalate containers cannot withstand. . Examples are shown below to further explain the effects of the present invention. The evaluation and measurement methods for the main characteristic values listed in Examples and Comparative Examples are as follows. (1) Glass transition temperature (Tg) PerkinElmer differential calorimeter (DSC-
1) at a heating rate of 10°C/min. (2) Heat filling shrinkage rate The unit weight (W) of the container immediately after molding and the approx.
After measuring the total weight (W ₁ ) of a container filled with water at 25° C. up to the mouth of the container using a Mettler balance, hot water at 70° C. to 80° C. is poured into the container up to the mouth of the container. After 30 minutes had elapsed, the hot water in the container was discarded, water was added again in the same manner as above, the total weight (W ₂ ) of the container was measured, and the volumetric shrinkage rate of the container was determined according to the following formula. (The specific volume of water at 25°C is 1) Volume shrinkage rate = W ₁ - W ₂ / W ₁ - W x 100% (3) Tensile yield stress, tensile rupture stress Specified by JIS K6301 from the body of the container. A dumbbell No. 3 test piece was punched out, and a strain rate of 50
The tension at yield and at break was measured in %/min and converted into stress per unit cross-sectional area of the original sample. Examples 1 to 4, Comparative Examples 1 to 4 Polyethylene terephthalate pellets with an intrinsic viscosity of 0.72 measured in an o-chlorophenol solution at 25°C and a Tg of 75°C were dried using a hot air dryer to reduce the moisture content.
After drying to 0.01% or less, it was molded using an injection molding machine IS-50 manufactured by Toshiba Machine Co., Ltd. and a water-cooled mold with a test tube-shaped cavity, with an outer diameter of 25 mm and a length of 95 mm.
A transparent bottomed parison with a wall thickness of 3 mm and a wall thickness of 3 mm was molded. The molding conditions are: discharge resin temperature 290℃±5℃, injection pressure 30Kg/cm ² (gauge pressure), mold temperature 30℃, injection/
The cooling time cycle is 8 seconds/10 seconds. After heating this bottomed parison to 95°C using a hot air circulation oven and an infrared heater, it has a cavity shaped like a small beer bottle with a mouth (threaded part) diameter of 25 mm, a body diameter of 64 mm, and a height of 180 mm. , transferred into a blowing mold maintained at various temperatures shown in Table 1, holding the open end, longitudinally stretched with a stretching rod,
Next, heated air at 90°C is immediately introduced to expand it in the radial direction at a blowing pressure of 7 kg/cm ² and also to stretch it in the circumferential direction. I made a beer bottle type container. Here, the blow molding equipment is Nikko Cautex V8
A partially modified mold blow molding machine was used. The blowing time was 10 seconds. Table 1 shows the results of measuring the transparency (visual observation), external appearance, and heat-filling shrinkage rate of the obtained container, and Table 2 shows the results of measuring the tensile strength.

【table】

[Table] As is clear from Table 1, if the mold temperature is set to below the glass transition temperature and at least 15°C lower than the glass transition temperature, it is possible to heat up to 70°C without impairing the transparency and appearance of the container. Even when filled with water, the volumetric shrinkage rate was less than 1.0%, indicating that the container can withstand high-temperature filling. Furthermore, as shown in Table 2, the containers of the present invention have significantly improved tensile strength and are extremely useful as containers for beverages such as carbonated drinks and beer. Examples 5 to 12, Comparative Examples 5 to 10 A bottomed parison was molded using the same raw materials and molding conditions as in Example 1, and the bottomed parison was heated to 95°C and then maintained at various temperatures shown in Table 3. The opening end was held in a blowing mold and stretched longitudinally. Then, heated air at various temperatures shown in Table 3 was immediately introduced to stretch the mold in the circumferential direction as well, as in Example 1. I made a polyester container. Here, the blow molding device, circumferential blow pressure, blow mold, etc. are the same as in Example 1. Table 3 shows the results of measuring the transparency (visual observation), appearance condition, and heat-filling shrinkage rate of the obtained container.

[Table] As is clear from Table 3, if the sum of the heated air temperature and the stretch blow mold temperature is in the range of 140°C to 190°C, the transparency and appearance of the container will be maintained almost unchanged. An excellent heat-resistant container with a volume shrinkage of 1.0% or less when filled with hot water at 70°C can be obtained. Examples 13 to 15 A bottomed parison was molded using the same raw materials and molding conditions as in Example 1, and after heating this bottomed parison to 95°C, it was transferred to a blowing mold maintained at a temperature of 75°C. Hold the open end, perform longitudinal stretching, and immediately
After introducing heated air at a temperature of 115°C and performing blow stretching (primary blow) for 5 seconds, the temperature was immediately changed to various temperatures shown in Table 4 and blowing (secondary blow) was performed for 5 seconds to cool it. . Here, the blow molding device, the lateral blowing pressure (including the cooling blowing pressure after stretching), etc. are the same as in Example 1. Table 4 shows the results of measuring the transparency (visual) appearance and heat-filling shrinkage rate of the obtained containers. As is clear from Table 4, by blowing cold air at room temperature or below room temperature after stretching, an excellent heat-resistant welder that does not deform can be obtained even when the mold temperature and the temperature of the primary blowing air are high.

【table】 [Brief explanation of the drawing]

1 to 5 are drawings for explaining the operating procedure of the biaxial stretch blow molding method. FIG. 6 is a drawing corresponding to FIGS. 3 and 4 for explaining the method of the present invention. 7... Bottomed parison, 13... Stretching blow mold, 14... Stretching rod, 16... Air flow, 18
... Hydraulic system, 19 ... Pressurized air tank, 22 ...
…heated air tank.

Claims (1)

[Claims] 1. When molding a biaxially stretched blow container made of thermoplastic polyester, a heated bottomed parison is axially heated by maintaining the temperature of the blow mold within a temperature range that satisfies the following formula (). A method for forming a thermoplastic polyester container, which comprises stretching the parison and blowing into the parison a pressurized gas heated to a temperature range satisfying the following formula (2) to expand and stretch the parison in the transverse direction. (Tg−15)<MT<Tg......() 140<(AT+MT)<190...() In the formula, Tg is the glass transition temperature of thermoplastic polyester (℃), and MT is the blowing mold temperature (℃)
and AT indicates the heated and pressurized gas temperature (°C).