JPH0327372B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a polyester hollow container with improved heat shrinkage resistance. In recent years, biaxially stretched and oriented hollow containers made of polyethylene terephthalate have improved mechanical strength, gas barrier properties,
Because it has excellent properties such as transparency and chemical resistance, it has made remarkable inroads into the food packaging and kitchenware fields, and has been used in containers for soy sauce, sauces, dressings, cooking oil, and dish detergent. For example, a biaxially stretched hollow container made of polyethylene terephthalate is molded using a blow mold kept at a low temperature such as room temperature. They tend to exhibit a large volume reduction when exposed to an atmosphere with a temperature higher than 10°C (°C) or when filled with a liquid at a high temperature. For this reason, the uses of conventionally produced polyethylene terephthalate biaxially stretched and oriented hollow containers are as follows:
It was limited to the field of filling contents at low temperatures, and could not be used in fields that required filling contents at high temperatures. By the way, in general, for polyethylene terephthalate molded products such as threads with a one-dimensional structure or films with a two-dimensional structure, a heat treatment called heat setting is performed after stretching to improve heat resistance, and the microcrystals generated during stretching are This process changes the crystal structure to a more stable crystal structure against heat and fixes it in that aligned state, as well as relieving the residual stress during stretching, and this treatment significantly improves the heat resistance of the molded product. . Similarly, in order to improve the heat resistance of biaxially stretched and oriented hollow containers made of polyester, it is necessary to improve the degree of crystallinity so that deformation due to residual stress during molding does not occur even at high temperatures. For this purpose, attempts have been made to improve the heat resistance of polyethylene terephthalate containers by molding them and then subjecting them to various heat treatments. This method is difficult to commercialize in practice because it not only significantly reduces productivity but also consumes a large amount of thermal energy. In order to solve such problems,
A method of adding a nucleating agent to polyester resin has been proposed in Publication No. 2342, but adding a nucleating agent not only impairs the transparency of the container, but also causes problems such as elution of the nucleating agent into the contents of the container. There is a risk of causing
This method has many practical problems. Another method is to increase the heat shrinkage resistance by raising the mold temperature close to the crystallization temperature of polyester and improving the crystallinity in a short time after blow molding, but molding cannot be achieved by blowing at high temperatures. Even if it is possible, it is not preferable because orientation of the molecular chains does not occur and no improvement in strength can be expected. In view of these circumstances, the present inventors have developed a biaxially stretched film that has excellent heat resistance by using only stretch blow molding without performing any heat setting treatment or adding additives such as nucleating agents. As a result of intensive research to provide a method for manufacturing oriented hollow containers, the present invention has been completed. That is, in the present invention, 80 mol% or more of the acid component is terephthalic acid, 80 mol% or more of the glycol component is ethylene glycol, has branches, and has a main exothermic peak and 1 Forming a rapidly cooled parison from a polyester resin exhibiting more than 10 secondary exothermic peaks or a mixture of the polyester resin and a polyethylene terephthalate resin, and then biaxially stretch blow molding the parison using a water-cooled blow mold. The purpose of this method is to provide a method for manufacturing a hollow container that has better heat resistance than ordinary polyester resin hollow containers. Note that at least the body of the hollow container manufactured by the method of the present invention is stretched and oriented in biaxial directions,
Here, being stretched and oriented in two axial directions means that the difference in refractive index in the thickness direction and the plane direction of the container is orthogonal to each other.
It means 0.04 or more, preferably 0.08 or more in any of the three plane directions. When polyester resin used for manufacturing hollow containers is analyzed using a differential scanning calorimeter, it is found that it is sufficiently crystallized because it is generally produced by solid phase polymerization, and even when the chips are measured as they are with a differential scanning calorimeter, no crystals are detected. The presence of an exothermic peak due to chemical reaction cannot be recognized, and it is not possible to know the difference in crystallization behavior between polyester resins. However, the polymer is heated and pressurized to 280°C using a heat press to form a sheet, which is then rapidly cooled by placing it in cold water at 0°C to form an amorphous polymer sheet. /
When measured at a heating rate of about minutes, an exothermic peak is observed between the glass transition temperature around 70°C and the melting temperature around 260°C. The position of this exothermic peak,
The size and number vary depending on the type of polyester, and the crystallization behavior of the resin can be estimated from these. The term "exothermic peak" as used in the present invention means a peak that appears during thermal analysis of such an amorphous sample. Polyethylene terephthalate, obtained by condensation of ethylene glycol and terephthalic acid,
As shown in Figure 1, only one crystallization exothermic peak is observed around 145°C. On the other hand, depending on the manufacturing method of polyester resin, as shown in FIG. 2, a polyester resin is produced which does not have a single exothermic peak but is divided into a main exothermic peak and a sub-exothermic peak. Normally, biaxially stretched hollow containers are manufactured by biaxially stretched polyester resin that exhibits the behavior shown in Figure 1, and the molded parison is rapidly cooled in a mold to a temperature range where crystallization is difficult to occur. The polyethylene terephthalate resin is then biaxially stretched and oriented by injecting compressed gas, and the polyethylene terephthalate resin in this case is cooled to near room temperature after blow molding. The crystallization rate of polyethylene terephthalate resin below this temperature is small, and the stress generated during stretch molding is retained, so if the container is exposed to a temperature above the glass transition temperature, it will easily deform, resulting in insufficient heat resistance. It is. On the other hand, in polyester resins that have a secondary exothermic peak, the temperature during stretch molding is close to the temperature range of the secondary exothermic peak, and crystallization occurs more easily than ordinary polyethylene terephthalate, even when molded under ordinary polyethylene terephthalate molding conditions. It is thought that the obtained hollow container is unlikely to be deformed due to residual stress even at high temperatures and has improved heat resistance. The phenomenon of showing a main exothermic peak and a sub-exothermic peak when analyzed by a differential scanning calorimeter is sometimes observed in polyester resins having branches as described below, and such polyester resins are used in the present invention. In this polyester resin, terephthalic acid accounts for 80 mol% or more of the acid component, preferably 90 mol% or more, and 80 mol% or more of the glycol component, preferably
It means a polyester in which 90 mol% or more is ethylene glycol, with the remainder being other acid components such as isophthalic acid, diphenyl ether-4,4'-dicarboxylic acid, naphthalene-1,4- or 1,6-dicarboxylic acid. , adipic acid, sebacic acid, decane-
1,10-dicarboxylic acid, hexahydroterephthalic acid, etc., and other glycol components such as propylene glycol, 1,4-butanediol, neobentyl glycol, diethylene glycol, cyclohexanedimethanol, 2,2-bis(4-
hydroxyphenyl)propane, 2,2-bis(4-hydroxyethoxyphenyl)propane, or a polyester containing p-oxybenzoic acid, p-hydroxyethoxybenzoic acid, etc. as an oxy acid, and this polyester contains substantially Contains a small amount of chain branching agent, but does not contain gel. Branching agents: pentaerythritol, glycerol, sorbitol, 1,2,6-hexanetriol, trimethylolethane, trimethylolpropane, trimethylolhexane, trimethylolbenzene-1,3,5, tripropyrrolbenzene-1,3,5 In addition to compounds having three or more hydroxyl groups such as , tributyrolbenzene-1,3,5, trimesic acid, trimellitic acid,
Pyromellitic acid, prenitic acid (1,2,3,
Examples include compounds having three or more carboxyl groups, such as (4-benzenetetracarboxylic acid). Amounts of these branching agents may range from about 0.025 to about 1.5 mole percent, preferably from about 0.05 to about 1.0 mole percent, based on the dicarboxylic acid component. Incidentally, it is preferable to use a chain terminator such as an aromatic monocarboxylic acid or an aliphatic monocarboxylic acid, and the amount thereof is in the range of about 0.25 to about 10 equivalents based on the number of moles of the chain branching agent, more preferably.
It ranges from 0.50 to about 5 equivalents. The above polyester can be obtained by a known polycondensation method. That is, a polyester is produced by polycondensing a dicarboxylic acid, a glycol, a branching agent, and optionally a chain terminator or an ester-forming derivative thereof under reduced pressure. In the present invention, biaxial stretch blow molding can be carried out using a commonly used biaxial stretch blow molding apparatus. In this molding, parison molding and biaxial stretch blow molding may be performed continuously in the same device, or parison molding and biaxial stretch blow molding may be performed in separate devices. In a continuous system, the polyester polymer is fed into a hopper dryer, dried, and then injection molded into a water-cooled mold using an injection molding machine to form a substantially amorphous material with a density of 1.35 or less. Thickness 1-4
Form a parison of mm. Next, this parison is adjusted to a temperature range that allows it to be stretched, and then biaxially stretched and oriented in a water-cooled blow-molding mold using a stretching rod and pressurized gas to produce a desired hollow container. The hollow container produced by the method of the present invention has improved heat resistance, so that the contents such as sake, mirin, vinegar, sauce, juice, etc.
Suitable for applications where the product is heat sterilized and then filled at high temperatures, that is, hot filling applications. Furthermore, since at least the body of the container is biaxially stretched and oriented, it has excellent pressure resistance and transparency. Hereinafter, the present invention will be explained in detail with reference to Examples. The measuring method for the biaxially stretched and oriented hollow containers mentioned in Examples and Comparative Examples is as follows. (1) Heat shrinkage rate Fill a bottle to the brim with 80°C hot water and leave it for 5 minutes. After 5 minutes, remove the hot water and fill with 20℃ water, measure the internal volume V after treatment, compare it with the internal volume V _O before treatment, and calculate the volume shrinkage rate V _S (%) using the following formula. Calculate with. V _S =V _O -V/V×100 (2) Degree of orientation The refractive index of the sample cut from the container in the thickness direction and in two orthogonal plane directions was measured using a polarizing microscope using the sodium D line. Biaxial orientation was determined when the difference in refractive index between the plane direction and the thickness direction was both 0.04 or more. Example 1 Trimethylolpropane and methyl benzoate were added to terephthalic acid at 0.33 mol% and 1.00%, respectively.
Polyethylene terephthalate containing mol % and having an intrinsic viscosity of 0.95 dl/g was synthesized by a conventional method. When an amorphous polymer sheet was prepared and the crystallization temperature was measured using a differential scanning calorimeter at a heating rate of 10°C/min, a main peak was observed at 145°C as shown in Figure 2.
A thermogram showing a subpeak at 121°C was obtained. This polymer was dried in a hopper dryer at 150°C for 5 hours, and then molded using an injection molding machine with an outer diameter of 24 mm.
A bottomed cylindrical parison with an inner diameter of 16 mm and a length of 160 mm was molded. Next, this parison is placed in an infrared heater while rotating and heated uniformly so that the temperature of the parison reaches approximately 110℃, and then inserted into a blow mold for molding and doubled in length in the longitudinal direction using a stretching rod. At the same time, compressed nitrogen was injected into the inside of the parison and stretch blowing was performed to obtain a bottle. When the degree of orientation of a sample cut from the body of the obtained bottle was measured, it was found to be biaxially oriented in the plane direction. Further, Table 1 shows the results of measuring the thermal shrinkage rate of the obtained bottles. The heat shrinkage rate is 2.5%,
Compared to the bottle molded from ordinary polyethylene terephthalate (intrinsic viscosity 0.80 dl/g) shown in Comparative Example 1, the heat shrinkage rate is smaller and the heat resistance is excellent. Example 2 The polyethylene terephthalate described in Example 1 was heated at 150° C. for 5 hours in a hot air dryer to obtain dried chips. This polymer was extruded into a cylinder using a conventional extruder, the tip was sealed, and then rapidly cooled to room temperature to obtain a parison. This parison is rotated and placed in an infrared heater device and heated uniformly so that the temperature of the parison reaches approximately 110℃.
The bottle was inserted into a blowing mold for forming, and a bottle with an areal stretching ratio of about 8 was obtained as in Example 1. The resulting bottle was biaxially oriented. Table 1 also shows the measurement results of the heat shrinkage rate. Example 3 Polyethylene terephthalate having an intrinsic viscosity of 1.10 dl/g and containing 0.2 mol% and 0.6 mol% of trimethylolpropane and methyl benzoate, respectively, based on terephthalic acid, was synthesized by a conventional method. On the other hand, polyethylene terephthalate containing no branching agent and having an intrinsic viscosity of 0.8 d8/g was also synthesized, and the two were chip-blended at a weight ratio of 1:1, and a bottle was molded in the same manner as in Example 1. The results of measuring the heat shrinkage rate of the bottle are shown in Table 1.The heat shrinkage rate is 4.0%, which shows that the heat resistance is improved compared to the polyethylene terephthalate bottle of the comparative example.Example 4 Pentaerythritol and benzoic acid Polyethylene terephthalate containing 0.2 mol % and 0.8 mol % of methyl based on terephthalic acid and having an intrinsic viscosity of 1.0 dl/g was synthesized by a conventional method.The polyethylene terephthalate resin described in Comparative Example 1 and this branched polyester and resin at a weight ratio of 3:2, and a bottle was molded in the same manner as in Example 2. Table 1 shows the heat shrinkage rate of the resulting bottle. Comparative Example 1 Commercially available polyethylene terephthalate for molding with an intrinsic viscosity of 0.8 dl/g was heated to 280°C using a hot press, and then poured into cold water at 0°C to form an amorphous polymer sheet. Measurement using a differential scanning calorimeter at a heating rate of 10°C/min revealed a single exothermic peak due to crystallization at 146°C and an endothermic peak due to crystal melting at 260°C, as shown in Figure 1. After drying this polymer in a hopper dryer at 150°C for 5 hours, it was molded into a mold with an outer diameter of 24 mm using an injection molding machine.
A bottomed cylindrical parison with an inner diameter of 16 mm and a length of 160 mm was molded. The parison is rapidly cooled to below 100℃,
It is substantially amorphous. This parison was placed in an infrared heater while rotating, heated uniformly so that the parison temperature reached approximately 110°C, and then inserted into a blowing mold for molding. Obtained. The heat shrinkage rate of the obtained bottle was measured and the results are shown in Table 1. The heat shrinkage rate is 12.5%, the volume change is large, and the heat resistance is poor.
When the bottle was filled with liquid at 80°C, the dimensions of the mouth part changed, making it difficult to seal it with a metal cap. Comparative Example 2 The polyethylene terephthalate resin described in Comparative Example 1 was molded into a parison in the same manner as in Example 2. The parison was rotated and uniformly heated in an infrared heater to a parison temperature of 125°C, and then inserted into a room temperature blow mold to obtain a bottle in the same manner as in Example 2. Table 1 shows the heat shrinkage rate of the obtained bottle. The heat shrinkage rate is as high as 11.2%, and the heat resistance is insufficient, so it cannot be used in applications that require hot filling.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is an example of a thermogram of ordinary amorphous polyethylene terephthalate, in which the vertical axis indicates heat input and output, and the upwardly convex peak indicates heat generation. The horizontal axis is temperature, and the higher the right, the higher the temperature. FIG. 2 is a thermogram of the polyester resin obtained in Example 1, and multiple exothermic peaks are observed.

Claims (1)

[Claims] 1 80 mol% or more of the acid component is terephthalic acid, 80 mol% or more of the glycol component is ethylene glycol, has branches, and has a main exothermic peak and one or more sub-exothermic peaks in analysis by differential scanning calorimeter. A hollow container characterized in that a rapidly cooled parison is formed from a polyester resin exhibiting an exothermic peak or a mixture of the polyester resin and a polyethylene terephthalate resin, and then the parison is biaxially stretch blow molded using a water-cooled blow mold. manufacturing method.