JPH0347176B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a polyester bottle, and more particularly to a polyethylene terephthalate bottle that has excellent transparency, gas barrier properties, and pressure deformation resistance and can be advantageously used as a container for food or beverages. [Prior art] Bottles obtained by biaxial stretch blow molding of thermoplastic polyester, particularly polyethylene terephthalate (hereinafter abbreviated as PET), have excellent properties such as mechanical strength, gas barrier properties, transparency, and chemical resistance. Because of this, they are widely used as containers for beverages, foods, cosmetics, etc. However, when such a PET bottle is used, for example, as a container for carbonated beverages in which carbon dioxide gas is dissolved under pressure, if the storage period is prolonged, the carbon dioxide gas in the content liquid will gradually be lost, resulting in a drawback that the product value will be lowered. . Various methods have been proposed to improve this drawback, such as a method of laminating resins with excellent gas barrier properties and PET, or a method of melt-mixing them. However, the bottles produced by this method are
Lamination of PET and barrier resin has drawbacks such as weak interlayer adhesion and peeling, while melt-mixing methods have drawbacks such as reduced bottle transparency. Furthermore, after using a PET bottle, it is difficult to separate the PET polymer and barrier resin when reusing the PET polymer for other purposes, or when reusing repropolymer generated during the bottle molding process for bottle molding. This has drawbacks such as problems in use. [Object of the Invention] An object of the present invention is to provide a bottle that is free from the above-mentioned drawbacks and has good transparency, gas barrier properties, and pressure deformation resistance. [Structure of the Invention] As a result of intensive research into polyester bottles that do not have the above-mentioned defects, the present inventor discovered that the defects can be improved if the bottle is made of a specific PET polymer and has specific physical properties. Reached. That is, the present invention provides a bottle made of a thermoplastic polyester resin whose main repeating unit is ethylene terephthalate, and whose thin body portion is biaxially oriented.
and copolymerization ratio (W (wt%)) of dicarboxylic acid and glycol components other than ethylene terephthalate
is within the range of formula (), the average degree of plane orientation of the thin wall portion is 0.125 or more, and the average wall thickness is 0.35 mm or more. IV≧0.02W ² +0.02W+0.66 ... Formula () (however, 0.5≦W≦3.0) The thermoplastic polyester resin in the present invention is
Its main repeating unit consists of ethylene terephthalate, and aromatic dicarboxylic acids such as isophthalic acid, naphthalene dicarboxylic acid, diphenyl dicarboxylic acid, diphenoxyethane dicarboxylic acid, diphenyl ether dicarboxylic acid, diphenyl sulfone dicarboxylic acid, etc.; Alicyclic dicarboxylic acids such as hydroterephthalic acid, hexahydroisophthalic acid, etc.; Alicyclic dicarboxylic acids such as adipic acid, sebacic acid, azelaic acid, etc.; p-β-
one or more difunctional carboxylic acids other than terephthalic acid, such as oxyacids such as hydroxyethoxybenzoic acid, epsilon-oxycaproic acid, and/or e.g. trimethylene glycol, tetramethylene glycol, hexamethylene glycol, decamethylene Glycol, neopentyl glycol, diethylene glycol, 1,1-cyclohexanedimethanol, 1,4-cyclohexanedimethanol,
Contains one or more diols other than ethylene glycol, such as 2,2-bis(4'-β-hydroxyethoxyphenyl)propane and bis(4'-β-hydroxyethoxyphenyl)sulfonic acid, as a copolymerization component. It is a polyester whose copolymerization ratio (W (wt% relative to the polymer weight)) and intrinsic viscosity (IV) fall within the range of formula (). IV≧0.02W ² +0.02W+0.66 () formula (however, 0.5≦W≦3.0) Particularly preferred is a polyester within the range of () formula. IV≧0.02W ² +0.07W+0.64 () formula (however, 0.5≦W≦2.5) When IV is lower than the range of () formula, it is difficult to obtain a bottle with good gas barrier properties. Furthermore, PET with a W lower than 0.5 crystallizes at too high a rate, making it impossible to obtain an amorphous preform. PET with a W larger than 3.0 has poor orientation and significantly increases deformation when pressurized with carbon dioxide gas. In the bottle of the present invention, the thin wall portion of the body is biaxially oriented with an average plane orientation degree of 0.125 or more, and the average wall thickness is
It is 0.35mm or more. The average plane orientation degree (hereinafter abbreviated as △nav) is a numerical value obtained from the measurement results of the axial refractive index (ny), circumferential refractive index (nx), and thickness direction refractive index (nz) of the bottle body. . △n _av = {(n _y − _nz ) + (n _x − _nz )}/2 Usually commercially available carbonated drink containers have △n _av ≒
0.120 to 0.123, but the present invention provides a highly oriented bottle with Δn _av ≧0.125, and preferably Δn _av ≧0.128, which significantly improves the pressure deformation resistance and gas barrier properties of the bottle. For the same reason, the average wall thickness of the body is 0.35 mm or more, preferably 0.38 mm or more. In addition, the bottle of the present invention has a
95 to 97 vol% water and 0°C for the volume of the water
After filling with 4.0 times the volume of carbon dioxide gas (pressure approximately 3.7 Kg/cm ² G at 20°C) at 1 atm and sealing the bottle, store it at 40°C for 10 days. It is preferable that the internal volume increase rate is 3% or less. The bottle of the present invention can be obtained, for example, by stretching a substantially amorphous preform in the axial direction under temperature conditions such that the degree of orientation falls within the above range (for example, 90°C to 130°C), and then blowing and expanding it in the lateral direction. It will be done. The stretching ratio during blow molding is 2 times or more in the axial direction,
It is preferable that the area magnification is 3 times or more in the lateral direction and 6 times or more in area magnification. Furthermore, the preferred shape of the bottle of the present invention is that the body is basically cylindrical, but it may be decoratively deformed with some ribs. Moreover, the bottom shape is preferably spherical and convex. [Example] Hereinafter, the present invention will be explained in detail with reference to Examples. The measurement conditions for the main physical property values are as follows. (1) Intrinsic viscosity [IV]: Measured at 35°C using o-chlorophenol as a solvent. (2) Density [ρ]: Measured at 30°C using a density gradient tube made from carbon tetrachloride and n-heptane. (3) Degree of orientation [△n]: A polarizing plate was attached to an Atsube refractometer, and the refractive index in the thickness direction and plane direction of the sample cut from the container was measured at a temperature of 25°C using sodium D line. , the difference between the two values was calculated. (4) Glass transition temperature [Tg]: A sample melted at 290°C and then rapidly cooled to 0°C was measured with a differential calorimeter (manufactured by Seiko Electronics Co., Ltd.).
Measured using DSC-20 model) at a heating rate of 10℃/min. Examples 1 to 9 and Comparative Examples 1 to 7 After drying RET chips containing IV, DEG (diethylene glycol), and IA (isophthalic acid) as copolymerization components shown in Table 1 in a hot air dryer,
A barrel diameter of 36mmφ and 8oz injection molding machine (DM-100 model manufactured by Meiki Seisakusho) is supplied to the hopper, and a hot runner type 2-cavity preform mold (outer diameter 24 to 25
mmφ, total length 175mm, body wall thickness 3.5mm, mouth screw diameter 28
A preform (weighing 49 g) was molded using 3 mm).
Injection molding conditions are cylinder set temperature 260-285
℃, hot runner temperature 290℃, molding cycle 35
Second, the mold cooling water temperature was 15°C. All of the obtained preforms had good transparency and were substantially amorphous (density 1.335 to 1.338). The preform thus obtained was molded using a biaxially oriented blow molding machine (RHB manufactured by Cincinnati Milacron).
-Blow molded using an L-type machine, with an outer diameter of 82 mm and a total height of 275 mm.
mm, round bottom, cylindrical body volume approximately 1045ml PET
Got a bottle. Table 1 shows the IV and body average characteristics of the obtained bottles. Bottle IV and bottle volume increase rate (△
V (%)) is illustrated in Fig. 1 using the DEG weight ratio (adding 1 part IA weight ratio) as a parameter.
From Fig 1, the results of reading the correlation between IV and DEG ratio where △V is 2.5%, 3.0%, 3.5% and 4.0% are shown.
It is illustrated in Fig.2. The correlation formula between DEG% (W) and IV in Fig. 2 is approximated by the following formula. When △V=2.5% IV=0.02W ² +0.07W+0.64 When △V=3.0% IV=0.02W ² +0.02W+0.66 When △V=3.5% IV=0.015W ² +0.015W+0. 645 When △V=4.0% IV=0.01W ² +0.02W+0.62 The bottle was filled with 1000 g of water and 14 g of citric acid, and the gas phase inside the bottle was replaced with carbon dioxide gas (hereinafter referred to as CO ₂ ). Afterwards, 14 g of baking soda (NaHCO ₃ ) weighed in a thin polyethylene bag was inserted into the mouth of the bottle without direct contact with the citric acid aqueous solution inside the bottle, and the bottle was immediately capped with an aluminum cap (lined with polyethylene). . After capping, the bottle is shaken so that the baking soda and citric acid aqueous solution inserted into the mouth of the bottle are sufficiently mixed to generate CO ₂ through a reaction, and the aqueous solution in which CO ₂ is dissolved under pressure is filled into the bottle. state. After storing the CO ₂ -filled bottle in an atmosphere of 40°C for 10 days, it was heated to 20°C.
After 12 hours, the CO ₂ pressure inside the bottle was measured. Next, the aluminum cap was opened and the volume inside the bottle was immediately measured. The measurement results are shown in Table-1. In the same manner, the bottle was stored at 40° C. for different days and the CO ₂ pressure change inside the bottle was measured, and from the obtained results, the number of storage days at which the internal pressure became 3.0 Kg/cm ² G or less was determined. The results are shown in Table-1.

[Table] As is clear from Table 1, the bottle of the present invention has significantly improved CO ₂ storage stability compared to the bottle shown in the comparative example.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the results of measuring the relationship between the copolymerization ratio of IV, DEG, etc. of bottle PET and the bottle internal volume increase rate after storage under CO ₂ pressure. FIG. 2 shows the relationship between the bottle IV and the copolymerization ratio of DEG, etc., in which the bottle internal volume increases at a constant rate, based on the results of FIG. 1.

Claims (1)

[Claims] 1. A bottle made of a thermoplastic polyester resin whose main repeating unit is ethylene terephthalate, and whose thin body portion is biaxially oriented,
The intrinsic viscosity (IV) of the polyester and the copolymerization ratio (W (wt%)) of a bifunctional carboxylic acid component other than terephthalic acid and a glycol component other than ethylene glycol are within the range of formula (), and the above-mentioned thin The average plane orientation degree of the part is 0.125 or more, the average wall thickness is
Polyester bottles that are 0.35mm or larger. IV≧0.02W ² +0.02W+0.66 ...Formula () (however, 0.5≦W≦3) 2 Fill the bottle with 95 to 97 vol% of water to the internal volume, and add water to the bottle at 0°C and 1 atm. Claim 1, wherein the bottle is filled with carbon dioxide gas equivalent to 4.0 times its capacity, sealed and capped, and stored at 40°C for 10 days, and then the bottle internal volume increases by 3% or less when the bottle is opened. Polyester bottle as described in section.