JPH0349815B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a polyester can-shaped container, and more specifically, a can-shaped container made of a thermoplastic polyester cylinder whose main repeating unit is ethylene terephthalate, with sealing plates integrally bonded to the openings at both ends. It concerns containers. [Prior Art] In recent years, due to the problem of depletion of petroleum resources, energy-saving plastic containers have come to be used instead of energy-intensive metal cans made of aluminum. These plastic containers are usually formed into a container shape by injection molding or deep drawing, but when conventional plastic containers are filled with drinking water containing carbon dioxide gas, etc., the carbon dioxide generated from the drinking water is released. The container is constantly under internal pressure due to the gas, which not only causes creep deformation of the container and significantly lowers its commercial value, but also causes the contents to leak out from the seal with the lid. Furthermore, when filling conventional plastic containers with contents that require high-temperature filling, there are problems such as deformation due to heat and failure to seal the lid completely. . [Problems to be Solved by the Invention] The present invention has been made by focusing on the above-mentioned circumstances, and has excellent pressure resistance and gas barrier properties, and has excellent protection performance against contents, and at the same time, it can withstand high temperatures. The object of the present invention is to provide a polyester can-shaped container that exhibits extremely little deformation shrinkage during filling and has excellent thermal stability. [Means for Solving the Problems] The present invention, which achieves the above object, is a can-shaped container formed by integrally bonding sealing plates to the openings at both ends of a thermoplastic polyester cylinder whose main repeating unit is ethylene terephthalate. The cylindrical body is stretched in at least one direction so that the degree of plane orientation Δn of the portion excluding the openings at both ends of the cylindrical body is 50×10 ^-3 or more, and the maximum thickness of the cylindrical body is 1.05 mm or less. In addition, the ratio of the thickness of the cylindrical body to the thickness of the sealing plate is 1 or more and 4 or less, and the volume shrinkage rate when filled with boiling water is reduced to 2% or less by heat treatment. That is. [Function] It is well known that the creep properties of polyester threads and films can be further improved by stretching thermoplastic polyester in an amorphous state to cause oriented crystallization. The present inventors focused on the above-mentioned properties of thermoplastic polyester, and conducted repeated research with the goal of creating a can-shaped container using this thermoplastic polyester, and decided to impart gas barrier properties and heat resistance to the can-shaped container. Thus, the present invention was completed. Although the polyester can-shaped container of the present invention is not limited by the manufacturing method, the following methods can be exemplified. That is, a polyester pipe is formed using an extruder, heated to a temperature of 90 to 120°C, which is suitable for stretching, and then pressurized gas is applied in the circumferential direction, or simultaneously or sequentially in the circumferential and axial directions. A stretched pipe is formed by stretching 2.8 times or more, and then heat-treated at a temperature that is at least 20°C higher than the glass transition temperature of polyester and at least 20°C lower than its melting point. A pressure-resistant can-shaped container is obtained by cutting the tube into a cylinder, and integrally joining sealing plates to the openings at both ends of the cylinder. The degree of plane orientation Δn of the portion of the cylindrical body used in the present invention excluding the openings at both ends must be 50×10 ^-3 or more. If Δn is less than 50×10 ^-3 , pressure resistance and gas barrier This results in insufficient properties, leading to creep deformation and seal leakage. The thickness of the cylinder part is 1.05mm due to the tightness of the stretched pipe.
The following is preferable, and even when forming a laminated cylinder with other resins, it is preferable that the polyester layer has a thickness of 1.05 mm or less. This makes it possible to further increase the sealing strength when sealing is performed using the sealing plate. The sealing plate is preferably made of a ductile metal such as aluminum or tinplate, but may also be a heat-resistant plastic or a composite plate of metal and plastic. In addition, when sealing the openings at both ends of the cylinder with a sealing plate, by setting the ratio between the thickness of the polyester in the cylinder and the thickness of the sealing plate to 1 or more and 4 or less, the difference between the materials of the thermoplastic polyester and the sealing plate can be avoided. problems based on,
That is, even if materials with different elastic moduli are integrally seamed, the sealing strength can be increased. Furthermore, by applying heat, for example, with a heating plate, to the portions corresponding to the seal portions at both ends during molding of the cylindrical portion, the degree of orientation can be lowered than that of the cylindrical portion, and the sealing strength can be increased. Note that seaming is preferred as the sealing method using a sealing plate.
Other methods include gluing and fusing, but
From the viewpoint of seal strength, it is recommended to use it together with seaming. The processing conditions for stretched pipes are at least 20℃ higher than the glass transition temperature of polyester and 20℃ higher than the melting point.
A lower temperature range is preferable, and heat treatment in this range improves heat resistance and makes it possible to produce a heat-resistant can-shaped container with a volume shrinkage of 2% or less when filled with boiling water. It is preferable that the heat treatment is carried out subsequent to the drawing in the process of manufacturing the drawn pipe, but it can also be carried out in a separate process. It is also possible to heat-treat the stretched pipe after cutting. During heat treatment, it is preferable to increase the internal pressure to prevent thermal shrinkage, or to insert an inner core to prevent shrinkage. The thermoplastic polyester containing ethylene terephthalate as a main repeating unit in the present invention usually has an acid component of 80 mol% or more, preferably 90 mol% or more of terephthalic acid, while a glycol component of
It means a polyester in which 80 mol% or more, preferably 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 2,6-dicarboxylic acid, adipic acid, sebacic acid, decane-1,10-dicarboxylic acid, hexahydroterephthalic acid, and as other glycol components propylene glycol-1,4-butanediol, neopentyl glycol, diethylene glycol , 1,6-hexylene glycol, cyclohexanedimethanol, 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(4
-hydroxyethoxyphenyl)propane is exemplified. The present invention also includes polyesters using p-oxybenzoic acid, p-hydroethoxybenzoic acid, etc. as the oxyacid. Alternatively, it may be a blend of two or more polyesters such that the content of ethylene terephthalate is 80 mol% or more by mixing polyethylene terephthalate with another thermoplastic polyester. Furthermore, the polyester in the present invention may contain additives such as colorants, ultraviolet absorbers, antistatic agents, thermal oxidation inhibitors, antibacterial agents, lubricants, and inorganic fillers in appropriate proportions, if necessary. . The thermoplastic polyester used in the present invention desirably has an intrinsic viscosity of 0.55 or more, preferably 0.6 or more, and more preferably 0.7 to 1.4. Intrinsic viscosity is the intrinsic viscosity when a solution of thermoplastic polyester dissolved in a phenol/tetrachloroethane mixed solvent (6/4 weight ratio) is measured at 30°C. The present invention also includes a can-shaped container made of a laminated cylinder of polyester and other resins such as metaxylylene group-containing polyamides, polyvinylidene chloride, and resins with better gas barrier properties such as acrylonitrile-styrene copolymers. It is. In addition, the evaluation method of the characteristic values of polyester can-shaped containers,
The measurement method is as follows. (1) Degree of orientation; attach a polarizing plate to the Atsube refractometer,
Measured using sodium D line at 25°C.
Let the refractive index in the axial and circumferential directions (both in the plane direction) be Nx and Ny, respectively, and the refractive index in the thickness direction be Nz,
Nx+Ny/2−Nz=Δn (birefringence) was calculated and used as the degree of plane orientation. (2) Volume shrinkage due to boiling water filling process: Fill a can-shaped container with boiling water and leave it for 5 minutes.
After 5 minutes, remove the hot water, fill with 20°C water, measure the internal volume (V) after treatment, and compare it with the internal volume (V ₀ ) before treatment to determine the volumetric shrinkage rate V _s (% )
is calculated using the following formula. V _s (%) = V ₀ −V / V ₀ ×100 [Example] Example 1 Toyobo polyester RT-560 (polyethylene terephthalate, intrinsic viscosity 1.0) was manufactured by Japan Steel Works.
Using a 40mmφ extruder with a pipe die, temperature regulator, and blower, it is formed into a pipe with an inner diameter of 15.8mm and an outer diameter of 17.7mm, and then the pipe temperature is set to 95mm.
Blow with pressurized air at
It was stretched twice to form a stretched pipe with an inner diameter of 52.4 mm and an outer diameter of 53.0 mm. The plane orientation degree Δn of this stretched pipe is 90
It was ×10 ^-3 . The stretched pipe was cut into a length of 140 mm, and flanges were then thermoformed on the openings at both ends using a hand press. Δn in that part was 40×10 ^-3 .
Aluminum lids with a thickness of 0.25 mm were sealed to the openings at both ends using a hand seamer manufactured by Osaka Can. Pressurized air was applied to this container (internal pressure) to measure the pressure resistance. As a result, no seal leakage occurred even at a pressure of 7 kg/cm ² , and the container was excellent as a pressure-resistant container. Example 2 Using the same equipment as in Example 1, the stretching ratio was 3 times, and the thicknesses after stretching were 0.25 mm, 0.45 mm, 0.60 mm, and 1.05.
mm, 1.10mm, 1.35mm stretched pipe (Δn≒90×
10 ^-3 ) was molded. Cut this into a length of 140mm,
A 0.3 mm thick aluminum lid was seamed with a hand seamer made by Osaka Can Manufacturing Co., Ltd., and a pressure test was performed using pressurized air.
The results are shown in Table 1.

【table】

[Table] In Table 1, Nos. 2 to 4 are examples of the present invention, and the ratio of the thickness of the cylindrical body to the thickness of the sealing plate is within the range of 1 to 4, so they exhibit high gas barrier properties. ing. On the other hand, No. 1 and No. 6 are comparative examples in which the thickness ratio with the sealing plate is outside the range of the present invention, and seal leakage occurs at the joint position of the sealing plate. No. 5 is a comparative example in which the thickness ratio to the sealing plate was within the range of the present invention, but the thickness of the cylindrical body was outside the range of the present invention, and seal leakage also occurred. Example 3 A heat setting device was added to the process of Example 1, and after stretching, heat setting was performed at 170°C for about 10 seconds.
The pipe was formed. This was cut into a length of 140 mm to produce a container body, and flanges were thermoformed at both end openings in a mold using a hand press machine. Δn of the body was 90×10 ⁻³ and Δn of the flange was 30×10 ⁻³ . Then on one of the open ends
A 0.25 mm thick aluminum lid was sealed. The volumetric shrinkage rate of the container thus obtained when filled with boiling water was measured and found to be 1.7%. The container had excellent transparency even after being filled with boiling water and was an excellent heat-resistant container. Also, the pressure resistance of containers sealed at both ends is 7.
It showed excellent pressure resistance of more than Kg/cm ² . Comparative example 1 Toyobo polyester RT-560 (1V=1.0),
Using a Vδ/s blow molding machine manufactured by Japan Steel Works, the inner diameter
A cylindrical molded product with a diameter of 52.4 mm, an outer diameter of 53.0 mm, and a length of 160 mm was molded (Δn≒10×10 ^-3 ), and both ends were cut to form a cylindrical product with a diameter of 140 mm.
mm in length, a 0.25 mm thick aluminum lid was sealed, and a pressure test was performed using pressurized air. pressure
At 4.5Kg/cm ² the center of the can was deformed, and at 5.0Kg/cm ² it began to leak from the seal. In addition, one end of the opening of a tube formed in the same manner was covered with aluminum, and the tube was filled with boiling water. Deformation occurred immediately after filling, resulting in considerable deformation of the cylinder shape and whitening and devitrification. The container was determined to be unsuitable as a pressure-resistant container or a heat-resistant container. [Effects of the Invention] Since the present invention is configured as described above, it is possible to provide a polyester can-shaped container that has excellent protection performance for the contents and also has excellent thermal stability even when filled at high temperatures. Summer.

Claims (1)

[Scope of Claims] 1. A can-shaped container formed by integrally bonding sealing plates to the openings at both ends of a thermoplastic polyester cylinder whose main repeating unit is ethylene terephthalate,
The cylindrical body is stretched in at least one direction so that the plane orientation degree Δn of the portion excluding the openings at both ends of the cylindrical body is 50×
10 ^-3 or more, and the maximum thickness of the cylindrical body is 1.05 mm or less, and the ratio of the thickness of the cylindrical body to the thickness of the sealing plate is 1 or more and 4 or less, and further heat treatment is performed to prevent boiling. A polyester can-shaped container characterized by having a volume shrinkage rate of 2% or less when filled with water. 2. The polyester can shape according to claim 1, wherein the degree of orientation Δn of the openings at both ends of the cylinder (the joints with the sealing plate) is lower than that of the main part of the cylinder, or is not oriented. container.