JPH0443494B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a three-piece two-metal end can made of polyester. The present invention relates to a method for efficiently manufacturing composite cans with sealed metal ends with high precision and high productivity.

(Prior art) A composite container formed by wrapping a plastic container body and a metal lid together at their engaging ends was developed in the 1970s.
As seen in Publication No. 25894, it has been known for a long time, and a composite container using polyester such as polyethylene terephthalate (PET), which has excellent transparency, flavor retention, and mechanical properties, as a plastic container body has also been disclosed. This is already known from Publication No. 55-3915. Further, this latter publication describes that defects such as flange cracking can be prevented by maintaining the seamed portion with the metal lid at a temperature near the glass transition point of the polyester resin.

Recently, as a method for manufacturing polyester can bodies for seaming, Japanese Patent Application Laid-Open No. 59-207216 discloses a method in which a biaxially stretched pipe is held on a mandle and heat set, and then the pipe is held in a predetermined position. It is described that the can body is cut to size and then flanged to form a can body for seaming.

(Problems to be Solved by the Invention) However, in the case of polyester container bodies, unlike in the case of metal can bodies, it is often difficult to process flanges with good dimensional accuracy, resulting in insufficient engagement between the body hook and cover hook. This often leads to leakage.

In addition, when seaming with a metal lid, it is necessary to form seaming flanges at both open ends of the polyester body, but a special process is required to form these flanges, and the number of processes is large. There are many problems, and productivity is low.

Therefore, the technical problem of the present invention is to provide a composite can consisting of a polyester container body that is open at both ends and a metal lid that is seamed at both ends, in which a seamed portion with high dimensional accuracy is formed, and the seamed portion is The polyester portions are also reliably engaged and fixed, and as a result, the pressure-resistant sealing performance of the seamed portion is significantly improved.

Another technical object of the present invention is to provide a method for reliably manufacturing the above-mentioned composite cans with a small number of steps and with high productivity.

(Means for Solving the Problems) According to the present invention, three steps are adopted, which consist of tightening both open ends of a seamless can body made of polyester and a metal lid.
In the method for manufacturing a two-piece metal end can, a single-layer or multi-layer pipe made of polyester, which has been formed in advance by an extrusion method, is held at the stretching temperature of polyester, and both ends of the pipe are gripped to form the final can. In a split mold comprising a plurality of circumferential parts corresponding to the body of the can body and an increasing diameter groove located between the circumferential parts and/or at the end of the circumferential part and corresponding to the can body flange part. At the same time as tensile stretching in the axial direction, blow stretching is performed in the circumferential direction, and the obtained blow molded body is cut at the end of the increasing diameter part and formed into a biaxially stretched polyester can body having flanges at both open ends. A method of manufacturing a three-piece two-metal end can is provided.

(Function) As shown in FIG. 1, the present invention stretches the pipe 10 made of thermoplastic polyester in the axial direction (stretching in the direction of the arrow), and then blow-stretching it in the circumferential direction, thereby forming the pipe 10 on the circumferential wall of the can body. The first feature lies in the production of a hollow molded body having a flange that is integrated with the can lid and has a flange that can be immediately used for seaming with the can lid.

Fig. 2 shows a precursor molded body, that is, a hollow molded body 1, used for manufacturing a seamless polyester can body, and this hollow molded body 1 is blown in a cavity mold corresponding to this hollow molded body. Formed by molding. That is, the axially extending pipe has both sides 2a,
2b is pinched off, and a fluid is blown through the blowing needle hole 3, thereby shaping it into a predetermined shape as described below.

This hollow molded body 1 has vertically closed ends 4
a, 4b, and a connecting portion 5 with a small diameter in the center.
It has an upper part 6a and a lower part 6b via. The upper part 6a and the lower part 6b are provided with a plurality of circumferential parts 7a, 7 having diameter and height dimensions corresponding to the final can body.
b, and there is an outward bulging part 8 with an increased diameter between the plurality of circumferential parts 7a and 7b, and there is also an outward bulging part 8 above the uppermost circumferential part 7a. Further, outwardly bulging portions 8 are also provided below the lowermost circumferential portion 7b. When this hollow molded body 1 is cut at the position A-A of the outwardly bulging portion 8, as shown in FIG. 13 is easily obtained.

According to the present invention, the formation of the seaming flanges 12, 12 provides the body with excellent mechanical strength, creep resistance, and even transparency without requiring special flanging operations. The advantage of being formed all at once in the biaxial stretching blowing process is achieved, and since the flange part is formed in the blow molding process described above, it also has very high dimensional accuracy.

Moreover, extruding polyester to make pipe and making can bodies from the pipe provides several additional advantages. One of these is that there is no melt viscosity restriction as in injection molding, which allows the use of high molecular weight polyesters, resulting in significant improvements in the mechanical strength and molecular orientation of the final can body. Also, since extrusion into pipes is continuous molding, efficiency is improved. Furthermore, it is possible to simultaneously coextrude an ethylene-vinyl alcohol copolymer layer and an adhesive layer, making multilayering easy and accurate.

Furthermore, since the seaming flange is also given biaxial molecular orientation, it has a structure that is strong against seaming with the metal lid.

In FIG. 4 showing a three-piece two-metal end can according to the present invention, this can is obtained by placing a metal lid 14 on the flange portions 12, 12 of the polyester can body 13 shown in FIG. It will be done. Since both ends of the polyester can body 13 are fixed with rigid metal lids, the container has excellent pressure resistance and heat resistance.

(Operations and Effects of the Invention) According to the present invention described above, polyester can bodies equipped with flanges with good dimensional accuracy and excellent mechanical strength can be produced efficiently and at a high production rate, resulting in improved sealing performance and pressure resistance. It has become possible to industrially manufacture 3-piece 2-metal end cans with excellent properties.

(Description of preferred embodiments of the invention) The thermoplastic polyester containing ethylene terephthalate as a main repeating unit used in the present invention usually has an acid component of 80 mol% or more, preferably 90 mol% or more of terephthalic acid, and a glycol component of It means a polyester in which 80 mol% or more, preferably 90 mol% or more, is ethylene glycol, with the remaining other acid components being 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 other glycol components such as 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, or oxyacid It means a polyester containing p-oxybenzoic acid, p-hydroethoxybenzoic acid, etc. Further, a polyfunctional component having trifunctionality or more may be copolymerized within a range that does not impair moldability. Further, it may be a mixed polyester of two or more types such that polyethylene terephthalate is mixed with another thermoplastic polyester so that the content of ethylene terephthalate is 80 mol% or more.

In addition, the polyester in the present invention can contain additives such as colorants, ultraviolet absorbers, antistatic agents, thermal oxidative deterioration inhibitors, antibacterial agents, lubricants, and inorganic fillers in appropriate proportions as necessary. .

The thermoplastic polyester used in the present invention needs to have an intrinsic viscosity of 0.7 or more, preferably 0.8 or more, and more preferably 0.9 to 2.5. The intrinsic viscosity is the intrinsic viscosity measured at 30°C of a solution of polyester dissolved in a mixed solvent of phenol/tetrachloroethane (6/4 weight ratio). The present invention also provides a laminated cylinder or coating polyester made of polyester and a resin having better gas barrier properties such as metaxylylene group-containing polyamide, polyvinylidene chloride, acrylonitrile styrene copolymer, or ethylene vinyl alcohol copolymer. It also includes a can-shaped container made of a cylindrical body.

In order to manufacture a polyester pipe, it is melt-extruded and molded using a die of a predetermined shape of a thermoplastic polyester extrusion molding machine. When the container body is particularly intended to have transparency, the melt-extruded pipe is cooled to below room temperature and rapidly cooled with a sizer for regulating the shape of the pipe to form an amorphous pipe.

Stretch blow molding of a pipe into a hollow precursor molding involves cutting the pipe to an appropriate length, heating it to a polyester stretching temperature of, for example, 85 to 110°C, and then holding it with a clamp and stretching it in the axial direction. At the same time, blow stretching is performed in the circumferential direction within a split mold. The axial stretching ratio is preferably 1.2 to 5.0 times, particularly 1.5 to 3.0 times, while the circumferential stretching ratio is preferably 1.1 to 4.5 times, particularly 1.3 to 3.5 times.

The shape of the hollow precursor molded body 1 is not limited to that shown in FIG. 2, and, for example, the shape shown in FIG. 5 or any other shape may be used. Further, the shape of the circumferential side wall portion is not limited to a cylindrical one, but may be any shape such as a barrel shape, an ellipse shape, or a square shape, or may have a neck-in structure directly below the flange portion. .

The outwardly bulging portion of the formed hollow precursor molded body is cut to produce a plurality of can body members from one precursor molded body.

The lid of the can is made of tin-plated steel plate, which is tin-free.
It is made of various surface-treated steel plates such as steel (electrolytic chromic acid treated steel plates) and light metals such as aluminum, and the surface is coated with epoxy-phenol paint, epoxy-
Those provided with a protective coating such as urea paint, epoxy-acrylic paint, epoxy-vinyl paint, vinyl-phenol paint, etc. are used. A circumferential groove is provided around the can lid for engagement with the seamed end of the container body, and the groove is lined with a sealing rubber composition. The center panel portion of the can lid can be provided with a known easy-to-open mechanism.

The polyester body and the metal lid can be easily seamed using a seamer which is known per se and is conventionally used for seaming metal cans.

(Examples) Example 1 Polyethylene terephthalate having an intrinsic viscosity of 1.0 was melt-extruded to form a pipe with an inner diameter of 25 mm and a wall thickness of 4 mm. Cut this pipe to the specified size of 200mm,
After heating to a stretching temperature of approximately 100°C, both ends of the pipe are held with clamping pieces and stretched approximately 2.5 times in the axial direction, and circumferentially in a mold having a cavity shaped as shown in Figure 2. A precursor molded body was obtained by blow stretching approximately 3.0 times. This precursor molded body was cut at the end of the increasing diameter portion (the tip of the bulging portion) to form a can body with flanges formed at both ends. The wall thickness of this can body was 0.5 mm. A metal lid was double-sealed to one end of the can body, and after filling with 250 c.c. of cola, a metal lid was double-sealed to the other end.

In a storage test of this sealed can at room temperature for one month, it was found to be in good condition with no leakage from the seam and no bulging of the body.

Example 2 It has an inner and outer layer made of polyethylene terephthalate with an intrinsic viscosity of 1.0, an intermediate layer made of an ethylene-vinyl alcohol copolymer, and an adhesive layer made of a nylon 6/nylon 66 copolymer polyamide interposed between the inner and outer layers and the intermediate layer. A multilayer pipe was coextruded.
This pipe has an inner diameter of 25mm and an inner wall thickness of 12mm/
The adhesive layer was 1.5 mm/intermediate layer 3 mm/adhesive layer 1.5 mm/outer layer 7 mm.

Cut this pipe to the specified size of 150 mm, and approximately 100 mm.
After heating to a stretching temperature of 120°C, both ends of the pipe are held with clamping pieces and stretched approximately 2.5 times in the axial direction, and the pipe is heated to approximately 120°C and has a cavity shaped as shown in Figure 2. A precursor molded body was obtained by blow stretching approximately 3.0 times in the circumferential direction in the mold. This precursor molded body was cut at the end of the increased diameter portion (flange portion) to form a can body with flanges formed at both ends. A metal lid is double-sealed to one end of this can body, and 85
℃ gas volume 2.0 carbonated youth
After filling with 250 c.c., a metal lid was double-sealed on the other end.

In a storage test of this sealed can at 37°C for one month, there was no leakage from the seam and no deformation of the body.
Furthermore, there was almost no loss of carbon dioxide gas, and no discoloration or change in taste of the contents was observed.

[Brief explanation of drawings]

Figure 1 is a front view of a pipe with a partially cut-out cross section, Figure 2 is a cross-sectional view of a precursor molded body, Figure 3 is a cross-sectional view of a can body, and Figure 4 is a three-piece piece with a partially cut-out cross section. 2 is a front view of the metal end can, and FIG. 5 is a sectional view of another precursor molded body. 1... Precursor molded body, 7a, 7b... Circumferential part, 8
...Bulging portion, 10... Pipe, 11... Circumferential body, 12... Sealing flange, 13... Can body, 1
4...Metal lid.

Claims (1)

[Claims] 1. A method for manufacturing a three-piece two-metal end can, which comprises wrapping both open ends of a seamless polyester can body and a metal lid, comprising: A single-layer or multi-layer pipe made mainly of polyester is held at the polyester stretching temperature, and both ends of the pipe are gripped to form a plurality of circumferential portions corresponding to the body of the final can body, and between the circumferential portions and The blow-molded product obtained by stretching in the axial direction and blow-stretching in the circumferential direction in a split mold having an increasing diameter groove located at the end of the circumferential part and corresponding to the can body flange part. 1. A method for producing a three-piece two-metal end can, which comprises cutting the polyester at the end of the increased diameter portion to form a biaxially oriented polyester can body having flanges at both open ends.