JPH0411101B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for seaming plastic cans, and more specifically, a method for making it easier for the plastic body hook to come out during double seaming, and for sealing the seamed part. This article relates to improvements in seaming methods to increase reliability.

(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, in Japanese Patent Application Laid-open No. 60-45146,
In this type of composite container, it is described that the thermoplastic polyester in the seam portion is whitened by thermal crystallization.

(Problem to be Solved by the Invention) However, in order to double-seal the end of the plastic container body and the metal lid, the plastic end must be bent approximately 180 degrees, and the plastic end must be mechanically connected to the metal lid end. Although it is necessary to have a strong engagement, plastic has poor bendability compared to metal.
Moreover, it has a characteristic of being poor in rigidity compared to metal.

For this reason, in double-sealed cans using plastic container bodies, it is difficult to ensure a sufficiently large overlap width between the body hook and cover hook, which is said to be the most important for sealing, and the sealing performance of the seamed portion is However, the results are still not fully satisfactory. In addition, it is often difficult to mechanically firmly engage and fix the seaming end of the plastic container body in the double seaming part, and the seaming end of the container body may come off, resulting in a sufficient pressure-resistant seal. The disadvantage is that you cannot gain power.

Therefore, the present invention provides a plastic can with a metal lid in which double seaming is performed between the metal lid and the opening end of the plastic container body, in which the overlap width between the body hook and the cover hook can be made sufficiently large. Moreover, it is an object of the present invention to provide a means for firmly mechanically fixing the seaming end of a plastic container body within a double seaming part.

(Means for Solving the Problems) The present invention provides a method for seaming a plastic can body having a seaming flange at an open end and a metal lid having a seaming end around the plastic can body. After thermally forming a flange part inclined downward from the horizontal plane by 5 to 45 degrees on the body, and forming the flange part at a temperature in the range of above the glass transition point Tg and below the normal melting point, the flange part is attached to the metal lid. It is characterized by engaging with the seaming end to perform double seaming,
With this, the above problem can be solved.

(Function) In FIG. 1 showing the main parts of the plastic can body used in the present invention, the can body 1 has a circumferential side wall portion 4 having an inner circumferential surface 2 and an outer circumferential surface 3. A flange portion 6 is provided at the open end of 4 with a root 5 interposed therebetween. While the conventional seaming flange part is located on the horizontal plane H, a remarkable feature is that the flange part 6 is provided downward at an angle α from the horizontal plane H. α is set between 5 and 45 degrees, particularly between 5 and 40 degrees.

In FIGS. 2A and 2B for explaining the process of seaming the plastic can body 1 and the metal lid, the metal lid 10 is
has a flat panel portion 11, a countersink portion 12 having a V-shaped cross section is provided on the outer periphery of the panel portion 11, and a groove portion 13 and a curl portion 14 are further provided on the outer periphery. In FIG. 2, the groove 13
is shown with its opening facing downward, and sealing compound 1 is applied to this groove 13.
5 is applied by lining. The outermost curling portion 14 has its tip curved inward.

The metal lid 10 is attached to the plastic container body 1 such that the flange portion 6 of the body is inserted into the gap of the groove portion 13.
is combined with the upward lift pressure against the container body 1.
P ₁ is applied, and a radially inward seaming pressure P ₂ is applied to the lid curl portion 14 to deform the lid curl portion 14, thereby performing double seaming.

In FIG. 3, which shows the structure of the double seam portion 20 formed, the plastic container body 1 has a downward body hook 21, and this body hook 21 is
The flange portion 6 shown in FIG. 1 is formed by forcibly bending downward together with the curled portion of the metal lid 10 for tightening. On the other hand, the metal lid 10 has a cover hook 22 that faces upward in the tightened state, with an outer circumferential portion 23 on the outer circumferential side of the cover hook 22 and a counter sink portion 2 on the inner circumferential side of the cover hook 22.
It has 4. Thus, the body hook 21 of the plastic container body is connected to the cover hook 22 of the metal lid.
The straight top portion 25 of the plastic container body is engaged with a countersink portion 24 of the metal lid, or is further sandwiched between the countersink portion 24 and the cover hook 22. Furthermore, there is a lower gap 26 at the tip of the body hook 21, and an upper gap 27 at the tip of the cover hook 22.

According to the present invention, when a plastic container body is provided with a flange portion 6 whose tip is inclined downward from a horizontal plane by 5 to 45 degrees, an overlap portion where a body hook portion 21 and a cover hook portion 22 overlap is formed.
It becomes possible to make the width of the OL sufficiently large,
Furthermore, this is based on the knowledge that seaming workability and sealing reliability are significantly improved.

Now, when sealing a flanged container body made of polyethylene terephthalate with a metal lid, the inclination angle α of the flange part from the horizontal plane and the lift pressure of the container body required to cause deformation of this inclination angle α P ₁
Figure 4 shows the relationship between . In other words, according to the results shown in Fig. 4, the lift pressure required for seaming is significant at the initial stage when the flange is undeformed, and when the deformation angle becomes large to a certain extent, the required lift pressure becomes less than the initial lift pressure. It becomes clear that much less is required.

As described above, according to the present invention, by attaching a reverse taper with an inclination angle α of 5 to 45 degrees to the flange, the lift pressure required to form the body hook is lower than that of a conventional flanged container body. Approximately 30 to
This makes it possible to reduce this to 60%, and as a result, it becomes easier to apply the body lift, and it also becomes possible to make the overlap width OL sufficiently large. In addition, when comparing plastic container bodies with the same thickness, it is difficult to apply large lifting pressure to metal container bodies because the buckling pressure is lower than that of metal container bodies. A significant advantage is that it is possible to perform good body lifting and complete seaming with a relatively small lift pressure.

It is important to keep the inclination angle α within the above range; if it is smaller than the above range, the effect of lowering the lift pressure during seaming and improving the body hook extension will be insufficient; If the seaming pressure P ₂ is also large, it becomes difficult to push the tip of the curled portion of the metal lid inward from the tip of the body flange portion, and the double seaming operation itself tends to become difficult. In addition, the present invention further combines the strong seaming or sealing reliability of the seaming part,
When forming the flange, the temperature should be adjusted to the glass transition point.
It is important to keep the temperature above Tg. If the heating temperature falls below the glass transition point, stress will be present in the flange during formation, so during subsequent tightening,
It cannot withstand lift pressure and seaming pressure, making it difficult to achieve a strong seal. Further, it is desirable that the heating temperature be below the melting point. When the heating temperature exceeds the normal melting point,
Naturally, the moldability of the resin deteriorates due to melting and the like.

(Operations and Effects of the Invention) According to the present invention as described above, double seaming is performed between the plastic container body and the metal lid with good seaming workability and excellent sealing reliability and pressure-resistant sealing force. This makes it possible to reliably prevent leakage problems even for contents that have their own pressure, such as carbonated drinks and beer, or contents that have a reduced pressure or vacuum inside. Ta.

(Description of Preferred Embodiments of the Invention) The plastic container body used in the present invention may be made of any plastic, such as polyolefin such as polyethylene, polypropylene, ethylene-propylene copolymer, or ionomer; polyester such as polyethylene terephthalate; nylon 6, nylon 6 , 6, polyamides such as nylon 6/nylon 6,6 copolyamide; various polycarbonates;
It can be made of any resin such as polyvinyl chloride resin; vinylidene chloride resin; polystyrene, styrene-butadiene copolymer, etc. These resins may be used alone in the container body, or may be used in the form of a blend of two or more, and may be used in the form of a laminate or coating structure of multiple resins to form the container body. It's okay to be hit. Suitable examples of laminates include inner and outer layers of polyolefin or polyester and an intermediate layer of gas barrier resin, such as ethylene-vinyl alcohol copolymer, polyamide, vinylidene chloride resin, etc., depending on the appropriate coating structure. Examples include those in which a vinylidene chloride resin coating layer is provided on the inner and/or outer surfaces of polyolefin, polyester, polycarbonate, or styrene resin.

The plastic container body of the present invention may have a cylindrical shape with both ends open, as shown in FIG. It can be something. Further, in any of these cases, a neck-in portion 31 narrowed to a small diameter may exist directly below the flange portion 6.

The plastic container body 1 can be obtained by any molding method, such as injection molding, extrusion molding, blow molding, stretch blow molding, drawing or drawing and ironing.

The circumferential side wall 4 of the plastic container body 1 may be substantially unoriented, but from the viewpoint of mechanical strength, rigidity, impact resistance, gas barrier properties, transparency, etc., it may be oriented in at least one direction, preferably in two directions. It is preferable that the molecules are oriented in this manner. For example, a container body with biaxially oriented molecules can be produced by stretching a preformed pipe or preform in the axial direction.
A container obtained by expanding and stretching in the circumferential direction and having molecules oriented in the axial direction can be obtained by stretching a sheet, pipe, or other preform by means of tensile stretching, drawing, drawing and ironing, etc. .

Although the present invention is applicable to the various plastics mentioned above, it is particularly advantageous to containers made of thermoplastic polyesters, particularly polyesters containing ethylene terephthalate repeating units as a main component. Here, thermoplastic polyester whose main repeating unit is ethylene terephthalate is usually 80 mol% of the acid component.
Above, preferably 90 mol% or more is terephthalic acid, and 80 mol% of the glycol component, preferably 90 mol% or more
It means a polyester in which ethylene glycol accounts for mol% or more, and the remaining acid components include 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, hexacidroterephthalic acid, and other glycol components such as propylene glycol, 1,4-butanediol, neopentyl glycol, diethylene glycol, 1,6-hexylene glycol, cyclohexanedimethanol,
Polyester containing 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(4-hydroxyethoxyphenyl)propane, or p-oxybenzoic acid, p-hydroethoxybenzoic acid, etc. as an oxyacid means. 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 the content of ethylene terephthalate is 80 mol % or more by mixing polyester terephthalate and another thermoplastic polyester.

The thermoplastic polyester used must have an intrinsic viscosity of 0.55 or more, preferably 0.6
Above, it more preferably has an intrinsic viscosity of 0.7 to 1.4. 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 applies to polyesters and other resins such as metaxylylene group-containing polyamides, polyvinylidene chloride, acrylonitrile styrene copolymers,
It also includes a can-shaped container made of a laminated cylinder with a resin having better gas barrier properties such as an ethylene vinyl alcohol copolymer or a coated polyester cylinder. This polyester container is
Density at 20℃ is 1.335g/cc or more, especially 1.360
It is desirable that the crystallization is oriented so that the ratio of
It is desirable that heat fixation is performed.

In the plastic container body used in the present invention,
Although the thickness T _W of the circumferential side wall portion 4 varies depending on the type of plastic, it is generally preferable to have a thickness of 0.2 to 1.0 mm, particularly 0.2 to 0.8 mm, while the thickness T _F of the flange portion 6 is 0.1 to 0.8mm, especially
It is preferably in the range of 0.15 to 0.6 mm. The thickness of the circumferential side wall portion and the thickness of the flange portion may be the same or may be different from each other. Although the radial dimension of the flange portion 6 varies depending on the dimensions of the entire container, it is generally within the range of 2 to 5 mm, particularly preferably within the range of 2 to 4 mm.

In FIGS. 7 and 8 illustrating the process for forming the slanted inversely tapered flange shown in FIG. 1, a support member 4 supporting a cylindrical container body 1
1 and the flanging die 42, the flange portion can be easily formed. The support member 41 and the flanging die 42 are provided coaxially and movably relative to each other in the axial direction, and the support member 41 tightly holds the container body 1 so as not to shift in the axial direction. , and the upper part thereof is provided with a molding surface 43 having a shape and dimensions corresponding to the lower surface of the flange portion 6 in FIG. On the other hand, the flanging die 42 has a tip portion 44 that is inserted into the interior of the body portion 1, and has a molding surface 45 around the tip portion 44 having a shape and size corresponding to the upper surface of the flange portion. When these molded members engage with each other as shown in FIG. 8, the flange portion 6 according to the present invention is formed. During this forming process, it is preferable to heat the processed part of the plastic can body to a temperature higher than the glass transition point of the plastic in the later seaming process, and of course, the temperature should be kept at a temperature that is not too high, i.e., the melting point that is normally considered. The heating should be below.

Of course, it should be understood that the formation of the flange portion in the present invention is not limited to that shown in the drawings, and that any form can be used.

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 seaming 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 thickness of the can lid varies depending on the thickness of the metal material, but it is generally 0.15 to 0.50 mm, especially 0.20 to 0.50 mm.
A value in the range of 0.45mm is good.

Figure 9 shows a suitable example of the can lid,
An annular rim portion 1 is provided around the center panel portion 11.
A circumferential tightening groove 13 is provided through the sealing member 2, and a lining layer 15 of a sealing rubber composition is provided within this groove. A score 17 is provided on the center panel portion 11 to define a portion 16 to be opened.
An opening piece 18 is attached to the portion 16 to be opened via a fixing member 19 such as a rivet.

For the double seaming of the plastic container body and the can lid, a seamer conventionally used for seaming metal cans can be used.

According to the present invention, it is easy to make the overlap width between the body hook and the cover hook 0.5 mm or more, particularly 0.7 mm or more.

(Example) Example 1 Polyethylene terephthalate was extruded using a conventional method to form a product with an outer diameter of 66 mm, an inner diameter of 65.2 mm, and a wall thickness of 0.4 mm.
A cylindrical body was made. Next, both ends of this plastic body were cut to maintain a constant height of 120 mm, and then thermoforming was carried out to form an inclined flange as shown in FIG. At this time, the thermoforming conditions were to heat the processed part of the plastic can body to form the flange part, and in this case, the temperature was approximately 75°C, which is higher than the glass transition point Tg of the polyethylene terephthalate.
The processed part was heated to perform thermoforming. At this time, the inclination angle of the flange die and support plate was 30 degrees.

The various characteristic values of the plastic can body obtained at this time were as follows.

Thickness of body wall 0.4mm Thickness of flange 0.4mm Incline angle of flange 30±1 degree Flange length 3mm Body height 114mm A metal lid (plate) is attached to one side of the plastic can body which has a flange with this inclination angle. Thickness 0.39mm,
5052 aluminum material), filled with carbonated water at 4.0 gas volume in a filling machine, and double-sealed about 2000 easy-open type aluminum lids using a high-speed seamer with a seaming speed of 500 cans per minute. No trouble occurred during the seaming work.

At this time, the lifter pressure when tightening both the top and bottom metal lids was 50 kgf.

In addition, the seaming part after filling is cut out and overlapped.
As a result of measuring the width of the OL (50 cans measured), a length of 0.8 mm or more was secured in all cases, and good seaming performance was obtained.

Furthermore, these filled plastic cans (500 cans)
When stored at 37°C for 24 hours, no aluminum lids were found to have come off due to internal pressure.

In addition, we performed a drop test from a height of 1 m using the same filled plastic cans packed in cartons, but no aluminum lids were found to come off or any leaks were found, and no pressure drop was confirmed when measuring the internal pressure. Nakatsuta.

Comparative Example 1 A plastic can similar to that of Example 1 was produced except that the flange portion was formed horizontally. At this time, the lifter pressure during seaming was set to 50 Kgf as in Example 1, but sufficient body hooking was not achieved and approximately 100 Kgf was required. When these cans were subjected to a storage test, 375 out of 500 had aluminum lids coming off and leaking. We also observed the seaming condition and found that the overlap width was 0 to 0.7.
mm and the variation was very large.

Comparative Example 2 A plastic can was produced in the same manner as in Example 1 except that the inclination angle of the flange portion was formed at 60 degrees. At this time, the lifter pressure was 50Kgf, which is the same as in Example 1, but the overlap width was not secured, and there were many cases where the cover hook part and the two plates on the outer periphery of the aluminum lid were tightened. Filling and seaming were stopped midway through before it reached the point where it could be used for filling and storage.

Comparative Example 3 A plastic can was produced in the same manner as in Example 1, except that the processed part forming the flange was molded at room temperature, but the flange length required in the present invention was Also, the inclination angle could not be obtained, resulting in can bodies with large dimensional variations.

In addition, we tried seaming the plastic can bodies of the plastic can bodies for which we had obtained a tilt angle, but in most cases, not only could we not obtain the desired body hook, but the flanges frequently cracked during the seaming process, resulting in leakage and being unusable. It was possible.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the main parts of a plastic can body formed by the method of the present invention, FIG.
Fig. B is an explanatory diagram showing the seaming process, Fig. 3 is an enlarged sectional view showing the structure of the double seaming part, Fig. 4 is a diagram showing the relationship between the inclination angle α of the flange part and the lift pressure P ₁ ,
5 and 6 are cross-sectional views showing examples of container bodies showing preferred embodiments of the method of the present invention, and FIGS. 7 and 8 show examples of the method of manufacturing container bodies according to the present invention. The drawings and FIG. 9 are drawings showing a preferred example of the metal lid. 1... Can body, 4... Circumferential side wall part, 6... Flange part,
DESCRIPTION OF SYMBOLS 10... Metal lid, 11... Panel part, 12... Counter sink part, 13... Groove part, 14... Curl part, 15
...Sealing compound, 21...Body hook, 22...Cover hook, 25...Straight top, 26...Lower gap, 27...Upper gap, 31
...Neck-in part, 41... Supporting member, 42... Flange die, 43... Molding surface.

Claims (1)

[Claims] 1. A method of seaming a plastic can body having a seaming flange at the open end and a metal lid having a seaming end around the periphery, the method comprising seaming the plastic can body at an angle of 5 to 45 degrees downward from the horizontal plane. After the inclined flange is thermally formed and the temperature at the time of thermal formation is higher than the glass transition point Tg of the plastic, the flange is engaged with the seaming end of the metal lid to perform double seaming. A method for seaming plastic cans, characterized by performing the following steps.