JPS6139556Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sealed container, and more particularly to a sealed container in which a lid member is thermally bonded to the open end of a container body formed of a laminate containing paper materials. Sealed containers made of polyethylene processed paper with a lid heat-bonded to the open end of the container body, such as the curl or flange, are used, for example, to seal dairy products such as fermented milk. Adhesive strength (also called sealing strength) is determined by laws and regulations, and must meet the condition that there is no damage to the thermally bonded part or air leakage when air is pressurized until the internal pressure reaches 100 mmHg in 10 seconds. It is stipulated that
Therefore, conventional lids, such as those shown in FIG. 1, have an outer layer 1a made of aluminum foil, an intermediate layer 1b made of polyethylene film, and an inner layer 1c made of a hot melt layer mainly composed of ethylene-vinyl acetate copolymer and wax. In order to open a sealed container which is thermally bonded to the curled part 3 at the open end of the container body 2, the outer layer 2a and the inner layer 2c are made of polyethylene film, and the middle layer 2b is made of paper material. When peeling from the container, there is a gap between the inner layer 1c of the lid and the inner layer 2c of the container body, and between the inner layer 1c of the lid and the intermediate layer 1.
Because the adhesive force between b is strong, inner layer 1c and inner layer 2c
The paper does not peel off at the boundary surface of the intermediate layer 2b, but peels off easily through the inside of the paper material of the intermediate layer 2b as shown in the figure. This is because paper materials generally have a layered structure, and delamination between the layers occurs relatively easily. Therefore, fluffy paper fibers are irregularly exposed on the peeling surface 4 of the container body 2, which impairs the appearance and sometimes gives the consumer a sense of uncleanliness. On the other hand, in an attempt to prevent such delamination inside the paper material, the inner layer 1c
If the thermal adhesive force between the inner layer 2c and the inner layer 2c is weakened, the above-mentioned legal regulations are likely not to be satisfied. The present invention aims to solve the problems of the prior art as described above. In order to achieve the above object, the present invention provides a sealed container formed by thermally bonding a lid material to an open end such as a curled portion or a flange portion of a container body, in which the lid material has a metal foil as an outer layer and a metal foil as an intermediate layer. A film mainly composed of a propylene-ethylene copolymer or a blend of polypropylene and polyethylene as the inner layer, an ethylene-vinyl acetate copolymer as the inner layer,
The open end of the container body is made of a laminate having a hot melt layer mainly composed of wax and a tackifying agent, and the open end of the container body is made of a paper material laminated with a polyethylene film on at least one side, the surface facing the lid material being a polyethylene layer. The present invention provides a sealed container characterized in that the hot melt layer and the polyethylene layer are thermally bonded. The present invention will be described below with reference to drawings showing embodiments. In FIG. 2, 10 is a sealed container (the filled contents are not shown), and is formed by thermally bonding a lid 11 to the upper surface of a curled portion 13 that is the open end of the container body 12. . The lid portion 11 has an outer layer 11a, an intermediate layer 11b, and an inner layer 11c. The outer layer 11a is made of metal foil such as soft aluminum foil (including those with a printed film or baked coating formed on the outer surface), and its thickness is usually about 30 to 30 mm.
It is 50 μm. If it is thinner than about 30 μm, the strength of the lid portion 11 (for example, internal pressure resistance strength) will decrease, and the lid portion 11
When the peripheral edge 11d protruding from the curled part 13 is bent so as to contact the outer periphery of the curled part 13 (not shown), the plastic effect of the metal foil is weakened because the thickness of the metal foil is thin, and the lid cannot be used as a lid. This is because the elasticity becomes strong and the bent state cannot be maintained. On the other hand, even if it is thicker than 50 μm, the above effect does not particularly increase.
Rather, this results in higher material costs. The outer layer 11a made of metal foil enhances other gas barrier properties,
Alternatively, it has the advantage of enabling thermal bonding by high-frequency induction heating. The intermediate layer 11b is made of a film mainly composed of a propylene-ethylene copolymer or a blend of polypropylene and polyethylene. As the propylene-ethylene copolymer, both block copolymers and random copolymers can be used. It may also be a film. Alternatively, the film may be formed by blending polypropylene, polyethylene, and a small amount of ethylene-vinyl acetate copolymer. In either case, the ethylene component in the film forming the intermediate layer 11b is preferably 3 to 40% by weight. This is because if it is less than 3% by weight, the adhesive strength with the inner layer 11c described below will decrease, and the internal pressure resistance will no longer satisfy the above-mentioned legal regulations. On the other hand, the adhesive force with the inner layer 11c, which is more than 40% by weight, is too strong, and when the lid part 11 is peeled off, the inner layer 11c and the intermediate layer 11b do not separate, resulting in curled parts or This is because delamination of the paper material occurs. Further, the content of the ethylene-vinyl acetate copolymer in the film forming the intermediate layer 11b is 20
It is desirable that it is less than % by weight. If it is more than 20% by weight, the adhesive force between the intermediate layer 11b and the inner layer 11c will be too strong, and when the lid part 11 is peeled off, the paper material in the curled part will be delaminated, which is not preferable. . Thickness of intermediate layer 11b: 15 to 30 μm
It is preferable that If it is thinner than 15 μm, the curl portion 13 corresponding to the side joint portion 15 of the container body 12
This is because pinholes are likely to occur during thermal bonding in the step portion (not shown), which impairs the sealing performance.
On the other hand, if it is thicker than 30 μm, the punching property and heat transfer properties are also reduced, resulting in a reduction in thermal adhesion and an increase in the cost of the material. The outer layer 11a and the intermediate layer 11b are formed by extrusion coating or dry lamination by interposing an anchor cord agent (for example, titanium ester) or an adhesive (for example, urethane adhesive, acid-modified polyolefin resin, etc.) (not shown). They are then laminated. The inner layer 11c is a hot melt layer mainly containing ethylene-vinyl acetate copolymer, wax, and tackifier. The content of ethylene-vinyl acetate copolymer in the hot melt layer is 30 to 60% by weight
It is desirable that If it is less than 30% by weight,
This is because the thermal adhesive strength with the polyethylene layer (in the curled portion 13) forming the inner layer 12c of the container body 12 may be reduced, and the internal pressure resistance strength may no longer satisfy the above-mentioned rule. Further, the hot melt layer is usually formed by coating the surface of the intermediate layer 11b in a molten state with a gravure cylinder, but if it exceeds 60% by weight, the viscosity becomes too high and the above coating becomes difficult. . As the wax, polyethylene wax, paraffin wax, microcrystalline wax, etc. are used. The content of wax in the hot melt layer is preferably 30 to 50% by weight. If it is less than 30% by weight, the viscosity will be too high and it will be difficult to apply the above coating, while if it is more than 50% by weight, the viscosity will be too low and it will be difficult to apply the above coating uniformly. It is. Examples of the tackifier include petroleum resins, terpene resins, rosin esters, and the like. The content of the tackifying agent in the hot melt layer is preferably 5 to 30% (by weight). If it is less than 5% by weight, the adhesive strength with the intermediate layer 11b may decrease, and the internal pressure strength may not meet the legal regulations.On the other hand, if it is more than 30% by weight, the adhesive strength with the intermediate layer 11b will be strong. This is because when the lid part 11 is peeled off, the intermediate layer 11b and the inner layer 11c are not separated, and the paper material that is the intermediate layer 13b of the curled part 13 is separated. In addition to the above, the hot melt layer usually contains about 0.3 to 1.0% by weight of a lubricant (eg, silicone oil). inner layer 1
1c, that is, the thickness of the hot melt layer is preferably 20 to 50 μm. This is because if it is thinner than 20 μm, pinholes are likely to occur in the portion of the curled portion 13 facing the side surface joint portion 15 during thermal bonding, while if it is thicker than 50 μm, it will result in decreased punching properties and increased material costs. Container body 12 and paper material as main layer (usually thickness 200~
400 μm), and at least the layer (inner layer 12c in FIG. 2) forming the surface facing the lid member 11 is made of polyethylene film (thickness preferably 50 to 100 μm). This is to make the container body 12 moisture-proof and waterproof, and to ensure good thermal adhesion with the inner layer 11c of the lid material. Although the outer layer 12a in FIG. 2 is made of polyethylene film, it may be made of other materials (eg, vinylidene chloride film, etc.). The curl part 13 of the lid part 11 and the container body 12 is formed by a known method such as a hot plate pressure bonding method, a high frequency induction heating method (provided that the lid material 11 includes a metal foil layer), an impulse sealing method, etc. 160～200゜C×0.1
The thermal bonding portion 14 is formed by heating and pressing for ~1.0 seconds. In order to peel off the heat-bonded lid 11, when the peripheral edge 11d of the lid is picked up with fingers and pulled up, the transparent lower layer 11c of the lid at the heat-bonded part 14 is removed, as shown in FIG. ' is separated from the intermediate layer 11b and remains adhered to the inner layer 12c of the container body. Therefore, interlayer peeling does not occur in the paper material that is the middle layer 12b of the container body, and the upper surface of the curled portion 13 after opening is beautiful and clean. In the above embodiments, the open end portion is a curled portion that curves outward, but it may also be a curled portion that curves inward. In this case, the outer layer of the container body must be made of polyethylene film. Further, the open end portion may be a flange portion. According to the present invention, since the intermediate layer of the lid is made of a film mainly made of propylene-ethylene copolymer or a blend of polypropylene and polyethylene, the lid and the opening end of the container body are firmly bonded by heat. Even if the sealing strength meets legal regulations, the paper material at the opening edge can be easily opened without delamination, and the top surface of the opening edge after opening is beautiful and clean. have an effect. Examples will be described below. Example The middle layer 12b is made of paperboard with a thickness of 270 μm, and the inner layer 12c and the outer layer 12a have a thickness of 60 μm and
Made of 20μm polyethylene film, diameter 70
A container body 12 for filling fermented milk of the type shown in FIG. 2 with a length of 70 mm and a height of 70 mm was prepared. Also, the outer layer 11a
is a soft aluminum foil with a thickness of 40 μm, intermediate layer 1
1b is propylene with an ethylene content of about 7% by weight.
A 20 μm thick film made of ethylene random copolymer ((registered trademark) Torejuan No. 3401, manufactured by Toray Industries, Inc.) (both were dry laminated via a urethane adhesive), and A lid part 11 having an inner layer 11c having a thickness of 40 μm and having various formulations as shown.
A sealed container 10 was prepared by heating and pressing at approximately 180° C. for 1 second using a hot plate method to thermally bond the lid portion 11 to the curled portion 13 of the container body. Note that, except for the fact that the intermediate layer 11b of the lid part 11 for comparison was made of a low-density polyethylene film,
A sealed container was produced in the same manner as in the example. The results of testing for container damage or air leakage when compressed air was introduced from the body of each of the above sealed containers (n=10) and the internal pressure was increased to 100 mmHg for 10 seconds, and the curled portion 13 after opening. Table 1 shows the appearance of the top surface. 【table】

[Brief explanation of the drawing]

Fig. 1 is a longitudinal cross-sectional view of the main part showing a state in which a sealed container is being opened as a comparative example, Fig. 2 is a partially cutaway front view of a sealed container according to an embodiment of the present invention, and Fig. 3 is a partially cutaway view of the sealed container according to an embodiment of the present invention. FIG. 2 is a longitudinal cross-sectional view of a main part showing a state in which the sealed container is being opened. 10... Sealed container, 11... Lid, 11a...
Outer layer, 11b...middle layer, 11c...inner layer, 12
... Container body, 12b ... Middle layer (paper material), 12
c...Inner layer (polyethylene film layer), 13...
... Curled part (opening end), 14... Heat bonding part.

Claims (1)

[Scope of utility model registration request] In a sealed container formed by thermally bonding a lid material to an open end such as a curled portion or a flange portion of a container body, the lid material has a metal foil as an outer layer and a propylene-ethylene copolymer or polypropylene as an intermediate layer. It consists of a laminate having a film mainly composed of a polyethylene blend, and a hot melt layer mainly composed of an ethylene-vinyl acetate copolymer, wax, and a tackifying agent as an inner layer, and the opening end of the container body is connected to the lid material. 1. A sealed container characterized in that opposing surfaces are made of a polyethylene layer, at least one side is made of a paper material laminated with a polyethylene film, and the hot melt layer and the polyethylene layer are thermally bonded.