JP3014510B2 - Sealed container - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sealed container having excellent storage stability and physical properties.

[0002]

2. Description of the Related Art Conventionally, a storage container using plastic has a structure in which an ethylene-vinyl alcohol copolymer or a vinylidene chloride copolymer is used as a gas barrier layer, and both sides are laminated with a polyolefin such as polypropylene or polyethylene. Has been used. These have been widely used as having both gas barrier properties and sealing properties with the lid. However, as the research on the deterioration of the contents progresses, in the container containing the polyolefin in the innermost layer, the innermost layer adsorbs the flavor of the contents, or the odor component of the resin layer of the innermost layer is transferred to the contents. It was found that the innermost layer other than the polyolefin was required.

As containers having these flavor characteristics, containers having an inner layer of polyethylene terephthalate or ethylene vinyl alcohol copolymer have been proposed.
These can be used for hot-filled contents or pasteurized (100 ° C or less) contents, but should be used for high-temperature sterilization (retort foods) because of the drawback that the innermost layer is softened by heat. Could not be done. On the other hand, polycarbonate was considered as a resin to compensate for these disadvantages, but in combination with other resins, because polycarbonate is a heat-resistant resin, when vacuum forming or the like is performed in a multilayer sheet layer, molding cannot be performed satisfactorily. Had the disadvantage that Also, for the polycarbonate according to the present invention,
Few lids exhibit easy-opening properties, and have the disadvantage that the sealing properties are impaired due to contamination of the sealing surface by the contents or hot water sterilization after sealing.

[0004]

SUMMARY OF THE INVENTION The present invention has been made as a result of various studies to solve these problems of the conventional hermetically sealed container. An object of the present invention is to provide a container which does not impair the flavor of various foods, and which is excellent in preservability, sealability, and easy-openability.

[0005]

According to the present invention, a polycarbonate (A), a polypropylene (B), and an ethylene vinyl alcohol copolymer (C) are prepared from the innermost layer of a container by AB.
The innermost polycarbonate layer (A) is 10% or less of the total thickness, the melt flow rate of polypropylene as the constituent resin is 2.0 or less, and the polypropylene layer is Is 50% or more of the whole, the laminate strength of the (A) layer as the seal layer and the corresponding adjacent layer (B) is 300 to 2
000 g / 25 mm, wherein a container provided with an infinite number of minute concave portions on a part or all of the peripheral surface of the container flange portion is sealed with a gas-barrier lid with a sealing strength exceeding the laminate strength. It is a sealed container.

As the polycarbonate used in the present invention, any polycarbonate can be used. Further, a mixture of a small amount of polyethylene terephthalate or the like can be used as long as the flavor characteristics are not affected.

As long as the polypropylene used in the present invention has a melt flow rate of 2.0 or less, various polypropylenes such as homopoly, copoly and random can be used. Further, other resins such as polyethylene may be mixed as long as the melt flow rate is not changed.

As the ethylene vinyl alcohol copolymer used in the present invention, any copolymer can be used as long as the ethylene copolymerization ratio is 20 to 45%.

As a method for laminating these resins, known laminating techniques such as a coextrusion method, a coextrusion laminating method, an extruding laminating method and a dry laminating method are used. In order to bond the respective resins for lamination, an adhesive or an adhesive resin suitable between the individual resins is used. Further, as a method of forming these multilayer sheets into a container, generally, a vacuum forming method, a pressure forming method, or a vacuum pressure forming method is used.

As the lid material used in the present invention, any material can be used as long as it can seal with the innermost layer and has gas barrier properties. For example, there are a three-layer film of polycarbonate as a sealant layer, a vinylidene chloride copolymer as a barrier layer, a nylon film as an outermost layer, a heat-sealing polyethylene terephthalate as a sealant layer, an aluminum foil as a barrier layer, and a polyethylene terephthalate as an outermost layer. Further, the lid is not limited to a film shape, but may be a molded product. For example, a multi-layer sheet in which the sealant is heat-sealable polyethylene terephthalate and the barrier layer is an ethylene vinyl alcohol copolymer and the outer layer is polypropylene can be formed into a drop lid shape by vacuum forming and used. As a method for welding these lids and the main body container, a known heat sealing method, ultrasonic sealing method, and high-frequency sealing method are used.

In the present invention, a method for forming a minute concave portion on a part or all of the peripheral portion of the flange portion of the container includes ultrasonic treatment, heating or cold pressing, pressurization using high frequency, and the like. It can be performed by an appropriate method. FIG. 1 is a cross-sectional view showing a sealed container of the present invention, wherein 1 is a container main body, 2 is a flange portion, and 3 is a lid material. On the upper surface of the flange, as shown in FIG. 2, countless minute concave portions 4 are formed in advance. Among them, the method of performing ultrasonic treatment using a convex ultrasonic horn is most effective in that a uniform and fine concave pattern can be formed on the entire surface of the flange. It is desirable that the number of minute concave portions formed is in the range of 50 to 500, but it is not particularly limited. Thus, a sealed container is manufactured by superposing the sealant layer 5 of the lid member 3 and the flange portion 2 of the container main body 1 having the innumerable minute concave portions formed on the upper surface in a state of FIG.

[0012]

The operation of the present invention will be described. The innermost polycarbonate layer used in the container of the present invention is used for protecting the flavor of the contents. Further, polycarbonate is excellent in heat resistance among thermoplastic resins and can be used for foods requiring retort sterilization or the like. However, polycarbonate requires a large amount of heat at the time of container heat molding because of its heat resistance. Further, it is said that the drawdown at the time of heating the sheet is large, and is generally not suitable for the vacuum forming method and the pressure forming method of the sheet heat forming type. In the present invention, therefore, the thickness of the polycarbonate is set to 1% of the total thickness.
This problem is solved by controlling the content to 0% or less and selecting a polypropylene layer described later. As for the suitability of the flavor to the contents, it is desirable that the above-mentioned thickness ratio can achieve a sufficient function, and it is more preferable to suppress the content to 5% or less.

The polypropylene layer used in the present invention is used as a strength maintaining layer, a water vapor barrier layer, and a moldability improving layer. In the present invention, the reason why the thickness ratio of the polypropylene layer is specified to be 50% or more and the melt flow rate of the used polypropylene is set to 2.0 or less is because the container moldability is involved. In the thermoforming of a sheet mainly composed of polypropylene, the melt flow rate of the resin used for the formed sheet greatly affects the moldability.
In other words, in the case of polypropylene, if the melt flow rate is large, the drawdown during heating is correspondingly large, and a satisfactory molded product cannot be obtained. The reason why the thickness ratio of the polypropylene layer is specified in the present invention is that if the polypropylene layer has a thickness ratio of 50% or less, the drawdown at the time of molding becomes large as described above, which is inconvenient for container molding. This is to minimize the water absorption of the ethylene vinyl alcohol copolymer as the gas barrier layer during retort sterilization. The ethylene vinyl alcohol copolymer serving as the gas barrier layer has the most excellent oxygen gas barrier property among general-purpose thermoplastic resins, but its barrier property is reduced by water absorption. In addition, this tendency of water absorption increases as the temperature increases, and when a container is treated in heated water, an outer moisture protection layer is required. For this reason, the outer water vapor barrier layer needs to have a certain thickness.

When polycarbonate is used as the sealing layer, various sealing methods such as heat sealing, ultrasonic sealing, and high frequency sealing can be considered. However, when a lid material that can be welded to polycarbonate is used, a general method is used. It is difficult to provide easy-opening properties, and there is also a slight amount of lid sealant that can provide easy-opening properties.However, after filling and sealing the contents, heat treatment, etc., impairs the sealability. there were.

However, in the container sealed by the process used in the present invention, as shown in FIG. 4, the sealant layer 5 of the lid 3 is completely filled in the minute concave portion formed on the upper surface of the flange portion 2. ing. Therefore, it is structurally strong and the pressure resistance against external pressure and internal pressure is extremely stable. In this case, the adhesive force at the Y point at the bottom of the concave portion is relatively weaker than the adhesive force at the position A where the sealing pressure is high.

When the lid material 3 is pulled upward, peeling occurs when the lid material 3 is pulled upward, as shown in FIG. 5, peeling occurs between a portion having a strong adhesive force, that is, between the (A) layer and the (B) layer, and a small amount is formed inside the container flange portion. The sealant layer (A) is broken due to the concave portion, and the pattern in which the container and the cover material are separated continuously advances. In this process, the unique strong and weak adhesive mechanism according to the present invention works skillfully, so that easy opening without a sense of resistance becomes possible.

[0017]

EXAMPLES The effects of the present invention will be described below with reference to examples. Table 1 shows the configurations of three types of multilayer sheets used in the present invention and four types of multilayer sheets used for comparison. These multilayer sheets were prepared by a co-extrusion method. These multi-layered sheets are 80 mm in diameter and 50 m in height using an indirect heating type vacuum forming machine.
m, a container with a bottom diameter of 40 mmφ is filled with two kinds of contents, orange juice and curry, the former is hot-filled at 60 ° C. After storage for one month, the storage stability and flavor suitability were compared. In addition, comparative evaluation was also performed on moldability during thermoforming. Table 2 shows the results.

In the container having the structure of Example 1 shown in Table 1, the laminate strength of the sealant layer and the adjacent layer was set to 100.
A convex ultrasonic wave having a projection number of 256 / cm ² is applied to the upper surface of the flange portion of the container according to the present invention adjusted to have a width of 0 g / 25 mm and subjected to ultrasonic treatment to form an infinite number of minute concave portions over the entire area. did. The lid material used was a laminate obtained by dry laminating a sealant layer (thickness: 30 μm) made of polycarbonate and 6-6 nylon (thickness: 25 μm). A sealant layer of a lid material was placed on the upper surface of the flange portion of the container, and heat-sealed twice under the conditions of a surface pressure of 10 kg / cm ² , a temperature of 210 ° C. and a time of 1.5 seconds. When the lids were opened for the 20 sealed containers thus manufactured, all the containers were opened smoothly with a light opening feeling to the end, and the state of the opening surface was good.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

According to the present invention, a container which does not cause a change in the flavor of the contents can be obtained as compared with a conventional multi-layer plastic barrier container. In addition, the conventional molding method can be used, and a molded product as inexpensive as the conventional one can be manufactured. Further, by sealing the lid and the container in which countless minute recesses were formed, the lid could be opened with a smooth opening feeling.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a sealed container of the present invention.

FIG. 2 is a plan view of the container showing a state in which a lid is half-opened.

FIG. 3

FIG. 4 is an enlarged cross-sectional view showing a process of sealing a lid member.

FIG. 5 is an enlarged sectional view of a flange portion showing a state in which a lid is opened.

Claims (1)

(57) [Claims] 1. Polycarbonate (A), polypropylene (B), ethylene vinyl alcohol copolymer (C)
Are laminated in the order of ABCB from the innermost layer of the container, the polycarbonate layer (A) of the innermost layer is 10% or less of the total thickness, and the melt flow rate of polypropylene as the constituent resin is Is not more than 2.0 and the polypropylene layer is 50% or more of the whole, the laminate strength between the polycarbonate layer (A) and the corresponding adjacent polypropylene layer (B) is 300 to 20.
00g / 25 mm, wherein a container provided with an infinite number of minute recesses on a part or all of the peripheral surface of the container flange portion is sealed with a gas-barrier lid with a sealing strength exceeding the laminate strength. And sealed container.