JPH0577865A - Sealed container - Google Patents

Abstract

PURPOSE:To obtain a container which provides an excellent preservability without impairing the flavor of foods by sealing the container provided with very small recess parts with a gas-barrier lid by a sealing strength exceeding the laminate strength of a specific value. CONSTITUTION:The wall of a container 1 is constituted of a polycarbonate layer A, a polypropylene layer B, an ethylenevinyl alcohol copolymer layer C and the polypropylene layer B formed in that order from the innermost layer. The total container wall consists of at most 10% of the polycarbonate layer A and at least 50% of the polypropylene layer B and the polypropylene layer B has a melt flow rate of at most 2.0. To open a container easily, very small recess parts 4 are preformed on the upper surface of the flange 2 of the container in an infinite number by using an ultrasonic horn having a raised shape. This container is sealed with a gas-barrier lid 3 by a sealing strength exceeding the laminate strength of 300-2000/25mm.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Conventionally, storage containers made of plastic have a construction in which ethylene vinyl alcohol copolymer or vinylidene chloride copolymer is used as a gas barrier layer, and both sides thereof are laminated with a polyolefin such as polypropylene or polyethylene. Has been used. These have been heavily used as those having both gas barrier properties and sealing properties with lids. However, as researches such as alteration of contents proceed, in containers containing polyolefin in the innermost layer, the flavor of the contents is adsorbed by the innermost layer, or the odorous component of the resin layer of the innermost layer is transferred to the contents. It was found that the innermost layer other than polyolefin was required.

As containers having these flavor characteristics, containers having polyethylene terephthalate or ethylene vinyl alcohol copolymer as an inner layer have been proposed.
These can be used for hot-filled contents and pasteurized (100 ° C or less) contents, but for high-temperature sterilization (retort foods), the innermost layer has the disadvantage of being softened by heat. I couldn't. On the other hand, polycarbonate was considered as a resin that compensates for these drawbacks, but when combined with other resins, polycarbonate is a heat-resistant resin, and therefore, when vacuum forming or the like is performed with a multilayer sheet layer, the molding cannot be satisfied. It had the drawback. Further, with respect to the polycarbonate according to the present invention,
There are few lids that exhibit easy-opening property, and there is a drawback that the sealing property is impaired due to contamination of the sealing surface with the contents or hot water sterilization after sealing.

[0004]

The present invention has been made as a result of various studies in order to solve these problems of the conventional hermetically sealed container, and the object thereof is the contents depending on the container. An object of the present invention is to provide a container which is excellent in storability, hermeticity, and easy opening without damaging the flavor of various foods.

[0005]

According to the present invention, polycarbonate (A), polypropylene (B) and ethylene vinyl alcohol copolymer (C) are used in the order of AB from the innermost layer of the container.
-CB is laminated in this order, 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 In a container in which the ratio is 50% or more of the total, the laminate strength between the layer (A) as a seal layer and the adjacent layer (B) corresponding thereto is 300 to 2
000 g / 25 mm, characterized in that a container having innumerable minute recesses on a part or all of the peripheral surface of the container flange is sealed with a lid having gas barrier properties with a sealing strength exceeding the above-mentioned laminating strength. It is a sealed container.

Any polycarbonate can be used as the polycarbonate used in the present invention. In addition, a mixture of a small amount of polyethylene terephthalate or the like may be used as long as the flavor characteristics are not affected.

As the polypropylene used in the present invention, various polypropylenes such as homo, copoly and random can be used as long as the melt flow rate is 2.0 or less. Further, other resins such as polyethylene may be mixed within a range that does not change the melt flow rate.

Any ethylene vinyl alcohol copolymer can be used in the present invention 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 extrusion laminating method and a dry laminating method are used. Further, in order to bond the resins to each other for stacking them, an adhesive suitable for the individual resins or an adhesive resin is used. As a method of molding these multilayer sheets into a container, a vacuum forming method, a pressure forming method, and a vacuum pressure forming method are generally used.

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

In the present invention, as a method of forming a minute concave portion on the peripheral surface of a part or the whole of the flange portion of the container, ultrasonic treatment, heating or cold pressing, pressurization using high frequency, etc. It can be performed by an appropriate method. FIG. 1 is a cross-sectional view showing a sealed container of the present invention, 1 is a container body, 2 is a flange portion, and 3 is a lid member. In addition, as shown in FIG. 2, innumerable minute recesses 4 are formed in advance on the upper surface of the flange. Of these, the method of 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. The number of minute recesses formed is preferably in the range of 50 to 500, but is not particularly limited. In this way, the flange portion 2 of the container body 1 having innumerable minute recesses formed on the upper surface thereof and the sealant layer 5 of the lid member 3 are overlaid in the state of FIG. 3 and heat-sealed to manufacture a sealed container.

[0012]

The function of the present invention will be described. The innermost polycarbonate layer used in the container of the present invention is used for flavor protection of the contents. Polycarbonate has excellent heat resistance among thermoplastic resins and can be used for foods that require retort sterilization. However, because of its heat resistance, polycarbonate requires a large amount of heat during container heat molding. Further, the drawdown during heating of the sheet is large, and it is generally said that it is not suitable for the sheet heating molding type vacuum forming method and the pressure forming method. Therefore, in the present invention, therefore, the thickness of the polycarbonate is less than 1 of the total thickness.
This problem is solved by suppressing the content to 0% or less and selecting a polypropylene layer described later. Regarding the flavor suitability for the contents, a sufficient function can be achieved with the above-mentioned thickness ratio, and it is rather preferable to suppress it to 5% or less.

The polypropylene layer used in the present invention is used as a strength retaining layer, a water vapor barrier layer and a moldability improving layer. In the present invention, the thickness ratio of the polypropylene layer is specified to be 50% or more, and the melt flow rate of the polypropylene used is set to 2.0 or less because it relates to the moldability of the container. In thermoforming of a sheet mainly composed of polypropylene, the melt flow rate of the resin used for the formed sheet is greatly related to its formability.
That is, in the case of polypropylene, if the melt flow rate is large, the drawdown at the time of heating becomes large, and a satisfactory molded product cannot be obtained. Further, the thickness ratio of the polypropylene layer is defined in the present invention, when the thickness ratio of the polypropylene layer is 50% or less, the drawdown at the time of molding becomes large as described above, which is inconvenient for container molding. And to reduce the water absorption of the ethylene vinyl alcohol copolymer, which is the gas barrier layer, during retort sterilization as much as possible. The ethylene vinyl alcohol copolymer, which is the gas barrier layer, has the best oxygen gas barrier property among general-purpose thermoplastic resins, but its water-absorbing property lowers its barrier property. Further, this tendency of water absorption increases as the temperature rises, and when treating the container in heated water, an outer moisture protection layer is required. Therefore, the water vapor barrier layer as the outer layer needs to have a certain thickness.

When polycarbonate is used as the seal layer, various sealing methods such as heat sealing, ultrasonic sealing and high frequency sealing are conceivable. However, it is common to use a lid material that can be welded to polycarbonate. It is difficult to impart easy-opening property to the product, and there are only a few sealant sealants that can provide easy-opening property, but there is a drawback that the sealing property is impaired when heat treatment is performed after filling and sealing the contents. 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 member 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. Regarding the adhesiveness in this case, the adhesive force at the point Y on the bottom of the recess is relatively weaker than the adhesive force at the position A where the sealing pressure is high.

When the lid 3 is pulled upward, peeling at the time of opening causes peeling between a portion having a strong adhesive force, that is, between the (A) layer and the (B) layer as shown in FIG. Due to the recesses, the sealant layer (A) is destroyed, and the pattern in which the container and the lid material are separated continuously progresses. In this process, the peculiar strong and weak adhesion mechanism according to the present invention works skillfully to enable easy opening without resistance.

[0017]

EXAMPLES The effects of the present invention will be described with reference to the following examples. Table 1 shows the configurations of the three types of multilayer sheets used for comparison with Example 3 used in the present invention. These multilayer sheets were prepared by the coextrusion method. These multi-layer sheets use an indirect heating type vacuum forming machine and have a diameter of 80 mm and a height of 50 m.
Create a container with m and bottom diameter of 40 mmφ and fill it with two types of orange juice and curry as the contents. The former is hot filling at 60 ° C, the latter is 120 ° C for 30 minutes after filling, and then at room temperature. Storage was carried out for 1 month, and the storability and flavor suitability were compared. In addition, comparative evaluation was also performed on the moldability during thermoforming. The results are shown in Table 2.

In the container having the constitution of Example 1 in Table 1, the laminate strength of the sealant layer and its adjacent layer was 100.
Ultrasonic treatment is performed by applying convex ultrasonic waves having a projection number of 256 pieces / cm ² 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 innumerable minute concave portions are formed in the entire area. did. As the lid material, a sealant layer (thickness 30 μm) made of polycarbonate and dry laminated with 6-6 nylon (thickness 25 μm) was used. The sealant layer of the 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 and a temperature of 210 ° C. for 1.5 seconds. When the lids of the 20 sealed containers produced in this manner were opened, all the containers had a light opening feeling and could be smoothly opened to the end, and the state of the opened surface was also good.

[0019]

[Table 1]

[0020]

[Table 2]

[0021]

According to the present invention, a container in which the flavor of the contents is not changed is obtained as compared with the conventional plastic barrier multilayer container. In addition, the conventional molding method can be used, and an inexpensive molded product similar to the conventional one can be manufactured. Furthermore, by sealing the container with the innumerable minute recesses and the lid member, the lid member could be opened with a smooth opening feeling.

[Brief description of 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 where the lid is half opened.

[Figure 3]

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

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

Claims (1)

[Claims] 1. Polycarbonate (A), polypropylene (B), ethylene vinyl alcohol copolymer (C)
Is laminated in the order of A-B-C-B 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 which is the constituent resin. Is 2.0 or less, and the polypropylene layer is 50% or more of the whole, in the container, the lamination strength between the polycarbonate layer (A) and the corresponding polypropylene layer (B) adjacent thereto is 300 to 20.
A container having a count of 00 g / 25 mm and innumerable minute recesses on a part or all of the peripheral surface of the container flange is sealed by a lid having a gas barrier property with a sealing strength exceeding the laminating strength. And a sealed container.