JPH08174777A - Molding laminated sheet for food container or the like - Google Patents

Abstract

PURPOSE: To obtain a molding laminated sheet having a good heat sealing property, bending stiffness, and impact resistance together by a method wherein an impact resistance layer, a rigid layer fixed to its both sides, and a heat sealing layer fixed to at least its one side are combined. CONSTITUTION: For an impact resistant layer 1 of a laminated sheet S, a highly impact resistant resin among general olefin resins, for example, a polypropylene copolymer synthetic resin or the like is used singly, or by blending two or more kinds. As a synthetic resin forming a rigid layer 2, an olefin resin of high rigidity at an ordinary temperature, for example, polypropylene homopolymer is provided. That is, as the impact resistant layer 1, a block copolymer of polypropylene and polyethylene is used. Polypropylene homopolymer is preferable for combination as the rigid layers 2, 2. As the synthetic resin forming a heatsealing layer 3, a polypropylene random copolymer of a low thermosoftening temperature, for example, that of 120 deg.C-150 deg.C of the crystal melting point is used, adjusted so as to be 1-10% of the whole, and molded by co-extrusion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to, for example, oysters, clams,
A laminated sheet for thermoforming a food packaging container (hereinafter simply referred to as "container") which is packaged with almost full water like food such as tokoroten and tofu, and whose opening edge is heat-sealed with a sealing film of a lid. .

[0002]

2. Description of the Related Art Conventionally, for example, oysters sold in the supermarket are packed in a container together with almost full water. Thus, the molding sheet of the container for storing the food is kneaded and extruded by blending the raw material synthetic resin so that good heat-sealing characteristics, good rigidity, and good impact resistance can be obtained in good balance. A single-layer container is manufactured by vacuum forming or pressure forming of such a sheet. And, especially for the purpose of improving the heat-sealing property, a film having good heat-sealing property is laminated on the surface of a single-layer synthetic resin sheet in which rigidity and impact resistance are harmonized, or a container having good heat-sealing property is laminated. It is manufactured by forming a two-layer sheet by coating a synthetic resin and molding it.

[0003]

The single-layer sheet for molding the above-mentioned container is made of a synthetic resin having good impact resistance, a synthetic resin having good rigidity, and a synthetic resin having good heat-sealing characteristics. Since it was created by kneading and extruding,
The synthetic resins having the respective characteristics are diffused throughout the sheet, and the characteristics of the respective synthetic resins cannot be effectively utilized. As a result, the characteristics of the heat-sealed container produced are also
The characteristics of the raw material synthetic resin used cannot be fully utilized. Specifically, the synthetic resin having good heat-sealing property has particularly low rigidity strength, and the synthetic resin having high rigidity strength does not have good heat-sealing property or impact resistance, and has high impact resistance. This is because they have contradictory tendencies that heat sealability and rigidity are not sufficient. Therefore, when these synthetic resins are mixed and kneaded and extruded, a composition for improving one property is sacrificed for the other property.

Further, it has been proposed to thicken the entire sheet in order to compensate for the decrease in rigidity and strength caused by improving the heat sealability and impact resistance, but this leads to an increase in material cost and a container. It is required to further improve the heat sealability and impact resistance of the sheet. In addition, it takes time to cool after molding by increasing the thickness of the sheet material, and crystals in the synthetic resin grow and impact on the flange in particular. There was also a tendency to decrease the sex.

In order to solve such a problem, there is a two-layer sheet obtained by laminating or coating a film having a good heat-sealing property on the above-mentioned single-layer sheet having a balance between rigidity and impact resistance. Film thickness
If the thickness is less than 10 μm, unevenness and wrinkles are likely to occur, yield is reduced, and in order to prevent peeling of the laminated film, pretreatment such as corona treatment and adhesive application is performed on the single layer sheet. However, there is a problem that it is necessary to increase the adhesive strength of the film, and there is a similar problem with the coated film, which also results in cost hindrance.

Conventionally, in the container seal for the same purpose as that of the present invention, the processing speed is raised to the limit in order to improve the working efficiency, and further, the inside of the container is filled with water in a substantially full state. Since the heat is absorbed by the filling water through the seal film from the heat sink, the heat radiation amount of the heat sealing mold during sealing is large, and the sealing surface temperature of the heat sealing mold is substantially lower than the set temperature of the sealing device. I often do Therefore, in many cases, insufficient sealing causes poor sealing. On the contrary, in the conventional work, when the sealing work is once stopped and then the sealing work is started again, the sealing surface temperature of the heat-sealing die has risen to the vicinity of the upper limit of the set temperature range. It may be in an overheated state, and in such a case, a part of the seal film may be melt-cut by the overheated seal die and a hole may be opened in the sealed film.

Therefore, an object of the present invention is to provide a laminated sheet for molding such as a food container having good heat-sealing characteristics, bending rigidity and impact resistance by appropriately combining synthetic resins having different characteristics. Especially.

[0008] Another object of the present invention is a molding laminate for a food container or the like, which can inexpensively and stably manufacture a container capable of obtaining good heat sealability, high rigidity and high impact resistance. To provide a seat.

[0009]

The first feature of the present invention is to:
An impact resistant layer and a rigid layer adhered to both sides of this impact resistant layer,
The heat-sealing layer is fixed to at least one surface of the rigid layer.

A second feature is that the impact resistant layer is a polypropylene block copolymer, or polypropylene and α.
-It is composed of a synthetic resin mixed with an olefin copolymer type modifier.

A third feature is that the rigid layer is made of polypropylene homopolymer.

A fourth characteristic is that the heat-sealing layer is a random copolymer of polypropylene and polyethylene (hereinafter referred to as "polypropylene random copolymer") having a crystal melting point in the range of 120 ° C. to 150 ° C. and its thickness. 1% or more and 10% of the total thickness of the laminated sheet
Where it is:

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 3, a food product such as oyster 11 is stored in a container 10 together with water 12, and a seal film 13 is welded by a sealing mold 14 on the upper surface of the edge 10a of the upper end opening. Yes, the oysters thus enclosed in the container are sold at the store. The seal film 13 has a multi-layer structure in which nylon is on the upper surface and polypropylene is on the lower surface, and this container was conventionally a single-layer polypropylene as described above, but this container 10 is a laminated layer according to the present invention. The sheet S is molded.

As shown in FIG. 1, a laminated sheet S according to the present invention comprises an impact resistant layer 1, rigid layers 2 and 2 on both outer surfaces of the impact resistant layer, and a heat seal layer 3 on the upper surface of the rigid layer. And are fixed by coextrusion molding.

The impact-resistant layer 1 differs depending on the type of synthetic resin constituting the rigid layer 2, but when an olefin resin is used for this rigid layer, a general olefin resin which is less likely to peel off from the olefin resin. Among them, those having as high impact resistance as possible may be used, and examples thereof include polypropylene copolymer, high-density polyethylene, low-density polyethylene, polybutene, and α-for a random copolymer or block copolymer of polypropylene and polyethylene. Examples thereof include a synthetic resin and the like in which an olefin-based copolymer modifier is mixed, and these may be used alone, or two or more kinds may be blended and used.

Examples of the α-olefin-based copolymer modifier include elastic materials such as ethylene propylene rubber, ethylene butylene rubber, and propylene butylene rubber. These may be random copolymers or partially block copolymers.

As the synthetic resin forming the rigid layer 2, a generally used olefin resin having a rigidity as high as possible at room temperature may be used, and examples thereof include polypropylene homopolymer. When polypropylene homopolymer is used for the rigid layer 2, it tends to be less likely to be softened by heating when molding the container 10, but since the rigid layer is arranged near the surface of the laminated sheet 3, the heating efficiency is high. As a result, the softening speed of the laminated sheet is increased and the molding shot time is shortened.

When transparency is not required, it is effective as a method for increasing the rigidity of the container to add a commonly used inorganic or organic filler to the rigid layers 2 and 2.

Specifically, a block copolymer of polypropylene and polyethylene is used as the impact resistant layer 1,
Considering factors such as adhesiveness between layers, transparency, and rigidity, the rigid layers 2 and 2 are preferably a polypropylene homopolymer in combination. The thickness ratio between the rigid layer 2 and the impact resistant layer 1 may be appropriately determined in consideration of the finally required rigidity strength and impact resistance.

As the synthetic resin for forming the heat-sealing layer 3, among the commonly used polypropylene random copolymers, those having a thermal softening temperature as low as possible, for example, those having a crystal melting point of 120 ° C. or more and 150 ° C. or less are used. Used as is, as the thickness of the heat-sealing layer on one side of the sheet, 1% to 10% of the total sheet thickness, preferably 1%
Coextrusion molding may be performed by adjusting the content to be 5%. The polypropylene random copolymer disposed as the outermost layer as the heat-sealing layer 3 of the container 10 has a low melting temperature,
When the sealing film 13 is overlaid on the edge portion 10a, which is the heat-sealing surface, and heat-sealed, it is possible to fuse even at a lower temperature than before even if the heating efficiency is lowered by interposing this film or water. Therefore, the defective rate in heat sealing is reduced. In addition, since the sealing temperature is lowered, it is possible to prevent the rigid layer and the impact resistant layer from generating and growing crystals due to heating, and thus it is possible to prevent the generation of cracks due to the resin crystals.

FIG. 2 shows another embodiment. In this laminated sheet Sa, the heat-sealing layers 3 and 3 are welded to both surfaces of the rigid layers 2 and 2, and the other constitution is the same as the above-mentioned drawing. This is substantially the same as the embodiment shown in FIG.

According to this embodiment, since the laminated sheet Sa wound in a tubular shape does not specify the front and back sides, the edge portion 1 of the container 10 is always kept regardless of whether it is pulled out from above or below.
The sealing surface of 0a can be used as a sealing layer.

Next, an experimental example of the present invention will be described. The measurement of each inspection item in the following experiments of the present invention was performed by the following method. [Flexural Modulus] According to JIS K7203. [Deformation resistance of the container] 220mm length x 1 width from the sheet
A container of 36 mm and a depth of 23 mm was formed by pressure molding, and as shown in FIG. 4, the edge portion 10a of the container 10 was placed on the bar-shaped fulcrums B and B having a fulcrum distance of 180 mm and attached to the Shimadzu autograph from above. The bottom portion of the container was pressed using the specified plug P, and the stress when deformed by 10 mm was measured. [Impact resistance] According to ASTM D781. [Film peeling strength] According to JIS Z1707. [Drop test] The impact resistance of the container is that the container is filled with water and sealed with a nylon-polypropylene laminated film to make 20 pieces each, which are stacked in 5 steps and placed in a corrugated cardboard box at 0 ° C. Leave it in the environment for 48 hours and set the height to 1.
The container was dropped from 5 m onto flat concrete, and the destruction rate of the container was obtained.

Experimental Example 1 Polypropylene-polyethylene random copolymer XF1800 manufactured by Chisso Corporation as the heat-sealing layer 3, polypropylene homopolymer HT6004 manufactured by Chisso Corporation as the rigid layers 2 and 2, polypropylene-polyethylene manufactured by Chisso Corporation as the impact resistance layer 1. Total of 24 block copolymers F3020
μm, total 160 μm, 216 μm, manufactured by coextrusion molding and subjected to predetermined measurement.
The results shown in are obtained.

[0026]

[Table 1]

Experimental Example 2 A container 10 was prepared by pressure molding using the sheet prepared in Experimental Example 1 and the deformation resistance of the container was measured by the method shown in FIG. 4, and the results shown in Table 1 were obtained. .

Comparative Example 1 Polypropylene-polyethylene block copolymer F3020 manufactured by Chisso Corporation and polypropylene-polyethylene random copolymer XF1800 manufactured by Chisso Corporation were used as sheet materials, respectively.
Wt%, 60Wt% kneading and extruding, 0.4mm
When a single-layer sheet having a thickness was manufactured and predetermined measurements were performed, the results shown in Table 1 were obtained.

COMPARATIVE EXAMPLE 2 Using the sheet produced in Comparative Example 1, a sealing container was prepared by pressure molding, and as shown in FIG.
When the deformation resistance of the container was measured by the method shown in Table 1, the results shown in Table 1 were obtained.

By the way, in the container formed by the laminated sheet according to the present invention, since the rigid layers 2 and 2 having inferior impact resistance are arranged on the outer side of the impact resistant layer 1, the impact applied from the outside has a small thickness. Will be added to this rigid layer via the heat-sealing layer 1. Therefore, the impact resistant layer 1 is formed on both sides of the rigid layer 2.
Although it was expected that brittle fracture would occur more easily than the case where the container was placed, contrary to that expectation, this container is comparable to the container with impact resistant layers on both sides of the rigid layer as a comparison. It showed impact resistance.

[0031]

According to the present invention, good heat sealability, high bending rigidity, and high impact resistance can be obtained, and a container can be manufactured inexpensively and stably. Further, since the rigid layers are arranged on both sides of the impact resistant layer, the deformation stress when the laminated sheet is bent can be concentrated on the rigid layer, and the bending moment of this sheet can be effectively increased. Therefore, the container made from this sheet can also have high rigidity and strength, and the impact resistant layer absorbs the deformation applied locally and suddenly by the impact, so that the container can be made by the impact resistant layer. Prevents the occurrence of cracks that lead to the cracking of. Since the rigid layer with low impact resistance is separated into two layers sandwiching the impact resistant layer, even if a crack occurs in one rigid layer, the crack propagation in the intermediate impact resistant layer to the opposite rigid layer is prevented. Can be prevented.

The container made from the laminated sheet of the present invention can improve the flexural strength by about 34% as compared with the conventional container. Therefore, even if the thickness of this sheet is reduced by about 10%, it is almost the same as the conventional one. It is possible to manufacture a container having the above-mentioned flexural strength characteristics.

Further, since the temperature of the heating mold for sealing is low, the same effect can be obtained when the heater capacity of the conventional sealing device is relatively large, and the sealing time can be shortened. .

The effect of preventing insufficient heating due to such a cause can be obtained by improving the relative heating efficiency as compared with the conventional container having the same purpose as that of the present invention. The reduction of the sealing temperature realized by the present invention also exerts an effect of preventing the base material of the sealing film from being melted, and as a result, the efficiency of the sealing operation can be improved and a stable sealing effect can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view.

FIG. 2 is a cross-sectional view showing another embodiment.

FIG. 3 is a sectional view showing a state in which a sheet film is welded to a container formed of the sheet of the present invention.

FIG. 4 is a perspective view showing a method for testing the deformation resistance of a container formed of the sheet of the present invention.

[Explanation of symbols]

 1 Impact resistant layer 2 Rigid layer 3 Heat seal layer

Claims (4)

[Claims] 1. A molding laminate for a food container or the like, comprising an impact resistant layer, a rigid layer adhered to both surfaces of the impact resistant layer, and a heat seal layer adhered to at least one surface of the rigid layer. Sheet. 2. The impact resistant layer according to claim 1, wherein the impact resistant layer is a polypropylene block copolymer, or polypropylene and α-.
A laminated sheet for molding a food container or the like, which is made of a synthetic resin mixed with an olefin copolymer type modifier. 3. A laminated sheet for molding a food container or the like, wherein the rigid layer according to claim 1 is made of polypropylene homopolymer. 4. The heat-sealing layer according to claim 1, which is a random copolymer of polypropylene and polyethylene having a crystalline melting point in the range of 120 ° C. or more and 150 ° C. or less, the thickness of which is 1 of the total thickness of the laminated sheet. % Or more and 10% or less, a laminated sheet for molding such as food containers.