JP2000000941A - Composite multilayered sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite multilayered sheet reconciling hermetical sealability and the easy openability due to ply separation, capable of withstanding a severe heat-sterilizing condition and suitable for a packaging container good in opening feel. SOLUTION: In a multilayered sheet comprising at least two layers of a seal layer having release function and the support layer on the outside of the seal layer, the seal layer comprises a high density polyethylenic resin, a straight chain low density polyethylenic resin, a polystyrenic resin and a compatibilizing agent for the polyethylenic resin and the polystyrenic resin and the support layer comprises a polyolefinic resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite multilayer sheet for packaging and containers, which is excellent in openability, impact resistance and heat resistance. More specifically, as a packaging material for foods and beverages, the pressure applied during heat sterilization, it has a sealing property to withstand heat, and has an easy-opening property, peels off only at the seal part, and has a good appearance of the peeled surface. The present invention relates to a composite multilayer sheet for packaging and containers, and particularly to a multilayer sheet excellent in resistance to vibration and impact applied to a lid material when used as a container.

[0002]

2. Description of the Related Art As a packaging container for foods, beverages and the like, an easily openable plastic sealed container whose lid can be easily opened is generally used. As a conventional method of opening a container, a conventional method of opening the container controls the sealing strength with the container by changing the composition of the resin constituting the sealing layer of the lid material (normally 500 to 1500 g / 15 mm, peeling speed: 300m
m / min), an interface peeling type in which the interface between the lid member and the container was peeled off and opened, and a cohesive peeling type were generally used. However, the sealing strength depends on the sealing conditions, ambient temperature,
It is easily affected by the adhesion of the contents to the interface between the bottom material and the lid material, which causes the seal strength to vary. Often, the sealing strength is set high to prevent leakage of the contents, thereby deteriorating the feeling of opening, and conversely, giving priority to the peeling feeling causes a problem of leakage due to poor sealing.

In order to solve these problems, there has been proposed a method of opening a container by delamination between a sealing layer and a layer adjacent thereto as a container having both excellent sealing properties and easy opening properties. There is a disadvantage that the layer does not break well and the contents are difficult to remove. Further, a structure in which a cut is formed in a flange portion to facilitate separation of a peeling layer from an adjacent layer has been proposed (Japanese Patent Application Laid-Open Nos. 62-251363 and 63-25037).
No.). However, in the case of the container having such a structure, since the outside of the cut portion must be sealed in the manufacturing stage, there is a structural problem that requires strict control of the position setting at the time of sealing. In addition, in the method of peeling the main body container sealing layer, it is necessary to start peeling from the peripheral end because of sealing to the peripheral end of the flange portion, and therefore, there are restrictions on the surface of the container shape. There are drawbacks.

Further, as described in Japanese Patent Application Laid-Open No. 2-98560, a weakening line for starting peeling and a weakening line for stopping peeling are provided outside the flange portion and a weakening line for stopping peeling is provided inside the flange portion. A structure that eliminates the manufacturing inconvenience of having to precisely set the positional accuracy of the panel has also been proposed. However, in the case of this structural container, there is a drawback that a step of forming a weakening line on the outside and inside of the flange portion and further installing a hole is required, and the cost is high.

As a measure for solving this drawback, Japanese Patent Laid-Open Publication No.
As described in JP-A-148264, the use of a container in which the innermost layer thickness of the sealing portion with the lid material of the flange portion, the innermost layer thickness of the inflection point portion, the breaking strength of the innermost layer material, and the like are used, A structure that can be easily opened with only a seal has also been proposed. However, in the case of this structural container, special molds and clamps are required to mold the inflection point, and after opening the lid material, the inside of the flange from the inner edge of the innermost seal portion or the flange section is changed. There is a disadvantage that the innermost layer unsealed portion at the curved point adheres to the lid material and impairs the appearance.

In order to solve these problems,
A method in which at least two or more high-density polyethylene resins having different melt flow rates are blended in a sealing layer in order to achieve both sealing properties and easy-opening properties by delamination by providing only a flat seal on the container flange portion (Japanese Patent Laid-Open No. Hei 3- 10853
No. 9, JP-A-8-142278). However, since the cutability of the seal layer is good, it is also vulnerable to shock and vibration applied to the lid material due to its brittleness, and there is a high risk of leakage of the contents during distribution of the product.

[0007]

SUMMARY OF THE INVENTION In the prior art, the present invention provides a flat seal on a container flange without inconvenience in the manufacturing process or restrictions on the shape of the container, which is a contradictory performance in the prior art. The object of the present invention is to provide a composite multilayer sheet for a container, which is compatible with the conventional method, and which withstands more severe heat sterilization conditions than before and has sufficient resistance to vibration and impact applied during product distribution.

[0008]

According to the present invention, there is provided a multilayer sheet comprising at least two layers of a sealing layer having a peeling function and a support layer outside the sealing layer, wherein the sealing layer is made of a high-density polyethylene resin. A chain low-density polyethylene-based resin, a polystyrene-based resin, and a compatibilizer for compatibilizing a polyethylene-based resin and a polystyrene-based resin,
The support layer is a composite multilayer sheet made of a polyolefin-based resin. Preferably, the sealing layer has a high-density polyethylene resin of 92 to 55% by weight and a linear polyethylene resin of 5 to 55% by weight.
30% by weight, 3 to 15% by weight of polystyrene resin, and 1 to 100 parts by weight of these resins in total,
It is a composite multilayer sheet that is blended at a ratio of 10 parts by weight, has a seal layer thickness of 3 to 30 μm, and has a polyolefin-based resin of a polypropylene-based resin.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A high-density polyethylene resin (hereinafter referred to as HDPE) 9 is used for a sealing layer used in the present invention.
2 to 55% by weight of a linear polyethylene resin (hereinafter referred to as L
5 to 30% by weight of LDPE, 3 to 15% by weight of polystyrene resin (hereinafter, referred to as PS), and 1 to 10 parts by weight of a compatibilizer based on 100 parts by weight of these resins in total. Is preferred. A more preferable blending ratio is LLDPE to 70 to 80% by weight of HDPE.
20 to 15% by weight, PS 10 to 5% by weight, easy to open,
Good impact resistance and heat resistance can be obtained. LLDPE
If less than 5%, sufficient impact resistance cannot be obtained, and 30%
If it exceeds, the heat resistance decreases. The amount of PS in the seal layer is 1
If it exceeds 5%, the heat resistance is reduced, and a problem of odor peculiar to PS is caused, so that it cannot withstand actual use. If it is less than 3%, the layer cut property of the seal is deteriorated, and the appearance may be impaired by fluffing or stringing of the opened surface.

The HDPE used in the present invention is not specifically defined, but has a density of 0.941 g / cm ³ or more (JIS
K 6760) are preferred. The tensile strength at break of LLDPE is 200 to 400 kg / cm ² (ASTM D
638) is preferred. Breaking strength 200kg
/ If cm less than ² sufficient resistance to vibration, impact resistance can not be obtained, which may damage the cutting of the seal layer during unsealing and exceeds 400 Kg / cm ^2. The PS is desirably GPPS (general grade), but HIPS (high impact grade) in which a rubber component is copolymerized may be used as long as the cut property is not impaired. The compatibilizer is not particularly limited as long as it compatibilizes the polyethylene resin and the polystyrene resin, and examples thereof include a graft copolymer resin in which the main chain is made of a polyethylene component and the side chain is made of styrene. .

The thickness of the sealing layer is preferably from 3 to 30 μm, more preferably from 5 to 20 μm. If the thickness is less than 3 μm, insufficient sealing or a decrease in resistance to shock and vibration may be caused. On the other hand, if the thickness exceeds 30 μm, the cuttability may be deteriorated and the feeling of opening may be impaired, or the appearance due to fluffing or stringing may be impaired.

The resin of the adjacent layer used in the present invention is preferably a polyolefin resin from the viewpoint of easy opening. For example, polyethylene, polypropylene, a copolymer thereof or the like is used, and more preferably, a polypropylene resin is used. is there. A polypropylene resin having a melt flow rate of 0.5 to 5 g / min is desirable for extrusion molding. In addition, homopolypropylene resin is desirable in order to maintain heat resistance. However, when heat resistance is not required and characteristics are not impaired, other olefin-based or copolymer-based resins such as ethylene may be used alone or as a blend. It does not matter. When the melt flow rate of the polypropylene-based resin is less than 0.5 g / min, the spread of the resin is poor. When the melt flow rate exceeds 5 g / min, the resin sags, which hinders sheeting.

The layer adjacent to the sealant is not limited to a single layer of the polyolefin resin. For example, if it is necessary to improve the oxygen barrier property, an ethylene-vinyl acetate copolymer may be sandwiched between the intermediate layers via an adhesive layer. Necessary resins may be laminated according to required characteristics to form a multilayer structure.

Further, a polyethylene resin may be added to the layer adjacent to the sealant, if necessary.

The multilayer sheet of the present invention can be produced by a coextrusion method, a dry lamination method, or an extrusion lamination method.

[0016]

The present invention will be described with reference to the following examples, which are illustrative only and do not limit the present invention. << Examples 1 to 6, Comparative Examples 1 to 6 >> The sealing layers of Examples 1 to 6 and Comparative Examples 1 to 6 were composed of the resins and sealing layer thicknesses shown in Tables 1 and 2. The adjacent layer is a homopolypropylene resin having a thickness of 750 μm (MFR = 2.5 g / 10 mi).
n), adhesive layer (maleic anhydride-modified polypropylene resin), oxygen gas barrier layer (saponified ethylene-vinyl acetate copolymer), adhesive layer (maleic anhydride-modified polypropylene resin), homopolypropylene resin (MFR =
After forming a sheet by a co-extrusion method, the sealing layer was extruded and bonded by a lamination method to form a multilayer sheet having a 6-layer structure.
In addition, as the additive to be added to the seal layer and compatibilizing the polyethylene resin and the polystyrene resin, a graft copolymer resin having a main chain composed of a polyethylene component and a side chain composed of styrene was used.

In the evaluation in a container, the multilayer sheet was vacuumed,
It is formed into a 65 mmφ, 70 cc flanged (flange width 5 mm) round-shaped container by air pressure molding, and 60 ° C.
After filling with hot water, using a hollow ring-shaped sealing plate, the temperature was 180 ° C., the surface pressure was 15 kg / cm ² , and the sealing time was 1.
Seal with the lid twice under the condition of 5 seconds.
What was retorted under the conditions of min was used. The lid material is polyethylene terephthalate resin (thickness: 15 μm)
Using a film of / nylon resin (thickness 15 μm) / linear low-density polyethylene resin (thickness 60 μm), the linear low-density polyethylene resin side was used as the seal side.

The evaluation was performed by the following method. The puncture pressure was evaluated in a container having a lid material sealed using a sealing strength tester based on an internal pressure resistance test method (Sumitomo Bakelite Co., Ltd. method). The peel feeling was evaluated using a container in which the lid material was sealed, and the lid material was peeled by hand, and those that could be easily peeled were rated as ○, those with some resistance but peelable were rated as Δ, and those that could not be peeled were rated X. The odor was evaluated by using pure water for the contents, opening the package after retort treatment (121 ° C., 30 minutes), and performing a sensory evaluation on the odor generated. Those that were not bothersome, those that smelled slightly, and those that clearly felt an odor were evaluated as x.

Heat resistance was measured using a container with a lid sealed.
It was immersed in pressurized hot water at 20 ° C. for 30 minutes and observed whether or not the seal portion was broken. A sample without damage was rated as "O", a sample with damage, and a sample with signs of damage as "X". Impact resistance was measured using a container with a lid material sealed.
After sealing in a m-thick cardboard case, the container was dropped on a concrete floor from a height of 1 m to observe the damage state of the container. The number of drops at which damage to the container began was measured. The evaluation results of puncture pressure, peel feeling, odor, heat resistance and impact resistance are shown in Tables 1 and 2.

[0020]

[Table 1]

[0021]

[Table 2]

[0022]

According to the present invention, the package made by using the multilayer sheet according to the present invention achieves both the sealing performance, which is a reciprocal performance, and the easy-openability due to delamination without inconvenience in the production process and without restriction on the shape of the container. In addition, it can withstand more severe heat sterilization conditions than before, has sufficient resistance to vibration and impact applied during product distribution, and has a good opening feeling with little flapping when opening.

Claims (4)

[Claims] 1. A multilayer sheet comprising at least two layers of a seal layer having a peeling function and a support layer outside the seal layer, wherein the seal layer is a high-density polyethylene resin.
A composite multilayer sheet comprising a linear low-density polyethylene-based resin, a polystyrene-based resin, and a compatibilizer for compatibilizing a polyethylene-based resin and a polystyrene-based resin, and wherein the support layer comprises a polyolefin-based resin. 2. The sealing layer is made of a high-density polyethylene resin 9.
2 to 55% by weight, 5 to 30% by weight of a linear polyethylene resin, 3 to 15% by weight of a polystyrene resin, and 1 to 10 parts by weight of a compatibilizer based on 100 parts by weight of these resins in total. The composite multilayer sheet according to claim 1, which is blended. 3. The composite multilayer sheet according to claim 1, wherein the thickness of the sealing layer is 3 to 30 μm. 4. The composite multilayer sheet according to claim 1, wherein the polyolefin resin is a polypropylene resin.