JP2590337B2 - Multilayer container for multi-layer container thermoforming - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a multi-layer sheet for thermoforming a multi-layer container which enables easy opening of the obtained packaging container. More specifically, the present invention has a wide range of conditions for heat sealing with a lid material and excellent sealing properties, is easy to open, has a stable opening force, and has a good appearance of a peeled surface after opening. The present invention relates to a multilayer sheet suitably used for producing an easily openable packaging container having excellent boil and retort treatment.

[Conventional technology]

2. Description of the Related Art Conventionally, a container in which a lid material is heat-sealed to a container main body flange portion is frequently used for packaging food. In this case, if the heat sealing strength is increased to improve the sealing property of the container,
The opening property at the time of use deteriorates, which is not practical. Attempts have been made to solve this problem by selecting a combination of resins for the seal layer or a resin blend. However, none satisfying these conflicting requirements has been obtained. This is because the heat sealing strength is greatly affected not only by the resin itself but also by sealing conditions such as temperature, pressure and time at the time of sealing, and the influence of impurities such as fillers and the like.

On the other hand, boil and retort sterilization of foods has recently been performed, and higher sealing properties and heat resistance are required. A long-awaited packaging container and a multilayer sheet suitable for the production of this container are expected. Have been.

[Problems to be solved by the invention]

The present invention, when formed into a multilayer container, and heat-sealed with the lid to form a packaging container, when opening the packaging container, easy to open, the opening force is stable, in addition to the lid material Provided is a multi-layer container thermoforming multi-layer sheet suitable for producing an easily-openable packaging container which has an excellent release surface appearance, is excellent in boil and retort treatment, has excellent heat resistance and is easily opened by a completely new opening method. It is the purpose.

[Means for solving the problem]

That is, the present invention is a method of thermoforming a multilayer container,
A multilayer sheet that is heat-sealed at a strength of 2.0 kg / 15 mm or more to become a packaging container, comprising at least a peelable surface layer and a layer in contact with the peelable surface layer, wherein the peelable surface layer is made of a high-density polyethylene resin, The layer in contact with the releasable surface layer is made of a mixed resin in which a polypropylene-based resin and a polyethylene-based resin are mixed in a weight ratio of 60:40 to 95: 5, and opening of the packaging container starts from delamination of the two layers. As described above, the present invention provides a multilayer sheet for thermoforming a multilayer container, wherein the two layers have a delamination strength of 1.5 kg / 15 mm or less.

Hereinafter, the present invention will be described in detail with reference to the drawings. First
The figure is a cross-sectional view of the multilayer sheet for thermoforming of the multilayer container of the present invention, wherein 2 is a peelable surface layer, and 1 is a layer in contact with it.

The peelable surface layer is a resin layer that can be heat-sealed with the lid material. The peelable surface layer is integrally formed with a resin layer that comes into contact with the cover material so that the peel strength is 1.5 kg / 15 mm (pulling speed 300 mm / min) or less. It is multilayered.

When the multi-layer sheet is formed into a multi-layer container having a flange portion, the releasable surface layer and the lid material at the flange portion and 2.
It is made of a material that can be heat-sealed with a strength of 0 kg / 15 mm or more, preferably 2.5 kg or more. And the peel strength between the peelable surface layer and the layer in contact therewith is 1.5 kg / 15 mm or less,
It is preferably 1.3 kg / 15 mm or less, which is smaller than the peeling strength of the lid material and the peelable surface layer, so that when the lid material is peeled from the container, it is peeled between the peelable surface layer and the layer in contact with the peelable surface layer. It has become.

The releasable surface layer and the layer in contact therewith are preferably the innermost layer of the multilayer sheet (hereinafter referred to as the inner layer of the container when the multilayer container is formed) and the layer in contact therewith. If the lid material is peeled off, as long as it has the feature of the present invention in which the multi-layer sheet is peeled off and opened, another layer such as a sealing layer may be provided on the innermost layer if necessary inside the innermost layer of the container. Good.

Examples of the high-density polyethylene resin used for the high-density polyethylene resin layer of the peelable surface layer include propylene, butene-1, and pentene- in addition to ethylene homopolymer.
Copolymers with α-olefins such as 1,3-methylbutene-1 and 4-methylpentene-1 are exemplified. In this copolymer, the proportion of the copolymerized monomer is preferably 10 mol% or less. The high-density polyethylene resin preferably has a density in the range of 0.940 to 0.975 g / cm ³ , and may be a mixture of those having different densities and molecular weight distributions.

Examples of the polypropylene resin used for the mixed resin of the peelable surface layer and the layer in contact with the peelable layer include, in addition to a highly crystalline propylene homopolymer, ethylene, butene-1, pentene-1, pentene-1, 3-methylbutene-1, 4, and the like. -Methylpentene-
And a random copolymer with an α-olefin such as 1, or a mixture thereof. The random copolymer may be a mixture with a homopolypropylene obtained by multi-stage polymerization. In the above-mentioned copolymer, those having a proportion of a copolymer monomer of 10 mol% or less are preferable. Further, these polypropylene resins preferably have a melt index in the range of 0.1 to 20.

As the polyethylene resin used for the mixed resin,
Any of low density (high pressure method low density polyethylene, linear low density polyethylene, etc.), medium density and high density polyethylene can be used. In addition to ethylene homopolymer, propylene, butene-1, Penten-1,
A random or block copolymer with α-olefin such as 3-methylbutene-1, 4-methylpentene-1 or vinyl acetate, or a mixture thereof can also be used. In the copolymer, the proportion of the copolymerized monomer is preferably 10 mol% or less. These polyethylene resins have a melt index of 0.
Those having a density in the range of 02 to 50 and a density in the range of 0.900 to 0.975 g / cm ³ are preferred.

The ratio between the polypropylene resin and the polyethylene resin is in the range of 60:40 to 95: 5 on a weight basis.
Outside this range, a predetermined peel strength cannot be obtained.

Further, if desired, a third resin component can be added to the resin mixture to improve its compatibility. As such a third resin component, for example, a modified polyolefin modified with an unsaturated carboxylic acid or a derivative thereof, an ethylene-vinyl acetate copolymer, an ethylene-acrylate copolymer, an ethylene-propylene rubber,
Ethylene-propylene-diene rubber, polybutene, polyisobutylene, polybutadiene rubber, polyisoprene rubber, atactic poly-4-methylpentene
1, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ion-crosslinked olefin copolymer (ionomer), and the like, each of which may be used alone or in combination of two or more. These third components are preferably used in an amount of 30 parts by weight or less per 100 parts by weight of the polypropylene resin.

The multilayer sheet of the present invention may be used as it is to constitute a container body, but for the purpose of improving gas barrier properties and reducing deformation of the container, it is used as a multilayer sheet of three or more layers using other materials. Is also good. Examples of the other layers include those having excellent gas barrier properties such as resin layers such as ethylene-vinyl alcohol copolymer, polyvinylidene chloride, nylon, and polyethylene terephthalate, and aluminum vapor deposition layers. Further, a resin layer containing 10 to 80% by weight of an inorganic filler may be provided.

As a method for producing the multilayer sheet, a method commonly used for lamination processing, for example, a method such as extrusion lamination, hot melt lamination, dry lamination, or wet lamination can be used in addition to a normal coextrusion molding method.

The thickness of the mixed resin layer and the high-density polyethylene resin layer is
Usually, it is preferably in the range of 10 to 1000 μm, preferably 20 to 500 μm.

FIG. 2 is a partial cross-sectional view of one embodiment of the easily-openable packaging container manufactured using the multilayer sheet of the present invention. A is a multilayer container body having a multilayer structure, 2 is the innermost layer of the multilayer container body, and 1 is a layer in contact with the innermost layer. This multilayer container body
Usually, it is obtained by obtaining the multilayer sheet by co-extrusion or the like, and subjecting the multilayer sheet to thermoforming such as vacuum forming or pressure forming.

B is a lid material for the container, which has an innermost layer 2 of the multilayer container main body, a sealant layer 3 having easy heat sealing properties, and substrates 4 and 5. Reference numeral 6 denotes a heat seal portion, in which the container main body and the lid member are heat-sealed in a ring shape at a container main body opening flange portion. The shape of the container is not particularly limited, and is generally a circle, a square, or the like, and is heat-sealed annularly along a flange portion having this shape.

The material B is a three-layer film in the figure, but may be a single-layer film or a multilayer film, and there is no particular limitation. The case where a three-layer film is used will be described. Substrates 4 and 5 made of a plastic single-layer film, a multilayer film, paper, aluminum foil, or a composite material thereof are used together with polyethylene, polypropylene, ethylene-α-olefin. It comprises a sealant layer 3 made of a resin having easy heat sealing properties and an innermost layer 2 of a container body made of a polymer, ethylene-vinyl acetate copolymer or the like.

An annular cut 7 is provided in the flange portion of the multilayer container body inside the annular heat seal portion. The cut is usually provided by a stamping die or the like having an annular blade, and any shape may be used as long as the release layer can be easily cut when the cover material is peeled off, and the shape and depth are not particularly limited. Only a part of the release layer may be cut. Further, the annular cut may be made over the entire circumference, or a part thereof may be left. When leaving a part of the lid material without peeling it off, make sure not to cut only that part.

In the packaging container shown in the figure, a space is provided between the inner end of the heat seal portion and the cut. The length t of this interval is usually 0.5 mm to 10 mm, preferably 1.5 to 5 mm. If this length is less than 0.5 mm, the peel strength from the inside of the container will not be much greater than the peel strength from the outside, and 10 mm
Beyond is impractical.

It is preferable to provide the knob portion 8 in which the outer edge of the lid material is protruded outside the multilayer container body, because the lid is easily gripped when the lid is opened and peeled.

[Action]

When the product is sealed in a container manufactured using the multilayer sheet of the present invention and the lid B is heat-sealed, it can be easily opened by the following operation.

For example, in FIG. 2, the knob portion 8 is lifted upward, so that the innermost layer 2 of the multilayer container main body A and the layer 1 in contact therewith are separated, and the innermost layer is separated to the cut 7. Subsequently, peeling progresses between the layers 2 and 3,
The lid is peeled off. Therefore, even when the lid member and the multilayer container main body are hardly peeled off and heat-sealed, they can be easily opened. Also,
Compared with the conventional method of peeling off from the sealing surface, there is no notch effect due to incomplete sealing at the seal end, no difference in sealing conditions, no influence of foreign substances, etc., and the opening force can be stabilized. In particular, when heat-sealing the lid material, there is no need to consider peelability at all. Therefore, the selection of the lid material and the sealing conditions can be selected so as to obtain a high heat sealing strength, so that the sealing is facilitated.

When the interval t is provided as shown in FIG. 2, the peel strength from the inside becomes larger than the peel strength from the outside, and a container having good heat resistance to boil and retort treatment can be obtained. The reason for this is not obvious, but when peeling from the inside, stress concentrates at point X in the figure, and the peeling strength from point Y becomes the shearing force on the YZ plane, so the peeling strength from the inside increases. It seems to have been.

〔Example〕

Next, the present invention will be described in more detail with reference to Examples.
The present invention is not limited in any way by these examples.

Example 1 A multilayer sheet having a layer constitution as shown in FIG. 1 was obtained by co-extrusion molding (layer a thickness 200 μm, layer b thickness 50 μm).
m).

a: Polypropylene resin [Idemitsu Petrochemical Co., Ltd. Idemitsu Polypro E-100G, density 0.91 g / Scm ² , MI 0.6 g / 10 min] 80
Parts by weight and low-density polyethylene resin (Toyo Soda Kogyo Co., Ltd., Petrocene 172, density 0.92 g / cm ³ , MI 0.3 g / 10
B) High-density polyethylene [Idemitsu Petrochemical Co., Ltd., Idemitsu Polyethylene 440M, density 0.954g /, MI 0.9g / 10min] Heat the multilayer sheet to a temperature at which it can be molded and apply vacuum. A multi-layer container main body A with a flange as shown in FIG. 2 was formed by air pressure molding.

A cut 7 having a depth of 70 μm was made in the flange portion of this multilayer container so that t was 2 mm and 4 mm.

After filling this multilayer container with water, a lid material film B; e: d:
c [Oriented nylon (ONY): polyvinylidene chloride (PVD
C): Linear low density polyethylene (LLDPE) = 15:20:40
(Mμ)] was heat-sealed under the conditions of a temperature of 170 ° C., a pressure of 1.5 kg / cm ³ , and 1.5 seconds using a linear low-density polyethylene surface as a sealing layer, and a retort treatment was performed at 120 ° C. for 30 minutes. There were no broken bags. The opening force of this container is about 0.9kg / 15mm before retort, and about 0.6kg / 15mm after retort.
It was 15 mm. Also, this packaging container is easily peeled between the container layers from the outer end of the flange seal portion when the lid material is peeled off,
The peeled surface was also clean.

[Effects of the Invention] The easily-openable packaging container manufactured by using the multilayer sheet for hot-molding of the multilayer container of the present invention has high sealing strength, excellent sealing property, easy opening, and stable opening force. In addition, it has excellent features such as a good appearance of the peeling surface, a peel strength from the inside of the container larger than a peel strength from the outside, good heat resistance, boil and retort treatment, etc. They are particularly suitable for use as food packaging containers for retort foods and boiled foods.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of one embodiment of the multilayer sheet of the present invention, wherein 1 is a layer in contact with a peelable surface layer, and 2 is a peelable surface layer. FIG. 2 is a partial cross-sectional view of one embodiment of a packaging container manufactured using the multilayer sheet of the present invention. In the drawing, reference numeral A denotes a multilayer container main body, B denotes a cover material, and 1 denotes an innermost layer of the multilayer container main body. The contacting layer, 2 is the innermost layer of the multilayer container main body, 3 is the sealant layer, 4 and 5 are the base material, 6 is the heat seal portion, 7 is the cut, and 8 is the knob portion.

Claims (1)

(57) [Claims] 1. Thermoformed into a multi-layer container, 2.0kg / 15mm with lid
A multilayer sheet that is heat-sealed with the above strength to become a packaging container, comprising at least a peelable surface layer and a layer in contact with the peelable surface layer, wherein the peelable surface layer is made of a high-density polyethylene resin, and the peelable surface layer The layer in contact with is made of a mixed resin in which a polypropylene-based resin and a polyethylene-based resin are mixed at a weight ratio of 60:40 to 95: 5, and the opening of the packaging container is started by delamination of the two layers. , Said 2
A multilayer sheet for thermoforming a multilayer container having a layer delamination strength of 1.5 kg / 15 mm or less.