JP3094303B2 - Multilayer sheets and easy-open containers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a multilayer sheet suitably used in the field of packaging, especially for manufacturing containers, and for storing foods, medicines, cosmetics, etc. manufactured using the same. The present invention relates to an easily openable container having excellent sealing and opening properties for packaging.

[Conventional technology]

Polystyrene-based sealed containers are often used as sealed containers for storing and packaging dessert foods, dairy products, and the like.

In the case of a polystyrene-based sealed container, the better the sealing property, the worse the opening property. Therefore, in order to improve the opening property, an aluminum foil or a plastic film coated with a hot-melt adhesive or a lacquer-type adhesive is generally used as a cover material. However, such containers are not sufficiently openable, and most of them are difficult to open for infants, boys and girls. There are also problems such as poor oil resistance and increased cost. In particular, tofu containers are made of polystyrene
Although the CPP film is laminated and the lid material is sealed by heat sealing, it is difficult to open this container, and the housewife cuts the film using a kitchen knife, opens the container, takes out the tofu, I have.

All of these containers have difficulty in opening, and the use of a lid with a special sealant to improve the opening is expensive. A container is desired.

[Problems to be solved by the invention]

An object of the present invention is to provide a multilayer sheet suitably used for manufacturing an easily-openable container using a styrene-based resin as a base material, in which a heat-sealing layer and an opening-peeling layer are separated.

Another object of the present invention is to provide an easily-openable container having excellent heat-sealing properties, sealing properties and openability using the above-mentioned multilayer sheets, and using a styrene-based resin as a base material.

[Means for solving the problem]

The present inventor has conducted intensive studies in order to achieve the above object, and as a result, has found that the above problem can be solved by forming a multilayer sheet used for manufacturing an easily-openable container into a specific layer configuration. Based on this, the present invention has been completed.

That is, in the present invention, a base material layer (C) made of a styrene-based resin is added with 0 to 15% by weight of a thermoplastic elastomer mainly composed of a styrene-butadiene copolymer and 0 to 25% by weight of an ethylene-based polymer. A surface layer (A) composed of a polyolefin resin via an intermediate layer (B) composed of a styrene-based resin layer containing 3 to 25% by weight of (B) and (C). Peel strength (A) (B)
An object of the present invention is to provide a multilayer sheet having a multilayer structure having a larger interlayer peel strength.

The multilayer sheets having a multilayer structure of the present invention will be described with reference to FIG.

FIG. 1 is a schematic view illustrating an example of a multilayer sheet having a multilayer structure according to the present invention.

These multilayer sheets are composed of a surface layer of (A), an intermediate layer of (B) and a base layer of (C).

The surface layer of (A) is a layer that becomes an easily peelable layer when molded into a container, and is made of a polyolefin resin. As the polyolefin resin, high density polyethylene, linear low density polyethylene, low density polyethylene, polypropylene or a mixture thereof is preferable. A necessary amount of a white pigment such as titanium oxide or other color pigments may be added to these polyolefin resins as needed. Further, polystyrene may be added in an amount of 15% by weight or less. If an amount of polystyrene exceeding 15% by weight is added, poor appearance of the obtained multilayer sheet is caused by poor mixing with the above-mentioned polyolefin resin, or the adhesive strength with (B) becomes too large (A). (B) In some cases, easy peelability may not be exhibited.

The intermediate layer (B) is a peel strength adjusting layer and is made of a styrene resin layer. In the present invention, the styrene-based resin layer comprises 0 to 15% by weight of a thermoplastic elastomer mainly composed of a styrene-butadiene copolymer and 0 to 25% by weight of an ethylene-based polymer, and the total of both is 3 to 25% by weight. It is indispensable to contain it as follows. When the ethylene-based polymer is not contained, it contains 3 to 15% by weight of a thermoplastic elastomer mainly composed of a styrene-butadiene copolymer. When no thermoplastic elastomer mainly composed of a styrene-butadiene copolymer is contained, 3 to 25% by weight of an ethylene polymer is used.
It contains.

When the total content of the thermoplastic elastomer mainly containing the styrene-butadiene copolymer and the ethylene-based polymer exceeds 25% by weight, the peel strength between (A) and (B) becomes too strong. For example, when 4% by weight of a thermoplastic elastomer mainly composed of a styrene-butadiene copolymer is contained, the content of the ethylene-based polymer is preferably 21% by weight or less (A).
(B) shows easy peelability, and if it exceeds 21% by weight, (A)
The peel strength between (B) becomes too strong. If the total of both is less than 3% by weight, the peel strength between (A) and (B) becomes too weak, and the obtained container has insufficient sealing performance. When the amount of the thermoplastic elastomer mainly composed of the styrene-butadiene copolymer exceeds 15% by weight, the peel strength between (A) and (B) becomes too strong.

Examples of the ethylene polymer include high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), ethylene-vinyl acetate copolymer (EVA), ethylene-α-olefin copolymer, ethylene -Propylene copolymers and ethylene-β olefin copolymers can be suitably used.

Examples of the thermoplastic elastomer mainly composed of a styrene-butadiene copolymer include styrene-butadiene-styrene block copolymer (SBS) and styrene-butadiene block copolymer (SBS).
Butadiene-block copolymer (SB) and the like can be suitably used.

The base layer of (C) is made of a styrene resin. As the styrene-based resin, impact-resistant polystyrene, general-purpose polystyrene, acid-modified polystyrene, syndiotactic polystyrene, a mixture thereof, or a mixture of these and a styrene-based elastomer is preferable. By using a styrene-based resin, the rigidity of the container can be improved. Further, as long as the adhesive strength with (B) is within a sufficient range, the base material layer is allowed to contain scrap generated during the production of the multilayer structure of the present invention or scrap generated during the molding of the container, so that the cost can be reduced. it can.

The multilayer sheet of the present invention has the above three layers (A), (B) and (C), and the delamination strength between (B) and (C) is higher than the delamination strength between (A) and (B). It needs to be big. As the delamination strength between (A) and (B) and between (B) and (C), the delamination strength between (A) and (B) is 0.2 to 2.0 kg.
/ 15mm (pulling speed 300mm / min) and (B) (C)
The delamination strength between (A) and (B) is 1.
It is preferably at least one time. By setting the delamination strength between (A) and (B) and between (B) and (C) in this way, the separation between the surface layer of (A) and the intermediate layer of (B) is facilitated, The separation between the intermediate layer (B) and the base material layer (C) can be made difficult. As a result, when the multilayer sheets are used as a container, the sealing property and the easy opening property can be simultaneously obtained.

Control of each delamination strength can be easily performed by appropriately selecting the resin composition of the resin material as described above.

Although the thickness of each layer is not particularly limited, the thickness of (A) is a thickness capable of delamination, and is usually 2 to 400 μm,
Preferably it is 5-200 μm. Further, the thickness of (B) is preferably 30% or less, preferably 20% or less of the total thickness of the multilayer sheets in consideration of film forming properties, and is usually 5 to 300 μm.
m. The thickness of (C) is not particularly limited, and is usually
10 to 3000 μm. The ratio of the thickness of each layer is not particularly limited, but the thickness of (B) is preferably smaller than the thickness of (C) in consideration of heat resistance.

FIG. 1 shows a multilayer sheet composed of three layers (A), (B) and (C), but the present invention is not limited to this. On the side of (C) of the present invention opposite to (B), a layer made of another material may be further provided for the purpose of improving oxygen gas barrier properties and reducing deformation when the container is used. As a layer made of another material, for example, ethylene-
Resin layer such as vinyl alcohol copolymer (EVOH), polyvinyldene chloride (PVDC), nylon, polyethylene terephthalate, aluminum vapor deposition layer, aluminum foil, aluminum,
Those having excellent gas barrier properties, such as iron and copper, may be mentioned. Here, as the EVOH, the content of the ethylene unit is 25 to
Those having 60 mol% are suitably used. As PVDC, a vinylidene chloride-vinyl chloride copolymer or a vinylidene chloride-methacrylic acid copolymer is preferably used. The layer made of these other materials may be only one layer,
It may be a multilayer body composed of two or more layers, or a resin layer containing 10 to 80% by weight of an inorganic filler. Further, a composite material with metal, paper, or the like may be used. Also,
An adhesive resin layer may be provided between these layers as necessary.

The multilayer sheets having a multilayer structure composed of (A), (B) and (C) of the present invention can be obtained by coextrusion or mineralization using the above-mentioned resin. As the coextrusion molding method, for example, (A), (B) and (C) are melt-extruded using different extruders, and are laminated by a feed block and formed into a film by a flat die, or a multilayer method. A method of laminating and forming a film in a die using a die may be used. As the lamination, for example, a method such as extrusion lamination, hot melt lamination, dry lamination, or wet lamination can be used. Usually, a co-extrusion laminating method of co-extruding a two-layer structure composed of (A) and (B) and laminating this with (C) is preferably used.

The present invention also has a multi-layer comprising the above-mentioned (A), (B) and (C) having an opening peripheral portion for sealing the lid member in a ring shape, the peripheral portion having the sealing surface as (A). An object of the present invention is to provide an easily-openable container having a structure.

This easily openable container is obtained by heating and melting the above-mentioned multilayer sheet and shaping it into a desired shape, and can be suitably obtained by ordinary vacuum forming, pressure forming or the like. Further, it can also be obtained by molding by injection molding, injection blow molding, blow molding or the like using the resin.

The shape of the peripheral edge of the opening of the easily-openable container is not particularly limited, but is usually a circle, a square, or the like, and the peripheral portion of this shape is annularly heated. The container may be cup-shaped or tray-shaped.

The easily-openable container of the present invention is a hermetically sealed container in which the lid material is sealed at the periphery of the opening.

As the lid material, a sealant layer made of the same or similar resin having excellent heat adhesion to the surface layer (A) at the periphery of the opening of the easily-openable container is used. In particular, when (A) is polyethylene, it is generally preferable to use a lid member having a sealant layer mainly composed of the same polyethylene. However, linear low-density polyethylene has good adhesion to different kinds of polyethylene, and can be used commonly for the same kind and different kinds of polyethylene.
When (A) is polypropylene, the same polypropylene may be used, but it is preferable to use a polypropylene random copolymer having a wide sealing condition. Further, an aluminum foil, a heat-resistant film, or the like may be provided outside the sealant layer.

FIG. 2 is an explanatory sectional view showing an example of the easily-openable container of the present invention.

1 is a surface layer, 2 is an intermediate layer, and 3 is a base material layer. 1,
Reference numerals 2 and 3 each have a multilayer structure including the above (A), (B) and (C), and form a container opening peripheral portion 4. 5
Is a lid material, which is heat-sealed annularly with the upper surface of the peripheral edge of the container opening to form a sealed container. Reference numeral 8 denotes a knob provided to facilitate peeling of the lid member.

When the thickness of the surface layer 1 of the easily-openable container is set to 10 μm or less, the container heat-sealed with the lid member has easy-openability at the time of opening as shown in FIG. That is, the second
In the figure, the knob 8 is lifted upward when the easy-open container is opened. Then, it peels between the surface layer 1 and the intermediate layer 2 of the multilayer container, the surface layer peels to the seal end, and is peeled off together with the lid material. Next, the surface layer 1 is cut at the seal end, and the container is opened. Therefore,
Even if the lid material and the surface layer of the multilayer container are hardly peeled off and heat sealed, they can be easily opened.

When the thickness of the surface layer of the easily-openable container exceeds 10 μm, the same easy-openability can be obtained by providing a weakening line inside the annular seal portion of the surface layer of the container. As the weakening line, a continuous half notch having a depth equal to or greater than the thickness of the surface layer is preferable.

FIG. 3 is a partial cross-sectional view showing an example in which a weakening line is provided on the surface layer of the easily-openable container of the present invention.

1 is a surface layer, 2 is an intermediate layer, and 3 is a base material layer. 1,
Reference numerals 2 and 3 each have a multilayer structure including the above (A), (B) and (C), and form a container opening peripheral portion 4. 5
Is packaged by a lid material, which is heat-sealed annularly with the upper surface of the peripheral edge of the container opening. A weakening line 7 is provided inside the annular seal portion 6 of the surface layer 1. The weakening line is used to cut the surface layer inside the peripheral edge of the container opening when the lid material is opened and the surface layer is peeled off, and is usually provided as an annular notch, but when removing the lid material Any material can be used as long as it can easily cut the surface layer. Note that the distance t between the inner peripheral edge of the heat seal and the weakening line is 10 mm or less, particularly
It is preferable that the thickness be 0.2 mm or more and 10 mm or less. Reference numeral 8 denotes a knob provided to facilitate peeling of the lid member.

To open the easy-open container, the knob 8 is lifted upward in FIG. Then, the surface layer 1 and the intermediate layer 2 of the multilayer container are peeled off, the surface layer is peeled up to the weakening line 7, and peeled off together with the lid material. Next, the surface layer is cut at the line of weakness, and the container is opened. Therefore, even if the lid member and the surface layer of the multilayer container are hardly peeled off and heat-sealed, they can be easily opened.

In order to open the container, instead of the above weakening line, a thin portion is provided on the surface layer at the inflection point portion of the inner surface of the container from the side wall to the peripheral portion of the container body, and breakage of the surface layer is performed at that portion. May be performed. That is, the thickness of the surface layer of the seal portion with the lid material at the peripheral portion is S μm, the thickness of the surface layer at the inflection point portion on the inner surface of the container from the side wall to the peripheral portion of the container body is T μm, and the breaking strength of the surface layer material. Is U kg / cm ² , S ≧ 1.1 × T,
T ≦ (1.33 / U) × 10 ⁴ , and the breaking strength of the surface layer at the inflection point is made smaller than the peel strength of the surface layer and the intermediate layer.

FIG. 4 is a partial cross-sectional view showing an example of an easily-openable container in which a thin portion is provided on a surface layer at a point of inflection on the inner surface of the container from the side wall to the peripheral edge of the container body. This easy-open container has a thin portion of the surface layer at an inflection point 9 on the inner surface of the container from the side wall to the peripheral portion of the container instead of the weakening line in FIG. The thickness of the thin portion is T μm. The thickness of the surface layer of the sealing portion 6 with the lid member 5 at the periphery is S μm. When opening the lid material sealed at the periphery, the surface layer is broken at the inflection point 9 and peeled off together with the lid material.

Here, when there is a peripheral step between the peripheral portion and the side wall of the container body, a thin portion (thickness T ′) is formed on the surface layer of the inflection point portion on the inner surface of the container from the side wall of the container body to the peripheral step. μm). When the peripheral portion has a rim portion or a rim roll portion, a thin portion (thickness T ″ μm) is also provided on the surface layer of the inflection point portion from the peripheral portion to the rim portion or the rim roll portion. However, if the surface layer can be broken, the container can be easily opened even if there is a rim portion or a rim roll portion.

The thickness (μm) S, T of the surface layer and the breaking strength (kg
/ cm ² ) U, it is necessary that the above relational expression be satisfied. The same applies to the relationship between S, T ', and U, and the relationship between S, T ", and U. If the thickness of S is small, the sealing strength of the sealant decreases, and the sealant cannot be said to be a sealed container.
If the thicknesses of T, T 'and T "are too large, the surface layer cannot be broken and the package cannot be opened.

The multilayer sheet of the present invention can be used not only as a container, but also as a lid material of an easily-openable container that is opened by utilizing delamination of a bag-like package or a lid material.

〔Example〕

Hereinafter, the present invention will be described in detail based on examples,
The present invention is not limited to this.

Examples 1 to 15 and Comparative Examples 1 to 8 Table 1 shows multilayer sheets of the present invention manufactured in Examples 1 to 15, and Table 2 shows comparative multilayer sheets manufactured in Comparative Examples 1 to 8. The peel strength between the constituent resin and the interlayer, and the peelability when an easy-open container is manufactured using this multilayer sheet and heat-sealed with a lid material are shown. The production of multilayer sheets and easy-open containers was performed as follows.

 The symbols in the table indicate the following.

PE ₁ : High density polyethylene Idemitsu Petrochemical Co., Ltd., Idemitsu polyethylene 110J
(MI value 13g / 10min) PE ₂ : High density polyethylene Idemitsu Petrochemical Co., Ltd., Idemitsu polyethylene 210J
(MI value: 5.8 g / 10 min) PE ₃ : High density polyethylene Idemitsu Petrochemical Co., Ltd., Idemitsu polyethylene 440M
(MI value 0.9 g / 10 min) PE ₄ : Low-density polyethylene manufactured by Tosoh Corporation, Petrocene 205 (MI value 3 g / 10 min)
Min) PE ₅ : ethylene-olefin copolymer manufactured by Mitsui Petrochemical Industry Co., Ltd., Toughmer A-4085 (MI value 3.6 g / 10 min (190
℃)) PE ₆ : Propylene-olefin copolymer Tuffmer XR-1071 manufactured by Mitsui Petrochemical Industry Co., Ltd.
(MI value: 3.6 g / 10 min (190 ° C)) EVA: Ethylene vinyl acetate copolymer manufactured by Tosoh Corporation, Ultracene UE540F (MI value: 3 g
/ 10 min) PP: polypropylene Idemitsu Petrochemical Co., Ltd., Idemitsu Horipro F-744N
(MI value 7g / 10min) GPPS ₁ : General polystyrene Idemitsu Styrol HH30E (M, manufactured by Idemitsu Petrochemical Co., Ltd.)
I value 4g / 10min) GPPS ₂ : Acid-modified polystyrene Idemitsu Petrochemical Co., Ltd., Idemitsu Moremax UG830
(MI value 2g / 10min) HIPS ₁ : High impact polystyrene Idemitsu Styrol ET-60 manufactured by Idemitsu Petrochemical Co., Ltd.
(MI value 2g / 10min) HIPS ₂ : Acid-modified polystyrene Idemitsu Petrochemical Co., Ltd., Idemitsu Moremax UH830
(MI value 0.7 g / 10 min) SBS: Styrene-butadiene-based elastomer JSR TR2000 (MI value 3 g /
10 minutes) Multilayer sheet (A), (B) and (C) by three extruders, extruder A (screw diameter 50 mm), extruder B (screw diameter 50 mm) and extruder C (screw diameter 65 mm). Were simultaneously extruded, and a three-layer three-layer sheet shown in FIG. 1 was obtained using a feed block and a flat die. The peel strength at each layer boundary surface of the obtained multilayer sheet was measured. Further, the thickness of each layer of (A), (B) and (C) was measured. The results are shown in Table 1.

Here, the peel strength between layers adopts the value at 180 ° peeling, the sample width at this time is 15 mm, the peeling speed is 300 mm /
Minutes.

Easy-Opening Container A round container having a diameter of 72 mm and a drawing ratio of 0.3 as shown in FIG. 2 was obtained by vacuum molding using the multilayer sheet obtained above. The container was notched at the periphery of the flange as a weakening line. After filling these containers with water, using a resin film (80 μm) of the same type as the container surface layer (seal side), heat-sealing with the inner peripheral edge of the heat seal and the weakened line t = 1.5 mm, and then peeling and opening. As a result, all the containers obtained by using the multilayer sheet of the present invention showed excellent peelability.

In addition, the acid-modified polystyrenes described in Examples 12, 13, and 15 were excellent in heat resistance, and thus were excellent in hot filling suitability for foods and the like. For example, Example 12 was capable of hot filling at 95 ° C., and Examples 13 and 15 were not only capable of hot filling but also capable of sterilizing boil at 95 ° C. Except for Examples 13 and 15, the limit was 80-83 ° C.

In a comparative example, a polyethylene polymer or styrene
If the amount of the thermoplastic elastomer mainly composed of a butadiene copolymer was too large, the adhesive force with the polyolefin of (A) was increased, and easy peelability was not obtained. On the other hand, if the amount is too small, the peel strength becomes weak, so that the sealing property cannot be sufficiently obtained, and thus the method is not suitable for the operation.

Example 16 Using the multi-layer sheet of Example 1 shown in Table 1, a plug having a diameter of 72 mm as shown in FIG.
A round container with a drawing ratio of 0.5 was obtained. At the time of air pressure forming with plug assist, the multilayer sheet was gripped by a clamp and a mold, and the container forming conditions were as shown in Table 3. The resulting container had a thin portion at the inflection point 9 as shown in FIG. After filling the container with water, heat sealing was performed using a resin film. Thereafter, when the suitability for peeling was evaluated, easy peelability was exhibited, and finally, the lid material and the container body were easily separated at the inflection point portion of the container, and all showed excellent results.

[Effects of the Invention] According to the present invention, multilayer sheets having a controlled delamination strength can be obtained using a styrene-based resin as a base material.

According to the present invention, it is also possible to obtain an easily-openable container having excellent heat-sealing properties, sealing properties and openability and using a styrene-based resin as a base material, using the above-mentioned multilayer sheets.

[Brief description of the drawings]

FIG. 1 is a schematic view illustrating an example of the multilayer sheets of the present invention. FIG. 2 is an explanatory sectional view showing an example of the easily-openable container of the present invention. FIG. 3 is a partial cross-sectional view showing an example in which a weakening line is provided on the surface layer of the easily-openable container of the present invention. FIG. 4 is a partial cross-sectional view showing an example in which a thin portion is provided on a surface layer of the easily-openable container of the present invention. DESCRIPTION OF SYMBOLS (A) Surface layer, (B) Intermediate layer (C) Base layer 1 ... Surface layer, 2 ... Intermediate layer 3 ... Base layer, 4 ... Opening edge 5 ... Lid material, 6 Seal part 7 Weak line, 8 Knob part 9 Inflection point part

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) B32B 1/00-35/00 B65D 65/40

Claims (7)

(57) [Claims] 1. A base material layer (C) comprising a styrene resin,
From a styrene-based resin layer containing 0 to 15% by weight of a thermoplastic elastomer mainly composed of a styrene-butadiene copolymer and 0 to 25% by weight of an ethylene-based polymer so that the total amount of both is 3 to 25% by weight. A surface layer (A) made of a polyolefin resin via an intermediate layer (B)
Multilayer sheets having a multilayer structure in which the delamination strength between (B) and (C) is greater than the delamination strength between (A) and (B). 2. A base material layer (C) comprising a styrene resin,
A surface layer (A) composed of a polyolefin resin is formed via an intermediate layer (B) composed of a styrene-based resin layer containing 3 to 15% by weight of a thermoplastic elastomer mainly composed of a styrene-butadiene copolymer. A multilayer sheet having a multilayer structure in which the delamination strength between (B) and (B) is greater than the delamination strength between (A) and (B). 3. A base material layer (C) comprising a styrene resin,
A surface layer (A) composed of a polyolefin resin is formed via an intermediate layer (B) composed of a styrene-based resin layer containing 3 to 25% by weight of an ethylene-based polymer. Multilayer sheets having a multilayer structure in which the delamination strength is higher than the delamination strength between (A) and (B). 4. A delamination strength between (A) and (B) is 0.2 to 2.0.
kg / 15mm (pulling speed 300mm / min) and (B)
The multilayer sheet according to any one of claims 1 to 3, wherein the delamination strength between (C) and 1.1 (D) is at least 1.1 times the delamination strength between (A) and (B). 5. The method according to claim 1, further comprising an opening peripheral portion for sealing the lid member in an annular shape, wherein the peripheral portion has a sealing surface of (A). An easily openable container having a multilayer structure comprising C). 6. A container having an opening peripheral portion for sealing a lid material in an annular shape, wherein the peripheral portion has a sealing surface (A). ) And (C), wherein an easy-open container having an annular weakening line provided inside the annular seal portion of the surface layer (A). 7. A container having an opening peripheral portion for sealing a lid material in an annular shape, wherein the peripheral portion has a sealing surface (A). ) And (C), the thickness of the surface layer of the seal portion with the lid material at the peripheral edge is S μm, and the thickness of the inflection point portion on the inner surface of the container from the side wall to the peripheral portion of the container body. When the thickness of the surface layer is T μm and the breaking strength of the surface layer material is Ukg / cm ² ,
An easily openable container, wherein S ≧ 1.1 × T, T ≦ (1.33 / U) × 10 ⁴ and the breaking strength of the surface layer at the inflection point is smaller than the peel strength of the surface layer and the intermediate layer.