JP2002059969A - Food container made of foamed polystyrene with label - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a food container made of a foamed polystyrene with a label on which the label with excellent moisture resistance and being heat- shrinkable can be tightly mounted under a mild condition. SOLUTION: The food container made of the foamed polystyrene with the label is prepared by mounting the heat-shrinkable label in which a printing layer is provided on at least one face of a base film constituted of a surface layer consisting of a non-crystalline olefin polymer with a glass transition temperature (Tg) in the range of 60-150 deg.C and a central layer consisting of a propylene polymer. Heat shrinkage rate of the above described base film is in the range of 30-80% in the main orientation direction when it is immersed e.g. in hot water at 90 deg.C for 10 sec.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a foamed polystyrene food container having excellent moisture resistance.

[0002]

2. Description of the Related Art As described in Japanese Patent Publication No. 62-13946, a heat-shrinkable label made of a plastic film such as polystyrene, polypropylene, or polyester is placed on a foamed plastic container used as a container for an instant food. It is known that the appearance of the water vapor is enhanced by attaching a, and the water vapor barrier property is enhanced. Among them, a heat-shrinkable label made of a polypropylene film is particularly excellent in moisture-proof property.

However, in order to attach a commonly used heat-shrinkable label made of polypropylene to a container made of expanded polystyrene with high adhesiveness, a relatively high temperature (for example, about 200 ° C.) Because a large amount of heat is required, such as spraying, there is a risk that the expanded polystyrene container may undergo secondary foaming due to the heat.

[0004]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a labeled foamed polystyrene food container which has excellent moisture proofing properties and which can be tightly fitted with a heat-shrinkable label under mild conditions. .

[0005]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, when the base film of the heat-shrinkable label to be mounted on the expanded polystyrene container has a multilayer structure made of a specific polymer, it has a high It has been found that the label can be tightly attached to the container even at a relatively low temperature and calorific value while keeping the moisture proof, and the secondary foaming of the container can be prevented.
The present invention has been completed.

That is, the present invention provides a foamed polystyrene container having a surface layer made of an amorphous olefin polymer having a glass transition temperature (Tg) in the range of 60 to 150 ° C. and a center layer made of a propylene polymer. And a heat-shrinkable label provided with a print layer on at least one surface of the base film constituted by the above.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings as necessary. FIG. 1 is a schematic view showing an example of a process for producing a labeled expanded polystyrene food container of the present invention, and FIG. 2 is a schematic cross section showing an example of a heat-shrinkable label in the labeled expanded polystyrene food container of the present invention. FIG. In the drawing, 1 indicates a container made of expanded polystyrene, and 2 indicates a heat-shrinkable label attached to the container.

The heat-shrinkable label 2 includes a base film 6
And the printing layer 3 provided on one surface of the base film 6
And the base film 6 has a surface layer 5
/ Central layer 4 / surface layer 5.

The center layer 4 is made of a propylene polymer. Various polymers containing propylene as a constituent monomer can be used as the propylene-based polymer, and a typical example thereof is an ethylene-propylene random copolymer. In this ethylene-propylene random copolymer, the ratio of ethylene to propylene is, for example, the former / the latter (weight ratio) = 2 / 98-5 /
It is about 95. The ethylene-propylene random copolymer can be obtained by a conventional polymerization method, but a commercially available product can also be used.

The central layer 4 may contain, in addition to the propylene polymer, at least one resin selected from a hydrogenated petroleum resin and a hydrogenated terpene resin, if necessary. By including such a resin in the center layer 4, transparency, stiffness, heat shrinkability at low temperatures, and the like can be improved. The hydrogenated petroleum resin is a resin obtained by hydrogenating an aromatic petroleum resin, and the hydrogenated terpene resin is a resin obtained by hydrogenating a terpene resin such as a terpene resin or an aromatic modified terpene resin. And commercial products can be used.

The amount of the resin to be used can be appropriately selected within a range not to impair the film-forming properties and the like, but is generally about 0 to 60 parts by weight, preferably 20 to 50 parts by weight, per 100 parts by weight of the propylene-based polymer. It is about parts by weight.

The center layer 4 may further contain a small amount of another polymer, if necessary. The thickness of the central layer 4 is, for example, about 10 to 80 μm, and preferably about 20 to 50 μm.

The surface layers 5 and 5 have a glass transition temperature (Tg)
Is formed of an amorphous olefin-based polymer in the range of 60 to 150 ° C, preferably 60 to 100 ° C, particularly preferably 60 to 80 ° C. When the glass transition temperature is lower than 60 ° C., the heat resistance is inferior, and when it exceeds 150 ° C., the label tends to be brittle.

The amorphous olefin polymer includes:
It is not particularly limited as long as it is amorphous and the glass transition temperature is in the above range, and typical examples thereof include (A) ethylene, propylene, 1-butene, 1-hexene, and 4-methyl-1-pentene. α-olefin and at least one
Copolymers with various types of cyclic olefins (hereinafter sometimes referred to as “cyclic olefin copolymers”), and (B) ring-opened polymers of cyclic olefins or hydrogenated products thereof.

Cyclic in the polymers (A) and (B)
Examples of the olefin include bicyclo [2.2.1].
Hept-2-ene (norbornene), tetracyclo
[4.4.0.1^2,5. 1^7,10] -3-dodecene, hex
Sacyclo [6.6.1.1^3,6. 1 ^10,13. 0^2,7. 0
^9,14] -4-heptadecene, octacyclo [8.8.
0.1^{2, 9}. 1^4,7. 1^11,18. 1^13,16. 0^3,8.
0^12,17] -5-docosene, pentacyclo [6.6.
1.1^3,6. 0^2,7. 0^9,14] -4-Hexadecene, hep
Tacyclo-5-icosene, heptacyclo-5-hemico
Sen, tricyclo [4.3.0.1^{2, Five}] -3-Dece
, Tricyclo [4.3.0.1^2,5] -3-Undesse
Pentacyclo [6.5.1.1^3,6. 0^2,7.
0^9,14] -4-pentadecene, pentacyclopentadeca
Diene, pentacyclo [4.7.0.1^2,5. 0^8,13.
1^9,12] -3-pentadecene, nonacyclo [9.10.
1.1^4,7. 1^13,20. 1^15,18. 0^{Two ,Ten}. 0^12,21. 0
^14,19Polycyclic cyclic olefins such as -5-pentacocene
And the like. These cyclic olefins have
S such as methoxycarbonyl and ethoxycarbonyl groups
Alkyl group such as ter group, methyl group, haloalkyl group,
It may have a substituent such as a cyano group or a halogen atom.
No.

The cyclic olefin copolymer (A) is prepared by, for example, reacting the α-olefin and the cyclic olefin in a hydrocarbon solvent such as hexane, heptane, octane, cyclohexane, benzene, toluene, or xylene, so-called Ziegler catalyst. Or by polymerization using a catalyst such as the above-mentioned metallocene catalyst. Such a cyclic olefin copolymer (A) is commercially available, and for example, trade name “Apel” (manufactured by Mitsui Chemicals, Inc.) can be used.

The ring-opened polymer of a cyclic olefin or a hydrogenated product thereof (B) is obtained, for example, by subjecting the cyclic olefin to metathesis polymerization (ring-opening polymerization) using a molybdenum compound or a tungsten compound as a catalyst. The polymer can be produced by further hydrogenating the obtained polymer. Such a polymer (B) is commercially available. For example, trade names "ARTON" (manufactured by Nippon Synthetic Rubber Co., Ltd.), trade names "ZEONEX" and "ZEONOR" (manufactured by Nippon Zeon Co., Ltd.) are used. it can.

The preferred amorphous cyclic olefin polymer is the above-mentioned cyclic olefin copolymer (A). Among them, ethylene and bicyclo [2.2.1] hept-2-ene (norbornene) or tetracyclo [4.4.0.1
^2,5 . Copolymers with [ ^1,7,10 ] -3-dodecene are preferred, and those having an ethylene content in the range of 60 to 85 mol% (particularly 70 to 80 mol%) are particularly preferred.

The surface layers 5 and 5 may be formed of one or more of the above-mentioned amorphous cyclic olefin polymers.
Further, other polymers may be contained in a small amount as required.

The thickness of each of the surface layers 5 is, for example, about 0.5 to 15 μm, and preferably about 1 to 10 μm. The ratio of the total thickness of both surface layers 5 and 5 to the thickness of base film 2 is, for example, about 3 to 50%, and preferably about 5 to 30%. If this ratio is less than 3%, a high temperature is required during heat shrinkage. In addition, since the amorphous cyclic olefin polymer is relatively expensive, the ratio is preferably set to 50% or less.

The surface of the surface layer 5 on the printing layer 3 side may be subjected to a conventional surface treatment such as corona discharge treatment or plasma treatment in order to improve printability. The center layer 4 and the surface layers 5 and 5 may be provided with a lubricant, a filler, inorganic fine particles, a heat stabilizer, an antioxidant, an ultraviolet absorber, an antistatic agent, a flame retardant, a coloring agent, and the like, if necessary. Various additives may be added.

The center layer 4 and the surface layers 5 and 5 may be each composed of a plurality of layers. In addition, another resin layer may be provided between the center layer 4 and the surface layers 5 and 5 as long as the heat shrinkage and the rigidity are not impaired. Alternatively, an overcoat layer made of an acrylic resin or the like may be provided.

The base film 6 can be manufactured by a conventional method used for manufacturing a laminated film, for example, a coextrusion method. For example, the base film 6 shown in FIG. 2 is formed by combining a resin composition containing the resin forming the center layer 4 and a resin composition containing the resin forming the surface layers 5 and 5 with a T-die, and Is feed block 2 kinds 3
It can be obtained by melt-extrusion using a layered extruder, cooling by a cooling roll, and then performing a stretching treatment (uniaxial stretching or biaxial stretching). Note that an annular die can be used instead of the T die. In the present invention, since both the center layer 4 and the surface layers 5 and 5 are formed of an olefin-based polymer, they can be laminated without using an adhesive.

The stretching can be performed by any of a tenter method and a tube method. The stretching process is usually performed at 70
At a temperature of ~ 150 ° C, in the width direction (lateral direction; TD direction)
The stretching is carried out by stretching 4 to 8 times, preferably about 5 to 7 times. In addition, if necessary, the length direction (vertical direction;
The stretching treatment can be performed at a low stretching ratio (for example, about 1.5 times or less) also in the MD direction. The base film 6 thus obtained is in the width direction (the direction in which the stretching process is performed).
Has an orientation and shows heat shrinkage in the direction.

The base film 6 is placed in warm water at 90 ° C. for 10 minutes.
The thermal shrinkage in the main orientation direction X (direction in which the stretching treatment was mainly performed; for example, the width direction) when immersed for 2 seconds is, for example, 3
It is about 0 to 80%, preferably about 40 to 70%.
The heat-shrinkable label made of such a base film can be heat-shrinked at a low temperature and a low calorific value, and can be easily and easily attached to a container having a curved surface, for example. The heat shrinkage is obtained by the following equation. Heat shrinkage (%) = [｛(original length in direction X) − (direction X
Length after immersion)｝ / (original length in direction X)] × 100

The heat shrinkage can be adjusted by appropriately selecting the type of resin constituting the central layer 4 and the surface layers 5 and 5 of the base film 6, the stretching conditions such as the stretching ratio, and the like.

The heat-shrinkable label 2 of the present invention is formed by printing desired images and characters on at least one surface of the base film 6 obtained as described above by a conventional printing method such as gravure printing. It can be manufactured by forming the layer 3. Then, after forming the print layer 3, it is usually cut into a long band shape having a desired width, and the print surface is turned inside, and the base film 6 is rounded into a cylindrical shape so that the direction X is the circumferential direction, After adhering the both sides with an organic solvent, heat fusion, or the like, by cutting the desired length as required, a tubular heat-shrinkable label can be obtained. The heat-shrinkable label formed in a cylindrical shape as described above can be tightly and easily mounted on a container having a body such as a cylindrical shape or an inverted truncated cone.

The printing ink for forming the printing layer 3 is not particularly limited, and any of a water-based ink, an oil-based ink, and the like may be used according to the application.

Since the surface layers 5 and 5 can be welded with an organic solvent, the bonding with the organic solvent is more preferable than the thermal fusion in which the shrinkage of the bonding portion is deteriorated. In addition, the heat-shrinkable label center-sealed by the organic solvent does not have wrinkles at the joints and exhibits an excellent appearance. Examples of the organic solvent include hydrocarbons such as pentane, hexane, cyclohexane, methylcyclohexane, benzene, and toluene; halogenated hydrocarbons such as methyl chloride, methylene chloride, chloroform, ethyl chloride, 1,2-dichloroethane, and propyl chloride. Linear or cyclic ethers such as diethyl ether, diisopropyl ether, dibutyl ether, ethylene glycol dimethyl ether, tetrahydrofuran and dioxane; ketones such as acetone, methyl ethyl ketone and cyclohexanone; one kind such as esters such as methyl acetate, ethyl acetate and butyl acetate; Several mixtures are mentioned. Among these, the boiling point is 20-
An organic solvent of about 120 ° C., especially about 50 to 105 ° C. is preferable in terms of workability and the like.

An adhesive layer is provided on at least the upper end, preferably the upper and lower ends of the tubular heat-shrinkable label, and is adhered to the container at the time of heat shrinkage. Can be reliably prevented. Furthermore, by providing an adhesive layer over the entire upper and lower ends on the inner side of the tubular heat-shrinkable label and adhering to the upper and lower ends of the container, the water vapor barrier property (moisture resistance) can be further enhanced. it can.

As the adhesive constituting the adhesive layer,
There is no particular limitation as long as the above-mentioned effects can be achieved. However, it is preferable to use a heat-sensitive adhesive which generates adhesiveness by softening or melting during heat shrinkage of the label. The heat-sensitive adhesive is roughly classified into a hot melt adhesive and a delayed tack adhesive.

The hot-melt type adhesive is an adhesive having hot-melt property and tackiness, and is usually composed of a base polymer, a tackifier, a wax and the like. The hot-melt adhesive has a base polymer of ethylene-vinyl alcohol copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate An olefin-based hot-melt adhesive which is an olefin-based resin such as a copolymer; the base polymer is styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene- Rubber-based hot-melt adhesive which is a thermoplastic elastomer such as ethylene-butylene-styrene-block copolymer (SEBS) and styrene-ethylene-propylene-styrene block copolymer (SEPS); polyester whose base polymer is polyester Hot melt type Chakuzai; base polymer include a polyamide-based hot-melt adhesive is a polyamide.

Examples of the tackifier include rosin resins (rosin, polymerized rosin, hydrogenated rosin and derivatives thereof, resin acid dimer, etc.), terpene resins (terpene resin, aromatic modified terpene resin, hydrogenated resin) Examples include terpene resins, terpene-phenol resins, etc., petroleum resins (aliphatic, aromatic, alicyclic), cumarone-indene resins, styrene resins, phenol resins, and the like. The tackifiers can be used alone or in combination of two or more.

On the other hand, in the delayed tack type adhesive, the adhesive surface after application and drying does not show tackiness at room temperature, but the tackiness is developed by heating and the tackiness is maintained for a certain period after cooling. It is an adhesive that lasts (for several minutes to several days) and is usually composed of a thermoplastic resin, a solid plasticizer (crystalline plasticizer), a tackifier, and the like.

Examples of the thermoplastic resin include polyacrylate, styrene-acrylate copolymer, styrene-butadiene copolymer, ethylene-vinyl acetate copolymer, polyvinyl acetate, and vinyl acetate-acrylic acid. Examples include an ester copolymer, an ethylene-vinyl chloride copolymer, an ethylene-acrylic acid ester copolymer, an ethylene-acrylic acid copolymer, polybutadiene, polyurethane, and a styrene-isoprene block copolymer. Among them, an acrylic polymer containing an acrylic acid ester as a monomer component, a vinyl acetate polymer containing vinyl acetate as a monomer component, a styrene polymer containing styrene as a monomer component, and the like are preferable. These thermoplastic resins may be used alone or in combination of two or more.

Examples of the solid plasticizer include phthalates such as diphenyl phthalate, dihexyl phthalate, dicyclohexyl phthalate and dihydroabiethyl phthalate; isophthalates such as dimethyl isophthalate; terephthalates Benzoic acid esters such as sucrose benzoate, ethylene glycol dibenzoate, trimethylolethane tribenzoate and pentaerythritol tetrabenzoate; acetates such as sucrose octaacetate; citrates such as tricyclohexyl citrate Sulfonamides such as N-cyclohexyl-p-toluenesulfonamide;
It is not limited to these. These solid plasticizers can be used alone or in combination of two or more. Also,
As the tackifier, the same as described above can be used.

The delayed tack type adhesive may contain known or commonly used additives such as a dispersant, an antifoaming agent and a thickener, if necessary.

The container 1 made of expanded polystyrene is not particularly limited as long as it is a container formed of a foam of a styrene-based polymer such as polystyrene. A container manufactured by bead expansion (for example, a vertical cup noodle container or the like) ), A container (for example, a bowl-shaped container) obtained by molding a foamed sheet, and the like. INDUSTRIAL APPLICABILITY The present invention is particularly useful for a container manufactured by bead foaming, which is mainly composed of closed cells and is likely to cause secondary foaming (refoaming) by heating.

The shape of the expanded polystyrene container 1 is not particularly limited. For example, various containers formed of a styrene-based polymer such as a bottomed cylindrical container such as a vertical cup-shaped container having a tapered side wall may be used. Can be used. The type of contents to be filled in the container 1 is not particularly limited, but the present invention is particularly useful as a labeled container for foods sensitive to moisture such as instant foods (such as instant noodles).

As a method of mounting the heat-shrinkable label 2 on the expanded polystyrene container 1, a known or commonly used method can be applied. For example, a heat-shrinkable label 2 formed in a cylindrical shape is supplied to an automatic label mounting device, cut into a required length, and then fitted over a container 1 normally filled with contents, and passed through a hot air tunnel at a predetermined temperature. The heat-shrinkable label 2 can be attached to the container 1 by causing the heat-shrinkable label 2 to be heated by radiant heat such as infrared rays. Since the amount of heating varies depending on the balance between temperature, air flow, and time, it cannot be unconditionally determined.
The label can be tightly mounted on the container even when the label is thermally contracted with hot air at a relatively low temperature of about 0 to 180 ° C, particularly about 140 to 160 ° C.

[0041]

According to the present invention, since the base film constituting the heat-shrinkable label has a central layer made of a propylene-based polymer, the heat-shrinkable label exhibits a high water vapor barrier property when mounted on a foamed polystyrene container, The contents can be prevented from getting wet. Moreover, in the present invention, since the base film has a surface layer made of an amorphous olefin polymer, it can be tightly closed to the container even at a relatively low temperature (a small heating amount) during heat shrinkage. Can be attached to Therefore, the expanded polystyrene container does not undergo secondary expansion due to heat, and the strength and appearance of the container are not impaired.

[0042]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

Example 1 100 parts by weight of a commercially available ethylene-propylene random copolymer (ethylene content: 4.2% by weight) and 45 parts by weight of a hydrogenated petroleum resin (trade name "Alcon", manufactured by Arakawa Chemical Industries, Ltd.) (A1), 100 parts by weight of an amorphous cyclic olefin polymer (trade name “Apel APL6509”, Tg80 ° C., density 1.02 g / cm ³ , manufactured by Mitsui Chemicals, Inc.) and inorganic fine particles ( Spherical silica, average particle size 1.5 μm)
The mixture (b1) with 0.5 part by weight was co-extruded from a T-die at a temperature of 260 ° C. using a feed block two-type / three-layer extruder, and then at 100 ° C. in the width direction (TD).
(B1)
50 μm (thickness of the central layer (a1): 40 μm, thickness of the surface layer (b1): 5 μm each having a layer configuration of / (a1) / (b1)
m) was obtained. A test piece of 10 cm × 10 cm (length in the width direction (TD direction) × length in the length direction (MD direction)) was cut out from the base film, and the test piece was immersed in warm water at 90 ° C. for 10 seconds. Then, the length in the width direction (TD direction) of the base film was measured, and the heat shrinkage was calculated by the above equation, and it was 50%. One surface of the base film obtained above is subjected to gravure printing of a design consisting of eight colors using a reactive urethane-based ink to form a print layer, and an acrylic resin for preventing damage on the other surface. Was formed and wound into a roll. After slitting the obtained printing roll into a predetermined width to form a plurality of rolls, each roll is rewound and formed into a cylindrical shape such that the width direction (TD direction) of the base film is the circumferential direction. It was rolled up and both ends were adhered with an organic solvent (cyclohexane) to obtain a long continuous heat-shrinkable label. This continuous heat-shrinkable label is supplied to an automatic label mounting apparatus, cut into each label, and then externally fitted into an inverted truncated cone-shaped vertical cup noodle container (internal volume of about 400 ml) containing instant noodles. Then, the label was attached to the container by passing through a hot-air heating tunnel (temperature: 140 to 160 ° C.) and thermally shrinking. No secondary foaming was observed in the container, and the label was easily attached to the container and finished. Further, when the thus-obtained labeled container with instant noodles was stored for a long period of time, a high moisture-proof effect was recognized.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a process for producing a labeled expanded polystyrene food container of the present invention.

FIG. 2 is a schematic cross-sectional view showing one example of a heat-shrinkable label in a labeled expanded polystyrene food container of the present invention.

[Explanation of symbols]

 Reference Signs List 1 container made of expanded polystyrene 2 heat-shrinkable label 3 printing layer 4 center layer 5 surface layer 6 base film

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yasuo Ose 5-3-1-18 Imazukita, Tsurumi-ku, Osaka F-Term in Fuji Seal Co., Ltd. (Reference) 3E067 AB01 BA07B BA21C BB14C BB16C BB17B BB25C BC03B BC03C CA01 CA05 EE02 EE04 FA04 FB01 FC01

Claims (2)

[Claims] 1. A foamed polystyrene container comprising a surface layer made of an amorphous olefin polymer having a glass transition temperature (Tg) in the range of 60 to 150 ° C. and a central layer made of a propylene polymer. A labeled expanded polystyrene food container having a heat-shrinkable label provided with a printed layer on at least one surface of the base film. 2. The main orientation direction when the base film is immersed in warm water having a heat shrinkage of 90 ° C. for 10 seconds.
The food container made of expanded polystyrene with a label according to claim 1, which is in the range of ~ 80%.