JP2001071435A - Film for skin pack packaging - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of chlorine gas during incineration by a method in which a film for skin pack packaging is formed from a sealable resin layer to constitute a surface facing a mold and an opposite side surface and a stretched polyamide resin layer, and in its one direction, heat shrinkage stress is set up at a specified width or below, and a heat shrinkage percentage is set up at a specified value or above. SOLUTION: A film for skin pack packaging is composed of a resin layer 31 using a polyolefin resin which is to constitute a surface facing a mold and an opposite side surface and is sealable, such as polypropylene, a propyleneethylene copolymer, straight chain ultra-low density polyethylene, and straight chain low density polyethylene; and a stretched polyamide resin layer 32 using an aliphatic polyamide which has a melting point by about 15 deg.C higher than a film heating temperature, such as nylon 6, and nylon 66. In its one direction, heat shrinkage stress at a film heating temperature is set up at 200 g/15 mm width or below, and a heat shrinkage percentage is set up at 3% or above.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film for skin pack packaging including a step of vacuum drawing into a heated mold having a recess, and more particularly to a multilayer film including a stretched polyamide resin layer. The film for packaging a skin pack of the present invention is preferably used particularly for food packaging including meat.

[0002]

2. Description of the Related Art Conventionally, in the field of food packaging, a packaging form having a beautiful appearance has been preferred. In particular, skin pack packaging is used for food packaging such as bacon, sausage, ham, meat, cheese, etc., since the packaging film is closely packed along the shape of the article to be packaged, and the packaging has good appearance without wrinkles. Have been. The basic technique of skin pack packaging is to place a packaged object on a base film or sheet (sometimes referred to as "bottom material") and then heat and soften a skin made of a thermoplastic resin. Pack packaging film (hereinafter often referred to as "skin film")
(Referred to as “package”), degassing, and bringing the skin film into close contact with the shape of the article to be packaged.

[0003] Various methods have been proposed as a skin pack packaging method. Among them, a skin film is drawn by a vacuum mold provided with a heater, and then the skin film is formed by a recess in the skin film formed by drawing. After covering the packaged material on the base film, vacuuming the space between the two films and using the elastic recovery property of the skin film to adhere to the packaged material is easy, while maintaining the original shape of the packaged material and easily automated. Is possible.

FIGS. 1 to 4 are sketches including a mold section.
The above-mentioned skin pack packaging method will be described in more detail with reference to (1) a skin film 3 and a recess 4a at a position covering an object to be packaged 2 placed on a bottom material 1 which is a base film or sheet. The concave portion 4a of the vacuum mold 4 having a vacuum hole 4b and a heater (not shown) is arranged (FIG. 1), and (2) the mold 4 heated to about 110 to 160 ° C.
The air in the recess 4a on the skin film 3 is evacuated from the vacuum hole 4b through the vacuum hole 4b, and the skin film 3 is heated in close contact with the recess of the mold 4 by drawing (FIG. 2). (3) Next, the air between the skin film 3 and the packaged object 2 is evacuated (FIG. 3), and (4) the deaeration from the vacuum hole 4b is stopped, and the inside of the recess 4a of the mold 4 is moved. After the skin film 3 is brought into close contact with the packaged object 1 by its elastic recovery force by returning to normal pressure, the lower side of the skin film 3 is deaerated (FIG. 4). Then, immediately, the bottom material 1 and the skin film 3 are heat-sealed at the contact overlapping position SP of the bottom material 1 and the skin film 3 around the packaged object 2 and, if necessary, the bottom outside the seal portion SP. By cutting and separating the material 1 and the skin film 3, the skin pack packaging is completed, and a product package is obtained.

[0005] The above-mentioned skin pack packaging method is a packaging method different from general drawing packaging because a preformed skin film is brought into close contact with an object to be packaged in a heated and softened state. That is, in the general draw-packing method, a film is previously formed into a predetermined shape such as a container using a metal mold, and then the object to be packaged is filled, followed by vacuum packaging. As a problem of this method, a void is likely to remain between the container and the packaged object, and the packaged material, for example, ham, bacon, etc., is accumulated in the void portion, and the appearance of the meat juice is impaired or causes decay. There are things. Further, in the general drawing and packaging method, it is necessary to match the shape of the container to the object to be packaged, and a mold corresponding to the object to be packaged must be prepared.

[0006] On the other hand, in the above-mentioned skin pack packaging method, a skin film preliminarily drawn by a vacuum mold is placed on a package in a heated and softened state, and the elastic recovery property allows the package to be packaged. Adhere to objects. According to the skin pack packaging method, not only can the skin film and the object to be packaged be uniformly adhered to each other, but also beautiful packaging can be performed even when the shape of, for example, sliced bacon is shifted and arranged.

[0007] The skin film used in the skin pack packaging method is required to have the following performance.

First, the skin film is usually required to be capable of being drawn at a drawing depth of about 10 to 25 mm. In order to automatically pack skins of various shapes into the package, it is necessary to draw the
It is required that the drawing depth be large to some extent.

Secondly, the skin film has a resilience (usually rubber elasticity) in order to adhere to the contents after drawing at a molding temperature (mold (heating) temperature, generally 110 to 160 ° C.). Is required, and it is required that a large stress is not generated when the film is stretched during drawing. In skin pack packaging, the skin film is preliminarily drawn and formed by applying stress in a vacuum mold, and after covering the article to be packaged, the stress is removed to bring the skin film into close contact with the article to be packaged. It is necessary to have resilience in a degraded state. That is, in the forming temperature range, it is required that the preform draw forming has a large form recoverability to the elongation of the skin film. If the recoverability of the skin film is insufficient, the stretched portion of the drawn film becomes an excess portion, causing wrinkles on the surface of the package and impairing the appearance. However, in the case of a film having a large heat shrinkage stress such as a conventional heat-shrinkable stretched film or a film having a large residual stress such as an elastic film, the packaged object is compressed and deformed, and the gravy is squeezed out. Inconveniences, such as the cause of deterioration, occur.

Third, the skin film is required to have such heat resistance as not to be fused to a heated vacuum mold (hot plate) when drawing by a vacuum mold. Generally, a multilayer laminated film is used as the skin film, and the outermost layer thereof is required to have heat resistance to such an extent that fusion to a hot plate does not occur. Fourth, skin films are required to have excellent transparency and gloss in order to increase the commercial value of the packaged items. Fifth, the skin film is required to have an oxygen gas barrier property for packaging of contents that need to prevent decay. Further, when heat sealing is performed, heat sealing properties with the substrate are required.

Conventionally, as a skin film satisfying such physical properties, for example, soft vinyl chloride (PVC) /
Unstretched co-extruded laminated film composed of vinylidene chloride copolymer (PVDC) / polyolefin (Japanese Patent Publication 6-2
485), ethylene-vinyl acetate copolymer (EV
A) A laminated film composed of / PVDC / EVA (JP-B-57-23607), a laminated film composed of EVA / PVDC / soft PVC (JP-B-56-49206) and the like have been used. Among these, a laminated film containing soft PVC is particularly preferable as a layer having a large elastic recovery rate and a rubber elastic property in a skin film. However, in recent years, due to environmental problems, packaging materials that do not generate chlorine gas during incineration have been demanded.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to provide a skin pack packaging film which has good suitability for skin pack packaging and does not generate chlorine gas during incineration.

[0013]

According to the study of the present inventors, most of the suitability for a skin film was appropriately selected in relation to a film heating temperature (skin pack forming temperature) for forming a skin pack. Using a stretched layer of a polyamide resin having a melting point, using a multilayer film including a resin layer that assists sealing properties, and controlling the degree of stretching of the polyamide resin layer, the heat shrinkage stress and the heat shrinkage at the skin pack molding temperature. Was found to be satisfied by a properly set multilayer film. The skin pack packaging film (skin film) of the present invention is based on such knowledge, and more specifically, is a skin pack packaging film including a step of drawing into a heated mold having a recess. A sealable resin layer (a) that should constitute a surface opposite to the mold facing surface, and a stretched polyamide resin layer made of a polyamide resin having a melting point about 15 ° C. or more higher than the film heating temperature ( b) at least two layers;
In at least one direction, at a film heating temperature, the heat shrinkage stress is 200 g / 15 mm width or less, and the heat shrinkage rate is 3% or more.

Hereinafter, preferred embodiments of the present invention will be described in detail.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The skin pack packaging method itself using the skin pack packaging film (skin film) of the present invention is not fundamentally different from that described with reference to FIGS. However, the film heating temperature can be set wider as compared with the conventional PVC skin film, because the range of selecting the melting point of the polyamide resin constituting the polyamide resin layer (b) is wider. However, the sealing resin layer (a)
90 to 170 ° C., furthermore, 110 to 15 in consideration of the constituent material of other layers such as
A temperature range of 0 ° C. is preferably used. Heating temperature is 90
When the temperature is lower than 0 ° C, shrinkage is reduced, and wrinkles are easily generated on the surface of the package after the skin pack. When the heating temperature exceeds 170 ° C., the film is melted, and the film is easily broken during skin molding. The most preferred film heating temperature, including the applicability of conventional skin pack molding machines, is believed to be around 120 ° C. The configuration of each layer of the skin film of the present invention is determined mainly in relation to the film heating temperature (skin pack molding temperature).

The heating time in the skin pack packaging (from the start of evacuation through the mold vacuum holes 4b in FIG.
Of the skin film 3 from the lower space to the start of evacuation from the lower space) is preferably 0.5 to 5 seconds, particularly about 1 to 3 seconds. From the start of evacuation, the time for releasing the vacuum in the upper space of the skin film 3 in FIG. 4 and maintaining the vacuum in the lower space of the skin film 3) is preferably about 1 to 5 seconds.

Strictly speaking, the film heating temperature related to the constitution of each layer of the skin film of the present invention is the heating temperature of the skin film itself, not the heating temperature of the mold 4. In particular, when the heating time is short, there may be a difference between the two. However, such a short heating time that causes a difference between the two temperatures is not always preferable for stable skin pack molding. Therefore, in general, the film heating temperature is considered to be equivalent to the mold heating temperature. No problem.

The sealing temperature after skin packaging may be appropriately set according to the resin used for the sealing layer (a). The set temperature of the seal bar is generally 100 ° C. to 100 ° C.
It is in the range of 240 ° C, preferably in the range of 130 to 220 ° C. If the set temperature is too low, the sealing strength tends to be insufficient, and if it is too high, the surface resin on the side opposite to the sealing surface tends to stick to the seal bar.

In the most basic form of the skin film of the present invention, as shown in FIG. 5, a two-layer laminate structure of a sealing resin layer (a) 31 and a stretched polyamide resin layer (b) 32 Take. However, as shown in FIG. 6, a functional intermediate layer (d) 33 such as a gas barrier resin layer can be inserted between the layers, and further, as shown in FIGS. 7 to 9, for example, surface properties such as printability. In consideration of the above, the outer surface layer (c) 34 may be provided. Further, an adhesive resin layer can be arbitrarily inserted between the respective layers, and an arbitrary intermediate layer such as an additional polyamide resin layer can be inserted.

More specifically, the sealing resin layer (a) 31
May be made of a resin that can be sealed, but in particular polypropylene, propylene-
Ethylene copolymer, linear ultra low density polyethylene, linear low density polyethylene, low density polyethylene polymerized by high pressure method, ethylene-vinyl acetate copolymer, ionomer resin, ethylene- (meth) acrylic acid copolymer Coalescing,
Polyolefin-based resins such as an ethylene- (meth) acrylic acid-unsaturated carboxylic acid ester copolymer and an ethylene-ethyl acrylate copolymer are preferably used. These may be used alone or as a mixture of two or more. The melting point of the resin used for the sealing resin layer (a) is determined by the polyamide resin layer (b) constituting the opposite outer surface layer.
32 (FIGS. 5 and 6) or other outer surface layer (c) 34
The melting point of the constituent resin shown in FIGS. When the melting point of the resin used for the sealing resin layer (a) is higher than the melting point of the resin used for the outer surface layer (b) or (c), when the inner surface is melted during sealing after skin packaging,
Since the outer surface also melts, sealing becomes difficult.

The polyamide resin layer (b) most characteristic of the skin film of the present invention has a melting point of about 15 ° C. or more, preferably 20 ° C. or more, more preferably 4 ° C. or more than the skin pack molding temperature.
It is made of a stretched polyamide resin having a melting point higher than 0 ° C., especially higher than 60 ° C. A skin film containing a polyamide resin layer (b) having a melting point of less than the skin pack molding temperature + 15 ° C. is plastically deformed by melting at the time of skin packaging, and the recoverability of the film tends to be insufficient. As a result, wrinkles occur after packaging, and the appearance of the package tends to be unsatisfactory.

Preferred polyamide resin species constituting the polyamide resin layer (b) include nylon 6 and nylon 6
6, nylon 69, nylon 610, nylon 612,
Aliphatic polyamide polymers such as nylon 11 and nylon 12, nylon 6-66 (representing a copolymer of nylon 6 and nylon 66, and similarly described below), nylon 6-66
And aliphatic polyamide copolymers such as 10, nylon 6-12, nylon 6-69, nylon 6-610, and nylon 66-69. Of these, nylon 6-66 and nylon 6-12 are particularly preferred in terms of moldability. These aliphatic polyamides (co)
The polymers can be used alone or as a blend of two or more. At the time of blending, there is a high probability of being affected by the polyamide resin having a low melting point. Therefore, the resin that does not satisfy the requirement of the melting point determined by the relationship with the skin pack molding temperature is preferably less than 30% by weight, particularly preferably less than 20% by weight. In addition, blends of these aliphatic polyamide (co) polymers with aromatic polyamides are also used. Here, the aromatic polyamide refers to a polyamide in which at least a part of at least one of a diamine and a dicarboxylic acid has an aromatic unit, and is particularly preferably a copolyamide. For example, nylon 6
A copolymer of an aliphatic nylon such as 6-610-MXD6 (MXD6 is an abbreviation for meta-xylylene adipamide) and an aromatic polyamide containing an aromatic diamine unit, nylon 6
Aliphatic polyamides such as 6-69-6I (6I is an abbreviation for hexamethylene isophthalamide), nylon 6-6I, nylon 66-6I, and nylon 6I-6T (6T is an abbreviation for hexamethylene terephthalamide); A copolymer with a copolymerized aromatic polyamide containing a carboxylic acid unit may be mentioned. As these polyamide resins, those having a melting point of 160 to 210 ° C., alone or in combination, are preferably used. The intermediate layer (b) includes an olefin resin modified with an acid such as maleic acid or an anhydride thereof, an ethylene-acrylic acid copolymer, an ethylene-methacrylic acid copolymer, an ionomer resin, an ethylene-vinyl acetate copolymer. A thermoplastic resin other than a polyamide resin such as a saponified polymer may be contained up to about 30% by weight.

The polyamide resin layer (b) needs to be stretched in at least one direction, preferably in the longitudinal / lateral biaxial direction. This is to ensure elastic recovery during skin packaging. Stretching can be performed, for example, on the entire laminate film as shown in FIGS.
If necessary, another layer may be laminated after stretching some of the layers including the polyamide resin layer (b). The degree of stretching required is such that the skin film of the present invention in the final laminated form has a heat shrinkage stress at a skin pack molding temperature of at least one direction of 200.
g / 15 mm width or less, a degree that can provide a heat shrinkage of 3% or more.

If necessary, however, in many cases, preferably used outer surface layer (c) 34 (for example, FIGS. 7 to 9)
The melting point is the skin pack molding temperature + about 5 ° C
It is composed of the thermoplastic resin described above. If a thermoplastic resin having a melting point of less than the skin pack molding temperature + 5 ° C. is used, surface contamination is likely to occur due to contact with a hot plate (die) during skin packaging, and as a result, gloss after packaging deteriorates, The beauty of the package appearance may be impaired. Examples of preferred thermoplastic resins constituting the outer surface layer (c) are listed below.

For example, polyolefin resins such as polypropylene, propylene-ethylene copolymer, linear low density polyethylene, medium density polyethylene and high density polyethylene can be mentioned. These may be used alone or as a mixture of two or more. In addition, other resins, for example, an ethylene-vinyl acetate copolymer, an ionomer resin, an ethylene-based copolymer such as an ethylene-methacrylic acid copolymer, and a melting point that does not satisfy the above requirements, as long as the heat resistance is not significantly impaired. The propylene-ethylene copolymer may be mixed at a ratio of 30% by weight or less, preferably 20% by weight or less.

Further, a polyamide resin selected from the polyamide resin types listed as those constituting the polyamide resin layer (b) may be used.

As another preferable example of the resin constituting the outer surface layer (c), a polyester resin is given.

The dicarboxylic acid component constituting the polyester resin may be any one which can obtain a polyester by a usual production method. In addition to the above-mentioned terephthalic acid and isophthalic acid, for example, a dimer of unsaturated fatty acid may be used. Dimer acid, adipic acid, oxalic acid, malonic acid, succinic acid, azelaic acid, sebacic acid, phthalic acid, 5-tert-butylisophthalic acid, naphthalenedicarboxylic acid, diphenylether dicarboxylic acid, cyclohexanedicarboxylic acid, etc. More than one species may be used. The diol component constituting the polyester-based resin may be any one that can obtain a polyester by a normal production method. Examples thereof include ethylene glycol, propylene glycol, tetramethylene glycol, neopentyl glycol, hexamethylene glycol, and diethylene glycol. , Polyalkylene glycol, 1,4-cyclohexanedimethanol, 2-alkyl-1,3-propanediol, and the like, and two or more kinds may be used.

Among them, preferred are aromatic polyester resins containing an aromatic dicarboxylic acid component, and particularly preferred are polyesters of terephthalic acid as a dicarboxylic acid component and a diol having 10 or less carbon atoms, for example, Polyethylene terephthalate, polybutylene terephthalate and the like are used, and a part of terephthalic acid, preferably up to 30 mol%, more preferably up to 15 mol%,
Is replaced with another dicarboxylic acid, for example, isophthalic acid, or a part of a diol component such as ethylene glycol is replaced with another diol, for example, 1,4-
Copolymerized polyester resins replaced with cyclohexanedimethanol are also preferably used. Further, two or more different types of polyester resins may be used as a mixture.

As the polyester resin, those having an intrinsic viscosity of about 0.6 to 1.2 are preferably used. The polyester resin constituting the outer surface layer (c) includes, for example,
Up to 20% by weight of a thermoplastic elastomer other than a polyester-based resin such as a thermoplastic elastomer typified by a thermoplastic polyurethane or a polyolefin-based resin modified with an acid such as maleic acid or an anhydride thereof can be contained.

The resin constituting the functional intermediate layer (d) provided as required (for example, the layer 33 shown in FIGS. 6, 8 and 9) is, for example, a chlorine-free gas barrier resin. Examples thereof include saponified ethylene-vinyl acetate copolymer (EVOH); nylon MXD6, nylon 6I-6T, and the like. Among these, E
VOH is preferably used because of its excellent moldability.

The adhesive resin layer can be provided as an intermediate layer, if necessary, when the adhesive strength between the above layers is not sufficient. More preferably, EE is used as the adhesive resin.
A, EAA, EMAA, IO, acid-modified polyolefins (unsaturated carboxylic acids such as maleic acid and fumaric acid, unsaturated carboxylic acid anhydrides, unsaturated carboxylic acid esters, metal salts, etc. For example, acid-modified VLDPE, acid-modified LLD
PE, acid-modified EEA, acid-modified EVA, acid-modified PP, acid-modified PP-Et) and the like can be used. Suitable examples include acid-modified polyolefins modified with acids such as maleic acid or anhydrides thereof.

In the above-mentioned layer constitution, a lubricant and an antistatic agent can be added to any of the layers.

Examples of the lubricant used include hydrocarbon lubricants, fatty acid lubricants, aliphatic amide lubricants, ester lubricants, metal soaps and the like. The lubricant may be liquid or solid. Specifically, examples of the hydrocarbon-based lubricant include liquid paraffin, natural paraffin, polyethylene wax, micro wax and the like. Examples of the fatty acid-based lubricant include stearic acid and lauric acid. Examples of the aliphatic amide lubricant include stearamide, palmitamide, N-oleyl palmitamide, behenamide, erucamide, arachidic amide, oleamide, erucamide,
Methylene bis-stearamide, ethylene bis-stearamide and the like can be mentioned. Examples of the ester lubricant include butyl stearate, hydrogenated castor oil, ethylene glycol monostearate, and monoglyceride stearate. The metal soap is derived from a fatty acid having 12 to 30 carbon atoms, and typically includes zinc stearate and calcium stearate. Among these lubricants, fatty acid amide-based lubricants and metal soaps are preferably used because they have excellent compatibility with polyolefin resins.

Known inorganic lubricants (anti-blocking agents) such as silica and zeolite can be added to both outer layers.

Lubricants such as aliphatic amides and silica can be added in the form of a masterbatch. The preferable addition amount is 0.1% in the case of a master batch containing 20% by weight of a lubricant.
To 10% by weight.

As an antistatic agent, a surfactant is preferably used. Examples of the surfactant include an anionic surfactant, a cationic surfactant, a nonionic surfactant,
Amphoteric surfactants and mixtures thereof can be used. The antistatic agent is added in an amount of 0.1 to the resin of the layer to be added.
It is preferably added in an amount of from 0.05 to 2% by weight, more preferably from 0.1 to 1% by weight.

Preferred embodiments of the layer structure of the skin film of the present invention are described below. However, these are merely examples, and the present invention is not limited to only these.

From outer layer to inner layer (1) polypropylene resin / polyamide resin / seal layer resin (FIG. 7) (2) polypropylene resin / polyamide resin / non-chlorine gas barrier resin / seal layer resin (FIG. 8) (3) polypropylene Resin / polyamide resin / non-chlorine gas barrier resin / polyamide resin / seal layer resin (4) PET resin / polyamide resin / seal layer resin (FIG. 7) (5) PET resin / polyamide resin / non-chlorine gas barrier resin / Seal layer resin (FIG. 8) (6) Polyamide resin / EVOH / Seal layer resin (FIG. 6) (7) Polyamide resin / EVOH / Polyamide resin / Seal layer resin In the above configuration, if the interlayer adhesiveness is poor, it is appropriately bonded. Layers can be provided.

The skin film of the present invention has a thickness of 10 to 150 μm, especially 15
It is preferable to form a multilayer film having a thickness in the range of 120 to 120 μm.

More specifically, the outer surface layer (c) has a thickness of 0.5
The thickness of the polyamide resin layer (b) is preferably from 3 to 40 μm, particularly from 4 to 30 μm, and the thickness of the sealing resin layer (c) is preferably from 5 to 70 μm, particularly from 10 to 60 μm.

A plurality of adhesive resin layers can be provided, and the thickness thereof is preferably in the range of 0.5 to 5 μm.

The skin film of the present invention may be produced by co-stretching a co-extruded unstretched multilayer film having a full-layer constitution by a known method such as an inflation method or a tenter method, or a polyamide resin layer ( The desired layer structure may be obtained by laminating the stretched film containing b) and the unstretched film or the stretched films by a known laminating method.

The skin film of the present invention thus obtained has a dry heat shrinkage at a film heating temperature (typically 120 ° C.) of at least one direction, preferably in both the longitudinal and transverse directions. %, And if it is less than 3%, wrinkles are likely to be formed after packaging. Further, the heat shrink force at the film heating temperature (typically 120 ° C.) is 200 g / 15 mm width or less, preferably 180 g / 15 mm width or less, more preferably 180 g / 15 mm width or less in at least one direction, preferably in both the vertical direction and the horizontal direction. It is 160 g / 15 mm width or less. If the heat shrinkage exceeds the upper limit, the content becomes difficult to maintain its original shape, and the appearance after packaging tends to be unsatisfactory.

Before or after stretching in the above-mentioned method for producing the skin film of the present invention, irradiation can be performed by a known method. Irradiation improves stretchability, heat resistance, mechanical strength, and the like, as compared with those not irradiated. In the present invention, known radiation such as α-rays, β-rays, electron beams, and γ-rays can be used. From the viewpoint of the cross-linking effect before and after irradiation, electron beams and γ-rays are preferable, and among them, electron beams are advantageous in terms of handleability and high processing ability in producing a molded product.

The above-described radiation irradiation conditions may be appropriately set according to the intended use. For example, in the case of an electron beam, the acceleration voltage is in the range of 150 to 500 kV, and the irradiation dose is. The range is preferably 10 to 200 kilogray (kGy), and in the case of γ-rays, the dose rate is preferably in the range of 0.05 to 3 kGy / hour.

The inner surface, outer surface, or both surfaces of the skin film of the present invention may be subjected to corona discharge treatment, plasma treatment, or flame treatment.

[0048]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In addition, the measuring method of the physical property described in this specification is as follows.

<Physical Property Measurement Method> Dry heat shrinkage A gear oven (MOG 600 manufactured by Robert Co., Ltd.) in which cardboard paper having a thickness of 3 mm is laid on a net shelf.
Mold) to the measurement temperature. The film samples marked in the machine direction (longitudinal direction, MD) and the direction perpendicular to the machine direction (horizontal direction, TD) of the skin film at a distance of 10 cm are placed therein. At this time, the door of the gear oven should be closed immediately after the sample is put. The time during which the door is vacant shall be within 3 seconds. Close the door, leave the sample film for measurement in a gear oven for 30 seconds, take it out and allow it to cool. Then, measure the marked distance and
The ratio of the reduction value from 0 cm to the original length of 10 cm was expressed as a percentage. One sample was tested five times, and the dry heat shrinkage was indicated as an average value in each of the vertical and horizontal directions.

2. Heat shrinkage stress From the obtained skin film, along its longitudinal direction (MD) and transverse direction (TD), each 150 mm length, 15 mm
Cut out the width of the sample film strip. Instron 55
Using a 65-type universal testing machine and an Instron 3119 type constant temperature bath, the sample film band was set in a constant temperature bath maintained at 23 ° C. with a distance between grippers of 100 mm, and then the constant temperature bath was moved at a rate of 2 ° C./min. To raise the temperature. When the temperature of the thermostat reaches 30 ° C., an initial load of 10 g is applied, and then the measurement is started, and the measurement is performed until the temperature of the thermostat reaches the measurement temperature + 10 to 20 ° C. On the way, the heat shrinkage stress value at the measurement temperature (skin packaging molding temperature (standard = 120 ° C.)) is measured.

3. Recovery rate Each of the obtained skin films was 100 mm long, 10 mm long along the machine direction (MD) and the transverse direction (TD).
A sample film strip of width is cut out and marked in the length direction of the film strip at a distance of 50 mm. Using a 5565 universal testing machine manufactured by Instron and a thermostat manufactured by Instron 3119, the sample film band was measured at the measurement temperature (standard =
(120 ° C) in a thermostat kept at a distance of 50mm
Set with. When setting the sample film, make sure that the sample film does not shrink due to the heat in the thermostat so that the sample mark and the end of the gripper are aligned. When the sample film is set, the temperature of the thermostat decreases by about 20 ° C. After the temperature of the thermostat returns to the measurement temperature, the distance between the grippers is 50 mm.
Pull at 0 mm / min to an elongation of 40% (20 mm as elongation) and immediately return the gripper to the position before pulling. The sample film was taken out of the thermostat, the length X between marks after cooling was measured, and the recovery rate was calculated according to the following equation.

Recovery rate (%) = [(50 + 20−X) / 20] × 100

4. Skin pack packaging suitability test The skin films of Examples and Comparative Examples, and a commercially available skin pack packaging base film (thickness: 150 µm) were used. Lay the paper backing on the base film, and put 6 sliced bacon (200g) on it.
Mold for a skin pack test chamber manufactured by Omori Machinery Co., Ltd. (depth 18 mm, length 120 mm, width 245 mm,
Skin pack packaging was performed at the bottom corner (7.5R). In the skin pack packaging, referring to FIGS. 1 to 4, the heating temperature of the mold 4 is set and maintained at a predetermined constant temperature (standard = 120 ° C.), the heating time is 2 seconds, and the vacuum time is 3 seconds. Set and went. Skin pack packaging suitability was evaluated according to the following criteria.

(1) Wrinkles A ⁺ : Wrinkles are not present on the entire surface and the appearance is beautiful. A: Although short and shallow wrinkles are generated only at the filling portion corner, no wrinkles are generated on the bacon surface and the bacon has a beautiful appearance. B: Shallow wrinkles occurred on the entire surface, and there was a problem in appearance. C: Deep wrinkles occurred on the entire surface, and there was a problem in appearance. (2) Surface roughness A: The skin film after packaging was excellent in surface gloss and had a beautiful appearance. C: Large irregularities were present on the surface of the skin film after packaging, and the surface gloss was deteriorated. (3) Crushing of Contents A: The corners of bacon after packaging were hardly crushed, and the original shape of the contents was almost maintained. C: The corners of the bacon after packaging disappeared at all, and the original shape of the contents was not maintained.

<Film Production Examples> Next, production examples of skin films according to Examples and Comparative Examples will be described. Some of the resins used in the following production examples are indicated by abbreviations, and the contents are collectively shown in Table 1 below.

(Example 1) The layer constitution was such that co-PET (1) / co-PET (1) /
M-PE (1) / Ny6-66 (5) / EVOH (3)
/ M-PE (1) / VLDPE (14)
Each resin was extruded with a plurality of extruders, and the melted resin was introduced into an annular die, where it was melt-bonded so as to have the above-mentioned layer configuration and co-extruded. The molten tubular body flowing out of the die outlet was rapidly cooled in a water bath to obtain a flat tubular body. Next, after passing the flat tubular body through a warm water bath at 90 ° C,
Simultaneous biaxial stretching at a stretch ratio of 3.0 times in the machine direction (MD) and 3.0 times in the transverse direction (TD) by the inflation method while forming a bubble-shaped tubular film while cooling with an air ring at 15 to 20 ° C. did. Next, the biaxially stretched film is guided into a heat-treated tube having a tube length of 2 m to form a bubble-shaped tubular film, which is heated to 70 ° C. by steam blown out from a blowout port, relaxed 10% in a longitudinal direction, and a transverse direction. Heat for 2 seconds while relaxing 10% to a thickness of 25
A μm biaxially stretched skin film was produced.

The measurement results of the dry heat shrinkage, the heat shrinkage stress, and the recovery rate of the obtained skin film, and the results of the skin pack packaging suitability test at a skin packaging temperature of 120 ° C. were obtained in the skin films obtained in Examples and Comparative Examples described later. The results are shown in Table 2 below.

Example 2 As a polyamide film,
Nylon 6 / MXD6 / Nylon 6 (thickness ratio = 1/1 /
A heat-shrinkable multilayer film having a layer structure of 1) (available from Mitsubishi Chemical Kojin Pax Co., Ltd., Super Neal SPR SH, total thickness: 15 μm, hereinafter abbreviated as “PA-1”) was prepared. Separately, PP-2 was melt-extruded using an extruder as a polypropylene film, and a 15 μm thick polypropylene-based unstretched film (hereinafter abbreviated as “CPP”) was obtained by a T-die method. (Note that “MXD6” means polymethaxylylene adipamide, and the melting point was determined to be 240 ° C. as a result of DSC (differential scanning calorimetry) of the laminated film “PA-1”.

The above PA-1 and CPP were treated with a polyurethane adhesive (“TM590” manufactured by Toyo Morton Co., Ltd.)
"CAT56") and dry-laminated using CPP
A laminated skin film having a structure of {PA-1} CPP and a thickness of 49 μm was obtained (‖ indicates a dry laminate adhesive layer).

(Example 3) The layer constitution is such that PP-Et (10) /
MPE (1.5) / Ny6-66 (12) / EVOH
Each resin is extruded with a plurality of extruders so that (4) / M-PE (1.5) / PP-Et (15), and the melted resin is introduced into an annular die. They were melt-bonded to form a layer structure and co-extruded. The molten tubular body flowing out of the die outlet was rapidly cooled in a water bath to obtain a flat tubular body. Next, after passing the flat tubular body through a hot water bath at 90 ° C., a bubble-shaped tubular body film is formed.
2.8 times in the machine direction (MD) and 2.8 in the transverse direction (TD) by the inflation method while cooling with an air ring at ℃.
The film was simultaneously biaxially stretched at twice the draw ratio. Next, the biaxially stretched film is guided into a heat treatment tube having a tube length of 2 m to form a bubble-shaped tubular film, which is heated to 80 ° C. by steam blown out from an outlet, relaxed 10% in a longitudinal direction, and a transverse direction. The film was heat-treated for 2 seconds while being relaxed by 10% to produce a 44 μm-thick biaxially stretched multilayer film.

(Example 4) EVOH (4) / Ny6-66 in a layer structure in order from outside to inside with a thickness ratio shown in parentheses.
(12) / M-PE (1.5) / VLDPE (20), and a biaxially stretched skin film having a total thickness of 37.5 μm was produced in the same manner as in Example 3 except for the layer structure.

(Comparative Example 1) In Example 2, instead of CPP, a biaxially stretched polypropylene film (Kojin Polyset, thickness: 15 μm, hereinafter abbreviated as “OPP”) was used in place of CPP as the polypropylene film. Except for using OPP @ PA-1 in the same manner as in Example 2.
A laminated skin film having a thickness of 49 μm and having a structure of ‖OPP was obtained.

(Comparative Example 2) The layer constitution was such that PP-Et (3) / M
-PE (1.5) / NY-2 (14) / EVOH (3)
Each of the resins is extruded by a plurality of extruders so that /M-PE(1.5)/VLDPE(18) is obtained, and the melted resin is introduced into an annular die. And co-extruded. The molten tubular body flowing out of the die outlet was rapidly cooled in a water bath to obtain a flat tubular body. Next, after passing the flat tubular body through a hot water bath at 90 ° C., it is formed into a bubble-shaped tubular body film and cooled by an air ring at 15 to 20 ° C. by 2.3 times in the longitudinal direction (MD) by an inflation method. The film was simultaneously biaxially stretched in the transverse direction (TD) at a draw ratio of 2.6 times. Next, the biaxially stretched film is guided into a heat-treated tube having a tube length of 2 m, and is formed into a bubble-shaped tubular film. Heat-treated for 2 seconds while relaxing 10% to a thickness of 41
A μm biaxially skinned skin film was produced.

(Comparative Example 3) The layer structure was VLDPE (10) /
M-PE (1.5) / Ny6-66 (12) / EVOH
(4) / M-PE (1.5) / VLDPE (20) Each resin is extruded with a plurality of extruders, and the melted resin is introduced into an annular die so that the layer structure is obtained. And were co-extruded. The molten tubular body flowing out of the die outlet was rapidly cooled in a water bath to obtain a flat tubular body. Next, after passing the flat tubular body through a hot water bath at 90 ° C., a bubble-shaped tubular body film is formed.
2.8 times in the machine direction (MD) and 2.8 in the transverse direction (TD) by the inflation method while cooling with an air ring at ℃.
The film was simultaneously biaxially stretched at twice the draw ratio. Next, the biaxially stretched film is guided into a heat treatment tube having a tube length of 2 m to form a bubble-shaped tubular film, which is heated to 80 ° C. by steam blown out from an outlet, relaxed 10% in a longitudinal direction, and a transverse direction. The film was heat-treated for 2 seconds while being relaxed by 10% to produce a biaxially stretched skin film having a thickness of 49 μm.

(Comparative Example 4) The layer structure was such that VLDPE (10) / M
-PE (1.5) / Ny6-12 (8) / EVOH
(3) / M-PE (1.5) / VLDPE (10), and a biaxially stretched skin film having a total thickness of 34 μm
Except for the layer configuration, it was manufactured in the same manner as in Comparative Example 3.

(Comparative Example 5) The layer constitution was such that PP-Et (15) /
M-PE (2) / Ny6 (15) / M-PE (2) / V
Each resin was extruded with a plurality of extruders so as to become LDPE (20), and the melted resin was introduced into a T-die, where it was melt-bonded so as to have the above-mentioned layer structure and co-extruded. The melt flowing out of the die outlet was quenched with a chill roll to obtain an unstretched skin film having a thickness of 54 μm.

(Comparative Example 6) PET (12) / M−
Each resin is extruded with a plurality of extruders so that PE (2) / Ny6-66 (15) is obtained, and the melted resin is introduced into a T-die. And co-extruded. The melt flowing out of the die outlet was quenched with a chill roll to obtain an unstretched skin film having a thickness of 29 μm.

The unstretched multilayer film and CPP were used in Example 1.
Dry-laminated in the same manner as described above, and co-PET / M
-PE / Ny6-66‖CPP thickness of 46 μm
Was obtained.

Comparative Example 7 In Example 2, PA-1 was used.
Instead of stretched nylon 6 film (Bonille RX, sold by Mitsubishi Chemical Kojin Pax Co., Ltd., thickness 15 μm, hereinafter referred to as “P
A-2)), except that the thickness 4 of the structure of CPP {PA-2} CPP was used.
A 9 μm laminated skin film was obtained.

The skin packaging temperature at 120 ° C. of the laminated skin film obtained in each of the above Examples and Comparative Examples was 12
Measurement results of the dry heat shrinkage at 0 ° C., heat shrinkage stress, and recovery rate,
Table 2 summarizes the skin pack suitability test results
It writes in.

[Skin Pack Packaging Temperature Suitability Test] With respect to the skin films obtained in Examples 1 and 4 and Comparative Examples 2 and 4, the skin packaging temperature was varied, and the skin packaging suitability test and shrinkage at the temperature were performed. The measurement of the rate and the contraction force was performed. The results are shown in Table 3 below together with the already measured results at 120 ° C. (shown in Table 2).

[0072]

[Table 1]

[0073]

[Table 2]

[0074]

[Table 3]

The following can be seen from the results in Table 2 above.
The skin films of Examples 1 to 4 satisfying the predetermined conditions of the present invention in relation to the skin packaging temperature of 120 ° C. show good skin packaging suitability.

On the other hand, the film of Comparative Example 1 had an excessive heat shrinkage stress, and the contents were crushed. The film of Comparative Example 2 has a low melting point (133 ° C.) of Ny6-12 contained in the polyamide resin layer (b) at 30% by weight in relation to the skin packaging temperature of 120 ° C., so that wrinkles remain on the appearance of the skin package. ing. In the film of Comparative Example 3, the melting point of the surface layer VLDPE (= 119 ° C.) was low, and the surface of the skin package was roughened. The film of Comparative Example 4 could not be evaluated due to tearing because both Comparative Examples 2 and 3 had a problem. In the films of Comparative Examples 5 and 6, since the polyamide resin layer (b) was not stretched, the appearance of the skin package was wrinkled. Although the film of Comparative Example 7 contained the stretched polyamide resin layer (b), the heat shrinkage stress was insufficient, and wrinkles remained on the surface of the skin package.

From the results in Table 3 above, the following can be seen with respect to the change in skin packaging temperature. The film of Example 1 shows good suitability for skin packaging in a wide temperature range of 90 to 170 ° C., and particularly at 170 ° C., has no wrinkles and has a beautiful appearance (A ⁺ ) over the entire surface. If the film of Example 4 has a temperature of 150 ° C. or more in relation to the melting point of EVOH (= 160 ° C.), surface contamination may occur. 1
The films of Comparative Examples 2 and 4, which do not show good skin-packing suitability at 20 ° C., also show good skin-packing suitability at a low skin-packing temperature at which the relative melting point condition of the polyamide resin layer is satisfied.

[0078]

As described above, according to the present invention, a stretched layer of a polyamide resin having a melting point appropriately selected in relation to the skin pack molding temperature is included, and the heat shrinkage rate and the heat shrinkage stress as a whole are determined. Is appropriately controlled to provide a non-chlorine-based skin pack packaging film having good skin pack packaging suitability.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a skin pack packaging step.

FIG. 2 is an explanatory diagram of a skin pack packaging step.

FIG. 3 is an explanatory view of a skin pack packaging step.

FIG. 4 is an explanatory diagram of a skin pack packaging step.

FIG. 5 is a schematic sectional view of one embodiment of the film for packaging a skin pack of the present invention.

FIG. 6 is a schematic sectional view of another embodiment of the skin pack packaging film of the present invention.

FIG. 7 is a schematic cross-sectional view of another embodiment of the skin pack packaging film of the present invention.

FIG. 8 is a schematic sectional view of another embodiment of the film for packaging a skin pack of the present invention.

FIG. 9 is a schematic sectional view of another embodiment of the film for packaging a skin pack of the present invention.

[Explanation of symbols]

 1: base film (bottom material) 2: packaged object 3: skin film 4: mold (4a: recess, 4b: vacuum hole) 31: seal resin layer (a) 32: stretched polyamide resin layer (b) 33 : Functional intermediate layer (d) 34: outer surface layer (c) SP: seal portion

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takeo Higashi 18-13 Kamitamari, Tamari-mura, Niibari-gun, Ibaraki Pref. F-term in the Resin Processing Technology Center, Kureha Chemical Industry Co., Ltd. BB25A CA01 CA04 CA24 EC28 FB01 FB05 3E086 AD18 BA04 BA15 BB51 BB67 CA01 CA04 CA05 CA22 DA02 DA08 4F100 AK01B AK01C AK04E AK07E AK42C AK42J AK46A AK48A AK48J AK63B BABA BA03 BA07 BA03 BA00 BA03 BA07 BA00 JA04C JB16C JD02D JK20 JL01 JL12B YY00 YY00A YY00C 4F208 AA04J AA08 AA24 AA29 AG01 AG03 AH81 MA01 MB01 MB11 MB29 MC01 MG04 MG12

Claims (13)

[Claims] 1. A film for skin pack packaging including a step of drawing into a heated mold having a concave portion, wherein the resin layer is a sealable resin layer which is to constitute a surface opposite to the mold facing surface. ) And a stretched polyamide resin layer (b) made of a polyamide resin having a melting point higher than the film heating temperature by about 15 ° C. or more, and heat shrink at at least one direction at the film heating temperature. A skin pack packaging film having a stress of 200 g / 15 mm width or less and a heat shrinkage of 3% or more. 2. The heat shrinkage stress at a film heating temperature in each of a longitudinal direction and a lateral direction is 200 g /
The film for packaging a skin pack according to claim 1, wherein the film has a width of 15 mm or less and a heat shrinkage of 3% or more. 3. The film for packaging a skin pack according to claim 1, wherein the polyamide resin layer (b) is a surface layer to constitute a mold facing surface. 4. The film for packaging a skin pack according to claim 1, further comprising a surface layer (c) made of a thermoplastic resin having a melting point higher than the film heating temperature by about 5 ° C. or more to constitute the mold facing surface. . 5. The film for packaging a skin pack according to claim 4, wherein the surface layer (c) is made of a thermoplastic resin having a melting point of about 125 ° C. or higher. 6. The polyamide resin constituting the polyamide resin layer (a) has a melting point of about 140 ° C. or higher.
5. The film for packaging a skin pack according to any one of items 5 to 5. 7. The skin pack packaging film according to claim 1, further comprising an intermediate layer (d) made of a gas barrier resin. 8. The package for skin pack packaging according to claim 1, further comprising an intermediate layer (e) made of an adhesive resin obtained by modifying a polyethylene resin and / or a polypropylene resin with an acid or an acid anhydride. the film. 9. The skin pack packaging film according to claim 1, which is co-extruded. 10. The skin pack packaging film according to claim 1, which is biaxially stretched. 11. A resin layer (a) capable of at least sealing.
The skin pack packaging film according to any one of claims 1 to 8, wherein the film is laminated outside the die. 12. The skin pack packaging film according to claim 4, wherein at least the surface layer (c) is laminated outside a die. 13. The skin pack packaging film according to claim 1, which has at least three intermediate layers and has a symmetric structure.