JP3144035B2 - Packaging film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a packaging film used for food packaging and the like. More specifically, the present invention relates to a stretched laminated film suitable for a packaging film having excellent cuttability, transparency, heat resistance, adhesiveness, gas barrier properties, non-heat shrinkage, and food safety.

[0002]

2. Description of the Related Art Conventionally, as a wrapping film used for food packaging, a film mainly composed of polyvinylidene chloride, polyethylene or polyvinyl chloride is known. These wrap films are often used to heat foods and the like in microwave ovens, so they have good adhesiveness, but they do not shrink, melt, discolor, etc. at high temperatures, that is, heat resistance Is required to be excellent.

[0003]

However, polyvinylidene chloride-based films have a disadvantage that shrinkage upon heating is large, and polyethylene-based films come in contact with oily substances (for example, meat and tempura) and have high heat. In such a case, there is a disadvantage that the film is melted, and further, the polyvinyl chloride-based film has a problem of causing a whitening phenomenon when it comes into contact with boiling hot water.

[0004] On the other hand, polyester resins such as polyethylene terephthalate resin (hereinafter referred to as PET) are known as resins having heat resistance as packaging films. PET has excellent heat resistance and mechanical strength, but it is difficult to impart tackiness, and thus it is difficult to apply a single-layer film to a wrap film.
Further, such a wrapping film has the following problems in cutability (easiness of cutting). That is, the wrapping film is usually stored in a case such as a paper tube,
The film is pulled against a cutting blade called a “saw blade” attached to the case and cut into an appropriate length.

[0005] As a "saw blade" used for cutting a film, a simple blade which is generally obtained by punching an iron plate having a thickness of about 0.2 mm into a saw shape is used. For cases that support
A coated cardboard paper box of about 0 g / m ² is used, and the rigidity is extremely low. This kind of film is required to be easily cut according to the user's will even with such a simple cutting mechanism, but in reality, the case and the "saw blade" are only deformed. Instead, the film may be deformed, or cutting may occur at a position outside the “saw blade”. Specifically, the conventional polyvinylidene chloride-based film, when a tear is formed in a part of the film at the time of cutting, the tear spreads,
There is a tendency to cut diagonally without being cut along the "saw blade". Further, the conventional polyethylene-based film requires a considerable tensile force at the time of cutting, so that not only the case is bent but also the film may be deformed.

In recent years, from the viewpoint of the environment and the like, a packaging film that does not generate chlorine or the like during use or incineration has been required. The present inventors have proposed a packaging film in which the inner and outer layers are made of a polypropylene-based resin composition, and the intermediate layer is made of an aliphatic polyamide resin, as a packaging film having good cut properties and the like and no generation of chlorine. (Japanese Patent Application Nos. 2-321605 and 3-13550,
Nos. 3-15547 and 3-283346).

[0007]

Means for Solving the Problems As a result of further intensive studies, the present inventors have used a polyester resin such as PET as the intermediate layer, and have a polypropylene resin composition having a specific composition on both sides thereof. The above problems are solved by stretching the unstretched laminated film in which the layers are laminated, and the cut property, the transparency, the heat resistance, and the like, without impairing the original properties (heat resistance and mechanical strength) of the polyester resin. The present inventors have found that a packaging film excellent in adhesiveness, gas barrier property, non-heat shrinkage property and food safety, particularly excellent in heat resistance and cutability, and furthermore from the viewpoint of environmental problems can be obtained.

That is, the gist of the present invention is to provide at least three layers of an outer layer, an intermediate layer and an inner layer, wherein the outer layer and the inner layer are (A) 100 parts by weight of a polypropylene resin, and (B) 2 to 30 parts by weight of polybutene or polyisobutylene. And (C) 0.2 to 5 parts by weight of a polyglycerin fatty acid ester, wherein the intermediate layer is obtained by stretching a laminated film of (D) a polyester resin. (A) the outer layer and the inner layer have a shear peel strength of 0.4
180 ° peel strength of 4 g / 50 mm or less at kg / cm ² or more,
(B) tensile elongation at break in the direction parallel to the take-off direction is 20
0% or less, and (c) the ratio of the tensile elongation at break (parallel / perpendicular) in the direction parallel to the take-off direction and the direction perpendicular to the take-off direction is 3 or less,
The present invention resides in a packaging film, wherein the thickness of the entire film is 40 μm or less, and the thickness of the intermediate layer is in the range of 10 to 90% of the total thickness of the film.

Hereinafter, the present invention will be described specifically. The packaging film of the present invention is composed of at least three layers: an outer layer, an intermediate layer, and an inner layer. The outer layer and the inner layer of the film are (A) 100 parts by weight of a polypropylene resin,
(B) 2 to 30 parts by weight of polybutene or polyisobutylene and (C) 0.2 to 5 polyglycerol fatty acid ester
It is formed from a polypropylene resin composition consisting of parts by weight. The intermediate layer is formed from (D) a polyester resin.

The above-mentioned polypropylene resin composition (A)
The components of the polypropylene resin are (B) and (C)
It is incorporated in a larger amount than the components and is used as a base material of the composition. The polypropylene resin that can be used here may be a propylene homopolymer or a copolymer of propylene with a small amount of another copolymer component (eg, ethylene, butene, etc.). Examples of the propylene homopolymer include isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene. Of these, isotactic polypropylene is preferable. Furthermore, the copolymer of propylene and other copolymer components such as ethylene may be any of a random copolymer and a block copolymer,
Propylene-ethylene random copolymers having an ethylene content of 1 to 5% by weight are preferred. The physical properties of the polypropylene resin as the component (A) may be appropriately selected according to various applications and conditions, and usually, the melt flow rate (M
FR) 0.5 to 20 g / 10 min (measured at 230 ° C. under a load of 2.16 kg according to JIS K 6758)
With a density of 0.89 to 0.91 g / cm ³ , especially MFR
Those having a density of 3 to 15 g / 10 min and a density of 0.893 to 0.905 are preferred.

The above-mentioned polypropylene resin component (B)
The component polybutene or polyisobutylene acts as a thickener and imparts excellent tackiness to the film. The physical properties of polybutene or polyisobutylene used here are
There is no particular limitation as it can be appropriately determined according to the amount of the composition, the type of the other components, the intended use of the composition, and the like.
Usually, the number average molecular weight is 200 to 3000, particularly 400 to
2000 and a viscosity of 300-50,000 cps, especially 5
Those having a range of 00 to 15000 cps are preferable. The amount of the polybutene or polyisobutylene is 2 to 3 parts per 100 parts by weight of the polypropylene resin as the component (A).
0 parts by weight, preferably 5 to 20 parts by weight. If the amount is less than 2 parts by weight, sufficient tackiness will not be exhibited.
If the amount exceeds 0 parts by weight, stickiness due to a large amount of bleeding occurs, and heat resistance is undesirably reduced.

The above-mentioned polypropylene resin composition (C)
The polyglycerin fatty acid ester as the component increases the adhesiveness of the film by being used in combination with the polybutene or polyisobutylene as the component (B). The polyglycerin fatty acid ester is a compound in which at least one of the hydroxyl groups of the condensation polymer of glycerin is esterified with a higher fatty acid having 8 to 22 carbon atoms. The glycerin condensation polymer has a degree of polymerization of usually 2 to 10, preferably 2
To 6, particularly preferably 2 to 3, condensation polymers. Among the hydroxyl groups of the glycerin condensation polymer, the number of esterified hydroxyl groups is one or more, preferably one or more and 70% or less of the number of hydroxyl groups, more preferably one or more and 60% of the number of hydroxyl groups. It is as follows. Higher fatty acids have 8 or more carbon atoms
As long as it is 22 fatty acids, it may be saturated or unsaturated, and is preferably a fatty acid having 10 to 18 carbon atoms. Examples of the polyglycerin fatty acid ester include diglycerin monolaurate, diglycerin monopalmitate,
Examples thereof include diglycerin monooleate, diglycerin monostearate, diglycerindiolate, and triglycerin monooleate. Preferably, diglycerin monooleate and diglycerin monolaurate are used.

These polyglycerin fatty acid esters may of course be used in combination of two or more. The amount of the polyglycerin fatty acid ester is 0.2 to 5, preferably 0.5 to 3 parts by weight per 100 parts by weight of the polypropylene resin as the component (A). If the amount is less than 0.2 parts by weight, the synergistic effect with the component (B) polybutene or polyisobutylene does not occur. Conversely, if the amount exceeds 5 parts by weight, stickiness or odor due to a large amount of bleeding occurs, It is not preferable because the gel frequently occurs.

On the other hand, the polyester resin constituting the intermediate layer of the packaging film of the present invention is a thermoplastic polyester resin obtained by polycondensation of a dibasic acid and a dihydric alcohol. For example, a saturated polyester formed from terephthalic acid or a derivative thereof and ethylene glycol is preferable. As the terephthalic acid derivative among the main acid components of the present resin, a lower alkyl ester of terephthalic acid is preferable, and an alkyl ester of terephthalic acid having 1 to 4 carbon atoms, particularly, dimethyl terephthalate is preferable.

In the present invention, a part of the main acid component,
Usually, 2 to 20% of other acid components such as dicarboxylic acid or oxycarboxylic acid other than terephthalic acid, specifically,
It may be replaced with isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, para-hydroxyethoxybenzoic acid, adipic acid, sebacic acid or the like or a lower alkyl ester thereof.

The main glycol component of the polyester resin of the present invention is ethylene glycol, and a part, usually 2 to 20%, of other glycol components such as trimethylene glycol, tetramethylene glycol, hexamethylene glycol, Pentyl glycol,
It may be replaced with 1,4-cyclohexanedimethanol or the like.

In any case, the polyester resin referred to in the present invention refers to a polyester whose main constituent component, for example, 80 mol% or more is an ethylene terephthalate unit.
In particular, the polyester resin of the present invention comprises 50 mol% of terephthalic acid and 50 mol% of ethylene glycol, and has a molecular weight of 10,000 to 30,000, preferably 17
2,000 to 22,000 polyethylene terephthalate (P
ET) is preferable because it exhibits good heat resistance without impairing the transparency and moldability required for the packaging film.

The intrinsic viscosity [η] of the present invention is from 0.4 to 1.0, preferably from 0.1 to 1.0, from the viewpoint of film formability.
5 or more and 0.8 or less are appropriate. The packaging film of the present invention is obtained by first forming an unstretched laminated film in which an outer layer and an inner layer are made of the above-mentioned polypropylene resin composition and the intermediate layer is made of the above-mentioned polyester resin by an arbitrary laminating method. Is formed by stretching.

The method for producing an unstretched laminated film (lamination method) includes thermal adhesion, extrusion or dry lamination,
Coextrusion and the like can be mentioned, and particularly preferred is molding by coextrusion. As the co-extrusion molding, a T-die molding method, an air-cooled or water-cooled inflation molding method is adopted, and among these, a T-die molding method or a water-cooled inflation molding method is preferable. That is, by quenching the melt-extruded resin by the above-mentioned molding method, a film having more excellent transparency can be obtained.

At this time, the thickness of the outer layer and the inner layer is usually 1
The thickness of the intermediate layer is usually from 5 to 200 μm, preferably from 20 to 100 μm.
The unstretched laminated film is formed to have a μ, preferably 10 to 50 μ. Further, when an adhesive layer is provided between the intermediate layer, the outer layer, and the inner layer, the thickness is usually 2 to 2.
It is good to choose 40μ, preferably 4-20μ.

The unstretched multilayer film obtained by the above-mentioned coextrusion molding is then subjected to film longitudinal (parallel to film take-off) and transverse (vertical to film take-up) directions. Stretch in at least one direction. The stretching ratio is usually 2 to 6 for each direction.
The film is stretched uniaxially or biaxially by a factor of, preferably 3 to 5 times. In the case of uniaxial stretching, 1
It is preferable to use an axially stretched film. If the stretching ratio is less than 2 times, the cutability of the film will be reduced, and if it is more than 6 times, the stretchability will be reduced and the film will break or the film will be unevenly stretched. The stretching treatment is performed by heating the unstretched film as it is or by slitting the unstretched film to a predetermined width, for example, by changing the circumferential speed of a stretching roll to stretch the film in the take-off direction, that is, in the longitudinal direction, and then tenter stretching method. And a method of stretching in the transverse direction. The preheating temperature in the stretching treatment is generally not more than about 10 ° C. lower than the melting point of the polypropylene resin, preferably in the range of 70 to 140 ° C.

The heat setting temperature after stretching is preferably higher than the preheating temperature, and is preferably as high as possible in order to prevent wrinkling of the film and shrinkage at a high temperature. About 10 from the melting point of
It is preferable to carry out the reaction at a temperature lower by lower than 0 ° C, preferably in the range of 80 to 150 ° C. When the preheating and heat setting temperature is higher than a temperature about 10 ° C. lower than the melting point of the polypropylene resin, the film is melt-adhered to the stretching roll, and when the preheating temperature is lower than 70 ° C., the PET is insufficiently preheated. It is preferable that the stretching be performed in the above range since stretching becomes difficult and the film is likely to break.

The thickness of the packaging film of the present invention is 4
0 μm or less, preferably 2 to 30 μm, more preferably 5 to 20 μm, and the thickness of the intermediate layer is 10 to 90%, preferably 1 to 90% of the thickness of the entire film.
The range is 5 to 40%. The thickness of the film is 40 μm
If it is larger, the tear strength at the time of cutting the film becomes too large, which is not suitable for the use of a wrap film.

If the thickness of the intermediate layer is less than 10% of the total thickness, the original heat resistance, mechanical strength, etc. of PET cannot be maintained. The thickness of the intermediate layer is preferably at least 15% of the total thickness. On the other hand, if it is larger than 90%, the thickness of the polypropylene layer becomes small, and it becomes difficult to uniformly cover the intermediate layer by co-extrusion. It is also disadvantageous in terms of cost. The thickness of the intermediate layer is preferably 80% or less of the total thickness.

The layer structure of the stretched laminated film of the present invention consists essentially of at least three resin layers of an outer layer / intermediate layer / inner layer, but other layers may be used without departing from the gist of the present invention. It is possible to add four resin layers to form a structure having four or more layers. Such a structure having four or more layers includes, for example, a structure having an adhesive layer or the like between an outer layer and an intermediate layer, or an inner layer and an intermediate layer, or a structure further provided with a resin layer outside the outer layer or inside the inner layer. Is mentioned.

Further, by adding an appropriate adhesive component to each layer, it is possible to prevent peeling between the layers without providing an adhesive layer and keeping the three-layer structure. In particular, in the present invention, a three-layer, five-layer structure in which an adhesive layer made of a modified polyolefin resin is provided between the outer layer and the intermediate layer and the inner layer and the intermediate layer impairs the transparency and moldability of the packaging film. It is suitable without any. Examples of the modified polyolefin resin include those obtained by adding a polar group such as an unsaturated carboxylic acid such as maleic anhydride or a derivative thereof to a polyolefin resin such as polyethylene or polypropylene by graft modification. As the resin to be grafted, the same polypropylene resin as that used for the inner and outer layers is preferable in terms of adhesiveness and the like.

From the viewpoint of adhesion to the polyester resin of the intermediate layer, the amount of grafting of unsaturated carboxylic acid and the like, particularly, a modified monomer of maleic anhydride is 0.01 to 0.01% based on the weight of the base resin to be grafted. A range of from 10 to 10% by weight is preferred. More preferably, it is 0.01 to 3% by weight. Such adhesive layers are preferably provided so as to be in the range of 2 to 20%, preferably 3 to 10%, respectively, of the entire thickness of the packaging film of the present invention.

The packaging film of the present invention thus obtained has an outer layer and an inner layer having a shear peel strength of 0.4 kg / cm ² or more, preferably 0.5 to ^2.5 kg / cm ² , and 180 °
Peel strength is 4 g / 50 mm or less, preferably 1-3 g /
It has a value in the range of 50 mm. The tensile elongation at break in the direction parallel to the take-off direction is 200% or less, preferably 5%.
At 0 to 150%, the ratio of the tensile elongation at break (parallel / perpendicular) in the direction parallel to the take-off direction and the direction perpendicular to the take-up direction has a value of 3 or less, preferably in the range of 0.1 to 2.

The above values are values obtained by measuring according to the measurement method described later, and the shear peel strength and the 180 ° peel strength indicate the degree of tackiness of the packaging film of the present invention. The ratio between the breaking elongation and the tensile breaking elongation indicates the degree of cutability.

[0030]

EXAMPLES Hereinafter, specific embodiments of the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples unless it exceeds the gist thereof.
The measurement in the examples was performed by the following method.

(1) Transparency (haze value) Measured with a haze meter according to JIS K6714. The measurement results are expressed in%.

(2) Heat Resistance Temperature Paper is placed on the top and bottom 25 mm of a strip-shaped film sample piece having a width of 30 mm and a length of 14 cm, and a weight of 10 g is lowered. The maximum ambient temperature that could not be cut in one hour was measured at 10 ° C intervals. (Refer to the description of Tokyo Metropolitan Ordinance No. 1072, “Quality Display of Wrap Film”).

(3) Thermal Shrinkage Rate The film was formed into a sample having a diameter of 10 mm by a punching jig.
Soak it in an aluminum pan containing silicone oil,
This aluminum pan is placed on a hot plate at 140 ° C.
Although the temperature of the hot plate temporarily drops because heat is taken by the aluminum pan, a sample is taken out 45 seconds after the temperature reaches 140 ° C., and the size change is measured. The measurement results are expressed in%.

(4) Cutability The film was wound around a core tube, housed in a wrap film case, subjected to a cutting test with a saw blade, and evaluated on a four-point scale (good, normal, slightly poor, poor). As a standard for evaluation, the cut level of a commercially available wrap film was evaluated as normal.

(5) Adhesive Strength Lightly superimpose two films, and apply 25 on the film.
mmφ, linear pressure 0.3kg / c with roll of 150mm width
m, three times, and the force required for shearing and peeling the two films within 5 minutes and for peeling in the direction of 180 ° C. were measured under the conditions shown in Table 1 using an Instron type tensile tester.

[0036]

[Table 1]

(6) Method of measuring tensile elongation at break and its ratio Tensile elongation at break was measured in both the vertical and horizontal directions, that is, in the direction parallel to the take-up direction and in the direction perpendicular to the take-up direction, in accordance with JIS C 2318. The ratio between the parallel direction and the vertical direction was determined from these values.

Examples 1-4, Comparative Examples 1-8 As the polypropylene resin (A), propylene was used.
Ethylene random copolymer (MFR = 9.0, density 0.
896 ethylene content 2.5%; trade name, Mitsubishi Polypro 6500J, manufactured by Mitsubishi Kasei Corporation, and polybutene (average molecular weight: 580, viscosity: 2000 cps at 25) as a component (B).
° C: Nissan Polybutene 0 manufactured by NOF Corporation
15SH) was mixed with a blender using diglycerin monooleate (manufactured by Riken Vitamin Co., Ltd.) as the component (C), with the blending amounts of the components shown in Table 2. Then, it pelletized on the extrusion conditions of 220 degreeC using the twin screw extruder of 30 mm in diameter, and manufactured the polypropylene-type resin composition.

Next, the above-mentioned polypropylene-based resin composition was extruded into an extruder No. 50 mm in diameter using a 450 mm wide three-layer five-layer coextrusion T-die molding machine. And a polyethylene terephthalate resin having a molecular weight of 20,000, intrinsic viscosity [η] = 0.60 dl / g, manufactured by Mitsubishi Kasei Co., Ltd. as an extruder N having a diameter of 40 mm.
o. 2, and an adhesive polyolefin resin (adhesive polyolefin resin, manufactured by Mitsubishi Kasei Corporation, Novatec-AP006T) having a diameter of 40 mm.
o. 3 was put. This was simultaneously extruded at a die temperature of 280 ° C., formed into a film under the conditions of a chill roll temperature of 30 ° C. and a take-up speed of 20 m / min, and formed into an outer layer (polypropylene resin composition).
/ Adhesive layer (adhesive resin) / Intermediate layer (PET) / Adhesive layer (adhesive resin) / Inner layer (polypropylene resin composition)
170 μm thick three-layer five-layer film was obtained. Table 2 shows the layer ratio of each layer.

Next, the film was longitudinally stretched in a roll at a preheating temperature of 90 ° C. and a heat setting temperature of 120 ° C. at a magnification shown in Table 2.
Tenter transverse stretching was performed to obtain a stretched multilayer film having a film thickness of 10 μm. The transparency, heat resistance temperature, heat shrinkage, cutability and adhesive strength of the obtained film were measured. Table 3 shows the results.

In Comparative Example 2, streaks occurred due to excessive addition of the component (C) to the raw film, and a good film was not obtained. In Comparative Example 5, breakage occurred during stretching, and sampling was impossible. , The film physical properties could not be evaluated. Further, the cutting properties of Comparative Examples 6 and 8 were slightly poor because the film was slightly stretched and it was difficult to cut.

[0042]

[Effects of the Invention] The packaging film of the present invention can be cut easily.
It is excellent in transparency, heat resistance, adhesiveness, gas barrier properties and non-heat shrinkage, and also excellent in food safety. Therefore, the present packaging film is particularly suitable as a wrap film for food packaging and the like. Furthermore, the present packaging film has no problem of chlorine generation and is suitable from an environmental point of view.

[0043]

[Table 2]

[0044]

[Table 3]

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI B29K 23:00 67:00 B29L 9:00 (56) References JP-A-3-175030 (JP, A) JP-A-4- JP-A-5-177789 (JP, A) JP-A-4-249150 (JP, A) JP-A-4-249131 (JP, A) JP-A-54-36359 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B32B 1/00-35/00

Claims (6)

(57) [Claims] At least three of an outer layer, an intermediate layer and an inner layer
And (B) 2 to 30 parts by weight of polybutene or polyisobutylene, and (C) 0.2 to 5 parts by weight of polyglycerin fatty acid ester. The intermediate layer is a stretched film obtained by stretching a laminated film comprising (D) a polyester resin, wherein the (a) outer layer and the inner layer have a shear peel strength of 0.4.
180 ° peel strength of 4 g / 50 mm or less at kg / cm ² or more,
(B) tensile elongation at break in the direction parallel to the take-off direction is 20
0% or less, and (c) the ratio of the tensile elongation at break (parallel / perpendicular) in the direction parallel to the take-off direction and the direction perpendicular to the take-off direction is 3 or less,
A packaging film, wherein the thickness of the entire film is 40 μm or less, and the thickness of the intermediate layer is in the range of 10 to 90% of the total thickness of the film. 2. The packaging film according to claim 1, wherein an adhesive layer is provided between the intermediate layer and the outer and inner layers. 3. The packaging film according to claim 2, wherein the adhesive layer is made of a modified polyolefin resin. 4. The packaging film according to claim 1, wherein a coextrusion method is used as a method for producing the unstretched laminated film. 5. The packaging film according to claim 1, which is obtained by biaxially stretching an unstretched laminated film in a machine direction and a transverse direction of the film. 6. The film obtained by uniaxially stretching an unstretched laminated film in the machine direction of the film.
The packaging film of the above.