JP2001240114A - Film for packaging food - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyolefin film which has high transparency, softness, restoring ability, and heat sealability, and is suitable for use in a manual packaging and moreover suitable for use in an automatic packaging such as a push-up type automatic packaging. SOLUTION: A core layer is formed from an elastic polymeric amorphous propylene homopolymer, and a layer made of a polyethylene resin, as a coating layer, is superposed on each side of the core layer, thereby forming a three layered construction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an article packaging film, and more particularly to a food packaging film having excellent transparency, flexibility, resilience, and heat sealability.

[0002]

2. Description of the Related Art A number of stretch films having excellent transparency, flexibility and heat sealability have been developed for packaging foods, especially for fresh foods such as meat, fresh fish, fruits and vegetables, and food packaging films (hereinafter referred to as "films"). (Referred to simply as film). Such a film packaging method includes manual packaging using a handler wrapper, or automatic packaging using a push-up type automatic packaging machine, a pillow type automatic packaging machine, or the like. Also, as the film, for example,
As disclosed in JP-A-6-256538, a three-layer structure in which a polypropylene resin specified by a cross separation method is used as a core layer, and an ethylene-vinyl acetate copolymer is laminated as a coating layer on both sides of the core layer Have been proposed.

[0003]

However, in the film proposed above, the mechanical strength of the film is extremely high because the average molecular weight of the polypropylene resin used for the core layer is large and the rubber elasticity is strong. For this reason, although there is an advantage that holes in the film caused by tearing of the film at the time of packaging and protrusions of the packaged object are eliminated, when the tray is packaged, the film at the bottom of the tray may peel off after packaging due to the effect of rubber elasticity. However, there was a problem in the sealing property. Furthermore, since the film is too soft, there is also a problem that the tension of the film after packaging is weak, the film remains slack, and the appearance is deteriorated. The present invention has been made in view of the above problems, transparency, flexibility, resilience,
An object of the present invention is to provide a polyolefin-based film which is excellent in heat sealing property and used in hand packaging, that is, excellent in hand packaging suitability.

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above problems, and as a result, have adopted an elastic high molecular weight amorphous propylene homopolymer as the core layer instead of the conventional polypropylene resin. The inventors have found that the above problem can be solved by forming a film having a layer made of a polyethylene resin on both sides of the core layer, thereby completing the present invention. That is, the film of the present invention has a core layer made of an elastic high molecular weight amorphous propylene homopolymer having specific properties shown in the following A) to D), and a layer made of a polyethylene resin as a coating layer on both sides of the core layer. Is characterized in that it is composed of three layers. A) Melting point: 145-165 ° C. B) The heat of fusion is 16.7-41.8 J / g. C) MFR at 230 ° C of 1 to 30 g / 10 minutes. D) The diethyl ether soluble fraction of the polymer is 35 to
50 wt%, and the intrinsic viscosity of the soluble fraction is 1.0 d.
1 / g or less, and the soluble fraction has no melting point above 40 ° C.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, an elastic high molecular weight amorphous propylene homopolymer used as a core layer is
A) melting point of 145 to 165 ° C, B) heat of fusion of 16.7 to
41.8 J / g, C) MFR at 230 ° C. of 1 to 3
0 g / 10 min, D) the diethyl ether soluble fraction of the polymer is 35-50 wt%, the intrinsic viscosity of the soluble fraction is 1.0 dl / g or less, and the soluble fraction is 4 wt.
It is a propylene homopolymer having the property of not having a melting point of 0 ° C. or higher.

[0006] The melting point and heat of fusion are determined by ASTM D-34.
It measures using a differential scanning calorimeter according to 81. The melting point is in the range of 145 to 165C. This melting point is 14
If the temperature is lower than 5 ° C., heat seal heat resistance cannot be obtained. Further, since the polymer is a propylene homopolymer, the melting point does not exceed 165 ° C. The heat of fusion is 1
It is in the range of 6.7-41.8 J / g. If the heat of fusion is less than 16.7 J / g, the rigidity of the propylene homopolymer will be lost, and the film after packaging will loosen. On the other hand, if it exceeds 41.8 J / g, crystals of propylene homopolymer are formed, and the transparency of the film is significantly impaired. MFR is ASTM D
230 ° C, load 21.18 according to -1238
It is measured by N (2.16 kgf). MFR is 1 to
The range is 30 g / 10 min, preferably 1 to 20 g / 10 min, more preferably 1 to 15 g / 10 min. This MF
When R is less than 1 g / 10 minutes, the melt viscosity at the time of melting is high, so that the flow of the molten resin tends to be non-uniform, and the thickness accuracy of the film cannot be obtained. On the other hand, if it exceeds 30 g / 10 minutes, the melt tension at the time of melting is reduced, so that the bubble stability particularly during inflation molding is impaired.

[0007] The diethyl ether soluble fraction and the intrinsic viscosity are described in Japanese Patent No. 2,845,412 and Japanese Patent No. 291.
It is measured by the method described in JP-A-2483. First, the measurement of the diethyl ether-soluble fraction is as follows. A 6 g sample of the polymer was placed in a cellulose thimble,
The thimble is placed in a vertical cylinder in a round bottom flask containing diethyl ether as a solvent. Attach a reflux condenser to the top of the round bottom flask and continue extraction with boiling diethyl ether for 16 hours. The extracted sample portion is the diethyl ether soluble fraction.

Next, the measurement of the intrinsic viscosity is as follows.
A 0.05 g sample was weighed with BHT (2,6-di-t-butyl-4).
-Methylphenol) in 100 ml of decahydronaphthalene containing 0.1 g / l, and the mixture was heated and stirred at 135 ° C. for 2 hours under a nitrogen stream, and the mixture was passed through a filter paper rod to obtain Cann.
Pour into an on-Ubbeloda viscometer, measure the extraction time at 135 ° C. and compare with the effluent time of the solvent alone. The intrinsic viscosity is
It is calculated by the following equation. (Intrinsic viscosity) = [ln (T /
T ₀ )] / C where T is the outflow time of the mixture, T ₀ is the outflow time of the solvent, and C is the sample concentration in g / dl.

The soluble fraction of diethyl ether is 35 to 5
It is within the range of 0 wt%. When the content of the diethyl ether-soluble fraction is less than 35% by weight, crystals of a propylene homopolymer are formed, so that the elasticity is increased and the film is hardened, and the sealing property of the film is reduced, and the transparency is significantly impaired. On the other hand, if it exceeds 50 wt%, the melting point does not reach 145 ° C., and heat sealing heat resistance cannot be obtained. The intrinsic viscosity of the diethyl ether-soluble fraction is 1.0 dl / g or less, and this value is 1.0 dl / g.
If it exceeds dl / g, the average molecular weight of the polymer of the soluble fraction becomes large, so that the dispersibility of the polymer of the soluble fraction in the propylene homopolymer is reduced and transparency is impaired. Furthermore, it is necessary that the soluble fraction does not have a melting point at 40 ° C. or higher. When the melting point exceeds 40 ° C., the polymer of the soluble fraction has crystallinity, and the propylene homopolymer It becomes difficult to eliminate crystallinity.

As described above, the elastic high molecular weight amorphous propylene homopolymer used in the present invention contains 35 to 50% by weight of a diethyl ether-soluble fraction, so that the characteristic of the propylene homopolymer alone is 145 to 165 ° C.
While maintaining the high melting point of, the propylene homopolymer alone and transparency, not having the flexibility and resilience suitable for use in the core layer of the polyolefin-based film, has both the film transverse direction described below. Tensile modulus and 50% tensile stress in the transverse direction of the film are in the desired range, and a film suitable for use in hand packaging is obtained.
The obtained film has good suitability for automatic packaging machines even when used in a push-up type automatic packaging machine.

By using the elastic high molecular weight amorphous propylene homopolymer alone for the core layer of the film of the present invention, it is possible to obtain a film suitable for use in hand-wrapping, and furthermore, use in a push-up type automatic packaging machine. However, for the purpose of adjusting the physical properties according to the usage of the film, hydrogenated petroleum resin, styrene-based thermoplastic elastomer, olefin-based thermoplastic elastomer, polyethylene-based resin, other than elastic high molecular weight amorphous propylene homopolymer A core layer can also be formed as a resin composition by mixing a polypropylene resin or the like. Surfactants such as monoglycerin fatty acid ester, polyglycerin fatty acid ester, sorbitan fatty acid ester, and polyoxyethylene alkyl ether can be added to the resin or resin composition forming the core layer. Specific examples of these include monoglycerin laurate, monoglycerin oleate, polyglycerin laurate, polyglycerin oleate, sorbitan laurate, sorbitan oleate, polyoxyethylene lauryl ether and the like. For the purpose of preventing thermal oxidation deterioration during molding, a phenolic antioxidant functioning as a radical scavenger or a phosphorus antioxidant functioning as a peroxide decomposing agent can be added.

In the present invention, examples of the polyethylene resin used as the coating layer include ethylene-vinyl acetate copolymer, linear low-density polyethylene, low-density polyethylene and the like. , An ethylene-vinyl acetate copolymer, and a linear low-density polyethylene are preferred. The ethylene-vinyl acetate copolymer has an MFR of 0.1 to 15 g / 10 min (at a temperature of 190 ° C. and a load of 21.1 minutes).
8N (2.16 kgf), vinyl acetate content 5-20
wt% range, preferably 10-15 wt%. If the vinyl acetate content is less than 5% by weight, no self-adhesiveness is obtained because no adhesiveness is exhibited. On the other hand, if it exceeds 20 wt%, the adhesiveness is too strong and the suitability for packaging is impaired. The glass transition temperature of this ethylene-vinyl acetate copolymer is -30.
C. to -50.degree. C., and excellent in flexibility. Further, the melting point is 100 ° C. or less, and the low-temperature heat sealability is excellent. As the linear low-density polyethylene, α
-Those having an olefin content of 10 to 30 wt% are preferred. If the content is less than 10 wt%, the melting point is 100%.
C., it cannot provide low-temperature heat sealability. Further, the glass transition temperature does not become lower than −30 ° C. On the other hand,
If it exceeds 30% by weight, the adhesiveness is too strong and the suitability for packaging is impaired.

For the purpose of imparting self-adhesiveness, slipperiness, antifogging property, etc., to the polyethylene resin forming the coating layer,
Monoglycerin fatty acid ester, acetylated monoglycerin fatty acid ester, polyglycerin fatty acid ester,
Surfactants such as sorbitan fatty acid esters and polyoxyethylene alkyl ethers can be added. Specific examples of these include monoglycerin laurate, monoglycerin oleate, monoglycerin monoacetomonolaurate, monoglycerin monoacetomonolaurate, monoglycerin diacetmonolaurate, monoglycerin diacetmonolaurate, polyglycerin laurate, polyglycerol Glycerin oleate, sorbitan laurate, sorbitan oleate, polyoxyethylene lauryl ether and the like can be mentioned. Further, similarly to the core layer, a phenolic antioxidant or a phosphorus-based antioxidant can be added.

The film of the present invention is produced by a method such as a multilayer inflation method or a multilayer T-die method. In particular, the multilayer inflation method is preferably employed. In this multilayer inflation method, specifically, using three extruders, a molten resin of each of the above resin compositions corresponding to the core layer and the coating layers on both sides thereof is passed through a three-layer inflation die to a predetermined layer. 180 to get the thickness
Co-extrude at ~ 220 ° C. Next, the molten resin film is blown up while being cooled by cooling air at 10 to 30 ° C. so that the blow-up ratio is in the range of 3 to 10. Thereafter, the film is folded by a pinch roll in a take-up machine, and wound up to a predetermined thickness and width by a take-up machine to produce a film. At this time, if the blow-up ratio is less than 3, the resin is undesirably oriented along the molding direction (vertical direction of the film). On the other hand, if the blow-up ratio exceeds 10, bubbles at the time of blow-up become unstable and film formation cannot be performed.

The thickness of the film of the present invention is not particularly limited as long as it can be applied as a film for wrapping articles, but is preferably in the range of 8 to 25 μm. Further, the thickness of the core layer is preferably in the range of 3 to 20 μm, and the thickness of the coating layer is preferably at least 1 μm. When the thickness of the core layer is less than 3 μm, the heat sealing heat resistance may be impaired. On the other hand, when the thickness of the core layer exceeds 20 μm, the polyethylene-based resin layer becomes thin and the low-temperature heat sealing property is impaired. May be

The film of the present invention having the above-mentioned structure has excellent properties, but has a 50% tensile stress in the transverse direction of the film (JIS K7) which is a measure of the flexibility of the film.
Compliant 113) is preferably in the range of 4.00~9.00N / mm ^2, in particular in the range of 4.50~8.50N / mm ² is more preferable. If this value is less than 4.00 N / mm ² , the film is too soft and the tension of the film after packaging is weak, and when the packaged products are stacked at the time of display, the film is loosened by the weight of the products. On the other hand, 9.00 N / mm ²
If it exceeds, the film becomes hard and hard to stretch, the film at the bottom of the tray is peeled off, and there is a problem in the sealing property. In addition, the tray may be broken at the time of packaging with an automatic push-up type packaging machine.

The tensile modulus in the transverse direction of the film (JIS K
7113) 30.00 to 80.00 N / mm
The range of ² is preferable, and especially 35.00 to 75.00 N /
The range of mm ² is more preferable. This value is 30.00N /
If it is less than ² mm, the elasticity of the rubber is weak and wrinkles remain on the film after packaging. On the other hand, if it exceeds 80.00 N / mm ² , the rubber elasticity is so strong that the film at the bottom of the tray peels off after packaging. The film of the present invention can provide a desired tensile stress and tensile elastic modulus by using an elastic high molecular weight amorphous propylene homopolymer for the core layer. Can be granted. Further, by using a polyethylene resin for the coating layer, a low-temperature heat sealing property can be imparted.

[0018]

EXAMPLES A three-layer film having a composition shown in Table 1 and comprising a core layer and coating layers on both sides thereof was produced by a multilayer inflation method. That is, using three extruders, the molten resin was co-extruded from a three-layer inflation die at 200 ° C. so that the thicknesses of the core layer and the coating layer become the values shown in Table 1 above. The resin film was blown up six times while being cooled by cooling air at 20 ° C. Then, it was folded with a pinch roll in a take-up machine, and wound up with a take-up machine to a thickness of 12 μm and a width of 35 cm. The details of the resin used in each layer are as follows.

[Core layer] Elastic high molecular weight amorphous propylene homopolymer; Type I: FPO-WL102: manufactured by Huntsman, trade name, melting point 155 ° C, heat of fusion 32.2 J / g, MFR5.
5 g / 10 min (230 ° C.), diethyl ether soluble fraction 42.8 wt%, intrinsic viscosity (diethyl ether soluble fraction) 0.93 dl / g Type II: FPO-WL107: manufactured by Huntsman, trade name, melting point 154 ° C. , Heat of fusion 25.5 J / g, MFR1
0.0 g / 10 min (230 ° C.), diethyl ether soluble fraction 44.0 wt%, intrinsic viscosity (diethyl ether soluble fraction) 0.82 dl / g Olefinic thermoplastic elastomer Adflex KS-081P: Montel SDK -Sunrise, trade name, melting point 162 ° C, MFR
0.8 g / 10 minutes (230 ° C), JP-A-6-25653
Resin elution amount measured by the cross-fractionation method described in JP-A No. 9; 44.8 wt% at 10 ° C, and 28.1 at 10 to 65 ° C.
wt%, 16.6 wt% at 65-90 ° C, 90-125
Propylene-ethylene copolymer Sumitomo Noblen S-131: manufactured by Sumitomo Chemical Co., Ltd., trade name, propylene-ethylene random copolymer, ethylene content 5 wt%, melting point 143 ° C, MFR 1.2 g / 10
Minute

[Coating layer] Ethylene-vinyl acetate copolymer; NUC-3758: manufactured by Nippon Unicar, trade name, vinyl acetate content 15 wt%, MFR 2.2 g / 10 min, glass transition temperature -32 ° C. AFFINITY EG8100: Dow Chemical Japan, trade name, ethylene-octene copolymer, octene content 24 wt%, MFR 1.0 g / 10 min, glass transition temperature -50 ° C

The physical properties of the obtained film were measured and evaluated by the following methods, and the results are shown in Table 2. [Transparency (Haze%)] Measured with one film according to JIS K7105. If this value is 2.0% or less, it is practically preferable.

[Tensile properties]-50% tensile stress; measured at a tensile speed of 200 m / min according to JIS K7113. -Tensile modulus: Measured at a tensile speed of 5 m / min according to JIS K7113.

[Resilience] An iron ball weighing 30 g (diameter of about 2 c) is placed on the stretched film.
m), which was pressed in 2 cm and removed, and then the film was evaluated as “Δ” (good) when the dents and wrinkles were restored within 10 seconds, and were evaluated as “x” (poor) when it was not restored.

[Heat sealability] Low temperature heat sealability; PSP with 200 g weight
(Polystyrene paper) Tray SK-20 [product name, manufactured by Chuo Chemical Co., Ltd.] was hand-wrapped using a hand wrapper, and left on a hot plate having a surface temperature of 100 ° C. for 2 seconds to check the situation. . "〇" indicates that the film was fused and heat-sealed at the part where multiple films were stacked.
(Good), and the case where heat sealing was not performed was evaluated as “x” (poor). Heat seal heat resistance: Packaging was carried out in the same manner as above, and the condition was confirmed by leaving the product on a hot plate having a surface temperature of 145 ° C. for 2 seconds. In a portion where a plurality of films overlap, the film is fused and heat-sealed. In a case where no hole is generated in one film portion, “と し” (good) indicates that a hole is generated. The case was evaluated as "x" (poor).

[Packing suitability] Hand wrapping suitability; 200g using hand wrapper
The SK-20 (supplied) tray containing the weight of No. was packed in 50 packs and the packing condition was checked. a. Wrinkles and looseness: The case where the occurrence of wrinkles and looseness was 2 packs or less was evaluated as “Δ”, and the case of 3 packs or more was evaluated as “x”. b. Sealing property: Peeling of bottom seal and generation of holes
The case of less than a pack was evaluated as “Δ”, and the case of three or more packs was evaluated as “×”. c. Torn; "〇" when the occurrence of torn is 2 packs or less
The case of three or more packs was evaluated as “×”. . Suitable for automatic packaging machine; push-up type automatic packaging machine Wmini
Using Mark II (trade name, manufactured by Ishida), 20
SK-20 (supra) tray with 0g weight is 100
The package was packed and the packaging condition was checked. a. Bottom state: The case where the package in which the film did not reach the bottom of the tray was 2 packs or less was evaluated as “〇”, and the case where 3 packs or more was evaluated as “x”. b. Tray cracking: The case where the occurrence of tray cracking was 0 pack was evaluated as “Δ”, and the case of 1 pack or more was evaluated as “X”. c. Wrinkles and looseness: The case where the occurrence of wrinkles and looseness was 2 packs or less was evaluated as “Δ”, and the case of 3 packs or more was evaluated as “x”. d. Sealing property: Peeling of bottom seal and generation of holes
The case of less than a pack was evaluated as “Δ”, and the case of three or more packs was evaluated as “×”. e. Torn; "〇" when the occurrence of torn is 2 packs or less
The case of three or more packs was evaluated as “×”.

[Evaluation Results] As is clear from the results shown in Table 2, the films of the examples all exhibited excellent properties, whereas the films of the comparative examples were inferior in any of the properties. And inferior to the film of the present invention.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

According to the film of the present invention, transparency, flexibility, resilience and heat sealability are excellent, and particularly, tensile stress,
With a tensile modulus in a specific range suitable for practical use, it is a film suitable for use in hand wrapping, and also has an automatic wrapping machine suitability suitable for use in a push-up type automatic wrapping machine. ing.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3E086 AB01 AD13 AD17 BA04 BA15 BA33 BB21 BB51 BB66 CA01 4F100 AK04B AK04C AK06 AK07A AK64 AK68 AL09 BA03 BA10B BA10C BA16 EH20 GB23 JA04A JA06A JA07A J11AJK12 J07AJL01

Claims (1)

[Claims] 1. A three-layer structure in which an elastic high molecular weight amorphous propylene homopolymer having the following properties A) to D) is used as a core layer, and a layer made of a polyethylene resin is laminated on both sides of the core layer as a coating layer. A food packaging film comprising: A) Melting point: 145-165 ° C. B) The heat of fusion is 16.7-41.8 J / g. C) MFR at 230 ° C of 1 to 30 g / 10 minutes. D) The diethyl ether soluble fraction of the polymer is 35 to
50 wt%, and the intrinsic viscosity of the soluble fraction is 1.0 d.
1 / g or less, and the soluble fraction has no melting point above 40 ° C.