JPH0662728A - Freshness retaining film - Google Patents

Abstract

PURPOSE:To obtain a freshness retaining film, having a high PR value which is a ratio of the carbon dioxide permeability to the oxygen permeability and hardly causing the blocking by constructing the interlayer and both the inner and outer surface layers from respective specific mixtures. CONSTITUTION:The freshness retaining film is composed of a three- or more multilayered film. The interlayer is constructed from a mixture of an ethylene- vinyl acetate copolymer or ethylene-ethyl acrylate copolymer with a polyamide. Both the inner and outer surface layers are formed from any of low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer with <=8wt.% vinyl acetate content, polypropylene, polystyrene and polybutadiene or a mixture thereof. The thickness ratio is preferably within the range of (1/1) to (5/1) of the interlayer/sum total of layers other than the interlayer. The PR is >=5 based on the whole film according to characteristics of the interlayer. Thereby, the hermetically sealing packaging film capable of optimizing the O2 and CO2 concentrations and retaining the freshness can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a freshness-keeping film for fruits and vegetables and flowers (hereinafter sometimes referred to as fruits and vegetables). More specifically, the present invention relates to a hermetic packaging film for packaging fruits and vegetables, flowers, etc. in a packaging bag and optimizing the O ₂ and CO ₂ concentrations in the atmosphere to maintain freshness.

[0002]

2. Description of the Related Art In recent years, consumers' needs for freshness of fruits and vegetables and flowers are high, and how to keep the freshness after harvesting is very important together with the cultivation technique of fruits and vegetables. In order to meet such demands, development of a packaging film focused on keeping freshness is under way, and for example, a method of removing ethylene which causes aging of plants (Japanese Patent Laid-Open No. 63-
309137, JP-A-63-110186), a method of activating cells by generating far infrared rays (JP-A-62-2).
10973) and humidity control in the bag (Japanese Patent Laid-Open No. 58-1936).
78), a method based on an antifogging effect (Japanese Patent Laid-Open No. 62-1104
9), a method based on an antibacterial effect (Japanese Patent Laid-Open No. 61-14823)
Various measures such as 6) have been proposed. However, an effective freshness-keeping method for a wide variety of fruits and vegetables has not been found. In other words, although a freshness-retaining effect can be seen in each individual special case, it is very difficult to obtain the same effect with other fruits and vegetables.

Generally, the cause of deterioration in freshness of fruits and vegetables is temperature,
Oxygen, carbon dioxide gas concentration, ethylene concentration, humidity,
Light, bacteria, etc. It is known that the respiration rate of fruits and vegetables and the ethylene production rate are reduced by lowering the most influential temperature within the range where low temperature damage does not occur. Furthermore, regarding the concentrations of oxygen and carbon dioxide, which are the next most important factors, the gas condition most effective for maintaining the freshness of individual fruits and vegetables has been proposed as the CA storage condition. However, the facility of the CA storage for mechanically creating the CA storage condition is very expensive, and thus the penetration rate is low. Therefore, the development of a film that can easily create CA storage conditions by wrapping with a plastic film to balance the breathability of fruits and vegetables and the gas permeability of the film has been promoted (Japanese Patent Laid-Open Nos. 61-216640 and 61-61640).
-227732, 63-102634). However, since it is impossible to create various CA storage gas conditions with a single film, it occurs that certain fruits and vegetables have a freshness-retaining effect but no effect on other fruits and vegetables.

Further, a freshness-keeping container for controlling the gas permeation amount according to the respiration amount of fruits and vegetables has been reported (JP-A-63-152638, JP-A-1-30962).
1) However, in this method, control is performed according to the area and type of the film used for the gas permeable panel in the gas impermeable container, so it is applied to corrugated cardboard boxes, styrofoam boxes, etc. currently used for distribution. There is a problem that you can not.

[0005]

There is a report by the present inventors regarding a method of designing a film in which the bag has CA storage conditions only by hermetically packaging based on the CA storage conditions and respiration rate of fruits and vegetables ( Mitsubishi Kasei R & D Review Vol
5, No2 (1991), P84~P90 ), the optimum film fruits or vegetables CA storage condition is O ₂ ≦ 6 vol% and CO ₂ ≦ 4 vol%, the carbon dioxide permeability to oxygen permeability (Po ₂₎ (Pco ₂ ) Ratio PR is 6 ≦ PR ≦ 1
Must have a large value of 2 and must meet this characteristic value,
And there is currently no practical packaging film.

[0006]

The object of the present invention is to provide PR
The value of (= Pco ₂ / Po ₂ ) is as large as 5.0 or more, the film blocking is small, and the vegetables are practical.
An object of the present invention is to provide a freshness-keeping film for packaging fruits and vegetables, cut flowers, flowers such as potted plants, plants such as mushrooms and sealing them with a heat seal, a rubber band, a string, etc.

The gist of the present invention consists of a multilayer film of three or more layers, the intermediate layer of which is (a) ethylene-vinyl acetate copolymer (EVA) or ethylene-ethyl acrylate copolymer (EEA) and (b). It is made of a mixture with polyamide, and the inner and outer surface layers are made of low density polyethylene (LDP).
E), linear low density polyethylene (LLDPE), any one of ethylene-vinyl acetate copolymer (EVA) having a vinyl acetate content of 8% by weight or less, polypropylene (PP), polystyrene (PS), polybutadiene (PBD) , Or a mixture thereof, in the freshness-preserving film.

The multi-layer film used in the present invention is 3
Layers having the above constitution, comprising an intermediate layer made of an ethylene-vinyl acetate copolymer (EVA) or an ethylene-ethyl acrylate copolymer (EEA) or a mixed resin composition of a mixture of these and a polyamide and another resin. It has an inner surface layer, an outer surface layer, and optionally an adhesive layer for adhering them. The thickness ratio is preferably in the range of intermediate layer / sum of layers other than intermediate layer = 1/1 to 5/1, and PR of the film as a whole is 5 or more depending on the characteristics of the intermediate layer. The EVA used in the intermediate layer preferably has a vinyl acetate content (VA) of 8 to 40% by weight, and the EEA preferably has an ethyl acrylate content (EA) of 8 to 40% by weight. When the layer used as the intermediate layer is EVA or EEA single layer, the PR becomes high, but at the same time, the O ₂ and CO ₂ transmittances also increase.

In a multilayer film, a layer having a large gas permeability has a small effect on the overall gas permeability. Therefore, when EVA or EEA alone is used as the intermediate layer of the multilayer film, the effect of the intermediate layer on the PR of the entire multilayer film. Power is O ₂ , C
It becomes small because the O ₂ transmittance is large. So P in the middle layer
Polyamide is added to EVA or EEA in order to reduce the O ₂ and CO ₂ permeabilities and increase the influence on PR without lowering R. At this time, polyethylene (preferably low-density polyethylene) may be further added to EVA or EEA at a weight ratio of (EVA / polyethylene) of 1/0 to 1/4, preferably 1/0 to 1/1. good. The mixing ratio of the polyamide is preferably 2 to 30% by weight based on the total weight of the intermediate layer. If it is 2% by weight or less, the barrier property is not so much increased by the addition of polyamide, and if 30% by weight or more of polyamide is added, the dispersibility in EVA or EEA is poor and it becomes opaque. EE to keep transparency
A can be replaced by low density polyethylene or linear low density polyethylene in a proportion of 50% by weight or less. This low-density polyethylene or linear low-density polyethylene preferably has a density of 0.94 g / cm ³ or less and a melt index of 0.5 to 3.0 g / 10 min (190 ° C). , And copolymers with other α-olefins can also be used. Further, by adding an unsaturated carboxylic acid-modified polyolefin to these mixtures, the dispersibility of the polyamide in EVA or EEA can be increased, and the PR itself can also be increased.

The unsaturated carboxylic acid-modified polyolefin is a polyolefin resin graft-modified with an unsaturated carboxylic acid such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid or a derivative thereof, and particularly grafted with maleic anhydride. Modified polyolefins are preferred. The amount of the unsaturated carboxylic acid grafted is 0.01 to 5 parts by weight, preferably 0.02 to 0.5 part by weight, based on 100 parts by weight of the polyolefin. The unsaturated carboxylic acid-modified polyolefin has a melt index of 0.5 to 20 g / 10 min, preferably 1.0 to
About 10 g / 10 minutes is preferable. The mixing amount of the unsaturated carboxylic acid-modified polyolefin is EVA or EEA.
It is desirable that the proportion of the polyamide and the mixture of polyamide is about 2 to 10% by weight, and if it is less than 2% by weight, the dispersing effect of the polyamide cannot be expected, and if it is more than 10% by weight, further improvement of the dispersing effect is not recognized.

For both the inner and outer surface layers, EVA having a VA of 8% by weight or less, low density polyethylene, linear low density polyethylene, polypropylene, polystyrene, polybutadiene, or a mixture thereof is used. The main function of both the inner and outer surface layers is to prevent blocking. When the adhesiveness between the intermediate layer and the inner and outer surface layers is poor in practical use, an adhesive layer is provided between them. As the adhesive layer, the above-mentioned unsaturated carboxylic acid-modified polyolefin can be preferably used.

When polypropylene, polystyrene, or polybutadiene is used for the surface layer, it is preferable to use an EVA-based unsaturated carboxylic acid-modified polyolefin as an adhesive for the adhesive effect. The thickness ratio between the intermediate layer and the other layers is preferably 1/1 to 5/1. If the ratio is 1/1 or less, the influence of the characteristic value of the intermediate layer on the entire multilayer film is too small, and the PR cannot be sufficiently increased, and if it is 5/1 or more, problems such as film strength and moldability are large. The total thickness of the film varies depending on the respiration rate and temperature of fruits and vegetables in the package and the temperature, but it is practically 15 μm to 1 μm.
The range of 00 μm is desirable.

A known method can be used for forming the film. Since it is a multilayer film, it can be formed by a multi-layer coextrusion inflation method, a T-die method, or a lamination method. Incidentally, plasticizers, heat stabilizers, antioxidants, fillers, lubricants, antiblocking agents, ultraviolet absorbers, colorants, modifiers, etc. usually added to resins may be used as necessary. . Also, an antibacterial agent, which is important for maintaining freshness,
It is also possible to add an antifogging agent, an ethylene removing agent, and the like.

[0014]

The present invention will be described below with reference to examples, but the present invention is not limited to these examples. In addition, the measurement of Pco ₂ and Po _{2 in} the examples is performed by a pressure type gas permeability measuring method (Gasperm-100 type manufactured by JASCO Corporation).
At 23 ° C.

EXAMPLE 1 EVA (V213K, VA manufactured by Mitsubishi Petrochemical Co., Ltd.) was used for both the inner and outer surface layers.
= 5% by weight), EVA (V403 manufactured by Mitsubishi Petrochemical Co., Ltd.) in the middle layer
E, VA = 15% by weight) 80% by weight, polyamide (1020 CAZ manufactured by Mitsubishi Kasei) 13% by weight, unsaturated carboxylic acid modified polyolefin (AP730T manufactured by Mitsubishi Kasei) 7
A 60 μm-thick three-layer film was formed by a three-layer coextrusion inflation method using the mixture by weight. Thickness ratio is 1
It was / 8/1. O ₂ and CO ₂ transmittance P of this film
When o ₂ and Pco ₂ are measured,

[0016]

## EQU1 ## Po ₂ = 3540 [CC / Day. m ² . atn] Pco ₂ = 22300 [CC / Day. m ² . atn] and PR = 6.30.

Example 2 Low density polyethylene (F1 manufactured by Mitsubishi Kasei Co., Ltd.) was used for both the inner and outer surface layers.
31), EEA (Mitsui DuPont Chemical Co. A
710, ethyl acrylate content 15% by weight) 80% by weight, polyamide (Mitsubishi Chemical's EN2250CS) 1
Using a mixture of 6% by weight and 4% by weight of an unsaturated carboxylic acid-modified polyolefin (AP730T manufactured by Mitsubishi Kasei Co., Ltd.), a three-layer film having a thickness of 60 μm was formed by a three-layer coextrusion inflation method. The thickness ratio was 1/8/1. When the O ₂ and CO ₂ transmittances Po ₂ and Pco ₂ of this film were measured,

[0018]

## EQU00002 ## Po ₂ = 4100 [CC / Day. m ² . atn] Pco ₂ = 25420 [CC / Day. m ² . atn] and PR = 6.20.

Example 3 Instead of using 80% by weight of EEA in the intermediate layer, the same EEA was used.
50% by weight and low density polyethylene (F1 manufactured by Mitsubishi Kasei)
31) was used at 30% by weight. Otherwise, in the same manner as in Example 2, a 3-layer film having a thickness of 60 μm was formed. The thickness ratio was 1/8/1. When the O ₂ and CO ₂ transmittances Po ₂ and Pco ₂ of this film were measured,

[0020]

## EQU00003 ## Po ₂ = 3600 [CC / Day. m ² . atn] Pco ₂ = 21000 [CC / Day. m ² . atn] and PR = 5.83.

Comparative Example 1 A three-layer film was formed in the same manner as in Example 1 except that only EVA (V403E) was used as the intermediate layer. (Thickness 60 μm)

[0022]

## EQU00004 ## Po ₂ = 6000 [CC / Day. m ² . atn] Pco ₂ = 28000 [CC / Day. m ² . atn] and PR = 4.67. Met.

Comparative Example 2 EVA (V403E) single layer film was molded by the inflation method. The thickness was 50 μm.

[0024]

## EQU00005 ## Po ₂ = 6480 [CC / Day. m ² . atn] Pco ₂ = 34700 [CC / Day. m ² . atn] and PR = 5.36. The film was heavily blocked and impractical.

Comparative Example 3 An LDPE (F131 manufactured by Mitsubishi Kasei) single layer film was formed by an inflation method. The thickness was 50 μm.

[0026]

[Equation 6] Po ₂ = 5550 [CC / Day. m ² . atn] Pco ₂ = 19000 [CC / Day. m ² . atn] and PR = 3.45.

Using the films of Examples and Comparative Examples, eight apples (Fuji) (2.4 kg) were hermetically sealed and packed (30 c
The bag was stored at 23 ° C. for 20 days. Table 1 shows the O ₂ and CO ₂ concentrations in the bag and the results of quality inspection after 20 days.

[0028]

[Table 1] Acidity: Mass of malic acid in 100 ml of fruit juice Sugar content: Brix sugar content meter hardness: Fruit hardness meter (Kiya Seisakusho) value Taste: 5 grade (5 good → 1 bad)

[0029]

EFFECTS OF THE INVENTION According to the present invention, it is possible to provide a practical freshness-keeping film with the O ₂ and CO ₂ concentrations in the bag being optimal for keeping the freshness only by packaging the fruits and vegetables and the flowers.

Claims (4)

[Claims] 1. A multilayer film comprising three or more layers, the intermediate layer of which is composed of a mixture of (a) an ethylene-vinyl acetate copolymer or an ethylene-ethyl acrylate copolymer and (b) a polyamide. The layer is any one of low density polyethylene, linear low density polyethylene, ethylene-vinyl acetate copolymer having a vinyl acetate content of 8% by weight or less, polypropylene, polystyrene, or polybutadiene,
Alternatively, a freshness-keeping film comprising a mixture thereof. 2. The freshness-retaining film according to claim 1, wherein the multilayer film has a thickness constitution of intermediate layer / sum of layers other than intermediate layer = 1/1 to 5/1. 3. The ethylene-vinyl acetate copolymer of the intermediate layer has a vinyl acetate content of 8 to 40% by weight, and the ethylene-ethyl acrylate copolymer has an ethyl acrylate content of 8 to 40% by weight. 2 of the total amount of the middle layer
3. A mixture of ˜30% by weight.
Alternatively, the freshness-keeping film according to claim 2. 4. The freshness-keeping film according to claim 1, wherein the intermediate layer is mixed with 2 to 10% by weight of an unsaturated carboxylic acid-modified polyolefin.