JP2000326455A - Film for stretch pavckaging - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the film for stretch packaging excellent in fundamental properties for stretch packaging such as transparency, strength, flexibility, stretchability or the like and having excellent adhesive nsss sand rustproof properties. SOLUTION: A skin layer formed from an ethylene/vinyl acetate copolymer resin is laminated to the single surface of an intermediate layer comprising a low density polyethylene resin with a density of 0.920-0.935 g/cm3 containing a vaporizable rustproof agent and a skin layer formed from an olefinic resin is laminated to the other surface of the intermediate layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a stretch packaging film suitable mainly for packaging steel coils.

[0002]

2. Description of the Related Art Since a steel coil is easily rusted, packaging using a moisture-proof polyethylene film or rust-proof paper has been conventionally performed. However, in the former case, the rust prevention is insufficient, and even if a relatively thick film of, for example, about 100 μm is used, there is a problem that the end face of the steel coil is particularly susceptible to rust during storage, and packaging work is difficult. Is troublesome and the workability is not good.

[0003] In the latter case, a long automatic packaging line and packaging equipment are required, so that it is economically impractical and the rust-proof paper is opaque, so that the appearance of the steel coil is poor. There is a problem that the inspection cannot be performed, or a problem that the adhesive applied to the rust-preventive paper is difficult to be separated from the paper, so that it cannot be substantially recycled.

On the other hand, from the viewpoint of emphasizing environmental protection in recent years, with the increasing demand for paperless steel coil packaging, stretch packaging of steel coils using a film for stretch packaging has attracted attention, and its practical application has been actively studied. ing.

[0005] The above-mentioned stretch wrapping film for steel coils has excellent basic properties required for a stretch wrapping film such as transparency, strength, flexibility and stretchability.
In addition, it is required to have excellent tackiness (self-adhesiveness) and rust prevention.

In general, in the case of a film for stretch packaging, it is necessary to reduce the thickness of the film in order to ensure excellent flexibility. There is a problem that the coil tends to rust during storage.

To cope with the above problems, a large amount of a rust inhibitor is contained in a film for stretch packaging. However, as the content of the rust inhibitor increases, the rust on the film surface increases. The bleed-out of the agent also increases, and even if the tackifier is contained in the film, the function of the tackifier is impaired by the bleed-out rust preventive, and the tackiness of the film becomes insufficient. . If the adhesiveness of the film is insufficient, a void is formed between the stretch-wrapped film and the steel coil after the stretch packaging, and moisture penetrates from the void to rust the steel coil.

As a stretch wrapping film provided with rustproofing properties, for example, Japanese Patent Publication No. 5-69708 discloses
"It is characterized by comprising at least one polyolefin resin layer containing at least one nitrite and at least one polyolefin resin layer containing at least one ammonium compound and / or at least one urea compound. Rustproof multilayer film (stretch packaging film) ".

[0009] However, although the stretch packaging film disclosed in the above disclosure has good rust prevention and sustainability, it has poor tackiness, so it is necessary to perform heat bonding (heat sealing) at the time of packaging. There is a problem that there is a restriction on the point.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned conventional problems, the present invention is excellent in basic performance required as a film for stretch wrapping such as transparency, strength, flexibility and stretchability. It is an object of the present invention to provide a stretch packaging film having both tackiness and rust resistance.

[0011]

The stretch packaging film according to the present invention (hereinafter, simply referred to as "film") comprises:
An intermediate layer comprising a low-density polyethylene resin having a density of 0.920 to 0.935 g / cm ³ and a vaporizable rust inhibitor is formed from an ethylene-vinyl acetate copolymer resin on one surface (the inner surface during stretch packaging). And a skin layer formed of an olefin-based resin is stacked on the other surface of the intermediate layer (the outer surface during stretch packaging).

In the film according to the present invention, a low-density polyethylene resin is used as a main component of the intermediate layer.

The type of the low-density polyethylene resin is not particularly limited, and may be a normal low-density polyethylene resin (LDPE) produced by a high-pressure method, or a straight-chain polyethylene resin produced by a medium-pressure method. Low-density polyethylene resin (L-LDPE). Further, these low-density polyethylene resins may be used alone or in combination.

In the present invention, the low-density polyethylene resin must have a density in the range of 0.920 to 0.935 g / cm ³ , preferably 0.922 to 0.935 g / cm ^3.
It is in the range of 0.927 g / cm ³ .

The density of the low density polyethylene resin is 0.92
If it is less than 0 g / cm ³ , the film becomes too soft, and problems such as breakage of the film and generation of wrinkles due to excessive elongation during stretch packaging are likely to occur.

[0016] Usually, for stretch packaging of steel coils,
A film having a thickness of about 60 μm and a width of about 250 mm is used. This is because when the film is stretched, the film is stretched and the width is clogged due to necking. Therefore, if the film width is less than about 250 mm, particularly 200 mm or less, it is possible to prevent the film from being easily broken or having wrinkles. However, the same trouble is caused by the low density polyethylene resin having a density of 0.920 g / c.
It is also likely to occur when it is less than m ³ .

The low-density polyethylene resin has a density of 0.
If it exceeds 935 g / cm ³ , the compatibility with the later-described volatile rust inhibitor will be reduced, and the bleed out of the volatile rust inhibitor on the film surface will be increased, and the adhesion of the film and the whitening phenomenon will be reduced. Generation and the like become remarkable.

The intermediate layer of the film according to the present invention contains a vaporizable rust inhibitor. The type of the vaporizable rust inhibitor is not particularly limited, and examples thereof include a nitrite, an ammonium compound, a urea-based compound and a mixture thereof, and one or more of these are suitable. Among them, a mixture of a nitrite and an ammonium compound and / or a urea-based compound is more preferably used.

By using a mixture of a nitrite and an ammonium compound and / or a urea compound as a vaporizable rust preventive, these absorb moisture in the air to cause hydrolysis and neutralization reaction, so that ammonium nitrite, Produces a highly volatile rust preventive such as ammonia and nitrous acid, and exhibits an excellent rust preventive effect.

The nitrite is not particularly limited, but includes, for example, sodium nitrite, potassium nitrite, calcium nitrite, magnesium nitrite and the like. One or more of these are preferably used. Can be

The ammonium compound is not particularly restricted but includes, for example, ammonium benzoate,
Examples thereof include ammonium phthalate, ammonium stearate, ammonium palmitate, and ammonium oleate. One or more of these are suitably used.

The urea-based compound is not particularly restricted but includes, for example, urea, urotropin, phenyl carbamate and the like, and one or more of these are preferably used.

In the film according to the present invention, a skin layer formed of an ethylene-vinyl acetate copolymer resin (hereinafter referred to as "EVA") is laminated on one surface of the above-mentioned intermediate layer (the inner surface at the time of stretch packaging). It is necessary to be.

The skin layer laminated on one side (the inner surface at the time of stretch packaging) is a layer that comes into contact with the steel coil at the time of stretch packaging. Flexibility, stretchability, etc. are required.

The EVA is not particularly limited, but preferably has a vinyl acetate content of 10 to 25% by weight. If the vinyl acetate content is less than 10% by weight, the flexibility and tackiness may be insufficient.
If it exceeds 5% by weight, flexibility and tackiness may be excessive, and handling operability may decrease.

In the film according to the present invention, it is necessary that a skin layer formed of an olefin resin is laminated on the other surface of the above-mentioned intermediate layer (the outer surface at the time of stretch packaging).

The skin layer laminated on the other surface (the outer surface at the time of stretch packaging) is a layer mainly exhibiting the function of adhesive release, and has good transparency, moderate strength, flexibility and the like. Just do it.

The olefin resin is not particularly limited, but examples thereof include a low density polyethylene resin,
Linear low-density polyethylene resin, medium-density polyethylene resin, high-density polyethylene resin, EVA, polypropylene resin, copolymerized resin of α-olefin and propylene such as ethylene-propylene copolymerized resin, hydrogenated polybutadiene resin and the like. One or more of these are suitably used.

On the skin layer laminated on the outer surface at the time of the stretch packaging, for example, a nylon resin is used to enhance the durability of the rust-preventive effect and to prevent the volatile rust-preventive agent from being dissipated in the film production process. A layer made of a resin having a high gas-shielding property such as EVOH resin or EVOH resin may be further laminated.

The film according to the present invention comprises the intermediate layer, the skin layer formed of the EVA laminated on one surface of the intermediate layer (the inner surface during stretch packaging) and the other surface of the intermediate layer (the outer surface during stretch packaging). It has at least three layers consisting of a skin layer formed from the olefin-based resin to be laminated.

The film according to the present invention preferably contains a tackifier in order to improve the tackiness. When the tackifier is contained, at least the surface layer formed from EVA which is the inner surface at the time of stretch packaging is used. Should contain a tackifier. However, when the film is stored for a long time after film formation, if there is a concentration gradient between the layers, the concentration of the skin in the skin layer will be reduced due to the migration phenomenon of the tackifier, resulting in reduced adhesiveness. Therefore, it is most preferable to include it in all layers.

The tackifier is not particularly restricted but includes, for example, liquid rubber and various conventionally known pressure-sensitive resins. One or more of these are preferably used. Among them, liquid rubber is more preferably used.

The liquid rubber is not particularly restricted but includes, for example, liquid polybutene, liquid polyisobutylene, liquid butyl rubber, liquid polybutadiene, liquid polyisoprene, liquid polychloroprene and the like. More than one species is preferably used.

The content of the tackifier is not particularly limited, but the content of the resin 1 used as a main component of each layer is not limited.
The amount of the tackifier is preferably 3 to 10 parts by weight, more preferably 5 to 7 parts by weight, based on 00 parts by weight.

Resin 100 used as a main component of each layer
When the content of the tackifier with respect to parts by weight is less than 3 parts by weight, a sufficient effect of improving the tackiness may not be obtained. Conversely, when the content exceeds 10 parts by weight, the tackiness becomes too strong, Extrusion molding of the film becomes difficult, wrinkles are easily generated at the time of winding, or bamboo-shaped winding deviation due to aging in the wound film is easily generated,
Various problems may occur during production, storage, use, and the like, such as the rollability of the wound film becomes poor and troubles of the packaging machine are likely to occur.

Each layer of the film according to the present invention may contain, if necessary, a filler, a softener, a plasticizer, a surfactant, a coupling agent, a stabilizer, an oxidizing agent as long as the object of the present invention is not hindered. One or more of various additives such as an inhibitor, an ultraviolet absorber, a colorant, a flame retardant, and an antistatic agent may be contained.

The thickness of the film according to the present invention is not particularly limited, but is preferably 30 to 100 μm, and more preferably 40 to 80 μm.

When the thickness of the film is less than 30 μm,
The strength of the film may be insufficient and the practicality may be poor. On the other hand, if it exceeds 100 μm, the flexibility of the film may be poor and tight winding around the steel coil may be difficult.

The thickness ratio of each layer constituting the film according to the present invention is not particularly limited, but the ratio of the skin layer formed of EVA / the intermediate layer / the skin layer formed of the olefin resin is 3 /. It is preferably from 1/3 to 1/6/1, more preferably from 2/1/2 to 1/4/1.

In the above thickness ratio, if the thickness of the intermediate layer is less than 1/3 of the thickness of the skin layer, the intermediate layer becomes relatively too thin, so that the rust prevention effect, particularly the initial rust prevention effect, is insufficient. In order to obtain a sufficient rust preventive effect, it is necessary to include a large amount of a vaporizable rust preventive in the intermediate layer, and the moldability of the film may be reduced.

Conversely, if the thickness of the intermediate layer exceeds 6 times the thickness of the skin layer, the surface layer becomes too thin, and the bleed-out of the vaporizable rust inhibitor becomes large, and the adhesiveness and stretchability are increased. May decrease.

The method of forming a film according to the present invention is not particularly limited, and various known methods such as coextrusion and extrusion lamination may be employed.
It is preferable to adopt a co-extrusion method which is excellent in productivity.

The film thus obtained may have been subjected to decoration such as coloring or printing, depending on the application and purpose of use.

The stretch wrapping film according to the present invention comprises, as an intermediate layer, a layer comprising a low-density polyethylene resin having a specific range of density and a volatilizable rust preventive, and one side of the intermediate layer (when stretch-wrapped). It has at least a three-layer structure in which a skin layer formed from EVA is laminated on the inner surface) and a skin layer formed from an olefin-based resin is laminated on the other surface of the intermediate layer (the outer surface during stretch packaging). Excellent balance of basic performance required as a film for stretch wrapping such as flexibility, strength, flexibility, stretchability, etc. Demonstrate sustainability.

Further, since a skin layer formed of EVA is laminated on the inner surface at the time of stretch packaging, excellent adhesiveness (self-adhesiveness) is exhibited. Further, the above E
By including a tackifier such as a liquid rubber in the skin layer formed of VA, the above-mentioned tackiness is further improved.

[0046]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

(Example 1)

(1) Preparation of stretch packaging film As a resin for forming an intermediate layer, a low-density polyethylene resin (density: 0.927 g / cm ³ , MFR: 4.0) was added to 100 parts by weight of a vaporizable rust inhibitor. (A mixture of nitrite, ammonium compound and urea) A composition was prepared by adding 3 parts by weight. Further, EVA is used as a resin for forming a skin layer (hereinafter referred to as “inner layer”) which becomes an inner surface during stretch packaging.
(Vinyl acetate content: 19% by weight, density: 0.940 g)
/ Cm ³ , MFR: 2.5). Further, a linear low-density polyethylene resin (density: 0.920 g / cm ³ , MFR: 2.1) was prepared as a resin for forming a skin layer (hereinafter, referred to as “outer layer”) which becomes an outer surface during stretch packaging. .

Next, a film for stretch packaging was produced by a three-layer, three-layer coextrusion molding method using the three resins obtained above. The film thickness of the obtained film for stretch packaging was 60 μm. The thickness of each layer was 25 μm for the inner layer, 10 μm for the intermediate layer, and 25 μm for the outer layer.

(2) Evaluation The performance (transparency, adhesive strength, rust prevention effect) of the stretch packaging film obtained above was evaluated by the following method. The results were as shown in Table 1.

Transparency The haze value (%) of the film for stretch packaging was measured according to JIS K-7105 “Testing method for optical properties of plastics”.

Adhesive strength The inner layer and the outer layer of the stretch packaging film
After being left in an atmosphere of 23 ° C. for 24 hours in a state where a load of 40 kg is uniformly applied to an area of 50 mm × 200 mm,
The peel strength (g / 200 mm) was measured.

Rust prevention effect 60 mm × 90 mm using stretch packaging film
Was prepared. Next, a steel plate (1 mm × 3 mm) which was mechanically polished with # 400 paper and washed with solvent naphtha.
0 mm x 50 mm) in the bag obtained above,
1 ml of a 0.1% by weight saline solution was injected, and the mouth of the bag was heat-sealed. Then, after leaving the bag in an atmosphere of 20 ° C. for 24 hours (initial) and after leaving it for one month (after a lapse of time), the steel sheet was taken out, and the occurrence of rust was visually observed. The effect was evaluated. [Judgment Criteria] ○ No rust was observed × No rust was observed

Example 2 In the production of a stretch packaging film, the thickness of each layer was set to 10 μm for the inner layer and 4
A stretch packaging film having a thickness of 60 μm was obtained in the same manner as in Example 1 except that the thickness was 0 μm and the outer layer was 10 μm.

Example 3 As a resin for forming an intermediate layer, a low-density polyethylene resin (density: 0.927 g / cm ³ ,
(MFR: 4.0) 100 parts by weight, vaporizable rust inhibitor (mixture of nitrite, ammonium compound and urea)
A composition was prepared by adding 3 parts by weight and 5 parts by weight of liquid polybutene. EVA is used as the resin for forming the inner layer.
(Vinyl acetate content: 19% by weight, density: 0.940 g)
/ Cm ³ , MFR: 2.5) A composition was prepared by adding 5 parts by weight of liquid polybutene to 100 parts by weight.
Further, as a resin for forming the outer layer, a linear low-density polyethylene resin (density: 0.920 g / cm ³ , MFR: 2.
1) A composition was prepared by adding 5 parts by weight of liquid polybutene to 100 parts by weight.

A stretch packaging film was produced in the same manner as in Example 1 except that the three types of resins obtained above were used. The film thickness of the obtained film for stretch packaging was 60 μm. The thickness of each layer was 25 μm for the inner layer, 10 μm for the intermediate layer, and 25 μm for the outer layer.

Example 4 In the production of a stretch packaging film, the thickness of each layer was set to 10 μm for the inner layer and 4
A stretch packaging film having a thickness of 60 μm was obtained in the same manner as in Example 3 except that the thickness was 0 μm and the outer layer was 10 μm.

Example 5 In the production of a film for stretch packaging, a composition comprising 5 parts by weight of liquid polybutene added to 100 parts by weight of EVA having a vinyl acetate content of 5% by weight was used as an inner layer forming resin. A stretch wrapping film having a film thickness of 60 μm was obtained in the same manner as in Example 3 except for the fact that the wrapping was performed.

Example 6 In the production of a stretch packaging film, the film thickness was changed in the same manner as in Example 3 except that the amount of liquid polybutene added to the resin for forming each layer was 2 parts by weight. A 60 μm stretch packaging film was obtained.

(Comparative Example 1) A film having a thickness of 60 μm was prepared in the same manner as in Example 1 except that a volatile rust preventive was not contained in the resin for forming the intermediate layer in the production of the film for stretch packaging. An inner layer 25 μm, an intermediate layer 10 μm, and an outer layer 25 μm) were obtained.

Comparative Example 2 A stretch wrapping film was produced in the same manner as in Example 1 except that only the resin for forming the intermediate layer was used without using the resin for forming the inner layer and the resin for forming the outer layer. Thus, a single-layer stretch packaging film having a thickness of 60 μm was obtained.

(Comparative Example 3)

In the production of the stretch packaging film, a film thickness of 60% was obtained in the same manner as in Example 3 except that no volatile rust preventive agent was contained in the resin for forming the intermediate layer.
μm (inner layer 25 μm, middle layer 10 μm, outer layer 25 μm)
Was obtained.

Comparative Example 4 A stretch wrapping film was produced in the same manner as in Example 3 except that only the resin for forming the intermediate layer was used without using the resin for forming the inner layer and the resin for forming the outer layer. Thus, a single-layer stretch packaging film having a thickness of 60 μm was obtained.

The performance of the nine types of stretch packaging films obtained in Examples 2 to 6 and Comparative Examples 1 to 4 was evaluated in the same manner as in Example 1. The results are shown in Table 1. In the evaluation of the rust-preventive effect, the stretch-wrapping films of Comparative Examples 1 and 3 had poor rust-preventive properties after being left for 24 hours (initial), and thus were evaluated after being left for one month (after lapse of time). Did not.

[0066]

[Table 1]

As is clear from Table 1, the films for stretch packaging of Examples 1 to 6 according to the present invention were excellent in all of transparency, tackiness, and rust prevention effect at initial stage and after aging.

On the other hand, the stretch packaging films of Comparative Examples 1 and 3, in which the intermediate layer did not contain a vaporizable rust preventive, had excellent transparency and tackiness, but had an initial rust preventive effect. Already bad.

The single-layer stretch packaging films of Comparative Examples 2 and 4, which were prepared using only the resin for forming the intermediate layer without using the resin for forming the inner layer and the resin for forming the outer layer, exhibited an initial rustproof effect. Was excellent, but the rust-proofing effect after aging was poor, and the transparency and tackiness were poor.

[0070]

As described above, the stretch wrapping film according to the present invention has excellent basic properties required for a stretch wrapping film such as transparency, strength, flexibility and stretchability, and has excellent adhesiveness. Since it has both (self-adhesiveness), rust prevention and its durability, it is suitably used for stretch packaging of easily rusted metal coils such as steel coils.

Continued on the front page F term (reference) 4F100 AH03H AK03C AK06A AK09 AK68B BA03 BA07 BA10B BA10C CA14 EH20 EH202 GB17 JA13A JB02 YY00A 4J002 BB031 DF006 EG017 EG077 EG107 ET018 GG02

Claims (1)

[Claims] (1) a density of 0.920 to 0.935 g / cm;
A skin layer formed from an ethylene-vinyl acetate copolymer resin is laminated on one surface of an intermediate layer containing a vaporizable rust inhibitor in the low-density polyethylene resin of ^{3, and} an olefin resin is formed on the other surface of the intermediate layer. A film for stretch packaging, wherein the formed skin layers are laminated.