JPH04277541A - Stretched film - Google Patents

Abstract

PURPOSE:To provide a stretched film excellent in stickiness, mechanical strengths (e.g. tear resistance, breaking strength, and elongation at break), transparency, and stretchability and esp, excellent in biaxial stretchability. CONSTITUTION:A stretched film which contains at least 80wt.% mixture of the same kinds of ethylene-4-12C alpha-olefin copolymers having different alpha-olefin contents and has a density of 0.87-0.94g/cm<3>, a melt flow rate of 0.5-20g/10min, and an alpha-olefin content of 5-25wt.%.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a stretch film, and more specifically, it is a stretch film that has excellent mechanical strength such as tear resistance, breaking strength, and elongation at break, as well as transparency and self-adhesiveness, and has good stretchability. It provides film.

0002

2. Description of the Related Art In recent years, stretch packaging, in which a film is stretched and wrapped around unitized cargo on a pallet, has become popular in industry as an energy-saving packaging method. Stretch packaging films used in these applications are required to have self-adhesive properties, be able to achieve a large stretching ratio without causing uneven stretching or stretch breakage during stretch packaging, and have strong strength against protrusions. ing.

Conventionally, polyethylene resins, ethylene-vinyl acetate copolymer resins, polyvinyl chloride resins, and the like have been commonly used as these stretch films.

Recently, in addition to polyethylene resins and ethylene-vinyl acetate copolymer resins, ethylene-α-olefin copolymers have been used because of their excellent mechanical strength, transparency, stretchability, self-adhesiveness, etc. Linear low-density polyethylene (LLDPE) alone, or mixtures and laminates with ethylene-vinyl acetate copolymer are rapidly becoming popular (Japanese Patent Publication No. 18983/1983, Utility Model Application Publication No. 56-7
Publication No. 4737, etc.).

[0005] Recently, labor-saving stretch films,
From the viewpoint of simplification of workability, etc., a film with a higher level of performance is required. Further improvements in properties such as axial stretchability), puncture resistance, and cohesive strength are desired.

[0006]

[Problems to be Solved by the Invention] The present invention has been made as a result of intensive studies in view of the above-mentioned problems, and its objectives are to improve self-adhesiveness, tear propagation resistance, breaking strength, breaking elongation, etc. The object of the present invention is to provide a stretch film having good mechanical strength, transparency, and stretchability, and particularly to provide a stretch film having excellent biaxial stretchability.

[0007]

[Means for Solving the Problems] The present invention provides the same type of ethylene with different α-olefin contents and α-
Contains 80% by weight or more of a mixture of copolymers with olefins, and has the following a) to c): a) density of 0.87 to 0.94 g/cm3, b) melt flow rate of 0.5 to 20 g/10 c) α-olefin content of 5 to 25% by weight.

The present invention will be explained in detail below.

The stretch film of the present invention has a) a density of 0.87 to 0.94 g/cm3, b) a melt flow rate of 0.5 to 20 g/10 min, and c) an α-olefin content of 5 to 25 wt. %, and is made of a resin composition containing 80% by weight or more of a mixture of copolymers of the same type of ethylene and α-olefin having 4 to 12 carbon atoms and having different α-olefin contents.

A mixture of these homogeneous ethylene-α-olefin copolymers has a density of 0.87 to 0.94 g/cm
3, preferably in the range of 0.89 to 0.92 g/cm3. The density is 0.87g/cm
If it is less than 0.94, the mechanical strength of the film will not be sufficient and the binding force after stretching will not be sufficient.
If it exceeds g/cm3, the stretchability will be impaired.

The melt flow rate (MFR) of the ethylene-α-olefin copolymer mixture is 0.5 to 20.
g/10 minutes. If the MFR is less than 0.5 g/10 minutes, the stretchability cannot be said to be sufficient,
If it exceeds 20 g/10 minutes, mechanical strength will decrease.

The α-olefins having 4 to 12 carbon atoms include butene-1, hexene-1, 4-methylpentene-1,
, octene-1, etc., but preferably carbon number 5
The higher monomers mentioned above are desirable from the viewpoint of elongation and strength.

Regarding the type of α-olefin, it is important to adjust the α-olefin content to a range of 5 to 25% by weight, preferably 7 to 20% by weight by mixing several types of α-olefins of the same type. If the content is less than 5% by weight, the elongation will be insufficient and the stretchability will be poor. Moreover, if it exceeds 25% by weight, the mechanical strength will decrease, which is not preferable.

In addition, in order to achieve the object of the present invention, the stretch film of the present invention contains 80% by weight or more of a mixture of a copolymer of the same type of ethylene and an α-olefin having 4 to 12 carbon atoms. It is necessary that the stretching ratio in the longitudinal direction satisfies at least 200% or more, and more preferably, the stretching ratio in the longitudinal direction by simultaneous or sequential biaxial stretching is 20%.
It is desirable that the lateral stretching ratio is 0% or more and the lateral stretching ratio is 150% or more.

In order to easily achieve this object, it is preferable to use an ethylene-α-olefin copolymer having a wide molecular weight distribution, for example, a density of 0.87 to 0. .94g/cm
3, [ηl] 1.2-6.0 dl/g high molecular weight component 10-70% by weight and density 0.90-0.96 g/cm3
, [η2] 0.3 to 1.5 dl/g low molecular weight component 3
It is preferable to use an ethylene-α-olefin copolymer having a wide molecular weight distribution, consisting of 0 to 90% by weight and satisfying η1>η2. These ethylene-α-olefin copolymers are generally prepared by a multistage polymerization method, a melt blending method, or the like.

In the present invention, although the cause is not well understood, by combining at least two types of ethylene-α-olefin copolymers having the same type of α-olefin with different α-olefin contents, stretching methods (uniaxial and biaxial) can be applied. This results in a dramatic improvement in the axial stretchability.

Further, the stretch film of the present invention can be made of ethylene-vinyl acetate copolymer, other ethylene-α-olefin copolymer, ethylene-unsaturated carboxylic acid or its derivative copolymer, low density polyethylene, etc. weight%
However, it is necessary that the ethylene-α-olefin copolymer mixture contains 80% by weight or more.

[0018] If the content of the ethylene-α-olefin copolymer mixture containing the same type of α-olefin in the stretch film composition is less than 80% by weight, the elongation of the stretch film will be insufficient and the drawability will be impaired.

Furthermore, these films may be used as multilayer laminates, such as two or three layers. Examples of this multilayer method include, but are not particularly limited to, coextrusion inflation molding, coextrusion T-die molding, coextrusion coating, and the like.

[0020] Among the above-mentioned forming methods, the use of a blown film is preferable because it can be made into a multilayer film by pinching the film during production.

[0021] When the same type of resin is multi-layered in this way, foreign matter such as gel is present in the film, and even if a hole is formed in one side of the film, the hole will propagate to the other side of the film. This eliminates the risk of the spread of rumors.

[0022] The film may be multilayered by using other types of ethylene-α-olefin copolymers, ethylene-vinyl acetate copolymers, ethylene-unsaturated carboxylic acid or its derivative copolymers, high-pressure low-density polyethylene, etc. Lamination with different resins is also preferably carried out. That is, this is because the multilayer film can utilize the characteristics of each different resin in addition to the above-mentioned effects.

[0023] The thickness of the original stretch film of the present invention is:
The thickness is appropriately selected within the range of 10 to 200 μm, preferably 15 to 180 μm, and more preferably 20 to 150 μm.

In the present invention, a lubricant, tackifier, filler, etc. may be added if necessary.

The lubricants include fatty acid amides such as oleic acid amide, stearic acid amide, and erucic acid amide; fatty acid glycerin ester compounds such as stearic acid monoglyceride, stearic acid diglyceride, oleic acid monoglyceride, and oleic acid diglyceride, and their polyethylene glycols. Examples include additives.

[0026] Examples of fillers include inorganic substances such as light and heavy calcium carbonate, talc, silica, and zeolite.

Tackifiers include castor oil derivatives, polybutene, polyisobutylene, amorphous polypropylene, polyterpenes, sorbitan fatty acid esters, rosin and rosin derivatives, petroleum resins and their hydrogenated products, microcrystalline wax, and the like. Examples include fire, rubber, etc. These tackifiers have a resin component of 10
It can be blended in a range of 0.5 to 20 parts by weight relative to 0 parts by weight.

[0028]

[Examples] Hereinafter, the present invention will be described in detail based on Examples. [Resin used]

A) Ethylene-α-olefin copolymer

[
1) Ethylene-octene-1 copolymer A (density 0.920 g/cm3, MFR 1.0 g/min, octene-1 content 8% by weight, trade name: Dowlex 2045)
, The Dow Chemical Co. )

2) Ethylene-octene-1 copolymer B (
Density 0.905g/cm3, MFR 0.8g/10min, Octene-1 content 13% by weight, Product name: Atein 40
03, The Dow Chemical Co. )

3) Ethylene-butene-1 copolymer (density 0.920 g/cm3, MFR 1.0 g/min, butene-1 content 6.4% by weight, trade name: Mitsubishi UF230, manufactured by Mitsubishi Yuka Co., Ltd.)

B) High pressure low density polyethylene (density 0.
924g/cm3, MFR=1.0g/10min, product name: Nisseki Rexron F22N, manufactured by Nippon Petrochemical Co., Ltd.)

00
34] C) Ethylene-vinyl acetate copolymer (VA content 1
5% by weight, MFR 1.5g/10min, product name: Nisseki Rexron Eva V270, manufactured by Nippon Petrochemicals Co., Ltd.)

[0035]
Examples 1 to 4 and Comparative Examples 1 to 5 Ethylene-octene-1 copolymer A and ethylene-octene-1 copolymer B were blended in the proportions shown in Table 1, and further contained 52% by weight of polybutene as a tackifier. 12 parts by weight of the masterbatch was added to 100 parts by weight of the total resin content. Using the prepared pellets thus obtained, stretch films with a width of 500 mm and a thickness of 12.5 μm and 20 μm were created by pinching the film with a width of 500 mm and a thickness of 12.5 μm and 20 μm using inflation molding (Examples 1 to 4 and Comparison Examples 1-2).

Stretch films were also prepared using high-pressure low-density polyethylene, ethylene-vinyl acetate copolymer, and ethylene-butene-1 copolymer in the same manner (Comparative Examples 3 to 5).

Furthermore, a single layer film having a thickness of 25 μm was separately produced by an inflation method.

Using these films, Japanese Patent Application No. 2-1
Biaxial stretching stretch wrapping machine (actual machine) No. 35243,
Table 1 shows the results of evaluating the stretchability of the film by biaxially stretching 200% in the machine direction and 370% in the transverse direction.

(Evaluation method) ◎...Best biaxial stretchability ○...Good biaxial stretchability△...
…poor biaxial stretching property ×……biaxial stretching property not possible

0
040]

[Table 1]

Examples 5 to 9 and Comparative Examples 6 to 8 Ethylene-octene-1 copolymer A, ethylene-octene-1
1 Copolymer B, low density polyethylene and ethylene-vinyl acetate copolymer were blended in the proportions shown in Table 2, and a masterbatch containing 52% by weight of polybutene as a tackifier was added to a total resin content of 100 parts by weight. 12 parts by weight was added to the total amount. Using the prepared pellets thus obtained, a film width of 500 mm was formed by inflation molding.
Pinch the thickness 12.5 μm and 20 μm to make the thickness 25
Stretch films of μm and 40 μm were created.

[0042] Separately, the thickness is 2 by the inflation method.
A 5 μm single layer film was created.

Using these films, patent application No. 2-1
Table 2 shows the results of evaluation in the same manner as in Example 1 using the biaxial stretching stretch packaging machine No. 35243 (actual machine).

[0044]

[Table 2]

[0045]

[Effects of the Invention] The present invention improves mechanical strength such as self-adhesiveness, tear propagation resistance, breaking strength, and elongation at break, transparency,
A stretch film with good stretchability is obtained, and this stretch film is particularly excellent in biaxial stretchability.

Claims (6)

[Claims] Claim 1: Contains 80% by weight or more of a mixture of a copolymer of the same type of ethylene and an α-olefin having 4 to 12 carbon atoms with different α-olefin contents, and has the following a) to c):
It is characterized by satisfying a) a density of 0.87 to 0.94 g/cm3, b) a melt flow rate of 0.5 to 20 g/10 min, and c) an α-olefin content of 5 to 25% by weight. Stretch film. 2. The stretch film has a longitudinal stretching ratio of 200% or more and a transverse stretching ratio of 150% or more by d) biaxial stretching.
% or more. Stretch film according to claim 1. 3. The ethylene-α-olefin copolymer has a density of 0.87 to 0.94 g/cm3, [η1]
10 to 70% by weight of high molecular weight components of 1.2 to 6.0 dl/g and density of 0.90 to 0.96 g/cm3, [η2]0
．． 30-90% by weight of low molecular weight components of 3-1.5dl/g
Ethylene -α- consisting of and satisfying η1>η2
The stretch film according to claim 1 or 2, comprising an olefin copolymer. 4. Contains 80% by weight or more of a mixture of a copolymer of the same type of ethylene and an α-olefin having 4 to 12 carbon atoms with different α-olefin contents, and the following a) to c):
It is characterized by satisfying a) a density of 0.87 to 0.94 g/cm3, b) a melt flow rate of 0.5 to 20 g/10 min, and c) an α-olefin content of 5 to 25% by weight. The stretch film according to any one of claims 1 to 3, wherein the film is multilayered. 5. The film of claim 1 or claim 4 is further coated with another type of ethylene-α-olefin copolymer, ethylene-
A stretch film comprising a laminated film made of at least one selected from the group of vinyl acetate copolymer, ethylene-unsaturated carboxylic acid or its derivative copolymer, and low-density polyethylene. 6. Claim 1, wherein 0.5 to 20 parts by weight of a tackifier is added to 100 parts by weight of the resin composition.
5. The stretch film according to any one of .