JP2003276081A - Uniaxially oriented polyethylene film and its use - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a uniaxially oriented polyethylene film which is excellent in transparency, rigidity, balance of tear strength between MD and TD, shock resistance, heat sealability and shrink packaging property, and a packaging film which is excellent in maintenance of freshness of contents when used as a packaging material appearance and holding of the contents when shrink- packed. <P>SOLUTION: The uniaxially oriented polyethylene film is provided by orienting in MD a film containing at least one layer comprising at-least one kind of an ethylene based polymer having a density of 0.880-0.970 g/cm<SP>3</SP>and having a decane soluble component quantity rate (W (wt.%)) and a density (d (g/cm<SP>3</SP>)) which satisfy the relations that W<80×exp(-100(d-0.88))+0.1 when MFR≤10 g/10 min and W<80×(MFR-9)<SP>0.26</SP>×exp(-100(d-0.88))+0.1 when MFR>10 g/10 min, by passing the film between a heating roll and a roll rotating at a speed different from that of the heating roll. The shrink packaging film is composed of this film. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a uniaxially stretched polyethylene-based film and its use, and more particularly, transparency, rigidity, balance of tear strength in machine direction (MD) and transverse direction (TD), and impact resistance. Uniaxially stretched polyethylene film having excellent heat-sealing property and shrink pack property, and a shrink wrapping film having excellent freshness retention property of contents when used as a packaging material, good appearance, and retention property of contents when shrinked .

[0002]

BACKGROUND OF THE INVENTION Packaging films made of polyethylene or a resin composition containing polyethylene as a main component are excellent in transparency, strength characteristics, chemical resistance, and bag-making processability, and are therefore used in various applications. However, a stretched film using a conventional polyethylene has a weak strength in the stretching direction, and easily breaks the bag when the contents are put in, which damages the contents or makes it difficult to heat seal as a bag-making product. There were drawbacks such as difficult processing and poor appearance.

Therefore, a uniaxially stretched polyethylene-based film having excellent transparency, rigidity, balance of tear strength in the machine direction (MD) and transverse direction (TD), impact resistance, heat sealability, and shrink pack property, and the film are used. The emergence of such shrink wrapping films is desired.

[0004]

It is an object of the present invention to solve the problems associated with the prior art as described above, and to provide transparency, rigidity,
To provide a uniaxially stretched polyethylene-based film excellent in balance of tear strength in the machine direction (MD) and transverse direction (TD), impact resistance, heat sealability, and shrink pack property, and a film for shrink packaging comprising the film. Has an aim.

[0005]

SUMMARY OF THE INVENTION The uniaxially stretched polyethylene film according to the present invention has (i) a density of 0.880 to 0.970 g / c.
m ² and (ii) when the decane-soluble component amount rate (W (wt%)) and the density (d (g / cm ³ )) at 23 ° C. are MFR ≦ 10 g / 10 minutes, W <80 × exp (−100 (d−0.88)) + 0.1 MFR> When 10 g / 10 min, W <80 × (MFR−9) ^0.26 × exp (−100 (d−
0.88)) + 0.1, a single layer or a multi-layer film containing at least one layer made of at least one ethylene-based polymer, the heating roll and a speed different from that of the roll. It is characterized in that it is stretched in the MD (longitudinal direction) by passing it through a roll that is rotating at.

The shrink wrapping film according to the present invention is characterized by comprising the above-mentioned uniaxially stretched polyethylene film according to the present invention. In addition, in this specification, the term "polymer" of an ethylene-based polymer includes not only a homopolymer but also a copolymer.

[0007]

DETAILED DESCRIPTION OF THE INVENTION The uniaxially stretched polyethylene film according to the present invention and its use will be specifically described below. The uniaxially stretched polyethylene-based film according to the present invention has a specific density, and the decane-soluble component amount ratio (W (% by weight)) and the density (d (g / cm ³ )) at 23 ° C.
Is a uniaxially stretched monolayer or multi-layer film having at least one layer composed of at least one ethylene polymer having a specific relationship with.

Ethylene Polymer The ethylene polymer used in the present invention is an ethylene homopolymer or a random or block copolymer composed of ethylene and another monomer. As the other monomer, specifically, propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, 1-
Examples thereof include α-olefins having 3 to 20 carbon atoms such as dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene and 1-eicosene. Among them, having 4 to 8 carbon atoms
Α-olefins are preferred.

Specific examples of the copolymer of ethylene and other monomers include ethylene / α such as ethylene / 4-methyl-1-pentene copolymer and ethylene / 1-hexene copolymer.
-Examples include olefin copolymers. The ethylene polymer used in the present invention may be one kind of (co) polymer selected from the above-mentioned ethylene homopolymers and copolymers of ethylene and other monomers. Alternatively, a mixture of two or more kinds may be used. Particularly preferred is a copolymer of ethylene and at least one α-olefin selected from α-olefins having 4 to 8 carbon atoms.

In the ethylene / α-olefin copolymer, the constitutional unit derived from ethylene is 65 to 99% by weight, preferably 70 to 98% by weight, more preferably 7% by weight.
The structural unit, which is present in an amount of 5 to 96% by weight and is derived from an α-olefin having 3 to 20 carbon atoms, is 1 to 35% by weight, preferably 2 to 30% by weight, more preferably 4 to
It is preferably present in an amount of 25% by weight.

The ethylene polymer used in the present invention is
The density is 0.880 to 0.970 g / cm ³ , preferably 0.890 to 965 g / cm ³ , and more preferably 0.1.
It is in the range of 900 to 0.950 g / cm ³ . When an ethylene polymer having a density within the above range is used, transparency, rigidity, balance of tear strength between longitudinal direction (MD) and transverse direction (TD), impact resistance, heat sealability, and shrinkability are particularly improved. An excellent film is obtained.

This density is 2.16k at 190 ° C.
This is a value obtained by treating the strand obtained at the time of measuring the melt flow rate (MFR) under g load for 2 hours at 120 ° C., gradually cooling to room temperature over 1 hour, and then measuring with a density gradient tube. Also, this melt flow rate (MFR)
Is 190 ° C. according to ASTM D-1238,
It is a value measured under the condition of 2.16 kg load.

The melt flow rate (ASTM D-1238, 190 ° C., 2.16 kg load) of the ethylene-based polymer is usually 0.1 to 10.
100 g / 10 minutes, preferably 0.3 to 50 g / 10
Min, more preferably 0.5 to 20 g / 10 min. In addition, the ethylene polymer used in the present invention has a decane-soluble component amount ratio (W (% by weight)) and a density (d (g / cm ³ )) at 23 ° C. of MF.
When R ≦ 10 g / 10 minutes, W <80 × exp (−100 (d−0.88)) + 0.1, preferably W <60 × exp (−100 (d−0.88)) + 0.1. Preferably, when W <40 × exp (−100 (d−0.88)) + 0.1 MFR> 10 g / 10 minutes, W <80 × (MFR-9) ^0.26 × exp (−100 (d−
0.88)) + 0.1 is satisfied.

It can be said that the ethylene-based polymer satisfying such a relationship has a narrow composition distribution. Since this ethylene polymer has a narrow composition distribution, it is possible to obtain a film that is not sticky. As described above, the ethylene-based polymer used in the present invention is, for example, homopolymerization of ethylene in the presence of a metallocene-based catalyst, or at least one selected from ethylene and an α-olefin having 4 to 20 carbon atoms. It is obtained by copolymerizing with α-olefin.

The metallocene catalyst is, for example, (1) a transition metal compound such as bis (n-propylcyclopentadienyl) zirconium dichloride, bis (n-butylmethylcyclopentadienyl) zirconium dichloride,
(2) Benzene-soluble aluminoxane or benzene-insoluble organoaluminum oxy compound, (3) Si
A fine particle carrier made of O ₂ , Al ₂ O ₃ or the like having a particle size of 10 to 300 μm, and used as necessary, (4)
It is prepared by contacting an organoaluminum compound such as (Me ₂ AlO) _n or (Et ₂ AlO) _n .

Here, Me is a methyl group and Et is an ethyl group. As a specific example of an ethylene polymer prepared by using this metallocene catalyst, JP-A-9-183816 is available.
The ethylene / α-olefin copolymers described in JP-A No. 1994-200242 can be mentioned. Uniaxially Stretched Polyethylene-based Film The uniaxially stretched polyethylene-based film according to the present invention is a monolayer film made of the above-mentioned at least one ethylene polymer or at least one layer made of the above-mentioned at least one ethylene polymer. It is obtained by uniaxially stretching the multilayer film.

The above-mentioned monolayer film can be produced by a conventionally known method for molding a polyethylene-based monolayer film, for example, an inflation film molding method. The above-mentioned multilayer film can also be produced by a conventionally known method for molding a polyethylene-based multilayer film, such as an inflation film molding method. The multilayer film in the present invention has at least one layer made of the above-mentioned at least one ethylene-based polymer, and other layers include, for example, polyamide such as nylon, polyester such as PET, polypropylene, and ethylene. A layer made of a vinyl alcohol copolymer (EVOH), a random copolymer (COC) of ethylene and a cyclic polyolefin represented by norbornene, or a polymer that can be an adhesive layer such as an acid-modified polyolefin as necessary. Is mentioned.

The layer structure of the multilayer film is, for example, polyethylene-based layer / adhesive layer / polyamide layer, polyethylene-based layer / adhesive layer / polyester layer, polyethylene-based layer / COC layer / polyethylene layer / adhesive layer / EVOH layer, or each. And the like. Uniaxial stretching of these films in MD (machine direction)
It is carried out by passing these monolayer or multilayer films between a heating roll and a roll rotating at a different speed from the heating roll. This uniaxially stretching method itself is conventionally known.

The surface temperature of the heating roll (corresponding to the stretching temperature) is usually 70 to 110 ° C. The rotation speeds of the heating roll and the other rolls are appropriately determined depending on the draw ratio and the like, but the rotation speed of the roll rotating at a speed different from that of the heating roll is higher. The draw ratio of the uniaxial stretching is usually 2 to 16 times, preferably 4 to 12 times, more preferably 5 to 10 times.

The uniaxially stretched polyethylene film according to the present invention obtained as described above has a ratio (TRR; MD / TD) of Elmendorf tear strength (ASTM D1922) in MD (longitudinal direction) and TD (transverse direction). )
Is 0.5 or more, the film width is 15 mm, the heat seal strength per 1 μm of the film thickness is 0.2 N or more, and the shrinkage rate at 120 ° C. in MD (longitudinal direction) of the film is 60%. More preferably, the dart impact strength per unit thickness (ASTM D1709) is more preferably 16 g / μm or more, and further, the haze value (PHZ) of the film before being passed between the rolls (before stretching). It is particularly preferable that the value [PHZ / HZ] obtained by dividing by the haze value (HZ) after passing the film between the rolls (after stretching) is 4 or more.

The haze value is based on ASTM D10.
It is a value measured according to 03. The thickness of the uniaxially stretched polyethylene film according to the present invention depends on its specific use, but when it is used for shrink packaging, for example, it is usually 10 to 120 μm, preferably 20 to
It is preferably 80 μm. The uniaxially stretched polyethylene film according to the present invention has transparency, rigidity, and a longitudinal direction (M
D) and transverse direction (TD) tear strength balance, impact resistance, heat sealability and shrink pack property are excellent, and it is suitable as a film for shrink packaging.

Shrink Wrap Film The shrink wrap film of the present invention comprises the above-mentioned uniaxially stretched polyethylene film of the present invention.
This film is excellent in transparency, rigidity, balance of tear strength in the machine direction (MD) and transverse direction (TD), impact resistance, heat sealability, and shrink pack property, and therefore is a stretched film made of conventional polyethylene. Compared to the above, the bag is less likely to be broken when the contents are put therein, the bag can be easily processed, and the appearance is also good.

[0023]

INDUSTRIAL APPLICABILITY According to the present invention, a uniaxially stretched polyethylene system having excellent transparency, rigidity, tear strength balance in the machine direction (MD) and transverse direction (TD), impact resistance, heat sealing property and shrink pack property. A film can be provided. Therefore, the uniaxially stretched polyethylene-based film according to the present invention is suitable as a material for, for example, vegetable packaging, shrink film, shrink label, meat packaging, direct mail bag, protective film, printing substrate and the like.

Further, since the shrink wrapping film according to the present invention comprises the above uniaxially stretched polyethylene film, it retains the freshness of the contents when used as a packaging material,
The effect is that it looks good and has excellent retention of the contents when shrinked.

[0025]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples. The polyethylene density, MFR, and decane-soluble component amount ratio (W) at 23 ° C. were measured according to the following methods. (1) Density Density was measured by measuring the melt flow rate (MFR) at 190 ° C under a load of 2.16 kg, heat-treating the strand at 120 ° C for 2 hours, gradually cooling to room temperature over 1 hour, and then using a density gradient tube. To measure. (2) MFR MFR is 19 according to ASTM D1238-65T.
It is measured under the condition of 0 ° C. and 2.16 kg load. (3) n-Decane soluble component amount ratio (W) at 23 ° C The n-decane soluble component amount ratio (W) at 23 ° C was measured by adding about 3 g of polyethylene to 450 ml of n-decane and dissolving at 145 ° C. After that, the mixture is cooled to 23 ° C., the n-decane-insoluble portion is removed by filtration, and the n-decane-soluble portion is recovered from the filtrate. And this n-decane soluble component amount rate (W) is calculated and calculated | required by the following formula.

W [wt%] = [W ₁ / (W ₁ + W ₂ )] × 100 W ₁ : Weight of n-decane-soluble portion W ₂ : Weight of n-decane-insoluble portion Amount of n-decane-soluble component The smaller the number, the narrower the composition distribution.

[0027]

Example 1 Polyethylene produced using a metallocene catalyst (density = 0.928 g / cm ³ , MFR (19
(0 ° C.) = 0.9 g / 10 min, the decane-soluble component amount ratio (W) = 0.6% by weight at 23 ° C. was subjected to inflation molding to prepare a single-layer film having a thickness of 240 μm, which was subjected to surface temperature (stretching). A uniaxially stretched film having a thickness of 30 μm was produced by passing it between a pair of rolls having a heating temperature of 90 ° C. and a roll not heated and stretching it by 8 times in the take-up direction.

With respect to the obtained uniaxially stretched film, the optical properties, tensile properties, strength and heat sealability are as follows.
Each test was conducted according to the following method. The result is first
Shown in the table. (1) Haze (PHZ), (HZ) Haze (PHZ) is for a film before stretching, and haze (HZ) is for a uniaxially stretched film.
It was measured according to D1003. (2) Gloss Gloss was measured according to ASTM D1003. (3) Tension initial elastic modulus A dumbbell of a size conforming to JIS K6718 is used as a punching test piece. MD (longitudinal direction) is punched parallel to the film pulling direction, and TD is punching perpendicular to the film pulling direction. (Horizontal direction).

A test piece is set on an air chuck of an Instron type universal material testing machine and a tensile test is conducted at a chuck distance of 86 mm and a tensile speed of 200 mm / min. The inclination with respect to the displacement of the initial stress is taken as the tensile initial elastic modulus. (4) Elmendorf Tear Strength (TR) The Elmendorf tear strength is measured using an Elmendorf tear tester manufactured by Toyo Seiki Seisakusho, in accordance with ASTM D1922. MD (longitudinal direction) when the cut is made in the take-up direction, and TD (transverse direction) when the cut is made at a right angle to the take-up direction. (5) Dirt impact strength Dirt impact strength was measured under the following conditions according to ASTM D1709.

<Conditions> A test piece is clamped by an air clamp method, a hemispherical dart is dropped from a position of a certain height, and the load at which the test piece is broken by 50% is read from the graph. The number of drops of one level is 10 and the method A is used. (6) Shrinkage rate The shrinkage rate was measured under the following conditions.

<Conditions> The film or the square plate marked with the shrinkage rate test after heating the film or the square plate is heat-treated in an air oven at a constant temperature for a fixed time, and the gap between the marked lines after the treatment is increased. The length is measured to determine the shrinkage rate. The distance between marked lines is 100 mm, the test temperature is 120 ° C, and the heating time is 3
0 seconds. (7) Heat seal strength The heat seal strength was measured under the following conditions. <Conditions> When a test piece with a width of 15 mm is taken from a film or a sealed film product that has been sealed at various temperatures using a heat sealer and a tensile load of 180 ° is applied using a tensile tester. Obtain the peel strength of the heat-sealed part.

[0032]

Example 2 In Example 1, a polyethylene produced by using a metallocene catalyst in place of the polyethylene of Example 1 (density = 0.928 g / cm ³ , MFR (1
90 ° C.) = 1.8 g / 10 min, decane soluble component amount ratio (W) = 23% by weight at 23 ° C.) was used, and the stretching temperature was 70 ° C. in the same manner as in Example 1. A uniaxially stretched film having a draw ratio of 8 times and a thickness of 30 μm was produced.

With respect to the obtained uniaxially stretched film, optical properties, tensile properties, strength and heat sealability were evaluated.
Each test was conducted according to the method described above. The results are shown in Table 1.

[0034]

Example 3 In Example 2, polyethylene produced using a metallocene catalyst (density = 0.920 g / c)
m ³ , MFR (190 ° C) = 3.8g / 10 minutes, 23 ° C
A decane soluble component amount ratio (W) = 0.4% by weight in Example 2 was produced by T-die molding to form a film having a thickness of 240 μm.
In the same manner as in Example 2 except that the stretching ratio was 6 times,
A uniaxially stretched film having a thickness of 30 μm was produced.

With respect to the obtained uniaxially stretched film, the optical properties, tensile properties, strength and heat sealability were
Each test was conducted according to the method described above. The results are shown in Table 1.

[0036]

Comparative Example 1 In Example 1, instead of the polyethylene of Example 1, the polyethylene shown in Table 1 (density = 0.
925 g / cm ³ , MFR (190 ° C) = 0.9 g / 1
Decane soluble component amount ratio (W) at 0 ° C. and 23 ° C. = 6.
A uniaxially stretched film having a stretching ratio of 8 times and a thickness of 30 μm was produced in the same manner as in Example 1 except that 8% by weight) was used.

With respect to the obtained uniaxially stretched film, optical properties, tensile properties, strength and heat sealability
Each test was conducted according to the method described above. The results are shown in Table 1.

[0038]

Comparative Example 2 In Example 1, instead of the polyethylene of Example 1, the polyethylene shown in Table 1 (density = 0.
925 g / cm ³ , MFR (190 ° C) = 1.2 g / 1
Decane soluble component amount ratio (W) at 0 ° C. and 23 ° C. = 5.
Uniaxially stretched film having a thickness of 20 μm was produced in the same manner as in Example 1 except that the stretching temperature was 80 ° C. and the stretching ratio was 6 times.

With respect to the obtained uniaxially stretched film, the optical properties, tensile properties, strength and heat sealability were
Each test was conducted according to the method described above. The results are shown in Table 1.

[0040]

Comparative Example 3 Using the same polyethylene as in Example 1, an unstretched film having a thickness of 30 μm was produced by inflation molding. The obtained unstretched film was subjected to each test according to the above-mentioned methods for optical properties, tensile properties, strength and heat sealability.

The results are shown in Table 1. In addition, (*) and (**) in Table 1 are as follows. (*): 80 × exp (−100 (d−0.88)) +
TRR with a value of 0.1 (**): MD (longitudinal direction) and TD of the film
Elmendorf tear strength ratio (MD) (MD)
/ TD)

[0042]

[Table 1]

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) B29L 9:00 B29L 9:00 C08L 23:04 C08L 23:04 (72) Inventor Akihiko Yamamoto Chiba Ichihara City Chikusaigan 3 Mitsui Chemicals Stock Association Internal F-term (reference) 4F071 AA15 AF14 AF16 AF23 AF43 AF59 AF61 AH04 BB07 BC01 4F210 AA04 AC03 AE01 AG01 AH54 AR12 QA03 QC02 QD13 QG01 QG02 QG18 QM02 QM03 RA05 RC02 RG02 RG02 RG02 RG02

Claims (6)

[Claims] 1. A density of (i) 0.880 to 0.970 g /
in the range of cm ^3, (ii) decane-soluble component ratio at 23 ° C. and (W (% by weight)) Density ^{(d (g / cm 3)} ) and is, when the MFR ≦ 10 g / 10 min, W <80 × exp (−100 (d−0.88)) + 0.1 MFR> When 10 g / 10 min, W <80 × (MFR−9) ^0.26 × exp (−100 (d−
0.88)) + 0.1, a single layer or a multi-layer film containing at least one layer made of at least one ethylene-based polymer, the heating roll and a speed different from that of the roll. A uniaxially stretched polyethylene-based film, characterized in that it is stretched in the MD (longitudinal direction) by being passed through a roll that is rotating in the above. 2. A ratio (TRR; MD / TD) of Elmendorf tear strength (ASTM D1922) in MD (longitudinal direction) and TD (horizontal direction) is 0.5 or more, and heat per film width 15 mm and film thickness 1 μm. The uniaxially stretched polyethylene-based film according to claim 1, which has a seal strength of 0.2 N or more. 3. 1 in MD (longitudinal direction) of the film
The uniaxially stretched polyethylene-based film according to claim 2, which has a shrinkage ratio of 20% or more of 60% or more. 4. The uniaxially stretched polyethylene film according to claim 3, which has a dirt impact strength per unit thickness (ASTM D1709) of 16 g / μm or more. 5. A value obtained by dividing the haze value (PHZ) of the film before passing it between the rolls (before stretching) by the haze value (HZ) after passing the film between the rolls (after stretching). PHZ / HZ] is 4 or more, and the uniaxially stretched polyethylene-based film according to claim 4. 6. A shrink wrapping film comprising the uniaxially stretched polyethylene film according to any one of claims 1 to 5.