JP2010270227A - Biaxially oriented ethylene-based copolymer film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biaxially oriented ethylene-based copolymer film excellent in bending resistance such as pinhole resistance, and suitable for a packaging material of a product such as a frozen food. <P>SOLUTION: The biaxially oriented ethylene-based copolymer film is a biaxially oriented film having a tensile modulus within a range of 300-3,000 MPa in any of orientation directions, a stress of 50-300 MPa at the breaking point in any of orientation directions, and values of ΔNxz(Nx-Nz) and ΔNyz(Ny-Nz) of the refractive indexes thereof each within the range of from 5×10<SP>-3</SP>to 4.5×10<SP>-2</SP>. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a biaxially stretched ethylene copolymer film that is excellent in bending resistance such as pinhole resistance and suitable for packaging materials for frozen foods and other products.

  The ethylene / α-olefin copolymer, which is a linear low density polyethylene (LLDPE), has better transparency, stress cracking resistance, low temperature heat sealability, heat seal strength, impact resistance, etc. than high pressure method low density polyethylene. It is excellent and is widely used as a sealant for food packaging taking advantage of its characteristics. Among them, the ethylene / α-olefin copolymer polymerized with a single site catalyst is further excellent in transparency, low-temperature heat sealability, contaminant sealability, and hot tack property.

As a method for improving the transparency, mechanical strength and the like of an ethylene / α-olefin copolymer film, biaxial stretching of the ethylene / α-olefin copolymer has been conventionally performed.
Patent Document 1 (Japanese Patent Application Laid-Open No. 2005-89693) discloses a stretched film made of a resin composition comprising two kinds of ethylene / α-olefin copolymers having different densities and high-density polyethylene.
Patent Document 4 (Japanese Patent Laid-Open No. 2006-239877) discloses a layer composed of a resin composition (α) composed of two types of ethylene / α-olefin copolymers having different densities and a high-pressure low-density polyethylene, and a polyethylene composition (β And a layered film in which the layer composed of the resin composition (α) is stretched.
In these Patent Documents 1 and 4, it is described that the stretching mode is uniaxial stretching or biaxial sequential stretching or simultaneous stretching. However, as a preferred mode, a stretched single layer film is further stretched. A uniaxially stretched film uniaxially stretched about 2 to 15 times is described, and also in the examples, a uniaxially stretched film using a heating roll is described.
Patent Document 2 (Japanese Patent Application Laid-Open No. 2005-298642) discloses a biaxially stretched ethylene polymer film that can be easily torn in both longitudinal and lateral directions, and is excellent in transparency and shrinkage. It is disclosed that an ethylene / α-olefin copolymer and an ethylene-based polymer are used.
Patent Document 3 (Japanese Patent Application Laid-Open No. 2006-181831) discloses a biaxially stretched ethylene polymer multilayer that can be easily torn in both longitudinal and lateral directions, has excellent transparency and shrinkage, and also has excellent heat sealability and bending resistance. A film is disclosed, and it is disclosed that the base material layer is composed of an ethylene / α-olefin copolymer having a specific density combination.
Patent Document 9 and Patent Document 10 disclose that a base film is biaxially stretched in the longitudinal (MD) direction and the lateral (TD) direction by a flat method (tenter method).
These conventional biaxially stretched films made of an ethylene / α-olefin copolymer are insufficient in pinhole resistance and bending resistance, and further improvements are required as other packaging materials such as frozen foods.
In addition, the conventional technique has limitations such as the use of a composition in which a specific ethylene / α-olefin copolymer is combined in order to obtain excellent bending resistance.

JP 2005-89693 A JP 2005-298642 A JP 2006-181831 A JP 2006-239877 A

  An object of the present invention is to provide a biaxially stretched ethylene polymer film excellent in bending resistance such as pinhole resistance.

According to the present invention, the following biaxially stretched ethylene polymer film is provided to solve the above problems.
That is, the present invention is a biaxially stretched film whose tensile modulus is in the range of 300 to 3000 MPa in any stretching direction and whose stress at break is 50 to 300 MPa in any stretching direction. Furthermore, the values of ΔNxz (Nx−Nz) and ΔNyz (Ny−Nz) are both 5 × 10 ⁻³ to 4.5 × 10 ⁻² , and the biaxially stretched ethylene copolymer film is characterized in that About.
The crystallinity value of the biaxially stretched film of the present invention is desirably 50 to 65%. Further, the ethylene copolymer used is an ethylene / α-olefin random copolymer having a density of 895 to 945 Kg / m 3 (the α-olefin is an α-olefin having 4 to 10 carbon atoms). Further, an ethylene copolymer composition comprising an ethylene / α-olefin random copolymer having a density of 895 to 945 Kg / m 3 and a high-pressure low-density polyethylene having a density of 910 to 935 Kg / m 3 is desirable. .

  The biaxially stretched ethylene copolymer of the present invention is excellent in flexibility such as pinhole resistance and transparency, and is suitable as various packaging materials including frozen foods.

The biaxially stretched ethylene copolymer film according to the present invention will be described.
As the ethylene copolymer used in the film of the present invention, a copolymer of ethylene and an α-olefin having 4 to 10 carbon atoms is suitable. Examples of the α-olefin include propylene, 1-butene, 1-heptene, 1-hexene, 1-octene, 4-methyl-1-pentene and the like. Among these ethylene copolymers, a random copolymer obtained by copolymerizing an α-olefin having 4 to 10 carbon atoms with ethylene is preferable. An ethylene-1-butene copolymer, ethylene-1- Examples include a hexene copolymer, an ethylene-1-octene copolymer, and an ethylene-4-methyl-1-pentene copolymer.

The density of these ethylene copolymers is preferably 895 to 945 Kg / m 3, particularly 900 to 940 Kg / m 3, and the melt flow rate (MFR: ASTM D1238 load 2160 g, temperature 190 ° C.) is particularly possible as long as film forming is possible. Although not limited, it is usually 0.5 to 15 g / 10 minutes, preferably 0.8 to 8 g / 10 minutes.
These ethylene polymers are obtained by appropriately selecting a single site catalyst such as a Ziegler catalyst or a metallocene catalyst, and other catalysts, and adjusting the composition distribution (density distribution) of the resulting ethylene copolymer. Can do. Further, these ethylene copolymers having different densities are appropriately mixed and used.

In the present invention, the ethylene copolymer is preferably prepared by a production method using a single site catalyst such as a metallocene catalyst. For example, a catalyst containing a metallocene compound includes (a) a metallocene compound of a transition metal and (b) It is preferably formed from an organoaluminum oxy compound and (c) a carrier, and if necessary, may be formed from these components and (d) an organoaluminum compound and / or an organoboron compound.
An olefin polymerization catalyst containing a metallocene compound and a method for preparing an ethylene copolymer using the catalyst are described, for example, in JP-A-8-269270.
Among the ethylene copolymers of the present invention, the molecular weight distribution (Mw / Mn) of an ethylene copolymer obtained using a single site catalyst or the like is usually 1.5 to 4.0, preferably 1.8 to It is in the range of 3.5. This Mw / Mn can be measured by gel permeation chromatography (GPC).

In the present invention, it is desirable to blend the ethylene copolymer with high-pressure low-density polyethylene to increase its melt tension.
The density of the high-pressure low-density polyethylene to be blended is usually 910 to 935 kg / m @ 3, preferably 915 to 930 kg / m @ 3, and is a homopolymer of ethylene polymerized under high pressure or other than 5 weight percent (%) or less. Of the α-olefin or a vinyl compound such as vinyl acetate.
The melt flow rate (MFR: ASTM D1238 load 2160 g, temperature 190 ° C.) is not particularly limited as long as the high-pressure low-density polyethylene can be formed into a film, but it is usually 0.5 to 15 g / 10 minutes, preferably 0.8. 8-8 g / 10 min.
The blending amount of the high-pressure method low density polyethylene is usually 5 to 45 weight percent (%) in the composition after blending, preferably 10 to 40 weight percent (%). Thereby, the density of the composition after blending is 895 to 945 Kg / m 3, and the melt flow rate (MFR: ASTM D1238 load 2160 g, temperature 190 ° C.) is 0.5 to 15 g / 10 minutes, preferably 0.8 to 8 g / It is desirable to adjust to 10 minutes.

The ethylene-based copolymer used in the present invention, or even the high-pressure method low-density polyethylene, is usually used in the range of the antioxidant, weathering stabilizer, antistatic agent, and antifogging agent as long as the object of the present invention is not impaired. An additive such as an anti-blocking agent, a lubricant, a nucleating agent, a pigment, or other polymers can be blended as necessary.
The ethylene-based copolymer and the high-pressure method low-density polyethylene, or further additives are dry blended with a Henschel mixer, tumbler blender, V-blender or the like, or after dry blending, a single-screw extruder, a multi-screw extruder, It can be prepared by melt-kneading with a Banbury mixer or the like.

  The biaxially stretched ethylene-based copolymer film of the present invention is molded using a composition with the above-mentioned ethylene-based copolymer, preferably a high-pressure method low-density polyethylene.

  The biaxially stretched ethylene-based copolymer film is formed by a flat method (tenter method), with a draw ratio in one direction of 3 to 15 times, preferably 5 to 5 (MD) and transverse (TD). It is carried out by biaxially stretching in the machine direction (MD) direction and the transverse direction (TD) in the range of 12 times and a draw ratio in the other direction of 3 to 15 times, preferably 5 to 12 times. Biaxial stretching may be simultaneous biaxial stretching or sequential biaxial stretching. Among these methods, a biaxially stretched ethylene copolymer film obtained by a flat method is preferable because it is more excellent in transparency.

The biaxially stretched ethylene copolymer of the present invention is desirably stretched and molded by a flat method. That is, in order to form by sequential biaxial stretching, the temperature of the sheet obtained by extrusion molding is 60 to 110 ° C., more preferably 70 to 90 ° C., and the sheet is further stretched in the longitudinal direction, and further 60 to 120 ° C. It is desirable to stretch in the transverse direction in the temperature range.
Moreover, in order to shape | mold by simultaneous biaxial stretching, the temperature of the sheet | seat obtained by extrusion molding is 60-110 degreeC, More preferably, it is 70-90 degreeC, and each of length (MD) and width (TD) is 3 each. It is desirable to perform simultaneous biaxial stretching at a stretching ratio of 15 times.
In addition, after biaxial stretching, you may heat-set depending on a use. The temperature of the heat set can be changed according to the desired heat shrinkage rate, but is usually about 80 to 140 ° C.
Although the thickness of the biaxially stretched ethylene polymer film of the present invention can be variously determined depending on the application, it is usually 5 to 200 μm, preferably 15 to 130 μm.

The biaxially stretched film of the present invention obtained by the above method has the following physical properties.
(1) Elastic modulus:
Range of 300 to 3000 MPa in any stretching direction (2) Stress at break:
Range of 50 to 300 MPa in any stretching direction (3) Values of refractive indices ΔNxz (Nx−Nz) and ΔNyz (Ny−Nz):
5 × 10 ⁻³ to 4.5 × 10 ⁻²

Further, the biaxially stretched ethylene copolymer film of the present invention has a refractive index in the above range and a value of ΔNp (1/2 (ΔNxz + ΔNyz)) which is the degree of plane orientation is from 1 × 10 ^−2. A film that is 3 × 10 ⁻² is particularly suitable.

Furthermore, the biaxially stretched ethylene copolymer film of the present invention is particularly preferably a film having a crystallinity value of 50 to 65 percent (%).
As described above, the biaxially stretched ethylene copolymer film having the refractive index and the degree of plane orientation, or the crystallinity, in the above range has an excellent balance of film strength.

  Further, among the biaxially stretched ethylene copolymer films of the present invention, those having the following physical properties are particularly suitable. That is, the haze (cloudiness value, the value of 4 films) is 5 to 30%, the thermal shrinkage rate (at 100 ° C.) is in the range of 1 to 15% in any stretching direction, and the tear strength is any stretching. It is a biaxially stretched film whose direction is also 5 to 120 N / cm.

  The biaxially stretched ethylene copolymer film of the present invention has a film surface, for example, corona treatment, flame treatment, in order to improve printability or adhesion with other films including a base material layer described later. Surface activation treatment such as plasma treatment or undercoat treatment may be performed.

  The biaxially stretched ethylene polymer film of the present invention can be used as a single layer, but other film base materials, for example, a sheet-like or film-like material made of a thermoplastic resin, a base material layer made of paper, aluminum foil, etc. You may laminate. When a thermoplastic resin is used as such a film substrate, various known thermoplastic resins such as polyolefin (polyethylene, polypropylene, poly-4-methyl-1-pentene, polybutene, etc.), polyester (polyethylene terephthalate, polybutylene terephthalate, Polyethylene naphthalate, etc.), polyamide (nylon-6, nylon-66, polymetaxylene adipamide, etc.), polyvinyl chloride, polyimide, ethylene / vinyl acetate copolymer or saponified product thereof, polyvinyl alcohol, polyacrylonitrile, polycarbonate , Polystyrene, ionomer, or a mixture thereof. Of these, thermoplastic resins having good stretchability and transparency, such as polypropylene, polyethylene terephthalate, and polyamide, are preferable.

  Moreover, the film base material which consists of these thermoplastic resin films may be a non-stretched film or a stretched film, or one or more kinds of coextrusion molding, extrusion lamination, dry lamination, thermal lamination. The laminated body obtained by etc. may be sufficient. Among them, a biaxially stretched thermoplastic film, particularly a biaxially stretched thermoplastic film made of polypropylene, polyethylene terephthalate, or polyamide is preferable.

  The biaxially stretched ethylene copolymer film of the present invention has a film surface, for example, corona treatment, flame treatment, in order to improve printability or adhesion with other films including a base material layer described later. Surface activation treatment such as plasma treatment or undercoat treatment may be performed.

[Example]
EXAMPLES Next, although this invention is demonstrated through an Example, this invention is not limited by these Examples.
Various test methods and evaluation methods in the present invention are as follows.

(1) Refractive index, degree of plane orientation
The refractive index of the film was measured in accordance with JIS K 7142 using the Abbe refractometer DR-M2 (manufactured by Atago Co., Ltd.) in accordance with JIS K7142.
That is, using the D-line (wavelength 589 nm) as measurement light, the refractive indexes Nx, Ny, and Nz in the three orthogonal directions of the film are measured, and the following refractive index and plane orientation degree are obtained from the numerical values obtained by the measurement. Asked.
Refractive index in the longitudinal direction (MD) of the Nx film Ny Refractive index in the width direction (TD) of the Ny film Refractive index in the thickness direction of the Nz film Values of ΔNxz (Nx−Nz) and ΔNyz (Ny−Nz) which are refractive indexes Value of ΔNp (1/2 (ΔNxz + ΔNyz)) which is the degree of orientation (2) Melt flow rate (g / 10 min)
Based on ASTM D1238, the load was 2160 g and the temperature was 190 ° C.
(3) Density (Kg / m3)
Based on JIS K7112, it measured by D method (density gradient tube).
(4) Crystallinity Based on the density determined with a density gradient tube, the crystallinity was determined from the ratio of the density of complete crystal and complete amorphous of polyethylene.

(5) Pinhole resistance Using a tester industry gelvo flex tester, a test piece having a width of 210 mm and a length of 297 mm was cut out from the multilayer film, and bent at a bending angle of 440 degrees and a bending speed of 40 times / min. Under each atmosphere, 3000 bending tests were performed, a bag was made with the test piece after the bending test, and the number of pinholes was measured with an ageless seal check made by Mitsubishi Gas Chemical.

(6) Haze (cloudiness value) (%)
The haze of the four films was measured according to JIS K 7136 using Haze Meter (NDH-2000 manufactured by Nippon Denshoku Industries Co., Ltd.).

(7) Elastic modulus, stress at break point A strip-shaped test piece having a width of 15 mm and a length of 200 mm is cut out from the film so that the length direction is the film flow direction (MD) and the width direction (TD). Using a Tensilon RT1225 type, the elastic modulus and stress at break were measured according to JIS K 7127.

(8) Tear strength (N / cm)
With reference to JIS P8116 and ASTM 1922, a light load tear tester (manufactured by Toyo Seiki Seisakusho: capacity weight B: 79 g attached to the left end of the pendulum) was used, and the length was 63.5 mm in the tear direction. ) And a rectangular test piece having a width of 50 mm (short side) in a direction perpendicular to the tearing direction, and a 12.7 mm incision is made in the center of the short side from the end to prepare a plurality of test pieces. After that, a preliminary test is performed by stacking a plurality of test pieces so that the indicator (placement needle) of the testing machine is within the range of 20 to 80, and the tear test is performed after adjusting the number of test pieces used for measurement. The tear strength (N / cm) was determined by the following formula. The measurement range (R) of the testing machine was 200.

T = (A × 0.001 × 9.81 × R / 100) / (t)
T: Tear strength (N / cm)
A: Value indicated by the pointer (g)
t: Total thickness of stacked specimens (cm)

(9) Thermal contraction rate (%)
A test piece having a width of 100 mm and a length of 100 mm was cut out so that the length direction of the film would be the film flow direction (MD) and the width direction (TD), and this was left in an oven at a predetermined temperature for 15 minutes and then taken out. The dimensional change of the test piece after cooling to room temperature was measured, and the shrinkage was measured.

The polymers and compositions used in the examples and comparative examples of the present invention are as follows.

[Examples 1 to 6]
A sheet having a thickness of about 2 mm was formed from an ethylene / 1-hexene random copolymer (melt flow rate 2 g / 10 minutes, 190 ° C.) by melt extrusion using a T-die.
Using this sheet, the longitudinal direction (MD) was stretched by a roll, and then the transverse direction (TD) was stretched by a tenter. The temperature for stretching by a roll is 80 to 100 ° C, and the temperature for stretching by a tenter is 80 to 110 ° C. The respective draw ratios are shown in Table 1.
Table 1 shows physical property values of the obtained biaxially stretched film.

Table 1

  As is apparent from Table 1, the biaxially stretched ethylene copolymer film of the present invention is particularly excellent in bending resistance such as pinhole resistance.

The biaxially stretched ethylene copolymer film of the present invention is excellent in bending resistance such as pinhole resistance, and is laminated alone or on a film of other materials such as polypropylene, PET, nylon, etc. Thus, it can be used for packaging materials and other various uses.
For example, since it is excellent in bending resistance such as pinhole resistance, it is suitable for packaging materials such as dried fish, crustaceans, fresh fish, frozen foods, ice and cold insulation, and packaging materials such as trays. Further, it is suitable for use as a sealant layer laminated on nylon, PET, polypropylene or the like, and is suitable as a sealant inner layer for spout bags and standing pouches.

Claims (5)

A biaxially stretched film having a tensile modulus in the range of 250 to 3000 MPa in any stretching direction, a stress at break of 50 to 300 MPa in any stretching direction, and a refractive index thereof. A value of ΔNxz (Nx−Nz) and ΔNyz (Ny−Nz), both of which are 5 × 10 ⁻³ to 4.5 × 10 ⁻² , is a biaxially stretched ethylene copolymer film.   2. The film according to claim 1, wherein the crystallinity value is 50 to 65%.   The ethylene copolymer is an ethylene / α-olefin random copolymer (α-olefin is an α-olefin having 4 to 10 carbon atoms) having a density of 895 to 945 Kg / m 3. Item 3. The film according to any one of Items 1 and 2.   The ethylene copolymer is an ethylene copolymer composition comprising an ethylene / α-olefin random copolymer having a density of 895 to 945 kg / m 3 and a high-pressure low-density polyethylene having a density of 910 to 935 kg / m 3. The film according to claim 1, wherein:   5. The film according to claim 1, wherein the value of haze (4 sheets) is 5 to 30%.