JPH08323941A - Oriented multi-layer polypropylene film - Google Patents

Abstract

PURPOSE: To manufacture a film, which is not disturbing optical properties such as transparency, gloss and the like as remarkable features of an oriented propylene film, superior interlaminar bonding properties, and an excellent low- temperature heat sealability. CONSTITUTION: An oriented multi-layer propylene film is composed of an oriented crystalline propylene layer and a straight-chain ethylene/α-olefin copolymer layer formed at least on one face of the oriented crystalline propylene layer by copolymerizing ethylene and 3-12C α-olefin and having the density of 0.860-0.930g/cm<3> and Mw/Mn of 3 or less and the ratio of the average branching number of 1.3 or less in a low molecular-weight area of 30wt.% to the average branching number in a high-molecular weight area of 30wt.%.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a stretched multilayer polypropylene film. More specifically, it relates to a stretched multilayer polypropylene film having excellent transparency and good low-temperature heat sealability.

[0002]

2. Description of the Related Art Crystalline polypropylene films have mechanical properties such as tear strength, rigidity and impact strength, gloss,
It is widely used in the field of packaging, especially food packaging, because it has excellent optical properties such as transparency and food hygiene such as nontoxicity and odorlessness. However, the polypropylene stretched film has a very poor heat-sealing property as a single layer, and when heat-sealed at a temperature at which it can be heat-sealed, heat shrinkage occurs, and heat-sealing cannot be practically performed.

As a method for improving this drawback, several methods have already been proposed in which a resin having a low melting point is laminated on at least one side of a crystalline polypropylene film. As a lamination method, there are a method of coating a stretched base material with a low melting point resin in a solution or a molten state, and a method of laminating a film-like low melting point resin on the base material with heat or an adhesive. Further, many proposals have been made such as a method of laminating a low melting point resin on an unstretched polypropylene film or a method of extruding a crystalline polypropylene and a low melting point resin into a sheet by a coextrusion method and then uniaxially or biaxially stretching. .

For example, in JP-A-46-31478 and JP-A-49-14343, by using a propylene / ethylene random copolymer, one having relatively good transparency and low temperature heat sealability can be obtained. ing.
Further, JP-A-55-145713 and JP-A-56-
No. 10509 discloses propylene, ethylene and carbon number 5.
It has been proposed to use a terpolymer with ~ 12 linear α-olefins. However, in these cases, it is desirable to increase the content of ethylene or higher α-olefin in order to improve the low temperature heat-sealing property, but as the content thereof increases, the blocking property and the slip property of the film deteriorate. For this reason, generally, an antiblocking agent such as silica is added to prevent the blocking resistance from being deteriorated. On the other hand, the addition of an anti-blocking agent impairs the optical properties such as film transparency and gloss, which deteriorates the optical properties that are a major feature of the polypropylene biaxially stretched film, and improves the heat sealability. Has a limit. Further, in JP-A-41-11353, it is proposed to laminate an ethylene-based polymer, such as an ethylene / vinyl acetate copolymer or a medium / low density polyethylene, which has a good heat-sealing property, on at least one side of a stretched polypropylene film. There is.
However, these ethylene-based polymers have weak interlayer adhesion with the polypropylene resin, and the transparency is significantly lowered.

[0005]

[Problems to be Solved by the Invention] Under these circumstances,
It is an object of the present invention to provide a film which does not impair the optical properties such as transparency and gloss which are major features of a stretched polypropylene film, has excellent interlayer adhesion, and has good low temperature heat sealability.

[0006]

As a result of intensive studies, the present inventors have found that a crystalline polypropylene layer obtained by stretching a linear ethylene / α-olefin copolymer having a specific molecular weight distribution and branching degree distribution is used. It has been found that by laminating it on at least one side, its transparency, glossiness, interlayer adhesion and heat sealability are improved. That is, the present invention
Obtained by copolymerizing ethylene and an α-olefin having 3 to 12 carbon atoms, the density is 0.860 to 0.930 g / cm 3.
³ , the molecular weight distribution obtained by GPC is 3 or less, G
A linear ethylene / α-olefin copolymer having a ratio of the average branch number in the low molecular weight region of 30 wt% to 1.3 in the high molecular weight region of 30 wt% fractionated by PC is 1.3 or less on at least one side. The crystalline polypropylene used as the base material layer, which is used as the heat-sealing layer, is obtained by propylene homopolymer, or by copolymerizing propylene and an α-olefin having 2 or 4 to 12 carbon atoms in one stage or in multiple stages. The present invention relates to a stretched multilayer polypropylene film characterized by using a copolymer with propylene. Hereinafter, the present invention will be described in detail.

Linear ethylene / α-used in the present invention
The olefin copolymer is a copolymer of ethylene and an α-olefin having 3 to 12 carbon atoms and has a density of 0.86.
The ratio (M) of the weight average molecular weight (Mw) and the number average molecular weight (Mn) determined by GPC at 0 to 0.930 g / cm ^3.
w / Mn) is 3 or less, and the low molecular weight region 3 with respect to the average number of branches in the high molecular weight region 30 wt% fractionated by GPC 3
The ratio of the average number of branches in 0 wt% is 1.3 or less. If the density exceeds this range, the transparency and heat sealing properties required for the product cannot be satisfied, and Mw /
If the ratio of Mn and the number of branches is outside this range, not only transparency but also interlayer adhesion to the substrate will be insufficient. Also, 19
The melt flow rate (MFR) measured under 0 ° C. and a load of 2160 g is preferably 0.5 to 50 g / 10 minutes. If the MFR is less than 0.5 g / 10 min, the load during extrusion will be large and molding will be difficult, and if it exceeds 50 g / 10 min, the uneven thickness accuracy of the product will decrease and it will not be put to practical use.

The Mw / Mn and the average number of branches in each region in the present invention are specifically determined as follows.

Waters 150C ALC / GP
C (column: manufactured by Tosoh Corporation, GMHHR-H (S),
Solvent 1,2,4-trichlorobenzene)
Mw and Mn were measured by the PC method, and Mw / Mn was calculated. The column elution volume was calibrated by the universal calibration method using standard polystyrene manufactured by Tosoh Corporation.

Of the total amount eluted by GPC, the first eluted 30 wt% is the high molecular weight region, the subsequently eluted eluent is the peak molecular weight region, and the last eluted 30 wt% is the low molecular weight region. The molecular weight range. The average number of branches of each molecular weight region component fractionated in this way was calculated as the number of short chain branches per 1000 carbon atoms by connecting FT-IR (1760X manufactured by Perkin Elmer Co., Ltd.) as a detector of the above measuring device. I asked.

Such a linear low density ethylene / α-olefin copolymer can be produced, for example, by the method disclosed in the following publications. JP-A-60-35006, JP-A-60-3500
7, JP-A-60-35008, JP-A-3-16308
8, JP-A-61-296008, JP-A-63-2280
4 Japanese Patent Application Laid-Open No. 58-19309, Japanese Patent Application No. 60-00862,
JP-A-63-61010, JP-A-63-152608,
JP-A-63-264606, JP-A-63-28070
3, JP-A-64-6003, JP-A-1-95110, JP-A-3-62806, JP-A-1-259004, JP-A-64-45406, JP-A-60-106808, JP-A-60-137911, and JP-A-60-137911. 61-296008, Patent publication 63-501369, JP-A 61-221207,
JP-A-2-22307, JP-A-2-173110, JP-A-2-302410, JP-A-1-129003, JP-A1-210404, JP-A-3-66710, JP-A-3-
70710, JP-A-1-207248, JP-A-63-2.
22177, JP-A-63-222178, and JP-A-63-222.
222179, JP-A-1-12407, JP-A-1-30
1704, JP-A-1-319489, and JP-A-3-744
12, JP-A-61-264010, JP-A-1-2756
09, JP-A-63-251405, JP-A-64-742.
02, JP-A-2-41303, JP-A-131488, JP-A-3-56508, JP-A-3-70708 and JP-A-3.
-70709, Japanese Patent Application No. 60-00862 and the like.

The method for producing a linear low-density ethylene / α-olefin copolymer which can be used in the present invention will be described below based on their contents. The linear low-density ethylene / α-olefin copolymer is, for example, an organic transition metal compound (I) containing a cyclopentadienyl derivative, and a compound (II) which reacts with the organic transition metal compound (I) to form an ionic complex. ) And / or organometallic compound (III)
In the presence of a catalyst consisting of ethylene and α having 3 to 12 carbon atoms
-It can be preferably produced by copolymerizing an olefin.

As the α-olefin having 3 to 12 carbon atoms, propylene, butene-1,4-methylpentene-
1,3-methylbutene-1, pentene-1, hexene-
1, heptene-1, octene-1, nonene-1, decene-1, undecene-1, dodecene-1, tridecene-
1, tetradecene-1, pentadecene-1, hexadecene-1, heptadecene-1, octadecene-1, nonadecene-1, eicosene-1 and the like.

The polymerization method used can be exemplified as follows.

When the solution polymerization method is used, the polymerization conditions may be as follows. That is, the polymerization temperature is 120 in consideration of the fact that the copolymer is in a solution state and the productivity is increased.
It is necessary to be higher than or equal to ° C. The upper limit of the polymerization temperature is not particularly limited, but it is preferably atmospheric pressure or higher in order to suppress the chain transfer reaction which causes a decrease in the molecular weight and to increase the 30 property in order not to decrease the catalyst efficiency.

In the high pressure polymerization method, the polymerization conditions are as follows. The polymerization temperature needs to be 120 ° C. or higher in consideration of the fact that the copolymer is in a molten state and the productivity is improved. The upper limit of the polymerization temperature is not particularly limited, but suppresses the chain transfer reaction that causes a decrease in the molecular weight,
In addition, the temperature is preferably 300 ° C. or lower so as not to reduce the catalyst efficiency. The pressure during the polymerization is not particularly limited, but is preferably 500 kgf / cm ² or more so that the polymerization conditions can be stably obtained in the high pressure process.

Further, in the gas phase polymerization method, the high temperature is not preferable because the copolymer is in a powder state, and it is necessary that the temperature is 100 ° C. or lower. The lower limit of the polymerization temperature is not particularly limited, but it is preferably 50 ° C. or higher in order to improve productivity.

Linear low density ethylene / α in the present invention
-The olefin copolymer, if necessary, an antioxidant, a weather resistance stabilizer, an antistatic agent, a lubricant, an antiblocking agent, etc.
Additives usually used for polyolefins may be added.

The crystalline polypropylene used for the base material layer is a Ziegler-Natta catalyst which is used in combination with a so-called solid titanium-containing transition metal component and an organic component.
In particular, using a catalyst in which the transition metal component is titanium, magnesium and halogen as an essential component and a solid component containing an electron donating compound as an optional component or titanium trichloride, and the organic component is an organic aluminum compound, slurry polymerization, gas phase Polymerization, bulk polymerization, solution polymerization or the like or a combination thereof, a propylene homopolymer obtained by homopolymerizing propylene in a single stage or multiple stages, or propylene and an α-olefin having 2 or 4 to 12 carbon atoms. It is a copolymer with propylene obtained by copolymerizing in one stage or multiple stages.

Further, various additives generally blended with polypropylene, such as an antioxidant, a lubricant, an antistatic agent, an antiblocking agent and the like, can be appropriately blended with the copolymer.

As the method for producing the stretched multilayer polypropylene film of the present invention, any of the known production methods such as the above-mentioned coating method, extrusion coating method, dry laminating method and coextrusion method can be used.

[0022]

EXAMPLES The effects of the present invention will be explained below with reference to examples, but the present invention is not limited to these.

In the examples, MFR, density, melting point, haze, heat sealing temperature and delamination are measured by the following methods.

(1) Melt Flow Rate (MFR) The melt flow rate (MFR) was measured according to JIS K 6760.

(2) Density The measurement was performed according to JIS K 6760.

(3) Melting point A sample of 80 was used using RDC-220 type manufactured by Seiko Denshi KK
After heating at 230 ° C for 5 minutes at a constant rate of temperature increase of 10 ° C / min.
The temperature is decreased at a constant rate in minutes, and the temperature is decreased to −10 ° C. and then held for 5 minutes.
Then, the temperature was raised at a constant rate of 10 ° C./min, and the melting point (point indicating the maximum endotherm) was determined.

(4) Haze Measurement was carried out according to ASTM D1003.

(5) Heat-sealing temperature Laminated films are superposed on each other at a pressure of ² kgf / cm ²
Heat sealing was performed for 2 seconds, and the temperature at which the peeling strength of 15 mm width (peeling speed 300 mm / min) was 200 g was determined.

(6) Peeling between layers Heat sealing was performed in the same manner as in (5), and the peeled state at that time was visually confirmed.

Reference Example Synthesis of Ethylene / α-Olefin Copolymer Polymerization was carried out using a reactor equipped for the high temperature and high pressure method. Ethylene and hexene were continuously injected into the reactor so that the total pressure was 950 kg / cm ² and the hexene concentration was 3
It was set to be 1.4 mol%. And one reactor
It was stirred at 500 rpm.

On the other hand, in a separate container, a toluene solution of diphenylmethylene (cyclopentadienyl) (fluorenyl) zirconium dicorolide as the organic transition metal compound (I) containing the cyclopentadienyl derivative was added to the organometallic compound (III ), A toluene solution of triisobutylaluminum was added so that the amount of aluminum was 250 times mol per zirconium. Furthermore, a compound (I) which reacts with the catalyst component to form an ionic complex.
As I), a toluene solution of N, N-dimethylanilinium tetrakis (pentafluorophenyl) borate was added so that the amount of boron was 2 times the mol of zirconium to obtain a catalyst solution.

The resulting catalyst solution was fed to the reactor at a rate of 120 cm ³ / hour, and the temperature of the reactor was set to 193 ° C. to carry out continuous polymerization. The polymerized polymer particles were withdrawn and discharged into a tank.

Example 1 Polymerized using the metallocene-type catalyst of Reference Example, the density was 0.900 g / cm ³ , the MFR was 3.0 g / 10 minutes, and G
The ratio of the average number of branches in the low molecular weight region 30 wt% to the average number of branches in the high molecular weight region 30 wt% fractionated by PC is 1.1, and the molecular weight distribution by GPC Mw / Mn = 1.
The ethylene / butene-1 copolymer of No. 8 was used as a heat-sealing layer, and polypropylene was used as a base material layer (trade name “UP Polypro” YD101-B, M manufactured by Tosoh Corporation).
FR = 1.7g / 10min), and 45mmφ, 35m
After forming a 1-mm-thick double-layer sheet (base material layer: 0.9 mm, heat-sealing layer: 0.1 mm) with an mφ double-layer extruder, it is vertically stretched at a stretching temperature of 155 ° C. with a small biaxial stretching device.
The stretched multi-layer film having a thickness of 25 μ was obtained by stretching it twice and horizontally to 8 times.

Example 2 Polymerized using the metallocene-type catalyst of Reference Example, the density was 0.910 g / cm ³ , the MFR was 3.0 g / 10 minutes, and G
The ratio of the average number of branches in the low molecular weight region 30 wt% to the average number of branches in the high molecular weight region 30 wt% fractionated by PC is 1.1, and the molecular weight distribution by GPC Mw / Mn = 1.
Using the ethylene / butene-1 copolymer of No. 8, a stretched multilayer film was obtained in the same manner as in Example 1.

Comparative Example 1 Polymerized with a Ziegler type catalyst, having a density of 0.90
0 g / cm ³ , MFR 3.0 g / 10 min, ratio of the average branch number in the low molecular weight region 30 wt% to the average branch number in the high molecular weight region 30 wt% fractionated by GPC is 5,
A stretched multilayer film was obtained in the same manner as in Example 1 except that an ethylene / butene-1 copolymer having a molecular weight distribution Mw / Mn = 5 by GPC was used for the heat seal layer.

Comparative Example 2 Tosoh Polypro F6073UC (propylene / ethylene / butene-1 terpolymer, MFR was used for the heat seal layer.
= 7.0 g / 10 min) was used to obtain a stretched multilayer film in the same manner as in Example 1.

[0037]

[Table 1]

[0038]

INDUSTRIAL APPLICABILITY As described above, the present invention provides a stretched multilayer film having improved transparency and interlayer adhesiveness as compared with the conventional stretched multilayer film and further excellent in low temperature heat sealability.

Claims (1)

[Claims] 1. A stretched crystalline polypropylene layer and a copolymer obtained by copolymerizing ethylene and an α-olefin having 3 to 12 carbon atoms on at least one surface thereof (a) has a density of 0.8.
Weight average molecular weight (Mw) and number average molecular weight (M) determined by gel permeation chromatography (hereinafter referred to as GPC) (b) at 60 to 0.930 g / cm ^3.
The ratio (Mw / Mn) of n) is 3 or less, and (c) the ratio of the average number of branches in the low molecular weight region 30 wt% to the average number of branches in the high molecular weight region 30 wt% fractionated by GPC is 1.
A stretched multilayer polypropylene film comprising a linear ethylene / α-olefin copolymer layer having a number of 3 or less.