JP3132462B2 - Low density polyethylene film, polyethylene mixture and its film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-density polyethylene film, a polyethylene mixture and a film having excellent physical properties. More specifically, the present invention relates to a low density polyethylene film, a polyethylene mixture and a film thereof which highly satisfy properties required for packaging applications such as heat sealing properties, transparency, gloss, stiffness, impact strength, and tear strength.

[0002]

2. Description of the Related Art Low-density polyethylene is widely used in the form of a film because of its excellent waterproofness and moisture-proofness, moderate flexibility, relatively good transparency, and relatively good strength. Further, since heat sealing can be performed at a relatively low temperature and the sealing strength is good, it is often used as a packaging film in a single layer or a multilayer form with another thin film material.

[0003] In recent years, there has been a strong demand for packaging films capable of increasing the filling speed. Increasing the filling speed means increasing the film feeding speed, shortening the heat sealing time, and shortening the time until the load of the contents is applied to the sealing surface immediately after the heat sealing. A film that exhibits heat sealability at low temperatures and does not peel off even if the load of the contents is applied while the seal is still hot immediately after heat sealing (good hot tack) is necessary. In addition, composite films are manufactured by various methods, but a wide range of materials can be combined, and a composite film with beautiful printing can be manufactured. If there is no waist, wrinkles are likely to occur, and for high-speed processing, the strength of the waist is also important. Furthermore, transparency and gloss increase the display value of the packaged contents, and resistance to impact and tearing in any direction is equally important because it enhances the inherent function of the package in protecting the articles.

[0004] Low-density polyethylene is roughly classified into the following two types according to its production method or molecular structure. One is
It is an ethylene polymer produced by a radical polymerization method under high pressure and high temperature and having essentially short-chain branches and long-chain branches. It is thought that short-chain branching is generated by the intramolecular transfer reaction of the growing polymer radical and long-chain branch is generated by the intermolecular transfer reaction. Since α-olefins have a large chain transfer constant in radical polymerization, only a small amount of α-olefins is copolymerized, even if present, in high-molecular-weight low-density polyethylene used as a synthetic resin.

The other is a copolymer of ethylene and an α-olefin by a transition metal catalyzed polymerization represented by a Ziegler catalyzed polymerization. Due to the copolymerization of the α-olefin, short-chain branches having two carbon atoms less than the number of carbon atoms are generated, and the density of the polymer decreases. The latter usually has no long-chain branching and is therefore also referred to as linear low-density polyethylene (L-LDPE). The former was historically invented earlier than the latter, so it was conventionally simply called low-density polyethylene, but it is called branched low-density polyethylene (B-LDPE) to clearly distinguish it from L-LDPE. To

In general, a polymer substance is a mixture of various molecules, and it is widely accepted that the physical properties change depending on the distribution mode. Analysis of distribution style, quantitative and mechanistic elucidation of the relationship between distribution style and various physical properties,
The invention of a polymer substance having improved physical properties by a new distribution mode has become one of the main subjects of polymer science both academically and industrially.

[0007] For low-density polyethylene, the distribution related to molecular weight (molecular weight distribution) and the distribution related to short-chain branching degree (short-chain branching degree distribution) are physically important. While B-LDPE has a broad molecular weight distribution and a relatively narrow short-chain branching distribution, L-LDPE is generally known to have a relatively broad short-chain branching distribution (eg, S. Hosoda: Polymer
J., 20, 383 (1988)). In addition, since the short-chain branching in the L-LDPE molecule is generated by copolymerizing an α-olefin as a comonomer, the distribution of the short-chain branching degree of L-LDPE is also called a comonomer distribution or a (copolymerization) composition distribution. .

The relationship between the composition distribution and physical properties of L-LDPE is as follows.
Various publications have been published. JP-B-46-21212 is one of the earliest publications that has pointed out the importance of comonomer distribution in partially crystalline ethylene-α-olefin copolymers. Here, a copolymer having a uniform distribution of comonomer between molecules has a lower extruded film, higher impact strength, and superior physical properties in the machine direction and its lateral direction, compared to a non-uniform copolymer. "Equilibrium" is disclosed, including examples of the physical properties of blown films of homogeneous and heterogeneous copolymers having a melt index near 2 and a density near 0.919. Here, the copolymer having a uniform comonomer distribution is obtained by copolymerizing ethylene and an α-olefin in the presence of a catalyst prepared by mixing a specific organoaluminum compound and a specific vanadium compound. ing. It also discloses graphically that the homogeneity of the comonomer distribution is identified by the relationship between the density and the melting point of the copolymer. That is, the density of the homogeneous copolymer is lower than the density of the heterogeneous copolymer having the same comonomer content.

[0009] However, there is no description about heat sealing properties and hot tack properties, which are important properties of the low density polyethylene film, and no mention is made of use as a composite film. Later, as shown in Comparative Examples of the present specification, such a homogeneous copolymer has a very narrow heat seal temperature range exhibiting good hot tack properties (and also has a low temperature heat seal property despite low rigidity). Insufficient), although having the above relatively excellent other properties, is practically impractical as a packaging film.

JP-A-59-66405 discloses that a copolymer film of ethylene having a plurality of melting points and an α-olefin having 4 or more carbon atoms has excellent low-temperature heat sealability and high heat resistance. It has been shown. All of the copolymers described in the examples show three melting points, the highest being 124 ° C.
And the lowest melting point lies between 104 and 106 ° C. However, there is no description about hot tack property, and no mention is made of use as a composite film.

JP-A-60-88016 discloses ethylene α
-In the olefin random copolymer, the copolymer specified by a combination of its composition distribution characteristics, branching characteristics, randomness characteristics, DSC melting point characteristics, crystallinity, molecular weight distribution, etc., has mechanical characteristics and optical characteristics. It is disclosed that it has excellent properties such as blocking resistance, heat resistance, and low-temperature heat-sealing property, and has these properties in a well-balanced manner. Regarding the composition distribution characteristics, it is essential that the composition distribution parameter derived by a specific method is equal to or less than a specific value, which means that the composition distribution must be sufficiently narrow. Regarding DSC characteristics, the maximum melting point is in a specific temperature range of 125 ° C or less, the temperature difference between the highest melting point and the lowest melting point is in a certain range, the temperature difference between the highest melting point and the second highest melting point. Is in a specific range, and it is essential that the heat of fusion of crystals at the highest melting point is not more than a specific ratio to the total heat of fusion of crystals.These prerequisites are that the copolymer is not Although it is a heterogeneous copolymer described in 212212, it means that it must be close to a homogeneous copolymer. Further, if the maximum melting point exceeds 125 ° C. and is too high, or if the proportion of the heat of crystal melting of the maximum melting point is too large, the film properties such as low-temperature heat sealability are inferior. Moreover, there is no description about hot tack property here,
There is no mention of use as a composite film. Later, as shown in Comparative Examples of this specification, such an ethylene copolymer is unsatisfactory in film physical properties such as low-temperature heat sealability and hot tack property.

[0012] The composition distribution can also be changed by homogeneously mixing ethylene copolymers (which may also include ethylene homopolymers) having different comonomer contents. In particular, an arbitrary composition distribution can be created in principle by mixing a plurality of homogeneous copolymers.

Japanese Patent Publication No. 57-37616 discloses 0.94 to 0.97 g.
High-density polyethylene 95 to 50 parts by weight of a density of / cm ^3, preferably a 90 to 70 parts by weight, 0.86~0.91g / cm ^3, preferably
Specific ethylene / 1-butene random copolymer polymerized with a vanadium catalyst having a density of 0.88 to 0.90 g / cm ³
A polyolefin film for packaging is disclosed which is made from a mixture of 5 to 50 parts by weight, preferably 10 to 30 parts by weight. However, the films disclosed herein are:
The waist (rigidity) is significantly higher than the film made of B-LDPE,
It cannot be called a low-density polyethylene film.
Ethylene / 1-butene random copolymer (specifically, 0.1.
889 g / cm ³ ), the ratio of which is higher than the above range, and a film of a mixture having the same rigidity as the B-LDPE film is also described, but the blocking becomes so severe that it cannot be measured. . Further, there is no specific description about the heat sealing property, and no mention is made of the hot tack property.

[0014]

In order to achieve a higher filling speed, which has been strongly demanded in recent years, in a packaging film, it is necessary to have an excellent heat sealing property, especially a hot tack property. Indispensable, furthermore, transparency and gloss are required to enhance the display value of the contents as a packaging film, and high impact strength and large tear strength in any direction are required to enhance the original function of packaging, which is the protection of articles Is as described above. However, conventionally known low-density polyethylene films have been unsatisfactory in their overall physical properties. Accordingly, an object of the present invention is to provide a low-density polyethylene-based film and a material thereof that are most suitable for packaging applications that satisfy all of the above physical properties.

[0015]

Means for Solving the Problems The present inventors have studied in detail the mechanism of developing heat sealing properties, particularly hot tack properties, which are important properties in low density polyethylene for packaging films. The heat sealing process is a process in which the temperature of the film is increased by the heat from the seal bar heated to a predetermined temperature, and the film is allowed to cool after the seal bar is detached. As a result of examining mainly the relationship between the heat sealing property and the hot tack property, it has been found that a specific heat transfer behavior is required to obtain highly excellent heat sealing properties. Furthermore, the low-density polyethylene having such a specific heat transfer behavior is unexpectedly used for the transparency, gloss, waist strength (rigidity), impact strength, and tear strength direction required for a packaging film. Have also been found to be highly satisfactory.

That is, the present invention relates to (1) a temperature rise thermogram measured by a differential scanning calorimeter having a density of 0.895 to 0.915 g / cm ³ , cooled slowly after complete melting, and An endothermic peak is observed within the range, and the endothermic amount of the endothermic peak is relative to the total amount of heat.
0.8 or more, α-olefin content is 2.0 to 10 mol
% Of a random copolymer of ethylene and an α-olefin having 3 to 10 carbon atoms (I) in a proportion of 60 to 99 parts by weight and a density of 0.945 g / cm ³ or more. In the thermogram measured with a thermometer, the thermogram consists of 40 to 1 part by weight of high density polyethylene (II) having an endothermic peak at 125 ° C. or higher, has a density of 0.900 to 0.930 g / cm ³ and a melt flow rate of 0.1 Or 100g
/ 10 minutes, wherein the total amount of the random copolymer (I) and the high-density polyethylene (II) is 100 parts by weight, (2) 3. And (3) a composite film wherein at least one surface layer is a layer comprising the film according to claim 3 .

As described in the section of the prior art, conventionally,
It has been considered that a linear low-density polyethylene having a narrow composition distribution and close to or having a uniform composition gives a film having excellent transparency, impact strength, low-temperature heat sealability, and the like. If the DSC shows multiple melting points,
The maximum melting point is not too high, and the smaller the heat of crystal fusion,
It has been considered preferable in view of the film physical properties. On the other hand, unlike the above concept, the low-density polyethylene used in the present invention has a non-uniform composition distribution and preferably has a maximum melting point as high as possible within the range permitted by polyethylene. Compared with the film using linear polyethylene based on the conventional concept, the film of the present invention has a higher stiffness (higher rigidity), superior transparency and gloss, a large impact strength, and a processed tear strength. Direction, the direction perpendicular to the direction, the temperature at which the heat sealing property is developed is low, the temperature at which the hot tack property is developed is low, and the temperature range is wide. Is better. Hereinafter, each item will be described.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION

(1) Density and Melt Flow Rate The density of the polyethylene according to the present invention is measured after annealing at 100 ° C. for 1 hour according to JIS K6760, and is from 0.900 to 0.93.
0 g / cm ³ , preferably 0.905 to 0.925 g / cm ³ .
The film of the present invention has a high stiffness (high elastic modulus) in proportion to the density of the polyethylene used, but if the density is lower than this, the stiffness of the film becomes weak, and wrinkles are easily generated in the laminating step. Is not preferred. On the other hand, if the density is higher than this, the temperature at which the heat sealing property and the hot tack property are developed becomes too high, and it is difficult to achieve high speed packaging and filling. The melt flow rate (MFR) of the polyethylene according to the present invention is measured according to JIS K6760,
It is in the range of 0.1 to 100 g / 10 minutes. Suitable MFR
Depends on the choice of the film production method, and is preferably 0.1 to 10 g / 10 minutes by the inflation method, more preferably
0.2 to 5 g / 10 minutes, 0.5 to 50 g / 10 by T-die method
Min, more preferably 1 to 10 g / 10 min, and in the extrusion lamination method, it is 1 to 100 g / 10 min, more preferably 2 to 50 g / 10 min. In general, the lower the MFR,
Although the strength of the film increases, the extrusion load during film processing increases, and the higher the MFR, the lower the strength of the film,
It is easy to process a thin film at high speed.

(2) α-olefin The α-olefin to be copolymerized with ethylene in the present invention has 3 to 10 carbon atoms and has the general formula R—CH ＝ CH ₂ (where R is 1 to 8 carbon atoms).
Specific examples of which include propylene, butene-1, pentene-1, hexene-1, heptene-1, octene-1, and nonene-
1, decene-1, 4-methylpentene-1, 4-methylhexene-1, 4,4-dimethylpentene-1 and the like. Among these α-olefins, the propylene-based ones have relatively little improvement effect of the present invention, and α-olefins having 4 or more carbon atoms are preferable, and in particular, butene-1, pentene-1,
Hexene-1, octene-1, 4-methylpentene-1
And the like are preferable from the viewpoint of monomer availability, copolymerizability and the quality of the obtained copolymer. These α-olefins can be used in combination of two or more.

(3) Thermal transition behavior The most important requirement in the present invention is the thermal transition behavior described in detail below. It is now customary to measure the thermal transition behavior of polymers by differential scanning calorimetry (DSC),
The relationship between the heat generation or heat absorption rate and the temperature is called a thermogram. This thermogram reflects the lamella thickness distribution of the polymer, and it is known that the lamella thickness distribution is affected by the composition distribution and thermal history of the polymer (eg, S. Hosoda: Polymer J., 20, 383 (198
8)). The measurement of the thermal transition behavior in the present invention is divided into a case where it is desired to obtain knowledge about the composition distribution inherent in the polymer and a case where it is desired to obtain knowledge about the lamellar thickness distribution of the formed film. Hereinafter, the method will be described. When it is desired to obtain information on the composition distribution inherent in the polymer In this case, after complete melting, the polymer is gradually cooled, and then a temperature rise thermogram is measured. Since the thermal transition behavior of a polymer depends on its thermal history, it must be measured by eliminating it in advance. Further, as shown in the examples and the drawings, if the cooling rate is not sufficiently low, the peak may be apparently split in the subsequent heating process. This is considered to be because the lamellar crystals that could not grow sufficiently under rapid cooling melt and recrystallize during the heating process. Therefore, in the present invention, after holding (pre-melt) in DSC at 150 ° C. for 5 minutes,
Cool to 40 ° C. at a rate of temperature drop of 40 ° C./min to obtain a thermogram after cooling, and then heat up to 150 ° C. at a rate of rate of 10 ° C./min to obtain a temperature rise thermogram. On each thermogram, a straight line is connected between the temperature at which the first heat generation starts and 50 ° C., or between 50 ° C. and the temperature at which all endotherms are completed, and is used as a baseline for obtaining the calorific value. In the present invention, the “peak” clearly indicates a maximum on the endothermic side, and is simply a shoulder (shoulder) shape identified by an inflection point, or 1/1 of the maximum peak intensity in the thermogram.
Anything that looks like a peak with a small change of less than 10 is not considered a “peak”. This is because, as described below, the present invention does not make a minute change in the thermogram a problem. The endothermic peak in the present invention is its half width (Wa1 / 2)
Is preferably 30 ° C. or lower, more preferably 27 ° C. or lower, particularly preferably 25 ° C. or lower. Wa1 / 2 is the temperature difference between two points where the line drawn parallel to the baseline from the midpoint of the perpendicular drawn from the peak to the baseline intersects the melting thermogram. Here, when the line intersects the boundary line with the adjacent peak before intersecting with the thermogram, the temperature difference between this temperature and the other intersection is taken. If Wa1 / 2 exceeds 30 ° C., the heat seal strength on the low temperature side and the peel distance during hot tack become large, which is not preferable.

When it is desired to obtain information on the lamellar thickness distribution of the formed film: In the low-density polyethylene film of the present invention, a temperature rise thermogram is measured directly from the film state. The crystal melting behavior of a molded article is determined by the composition distribution of the polymer itself and various thermal histories during and after processing. Therefore, when it is desired to know the thermal melting behavior of the film itself, it is necessary to directly measure the film without subjecting the film to thermal treatment before measurement. For this reason, in the present invention, the film is placed in a DSC
Heat at a heating rate of 0 ° C./min to obtain a heating thermogram. For this thermogram, a melting peak temperature, a melting peak calorific value, and a half width of a peak are calculated in the same manner as described above. However, in this case, since it is necessary to give importance to the lamella thickness distribution due to the heat history received so far, a peak is recognized if there is a change of 5% or more of the maximum peak intensity. Films made using conventional L-LDPE by the processing method described below exhibit essentially a single broad endothermic peak in their heating thermogram. On the other hand, the film of the present invention is characterized by exhibiting a plurality of distinct endothermic peaks in the heating thermogram as described below. In the heating thermogram of the low-density polyethylene film used in the present invention,
First, in the range of 75 to 100 ° C, preferably 80 to 95
It is necessary that the endothermic peak (a) is observed within the range of ° C. A plurality of endothermic peaks (a) may be observed within the above temperature range. When the peak temperature of the endothermic peak (a) is higher than this range, heat sealing properties and hot tack properties are not exhibited from a sufficiently low temperature.

In the heating thermogram of the polyethylene film used in the present invention, it is necessary that an endothermic peak (b) be observed at 120 ° C. or higher. The presence of the endothermic peak (a) alone does not make the temperature at which hot tack and heat seal properties are developed sufficiently low, and the temperature range at which hot tack is developed is so narrow that it is practically impractical. When the endothermic amount ΔHb of the endothermic peak (b) is the ratio of the endothermic peak (a) to the endothermic amount ΔHa, that is, ΔHb / ΔHa is 0.03 or more, preferably 0.05 or more, and more preferably 0.10 or more, the heat sealing property or hot tack property Is developed from a sufficiently low temperature. On the other hand, if ΔHb / ΔHa is greater than 2.0,
The temperature at which the hot tack property and the heat sealing property are developed is undesirably high. Therefore, ΔHb / ΔHa is 2.0 or less, preferably 1.5 or less, and more preferably 1.0 or less. When the temperature of the endothermic peak (b) is lower than 120 ° C., the temperature range in which the hot tack property is exhibited becomes narrow. Endothermic peak (b) is 1
It is preferably present at a temperature of 22 ° C. or higher. However, since the melting point of polyethylene does not exceed 140 ° C., the peak temperature of the endothermic peak (b) is lower than this. A plurality of endothermic peaks (b) may be observed within the above temperature range.

The present invention does not prevent the endothermic peaks other than the above-mentioned endothermic peaks (a) and (b) from being present in the temperature rising thermogram of the polyethylene film of the present invention. In order to exert the effect, the ratio of the sum of ΔHa and ΔHb to the total heat absorption ΔHt, that is, (ΔHa
+ ΔHb) / ΔHt is 0.6 or more, further 0.7 or more, especially 0.75
It is preferable that it is above. The endothermic peak (a) of the polyethylene film of the present invention has a half width (Wa1 / 2) of 27 ° C. or lower, preferably 25 ° C. or lower, particularly preferably 23 ° C. or lower. Wa1 / 2
Is the temperature difference between the two points where the line drawn parallel to the baseline from the midpoint of the perpendicular drawn from peak (a) to the baseline intersects the melting thermogram. Here, when the line intersects the boundary line with the adjacent peak before intersecting with the thermogram, the temperature difference between this temperature and the other intersection is taken.
If Wa1 / 2 exceeds 27 ° C., the heat seal strength on the low temperature side and the peel distance during hot tack become large, which is not preferable.

(4) Polyethylene mixture The polyethylene mixture of the present invention has a density of 0.895 to 0.9.
15 g / cm ^3, and preferably be from 0.900 0.910g / cm ^3,
A copolymer of ethylene having an α-olefin content of 2.0 to 10.0 mol% and an α-olefin having 3 to 10 carbon atoms, which has a DSC heating thermogram of 80 to 100 ° C., preferably 85 to 95 ° C. An endothermic peak is observed within the range,
99 to 60 parts by weight of a random copolymer (I) of ethylene having 3 to 10 carbon atoms and an α-olefin having an endotherm of 0.8 or more with respect to the total endotherm, and a density of 0.945 or more. Above 125 ° C in the DSC heating thermogram,
Preferably, it can be obtained by mixing with 1 to 40 parts by weight of high density polyethylene (II) having an endothermic peak observed at 130 ° C. or higher. Here, the total amount of the random copolymer (I) and the high-density polyethylene (II) is 100 parts by weight.

The random copolymer (I) was prepared by the present applicant in Showa 6
Japanese Patent Application No. 63-1 entitled "Method for producing ethylene-α-olefin copolymer" filed on June 8, 2013
It can be obtained by the method described in 42522. That is, in a hydrocarbon solvent, (a) a vanadium compound represented by the formula of VO (OR) _n X _3-n (where R is a hydrocarbon group, X is a halogen, 0 <n <3) as a transition metal component, and (b) R ' _m AlX _3-m (where R' is a hydrocarbon group, X is a halogen, 1 <m <3) as an organometallic component, and (c) an organic aluminum compound represented by the following general formula: Formula R "(C = O) OR '" (where R "is an organic group having 1 to 20 carbon atoms and partially or entirely halogen-substituted, and R'" is a hydrocarbon group having 1 to 20 carbon atoms) ) (M)
When ethylene and an α-olefin having 3 to 10 carbon atoms are copolymerized using a catalyst system formed from the above, Al / V (molar ratio) is 2.5 or more and M / V (molar ratio) is
Under a catalyst condition of 1.5 or more, a polymerization temperature of 40 ° C. was set with a molar ratio of ethylene to α-olefin of 35/65 to 60/40.
It is obtained by copolymerization at a temperature of from 80 ° C. to 80 ° C. in the state where a hydrocarbon solvent-insoluble polymer (slurry part) and a hydrocarbon solvent-soluble polymer (solution part) are present. Also random copolymer (I)
Described in Japanese Patent Application Laid-Open No. 60-226514 filed by the applicant of the present invention `` a method for producing an ethylene copolymer '', the vanadium compound obtained by reacting vanadium trichloride and an alcohol with the (a) transition metal It can also be obtained by polymerizing similarly using as a component. Random copolymer (I)
Can also be obtained by the method described in JP-B-46-21212 and the like. As an α-olefin,
Those having 4 to 10 carbon atoms are preferred. Α with 6 or more carbon atoms
When an olefin is used, it is preferable to use a vanadium compound described in JP-A-60-226514.

The high-density polyethylene (II) is a homopolymer of ethylene and / or a copolymer of ethylene and an α-olefin having 3 to 10 carbon atoms, among which are commercially available as high-density polyethylene. You can choose from. Random copolymer (I) and high density polyethylene
The MFR of (II) can be arbitrarily selected within the range of 0.01 to 1000 g / 10 min, as long as the MFR of the mixture is 0.1 to 100 g / 10 min. At this time, it can be assumed that the logarithm of MFR is almost additive. The mixing ratio (parts by weight) of the random copolymer (I) and the high-density polyethylene (II) is preferably from 98 to 70/2 to 30, more preferably
97-80 / 3-20. A uniform mixture can be obtained by kneading the random copolymer (I) and the high-density polyethylene (II) at a temperature at which both components are melted. As the kneader, any of a batch type or a continuous type, a single-screw or multi-screw screw type can be used, but an extruder in a film production machine can also be used.

(5) Production of Film The low-density polyethylene film of the present invention comprises the above (3) and (4)
Can be produced at a temperature at which the raw material resin is melted by a known technique such as an inflation method or a T-die method. The inflation method is also called blow molding method, in which resin melt-kneaded by an extruder is extruded into a tube through a circular slit of a die, and the pressure of gas (usually air) blown into the tube is adjusted. By doing so, films with a wide range of widths can be produced. The ratio of the width of the film to the diameter of the circular slit is called the blow-up ratio (BUR). The thickness of the film can be adjusted by selecting the resin extrusion speed and BUR. The extruded tube is cooled by gas (usually air) and / or liquid (usually water) from the outside. The method of cooling with water is called a water-cooled inflation method and is used to obtain a film having excellent transparency, but it is troublesome to change the width of the film. In addition, a method of performing cooling by air is called an air cooling inflation method, and various cooling devices and methods have been proposed, but when roughly classified, there are a method of performing air cooling in one stage and a method of performing air cooling in multiple stages. Conventionally, L-LDPE single-stage air-cooled inflation film has insufficient transparency, and a multi-stage air-cooling system has been proposed to improve this. However, with the multi-stage air-cooling system, it is not easy to change the film width, and water-cooled inflation is not possible. As with the process, the characteristics of the inflation process that many kinds of films can be produced economically with one machine are lost. In the present invention, a film having extremely excellent transparency can be obtained even by the one-stage air-cooled inflation method. In the present invention, it is a matter of course that a film having excellent transparency can be obtained by a water-cooled inflation method or a multi-stage air-cooled inflation method. The resin temperature during processing is usually selected from the range of the complete melting temperature to 250 ° C.

The T-die method is also called a casting method, in which a resin melt-kneaded by an extruder is extruded through parallel slits of the die and cooled by being brought into contact with a roll through which a coolant such as water passes. Generally, a film having good transparency and good thickness accuracy can be manufactured. The thickness of the film can be adjusted by selecting the resin extrusion speed and the film take-up speed. The resin temperature during processing is usually selected from the range of the complete melting temperature to 350 ° C. The thickness of the monolayer film comprising the polyethylene mixture of the present invention is preferably 5 to 500 μm, particularly preferably 10 to 100 μm. If the thickness is smaller than this range, processing is difficult and handling is difficult when lamination is performed. If the thickness is too large, processing is difficult and heat sealing properties are hardly exhibited.

(6) Composite Film The film of the present invention must be in the form of a composite film with another substrate in order to sufficiently exhibit its excellent heat sealing properties. It is desirable that the surface be present as a surface layer on one side. The substrate can be selected from any polymer capable of forming a film, cellophane, paper, paperboard, woven fabric, aluminum foil and the like. Examples of the polymer capable of forming a film include nylon 6, nylon 66, nylon 11,
Polyamide resins such as nylon 12, polyester resins such as polyethylene terephthalate and polybutylene terephthalate, polypropylene, poly 1-butene, poly-4-methyl-1-pentene, polyethylene, ethylene-vinyl acetate copolymer, ethylene・ Polyolefin resins such as methacrylic acid ester copolymer, ethylene / acrylic acid ester copolymer, ethylene / methacrylic acid copolymer, ethylene / acrylic acid copolymer, ionomer, polyvinylidene chloride, polyvinyl chloride, polystyrene, From polyvinyl alcohol, ethylene vinyl alcohol copolymer etc., each gas barrier property, printability, transparency, rigidity,
It can be selected depending on the purpose of forming the composite film in consideration of the adhesiveness and the like. When the substrate is stretchable, particularly when the film properties are improved by stretching such as polyamide resin, polyester resin or polypropylene, the substrate may be stretched uniaxially or biaxially.

When in the form of a composite film, the low-density polyethylene layer of the present invention preferably has a thickness of 1 to 500 μm, especially 10 to 100 μm. The thickness of the substrate layer is arbitrary and can be selected according to the purpose. In addition, combining a plurality of base materials with various configurations is already widely performed, and can be employed in the present invention. In the present invention, the composite film having two or more layers is a dry lamination method, a wet lamination method, a sandwich lamination method, a lamination method such as a hot melt lamination method, a co-extrusion method,
It can be manufactured by a known technique such as an extrusion coating method (also called an extrusion lamination method) and a combination thereof.

In the lamination method, the film of the present invention obtained by the method described in the description of the single-layer film or the composite film described herein and another substrate are mixed with a solvent-based adhesive, an aqueous-based adhesive, Laminate with hot melt adhesive, molten polymer, etc. In the co-extrusion method, a melt-extruded polyethylene mixture according to the present invention and another melt-extruded polymer are mixed in a die and / or in a die.
Or contact outside. In the extrusion coating method, at least one surface of another substrate or the composite film described herein is coated with a melted and extruded polyethylene mixture film of the present invention or a molten polymer film obtained by the above-mentioned coextrusion method. Further details of these are described in "Handbook of Laminating Processes" issued by Processing Technology Research Group. In the composite film thus produced, if the substrate can be uniaxially or biaxially stretched, further uniaxial or biaxial stretching can be added. A stretched composite film in which the thickness of the layer is reduced to about 1 μm can be obtained. Stretching can be performed by heating the composite film to a temperature range in which the substrate can be stretched by a known method such as a tenter stretching method, an inflation stretching method, or a roll stretching method, and further heat-set if necessary.

(7) Additives The film and the mixture of the present invention may contain known additives such as an antioxidant, a weathering agent, a lubricant, an antiblocking agent, an antistatic agent, an antifogging agent, a dripless agent, a pigment and a filler. Can be contained. (8) Uses The film of the present invention has strong stiffness (high rigidity), excellent transparency and gloss, high impact strength, good balance of tear strength between directions, and low temperature at which heat sealability is exhibited. All of the important properties of packaging films that have a wide temperature range are excellent, so liquids such as foods, milk, soups, etc. packaged with water, such as pickles, in the form of single-layer films or composite films Foods,
It can be used for packaging various contents, such as packaging of dried foods such as confectionery and processed meats such as ham and sausage.

[0033]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the scope of the invention. First, methods for measuring physical properties in the following examples and comparative examples will be described. (1) Density According to the method specified in JIS K6760. After annealing for 1 hour in water at 100 ° C., the density was measured. (2) Melt flow rate (MFR) In accordance with the method specified in JIS K6760. (3) Differential scanning calorimeter (DSC) DSC-7 manufactured by Perkielmer was used. When measuring the temperature rise thermogram after slow cooling after complete melting, place about 10 mg of specimen cut out from a sheet of about 0.5 mm thickness created by hot press into a sample pan for DSC measurement, D
The pre-melt was performed at 150 ° C. for 5 minutes in the SC, the temperature was lowered to 40 ° C. at 1 ° C./min, and the temperature was maintained for 5 minutes, and then the temperature was raised to 150 ° C. at a rate of 10 ° C./min to obtain a thermogram. When directly measuring the temperature rise thermogram from the film state Put about 10 mg of the film stacked on several sheets into a sample pan for DSC measurement, hold in DSC at 40 ° C for 5 minutes, and then 1 ° C at 10 ° C / min.
The temperature was raised to 50 ° C. to obtain a thermogram. (4) Haze (Haze) The method specified in ASTM D1003 was followed. The smaller this value is, the better the transparency is. (5) Gloss (gloss) According to the method specified in JIS Z8741. The greater the value, the better the gloss.

(6) 1% Secant Modulus A width of 2 in the machine direction (MD) or the perpendicular direction (TD) of the film.
cm specimen and cut into a tensile tester with a distance between chucks of 6
cm, tensile at a speed of 5 mm / min, and 1% elongation, calculated from the stress at 100 × (stress) / (cross-sectional area). (7) Dart impact strength According to the method A of ASTM D1709. (8) Elmendorf tear strength The method specified in JIS Z1702 was used. (9) Heat sealing property The polyethylene layers of the two composite films are combined,
Using a heat sealer manufactured by Tester Sangyo Co., Ltd., seal width 10 mm under conditions of seal surface pressure 1.0 kg / cm ² and seal time 1.0 second.
Was heat-sealed. Heat sealing was performed in the same manner while changing the temperature of the seal bar (heat sealing temperature) by 5 ° C. From this, a 15 mm wide specimen was cut out in the direction perpendicular to the sealing surface, and 200 mm /
The 180 ° peel strength was measured at a rate of minutes. (10) Hot tack property The polyethylene layers of the composite film cut to a width of 15 mm were put together, a load of 30 g was applied to one side via a pulley, and a seal surface pressure of 1.3 was applied using a heat sealer manufactured by Tester Sangyo Co., Ltd. Heat sealing was performed with a sealing width of 20 mm under the conditions of kg / cm ² and a sealing time of 0.3 seconds. Since the load dropped at the same time as the end of the seal, and a peeling force due to the load was applied to the seal surface 0.14 seconds after the end of the seal, the actual peeled length was measured. The same test was performed by changing the temperature of the seal bar (heat sealing temperature) in steps of 5 ° C.

Examples 1 to 11 and Comparative Examples 1, 2, 5, and 7 (1) Production of random copolymer (I) In the lower part of a tank type reactor equipped with a stirrer having a content of 200 liters, n-
A solution in which predetermined ethylene and butene-1 were dissolved in hexane was continuously supplied at a fixed amount / hour of 80 kg / hour of n-hexane and a constant amount / hour of ethylene and 1-butene, respectively. Vanadyl trichloride, ethylaluminum sesquichloride, and n-butyl perchlorcrotonate were continuously supplied at a constant rate / hour from separate supply lines. The temperature inside the reactor was controlled at 40 ° C. or 50 ° C. by circulating cooling water through a jacket attached to the outside of the reactor. The polymerization solution was continuously withdrawn from the top of the reactor so that the inside of the reactor was always full, the polymerization reaction with a small amount of methanol added was stopped, and after demonomerization and washing with water, the solvent was steam-stripped. , Take out the solid copolymer,
Drying at 80 ° C. under reduced pressure gave an ethylene-1-butene random copolymer. Table 1 shows the polymerization conditions of each copolymer, the rate of formation of the copolymer, the density of the obtained copolymer, the MFR, and the value of the endothermic peak in the DSC thermogram measured after cooling after complete melting.

(2) Mixture of random copolymer (I) and high-density polyethylene (II) Each of random copolymers IA to IE obtained in (1) above and Nissan polyethylene (Table 2) (Registered trademark) 101
0 (II-A), 2010 (II-B), or 1070 (II-C) at a ratio shown in Table 3 or Table 4 using a # 0 intensive mixer manufactured by Nippon Roll Manufacturing Co., Ltd. Several 35rpm, 10 at 150 ℃
Kneaded for minutes. At this time, 0.20 parts by weight of calcium stearate, 0.15 parts by weight of Irganox (registered trademark) 1076, 0.10 part by weight of Sandstarb (registered trademark) P-EPQ, 0.10 part by weight of erucamide To
0.08 parts by weight and 0.10 parts by weight (Examples 1 to 3, Comparative Examples 1 and 3) or 0.40 parts by weight (Examples 4 to 11, Comparative Examples 5, 6, and 7) of a silica-based antiblocking agent were added. The Nissan polyethylene used here is an ethylene-1-butene copolymer from infrared spectrum analysis. Table 2 shows the density of each high-density polyethylene (II), the MFR, the value of the endothermic peak in the DSC heating thermogram measured after cooling after complete melting, and the half-value width of the endothermic peak. The density of the homogeneous mixture thus obtained, MFR, endothermic peak temperature in the DSC thermogram measured after cooling after complete melting,
Tables 3 and 4 show ΔHb / ΔHa, (ΔHa + ΔHb) / ΔHt, and Wa1 / 2.

(3) Production of Film Inflation Method (Examples 1 to 10, Comparative Examples 1, 2, 5, 7) Die diameter 125 m
m, die lip 2.0 mm spiral die and one step air ring with iris, using a Placo inflation molding machine K-40R, extrusion speed of 24 kg / hour, 170
With the die set temperature of ℃ and the blow-up ratio of 1.8,
From the uniform mixture obtained in the above (2), a film having a thickness of 30 μm was obtained. The physical properties of the film thus obtained are shown in Tables 3 and 4. The film to be used in the production of the following composite film was subjected to corona treatment by a corona treatment machine attached to the apparatus so that the surface tension became 42 to 45 dyne / cm. T-die method (Example 11) Extruder with 50 mm inner diameter, die width 400 mm, die gap 0.7
Using a Tanabe plastic T-die film forming machine equipped with a T-die of mm and a semi-matte roll, a 30 μm thick film was obtained at a processing temperature of 270 ° C., an extrusion rate of 6.4 kg / hour, and a chill roll temperature of 75 ° C. The corona treatment was performed by a corona treatment machine attached to the apparatus so that the surface tension became 42 to 45 dyne / cm. Table 4 shows the physical properties of the film thus obtained.

(4) Production of composite film Sandwich lamination method (Examples 1-3, Comparative Examples 1 and 2) stretched nylon (thickness 15
μm) / LDPE (thickness: 20 μm) base film and the film obtained in (3) above, using Sumitomo Heavy Industries 65mmφ extruder and Tanabe Plastics Machinery L550 type laminator, resin temperature 320 ℃ By extruding L705 in the middle, a sandwich / lamination composite film having an intermediate layer thickness of 30 μm was obtained. Table 5 shows the heat sealing property of the composite film thus obtained, and Table 6 shows the hot tack property. Dry lamination method (Examples 4 to 11, Comparative Examples 5, 6, and 7) Using a desktop test coater manufactured by Yasui Seiki, dry the film obtained in (3) above to 2 g / m ² after drying. A 15 μm-thick stretched nylon base film coated with a urethane-based adhesive is pressed at 40 ° C. at 3 g / cm ² , and then heated and heated at 40 ° C. for 2 days to obtain a dry lamination composite film. Was. Table 7 shows the heat sealing property and Table 8 shows the hot tack property of the composite film thus obtained.

Comparative Example 3 A prototype of Sumikasen-L (registered trademark) manufactured by Sumitomo Chemical Co., Ltd. having a density of 0.913 and an MFR of 1.9 (infrared absorption spectrum analysis indicates that the copolymer is an ethylene-1-butene copolymer. )
Example 2 except that is used instead of the homogeneous mixture of Example 2.
(3) and (4). Endothermic peaks in the DSC thermogram measured after slow cooling after complete melting of the prototype were observed at 103.0 and 120.4 ° C, and showed a minimum value of the temperature rising thermogram at 112.0 ° C between both endothermic peaks. This one
The ratio of the heat absorption on the high temperature side to the heat absorption on the low temperature side at 12.0 ° C was 0.42, and the half value width of the low temperature side peak was 34.2 ° C. The DSC thermogram obtained by directly raising the temperature of the film thus obtained had a peak only at 116.0 ° C., and had a half width of 29.8 ° C. The properties of the film and the composite film thus obtained are shown in Table 3 and Tables 5 and 6.

COMPARATIVE EXAMPLE 4 Ultzex (registered trademark) 1520L manufactured by Mitsui Petrochemical Industry Co., Ltd. (density 0.913, MFR 2.5, 9.1% by weight of 4-methyl-1-pentene was copolymerized by infrared absorption spectrum analysis) Example 2 (3) and (4) except that ethylene-4-methyl-1 pentene copolymer) was used instead of the homogeneous mixture of Example 2. However, since 0.15 parts by weight of the antiblocking agent was analyzed per 100 parts by weight of the raw material pellets, no additional antiblocking agent was added. The endothermic peak in the DSC thermogram measured after slow cooling after complete melting of the sample was 102.3.
And 119.3 ° C, and showed a minimum value of the heating thermogram at 115.4 ° C between both endothermic peaks. The ratio of the heat absorption on the high temperature side to the heat absorption on the low temperature side at 115.4 ° C is 0.
19. The half value width of the low temperature side peak was 31.0 ° C. The DSC thermogram obtained by directly raising the temperature of the film thus obtained had a broad distribution having a peak only at 109.4 ° C., and its half-value width was 27.6 ° C. The properties of the film and the composite film thus obtained are shown in Table 3 and Tables 5 and 6.

Comparative Example 6 A prototype of Sumikasen-L (registered trademark) manufactured by Sumitomo Chemical Co., Ltd., having a density of 0.914 and an MFR of 2.7 (infrared absorption spectrum analysis shows that it is an ethylene-1-butene copolymer. )
In the same manner as in Example 9, (3) and (4), except that a sample prepared by melting and kneading 0.40 part by weight of a silica-based antiblocking agent was used instead of the homogeneous mixture of Example 9. Endothermic peaks in the DSC thermograms measured after the above sample was completely cooled after complete melting were observed at 101.4 ° C and 120.3 ° C, and showed a minimum value of the temperature rising thermogram at 111.8 ° C between both endothermic peaks. The ratio of the high-temperature endotherm to the low-temperature endotherm at 111.8 ° C is 0.33, and the half-value width of the low-temperature peak is
31.6 ° C. The DSC thermogram obtained by directly raising the temperature of the film thus obtained had a peak only at 109.5 ° C. and had a half width of 27.8 ° C. The properties of the films and composite films thus obtained are shown in Table 4 and Tables 7 and 8.

Example 12, Comparative Example 8 (1) Synthesis of vanadium catalyst (a) Vanadium trichloride was placed in a 100 ml flask purged with argon.
0.033 mol of n-heptane and 26 ml of n-heptane were added and the temperature was raised to 50 ° C
Then, add 0.165 mol of methyl alcohol and add argon gas.
The reaction was carried out at 50 ° C. for 1 hour with stirring in a stream. After the reaction, the supernatant
The liquid is drawn out with a glass filter and then with 25 ml of n-heptane.
After washing three times and drying under reduced pressure, the residue was insoluble in n-heptane.
A dark green solid powdery vanadium compound was obtained. This vanaji
Analysis of the composition of the uranium compound shows that vanadium atoms are 21 weight
%, 42% by weight of chlorine atom, CH_ThreeOH was 40% by weight.
Therefore, this vanadium compound is VCl _Three・ 3.0CH_ThreeOH (general
Formula V (OR)_mCl_3-m・_nROH m and n are 0 and 3.0)
The compound was The X-ray powder of this compound
The spectrum shows a spectrum unique to vanadium trichloride.
Was not. (2) Production of random copolymer I-G n-hexane 60
Liter, 1-hexene 3.8 kg, ethyl aluminum
400 ml of a 10 wt% hexane solution of schichloride was supplied.
Circulating warm water to the jacket installed outside the reactor
The temperature inside the reactor was raised to 30 ° C. Next, 1.5kg of hydrogen
cm^Two, Ethylene 4.5kg / cm^TwoTo the vanaji
Catalyst (a) 1.58 g and ethyl aluminum sesquichloride
A mixture of 70 ml of a 10 wt% hexane solution of
Started. 1 mmol / ml perchloroc divided into 5 times every 20 minutes
1.25 ml of the n-butyl rotonate solution was added. Reaction
Ethylene was supplied in such a manner that the total pressure was constant. Again
By circulating cooling water through the jacket, the temperature in the reactor
The temperature was kept at 30 ° C. Two hours after the start of the polymerization,
Purge the gas and add the contents to a large amount of methanol for precipitation.
A precipitate was obtained. These are filtered and the solid is dried.
Thus, an ethylene-1-hexene random copolymer was obtained. This
MFR of the copolymer obtained as above
Table 4 shows the DSC thermogram measurement results
Show.

(3) Mixture of random copolymer and high-density polyethylene The random copolymer IG obtained in the above (2) was prepared in Example 9
Nissan polyethylene 1010 (II-A) under the same conditions as (2)
And mixed. Table 4 shows the MFR of the copolymer thus obtained and the DSC thermogram measured after complete melting and then cooling. (4) Production of Film and Composite Film Using the polyethylene pellets obtained in the above (3), the procedure was carried out in exactly the same manner as in (3) and (4) of Example 10. Table 4 shows each measured value of the DSC thermogram measured directly from the obtained film. The properties of the films and composite films thus obtained are shown in Table 4 and Tables 7 and 8.

Comparative Example 9 A prototype of Sumikasen α (registered trademark) manufactured by Sumitomo Chemical Co., Ltd. having a density of 0.913 and an MFR of 2.0 (an ethylene-1-hexene copolymer based on infrared absorption spectrum analysis)
The procedure of Example 12 (3) was repeated except that a sample prepared by melting and kneading 0.40 part by weight of a silica antiblocking agent was used instead of the homogeneous mixture of Example 12. Endothermic peaks in the DSC thermogram measured after the sample was completely melted and then cooled slowly were observed at 103.6 ° C. and 121.0 ° C., and the minimum value of the temperature rising thermogram was shown at 114.0 ° C. between both endothermic peaks. The ratio of the heat absorption on the high temperature side to the heat absorption on the low temperature side at 114.0 ° C is 0.30, and the half value width of the low temperature side peak is 33.4.
° C. The DSC thermogram obtained by directly raising the temperature of the film thus obtained had a peak only at 109.4 ° C. and had a half width of 29.2 ° C. The properties of the films and composite films thus obtained are shown in Table 4 and Tables 7 and 8.

Uniform mixture of Examples 1 to 3, Comparative Example 4
Table 1 shows the endothermic peak temperatures in the thermograms obtained when the rate of the temperature lowering process was set to 1 ° C./min and 10 ° C./min. It is shown in FIG. FIGS. 1 to 4 show temperature rising thermograms of Example 2 and Comparative Example 4 with different temperature lowering conditions. In the figure, the horizontal axis represents temperature, and the vertical axis represents peak height (endotherm). From the comparison between FIGS. 1 and 2 and FIGS. 3 and 4, the case where the endothermic peak on the high temperature side, which was one at the time of the cooling rate of 1 ° C./min, splits when the cooling rate was increased to 10 ° C./min. It turns out that there is. It is considered that this fission occurred due to the melting and recrystallization of the lamellar crystals that could not grow sufficiently under rapid cooling during the heating process. Note that a straight line substantially parallel to the temperature axis (horizontal axis) in FIGS. 1 and 2 indicates a baseline, and a vertical straight line indicates a temperature at which a thermogram shows a minimum value between endothermic peaks. The endothermic amount of each peak is calculated at the boundary. Also obtained from the films of Example 2 and Comparative Example 4.
FIGS. 5 and 6 show the DSC heating thermogram. The film of Example 2 has distinct peaks at 92.2 ° C and 125.8 ° C, while the film of Comparative Example 4 shows a broad melting pattern with a peak at 109.0 ° C. Example 2 in Tables 5 and 6 is better than Comparative Examples 3 and 4, or Example 5 in Tables 7 and 8.
10 indicates that heat sealing and hot tack properties are exhibited at a lower temperature than Comparative Example 9 compared to Comparative Example 6, and that the temperature range in which hot tack properties are exhibited is remarkably wide. Further, in Table 8, it can be seen that Comparative Example 5 has a longer minimum peeling distance of hot tack and lower strength than Examples 4 and 5 having the same density. Also, comparing the same density in Tables 3 and 4, the examples are much more excellent in transparency (haze), gloss (gross) and impact strength than conventional L-LDPE films, Elastic modulus) is also strong. Thus, the film of the present invention is remarkably excellent as a packaging film as compared with the conventional film.

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

[Table 3]

[0049]

[Table 4]

[0050]

[Table 5]

[0051]

[Table 6]

[0052]

[Table 7]

[0053]

[Table 8]

[0054]

[Table 9]

[0055]

As described above, according to the present invention, the present invention is most suitable for use in packaging which highly satisfies all the physical properties such as heat sealing property, hot tack property, transparency, gloss, waist, impact strength and tear strength. A low-density polyethylene-based film and its material can be provided.

[Brief description of the drawings]

FIG. 1 is a drawing showing a temperature rise thermogram of Example 2 at a rate of 10 ° C./min after a fall in temperature at a rate of 1 ° C./min.

FIG. 2 is a drawing showing a temperature rise thermogram of Comparative Example 4 at a rate of 10 ° C./min after a fall in temperature at a rate of 1 ° C./min.

FIG. 3 is a drawing showing a temperature rising thermogram of Example 2 at a rate of 10 ° C./min after a temperature drop at a rate of 10 ° C./min.

FIG. 4 is a drawing showing a temperature rise thermogram of Comparative Example 4 at a rate of 10 ° C./min after a fall in temperature at a rate of 10 ° C./min.

FIG. 5 is a drawing showing a temperature rising thermogram of Example 2 at a rate of 10 ° C./min directly measured from a film state.

FIG. 6 is a drawing showing a temperature rise thermogram of Comparative Example 4 at a rate of 10 ° C./min directly measured from a film state.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masashi Hanba 5-1, Anesaki Beach, Ichihara-shi, Chiba Sumitomo Chemical Co., Ltd. (72) Inventor Akio Imai 5-1, Anesaki Beach, Ichihara-shi, Chiba Sumitomo Chemical Co., Ltd. (72) Inventor Kiyoyuki Sugimori 5-1, Anesaki Beach, Ichihara-shi, Chiba Sumitomo Chemical Co., Ltd. (58) Field surveyed (Int.Cl. ⁷ , DB name) C08J 5/18 CES B32B 27/32 103 C08L 23/06 C08L 23/08

Claims (3)

(57) [Claims] 1. An endothermic peak is observed within a range of 80 to 100 ° C. in a temperature rising thermogram measured by a differential scanning calorimeter after a density is 0.895 to 0.915 g / cm ³ , cooled slowly after complete melting, and The endothermic amount of the endothermic peak is 0.8 or more with respect to the total amount of heat, the α-olefin content is 2.0 to
10.0 mol% of a random copolymer of ethylene and an α-olefin having 3 to 10 carbon atoms (I) 60 to 99 parts by weight and a density of not less than 0.945 g / cm ³ , and after being completely melted and gradually cooled, differential It consists of 40 to 1 parts by weight of high-density polyethylene (II) whose endothermic peak is observed at 125 ° C. or higher in a heating thermogram measured by a scanning calorimeter, and has a density of 0.90
0 to 0.930 g / cm ³ , melt flow rate 0.1 to 1
A polyethylene mixture characterized by being 100 g / 10 minutes (provided that the total amount of the random copolymer (I) and the high-density polyethylene (II) is 100 parts by weight). 2. A film comprising the polyethylene mixture according to claim 1 . 3. A composite film wherein at least one surface layer is a layer comprising the film according to claim 2 .