JPH08134284A - Stretched polyethylene resin film - Google Patents

Abstract

PURPOSE: To obtain a thin crosslinked or uncrosslinked stretched polyethylene resin film that has a good stretchability, has been stretched at a high stretch ratio, is tough, and has a high transparency. CONSTITUTION: This stretched polyethylene resin film is obtained by stretching at least uniaxially a polyethylene resin obtained by using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst. The polyethylene resin has a density of 0.860 to 950g/cm<3> , the difference between the temperature at which 10wt.% oozing of the polyethylene resin occurs by the cross fractionation method and the temperature at which 100wt.% oozing occurs is 30 deg.C or less, and the ratio of the weight-average molecular weight to the number-average molecular weight is from 1.5 to 3.5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stretched polyethylene resin film, more specifically, a thin cross-linked or non-crosslinked film having good stretchability, toughness stretched at a high stretch ratio, and high transparency. The present invention relates to a polyethylene resin stretched film.

[0002]

2. Description of the Related Art Stretched films of polyethylene resin are
Utilizing its properties such as toughness, high transparency and twistability, it has been widely used as a twist packaging film, a shrink packaging film, and the like. The type of polyethylene-based resin is selected according to the purpose of use, for example, low density polyethylene is used when especially flexibility is required, but when more toughness is required, linear chain resin is used. Low density polyethylene or a resin composition comprising low density polyethylene and linear low density polyethylene is used (see, for example, Japanese Patent Publication No. 61-57334). But,
With the above low-density polyethylene, only a stretched film having a low stretch ratio and a large thickness can be obtained, and linear low-density polyethylene is exclusively used for obtaining a thin stretched film, but this is not enough in terms of toughness. Absent.

Linear low-density polyethylene is a copolymer of ethylene and α-olefin. When a resin containing an increased amount of α-olefin as a copolymer component is used to increase flexibility, Such a resin is generally a polymer component having a low molecular weight in which a copolymerization component is introduced into the molecular chain and a polymer component having a high molecular weight in which the copolymerization component is hardly introduced, and thus lacks stretchability, Since the film often breaks during the stretching process, a stretched film with a high stretch ratio or a thin stretched film cannot be obtained, and thus the toughness of the obtained stretched film is not sufficient.

On the other hand, in recent years, various studies have been conducted on a method of polymerizing a polyolefin having a narrow molecular weight distribution, in which a copolymerization component is uniformly distributed in a molecular chain by using a metallocene compound as an α-olefin polymerization catalyst. (For example, Japanese Patent Laid-Open Nos. 3-188092 and 4-2.
79592, etc.), the possibility of new polyethylene resins is expected. However, up to now, no research and proposal have been made regarding the stretching of a polyethylene resin using a metallocene catalyst.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a thin stretched polyethylene resin film having good stretchability, stretched at a high stretch ratio, toughness and high transparency.

As a result of intensive studies, the present inventors have found that the above object can be achieved by using a polyethylene-based resin obtained by using a metallocene compound as a polymerization catalyst or a polyethylene-based resin having specific physical properties. The present invention has been completed based on the findings.

[0007]

According to the present invention, a polyethylene resin stretched film obtained by stretching a polyethylene resin obtained by using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst in at least one axial direction. Will be provided. Further, according to the present invention, the density is 0.860-0.
950 g / cm ³ , 10 by cross fractionation method
The range of the wt% elution temperature and the 100 wt% elution end temperature is 30
The value of weight average molecular weight / number average molecular weight (Mw / Mn), which is not higher than 0 ° C. and is a measure of the molecular weight distribution, is 1.5 to
There is provided a polyethylene-based resin stretched film obtained by stretching the polyethylene-based resin of 3.5 in at least a uniaxial direction.

The present invention will be described in detail below. Polyethylene Resin As the polyethylene resin used in the present invention, a homopolymer of ethylene or a copolymer of ethylene and α-olefin can be mentioned. Examples of the α-olefin include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene and the like.

The polyethylene resin used in the present invention is
First, a polyethylene-based resin obtained by polymerizing ethylene or ethylene and an α-olefin by using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst, preferably a differential scanning calorimeter (DSC). ), There is one crystal melting peak, and the range of the melting peak temperature and the temperature until the melting of all the crystals is 20 ° C. or less.

The polyethylene resin used in the present invention is
Second, the density is 0.840 to 0.950 g / cm ³ , and the range of the temperature at the time of elution being 10% by weight to the completion of elution of 100% by weight by the cross fractionation method described below is 30 ° C or less. And the value of Mw / Mn is 1.5 to 3.
5 of them. Such a polyethylene resin can be preferably obtained by using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst.

Metallocene Compound In the present invention, a polyethylene resin obtained by using a metallocene compound (metallocene catalyst) as a polymerization catalyst can be used. The metallocene compound generally refers to a compound having a structure in which a transition metal is sandwiched between π-electron unsaturated compounds, and a bis (cyclopentadienyl) metal complex is typical. More specifically, as the metallocene compound in the present invention, a tetravalent transition metal such as titanium, zirconium, nickel, palladium, hafnium, or platinum is provided with one or more cyclopentadienyl rings or an analogue thereof as a ligand ( The compound which exists as a ligand) is mentioned.

Specific examples of the ligand include a cyclopentadienyl ring; a cyclopentadienyl ring substituted with a hydrocarbon group, a substituted hydrocarbon group or a hydrocarbon-substituted metalloid group; a cyclopentadienyl oligomer ring; an indenyl ring And an indenyl ring substituted with a hydrocarbon group, a substituted hydrocarbon group or a hydrocarbon-substituted metalloid group, and the like. In addition to these π-electron unsaturated compounds, as ligands, monovalent anion ligands such as chlorine and bromine, or divalent anion chelate ligands, hydrocarbons, alkoxides, arylamides, aryloxides, amides, arylamides , Phosphide, arylphosphide and the like may be coordinate-bonded to the transition metal atom.

Examples of the hydrocarbon group substituting the cyclopentadienyl ring include, for example, methyl, ethyl, propyl, butyl, amyl, isoamyl, hexyl, isobutyl, heptyl, octyl, nonyl, decyl, cetyl, 2-ethylhexyl, phenyl. Etc.

Examples of such metallocene compounds include cyclopentadienyltitanium tris (dimethylamide), methylcyclopentadienyltitanium tris (dimethylamide), bis (cyclopentadienyl) titanium dichloride, dimethylsilyltetramethyl. Cyclopentadienyl-tert-butylamide zirconium dichloride, dimethylsilyltetramethylcyclopentadienyl-tert-butylamide hafnium dichloride, dimethylsilyltetramethylcyclopentadienyl-pn-butylphenylamide zirconium chloride, methylphenylsilyl Tetramethylcyclopentadienyl-tert-butylamide hafnium dichloride, indenyl titanium tris (dimethylamide), indenyl tita Umutorisu (diethylamide), indenyl titanium tris (di -n- propyl amide), indenyl titanium bis (di -n- butylamide) (di -n- propyl amide) and the like.

The metallocene compound exerts a function as a catalyst during the polymerization of various olefins by changing the kind of metal and the structure of the ligand and combining it with a specific cocatalyst (cocatalyst). More specifically, the polymerization is usually carried out in a catalyst system in which methylaluminoxane (MAO) as a cocatalyst, a boron compound or the like is added to these metallocene compounds. The ratio of the cocatalyst used to the metallocene compound is 1
0 to 1,000,000 molar times, preferably 50 to 5,
It is 000 mole times.

The polymerization conditions are not particularly limited, and for example, a solution polymerization method using an inert medium, a bulk polymerization method in which an inert medium does not substantially exist, a gas phase polymerization method and the like can be used. Usually, the polymerization temperature is −100 ° C. to 300 ° C., and the polymerization pressure is usually atmospheric pressure to 100 kg / cm ² .

The metallocene catalyst is characterized in that the properties of active sites are uniform. Since each active site of the metallocene catalyst has the same activity, the homogeneity of the molecular weight, the molecular weight distribution, the composition, and the composition distribution of the polymer to be synthesized is improved.
Therefore, the polyolefins polymerized with these metallocene catalysts have a narrow molecular weight distribution, and in the case of copolymers, the copolymer components are introduced in almost equal proportions in every molecular weight component. Examples of the polyethylene-based resin obtained by using the metallocene compound as a polymerization catalyst include CGCT manufactured by Dow Chemical Co., and EXACT manufactured by Exxon Chemical Co.
Are commercially available.

Cross fractionation method The cross fractionation method used in the present invention is as follows. First, a polyethylene resin is dissolved in o-dichlorobenzene at 140 ° C or a temperature at which the polyethylene resin is completely dissolved, and then cooled at a constant rate to form a thin polymer layer on the surface of an inert carrier prepared in advance. It is generated in the order of high crystallinity and in the order of high molecular weight. next,
The temperature is raised continuously or stepwise, and the concentration of the eluted components is detected to measure the composition distribution (crystallinity distribution).
The temperature rising elution fractionation (Temperature R
ising Elution Fractionati
on; TREF). At the same time, the sequentially eluted components were added to the high temperature GPC (Size Exclusion Chr.
The molecular weight and the molecular weight distribution are measured by analysis by omatograph (SEC). In the present invention, the above-mentioned data was measured using a cross fractionation chromatograph apparatus (Model CFC-T150A manufactured by Mitsubishi Petrochemical Co., Ltd.) equipped with both the above-mentioned temperature rising elution fractionation part and high temperature GPC part as a system.

In the polyethylene resin used in the present invention, the range of the temperature at which 10% by weight is eluted by the cross fractionation method and the temperature at which 100% by weight is completed is usually 30 ° C. or less, preferably 28 ° C. or less. If this temperature range exceeds 30 ° C,
In the polyethylene resin, a component having high crystallinity and a component having low crystallinity are present at the same time, and the stretching suitability is lowered,
When the film is stretched, the film may be broken or the film may be unevenly stretched, resulting in unevenness of the film surface, which makes it difficult to increase the stretching ratio.

The polyethylene resin used in the present invention has a Mw / Mn value measured by the cross fractionation method,
Usually, it is within the range of 1.5 to 3.5, preferably 1.7 to 3.0. If this value is less than 1.5,
Although the strength of the stretched film is improved, the resin becomes difficult to flow when melted, which makes molding difficult. On the other hand, this value is 3.5
When the value exceeds the above range, the variation in the molecular weight distribution becomes large, and the abundance ratio of low molecular weight molecules and high molecular weight molecules increases, and the stretching suitability decreases, causing film breakage during stretching and uneven film surface due to uneven stretching. Therefore, it becomes difficult to obtain a large draw ratio. That is, it is difficult to obtain a thin and tough stretched film having a high stretch ratio.

Differential Scanning Calorimetric Analysis Differential scanning calorimetric analysis in the present invention was carried out by the following method. About 10 mg of a polyethylene resin sample was put in an aluminum pan and measured with a differential scanning calorimeter (DSC) (SSC5200 manufactured by Seiko Instruments Inc.). The measurement conditions are
After the sample was once melted, it was cooled to −50 ° C. at a rate of 5 ° C./minute, and then heated at a rate of 5 ° C./minute for measurement.

The polyethylene resin used in the present invention usually has one crystal melting peak in differential scanning calorimetry, and has a melting peak temperature and a temperature range within 20 ° C. until all the crystals are melted. Is preferred. The single crystal melting peak includes the case where the peak is not clearly divided into two or more peaks.

The presence of a plurality of crystal melting peaks means the presence of a plurality of components having different crystallinity, in which case the ductility at the time of stretching is lowered, and a stretched film having a high stretch ratio is obtained. Becomes difficult. Melting peak is 1
However, if the temperature range from the melting peak temperature to the end of melting of all the crystals exceeds 20 ° C., the difference in crystallinity between the polyethylene molecules having high crystallinity and the one having low crystallinity becomes large, After all, the stretchability during stretching is lowered, and it becomes difficult to obtain a stretched film having a high stretch ratio.

Density The polyethylene resin used in the present invention usually has a density of 0.860 to 0.950 g / cm ³ , preferably 0.8.
It is in the range of 70 to 0.945 g / cm ³ . When the density is less than 0.860 g / cm ³ , the crystallinity of the polyethylene resin is low and the heat resistance of the stretched film is reduced. On the other hand, if it exceeds 0.950 g / cm ³ , problems will occur in the flexibility and elongation of the obtained stretched film.

Optional Ingredients In the present invention, within the range that does not impair the object of the present invention, the above-mentioned polyethylene-based resin may be replaced with another thermoplastic resin,
For example, a low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, polypropylene, ethylene-propylene rubber, polyvinyl acetate, polybutene, etc. may be added to form a stretched film. The blending ratio of the other thermoplastic resin is usually 30% by weight or less based on the whole resin component. Among these thermoplastic resins, linear low density polyethylene is preferable. In the present invention, within the range that does not impair the physical properties of the polyethylene resin stretched film, phenol type, phosphorus type, amine type,
Sulfur-based antioxidants, metal damage inhibitors, flame retardants, fillers, antistatic agents, stabilizers, pigments and the like may be added.

Crosslinking The polyethylene resin in the present invention may be crosslinked depending on the heat resistance of the finally obtained stretched film and the stretching method. As a general crosslinking method,
Examples include a method of thermally decomposing a radical generator such as a peroxide mixed in a resin to crosslink, crosslinking by irradiation of ionizing radiation, crosslinking by irradiation of ionizing radiation in the presence of a polyfunctional monomer, and silane crosslinking. .

Production Method of Stretched Film The production method of the stretched film of the present invention is not particularly limited. For example, there may be mentioned a tenter stretching method, a roll stretching method, a stretching method using another stretching device, or a tubular stretching method after forming a raw sheet of the above-mentioned polyethylene resin by a T-die method. These stretching processing methods may be performed on only one axis of the film, or may be performed on two axes. Further, a plurality of devices may be used in combination, and for example, a sequential stretching method of performing tenter transverse axis stretching may be adopted as a post-process of roll longitudinal uniaxial stretching.

[0028]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. Gap, suitability during stretching (stretch ratio, thin wall limit) and physical properties of stretched film at the maximum stretchable ratio (tensile strength, Elmendorf tear strength)
The measuring method and the evaluating method of are as follows.

1. Stretching ratio: The suitability at the time of stretching was determined by the ratio that can be stretched according to the following criteria. ◯: The film was not cut during stretching, and the obtained film had a good appearance. Δ: The film was not cut during stretching, but the obtained film had unevenness and had a poor appearance. X: The film is often cut during stretching, which makes industrial production difficult.

2. Thin-wall limit: The stretched film thickness obtained when the suitability at the time of stretching was set to the maximum drawable ratio based on the criteria of the preceding paragraph was determined as the thin-wall limit.

3. Tensile strength: The strength of the obtained film in the stretching (vertical) direction was measured according to JIS Z 1702.

4. Elmendorf tear strength: JIS P
According to 8116, stretching of the obtained film (vertical)
The strength in the direction was measured.

Example 1 A polyethylene-based resin (exxon resin) obtained by using a metallocene compound as a polymerization catalyst.
EXACT3027 manufactured by Chemical Co .: Density = 0.900 g
/ Cm ³ ; Mw / Mn = 2.0; Measurement results by the cross fractionation method and DSC are shown in Table 1. ) T
A die sheet is used to produce a 0.12 mm thick blank sheet at a mold temperature of 230 ° C., and then an electron beam of 700 kV is applied to this sheet.
Irradiation was performed at an acceleration voltage of 4.0 Mrad. Next, the irradiation element sheet was longitudinally uniaxially stretched by a roll stretching method at a stretching temperature of 90 ° C. and a stretching ratio of 3 to 6 to obtain a stretched film. With respect to the obtained polyethylene-based resin stretched film, suitability at the time of stretching (stretching ratio, thin wall limit) and physical properties of the stretched film (tensile strength, Elmendorf tear strength) were measured and evaluated. The results are shown in Table 1.

Example 2 A polyethylene-based resin (exxon resin) obtained by using a metallocene compound as a polymerization catalyst.
EXACT3001: manufactured by Chemical Co., Ltd. Density = 0.910 g
/ Cm ³ ; Mw / Mn = 2.0; Measurement results by the cross fractionation method and DSC are shown in Table 1. ) Using a T-die method at a mold temperature of 230 ° C. and a thickness of 0.12 m.
Immediately after producing the elementary sheet of m, longitudinal uniaxial stretching was carried out in the same manner as in Example 1 to obtain a stretched film. The obtained polyethylene resin stretched film was measured and evaluated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 1) Linear low-density polyethylene resin (made by Idemitsu Petrochemical Co., Ltd., trade name: 1044D, density =
0.925 g / cm ³ ; weight average molecular weight / number average molecular weight = 4.0) was used to prepare a raw sheet by the T-die method in the same manner as in Example 1, followed by electron beam irradiation, and this was uniaxially longitudinally aligned. Stretching was performed to obtain a stretched film. The obtained polyethylene resin stretched film was measured and evaluated in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 2 Linear low-density polyethylene resin (manufactured by Tosoh Corporation, trade name: 43-1, density = 0.905)
g / cm ³ ; weight average molecular weight / number average molecular weight = 4.4)
Was used to prepare a raw sheet by the T-die method in the same manner as in Example 2, and then longitudinally uniaxially stretched to obtain a stretched film. The obtained polyethylene resin stretched film was measured and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0037]

[Table 1]

[0038]

EFFECTS OF THE INVENTION According to the present invention, there is provided a polyethylene resin stretched film which has been stretched to a high stretch ratio and has a thin wall and is excellent in beauty, flexibility, toughness and twistability. The non-crosslinked stretched film is also excellent in recyclability. Therefore, by using the stretched polyethylene resin film of the present invention, it is possible to provide a package which is uniformly beautiful and has excellent flexibility and toughness in twist packaging and other light packaging fields in which twistability is utilized.

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Claims (5)

[Claims] 1. A polyethylene resin stretched film obtained by stretching a polyethylene resin obtained by using a metallocene compound containing a tetravalent transition metal as a polymerization catalyst in at least a uniaxial direction. 2. The polyethylene resin has one crystal melting peak measured by using a differential scanning calorimeter (DSC), and has a melting peak temperature and a temperature range until melting of all crystals is 20. The polyethylene-based resin stretched film according to claim 1, which has a temperature within the range of ° C. 3. The polyethylene resin has a density of 0.86.
0 to 0.950 g / cm ³ , the range between the temperature at which 10% by weight is eluted and the temperature at which 100% by weight is dissolved by the cross fractionation method is 30 ° C. or less, and the value of weight average molecular weight / number average molecular weight 3. The stretched polyethylene resin film according to claim 1, wherein the stretched film is 1.5 to 3.5. 4. The density is 0.860 to 0.950 g / cm.
³ , the range between the temperature at which 10% by weight elution and the temperature at which 100% by weight elution ends by the cross fractionation method is 30 ° C. or less, and the value of weight average molecular weight / number average molecular weight is 1.5 to 3. A polyethylene-based resin stretched film obtained by stretching the polyethylene-based resin of 5 in at least a uniaxial direction. 5. The polyethylene resin has one crystal melting peak measured by using a differential scanning calorimeter (DSC), and the melting peak temperature and the temperature range until the melting of all crystals is 20. The polyethylene-based resin stretched film according to claim 4, which has a temperature within the range of ° C.