Polyolefin resin composition and stretch film using the same

Abstract

The present invention provides polyolefin resin composition exhibiting excellent long term durability as well as improved properties, and an article prepared using the same.

Claims

1. A polyolefin resin composition comprising i) a homopolyethylene having a melt index of 0.8 g/10 min or less measured, at 190° C. under a load of 2.16 kg according to ASTM D1238; and ii) an ethylene copolymer comprising a repeat unit derived from an alpha olefin having a carbon number of 4 or more, and the ethylene copolymer has a melt index of 0.5 g/10 min or less measured at 190° C. under a load of 2.16 kg according to ASTM D1238, and an average short chain branch (SCB) number of 6 or less per 1,000 carbon atoms in a molecular weight distribution graph measured by GPC-FTIR, wherein the short chain branch has a carbon number of 4 to 7; wherein the homopolyethylene and the ethylene copolymer are present at a weight ratio of 3:1 to 1:3, and wherein the polyolefin resin composition fulfills the following requirements 1) to 5): 1) a density of 0.930 to 0.960 g/cc measured according to ASTM D1505, 2) a melt index of 0.1 to 0.5 g/10 min measured at 190° C. under a load of 2.16 kg according to ASTM D1238, 3) a melt flow rate ratio (MI.sub.5/MI.sub.2.16) of less than 3.1, 4) a molecular weight distribution of 2.5 to 4.2, 5) a normalized viscosity of 20 to 30% according to the following Equation 1: $\begin{array}{cc}\mathrm{normalized}\mathrm{viscosity}=\left(\frac{\mathrm{Mf}-\mathrm{Mi}}{\mathrm{Mi}}\right)\times 100& \left[\mathrm{Equation}1\right]\end{array}$ wherein: Mi is an initial viscosity of a polyolefin resin composition, which is measured at 240° C., under oxygen free conditions, and Mf is a viscosity of a polyolefin resin composition, which is measured after the polyolefin resin composition is stored at 240° C. for 2,000 seconds under the presence of oxygen.

2. The polyolefin resin composition according to claim 1, wherein the polyolefin resin composition has a weight average molecular weight of 50,000 to 250,000 g/mol measured by gel permeation chromatography.

3. The polyolefin resin composition according to claim 1, wherein the polyolefin resin composition has a tensile strength of greater than 2.0 gf/den, as measured according to ASTM D1709A by forming it into a film having a thickness of 100 μm.

4. The polyolefin resin composition according to claim 1, wherein the polyolefin resin composition has a residual stress of less than 1% measured according to dynamic mechanical analysis (DMA) at 100 s, 140° C.

5. The polyolefin resin composition according to claim 1, wherein the polyolefin resin composition has a density of 0.940 to 0.950 g/cc measured according to ASTM D1505, a melt index of 0.2 to 0.5 g/10 min measured at 190° C. under a load of 2.16 kg according to ASTM D1238, a melt flow rate ratio (MI.sub.5/MI.sub.2.16) of 2 to 3, a molecular weight distribution of 2.5 to 4.0, a normalized viscosity of 25 to 30% according to Equation 1, and a residual stress of 0.1 to 0.4% measured according to dynamic mechanical analysis (DMA) at 100 s, 140° C.

6. The polyolefin resin composition according to claim 1, wherein the homopolyethylene has a melt index of 0.4 to 0.8 g/10 min measured at 190° C. under a load of 2.16 kg according to ASTM D1238, and a density of 0.940 to 0.960 g/cc measured according to ASTM D1505.

7. The polyolefin resin composition according to claim 1, wherein the alpha olefin having a carbon number of 4 or more is 1-butene.

8. The polyolefin resin composition according to claim 1, wherein the ethylene copolymer has a melt index of 0.1 to 0.4 g/10 min measured at 190° C. under a load of 2.16 kg according to ASTM D1238, an average SCB number of 3 to 6 per 1,000 carbon atoms in a molecular weight distribution graph measured by GPC-FTIR, and a density of 0.940 to 0.950 g/cc measured according to ASTM D1505.

9. A method for preparing a polyolefin resin composition comprising: polymerizing ethylene and an alpha olefin having a carbon number of 4 or more, while introducing hydrogen in an amount of 0.1 to 0.5 g/hr, in the presence of a hybrid supported catalyst in which a first transition metal compound of the following Chemical Formula 1 and a second transition metal compound of the following Chemical Formula 2 are supported together on a carrier, to prepare an ethylene copolymer comprising a repeat unit derived from the alpha olefin having a carbon number of 4 or more, wherein the ethylene copolymer has a melt index of 0.5 g/10 min or less measured at 190° C. under a load of 2.16 kg according to ASTM D1238, and an average short chain branch (SCB) number of 6 or less per 1,000 carbon atoms in a molecular weight distribution graph measured by GPC-FTIR; and mixing the ethylene copolymer with a homopolyethylene having a melt index of 0.8 g/10 min or less measured at 190° C. under a load of 2.16 kg according to ASTM D1238 at a weight ratio of 3:1 to 1:3, wherein the alpha olefin is introduced in an amount of 2.0 to 3.0 ml/min, based on an introduction of 10 kg/hr of the ethylene,
(Cp.sup.1(R.sup.a).sub.x).sub.n(Cp.sup.2(R.sup.b).sub.y)M.sup.1Z.sup.1.sub.3-n   [Chemical Formula 1] wherein, in Chemical Formula 1, M.sup.1 is Group 4 transition metal; Cp.sup.1 and Cp.sup.2 are identical or different, and are each independently, cyclopentadienyl, indenyl, 4,5,6,7-tetrahydro-1-indenyl or fluorenyl radical, each of which is unsubstituted or substituted with a C1 to C20 hydrocarbon group; R.sup.a and R.sup.b identical or different, and are each independently, hydrogen, C1 to C20 alkyl, C1 to C10 alkoxy, C2 to C20 alkoxyalkyl, C6 to C20 aryl, C6 to C10 aryloxy, C2 to C20 alkenyl, C7 to C40 alkylaryl, C7 to C40 arylalkyl, C8 to C40 arylalkenyl, or C2 to C10 alkynyl; Z.sup.1 is halogen atom, C1 to C20 alkyl, C2 to C10 alkenyl, C7 to C40 alkylaryl, C7 to C40 arylalkyl, C6 to C20 aryl, substituted or unsubstituted C1 to C20 alkylidene, substituted or unsubstituted amino group, C2 to C20 alkylalkoxy, or C7 to C40 arylalkoxy; n is 0 or 1, x and y are each independently, an integer of 0 to 4,
(Cp.sup.3(R.sup.e).sub.z)B.sup.2(J)M.sup.2Z.sup.2.sub.2   [Chemical Formula 2] wherein, in Chemical Formula 2, M.sup.2 is Group 4 transition metal; Cp.sup.3 is cyclopentadienyl, indenyl, 4,5,6,7-tetrahydro-1-indenyl or fluorenyl radical, each of which is unsubstituted or substituted with a C1 to C20 hydrocarbon group; R.sup.e is hydrogen, C1 to C20 alkyl, C1 to C10 alkoxy, C2 to C20 alkoxyalkyl, C6 to C20 aryl, C6 to C10 aryloxy, C2 to C20 alkenyl, C7 to C40 alkylaryl, C7 to C40 arylalkyl, C8 to C40 arylalkenyl, or C2 to C10 alkynyl; Z.sup.2 is halogen atom, C1 to C20 alkyl, C2 to C10 alkenyl, C7 to C40 alkylaryl, C7 to C40 arylalkyl, C6 to C20 aryl, substituted or unsubstituted C1 to C20 alkylidene, substituted or unsubstituted amino group, C2 to C20 alkylalkoxy, or C7 to C40 arylalkoxy; B.sup.2 is one or more radicals containing carbon, germanium, silicon, phosphorus or nitrogen atom or combinations thereof, which crosslink the (Cp.sup.3(R.sup.e).sub.z) ring with J; J is selected from the group consisting of NR.sup.f, O, PR.sup.f and S, R.sup.f is substituted or unsubstituted C1 to C20 alkyl, or substituted or unsubstituted C6 to C20 aryl, and z is an integer of 0 to 4.

10. The method for preparing a polyolefin resin composition according to claim 9, further comprising a step of homopolymerizing ethylene while introducing hydrogen in an amount of 0.1 to 1 g/hr, in the presence of a hybrid supported catalyst in which a first transition metal compound of the above Chemical Formula 1 and a second transition metal compound of the above Chemical Formula 2 are supported together on a carrier, to prepare the homopolyethylene having a melt index of 0.8 g/10 min or less measured at 190° C. under a load of 2.16 kg according to ASTM D1238, after preparing the ethylene copolymer and before mixing the ethylene copolymer and the homopolyethylene, or before preparing the ethylene copolymer.

11. The method for preparing a polyolefin resin composition according to claim 9, wherein the first transition metal compound is selected from the group consisting of the following compounds: ##STR00007## ##STR00008## ##STR00009##

12. The method for preparing a polyolefin resin composition according to claim 9, wherein the second transition metal compound is selected from the group consisting of the following compounds: ##STR00010## ##STR00011##

13. An article prepared with the polyolefin resin composition according to claim 1.

14. The article according to claim 13, wherein the article is a stretch film or a bale net.

15. The polyolefin resin composition according to claim 1, wherein the repeat unit derived from the alpha olefin having a carbon number of 4 or more is included in an amount of 1 to 5 mol % in the ethylene copolymer.

16. The method for preparing a polyolefin resin composition according to claim 9, wherein in Chemical Formula 2, B.sup.2 is a divalent silane substituted by hydrogen, C1-20 alkyl, C1-20 alkoxy, or C2-20 alkoxyalkyl.

17. The method for preparing a polyolefin resin composition according to claim 9, wherein the first transition metal compound and the second transition metal compound are included at a mole ratio of 1:0.1 to 1:0.9 on the hybrid supported catalyst.

18. The method for preparing a polyolefin resin composition according to claim 9, wherein the polymerizing of the ethylene and the alpha olefin having a carbon number of 4 or more is performed at a temperature of 25 to 500° C., and at a polymerization pressure of 1 to 100 Kgf/cm.sup.2.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 and FIG. 2 are drawings respectively showing the molecular weight distribution curves (full line) and SCB number distributions per 1000 carbon atoms (dots) of the ethylene copolymers prepared in Preparation Example 1 and Preparation Example 2.

(2) FIG. 3 is a drawing showing the molecular weight distribution curve (full line) and SCB number distribution per 1000 carbon atoms (dots) of the polymer in the resin composition used in Comparative Example 4.

MODE FOR INVENTION

(3) The present invention will be explained in more detail in the following examples. However, these examples are presented only as the illustrations of the present invention, and the scope of the present invention is not limited thereby.

(4) Synthesis Example: Preparation of Hybrid Supported Catalyst

(5) Into a 20 L SUS high pressure reactor, 6.0 kg of a toluene solution was introduced and the temperature of the reactor was maintained at 40° C. And, 1,000 g of silica (SYLOPOL™ 948, manufactured by Grace Davison) dehydrated by applying vacuum at 600° C. for 12 hours was introduced into the reactor, and sufficiently dispersed, and then, 80 g of a first metallocene compound (I) of the following structure was dissolved in toluene and introduced, and the resulting solution was stirred at 40° C. for 2 hours to react. Thereafter, stirring was stopped, followed by settling for 30 minutes, and decantation of the reaction solution.

(6) Into the reactor, 2.5 kg of toluene was introduced, 9.4 kg of a solution of 10 wt % methylaluminoxane (MAO)/toluene was introduced, and then, the solution was stirred at 40° C., 200 rpm for 12 hours. After the reaction, stirring was stopped, followed by settling for 30 minutes, and decantation of the reaction solution. And, 3.0 kg of toluene was introduced and stirred for 10 minutes, and then, stirring was stopped, followed by settling for 30 minutes, and decantation of the reaction solution.

(7) Into the reactor, 3.0 kg of toluene was introduced, 314 mL of a solution of 29.2 wt % second metallocene compound (II) of the following structure/toluene was introduced, and then, the resulting solution was stirred at 40° C., 200 rpm for 12 hours. After lowering the temperature of the reactor to a room temperature, stirring was stopped, followed by settling for 30 minutes, and decantation of the reaction solution.

(8) Into the reactor, 2.0 kg of toluene was introduced and stirred for 10 minutes, and then, stirring was stopped, followed by settling for 30 minutes, and decantation of the toluene solution.

(9) Into the reactor, 3.0 kg of hexane was introduced, and the hexane slurry was transferred to a filter dryer, and the hexane solution was filtered. Drying under reduced pressure at 40° C. for 4 hours gave 890 g-SiO.sub.2 hybrid supported catalyst.

(10) ##STR00006##

PREPARATION EXAMPLE 1

Preparation of Ethylene Copolymer (COMO)

(11) In the presence of the hybrid supported catalyst prepared in Synthesis Example, ethylene copolymer was prepared using a hexane slurry stirred tank reactor, by unimodal operation of one reactor. As comonomers, 1-butene was used, and the reactor pressure was maintained at 40 bar, and the polymerization temperature was maintained at 90° C.

(12) Ethylene feed : 10.0 kg/hr

(13) Hydrogen input: 0.2 g/hr

(14) 1-butene input: 2.5 ml/min.

PREPARATION EXAMPLE 2

Preparation of Ethylene Copolymer (COMO)

(15) Ethylene copolymer was prepared by the same method as Preparation Example 1, except that hydrogen input was changed to 0.7 g/hr.

PREPARATION EXAMPLE 3

Preparation of Ethylene Copolymer (COMO)

(16) Ethylene copolymer was prepared by the same method as Preparation Example 1, except that 1-butene input was changed to 3.5 ml/min.

PREPARATION EXAMPLE 4

Preparation of Homopolyethylene (HOMO)

(17) In the presence of the hybrid supported catalyst prepared in Synthesis Example, homopolyethylene was prepared using a hexane slurry stirred tank reactor, by unimodal operation of one reactor (MI=0.6 g/10 min, density=0.952 g/cc, see Table 1 below). The reactor pressure was maintained at 40 bar, and the polymerization temperature was maintained at 90° C.

(18) Ethylene feed : 10.0 kg/hr

(19) Hydrogen input: 0.7 g/hr

PREPARATION EXAMPLE 5

Preparation of Homopolyethylene (HOMO)

(20) Homopolyethylene was prepared by the same method as Preparation Example 4, except that hydrogen input was changed to 2.0 g/hr (MI=1.3 g/10 min, density=0.954 g/cc, see Table 1 below).

EXAMPLE 1

Preparation of a Polyolefin Resin Composition

(21) As shown in the following Table 1, the homopolyethylene prepared in Preparation Example 4 and the ethylene copolymer prepared in Preparation Example 1 were mixed at a weight ratio of 1:1 to prepare a resin composition.

EXAMPLE 2

Preparation of a Polyolefin Resin Composition

(22) As shown in the following Table 1, the homopolyethylene prepared in Preparation Example 4 and the ethylene copolymer prepared in Preparation Example 1 were mixed at a weight ratio of 1:3 to prepare a resin composition.

COMPARATIVE EXAMPLE 1

Preparation of a Polyolefin Resin Composition

(23) As shown in the following Table 1, the homopolyethylene (HOMO) prepared in Preparation Example 4 was used alone.

COMPARATIVE EXAMPLE 2

Preparation of a Polyolefin Resin Composition

(24) As shown in the following Table 1, the ethylene copolymer (COMO) prepared in Preparation Example 1 was used alone.

COMPARATIVE EXAMPLE 3

Preparation of a Polyolefin Resin Composition

(25) As shown in the following Table 1, the ethylene copolymer (COMO) prepared in Preparation Example 2 was used alone.

COMPARATIVE EXAMPLE 4

Preparation of a Polyolefin Resin Composition

(26) As a polyolefin resin composition, ACP7740-F3™ from Basell Company was used (MI: 0.6 g/10 min (measured at 190° C. under a load of 2.16 kg according to ASTM D1238), density: 0.946 g/cc, SCB number per 1000 carbon atoms (SCB per 1000 TC): 4).

COMPARATIVE EXAMPLE 5

Preparation of a Polyolefin Resin Composition

(27) As shown in the following Table 1, the homopolyethylene (HOMO) prepared in Preparation Example 4 and the ethylene copolymer (COMO) prepared in Preparation Example 1 were mixed at a weight ratio of 5:1 to prepare a resin composition.

COMPARATIVE EXAMPLE 6

Preparation of a Polyolefin Resin Composition

(28) As shown in the following Table 1, the homopolyethylene (HOMO) prepared in Preparation Example 4 and the ethylene copolymer (COMO) prepared in Preparation Example 1 were mixed at a weight ratio of 1:5 to prepare a resin composition.

COMPARATIVE EXAMPLE 7

Preparation of a Polyolefin Resin Composition

(29) As shown in the following Table 1, the homopolyethylene (HOMO) prepared in Preparation Example 4 and the ethylene copolymer (COMO) prepared in Preparation Example 2 were mixed at a weight ratio of 1:1 to prepare a resin composition.

COMPARATIVE EXAMPLE 8

Preparation of a Polyolefin Resin Composition

(30) As shown in the following Table 1, the homopolyethylene (HOMO) prepared in Preparation Example 4 and the ethylene copolymer (COMO) prepared in Preparation Example 3 were mixed at a weight ratio of 1:1 to prepare a resin composition.

COMPARATIVE EXAMPLE 9

Preparation of a Polyolefin Resin Composition

(31) As shown in the following Table 1, a resin composition was prepared by the same method as Example 1, except that the homopolyethylene (HOMO) prepared in Preparation Example 5 was used as homopolyethylene (HOMO).

(32) TABLE-US-00001 TABLE 1 Example Comparative Example 1 2 1 2 3 5 6 7 8 9 HOMO Preparation 4 4 4 — — 4 4 4 4 5 Example No. Hydrogen 0.7 0.7 0.7 — — 0.7 0.7 0.7 0.7 2 input(g/hr) MI (g/10 min) 0.6 0.6 0.6 — — 0.6 0.6 0.6 0.6 1.3 density (g/cc) 0.952 0.952 0.952 — — 0.952 0.952 0.952 0.952 0.954 COMO COMO Preparation 1 1 — 1 2 1 1 2 3 1 Example No. Hydrogen 0.2 0.2 — 0.2 0.7 0.2 0.2 0.7 0.2 0.2 input(g/hr) 1-butene 2.5 2.5 — 2.5 2.5 2.5 2.5 2.5 3.5 2.5 input(ml/min) MI (g/10 min) 0.4 0.4 — 0.4 0.6 0.4 0.4 0.6 0.4 0.4 density 0.946 0.946 — 0.946 0.946 0.946 0.946 0.946 0.942 0.946 (g/cc) SCB per 4 4 — 4 4 4 4 4 8 4 1000TC (number) HOMO:COMO 1:1 1:3 HOMO COMO COMO 5:1 1:5 1:1 1:1 1:1 weight ratio alone alone alone

(33) In the Table 1, density was measured according to ASTM D1505.

(34) Melt index (MI) was measured at 190° C. under a load of 2.16 kg according to ASTM D1238.

(35) SCB (short chain branch; number/1,000 C) was measured as follows. The molecular weight distribution curves of the polymer chains making up the ethylene copolymers prepared in Preparation Examples 1 and 2 were derived using GPC (Gel Permeation Chromatography), and indicated as continuous curves in FIG. 1 and FIG. 2. And, each ethylene copolymer was analyzed by FT-IR to derive the distribution of SCB per 1000 carbon atoms (right Y-axis) according to the molecular weight of the polymer chains (X-axis), which is then indicated as a discontinuous dotted line in FIG. 1 and FIG. 2. From the above results, the average value of SCB per 1000 carbon atoms for the whole molecular weight ranges was measured.

(36) FIG. 1 and FIG. 2 are drawings respectively showing the molecular weight distribution curves (full lines) and the distributions of SCB per 1000 carbon atoms (dotted lines) of the ethylene copolymers prepared in Preparation Example 1 and Preparation Example 2.

(37) For comparison, the molecular weight distribution curve (full line) and the distribution of SCB per 1000 carbon atoms (dotted line) of the polymer in the polyolefin resin composition used in Comparative Example 4 were derived by the same method, and shown in FIG. 3. For reference, the average SCB per 1000 carbon atoms in the polymer of Comparative Example 4 was 4.

EXPERIMENTAL EXAMPLE

(38) For the polyolefin resin compositions prepared in Examples and Comparative Examples, the properties were measured as follows, and the results were shown in the following Table 2.

(39) 1) Density (g/cc): measured according to ASTM D1505.

(40) 2) Melt index (MI; g/10 min): measured at 190° C. under a load of 2.16 kg according to ASTM D1238, and indicated as the weight (g) of polymer molten for 10 minutes.

(41) 3) Melt flow rate ratio (MFRR, MI.sub.5/MI.sub.2.16): MI.sub.5 was measured at 190° C. under a load of 5 kg according to ASTM D1238, and then, MFRR was obtained from the ratio of MI.sub.5 to MI.sub.2.16 measured at 190° C. under a load of 2.16 kg according to ASTM D1238.

(42) 4) Weight average molecular weight (Mw; g/mol) and molecular weight distribution (MWD): The weight average molecular weight (Mw) and the number average molecular weight (Mn) of polymer were measured by GPC (gel permeation chromatography, manufactured by Waters Corp.), and molecular weight distribution (MWD) was calculated by dividing the weight average molecular weight by the number average molecular weight.

(43) Specifically, it was measured using Polymer Laboratories PLgel MIX-B 300 mm length column and Waters PL-GPC220 equipment. The evaluation temperature was 160° C., 1,2,4-trichlorobenzene was used as a solvent, and the flow rate was 1 mL/min. A sample was prepared at a concentration of 10 mg/10 mL, and then, fed in an amount of 200 μL. Using a calibration curve obtained using polystyrene standard, Mw and Mn values were derived. As polystyrene standard product, 9 kinds having molecular weights (g/mol) of 2,000/10,000/30,000/70,000/200,000/700,000/2,000,000/4,000,000/10,000,000 were used.

(44) 5) Tensile strength (gf/den): The resin compositions prepared in Examples and Comparative Examples were respectively molded into a film having a thickness of 100 μm, and tensile strength was measured according to ASTM D1709A.

(45) Specifically, under the following molding conditions, the resin composition was molded by a T-die method to prepare a film with a thickness of 100 μm and a width of 600 nm.

(46) [Molding Conditions]

(47) Molding machine: 40 mm diameter T-die molding machine screw: L/D 24

(48) screw rpm: 60, molding temperature: 280° C.

(49) 6) Normalized viscosity (%): Normalized viscosity was measured based on change in rheological properties, and from the result, long term durability was evaluated.

(50) Specifically, the initial viscosity (Mi) was measured at 240° C. under oxygen free conditions using Discovery Hybrid Rheometer (DHR2, TA Instruments), and then, viscosity after storage (Mf) at 240° C. under the presence of oxygen for 2000 seconds was measured, and change in rheological properties was observed, and normalized viscosity (%) was calculated according to the following Equation 1. The smaller value is favorable in terms of long term durability.

(51) $\begin{array}{cc}\mathrm{normalized}\mathrm{viscosity}=\left(\frac{\mathrm{Mf}-\mathrm{Mi}}{\mathrm{Mi}}\right)\times 100& \left[\mathrm{Equation}1\right]\end{array}$

(52) Mi: the initial viscosity of a polyolefin resin composition (measured at 240° C., under oxygen free conditions)

(53) Mf: the viscosity of a polyolefin resin composition, measured after the polyolefin resin composition is stored at 240° C. for 2,000 seconds under the presence of oxygen.

(54) 7) Residual stress (at 100 s, 140° C.): measured according to DMA (Dynamic Mechanical Analysis). Specifically, each resin composition according to Examples and Comparative Examples was taken, and 200% strain was applied at 140° C., and then, residual stress change was observed for 100 seconds. Using Discovery Hybrid Rheometer (DHR) of TA Instruments, each resin composition was sufficiently loaded as a sample between the upper and the lower plates respectively having diameter of 25 mm, and dissolved at 140° C., and then, fixed with a gap of 1 mm, and residual stress was measured.

(55) 8) Processibility: Bale nets were prepared using the resin compositions of Examples and Comparative Examples. Specifically, each resin composition according to Examples and Comparative Examples was taken to prepare a HDPE film, which is then cut in a machine direction, and drawn 8 times to prepare a bale net, and at this time, the processibility of the resin composition was evaluated according to the following standard.

(56) Good: capable of easily preparing a bale net through drawing

(57) Poor: the film is broken while progressing drawing for the preparation of a bale net

(58) TABLE-US-00002 TABLE 2 Example Comparative Example 1 2 1 2 3 4 5 6 7 8 9 Density(g/cc) 0.948 0.947 0.952 0.946 0.946 0.946 0.951 0.946 0.948 0.945 0.949 MI (g/10 min) 0.5 0.4 0.6 0.4 0.6 0.6 0.6 0.4 0.5 0.5 1.0 MFRR 3.0 3.0 2.9 2.9 2.9 3.3 2.9 2.9 3.0 3.3 3.7 Mw(g/mol, 190K 190K 190K 190K 180K 190K 190K 180K 180K 180K 170K K = x10.sup.3) MWD 4.0 4.0 3.0 4.0 4.0 5.0 4.0 4.0 4.4 4.7 5.0 Tensile 2.5< 2.4 2.5< 2.0< 1.7 1.7 2.2 1.8 2.5< 2.0 1.5 strength (gf/den) Normalized 26 27 24 33 35 22 26 33 34 37 — viscosity (%) Residual 0.30 — — 0.44 0.22 0.18 — — — — — stress(at 100 s, 140° C.) (%) processibility good — Cannnot good good Good — — — — — be processed In the Table 2, “—” means not being measured.

(59) As the result of experiments, the resin compositions of Examples 1 and 2 wherein homopolyethylene, and ethylene copolymer prepared in Preparation Example 1 having MI of 0.5 g/10 min or less and SCB of 6 or less are used at the optimum mixing ratio, exhibited excellent effects in terms of processibility and long term durability as well as basic properties, and particularly, exhibited tensile strength greater than 2.0 gf/den, thus also exhibiting remarkably improved effect in terms of mechanical properties.