GB2323364A - Polyethylene resin composition and film thereof - Google Patents

Abstract

A polyethylene resin composition comprising 80 to 99.5% by weight of the following component (A) and 20 to 0.5% by weight of the following component (B): component (A): an ethylene-α-olefin copolymer comprising ethylene and an α-olefin having 3 to 18 carbon atoms wherein the melt flow rate is from 0.1 to 50 g/10 minutes, the density is from 0.900 to 0.940 g/cm<SP>3</SP>, the molecular weight distribution Mw/Mn determined by GPC is from 1.5 to 4, and the composition distribution variation coefficient Cx Cx=#/SCBave. (1) is 0.5 or less; and component (B): a high-density polyethylene wherein the melt flow rate is from 0.1 to 20 g/10 minutes, the density is 0.940 g/cm<SP>3</SP> or more, and the value of [g]* defined by the following equation (2) is from 0.2 to 0.8: [g]* = [#]/[#] 1 (2) In the above formulae: # =standard deviation of the composition distribution and SCBave. = average number of short chain branches per 1000 C atoms; and [#]=intrinsic viscosity of [B] in tetralin at 135‹C, and [#] 1 =intrinsic viscosity of a HDPE of same Mw as [B] calculated from [#] 1 =4.86x10<SP>-4</SP>[Mw]<SP>0.705</SP> where [Mw] is the wt. average MW of [B] by the GPC-LALLS method.

Description

2323364 POLYETHYLENE RESIN COMPOSITION AND FILM THEREOF

BACKGROUND OF THE INVENTION Field of invention

The present invention relates to a polyethylene resin composition wherein the transparency and the stiffness are improved by maintaining the impact resistance strength, anti-blocking property and heat sealing property, and a f ilm thereof.

Prior art

One of the usage for polyethylene resins includes a packaging film. For the packaging film, a good transparency (contents can be sufficiently seen from outside), an ef f icient stif f ness, an excellent auto-f illing suitability and an excellent anti-blocking property are required.

For example, Japanese Patent Kokai Publication No. Hei 2-150442 discloses a technique of improving the transparency and the stiffness by using a resin composition comprising an ethylene- a-olef in copolymer and a highdensity polyethylene wherein the ratio of a melt flow rate of the ethylene- a-olef in copolymer to that of the high-density ethylene is adjusted to the valuewithinthe specifidrange.

- 1 However, this resin composition is unsatisfactory in view of an improvement in transparency, anti-blocking property, impact resistance strength and heat sealing property at a high level with a good balance, because the composition distribution variation coefficient Cx exceeds 0.5.

Variousliteratures indicates that the anti-blocking property has improved in homogenous polyethylenes such as an ethylene- a-olef in copolymer obtained by using a metallocene catalyst which has been recently developed It became apparent that the ethylene- a -olef in copolymer obtained by using a metallocene catalyst is remarkably superior in transparency at the ultra low-density region such as 0.890 g/CM3, but is inferior in transparency at the high-density region at which a rigidity is generally required. Therefore, a material having a well-balanced transparency, a stiffness, an impact residence strength, an anti-blocking property and a heat sealing property has been desired.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a polyethylene resin composition wherein the transparency and the stiffness are improved by maintaining an impact residence strength, an anti-blocking property and a heat 2 - sealing property, and a film thereof.

That is, the present invention provides a polyethylene resin composition comprising 80 to 99.5 % by weight of the following component (A) and 20 to 0.5 % by weight of the following component (B):

component (A): an ethylene- a-olef in copolymer comprising ethylene and an a-olefin having 3 to 18 carbon atoms wherein the melt flow rate is from 0.1 to 50 g/10 minutes, the density is from 0.900 to 0.940 g/CM3, the molecular weight distribution Mw/Mn determined by GPC is f rom 1.5 to 4, and a composition distribution variation coefficient Cx determined by the following equation (1) is 0.5 or less:

Cx = CF/SCBave. (1) (wherein or represents a standard deviation of the composition distribution, and SCBave. represents an average value of a short-chain branch per 1000 carbon atoms (l/1000 C)); and component (B): a high-dens ity polyethylene wherein the melt flow rate is from 0.1 to 20 g/10 minutes, the density is 0.940 g/cm' or more, and a value of [g] defined by the following equation (2):

[g) = [77]/[77], (2) [(wherein [771 represents an intrinsic viscosity of the - 3 component (B) measured in a tetralin solution at 135 T, and [77], represents an intrinsic viscosity of a highdensity polyethylene having the same weight-average molecular weight as that of the component (B) and is calculated by the following equation (3) is from 0.2 to 0.8:

[ 77], = 4.86 X 10 -4[MW] 0.705 (3) (wherein [Mw] represents the weightaverage molecular weight (determined by the GPC-LALLS method) of the component (B))].

The present invention also provides a film comprising the above polyethylene resin composition.

The present invention also provides a multilayer f ilm. wherein at least one surf ace layer is a layer of the above polyethylene resin composition.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described in detail hereinafter.

The component (A) is an ethylene-ct-olef in copolymer comprising ethylene and the a -olef in having 3 to 18 carbon atoms wherein the melt flow rate is from 0.1 to 50 g/10 minutes, the density is from 0.900 to 0.940 g/cm3, the molecular weight distribution Mw/Mn determined by GPC is from 1.5 to 4, and a composition distribution variation - 4 coefficient 0.5 or less:

Cx determined by the following equation (1) is Cx = Or/SCBave. (1) (wherein or represents a standard deviation of the composition distribution, and SCBave. represents an average value of a short-chain branch per 1000 carbon atoms (l/1000 C)).

The a-olefin of the component (A) includes a-olefin having 3 to 18 carbon atoms, such as propylene, butene-1, hexene-1, 4-methylpentene-1, octene-1, decene-1, etc.. a -olef ins having 6 to 8 carbon atoms are preferable. The a -olef ins can be used alone or in combination thereof. When the number of carbon atoms of the a -olef in is too large, the production cost is high and, therefore, it is difficult to perform a commercial production.

The content of a-olefin of the component (A) is normally from 2 to 25% by weight, preferably from 4 to 18% by weight.

The melt f low rate of the component (A) is f rom 0. 1 to 5 0 g / 10 minutes, pref erably f rom 0. 5 to 2 0 g / 10 minutes. When the melt flow rate is too low, the processability becomes inferior. On the other hand, when the melt flow rate is too large, the strength and the processability becomes inferior.

The density of the component (A) is from 0.900 to 0.940 g/cm', pref erably f rom 0. 905 to 0. 938 g/CM3. When the density is too low, the anti-blocking property is inferior. on the other hand, when the density is too high, the strength and transparency are inferior.

The molecular distribution Mw/Mn of the component (A) determined by GPC is f rom 1. 5 to 4, pref erably f rom 2 to 3. When the molecular distribution is too narrow, the processability is inferior. on the other hand, when it is too wide, the strength is weakened.

The composition distribution variation coefficient Cx of the component (A) determined by the above equation (1) is 0.5 or less, preferably from 0.2 to 0.4. When Cx exceeds 0. 5, the strength is weakened and the antiblocking property is inferior.

The measurement method of the composition distribution variation coefficient Cx is summarized as follows.

The ethylene- a-olef in copolymer of the present invention is'dissolved in a solvent heated to a predetermined temperature and the solution is poured into a column in a column oven, and then the temperature of the oven is decreased.

Subsequently, the temperature is raised to a predetermined temperature and then a relative concentration 6 - and a branching degree of the copolymer eluted during the temperature rise are measured by FT-IR which is connected to the column. The temperature is raised to a final temperature while the relative concentration and branching degree of the copolymer eluted at each set temperature are measured.

A composition distribution curve is determined by the resulting relative concentration and branching degree to obtain a composition distribution variation coefficient Cx representing an average composition and a broad range of distribution.

A method for preparing the component (A) of the present invention includes the following methods.

Namely, ethylene and the a-olefin having 3 to 18 carbon atoms are polymerized by using a homogenous catalyst such as metallocene catalysts etc. under a gas-solid, liquidsolid or homogenous liquid phase in the presence or absence of a solvent. The polymerization temperature is normally from 30 to 300T and the polymerization pressure is from an atmospheric pressure to 3000 kg/cm2.

The component (B) of the present invention is a high-density polyethylene wherein the melt flowrateis from 0.1 to 20 g/10 minutes, the density is from 0.940 g/cm' or more, and a value of [ g] def ined by the f ollowing equation 7 - (2) is from 0.2 to 0.8:

191 = 1771/177 11 (2) [(wherein [ 77] represents an intrinsic viscosity of the component (B) determined in a tetralin solution at 135 OC, [77], represents an intrinsic viscosity of a high-density polyethylene having the same weight average molecular weight as that of the component (B) and is determined by the following equation (3):

[ 77], = 4.86 X 10-4 [Mw]0705 (3) (wherein [Mw] represents a weightaverage molecular weight (determined by the GPC-LALLS method) of the component (B)].

The melt flow rate of the component (B) is from 0. 1 to 20 g/10 minutes, preferably from 0.5 to 10 g/10 minutes. When the melt flow rate is too low, so-called fish eye arises because of poor mixing, which results in poor appearance. Furthermore, pinholes are caused by an adhesive in the laminated film. On the other hand, when the melt flow rate is too large, the strength becomes poor The density of the component (B) is 0.940 or more, preferably from 0.945 to 0.955 g/CIR3. When the density is too low, the stiffness is inferior.

The value of [g] of the component (B) defined by the above equation (2) is from 0.2 to 0.8, preferably from 0.3 to 0. 6. when the value of [ g is too small, the deterioration of the dispersion, the appearance and the transparency arises. On the other hand, when the value of [g] is too large, the improving effect of the transparency is insufficient.

The weight- average molecular weight of the component (B) is measured by the GPC-LALLS (Gel Permeation Chromatography-Low angle Laser Light Scattering method).

The equation (3) is described, for example, in H. Rachapudy, G.G. Smith, V.R. Raju, and W.W. Glassley, J. Polym. Sci., Polym. Phys. Ed., 17, 1211(1979).

A method of producing the component (B) includes the following method. That is, ethylene alone, or ethylene and a small amount of a -olef in having 3 to 18 carbon atoms are polymerized by using a Ziegler-Natta catalyst or a metallocene catalyst under a gas-solid, liquid-solid or homogenous liquid phase in the presence or absence of a solvent.. The polymerization temperature is normally from 30 to 300 T and the polymerization pressure is from an atmospheric pressure to 3000 kg /CM2. The high-density polyethylene can be selected from commercially available ones.

The polyethylene resin composition of the present invention comprises 80 to 99.5 % by weight, preferably 90 to 99 % by weight, of the above component (A) and 20 to 0.5 % by weight, preferably 10 to 1 % by weight of the above component (B). When the amount of the component (A) is too small (or the amount of the component (B) is too large), the stiffness becomes large but the strength and the heat sealing property are lowered. on the other hand, when the amount of the component (A) is too large (or the amount of the component (B) is too small), the improving effect of the transparency is inferior.

A method of producing the polyethylene resin composition of the present invention is not specifically limited, but may be carried out by mixing the component (A) and component (B) using a known apparatus such as a single screw extruder, a twin screw extruder, a Banbury mixer and the like. Pellets of the component (A) and the component (B) may also be mixed by using a tumble mixer and the like.

If necessary, antioxidants, lubricants, antiblocking agents, antistatic agents, neutralizing agents, etc. may be contained in the polyethylene resin composition of the present invention.

The polyethylene resin composition of the present invention can be processed into a film by using a known processing method such as an inflation processing, a T-die film processing and the like. The film of the present invention is most suitable as a packaging film.

According to the present invention, it is also possible - 10 to form a multilayer f ilm wherein at least one surf ace layer is the layer of the polyethylene resin composition.

Furthermore, a single layer film or a multilayer film composed of the polyethylene resin composition can be used as a laminated film by laminating with the following base materials.

Examples of the base material include, for example, any polymer having f ilm-forming properties, paper, aluminum f oil, cellophane and the like. Examples of the polymer include, for example, high-density polyethylene, medium-density polyethylene, low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-acrylate copolymer, ionomer, olefin polymer (e.g. polypropylene, poly-l-butene, poly4-methyl-l-pentene, etc.), vinyl polymer (e.g. polyvinyl chloride, polyvinylidene chloride, polystyrene, polyacrylate, polyacrylonitorile, etc.), polyamide (e.g. nylon 6, nylon 66, nylon 7, nylon 10, nylon 11, nylon 12, nylon 6 10, polymetaxylyleneadipamide, etc.), polyester (e. g. polyethylene terephthalate, polyethylene terephthalate/isophthalate, polybutylene terephthalate, etc.), polyvinyl alcohol, ethylene-vinyl alcohol copolymer, polycarbonate and the like. These base materials can be selected appropriately depending on the purpose and kind of articles to be packaged.

As the method of producing the laminated film, for example, a known method such as a laminating method (e.g. dry laminating method, wet laminating method, sand laminating method, hot melt laminating method, etc.), a co-extrusion method, an extrusion laminating method or a combination thereof can be used.

As described above, the present invention can provide a polyethylene resin composition wherein the transparency and the stiffness are improved by maintaining the impact resistance strength, the anti-blocking property and the heat sealing property, and a film thereof.

The following Examples and comparative Examples further illustrate the present invention in detail but are not to be construed to limit the scope thereof.

The measuring method of physical properties is as follows. (1) Density It was measured according to the method def ined in JIS K6760. (2) Melt flow rate (MFR) It was measured according to the method defined in JIS K6760. The load was set to 2.16 kg and the temperature was - 12 set to 190 T. (3) Molecular weight distribution Mw/Mn It was measured under the following conditions by Gel permeation chromatography (GPC).

Apparatus: GPC device, Model 150C, manufactured by Nippon Waters Co., Ltd.

Column: TSK GMH-6, manufactured by Tosoh Co., Ltd.

Solvent: ortho-dichlorobenzene (ODCB) Temperature: 135T.

Flow rate: I ml/minute Pouring concentartion: 10 mg/10 ml ODCB (pouring volume: 500 U 1) - The weight-average molecular weight Mw and numberaverage molecular weight Mn, which were reduced from a calibration curve using a standard polystyrene, were determined and then Mw/Mn was calculated. (4) Composition distribution variation curve (Cx) It was measured by a multifunctional LC manufactured by Tosoh Co., Ltd. An ethylene- a-olef in copolymer used in the present invention was dissolved in an ODCB solvent heated to a predetermined temperature 14 0 T (concentration: 0. 2 g/ 20 ml). The solution (6 ml) was charged in a column filled with sea sands in a column oven, and the temperature of the oven was lowered to 1250C at a rate of 40T / 60 min. and 13 - further lowered from 125T to -140C for 14 hours. Subsequently, the temperature was raised to a predetermined temperature at a rate of 100C / 60 min. and a relative concentration and a branching degree of the copolymer eluted during the temperature rise were measured by FT-IR connected to the column. Seven measurement points are set in the temperature range of 100C. The temperature was raised to the f inal temperature 125T while the relative concentration and branching degree of the eluted copolymer were measured at every set temperature.

Branching degree at every 10C was calculated from a calibration curve obtained from the branching degree of the known polymer and the elution temperature. A composition distribution curve was obtained from the resulting relative concentrations and branching degree, and then a composition distribution variation coefficient Cx representing an average composition and width of distribution was obtained from this curve. (5) [g] A LALLS device (KMX-6) manufactured by Chromatix Co. was connected to a GPC device (HLC811) manufactured by Tosoh Co., Ltd., and then [g] was measured by using 1,2,4trichlorobenzene as a solvent under the conditions of a concentration of 0. 5 % by weight, a temperature of 14 0 'C and - 14 a flow rate of 1 ml/minute. (6) Haze It was measured by the method defined in ASTM D1003. The smaller this value becomes, the better the transparency is. A film obtained by T-die processing was used as a test piece.

(7) 1% Secant Modulus A test piece having a width of 2 cm was cut in the machine direction (MD) or transverse direction (TD) of the film, and each test piece was mounted to a tensile tester at a distance between chucks of 6 cm. The test piece was stretched at a rate of 5 mm/minute. The 1% secant modulus was calculated from the stress at 1% elongation using an equation of 100 x (Stress) / (Cross section) [ kg/cm]. A f ilm obtained by T-die process was used as a test piece.

(8) Anti-blocking property The films were laminated each other and 40 kg/100cm 2 of load was applied to the laminated film, and then conditioning was carried out at 40T for one week. Then, a force required to peeling [g/100 CM 2] was measured by applying a peeling force to the adhesion portion (100 cm') of each sample at a load transfer rate of 20 g/min., using a vertical peeling type blocking tester, under the conditions of a humidity 50 % RH and a temperature of 23T. The smaller this - value becomes, the better the anti-blocking property is. A film obtained by T-die processing was used as a test piece. (9) Dart impact It was measured according to the method described in ASTM D1709 A. A film obtained by T-die processing was used as a test piece. (10) Heat sealing property A laminated f ilm was folded so that the inside portion becomes a film obtained by T-die processing and then heat-sealed (sealing width: 10 mm) by using a heat sealer manufactured by Tester Sangyo Co. under the conditions of a seal surface pressure of 1 kg/cm' and a sealing time of 1. 0 second. In the same manner as described above, heat sealing is performed by changing the temperature (heat sealing temperature) of a sealing bar by 5C. Then, a test piece having a width of 15 mm was cut from the resultant in the direction which is vertical to the sealing surface, and a 1800 peeling strength is measured at a rate of 200 mm/minute using a tensile testing machine.

The temperature at which the heat sealing strength is 4 kg/15mm width is represented as a measure of the sealing property. The lower the value, the better sealing ability is. Examples 1 to 3 and Comparative Examples 1 to 3 16 - To the total amount of 100 parts by weight of the component (A) and component (B) shown in Table 1, 0. 03 parts by weight of erucic acid amide (lubricant), 0.02 parts by weight of ethylene bis oleic acid amide (lubricant) and 0.3 parts by weight of aluminosilicate (anti-blocking agent) were blended, followed by mixing using a mixer to obtain a resin composition. The above lubricants and anti-blocking agent were used as a master batch comprising the component (A) and those having the concentration of 2% by weight and 10% by weight.

Then, the resin composition was processed by using a T-die film processing machine equipped with a 40 mm/50 mm co-extruder (L/D=32) (manufactured by Modern Machinery Co., Ltd., width of die: 600 mm, gap of lip: 0.9mm) under the conditions of a processing temperature of 240T, an extruder rate of 30 kg/h and a chill-roll temperature of 7ST to obtain a f ilm having a thickness of 50 11 m. one surf ace of the f ilm was subjected to a corona treatment whose wet tension is 42 dyne/cm.

This f ilm and a biaxially- stretched f ilm (emblem) base having a thickness of 15 am were subjected to a dry laminating processing using a Test Coater MGD-280 manufactured by Yasui Seiki Co., Ltd., to obtain a laminated f ilm having the construction of nylon/res in composition f ilm.

17 - In the dry laminating processing, TakelackA310/TakenateA-3 manufactured by Takeda Chemical Industries Ltd. as a two-component curing type polyurethane adhesive was used and aging was carried out for 48 hours at 40T after lamination.

The results are shown in Table 1. Comparative Examples 4 to 6 According to the same manner as described in Example 1 except for blending 0.5 parts by weight of aluminosilicate to 100 parts by weight of total amount of the composition (A) and composition (B) shown in Table 2, a resin composition was obtained, respectively. According to the same manner as that described in Example 1, a f ilm and a laminated f ilm were produced, respectively.

The results are shown in Table 2. Examples 4 to 5 According to the same manner as that described in Example 1 except for blending 0.03 parts by weight of erucic acid amide (lubricant), 0. 02 parts by weight of ethylene bis oleic acid amide (lubricant) and 0.5 parts by weight of aluminosilicate (anti-blocking agent) to 100 parts by weight of the total amount of the component (A) and component (B) shown in Table 3 to obtain a resin composition, respectively.

According the same manner as that described in Example 1, a film and a laminated film were produced, respectively.

18 The results are shown in Table 3.

- 19 <Table l>

Example Comparative example 1 2 3 1 2 3 Component (A) Amount (%by weight)' 97 97 93 100 100 Kind -2 Al A2 A2 Al A2 Density (g/cm) 0.915 0.920 0.920 0.915 0.920 MFR (g/10 minutes) 4 4 4 4 4 MwIMn 2.0 2.1 2.1 2.0 2.1 Cx 0.31 0.36 0.36 0.31 0.36 Component (B) Amount (%by weight)' 3 3 7 0 0 Kind -3 Bl Bl B2 - - Density (g/cm3) 0.947 0.947 0.954 MFR (g/10 minutes) 0.95 0.95 1.2 191 0.34 0.34 0.52 - - Haze % 2.4 3.1 4.5 5.3 7.8 1% SM MD kg/cm2 1120 1380 1530 1100 1300 1% SM TD kg/cm2 1140 1460 1650 1100 1300 Anti-blocking 34 32 30 36 30 property g/lOOcm2 Dart impact kg-cm/m NB 1100 970 NB 1380 Heat sealing 117 122 125 117 122 temperature 'C 97 A2 0.920 4 2.1 0.36 3 B3 0.960 0.90 1.0 5.1 1130 1150 36 NB <Table 2>

Comparative example 4 5 6 Component (A) Amount (%by weight)' 97 97 100 Kind-2 A3 A4 A4 Density (g/cm) 0.912 0.921 0.921 MFR (g/10 minutes) 2 2 2 Mw/Mn 3.6 3.7 3.7 Cx 0.52 0.56 0.56 Component (B) Amount (%by weight)' 3 3 0 Kind -3 Bl Bl Density (g/cm) 0.947 0.947 MFR (g/10 minutes) 0.95 0.95 [g] 0.34 0.34 - Haze % 3.9 4.8 5.7 1% SM MD kg/cm2 970 1480 1430 1% SM TD kg /CM2 1020 1610 1520 Anti-blocking 47 30 20 property g/100cm2 Dart impact kg-cm/m 1330 380 470 Heat sealing 120 122 122 temperature. C 1: Amount (% by weight): Component (A) + Component (B) % by weight.

2: Kind of component (A) - 21 <Tabel 3> Example

4 5 Component (A) Amount (%by weight)" 97 97 Kind -2 A5 A6 Density (g/cm) 0.914 0.920 MFR (g/10 minutes) 2.0 2.1 Mw/Mn 2.4 2.3 Cx 0.49 0.50 Component (B) Amount (%by weight)' 3 3 Kind2 B1 B1 Density (g/cm3) 0.947 0.947 MFR (g/10 minutes) 0.95 0.95 [g) 0.34 0.34 Haze % 3.6 4.4 1% SM MD kg/cm2 1020 1450 1% SM TD kg/c& 1040 1510 Anti-blocking property 28 20 g/100Cm2 Dart impact kg.cm/m NB 880 Heat sealing 115 122 temperature 'C 22 - Al: Evolue, SP1540 manufactured by Nippon Evolue Co., Ltd A2: Evolue, SP2040 manufactured by Nippon Evolue Co., Ltd Al is an ethylene-hexene-1 copolymer obtained by polymerizing using a metallocene catalyst (content of hexene-1: 11.1% by weight). A2 is an ethylene-hexene-I copolymer obtained by polymerizing using a metallocene catalyst (content of hexene-1: 8.6 % by weight). A3: Sumikathene L a, FZ201-0 manufactured by Sumitomo Chemical Co., Ltd.

(Arm) A4: Sumikathenela, FZ202-0 manufactured by Sumitomo Chemical Co., Ltd.

A3 is an ethylene-hexene-1 copolymer obtained by copolymerizing using a Ziegler-Natta catalyst (content of hexene-1: 13.6 % by weight). A4 is an ethylene-hexene-1 copolymer obtained by copolymerizing using a ZieglerNatta catalyst (content of hexene-1: 9.4 % by weight). A5: Sumikasen Hi a, CW2 0 01 manufactured by Sumitomo Chemical Co., Ltd. A6: Sumikasen Hi a, CW2002 manufactured by Sumitomo Chemical Co., Ltd.

A5 is an ethylene-hexene-1 copolymer obtained by copolymerizing using a Ziegler-Natta catalyst (content of hexene-1: 12.7 % by weight). A6 is an ethylene-hexene-I copolymer obtained by copolymerizing using a ZieglerNatta - 23 catalyst (content of hexene-1: 9.2 % by weight). 3 Kind of component (B) Bl: Idemitsu polyethylene 440M manufactured by Idemitsu petrochemical Co., Ltd. B2: Showlex F5012M manufactured by Showa Denko Co., Ltd. B3: Chemirez 2010 manufactured by Maruzen Polymer Co., Ltd Bl, B2 and B3 are high-density polyethylenes. 4: NB shows no breaking at critical point for measurement

Claims (9)

1. A polyethylene resin composition comprising 80 to 99.5% by weight of the following component (A) and 20 to 0.5% by weight of the following component (B):

component (A): an ethylene-a-olefin copolymer comprising ethylene and an a-olefin having 3 to 18 carbon atoms wherein the melt flow rate is from 0. 1 to 50 g/10 minutes, the density is from 0.900 to 0.940 g/CM3, the molecular weight distribution Mw/Mn determined by GPC is from 1.5 to 4, and the composition distribution variation coefficient Cx determined by the following equation (1) is 0. 5 or less:

Cx = u/SCBave. wherein a represents the standard deviation of the composition distribution, and SCBave. represents the average number of short-chain branches per 1000 carbon atoms (1/1000 C); and component (B): a high-density polyethylene wherein (1) the melt flow rate is from 0.1 to 20 9/10 minutes, the density is 0.940 g/CM3 or more, and the value of [g] defined by the following equation (2) is from 0.2 to 0.8:

191 = 1771/17711 wherein [771 represents the intrinsic viscosity of component (B) measured in a tetralin solution at 1350C, and [n], represents the intrinsic viscosity of a high-density polyethylene having the same weight-average molecular weight as component (B) calculated by the following equation (3):

[1711 = 4.86 x 10-4 [MW] 0.705 (3) (2) - 26 wherein [Mw] represents the weight average molecular weight determined by the GPC-LALLS method of component (B).

2. A composition according to claim 1, wherein component (A) is an ethylene-a-olefin copolymer polymerized in the presence of a metallocene catalyst.

3. A composition according to claim 1 or 2, wherein the molecular weight distribution Mw/Mn determined by GPC of component (A) is from 2 to 3.

4. A composition according to any one of claims 1 to 3, wherein the composition distribution variation coefficient of component (A) is from 0. 2 to 0.4.

5. A film comprising a polyethylene resin composition according to any one of claims 1 to 4.

6. A multilayer film wherein at least one surface layer is a layer of a polyethylene resin composition according to any one of claims 1 to 4.

7. A composition according to claim 1, substantially as hereinbefore described in any one of Examples 1 to 5.

8. A film according to claim 5, substantially as hereinbefore described in any one of Examples 1 to 5.

9. A multilayer film according to claim 6, substantially as hereinbefore described in any one of Examples 1 to 5.