KR101862928B1 - Linear Medium Density Polyethylene Resin Composition and Article Produced with the Same - Google Patents

Abstract

TECHNICAL FIELD The present invention relates to a linear medium density polyethylene resin composition and a molded article made therefrom, and more particularly to a linear medium density polyethylene resin composition suitable for use in rotational molding and a molded article made therefrom.
The linear medium density polyethylene resin composition according to the present invention is a linear medium density polyethylene resin composition comprising silicon, titanium, magnesium and a polyethylene resin, wherein the composition distribution width index (CDBI) is 60% or less, / Ti) is in the range of 0.01 to 1.

Description

TECHNICAL FIELD [0001] The present invention relates to a linear medium density polyethylene resin composition and a molded article produced therefrom,

TECHNICAL FIELD The present invention relates to a linear medium density polyethylene resin composition and a molded article made therefrom, and more particularly to a linear medium density polyethylene resin composition suitable for use in rotational molding and a molded article made therefrom.

Rotational molding is a molding method applied to the production of large-sized containers with empty spaces or complex shaped products. It can be applied to the manufacture of various products such as chemical tanks, recreational transportation vehicles, containers, medium-sized playground equipment and offshore structures There is a way. This method is advantageous in producing a small quantity of various products because it is easy to produce and replace various products according to the production of a mold, and also has a merit that a large product can be produced economically.

Almost all common thermoplastic resins can be used for rotational molding, but polyethylene is the most used with more than 80%. Particularly, a linear medium density polyethylene having good flowability capable of forming a container in a molten state and having good mechanical properties such as low temperature impact strength is widely used.

Crushed powder-type polyethylene which passes through 35 mesh is used for the rotation molding method without pressure or shear stress and heat and biaxial rotation. Pinhole-like defects are generated in the appearance of the molding when the sintering between the powders is slow Therefore, the faster the sintering between the powders, the better the appearance.

KP 10-2004-7017709 discloses a polyethylene for rotational molding which is produced by copolymerizing ethylene and an alpha-olefin in the same gas phase reactor as the present invention, and a method for producing the same, but does not suggest a method for reducing the occurrence of pinholes, Indu Chaudhary et al., &Quot; Processing Enhancers for Rotational Molding of Polyethylene ", Polymer Engineering and Science, October 2001, Vol. 41, No. 10, a blend of low molecular weight additives such as mineral oil and glycerol monostearate has been introduced to improve powder sintering, but its relation to mechanical properties has not been verified. In addition, KP10-1011168 claims to improve the appearance with an improved metallocene catalyst, but it is not an improvement of the Ziegler-Natta catalyst-based linear medium density polyethylene product, which accounts for most of the rotational molding.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide a linear medium density polyethylene resin composition and a molded article which exhibit excellent appearance due to less occurrence of surface pinholes due to powder sintering characteristics at the time of molding.

According to an aspect of the present invention,

1. A linear medium density polyethylene resin composition comprising silicon, titanium, magnesium and a polyethylene resin,

The composition distribution width index (CDBI) is 60% or less,

Wherein the molar ratio of the silicon to titanium (Si / Ti) is 0.01 to 1. The linear medium-density polyethylene resin composition for rotary molding according to claim 1,

Another aspect of the present invention relates to a molded article made of the polyethylene resin composition.

The polyethylene resin composition according to the present invention exhibits excellent powder sintering characteristics at the time of molding, resulting in less appearance of surface pinholes and excellent appearance.

In particular, it exhibits the desired results when used in rotational molding, and thus can be usefully used in the production of various molded articles.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graphical illustration of a process for the preparation of a polymeric material according to the method of Bharat Indu Chaudhary et al., &Quot; Processing Enhancers for Rotational Molding of Polyethylene ", Polymer Engineering and Science, October 2001, 41, No. 10 is a schematic view for explaining a method of setting a sintering type according to a sintering time measuring method disclosed in Japanese Unexamined Patent Application,

Hereinafter, the present invention will be described in more detail.

The present invention provides a linear medium density polyethylene resin composition capable of shortening the cycle time by the powder sintering property at the time of molding.

A polyethylene resin composition according to an embodiment of the present invention is a linear, medium-density polyethylene resin composition comprising silicon, titanium, magnesium and a polyethylene resin, wherein the composition distribution breadth index (CDBI) And the molar ratio of silicon to titanium (Si / Ti) is 0.01 to 1.

According to one embodiment of the present invention, it is preferable to include Si, Ti, and Mg.

Particularly, even if Si is not contained and the CDBI is 60% or less, the sintering property is not improved, and pinholes are more likely to appear on the outer surface when the final product is molded, which is not preferable.

According to one embodiment of the present invention, the molar ratio of Si / Ti is preferably 0.01 to 1. If the molar ratio of Si / Ti in the polyethylene resin composition is less than 0.01, the effect of improving the appearance may be lowered. If the molar ratio of Si / Ti is more than 1, the molding of the polyethylene resin composition may be deteriorated.

The composition distribution width index according to the present invention was calculated from data measured at a crystallization rate of 0.2 / min using CRTSTAF (Crystallization analysis Fractionation). Here, the composition distribution width index represents the weight percentage of the copolymer contained within 50% of the mol% at 50% of the cumulative fraction of the copolymer distribution curve. For example, a relatively high compositional distribution width index indicates that most polymers have a comonomer content that is within 50% of the intermediate comonomer content, which means that the polymer is relatively uniform.

According to an embodiment of the present invention, the CDBI is preferably 60% or less, and when the CDBI is more than 60%, the sintering time becomes long and pinholes on the surface are increased.

According to one embodiment of the present invention, the melt index (ASTM D1238, 230 DEG C, 2.16 kg) of the linear medium density polyethylene is 1 to 15 g / 10 min, preferably 3 to 10 g / 10 min. When the MI is less than 1 g / 10 min, the flowability is lowered and rotational molding is difficult. When the MI is 15 g / 10 min or more, the low temperature impact strength and the environmental stress crack resistance (ESCR) .

According to an embodiment of the present invention, the density of the linear medium density polyethylene (ASTM D 1505, 23 ° C) is 0.930 to 0.945 g / cm ³ , preferably 0.934 to 0.941 g / cm ³ . When the amount is lower than the above range, the bending strength is lowered and generally the basic required physical properties of the rotary molded article containing the contents such as water can not be matched. When it is higher than the above range, the low temperature impact strength and the environmental stress crack resistance (ESCR) There may be a problem with the long-term storage stability.

According to one embodiment of the present invention, 0.01 to 0.5 part by weight, preferably 0.05 to 0.2 part by weight, preferably 0.01 to 0.3 part by weight, preferably 0.05 to 0.2 part by weight of an antioxidant is added to 100 parts by weight of the total amount of the polyethylene resin composition And 0.01 to 0.5 parts by weight, preferably 0.1 to 0.3 parts by weight of a UV stabilizer.

If the content of the antioxidant is less than 0.01 parts by weight, discoloration during storage and viscosity change during processing may occur. If the content of the antioxidant exceeds 0.5 parts by weight, the mechanical properties of the resin may be deteriorated. If the content of the neutralizing agent is less than 0.01 parts by weight, discoloration and viscosity change during processing may occur. If the amount of the neutralizing agent is more than 0.3 parts by weight, changes in physical properties such as color and strength may occur. The UV stabilizer content is less than 0.01 part by weight and there are problems such as color discoloration and impact strength lowering in outdoor storage, and if it exceeds 0.5 part by weight, the mechanical properties of the resin may be lowered.

Representative examples of the antioxidant include 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene (1,3,5- , 4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene, 1,6-bis [3- (3,5- (3,5-di-tert-butyl-4-hydroxyphenyl) propionamido] hexane), 1,6-bis [3- Butyl-4-hydroxyphenyl) propionamido] propane), tetrakis [methylene (3,5 4-hydroxyhydrocinnamate)] methane), bis (2,6-di-tert-butyl-4-hydroxyhydrocinnamate) Di-tert-butyl-4-methylphenyl) pentaerythritol-di-phosphite), bis (2,4-di-tert- butylphenyl) pentaerythritol- Bis (2,4-di-tert-butylphenyl) pentraerythritol-di-phosphite) and the like.

Representative examples of the neutralizing agent may include calcium stearate, zinc stearate, magnesium aluminum hydroxycarbonate, zinc oxide, magnesium hydroxystearic acid, or a mixture thereof.

In addition to the above components, other commonly used additives such as a nucleating agent, a heat stabilizer, a weather stabilizer, an antistatic agent, a lubricant, a slip agent, a flame retardant, a pigment and a dye may be blended according to the purpose.

According to an embodiment of the present invention, the polyethylene resin is prepared using a solid catalyst for gas phase polymerization, and the solid catalyst for gas phase polymerization comprises the following steps: Lt; / RTI >

(1) reacting a metal magnesium (Mg) with an organic halide compound represented by the following formula (A) to produce an organic magnesium halide;

R ¹ X (A)

(Wherein R1 is an alkyl group having 1 to 10 carbon atoms, and X is chlorine, bromine or iodine);

(2) a step of reacting the titanium tetravalent titanium compound represented by the following formula (B) in the reaction of the step (1) to prepare a catalyst intermediate,

Ti (OR ₂ ) _m Cl _{4 - m} (B)

(Wherein R ² is an alkyl group having 1 to 10 carbon atoms, and m is an integer or a number of 0 to 4);

(3) adding an alkoxysilane compound represented by the following formula (C) during the reaction of the step (2) or after completing the reaction of the step (2)

R ³ _n Si (OR ⁴ ) _{4 - n} (C)

(Wherein R ³ and R ⁴ are each an alkyl group having 1 to 10 carbon atoms, n is an integer of 0, 1 or 2, and when n is 2, two R 4 s are the same or different).

Examples of the alkoxysilane compound represented by R ³ _n Si (OR ⁴ ) _{4 - n} used as an electron donor material in the step (3) include tetramethoxysilane, methyltrimethoxysilane, dimethyltrimethoxysilane , Trimethylmethoxysilane, ethyltrimethoxysilane, diethyldimethoxysilane, triethylmethoxysilane, vinyltrimethoxysilane, divinyldimethoxysilane, propyltrimethoxysilane, dipropyldimethoxysilane, tripropyl But are not limited to, methoxysilane, isopropyltrimethoxysilane, diisopropyldimethoxysilane, triisopropylmethoxysilane, butyltrimethoxysilane, dibutyldimethoxysilane, tributylmethoxysilane, isobutyltrimethoxysilane, Diisobutyldimethoxysilane, diisobutyldimethoxysilane, triisobutylmethoxysilane, cyclopentyltrimethoxysilane, dicyclopentyldimethoxysilane, cyclopentylmethyldimethoxysilane, cyclohexyltrimethoxysilane, dicyclohexyldimethoxysilane , Cyclohexylmethyldimethoxysilane, tetraethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, trimethylethoxysilane, ethyltriethoxysilane, diethyldiethoxysilane, triethylmethoxysilane, vinyltriethoxysilane, Propyltriethoxysilane, dipropyldiethoxysilane, tripropylethoxysilane, isopropyltriethoxysilane, diisopropyldiethoxysilane, triisopropylethoxysilane, butyltriethoxysilane, dipropyltriethoxysilane, dipropyltriethoxysilane, But are not limited to, ethoxysilane, dibutyldiethoxysilane, tributylethoxysilane, isobutyltriethoxysilane, diisobutyldiethoxysilane, triisobutylethoxysilane, cyclopentyltriethoxysilane, dicyclopentyldiethoxysilane, Cyclopentylmethyldiethoxysilane, cyclohexyltriethoxysilane, dicyclohexyldiethoxysilane, cyclohexylmethyldiethoxysilane, tetrapropoxysilane, methyltripropoxysilane, methyltripropoxysilane, Methyldipropoxysilane, trimethylpropoxysilane, ethyltripropoxysilane, diethyldipropoxysilane, vinyltripropoxysilane, divinyldipropoxysilane, propyltripropoxysilane, dipropyldipropoxysilane, Isopropyltripropoxysilane, diisopropyldipropoxysilane, butyltripropoxysilane, dibutyldipropoxysilane, isobutyltripropoxysilane, diisobutyldipropoxysilane, cyclopentyltripropoxysilane, cyclopentyltripropoxysilane, , Dicyclopentyldipropoxysilane, cyclopentylmethyldipropoxysilane, cyclohexyltripropoxysilane, dicyclohexyldipropoxysilane, and cyclohexylmethyldipropoxysilane. Of these, one or two of them Or more can be used.

In the present invention, each of the reactions of steps (1), (2) and (3) is carried out in the presence of an organic solvent. Examples of the organic solvent include hexane, heptane, cyclohexane, methyl Aliphatic hydrocarbons such as cyclopentane, octane, isooctane, nonane, decane and kerosene may be used as well as aromatic hydrocarbons such as toluene and xylene. More preferred are aromatic hydrocarbons such as hexane, heptane, cyclohexane, methylcyclopentane, Etc. may be used.

Each of the reactions of steps (1), (2) and (3) is performed at a temperature of 20 to 150 ° C, more advantageously 60 to 90 ° C, for efficient reaction.

The solid catalyst prepared according to the present invention may be directly added to the polymerization reactor in the presence of a cocatalyst during polymerization or may be prepared by prepolymerization of one or more olefins in the presence of a cocatalyst in an inert liquid such as an aliphatic hydrocarbon Or may be introduced into the reactor in the form of a prepolymer.

The cocatalyst may be a trialkylaluminum compound having a structure of AlR ⁵ ₃ (wherein R ⁵ is an alkyl group having 1 to 16 carbon atoms, more preferably 2 to 12 carbon atoms). Examples of such a trialkylaluminum compound include triethylaluminum, trimethylaluminum, trinormalpropylaluminum, trinormalbutylaluminum, triisobutylaluminum, trinormalhexylaluminum, trinormaloctalaluminum, tri-2-methylpentylaluminum and the like have. Of these, triethylaluminum, triisobutylaluminum, trinormalhexylaluminum, trinormaloctylaluminum and the like are preferable.

In the present invention, ethylene and alpha-olefin copolymerization is generally carried out at a pressure of 30 bar or less and at a temperature between 40 and 120 < 0 > C. This polymerization reaction is carried out by continuously introducing monomers composed of ethylene or other alpha-olefins into the reactor filled with gaseous ethylene, by bringing gaseous monomers directly into contact with the catalyst system. The alpha-olefin is preferably propylene, 1-butene, 1-hexene, 4-methyl-1-pentene and the like. The polymerization is generally carried out in the presence of a chain growth inhibitor such as hydrogen to control the molecular weight of the polymer, and it is preferable that the volume ratio of hydrogen used for the olefin used in the reaction ranges from 1 to 10%.

The method for measuring the physical properties of the linear medium density polyethylene for rotational molding produced according to the present invention is as follows.

Measurement of the content of each metal composition

The content of the metal component in the resin composition prepared according to the present invention was measured by an X-ray fluorescence (XRF) method. The results are shown in Table 2 .

Melt flow index (melt index, MI)

Lt; RTI ID = 0.0 > 190 C < / RTI > according to ASTM D1238.

density

Measured according to ASTM D1505.

MFRR ( MFRR - Melt Flow Rate Ratio, Melt flow rate ratio )

MI21.6 (21.6 kg load, melt flow index at 190 DEG C) / MI2.16 (2.16 kg load, melt flow index at 190 DEG C)

Flexural modulus ( Flexural modulus )

ASTM D790.

Izod  impact strength ( Izod  Impact strength)

And measured according to ASTM D256.

FNCT (Full Notched Creep Test)

iPT Tensile Creep Tester, Model MOD1719, and measured in accordance with ISO 16770. Igepal 2% solution, and the temperature was set at 50 ° C.

Shore hardness (D scale)

And measured according to ASTM D2240.

Tm (Melting temperature), Tc ( Crystallization temperature )

Was measured at a heating rate of 10 DEG C / min and a cooling rate using DSC (Differential Scanning Calorimeter).

Sintering time

Bharat Indu Chaudhary et al., &Quot; Processing Enhancers for Rotational Molding of Polyethylene ", Polymer Engineering and Science, October 2001, Vol. 41, No. 10 < / RTI > A micro-pellet was produced in a cylindrical shape using 0.5 mm diameter, 0.5 mm height mold and hot press. The micro-pellet was placed on a glass plate set at 130 ° C as a hot stage as shown in Fig. 1 and measured with an optical microscope. In the present invention, the time when the neck radius / particle radius (Y / A) reaches 0.8 is set as the sintering time.

The symbols in FIG. 1 are as follows:

a: particle radius,

a0: initial particle radius,

y: neck radius,

L is the length of the sintered particles,

W: width of the sintered particles (width of the sintered particles)

Pinhole  Number

The pelletized resin was pulverized into a 35 mesh in a pulverizer, and then subjected to rotational molding using a box mold of 15.24 cm x 15.24 cm x 20.32 cm. The thickness of the box wall used was 3 mm. The test sample was molded and die-cut (DIE-CUT) from the mold. The number of pinholes within a 5 cm x 5 cm area was confirmed using an optical microscope (magnification: 10 times), and the number of pinholes per cm 2 was calculated.

Hereinafter, the present invention will be described in more detail with reference to the following examples and comparative examples so that those skilled in the art can easily carry out the present invention. The following examples are only illustrative of the present invention and do not limit the scope of protection of the present invention.

Example  1 to 4, Comparative Example  1-2

[Production of catalyst]

47.8 g (1.968 moles) of magnesium and 5.0 g (0.02 moles) of iodine were suspended in 2400 ml of purified heptane in a 5 liter glass reactor equipped with a mechanical stirrer. 44.9 ml (0.165 mole) of tetrabutoxy titanium and 22.8 ml (0.205 mole) of titanium tetrachloride were poured into the mixture, and then 318 ml (3.05 mole) of 1-chlorobutane was added dropwise over 4 hours Respectively. After the completion of the addition, a further reaction was carried out for 2 hours, followed by washing with a sufficient amount of hexane four times. Then, 8.240 ml (0.037 mol) of tetraethoxysilane was added thereto, followed by further reaction at 60 for 1 hour. The catalyst thus obtained was stored in purified hexane in a slurry state.

[Ethylene and alpha-olefin copolymerization]

Polyethylene was polymerized in the gas-phase fluidized bed reactor with the catalyst prepared above, the co-catalyst trinuclear octylaluminum (TnOA) and the polymerization conditions shown in Table 1 below.

[ Granulation ]

0.05 parts by weight of Irganox-1010, 0.1 parts by weight of Irgafos-168, 0.1 parts by weight of calcium stearate and 0.2 parts by weight of Chimassorb 944FDL were mixed in a Henschel mixer and then granulated in a pelletizer using a twin screw extruder Respectively.

Comparative Example  3

[Production of catalyst]

47.8 g (1.968 moles) of magnesium and 5.0 g (0.02 moles) of iodine were suspended in 2400 ml of purified heptane in a 5 liter glass reactor equipped with a mechanical stirrer. 44.9 ml (0.165 mole) of tetrabutoxy titanium and 22.8 ml (0.205 mole) of titanium tetrachloride were poured into the mixture, and then 318 ml (3.05 mole) of 1-chlorobutane was added dropwise over 4 hours Respectively. After the completion of the addition, a further reaction was carried out for 2 hours, followed by washing with a sufficient amount of hexane four times. The catalyst thus obtained was stored in purified hexane in a slurry state.

[Ethylene and alpha-olefin copolymerization]

Polyethylene was polymerized in the gas-phase fluidized bed reactor with the catalyst prepared above, the co-catalyst trinuclear octylaluminum (TnOA) and the polymerization conditions shown in Table 1 below.

[ Granulation ]

0.05 parts by weight of Irganox-1010, 0.1 parts by weight of Irgafos-168, 0.1 parts by weight of calcium stearate and 0.2 parts by weight of Chimassorb 944FDL were mixed in a Henschel mixer and then granulated in a pelletizer using a twin screw extruder Respectively.

Comparative Example  4

Versalis's linear medium density polyethylene RP50U

Comparative Example  5

Qenos's linear medium density polyethylene LL711UV

unit Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Polymerization temperature ℃ 90 90 90 90 90 90 90 Polymerization pressure kgf / cm2 19.5 19.5 19.5 19.5 19.5 19.5 19.5 Ethylene mol% 37.6 40.4 30.3 52.0 41.2 51.6 45.6 Hydrogen mol% 13.8 11.2 18.6 9.5 10.8 9.4 9.9 1-butene mol% 3.9 3.4 3.0 0 3.3 0 3.6 1-hexene mol% 0 0 0 1.9 0 2 0 Bed Weight kg 70 70 70 70 35 35 35 Residence time hr 7.4 7.4 7.4 7.4 3.7 3.7 7.4 output kg / hr 9.4 9.4 9.4 9.4 9.4 9.4 9.4

unit Example Comparative Example One 2 3 4 One 2 3 4 5 MI g / 10 min. 5.5 3.8 10.3 3.1 3.7 3.0 3.4 9.5 3.1 MFRR - 27 29 30 28 26 25 27 25 23 Density g / cm3 0.934 0.936 0.934 0.938 0.936 0.938 0.937 0.935 0.938 Tm ℃ 124 125 124 127 125 127 126 124 127 Tc ℃ 114 114 113 117 114 117 116 113 115 CDBI 54.3 58.1 48.6 56.9 62.1 63.5 61.5 61.2 65.4 Flexural modulus kgf / cm ² 4,400 4,900 4,300 5,100 5,000 5,200 5,100 4,500 5100 Shore hardness D scale 54 55 54 55 55 55 55 54 55 Izod impact strength, 23 캜 kgcm / cm No break No break No break No break No break No break No break No break No break Izod impact strength, -20 ° C kgcm / cm 11.4 9.5 9.6 7.6 9.8 7.7 8.6 8.9 7.7 FNCT, 50 DEG C, 5 MPa hr 21 43 7 86 36 87 30 7 65 Sintering time sec 210 230 160 240 280 340 300 270 370 Number of pin holes holes / cm ² One 2 0 4 8 38 12 7 48 Si / Ti molar ratio 0.08 0.1 0.09 0.11 0.08 0.1 - - ¹⁾ - ²⁾

¹⁾ and ²⁾ can not be confirmed by third-party products.

When the Si / Ti molar ratio of the resin composition prepared as shown in Table 2 falls within the range of the present invention, when the composition distribution width index (CDBI) is 60% or less, have. However, even though they belong to the same range of Si / Ti molar ratios, in the case of Comparative Examples 1 and 2, when the CDBI exceeds 60%, a desired result is not obtained.

Claims (8)

1. A linear medium density polyethylene resin composition comprising silicon, titanium, magnesium and a polyethylene resin,
The composition distribution width index (CDBI) is 60% or less,
Wherein the molar ratio of silicon to titanium (Si / Ti) is 0.01 to 1,
The linear medium density polyethylene has a melt index (ASTM D 1238, 190 캜, 2.16 kg) of 1 to 15 g / 10 min,
Wherein the linear medium density polyethylene has a density (ASTM D 1505, 23 캜) of 0.930 to 0.945 g / cm ³ . delete delete delete The method according to claim 1,
Characterized by further comprising at least one selected from the group consisting of 0.01 to 0.5 parts by weight of an antioxidant, 0.01 to 0.3 parts by weight of a neutralizing agent and 0.01 to 0.5 parts by weight of a UV stabilizer based on 100 parts by weight of the total of the linear medium density polyethylene resin composition. Medium density polyethylene resin composition. The method according to claim 1,
The polyethylene resin is prepared using a solid catalyst for gas phase polymerization,
The solid catalyst for gas phase polymerization
A linear medium density polyethylene resin composition comprising the steps of:
(1) reacting a metal magnesium (Mg) with an organic halide compound represented by the following formula (A) to produce an organic magnesium halide;
R ¹ X (A)
(Wherein R ¹ is an alkyl group having 1 to 10 carbon atoms, and X is chlorine, bromine or iodine);
(2) a step of reacting the titanium tetravalent titanium compound represented by the following formula (B) in the reaction of the step (1) to prepare a catalyst intermediate,
Ti (OR ² ) _m Cl _4-m (B)
(Wherein R ² is an alkyl group having 1 to 10 carbon atoms, and m is an integer or a number of 0 to 4);
(3) adding an alkoxysilane compound represented by the following formula (C) during the reaction of the step (2) or after completing the reaction of the step (2)
R ³ _n Si (OR ⁴ ) _4-n (C)
(Wherein R ³ and R ⁴ are each an alkyl group having 1 to 10 carbon atoms, n is an integer of 0, 1 or 2, and when n is 2, two R 4 s are the same or different). The linear medium density polyethylene resin composition according to claim 1, wherein the linear medium density polyethylene resin composition is used for rotational molding. A molded article made from the linear medium density polyethylene resin composition according to any one of claims 1 to 7.

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