WO2026010482A1 - Polyethylene resin composition - Google Patents

Abstract

The present invention provides a polyethylene resin composition comprising polyethylene, a neutralizing agent such as metal stearate, and an antioxidant. The polyethylene resin composition is used to manufacture a stretched film and does not cause processing defects such as butterfly patterns on the surface of a film or yellowing during stretching, thus having improved thermal stability.

Description

polyethylene resin composition

Cross-citation with related application(s)

This application claims the benefit of priority to Korean Patent Application No. 10-2024-0086288, filed July 1, 2024, and Korean Patent Application No. 10-2025-0083608, filed June 24, 2025, the entire contents of which are incorporated herein by reference.

The present invention relates to a polyethylene resin composition having improved thermal stability, which enables the production of a stretched film without concern for processing defects.

Conventional multilayer film packaging materials used composite materials blending polyamide (PA), polyethylene terephthalate (PET), and polypropylene (PP). However, with increasing consumer concern for the environment, single-material packaging materials that are easily recyclable are gaining attention. Accordingly, the food packaging and distribution industries are increasingly manufacturing "all-PE" films using only the general-purpose material polyethylene (PE). However, compared to resins like polypropylene and polyethylene terephthalate, polyethylene has disadvantages such as lower heat resistance, stiffness, and transparency.

To solve this problem, active development is being conducted on technologies to increase mechanical properties by uniaxially or biaxially stretching blown and cast films.

However, the polyethylene used for this technology must have excellent film stretchability and mechanical properties, and must also maintain an appropriate level of transparency.

In particular, in the case of high-density polyethylene (HDPE) used in the stretching process, since processing is typically carried out over a wide temperature range from 190℃ to a maximum of 270℃, it is important to minimize deformation or deterioration of the polymer resin's properties by adding appropriate antioxidants and neutralizing agents.

In order to solve the problems of the above-mentioned prior art, the present invention aims to provide a polyethylene resin composition having improved thermal stability, which enables the production of a stretched film without concern about the occurrence of processing defects.

In order to solve the above problem, according to the present invention, a polyethylene resin composition comprising polyethylene having an MFRR (MFR _21.6 /MFR _2.16 ) of 15 to 60, a neutralizing agent of a stearic acid metal salt, and an antioxidant, wherein the polyethylene resin composition satisfies the following conditions (i) to (iii):

(i) a density of 0.9400 to 0.9700 g/cm3 as measured according to ASTM D 792;

(ii) a melt index of 0.50 to 3.00 g/10 min measured under a load of 2.16 kg at 190°C according to ASTM D 1238;

(iii) molecular weight distribution of 10.00 or more; and

Using a rotary rheometer, steps 1 to 3 are sequentially performed according to the following measurement conditions, and the complex viscosity and phase angle at each step are measured, and the complex viscosity value of the first point with the lowest angular frequency is referred to as the zero shear viscosity, and the slope value (b) in the relationship y = a + bx obtained by fitting 7 points of the vGP plot (van. Gurp-Palmen plot) to a straight line model is referred to as the phase angle slope. When the zero shear viscosity and the phase angle slope at steps 1 and 3 are calculated, the polyethylene resin composition satisfies the following conditions (iv) to (vi):

(iv) The change in zero shear viscosity calculated from the difference between the zero shear viscosity in step 1 and the zero shear viscosity in step 3 is 10,000 Pa·s or less;

(v) the zero shear viscosity in step 1 below is 3,000 to 14,000 Pa·s;

(vi) The phase angle slope change is 55 or less;

<Measurement conditions>

Step 1: Temperature 230℃, Frequency 0.1 to 100Hz sweep, Strain 0.5%, oscillation

Step 2: Temperature 230℃, Frequency fixed at 1Hz, Strain 0.5%, oscillation for 30 minutes

Step 3: Temperature 230℃, Frequency 0.1 to 100Hz sweep, Strain 0.5%, oscillation.

In addition, according to the present invention, a stretched film comprising the polyethylene resin composition is provided.

The terminology used herein is for the purpose of describing exemplary embodiments only and is not intended to limit the present invention.

Singular expressions include plural expressions unless the context clearly indicates otherwise.

In this specification, the terms “comprise,” “include,” or “have” are intended to describe a feature, number, step, component, or combination thereof implemented, but do not exclude the possibility of one or more other features, numbers, steps, components, combinations, or additions thereof.

In addition, the terms "about," "substantially," and the like used throughout this specification are used in a meaning that is at or close to the numerical value when manufacturing and material tolerances inherent to the meanings mentioned are presented, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosure in which exact or absolute values are mentioned to aid understanding of the present invention.

Also, throughout this specification, the term “polyethylene” or “ethylene (co)polymer” is a concept that includes both ethylene homopolymer and/or copolymer of ethylene and alpha-olefin.

Unless otherwise defined herein, “copolymerization” may mean block copolymerization, random copolymerization, graft copolymerization or alternating copolymerization, and “copolymer” may mean block copolymer, random copolymer, graft copolymer or alternating copolymer.

The present invention is susceptible to various modifications and takes various forms. Specific examples are illustrated and described in detail below. However, this does not limit the invention to a specific disclosed form, but rather encompasses all modifications, equivalents, and alternatives falling within the spirit and technical scope of the present invention.

Hereinafter, the present invention will be described in detail.

(polyethylene resin composition)

In the case of high-density polyethylene (HDPE), which is commonly used in the stretching process, processing is carried out over a wide temperature range, so it is important to minimize deformation or deterioration of the polymer resin during the process.

Accordingly, the present invention finds out the property requirements related to the thermal stability of a polyethylene resin composition for a uniaxial or biaxially oriented film, and controls these property requirements together with the components of the resin composition, particularly an antioxidant and a neutralizing agent, thereby producing a polyethylene resin composition having excellent thermal stability and capable of producing a oriented film without concern for occurrence of processing defects.

Specifically, the polyethylene resin composition according to the present invention comprises polyethylene having an MFRR (MFR _21.6 /MFR _2.16 ) of 15 to 60, a stearic acid metal salt as a neutralizing agent, and an antioxidant.

The above polyethylene resin composition satisfies the following conditions (i) to (iii):

(i) a density of 0.9400 to 0.9700 g/cm3 as measured according to ASTM D 792;

(ii) a melt index of 0.50 to 3.00 g/10 min measured under a load of 2.16 kg at 190°C according to ASTM D 1238;

(iii) molecular weight distribution of 10.00 or more; and

Using a rotary rheometer, steps 1 to 3 are sequentially performed according to the following measurement conditions, and the complex viscosity and phase angle at each step are measured, and the complex viscosity value of the first point with the lowest angular frequency is referred to as the zero shear viscosity, and the slope value (b) in the relationship y = a + bx obtained by fitting 7 points of the vGP plot (van. Gurp-Palmen plot) to a straight line model is referred to as the phase angle slope. When the zero shear viscosity and the phase angle slope at steps 1 and 3 are calculated, the polyethylene resin composition satisfies the following conditions (iv) to (vi):

(iv) The change in zero shear viscosity calculated from the difference between the zero shear viscosity in step 1 and the zero shear viscosity in step 3 is 10,000 Pa·s or less;

(v) the zero shear viscosity in step 1 below is 3,000 to 14,000 Pa·s;

(vi) The phase angle slope change is 55 or less;

<Measurement conditions>

Step 1: Temperature 230℃, Frequency 0.1 to 100Hz sweep, Strain 0.5%, oscillation

Step 2: Temperature 230℃, Frequency fixed at 1Hz, Strain 0.5%, oscillation for 30 minutes

Step 3: Temperature 230℃, Frequency 0.1 to 100Hz sweep, Strain 0.5%, oscillation.

Specifically, the polyethylene resin composition according to the present invention has a density of 0.9400 to 0.9700 g/cm3 as measured according to ASTM D 792.

The density of the polyethylene resin composition affects the rigidity of the stretched film. If the density of the polyethylene resin composition is less than 0.9400 g/cm ³ , there is a concern that the rigidity of the stretched film may be reduced, and if it exceeds 0.9700 g/cm ³ , the stretchability of the film may be reduced due to excessively high density. More specifically, the density of the polyethylene resin composition may be 0.9400 g/cm ³ or more, or 0.9450 g/cm ³ or more, or 0.9460 g/cm ³ or more, or 0.9465 g/cm ³ or more, and 0.9700 g/cm ³ or less, or 0.9600 g/cm ³ or less, or 0.9550 g/cm ³ or less, or 0.9520 g/cm ³ or less.

In addition, the polyethylene resin composition exhibits a melting index (MI _2.16 ) of 0.50 to 3.00 g/10 min along with a high density as described above.

The melt index of polyethylene resin compositions affects film processability and dimensional stability during the production of stretched films. If the MI _2.16 is less than 0.50 g/10 min, increased processing pressure may lead to reduced processability. If it exceeds 3.00 g/10 min, high fluidity may result in poor bubble stability, potentially resulting in film thickness variations. More specifically, the polyethylene resin composition may exhibit an MI 2.16 of 0.50 g/10 min or more, or 0.80 g/10 min or more, or 1.00 g/10 min or more, or 1.20 g/10 min or more, or more than 1.20 g/10 min, or 1.25 g/10 min or more, and 3.00 g/10 min or less, or 2.50 g/10 min or less, or 2.00 g/10 min or less, or 1.50 g/10 min or less, or _1.35 g/10 min or less.

Meanwhile, in the present invention, the melting index of the polyethylene resin composition can be measured under a load of 2.16 kg at 190°C according to ASTM D1238, and is expressed as the weight (g) of the polymer after melting for 10 minutes.

In addition, the polyethylene resin composition exhibits a broad molecular weight distribution of 10.00 or more.

The molecular weight distribution of a polyethylene resin composition affects processability. If the molecular weight distribution is narrow, less than 10, bubble stability may be reduced during blown film production and resin flowability may be reduced during cast film production. Specifically, since the polyethylene resin composition has a broad molecular weight distribution of 10 or more, it may exhibit improved processability and stretchability during stretched film production. More specifically, the polyethylene resin composition may have a molecular weight distribution of 10.00 or more, or 10.50 or more, or 10.60 or more, or 10.65 or more, and 15.00 or less, or 12.00 or less, or 11.50 or less, or 11.25 or less.

In the present invention, the molecular weight distribution of the polyethylene resin composition can be determined by measuring the weight average molecular weight (Mw) and number average molecular weight (Mn) of polyethylene using gel permeation chromatography (GPC), and calculating the molecular weight distribution (Mw/Mn, polydispersity index) by dividing the weight average molecular weight by the number average molecular weight. Specific measurement methods and conditions are as described in the following test examples.

Meanwhile, when polymers are exposed to high temperature and oxygen conditions, thermo-oxidative degradation occurs, which can cause both chain scission and crosslinking.

Chain scission reduces the molecular weight of the polymer, lowering its viscosity. Furthermore, the molecular weight distribution decreases, diminishing shear thinning behavior. Therefore, while viscosity changes at high shear are minimal, the viscosity at zero shear shows significant differences before and after thermal-oxidative degradation. This chain scission can cause yellowing and carbonization during film extrusion, fracture during stretching, and ultimately, reduce film strength.

Furthermore, when crosslinking occurs, the molecular weight increases due to increased connections between polymer chains. This can be confirmed in the vGP plot. Specifically, before thermal oxidative degradation, the polymer exhibits viscous properties with a high phase angle in the low frequency region. However, after degradation, the phase angle decreases rapidly and elastic properties are observed. Therefore, if crosslinking occurs when thermal stability is low, the relevant portion will tear unevenly during film stretching, resulting in processing defects such as a butterfly pattern on the film surface.

Accordingly, in the present invention, the thermal behavior of the polymer as described above was studied, and as a result, when the thermal stability is high, chain scission and crosslinking of the polymer are reduced, and as a result, the change in complex viscosity and phase angle before and after thermal oxidative decomposition is small, and also, when the thermal stability is high, the crosslinking of the polymer is reduced, the phase angle decrease time is shortened, and as a result, the inflection point of the phase angle is lowered, and using this, the thermal stability of the polyethylene resin composition was defined as the change in zero shear viscosity (Delta Zero shear viscosity), the change in phase angle slope (Delta Phase angle slope), and the inflection point of the phase angle, and each range was optimized.

Specifically, the polyethylene resin composition according to the present invention sequentially performs steps 1 to 3 according to the following measurement conditions, and measures the complex viscosity at each step using a rotational rheometer (ARES), and then, when the complex viscosity value of the first point with the lowest angular frequency is defined as the zero shear viscosity, the zero shear viscosities at steps 1 and 3 are each obtained, and a value calculated from the difference between the zero shear viscosity at step 1 and the zero shear viscosity at step 3, specifically, a value obtained by subtracting the zero shear viscosity at step 1 from the zero shear viscosity at step 3, the change in zero shear viscosity (Delta Zero shear viscosity) (Δ _{Zero shear viscosity} = manufacturing shear viscosity at step 3 - zero shear viscosity at step 1) is 10,000 Pa·s or less.

<Measurement conditions>

Step 1: Temperature 230℃, Frequency 0.1 to 100Hz sweep, Strain 0.5%, oscillation

Step 2: Temperature 230℃, Frequency fixed at 1Hz, Strain 0.5%, oscillation for 30 minutes

Step 3: Temperature 230℃, Frequency 0.1 to 100Hz sweep, Strain 0.5%, oscillation.

More specifically, the polyethylene resin composition may have a zero shear viscosity change of 10,000 Pa·s or less, or 9,000 Pa·s or less, or 8,950 Pa·s or less, and may exhibit excellent thermal stability due to such a low zero shear viscosity change. Meanwhile, since the thermal stability is excellent as the zero shear viscosity change is smaller, the lower limit is not particularly limited, but may be 1,000 Pa·s or more, or 5,000 Pa·s or more, or 7,000 Pa·s or more, or 7,300 Pa·s or more.

In addition, the polyethylene resin composition may have a zero shear viscosity of 3,000 to 14,000 Pa·s when the composite viscosity value of the first point with the lowest angular frequency is defined as the zero shear viscosity after measuring the composite viscosity under the conditions of temperature 230°C, frequency 0.1 to 100 Hz sweep, strain 0.5%, and oscillation using a rotary rheometer as in step 1. If the zero shear viscosity of the polyethylene resin composition is less than 3,000 Pa·s, yellowing and carbonization may occur during film extrusion, or breakage may occur during stretching, and the strength may decrease during film manufacturing. On the other hand, if the zero shear viscosity exceeds 14,000 Pa·s, the processing load may be high during film extrusion, which may decrease the film processability.

In addition, the polyethylene resin composition may be measured by sequentially performing steps 1 to 3 according to the measurement conditions using a rotary rheometer, and the phase angle at each step may be measured, and the slope value (b) in the relationship y = a + bx obtained by fitting 7 points of the vGP plot (van. Gurp-Palmen plot) to a straight line model may be referred to as the phase angle slope, and the phase angle slopes at steps 1 and 3 may be obtained, respectively, and the change in the phase angle slope (Delta Phase angle slope) (Δ _{phase angle slope} = phase angle slope of step 3 - phase angle slope of step 1) may be 55 or less, more specifically, 54 or less, or 53 or less. Since the smaller the phase angle slope change, the better the thermal stability, the lower limit value is not particularly limited, but it can be 10 or more, or 30 or more, or 40 or more, or 45 or more.

In addition, the polyethylene resin composition is oscillated for 30 minutes under high temperature and oxygen conditions of 230°C, a frequency of 1 Hz, as in step 2, using a rotary rheometer, and the phase angle change over time (Step time) is measured. Then, a graph of a phase angle change curve (x-axis: time, y-axis: phase angle) is derived from the result, and a tangent line is drawn before and after the phase angle data in the phase angle change curve. When the point where the two tangent lines meet, that is, the point where the convexity or concaveness of the phase angle change curve changes, that is, the point where the phase angle slope changes from positive to negative or negative to positive, is called an inflection point (s), the inflection point of the phase angle may be 700 seconds or more, or 720 seconds or more, or 730 seconds or more. Since the higher the inflection point of the phase angle is, the better the thermal stability, the upper limit is not particularly limited, but may be 900 seconds or less, or 880 seconds or less.

Meanwhile, in the present invention, the change in zero shear viscosity, the change in phase angle, the inflection point of the zero shear viscosity and the phase angle are calculated by measuring the complex viscosity and phase angle in steps 1 to 3 according to the measurement conditions using a rotational rheometer (ARES Rheometer), and using the values. At this time, the specimen is manufactured by placing a pellet of a polyethylene resin composition on a rheometer, melting it, and pressing it with a gap of 1 mm. The method of measuring the change in zero shear viscosity, the change in phase angle, and the inflection point of the phase angle is described in more detail in the following experimental examples.

The polyethylene resin composition having the above properties specifically includes polyethylene, an antioxidant, and a neutralizing agent. Each component is described in detail below.

(polyethylene)

The polyethylene resin composition according to the present invention comprises polyethylene having an MFRR (MFR _21.6 /MFR _2.16 ) of 15 to 60.

As polyethylene satisfies the above-described MFRR conditions, a polyethylene resin composition satisfying the physical property requirements defined in the present invention can be easily implemented, and as a result, the polyethylene resin composition produced has improved thermal stability, so that a stretched film can be produced without concern about the occurrence of processing defects.

Specifically, the polyethylene may have an MFRR (MFR _21.6 /MFR _2.16 ) of 15.0 or more, or 20.0 or more, or 25.0 or more, or 25.5 or more, or 25.8 or more, and 60 or less, or 55 or less, or 50 or less, or 48.0 or less, or 45.0 or less, or 40.0 or less, or 35.0 or less, or 30.0 or less, or 28.0 or less, or 26.5 or less, or 26.1 or less.

Meanwhile, the MFR _21.6 of the above MFRR is measured at 190°C and under a load of 21.6 kg according to ISO 1133, and the MFR _2.16 is measured at 190°C and under a load of 2.16 kg according to ISO 1133.

In addition, the polyethylene may satisfy the following conditions (b1) and (b2):

(b1) Melt index (MI _2.16 ) measured according to ASTM D 1238: 0.5 to 3.0 g/10 min.

(b2) Density measured according to ASTM D 792: 0.940 to 0.970 g/cm ³ .

Specifically, the polyethylene may have a melt index (MI _2.16 ) measured according to ASTM D 1238 of 0.50 g/10 min or more, or 0.80 g/10 min or more, or 1.00 g/10 min or more, or 1.20 g/10 min or more, or greater than 1.20 g/10 min, or 1.30 g/10 min or more, or 1.32 g/10 min or more, and 3.00 g/10 min or less, or 2.50 g/10 min or less, or 2.00 g/10 min or less, or 1.50 g/10 min or less, or 1.35 g/10 min or less.

In addition, the polyethylene has a density of 0.940 to 0.970 as measured according to ASTM D 792. g/cm ^3. If the density of polyethylene is less than 0.940 g/cm ³ , there is a risk that the rigidity of the stretched film will decrease, and if it is less than 0.970 g/cm 3, there is a risk that the rigidity of the stretched film will decrease. If it exceeds g/cm ³ , the extensibility of the film may be reduced due to an excessively high density. More specifically, the polyethylene may have a density of 0.940 g/cm ³ or more, or 0.941 g/cm ³ or more, or 0.945 g/cm ³ or more, and 0.970 g/cm ³ or less, or 0.965 g/cm ³ or less, or 0.960 g/cm ³ or less, or 0.954 g/cm ³ or less.

Meanwhile, the polyethylene may be a copolymer of ethylene and an alpha-olefin having 3 to 20 carbon atoms. More specifically, it may be a copolymer of ethylene and an alpha-olefin having 4 to 10 carbon atoms. Even more specifically, the polyethylene may be a copolymer of ethylene and 1-hexene.

In addition, the above polyethylene can be produced by polymerizing ethylene and an olefin monomer having 3 to 20 carbon atoms in the presence of a hybrid supported metallocene catalyst including, for example, at least one first metallocene compound selected from compounds represented by the following chemical formula 1; at least one second metallocene compound selected from compounds represented by the following chemical formula 2; and a carrier supporting the first and second metallocene compounds:

[Chemical Formula 1]

In the above chemical formula 1,

M ₁ is a group 4 transition metal,

X ₁₁ and X ₁₂ are each independently a substituted or unsubstituted C _1-20 alkyl or halogen,

R ₁ to R ₅ and R ₇ to R ₁₂ are each independently hydrogen, substituted or unsubstituted C _1-20 alkyl, substituted or unsubstituted C _6-60 aryl, or -(CH ₂ ) _n1 -OR ₁₃ ,

R ₆ is substituted or unsubstituted C _1-20 alkyl, substituted or unsubstituted C _6-60 aryl, or -(CH ₂ ) _n1 -OR ₁₃ ,

At least one of R ₁ to R ₁₂ is -(CH ₂ ) _n1 -OR ₁₃ ,

R ₁₃ is substituted or unsubstituted C _1-20 alkyl,

n1 is an integer from 0 to 10,

[Chemical Formula 2]

In the above chemical formula 2,

M ₂ is a group 4 transition metal,

X ₂₁ and X ₂₂ are each independently a substituted or unsubstituted C _1-20 alkyl or halogen,

T ₂ is C (carbon) or Si (silicon),

Q ₂₁ and Q ₂₂ are each independently a substituted or unsubstituted C _1-20 alkyl, a substituted or unsubstituted C _6-60 aryl, or -(CH ₂ ) _n2 -OR ₃₂ , or Q ₂₁ and Q ₂₂ combine with each other to form a substituted or unsubstituted C _3-20 cycloalkyl ring,

R ₂₀ to R ₃₁ are each independently hydrogen, substituted or unsubstituted C _1-20 alkyl, substituted or unsubstituted C _6-60 aryl, or -(CH ₂ ) _n2 -OR ₃₂ , or two adjacent ones of R ₂₀ to R ₃₁ combine to form a substituted or unsubstituted C _3-20 cycloalkyl ring,

At least one of R ₂₀ to R ₃₁ , Q ₂₁ and Q ₂₂ is -(CH ₂ ) _n2 -OR ₃₂ ,

R ₃₂ is substituted or unsubstituted C _1-20 alkyl,

n2 is an integer from 0 to 10.

In the present invention, the substituents of the chemical formula are described more specifically as follows.

The halogen can be fluorine (F), chlorine (Cl), bromine (Br), or iodine (I).

The C _1-20 alkyl may be a straight-chain, branched-chain or cyclic alkyl. Specifically, the C _1-20 alkyl may be a straight-chain alkyl having 1 to 20 carbon atoms; a straight-chain alkyl having 1 to 10 carbon atoms; a straight-chain alkyl having 1 to 5 carbon atoms; a branched-chain or cyclic alkyl having 3 to 20 carbon atoms; a branched-chain or cyclic alkyl having 3 to 15 carbon atoms; or a branched-chain or cyclic alkyl having 3 to 10 carbon atoms. More specifically, the alkyl having 1 to 20 carbon atoms may be a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, an iso-butyl group, a tert-butyl group, an n-pentyl group, an iso-pentyl group or a cyclohexyl group.

The C _3-20 cycloalkyl ring may be a ring composed of carbon atoms. It may be a hydrocarbon ring having 3 to 20 carbon atoms; a hydrocarbon ring having 3 to 15 carbon atoms; or a hydrocarbon ring having 3 to 10 carbon atoms. More specifically, the C _3-20 cycloalkyl ring may be a cyclopropene ring, a cyclobutene ring, a cyclopentene ring, a cyclohexene ring, or the like.

C _2-20 alkenyl may be straight-chain, branched-chain or cyclic alkenyl. Specifically, the C _2-20 alkenyl may be straight-chain alkenyl having 2 to 20 carbon atoms, straight-chain alkenyl having 2 to 10 carbon atoms, straight-chain alkenyl having 2 to 5 carbon atoms, branched-chain alkenyl having 3 to 20 carbon atoms, branched-chain alkenyl having 3 to 15 carbon atoms, branched-chain alkenyl having 3 to 10 carbon atoms, cyclic alkenyl having 5 to 20 carbon atoms or cyclic alkenyl having 5 to 10 carbon atoms. More specifically, the C _2-20 alkenyl may be ethenyl, propenyl, butenyl, pentenyl or cyclohexenyl.

C _1-20 alkoxy may be a straight-chain, branched-chain or cyclic alkoxy group. Specifically, the C _1-20 alkoxy may be a straight-chain alkoxy group having 1 to 20 carbon atoms; a straight-chain alkoxy group having 1 to 10 carbon atoms; a straight-chain alkoxy group having 1 to 5 carbon atoms; a branched-chain or cyclic alkoxy group having 3 to 20 carbon atoms; a branched-chain or cyclic alkoxy group having 3 to 15 carbon atoms; or a branched-chain or cyclic alkoxy group having 3 to 10 carbon atoms. More specifically, the alkoxy group having 1 to 20 carbon atoms may be a methoxy group, an ethoxy group, an n-propoxy group, an iso-propoxy group, an n-butoxy group, an iso-butoxy group, a tert-butoxy group, an n-pentoxy group, an iso-pentoxy group, a neo-pentoxy group or a cyclohexene group.

C _2-20 alkoxyalkyl may be a substituent having a structure including -R _y -OR _z in which one or more hydrogens of alkyl (-R _y ) are replaced with alkoxy (-OR _z ). Specifically, the alkoxyalkyl having C2 to C20 carbon atoms may be a methoxymethyl group, a methoxyethyl group, an ethoxymethyl group, an iso-propoxymethyl group, an iso-propoxyethyl group, an iso-propoxyhectyl group, a tert-butoxymethyl group, a tert-butoxyethyl group, or a tert-butoxyhexyl group.

C _6-60 aryl may refer to a monocyclic, bicyclic or tricyclic aromatic hydrocarbon. Specifically, the C6 to C60 aryl may be a phenyl group, a naphthyl group or anthracenyl group.

C _7-20 alkylaryl may refer to a substituent in which one or more hydrogens of aryl are replaced by alkyl. Specifically, the C _7-20 alkylaryl may be methylphenyl, ethylphenyl, n-propylphenyl, iso-propylphenyl, n-butylphenyl, iso-butylphenyl, tert-butylphenyl, or cyclohexylphenyl.

C _7-20 arylalkyl may refer to a substituent in which one or more hydrogens of alkyl are replaced by aryl. Specifically, the C _7-20 arylalkyl may be a benzyl group, phenylpropyl, or phenylhexyl.

Also, group 4 transition metals can include titanium, zirconium, and hafnium.

The above hybrid supported metallocene catalyst is a hybrid catalyst comprising a first metallocene compound having a high molecular weight and high crystallinity and a second metallocene compound having a low molecular weight and low crystallinity.

In single-reactor copolymerization using a hybrid supported metallocene catalyst, it is important to control the expression of differences in polymerization characteristics between the metallocene compounds constituting the hybrid supported metallocene catalyst under a single copolymerization condition. In particular, to obtain polyethylene suitable for biaxial stretching, both high-molecular-weight, high-crystallinity components and low-molecular-weight, low-crystallinity components must be present together. Accordingly, in the present invention, a hybrid supported metallocene catalyst obtained by combining the first and second metallocene compounds was used to produce polyethylene exhibiting respective characteristics under a single copolymerization condition.

The first metallocene compound represented by the above chemical formula 1 has the characteristics of a lower polymerization rate of the comonomer and a higher polymerization rate of the ethylene monomer compared to the second metallocene compound due to the structure of the non-bridged ligand bonded to the central metal. As a result, under ethylene/1-hexene copolymerization conditions, it can express a high molecular weight, high crystallinity polyethylene with a small number of SCBs and a high Mw.

Meanwhile, the second metallocene compound represented by Chemical Formula 2 has a higher polymerization rate of comonomer and a lower polymerization rate of ethylene monomer compared to the first metallocene compound due to the bridge-type ligand structure bonded to the central metal. As a result, it can express a low molecular weight, low crystallinity polyethylene with a high SCB and a low Mw under ethylene/1-hexene copolymerization conditions.

Specifically, the central metal (M ₁ ) of chemical formula 1 may be a Group 4 transition metal, specifically Ti, Zr, or Hf, and more specifically Zr or Hf.

Specifically, X ₁₁ and X ₁₂ can each independently be methyl or chloro, and more specifically, X ₁₁ and X ₁₂ can both be methyl, or both can be chloro.

Specifically, R ₁ to R ₅ and R ₇ to R ₁₂ are each independently hydrogen, substituted or unsubstituted C _1-20 alkyl, substituted or unsubstituted C _6-20 aryl, or -(CH ₂ ) _n1 -OR ₁₃ , and R ₆ is substituted or unsubstituted C _1-20 alkyl, substituted or unsubstituted C _6-20 aryl, or -(CH ₂ ) _n1 -OR ₁₃ , provided that one or both of R ₁ to R ₅ and R ₇ to R ₁₂ can be -(CH ₂ ) _n1 -OR ₁₃ .

Specifically, R ₁ to R ₅ can each independently be hydrogen, methyl, isopropyl, n-butyl, phenyl, or -(CH ₂ ) _n1 -OR _13. More specifically, R ₁ to R ₅ can each independently be hydrogen, methyl, n-butyl, phenyl, or tertbutoxyhexyl.

Specifically, either R ₇ or R ₈ may be -(CH ₂ ) _n1 -OR ₁₃ , and the remainder and R ₁ to R _5, and R ₉ to R ₁₂ may each independently be hydrogen, a substituted or unsubstituted C _1-20 alkyl, a substituted or unsubstituted C _6-60 aryl, or -(CH ₂ ) _n1 -OR ₁₃ .

Specifically, either R ₇ or R ₈ may be -(CH ₂ ) _n1 -OR ₁₃ , while the remainder and R ₉ to R ₁₂ may each be hydrogen. More specifically, either R ₇ or R ₈ may be tert-butoxy hexyl, while the remainder and R ₉ to R ₁₂ may each be hydrogen.

Specifically, R ₁₃ may be tertbutyl.

Specifically, R ₆ is a substituted or unsubstituted C _1-20 alkyl, or a substituted or unsubstituted C _6-60 aryl, wherein the C _1-20 alkyl and C _6-60 aryl may each be independently substituted with C _6-12 aryl or Si(R') ₃ , wherein R' may be C _1-20 alkyl or C _6-10 aryl. More specifically, R ₆ can be unsubstituted C _1-20 alkyl, C _{1-20 alkyl substituted with C 6-12} aryl, C _1-20 alkyl substituted with Si(R') ₃ , unsubstituted C _6-30 aryl, C _6-30 aryl substituted with C _6-12 aryl, C _6-30 aryl substituted with Si(R') ₃ , wherein R' can be C _1-20 alkyl or C _{6-10 aryl} .

More specifically, R ₆ may be an unsubstituted C _1-20 alkyl or C _6-20 aryl, or a C _1-20 alkyl or C _6-20 aryl substituted with phenyl, trimethylsilyl, or triphenylsilyl. Even more specifically, R ₆ may be methyl, ethyl, isopropyl, benzyl, trimethylsilyl methyl, or phenyl.

Specifically, n1 may be an integer from 4 to 10, more specifically, n1 may be an integer from 4 to 7, and even more specifically, n1 may be 6.

Specifically, the first metallocene compound represented by the above chemical formula 1 may be any one selected from the group consisting of:

.

Meanwhile, the method for producing the first metallocene compound represented by the above chemical formula 1 is not particularly limited, but may be produced by a method such as the following reaction scheme 1, for example.

The compound represented by the above chemical formula 1 is difficult to synthesize due to the steric hindrance of the indene ligand, but the compound represented by the above chemical formula 1 can be produced in high yield and high purity according to a method such as the following reaction scheme 1.

Accordingly, according to one embodiment of the present invention, the compound represented by the chemical formula 1 is

A step of preparing a ligand of chemical formula 1-3 by reacting a compound represented by chemical formula 1-1 with a compound represented by chemical formula 1-2; and

It can be produced by a production method including a step of reacting a ligand of Chemical Formula 1-3, a compound represented by Chemical Formula 1-4, and a halogen salt of a transition metal represented by Chemical Formula 1-5:

[Reaction Formula 1]

In the above reaction formula 1,

M ₁ , X ₁₁ , X ₁₂ and R ₁ to R ₁₂ are as defined in the above chemical formula 1,

X' is each independently a halogen.

Specifically, the central metal (M ₂ ) of chemical formula 2 may be a Group 4 transition metal such as Ti, Zr, or Hf, and more specifically, may be Zr.

Specifically, X ₂₁ and X ₂₂ can each independently be methyl or chloro, and more specifically, X ₂₁ and X ₂₂ can each be chloro.

Specifically, T ₂ can be C (carbon).

Specifically, at least one of R ₂₀ to R ₃₁ , Q ₂₁ and Q ₂₂ may be -(CH ₂ ) _n2 -OR ₃₂ . More specifically, at least one of R ₂₀ to R ₂₅ , Q ₂₁ and Q ₂₂ may be -(CH ₂ ) _n2 -OR ₃₂ . More specifically, one or both of R ₂₀ to R ₃₁ , Q ₂₁ and Q ₂₂ may be -(CH ₂ ) _n2 -OR ₃₂ . More specifically, one or both of R ₂₀ to R ₂₅ , Q ₂₁ and Q ₂₂ may be -(CH ₂ ) _n2 -OR ₃₂ . Even more specifically, one or both of R ₂₀ to R ₂₅ , Q ₂₁ and Q ₂₂ may be tertbutoxy hexyl.

Specifically, Q ₂₁ and Q ₂₂ are each independently a substituted or unsubstituted C _1-20 alkyl, a substituted or unsubstituted C _6-20 aryl, or -(CH ₂ ) _n2 -OR ₃₂ , or Q ₂₁ and Q ₂₂ may combine with each other to form a substituted or unsubstituted C _3-20 cycloalkyl ring. More specifically, Q ₂₁ and Q ₂₂ are each independently methyl, ethyl, isopropyl, phenyl, or -(CH ₂ ) _n2 -OR ₃₂ , or Q ₂₁ and Q ₂₂ may combine with each other to form a cyclopentene ring or a cyclohexene ring.

Specifically, R ₂₀ to R ₂₃ can each independently be hydrogen, C _1-20 alkyl, C _6-20 aryl, or -(CH ₂ ) _n2 -OR ₃₂ , and more specifically, R ₂₀ to R ₂₃ can each independently be hydrogen, methyl, n-butyl, phenyl, or tert-butoxy hexyl. More specifically, one of R ₂₀ to R ₂₃ can be tert-butoxy hexyl or n-butyl, and the other can be hydrogen, or two of R ₂₀ to R ₂₃ can each independently be methyl, n-butyl, or phenyl, and the other can be hydrogen.

Specifically, R ₂₄ to R ₃₁ are each independently hydrogen, C _1-10 alkyl, C _6-20 aryl, or -(CH ₂ ) _n2 -OR ₃₂ , or two adjacent ones of R ₂₄ to R ₃₁ may combine to form a substituted or unsubstituted C _3-10 cycloalkyl ring. More specifically, R ₂₄ to R ₃₁ are each independently hydrogen, tert-butyl, or tert-butoxy hexyl, or two adjacent ones of R ₂₄ to R ₃₁ may combine to form a cyclohexane ring substituted with four methyls.

Specifically, R ₃₂ may be tertbutyl.

Specifically, n2 may be an integer from 4 to 10, more specifically, n2 may be an integer from 4 to 7, and even more specifically, n2 may be 6.

Specifically, the metallocene compound represented by the above chemical formula 2 may be any one selected from the group consisting of:

.

Meanwhile, the method for producing the second metallocene compound represented by the above chemical formula 2 is not particularly limited, but may be produced by a method such as the following reaction formula 2, for example.

The compound represented by the above chemical formula 2 is difficult to synthesize due to the steric hindrance of the indene ligand, but the compound represented by the above chemical formula 2 can be produced in high yield and high purity according to a method such as the following reaction scheme 2.

Accordingly, according to one embodiment of the present invention, the compound represented by the chemical formula 2 is

A step of producing a compound represented by chemical formula 2-3 by reacting a compound represented by chemical formula 2-1 with a compound represented by chemical formula 2-2;

A step of preparing a ligand of chemical formula 2-5 by reacting a compound represented by chemical formula 2-3 with a compound represented by chemical formula 2-4; and

It can be produced by a production method including a step of reacting a ligand of Chemical Formula 2-5 with a halogen salt of a transition metal represented by Chemical Formula 2-6:

[Reaction Formula 2]

In the above reaction formula 2,

M ₂ , X ₂₁ , X ₂₂ , T ₂ , Q ₂₁ , Q ₂₂ and R ₂₀ to R ₃₁ are as defined in the above chemical formula 2,

X" is each independently a halogen.

Meanwhile, in the hybrid supported metallocene catalyst, the first metallocene compound and the second metallocene compound may be supported at a molar ratio of 1:1 to 25:1, or 2:1 to 25:1, or 3:1 to 25:1, or 3:1 to 23:1, or 3:1 to 20:1. When the ratio of the first metallocene compound and the second metallocene compound is less than 1:1, the high crystallinity content is low, making it difficult for the stretched film to have heat resistance, and when the ratio of the first metallocene compound and the second metallocene compound exceeds 25:1, the low crystallinity content is low, making biaxial stretching processability difficult.

In addition, in the hybrid supported metallocene catalyst, a carrier having a highly reactive hydroxyl group, silanol group, or siloxane group on the surface can be used as a carrier for supporting the first metallocene compound and the second metallocene compound, and for this purpose, a carrier whose surface has been modified by calcination or whose surface has had moisture removed by drying can be used. Specifically, silica such as silica prepared by calcining silica gel, silica dried at high temperature, etc.; silica-alumina; and silica-magnesia; etc. can be used, and these can typically contain oxides, carbonates, sulfates, and nitrate components such as Na ₂ O, K ₂ CO ₃ , BaSO ₄ , and Mg(NO ₃ ) ₂ .

In addition, when used in a supported catalyst state, the particle shape and bulk density of the polymer produced are excellent, and it can be suitably used in conventional slurry polymerization, bulk polymerization, and gas phase polymerization processes. In addition, among various carriers, since the functional group of the transition metal compound is chemically bonded and supported in the silica carrier, almost no catalyst is liberated from the surface of the carrier in the ethylene polymerization process, and as a result, when producing a polyethylene copolymer by slurry or gas phase polymerization, fouling caused by adhesion of the reactor wall or polymer particles to each other can be minimized.

In addition, when supported on the carrier, the first and second metallocene compounds may be supported in an amount of, for example, 1 mmol or more, or 10 mmol or more, and 500 mmol or less, or 300 mmol or less, based on 1,000 g of the carrier. When supported in the above amount range, it may exhibit appropriate supported catalytic activity, which may be advantageous in terms of maintaining the activity of the catalyst and economic efficiency.

In addition, the above hybrid metallocene catalyst may further include a cocatalyst in order to improve high activity and process stability.

Specifically, the cocatalyst may include at least one compound represented by the following chemical formula 3.

[Chemical Formula 3]

-[Al(R ₄₁ )-O]a-

In the above chemical formula 3,

R ₄₁ is halogen; or C _1-20 hydrocarbyl substituted or unsubstituted by halogen;

a is an integer greater than or equal to 2.

Meanwhile, in the present specification, a hydrocarbyl group is a monovalent functional group in the form of removing a hydrogen atom from a hydrocarbon, and may include an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an aralkyl group, an aralkenyl group, an aralkynyl group, an alkylaryl group, an alkenylaryl group, and an alkynylaryl group. In addition, the hydrocarbyl group having 1 to 20 carbon atoms may be a hydrocarbyl group having 1 to 15 carbon atoms or 1 to 10 carbon atoms. Specifically, the hydrocarbyl group having 1 to 20 carbon atoms is a straight-chain, branched-chain, or cyclic alkyl group such as a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, an iso-butyl group, a tert-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, or a cyclohexyl group; Or it may be an aryl group such as a phenyl group, a naphthyl group, or anthracenyl group.

Examples of compounds represented by the above chemical formula 3 include alkylaluminoxane compounds such as methylaluminoxane, ethylaluminoxane, isobutylaluminoxane, or butylaluminoxane, and any one of these or a mixture of two or more thereof may be used.

The above alkylaluminoxane compound can further enhance catalytic activity by including a metal element that stabilizes the first and second metallocene compounds and acts as a Lewis acid to form a bond through a Lewis acid-base interaction with a functional group introduced into a bridge group of the second metallocene compound.

In addition, the amount of the cocatalyst used can be appropriately adjusted depending on the properties or effects of the desired catalyst and polyethylene. For example, when silica is used as the carrier, the cocatalyst can be supported in an amount of 100 g or more, or 500 g or more, or 750 g or more, and 6000 g or less, or 5500 g or less, or 5400 g or less, based on 1,000 g of silica.

The hybrid metallocene catalyst according to the present invention having the above-described configuration can be produced by a production method including a step of supporting a promoter compound on a support, and a step of supporting the first and second transition metal compounds on the support. At this time, the supporting order of the promoter and the first and second transition metal compounds can be changed as needed, and the supporting order of the first and second transition metal compounds can also be changed as needed. The first and second transition metal compounds may be supported simultaneously. Considering the effect of the supported catalyst having a structure determined according to the supporting order, among these, supporting the promoter on the support and then sequentially supporting the first and second transition metal compounds can enable the produced supported catalyst to realize high catalytic activity and better process stability in the production process of a polyethylene copolymer.

As described above, the hybrid supported metallocene catalyst can exhibit excellent catalytic activity by including first and second metallocene compounds having specific structures. Accordingly, the hybrid supported metallocene catalyst can be suitably used for the polymerization of ethylene and olefin monomers.

The above-mentioned hybrid supported metallocene catalyst can be dissolved or diluted and injected into an aliphatic hydrocarbon solvent having 4 to 12 carbon atoms, such as isobutane, pentane, hexane, heptane, nonane, decane, and their isomers, an aromatic hydrocarbon solvent such as toluene and benzene, a hydrocarbon solvent substituted with a chlorine atom such as dichloromethane and chlorobenzene, etc. It is preferable to use the solvent used here after removing a small amount of water or air, etc. that act as catalyst poisons, by treating it with a small amount of alkyl aluminum, and it is also possible to carry out the process using an additional cocatalyst.

Meanwhile, as the olefin monomer polymerized with ethylene, ethylene, alpha-olefin, cyclic olefin, diene olefin or triene olefin having two or more double bonds can be used.

Specific examples of the above olefin monomers include ethylene, propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-undecene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-eicosene, norbornene, norbornadiene, ethylidenenorbornene, phenylnorbornene, vinylnorbornene, dicyclopentadiene, 1,4-butadiene, 1,5-pentadiene, 1,6-hexadiene, styrene, alpha-methylstyrene, divinylbenzene, 3-chloromethylstyrene, etc., and two or more of these monomers may be mixed and copolymerized. More specifically, the above olefin monomer may be 1-hexene.

The amount of the olefin monomer added may be determined depending on the properties of the polyethylene copolymer to be manufactured. For example, considering the properties of the polyethylene copolymer to be implemented in the present invention, the olefin monomer may be added in an amount of 3.0 to 10.0 wt%, or 5.0 to 8.0 wt%, based on the total weight of ethylene.

In addition, the above polymerization reaction is performed under the condition of hydrogen input.

Specifically, the hydrogen may be introduced in an amount of 5 to 120 ppm based on the total weight of ethylene, which is a monomer. More specifically, it may be introduced in an amount of 5 ppm or more, or 10 ppm or more, or 15 ppm or more, or 20 ppm or more, or 22 ppm or more, and 120 ppm or less, or 100 ppm or less, or 50 ppm or less, or 40 ppm or less, or 35 ppm or less, or 30 ppm or less, based on the total weight of ethylene.

When injected within the above range, it is easier to implement the properties of the polyethylene described above.

Additionally, the polymerization reaction can be carried out as a gas phase polymerization reaction or a slurry polymerization reaction.

Accordingly, it can be performed using a single gas phase polymerization reactor, a continuous slurry polymerization reactor, or a loop slurry reactor.

In addition, the polymerization reaction may be carried out at a temperature of 40°C or higher, or 60°C or higher, or 80°C or higher, and 110°C or lower, or 100°C or lower, or 90°C or lower. In addition, when the pressure conditions are further controlled during the polymerization reaction, the polymerization reaction may be carried out under a pressure of 5 bar or higher, or 10 bar or higher, or 20 bar or higher, and 50 bar or lower, or 45 bar or lower, or 40 bar or lower. When polymerization is carried out under such temperatures and pressures, the desired physical properties of polyethylene can be more easily realized.

The above polyethylene is produced using a catalyst that hybridizes a metallocene compound exhibiting high molecular weight and high crystallinity with a metallocene compound exhibiting low molecular weight and low crystallinity, thereby having a high crystallinity content and an improved main chain average molecular weight of the high crystallinity fraction. Accordingly, when producing a stretched film using the above polyethylene, the thermal stability of the stretched film can be improved.

(corrector)

In the polyethylene resin composition according to the present invention, the neutralizing agent includes a stearic acid metal salt.

The metal cation contained in the stearic acid metal salt acts as a nucleation point when polyethylene gradually decreases its temperature from a temperature above its melting point to reach its crystallization temperature, thereby densifying the size of the polymer crystals and simultaneously increasing the degree of crystallinity. In addition, since the metal cation exists in the form of a divalent cation, it can separate into two fatty acid forms at a temperature above the melting point of polyethylene, and can combine with the fatty acid or the polymer at a temperature below the melting point of polyethylene. When combined with the crystallized polymer terminal, it forms a crystal structure with a uniform intercrystalline distance and prevents the formation of ultra-high molecular weight molecules, thereby improving the haze characteristics, which is the transparency of the film. In addition, when blended with polyethylene, it lowers the melt viscosity of the resin composition, thereby improving the flowability and, as a result, the molding processability.

The above stearic acid metal salt may be a stearic acid metal salt containing an alkaline earth metal of Group 2 or a transition metal of Group 12 in the periodic table as a metal. Among various metal elements, these metal elements have divalent cations, making it easy to combine with fatty acids having OH- groups such as stearate series in the form of fatty acid salts. In addition, the fatty acid salt produced using the metal elements has a melting point of 125 to 130°C, which is similar to or slightly higher than the melting point of polyethylene. As a result, the liquid polyethylene crystallizes during the crystallization process, thereby increasing the uniformity of the crystal arrangement, and also increasing the degree of crystallinity during film production. More specifically, the metal may be Mg, Ca, Sr, Ba, Cd, or Zn, and even more specifically, may be Ca, Mg, or Zn.

Specific examples of the above stearic acid metal salt include calcium stearate (Ca-St), zinc stearate, or magnesium stearate, and any one of these or a mixture of two or more thereof may be used.

The neutralizing agent may be included in an amount of 100 to 2000 ppm based on the total weight of polyethylene. More specifically, if the content of the metal cation in the polyethylene resin composition is less than 100 ppm, the effect of improving crystallinity and crystal orientation uniformity is minimal, and if it exceeds 2000 ppm, the metal cation may leach out, thereby reducing the smoothness of the film surface, or may become a source of contamination, thereby reducing transparency. More specifically, the neutralizing agent may be included in an amount of 100 ppm or more, or 500 ppm or more, or 800 ppm or more, or 1000 ppm or more, and 2000 ppm or less, or 1800 ppm or less, or 1500 ppm or less, or 1200 ppm or less based on the total weight of polyethylene.

(antioxidant)

In the polyethylene resin composition according to the present invention, the antioxidant specifically includes a primary antioxidant and a secondary antioxidant.

The above primary antioxidant functions as a radical scavenger, reacting with radicals generated within polyethylene to stabilize it. The primary antioxidant releases its own hydrogen to stabilize the radicals, transforming itself into a radical that remains stable through resonance or electron rearrangement. Specific examples of primary antioxidants include phenolic compounds and aromatic amine compounds, and any one of these compounds or a mixture of two or more thereof may be used.

In addition, specific examples of the phenolic compound include pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, and the like, and any one or a mixture of two or more of these may be used. In addition, examples of the aromatic amine compound include phenylnaphthylamine, 4,4'-(α,α-dimethylbenzyl)diphenylamine, and N,N'-di-2-naphthyl-p-phenylenediamine, and the like, and any one or a mixture of two or more of these may be used. Alternatively, commercially available Irganox™ 1010 (BASF), Irganox™ 3114 (BASF), or Irganox™ 1076 (BASF) may be used.

Additionally, secondary antioxidants function as peroxide decomposers and are excellent for improving high-temperature heat resistance, processability, and preventing discoloration. Specific examples of secondary antioxidants include phosphite compounds and sulfur compounds, and one or a mixture of two or more of these may be used.

Examples of the above phosphite compounds include tris(2,4-di-tert.-butylphenyl)phosphite, bis(2,4-di-tert.-butylphenyl)pentaerythritol diphosphite, and bis(2,4-dicumylphenyl)pentaerythritol diphosphite, and any one of these or a mixture of two or more thereof may be used. In addition, commercially available Irgafos™ 168 (manufactured by BASF) or Cyanox™ 1790 (manufactured by CYTEC) may also be used.

The antioxidant may be included in an amount of 500 to 2200 ppm based on the total weight of polyethylene. More specifically, the antioxidant may be included in an amount of 500 ppm or more, or 800 ppm or more, or 1000 ppm or more, and 2200 ppm or less, or 2100 ppm or less, or 2000 ppm or less based on the total weight of the polyethylene resin composition.

In addition, the primary antioxidant and the secondary antioxidant may be included in a weight ratio of 1:1 to 1:2 under the condition that the content range of the antioxidant is satisfied. More specifically, the weight ratio of the primary antioxidant and the secondary antioxidant may be 1:1 to 1:1.2, or 1:1.2 to 1:2. When included in the weight ratio described above, the thermal stability of the polyethylene resin composition and the effect of improving the physical properties of the film produced are more excellent.

Meanwhile, the polyethylene resin composition according to the present invention may further include one or more additives, such as a nucleating agent, a slip agent, an anti-blocking agent, a UV stabilizer, and an antistatic agent, in addition to the polyethylene, antioxidant, and neutralizing agent described above. The content of the additives is not particularly limited, and may be, for example, 500 ppm or more, or 700 ppm or more, or 1,000 ppm or more, and 2,500 ppm or less, or 1,500 ppm or less, based on the total weight of the polyethylene.

(Method for producing polyethylene resin composition)

The polyethylene resin composition according to the present invention can be prepared by mixing the polyethylene, antioxidant, neutralizer, and optionally other additives in an amount that satisfies the physical property requirements of the polyethylene resin composition described above. Accordingly, the present invention provides a method for preparing a polyethylene resin composition, comprising the step of mixing the polyethylene, antioxidant, neutralizer, and optionally other additives in the amounts described above. The mixing method is not particularly limited, and conventional mixing processes and mixing devices can be used.

In addition, the method for producing the polyethylene resin composition may further include a melting and extrusion step after the mixing process. A pellet-shaped polyethylene resin composition can be produced through the melting and extrusion process described above.

After the polymerization reaction for the production of the above polyethylene, the polymer product is obtained in powder form. Therefore, the types of antioxidants that can be used are limited. Furthermore, the antioxidant content varies significantly from powder to powder, resulting in significant variations in the physical properties of products manufactured using the polymer. However, performing a melting and extrusion process allows the components, including the antioxidant, to be uniformly mixed, resulting in products with uniform physical properties.

Meanwhile, in the present invention, the term "pellet" or "pellet-type" refers to small particles or pieces formed by extrusion of a raw material, and includes all shapes classified as pellets in the relevant technical field, such as circular, flat, sliver, polygonal, and rod-shaped. In addition, the size of the pellet is appropriately determined according to the use and shape and is not particularly limited. However, in order to be able to distinguish it from powder having a small average diameter of about 1 mm, the pellet in the present invention is defined as having an average diameter of 2 mm or more. Here, the "diameter" is the longest distance among any straight line distances on the outer surface of the pellet, and can be measured using an imaging microscope or the like.

The above melt extrusion process can be performed using a conventional extruder, and the specific method and conditions are not particularly limited as long as the morphological conditions of the pellet are satisfied.

Additionally, the above melting and extrusion process can be performed according to a conventional method. For example, it can be performed at an extrusion temperature of 180 to 220°C, or 180 to 210°C, using an extruder such as a twin screw extruder.

A polyethylene resin composition satisfying the aforementioned physical property conditions is produced using the above-described manufacturing method. The produced polyethylene resin composition exhibits excellent thermal stability, thereby eliminating the risk of processing defects such as butterfly patterns on the film surface or yellowing during the production of a stretched film. Furthermore, the produced biaxially stretched film exhibits excellent stretching and tensile strength characteristics, along with appearance characteristics.

(extension film)

Accordingly, according to the present invention, a stretched film, specifically a biaxially stretched film, is provided, manufactured using the above polyethylene resin composition.

The above-mentioned stretch film can be manufactured according to a conventional film manufacturing method, except that the above-mentioned polyethylene resin composition is used.

For example, a stretched film according to the present invention can be manufactured according to the following stretching conditions, and more specific film manufacturing methods and conditions are as described in the examples described below.

- Using Bruckner Lab extruder line Using Lab extruder line (L/D ratio: 42, Screw diameter: 25 mm, Melt/T-Die temperature: 220 ℃) to manufacture 0.75 mm thick polyethylene sheet

- Biaxial stretching of a polyethylene sheet measuring 50 mm × 50 mm in length × width was performed using Ocean Science's COAD.521 stretching equipment.

- Sequential stretching (MD→TD) is performed after preheating at 120 to 127 ℃ for 90 seconds each.

The above-mentioned stretchable film exhibits excellent stretchability as it contains the above-mentioned polyethylene resin composition.

Specifically, the stretched film may be a biaxially stretched film having a machine direction (MD) stretch ratio of 5 or more, or 5 to 8, and a transverse direction (TD) stretch ratio of 8 or more, or 8 to 10, when the thickness is 10 to 100 μm.

In addition, the above-mentioned stretched film exhibits excellent appearance characteristics without occurrence of processing defects such as butterfly patterns or yellowing on the film surface due to the excellent thermal stability of the above-mentioned polyethylene resin composition.

The polyethylene resin composition according to the present invention has improved thermal stability, and thus enables the production of a stretched film without concern about processing defects.

Figure 1 is a graph showing the results of observing changes in the composite viscosity according to angular frequency of the polyethylene resin compositions of Examples 2-2 and 2-3 and Comparative Examples 2-1 and 2-2.

Figure 2 is a graph showing the results of observing the phase angle change according to the complex modulus of the polyethylene resin compositions of Examples 2-2 and 2-3 and Comparative Examples 2-1 and 2-2.

Figure 3 is a graph showing a phase angle inflection point in a phase angle change curve over time of the polyethylene resin compositions of Example 2-3 and Comparative Example 2-1.

Hereinafter, preferred examples are presented to aid understanding of the present invention. However, the following examples are provided solely to facilitate understanding of the present invention and are not intended to limit the scope of the present invention.

<Preparation of metallocene compounds>

Synthesis Example 1-1: Preparation of the first metallocene compound (A1)

(A1)

(1) Synthesis of ligands

Under Ar, 27.2 g (100 mmol) of 3-(6- tert -butoxyhexyl)-1 H -indene and 250 mL of n- hexane were added to a dried 2 L Schlenk flask. After cooling to -78 °C, 42 mL (1.05 eq., 105 mmol) of 2.5 M n-BuLi in hexane was added dropwise. The reaction mixture was slowly warmed to room temperature and stirred for 8 h. After cooling again to -78 °C, 21.3 g (1.5 eq., 150 mmol) of iodomethane was added dropwise. After slowly warming to room temperature and stirring for 24 hours, the organic layer was separated using water and diethyl ether and dried over MgSO ₄ to obtain 24.1 g (84.2 mmol, 84.2% yield) of 3-(6- tert -butoxyhexyl)-1-methyl-1 H -indene.

^1H NMR (500 MHz, CDCl ₃ ): 1.12 (9H, s), 1.29 (3H, d), 1.42 (4H, m), 1.56 (2H, m), 1.70 (2H, m), 2.52 (2H, t), 3.34 (2H, t), 3.42 (1H, m), 6.25 (1H, brs), 7.21 (1H, t), 7.25-7.32 (2H, m), 7.40 (1H, d).

　

(2) Synthesis of metallocene compounds

Under Ar, 5.73 g (20 mmol) of the ligand synthesized above and 70 mL of diethyl ether were added to a dried 250 mL Schlenk flask. After cooling to -78 °C, 8.4 mL (1.05 eq., 21 mmol) of 2.5 M n-BuLi in hexane was added dropwise. The reaction mixture was slowly warmed to room temperature and stirred for 8 hours. After cooling again to -78 °C, 8.46 g (1.0 eq., 20 mmol) of (1- n -butyl-3-methylcyclopentadienyl)ZrCl ₃ dimethoxyethane complex was added together with 30 mL of diethyl ether. After slowly warming to room temperature and stirring for 24 hours, the reaction mixture was dried under reduced pressure, and dichloromethane was added. The resulting suspension was filtered under Ar to remove LiCl, the filtrate was dried under reduced pressure, and n -hexane was added. The resulting suspension was filtered under Ar to obtain 7.52 g (12.9 mmol, 64.5% yield) of a solid metallocene compound (A1).

^1H NMR (500 MHz, CDCl ₃ ): 0.77-0.81 (3H, m), 1.09 (9H, s), 1.16-1.28 (6H, m), 1.48-1.56 (6H, m), 1.95 (3H, d), 2.14 (1H, m), 2.42 (4H, m), 2.68 (1H, m), 2.90 (1H, m), 3.23 (2H, t), 4.97 (1H, dt), 5.11 (1H, dt), 5.76 (1H, t), 6.41 (1H, brs), 7.13-7.15 (2H, m), 7.46-7.48 (2H, m).

Synthesis Example 1-2: Preparation of the first metallocene compound (A2)

(A2)

(1) Synthesis of ligands

Under Ar, 120 g (440 mmol) of 3-(6- tert -butoxyhexyl)-1 H -indene and 1.1 L of n- hexane were added to a dried 2 L Schlenk flask. After cooling to -78 °C, 185 mL (1.05 eq., 462.5 mmol) of 2.5 M n-BuLi in hexane was added dropwise. The reaction mixture was slowly warmed to room temperature and stirred for 8 h. After cooling again to -78 °C, 82.8 g (1.1 eq., 484 mmol) of benzyl bromide was added dropwise. After slowly warming to room temperature and stirring for 24 hours, the organic layer was separated using water and diethyl ether and dried over MgSO ₄ to obtain 137 g (377 mmol, 85.7% yield) of 3-(6- tert -butoxyhexyl)-1-benzyl-1 H -indene.

^1H NMR (500 MHz, CDCl ₃ ): 1.22 (9H, s), 1.32 (4H, m), 1.44 (2H, m), 1.57 (2H, m), 1.73 (2H, m), 2.59 (2H, m), 3.38 (2H, t), 3.75 (1H, m), 6.14 (1H, brs), 7.14-7.45 (9H, m).

(2) Synthesis of metallocene compounds

Under Ar, 9.06 g (25 mmol) of the ligand synthesized above and 90 mL of diethyl ether were added to a dried 250 mL Schlenk flask. After cooling to -78 °C, 11 mL (1.05 eq., 27.5 mmol) of 2.5 M n-BuLi in hexane was added dropwise. The reaction mixture was slowly warmed to room temperature and stirred for 8 hours. After cooling again to -78 °C, 10.6 g (1.0 eq., 25 mmol) of (1- n -butyl-3-methylcyclopentadienyl)ZrCl ₃ dimethoxyethane complex was added together with 30 mL of diethyl ether. After slowly warming to room temperature and stirring for 24 hours, the reaction mixture was dried under reduced pressure and dichloromethane was added. The resulting suspension was filtered under Ar to remove LiCl, the filtrate was dried under reduced pressure, and n -hexane was added. The resulting suspension was filtered under Ar to obtain 8.76 g (13.3 mmol, 53.2% yield) of a solid metallocene compound (A2).

¹ H NMR (500 MHz, CDCl ₃ ): 0.88-0.91 (3H, m), 1.22 (9H, s), 1.29-1.40 (8H, m), 1.52-1.76 (4H, m), 2.06 (3H, s), 2.11-2.22 (2H, m), 2.59-2.68 (2H, m), 2.99-3.07 (2H, m), 3.34 (2H, t), 4.43 (1H, dt), 5.21 (1H, dt), 5.78 (1H, t), 6.47 (1H, brs), 7.11-7.63 (9H, m).

Synthesis Example 1-3: Preparation of the first metallocene compound (A3)

(A3)

Under Ar, 5.73 g (20 mmol) of the ligand synthesized in (1) of Synthesis Example 1-1 and 70 mL of diethyl ether were added to a dried 250 mL Schlenk flask. After cooling to -78 °C, 8.4 mL (1.05 eq., 21 mmol) of 2.5 M n-BuLi in hexane was added dropwise. The reaction mixture was slowly warmed to room temperature and stirred for 8 hours. After cooling again to -78 °C, 8.12 g (1.0 eq., 20 mmol) of (tetramethylcyclopentadienyl)HfCl ₃ was added together with 30 mL of diethyl ether. After slowly warming to room temperature and stirring for 24 hours, the reaction mixture was dried under reduced pressure and toluene was added. The resulting suspension was filtered under Ar to remove LiCl, and 20 mL (3.0 eq., 60 mmol) of 3.0 M methylmagnesium bromide in diethyl ether was added dropwise to the filtrate. The reaction mixture was heated to 80 °C and stirred for 2 days. After cooling to room temperature, 1,4-dioxane was added. The resulting suspension was filtered under Ar to remove the Mg salt, and the reaction mixture was dried under reduced pressure to obtain 7.80 g (12.7 mmol, 63.4% yield) of an oily metallocene compound (A3).

¹ H NMR (500 MHz, CDCl ₃ ): -1.39 (6H, d), 1.17 (9H, s), 1.30-1.37 (4H, m), 1.45-1.70 (4H, m), 1.81-1.90 (12H, m), 2.27 (3H, s), 2.30-2.41 (1H, m), 2.72-2.80 (1H, m), 3.30 (2H, t), 4.92 (1H, brs), 5.56 (1H, brs), 7.10-7.19 (2H, m), 7.39-7.46 (2H, m).

Synthesis Example 2-1: Preparation of a second metallocene compound (B1)

(B1)

(1) Synthesis of ligands

Under Ar, 100 g (450 mmol) of 2-(6- tert -butoxyhexyl)cyclopentadiene, 103 g (2.0 eq., 900 mmol) of 2,4-dimethyl-3-pentanone, and 1 L of ethanol were added to a dried 250 mL Schlenk flask. After cooling to 0 °C, 48.0 g (1.5 eq., 675 mmol) of pyrrolidine was added dropwise. The reaction mixture was slowly warmed to room temperature and stirred for 24 h. After cooling the reaction mixture to 0 °C, 1 L of 10 vol% aq. acetic acid was added and stirred for 30 min. The organic layer was separated using water and diethyl ether and dried over MgSO ₄ to obtain 44.9 g (141 mmol, 31.3% yield) of 2-(6- tert -butoxyhexyl)-5-(2,4-dimethylpentan-3-ylidene)-cyclopenta-1,3-diene.

Under Ar, 1.66 g (10 mmol) of fluorene and 40 mL of tetrahydrofuran were added to another dried 250 mL Schlenk flask. After cooling to -78 °C, 4.8 mL (1.2 eq., 12 mmol) of 2.5 M n-BuLi in hexane was added dropwise. The reaction mixture was slowly warmed to room temperature and stirred for 8 h. After cooling to -78 °C, 3.19 g (1.0 eq., 10 mmol) of 2-(6- tert -butoxyhexyl)-5-(2,4-dimethylpentan-3-ylidene)-cyclopenta-1,3-diene synthesized above was added together with 10 mL of tetrahydrofuran. After slowly warming to room temperature and stirring for 24 hours, the organic layer was separated using water and diethyl ether and dried over MgSO ₄ to obtain 3.94 g (8.12 mmol, 81.2% yield) of ligand.

¹ H NMR (500 MHz, CDCl ₃ ): 0.87 (12H, d), 1.12 (9H, s), 1.34 (2H, m), 1.41 (2H, m), 1.46 (2H, m), 1.55 (4H, m), 2.18 (2H, t), 2.91 (2H, d), 3.36 (2H, t), 3.73 (1H, s), 6.15 (1H, t), 6.25 (1H, brs), 7.25-7.44 (4H, m), 7.55 (2H, dd), 7.90 (2H, dd).

　

(2) Synthesis of metallocene compounds

Under Ar, 3.94 g (8.12 mmol) of the ligand synthesized above, 5 mL of methyl t -butyl ether, and 20 mL of toluene were added to a dried 250 mL Schlenk flask. After cooling to -78 °C, 7.1 mL (2.2 eq., 17.8 mmol) of a 2.5 M n-BuLi in hexane solution was added dropwise. The reaction mixture was slowly warmed to room temperature and stirred for 8 hours. After cooling to -78 °C, 3.06 g (1.0 eq., 8.12 mmol) of ZrCl ₄ (THF) ₂ was added together with 5 mL of methyl t -butyl ether. After slowly warming to room temperature and stirring for 24 hours, the reaction mixture was dried under reduced pressure at room temperature to remove methyl t -butyl ether. The resulting toluene suspension was filtered under Ar to remove LiCl, the filtrate was dried under reduced pressure at 50°C, and n -hexane was added. The resulting suspension was filtered under Ar to obtain 2.61 g (4.04 mmol, 49.8% yield) of a solid metallocene compound (B1).

¹ H NMR (500 MHz, C ₆ D ₆ ): ¹ H NMR (500 MHz, C ₆ D ₆ ): 0.91 (12H, d), 1.13 (9H, s), 1.15-1.38 (6H, m), 1.40-1.55 (6H, m), 3.22 (2H, t), 5.32-6.12 (3H, m), 7.20-7.32 (2H, t), 7.47-7.55 (2H, dd), 7.72 (2H, d), 7.93 (2H, t).

<Manufacture of supported catalysts>

Manufacturing Example 1: Manufacturing of Catalyst 1

Silica (SP 952, manufactured by Grace Davision) was dehydrated and dried under vacuum at 200°C for 12 hours.

800 g of dried silica was placed in a 20 L SUS reactor, and 6 kg of methylaluminoxane (MAO) solution (10 wt% in toluene) in toluene solution was added, and the mixture was slowly reacted with stirring at 70 ° C. for 1 hour. After completion of the reaction, the mixture was washed several times with a sufficient amount of toluene until the unreacted aluminum compound was completely removed. A solution prepared by dissolving 25.4 g of the first metallocene compound (A1) and 2.8 g of the second metallocene compound (B1) in toluene was sequentially added to the reactor, and the mixture was reacted with stirring at 40 ° C. for 4 hours. After washing with a sufficient amount of toluene, the mixture was vacuum-dried to obtain a hybrid supported metallocene catalyst 1 as a solid powder.

Manufacturing Examples 2 and 3

Hybrid supported metallocene catalysts 2 and 3 were prepared in the same manner as in Preparation Example 1, except that the types and contents of metallocene compounds were used as described in Table 1 below instead of 25.4 g of the first metallocene compound (A1) and 2.8 g of the second metallocene compound (B1).

Manufacturing example catalyst First metallocene compound Second metallocene compound Molar ratio of first metallocene compound: second metallocene compound First metallocene
Compound input (g) Second metallocene
Compound input (g) Manufacturing Example 1 Catalyst 1 A1 B1 10:1 25.4 2.8 Manufacturing Example 2 Catalyst 2 A2 B1 20:1 30.1 1.5 Manufacturing Example 3 Catalyst 3 A3 B1 3:1 22.1 7.7

<Manufacturing of polyethylene>

Example 1-1

The polymerization reactor was a continuous reactor using an isobutane slurry loop process, with a reactor volume of 140 L and a reaction flow rate of approximately 7 m/s. The gases (ethylene, hydrogen) and comonomers required for polymerization were continuously fed continuously and the individual flow rates were adjusted to suit the target product. The concentrations of all gases and the comonomer 1-hexene were confirmed by an online gas chromatograph. The supported catalyst was fed as isobutane slurry, the reactor pressure was maintained at 40 bar, and the polymerization temperature was 80°C. The ethylene input for polyethylene production, the input amounts of the solvent i-butane, the 1-hexene/ethylene input ratio, and the hydrogen/ethylene input ratio are shown in Table 2 below.

Examples 1-2 and 1-3

Polyethylene was manufactured in the same manner as in Example 1, except that the conditions described in Table 2 below were changed.

Comparative Examples 1-1 to 1-3

Polyethylene was manufactured in the same manner as in Example 1, except that the conditions described in Table 2 below were changed.

The physical properties of the polyethylene manufactured in Examples 1-1 to 1-3 and Comparative Examples 1-1 to 1-3 were measured using the following methods, and the results are shown in Table 2 below.

(1) MI _2.16

Melt Index (MI _2.16 ) was measured according to ASTM D1238 (condition E, 190 ℃, 2.16 kg load).

(2) MFRR (MFR _21.6 /MFR _2.16 )

Melt Flow Rate Ratio (MFRR, MFR _21.6 / MFR _2.16 ) was calculated by dividing MFR _21.6 by MFR _2.16 , where MFR _21.6 was measured at a temperature of 190 ℃ and a load of 21.6 kg according to ISO 1133, and MFR _2.16 was measured at a temperature of 190 ℃ and a load of 2.16 kg according to ISO 1133.

(3) Density (g/cm ³ )

Density (g/cm ³ ) was measured according to the American Society for Testing and Materials standard ASTM D 792.

In the above table, wt% and ppmw are based on the total weight of ethylene.

<Manufacture of polyethylene resin composition>

Example 2-1

Based on the total weight of the polyethylene obtained in Example 1-1, 500 ppm of Irganox™ 1010 from BASF as a primary antioxidant, 500 ppm of Irgafos™ 168 from BASF as a secondary antioxidant, and 1000 ppm of calcium stearate (Ca-St) as a neutralizer were added and mixed, and then extruded at an extrusion temperature of 190°C using a twin screw extruder (TEK 30 MHS, manufactured by SMPLATECH CO., diameter 32 pi, L/D=40) to prepare a polyethylene resin composition in the form of pellets.

Examples 2-2 to 2-5

A polyethylene resin composition was manufactured in the same manner as in Example 2-1, except that the conditions described in Table 3 below were changed.

Example 2-6

A polyethylene resin composition was prepared in the same manner as in Example 2-1, except that Songnox™ 1010 from Songwon Industrial Co., Ltd. was used instead of Irganox 1010 as a primary antioxidant, and Songnox™ 1680 from Songwon Industrial Co., Ltd. was used instead of Irgafos 168 as a secondary antioxidant, in an amount of 500 ppm based on the total weight of polyethylene obtained in Example 1-1.

Example 2-7

A polyethylene resin composition was prepared in the same manner as in Example 2-1, except that 1000 ppm of zinc stearate (Zn-St) was added instead of calcium stearate based on the total weight of the polyethylene obtained in Example 1-1.

Comparative Examples 2-1 to 2-5

A polyethylene resin composition was manufactured in the same manner as in Example 2-1, except that the conditions described in Table 3 below were changed.

Comparative Example 2-6

A polyethylene resin composition was prepared in the same manner as in Example 1, except that high-density polyethylene (I) having a melting index of 1.0 g/10 min, a density of 0.9600 g/cm3, and a molecular weight distribution of 4.5 was used.

Comparative Example 2-7

A polyethylene resin composition was prepared in the same manner as in Example 2-1, except that no neutralizing agent was added.

Comparative Example 2-8

A polyethylene resin composition was manufactured in the same manner as in Example 2-1, except that the conditions described in Table 3 below were changed.

In the above table, ppmw is based on the total weight of polyethylene.

Additionally, the primary antioxidant is Irganox™ 1010 from BASF, and the secondary antioxidant is Irgafos™ 168 from BASF.

Also, Ca-St is an abbreviation for calcium stearate, and DHT-4A™ is a synthetic hydrotalcite manufactured by Kyowa.

Experimental Example 2

The physical properties of the polyethylene resin compositions manufactured in the examples and comparative examples were measured and evaluated as follows, and the results are shown in Table 4, Fig. 1, and Fig. 2, respectively.

(1) Density: Measured according to ASTM D 792 standard

(2) Melt Index (MI _2.16 ): Measured according to ASTM D1238 (condition E, 190 ℃, 2.16 kg load).

(3) Thermal stability evaluation

Thermal stability was evaluated using an ARES Rheometer (TA Instruments, 25 mm Parallel Plate Geometry).

First, the pellets manufactured in the above examples or comparative examples were placed on the Geometry, melted, pressed with a gap of 1 mm to manufacture a specimen, and then loaded. Thereafter, steps 1 to 3 were sequentially performed under the following conditions, and the complex viscosity and phase angle at each step were measured.

<Measurement conditions>

Step 1: Temperature 230℃, Frequency 0.1~100Hz sweep, Strain 0.5%, oscillation

Step 2: Temperature 230℃, Frequency fixed at 1Hz, Strain 0.5%, oscillation for 30 minutes

Step 3: Temperature 230℃, Frequency 0.1~100Hz sweep, Strain 0.5%, oscillation

After measuring the complex viscosity and phase angle in steps 1 and 3, respectively, the complex viscosity value of the first point (0.628319 rad/s) with the lowest angular frequency was called zero shear viscosity, and when the slope value (b) in the relationship y = a + bx obtained by fitting 7 points of the vGP plot with the straight line model of Trios software was called phase angle slope, the zero shear viscosity and phase angle slope in steps 1 and 3 were calculated, respectively, and the changes were called zero shear viscosity change (Delta Zero shear viscosity) and phase angle slope change (Delta Phase angle slope), respectively.

Meanwhile, the inflection point of the phase angle was measured by oscillating for 30 minutes under high temperature and oxygen conditions of 230℃, with a frequency of 1Hz fixed, using a rotary rheometer as in step 2 after performing step 1, and drawing tangents before and after the phase angle data, and quantifying the point where the two tangents meet as the inflection point (s).

FIG. 1 is a graph showing the results of observing changes in complex viscosity according to angular frequency of the polyethylene resin compositions of Examples 2-2 and 2-3 and Comparative Examples 2-1 and 2-2, and FIG. 2 is a graph showing the results of observing changes in phase angle according to complex modulus of the polyethylene resin compositions of Examples 2-2 and 2-3 and Comparative Examples 2-1 and 2-2.

In addition, Fig. 3 is a graph showing a phase angle inflection point in a phase angle change curve over time of the polyethylene resin compositions of Example 2-3 and Comparative Example 2-1.

(4) Fair Issue Evaluation

Using the polyethylene resin compositions manufactured in the above examples and comparative examples, a stretched film was manufactured under the following conditions, and the occurrence of processing defects and yellowing in the stretched film during and after the manufacturing process was observed.

- Manufacture of polyethylene resin composition sheet with a thickness of 0.75 mm using Bruckner Lab extruder line (L/D ratio: 42, Screw diameter: 25 mm, Melt/T-Die temperature: 220 ℃)

- Biaxial stretching was performed on a polyethylene resin composition sheet measuring 50 mm × 50 mm in length × width using Ocean Science's COAD.521 stretching equipment.

- After preheating at 124℃ for 90 seconds each, sequential stretching (MD direction → TD direction) is performed at a stretching ratio of 5X8 (MDXTD).

Experimental results showed that when a film was manufactured and stretched using the polyethylene resin composition of the example, no processing defects, such as butterfly patterns, or yellowing occurred on the film surface. This indicates that the polyethylene resin composition of the example possesses excellent thermal stability.

Meanwhile, in the case of the polyethylene resin compositions of Comparative Examples 2-1 and 2-3, due to the high Delta Phase angle slope, the stretched portion was unevenly torn during film stretching, and a butterfly pattern occurred on the film surface. In addition, even in the case of Comparative Example 2-5, which had a high melting index and low density even when the Delta Phase angle slope condition was satisfied, a butterfly pattern occurred on the film surface during film stretching.

In addition, in the case of the polyethylene resin composition of Comparative Example 2-2, yellowing occurred during film stretching due to high Delta Zero shear viscosity, and in the case of the polyethylene resin composition of Comparative Example 2-4, which has high Delta Zero shear viscosity, low melting index, and low density, yellowing also occurred during film stretching.

In addition, the resin composition of Comparative Example 2-6, which had a high Delta Zero shear viscosity and Delta Phase angle slope, and a narrow molecular weight distribution, exhibited both a butterfly pattern and yellowing during film stretching. In addition, the resin compositions of Comparative Example 2-7, which had a high Delta Phase angle slope, and Comparative Example 2-8, which had a high Delta Phase angle slope and a high melting index, also exhibited both a butterfly pattern and yellowing during film stretching.

From these experimental results, it can be seen that the density, melt index, molecular weight distribution, Delta Zero shear viscosity, and Delta Phase angle slope of a polyethylene resin composition affect the thermal stability of the resin composition, and when the above properties are combined and controlled within an optimal range, the polyethylene resin composition has excellent thermal stability, and as a result, a stable stretching process can be achieved without butterfly patterns and yellowing occurring during film stretching.

Claims (14)

A polyethylene resin composition comprising polyethylene having an MFRR (MFR _21.6 /MFR _2.16 ) of 15 to 60, a neutralizing agent of a stearic acid metal salt, and an antioxidant, The above polyethylene resin composition satisfies the following conditions (i) to (iii): (i) a density of 0.9400 to 0.9700 g/cm3 as measured according to ASTM D 792; (ii) a melt index of 0.50 to 3.00 g/10 min measured under a load of 2.16 kg at 190°C according to ASTM D 1238; (iii) molecular weight distribution of 10.00 or more; and Using a rotary rheometer, steps 1 to 3 are sequentially performed according to the following measurement conditions, and the complex viscosity and phase angle at each step are measured, and the complex viscosity value of the first point with the lowest angular frequency is referred to as the zero shear viscosity, and the slope value (b) in the relationship y = a + bx obtained by fitting 7 points of the vGP plot (van. Gurp-Palmen plot) to a straight line model is referred to as the phase angle slope. When the zero shear viscosity and the phase angle slope at steps 1 and 3 are calculated, the polyethylene resin composition satisfies the conditions of (iv) to (vi): (iv) The change in zero shear viscosity calculated from the difference between the zero shear viscosity in step 1 and the zero shear viscosity in step 3 is 10,000 Pa·s or less; (v) the zero shear viscosity in step 1 below is 3,000 to 14,000 Pa·s; (vi) The phase angle slope change is 55 or less; <Measurement conditions> Step 1: Temperature 230℃, Frequency 0.1 to 100Hz sweep, Strain 0.5%, oscillation Step 2: Temperature 230℃, Frequency fixed at 1Hz, Strain 0.5%, oscillation for 30 minutes Step 3: Temperature 230℃, Frequency 0.1 to 100Hz sweep, Strain 0.5%, oscillation. In the first paragraph, The polyethylene resin composition, after performing step 1, is oscillated for 30 minutes under high temperature and oxygen conditions of 230°C, with a frequency of 1 Hz fixed, using a rotary rheological property measuring device, and when a phase angle change over time is measured and a graph of a phase angle change curve is derived from the results, the polyethylene resin composition has a phase angle inflection point of 700 seconds or longer in the phase angle change curve. In the first paragraph, A polyethylene resin composition, wherein the neutralizing agent is included in an amount of 100 to 2000 ppm based on the total weight of polyethylene. In the first paragraph, A polyethylene resin composition wherein the above stearic acid metal salt is a stearic acid metal salt containing an alkaline earth metal of Group 2 or a transition metal of Group 12. In the first paragraph, A polyethylene resin composition wherein the stearic acid metal salt comprises calcium stearate, zinc stearate, magnesium stearate or a mixture thereof. In the first paragraph, A polyethylene resin composition, wherein the antioxidant is included in an amount of 500 to 2200 ppm based on the total weight of polyethylene. In the first paragraph, The above antioxidant is a polyethylene resin composition comprising a primary antioxidant and a secondary antioxidant in a weight ratio of 1:1 to 1:2. In paragraph 7, A polyethylene resin composition, wherein the primary antioxidant comprises a phenolic compound, an aromatic amine compound, or a mixture thereof. In paragraph 7, A polyethylene resin composition comprising the primary antioxidant, pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, phenylnaphthylamine, 4,4'-(α,α-dimethylbenzyl)diphenylamine, N,N'-di-2-naphthyl-p-phenylenediamine or a mixture thereof. In paragraph 7, A polyethylene resin composition, wherein the secondary antioxidant comprises a phosphite compound, a sulfur compound, or a mixture thereof. In paragraph 7, A polyethylene resin composition, wherein the secondary antioxidant comprises tris(2,4-di-tert.-butylphenyl)phosphite, bis(2,4-di-tert.-butylphenyl)pentaerythritol diphosphite, bis(2,4-dicumylphenyl)pentaerythritol diphosphite, or a mixture thereof. In the first paragraph, The above polyethylene is a polyethylene resin composition that satisfies the conditions of (b1) and (b2) below: (b1) Melt index (MI _2.16 ) measured according to ASTM D 1238: 0.5 to 3.0 g/10 min. (b2) Density measured according to ASTM D 792: 0.940 to 0.970 g/cm ³ . In the first paragraph, The above polyethylene is a polyethylene resin composition which is a copolymer of ethylene and 1-hexene. A stretched film comprising a polyethylene resin composition according to claim 1.