Polyethylene resin composition for cover, manufacturing method therefor, and molded article

Abstract

Disclosed is a polyethylene resin composition for a bottle cap comprising a second polyethylene resin formed by continuous polymerization in a first reactor and a second reactor, in which a first polyethylene resin formed by polymerization in the first reactor has a weight average molecular weight of 0.8 * 105 g / mol to 1.7 * 105 g / mol and a molecular weight distribution of 4 to 9, the molecular weight distribution is defined as the ratio of the weight average molecular weight to the number average molecular weight, and a second polyethylene resin formed by polymerization of the first polyethylene resin transferred to the second reactor has a weight average molecular weight of 0.9 * 105 g / mol to 1.8 * 105 g / mol and a molecular weight distribution of 5 to 10, the molecular weight distribution is defined as a ratio of weight-average molecular weight to number-average molecular weight, and a ratio of weight-average molecular weight of the second polyethylene resin to weight-average molecular weight of the first polyethylene resin is 1.0 to 1.15.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of Korean Patent Application No. 10-2023-0175171 filed in the Korean Intellectual Property Office on December 6, 2023, the disclosure of which is incorporated herein by reference in its entirety. background 1. Technical Field

[0002] Embodiments of the present disclosure relate to a polyethylene resin composition for a bottle cap, a method for preparing the same, and a molded article produced therefrom. 2. Background technology

[0003] The use of plastics as bottle cap materials for glass bottles and beverage containers, such as polyethylene terephthalate (PET), is increasing due to the diversification of packaging containers and the expansion of recycling in environmental terms.

[0004] High-density polyethylene (HDPE) and polypropylene (PP) are mainly used as plastic bottle cap materials. Bottle caps made of these materials are more widely used due to advantages such as lighter weight, less corrosion, better moldability and the ability to form various designs compared to conventional aluminum bottle caps. In particular, HDPE is advantageously softer than polypropylene and is able to maintain the tightness of the contents without the use of a liner, unlike polypropylene bottle caps that require a separate liner to seal the beverage container.

[0005] One physical property essential to a screw cap is the opening torque of the cap, which means the force required to open the cap by twisting it to drink the beverage. When the opening torque is too large, the elderly and children cannot open the beverage, and when the opening torque is too small, there is a problem that the contents cannot be effectively preserved. Therefore, the range of the opening torque of the cap is usually important.

[0006] The information disclosed in this section is provided only for enhancement of understanding of the background of the present disclosure and therefore may contain information that does not constitute prior art. Summary of the invention

[0007] Embodiments of the present disclosure provide a polyethylene resin composition for a bottle cap, which is capable of providing a molded article having constant openability.

[0008] Another embodiment of the present disclosure provides a method of preparing a polyethylene resin composition for a bottle cap.

[0009] Another embodiment provides a molded article produced from the polyethylene resin composition for bottle caps.

[0010] One embodiment of the present disclosure provides a polyethylene resin composition for a bottle cap, which comprises a second polyethylene resin formed by continuous polymerization in a first reactor and a second reactor, wherein the first polyethylene resin formed by polymerization in the first reactor has a molecular weight of 0.8×10 5 g / mol to 1.7×10 5 The weight average molecular weight (Mw _1st ) and a molecular weight distribution (Mw _1st / Mn _1st , MWD _1st ), the molecular weight distribution (Mw _1st / Mn _1st , MWD _1st ) is defined as the weight average molecular weight (Mw _1st ) and number average molecular weight (Mn _1st ) ratio, the second polyethylene resin formed by the polymerization of the first polyethylene resin transferred to the second reactor has a ratio of 0.9×10 5 g / mol to 1.8×10 5 The weight average molecular weight (Mw _2nd ) and a molecular weight distribution (Mw _2nd / Mn _2nd , MWD _2nd ), the molecular weight distribution (Mw _2nd / Mn _2nd , MWD _2nd ) is defined as the weight average molecular weight (Mw _2nd ) and number average molecular weight (Mn _2nd ) ratio, and the weight average molecular weight (Mw _2nd ) and the weight average molecular weight (Mw _1st ) ratio (Mw _2nd / Mw _1st ) is 1.0 to 1.15.

[0011] The molecular weight distribution (MWD) of the second polyethylene resin _2nd ) and the molecular weight distribution (MWD) of the first polyethylene resin _1st ) ratio (MWD _2nd / MWD _1st ) can be from 1.0 to 1.4.

[0012] The first polyethylene resin may be present in an amount of about 40 wt % to about 60 wt % based on the total amount of the polyethylene resin composition.

[0013] The polyethylene resin composition may have a melt flow index (2.16 kg, 190° C.) of 2.0 g / 10 min to 10.0 g / 10 min.

[0014] The polyethylene resin composition may have a melt flow rate ratio (MFRR) of 25 to 35.

[0015] The density of the polyethylene resin composition can be 0.950 g / cm 3 Up to 0.965g / cm 3 .

[0016] Another embodiment provides a method for preparing a polyethylene resin composition for bottle caps, the method comprising: supplying a monomer, a catalyst, a comonomer, and hydrogen to a first reactor, transferring a first polyethylene resin formed by polymerization in the first reactor to a second reactor, and further supplying a monomer, a catalyst, a comonomer, and hydrogen to the second reactor to prepare a second polyethylene resin, wherein the hydrogen supplied to the first reactor is supplied at a supply ratio of 150 mg / kg to 300 mg / kg relative to the monomer, and the hydrogen supplied to the second reactor is supplied at a supply ratio of 200 mg / kg to 400 mg / kg relative to the monomer, and the first polyethylene resin is transferred to the second reactor in an amount of 40 wt % to 60 wt % relative to the total amount of the polyethylene resin composition.

[0017] The comonomer supplied to the first reactor may be supplied at a supply ratio of 5 g / kg to 40 g / kg with respect to the monomer.

[0018] The comonomer supplied to the second reactor may be supplied at a supply ratio of 10 g / kg to 60 g / kg relative to the monomer.

[0019] Another embodiment provides a molded article produced from the polyethylene resin composition for bottle caps.

[0020] The molded article may be a bottle cap. DETAILED DESCRIPTION

[0021] The embodiments are provided to more fully explain the present disclosure to those of ordinary skill in the art, the following embodiments may be modified in various other forms, and the scope of the present disclosure is not limited to the following embodiments.

[0022] One embodiment includes a polyethylene resin composition for bottle caps, which includes a second polyethylene resin formed by continuous polymerization in a first reactor and a second reactor, wherein the first polyethylene resin formed by polymerization in the first reactor has a molecular weight of 0.8×10 5 g / mol to 1.7×10 5 The weight average molecular weight (Mw _1st ) and a molecular weight distribution (Mw_1st / Mn _1st , MWD _1st ), the molecular weight distribution (Mw _1st / Mn _1st , MWD _1st ) is defined as the weight average molecular weight (Mw _1st ) and number average molecular weight (Mn _1st ), and the second polyethylene resin formed by polymerizing the first polyethylene resin transferred to the second reactor has a ratio of 0.9×10 5 g / mol to 1.8×10 5 The weight average molecular weight (Mw _2nd ) and a molecular weight distribution (Mw _2nd / Mn _2nd , MWD _2nd ), the molecular weight distribution (Mw _2nd / Mn _2nd , MWD _2nd ) is defined as the weight average molecular weight (Mw _2nd ) and number average molecular weight (Mn _2nd ) ratio, and the weight average molecular weight (Mw _2nd ) and the weight average molecular weight (Mw _1st ) ratio (Mw _2nd / Mw _1st ) is 1.0 to 1.15.

[0023] The polyethylene resin composition for bottle caps according to one embodiment can be formed by continuous polymerization using a two-stage reactor including a first reactor and a second reactor connected in series. Specifically, the first polyethylene resin is mainly formed by polymerization in the first reactor, and the first polyethylene resin obtained thereby is transferred to the second reactor and subjected to secondary polymerization to form the second polyethylene resin.

[0024] The first polyethylene resin formed by the polymerization in the first reactor has a molecular weight of 0.8×10 5 g / mol to 1.7×10 5 The weight average molecular weight (Mw _1st ) and 4 to 9 are defined as the weight average molecular weight (Mw _1st ) and number average molecular weight (Mn _1st ) ratio (Mw _1st / Mn _1st , MWD _1st ). For example, the first polyethylene resin has a 5 g / mol to 1.5×10 5The weight average molecular weight (Mw _1st ) and a molecular weight distribution (Mw _1st / Mn _1st , MWD _1st ). When the weight average molecular weight (Mw _1st ) and molecular weight distribution (Mw _1st / Mn _1st , MWD _1st ) falls within the above range, the opening torque falls within the range of 100 N·cm to 150 N·cm, thereby providing a molded product having constant opening properties as well as excellent impact strength and processability.

[0025] The second polyethylene resin formed by polymerizing the first polyethylene resin transferred to the second reactor has a molecular weight of 0.9×10 5 g / mol to 1.8×10 5 The weight average molecular weight (Mw _2nd ) and 5 to 10 are defined as the weight average molecular weight (Mw _2nd ) and number average molecular weight (Mn _2nd ) ratio (Mw _2nd / Mn _2nd , MWD _2nd ). For example, the second polyethylene resin has a 5 g / mol to 1.6×10 5 The weight average molecular weight (Mw _2nd ) and a molecular weight distribution (Mw _2nd / Mn _2nd , MWD _2nd ). When the weight average molecular weight (Mw _2nd ) and molecular weight distribution (Mw _2nd / Mn _2nd , MWD _2nd ) falls within the above range, the opening torque falls within the range of 100 N·cm to 150 N·cm, thereby providing a molded product having constant opening properties as well as excellent impact strength and processability.

[0026] The first polyethylene resin and the second polyethylene resin may be ethylene and carbon atoms C 3 To C 20 The copolymer of α-olefins and may be ethylene and, for example, C 4 To C 8 α-olefins or C 5 To C 8 Copolymers of α-olefins.

[0027] The weight average molecular weight (Mw) of the second polyethylene resin of the polyethylene resin composition for bottle caps _2nd ) and the weight average molecular weight (Mw _1st ) ratio (Mw _2nd / Mw _1st ) may be 1.0 to 1.15. For example, the ratio (Mw _2nd / Mw _1st ) can be 1.02 to 1.10. When the ratio (Mw _2nd / Mw _1st ) falls within the above-defined range, the opening torque falls within the range of 100 N·cm to 150 N·cm, thereby providing a molded product with constant opening properties.

[0028] The molecular weight distribution (MWD) of the second polyethylene resin _2nd ) and the molecular weight distribution (MWD) of the first polyethylene resin _1st ) ratio (MWD _2nd / MWD _1st ) may fall within the range of 1.0 to 1.4, for example, 1.0 to 1.2. When the molecular weight distribution index ratio (MWD _2nd / MWD _1st ) falls within the above-defined range, the opening torque falls within the range of 100 N·cm to 150 N·cm, thereby providing a molded product with constant opening properties.

[0029] The first polyethylene resin may be present in an amount of 40 wt % to 60 wt % based on the total amount of the polyethylene resin composition. When the first polyethylene resin is present within this content range, the opening torque falls within the range of 100 N·cm to 150 N·cm, so that the opening property of the molded product can be constant.

[0030] The melt flow index (2.16 kg, 190° C.) of the polyethylene resin composition for bottle caps may be 2.0 g / 10 min to 10.0 g / 10 min. That is, under a load of 2.16 kg at 190° C., the melt flow index may be 2.0 g / 10 min to 10.0 g / 10 min, for example, 2.0 g / 10 min to 8.5 g / 10 min (2.16 kg, 190° C.). When the melt flow index falls within this range, the polyethylene resin composition for bottle caps has excellent fluidity, and thus excellent processing properties may be ensured.

[0031] The melt flow rate ratio (MFRR) of the polyethylene resin composition for bottle caps may be 25 to 35, for example, 27 to 35. When the melt flow rate ratio (MFRR) falls within the above-defined range, the opening torque falls within the range of 100 N·cm to 150 N·cm, and thus the opening property of the molded product can be constant.

[0032] The density of the polyethylene resin composition for bottle caps can be 0.950 g / cm 3 Up to 0.965g / cm 3 , for example 0.953 g / cm 3 Up to 0.963g / cm 3 When the density falls within the above-defined range, the opening torque falls within the range of 100 N·cm to 150 N·cm, and thus the opening property of the molded product can be constant.

[0033] The flexural modulus of the polyethylene resin composition for bottle caps may be 8,000 kgf / cm 2 Up to 11,000kgf / cm 2 , for example 8,500kgf / cm 2 Up to 11,000kgf / cm 2 When the flexural modulus falls within the above-defined range, the opening torque falls within the range of 100 N·cm to 150 N·cm, and thus a molded product having constant opening properties as well as excellent impact strength and processability can be provided.

[0034] The polyethylene resin composition for a bottle cap according to another embodiment may further include an antioxidant, a neutralizer, a slip agent, or a combination thereof in addition to the first polyethylene resin and the second polyethylene resin.

[0035] The antioxidant may include 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, 1,6-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionamido]hexane, 1,6-bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionamido]propane, tetrakis[methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate)]methane, bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol-diphosphite, bis(2,4-di-tert-butylphenyl)pentaerythritol-diphosphite, or a combination thereof.

[0036] The antioxidant may be present in an amount of 0.01 to 0.5 parts by weight, for example 0.05 to 0.2 parts by weight, based on 100 parts by weight of the polyethylene resin composition for bottle caps. When the antioxidant is present within this content range, excellent processing properties may be obtained, viscosity changes may not occur during processing, and discoloration is not likely to occur during storage.

[0037] The neutralizer may include calcium stearate, zinc stearate, hydroxy magnesium aluminum carbonate, zinc oxide, hydroxy magnesium stearate or a combination thereof. Based on 100 parts by weight of the polyethylene resin composition, the neutralizer may be present in an amount of 0.01 to 0.3 parts by weight, for example 0.05 to 0.2 parts by weight. When the neutralizer is present within this content range, excellent processing properties may be obtained, there is no viscosity change during processing, and physical properties such as strength may be maintained.

[0038] The slip agent may include erucic acid amide, oleic acid amide, behenic acid amide, stearic acid amide or a combination thereof. Based on 100 parts by weight of the polyethylene resin composition, the slip agent may be present in an amount of 0.01 to 0.5 parts by weight, such as 0.05 to 0.2 parts by weight. When the slip agent is present within this content range, the bottle cap can be easily opened due to the low opening torque, and the odor problem caused by the bottle cap can be prevented.

[0039] Another embodiment provides a method for preparing a polyethylene resin composition for bottle caps, comprising: supplying monomers, catalysts, comonomers and hydrogen to a first reactor; transferring a first polyethylene resin formed by polymerization in the first reactor to a second reactor; and further supplying monomers, catalysts, comonomers and hydrogen to the second reactor to prepare a second polyethylene resin, wherein the hydrogen supplied to the first reactor is supplied at a supply ratio of 150 mg / kg to 300 mg / kg relative to the monomer, and the hydrogen supplied to the second reactor is supplied at a supply ratio of 200 to 400 mg / kg relative to the monomer, and the first polyethylene resin is transferred to the second reactor in an amount of 40 wt % to 60 wt % relative to the total amount of the polyethylene resin composition.

[0040] The polymerization in the first reactor and the second reactor can be carried out in the presence of a Ziegler-Natta catalyst. The Ziegler-Natta catalyst is a catalyst known as a conventional Ziegler-Natta catalyst, which is a transition metal compound of Group IV, Group V or Group VI of the periodic table as a main catalyst. Among them, the Ziegler-Natta catalyst can be a halogenated complex composed of magnesium and titanium or magnesium and vanadium.

[0041] The comonomer may be C 3 To C 20α -Olefins, such as C 4 To C 8 α-olefins, or C 5 To C 8α-olefin. The comonomer supplied to the first reactor can be supplied at a supply ratio of 5g / kg to 40g / kg relative to the monomer, for example, it can be supplied at a supply ratio of 10g / kg to 30g / kg. In addition, the comonomer supplied to the second reactor can be supplied at a supply ratio of 10g / kg to 60g / kg relative to the monomer, for example, at a supply ratio of 20g / kg to 50g / kg. When the comonomer is supplied to the first reactor and the second reactor in the range of this supply ratio, a polyethylene resin composition for a bottle cap having an opening torque of 100·N·cm to 150N·cm can be prepared, and a molded product having constant opening properties while exhibiting excellent impact strength and processing properties is provided.

[0042] When the first polyethylene resin and the second polyethylene resin are formed in the first reactor and the second reactor, respectively, the resins can be polymerized together by supplying hydrogen thereto. Hydrogen can be supplied to the first reactor at a supply ratio of 150 to 300 mg / kg relative to the monomer, for example, at a supply ratio of 160 to 280 g / kg. In addition, hydrogen can be supplied to the second reactor at a supply ratio of 200 to 400 mg / kg relative to the monomer, for example, at a supply ratio of 230 to 380 g / kg.

[0043] When the supply ratio of the hydrogen supplied to the first reactor and the second reactor falls within the above range, the polyethylene resin composition for a bottle cap has excellent fluidity and processability and high impact strength.

[0044] The first polyethylene resin may be transferred to the second reactor in an amount of 40 to 60 wt % based on the total amount of the polyethylene resin composition. When the content of the first polyethylene resin transferred to the second reactor falls within the above-defined range, the opening torque falls within the range of 100 to 150 N·cm, and thus a molded product having a constant opening property can be provided.

[0045] The polymerization in the first reactor may be carried out at a pressure of 40 to 50 bar and a temperature of 70 to 100° C. for a residence time of 40 to 70 minutes, for example, at a pressure of 42 to 48 bar and a temperature of 80 to 100° C. for a residence time of 50 to 65 minutes. In addition, the polymerization in the second reactor may be carried out at a pressure of 40 to 50 bar and a temperature of 80 to 110° C. for a residence time of 20 to 50 minutes, for example, at a pressure of 42 to 48 bar and a temperature of 90 to 105° C. for a residence time of 25 to 40 minutes. When the process conditions do not fall within the above range, productivity may decrease, and production costs may increase.

[0046] Another embodiment provides a molded article produced from the polyethylene resin composition for bottle caps.

[0047] The molded article may be a bottle cap, for example a lightweight and thin bottle cap.

[0048] The specific embodiments of the present disclosure will be described below. However, the embodiments described below are only provided to give examples or illustrate the present disclosure in detail and should not be construed as limiting the scope of the present disclosure. In addition, other details that those skilled in the art can fully think of technically will not be repeated.

[0049] (Preparation of polyethylene resin composition)

[0050] Example 1

[0051] Two 90 L reactors of the respective stages were connected in series by continuous slurry polymerization, a known Ziegler-Natta catalyst containing magnesium and titanium was prepared by a conventional method as a main catalyst, and polymerization was performed using 1-hexene as a comonomer.

[0052] Ethylene as a monomer and 1-hexene as a comonomer are supplied to the first reactor and the second reactor to polymerize a polyethylene resin of a copolymer. The first polyethylene resin formed by polymerization in the first reactor is transferred to the second reactor as a copolymer and then continuously polymerized in the second reactor to form a second polyethylene resin. The ratio of the polymerization amount in the first reactor to the polymerization amount in the second reactor is a weight ratio of 50 / 50.

[0053] At this time, the polymerization temperature of the first reactor was 95°C, and the polymerization temperature of the second reactor was 98°C. 2 ) is 21 g / kg to supply 1-hexene as a comonomer to the first reactor, and the comonomer is 1-heptene at a supply ratio of 21 g / kg relative to ethylene (C 2 ) was supplied with hydrogen at a supply ratio of 260 mg / kg. 2 ) is 34 g / kg, and 1-hexene is supplied to the second reactor as a comonomer, and the feed ratio relative to ethylene (C 2 ) was supplied with hydrogen at a supply ratio of 285 mg / kg.

[0054] 100 parts by weight of the powdered polyethylene resin obtained above was mixed with 0.025 parts by weight of Iragnox-1010 as an antioxidant, 0.05 parts by weight of Irgafos-168 and 0.1 parts by weight of calcium stearate as a neutralizer using a Henschel mixer, and then a polyethylene resin composition in the form of pellets was prepared using a twin-screw extruder.

[0055] The polymerization conditions in the first reactor and the second reactor of Examples 1 to 4 and Comparative Examples 1 to 7 are shown in Table 1 and Table 2, respectively.

[0056] Example 2

[0057] A polyethylene resin composition was prepared in the same manner as in Example 1, except that the conditions shown in the following Table 1 were used.

[0058] That is, relative to ethylene (C 2 ) is 13 g / kg to supply 1-hexene as a comonomer to the first reactor, and the comonomer is 10 g / kg relative to ethylene (C 2 ) was supplied with hydrogen at a supply ratio of 270 mg / kg. 2 ) is 22 g / kg to supply 1-hexene as a comonomer to the second reactor, and the comonomer is 1-heptene at a supply ratio of 22 g / kg relative to ethylene (C 2 ) was supplied with hydrogen at a supply ratio of 290 mg / kg.

[0059] Example 3

[0060] A polyethylene resin composition was prepared in the same manner as in Example 1, except that the conditions shown in the following Table 1 were used.

[0061] That is, relative to ethylene (C 2 ) is 23 g / kg to supply 1-hexene as a comonomer to the first reactor, and the comonomer is 1-heptene at a supply ratio of 23 g / kg relative to ethylene (C 2 ) was supplied with hydrogen at a supply ratio of 170 mg / kg. 2 ) is 39 g / kg to supply 1-hexene as a comonomer to the second reactor, and the supply ratio relative to ethylene (C 2 ) was supplied with hydrogen at a supply ratio of 250 mg / kg.

[0062] Example 4

[0063] A polyethylene resin composition was prepared in the same manner as in Example 1, except that the conditions shown in the following Table 1 were used.

[0064] That is, relative to ethylene (C 2 ) is 24 g / kg to supply 1-hexene as a comonomer to the first reactor, and the comonomer is 1-heptene at a supply ratio of 24 g / kg relative to ethylene (C 2 ) was supplied with hydrogen at a supply ratio of 265 mg / kg. 2 ) is 35 g / kg, and 1-hexene is supplied to the second reactor as a comonomer, and the supply ratio relative to ethylene (C 2 ) was supplied with hydrogen at a supply ratio of 375 mg / kg.

[0065] Comparative Example 1

[0066] A polyethylene resin composition was prepared in the same manner as in Example 1, except that the conditions shown in Table 2 below were used.

[0067] That is, relative to ethylene (C 2 ) is 14 g / kg to supply 1-hexene as a comonomer to the first reactor, and the comonomer is 1-heptene at a supply ratio of 14 g / kg relative to ethylene (C 2 ) was supplied with hydrogen at a supply ratio of 320 mg / kg. 2 ) is 22 g / kg to supply 1-hexene as a comonomer to the second reactor, and the comonomer is 1-heptene at a supply ratio of 22 g / kg relative to ethylene (C 2 ) is supplied with 290 mg / kg of hydrogen.

[0068] The properties of the first polyethylene resin, the second polyethylene resin and the polyethylene resin composition according to each comparative example are shown in Table 4 below.

[0069] Comparative Example 2

[0070] A polyethylene resin composition was prepared in the same manner as in Example 1, except that the conditions shown in Table 2 below were used.

[0071] That is, relative to ethylene (C 2 ) is 7 g / kg to supply 1-hexene as a comonomer to the first reactor, and the comonomer is 1-heptene at a supply ratio of 7 g / kg relative to ethylene (C 2 ) was supplied with hydrogen at a supply ratio of 490 mg / kg. 2 ) is 13 g / kg to supply 1-hexene as a comonomer to the second reactor, and the comonomer is 10 g / kg relative to ethylene (C 2 ) was supplied with hydrogen at a supply ratio of 130 mg / kg.

[0072] Comparative Example 3

[0073] A polyethylene resin composition was prepared in the same manner as in Example 1, except that the conditions shown in Table 2 below were used.

[0074] That is, relative to ethylene (C 2 ) is 18 g / kg to supply 1-hexene as a comonomer to the first reactor, and the comonomer is 1-heptene at a supply ratio of 18 g / kg relative to ethylene (C 2 ) was supplied with hydrogen at a supply ratio of 290 mg / kg. 2 ) is 32 g / kg to supply 1-hexene as a comonomer to the second reactor, and the comonomer is 1-heptene at a supply ratio of 32 g / kg relative to ethylene (C 2) was supplied with hydrogen at a supply ratio of 460 mg / kg.

[0075] Comparative Example 4

[0076] A polyethylene resin composition was prepared in the same manner as in Example 1, except that the conditions shown in Table 2 below were used.

[0077] That is, relative to ethylene (C 2 ) is 20 g / kg to supply 1-hexene as a comonomer to the first reactor, and the comonomer is 1-heptene at a supply ratio of 20 g / kg relative to ethylene (C 2 ) was supplied with hydrogen at a supply ratio of 210 mg / kg. 2 ) is 38 g / kg to supply 1-hexene as a comonomer to the second reactor, and the supply ratio relative to ethylene (C 2 ) was supplied with hydrogen at a supply ratio of 370 mg / kg. The ratio of the polymerization amount in the first reactor to the polymerization amount in the second reactor was a weight ratio of 38 / 62.

[0078] Comparative Example 5

[0079] A polyethylene resin composition was prepared in the same manner as in Example 1, except that the conditions shown in Table 2 below were used.

[0080] That is, relative to ethylene (C 2 ) is 35 g / kg to supply 1-hexene as a comonomer to the first reactor, and the comonomer is 1-heptene at a supply ratio of 35 g / kg relative to ethylene (C 2 ) was supplied with hydrogen at a supply ratio of 980 mg / kg. No comonomer was supplied to the second reactor, and the comonomer was 1.5 mmol / L relative to ethylene (C 2 ) was supplied with hydrogen at a supply ratio of 110 mg / kg. The ratio of the polymerization amount in the first reactor to the polymerization amount in the second reactor was a weight ratio of 49 / 51.

[0081] Comparative Example 6

[0082] A polyethylene resin composition was prepared in the same manner as in Example 1, except that the conditions shown in Table 2 below were used.

[0083] That is, relative to ethylene (C 2 ) is 27 g / kg to supply 1-hexene as a comonomer to the first reactor, and the comonomer is 1-heptene at a supply ratio of 27 g / kg relative to ethylene (C 2 ) was supplied with hydrogen at a supply ratio of 230 mg / kg. No comonomer was supplied to the second reactor, and the comonomer was 2.0 mg / kg relative to ethylene (C 2) was supplied with hydrogen at a supply ratio of 170 mg / kg. The ratio of the polymerization amount in the first reactor to the polymerization amount in the second reactor was a weight ratio of 49 / 51.

[0084] Comparative Example 7

[0085] A polyethylene resin composition was prepared in the same manner as in Example 1, except that the conditions shown in Table 2 below were used.

[0086] That is, relative to ethylene (C 2 ) is 26 g / kg to supply 1-hexene as a comonomer to the first reactor, and the comonomer is 1-heptene at a supply ratio of 26 g / kg relative to ethylene (C 2 ) was supplied with hydrogen at a supply ratio of 57 mg / kg. No comonomer was supplied to the second reactor, and the comonomer was 1.5 mg / kg relative to ethylene (C 2 ) was supplied with hydrogen at a supply ratio of 80 mg / kg. The ratio of the polymerization amount in the first reactor to the polymerization amount in the second reactor was a weight ratio of 49 / 51.

[0087] [Table 1].

[0088] [Table 2]

[0089] Test 1: Measurement of physical properties of polyethylene resin compositions

[0090] The following physical properties of the first polyethylene resin, the second polyethylene resin and the polyethylene resin composition according to Examples 1 to 4 and Comparative Examples 1 to 7 were measured and the results are shown in Tables 3 and 4 below.

[0091] Melt flow index (MI)

[0092] Melt flow index (MI) was measured according to ASTM D1238 at 190°C with loads of 2.16 kg and 21.6 kg.

[0093] Melt Flow Rate Ratio (MFRR)

[0094] MI 21.6 (Melt flow index measured at 190°C with a load of 21.6 kg) / MI 2.16 (Melt flow index measured at 190°C with 2.16 kg load).

[0095] density

[0096] Measured according to ASTM D1505.

[0097] Molecular weight distribution (MWD)

[0098] The molecular weight distribution is defined as the ratio of the number average molecular weight (Mn) to the weight average molecular weight (Mw) Mw / Mn. The molecular weight is measured by gel permeation chromatography (GPC).

[0099] Spiral Flow Length (SFL)

[0100] The molding machine used in this article is a model SI80III-F200 from Toyo, the mold is an Archimedean screw mold with a width of 10 mm, a thickness of 2 mm, and a maximum length of 2,000 mm, and the injection molding is carried out under the following conditions: injection pressure is 1,000 kgf / cm 2 , the injection temperature was 235°C, the injection speed was 30 mm / sec, and the mold temperature was 50°C, and the cooling time was 10 seconds.

[0101] Izod impact strength

[0102] After injection molding into a specimen having ASTM-4 dimensions and aging for 48 hours, the Izod impact strength was measured at 23° C. according to ASTM D256.

[0103] Flexural modulus

[0104] Flexural modulus was measured at 23°C according to ASTM D790 after injection molding into specimens having ASTM-4 dimensions and aging for 48 hours.

[0105] Bottle cap molding

[0106] The bottle caps were molded using an injection molding machine having 48 cavities and a size of 28 mm, and the molding was performed at an injection temperature of 250° C., an injection pressure of 175 bar, an injection speed of 160 mm / sec, and an injection holding pressure of 45 bar.

[0107] Opening torque

[0108] The molded bottle cap was annealed at room temperature for 48 hours, a 500 mL polyethylene terephthalate container was filled with 90% water, and then the bottle cap was closed with a force of 18 lb-in. The torque was measured 100 times using a torque meter. The number of times the opening torque exceeded the range of 100 N·cm 150 N·cm in 100 times was defined as the defect rate.

[0109] [Table 3]

[0110] [Table 4]

[0111] As can be seen from Tables 3 and 4 above, the melt flow index of the polyethylene resin composition of Examples 1 to 4 is in the range of 2.0 g / 10 min to 10.0 g / 10 min, indicating excellent fluidity and processability. In addition, the Izod impact strength of the polyethylene resin composition is 5 kJ / m 2 or higher, indicating excellent impact strength when used as a bottle cap. In addition, the flexural modulus of the polyethylene resin composition was 8,000 kgf / cm 2 Up to 11,000kgf / cm 2 , which means that the composition is flexible, thus allowing the contents to be kept sealed without the use of a separate liner.

[0112] Furthermore, the opening torques of the bottle caps produced from the polyethylene resin compositions of Examples 1 to 4 were 100 to 150 N·cm, and therefore, the defect rate was zero in all cases, indicating that molded products having consistent opening properties could be provided.

[0113] Meanwhile, the polyethylene resin compositions of Comparative Examples 1 to 7 exhibited excellent fluidity and Izod impact strength, while the opening torque of the bottle caps produced from the polyethylene resin compositions of Comparative Examples 1 to 7 was outside the range of 100 N·cm to 150 N·cm, and thus the defect rate increased significantly. Therefore, the polyethylene resin composition for a bottle cap according to one embodiment has an opening torque of 100 N·cm to 150 N·cm, thereby providing a molded product having constant opening properties as well as excellent processability and impact strength.

[0114] As apparent from the above description, the polyethylene resin composition for a bottle cap according to one embodiment exhibits an opening torque of 100 to 150 N·cm, thus providing a molded product having constant opening properties as well as excellent processability and impact strength.

[0115] Although the preferred embodiments of the present disclosure have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the disclosure as disclosed in the accompanying claims.

Claims

1. A polyethylene resin composition for bottle caps, the polyethylene resin composition comprising a second polyethylene resin formed by continuous polymerization in a first reactor and a second reactor, in, The first polyethylene resin formed by the polymerization in the first reactor has a molecular weight of 0.8×10 5 g / mol to 1.7×10 5 The weight average molecular weight (Mw _1st ) and a molecular weight distribution (Mw _1st / Mn _1st , MWD _1st ), the molecular weight distribution (Mw _1st / Mn _1st , MWD _1st ) is defined as the weight average molecular weight (Mw _1st ) and number average molecular weight (Mn _1st ), The second polyethylene resin formed by polymerization of the first polyethylene resin transferred to the second reactor has a molecular weight of 0.9×10 5 g / mol to 1.8×10 5 The weight average molecular weight (Mw _2nd ) and a molecular weight distribution (Mw _2nd / Mn _2nd , MWD _2nd ), the molecular weight distribution is defined as the weight average molecular weight (Mw _2nd ) and number average molecular weight (Mn _2nd ) and The weight average molecular weight (Mw) of the second polyethylene resin _2nd ) and the weight average molecular weight (Mw _1st ) ratio (Mw _2nd / Mw _1st ) is 1.0 to 1.

15.

2. The polyethylene resin composition according to claim 1, wherein The molecular weight distribution (MWD) of the second polyethylene resin _2nd ) and the molecular weight distribution (MWD) of the first polyethylene resin _1st ) ratio (MWD _2nd / MWD _1st ) is 1.0 to 1.

4.

3. The polyethylene resin composition according to claim 1, wherein The first polyethylene resin is present in an amount of 40 wt % to 60 wt % based on the total amount of the polyethylene resin composition.

4. The polyethylene resin composition according to claim 1, wherein The polyethylene resin composition has a melt flow index of 2.0 g / 10 min to 10.0 g / 10 min when measured at 190° C. with a load of 21.6 kg.

5. The polyethylene resin composition according to claim 1, wherein The polyethylene resin composition has a melt flow rate ratio of 25 to 35.

6. The polyethylene resin composition according to claim 1, wherein The density of the polyethylene resin composition is 0.950 g / cm 3 Up to 0.965g / cm 3 .

7. A method for preparing a polyethylene resin composition for a bottle cap, the method comprising: supplying monomer, catalyst, comonomer and hydrogen to the first reactor; transferring a first polyethylene resin formed by polymerization in the first reactor to a second reactor; as well as further supplying monomer, catalyst, comonomer and hydrogen to the second reactor to produce a second polyethylene resin, wherein hydrogen is supplied to the first reactor at a supply ratio of 150 to 300 mg / kg relative to the monomer, and hydrogen is supplied to the second reactor at a supply ratio of 200 to 400 mg / kg relative to the monomer, and the first polyethylene resin is transferred to the second reactor in an amount of 40 to 60 wt % relative to the total amount of the polyethylene resin composition.

8. The method according to claim 7, wherein: The comonomer supplied to the first reactor is supplied at a supply ratio of 5 g / kg to 40 g / kg relative to the monomer.

9. The method according to claim 7, wherein: The comonomer supplied to the second reactor is supplied at a supply ratio of 10 g / kg to 60 g / kg relative to the monomer.

10. A molded article produced from the polyethylene resin composition for bottle caps according to any one of claims 1 to 6.

11. The molded article according to claim 10, wherein The molded article is a bottle cap.

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