阅读说明：本技术 聚乙烯树脂组合物及由其制备的二次电池用分离膜 (Polyethylene resin composition and separation membrane for secondary battery prepared from same ) 是由 韩礼恩 金东镇 韩在爀 朴智溶 于 2021-05-10 设计创作，主要内容包括：本发明涉及聚乙烯树脂组合物及利用该聚乙烯树脂组合物制备的二次电池用分离膜,上述聚乙烯树脂组合物包含具有相对较高的高负荷熔体流动指数的乙烯均聚物(A)20重量％至80重量％；和具有相对较低的高负荷熔体流动指数的乙烯均聚物(B)20重量％至80重量％；上述乙烯均聚物的高负荷熔体流动指数(190℃、21.6kg)之比(A/B)为3～500。根据本发明,聚乙烯树脂组合物可以在发挥优秀加工性的同时,确保应用其的成型品的孔隙率等机械物性。(The present invention relates to a polyethylene resin composition comprising 20 to 80% by weight of an ethylene homopolymer (a) having a relatively high load melt flow index; and 20 to 80 wt.% of an ethylene homopolymer (B) having a relatively low high load melt flow index; the ethylene homopolymer has a ratio (A/B) of high load melt flow index (190 ℃, 21.6kg) of 3 to 500. According to the present invention, the polyethylene resin composition can ensure mechanical properties such as porosity of a molded article using the polyethylene resin composition while exhibiting excellent processability.)

1. A polyethylene resin composition characterized in that,

comprising 20 to 80% by weight of a high-ethylene homopolymer A having a relatively high melt flow index at 190 ℃ under a high load, measured at 21.6kg, and 20 to 80% by weight of a low-ethylene homopolymer B having a relatively low melt flow index at 190 ℃ under a high load, measured at 21.6 kg;

the ratio A/B of the high-load melt flow index measured at 190 ℃ under 21.6kg of the high-ethylene homopolymer A to the low-ethylene homopolymer B is 3 to 500.

2. The polyethylene resin composition according to claim 1,

the high-load melt flow index of the high-ethylene homopolymer A is 0.3g/10 min to 5.0g/10 min measured at 190 ℃ under the condition of 21.6kg,

the low-ethylene homopolymer B has a high-load melt flow index of 0.01g/10 min to 0.10g/10 min, measured at 190 ℃ under the condition of 21.6 kg.

3. The polyethylene resin composition according to claim 1,

the polyethylene resin composition has a high load melt flow index of 0.3g/10 min to 2.0g/10 min measured at 190 ℃ under 21.6 kg.

4. The polyethylene resin composition according to claim 1,

the polyethylene resin composition has a density of 0.935g/cm³To 0.960g/cm³。

5. The polyethylene resin composition according to claim 1,

the polyethylene resin composition further comprises 0.01 to 0.5 parts by weight of an antioxidant, 0.01 to 0.3 parts by weight of a neutralizer or a mixture thereof, based on 100 parts by weight of the polyethylene resin composition.

6. The polyethylene resin composition according to claim 5,

the antioxidant is one or more selected from 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 and bis (2,4-di-tert-butylphenyl) pentaerythritol diphosphite.

7. The polyethylene resin composition according to claim 5,

the neutralizer is calcium stearate, zinc stearate, magnesium aluminum hydroxycarbonate, zinc oxide, magnesium hydroxystearate or a mixture thereof.

8. A separation membrane for a secondary battery prepared using the polyethylene resin composition according to any one of claims 1 to 7.

Technical Field

The present invention relates to a bimodal (bimodal) polyethylene resin composition capable of ensuring mechanical properties of a molded article while exhibiting excellent processability, and a separation membrane for a secondary battery prepared therefrom.

Background

A secondary battery, particularly a separation membrane for a lithium secondary battery, is used as a porous thin film existing between a positive electrode and a negative electrode of the secondary battery, in order to prevent direct short-circuiting between the positive electrode and the negative electrode while allowing an electrolyte and lithium cations to easily permeate therethrough during charge and discharge of the battery.

The separator for a lithium secondary battery is required to have characteristics of separating a positive electrode and a negative electrode to achieve electrical insulation, and improving permeability of lithium ions and ion conduction by virtue of high porosity. In addition, the separator should have mechanical strength that can be endured by external impact or during high-speed winding during battery assembly, and prevent ignition and explosion of the battery due to thermal contraction of the separator caused by overcharge, high-temperature exposure, and the like.

Therefore, continuous research is being conducted on a composition that can ensure mechanical properties, particularly high porosity, of a separation membrane while exhibiting excellent processability when formed into a microporous separation membrane.

Disclosure of Invention

The purpose of the present invention is to provide a bimodal (bimodal) polyethylene resin composition that can ensure the mechanical properties of a molded article to which the bimodal polyethylene resin composition is applied while exhibiting excellent processability, and a separation membrane for a secondary battery produced from the bimodal polyethylene resin composition.

To achieve the object, the present invention provides a polyethylene resin composition characterized by comprising 20 to 80% by weight of a high-ethylene homopolymer (a) having a relatively high load melt flow index (190 ℃, 21.6kg), and 20 to 80% by weight of a low-ethylene homopolymer (B) having a relatively low high load melt flow index (190 ℃, 21.6 kg); the ratio (A/B) of the high-load melt flow index (190 ℃, 21.6kg) of the high-ethylene homopolymer (A) to the low-ethylene homopolymer (B) is 3 to 500.

The polyethylene resin composition of the present invention can ensure mechanical properties such as porosity of a molded article using the polyethylene resin composition while exhibiting excellent processability.

Detailed Description

The present invention is explained in more detail below.

The present invention provides a polyethylene resin composition characterized by comprising 20 to 80% by weight of a high-ethylene homopolymer (A) having a relatively high load melt flow index (190 ℃, 21.6kg) and 20 to 80% by weight of a low-ethylene homopolymer (B) having a relatively low high load melt flow index (190 ℃, 21.6 kg); the ratio (A/B) of the high-load melt flow index (190 ℃, 21.6kg) of the high-ethylene homopolymer (A) to the low-ethylene homopolymer (B) is 3 to 500.

In the present specification, "high ethylene homopolymer (A)" means an ethylene homopolymer (A) having a relatively high load melt flow index (190 ℃, 21.6 kg).

In the present specification, "low ethylene homopolymer (B)" means an ethylene homopolymer (B) having a relatively low high load melt flow index (190 ℃, 21.6 kg).

If the ratio of the high load melt flow index (190 ℃, 21.6kg) of the ethylene homopolymer (A, B) is less than 3, the processability is lowered, and if it exceeds 500, the mechanical properties are lowered.

According to the invention, the ethylene homopolymer (A, B) may have a ratio of high load melt flow index (190 ℃, 21.6kg) of 3 to 500, preferably 5 to 100.

The ethylene homopolymer (A) had a melt flow index of 0.3g/10 min to 5.0g/10 min as measured at 190 ℃ under a 21.6kg load. When the melt flow index of the ethylene homopolymer (A) is less than 0.3g/10 min under a high load (21.6kg, 190 ℃), the flowability of the resin is lowered during extrusion processing of the film, and the processability is lowered, so that the density of the extruded film is too high, and there is a fear that the micropores intended for the present invention cannot be normally formed during stretching. If the melt flow index under high load exceeds 5.0g/10 minutes, there is a fear that pores are not normally formed during elongation processing and mechanical properties such as tensile strength of the film are deteriorated.

The ethylene homopolymer (a) may be contained in an amount of 20 to 80% by weight, for example, 30 to 60% by weight, based on 100% by weight of the total composition. When the ethylene homopolymer (A) is less than 20% by weight, the improvement of processability is limited, and when it exceeds 80% by weight, the physical properties are deteriorated.

The ethylene homopolymer (B) had a melt flow index of 0.01g/10 min to 0.1g/10 min as measured at 190 ℃ under a 21.6kg load. If the melt flow index of the ethylene homopolymer (B) is less than 0.01g/10 min, the processability tends to be low, and the film appearance such as fish eyes tends to be poor, while if the melt flow index exceeds 0.1g/10 min, the mechanical properties tend to be low.

The ethylene homopolymer (B) may be contained in an amount of 20 to 80% by weight, relative to 100% by weight of the composition. When the ethylene homopolymer (B) is less than 20% by weight, the processability is excellent, but the mechanical properties may be deteriorated, and when it exceeds 80% by weight, the mechanical properties are excellent, but the processability is deteriorated.

The polyethylene resin composition of the present invention may be a mixture of the ethylene homopolymer (a) and the ethylene homopolymer (B). The high load melt flow index of the above polyethylene resin composition is 0.3g/10 min to 2.0g/10 min when measured under a 21.6kg load at 190 ℃.

The density of the polyethylene resin composition may be 0.935g/cm³To 0.960g/cm³. When the density is lower than the above range, there is a fear that the mechanical strength of the membrane becomes weak, and when the density is higher than the above range, the separation membrane may be difficult to mold.

The polyethylene resin composition of the present invention may further comprise 0.01 to 0.5 parts by weight, preferably 0.05 to 0.2 parts by weight of an antioxidant and 0.01 to 0.3 parts by weight, preferably 0.05 to 0.2 parts by weight of a neutralizing agent, relative to 100 parts by weight of the total composition.

If the content of the antioxidant is less than 0.01 part by weight, there are problems such as viscosity change during processing and unevenness of the film surface, and if it exceeds 0.5 part by weight, there are problems such as appearance of the film surface and contamination of the roll due to migration (migration) of the antioxidant to the film surface.

Representative examples of the antioxidant include 1,3,5-Trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) benzene (1,3, 5-trimethy-2, 4,6-tris (3,5-di-tert-butyl-4-hydroxyphenyl) bezene), 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 ] hexane), 1,6-Bis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionamido ] propane (1,6-Bis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionamido ] propane, Tetrakis [ methylene (3,5-di-tert-butyl-4-hydroxyhydrocinnamate) ] methane (tetrakis [ methyl (3,5-di-tert-butyl-4-hydroxyhydrocinnamate) ] methane), Bis (2,6-di-tert-butyl-4-methylphenyl) pentaerythritol diphosphite (Bis (2,6-di-tert-butyl-4-methylphenyl) pentaerythrityl-di-phoshphite), and Bis (2,4-di-tert-butylphenyl pentaerythritol diphosphite (Bis (2,4-di-tert-butylphenyl) pentaerythrityl-di-phoshphite), and the like.

The polyethylene resin composition of the present invention may further comprise 0.01 to 0.3 parts by weight of a neutralizing agent, relative to 100 parts by weight of the total composition. If the content of the neutralizing agent is less than 0.01 parts by weight, discoloration and viscosity change occur during processing, and if it exceeds 0.3 parts by weight, the neutralizing agent migrates (migration) to the film surface, resulting in problems such as film surface appearance and roll contamination.

As representative examples of the above-mentioned neutralizing agent, calcium stearate, zinc stearate, magnesium aluminum hydroxycarbonate, zinc oxide, magnesium hydroxystearate, or a mixture thereof, and the like can be included.

The method for producing the above-mentioned polyethylene resin composition is not particularly limited, and a known production method of a polyethylene resin composition can be usually used as it is or with appropriate modification. For example, it can be prepared according to the preparation method of ultra-high molecular weight polyethylene disclosed in korean patent No. R10-1826447.

The polyethylene resin composition of the present invention can be prepared into a microporous separation membrane used as a separation membrane for a secondary battery. As one example, the secondary battery may be a lithium secondary battery. The above separation membrane may have a thickness of 1 μm to 100 μm, for example, 1 μm to 50 μm, and may have a porosity of 20% to 99%, for example, 40% to 70%, but is not limited thereto.

The separation membrane for a secondary battery using the above polyethylene resin composition can be easily prepared by a person of ordinary skill according to a method known in the corresponding technical field.

As an example, it may include: (1) a step of extruding the polyethylene resin composition together with paraffin oil, passing between a casting roll (casting roll) and a nip roll (nip roll) to prepare a gel-like sheet; (2) a step of preparing a film by stretching the gel sheet; (3) forming micropores in the film; (4) and (4) a heat setting step.

In the step (1), the resin composition is charged and melted together with the paraffin oil at a temperature of 180 to 250 ℃ using, for example, a twin-screw extruder, and a gel sheet is prepared by T-molding.

In the step (2), the gel-like sheet prepared in the step (1) may be stretched 5 to 15 times in the longitudinal direction (machine direction) and the transverse direction (transverse direction) sequentially or simultaneously to prepare a film.

In the above step (3), the stretched membrane is immersed in an extraction solvent such as a hydrocarbon such as pentane, hexane, heptane or the like, a chlorinated hydrocarbon such as dichloromethane, carbon tetrachloride or the like, a fluorinated hydrocarbon, diethyl ether or the like to remove the paraffin-based oil, thereby forming micropores in the membrane.

In the step (4), heat setting is performed at 110 to 150 ℃ to remove residual stress.

The following examples are given to illustrate preferred embodiments of the present invention, but they are given only for the purpose of facilitating understanding of the present invention and are not intended to limit the scope of the present invention.

Preparation of separation membrane: microporous membrane prepared using polyethylene resin

The polyethylene resin compositions used in examples 1 to 6 and comparative examples 1 to 3 are collated in tables 1 and 2 below. Irganox 1010(i-1010), Irgafos 168(i-168) and calcium stearate (calcium stearate) were added as additives in amounts of 2000 ppm by weight, 2000 ppm by weight and 2000 ppm by weight, respectively, based on 100 parts by weight of the total composition, and the mixture was all charged into a Henschel mixer (Henschel mixer) at once and kneaded. The kneaded powdery resin composition was charged into a kneading extruder (HANKOOK E.M, 32mm double-head extruder) together with a paraffin oil (LP 350F, yoto oil chemical corporation) (30 wt% resin, 70 wt% paraffin oil), kneaded at 200 ℃, and extruded into a T-die to prepare a gel sheet. After the gel sheet was stretched 8 times in the longitudinal direction (machine direction) and the transverse direction (transverse direction) at the same time to prepare a film, the film was immersed in a dichloromethane extraction solvent to remove paraffin oil, thereby preparing a microporous film (separation film).

[ TABLE 1 ]

[ TABLE 2 ]

Physical property measurement/evaluation item and test method thereof

The physical properties of the separation membranes prepared in examples 1 to 6 and comparative examples 1 to 3 were measured as follows.

High load melt flow index (HLMI)

The measurement was carried out at 190 ℃ under a 21.6kg load according to ASTM D1238.

Density (Density)

Measurements were made according to ASTM D1505.

Thickness of

The thickness of the film was measured according to ASTM D374.

Degree of ventilation

According to Japanese Industrial Standard (JIS)Erley (GURLEY) measurements at ambient temperature of 100mL of air at 4.8 inches H₂O passing through 1 inch square (inch) at a specified pressure²) The time (seconds) required for the microporous membrane.

Puncture strength (punture)

The puncture strength was measured at a speed of 10 mm/sec using a KES-G5 instrument of Kato Tech, Inc., Japan, using a tip accessory (tip) having a tip end portion diameter of 1 mm.

Porosity of the material

The porous film was cut into 50m in the longitudinal direction and the transverse direction, respectively, and the thickness and the weight were measured, and the density was calculated. I.e. the volume is measured in longitudinal x transverse x thickness, the density (p)₁) Calculated as the measured weight divided by the volume. The net density (. rho.) of the resin₀) Film density (. rho.) corresponding to the above measurement₁) The porosity (P) was calculated by substituting the following formula, and the net density of the polyethylene confirmed in the present invention was 0.946g/cm³，

P(％)＝(ρ₀-ρ₁)/ρ₀×100。

Tensile strength

The measurements were carried out in an Instron Universal Testing Machine (UTM) according to ASTM D3763.

Referring to tables 1 and 2, the separation membranes of the examples showed excellent processability, and physical properties such as porosity and mechanical strength were confirmed to be equal to or higher than those of the comparative examples. In particular, it was confirmed that the ratio (a/B) of the high ethylene homopolymer (a) to the low ethylene homopolymer (B) in each of comparative examples 2 and 3 is out of the preferable range (3 to 500) of the present invention, and the physical properties of the separation film are very poor.

In addition, comparing examples 1 to 3 with examples 4 to 6, it can be confirmed that the resin having a preferable high load melt flow index is more excellent in processability.