This application claims the benefit of priority based on Korean Patent Application No. 10-2018-0052044 dated May 04, 2018, and all contents disclosed in the literature of the Korean patent application are incorporated as a part of this specification. [3] [Technical field] [4] The present invention relates to an olefin-based copolymer and a method for preparing the same, and more particularly, to a low-density olefin-based copolymer having improved physical properties such as hardness, flexural strength, and tear strength while having high fluidity and a method for preparing the same. background [5] Olefin polymerization catalyst systems can be classified into Ziegler-Natta and metallocene catalyst systems, and these two highly active catalyst systems have been developed according to their respective characteristics. Ziegler-Natta catalyst has been widely applied to existing commercial processes since its invention in the 1950s. There is a problem in that there is a limit in securing the desired physical properties because the composition distribution is not uniform. [6] On the other hand, the metallocene catalyst is composed of a combination of a main catalyst containing a transition metal compound as a main component and a cocatalyst containing an organometallic compound containing aluminum as a main component. Such a catalyst is a homogeneous complex catalyst and is a single site catalyst. The molecular weight distribution is narrow depending on the single active point characteristic, and a polymer with a uniform composition distribution of the comonomer is obtained. It has properties that can change crystallinity, etc. [7] U.S. Patent No. 5,914,289 discloses a method of controlling the molecular weight and molecular weight distribution of a polymer using a metallocene catalyst supported on each carrier, but the amount of solvent used in preparing the supported catalyst and preparation time are required. , the inconvenience of having to support each of the metallocene catalysts to be used on a carrier followed. [8] Korean Patent Application No. 10-2003-0012308 discloses a method of controlling molecular weight distribution by supporting a double-nuclear metallocene catalyst and a single-nuclear metallocene catalyst together with an activator on a carrier to change the combination of catalysts in the reactor and polymerization is starting. However, this method has a limitation in simultaneously realizing the characteristics of each catalyst, and also has a disadvantage in that the metallocene catalyst portion is released from the carrier component of the finished catalyst, thereby causing fouling in the reactor. [9] On the other hand, linear low-density polyethylene is produced by copolymerizing ethylene and alpha olefin at low pressure using a polymerization catalyst, and is a resin having a narrow molecular weight distribution, short-chain branches of a constant length, and no long-chain branches. The linear low-density polyethylene film has high breaking strength and elongation along with the characteristics of general polyethylene, and has excellent tear strength and drop impact strength. are doing [10] However, most of the linear low-density polyethylene using 1-butene or 1-hexene as a comonomer is produced in a single gas phase reactor or a single loop slurry reactor, and the productivity is high compared to the process using 1-octene comonomer, but these products are also used Due to limitations in catalyst technology and process technology, the physical properties are significantly inferior to those in the case of using 1-octene comonomer, and the molecular weight distribution is narrow, resulting in poor processability. [11] In US Patent No. 4,935,474, two or more metallocene compounds are used to report a polyethylene production method having a broad molecular weight distribution. U.S. Patent No. 6,828,394 reports on a method for producing polyethylene, which has excellent processability and is particularly suitable for films, by using a mixture of those having good comonomer binding properties and those not having good comonomer binding properties. In addition, U.S. Patent Nos. 6,841,631 and 6,894,128 disclose that at least two types of metal compounds are used as a metallocene-based catalyst to prepare polyethylene having a bicrystalline or polycrystalline molecular weight distribution, and thus for use in films, blow molding, pipes, etc. reported to be applicable. However, these products have improved processability, but the dispersion state by molecular weight within the unit particles is not uniform, so the extrusion appearance is rough and the physical properties are not stable even under relatively good extrusion conditions. [12] Against this background, there is a constant demand for the production of better products with a balance between physical properties and processability, and in particular, the need for a polyethylene copolymer having excellent processability is further demanded. DETAILED DESCRIPTION OF THE INVENTION technical challenge [13] An object of the present invention is to provide a low-density olefin-based copolymer having improved physical properties such as hardness, flexural strength, and tear strength while having high fluidity. [14] In addition, another object to be solved by the present invention is to provide a method for producing the olefin-based copolymer. means of solving the problem [15] In order to solve the above problems, the present invention (1) the density (d) is 0.85 to 0.89 g / cc, (2) the melt index (Melt Index, MI, 190 ℃, 2.16 kg load condition) 15 g/10 min to 100 g/10 min, (3) hardness, density, and MI satisfy Equation 1 below, and (4) 15 wt% to 45 wt% of alpha olefin-derived repeating units measured through nuclear magnetic spectroscopy. , to provide an olefin-based copolymer. [16] [Equation 1] [17] Hardness = 0.0082×MI 2 -0.99×Density×MI+A [18] (A is 97×density [193] [194] Preparation of chloro- 1-(1,2-dimethyl-3H- benzo[b]cyclopenta[d]thiophen- 3-yl)-1,1-( methyl )(phenyl)silane [195] In a 250 ml Schlenk flask, put 10 g (1.0 eq, 49.925 mmol) of 1,2-dimethyl-3H-benzo [b] cyclopenta [d] thiophene and 100 ml of THF, and 22 ml of n-BuLi (1.1 eq, 54.918 mmol, 2.5 M in hexane) was added dropwise at -30 °C, followed by stirring at room temperature for 3 hours. The stirred Li-complex THF solution was cannulated at -78 °C in a Schlenk flask containing 8.1 ml (1.0 eq, 49.925 mmol) of dichloro(methyl)(phenyl)silane and 70 ml of THF, followed by stirring at room temperature overnight. After stirring, the mixture was dried in vacuo, and extracted with 100 ml of hexane. [196] [197] [Preparation of transition metal compound] [198] Preparation of N- tert -butyl-1-(1,2-dimethyl-3H- benzo[b]cyclopenta[d]thiophen- 3-yl)-1,1-( methyl )(phenyl)silanamine [199] t-BuNH in 100 ml of extracted chloro-1-(1,2-dimethyl-3H-benzo[b]cyclopenta[d]thiophen-3-yl)-1,1-(methyl)(phenyl)silane hexane solution 2 42 ml (8 eq, 399.4 mmol) was added at room temperature, followed by stirring at room temperature overnight. After stirring, the mixture was dried in vacuo, and extracted with 150 ml of hexane. After solvent drying, 13.36 g (68 %, dr = 1:1) of a yellow solid was obtained. [200] 1 H NMR (CDCl 3 , 500 MHz): δ 7.93 (t, 2H), 7.79 (d,1H), 7.71 (d,1H), 7.60 (d, 2H), 7.48 (d, 2H), 7.40-7.10 (m, 10H, aromatic), 3.62 (s, 1H), 3.60 (s, 1H), 2.28 (s, 6H), 2.09 (s, 3H), 1.76 (s, 3H), 1.12 (s, 18H), 0.23 (s, 3H), 0.13 (s, 3H) [201] [202] In a 100 ml Schlenk flask, put 4.93 g (12.575 mmol, 1.0 eq) of the ligand compound of Formula 2-4 and 50 ml (0.2M) of toluene, and 10.3 ml (25.779 mmol, 2.05 eq, 2.5M in hexane) of n-BuLi. was added dropwise at -30°C, followed by stirring at room temperature overnight. After stirring, 12.6 ml (37.725 mmol, 3.0 eq, 3.0 M in diethyl ether) of MeMgBr was added dropwise, and then TiCl 4 13.2 ml (13.204 mmol, 1.05 eq, 1.0 M in toluene) was added in order and stirred at room temperature overnight. . After stirring, the mixture was vacuum dried, extracted with 150 ml of hexane, and the solvent was removed to 50 ml, and then 4 ml (37.725 mmol, 3.0eq) of DME was added dropwise, followed by stirring at room temperature overnight. After vacuum drying again, the mixture was extracted with 150 ml of hexane. After solvent drying, 2.23 g (38 %, dr = 1:0.5) of a brown solid was obtained. [203] 1 H NMR (CDCl 3 , 500 MHz): δ 7.98 (d, 1H), 7.94 (d, 1H), 7.71 (t, 6H), 7.50-7.30 (10H), 2.66 (s, 3H), 2.61 (s) , 3H), 2.15 (s, 3H), 1.62 (s, 9H), 1.56 (s, 9H), 1.53 (s, 3H), 0.93 (s, 3H), 0.31 (s, 3H), 0.58 (s, 3H), 0.51 (s, 3H), -0.26 (s, 3H), -0.39 (s, 3H) [204] [205] Preparation Example 2: Preparation of transition metal compound 2 [206] [Preparation of ligand compound] [207] [208] In a 100 mL Schlenk flask, quantify 4.65 g (15.88 mmol) of chloro-1-(1,2-dimethyl-3H-benzo[b]cyclopenta[d]thiophen-3-yl)-1,1-dimethylsilane After addition, 80 mL of THF was added thereto. After adding tBuNH 2 (4eq, 6.68 mL) at room temperature, the reaction was conducted at room temperature for 3 days. After the reaction, THF was removed and then filtered with hexane. After solvent drying, a yellow liquid was obtained in a yield of 4.50 g (86%). [209] 1 H-NMR (in CDCl 3 , 500 MHz): 7.99 (d, 1H), 7.83 (d, 1H), 7.35 (dd, 1H), 7.24 (dd, 1H), 3.49 (s, 1H), 2.37 ( s, 3H), 2.17(s, 3H), 1.27(s, 9H), 0.19(s, 3H), -0.17(s, 3H). [210] [211] [Preparation of transition metal compound] [212] [213] N-tert-butyl-1-(1,2-dimethyl-3H-benzo[b]cyclopenta[d]thiophen-3-yl)-1,1-dimethylsilane prepared above in a 50 mL Schlenk flask An amine (1.06g, 3.22mmol/1.0eq) and 16.0 mL (0.2 M) of MTBE were added and stirred first. n-BuLi (2.64 mL, 6.60 mmol/2.05eq, 2.5 M in THF) was added at -40°C, and the reaction was carried out at room temperature overnight. Thereafter, MeMgBr (2.68 mL, 8.05 mmol/2.5eq, 3.0 M in diethyl ether) was slowly added dropwise at -40°C, and then TiCl4 (2.68 mL, 3.22 mmol/1.0eq, 1.0 M in toluene) was added in this order. and reacted overnight at room temperature. Then, the reaction mixture was filtered through Celite using hexane. After solvent drying, a brown solid was obtained in a yield of 1.07 g (82%). [214] 1 H-NMR (in CDCl 3 , 500 MHz): 7.99 (d, 1H), 7.68 (d, 1H), 7.40 (dd, 1H), 7.30 (dd, 1H), 3.22 (s, 1H), 2.67 ( s, 3H), 2.05 (s, 3H), 1.54 (s, 9H), 0.58 (s, 3H), 0.57 (s, 3H), 0.40 (s, 3H), -0.45 (s, 3H). [215] [216] Example 1 [217] After the 1.5L autoclave continuous process reactor was charged with hexane solvent (5 kg/h) and 1-octene (2 kg/h), the temperature at the top of the reactor was preheated to 136° C. Triisobutylaluminum compound (0.05 mmol/min) ), the transition metal compound (0.45 μmol/min) obtained in Preparation Example 1, and dimethylanilinium tetrakis(pentafluorophenyl) borate cocatalyst (1.35 μmol/min) were simultaneously introduced into the reactor as a catalyst. Ethylene (0.87 kg/h) hydrogen gas (28 cc/min) was introduced into the autoclave reactor and maintained at 136° C. for at least 30 minutes in a continuous process at a pressure of 89 bar to proceed with a copolymerization reaction to obtain a copolymer. After drying for more than 12 hours, the physical properties were measured. [218] [219] Examples 2 to 8 [220] As shown in Table 1 below, a copolymer was prepared in the same manner as in Example 1, except that the content of each material was changed. [221] [222] Comparative Examples 1 to 7 [223] As Comparative Example 1, Solumer 8730L (manufactured by SK Innovation) was purchased and used, as Comparative Example 3, DF7350 (manufactured by Mitsui) was purchased and used, and as Comparative Example 4, LC875 (manufactured by LG Chem) was purchased and used. [224] Comparative Examples 2, 5, and 6 were the same method as in Example 1, except that the transition metal compound obtained in Preparation Example 2 was used as a catalyst and the content of each material was changed as shown in Table 1 below. A copolymer was prepared. [225] Comparative Example 7 uses the transition metal compound obtained in Preparation Example 1 as a catalyst and does not introduce hydrogen gas, and is the same as in Example 1, except that the content of each material is changed as shown in Table 1 below. The copolymer was prepared by the method. [226] [227] [Table 1] Catalyst (μmol/min) Cocatalyst (μmol/min) TiBAl (mmol/min) Ethylene (kg/h) Hydrogen (cc/min) Alpha Olefin Monomer Reaction temperature (℃) 1-octene (kg/h) 1-butene (kg/h) Example 1 0.45 1.35 0.05 0.87 28 2.00 - 136 Example 2 0.60 1.80 0.05 0.87 20 2.00 - 150 Example 3 0.60 1.80 0.05 0.87 35 2.00 - 149 Example 4 0.25 0.75 0.05 0.87 30 - 0.80 135 Example 5 0.27 0.81 0.05 0.87 34 - 0.90 135 Example 6 0.38 1.14 0.05 0.87 19 - 0.91 151 Example 7 0.25 0.75 0.05 0.87 45 - 0.90 135 Example 8 0.40 2.40 0.05 0.87 30 - 1.00 150 Comparative Example 2 0.70 2.10 0.05 0.87 0 2.20 - 150 Comparative Example 5 0.37 1.11 0.05 0.87 0 - 1.00 150 Comparative Example 6 0.38 1.14 0.05 0.87 0 - 1.00 151 Comparative Example 7 0.40 2.40 0.05 0.87 0 - 1.00 151 [228] Experimental Example 1 [229] The copolymers of Examples 1 to 8 and Comparative Examples 1 to 7 were evaluated for physical properties according to the following method, and are shown in Table 2 below. [230] 1) Density of the polymer [231] Measured by ASTM D-792. [232] 2) Melt Index (MI) of the polymer [233] It was measured by ASTM D-1238 (Condition E, 190°C, 2.16 kg load). [234] 3) Weight average molecular weight (g/mol) and molecular weight distribution (MWD) [235] The number average molecular weight (Mn) and the weight average molecular weight (Mw) were respectively measured using gel permeation chromatography (GPC), and the molecular weight distribution was calculated by dividing the weight average molecular weight by the number average molecular weight. [236] - Column: PL Olexis [237] - Solvent: TCB (Trichlorobenzene) [238] - Flow rate: 1.0 ml/min [239] - Sample concentration: 1.0 mg/ml [240] - Injection volume: 200 μl [241] - Column temperature: 160℃ [242] - Detector: Agilent High Temperature RI detector [243] - Standard: Polystyrene (corrected by cubic function) [244] 4) Measurement of hardness (shore A) [245] Hardness was measured according to ASTM D2240 standard using TECLOCK's GC610 STAND for Durometer and Mitutoyo's Shore Durometer Type A. [246] 5) Determination of comonomer content [247] Take ~50mg of the sample, put it in a vial, add 1ml of TCE-d2 solvent, melt the sample completely with a heat gun, and transfer it to the NMR tube. 1H NMR was measured at Number of Scan (ns) = 2048 (3h 30min), measuring temperature 393K, and then the polymer was reprecipitated before NMR analysis to remove residual 1-octene or 1-butene that may be present in the specimen. . Specifically, 1 g of the polymer was completely dissolved in chloroform at 70° C., and the resulting polymer solution was slowly poured into 300 ml of methanol with stirring to reprecipitate the polymer, and then the reprecipitated polymer was vacuum dried at room temperature. The above process was repeated once more to obtain a polymer from which residual 1-octene or 1-butene was removed. [248] A 50 mg specimen of the polymer obtained above was dissolved in 1 ml of TCE-d2 solvent. Using the Bruker AVANCEⅢ 500MHz NMR equipment, 2048 measurements were made at room temperature with an acquisition time of 3 seconds and a pulse angle of 30°. The comonomer content was calculated using the integral value of the ethylene, 1-butene, and 1-octene peaks in the range of 0.5 to 1.5 ppm. The number of double bonds was calculated based on the integral value of the double bonds in the 4.5-6.0 ppm region. Macromolecules 2014, 47, 3782-3790. [249] [Table 2] Density (g/mL) MI (g/10min) Mw MWD %[1-C8](wt%) %[1-C4](wt%) Hardness Example 1 0.869 33.7 46000 2.05 35.8 0 66.2 Example 2 0.873 17.0 55000 1.99 34.6 0 74.7 Example 3 0.874 45.0 42000 1.98 33.9 0 65.7 Example 4 0.875 20.0 53000 2.03 0 25.2 71.1 Example 5 0.871 32.4 47000 2.01 0 27.0 67.1 Example 6 0.868 34.3 46000 2.00 0 27.9 66.5 Example 7 0.872 62.0 32000 2.02 0 27.6 64.5 Example 8 0.865 58.2 35000 2.04 0 30.0 62.1 Comparative Example 1 0.869 29.2 48000 2.34 37.9 0 61.4 Comparative Example 2 0.870 33.4 46000 2.30 36.1 0 64.1 Comparative Example 3 0.870 29.5 48000 1.93 0 26.8 65.8 Comparative Example 4 0.869 30.0 47000 2.33 0 28.8 61.2 Comparative Example 5 0.870 30.3 47000 2.16 0 28.2 64.7 Comparative Example 6 0.870 34.0 46000 2.35 0 28.8 63.6 Comparative Example 7 0.864 5.4 69000 2.18 0 29.1 48.9 [250] Experimental Example 2 [251] The olefinic copolymers of Examples 1, 5, 7 and Comparative Examples 1 to 6 were measured for tear strength, elongation, and flexural modulus according to the following method, and are shown in Table 3 below. [252] 1) Polymer tear strength and elongation [253] The olefinic copolymers of Examples 1, 5, 7 and Comparative Examples 1 to 6 were each extruded and prepared into pellets, and then the tear strength and tensile elongation at breakage were measured according to ASTM D638 (50 mm/min). did. [254] 2) flexural modulus of the polymer [255] The flexural modulus (Secant 1%) was measured according to ASTM D790. [256] [Table 3] Types of comonomers Density (g/mL) MI (g/10min) Tear strength (kgf/cm 2) Elongation (%) Flexural modulus (Secant 1%) (kgf/cm 2 ) Example 1 1-octene 0.869 33.7 33.5 1,000 or more 12.0 Comparative Example 1 1-octene 0.869 29.2 32.6 1,000 or more 10.9 Comparative Example 2 1-octene 0.870 33.4 29.1 1,000 or more 10.5 Example 5 1-butene 0.871 32.4 26.7 700 16.2 Example 7 1-butene 0.868 34.3 28.6 550 15.7 Comparative Example 3 1-butene 0.870 29.5 25.6 500 15.6 Comparative Example 4 1-butene 0.869 30.0 21.3 700 12.3 Comparative Example 5 1-butene 0.870 30.3 23.8 600 14.9 Comparative Example 6 1-butene 0.870 34.0 27.5 436 14.5 [257] The olefin-based copolymer according to the present invention is a low-density olefin-based copolymer and may exhibit increased tear strength, elongation and flexural modulus at a density and melt index equivalent to that of a conventional olefin-based copolymer. Specifically, in Table 3 above, when the olefinic copolymers prepared using the same comonomer (alpha-olefin monomer) rule and exhibiting the same density and MI are compared with each other, the olefinic copolymer of Examples has improved hardness. It can be confirmed that Equation 1 is satisfied, and as a result, it exhibits higher tear strength and flexural modulus with equal or superior elongation compared to the olefin-based copolymer of Comparative Example. [258] When the hardness, density, and MI of the olefinic copolymers of Example 1 and Comparative Examples 1 and 2 are substituted into Equation 1, Example 1 satisfies the conditions of Equation 1, but Comparative Example 1 and Comparative Example 1 In Example 2, the lower limit of the value of A was not reached and thus was not satisfied. Accordingly, the olefin-based copolymer of Example 1 exhibits higher tear strength and flexural modulus than the olefin-based copolymers of Comparative Examples 1 and 2, and also the molecular weight distribution (MWD) of the olefin-based copolymer of Example 1 The copolymer showed a smaller value than the olefinic copolymer of Comparative Examples 1 and 2. [259] In addition, when comparing Example 5 with Comparative Examples 4 and 5, as compared above, the olefinic copolymer of Example 5 satisfies the condition of Equation 1, but Comparative Examples 4 to 5 is Equation 1 does not satisfy the conditions of Accordingly, the olefin-based copolymer of Example 5 exhibits higher tear strength and flexural modulus than the olefin-based copolymers of Comparative Examples 4 to 5. [260] In addition, when the olefin-based copolymer of Example 7 is compared with the olefin-based copolymer of Comparative Example 6, it can be confirmed that it has better elongation, tear strength, and flexural strength. [261] Through these experiments, the olefin-based copolymer according to the present invention satisfies the conditions of Equation 1, and thus has higher tear strength and elongation than the conventional olefin-based copolymers such as Comparative Examples 1, 3 and 4 and flexural modulus. [262] In addition, the olefin-based copolymer according to the present invention is prepared by polymerizing an olefin-based monomer by adding hydrogen at 10 to 100 cc/min in the presence of a catalyst composition for olefin polymerization including the transition metal compound of Formula 1, Although hydrogen improved the hardness of the olefin-based copolymer to improve tear strength, flexural modulus, and elongation, the olefin-based copolymers of Comparative Examples 2 and 5 to 7 polymerized without hydrogen input could not satisfy the conditions of Equation 1 and showed relatively low hardness, tear strength, flexural modulus, and physical properties such as elongation. [263] In particular, the olefin-based copolymers of Example 8 and Comparative Example 7 showed differences in physical properties depending on whether hydrogen was added even when the same content of each material was used in the presence of the same catalyst composition. Specifically, Comparative Example 7 The olefin-based copolymer exhibited a low MI, and could not satisfy the condition of Equation (1). Claims [Claim 1] (1) the density (d) is 0.85 to 0.89 g/cc, (2) the melt index (Melt Index, MI, 190 ° C, 2.16 kg load condition) is 15 g/10 min to 100 g/10 min, (3) ) hardness, density, and MI satisfy Equation 1 below, and (4) an alpha olefin-derived repeating unit measured through nuclear magnetic spectroscopy is 15 wt% to 45 wt%, an olefinic copolymer. [Equation 1] Hardness = 0.0082 × MI 2 -0.99 × Density × MI + A (A is 97 × Density