DESCRIPTION ETHYLENIC RESIN AND BLOW MOLDED ARTICLE OBTAINED THEREFROM [TECHNICAL FIELD] [0001] The present invention relates to a polyethylene-based resin excellent in strength and moldability and a blow molded article (a hollow molded article) composed of the resin. [BACKGROUND ART] [0002] Conventionally, there has been a major problem in the field of hollow molded articles of how the amount of resins used is reduced from the viewpoint of resource conservation and reduction of the volume of waste materials. In addition, in order to minimize the production cost, polyethylene which is easily molded has been desired to be provided. [0003] However, for example, in polyethylene used for a container of detergents and the like, especially in the field of hollow molded articles composed of a high density polyethylene, the wall thickness of a container is unavoidably increased in order to ensure the buckling strength required at the time of filling of the content liquid, transporting and the like, thereby resulting in the increase of the amount of resins used. When the wall thickness of a container is reduced in order to reduce the amount of resins used, a polyethylene resin having a high density and a high rigidity is required to be used in order to ensure the buckling strength. However, when a container obtained by using existing polyethylene materials having a high density and a high rigidity contains a detergent, a softener or a bleacher as a content liquid, the container frequently cracks because of poor environmental stress cracking resistance (ESCR), which prevents the container from the practical application. [0004] It is known that, when a polyethylene resin has a high molecular weight in order to ensure the ESCR, the melt flow rate (MFR) is decreased, thereby resulting in poor productivity because the fluidity at the time of molding is reduced. For example, Japanese Patent Application Laid-Open Publication No. 2003-507538 describes a polyethylene-based resin container having an ESCR improved by a conventionally known bimodal process. However, the resins described in Examples of the publication have an MFR of 7.3 (g/10 min) or lower under a load of 21.6 kg, in other words, have poor fluidity, and it is also difficult to consider that the resins are at the practical level in terms of moldability represented by melt tension and melt breaking drawing rate. [0005] With the background art described above, there has been desired the advent of a polyethylene-based resin for a hollow molded article composed of a high density polyethylene-based resin capable of preparing a polyethylene hollow molded article which is excellent in buckling strength even when the wall thickness is reduced and is excellent in environmental stress cracking resistance as well as moldability, and of a hollow molded article composed of the resin. [0006] In addition, in order to increase the productivity of hollow molded articles, there has been desired a resin which has a high melt tension and which is formed into a parison that can be cut easily. Further, it is an important requirement that the product skin should not be deteriorated, even when a hollow molded article is produced at a high speed in order to increase the productivity. [Patent Document 1] Japanese Patent Application Laid-Open Publication No. 2003-507538 [DISCLOSURE OF THE INVENTION] [PROBLEMS TO BE SOLVED BY THE INVENTION] [0007] An object of the present invention is to solve the problems associated with the conventional techniques as mentioned above, and to provide a polyethylene-based resin which has a high flexural modulus, an excellent buckling strength, an excellent ESCR of a bottle thereof and excellent moldability in spite of being resistant to environmental stress cracking, and a hollow molded article composed of the resin. [MEANS FOR SOLVING THE PROBLEMS] [0008] The ethylene-based resin of the present invention is characterized by simultaneously satisfying the following requirements [a] to [c]. [0009] [a] The environmental stress cracking resistance (ESCR), T, at 50°C is 500 hours o;r more in the case of a flexural modulus of 1000 MPa to 1500 MPa and is 100 hours or more in the case of a flexural modulus of 1500 MPa to 2000 MPa, as measured according to ASTM-D-1693. [0010] [b] The melt tension at 190°C is 50 (mN) or more. [0011] [c] The melt breaking drawing rate is 90 (m/min) or less . [0012] The preferred embodiment of an ethylene-based resin of the present invention simultaneously satisfies the requirements [a] to [c] and the following requirements [d] to [f]. [0013] [d] The flexural modulus, M (MPa), satisfies 1000≤M≤2000, as measured at 23°C according to ASTM-D-7 90 . [0014] [e] The MFR (g/10 min) is 0.10 or more and less than 2.0, as measured at 190°C under a load of 2.16 kg according to JIS K7210. [0015] [f] The MFR ratio of the MFR (g/10 min) under a load of 2.16 kg to the HLMFR (g/10 min) under a load of 21.6 kg (HLMFR/MFR) is 5 0 or more and less than 150,has measured at 190°C according to JIS K7210. [0016] Further, the present invention relates to a blow molded article, preferably a fuel tank, an industrial chemical can or a bottle container., which is formed from the above-mentioned ethylene-based resin. [EFFECT OF THE INVENTION] [0017] The ethylene-based resin of the present invention is excellent in rigidity and ESCR and excellent in stability and cutting property of a parison thereof, and a bottle formed from the resin is also excellent in appearance. The ethylene-based resin and the hollow molded article of the present invention may be suitably used for applications such -as containers for detergents, shampoos, conditioners, bleachers, fabric softeners, cosmetics, waxes, cooking oils, mayonnaise, green horseradish paste and the like, fuel tanks, industrial chemical cans, drums, water storage tanks and the like. [BEST MODE FOR CARRYING OUT THE INVENTION] [0018] Hereinafter, there will be explained in detail the ethylene-based resin related to the present invention, and the blow molded article composed of the resin. [0019] The ethylene-based resin of the present invention simultaneously satisfies the above-mentioned requirements [a] to [c] and preferably satisfies the requirements [d] to [f] in addition to the requirements [a] to [c]. Hereinafter, these requirements will be explained in detail . [0020] Requirement [a] The ethylene-based resin of the present invention has an environmental stress cracking resistance (ESCR), T, of 500 hours or more, preferably 600 hours or more and 1000 hours or less and more preferably 600 hours or more and 1000 hours or less, as measured according to ASTM-D-1698, in the case of a flexural modulus of 1000 MPa or more and less than 1500 MPa. In the case of a flexural modulus of 1500 MPa or more and less than 2000 MPa, the ethylene-based resin has an environmental stress cracking resistance, T, of 100 hours or more, preferably 100 hours or more and 500 hours or less and more preferably 150 hours or more and 500 hours or less. [0021] The use of the above-mentioned ethylene-based resin prevents the occurrence of environmental stress cracking in spite of the high rigidity. [0022] In an ethylene-based polymer (E) described later, the T of the ethylene-based resin may be adjusted within the above range by copolymerizing the ethylene main chain with 0.01 to 0.5% by mol of skeletons derived from α-olefins having 3 to 20 carbon atoms such as propylene, butene-1, hexene-1, 4-methylpentene-l, octene-1 and the like, preferably butene-1, hexene-1, 4-methylpentene-l and octene-1. The amount of the comonomer to be copolymerized may be reduced to decrease the T, and conversely the amount of the comonomer may be increased to increase the T. [0023] Requirement [b] The ethylene-based resin of the present invention has a melt tension at 190°C of 50 (mN) or more, preferably 50 (mN) or more and 300 (mN) or less, and more preferably 55 (mN) or more and 300 (mN) or less. [0024] The melt tension of 50 (mN) or more ensures stability of a parison during extrusion. [0025] Examples of methods for increasing the melt tension of the ethylene-based resin include blending a polyethylene having a low MFR or a polyethylene having a long chain branch. It is well-known that the polyethylene having a low MFR may be obtained by controlling the ratio of hydrogen to ethylene at the time of polymerization. The polyethylenes having a long chain branch include a high-pressure polyethylene, a polyethylene polymerized using a chromium-based catalyst, and a polyethylene polymerized using metallocene. In other words, the melt tension of the ethylene-based resin may be adjusted to the above range by controlling the blending amount of the polyethylene having a low MFR and the polyethylene having a long chain branch. [0026] Requirement [c] The ethylene-based resin of the present invention has a melt breaking drawing rate of 90 (m/min) or less and preferably 1 (m/min) or more and 8 0 (m/min) or less. [0027] The melt breaking drawing rate of 90 (m/min) or less ensures excellent cutting properties in cutting a parison. [0028] Examples of methods for reducing the melt breaking drawing rate of the ethylene-based resin include blending a polyethylene having a low MFR or a polyethylene having a long chain branch. It is well-known that the polyethylene having a low MFR may be obtained by controlling the ratio of hydrogen to ethylene at the time of polymerization. The polyethylenes having a long chain branch include a high-pressure polyethylene, a polyethylene polymerized using a chromium-based catalyst and a polyethylene polymerized using a metallocene catalyst. In other words, the melt breaking drawing rate of the ethylene-based resin may be adjusted to the above range by controlling the blending amount of the polyethylene having a low MFR and the polyethylene having a long chain branch. [0029] Requirement [d] The ethylene-based resin of the present invention has a flexural modulus, M, of 1000 MPa or more and 2000 MPa or less, preferably 1100 MPa or more and 1800 MPa or less and more preferably 1200 MPa or more and 1700 MPa or less, as measured in accordance with JIS K6922-2. The ethylene-based resin having this high rigidity forms a bottle which is a hollow molded article with increased buckling strength. In addition, as a result of the bottle's buckling strength being increased due to high elastic modulus, the wall thickness of the hollow molded article may be reduced. [0030] Examples of methods for increasing the flexural modulus of the ethylene-based resin include increasing the density of the resin. Methods which can increase the density of the polyethylene resin, for example, include reducing the comonomer amount at the time of polymerization, as is well known in the art. [0031] Requirement [e] The ethylene-based resin of the present invention has a melt flow rate in the range of preferably 0.1 to 20 (g/10 min) and more preferably 0.2 to 1.5 (g/10 min) , as measured at 190°C under a load of 2.16 kg according to JIS K7210. The ethylene-based resin having this melt flow rate shows good moldability, in detail, it maintains suitable fluidity at the time of molding and has excellent extrusion properties. [0032] Requirement [f] The ethylene-based resin of the present invention has a value (HLMFR/MFR) of 50 or more and less than 150 and preferably 70 or more and less than 125, which is calculated by dividing a value of a melt flow rate (HLMFR) measured under a load of 21.6 kg by a value of a melt flow rate (MFR) measured under a load of 2.16 kg. The polyethylene-based resin having a value of HLMFR/MFR to the above range forms a hollow molded article excellent in appearance. [0033] Examples of methods for increasing the value of HLMFR/MFR of the ethylene-based resin include broadening the molecular weight distribution by blending ethylene-based resins having different molecular weights or by performing continuous two-stage polymerization. The value of HLMFR/MFR of the ethylene-based resin may be adjusted to the above range by controlling the molecular weight distribution as mentioned above. [0034] Furthermore, a preferred embodiment of the present invention is a hollow molded article, which may be monolayer or multilayer. Such hollow molded articles are suitably used for a fuel tank, an industrial chemical can and a bottle container for storing a detergent, a bleacher, a softener or the like. [0035] Hereinafter, there will be specifically explained the ethylene-based resin related to the present invention and the blow molded article, preferably the hollow molded article using the resin. [0036] Ethylene-Based Resin The ethylene-based resin of the present invention is not particularly limited in constituents, composition ratio and constitution method as long as it satisfies the above requirements [a] to [c], preferably the above requirements [d] to [f ] in addition to the above requirements [a] to [c] . In general, it is prepared by using an ethylene-based polymer (E) described later as an essential component and blending the polymer with an olefin-based resin (R) in which the above requirement [a] is different from that of the ethylene-based polymer (E) so that the blend will satisfy the above requirements [a] to [c], preferably [a] to [f]. Examples of the olefin-based resins (R) specifically include an ethylene-based polymer, a propylene-based polymer, a butene-based polymer, a 4-methyl-l-pentene-based polymer, a 3-methyl-l-butene-based polymer, a 1-hexene-based polymer, a 1-octene-based polymer and the like. Among these, an ethylene-based polymer (E') in which the above requirement [a] is different from that of the ethylene-based polymer (E) is preferred. Such ethylene-based polymers (E') include low density polyethylenes produced by using a Ziegler-Natta catalyst such as ULTZEX 15150J, ULTZEX 20100J (trade names, manufactured by Prime Polymer Co., Ltd.) and the like; low density polyethylenes produced by using a metallocene catalyst such as EVOLUE SP1540, EVOLUE SP2040 (trade names, manufactured by Prime Polymer Co., Ltd.) and the like; high-pressure low density polyethylenes such as MIRASON 11P, MIRASON 14P (trade names, manufactured by Prime Polymer Co., Ltd.) and the like; and high density polyethylenes such as HI-ZEX 7800M, HI-ZEX 1810J (trade names, manufactured by Prime Polymer Co., Ltd.) and the like. Of the ethylene-based polymers (E' ) , the high-pressure low density polyethylenes, the high density polyethylenes and the linear low density polyethylenes are preferred. [0037] In the ethylene-based resin of the present invention, the total amount of the ethylene-based polymer (E) and the ethylene-based polymer (Ef) based on the ethylene-based resin accounts for typically 70% by. weight or more, preferably 80% by weight or more, more preferably 90% by weight or more and especially preferably 100% by weight. In addition, the composition ratio of the ethylene-based polymer (E' ) to the total of the ethylene-based polymer (E) and the ethylene-based polymer (E') in the ethylene-based resin of the present invention is typically 50% by weight or less, preferably 30% by weight or less and more preferably 20% by weight or less. Furthermore, the ethylene-based polymers (E) may be used singly or in combination of two or more kinds. [0038] Next, there will be explained a method for producing the ethylene-based polymer (E) related to the present invention. [0039] Production Method for Ethylene-Based Polymer (E) The ethylene-based polymer (E) related to the present invention may be obtained, for example, by homopolymerizing ethylene or copolymerizing ethylene with an a-olefin having 3 to 20 carbon atoms in the presence of a catalyst for olefin polymerization formed from (A) a transition metal compound in which a cyclopentadienyl group and a fluorenyl group are bonded by covalent bond crosslinking containing a Group 14 atom; (B) at least one compound selected from (B-l) an organometallic compound, (B-2) an organoaluminum oxy compound and (B-3) a compound which reacts with the transition metal compound to form an ion pair; and (C) a carrier. [0040] In further detail, the above (A), (B) and (C) used in the invention are as follows. [0041] (A) Transition Metal Compound As the transition metal compounds (A) , there are preferably used the transition metal compounds represented by the general formulae (1) and (2) described below. [0042] [Chemical Formula 1] (Formula Removed) [004 3] [Chemical Formula 2 J (Formula Removed) [0044] [In the above general formulae (1) and (2), R7, R8, R9, R10, R11, R12, R13, R14, R15, R16, R17, R18, R19 and R20 are selected from a hydrogen atom, a hydrocarbon group and a silicon-containing hydrocarbon group and may be the same or different, two adjacent substituents from R7 to R18 may be bonded together to form a ring, A is a divalent hydrocarbon group having 2 to 20 carbon atoms which may contain a partially unsaturated bond and/or an aromatic ring and forms a ring structure together with Y, A may contain two or more ring structures including the ring that it forms together with Y, Y is carbon or silicon, M is a metal selected from Group 4 in the Periodic Table, Q may be the same or different from each other and is selected from a halogen, a hydrocarbon group, an anionic ligand and a neutral ligand which can coordinate with a lone electron pair, and j is an integer from 1 to 4 . ] In the present invention, among the transition metal compounds represented by the above general formulae (1) and (2) , a compound in which. R7 to R10 are each a hydrogen atom, Y is a carbon atom, M is Zr and j is 2 is preferably used. [0045] The transition metal compound (A) used in Examples described later is specifically represented by the following general formula (3), but the present invention is not at all limited thereto. [0046] [Chemical Formula 3] (Formula Removed) [0047] The structure of the transition metal compound was determined by using 270 MHz IH-NMR (GSH-270, manufactured by JEOL Ltd.) and FD-Mass Spectrometer (SX-102A, manufactured by JEOL Ltd.). [0048] The transition metal compound (A) represented by the above general formula (1) or (2) may be prepared, for example, according to a method described in WO 2001/27124. [0049] (B-l) Qrganometallic Compound The organometallic compounds (B-l) used if necessary in the present invention include specifically an organoaluminum compound as described below. [0050] General Formula RamAl (ORb) nHpXq (In the formula, Ra and Rb may be the same or different from each other and. represent a hydrocarbon group having 1 to 15 carbon atoms, preferably having 1 to 4 carbon atoms, X represents a halogen atom, m is a number of 0