Polyethylene for film

Abstract

To provide a polyethylene having improved balance of ease of handling or the like and to provide a method for producing the same.SOLUTION: There is provided a polyethylene having a ratio (Mz / Mw) of Mz (Z-average molecular weight) to Mw (weight average molecular weight) of 3.4 or more and 4.0 or less in the integral distribution curve of the polyethylene evaluated by gel permeation chromatography and a light scattering area ratio (RLS) represented by the following (expression 1) of 2.5 or more and 4.0 or less. RLS=LS / LS' (Expression 1) (where, Ls represents the light scattering area of a solution obtained by dissolving 40 mg of the polyethylene in 20 mL of ortho-dichlorobenzene. LS' represents the light scattering area of a solution obtained by dissolving 40 mg of a standard polystyrene having an average molecular weight of 1000 in 20 mL of ortho-dichlorobenzene.)SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to polyethylene and a method for producing the same. [Background technology]

[0002] Polyethylene is processed into a wide variety of films, including heavy-duty bags, shrink wrap, general packaging, thin films, protective films, extrusion laminates, extrusion-molded films, and foam-molded films. Low-density polyethylene (LDPE), produced by high-pressure radical polymerization, is particularly well-suited for extrusion laminates and protective films. Protective films are laminated (attached) to optical materials or metal plates to protect them. For example, they are used as protective films to protect film-type etching resists (dry film resists, or DFRs) used in circuit board circuit formation. To manufacture such films, a good balance of polyethylene's ease of handling is required.

[0003] Patent Document 1 describes a protective film for DFR made of polyethylene obtained by high-pressure radical polymerization, and a protective film for DFR made of polyethylene film in which the density of fisheyes present in the film falls within a specific range. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-60426 Summary of the Invention [Problem to be solved by the invention]

[0005] Under these circumstances, the problem to be solved by the present invention is to provide a polyethylene having an improved balance between ease of handling of the film and ease of detecting defects in the film (fish eyes, air entrapment), and a method for producing the same. [Means for solving the problem]

[0006] The present inventors have conducted extensive research in light of the above background and have completed the present invention. That is, the present invention is as follows. [1] In an integral distribution curve of the polyethylene evaluated by gel permeation chromatography, the ratio (Mz / Mw) of Mz (Z-average molecular weight) to Mw (weight-average molecular weight) of the polyethylene is 3.4 or more and 4.0 or less; The light scattering area ratio (R LS ) is 2.5 or more and 4.0 or less. R LS =LS / LS' (Equation 1) (In the formula, LS represents the light scattering area of ​​a solution obtained by dissolving 40 mg of the polyethylene in 20 mL of orthodichlorobenzene. LS' indicates the light scattering area of ​​a solution in which 40 mg of standard polystyrene with a number average molecular weight of 1000 is dissolved in 20 mL of orthodichlorobenzene. Below, [2] to [8] are each preferred aspects or embodiments of the present invention. [2] Mz / Mw is 3.5 or more and 3.8 or less, Light scattering area ratio (R LS ) is 2.8 or more and 3.8 or less. [3] The polyethylene according to either [1] or [2], wherein the polyethylene is a high-pressure low-density polyethylene. [4] A film made of polyethylene according to any one of [1] to [3]. [5] A protective film for dry film resist, comprising the polyethylene according to any one of [1] to [3]. [6] A method for producing the polyethylene according to any one of [1] to [3], comprising the following steps: Chain transfer agent (CTA) supplying step: a step of supplying ethane, propane, and propylene as chain transfer agents (CTAs) from a chain transfer agent (CTA) supplying pipe (17) controlled at a pressure of 0.01 to 0.1 MPa and a temperature of 10 to 60°C to an unreacted low-pressure ethylene supplying pipe (16) controlled at a pressure of 0.01 to 0.1 MPa and a temperature of 10 to 60°C, and adjusting the ratio of the propane concentration to the total CTA concentration to 0.70 to 0.95 (note that the concentrations are on a volume basis, and the sum of the volumes of ethylene, ethane, propane, and propylene is taken as 100% by volume). [7] The method according to [6], further comprising the steps of: · Compression process: the process of compressing ethylene; Reaction step: supplying compressed ethylene and a polymerization initiator to a reactor (4) and polymerizing the ethylene at a reactor pressure of 170-220 MPa and a reaction temperature of 220-270°C to produce polyethylene; Separation step: a step of separating the polyethylene produced in the reactor (4) from unreacted ethylene in a high-pressure separator (5), withdrawing the produced polyethylene from the high-pressure separator (5) and supplying it to a low-pressure separator (8) through an extraction pipe (7), separating the unreacted ethylene contained in the polyethylene in the low-pressure separator (8), and withdrawing the polyethylene; unreacted low-pressure ethylene recycling step: a step of supplying unreacted low-pressure ethylene separated in the low-pressure separator (8) at a pressure of 0.01 to 0.1 MPa and a temperature of 150 to 220°C to an unreacted ethylene holding drum (15) through an unreacted low-pressure ethylene supply pipe (9); and Fresh ethylene supply step: a step of supplying fresh ethylene from the fresh ethylene pipe (14) to the ethylene pipe (13). [8] The method according to either [6] or [7], further comprising the following steps: Unreacted high-pressure ethylene recycling process: A process in which the unreacted ethylene separated in the high-pressure separator (5) is decompressed through the unreacted high-pressure ethylene supply pipe (6) and the decompressed unreacted ethylene is supplied to the secondary compressor (3). [Effects of the Invention]

[0007] According to the present invention, by carrying out the chain transfer agent (CTA) supplying step in a high-pressure polyethylene production process by supplying a specific chain transfer agent (CTA) at a specific pressure and temperature and at a specific concentration, it is possible to produce polyethylene with an improved balance between ease of film handling and ease of detection of film defects (fish eyes, air entrapment). The present invention is characterized by the ratio (Mz / Mw) of Mz (Z-average molecular weight) to Mw (weight-average molecular weight) of polyethylene and the light scattering area ratio (R LS ) is related to the balance between the haze and clarity ratio, and the ratio (Mz / Mw) and the light scattering area ratio (R LS By setting the clarity ratio (MD / TD difference of rectilinear transmitted light (anisotropy)), the balance between haze and a low clarity ratio is improved, thereby producing polyethylene with an improved balance between film ease of handling and ease of detecting film defects (fisheyes and air entrapment). The ease of handling of a film can be evaluated as the unevenness of the film surface, for example, the film's haze. The ease of detecting film defects (fisheyes and air entrapment) can be evaluated as a low clarity ratio of the film. By obtaining a film with a low clarity ratio (MD / TD difference of rectilinear transmitted light (anisotropy)), film defects (fisheyes and air entrapment) can be easily detected. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 shows a schematic process diagram of one embodiment of the method and apparatus for producing high-pressure polyethylene according to the present invention. [Figure 2]FIG. 2 shows a schematic diagram of an LS (light scattering detector) chromatogram for measuring the light scattering area of ​​the polyethylenes produced in Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0009] <Polyethylene> The polyethylene of the present invention is: In an integral distribution curve of the polyethylene evaluated by gel permeation chromatography, the ratio (Mz / Mw) of Mz (Z-average molecular weight) to Mw (weight-average molecular weight) of the polyethylene is 3.4 or more and 4.0 or less; The light scattering area ratio (R LS ) is 2.5 or more and 4.0 or less. R LS =LS / LS' (Equation 1) (In the formula, LS represents the light scattering area of ​​a solution obtained by dissolving 40 mg of the polyethylene in 20 mL of orthodichlorobenzene. LS' indicates the light scattering area of ​​a solution in which 40 mg of standard polystyrene with a number average molecular weight of 1000 is dissolved in 20 mL of orthodichlorobenzene. From the viewpoint of ease of handling of the film, that is, obtaining a film with an appropriate haze, Mz / Mw is preferably 3.5 or more and 3.8 or less. Light scattering area ratio (R LS ) is preferably 2.8 or more and 3.8 or less from the viewpoint of ease of handling of the film, that is, from the viewpoint of obtaining a film with an appropriate haze. The polyethylene is preferably a high-pressure low-density polyethylene. The film of the present invention made of the above polyethylene is preferred. The protective film for a dry film resist of the present invention is preferably made of the above polyethylene. The method for producing the film and the protective film for dry film resist from polyethylene is not particularly limited, and they can be produced by methods well known to those skilled in the art.

[0010] From the viewpoint of film processability, the MFR is preferably 1 g / 10 min or more and 6 g / 10 min or less, and more preferably 2.5 g / 10 min or more and 4.5 g / 10 min or less. If the MFR is less than 1 g / 10 min, it becomes difficult to form a thin film, and if it is higher than 6 g / 10 min, the uniformity of the film thickness decreases.

[0011] The density is 917 kg / m from the viewpoint of film handling. 3 More than 930kg / m 3 It is preferable that the resistance is 921 kg / m or less, and more preferably 921 kg / m 3 More than 926kg / m 3 It is more preferable that the density is 917 kg / m or less. 3 If the tension is less than 930 kg / m, the film will not be easily unwound. 3 If the temperature is higher, it becomes difficult to peel the film from the resist after it has been attached to the resist.

[0012] From the viewpoint of film processability, the shrinkage factor g' is preferably 0.10 or more and 0.40 or less, more preferably 0.15 or more and 0.35 or less, and even more preferably 0.19 or more and 0.24 or less. If the shrinkage factor g' is less than 0.10, it becomes difficult to form a thin film, and if it is higher than 0.40, the uniformity of the film thickness decreases.

[0013] <One embodiment of manufacturing method and manufacturing device> An embodiment of the production method according to the present invention and a production apparatus preferably used in the production method will be described in detail below with reference to FIG. Ethylene gas is supplied from the rear stage of the primary compressor (2) to the secondary compressor (3) through a high-pressure ethylene pipe (18), and then supplied to a polymerization reactor (4), where a polymerization initiator is added to polymerize the ethylene. The polymerization mixture is discharged from the polymerization reactor (4) into a high-pressure separator (5) where it is separated into the produced polymer and unreacted ethylene gas. The polymer separated in the high-pressure separator (5) is withdrawn through a polyethylene withdrawal pipe (7) into a low-pressure separator (8) where it is further separated into an ethylene polymer and unreacted ethylene gas. The ethylene polymer is withdrawn through a polyethylene withdrawal pipe (10) and pelletized in a granulator. The unreacted ethylene gas separated in the low-pressure separator (8) is supplied to an unreacted ethylene holding drum (15) through an unreacted low-pressure ethylene pipe (9). The unreacted ethylene gas held in the unreacted ethylene holding drum (15) is supplied to the first compressor front stage 1 through an ethylene pipe (16), and a chain transfer agent (CTA) (17) is supplied to the ethylene pipe (16) to supply the unreacted ethylene gas to the first compressor front stage (1). Unreacted ethylene gas and a chain transfer agent (CTA) are compressed in the first stage (1) of the primary compressor and supplied to the second stage (2) of the primary compressor through an ethylene pipe (13). The unreacted ethylene gas separated in the high-pressure separator (5) is passed through an unreacted high-pressure ethylene pipe (6), and the entire amount (100 weight percent) of the unreacted ethylene gas is supplied to the inlet pipe of the secondary compressor (3). Fresh ethylene gas is supplied from a fresh ethylene supply pipe (14) through an ethylene pipe (13) to the primary compressor rear stage (2). A mixture of unreacted ethylene gas and a chain transfer agent (CTA) supplied from the first compressor upstream stage (1) and fresh ethylene gas is compressed in the first compressor downstream stage (2) and supplied to the secondary compressor (3). Ethylene gas compressed by a secondary compressor (3) and a chain transfer agent (CTA) are fed to a polymerization reactor (4) to carry out a continuous polymerization reaction. <Manufacturing equipment> A manufacturing apparatus preferably used in the manufacturing method of the present invention is For example, a high-pressure polyethylene manufacturing plant equipped with one or more of the following facilities: · Primary compressor front stage (1): Compressor that compresses ethylene; Primary compressor rear stage (2): a compressor that further compresses the ethylene supplied from the primary compressor front stage (1); Secondary compressor (3): a compressor that further compresses the ethylene supplied from the downstream of the primary compressor (2); Reactor (4): a reactor for polymerizing ethylene using ethylene supplied from the secondary compressor (3) and a polymerization initiator supplied to the reactor (4) to produce polyethylene; High-pressure separator (5): a high-pressure separator that receives the polyethylene obtained in the reactor (4) and unreacted ethylene from the reactor (4) and separates the polyethylene from the unreacted high-pressure ethylene; Unreacted high-pressure ethylene supply pipe (6): a pipe for supplying the unreacted high-pressure ethylene separated in the high-pressure separator (5) to the secondary compressor (3); Polyethylene withdrawal pipe (7): A pipe for withdrawing the polyethylene separated in the high-pressure separator (5) from the high-pressure separator (5) and supplying it to the low-pressure separator (8); Low-pressure separator (8): a separator for separating the unreacted low-pressure ethylene contained in the polyethylene separated in the high-pressure separator (5) and supplied through the polyethylene withdrawal pipe (7) from the polyethylene; Unreacted low-pressure ethylene supply pipe (9): a pipe for supplying the unreacted low-pressure ethylene separated in the low-pressure separator (8) to the unreacted ethylene holding drum (15); Polyethylene extraction pipe (10): Pipe for extracting the polyethylene separated in the low-pressure separator (8); Ethylene supply pipe (13): a pipe connecting the upstream section (1) of the primary compressor and the downstream section (2) of the primary compressor, for supplying compressed unreacted ethylene from the upstream section (1) of the primary compressor to the downstream section (2) of the primary compressor, and merging with the fresh ethylene supply pipe (14); Fresh ethylene supply pipe (14): a pipe connected to the ethylene supply pipe (13) for supplying fresh ethylene; Unreacted ethylene holding drum (15): a drum for holding the unreacted low-pressure ethylene supplied through the unreacted low-pressure ethylene supply pipe (9); Unreacted low-pressure ethylene supply pipe (16): A pipe connecting the unreacted ethylene holding drum (15) and the front stage of the primary compressor (1) and supplying unreacted low-pressure ethylene from the unreacted ethylene holding drum (15) to the front stage of the primary compressor (1); and Chain transfer agent (CTA) supply pipe (17): A pipe connected to the unreacted low-pressure ethylene supply pipe (16) and supplying a chain transfer agent (CTA).

[0014] Front stage of primary compressor (1) The primary compressor front stage (1) is a compressor that compresses ethylene within a range of, for example, 0.04 MPa to 3 MPa.

[0015] Primary compressor rear stage (2) The primary compressor rear stage (2) is a compressor that compresses the ethylene supplied from the primary compressor front stage (1) to a pressure in the range of, for example, 3 MPa to 20 MPa.

[0016] Secondary compressor (3) The secondary compressor (3) is a compressor that compresses the ethylene supplied from the primary compressor rear stage (2) to a pressure in the range of, for example, 20 MPa to 200 MPa.

[0017] reactor (4) The reactor (4) is a reactor in which ethylene supplied from the secondary compressor (3) and a polymerization initiator supplied to the reactor (4) are polymerized to produce polyethylene. The reactor (4) may be either a tubular reactor or a tank-type reactor, and the high-pressure polymerization of ethylene can be carried out using a polymerization initiator such as oxygen or a peroxide under conditions of a pressure of, for example, 20 MPa or higher, preferably 100 to 500 MPa, and more preferably 100 to 400 MPa, and a temperature of, for example, 100°C or higher, preferably 100 to 400°C, more preferably 150 to 350°C, and even more preferably 150 to 300°C. The ethylene stream entering the reactor (4) may contain a comonomer and a chain transfer agent in addition to the polymerization initiator.

[0018] High-pressure separator (5) The high-pressure separator (5) is a high-pressure separator to which the polyethylene obtained in the reactor (4) under reduced pressure and unreacted ethylene are supplied, and which separates the polyethylene from the unreacted high-pressure ethylene. The reaction mixture containing the polymer produced in the reactor (4), unreacted ethylene gas, polymerization by-products, solvent, lubricating oil, etc., is optionally passed through a pressure control valve and enters the high-pressure separator (5) where it is released under reduced pressure, and a portion of the polymer contained in the reaction mixture is separated at a pressure of, for example, 10 to 100 MPa, preferably 15 to 100 MPa, more preferably 70 MPa or less, and at a temperature of, for example, 200 to 260°C.

[0019] The separated polymer contains almost no low molecular weight compounds having a weight average molecular weight of 5,000 or less. The polymer separated in the high-pressure separator (5) is sent to the low-pressure separator (8) where unreacted ethylene gas remaining in the polymer is separated and removed, and then the polymer is taken out as product polyethylene from the polyethylene withdrawal pipe (10).

[0020] Unreacted high pressure ethylene supply pipe (6) The unreacted high-pressure ethylene supply pipe (6) is a pipe for supplying the unreacted high-pressure ethylene separated in the high-pressure separator (5) to the secondary compressor (3).

[0021] Polyethylene extraction pipe (7) The polyethylene withdrawal pipe (7) is a pipe for withdrawing the polyethylene separated in the high-pressure separator (5) from the high-pressure separator (5) and supplying it to the low-pressure separator (8).

[0022] Low Pressure Separator (8) The low-pressure separator (8) is a separator for separating polyethylene from unreacted low-pressure ethylene contained in the polyethylene separated in the high-pressure separator (5) and supplied through the polyethylene withdrawal pipe (7). The unreacted gas separated as the head in the low-pressure separator (8), for example at a temperature of about 200 to 250°C, is cooled to 20 to 50°C, for example, in a cooler, and then sent to, for example, a separator to remove impurities such as solvent. The unreacted gaseous ethylene from which the impurities have been removed is returned to the inlet of the front stage (1) of the primary compressor through the unreacted low-pressure ethylene supply pipe (16).

[0023] Unreacted low-pressure ethylene supply pipe (9) The unreacted low-pressure ethylene supply pipe (9) is a pipe for supplying the unreacted low-pressure ethylene separated in the low-pressure separator (8) to the upstream stage of the primary compressor. The pressure inside the unreacted low-pressure ethylene supply pipe (9) can be controlled to, for example, 0.01 to 0.1 MPa and the temperature to, for example, 150 to 220°C.

[0024] Polyethylene extraction pipe (10) The polyethylene withdrawal pipe (10) is a pipe for withdrawing the polyethylene separated in the low-pressure separator (8). The polyethylene withdrawn from the polyethylene withdrawal pipe (10) can be processed into a pellet product by passing through an extruder, a cooler, a granulator, etc. The obtained polyethylene can be a low-density polyethylene, for example, 910 to 920 kg / m 3 It has a density of

[0025] Ethylene supply piping (13) The ethylene supply pipe (13) connects the primary compressor front stage (1) and the primary compressor rear stage (2) and is a pipe for supplying unreacted ethylene compressed to, for example, 0.04 MPa to 3 MPa from the primary compressor front stage (1) to the primary compressor rear stage (2), and merges with the fresh ethylene supply pipe (14).

[0026] Fresh ethylene supply piping (14) The fresh ethylene supply pipe (14) is connected to the ethylene supply pipe (13) and is a pipe for supplying fresh ethylene. For example, fresh ethylene gas of 0.8 MPa to 3 MPa is supplied. In one embodiment, raw material ethylene gas is sent from a fresh ethylene supply pipe (14) to the rear stage (2) of the primary compressor, where it is compressed to a pressure in the range of, for example, 3 MPa to 20 MPa, and then further compressed to a pressure in the range of, for example, 20 MPa to 200 MPa by the secondary compressor (3). The gas pressurized to the polymerization pressure is sent to the reactor (4), where it is polymerized using an oxygen or peroxide initiator at a predetermined temperature of, for example, 150 to 300°C.

[0027] Unreacted ethylene holding drum (15) The unreacted ethylene holding drum (15) is a drum that holds the unreacted low-pressure ethylene supplied through the unreacted low-pressure ethylene supply pipe (9) at a pressure of, for example, 0.01 to 0.1 MPa and a temperature of, for example, 10 to 60°C.

[0028] Unreacted low-pressure ethylene supply pipe (16) The unreacted low-pressure ethylene supply pipe (16) connects the unreacted ethylene holding drum (15) and the primary compressor front stage (1), and is a pipe for supplying unreacted low-pressure ethylene from the unreacted ethylene holding drum (15) to the primary compressor front stage (1). The pressure inside the unreacted low-pressure ethylene supply pipe (16) can be controlled to, for example, 0.01 to 0.1 MPa and the temperature to, for example, 10 to 60°C.

[0029] Chain Transfer Agent (CTA) Supply Pipe (17) The chain transfer agent (CTA) supply pipe (17) is connected to the unreacted low-pressure ethylene supply pipe (16) and is a pipe for supplying a chain transfer agent (CTA). The pressure inside the chain transfer agent (CTA) supply pipe (17) can be controlled to, for example, 0.01 to 0.1 MPa and the temperature can be controlled to, for example, 10 to 60°C.

[0030] High-pressure ethylene piping (18) The high-pressure ethylene pipe (18) connects the primary compressor rear stage (2) and the secondary compressor (3), and is a pipe for supplying unreacted high-pressure ethylene separated in the high-pressure separator (5) from the unreacted high-pressure ethylene supply pipe (6) to the secondary compressor (3), and for supplying ethylene from the primary compressor rear stage (2) to the secondary compressor (3). The pressure inside the high-pressure ethylene pipe (18) can be controlled to, for example, 10 MPa to 20 MPa and a temperature of, for example, 10 to 60°C.

[0031] <Manufacturing method> The manufacturing method of the present invention comprises: A method for producing high-pressure polyethylene, comprising the steps of: Chain transfer agent (CTA) supplying step: a step of supplying ethane, propane, and propylene as chain transfer agents (CTAs) from a chain transfer agent (CTA) supplying pipe (17) controlled at a pressure of 0.01 to 0.1 MPa and a temperature of 10 to 60°C to an unreacted low-pressure ethylene supplying pipe (16) controlled at a pressure of 0.01 to 0.1 MPa and a temperature of 10 to 60°C, and adjusting the ratio of the propane concentration to the total CTA concentration to 0.70 to 0.95 (note that the concentrations are on a volume basis, and the sum of the volumes of ethylene, ethane, propane, and propylene is taken as 100% by volume). The production method of the present invention is preferably the method for producing the above polyethylene of the present invention. The production method of the present invention preferably further comprises the following steps: · Compression process: the process of compressing ethylene; Reaction step: supplying compressed ethylene and a polymerization initiator to a reactor (4) and polymerizing the ethylene at a reactor pressure of 170-220 MPa and a reaction temperature of 220-270°C to produce polyethylene; Separation step: a step of separating the polyethylene produced in the reactor (4) from unreacted ethylene in a high-pressure separator (5), withdrawing the produced polyethylene from the high-pressure separator (5) and supplying it to a low-pressure separator (8) through an extraction pipe (7), separating the unreacted ethylene contained in the polyethylene in the low-pressure separator (8), and withdrawing the polyethylene; unreacted low-pressure ethylene recycling step: a step of supplying unreacted low-pressure ethylene separated in the low-pressure separator (8) at a pressure of 0.01 to 0.1 MPa and a temperature of 150 to 220°C to an unreacted ethylene holding drum (15) through an unreacted low-pressure ethylene supply pipe (9); and Fresh ethylene supply step: a step of supplying fresh ethylene from the fresh ethylene pipe (14) to the ethylene pipe (13). The production method of the present invention preferably further comprises the following steps: Unreacted high-pressure ethylene recycling process: A process in which the unreacted ethylene separated in the high-pressure separator (5) is decompressed through the unreacted high-pressure ethylene supply pipe (6) and the decompressed unreacted ethylene is supplied to the secondary compressor (3).

[0032] Compression process The compression step is not limited to one stage, but may include a step of compressing in two or more stages. For example, the compression process may be The ethylene is compressed by the first stage of the primary compressor (1) to a pressure in the range of, for example, 0.04 MPa to 3 MPa, The ethylene compressed in the first stage of the primary compressor (1) is compressed in the second stage of the primary compressor (2) to a pressure in the range of, for example, 3 MPa to 20 MPa, This is a step in which ethylene compressed in the rear stage of the primary compressor (2) is compressed in the secondary compressor (3) to a pressure in the range of, for example, 20 MPa to 200 MPa.

[0033] Reaction process The reaction process is In this step, ethylene compressed by the secondary compressor (3) and a polymerization initiator are fed to the reactor (4) to polymerize the ethylene and produce polyethylene. The detailed operating conditions for the reaction step are the same as those described above in the description of the reactor (4).

[0034] Separation process The separation process is The polyethylene produced in the reactor (4) and unreacted ethylene are separated in a high-pressure separator (5), The produced polyethylene is extracted from the high-pressure separator (5) and fed to the low-pressure separator (8) through an extraction pipe (7). This is the process where unreacted ethylene contained in the polyethylene is separated in a low-pressure separator (8) and the polyethylene is extracted. The detailed operating conditions for the separation process in the high-pressure separator (5) and the low-pressure separator (8) are the same as those described above for the high-pressure separator (5) and the low-pressure separator (8).

[0035] Unreacted high-pressure ethylene recycling process The unreacted high-pressure ethylene recycling process is In this step, the unreacted ethylene separated in the high-pressure separator (5) is passed through an unreacted high-pressure ethylene supply pipe (6) and is supplied to the secondary compressor (3). As the detailed operating conditions for the unreacted high-pressure ethylene recycling step, the conditions described above in the description of the unreacted high-pressure ethylene supply pipe (6) can be applied.

[0036] Unreacted low-pressure ethylene recycling process The unreacted low-pressure ethylene recycling process is In this step, the unreacted low-pressure ethylene separated in the low-pressure separator (8) is fed to the unreacted ethylene holding drum (15) through the unreacted low-pressure ethylene feed pipe (9). As the detailed operating conditions of the unreacted low-pressure ethylene recycling step, the conditions described above in the description of the low-pressure separator (8), the unreacted low-pressure ethylene supply pipe (9), and the unreacted ethylene holding drum (15) can be applied.

[0037] Chain transfer agent (CTA) supply process The chain transfer agent (CTA) supply step is a step of supplying a chain transfer agent (CTA) from a chain transfer agent (CTA) supply pipe (17) to the unreacted low-pressure ethylene supply pipe (16). As the detailed operating conditions of the chain transfer agent (CTA) supplying step, the conditions described above in the description of the chain transfer agent (CTA) supplying pipe (17) and the unreacted low-pressure ethylene supplying pipe (16) can be applied.

[0038] Fresh ethylene supply process The fresh ethylene supply process is Fresh ethylene is supplied from a fresh ethylene supply pipe (14) to an ethylene supply pipe (13), This is a process in which the ethylene is supplied to the downstream stage (2) of the primary compressor through the ethylene supply pipe (13). As detailed operating conditions for the fresh ethylene supply step, the conditions described above in the description of the fresh ethylene supply pipe (14) and the ethylene supply pipe (13) can be applied.

[0039] The present invention can be carried out using a high-pressure ethylene polymerization unit equipped with a high-pressure circulating gas system. In the present invention, all polymerization initiators and chain transfer agents known to be used in the polymerization or copolymerization of ethylene can be used.

[0040] <Polymerization initiator> In the present invention, any polymerization initiator known to be used in the polymerization or copolymerization of ethylene can be used. Suitable examples of the polymerization initiator include organic peroxides such as hydrogen peroxide, lauroyl peroxide, dipropionyl peroxide, benzoyl peroxide, di-tert-butyl peroxide, tert-butyl hydroperoxide, trimethylhexanoyl peroxide, diisopropyl peroxydicarbonate, tert-butyl peracetate, and tert-butyl perisobutyrate; hydrogen peroxide; molecular oxygen; azo compounds such as azobisisobutyronitrile and azoisobutylvaleronitrile; t-butyl peroxybenzoate, t-butylperoxy-2-ethylhexanoate, t-butylperoxyisopropyl carbonate; and oxygen.

[0041] <Chain transfer agent> In the present invention, any chain transfer agent known to be used in the polymerization or copolymerization of ethylene can be used. Suitable examples of the chain transfer agent include paraffin hydrocarbons such as ethane, propane, butane, heptane, hexane, and pentane; α-olefins such as propylene, butene-1, hexene-1, and 3-methylbutene-1; aldehydes such as formaldehyde, acetaldehyde, propylene aldehyde, and n-butylaldehyde; ketones such as acetone, methyl ethyl ketone, diethyl ketone, diisopropyl ketone, cyclohexanone, and methyl isopropyl ketone; aromatic hydrocarbons; and chlorinated hydrocarbons. Preferably, ethane, propane, and propylene are supplied as the chain transfer agent (CTA), and the ratio of the propane concentration to the total CTA concentration is adjusted to preferably 0.75 to 0.93 before supplying the chain transfer agent (CTA) (note that the concentrations are based on volume, and the sum of the volumes of ethylene, ethane, propane, and propylene is taken as 100% by volume).

[0042] <Comonomer> The apparatus and method of the present invention are also applicable to the copolymerization of ethylene with other comonomers that are copolymerizable with ethylene. In the present invention, any comonomer known to copolymerize with ethylene can be used, such as compounds having an ethylenically unsaturated group, including, for example, acrylic acid, methacrylic acid and their alkyl esters, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, vinyl chloride, vinylitine chloride, vinyl fluoride, vinyl acetate, vinyl propionate, N-vinyl imide compounds, vinyl aryl compounds, vinyl ether compounds, and vinyl ketone compounds. The comonomer can be used such that it is present in the resulting copolymerization in an amount greater than 0% by weight and up to about 50% by weight, preferably up to about 40% by weight, more preferably up to about 30% by weight, and even more preferably up to about 20% by weight. The comonomer can be added to any equipment or process, for example, from the vicinity of the compressor to the vicinity of the reactor. [Example]

[0043] <Methods for measuring the physical properties of polyethylene> The physical properties of the polyethylenes produced in the following examples and comparative examples were measured according to the following methods.

[0044] (1) Melt flow rate (MFR, unit: g / 10 min) The melt flow rate was measured by Method A in accordance with JIS K7210-1995 under conditions of a load of 21.18 N and a temperature of 190°C.

[0045] (2) Density (unit: kg / m 3 ) After annealing as specified in JIS K6922-2, measurement was performed by Method A in accordance with the method specified in JIS K7112.

[0046] (3) Mz / Mw (M indicates the molecular weight in terms of polyethylene) The molecular weight distribution of polyethylene and various polyethylene-equivalent molecular weights (number average molecular weight Mn, weight average molecular weight Mw, z-average molecular weight Mz) are determined by gel permeation chromatography (GPC). GPC measurements to determine Mz / Mw are performed under the following conditions. Based on the description in ISO16014-1, the baseline on the chromatogram is specified and peaks are designated. (GPC equipment and software) Apparatus: HLC-8321GPC / HT (Tosoh Corporation) (Measurement conditions) GPC column: TSKgel GMHHR-H(S)HT 7.8mm ID x 300mm (Tosoh Corporation), 3 columns Mobile phase: Orthodichlorobenzene (Wako Pure Chemical Industries, Ltd., special grade) to which dibutylhydroxytoluene (BHT) was added at a concentration of 0.1 w / V, i.e., 0.1 g / 100 mL. Flow rate: 1mL / min Column oven temperature: 140°C Autosampler temperature: 140℃ System oven temperature: 40°C Detection: Refractive index detector (RID) RID cell temperature: 140℃ Sample solution injection volume: 300 μL GPC column calibration standard: Weigh out the standard polystyrene manufactured by Tosoh Corporation in the combinations shown in the table below, add 5 mL of orthodichlorobenzene (same composition as the mobile phase), and leave to stand at room temperature for 120 minutes to dissolve. [Table 0] (Sample solution preparation conditions) Solvent: Orthodichlorobenzene (Wako Pure Chemical Industries, Ltd., special grade) to which BHT was added at a concentration of 0.1 w / V (0.1 g / 100 mL) was used. Sample solution concentration: 1 mg / mL Automatic dissolution shaker: DF-8020 (Tosoh Corporation) Dissolution conditions: 5 mg of sample was sealed in a 1000 mesh SUS wire bag, the wire bag containing the sample was placed in a test tube, 5 mL of solvent was added to the test tube, the test tube was covered with aluminum foil, the test tube was placed in a shaker, and the mixture was stirred at 140°C for 120 minutes at a stirring speed of 60 strokes per minute.

[0047] (4) Light scattering area ratio (R LS ) calculation The light scattering area ratio was calculated using a liquid chromatography (LC) device equipped with a light scattering detector by measuring the light scattering area LS of a solution in which the polyethylene of each Example and Comparative Example was dissolved in orthodichlorobenzene at a concentration of 2 mg / mL, and the light scattering area LS' of a solution in which standard polystyrene F10 (number average molecular weight 1000) manufactured by Tosoh Corporation was dissolved in orthodichlorobenzene at a concentration of 2 mg / mL, and then using the following formula: R LS =LS / LS' (Equation 1) Light scattering area ratio (R LS ), that is, the larger the light scattering area LS of a solution of polyethylene dissolved in orthodichlorobenzene, the greater the amount of ultra-high molecular weight components in the polyethylene. The measurement conditions are as follows: LC device: HLC-8121GPC / HT (Tosoh Corporation) Light scattering detector: PD2040 (Precision Detectors) Laser light source: Wavelength 685nm GPC column: None Sample solution concentration: 2mg / mL ·Injection volume: 300μL ·Measurement temperature: 140℃ Dissolution conditions: Stir at 145°C for 2 hours Automatic dissolution shaker: DF-8020 (Tosoh Corporation) Solvent and mobile phase: Orthodichlorobenzene containing 0.1 w / V BHT (Wako Pure Chemical Industries, Ltd., special grade) ·Mobile phase flow rate: 1.0mL / min Specifically, a light scattering detector (LS) was connected to the LC system. The scattering angle used for light scattering detection was 90°. The LS was installed in the column oven of the LC system. The sample was dissolved as follows: 40.0 mg of sample and 20.0 mL of solvent were placed in a 30 mL screw vial and sealed. The screw vial was then placed in a DF-8020 (Tosoh Corporation) and stirred at 140 °C for 2 hours to dissolve the sample. The sample solution obtained by this method was filtered using a 10 μm pore size cylindrical filter (Whatman cylindrical filter, 18 mm diameter x 55 mm length, model number: 2800-185) prior to analysis. Filtration was performed at 140 °C or higher to prevent sample precipitation. The cylindrical filter was immersed in the sample solution and allowed to stand for 5 minutes to equilibrate, after which the sample solution leached into the cylindrical filter was subjected to analysis. Filtration was performed within 20 minutes to avoid changes in the concentration of the sample solution due to solvent evaporation. To avoid capturing ultra-high molecular weight components in the column, a GPC column and a guard column were not used. To obtain the chromatogram, a 5-m-long stainless steel pipe with an inner diameter of 0.75 mm was attached between the sample injection port and the LS detector, and the temperature of the sample injection port and each detector was set to 140°C. The obtained LS chromatogram was subjected to baseline processing, and the light scattering area was calculated (see Figure 2). The light scattering area was determined using Malvern's data processing software OmniSEC (version 4.7).

[0048] (5) Calculation of the contraction factor g' The shrinkage factor g' of the sample was measured by a gel permeation chromatograph (3D-GPC) equipped with a differential refractive index detector, a viscosity detector, and a light scattering detector. A Tosoh HLC-8121GPC / HT GPC system equipped with a refractive index detector (RI) was used. A Precision Detectors PD2040 light scattering detector (LS) was connected to the GPC system. The scattering angle used for light scattering detection was 90°. A Viscotek H502 viscosity detector (VISC) was also connected to the GPC system. The LS and VISC were installed in the column oven of the GPC system and connected in the following order: LS, RI, VISC. Malvern's polystyrene standard Polycal TDS-PS-N (weight-average molecular weight Mw 104,349, polydispersity index 1.04) was used at a solution concentration of 1 mg / mL for calibration of the LS and VISC and for correction of the delay volume between the detectors. The mobile phase and solvent were orthodichlorobenzene with dibutylhydroxytoluene added at a concentration of 0.5 mg / mL as a stabilizer. The sample was dissolved at 145°C for 2 hours with stirring. The flow rate was 1 mL / min. Three Tosoh GMHHR-H(S) HT columns were used in series. The temperature of the column, sample injection port, and each detector was 140°C. The sample solution concentration was 2 mg / mL. The sample solution injection volume (sample loop volume) was 0.3 mL. The refractive index increment (dn / dc) of NIST 1475a and the sample in orthodichlorobenzene was -0.078 mL / g. The dn / dc of the polystyrene standard was 0.079 mL / g. The absolute molecular weight and intrinsic viscosity ([η]) were calculated from the data from each detector using Malvern's data processing software OmniSEC (version 4.7) with reference to the literature, "Size Exclusion Chromatography, Springer (1999)." The refractive index increment is the rate of change in refractive index with respect to a change in concentration. (Calculation of contraction factor g') The shrinkage factor g' was calculated from the ratio ([η]sample / [η]PE) of the intrinsic viscosity ([η]sample) obtained by measuring the sample using the above-mentioned device to the intrinsic viscosity ([η]PE) of linear polyethylene. The weight average value of the above intrinsic viscosity ratios in the range of the common logarithm logM of the absolute molecular weight from 5.0 to 6.5 was used as the g' of the sample. Here, [η]PE of linear polypropylene was calculated using the following formula described in "Size Exclusion Chromatography, Springer (1999)." [η]PE = K0× M^ α0(dl / g) Equation (I) where M is the absolute molecular weight. α0 and K0 in formula (I) were determined by the following method. α0 is a value obtained by a method comprising: plotting measured data with the logarithm of the absolute molecular weight of polyethylene standard substance 1475a on the horizontal axis and the logarithm of the intrinsic viscosity of polyethylene standard substance 1475a on the vertical axis; performing least-squares approximation of the logarithm of the absolute molecular weight and the logarithm of the intrinsic viscosity using formula (II) within the range of the horizontal axis from the logarithm of the weight-average molecular weight of polyethylene standard substance 1475a to the logarithm of the z-average molecular weight; and defining the value of the slope of the straight line representing formula (II) as α0. log[η0]=α0logM0+logK0(II) (In formula (II), [η] represents the intrinsic viscosity (unit: dl / g) of polyethylene standard substance 1475a, M represents the absolute molecular weight of polyethylene standard substance 1475a, and K is a constant.) <Measurement conditions> GPC equipment: Tosoh HLC-8121GPC / HT Light scattering detector: Precision Detectors PD2040 Differential pressure viscometer: Viscotek H502 GPC column: Tosoh GMHHR-H(S)HT x 3 Sample solution concentration: 2mg / ml Injection volume: 0.3ml Measurement temperature: 140℃ Dissolution conditions: Stir at 145°C for 2 hours Solvent and mobile phase: Orthodichlorobenzene (Wako special grade) containing 0.05 wt% dibutylhydroxytoluene Mobile phase flow rate: 1mL / min Measurement time: Approximately 1 hour

[0049] (6) Polyethylene film production An inflation film was produced under the following processing conditions. Processing equipment: Placo L-40A Screw diameter: 40mmΦ L / D:26 Die diameter: 75mmφ Lip gap: 1.0mm Set temperature: 150℃ BUR:1.78 Film thickness: 60 μm Screw rotation speed: 60 rpm Pulling machine: Tajima Kogyo Co., Ltd. TW2B

[0050] (7) Haze measurement The haze of the formed inflation film was measured using an integrating sphere light transmittance measuring device (Direct Reading Haze Meter, Toyo Seiki Seisakusho Co., Ltd.) in accordance with ASTM D 1003. The smaller this value, the higher the transparency.

[0051] (8) Clarity ratio measurement The clarity (unit: %) in the machine direction (MD) and the transverse direction (TD) of the film were measured using a transparency meter (TM-1D model, manufactured by Murakami Color Research Laboratory Co., Ltd.) conforming to ASTM D 1746 for the formed inflation film, and the clarity (unit: %) was calculated using the following formula: The smaller this value, the smaller the optical anisotropy. Clarity ratio = (MD clarity - TD clarity) / [(MD Clarity + TD Clarity) / 2]

[0052] [Examples and Comparative Examples] The present invention will be described below with reference to examples and comparative examples.

[0053] Table 1 shows the physical properties of the polyethylenes produced in Examples 1 to 3 and Comparative Examples 1 to 4 below. [Table 1]

[0054] Examples 1, 2, and 3 and Comparative Examples 1, 2, 3, and 4 Ethylene gas was supplied from secondary compressor 3 to reactor 4 at a rate of 14.2 to 15.3 ton / h (listed in Table 2), and ethylene was polymerized by adding t-butyl peroxybenzoate, t-butyl peroxyisopropyl carbonate, or t-butyl peroxy-2-ethylhexanoate (listed in Table 2) as a polymerization initiator under conditions of a pressure of 164 to 220 MPa (listed in Table 2) and a temperature of 232 to 261°C (listed in Table 2) in reactor 4. The amount of polymer produced was 2.3 to 2.8 ton / h (listed in Table 2). The polymerization mixture was discharged from the polymerization reactor 4 to a high-pressure separator 5 at 18.9 to 20.1 MPa (listed in Table 2), where it was separated into the produced polymer and unreacted ethylene gas at 248 to 260°C (listed in Table 2). The produced polymer separated in the high-pressure separator 5 was discharged through a polyethylene discharge pipe 7 into a low-pressure separator 8 at 0.044 to 0.045 MPa (shown in Table 2), where it was further separated into the produced polymer and unreacted ethylene gas at 191 to 201°C (shown in Table 2). The produced polymer was discharged through a polyethylene discharge pipe 10 and pelletized in a granulator. The unreacted ethylene gas separated in the low-pressure separator 8 was supplied to an unreacted ethylene holding drum 15 at a temperature of 22 to 42°C (listed in Table 2) under 0.040 MPa through an unreacted low-pressure ethylene piping 9. The unreacted ethylene gas at 0.040 MPa held in the unreacted ethylene holding drum 15 was supplied to the primary compressor upstream stage 1 through an ethylene piping 16, and ethane, propane, and propylene were supplied to the ethylene piping 16 as a chain transfer agent (CTA) 17. Unreacted ethylene gas, ethane, propane, and propylene were compressed to 2.9 to 3.1 MPa (listed in Table 2) in the first stage 1 of the primary compressor and supplied to the second stage 2 of the primary compressor through an ethylene pipe 13. The unreacted ethylene gas separated in the high-pressure separator 5 was decompressed to 17.2 to 18.2 MPa (listed in Table 2) through the unreacted high-pressure ethylene piping 6, and the entire amount of the unreacted ethylene gas (100 weight percent) was supplied to the inlet piping of the secondary compressor 3. Fresh ethylene gas at 3.0 MPa was supplied from fresh ethylene supply pipe 14 through ethylene pipe 13 to the primary compressor rear stage 2. The mixed ethylene gas of unreacted ethylene gas, ethane, propane, propylene, and fresh ethylene gas supplied from the upstream stage 1 of the primary compressor was compressed to 18.3 to 19.5 MPa (listed in Table 2) in the downstream stage 2 of the primary compressor and supplied to the secondary compressor 3. Ethylene gas, ethane, propane, and propylene compressed to 166 to 220 MPa (listed in Table 2) by a secondary compressor 3 were supplied to a polymerization reactor 4, where the polymerization reaction was carried out continuously. The concentrations of the chain transfer agents (CTAs) ethane, propane, and propylene were measured using a gas chromatograph installed in the high-pressure ethylene pipe 18, and the concentration of all CTAs (ethane, propane, propylene) in the total gas amount (ethylene, ethane, propane, propylene) was adjusted to 2.15 to 3.44 vol.% (listed in Table 2), and the ratio of the propane concentration to the total CTA (ethane, propane, propylene) concentration was adjusted to 0.31 to 0.91 (listed in Table 2).

[0055] [Table 2]

[0056] From the results in Tables 1 and 2, it was confirmed that in Examples 1 to 3, in which the ratio of the propane concentration to the total CTA concentration in the chain transfer agent (CTA) supply process was adjusted to a specific ratio (0.70 to 0.95), the haze and clarity ratio of the resulting films were lower than in Comparative Examples 1 to 4, in which the ratio was outside the specific range. [Industrial Applicability]

[0057] According to the present invention, the chain transfer agent (CTA) supplying step in a high-pressure polyethylene production process is carried out by supplying a specific chain transfer agent (CTA) at a specific pressure and temperature in a specific concentration ratio, thereby making it possible to produce polyethylene with an improved balance between ease of film handling and ease of detection of film defects (fish eyes, air entrapment). The polyethylene of the present invention can be used for a wide variety of films, such as heavy-duty bags, shrink films, general packaging, thin films, protective films (protective films), extrusion laminated films, extrusion-molded films, and foam-molded films.The polyethylene of the present invention can be suitably used for applications such as various parts for home appliances, various housing equipment parts, various industrial parts, various building material parts, and various interior and exterior parts for automobiles, and is highly applicable in various industrial fields, such as the electrical and electronics industry, household products industry, transportation machinery industry, and building and construction industry.

Claims

1. In an integral distribution curve of the polyethylene evaluated by gel permeation chromatography, the ratio (Mz / Mw) of Mz (Z-average molecular weight) to Mw (weight-average molecular weight) of the polyethylene is 3.4 or more and 4.0 or less; The light scattering area ratio (R ＬＳ ) is 2.5 or more and 4.0 or less, R ＬＳ =L / LL' (Formula 1) (In the formula, LS represents the light scattering area of ​​a solution obtained by dissolving 40 mg of the polyethylene in 20 mL of orthodichlorobenzene. LS' indicates the light scattering area of ​​a solution in which 40 mg of standard polystyrene having a number average molecular weight of 1,000 is dissolved in 20 mL of orthodichlorobenzene. Polyethylene produced by a high-pressure polyethylene production method comprising the steps of: Chain transfer agent (CTA) supplying step: a step of supplying ethane, propane, and propylene as chain transfer agents (CTA) from a chain transfer agent (CTA) supplying pipe (17) whose interior is controlled at a pressure of 0.01 to 0.1 MPa and a temperature of 10 to 60°C to an unreacted low-pressure ethylene supplying pipe (16) whose interior is controlled at a pressure of 0.01 to 0.1 MPa and a temperature of 10 to 60°C, and adjusting the ratio of the propane concentration to the total CTA concentration to 0.70 to 0.95 (wherein the concentrations are concentrations on a volume basis, and the sum of the volumes of ethylene, ethane, propane, and propylene is taken as 100% by volume), The total CTA (ethane, propane, propylene) concentration in the total gas (ethylene, ethane, propane, propylene) is 2.15 to 3.44% by volume, The propane concentration in the total amount of gas (ethylene, ethane, propane, propylene) is 1.88 to 3.12% by volume, The propylene concentration comprises 0% by volume.

2. Mz / Mw is 3.5 or more and 3.8 or less, Light scattering area ratio (R ＬＳ 2. The polyethylene according to claim 1, wherein the σ is 2.8 or more and 3.8 or less.

3. The polyethylene according to claim 1 or claim 2, wherein the polyethylene is a high-pressure low-density polyethylene.

4. A film made of the polyethylene according to any one of claims 1 to 3.

5. A protective film for a dry film resist, comprising the polyethylene according to any one of claims 1 to 3.

6. A method for producing the polyethylene according to any one of claims 1 to 3, comprising the steps of: Chain transfer agent (CTA) supplying step: a step of supplying ethane, propane, and propylene as chain transfer agents (CTA) from a chain transfer agent (CTA) supplying pipe (17) whose interior is controlled at a pressure of 0.01 to 0.1 MPa and a temperature of 10 to 60°C to an unreacted low-pressure ethylene supplying pipe (16) whose interior is controlled at a pressure of 0.01 to 0.1 MPa and a temperature of 10 to 60°C, and adjusting the ratio of the propane concentration to the total CTA concentration to 0.70 to 0.95 (wherein the concentrations are concentrations on a volume basis, and the sum of the volumes of ethylene, ethane, propane, and propylene is taken as 100% by volume), The total CTA (ethane, propane, propylene) concentration in the total gas (ethylene, ethane, propane, propylene) is 2.15 to 3.44% by volume, The propane concentration in the total amount of gas (ethylene, ethane, propane, propylene) is 1.88 to 3.12% by volume, The propylene concentration comprises 0% by volume.

7. The method of claim 6 further comprising the steps of: Compression step: a step of compressing ethylene; Reaction step: supplying compressed ethylene and a polymerization initiator to a reactor (4) and polymerizing ethylene at a reactor pressure of 170 to 220 MPa and a reaction temperature of 220 to 270°C to produce polyethylene; Separation step: a step of separating the polyethylene produced in the reactor (4) from unreacted ethylene in a high-pressure separator (5), withdrawing the produced polyethylene from the high-pressure separator (5) and supplying it to a low-pressure separator (8) through an extraction pipe (7), separating the unreacted ethylene contained in the polyethylene in the low-pressure separator (8), and withdrawing the polyethylene; - Unreacted low-pressure ethylene recycling step: A step of supplying unreacted low-pressure ethylene separated in the low-pressure separator (8) at a pressure of 0.01 to 0.1 MPa and a temperature of 150 to 220°C to an unreacted ethylene holding drum (15) through an unreacted low-pressure ethylene supply pipe (9); and Fresh ethylene supply step: a step of supplying fresh ethylene from the fresh ethylene pipe (14) to the ethylene pipe (13).

8. The method of claim 6 or claim 7, further comprising the steps of: Unreacted high-pressure ethylene recycling step: a step of reducing the pressure of the unreacted ethylene separated in the high-pressure separator (5) through an unreacted high-pressure ethylene supply pipe (6) and supplying the reduced-pressure unreacted ethylene to the secondary compressor (3).

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