Name of the invention: Ethylene vinyl acetate copolymer and its manufacturing method
Technical field
[One]
Cross-reference with related application(s)
[2]
This application claims the benefit of priority based on Korean Patent Application No. 10-2018-0147748 filed on November 26, 2018, and includes all the contents disclosed in the documents of the Korean patent application as part of this specification.
[3]
The present invention relates to an ethylene vinyl acetate copolymer and a method for producing the same, and more particularly, to an ethylene vinyl acetate copolymer having excellent physical properties such as mechanical strength with high crosslinking degree and a method for producing the same.
Background
[4]
Ethylene vinyl acetate is a copolymer of ethylene and vinyl acetate. Depending on the content of vinyl acetate, the range of use is very wide, ranging from hard materials to soft materials such as hot melt adhesives, and is more crystalline than polyethylene. It has the characteristics of low temperature and excellent impact resistance.
[5]
In addition, ethylene vinyl acetate has a thermoplastic polymer or rubbery character, has excellent electrical insulation and voltage resistance, and has excellent transparency, barrier properties, adhesion, and UV properties. It is widely used for tapes, adhesives, and various sheets, and in recent years, its use area is expanding with a protective film or encapsulant for photovoltaic devices such as solar cells.
[6]
In general, ethylene vinyl acetate copolymer can be prepared in an autoclave or tubular reactor. Vinyl acetate has a narrow molecular weight distribution, and it is common to select and manufacture a reactor according to the application.
[7]
However, in the case of using an autoclave reactor in which back-mixing occurs, a tubular reactor in which mixing occurs due to a turbulent plug flow can be used because a uniform and high reaction temperature can be maintained. Compared to the case of use, there is an advantage of producing an ethylene vinyl acetate copolymer having a higher content of vinyl acetate.
[8]
Meanwhile, ethylene vinyl acetate copolymers are known to have high transparency and adhesion, but generally have low mechanical strength compared to polyethylene.
[9]
Recently, ethylene vinyl acetate copolymer products are often used as an encapsulant that protects the cells of a solar module from moisture and dust. In this case, the better the mechanical strength, the higher the encapsulant performance can be.
[10]
Therefore, there is a need for research on a manufacturing method for improving the mechanical strength of ethylene vinyl acetate copolymer.
Detailed description of the invention
Technical challenge
[11]
The present invention is to solve the above problems, to provide an ethylene vinyl acetate copolymer having a high degree of crosslinking even with the use of a reduced crosslinking agent by controlling the temperature difference in the autoclave reactor and the input ratio of the initiator during polymerization, and a manufacturing method thereof. will be.
Means of solving the task
[12]
In order to solve the above problems, according to an embodiment of the present invention, an ethylene vinyl acetate copolymer satisfying the following conditions (1) to (4) is provided:
[13]
(1) Degree of crosslinking: more than 89%
[14]
(2) Content of vinyl acetate: 25 to 35% by weight based on the total weight of the copolymer
[15]
(3) Melt Index (190° C., 2.16 kg): 10 to 20 g/10 minutes
[16]
(4) Ratio of η*/[η]: 7500 to 9500
[17]
(η* is the zero shear viscosity measured at 160°C, and [η] is the intrinsic viscosity measured at 25°C)
[18]
In addition, according to another embodiment of the invention, in the presence of an initiator, comprising the step of polymerizing an ethylene monomer and a vinyl acetate monomer in an autoclave reactor,
[19]
The reactor comprises at least three or more reaction zones,
[20]
The initiator is added to the top and bottom of the reactor, and the amount of the initiator is added to the bottom of the reactor is 12 to 22% by weight of the total initiator content,
[21]
The relationship between the temperature of one or more reaction zones from the bottom (T1)> the temperature of one or more reaction zones from the top (T2)> the temperature of one or more reaction zones (T3) in between,
[22]
The difference ΔT between T1 and T2 satisfies 20 to 40° C., and a method for producing an ethylene vinyl acetate copolymer is provided.
Effects of the Invention
[23]
The ethylene vinyl acetate copolymer according to the present invention can exhibit excellent effects in terms of mechanical strength, etc., having optimized physical properties with high crosslinking degree. Accordingly, it can be usefully used for a solar module.
[24]
In addition, the method for producing an ethylene vinyl acetate copolymer according to the present invention can produce an ethylene vinyl acetate copolymer having a high degree of crosslinking even with a reduced amount of crosslinking agent by controlling the temperature difference in the autoclave reactor and the ratio of the initiator input during polymerization.
Mode for carrying out the invention
[25]
The terms used in the present specification are only used to describe exemplary embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present specification, terms such as "comprise", "include" or "have" are intended to designate the existence of a feature, step, component, or a combination of the implemented features, one or more other features or steps, It is to be understood that the possibility of the presence or addition of components, or combinations thereof, is not excluded in advance.
[26]
In the present specification, unless otherwise specified, "room temperature" means a temperature of 23±2°C, specifically 25°C.
[27]
The present invention will be described in detail below and exemplifying specific embodiments, which can be made various changes and have various forms. However, this is not intended to limit the present invention to a specific form disclosed, it should be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention.
[28]
Hereinafter, a method for preparing an ethylene vinyl acetate copolymer according to a specific embodiment of the present invention will be described in more detail.
[29]
The ethylene vinyl acetate copolymer according to an embodiment of the present invention satisfies the following conditions (1) to (4):
[30]
(1) Degree of crosslinking: more than 89%
[31]
(2) Content of vinyl acetate: 25 to 35% by weight based on the total weight of the copolymer
[32]
(3) Melt Index (190° C., 2.16 kg): 10 to 20 g/10 minutes
[33]
(4) Ratio of η*/[η]: 7500 to 9500
[34]
(η* is the zero shear viscosity measured at 160°C, and [η] is the intrinsic viscosity measured at 25°C)
[35]
The degree of crosslinking of the ethylene vinyl acetate copolymer may be increased when a portion of a peak molecular weight (Mp) or more is increased on gel permeation chromatography (GPC). As a method of increasing the portion above Mp, there are methods of increasing high molecular weight and long chain branch (LCB).
[36]
In the present invention, the degree of crosslinking of the ethylene vinyl acetate copolymer can be increased by reducing the amount of the crosslinking agent used by controlling the temperature difference in the autoclave reactor and the initiator input ratio during polymerization as described below.
[37]
Specifically, the ethylene vinyl acetate copolymer according to an embodiment of the present invention has a crosslinking degree of 89% or more. By having such a high degree of crosslinking, it is possible to exhibit improved mechanical strength characteristics while maintaining excellent adhesion. If the degree of crosslinking is less than 89%, there is a concern of a decrease in mechanical strength properties and adhesion. More specifically, the ethylene vinyl acetate copolymer has a degree of crosslinking of 89 to 95%, or 89 to 93%.
[38]
In the present invention, the degree of crosslinking of the ethylene vinyl acetate copolymer is measured by adding a crosslinking agent to the ethylene vinyl acetate copolymer, preparing a film, and after thermal lamination, standing in toluene, and then drying the sheet. And, it can be determined from the weight ratio of the sheet after standing and drying to the weight of the sheet before toluene standing. Specifically, as a base resin, an ethylene vinyl acetate (EV) copolymer was mixed with a crosslinking agent to form a sheet, and then crosslinked in a laminating equipment at 140°C for 14 minutes and 30 seconds, and the crosslinked sheet was made into toluene. After standing at for 15 hours, it was dried for 3 hours and the weight was measured. The crosslinking degree is calculated according to Equation 1 below using the measured weight of the sheet before toluene stationary (W i ) and the weight of the sheet after drying (W d ).
[39]
[Equation 1]
[40]

[41]
In addition, the ethylene vinyl acetate copolymer has a vinyl acetate content of 25 to 35% by weight based on the total weight of the copolymer.
[42]
If the content of vinyl acetate in the ethylene vinyl acetate copolymer is less than 25% by weight, elasticity, elasticity, and adhesion may be deteriorated, and if it exceeds 35% by weight, there is a concern that weather resistance may decrease. More specifically, it has a vinyl acetate content of 27 to 30% by weight, or 27.9 to 29% by weight, or 27.9 to 28.5% by weight based on the total weight of the copolymer.
[43]
In addition, the ethylene vinyl acetate copolymer may have a melt index (MI) of 10 to 20 g/10 minutes measured by a load of 190°C and 2.16 kg. As described above, by having a high degree of crosslinking and a low melt index within the above range, along with a high degree of crosslinking and a vinyl acetate content, excellent processability can be exhibited while maintaining excellent mechanical properties. If the melt index of the ethylene vinyl acetate copolymer is less than 10 g/10 minutes, there is a concern of deterioration in processability. More specifically, the melt index of the ethylene vinyl acetate copolymer may be 14 to 19 g/10 minutes.
[44]
In addition, the ethylene vinyl acetate copolymer may have a ratio of η*/[η] of 7500 to 9500, or 7500 to 9000.
[45]
Meanwhile, the complex viscosity at zero shear of η* at the ratio of η*/[η] means the viscosity at each angular frequency of 0, and a rotational rheometer It is a parameter obtained through a dedicated analysis program installed in a rotary rheometer as data points of the frequency sweep measured in the range of actual measurable frequencies using. The frequency sweep is measured at 160° C. using a rotary rheometer. In addition, the intrinsic viscosity of [η] is a value obtained by extrapolating the reduced viscosity or the inherent viscosity of the polymer solution to the polymer concentration 0, and the Newtonian viscosity using a rotational rheometer Is obtained by measuring. In the present invention, the zero shear viscosity of η* was measured at 160°C by a melt viscosity measurement method using a rotational rheometer, and the intrinsic viscosity of [η] was measured at room temperature using a rotational rheometer, specifically 25 It was measured at °C.
[46]
In addition to the conditions of (1) to (4), the ethylene vinyl acetate copolymer may have a number average molecular weight (Mn) of 18,000 to 23,000 g/mol. By having a high number average molecular weight in the above range, a high degree of crosslinking can be implemented. More specifically, it may be 19,000 to 21,000 g/mol.
[47]
In addition, the ethylene vinyl acetate copolymer may have a molecular weight distribution (MWD) of 3.0 to 4.0. The molecular weight distribution means the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) (Mw/Mn), and by having a molecular weight distribution within the above-described range, processability and mechanical strength can be well balanced. More specifically, it may have a molecular weight distribution of 3.2 to 3.5.
[48]
Meanwhile, in the present invention, the molecular weight distribution, weight average molecular weight, and number average molecular weight can be measured using size exclusion chromatography (SEC). Specifically, in the present invention, after dissolving an ethylene vinyl acetate copolymer sample in 1,2,4-TCB (Trichlorobenzene), using 1,2,4-TCB as a mobile phase, conditions of a temperature of 125°C and a flow rate of 1 ml/min Below, the weight average molecular weight (Mw) and the number average molecular weight (Mn) were respectively calculated, and molecular weight distribution (ratio of weight average molecular weight/number average molecular weight) was calculated from the values. At this time, as the column of SEC, PLgel 10 μm Mixed-B (manufactured by Agilent), etc. may be used.
[49]
The above-described ethylene vinyl acetate copolymer reduces the temperature difference in the reactor during polymerization using an autoclave reactor, and adjusts the amount of initiator introduced into the upper and lower portions of the reactor to control the gas flow rate of the reactor. Features can be implemented.
[50]
Specifically, ethylene vinyl acetate according to an embodiment of the present invention may be prepared by a manufacturing method comprising polymerizing an ethylene monomer and a vinyl acetate monomer in an autoclave reactor in the presence of an initiator, At this time, the reactor includes at least three reaction zones, and the temperature of one or more reaction zones from the bottom (T1)> the temperature of the one or more reaction zones from the top (T2)> one or more reaction zones in between (T3) ), and the difference ΔT between T1 and T2 satisfies 20 to 40°C.
[51]
More specifically, the reactor includes 11 stages of the reaction zone, T1 is the temperature of the 5 stages from the bottom, T2 is the temperature of the 4 stages from the top, and T3 is 2 in between. It may be the temperature of the open reaction zone.
[52]
If the ΔT exceeds 40° C. and the temperature difference in the reactor is too large, the stability of the polymerization reaction may be affected. The lower the temperature difference in the reactor, the more advantageous in terms of reaction stability, but since the desired degree of crosslinking may not be achieved due to an increase in Wax, etc., the ΔT is preferably in the range of 20 to 40°C.
[53]
Meanwhile, the temperature in each reaction region of the autoclave reactor may be measured by a thermocouple installed in the corresponding region, and in the present invention, the temperature at the top of each reaction region was measured. For example, in an 11-stage reactor, T1 is the temperature measured in the 5th stage, T2 is the temperature measured in the 11th stage, and T3 is the temperature measured in the 7th stage.
[54]
Under conditions satisfying the above ΔT, the temperature in the autoclave reactor may be 150 to 220°C, T1 may be 180 to 220°C, T2 may be 160 to 190°C, and T3 may be lower than T2. By performing in the temperature range optimized according to the position in the reactor as described above, the degree of crosslinking and the polymerization conversion rate can be increased, and as a result, productivity can be increased.
[55]
In addition, in the production method of the ethylene vinyl acetate copolymer of the present invention, the initiator is divided into the upper and lower ends of the reactor, and the amount of the initiator added to the lower end of the reactor is 12 to 22 based on the total amount of initiator introduced into the reactor. It meets the weight percent range.
[56]
When the initiator is dividedly injected into the top and bottom of the reactor, the flow rate of the monomer supplied in the gaseous phase can be appropriately distributed to the top and bottom of the reactor. That is, since the gaseous monomers are collected in the zone where the initiator is supplied, the flow rate of the gas in the reactor can be adjusted by adjusting the content of the initiator introduced at the top and bottom of the reactor.
[57]
At this time, if the amount of the initiator added to the bottom of the reactor is less than 12% by weight of the total amount of the initiator, the effect of controlling the gas flow cannot be secured, so it is difficult to prepare an ethylene vinyl acetate copolymer having the above-described physical properties, and exceeds 22% by weight. If so, there may be a problem with the reaction stability.
[58]
In addition, the pressure of the autoclave reactor may be 1800 to 2100 bar under conditions that satisfy the above temperature range and the amount of initiator input.
[59]
The pressure in the reactor means the pressure measured by the pressure sensor inside the reactor, and by being carried out under the pressure in the above range, an ethylene vinyl acetate copolymer having mechanical properties such as superior tensile strength can be prepared with a high conversion rate. .
[60]
In addition, in the method for preparing the ethylene vinyl acetate copolymer, the vinyl acetate monomer and the ethylene monomer are each added in a gas phase, and at this time, the temperature of the monomers introduced into the autoclave reactor is 10 to 50 °C, more specifically 30 to It may be 50 °C.
[61]
In addition, the vinyl acetate monomer may be used in 25 to 35% by weight, more specifically 27 to 30% by weight, based on the total amount of the ethylene monomer and the vinyl acetate monomer.
[62]
On the other hand, the initiator used in the manufacturing method of the ethylene vinyl acetate copolymer is an organic peroxide-based low-temperature initiator; Alternatively, it may be a high-temperature initiator, and any one or a mixture of two or more of them may be used.
[63]
The low-temperature initiator refers to an initiator capable of initiating and/or accelerating the reaction between the ethylene monomer and the vinyl acetate monomer at a temperature of 130°C or more and less than 170°C, and the high-temperature initiator refers to the reaction at a temperature of 170°C or more and 230°C or less. It refers to an initiator capable of initiating and/or promoting at.
[64]
In general, in the case of using only one initiator in the manufacture of an ethylene vinyl acetate copolymer, when the operating temperature is too low, the initiator cannot react, and when the reaction temperature is too high, the initiator is decomposed before polymerization of the copolymer, thereby increasing the initiator efficiency. Falling or runaway reactions may occur.
[65]
On the other hand, according to the manufacturing method of the ethylene vinyl acetate copolymer of one embodiment of the present invention, polymerization is performed by setting the polymerization temperature differently according to the position of the reactor, and an organic peroxide-based low-temperature initiator and a high-temperature initiator are mixed as an initiator. As used, the degree of polymerization can be controlled according to each temperature range.
[66]
Specifically, according to an embodiment of the present invention, the low-temperature initiator and the high-temperature initiator may be used in a weight ratio of 5:95 to 95:5. When used in the above mixing ratio, polymerization efficiency can be increased by controlling the degree of polymerization reaction according to each temperature range. More specifically, it may be used in a weight ratio of 10:90 to 90:10, or a weight ratio of 20:80 to 70:30.
[67]
The low-temperature initiator has a characteristic capable of initiating a polymerization reaction at a temperature lower than a general high-pressure radical polymerization reaction temperature, for example, DIPND (1,4-di(2-neodecanoylperoxyisopropyl)benzene), CUPND (Cumylperoxy neodecanoate). , SBPC(Di(sec-butyl) peroxydicarbonate), NBPC(Di(n-butyl)peroxydicarbonate), EHP(Di(2-ethylhexyl) peroxydicarbonate), TAPND(Tert-amylperoxyneodecanoate) and TBPND(Tert-butyl peroxyneodecanoate) One or more compounds selected from the group may be used.
[68]
In addition, the high-temperature initiator has a characteristic capable of initiating a polymerization reaction at a temperature higher than a general high-pressure radical polymerization reaction temperature, for example, TAPPI (Tert-amylperoxy pivalate), TBPPI (Tert-butylperoxy pivalate), INP ( Di(3,5,5-trimethylhexanoyl) peroxide), TAPEH (Tert-amylperoxy 2-ethylhexanoate), TBPEH (Tert-butylperoxy 2-ethylhexanoate), TBPIB (Tert-butylperoxy-isobutyrate), TBPIN (Tert-butylperoxy-3, At least one compound selected from the group consisting of 5,5-trimethylhexanoate) and TBPA (Tert-butylperoxyacetate) may be used.
[69]
In addition, the low-temperature initiator and the high-temperature initiator may be used by diluting the initiator stock solution in a hydrocarbon solvent in an amount of 20 to 80% by weight, preferably 30 to 70% by weight. In this case, the hydrocarbon solvent is, for example, n-decane, n-octane, iso-dodecane, and iso-octane. One or more selected from the above can be used, or a hydrocarbon mixture commercial product, Isopar series solvent can be used.
[70]
In addition, the total amount of the initiator including the low-temperature initiator and the high-temperature initiator is about 60 ppm or more, or about 70 ppm or more, or about 80 ppm or more, and about 170 ppm or less based on the total monomer weight of the ethylene monomer and vinyl acetate monomer. , Or about 160 ppm or less, or about 150 ppm or less. If the amount of the initiator is too small, the reaction may not proceed properly, and if the amount of the initiator is too large, a runaway reaction may occur due to an abnormal reaction.
[71]
As described above, by controlling the temperature difference in the autoclave reactor and controlling the gas flow rate according to the adjustment of the initiator input ratio, while having a high degree of crosslinking and a vinyl acetate content, MI is reduced, and the ratio of η*/[η] is optimized. Ethylene vinyl acetate copolymer can be prepared.
[72]
The ethylene vinyl acetate copolymer may exhibit improved mechanical strength along with excellent transparency, adhesion, and processability due to its optimized physical properties. Accordingly, the ethylene vinyl acetate copolymer can be used for packaging materials, wire coverings, electrical insulation products, tapes, adhesives, various sheets, and protective films or sealing materials for photovoltaic devices such as solar cells. It can be useful as a protective film for a photoelectric device requiring strength characteristics.
[73]
Accordingly, according to another embodiment of the present invention, a molded article including the above-described ethylene vinyl acetate copolymer, more specifically, a protective film or encapsulant for a photoelectric device is provided.
[74]
The invention will be described in more detail in the following examples. However, the following examples are merely illustrative of the present invention, and the contents of the present invention are not limited by the following examples.
[75]

[76]
Examples and Comparative Examples
[77]
An autoclave reactor including an 11-stage reactor (first stage to fifth stage reactor: lower end (T1), sixth stage to seventh stage reactor: intermediate unit (T3), 8th stage to 11th stage reactor: In the upper part (divided by T2)), 72% by weight of an ethylene monomer and 28% by weight of a vinyl acetate monomer were added, and the initiators of TBPND and TBPPI were used, and reacted under the process conditions shown in Table 1 to obtain an ethylene vinyl acetate copolymer. Prepared. At this time, the autoclave reactor was set to lower the temperature in the order of T1>T2>T3 within a temperature range of 150 to 220°C.
[78]
[Table 1]
[79]
In Table 1, ΔT is the difference between T1 and T2 (T1-T2), where T1 and T2 are temperatures in the fifth and eleventh stage reactors, respectively.
[80]
In addition, the input amount of the initiator at the bottom is a percentage of the total amount of initiator introduced into the reactor.
[81]
Experimental example
[82]
The physical properties of the ethylene vinyl acetate copolymers of Examples 1 to 2 and Comparative Examples 1 to 2 prepared above were measured by the following method, and are shown in Table 2.
[83]
(1) Vinyl acetate (VA) content (% by weight): It was measured using near infrared spectroscopy (NIR).
[84]
(2) Degree of crosslinking (%): t-butyl peroxy 2-ethylhexyl carbonate as a crosslinking agent in 500 g of each of the ethylene vinyl acetate (EV) copolymers prepared in the above Examples and Comparative Examples as a base resin (tert-butyl peroxy 2-ethylhexyl carbonate, TBEC) 4 ml, triallyl isocyanurate (TAIC) 2.5 ml, and silane 1 ml were soaked and produced as a sheet in an extruder. . The prepared sheet was crosslinked in a laminating equipment at 140° C. for 14 minutes and 30 seconds, and then allowed to stand in toluene for 15 hours, and dried in a convection oven for 3 hours, and then the weight was measured. The degree of crosslinking was calculated according to Equation 1 below by using the sheet weight (W i ) before toluene stationary and the sheet weight (W d ) after drying .
[85]
[Equation 1]
[86]

[87]
(3) Melt Index (MI, 2.16 kg): It was measured with a load of 2.16 kg at 230° C. according to ASTM D1238, and expressed as the weight (g) of the polymer melted for 10 minutes.
[88]
(4) Molecular weight distribution (MWD) and number average molecular weight (Mn): Measured using size exclusion chromatography (SEC). Measured with a PL-GPC instrument (manufactured by Agilent) using a column of PLgel 10㎛ Mixed-B (manufactured by Agilent), and a temperature of 125°C using 1,2,4-TCB (1,2,4-Trichlorobenzene) as the mobile phase. And a flow rate of 1 ml/min. Specifically, the ethylene vinyl acetate copolymer samples in the above Examples and Comparative Examples were dissolved in 1,2,4-TCB at a concentration of 10 mg/10 mL, respectively, and then supplied in an amount of 200 μL, using a styrene standard. The weight average molecular weight (Mw) and the number average molecular weight (Mn) were derived using the formed calibration curve, and the molecular weight distribution (ratio of the weight average molecular weight/number average molecular weight) was calculated from the values. At this time, the molecular weight of the polystyrene standard was 9,475,000, 597,500, 19,920, 3,507,000, 224,900, 9,960, 1,956,000, 74,800, 2,980.
[89]
(5) Ratio of η*/[η]
[90]
The zero shear viscosity of η* was measured at 160°C with a melt viscosity measurement method using a rotational rheometer, and the intrinsic viscosity of [η] was measured at 25°C using a rotational rheometer.
[91]
[Table 2]
[92]
As a result of the experiment, the ethylene vinyl acetate copolymers of Examples 1 to 4 prepared by controlling the input amount of the initiator at the bottom of the reactor and the temperature of the reactor in a certain range according to the present invention have a high degree of crosslinking and η*/[ η].
[93]
Claims
[Claim 1]
Ethylene vinyl acetate copolymer satisfying the following conditions (1) to (4): (1) Crosslinking degree: 89% or more (2) Content of vinyl acetate: 25 to 35% by weight based on the total weight of the copolymer (3) Melt Index (190°C, 2.16kg): 10 to 20 g/10 minutes (4) Ratio of η*/[η]: 7500 to 9500 (η* is the zero shear viscosity measured at 160°C, and [η] is It is the intrinsic viscosity measured at 25℃)
[Claim 2]
The ethylene vinyl acetate copolymer of claim 1, wherein the ethylene vinyl acetate copolymer has a number average molecular weight of 18,000 to 23,000 g/mol.
[Claim 3]
The ethylene vinyl acetate copolymer of claim 1, wherein the ethylene vinyl acetate copolymer has a molecular weight distribution of 3.0 to 4.0.
[Claim 4]
The ethylene vinyl acetate copolymer of claim 1, wherein the ethylene vinyl acetate copolymer has a degree of crosslinking of 89 to 93%.
[Claim 5]
In the presence of an initiator, comprising the step of polymerizing the ethylene monomer and the vinyl acetate monomer in an autoclave reactor, the reactor comprises at least three or more reaction zones, the initiator is introduced to the top and bottom of the reactor, The amount of the initiator introduced to the bottom is 12 to 22% by weight of the total initiator content, and the temperature of the reaction zone at least one stage from the bottom (T1)> the temperature of the reaction zone at least one stage from the top (T2)> A method for producing an ethylene vinyl acetate copolymer, wherein the relationship between the temperature of the reaction region (T3) is satisfied, and the difference ΔT between T1 and T2 is 20 to 40°C.
[Claim 6]
The method of claim 5, wherein the reactor includes 11 stages of the reaction zone, T1 is the temperature of the 5 stages from the bottom, T2 is the temperature of the 4 stages from the top, and T3 is between A method for producing an ethylene vinyl acetate copolymer, which is the temperature of the two stages of the reaction zone.
[Claim 7]
The method of claim 5, wherein the pressure of the autoclave reactor is 1,800 to 2,100 bar.
[Claim 8]
The method of claim 5, wherein the temperature of the monomers introduced into the autoclave reactor is 10 to 50°C.
[Claim 9]
The method of claim 5, wherein the vinyl acetate monomer is contained in an amount of 25 to 35% by weight based on 100% by weight of the total of the ethylene monomer and the vinyl acetate monomer.
[Claim 10]
The method of claim 5, wherein the initiator comprises a low-temperature initiator that initiates a reaction between the ethylene monomer and the vinyl acetate monomer at a temperature of 130°C or more and less than 170°C; A method for producing an ethylene vinyl acetate copolymer comprising a high-temperature initiator starting at a temperature of 170° C. or more and 230° C. or less in a weight ratio of 5:95 to 95:5.
[Claim 11]
The method of claim 10, wherein the low-temperature initiator is 1,4-di(2-neodecanoylperoxyisopropyl)benzene, cumylperoxy neodecanoate, di(sec-butyl)peroxydicarbonate, di( At least one selected from the group consisting of n-butyl) peroxydicarbonate, di(2-ethylhexyl)peroxydicarbonate, tert-amylperoxyneodecanoate and tert-butyl peroxyneodecanoate Including a compound, wherein the high-temperature initiator is tert-amylperoxy pivalate, tert-butylperoxypivalate, di(3,5,5-trimethylhexanoyl) peroxide, tert-amylperoxy 2-ethylhexano 8, tert-butylperoxy 2-ethylhexanoate, tert-butylperoxy isobutyrate, tert-butylperoxy-3,5,5-trimethylhexanoate and tert-butylperoxyacetate selected from the group consisting of A method for producing an ethylene vinyl acetate copolymer comprising at least one compound.