Process for the preparation of ethylene-acrylic acid copolymers

Abstract

The method for preparing ethylene-acrylic acid copolymer of the present invention controls the discharge temperature of the prepared copolymer to 200-300°C to discharge the copolymer strands, thereby minimizing strand necking and providing excellent workability, processability, and moldability, as well as easy adjustment of the melt index (MI). Furthermore, the ethylene-acrylic acid copolymer prepared by the method has high melt strength.

Description

Technical Field

[0001] This invention relates to a method for preparing ethylene-acrylic acid copolymers, and more specifically, to a method for preparing ethylene-acrylic acid copolymers that minimizes necking and improves workability and processability. Background Technology

[0002] Ethylene-acrylic acid copolymer (EAA) is a high-value-added chemical product used in various fields, mainly as a functional adhesive resin, such as an adhesive for thin packaging materials like milk cartons and aluminum foil for detergents.

[0003] The preparation process of this ethylene-acrylic acid copolymer requires high-pressure facilities and advanced technical capabilities, such as producing the product under high acidity. For example, the copolymerization of ethylene monomers and carboxylic acid monomers utilizes a high-pressure free radical copolymerization system, specifically carried out in an autoclave reactor or a tubular reactor.

[0004] Ethylene-acrylic acid copolymer adhesives require excellent workability, processability, and high adhesion properties, and particularly high melt strength (melt tension). Specifically, during polymer preparation, factors that can reduce workability, processability, and moldability are particularly problematic, with necking being a significant issue. Necking occurs when the strand or film produced by monomer polymerization is discharged, causing shrinkage at the discharge end and creating a difference between the die width and the discharge width, thus reducing workability, processability, and moldability. Furthermore, in the preparation of vinyl copolymers polymerized from ethylene monomers and other comonomers, when high melt strength (melt tension) is required, especially under conditions requiring even higher melt strength, the practical solution is often simply to replace the comonomers with other comonomers. Therefore, to date, no other solutions have been proposed for increasing the melt strength of ethylene-acrylic acid copolymers.

[0005] As mentioned above, there are clear limitations in improving melt strength, workability, processability, and moldability when preparing ethylene-acrylic acid copolymers. Therefore, the object of the present invention is to provide an ethylene-acrylic acid copolymer with high melt strength and improved workability, processability, and moldability.

[0006] [Existing technical documents]

[0007] [Patent Literature]

[0008] (Patent Document 1) Korean Patent Publication No. 10-1861878 (May 21, 2018) Summary of the Invention

[0009] Technical problems to be solved

[0010] The purpose of this invention is to provide a method for preparing ethylene-acrylic acid copolymers that minimizes necking and has excellent workability, processability and moldability.

[0011] Another object of the present invention is to provide a method for preparing an ethylene-acrylic acid copolymer with high melt strength.

[0012] Another object of the present invention is to provide a method for preparing an ethylene-acrylic acid copolymer with an easily adjustable melt index (MI).

[0013] Technical solution

[0014] The method for preparing ethylene-acrylic acid copolymer of the present invention is characterized by comprising: a polymerization step of copolymerizing ethylene monomer and acrylic acid comonomer to prepare ethylene-acrylic acid copolymer; and a discharge step of discharging said ethylene-acrylic acid copolymer to obtain strands, wherein the discharge temperature of the strands in the discharge step is controlled at 200-300°C.

[0015] In one embodiment of the present invention, the dwell time of the strand in the discharge step can be 5-60 seconds.

[0016] In one embodiment of the present invention, the carboxyl groups in the discharged strands during the discharge step can undergo a dehydration reaction to form an anhydride structure.

[0017] In one embodiment of the invention, the acrylic acid content of the strand can be 1-30% by weight.

[0018] In one embodiment of the present invention, the weight-average molecular weight / number-average molecular weight (Mw / Mn) of the strand can be 4.5-15.

[0019] In one embodiment of the present invention, the polymerization temperature and polymerization pressure in the polymerization step can be 150-350°C and 1000-5000 bar, respectively.

[0020] In one embodiment of the invention, the polymerization in the polymerization step can be carried out by an initiator mixture containing a free radical initiator and a diluent solvent, and the diluent solvent can be Isopar-H.

[0021] In one embodiment of the invention, the melt strength (melt tension) of the strand obtained by the discharge step (Gottfert Rheotensometer, 160°C, ASTM D1238-E) can be 120-200 mN.

[0022] In one embodiment of the invention, the melt index (190°C / 2.16 kg, ASTM D 1238) of the strand obtained by discharge in the discharge step can be 5-15.

[0023] In one embodiment of the invention, the necking (drawdown speed of the strands obtained by the discharge step is 440 feet / min) can be less than 3.3 inches.

[0024] Beneficial effects

[0025] The method for preparing ethylene-acrylic acid copolymer of the present invention can minimize necking of the prepared copolymer molded articles and has excellent workability, processability and moldability.

[0026] Furthermore, the method for preparing ethylene-acrylic acid copolymer of the present invention has the effect of easily adjusting the melt index (MI) of the copolymer, and also has the effect of the ethylene-acrylic acid copolymer having high melt strength. Attached Figure Description

[0027] Figure 1 A process diagram illustrating the preparation of an ethylene-acrylic acid copolymer according to an embodiment of the present invention is shown.

[0028] Explanation of reference numerals in the attached figures

[0029] 100: Supply Department, 110: First Supply Department, 120: Primary Compressor

[0030] 130: Second Supply Department; 140: High-Pressure Compressor (Secondary Compressor)

[0031] 200: Reactor; 310: High-pressure separator.

[0032] 320: Low-pressure separator; 400: Filter section.

[0033] 10: Supply pipeline; 20: Low-pressure circulation pipeline; 30: High-pressure circulation pipeline.

[0034] A: Ethylene-acrylic acid copolymer, B: Impurities Detailed Implementation

[0035] The method for preparing ethylene-acrylic acid copolymer of the present invention will be described in detail below with reference to the accompanying drawings.

[0036] The accompanying drawings described in this specification are provided as examples to fully convey the concept of the invention to those skilled in the art. Therefore, the invention is not limited to the drawings provided, and may be implemented through other embodiments. The drawings may be enlarged to illustrate the concept of the invention.

[0037] Unless otherwise defined, the technical and scientific terms used in this specification have the same meanings as commonly understood by one of ordinary skill in the art to which this invention pertains, and descriptions of well-known functions and structures that may unnecessarily obscure the gist of the invention are omitted in the following description and drawings.

[0038] The numerical ranges used in this specification include lower and upper limits, all values ​​within those limits, increments logically derived from the form and magnitude of the defined ranges, all values ​​defined therein, and all possible combinations of the upper and lower limits of numerical ranges defined in different forms. Unless otherwise defined, values ​​outside the defined numerical ranges that may arise in this specification due to experimental errors or rounding are also included within the defined numerical ranges.

[0039] The word “comprising” or “including” as used in this specification is an open-ended description that has the same meaning as expressions such as “possessing,” “containing,” “having,” “characterized in,” etc., and does not exclude elements, materials, or processes that are not further listed.

[0040] Unless otherwise specified, the singular form of the terms used in this specification may be interpreted to also include the plural form.

[0041] Unless otherwise defined, the percentage (%) used in this specification indicates weight unless otherwise specified.

[0042] The term "neckback" as described in this specification refers to the difference between the die width and the ejection width in the work-in-process. Unless otherwise defined, the "neckback" value can be measured as follows: using a Black-Clawson extrusion coater with an extrusion speed of 440 feet per minute to form a 1 mm coating thickness, the Black-Clawson extrusion coater having an extrusion speed of 250 pounds per hour, a 30-inch wide die with a 24-inch deckling at 600°F, and a die gap of 25 mm, the extrusion coater having a diameter of 3.5 inches and an L / D ratio of 30:1.

[0043] The “drawing speed” described in this specification refers to the speed at which the molten polymer breaks off from the mold or the speed at which edge instability occurs.

[0044] Melt tension, as described in this specification, refers to the force required to stretch a molten extrudate through a die using a standard plasticity tester as specified in ASTM D 1238-E, at a traction speed that allows the melt strength to stabilize above the melting point before the fracture velocity. This melt strength can be expressed in centinewtons (cN) or millinenewtons (mN) and, unless otherwise defined, can be measured using a Gotford tensile rheometer. As a concrete example, melt strength can be measured by stretching a strand of wire discharged at 160°C through a gear on a tensile rheometer device at an initial linear velocity of 11.2 mm / s at a speed of 2.4 mm / s. 2 The acceleration increases the rotational speed of the gear, and the force on the strand converges at the measured value.

[0045] Previously, the preparation of ethylene-acrylic acid copolymers suffered from reduced workability, processability, and moldability due to necking, as well as low adhesive properties and melt strength (melt tension). Until now, the only practical solution to this problem has been to replace the acrylic acid comonomer with other comonomers. Therefore, the object of this invention is to provide a method for preparing ethylene-acrylic acid copolymers that, compared to conventional methods, offer higher adhesive properties and melt strength, while improving workability, processability, and moldability.

[0046] As an embodiment thereof, the method for preparing ethylene-acrylic acid copolymer of the present invention is characterized by comprising: a polymerization step of copolymerizing ethylene monomer and acrylic acid comonomer to prepare ethylene-acrylic acid copolymer; and a discharge step of discharging said ethylene-acrylic acid copolymer to obtain strand, wherein the discharge temperature range of the strand in the discharge step is controlled at 200-300°C, preferably at 250-300°C, and more preferably at 270-300°C.

[0047] When the temperature of the strand is not controlled within the aforementioned discharge temperature range, severe necking occurs as in existing technologies, resulting in reduced workability, processability, and moldability. Not only does the melt strength (melt tension) decrease, but it also becomes difficult to adjust to the desired melt index (MI). Specifically, the ethylene-acrylic acid copolymer prepared by the polymerization reaction of the monomers in the reactor of the polymerization step is conveyed to the discharge device and discharged through the die. If the discharge temperature does not meet the aforementioned discharge temperature range, severe necking occurs as in existing technologies, resulting in reduced workability, processability, and moldability. Not only does the melt strength decrease, but it also becomes difficult to adjust to the desired melt index. During discharge, when the strand remains at temperatures exceeding 300°C, thermal degradation occurs, causing the polymer backbone to break, which may weaken the melt strength.

[0048] As described above, in this invention, by controlling the discharge temperature of the strand within the aforementioned temperature range during the preparation of the ethylene-acrylic acid copolymer, various effects are achieved, such as minimizing necking, improving workability, processability, and moldability, enhancing adhesive properties, and increasing melt strength. Specifically, when the discharge temperature of the strand is controlled within the aforementioned temperature range, the carboxyl groups in the strand, i.e., the polymer, undergo a dehydration reaction during the discharge step to form an anhydride structure. By controlling the discharge temperature within the aforementioned temperature range, the copolymer prepared in the polymerization step contains an anhydride structure during the discharge step, thereby significantly improving physical properties such as adhesive strength and workability-related physical properties such as melt strength. In particular, while existing technologies have limitations in improving necking under conditions requiring higher melt strength, this invention achieves the effect of significantly improving necking while maintaining high melt strength through a simple method of controlling the discharge temperature. Therefore, the method for preparing copolymers according to this invention is a very useful method in the preparation of ethylene-acrylic acid copolymers, achieving both high melt strength and low necking.

[0049] As described above, in the method for preparing ethylene-acrylic acid copolymer of the present invention, in the discharge step, an anhydride structure is formed by dehydrating the carboxyl groups in the strand, so the strand obtained by discharge contains anhydride structural units and significantly improves melt strength.

[0050] At this point, the residence time of the strand during discharge in the discharge step only needs to be sufficient to form an appropriate amount of anhydride structural units in the polymer to achieve the above-mentioned effect. The residence time is preferably 5-60 seconds, more preferably 10-50 seconds, further preferably 15-40 seconds, and even more preferably 15-30 seconds. When the residence time of the strand during discharge meets the above range, the carboxyl groups in the strand appropriately form anhydride structures, thereby achieving high melt strength while minimizing necking.

[0051] As described above, in the preparation of the ethylene-acrylic acid copolymer in this invention, by controlling the discharge temperature during the discharge of the strands in the discharge step to form anhydride structural units, high melt strength and minimization of necking can be achieved. In contrast, in the case of vinyl copolymers without using acrylic acid comonomers, anhydride structural units cannot be formed due to the lack of carboxyl groups, thus not only is high melt strength unattainable, but necking cannot be minimized either.

[0052] The content of anhydride structural units in the strands obtained during the discharge step can be controlled by adjusting the discharge temperature and residence time, as long as the aforementioned effects can be achieved. As a preferred example, the ratio of total anhydride structural units to total carboxyl structural units in the copolymer of the strands can be from 0.0001 to 0.1:1, preferably from 0.0005 to 0.05:1.

[0053] The acrylic acid content in the ethylene-acrylic acid copolymer of the present invention (i.e., the strand prepared by the discharge step) is not particularly limited, but the acrylic acid content in the total weight of the copolymer can be 1-30% by weight, preferably 3-25% by weight, and more preferably 5-20% by weight.

[0054] The weight-average molecular weight of the ethylene-acrylic acid copolymer of the present invention (i.e., the strand prepared after the discharge step) is not particularly limited. As an example, it can be 30,000-200,000 g / mol, more specifically 30,000-150,000 g / mol, and even more specifically 70,000-130,000 g / mol. Furthermore, the molecular weight distribution (polydispersity index, PI) of the strand prepared after the discharge step is not particularly limited, but as an example, the weight-average molecular weight / number-average molecular weight (Mw / Mn) can be 4.5-15, preferably 5-10. However, this is merely an illustrative example and should not be construed as limiting the invention to this.

[0055] The ethylene-acrylic acid copolymer of the present invention (i.e., the strand obtained by discharge in the discharge step) has a melt strength (melt tension) (Gottford tensile rheometer, 160°C, ASTM D 1238-E) of 120 mN or more, specifically 120-200 mN, more preferably 130 mN or more, specifically 130-200 mN, thereby achieving high melt strength.

[0056] The melt index (190°C / 2.16 kg, ASTM D 1238) of the ethylene-acrylic acid copolymer of the present invention (i.e., the strand obtained by discharge in the discharge step) can be 5-15, specifically 9-15.

[0057] The ethylene-acrylic acid copolymer of the present invention (i.e., the strand obtained by discharge in the discharge step) has a necking (drawing speed of 440 feet / minute) of 3.3 inches or less, preferably 3.0 inches or less, a significantly low difference between the die width and the discharge width, and has excellent moldability and processability.

[0058] The method for preparing ethylene-acrylic acid copolymer of the present invention may further include a granulation step after the discharge step. By further passing through a granulation step in which the strands obtained in the discharge step are cut to be suitable for molding, processing and other processes, granules of a specified size can be obtained.

[0059] The aforementioned effect is achieved by performing the polymerization step prior to the discharge step, and the polymerization step can be carried out using conventional polymerization methods for ethylene-acrylic acid copolymers. Preferably, the polymerization step utilizes a polymerization method performed under high temperature and high pressure conditions, which will be specifically described below.

[0060] In one embodiment of the present invention, the polymerization step can be carried out by a polymerization apparatus including a supply unit 100 and a circulation unit. The supply unit 100 supplies a compressed material, formed by secondary compression of a mixture comprising ethylene monomer, a monomer containing an acrylic acid comonomer, and a polar solvent, which has been compressed once by a primary compressor 120, to the reactor 200 using a high-pressure compressor 140. The circulation unit filters unreacted residues separated from the discharge from the reactor 200 and supplies them to the front end of the primary compressor 120 or the high-pressure compressor 140. Here, "discharge" refers to the material discharged after the ethylene-acrylic acid polymerization reaction inside the reactor 200 in the process of preparing the ethylene-acrylic acid copolymer, and may contain both the ethylene copolymer and unreacted residues. Furthermore, "unreacted residues" are substances other than the ethylene-acrylic acid copolymer in the process of preparing the ethylene-acrylic acid copolymer; specifically, they may include unreacted ethylene monomers, unreacted acrylic acid comonomers, solvents, initiators, other additives, etc.

[0061] Specifically, the supply unit 100 may include a first supply unit 110 and a second supply unit 130, wherein the first supply unit 110 supplies ethylene monomer and the second supply unit supplies acrylic acid comonomer. In describing the reaction mixture supply process, the ethylene monomer supplied by the first supply unit 110 is compressed by a primary compressor 120 to form a primary compressed product. A high-pressure compressor 140, acting as a secondary compressor, then compresses a mixture containing the acrylic acid comonomer supplied by the second supply unit 130 and the primary compressed product to form a secondary compressed product. The formed secondary compressed product is supplied to a reactor 200, where the ethylene monomer and acrylic acid comonomer copolymerize to synthesize an ethylene-acrylic acid copolymer.

[0062] That is, the polymerization step may include the following steps: a reactant supply step in which a compressed material containing monomers, comonomers, and solvent, compressed by a high-pressure compressor 140, is supplied to the reactor 200 via a supply line 10; and a reaction step in which the compressed material reacts in the reactor 200. As described above, the monomers and solvent are supplied to the high-pressure compressor 140 via the supply section 100 to prevent the high-pressure compressor 140 from becoming clogged.

[0063] Furthermore, the polymerization step can also include a first circulation step and a second circulation step. In the first circulation step, the effluent discharged from the reactor 200 is filtered and separated by a high-pressure separator 310 to obtain unreacted residue. This unreacted residue is supplied to the front end of the high-pressure compressor 140 through a high-pressure circulation line 30. In the second circulation step, the substance filtered by the high-pressure separator 310 is filtered and separated again by a low-pressure separator 320 to obtain unreacted residue. This unreacted residue is supplied to the front end of the primary compressor 120 through a low-pressure circulation line 20. The steps described above can be performed through the circulation section, where unreacted monomers and solvents in the compressed material from the supply section 100 to the high-pressure compressor 140 are again supplied to the front end of the high-pressure compressor 140 or the primary compressor 120 through the circulation section. Therefore, in the entire polymerization reaction, the above-mentioned effects can be achieved while producing ethylene-acrylic acid copolymers with high efficiency.

[0064] Specifically, in the first cycle step, a filter unit 400 is provided that can filter and separate unreacted residues, thereby discharging impurities to the outside. Impurities other than unreacted residues can also be removed through filtration and separation. Furthermore, if the filter unit 400 becomes clogged due to excessive impurities, additional pipelines can be provided.

[0065] Furthermore, in the second circulation step, residual unreacted residue can be supplied to the primary compressor 120. This residual unreacted residue is obtained by secondary filtration and separation of the effluent from which unreacted residue has been separated in the first filtration. That is, the polymerization step may further include the following step: in the circulation section, residual unreacted residue separated by secondary filtration of the effluent from which unreacted residue has been removed is supplied to the front end of the primary compressor 120. Therefore, since solvent can be delivered to the front end of the primary compressor 120 supplying ethylene monomer, solvent is transported throughout the polymerization unit, suppressing blockage and removing various foreign matter remaining inside the preparation unit.

[0066] The solvent can be any medium that allows the ethylene monomer and the acrylic acid comonomer to undergo a copolymerization reaction, such as a low-boiling-point polar solvent. As a specific example, the solvent may contain one or more of the following: methanol, ethanol, isopropyl alcohol, methylethyl ketone, tetrahydrofuran, acetone, ethyl acetate, propyl acetate, butyl acetate, 2-methoxyethanol, and 2-ethoxyethanol. However, this is merely a preferred example and should not be construed as limiting the invention to this.

[0067] The mixing ratio of ethylene monomer, acrylic acid comonomer, and solvent can be appropriately controlled to prepare ethylene-acrylic acid copolymers with acrylic acid content within the aforementioned range. For example, relative to 100 parts by weight of ethylene monomer, the acrylic acid comonomer can be 1-20 parts by weight, and the solvent can be 1-20 parts by weight. Specifically, the acrylic acid comonomer can be 3-10 parts by weight, and the solvent can be 3-10 parts by weight. However, this is merely an illustrative example and should not be construed as limiting the invention thereto.

[0068] The polymerization in the polymerization step can be initiated by an initiator, such as free radical polymerization. Therefore, the compressed material supplied to the reactor 200 also contains an initiator, specifically, preferably a free radical initiator, under which the monomers react to carry out polymerization. As a preferred example, the polymerization can preferably be carried out using an initiator mixture containing a free radical initiator and a diluent solvent. The amount of initiator used is only required to initiate the free radical polymerization reaction; for example, based on 100 parts by weight of the whole monomer, 0.001-1 parts by weight of the initiator can be used. Furthermore, the amount of diluent used can be appropriately adjusted; for example, 5-1000 parts by weight of diluent solvent can be used relative to 1 part by weight of initiator. However, this is merely an illustrative example and should not be construed as limiting the invention thereto.

[0069] As a specific example, the free radical initiator can be any type that enables the free radical polymerization of ethylene monomer and acrylic acid comonomer, and may include any one or more peroxy organic peroxides selected from peroxy carbonates, peroxydicarbonates, peroxy esters, and peroxy ketals. However, this is merely an illustrative example and should not be construed as limiting the invention thereto.

[0070] The diluting solvent can be a known initiator diluting solvent, such as an alkane-based solvent. More preferably, when Isopar-H, an alkane-based solvent, is used as the diluting solvent, a uniform copolymer can be prepared, quality reduction such as molecular weight reduction can be prevented, and a product with excellent constant melt strength equivalent throughout the entire strand can be provided.

[0071] In one embodiment of the invention, the compressed material supplied to the reactor 200 may further include a chain transfer agent. As a non-limiting example, the chain transfer agent may be: aliphatic and olefinic hydrocarbons, such as saturated hydrocarbons having six or more carbon atoms, such as compounds like hexane, cyclohexane, and octane; ketone compounds such as acetone, diethyl ketone, and dipentyl ketone; aldehyde compounds such as formaldehyde and acetaldehyde; and alcohol compounds such as methanol, ethanol, propanol, and butanol. When using a chain transfer agent, the amount of the chain transfer agent used is not significantly limited; for example, 0.1-20 parts by weight of the chain transfer agent may be used relative to 100 parts by weight of the entire monomer. However, this is merely an illustrative example and should not be construed as limiting the invention thereto.

[0072] As described above, the polymerization step is preferably carried out under high temperature and high pressure conditions controlled by a compressor and / or temperature control. As a specific example, more preferably, in order to better achieve the above-mentioned effects, the polymerization step can be carried out under polymerization conditions of 150-350°C and 1000-5000 bar, preferably 200-300°C and 1200-3000 bar, respectively.

[0073] The reactor 200 used in the polymerization step can be any known reactor used for polymerization reactions, such as a batch reactor (e.g., autoclave), a continuous stirred tank reactor (CSTR), a tubular reactor, or any other type of reactor.

[0074] Figure 1 The diagram shows a process diagram for preparing an ethylene-acrylic acid copolymer according to an embodiment of the present invention. Hereinafter, reference will be made to... Figure 1 The polymerization process of the polymerization step is described in detail.

[0075] Reference Figure 1 To perform the polymerization step, a polymerization apparatus for preparing ethylene-acrylic acid copolymers can be used, the apparatus comprising: a primary compressor 120 for primary compression of ethylene supplied by a first supply unit 110; a high-pressure compressor 140 for secondary compression of a mixture comprising the primary compressed ethylene, a comonomer containing carboxylic acid supplied by a second supply unit 130, and a polar solvent; a supply line 10 for supplying the compressed material from the high-pressure compressor 140 to a reactor 200; a high-pressure separator 310 for primary filtration of the effluent from the reactor 200 to separate unreacted residues; and a high-pressure circulation line 30 for supplying the unreacted residues separated by the high-pressure separator 310 to the front end of the high-pressure compressor 140.

[0076] In one embodiment of the invention, the primary compressor 120, the hyper compressor 140, the reactor (autoclave reactor) 200, the high pressure separator (HPS) 310, and the low pressure separator (LPS) 320 can be made using existing, known vinyl polymer preparation apparatus.

[0077] In one embodiment of the invention, a filter unit 400 may be provided, located at the rear end of the high-pressure circulation line 30, which can filter and remove impurities. The filter unit 400 removes impurities other than unreacted monomers and solvents, and the unreacted residue containing the unreacted monomers and solvents with impurities removed is transported to the front end of the high-pressure compressor 140 through the high-pressure circulation line 30.

[0078] In one embodiment of the invention, a low-pressure separator 320 and a low-pressure circulation line 20 may be provided. The low-pressure separator 320 performs secondary filtration on the effluent from the high-pressure separator 310 to separate residual unreacted residues, forming an ethylene-acrylic acid copolymer, and discharges the formed ethylene-acrylic acid copolymer. The low-pressure circulation line 20 supplies the unreacted residues separated in the low-pressure separator 320 to the front end of the primary compressor 120. The low-pressure separator 320 and low-pressure circulation line 20, as described above, further remove unreacted residues, thereby enabling the preparation of a high-purity ethylene-acrylic acid copolymer. Furthermore, by supplying the unreacted residues containing ethylene and a polar solvent to the primary compressor 120 side, high process efficiency can be achieved.

[0079] The present invention will be described in detail below through embodiments. These embodiments are used to illustrate the present invention in more detail, and the scope of the present invention is not limited to the following embodiments.

[0080] [Example 1]

[0081] like Figure 1 As shown, ethylene monomer will undergo a single compression in a compressor at a temperature of 30°C and a pressure of 200 bar to a 3m... 3 An average flow rate of / minute is supplied to the secondary compressor, and a mixture of acrylic acid comonomer and ethyl acetate, mixed at a weight ratio of 10:1, is fed at 0.004m³. 3 An average flow rate of [value missing] / minute is supplied to the secondary compressor. A secondary pressure is applied in the secondary compressor at a temperature of 20°C and a pressure of 200 bar to form a compressed material. The compressed material and initiator mixture supplied by the secondary compressor are then [discharged at] 0.4 m [unit missing]. 3 An average flow rate of [value missing] / minute is supplied to the reactor, regulating the internal temperature to 250°C and pressure to 2250 bar, thereby initiating the polymerization reaction. At this time, the initiator mixture solution is a mixture of 10% by weight of the initiator (tert-Butyl peroxyacetate) diluted in a diluent (Isopar-H, ExxonMobil). Furthermore, the effluent discharged from the reactor is [value missing] at a rate of 1.3 m [value missing]. 3 An average flow rate of [value] / minute is supplied to the high-pressure separator. Unreacted residue separated by the high-pressure separator is circulated through a 1.4m [flow rate] pipeline. 3 The average flow rate of [amount] / minute is then supplied to the secondary compressor. The discharge, after primary removal of unreacted residues by the high-pressure separator, is supplied to the low-pressure separator for secondary removal of unreacted residues. The unreacted residues removed in the low-pressure separator are discharged at a rate of 5.0 m³ / min. 3 An average flow rate of / minute is supplied again to the primary compressor, and in the low-pressure separator, an ethylene-acrylic acid copolymer with an acrylic acid content of 9.7% by weight, after removing unreacted residues, is produced.

[0082] Next, the ethylene-acrylic acid copolymer is conveyed to a discharge device, from which it is discharged from a mold to obtain a strand. At this time, the ambient temperature around the device is 25°C, and the temperature of the strand during discharge and the residence time during discharge are controlled to be maintained at 280°C and 22 seconds, respectively.

[0083] Furthermore, the acrylic acid content, discharge temperature, residence time, melt strength (melt tension), melt index (MI), and necking of the ethylene-acrylic acid copolymer strands were measured and their values ​​are shown in Table 1 below. The melt strength value was calculated as follows: The test was conducted according to ASTM D 1238-E standard. Specifically, a tensile rheometer (Gottefert) was installed at the lower end of the discharge device. The strands discharged from the discharge device were hung on the gear of the device at 0.5 mm intervals, and then the initial rotational speed of the gear was 11.2 mm / s followed by a further rotation at 2.4 mm / s. 2 The constant acceleration is used to increase the rotational speed, and the force on the strand is measured. The value of the force on the strand at convergence is calculated. Furthermore, the melt index is calculated as follows: Tests are conducted according to ASTM D 1238. Specifically, using a melt index tester (MI tester, Gottfert), the copolymer is added to a 9.55 mm diameter barrel at 190°C, and a 2.16 kg weight is used to press it through a 2.095 mm diameter capillary. The amount discharged over 10 minutes is measured for calculation.

[0084] [Example 2]

[0085] Except for adjusting the monomer flow rate in Example 1 to meet the acrylic acid content in Table 1 below, thereby preparing an ethylene-acrylic acid copolymer with an acrylic acid content of 8.0% by weight, the ethylene-acrylic acid copolymer strands were obtained by the same method as in Example 1.

[0086] [Example 3]

[0087] Except that the residence time during discharge was set to 4 seconds in Example 1, ethylene-acrylic acid copolymer strands were obtained by the same method as in Example 1.

[0088] [Comparative Example 1]

[0089] Except that the temperature of the strands was not controlled in Example 1, ethylene-acrylic acid copolymer strands were obtained by the same method as in Example 1. In this case, the temperature of the uncontrolled strands was 190°C.

[0090] [Comparative Example 2]

[0091] Except that methyl acrylate was used instead of acrylic acid as a comonomer in Example 1, vinyl copolymer strands were obtained by the same method as in Example 1.

[0092] [Table 1]

[0093]

Claims

1. A method for preparing ethylene-acrylic acid copolymer, characterized in that, include: The polymerization step of copolymerizing ethylene monomer and acrylic acid comonomer to prepare ethylene-acrylic acid copolymer; as well as The step of discharging the ethylene-acrylic acid copolymer to obtain the stranded thread is described. The discharge temperature of the strands in the discharge step is controlled at 250-300℃. During the discharge step, the carboxyl groups in the discharged strands undergo a dehydration reaction to form an anhydride structure. The retention time of the strands in the discharge step is 5-60 seconds.

2. The method for preparing ethylene-acrylic acid copolymer according to claim 1, wherein, The acrylic acid content of the strand is 1-30% by weight.

3. The method for preparing ethylene-acrylic acid copolymer according to claim 1, wherein, The weight-average molecular weight / number-average molecular weight (Mw / Mn) of the strands is 4.5-15.

4. The method for preparing ethylene-acrylic acid copolymer according to claim 1, wherein, The polymerization temperature and polymerization pressure in the polymerization step are 150-350℃ and 1000-5000 bar, respectively.

5. The method for preparing ethylene-acrylic acid copolymer according to claim 1, wherein, The polymerization in the polymerization step is carried out by an initiator mixture containing a free radical initiator and a diluent solvent, wherein the diluent solvent is Isopar-H.

6. The method for preparing ethylene-acrylic acid copolymer according to claim 1, wherein, The melt strength, or melt tension, of the strands obtained by the discharge step, measured on a Gotford tensile rheometer at 160°C and ASTM D 1238-E is 120-200 mN.

7. The method for preparing ethylene-acrylic acid copolymer according to claim 1, wherein, The melt flow index of the strands obtained by the discharge step, measured at 190°C / 2.16kg and ASTM D 1238, is 5-15.

8. The method for preparing ethylene-acrylic acid copolymer according to claim 1, wherein, The strands obtained by the discharge step have a necking of less than 3.3 inches at a drawing speed of 440 feet per minute.

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