Method of manufacturing ethylene vinyl acetate copolymer

Abstract

To provide a method of preparing an ethylene vinyl acetate copolymer, as a solvent, using alkyl acetate, which has a low chain transfer constant and is easily separated from monomers in an ethylene vinyl acetate polymerization process and to provide a method of preparing an ethylene vinyl acetate copolymer that easily controls the molecular weight of the ethylene vinyl acetate copolymer and is applicable to ultra-high molecular weight ethylene vinyl acetate copolymer rubber.SOLUTION: There is provided a method of preparing ethylene vinyl acetate copolymer, comprising the step of adding a monomer comprising ethylene and vinyl acetate, and a solvent comprising alkyl acetate to a reactor and performing polymerization.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing an ethylene-vinyl acetate copolymer. [Background technology]

[0002] Ethylene vinyl acetate copolymer is a polymer copolymer in which ethylene and vinyl acetate are randomly copolymerized, and is known as a polymer that exhibits properties similar to rubber due to its excellent flexibility and elasticity. Such ethylene vinyl acetate copolymers exhibit different physical properties depending on the molecular weight or vinyl acetate content, and are generally used in various applications such as solar cell encapsulants, shoe soles, coated paper, and agricultural films due to their excellent transparency and adhesive strength. In addition, high molecular weight vinyl acetate can be used for special applications such as undersea cables, and ethylene vinyl acetate copolymers with a high vinyl acetate content can be converted into ethylene vinyl alcohol with excellent gas barrier properties by additional saponification reaction. The converted ethylene vinyl alcohol can be used in a wide range of fields such as films, containers, and fibers due to its excellent gas barrier properties and chemical resistance, and is particularly used as an important element in fields requiring gas barrier properties such as fresh food packaging and automobile gas tanks.

[0003] Generally, ethylene vinyl acetate copolymer is industrially produced by using vinyl acetate monomer, ethylene, and an initiator as raw materials, and is produced by a high-temperature and high-pressure gas phase polymerization method or a low-temperature and low-pressure solution polymerization method. In particular, the production method of ethylene vinyl acetate copolymer with a high vinyl acetate content is generally a low-temperature and low-pressure solution polymerization method, in which a C1-C4 alcohol is used as an additional solvent.

[0004] In the solution polymerization method, the additional solvent is used to reduce the viscosity in the polymerization reactor and effectively remove the heat of polymerization generated during the ethylene vinyl acetate polymerization process, and is generally used at 2 to 20 wt% of the total reaction medium. Depending on the type of alcohol used, a chain transfer reaction occurs in which the active site of the polymerization reaction is transferred to the alcohol, and this chain transfer reaction leads to the termination or branching of polymer growth, hindering the increase in molecular weight of linear polymers.

[0005] In order to prevent this phenomenon, a method of using an alcohol with a low chain transfer constant, such as tert-butyl alcohol, alone or in combination has been proposed. However, due to its relatively high price, high boiling point, and the formation of an azeotrope with the monomer, separation efficiency is reduced in the downstream process, especially in the unreacted monomer recovery process, making it difficult to apply. Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, the present invention provides a method for producing an ethylene-vinyl acetate copolymer using, as a solvent, an alkyl acetate which has a low chain transfer constant and is easily separated from the monomer in the ethylene-vinyl acetate polymerization step.

[0007] In addition, the present invention provides a production method that makes it easy to adjust the molecular weight of ethylene-vinyl acetate copolymer and is applicable to rubbers of ethylene-vinyl acetate copolymers having ultra-high molecular weights. [Means for solving the problem]

[0008] One embodiment provides a method for producing an ethylene-vinyl acetate copolymer, comprising the steps of feeding monomers including ethylene and vinyl acetate, and a solvent including an alkyl acetate into a reactor and polymerizing the monomers.

[0009] The alkyl acetate may have a boiling point of 57°C to 126°C.

[0010] The alkyl acetate may be at least one selected from ethyl acetate, methyl acetate, propyl acetate, butyl acetate, and dimethyl acetate.

[0011] The solvent may be added in an amount of 2.5% by weight to 50% by weight based on the total amount of the monomer and the solvent.

[0012] The polymerizing step may further include an initiator including an azobis-based compound, benzoyl peroxide (BPO), or a combination thereof, and the azobis-based compound may include azobisisobutyronitrile (AIBN), azobisdimethylvaleronitrile (ADVN), or a combination thereof.

[0013] The ethylene-vinyl acetate copolymer may have a weight average molecular weight (Mw) of 150,000 g / mol to 500,000 g / mol.

[0014] The ethylene-vinyl acetate copolymer may contain 40 mol % to 80 mol % vinyl acetate. Effect of the Invention

[0015] According to one embodiment, the physical properties of the product can be improved by obtaining an ethylene vinyl acetate copolymer having a high molecular weight, and it is also applicable to rubber of an ethylene vinyl acetate copolymer having an ultra-high molecular weight. In addition, by using the above method, the unreacted vinyl acetate and the alkyl acetate solvent do not form an azeotropic mixture, so that the subsequent separation process is easy. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Although the present invention is described in detail below so as to be easily understood by those skilled in the art, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0017] According to an embodiment, the ethylene-vinyl acetate copolymer may be prepared by feeding monomers and a solvent into a reactor and polymerizing the monomers, where the monomers include ethylene and vinyl acetate, and the solvent includes an alkyl acetate.

[0018] Conventionally, C1-C4 alcohols such as methanol have been used as solvents in the polymerization step for producing ethylene vinyl acetate copolymers. However, in this case, there is a limit to the control of the molecular weight of the ethylene vinyl acetate (EVA) copolymer, it is difficult to obtain a high molecular weight resin, and later, unreacted vinyl acetate and alcohol often form an azeotropic mixture, making it difficult to separate.

[0019] The term "azeotrope" is used in the usual sense in the art, that is, in a liquid with a particular component ratio, when the component ratio of the solution and the vapor become the same when the liquid boils at a certain temperature without changing the component ratio like a pure liquid. The equilibrium temperature, which is the boiling point of the azeotrope, is called the azeotropic point, and the azeotropic state in which the component ratio of the solution and the vapor are the same changes depending on the pressure, and the azeotropic point indicates the minimum or maximum value on the boiling point curve that shows the relationship between the component ratio and the boiling point.

[0020] Meanwhile, according to one embodiment, by using an alkyl acetate having a low chain transfer constant as a solvent for polymerization, an ethylene vinyl acetate (EVA) copolymer having a high molecular weight can be obtained, and therefore the physical properties of the product can be improved. In addition, since unreacted vinyl acetate and alkyl acetate do not form an azeotropic mixture, separation is easy.

[0021] The alkyl acetate used as the solvent may have a boiling point of 57° C. to 126° C., for example, 57° C. to 102° C., or 57° C. to 80° C. By using an alkyl acetate having a boiling point within the above range as a solvent, an ethylene vinyl acetate (EVA) copolymer with a high molecular weight can be obtained.

[0022] The alkyl acetate used as the solvent may be, for example, at least one selected from ethyl acetate, methyl acetate, propyl acetate, butyl acetate, and dimethyl acetate, and more specifically, may be ethyl acetate or methyl acetate.

[0023] The solvent may be added in an amount of 2.5% by weight to 50% by weight, for example, 5% by weight to 30% by weight, 9% by weight to 30% by weight, or 9% by weight to 15% by weight, based on the total amount of the monomer and the solvent. When the solvent is added within the above content range, an ethylene vinyl acetate (EVA) copolymer having a high molecular weight can be obtained during polymerization.

[0024] The polymerization may be carried out by further charging an initiator.

[0025] The initiator may include an azobis compound, benzoyl peroxide (BPO), or a combination thereof, and the azobis compound may include azobisisobutyronitrile (AIBN), azobisdimethylvaleronitrile (ADVN), or a combination thereof.

[0026] The ethylene vinyl acetate copolymer obtained by the polymerization may have a weight average molecular weight (Mw) of 150,000 g / mol to 500,000 g / mol, for example, a weight average molecular weight (Mw) of 150,000 g / mol to 400,000 g / mol, 250,000 g / mol to 400,000 g / mol, or 350,000 g / mol to 400,000 g / mol. The ethylene vinyl acetate copolymer having a weight average molecular weight (Mw) within the above range has improved physical properties and can be applied to rubber of an ethylene vinyl acetate copolymer with an ultra-high molecular weight.

[0027] The ethylene-vinyl acetate copolymer obtained by the polymerization may contain 40 mol% to 80 mol% of vinyl acetate, for example, 56 mol% to 72 mol% of vinyl acetate. Ethylene-vinyl acetate copolymers containing vinyl acetate within the above range have improved physical properties and can be used for rubbers of ultra-high molecular weight ethylene-vinyl acetate copolymers.

[0028] Specific examples of the present invention will be presented below. However, the following examples are merely intended to specifically illustrate or explain the present invention, and the present invention should not be limited by these examples. Furthermore, the contents not described here can be fully inferred by those skilled in the art, and therefore the description thereof will be omitted.

[0029] (Production of ethylene vinyl acetate copolymer) Example 1 21.5% by weight of ethylene, 69.3% by weight of vinyl acetate, and 9.2% by weight of ethyl acetate having a boiling point of 77°C as a solvent were charged into a reactor, and a polymerization reaction was carried out under conditions of 60°C and an ethylene pressure of 40 kg / cm2 to produce an ethylene-vinyl acetate (EVA) copolymer containing 71.3 mol% of vinyl acetate.

[0030] Example 2 An ethylene vinyl acetate (EVA) copolymer was produced in the same manner as in Example 1, except that methyl acetate having a boiling point of 57° C. was used instead of ethyl acetate used as the solvent in Example 1.

[0031] Comparative Example 1 An ethylene vinyl acetate (EVA) copolymer was produced in the same manner as in Example 1, except that ethanol was used instead of the ethyl acetate used as the solvent in Example 1.

[0032] Comparative Example 2 An ethylene vinyl acetate (EVA) copolymer was produced in the same manner as in Example 1, except that methanol was used instead of the ethyl acetate used as the solvent in Example 1.

[0033] Evaluation 1: Measurement of molecular weight of ethylene vinyl acetate (EVA) copolymer In order to confirm the molecular weight of the ethylene vinyl acetate (EVA) copolymers prepared in Examples 1 and 2 and Comparative Examples 1 and 2, the weight average molecular weight (Mw) was measured using a gel permeation chromatography (GPC) device, and the results are shown in Table 1 below.

[0034] [Table 1]

[0035] From Table 1 above, it can be seen that the molecular weights of the ethylene vinyl acetate (EVA) copolymers prepared in Examples 1 and 2 are higher than those of Comparative Examples 1 and 2. Therefore, according to one embodiment, it can be seen that the ethylene vinyl acetate copolymer has a high molecular weight applicable to rubber, and the physical properties of the product can be improved.

[0036] Evaluation 2: Whether or not azeotropes are formed between vinyl acetate and the solvent The solvents used in the above Examples 1 and 2 and Comparative Examples 1 and 2 do not form an azeotrope with vinyl acetate and can be separated by simple distillation, or they form an azeotrope and should be separated using an extractant, etc., as shown in Table 2 below.

[0037] [Table 2]

[0038] From this, it can be seen that in Examples 1 and 2, no azeotropic mixture is formed and separation is possible by simple distillation, whereas in the Comparative Examples, all of the mixtures form azeotropic mixtures and require a separate separation process.

[0039] Although the preferred embodiment of the present invention has been described above, the present invention is not limited thereto, and can be embodied in various modifications within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and it is natural that these modifications also fall within the scope of the present invention.

Claims

1. A method for producing an ethylene-vinyl acetate copolymer, comprising the steps of: feeding monomers including ethylene and vinyl acetate, and a solvent including an alkyl acetate into a reactor, and polymerizing the monomers.

2. The method for producing ethylene-vinyl acetate copolymer according to claim 1, wherein the alkyl acetate has a boiling point of 57°C to 126°C.

3. The method for producing an ethylene-vinyl acetate copolymer according to claim 1, wherein the alkyl acetate is at least one selected from the group consisting of ethyl acetate, methyl acetate, propyl acetate, butyl acetate, and dimethyl acetate.

4. The method for producing ethylene-vinyl acetate copolymer according to claim 1, wherein the solvent is added in an amount of 2.5% by weight to 50% by weight based on the total amount of the monomers and the solvent.

5. The polymerizing step further includes adding an initiator including an azobis compound, benzoyl peroxide (BPO), or a combination thereof; The method for producing ethylene-vinyl acetate copolymer according to claim 1 , wherein the azobis-based compound comprises azobisisobutyronitrile (AIBN), azobisdimethylvaleronitrile (ADVN), or a combination thereof.

6. The method for producing ethylene-vinyl acetate copolymer according to claim 1, wherein the ethylene-vinyl acetate copolymer has a weight average molecular weight (Mw) of 150,000 g / mol to 500,000 g / mol.

7. The method for producing an ethylene-vinyl acetate copolymer according to claim 1, wherein the ethylene-vinyl acetate copolymer contains 40 mol% to 80 mol% vinyl acetate.

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