Ethylene-vinyl alcohol resin as well as preparation method and application thereof

Abstract

The invention relates to the technical field of preparation of ethylene-vinyl alcohol resin, and discloses ethylene-vinyl alcohol resin as well as a preparation method and application thereof. The preparation method comprises the following steps: (1) contacting vinyl acetate, an initiator, monohydric alcohol and ethylene in a closed container for constant-temperature and constant-pressure reaction; (2) carrying out residual monomer removal, alcoholysis saponification, heating filtration, washing and drying treatment on the obtained product to obtain ethylene-vinyl alcohol resin; the step of heating and filtering comprises the following steps: adding hot water into a saponified substance obtained by alcoholysis and saponification, and heating to obtain a homogeneous solution; and cooling to 20-50 DEG C to separate out an insoluble substance, and removing the soluble substance to obtain the insoluble substance EVOH. The ethylene content in the prepared ethylene-vinyl alcohol resin is 20-60 mol%, and the ethylene-vinyl alcohol resin has the advantages of good barrier property, high decomposition temperature, high oxidation induction temperature, no fisheye in the processing application process, and difficult thermal oxidation and thermal decomposition.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of ethylene-vinyl alcohol resins, and particularly relates to an ethylene-vinyl alcohol resin, a preparation method thereof, and an application thereof. Background Art

[0002] Ethylene-vinyl alcohol resin (EVOH) is a thermoplastic resin obtained by saponifying an ethylene-vinyl ester copolymer obtained by copolymerizing ethylene and a vinyl ester monomer. Due to its excellent transparency, oxygen barrier property, aroma retention property, solvent resistance, oil resistance, mechanical strength, etc., it is formed into films, sheets, containers, etc., and is widely used in various packaging materials such as food, medicine, industrial drugs, pesticides, etc.

[0003] Packaging materials are usually obtained by melt molding. Therefore, EVOH is required to have excellent thermoplastic properties during melt molding, such as no gels, few crystal points, and little yellowing. The main factor affecting the thermoplastic properties of EVOH is the thermal degradation of EVOH. Alvarez et al. calculated the degradation kinetics of three kinds of EVOH with ethylene contents of 32%, 38%, and 44% in a nitrogen atmosphere, and proposed that the thermal stability of EVOH increases with the increase of ethylene content. However, as is well known, with the increase of ethylene content, the barrier property of EVOH will decrease. Deng Zhaoyi et al. studied the degradation behavior of EVOH with different degrees of polymerization and found that the size of the degree of polymerization is closely related to the degradation behavior.

[0004] Currently, the common practice is to improve the thermoplastic properties of EVOH by adding carboxylic acid compounds, boron compounds, phosphoric acid compounds, etc., but the problem has not been solved at the source.

[0005] Therefore, it is of great significance to research and develop an ethylene-vinyl alcohol resin and a preparation method thereof. Summary of the Invention

[0006] The purpose of the present invention is to overcome the defect problems of "fish eyes", easy thermal oxidation and thermal decomposition with yellowing during the processing and application of ethylene-vinyl alcohol resins prepared by the prior art, and to provide an ethylene-vinyl alcohol resin, a preparation method thereof, and an application thereof. The ethylene-vinyl alcohol resin prepared by the method provided by the present invention has an ethylene content of 20-60 mol%, has good barrier properties, a relatively high decomposition temperature, a relatively high oxidation induction temperature, no "fish eyes" during the processing and application process, and is not easily thermally oxidized and thermally decomposed.

[0007] In order to achieve the above purpose, the first aspect of the present invention provides a preparation method of an ethylene-vinyl alcohol resin, wherein the preparation method comprises the following steps:

[0008] (1) Contacting vinyl acetate, an initiator, a monohydric alcohol with ethylene in a closed container for a constant temperature and constant pressure reaction;

[0009] (2) Subject the product obtained in step (1) to treatments of removing residual monomers, alcoholysis saponification, heating filtration, washing and drying to obtain ethylene-vinyl alcohol resin;

[0010] Among them, the conditions of the heating filtration treatment include: adding hot water to the saponified product obtained by alcoholysis saponification and heating to obtain a homogeneous solution; then cooling to 20 - 50 °C to precipitate insoluble substances, removing soluble substances, and obtaining insoluble EVOH.

[0011] The second aspect of the present invention provides an ethylene-vinyl alcohol resin prepared by the aforementioned preparation method.

[0012] The third aspect of the present invention provides an application of the aforementioned ethylene-vinyl alcohol resin in the packaging industry.

[0013] Through the above technical solution, by using the preparation method of the ethylene-vinyl alcohol resin of the present invention and removing soluble substances through heating filtration, it is possible to make the ethylene content in the prepared ethylene-vinyl alcohol resin be 20 - 60 mol%, have good barrier properties, and at the same time have a relatively high decomposition temperature and oxidation induction temperature, without "fish eyes" during the processing application process and being not prone to thermal oxidation and thermal decomposition. Detailed Embodiments

[0014] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0015] As described above, the first aspect of the present invention provides a preparation method of ethylene-vinyl alcohol resin, among which, the preparation method includes the following steps:

[0016] (1) Contact vinyl acetate, initiator, monohydric alcohol and ethylene in a closed container for isothermal and isobaric reaction;

[0017] (2) Subject the product obtained in step (1) to treatments of removing residual monomers, alcoholysis saponification, heating filtration, washing and drying to obtain ethylene-vinyl alcohol resin;

[0018] Among them, the conditions of the heating filtration treatment include: adding hot water to the saponified product obtained by alcoholysis saponification and heating to obtain a homogeneous solution; then cooling to 20 - 50 °C to precipitate insoluble substances, removing soluble substances, and obtaining insoluble EVOH.

[0019] The inventors of the present invention found that during the preparation of ethylene-vinyl alcohol resin (EVOH), hot water was added and the temperature was raised to obtain a homogeneous solution; then the temperature was lowered to 20-50°C to precipitate insoluble substances; in a further preferred case, hot water was added and the temperature was raised to 90-110°C to obtain a homogeneous solution; then the temperature was lowered to 20-50°C, and in a further preferred case, when the temperature was lowered to 20-50°C and held at a constant temperature for more than 1 h, insoluble substances were precipitated, and the solution was filtered while it was hot to remove soluble substances, obtaining the precipitated EVOH. Since the filtered solution contains EVOH with a relatively small molecular weight, it affects the processing performance of the product, and at the same time, this is the reason why a thermoplastic ethylene-vinyl alcohol resin with excellent properties can be obtained through heating and filtration treatment.

[0020] According to the present invention, in a preferred case, the conditions of the heating and filtration treatment include: after heating and cooling, it is also necessary to hold at a constant temperature for 1-2 h within the temperature range of cooling.

[0021] According to the present invention, the temperature of heating and cooling affects the molecular weight of the prepared ethylene-vinyl alcohol resin. The larger the molecular weight, the higher the temperature required for dissolution, and at the same time, higher temperatures will cause precipitation.

[0022] According to the present invention, in a preferred case, during the process of neutralizing the saponified product obtained by alcoholysis saponification by dropwise adding hot water, based on the total weight of the mixed solvent, the hot water in the mixed solvent accounts for 30-70% by weight, preferably 30-55% by weight, more preferably 30-48% by weight. In the present invention, the proportion of hot water in the mixed solvent is adjusted according to the ethylene content of the prepared EVOH resin. The lower the ethylene content, the higher the proportion of the hot water. In the present invention, the hot water refers to water with a temperature of 40-100°C, preferably 60-100°C, more preferably 90-100°C.

[0023] According to the present invention, in step (1), the reaction is terminated when the conversion rate of vinyl acetate is 30-60% by weight; in the present invention, a terminator can be used to end the polymerization, and the terminator is selected from sorbic acid; in a preferred case, the reaction is terminated when the conversion rate of vinyl acetate is 40-50%. In the present invention, if the conversion rate is too low, the product yield is affected; if the conversion rate is too high, the increase in insoluble substances is obvious.

[0024] According to the present invention, relative to 100 parts by weight of the vinyl acetate, the amount of the initiator is 0.01 - 0.1 parts by weight, and the amount of the monohydric alcohol is 5 - 50 parts by weight; preferably, relative to 100 parts by weight of the vinyl acetate, the amount of the initiator is 0.03 - 0.06 parts by weight, and the amount of the monohydric alcohol is 10 - 20 parts by weight; more preferably, relative to 100 parts by weight of the vinyl acetate, the amount of the initiator is 0.032 - 0.052 parts by weight. In the present invention, by controlling the amounts of the respective reaction materials within the foregoing ranges, an EVOH resin with excellent thermoplasticity can be obtained.

[0025] According to the present invention, the conditions for the isothermal and isobaric reaction include: a pressure of 10 - 60 bar and a polymerization temperature of 50 - 70 °C; preferably, the conditions for the isothermal and isobaric reaction include: a pressure of 30 - 55 bar and a polymerization temperature of 52 - 60 °C.

[0026] In the present invention, the pressure is highly related to the ethylene content of the EVOH to be prepared. It is adjusted according to the ratio of methanol to VAC. If the pressure is too low, the ethylene content of the resin will be too low, which is not conducive to processing; if the pressure is too high, the ethylene content of the resin will be too high, reducing the barrier performance of the resin.

[0027] In the present invention, if the temperature is too low, the reaction will be too slow; if the temperature is too high, the molecular chain segments will be arranged more randomly, the molecular weight distribution will be wide, and the reaction is prone to explosive polymerization and uncontrollable.

[0028] According to the present invention, the initiator is selected from one or more of azo initiators, peroxide initiators, and organic peroxides.

[0029] According to the present invention, the azo initiator is selected from one or more of azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, and azobis(2-methylbutyronitrile); preferably, the azo initiator is azobisisobutyronitrile and / or azobisisoheptonitrile.

[0030] According to the present invention, the peroxide initiator is selected from one or more of hydrogen peroxide, ammonium persulfate, and potassium persulfate.

[0031] According to the present invention, the organic peroxide is selected from one or more of benzoyl peroxide, tert-butyl benzoyl peroxide, methyl ethyl ketone peroxide, diisobutyryl peroxide, tert-amyl peroxyneodecanoate, bis(4-tert-butylcyclohexyl) peroxydicarbonate, tert-amyl peroxypivalate, tert-butyl peroxyacetate, and dibutyl peroxydicarbonate; preferably, the organic peroxide is selected from tert-amyl peroxyneodecanoate and / or tert-amyl peroxypivalate.

[0032] According to the present invention, the monohydric alcohol is C1 -C 4 monohydric alcohol; preferably, the monohydric alcohol is selected from one or more of methanol, ethanol, propanol, n-butanol, isobutanol, tert-butanol, dimethyl methanol, and 3-methyl-2-butanol; more preferably, the monohydric alcohol is selected from one or more of methanol, ethanol, propanol, and tert-butanol.

[0033] According to the present invention, the residual monomers can be removed by rotary evaporation drying or by solvent replacement. After removing the residual monomers, the total content of vinyl acetate is below 200 ppm, preferably below 50 ppm, and more preferably 2 - 50 ppm.

[0034] According to the present invention, for the alcoholysis saponification, an alkali solution is added for alcoholysis. First, the obtained EVAc solution is added to a methanol solution of NaOH for alcoholysis saponification.

[0035] In the present invention, the alcoholysis saponification can be any one of homogeneous saponification method, solvent dispersion saponification method, and melting saponification method, preferably the homogeneous saponification method or the solvent dispersion saponification method.

[0036] According to the present invention, after the alcoholysis saponification treatment, the degree of alcoholysis is 99.0 - 99.9 mol%.

[0037] According to the present invention, the washing includes pickling and water washing. Preferably, pickling is carried out with an aqueous acetic acid solution, and the concentration of the aqueous acetic acid solution is 50 - 1000 ppm. In the present invention, the water washing is preferably carried out 3 - 6 times.

[0038] According to the present invention, for the drying, it is dried at 50 - 120 °C for 5 - 24 hours, and at this time its volatile content reaches 0.1 - 0.5%.

[0039] According to a preferred specific embodiment of the present invention, a method for preparing an ethylene-vinyl alcohol resin includes the following steps:

[0040] 100 parts of VAC, 10 - 20 parts of monohydric alcohol, and 0.032 - 0.052 parts of initiator are added to a closed container, replaced with 7 bar of ethylene gas 3 times, and then ethylene gas is introduced to keep the pressure at 30 - 55 bar, stirred, heated to 52 - 60 °C, and the reaction starts under constant temperature and pressure. When the VAC conversion rate reaches 40 - 50%, a terminator is added to end the polymerization. Then, the residual monomers are removed, alcoholysis saponification is carried out, the temperature is raised for filtration, washing, and drying to obtain an EVOH resin with excellent thermoplastic properties.

[0041] The third aspect of the present invention provides an ethylene-vinyl alcohol resin prepared by the aforementioned preparation method.

[0042] According to the present invention, the "fish eyes" of the ethylene-vinyl alcohol resin are 0; preferably, the decomposition temperature of the ethylene-vinyl alcohol resin is 360-400 °C, preferably 370-395 °C, more preferably 376-392 °C; the oxidation induction temperature of the ethylene-vinyl alcohol resin is 190-220 °C, preferably 190-215 °C, more preferably 193-212 °C.

[0043] According to the present invention, the weight-average molecular weight of the ethylene-vinyl alcohol resin is 10,000-400,000, and the ethylene content of the ethylene-vinyl alcohol resin is 20-60 mol%. Preferably, the weight-average molecular weight of the ethylene-vinyl alcohol resin is 50,000-200,000, and the ethylene content of the ethylene-vinyl alcohol resin is 27-46 mol%, more preferably 31.5-44.5 mol%.

[0044] The fourth aspect of the present invention provides an application of the aforementioned ethylene-vinyl alcohol resin in the packaging industry.

[0045] According to the present invention, the packaging industry includes one or more of food packaging, pharmaceutical packaging, cosmetic packaging, and automobile fuel tanks.

[0046] The present invention will be described in detail below through examples.

[0047] In the following examples and comparative examples:

[0048] The "fish eyes" parameter is measured by the method of "Determination of 'fish eyes' of general-purpose polyvinyl chloride resin" in GB / T 4611-2008;

[0049] The thermal decomposition temperature and oxidation induction temperature are measured by the method of differential scanning calorimetry (DSC) of plastics in GB / T19466.2;

[0050] The weight-average molecular weight and molecular weight distribution parameters are used to measure the molecular weight and molecular weight distribution of the EVOH sample by high-temperature gel chromatography (GPC, PL-GPC220, Aglient Co., USA). The solvent is dimethyl sulfoxide, the test temperature is 70 °C, the sample concentration is 0.1 mg / ml, and the feed volume is 100.0 μl;

[0051] The volatile matter and alcoholysis degree parameters are measured by the internal control standard of Chongqing Chuanwei Chemical Co., Ltd. (CWHG) of Sinopec Group;

[0052] The ethylene content is determined according to GB / T41877.2.

[0053] The raw materials VAC and methanol are all produced by Chongqing Chuanwei Chemical Co., Ltd. (CWHG) of Sinopec Group.

[0054] The ethylene is cylinder ethylene with a purity of 99.9%, which is a commercially available product from Dalian Dete Gas Co., Ltd.

[0055] Unless otherwise specified, all are in parts by weight and weight percentages hereinafter.

[0056] "Parts" all refer to "parts by weight".

[0057] Example 1

[0058] (1) Add 100 parts by weight of VAC, 15 parts by weight of methanol and 0.038 parts by weight of initiator tert-amyl peroxyneodecanoate into a 3-L high-pressure reactor; displace with 7 bar of ethylene gas for 3 times, then introduce ethylene gas to keep the pressure at 48 bar, stir, heat up to 58 °C, and start the reaction at constant temperature and pressure;

[0059] (2) When the conversion rate of VAC reaches 49%, add 0.052 parts of sorbic acid to end the polymerization;

[0060] (3) Then adopt the method of adding methanol in multiple batches and heating up to displace VAC to remove the residual monomer. After removal, the VAC content is 47 ppm; for the EVAc methanol solution obtained above; then add 18 parts by weight of NaOH methanol solution for saponification, and remove the by-product methyl acetate at the same time. After alcoholysis saponification, the degree of alcoholysis is 99.2 (mol)%;

[0061] (4) Dropwise add hot water at 90 °C to make the hot water in the mixed solvent account for 38% (weight ratio), then heat up to 93 °C to obtain a homogeneous solution; then cool down to 28 °C and keep it constant for 1.5 h to precipitate insoluble substances, filter while it is hot to remove the soluble substances, and obtain insoluble EVOH. Then wash it once with an acetic acid aqueous solution with a concentration of 800 ppm and wash it 3 times with water, and dry it at 85 °C for 16 hours. At this time, the volatile content of EVOH is 0.2%, and an EVOH resin is obtained.

[0062] Example 2

[0063] This example is to illustrate the ethylene-vinyl alcohol resin prepared by the method of the present invention.

[0064] (1) Add 100 parts by weight of VAC, 18 parts by weight of ethanol and 0.035 parts by weight of initiator tert-amyl peroxypivalate into a 3-L high-pressure reactor; displace with 7 bar of ethylene gas for 3 times, then introduce ethylene gas to keep the pressure at 53 bar, stir, heat up to 56 °C, and start the reaction at constant temperature and pressure;

[0065] (2) When the conversion rate of VAC reaches 47%, add 0.048 parts of sorbic acid to end the polymerization;

[0066] (3) Remove the residual monomers by rotary evaporation and drying, and prepare an EVAc methanol solution with methanol. After removal, the VAC content is 23 ppm. Take the EVAc methanol solution obtained above; then add 19 parts by weight of NaOH methanol solution for saponification, and remove the by-product methyl acetate at the same time. After alcoholysis and saponification, the degree of alcoholysis is 99.5 (mol)%;

[0067] (4) Add hot water at 90 °C to make the hot water in the mixed solvent account for 32% (weight ratio), then heat up to 108 °C to obtain a homogeneous solution; then cool down to 20 °C and keep it at a constant temperature for 1 h to precipitate insoluble substances, filter while it is hot, filter while it is hot, remove the soluble substances, and obtain insoluble EVOH. Then, wash it once with an aqueous acetic acid solution with a concentration of 950 ppm and wash it 5 times with water, and dry it at 110 °C for 10 hours. At this time, the volatile content of EVOH is 0.1%, and the EVOH resin is obtained.

[0068] Example 3

[0069] This example is to illustrate the ethylene-vinyl alcohol resin prepared by the method of the present invention.

[0070] (1) Add 100 parts by weight of VAC, 12 parts by weight of tert-butanol and 0.05 part by weight of initiator azobisisobutyronitrile to a 3 L high-pressure reactor; displace with 7 bar of ethylene gas 3 times, and then introduce ethylene gas to keep the pressure at 32 bar, stir, heat up to 55 °C, and start the reaction at a constant temperature and pressure;

[0071] (2) When the VAC conversion rate reaches 45%, add 0.082 parts of sorbic acid to end the polymerization;

[0072] (3) Remove the residual monomers by rotary evaporation and drying, and prepare an EVAc methanol solution with methanol. After removal, the VAC content is 35 ppm. Take the EVAc methanol solution obtained above; then add 25 parts by weight of NaOH methanol solution for saponification, and remove the by-product methyl acetate at the same time. After alcoholysis and saponification, the degree of alcoholysis is 99.6 (mol)%;

[0073] (4) Add hot water at 90 °C to make the hot water in the mixed solvent account for 48% (weight ratio), then heat up to 105 °C to obtain a homogeneous solution; then cool down to 35 °C and keep it at a constant temperature for 2 h to precipitate insoluble substances, filter while it is hot, remove the soluble substances, and obtain insoluble EVOH. Then, wash it once with an aqueous acetic acid solution with a concentration of 700 ppm and wash it 4 times with water, and dry it at 50 °C for 24 hours. At this time, the volatile content of EVOH is 0.5%, and the EVOH resin is obtained.

[0074] Example 4

[0075] This example is to illustrate the ethylene-vinyl alcohol resin prepared by the method of the present invention.

[0076] (1) Add 100 parts by weight of VAC, 17 parts by weight of propanol, and 0.048 part by weight of the initiator azobisisoheptonitrile into a 3-L high-pressure reactor; displace with 7 bar of ethylene gas three times, then introduce ethylene gas to keep the pressure at 40 bar, stir, heat up to 58 °C, and start the reaction under constant temperature and pressure;

[0077] (2) When the conversion rate of VAC reaches 47%, add 0.052 parts of sorbic acid to end the polymerization;

[0078] (3) Then remove the residual monomers by rotary evaporation and drying, prepare an EVAc methanol solution with methanol, and the VAC content after removal is 31 ppm. For the EVAc methanol solution obtained above; then add 22 parts by weight of NaOH methanol solution for saponification, and remove the by-product methyl acetate at the same time. The degree of alcoholysis after alcoholysis saponification is 99.4 (mol)%;

[0079] (4) Dropwise add hot water at 90 °C to make the hot water in the mixed solvent account for 42% (weight ratio), then heat up to 102 °C to obtain a homogeneous solution; then cool down to 50 °C and keep it constant for 1.5 h to precipitate insoluble substances, filter while it is hot, remove the soluble substances, and obtain the insoluble substance EVOH. Then wash it once with an aqueous acetic acid solution with a concentration of 550 ppm and wash it three times with water, and dry it at 85 °C for 16 hours. At this time, the volatile content of EVOH is 0.2%, and the EVOH resin is obtained.

[0080] Example 5

[0081] This example is to illustrate the ethylene-vinyl alcohol resin prepared by the method of the present invention.

[0082] (1) Add 100 parts by weight of VAC, 10 parts by weight of tert-butanol, and 0.034 part by weight of the initiator dibutyl peroxydicarbonate into a 3-L high-pressure reactor; displace with 7 bar of ethylene gas three times, then introduce ethylene gas to keep the pressure at 50 bar, stir, heat up to 56 °C, and start the reaction under constant temperature and pressure;

[0083] (2) When the conversion rate of VAC reaches 49%, add 0.056 parts of sorbic acid to end the polymerization;

[0084] (3) Then remove the residual monomers by rotary evaporation and drying, prepare an EVAc methanol solution with methanol, and the VAC content after removal is 22 ppm. For the EVAc methanol solution obtained above; then add 25 parts by weight of NaOH methanol solution for saponification, and remove the by-product methyl acetate at the same time. The degree of alcoholysis after alcoholysis saponification is 99.7 (mol)%;

[0085] (4) Add hot water at 90 °C to make the hot water in the mixed solvent account for 30% (by weight), then heat up to 92 °C to obtain a homogeneous solution; then cool down to 45 °C and keep it at a constant temperature for 1.5 h to precipitate insoluble substances, filter while it is hot to remove soluble substances, and obtain insoluble EVOH. Then, wash it once with an aqueous acetic acid solution with a concentration of 680 ppm and wash it four times with water, and dry it at 88 °C for 14 hours. At this time, the volatile content of EVOH is 0.3%, and an EVOH resin is obtained.

[0086] Comparative Example 1

[0087] Prepare ethylene-vinyl alcohol resin according to the same method as in Example 1, the difference is that: in step (4), instead of "adding hot water at 90 °C to make the hot water in the mixed solvent account for 38% (by weight), then heating up to 93 °C to obtain a homogeneous solution; then cooling down to 28 °C and keeping it at a constant temperature for 1.5 h to precipitate insoluble substances, filtering while it is hot to remove soluble substances, and obtaining insoluble EVOH", directly carry out the pickling and water washing steps.

[0088] As a result, an ethylene-vinyl alcohol resin is obtained.

[0089] Comparative Example 2

[0090] Prepare ethylene-vinyl alcohol resin according to the same method as in Example 1, the difference is that: in step (4), modify "then cooling down to 28 °C and keeping it at a constant temperature for 1.5 h to precipitate insoluble substances" to "then cooling down to 28 °C and keeping it at a constant temperature for 0.5 h to precipitate insoluble substances".

[0091] As a result, an ethylene-vinyl alcohol resin is obtained, and the yield is 15% lower than that of Example 1.

[0092] Comparative Example 3

[0093] Prepare ethylene-vinyl alcohol resin according to the same method as in Example 1, the difference is that: in step (4), modify "then cooling down to 28 °C and keeping it at a constant temperature for 1.5 h to precipitate insoluble substances" to "then cooling down to 55 °C and keeping it at a constant temperature for 1.5 h to precipitate insoluble substances".

[0094] As a result, an ethylene-vinyl alcohol resin is obtained, and the yield is 23% lower than that of Example 1.

[0095] Comparative Example 4

[0096] Prepare ethylene-vinyl alcohol resin according to the same method as in Example 1, the difference is that: in step (4), modify "adding hot water at 90 °C to make the hot water in the mixed solvent account for 38% (by weight), then heating up to 93 °C to obtain a homogeneous solution" to "adding hot water at 90 °C to make the hot water in the mixed solvent account for 28% (by weight), then heating up to 93 °C to obtain a homogeneous solution". In this Comparative Example 4, the hot water in the mixed solvent accounts for 28% (by weight), and a homogeneous solution cannot be formed, and soluble substances cannot be removed after filtration.

[0097] As a result, an ethylene-vinyl alcohol resin is obtained.

[0098] Test Examples

[0099] The ethylene-vinyl alcohol resins prepared in Examples 1-5 and Comparative Examples 1-4 were tested for various parameters, and the results are shown in Table 1.

[0100] Table 1

[0101]

[0102] It can be seen from the results in Table 1 that the ethylene-vinyl alcohol resin prepared by the preparation method of the present invention has an ethylene content of 31.5-44.5 mol%, has good barrier properties, a relatively high decomposition temperature, a relatively high oxidation induction temperature, no "fish eyes" during the processing and application process, and is a thermoplastic ethylene-vinyl alcohol resin with excellent properties, which is very suitable for use in the packaging industry, especially can be widely used in the fields of food packaging, pharmaceutical packaging, cosmetic packaging, automobile fuel tanks, etc.

[0103] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the technical concept scope of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A preparation method of ethylene-vinyl alcohol resin, characterized in that, the preparation method comprises the following steps: (1) Contact vinyl acetate, an initiator, a monohydric alcohol and ethylene in a closed container for an isothermal and isobaric reaction; (2) Perform treatment of removing residual monomers, alcoholysis saponification, heating and filtration, washing and drying on the product obtained in step (1) to obtain ethylene-vinyl alcohol resin; wherein, the conditions of the heating and filtration treatment include: adding hot water to the saponified product obtained by alcoholysis saponification and heating to obtain a homogeneous solution; then cooling to 20-50 °C to precipitate insoluble substances, removing soluble substances, and obtaining insoluble EVOH.

2. The preparation method according to claim 1, wherein, the conditions of the heating and filtration treatment include: heating to 90-110 °C, and then cooling to 20-50 °C; preferably, the conditions of the heating and filtration treatment include: heating to 93-108 °C, then cooling to 25-50 °C and maintaining a constant temperature for more than 1 h; more preferably, maintaining a constant temperature for 1-2 h.

3. The preparation method according to claim 1 or 2, during the process of adding the hot water to neutralize the saponified product obtained by alcoholysis saponification, the amount of the hot water is 30-70% by weight, preferably 30-55% by weight based on the total weight of the mixed solvent.

4. The preparation method according to claim 1, wherein, in step (1), the reaction is terminated when the conversion rate of vinyl acetate is 30-60%; preferably, the reaction is terminated when the conversion rate of vinyl acetate is 40-50%.

5. The preparation method according to any one of claims 1-4, wherein, relative to 100 parts by weight of the vinyl acetate, the amount of the initiator is 0.01-0.1 part by weight, and the amount of the monohydric alcohol is 5-50 parts by weight; preferably, relative to 100 parts by weight of the vinyl acetate, the amount of the initiator is 0.03-0.06 part by weight, and the amount of the monohydric alcohol is 10-20 parts by weight.

6. The preparation method according to claim 1, wherein, the conditions of the isothermal and isobaric reaction include: the pressure is 10-60 bar, and the polymerization temperature is 50-70 °C; preferably, the conditions of the isothermal and isobaric reaction include: the pressure is 30-55 bar, and the polymerization temperature is 52-60 °C.

7. The preparation method according to claim 1, wherein, after removing the residual monomers, the total content of vinyl acetate is below 200 ppm, preferably below 50 ppm; and / or, during the alcoholysis saponification treatment, the degree of alcoholysis is 99-99.9 mol%.

8. The preparation method according to claim 1 or 5, wherein, the initiator is selected from one or more of azo initiators, peroxide initiators and organic peroxides; preferably, the azo initiator is selected from one or more of azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate and azobis(2-methylbutyronitrile); preferably, the peroxide initiator is selected from one or more of hydrogen peroxide, ammonium persulfate and potassium persulfate; Preferably, the organic peroxide is selected from one or more of benzoyl peroxide, tert-butyl peroxybenzoate, methyl ethyl ketone peroxide, diisobutyryl peroxide, tert-amyl peroxyneodecanoate, bis(4-tert-butylcyclohexyl) peroxydicarbonate, tert-amyl peroxy pivalate, tert-butyl peroxyacetate, and dibutyl peroxydicarbonate.

9. An ethylene-vinyl alcohol resin prepared by the preparation method according to any one of claims 1-8.

10. The ethylene-vinyl alcohol resin according to claim 9, wherein, the decomposition temperature of the ethylene-vinyl alcohol resin is 360-400 °C, preferably 370-395 °C; and / or, the oxidation induction temperature of the ethylene-vinyl alcohol resin is 190-220 °C, preferably 190-215 °C.

11. Use of the ethylene-vinyl alcohol resin according to claim 9 or 10 in the packaging industry.

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