Ethanolysis method of ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol resin particles, and applications

Abstract

The present application relates to the field of resin, and discloses a kind of alcoholysis method of ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol resin particle and application.The method comprises: (1) after mixing the polymerization solution containing ethylene-vinyl acetate copolymer and the first alkaline catalyst solution, first alcoholysis is carried out;The product of first alcoholysis is divided into stream A and stream B;(2) after mixing stream A and optionally second alkaline catalyst solution, second alcoholysis is carried out;(3) stream B and the product of second alcoholysis are mixed, formed, dried, and ethylene-vinyl alcohol resin particle is obtained.The ethylene-vinyl alcohol resin particle prepared by the method of the present application can improve the bonding performance while maintaining high barrier properties, and improve the processability of the product.

Description

Technical Field

[0001] This invention relates to the field of resins, and more specifically to a method for the alcoholysis of ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol resin particles, and their applications. Background Technology

[0002] Ethylene-vinyl alcohol copolymer (EVOH) is a novel polymeric synthetic material that combines the processability of ethylene polymers with the gas barrier properties of vinyl alcohol polymers. It possesses excellent gas barrier properties, water resistance, oil resistance, and ammonia barrier properties. EVOH, along with polyvinylidene chloride (PVDC) and polyamide (PA), is considered one of the world's three major high-barrier resins. In the 1950s, DuPont first produced EVOH resin through copolymerization and alcoholysis of ethylene and vinyl acetate (VAc).

[0003] In existing EVOH production processes, EVOH is generally produced by polymerizing ethylene and vinyl acetate using conventional methods such as emulsion polymerization, solution polymerization, or suspension polymerization, followed by saponification. In solution polymerization, alcohols with no more than four carbon atoms are typically used as solvents, with methanol being the preferred choice. The resulting ethylene-vinyl acetate copolymer solution contains the solvent methanol and unreacted vinyl acetate monomers. Utilizing the azeotropic properties of methanol and vinyl acetate in a distillation column, the unreacted vinyl acetate is removed by adding methanol solution or blowing in methanol vapor. The solution then enters an alcoholysis unit, where methyl acetate is removed by distillation, yielding EVOH with a degree of alcoholysis of over 99%, but generally below 99.5%. The alcoholysis of ethylene-vinyl acetate copolymers can be carried out using a batch alcoholysis method. CN104098733A discloses a method for the alcoholysis of ethylene-vinyl acetate copolymers, which involves alcoholysis at a pressure of -4 to 0 atmospheres, a reaction temperature of 40-85℃, and a reaction time of 4-7 hours, followed by neutralization and washing to obtain EVOH product. The main drawbacks of this method are long reaction time and low production efficiency. Alternatively, the alcoholysis of ethylene-vinyl acetate copolymers can be carried out using a tower alcoholysis method. CN1196724C discloses a method for manufacturing ethylene-vinyl acetate copolymer saponification products using a tower saponification reactor. The ethylene-vinyl acetate copolymer is added from the top of the tower, and the catalyst and alkali solution are added from the top and middle of the tower. A small amount of water is added to control product quality. The catalysts used for alcoholysis are usually methanol solutions such as sodium hydroxide and potassium hydroxide. Patent application CN115433301A discloses the use of an acidic deep eutectic solvent of choline chloride-p-toluenesulfonic acid for alcoholysis, which can effectively reduce the problem of metal ions affecting product quality when using sodium hydroxide, and the solvent can be recycled multiple times. However, no specific method for solvent recovery is mentioned.

[0004] To improve the barrier properties of EVOH, the degree of alcoholysis is usually required to reach above 99.3 mol%, or even above 99.5 mol%. As the degree of alcoholysis of EVOH increases, the number of hydroxyl groups in the molecular chain increases, which worsens the adhesion performance of EVOH materials to polyethylene / polypropylene. In order to improve the adhesion performance, the degree of alcoholysis of EVOH is reduced to improve the adhesion, but at the same time, the barrier properties of EVOH are reduced. EVOH products cannot simultaneously maintain a high barrier and adhesion performance. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned problems existing in the prior art and to provide a method for alcoholysis of ethylene-vinyl acetate copolymer, ethylene-vinyl alcohol resin particles and their applications. The ethylene-vinyl alcohol resin particles prepared by this method can improve the bonding performance and improve the processability while maintaining high barrier properties.

[0006] To achieve the above objectives, a first aspect of the present invention provides a method for the alcoholysis of ethylene-vinyl acetate copolymer, the method comprising: (1) After mixing the polymerization solution containing ethylene-vinyl acetate copolymer and the first alkaline catalyst solution, a first alcoholysis is carried out; the products of the first alcoholysis are divided into stream A and stream B; (2) After mixing the feed stream A with the optional second alkaline catalyst solution, a second alcoholysis is carried out; (3) Mix, shape, wash and dry the product of the second alcoholysis of the material stream B to obtain ethylene-vinyl alcohol resin particles.

[0007] A second aspect of the present invention provides ethylene-vinyl alcohol resin particles prepared by the method described in the first aspect above.

[0008] A third aspect of the present invention provides the application of the ethylene-vinyl alcohol resin particles described in the second aspect above.

[0009] Through the above technical solution, the present invention divides the product after the first alcoholysis reaction into two streams, one of which undergoes a second alcoholysis. The product of the second alcoholysis is mixed with the other stream after the first alcoholysis reaction, shaped, and dried to obtain ethylene-vinyl alcohol resin particles. The ethylene-vinyl alcohol resin particles obtained in this way can improve the bonding performance and improve the processability of the product while maintaining high barrier performance. Attached Figure Description

[0010] Figure 1 This is a flowchart of the production process of the present invention.

[0011] Explanation of reference numerals in the attached figures 1 is alcoholysis unit 1; 2 is alcoholysis unit 2; 3 and 4 are transfer pumps; 101 and 102 are material input pipelines; 103 and 105 are gas output pipelines; 104 is the connecting pipeline for conveying material flow A from 1 to 2; 106 is the output pipeline for the product after alcoholysis from 2; 107 is the output pipeline for material flow B. Detailed Implementation

[0012] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0013] The first aspect of this invention provides a method for the alcoholysis of ethylene-vinyl acetate copolymer, the method comprising: (1) After mixing the polymerization solution containing ethylene-vinyl acetate copolymer and the first alkaline catalyst solution, a first alcoholysis is carried out; the products of the first alcoholysis are divided into stream A and stream B; (2) After mixing the feed stream A with the optional second alkaline catalyst solution, a second alcoholysis is carried out; (3) Mix, shape, wash and dry the product of the second alcoholysis of the material stream B to obtain ethylene-vinyl alcohol resin particles.

[0014] In this invention, the product of the first alcoholysis is mixed with the product of the second alcoholysis with a high degree of alcoholysis. The mixed polymerization solution contains ethylene-vinyl alcohol copolymers with low and high degrees of alcoholysis. After molding and drying, ethylene-vinyl alcohol resin particles are obtained. The ethylene-vinyl alcohol resin particles obtained in this way can improve the bonding performance and improve the processability of the product while maintaining high barrier properties.

[0015] In this invention, when the mass concentration of ethylene-vinyl acetate copolymer in the polymerization solution is too low, a large amount of energy is required during the alcoholysis process; when the concentration is too high, the viscosity of the polymerization solution increases, making transportation difficult. Preferably, the mass concentration of ethylene-vinyl acetate copolymer in the polymerization solution is 30-50 wt%.

[0016] In this invention, there is no particular limitation on the solvent of the polymerization solution containing ethylene-vinyl acetate copolymer, as long as it can facilitate the alcoholysis of ethylene-vinyl acetate copolymer. Preferably, the solvent is a C1-C4 alcohol solvent, preferably at least one of methanol, ethanol, propanol, ethylene glycol, n-butanol and tert-butanol, and more preferably methanol.

[0017] In this invention, based on the total molar amount of the ethylene-vinyl acetate copolymer, preferably, the content of structural units from ethylene in the ethylene-vinyl acetate copolymer is 15-60 mol%, which can be any two values ​​within the range of 15 mol%, 20 mol%, 25 mol%, 30 mol%, 35 mol%, 40 mol%, 45 mol%, 50 mol%, 55 mol%, 60 mol%, or more, and more preferably 20-50 mol%.

[0018] In this invention, the weight-average molecular weight of the ethylene-vinyl acetate copolymer is 30,000-200,000 g / mol, which can be any two values ​​of 30,000 g / mol, 60,000 g / mol, 100,000 g / mol, 150,000 g / mol, 200,000 g / mol or more, or values ​​within that range. Preferably, the weight-average molecular weight of the ethylene-vinyl acetate copolymer is 50,000-150,000 g / mol, and the molecular weight distribution index is 1-4, which can be any two values ​​of 1.2, 2, 2.5, 3, 3.5, 4 or more, or values ​​within that range.

[0019] In this invention, in order to alcoholyze the ethylene-vinyl acetate copolymer, the polymerization solution of the ethylene-vinyl acetate copolymer is mixed with an alkaline catalyst solution in the alcoholysis device 1 for alcoholysis.

[0020] In this invention, there is no particular limitation on the type of alcoholysis device 1. Preferably, the alcoholysis device 1 is a batch or tower type production device with a stirring device, which is beneficial to promoting the alcoholysis of ethylene-vinyl acetate copolymer.

[0021] According to the present invention, preferably, the alkaline catalyst solution is an alcoholic solution of an alkali. There is no particular limitation on the solvent of the alkaline catalyst solution; to reduce the cost of solvent recovery, it can be a C1-C4 alcohol solvent, preferably at least one selected from methanol, ethanol, propanol, ethylene glycol, n-butanol, and tert-butanol, and more preferably methanol. Mixing the alkaline alcoholic solution with the polymerization solution of the ethylene-vinyl acetate copolymer in the aforementioned preferred case can better promote the alcoholysis of the ethylene-vinyl acetate copolymer.

[0022] In this invention, there is no particular limitation on the mass concentration of alkali in the alkaline catalyst solution, as long as it is sufficient to cause alcoholysis of the ethylene-vinyl acetate copolymer. Preferably, it is 1-10 wt%, and can be any two values ​​within the range of 1 wt%, 1.5 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, or more.

[0023] In this invention, there is no particular limitation on the type of alkaline catalyst; any conventional type of alkali in the art can be used, preferably sodium hydroxide and / or potassium hydroxide.

[0024] In this invention, in order to enable the alcoholysis of the ethylene-vinyl acetate copolymer, the weight ratio of the polymerization solution of the ethylene-vinyl acetate copolymer to the alkaline catalyst solution is 1:0.01-0.2, which can be 1:0.02, 1:0.05, 1:0.1, 1:0.2 or any two of the above values ​​within a range.

[0025] In this invention, controlling the weight ratio of the polymerization solution of the ethylene-vinyl acetate copolymer to the alkaline catalyst solution to meet the above-mentioned range can not only reduce the amount of solvent, but also reduce the recycling cost.

[0026] More preferably, the weight ratio of the polymerization solution of the ethylene-vinyl acetate copolymer to the alkaline catalyst solution is 1:0.02-0.1.

[0027] In this invention, there is no particular limitation on the temperature of the first alcoholysis. It is sufficient to allow the ethylene-vinyl acetate copolymer in the alcoholysis device 1 to be successfully alcoholyzed. Preferably, the temperature is 60-110°C, which can be any two of the following values: 60°C, 70°C, 80°C, 85°C, 90°C, 100°C, 105°C, 110°C, or more preferably 70-100°C.

[0028] In this invention, there is no particular limitation on the time of the first alcoholysis, as long as the ethylene-vinyl acetate copolymer in the alcoholysis device 1 can be successfully alcoholyzed. Preferably, it is 0.2-2h, which can be any two of the following values: 0.2h, 0.3h, 0.4h, 0.5h, 0.6h, 0.8h, 0.9h, 1h, 1.3h, 1.5h, 2h, or a value within the range of any two of the above values. More preferably, it is 0.3-1h.

[0029] In this invention, controlling the conditions of the first alcoholysis within the above-mentioned range not only makes it easy to control and reduce the amount of alkaline catalyst solution used in production, but also increases the degree of alcoholysis of the product of the first alcoholysis.

[0030] In this invention, the degree of alcoholysis of the first alcoholysis product can be further controlled by adjusting the amount of alkaline catalyst added and the reaction temperature. The inventors of this invention discovered that if the degree of alcoholysis of the first alcoholysis product is too low, it increases the production load of the alcoholysis unit 2, affecting the degree of alcoholysis of the second alcoholysis product; if the degree of alcoholysis of the first alcoholysis product is too high, a large amount of alkaline catalyst solution needs to be added, increasing the residual alkaline impurities and affecting the quality of the final ethylene-vinyl alcohol resin particles. Preferably, the degree of alcoholysis of the first alcoholysis product in the alcoholysis unit 1 is controlled to be 85-98 mol%.

[0031] In this invention, when the degree of alcoholysis of the first alcoholysis product meets the above-mentioned range, it is mixed with the second alcoholysis product, and after molding and drying, the resulting ethylene-vinyl alcohol resin particles can improve the bonding performance while maintaining high barrier properties.

[0032] More preferably, the degree of alcoholysis of the product of the first alcoholysis is 90-96 mol. In this invention, the methyl acetate byproduct generated from the first alcoholysis is sent out through pipeline 103 and enters the solvent recovery device.

[0033] In this invention, the product of the first alcoholysis is divided into stream A and stream B. Stream A is pumped by pump 3 and enters the alcoholysis device 2 through pipeline 104 for the second alcoholysis.

[0034] In this invention, the quality of the ethylene-vinyl alcohol resin particles obtained from the final ethylene-vinyl alcohol copolymer mixture is controlled by controlling the mass ratio of material flow A to material flow B. Preferably, the mass ratio of material flow A to material flow B is 1:0.01-0.3, and more preferably 1:0.02-0.1.

[0035] More preferably, the mass ratio of material flow A to material flow B is 1:0.03-0.06.

[0036] In this invention, feed stream A and optionally a second alkaline catalyst solution are mixed and then subjected to a second alcoholysis. There are no particular limitations on the conditions for the second alcoholysis, as long as the vinyl acetate copolymer in the alcoholysis device 2 undergoes successful alcoholysis. Preferably, the conditions for the second alcoholysis include: a temperature of 70-130°C, which can be any two of the following values: 70°C, 80°C, 85°C, 90°C, 100°C, 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, or values ​​within that range; and a time of 0.2-2 hours, which can be any two of the following values: 0.2 hours, 0.3 hours, 0.4 hours, 0.5 hours, 0.6 hours, 0.8 hours, 0.9 hours, 1 hour, 1.3 hours, 1.5 hours, 2 hours, or values ​​within that range.

[0037] In this invention, controlling the conditions of the second alcoholysis within the above range can increase the degree of alcoholysis of the product of the second alcoholysis. Preferably, the degree of alcoholysis of the product of the second alcoholysis is not less than 98 mol.

[0038] Furthermore, the conditions for the second alcoholysis include: a temperature of 80-120°C, which can be any two values ​​of 80°C, 85°C, 90°C, 100°C, 105°C, 110°C, 115°C, 120°C or above, and a time of 0.3-1 h, which can be any two values ​​of 0.3 h, 0.4 h, 0.5 h, 0.6 h, 0.8 h, 0.9 h, 1 h or above, and a time ...-1 h.

[0039] In this invention, there are no special requirements for the amount of the second alkaline catalyst solution, as long as the degree of alcoholysis of the second alcoholysis product meets the requirements of this invention.

[0040] According to a preferred embodiment of the present invention, in order to further reduce the cost of alcoholysis, no additional alkaline catalyst may be added to the alcoholysis device 2.

[0041] In this invention, in order to facilitate the discharge of methyl acetate produced by the second alcoholysis, methanol solvent can be added. The methyl acetate byproduct produced by the second alcoholysis is sent out from pipeline 105 and enters the solvent recovery device.

[0042] In this invention, the method further includes removing the catalyst from the ethylene-vinyl alcohol resin particles obtained in step (3). Specifically, the particles are washed by soaking them in hot water at 20-80°C. The washed particles are then sent to a drying device, and the hot water containing residual catalyst is sent to a wastewater treatment device.

[0043] A second aspect of the present invention provides ethylene-vinyl alcohol resin particles prepared by the method described in the first aspect above.

[0044] According to the present invention, preferably, the ethylene-vinyl alcohol resin particles comprise ethylene-vinyl alcohol copolymer I and ethylene-vinyl alcohol copolymer II.

[0045] In this invention, the ethylene-vinyl alcohol copolymer I is the product of the second alcoholysis, and the ethylene-vinyl alcohol copolymer II is the product of the first alcoholysis.

[0046] According to the present invention, preferably, the degree of alcoholysis of ethylene-vinyl alcohol copolymer I is not less than 98 mol%, more preferably 98-99.9 mol%.

[0047] According to the present invention, preferably, the degree of alcoholysis of ethylene-vinyl alcohol copolymer II is 85-98 mol%, more preferably 90-96 mol%.

[0048] In this invention, by controlling the degree of hydrolysis of ethylene-vinyl alcohol copolymer I and ethylene-vinyl alcohol copolymer II to meet the above-mentioned preferred range, the quality of the final ethylene-vinyl alcohol resin particles can be further controlled.

[0049] In this invention, the quality of the final ethylene-vinyl alcohol resin particles is controlled by controlling the mass ratio of the polymerization solution containing ethylene-vinyl alcohol copolymer I to the polymerization solution containing ethylene-vinyl alcohol copolymer II. Preferably, the mass ratio of the polymerization solution containing ethylene-vinyl alcohol copolymer I to the polymerization solution containing ethylene-vinyl alcohol copolymer II is 1:0.01-0.3, and more preferably 1:0.02-0.1.

[0050] More preferably, the mass ratio of the polymerization solution containing ethylene-vinyl alcohol copolymer I to the polymerization solution containing ethylene-vinyl alcohol copolymer II is 1:0.03-0.06.

[0051] In this invention, the structural units derived from ethylene in the ethylene-vinyl alcohol copolymer I and ethylene-vinyl alcohol copolymer II are consistent with the ethylene-vinyl acetate copolymer in the raw materials. The total content of the structural units derived from ethylene in ethylene-vinyl alcohol copolymer I and ethylene-vinyl alcohol copolymer II is 15-60 mol%, which can be any two values ​​within the range of 15 mol%, 20 mol%, 25 mol%, 30 mol%, 35 mol%, 40 mol%, 45 mol%, 50 mol%, 55 mol%, 60 mol%, or more, preferably 20-50 mol%.

[0052] A third aspect of this invention provides the application of the ethylene-vinyl alcohol resin particles described in the second aspect above in at least one of packaging materials, underfloor heating pipes, and automotive fuel tanks. In this invention, the packaging materials include, but are not limited to, food packaging materials and pharmaceutical packaging materials.

[0053] The following combination Figure 1 The most preferred embodiment of the present invention will be described in detail below: (1) The polymerization solution containing ethylene-vinyl acetate copolymer and the first alkaline catalyst solution are respectively introduced into 1 through pipelines 101 and 102 for mixing and first alcoholysis; the methyl acetate byproduct generated by the first alcoholysis is sent out from 103 and enters the solvent recovery device. The products of the first alcoholysis are divided into stream A and stream B. The weight ratio of the polymerization solution containing ethylene-vinyl acetate copolymer to the first alkaline catalyst solution is 1:0.01-0.1, the degree of alcoholysis of the first alcoholysis product is 90-96 mol%, and the mass ratio of stream A to stream B is 1:0.03-0.06; (2) Flow A is fed into 2 via 104 through 3 for the second alcoholysis. The methyl acetate byproduct generated by the second alcoholysis is sent out through pipeline 105 and enters the solvent recovery unit. The degree of alcoholysis of the second alcoholysis product is 99-99.9 mol%. (3) The product of the second alcoholysis is mixed with the material flow B sent through 3 via 106 via 4, shaped and dried to obtain ethylene-vinyl alcohol resin particles.

[0054] The present invention will be described in detail below through examples. Unless otherwise specified, the reagents used in the following examples and comparative examples are commercially available.

[0055] Test methods for weight-average molecular weight and molecular weight distribution: determined by GPC method.

[0056] The method for testing the degree of alcoholysis is as follows: Dry EVOH is pulverized to 100 mesh, successively extracted and purified with deionized water, and dried at 120℃. The obtained ethylene-vinyl alcohol copolymer is subjected to NMR analysis under the following conditions, and the degree of alcoholysis is determined using the following analytical method: Analysis Method: From the spectrum measured at 40℃, the integral values ​​(I1) of the peak with a chemical shift of 3.7–4 ppm and (I2) of the peak with a chemical shift of 0.6–1.8 ppm are calculated. From the spectrum measured at 95℃, the integral values ​​(I3) of the peak with a chemical shift of 3.1–3.7 ppm, (I4) of the peak with a chemical shift of 0.6–1.8 ppm, and (I5) of the peak with a chemical shift of 1.9–2.1 ppm are calculated. Here, the peak with a chemical shift of 0.6–1.8 ppm mainly originates from methylene protons, and the peak with a chemical shift of 1.9–2.1 ppm originates from methyl protons in the un-hydrolyzed vinyl acetate unit. The degree of hydrolysis is calculated from these integral values ​​using Equation 1 below: Degree of alcoholysis (mol%) = (Equation 1) Ethylene-vinyl alcohol resin particle adhesion test: HDPE, PE-g-MAH (PE grafted maleic anhydride) adhesive layer, and ethylene-vinyl alcohol resin particles were extruded into sheets from the outside to the inside. The thickness was controlled by the amount of each component added. The thicknesses from the outside to the inside were 300 μm for the HDPE layer, 100 μm for the adhesive layer, and 120 μm for the ethylene-vinyl alcohol resin layer. Strips of 200 mm × 12.7 mm were cut from the sheets. After peeling the samples along the adhesive layer and ethylene-vinyl alcohol resin particles for a certain distance, the peeled ends were clamped onto a universal tensile testing machine for testing. The test temperature was 23℃, the tensile speed was 100 mm / min, and three sets of parallel tests were conducted. The average peel strength was used for characterization.

[0057] Ethylene-vinyl alcohol resin particle barrier performance: The barrier performance of the product was tested using a Mocon ox-tran2 / 12 instrument. A multilayer film sample (10.5×10.5cm) was taken and cut into a square according to the test chamber. The thickness of the film (μm) was tested. The film was placed on a sealing surface coated with grease, the top of the test chamber was covered and the screws were fixed. The test temperature (20℃) and humidity (65%RH) were set, and compressed air was introduced to test its performance.

[0058] Example 1 (1) The polymerization solution containing ethylene-vinyl acetate copolymer (solid content 40wt%, ethylene content 32mol%, weight average molecular weight of ethylene-vinyl acetate copolymer 98,000 g / mol, molecular weight distribution 1.72) enters the alcoholysis unit 1 through 101, and the sodium hydroxide-methanol solution (solid content 4wt%) enters through 102. The weight ratio of the polymerization solution containing ethylene-vinyl acetate copolymer to the sodium hydroxide-methanol solution is 1:0.05. The temperature of the first alcoholysis is 90℃, the time is 0.8h, the rotation speed of the alcoholysis unit 1 is 60 rpm, and the methyl acetate generated after alcoholysis is discharged through pipeline 103. The flow rate of material flow A in the product of the first alcoholysis is 1080 kg / h, and the flow rate of material flow B is 55 kg / h. The degree of alcoholysis of the product after the first alcoholysis is analyzed to be 92 mol%. (2) Flow A is pumped by pump 3 through 104 into alcoholysis unit 2 for a second alcoholysis. The temperature of the second alcoholysis is 110℃ and the time is 1h. The methyl acetate produced by alcoholysis is discharged through pipeline 105. The degree of alcoholysis of the product after the second alcoholysis is analyzed to be 99.5 mol%. (3) The product after the second alcoholysis is mixed with the material flow B, which is pumped by pump 3 via pump 107, through pump 4 at 106, and then shaped and dried to obtain ethylene-vinyl alcohol resin particles. The obtained ethylene-vinyl alcohol resin particles have a good appearance. The various parameters of the ethylene-vinyl alcohol resin particles are shown in Table 1.

[0059] Example 2 (1) The polymerization solution containing ethylene-vinyl acetate copolymer (solid content 35.5 wt%, ethylene content 32 mol%, weight average molecular weight of ethylene-vinyl acetate copolymer 82,000 g / mol, molecular weight distribution 1.62) enters the alcoholysis unit 1 through 101, and the sodium hydroxide-methanol solution (solid content 4 wt%) enters through 102. The weight ratio of the polymerization solution containing ethylene-vinyl acetate copolymer to the sodium hydroxide-methanol solution is 1:0.08. The temperature of the first alcoholysis is 90℃, the time is 1 h, the rotation speed of the alcoholysis unit 1 is 60 rpm, and the methyl acetate generated after alcoholysis is discharged through pipeline 103. The flow rate of material stream A in the product of the first alcoholysis is 990 kg / h, and the flow rate of material stream B is 42 kg / h. The degree of alcoholysis of the product after the first alcoholysis is analyzed to be 91 mol%. (2) Flow A is pumped by pump 3 through 104 into alcoholysis unit 2 for a second alcoholysis. The temperature of the second alcoholysis is 109℃ and the time is 0.7h. The methyl acetate produced by alcoholysis is discharged through pipeline 105. The degree of alcoholysis of the product after the second alcoholysis is analyzed to be 99.4 mol%. (3) The product after the second alcoholysis is mixed with the material flow B, which is pumped by pump 3 via pump 107, through pump 4 at 106, and then shaped and dried to obtain ethylene-vinyl alcohol resin particles. The obtained ethylene-vinyl alcohol resin particles have a good appearance. The various parameters of the ethylene-vinyl alcohol resin particles are shown in Table 1.

[0060] Example 3 (1) A polymerization solution containing ethylene-vinyl acetate copolymer (solid content 40wt%, ethylene content 32mol%, weight average molecular weight of ethylene-vinyl acetate copolymer 65,000 g / mol, molecular weight distribution 1.42) enters alcoholysis unit 1 through 101, and a sodium hydroxide-methanol solution (solid content 4wt%) enters through 102. The weight ratio of the polymerization solution containing ethylene-vinyl acetate copolymer to the sodium hydroxide-methanol solution is 1:0.03. The temperature of the first alcoholysis is 80℃, the time is 0.6h, the rotation speed of alcoholysis unit 1 is 60 rpm, and the methyl acetate generated after alcoholysis is discharged through pipeline 103. The flow rate of material stream A in the product of the first alcoholysis is 1080 kg / h, and the flow rate of material stream B is 55 kg / h. The degree of alcoholysis of the product after the first alcoholysis is analyzed to be 86 mol%. (2) Flow A is pumped by pump 3 through 104 into alcoholysis unit 2 for a second alcoholysis. The temperature of the second alcoholysis is 110℃ and the time is 1h. The methyl acetate produced by alcoholysis is discharged through pipeline 105. The degree of alcoholysis of the product after the second alcoholysis is analyzed to be 99.1 mol%. (3) The product after the second alcoholysis is mixed with the material flow B through pump 3 through pump 3 through pump 107 via pump 4, and then shaped and dried to obtain ethylene-vinyl alcohol resin particles. The obtained ethylene-vinyl alcohol resin particles have a good appearance. The various parameters of the ethylene-vinyl alcohol resin particles are shown in Table 1.

[0061] Example 4 (1) A polymerization solution containing ethylene-vinyl acetate copolymer (solid content 40wt%, ethylene content 32mol%, weight average molecular weight of ethylene-vinyl acetate copolymer 74,000 g / mol, molecular weight distribution 2.15) enters alcoholysis unit 1 through 101, and a sodium hydroxide-methanol solution (solid content 4wt%) enters through 102. The weight ratio of the polymerization solution containing ethylene-vinyl acetate copolymer to the sodium hydroxide-methanol solution is 1:0.05. The temperature of the first alcoholysis is 90℃, the time is 0.8h, the rotation speed of alcoholysis unit 1 is 60 rpm, and the methyl acetate generated after alcoholysis is discharged through pipeline 103. The flow rate of material stream A in the product of the first alcoholysis is 1000 kg / h, and the flow rate of material stream B is 350 kg / h. The degree of alcoholysis of the product after the first alcoholysis is analyzed to be 92 mol%. (2) Flow A is pumped by pump 3 through 104 into alcoholysis unit 2 for a second alcoholysis. The temperature of the second alcoholysis is 110℃ and the time is 1h. The methyl acetate produced by alcoholysis is discharged through pipeline 105. The degree of alcoholysis of the product after the second alcoholysis is analyzed to be 99.5 mol%. (3) The product after the second alcoholysis is mixed with the material flow B through pump 3 through pump 3 through pump 107 via pump 4, and then shaped and dried to obtain ethylene-vinyl alcohol resin particles. The obtained ethylene-vinyl alcohol resin particles have a good appearance. The various parameters of the ethylene-vinyl alcohol resin particles are shown in Table 1.

[0062] Example 5 (1) The polymerization solution containing ethylene-vinyl acetate copolymer (solid content 40wt%, ethylene content 32mol%, weight average molecular weight of ethylene-vinyl acetate copolymer 128,000 g / mol, molecular weight distribution 2.45) enters the alcoholysis unit 1 through 101, and the sodium hydroxide-methanol solution (solid content 4wt%) enters through 102. The weight ratio of the polymerization solution containing ethylene-vinyl acetate copolymer to the sodium hydroxide-methanol solution is 1:0.05. The temperature of the first alcoholysis is 90℃, the time is 0.8h, the rotation speed of the alcoholysis unit 1 is 60 rpm, and the methyl acetate generated after alcoholysis is discharged through pipeline 103. The flow rate of material flow A in the product of the first alcoholysis is 1080 kg / h, and the flow rate of material flow B is 55 kg / h. The degree of alcoholysis of the product after the first alcoholysis is analyzed to be 92 mol%. (2) Flow A is pumped by pump 3 through 104 into alcoholysis unit 2 for a second alcoholysis. The temperature of the second alcoholysis is 95℃ and the time is 1h. The methyl acetate produced by alcoholysis is discharged through pipeline 105. The degree of alcoholysis of the product after the second alcoholysis is analyzed to be 98.8 mol%. (3) The product after the second alcoholysis is mixed with the material flow B through pump 3 through pump 3 through pump 107 via pump 4, and then shaped and dried to obtain ethylene-vinyl alcohol resin particles. The obtained ethylene-vinyl alcohol resin particles have a good appearance. The various parameters of the ethylene-vinyl alcohol resin particles are shown in Table 1.

[0063] Example 6 (1) A polymerization solution containing ethylene-vinyl acetate copolymer (solid content 40wt%, ethylene content 32mol%, weight average molecular weight of ethylene-vinyl acetate copolymer 98,000 g / mol, molecular weight distribution 1.72) enters alcoholysis unit 1 through 101, and a sodium hydroxide-methanol solution (solid content 4wt%) enters through 102. The weight ratio of the polymerization solution containing ethylene-vinyl acetate copolymer to the sodium hydroxide-methanol solution is 1:0.05. The temperature of the first alcoholysis is 90℃, the time is 0.8h, the rotation speed of alcoholysis unit 1 is 60 rpm, and the methyl acetate generated after alcoholysis is discharged through pipeline 103. The flow rate of material stream A in the product of the first alcoholysis is 1000 kg / h, and the flow rate of material stream B is 130 kg / h. The degree of alcoholysis of the product after the first alcoholysis is analyzed to be 92 mol%. (2) Flow A is pumped by pump 3 through 104 into alcoholysis unit 2 for a second alcoholysis. The temperature of the second alcoholysis is 95℃ and the time is 1h. The methyl acetate produced by alcoholysis is discharged through pipeline 105. The degree of alcoholysis of the product after the second alcoholysis is analyzed to be 98.8 mol%. (3) The product after the second alcoholysis is mixed with the material flow B through pump 3 through pump 3 through pump 107 via pump 4, and then shaped and dried to obtain ethylene-vinyl alcohol resin particles. The obtained ethylene-vinyl alcohol resin particles have a good appearance. The various parameters of the ethylene-vinyl alcohol resin particles are shown in Table 1.

[0064] Comparative Example 1 The method is the same as in Example 1, except that all the material in alcoholysis unit 1 is fed into alcoholysis unit 2 for alcoholysis. The degree of alcoholysis of the product after the first alcoholysis is 92 mol%, and the degree of alcoholysis of the product after the second alcoholysis is 99.5 mol%. The peel strength of the obtained ethylene-vinyl alcohol resin particles is reduced. The parameters of the obtained ethylene-vinyl alcohol resin particles are shown in Table 1.

[0065] Comparative Example 2 Following the method of Example 1, the difference was that the solid content of the polymerization solution containing the ethylene-vinyl acetate copolymer was 58 wt% (ethylene content was 32 mol%, the weight-average molecular weight of the ethylene-vinyl acetate copolymer was 129,000 g / mol, and the molecular weight distribution was 2.15). All the material from alcoholysis unit 1 was fed into alcoholysis unit 2 for alcoholysis. The degree of alcoholysis of the first alcoholysis product was 87.3 mol%, and the degree of alcoholysis of the second alcoholysis product was 98.5 mol%. During the operation of transfer pumps 3 and 4, the current value increased. The degree of alcoholysis of the product after alcoholysis in alcoholysis unit 1 was low, and transfer pump 4 even tripped, affecting the normal operation of the unit. The parameters of the obtained ethylene-vinyl alcohol resin particles are shown in Table 1.

[0066] Table 1

[0067] Continued from Table 1

[0068] As shown in Table 1, to improve the barrier properties of the product, the degree of alcoholysis needs to be increased, but the peeling performance of the product decreases; conversely, to improve the peeling performance, the degree of alcoholysis needs to be decreased, but the barrier properties of the product decrease. To resolve these contradictions, the ethylene-vinyl alcohol resin particles obtained by the method of this invention can improve the bonding performance and processability while maintaining high barrier properties.

[0069] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for the alcoholysis of ethylene-vinyl acetate copolymer, characterized in that, The method includes: (1) After mixing the polymerization solution containing ethylene-vinyl acetate copolymer and the first alkaline catalyst solution, a first alcoholysis is carried out; the products of the first alcoholysis are divided into stream A and stream B; (2) After mixing the feed stream A with the optional second alkaline catalyst solution, a second alcoholysis is carried out; (3) Mix the material flow B and the product of the second alcoholysis, shape and dry them to obtain ethylene-vinyl alcohol resin particles.

2. The alcoholysis method according to claim 1, wherein, The polymerization solution containing ethylene-vinyl acetate copolymer has a mass concentration of 30-50 wt% for the ethylene-vinyl acetate copolymer. Preferably, the solvent of the polymerization solution containing the ethylene-vinyl acetate copolymer is a C1-C4 alcohol solvent, preferably at least one selected from methanol, ethanol, propanol, ethylene glycol, n-butanol and tert-butanol, and more preferably methanol.

3. The alcoholysis method according to claim 1 or 2, wherein, Based on the total molar amount of the ethylene-vinyl acetate copolymer, the content of structural units derived from ethylene in the ethylene-vinyl acetate copolymer is 15-60 mol%, preferably 20-50 mol%; Preferably, the ethylene-vinyl acetate copolymer has a weight-average molecular weight of 30,000-200,000 g / mol and a molecular weight distribution index of 1-4.

4. The alcoholysis method according to claim 1 or 2, wherein, The alkaline catalyst solution is an alcoholic solution of an alkali; Preferably, the mass concentration of alkali in the alkaline catalyst solution is 1-10 wt%. Preferably, the weight ratio of the polymerization solution containing ethylene-vinyl acetate copolymer to the alkaline catalyst solution is 1:0.01-0.

2.

5. The alcoholysis method according to claim 1 or 2, wherein, The conditions for the first alcoholysis include: a temperature of 60-110℃ and a time of 0.2-2h; Preferably, the degree of alcoholysis of the product of the first alcoholysis is 85-98 mol%, more preferably 90-96 mol.

6. The alcoholysis method according to claim 1 or 2, wherein, The mass ratio of material flow A to material flow B is 1:0.01-0.3, preferably 1:0.02-0.1, and more preferably 1:0.03-0.

06.

7. The alcoholysis method according to claim 1 or 2, wherein, The conditions for the second alcoholysis include: a temperature of 70-130℃ and a time of 0.2-2h; Preferably, the degree of alcoholysis of the product of the second alcoholysis is not less than 98 mol.

8. Ethylene-vinyl alcohol resin particles prepared by any one of the alcoholysis methods according to claims 1-7.

9. The ethylene-vinyl alcohol resin particles according to claim 8, wherein, The ethylene-vinyl alcohol resin particles include ethylene-vinyl alcohol copolymer I and ethylene-vinyl alcohol copolymer II; Preferably, the degree of alcoholysis of ethylene-vinyl alcohol copolymer I is 98-99.9 mol%; Preferably, the degree of alcoholysis of the ethylene-vinyl alcohol copolymer II is 90-96 mol%; Preferably, the total content of structural units derived from ethylene in ethylene-vinyl alcohol copolymer I and ethylene-vinyl alcohol copolymer II is 15-60 mol%, more preferably 20-50 mol.

10. The use of the ethylene-vinyl alcohol resin particles of claim 8 or 9 in at least one of packaging materials, underfloor heating pipes, and automotive fuel tanks.

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