An ethylene-vinyl alcohol copolymer resin composition and a method for producing the same

Abstract

The present application discloses an ethylene-vinyl alcohol copolymer (EVOH) resin composition, which is prepared by ethylene-vinyl acetate copolymerization reaction, and the content of polyvinyl alcohol in the EVOH resin composition is less than 5000 ppm. The present application can reduce the content of polyvinyl alcohol in the EVOH resin composition, thereby improving the yellowing resistance and processing stability of the EVOH resin composition in the melting process, and the prepared multilayer sheet, film and container are not prone to have defects such as crystal points and stripes.

Description

Technical Field

[0001] This invention relates to the field of ethylene-vinyl alcohol copolymers, specifically to an ethylene-vinyl alcohol copolymer resin composition and its preparation method. Background Technology

[0002] Ethylene-vinyl alcohol copolymer (EVOH), especially EVOH with an ethylene content of 20-50 mol%, has excellent gas barrier properties, approximately 10,000 times that of ordinary polyethylene. Combined with its transparency, processability, solvent resistance, and antistatic properties, it is widely used in packaging materials, automotive fuel tanks, oxygen-barrier underfloor heating pipes, textile materials, and medical materials.

[0003] Chinese patent document CN114426753A discloses an ethylene-vinyl alcohol copolymer composition and its preparation method: the composition includes an ethylene-vinyl alcohol copolymer, a carboxyl-containing substance, a potassium salt, and a sodium salt, wherein the carboxyl-containing substance includes acetic acid and a carboxylic acid containing a carbon-carbon double bond; the preparation method of the composition includes the following steps: the ethylene-vinyl acetate copolymer obtained by polymerization is alcoholyzed with sodium hydroxide, then granulated, and then washed, during which acetic acid and a carboxylic acid containing a carbon-carbon double bond are added for washing, and then potassium salt is added.

[0004] The prior art has the following drawbacks: the multilayer sheets, films and containers made from the EVOH resin composition are prone to defects such as crystal points and streaks. Summary of the Invention

[0005] On one hand, the present invention provides an EVOH resin composition, which is obtained by ethylene-vinyl acetate copolymerization reaction, wherein the content of polyvinyl alcohol in the EVOH resin composition is <5000ppm.

[0006] Furthermore, it also includes a step of depressurizing and flash evaporation after the ethylene-vinyl acetate copolymerization reaction is terminated by lowering the temperature; this can further ensure that the multilayer sheets, films and containers made from the obtained EVOH resin composition will not have defects such as crystal points and streaks.

[0007] Furthermore, the temperature is lowered to 10-30°C; this further ensures that the multilayer sheets, films, and containers made from the obtained EVOH resin composition will not produce defects such as crystal points and streaks.

[0008] Furthermore, the termination is achieved by adding a terminating agent, which further ensures that the multilayer sheets, films, and containers made from the obtained EVOH resin composition will not produce defects such as crystal points and streaks.

[0009] Furthermore, the content of the terminator is 100-5000 ppm of EVOH; this further ensures that the multilayer sheets, films, and containers made from the obtained EVOH resin composition will not produce defects such as crystal points and streaks.

[0010] Secondly, the present invention provides a method for preparing the EVOH resin composition of the present invention, comprising performing an alcoholysis reaction after ethylene-vinyl acetate copolymerization, lowering the temperature to 10-30°C after ethylene-vinyl acetate copolymerization, adding a terminator, depressurizing and flash evaporating, and then passing a solvent through for distillation to obtain an alcohol solution of ethylene-vinyl acetate copolymer.

[0011] Furthermore, the method also includes adding the alcoholic solution of EVOH obtained from alcoholysis to the additive solution, extruding the resulting EVOH solution into an aqueous solution at 0-10°C, cutting it into granules, and washing it; this can further ensure that the multilayer sheets, films, and containers made from the obtained EVOH resin composition will not have defects such as crystal points and streaks.

[0012] Furthermore, the additive is a heat stabilizer and / or an antioxidant; this further ensures that multilayer sheets, films, and containers made from the obtained EVOH resin composition will not produce defects such as crystal points and streaks.

[0013] Furthermore, the additive is one or more of carboxylic acids, alkali metal salts, alkaline earth metal salts, boric acid and its salts, and phosphoric acid and its salts; this further ensures that the multilayer sheets, films, and containers made from the obtained EVOH resin composition will not have defects such as crystal points and streaks.

[0014] Thirdly, the present invention provides the application of the EVOH resin composition described herein in membranes, multilayer sheets and containers.

[0015] The present invention has the following beneficial effects:

[0016] 1. The EVOH resin composition of the present invention can eliminate active free radicals in the polymerization system during processing. In the process from the subsequent depressurization and removal of ethylene monomer to the removal of vinyl acetate monomer, it reduces the self-polymerization of vinyl acetate to polyvinyl acetate, thereby reducing the amount of polyvinyl alcohol (PVA) generated in the subsequent alcoholysis process, so that the content of PVA in the polyvinyl acetate homopolymer is less than 5000 ppm. Therefore, the processing performance of the EVOH resin composition prepared by the present invention is significantly improved.

[0017] 2. The EVOH resin composition of the present invention can significantly reduce yellowing at high temperatures and reduce the number of defects after melt blown film processing.

[0018] 3. Multilayer sheets, films, and containers made from the EVOH resin composition of the present invention are less prone to defects such as crystal points and streaks. Detailed Implementation

[0019] The examples provided are for illustrative purposes only and are not intended to limit the scope of the invention. Therefore, non-essential modifications and adjustments made to the embodiments by those skilled in the art based on the above description are still within the protection scope of this invention.

[0020] 1. Definition

[0021] (1) Depressurization flash evaporation: The process of evaporating and vaporizing low-boiling-point substances by rapidly releasing pressure.

[0022] (2) Polymerization reaction: The process of converting low molecular weight monomers into high molecular weight polymers.

[0023] (3) Alcohololysis: the reaction in which acyl halides, acid anhydrides, esters, etc. are decomposed by alcohols to generate esters and other compounds.

[0024] (4) Distillation: is a thermodynamic separation process that utilizes the different boiling points of the components in a mixed liquid or liquid-solid system to evaporate the low-boiling-point components and then condense them to separate the entire component. It is a unit operation process that combines evaporation and condensation.

[0025] 2. Various preferred solutions involving the scope

[0026] (1) In this invention, EVOH can be polymerized by solution polymerization, emulsion polymerization or suspension polymerization, preferably by free radical solution polymerization.

[0027] (2) The ethylene-vinyl acetate copolymerization reaction in EVOH in this invention is prepared by using a solvent, an initiator, vinyl acetate, and ethylene as raw materials; the solvent is an alcohol solvent, which is an alcohol with 1-4 carbon atoms, such as one or more of methanol, ethanol, propanol, ethylene glycol, n-butanol, and tert-butanol; the initiator is an azo initiator or a peroxide initiator, wherein the azo initiator can be an oil-soluble initiator such as azobisisobutyronitrile, azobisisovalerate, azoisobutylcyanoformamide, etc. One or more of dicyclohexylformonitrile and dimethyl azobisisobutyrate; the peroxide initiator may be one or more of organic peroxides such as benzoyl peroxide, tert-butyl peroxide, methyl ethyl ketone peroxide, diisobutyryl peroxide, tert-pentyl peroxydecanoate, bis(4-tert-butylcyclohexyl peroxydicarbonate), tert-pentyl peroxydipentanoate, tert-butyl peroxyacetate, and bisbutyl peroxydicarbonate; or one or more of inorganic peroxides such as hydrogen peroxide, ammonium persulfate, and potassium persulfate.

[0028] 3. Detection Method

[0029] 1) Test method for PVA in EVOH: Accurately weigh 10g of EVOH sample into a 500mL beaker, add 300-400mL of distilled water, heat to boiling on an electric stove with a glass rod and stir until about 100mL of water evaporates from the beaker, then filter into a 500mL volumetric flask. Repeat the operation at least 3 times, then dilute the 500mL volumetric flask to volume. Take 10.00mL of the sample from the volumetric flask and place it in a 20mL graduated test tube, add 4.00mL of boric acid solution and 1mL of iodine-potassium iodide solution, dilute to the mark with water, shake well, and measure the absorbance at 640nm using a 1cm cuvette, with a reagent blank as a reference.

[0030] 2) Method for determining the number of surface defects in membrane products: A 30cm*24cm membrane sample was prepared using an SG-45 blown film machine, and the surface defects in the membrane were analyzed using a surface defect analyzer MVT-SIS. The number of defects larger than 0.5mm*0.5mm in the sample was counted.

[0031] Example 1

[0032] 100 parts of vinyl acetate, 12 parts of methanol, and 0.1 parts of azobisisobutyronitrile (AIBN) were added to a pressure polymerization reactor equipped with a jacket, stirrer, raw material inlet, temperature and pressure gauge, and reaction product outlet. The temperature was raised to 60°C, and the ethylene pressure was maintained at 3.8 MPaG. After reacting for 4 hours with stirring, the pressure was kept constant, and the temperature was lowered to 28°C. Then, 1000 ppm of copper acetate, a terminator relative to the generated ethylene-vinyl acetate copolymer, was added. After stirring for 1 hour, the pressure was released and the ethylene was flash-evaporated to remove it. Unreacted vinyl acetate was removed by distillation with methanol. The ethylene content in the obtained copolymer was tested to be 32 mol.

[0033] The methanol solution of the obtained ethylene-vinyl acetate copolymer was prepared into a 28% (w / w) solution with methanol, and then an alkaline solution was added for alcoholysis. The alkaline solution was a methanol solution of NaOH, and the molar ratio of the alkaline solution to the ethylene-vinyl acetate copolymer was controlled at 0.5:1. After alcoholysis, an EVOH methanol solution was obtained.

[0034] Add 0.3 parts by weight of the additive solution relative to the EVOH solid to the obtained EVOH methanol solution and stir until homogeneous; wherein the additive and its content are 200 ppm propionic acid, 300 ppm boric acid, and 400 ppm sodium dihydrogen phosphate relative to the weight of the EVOH solid.

[0035] The EVOH methanol solution obtained from alcoholysis was extruded into an aqueous solution at 5°C using an extruder equipped with a perforated plate. After precipitating into strips, the strips were cut into granules using a standard cutting method. The EVOH granules were then washed with water in a stirred tank for 2 hours each time, repeated twice. During the third wash, 0.01 parts by weight of acetic acid relative to the EVOH solids were added for acid washing, followed by centrifugation, dehydration, and drying to obtain the EVOH granules.

[0036] The EVOH particles obtained after drying were tested and found to contain 3600 ppm of homopolymer PVA. After heat treatment at 150℃ for 5 hours, the yellowness index increased by ΔYI=11.

[0037] The dried EVOH particles were extruded and blown into a film using a single screw. After 10 hours of continuous operation, the number of surface defects in the EVOH film was found to be 14, and the change in screw current ΔA = 1A.

[0038] Example 2

[0039] 100 parts of vinyl acetate, 12 parts of methanol, and 0.1 parts of pentyl peroxypentate were added to a pressure polymerization reactor equipped with a jacket, stirrer, raw material inlet, temperature and pressure gauge, and reaction product outlet. The temperature was raised to 60°C, and the ethylene pressure was maintained at 4.3 MPaG. After reacting for 4 hours with stirring, the pressure was kept constant, and the temperature was lowered to 20°C. Then, 1500 ppm of copper acetate, a terminator relative to the generated ethylene-vinyl acetate copolymer, was added. After stirring for 1 hour, the pressure was released and the ethylene was removed by flash evaporation. Unreacted vinyl acetate was removed by distillation with methanol. The ethylene content in the obtained copolymer was tested to be 38 mol.

[0040] The methanol solution of the obtained ethylene-vinyl acetate copolymer was prepared into a 38% (w / w) solution with methanol, and then an alkaline solution was added for alcoholysis. The alkaline solution was a methanol solution of NaOH, and the molar ratio of the alkaline solution to the ethylene-vinyl acetate copolymer was controlled at 0.12:1. After alcoholysis, an EVOH methanol solution was obtained.

[0041] Add 0.6 parts by weight of additive solution relative to the EVOH solid to the obtained EVOH methanol solution and stir until homogeneous; wherein the additive and its content are 300 ppm acetic acid, 200 ppm boric acid or 600 ppm sodium dihydrogen phosphate relative to the weight of EVOH solid.

[0042] The EVOH methanol solution obtained from alcoholysis was extruded into an aqueous solution at 5°C using an extruder equipped with a perforated plate. The precipitated strips were then cut into granules using a standard cutting method. The EVOH granules were washed with water in a stirred tank for 2 hours each time, repeated twice. During the third wash, 0.05 parts by weight of acetic acid relative to the EVOH solids were added for acid washing, followed by centrifugation, dehydration, and drying to obtain the final EVOH granules.

[0043] The EVOH particles obtained after drying were tested and found to contain 3100 ppm of homopolymer PVA. After heat treatment at 150℃ for 5 hours, the yellowness index increased by ΔYI=9.

[0044] The dried EVOH particles were extruded and blown into a film using a single screw. After 10 hours of continuous operation, the number of surface defects in the EVOH film was found to be 13, and the change in screw current ΔA = 1A.

[0045] Example 3

[0046] 100 parts of vinyl acetate, 12 parts of methanol, and 0.1 parts of pentyl peroxypentate were added to a pressure polymerization reactor equipped with a jacket, stirrer, raw material inlet, temperature and pressure gauge, and reaction product outlet. The temperature was raised to 60°C, and the ethylene pressure was maintained at 3.6 MPaG. After reacting for 4 hours with stirring, the pressure was kept constant, and the temperature was lowered to 28°C. Then, 2200 ppm of copper acetate as a terminator relative to the generated ethylene-vinyl acetate copolymer was added. After stirring for 1 hour, the pressure was released and the ethylene was removed by flash evaporation. Unreacted vinyl acetate was removed by distillation with methanol. The ethylene content in the obtained copolymer was tested to be 32 mol.

[0047] The methanol solution of the obtained ethylene-vinyl acetate copolymer was prepared into a 35% (w / w) solution with methanol, and then an alkaline solution was added for alcoholysis. The alkaline solution was a methanol solution of NaOH, and the molar ratio of the alkaline solution to the ethylene-vinyl acetate copolymer was controlled at 0.08:1. After alcoholysis, an EVOH methanol solution was obtained.

[0048] Add 0.8 parts by weight of the additive solution relative to the EVOH solid to the obtained EVOH methanol solution and stir until homogeneous; wherein the additive and its content are 300 ppm of acetic acid, 300 ppm of boric acid or 600 ppm of potassium dihydrogen phosphate relative to the weight of the EVOH solid.

[0049] The EVOH methanol solution obtained from alcoholysis was extruded into an aqueous solution at 5°C using an extruder equipped with a perforated plate. The precipitated strips were then cut into granules using a standard cutting method. The EVOH granules were washed with water in a stirred tank for 2 hours each time, repeated twice. During the third wash, 0.05 parts by weight of acetic acid relative to the EVOH solids were added for acid washing, followed by centrifugation, dehydration, and drying to obtain the final EVOH granules.

[0050] The EVOH particles obtained after drying were tested and found to contain 2600 ppm of homopolymer PVA. After heat treatment at 150℃ for 5 hours, the yellowness index increased by ΔYI=7.

[0051] The dried EVOH particles were extruded and blown into a film using a single screw. After 10 hours of continuous operation, the number of surface defects on the EVOH film was found to be 10, and the change in screw current ΔA = 1A.

[0052] Comparative Example 1

[0053] 100 parts of vinyl acetate, 12 parts of methanol, and 0.1 parts of pentyl peroxypentate were added to a pressure polymerization reactor equipped with a jacket, stirrer, raw material inlet, temperature and pressure gauge, and reaction product outlet. The temperature was raised to 60°C, and the ethylene pressure was maintained at 4.3 MPaG. After reacting for 4 hours with stirring, the pressure was kept constant, and the temperature was lowered to 45°C. Then, 1500 ppm of copper acetate, a terminator relative to the generated ethylene-vinyl acetate copolymer, was added. After stirring for 1 hour, the pressure was released and the ethylene was removed by flash evaporation. Unreacted vinyl acetate was removed by distillation with methanol. The ethylene content of the obtained copolymer was tested to be 38 mol.

[0054] The methanol solution of the obtained ethylene-vinyl acetate copolymer was prepared into a 38% (w / w) solution with methanol, and then an alkaline solution was added for alcoholysis. The alkaline solution was a methanol solution of NaOH, and the molar ratio of the alkaline solution to the ethylene-vinyl acetate copolymer was controlled at 0.12:1. After alcoholysis, an EVOH methanol solution was obtained.

[0055] Add 0.6 parts by weight of additive solution relative to the EVOH solid to the obtained EVOH methanol solution and stir until homogeneous; wherein the additive and its content are 300 ppm acetic acid, 200 ppm boric acid or 600 ppm sodium dihydrogen phosphate relative to the weight of EVOH solid.

[0056] The EVOH methanol solution obtained from alcoholysis was extruded into an aqueous solution at 5°C using an extruder equipped with a perforated plate. The precipitated strips were then cut into granules using a standard cutting method. The EVOH granules were washed with water in a stirred tank for 2 hours each time, repeated twice. During the third wash, 0.05 parts by weight of acetic acid relative to the EVOH solids were added for acid washing, followed by centrifugation, dehydration, and drying to obtain the final EVOH granules.

[0057] The EVOH particles obtained after drying were tested and found to contain 7800 ppm of homopolymer PVA. After heat treatment at 150℃ for 5 hours, the yellowness index increased by ΔYI=18.

[0058] The dried EVOH particles were extruded and blown into a film using a single screw. After 10 hours of continuous operation, the number of surface defects in the EVOH film was found to be 22, and the change in screw current ΔA = 2A.

[0059] Comparative Example 2

[0060] 100 parts of vinyl acetate, 12 parts of methanol, and 0.1 parts of azobisisobutyronitrile (AIBN) were added to a pressure polymerization reactor equipped with a jacket, stirrer, raw material inlet, temperature and pressure gauge, and reaction product outlet. The temperature was raised to 60°C, and the ethylene pressure was maintained at 3.8 MPaG. After reacting for 4 hours with stirring, the pressure was kept constant, and the temperature was lowered to 50°C. Then, 1000 ppm of copper acetate, a terminator relative to the generated ethylene-vinyl acetate copolymer, was added. After stirring for 1 hour, the pressure was released and the ethylene was flash-evaporated to remove it. Unreacted vinyl acetate was removed by distillation with methanol. The ethylene content in the obtained copolymer was tested to be 32 mol.

[0061] The methanol solution of the obtained ethylene-vinyl acetate copolymer was prepared into a 32% (w / w) solution with methanol, and then an alkaline solution was added for alcoholysis. The alkaline solution was a methanol solution of NaOH, and the molar ratio of the alkaline solution to the ethylene-vinyl acetate copolymer was controlled at 0.5:1. After alcoholysis, an EVOH methanol solution was obtained.

[0062] Add 0.3 parts by weight of the additive solution relative to the EVOH solid to the obtained EVOH methanol solution and stir until homogeneous; wherein the additive and its content are 200 ppm propionic acid, 300 ppm boric acid, and 400 ppm sodium dihydrogen phosphate relative to the weight of the EVOH solid.

[0063] The EVOH methanol solution obtained from alcoholysis was extruded into an aqueous solution at 5°C using an extruder equipped with a perforated plate. The precipitated strips were then cut into granules using a standard cutting method. The EVOH granules were washed with water in a stirred tank for 2 hours each time, repeated twice. After centrifugation and dehydration, the EVOH granules were dried to obtain the final EVOH granules.

[0064] The EVOH particles obtained after drying were tested and found to contain 9100 ppm of homopolymer PVA. After heat treatment at 150℃ for 5 hours, the yellowness index increased by ΔYI=20.

[0065] The dried EVOH particles were extruded and blown into a film using a single screw. After 10 hours of continuous operation, the number of surface defects in the EVOH film was found to be 24, and the change in screw current ΔA = 2A.

[0066] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing an EVOH resin composition, comprising an alcoholysis reaction following an ethylene-vinyl acetate copolymerization reaction, characterized in that: After the copolymerization reaction of ethylene-vinyl acetate, the temperature is lowered to 10-30℃, a terminator is added, the pressure is released and the mixture is flash-evaporated, and then the solvent is introduced for distillation to obtain an alcohol solution of ethylene-vinyl acetate copolymer. The polyvinyl alcohol content in the EVOH resin composition is <5000ppm; The content of the terminator is 1000-1500 ppm of ethylene-vinyl acetate copolymer.

2. The preparation method according to claim 1, characterized in that: It also includes adding an alcoholic solution of EVOH obtained from alcoholysis to an additive solution, extruding the resulting EVOH solution into an aqueous solution at 0-10℃, cutting it into granules, and then washing it.

3. The preparation method according to claim 2, characterized in that: The additive is a heat stabilizer and / or an antioxidant.

4. The preparation method according to claim 3, characterized in that: The additive is one or more of the following: carboxylic acid, alkali metal salt, alkaline earth metal salt, boric acid and its salt, and phosphoric acid and its salt.