Ethylene-vinyl acetate copolymer emulsion as well as preparation method and application thereof

Abstract

The invention relates to the field of emulsion polymerization, in particular to ethylene-vinyl acetate copolymer emulsion as well as a preparation method and application thereof. The preparation method comprises the following steps: carrying out polymerization reaction on vinyl acetate, ethylene, protective colloid and an initiator, and then adding a pH regulator, a defoaming agent and a bactericide to obtain ethylene-vinyl acetate copolymer emulsion; wherein the protective colloid is modified polyvinyl alcohol, and a macromolecular main chain of the modified polyvinyl alcohol contains a C = C structure, a C = C-C = C structure and a C = C-C = C-C = C structure; the specific preparation method is a continuous process, is efficient and simple and is beneficial to mass production, a step-by-step polymerization method is further adopted, the uniformity of the prepared ethylene-vinyl acetate copolymer emulsion is improved, and an emulsion film prepared from the emulsion is high in tensile strength.

Description

Technical Field

[0001] The present invention relates to the field of emulsion polymerization, and particularly to an ethylene-vinyl acetate copolymer emulsion, a preparation method thereof and an application thereof. Background Art

[0002] The copolymer of ethylene and vinyl acetate is an important product among ethylene copolymers, which is generally collectively referred to as EVA abroad. However, in China, according to the different vinyl acetate contents, the copolymer of ethylene and vinyl acetate is divided into EVA resin, EVA rubber and VAE emulsion. The VAE emulsion product has high strength, non-toxic and environmental protection, and excellent bonding performance, and can be used in the fields of textile, light industry, coating, plastic toughening, building compounding material, polymer blending coating, rubber modification, etc.

[0003] CN101041704A provides an ethylene-vinyl acetate copolymer stabilized by an emulsifying system composed of a reactive anionic emulsifier and a non-ionic emulsifier to obtain an ethylene-vinyl acetate polymer emulsion with excellent water resistance and bonding performance, which involves using polyvinyl alcohol as a protective colloid to improve the water resistance and bonding strength of the ethylene-vinyl acetate copolymer powder. The reactive anionic emulsifier is one or a mixture of phosphate esters, 2-allyl types or acrylamide types.

[0004] However, the existing ethylene-vinyl acetate emulsion has poor uniformity, is easy to stratify and has poor film-forming property, and the strength of the prepared ethylene-vinyl acetate emulsion is low and it is easy to crack. Summary of the Invention

[0005] The object of the present invention is to overcome the problems of poor uniformity of the existing ethylene-vinyl acetate emulsion and low strength of the emulsion film prepared from the emulsion, and to provide an ethylene-vinyl acetate copolymer emulsion, a preparation method thereof and an application thereof. The ethylene-vinyl acetate copolymer emulsion prepared by this preparation method has good uniformity, and the tensile strength of the emulsion film prepared from the emulsion is high.

[0006] To achieve the above object, in the first aspect of the present invention, a preparation method of an ethylene-vinyl acetate copolymer emulsion is provided, wherein the preparation method includes polymerizing vinyl acetate, ethylene, a protective colloid and an initiator, and then adding a pH regulator, an antifoaming agent and a bactericide to obtain the ethylene-vinyl acetate copolymer emulsion;

[0007] Wherein, the protective colloid is a modified polyvinyl alcohol, and in the macromolecular main chain of the modified polyvinyl alcohol, there are C=C structures, C=C-C=C structures and C=C-C=C-C=C structures.

[0008] In the second aspect of the present invention, an ethylene-vinyl acetate copolymer emulsion prepared by the foregoing preparation method is provided.

[0009] The third aspect of the present invention provides the application of the aforementioned ethylene-vinyl acetate copolymer emulsion in the field of membranes.

[0010] Through the above technical solutions, the beneficial effects of the present invention are as follows:

[0011] The specific preparation method is a continuous process, which is efficient and simple, and is conducive to mass production; further, the method of stepwise polymerization is adopted to improve the uniformity of the prepared ethylene-vinyl acetate copolymer emulsion, and the tensile strength of the emulsion film prepared with this emulsion is large. Detailed implementation manners

[0012] 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.

[0013] The first aspect of the present invention provides a method for preparing an ethylene-vinyl acetate copolymer emulsion, wherein the preparation method includes polymerizing vinyl acetate, ethylene, a protective colloid, and an initiator, and then adding a pH regulator, an antifoaming agent, and a bactericide to obtain an ethylene-vinyl acetate copolymer emulsion;

[0014] Wherein, the protective colloid is a modified polyvinyl alcohol, and in the macromolecular main chain of the modified polyvinyl alcohol, there are C=C structures, C=C-C=C structures, and C=C-C=C-C=C structures.

[0015] In the present invention, the specific preparation method is a continuous process, which is simple and convenient, and the prepared ethylene-vinyl acetate copolymer emulsion has excellent uniformity.

[0016] In a particularly preferred embodiment, the preparation method of the protective colloid is as follows: S1. Mix vinyl acetate monomer, methanol, a modifier, and an initiator for polymerization reaction to obtain a polyvinyl acetate methanol solution, and then purify, alcoholize, and separate to obtain particles;

[0017] S2. Dry the particles to obtain the modified polyvinyl alcohol;

[0018] Wherein, the modifier is a straight-chain dialdehyde of C 2 -C 6 ;

[0019] Wherein, the drying includes primary drying, secondary drying, and tertiary drying;

[0020] The conditions for the primary drying include: the temperature of the primary drying is 65-80°C;

[0021] The conditions for the secondary drying include: the temperature for the secondary drying is 85 - 100 °C;

[0022] The conditions for the tertiary drying include: the temperature for the tertiary drying is 110 - 140 °C.

[0023] The specific modifier and the drying method act synergistically, resulting in a higher content of conjugated double bonds in the prepared modified polyvinyl alcohol, better solubility of the resin, and less foam during the dissolution process. The appearance of this polyvinyl alcohol resin enriches the types of modified polyvinyl alcohol and provides a reliable guarantee for the stability of the unsaturated monomer copolymerization system.

[0024] Purification process: Adding methanol to the polyvinyl acetate methanol solution multiple times can remove the unreacted vinyl acetate monomer more thoroughly. In the subsequent alcoholysis reaction process, the polyvinyl alcohol particles obtained have a whiter color, consume less alkali solution, and have a lower sodium acetate content in the product. It is preferably added 5 - 10 times, and the unreacted vinyl acetate monomer is blown out by heating to 70 - 80 °C. In a particularly preferred embodiment, the weight ratio of the methanol to the polyvinyl acetate methanol solution is 2 - 3:1.

[0025] Alcoholysis process: Adjust the concentration of the purified polyvinyl acetate solution with methanol; in the new polyvinyl acetate methanol solution, after adjusting the concentration of polyvinyl acetate to 10 - 20 wt%, perform a water bath treatment. The conditions for the water bath treatment are that the temperature of the water bath is 30 - 50 °C and the time of the water bath is 30 - 60 min; add sodium hydroxide methanol solution to the solution after the water bath treatment for alcoholysis. The conditions for the alcoholysis are that the temperature of the alcoholysis is 30 - 50 °C and the time of the alcoholysis is 10 - 60 min. Among them, in the sodium hydroxide methanol solution, the content of sodium hydroxide is 2.5 - 6.2 wt%.

[0026] In a particularly preferred embodiment, azobisisobutyronitrile is added to initiate the polymerization reaction of vinyl acetate; a linear aldehyde is used as a chain transfer agent to perform end group capping to terminate the polymerization reaction of vinyl acetate; the macromolecular chain is subjected to alcoholysis, and in the structure is converted into dried to cause the elimination of -OH, and finally C=C structure, C=C-C=C structure, and C=C-C=C-C=C structure are obtained.

[0027] The specific drying method can obtain more C=C-C=C structure and C=C-C=C-C=C structure, resulting in a higher content of conjugated double bonds in the finally prepared modified polyvinyl alcohol and obtaining a more stable polymerization protection system.

[0028] According to the present invention, the degree of polymerization of the modified polyvinyl alcohol is 1000 - 2500, preferably 1100 - 2400.

[0029] According to the present invention, the macromolecular main chain contains the group -CO-R-CO-; wherein, R is selected from -CH(CH 2 ) 2 CH-, -CH(CH 2 ) 3 CH- and -CH(CH 2 ) 4 CH- and at least one of them. For example, it can be -CH(CH 2 ) 2 CH-, -CH(CH 2 ) 3 CH- or -CH(CH 2 ) 4 CH-. When adding two aldehydes as modifiers, R can also be CH(CH 2 ) 2 CH- and -CH(CH 2 ) 4 CH-.

[0030] According to the present invention, the degree of alcoholysis of the polyvinyl alcohol is 85-95%, preferably 86-90%.

[0031] According to the present invention, for the polyvinyl alcohol, the ultraviolet absorption value at 215 nm is 0.05-0.25, the ultraviolet absorption value at 280 nm is 0.1-0.4, and the ultraviolet absorption value at 320 nm is 0.08-0.35.

[0032] Furthermore, for the polyvinyl alcohol, the ultraviolet absorption value at 215 nm is 0.06-0.22, the ultraviolet absorption value at 280 nm is 0.12-0.36, and the ultraviolet absorption value at 320 nm is 0.1-0.32.

[0033] According to the present invention, at 90 °C, the modified polyvinyl alcohol is configured into a 4 wt% aqueous solution of polyvinyl alcohol, and the viscosity of the 4 wt% aqueous solution of polyvinyl alcohol is 10-60 mPa·s, preferably 13-50 mPa·s.

[0034] According to the present invention, the pressure of ethylene is 2-6 MPa, preferably 3-5 MPa.

[0035] According to the present invention, in the preparation method, the specific steps of adding an initiator for the polymerization reaction include: adding a first initiator for the first polymerization and adding a second initiator for the second polymerization.

[0036] In the present invention, the preparation method of adding the initiator step by step can further promote the smooth and controllable reaction, making the prepared emulsion have excellent uniformity.

[0037] According to the present invention, the conditions for the first polymerization include: the polymerization temperature is 50 - 70°C, preferably 55 - 65°C; the polymerization time is 1 - 4 h, preferably 2 - 3 h.

[0038] According to the present invention, the conditions for the second polymerization include: the polymerization temperature is 75 - 90°C, preferably 80 - 85°C; the polymerization time is 1 - 5 h, preferably 2 - 4 h.

[0039] According to the present invention, the weight ratio of vinyl acetate to ethylene is 1:0.05 - 0.15, preferably 1:0.07 - 0.12.

[0040] According to the present invention, the weight ratio of vinyl acetate to the protective colloid is 1:0.05 - 0.2.

[0041] In the present invention, when the amounts of vinyl acetate and the protective colloid meet the above ranges, good uniformity is achieved, which can meet the requirements of automatic mechanized sizing and improve the adhesive strength of the emulsion.

[0042] Further, the weight ratio of vinyl acetate to the protective colloid is 1:0.07 - 0.15.

[0043] According to the present invention, the weight ratio of vinyl acetate to the first initiator is 1:0.0001 - 0.0018, preferably 1:0.0003 - 0.0015.

[0044] According to the present invention, the weight ratio of vinyl acetate to the second initiator is 1:0.0014 - 0.007, preferably 1:0.0018 - 0.006.

[0045] According to the present invention, the weight ratio of vinyl acetate to the pH regulator is 1:0.0008 - 0.03, preferably 1:0.001 - 0.02.

[0046] According to the present invention, the weight ratio of vinyl acetate to the defoamer is 1:0.0012 - 0.0036, preferably 1:0.0016 - 0.003.

[0047] According to the present invention, the weight ratio of vinyl acetate to the bactericide is 1:0.001 - 0.004, preferably 1:0.0015 - 0.0035.

[0048] According to the present invention, the first initiator and the second initiator are each independently selected from thermal decomposition initiators and / or redox initiators.

[0049] According to the present invention, the thermal decomposition initiator is selected from potassium persulfate and / or ammonium persulfate.

[0050] According to the present invention, the redox initiator is selected from tartrate-hydrogen peroxide and / or persulfate-bisulfite.

[0051] In the present invention, a specific redox initiator system has a high initiation efficiency, can reduce the initiation activation energy, and promote the polymerization reaction.

[0052] Furthermore, the first initiator and the second initiator are each independently selected from potassium persulfate and / or tartrate-hydrogen peroxide.

[0053] Even further, the first initiator and the second initiator are each independently selected from sodium tartrate-hydrogen peroxide.

[0054] According to the present invention, the pH regulator is selected from at least one of sodium bicarbonate, potassium bicarbonate, sodium acetate, sodium carbonate, potassium hydrogen phosphate, and sodium dihydrogen phosphate, and preferably sodium carbonate and / or sodium bicarbonate.

[0055] In the present invention, adjusting the pH of the system can ensure the stability and uniformity of the emulsion system during storage, and improve the storage time; wherein, the system refers to the emulsion containing vinyl acetate, ethylene, protective colloid, and initiator solution after the polymerization reaction.

[0056] According to the present invention, the defoamer is selected from silicone oil defoamers and / or mineral oil defoamers, and preferably silicone oil defoamers.

[0057] According to the present invention, the bactericide is selected from 1,2-benzisothiazolin-3-one bactericides and / or Kathon bactericides, and preferably Kathon bactericides.

[0058] The second aspect of the present invention provides an ethylene-vinyl acetate copolymer emulsion prepared by the foregoing preparation method.

[0059] In the present invention, the emulsion can stably exist, has excellent uniformity, and the emulsion film prepared from the emulsion has excellent tensile strength.

[0060] According to the present invention, the ethylene-vinyl acetate copolymer emulsion contains an ethylene-vinyl acetate copolymer.

[0061] According to the present invention, the weight-average molecular weight of the ethylene-vinyl acetate copolymer is 450,000 - 750,000 g / mol.

[0062] In the present invention, the inventors unexpectedly found that the ethylene-vinyl acetate copolymer with a specific weight-average molecular weight within the above range has excellent uniformity.

[0063] Furthermore, the weight-average molecular weight of the ethylene-vinyl acetate copolymer is 480,000 - 650,000 g / mol.

[0064] According to the present invention, the particle size distribution of the ethylene-vinyl acetate copolymer emulsion is 0.04 - 10 μm, preferably 0.1 - 8 μm.

[0065] In the present invention, the particle size distribution of the ethylene-vinyl acetate copolymer emulsion can characterize the uniformity of the emulsion. The specific test method is as follows: Using water as the dispersion liquid, the emulsion is dropped into water and fully dispersed until a set light shielding ratio is reached. After the system is stable, it is analyzed using a MasterSizer 2000 laser particle size analyzer. When the particle size distribution range is large, the emulsion is prone to coalescence during storage and will quickly settle out, resulting in layering of the emulsion. The value of the particle size distribution range refers to the absolute value of the difference between the left and right endpoints of the range.

[0066] According to the present invention, the ethylene-vinyl acetate copolymer emulsion may further include an ethylene-vinyl acetate copolymer, vinyl acetate, ethylene, a protective colloid, an initiator, a pH regulator, an antifoaming agent, and a bactericide. The weight ratio of the ethylene-vinyl acetate copolymer to the protective colloid is 1:0.03 - 0.15. In the present invention, when the amounts of the ethylene-vinyl acetate copolymer and the protective colloid meet the above range, it has good uniformity and can meet the requirements of automatic mechanized sizing. Further, in the ethylene-vinyl acetate copolymer emulsion, the weight ratio of the ethylene-vinyl acetate copolymer to the protective colloid is 1:0.04 - 0.12.

[0067] The third aspect of the present invention provides an application of the aforementioned ethylene-vinyl acetate copolymer emulsion in the field of membranes.

[0068] To prepare the emulsion into an emulsion film, conventional methods in the art can be used. In a preferred embodiment, the method for preparing an ethylene-vinyl acetate copolymer emulsion film from an ethylene-vinyl acetate copolymer emulsion is a conventional method in the art. In a particularly preferred embodiment, 20 - 25 g of the ethylene-vinyl acetate copolymer emulsion is coated on a 300×400 mm film applicator, and the excess emulsion is scraped off from the film applicator with a stainless steel sheet; the film is dried for 72 h under the conditions of a temperature of 25 ± 0.5 °C and a humidity of 50 ± 10%, obtaining an ethylene-vinyl acetate copolymer emulsion film. The thickness of the film obtained by this method is related to the film applicator and does not affect its tensile strength. The thickness of the prepared emulsion film is 0.5 - 1 mm.

[0069] The present invention will be described in detail below through examples.

[0070] Test method for the degree of polymerization of polyvinyl alcohol: Test is carried out in accordance with the provisions of GB / T 12010.5 - 2010.

[0071] Test method for the degree of alcoholysis of polyvinyl alcohol: Test is carried out in accordance with the provisions in Appendix D of GB / T 12010.2 - 2010.

[0072] Test method for ultraviolet absorption value of polyvinyl alcohol: Using an ultraviolet / visible spectrometer UV-3700 (Shimadzu, Japan), with a solution concentration of 0.1%, perform ultraviolet absorption tests, and measure the ultraviolet absorption values at 215 nm, 280 nm, and 320 nm respectively.

[0073] Test method for viscosity of polyvinyl alcohol: According to the regulations in Appendix E of GB / T12010.2-2010, use a Brookfield viscometer for testing, and the test temperature is 20 °C.

[0074] The weight-average molecular weight of ethylene-vinyl acetate copolymer is measured using a multi-detector gel permeation chromatograph LC-20AD.

[0075] The particle size distribution of ethylene-vinyl acetate copolymer emulsion is measured using a Mastersizer 2000 laser particle size analyzer.

[0076] The tensile strength of ethylene-vinyl acetate copolymer emulsion film is measured using the tensile strength detection method in "Plastic Film and Sheet Tensile Test" of GB / T10801-2006.

[0077] Nitrogen, ethylene, vinyl acetate, methanol, adipic dialdehyde, succinic dialdehyde, azobisisobutyronitrile, acetic acid, potassium persulfate, sodium bicarbonate, sodium tartrate, hydrogen peroxide, ammonium persulfate, potassium persulfate, sodium acetate, sodium hydrogen phosphate, defoamer 4201A, defoamer DCA-422, defoamer ZK682, defoamer DF-6983, fungicide FF-02, carbendazim fungicide, fungicide K12N, fungicide K20, etc. are all commercially purchased.

[0078] Example 1

[0079] Step 1. Preparation method of protective colloid:

[0080] S1. Polymerization reaction

[0081] Add 100 parts by weight of vinyl acetate, 5 parts by weight of methanol, 2.4 parts by weight of adipic dialdehyde, and 0.01 part by weight of azobisisobutyronitrile to the reaction kettle, and carry out polymerization reaction. The temperature of the polymerization reaction is 62 °C, and the time of the polymerization reaction is 5 h;

[0082] Purification:

[0083] Add 250 parts by weight of methanol to the polyvinyl acetate methanol solution in 4 portions, heat up to 75 °C to blow out the unreacted vinyl acetate, and carry out purification;

[0084] Alcoholysis:

[0085] Methanol is added to the partially purified polyvinyl acetate solution to prepare a new polyvinyl acetate methanol solution. In the new polyvinyl acetate methanol solution, the concentration of polyvinyl acetate is 15 wt%. Water bath treatment is carried out at a water bath temperature of 50 °C for 30 min. 0.46 parts by weight of sodium hydroxide methanol solution (the content of sodium hydroxide is 6.2 wt%) is added to the solution after water bath treatment, and alcoholysis is carried out at an alcoholysis temperature of 50 °C for 60 min; 0.035 parts by weight of acetic acid is added to terminate the reaction;

[0086] Separation:

[0087] The alcoholized polyvinyl alcohol is separated by a centrifuge to obtain polyvinyl alcohol pretreatment particles;

[0088] S2. Drying treatment

[0089] The obtained polyvinyl alcohol pretreatment particles are dried. The temperature of the first-stage drying is 75 °C for 1 h; the temperature of the second-stage drying is 90 °C for 0.5 h; the temperature of the third-stage drying is 130 °C for 2 h to obtain modified polyvinyl alcohol A1;

[0090] The macromolecular main chain of modified polyvinyl alcohol A1 contains the group -CO-R-CO-; where R is -CH(CH 2 ) 4 CH-.

[0091] Step 2. Preparation of ethylene-vinyl acetate copolymer emulsion

[0092] Perform two gas replacements with nitrogen at 5 MPa and one gas replacement with ethylene at 3 MPa. Add 1000 parts by weight of vinyl acetate, 120 parts by weight of ethylene, 90 parts by weight of modified polyvinyl alcohol A1, 770 parts by weight of water, and 5 parts by weight of potassium persulfate solution (6 parts by weight of potassium persulfate and 94 parts by weight of water) for the first polymerization. The weight ratio of vinyl acetate to ethylene is 1:0.12; the weight ratio of vinyl acetate to modified polyvinyl alcohol A1 is 1:0.09; the weight ratio of vinyl acetate to the first initiator is 1:0.0003. The conditions for the first polymerization include: a polymerization temperature of 65 °C and a polymerization time of 3 h. Add 80 parts by weight of potassium persulfate for the second polymerization. The weight ratio of vinyl acetate to the second initiator is 1:0.0048. The conditions for the second polymerization include: a polymerization temperature of 88 °C and a polymerization time of 1.5 h. Cool down to 25 °C, and then add 2 parts by weight of sodium bicarbonate, 1.6 parts by weight of defoamer 4201A, and 3 parts by weight of fungicide FF-02. The weight ratio of vinyl acetate to sodium bicarbonate is 1:0.002; the weight ratio of vinyl acetate to defoamer 4201A is 1:0.0016; the weight ratio of vinyl acetate to fungicide FF-02 is 1:0.003 to obtain ethylene-vinyl acetate copolymer emulsion B1.

[0093] Example 2

[0094] Step 1. Preparation method of protective colloid:

[0095] S1. Polymerization reaction

[0096] Add 100 parts by weight of vinyl acetate, 20 parts by weight of methanol, 1.5 parts by weight of glutaraldehyde, and 0.014 parts by weight of azobisisobutyronitrile to the reaction kettle for polymerization reaction. The temperature of the polymerization reaction is 60 °C, and the time of the polymerization reaction is 4 h.

[0097] Purification:

[0098] Add 200 parts by weight of methanol to the polyvinyl acetate methanol solution in 4 portions, heat up to 80 °C to blow out the unreacted vinyl acetate for purification.

[0099] Alcoholysis:

[0100] Add methanol to the partially purified polyvinyl acetate solution to prepare a new polyvinyl acetate methanol solution. In the new polyvinyl acetate methanol solution, the concentration of polyvinyl acetate is 20 wt%. Perform a water bath treatment. The temperature of the water bath is 50 °C, and the time of the water bath is 30 min. Add 0.46 parts by weight of sodium hydroxide methanol solution (the content of sodium hydroxide is 6.2 wt%) to the solution after the water bath treatment for alcoholysis. The temperature of alcoholysis is 50 °C, and the time of alcoholysis is 60 min. Add 0.035 parts by weight of acetic acid to terminate the reaction.

[0101] Separation:

[0102] Use a centrifuge to separate the polyvinyl alcohol after alcoholysis to obtain polyvinyl alcohol pretreatment particles;

[0103] S2. Drying treatment

[0104] Dry the obtained polyvinyl alcohol pretreatment particles. The temperature of the first-stage drying is 75 °C, and the time of the first-stage drying is 1 h; the temperature of the second-stage drying is 90 °C, and the time of the second-stage drying is 0.5 h; the temperature of the third-stage drying is 130 °C, and the time of the third-stage drying is 2 h to obtain modified polyvinyl alcohol A2;

[0105] The groups contained in the macromolecular main chain of modified polyvinyl alcohol A2 are -CO-R-CO-; among them, R is -CH(CH 2 ) 3 CH-.

[0106] Step 2. Preparation of ethylene-vinyl acetate copolymer emulsion

[0107] Perform two gas replacements with nitrogen at 5 MPa and one gas replacement with ethylene at 3 MPa. Add 1000 parts by weight of vinyl acetate, 70 parts by weight of ethylene, 90 parts by weight of modified polyvinyl alcohol A2, 765 parts by weight of water, and 5 parts by weight of sodium tartrate-hydrogen peroxide solution (3 parts by weight of sodium tartrate, 1 part by weight of hydrogen peroxide, and 48 parts by weight of water) for the first polymerization. The weight ratio of vinyl acetate to ethylene is 1:0.07; the weight ratio of vinyl acetate to modified polyvinyl alcohol A2 is 1:0.09; the weight ratio of vinyl acetate to the first initiator is 1:0.0003; the conditions for the first polymerization include: the polymerization temperature is 55 °C, and the polymerization time is 4 h; add 70 parts by weight of potassium persulfate for the second polymerization. The weight ratio of vinyl acetate to the second initiator is 1:0.0054; the conditions for the second polymerization include: the polymerization temperature is 90 °C, and the polymerization time is 1 h; cool down to 30 °C, and then add 2 parts by weight of sodium carbonate, 3 parts by weight of defoamer DCA-422, and 2.5 parts by weight of Kathon fungicide; the weight ratio of vinyl acetate to sodium carbonate is 1:0.002; the weight ratio of vinyl acetate to defoamer DCA-422 is 1:0.003; the weight ratio of vinyl acetate to Kathon fungicide is 1:0.0025 to obtain ethylene-vinyl acetate copolymer emulsion B2.

[0108] Example 3

[0109] Step 1. Preparation method of protective colloid:

[0110] S1. Polymerization reaction

[0111] Add 100 parts by weight of vinyl acetate, 3 parts by weight of methanol, 1 part by weight of succinaldehyde and 0.005 part by weight of azobisisobutyronitrile to a reaction kettle for polymerization reaction. The temperature of the polymerization reaction is 64 °C and the time of the polymerization reaction is 8 h;

[0112] Purification:

[0113] Add 300 parts by weight of methanol to the polyvinyl acetate methanol solution in 5 portions, heat up to 70 °C to blow out the unreacted vinyl acetate for purification;

[0114] Alcoholysis:

[0115] Add methanol to the partially purified polyvinyl acetate solution to prepare a new polyvinyl acetate methanol solution. In the new polyvinyl acetate methanol solution, the concentration of polyvinyl acetate is 10 wt%, perform a water bath treatment. The temperature of the water bath is 50 °C and the time of the water bath is 30 min. Add 0.46 part by weight of sodium hydroxide methanol solution (the content of sodium hydroxide is 6.2 wt%) to the solution after the water bath treatment for alcoholysis. The temperature of the alcoholysis is 50 °C and the time of the alcoholysis is 60 min; add 0.035 part by weight of acetic acid to terminate the reaction;

[0116] Separation:

[0117] Use a centrifuge to separate the alcoholyzed polyvinyl alcohol to obtain polyvinyl alcohol pretreatment particles;

[0118] S2. Drying treatment

[0119] Dry the obtained polyvinyl alcohol pretreatment particles. The temperature of the first-stage drying is 70 °C and the time of the first-stage drying is 0.5 h; the temperature of the second-stage drying is 85 °C and the time of the second-stage drying is 1 h; the temperature of the third-stage drying is 110 °C and the time of the third-stage drying is 3.5 h to obtain modified polyvinyl alcohol A3;

[0120] The groups contained in the macromolecular main chain of modified polyvinyl alcohol A3 are -CO-R-CO-; where R is -CH(CH 2 ) 2 CH-.

[0121] Step 2. Prepare ethylene-vinyl acetate copolymer emulsion

[0122] Two gas replacements were carried out with nitrogen at 5 MPa, and one gas replacement was carried out with ethylene at 3 MPa. 1000 parts by weight of vinyl acetate, 105 parts by weight of ethylene, 75 parts by weight of modified polyvinyl alcohol A3, 732 parts by weight of water, and 7 parts by weight of ammonium persulfate solution (2 parts by weight of ammonium persulfate and 98 parts by weight of water) were added for the first polymerization. The weight ratio of vinyl acetate to ethylene was 1:0.105; the weight ratio of vinyl acetate to modified polyvinyl alcohol A3 was 1:0.075; the weight ratio of vinyl acetate to the first initiator was 1:0.00014. The conditions for the first polymerization included: the polymerization temperature was 60 °C, and the polymerization time was 3.5 h. 75 parts by weight of ammonium persulfate was added for the second polymerization. The weight ratio of vinyl acetate to the second initiator was 1:0.0015. The conditions for the second polymerization included: the polymerization temperature was 85 °C, and the polymerization time was 1 h. The temperature was lowered to 30 °C, and then 2.5 parts by weight of sodium acetate, 2 parts by weight of defoamer ZK682, and 1 part by weight of fungicide K12N were added. The weight ratio of vinyl acetate to sodium acetate was 1:0.0025; the weight ratio of vinyl acetate to defoamer ZK682 was 1:0.002; the weight ratio of vinyl acetate to fungicide K12N was 1:0.001, and ethylene-vinyl acetate copolymer emulsion B3 was obtained.

[0123] Example 4

[0124] 100 parts by weight of vinyl acetate, 15 parts by weight of methanol, 1 part by weight of butanedial, 1 part by weight of adipodial, and 0.008 parts by weight of azobisisobutyronitrile were added to the reaction kettle for polymerization reaction. The temperature of the polymerization reaction was 61 °C, and the time of the polymerization reaction was 6 h.

[0125] Purification:

[0126] 280 parts by weight of methanol was added to the polyvinyl acetate methanol solution in 5 portions, and the temperature was raised to 75 °C to blow out the unreacted vinyl acetate for purification.

[0127] Alcoholysis:

[0128] Methanol was added to the partially purified polyvinyl acetate solution to prepare a new polyvinyl acetate methanol solution. In the new polyvinyl acetate methanol solution, the concentration of polyvinyl acetate was 18 wt%. A water bath treatment was carried out. The temperature of the water bath was 50 °C, and the time of the water bath was 30 min. 0.46 parts by weight of sodium hydroxide methanol solution (the content of sodium hydroxide was 6.2 wt%) was added to the solution after the water bath treatment for alcoholysis. The temperature of the alcoholysis was 50 °C, and the time of the alcoholysis was 60 min. 0.035 parts by weight of acetic acid was added to terminate the reaction.

[0129] Separation:

[0130] Use a centrifuge to separate the polyvinyl alcohol after alcoholysis to obtain polyvinyl alcohol pretreatment particles;

[0131] S2. Drying treatment

[0132] Dry the obtained polyvinyl alcohol pretreatment particles. The temperature of the first-stage drying is 75 °C, and the time of the first-stage drying is 1 h; the temperature of the second-stage drying is 85 °C, and the time of the second-stage drying is 1 h; the temperature of the third-stage drying is 110 °C, and the time of the third-stage drying is 1.5 h to obtain modified polyvinyl alcohol A4;

[0133] The group contained in the macromolecular main chain of modified polyvinyl alcohol A4 is -CO-R-CO-; wherein, R is -CH(CH 2 ) 2 CH- and -CH(CH 2 ) 4 CH-.

[0134] Step 2. Prepare ethylene-vinyl acetate copolymer emulsion

[0135] Perform two gas replacements with nitrogen at 5 MPa and one gas replacement with ethylene at 3 MPa. Add 1000 parts by weight of vinyl acetate, 90 parts by weight of ethylene, 110 parts by weight of modified polyvinyl alcohol A4, 759 parts by weight of water, and 7 parts by weight of potassium persulfate solution (5 parts by weight of potassium persulfate and 95 parts by weight of water) for the first polymerization. The weight ratio of vinyl acetate to ethylene is 1:0.09; the weight ratio of vinyl acetate to modified polyvinyl alcohol A4 is 1:0.11; the weight ratio of vinyl acetate to the first initiator is 1:0.00035; the conditions for the first polymerization include: the polymerization temperature is 65 °C, and the polymerization time is 3.5 h; add 78 parts by weight of potassium persulfate for the second polymerization. The weight ratio of vinyl acetate to the second initiator is 1:0.0039; the conditions for the second polymerization include: the polymerization temperature is 88 °C, and the polymerization time is 0.8 h; cool down to 35 °C, and then add 2 parts by weight of sodium hydrogen phosphate, 2.5 parts by weight of defoamer DF-6983, and 2 parts by weight of fungicide K20; the weight ratio of vinyl acetate to sodium hydrogen phosphate is 1:0.002; the weight ratio of vinyl acetate to defoamer DF-6983 is 1:0.0025; the weight ratio of vinyl acetate to fungicide K20 is 1:0.002 to obtain ethylene-vinyl acetate copolymer emulsion B4.

[0136] Example 5

[0137] Step 1. In the manner of Example 1.

[0138] Step 2: In the same manner as in Example 1, except that "adding 1000 parts by weight of vinyl acetate, 120 parts by weight of ethylene, and 50 parts by weight of modified polyvinyl alcohol A1" is used to replace "adding 1000 parts by weight of vinyl acetate, 120 parts by weight of ethylene, and 90 parts by weight of modified polyvinyl alcohol A1" to obtain ethylene-vinyl acetate copolymer emulsion B5.

[0139] Example 6

[0140] Step 1: In the same manner as in Example 1.

[0141] Step 2: In the same manner as in Example 1, except that nitrogen at 5 MPa is used for gas replacement twice and ethylene at 3 MPa is used for gas replacement once, and 1000 parts by weight of vinyl acetate, 120 parts by weight of ethylene, 90 parts by weight of modified polyvinyl alcohol A1, 770 parts by weight of water, and 85 parts by weight of potassium persulfate solution (6 parts by weight of potassium persulfate and 94 parts by weight of water) are added for polymerization. The weight ratio of vinyl acetate to ethylene is 1:0.12; the weight ratio of vinyl acetate to modified polyvinyl alcohol is 1:0.09; the weight ratio of vinyl acetate to initiator is 1:0.0051. The polymerization conditions include: the polymerization temperature is 88 °C and the polymerization time is 4.5 h. After cooling to 25 °C, 2 parts by weight of sodium bicarbonate, 1.6 parts by weight of defoamer 4201A, and 3 parts by weight of fungicide FF-02 are added. The weight ratio of vinyl acetate to sodium bicarbonate is 1:0.002; the weight ratio of vinyl acetate to defoamer 4201A is 1:0.0016; the weight ratio of vinyl acetate to fungicide FF-02 is 1:0.003 to obtain ethylene-vinyl acetate copolymer emulsion B6.

[0142] Comparative Example 1

[0143] Step 1: Conventional commercially available PVA1788 is used as protective colloid D1.

[0144] Step 2

[0145] Two gas replacements were carried out with nitrogen at 5 MPa, and one gas replacement was carried out with ethylene at 3 MPa. 1000 parts by weight of vinyl acetate A1, 120 parts by weight of ethylene, 90 parts by weight of modified polyvinyl alcohol D1, 770 parts by weight of water, and 5 parts by weight of potassium persulfate solution (6 parts by weight of potassium persulfate and 94 parts by weight of water) were added for the first polymerization. The weight ratio of vinyl acetate to ethylene was 1:0.12; the weight ratio of vinyl acetate to modified polyvinyl alcohol was 1:0.09; the weight ratio of vinyl acetate to the first initiator was 1:0.0003. The conditions for the first polymerization included: the polymerization temperature was 65 °C, and the polymerization time was 3 h. 80 parts by weight of potassium persulfate was added for the second polymerization. The weight ratio of vinyl acetate to the second initiator was 1:0.0048. The conditions for the second polymerization included: the polymerization temperature was 88 °C, and the polymerization time was 1.5 h. The temperature was lowered to 25 °C, and then 2 parts by weight of sodium bicarbonate, 1.6 parts by weight of defoamer DF-692, and 3 parts by weight of fungicide FF-02 were added. The weight ratio of vinyl acetate to sodium bicarbonate was 1:0.002; the weight ratio of vinyl acetate to defoamer DF-692 was 1:0.0016; the weight ratio of vinyl acetate to fungicide FF-02 was 1:0.003, and ethylene-vinyl acetate copolymer emulsion DA1 was obtained.

[0146] The modified polyvinyl alcohol obtained in the examples and the polyvinyl alcohol in the comparative examples were tested, and the results are shown in Table 1. The obtained emulsions were tested, and the results are shown in Table 2.

[0147] Table 1

[0148]

[0149] Table 2

[0150] Weight-average molecular weight (ten thousand g / mol) Particle size distribution (μm) B1 63.7 0.18-5.6 B2 56.6 0.2-6.5 B3 52.5 0.15-8 B4 51.1 0.11-7.6 B5 46.8 0.05-10.2 B6 44.1 0.03-9.8 DB1 40.9 0.04-13.1

[0151] Preparation Example 1

[0152] 25 g of ethylene-vinyl acetate copolymer emulsion B1 was coated on a 300×400 mm film applicator, and the excess emulsion was scraped off from the film applicator with a stainless steel sheet. The film was dried for 72 h under the conditions of a temperature of 25 ± 0.5 °C and a humidity of 50 ± 10%, and ethylene-vinyl acetate copolymer emulsion film C1 with a thickness of 0.8 mm was obtained.

[0153] Preparation Examples C2 - C6 and Preparation Example DC1 were all carried out in the same manner as Preparation Example C1, and the thicknesses of the obtained emulsion films were all 0.8 mm. The results of the tensile strength are shown in Table 3.

[0154] Table 3

[0155] Tensile strength (MPa) C1 7.13 C2 6.58 C3 5.63 C4 5.49 C5 5.15 C6 4.56 DC1 4.01

[0156] It can be seen from the results in Table 1, Table 2 and Table 3 that the ethylene-vinyl acetate copolymer emulsion prepared by the preparation method of the present invention has good uniformity, and the tensile strength of the emulsion film prepared by using this emulsion is high.

[0157] Furthermore, by comparing Example 1 with Example 6, it can be known that by using the stepwise polymerization method, the uniformity of the prepared emulsion is better, the tensile strength is greater, and the performance of the film is more excellent.

[0158] By comparing Example 1 with Comparative Example 1, it can be known that the specific protective colloid of the present invention can make the prepared emulsion have a uniform distribution (the absolute value of the particle size distribution range is small), and the tensile strength of the emulsion film prepared by using this emulsion is high; by comparing Example 1 with Example 5, it can be known that the dosage of the vinyl acetate protective colloid further affects its particle size distribution.

[0159] 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 technical concept 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 acetate copolymer emulsion, characterized in that, the preparation method includes polymerizing vinyl acetate, ethylene, protective colloid, and initiator, and then adding a pH regulator, defoamer, and bactericide to obtain ethylene-vinyl acetate copolymer emulsion; wherein, the protective colloid is modified polyvinyl alcohol, and in the macromolecular main chain of the modified polyvinyl alcohol, there are C=C structures, C=C-C=C structures, and C=C-C=C-C=C structures.

2. According to the preparation method described in claim 1, wherein, the polymerization degree of the modified polyvinyl alcohol is 1000-2500, preferably 1100-2400; and / or, containing the group -CO-R-CO- in the macromolecular main chain; wherein, R is selected from -CH(CH 2 ) 2 CH-, -CH(CH 2 ) 3 CH- and -CH(CH 2 ) 4 CH-, at least one of them; and / or, the alcoholysis degree of the polyvinyl alcohol is 85-95%, preferably 86-90%; and / or, for the polyvinyl alcohol, the ultraviolet absorption value at 215nm is 0.05-0.25, the ultraviolet absorption value at 280nm is 0.1-0.4, and the ultraviolet absorption value at 320nm is 0.08-0.35; preferably, the ultraviolet absorption value of the polyvinyl alcohol at 215nm is 0.06-0.22, the ultraviolet absorption value at 280nm is 0.12-0.36, and the ultraviolet absorption value at 320nm is 0.1-0.32; and / or, at 90℃, the modified polyvinyl alcohol is configured into a 4wt% aqueous solution of polyvinyl alcohol, and the viscosity of the 4wt% aqueous solution of polyvinyl alcohol is 10-60mPa·s, preferably 13-50mPa·s.

3. According to the preparation method described in claim 1 or 2, wherein, the pressure of ethylene is 2-6MPa, preferably 3-5MPa; preferably, in the preparation method, the specific steps of adding an initiator for the polymerization reaction include: adding a first initiator for the first polymerization, and adding a second initiator for the second polymerization; preferably, the conditions for the first polymerization include: the polymerization temperature is 50-70℃, preferably 55-65℃; the polymerization time is 1-4h, preferably 2-3h; preferably, the conditions for the second polymerization include: the polymerization temperature is 75-90℃, preferably 80-88℃; the polymerization time is 1-5h, preferably 2-4h.

4. According to the preparation method described in claim 3, wherein, the weight ratio of vinyl acetate to ethylene is 1:0.05-0.15, preferably 1:0.07-0.12; and / or, the weight ratio of vinyl acetate to the protective colloid is 1:0.05-0.2, preferably 1:0.07-0.15; and / or, the weight ratio of vinyl acetate to the first initiator is 1:0.0001-0.0018, preferably 1:0.0003-0.0015; and / or, the weight ratio of vinyl acetate to the second initiator is 1:0.0014-0.007, preferably 1:0.0018-0.006; and / or, the weight ratio of vinyl acetate to the pH regulator is 1:0.0008-0.03, preferably 1:0.001-0.02; And / or, the weight ratio of the vinyl acetate to the defoamer is 1:0.0012 - 0.0036, preferably 1:0.0016 - 0.003; And / or, the weight ratio of the vinyl acetate to the bactericide is 1:0.001 - 0.004, preferably 1:0.0015 - 0.0035.

5. The preparation method according to claim 3 or 4, wherein, The first initiator and the second initiator are each independently selected from thermal decomposition initiators and / or redox initiators; Preferably, the thermal decomposition initiator is selected from potassium persulfate and / or ammonium persulfate; Preferably, the redox initiator is selected from tartrate-hydrogen peroxide and / or persulfate-bisulfite; Preferably, the first initiator and the second initiator are each independently selected from potassium persulfate and / or tartrate-hydrogen peroxide.

6. The preparation method according to any one of claims 1 - 5, wherein, The pH regulator is selected from at least one of sodium bicarbonate, potassium bicarbonate, sodium acetate, sodium carbonate, potassium hydrogen phosphate and sodium dihydrogen phosphate, preferably sodium carbonate and / or sodium bicarbonate; Preferably, the defoamer is selected from silicone oil defoamers and / or mineral oil defoamers, preferably silicone oil defoamers; Preferably, the bactericide is selected from 1,2-benzisothiazolin-3-one bactericides and / or Kathon bactericides, preferably Kathon bactericides.

7. An ethylene-vinyl acetate copolymer emulsion prepared by the preparation method according to any one of claims 1 - 6.

8. The ethylene-vinyl acetate copolymer emulsion according to claim 7, wherein, The ethylene-vinyl acetate copolymer emulsion contains an ethylene-vinyl acetate copolymer.

9. The ethylene-vinyl acetate copolymer emulsion according to claim 7 or 8, wherein, The weight-average molecular weight of the ethylene-vinyl acetate copolymer is 450,000 - 750,000 g / mol, preferably 480,000 - 650,000 g / mol; Preferably, the particle size distribution of the ethylene-vinyl acetate copolymer emulsion is 0.04 - 10 μm, preferably 0.1 - 8 μm.

10. The application of the ethylene-vinyl acetate copolymer emulsion according to any one of claims 7 - 9 in the field of membranes.

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