Vinyl acetate copolymer emulsions, methods of making and using the same

Abstract

This invention relates to the field of vinyl acetate technology, and discloses a vinyl acetate copolymer emulsion, its preparation method and application. The method includes: (1) mixing a first vinyl acetate, a first polyvinyl alcohol, a reactive emulsifier, a reducing agent and water in the presence of ethylene, and then adding a first initiator to carry out a first reaction; (2) mixing the reaction product of step (1), a second polyvinyl alcohol and a second vinyl acetate, adjusting the pH to 4-5, and then adding a second initiator to carry out a second reaction to obtain a vinyl acetate copolymer emulsion; wherein, in step (1), based on 100 parts by weight of the first vinyl acetate, the first polyvinyl alcohol is 2-5 parts by weight, and the reactive emulsifier is 0.1-1 parts by weight; in step (2), the apparent viscosity of a 4 wt% aqueous solution of the second polyvinyl alcohol at 20°C is 2-8 mPa·s; after the vinyl acetate copolymer emulsion is mixed with an alcohol solvent, the vinyl acetate copolymer emulsion can still remain stable.

Description

Technical Field

[0001] This invention relates to the field of vinyl acetate technology, specifically to a vinyl acetate copolymer emulsion, its preparation method, and its application. Background Technology

[0002] Packaging printing enhances the appearance of products. Lamination of paper products with paper products, paper products with plastic film, and plastic printed materials with plastic film is widely used in book covers, shopping bags, product packaging, outdoor advertising, wine boxes, and flexible food packaging. Adhesives used in packaging lamination require good coating wettability, high bonding strength, good transparency, and the absence of bubbling, yellowing, and wrinkling.

[0003] Vinyl acetate-ethylene copolymer emulsion (VAE) is a water-based, environmentally friendly product with high cost-effectiveness and a wide range of applications, maintaining rapid growth for many years. Packaging is an important application area for VAE emulsions, and improving the drying speed and tack strength of the emulsion is a goal pursued by many technical personnel.

[0004] Increasing the solids content is one of the technical methods to improve the drying speed of emulsions. Wu Huijiang (“Development of High Solids Content Vinyl Acetate-Ethylene Copolymer Emulsion”, Wu Huijiang, Adhesion, 2003, No. 4, pp. 15-17) disclosed a method for preparing a vinyl acetate-ethylene copolymer emulsion with a solids content of around 60%. This product has high solids content, low viscosity, good flexibility, and significantly improved initial tack, fast drying speed, and water resistance compared to conventional products. Liu Bingpo (“New VAE Emulsion and Its Application in Adhesives”, Liu Bingpo, China Adhesives, 2003, No. 7, pp. 24-26) disclosed the development of a new variety of VAE emulsion using a continuous polymerization process in a high-pressure ring reactor. By adjusting the type and amount of protective colloid based on ordinary VAE models and using a novel redox initiation system, a VAE emulsion with a solids content of 65% was produced. The product exhibits excellent adhesive strength and drying speed. Liu Hongwei (“Preparation of High Solids Content Polyvinyl Acetate Emulsion by Seed Method”, Liu Hongwei, Polymer Materials Science and Engineering, 2008, No. 3) disclosed a method for synthesizing polyvinyl acetate emulsion with a solids content of not less than 60% using a semi-finished VAE emulsion as a seed, employing an oxidation-reduction initiation system and a semi-continuous emulsion polymerization process. The product's curing speed and initial tack are far superior to conventional polyvinyl acetate emulsions. Other methods can also improve the drying speed of the emulsion. CN115785777A discloses a method for preparing a low-temperature fast-drying waterproof coating. This invention includes a component A liquid and a component B powder. The component A liquid includes an acrylic-modified alkyd resin emulsion, an alkyd resin drier, and a naphthenic acid aqueous solution; the component B powder includes aluminoferrite cement and a photocatalyst. This invention's technical solution can achieve rapid drying of the coating film even in low-temperature and high-humidity environments without affecting subsequent construction. CN115703945A discloses a method for preparing an adhesive coating based on demulsification-induced rapid curing technology. This invention includes steps such as substrate treatment, emulsion preparation, demulsification-induced rapid curing technology to prepare a polymer coating, and coating adhesion. In VAE applications, some users add low-boiling-point solvents to the emulsion to improve the bonding speed and strength of the product. However, environmentally friendly low-boiling-point alcohol solvents such as ethanol can cause emulsion gelation when added directly, and therefore need to be mixed with water or other solvents before addition. This makes it difficult to manufacture adhesives with high alcohol solvent content.

[0005] In summary, my country's main methods for addressing the rapid drying of emulsions include increasing the solid content, demulsification, and adding solvents. While increasing the solid content can improve the drying speed, it is rarely used in packaging applications because it doesn't improve the wettability of the emulsion with low surface tension substrates. Adding solvents is also less common due to environmental restrictions on common solvents and the insufficient amount of low-boiling-point alcohols added, which often fails to achieve the desired drying speed. Other techniques, such as demulsification, are also limited in use due to their inherent limitations. Summary of the Invention

[0006] The purpose of this invention is to overcome the problem of emulsion gelation caused by adding alcohol solvents to vinyl acetate-ethylene copolymer emulsions in the prior art, and to provide a vinyl acetate copolymer emulsion, its preparation method and application, wherein the vinyl acetate copolymer emulsion can remain stable after being mixed with alcohol solvents.

[0007] To achieve the above objectives, a first aspect of the present invention provides a method for preparing a vinyl acetate copolymer emulsion, wherein the method includes:

[0008] (1) In the presence of ethylene, the first vinyl acetate, the first polyvinyl alcohol, the reactive emulsifier, the reducing agent and water are mixed and then the first initiator is added to carry out the first reaction;

[0009] (2) After mixing the reaction product of step (1), the second polyvinyl alcohol and the second vinyl acetate, the pH is adjusted to 4-5, and the second initiator is added to carry out the second reaction to obtain the vinyl acetate copolymer emulsion.

[0010] In step (1), based on 100 parts by weight of the first vinyl acetate, the first polyvinyl alcohol is 2-5 parts by weight, and the reactive emulsifier is 0.1-1 parts by weight.

[0011] In step (2), the apparent viscosity of the 4 wt% aqueous solution of the second polyvinyl alcohol at 20°C is 2-8 mPa·s.

[0012] A second aspect of the present invention provides a vinyl acetate copolymer emulsion prepared by the above method.

[0013] A third aspect of the present invention provides an application of the above-mentioned vinyl acetate copolymer emulsion as an adhesive.

[0014] Through the above technical solutions, the vinyl acetate copolymer emulsion, its preparation method, and its application provided by the present invention have the following beneficial effects:

[0015] This invention employs a reactive emulsifier to carry out a first reaction with vinyl acetate and ethylene. The resulting reaction product then undergoes a second reaction with polyvinyl alcohol and vinyl acetate of a specific viscosity, thereby obtaining a vinyl acetate copolymer with a high polyvinyl alcohol graft content. Under the combined action of the reactive emulsifier, the stability of the vinyl acetate-ethylene copolymer after mixing with alcohol solvents is improved. Detailed Implementation

[0016] 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.

[0017] In this invention, unless otherwise specified, "first" and "second" do not indicate a sequence, but are only used to distinguish that they are not the same material or step. For example, in "first initiator" and "second initiator", "first" and "second" are only used to indicate that they are initiators that are not in the same step.

[0018] The first aspect of this invention provides a method for preparing a vinyl acetate copolymer emulsion, wherein the method includes:

[0019] (1) In the presence of ethylene, the first vinyl acetate, the first polyvinyl alcohol, the reactive emulsifier, the reducing agent and water are mixed and then the first initiator is added to carry out the first reaction;

[0020] (2) After mixing the reaction product of step (1), the second polyvinyl alcohol and the second vinyl acetate, the pH is adjusted to 4-5, and the second initiator is added to carry out the second reaction to obtain the vinyl acetate copolymer emulsion.

[0021] In step (1), based on 100 parts by weight of the first vinyl acetate, the first polyvinyl alcohol is 2-5 parts by weight, and the reactive emulsifier is 0.1-1 parts by weight.

[0022] In step (2), the apparent viscosity of the 4 wt% aqueous solution of the second polyvinyl alcohol at 20°C is 2-8 mPa·s.

[0023] This invention employs a reactive emulsifier to carry out a first reaction with vinyl acetate and ethylene. The resulting reaction product then undergoes a second reaction with polyvinyl alcohol and vinyl acetate of a specific viscosity, thereby obtaining a vinyl acetate copolymer with a high polyvinyl alcohol graft content. Under the combined action of the reactive emulsifier, the stability of the vinyl acetate-ethylene copolymer after mixing with alcohol solvents is improved.

[0024] In this invention, there are no particular limitations on the method for adjusting the pH of the reaction system; for example, a pH adjuster can be used. In this invention, the pH adjuster is an aqueous solution of sodium hydroxide and / or an aqueous solution of sodium bicarbonate, preferably an aqueous solution of sodium hydroxide. Preferably, the concentration of the pH adjuster is 5-15 wt%.

[0025] In this invention, the weight parts and the parts can be grams or kilograms; for example, 1 weight part can represent 1 gram or 1 kilogram; 1 part can be 1 gram or 1 kilogram.

[0026] Further, in step (1), based on 100 parts by weight of the first vinyl acetate, the first polyvinyl alcohol is 3.2-4.5 parts by weight, and the reactive emulsifier is 0.2-0.8 parts by weight. When the amounts of the first vinyl acetate, the first polyvinyl alcohol, and the reactive emulsifier meet the above ranges, the first vinyl acetate, ethylene, and the reactive emulsifier react to generate a vinyl acetate copolymer; the first polyvinyl alcohol plays a role in improving the stability of the emulsion during the reaction process, but because the amount of the first polyvinyl alcohol is relatively small compared to the first vinyl acetate and its reactivity is poor, the first polyvinyl alcohol is not easy to react with the first vinyl acetate.

[0027] In this invention, there is no special limitation on the amount of water used in step (1), and it can be added and adjusted according to the conventional dosage in the art. For example, based on 100 parts by weight of vinyl acetate, the amount of water added is 50-65 parts by weight.

[0028] According to the present invention, in step (1), the amount of ethylene introduced is such that the pressure of the first reaction is 3-7 MPa.

[0029] According to the present invention, in step (1), the reducing agent is 0.1-0.4 parts by weight, based on 100 parts by weight of vinyl acetate.

[0030] Further, in step (1), based on 100 parts by weight of vinyl acetate, the reducing agent is 0.1-0.3 parts by weight.

[0031] According to the present invention, in step (1), based on 100 parts by weight of the first vinyl acetate, the first initiator is 0.05-0.5 parts by weight.

[0032] Further, in step (1), based on 100 parts by weight of vinyl acetate, the reducing agent is 0.1-0.4 parts by weight.

[0033] According to the present invention, in step (1), the temperature of the first reaction is 50-82°C.

[0034] Furthermore, in step (1), the temperature of the first reaction is 78-82℃.

[0035] According to the present invention, the reducing agent is selected from at least one of ascorbic acid, sodium isoascorbate, zinc formaldehyde sulfoxylate, and sodium formaldehyde sulfoxylate.

[0036] According to the present invention, the reactive emulsifier is an emulsifier containing carbon-carbon double bonds.

[0037] Furthermore, the reactive emulsifier is selected from at least one of sodium vinyl sulfonate, allyl polyether, and allyloxynonylphenol sulfonate.

[0038] According to the present invention, the first initiator is selected from at least one of hydrogen peroxide, potassium persulfate and tert-butyl hydroperoxide.

[0039] Furthermore, the first initiator is hydrogen peroxide.

[0040] According to the present invention, the addition rate of the first initiator is 0.15-0.3 parts / min.

[0041] Furthermore, the addition rate of the first initiator is 0.2-0.25 parts / min.

[0042] In this invention, the apparent viscosity of a 4 wt% aqueous solution of the first polyvinyl alcohol at 20°C is 2-30 mPa·s.

[0043] In this invention, the degree of alcoholysis of the first polyvinyl alcohol is 85-89%.

[0044] In this invention, the first polyvinyl alcohol can be commercially available, and for example, it can be at least one selected from polyvinyl alcohol 0388, polyvinyl alcohol 0488, polyvinyl alcohol 0588, polyvinyl alcohol 1788, and polyvinyl alcohol 2088. Preferably, the first polyvinyl alcohol is polyvinyl alcohol 0588 and polyvinyl alcohol 1788. Preferably, the mass ratio of polyvinyl alcohol 0588 to polyvinyl alcohol 1788 is 1:4-6.

[0045] In this invention, the first polyvinyl alcohol is added to the reaction system in the form of an aqueous solution of polyvinyl alcohol. The concentration of the first aqueous solution of polyvinyl alcohol is not particularly limited in this invention, and those skilled in the art can adjust the concentration of the aqueous solution of polyvinyl alcohol according to the reaction conditions. Preferably, the concentration of the first aqueous solution of polyvinyl alcohol is 7-13 wt%.

[0046] In this invention, the method for preparing vinyl acetate copolymer further includes: removing ethylene from the product after the first reaction. Preferably, the ethylene is removed from the product after the first reaction in a degassing tank.

[0047] According to a preferred embodiment of the present invention, step (1) includes: in the presence of ethylene, mixing first vinyl acetate A, first polyvinyl alcohol, emulsifier and water, heating to 50-60°C, and pressurizing to 3.8-4.3 MPa, adding first initiator, and when heating to 75-85°C and pressurizing to 6-6.5 MPa, adding first vinyl acetate B, stopping the introduction of ethylene gas, and when the pressure is less than or equal to 1.5 MPa, the reaction ends.

[0048] According to a preferred embodiment of the present invention, the amount of the first vinyl acetate A is 30-70 wt%, based on the total mass of the first vinyl acetate.

[0049] According to a preferred embodiment of the present invention, the addition rate of the first initiator is 0.15-0.3 parts / min.

[0050] According to a preferred embodiment of the present invention, the addition rate of the first vinyl acetate B is 0.2-0.6 parts / min.

[0051] Further, in step (2), the apparent viscosity of the 4wt% aqueous solution of the second polyvinyl alcohol at 20°C is 3-6 mPa·s.

[0052] According to the present invention, the degree of alcoholysis of the second polyvinyl alcohol is 85-89%.

[0053] In this invention, when the degree of hydrolysis of the second polyvinyl alcohol meets the above-mentioned range, it is easy to form a graft with vinyl acetate, and the graft is easily adsorbed onto the surface of the latex particles, making the latex particles more stable.

[0054] Furthermore, the degree of alcoholysis of the second polyvinyl alcohol is 86-88.5%.

[0055] In this invention, the second polyvinyl alcohol can be commercially available, for example, at least one of polyvinyl alcohol 0388, polyvinyl alcohol 0488 and polyvinyl alcohol 0588 can be selected.

[0056] In this invention, the second polyvinyl alcohol is added to the reaction system in the form of an aqueous solution of polyvinyl alcohol. The concentration of the aqueous solution of polyvinyl alcohol is not particularly limited in this invention, and those skilled in the art can adjust the concentration of the aqueous solution of polyvinyl alcohol according to the reaction conditions. Preferably, the concentration of the second aqueous solution of polyvinyl alcohol is 17-23 wt%.

[0057] According to the present invention, the second initiator is selected from at least one of hydrogen peroxide, potassium persulfate and tert-butyl hydroperoxide.

[0058] Furthermore, the second initiator is potassium persulfate.

[0059] In this invention, the second initiator is added to the reaction system in the form of an aqueous initiator solution. The concentration of the aqueous initiator solution is not particularly limited in this invention, and those skilled in the art can adjust the concentration according to the reaction conditions. Preferably, the concentration of the aqueous initiator solution is 3-5 wt%.

[0060] According to the present invention, the temperature of the second reaction is 55-85°C.

[0061] Furthermore, the temperature of the second reaction is 78-82°C.

[0062] According to the present invention, in step (2), based on 100 parts by weight of the first vinyl acetate, the amount of the second polyvinyl alcohol is 0.3-1.5 parts by weight, the amount of the second vinyl acetate is 4-5.5 parts by weight, and the amount of the second initiator is 0.05-0.3 parts by weight.

[0063] In this invention, when the amounts of the second polyvinyl alcohol, the second vinyl acetate, and the second initiator meet the above-mentioned ranges, the resulting vinyl acetate copolymer emulsion exhibits higher stability after being mixed with ethanol.

[0064] Further, in step (2), based on 100 parts by weight of the first vinyl acetate, the amount of the second polyvinyl alcohol is 0.5-1 parts by weight, the amount of the second vinyl acetate is 4.5-5 parts by weight, and the amount of the second initiator is 0.1-0.25 parts by weight.

[0065] According to a preferred embodiment of the present invention, based on 100 parts by weight of the first vinyl acetate, the amount of the second polyvinyl alcohol is 0.6-0.9 parts by weight, the amount of the second vinyl acetate is 5.7-5 parts by weight, and the amount of the second initiator is 0.15-0.25 parts by weight.

[0066] According to a preferred embodiment of the present invention, step (2) includes: mixing the reaction product of step (1) and the second polyvinyl alcohol, adjusting the pH to 4-5, adding the second initiator A, and then adding the second vinyl acetate and the second initiator B to carry out the second reaction.

[0067] In this invention, the second initiator A is added first to increase the concentration of free radicals generated by the initiator in the reaction system. These free radicals produce α-hydrogen opposite the acetyl group on the polyvinyl alcohol molecular chain, generating a large number of active sites, which facilitates the subsequent grafting reaction of the second vinyl acetate and the second initiator B on these active sites.

[0068] According to a preferred embodiment of the present invention, the amount of the second initiator A is 40-85 wt%, based on the total mass of the second initiator.

[0069] According to the present invention, the addition rate of the second vinyl acetate is 0.04-0.1 parts / min.

[0070] In this invention, when the addition rate of the second vinyl acetate meets the above-mentioned range, the obtained vinyl acetate copolymer emulsion has better stability.

[0071] Furthermore, the addition rate of the second vinyl acetate is 0.04-0.07 parts / min.

[0072] According to the present invention, the addition rate of the second initiator B is 0.003-0.1 parts / min.

[0073] A second aspect of the present invention provides a vinyl acetate copolymer emulsion prepared by the above method.

[0074] According to the present invention, the apparent viscosity of the vinyl acetate copolymer emulsion at 25±0.1℃ is 400-1000 mPa·s.

[0075] Furthermore, the apparent viscosity of the vinyl acetate copolymer emulsion at 25±0.1℃ is 500-900 mPa·s.

[0076] In this invention, the graft content of the vinyl acetate copolymer emulsion is 50-65 wt%.

[0077] In this invention, the graft content of the vinyl acetate copolymer emulsion refers to the mass content of the vinyl acetate copolymer emulsion (based on dry solids content) that is insoluble in acetone and water. Specifically, acetone and water can extract unreacted monomers, reducing agents, initiators, and oligomers from the vinyl acetate copolymer emulsion. When the graft content of the vinyl acetate copolymer emulsion meets the above-mentioned range, the vinyl acetate copolymer emulsion exhibits higher stability after being mixed with alcohol solvents.

[0078] Furthermore, the graft content of the vinyl acetate copolymer emulsion is 55-60 wt%.

[0079] A third aspect of the present invention provides an application of the above-mentioned vinyl acetate copolymer emulsion as an adhesive.

[0080] The present invention will be described in detail below through embodiments.

[0081] In the following examples and comparative examples, parts by weight and parts refer to grams.

[0082] Solid content of vinyl acetate copolymer emulsion: tested according to the test methods of the corresponding indicators in the national standard GB / T27573-2011 Vinyl acetate-ethylene copolymer emulsion.

[0083] The apparent viscosity of the vinyl acetate copolymer emulsion at 25±0.1℃ was tested according to the viscosity test method in the national standard GB / T27573-2011 Vinyl acetate-ethylene copolymer emulsion. The test temperature was 25±0.1℃, the instrument model was Brookfield LVDV-II+, the rotor model was No. 3 shaft, and the speed was 60 rpm.

[0084] Test method for compatibility of vinyl acetate copolymer emulsion with ethanol: Weigh 200g of vinyl acetate copolymer emulsion and add it to a 500mL glass bottle. While stirring, add 200g of anhydrous ethanol to the empty bottle and stir evenly to obtain the emulsion sample with a vinyl acetate copolymer emulsion:ethanol ratio of 1:1. Then, store the emulsion sample in a 50℃ constant temperature drying oven for 7 days and observe the change in emulsion viscosity. A viscosity change within 15% and no precipitation or flocculation in the emulsion are considered acceptable.

[0085] Calculate the viscosity change rate according to Formula 1; the viscosity change is considered acceptable if it is within 15% and the emulsion does not show any precipitation or flocculation.

[0086]

[0087] Graft content: The vinyl acetate copolymer emulsion was formed into a thin film on a glass plate using a 400 μm film-forming device. The film was then dried at room temperature until transparent to obtain the emulsion membrane. 1.5 g of the emulsion membrane was placed in a pre-weighed 100 mL beaker (m1) with folded filter paper and dried in an oven at 105 °C until constant weight (approximately 5 h). The mass of the beaker, filter paper, and dried membrane was recorded as m2. The dried emulsion membrane and filter paper were placed together in a Soxhlet extractor. 200 mL of acetone reagent was added to a 500 mL dry ground glass flask. The extraction apparatus was installed, and extraction was performed in an 80 °C water bath for 24 h. After 24 h of extraction, the emulsion membrane and filter paper were removed together, placed in a beaker, and dried in an oven at 105 °C until constant weight (approximately 5 h). The dried membrane and filter paper after acetone extraction were placed in a Soxhlet extractor, and 200 mL of pure water was added to a 500 mL dry ground glass flask. The extract was carried out in an oil bath at 120 °C for 24 h. The emulsion membrane and filter paper after 24 h of extraction were taken out together and placed in a beaker. The beaker was dried in an oven at 105 °C until constant weight (about 5 h). The mass of the beaker, filter paper and the dried membrane after the second extraction was recorded as m3. The content of grafted material in the latex particles was calculated according to formula (2).

[0088]

[0089] Where m1 is the mass (g) of the beaker and filter paper; m2 is the mass (g) of the beaker, filter paper, and dry film; m3 is the mass (g) of the beaker, filter paper, and the dry film after acetone extraction followed by pure water extraction. Apparent viscosity of polyvinyl alcohol: A 4wt% aqueous solution of polyvinyl alcohol was prepared and tested using a Brookfield viscometer with rotor #0 at 20°C.

[0090] The apparent viscosity of polyvinyl alcohol 0588 is 5 mPa·s, and the degree of alcoholysis is 87%.

[0091] The apparent viscosity of polyvinyl alcohol 1788 is 22 mPa·s, and the degree of alcoholysis is 87%.

[0092] The apparent viscosity of polyvinyl alcohol 0388 is 3.5 mPa·s, and the degree of alcoholysis is 87%.

[0093] The apparent viscosity of polyvinyl alcohol 0488 is 4.5 mPa·s, and the degree of alcoholysis is 87%.

[0094] Example 1

[0095] (1) After purging the reactor with nitrogen three times, add water and the first polyvinyl alcohol aqueous solution (the mass ratio of polyvinyl alcohol 0588 to polyvinyl alcohol 1788 is 1:5, and the concentration is 10wt%) to the reactor, start the stirrer, and add water, emulsifier sodium vinyl sulfonate (SVS), sodium isoascorbate in sequence, and finally add the first vinyl acetate A as the initial monomer (based on the total mass of the first vinyl acetate, the amount of the first vinyl acetate A is 67.2wt%).

[0096] After mixing, ethylene is introduced to bring the pressure to 4.0 MPa and the temperature to 58°C. Then, the first initiator (1.8 wt% hydrogen peroxide, with an addition rate of 0.2 parts / min) is added.

[0097] When the temperature of the reactants rises to 80°C, the ethylene pressure is simultaneously increased to 6 MPa, and then first vinyl acetate B is added (the addition rate of first vinyl acetate B is 0.3 parts / min); during the addition of first vinyl acetate B, the ethylene pressure is maintained at 6 MPa.

[0098] Based on 100 parts by weight of the first vinyl acetate, the first polyvinyl alcohol is 3.9 parts by weight, the reactive emulsifier is 0.2 parts by weight, the reducing agent is 0.1 parts by weight, and the first initiator is 0.1 parts by weight.

[0099] After the second vinyl acetate B is added, the ethylene feed switch is turned off, and the reaction temperature is maintained at 80°C. When the ethylene pressure is lower than 1.5 MPa, the reaction ends. The ethylene in the reaction product is removed through a degassing tank.

[0100] (2) Under stirring conditions, the second polyvinyl alcohol aqueous solution (20 wt% polyvinyl alcohol 0388 aqueous solution) is mixed evenly with the reaction product of step 1, and the pH is adjusted to 4 by sodium hydroxide solution (10 wt%).

[0101] At 80°C, after adding the second initiator A (4 wt% potassium persulfate aqueous solution) and stirring for 20 min, the second vinyl acetate and the second initiator B (the addition rate of the second vinyl acetate was 0.06 parts / min and the addition rate of the second initiator B was 0.004 parts / min) were added. The amount of the second initiator A was 83.3 wt% based on the total mass of the second initiator.

[0102] After vinyl acetate is added, the remaining second initiator B is quickly added to the degassing tank, and the reaction is carried out at 80°C for 30 minutes under stirring conditions.

[0103] Based on 100 parts by weight of the first vinyl acetate, the amount of the second polyvinyl alcohol is 0.6 parts by weight, the amount of the second vinyl acetate is 4.8 parts by weight, and the amount of the second initiator is 0.12 parts by weight.

[0104] After the heat preservation reaction was completed, the mixture was cooled, filtered, and discharged to obtain a vinyl acetate copolymer emulsion. The test results of the vinyl acetate copolymer emulsion are shown in Table 1.

[0105] Example 2

[0106] (1) Replace the reactor with nitrogen three times, then add water and the first polyvinyl alcohol aqueous solution (the mass ratio of polyvinyl alcohol 0588 to polyvinyl alcohol 1788 is 1:5, and the concentration is 10wt%) to the reactor, start the stirrer, and add water, emulsifier allyl polyether (AE-100), ascorbic acid in sequence, and finally add the first vinyl acetate A as the initial monomer (based on the total mass of the first vinyl acetate, the amount of the first vinyl acetate A is 30wt%).

[0107] After mixing, ethylene is introduced to bring the pressure to 3.8 MPa and the temperature to 50°C. Then, the first initiator (1.8 wt% hydrogen peroxide, with an addition rate of 0.2 parts / min) is added.

[0108] When the temperature of the reactants rises to 80°C, the ethylene pressure is simultaneously increased to 6.2 MPa, and first vinyl acetate B is added (the addition rate of first vinyl acetate B is 0.6 parts / min); during the addition of first vinyl acetate B, the ethylene pressure is maintained at 6.2 MPa;

[0109] Based on 100 parts by weight of vinyl acetate, the first polyvinyl alcohol is 4.3 parts by weight, the reactive emulsifier is 0.8 parts by weight, the reducing agent is 0.3 parts by weight, and the first initiator is 0.1 parts by weight.

[0110] After the second vinyl acetate B is added, the ethylene feed switch is turned off, and the reaction temperature is maintained at 80°C. When the ethylene pressure is lower than 1.5 MPa, the reaction ends. The ethylene in the reaction product is removed through a degassing tank.

[0111] (2) Under stirring conditions, the second polyvinyl alcohol aqueous solution (20 wt% polyvinyl alcohol 0488 aqueous solution) is mixed evenly with the reaction product of step 1, and the pH is adjusted to 4 by sodium hydroxide solution (10 wt%).

[0112] At 80°C, the second initiator A (4 wt% potassium persulfate aqueous solution) was added and stirred for 20 min; then the second vinyl acetate and the second initiator B were added (the addition rate of the second vinyl acetate was 0.06 parts / min, and the addition rate of the second initiator B was 0.014 parts / min), wherein, based on the total mass of the second initiator, the amount of the second initiator A was 66.7 wt%.

[0113] After vinyl acetate is added, the remaining second initiator B is quickly added to the degassing tank, and the reaction is carried out at 80°C for 30 minutes under stirring conditions.

[0114] Based on 100 parts by weight of the first vinyl acetate, the amount of the second polyvinyl alcohol is 1 part by weight, the amount of the second vinyl acetate is 5 parts by weight, and the amount of the second initiator is 0.23 parts by weight.

[0115] After the heat preservation reaction was completed, the mixture was cooled, filtered, and discharged to obtain a vinyl acetate copolymer emulsion. The test results of the vinyl acetate copolymer emulsion are shown in Table 1.

[0116] Example 3

[0117] (1) Replace the reactor with nitrogen three times, then add water and the first polyvinyl alcohol aqueous solution (the mass ratio of polyvinyl alcohol 0588 to polyvinyl alcohol 1788 is 1:5, and the concentration is 10wt%) to the reactor, start the stirrer, and add water, emulsifier allyloxynonylphenol sulfonate (DNS-86), zinc oxide in sequence, and finally add the first vinyl acetate A as the initial monomer (based on the total mass of the first vinyl acetate, the amount of the first vinyl acetate A is 50wt%).

[0118] After mixing, ethylene is introduced to bring the pressure to 4.1 MPa and the temperature to 54°C. Then, the first initiator (5.2 wt% tert-butyl hydrogen peroxide, with an addition rate of 0.2 parts / min) is added.

[0119] When the temperature of the reactants rises to 80°C, the ethylene pressure is simultaneously increased to 6.4 MPa, and first vinyl acetate B is added (the addition rate of first vinyl acetate B is 0.4 parts / min); during the addition of first vinyl acetate B, the ethylene pressure is maintained at 6.4 MPa.

[0120] Based on 100 parts by weight of the first vinyl acetate, the first polyvinyl alcohol is 4.4 parts by weight, the reactive emulsifier is 0.7 parts by weight, the reducing agent is 0.3 parts by weight, and the first initiator is 0.4 parts by weight.

[0121] After the second vinyl acetate B is added, the ethylene feed switch is turned off, and the reaction temperature is maintained at 80°C. When the ethylene pressure is lower than 1.5 MPa, the reaction ends. The ethylene in the reaction product is removed through a degassing tank.

[0122] (2) Under stirring conditions, the second polyvinyl alcohol aqueous solution (20 wt% polyvinyl alcohol 0588 aqueous solution) is mixed evenly with the reaction product of step 1, and the pH is adjusted to 4 by sodium hydroxide solution (10 wt%).

[0123] At 80°C, after adding the second initiator A (4 wt% potassium persulfate aqueous solution) and stirring for 20 min, the second vinyl acetate and the second initiator B (the addition rate of the second vinyl acetate was 0.06 parts / min, and the addition rate of the second initiator B was 0.093 parts / min) were added, wherein, based on the total mass of the second initiator, the amount of the second initiator A was 75 wt%.

[0124] After vinyl acetate is added, the remaining second initiator B is quickly added to the degassing tank, and the reaction is carried out at 80°C for 30 minutes under stirring conditions.

[0125] Based on 100 parts by weight of the first vinyl acetate, the amount of the second polyvinyl alcohol is 0.8 parts by weight, the amount of the second vinyl acetate is 4.9 parts by weight, and the amount of the second initiator is 0.2 parts by weight.

[0126] After the heat preservation reaction was completed, the mixture was cooled, filtered, and discharged to obtain a vinyl acetate copolymer emulsion. The test results of the vinyl acetate copolymer emulsion are shown in Table 1.

[0127] Example 4

[0128] (1) Replace the reactor with nitrogen three times, then add water and the first polyvinyl alcohol aqueous solution (the mass ratio of polyvinyl alcohol 0588 to polyvinyl alcohol 1788 is 1:5, and the concentration is 10wt%) to the reactor, start the stirrer, and add water, emulsifier allyloxynonylphenol sulfonate (DNS-86), sodium formaldehyde sulfoxylate (sodium formaldehyde sulfoxylate) in sequence, and finally add the first vinyl acetate A as the initial monomer (based on the total mass of the first vinyl acetate, the amount of the first vinyl acetate A is 52.8wt%).

[0129] After mixing, ethylene is introduced to bring the pressure to 4.0 MPa and the temperature to 52°C. Then, the first initiator (1.8 wt% hydrogen peroxide, with an addition rate of 0.2 parts / min) is added.

[0130] When the temperature of the reactants rises to 80°C, the ethylene pressure is simultaneously increased to 6.3 MPa, and first vinyl acetate B is added (the addition rate of first vinyl acetate B is 0.4 parts / min); during the addition of first vinyl acetate B, the ethylene pressure is maintained at 6.3 MPa.

[0131] Based on 100 parts by weight of the first vinyl acetate, the first polyvinyl alcohol is 4.5 parts by weight, the reactive emulsifier is 0.3 parts by weight, the reducing agent is 0.2 parts by weight, and the first initiator is 0.2 parts by weight.

[0132] After the second vinyl acetate B is added, the ethylene feed switch is turned off, and the reaction temperature is maintained at 80°C. When the ethylene pressure is lower than 1.5 MPa, the reaction ends. The ethylene in the reaction product is removed through a degassing tank.

[0133] (2) Under stirring conditions, the second polyvinyl alcohol aqueous solution (20 wt% polyvinyl alcohol 0388 aqueous solution) is mixed evenly with the reaction product of step 1, and the pH is adjusted to 4 by sodium hydroxide solution (10 wt%).

[0134] At 80°C, the second initiator A (4 wt% potassium persulfate aqueous solution) was added and stirred for 20 min; then the second vinyl acetate and the second initiator B were added (the addition rate of the second vinyl acetate was 0.04 parts / min, and the addition rate of the second initiator B was 0.004 parts / min); wherein, based on the total mass of the second initiator, the amount of the second initiator A was 77 wt%.

[0135] After vinyl acetate is added, the remaining second initiator B is quickly added to the degassing tank and reacted at 80°C for 30 minutes under stirring conditions.

[0136] Based on 100 parts by weight of the first vinyl acetate, the amount of the second polyvinyl alcohol is 0.8 parts by weight, the amount of the second vinyl acetate is 5 parts by weight, and the amount of the second initiator is 0.25 parts by weight.

[0137] After the heat treatment reaction was completed, the mixture was cooled, filtered, and discharged to obtain a vinyl acetate copolymer emulsion. The test results of the vinyl acetate copolymer emulsion are shown in Table 1.

[0138] Example 5

[0139] (1) Replace the reactor with nitrogen three times, then add water and the first polyvinyl alcohol aqueous solution (the mass ratio of polyvinyl alcohol 0588 to polyvinyl alcohol 1788 is 1:5, and the concentration is 10wt%) to the reactor, start the stirrer, and add water, emulsifier allyloxynonylphenol sulfonate (DNS-86), ascorbic acid in sequence, and finally add the first vinyl acetate A as the initial monomer (based on the total mass of the first vinyl acetate, the amount of the first vinyl acetate A is 68.5wt%).

[0140] After mixing, ethylene is introduced to bring the pressure to 4.0 MPa and the temperature to 50°C. Then, the first initiator (1.8 wt% hydrogen peroxide, with an addition rate of 0.2 parts / min) is added.

[0141] When the temperature of the reactants rises to 80°C, the ethylene pressure is simultaneously increased to 6.0 MPa, and first vinyl acetate B is added (the addition rate of first vinyl acetate B is 0.3 parts / min); during the addition of first vinyl acetate B, the ethylene pressure is maintained at 6.4 MPa;

[0142] Based on 100 parts by weight of the first vinyl acetate, the first polyvinyl alcohol is 4.1 parts by weight, the reactive emulsifier is 0.7 parts by weight, the reducing agent is 0.3 parts by weight, and the first initiator is 0.4 parts by weight.

[0143] After the second vinyl acetate B is added, the ethylene feed switch is turned off, and the reaction temperature is maintained at 80°C. When the ethylene pressure is lower than 1.5 MPa, the reaction ends. The ethylene in the reaction product is removed through a degassing tank.

[0144] (2) Under stirring conditions, the second polyvinyl alcohol aqueous solution (20 wt% polyvinyl alcohol 0388 aqueous solution) is mixed evenly with the reaction product of step 1, and the pH is adjusted to 4 by sodium hydroxide solution (10 wt%).

[0145] At 80°C, the second initiator A (4 wt% potassium persulfate aqueous solution) was added and stirred for 20 min; then the second vinyl acetate and the second initiator B were added (the addition rate of the second vinyl acetate was 0.05 parts / min, and the addition rate of the second initiator B was 0.005 parts / min); wherein, based on the total mass of the second initiator, the amount of the second initiator A was 83 wt%.

[0146] After vinyl acetate is added, the remaining second initiator B is quickly added to the degassing tank and reacted at 80°C for 30 minutes under stirring conditions.

[0147] Based on 100 parts by weight of the first vinyl acetate, the amount of the second polyvinyl alcohol is 0.7 parts by weight, the amount of the second vinyl acetate is 4.9 parts by weight, and the amount of the second initiator is 0.2 parts by weight.

[0148] After the heat treatment reaction was completed, the mixture was cooled, filtered, and discharged to obtain a vinyl acetate copolymer emulsion. The test results of the vinyl acetate copolymer emulsion are shown in Table 1.

[0149] Example 6

[0150] The vinyl acetate copolymer emulsion was prepared according to the method of Example 1, except that in step (2), based on 100 parts by weight of the first vinyl acetate, the amount of the second polyvinyl alcohol was 0.3 parts by weight, the amount of the second vinyl acetate was 4 parts by weight, and the amount of the second initiator was 0.2 parts by weight. The test results of the obtained vinyl acetate copolymer emulsion are shown in Table 1.

[0151] Example 7

[0152] The vinyl acetate copolymer emulsion was prepared according to the method of Example 1, except that in step (2), based on 100 parts by weight of the first vinyl acetate, the amount of the second polyvinyl alcohol was 1.7 parts by weight, the amount of the second vinyl acetate was 6 parts by weight, and the amount of the second initiator was 0.2 parts by weight. The test results of the obtained vinyl acetate copolymer emulsion are shown in Table 1.

[0153] Example 8

[0154] Vinyl acetate copolymer emulsions were prepared according to the method of Example 1, except that in step (2), the addition rate of the second vinyl acetate was 0.1 parts / min. The test results of the obtained vinyl acetate copolymer emulsions are shown in Table 1.

[0155] Comparative Example 1

[0156] Vinyl acetate copolymer emulsions were prepared according to the method of Example 1, except that in step (2), the second polyvinyl alcohol aqueous solution used was a 20 wt% aqueous solution of polyvinyl alcohol 1788. The test results of the obtained vinyl acetate copolymer emulsions are shown in Table 1.

[0157] Comparative Example 2

[0158] Vinyl acetate copolymer emulsion was prepared according to the method of Example 1, except that step (2) was omitted. Specifically, the product prepared in step (1) was cooled, filtered, and discharged to obtain the copolymer emulsion. The test results of the copolymer emulsion are shown in Table 1.

[0159] Comparative Example 3

[0160] A vinyl acetate copolymer emulsion was prepared according to the method of Example 1, except that a second vinyl acetate was not added in step (2). The copolymer emulsion was obtained. The test results of the copolymer emulsion are shown in Table 1.

[0161] Table 1

[0162]

[0163]

[0164] The results show that the vinyl acetate copolymer emulsion prepared by the present invention has a higher graft content. After the vinyl acetate copolymer emulsion is blended with ethanol at a ratio of 1:1, the viscosity change rate of the emulsion is low, indicating that the vinyl acetate copolymer emulsion has high stability.

[0165] 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 preparing a vinyl acetate copolymer emulsion, characterized in that, The method includes: (1) In the presence of ethylene, the first vinyl acetate, the first polyvinyl alcohol, the reactive emulsifier, the reducing agent and water are mixed and then the first initiator is added to carry out the first reaction; (2) After mixing the reaction product of step (1), the second polyvinyl alcohol and the second vinyl acetate, the pH is adjusted to 4-5, and the second initiator is added to carry out the second reaction to obtain the vinyl acetate copolymer emulsion. In step (1), based on 100 parts by weight of the first vinyl acetate, the first polyvinyl alcohol is 2-5 parts by weight, and the reactive emulsifier is 0.1-1 parts by weight. In step (2), the apparent viscosity of the 4 wt% aqueous solution of the second polyvinyl alcohol at 20°C is 2-8 mPa·s.

2. The method according to claim 1, wherein, In step (1), based on 100 parts by weight of the first vinyl acetate, the first polyvinyl alcohol is 3.2-4.5 parts by weight, and the reactive emulsifier is 0.2-0.8 parts by weight; Preferably, the amount of ethylene introduced is such that the pressure of the first reaction is 3-7 MPa.

3. The method according to claim 1 or 2, wherein, In step (1), based on 100 parts by weight of vinyl acetate, the reducing agent is 0.1-0.4 parts by weight, preferably 0.1-0.3 parts by weight; Preferably, in step (1), based on 100 parts by weight of the first vinyl acetate, the first initiator is 0.05-0.5 parts by weight, preferably 0.1-0.4 parts by weight.

4. The method according to claim 1 or 2, wherein, In step (1), the temperature of the first reaction is 78-82℃; Preferably, the reducing agent is selected from at least one of ascorbic acid, sodium isoascorbate, zinc formaldehyde sulfoxylate, and sodium formaldehyde sulfoxylate; Preferably, the reactive emulsifier is an emulsifier containing carbon-carbon double bonds; Preferably, the first initiator is selected from at least one of hydrogen peroxide, potassium persulfate, and tert-butyl hydroperoxide; Preferably, the addition rate of the first initiator is 0.15-0.3 parts / min, more preferably 0.2-0.25 parts / min.

5. The method according to claim 1 or 2, wherein, In step (2), the apparent viscosity of the 4wt% aqueous solution of the second polyvinyl alcohol at 20°C is 3-6 mPa·s; Preferably, the degree of alcoholysis of the second polyvinyl alcohol is 85-89%, more preferably 86-88.5%; Preferably, the second initiator is selected from at least one of hydrogen peroxide, potassium persulfate, and tert-butyl hydroperoxide; Preferably, the temperature of the second reaction is 55-85°C, more preferably 78-82°C.

6. The method according to claim 1 or 2, wherein, In step (2), based on 100 parts by weight of the first vinyl acetate, the amount of the second polyvinyl alcohol is 0.3-1.5 parts by weight, preferably 0.5-1 parts by weight; the amount of the second vinyl acetate is 4-5.5 parts by weight, preferably 4.5-5 parts by weight; and the amount of the second initiator is 0.05-0.3 parts by weight, preferably 0.1-0.25 parts by weight.

7. The method according to claim 1 or 2, wherein, Step (2) includes: mixing the reaction product of step (1) and the second polyvinyl alcohol, adjusting the pH to 4-5, adding the second initiator A, and then adding the second vinyl acetate and the second initiator B to carry out the second reaction.

8. The method according to claim 7, wherein, Based on the total mass of the second initiator, the amount of the second initiator A is 40-85 wt%. Preferably, the addition rate of the second vinyl acetate is 0.04-0.1 parts / min, more preferably 0.04-0.07 parts / min; Preferably, the addition rate of the second initiator B is 0.003-0.1 parts / min.

9. A vinyl acetate copolymer emulsion prepared by the method according to any one of claims 1-8; Preferably, the apparent viscosity of the vinyl acetate copolymer emulsion at 25±0.1℃ is 400-1000 mPa·s, more preferably 500-900 mPa·s.

10. The use of the vinyl acetate copolymer emulsion of claim 9 as an adhesive.

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