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

Abstract

The present application relates to the technical field of vinyl acetate, and discloses a vinyl acetate copolymer emulsion, a preparation method and application thereof, which comprises the following steps: (1) in the presence of ethylene, a first vinyl acetate, a first polyvinyl alcohol, a reactive emulsifier, a reducing agent and water are mixed, and then a first initiator is added to perform a first reaction; (2) the reaction product of step 1, a second polyvinyl alcohol, a second vinyl acetate and a monomer A of formula I are mixed, the pH is adjusted to 4-5, a second initiator is added to perform a second reaction, and then methanol and / or ethanol are mixed to obtain the vinyl acetate copolymer emulsion; in formula I, n is 0 or 1, and m is an integer of 1-3; 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 0.2-1 part by weight. The prepared vinyl acetate copolymer emulsion has the characteristics of fast drying speed, short film forming time and high peeling strength.

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 films, and plastic printed materials with plastic films 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 no bubbling, yellowing, or wrinkling. Currently, the adhesives used in packaging lamination in my country are mainly solvent-based and water-based. Water-based adhesives are gaining attention due to their environmental friendliness, but their application is limited by the high latent heat of water volatilization and slow drying speed.

[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. Summary of the Invention

[0004] The purpose of this invention is to overcome the problem of slow drying speed of vinyl acetate copolymer emulsions in the prior art, and to provide a vinyl acetate copolymer emulsion, its preparation method and application. The vinyl acetate copolymer emulsion prepared by the method of this invention has the characteristics of fast drying speed, short film-forming time and high peel strength.

[0005] 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:

[0006] (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;

[0007] (2) After mixing the reaction product of step (1), the second polyvinyl alcohol, the second vinyl acetate and monomer A shown in Formula I, the pH is adjusted to 4-5, the second initiator is added to carry out the second reaction, and then it is mixed with methanol and / or ethanol to obtain the vinyl acetate copolymer emulsion.

[0008]

[0009] In Equation I, n is 0 or 1, and m is an integer from 1 to 3;

[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 0.2-1 parts by weight.

[0011] A second aspect of the present invention provides a vinyl acetate copolymer emulsion prepared by the above method.

[0012] A third aspect of the present invention provides an application of the above-mentioned vinyl acetate copolymer emulsion as an adhesive.

[0013] 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:

[0014] This invention employs a reactive emulsifier to undergo a first reaction with vinyl acetate and ethylene. The resulting reaction product then undergoes a second reaction with polyvinyl alcohol, vinyl acetate, and monomer A as shown in Formula I. This process improves the stability of the vinyl acetate copolymer emulsion when mixed with alcohol solvents. The resulting vinyl acetate copolymer emulsion exhibits rapid drying and short film-forming time. Furthermore, the obtained vinyl acetate copolymer emulsion has low surface tension, enhancing its wettability and adhesion to plastic films. Moreover, the introduced monomer A contains long-chain carboxyl groups, which, by utilizing the reactivity of these carboxyl groups with hydroxyl and other carboxyl groups on the surface of the substrate, improve the adhesion between the vinyl acetate copolymer emulsion and the substrate surface. Detailed Implementation

[0015] 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.

[0016] The first aspect of this invention provides a method for preparing a vinyl acetate copolymer emulsion, wherein the method includes:

[0017] (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;

[0018] (2) After mixing the reaction product of step (1), the second polyvinyl alcohol, the second vinyl acetate and monomer A shown in Formula I, the pH is adjusted to 4-5, the second initiator is added to carry out the second reaction, and then it is mixed with methanol and / or ethanol to obtain the vinyl acetate copolymer emulsion.

[0019]

[0020] In Equation I, n is 0 or 1, and m is an integer from 1 to 3;

[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 0.2-1 parts by weight.

[0022] This invention employs a reactive emulsifier to undergo a first reaction with vinyl acetate and ethylene. The resulting reaction product then undergoes a second reaction with polyvinyl alcohol, vinyl acetate, and monomer A as shown in Formula I. This process improves the stability of the vinyl acetate copolymer emulsion after mixing with alcohol solvents, resulting in a vinyl acetate copolymer emulsion with fast drying speed and short film-forming time. Furthermore, the obtained vinyl acetate copolymer emulsion exhibits low surface tension, enhancing its wettability and adhesion to plastic films. Moreover, the introduced monomer A contains long-chain carboxyl groups, which, by utilizing the reactivity of these carboxyl groups with hydroxyl and other carboxyl groups on the surface of the substrate, improve the adhesion between the vinyl acetate copolymer emulsion and the substrate surface.

[0023] 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.

[0024] Furthermore, the reactive emulsifier used in step (1) can have a synergistic effect with polyvinyl alcohol, thereby improving the stability of the vinyl acetate copolymer emulsion after mixing with alcohol solvents.

[0025] 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%.

[0026] In this invention, 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 0.2-1 parts by weight. When the amounts of the first vinyl acetate, the first polyvinyl alcohol, and the reactive emulsifier meet the above range, 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. However, since 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] Further, in step (1), based on 100 parts by weight of the first vinyl acetate, the first polyvinyl alcohol is 4-4.5 parts by weight, and the reactive emulsifier is 0.3-0.7 parts by weight.

[0028] 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 50-70 parts by weight.

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

[0030] Further, in step (1), based on 100 parts by weight of vinyl acetate, the amount of reducing agent used is 0.15-0.35 parts by weight.

[0031] According to the present invention, in step (1), based on 100 parts by weight of the first vinyl acetate, the amount of the first initiator is 0.1-0.4 parts by weight.

[0032] Further, in step (1), based on 100 parts by weight of the first vinyl acetate, the amount of the first initiator is 0.18-0.32 parts by weight.

[0033] According to the present invention, the amount of ethylene introduced is such that the pressure of the first reaction is 3-7 MPa.

[0034] Furthermore, the amount of ethylene introduced makes the pressure of the first reaction 3.5-6.5 MPa.

[0035] According to the present invention, in step (1), the temperature of the first reaction is 50-82°C.

[0036] Furthermore, in step (1), the temperature of the first reaction is 78-82℃.

[0037] 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.

[0038] According to the present invention, the reactive emulsifier is an emulsifier containing carbon-carbon double bonds.

[0039] Furthermore, the reactive emulsifier is selected from at least one of sodium vinyl sulfonate, allyl polyether, and allyloxynonylphenol sulfonate.

[0040] According to the present invention, the first initiator is selected from at least one of hydrogen peroxide, potassium persulfate and tert-butyl hydroperoxide.

[0041] Furthermore, the first initiator is hydrogen peroxide.

[0042] According to the present invention, the addition rate of the first initiator is 0.15-0.3 parts / min.

[0043] 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.

[0044] In this invention, the degree of alcoholysis of the first polyvinyl alcohol is 85-89%.

[0045] 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.

[0046] 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%.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] According to a preferred embodiment of the present invention, the addition rate of the first initiator is 0.15-0.3 parts / min.

[0051] 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.

[0052] Furthermore, the structure of monomer A in step (2) is shown in formula I;

[0053]

[0054] Furthermore, in Equation I, n is 0 and m is an integer from 1 to 3.

[0055] According to a preferred embodiment of the present invention, the monomer A is β-acryloyloxypropionic acid (n is 0, m is 2).

[0056] According to the present invention, in step (2), the apparent viscosity of the 4wt% aqueous solution of the second polyvinyl alcohol at 20°C is 2-8 mPa·s.

[0057] In this invention, when the apparent viscosity of the second polyvinyl alcohol meets the above-mentioned range, the degree of polymerization of polyvinyl alcohol is small, polyvinyl alcohol is easy to diffuse, and the graft formed with vinyl acetate is easily adsorbed onto the surface of latex particles, making the latex particles more stable.

[0058] Furthermore, the apparent viscosity of a 4 wt% aqueous solution of the second polyvinyl alcohol at 20°C is 3-6 mPa·s.

[0059] According to the present invention, the degree of alcoholysis of the second polyvinyl alcohol is 85-89%.

[0060] In this invention, when the degree of hydrolysis of the second polyvinyl alcohol meets the above-mentioned range, a graft formed with vinyl acetate is formed, and the graft is easily adsorbed onto the surface of the latex particles, making the latex particles more stable.

[0061] Furthermore, the degree of alcoholysis of the second polyvinyl alcohol is 86-88.5%.

[0062] 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.

[0063] 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%.

[0064] According to the present invention, the second initiator is selected from at least one of hydrogen peroxide, potassium persulfate and tert-butyl hydroperoxide.

[0065] Furthermore, the second initiator is potassium persulfate.

[0066] 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%.

[0067] According to the present invention, the temperature of the second reaction is 55-85°C.

[0068] Furthermore, the temperature of the second reaction is 78-82°C.

[0069] 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, the amount of monomer A is 0.02-0.15 parts by weight, and the amount of the second initiator is 0.05-0.3 parts by weight.

[0070] In this invention, when the amounts of the second polyvinyl alcohol, the second vinyl acetate, and monomer A meet the above-mentioned range, the resulting vinyl acetate copolymer emulsion dries quickly, has a short film-forming time, and exhibits high adhesion to the substrate surface.

[0071] 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, the amount of monomer A is 0.03-0.1 parts by weight, and the amount of the second initiator is 0.1-0.25 parts by weight.

[0072] According to the present invention, the amount of ethanol added is 80-100 wt% of the mass of the emulsion after the second reaction.

[0073] Furthermore, the amount of ethanol added is 40-70 wt% of the emulsion mass after the second reaction.

[0074] 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 a mixed monomer containing the second vinyl acetate and monomer A, as well as the second initiator B to carry out the second reaction.

[0075] 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, monomer A, and second initiator B on these active sites.

[0076] 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.

[0077] According to a preferred embodiment of the present invention, the addition rate of the mixed monomers is 0.04-0.1 parts / min.

[0078] In this invention, when the addition rate of the mixed monomers meets the above-mentioned range, the polymerization of the second vinyl acetate with monomer A is more uniform, and the obtained vinyl acetate copolymer emulsion has better adhesion.

[0079] Furthermore, the addition rate of the mixed monomers is 0.04-0.06 parts / min.

[0080] According to a preferred embodiment of the present invention, the addition rate of the second initiator B is 0.003-0.1 parts / min.

[0081] A second aspect of the present invention provides a vinyl acetate copolymer emulsion prepared by the above method.

[0082] In this invention, the vinyl acetate copolymer emulsion includes vinyl acetate copolymer, water, ethanol and / or methanol.

[0083] According to the present invention, the apparent viscosity of the vinyl acetate copolymer emulsion at 25±0.1℃ is 200-500 mPa·s.

[0084] Furthermore, the apparent viscosity of the vinyl acetate copolymer emulsion at 25±0.1℃ is 250-430 mPa·s.

[0085] In this invention, the graft content of the vinyl acetate copolymer emulsion is 50-65 wt%.

[0086] 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.

[0087] Furthermore, the graft content of the vinyl acetate copolymer emulsion is 55-60 wt%.

[0088] According to the present invention, the solid content of the vinyl acetate copolymer emulsion is 25-45 wt%.

[0089] Furthermore, the solid content of the vinyl acetate copolymer emulsion is 27-40 wt%.

[0090] A third aspect of the present invention provides an application of the above-mentioned vinyl acetate copolymer emulsion as an adhesive.

[0091] The present invention will be described in detail below through embodiments.

[0092] In the following examples and comparative examples, parts by weight and parts refer to grams.

[0093] 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.

[0094] 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.

[0095] Film-forming time: The actual drying time was measured using the blade method in GB / T 1728-2020 "Determination of Drying Time of Paint Film and Putty Film".

[0096] Surface tension: Tested using the ring method. A ring made of thin platinum wire is inserted into the liquid and then slowly pulled upwards to form a liquid film. The force required to raise the ring to its current height is measured, and the surface tension is calculated accordingly.

[0097] Peel strength of biaxially oriented polypropylene film (BOPP film) and paper composite: Testing was conducted according to GB / T2791-1995 "Adhesives T-Peel Strength Test Method: Flexible Materials vs. Rigid Materials". Sample preparation involved applying a vinyl acetate copolymer emulsion to the front sides of both the BOPP film and white cardboard using a 50μm coater, drying with a hairdryer, applying 5kg of pressure for 15 minutes, and then preparing 10mm × 15mm samples for T-peel testing.

[0098] Graft content: Using a 400 μm membrane-forming device, a thin film was formed on a glass plate from the vinyl acetate copolymer emulsion (i.e., the product of the second reaction) without the addition of ethanol and / or methanol. The film was 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 (1).

[0099]

[0100] 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 and subsequent extraction with pure water.

[0101] Apparent viscosity of polyvinyl alcohol: Prepare a 4 wt% aqueous solution of polyvinyl alcohol and test it using a Brookfield viscometer with rotor No. 0 at 20°C.

[0102] The apparent viscosity of polyvinyl alcohol 0588 is 5 mPa·s, and the degree of alcoholysis is 87%.

[0103] The apparent viscosity of polyvinyl alcohol 1788 is 22 mPa·s, and the degree of alcoholysis is 87%.

[0104] The apparent viscosity of polyvinyl alcohol 0388 is 3.5 mPa·s, and the degree of alcoholysis is 87%.

[0105] The apparent viscosity of polyvinyl alcohol 0488 is 4.5 mPa·s, and the degree of alcoholysis is 87%.

[0106] Monomer A: β-Acryloyloxypropionic acid (n is 0, m is 2).

[0107] Example 1

[0108] (1) Replace the reactor with nitrogen three times, and add water and the first polyvinyl alcohol aqueous solution (the mass ratio of polyvinyl alcohol 0388, polyvinyl alcohol 0588 and polyvinyl alcohol 1788 is 1:2:6, and the concentration is 10wt%) to the reactor. Start the stirrer, and add water, emulsifier allyloxynonylphenol sulfonate (DNS-86), sodium isoascorbate in sequence. 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 53wt%).

[0109] 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.

[0110] 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, and the reaction temperature is maintained at 80°C.

[0111] 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 0.5 parts by weight, the reducing agent is 0.2 parts by weight, and the first initiator is 0.2 parts by weight.

[0112] After the first 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 main reaction ends. Ethylene is removed from the reaction products through a degassing tank.

[0113] (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%).

[0114] At 80°C, the second initiator A (4 wt% potassium persulfate aqueous solution) was added and stirred for 20 min; then, a mixed monomer (second vinyl acetate and monomer A, the mixed monomer being added at a rate of 0.04 parts / min) was added, along with the second initiator B (the second initiator B being added at a rate of 0.004 parts / min); wherein, based on the total mass of the second initiator, the amount of the second initiator A was 77 wt%.

[0115] After the mixed monomers are added, the remaining initiator is quickly added to the degassing tank and kept at 80°C with stirring for 30 minutes. Specifically, based on 100 parts by weight of the first vinyl acetate, the amount of the second polyvinyl alcohol is 0.75 parts by weight, the amount of the second vinyl acetate is 5 parts by weight, the amount of monomer A is 0.05 parts by weight, and the amount of the second initiator is 0.25 parts by weight.

[0116] After the heat preservation was completed, the temperature was lowered to 30°C, and 80 wt% ethanol of the emulsion was added. The mixture was stirred evenly, filtered, and discharged to obtain a vinyl acetate copolymer emulsion. The test results of the vinyl acetate copolymer emulsion are shown in Table 1.

[0117] Example 2

[0118] (1) Replace the reactor with nitrogen three times, and then add water and the first polyvinyl alcohol aqueous solution (the mass ratio of polyvinyl alcohol 0388, polyvinyl alcohol 0588 and polyvinyl alcohol 1788 is 1:2:6, and the concentration is 10wt%) to the reactor. Start the stirrer and add water, emulsifier allyloxynonylphenol sulfonate (DNS-86), ascorbic acid in sequence. 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 69wt%).

[0119] After mixing, ethylene is introduced to bring the pressure to 4.0 MPa and the temperature to 50°C. Then, the first initiator (4.6 wt% tert-butyl hydrogen peroxide, with an addition rate of 0.2 parts / min) is added.

[0120] 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, and the reaction temperature is maintained at 80°C.

[0121] Based on 100 parts by weight of the first vinyl acetate, the first polyvinyl alcohol is 2.9 parts by weight, the reactive emulsifier is 0.5 parts by weight, the reducing agent is 0.3 parts by weight, and the first initiator is 0.4 parts by weight.

[0122] After the first 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 main reaction ends. Ethylene is removed from the reaction products through a degassing tank.

[0123] (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%).

[0124] At 80°C, the second initiator A (4 wt% potassium persulfate aqueous solution) was added and stirred for 20 min; then, a mixed monomer (second vinyl acetate and monomer A, the mixed monomer being added at a rate of 0.05 parts / min) was added, along with the second initiator B (the second initiator B being added at a rate of 0.005 parts / min); wherein, based on the total mass of the second initiator, the amount of the second initiator A was 83 wt%.

[0125] After the mixed monomers are added, the remaining initiator is quickly added to the degassing tank and kept at 80°C for 30 minutes. 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, the amount of monomer A is 0.07 parts by weight, and the amount of the second initiator is 0.2 parts by weight.

[0126] After the heat preservation was completed, the temperature was lowered to 30°C, and 80 wt% ethanol of the emulsion was added. The mixture was stirred evenly, 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 3

[0128] (1) Replace the reactor with nitrogen three times, and then add water and the first polyvinyl alcohol aqueous solution (the mass ratio of polyvinyl alcohol 0388, polyvinyl alcohol 0588 and polyvinyl alcohol 1788 is 1:2:6, and the concentration is 10wt%) to the reactor. Start the stirrer and add water, emulsifier sodium vinyl sulfonate (SVS), ascorbic acid in sequence. 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 67wt%).

[0129] 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.

[0130] 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 6.0 MPa, and the reaction temperature is maintained at 80°C.

[0131] 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 0.5 parts by weight, the reducing agent is 0.2 parts by weight, and the first initiator is 0.1 parts by weight.

[0132] After the first 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 main reaction ends. Ethylene is removed from the reaction products 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, a mixed monomer (second vinyl acetate and monomer A, the mixed monomer being added at a rate of 0.06 parts / min) was added, along with the second initiator B (the second initiator B being added at a rate of 0.004 parts / min); wherein, based on the total mass of the second initiator, the amount of the second initiator A was 83 wt%.

[0135] After the mixed monomers are added, the remaining initiator is quickly added to the degassing tank and kept at 80°C for 30 minutes. 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, the amount of monomer A is 0.02 parts by weight, and the amount of the second initiator is 0.12 parts by weight.

[0136] After the heat preservation was completed, the temperature was lowered to 30°C, and 90 wt% ethanol of the emulsion was added. The mixture was stirred evenly, filtered, and discharged to obtain a vinyl acetate copolymer emulsion. The test results of the vinyl acetate copolymer emulsion are shown in Table 1.

[0137] Example 4

[0138] (1) Replace the reactor with nitrogen three times, and then add water and the first polyvinyl alcohol aqueous solution (the mass ratio of polyvinyl alcohol 0388, polyvinyl alcohol 0588 and polyvinyl alcohol 1788 is 1:2:6, and the concentration is 10wt%) to the reactor. Start the stirrer and add water, emulsifier allyl polyether (AE-100), ascorbic acid in sequence. 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%).

[0139] 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.

[0140] 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, and the reaction temperature is maintained at 80°C.

[0141] Based on 100 parts by weight of the first vinyl acetate, the first polyvinyl alcohol is 4.3 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 0.1 parts by weight.

[0142] After the first 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 main reaction ends. Ethylene is removed from the reaction products through a degassing tank.

[0143] (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%).

[0144] At 80°C, the second initiator A (4 wt% potassium persulfate aqueous solution) was added and stirred for 20 min; then, a mixed monomer (second vinyl acetate and monomer A, the mixed monomer being added at a rate of 0.06 parts / min) was added, along with the second initiator B (the second initiator B being added at a rate of 0.014 parts / min); wherein, based on the total mass of the second initiator, the amount of the second initiator A was 67 wt%.

[0145] After the mixed monomers are added, the remaining initiator is quickly added to the degassing tank and kept at 80°C for 30 minutes. The amount of the second polyvinyl alcohol is 1 part by weight, the amount of the second vinyl acetate is 5 parts by weight, the amount of monomer A is 0.1 parts by weight, and the amount of the second initiator is 0.23 parts by weight.

[0146] After the heat preservation was completed, the temperature was lowered to 30°C, 100% ethanol by weight of the emulsion was added, stirred evenly, filtered, and discharged to obtain vinyl acetate copolymer emulsion. The test results of the vinyl acetate copolymer emulsion are shown in Table 1.

[0147] Example 5

[0148] (1) Replace the reactor with nitrogen three times, and then add water and the first polyvinyl alcohol aqueous solution (the mass ratio of polyvinyl alcohol 0388, polyvinyl alcohol 0588 and polyvinyl alcohol 1788 is 1:2:6, 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. 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%).

[0149] 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.

[0150] 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 0.4 parts / min); during the addition of first vinyl acetate B, the ethylene pressure is maintained at 6.2 MPa, and the reaction temperature is maintained at 80°C.

[0151] Based on 100 parts by weight of vinyl acetate, the first polyvinyl alcohol is 4.4 parts by weight, the reactive emulsifier is 0.6 parts by weight, the reducing agent is 0.3 parts by weight, and the first initiator is 0.4 parts by weight.

[0152] After the first 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 main reaction ends. Ethylene is removed from the reaction products through a degassing tank.

[0153] (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%).

[0154] At 80°C, the second initiator A (4 wt% potassium persulfate aqueous solution) was added and stirred for 20 min; then, a mixed monomer (second vinyl acetate and monomer A, with the mixed monomer added at a rate of 0.06 parts / min) was added, along with the second initiator B (with the second initiator B added at a rate of 0.093 parts / min); wherein, based on the total mass of the second initiator, the amount of the second initiator A was 75 wt%.

[0155] After the mixed monomers are added, the remaining initiator is quickly added to the degassing tank and kept at 80°C for 30 minutes. 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, the amount of monomer A is 0.07 parts by weight, and the amount of the second initiator is 0.2 parts by weight.

[0156] After the heat preservation was completed, the temperature was lowered to 30°C, 100% ethanol by weight of the emulsion was added, stirred evenly, filtered, and discharged to obtain vinyl acetate copolymer emulsion. The test results of the vinyl acetate copolymer emulsion are shown in Table 1.

[0157] Example 6

[0158] 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 1.5 parts by weight, the amount of the second vinyl acetate was 4.5 parts by weight, the amount of monomer A was 0.15 parts by weight, and the amount of the second initiator was 0.25 parts by weight.

[0159] Example 7

[0160] 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 0.2 parts by weight, the amount of the second vinyl acetate was 3.5 parts by weight, the amount of monomer A was 0.01 parts by weight, and the amount of the second initiator was 0.25 parts by weight.

[0161] Example 8

[0162] Vinyl acetate copolymer emulsions were prepared according to the method in Example 1, except that the addition rate of the mixed monomers was 0.15 parts / min. The test results of the obtained vinyl acetate copolymer emulsions are shown in Table 1.

[0163] Comparative Example 1

[0164] Vinyl acetate copolymer emulsions were prepared according to the method of Example 1, except that monomer A was not added in step (2). The test results of the vinyl acetate copolymer emulsions are shown in Table 1.

[0165] Comparative Example 2

[0166] Vinyl acetate copolymer emulsion was prepared according to the method of Example 1, except that in step (2), no second vinyl acetate was added, and monomer A of equal mass was used to replace the second vinyl acetate; gel was generated during the second reaction.

[0167] Comparative Example 3

[0168] Vinyl acetate copolymer emulsions were prepared according to the method in Example 1, except that methacrylic acid was used instead of β-acryloyloxypropionic acid. The test results of the vinyl acetate copolymer emulsions are shown in Table 1.

[0169] Comparative Example 4

[0170] The vinyl acetate copolymer emulsion was prepared according to the method of Example 1, except that no second polyvinyl alcohol was added in step (2), and a gel was generated when the product obtained from the second reaction in step (2) was mixed with ethanol.

[0171] Comparative Example 5

[0172] Vinyl acetate copolymer emulsion was prepared according to the method of Example 1, except that the pH of the reaction system was 3, and gel was generated during the second reaction.

[0173] Comparative Example 6

[0174] The vinyl acetate copolymer emulsion was prepared according to the method of Example 1, except that in step (1), dodecylphenol polyoxyethylene ether (OP-10) was used to replace the emulsifier allyloxynonylphenol sulfonate (DNS-86), and when the product obtained from the second reaction in step (2) was mixed with ethanol, a gel was formed.

[0175] Table 1

[0176]

[0177]

[0178] As shown in Table 1, the vinyl acetate copolymer emulsion prepared by this invention has a higher graft content, resulting in good compatibility with ethanol. The vinyl acetate copolymer emulsion of this invention exhibits high peel strength and fast film-forming speed in BOPP film-paper composites. This demonstrates that the vinyl acetate copolymer emulsion of this invention has a fast film-forming speed and high adhesion strength to low surface tension substrates.

[0179] 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, the second vinyl acetate and monomer A shown in Formula I, the pH is adjusted to 4-5, the second initiator is added to carry out the second reaction, and then it is mixed with methanol and / or ethanol to obtain the vinyl acetate copolymer emulsion. In Equation I, n is 0 or 1, and m is an integer from 1 to 3; 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 0.2-1 parts by weight.

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 4-4.5 parts by weight, and the reactive emulsifier is 0.3-0.7 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 amount of reducing agent used is 0.1-0.4 parts by weight; Preferably, in step (1), based on 100 parts by weight of the first vinyl acetate, the amount of the first initiator is 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 50-82℃; 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.

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 2-8 mPa·s, preferably 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, the amount of monomer A is 0.02-0.15 parts by weight, preferably 0.03-0.1 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; Preferably, the amount of ethanol added is 80-100 wt% of the emulsion mass after the second reaction, and more preferably 40-70 wt%.

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 a mixed monomer containing the second vinyl acetate and monomer A, as well as 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 mixed monomers is 0.04-0.1 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 200-500 mPa·s, more preferably 250-430 mPa·s; Preferably, the solid content of the vinyl acetate copolymer emulsion is 25-45 wt%.

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

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