阅读说明：本技术 一种低游离甲醛的乙酸乙烯酯-乙烯共聚乳液的制备方法 (Preparation method of vinyl acetate-ethylene copolymer emulsion with low free formaldehyde ) 是由 袁大兵 蒋红光 何盛教 苏猛 石显伟 韦忠国 韦慧 牙金艳 黄栋 文志康 何伟忠 于 2021-08-26 设计创作，主要内容包括：本发明公开了一种低游离甲醛的乙酸乙烯酯-乙烯共聚乳液的制备方法,加入乙酸乙烯酯、表面活性剂、氧化剂制备乙酸乙烯酯-乙烯共聚乳液,在制备过程的熟化期阶段加入甲醛捕捉剂水溶液,中和共聚乳液中的游离甲醛,达到降低共聚乳液中游离甲醛含量的目的。本发明在不改变原乙酸乙烯酯-乙烯共聚乳液粘度和固含量的前提下,通过添加甲醛捕捉剂水溶液降低游离甲醛含量,制备工艺过程简单,容易实现工业化。(The invention discloses a preparation method of vinyl acetate-ethylene copolymer emulsion with low free formaldehyde, which comprises the steps of adding vinyl acetate, a surfactant and an oxidant to prepare the vinyl acetate-ethylene copolymer emulsion, adding a formaldehyde catcher water solution in the curing period of the preparation process to neutralize the free formaldehyde in the copolymer emulsion, thereby achieving the purpose of reducing the content of the free formaldehyde in the copolymer emulsion. The invention reduces the content of free formaldehyde by adding the aqueous solution of the formaldehyde catching agent on the premise of not changing the viscosity and the solid content of the original vinyl acetate-ethylene copolymer emulsion, has simple preparation process and is easy to realize industrialization.)

1. A preparation method of vinyl acetate-ethylene copolymer emulsion with low free formaldehyde is characterized in that: adding vinyl acetate, a surfactant and an oxidant to prepare vinyl acetate-ethylene copolymer emulsion, adding a formaldehyde scavenger aqueous solution in the curing period of the preparation process to neutralize free formaldehyde in the copolymer emulsion, thereby achieving the purpose of reducing the content of the free formaldehyde in the copolymer emulsion; the mass of the added formaldehyde scavenger aqueous solution is 5.3-5.6% of the total mass of the vinyl acetate; the temperature of the formaldehyde scavenger aqueous solution is maintained at 55-65 ℃.

2. The method of claim 1, wherein: the formaldehyde scavenger aqueous solution is prepared by mixing a formaldehyde scavenger and water according to the mass ratio of 1: 1; the formaldehyde catching agent is GW 21-2.

3. The method according to claim 1, wherein the vinyl acetate-ethylene copolymer emulsion with low free formaldehyde content is prepared by the following steps:

(1) adding initial monomer vinyl acetate and a surfactant solution into a reactor for min, continuously adding an oxidant hydrogen peroxide solution under the conditions of ethylene atmosphere and pressure of 1.5-6.0MPa to initiate reaction, stirring for reaction for 100-120min, adding continuous monomer vinyl acetate in the reaction process, controlling the temperature to be 78-82 ℃ in the reaction process, after the continuous monomer vinyl acetate is completely added, the reaction temperature to be lower than 77 ℃, adding a formaldehyde scavenger aqueous solution in a curing period, and removing residual ethylene after 3min after the formaldehyde scavenger aqueous solution is completely added; the mass of the added formaldehyde scavenger aqueous solution is 5.3-5.6% of the total mass of the monomer vinyl acetate; the temperature of the formaldehyde scavenger aqueous solution is maintained at 55-65 ℃;

(2) adding water to the reaction liquid from which the residual ethylene is removed in the step (1) to adjust the content of nonvolatile components, adding a reducing agent FF6M and tert-butyl peroxybenzoate to reduce the content of vinyl acetate, adjusting the pH value of sodium bicarbonate, removing residual fine bubbles in the emulsion by an antifoaming agent, stirring uniformly, and filtering to remove scum to obtain the low-formaldehyde vinyl acetate-ethylene copolymer emulsion GW-705 emulsion with low free formaldehyde.

4. The method of claim 1, wherein: the surfactant solution in the step (1) is a mixed solution obtained by mixing water, compound polyvinyl alcohol and a reducing agent zinc formaldehyde sulfoxylate in a container, heating to 75-85 ℃, and uniformly stirring; the mass ratio of water, compound polyvinyl alcohol and reducing agent zinc sulfoxylate formaldehyde in the surfactant solution is 313-376: 17-21: 1.0 to 1.2.

5. The method according to claim 4, wherein: the compound polyvinyl alcohol is prepared by mixing polyvinyl alcohol 05-88 and polyvinyl alcohol 17-88 according to a mass ratio of 1-1.2: 3-3.5.

6. The method of claim 1, wherein: in the step (1), the mass percentage of the oxidant hydrogen peroxide solution is 1.2-2.0%, and the total mass of the oxidant hydrogen peroxide solution is 6.8-7.5% of the total mass of the monomer vinyl acetate.

7. The method of claim 1, wherein: the mass ratio of the initial monomer vinyl acetate to the continuous monomer vinyl acetate in the step (1) is 2.0-2.5: 1.

8. The method of claim 1, wherein: in the step (1), continuous monomer vinyl acetate is added in three batches in the reaction process, and the adding amount of each batch is equal; the specific adding time is that the reaction is added when the reaction is carried out for 10min, 30min and 50min, the adding time is 15min at each time interval, and then the adding is stopped for 5min and is continued.

9. The method of claim 1, wherein: in the step (2), the mass ratio of the addition amount of the reducing agent FF6M to the reaction liquid is 0.2-0.3: 1000, parts by weight; the mass ratio of the addition amount of the tert-butyl peroxybenzoate to the reaction liquid is (0.15-0.3): 1000, parts by weight; the mass ratio of the addition amount of the sodium bicarbonate to the reaction liquid is 1.5-2.2: 1000, parts by weight; the mass ratio of the addition amount of the defoaming agent to the reaction liquid is 1.5-2.0: 1000, parts by weight; and the mass ratio of the addition amount of the nonvolatile components to the reaction liquid is adjusted to 10-13: 1000 by using water.

Technical Field

The invention relates to a preparation method of vinyl acetate-ethylene copolymer emulsion, in particular to a preparation method of vinyl acetate-ethylene copolymer emulsion with low free formaldehyde.

Background

Vinyl acetate-ethylene copolymer emulsion (namely VAE emulsion) introduces ethylene molecular chains into polyvinyl acetate molecules, so that acetyl groups generate discontinuity, the rotational freedom degree of a high molecular chain is increased, the space obstruction is reduced, and the main chain of a high polymer becomes soft. Meanwhile, ethylene is used as an internal plasticizer of the copolymer, so that the VAE polymer has internal plasticization, and the plasticizer cannot migrate, thereby avoiding the aging of the polymer performance. The VAE emulsion not only has good stability to ultraviolet rays, but also has good acid and alkali resistance, and is widely applied to the fields of adhesives, waterproof coatings, interior decoration, outdoor heat preservation, carpets, non-woven fabrics, paper industry processing, cement modification and the like.

The E0-level national environmental standard is described in "impregnated paper laminated wood flooring" GB/T18102-2007, in which the indoor mandatory standard for the limit of formaldehyde emission in artificial boards and their products is specified, and the limit of formaldehyde in water-based adhesives: formaldehyde acetal, polyvinyl acetate adhesive and rubber adhesive are less than or equal to 1 g/kg; the amount of harmful substances in the interior wall coating is limited: the limit of free formaldehyde of the interior wall coating (synthetic resin emulsion interior wall coating) is less than or equal to 0.1 mg/kg; the amount of harmful substances in the interior wall coating is limited: the limit of free formaldehyde of the interior wall coating (synthetic resin emulsion interior wall coating) is less than or equal to 0.1 mg/kg.

At present, vinyl acetate-ethylene copolymer emulsion products have a plurality of models, each model has unique performance advantages, but the content of free formaldehyde in most copolymer emulsions is 0.18-0.3 mg/kg. The original GW-705 has excellent initial viscosity and mechanical stability, higher viscosity and consistency, application performances of high curing speed, strong bonding force and the like, but the content of free formaldehyde is kept between 0.18 and 0.25mg/kg, and the standard requirement of the interior wall coating cannot be met.

Disclosure of Invention

Aiming at the technical problems, the invention provides a preparation method of vinyl acetate-ethylene copolymer emulsion with low free formaldehyde, aiming at obtaining vinyl acetate-ethylene copolymer emulsion with good mechanical stability, good rheological property, high flexibility, good film forming property and low free formaldehyde content, namely GW-705 low formaldehyde emulsion.

In order to achieve the purpose, the technical scheme provided by the invention is as follows:

a preparation method of vinyl acetate-ethylene copolymer emulsion with low free formaldehyde comprises the steps of adding vinyl acetate, a surfactant and an oxidant to prepare the vinyl acetate-ethylene copolymer emulsion, adding a formaldehyde catcher water solution in the curing period of the preparation process to neutralize the free formaldehyde in the copolymer emulsion, thereby achieving the purpose of reducing the content of the free formaldehyde in the copolymer emulsion; the formaldehyde scavenger aqueous solution is obtained by mixing a formaldehyde scavenger and deionized water according to the mass ratio of 1:1, wherein the addition mass of the formaldehyde scavenger aqueous solution is 5.3-5.6% of the total mass of vinyl acetate (the total mass of vinyl acetate refers to the total mass of initial monomer vinyl acetate + continuous monomer vinyl acetate); the formaldehyde trapping agent is GW21-2, and the temperature of the formaldehyde trapping agent aqueous solution is maintained at 55-65 ℃.

Preferably, the preparation method of the vinyl acetate-ethylene copolymerization emulsion with low free formaldehyde comprises the following operation steps:

(1) adding initial monomer vinyl acetate and surfactant solution into a reactor for min, continuously dropwise adding oxidant hydrogen peroxide solution under the conditions of ethylene atmosphere and pressure of 1.5-6.0MPa to initiate reaction, stirring for reaction for 120min, adding continuous monomer vinyl acetate in the reaction process, controlling the temperature to be 78-82 ℃ in the reaction process, after the continuous monomer vinyl acetate is completely added, the reaction temperature is lower than 77 ℃ and the adding rate of the oxidant hydrogen peroxide solution is increased to 100%, then entering a curing period, adding formaldehyde scavenger aqueous solution in the curing period, stopping adding the hydrogen peroxide solution 3min after the formaldehyde scavenger aqueous solution is completely added, and after the reaction is finished, placing the reaction solution into a flash evaporator to remove residual ethylene; the mass of the added formaldehyde scavenger aqueous solution is 5.3-5.6% of the total mass of the monomer vinyl acetate (the total mass of the monomer vinyl acetate refers to the total of initial monomer vinyl acetate and continuous monomer vinyl acetate); the temperature of the formaldehyde scavenger aqueous solution is maintained at 55-65 ℃;

(2) adding deionized water into the reaction liquid from which the residual ethylene is removed in the step (1) to adjust the content of nonvolatile components, adding a reducing agent FF6M and tert-butyl peroxybenzoate to reduce the content of vinyl acetate, adjusting the pH value of sodium bicarbonate, removing residual fine bubbles in the emulsion by using an antifoaming agent, uniformly stirring, and filtering to remove scum to obtain the low-formaldehyde vinyl acetate-ethylene copolymer emulsion GW-705 emulsion with low free formaldehyde.

Preferably, the surfactant solution in the step (1) is a mixed solution obtained by mixing deionized water, compound polyvinyl alcohol and a reducing agent zinc formaldehyde sulfoxylate in a container, heating to 75-85 ℃, and uniformly stirring; the mass ratio of the deionized water to the compound polyvinyl alcohol to the reducing agent zinc formaldehyde sulfoxylate in the surfactant solution is 313-376: 17-21: 1.0 to 1.2.

Preferably, the compound polyvinyl alcohol is prepared by mixing polyvinyl alcohol 05-88 and polyvinyl alcohol 17-88 according to the mass ratio of 1-1.2: 3-3.5.

Preferably, in the step (1), the mass percentage of the oxidant hydrogen peroxide solution is 1.2-2.0%, and the total mass of the oxidant hydrogen peroxide solution is 6.8-7.5% of the total mass of the monomer vinyl acetate (initial monomer vinyl acetate and continuous monomer vinyl acetate).

Preferably, the aqueous solution of the formaldehyde scavenger in the step (1) is prepared by mixing a formaldehyde scavenger and deionized water according to a mass ratio of 1: 1; the formaldehyde catching agent is GW 21-2.

Preferably, the ratio of the mass of the initial monomeric vinyl acetate to the mass of the continuous monomeric vinyl acetate in step (1) is 2.0 to 2.5: 1.

Preferably, in the step (1), the continuous monomer vinyl acetate is added in three batches in the reaction process, and the addition amount of each batch is equal; the specific adding time is that the reaction is added when the reaction is carried out for 10min, 30min and 50min, the adding time is 15min at each time interval, and then the adding is stopped for 5min and is continued.

Preferably, the mass ratio of the addition amount of the reducing agent FF6M to the reaction liquid in the step (2) is 0.2-0.3: 1000, parts by weight; the mass ratio of the addition amount of the tert-butyl peroxybenzoate to the reaction liquid is (0.15-0.3): 1000, parts by weight; the mass ratio of the addition amount of the sodium bicarbonate to the reaction liquid is 1.5-2.2: 1000, parts by weight; the mass ratio of the addition amount of the defoaming agent to the reaction liquid is 1.5-2.0: 1000, parts by weight; and adjusting the mass ratio of the addition amount of the nonvolatile components to the reaction liquid to be 10-13: 1000 by using the deionized water.

Compared with the prior art, the invention has the following beneficial effects:

the low-free-formaldehyde vinyl acetate-ethylene copolymer emulsion GW-705 prepared by the invention has the free formaldehyde content of less than or equal to 0.08mg/kg, makes up for the defect of the existing vinyl acetate-ethylene copolymer emulsion in the low-formaldehyde field, and can meet the higher environmental protection requirements of the vinyl acetate-ethylene copolymer emulsion in the fields of adhesives, waterproof coatings, indoor decoration, outdoor heat preservation, carpet, non-woven fabrics, paper industry processing, cement modification and the like; further, on the premise of not changing the viscosity and solid content of the original vinyl acetate-ethylene copolymer emulsion, the content of free formaldehyde is reduced by adding the aqueous solution of the formaldehyde catching agent, the preparation process is simple, and industrialization is easy to realize.

Detailed Description

The following detailed description is to be read in connection with specific embodiments, but it should be understood that the scope of the invention is not limited to the specific embodiments. The raw materials and reagents used in the examples were all commercially available unless otherwise specified. The oxidant hydrogen peroxide solution used in the following examples is 150kg of hydrogen peroxide solution with a mass concentration of 35%, and the hydrogen peroxide solution is diluted to have a mass concentration of 1.2-2.0%. The formaldehyde scavenger is a commercially available formaldehyde scavenger with model number of GW 21-2. The reducing agent FF6M and the reducing agent zinc sulfoxylate are two different chemicals, both of which are commercially available.

The vinyl acetate used in the following examples has a purity of 99.5% or more, wherein the initial monomeric vinyl acetate and the continuous monomeric vinyl acetate are the same material, but are added in a different order, hence the designations; the monomer vinyl acetate described in the examples refers to the generic term of initial monomer vinyl acetate + continuous monomer vinyl acetate.

Example 1

A preparation method of a low free formaldehyde vinyl acetate-ethylene copolymer emulsion comprises the following operation steps:

(1) taking deionized water as a solvent, mixing 250kg of compound polyvinyl alcohol (obtained by mixing polyvinyl alcohol 05-88 and polyvinyl alcohol 17-88 according to a mass ratio of 1: 3.0) and 12.5kg of zinc sulfoxylate formaldehyde serving as a reducing agent in a container, heating to 85 ℃, uniformly stirring, and preparing 4600kg of mixed solution serving as a surfactant solution for later use; then adding 1050kg of formaldehyde scavenger with the model number of GW21-2 and 1050kg of deionized water into the rear additive tank, uniformly mixing to prepare a 50% formaldehyde scavenger aqueous solution, and maintaining the temperature of the formaldehyde scavenger aqueous solution at 55-65 ℃ for later use;

3850kg of initial monomer vinyl acetate and 4600kg of surfactant solution for later use are added into a polymerization kettle with a stirrer and an external heat removal device, the stirrer and a circulating pump are started, the temperature is raised to 50-60 ℃, ethylene is introduced and is boosted to 3.8MPa, 1.82 percent by mass of oxidant hydrogen peroxide solution is dripped, the stirring reaction is carried out for 120min, the oxidant hydrogen peroxide is added, the reaction is started, continuous monomer vinyl acetate is added when the reaction time is 10min, the reaction is started, the continuous monomer vinyl acetate is added in three batches, 530kg of continuous monomer vinyl acetate is added in each batch, the adding time is 10min, 30min and 50min, the adding time is 15min in each time interval, then the adding is stopped for 5min, the total amount of the continuous monomer vinyl acetate is 1590kg, the ratio of the mass of the initial monomer vinyl acetate to the mass of the continuous monomer vinyl acetate is 2.42:1, releasing heat in the reaction process, finally controlling the reaction temperature to be 78-82 ℃ for reaction, when the reaction is overheated, using circulating cooling water of a reactor heat exchanger to cool, continuously adding ethylene to increase the pressure to 5.9MPa, stopping adding ethylene, setting the pressure of the reactor to be 1.8MPa when the reaction time reaches 78min, automatically controlling the adding rate of an oxidant by an oxidant feeding pump according to the reaction temperature, adjusting the oxidant to be added at a rate of 100% when the reaction time reaches 120min, controlling the total adding amount of the oxidant hydrogen peroxide with the concentration of 1.82% to be 370 kg, adding the oxidant at a rate of 100%, reaching the curing period, simultaneously adding 300kg of the standby formaldehyde scavenger aqueous solution at a rate of 30-40 kg/min (the adding mass of the formaldehyde scavenger aqueous solution is 5.5% of the mass of monomer vinyl acetate), stopping adding the hydrogen peroxide solution 3min after the formaldehyde scavenger aqueous solution is added, and after the reaction is finished, putting the reaction liquid into a flash evaporator to remove residual ethylene;

(2) adding 10kg of deionized water into the reaction liquid from which the residual ethylene is removed in the step (1) according to the amount of 10kg of deionized water added into each ton of reaction liquid to adjust the content of nonvolatile components in the reaction liquid, adding 0.2kg of a reducing agent FF6M into each ton of reaction liquid, adding 0.15kg of tert-butyl peroxybenzoate into each ton of reaction liquid to reduce the content of vinyl acetate in the reaction liquid, adding 1.5kg of sodium bicarbonate into each ton of reaction liquid to adjust the pH value of the reaction liquid, adding 1.5kg of a defoaming agent into each ton of reaction liquid to remove residual fine bubbles in the reaction liquid, stirring uniformly, filtering to remove filter residues, cooling to 25-35 ℃ by circulating cooling water, and obtaining the low-formaldehyde vinyl acetate-ethylene copolymer emulsion GW-705 emulsion with low free formaldehyde.

Example 2

A preparation method of a low free formaldehyde vinyl acetate-ethylene copolymer emulsion comprises the following operation steps:

(1) taking deionized water as a solvent, mixing 250kg of compound polyvinyl alcohol (obtained by mixing polyvinyl alcohol 05-88 and polyvinyl alcohol 17-88 according to a mass ratio of 1.2: 3.5) and 13.0kg of zinc sulfoxylate formaldehyde serving as a reducing agent in a container, heating to 85 ℃, uniformly stirring, and preparing 4750kg of mixed solution serving as a surfactant solution for later use; then adding 1050kg of formaldehyde scavenger with the model number of GW21-2 and 1050kg of deionized water into the rear additive tank, uniformly mixing to prepare a 50% formaldehyde scavenger aqueous solution, and maintaining the temperature of the formaldehyde scavenger aqueous solution at 55-65 ℃ for later use;

3580kg of initial monomer vinyl acetate and 4750kg of the spare surfactant solution are added into a polymerization kettle with a stirrer and an external heat removal device, the stirrer and a circulating pump are started, the temperature is raised to 50-60 ℃, ethylene is introduced and is boosted to 3.8MPa, 1.80 percent by mass of oxidant hydrogen peroxide solution is dripped, the stirring reaction is carried out for 100min, the oxidant hydrogen peroxide is added, the reaction is started, continuous monomer vinyl acetate is added at the 10 th min of the reaction (the continuous monomer vinyl acetate is added in three batches, the adding amount of each batch is equal, the adding time is 10min, 30min and 50min of the reaction, the adding time is 15min at each time interval, then the adding is stopped for 5min, the adding is continued, the total amount of the continuous monomer vinyl acetate is 1750kg, the ratio of the mass of the initial monomer vinyl acetate to the mass of the continuous monomer vinyl acetate is 2.05:1, the heat is released in the reaction process, the reaction temperature is finally controlled to be 78-82 ℃ for reaction, when the reaction is overheated, the reactor heat exchanger is used for cooling by circulating cooling water, the ethylene is continuously added, the pressure is increased to 5.9MPa, the ethylene is stopped to be added, the reactor pressure is set to be 1.8MPa when the reaction time reaches 70min, the adding rate of the oxidant is automatically controlled by an oxidant adding pump according to the reaction temperature, the oxidant is adjusted to be added at a rate of 100% when the reaction time reaches 120min, the total adding amount of the oxidant hydrogen peroxide with the concentration of 1.80% is controlled to be 365-375 kgkg, the oxidant is added at a rate of 100%, the aging period is reached, 300kg of the standby formaldehyde scavenger aqueous solution is added at a rate of 30-40 kg/min (the adding mass of the formaldehyde scavenger aqueous solution is 5.6% of the mass of monomer vinyl acetate), the hydrogen peroxide solution is stopped to be added 3min after the formaldehyde scavenger aqueous solution is added, and after the reaction is finished, putting the reaction solution into a flash evaporator to remove residual ethylene, and filtering to remove scum;

(2) adding 13kg of deionized water into the reaction liquid from which the residual ethylene is removed in the step (1) according to the amount of 13kg of deionized water added per ton of the reaction liquid to adjust the content of nonvolatile components in the reaction liquid, adding 0.3kg of a reducing agent FF6M per ton of the reaction liquid, adding 0.3kg of tert-butyl peroxybenzoate into the reaction liquid per ton to reduce the content of vinyl acetate in the reaction liquid, adding 2.2kg of sodium bicarbonate into the reaction liquid per ton to adjust the pH value of the reaction liquid, adding 2.0kg of a defoaming agent per ton of the reaction liquid to remove residual fine bubbles in the reaction liquid, stirring uniformly, filtering to remove filter residues, cooling to 25-35 ℃ by circulating cooling water, and obtaining the low-formaldehyde vinyl acetate-ethylene copolymer emulsion GW-705 emulsion with low free formaldehyde.

Example 3

A preparation method of a low free formaldehyde vinyl acetate-ethylene copolymer emulsion comprises the following operation steps:

(1) taking deionized water as a solvent, mixing 250kg of compound polyvinyl alcohol (obtained by mixing polyvinyl alcohol 05-88 and polyvinyl alcohol 17-88 according to a mass ratio of 1: 2.5) and 12.8kg of zinc sulfoxylate formaldehyde serving as a reducing agent in a container, heating to 85 ℃, uniformly stirring, and preparing 4700kg of mixed solution serving as a surfactant solution for later use; then adding 1050kg of formaldehyde scavenger with the model number of GW21-2 and 1050kg of deionized water into the rear additive tank, uniformly mixing to prepare a 50% formaldehyde scavenger aqueous solution, and maintaining the temperature of the formaldehyde scavenger aqueous solution at 55-65 ℃ for later use;

adding 3800kg of initial monomer vinyl acetate and 4700kg of the surfactant solution for later use into a polymerization kettle with a stirrer and an external heat removal device, starting the stirrer and a circulating pump, heating to 50-60 ℃, introducing ethylene, boosting to 3.8MPa, dropwise adding 1.82% by mass of oxidant hydrogen peroxide solution, stirring for reaction for 110min, adding the oxidant hydrogen peroxide, starting timing, starting to add continuous monomer vinyl acetate (the continuous monomer vinyl acetate is added in three batches, the adding amount of each batch is equal, the adding time is 10min, 30min and 50min after reaction, the adding time is 15min at each time interval, stopping adding for 5min, continuing adding, the total amount of the continuous monomer vinyl acetate is 1650kg, and the mass ratio of the initial monomer vinyl acetate to the continuous monomer vinyl acetate is 2.3:1, the heat is released in the reaction process, the reaction temperature is finally controlled to be 78-82 ℃ for reaction, when the reaction is overheated, the reactor heat exchanger is used for cooling by circulating cooling water, the ethylene is continuously added, the pressure is increased to 5.9MPa, the ethylene is stopped to be added, the reactor pressure is set to be 1.8MPa when the reaction time reaches 70min, the adding rate of the oxidant is automatically controlled by an oxidant adding pump according to the reaction temperature, the oxidant is adjusted to be added at the rate of 100% when the reaction time reaches 120min, the total adding amount of the oxidant hydrogen peroxide with the mass percent of 1.82% is controlled to be 368-380 kg, the oxidant is added at the rate of 100%, the aging period is reached, 300kg of the standby formaldehyde scavenger aqueous solution is added at the rate of 30-40 kg/min (the adding mass of the formaldehyde scavenger aqueous solution is 5.5% of the mass of the monomer vinyl acetate), the hydrogen peroxide solution is stopped to be added 3min after the formaldehyde scavenger aqueous solution is completely added, after the reaction is finished, putting the reaction solution into a flash evaporator to remove residual ethylene, and filtering to remove scum;

(2) adding 11kg of deionized water into the reaction liquid from which the residual ethylene is removed in the step (1) according to the amount of 11kg of deionized water added per ton of the reaction liquid to adjust the content of nonvolatile components in the reaction liquid, adding 0.2kg of a reducing agent FF6M per ton of the reaction liquid, adding 0.22kg of tert-butyl peroxybenzoate into the reaction liquid per ton to reduce the content of vinyl acetate in the reaction liquid, adding 1.8kg of sodium bicarbonate into the reaction liquid per ton to adjust the pH value of the reaction liquid, adding 1.8kg of a defoaming agent per ton of the reaction liquid to remove residual fine bubbles in the reaction liquid, stirring uniformly, filtering to remove filter residues, cooling to 25-35 ℃ by circulating cooling water, and obtaining the low-formaldehyde vinyl acetate-ethylene copolymer emulsion GW-705 emulsion with low free formaldehyde.

Comparative example 1

In the step (1), the total amount of 1.82% oxidant hydrogen peroxide is controlled to be 370-380 kg, oxidant hydrogen peroxide solution is added at a rate of 100%, after the addition is finished, the reaction solution is placed in a flash evaporator, then 300kg of the standby formaldehyde scavenger aqueous solution (the addition mass of the formaldehyde scavenger aqueous solution is 5.5% of the mass of the monomer vinyl acetate) is added in the flash evaporator, stirring is started for 15min and then stopped, residual ethylene is removed, and scum is removed through filtration; the rest of the operation was the same as in example 1.

The product indices obtained in examples 1, 2, 3 and comparative example 1 are compared in Table 1:

TABLE 1

The comparison table of the quality performance important index test results of the prepared vinyl acetate-ethylene copolymer emulsion GW-705 with low free formaldehyde and the conventional GW-705 is shown in Table 2:

TABLE 2

As can be seen from the data in Table 1, the free formaldehyde content in the products of examples 1, 2 and 3 is lower than 0.1mg/kg, and the chemical and physical properties are basically maintained, but the free formaldehyde content in the product of comparative example 1 is lower than that of the ordinary GW-705 emulsion, but still higher than that of the product of comparative example 1, and the requirement that the limit amount of harmful substances in interior wall coating is less than or equal to 0.1mg/kg is not met, and the GW-705 with low free formaldehyde content is usually produced by adopting the products of examples 1, 2 and 3; as can be seen from the data in Table 2, compared with the conventional GW-705, the GW-705 with low free formaldehyde basically maintains the chemical and physical properties, only reduces the free formaldehyde content, and maintains the original characteristics of the GW-705 while reducing the free formaldehyde content; as can be seen from the data in tables 1 and 2, the low free formaldehyde GW-705 content of the invention is less than or equal to 0.08mg/kg, meets the requirement that the limited free formaldehyde content of harmful substances in interior wall coatings is less than or equal to 0.1mg/kg, and can be widely applied to the fields of adhesives, coatings, cement modifiers, paper processing and the like.

The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. It is not intended to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and its practical application to enable one skilled in the art to make and use various exemplary embodiments of the invention and various alternatives and modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims and their equivalents.