Polymer emulsion preparation method capable of reducing monomer residual quantity

Abstract

The invention discloses a polymer emulsion preparation method capable of reducing monomer residual quantity, which comprises the following steps: S1, mixing a main monomer, a hard monomer, a functional monomer, an oil-soluble peroxide initiator, a first part of emulsifier and a first part of deionized water, and pre-emulsifying to obtain pre-emulsified liquid; s2, dividing the water-soluble initiator into two parts: a first part of the water-soluble initiator and a second part of the water-soluble initiator, wherein the second part of the water-soluble initiator is prepared into a water-soluble initiator solution; adding the remaining second part of the emulsifier and the second part of the deionized water into the reaction kettle, stirring, heating, and adding the pH regulator and the first part of the water-soluble initiator; adding part of the pre-emulsion into a reaction kettle, and then dropwise adding the rest of the pre-emulsion and a water-soluble initiator solution; s3, preparing a reducing agent into a reducing agent aqueous solution, dropwise adding the reducing agent aqueous solution into the reaction kettle, and heating for reaction after dropwise adding is completed; and S4, cooling and filtering to obtain the polymer emulsion with low monomer residual quantity.

Description

Technical Field

[0001] The invention relates to the field of organic preparation, and in particular to a method for preparing a polymer emulsion with reduced monomer residual amount. Background Art

[0002] Polymer emulsion is a colloidal solution formed by polymer particles dispersed in water. It is widely used in coatings, adhesives, textiles, paper processing and other fields. Polymer emulsion is usually prepared from monomers through emulsion polymerization. Since the product contains a certain amount of unreacted monomers, it will be released in the form of VOC after the polymerization reaction. Effective removal methods are needed to reduce its impact on the environment and human health.

[0003] At present, it is a common practice to add initiators or redox initiators in the later stage of the polymerization reaction to eliminate the residual monomers that have not been completely reacted, and it has a certain effect. However, the initiators or peroxide initiators added in the later stage can only act on the surface of the micelles, and it is difficult to initiate the unreacted monomers inside the micelles. Therefore, it is difficult to reduce the residual monomers to less than 500 ppm. Generally, steam stripping is required to further reduce the residual monomer content. However, the equipment cost of the steam stripping method is high, the operation is complicated, and it takes a long time.

[0004] Therefore, it is necessary to improve the existing technology to provide a more reliable solution. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing a polymer emulsion with reduced monomer residual amount in view of the above-mentioned deficiencies in the prior art.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing a polymer emulsion with reduced monomer residual amount, comprising the following steps:

[0007] S1, pre-emulsifying the main monomer, the hard monomer, the functional monomer, the oil-soluble peroxide initiator, the first part of the emulsifier and the first part of the deionized water to obtain a pre-emulsified liquid;

[0008] S2, dividing the water-soluble initiator into two parts: a first part of the water-soluble initiator and a second part of the water-soluble initiator, wherein the second part of the water-soluble initiator is prepared into a water-soluble initiator solution using deionized water;

[0009] The remaining second part of the emulsifier and the second part of the deionized water are added to the reaction kettle for stirring and heating, and a pH regulator and the first part of the water-soluble initiator are added;

[0010] Add part of the pre-emulsion prepared in step S1 into the reaction kettle, and then dropwise add the remaining pre-emulsion and the water-soluble initiator solution;

[0011] S3, preparing a reducing agent aqueous solution with deionized water and then adding it dropwise to the reactor, and heating the reactor to react after the addition is complete;

[0012] S4, after the reaction is completed, the temperature is lowered, and then filtered to obtain a polymer emulsion with low monomer residual content. Preferably, the method for preparing a polymer emulsion with low monomer residual content comprises the following steps:

[0013] S1, pre-emulsifying the main monomer, the hard monomer, the functional monomer, the oil-soluble peroxide initiator, the first part of the emulsifier and the first part of the deionized water to obtain a pre-emulsified liquid;

[0014] S2, dividing the water-soluble initiator into two parts: a first part of the water-soluble initiator and a second part of the water-soluble initiator, wherein the second part of the water-soluble initiator is prepared into a water-soluble initiator solution using deionized water;

[0015] The remaining second part of the emulsifier and the second part of the deionized water are added to the reaction kettle for stirring, and the temperature is raised to 75-83° C., and a pH regulator and the first part of the water-soluble initiator are added;

[0016] Take part of the pre-emulsion prepared in step S1 and add it to the reactor. After reacting for 2-10 minutes, start to dropwise add the remaining part of the pre-emulsion and the water-soluble initiator solution. The dropping time is controlled to be 1-4 hours.

[0017] S3, preparing a reducing agent aqueous solution with deionized water and then adding it dropwise to the reactor, controlling the adding time to be 5-30 min, and keeping the temperature at 80-88° C. for 1-4 h after the adding is completed;

[0018] S4. After the heat preservation is completed, the temperature is lowered to below 40-60°C, and then filtered to obtain a polymer emulsion with low monomer residual content.

[0019] Preferably, the method for preparing a polymer emulsion with reduced monomer residual amount comprises the following steps:

[0020] S1, pre-emulsifying the main monomer, the hard monomer, the functional monomer, the oil-soluble peroxide initiator, the first part of the emulsifier and the first part of the deionized water to obtain a pre-emulsified liquid;

[0021] S2, dividing the water-soluble initiator into two parts: a first part of the water-soluble initiator and a second part of the water-soluble initiator, wherein the second part of the water-soluble initiator is prepared into a water-soluble initiator solution using deionized water;

[0022] The remaining second part of the emulsifier and the second part of the deionized water are added to the reaction kettle for stirring, and the temperature is raised to 80° C., and a pH adjuster and the first part of the water-soluble initiator are added;

[0023] Take part of the pre-emulsion prepared in step S1 and add it to the reactor. After reacting for 5 minutes, start to dropwise add the remaining part of the pre-emulsion and the water-soluble initiator solution. The dropping time is controlled to be 2 hours.

[0024] S3, prepare a reducing agent aqueous solution with deionized water and then add it dropwise to the reactor, control the dropping time to be 15 minutes, and after the dropping is completed, heat it to 84°C and keep it warm for 2 hours;

[0025] S4. After the heat preservation is completed, the temperature is lowered to below 50° C., and then filtered to obtain a polymer emulsion with a low monomer residual content.

[0026] Preferably, the mass ratio of the first part of the emulsifier to the second part of the emulsifier is 2:1;

[0027] The mass ratio of the first part of deionized water to the second part of deionized water is 1:2;

[0028] The mass ratio of the first part of water-soluble initiator to the second part of water-soluble initiator is 1:2;

[0029] Preferably, the mass concentration of the water-soluble initiator in the water-soluble initiator solution is 2-8%;

[0030] In the reducing agent aqueous solution, the mass concentration of the reducing agent is 1.5-7%;

[0031] Preferably, by weight: the main monomer is 45-50 parts, the hard monomer is 10-15 parts, the functional monomer is 0.5-1.5 parts, the sum of the first part of the emulsifier and the second part of the emulsifier is 0.1-0.4 parts, the sum of the first part of the deionized water and the second part of the deionized water is 40-50 parts, the pH adjuster is 0.05-0.1 parts, the sum of the first part of the water-soluble initiator and the second part of the water-soluble initiator is 0.1-0.3 parts, the oil-soluble peroxide initiator is 0.05-0.1 parts, and the reducing agent is 0.05-0.1 parts.

[0032] Preferably, the main monomer is at least one of butyl acrylate and isooctyl acrylate;

[0033] The hard monomer is at least one of methyl acrylate, methyl methacrylate, n-butyl methacrylate, styrene and acrylonitrile;

[0034] The functional monomer is at least one of acrylic acid, methacrylic acid, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl acrylate, glycidyl methacrylate, ethylene glycol dimethacrylate, and β-carboxyethyl acrylate.

[0035] Preferably, the water-soluble initiator is at least one of ammonium persulfate and potassium persulfate;

[0036] The oil-soluble peroxide initiator of the present invention is di-tert-butyl peroxide.

[0037] Preferably, the reducing agent is at least one of sodium sulfite, sodium bisulfite and ascorbic acid.

[0038] Preferably, the emulsifier is at least one of anionic emulsifiers selected from sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium dodecyl diphenyl ether disulfonate, and sodium alkylphenol polyoxyethylene sulfate;

[0039] The pH regulator of the present invention is at least one of sodium bicarbonate and sodium hydroxide.

[0040] The beneficial effects of the present invention are:

[0041] The present invention provides a method for preparing a polymer emulsion with reduced residual monomer content, wherein an oil-soluble initiator with a high reaction temperature is emulsified together with a monomer in the emulsification stage, and before a reducing agent is added, the oil-soluble initiator basically does not react due to its high reaction temperature, but enters into latex particles together with the monomer; in the later stage, the reducing agent is added to reduce the activation energy of the oil-soluble initiator, and the oil-soluble initiator in the system begins to decompose and generate free radicals, which can consume unreacted monomers in the latex particles and reduce the overall residual monomer content. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 GC-FID spectrum of polymer emulsion 1 prepared in Example 1;

[0043] Figure 2 GC-FID spectrum of polymer emulsion 2 prepared in Example 2;

[0044] Figure 3 GC-FID spectrum of polymer emulsion 3 prepared in Comparative Example 1;

[0045] Figure 4 This is the GC-FID spectrum of polymer emulsion 4 prepared in Comparative Example 2. DETAILED DESCRIPTION

[0046] The present invention is further described in detail below in conjunction with embodiments so that those skilled in the art can implement the invention with reference to the description.

[0047] It should be understood that the terms such as “having”, “including” and “comprising” used herein do not exclude the existence or addition of one or more other elements or combinations thereof.

[0048] The test methods used in the following examples are conventional methods unless otherwise specified. The materials and reagents used in the following examples are all commercially available unless otherwise specified. In the following examples, if no specific conditions are specified, the experiments were carried out under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used, if the manufacturer is not specified, are all conventional products that can be purchased commercially.

[0049] The invention provides a method for preparing a polymer emulsion with reduced monomer residual amount. The method comprises the following steps: emulsifying an oil-soluble peroxide initiator together with a monomer, so that the oil-soluble peroxide initiator can fully enter micelles and latex particles during a reaction; and dropping a reducing agent in the later stage of the reaction to reduce the half-life of the oil-soluble peroxide initiator so that the initiator can be initiated at the current temperature. Since the oil-soluble peroxide already exists in the latex particles, the unreacted monomers in the latex particles can be treated well. The method comprises the following steps:

[0050] S1, pre-emulsifying the main monomer, the hard monomer, the functional monomer, the oil-soluble peroxide initiator, the first part of the emulsifier and the first part of the deionized water to obtain a pre-emulsified liquid;

[0051] S2, dividing the water-soluble initiator into two parts: a first part of the water-soluble initiator and a second part of the water-soluble initiator, wherein the second part of the water-soluble initiator is prepared into a water-soluble initiator solution using deionized water;

[0052] The remaining second part of the emulsifier and the second part of the deionized water are added to the reaction kettle for stirring and heating, and a pH regulator and the first part of the water-soluble initiator are added;

[0053] Add part of the pre-emulsion prepared in step S1 into the reaction kettle, and then dropwise add the remaining pre-emulsion and the water-soluble initiator solution;

[0054] S3, preparing a reducing agent aqueous solution with deionized water and then adding it dropwise to the reactor, and heating the reactor to react after the addition is complete;

[0055] S4. After the reaction is completed, the temperature is lowered and then filtered to obtain a polymer emulsion with a low monomer residual content.

[0056] In a preferred embodiment, the method for preparing a polymer emulsion with reduced monomer residual amount comprises the following steps:

[0057] S1, pre-emulsifying the main monomer, the hard monomer, the functional monomer, the oil-soluble peroxide initiator, the first part of the emulsifier and the first part of the deionized water to obtain a pre-emulsified liquid;

[0058] S2, dividing the water-soluble initiator into two parts: a first part of the water-soluble initiator and a second part of the water-soluble initiator, wherein the second part of the water-soluble initiator is prepared into a water-soluble initiator solution using deionized water;

[0059] The remaining second part of the emulsifier and the second part of the deionized water are added to the reaction kettle for stirring, and the temperature is raised to 75-83° C., and a pH regulator and the first part of the water-soluble initiator are added;

[0060] Take part of the pre-emulsion prepared in step S1 and add it to the reactor. After reacting for 2-10 minutes, start to dropwise add the remaining part of the pre-emulsion and the water-soluble initiator solution. The dropping time is controlled to be 1-4 hours.

[0061] S3, preparing a reducing agent aqueous solution with deionized water and then adding it dropwise to the reactor, controlling the adding time to be 5-30 min, and keeping the temperature at 80-88° C. for 1-4 h after the adding is completed;

[0062] S4. After the heat preservation is completed, the temperature is lowered to below 40-60°C, and then filtered to obtain a polymer emulsion with low monomer residual content.

[0063] In a more preferred embodiment, the method for preparing a polymer emulsion with reduced monomer residual amount comprises the following steps:

[0064] S1, pre-emulsifying the main monomer, the hard monomer, the functional monomer, the oil-soluble peroxide initiator, the first part of the emulsifier and the first part of the deionized water to obtain a pre-emulsified liquid;

[0065] S2, dividing the water-soluble initiator into two parts: a first part of the water-soluble initiator and a second part of the water-soluble initiator, wherein the second part of the water-soluble initiator is prepared into a water-soluble initiator solution using deionized water;

[0066] The remaining second part of the emulsifier and the second part of the deionized water are added to the reaction kettle for stirring, and the temperature is raised to 80° C., and a pH adjuster and the first part of the water-soluble initiator are added;

[0067] Take part of the pre-emulsion prepared in step S1 and add it to the reactor. After reacting for 5 minutes, start to dropwise add the remaining part of the pre-emulsion and the water-soluble initiator solution. The dropping time is controlled to be 2 hours.

[0068] S3, prepare a reducing agent aqueous solution with deionized water and then add it dropwise to the reactor, control the dropping time to be 15 minutes, and after the dropping is completed, heat it to 84°C and keep it warm for 2 hours;

[0069] S4. After the heat preservation is completed, the temperature is lowered to below 50° C., and then filtered to obtain a polymer emulsion with a low monomer residual content.

[0070] In a preferred embodiment, the mass ratio of the first part of the emulsifier to the second part of the emulsifier is 2:1.

[0071] In a preferred embodiment, the mass ratio of the first part of deionized water to the second part of deionized water is 1:2.

[0072] In a preferred embodiment, the mass ratio of the first part of the water-soluble initiator to the second part of the water-soluble initiator is 1:2.

[0073] In a preferred embodiment, the mass concentration of the water-soluble initiator in the water-soluble initiator solution is 2-8%.

[0074] In a preferred embodiment, the mass concentration of the reducing agent in the reducing agent aqueous solution is 1.5-7%.

[0075] In a preferred embodiment, by weight: the main monomer is 45-50 parts, the hard monomer is 10-15 parts, the functional monomer is 0.5-1.5 parts, the sum of the first part of the emulsifier and the second part of the emulsifier is 0.1-0.4 parts, the sum of the first part of the deionized water and the second part of the deionized water is 40-50 parts, the pH adjuster is 0.05-0.1 parts, the sum of the first part of the water-soluble initiator and the second part of the water-soluble initiator is 0.1-0.3 parts, the oil-soluble peroxide initiator is 0.05-0.1 parts, and the reducing agent is 0.05-0.1 parts.

[0076] In a preferred embodiment, the main monomer is at least one of butyl acrylate and isooctyl acrylate.

[0077] In a preferred embodiment, the hard monomer is at least one of methyl acrylate, methyl methacrylate, n-butyl methacrylate, styrene and acrylonitrile.

[0078] In a preferred embodiment, the functional monomer is at least one of acrylic acid, methacrylic acid, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl acrylate, glycidyl methacrylate, ethylene glycol dimethacrylate, and β-carboxyethyl acrylate.

[0079] In a preferred embodiment, the water-soluble initiator is at least one of ammonium persulfate and potassium persulfate.

[0080] In a preferred embodiment, the oil-soluble peroxide initiator of the present invention is di-tert-butyl peroxide (DTBP).

[0081] In a preferred embodiment, the reducing agent is at least one of sodium sulfite, sodium bisulfite, and ascorbic acid.

[0082] In a preferred embodiment, the emulsifier is at least one of anionic emulsifiers selected from sodium dodecyl sulfate (SDS), sodium dodecylbenzene sulfonate (SDBS), sodium dodecyl diphenyl ether disulfonate (2A-1), and sodium alkylphenol polyoxyethylene sulfate.

[0083] In a preferred embodiment, the pH regulator of the present invention is at least one of sodium bicarbonate and sodium hydroxide.

[0084] The present invention selects an oil-soluble initiator with a higher reaction temperature when no reducing agent is added, which will not participate in the reaction in advance in the early stage and can be emulsified together with the monomer; in the later stage of the reaction, by adding a reducing agent, the activation energy of the oil-soluble initiator is reduced, free radicals can be generated inside the latex particles, and the residual monomer content is reduced.

[0085] The above is the overall concept of the present invention, and detailed embodiments and comparative examples are provided below on the basis of the overall concept of the present invention to further illustrate the present invention.

[0086] Example 1

[0087] An emulsion polymerization method for reducing the amount of residual monomers comprises the following steps:

[0088] S1, weigh 0.8 g of sodium dodecyl sulfate and 70 g of deionized water, mix and stir until foam is generated, weigh 215 g of butyl acrylate, 60 g of methyl methacrylate, 6 g of acrylic acid, and 0.35 g of di-tert-butyl peroxide, mix thoroughly and add to the mixed solution of sodium dodecyl sulfate and deionized water, and continue stirring for 20 min to obtain a pre-emulsion;

[0089] S2, weigh 0.4 g of sodium dodecyl sulfate and 140 g of deionized water into a reaction kettle, stir and heat to 80°C, add 0.35 g of sodium bicarbonate and 0.4 g of ammonium persulfate;

[0090] 5 g of the pre-emulsion was added to the reactor and reacted for 5 min. 0.8 g of ammonium persulfate was weighed and dissolved in 20 g of water to prepare a water-soluble initiator aqueous solution. The water-soluble initiator solution and the remaining pre-emulsion were added dropwise at the same time for 2 h.

[0091] S3, add a solution of 0.35g sodium sulfite and 10g water dropwise for 15min, after the sodium sulfite aqueous solution is added dropwise, raise the temperature to 84°C and keep warm for 2h;

[0092] S4. Cooling to 50° C. and filtering with a 200-mesh nickel screen to obtain polymer emulsion 1.

[0093] Example 2

[0094] An emulsion polymerization method for reducing the amount of residual monomers comprises the following steps:

[0095] S1, weighing 0.8 g of sodium dodecyl diphenyl oxide disulfonate, 70 g of deionized water, and stirring until foam is generated, weighing 215 g of butyl acrylate, 60 g of n-butyl methacrylate, 6 g of methacrylic acid, and 0.35 g of di-tert-butyl peroxide, mixing thoroughly, adding to the mixed solution of the sodium dodecyl diphenyl oxide disulfonate and deionized water, and continuing to stir for 20 min to obtain a pre-emulsion;

[0096] S2, weigh 0.4 g of sodium dodecyl diphenyl ether disulfonate and 140 g of deionized water into a reactor, stir and heat to 80°C, add 0.35 g of sodium bicarbonate and 0.4 g of potassium persulfate;

[0097] 5 g of the pre-emulsion was added to the reactor and reacted for 5 min. 0.8 g of potassium persulfate was weighed and dissolved in 20 g of water to prepare a water-soluble initiator aqueous solution, and the water-soluble initiator solution and the remaining pre-emulsion were added dropwise at the same time for 2 h.

[0098] S3, add a solution of 0.35g sodium sulfite and 10g water dropwise for 15min, after the sodium sulfite aqueous solution is added dropwise, raise the temperature to 84°C and keep warm for 2h;

[0099] S4. Cool down to 50° C. and filter through a 200-mesh nickel screen to obtain polymer emulsion 2.

[0100] Comparative Example 1

[0101] Comparative Example 1 is substantially the same as Example 1, except that no peroxide initiator and reducing agent are used. The specific steps are as follows:

[0102] S1, weigh 0.8 g of sodium dodecyl sulfate and 70 g of deionized water, mix and stir until foam is generated, weigh 215 g of butyl acrylate, 60 g of methyl methacrylate and 6 g of acrylic acid, mix thoroughly and add to the mixed solution of sodium dodecyl sulfate and deionized water, and continue stirring for 20 min to obtain a pre-emulsion;

[0103] S2, weigh 0.4 g of sodium dodecyl sulfate and 140 g of deionized water into a reaction kettle, stir and heat to 80°C, add 0.35 g of sodium bicarbonate and 0.4 g of ammonium persulfate;

[0104] Take 5g of the pre-emulsion and add it to the reactor for 5 minutes. Weigh 0.8g of ammonium persulfate and dissolve it in 20g of water to prepare a water-soluble initiator aqueous solution, and start dripping the water-soluble initiator solution and the remaining pre-emulsion at the same time for 2h;

[0105] S3, raise the temperature to 84°C and keep warm for 2h;

[0106] S4. Cool down to 50° C. and filter with a 200-mesh nickel screen to obtain polymer emulsion 3.

[0107] Comparative Example 2

[0108] Comparative Example 1 is basically the same as Example 2, except that the peroxide initiator and the reducing agent are added dropwise simultaneously in the late stage of the reaction. The specific steps are as follows:

[0109] S1, weighing 0.8 g of sodium dodecyl diphenyl oxide disulfonate, 70 g of deionized water, and stirring until foam is generated, weighing 215 g of butyl acrylate, 60 g of n-butyl methacrylate, and 6 g of methacrylic acid, mixing them thoroughly, adding them to the mixed solution of the sodium dodecyl diphenyl oxide disulfonate and deionized water, and continuing to stir for 20 min to obtain a pre-emulsion;

[0110] S2, weigh 0.4 g of sodium dodecyl diphenyl ether disulfonate and 140 g of deionized water into a reactor, stir and heat to 80°C, add 0.35 g of sodium bicarbonate and 0.4 g of potassium persulfate;

[0111] 5 g of the pre-emulsion was added to the reactor and reacted for 5 min. 0.8 g of potassium persulfate was weighed and dissolved in 20 g of water to prepare a water-soluble initiator aqueous solution, and the water-soluble initiator solution and the remaining pre-emulsion were added dropwise at the same time for 2 h.

[0112] S3, add 0.35g of a solution of sodium sulfite and 10g of water and 0.35g of di-tert-butyl peroxide dropwise for 15min. After the addition is complete, raise the temperature to 84°C and keep warm for 2h;

[0113] S4, cooling to 50°C, and filtering with a 200-mesh nickel screen to obtain polymer emulsion 4.

[0114] The residual monomer volatiles of the emulsions obtained in the above embodiment and the comparative example were detected by headspace gas chromatography, and the results are shown in Table 1 below:

[0115] Table 1

[0116]

[0117]

[0118] It can be seen from the test results of the embodiments and comparative examples that the emulsion obtained by the method of the present invention has a low content of residual monomer volatiles, which is less than 500 ppm.

[0119] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to specific details.

Claims

1. A method for preparing a polymer emulsion with reduced monomer residual amount, characterized in that: The following steps are involved: S1, pre-emulsifying the main monomer, the hard monomer, the functional monomer, the oil-soluble peroxide initiator, the first part of the emulsifier and the first part of the deionized water to obtain a pre-emulsified liquid; S2, dividing the water-soluble initiator into two parts: a first part of the water-soluble initiator and a second part of the water-soluble initiator, wherein the second part of the water-soluble initiator is prepared into a water-soluble initiator solution using deionized water; The remaining second part of the emulsifier and the second part of the deionized water are added to the reaction kettle for stirring and heating, and a pH regulator and the first part of the water-soluble initiator are added; Add part of the pre-emulsion prepared in step S1 into the reaction kettle, and then dropwise add the remaining pre-emulsion and the water-soluble initiator solution; S3, preparing a reducing agent aqueous solution with deionized water and then adding it dropwise to the reactor, and heating the reactor to react after the addition is complete; S4. After the reaction is completed, the temperature is lowered and then filtered to obtain a polymer emulsion with a low monomer residual content.

2. The method for preparing a polymer emulsion with reduced monomer residual amount according to claim 1, characterized in that: The following steps are involved: S1, pre-emulsifying the main monomer, the hard monomer, the functional monomer, the oil-soluble peroxide initiator, the first part of the emulsifier and the first part of the deionized water to obtain a pre-emulsified liquid; S2, dividing the water-soluble initiator into two parts: a first part of the water-soluble initiator and a second part of the water-soluble initiator, wherein the second part of the water-soluble initiator is prepared into a water-soluble initiator solution using deionized water; The remaining second part of the emulsifier and the second part of the deionized water are added to the reaction kettle for stirring, and the temperature is raised to 75-83° C., and a pH regulator and the first part of the water-soluble initiator are added; Take part of the pre-emulsion prepared in step S1 and add it to the reactor. After reacting for 2-10 minutes, start to dropwise add the remaining part of the pre-emulsion and the water-soluble initiator solution. The dropping time is controlled to be 1-4 hours. S3, preparing a reducing agent aqueous solution with deionized water and then adding it dropwise to the reactor, controlling the adding time to be 5-30 min, and keeping the temperature at 80-88° C. for 1-4 h after the adding is completed; S4. After the heat preservation is completed, the temperature is lowered to below 40-60°C, and then filtered to obtain a polymer emulsion with low monomer residual content.

3. The method for preparing a polymer emulsion with reduced monomer residual amount according to claim 2, characterized in that: The following steps are involved: S1, pre-emulsifying the main monomer, the hard monomer, the functional monomer, the oil-soluble peroxide initiator, the first part of the emulsifier and the first part of the deionized water to obtain a pre-emulsified liquid; S2, dividing the water-soluble initiator into two parts: a first part of the water-soluble initiator and a second part of the water-soluble initiator, wherein the second part of the water-soluble initiator is prepared into a water-soluble initiator solution using deionized water; The remaining second part of the emulsifier and the second part of the deionized water are added to the reaction kettle for stirring, and the temperature is raised to 80° C., and a pH adjuster and the first part of the water-soluble initiator are added; Take part of the pre-emulsion prepared in step S1 and add it to the reactor. After reacting for 5 minutes, start to dropwise add the remaining part of the pre-emulsion and the water-soluble initiator solution. The dropping time is controlled to be 2 hours. S3, prepare a reducing agent aqueous solution with deionized water and then add it dropwise to the reactor, control the dropping time to be 15 minutes, and after the dropping is completed, heat it to 84°C and keep it warm for 2 hours; S4. After the heat preservation is completed, the temperature is lowered to below 50° C., and then filtered to obtain a polymer emulsion with a low monomer residual content.

4. The method for preparing a polymer emulsion with reduced monomer residual amount according to claim 1, characterized in that: The mass ratio of the first part of emulsifier to the second part of emulsifier is 2:1; The mass ratio of the first part of deionized water to the second part of deionized water is 1:2; The mass ratio of the first part of the water-soluble initiator to the second part of the water-soluble initiator is 1:

2.

5. The method for preparing a polymer emulsion with reduced monomer residual amount according to claim 1, characterized in that: In the water-soluble initiator solution, the mass concentration of the water-soluble initiator is 2-8%; In the reducing agent aqueous solution, the mass concentration of the reducing agent is 1.5-7%.

6. The method for preparing a polymer emulsion with reduced monomer residual amount according to claim 1, characterized in that: In parts by weight: the main monomer is 45-50 parts, the hard monomer is 10-15 parts, the functional monomer is 0.5-1.5 parts, the sum of the first part of the emulsifier and the second part of the emulsifier is 0.1-0.4 parts, the sum of the first part of the deionized water and the second part of the deionized water is 40-50 parts, the pH adjuster is 0.05-0.1 parts, the sum of the first part of the water-soluble initiator and the second part of the water-soluble initiator is 0.1-0.3 parts, the oil-soluble peroxide initiator is 0.05-0.1 parts, and the reducing agent is 0.05-0.1 parts.

7. The method for preparing a polymer emulsion with reduced monomer residual amount according to claim 1, characterized in that: The main monomer is at least one of butyl acrylate and isooctyl acrylate; The hard monomer is at least one of methyl acrylate, methyl methacrylate, n-butyl methacrylate, styrene and acrylonitrile; The functional monomer is at least one of acrylic acid, methacrylic acid, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl acrylate, glycidyl methacrylate, ethylene glycol dimethacrylate, and β-carboxyethyl acrylate.

8. The method for preparing a polymer emulsion with reduced monomer residual amount according to claim 1, characterized in that: The water-soluble initiator is at least one of ammonium persulfate and potassium persulfate; The oil-soluble peroxide initiator of the present invention is di-tert-butyl peroxide.

9. The method for preparing a polymer emulsion with reduced monomer residual amount according to claim 1, characterized in that: The reducing agent is at least one of sodium sulfite, sodium bisulfite and ascorbic acid.

10. The method for preparing a polymer emulsion with reduced monomer residual amount according to claim 1, characterized in that: The emulsifier is at least one of anionic emulsifiers selected from sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, sodium dodecyl diphenyl ether disulfonate, and sodium alkylphenol polyoxyethylene sulfate; The pH regulator of the present invention is at least one of sodium bicarbonate and sodium hydroxide.

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