An emulsion type low temperature pressure sensitive adhesive and a method for preparing the same

Abstract

The application discloses an emulsion type low-temperature pressure-sensitive adhesive and a preparation method thereof. The emulsion type low-temperature pressure-sensitive adhesive comprises, in parts by weight, 20 parts of alkyl acrylate soft monomer, 10-40 parts of alkoxy polyethylene glycol acrylate monomer, 0.1-0.5 parts of functional monomer, 0.01-0.05 parts of pH regulator, 0.01-0.05 parts of chain transfer agent, 0.3-0.9 parts of emulsifier, 0.05-0.3 parts of initiator, 0.5-2 parts of rheological auxiliary agent and 15-30 parts of water. The initial tack and low-temperature resistance of the emulsion pressure-sensitive adhesive are greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of pressure-sensitive adhesive technology, and particularly relates to an emulsion-type low-temperature pressure-sensitive adhesive and its preparation method. Background Technology

[0002] Pressure-sensitive adhesives (PSAs) are viscoelastic materials that possess both liquid viscosity and solid elasticity. Their applications primarily include tapes, films, labels, and protective films. Currently, global PSA production exceeds one million tons, and they are widely used in the electronics, electrical appliances, aerospace, and packaging industries, making them a crucial industrial material.

[0003] Currently, pressure-sensitive adhesives (PSAs) used in actual production mainly include three types: solvent-based, hot-melt, and emulsion-based. Solvent-based PSAs typically contain over 50% solvent, causing serious environmental pollution and posing safety hazards during production. While hot-melt PSAs do not contain solvents, their production and coating temperatures exceed 130°C, resulting in very high energy consumption. Furthermore, hot-melt PSAs are usually based on unsaturated styrene-isoprene-styrene copolymers, leading to poor aging resistance. Compared to solvent-based and hot-melt PSAs, emulsion-based PSAs are much more environmentally friendly, have a safer production process, relatively lower energy consumption, and excellent aging resistance, thus attracting widespread research and application. Currently widely used emulsion-based PSAs typically exhibit good initial tack and holding power at room temperature and higher temperatures; however, due to their high glass transition temperature, their adhesion at low temperatures is poor, and they may even lack tack under extremely cold conditions (< -20°C).

[0004] Patent CN116023603A discloses an acrylate polymer, a pressure-sensitive adhesive composition, and a protective film. This pressure-sensitive adhesive is obtained through solution polymerization, which poses environmental pollution problems. More importantly, this pressure-sensitive adhesive only uses polyethylene glycol acrylate derivative ultra-flexible monomers without chain transfer agents or rheology modifiers, resulting in poor low-temperature performance. Patent CN108587527B discloses a method for preparing a low-temperature acrylate pressure-sensitive adhesive, using C8-C10 branched acrylate monomers. Compared with conventional acrylate emulsion pressure-sensitive adhesives, it has certain low-temperature resistance; however, it does not use chain transfer agents to reduce molecular weight, long-branched emulsifiers to lower the glass transition temperature, or rheology modifiers to further reduce low-temperature fluidity during polymerization. Therefore, its minimum operating temperature is only -20°C, and it cannot be used at temperatures as low as -30°C.

[0005] Conventional acrylic pressure-sensitive adhesives fail at low temperatures primarily in two ways: firstly, for adhesives about to be applied, the molecular movement is difficult at low temperatures, making it hard to quickly wet the bonded surface, resulting in low adhesive strength; secondly, for already bonded pressure-sensitive adhesive products, the temperature drop causes the adhesive to harden and detach. To meet the low-temperature requirements of modern industry, there is an urgent need to improve existing conventional emulsion pressure-sensitive adhesives. This can be achieved through molecular design and formulation optimization to improve the low-temperature flowability of these adhesives, thereby obtaining high-performance emulsion-type low-temperature pressure-sensitive adhesives. Summary of the Invention

[0006] This invention provides an emulsion-type low-temperature pressure-sensitive adhesive and its preparation method, which enables the pressure-sensitive adhesive to have excellent low-temperature bonding performance and significantly improves the initial tack and holding power of the pressure-sensitive adhesive in low-temperature environments.

[0007] To achieve the above objectives, the present invention provides an emulsion-type low-temperature pressure-sensitive adhesive, comprising, by weight, 20 parts of alkyl acrylate soft monomer, 10-40 parts of alkoxy polyethylene glycol acrylate monomer, 0.1-0.5 parts of functional monomer, 0.01-0.05 parts of pH adjuster, 0.01-0.05 parts of chain transfer agent, 0.3-0.9 parts of emulsifier, 0.05-0.3 parts of initiator, 0.5-2 parts of rheology modifier, and 15-30 parts of water.

[0008] The alkyl acrylate soft monomer is one of butyl acrylate, isooctyl acrylate, n-octyl acrylate, and cyclohexyl acrylate.

[0009] The alkoxy polyethylene glycol acrylate monomer is one of methoxy polyethylene glycol acrylate, phenoxy polyethylene glycol acrylate, and nonylphenoxy polyethylene glycol acrylate.

[0010] The functional monomer is one of acrylic acid and methacrylic acid.

[0011] The pH adjuster is either sodium bicarbonate or sodium carbonate.

[0012] The chain transfer agent is one of dodecyl mercaptan or mercaptoethanol.

[0013] The emulsifier is one of sodium dodecyl sulfate, sodium nonylphenol polyoxyethylene ether sulfate, and ammonium allyloxynonylphenol polyoxyethylene ether sulfate.

[0014] The initiator is one of ammonium persulfate or potassium persulfate.

[0015] The rheology modifier is one of dodecyl alcohol ester, propylene glycol butyl ether, and propylene glycol methyl ether acetate.

[0016] A method for preparing an emulsion-type low-temperature pressure-sensitive adhesive includes the following steps:

[0017] S1. Add monomer, chain transfer agent, emulsifier and initiator to half water in weight ratio and stir to obtain preemulsion;

[0018] S2. Add the other half of the water and pH adjuster to the reaction vessel, heat to 80°C, and then add the pre-emulsion dropwise. After the dropwise addition is complete, continue the reaction for 1 hour. After cooling, add the rheology modifier and stir well to obtain the emulsion-type low-temperature pressure-sensitive adhesive.

[0019] By weight, the composition includes 20 parts alkyl acrylate soft monomer, 10-40 parts alkoxy polyethylene glycol acrylate monomer, 0.1-0.5 parts functional monomer, 0.01-0.05 parts pH adjuster, 0.01-0.05 parts chain transfer agent, 0.3-0.9 parts emulsifier, 0.05-0.3 parts initiator, 0.5-2 parts rheology modifier, and 15-30 parts water.

[0020] Beneficial effects:

[0021] An environmentally friendly low-temperature pressure-sensitive adhesive is provided through emulsion polymerization using water as a medium.

[0022] The emulsion-type low-temperature pressure-sensitive adhesive of the present invention contains alkoxy polyethylene glycol acrylate, and the flexible polyethylene glycol segment has a lower glass transition temperature and excellent low-temperature fluidity, which can significantly improve the initial tack and low-temperature resistance of traditional emulsion pressure-sensitive adhesives.

[0023] The emulsion-type low-temperature pressure-sensitive adhesive of the present invention has a reduced molecular weight and glass transition temperature due to the addition of a chain transfer agent during the preparation process, thereby improving the fluidity and adhesion of the pressure-sensitive adhesive at low temperatures.

[0024] The emulsion-type low-temperature pressure-sensitive adhesive of the present invention contains long-branched emulsifier segments, which can effectively reduce the glass transition temperature of the pressure-sensitive adhesive and improve its low-temperature fluidity.

[0025] The emulsion-type low-temperature pressure-sensitive adhesive of the present invention contains a rheology modifier, which can further improve the low-temperature fluidity of the pressure-sensitive adhesive and prevent it from hardening and losing its tack at low temperatures. Detailed Implementation

[0026] The technical solution of the present invention will be described below through specific embodiments.

[0027] An emulsion-type low-temperature pressure-sensitive adhesive, by weight, comprises 20 parts of alkyl acrylate soft monomer, 10-40 parts of alkoxy polyethylene glycol acrylate monomer, 0.1-0.5 parts of functional monomer, 0.01-0.05 parts of pH adjuster, 0.01-0.05 parts of chain transfer agent, 0.3-0.9 parts of emulsifier, 0.05-0.3 parts of initiator, 0.5-2 parts of rheology modifier, and 15-30 parts of water.

[0028] Furthermore, the alkyl acrylate soft monomer is one of butyl acrylate, isooctyl acrylate, n-octyl acrylate, and cyclohexyl acrylate. Preferably, the alkyl acrylate soft monomer is isooctyl acrylate, which has a lower glass transition temperature and better flowability at low temperatures.

[0029] Furthermore, the alkoxy polyethylene glycol acrylate monomer is one of methoxy polyethylene glycol acrylate, phenoxy polyethylene glycol acrylate, and nonylphenoxy polyethylene glycol acrylate.

[0030] Low-temperature pressure-sensitive adhesives prepared from alkoxy polyethylene glycol acrylate monomers exhibit lower glass transition temperatures and superior low-temperature flowability compared to traditional alkyl acrylate soft monomers. Therefore, they can improve the initial tack and low-temperature resistance of traditional emulsion pressure-sensitive adhesives.

[0031] Furthermore, the functional monomer is one of acrylic acid and methacrylic acid.

[0032] Furthermore, the pH adjuster is either sodium bicarbonate or sodium carbonate.

[0033] Furthermore, the chain transfer agent is one of dodecyl mercaptan or mercaptoethanol. Preferably, the chain transfer agent is dodecyl mercaptan, which has less odor and volatility.

[0034] This invention incorporates a chain transfer agent during the preparation of emulsion-type pressure-sensitive adhesives, which significantly reduces the molecular weight of the resulting pressure-sensitive adhesive, thereby lowering the glass transition temperature of the polymer and improving the fluidity and adhesion of the pressure-sensitive adhesive at low temperatures. Conventional emulsion-type pressure-sensitive adhesives, due to the absence of a chain transfer agent in their preparation, result in very large molecular weights and high glass transition temperatures, limiting their applicability to room temperature and higher temperatures.

[0035] The emulsifier is one of sodium dodecyl sulfate, sodium nonylphenol polyoxyethylene ether sulfate, and ammonium allyloxynonylphenol polyoxyethylene ether sulfate.

[0036] The initiator is one of ammonium persulfate or potassium persulfate.

[0037] The rheology modifier is one of dodecyl alcohol ester, propylene glycol butyl ether, and propylene glycol methyl ether acetate. The rheology modifier can further improve the low-temperature flowability of the pressure-sensitive adhesive and prevent it from hardening and losing its tackiness at low temperatures.

[0038] Example 1

[0039] An emulsion-type low-temperature pressure-sensitive adhesive is prepared from the following raw materials in parts by weight: 20 parts butyl acrylate, 10 parts methoxy polyethylene glycol acrylate, 0.1 parts acrylic acid, 0.01 parts sodium bicarbonate, 0.05 parts dodecyl mercaptan, 0.3 parts sodium dodecyl sulfate, 0.05 parts ammonium persulfate, 0.5 parts dodecyl alcohol ester, and 20 parts water.

[0040] A method for preparing an emulsion-type low-temperature pressure-sensitive adhesive is as follows: butyl acrylate, methoxy polyethylene glycol acrylate, acrylic acid, dodecyl mercaptan, sodium dodecyl sulfate, and ammonium persulfate are added to 10 parts of water and stirred to obtain a pre-emulsion; 10 parts of water and sodium bicarbonate are added to a reaction vessel, heated to 80°C, and the pre-emulsion is added dropwise. After the dropwise addition is completed in 3 hours, the reaction continues for 1 hour. After cooling, dodecyl alcohol ester is added and stirred until homogeneous to obtain the emulsion-type low-temperature pressure-sensitive adhesive.

[0041] Example 2

[0042] An emulsion-type low-temperature pressure-sensitive adhesive is prepared from the following raw materials in parts by weight: 20 parts isooctyl acrylate, 30 parts phenoxy polyethylene glycol acrylate, 0.3 parts methacrylic acid, 0.03 parts sodium carbonate, 0.01 parts mercaptoethanol, 0.6 parts nonylphenol polyoxyethylene ether sodium sulfate, 0.2 parts potassium persulfate, 1 part propylene glycol butyl ether, and 15 parts water.

[0043] A method for preparing an emulsion-type low-temperature pressure-sensitive adhesive is as follows: Isooctyl acrylate, phenoxy polyethylene glycol acrylate, methacrylic acid, mercaptoethanol, sodium nonylphenol polyoxyethylene ether sulfate, and potassium persulfate are added to 7.5 parts of water and stirred to obtain a pre-emulsion; 7.5 parts of water and sodium carbonate are added to a reaction vessel, heated to 80°C, and the pre-emulsion is added dropwise. After the dropwise addition is completed in 3 hours, the reaction continues for 1 hour. After cooling, propylene glycol butyl ether is added and stirred until homogeneous to obtain the emulsion-type low-temperature pressure-sensitive adhesive.

[0044] Example 3

[0045] An emulsion-type low-temperature pressure-sensitive adhesive is prepared from the following raw materials in parts by weight: 20 parts isooctyl acrylate, 40 parts nonylphenoxy polyethylene glycol acrylate, 0.3 parts acrylic acid, 0.03 parts sodium carbonate, 0.03 parts dodecyl mercaptan, 0.8 parts allyloxynonylphenol polyoxyethylene ether ammonium sulfate, 0.2 parts ammonium persulfate, 1.5 parts propylene glycol methyl ether acetate, and 30 parts water.

[0046] A method for preparing an emulsion-type low-temperature pressure-sensitive adhesive is as follows: isooctyl acrylate, nonylphenoxy polyethylene glycol acrylate, acrylic acid, dodecyl mercaptan, allyloxynonylphenol polyoxyethylene ether ammonium sulfate, and ammonium persulfate are added to 15 parts of water and stirred to obtain a pre-emulsion; 15 parts of water and sodium carbonate are added to a reaction vessel, heated to 80°C, and the pre-emulsion is added dropwise. After the dropwise addition is completed in 3 hours, the reaction continues for 1 hour. After cooling, propylene glycol methyl ether acetate is added and stirred until homogeneous to obtain the emulsion-type low-temperature pressure-sensitive adhesive.

[0047] Example 4

[0048] An emulsion-type low-temperature pressure-sensitive adhesive is prepared from the following raw materials in parts by weight: 20 parts isooctyl acrylate, 40 parts methoxy polyethylene glycol acrylate, 0.5 parts acrylic acid, 0.05 parts sodium bicarbonate, 0.01 parts dodecyl mercaptan, 0.9 parts allyloxynonylphenol polyoxyethylene ether ammonium sulfate, 0.3 parts ammonium persulfate, 2 parts dodecyl alcohol ester, and 30 parts water.

[0049] A method for preparing an emulsion-type low-temperature pressure-sensitive adhesive is as follows: isooctyl acrylate, methoxy polyethylene glycol acrylate, acrylic acid, dodecyl mercaptan, allyloxy nonylphenol polyoxyethylene ether ammonium sulfate, and ammonium persulfate are added to 15 parts of water and stirred to obtain a pre-emulsion; 15 parts of water and sodium bicarbonate are added to a reaction vessel, heated to 80°C, and the pre-emulsion is added dropwise. After the dropwise addition is completed in 3 hours, the reaction continues for 1 hour. After cooling, dodecyl alcohol ester is added and stirred until homogeneous to obtain the emulsion-type low-temperature pressure-sensitive adhesive.

[0050] Comparative Example 1:

[0051] The methoxy polyethylene glycol acrylate in Example 4 was replaced with butyl acrylate, and everything else was the same as in Example 4.

[0052] Comparative Example 2:

[0053] In Example 4, methoxy polyethylene glycol acrylate was replaced with butyl acrylate, and allyloxynonylphenol polyoxyethylene ether ammonium sulfate was replaced with sodium dodecyl sulfate. Otherwise, the same rules as in Example 4 were followed.

[0054] Comparative Example 3:

[0055] In Example 4, methoxy polyethylene glycol acrylate was replaced with butyl acrylate, allyloxynonylphenol polyoxyethylene ether ammonium sulfate was replaced with sodium dodecyl sulfate, and dodecyl alcohol ester was not added; otherwise, it was the same as in Example 4.

[0056] Comparative Example 4:

[0057] The dodecyl alcohol ester and allyloxynonylphenol polyoxyethylene ether ammonium sulfate in Example 4 were removed, and the rest were the same as in Example 4.

[0058] Comparative Example 5:

[0059] The methoxy polyethylene glycol acrylate in Example 4 was replaced with butyl acrylate, and dodecyl alcohol ester was not added; otherwise, it was the same as in Example 4.

[0060] Comparative Example 6:

[0061] The methoxy polyethylene glycol acrylate in Example 4 was replaced with butyl acrylate, and allyloxynonylphenol polyoxyethylene ether ammonium sulfate was not added; otherwise, it was the same as in Example 4.

[0062] Main performance indicators and measurement methods of this invention:

[0063] The emulsion pressure-sensitive adhesives of the above examples and comparative examples were coated on PET films. Under conditions of -30°C, the initial tack, peel strength and holding power of the obtained pressure-sensitive adhesives were tested according to the national standard GB / T31125-2014 initial tack test method, GB / T2792-1998 180° peel strength test method for pressure-sensitive tapes, and GB / T4851-1998 holding power test method for pressure-sensitive tapes. The results are shown in Table 1.

[0064] Table 1. Performance test results of pressure-sensitive adhesive

[0065] performance Initial tack (N) Peel strength (N / 25mm) Holding power (h) Example 1 10.3 11.4 ＞48 Example 2 11.2 12.6 ＞48 Example 3 12.6 14.5 ＞48 Example 4 12.5 15.1 ＞48 Comparative Example 1 3.6 6.5 6.8 Comparative Example 2 2.5 3.8 2.2 Comparative Example 3 0.8 1.2 0.5 Comparative Example 4 2.4 4.5 3.8 Comparative Example 5 1.0 1.7 0.8 Comparative Example 6 1.8 2.2 1.5

[0066] As shown in Table 1, the emulsion-type low-temperature pressure-sensitive adhesive obtained in this invention exhibits excellent initial tack, peel strength, and holding power under extremely cold conditions, meeting the requirements for low-temperature use of emulsion-type pressure-sensitive adhesives. The low-temperature performance of the emulsion-type low-temperature pressure-sensitive adhesive obtained in Example 4 demonstrates that it still maintains good adhesive properties after being frozen at -30°C for 48 hours. Example 4, due to the synergistic effect of integrating the flexibility of alkoxylated polyethylene glycol acrylate monomers, the plasticizing effect of long-chain emulsifiers, and the softening effect of rheology modifiers, exhibits excellent flowability and good low-temperature adhesive performance at low temperatures.

[0067] Compared to Example 4, Comparative Examples 5 and 6 replaced the flexible methoxy polyethylene glycol acrylate with the traditional soft monomer butyl acrylate. Furthermore, Comparative Example 5 did not add dodecyl alcohol ester (rheology modifier), and Comparative Example 6 did not add allyloxynonylphenol polyoxyethylene ether ammonium sulfate (long-chain emulsifier). As a result, the glass transition temperature of the pressure-sensitive adhesive increased, the flow properties at low temperatures decreased significantly, and the adhesion was also significantly reduced.

[0068] Comparative Example 1, compared to Comparative Examples 5 and 6, simultaneously added a rheology modifier and a long-chain branched emulsifier, resulting in a slightly lower glass transition temperature of the pressure-sensitive adhesive, thus improving its low-temperature adhesion performance by 1-2 times. Comparative Example 2, compared to Comparative Example 1, replaced the long-chain branched reactive emulsifier with the traditional emulsifier sodium dodecyl sulfate, causing the glass transition temperature of the pressure-sensitive adhesive to continue to rise, thus further reducing its low-temperature adhesion performance. Comparative Example 3, compared to Comparative Example 2, further removed the rheology modifier, resulting in even worse molecular chain flowability at low temperatures, thus exhibiting the worst low-temperature performance. Comparative Example 4, compared to Comparative Example 3, only possessed the flexibility of alkoxy polyethylene glycol acrylate monomers, lacking the plasticizing effect of long-chain emulsifiers and the softening effect of rheology modifiers, therefore exhibiting poor low-temperature adhesion performance.

[0069] This invention significantly reduces the glass transition temperature of pressure-sensitive adhesives by introducing flexible polyethylene glycol segments, long-chain reactive emulsifiers, and rheology modifiers. The resulting pressure-sensitive adhesive exhibits excellent fluidity at low temperatures, effectively wetting the bonding surfaces and thus demonstrating good low-temperature adhesion. The high flexibility of the alkoxy polyethylene glycol acrylate monomer endows the entire macromolecular chain with mobility, thereby maintaining the material's softness and viscoelasticity. Furthermore, the ether oxygen bonds (-O-) of the alkoxy polyethylene glycol acrylate monomer introduce polarity into the polymer, which helps improve affinity and wettability to certain polar substrates (such as glass and some plastics), potentially enhancing interfacial adhesion.

[0070] Rheology modifiers enhance the affinity between themselves and alkoxy polyethylene glycol acrylate monomers through their hydroxyl or ester carbonyl oxygen groups. This allows them to disperse within the alkoxy polyethylene glycol acrylate monomers without phase separation. This physically expands the polymer backbone, increasing the distance between the polymer chains and weakening the intermolecular forces. This steric hindrance significantly reduces the energy required for molecular chain rotation and movement, thus drastically lowering the polymer's glass transition temperature (Tg). A lower Tg means the polymer transitions from a soft, elastic state to a hard, brittle glassy state at lower temperatures, ensuring its basic tackiness at low temperatures. By imparting flexibility and flowability to the polymer at low temperatures, adhesives can better wet and penetrate the surfaces of adherends, laying the foundation for strong adhesion.

[0071] Emulsifiers disperse hydrophobic monomers into tiny droplets, forming a stable emulsion system and improving the water and solvent resistance of the film.

[0072] Chain transfer agents can efficiently regulate the growth of the polymer backbone, significantly reducing the molecular weight. This lowers the molecular weight and glass transition temperature of the pressure-sensitive adhesive, improving its flowability and adhesion at low temperatures.

[0073] It should be understood that the above description of the preferred embodiments is quite detailed, but it should not be considered as a limitation on the scope of protection of this invention. Those skilled in the art, under the guidance of this invention, can make substitutions or modifications without departing from the scope of protection of the claims of this invention, and all such substitutions or modifications fall within the scope of protection of this invention. The scope of protection of this invention should be determined by the appended claims.

Claims

1. An emulsion type cryogenic pressure sensitive adhesive, characterized by, The emulsion type low temperature pressure sensitive adhesive is prepared from the following components by weight: 20 parts of alkyl acrylate soft monomer, 10-40 parts of alkoxy polyethylene glycol acrylate monomer, 0.1-0.5 parts of functional monomer, 0.01-0.05 parts of pH regulator, 0.01-0.05 parts of chain transfer agent, 0.3-0.9 parts of emulsifier containing long chain branch, 0.05-0.3 parts of initiator, 0.5-2 parts of rheological auxiliary agent, and 15-30 parts of water. The functional monomer is selected from one of acrylic acid and methacrylic acid. The emulsifier containing long chain branch is selected from one of sodium nonylphenol polyoxyethylene ether sulfate and ammonium allyloxy nonylphenol polyoxyethylene ether sulfate. The rheological auxiliary agent is selected from one of dodecanol ester, propylene glycol butyl ether, and propylene glycol methyl ether acetate.

2. The emulsion type cryogenic pressure sensitive adhesive according to claim 1, characterized by, The alkyl acrylate soft monomer is one of butyl acrylate, isooctyl acrylate, n-octyl acrylate, and cyclohexyl acrylate.

3. The emulsion type cryogenic pressure sensitive adhesive according to claim 1, characterized by, The alkoxy polyethylene glycol acrylate monomer is methoxy polyethylene glycol acrylate.

4. The emulsion type cryogenic pressure sensitive adhesive according to claim 1, characterized by, The pH regulator is one of sodium bicarbonate and sodium carbonate.

5. The emulsion type cryogenic pressure sensitive adhesive according to claim 1, characterized in that, The chain transfer agent is one of dodecyl mercaptan and mercaptoethanol.

6. The emulsion type cryogenic pressure sensitive adhesive according to claim 1, characterized by, The initiator is one of ammonium persulfate and potassium persulfate.

7. A process for the preparation of an emulsion cryogenic pressure sensitive adhesive according to any one of claims 1 to 6, characterized in that, The emulsion type low temperature pressure sensitive adhesive is prepared from the following components by weight: 20 parts of alkyl acrylate soft monomer, 10-40 parts of alkoxy polyethylene glycol acrylate monomer, 0.1-0.5 parts of functional monomer, 0.01-0.05 parts of pH regulator, 0.01-0.05 parts of chain transfer agent, 0.3-0.9 parts of emulsifier containing long chain branch, 0.05-0.3 parts of initiator, 0.5-2 parts of rheological auxiliary agent, and 15-30 parts of water. The functional monomer is selected from one of acrylic acid and methacrylic acid. The emulsifier containing long chain branch is selected from one of sodium nonylphenol polyoxyethylene ether sulfate and ammonium allyloxy nonylphenol polyoxyethylene ether sulfate. The rheological auxiliary agent is selected from one of dodecanol ester, propylene glycol butyl ether, and propylene glycol methyl ether acetate. ​ ​ ​