A hollow sphere structure acrylic emulsion and preparation method thereof

Abstract

The invention discloses a novel hollow sphere structured acrylic emulsion and a preparation method thereof, belonging to the technical field of acrylic emulsion processing, and is used to solve the technical problem that the thermal insulation performance of the acrylic emulsion in the prior art is poor and the storage stability needs to be further improved. The invention comprises the following steps: adding composite polyurethane, N-methylpyrrolidone and a stabilizer into a reaction kettle, raising the temperature of the reaction kettle to 70-80 DEG C, and stirring the reaction kettle until the system is dissolved to obtain a composite polyurethane solution. The invention uses the prepared waterborne polyurethane as a core layer, sequentially coats the waterborne polyurethane with polysiloxane and coats the waterborne polyurethane with acrylic acid, optimizes the composition of the emulsification system, and effectively improves the storage stability of the acrylic emulsion, and also improves the thermal insulation performance and low-temperature flexibility of a coating prepared from the waterborne polyurethane.

Description

Technical Field

[0001] The invention relates to the technical field of acrylic emulsion processing, and in particular to a novel hollow sphere structured acrylic emulsion and a preparation method thereof. Background Art

[0002] Acrylate emulsion refers to a polymer aqueous dispersion obtained by emulsion polymerization of acrylic monomers. This type of emulsion is widely used in coatings, adhesives, textiles, leather processing and building waterproofing. It is highly favored for its excellent adhesion, crack resistance, frost resistance, impermeability and other properties.

[0003] In the prior art, a Chinese invention patent with publication number CN115353582B discloses a heat-insulating acrylic emulsion, a reflective heat-insulating waterproof coating, and a preparation method and application thereof. The raw materials for preparing the heat-insulating acrylic emulsion include a combination of butyl acrylate, styrene, organic polymer hollow microspheres, an initiator, a surfactant, a pH adjuster and water; the organic polymer hollow microspheres are added to the raw materials for preparation, and the latex particles formed during the polymerization of the acrylic emulsion can perform surface chemical coating on the organic polymer hollow microspheres, thereby obtaining hollow acrylic latex particles, which greatly improves the heat-insulating performance and storage stability of the heat-insulating acrylic emulsion, thereby making the reflective heat-insulating waterproof coating prepared by the heat-insulating acrylic emulsion have both excellent storage stability and reflective heat-insulating performance, and can be combined with specific pigments to form different colors, which helps to reduce visual stimulation to the human body.

[0004] However, in the emulsion polymerization process of preparing acrylic emulsion, hydrophilic monomers tend to react closer to the water phase and gather in the outer layer of the latex particles to form a hydrophilic shell, while hydrophobic monomers tend to react away from the water phase and gather inside the latex particles to form a hydrophobic core, thus forming a "hydrophilic in the shell, lipophilic in the core" structure. There is a large interfacial tension between the hydrophilic groups of the shell layer and the hydrophobic groups of the core layer. This interfacial tension will gradually increase during long-term storage, resulting in the instability of the emulsion structure. The storage stability needs to be further improved, and the oily core cannot achieve a "vacuum" effect and has poor thermal insulation performance. When preparing acrylic emulsion coatings, hollow microspheres are usually added to them to improve their thermal insulation and heat preservation properties.

[0005] In view of the technical defects in this aspect, a solution is now proposed. Summary of the invention

[0006] The object of the present invention is to provide a novel hollow sphere structured acrylic emulsion and a preparation method thereof, so as to solve the technical problems that the thermal insulation performance of the acrylic emulsion in the prior art is poor and the storage stability needs to be further improved.

[0007] The purpose of the present invention can be achieved by the following technical scheme: A method for preparing a novel hollow sphere structure acrylic emulsion comprises the following steps:

[0008] S1. Add composite polyurethane, N-methylpyrrolidone and stabilizer into a reactor, raise the temperature of the reactor to 70-80° C., and stir until the system is dissolved to obtain a composite polyurethane solution;

[0009] S2. Add an emulsifier and an acrylate mixture to a reactor containing the composite polyurethane solution, keep warm and stir for 20-30 minutes, add an initiator to the reactor, keep warm and stir for 3-5 hours, and lower the temperature of the reactor to room temperature to obtain an acrylate emulsion.

[0010] The synthetic reaction principle of acrylic emulsion is:

[0011] The composite polyurethane is dissolved in N-methylpyrrolidone and then emulsified with an emulsifier to promote uniform dispersion of polyurethane microspheres in the emulsification system. Under the action of an initiator, the olefin double bonds on the acrylate mixture and the olefin double bonds on the polyurethane microspheres undergo free radical addition reaction to form a polyolefin coating layer on the outside of the polyurethane microspheres, thereby preparing an acrylic emulsion.

[0012] Furthermore, the dosage ratio of the composite polyurethane, N-methylpyrrolidone, stabilizer, emulsifier, acrylate mixture and initiator is 14-16g:30mL:3g:20mL:10-12g:0.1g, the stabilizer is polyvinylpyrrolidone, the emulsifier is composed of purified water, sodium lauryl sulfate, Tween-80 and Span-20 in a dosage ratio of 35mL:2g:1g:1g, the acrylate mixture is composed of silane-modified acrylate, butyl methacrylate, isooctyl acrylate and methyl acrylate in a weight ratio of 4:2:3:2, and the initiator is potassium persulfate.

[0013] Furthermore, the preparation method of silane-modified acrylate is as follows: dodecamethylcyclohexasiloxane, 2-methyl-2-acrylic acid (dimethoxymethylsilyl) methyl ester, and N,N-dimethylformamide are added to a nitrogen-protected reactor and stirred, the temperature of the reactor is increased to 75-85°C, a catalyst is added to the reactor, the reaction is kept warm for 6-8 hours, and the silane-modified acrylate is obtained by post-treatment.

[0014] The reaction formula involved in the synthesis of silane-modified acrylate is:

[0015]

[0016] The reaction principle involved in the synthesis of silane-modified acrylates is:

[0017] Potassium hydroxide is a strong base. Dodecamethylcyclohexasiloxane and 2-methyl-2-acrylic acid (dimethoxymethylsilyl) methyl ester are hydrolyzed under the action of potassium hydroxide to form active groups with silanol groups. The silanol groups are self-assembled to form silane-modified acrylates with acrylate-modified long straight-chain polysiloxane structures.

[0018] Furthermore, the dosage ratio of the dodecamethylcyclohexasiloxane and 2-methyl-2-acrylic acid (dimethoxymethylsilyl) methyl ester is 5 mol:3 mol, the dosage ratio of the dodecamethylcyclohexasiloxane, N,N-dimethylformamide and the catalyst is 5 g:30 mL:2 g, the catalyst is a 40 wt% potassium hydroxide solution, and the post-treatment comprises: after the reaction is completed, the temperature of the reactor is increased to 92-96° C., and the reaction kettle is distilled under reduced pressure until no liquid is produced, the temperature of the reactor is lowered to room temperature, toluene is added to the reactor, and stirred until the system is dissolved, purified water is added to the reactor, and the mixture is stirred and dispersed for 20-30 minutes, and the mixture is allowed to stand for separation, and the organic phase is washed with purified water 3 times and then transferred to a rotary evaporator with an oil bath temperature of 92-96° C., and distilled under reduced pressure until no liquid is produced to obtain silane-modified acrylate.

[0019] Further, the composite polyurethane is processed by the following steps:

[0020] A1. Add polyethylene glycol, modified pentanediol, o-toluene diisocyanate, N-methylpyrrolidone and a catalyst into a nitrogen-protected reactor and stir. Raise the temperature of the reactor to 70-80° C. and keep the temperature for 40-60 minutes to obtain a prepolymer solution.

[0021] A2, add chain extender to the reactor containing prepolymer solution, keep warm for 50-60min, add end-capping agent to the reactor, keep warm for 60-70min, add triethylamine to the reactor, adjust the pH of the system to 8.5-9.5, and obtain polyurethane solution;

[0022] The reaction equations involved in the synthesis of polyurethane solutions include:

[0023]

[0024]

[0025] Where:

[0026] R1

[0027] R2:

[0028] R3:

[0029] The reaction principle involved in the synthesis of polyurethane solution is:

[0030] During the reaction, the hydroxyl groups of polyethylene glycol and modified pentanediol react with the isocyanate groups of o-toluene diisocyanate to generate triethoxysilane-modified polyurethane prepolymers containing urethane bonds. 1,3,5-triaminobenzene is added to the reaction as a chain extender, and they react with the isocyanate groups in the prepolymer to further extend the molecular chains of the polyurethane. Ethanolamine is used in excess to terminate the hydroxyl groups on the polyurethane molecular chains to prepare a polyurethane solution.

[0031] A3. The speed of the reactor is set to 570-630 r / min, and the siloxane dispersion solution is added to the reactor containing the polyurethane solution. The mixture is stirred at the temperature for 10-12 hours, and then post-treated to obtain a composite polyurethane.

[0032] The synthetic reaction principle of composite polyurethane is:

[0033] After the siloxane dispersion is added to the polyurethane solution, sodium carboxymethyl cellulose can form a thin film on the oil-water interface to reduce the interfacial tension. Under the shear force of rapid stirring, it promotes the formation and stabilization of emulsification, and forms droplet-shaped microspheres in the reaction system. Allyl triethoxysilane, 1,2-bis(triethoxysilyl)ethane, ethyl orthosilicate and the siloxane on the polyurethane molecules are self-assembled after hydrolysis in an alkaline environment, and an olefin-modified polysiloxane coating layer is formed on the outside of the polyurethane microspheres. After reduced pressure distillation, the low-boiling point small molecule materials are evaporated to prepare a composite polyurethane.

[0034] Furthermore, during the preparation of the polyurethane solution, the molar ratio of hydroxyl group to isocyanate group is 1:1.05, the dosage ratio of the polyethylene glycol, modified pentylene glycol, N-methyl pyrrolidone, catalyst, chain extender, end capping agent and siloxane dispersion is 40g:10g:200mL:0.5g:4g:3g:110g, the chain extender is 1,3,5-triaminobenzene, the end capping agent is ethanolamine, the catalyst is dibutyltin dilaurate, the siloxane dispersion is composed of allyltriethoxysilane, 1,2-bis(triethoxysilyl)ethane, tetraethyl orthosilicate, sodium carboxymethyl cellulose and purified water in a dosage ratio of 3g:5g:2g:10g:90mL, and the post-treatment includes: after the reaction is completed, the temperature of the reactor is increased to 100-110°C, and the solvent is evaporated under reduced pressure to obtain a composite polyurethane.

[0035] Furthermore, the preparation method of modified pentanediol is: 2-aminopentane-1,5-diol, isocyanatepropyltriethoxysilane and tetrahydrofuran are added to a nitrogen-protected reactor and stirred, the temperature of the reactor is increased to reflux, the reaction is kept warm for 60-80 minutes, and the modified pentanediol is obtained by post-treatment.

[0036] The reaction formula involved in the synthesis of modified pentanediol is:

[0037]

[0038] The reaction principle involved in the synthesis of modified pentanediol is:

[0039] During the reaction with isocyanate group, amino group is more likely to react with isocyanate group than hydroxyl group. By controlling the dosage ratio of the reactants, the amino group on 2-aminopentane-1,5-diol and the isocyanate group on isocyanatepropyltriethoxysilane are condensed at 1 mol:01 mol to prepare modified pentanediol with dihydroxy-modified triethoxysilane. The mass spectrometry analysis data are: m / z: 366.2186 (100.0%), 367.2220 (16.2%), 367.2182 (5.1%), 368.2155 (3.3%), 368.2229 (1.2%), 368.2253 (1.2%), Elemental Analysis: C, 49.15; H, 9.35; N, 7.64; O, 26.19; Si, 7.66.

[0040] Furthermore, the usage ratio of the 2-aminopentane-1,5-diol and isocyanatepropyltriethoxysilane is 1 mol:1 mol, the usage ratio of isocyanatepropyltriethoxysilane and tetrahydrofuran is 1 g:5 mL, and the post-treatment includes: after the reaction is completed, distilling off the solvent under reduced pressure to obtain modified pentanediol.

[0041] Among them, a novel hollow sphere structure acrylic emulsion is provided, and the novel hollow sphere structure acrylic emulsion is prepared by a novel hollow sphere structure acrylic emulsion preparation method.

[0042] The present invention has the following beneficial effects:

[0043] 1. The novel hollow sphere structured acrylic emulsion of the present invention forms an acrylic emulsion with a core-shell structure by coating a modified polysiloxane support layer on the surface of a hydrophilic polyurethane microsphere, using olefins on the polysiloxane support layer as reactive sites, and modifying polyacrylic acid monomers on the surface of a composite polyurethane. The core layer of the acrylic emulsion exhibits hydrophilicity, and the shell layer exhibits lipophilicity, so that water molecules in the core of the emulsion are volatilized to form a "vacuum core", breaking through the characteristic of "hydrophilicity in the shell and lipophilicity in the core" of traditional acrylic emulsions, thereby improving the thermal insulation performance of the acrylic emulsion material, and improving the storage stability of the acrylic emulsion by optimizing the composition of the emulsifier and matching the polyurethane microsphere structure with a special structure. The polyurethane microspheres, as the core layer material, have good flexibility and elasticity. After being coated with the polysiloxane support layer and the polyacrylic acid monomer, the flexibility of the core layer is further increased, and the internal stress concentration and crack propagation of the material at low temperatures are reduced, thereby improving the low-temperature flexibility.

[0044] 2. The novel hollow sphere structure acrylic emulsion of the present invention uses polyethylene glycol, modified pentylene glycol and o-toluene diisocyanate as reaction monomers, 1,3,5-triaminobenzene as chain extender, and ethanolamine as end-capping agent to prepare highly cross-linked polyurethane with triethoxysilane modified hydroxyl end-capping. Modified pentylene glycol and polyethylene glycol are used as polyols, which themselves have good hydrophilicity. The hydroxyl group reacts with the isocyanate group to form a carbamate bond, which not only constructs the skeleton of the polyurethane, but also allows the hydrophilicity of the modified pentylene glycol to be retained in the polyurethane core layer. The hydrophilic core layer can attract and retain a certain amount of water molecules, which form tiny water layers or water channels in the emulsion. During the film-forming process of the emulsion, the water molecules evaporate and leave tiny pores or channels, forming a porous "vacuum core layer" inside the polysiloxane layer, reducing heat conduction, thereby improving the thermal insulation performance of the material. The soft and hard segments in the urethane molecular chain cooperate with each other, so that the polyurethane maintains a certain strength while also having good flexibility. The polyurethane solution is emulsified and dispersed by the silicone dispersion, and the sodium hydroxymethyl cellulose molecules form an adsorption layer at the oil-water interface to reduce the interfacial tension. The hydrophilic groups and hydrophobic groups on the polyurethane molecular chain will also participate in the stability of the emulsion, promote the formation of the emulsion, form polyurethane microspheres, and coat the outside of the polysiloxane layer. The polysiloxane coating layer is a polymer with a silicon-oxygen bond as the main chain, and its molecular chain has a high degree of flexibility and low-temperature resistance. When the polysiloxane layer is coated on the surface of the polyurethane microsphere, this flexibility will be transferred to the polyurethane microsphere, thereby improving its overall low-temperature flexibility. In addition, the polysilane coating layer can also effectively support the polyurethane core layer, prevent the core layer from deforming after water loss, maintain the smooth surface of the microspheres in the acrylic emulsion, and thereby improve the hemispherical emissivity of the material.

[0045] 3. The novel hollow sphere structured acrylic emulsion of the present invention is prepared by preparing an acrylic ester mixture composed of silane-modified acrylic ester of acrylic ester-modified polysiloxane and butyl methacrylate, isooctyl acrylate, and methyl acrylate, and in an emulsification system, a free radical initiator is initiated to form a polyacrylate coating on the outside of the composite polyurethane material to prepare the acrylic ester emulsion; by optimizing the composition of the emulsifier, an amphiphilic emulsifier is prepared, the hydrophobic groups of the emulsifier molecules tend to attract each other with the non-polar parts on the acrylic ester molecular chain, while the hydrophilic groups face the water phase and combine with the hydrophilic core layer, so that the acrylic ester forms a water-oil-water dispersion system in the emulsion, thereby maintaining It maintains uniform and stable dispersion of acrylates and improves the storage stability of acrylate emulsions. The molecular chains of acrylates and composite polyurethanes are cross-linked by chemical bonds at the interface to form a more complex network structure, which increases the tortuosity of the heat conduction path, requiring more time and energy to transfer heat, thereby hindering heat conduction and further improving thermal insulation properties. This complex cross-linked structure further enhances the connection strength between the polyacrylate and polysiloxane layers, allowing the material to resist external stress under low temperature conditions and prevent brittle fracture of the material due to temperature reduction, thereby maintaining the integrity and flexibility of the material and further improving the hemispherical emissivity of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0047] Figure 1 This is a scanning electron microscope photo of the acrylic emulsion in the present invention (1 μm);

[0048] Figure 2 This is a scanning electron microscope photograph (200 nm) of the acrylic emulsion in the present invention. DETAILED DESCRIPTION

[0049] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] In this application, polyethylene glycol is selected from Nantong Yongle Chemical Co., Ltd., with a molecular weight of 560-660 and a moisture content of less than 0.1%; polyvinyl pyrrolidone is selected from Huzhou Shenhua Polymer Materials Co., Ltd., with a density of 1.69 g / cm 3 .

[0051] Example 1

[0052] This embodiment provides a method for preparing a novel hollow sphere structured acrylic emulsion, comprising the following steps:

[0053] S1. Preparation of modified pentanediol

[0054] Weigh: 119.2 g of 2-aminopentane-1,5-diol, 247.4 g of isocyanatepropyltriethoxysilane and 1237 mL of tetrahydrofuran, add into a nitrogen-protected reactor and stir, raise the temperature of the reactor to 64° C., reflux the system, keep the temperature for 60 min, evaporate the solvent under reduced pressure to obtain modified pentanediol.

[0055] S2. Preparation of polyurethane solution

[0056] Weigh: 200 g of polyethylene glycol, 50 g of modified pentanediol, 1000 mL of N-methylpyrrolidone and 2.5 g of dibutyltin dilaurate, add them to a nitrogen-protected reactor and stir, weigh o-toluene diisocyanate according to a molar ratio of hydroxyl group to isocyanate group of 1:1.05 and add it to the reactor, raise the temperature of the reactor to 70°C, keep the reaction for 40 minutes, add 1,3,5-triaminobenzene 20 g to the reactor, keep the reaction for 50 minutes, add 15 g of ethanolamine to the reactor, keep the reaction for 60 minutes, add triethylamine to the reactor, adjust the pH of the system to 8.5, and obtain a polyurethane solution.

[0057] S3. Preparation of composite polyurethane

[0058] Allyl triethoxysilane, 1,2-bis(triethoxysilyl)ethane, ethyl orthosilicate, sodium carboxymethyl cellulose and purified water were mixed uniformly in an amount ratio of 3 g:5 g:2 g:10 g:90 mL to obtain a siloxane dispersion;

[0059] The speed of the reactor was set to 570 r / min, 550 g of the siloxane dispersion solution was added to the reactor containing the polyurethane solution, and the mixture was stirred for 10 h. The temperature of the reactor was raised to 100° C., and the solvent was evaporated under reduced pressure to obtain a composite polyurethane.

[0060] S4. Preparation of silane-modified acrylic acid

[0061] Weigh: 222.5 g of dodecamethylcyclohexasiloxane, 61.3 g of 2-methyl-2-acrylic acid (dimethoxymethylsilyl) methyl ester, and 1335 mL of N,N-dimethylformamide, add them to a nitrogen-protected reactor and stir, raise the temperature of the reactor to 75°C, add 89 g of 40 wt% potassium hydroxide aqueous solution to the reactor, keep the reaction for 6 hours, raise the temperature of the reactor to 92°C, and distill under reduced pressure until no liquid is produced. The temperature of the reactor is lowered to room temperature, 1 L of toluene is added to the reactor, stirred until the system is dissolved, 300 mL of purified water is added to the reactor, stirred and dispersed for 20 minutes, and allowed to stand for liquid separation. The organic phase is washed 3 times with purified water and then transferred to a rotary evaporator with an oil bath temperature of 92°C, and distilled under reduced pressure until no liquid is produced to obtain silane-modified acrylate.

[0062] S5. Preparation of acrylic emulsion

[0063] Weigh: 140 g of composite polyurethane, 300 mL of N-methylpyrrolidone, and 30 g of polyvinylpyrrolidone, add them into a reactor, raise the temperature of the reactor to 70° C., and stir at this temperature until the system is dissolved to obtain a composite polyurethane solution;

[0064] Purified water, sodium lauryl sulfate, Tween-80 and Span-20 were mixed uniformly in a ratio of 35 mL:2 g:1 g:1 g to obtain an emulsifier;

[0065] Silane-modified acrylate, butyl methacrylate, isooctyl acrylate, and methyl acrylate are uniformly mixed in a weight ratio of 4:2:3:2 to obtain an acrylate mixture;

[0066] Add 200 mL of emulsifier and 100 g of acrylate mixture to the reactor containing the composite polyurethane solution, stir and keep warm for 20 min, add 1 g of potassium persulfate to the reactor, stir and keep warm for 3 h, lower the temperature of the reactor to room temperature, and obtain an acrylate emulsion with a particle size of 3-6 μm.

[0067] Example 2

[0068] This embodiment provides a method for preparing a novel hollow sphere structured acrylic emulsion, comprising the following steps:

[0069] S1. Preparation of modified pentanediol

[0070] Weigh: 119.2 g of 2-aminopentane-1,5-diol, 247.4 g of isocyanatepropyltriethoxysilane and 1237 mL of tetrahydrofuran, add into a nitrogen-protected reactor and stir, raise the temperature of the reactor to 65° C., reflux the system, keep the temperature for 70 min, evaporate the solvent under reduced pressure to obtain modified pentanediol.

[0071] S2. Preparation of polyurethane solution

[0072] Weigh: 200 g of polyethylene glycol, 50 g of modified pentanediol, 1000 mL of N-methylpyrrolidone and 2.5 g of dibutyltin dilaurate, add them to a nitrogen-protected reactor and stir, weigh o-toluene diisocyanate according to a molar ratio of hydroxyl group to isocyanate group of 1:1.05 and add it to the reactor, raise the temperature of the reactor to 75°C, keep the reaction for 50 min, add 1,3,5-triaminobenzene 20 g to the reactor, keep the reaction for 55 min, add 15 g of ethanolamine to the reactor, keep the reaction for 65 min, add triethylamine to the reactor, adjust the pH of the system to 9.0, and obtain a polyurethane solution.

[0073] S3. Preparation of composite polyurethane

[0074] Allyl triethoxysilane, 1,2-bis(triethoxysilyl)ethane, ethyl orthosilicate, sodium carboxymethyl cellulose and purified water were mixed uniformly in an amount ratio of 3 g:5 g:2 g:10 g:90 mL to obtain a siloxane dispersion;

[0075] The speed of the reactor was set to 600 r / min, 550 g of the siloxane dispersion solution was added to the reactor containing the polyurethane solution, and the mixture was stirred for 11 h. The temperature of the reactor was raised to 105° C., and the solvent was evaporated under reduced pressure to obtain a composite polyurethane.

[0076] S4. Preparation of silane-modified acrylic acid

[0077] Weigh: 222.5 g of dodecamethylcyclohexasiloxane, 61.3 g of 2-methyl-2-acrylic acid (dimethoxymethylsilyl) methyl ester, and 1335 mL of N,N-dimethylformamide, add them to a nitrogen-protected reactor and stir, raise the temperature of the reactor to 80°C, add 89 g of 40 wt% potassium hydroxide aqueous solution to the reactor, keep warm for 7 hours, raise the temperature of the reactor to 94°C, and distill under reduced pressure until no liquid is produced. The temperature of the reactor is lowered to room temperature, 1 L of toluene is added to the reactor, stirred until the system is dissolved, 300 mL of purified water is added to the reactor, stirred and dispersed for 25 minutes, and allowed to stand for separation. The organic phase is washed 3 times with purified water and then transferred to a rotary evaporator with an oil bath temperature of 94°C, and distilled under reduced pressure until no liquid is produced to obtain silane-modified acrylate.

[0078] S5. Preparation of acrylic emulsion

[0079] Weigh: 150 g of composite polyurethane, 300 mL of N-methylpyrrolidone, and 30 g of polyvinylpyrrolidone, add them into a reactor, raise the temperature of the reactor to 75° C., and stir at this temperature until the system is dissolved to obtain a composite polyurethane solution;

[0080] Purified water, sodium lauryl sulfate, Tween-80 and Span-20 were mixed uniformly in a ratio of 35 mL:2 g:1 g:1 g to obtain an emulsifier;

[0081] Silane-modified acrylate, butyl methacrylate, isooctyl acrylate, and methyl acrylate are uniformly mixed in a weight ratio of 4:2:3:2 to obtain an acrylate mixture;

[0082] Add 200 mL of emulsifier and 110 g of acrylate mixture to the reactor containing the composite polyurethane solution, stir and keep warm for 25 minutes, add 1 g of potassium persulfate to the reactor, stir and keep warm for 4 hours, and lower the temperature of the reactor to room temperature to obtain an acrylate emulsion with a particle size of 3-6 μm.

[0083] Example 3

[0084] This embodiment provides a method for preparing a novel hollow sphere structured acrylic emulsion, comprising the following steps:

[0085] S1. Preparation of modified pentanediol

[0086] Weigh: 119.2 g of 2-aminopentane-1,5-diol, 247.4 g of isocyanatepropyltriethoxysilane and 1237 mL of tetrahydrofuran, add into a nitrogen-protected reactor and stir, raise the temperature of the reactor to 66° C., reflux the system, keep the temperature for 80 min, evaporate the solvent under reduced pressure to obtain modified pentanediol.

[0087] S2. Preparation of polyurethane solution

[0088] Weigh: 200 g of polyethylene glycol, 50 g of modified pentanediol, 1000 mL of N-methylpyrrolidone and 2.5 g of dibutyltin dilaurate, add them to a nitrogen-protected reactor and stir, weigh o-toluene diisocyanate according to a molar ratio of hydroxyl group to isocyanate group of 1:1.05 and add it to the reactor, raise the temperature of the reactor to 80°C, keep the reaction for 60 min, add 20 g of 1,3,5-triaminobenzene to the reactor, keep the reaction for 60 min, add 15 g of ethanolamine to the reactor, keep the reaction for 70 min, add triethylamine to the reactor, adjust the pH of the system to 9.5, and obtain a polyurethane solution.

[0089] S3. Preparation of composite polyurethane

[0090] Allyl triethoxysilane, 1,2-bis(triethoxysilyl)ethane, ethyl orthosilicate, sodium carboxymethyl cellulose and purified water were mixed uniformly in an amount ratio of 3 g:5 g:2 g:10 g:90 mL to obtain a siloxane dispersion;

[0091] The speed of the reactor was set to 630 r / min, 550 g of the siloxane dispersion solution was added to the reactor containing the polyurethane solution, and the mixture was stirred for 12 h. The temperature of the reactor was raised to 110° C., and the solvent was evaporated under reduced pressure to obtain a composite polyurethane.

[0092] S4. Preparation of silane-modified acrylic acid

[0093] Weigh: 222.5 g of dodecamethylcyclohexasiloxane, 61.3 g of 2-methyl-2-acrylic acid (dimethoxymethylsilyl) methyl ester, and 1335 mL of N,N-dimethylformamide, add them to a nitrogen-protected reactor and stir, raise the temperature of the reactor to 85°C, add 89 g of 40 wt% potassium hydroxide aqueous solution to the reactor, keep the reaction for 8 hours, raise the temperature of the reactor to 96°C, and distill under reduced pressure until no liquid is produced. The temperature of the reactor is lowered to room temperature, 1 L of toluene is added to the reactor, stirred until the system is dissolved, 300 mL of purified water is added to the reactor, stirred and dispersed for 30 minutes, and allowed to stand for separation. The organic phase is washed 3 times with purified water and then transferred to a rotary evaporator with an oil bath temperature of 96°C, and distilled under reduced pressure until no liquid is produced to obtain silane-modified acrylate.

[0094] S5. Preparation of acrylic emulsion

[0095] Weigh: 140-160 g of composite polyurethane, 300 mL of N-methylpyrrolidone, and 30 g of polyvinylpyrrolidone, add them into a reaction kettle, raise the temperature of the reaction kettle to 80° C., and stir to obtain a composite polyurethane solution while keeping the temperature high until the system is dissolved;

[0096] Purified water, sodium lauryl sulfate, Tween-80 and Span-20 were mixed uniformly in a ratio of 35 mL:2 g:1 g:1 g to obtain an emulsifier;

[0097] Silane-modified acrylate, butyl methacrylate, isooctyl acrylate, and methyl acrylate are uniformly mixed in a weight ratio of 4:2:3:2 to obtain an acrylate mixture;

[0098] Add 200 mL of emulsifier and 120 g of acrylate mixture to the reactor containing the composite polyurethane solution, stir and keep warm for 30 minutes, add 1 g of potassium persulfate to the reactor, stir and keep warm for 5 hours, lower the temperature of the reactor to room temperature, and obtain an acrylate emulsion with a particle size of 3-6 μm.

[0099] Comparative Example 1

[0100] The difference between this comparative example and Example 3 is that step S1 is eliminated and pentanediol is used to replace the modified pentanediol in step S2.

[0101] Comparative Example 2

[0102] The difference between this comparative example and Example 3 is that no allyltriethoxysilane is added to the siloxane dispersion in step S3.

[0103] Comparative Example 3

[0104] The difference between this comparative example and Example 3 is that step S4 is omitted and no silane-modified acrylate is added to the acrylate mixture in step S5.

[0105] Performance Testing:

[0106] The storage stability and thermal insulation performance of the acrylic emulsions prepared in Examples 1-3 and Comparative Examples 1-3 were tested, wherein the storage stability was measured with reference to the standard GB / T 20623-2006 "Emulsions for Building Coatings", and the thermal insulation performance was used as a reference. The acrylic emulsion prepared by the present invention was substituted for the acrylic emulsion and the organic polymer hollow microspheres in the reflective thermal insulation and waterproof coating in the invention patent with publication number CN115353582B to prepare a coating sample, and the thermal conductivity, hemispherical emissivity, elongation at break and low-temperature flexibility (0°C, diameter 4 mm) of the coating sample were tested with reference to the standard GB / T25261-2018 "Reflective Thermal Insulation Coatings for Buildings". The specific test results are shown in Table 1 below.

[0107] Table 1-Performance test data of samples

[0108]

[0109]

[0110] Data Analysis:

[0111] Comparative analysis of the data in Table 1 above shows that the acrylic emulsion prepared by the present invention has good storage stability. The thermal conductivity of the coating sample prepared by the acrylic emulsion is reduced to 0.091 W / (m·k), the hemispherical emissivity reaches 0.91, and the sample has good low-temperature flexibility. All properties are better than those of the comparative example.

[0112] Description: The present invention prepares waterborne polyurethane and uses it as the core layer, and sequentially coats it with polysiloxane and acrylic acid, thereby optimizing the composition of the emulsification system, which not only effectively improves the storage stability of the acrylic ester emulsion, but also improves the thermal insulation performance and low-temperature flexibility of the coating prepared therefrom.

[0113] The above contents are merely examples and explanations of the structure of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the structure of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

[0114] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0115] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only specific implementation methods. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a hollow sphere structured acrylic emulsion, characterized in that: The following steps are involved: S1. Add composite polyurethane, N-methylpyrrolidone and stabilizer into a reactor, raise the temperature of the reactor to 70-80° C., and stir until the system is dissolved to obtain a composite polyurethane solution; S2, add an emulsifier and an acrylate mixture to a reactor containing a composite polyurethane solution, keep warm and stir for 20-30 min, add an initiator to the reactor, keep warm and stir for 3-5 h, lower the temperature of the reactor to room temperature, and obtain an acrylate emulsion, wherein the acrylate mixture is composed of silane-modified acrylate, butyl methacrylate, isooctyl acrylate, and methyl acrylate in a weight ratio of 4:2:3:2; The preparation method of silane-modified acrylate is as follows: dodecamethylcyclohexasiloxane, 2-methyl-2-acrylic acid (dimethoxymethylsilyl) methyl ester and N,N-dimethylformamide are added to a nitrogen-protected reactor and stirred, the temperature of the reactor is increased to 75-85° C., a catalyst is added to the reactor, the reaction is carried out by heat preservation for 6-8 hours, and the silane-modified acrylate is obtained by post-treatment; Composite polyurethane is processed by the following steps: A1. Add polyethylene glycol, modified pentanediol, o-toluene diisocyanate, N-methylpyrrolidone and a catalyst into a nitrogen-protected reactor and stir. Raise the temperature of the reactor to 70-80° C. and keep the temperature for 40-60 minutes to obtain a prepolymer solution. A2, add chain extender to the reactor containing prepolymer solution, keep warm for 50-60min, add end-capping agent to the reactor, keep warm for 60-70min, add triethylamine to the reactor, adjust the pH of the system to 8.5-9.5, and obtain polyurethane solution; A3, the speed of the reactor is set to 570-630r / min, and a siloxane dispersion is added to the reactor containing the polyurethane solution, and the mixture is stirred at a temperature of 10-12h, and post-treated to obtain a composite polyurethane, wherein the siloxane dispersion is composed of allyltriethoxysilane, 1,2-bis(triethoxysilyl)ethane, tetraethyl orthosilicate, sodium carboxymethyl cellulose and purified water in a dosage ratio of 3g:5g:2g:10g:90mL; The preparation method of modified pentanediol is as follows: 2-aminopentane-1,5-diol, isocyanatepropyltriethoxysilane and tetrahydrofuran are added into a nitrogen-protected reactor and stirred, the temperature of the reactor is increased to reflux, the reaction is kept warm for 60-80 minutes, and the modified pentanediol is obtained by post-treatment.

2. The method for preparing a hollow sphere structured acrylic emulsion according to claim 1, characterized in that: The dosage ratio of the composite polyurethane, N-methylpyrrolidone, stabilizer, emulsifier, acrylate mixture and initiator is 14-16g:30mL:3g:20mL:10-12g:0.1g, the stabilizer is polyvinylpyrrolidone, the emulsifier is composed of purified water, sodium lauryl sulfate, Tween-80 and Span-20 in a dosage ratio of 35mL:2g:1g:1g, and the initiator is potassium persulfate.

3. The method for preparing a hollow sphere structure acrylic emulsion according to claim 1, characterized in that: The dosage ratio of dodecamethylcyclohexasiloxane and 2-methyl-2-acrylic acid (dimethoxymethylsilyl) methyl ester is 5 mol:3 mol, the dosage ratio of dodecamethylcyclohexasiloxane, N,N-dimethylformamide and catalyst is 5 g:30 mL:2 g, and the catalyst is 40 wt% potassium hydroxide solution.

4. The method for preparing a hollow sphere structure acrylic emulsion according to claim 1, characterized in that: During the preparation of the polyurethane solution, the molar ratio of hydroxyl group to isocyanate group is 1:1.05, the dosage ratio of the polyethylene glycol, modified pentylene glycol, N-methylpyrrolidone, catalyst, chain extender, end capping agent and silicone dispersion is 40g:10g:200mL:0.5g:4g:3g:110g, the chain extender is 1,3,5-triaminobenzene, the end capping agent is ethanolamine, and the catalyst is dibutyltin dilaurate.

5. The method for preparing a hollow sphere structured acrylic emulsion according to claim 1, characterized in that: The usage ratio of the 2-aminopentane-1,5-diol and isocyanatepropyltriethoxysilane is 1 mol:1 mol, and the usage ratio of isocyanatepropyltriethoxysilane and tetrahydrofuran is 1 g:5 mL.

6. A hollow sphere structured acrylic emulsion, characterized in that: The hollow sphere structured acrylic emulsion is prepared according to the method for preparing a hollow sphere structured acrylic emulsion according to any one of claims 1 to 5.

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