Waterborne polyurethane modified acrylate composite emulsion and preparation method thereof

Abstract

The invention relates to the field of polymer emulsions, and particularly discloses a waterborne polyurethane modified acrylate composite emulsion and a preparation method thereof. The waterborne polyurethane modified acrylate composite emulsion is prepared from the following raw materials in parts by weight: 20 to 40 parts of castor oil-based polyurethane prepolymer, 20 to 40 parts of acrylate monomer, 0.5 to 1 part of composite initiator, 0.5 to 0.8 part of chain extender, 1 to 3 parts of neutralizer, 30 to 50 parts of water and 10 to 20 parts of silica sol, according to the waterborne polyurethane modified acrylate composite emulsion prepared in the invention, the castor oil-based polyurethane prepolymer is adopted to provide active sites for graft copolymerization of waterborne polyurethane and acrylate monomers, so that the crosslinking degree of the polymer is improved, and the film forming uniformity and water resistance of a film are improved.

Description

Technical Field

[0001] The present application relates to the field of polymer emulsions, and in particular to an aqueous polyurethane-modified acrylate composite emulsion and a preparation method thereof. Background Art

[0002] Acrylate and polyurethane emulsions, as important water-based coating binders, offer advantages in environmental friendliness and functionality. However, the insufficient water and weather resistance of acrylate emulsions alone limits their application outdoors or in high-humidity environments. Polyurethane emulsions are expensive and prone to microphase separation, affecting coating uniformity and gloss.

[0003] There are several traditional methods for preparing aqueous composite emulsions. A common approach involves synthesizing a single polymer: first synthesizing a waterborne polyurethane emulsion or an acrylic emulsion separately, and then simply physically mixing the two emulsions. This method is relatively simple to operate, requiring only the two prepared emulsions to be mixed uniformly in a certain proportion under stirring. However, simple physical mixing methods struggle to achieve effective bonding between the two polymers, resulting in poor emulsion stability and prone to delamination and demulsification.

[0004] Another approach is stepwise polymerization, where one polymer is first synthesized as a seed, and then another polymer is polymerized on top of it. While stepwise polymerization can improve bonding to a certain extent, it is complex and requires high control over reaction conditions, and can easily lead to poor compatibility between the polymers. Summary of the Invention

[0005] In order to improve the deficiencies of existing aqueous polyurethane and acrylate composite emulsions, the present application provides an aqueous polyurethane modified acrylate composite emulsion and a preparation method thereof.

[0006] In a first aspect, the present application provides a waterborne polyurethane-modified acrylate composite emulsion, which adopts the following technical solution: A waterborne polyurethane-modified acrylate composite emulsion comprises the following raw materials in parts by weight: 20-40 parts of castor oil-based polyurethane prepolymer, 20-40 parts of acrylate monomer, 0.5-1 part of composite initiator, 0.5-0.8 part of chain extender, 1-3 parts of neutralizer, 30-50 parts of water, and 10-20 parts of silica sol.

[0007] By adopting the above technical solution, castor oil can improve the low-temperature performance and water resistance of polyurethane prepolymers. The unsaturated carbon-carbon double bonds and methylene groups in castor oil can provide active sites for the graft copolymerization of waterborne polyurethane with acrylic monomers. The excess carbon-carbon double bonds can also increase the crosslinking degree of the polymer through oxidative crosslinking, improving the film formation uniformity and water resistance of the coating. The silica sol has a large number of silanol bonds on the surface, which can provide conditions for reaction with isocyanates on the polyurethane. At the same time, the Si-O-Si groups can also form a film on their own, which can improve the water resistance and strength of the coating.

[0008] Preferably, the castor oil-based polyurethane prepolymer comprises the following raw materials in parts by weight: 40-50 parts of isocyanate, 50-60 parts of polyester polyol, 1-3 parts of dimethylol propionic acid, and 5-8 parts of castor oil.

[0009] By adopting the above technical solution, dimethylolpropionic acid uses its own hydroxyl and carboxyl groups to play a hydrophilic chain extension role, which can promote the formed polyurethane prepolymer to be evenly dispersed in water, which is conducive to subsequent compounding with acrylates, reducing the use of external emulsifiers, and further reducing the impact of external emulsifiers on the water resistance of the coating, thereby improving the water resistance of the coating.

[0010] Preferably, the method for preparing the castor oil-based polyurethane prepolymer comprises the following specific steps: mixing isocyanate, polyester polyol and castor oil, heating the mixture for reaction, cooling the mixture, adding dimethylol propionic acid and continuing the reaction at the same temperature to obtain the castor oil-based polyurethane prepolymer.

[0011] Preferably, the heating temperature is 80-90°C, and the cooling temperature is 70-80°C.

[0012] Preferably, the composite initiator is a mixture of azobisisobutyronitrile and ammonium persulfate, and the mass ratio of the azobisisobutyronitrile to the ammonium persulfate is (0.8-1.2):1.

[0013] By adopting the above technical solution, azobisisobutyronitrile and ammonium persulfate are used as composite initiators, azobisisobutyronitrile is dissolved in the hydrophobic chain segments of acrylate and castor oil-based polyurethane prepolymer to decompose and generate free radicals, and ammonium persulfate is used to initiate the reaction of the active sites of the water-soluble acrylate monomer and the polyurethane prepolymer, thereby improving the reaction efficiency of the composite emulsion system, improving the graft copolymerization conversion rate of the polyurethane prepolymer and the acrylate, and enhancing the interfacial bonding between the polyurethane and the acrylate.

[0014] Preferably, the acrylic acid ester monomers include methyl methacrylate, butyl acrylate, and hydroxypropyl methacrylate, and the mass ratio of the methyl methacrylate, butyl acrylate, and hydroxypropyl methacrylate is 1:(0.5-0.8):(0.3-0.5).

[0015] Preferably, the silica sol is modified with a silane coupling agent in advance, which comprises the following specific steps: mixing the silica sol with isopropyl alcohol, then adding the silane coupling agent, mixing, dispersing them uniformly, reacting them, and filtering to obtain the modified silica sol.

[0016] By adopting the above technical solution, the silica sol is modified in advance using a silane coupling agent, and then the modified silica sol is introduced into the polyurethane-acrylate composite emulsion. The alkyl group in the silane coupling agent is used to provide a better steric hindrance protection for the silica sol, thereby reducing the aggregation reaction of the silica sol particles, avoiding the agglomeration and flocculation of the silica sol in the composite emulsion system, and improving the dispersibility of the composite emulsion system.

[0017] Preferably, the mass ratio of the silica sol, isopropyl alcohol and silane coupling agent is 1:(2-3):(1-1.5).

[0018] In a second aspect, the present application provides a method for preparing an aqueous polyurethane-modified acrylate composite emulsion, which adopts the following technical solution: A method for preparing a waterborne polyurethane-modified acrylate composite emulsion comprises the following specific steps: mixing a castor oil-based polyurethane prepolymer, an acrylate monomer, a silica sol, and water, uniformly dispersing the mixture, adding a composite initiator and a chain extender, heating the mixture for reaction, and finally neutralizing the mixture with a neutralizer to obtain the waterborne polyurethane-modified acrylate composite emulsion.

[0019] By adopting the above technical solution, the prepared composite emulsion can form a uniform and glossy coating, maintain good water resistance, and reduce the occurrence of stratification.

[0020] Preferably, the heating temperature is 70-80°C.

[0021] In summary, this application has the following beneficial effects: 1. Since castor oil is added to the polyurethane prepolymer raw material in this application, the water resistance of the coating can be improved. The active groups of castor oil can improve the grafting effect of the polyurethane prepolymer and the acrylate monomer, increase the cross-linking degree of the composite emulsion system, form a uniform coating, and at the same time improve the water resistance of the coating.

[0022] 2. In this application, silica sol is added to the composite emulsion system to enhance the water resistance and strength of the coating. At the same time, a silane coupling agent is used to modify the silica sol to promote the uniform dispersion of the silica sol in the composite emulsion system, thereby improving the uniformity and film-forming effect of the coating. DETAILED DESCRIPTION

[0023] The present application is further described in detail below with reference to the embodiments.

[0024] All raw materials in the examples are commercially available. Example

[0025] Example 1 This embodiment provides a waterborne polyurethane-modified acrylate composite emulsion comprising the following raw materials in parts by weight: 30 kg of castor oil-based polyurethane prepolymer, 30 kg of acrylate monomer, 0.8 kg of composite initiator, 0.7 kg of chain extender, 2 kg of neutralizer, 40 kg of water, and 15 kg of silica sol. The castor oil-based polyurethane prepolymer comprises the following raw materials in parts by weight: 45 kg of isocyanate, 55 kg of polyester polyol, 2 kg of dimethylolpropionic acid, and 7 kg of castor oil.

[0026] The composite initiator is a mixture of azobisisobutyronitrile and ammonium persulfate, the mass ratio of azobisisobutyronitrile to ammonium persulfate is 1.2:1, the chain extender is ethylenediamine, the neutralizer is triethylamine, the average particle size of the silica sol is 100 nm, the isocyanate is toluene diisocyanate, the polyester polyol is polybutylene adipate diol, the number average molecular weight of polybutylene adipate diol is 1000, the acrylate monomers are methyl methacrylate, butyl acrylate, and hydroxypropyl methacrylate, and the mass ratio of methyl methacrylate, butyl acrylate, and hydroxypropyl methacrylate is 1:0.7:0.4 The preparation method of the waterborne polyurethane modified acrylate composite emulsion comprises the following specific steps: S1: Mix isocyanate, polyester polyol and castor oil, heat to 85°C and react for 1 hour, then cool to 75°C, add dimethylol propionic acid and continue to react at this temperature for 1 hour to obtain a castor oil-based polyurethane prepolymer.

[0027] S2: Mix castor oil-based polyurethane prepolymer, acrylic ester monomer, silica sol and water, disperse them evenly, then add composite initiator and chain extender, heat to 75°C and react for 5 hours, and finally add neutralizer to neutralize to obtain waterborne polyurethane modified acrylate composite emulsion.

[0028] Example 2 The difference between Example 2 and Example 1 is that the amount of castor oil-based polyurethane prepolymer used in the raw material of the water-based polyurethane modified acrylate composite emulsion is 20 kg, the amount of acrylate used is 40 kg of monomer, the amount of composite initiator used is 0.5 kg, the amount of chain extender used is 0.8 kg, the amount of neutralizer used is 1 kg, the amount of water used is 30 kg, and the amount of silica sol used is 10 kg.

[0029] Example 3 The difference between Example 3 and Example 1 is that the amount of castor oil-based polyurethane prepolymer used in the raw material of the water-based polyurethane modified acrylate composite emulsion is 40 kg, the amount of acrylate used is 20 kg of monomer, the amount of composite initiator used is 1 kg, the amount of chain extender used is 0.5 kg, the amount of neutralizer used is 3 kg, the amount of water used is 50 kg, and the amount of silica sol used is 20 kg.

[0030] Example 4 The difference between Example 4 and Example 1 is that the amount of isocyanate used in the castor oil-based polyurethane prepolymer raw material is 40 kg, the amount of polyester polyol used is 60 kg, the amount of dimethylol propionic acid used is 3 kg, and the amount of castor oil used is 8 kg.

[0031] Example 5 The difference between Example 5 and Example 1 is that the amount of isocyanate used in the castor oil-based polyurethane prepolymer raw material is 50 kg, the amount of polyester polyol used is 50 kg, the amount of dimethylol propionic acid used is 1 kg, and the amount of castor oil used is 5 kg.

[0032] Example 6 The difference between Example 6 and Example 1 is that the mass ratio of azobisisobutyronitrile and ammonium persulfate in the composite initiator is 0.8:1.

[0033] Example 7 The difference between Example 7 and Example 1 is that the mass ratio of methyl methacrylate, butyl acrylate, and hydroxypropyl methacrylate in the acrylic ester monomer is 1:0.5:0.5.

[0034] Example 8 The difference between Example 8 and Example 1 is that the mass ratio of methyl methacrylate, butyl acrylate, and hydroxypropyl methacrylate in the acrylic ester monomer is 1:0.8:0.3.

[0035] Example 9 The difference between Example 9 and Example 1 is that the silica sol is pre-modified with a silane coupling agent.

[0036] The preparation method of the waterborne polyurethane modified acrylate composite emulsion comprises the following specific steps: S1: Mix isocyanate, polyester polyol and castor oil, heat to 85°C and react for 1 hour, then cool to 75°C, add dimethylol propionic acid and continue to react at this temperature for 1 hour to obtain a castor oil-based polyurethane prepolymer.

[0037] S2: Mix the silica sol with isopropyl alcohol, and then add a silane coupling agent to mix. The mass ratio of the silica sol, isopropyl alcohol, and the silane coupling agent is 1:2:1.5. After uniform dispersion, react and filter to obtain a modified silica sol.

[0038] S3: Mix castor oil-based polyurethane prepolymer, acrylate monomer, modified silica sol and water, disperse them evenly, then add composite initiator and chain extender, heat to 75°C and react for 5 hours, and finally add neutralizer to neutralize to obtain waterborne polyurethane modified acrylate composite emulsion.

[0039] Example 10 The difference between Example 10 and Example 1 is that the mass ratio of silica sol, isopropyl alcohol and silane coupling agent is 1:3:1.

[0040] Comparative Example Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the aqueous polyurethane-modified acrylate composite emulsion does not use silica sol.

[0041] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the aqueous polyurethane-modified acrylate composite emulsion uses an equal amount of polyester-type aqueous polyurethane prepolymer instead of castor oil-based polyurethane prepolymer, wherein the polyester-type aqueous polyurethane prepolymer is purchased from Jiangsu Qianmeite Polyurethane New Materials Co., Ltd. K1230.

[0042] Performance testing According to the aqueous polyurethane-modified acrylate composite emulsions provided in Examples 1-10 and Comparative Examples 1-2 of the present application, the appearance of the emulsions was observed and the following performance tests were performed. The specific test results are shown in Table 1.

[0043] Detection method 1. Water resistance The coating film formed by the water-based polyurethane modified acrylate composite emulsion was cut into 3cm×3cm, the sample mass was measured at room temperature, and then it was immersed in deionized water at room temperature. After 24 hours, the sample was taken out and quickly wiped dry and weighed. The percentage increase in the mass of the sample was the water absorption rate.

[0044] 2. Gloss With reference to the standard GB / T9754-2007 "Determination of specular gloss at 20°, 60° and 85° of paints and varnishes without metallic pigments", the gloss of the composite emulsion coating prepared in this application at 60° was tested.

[0045] 3. Hardness The coating film hardness of the waterborne polyurethane-modified acrylate composite emulsion prepared in this application was tested with reference to the standard GB / T 6739-2006 "Paints and varnishes - Determination of film hardness by pencil method".

[0046] Table 1: Performance test results data table It can be seen from the performance test results that the water-based polyurethane-modified acrylate composite emulsion prepared in this application has good stability, a transparent appearance, and can form a uniform and glossy coating film. Through the synergistic effect of each component, the cross-linking degree in the composite emulsion system is improved, thereby improving the water resistance and hardness of the coating film.

[0047] By comparing Comparative Examples 1-2 with Example 1, it can be seen that Comparative Example 1 does not use silica sol, and Comparative Example 2 uses conventional polyester polyurethane prepolymer instead of castor oil-based polyurethane prepolymer. From the performance test results, it can be seen that the strength of the coating prepared in Comparative Example 1 is significantly reduced, and the water resistance and stability of the composite emulsion prepared in Comparative Example 2 are reduced.

[0048] Comparison between Examples 9-10 and Example 1 shows that pre-modification of the silica sol with a silane coupling agent can promote uniform dispersion of the modified silica sol in the composite emulsion system, thereby improving the uniformity, gloss and hardness of the coating film.

[0049] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A waterborne polyurethane modified acrylate composite emulsion, characterized in that: The invention comprises the following raw materials in parts by weight: 20-40 parts of castor oil-based polyurethane prepolymer, 20-40 parts of acrylate monomer, 0.5-1 part of composite initiator, 0.5-0.8 part of chain extender, 1-3 parts of neutralizer, 30-50 parts of water and 10-20 parts of silica sol.

2. The aqueous polyurethane modified acrylate composite emulsion according to claim 1, characterized in that: The castor oil-based polyurethane prepolymer comprises the following raw materials in parts by weight: 40-50 parts of isocyanate, 50-60 parts of polyester polyol, 1-3 parts of dimethylol propionic acid, and 5-8 parts of castor oil.

3. The aqueous polyurethane modified acrylate composite emulsion according to claim 2, characterized in that: The method for preparing the castor oil-based polyurethane prepolymer comprises the following specific steps: mixing isocyanate, polyester polyol and castor oil, heating the mixture for reaction, cooling the mixture, adding dimethylol propionic acid and continuing the reaction at the same temperature to obtain the castor oil-based polyurethane prepolymer.

4. The aqueous polyurethane modified acrylate composite emulsion according to claim 3, characterized in that: The heating temperature is 80-90°C, and the cooling temperature is 70-80°C.

5. The aqueous polyurethane modified acrylate composite emulsion according to claim 1, characterized in that: The composite initiator is a mixture of azobisisobutyronitrile and ammonium persulfate, and the mass ratio of the azobisisobutyronitrile to the ammonium persulfate is (0.8-1.2):

1.

6. The aqueous polyurethane modified acrylate composite emulsion according to claim 1, characterized in that: The acrylic acid ester monomers include methyl methacrylate, butyl acrylate, and hydroxypropyl methacrylate, and the mass ratio of the methyl methacrylate, butyl acrylate, and hydroxypropyl methacrylate is 1: (0.5-0.8): (0.3-0.5).

7. The aqueous polyurethane modified acrylate composite emulsion according to claim 1, characterized in that: The silica sol is modified with a silane coupling agent in advance, which includes the following specific steps: mixing the silica sol with isopropyl alcohol, then adding the silane coupling agent, mixing, uniformly dispersing, reacting, and filtering to obtain the modified silica sol.

8. The aqueous polyurethane modified acrylate composite emulsion according to claim 7, characterized in that: The mass ratio of the silica sol, isopropyl alcohol and silane coupling agent is 1:(2-3):(1-1.5).

9. A method for preparing the aqueous polyurethane modified acrylate composite emulsion according to any one of claims 1 to 8, characterized in that: The method comprises the following specific steps: mixing castor oil-based polyurethane prepolymer, acrylate monomer, silica sol and water, dispersing them uniformly, adding composite initiator and chain extender, heating for reaction, and finally neutralizing with a neutralizer to obtain waterborne polyurethane modified acrylate composite emulsion.

10. The method for preparing the aqueous polyurethane modified acrylate composite emulsion according to any one of claim 9, characterized in that: The heating temperature is 70-80°C.

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