Hydrophobic acrylic organosilicon polyurethane coating and preparation method thereof

Abstract

The invention relates to a preparation method of a hydrophobic acrylic organosilicon polyurethane coating, which comprises the following steps: initiating a silane coupling agent to graft methacrylic acid through an initiator, substituting a double bond to synthesize silane modified methacrylic acid Si-MA, introducing Si-MA into polyurethane through a copolymerization method in the polyurethane synthesis process, and introducing an organosilicon hydrophobic chain segment into the structure; si-MA is firstly dissolved in a methanol solution, self-polymerization of silanol bonds can be avoided, the reaction activity is guaranteed, silane contains three silanol bonds after hydrolysis, two silanol bonds are used for a chain extension reaction, the remaining silanol bonds can be subjected to self-crosslinking after curing to form a net structure, the strength of the system is further improved, and a core-shell structure with a better hydrophobic effect is formed; the molecular weight of silane is small, so that the particle size of the coating is reduced, and the hardness is moderate; according to the hydrophobic polyurethane coating prepared by the method disclosed by the invention, an organosilicon hydrophobic chain segment Si-MA is introduced, so that the free energy of the surface of the coating is reduced, the water resistance of the surface is enhanced, and the application prospect is wide.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coatings, in particular to a hydrophobic acrylic organic silicon polyurethane coating and a preparation method thereof. BACKGROUND

[0002] Waterborne polyurethane is an environmentally friendly new material, which maintains the wear resistance of solvent-based polyurethane, and has the characteristics of low VOC (low volatile organic compounds) content, making it widely used in many fields. However, due to the introduction of hydrophilic groups to produce self-emulsification effect, the surface of the waterborne polyurethane is hydrophilic, and the overall water resistance is reduced, which limits its further promotion. At present, most of the methods choose copolymerization to introduce organosilicon chain segments into the structure in the form of chemical bonds to obtain organosilicon-modified waterborne polyurethane composite coating. In order to introduce organosilicon hydrophobic chain segments into the structure, reduce the surface free energy of the coating, and enhance the water resistance of the surface, the excellent mechanical properties of polyurethane and the excellent water resistance of organosilicon are combined. Most of them use amino-terminated polydimethylsiloxane or hydroxyl-terminated polydimethylsiloxane as raw materials to replace part of the polyol and combine with isocyanate to introduce organosilicon chain segments. However, these two raw materials are used to replace polyols to introduce chain segments, and too much will increase the hardness of the coating, reduce the elasticity, ductility and impact resistance, and increase the processing viscosity. Too little has little effect on the hydrophobic performance and surface tension of the coating, and cannot play a hydrophobic role. As a chain extender, it does not contain carboxyl structure, and needs to introduce acrylic acid additionally. The molecular weight will increase, and the fineness and viscosity of the coating cannot be controlled. Therefore, how to prepare an organosilicon-modified polyurethane coating with small particles, good hydrophobic performance, high hardness and strength, and multiple performances has great research value and application potential. SUMMARY

[0003] In view of the deficiencies of the prior art, the present application provides a hydrophobic acrylic organic silicon polyurethane coating and a preparation method thereof.

[0004] The technical scheme of the present application is as follows: A preparation method of a hydrophobic acrylic organic silicon polyurethane coating, comprising the following steps, S1. After stirring and reacting methyl methacrylate and silane in a solvent, an initiator is added, and the reaction is continued, and then a silane-modified methyl methacrylate is obtained. The silane-modified methyl methacrylate is dissolved in a methanol aqueous solution to obtain solution A; S2. Solution A is added dropwise into a polyurethane prepolymer dispersion to obtain solution B; S3. An acrylic butyl ester aqueous solution containing potassium persulfate is added to solution B for emulsification reaction, and then heated and reacted. Organic amine is added, and after stirring, a hydrophobic acrylic organic silicon polyurethane coating is obtained.

[0005] Furthermore, in step S1, the solvent is one or more of toluene, xylene, and decahydronaphthalene; the initiator is one or more of dibenzoyl peroxide BPO, dicumyl peroxide DCP, tert-butyl perbenzoate TPB, and dilauroyl peroxide LPO; and the silane is one or more of vinyltrimethoxysilane and vinyltriethoxysilane.

[0006] Furthermore, in step S1, the methacrylic acid is 1-5 parts by mass, the silane is 0.01-0.15 parts by mass, the initiator is 0.0002-0.0025 parts by mass, the methanol aqueous solution is 2-10 parts by mass, methanol:water = (5-20):1, and the solvent is 70-100 parts by mass.

[0007] Furthermore, the reaction in step S1 is specifically as follows: methacrylic acid and silane are added to a solvent and reacted for 30-40 minutes, and an initiator is added thereto and reacted at 70-130° C. for 30-120 minutes.

[0008] Furthermore, the process parameters of the reaction in step S2 are: at 70-80° C., a dropping rate of 0.1-0.2 g / min, the dropping is completed within half an hour, and the reaction is carried out for 4-6 hours.

[0009] Furthermore, the components in step S3 are 30-60 parts by mass of distilled water, 1-10 parts by mass of organic amine, 0.01-1 parts by mass of potassium persulfate, and 1-5 parts by mass of butyl acrylate.

[0010] Furthermore, the process parameters of the reaction in step S3 are as follows: emulsification for 30-60 minutes, rotary evaporation of acetone, and then heating to 60-80° C. for reaction.

[0011] Furthermore, the organic amine in step S3 is one or more of triethylamine, triethanolamine, and diethanolamine.

[0012] The hydrophobic acrylic organosilicon polyurethane coating is prepared by the above preparation method.

[0013] Compared with the prior art, the present invention has at least the following advantages: 1.The present application relates to a method for preparing a hydrophobic acrylic silicone polyurethane coating, a silane coupling agent is grafted with methyl methacrylate by an initiator to replace its double bond to synthesize silane modified methyl methacrylate Si-MA, Si-MA is introduced into polyurethane by a method of copolymerization in the process of polyurethane synthesis to obtain a hydrophobic acrylic silicone polyurethane coating Si-WPUA, and an organic silicon hydrophobic segment is introduced into the structure; Si-MA is dissolved in a methanol solution after synthesis, which can avoid silanol bond self-polymerization and ensure reaction activity; Si-MA is added into a polyurethane prepolymer in a dropwise manner, which can ensure that Si-MA preferentially reacts with excess isocyanate; after synthesizing Si-MA, three silanol bonds are contained after silane hydrolysis, two of which are used for chain extension reaction, and the remaining silanol bond can form a network structure after methanol volatilization in the coating construction process, further increasing the strength of the system, and a core-shell structure is formed, the silane segment tends to migrate to the surface of the coating, and the polyurethane acrylic segment (containing a polar group such as carboxylic acid) is more hydrophilic and tends to remain inside, after curing, a microstructure similar to a core-shell structure is formed, and the hydrophobic effect is better; the silane is one or more of vinyltrimethoxysilane and vinyltriethoxysilane, the molecular weight of the silane is small, which reduces the particle size of the coating and makes the hardness moderate.

[0014] 2.The present application relates to a hydrophobic acrylic silicone polyurethane coating, an organic silicon hydrophobic segment Si-MA is introduced, which reduces the free energy of the surface of the coating and enhances the water resistance of the surface; Si-MA has not only a hydroxyl group for isocyanate synthesis but also a hydrophilic carboxyl group, which combines two functions into one, can not only react with isocyanate and be used as a chain extender but also be used for end capping; the role of polybutyl acrylate is to improve the water resistance and mechanical properties of the coating. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to more clearly illustrate the specific embodiments of the present application, the drawings required to be used in the specific embodiments or prior art description will be briefly introduced below.

[0016] Figure 1 The FTIR-ATR characterization graph of the test example one of the present application. DETAILED DESCRIPTION

[0017] The present application will be further described below, and it is necessary to point out here that the following specific embodiments are only used to further illustrate the present application and cannot be understood as limiting the protection scope of the present application, and those skilled in the art can make some non-essential improvements and adjustments to the present application according to the above application content.

[0018] The materials used in the experiments and the experimental methods are generally and / or specifically described. Unless otherwise specified, the experimental methods or test methods involved are conventional methods; the reagents or instruments used are conventional products available on the market, prepared or used by conventional methods, unless otherwise specified.

[0019] Example 1 The preparation method of the hydrophobic acrylic silicone polyurethane coating (1) Preparation of silane-modified methacrylic acid: in a reaction vessel, 1 g of methacrylic acid MA and 0.01 g of A171 were dissolved in 70 g of toluene, stirred for 30 min, 0.0002 g of BPO initiator was added, and reacted at 70°C for 120 min. After the reaction was completed, it was washed with acetone to obtain silane-modified methacrylic acid Si-MA, which was dissolved in 2 g of methanol aqueous solution to obtain solution A, methanol: water = 10: 1; (2) Preparation of polyurethane prepolymer dispersion: 5 g of TDI, 3 g of PPG-1000, 20 g of acetone, and 0.001 g of dibutyltin dilaurate were mixed, and the polyurethane prepolymer dispersion was obtained after reaction at 70°C for 1 h under stirring conditions; (3) Solution A was added dropwise into the polyurethane prepolymer dispersion at 70°C, the dropping speed was 0.1 g / min, and the dropping was completed within half an hour. After reaction for 4 h, solution B was obtained; (4) At room temperature, 0.01 g of potassium persulfate, 1 g of butyl acrylate, and 30 g of distilled water were added to the flask under high-speed stirring at 400 r / min, and the emulsification was continued for 30 min. The acetone was removed by rotary evaporation, the temperature was raised to 60°C, and then 1 g of triethylamine was added and stirred uniformly to obtain the hydrophobic acrylic silicone polyurethane coating Si-WPUA.

[0020] The coating was poured into a polytetrafluoroethylene mold, placed in a 40ºC air-drying oven for 30 min, and then the cured film was dried in a vacuum oven at 70ºC for 2 h.

[0021] The preparation flow chart of this example is as follows: Example 2 The preparation method of the hydrophobic acrylic silicone polyurethane coating (1) Preparation of silane-modified methacrylic acid: in a reaction vessel, 5 g of methacrylic acid MA and 0.15 g of A172 were dissolved in 80 g of decaline, stirred for 30 min, 0.0025 g of TPB initiator was added, and reacted at 130°C for 30 min. After the reaction was completed, it was washed with acetone to obtain silane-modified methacrylic acid Si-MA, which was dissolved in 10 g of methanol aqueous solution to obtain solution A, methanol: water = 10: 1; (2) Preparation of polyurethane prepolymer dispersion: 20 g of MDI, 10 g of PCDL-1000, 30 g of acetone, and 0.01 g of dibutyltin dilaurate were mixed, and a polyurethane prepolymer dispersion was obtained after stirring at 90°C for 3 h; (3) At 80°C, solution A was added dropwise to the polyurethane prepolymer dispersion at a rate of 0.1 g / min, and the addition was completed within half an hour. After 6 h of reaction, solution B was obtained. (4) At room temperature, 0.1 g of potassium persulfate, 5 g of butyl acrylate, and 60 g of distilled water were added to the flask and stirred at 400 r / min for 30 min. The acetone was removed by rotary evaporation, the temperature was raised to 80°C, and then 10 g of triethylamine was added and stirred uniformly to obtain the hydrophobic acrylic silicone polyurethane coating Si-WPUA.

[0022] The above coating was poured into a polytetrafluoroethylene mold, placed in a 40ºC air-drying oven for 30 min, and then the cured film was dried in a vacuum oven at 70ºC for 2 h.

[0023] Example Three Preparation method of hydrophobic acrylic silicone polyurethane coating (1) Preparation of silane-modified methyl methacrylate: 5 g of methyl methacrylate MA and 0.15 g of A171 were dissolved in 100 g of toluene in a reaction vessel, stirred for 30 min, and then 0.002 g of DCP initiator was added. The reaction was carried out at 100°C for 90 min. After the reaction was completed, the silane-modified methyl methacrylate Si-MA was washed with acetone, and then dissolved in 10 g of methanol aqueous solution to obtain solution A (methanol: water = 10: 1). (2) Preparation of polyurethane prepolymer dispersion: 20 g of IPDI, 10 g of PPG-2000, and 0.005 g of dibutyltin dilaurate were mixed, and a polyurethane prepolymer dispersion was obtained after stirring at 80°C for 3 h; (3) At 80°C, solution A was added dropwise to the polyurethane prepolymer dispersion at a rate of 0.1 g / min, and the addition was completed within half an hour. After 6 h of reaction, solution B was obtained. (4) At room temperature, 0.05 g of potassium persulfate, 5 g of butyl acrylate, and 50 g of distilled water were added to the flask and stirred at 400 r / min for 30 min. The acetone was removed by rotary evaporation, the temperature was raised to 75°C, and then 8 g of triethylamine was added and stirred uniformly to obtain the hydrophobic acrylic silicone polyurethane coating Si-WPUA.

[0024] The above coating was poured into a polytetrafluoroethylene mold, placed in a 40ºC air-drying oven for 30 min, and then the cured film was dried in a vacuum oven at 70ºC for 2 h.

[0025] Comparative Example 1 The present comparative example is a method for preparing a waterborne polyurethane WPUA, comprising the following steps: (1) A polyurethane prepolymer dispersion was prepared by mixing 5 g of TDI, 3 g of PPG-1000, 20 g of acetone, 2 g of 2,2-dimethylol propionic acid, and 0.001 g of dibutyltin dilaurate under stirring at 70 °C for 1 h; (2) At room temperature, 0.01 g of potassium persulfate, 1 g of MA, 1 g of butyl acrylate, and 30 g of distilled water were added to the polyurethane prepolymer dispersion in a flask under high-speed stirring, and the emulsification was continued for 30 min. The acetone was removed by rotary evaporation, the temperature was raised to 60 °C, and then 1 g of triethylamine was added thereto and stirred uniformly to obtain a waterborne polyurethane WPUA.

[0026] The above coating was poured into a polytetrafluoroethylene mold, dried in a 40 °C air-drying oven for 30 min, and then the cured film was dried in a vacuum oven at 70 °C for 2 h.

[0027] Comparative Example 2 The present comparative example is a method for preparing a waterborne polyurethane WPUA containing silicon, which is different from Example 1 in that the silane-modified methyl methacrylate is replaced by a hydroxyl-terminated polydimethylsiloxane, comprising the following steps: (1) A polyurethane prepolymer dispersion was prepared by mixing 5 g of TDI, 3 g of PPG-1000, 20 g of acetone, 2 g of 2,2-dimethylol propionic acid, and 0.001 g of dibutyltin dilaurate under stirring at 70 °C for 1 h; (2) At 70 °C, 2 g of a hydroxyl-terminated polydimethylsiloxane solution was added dropwise to the polyurethane prepolymer dispersion, and after 4 h of reaction, solution B was obtained; (3) At room temperature, 0.01 g of potassium persulfate, 1 g of MA, 1 g of butyl acrylate, and 30 g of distilled water were added to solution B in a flask under high-speed stirring at 400 r / min, and the emulsification was continued for 30 min. The acetone was removed by rotary evaporation, the temperature was raised to 60 °C, and then 1 g of triethylamine was added thereto and stirred uniformly to obtain a waterborne polyurethane WPUA containing silicon.

[0028] The above coating was poured into a polytetrafluoroethylene mold, dried in a 40 °C air-drying oven for 30 min, and then the cured film was dried in a vacuum oven at 70 °C for 2 h.

[0029] Comparative Example 3 The present comparative example is a method for preparing a waterborne polyurethane WPUA containing silicon, which is different from Example 1 in that the 2,2-dimethylol propionic acid and the silane 171 are added to the polyurethane prepolymer dispersion in steps, comprising the following steps: (1) Preparation of polyurethane prepolymer dispersion: 5 g of TDI, 3 g of PPG-1000, 2 g of 2,2-dimethylol propionic acid, 20 g of acetone, and 0.001 g of dibutyltin dilaurate were mixed, and a polyurethane prepolymer dispersion was obtained after reaction at 70°C under stirring conditions for 1 h; (2) 0.01 g of A171 was added dropwise to the polyurethane prepolymer dispersion at 70°C, and solution B was obtained after reaction for 4 h; (3) At room temperature, 0.01 g of potassium persulfate, 1 g of butyl acrylate, and 30 g of distilled water were added to the flask under high-speed stirring at 400 r / min, and the emulsion was continuously stirred for 30 min, and acetone was removed by rotary evaporation, and the temperature was increased to 60°C, and then 1 g of triethylamine was added and stirred uniformly to obtain a silicon-containing waterborne polyurethane WPUA.

[0030] Test Example One This test example takes the hydrophobic acrylic silicone polyurethane coating Si-WPUA prepared in Example One as an example, and the FTIR-ATR characterization is carried out after curing.

[0031] The characterization results are shown in Figure 1 From the figure, it can be seen that the prepared and synthesized Si-WPUA has obvious infrared absorption peaks at 3330 cm -1 , 1717 cm -1 , and 2835 cm -1 , which are caused by the stretching vibration of C=O group in formate bond and CH3 group, respectively. The silicone-modified coating has Si-O-C asymmetric stretching vibration absorption peaks at 1255 cm -1 , 1003 cm -1 , and 813 cm -1 , respectively, and Si-CH3 rocking vibration absorption peaks, and a strong absorption peak at 1099 cm -1 , which is the infrared absorption peak of Si-O. Moreover, a multi-peak can be obviously observed at this position, and the peak is relatively wide, which is because there are a large number of Si-O-Si structures in the structure. In summary, the hydrophobic acrylic silicone polyurethane coating Si-WPUA can be successfully prepared by the method.

[0032] Test Example Two The performance of the coatings prepared in Examples 1-3 and Comparative Examples 1-3 was tested. The pencil method was used to determine the film hardness according to GB / T 6739, and the emulsion particle size was determined according to GB / T 1724. A contact angle measuring instrument was used to measure the static contact angle of water by adding 2 microliters of water droplets on the surface. The tensile properties were tested according to GB / T 1040-2006, and the test results are shown in Table 1 below: Table 1 Performance data of the composite coatings prepared in Examples 1-3 and Comparative Examples 1-2 As can be seen from Table 1, Examples 1-3 are superior to Comparative Examples in various aspects, especially using self-synthesized Si-MA, while achieving small average particle size, good hydrophobic effect, excellent tensile strength, elongation at break, and hardness effect. The condensation crosslinking between silanol in the silicone polyurethane coating prepared by the present application further improves the strength after drying.

[0033] The molecular weight of the hydroxyl-terminated polydimethylsiloxane in Comparative Example 2 is large, and the introduction of large molecular weight leads to an increase in coating hardness and a decrease in elongation at break. The fineness of the coating cannot be controlled. In the reaction system of Comparative Example 3, unhydrolyzed A171 is directly added to the polyurethane prepolymer dispersion, the water content in the system is insufficient, and the reaction proceeds synchronously (such as polyurethane chain growth), which leads to insufficient hydrolysis of silane, and part of the unhydrolyzed silane cannot form silanol and participate in crosslinking reaction, resulting in less siloxane structure and less introduction of hydrophobic segments, which has little effect on the hydrophobic performance and surface tension of the coating, and the hydrophobic effect is poor. The hardness is small, which leads to poor scratch resistance. In the Si-WPUA reaction system of the hydrophobic acrylic silicone polyurethane coating prepared by the present application, the silane has three silanol structures, two of which enter the chain segment, and the other silanol structure is used for intermolecular self-polymerization to form a three-dimensional crosslinked network, which enhances the mechanical strength and compactness of the coating. Thus, a core-shell structure is formed, the silane segment (containing hydrophobic Si-O-Si structure) tends to migrate to the surface of the coating (hydrophobic environment), and the polyurethane acrylic segment (containing polar groups such as carboxylic acid) is more hydrophilic and tends to stay inside. After curing, the silane forms a hydrophobic "shell" on the outer layer, and the polyurethane acrylic forms a "core" on the inner layer, forming a microstructure similar to a core-shell structure, which has better hydrophobic effect.

[0034] The above examples are only used to illustrate the technical solutions of the present application, but not limit the present application; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can be modified, or some or all of the technical features can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and the specification of the present application.

Claims

1. A method for preparing a hydrophobic acrylic silicone polyurethane coating, characterized in that: The following steps are included: S1. Methacrylic acid and silane were added to a solvent and stirred for reaction, an initiator was added thereto, and the reaction was continued by heating to obtain silane-modified methacrylic acid, which was dissolved in aqueous methanol to obtain a solution A; S2. Solution A was added dropwise to the polyurethane prepolymer dispersion to obtain solution B; S3. An aqueous solution of butyl acrylate containing potassium persulfate is added to solution B for emulsification reaction, and then an organic amine is added thereto after heating and reaction, and the mixture is stirred to obtain a hydrophobic acrylic silicone polyurethane coating.

2. The preparation method according to claim 1, characterized in that In step S1, the solvent is one or more of toluene, xylene, and decahydronaphthalene; the initiator is one or more of dibenzoyl peroxide (BPO), dicumyl peroxide (DCP), tert-butyl perbenzoate (TPB), and dilauroyl peroxide (LPO); and the silane is one or more of vinyltrimethoxysilane and vinyltriethoxysilane.

3. The preparation method according to claim 2, characterized in that In step S1, the methacrylic acid is 1-5 parts by mass, the silane is 0.01-0.15 parts by mass, the initiator is 0.0002-0.0025 parts by mass, the methanol aqueous solution is 2-10 parts by mass, methanol:water=(5-20):1, and the solvent is 70-100 parts by mass.

4. The preparation method according to any one of claims 1 to 3, characterized in that The reaction in step S1 is specifically as follows: methacrylic acid and silane are added to a solvent and reacted for 30-40 minutes, and an initiator is added thereto and reacted at 70-130° C. for 30-120 minutes.

5. The preparation method according to claim 4, characterized in that The process parameters of the reaction in step S2 are: at 70-80° C., a dropping rate of 0.1-0.2 g / min, the dropping is completed within half an hour, and the reaction is carried out for 4-6 hours.

6. The preparation method according to claim 5, characterized in that The components in step S3 are as follows: 30-60 parts by mass of distilled water, 1-10 parts by mass of an organic amine, 0.01-1 parts by mass of potassium persulfate, and 1-5 parts by mass of butyl acrylate.

7. The preparation method according to claim 6, characterized in that The process parameters of the reaction in step S3 are as follows: emulsification for 30-60 minutes, rotary evaporation of acetone, and then heating to 60-80° C. for reaction.

8. The preparation method according to any one of claims 5 to 7, characterized in that The organic amine in step S3 is one or more of triethylamine, triethanolamine, and diethanolamine.

9. A hydrophobic acrylic organosilicon polyurethane coating prepared by the preparation method according to any one of claims 1 to 8.

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