A method for producing a coating for bathtubs

Abstract

This invention belongs to the field of coating materials, specifically relating to a method for preparing a bathtub-specific coating. The method includes: 1) mixing monomers, initiator A, and an organic solvent uniformly for prepolymerization, then adding resin monomers, organic solvent, and initiator B to react and obtain a powder; 2) mixing inorganic particles with a siloxane polymer to obtain modified particles; 3) reacting isocyanate, a blocking agent, and an organic solvent to obtain a curing agent; 4) mixing reagents, color paste, and powder uniformly, then adding the curing agent to obtain a coating material, and alternately spraying the coating material and modified particles with a spray gun to cure and obtain the coating. The coating prepared by this invention is safe, non-toxic, odorless, has a smooth, burr-free surface, and is water-resistant, solvent-resistant, high-temperature resistant, weather-resistant, has strong adhesion, high hardness, wear-resistant, scratch-resistant, and impact-resistant.

Description

Technical Field

[0001] This invention belongs to the field of coating materials, and specifically relates to a method for preparing a coating for bathtubs. Background Technology

[0002] Existing bathtub coatings are broadly classified into two types: organic solvent-based coatings and water-based coatings. Organic solvent-based coatings generally contain pungent odors and many substances harmful to human health, primarily formaldehyde, benzene, and ethylene glycol ether solvents. The evaporation of these solvents poses environmental hazards and may corrode the acrylic substrate of the bathtub, causing "bathtub burning." Furthermore, these coatings have poor scratch resistance. Water-based coatings, on the other hand, can significantly reduce VOC content, lessen the environmental impact, and prevent "bathtub burning."

[0003] Water-based coatings include epoxy resin coatings, polyurethane coatings, polyacrylate coatings, and alkyd resin coatings. Epoxy resin coatings, after curing, form a recalcitrant and insoluble network structure, exhibiting strong adhesion, chemical resistance, abrasion resistance, and high hardness. However, they may develop micropores and cracks, leading to brittle fracture of the coating. Polyurethane water-resistant coatings are significantly affected by temperature; at temperatures between 5 and 8°C, heating or the addition of organic solvents is required for use. Polyacrylate coatings, on the other hand, suffer from poor abrasion resistance. Alkyd resin coatings possess good brushing and wetting properties, but also exhibit drawbacks such as slow film drying, low hardness, poor water and corrosion resistance, and poor weather resistance.

[0004] In addition, compared to organic solvents, water is less volatile, and under high humidity conditions, the coating is prone to sagging and uneven thickness after molding. Water's surface tension is much higher than that of solvents, causing wrinkles on the molded coating surface. Furthermore, water's conductivity is much higher than that of solvents, making electrostatic spraying unsuitable. Due to these numerous differences, it is necessary to develop a bathtub-specific coating and a method for molding water-based coatings. Summary of the Invention

[0005] Based on the above, in order to solve the problems of poor weather resistance, insufficient adhesion strength, and uneven thickness caused by sagging in water-based coatings, this invention proposes a method for preparing a bathtub-specific coating.

[0006] The purpose of this invention is:

[0007] 1. Improve the anti-sagging properties of coatings;

[0008] Second, ensure that the coating is water-resistant and weather-resistant, and will not delaminate from the bathtub substrate under long-term immersion in water;

[0009] 3. Improve the adhesion strength, hardness, and impact resistance of the coating.

[0010] To achieve the above objectives, the present invention adopts the following technical solution.

[0011] A method for preparing a coating specifically for bathtubs.

[0012] The method includes:

[0013] 1) Mix monomer, initiator A and organic solvent evenly for prepolymerization, add the mixture of resin monomer and organic solvent dropwise, and continue to add initiator B while stirring to carry out thermal reaction. Filter and dry to obtain powder.

[0014] 2) Take inorganic particles and disperse them evenly in an organic solvent, add siloxane polymer and mix evenly, then dry to obtain modified particles;

[0015] 3) Take isocyanate, sealant and organic solvent and carry out thermal reaction. After cooling, add neutralizer and mix evenly. Discharge to obtain curing agent;

[0016] 4) Mix the reagents, color paste, and powder evenly to obtain the coating. Add the curing agent to the coating and spray the coating and modified particles alternately through a spray gun while applying the coating at a temperature gradient. Curing will then result in the coating layer.

[0017] As a preferred option

[0018] The monomer mentioned in step 1) is butyl acrylate;

[0019] In step 1), the initiator A is benzoyl peroxide, and its dosage is 0.02-0.05 g / g monomer;

[0020] The organic solvent used in step 1) is ethanol, and the amount used is 2-5 mL / g monomer.

[0021] As a preferred option

[0022] The prepolymerization in step 1) is carried out at a constant temperature of 110-120°C for 0.5-1 hour.

[0023] As a preferred option

[0024] The dripping rate in step 1) is 1-2 mL / min.

[0025] Step 1) The resin monomer is methyl methacrylate and ethylene-vinyl alcohol copolymer;

[0026] The methyl methacrylate, ethylene-vinyl alcohol copolymer, and monomers are formulated in a mass ratio of (5-7):(1-3):4;

[0027] The organic solvent used in step 1) is ethanol, and the amount used is 2-5 mL / g resin monomer;

[0028] In step 1), the initiator B is benzoyl peroxide, and its dosage is 0.02-0.05 g / g resin monomer.

[0029] As a preferred option

[0030] The thermal reaction described in step 1) is carried out at 120–125°C for 0.5–1 hour.

[0031] As a preferred option

[0032] The inorganic particles mentioned in step 2) are silicon dioxide with a particle size of 5-8 μm;

[0033] The organic solvent in step 2) is anhydrous ethanol, and its dosage is 5-15 mL / g inorganic particles;

[0034] Step 2) The siloxane polymer is polydimethylsiloxane, and its dosage is 1-1.5 mL / g inorganic particles.

[0035] As a preferred option

[0036] Step 3) The isocyanate is isophorone diisocyanate;

[0037] The blocking agent in step 3) is 3,5-dimethylpyrazole, and its dosage is 0.5-0.6 g / mL isocyanate;

[0038] The organic solvent in step 3) is acetone, and the amount used is 1-5 mL / mL isocyanate.

[0039] As a preferred option

[0040] The thermal reaction described in step 3) is carried out at 60-65°C for 4-5 hours at a constant temperature.

[0041] The neutralizing agent in step 3) is triethylamine, and its dosage is 0.9 to 1 mL / mL isocyanate.

[0042] As a preferred option

[0043] The reagents, pigments, and powders described in step 4) are prepared in a mass ratio of 1:(1-2):(13-17);

[0044] The reagent is water;

[0045] Step 4) The amount of curing agent used is 15-18 wt% of the coating;

[0046] Step 4) The amount of modified particles used is 10-15 wt% of the coating.

[0047] As a preferred option

[0048] Step 4) describes the temperature gradient coating method as follows:

[0049] In an inert gas environment, the inert gas flow rate is set to 50-60 L / min, the spray gun temperature is set to 120-150℃, and the temperature is gradually reduced after every 3-5 sprays. The number of sprays is 10-20, and the total spray thickness is 0.4-0.8 mm.

[0050] Step 4) The curing is carried out at 80-90°C for 3-4 hours.

[0051] In this invention, the mechanical properties of the coating are controlled by adding the hard monomer methyl methacrylate, the soft monomer butyl acrylate, and the functional monomer ethylene-vinyl alcohol copolymer in steps, forming a "core-shell" structure where hard segments encapsulate soft segments. During prepolymerization, the viscosity of the coating increases slowly, resulting in a longer activation period and avoiding polymerization difficulties caused by excessive resin viscosity. As the amount of hard monomer increases, the drying time required for the coating becomes shorter, while its hardness and water resistance increase. However, excessive hard monomer leads to reduced coating flexibility and significantly increased brittleness, resulting in a significant decrease in the coating's impact resistance. The adhesion strength between the coating and the bathtub substrate decreases slightly, leading to a reduction in the coating's water resistance. Furthermore, to ensure moderate resin viscosity and stable storage, this invention selects BPO as an initiator. Experiments have shown that adding an appropriate amount of initiator results in a higher resin conversion rate.

[0052] Simultaneously, the addition time of the monomer mixture should be controlled. If the droplet acceleration is too slow, the diffusion rate of polymer molecules with different chain lengths will be uniform. Although the composition is uniform and the molecular weight distribution is narrow, the molecular weight of the coating is relatively low, its viscosity is low, the drying time is long, and the coating sagging is severe. If the droplet acceleration is too fast, it will lead to a significant increase in the molecular weight of the coating, and its relative molecular weight distribution will be wide, resulting in a large difference in the diffusion rate of different chain lengths. This will lead to excessively high local viscosity, causing not only uneven composition but also low solid content. If the three are mixed and activated, the coating viscosity may rise rapidly, resulting in excessively high local viscosity and difficulty in forming a "core-shell" structure, leading to poor impact resistance of the coating material. In addition, with the increase of functional monomer content and ethylene-vinyl alcohol copolymer content, the degree of cross-linking between coating components will be higher, thereby improving the adhesion strength of the coating. The steric hindrance of the groups and the synergistic protection of the ester groups by the polydimethylsiloxane-loaded silica (PDMS@SiO2) microspheres give the coating good water resistance.

[0053] PDMS@SiO2 microspheres can improve the high-temperature resistance and chemical stability of coatings. The microspheres dispersed in the coating can inhibit the slippage of resin macromolecules, thus improving the severe sagging problem during coating curing. They also act as dispersion reinforcement, enhancing the overall impact strength of the coating. During friction, the silicon-oxygen chains of PDMS migrate to the surface, reducing surface free energy and improving the coating's solvent and water resistance. PDMS@SiO2 microspheres also act as defoamers. However, introducing excessive PDMS negatively impacts the mechanical properties of the coating, but this problem can be compensated for by inorganic nanoparticles, which can also improve the coating's wear resistance. Characterization of the coating cross-section reveals ductile fracture, indicating that PDMS@SiO2 microspheres can enhance the coating's toughness.

[0054] The particulate matter on the coating surface increases with increasing SiO2 content, and the particles gradually aggregate and increase in size. To avoid this problem, this invention selects microspheres with a particle size of 5-8 μm, avoiding the use of excessively small particles, otherwise the particle surface energy will be large, making agglomeration more likely. In addition, the sedimentation phenomenon of SiO2 becomes more obvious with increasing SiO2 particle content, and the pore size of the coating increases. However, excessive SiO2 particles lead to the formation of a large number of agglomerated PDMS@SiO2 microspheres in the system. Moreover, the large-sized aggregates settle during static curing, leaving larger pores inside the coating. Pores are usually stress concentration points. In the experiment, it can be clearly seen that adding excessive SiO2 particles will cause cracks to appear around the stress points. Under the same load, the coating is more prone to cracking, and the dispersion strengthening effect of the coating is significantly reduced, resulting in a deterioration of its mechanical properties.

[0055] Under cyclic shear forces, the pure resin coating exhibits numerous cracks that propagate continuously, compressing abrasive debris to the vicinity of the contact area—a phenomenon characteristic of fatigue wear. This indicates insufficient toughness in the pure resin coating. While the addition of SiO2 microspheres, after prolonged friction, leads to abrasive wear, it still manages to penetrate the coating, accelerating its failure. PDMS@SiO2 microspheres, however, can reduce the coefficient of friction of the coating. Within a reasonable dosage range, the coefficient of friction of the coating remains relatively low.

[0056] At a certain temperature, the curing agent de-encapsulates to form isocyanate groups (-N=C=O) and end-capping agents. The resin dispersion contains a large number of hydroxyl groups, and the isocyanate groups react with the active hydrogen components to form more stable urethane bonds, further improving the toughness of the coating and thus enhancing its impact resistance. For industrial application, this invention selects 3,5-dimethylpyrazole for low-temperature de-encapsulation. Furthermore, this invention neutralizes the -COOH in the polymer chain with triethylamine. As the degree of neutralization increases, the dispersion becomes better, i.e., it is easier to disperse in water, and the stability is enhanced. Using an appropriate amount of triethylamine can ensure that the powder and modified particles are uniformly dispersed in water.

[0057] There is a difference in thermal expansion between the coating and the bathtub substrate. To enhance the high-temperature resistance of the resin-based coating, avoid the effects of different cooling rates inside and outside the coating, and strengthen the adhesion between the bathtub substrate and the coating, this invention uses a spray gun to apply the coating, followed by gradient cooling, and then curing. The raw materials are fully melted but do not decompose, and the heating time is greatly shortened, which is beneficial for industrial spraying of bathtubs. The fully molten particles are uniformly sprayed onto the bathtub substrate, and the high kinetic energy of the particles impacting the substrate results in high bonding strength between coating particles and high adhesion strength between the coating and the substrate. At the same time, there is heat loss during the spraying process. Therefore, this invention continuously gradient-cools the coating to prepare a coating with continuous composition, reducing the difference in thermal expansion between the coating and the bathtub substrate, and improving the adhesion strength between the coating and the substrate.

[0058] The beneficial effects of this invention are as follows:

[0059] (1) The coating prepared by the present invention is safe, non-toxic, odorless, and has a smooth and burr-free surface. It will not pollute the air or water quality when used.

[0060] (2) The coating prepared by this invention is water-resistant, solvent-resistant, high-temperature resistant, and weather-resistant;

[0061] (3) The coating prepared by the present invention has strong adhesion, high hardness, wear resistance, scratch resistance and impact resistance. Detailed Implementation

[0062] The present invention will be further described clearly and in detail below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0063] Unless otherwise specified, all raw materials used in the embodiments of the present invention are commercially available or obtainable by those skilled in the art; unless otherwise specified, all methods used in the embodiments of the present invention are methods mastered by those skilled in the art.

[0064] Example 1

[0065] A method for preparing a coating specifically for bathtubs, the method comprising:

[0066] 1) Take 20g butyl acrylate, 0.4g benzoyl peroxide and 40mL ethanol and mix them evenly. Keep the temperature at 110℃ for 1h. Separately take 25g methyl methacrylate, 5g ethylene-vinyl alcohol copolymer and 80mL ethanol to prepare a mixture. Add the mixture dropwise at a rate of 1mL / min. While stirring, continue to add 0.6g benzoyl peroxide. Keep the temperature at 120℃ for 1h. Filter and dry to obtain powder.

[0067] 2) Take 7.5g of silica with a particle size of 5μm and disperse it evenly in 40mL of anhydrous ethanol. Add 7.5mL of polydimethylsiloxane and mix evenly. Dry to obtain modified particles.

[0068] 3) Take 9 mL of isophorone diisocyanate, 4.5 g of 3,5-dimethylpyrazole and 25 mL of acetone, keep the temperature at 60℃ for 5 h, and after cooling, add 8.1 mL of triethylamine and mix well. Discharge to obtain the curing agent.

[0069] 4) Take water, pigment and powder obtained in step 1) and mix them in a mass ratio of 1:1:13 to obtain a coating. Add curing agent at 15wt% of the coating and spray the coating and modified particles alternately with equal mass on the acrylic substrate by spraying with a spray gun. At the same time, perform temperature gradient coating and keep the temperature at 80℃ for 4 hours to obtain the coating.

[0070] The amount of the modified particles is 10 wt% of the coating.

[0071] The temperature gradient coating method is as follows: in an inert gas environment, the inert gas flow rate is set to 50L / min, the spray gun temperature is 150℃, the temperature is reduced by 10℃ after every 5 sprays, and the spraying is repeated 20 times, with a total coating thickness of approximately 0.6mm.

[0072] The performance of the coating in this example was tested using the following methods.

[0073] 1. Water and solvent resistance test:

[0074] The coating obtained in this example was applied to the bathtub substrate to obtain a coating with a thickness of 2 mm and an area of ​​12.56 cm². 2At 20℃, the coating is immersed in a clear aqueous solution of Ca(OH)2 with a concentration of 0.02mol / L. After 7 days, if there is no delamination or blistering between the coating and the bathtub substrate, it is considered qualified; otherwise, it is considered unqualified.

[0075] 2. Abrasion resistance test:

[0076] The coating obtained in this example was applied to the bathtub substrate to obtain a coating with a thickness of 2 mm and an area of ​​12.56 cm². 2 The coating was subjected to tribological testing using a WTM-2E tribometer at 25℃ and 60-70% humidity. A load of 200g was applied, and the rotational speed was set to 750 r / min. Silicon nitride was used as the dual sphere. The wear volume of the surface scratches was characterized using a UP Lambda laser confocal three-dimensional profilometer, and its wear rate and coefficient of friction were calculated.

[0077]

[0078] In the formula: W is the wear rate; V is the volume of wear marks on the coating surface; L is the sliding distance of the dual ball; F is the normal load.

[0079] 3. Adhesion strength:

[0080] The test was conducted according to GB / T 1720-1979(1989) "Determination of Adhesion of Paint Film".

[0081] 4. Impact resistance:

[0082] Using a simply supported beam pendulum cone impact testing machine, the pendulum cone is hung vertically on the machine frame's boom. The pendulum is released, allowing the boom to crush the sample. The amount of impact absorbed by the sample is measured, and the impact strength of the sample is calculated using the following formula:

[0083]

[0084] In the formula: b is the width of the impacted sample; d represents the thickness of the impacted sample; A is the amount of impact absorbed by the sample.

[0085] 5. Tensile strength and elongation at break:

[0086] Cut the coating into a dumbbell shape without any notches. Take a 25mm section from the center of the dumbbell-shaped sample as the measurement area. Within this area, measure the thickness at three points (1, 2, and 3) at both ends and the middle. Calculate the average value and input it into the computer. Clamp the dumbbell-shaped sample at both ends using the universal testing machine clamps, ensuring the force direction coincides with the measurement area. Set the clamp distance to 70mm and zero the machine before operation. Stretch the sample until it breaks to obtain its tensile strength and elongation at break.

[0087] 6. High temperature resistance:

[0088] The coating obtained in this example was applied to the bathtub substrate to obtain a coating with a thickness of 2 mm and an area of ​​12.56 cm². 2 The coating was subjected to a constant temperature oil bath at 120℃, and the time from the start of the test to the appearance of cracks in the coating was recorded.

[0089] The results are as follows.

[0090]

[0091] Observations revealed that the coating prepared in this example is complete and continuous, odorless, and has a smooth, burr-free surface. According to the results in the table, the coating prepared in this example has an extremely low coefficient of friction, is wear-resistant, water-resistant, solvent-resistant, and high-temperature resistant, and also has excellent mechanical properties.

[0092] Example 2

[0093] A method for preparing a coating specifically for bathtubs, the method comprising:

[0094] 1) Take 20g butyl acrylate, 0.4g benzoyl peroxide and 40mL ethanol and mix them evenly. Keep the temperature at 110℃ for 1h. Separately take 30g methyl methacrylate, 5g ethylene-vinyl alcohol copolymer and 80mL ethanol to prepare a mixture. Add the mixture dropwise at a rate of 1mL / min. While stirring, continue to add 0.6g benzoyl peroxide. Keep the temperature at 120℃ for 1h. Filter and dry to obtain powder.

[0095] 2) Take 7.5g of silica with a particle size of 5μm and disperse it evenly in 40mL of anhydrous ethanol. Add 7.5mL of polydimethylsiloxane and mix evenly. Dry to obtain modified particles.

[0096] 3) Take 9 mL of isophorone diisocyanate, 4.5 g of 3,5-dimethylpyrazole and 25 mL of acetone, keep the temperature at 60℃ for 5 h, and after cooling, add 8.1 mL of triethylamine and mix well. Discharge to obtain the curing agent.

[0097] 4) Take water, pigment and powder obtained in step 1) and mix them in a mass ratio of 1:1:13 to obtain a coating. Add curing agent at 15wt% of the coating and spray the coating and modified particles alternately with equal mass on the acrylic substrate by spraying with a spray gun. At the same time, perform temperature gradient coating and keep the temperature at 80℃ for 4 hours to obtain the coating.

[0098] The amount of the modified particles is 10 wt% of the coating.

[0099] The temperature gradient coating method is as follows: in an inert gas environment, the inert gas flow rate is set to 50L / min, the spray gun temperature is 150℃, the temperature is reduced by 10℃ after every 5 sprays, and the spraying is repeated 20 times, with a total coating thickness of approximately 0.6mm.

[0100] The coating in this example was subjected to the same performance test as in Example 1, and the results are as follows.

[0101]

[0102] In this example, the coating requires a shorter drying time, and with the increase in the amount of hard monomer, various properties improve, especially the coating's adhesion strength on the acrylic substrate, its tensile strength is enhanced, and its mechanical properties are better.

[0103] Example 3

[0104] A method for preparing a coating specifically for bathtubs, the method comprising:

[0105] 1) Take 20g butyl acrylate, 0.4g benzoyl peroxide and 40mL ethanol and mix them evenly. Keep the temperature at 110℃ for 1h. Separately take 35g methyl methacrylate, 5g ethylene-vinyl alcohol copolymer and 80mL ethanol to prepare a mixture. Add the mixture dropwise at a rate of 1mL / min. While stirring, continue to add 0.6g benzoyl peroxide. Keep the temperature at 120℃ for 1h. Filter and dry to obtain powder.

[0106] 2) Take 7.5g of silica with a particle size of 5μm and disperse it evenly in 40mL of anhydrous ethanol. Add 7.5mL of polydimethylsiloxane and mix evenly. Dry to obtain modified particles.

[0107] 3) Take 9 mL of isophorone diisocyanate, 4.5 g of 3,5-dimethylpyrazole and 25 mL of acetone, keep the temperature at 60℃ for 5 h, and after cooling, add 8.1 mL of triethylamine and mix well. Discharge to obtain the curing agent.

[0108] 4) Take water, pigment and powder obtained in step 1) and mix them in a mass ratio of 1:1:13 to obtain a coating. Add curing agent at 15wt% of the coating and spray the coating and modified particles alternately with equal mass on the acrylic substrate by spraying with a spray gun. At the same time, perform temperature gradient coating and keep the temperature at 80℃ for 4 hours to obtain the coating.

[0109] The amount of the modified particles is 10 wt% of the coating.

[0110] The temperature gradient coating method is as follows: in an inert gas environment, the inert gas flow rate is set to 50L / min, the spray gun temperature is 150℃, the temperature is reduced by 10℃ after every 5 sprays, and the spraying is repeated 20 times, with a total coating thickness of approximately 0.6mm.

[0111] The coating in this example was subjected to the same performance test as in Example 1, and the results are as follows.

[0112]

[0113] In this example, the large amount of hard monomers reduces the coating's flexibility and increases its brittleness, thus reducing its impact resistance. Theoretically, a slight decrease in the adhesion strength between the coating and the bathtub substrate will lead to a reduction in the coating's water and solvent resistance.

[0114] Example 4

[0115] A method for preparing a coating specifically for bathtubs, the method comprising:

[0116] 1) Take 20g butyl acrylate, 0.4g benzoyl peroxide and 40mL ethanol and mix them evenly. Keep the temperature at 110℃ for 1h. Separately take 30g methyl methacrylate, 10g ethylene-vinyl alcohol copolymer and 80mL ethanol to prepare a mixture. Add the mixture dropwise at a rate of 1mL / min. While stirring, continue to add 0.6g benzoyl peroxide. Keep the temperature at 120℃ for 1h. Filter and dry to obtain powder.

[0117] 2) Take 7.5g of silica with a particle size of 5μm and disperse it evenly in 40mL of anhydrous ethanol. Add 7.5mL of polydimethylsiloxane and mix evenly. Dry to obtain modified particles.

[0118] 3) Take 9 mL of isophorone diisocyanate, 4.5 g of 3,5-dimethylpyrazole and 25 mL of acetone, keep the temperature at 60℃ for 5 h, and after cooling, add 8.1 mL of triethylamine and mix well. Discharge to obtain the curing agent.

[0119] 4) Take water, pigment and powder obtained in step 1) and mix them in a mass ratio of 1:1:13 to obtain a coating. Add curing agent at 15wt% of the coating and spray the coating and modified particles alternately with equal mass on the acrylic substrate by spraying with a spray gun. At the same time, perform temperature gradient coating and keep the temperature at 80℃ for 4 hours to obtain the coating.

[0120] The amount of the modified particles is 10 wt% of the coating.

[0121] The temperature gradient coating method is as follows: in an inert gas environment, the inert gas flow rate is set to 50L / min, the spray gun temperature is 150℃, the temperature is reduced by 10℃ after every 5 sprays, and the spraying is repeated 20 times, with a total coating thickness of approximately 0.6mm.

[0122] The coating in this example was subjected to the same performance test as in Example 1, and the results are as follows.

[0123]

[0124] In this example, as the content of functional monomers and ethylene-vinyl alcohol copolymers increases, the degree of cross-linking between coating components becomes higher, thereby improving the adhesion strength of the coating. The steric hindrance of the functional groups and the PDMS@SiO2 microspheres synergistically protect the ester groups, giving the coating good water and solvent resistance.

[0125] Comparative Example 1

[0126] A method for preparing a coating specifically for bathtubs, the method comprising:

[0127] 1) Take 20g butyl acrylate, 0.4g benzoyl peroxide and 40mL ethanol and mix them evenly. Keep the temperature at 110℃ for 1h. Separately take 30g methyl methacrylate, 5g ethylene-vinyl alcohol copolymer and 80mL ethanol to prepare a mixture. Add the mixture dropwise at a rate of 0.5mL / min. While stirring, continue to add 0.6g benzoyl peroxide. Keep the temperature at 120℃ for 1h. Filter and dry to obtain powder.

[0128] 2) Take 7.5g of silica with a particle size of 5μm and disperse it evenly in 40mL of anhydrous ethanol. Add 7.5mL of polydimethylsiloxane and mix evenly. Dry to obtain modified particles.

[0129] 3) Take 9 mL of isophorone diisocyanate, 4.5 g of 3,5-dimethylpyrazole and 25 mL of acetone, keep the temperature at 60℃ for 5 h, and after cooling, add 8.1 mL of triethylamine and mix well. Discharge to obtain the curing agent.

[0130] 4) Take water, pigment and powder obtained in step 1) and mix them in a mass ratio of 1:1:13 to obtain a coating. Add curing agent at 15wt% of the coating and spray the coating and modified particles alternately with equal mass on the acrylic substrate by spraying with a spray gun. At the same time, perform temperature gradient coating and keep the temperature at 80℃ for 4 hours to obtain the coating.

[0131] The amount of the modified particles is 10 wt% of the coating.

[0132] The temperature gradient coating method is as follows: in an inert gas environment, the inert gas flow rate is set to 50L / min, the spray gun temperature is 150℃, the temperature is reduced by 10℃ after every 5 sprays, and the spraying is repeated 20 times, with a total coating thickness of approximately 0.6mm.

[0133] The coating in this example was subjected to the same performance test as in Example 1, and the results are as follows.

[0134]

[0135] In this example, the rate of adding the mixture was too slow. Characterization revealed that although the product composition was uniform and the molecular weight distribution was narrow, the coating had a relatively low molecular weight and viscosity, requiring a longer drying time. This resulted in severe sagging and deformation of the coating, leading to an uneven surface and a significantly increased wear rate. Consequently, the mechanical properties of the coating in this example were significantly reduced.

[0136] Comparative Example 2

[0137] A method for preparing a coating specifically for bathtubs, the method comprising:

[0138] 1) Take 20g butyl acrylate, 0.4g benzoyl peroxide and 40mL ethanol and mix them evenly. Keep the temperature at 110℃ for 1h. Separately take 30g methyl methacrylate, 5g ethylene-vinyl alcohol copolymer and 80mL ethanol to prepare a mixture. Add the mixture dropwise at a rate of 2.5mL / min. While stirring, continue to add 0.6g benzoyl peroxide. Keep the temperature at 120℃ for 1h. Filter and dry to obtain powder.

[0139] 2) Take 7.5g of silica with a particle size of 5μm and disperse it evenly in 40mL of anhydrous ethanol. Add 7.5mL of polydimethylsiloxane and mix evenly. Dry to obtain modified particles.

[0140] 3) Take 9 mL of isophorone diisocyanate, 4.5 g of 3,5-dimethylpyrazole and 25 mL of acetone, keep the temperature at 60℃ for 5 h, and after cooling, add 8.1 mL of triethylamine and mix well. Discharge to obtain the curing agent.

[0141] 4) Take water, pigment and powder obtained in step 1) and mix them in a mass ratio of 1:1:13 to obtain a coating. Add curing agent at 15wt% of the coating and spray the coating and modified particles alternately with equal mass on the acrylic substrate by spraying with a spray gun. At the same time, perform temperature gradient coating and keep the temperature at 80℃ for 4 hours to obtain the coating.

[0142] The amount of the modified particles is 10 wt% of the coating.

[0143] The temperature gradient coating method is as follows: in an inert gas environment, the inert gas flow rate is set to 50L / min, the spray gun temperature is 150℃, the temperature is reduced by 10℃ after every 5 sprays, and the spraying is repeated 20 times, with a total coating thickness of approximately 0.6mm.

[0144] The coating in this example was subjected to the same performance test as in Example 1, and the results are as follows.

[0145]

[0146] In this example, the rapid addition of the mixture resulted in a significant increase in the molecular weight of the coating, with a wide relative molecular weight distribution. This led to substantial differences in diffusion rates for different chain lengths, causing excessively high local viscosity. Consequently, this not only resulted in component inhomogeneity but also a low solids content. Therefore, the coating performance in this case was significantly reduced.

[0147] Comparative Example 3

[0148] A method for preparing a coating specifically for bathtubs, the method comprising:

[0149] 1) Take 20g butyl acrylate, 30g methyl methacrylate, 5g ethylene-vinyl alcohol copolymer, 1g benzoyl peroxide and 120mL ethanol, mix them evenly, keep the temperature at 120℃ for 1h, filter and dry to obtain powder;

[0150] 2) Take 7.5g of silica with a particle size of 5μm and disperse it evenly in 40mL of anhydrous ethanol. Add 7.5mL of polydimethylsiloxane and mix evenly. Dry to obtain modified particles.

[0151] 3) Take 9 mL of isophorone diisocyanate, 4.5 g of 3,5-dimethylpyrazole and 25 mL of acetone, keep the temperature at 60℃ for 5 h, and after cooling, add 8.1 mL of triethylamine and mix well. Discharge to obtain the curing agent.

[0152] 4) Take water, pigment and powder obtained in step 1) and mix them in a mass ratio of 1:1:13 to obtain a coating. Add curing agent at 15wt% of the coating and spray the coating and modified particles alternately with equal mass on the acrylic substrate by spraying with a spray gun. At the same time, perform temperature gradient coating and keep the temperature at 80℃ for 4 hours to obtain the coating.

[0153] The amount of the modified particles is 10 wt% of the coating.

[0154] The temperature gradient coating method is as follows: in an inert gas environment, the inert gas flow rate is set to 50L / min, the spray gun temperature is 150℃, the temperature is reduced by 10℃ after every 5 sprays, and the spraying is repeated 20 times, with a total coating thickness of approximately 0.6mm.

[0155] The coating in this example was subjected to the same performance test as in Example 1, and the results are as follows.

[0156]

[0157]

[0158] In this example, when butyl acrylate, methyl methacrylate, and ethylene-vinyl alcohol copolymer were mixed and initiated to prepare the coating, the viscosity rose rapidly, with excessively high viscosity in some areas, resulting in extremely poor thixotropy. Such preparation makes it difficult to guarantee the formation of the target "core-shell" structure. According to the results in the table, the mechanical properties of the coating material, such as impact resistance, are significantly reduced.

[0159] Comparative Example 4

[0160] A method for preparing a coating specifically for bathtubs, the method comprising:

[0161] 1) Take 20g butyl acrylate, 0.4g benzoyl peroxide and 40mL ethanol and mix them evenly. Keep the temperature at 110℃ for 1h. Separately take 30g methyl methacrylate, 5g ethylene-vinyl alcohol copolymer and 80mL ethanol to prepare a mixture. Add the mixture dropwise at a rate of 1mL / min. While stirring, continue to add 0.6g benzoyl peroxide. Keep the temperature at 120℃ for 1h. Filter and dry to obtain powder.

[0162] 2) Take 7.5g of silica with a particle size of 3μm and disperse it evenly in 40mL of anhydrous ethanol. Add 7.5mL of polydimethylsiloxane and mix evenly. Dry to obtain modified particles.

[0163] 3) Take 9 mL of isophorone diisocyanate, 4.5 g of 3,5-dimethylpyrazole and 25 mL of acetone, keep the temperature at 60℃ for 5 h, and after cooling, add 8.1 mL of triethylamine and mix well. Discharge to obtain the curing agent.

[0164] 4) Take water, pigment and powder obtained in step 1) and mix them in a mass ratio of 1:1:13 to obtain a coating. Add curing agent at 15wt% of the coating and spray the coating and modified particles alternately with equal mass on the acrylic substrate by spraying with a spray gun. At the same time, perform temperature gradient coating and keep the temperature at 80℃ for 4 hours to obtain the coating.

[0165] The amount of the modified particles is 10 wt% of the coating.

[0166] The temperature gradient coating method is as follows: in an inert gas environment, the inert gas flow rate is set to 50L / min, the spray gun temperature is 150℃, the temperature is reduced by 10℃ after every 5 sprays, and the spraying is repeated 20 times, with a total coating thickness of approximately 0.6mm.

[0167] The coating in this example was subjected to the same performance test as in Example 1, and the results are as follows.

[0168]

[0169] The particulate matter on the coating surface increases with increasing SiO2 content. The particles gradually aggregate and increase in size. In this example, microspheres with a diameter of 3 μm were used. Small particles have higher surface energy and are prone to aggregation. Before curing, the coating composition is uneven. According to the results in the table, the coating's wear resistance decreases, making it easier to wear through, and its mechanical properties all decline to varying degrees.

[0170] Comparative Example 5

[0171] A method for preparing a coating specifically for bathtubs, the method comprising:

[0172] 1) Take 20g butyl acrylate, 0.4g benzoyl peroxide and 40mL ethanol and mix them evenly. Keep the temperature at 110℃ for 1h. Separately take 30g methyl methacrylate, 5g ethylene-vinyl alcohol copolymer and 80mL ethanol to prepare a mixture. Add the mixture dropwise at a rate of 1mL / min. While stirring, continue to add 0.6g benzoyl peroxide. Keep the temperature at 120℃ for 1h. Filter and dry to obtain powder.

[0173] 2) Take 8.5g of silica with a particle size of 5μm and disperse it evenly in 40mL of anhydrous ethanol. Add 7.5mL of polydimethylsiloxane and mix evenly. Dry to obtain modified particles.

[0174] 3) Take 9 mL of isophorone diisocyanate, 4.5 g of 3,5-dimethylpyrazole and 25 mL of acetone, keep the temperature at 60℃ for 5 h, and after cooling, add 8.1 mL of triethylamine and mix well. Discharge to obtain the curing agent.

[0175] 4) Take water, pigment and powder obtained in step 1) and mix them in a mass ratio of 1:1:13 to obtain a coating. Add curing agent at 15wt% of the coating and spray the coating and modified particles alternately with equal mass on the acrylic substrate by spraying with a spray gun. At the same time, perform temperature gradient coating and keep the temperature at 80℃ for 4 hours to obtain the coating.

[0176] The amount of the modified particles is 20 wt% of the coating.

[0177] The temperature gradient coating method is as follows: in an inert gas environment, the inert gas flow rate is set to 50L / min, the spray gun temperature is 150℃, the temperature is reduced by 10℃ after every 5 sprays, and the spraying is repeated 20 times, with a total coating thickness of approximately 0.6mm.

[0178] The coating in this example was subjected to the same performance test as in Example 1, and the results are as follows.

[0179]

[0180]

[0181] In this example, the excessive SiO2 particles led to the formation of a large number of aggregated PDMS@SiO2 microspheres in the system. Moreover, the large-sized aggregates settled during the static curing process, resulting in larger pores inside the coating. Pores are usually stress concentration points. In the experiment, it can be clearly seen that the addition of excessive SiO2 particles will cause cracks to appear around the stress points. Under the same load, the coating is more prone to cracking, and the dispersion strengthening effect of the coating is significantly reduced, which leads to a deterioration in its mechanical properties.

[0182] Comparative Example 6

[0183] A method for preparing a coating specifically for bathtubs, the method comprising:

[0184] 1) Take 20g butyl acrylate, 0.4g benzoyl peroxide and 40mL ethanol and mix them evenly. Keep the temperature at 110℃ for 1h. Separately take 30g methyl methacrylate, 5g ethylene-vinyl alcohol copolymer and 80mL ethanol to prepare a mixture. Add the mixture dropwise at a rate of 1mL / min. While stirring, continue to add 0.6g benzoyl peroxide. Keep the temperature at 120℃ for 1h. Filter and dry to obtain powder.

[0185] 2) Take 7.5g of silica with a particle size of 5μm and disperse it evenly in 40mL of anhydrous ethanol. Add 7.5mL of polydimethylsiloxane and mix evenly. Dry to obtain modified particles.

[0186] 3) Take 9 mL of isophorone diisocyanate, 4.5 g of 3,5-dimethylpyrazole and 25 mL of acetone, keep the temperature at 60℃ for 5 h, and after cooling, add 8.1 mL of triethylamine and mix well. Discharge to obtain the curing agent.

[0187] 4) Take water, pigment paste and powder obtained in step 1) and mix them in a mass ratio of 1:1:13 to obtain a coating. Add curing agent at 15wt% of the coating and spray the coating and modified particles alternately and in equal mass on the acrylic substrate with a spray gun. Under an inert gas environment, set the inert gas flow rate to 50L / min and the spray gun temperature to 150℃, repeat the spraying 20 times. The total spray thickness is about 0.6mm. Keep the temperature at 80℃ for 4h to obtain the coating.

[0188] The amount of the modified particles used is 10 wt% of the coating.

[0189] The coating in this example was subjected to the same performance test as in Example 1, and the results are as follows.

[0190]

[0191] The coating and the bathtub substrate have different thermal expansion rates, and there is heat loss during the spraying process. The different cooling rates inside and outside the coating also have a negative impact. Therefore, the adhesion strength between the coating and the acrylic substrate is significantly reduced.

Claims

1. A method for preparing a coating specifically for bathtubs, characterized in that, The method includes: 1) Take butyl acrylate, benzoyl peroxide and ethanol and mix them evenly for prepolymerization. Add a mixture of methyl methacrylate, ethylene-vinyl alcohol copolymer and ethanol dropwise. While stirring, continue to add benzoyl peroxide to carry out thermal reaction. Filter and dry to obtain powder. 2) Disperse silica evenly in anhydrous ethanol, add polydimethylsiloxane and mix evenly, then dry to obtain modified particles; 3) Take isophorone diisocyanate, 3,5-dimethylpyrazole and acetone for thermal reaction, and after cooling, add triethylamine and mix evenly to obtain curing agent; 4) After mixing water, pigment paste, and powder evenly, add curing agent to obtain coating. Spray the coating and modified particles alternately with a spray gun, and apply temperature gradient coating at the same time to cure and obtain coating. Step 1) The prepolymerization is carried out at 110–120 °C for 0.5–1 h. The dropping rate in step 1) is 1–2 mL / min; Step 1) The methyl methacrylate, ethylene-vinyl alcohol copolymer, and butyl acrylate are prepared in a mass ratio of (5-7):(1-3):4; Step 2) The silica particle size is 5–8 μm; Step 2) The amount of anhydrous ethanol used is 5-15 mL / g silicon dioxide; Step 2) The amount of polydimethylsiloxane used is 1–1.5 mL / g silicon dioxide; Step 3) The amount of 3,5-dimethylpyrazole used is 0.5–0.6 g / mL isophorone diisocyanate; Step 3) The amount of acetone used is 1-5 mL / mL isophorone diisocyanate; The thermal reaction described in step 3) is carried out at 60–65 °C for 4–5 h at a constant temperature. Step 3) The amount of triethylamine used is 0.9–1 mL / mL of isophorone diisocyanate; Step 4) The temperature gradient coating method is as follows: In an inert gas environment, the inert gas flow rate is set to 50-60 L / min, the spray gun temperature is set to 120-150 ℃, and the temperature is gradually reduced after every 3-5 sprays. The number of sprays is 10-20, and the total spray thickness is 0.4-0.8 mm. Step 4) The curing is carried out at a constant temperature of 80-90 ℃ for 3-4 h.

2. The method for preparing a bathtub-specific coating according to claim 1, characterized in that, The thermal reaction described in step 1) is carried out at 120–125 °C for 0.5–1 h.

3. The method for preparing a bathtub-specific coating according to claim 1, characterized in that, Step 4) The water, pigment, and powder are prepared in a mass ratio of 1:(1-2):(13-17); Step 4) The amount of curing agent used is 15-18 wt% of the total mass of water, pigment, and powder. Step 4) The amount of the modified particles used is 10-15 wt% of the coating.

Images