Reflective heat-insulation polyurethane coating and preparation method thereof

Abstract

The invention belongs to the technical field of coating preparation, and particularly relates to a reflective heat-insulation polyurethane coating and a preparation method thereof.The reflective heat-insulation polyurethane coating is prepared from, by mass, 30%-50% of waterborne polyurethane, 11%-18% of a reflective heat-insulation composite material, 5%-7% of rutile type titanium dioxide, 3%-7% of nano barium sulfate, 1%-5% of a defoaming agent, 0.2%-0.5% of a flatting agent and the balance water; the specific preparation method comprises the following steps: adding the waterborne polyurethane, the reflective thermal insulation composite material, the rutile type titanium dioxide, the nano barium sulfate, the defoaming agent and the flatting agent into water, and uniformly stirring and dispersing to obtain a reflective thermal insulation polyurethane coating; according to the coating prepared by the method, the dispersing performance is effectively improved, the uniformity is ensured, the surface tension of the coating is reduced, the conditions of shrinkage cavities and pinholes after film formation of the coating are effectively controlled, and the heat insulation performance is effectively improved through the modes of reflection, heat insulation and radiation refrigeration.

Description

Technical Field

[0001] The invention belongs to the technical field of coating preparation, and particularly relates to a reflective heat-insulating polyurethane coating and a preparation method thereof. Background Art

[0002] Energy conservation, consumption reduction, and improved economic efficiency are the goals of healthy and sustainable development in the industrial and construction sectors. Accordingly, thermal insulation coatings are widely used in building exteriors, the petrochemical industry, the metallurgical industry, and other fields. Commonly used thermal insulation coatings in the construction sector include reflective, barrier, radiant, and composite types. Regardless of the type of coating, improving thermal insulation performance is crucial.

[0003] At present, in order to improve thermal insulation performance, reflective materials such as titanium dioxide and barrier materials are usually added to thermal insulation coatings. The resulting coating can reduce heat accumulation by reflecting and blocking solar radiation heat, thereby improving thermal insulation performance to a certain extent. However, these materials generally have problems such as easy agglomeration and poor dispersion, which makes the coating unstable and limits the improvement of thermal insulation performance. Currently, modification treatment is often used to solve this problem. Although modification can improve dispersion to a certain extent, the effect is minimal. In the actual construction process, the coating film of thermal insulation coatings is prone to shrinkage holes and pinholes during construction, which affects the thermal insulation effect. Summary of the Invention

[0004] In response to the current technical problems, the present invention provides a reflective heat-insulating polyurethane coating and a preparation method thereof. The titanium dioxide in the coating is combined with nano-barium sulfate by coating hollow glass microspheres and modification, thereby solving the problem that the added materials are difficult to disperse and easy to agglomerate. In addition, the coating is combined with silicone-modified water-based polyurethane to effectively avoid the formation of shrinkage cavities and pinholes in the coating during the construction process. The coating significantly improves the heat insulation performance by combining rutile titanium dioxide, hollow glass microspheres and nano-barium sulfate with silicone-modified water-based polyurethane.

[0005] The technical solutions of the present invention are as follows:

[0006] A reflective heat-insulating polyurethane coating comprises, by mass percentage, 30-50% waterborne polyurethane, 11-18% reflective heat-insulating composite material, 5-7% rutile titanium dioxide, 3-7% nano-barium sulfate, 1-5% defoamer, 0.2-0.5% leveling agent, and the balance is water.

[0007] The nano-barium sulfate in the present invention has a solid particle size of 1 to 100 nm. As the material is ultra-fine, the nano-barium sulfate has excellent properties, such as small particle size, high surface energy, large specific surface area, and a large proportion of surface atoms. It also has three unique effects: small size effect, surface effect, and macroscopic quantum tunneling effect. Nano-barium sulfate utilizes its high surface activity to tightly bond with the matrix, and has advantages such as good compatibility, good dispersibility, and good adsorption. Compared with reflective thermal insulation composite materials, nano-barium sulfate, as a radiation cooling material, emphasizes the radiation effect of the material and emits heat into outer space, thereby achieving cooling without consuming any external energy. Importantly, nano-barium sulfate can also serve as a dispersant for pigments, ensuring uniform dispersion of titanium dioxide, reducing agglomeration, and reducing the formation of shrinkage holes and pinholes during the construction process.

[0008] Preferably, the waterborne polyurethane is silicone-modified waterborne polyurethane.

[0009] Further preferably, the specific method for silicone-modified waterborne polyurethane is as follows: eugenol-based diphenol, diisocyanate, polyester polyol and polyhydroxy hydrophilic chain extender are subjected to polymerization reaction and then neutralized with a neutralizer to obtain a waterborne polyurethane prepolymer; the waterborne polyurethane prepolymer, water and a post-chain extender are mixed, and the silicone-modified waterborne polyurethane is prepared through a chain extension reaction.

[0010] Preferably, the reflective heat-insulating composite material is titanium dioxide-coated hollow glass microspheres, and the hollow glass microspheres are 350-400 meshes.

[0011] More preferably, the inner layer of the titanium dioxide-coated hollow glass microspheres is hollow glass microspheres, and the outer layer is rutile titanium dioxide and anatase titanium dioxide, wherein the rutile titanium dioxide accounts for 93-95%.

[0012] Preferably, the specific method for modifying rutile titanium dioxide is as follows: titanium dioxide is taken into deionized water, stirred and mixed at room temperature and ultrasonically dispersed, sodium chloroacetate is added and sodium hydroxide solution is added dropwise to adjust the pH of the system to 11-13, and then placed in an oil bath at 100-120°C and heated for 3-6 hours. After the reaction is completed, it is washed with deionized water until neutral, and then centrifuged and dried to prepare carboxylated titanium dioxide.

[0013] Preferably, the particle size of the nano-barium sulfate is 1-100 nm.

[0014] Preferably, the particle size of rutile titanium dioxide is 100-200 nm.

[0015] A method for preparing a reflective heat-insulating polyurethane coating comprises the following steps: adding water-based polyurethane, a reflective heat-insulating composite material, rutile titanium dioxide, nano-barium sulfate, a defoaming agent, and a leveling agent into water, stirring and mixing the mixture to obtain the reflective heat-insulating coating.

[0016] A method for preparing a reflective heat-insulating polyurethane coating, the specific steps of the preparation method are as follows:

[0017] The defoamer and water are stirred and mixed evenly, and then rutile titanium dioxide, nano-barium sulfate and water are added and stirred and mixed evenly, and then water-based polyurethane, reflective thermal insulation composite material, leveling agent and water are added and stirred and mixed evenly to obtain a reflective thermal insulation coating.

[0018] At present, the improvement of the thermal insulation performance of thermal insulation coatings is limited by the following reasons: on the one hand, the added nanomaterials have poor dispersion and are easy to agglomerate; on the other hand, the surface tension is high, which makes the coating prone to the formation of shrinkage holes and pinholes, affecting the thermal insulation performance. Among them, shrinkage holes refer to the tendency of the coating to maintain a shrinkage drop shape and expose the substrate to form shrinkage holes. Pinholes refer to small holes on the surface of the dry film that are similar to those punctured by a needle tip. Excessive surface tension of the coating and uneven dispersion of nanomaterials will lead to the appearance of shrinkage holes and pinholes. The present invention introduces organosilicon into waterborne polyurethane, which can reduce the surface energy of the coating, form a low-surface-energy coating, improve hydrophobicity, and enhance anti-fouling ability to a certain extent. The preparation of titanium dioxide-coated hollow glass microspheres can solve the problem of easy agglomeration of some rutile titanium dioxide. The rutile titanium dioxide is first subjected to a carboxylation treatment, and the remaining rutile titanium dioxide is then mixed with nano-barium sulfate. The nano-barium sulfate serves as a pigment dispersant and effectively improves the dispersibility of the rutile titanium dioxide. Since the surface of the nano-barium sulfate is extremely active, the carboxylated titanium dioxide-coated hollow glass microspheres, the carboxylated rutile titanium dioxide, and the highly active nano-barium sulfate can form a stable structure, which is conducive to uniform dispersion in the coating and synergistically cooperates with other substances to exert an optimal effect. At the same time, the nano-barium sulfate has an efficient radiative cooling effect, the rutile titanium dioxide has an efficient reflective effect, and the hollow glass microspheres have an efficient thermal insulation effect. The three synergistically effectively improve the thermal insulation performance.

[0019] The present invention provides a reflective water-insulating polyurethane coating and a preparation method thereof. The coating prepared by the method effectively improves the dispersion performance of nanomaterials, reduces the surface tension of the coating, effectively controls the occurrence of shrinkage holes and pinholes after the coating is formed into a film, and effectively improves the thermal insulation performance through reflection, heat insulation and radiation cooling. DETAILED DESCRIPTION

[0020] The present invention will be further described below with reference to specific embodiments, but is not limited thereto.

[0021] The experimental methods described in the examples are conventional methods unless otherwise specified, and the reagents and materials used are commercially available unless otherwise specified.

[0022] Rutile titanium dioxide: purchased from Qinghe Chaotai Metal Materials Co., Ltd., model TIMP4; defoaming agent brand TEGO Foamex 810; leveling agent brand BYK-306.

[0023] The preparation method of silicone-modified waterborne polyurethane is as follows:

[0024] 2800 g of adipic acid, 1014 g of 1,4-butanediol, 698 g of ethylene glycol, and 0.2 g of tetraisopropyl titanate were added to a four-necked flask, heated to 135° C., and the distilled water was collected to obtain a polyester polyol.

[0025] 0.39 g of platinum catalyst and 16.42 g (0.1 mol) of eugenol were added to a three-necked flask equipped with a reflux condenser and a magnetic stirrer, and 20 mL of toluene was added. After nitrogen was passed through the flask for 30 minutes, the temperature was raised to 60° C., and 6.70 g (0.05 mol) of tetramethyldisiloxane was slowly added dropwise to the reaction system. During the reaction, the product was continuously subjected to nuclear magnetic resonance (NMR) analysis to observe the reaction extent of the eugenol until no double bonds appeared in the NMR spectrum. A total of 4.02 g (0.03 mol) of tetramethyldisiloxane was added. After the reaction, the solvent was removed using a rotary evaporator to obtain a light yellow viscous liquid with a yield of 95%.

[0026] 9.00 g of polyester polyol, 0.65 g of 2,2-dimethylol propionic acid and 0.42 g of eugenol-based diphenol (3% of the polyurethane prepolymer content) were added to a 100 mL four-necked flask equipped with a mechanical stirrer, a reflux condenser and a thermometer. The temperature was raised to 80 ° C. and stirred at 200 r / min for 30 min under a nitrogen atmosphere. Then 4 g of isophorone diisocyanate and 0.001 g of dibutyltin dilaurate catalyst were weighed and added to the four-necked flask. The reaction was continued until the N of the system was measured by the di-n-butylamine method. The reaction mixture was cooled to 50°C and 0.44 g of triethylamine was added to neutralize the carboxyl groups. During the reaction, a small amount of acetone was added to reduce the viscosity of the system. Neutralization was continued for 30 minutes, the oil bath was removed, and the reaction system was brought to room temperature. Deionized water was added dropwise under an ice-water bath, and 0.44 g of ethylenediamine was added for post-chain extension. Stirring was continued for 1.5 hours, the emulsion was transferred to a flask, and the acetone was evaporated using a rotary evaporator to obtain a silicone-modified waterborne polyurethane emulsion with a solids content of approximately 30%. Preparation method of carboxylated rutile titanium dioxide:

[0027] Take 2g of nano-rutile titanium dioxide and dissolve it in 300mL of deionized water, stir and mix it at room temperature and ultrasonically disperse it, add 2.5g of sodium chloroacetate and add dropwise a 0.1mol / L sodium hydroxide solution to adjust the pH of the system to 12, then place it in an oil bath and heat it at 115°C for 4h. After the reaction is completed, wash it with deionized water until it is neutral, then centrifuge and dry it to prepare carboxylated rutile titanium dioxide.

[0028] Carboxylated reflective thermal insulation composite material:

[0029] 3 g of hollow glass microspheres (particle size 400 mesh) were immersed in 100 ml of 90% ethanol aqueous solution, ultrasonicated at 25 ° C for 10 min, filtered and washed three times with distilled water, and the dried hollow glass microspheres were mixed with 0.15 g of initiator K2S2O8 and 15 g of methyl methacrylate (MMA), heated to 80 ° C and stirred for 4 h at a stirring speed of 100 r / min to obtain hollow glass microspheres grafted with methyl methacrylate polymer (PMMA);

[0030] 3 g of the hollow glass microspheres grafted with methyl methacrylate polymer prepared above were mixed with 12 g of hydrochloric acid having a concentration of 1 mol / L, and then a mixed solution of tetrabutyl titanate and anhydrous ethanol with a volume ratio of 1:2 was added (wherein tetrabutyl titanate was 45 g), and then a pH regulator (hydrochloric acid with a concentration of 0.1 mol / L) and a mixed solution of anhydrous ethanol with a mass ratio of 1:0.6 were added dropwise thereto (based on anhydrous ethanol, and the volume ratio of anhydrous ethanol to the mixed solution of tetrabutyl titanate and anhydrous ethanol was 1:2). The pH value of the system was controlled to be 1 during the addition process, and then stirred at a speed of 300 r / min for 40 min to form a gel, and the gel was coated on the surface of the hollow glass microspheres, and then aged at room temperature for 12 h, filtered, washed with anhydrous ethanol until neutral, and dried at 80 ° C for 10 h to obtain titanium dioxide-coated hollow glass microspheres;

[0031] Take 10g of the above-mentioned titanium dioxide-coated hollow glass microspheres and add them to 400mL of deionized water, stir and mix at room temperature and ultrasonically disperse them, add 4g of sodium chloroacetate and add dropwise a sodium hydroxide solution with a concentration of 0.1mol / L to adjust the pH of the system to 12, then place it in an oil bath and heat it at 115°C for 4h. After the reaction is completed, wash it with deionized water until neutral, then centrifuge and dry it to prepare carboxylated titanium dioxide-coated hollow glass microspheres, that is, carboxylated reflective thermal insulation composite materials.

[0032] Example 1

[0033] A preparation method of a reflective heat-insulating polyurethane coating:

[0034] 2% defoamer and water (1 / 3 of the total water) are stirred and mixed evenly, then 7% carboxylated rutile titanium dioxide, 5% nano-barium sulfate (average particle size 50 nm) and water (1 / 3 of the total water) are added and stirred and mixed evenly, and then 40% silicone-modified water-based polyurethane, 11% carboxylated reflective heat-insulating composite material, 0.4% leveling agent and water (1 / 3 of the total water) are added and stirred and mixed evenly to obtain a reflective heat-insulating polyurethane coating.

[0035] Example 2

[0036] A preparation method of a reflective water-insulating polyurethane coating:

[0037] 1% defoamer and water (1 / 3 of the total water) are stirred and mixed evenly, then 5% carboxylated rutile titanium dioxide, 3% nano-barium sulfate (average particle size 50 nm) and water (1 / 3 of the total water) are added and stirred and mixed evenly, and then 45% silicone-modified water-based polyurethane, 15% carboxylated reflective heat-insulating composite material, 0.3% leveling agent and water (1 / 3 of the total water) are added and stirred and mixed evenly to obtain a reflective heat-insulating polyurethane coating.

[0038] Example 3

[0039] A preparation method of a reflective water-insulating polyurethane coating:

[0040] 45% of silicone-modified waterborne polyurethane, 15% of carboxylated reflective heat-insulating composite material, 5% of carboxylated rutile titanium dioxide, 3% of nano-barium sulfate (average particle size 50 nm), 1% of defoaming agent, and 0.3% of leveling agent were added to water, and the mixture was stirred and mixed to obtain a reflective heat-insulating polyurethane coating.

[0041] Example 4

[0042] The difference from Example 2 is that the rutile titanium dioxide and the reflective heat-insulating composite material used are not subjected to carboxyl modification treatment. Other aspects are the same as Example 2.

[0043] Comparative Example 1

[0044] The difference from Example 2 is that water-based polyurethane (brand 5136 of Wuhan Shiquanxing New Materials Technology Co., Ltd.) is used, and the rest is the same as Example 2.

[0045] Comparative Example 2

[0046] The difference from Example 2 is that the amount of nano-barium sulfate added is 0, and the other aspects are the same as Example 2.

[0047] Comparative Example 3

[0048] The difference from Example 2 is that the amount of added carboxylated rutile titanium dioxide is 0, and the other aspects are the same as Example 2.

[0049] Comparative Example 4

[0050] The difference from Example 2 is that the amount of carboxylated rutile titanium dioxide added is 10%, and the other steps are the same as Example 2.

[0051] Comparative Example 5

[0052] Common commercially available reflective heat-insulating polyurethane coating.

[0053] Test example

[0054] The coatings prepared in the above examples and comparative examples were dip-coated on the substrate respectively. The curing temperature of the thermal insulation coating was 80°C and the curing time was 10 hours. The dry film thickness of the coating was controlled to be 1 mm. The thermal conductivity of the coating was tested using a thermal conductivity meter.

[0055] The coatings prepared in the above examples and comparative examples were dip-coated on substrates, respectively, and coatings were formed after the solvent evaporated. The dry film thickness of the coatings was controlled to be 0.5 mm. The solar reflectance and heat insulation / cooling performance of the coatings were then tested, and the shrinkage cavities and pinholes of the coatings were observed with the human eye.

[0056] Solar reflectance: The reflectance of the coating was measured at an incident angle of 5° using a UV-visible-near-infrared spectrophotometer Lambda950 in the wavelength range of 0.3 to 2.5 μm.

[0057] Cooling effect: Apply black enamel and the above-mentioned coating on an aluminum sheet with a dry film thickness of 0.5 mm. The room temperature is fixed at (25±1)°C. Use a 500W infrared lamp to simulate sunlight to irradiate the coating. By adjusting the distance from the infrared lamp to the test panel, the temperature of the black enamel is controlled within the range of (37±1)°C. Use a surface thermometer to detect the temperature of the back of the test panel (T1) and the surface temperature of the coating (T2). Record the data every 10 minutes until the temperature stabilizes. Calculate the cooling temperature (ΔT) using the formula (ΔT=T2-T1).

[0058] Table 1 is the test data of Examples 1-4 and Comparative Examples 1-5

[0059]

[0060] It is obvious from Table 1 that the solar reflectance, thermal conductivity, heat insulation / cooling effect, micropores and pinholes of the coatings prepared in Examples 1-4 are significantly better than those of the coatings in Comparative Examples 1-5; Example 3 changes the preparation method relative to Example 2, and its performance is affected, which can prove that different preparation methods can affect the performance of the coating; Example 4 uses rutile titanium dioxide that is not carboxylated relative to Example 2, and carboxylation of titanium dioxide is beneficial to the dispersion of titanium dioxide, so that the thermal insulation performance of the coating is improved, and it is also beneficial to avoid the appearance of micropores and shrinkage cavities; Comparative Example 1 uses water-based polyurethane that is not modified with silicone relative to Example 2, and its performance is significantly lower than that of Example 2, which can prove that the use of water-based polyurethane modified with silicone is beneficial to reducing the surface energy of the coating, effectively reducing the formation of micropores and pinholes, and improving the solar reflectance, thermal conductivity and thermal insulation effect; Comparative Example 2 does not use nano-barium sulfate relative to Example 2, and its coating performance is very poor because nano-barium sulfate Barium affects the dispersion of rutile titanium dioxide. Failure to add nano-barium sulfate causes titanium dioxide to agglomerate, affecting performance and the radiant cooling effect. After film formation, the coating is prone to the formation of shrinkage cavities and pinholes. Comparative Example 3, in contrast to Example 2, does not add additional carboxylated rutile titanium dioxide. The performance deteriorates because the amount of titanium dioxide added to the reflective thermal insulation composite material is relatively small, requiring additional rutile titanium dioxide to achieve optimal thermal insulation performance. Comparative Example 4, in contrast to Example 2, adds an excess of rutile titanium dioxide. It can be found that excessive rutile titanium dioxide, on the one hand, is not conducive to dispersion and is prone to the formation of shrinkage cavities and pinholes. On the other hand, it also causes the gaps between the particles in the coating to continuously decrease, affecting the thermal insulation effect. The reflective thermal insulation polyurethane coating prepared in accordance with the present invention achieves significant improvements in solar reflectance, thermal conductivity, thermal insulation / cooling effect, and micropores and pinholes compared to conventional commercially available reflective thermal insulation polyurethane coatings.

[0061] The present invention provides a reflective heat-insulating polyurethane coating and a preparation method thereof. The coating prepared by the method effectively improves the dispersion performance of nanomaterials, reduces the surface tension of the coating, effectively controls the occurrence of shrinkage holes and pinholes in the coating after film formation, and effectively improves the heat insulation performance through reflection, heat insulation and radiation cooling.

[0062] In this specification, references to the same or similar parts between the various embodiments can be made to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiment.

[0063] The foregoing is merely an embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application should all be included within the scope of the claims of the present application.

Claims

1. A reflective heat-insulating polyurethane coating, characterized in that: Calculated by mass percentage, it includes 30-50% waterborne polyurethane, 11-18% reflective heat insulation composite material, 5-7% rutile titanium dioxide, 3-7% nano barium sulfate, 1-5% defoaming agent, 0.2-0.5% leveling agent, and the balance is water.

2. The reflective heat-insulating polyurethane coating according to claim 1, characterized in that: The waterborne polyurethane is silicone-modified waterborne polyurethane.

3. The reflective heat-insulating polyurethane coating according to claim 2, characterized in that: The specific preparation method of the silicone-modified waterborne polyurethane is as follows: eugenol-based diphenol, diisocyanate, polyester polyol and polyhydroxy hydrophilic chain extender are subjected to polymerization reaction and then neutralized with a neutralizer to obtain a waterborne polyurethane prepolymer; the waterborne polyurethane prepolymer, water and a post-chain extender are mixed, and the silicone-modified waterborne polyurethane is prepared by a chain extension reaction.

4. The reflective heat-insulating polyurethane coating according to claim 1, characterized in that: The reflective heat-insulating composite material is hollow glass microspheres coated with titanium dioxide, and the hollow glass microspheres have a mesh size of 350-400.

5. The reflective heat-insulating polyurethane coating according to claim 4, characterized in that: The inner layer of the titanium dioxide-coated hollow glass microspheres is hollow glass microspheres, and the outer layer is rutile titanium dioxide and anatase titanium dioxide, wherein the rutile titanium dioxide accounts for 93-95%.

6. A reflective heat-insulating polyurethane coating according to claim 1 or 5, characterized in that: The specific method for modifying the rutile titanium dioxide is as follows: titanium dioxide is taken into deionized water, stirred and mixed at room temperature, and ultrasonically dispersed, sodium chloroacetate is added, and sodium hydroxide solution is added dropwise to adjust the pH of the system to 11-13, and then placed in an oil bath and heated at 100-120° C. for 3-6 hours. After the reaction is completed, it is washed with deionized water until neutral, and then centrifuged and dried to prepare carboxylated titanium dioxide.

7. The reflective heat-insulating polyurethane coating according to claim 1, characterized in that: The particle size of the nano-barium sulfate is 1-100 nm.

8. The reflective heat-insulating polyurethane coating according to claim 1, characterized in that: The particle size of the rutile titanium dioxide is 100-200 nm.

9. The method for preparing a reflective heat-insulating polyurethane coating according to any one of claims 1 to 8, characterized in that: The specific preparation method comprises the following steps: adding waterborne polyurethane, reflective heat-insulating composite material, rutile titanium dioxide, nano-barium sulfate, defoaming agent and leveling agent into water, stirring and mixing the mixture evenly to obtain reflective heat-insulating coating.

10. The method for preparing a reflective heat-insulating polyurethane coating according to claim 9, characterized in that: The specific preparation steps are as follows: The defoamer and water are stirred and mixed evenly, and then rutile titanium dioxide, nano-barium sulfate and water are added and stirred and mixed evenly, and then water-based polyurethane, reflective heat insulation composite material, leveling agent and water are added and stirred and mixed evenly to obtain a reflective heat insulation polyurethane coating.

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