Tung oil-based polyurethane film with bright structural color and preparation method of tung oil-based polyurethane film

Abstract

The invention relates to the field of high polymer materials, and particularly discloses a tung oil-based polyurethane film with a bright structural color and a preparation method of the tung oil-based polyurethane film. According to the polyurethane film, monodisperse spherical silicon dioxide, alkylene-terminated tung oil-based waterborne polyurethane emulsion, carbon black and an ultraviolet light initiator serve as main raw materials, and a network structure formed by crosslinking of long aliphatic side chains of the alkylene-terminated tung oil-based waterborne polyurethane emulsion is more beneficial to self-assembly of the monodisperse spherical silicon dioxide; the long aliphatic side chain crosslinking also endows the structural color polyurethane film with excellent hydrophobicity and tensile strength.

Description

Technical Field

[0001] The present application relates to the technical field of polymer materials, and more specifically, to a tung oil-based polyurethane film with bright structural colors and a preparation method thereof. Background Art

[0002] As the colors of consumer electronics become increasingly diverse, structural color films are often used to alter the appearance of these products. Structural color films are prepared by spatially arranging two or more dielectric materials with different refractive indices in an ordered / disordered manner to form a 3D periodic structure, creating a photonic crystal. Due to the presence of a photonic band gap, photonic crystals can modulate the propagation of electromagnetic waves, causing their band gap to fall within the visible light band, i.e., within the range of 380 to 780 nm. Electromagnetic waves with similar wavelengths cannot enter the crystal, but are selectively reflected by the photonic crystal layer, resulting in coherent diffraction on the periodically arranged photonic crystal surface. The constructive interference reflected light stimulates the human visual system, producing a vibrant structural color effect. Therefore, compared to traditional dyed films, structural color films offer advantages such as high brightness, excellent weather resistance, and iridescence.

[0003] At present, the defect of structural color film is that the color of structural color film comes from its microstructure, but under the action of external force, its microstructure is prone to irreversible changes, resulting in the loss of color or functional characteristics of the structural color film. The durability of structural color film needs to be improved. Summary of the Invention

[0004] In order to improve the durability of structural color films, the present application provides a tung oil-based polyurethane film with bright structural colors and a preparation method thereof.

[0005] In a first aspect, the present application provides a tung oil-based polyurethane film with bright structural colors, which adopts the following technical solution: A tung oil-based polyurethane film with bright structural colors is composed of the following raw materials in parts by weight: 40-60 parts of monodisperse spherical silica 35-45 parts of olefin-terminated tung oil-based waterborne polyurethane emulsion 5-7 parts carbon black 4-6 parts of ultraviolet light initiator; Among them, the olefin-terminated tung oil-based water-based polyurethane emulsion is obtained by reacting tung oil-based polyol, polyisocyanate and a capping agent in a weight ratio of (20-30):(15-32):(1-10), and one end of the capping agent is a carboxyl group or a hydroxyl group, and the other end is an olefin group.

[0006] Furthermore, the particle size of the olefin-terminated tung oil-based waterborne polyurethane emulsion is controlled between 50 and 90 nm.

[0007] Furthermore, the particle size dispersion coefficient of the olefin-terminated tung oil-based waterborne polyurethane emulsion is between 0.22 and 0.25.

[0008] Furthermore, the preparation method of the tung oil-based polyol is as follows: potassium hydroxide is used as a catalyst, tung oil and alcohol amine are subjected to an aminolysis reaction, wherein the weight ratio of tung oil, alcohol amine and potassium hydroxide is 1: (0.4-0.6): (0.006-0.008), the temperature is raised to 125-140° C., the reaction is kept warm for 6-8 hours, and the tung oil-based polyol is purified.

[0009] Furthermore, during the preparation of the tung oil-based polyol, the weight ratio of tung oil to potassium hydroxide is 1:0.0075.

[0010] Furthermore, the end-capping agent is any one or more of diethylene glycol monovinyl ether, hydroxyethyl acrylate and acrylic acid.

[0011] Furthermore, the preparation steps of the olefin-terminated tung oil-based waterborne polyurethane emulsion are as follows: The method comprises the following steps: blending tung oil-based polyol and a hydrophilic chain extender, controlling the reaction temperature at 80-85° C. under a protective atmosphere, adding polyisocyanate according to a weight ratio and reacting for 90-120 minutes; cooling to 60-70° C., adding a small molecule chain extender dropwise and reacting for 30-40 minutes; adding a capping agent dropwise and reacting for 40-60 minutes; cooling to 40-50° C., adding a neutralizing agent dropwise and reacting for 20-30 minutes; and emulsifying the obtained waterborne polyurethane acrylate to obtain an olefin-terminated tung oil-based waterborne polyurethane emulsion.

[0012] Furthermore, the particle size of the monodisperse spherical silica is in the range of 150 to 300 nm.

[0013] Furthermore, the particle size of the carbon black is in the range of 50 to 150 nm.

[0014] Furthermore, the ultraviolet light initiator is a water-soluble ultraviolet light initiator.

[0015] Furthermore, the water-soluble ultraviolet photoinitiator is selected from any one or more of benzoylpyridine oxalate, sodium anthraquinone-2-sulfonate, 2-hydroxy-3-(2-thioxanthoneoxy)propyltrimethylammonium chloride, 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone, and α-hydroxyisobutyrophenone.

[0016] In a second aspect, the present application provides a method for preparing a tung oil-based polyurethane film having a bright structural color, using the following technical solution: A method for preparing a tung oil-based polyurethane film with bright structural color comprises the following steps: Mixing: Compounding monodisperse spherical silica, tung oil-based waterborne polyurethane emulsion, carbon black and ultraviolet light initiator according to parts by weight, and blending to obtain a coating liquid; Film formation: The coating liquid is placed in a mold, annealed, and then UV-cured to obtain a tung oil-based polyurethane film with bright structural colors.

[0017] Furthermore, the carbon black is blended with monodisperse spherical silica, tung oil-based waterborne polyurethane emulsion and ultraviolet light initiator, and then ultrasonically dispersed, and then vortex-oscillated to obtain a coating liquid.

[0018] In summary, this application has at least the following advantages: 1. The present application uses tung oil polyol to first react with polyisocyanate to form a polyurethane prepolymer containing long aliphatic side chains, and then react with a capping agent. The active hydroxyl group or carboxyl group at one end of the capping agent reacts with the polyurethane prepolymer, and the olefin group is retained. The network structure formed by cross-linking the long aliphatic side chains of the olefin-terminated tung oil-based water-based polyurethane emulsion is more conducive to the self-assembly of monodisperse spherical silica. At the same time, the cross-linking of the long aliphatic side chains also gives the structural color polyurethane film relatively excellent hydrophobicity and tensile strength.

[0019] By controlling the particle sizes of the olefin-terminated tung oil-based waterborne polyurethane emulsion, monodisperse spherical silica, and carbon black, the tung oil-based waterborne polyurethane emulsion is enriched on the surfaces of the monodisperse spherical silica and carbon black. After curing, the monodisperse spherical silica and carbon black are evenly dispersed in the structural color polyurethane film. The moderate particle sizes of the monodisperse spherical silica and carbon black allow for good dispersion in the structural color polyurethane film. The smaller particle size of the monodisperse spherical silica also regularizes the propagation path during light interference and diffraction, improving the purity of the structural color polyurethane film. The carbon black also reduces incoherent scattering, further improving the purity and stability of the structural color polyurethane film. The structural color film exhibits gentle changes in light interference and reflection conditions at different incident angles, resulting in minimal color changes and a wider visible angle range.

[0020] The olefin-terminated tung oil-based water-based polyurethane emulsion undergoes cross-linking of the terminal olefin groups under the action of a photoinitiator. The structural color polyurethane film has a high internal cross-linking density. Combined with the wear-resistant reinforcing effect of carbon black, the structural color polyurethane film has excellent mechanical strength and is not easily subject to irreversible changes under the action of external forces.

[0021] 2. This application chooses to optimize the preparation parameters of tung oil-based polyol by controlling the weight ratio of tung oil and potassium hydroxide, so that the hydroxyl value of tung oil-based polyol is moderate. At the same time, tung oil-based polyol has fewer by-products and high purity, which helps to enhance the color stability of structural color polyurethane film.

[0022] 3. In this application, carbon black, monodisperse spherical silica and other ingredients are first ultrasonically dispersed and then vortex-oscillated. No additional stabilizer is required. The carbon black, monodisperse spherical silica and olefin-terminated tung oil-based water-based polyurethane emulsion form a uniform and stable suspension, which helps to improve the color rendering effect of the structural color polyurethane film. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 These are optical images of the polyurethane films obtained in Example 1 and Comparative Example 1.

[0024] Figure 2 1 and 2 are the reflection spectra of the polyurethane films obtained in Example 1 and Comparative Example 1.

[0025] Figure 3 These are SEM images of the polyurethane films obtained in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0026] This application is further described in conjunction with the following examples, comparative examples and test data.

[0027] Unless otherwise specified, the sources of the raw materials used in the preparation examples, examples and comparative examples of this application are as follows: Tung oil: Product No. TXHG-002, sourced from Shandong Tianxiang Chemical Co., Ltd. Carbon black, customized by Jiangsu Xianfeng Nano: Brand 1#, average particle size is 10-30nm; Brand 2#, average particle size is 50-150nm; Brand 3#, average particle size is 200-300nm.

[0028] Preparation Example of Monodisperse Spherical Silica Monodisperse spherical silica is prepared according to the following steps: Under a stirring rate of 500 rpm, anhydrous ethanol and deionized water were mixed at a volume ratio of 100:18 (mL / mL) at 55°C for 30 minutes; ammonia water and tetraethyl orthosilicate (TEOS) were added to the mixture in sequence, with the volume ratio of anhydrous ethanol to ammonia water and tetraethyl orthosilicate being 100:5:7.5 (mL / mL / mL), and the mixture was kept warm for 150 minutes; the mixture was placed in a fume hood and allowed to stand for 48 hours, and the lower white precipitate was removed; the mixture was centrifuged at a speed of 10,000 rpm for 15 minutes, the supernatant was discarded, and the lower white solid was ultrasonically dispersed in anhydrous ethanol, and the centrifugation, the supernatant was discarded, and the dispersion was repeated three times to obtain monodisperse spherical silica; finally, the product was uniformly dispersed in anhydrous ethanol by ultrasound to obtain a monodisperse spherical silica dispersion.

[0029] Preparation Example of Tung Oil-Based Polyol Preparation Example 1 Tung oil-based polyol is prepared according to the following steps: Prepare 134 parts of tung oil, 67 parts of diethanolamine and 1 part of potassium hydroxide according to weight; Pour diethanolamine doped with potassium hydroxide into the flask, stir continuously, and raise the reaction temperature to 135°C until the potassium hydroxide is completely dissolved; then add tung oil into the reaction system and react for 8 hours; When the reaction system was cooled to room temperature, the organic layer containing the tung oil-based polyol was extracted with petroleum ether and a saturated sodium chloride solution, and the water was removed with anhydrous sodium sulfate. Finally, the solvent was removed from the filtrate to obtain a brown-yellow tung oil-based polyol, and the hydroxyl value of the tung oil-based polyol was determined to be 206.7 mgKOH / g.

[0030] Preparation Example 2 Tung oil-based polyol is prepared according to the following steps: Prepare 134 parts of tung oil, 53.6 parts of diethanolamine and 0.8 parts of potassium hydroxide according to weight; Pour diethanolamine doped with potassium hydroxide into the flask, stir continuously, and raise the reaction temperature to 125°C until the potassium hydroxide is completely dissolved; then add tung oil into the reaction system and react for 8 hours; When the reaction system was cooled to room temperature, the sulfur organic layer containing tung oil-based polyol was extracted with petroleum ether and saturated sodium chloride solution, and water was removed with anhydrous sodium chloride. Finally, the solvent was removed from the filtrate to obtain brown-yellow tung oil-based polyol, and the hydroxyl value of the tung oil-based polyol was measured to be 182.9 mgKOH / g.

[0031] Preparation Example 3 Tung oil-based polyol is prepared according to the following steps: Prepare 134 parts of tung oil, 80.4 parts of diethanolamine and 1.1 parts of potassium hydroxide according to weight; Pour diethanolamine doped with potassium hydroxide into the flask, stir continuously, and raise the reaction temperature to 140°C until the potassium hydroxide is completely dissolved; then add tung oil into the reaction system and react for 6 hours; When the reaction system was cooled to room temperature, the organic layer containing the tung oil-based polyol was extracted with petroleum ether and a saturated sodium chloride solution, and the water was removed with anhydrous sodium sulfate. Finally, the solvent was removed from the filtrate to obtain a brown-yellow tung oil-based polyol, and the hydroxyl value of the tung oil-based polyol was determined to be 254.4 mgKOH / g.

[0032] Preparation Example of Olefin-Terminated Tung Oil-Based Waterborne Polyurethane Emulsion Preparation Example a The olefin-terminated tung oil-based waterborne polyurethane emulsion is prepared according to the following steps: The tung oil-based polyol prepared in Preparation Example 1 was vacuum dehydrated at 120° C. for 60 min; a hydrophilic chain extender, 2,2-dimethylol propionic acid, was added and vacuum dehydrated for 60 min; under nitrogen protection, the temperature was lowered to 80° C., isophorone diisocyanate was added dropwise and reacted for 90 min; the temperature was lowered to 60° C., a small molecule chain extender, 1,4-butanediol, was added dropwise and reacted for 30 min; a capping agent, diethylene glycol monovinyl ether, was added dropwise and reacted for 60 min; the temperature was lowered to 50° C., a neutralizing agent, triethylamine, was added dropwise and reacted for 30 min; the resulting olefin-terminated tung oil-based waterborne polyurethane was added to deionized water and emulsified at a speed of 1500 rpm for 30 min to prepare an olefin-terminated tung oil-based waterborne polyurethane emulsion with a particle size of 50 to 90 nm and a particle size dispersion coefficient of 0.23; The weight ratio of tung oil-based polyol, 2,2-dimethylol propionic acid, isophorone diisocyanate, 1,4-butanediol, diethylene glycol monovinyl ether, triethylamine and deionized water is 25:2:20:1:3:3:80.

[0033] Preparation Example bc The olefin-terminated tung oil-based waterborne polyurethane emulsion differs from that of Preparation Example a in that the source of the tung oil-based polyol is different, as follows: The source of the tung oil-based polyol in Example b is Preparation Example 2; The source of the tung oil-based polyol in Example c is Preparation Example 3; Preparation Example The olefin-terminated tung oil-based waterborne polyurethane emulsion differs from that of Preparation Example a in that the specific preparation parameters are different, as follows: In Preparation Example d, the tung oil-based polyol prepared in Preparation Example 1 was vacuum dehydrated at 120° C. for 60 minutes; a hydrophilic chain extender, 2,2-dimethylol propionic acid, was added and vacuum dehydrated for 60 minutes; under nitrogen protection, the temperature was lowered to 85° C., and isophorone diisocyanate was added dropwise to react for 90 minutes; the temperature was lowered to 65° C., and a small molecule chain extender, 1,4-butanediol, was added dropwise to react for 35 minutes; a capping agent, diethylene glycol monovinyl ether, was added dropwise to react for 50 minutes; the temperature was lowered to 45° C., and a neutralizing agent, triethylamine, was added dropwise to react for 25 minutes; the resulting olefin-terminated tung oil-based waterborne polyurethane was added to deionized water and emulsified at a speed of 1200 rpm for 30 minutes to prepare an olefin-terminated tung oil-based waterborne polyurethane emulsion with a particle size of 25 to 110 nm and a particle size dispersion coefficient of 0.25; The weight ratio of tung oil-based polyol, 2,2-dimethylol propionic acid, isophorone diisocyanate, 1,4-butanediol, diethylene glycol monovinyl ether, triethylamine and deionized water is 20:2:15:1:1:3:80; In Preparation Example e, the tung oil-based polyol prepared in Preparation Example 1 was vacuum dehydrated at 120° C. for 60 minutes; a hydrophilic chain extender, 2,2-dimethylol propionic acid, was added and vacuum dehydrated for 60 minutes; under nitrogen protection, the temperature was lowered to 80° C., and isophorone diisocyanate was added dropwise to react for 120 minutes; the temperature was lowered to 70° C., and a small molecule chain extender, 1,4-butanediol, was added dropwise to react for 30 minutes; a capping agent, diethylene glycol monovinyl ether, was added dropwise to react for 40 minutes; the temperature was lowered to 40° C., and a neutralizing agent, triethylamine, was added dropwise to react for 20 minutes; the resulting olefin-terminated tung oil-based waterborne polyurethane was added to deionized water and emulsified at a speed of 1000 rpm for 30 minutes to prepare an olefin-terminated tung oil-based waterborne polyurethane emulsion with a particle size of 60 to 150 nm and a particle size dispersion coefficient of 0.24; The weight ratio of tung oil-based polyol, 2,2-dimethylol propionic acid, isophorone diisocyanate, 1,4-butanediol, diethylene glycol monovinyl ether, triethylamine and deionized water is 30:2:32:1:10:3:80.

[0034] Examples 1-3 A tung oil-based polyurethane film with bright structural colors is prepared by preparing the following raw materials according to the following weight parts, the specific weight parts are shown in Table 1: Table 1. Weight parts of each raw material in Examples 1-3

[0035] Among them, the olefin-terminated tung oil-based water-based polyurethane emulsion is derived from Preparation Example a; the monodisperse spherical silica is a homemade product of this application, and after particle size screening, a monodisperse spherical silica product with a particle size range of 150 to 300 nm is selected; the particle size of carbon black is 50 to 150 nm; and the ultraviolet photoinitiator is 2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone.

[0036] Follow these steps to make it: Prepare monodisperse spherical silica, tung oil-based waterborne polyurethane emulsion, carbon black, and ultraviolet photoinitiator according to the weight parts shown in Table 1; Monodisperse spherical silica, olefin-terminated tung oil-based waterborne polyurethane emulsion, carbon black and ultraviolet photoinitiator were mixed and then ultrasonically dispersed at an ultrasonic dispersion power of 80 kW for 20 minutes. The coating solution was then vortexed for 30 minutes. The coating liquid was poured into a mold for annealing at 70°C. After annealing for 20 minutes, it was subjected to UV curing to produce a tung oil-based waterborne polyurethane film with bright structural colors.

[0037] Examples 4-7 A tung oil-based polyurethane film with bright structural colors, which differs from Example 1 in that the source of the olefin-terminated tung oil-based waterborne polyurethane emulsion is different, as follows: In Example 4, the olefin-terminated tung oil-based waterborne polyurethane emulsion is derived from Preparation Example b; In Example 5, the olefin-terminated tung oil-based waterborne polyurethane emulsion was derived from Preparation Example C; In Example 6, the olefin-terminated tung oil-based waterborne polyurethane emulsion is derived from Preparation Example d; In Example 7, the olefin-terminated tung oil-based waterborne polyurethane emulsion is derived from Preparation Example e.

[0038] Examples 8-9 A tung oil-based polyurethane film with bright structural colors, which differs from Example 1 in that the particle size of the carbon black is different, as follows: In Example 8, carbon black with a particle size range of 10 to 30 nm was selected instead of carbon black with a particle size range of 50 to 150 nm; In Example 9, carbon black with a particle size range of 200 to 300 nm is selected instead of carbon black with a particle size range of 50 to 150 nm.

[0039] Example 10

[0040] A tung oil-based polyurethane film with bright structural color is different from Example 1 in that the preparation steps are different. In this example, only the coating liquid is ultrasonically dispersed, the ultrasonic power is 80 kW, and the ultrasonic time is 60 minutes.

[0041] Comparative Example 1 A structural color polyurethane film, which differs from Example 1 in that: Poly(1,4-butylene glycol oxalate) (Mn=1000, from Maclean) was vacuum dehydrated at 120°C for 60 minutes; after cooling to 105°C, a hydrophilic chain extender 2,2-dimethylol propionic acid was added and vacuum dehydrated for 60 minutes; under nitrogen protection, the temperature was lowered to 85°C, isophorone diisocyanate was added dropwise and reacted for 90 minutes; the temperature was lowered to 60°C, a small molecule chain extender 1,4-butanediol was added dropwise and reacted for 30 minutes; a blocking agent diethylene glycol monovinyl ether was added dropwise and reacted for 60 minutes; the temperature was lowered to 50°C, a neutralizing agent triethylamine was added dropwise and reacted for 30 minutes; the resulting olefin-terminated waterborne polyurethane was added to deionized water and emulsified at a speed of 1500 rpm for 30 minutes to prepare an olefin-terminated waterborne polyurethane emulsion with a particle size of 45 to 95 nm. The weight ratio of poly(1,4-butylene glycol oxalate), 2,2-dimethylol propionic acid, isophorone diisocyanate, 1,4-butanediol, diethylene glycol monovinyl ether, triethylamine and deionized water is 18:2:20:1:3:3:80; Tung oil, water-based polyurethane emulsion, monodisperse spherical silica (particle size range of 150-300 nm), carbon black (particle size of 50-150 nm) and ultraviolet light initiator were blended in a weight ratio of 5:45:60:7:6, and after mixing, ultrasonic dispersion was performed at an ultrasonic dispersion power of 80 kW and an ultrasonic time of 20 min. The coating liquid was then vortexed for 30 min. The coating liquid was poured into a mold for annealing at 70°C. After annealing for 20 minutes, it was subjected to UV curing to produce a tung oil-based waterborne polyurethane film with bright structural colors.

[0042] Performance Testing The polyurethane films prepared in Examples 1-10 and Comparative Example 1 were subjected to the following tests: 1. Mechanical properties: Refer to standard GB / T 1040.1 2018 to test the elongation at break and tensile strength of polyurethane film; 2. Water contact angle: measured using a ZJ-6900 water drop angle tester; 3. Water absorption rate: The difference between the weight of the polyurethane film after soaking in deionized water at room temperature for 48 hours and the weight before soaking is expressed as a percentage of the weight before soaking; 4. Reflection peak position and half-peak width: measured using a UV-visible-near-infrared spectrometer Cary 5000 produced by Agilent Technologies.

[0043] Table 2. Performance test of structural color polyurethane films obtained in Examples 1-10 and Comparative Example 1

[0044] According to the above test data, we can see that: First, in Comparative Example 1, tung oil was directly blended with water-based polyurethane emulsion, carbon black, monodisperse spherical silica and other substances to impart hydrophobicity to the polyurethane film through blending modification. However, actual testing showed that: first, the compatibility between tung oil and water-based polyurethane emulsion was poor. Tung oil was highly hydrophobic, which easily led to agglomeration of monodisperse spherical silica particles and a widening of the particle size distribution. Figure 3 SEM observation shows that the orderliness of the microspheres in the polyurethane film is reduced. Secondly, physical mixing triggers the phase separation of the coating liquid, which leads to a significant decrease in the tensile strength and elongation at break of the cured polyurethane film, and the mechanical properties of the polyurethane film are reduced. Figure 2It can be seen that after tung oil addition, the half-width of the reflection peak of the polyurethane film increases, resulting in a decrease in color saturation and a blue shift in the maximum reflection wavelength. Finally, although direct tung oil addition can increase the water contact angle, the increased water droplet rolling angle actually reduces the actual hydrophobicity and increases the water absorption rate. Therefore, while direct tung oil addition can temporarily improve surface properties such as the static contact angle, it will destroy the orderly arrangement of microspheres required for structural color generation and lead to a significant decrease in mechanical properties and durability. This fully demonstrates that different methods of tung oil modification have a significant impact on the structural color of polyurethane films.

[0045] Second, in Examples 1-3 of the present application, the composition and content of the coating liquid were varied. As the content of monodisperse spherical silica increased, the content of the olefin-terminated tung oil-based aqueous polyurethane emulsion also increased. The polyurethane films produced in Examples 1-3 exhibited increased elongation at break, increased tensile strength, and decreased hydrophobicity as the content of monodisperse spherical silica decreased. Therefore, controlling the coating liquid composition within a moderate range ensures excellent mechanical properties and structural color development in the polyurethane films, with a narrow half-width at half-maximum (FWHM) of the reflection peak and excellent color saturation.

[0046] Third, in Examples 4-7 of this application, the source of the olefin-terminated tung oil-based waterborne polyurethane emulsion was varied. The tung oil-based polyols possessed a moderate hydroxyl value and particle size, achieving a balanced improvement in the polyurethane film's structural color vividness, mechanical properties, and hydrophobicity. While increasing the amount of diethanolamine helped increase the hydroxyl value of the tung oil-based polyol, it also resulted in impurities in the tung oil-based polyol affecting the reflection peak position and half-width of the reflection peak in the final polyurethane film.

[0047] Fourth, the carbon black particle size range was changed in Examples 8-9 of this application. If the carbon black particle size is too small, the olefin-terminated tung oil-based waterborne polyurethane will not be able to effectively disperse the carbon black, causing the carbon black to easily agglomerate, thereby affecting the orderly arrangement of the microspheres in the polyurethane film. If the carbon black particle size is too large, the carbon black will hinder the regular arrangement of the polyurethane film particles, resulting in an increase in the half-width of the reflection peak and a decrease in the color vividness of the polyurethane film.

[0048] Fifth, in Example 10 of the present application, the mixing method of the coating liquid is changed. It is difficult to ensure the uniform dispersion of the suspended particles in the coating liquid only by ultrasonic dispersion, which leads to the shift of the reflection peak position of the final polyurethane film, and the width of the half-peak width of the reflection peak is large, and the color vividness of the polyurethane film is reduced.

[0049] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0050] Furthermore, the above-described embodiments merely represent several implementation methods of the present application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention. It should be noted that a person of ordinary skill in the art may make a number of variations and improvements without departing from the concept of the present application, and these variations and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be based on the appended claims.

Claims

1. A tung oil-based polyurethane film with bright structural color, characterized in that: The raw material composition is as follows: 40-60 parts of monodisperse spherical silica 35-45 parts of olefin-terminated tung oil-based waterborne polyurethane emulsion 5-7 parts carbon black 4-6 parts of ultraviolet light initiator; Among them, the olefin-terminated tung oil-based water-based polyurethane emulsion is obtained by reacting tung oil-based polyol, polyisocyanate and a capping agent in a weight ratio of (20-30):(15-32):(1-10), and one end of the capping agent is a carboxyl group or a hydroxyl group, and the other end is an olefin group.

2. The tung oil-based polyurethane film with bright structural color according to claim 1, characterized in that: The particle size of the olefin-terminated tung oil-based waterborne polyurethane emulsion is controlled between 50 and 90 nm.

3. The tung oil-based polyurethane film with bright structural color according to claim 2, characterized in that: The particle size dispersion coefficient of the olefin-terminated tung oil-based waterborne polyurethane emulsion is between 0.22 and 0.

25.

4. The tung oil-based polyurethane film with bright structural color according to claim 1, characterized in that: The preparation method of the tung oil-based polyol is as follows: potassium hydroxide is used as a catalyst, tung oil and alcohol amine are subjected to an aminolysis reaction, wherein the weight ratio of tung oil, alcohol amine and potassium hydroxide is 1:(0.4-0.6):(0.006-0.008), the temperature is raised to 125-140° C., the temperature is kept for reaction for 6-8 hours, and the tung oil-based polyol is purified to obtain the tung oil-based polyol.

5. The tung oil-based polyurethane film with bright structural color according to claim 4, characterized in that: During the preparation of the tung oil-based polyol, the weight ratio of tung oil to potassium hydroxide is 1:0.0075.

6. The tung oil-based polyurethane film with bright structural color according to claim 1, characterized in that: The end-capping agent is any one or more of diethylene glycol monovinyl ether, hydroxyethyl acrylate and acrylic acid.

7. The tung oil-based polyurethane film with bright structural color according to claim 1, characterized in that: The preparation steps of the olefin-terminated tung oil-based waterborne polyurethane emulsion are as follows: The method comprises the following steps: blending tung oil-based polyol and a hydrophilic chain extender, controlling the reaction temperature at 80-85° C. under a protective atmosphere, adding polyisocyanate according to a weight ratio and reacting for 90-120 minutes; cooling to 60-70° C., adding a small molecule chain extender dropwise and reacting for 30-40 minutes; adding a capping agent dropwise and reacting for 40-60 minutes; cooling to 40-50° C., adding a neutralizing agent dropwise and reacting for 20-30 minutes; and emulsifying the obtained waterborne polyurethane acrylate to obtain an olefin-terminated tung oil-based waterborne polyurethane emulsion.

8. The tung oil-based polyurethane film with bright structural color according to claim 1, characterized in that: The particle size of the monodisperse spherical silicon dioxide is in the range of 150 to 300 nm.

9. The tung oil-based polyurethane film with bright structural color according to claim 1, characterized in that: The particle size of the carbon black is in the range of 50 to 150 nm.

10. The method for preparing a tung oil-based polyurethane film having a bright structural color according to any one of claims 1 to 9, characterized in that: The steps include: Mixing: Compounding monodisperse spherical silica, tung oil-based waterborne polyurethane emulsion, carbon black and ultraviolet light initiator according to parts by weight, and blending to obtain a coating liquid; Film formation: The coating liquid is placed in a mold, annealed, and then UV-cured to obtain a tung oil-based polyurethane film with bright structural colors.

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