A polyurethane emulsion sunscreen film and a preparation method thereof

Abstract

The application discloses a polyurethane emulsion sunscreen film and a preparation method thereof. The sunscreen agent is surface grafted and modified by a silane coupling agent, so that the sunscreen agent is connected with a polyurethane molecular chain in a covalent bond, thereby solving the problem of weak interface bonding force and easy falling in traditional physical blending. On this basis, the molecular structure of the polyurethane matrix is ingeniously designed, and the grafted sunscreen agent is actively guided to migrate and enrich on the surface of the coating in the emulsion film forming process. The "surface enrichment" structure makes the sunscreen agent concentrate on the surface of the ultraviolet light, realizes the maximization of the function, and thus a high ultraviolet protection factor is obtained under a low addition amount. Meanwhile, the internal matrix can keep its flexibility and mechanical integrity due to the avoidance of a large amount of filler filling, and the chemical bonding on the surface ensures the long-lasting and wash-resistant sunscreen function, so that the synergistic effect of high efficiency, durability and mechanical performance balance is finally achieved.

Description

Technical Field

[0001] This invention belongs to the field of polyurethane preparation, specifically relating to a polyurethane emulsion sunscreen film and its preparation method. Background Technology

[0002] Polyurethane (WPU) materials are widely used in coatings, textile coatings, and other fields due to their excellent film-forming properties, flexibility, and designability. Waterborne polyurethane emulsions use water as the dispersion medium, which aligns with environmental protection trends. However, the urethane bonds, urea groups, and aromatic isocyanate residues in the polyurethane molecular chain are highly sensitive to ultraviolet (UV) radiation. Long-term exposure to sunlight can easily lead to photo-oxidative degradation, resulting in yellowing, chalking, loss of mechanical properties, and damage to the substrate. Therefore, endowing WPU with excellent UV shielding properties is crucial for its high-end applications. A common technical approach to impart UV protection to polyurethane materials is to introduce UV-blocking agents, such as inorganic nanoparticles or organic UV absorbers. However, inorganic nanoparticles have poor compatibility with organic polymer matrices, are prone to agglomeration, and are mainly bound by weak physical forces. This leads to the sunscreen agent easily detaching from the coating during use, resulting in poor durability of the UV shielding function. Some studies have used chemical grafting methods to disperse UV-blocking agents in the polyurethane system to improve the problem of poor co-bonding between the two. However, sunscreen agents are usually randomly distributed in the matrix, with a large number of particles embedded inside the material. This prevents them from effectively blocking ultraviolet rays in the surface areas where they are most needed, resulting in low sun protection efficiency. These methods focus on improving dispersibility or introducing functional components, but they do not actively guide the sunscreen agents to be directionally enriched on the surface during film formation, thus failing to fundamentally solve the balance problem between the "effective utilization rate" and "functional durability" of sunscreen agents. Summary of the Invention

[0003] To address the problems of uneven sunscreen agent distribution, easy detachment, and poor durability in existing sunscreen materials, this invention provides a polyurethane emulsion sunscreen film and its preparation method. The sunscreen agent is surface-grafted and modified using a silane coupling agent, forming covalent bonds with the polyurethane molecular chains, thus solving the problems of weak interfacial bonding and easy detachment in traditional physical blending. Based on this, the molecular structure of the polyurethane matrix is ​​cleverly designed to actively guide the grafted sunscreen agent to migrate and accumulate on the coating surface during emulsion film formation. This "surface enrichment" structure concentrates the sunscreen agent on the surface exposed to ultraviolet radiation, maximizing its function and achieving a high UV protection factor with low additive amounts. Simultaneously, the internal matrix maintains its flexibility and mechanical integrity by avoiding excessive filler filling, while the surface chemical bonding ensures the long-lasting washability of the sunscreen function, ultimately achieving a synergistic effect of high efficiency, durability, and balanced mechanical properties.

[0004] Specifically, this is achieved through the following technical solution: (1) An amino-modified sunscreen is obtained by modifying the sunscreen with the silane coupling agent KH-550; the sunscreen is an inorganic sunscreen. (2) The diol, isocyanate monomer and catalyst are mixed and reacted, and then a hydrophilic chain extender and a low surface energy chain extender are added for chain extension modification; after the reaction is completed, the temperature is lowered, and a neutralizer and a diluent are added for neutralization reaction; then deionized water is added for emulsification; then an amino-modified sunscreen agent is added for reaction, and the diluent is removed under reduced pressure to obtain a polyurethane emulsion modified with sunscreen agent; (3) Under low-speed stirring, wetting agent, film-forming aid and leveling agent are added sequentially to the polyurethane emulsion modified with sunscreen agent, and stirring is continued for a period of time. The viscosity is adjusted by slowly adding an aqueous solution of thickener, and then defoamer is added. The speed is increased and stirring is continued for a period of time. The treated emulsion is applied to the substrate by means of scraping or other methods, and dried at a certain temperature to obtain a sunscreen film. Before adding thickener, the stirring speed of the system is 500~800 r / min, and the stirring time is 40~200 min; Preferably, after adding the thickener, the system stirring speed is 1000~2000 r / min, the stirring time is 40~200 min, the drying temperature is 60~90℃, and the drying time is 6~10 h.

[0005] Furthermore, the inorganic sunscreen agent is one or more of titanium dioxide and zinc oxide.

[0006] Further, the modification method described in step (1) is to add the silane coupling agent KH-550 to a mixed solution of ethanol and water, mix it evenly, and then drop it into the ethanol dispersion of the sunscreen agent, adjust the pH of the system to 8-9, and react for 3-6 hours.

[0007] Further, in step (2), the mass ratio of the diol, dicyanate monomer, catalyst, hydrophilic chain extender, low surface energy chain extender, neutralizer, diluent, amino-modified sunscreen agent, and deionized water is 100: (35~45): (0.1~0.2): (8~12): (3~6): (7~13): (50~80): (5~10): (260~420).

[0008] Further, in step (2), the diol includes one or more of polyether diols, polyester diols, or copolymers thereof, wherein the molecular weight of the diol is Mn=2500~3500; the isocyanate ester monomer includes one or more of isophorone diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, and lysine diisocyanate; the catalyst includes one or more of organozinc compounds and organobismuth compounds; the hydrophilic chain extender includes one or more of 2,2-dimethylolbutyric acid, sodium ethylenediamine ethanesulfonate, and diethylenetriamine; the low surface energy chain extender includes one or more of polybutadiene glycol, polyisoprene glycol, and aminopropyl-terminated polydimethylsiloxane; the neutralizing agent includes one or more of triethylamine, monoethanolamine, and ammonia water; and the diluent includes one or more of acetone, butanone, N-methylpyrrolidone, ethyl acetate, and butyl acetate.

[0009] Furthermore, the wetting agent includes one or more of alkyl sulfates, polyoxyethylene alkylphenol ethers, and polyoxyethylene fatty alcohol ethers; the film-forming aid includes one or more of propylene glycol phenyl ether, benzyl alcohol, and dodecyl alcohol ester; the leveling agent includes one or more of silicone leveling agents and acrylate leveling agents; and the thickener includes one or more of cellulose thickeners, polyacrylic acid thickeners, and polyurethane associative thickeners.

[0010] Furthermore, the mass ratio of the aqueous solution of the sunscreen-modified polyurethane emulsion, wetting agent, film-forming aid, leveling agent, thickener, and defoamer is (30~45):(0.5~3):(0.5~3):(0.3~2):(5~10):(0.5~1); the concentration of the aqueous solution of the thickener is 0.5~20wt%.

[0011] Further, in step (2), the reaction temperature of the diol and isocyanate is 60~95℃ and the reaction time is 2~5h; the reaction temperature after adding the hydrophilic chain extender and the dihydroxy chain extender is 60~95℃ and the reaction time is 3~7h; the temperature after cooling is 30~45℃; the neutralization reaction time is 10~35min; the emulsification temperature is 30~45℃ and the time is 25~35min; the reaction temperature with the amino-modified sunscreen agent is 40~50℃ and the time is 3~6h.

[0012] Furthermore, the stirring speed for emulsification in step (2) is 600-1000 r / min.

[0013] The present invention also provides a polyurethane emulsion sunscreen film prepared by the above method.

[0014] The advantages of this invention are: By combining specific sunscreen agent modification (grafting with silane coupling agent KH-550) with polyurethane molecular structure design (introducing low surface energy segments), the sunscreen agent is actively guided to migrate and accumulate on the surface during emulsion film formation. This allows the sunscreen agent to preferentially distribute on the outermost layer of the coating, forming a highly effective protective layer at the location where ultraviolet rays first reach. The polyurethane matrix inside the coating maintains its inherent flexibility and excellent mechanical properties, avoiding excessive interference and damage to the continuous phase of the entire matrix caused by a large amount of filler. The tensile strength can reach up to 18.3 MPa, and the elongation at break can reach up to 642%. This "surface enrichment" structure achieves a function-oriented distribution. At the same time, because the sunscreen agent is firmly bonded to the polyurethane chain through chemical grafting and is stably "locked" on the surface, the sun protection function is durable and long-lasting. Attached Figure Description

[0015] Figure 1 These are the test results for the UV transmittance of the sunscreen film. Detailed Implementation

[0016] The following examples are provided to further illustrate the present invention and are intended to explain the invention, not to limit its scope. Unless otherwise specified, all figures are expressed in parts by weight and weight percentages.

[0017] Unless otherwise specified, the raw materials used in this invention are all conventional commercially available products; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0018] The embodiments of the present invention will be further described below with reference to several examples.

[0019] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0020] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0021] Example 1 S1) Five parts of silane coupling agent KH-550 were added to a mixed solution of ethanol and water (pH=4). The hydrolysate was slowly added dropwise to 100 parts of titanium dioxide ethanol dispersion, and the system was adjusted to alkaline (pH=8). The reaction was carried out at 60°C for 5 hours. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain amino-modified titanium dioxide.

[0022] S2) 100 parts of polyether diol (Mn=2500), 35 parts of isophorone diisocyanate and 0.1 parts of organobismuth compound catalyst were mixed in a predetermined ratio and reacted at 75°C for 4 h; then 8 parts of 2,2-dimethylolbutyric acid and 3 parts of polybutadiene glycol were added for chain extension modification and reacted at 70°C for 6 h; after the reaction was completed, the temperature was lowered to 45°C, and 7 parts of triethylamine and 50 parts of acetone were added for neutralization reaction for 15 min; then 260 parts of deionized water were added for high-speed shear emulsification for 25 min at a shear rate of 800 r / min; then 5 parts of amino-modified titanium dioxide were added and reacted at 50°C for 6 h. After removing acetone under reduced pressure, a titanium dioxide-modified polyurethane emulsion was obtained.

[0023] S3) Under low-speed stirring, 0.5 parts of alkyl sulfate, 2 parts of dodecyl alcohol ester, and 0.3 parts of silicone leveling agent were added sequentially to 45 parts of titanium dioxide-modified polyurethane emulsion, and stirred at 800 rpm for 120 min. The viscosity was adjusted by slowly adding 5 parts of a 10% aqueous solution of cellulose thickener, followed by 0.5 parts of dimethylsiloxane, and water was added to bring the total volume to 100 parts. The stirring speed was increased to 1000 rpm, and the mixture was stirred for 100 min. The treated emulsion was then coated onto a substrate using methods such as scraping, and dried at 60°C for 10 h to obtain a sunscreen film.

[0024] Example 2 S1) Seven parts of silane coupling agent KH-550 were added to a mixed solution of ethanol and water (pH=5). The hydrolysate was slowly added dropwise to 100 parts of titanium dioxide ethanol dispersion, and the system was adjusted to alkaline (pH=9). The reaction was carried out at 60°C for 5 hours. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain amino-modified titanium dioxide.

[0025] S2) 100 parts of polyester diol (Mn=3500), 45 parts of isophorone diisocyanate and 0.2 parts of organobismuth compound catalyst were mixed in a predetermined ratio and reacted at 95°C for 2 h; then 8 parts of sodium ethylenediamine ethanesulfonate and 3 parts of polyisoprene diol were added for chain extension modification and reacted at 60°C for 7 h; after the reaction was completed, the temperature was lowered to 30°C, and 7 parts of triethylamine and 80 parts of acetone were added for neutralization reaction for 35 min; then 370 parts of deionized water were added for high-speed shear emulsification for 35 min at a shear rate of 1000 r / min; then 5 parts of amino-modified titanium dioxide were added and reacted at 40°C for 6 h. After removing acetone under reduced pressure, a titanium dioxide-modified polyurethane emulsion was obtained.

[0026] S3) Under low-speed stirring, 0.8 parts of alkyl sulfate, 2 parts of propylene glycol phenyl ether, and 2 parts of silicone leveling agent were added sequentially to 45 parts of titanium dioxide-modified polyurethane emulsion. The mixture was stirred at 800 rpm for 120 min. 5 parts of a 10% aqueous solution of cellulose thickener were slowly added to adjust the viscosity, followed by the addition of 1 part of dimethylsiloxane and water to bring the total volume to 100 parts. The stirring speed was increased to 1000 rpm, and the mixture was stirred for 100 min. The treated emulsion was then coated onto a substrate using methods such as scraping, and dried at 60°C for 10 h to obtain a sunscreen film.

[0027] Example 3 S1) Add 20 parts of silane coupling agent KH-550 to a mixed solution of ethanol and water (pH=5). Slowly add the hydrolysate dropwise to 100 parts of titanium dioxide ethanol dispersion, adjust the system to alkaline (pH=8), and react at 60℃ for 5 h. After the reaction is complete, centrifuge, wash, and dry to obtain amino-modified titanium dioxide.

[0028] S2) 100 parts of polyether diol (Mn=3500), 35 parts of isophorone diisocyanate and 0.1 parts of organozinc compound catalyst were mixed in a predetermined ratio and reacted at 60°C for 5 h; then 12 parts of 2,2-dimethylolbutyric acid and 6 parts of polybutadiene glycol were added for chain extension modification and reacted at 70°C for 5 h; after the reaction was completed, the temperature was lowered to 45°C, and 13 parts of triethylamine and 50 parts of butanone were added for neutralization reaction for 10 min; then 420 parts of deionized water were added for high-speed shear emulsification for 25 min at a shear rate of 600 r / min; then 5 parts of amino-modified titanium dioxide were added and reacted at 50°C for 3 h. After removing acetone under reduced pressure, a titanium dioxide-modified polyurethane emulsion was obtained.

[0029] S3) Under low-speed stirring, 3 parts of polyoxyethylene alkylphenol ether, 2 parts of dodecyl alcohol ester, and 0.3 parts of silicone leveling agent were added sequentially to 45 parts of titanium dioxide-modified polyurethane emulsion, and stirred at 800 rpm for 120 min. Ten parts of a 10% aqueous solution of cellulose thickener were slowly added to adjust the viscosity, followed by 0.5 parts of dimethylsiloxane, and water was added to bring the total volume to 100 parts. The stirring speed was increased to 1000 rpm, and the mixture was stirred for 100 min. The treated emulsion was then coated onto a substrate using methods such as scraping, and dried at 60°C for 10 h to obtain a sunscreen film.

[0030] Example 4 S1) Five parts of silane coupling agent KH-550 were added to a mixed solution of ethanol and water (pH=4). The hydrolysate was slowly added dropwise to 100 parts of titanium dioxide ethanol dispersion, and the system was adjusted to alkaline (pH=8). The reaction was carried out at 60°C for 5 hours. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain amino-modified titanium dioxide.

[0031] S2) 100 parts of polyether diol (Mn=2500), 35 parts of isophorone diisocyanate and 0.1 parts of organobismuth compound catalyst were mixed in a predetermined ratio and reacted at 75°C for 4 h; then 8 parts of 2,2-dimethylolbutyric acid and 3 parts of polybutadiene glycol were added for chain extension modification and reacted at 70°C for 6 h; after the reaction was completed, the temperature was lowered to 45°C, and 7 parts of triethylamine and 50 parts of acetone were added for neutralization reaction for 15 min; then 260 parts of deionized water were added for high-speed shear emulsification for 25 min at a shear rate of 800 r / min; then 7 parts of amino-modified titanium dioxide were added and reacted at 50°C for 6 h. After removing acetone under reduced pressure, a titanium dioxide-modified polyurethane emulsion was obtained.

[0032] S3) Under low-speed stirring, 0.5 parts of alkyl sulfate, 2 parts of dodecyl alcohol ester, and 0.3 parts of silicone leveling agent were added sequentially to 45 parts of titanium dioxide-modified polyurethane emulsion, and stirred at 800 rpm for 120 min. The viscosity was adjusted by slowly adding 5 parts of a 10% aqueous solution of cellulose thickener, followed by 0.5 parts of dimethylsiloxane, and water was added to bring the total volume to 100 parts. The stirring speed was increased to 1000 rpm, and the mixture was stirred for 100 min. The treated emulsion was then coated onto a substrate using methods such as scraping, and dried at 60°C for 10 h to obtain a sunscreen film.

[0033] Example 5 S1) Five parts of silane coupling agent KH-550 were added to a mixed solution of ethanol and water (pH=4). The hydrolysate was slowly added dropwise to 100 parts of titanium dioxide ethanol dispersion, and the system was adjusted to alkaline (pH=8). The reaction was carried out at 60°C for 5 hours. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain amino-modified titanium dioxide.

[0034] S2) 100 parts of polyether diol (Mn=2500), 35 parts of isophorone diisocyanate and 0.1 parts of organobismuth compound catalyst were mixed in a predetermined ratio and reacted at 75°C for 4 h; then 8 parts of 2,2-dimethylolbutyric acid and 3 parts of polybutadiene glycol were added for chain extension modification and reacted at 70°C for 6 h; after the reaction was completed, the temperature was lowered to 45°C, and 7 parts of triethylamine and 50 parts of acetone were added for neutralization reaction for 15 min; then 260 parts of deionized water were added for high-speed shear emulsification for 25 min at a shear rate of 800 r / min; then 10 parts of amino-modified titanium dioxide were added and reacted at 50°C for 6 h. After removing acetone under reduced pressure, a titanium dioxide-modified polyurethane emulsion was obtained.

[0035] S3) Under low-speed stirring, 0.5 parts of alkyl sulfate, 2 parts of dodecyl alcohol ester, and 0.3 parts of silicone leveling agent were added sequentially to 45 parts of titanium dioxide-modified polyurethane emulsion, and stirred at 800 rpm for 120 min. The viscosity was adjusted by slowly adding 5 parts of a 10% aqueous solution of cellulose thickener, followed by 0.5 parts of dimethylsiloxane, and water was added to bring the total volume to 100 parts. The stirring speed was increased to 1000 rpm, and the mixture was stirred for 100 min. The treated emulsion was then coated onto a substrate using methods such as scraping, and dried at 60°C for 10 h to obtain a sunscreen film.

[0036] Comparative Example 1 The difference from Example 1 is that no flexible segments were added. The specific preparation method is as follows: S1) Five parts of silane coupling agent KH-550 were added to a mixed solution of ethanol and water (pH=4). The hydrolysate was slowly added dropwise to 100 parts of titanium dioxide ethanol dispersion, and the system was adjusted to alkaline (pH=8). The reaction was carried out at 60°C for 5 hours. After the reaction was completed, the mixture was centrifuged, washed, and dried to obtain amino-modified titanium dioxide.

[0037] S2) 100 parts of polyether diol (Mn=2500), 35 parts of isophorone diisocyanate and 0.1 parts of organobismuth compound catalyst were mixed in a predetermined ratio and reacted at 75°C for 4 h; then 8 parts of 2,2-dihydroxymethylbutyric acid were added for chain extension modification and reacted at 70°C for 6 h; after the reaction was completed, the temperature was lowered to 45°C, and 7 parts of triethylamine and 50 parts of acetone were added for neutralization reaction for 15 min; then 260 parts of deionized water were added for high-speed shear emulsification for 25 min at a shear rate of 800 r / min; then 5 parts of amino-modified titanium dioxide were added and reacted at 50°C for 6 h. After removing acetone under reduced pressure, a titanium dioxide-modified polyurethane emulsion was obtained.

[0038] S3) Under low-speed stirring, 0.5 parts of alkyl sulfate, 2 parts of dodecyl alcohol ester, and 0.3 parts of silicone leveling agent were added sequentially to 45 parts of titanium dioxide-modified polyurethane emulsion, and stirred at 800 rpm for 120 min. The viscosity was adjusted by slowly adding 5 parts of a 10% aqueous solution of cellulose thickener, followed by 0.5 parts of dimethylsiloxane, and water was added to bring the total volume to 100 parts. The stirring speed was increased to 1000 rpm, and the mixture was stirred for 100 min. The treated emulsion was then coated onto a substrate using methods such as scraping, and dried at 60°C for 10 h to obtain a sunscreen film.

[0039] Comparative Example 2 The difference from Example 1 is that titanium dioxide was not added. The specific preparation method is as follows: S1) 100 parts of polyether diol (Mn=2500), 35 parts of isophorone diisocyanate and 0.1 parts of organobismuth compound catalyst were mixed in a predetermined ratio and reacted at 75°C for 4 h; then 8 parts of 2,2-dimethylolbutyric acid and 3 parts of polybutadiene glycol were added for chain extension modification and reacted at 70°C for 6 h; after the reaction was completed, the temperature was lowered to 45°C, and 7 parts of triethylamine and 50 parts of acetone were added for neutralization reaction for 15 min; then 260 parts of deionized water were added for high-speed shear emulsification for 25 min at a shear rate of 800 r / min, and reacted at 50°C for 6 h. After removing acetone under reduced pressure, a polyurethane emulsion was obtained.

[0040] S2) Under low-speed stirring, add 0.5 parts of alkyl sulfate, 2 parts of dodecyl alcohol ester, and 0.3 parts of silicone leveling agent sequentially to 45 parts of polyurethane emulsion, and stir at 800 rpm for 120 min. Slowly add 5 parts of a 10% aqueous solution of cellulose thickener to adjust the viscosity, then add 0.5 parts of dimethylsiloxane, and add water to bring the total to 100 parts. Increase the speed to 1000 rpm and stir for 100 min. Apply the treated emulsion to the substrate by means of scraping or other methods, and dry at 60°C for 10 h to obtain a sunscreen film.

[0041] Comparative Example 3 The difference from Example 1 is that the titanium dioxide was not modified. The specific preparation method is as follows: S1) 100 parts of polyether diol (Mn=2500), 35 parts of isophorone diisocyanate and 0.1 parts of organobismuth compound catalyst were mixed in a predetermined ratio and reacted at 75°C for 4 h; then 8 parts of 2,2-dimethylolbutyric acid and 3 parts of polybutadiene glycol were added for chain extension modification and reacted at 70°C for 6 h; after the reaction was completed, the temperature was lowered to 45°C, and 7 parts of triethylamine and 50 parts of acetone were added for neutralization reaction for 15 min; then 260 parts of deionized water were added for high-speed shear emulsification for 25 min at a shear rate of 800 r / min; then 5 parts of titanium dioxide were added and reacted at 50°C for 6 h. After removing acetone under reduced pressure, a polyurethane emulsion containing titanium dioxide was obtained.

[0042] S3) Under low-speed stirring, add 0.5 parts alkyl sulfate, 2 parts dodecyl alcohol ester, and 0.3 parts silicone leveling agent sequentially to 45 parts of a polyurethane emulsion containing titanium dioxide, and stir at 800 rpm for 120 min. Slowly add 5 parts of a 10% aqueous solution of cellulose thickener to adjust the viscosity, then add 0.5 parts dimethylsiloxane and add water to bring the total to 100 parts. Increase the speed to 1000 rpm and stir for 100 min. Apply the treated emulsion to a substrate by means of scraping or other methods, and dry at 60°C for 10 h to obtain a sunscreen film.

[0043] The prepared sample is placed on the sample holder of the spectrophotometer and scanned in the wavelength range of 290nm to 700nm. The transmittance is statistically analyzed at 340nm. The scanning interval is usually no more than 5nm.

[0044] Depend on Figure 1 It is evident that the flexible segment design promotes the surface orientation migration of the sunscreen agent during film formation, effectively enhancing the sun protection performance of the film. The unmodified sunscreen agent cannot accumulate on the surface of the sunscreen film and is dispersed within the polyurethane, thus failing to effectively block the photoaging of the polyurethane, and the strength of the polyurethane is significantly reduced compared to Example 1.

[0045] The test was performed using a universal testing machine according to the standard GB / T 1040.2-2022. The resin emulsion was placed into a dumbbell-shaped mold and placed in an environment with a temperature of 23℃±2℃ and a relative humidity of 50%±5% for 24 hours to adjust the condition, and then a dumbbell-shaped standard specimen was obtained. The test was performed at a tensile speed of 50 mm / min.

[0046] As shown in Table 1, the mechanical properties of the internal resin can be effectively improved after titanium dioxide is enriched on the surface.

[0047] Table 1. Mechanical property test results of Examples 1-5 and Comparative Examples 1-3 The above embodiments describe in detail the structure, features, and effects of the present invention. The above description is only a preferred embodiment of the present invention. Any changes made in accordance with the concept of the present invention, or equivalent embodiments modified to have equivalent changes, shall still fall within the scope of protection of the present invention if they do not exceed the scope covered by the specification.

Claims

1. A method for preparing a polyurethane emulsion sunscreen film, characterized in that, It includes the following steps: (1) An amino-modified sunscreen is obtained by modifying the sunscreen with the silane coupling agent KH-550; the sunscreen is an inorganic sunscreen. (2) The diol, isocyanate monomer and catalyst are mixed and reacted, and then a hydrophilic chain extender and a low surface energy chain extender are added for chain extension modification; after the reaction is completed, the temperature is lowered, and a neutralizer and a diluent are added for neutralization reaction; then deionized water is added for emulsification; then an amino-modified sunscreen agent is added for reaction, and the diluent is removed under reduced pressure to obtain a polyurethane emulsion modified with sunscreen agent; (3) Add wetting agent, film-forming aid and leveling agent to polyurethane emulsion modified with sunscreen agent, then add thickener and defoamer, stir evenly and then coat to obtain polyurethane emulsion sunscreen film.

2. The method according to claim 1, characterized in that, The inorganic sunscreen agent is one or more of titanium dioxide and zinc oxide.

3. The method according to claim 1, characterized in that, The modification method described in step (1) is to add silane coupling agent KH-550 to a mixed solution of ethanol and water, mix it evenly, and then drop it into the ethanol dispersion of sunscreen agent. Adjust the pH of the system to 8-9 and react for 3-6 hours.

4. The method according to claim 1, characterized in that, In step (2), the mass ratio of diol, dicyanate monomer, catalyst, hydrophilic chain extender, low surface energy chain extender, neutralizer, diluent, amino-modified sunscreen agent, and deionized water is 100: (35~45): (0.1~0.2): (8~12): (3~6): (7~13): (50~80): (5~10): (260~420).

5. The method according to claim 1, characterized in that, In step (2), the diol includes one or more of polyether diols, polyester diols, or copolymers thereof, wherein the molecular weight of the diol is Mn=2500~3500; the isocyanate ester monomer includes one or more of isophorone diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, and lysine diisocyanate; the catalyst includes one or more of organozinc compounds and organobismuth compounds; the hydrophilic chain extender includes one or more of 2,2-dimethylolbutyric acid, sodium ethylenediamine ethanesulfonate, and diethylenetriamine; the low surface energy chain extender includes one or more of polybutadiene glycol, polyisoprene glycol, and aminopropyl-terminated polydimethylsiloxane; the neutralizing agent includes one or more of triethylamine, monoethanolamine, and ammonia water; and the diluent includes one or more of acetone, butanone, N-methylpyrrolidone, ethyl acetate, and butyl acetate.

6. The method according to claim 1, characterized in that, The wetting agent includes one or more of alkyl sulfates, polyoxyethylene alkylphenol ethers, and polyoxyethylene fatty alcohol ethers; the film-forming aid includes one or more of propylene glycol phenyl ether, benzyl alcohol, and dodecyl alcohol ester; the leveling agent includes one or more of silicone leveling agents and acrylate leveling agents; and the thickener includes one or more of cellulose thickeners, polyacrylic acid thickeners, and polyurethane associative thickeners.

7. The method according to claim 1, characterized in that, The mass ratio of the aqueous solution of the sunscreen-modified polyurethane emulsion, wetting agent, film-forming aid, leveling agent, thickener, and defoamer is (30~45):(0.5~3):(0.5~3):(0.3~2):(5~10):(0.5~1); the concentration of the aqueous solution of the thickener is 0.5~20wt%.

8. The method according to claim 1, characterized in that, In step (2), the reaction temperature of the diol and isocyanate is 60~95℃ and the reaction time is 2~5h; the reaction temperature after adding the hydrophilic chain extender and the dihydroxy chain extender is 60~95℃ and the reaction time is 3~7h; the temperature after cooling is 30~45℃; the neutralization reaction time is 10~35min; the emulsification temperature is 30~45℃ and the time is 25~35min; the reaction temperature with the amino-modified sunscreen agent is 40~50℃ and the time is 3~6h.

9. The method according to claim 1, characterized in that, The stirring speed for emulsification in step (2) is 600-1000 r / min.

10. A polyurethane emulsion sunscreen film prepared by the method described in claim 1.

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