Ultraviolet absorbing polymer nanoparticles and preparation method thereof, and ultraviolet absorbing coating

Abstract

The present invention discloses ultraviolet-absorbing polymer nanoparticles, a preparation method thereof, and an ultraviolet-absorbing coating. The ultraviolet-absorbing polymer nanoparticles comprise microspheres encapsulating an ultraviolet absorber, the microspheres being formed from a first hydrophobic polymer; a first shell formed on the surface of the microspheres, the first shell being formed from a second hydrophobic polymer having weaker hydrophobicity than the first; and a second shell formed on the surface of the first shell, the second shell being formed from a hydrophilic polymer. The ultraviolet-absorbing polymer nanoparticles, through double encapsulation, have excellent stability, reduce the leakage rate of the ultraviolet absorber, and improve the durability of product performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and particularly relates to ultraviolet absorbing polymer nanoparticles with a double-layer core-shell structure, a method for preparing ultraviolet absorbing polymer nanoparticles based on a seed miniemulsion polymerization method, and an ultraviolet absorbing coating formed by the ultraviolet absorbing polymer nanoparticles. Background Art

[0002] Polymer nanoparticles can take the form of nanospheres or nanocapsules. Nanospheres are a framework system composed of a dense polymer network, with active molecules dispersed throughout the particle. Nanocapsules, on the other hand, are sac-like systems with a core-shell structure. Polymer nanoparticles can encapsulate active substances, isolating them from the surrounding medium to prevent rapid degradation while allowing for release of the active substance upon demand. Furthermore, polymer nanoparticles exhibit excellent storage stability and biocompatibility, leading to their widespread application in a wide range of fields.

[0003] Emulsion polymerization can be used to prepare polymer nanoparticles, offering advantages such as low reaction system viscosity, high polymerization rate, and high molecular weight of the resulting polymers. Seeded emulsion polymerization, with its advantages of improved emulsion stability, narrow particle size distribution, and ease of control, plays an important role in the design of latex particles and the preparation of various functional latexes. It is the most common and simplest method for preparing latexes with core-shell structures.

[0004] Previous studies have reported synthesizing a new dipolymer of benzotriazole UV-shielding material—2,2'-methylene-bis(4-tert-butyl-6-(4-chloro)benzotriazolyl)phenol—through diazotization, coupling, reduction, and Mannich reactions. This material can be added to acrylic coatings as a UV absorber. The synthesized 2,2'-methylene-bis(4-tert-butyl-6-(4-chloro)benzotriazolyl)phenol exhibits strong absorption in the 260-380 nm wavelength range. However, the synthesis of this new UV absorber is complex and exhibits poor compatibility with acrylic esters.

[0005] Furthermore, commercial UV absorbers were encapsulated in polymethyl methacrylate microspheres using an internal phase separation method. The microspheres were then incorporated into a transparent acrylic adhesive. The acrylic resin was then coated onto a wooden board and placed in an artificial UV chamber. The coating's efficiency after aging was monitored using a colorimeter, infrared spectroscopy, and transmission electron microscopy. This study compared the efficiency of free and encapsulated Tinuvin 1130 and Tinuvin 292 commercial UV absorbers. The results showed that coating efficiency was slightly improved when the encapsulated products were used. However, the encapsulation of the UV absorbers was insufficient, and incorporating the microspheres into the transparent acrylic resin resulted in discoloration.

[0006] In addition, publications CN110074993A and CN105287236A both disclose using polymers to encapsulate ultraviolet absorbers, thereby reducing direct contact between the ultraviolet absorbers and human skin. However, the use of polymers alone to encapsulate the ultraviolet absorbers leaves open the question of the sustained effect of the ultraviolet absorption capacity of the ultraviolet absorbers (i.e., the leakage rate of the encapsulated ultraviolet absorbers). Summary of the Invention

[0007] In view of this, it is necessary for the present invention to provide a UV-absorbing polymer nanoparticle, which encapsulates an oil-soluble UV absorber inside a microsphere formed by a first hydrophobic polymer as a core layer, and on the surface of the core layer are a first shell layer formed by a second hydrophobic monomer and a second shell layer formed by a hydrophilic monomer. Through double encapsulation, the leakage rate of the UV absorber is further reduced and the durability of the product performance is improved.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] The present invention first provides a UV-absorbing polymer nanoparticle, which comprises:

[0010] microspheres encapsulating an ultraviolet absorber, wherein the microspheres are formed from a first hydrophobic polymer;

[0011] a first shell layer formed on the surface of the microsphere, wherein the first shell layer is formed of a second hydrophobic polymer, and the hydrophobicity of the second hydrophobic polymer is weaker than that of the first hydrophobic polymer;

[0012] and a second shell layer formed on the surface of the first shell layer, wherein the second shell layer is formed of a hydrophilic polymer;

[0013] Preferably, the size of the UV-absorbing polymer nanoparticles is between 150-300 nm, the thickness of the first shell is between 20-40 nm, and the thickness of the second shell is between 10-20 nm.

[0014] In a further embodiment, the first hydrophobic polymer is polystyrene or polyethyl methacrylate, the second hydrophobic polymer is polymethyl methacrylate or polyvinyl acetate, and the hydrophilic polymer is polyacrylonitrile or polymethyl acrylate.

[0015] The present invention further discloses a method for preparing ultraviolet absorbing polymer nanoparticles, comprising the following steps:

[0016] mixing a first hydrophobic monomer, a cross-linking agent, a stabilizer, an oil-soluble UV absorber, and an oil-soluble initiator to obtain an oil phase;

[0017] mixing an emulsifier and deionized water to obtain an aqueous phase;

[0018] The oil phase is slowly added to the water phase while stirring, and subjected to homogenization, emulsification, heating and polymerization to obtain a seed miniemulsion;

[0019] slowly adding a second hydrophobic monomer to the seed miniemulsion and continuing polymerization to obtain a miniemulsion with a core-shell structure;

[0020] Slowly add a hydrophilic monomer into the core-shell structured miniemulsion and continue polymerization to obtain a double-layer core-shell structured miniemulsion.

[0021] In a further embodiment, the first hydrophobic monomer is styrene or ethyl methacrylate, the second hydrophobic monomer is methyl methacrylate or vinyl acetate, and the hydrophilic monomer is acrylonitrile or methyl acrylate.

[0022] In a further embodiment, the oil-soluble UV absorber is selected from one of 2,4-dihydroxybenzophenone and 2-hydroxy-4-methoxybenzophenone, or a combination of the two;

[0023] The cross-linking agent is selected from one of divinylbenzene, ethylene glycol dimethacrylate, ethylene glycol dimethacrylate, and propylene glycol dimethacrylate;

[0024] The co-stabilizer is selected from one of hexadecane, hexadecanol, octadecane, and octadecyl alcohol;

[0025] The oil-soluble initiator is selected from one of azobisisobutyronitrile, azobisisoheptanenitrile, cumene hydroperoxide and benzoyl peroxide.

[0026] In a further embodiment, based on the first hydrophobic monomer, the weight percentage of the crosslinking agent is 5-10%; the weight percentage of the oil-soluble initiator is 0.5-5%; the weight percentage of the stabilizer is 3-12%; and the weight percentage of the oil-soluble UV absorber is 1-5%.

[0027] In a further embodiment, the emulsifier is prepared by compounding any one of sodium lauryl sulfate, lauryl ammonium chloride, cetyl trimethyl ammonium chloride, and nonylphenol polyoxyethylene ether with a waterborne polyurethane macromolecule terminated with hydroxyethyl methacrylate in any proportion;

[0028] Preferably, the amount of the emulsifier is 0.3-3.0% by weight of the first hydrophobic monomer;

[0029] Preferably, the molecular weight of the hydroxyethyl methacrylate terminated aqueous polyurethane is between 20,000 and 60,000.

[0030] In a further embodiment, the amount of the second hydrophobic monomer is 80-150% of the weight of the first hydrophobic monomer; the addition rate of the second hydrophobic monomer is 0.5-2 mL / min, and the reaction time is 2-3 h.

[0031] In a further embodiment, the amount of the hydrophilic monomer is 80-120% of the weight of the first hydrophobic monomer; the addition rate of the hydrophilic monomer is 0.5-2 mL / min, and the reaction time is 2-3 h.

[0032] The present invention further discloses a UV absorbing coating, characterized in that it is prepared by incorporating the UV absorbing polymer nanoparticles as described above or the UV absorbing polymer nanoparticles prepared by the aforementioned preparation method into a substrate; preferably, the substrate is selected from acrylic resin or water-based polyurethane resin.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The UV-absorbing polymer nanoparticles have a double-layer core-shell structure, which seals the UV absorber inside, which helps to reduce the leakage of oil-soluble UV absorbers, increase their durability, and technically solve the problems of instability and short action time of UV absorbers.

[0035] The seed emulsion polymerization method plays an important role in the design of latex particles and the preparation of various functional latexes due to its advantages such as better emulsion stability, narrow particle size distribution, and easy control. It is the most common and simplest method for preparing high-solid content emulsions and emulsions with core-shell structures. The present invention utilizes the characteristics of the semi-continuous mini-emulsion polymerization process. First, the oil-soluble UV absorber is encapsulated into the interior of the first cross-linked hydrophobic polymer microspheres by mini-emulsion polymerization to prepare a seed mini-emulsion; then, the second hydrophobic monomer, hydrophilic monomer and other shell monomers are added dropwise by monomer addition to prepare a double-encapsulated UV-absorbing mini-emulsion; by using the semi-continuous addition method, the entire reaction process is always in a "starved state", monomers with different reactivity and water solubility can be copolymerized, and the hydrophilic groups are evenly dispersed on the particle surface, thereby improving the stability of the polymer. The present invention solves the problem of heat dissipation difficulty in the nucleation and growth stage of the mini-emulsion by using the semi-continuous mini-emulsion polymerization method, and can well control the stability of the polymerization reaction and the performance of the product.

[0036] The present invention encapsulates an oil-soluble UV absorber into the interior of a cross-linked first hydrophobic polymer microsphere as a seed, and performs double encapsulation by effectively controlling the phase separation between the cross-linked seed and the growing polymer phase, which is beneficial to reducing the leakage of the oil-soluble UV absorber and technically solves the problems of instability and short action time of the UV absorber.

[0037] The ultraviolet absorption coating prepared in the present invention has the advantages of being environmentally friendly and non-toxic, having good corrosion resistance, good weather resistance and sunlight resistance, high mechanical strength, good heat resistance, good sealing, large absorbance, simple preparation process, and easy control of the polymerization system, and can be industrially produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Schematic diagram of the structure of ultraviolet absorbing polymer nanoparticles in Example 1;

[0039] Figure 2 is the ultraviolet transmittance of the ultraviolet absorbing coating prepared in Examples 1-3;

[0040] Figure 3 is the ultraviolet transmittance of the ultraviolet absorbing coating prepared in Examples 4-7;

[0041] Figure 4 The UV transmittance of the UV absorbing coatings prepared in Example 6 and Comparative Example 1. DETAILED DESCRIPTION

[0042] The embodiments of the present invention are described in detail below. The embodiments described below are exemplary and are only used to explain the present invention, and are not to be construed as limiting the present invention.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0044] The first aspect of the present invention discloses a UV-absorbing polymer nanoparticle comprising:

[0045] microspheres encapsulating an ultraviolet absorber, wherein the microspheres are formed from a first hydrophobic polymer;

[0046] a first shell layer formed on the surface of the microsphere, wherein the first shell layer is formed of a second hydrophobic polymer, and the hydrophobicity of the second hydrophobic polymer is weaker than that of the first hydrophobic polymer;

[0047] and a second shell layer formed on the surface of the first shell layer, wherein the second shell layer is formed of a hydrophilic polymer.

[0048] By double encapsulating the ultraviolet absorber with a polymer, it is possible to effectively prevent the leakage of the ultraviolet absorber and improve its durability. In order to ensure that the ultraviolet absorbing polymer nanoparticles are latex particles of normal structure and have good stability, according to an embodiment of the present invention, preferably, the first hydrophobic polymer is polystyrene or polyethyl methacrylate, the second hydrophobic polymer is polymethyl methacrylate or polyvinyl acetate, and the hydrophilic polymer is polyacrylonitrile or polymethyl acrylate. It is understandable that different properties can be given to ultraviolet absorbing polymer nanoparticles by selecting different types of encapsulating polymers, such as the first hydrophobic polymer using polystyrene to give the emulsion water resistance, oil resistance, hardness, etc.; the second hydrophobic polymer using polymethyl methacrylate to give the emulsion chemical stability, weather resistance, excellent adhesion and elasticity, etc., and polymethyl methacrylate has a certain reflective ability to ultraviolet rays, and has the advantages of environmental protection, non-toxicity, high mechanical strength, and good heat resistance; the polyvinyl acetate selected by the second hydrophobic polymer gives the emulsion toughness and plasticity; the hydrophilic polymer using polyacrylonitrile to give the emulsion weather resistance, solvent resistance, etc. will not be elaborated here.

[0049] Preferably, the size of the UV-absorbing polymer nanoparticles is between 150-300 nm, the thickness of the first shell is between 20-40 nm, and the thickness of the second shell is between 10-20 nm.

[0050] The second aspect of the present invention discloses a method for preparing ultraviolet absorbing polymer nanoparticles, the main steps of which are:

[0051] Formation of nuclear layer

[0052] The core layer of the present invention is mainly formed by polymerizing a first hydrophobic monomer into microspheres, and the microspheres are encapsulated with an oil-soluble ultraviolet absorber. The present invention adopts a semi-continuous miniemulsion polymerization process. According to an embodiment of the present invention, the steps for preparing the core layer are as follows:

[0053] S1. Obtain oil phase and water phase respectively.

[0054] Prepare the oil phase: Mix the first hydrophobic monomer, cross-linking agent, stabilizer, oil-soluble UV absorber and oil-soluble initiator to obtain the oil phase. The purpose of mixing is to fully dissolve and mix the raw materials, and there is no special limitation. The first hydrophobic monomer is preferably styrene or ethyl methacrylate monomer; the oil-soluble UV absorber is not particularly limited, and conventional oil-soluble UV absorbers in the field can be used. According to an embodiment of the present invention, the oil-soluble UV absorber is selected from one or two of 2,4-dihydroxybenzophenone or 2-hydroxy-4-methoxybenzophenone. In addition, the cross-linking agent, stabilizer and oil-soluble initiator used in the oil phase are not particularly limited, and their function is to initiate the polymerization and cross-linking of the first hydrophobic monomer. Specifically, the addition of a cross-linking agent can make the polymer network more compact, further hinder the transmission of the ultraviolet absorber from the polymer matrix, and help reduce the leakage of oil-soluble ultraviolet absorbers and increase their durability. The stability of the miniemulsion is achieved through the synergistic effect of the emulsifier and the stabilizer. The stabilizer can work with the emulsifier to generate osmotic pressure to offset the Laplace pressure difference between large and small droplets, slowing down the diffusion of monomer molecules in the monomer droplets, thereby inhibiting the Ostwald aging of the emulsion and improving the stability of the monomer droplets. The addition of the above-mentioned auxiliary agent promotes the stability of the subsequent emulsion. Any auxiliary agent conventionally used in the miniemulsion polymerization process in the art can be used. Examples that can be mentioned include the cross-linking agent being selected from one of divinylbenzene, ethylene glycol dimethacrylate, ethylene glycol dimethacrylate, and propylene glycol dimethacrylate; the stabilizer being selected from one of hexadecane, hexadecanol, octadecane, and octadecyl alcohol; and the oil-soluble initiator being selected from one of azobisisobutyronitrile, azobisisoheptonitrile, isopropylbenzene hydroperoxide, and benzoyl peroxide.

[0055] It can be understood that in the oil phase, the added amount of the crosslinker, oil-soluble initiator, stabilizer and oil-soluble UV absorber can be adjusted according to the amount of the first hydrophobic monomer and the size of the microspheres. Preferably, in some specific embodiments of the present invention, based on the first hydrophobic monomer, the weight percentage of the crosslinker is 5-10%; the weight percentage of the oil-soluble initiator is 0.5-5%; the weight percentage of the stabilizer is 3-12%; and the weight percentage of the oil-soluble UV absorber is 1-5%.

[0056] Prepare the aqueous phase: Mix the emulsifier and deionized water to obtain the aqueous phase. Similar to the oil phase, the purpose of mixing is to fully dissolve and mix the raw materials, and there are no special restrictions. The emulsifier can be selected from the emulsifiers conventionally used in the miniemulsion polymerization process in the art. Preferably, in some specific embodiments of the present invention, the emulsifier is formed by mixing and compounding a first emulsifying component and a second emulsifying component in any proportion. The first emulsifying component is a surfactant, which can be any one of a cationic surfactant, an anionic surfactant or a nonionic surfactant. Specific examples include but are not limited to any one of sodium lauryl sulfate, lauryl ammonium chloride, hexadecyltrimethylammonium chloride, and nonylphenol polyoxyethylene ether. The second emulsifying component is a water-based polyurethane macromolecule terminated with hydroxyethyl methacrylate. Preferably, the molecular weight of the water-based polyurethane terminated with hydroxyethyl methacrylate is above 20,000, more preferably, between 20,000 and 60,000. Because the aqueous polyurethane macromolecules terminated with hydroxyethyl methacrylate have polymerization activity, their reactive functional groups participate in the miniemulsion polymerization reaction. While playing a conventional emulsifying role, they are covalently bonded to the surface of the polymer particles and become part of the polymer, thereby avoiding the emulsifier from being desorbed from the polymer particles or migrating in the latex film, greatly reducing the hydrophilic groups on the surface of the latex film, thereby improving the coating performance. According to an embodiment of the present invention, the aqueous polyurethane terminated with hydroxyethyl methacrylate can be prepared with reference to the prior art, as described in Wang X, Cui Y, Wang Y, et al. Preparation and characteristics of crosslinked fluorinated acrylate modified waterborne polyurethane for metal protection coating [J]. Progress in Organic Coatings, 2021, 158: 106371.

[0057] It is understandable that the amount of the emulsifier can be adjusted according to actual conditions. According to an embodiment of the present invention, the amount of the emulsifier is 0.3-3.0% by weight of the first hydrophobic monomer.

[0058] S2. Formation of nuclear layer.

[0059] The oil phase in step S1 is slowly added to the aqueous phase while stirring, and stirring is continued to mix thoroughly to form a pre-emulsion; the pre-emulsion is then homogenized and emulsified by high-speed shearing, preferably, the shear rate is 16000-20000rpm, to obtain a miniemulsion; finally, the miniemulsion is heated and polymerized to obtain a seed miniemulsion composed of a microsphere structure, wherein the oil-soluble ultraviolet absorber is encapsulated in the microspheres. It is understood that the heating polymerization temperature, time, etc. described in this step can be adjusted according to actual conditions. Specifically, the temperature can be selected according to the type of oil-soluble initiator and can initiate the polymerization of the first hydrophobic monomer. The polymerization time can be adjusted according to the amount of the first hydrophobic monomer and the size of the desired microspheres. In one or more embodiments of the present invention, the polymerization temperature is 35-80°C and the polymerization time is 1-2h.

[0060] Forming the first shell

[0061] Specifically, a second hydrophobic monomer is slowly added to the seed miniemulsion, and polymerization is continued to form a first shell layer to obtain a miniemulsion of a core-shell structure. Wherein, the second hydrophobic monomer is methyl methacrylate or vinyl acetate. According to an embodiment of the present invention, the second hydrophobic monomer is added to the seed miniemulsion by slowly dropping, and the dropping speed is preferably 0.5-2mL / min, and the reaction time is 2-3h. It is understood that the amount of the second hydrophobic monomer can be adjusted according to the size of the core layer microspheres and the thickness of the first shell layer. Preferably, the amount of the second hydrophobic monomer is 80-150% of the weight of the first hydrophobic monomer.

[0062] Forming the second shell

[0063] Specifically, a hydrophilic monomer is slowly added to the core-shell structure miniemulsion, and polymerization is continued to form a second shell layer to obtain a double-layer core-shell structure miniemulsion. The hydrophilic monomer is acrylonitrile or methyl acrylate. According to an embodiment of the present invention, the second hydrophobic monomer is slowly added to the seed miniemulsion by dropwise addition at a rate of preferably 0.5-2 mL / min, and the reaction time is 2-3 hours. The amount of the hydrophilic monomer is 80-120% by weight of the first hydrophobic monomer.

[0064] A third aspect of the present invention provides a UV-absorbing coating, prepared by incorporating the UV-absorbing polymer nanoparticles described in the first aspect of the present invention, or the UV-absorbing polymer nanoparticles prepared by the preparation method described in the second aspect of the present invention, into a substrate. The type of substrate is not particularly limited, and specific examples include, but are not limited to, water-based polyurethanes and polyacrylates.

[0065] The present invention is described below by means of specific examples. It should be noted that the following specific examples are for illustrative purposes only and do not limit the scope of the present invention in any way. In addition, unless otherwise specified, methods without specific conditions or steps are conventional methods, and the reagents and materials used are all commercially available.

[0066] Example 1

[0067] 9.0 g of styrene, 1.0 g of ethylene glycol dimethacrylate, 0.3 g of 2-hydroxy-4-methoxybenzophenone, 0.8 g of hexadecane, and 0.5 g of azobisisoheptanenitrile were magnetically stirred for 30 min to fully dissolve them as the oil phase;

[0068] 0.15 g of sodium lauryl sulfate and 3 g of hydroxyethyl methacrylate-terminated waterborne polyurethane macromolecules (molecular weight 30,000) were weighed and dissolved in deionized water with magnetic stirring for 30 min to fully dissolve them, which served as the aqueous phase.

[0069] The oil phase was slowly added to the water phase and magnetically stirred at room temperature for 30 min to form a pre-emulsion;

[0070] Then, the mixture was homogenized and emulsified at a shear rate of 16,000 rpm using a high-speed shearing device in an ice-water bath for 5 min to form a miniemulsion;

[0071] The miniemulsion was transferred to a three-necked flask equipped with a stirrer, a thermometer, and a reflux condenser. Nitrogen was introduced for 30 minutes under stirring to remove air from the system. The mixture was then kept in a water bath at 55°C for 2 hours to obtain a seed miniemulsion.

[0072] 12 g of methyl methacrylate monomer was added dropwise to the seed miniemulsion at a rate of 0.5 ml / min and polymerized for 2 h to form the first shell layer, thereby obtaining a core-shell structured miniemulsion.

[0073] 10 g of acrylonitrile monomer was added dropwise to the core-shell structured miniemulsion at a rate of 0.5 ml / min and the polymerization reaction was carried out for 3 h to form a second shell layer, thereby obtaining a double-layer core-shell structured miniemulsion.

[0074] The microstructure of the ultraviolet absorbing polymer nanoparticles prepared in this embodiment is as follows: Figure 1 As shown in , it can be seen that the interior is polystyrene microspheres encapsulated with ultraviolet absorbers, the first shell layer is polymethyl methacrylate, and the second shell layer is polyacrylonitrile.

[0075] Example 2

[0076] 9.0 g of styrene, 1.0 g of divinylbenzene, 0.3 g of 2-hydroxy-4-methoxybenzophenone, 0.8 g of hexadecane, and 0.5 g of benzoyl peroxide were magnetically stirred for 30 min to fully dissolve them as the oil phase;

[0077] 0.1 g of sodium dodecylbenzenesulfonate and 5 g of hydroxyethyl methacrylate-terminated waterborne polyurethane macromolecules (molecular weight 20,000) were weighed and dissolved in deionized water with magnetic stirring for 30 min to fully dissolve them, which served as the aqueous phase.

[0078] The oil phase was slowly added to the water phase and magnetically stirred at room temperature for 30 min to form a pre-emulsion;

[0079] Then, the mixture was homogenized and emulsified at a shear rate of 16,000 rpm using a high-speed shearing device in an ice-water bath for 5 min to form a miniemulsion;

[0080] The miniemulsion was transferred to a three-necked flask equipped with a stirrer, a thermometer, and a reflux condenser. Nitrogen was introduced for 30 minutes while stirring to remove air from the system. The mixture was then kept in a water bath at 70°C for 2 hours to obtain a seed miniemulsion.

[0081] 14 g of methyl methacrylate monomer was added dropwise to the seed miniemulsion at a rate of 0.5 ml / min and polymerized for 2 h to form the first shell layer, thereby obtaining a core-shell structured miniemulsion.

[0082] 12 g of methyl acrylate monomer was added dropwise to the core-shell structured miniemulsion at a rate of 0.5 ml / min, and the polymerization reaction was carried out for 3 h to form a second shell layer, thereby obtaining a double-layer core-shell miniemulsion.

[0083] Example 3

[0084] 12.0 g of ethyl methacrylate, 1.0 g of ethylene glycol dimethacrylate, 0.3 g of 2-hydroxy-4-methoxybenzophenone, 0.8 g of hexadecane, and 0.5 g of cumene hydroperoxide were magnetically stirred for 30 min to fully dissolve them as the oil phase;

[0085] Weigh 0.1 g of hexadecyltrimethylammonium chloride and 4 g of hydroxyethyl methacrylate-terminated waterborne polyurethane macromolecules (molecular weight 40,000) and dissolve them in deionized water with magnetic stirring for 30 min to fully dissolve them, which serves as the aqueous phase.

[0086] The oil phase was slowly added to the water phase and magnetically stirred at room temperature for 30 min to form a pre-emulsion;

[0087] Then, the mixture was homogenized and emulsified at a shear rate of 16,000 rpm using a high-speed shearing device in an ice-water bath for 5 min to form a miniemulsion;

[0088] The miniemulsion was transferred to a three-necked flask equipped with a stirrer, a thermometer, and a reflux condenser. Nitrogen was introduced for 30 minutes under stirring to remove air from the system. The mixture was then kept in a water bath at 75°C for 2 hours to obtain a seed miniemulsion.

[0089] 10 g of vinyl acetate monomer was added dropwise to the seed miniemulsion at a rate of 0.5 ml / min and polymerized for 2 h to form the first shell layer, thereby obtaining a core-shell structured miniemulsion.

[0090] 12 g of acrylonitrile monomer was added dropwise to the core-shell structured miniemulsion at a rate of 0.5 ml / min, and the polymerization reaction was carried out for 3 h to form a second shell layer, thereby obtaining a double-layer core-shell structured miniemulsion.

[0091] Example 4

[0092] 12.0 g of styrene, 1.0 g of divinylbenzene, 0.3 g of 2,4-dihydroxybenzophenone, 0.8 g of hexadecane, and 0.5 g of azobisisobutyronitrile were magnetically stirred for 30 min to fully dissolve them as the oil phase;

[0093] 0.15 g of sodium lauryl sulfate and 4 g of hydroxyethyl methacrylate-terminated waterborne polyurethane macromolecules (molecular weight 60,000) were weighed and dissolved in deionized water with magnetic stirring for 30 min to fully dissolve them, which served as the aqueous phase.

[0094] The oil phase was slowly added to the water phase and magnetically stirred at room temperature for 30 min to form a pre-emulsion;

[0095] Then, the mixture was homogenized and emulsified at a shear rate of 16,000 rpm using a high-speed shearing device in an ice-water bath for 5 min to form a miniemulsion;

[0096] The miniemulsion was transferred to a three-necked flask equipped with a stirrer, a thermometer, and a reflux condenser. Nitrogen was introduced for 30 minutes under stirring to remove air from the system. The mixture was then kept in a water bath at 65°C for 2 hours to obtain a seed miniemulsion.

[0097] 14 g of methyl methacrylate monomer was added dropwise to the seed miniemulsion at a rate of 0.5 ml / min and polymerized for 2 h to form the first shell layer, thereby obtaining a core-shell structured miniemulsion.

[0098] 12 g of methyl acrylate monomer was added dropwise to the core-shell structured miniemulsion at a rate of 0.5 ml / min, and the polymerization reaction was carried out for 3 h to form a second shell layer, thereby obtaining a double-layer core-shell structured miniemulsion.

[0099] Example 5

[0100] 10.0 g of ethyl methacrylate, 1.0 g of ethylene glycol dimethacrylate, 0.3 g of 2,4-dihydroxybenzophenone, 0.8 g of hexadecane, and 0.5 g of azobisisobutyronitrile were magnetically stirred for 30 min to fully dissolve them as the oil phase;

[0101] Weigh 0.15 g of hexadecyltrimethylammonium chloride and 4 g of hydroxyethyl methacrylate-terminated waterborne polyurethane macromolecules (molecular weight 50,000) and dissolve them in deionized water with magnetic stirring for 30 min to fully dissolve them, which serves as the aqueous phase.

[0102] The oil phase was slowly added to the water phase and magnetically stirred at room temperature for 30 min to form a pre-emulsion;

[0103] Then, the mixture was homogenized and emulsified at a shear rate of 16,000 rpm using a high-speed shearing device in an ice-water bath for 5 min to form a miniemulsion;

[0104] The miniemulsion was transferred to a three-necked flask equipped with a stirrer, a thermometer, and a reflux condenser. Nitrogen was introduced for 30 minutes under stirring to remove air from the system. The mixture was then kept in a water bath at 65°C for 2 hours to obtain a seed miniemulsion.

[0105] 15 g of vinyl acetate monomer was added dropwise to the seed miniemulsion at a rate of 0.5 ml / min and polymerized for 2 h to form the first shell layer, thereby obtaining a core-shell structured miniemulsion.

[0106] 10 g of acrylonitrile monomer was added dropwise to the core-shell structured miniemulsion at a rate of 0.5 ml / min and the polymerization reaction was carried out for 3 h to form a second shell layer, thereby obtaining a double-layer core-shell structured miniemulsion.

[0107] Example 6

[0108] 12.0 g of styrene, 1.0 g of divinylbenzene, 0.3 g of 2,4-dihydroxybenzophenone, 0.8 g of hexadecane, and 0.5 g of azobisisobutyronitrile were magnetically stirred for 30 min to fully dissolve them as the oil phase;

[0109] Weigh 0.1 g of sodium lauryl sulfate and 8 g of hydroxyethyl methacrylate-terminated waterborne polyurethane macromolecules (molecular weight 30,000) and dissolve them in deionized water with magnetic stirring for 30 min to fully dissolve them as the aqueous phase;

[0110] The oil phase was slowly added to the water phase and magnetically stirred at room temperature for 30 min to form a pre-emulsion;

[0111] Then, the mixture was homogenized and emulsified at a shear rate of 16,000 rpm using a high-speed shearing device in an ice-water bath for 5 min to form a miniemulsion;

[0112] The miniemulsion was transferred to a three-necked flask equipped with a stirrer, a thermometer, and a reflux condenser. Nitrogen was introduced for 30 minutes under stirring to remove air from the system. The mixture was then kept in a water bath at 65°C for 2 hours to obtain a seed miniemulsion.

[0113] 15 g of methyl methacrylate monomer was added dropwise to the seed miniemulsion at a rate of 0.5 ml / min and polymerized for 2 h to form the first shell layer, thereby obtaining a core-shell structured miniemulsion.

[0114] 13 g of methyl acrylate monomer was added dropwise to the miniemulsion at a rate of 0.5 ml / min and polymerized for 3 h to form a second shell layer, thereby obtaining a miniemulsion with a double-layer core-shell structure.

[0115] Example 7

[0116] 12.0 g of styrene, 1.0 g of divinylbenzene, 0.3 g of 2,4-dihydroxybenzophenone, 0.8 g of hexadecane, and 0.5 g of azobisisobutyronitrile were magnetically stirred for 30 min to fully dissolve them as the oil phase;

[0117] Weigh 0.45 g of sodium lauryl sulfate and dissolve it in deionized water with magnetic stirring for 30 min to fully dissolve it as the aqueous phase;

[0118] The oil phase was slowly added to the water phase and magnetically stirred at room temperature for 30 min to form a pre-emulsion;

[0119] Then, the mixture was homogenized and emulsified at a shear rate of 16,000 rpm using a high-speed shearing device in an ice-water bath for 5 min to form a miniemulsion;

[0120] The miniemulsion was transferred to a three-necked flask equipped with a stirrer, a thermometer, and a reflux condenser. Nitrogen was introduced for 30 minutes under stirring to remove air from the system. The mixture was then kept in a water bath at 65°C for 2 hours to obtain a seed miniemulsion.

[0121] 15 g of methyl methacrylate monomer was added dropwise to the seed miniemulsion at a rate of 0.5 ml / min and polymerized for 2 h to form the first shell layer, thereby obtaining a core-shell structured miniemulsion.

[0122] 13 g of methyl acrylate monomer was added dropwise to the miniemulsion at a rate of 0.5 ml / min and polymerized for 3 h to form a second shell layer, thereby obtaining a miniemulsion with a double-layer core-shell structure.

[0123] Comparative Example 1

[0124] This comparative example adopts the same implementation as Example 6, except that the ultraviolet absorber is encapsulated in microspheres formed of polymethyl methacrylate.

[0125] The specific preparation steps of this comparative example are as follows:

[0126] 15 g of methyl methacrylate monomer, 1.0 g of divinylbenzene, 0.3 g of 2,4-dihydroxybenzophenone, 0.8 g of hexadecane and 0.5 g of azobisisobutyronitrile were magnetically stirred for 30 min to fully dissolve them as the oil phase;

[0127] Weigh 0.1 g of sodium lauryl sulfate and 8 g of hydroxyethyl methacrylate-terminated waterborne polyurethane macromolecules (molecular weight 30,000) and dissolve them in deionized water with magnetic stirring for 30 min to fully dissolve them as the aqueous phase;

[0128] The oil phase was slowly added to the water phase and magnetically stirred at room temperature for 30 min to form a pre-emulsion;

[0129] Then, the mixture was homogenized and emulsified at a shear rate of 16,000 rpm using a high-speed shearing device in an ice-water bath for 5 min to form a miniemulsion;

[0130] The miniemulsion was transferred to a three-necked flask equipped with a stirrer, a thermometer and a reflux condenser. Nitrogen was passed through the flask for 30 minutes under stirring to exclude air from the system. The flask was reacted at a constant temperature of 65°C in a water bath for 2 hours to obtain a seed miniemulsion, i.e., polymethyl methacrylate microspheres sealed with a UV absorber.

[0131] Test Case

[0132] (1) At room temperature (25°C), the emulsion samples of Examples 1-7 and Comparative Example 1 were diluted with water to a concentration of 5 wt‰, and then the particle size and particle size distribution index (PDI) were measured using a laser dynamic light scattering (DLS); the emulsion viscosity was measured using an SNB-1 digital viscometer; and the emulsion was stored at room temperature (25°C) for 6 months, and the stability of the copolymer emulsion was observed. The results are shown in Table 1.

[0133] Table 1 Emulsion performance test results of double-layer core-shell structure in Examples 1-7

[0134] Z average particle size (nm) Particle Size Distribution Index (PDI) Viscosity (mpa·s) Storage stability Example 1 212.5 0.172 470 No precipitation Example 2 207.9 0.153 513 No precipitation Example 3 216.4 0.168 467 No precipitation Example 4 237.1 0.147 452 No precipitation Example 5 231.6 0.165 481 No precipitation Example 6 253.2 0.187 453 No precipitation Example 7 214.2 0.139 463 Slight precipitation Comparative Example 1 192.3 0.142 473 A small amount of precipitation

[0135] It can be seen from the test results in Table 1 that the ultraviolet absorbing polymer nanoparticles obtained in Examples 1-7 of the present invention and Comparative Example 1 have relatively uniform particle sizes, low emulsion viscosity, and good storage stability.

[0136] (2) The emulsion sample was evenly coated on a glass slide (thickness 30 μm) using a wire rod coater, dried at room temperature for 48 h, and its optical properties were measured using a UV-visible-near infrared spectrophotometer (HITACHI U-4100); the results are shown in Figure 2. Figure 2 、 Figure 3 and Figure 4 As shown. Figure 2 、 Figure 3 and Figure 4 It can be seen that the ultraviolet transmittance of the ultraviolet absorbing coatings obtained in Examples 1-7 and Comparative Example 1 is close to 0 in the (280-340 nm) band, which shows that the ultraviolet absorbing coatings obtained in Examples 1-7 and Comparative Example 1 can strongly absorb ultraviolet rays in the (280-340 nm) band.

[0137] (3) 0.01 g of UV-absorbing polymer nanoparticles was placed in 15 mL of ethanol in a 25 mL beaker and stirred continuously (100 rpm) for 0.5 h, 1 h, 2 h, 4 h, 8 h, 12 h, and 24 h. The UV absorption intensity of the supernatant after centrifugation was measured at a wavelength of 326 nm using a UV-visible spectrophotometer.

[0138] Table 2 UV absorber leakage test results in Examples 1-7 and Comparative Example 1

[0139] 0.5h 1h 2h 4h 8h 12h 24h Example 1 0.01 0.02 0.03 0.03 0.03 0.03 0.03 Example 2 0.02 0.03 0.04 0.04 0.04 0.04 0.04 Example 3 0.01 0.02 0.03 0.03 0.03 0.03 0.03 Example 4 0.01 0.02 0.03 0.03 0.03 0.03 0.03 Example 5 0.02 0.03 0.04 0.04 0.04 0.04 0.04 Example 6 0.01 0.02 0.03 0.03 0.03 0.03 0.03 Example 7 0.01 0.02 0.03 0.04 0.04 0.04 0.04 Comparative Example 1 0.02 0.04 0.06 0.07 0.08 0.09 0.11

[0140] As can be seen from Table 2, within 0-2h, as time increases, the ultraviolet absorption intensity of the ultraviolet absorbing polymer nanoparticles in absolute ethanol increases gradually among Examples 1-7, and remains essentially unchanged at 24h. This may be because the ultraviolet absorber on the ultraviolet absorbing polymer nanoparticle surface dissolves in the absolute ethanol. Therefore, the leakage of the ultraviolet absorber in the embodiments can be ignored essentially. And in Comparative Example 1, the ultraviolet absorption intensity is still increasing at 24h, which indicates that the single-layer encapsulation shortens the ultraviolet absorber action time.

[0141] 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.

[0142] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for preparing ultraviolet absorbing polymer nanoparticles, characterized in that: The following steps are involved: mixing a first hydrophobic monomer, a cross-linking agent, a stabilizer, an oil-soluble UV absorber, and an oil-soluble initiator to obtain an oil phase; An emulsifier and deionized water are mixed to obtain an aqueous phase, wherein the emulsifier is prepared by compounding any one of sodium lauryl sulfate, lauryl ammonium chloride, hexadecyltrimethylammonium chloride, and nonylphenol polyoxyethylene ether with a waterborne polyurethane macromolecule terminated with hydroxyethyl methacrylate in any proportion; The oil phase is slowly added to the water phase while stirring, and subjected to homogenization, emulsification, heating and polymerization to obtain a seed miniemulsion; slowly adding a second hydrophobic monomer to the seed miniemulsion and continuing polymerization to obtain a miniemulsion with a core-shell structure; Slowly adding a hydrophilic monomer to the core-shell structured miniemulsion and continuing polymerization to obtain a double-layer core-shell structured miniemulsion; The ultraviolet absorbing polymer nanoparticles include: microspheres encapsulating an ultraviolet absorber, wherein the microspheres are formed from a first hydrophobic polymer; a first shell layer formed on the surface of the microsphere, wherein the first shell layer is formed of a second hydrophobic polymer, and the hydrophobicity of the second hydrophobic polymer is weaker than that of the first hydrophobic polymer; and a second shell layer formed on the surface of the first shell layer, wherein the second shell layer is formed of a hydrophilic polymer.

2. The preparation method according to claim 1, wherein The size of the ultraviolet absorbing polymer nanoparticles is between 150-300 nm, the thickness of the first shell is between 20-40 nm, and the thickness of the second shell is between 10-20 nm.

3. The preparation method according to claim 1, wherein The first hydrophobic polymer is polystyrene or polyethyl methacrylate, the second hydrophobic polymer is polymethyl methacrylate or polyvinyl acetate, and the hydrophilic polymer is polyacrylonitrile or polymethyl acrylate.

4. The preparation method according to claim 1, wherein The first hydrophobic monomer is styrene or ethyl methacrylate, the second hydrophobic monomer is methyl methacrylate or vinyl acetate, and the hydrophilic monomer is acrylonitrile or methyl acrylate.

5. The preparation method according to claim 1, wherein The oil-soluble UV absorber is selected from one of 2,4-dihydroxybenzophenone and 2-hydroxy-4-methoxybenzophenone, or a combination of the two; The cross-linking agent is selected from one of divinylbenzene, ethylene glycol dimethacrylate, and propylene glycol dimethacrylate; The co-stabilizer is selected from one of hexadecane, hexadecanol, octadecane, and octadecyl alcohol; The oil-soluble initiator is selected from one of azobisisobutyronitrile, azobisisoheptanenitrile, cumene hydroperoxide and benzoyl peroxide.

6. The preparation method according to claim 1, wherein Based on the first hydrophobic monomer, the weight percentage of the crosslinking agent is 5-10%; the weight percentage of the oil-soluble initiator is 0.5-5%; the weight percentage of the stabilizer is 3-12%; and the weight percentage of the oil-soluble UV absorber is 1-5%.

7. The preparation method according to claim 1, wherein The amount of the emulsifier used is 0.3-3.0% by weight of the first hydrophobic monomer.

8. The preparation method according to claim 1, wherein The molecular weight of the hydroxyethyl methacrylate terminated aqueous polyurethane is between 20,000 and 60,000.

9. The preparation method according to claim 1, wherein The amount of the second hydrophobic monomer is 80-150% of the weight of the first hydrophobic monomer; the addition rate of the second hydrophobic monomer is 0.5-2 ml / min, and the reaction time is 2-3 hours.

10. The preparation method according to claim 1, wherein The amount of the hydrophilic monomer is 80-120% of the weight of the first hydrophobic monomer; the addition rate of the hydrophilic monomer is 0.5-2 ml / min, and the reaction time is 2-3 hours.

11. A UV absorbing coating, characterized in that: The ultraviolet absorbing polymer nanoparticles are prepared by mixing the ultraviolet absorbing polymer nanoparticles obtained by the preparation method according to any one of claims 1 to 10 into a substrate.

12. The ultraviolet absorbing coating according to claim 11, wherein The substrate is selected from acrylic resin or waterborne polyurethane resin.

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