Ultraviolet absorber and preparation method thereof

Abstract

The invention belongs to the field of ultraviolet absorber technology, and in particular to a kind of ultraviolet absorber and preparation method thereof, comprise the following steps: S1: in an oxygen-free atmosphere, 2,4-dihydroxybenzophenone, potassium carbonate and N, N-dimethylformamide are mixed, chlorodibenzoylmethane is added, temperature reaction is warmed up;Reaction solution is cooled to room temperature, poured into water, pH is adjusted to 7-8, extraction, washing, drying, compound A is obtained through chromatographic column;S2: compound A, emulsifier and polylysine solution are mixed, sodium carboxymethyl cellulose solution is added dropwise, and reacted after adjusting pH to 5-6;S3: glutaraldehyde solution is added to the system of step S2, reacted after adjusting pH to 6-8, and reactant is obtained;Reactant is centrifuged, supernatant is removed, suction filtration, washing, drying, ultraviolet absorber. The ultraviolet absorber provided by the present invention has excellent absorptive properties.

Description

Technical Field

[0001] The invention belongs to the technical field of ultraviolet absorbers, and particularly relates to an ultraviolet absorber and a preparation method thereof. Background Art

[0002] Ultraviolet rays contained in sunlight can cause harm to human health, the ecological environment, and material structures. To reduce or prevent the harm of ultraviolet rays to human health and material structures, adding ultraviolet absorbers is an effective method.

[0003] Ultraviolet absorbers are substances that strongly and selectively absorb high-energy ultraviolet light and convert it into energy, releasing or consuming it as heat or harmless, low-radiation radiation. They are commonly used in industries such as polymer materials, textile processing, and cosmetics. Common UV absorbers include benzophenones, benzotriazoles, hindered amines, substituted acrylonitriles, and triazines.

[0004] Chinese patent application document with application publication number CN107163206A discloses the preparation of a high molecular weight benzophenone compound and its application in light pollution-resistant plastics. The application document uses benzophenone and an excess of alkali metal sodium to generate a disodium benzophenone initiator, which reacts with toluene-2,4-diisocyanate in the presence of a catalyst, and then reacts with 4,4'-dihydroxybenzophenone under ethyl acetate reflux conditions to prepare the high molecular weight benzophenone compound. Although the application document modifies benzophenone, the prepared high molecular weight benzophenone compound mainly relies on the synergistic effect of the carbonyl group and the ortho-hydroxyl group, stabilizes the excited state through intramolecular hydrogen bonds, and has an absorption peak more concentrated in the UVB band (280-320nm), and has a poor ability to absorb the UVA band. Summary of the Invention

[0005] Existing ultraviolet absorbers have poor ability to absorb UVA band; in order to solve this problem, the present invention provides an ultraviolet absorber and a preparation method thereof.

[0006] In order to achieve the purpose of the present invention, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing an ultraviolet absorber, comprising the following steps:

[0008] S1: In an oxygen-free atmosphere, 2,4-dihydroxybenzophenone, potassium carbonate, and N,N-dimethylformamide were mixed uniformly, chlorodibenzoylmethane was added, and the temperature was raised to react; the reaction solution was cooled to room temperature, poured into water, the pH was adjusted to 7-8, extracted, washed, dried, and passed through a chromatographic column to obtain compound A;

[0009] S2: Compound A, an emulsifier, and a polylysine solution are mixed evenly, sodium carboxymethyl cellulose solution is added dropwise, and the pH is adjusted to 5-6 before reacting;

[0010] S3: adding glutaraldehyde solution to the system of step S2, adjusting the pH to 6-8 and then reacting to obtain a reactant; centrifuging the reactant, removing the supernatant, filtering, washing with water, and drying to obtain an ultraviolet absorber.

[0011] The reaction process of compound A is shown in Reaction Formula I:

[0012]

[0013] Reaction Formula Ⅰ

[0014] Preferably, in step S1, the molar ratio of 2,4-dihydroxybenzophenone, potassium carbonate and chlorodibenzoylmethane is 1:(1.3-1.5):(1.2-1.6).

[0015] By adopting the above technical solution, the dosage ratio of 2,4-dihydroxybenzophenone and chlorodibenzoylmethane is adjusted, the reaction conversion rate is improved, and the generation of by-products is reduced.

[0016] Preferably, in step S1, the temperature of the temperature-raising reaction is 65-75° C., and the reaction time is 3-5 hours.

[0017] Preferably, in step S2, the mass fraction of the polylysine solution is 1%-4%, the mass fraction of the sodium carboxymethyl cellulose solution is 1%-4%; the mass ratio of polylysine to sodium carboxymethyl cellulose is (1.05-1.15):1; and the amount of compound A used is 42%-48% of the total mass of polylysine and sodium carboxymethyl cellulose.

[0018] By adopting the above technical solution, the UV absorber produced by combining polylysine and sodium carboxymethyl cellulose at this ratio is spherical and uniformly coated. The UV absorber formed at this dosage of Compound A has a good morphology, with full and round particles. Too high a content can easily lead to low coating efficiency, while too low a content can easily affect the UV absorber's absorption properties.

[0019] Preferably, in step S2, the reaction temperature is 45-55° C., and the reaction time is 1-1.5 h.

[0020] Preferably, in step S2, the emulsifier is composed of Tween-80 and dioctyl sodium sulfosuccinate in a mass ratio of (1-1.2):1; the amount of the emulsifier is 0.5%-1% of the total mass of the polylysine solution and the sodium carboxymethylcellulose solution.

[0021] By adopting the above technical solution, the emulsifier is obtained by compounding two components: Tween-80 and dioctyl sodium sulfosuccinate. The ratio of the two components is adjusted to optimize the synergistic effect of nonionic and anionic surfactants, thereby improving the stability of the system.

[0022] Preferably, in step S3, the reaction temperature is 0-5°C, and the reaction time is 0.5-1h.

[0023] Preferably, the preparation method of chlorodibenzoylmethane comprises the following steps:

[0024] Dibenzoylmethane, pyridine, tetrahydrofuran and N-chlorosuccinimide are mixed evenly, and the mixture is heated and refluxed for reaction; the reaction solution is filtered, and the filtrate is subjected to rotary evaporation and passed through a chromatographic column to obtain chlorodibenzoylmethane.

[0025] The reaction process of chlorodibenzoylmethane is shown in Reaction Formula II:

[0026]

[0027] Reaction formula II

[0028] Preferably, the molar ratio of dibenzoylmethane, pyridine and N-chlorosuccinimide is 1:(1.05-1.2):(1.1-1.4); the temperature of the reflux is 75-80° C., and the reflux time is 1-3 h.

[0029] By adopting the above technical solution, under this ratio, the main product is monochlorodibenzoylmethane. A slight excess of N-chlorosuccinimide can avoid unreacted dibenzoylmethane residue. Too much N-chlorosuccinimide is likely to generate polychlorinated compounds, reducing the yield of the target product. The addition of pyridine can maintain an alkaline environment and promote the reaction.

[0030] In a second aspect, the present invention provides an ultraviolet absorber prepared by the above-mentioned method for preparing the ultraviolet absorber.

[0031] In summary, the beneficial effects of the present invention are:

[0032] (1) The present invention modifies 2,4-dihydroxybenzophenone by introducing a dibenzoylmethane structure that can absorb the UVA band into the molecular structure of 2,4-dihydroxybenzophenone that mainly absorbs the UVB band. The β-diketone skeleton and the benzene ring conjugated system in the dibenzoylmethane structure can effectively absorb the UVA band. The prepared compound A can absorb both UVA and UVB simultaneously. The 2,4-dihydroxybenzophenone molecular structure and the dibenzoylmethane structure are connected by an ether bond, which increases the conjugation range and reduces the photodegradation rate.

[0033] (2) The present invention coats compound A to form an outer shell layer, isolating compound A from direct contact with the external environment and delaying its photodegradation; at the same time, the outer shell layer can slowly and continuously release compound A, thus avoiding the problem of rapid release and rapid action of traditional ultraviolet absorbers causing premature failure of the protective effect;

[0034] (3) The ultraviolet absorber provided by the present invention has excellent absorption performance in the wavelength range of 280-380nm, indicating that the ultraviolet absorber provided by the present invention can absorb UVA and UVB simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a SEM image of the ultraviolet absorber of the present invention;

[0036] Figure 2 is the ultraviolet absorption spectrum of the ultraviolet absorber of the present invention;

[0037] Figure 3 This is the infrared spectrum of compound A prepared in the present invention;

[0038] Figure 4 This is the hydrogen nuclear magnetic resonance spectrum of compound A prepared in the present invention;

[0039] Figure 5 The figure is the hydrogen nuclear magnetic resonance spectrum of chlorodibenzoylmethane prepared by the present invention. DETAILED DESCRIPTION

[0040] The technical solution of the present invention is explained in detail below with reference to several representative embodiments of the present invention.

[0041] Unless otherwise specified, the experimental methods used in the following examples and comparative examples are all conventional methods. Unless otherwise specified, the materials, reagents, etc. used in the following examples and comparative examples are all commercially available.

[0042] Example 1

[0043] The ultraviolet absorber of this embodiment is prepared by the following preparation method of the ultraviolet absorber.

[0044] The preparation method of a UV absorber of this embodiment has the following specific preparation steps:

[0045] S1: Under an argon atmosphere, 2.14 g of 2,4-dihydroxybenzophenone, 1.8 g of potassium carbonate, and 100 mL of N,N-dimethylformamide were added sequentially to a three-necked flask, stirred for 0.5 h, and 3.36 g of chlorodibenzoylmethane was added. The temperature was raised to 75°C and the reaction was allowed to react for 4 h. The reaction solution was cooled to room temperature, poured into water, and the pH was adjusted to 7 with 1 mol / L dilute hydrochloric acid. The solution was extracted, washed, dried, and passed through a chromatographic column to obtain compound A; yield: 86.6%;

[0046] S2: 0.36 g of compound A, 0.16 g of Tween-80, 0.16 g of sodium dioctylsulfosuccinate, and 44 g of 1% polylysine solution were added to a beaker in sequence. The mixture was stirred at 10,000 rpm for 5 min. 20 g of 2% sodium carboxymethyl cellulose solution was added dropwise. The pH was adjusted to 5. The mixture was heated to 48°C and reacted for 1.3 h.

[0047] S3: Add glutaraldehyde solution to the system of step S2, adjust the pH to 7, place in ice water and cool to 2°C for reaction for 0.5h to obtain a reactant; centrifuge the reactant, remove the supernatant, filter, wash with water, and freeze-dry to obtain a UV absorber.

[0048] The SEM image of the UV absorber is shown in Figure 1 , the UV absorption spectrum of the UV absorber is shown in Figure 2 .

[0049] Depend on Figure 1 It can be seen that the ultraviolet absorber has an approximately spherical appearance, a particle size between 0.5-1 μm, and is relatively evenly dispersed without obvious agglomeration.

[0050] Depend on Figure 2 It can be seen that the UV absorber has maximum absorption peaks at wavelengths of 286nm and 355nm, and has significant absorption effects at wavelengths of 280-380nm.

[0051] The infrared spectrum of compound A is shown in Figure 3 .

[0052] Depend on Figure 3 It can be seen that 3002cm -1 The OH stretching vibration absorption peak of compound A is 1684 cm -1 The stretching vibration absorption peak of the benzoyl carbonyl C=O on compound A is 1625 cm -1 The stretching vibration absorption peak of the carbonyl C=O in the β-diketone carbonyl group of compound A is 1582 cm -1 , 1500cm -1 The stretching vibration of the benzene ring skeleton of compound A is at 751 cm -1 、701cm -1The absorption of CH on the benzene ring of compound A is 1221 cm -1 The stretching vibration of the aromatic ether bond COC on compound A is shown in FIG.

[0053] The H NMR spectrum of compound A is shown in Figure 4 .

[0054] Depend on Figure 4 It can be seen that δ6.52-6.59ppm (benzene ring H, 2H, m), δ6.70ppm (-CH, 1H, s), δ7.51-8.00ppm (benzene ring H, 16H, m), δ12.43ppm (-OH, 1H, s).

[0055] The hydrogen nuclear magnetic resonance spectrum combined with the infrared spectrum proved that the synthesized product was compound A.

[0056] The specific preparation steps of the preparation method of chlorodibenzoylmethane of the present embodiment are as follows:

[0057] 2.24 g of dibenzoylmethane, 0.87 g of pyridine, and 150 mL of tetrahydrofuran were added sequentially to a three-necked flask, stirred at 65°C for 0.5 h, and 1.6 g of N-chlorosuccinimide was added. The temperature was raised to 75°C and refluxed for 2 h. The reaction solution was filtered, and the filtrate was subjected to rotary evaporation and chromatography to obtain chlorodibenzoylmethane; yield: 79.5%.

[0058] The H NMR spectrum of chlorodibenzoylmethane is shown in Figure 5 .

[0059] Example 2

[0060] The ultraviolet absorber of this embodiment is prepared by the following preparation method of the ultraviolet absorber.

[0061] The preparation method of a UV absorber of this embodiment has the following specific preparation steps:

[0062] S1: Under argon atmosphere, 2.14 g of 2,4-dihydroxybenzophenone, 2.07 g of potassium carbonate, and 100 mL of N,N-dimethylformamide were added sequentially to a three-necked flask, stirred for 0.5 h, and 3.2 g of chlorodibenzoylmethane was added. The temperature was raised to 65°C and the reaction was allowed to react for 3 h. The reaction solution was cooled to room temperature, poured into water, and the pH was adjusted to 8 with 1 mol / L dilute hydrochloric acid. The solution was extracted, washed, dried, and passed through a chromatographic column to obtain compound A; yield: 84.2%;

[0063] S2: 0.54 g of compound A, 0.169 g of Tween-80, 0.141 g of sodium dioctylsulfosuccinate, and 31.5 g of 2% polylysine solution were added to a beaker in sequence. The mixture was stirred at 10,000 rpm for 5 min. 20 g of 3% sodium carboxymethylcellulose solution was added dropwise. The pH was adjusted to 5.5. The mixture was heated to 45°C and reacted for 1.2 h.

[0064] S3: Add glutaraldehyde solution to the system of step S2, adjust the pH to 8, place in ice water and cool to 0°C for reaction for 1 hour to obtain a reactant; centrifuge the reactant, remove the supernatant, filter, wash with water, and freeze-dry to obtain an ultraviolet absorber.

[0065] The specific preparation steps of the preparation method of chlorodibenzoylmethane of the present embodiment are as follows:

[0066] 2.24 g of dibenzoylmethane, 0.84 g of pyridine, and 150 mL of tetrahydrofuran were added sequentially to a three-necked flask, stirred at 65°C for 0.5 h, and 1.86 g of N-chlorosuccinimide was added. The temperature was raised to 77°C and refluxed for 3 h. The reaction solution was filtered, and the filtrate was subjected to rotary evaporation and chromatography to obtain chlorodibenzoylmethane; yield: 77.8%.

[0067] Example 3

[0068] The ultraviolet absorber of this embodiment is prepared by the following preparation method of the ultraviolet absorber.

[0069] The preparation method of a UV absorber of this embodiment has the following specific preparation steps:

[0070] S1: Under argon atmosphere, 2.14 g of 2,4-dihydroxybenzophenone, 1.94 g of potassium carbonate, and 100 mL of N,N-dimethylformamide were added sequentially to a three-necked flask, stirred for 0.5 h, and 3.88 g of chlorodibenzoylmethane was added. The temperature was raised to 70°C and the reaction was allowed to react for 5 h. The reaction solution was cooled to room temperature, poured into water, and the pH was adjusted to 7.5 with 1 mol / L dilute hydrochloric acid. The solution was extracted, washed, dried, and passed through a chromatographic column to obtain compound A; yield: 83.5%;

[0071] S2: 0.2 g of compound A, 0.141 g of Tween-80, 0.129 g of sodium dioctylsulfosuccinate, and 7.6 g of 3% polylysine solution were added to a beaker in sequence. The mixture was stirred at 10,000 rpm for 5 min. 20 g of 1% sodium carboxymethyl cellulose solution was added dropwise. The pH was adjusted to 6. The mixture was heated to 50°C and reacted for 1 h.

[0072] S3: Add glutaraldehyde solution to the system of step S2, adjust the pH to 6-8, place in ice water and cool to 0-5°C for reaction for 0.5-1h to obtain a reactant; centrifuge the reactant, remove the supernatant, filter, wash with water, and freeze-dry to obtain a UV absorber.

[0073] The specific preparation steps of the preparation method of chlorodibenzoylmethane of the present embodiment are as follows:

[0074] 2.24 g of dibenzoylmethane, 0.94 g of pyridine, and 150 mL of tetrahydrofuran were added sequentially to a three-necked flask, stirred at 65°C for 0.5 h, and 1.74 g of N-chlorosuccinimide was added. The temperature was raised to 80°C and refluxed for 1 h. The reaction solution was filtered, and the filtrate was subjected to rotary evaporation and chromatography to obtain chlorodibenzoylmethane; yield: 77.6%.

[0075] Example 4

[0076] The ultraviolet absorber of this embodiment is prepared by the following preparation method of the ultraviolet absorber.

[0077] The preparation method of a UV absorber of this embodiment has the following specific preparation steps:

[0078] S1: Under argon atmosphere, 2.14 g of 2,4-dihydroxybenzophenone, 1.94 g of potassium carbonate, and 100 mL of N,N-dimethylformamide were added sequentially to a three-necked flask, stirred for 0.5 h, and 4.13 g of chlorodibenzoylmethane was added. The temperature was raised to 70°C and the reaction was allowed to react for 5 h. The reaction solution was cooled to room temperature, poured into water, and the pH was adjusted to 7.5 with 1 mol / L dilute hydrochloric acid. The solution was extracted, washed, dried, and passed through a chromatographic column to obtain compound A; yield: 85.1%;

[0079] S2: 0.38 g of compound A, 0.125 g of Tween-80, 0.125 g of sodium dioctylsulfosuccinate, and 11 g of 3% polylysine solution were added to a beaker in sequence. The mixture was stirred at 10,000 rpm for 5 min, and 20 g of 4% sodium carboxymethylcellulose solution was added dropwise. The pH was adjusted to 5.5, and the mixture was heated to 50°C for reaction for 1.5 h.

[0080] S3: Add glutaraldehyde solution to the system of step S2, adjust the pH to 6-8, place in ice water and cool to 0-5°C for reaction for 0.5-1h to obtain a reactant; centrifuge the reactant, remove the supernatant, filter, wash with water, and freeze-dry to obtain a UV absorber.

[0081] The specific preparation steps of the preparation method of chlorodibenzoylmethane of the present embodiment are as follows:

[0082] 2.24 g of dibenzoylmethane, 0.91 g of pyridine, and 150 mL of tetrahydrofuran were added sequentially to a three-necked flask, stirred at 65°C for 0.5 h, and 1.47 g of N-chlorosuccinimide was added. The temperature was raised to 76°C and refluxed for 1.5 h. The reaction solution was filtered, and the filtrate was rotary evaporated and passed through a chromatographic column to obtain chlorodibenzoylmethane; yield: 78.3%.

[0083] Comparative Example 1

[0084] The difference from Example 1 is that the molar ratio of 2,4-dihydroxybenzophenone, potassium carbonate and chlorodibenzoylmethane in this comparative example is 1:3:2.5, and the rest is the same as Example 1.

[0085] Comparative Example 2

[0086] The difference from Example 1 is that the amount of compound A in this comparative example is 21% of the total mass of polylysine and sodium carboxymethyl cellulose, and the rest is the same as Example 1.

[0087] Comparative Example 3

[0088] The difference from Example 1 is that the amount of compound A used in this comparative example is 75% of the total mass of polylysine and sodium carboxymethyl cellulose, and the rest is the same as Example 1.

[0089] Comparative Example 4

[0090] The difference from Example 1 is that the mass ratio of polylysine to sodium carboxymethyl cellulose in this comparative example is 3.5:1, and the rest is the same as Example 1.

[0091] Comparative Example 5

[0092] The difference from Example 1 is that this comparative example uses an equal amount of 2,4-dihydroxybenzophenone instead of compound A, and the rest is the same as Example 1.

[0093] Comparative Example 6

[0094] The difference from Example 1 is that this comparative example does not carry out the preparation of step S2 and step S3, and directly uses compound A as the ultraviolet absorber. The rest is the same as Example 1.

[0095] Related tests

[0096] The ultraviolet absorbers prepared in Examples 1 to 4 and Comparative Examples 1 to 6 were added to the water-based saturated polyester resin coating in an amount of 1 wt %, respectively, and coated on steel plates, and baked to form 20 μm steel plate topcoat coatings. The ultraviolet accelerated aging test was carried out in accordance with GB / T 12754-2019 "Color Coated Steel Sheets and Steel Strips": the obtained steel plate topcoat coating was placed in an aging box, the ultraviolet lamp power was set to 300 W, the turntable speed was set to 10 r / min, and the temperature was set to 60°C. The aging performance level was determined according to the light source irradiation time, discoloration and gloss loss range. The test results are shown in Table 1.

[0097] Table 1 Test results

[0098]

[0099] By comparing Comparative Example 1 with Example 1, it can be seen that the ratio of 2,4-dihydroxybenzophenone, potassium carbonate and chlorodibenzoylmethane is adjusted in Comparative Example 1, and the performance of the ultraviolet absorber is not greatly affected, but the yield of the target product in Comparative Example 1 is 62.5%, and the by-products increase.

[0100] By comparing Comparative Examples 2 and 3 with Example 1, it can be seen that if the amount of Compound A is too small, the content of the effective ultraviolet absorber is low; if the amount of Compound A is too large, adhesion is easy to occur, resulting in agglomeration; both of these affect the aging resistance of the product.

[0101] From the comparison between Comparative Example 4 and Example 1, it can be seen that adjusting the mass ratio of polylysine to sodium carboxymethyl cellulose will lead to an imbalance in the charges carried by the two, incomplete reaction, and irregular shape of the final ultraviolet absorber, which affects the ultraviolet absorption performance.

[0102] From the comparison between Comparative Example 5 and Example 1, it can be seen that 2,4-dihydroxybenzophenone mainly absorbs ultraviolet rays in the UVB band. Therefore, the aging level (UVA) of Comparative Example 5 is weaker than the aging level (UVB), which proves that the compound A prepared by the present invention has good absorption of ultraviolet light in both UVA and UVB bands.

[0103] By comparing Comparative Example 6 with Example 1, it can be seen that the coating of Compound A in the present application can slowly release Compound A, which can avoid the problem of premature failure of the anti-aging effect caused by the rapid action of Compound A alone; therefore, Example 1 can last longer under ultraviolet light than Comparative Example 6, and the product with the addition of Example 1 has good aging resistance.

[0104] The above is an exemplary description of the present invention. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by other skilled in the art without expending creative labor shall fall within the scope of protection of the present invention.

Claims

1. A method for preparing an ultraviolet absorber, characterized in that: The steps include: S1: In an oxygen-free atmosphere, 2,4-dihydroxybenzophenone, potassium carbonate, and N,N-dimethylformamide were mixed uniformly, chlorodibenzoylmethane was added, and the temperature was raised to react; the reaction solution was cooled to room temperature, poured into water, the pH was adjusted to 7-8, extracted, washed, dried, and passed through a chromatographic column to obtain compound A; S2: Compound A, an emulsifier, and a polylysine solution are mixed evenly, sodium carboxymethyl cellulose solution is added dropwise, and the pH is adjusted to 5-6 before reacting; S3: adding glutaraldehyde solution to the system of step S2, adjusting the pH to 6-8 and reacting to obtain a reactant; centrifuging the reactant, removing the supernatant, filtering, washing with water, and drying to obtain an ultraviolet absorber; Wherein, the structure of compound A is shown in formula (1): ; Formula (1); In step S1, the molar ratio of 2,4-dihydroxybenzophenone, potassium carbonate, and chlorodibenzoylmethane is 1:(1.3-1.5):(1.2-1.6); the preparation method of chlorodibenzoylmethane comprises the following steps: uniformly mixing dibenzoylmethane, pyridine, tetrahydrofuran, and N-chlorosuccinimide, heating and refluxing the mixture; filtering the reaction solution, subjecting the filtrate to rotary evaporation, and passing the filtrate through a chromatographic column to obtain chlorodibenzoylmethane; In step S2, the mass ratio of polylysine to sodium carboxymethyl cellulose is (1.05-1.15):1; the amount of compound A used is 42%-48% of the total mass of polylysine and sodium carboxymethyl cellulose.

2. The method for preparing an ultraviolet absorber according to claim 1, wherein: In step S1, the temperature of the temperature-raising reaction is 65-75° C., and the reaction time is 3-5 hours.

3. The method for preparing an ultraviolet absorber according to claim 1, wherein: In the step S2, the mass fraction of the polylysine solution is 1%-4%, and the mass fraction of the sodium hydroxymethyl cellulose solution is 1%-4%.

4. The method for preparing an ultraviolet absorber according to claim 1, wherein: In step S2, the reaction temperature is 45-55° C., and the reaction time is 1-1.5 h.

5. The method for preparing an ultraviolet absorber according to claim 1, wherein: In step S2, the emulsifier is composed of Tween-80 and dioctyl sodium sulfosuccinate in a mass ratio of (1-1.2):1; the amount of the emulsifier is 0.5%-1% of the total mass of the polylysine solution and the sodium carboxymethylcellulose solution.

6. The method for preparing an ultraviolet absorber according to claim 1, wherein: In step S3, the reaction temperature is 0-5° C., and the reaction time is 0.5-1 h.

7. The method for preparing an ultraviolet absorber according to claim 1, wherein: The molar ratio of dibenzoylmethane, pyridine and N-chlorosuccinimide is 1:(1.05-1.2):(1.1-1.4); the temperature of the reflux is 75-80° C., and the reflux time is 1-3 hours.

8. An ultraviolet absorber prepared by the method for preparing the ultraviolet absorber according to any one of claims 1 to 7.

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