Ultraviolet light absorber and preparation method thereof

Abstract

The invention belongs to the technical field of ultraviolet light absorbers, and particularly relates to an ultraviolet light absorber and a preparation method thereof.The preparation method comprises the following steps that S1, in an oxygen-free atmosphere, 2, 4-dihydroxybenzophenone, potassium carbonate and N, N-dimethylformamide are evenly mixed, chlorodibenzoylmethane is added, and heating reaction is conducted; cooling the reaction liquid to room temperature, pouring into water, adjusting the pH value to 7-8, extracting, washing, drying, and passing through a chromatographic column to obtain a compound A; s2, uniformly mixing a compound A, an emulsifier and a polylysine solution, dropwise adding a sodium carboxymethyl cellulose solution, adjusting the pH value to 5-6, and carrying out a reaction; s3, adding a glutaraldehyde solution into the system in the step S2, adjusting the pH value to 6-8, and carrying out a reaction to obtain a reactant; and centrifuging the reactant, removing the supernate, carrying out suction filtration, washing with water, and drying to obtain the ultraviolet light absorber. The ultraviolet light absorber provided by the invention has excellent absorption performance.

Description

Technical Field

[0001] The present 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 can strongly and selectively absorb high-energy ultraviolet light and convert the energy, releasing or consuming the energy in the form of heat or harmless low radiation. They are commonly used in industries such as polymer materials, textile processing and cosmetics. Common ultraviolet absorbers mainly include benzophenone derivatives, benzotriazole derivatives, hindered amines, substituted acrylonitriles, triazines, etc.

[0004] The Chinese patent application document with the application publication number of CN107163206A discloses the preparation of a polymer benzophenone compound and its application in anti-light pollution plastics. This application document uses benzophenone and excessive sodium metal to generate a benzophenone disodium initiator, reacts with toluene-2,4-diisocyanate under the action of a catalyst, and then reacts with 4,4'-dihydroxybenzophenone under the reaction conditions of ethyl acetate reflux to prepare a polymer benzophenone compound. Although this application document modifies benzophenone, the prepared polymer benzophenone compound mainly relies on the synergistic effect of the carbonyl group and the ortho-hydroxy group to stabilize the excited state through intramolecular hydrogen bonding, and the absorption peak is more concentrated in the UVB band (280 - 320 nm), and the ability to absorb the UVA band is poor. Summary of the Invention

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

[0006] To achieve the purpose of the present invention, the following technical solutions are adopted in the present invention: In the first aspect, the present invention provides a preparation method of an ultraviolet absorber, including the following steps: S1: Under an anaerobic atmosphere, uniformly mix 2,4-dihydroxybenzophenone, potassium carbonate and N,N-dimethylformamide, add chlorodibenzoylmethane, and raise the temperature for reaction; cool the reaction solution to room temperature, pour it into water, adjust the pH to 7 - 8, extract, wash, dry, and pass through a chromatographic column to obtain compound A; S2: Uniformly mix compound A, an emulsifier and a polylysine solution, dropwise add a sodium carboxymethylcellulose solution, and react after adjusting the pH to 5 - 6; S3: Add glutaraldehyde solution to the system in step S2, adjust the pH to 6 - 8 and then carry out the reaction to obtain a reaction product; centrifuge the reaction product, remove the supernatant, carry out suction filtration, wash with water, and dry to obtain the ultraviolet absorber.

[0007] The reaction process of compound A is shown in Reaction Scheme Ⅰ:

[0008] Reaction Scheme Ⅰ Preferably, in step S1, the molar ratio of 2,4 - dihydroxybenzophenone, potassium carbonate to chlorodibenzoylmethane is 1∶(1.3 - 1.5)∶(1.2 - 1.6).

[0009] By adopting the above technical solution, the dosage ratio of 2,4 - dihydroxybenzophenone and chlorodibenzoylmethane is adjusted to improve the reaction conversion rate and reduce the generation of by - products.

[0010] Preferably, in step S1, the temperature for the temperature - rising reaction is 65 - 75°C and the reaction time is 3 - 5 h.

[0011] Preferably, in step S2, the mass fraction of the polylysine solution is 1% - 4%, and the mass fraction of the sodium carboxymethylcellulose solution is 1% - 4%; the mass ratio of polylysine to sodium carboxymethylcellulose is (1.05 - 1.15)∶1; the dosage of compound A is 42% - 48% of the total mass of polylysine and sodium carboxymethylcellulose.

[0012] By adopting the above technical solution, the ultraviolet absorber prepared from polylysine and sodium carboxymethylcellulose in this ratio is spherical and uniformly coated. The morphology of the ultraviolet absorber formed by compound A at this dosage is good, the particles are plump and round. Too high content is likely to lead to low coating rate, and too low content is likely to affect the absorption performance of the ultraviolet absorber.

[0013] Preferably, in step S2, the reaction temperature is 45 - 55°C and the reaction time is 1 - 1.5 h.

[0014] Preferably, in step S2, the emulsifier is composed of Tween - 80 and sodium dioctyl sulfosuccinate in a mass ratio of (1 - 1.2)∶1; the dosage of the emulsifier is 0.5% - 1% of the total mass of the polylysine solution and the sodium carboxymethylcellulose solution.

[0015] By adopting the above technical solution, the emulsifier is obtained by compounding two components, Tween - 80 and sodium dioctyl sulfosuccinate. By adjusting the ratio of the two components, the synergistic effect of non - ionic and anionic surfactants is optimized to improve the stability of the system.

[0016] Preferably, in step S3, the reaction temperature is 0-5°C and the reaction time is 0.5-1 h.

[0017] Preferably, the preparation method of the chlorodibenzoylmethane comprises the following steps: Mix dibenzoylmethane, pyridine, tetrahydrofuran and N-chlorosuccinimide evenly, heat up to reflux for reaction; filter the reaction solution, rotary evaporate the filtrate, and obtain chlorodibenzoylmethane by passing through a chromatographic column.

[0018] The reaction process of chlorodibenzoylmethane is shown in Reaction Formula II:

[0019] Reaction Formula II Preferably, the molar ratio of dibenzoylmethane, pyridine and N-chlorosuccinimide is 1:(1.05-1.2):(1.1-1.4); the temperature of the heating reflux is 75-80°C and the reflux time is 1-3 h.

[0020] By adopting the above technical scheme, under this ratio, the main product is monochlorodibenzoylmethane. A slight excess of N-chlorosuccinimide can avoid the residue of unreacted dibenzoylmethane. Too much N-chlorosuccinimide is likely to generate polychlorinated products, reducing the yield of the target product; the addition of pyridine can maintain an alkaline environment and promote the reaction.

[0021] In the second aspect, the present invention provides an ultraviolet absorber prepared by the above preparation method of the ultraviolet absorber.

[0022] In summary, the beneficial effects of the present invention are as follows: (1) The present invention modifies 2,4-dihydroxybenzophenone, introduces a dibenzoylmethane structure that can absorb the UVA band into the molecular structure of 2,4-dihydroxybenzophenone which mainly absorbs the UVB band. The β-diketone skeleton in the dibenzoylmethane structure and the benzene ring conjugate system can effectively absorb the UVA band, and the prepared compound A can absorb both UVA and UVB; the molecular structure of 2,4-dihydroxybenzophenone and the dibenzoylmethane structure are connected by an ether bond, increasing the conjugation range and reducing the photodegradation rate; (2) The present invention coats compound A to form an outer shell layer, isolating the direct contact between compound A and the external environment and delaying its photodegradation; at the same time, the outer shell layer can release compound A in a slow and continuous manner, avoiding the problem that the traditional ultraviolet absorber fails to provide protection prematurely due to rapid release and rapid action; (3) The ultraviolet absorber provided by the present invention has excellent absorption performance in the wavelength range of 280-380 nm, indicating that the ultraviolet absorber provided by the present invention can absorb both UVA and UVB. Description of the Drawings

[0023] Figure 1 SEM diagram of the ultraviolet absorber of the present invention; Figure 2 Ultraviolet absorption spectrum of the ultraviolet absorber of the present invention; Figure 3 Infrared spectrum of compound A prepared according to the present invention; Figure 4 1H NMR spectrum of compound A prepared according to the present invention; Figure 5 1H NMR spectrum of chlorodibenzoylmethane prepared according to the present invention. Detailed Description of the Invention

[0024] The technical solution of the present invention will be elaborated in detail below with reference to several representative embodiments of the present invention.

[0025] 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 can all be obtained from commercial sources.

[0026] Example 1 An ultraviolet absorber of this example is prepared by the following preparation method of the ultraviolet absorber.

[0027] A preparation method of an ultraviolet absorber of this example is as follows: 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 are successively added to a three-necked flask, stirred for 0.5 h, 3.36 g of chlorodibenzoylmethane is added, and the temperature is raised to 75 °C and reacted for 4 h; the reaction solution is cooled to room temperature, poured into water, and the pH is adjusted to 7 with 1 mol / L dilute hydrochloric acid, extracted, washed, dried, and passed through a chromatographic column to obtain compound A; yield: 86.6%; S2: 0.36 g of compound A, 0.16 g of Tween-80, 0.16 g of dioctyl sulfosuccinate and 44 g of a 1% polylysine solution are successively added to a beaker, stirred at a high speed of 10000 r / min for 5 min, 20 g of a 2% sodium carboxymethylcellulose solution is added dropwise, the pH is adjusted to 5, and the temperature is raised to 48 °C and reacted for 1.3 h; S3: Glutaraldehyde solution is added to the system of step S2, the pH is adjusted to 7, and then cooled to 2 °C in ice water and reacted for 0.5 h to obtain a reactant; the reactant is centrifuged, the supernatant is removed, filtered, washed with water, and freeze-dried to obtain an ultraviolet absorber. The SEM diagram of the ultraviolet absorber is shown inFigure 1 , the ultraviolet absorption spectrum of the ultraviolet absorber is shown in Figure 2 .

[0028] It can be seen from Figure 1 that the ultraviolet absorber presents an approximately spherical appearance, with a particle size between 0.5 - 1 μm, relatively uniform dispersion, and no obvious agglomeration phenomenon.

[0029] It can be seen from Figure 2 that the ultraviolet absorber has maximum absorption peaks at wavelengths of 286 nm and 355 nm, and has significant absorption effects at wavelengths of 280 - 380 nm.

[0030] The infrared spectrum of compound A is shown in Figure 3 .

[0031] It can be seen from Figure 3 that the absorption peak at 3002 cm -1 is the stretching vibration absorption peak of the hydroxyl O - H on compound A, the absorption peak at 1684 cm -1 is the stretching vibration absorption peak of the benzoyl carbonyl C = O on compound A, the absorption peak at 1625 cm -1 is the stretching vibration absorption peak of the carbonyl C = O in the β - diketone carbonyl on compound A, the absorption peaks at 1582 cm -1 , 1500 cm -1 etc. are the stretching vibrations of the benzene ring skeleton on compound A, the absorption peaks at 751 cm -1 , 701 cm -1 etc. are the characteristic absorptions of the benzene ring C - H on compound A, and the absorption peak at 1221 cm -1 is the stretching vibration of the aromatic ether bond C - O - C on compound A.

[0032] The nuclear magnetic resonance hydrogen spectrum of compound A is shown in Figure 4 .

[0033] It can be seen from Figure 4 that δ6.52 - 6.59 ppm (benzene ring H, 2H, m), δ6.70 ppm (-CH, 1H, s), δ7.51 - 8.00 ppm (benzene ring H, 16H, m), δ12.43 ppm (-OH, 1H, s).

[0034] The nuclear magnetic resonance hydrogen spectrum combined with the infrared spectrum proves that the synthesized product is compound A.

[0035] The specific preparation steps of the preparation method of chlorodibenzoylmethane in this example are as follows: 2.24 g of dibenzoylmethane, 0.87 g of pyridine and 150 mL of tetrahydrofuran were successively added to a three-necked flask, stirred at 65 °C for 0.5 h, 1.6 g of N-chlorosuccinimide was added, and the temperature was raised to 75 °C for reflux reaction for 2 h; the reaction solution was filtered, the filtrate was rotary evaporated, and passed through a chromatographic column to obtain chlorodibenzoylmethane; yield: 79.5%.

[0036] The nuclear magnetic resonance hydrogen spectrum of chlorodibenzoylmethane is shown in Figure 5 .

[0037] Example 2 A UV absorber of this example was prepared by the following preparation method of the UV absorber.

[0038] The preparation method of a UV absorber of this example is as follows: S1: Under an argon atmosphere, 2.14 g of 2,4-dihydroxybenzophenone, 2.07 g of potassium carbonate and 100 mL of N,N-dimethylformamide were successively added to a three-necked flask, stirred for 0.5 h, 3.2 g of chlorodibenzoylmethane was added, and the temperature was raised to 65 °C for reaction 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, extracted, washed, dried, and passed through a chromatographic column to obtain compound A; yield: 84.2%; S2: 0.54 g of compound A, 0.169 g of Tween-80, 0.141 g of dioctyl sulfosuccinate and 31.5 g of a 2% polylysine solution were successively added to a beaker, stirred at a high speed of 10000 r / min for 5 min, 20 g of a 3% sodium carboxymethylcellulose solution was added dropwise, the pH was adjusted to 5.5, and the temperature was raised to 45 °C for reaction for 1.2 h; S3: Glutaraldehyde solution was added to the system of step S2, the pH was adjusted to 8, and then cooled to 0 °C in ice water for reaction for 1 h to obtain a reactant; the reactant was centrifuged, the supernatant was removed, filtered by suction, washed with water, and freeze-dried to obtain a UV absorber.

[0039] The preparation method of chlorodibenzoylmethane in this example is as follows: 2.24 g of dibenzoylmethane, 0.84 g of pyridine and 150 mL of tetrahydrofuran were successively added to a three-necked flask, stirred at 65 °C for 0.5 h, 1.86 g of N-chlorosuccinimide was added, and the temperature was raised to 77 °C for reflux reaction for 3 h; the reaction solution was filtered, the filtrate was rotary evaporated, and passed through a chromatographic column to obtain chlorodibenzoylmethane; yield: 77.8%.

[0040] Example 3 A UV absorber of this example was prepared by the following preparation method of the UV absorber.

[0041] A preparation method of an ultraviolet absorber according to this embodiment is as follows: S1: Under an argon atmosphere, 2.14 g of 2,4-dihydroxybenzophenone, 1.94 g of potassium carbonate and 100 mL of N,N-dimethylformamide are successively added to a three-necked flask, stirred for 0.5 h, 3.88 g of chlorodibenzoyl methane is added, and the temperature is raised to 70 °C for reaction for 5 h; the reaction solution is cooled to room temperature, poured into water, and the pH is adjusted to 7.5 with 1 mol / L dilute hydrochloric acid, extracted, washed, dried, and passed through a chromatographic column to obtain compound A; yield: 83.5%; S2: 0.2 g of compound A, 0.141 g of Tween-80, 0.129 g of dioctyl sulfosuccinate and 7.6 g of a 3% polylysine solution are successively added to a beaker, stirred at a high speed of 10000 r / min for 5 min, 20 g of a 1% sodium carboxymethylcellulose solution is added dropwise, the pH is adjusted to 6, and the temperature is raised to 50 °C for reaction for 1 h; S3: Glutaraldehyde solution is added to the system in step S2, after adjusting the pH to 6 - 8, it is placed in ice water and cooled to 0 - 5 °C for reaction for 0.5 - 1 h to obtain a reactant; the reactant is centrifuged, the supernatant is removed, filtered by suction, washed with water, and freeze-dried to obtain the ultraviolet absorber.

[0042] The preparation method of chlorodibenzoyl methane in this embodiment is as follows: 2.24 g of dibenzoyl methane, 0.94 g of pyridine and 150 mL of tetrahydrofuran are successively added to a three-necked flask, stirred at 65 °C for 0.5 h, 1.74 g of N-chlorosuccinimide is added, and the temperature is raised to 80 °C for reflux reaction for 1 h; the reaction solution is filtered, the filtrate is rotary evaporated and passed through a chromatographic column to obtain chlorodibenzoyl methane; yield: 77.6%.

[0043] Example 4 An ultraviolet absorber according to this embodiment is prepared by the following preparation method of the ultraviolet absorber.

[0044] A preparation method of an ultraviolet absorber according to this embodiment is as follows: S1: Under an argon atmosphere, 2.14 g of 2,4-dihydroxybenzophenone, 1.94 g of potassium carbonate and 100 mL of N,N-dimethylformamide are successively added to a three-necked flask, stirred for 0.5 h, 4.13 g of chlorodibenzoyl methane is added, and the temperature is raised to 70 °C for reaction for 5 h; the reaction solution is cooled to room temperature, poured into water, and the pH is adjusted to 7.5 with 1 mol / L dilute hydrochloric acid, extracted, washed, dried, and passed through a chromatographic column to obtain compound A; yield: 85.1%; S2: Add 0.38 g of compound A, 0.125 g of Tween-80, 0.125 g of dioctyl sodium sulfosuccinate and 11 g of 3% polylysine solution into a beaker in sequence, stir at a high speed of 10,000 r / min for 5 min, add 20 g of 4% sodium carboxymethylcellulose solution dropwise, adjust the pH to 5.5, and raise the temperature to 50 °C for reaction for 1.5 h; S3: Add glutaraldehyde solution to the system of step S2, adjust the pH to 6 - 8, then place it in ice water to cool down to 0 - 5 °C for reaction for 0.5 - 1 h to obtain a reactant; centrifuge the reactant, remove the supernatant, carry out suction filtration, wash with water, and freeze-dry to obtain an ultraviolet absorber.

[0045] The specific preparation steps of the preparation method of chlorodibenzoylmethane in this example are as follows: Add 2.24 g of dibenzoylmethane, 0.91 g of pyridine and 150 mL of tetrahydrofuran into a three-necked flask in sequence, stir at 65 °C for 0.5 h, add 1.47 g of N-chlorosuccinimide, raise the temperature to 76 °C for reflux reaction for 1.5 h; filter the reaction solution, and obtain chlorodibenzoylmethane after rotary evaporation of the filtrate and passing through a chromatographic column; yield: 78.3%.

[0046] Comparative Example 1 The difference from Example 1 is that in this comparative example, the molar ratio of 2,4-dihydroxybenzophenone, potassium carbonate and chlorodibenzoylmethane is 1∶3∶2.5, and the rest are the same as in Example 1.

[0047] Comparative Example 2 The difference from Example 1 is that in this comparative example, the dosage of compound A is 21% of the total mass of polylysine and sodium carboxymethylcellulose, and the rest are the same as in Example 1.

[0048] Comparative Example 3 The difference from Example 1 is that in this comparative example, the dosage of compound A is 75% of the total mass of polylysine and sodium carboxymethylcellulose, and the rest are the same as in Example 1.

[0049] Comparative Example 4 The difference from Example 1 is that in this comparative example, the mass ratio of polylysine to sodium carboxymethylcellulose is 3.5∶1, and the rest are the same as in Example 1.

[0050] Comparative Example 5 The difference from Example 1 is that in this comparative example, an equal amount of 2,4-dihydroxybenzophenone is used to replace compound A, and the rest are the same as in Example 1.

[0051] Comparative Example 6 The difference from Example 1 is that in this comparative example, the preparations of Steps S2 and S3 are not carried out, and Compound A is directly used as the ultraviolet absorber, and the rest are the same as in Example 1.

[0052] Related tests The ultraviolet absorbers prepared in Examples 1 - 4 and Comparative Examples 1 - 6 were respectively added to the waterborne saturated polyester resin coating at an addition amount of 1 wt%, and were respectively coated on steel plates, and baked to form a 20 - μm steel plate topcoat coating. The ultraviolet accelerated aging test was carried out in accordance with GB / T 12754 - 2019 "Color Coated Steel Sheets and Strips": The obtained steel plate topcoat coatings were placed in an aging chamber, the power of the ultraviolet lamp was set to 300 W, the rotation speed of the turntable was 10 r / min, and the temperature was 60 °C. According to the light source irradiation duration, color change, and loss of gloss range, the aging performance level was determined, and the test results are shown in Table 1.

[0053] Table 1 Test results

[0054] It can be seen from the comparison between Comparative Example 1 and Example 1 that Comparative Example 1 adjusted the ratio of 2,4 - dihydroxybenzophenone, potassium carbonate, and chlorodibenzoylmethane, and there was not much impact on the performance of the ultraviolet absorber, but the yield of the target product in Comparative Example 1 was 62.5%, and the by - products increased.

[0055] It can be seen from the comparison between Comparative Examples 2 and 3 and Example 1 that when the amount of Compound A is too small, the content of the available ultraviolet absorber is low; when the amount of Compound A is too large, it is easy to stick and cause agglomeration phenomena; both affect the aging resistance performance of the product.

[0056] It can be seen from the comparison between Comparative Example 4 and Example 1 that adjusting the mass ratio of polylysine and sodium carboxymethylcellulose will cause the charges carried by the two to be unbalanced, the reaction is incomplete, resulting in an irregular shape of the final ultraviolet absorber and affecting the ultraviolet absorption performance.

[0057] It can be seen from the comparison between Comparative Example 5 and Example 1 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), proving that the Compound A prepared by the present invention has good absorption of ultraviolet light in both UVA and UVB bands.

[0058] It can be seen from the comparison between Comparative Example 6 and Example 1 that coating Compound A in the present application can slowly release Compound A, which can avoid the problem of premature failure of the aging resistance effect caused by the rapid action of using Compound A alone; therefore, Example 1 can last longer under ultraviolet light than Comparative Example 6, and the product added with Example 1 has good aging resistance performance.

[0059] The above has made 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 equivalent replacement that can be made by those skilled in the art without creative labor shall fall within the protection scope of the present invention.

Claims

1. A preparation method of an ultraviolet absorber, characterized in that, It includes the following steps: S1: Under an anaerobic atmosphere, mix 2,4-dihydroxybenzophenone, potassium carbonate and N,N-dimethylformamide evenly, add chlorodibenzoylmethane, and raise the temperature for reaction; cool the reaction solution to room temperature, pour it into water, adjust the pH to 7-8, extract, wash, dry, and pass through a chromatographic column to obtain compound A; S2: Mix compound A, an emulsifier and a polylysine solution evenly, dropwise add a sodium carboxymethylcellulose solution, and react after adjusting the pH to 5-6; S3: Add a glutaraldehyde solution to the system in step S2, react after adjusting the pH to 6-8 to obtain a reactant; centrifuge the reactant, remove the supernatant, filter by suction, wash with water, and dry to obtain an ultraviolet absorber; Among them, the structure of compound A is shown in formula (1): ; Formula (1).

2. The preparation method of an ultraviolet absorber according to claim 1, characterized in that, In the said step S1, the molar ratio of 2,4-dihydroxybenzophenone, potassium carbonate and chlorodibenzoylmethane is 1∶(1.3-1.5)∶(1.2-1.6).

3. The preparation method of an ultraviolet absorber according to claim 1, characterized in that, In the said step S1, the temperature for the temperature-raising reaction is 65-75°C, and the reaction time is 3-5 h.

4. The preparation method of an ultraviolet absorber according to claim 1, characterized in that, In the said step S2, the mass fraction of the polylysine solution is 1%-4%, and the mass fraction of the sodium carboxymethylcellulose solution is 1%-4%; the mass ratio of polylysine to sodium carboxymethylcellulose is (1.05-1.15)∶1; the dosage of compound A is 42%-48% of the total mass of polylysine and sodium carboxymethylcellulose.

5. The preparation method of an ultraviolet absorber according to claim 1, characterized in that, In the said step S2, the reaction temperature is 45-55°C, and the reaction time is 1-1.5 h.

6. The preparation method of an ultraviolet absorber according to claim 1, wherein, In the said step S2, the emulsifier is composed of Tween-80 and sodium dioctyl sulfosuccinate according to the mass ratio of (1-1.2)∶1; the dosage of the emulsifier is 0.5%-1% of the total mass of the polylysine solution and the sodium carboxymethylcellulose solution.

7. The preparation method of an ultraviolet absorber according to claim 1, characterized in that, In the said step S3, the reaction temperature is 0-5°C, and the reaction time is 0.5-1 h.

8. The preparation method of an ultraviolet absorber according to claim 1, characterized in that, In the said step S1, the preparation method of chlorodibenzoylmethane includes the following steps: Mix dibenzoylmethane, pyridine, tetrahydrofuran and N-chlorosuccinimide evenly, raise the temperature for reflux reaction; filter the reaction solution, and obtain chlorodibenzoylmethane after rotary evaporation of the filtrate and passing through a chromatographic column.

9. The preparation method of an ultraviolet absorber according to claim 8, characterized in that, The molar ratio of dibenzoylmethane, pyridine and N-chlorosuccinimide is 1∶(1.05-1.2)∶(1.1-1.4); the temperature for the temperature-raising reflux is 75-80°C, and the reflux time is 1-3 h.

10. An ultraviolet absorber prepared by the preparation method of the ultraviolet absorber according to any one of claims 1-9.

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