An ultraviolet blocking film, its preparation method and application

Abstract

This invention discloses an ultraviolet (UV) blocking film, its preparation method, and its application. The UV blocking film of this invention is made from the following raw materials in weight percentages: polyvinyl alcohol: 20%–40%; sodium carboxymethyl cellulose: 20%–30%; carbon quantum dots: 5%–10%; and water chestnut starch: 30%–45%. The preparation method of the UV blocking film of this invention includes the following steps: 1) preparing a polyvinyl alcohol solution, a sodium carboxymethyl cellulose solution, a carbon quantum dot dispersion, and a water chestnut starch solution; 2) preparing a gelatinized mixed slurry; and 3) casting the gelatinized mixed slurry into a film and then drying it to obtain the UV blocking film. The UV blocking film of this invention has advantages such as excellent UV blocking performance, good moisture barrier performance, high mechanical strength, high transparency, environmental friendliness, and biodegradability. It can be used as a packaging material, and its preparation method is simple and has low production cost, making it suitable for large-scale industrial production and application.

Description

Technical Field

[0001] This invention relates to the field of packaging materials technology, specifically to an ultraviolet blocking film, its preparation method, and its application. Background Technology

[0002] Food packaging is a crucial component of food products, effectively protecting them from biological, chemical, and physical damage. However, existing food packaging is susceptible to degradation when exposed to ultraviolet (UV) radiation from sunlight. The resulting degradation products directly contaminate the food, ultimately harming human health. Furthermore, UV radiation can decompose many nutrients in food, hindering storage and transportation. In addition, existing food packaging generally offers poor moisture barrier properties, which can also contaminate and damage food. Therefore, existing packaging materials are fundamentally inadequate to fully meet practical application requirements.

[0003] Therefore, it is of great significance to develop a food packaging material with excellent UV blocking performance, good moisture blocking performance, and environmental friendliness. Summary of the Invention

[0004] The purpose of this invention is to provide an ultraviolet blocking film, its preparation method, and its application.

[0005] The technical solution adopted in this invention is:

[0006] An ultraviolet-blocking film, which is made from the following raw materials by weight percentage:

[0007] Polyvinyl alcohol: 20%–40%;

[0008] Sodium carboxymethyl cellulose: 20%–30%;

[0009] Carbon quantum dots: 5%–10%;

[0010] Water chestnut starch: 30%–45%.

[0011] Preferably, the number average molecular weight of the polyvinyl alcohol is 250,000 to 300,000.

[0012] Preferably, the carbon quantum dots have a particle size of 5 nm to 10 nm.

[0013] Preferably, the carbon quantum dots are made from waste leather. Making carbon quantum dots from waste leather not only reduces environmental pollution caused by waste leather but also achieves the resource utilization of waste leather.

[0014] More preferably, the carbon quantum dots are prepared by a method comprising the following steps: removing chromium from waste leather, then adding it together with calcium oxide (CaO) to water for soaking to obtain a collagen extract, then subjecting the collagen extract to a microwave-assisted hydrothermal reaction, and finally freeze-drying to obtain carbon quantum dots.

[0015] Preferably, the specific operation of the chromium removal treatment is as follows: the waste leather is soaked in a sodium carbonate solution for soaking treatment, and then taken out and rinsed with water.

[0016] Preferably, the soaking treatment is carried out at a temperature of 70℃ to 90℃ for a treatment time of 20h to 30h.

[0017] Preferably, the weight ratio of the waste leather to calcium oxide is 1:0.1 to 0.4.

[0018] Preferably, the impregnation treatment is carried out at a temperature of 50℃ to 70℃ for a treatment time of 3h to 10h.

[0019] Preferably, the microwave-assisted hydrothermal reaction is carried out under conditions of microwave power of 500W to 1000W, temperature of 170℃ to 210℃, and reaction time of 40min to 90min.

[0020] Preferably, the particle size of the water chestnut starch is ≤50μm.

[0021] Preferably, the areal density of the ultraviolet blocking film is 13 g / m³. 2 ~20g / m 2 .

[0022] A method for preparing an ultraviolet blocking film as described above includes the following steps:

[0023] 1) Polyvinyl alcohol, sodium carboxymethyl cellulose, carbon quantum dots and water chestnut starch were dissolved / dispersed in water to prepare polyvinyl alcohol solution, sodium carboxymethyl cellulose solution, carbon quantum dot dispersion and water chestnut starch solution, respectively;

[0024] 2) Mix polyvinyl alcohol solution, sodium carboxymethyl cellulose solution, carbon quantum dot dispersion and water chestnut starch solution evenly, and then heat to carry out gelatinization reaction to obtain gelatinized mixed slurry;

[0025] 3) Cast the gelatinized slurry into a film and then dry it to obtain an ultraviolet blocking film.

[0026] Preferably, the polyvinyl alcohol solution in step 1) has a mass fraction of 4% to 8%.

[0027] Preferably, the sodium carboxymethyl cellulose solution in step 1) has a mass fraction of 5% to 6%.

[0028] Preferably, the concentration of the carbon quantum dot dispersion in step 1) is 0.005 g / mL to 0.01 g / mL.

[0029] Preferably, the carbon quantum dots in step 1) are dispersed by stirring, and the stirring is carried out at a temperature of 25℃~35℃ and a stirring speed of 350r / min~450r / min for 2h~3h.

[0030] Preferably, the mass fraction of the water chestnut starch solution in step 1) is 8% to 10%.

[0031] Preferably, the water chestnut starch in step 1) is dissolved by ultrasonic dispersion, with an ultrasonic power of 300W to 500W, a frequency of 15kHz to 25kHz, and an ultrasonic dispersion time of 10min to 15min.

[0032] Preferably, the gelatinization reaction in step 2) is carried out at a temperature of 80℃~85℃ for a reaction time of 10min~15min.

[0033] Preferably, the drying in step 3) is carried out at a temperature of 30℃~40℃ and a relative humidity of 35%~45%, and the drying time is 48h~72h.

[0034] A food packaging material comprising the aforementioned ultraviolet-blocking film.

[0035] The beneficial effects of the present invention are: the ultraviolet blocking film of the present invention has the advantages of excellent ultraviolet blocking performance, good moisture blocking performance, high mechanical strength, high transparency, green environmental protection, and biodegradability. It can be used as a packaging material, and its preparation method is simple and the production cost is low, making it suitable for large-scale industrial production and application.

[0036] Specifically:

[0037] 1) The ultraviolet blocking film of the present invention contains carbon quantum dots, which are rich in functional groups such as amino, hydroxyl, and carboxyl groups. They have the characteristics of low toxicity and good biocompatibility, and can convert ultraviolet rays that pass through the film into fluorescence, thereby giving the film excellent ultraviolet blocking performance (when carbon quantum dots are excited by direct irradiation from an external light source, they will undergo photon energy level transitions inside, thereby converting ultraviolet rays into fluorescence. Moreover, the fluorescence intensity of carbon quantum dots can remain stable after long-term ultraviolet irradiation, and they have strong photostability, making them suitable for preparing biodegradable, sustainable, green and naturally sourced ultraviolet protection films).

[0038] 2) The ultraviolet blocking film of the present invention contains natural polymer material water chestnut starch (also known as "water chestnut starch"), which has good water absorption and film-forming properties. Water chestnut starch molecules interact with water molecules through hydrogen bonds and then form a tight structure through gelatinization, thereby preventing further water penetration. It can absorb moisture in the packaging space while keeping moisture from passing through the film. This water-absorbing but waterproof property allows the film to keep the inside of the packaging dry while effectively preventing the intrusion of external moisture, thereby extending the shelf life of the product inside the packaging.

[0039] 3) The ultraviolet blocking film of the present invention has the advantages of excellent ultraviolet blocking performance, good moisture blocking performance, high mechanical strength, high transparency, green environmental protection and biodegradability. It can be applied in the food packaging field. Moreover, its preparation method is simple, safe and environmentally friendly, and has low production cost, making it suitable for large-scale industrial production and application. Attached Figure Description

[0040] Figure 1 The images show the appearance of the ultraviolet blocking films in Examples 1-4 and the film in Comparative Example 1.

[0041] Figure 2 This is an image of the film in Comparative Example 2.

[0042] Figure 3 The graph shows the UV blocking performance test results of the UV blocking films in Examples 1-4 and the film in Comparative Example 1.

[0043] Figure 4 The graph shows the water vapor transmission rate test results of the ultraviolet blocking films in Examples 1-4 and the film in Comparative Example 2.

[0044] Figure 5 The graph shows the water content and water solubility test results of the ultraviolet blocking films in Examples 1-4 and the film in Comparative Example 2. Detailed Implementation

[0045] The present invention will be further explained and described below with reference to specific embodiments.

[0046] The preparation methods of carbon quantum dots in Examples 1-4 and Comparative Example 2 are as follows: 5g of waste leather was chopped and soaked in a sodium carbonate solution with a pH of 9.5 at 80°C for 24h (to remove chromium). After filtration, the filtered solid was washed with deionized water and then added to 120g of deionized water, along with 0.8g of CaO. The mixture was stirred at 60°C for 5h to extract collagen extract. The collagen extract was then transferred to a polytetrafluoroethylene-lined digestion vessel and reacted at 800W microwave power and 190°C for 60min. After freeze-drying, carbon quantum dots (particle size of 5nm-10nm) were obtained.

[0047] Example 1:

[0048] An ultraviolet blocking film is prepared by the following method:

[0049] 1) Add 0.4g of polyvinyl alcohol (number average molecular weight 250,000) to 4.6g of deionized water and stir for 3 hours at 90℃ and 700 rpm to obtain an 8% polyvinyl alcohol solution. Add 0.25g of sodium carboxymethyl cellulose to 4.75g of deionized water and stir for 2 hours at 30℃ and 500 rpm to obtain a 5% sodium carboxymethyl cellulose solution. 0.05 g of carbon quantum dots were added to 10 g of deionized water and stirred for 2 h at 30 °C and 400 r / min to obtain a carbon quantum dot dispersion with a concentration of 0.005 g / mL. 0.3 g of water chestnut starch (particle size ≤ 50 μm) was added to 3.35 g of deionized water and ultrasonically dispersed for 10 min at 300 W and 20 kHz to obtain a water chestnut starch solution with a mass fraction of 8%.

[0050] 2) Mix polyvinyl alcohol solution, sodium carboxymethyl cellulose solution, carbon quantum dot dispersion and water chestnut starch solution, stir for 2 hours at 25℃ and 400 r / min, then heat to 85℃ and stir at a constant temperature for 10 minutes to obtain a gelatinized mixed slurry.

[0051] 3) The gelatinized slurry is cast into a film and then dried in a constant temperature and humidity chamber at 30℃ and 40% relative humidity for 72 hours to obtain an ultraviolet blocking film (area density of 13.01 g / m³). 2 ).

[0052] Example 2:

[0053] An ultraviolet blocking film is prepared by the following method:

[0054] 1) Add 0.3g of polyvinyl alcohol (number average molecular weight 300,000) to 4.7g of deionized water and stir for 3 hours at 90℃ and 700r / min to obtain a 6% polyvinyl alcohol solution. Add 0.285g of sodium carboxymethyl cellulose to 4.715g of deionized water and stir for 3 hours at 30℃ and 350r / min to obtain a 5.7% sodium carboxymethyl cellulose solution. Solution: 0.065 g of carbon quantum dots were added to 13 g of deionized water and stirred for 3 h at 35 °C and 400 r / min to obtain a carbon quantum dot dispersion with a concentration of 0.005 g / mL; 0.35 g of water chestnut starch (particle size ≤ 50 μm) was added to 3.15 g of deionized water and ultrasonically dispersed for 10 min at an ultrasonic power of 300 W and an ultrasonic frequency of 20 kHz to obtain a water chestnut starch solution with a mass fraction of 10%.

[0055] 2) Mix polyvinyl alcohol solution, sodium carboxymethyl cellulose solution, carbon quantum dot dispersion and water chestnut starch solution, stir for 3 hours at 25℃ and 350 r / min, then heat to 85℃ and stir at a constant temperature for 10 minutes to obtain a gelatinized mixed slurry.

[0056] 3) The gelatinized slurry is cast into a film and then dried in a constant temperature and humidity chamber at 30℃ and 40% relative humidity for 48 hours to obtain an ultraviolet blocking film (area density of 14.05 g / m³). 2 ).

[0057] Example 3:

[0058] An ultraviolet blocking film is prepared by the following method:

[0059] 1) Add 0.25g of polyvinyl alcohol (number average molecular weight 300,000) to 3.92g of deionized water and stir for 3 hours at 90℃ and 700r / min to obtain a 6% polyvinyl alcohol solution. Add 0.265g of sodium carboxymethyl cellulose to 4.735g of deionized water and stir for 2 hours at 35℃ and 400r / min to obtain a 5.3% sodium carboxymethyl cellulose solution. Vitamin B1 sodium solution; 0.085 g of carbon quantum dots were added to 17 g of deionized water and stirred for 3 h at 35 °C and 400 r / min to obtain a carbon quantum dot dispersion with a concentration of 0.005 g / mL; 0.4 g of water chestnut starch (particle size ≤ 50 μm) was added to 4 g of deionized water and ultrasonically dispersed for 10 min at an ultrasonic power of 300 W and an ultrasonic frequency of 20 kHz to obtain a water chestnut starch solution with a mass fraction of 9%;

[0060] 2) Mix polyvinyl alcohol solution, sodium carboxymethyl cellulose solution, carbon quantum dot dispersion and water chestnut starch solution, stir for 2 hours at 25℃ and 400 r / min, then heat to 85℃ and stir at a constant temperature for 10 minutes to obtain a gelatinized mixed slurry.

[0061] 3) The gelatinized slurry is cast into a film and then dried in a constant temperature and humidity chamber at 30℃ and 40% relative humidity for 60 hours to obtain an ultraviolet blocking film (area density of 14.30 g / m³). 2 ).

[0062] Example 4:

[0063] An ultraviolet blocking film is prepared by the following method:

[0064] 1) Add 0.2g of polyvinyl alcohol (number average molecular weight 250,000) to 4.8g of deionized water and stir for 3 hours at 90℃ and 700r / min to obtain a 4% polyvinyl alcohol solution. Add 0.25g of sodium carboxymethyl cellulose to 4.75g of deionized water and stir for 2 hours at 35℃ and 350r / min to obtain a 5% sodium carboxymethyl cellulose solution. Solution: 0.1 g of carbon quantum dots were added to 10 g of deionized water and stirred for 2 h at 35 °C and 350 r / min to obtain a carbon quantum dot dispersion with a concentration of 0.01 g / mL; 0.45 g of water chestnut starch (particle size ≤ 50 μm) was added to 4.5 g of deionized water and ultrasonically dispersed for 10 min at an ultrasonic power of 300 W and an ultrasonic frequency of 20 kHz to obtain a water chestnut starch solution with a mass fraction of 9%.

[0065] 2) Mix polyvinyl alcohol solution, sodium carboxymethyl cellulose solution, carbon quantum dot dispersion and water chestnut starch solution, stir for 2 hours at 25℃ and 400 r / min, then heat to 85℃ and stir at a constant temperature for 10 minutes to obtain a gelatinized mixed slurry.

[0066] 3) The gelatinized slurry is cast into a film and then dried in a constant temperature and humidity chamber at 30℃ and 40% relative humidity for 72 hours to obtain an ultraviolet blocking film (area density of 16.90 g / m³). 2 ).

[0067] Comparative Example 1:

[0068] A thin film, prepared by the following method:

[0069] 1) Add 0.3g of polyvinyl alcohol (number average molecular weight of 300,000) to 4.7g of deionized water and stir for 3h at 90℃ and 700r / min to obtain a 6% polyvinyl alcohol solution; add 0.3g of sodium carboxymethyl cellulose to 4.7g of deionized water and stir for 2h at 35℃ and 450r / min to obtain a 6% sodium carboxymethyl cellulose solution; add 0.4g of water chestnut starch (particle size ≤50μm) to 4g of deionized water and ultrasonically disperse for 10min at 300W and 20kHz to obtain a 9% water chestnut starch solution.

[0070] 2) Mix polyvinyl alcohol solution, sodium carboxymethyl cellulose solution and water chestnut starch solution, stir for 2 hours at 25℃ and 400 r / min, then heat to 85℃ and stir at a constant temperature for 10 minutes to obtain a gelatinized mixed slurry.

[0071] 3) The gelatinized slurry is cast into a film and then dried in a constant temperature and humidity chamber at 30℃ and 40% relative humidity for 72 hours to obtain a thin film (area density of 12.74 g / m³). 2 ).

[0072] Comparative Example 2:

[0073] A thin film, prepared by the following method:

[0074] 1) Add 0.4g of polyvinyl alcohol (number average molecular weight of 300,000) to 4.6g of deionized water and stir for 4h at 90℃ and 700r / min to obtain a polyvinyl alcohol solution with a mass fraction of 8%; add 0.3g of sodium carboxymethyl cellulose to 4.7g of deionized water and stir for 3h at 35℃ and 450r / min to obtain a sodium carboxymethyl cellulose solution with a mass fraction of 6%; add 0.1g of carbon quantum dots to 20g of deionized water and stir for 3h at 35℃ and 300r / min to obtain a carbon quantum dot dispersion with a concentration of 0.005g / mL.

[0075] 2) Mix polyvinyl alcohol solution, sodium carboxymethyl cellulose solution and carbon quantum dot dispersion, and stir for 2 hours at 25℃ and 400 r / min to obtain a mixed slurry;

[0076] 3) The mixed slurry is cast into a film, and then placed in a constant temperature and humidity chamber at 30℃ and 40% relative humidity for 48 hours to dry, thus obtaining a film (area density of 10.40 g / m³). 2 ).

[0077] Performance testing:

[0078] 1) The UV-blocking films from Examples 1-4 and the films from Comparative Examples 1-2 were cut into strips with a length of 5 cm and a width of 1 cm. After measuring the thickness, the mechanical properties were tested using an Instron 5967 universal testing machine (Instron Ltd., USA) at a tensile speed of 1.25 mm / min. The test results are shown in the table below:

[0079] Table 1. Mechanical property test results of the ultraviolet blocking films in Examples 1-4 and the films in Comparative Examples 1-2.

[0080] Test Project Sample thickness (μm) Tensile strength (MPa) Elongation at break (%) Example 1 37.21 138.26 4.82 Example 2 41.52 146.34 5.57 Example 3 38.33 154.11 6.75 Example 4 46.41 149.79 6.02 Comparative Example 1 42.50 129.21 4.12 Comparative Example 2 40.76 132.37 4.32

[0081] As shown in Table 1, the ultraviolet blocking films in Examples 1-4 have improved tensile strength compared with the films in Comparative Examples 1-2. Moreover, as the carbon quantum dot content increases, the tensile strength of the film first increases and then decreases. The tensile strength of the film reaches its maximum value when the weight percentage of carbon quantum dots reaches 8.5% (Example 3).

[0082] 2) The appearance diagrams of the ultraviolet blocking films in Examples 1-4 and the film in Comparative Example 1 are shown below. Figure 1 (The film sample is placed on a piece of white paper printed with the word "Transparency"), as shown in the image. The appearance of the film in Comparative Example 2 is as follows. Figure 2 (The thin film sample is placed on a piece of white paper printed with the word "Transparency") as shown.

[0083] Depend on Figure 1 and Figure 2 It can be seen that the ultraviolet blocking films in Examples 1-4 and the films in Comparative Examples 1-2 have high transparency and good light transmittance.

[0084] 3) The ultraviolet blocking performance of the ultraviolet blocking films in Examples 1-4 and the film in Comparative Example 1 was tested using a UV-1900 ultraviolet-visible spectrophotometer. The test results are as follows: Figure 3 As shown.

[0085] Depend on Figure 3 It can be seen that: compared with the film in Comparative Example 1, the transmittance of the ultraviolet blocking films in Examples 1 to 4 in the ultraviolet-A (315nm~400nm) and UV-B (280nm~315nm) bands is significantly reduced, indicating that they have excellent ultraviolet blocking performance; as the carbon quantum dot content of the ultraviolet blocking films in Examples 1 to 4 increases, the ultraviolet blocking performance of the films becomes better and better.

[0086] 4) The water vapor transmission rate (WVTR) test results of the ultraviolet blocking films in Examples 1-4 and the film in Comparative Example 2 are as follows: Figure 4 As shown, the test results for moisture content (MC) and water solubility (WS) are as follows: Figure 5 As shown.

[0087] The water vapor transmission rate (WVTR) test method is as follows: Seal a centrifuge tube containing 30 mL of deionized water with a thin-film sample, then place it in a desiccator containing color-changing silica gel and incubate at 25°C for 24 h. Calculate the WVTR (unit: g / m³) according to the following formula. 2 •s): WVTR=ΔW / (T×A), where ΔW is the weight loss of deionized water (in g), T is the storage time (in s), and A is the exposed area of ​​the membrane (in m²). 2 ).

[0088] The test methods for moisture content (MC) and water solubility (WS) are as follows: Cut the film sample into 50mm×50mm sheets, weigh them, and record the weight as M1 (in g). Dry the film sample at 105℃ to constant weight, weigh it again, and record the weight as M2 (in g). Place the dried film sample in a beaker containing 100mL of deionized water, seal it, soak it at room temperature for 24 hours, remove it, dry it again at 105℃ to constant weight, weigh it again, and record the weight as M3 (in g). Then calculate MC and WS according to the following formulas: MC (%) = (M1-M2) / M1×100%; WS (%) = (M2-M3) / M2×100%.

[0089] Depend on Figure 4 and Figure 5 It can be seen that the ultraviolet blocking films in Examples 1-4 have lower water vapor transmission rates compared to the film in Comparative Example 2. Furthermore, as the water vapor transmission rate of the ultraviolet blocking films in Examples 1-4 increases, the water content and water solubility of the films decrease slowly. In particular, the water content of the ultraviolet blocking film in Example 4 reaches about 30%, indicating that the film in Comparative Example 2 has relatively poor water barrier performance. In contrast, the ultraviolet blocking films in Examples 1-4 incorporate water chestnut starch, which has a unique water absorption function. Water chestnut starch can absorb moisture from the surrounding environment and reduce water transmission, thereby increasing the water barrier effect of the film and effectively improving its water absorption and barrier performance.

[0090] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An ultraviolet-blocking film, characterized in that, Made from the following raw materials by weight percentage: Polyvinyl alcohol: 20%–40%; Sodium carboxymethyl cellulose: 20%–30%; Carbon quantum dots: 5%–10%; Water chestnut starch: 30%–45%; The carbon quantum dots are prepared by a method including the following steps: chromium removal treatment of waste leather, followed by soaking in water with calcium oxide to obtain collagen extract, followed by microwave-assisted hydrothermal reaction of the collagen extract, and then freeze-drying to obtain carbon quantum dots. The ultraviolet blocking film is prepared by a method including the following steps: 1) Polyvinyl alcohol, sodium carboxymethyl cellulose, carbon quantum dots and water chestnut starch are dissolved / dispersed in water to prepare polyvinyl alcohol solution, sodium carboxymethyl cellulose solution, carbon quantum dot dispersion and water chestnut starch solution respectively; 2) Polyvinyl alcohol solution, sodium carboxymethyl cellulose solution, carbon quantum dot dispersion and water chestnut starch solution are mixed evenly and then heated to carry out a gelatinization reaction to obtain a gelatinized mixed slurry; 3) The gelatinized mixed slurry is cast into a film and then dried to obtain the ultraviolet blocking film.

2. The ultraviolet blocking film according to claim 1, characterized in that: The number average molecular weight of the polyvinyl alcohol is 250,000 to 300,000.

3. The ultraviolet blocking film according to claim 1, characterized in that: The carbon quantum dots have a particle size of 5 nm to 10 nm.

4. The ultraviolet blocking film according to any one of claims 1 to 3, characterized in that: The particle size of the water chestnut starch is ≤50µm.

5. The ultraviolet blocking film according to any one of claims 1 to 3, characterized in that: The areal density of the ultraviolet blocking film is 13 g / m³. 2 ~20g / m 2 .

6. The ultraviolet blocking film according to claim 1, characterized in that: The polyvinyl alcohol solution in step 1) has a mass fraction of 4% to 8%; the sodium carboxymethyl cellulose solution in step 1) has a mass fraction of 5% to 6%; the carbon quantum dot dispersion in step 1) has a concentration of 0.005 g / mL to 0.01 g / mL; and the water chestnut starch solution in step 1) has a mass fraction of 8% to 10%.

7. The ultraviolet blocking film according to claim 1 or 6, characterized in that: Step 2) The gelatinization reaction is carried out at a temperature of 80℃~85℃ for a reaction time of 10min~15min.

8. The ultraviolet blocking film according to claim 1 or 6, characterized in that: Step 3) The drying is carried out at a temperature of 30℃~40℃ and a relative humidity of 35%~45%, and the drying time is 48h~72h.

9. A food packaging material, characterized in that, It includes the ultraviolet blocking film according to any one of claims 1 to 8.

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