Preparation method of transparent flexible radiation refrigeration film based on TPU / PVDF

Abstract

The invention provides a preparation method of a transparent radiation refrigeration film based on TPU / PVDF. The radiation refrigeration film is a composite transparent radiation refrigeration film mainly prepared from TPU and PVDF. The main preparation method comprises the following steps: respectively mixing solid TPU powder and PVDF powder with a solvent N-N dimethylacetamide (DMAC), magnetically stirring, and uniformly dispersing to obtain a TPU transparent solution and a PVDF transparent solution in sequence; and cleaning the glass sheet by using the cleaning solution, and then sequentially washing the glass sheet for three times by using absolute ethyl alcohol and deionized water. Dripping the TPU transparent solution on the surface of a cleaned glass sheet, scraping the surface of a sample by using an adjustable scraper BEVS 1806B / 150 at a constant speed to form a flat coating, drying the glass sheet in a drying oven, dripping the PVDF transparent solution on the surface of the sample, scraping the surface of the sample by using the scraper at a constant speed, and drying the glass sheet in the drying oven. As the material is low in price and the preparation method is simple, the film has a wide application prospect in the fields of automobile protective films, outdoor high-voltage electrical equipment, building outer walls and ceilings, outdoor articles and agricultural greenhouses.

Description

Technical Field

[0001] A preparation method based on TPU / PVDF transparent flexible radiation cooling film belongs to the field of materials and energy, mainly involving the cooling problem of outdoor equipment such as buildings and automobiles. The radiation cooling film can effectively reduce the sub-ambient temperature. Background Art

[0002] The frequency of extreme climate events around the world in recent years has been alarming, especially the surge in hot weather and the gradual rise in temperature. This trend has led to further energy pressure on cooling systems in buildings, outdoor equipment and vehicles. It is predicted that various cooling methods will account for more than 10% of the world's annual electricity consumption. Passive daytime radiative cooling (PDRC) is an emerging technology that can significantly alleviate the above energy demand by using the cryosphere as a natural heat sink to effectively dissipate heat from the surface.

[0003] Generally speaking, PDRC utilizes advanced functional materials and sophisticated strategies to manipulate the optical properties of materials to achieve high reflectivity in the solar band and high emissivity in the mid-infrared (MIR) region. This allows thermal radiation to be effectively cooled through the atmospheric window to outer space. To optimize radiative cooling performance, materials are usually designed to have high reflectivity and emissivity, usually in the form of white coatings or films. However, the monotonous white color of these coatings or films obscures the original surface appearance of buildings or equipment and fails to meet the corresponding aesthetic requirements, hindering their widespread application in daily life, especially in the field of highly aesthetically designed automobiles. At the same time, as global temperatures continue to rise, the power consumption burden of automotive cooling systems is gradually increasing. Considering the gradual withdrawal of fuel vehicles from the market and the increasing popularity of electric vehicles, it has become particularly urgent to adopt zero-energy radiative cooling to reduce energy consumption for automotive cooling. Summary of the invention

[0004] A method for preparing a transparent flexible radiation cooling film based on TPU / PVDF. The radiation cooling film is prepared by calculating the ratio of TPU and NN dimethylacetamide, PVDF and NN dimethylacetamide, and using a scraping method to prepare a sample. The sample exhibits a transmittance of 71% (0.4-0.8μm) and an emissivity of 98% (4-25μm). The TPU / PVDF radiation cooling film can achieve a maximum average temperature drop of 17.3°C during the day. Because the invented material is low in price and the preparation method is simple, the film has broad application prospects in building and car clothing cooling.

[0005] A method for preparing a transparent flexible radiation cooling film based on TPU / PVDF, wherein the specific preparation steps are as follows: (1) Preparation of transparent TPU solution: Mix TPU powder and NN dimethylacetamide solution at 30°C for 2-4 hours to obtain a transparent TPU solution; (2) Preparation of transparent PVDF solution: Mix PVDF powder and N-N-dimethylacetamide solution at 30°C for 2-4 hours to obtain a transparent PVDF solution; (3) Coating film formation: Place a clean glass on a flat table, calibrate the BEVS 1806B / 150 adjustable scraper, drop the TPU transparent solution in step (1) onto the surface of the glass, and then scrape the sample at a uniform speed to form a flat coating. Finally, place the sample in an oven for drying, then drop the PVDF transparent solution in step (2) onto the surface of the sample, scrape the sample surface at a uniform speed with the scraper, and then place it in an oven for drying, thereby obtaining a TPU / PVDF-based transparent flexible radiative cooling film.

[0006] The added mass ratio of the TPU powder to NN dimethylacetamide is 1-2: 15-20.

[0007] The added mass ratio of the PVDF powder to NN dimethylacetamide is 3-6: 15-20.

[0008] The added mass ratio of the TPU powder: PVDF powder is 1~2: 3~6.

[0009] The oven temperature is set at 60-90°C, and the drying time is 20-30 minutes.

[0010] The distance between the scraper and the glass sheet, i.e. the thickness of the wet film, is 0.5 mm to 2.5 mm.

[0011] The beneficial effects of the present invention are: The TPU / PVDF film prepared by the present invention has excellent transparency, a transmittance of 71% for visible light, and excellent radiation cooling performance, showing an emissivity of 98% in the atmospheric transparent window band, and also has excellent stretchability and wear resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 Actual photo of the film prepared in Example 3.

[0013] Figure 2 SEM image of the film prepared in Example 2-3.

[0014] Figure 3 SEM images of the films prepared in Examples 1-3.

[0015] Figure 4 SEM image of the film prepared in Example 3.

[0016] Figure 5 In Example 3, thin film transmittance and emissivity spectra were prepared.

[0017] Figure 6 Comparative spectra of the emissivity of the films prepared in Examples 1-3, Examples 2-3 and Example 3.

[0018] Figure 7 Comparative spectra of the transmittance of the films prepared in Examples 1-3, Examples 2-3 and Example 3.

[0019] Figure 8 FTIR spectra of the thin films prepared in Examples 1-3, Examples 2-3 and Example 3.

[0020] Fig. 9 Schematic diagram of the outdoor cooling test device.

[0021] Fig.10 Temperature curves of the films prepared in Examples 1-3, Examples 2-3 and Example 3 during outdoor testing.

[0022] Fig.11 Temperature drop graphs of the films prepared in Examples 1-3, Examples 2-3 and Example 3 compared with aluminum sheets in outdoor testing.

[0023] Fig.12 Comparative temperature drop diagram of the film prepared in Example 3 on the outdoor car surface. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention.

[0025] Example 1 The present invention conducts experiments on TPU films of different thicknesses, and the experimental methods are as follows: Example 1-1 The specific preparation steps of TPU film are as follows: (1) Preparation of transparent TPU solution: TPU powder and NN dimethylacetamide solution were mixed at 30 °C for 3 h to obtain a TPU transparent solution; (2) Coating film formation: Place a clean glass sheet on a flat table, calibrate the BEVS 1806B / 150 adjustable scraper, set the distance between the scraper and the glass sheet to 0.5 mm, drop the TPU transparent solution in step (1) onto the surface of the glass sheet, and then scrape across the sample at a uniform speed to form a flat coating. Finally, place the sample in a 90°C oven and dry it for 20 min.

[0026] Example 1-2 Compared with Example 1-1, except that the distance between the scraper and the glass sheet is set to 1 mm, the rest is the same as Example 1-1.

[0027] Examples 1-3 Compared with Example 1-1, except that the distance between the scraper and the glass sheet is set to 1.5 mm, the rest is the same as Example 1-1.

[0028] Examples 1-4 Compared with Example 1-1, except that the distance between the scraper and the glass sheet is set to 2 mm, the rest is the same as Example 1-1.

[0029] Examples 1-5 Compared with Example 1-1, except that the distance between the scraper and the glass sheet is set to 2.5 mm, the rest is the same as Example 1-1.

[0030] Example 2 The present invention conducts experiments on TPU films of different thicknesses, and the experimental methods are as follows: Example 2-1 The specific preparation steps of PVDF film are as follows: (1) Preparation of transparent PVDF solution: PVDF powder and N-N-dimethylacetamide solution were mixed at 30°C for 2 h to obtain a transparent PVDF solution; (2) Coating film formation: Place a clean glass sheet on a flat table, calibrate the BEVS 1806B / 150 adjustable scraper, set the distance between the scraper and the glass sheet to 0.5 mm, drop the PVDF transparent solution in step (1) onto the surface of the glass sheet, and then scrape across the sample at a uniform speed to form a flat coating. Finally, place the sample in a 90°C oven and dry it for 30 min.

[0031] Example 2-2 Compared with Example 2-1, except that the distance between the scraper and the glass sheet is set to 1 mm, the rest is the same as Example 2-1.

[0032] Example 2-3 Compared with Example 2-1, except that the distance between the scraper and the glass sheet is set to 1.5 mm, the rest is the same as Example 22-1.

[0033] Embodiment 2-4 Compared with Example 2-1, except that the distance between the scraper and the glass sheet is set to 2 mm, the rest is the same as Example 2-1.

[0034] Embodiment 2-5 Compared with Example 2-1, except that the distance between the scraper and the glass sheet is set to 2.5 mm, the rest is the same as Example 2-1.

[0035] Example 3 The specific preparation steps of TPU / PVDF transparent flexible radiation cooling film are as follows: (1) Preparation of transparent TPU solution: TPU powder and NN dimethylacetamide solution were mixed at 30 °C for 3 h to obtain a TPU transparent solution; (2) Preparation of transparent PVDF solution: PVDF powder and N-N-dimethylacetamide solution were mixed at 30°C for 2 h to obtain a transparent PVDF solution; (3) Coating film formation: Place a clean glass on a flat table, calibrate a BEVS 1806B / 150 adjustable scraper, set the distance between the scraper and the glass sheet to 1.5 mm, drop the TPU transparent solution in step (1) onto the surface of the glass sheet, and then scrape the sample at a uniform speed to form a flat coating. Finally, place the sample in a 90°C oven for drying for 20 min, then drop the PVDF transparent solution in step (2) onto the surface of the sample, set the distance between the scraper and the glass sheet to 1.5 mm, scrape the sample surface with the scraper at a uniform speed, and then place the sample in a 90°C oven for drying for 30 min to obtain a TPU / PVDF-based transparent flexible radiative cooling film.

[0036] Figure 1 The actual picture of the film prepared in Example 3 shows that the film prepared in Example 3 has excellent transmittance and flexibility. Figure 2 SEM image of the film prepared in Example 2-3 shows the microscopic morphology and thickness of the film prepared in Example 2-3 is 56.1 microns. Figure 3 SEM images of the films prepared in Examples 1-3 show the microscopic morphology and thickness of the films prepared in Examples 1-3 to be 155 μm. Figure 4 SEM image of the film prepared in Example 3. It shows the microscopic morphology and thickness of the film prepared in Example 3 is 191 microns. Figure 5 Transmittance and emissivity spectra of the film prepared in Example 3. The transmittance of the film prepared in Example 3 was 71% and the emissivity was 98%. Figure 6 Comparison of the emissivity spectra of the films prepared in Examples 1-3, Examples 2-3 and Example 3. It is proved that the film prepared in Example 3 has the highest emissivity. Figure 7 Comparative spectra of the transmittance of the films prepared in Examples 1-3, Examples 2-3 and Example 3. Figure 8 FTIR spectra of the films prepared in Examples 1-3, Examples 2-3 and Example 3. It illustrates the molecular bonds of the prepared films. Fig. 9 Schematic diagram of the outdoor cooling test device. Fig.10The temperature curves of the films prepared in Examples 1-3, 2-3 and 3 during outdoor testing show that the film prepared in Example 3 has the lowest temperature. Fig.11 The temperature drop diagrams of the films prepared in Examples 1-3, Examples 2-3 and Example 3 compared with aluminum sheets in outdoor tests prove that the film prepared in Example 3 has the highest temperature drop effect. Fig.12 The temperature drop diagram of the film prepared in Example 3 on the outdoor car surface is compared. It proves that the film prepared in Example 3 has an excellent cooling effect on the outer surface of the car.

Claims

1. A method for preparing a transparent flexible radiation cooling film based on TPU / PVDF, characterized in that: The method comprises the following preparation steps: (1) Preparation of transparent TPU solution: Thermoplastic polyurethane elastomer TPU powder is stirred and mixed in NN dimethylacetamide solution to obtain a TPU transparent solution; (2) Preparation of transparent PVDF solution: polyvinylidene fluoride PVDF powder is stirred and mixed in N-N-dimethylacetamide solution to obtain a PVDF transparent solution; (3) Coating film formation: drip the TPU transparent solution in step (1) onto the surface of a glass sheet, then scrape the sample at a uniform speed to form a smooth coating, then place the sample in an oven for drying, then drip the PVDF transparent solution in step (2) onto the surface of the sample, scrape the sample surface at a uniform speed with a scraper, and then place it in an oven for drying to obtain a TPU / PVDF-based transparent flexible radiative cooling film.

2. The method for preparing the TPU / PVDF transparent flexible radiation cooling film according to claim 1, characterized in that: The added mass ratio of TPU powder:NN dimethylacetamide is 1~2: 15~20.

3. The method for preparing the TPU / PVDF transparent flexible radiation cooling film according to claim 1, characterized in that: The added mass ratio of PVDF powder:NN dimethylacetamide is 3~6:15~20.

4. The method for preparing the TPU / PVDF transparent flexible radiation cooling film according to claim 1, characterized in that: The added mass ratio of TPU powder: PVDF powder is 1~2: 3~6.

5. The method for preparing a TPU / PVDF transparent flexible radiation cooling film according to claim 1, characterized in that: The oven temperature in step (3) is set to 60-90°C and the drying time is 20-30 minutes.

Images