Method for evaluating near-infrared shielding performance of composite film

Abstract

The application relates to an evaluation method of near-infrared shielding performance of a composite film, and belongs to the field of detection. The evaluation method of near-infrared shielding performance of a composite film comprises the following steps: mixing a dispersion liquid of near-infrared shielding functional particles and an organic resin solution to obtain a coating film slurry; obtaining a composite film with near-infrared shielding function through a coating process; testing a transmission spectrum curve of the composite film by using an ultraviolet-visible-near-infrared spectrophotometer to obtain spectral transmittance values at different wavelengths; calculating an average light transmittance T Vis in a visible light band and an average light transmittance T NIR in a near-infrared light band; and calculating a transparent heat insulation index K to represent the near-infrared shielding performance. The application starts from the Lambert-Beer law, proposes a brand-new transparent heat insulation index K to evaluate and compare the near-infrared shielding performance of different films, and is suitable for reasonably comparing the near-infrared shielding performance of films with different visible light transmittances.

Description

Technical Field

[0001] This invention relates to a method for evaluating the near-infrared shielding performance of composite thin films, belonging to the field of testing. Background Technology

[0002] Near-infrared light accounts for more than 50% of solar radiation. As one of the main components of solar radiation energy, a large amount of near-infrared (NIR) light entering indoor spaces will place a certain burden on building temperature control energy consumption. Therefore, using energy-saving window materials that can shield near-infrared light is an effective means of achieving building energy conservation. Currently reported materials with near-infrared shielding function mainly include lanthanum hexaboride (LaB6), indium tin oxide (ITO), tin oxide (ATO), copper sulfide (CuS), vanadium dioxide (VO2), Low-E glass, and tungsten bronze (M). x WO3,M=Li,Na,K,Rb,Cs,NH4), etc.

[0003] Currently, in characterizing and evaluating the near-infrared shielding performance of composite films, many researchers often compare the transparency-heat insulation index, i.e., the ratio of visible light transmittance to near-infrared transmittance (T). vis / T NIR ) or difference (T) Vis -T NIR To compare the near-infrared shielding performance of different films, a method is used, but this requires the visible light transmittance of the film materials to be very similar to make the near-infrared shielding performance comparable. However, because the visible light transmittance of the prepared film materials may not be exactly the same due to slight differences in thickness, the evaluation of the near-infrared shielding performance of the films is usually quite subjective. Therefore, in order to evaluate and compare the near-infrared shielding performance of different film materials, it is necessary to propose a more reasonable transparency-heat insulation index and its calculation method. Summary of the Invention

[0004] This invention provides a novel transparency and heat insulation index for evaluating the near-infrared shielding performance of thin films and its calculation method.

[0005] A method for evaluating the near-infrared shielding performance of a composite thin film includes the following steps:

[0006] (1) Mix the dispersion of near-infrared shielding particles with an organic resin solution to obtain a coating slurry. Obtain a composite film with near-infrared shielding function through a coating process. Measure its transmittance spectrum curve using an ultraviolet-visible-near-infrared spectrophotometer to obtain the spectral transmittance values ​​at different wavelengths.

[0007] (2) Calculate the average light transmittance T in the visible light band using the following formula. Vis and average light transmittance T in the near-infrared band NIR;

[0008]

[0009] In the formula, T Vis T represents the average transmittance of visible light (380–780 nm). NIR The average transmittance in the near-infrared range (780–2500 nm), where S (λ) It is the relative spectral distribution of the solar spectrum (AM1.5 solar spectrum) passing through 1.5 times the vertical atmospheric thickness, T (λ) It is the spectral transmittance of the sample.

[0010] (3) The near-infrared shielding performance is characterized by calculating the transparency thermal insulation index K using the following formula.

[0011] A = lg(1 / T) = K λ bc ①

[0012]

[0013]

[0014] A higher K value indicates stronger near-infrared shielding performance.

[0015] Equation ① above is the basic expression of the Lambert-Beer law, where A is absorbance; T is transmittance, which is the ratio of emitted light intensity (I) to incident light intensity (I0); K λ λ is the molar absorptivity, which is related to the properties of the absorbing material and the wavelength λ of the incident light, and b is the thickness of the absorbing layer.

[0016] For the same thin film, the ratio of absorbance at different wavelengths is the ratio of molar absorptivity. For example, the absorbance A at a certain wavelength of near-infrared light. λ2 Absorbance A at a certain wavelength of visible light λ1 The ratio, as shown in equation ②, gives k as the ratio of their molar absorptivity. Similarly, the average near-infrared absorbance A... NIR Compared with average visible light absorbance A Vis From the ratio, we can obtain the average molar absorptivity K of near-infrared light in equation ③. λ,NIR The average molar absorptivity K of visible light λ,vis The ratio K, which can be defined here as the transparent thermal insulation index K.

[0017] Therefore, the physical meaning of the transparency heat insulation index K can be simply expressed as follows: averaging the energy of visible-near infrared (380-2500nm) photons, for every visible light photon (380-780nm) absorbed, K times the number of near infrared photons (780-2500nm) are absorbed. The meaning of K is to keep the visible light transmittance constant and compare the near infrared absorption intensity or near infrared light transmittance. Therefore, the transparency heat insulation index K is more reasonable for evaluating near infrared shielding performance.

[0018] Preferably, in step (1), the near-infrared shielding functional particles are alkali metal tungsten bronze (M) with a hexagonal structure. x WO3) particles, wherein M is one, two or three elements selected from Li, Na, K, Cs and Rb, and x = 0.2 to 0.35.

[0019] Preferably, in step (1), the concentration of the dispersion of the near-infrared shielding functional particles is 0.01-0.05 g / mL, and the solvent is one or more of the following: water, anhydrous ethanol, isopropanol, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone.

[0020] Preferably, in step (1), the organic resin is one or more of polyvinyl alcohol, polyvinyl butyral, polyurethane, and polymethyl methacrylate.

[0021] Preferably, the concentration of the organic resin solution is 5-30 wt%, and the solvent is one or more of the following: water, anhydrous ethanol, isopropanol, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone; the volume ratio of the near-infrared shielding functional particle dispersion to the organic resin solution is 1:2-8.

[0022] Preferably, in step (1), the coating process is to coat M on the surface of a glass or PET substrate using a roller coating method. x WO3 film.

[0023] Preferably, in step (1), the composite film has a thickness of 0.5 to 30 μm and has 1 to 10 coating layers.

[0024] Preferably, when using an ultraviolet-visible-near-infrared spectrophotometer to test its transmission spectrum curve, the wavelength range is set to 300–2500 nm.

[0025] The beneficial effects of this invention are as follows: This invention addresses the issue that during the testing and characterization of near-infrared shielding of thin films, the inconsistent film thickness leads to different visible light transmittance, making it difficult to reasonably evaluate the near-infrared shielding performance of the film due to the varying degrees of influence from film thickness and visible light transmittance. Based on the Lambert-Beer Law, this invention proposes a novel transparency and heat insulation index K to evaluate and compare the near-infrared shielding performance of different films, making it suitable for a reasonable comparison of the near-infrared shielding performance of films with different visible light transmittance. Attached Figure Description

[0026] Figure 1 (a) and (b) are the UV-Vis-NIR transmittance (UV-Vis-NIR) graphs of the 1-6 layer films prepared in Example 1, respectively, and the T... 560nm With T 1600nm The fitted curve. Detailed Implementation

[0027] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the invention, but do not limit the invention in any way.

[0028] Unless otherwise specified, the experimental methods described in the following examples are conventional methods; the reagents and materials described are commercially available unless otherwise specified.

[0029] Example 1

[0030] 1. A method for evaluating the near-infrared shielding performance of a composite thin film, comprising the following steps:

[0031] (1) Mix the dispersion of near-infrared shielding particles with an organic resin solution to obtain a coating slurry. Obtain a composite film with near-infrared shielding function through a coating process. Measure its transmittance spectrum curve using an ultraviolet-visible-near-infrared spectrophotometer to obtain the spectral transmittance values ​​at different wavelengths.

[0032] (2) Calculate the average light transmittance T in the visible light band using the following formula. Vis and average light transmittance T in the near-infrared band NIR ;

[0033]

[0034] In the formula, T Vis T represents the average transmittance of visible light (380–780 nm). NIR The average transmittance in the near-infrared range (780–2500 nm), where S (λ) It is the relative spectral distribution of the solar spectrum (AM1.5 solar spectrum) passing through 1.5 times the vertical atmospheric thickness, T (λ) It is the spectral transmittance of the sample.

[0035] (3) The near-infrared shielding performance is characterized by the transparency heat insulation index K calculated by the following formula. The larger the value, the stronger the near-infrared shielding performance.

[0036]

[0037] In step (1), the near-infrared shielding functional particles are cesium tungsten bronze powder sold by Hangzhou Jikang New Materials Co., Ltd., and 0.5g of Cs is taken. x WO3 powder was mixed with 7.5 mL of deionized water and ball-milled at 600 rpm for 4 hours. A 10 wt% PVA aqueous solution was used as the film-forming agent to obtain a coating slurry with a mass fraction of 1.2 wt%. M was then coated onto the surface of a glass substrate using a roller coating method. x WO3 film.

[0038] Coating with 1 to 6 layers of cesium tungsten bronze film.

[0039] The transmittance spectrum of the thin film was characterized using a UV-Vis-NIR spectrophotometer (Model Lambda 950, PerkinElmer), with a test range of 300–2500 nm and a step size of 10 nm.

[0040] Figure 1 (a)-(b) are transmittance spectra of cesium tungsten bronze films with different numbers and thicknesses, used to verify the applicability of the Lambert-Beer law. Figure 1 (a) It can be seen that the decrease in visible light transmittance and near-infrared light transmittance is not consistent with the decrease in film thickness. Table 1 shows the data based on... Figure 1 (a) Calculated average transmittance of visible and near-infrared rays, and the transparency thermal insulation index (difference ΔT = T) frequently used in existing research to evaluate near-infrared shielding performance. Vis -T NIR The ratio THI = T Vis / T NIR Calculation results. As can be seen from Table 1, with the increase of film thickness, both the difference ΔT and the ratio THI show significant changes, indicating that it is difficult to accurately and reasonably evaluate and compare the near-infrared shielding performance of different films using the difference ΔT and the ratio THI. However, the transparent heat insulation index K calculated by the molar absorptivity is less affected by the number of film layers and the thickness of the film. Figure 1 (b) is... Figure 1 (a) T 560 nm T 1600 nm The fitting calculation results show that the transmittance of the thin film at 560 nm and 1600 nm exhibits a k-power function relationship. Figure 1(b) The R-square of the fitted curve is close to 1, indicating that the film thickness has little effect on the value of k. This further proves the effectiveness of using K = log T(Vis) T (NIR) The evaluation of the near-infrared shielding performance of thin films is more accurate and reasonable.

[0041] Table 1

[0042]

[0043]

Claims

1. A method for evaluating the near-infrared shielding performance of a composite thin film, characterized in that, The steps include the following: (1) Mix the dispersion of near-infrared shielding particles with an organic resin solution to obtain a coating slurry. Obtain a composite film with near-infrared shielding function through a coating process. Measure its transmittance spectrum curve using an ultraviolet-visible-near-infrared spectrophotometer to obtain the spectral transmittance values ​​at different wavelengths. (2) Calculate the average light transmittance T in the visible light band using the following formula. Vis Average light transmittance T in the near-infrared band NIR ; In the formula, T Vis The average transmittance of visible light in the range of 380–780 nm. T NIR The average transmittance in the near-infrared range of 780–2500 nm, where S (λ) It is the relative spectral distribution of the AM1.5 solar spectrum, T (λ) It is the spectral transmittance of the sample; (3) The near-infrared shielding performance is characterized by calculating the transparent heat insulation index K using the following formula. 。 2. The method according to claim 1, characterized in that: A higher K value indicates stronger near-infrared shielding performance.

3. The method according to claim 1, characterized in that: In step (1), the near-infrared shielding functional particles are alkali metal tungsten bronze (M) with a hexagonal structure. x WO3) particles, where M is one, two, or three of the elements Li, Na, K, Cs, and Rb, and x = 0.2 to 0.

35.

4. The method according to claim 1, characterized in that: In step (1), the concentration of the dispersion of the near-infrared shielding functional particles is 0.01-0.05 g / mL, and the solvent is one or more of the following: water, anhydrous ethanol, isopropanol, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone.

5. The method according to claim 1, characterized in that: In step (1), the organic resin is one or more of polyvinyl alcohol, polyvinyl butyral, polyurethane, and polymethyl methacrylate; the concentration of the organic resin solution is 5-30 wt%, and the solvent is one or more of water, anhydrous ethanol, isopropanol, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone; the volume ratio of the near-infrared shielding functional particle dispersion to the organic resin solution is 1:2-8.

6. The method according to claim 1, characterized in that: In step (1), the coating process involves coating M onto the surface of a glass or PET substrate using a roller coating method. x WO3 film.

7. The method according to claim 1, characterized in that: When using an ultraviolet-visible-near-infrared spectrophotometer to test its transmission spectrum curve, the wavelength range is set to 300–2500 nm.

8. The method according to claim 1, characterized in that: In step (1), the composite film has a thickness of 0.5 to 30 μm and has 1 to 10 coating layers.

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