A method for testing the degree of crosslinking of composite white photovoltaic films

Abstract

This invention relates to the field of photovoltaic encapsulant film technology, and particularly to a method for testing the crosslinking degree of composite white photovoltaic encapsulant films. To address the problem that existing methods for testing the crosslinking degree of composite white photovoltaic encapsulant films often result in a significant discrepancy between the measured crosslinking degree and the actual crosslinking degree, this invention provides a method for testing the crosslinking degree of composite white photovoltaic encapsulant films. The composite white photovoltaic encapsulant film comprises a transparent layer and a white layer. The crosslinking degree of the composite white photovoltaic encapsulant film is calculated using the following formula: The crosslinking degree measured by this method is closer to the actual crosslinking degree and can more accurately reflect the degree of crosslinking of the resin in the composite white photovoltaic encapsulant film.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic encapsulant technology, and in particular to a method for testing the degree of crosslinking of composite white photovoltaic encapsulant films. Background Technology

[0002] Currently, the preparation and application of high-reflectivity white photovoltaic encapsulant films have become a research hotspot in the solar energy industry to improve the photoelectric conversion efficiency of solar cells. The high reflectivity of white photovoltaic encapsulant films can bring higher photoelectric conversion efficiency to photovoltaic modules. As a key encapsulation material for photovoltaic modules, photovoltaic encapsulant films undergo cross-linking after heating and lamination to form a stable three-dimensional network structure, providing excellent sealing and bonding for the photovoltaic modules. Generally, the higher the degree of cross-linking of the photovoltaic encapsulant film, the better its light transmittance and the significantly improved adhesion, which can improve the photoelectric conversion efficiency of the module; however, excessively high cross-linking can increase the risk of cracking during subsequent use, seriously affecting the outdoor lifespan of the module. Therefore, white photovoltaic encapsulant films with a suitable degree of cross-linking can provide high reliability and high-gain encapsulation and bonding performance, thereby ensuring the long-term operation of photovoltaic modules.

[0003] Existing composite white photovoltaic films (such as EVA films) consist of a transparent layer and a white layer. The different crosslinking degree test methods reported so far do not take into account the addition of titanium dioxide and the ratio between the transparent layer and the white layer. Therefore, there is a lack of a test method that can be applied to composite white photovoltaic films to obtain a test method that approximates the true crosslinking degree.

[0004] The existing method for calculating the degree of crosslinking (Method 1) is as follows: Wherein, C is the degree of crosslinking of the test film (%), W1 is the weight of the wire mesh (g), W2 is the weight of the wire mesh after the sample is loaded (g), and W3 is the weight of the wire mesh after drying and loading the sample (g).

[0005] The existing method for calculating the crosslinking degree of composite white photovoltaic film treats the main resin and titanium dioxide as a whole, without considering that the insolubility of titanium dioxide (in xylene solvent) and the ratio between the transparent layer and the white layer in the composite white photovoltaic film will affect the true crosslinking degree of the composite white photovoltaic film. Therefore, the obtained value is a reference value of the crosslinking degree, which differs greatly from the true crosslinking degree. Summary of the Invention

[0006] To address the problem that existing methods for testing the crosslinking degree of composite white photovoltaic films often yield results in a significant discrepancy between the measured crosslinking degree and the actual crosslinking degree. This invention provides a method for testing the crosslinking degree of composite white photovoltaic films. In addition to considering the sample quality of the composite white photovoltaic film before and after extraction, this method also takes into account the influence of the layer thickness ratio of the white layer to the transparent layer and the titanium dioxide content before and after extraction on the crosslinking degree. The crosslinking degree measured by this method is closer to the actual crosslinking degree and can more accurately reflect the degree of resin crosslinking in the composite white photovoltaic film, thus solving the problem of significant discrepancies between the measured crosslinking degree and the actual crosslinking degree in existing methods.

[0007] The crosslinking degree test method for composite white photovoltaic films refers to the test method for the crosslinking degree of the main resin in the composite white photovoltaic film.

[0008] The degree of crosslinking is defined as follows: During the lamination process of photovoltaic encapsulant film in the module, linear encapsulant film molecules undergo crosslinking reaction to form network encapsulant film molecules; that is, the main resin (referred to as resin) of the crosslinked photovoltaic encapsulant film includes linear encapsulant film molecules and network encapsulant film molecules. The mass percentage of network encapsulant film molecules in the main resin is called the degree of crosslinking.

[0009] The significance of measuring the degree of crosslinking is as follows: the higher the degree of crosslinking of the photovoltaic encapsulant film, the better its light transmittance and the significantly improved adhesion, which can improve the photoelectric conversion efficiency of the module. However, excessively high crosslinking degree also increases the risk of cracking of the encapsulant film during subsequent use, leading to the eventual failure of the module. Therefore, photovoltaic encapsulant films with an appropriate degree of crosslinking play an important role in improving the efficiency and long-term use of photovoltaic modules.

[0010] Photovoltaic encapsulant film is EVA film. The higher the degree of cross-linking, the less likely EVA is to crystallize; the lower the degree of crystallinity, the higher the light transmittance. EVA is a copolymer of ethylene and vinyl acetate. Its Chinese chemical name is ethylene-vinyl acetate copolymer, and its English chemical name is Ethylene Vinyl Acetate Copolymer.

[0011] To address the aforementioned technical problems, this invention provides a method for testing the crosslinking degree of a composite white photovoltaic film. The composite white photovoltaic film comprises a transparent layer and a white layer, and the method includes the following steps:

[0012] (1) Obtain the sample mass M1 of the composite white photovoltaic film, the mass percentage of titanium dioxide in the white layer of the composite white photovoltaic film A1, and the thickness ratio of the transparent layer to the white layer of the composite white photovoltaic film is 1:X;

[0013] (2) Extraction of the composite white photovoltaic film sample;

[0014] (3) Obtain the mass M2 of the composite white photovoltaic film sample after extraction, and the mass percentage of titanium dioxide in the extracted sample A2.

[0015] (4) Calculate the degree of crosslinking of the composite white photovoltaic film using the following formula:

[0016]

[0017] The white layer contains the main resin and titanium dioxide. The transparent layer is composed of the main resin (referred to as resin).

[0018] The main resin is the resin material in the photovoltaic film. The main resin is usually EVA or POE.

[0019] X is 1-4. The thickness ratio of the transparent layer to the white layer of the composite white photovoltaic film is 1:(1-4). The thickness ratio of the transparent layer to the white layer of the composite white photovoltaic film is 1:1, 1:2, 1:3, or 1:4.

[0020] The derivation process of the above formula for calculating the degree of crosslinking is as follows:

[0021] (1)

[0022] (2) The content of the main resin in the extracted composite white photovoltaic film = M2 × (1-A2)

[0023] (3)

[0024] (4)

[0025] Combining the above formulas, we can obtain the following results.

[0026] Furthermore, a method for testing the crosslinking degree of a composite white photovoltaic film includes the following steps:

[0027] (1) Weigh the wire mesh and denote its weight as W1 (g);

[0028] (2) Cut the cross-linked composite white film sample into pieces with a size of 0.2-0.5 cm. 2 The weight of the wire mesh containing the sample is W2 (g).

[0029] (3) The thickness ratio of the transparent layer to the white layer of the composite white film is 1:X, and the mass percentage of titanium dioxide in the white layer is A1.

[0030] (4) The wire mesh containing the composite white adhesive film sample was placed in the solvent for extraction;

[0031] (5) After the extraction is completed, the wire mesh containing the sample is dried, and the weight of the sample is W3 (g). The mass percentage of titanium dioxide in the sample after extraction is A2 (g).

[0032] (6) The main resin of the composite white photovoltaic film includes the main resin in the white layer and the main resin in the transparent layer.

[0033] The mass of the main resin in the white layer is: The mass of the main resin in the transparent layer is The content of the main resin in the extracted composite white photovoltaic film is (W3-W1)(1-A2). The degree of crosslinking C of the composite white photovoltaic film is calculated using the following formula:

[0034]

[0035]

[0036] Furthermore, the specific steps of the crosslinking degree test method for the composite white photovoltaic film are as follows:

[0037] (1) Using an electronic analytical balance with an accuracy of 0.1 mg / 10,000, weigh the wire mesh as W1 (g);

[0038] (2) Cut the cross-linked composite white film sample into pieces with a size of 0.2-0.5 cm. 2 The weight of the wire mesh containing the sample was measured as W2 (g) using an electronic analytical balance with an accuracy of 1 / 10,000.

[0039] (3) The thickness ratio of the transparent layer to the white layer of the composite white film is 1:X, and the mass percentage of titanium dioxide in the white layer is A1.

[0040] (4) The wire mesh containing the composite white adhesive film sample was placed in the solvent for extraction;

[0041] (5) After extraction, the wire mesh containing the sample is dried, and the weight of the sample is weighed using an electronic analytical balance with a strength of 0.01% as W3 (g). The mass percentage of titanium dioxide in the extracted sample is A2 (g).

[0042] (6) Separating the titanium dioxide and main resin in the composite white photovoltaic film allows for a more accurate reflection of the true cross-linking degree of the main resin in the composite white photovoltaic film. The main resin of the composite white photovoltaic film includes the main resin in the white layer and the main resin in the transparent layer.

[0043] The mass of the main resin in the white layer is approximately... The mass of the main resin in the transparent layer is The content of the main resin in the extracted composite white photovoltaic film is (W3-W1)(1-A2). The degree of crosslinking C of the composite white photovoltaic film is calculated using the following formula:

[0044]

[0045]

[0046] Furthermore, the composite white photovoltaic film is a composite white EVA photovoltaic film.

[0047] Furthermore, the extraction solvent is xylene.

[0048] Furthermore, the extraction temperature is 135-140℃, and the extraction time is 4-6 hours.

[0049] When the composite white film is an EVA film, the extraction conditions are as follows: xylene is used as the solvent, the solvent volume is 500-800 mL, the extraction temperature is 135-140℃, and the extraction time is 4-6 h.

[0050] Furthermore, the sample drying process is carried out in a vacuum drying oven at a temperature of 135-140℃ and a vacuum degree of 0.1MPa for a drying time of ≥3h.

[0051] Furthermore, in the aforementioned test method, in order to reduce the "swelling" of the composite white adhesive film in the solvent and its overflow from the wire mesh, the wire mesh in this invention is required to have a mesh count >120.

[0052] Furthermore, in the aforementioned test method, when the composite white film is an EVA film, that is, the main resin in the composite white film is EVA resin, the extraction conditions are as follows: xylene is used as the solvent, the solvent volume is 500-800 mL, the extraction temperature is set to 135-140℃, and the extraction time is 4-6 h.

[0053] Furthermore, in the aforementioned testing method, the sample drying process is carried out in a vacuum drying oven, with the temperature set at 135-140℃, the vacuum degree set at 0.1MPa, and the sample drying time >3h.

[0054] Furthermore, in the aforementioned testing method, the thickness ratio of the transparent layer to the white layer of the composite white adhesive film is obtained by measuring with a metallographic microscope or a laser microscope.

[0055] Furthermore, in the aforementioned testing method, the mass percentage of titanium dioxide in the sample before extraction is obtained by the titanium dioxide ratio provided by the manufacturer, or by thermogravimetric analysis, or by ash analysis, and the titanium dioxide content in the sample after extraction is obtained by thermogravimetric analysis or ash analysis.

[0056] In the crosslinking degree calculation method provided by this invention, since the titanium dioxide content in the white layer of the composite white film is low (usually less than 10%), the density of the white layer can be considered to be the same as that of the transparent layer, and the mass of the main resin in the white layer is approximately... This approximate mass is close to the mass of the main resin in the actual white layer.

[0057] The transparent layer is entirely composed of the main resin, and the mass of the resin in the transparent layer is... Therefore, the degree of crosslinking calculated by the formula provided by this invention is closer to the true degree of crosslinking than the existing formula for calculating the degree of crosslinking, and can more accurately reflect the degree of crosslinking of the resin in the composite white film.

[0058] Compared with the prior art, the crosslinking degree testing method provided by the present invention has the following advantages:

[0059] (1) This invention provides a crosslinking degree testing method suitable for composite white photovoltaic films, and the calculated crosslinking degree of the composite white photovoltaic film is closer to the true crosslinking degree. Photovoltaic cells require the crosslinked film to have good adhesion to the glass and backsheet, and also to meet the protection requirements for the solar cells. Typically, the crosslinking degree of white photovoltaic films (including white composite EVA films) for photovoltaic modules is usually controlled between 75% and 95%. Therefore, a more realistic crosslinking degree can more effectively assess whether the composite white photovoltaic film meets the requirements of photovoltaic modules.

[0060] (2) The method of the present invention fully considers the influence of the introduction of titanium dioxide and the difference in the thickness ratio of the transparent layer and the white layer on the crosslinking degree of the white photovoltaic film. With a more accurate crosslinking degree value, the content of the additives that control the crosslinking rate in the formulation can be adjusted, thereby guiding the design of the composite white photovoltaic film formulation and structure.

[0061] (3) The method of the present invention can obtain a more realistic degree of crosslinking of the composite white photovoltaic film simply and quickly by collecting data such as the titanium dioxide content and the thickness ratio of the transparent layer and the white layer provided by the manufacturer and substituting them into the test formula provided by the present invention. Attached Figure Description

[0062] Figure 1 This is a schematic diagram of the structure of an existing composite white photovoltaic film. Detailed Implementation

[0063] To better understand the structure of the present invention and the functional features and advantages it can achieve, the following detailed description will be provided in conjunction with preferred embodiments of the present invention:

[0064] like Figure 1As shown, the existing composite white photovoltaic film includes a transparent layer 10 and a white layer 20. The thickness of a typical white composite photovoltaic film is 400-700 μm. For example, if the thickness of the white composite photovoltaic film is 450 μm, and the thickness ratio of the transparent layer 10 to the white layer 20 is 1:2, the thickness of the transparent layer is 150 μm, and the thickness of the white layer is 300 μm.

[0065] Comparative Example 1

[0066] Using an electronic analytical balance with an accuracy of 0.1 mg / 10,000, the weight W1 of the steel wire mesh was measured to be 1.7625 g. The mesh size of the steel wire mesh was 120 mesh. The laminated composite white film sample was then cut into pieces with dimensions of approximately 0.3 cm. 2 Using an electronic analytical balance with an accuracy of 0.01%, the weight of the wire mesh W2 containing the sample was measured to be 2.365 g. The thickness ratio of the transparent layer to the white layer of the composite film was 1:1, and the titanium dioxide content in the white layer was 8.2% by mass. The wire mesh containing the composite white film sample was extracted in 500 mL of xylene at a temperature of 138 °C for 4 h. After extraction, the sample was dried in a vacuum drying oven at 140 °C for 3 h with a vacuum degree of 0.1 MPa. Using an electronic analytical balance with an accuracy of 0.01%, the weight of the dried wire mesh (including the extracted sample) W3 was measured to be 2.2813 g.

[0067] Example 1

[0068] Using an electronic analytical balance with an accuracy of 0.1 mg / 10,000, the weight W1 of the steel wire mesh was measured to be 1.8635 g. The mesh size of the steel wire mesh was 140 mesh. The laminated composite white film sample was then cut into pieces approximately 0.4 cm in size. 2 The weight of the wire mesh containing the sample, W2, was measured to be 2.4686 g using an electronic analytical balance with an accuracy of 0.01 g. The thickness ratio of the transparent layer to the white layer of the composite film was 1:1, and the mass percentage of titanium dioxide in the white layer, A1, was 8.2%. The wire mesh containing the composite white film sample was extracted in 500 mL of xylene at 138 °C for 4 h. After extraction, the sample was dried in a vacuum drying oven at 140 °C for 3 h with a vacuum degree of 0.1 MPa. The weight of the dried wire mesh, W3, was measured to be 2.3853 g using an electronic analytical balance with an accuracy of 0.01 g. Thermogravimetric analysis of the dried composite white film showed that its mass percentage of titanium dioxide, A2, was 10.2%.

[0069] The same sample was used in Implementation 1 and Comparison 1, only the method of calculating the degree of crosslinking was different.

[0070] Example 2

[0071] Using an electronic analytical balance with an accuracy of 0.1 mg / 10,000, the weight W1 of the steel wire mesh was measured to be 1.9519 g. The mesh size of the steel wire mesh was 170 mesh. The laminated composite white film sample was then cut into pieces with dimensions of approximately 0.5 cm. 2 The weight of the wire mesh containing the sample, W2, was measured to be 2.4775 g using an electronic analytical balance with an accuracy of 0.01 g / mL. The thickness ratio of the transparent layer to the white layer of the composite film was 1:2, and the mass percentage of titanium dioxide in the white layer, A1, was 8.3%. The wire mesh containing the composite white film sample was extracted in 700 mL of xylene at 135 °C for 5 h. After extraction, the sample was dried in a vacuum drying oven at 140 °C for 3 h with a vacuum degree of 0.1 MPa. The weight of the dried wire mesh, W3, was measured to be 2.4082 g using an electronic analytical balance with an accuracy of 0.01 g / mL. Thermogravimetric analysis of the dried composite white film showed that its mass percentage of titanium dioxide, A2, was 12.4%.

[0072] Example 3

[0073] Using an electronic analytical balance with an accuracy of 0.1 mg / 10,000, the weight W1 of the steel wire mesh was measured to be 2.0341 g. The mesh size of the steel wire mesh was 140 mesh. The laminated composite white film sample was then cut into pieces with dimensions of approximately 0.2 cm. 2 The weight of the wire mesh containing the sample, W2, was measured to be 2.5170 g using an electronic analytical balance with an accuracy of 0.01 g. The thickness ratio of the transparent layer to the white layer of the composite film was 1:3, and the titanium dioxide content (A1) in the white layer was 8.1%. The wire mesh containing the composite white film sample was extracted in 600 mL of xylene at 138 °C for 6 h. After extraction, the sample was dried in a vacuum drying oven at 140 °C for 4 h with a vacuum level of 0.1 MPa. The weight of the dried wire mesh, W3, was measured to be 2.4525 g using an electronic analytical balance with an accuracy of 0.01 g. Thermogravimetric analysis of the dried composite white film showed that its titanium dioxide content (A2) was 13.8%.

[0074] Example 4

[0075] Using an electronic analytical balance with an accuracy of 0.1 mg / 10,000, the weight W1 of the steel wire mesh was measured to be 1.6384 g. The mesh size of the steel wire mesh was 120 mesh. The laminated composite white film sample was then cut into pieces with dimensions of approximately 0.4 cm. 2The weight of the wire mesh containing the sample, W2, was measured to be 2.1602 g using an electronic analytical balance with an accuracy of 0.01 g. The thickness ratio of the transparent layer to the white layer of the composite film was 1:3, and the titanium dioxide content (A1) in the white layer was 8.2%. The wire mesh containing the composite white film sample was extracted in 800 mL of xylene at 140 °C for 5 h. After extraction, the sample was dried in a vacuum drying oven at 135 °C for 3 h with a vacuum level of 0.1 MPa. The weight of the dried wire mesh, W3, was measured to be 2.0942 g using an electronic analytical balance with an accuracy of 0.01 g. Thermogravimetric analysis of the dried composite white film showed that its titanium dioxide content (A2) was 13.6%.

[0076] Example 5

[0077] Using an electronic analytical balance with an accuracy of 0.1 mg / 10,000, the weight W1 of the steel wire mesh was measured to be 1.3269 g. The mesh size of the steel wire mesh was 170 mesh. The laminated composite white film sample was then cut into pieces with dimensions of approximately 0.4 cm. 2 The weight of the wire mesh containing the sample, W2, was 1.8254 g using an electronic analytical balance with an accuracy of 0.01 g. The thickness ratio of the transparent layer to the white layer of the composite film was 1:4, and the titanium dioxide content (A1) in the white layer was 8.3%. The wire mesh containing the composite white film sample was extracted in 800 mL of xylene at 135 °C for 6 h. After extraction, the sample was dried in a vacuum drying oven at 138 °C for 4 h with a vacuum of 0.1 MPa. The weight of the dried wire mesh, W3, was 1.7502 g using an electronic analytical balance with an accuracy of 0.01 g. Thermogravimetric analysis of the dried composite white film showed that its titanium dioxide content (A2) was 14.1%.

[0078] Comparative Example 1 calculates the degree of crosslinking using existing crosslinking degree calculation methods: Examples 1-5 use the crosslinking degree calculation method provided by this invention to calculate the crosslinking degree. The obtained crosslinking degrees are shown in Table 1.

[0079] Table 1 shows the specific parameters and crosslinking degree calculation results for Examples 1-5 and Comparative Example 1.

[0080]

[0081] The test results from the above embodiments and comparative examples show that the crosslinking degree testing method provided by the present invention is closer to the true crosslinking degree and more accurate than existing film measurement methods. Through the crosslinking degree results of Comparative Example 1 and Example 1, it can be seen that the crosslinking degree test method (Method 2) of the present invention yields a lower value than the existing crosslinking degree calculation method (Method 1), but both are within the acceptable crosslinking degree range, and more accurately reflect the true crosslinking degree of the composite white photovoltaic film. In particular, Examples 2-5 demonstrate that for composite white photovoltaic films with different layer thickness ratios, the crosslinking degree test method of the present invention can obtain accurate crosslinking degree values.

[0082] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. All equivalent variations and modifications made based on the content of the present invention are covered within the patent scope of the present invention.

Claims

1. A method for testing the crosslinking degree of a composite white photovoltaic adhesive film, the composite white photovoltaic adhesive film comprising a transparent layer and a white layer, characterized in that, The method includes the following steps: (1) Obtain the sample mass M1 of the composite white photovoltaic film, the mass percentage of titanium dioxide in the white layer of the composite white photovoltaic film A1, and the thickness ratio of the transparent layer to the white layer of the composite white photovoltaic film is 1:X; (2) Extraction of the composite white photovoltaic film sample; (3) The composite white photovoltaic film sample was extracted and dried to obtain the mass M2 of the composite white photovoltaic film sample and the mass percentage of titanium dioxide in the extracted and dried sample A2. (4) Calculate the degree of crosslinking of the composite white photovoltaic film using the following formula:

2. The method for testing the degree of crosslinking of the composite white photovoltaic film according to claim 1, characterized in that, The method includes the following steps: (1) Weigh the wire mesh and denote its weight as W1 (g); (2) The crosslinked composite white adhesive film sample was cut into small pieces with a size of 0.2-0.5 cm 2 , and the weight of the steel wire mesh with the sample was measured as W2 (g); (3) The thickness ratio of the transparent layer to the white layer of the composite white film is 1:X, and the mass percentage of titanium dioxide in the white layer is A1. (4) The wire mesh containing the composite white adhesive film sample was placed in a solvent for extraction; (5) After the extraction is completed, the wire mesh containing the sample is dried, and the weight of the sample is W3 (g). The mass percentage of titanium dioxide in the sample after extraction is A2 (g). (6) The main resin of the composite white photovoltaic film includes the main resin in the white layer and the main resin in the transparent layer. The mass of the main resin in the white layer is... The mass of the main resin in the transparent layer is The content of the main resin in the extracted composite white photovoltaic film is (W3-W1)(1-A2); the degree of crosslinking C of the composite white photovoltaic film is calculated according to the following formula:

3. The method for testing the degree of crosslinking of the composite white photovoltaic film according to claim 1 or 2, characterized in that, The composite white photovoltaic film is a composite white EVA photovoltaic film.

4. The method for testing the degree of crosslinking of the composite white photovoltaic film according to claim 3, characterized in that, The extraction solvent was xylene.

5. The method for testing the degree of crosslinking of the composite white photovoltaic film according to claim 4, characterized in that, The extraction temperature is 135-140℃, and the extraction time is 4-6 hours.

6. The method for testing the degree of crosslinking of the composite white photovoltaic film according to claim 2, characterized in that, When the composite white film is an EVA film, the extraction conditions are as follows: xylene is used as the solvent, the solvent volume is 500-800 mL, the extraction temperature is 135-140℃, and the extraction time is 4-6 h.

7. The method for testing the degree of crosslinking of the composite white photovoltaic film according to claim 1 or 2, characterized in that, The sample drying process was carried out in a vacuum drying oven at a temperature of 135-140℃ and a vacuum degree of 0.1MPa for a drying time of ≥3h.

8. The method for testing the degree of crosslinking of the composite white photovoltaic film according to claim 1 or 2, characterized in that, The white layer comprises a main resin and titanium dioxide, and the transparent layer is composed of the main resin.

9. The method for testing the degree of crosslinking of the composite white photovoltaic film according to claim 8, characterized in that, The main resin is EVA resin or POE resin.

10. The method for testing the degree of crosslinking of the composite white photovoltaic film according to claim 1 or 2, characterized in that, X is 1-4.

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