Test method for low temperature crosslinking degree of EVA adhesive film

Abstract

This invention discloses a method for testing the low-temperature crosslinking degree of EVA film, comprising the following steps: Step 1: Selecting a film sample as the first sample; Step 2: Laminating the first sample to form a second sample; Step 3: Cutting the second sample to form multiple third samples; then placing the third samples into a container and adding xylene to the container; Step 4: Placing the third samples into a dimethyl silicone oil bath for low-temperature extraction, with the extraction temperature set at 110±5℃; Step 5: Removing the third samples and drying them; Step 6: Cooling and drying the dried third samples; Step 7: Calculating the degree of crosslinking. This invention's method for testing the low-temperature crosslinking degree of EVA film utilizes a low-temperature heating extraction method to test the crosslinking degree, avoiding secondary crosslinking of the EVA film during continuous heating extraction, ensuring accurate characterization of the actual crosslinking degree of the EVA film, improving the accuracy of test data, and thus reducing the risk of photovoltaic module failure in outdoor environments.

Description

Technical Field

[0001] This invention belongs to the field of film testing technology. Specifically, this invention relates to a method for testing the degree of crosslinking of EVA films at low temperatures. Background Technology

[0002] Solar energy is a green, pollution-free, inexhaustible, and renewable clean energy source. Solar energy is utilized through two methods: photothermal conversion and photovoltaic conversion. Photovoltaic power generation utilizes the photothermal conversion method. Since solar cells cannot be directly exposed to air, rain, or other natural conditions, but photovoltaic modules are used outdoors, encapsulation of the solar cells is necessary. Currently, this is mainly achieved using a self-resistant, weather-resistant, highly adhesive, highly transparent, and elastic encapsulating film. This film is then bonded together with an upper protective material (glass) and a lower protective material (backsheet or glass). Finally, a junction box and frame are installed to form a photovoltaic module, ensuring a lifespan of 25-30 years outdoors.

[0003] In photovoltaic (PV) module encapsulation, the performance of the EVA (Polyethylene vinyl acetate) film used is crucial to the quality and lifespan of the PV module. The degree of crosslinking is a physical quantity used to characterize the extent of crosslinking in the EVA film. Its magnitude not only determines the mechanical properties of the cured EVA film, such as peel strength and tensile strength, but also affects the environmental aging performance of the PV module. Therefore, accurate and rapid measurement of the film's degree of crosslinking is particularly important.

[0004] The existing method for testing the degree of crosslinking of EVA film is mainly the electrothermal sleeve xylene extraction method. Although this method can test the crosslinking of EVA film after high-temperature lamination, the extraction is carried out at a high temperature of 140°C. At this temperature, EVA film that is not fully crosslinked during lamination will undergo secondary crosslinking, which will affect the determination of the final degree of crosslinking and thus affect the service life of EVA film.

[0005] This invention provides a method for testing the low-temperature crosslinking degree of EVA film, specifically addressing how to avoid deviations in test results caused by secondary crosslinking of EVA film, in order to accurately characterize the actual crosslinking degree of EVA film and ensure that photovoltaic modules can meet harsh outdoor operating conditions. Summary of the Invention

[0006] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention provides a low-temperature crosslinking degree testing method for EVA films, the purpose of which is to avoid the deviation in test results caused by secondary crosslinking of EVA films, ensure accurate characterization of the actual crosslinking degree of EVA films, and ensure that photovoltaic modules can meet harsh outdoor operating conditions.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a method for testing the low-temperature crosslinking degree of EVA film, comprising the following steps:

[0008] Step 1: Select a film sample as the first test sample;

[0009] Step 2: Lamination of the first sample to form the second sample;

[0010] Step 3: Cut the second sample to form multiple third samples; then put the third samples into a container and pour xylene into the container;

[0011] Step 4: Place the third sample into a dimethyl silicone oil bath for low-temperature extraction, with the extraction temperature set at 110±5℃.

[0012] Step 5: After removing the third sample, perform a drying process;

[0013] Step Six: Cool and dry the dried third sample;

[0014] Step 7: Calculate the degree of crosslinking;

[0015] In step seven, the degree of crosslinking of the EVA film is calculated using the following formula:

[0016] Degree of crosslinking (%) = (W2 / W1) * 100%

[0017] Wherein, W2 is the weight of the third sample obtained in step six, and W1 is the weight of the third sample obtained in step three.

[0018] The extraction temperature is set to 105℃, 110℃, or 115℃.

[0019] In step four, the extraction time is set to 12–16 hours.

[0020] In step five, the temperature for drying the third sample is set to 140°C, and the drying time is 8 hours.

[0021] In step two, the first sample, glass, and release film are placed in a lamination device for curing and cross-linking to form the second sample; two layers of the first sample are sandwiched between two layers of release film, and the glass is bonded to a layer of release film, with the glass located at the bottom layer.

[0022] The laminating equipment is a dual-cavity laminator.

[0023] In step three, the amount of xylene used is 100 ml.

[0024] In step four, the extraction equipment is an oil bath, and the dimethyl silicone oil occupies 2 / 3 of the volume of the oil bath.

[0025] In step six, the cooling time is set to 30 minutes.

[0026] The low-temperature crosslinking degree test method for EVA film of the present invention uses a low-temperature heating extraction test method to test the crosslinking degree, which can avoid secondary crosslinking of EVA film during continuous heating extraction, ensure accurate characterization of the actual crosslinking degree of EVA film, improve the accuracy of test data, and thus reduce the risk of failure of photovoltaic modules in outdoor environments. Detailed Implementation

[0027] The following description of the embodiments provides a more detailed explanation of the specific implementation of the present invention, with the aim of helping those skilled in the art to have a more complete, accurate, and in-depth understanding of the concept and technical solutions of the present invention, and facilitating its implementation.

[0028] This invention provides a method for testing the low-temperature crosslinking degree of EVA films, comprising the following steps:

[0029] Step 1: Select a film sample as the first test sample;

[0030] Step 2: Lamination of the first sample to form the second sample;

[0031] Step 3: Cut the second sample to form multiple third samples; then put the third samples into a container and pour xylene into the container;

[0032] Step 4: Place the third sample into a dimethyl silicone oil bath for low-temperature extraction, with the extraction temperature set at 110±5℃.

[0033] Step 5: After removing the third sample, perform a drying process;

[0034] Step Six: Cool and dry the dried third sample;

[0035] Step 7: Calculate the degree of crosslinking of the EVA film.

[0036] Specifically, the low-temperature crosslinking degree testing method for EVA film provided by this invention overcomes the shortcomings of existing technologies, avoids the deviation in test results caused by secondary crosslinking of EVA film, and can achieve accurate, scientific, and practical characterization of the actual crosslinking degree of the film, ensuring that photovoltaic modules can meet harsh outdoor usage conditions. EVA film is an encapsulation material used in photovoltaic modules between cells and glass, and between cells and backing materials.

[0037] In step one above, a sample was taken, and a 100mm*100mm piece of EVA film to be packaged was selected as the first sample. The cutting tools used were a utility knife and a steel ruler.

[0038] In step two above, the first sample, glass, and release film are placed in a laminating device for curing and cross-linking to form the second sample. The selected materials are stacked from top to bottom in the following order: glass, release film, first sample, first sample, and release film. Two layers of the first sample are sandwiched between two layers of release film, and the glass is bonded to one layer of release film, with the glass at the bottom layer.

[0039] In step two above, the lamination equipment is a dual-cavity laminator.

[0040] In step three above, the laminated sample is selected from the middle position of the second sample, which is 5mm*5mm in size, and cut into four small pieces of the third sample with uniform size. The total weight of the third sample is 1±0.05g.

[0041] In step three above, the container is a 250ml beaker, and the amount of xylene used is 100ml.

[0042] In step four above, the extraction equipment is an oil bath, and dimethyl silicone oil occupies 2 / 3 of the volume of the oil bath.

[0043] In step four above, the extraction time is set to 12–16 hours.

[0044] In step five above, the temperature for drying the third sample is set to 140°C and the drying time is 8 hours.

[0045] In step six above, the cooling time is set to 30 minutes.

[0046] In step seven above, the degree of crosslinking of the EVA film is calculated using the following formula:

[0047] Degree of crosslinking (%) = (W2 / W1) * 100%

[0048] Wherein, W2 is the weight of the third sample obtained in step six, and W1 is the weight of the third sample obtained in step three.

[0049] Example 1

[0050] As a first preferred example, this embodiment provides a method for testing the crosslinking degree of EVA film under low-temperature conditions, including glass placed on the front side of the battery cell, an EVA film, and an adhesive film between the battery cell and the back side material; the testing method includes the following steps:

[0051] Step 1: Sampling. Use a utility knife and a steel ruler to cut a 100mm*100mm EVA film to be packaged as the first sample.

[0052] Step 2: Lamination. Set the lamination parameters in advance. Stack the selected materials from top to bottom as follows: glass, release film, first sample, first sample, and release film. Place the glass-side down into the lamination equipment for curing and cross-linking to form the second sample.

[0053] Step 3: Sample preparation. Take a second sample (5mm x 5mm) from the center of the laminated sample. Cut the second sample into four uniformly sized third samples and weigh them (W1 = 0.95g). Place the third samples in a 250ml beaker and pour in 100ml of xylene to immerse the samples. Set aside for later use.

[0054] Step 4: Low-temperature extraction. Place the third sample prepared in Step 3 into the prepared dimethyl silicone oil bath device. The dimethyl silicone oil in the oil bath device should be higher than the xylene liquid level in the beaker. Set the extraction temperature to 105℃ and extract at this temperature for 12 hours. Then stop heating and use tweezers to take out the cross-linked third sample and place it on the tray.

[0055] Step 5: Drying. Place the third sample on the tray and the tray together into a vacuum drying oven to dry at 140°C for 8 hours.

[0056] Step 6: Cooling. Place the dried third sample in a desiccator and dry for 30 minutes.

[0057] Step 7: Calculation. Take out the third sample from the desiccator and weigh it. The weight of W2 is 0.76g. Calculate the degree of crosslinking of the EVA film using the following formula:

[0058] Degree of crosslinking (%) = W2 / W1 * 100% = 80.0%

[0059] In summary, the initial sample weight W1 was 0.95g, and the sample weight W2 after the experiment was 0.76g; the calculated crosslinking degree was 80.0%, which meets the crosslinking degree requirement, thus proving that the crosslinking degree of the EVA film under this lamination condition meets the requirements of the component end.

[0060] Example 2

[0061] As a second preferred example, this embodiment provides a method for testing the crosslinking degree of EVA film under low-temperature conditions, including glass placed on the front side of the battery cell, an EVA film, and a film between the battery cell and the back material; the testing method includes the following steps:

[0062] Step 1: Sampling. Use a utility knife and a steel ruler to cut a 100mm*100mm EVA film to be packaged as the first sample.

[0063] Step 2: Lamination. Set the lamination parameters in advance. Stack the selected materials from top to bottom as follows: glass, release film, EVA film, EVA film, and release film. Place the glass-side down into the laminator for curing and cross-linking to form the second sample.

[0064] Step 3: Sample preparation. Select a second sample, 5mm x 5mm in size, from the center of the laminated sample. Cut the second sample into four uniformly sized third samples and weigh them (W1 = 1.05g). Place the third samples into a 250ml beaker, then pour in 100ml of xylene to immerse the samples. Set aside for later use.

[0065] Step 4: Low-temperature extraction. Place the third sample prepared in Step 3 into the prepared dimethyl silicone oil bath device. The dimethyl silicone oil in the oil bath device should be higher than the xylene liquid level in the beaker. Set the extraction temperature to 115℃ and extract at this temperature for 16 hours. Then stop heating and use tweezers to take out the cross-linked third sample and place it on the tray.

[0066] Step 5: Drying. Place the sample on the tray and the tray together into a vacuum drying oven to dry at 140°C for 8 hours.

[0067] Step 6: Cooling. Place the dried third sample in a desiccator and dry for 30 minutes.

[0068] Step 7: Calculation. Take out the third sample from the desiccator and weigh it. The weight of W2 is 0.92g. Calculate the degree of crosslinking of the EVA film using the following formula:

[0069] Degree of crosslinking (%) = W2 / W1 * 100% = 87.6%

[0070] In summary, the initial sample weight W1 was 1.05g, and the sample weight W2 after the experiment was 0.92g; the calculated crosslinking degree was 87.6%, which meets the crosslinking degree requirement, thus proving that the crosslinking degree of the EVA film under this lamination condition meets the requirements of the component end.

[0071] Example 3

[0072] As a third preferred example, this embodiment provides a method for testing the crosslinking degree of EVA film under low-temperature conditions, including glass placed on the front side of the battery cell, an EVA film, and an adhesive film between the battery cell and the back side material; the testing method includes the following steps:

[0073] Step 1: Sampling. Use a utility knife and a steel ruler to cut a 100mm*100mm EVA film to be packaged as the first sample.

[0074] Step 2: Lamination. Set the lamination parameters in advance. Stack the selected materials from top to bottom as follows: glass, release film, EVA film, EVA film, and release film. Place the glass-side down into the laminator for curing and cross-linking to form the second sample.

[0075] Step 3: Sample preparation. Select a 5mm*5mm cross-linked EVA strip from the center of the laminated sample, and cut it into four uniform small pieces. Weigh each piece (W1) to 1g. Place the sample in a 250ml beaker, and then pour in 100ml of xylene to immerse the sample. Set aside for later use.

[0076] Step 4: Low-temperature extraction. Place the third sample prepared in Step 3 into the prepared dimethyl silicone oil bath device. The dimethyl silicone oil in the oil bath device should be higher than the xylene liquid level in the beaker. Set the extraction temperature to 110℃ and extract at this temperature for 14 hours. Then stop heating and use tweezers to take out the cross-linked third sample and place it on the tray.

[0077] Step 5: Drying. Place the third sample on the tray and the tray together into a vacuum drying oven to dry at 140°C for 8 hours.

[0078] Step 6: Cooling. Place the dried third sample in a desiccator and dry for 30 minutes.

[0079] Step 7: Calculation. Take out the third sample from the desiccator and weigh it. The weight of W2 is 0.85g. Calculate the degree of crosslinking of the EVA film using the following formula:

[0080] Degree of crosslinking (%) = W2 / W1 * 100% = 85.0%

[0081] In summary, the initial sample weight W1 was 1.0g, and the sample weight W2 after the experiment was 0.85g; the calculated crosslinking degree was 85.0%, which meets the crosslinking degree requirement, thus proving that the crosslinking degree of the EVA film under this lamination condition meets the requirements of the component end.

[0082] The specific embodiments described above further illustrate the technical solution and its beneficial effects. The above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, or improvements made within the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for testing the degree of crosslinking of EVA films at low temperatures, characterized in that, Including the following steps: Step 1: Select a film sample as the first test sample; Step 2: Lamination of the first sample to form the second sample; Step 3: Cut the second sample to form multiple third samples; then put the third samples into a container and pour xylene into the container; Step 4: Place the third sample into a dimethyl silicone oil bath for low-temperature extraction, with the extraction temperature set at 110±5℃. Step 5: After removing the third sample, perform a drying process; Step Six: Cool and dry the dried third sample; Step 7: Calculate the degree of crosslinking; In step seven, the degree of crosslinking of the EVA film is calculated using the following formula: Degree of crosslinking (%) = (W2 / W1) * 100% Wherein, W2 is the weight of the third sample obtained in step six, and W1 is the weight of the third sample obtained in step three.

2. The method for testing the low-temperature crosslinking degree of EVA film according to claim 1, characterized in that, The extraction temperature is set to 105℃, 110℃, or 115℃.

3. The method for testing the low-temperature crosslinking degree of EVA film according to claim 1, characterized in that, In step four, the extraction time is set to 12–16 hours.

4. The method for testing the low-temperature crosslinking degree of EVA film according to any one of claims 1 to 3, characterized in that, In step five, the temperature for drying the third sample is set to 140°C, and the drying time is 8 hours.

5. The method for testing the low-temperature crosslinking degree of EVA film according to any one of claims 1 to 3, characterized in that, In step two, the first sample, glass, and release film are placed in a lamination device for curing and cross-linking to form the second sample; two layers of the first sample are sandwiched between two layers of release film, and the glass is bonded to a layer of release film, with the glass located at the bottom layer.

6. The method for testing the low-temperature crosslinking degree of EVA film according to claim 5, characterized in that, The laminating equipment is a dual-cavity laminator.

7. The method for testing the low-temperature crosslinking degree of EVA film according to any one of claims 1 to 3, characterized in that, In step three, the amount of xylene used is 100 ml.

8. The method for testing the low-temperature crosslinking degree of EVA film according to any one of claims 1 to 3, characterized in that, In step four, the extraction equipment is an oil bath, and the dimethyl silicone oil occupies 2 / 3 of the volume of the oil bath.

9. The method for testing the low-temperature crosslinking degree of EVA film according to any one of claims 1 to 3, characterized in that, In step six, the cooling time is set to 30 minutes.