Method for detecting the pmma coating state of a diaphragm

Abstract

This invention discloses a method for detecting the PMMA coating status of a diaphragm. The method involves folding a diaphragm coated with PMMA to bring the PMMA coatings into contact, then wetting the diaphragm with ethyl acetate to disperse and soften the solid PMMA molecules, resulting in a viscous, gel-like form. The adhesion between the diaphragms is then tested using a tensile testing machine. By comparing the detected adhesion with the standard value of adhesion for a normally coated diaphragm, it can be determined whether the diaphragm has insufficient or missing PMMA coating. This method achieves a smaller standard deviation and allows for rapid detection of whether the diaphragm has insufficient or missing PMMA coating, solving the problem of the inability to quickly determine whether the PMMA coating on the diaphragm is insufficient or missing.

Description

Technical Field

[0001] This invention relates to the field of battery separator testing technology, and more specifically to a method for detecting the PMMA coating status of a separator. Background Technology

[0002] As the market for coated separators continues to expand, PMMA coatings for separators are gaining increasing penetration in mid-to-high-end power batteries and energy storage batteries due to their cost advantages and process compatibility. However, at room temperature, PMMA coatings are colorless, odorless, and transparent polymer films, making it visually impossible to determine whether PMMA is applied to the separator surface. If PMMA is missed or insufficiently applied, it will result in no adhesion or poor adhesion, making it easy for the separator and the positive and negative electrode plates of the battery cell to slip and delaminate, leading to misalignment and uneven thickness of the battery cell electrodes, directly causing rework or even scrapping of the battery cell.

[0003] Currently, the hot-pressing test is used to test whether the diaphragm surface is coated with PMMA. This test method is time-consuming and labor-intensive, and the test results have a large relative standard deviation and poor data stability. There is an urgent need for a method that can quickly determine whether the PMMA coating of the diaphragm is missing or insufficient. Summary of the Invention

[0004] This invention addresses the shortcomings of existing technologies by providing a method for detecting the PMMA coating status of diaphragms. This method can quickly detect whether there is any omission or insufficient PMMA coating on the diaphragm, and the detection results are accurate and efficient.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for detecting the PMMA coating state of a diaphragm includes the following steps: S1, Fold the diaphragm in half so that the PMMA coated surfaces on the diaphragm come into contact with each other, and cut the folded part of the diaphragm to obtain the test sample; S2, the test sample is completely wetted with ethyl acetate, then rolled and dried. S3. After drying, the test sample is pulled apart using a tensile testing machine to separate the PMMA coated surfaces that are in contact with each other, and the tensile parameters are recorded. S4. Calculate the average value of the recorded tensile parameters, and then divide the average value by the area of ​​the test sample to obtain the adhesive force value. S5, Apply the aforementioned steps S1-S4 to the normally coated diaphragm to obtain the standard value of the adhesion force of the normally coated diaphragm. S6, compare the adhesion strength value with the standard adhesion strength value of a normally coated diaphragm; The test results obtained through the above testing steps have a small standard deviation. By comparing them with the standard value of the adhesion force of a normally coated diaphragm, it is possible to quickly detect whether the diaphragm has missed or insufficient PMMA coating, thus solving the problem of not being able to quickly determine whether the PMMA coating of the diaphragm has missed or insufficient coating.

[0006] As a preferred embodiment, in step S1, the size of the test sample is 130mm*65mm.

[0007] As a preferred embodiment, in step S2, the mass percentage concentration of the ethyl acetate is 100%.

[0008] As a preferred option, in step S2, a pressure roller weighing two kg is used for reciprocating rolling.

[0009] As a preferred option, the reciprocating rollers are pressed three times.

[0010] As a preferred embodiment, in step S3, one side of the test sample is adhered to the test plate using a first double-sided adhesive, the area of ​​the first double-sided adhesive being greater than or equal to the area of ​​the test sample. Flexible paper is adhered to one end of the other side of the test sample using a second double-sided adhesive. The two test jaws of the tensile testing machine clamp the flexible paper and the test plate respectively.

[0011] As a preferred option, in step S3, the testing speed of the tensile testing machine is 80 mm / min, and after pre-stretching for 10 mm, it returns to its original position before being stretched again.

[0012] As a preferred embodiment, in step 2, the test sample is housed using a accommodating assembly, which includes a accommodating box and a cover plate. The accommodating box has a recessed cavity. In use, the test sample is placed inside the cavity, and the cover plate presses down on the test sample.

[0013] As a preferred embodiment, the area of ​​the cover plate is larger than the area of ​​the test sample.

[0014] As a preferred embodiment, the cover plate is provided with several through holes.

[0015] Compared with the prior art, the present invention has significant advantages and beneficial effects, specifically, 1. The membrane is wetted with ethyl acetate, which disperses and softens the solid PMMA molecules, eventually resulting in a viscous gel-like form. The adhesion between the membranes is then tested using a tensile testing machine. By comparing the detected adhesion with the standard value of the adhesion of a normally coated membrane, it can be determined whether the membrane has been missed or insufficiently coated with PMMA. This testing method has a smaller standard deviation and more accurate test results compared to the existing hot-pressing test method. 2. Compared with existing hot pressing testing methods, this method is faster and can avoid the interference of fluctuations in process parameters such as temperature, pressure, and holding time during hot pressing on the test results.

[0016] To more clearly illustrate the structural features, technical means, and specific objectives and functions achieved by the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: Attached Figure Description

[0017] Figure 1 This is a process flow diagram of an embodiment of the present invention; Figure 2 This is a flowchart of step S1, obtaining the test sample, in an embodiment of the present invention. Figure 3 This is a schematic diagram of the structure of the test sample in step S3 of an embodiment of the present invention.

[0018] Figure 4 This is a schematic diagram of the detection tool structure according to an embodiment of the present invention; Explanation of reference numerals in the attached diagram: 10. Receiving box; 11. Receiving cavity; 20. Cover plate; 21. Through hole; 30. Diaphragm; 31. PMMA; 32. Test plate; 33. Flexible paper; 34. First double-sided adhesive; 35. Second double-sided adhesive. Detailed Implementation

[0019] In the description of this invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the indicated position or element must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0020] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0021] like Figure 1-3 As shown, this invention discloses a method for detecting the PMMA coating state of a diaphragm, comprising the following steps: like Figure 2As shown in Figure S1, the diaphragm 30 is folded in half so that the PMMA31 coated surfaces on the diaphragm 30 come into contact with each other. The test sample is then prepared by cutting the folded part of the diaphragm 30. S2, the test sample was completely wetted with ethyl acetate, then rolled and dried. S3. After drying, the test sample is pulled apart using a tensile testing machine to separate the PMMA coated surfaces that are in contact with each other, and the tensile parameters are recorded. S4. Calculate the average value of the recorded tensile parameters, and then divide the average value by the area of ​​the test sample to obtain the adhesive force value. S5, the normally coated diaphragm 30 is subjected to the aforementioned steps S1-S4 to obtain the standard value of the adhesion force of the normally coated diaphragm 30. S6, compare the adhesion strength value with the standard adhesion strength value of a normally coated diaphragm; The test results obtained through the above test steps have a small standard deviation. By comparing them with the standard value, it is possible to quickly detect whether the diaphragm 30 has missed or insufficient PMMA31 coating, thus solving the problem of not being able to quickly determine whether the PMMA31 coating of the diaphragm 30 has missed or insufficient coating.

[0022] In step S1, the size of the test sample is 130mm*65mm.

[0023] In step S2, the mass percentage concentration of the ethyl acetate is 100%.

[0024] In step S2, a pressure roller weighing two kg is used for reciprocating rolling.

[0025] The reciprocating rollers are pressed three times.

[0026] In step S3, one side of the test sample is adhered to the test plate 32 using a first double-sided adhesive 34, the area of ​​which is greater than or equal to the area of ​​the test sample. Flexible paper 33 is adhered to one end of the other side of the test sample using a second double-sided adhesive 35. The test plate 32 and flexible paper 33 are then attached to the test sample in the following structure: Figure 3 As shown, the two test jaws of the tensile testing machine are clamped onto the flexible paper 33 and the test plate 32, respectively.

[0027] In step S3, the testing speed of the tensile testing machine is 80 mm / min. After pre-stretching for 10 mm, it returns to its original position and then performs the stretching again.

[0028] like Figure 4 As shown, in step 2, the test sample is contained using a accommodating assembly, which includes a accommodating box 10 and a cover plate 20. The accommodating box 10 has a recessed receiving cavity 11. In use, the test sample is placed in the receiving cavity 11 and the cover plate 20 is pressed on the test sample.

[0029] The area of ​​the cover plate 20 is larger than the area of ​​the test sample.

[0030] The cover plate 20 is provided with a plurality of through holes 21; by providing a plurality of through holes 21, gas can be discharged through the through holes 21 during rolling.

[0031] This invention uses ethyl acetate to wet the diaphragm 30, dispersing and softening the molecules of solid PMMA31, ultimately resulting in a viscous gel-like form. The adhesion between the diaphragms 30 is then tested using a tensile testing machine. By comparing the detected adhesion with the standard value of the adhesion of a normally coated diaphragm 30, it can be determined whether the diaphragm 30 has been missed or insufficiently coated with PMMA31. Compared with existing hot-pressing testing methods, this method is faster and can avoid the interference of fluctuations in process parameters such as temperature, pressure, and holding time during hot pressing on the test results.

[0032] The following examples and comparative examples further illustrate the technical solutions of this application, but this application is not limited to these examples.

[0033] In this invention, the testing steps of the traditional hot-pressing method are as follows: Fold the diaphragm in half 30° so that the side with the PMMA31 coating is in contact. After cutting the folded part, use a mold to stamp out a test sample of 130*65mm size. Place the test sample into a hot press, set the temperature to 60℃, the pressure to 0.6Mpa, and the hot pressing time to 75s.

[0034] After the hot pressing is completed, the test sample is removed and fixed onto the test plate 32 of the same size with double-sided tape. Then, a flexible paper 33 of the same size with thin strips of double-sided tape is attached to one end of the diaphragm 30 on the other side.

[0035] The upper clamp of the tensile testing machine holds flexible paper 33, and the lower clamp holds steel plate 32. The testing speed of the tensile testing machine is 80mm / min. After pre-stretching 10mm, it returns to the original position and then stretches again. After the test is completed, the adhesive force data obtained from the test is exported.

[0036] The method for calculating the relative standard deviation is as follows: Relative standard deviation = (standard deviation / mean) × 100%.

[0037] In this invention, the standard value of the adhesion force of a normally coated diaphragm is obtained by averaging the adhesion force values ​​of multiple normally coated diaphragms detected by the method of this invention. The dimensions and PMMA31 coating amount of the normally coated diaphragm during testing are consistent with the dimensions and predetermined PMMA31 coating amount of the test sample to be tested.

[0038] Example 1

[0039] PMMA31 was coated onto the diaphragm 30, and the surface density of the PMMA31 coating was tested using a Japanese Kurabo infrared thickness gauge. Ten portions of diaphragm 30 with a PMMA31 coating surface density of 0.90±0.1mg / 5000mm² were taken, and two test samples were prepared for each portion of diaphragm 30 through step S1. A total of 20 test samples were prepared in the above manner. Ten test samples were tested using the traditional hot-pressing test method, and another ten test samples were tested using the test method of this invention. The test results are shown in Table 1. Table 1

[0040] Example 2

[0041] PMMA31 was coated onto the diaphragm 30, and the surface density of the PMMA31 coating was tested using a Japanese Kurabo infrared thickness gauge. Ten portions of diaphragm 30 with PMMA31 coating surface density in the range of 1.35±0.1mg / 5000mm² were taken. Two test samples were prepared for each portion of diaphragm 30 through step S1. A total of 20 test samples were prepared in the above manner. Ten test samples were tested using the traditional hot-pressing test method, and another ten test samples were tested using the test method of this invention. The test results are shown in Table 2. Table 2 As shown in Table 1, the relative standard deviation of the test results using the traditional hot pressing method is 28.06%, while the relative standard deviation of the test results using the test method of this invention is 4.40. As shown in Table 2, the relative standard deviation of the test results using the traditional hot-pressing method is 16.41%, while the relative standard deviation of the test results using the test method of this invention is 4.89%. The results above show that the adhesive force measured by the test method of this invention has better repeatability, smaller relative standard deviation, and more accurate results.

[0042] Example 3

[0043] PMMA31 was coated onto the diaphragm 30, and the surface density of the PMMA31 coating was tested using a Japanese Kurabo infrared thickness gauge. Ten diaphragms 30 with PMMA31 coating surface densities in the range of 0.30-0.95 / 5000mm² were taken and test samples were prepared through step S1. A total of 10 test samples were prepared in the above manner. Ten test samples were tested using the test method of this invention; PMMA31 was coated onto the diaphragm 30, and the surface density of the PMMA31 coating was measured using a Japanese Kurabo infrared thickness gauge. Ten diaphragms 30 with a PMMA31 coating surface density in the range of 1.4±0.1mg / 5000mm² were taken and test samples were prepared through step S1. A total of 10 test samples were prepared in the above manner. Ten test samples were tested using the test method of this invention; Ten test samples were prepared by directly folding the diaphragm 30 without coating it with PMMA31. Ten test samples were tested using the test method of this invention; The test results are shown in Table 3: Table 3 From Table 3, we can see that... When the diaphragm 30 is coated with sufficient PMMA31, the average adhesion strength is 53.60 N / m, the minimum is 50.48 N / m, and the average PMMA31 coating amount is 1.4 mg / 5000 mm². However, when the diaphragm 30 is coated with insufficient PMMA31, the maximum adhesion strength is 45.24 N / m, and the maximum PMMA31 coating amount is 0.91 mg / 5000 mm². The adhesion strength measured by the method of this invention shows that when the PMMA31 coating amount is 1.4 ± 0.1 mg / 5000 mm², the adhesion strength is greater than 50 N / m. When the adhesion strength is less than 50 N / m, the diaphragm 30 has a problem of insufficient PMMA31 coating. The method of this invention can quickly determine whether the diaphragm 30 has a problem of insufficient PMMA31 coating.

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the actual technology of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for detecting the coating state of a PMMA coating on a diaphragm, characterized in that: Includes the following steps: S1, Fold the diaphragm in half so that the PMMA coated surfaces on the diaphragm come into contact with each other, and cut the folded part of the diaphragm to obtain the test sample; S2, the test sample is completely wetted with ethyl acetate, then rolled and dried. S3. After drying, the test sample is pulled apart using a tensile testing machine to separate the PMMA coated surfaces that are in contact with each other, and the tensile parameters are recorded. S4. Calculate the average value of the recorded tensile parameters, and then divide the average value by the area of ​​the test sample to obtain the adhesive force value. S5, Apply the aforementioned steps S1-S4 to the normally coated diaphragm to obtain the standard value of the adhesion force of the normally coated diaphragm. S6. Compare the adhesion strength value with the standard adhesion strength value of a normally coated diaphragm.

2. The method for detecting the coating state of a PMMA coating on a diaphragm according to claim 1, characterized in that, In step S1, the size of the test sample is 130mm*65mm.

3. The method for detecting the coating state of a PMMA coating on a diaphragm according to claim 1, characterized in that, In step S2, the mass percentage concentration of the ethyl acetate is 100%.

4. The method for detecting the coating state of a PMMA coating on a diaphragm according to claim 1, characterized in that, In step S2, a pressure roller weighing two kg is used for reciprocating rolling.

5. The method for detecting the coating state of a PMMA coating on a diaphragm according to claim 4, characterized in that, The reciprocating rollers are pressed three times.

6. The method for detecting the coating state of a PMMA coating on a diaphragm according to claim 1, characterized in that, In step S3, one side of the test sample is adhered to the test plate using the first double-sided adhesive, the area of ​​the first double-sided adhesive being greater than or equal to the area of ​​the test sample. The flexible paper is adhered to one end of the other side of the test sample using the second double-sided adhesive. The two test jaws of the tensile testing machine clamp the flexible paper and the test plate respectively.

7. The method for detecting the coating state of a PMMA coating on a diaphragm according to claim 6, characterized in that, In step S3, the testing speed of the tensile testing machine is 80 mm / min. After pre-stretching for 10 mm, it returns to its original position and then performs the stretching again.

8. The method for detecting the coating state of a PMMA coating on a diaphragm according to claim 1, characterized in that, In step 2, the test sample is contained using a accommodating assembly, which includes a accommodating box and a cover plate. The accommodating box has a recessed cavity. In use, the test sample is placed in the cavity and the cover plate is pressed on the test sample.

9. The method for detecting the coating state of a PMMA coating on a diaphragm according to claim 8, characterized in that, The area of ​​the cover plate is larger than the area of ​​the test sample.

10. The method for detecting the coating state of a PMMA coating on a diaphragm according to claim 9, characterized in that, The cover plate has several through holes.

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