A method for testing the areal density of a pmma coating

Abstract

The present application provides a kind of PMMA coating area density test method, the test method includes: providing separator sample, the separator sample includes base film and is arranged on the PMMA coating of base film;With the infrared detection device of filter being provided, the separator sample is tested, and the absorbance value is obtained, the transmission wavelength of the filter is 5.7-5.8 μm;The absorbance value is brought into absorbance-area density standard curve, and the PMMA coating area density is obtained.The present application is based on infrared technology and realizes quantitative detection, completely eliminates the influence of base film on detection, and obtains accurate PMMA coating area density.The test method has the characteristics of direct, fast and accurate, and can obtain PMMA coating area density data with high accuracy, small error and high reliability, to provide strong data support for the quality evaluation of secondary battery separator.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology, specifically relating to a method for testing the areal density of PMMA coatings. Background Technology

[0002] PMMA (polymethyl methacrylate, also known as "acrylic") fluorine-free coating is the mainstream environmentally friendly technology route to replace traditional PVDF fluorine-containing coatings in the field of lithium secondary battery separator coating. PMMA itself has a much lower density than PVDF, and as a polymer film, it is loose and porous, not a dense solid. Therefore, the surface density of PMMA coatings applied to the base film is relatively light, mostly around 0.6 mg / 5000 mm². 2 -1.5 mg / 5000 mm 2 If PMMA is missed or insufficiently applied, the adhesion of the electrode sheets will fail. After the battery cell is hot-pressed, gaps, warping, and misalignment will occur between the separator and the electrode sheets, directly causing rework or even scrapping of the battery cell. Moreover, since the PMMA coating has the effect of inhibiting thermal shrinkage, missed or insufficient application also poses a risk of uncontrolled thermal shrinkage. The PMMA coating is colorless and odorless at room temperature, and it is impossible to directly determine whether it is missed or insufficient by visual inspection. Therefore, the areal density of the PMMA coating is a key quality characteristic in the separator coating industry.

[0003] Currently, the industry uses a four-digit electronic balance to calculate the areal density of the PMMA coating using a subtraction method. This involves first weighing the total areal density of the PE base film and the PMMA coating, then subtracting the areal density of the PE base film without the PMMA coating. Since the areal density of the PE base film (taking a thickness of 5 μm as an example) typically fluctuates by 0.25 mg / 5000 mm², this method is less effective. 2 -0.5 mg / 5000 mm 2 This component accounts for 1 / 3 of the PMMA coating surface density and has a significant impact on the PMMA coating surface density test results. Therefore, the PMMA coating surface density obtained by the deduction method is inaccurate, the data is distorted, and there is a risk that the PMMA coating surface density is not within the specification range.

[0004] Therefore, there is an urgent need in the field for a method that can ignore the influence of the PE base film and directly and accurately detect the areal density of the PMMA coating. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for testing the areal density of PMMA coatings. This method utilizes infrared spectroscopy for quantitative detection, completely eliminating the influence of the base film, and enabling direct and rapid detection of the areal density of PMMA coatings, resulting in highly accurate and reliable test results.

[0006] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for testing the areal density of a PMMA coating, the method comprising: A diaphragm sample is provided, the diaphragm sample comprising a base membrane and a PMMA coating disposed on the base membrane; The absorbance value was obtained by testing the membrane sample using an infrared detection device equipped with a filter, wherein the transmission wavelength of the filter is 5.7-5.8 μm; The absorbance value was substituted into the absorbance-area density standard curve to obtain the area density of the PMMA coating.

[0007] The testing method proposed in this invention achieves quantitative detection based on infrared radiation. By setting a filter in the infrared detection device, infrared light of a specific wavelength that the PMMA coating is sensitive to passes through, while blocking infrared light of other wavelengths, thus completely eliminating the influence of the base film on the detection and obtaining the absorbance value of the PMMA coating. This absorbance value is then used in an absorbance-area density standard curve to obtain an accurate PMMA coating area density unaffected by the base film. The testing method of this invention is direct, rapid, and accurate, providing highly accurate, low-error, and reliable PMMA coating area density data, offering strong data support for the quality evaluation of secondary battery separators.

[0008] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The purpose and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0009] As a preferred embodiment of the present invention, the base film includes a PP base film, a PE base film, or a PP / PE composite base film, preferably a PE base film.

[0010] As a preferred embodiment of the present invention, the transmission wavelength of the filter is 5.79-5.8 μm, preferably 5.7954 μm.

[0011] Secondly, the present invention provides a calibration method for infrared detection of the areal density of a PMMA coating, the calibration method comprising: A number of diaphragm standards with PMMA coating areal density gradients are provided, the diaphragm standards comprising a base membrane and a PMMA coating disposed on the base membrane; The absorbance of the diaphragm standard was tested using an infrared detection device equipped with a filter; the transmission wavelength of the filter was 5.7-5.8 μm. The diaphragm standard was cleaned and weighed, and then the measured areal density was calculated according to the following formula I: Measured surface density = 5000 × (W1 - W2) / s (Equation I) In Formula I, the unit of the measured areal density is mg / 5000 mm². 2 W1 represents the mass of the diaphragm standard, in mg; W2 represents the mass of the diaphragm standard after cleaning, in mg; s represents the area of ​​the diaphragm standard, in mm. 2 ; Based on the measured absorbance and areal density values, an absorbance-areal density standard curve is plotted to complete the calibration.

[0012] As a preferred embodiment of the present invention, the PMMA coating surface density gradient of the diaphragm standard is 5-10.

[0013] As a preferred embodiment of the present invention, the PMMA coating of the diaphragm standard has an areal density of 0.5-1.3 mg / 5000 mm². 2 .

[0014] As a preferred embodiment of the present invention, the method for testing absorbance includes: The absorbance of the diaphragm standard is tested using an infrared detection device equipped with a filter. Each point is tested n times to obtain n test values. The average value is taken to obtain the absorbance; n≥2.

[0015] As a preferred embodiment of the present invention, 3≤n≤7.

[0016] As a preferred embodiment of the present invention, the transmission wavelength of the filter is 5.79-5.8 μm, preferably 5.7954 μm.

[0017] As a preferred embodiment of the present invention, the cleaning and weighing method includes: S1. The diaphragm standard is placed in dimethylacetamide for ultrasonic cleaning, then dried and weighed; S2. Repeat step S1 until the absolute value of the mass difference between two adjacent weighings is ≤0.02 mg, and obtain the mass W2 of the diaphragm standard after cleaning.

[0018] As a preferred embodiment of the present invention, the power of the ultrasonic cleaning is 500-1000 W.

[0019] As a preferred embodiment of the present invention, the ultrasonic cleaning time is 1-3 hours.

[0020] As a preferred embodiment of the present invention, the drying temperature is 60-100℃.

[0021] As a preferred embodiment of the present invention, the drying time is 30-60 min.

[0022] As a preferred embodiment of the present invention, the determination coefficient R of the absorbance-area density standard curve is... 2 >0.995.

[0023] Thirdly, the present invention provides an application of the PMMA coating areal density test method as described in the first aspect in secondary batteries.

[0024] As a preferred embodiment of the present invention, the test method is applied to the detection of lithium battery separators.

[0025] Compared with the prior art, the present invention has at least the following beneficial effects: This invention provides a method for testing the areal density of PMMA coatings, enabling quantitative detection based on infrared spectroscopy. This method completely eliminates the influence of the base film on the detection, yielding accurate PMMA coating areal density data. The method is direct, rapid, and accurate, providing highly accurate, low-error, and reliable PMMA coating areal density data, thus offering strong data support for the quality assessment of secondary battery separators. Attached Figure Description

[0026] Figure 1 The absorbance-area density standard curve obtained in Example 1 is shown. Detailed Implementation

[0027] To facilitate understanding of the present invention, specific embodiments are provided to further illustrate the technical solution of the present invention. Those skilled in the art should understand that the embodiments are merely illustrative of the present invention and should not be considered as specific limitations thereof.

[0028] The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used herein, are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not limited to those elements and may also include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0029] In this invention, features marked with "one," "two," or "three" may explicitly or implicitly include one or more of those features, used to distinguish and describe features, without any order or emphasis. In the description of this invention, unless otherwise stated, "multiple" means two or more.

[0030] PMMA coating areal density is a key quality characteristic in the secondary battery separator industry. Current technology uses a subtraction method to determine PMMA coating areal density. However, due to significant fluctuations in the areal density within the roll of PE base film, the PMMA coating areal density test results are inaccurate, leading to data distortion and the risk that the PMMA coating areal density may not be within the specified range.

[0031] To overcome the shortcomings of existing PMMA coating areal density tests, which are greatly affected by the base film and produce inaccurate data, one specific embodiment of the present invention provides a method for testing the areal density of a PMMA coating, the method comprising: A diaphragm sample is provided, the diaphragm sample comprising a base membrane and a PMMA coating disposed on the base membrane; The absorbance value was obtained by testing the membrane sample using an infrared detection device equipped with a filter, wherein the transmission wavelength of the filter is 5.7-5.8 μm; The absorbance value was substituted into the absorbance-area density standard curve to obtain the area density of the PMMA coating.

[0032] This invention utilizes infrared technology for quantitative detection. Specifically, it employs an infrared (IR) detection device to detect different substances (base film, PMMA coating): Infrared density detection is based on the Lambert-Beer law, the core of which is that different substances have different absorption intensities at specific infrared wavelengths, and the absorption amount is linearly related to the mass per unit area (area density) of the substance. This invention has found that the specific infrared wavelength sensitive to the base film (e.g., PE polyethylene base film, where CH bond stretching vibrations occur) is 3.3-3.5 μm, while the specific infrared wavelength sensitive to the PMMA coating (polymethyl methacrylate, where the C=O carbonyl group in the ester group strongly absorbs) is 5.7-5.8 μm. Simultaneously, the base film does not absorb in this wavelength range (5.7-5.8 μm), so its influence can be ignored. Based on this, the present invention incorporates a filter in the infrared detection device. Infrared light passes through the filter, allowing only infrared light of specific wavelengths sensitive to the PMMA coating to pass through, while other wavelengths are effectively blocked. After penetrating the membrane sample via an infrared generator, the infrared detector receives and records the absorbance of the PMMA coating (Abs, i.e., the absorption intensity of the PMMA coating for a specific infrared wavelength). The specific filter completely eliminates the influence of the base film on the detection, yielding the absorbance value of the PMMA coating. This absorbance value is then substituted into a pre-calibrated absorbance-area density standard curve to convert the absorbance value into an accurate PMMA coating area density unaffected by the base film. The testing method provided by this invention is direct, rapid, and accurate, providing highly accurate, low-error, and reliable PMMA coating area density data, offering strong data support for the quality evaluation of secondary battery separators.

[0033] In a preferred embodiment, the base film includes a PP base film, a PE base film, or a PP / PE composite base film, preferably a PE base film.

[0034] In this invention, the transmission wavelength of the filter is 5.7-5.8 μm, for example, it can be 5.72 μm, 5.74 μm, 5.75 μm, 5.76 μm, 5.78 μm, 5.79 μm, 5.792 μm, 5.794 μm, 5.795 μm, 5.796 μm, 5.797 μm, 5.798 μm or 5.799 μm, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, this invention will not exhaustively list the specific values ​​included in the range; preferably, the transmission wavelength of the filter is 5.79-5.8 μm, and more preferably 5.7954 μm.

[0035] Another specific embodiment of the present invention provides a calibration method for infrared detection of PMMA coating areal density, the calibration method comprising: A number of diaphragm standards with PMMA coating areal density gradients are provided, the diaphragm standards comprising a base membrane and a PMMA coating disposed on the base membrane; The absorbance of the diaphragm standard was tested using an infrared detection device equipped with a filter; the transmission wavelength of the filter was 5.7-5.8 μm. The diaphragm standard was cleaned and weighed, and then the measured areal density was calculated according to the following formula I: Measured surface density = 5000 × (W1 - W2) / s (Equation I) In Formula I, the unit of the measured areal density is mg / 5000 mm². 2 W1 represents the mass of the diaphragm standard (i.e., the mass before cleaning), in mg; W2 represents the mass of the diaphragm standard after cleaning, in mg; s represents the area of ​​the diaphragm standard, in mm. 2 ; Based on the measured absorbance and areal density values, an absorbance-areal density standard curve is plotted to complete the calibration.

[0036] In the PMMA coating areal density test method provided by the present invention, the absorbance-area density standard curve can be obtained by the calibration method. First, the diaphragm standard is subjected to infrared detection to obtain the absorbance of the PMMA coating which is not affected by the base film and is accurate. Then, the areal density is measured by cleaning and weighing. Based on the absorbance and areal density measured values, an accurate absorbance-area density standard curve is established.

[0037] For example, a diaphragm standard with a PMMA coating surface density gradient can be prepared by adjusting the roller speed ratio.

[0038] In a preferred embodiment, the PMMA coating surface density gradient of the diaphragm standard is 5-10, for example, 5, 6, 7, 8, 9 or 10.

[0039] In a preferred embodiment, the PMMA coating areal density of the diaphragm standard is 0.5-1.3 mg / 5000 mm². 2 For example, it could be 0.55 mg / 5000 mm. 2 0.6 mg / 5000 mm 2 0.7 mg / 5000 mm 2 0.8 mg / 5000 mm 2 0.9 mg / 5000 mm 2 1 mg / 5000 mm 2 1.1 mg / 5000 mm 2 Or 1.2 mg / 5000 mm 2 And the specific point values ​​between the above-mentioned point values, due to space limitations and for the sake of brevity, this invention will not exhaustively list the specific point values ​​included in the range, preferably 0.6-1.3 mg / 5000 mm. 2 (Samples covering the tolerance range).

[0040] For example, the PMMA coating areal density gradient of the diaphragm standard has seven gradients, each being 0.6 mg / 5000 mm². 2 0.7 mg / 5000 mm 2 0.8 mg / 5000 mm 2 0.9 mg / 5000 mm 2 1 mg / 5000 mm 2 1.1 mg / 5000mm 2 1.2 mg / 5000 mm 2 .

[0041] The transmission wavelength of the filter used in the calibration method is 5.7-5.8 μm, for example, it can be 5.72 μm, 5.74 μm, 5.75 μm, 5.76 μm, 5.78 μm, 5.79 μm, 5.792 μm, 5.794 μm, 5.795 μm, 5.796 μm, 5.797 μm, 5.798 μm or 5.799 μm, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range; preferably, the transmission wavelength of the filter is 5.79-5.8 μm, and more preferably 5.7954 μm.

[0042] In a preferred embodiment, the absorbance testing method includes: The absorbance of the diaphragm standard is tested using an infrared detection device equipped with a filter. Each point is tested n times to obtain n test values. The average value is taken to obtain the absorbance. n≥2, for example, n can be 2, 3, 4, 5, 6, 7, 8, 9, 10, etc.

[0043] In a preferred embodiment, 3 ≤ n ≤ 7.

[0044] In a preferred embodiment, the cleaning and weighing method includes: S1. The diaphragm standard is placed in dimethylacetamide for ultrasonic cleaning, then dried and weighed; S2. Repeat step S1 until the absolute value of the mass difference between two adjacent weighings is ≤0.02 mg (e.g., 0, 0.001 mg, 0.002 mg, 0.003 mg, 0.005 mg, 0.008 mg, 0.01 mg, 0.012 mg, 0.013 mg, 0.015 mg, 0.016 mg, 0.018 mg, 0.019 mg, etc., preferably ≤0.017 mg), to obtain the mass W2 of the diaphragm standard after cleaning (i.e., the mass obtained by weighing after the last cleaning and drying is W2).

[0045] This invention uses dimethylacetamide (DMAC) as a cleaning solvent. As a highly polar aprotic solvent, DMAC can penetrate and swell the PMMA coating through similar-phase dissolution, breaking the inter-molecular forces and causing it to dissolve and peel off, thus achieving selective and efficient cleaning of the PMMA coating without damaging the base film.

[0046] In a preferred embodiment, the power of the ultrasonic cleaning is 500-1000 W, for example, it can be 550 W, 600 W, 650 W, 700 W, 750 W, 800 W, 850 W, 900 W or 950 W, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range, but 750-850 W is preferred.

[0047] In a preferred embodiment, the ultrasonic cleaning time is 1-3 hours, for example, 1.2 hours, 1.4 hours, 1.5 hours, 1.6 hours, 1.8 hours, 2 hours, 2.2 hours, 2.4 hours, 2.5 hours, 2.6 hours, or 2.8 hours, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific values ​​included in the range.

[0048] In a preferred embodiment, the drying temperature is 60-100°C, for example, it can be 65°C, 70°C, 75°C, 80°C, 85°C, 90°C or 95°C, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0049] In a preferred embodiment, the drying time is 10-60 min, for example, it can be 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min or 55 min, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range, but 30-60 min is preferred.

[0050] For example, the weighing is performed using a five-digit electronic scale (unit: g), and each sample is weighed ≥2 times (e.g., 3 times, 4 times, 5 times, etc., preferably 3 times), and the average value is taken.

[0051] In a preferred embodiment, the calibration method includes the following steps: (1) Provide a (5≤a≤10) diaphragm standard with PMMA coating surface density gradient, the diaphragm standard comprising a base film and a PMMA coating disposed on the base film; (2) Using an infrared detection device with a filter, the diaphragm standard is randomly placed on the probe of the infrared detection device. Each diaphragm standard has m points (m≥2, for example, m can be 3, 4, 5, 6, 7, 8, etc., preferably 2≤m≤5) for testing. Each point is tested n times (3≤n≤7) to obtain n test values. The average value is taken to obtain the absorbance at the corresponding point (a total of m×a absorbance data). (3) According to the points, the samples are stamped and sampled using a die to obtain m×a samples; each sample is weighed to obtain W1 (unit is mg). (4) Place each sample in dimethylacetamide and ultrasonically clean it for 1-3 h at a power of 500-1000 W. After cleaning, dry it at 60-100℃ for 10-60 min and weigh it. (5) Repeat step (4) until the absolute value of the mass difference between two adjacent weighings is ≤0.02 mg, and take the mass obtained from the last weighing as W2 (in mg). Calculate the measured areal density (unit: mg / 5000 mm²). 2 ): Measured surface density = 5000 × (W1 - W2) / s, where s is the area of ​​the sample in mm.2 ; (6) Based on the measured values ​​of absorbance and areal density, draw / fit the absorbance-areal density standard curve to complete the calibration.

[0052] For example, the probe of the infrared detection device has a size of 30 mm × 20 mm.

[0053] For example, the die-cutting mold has a size of 30 mm × 30 mm, and the sample obtained by stamping has a size of 30 mm × 30 mm and an area s of 900 mm². 2 .

[0054] In a preferred embodiment, the coefficient of determination R of the absorbance-area density standard curve 2 >0.995, for example, it can be 0.9955, 0.996, 0.9965, 0.997, 0.9975, 0.998, 0.9985, 0.999 or 0.9995, etc.

[0055] Another specific embodiment of the present invention provides an application of the PMMA coating areal density test method as described in the foregoing specific embodiments in secondary batteries.

[0056] In a preferred embodiment, the PMMA coating areal density testing method is applied to the testing of lithium battery separators.

[0057] The following describes in detail the calibration method and test method for the infrared detection of PMMA coating surface density provided by the present invention using several embodiments as examples. However, the calibration method and test method for the infrared detection of PMMA coating surface density provided by the present invention are not limited to these embodiments.

[0058] Example 1 A calibration method for infrared detection of PMMA coating areal density includes the following steps: (1) Provide 7 diaphragm standards with PMMA coating areal density gradients. The diaphragm standard comprises a PE base film and a PMMA coating disposed on the PE base film. It is prepared on the PE base film by adjusting the roller speed ratio. The standard covering the tolerance range is 0.6 mg / 5000 mm. 2 -1.3 mg / 5000 mm 2 ; (2) Determine the infrared wavelength that is only affected by the surface density of the PMMA coating and install the filter. Tests conducted on laboratory spectroscopy equipment revealed that the PMMA coating (polymethyl methacrylate: ester group C=O carbonyl group with strong absorption) is sensitive to a specific infrared wavelength of 5.7954 μm. The PE base film does not absorb in this wavelength band, so the influence of the PE base film can be ignored. Therefore, the transmission wavelength of the filter is 5.7954 μm, and it is installed in an infrared detection device (RX410, KURABO, Japan).

[0059] (3) Test the absorbance of diaphragm standards of different gradients to a specific infrared wavelength. After zeroing the infrared detection device, the diaphragm standard is randomly placed on the worktable of the infrared detection device and fixed with a magnetic strip to keep the membrane surface flat and wrinkle-free. Three points are taken for each diaphragm standard (the test positions of each point are marked) for testing. Each point is tested repeatedly 5 times and the average value is taken as the absorbance of that point. Finally, absorbance data are obtained at 21 fixed points (7 gradients × 3 points).

[0060] (4) Clean the PMMA coating and weigh it. According to the marked points, 21 samples were obtained by stamping using a die with a length and width of 30 mm × 30 mm. Each sample was weighed using a five-digit electronic scale (weighed 3 times and the average value was taken) to obtain W1 (unit: mg). The sample was immersed in dimethylacetamide and cleaned for 2 hours using an ultrasonic device with a power of 800 W. After removal, it was placed in an oven at 80°C for 30 minutes and weighed using a five-digit electronic scale. The cleaning-drying-weighing steps were repeated until the mass obtained from two adjacent weighings did not change. The obtained mass was W2 (in mg).

[0061] (5) Calculate the measured values ​​of areal density for different gradients (unit: mg / 5000 mm²). 2 ): Measured surface density = 5000 × (W1 - W2) / s, where s is the area of ​​the sample (900 mm²). 2 Finally, the measured areal density values ​​of 21 samples were obtained.

[0062] (6) Fitting and plotting the standard curve The 21 absorbance data (x) were fitted with the measured areal density values ​​(y) to form a nonlinear regression relationship, with a determination coefficient R. 2 >0.995, obtain the absorbance-area density standard curve, input the absorbance-area density standard curve into the infrared device to complete the calibration.

[0063] The absorbance data (x) and measured areal density (y) of this embodiment are shown in Table 1. The standard curve of absorbance-areal density obtained by fitting and plotting is shown in Table 1. Figure 1As shown, y = -552.79x 2 + 50.333x + 0.3327, R 2 = 0.9971.

[0064] Table 1 Example 2 A method for testing the areal density of a PMMA coating includes the following steps: (1) Provide a diaphragm sample, the diaphragm sample comprising a PE base film and a PMMA coating disposed on the PE base film; (2) A filter with a wavelength of 5.7954 μm was installed in an infrared detection device, and the absorbance value was obtained by testing the membrane sample using the infrared detection device. (3) Substitute the absorbance value into the absorbance-area density standard curve provided in Example 1 to obtain the PMMA coating area density, referred to as "IR test value", and the data is shown in Table 2.

[0065] To verify the accuracy and reliability of the testing method provided in this embodiment, the diaphragm sample was tested using both the electronic celestial density subtraction method and the cleaning method, specifically including: (A) Electronic Surface Density Subtraction Method: Samples were taken by stamping using a 100 mm × 50 mm die (one PE base film with PMMA coating and one adjacent PE base film sample). First, the weight (mg) of the PE base film with PMMA coating sample y1 was measured, then the weight (mg) of the adjacent PE base film sample y2 was measured. Therefore, the areal density of the PMMA coating (mg / 5000 mm²) was calculated. 2 The result is y1-y2, and the subtraction test value is obtained. The data is shown in Table 2.

[0066] (B) Cleaning method: Immerse the diaphragm sample in dimethylacetamide and clean it for 2 hours using an ultrasonic device at 800W. After cleaning, place it in an oven at 80℃ for 30 minutes and weigh it using a five-digit electronic scale. Repeat the cleaning-drying-weighing steps until the mass obtained from two consecutive weighings is unchanged. The obtained mass is W2 (in mg). Surface density = 5000 × (W1 - W2) / s, where s is the area of ​​the sample (in mm). 2 The measured values ​​obtained by the cleaning method are shown in Table 2.

[0067] Table 2 As can be seen from Examples 1 and 2, the present invention obtains a specific wavelength of infrared light that is only affected by the surface density of the PMMA coating through laboratory testing. The absorbance of the PMMA coating is tested and recorded using an infrared detection device, and the absorbance is fitted and regressed with the actual surface density data of the PMMA coating obtained by the cleaning method to obtain an absorbance-surface density standard curve. The infrared detection device converts the absorbance of the PMMA coating into the final surface density of the PMMA coating through the calibrated absorbance-surface density standard curve. This method effectively removes the test influence caused by the surface density fluctuation of the base film itself in the electronic balance subtraction method.

[0068] As shown in Table 2, the infrared-based testing method proposed in this invention has a much smaller detection error for the surface density of PMMA coatings than the electronic balance subtraction method. The average absolute error between the cleaning method and the electronic balance subtraction method is 0.09 mg / 5000mm. 2 The average absolute error between the cleaning method and the infrared detection method is 0.01 mg / 5000 mm. 2 Therefore, the test method described in this invention can obtain PMMA coating areal density data with high accuracy, small error, and high reliability.

[0069] The present invention has been illustrated through the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for testing the areal density of a PMMA coating, characterized in that, The testing method includes: A diaphragm sample is provided, the diaphragm sample comprising a base membrane and a PMMA coating disposed on the base membrane; The absorbance value was obtained by testing the membrane sample using an infrared detection device equipped with a filter, wherein the transmission wavelength of the filter is 5.7-5.8 μm; The absorbance value was substituted into the absorbance-area density standard curve to obtain the area density of the PMMA coating.

2. The test method according to claim 1, characterized in that, The base film includes PP base film, PE base film or PP / PE composite base film, preferably PE base film.

3. The test method according to claim 1, characterized in that, The transmission wavelength of the filter is 5.79-5.8 μm, preferably 5.7954 μm.

4. A method for calibrating the areal density of a PMMA coating using infrared detection, characterized in that, The calibration method includes: A number of diaphragm standards with PMMA coating areal density gradients are provided, the diaphragm standards comprising a base membrane and a PMMA coating disposed on the base membrane; The absorbance of the diaphragm standard was tested using an infrared detection device equipped with a filter; the transmission wavelength of the filter was 5.7-5.8 μm. The diaphragm standard was cleaned and weighed, and then the measured areal density was calculated according to the following formula I: Measured surface density = 5000 × (W1 - W2) / s (Equation I) The measured areal density is expressed in mg / 5000 mm². 2 W1 represents the mass of the diaphragm standard, in mg; W2 represents the mass of the diaphragm standard after cleaning, in mg; s represents the area of ​​the diaphragm standard, in mm. 2 ; Based on the measured absorbance and areal density values, an absorbance-areal density standard curve is plotted to complete the calibration.

5. The calibration method according to claim 4, characterized in that, The PMMA coating areal density gradient of the diaphragm standard is 5-10. And / or, the PMMA coating areal density of the diaphragm standard is 0.5-1.3 mg / 5000 mm². 2 .

6. The calibration method according to claim 4, characterized in that, The absorbance testing method includes: The absorbance of the diaphragm standard is tested using an infrared detection device equipped with a filter. The test is performed n times at each point to obtain n test values. The average value is taken to obtain the absorbance; n≥2. Preferably, 3 ≤ n ≤ 7.

7. The calibration method according to claim 4, characterized in that, The transmission wavelength of the filter is 5.79-5.8 μm, preferably 5.7954 μm.

8. The calibration method according to claim 4, characterized in that, The cleaning and weighing methods include: S1. The diaphragm standard is placed in dimethylacetamide for ultrasonic cleaning, then dried and weighed; S2. Repeat step S1 until the absolute value of the mass difference between two adjacent weighings is ≤0.02 mg, and obtain the mass W2 of the diaphragm standard after cleaning. Preferably, the ultrasonic cleaning power is 500-1000 W and the time is 1-3 h; Preferably, the drying temperature is 60-100℃ and the time is 30-60 min.

9. The calibration method according to claim 4, characterized in that, The coefficient of determination R of the absorbance-area density standard curve 2 >0.

995.

10. The application of a method for testing the areal density of a PMMA coating as described in any one of claims 1-3 in secondary batteries.

Images