A Detection Method for Low Concentration Acid Value in Photovoltaic Adhesive Film

Abstract

The present invention provides a method for detecting the acid value in a low concentration in a photovoltaic adhesive film. The method includes the following steps: preparation of a sample to be tested; testing stage: first, the content and types of volatile acids of the sample to be tested are detected by headspace gas chromatography-mass spectrometry (HS-GC-MS), then the sample after headspace treatment is recovered and placed in a solvent, and swelling extraction is carried out by water bath ultrasonic treatment to obtain an extraction solution. After titration testing with an automatic potentiometric titrator in combination with an indicator, the acid value C is obtained; analysis of the test results. For the first time, it is proposed to combine headspace gas chromatography-mass spectrometry (HS-GC-MS) with full-automatic potentiometric titration to detect the acid value in the adhesive film. The combination of back titration and indicator method is used to improve the accuracy of detection, and for the first time, it is innovatively proposed to simulate the aging environment in a headspace vial to more accurately and comprehensively detect the acid value of the photovoltaic adhesive film.

Description

Technical Field

[0001] The present invention relates to the field of photovoltaic cell encapsulation films, and specifically to a method for detecting low concentration acid value in photovoltaic films. Background Technique

[0002] Photovoltaic films are one of the core materials in the encapsulation link of photovoltaic modules, and play a crucial role in the life and power generation efficiency of solar cells. The quality of photovoltaic films is of vital importance for the protection of batteries. In the prior art, currently, relatively mature photovoltaic module encapsulation film materials at home and abroad include EVA, POE, EP (films containing EVA raw materials), etc. However, due to their structural and performance reasons, EVA and EP films are prone to cause the degradation of EVA film molecular chains under long-term aging and water vapor influence, releasing acidic substances such as acetic acid, acid-containing organic substances, and polyacids. These acidic substances will corrode the surface and solder ribbons of the battery chips, and at the same time will further promote the aging of the film. For POE films, although they are relatively stable in structure, there will be residual decomposition of some organic additives in the encapsulation film formulation design, resulting in the generation of acidic substances, thus causing corrosion of the battery chips and solder ribbons. The existence of these problems will directly affect the power generation efficiency and battery life.

[0003] Due to the low concentration of acidic substances in the film, there are great difficulties in acid value testing. Currently, for the acid value testing of films, Chinese Patent CN202211274306.7 discloses a test and evaluation method for corrosion resistance, and uses the acid-base titration method to measure the acid value of the film. However, due to the low content of acid value in the film, there may be large errors for traditional acid-base titration. Chinese Patent CN202211586465.0 uses LC-MS to test the film precipitation solution, and can analyze the substances and contents of acids in the solution. However, the acids in the film are extremely easy to escape. During the aging sample preparation and film precipitation process, acetic acid and some volatile acidic substances are extremely easy to escape, resulting in deviations in the acid value results during the testing process, and the corrosion effects of this part of acidic substances on solar cells and solder ribbons cannot be ignored. The present invention provides a method for detecting low concentration acid value in photovoltaic films, which simulates the generation of aging acidic substances and the volatilization of acidic substances, and can more comprehensively and accurately analyze and characterize the actual content of acid value in the film, providing a reference for the formulation design and additive selection of encapsulation films. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a method for detecting low concentration acid value in photovoltaic films, which can more comprehensively and accurately analyze and characterize the actual content of acid value in the film, and provides a reference for the formulation design and additive selection of encapsulation films.

[0005] To achieve the above objectives, the present invention is realized through the following technical solutions:

[0006] A method for detecting low concentration acid value in a photovoltaic encapsulant film is carried out according to the following steps:

[0007] It mainly combines quantitative analysis by headspace gas chromatography-mass spectrometry (HS-GC-MS) and testing with an automatic potentiometric titrator. The testing method includes the following steps:

[0008] (a) Preparation of the sample to be tested;

[0009] (b) Testing stage: First, use HS-GC-MS to test the content and types of volatile acids in the sample to be tested. Then, recover the sample after headspace treatment and place it in a solvent. After swelling extraction by water bath ultrasonic treatment, an extraction solution is obtained. After titration testing with an automatic potentiometric titrator combined with an indicator, the acid value C is obtained;

[0010] (c) Analysis of the test results.

[0011] 1. The method for detecting low concentration acid value in a photovoltaic encapsulant film according to claim 1, characterized in that it is carried out according to the following steps:

[0012] In step (a), the method for preparing the sample by high-temperature and high-humidity aging is to laminate it into a component or place the laminated encapsulant film in a headspace vial;

[0013] In step (b), for the HS-GC-MS method, the test environment settings are as follows: the temperature of the sample thermostat is set at 50 - 150 °C, the temperature of the injection valve is set at 100 - 170 °C, the temperature of the transfer line is set at 130 - 200 °C, the column temperature: 50 - 60 °C, the column flow rate is 1 - 2 ml / min, and the high-purity nitrogen gas flow rate is 1 - 3 ml / min;

[0014] Its detection steps are as follows: First, seal the sample to be tested in a headspace vial with a mass of M (g), place it in a thermostat and heat for 30 - 60 min, then inject the sample by headspace and conduct HS-GC-MS testing. According to the comparison with the standard curve, the acid content m x (g) in the sample is obtained.

[0015] Preferably, in step (a), the preparation of the sample after high-temperature and high-humidity aging in a headspace vial is carried out according to the following specific steps: Place the laminated encapsulant film into a headspace vial, then add 0.01 - 2 ml of deionized water into the headspace vial, cover and seal it, place it in a high-temperature and high-humidity aging chamber, simulate the high-temperature aging environment in the headspace vial, and the treatment time is 96 - 192 h;

[0016] In step (b), the standard curve is the standard curve of acetic acid solution, with a concentration range of 0 - 1000 ppm. The standard curve S = ma + b of the measured acetic acid content and peak area is obtained, where S is the peak area, m is the mass of acetic acid, and a, b are coefficients;

[0017] The acid content is measured by HS-GC-MS, and through the calculation formula:

[0018] C x = m x ×1000×56.1×1000 / (M×60.05)

[0019] the acid value C can be obtained x ; where C x is the acid value in the adhesive film, m x is the acid content measured by HS-GC-MS, and M is the mass of the sample for headspace injection.

[0020] Preferably, in step (a), the lamination temperature is 135 - 150 °C, the treatment time is 15 - 30 min; the high-temperature aging treatment temperature is 100 - 120 °C, the humidity is 95 - 100% RH, and the treatment time is 96 - 192 h.

[0021] Preferably, in step (b), the solvent is at least one of ethanol, methanol, isopropanol, toluene, xylene, n-heptane, n-octane, deionized water;

[0022] the water bath ultrasonic frequency is 70 - 90 kHz, the water bath temperature is 20 - 60 °C, and the ultrasonic time is 30 - 60 min;

[0023] analyzed and tested by an automatic potentiometric titrator, the titration speed is 0.1 - 0.01 ml, and the stirring speed is 500 - 1500 r / min;

[0024] the indicator is one of phenolphthalein and bromothymol blue.

[0025] Preferably, in step (b),

[0026] the solvent is one of ethanol, n-heptane, xylene, a 1:1 mixture of ethanol and n-heptane, and a 1:1 mixture of ethanol and deionized water; the volume of the solvent is 50 - 100 ml;

[0027] the titration test is alkali titration and back titration, because the organic acids in the adhesive film are mainly weak acids.

[0028] Preferably, in step (b), the titration test is back titration. The back titration uses a standard concentration of alkali solution to react with the extract by stirring, uses an acid to conduct potentiometric titration on the test solution, synchronously confirms the titration end point through the potential and the indicator, and through the calculation formula:

[0029] C = 56.1×1000×[C1×V1 - C2×(V2 - V0)] / M0

[0030] the acid value C can be obtained, where C is the acid value measured by an automatic potentiometric titrator, C1 is the molar concentration of the standard base solution, V1 is the volume of the standard base added, C2 is the molar concentration of the acid, V2 is the volume of the acid solution consumed at the titration endpoint, V0 is the volume of the acid solution consumed by the blank sample, and M0 is the weight of the adhesive film.

[0031] Preferably, the standard base solution is one of an ethanol solution of sodium hydroxide and an ethanol solution of potassium hydroxide, and the molar concentration is 0.01 mol / L to 0.1 mol / L.

[0032] The volume ratio of the standard base solution to the extraction solution added is 1:50 to 1:100;

[0033] The acid solution is a hydrochloric acid ethanol solution with a concentration of 0.01 to 0.1 mol / L.

[0034] Preferably, in step (c), the test result analysis is that the acid value content measured by HG-GC-MS and the acid mass content measured by the back titration method pass through the formula:

[0035] AN = C + C x ,

[0036] and measured, where AN is the acid value of the sample to be tested.

[0037] Preferably, the mass of the photovoltaic adhesive film is 5 to 12 g;

[0038] In step (a), the photovoltaic adhesive film is one of ethylene-vinyl acetate copolymer (EVA), polyolefin elastomer (POE), and an adhesive film containing EVA raw material (EP);

[0039] In step (a), the sample to be tested is: (1) an unlaminated encapsulation adhesive film; (2) an encapsulation adhesive film after lamination and crosslinking; (3) a sample after high-temperature and high-humidity aging; (4) polymer particles.

[0040] The gain effect of adopting the technical solution of the present invention is:

[0041] In practice, after the photovoltaic encapsulation film has experienced long-term environmental aging and water vapor intrusion, the molecular chains of the film itself are likely to degrade, releasing a part of acid. In addition, some organic additives added to the encapsulation film will also decompose to produce some acidic substances after aging. These acidic organic substances include one or more of acetic acid, carboxylic acid organic substances, phenol, carbonic acid or silanol. In a long-term aging and humid environment, they will corrode the surface of the battery chip and the welding strip, thus affecting the life and power generation efficiency of the module. However, the concentration of these acidic organic substances is relatively low, and acetic acid is extremely volatile and easy to escape. It is difficult for ordinary acid value tests to accurately reflect the true situation of the acid value of the encapsulated module. Based on the above situation, the present invention simulates the actual application (long-term aging and water vapor intrusion) through high temperature and high humidity, obtains the content of acidic substances generated in the film (i.e., C), comprehensively considers the existence of low-concentration acids, weak acids, and acetic acid that is extremely easy to escape, uses a headspace bottle to simulate the high temperature and high humidity aging environment, and innovatively proposes for the first time to combine the headspace GC-MS method with the automatic potentiometric method. By adopting the back titration method and an indicator, the error brought during the test is further reduced, and the acid value situation of the encapsulation film after aging can be accurately analyzed. By analyzing the acid value content in the encapsulation film and combining the corrosion situation of the sample module in the EL, the potential failure risk to the encapsulation film can be inferred. This detection method comprehensively analyzes the acid value content in the film, has higher detection accuracy, the test results have guiding significance for the encapsulation film, and the evaluation reliability is higher. Detailed implementation manners

[0042] The following will combine the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0043] The conditions of the HC-GC-MS analysis method used in the following embodiments are as follows:

[0044] The temperature of the sample constant temperature bath is 90 °C; the temperature of the transmission line is 130 °C; the injection time is 1.0 min

[0045] Chromatographic conditions: Carrier gas: High-purity nitrogen, concentration: 99.99%; Carrier gas flow rate: 2.0 ml / min; Injection mode: Split; Injection port temperature: 260 °C, starting temperature 50 °C, heating rate 10 °C / min, maintaining for 21 min; Total flow rate 405 ml / min; Column flow rate: 2 ml / min; Purge flow rate: 3 ml / min.

[0046] The automatic potentiometric titration conditions used in the following embodiments are as follows: The speed is 0.01 ml; the stirring speed is 800 r / min; the temperature is 25 °C; the titration is carried out under a nitrogen atmosphere in a closed condition.

[0047] Drawing of the standard curve in the present invention: Five groups of standard aqueous acetic acid solutions were accurately prepared by the constant volume method, with concentrations of 9.98 mg / L, 52.46 mg / L, 154.44 mg / L, 663.55 mg / L, and 984.76 mg / L. 2 ml of each solution was taken and added to a 10 ml headspace vial. The peak area S was obtained through HS-GC-MS testing. Three sets of data were measured for each group, and the regression equation of acetic acid was obtained based on the average value of each group: S = 516.84m + 16.45.

[0048] Example 1:

[0049] Preparation of the sample to be measured: The unlaminated EVA film was used as the sample to be measured, with a sample mass of 10 g. The sample was cut into small fragments of about 5 mm × 5 mm.

[0050] Testing stage: The cut fragments were added to a 60 ml headspace vial and tested by HG-GC-MS. Through formula C x = m x ×1000×56.1×1000 / (M×60.05), C was measured to be 8.03 μg KOH / g. x It was 8.03 μg KOH / g.

[0051] The tested sample was taken out from the headspace vial and placed in a 60 ml mixed solution of ethanol and n-heptane at a ratio of 1:1, sealed with nitrogen, and ultrasonically treated for 30 min at 90 kHz in a 30 °C water bath to obtain the solution to be measured.

[0052] 5 ml of 0.01 mol / L standard potassium hydroxide solution was added to the solution to be measured, 0.2 g of phenolphthalein was added as an indicator, and the 0.01 mol / L standard hydrochloric acid solution was titrated using an automatic potentiometric titrator. The titration end point was confirmed synchronously by the potential and the indicator.

[0053] Through formula C = 56.1×1000×[C1×V1 - C2×(V2 - V0)] / M0, C was measured to be 15.21 μg KOH / g.

[0054] The test result was obtained through formula AN = C + C x , and the acid value AN of the film was 23.24 μg KOH / g.

[0055] Example 2:

[0056] The difference from Example 1 is that the sample to be measured is the laminated EVA film, and the sample preparation is 12 g.

[0057] Through formula C x = m x ×1000×56.1×1000 / (M×60.05), C was measured to be 7.13 μg KOH / g. x It was 7.13 μg KOH / g.

[0058] The acid value C is measured by the formula C = 56.1×1000×[C1×V1 - C2×(V2 - V0)] / M0, and C is 9.21 μg KOH / g.

[0059] The test result is calculated by the formula AN = C + C x , and the acid value AN of the adhesive film is 16.34 μg KOH / g.

[0060] Example 3:

[0061] The difference from Example 1 is that the sample to be tested is an EVA adhesive film after high-temperature and high-humidity aging. The adhesive film, glass with a size of 25 cm × 25 cm, and the backplane are laminated in this order. The pressure-bearing temperature is 145 °C, and the lamination time is 15 min. After removing the excess adhesive film from the edge of the laminated part, the periphery is sealed with tape and placed in an aging oven at 120 °C and 100% RH for 96 h. After the treatment is completed, the middle part of the laminated part is taken for acid value testing.

[0062] By the formula C x = m x ×1000×56.1×1000 / (M×60.05), C is measured to be x 63.33 μg KOH / g.

[0063] The acid value C is measured by the formula C = 56.1×1000×[C1×V1 - C2×(V2 - V0)] / M0, and C is 60.58 μg KOH / g.

[0064] The test result is calculated by the formula AN = C + C x , and the acid value AN of the adhesive film is 123.91 μg KOH / g.

[0065] Example 4:

[0066] The difference from Example 3 is that the aging time is 192 h.

[0067] By the formula C x = m x ×1000×56.1×1000 / (M×60.05), C is measured to be x 102.56 μg KOH / g.

[0068] The acid value C is measured by the formula C = 56.1×1000×[C1×V1 - C2×(V2 - V0)] / M0, and C is 62.58 μg KOH / g.

[0069] The test result is calculated by the formula AN = C + C x , and the acid value AN of the adhesive film is 165.14 μg KOH / g.

[0070] Embodiment 5:

[0071] The difference from implementation 3 is that the laminated packaging film is placed in a headspace bottle, and then 0.01 ml of deionized water is added to the headspace bottle, which is sealed with a cover and placed in a 120°C, 100% RH humidity aging box for a simulated aging experiment for 96 hours, followed by HC-GC-HS testing and back titration testing.

[0072] Through formula C x =m x ×1000×56.1×1000 / (M×60.05), measured C x It is 181.56μgKOH / g.

[0073] Through the formula C = 56.1×1000×[C1×V1-C2×(V2-V0)] / M0, C was measured to be 71.48 μgKOH / g.

[0074] The test results are obtained by the formula AN=C+C x The acid value AN of the film is 253.04 μgKOH / g.

[0075] Embodiment 6:

[0076] The difference from implementation 4 is that 0.5 ml of deionized water is added to the headspace bottle.

[0077] Through formula C x =m x ×1000×56.1×1000 / (M×60.05), measured C x The measured C is 74.25 μg KOH / g. The test result is obtained by the formula AN=C+C x The acid value AN of the film is 386.49 μgKOH / g.

[0078] Embodiment 7:

[0079] The difference from implementation 4 is that 1 ml of deionized water is added to the headspace bottle.

[0080] Through formula C x =m x ×1000×56.1×1000 / (M×60.05), measured C x The measured C is 75.29 μg KOH / g. The test result is obtained by the formula AN=C+C x, the acid value AN of the adhesive film is 425.57 μg KOH / g.

[0081] Example 8:

[0082] The difference from Example 4 is that 1.5 ml of deionized water is added to the headspace vial.

[0083] Through formula C x = m x × 1000 × 56.1 × 1000 / (M × 60.05), C is measured to be 381.56 μg KOH / g. Through formula C = 56.1 × 1000 × [C1 × V1 - C2 × (V2 - V0)] / M0, C is measured to be 74.35 μg KOH / g. The test result is through formula AN = C + C x , and the acid value AN of the adhesive film is 455.91 μg KOH / g. x

[0084] Example 9:

[0085] The difference from Example 4 is that 2 ml of deionized water is added to the headspace vial.

[0086] Through formula C x = m x × 1000 × 56.1 × 1000 / (M × 60.05), C is measured to be 383.14 μg KOH / g. Through formula C = 56.1 × 1000 × [C1 × V1 - C2 × (V2 - V0)] / M0, C is measured to be 72.87 μg KOH / g. The test result is through formula AN = C + C x , and the acid value AN of the adhesive film is 456.01 μg KOH / g. x

[0087] Example 10:

[0088] The difference from Example 9 is that: the aging time is changed to 192 h.

[0089] Through formula C x = m x × 1000 × 56.1 × 1000 / (M × 60.05), C is measured to be 460.35 μg KOH / g. Through formula C = 56.1 × 1000 × [C1 × V1 - C2 × (V2 - V0)] / M0, C is measured to be 130.84 μg KOH / g. x

[0090] The test result is through formula AN = C + C x , and the acid value AN of the adhesive film is 591.19 μg KOH / g.

[0091] Example 11:

[0092] The difference from Example 1 is that the sample to be tested is EVA particles.

[0093] Through formula C x = m x ×1000×56.1×1000 / (M×60.05), C is measured to be 12.25 μg KOH / g. x It is 12.25 μg KOH / g.

[0094] Through formula C = 56.1×1000×[C1×V1 - C2×(V2 - V0)] / M0, C is measured to be 5.78 μg KOH / g.

[0095] The test result is through formula AN = C + C x and the acid value AN of the adhesive film is 18.03 μg KOH / g.

[0096] Example 12:

[0097] The difference from Example 1 is that the sample to be tested is an unlaminated POE adhesive film and the sample mass is 5 g.

[0098] The acetic acid content is not detected by HC-GC-MS, that is, C x is 0.

[0099] Through formula C = 56.1×1000×[C1×V1 - C2×(V2 - V0)] / M0, C is measured to be 19.78 μg KOH / g.

[0100] The test result is through formula AN = C + C x and the acid value AN of the adhesive film is 19.78 μg KOH / g.

[0101] Example 13

[0102] The difference from Example 12 is that the sample to be tested is a laminated POE adhesive film.

[0103] The acetic acid content is not detected by HC-GC-MS, that is, C x is 0.

[0104] Through formula C = 56.1×1000×[C1×V1 - C2×(V2 - V0)] / M0, C is measured to be 8.69 μg KOH / g.

[0105] The test result is through formula AN = C + C x and the acid value AN of the adhesive film is 8.69 μg KOH / g.

[0106] Example 14

[0107] The difference from Example 9 is that the sample to be tested is a laminated POE adhesive film

[0108] The acetic acid content was not detected by HC-GC-MS, i.e., C x was 0.

[0109] By formula C = 56.1×1000×[C1×V1−C2×(V2−V0)] / M0, C was measured to be 108.79 μg KOH / g.

[0110] The test result was calculated by formula AN = C + C x , and the acid value AN of the adhesive film was 108.79 μg KOH / g.

[0111] The acid value test results are as follows:

[0112] Serial number C (μg KOH / g) CX μg KOH / g AN μg KOH / g Remarks Example 1 8.03 15.21 23.24 Unlaminated Example 2 7.13 9.21 16.34 Laminated Example 3 63.33 60.58 123.91 Laminated and aged Example 4 102.56 62.58 165.14 Laminated and aged Example 5 181.56 71.48 253.04 Laminated, headspace bottle aged Example 6 312.24 74.25 386.49 Laminated, headspace bottle aged Example 7 350.28 75.29 425.57 Laminated, headspace bottle aged Example 8 381.56 74.35 455.91 Laminated, headspace bottle aged Example 9 383.14 72.87 456.01 Laminated, headspace bottle aged Example 10 460.35 130.84 591.19 Laminated, headspace bottle aged Example 11 12.25 5.78 18.03 Particles are laminated Example 12 0 19.78 19.78 Unlaminated Example 13 0 8.69 8.69 Laminated Example 14 0 108.79 108.79 Laminated, headspace bottle aged

[0113] By comparing the above examples, it was found that the EVA encapsulation adhesive film would release more acidic substances after aging, mainly acetic acid. And by comparing Example 4 and Example 10, a large amount of acidic substances were generated and volatilized during the aging process. Therefore, the method of simulating aging in a headspace vial could more accurately measure the true acid value level. The acid value of the POE adhesive film was more caused by the addition of additives and auxiliary materials. The type and acid value of the auxiliary materials could be further determined by adjusting the relevant parameters according to the above HC-GC-MS test method.

[0114] Finally, it should be noted that the above implementation manners are only the preferred implementation manners of the present invention and cannot be used to limit the protection scope of this patent. Any non-substantial changes and transformations made by those skilled in the art to this invention patent fall within the protection scope required by this invention patent.

Claims

1. A method for detecting low concentration acid value in a photovoltaic adhesive film, characterized in that, Proceed as follows: Through the combination of headspace gas chromatography-mass spectrometry (HS-GC-MS) quantitative analysis and back-titration testing with an automatic potentiometric titrator, the testing method includes the following steps: (a) Preparation of the sample to be tested: Place the sample in a headspace vial for high-temperature and high-humidity aging; (b) Testing stage: First, use HS-GC-MS to test the content and types of volatile acids in the sample to be tested, and calculate the acid value Cx; then recover the sample after headspace treatment and place it in a solvent, perform swelling extraction through water bath ultrasonic treatment to obtain an extraction solution, and perform back-titration testing with an automatic potentiometric titrator combined with an indicator to obtain the acid value C; (c) Analysis of test results: The analysis of the test results is that the acid value measured by HG-GC-MS and the acid value measured by the back-titration method are obtained through the formula: AN = C + Cx, where AN is the acid value of the sample to be tested.

2. The method for detecting low-concentration acid value in a photovoltaic encapsulant film according to claim 1, wherein: In step (a), place the laminated encapsulant film in a headspace vial; In step (b), for the HS-GC-MS method, the testing environment settings are as follows: the temperature of the sample thermostat is set at 50 - 150 °C, the temperature of the injection valve is set at 100 - 170 °C, the temperature of the transfer line is set at 130 - 200 °C, the column temperature: 50 - 60 °C, the column flow rate is 1 - 2 ml / min, and the high-purity nitrogen gas flow rate is 1 - 3 ml / min; The detection steps are as follows: First, seal the sample to be tested in a headspace vial with a mass of M (g), place it in a thermostat and heat for 30 - 60 min, then perform headspace injection and conduct HS-GC-MS testing, and obtain the acid content mx (g) in the sample according to the comparison standard curve.

3. The method for detecting low-concentration acid value in a photovoltaic encapsulant film according to claim 2, wherein: In step (a), the specific steps are as follows: Place the laminated encapsulant film into a headspace vial, then add 0.01 - 2 ml of deionized water to the headspace vial, cover and seal it, place it in a high-temperature and high-humidity aging chamber, simulate a high-temperature aging environment in the headspace vial, and the treatment time is 96 - 192 h; In step (b), the standard curve is the standard curve of acetic acid solution, with a concentration range of 0 - 1000 ppm. The standard curve of the measured acetic acid content and the peak area is S = ma + b, where S is the peak area, m is the mass of acetic acid, and a and b are coefficients; The acid content is measured by HS-GC-MS, and through the calculation formula: Cx = mx × 1000 × 56.1 × 1000 / (M × 60.05) the acid value Cx can be obtained; where Cx is the acid value in the encapsulant film, the unit of the acid value is μgKOH / g, mx is the acid content measured by HS-GC-MS, and M is the mass of the sample for headspace injection.

4. The method for detecting low-concentration acid value in a photovoltaic encapsulant film according to claim 3, wherein: In step (a), the lamination temperature is 135 - 150 °C, the treatment time is 15 - 30 min; the high-temperature aging treatment temperature is 100 - 120 °C, the humidity is 95 - 100% RH, and the treatment time is 96 - 192 h.

5. The detection method for low concentration acid value in a photovoltaic adhesive film according to claim 1, wherein: In step (b), the solvent is at least one of ethanol, methanol, isopropanol, toluene, xylene, n - heptane, n - octane, and deionized water; The water - bath ultrasonic frequency is 70 - 90 kHZ, the water - bath temperature is 20 - 60 °C, and the ultrasonic time is 30 - 60 min; Analyze and test with an automatic potentiometric titrator, the titration speed is 0.1 - 0.01 ml / s, and the stirring speed is 500 - 1500 r / min; The indicator is one of phenolphthalein and bromothymol blue.

6. The detection method for low concentration acid value in a photovoltaic adhesive film according to claim 5, wherein: In step (b), The solvent is one of a 1:1 mixture of ethanol and n - heptane and a 1:1 mixture of ethanol and deionized water; the volume of the solvent is 50 - 100 ml; The titration test is alkali titration and back - titration. Since the organic acids in the adhesive film are mainly weak acids.

7. The detection method for low concentration acid value in a photovoltaic adhesive film according to claim 6, wherein: In step (b), the titration test is back - titration. The back - titration is to stir - react the standard alkali solution with the extract, and use an acid to conduct potentiometric titration on the test solution. The titration end - point is confirmed synchronously by the potential and the indicator. Through the calculation formula: C = 56.1×1000×[C1×V1−C2×(V2−V0)] / M0 The acid value C can be obtained. The unit of the acid value is μgKOH / g, where C is the acid value measured by the automatic potentiometric titrator, C1 is the molar concentration of the standard alkali solution, V1 is the volume of the standard alkali solution added, C2 is the molar concentration of the acid, V2 is the volume of the acid solution consumed at the titration end - point, V0 is the volume of the acid solution consumed by the blank sample, and M0 is the weight of the adhesive film.

8. The detection method for low concentration acid value in a photovoltaic adhesive film according to claim 7, wherein: The standard alkali solution is one of an ethanol solution of sodium hydroxide and an ethanol solution of potassium hydroxide, and the molar concentration is 0.01 mol / L - 0.1 mol / L; The volume ratio of the added standard alkali solution to the extract is 1:50 - 1:100; The acid solution is a hydrochloric acid ethanol solution, and the concentration is 0.01 - 0.1 mol / L.

9. The detection method for low concentration acid value in a photovoltaic adhesive film according to claim 1, wherein: The mass of the photovoltaic adhesive film is 5 - 12 g; In step (a), the photovoltaic adhesive film is one of ethylene - vinyl acetate copolymer (EVA), polyolefin elastomer (POE), and an adhesive film containing EVA raw material (EP); In step (a), the test sample is one of the following: an un - laminated encapsulation adhesive film; an encapsulation adhesive film after lamination and cross - linking; polymer particles.