A method for evaluating the corrosiveness of potting materials

Abstract

The present invention discloses a method for evaluating the corrosiveness of a potting material, comprising a water absorption test step, wherein a potting material sample S1 of a certain mass is taken and the water absorption rate of the potting material sample S1 is detected; a conductivity test step, wherein a potting material sample S2 of a certain mass is taken and the conductivity of the potting material sample S2 is detected; a gel content test step, wherein a potting material sample S3 of a certain mass is taken and the gel content of the potting material sample S3 is detected; and a pH value test step, wherein a potting material sample S4 of a certain mass is taken and the pH value of the potting material sample S4 is detected; the potting material samples S1, S2 and S3 have the same mass. The method for evaluating the corrosiveness of a potting material of the present invention can comprehensively evaluate the corrosiveness of the potting material by testing the water absorption, conductivity, gel content and pH value of the potting material.

Description

Technical Field

[0001] The present invention relates to the technical field of metallized film capacitors, and in particular to a method for evaluating the corrosiveness of a potting material. Background Art

[0002] At present, metal film capacitors are mainly formed by winding metal film, that is, a metal coating is set on the film for conductivity, and then the electrode core formed by the metal film is encapsulated in the capacitor shell through a potting material (such as resin, catalyst and filler, etc.). However, during the use of the electrode, the water absorption performance and composition of the potting material itself will affect the corrosion of the metal film and affect the use of the electrode.

[0003] Metallized film capacitors are typically made from two layers of micron-thick polypropylene dielectric film with a single-sided nano-metal coating evaporated onto the capacitor. The process involves staggered winding, end-face gold spraying, heat setting, and potting. Metallized film capacitors possess the self-healing property of restoring insulation in the event of a partial breakdown, leading to their widespread use in home appliances, reactive power compensation, harmonic control, wind power generation, photovoltaic power generation, and DC transmission. As their applications expand and operating conditions become increasingly demanding, the requirements for metallized film capacitors, particularly their lifespan, are also increasing. Potting compounds, a key material for protecting metallized film capacitor components, have a significant impact on their lifespan due to their corrosive properties. Currently, industry evaluation of potting compound corrosiveness relies primarily on long-term endurance testing of finished capacitors. These testing cycles are lengthy and involve numerous influencing factors, and the corrosiveness of the potting compound itself cannot be evaluated based on its inherent properties. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the purpose of the present invention is to provide a method for evaluating the corrosiveness of a potting material, which can comprehensively evaluate the corrosiveness of the potting material by testing its water absorption, electrical conductivity, gel content and pH value.

[0005] The purpose of the present invention is achieved by the following technical solutions:

[0006] A method for evaluating the corrosiveness of a potting material, comprising:

[0007] The water absorption test step is to take a certain mass of potting material sample S1 and test the water absorption rate of the potting material sample S1;

[0008] Conductivity test step: taking a certain mass of potting material sample S2 and testing the conductivity of the potting material sample S2;

[0009] Gel content testing step: taking a certain mass of potting material sample S3 and testing the gel content of the potting material sample S3;

[0010] pH value testing step: taking a certain mass of potting material sample S4 and testing the pH value of the potting material sample S4;

[0011] The potting material samples S1, S2, and S3 have the same quality.

[0012] Furthermore, in the water absorption test step,

[0013] Take 10g of potting material sample S1 with a thickness of 1-2mm, first dry it in a 105℃ forced air oven for 2h, weigh it, soak it in boiling water for 2h, then place it in 23℃ distilled water to cool for 15min, wipe off the visible water droplets on the surface, and weigh it again. Calculate its water absorption rate based on the mass difference between the potting material before and after the test.

[0014] Furthermore, in the conductivity testing step,

[0015] Take 10g of potting material sample S2 with a particle size of less than 3mm, add deionized water to 100mL, then put it into 95℃ water for treatment for 20h, and then cool it to room temperature. The conductivity of its water immersion liquid is calculated by the difference in the conductivity of the aqueous solution before and after the test.

[0016] Furthermore, in the gel content testing step,

[0017] Take 10g of potting material sample S3 with a particle size of less than 3mm, add 100mL of organic solvent, seal it, and place it at room temperature for 48h. After pouring out the solvent, evaporate the solvent in an oven at room temperature and 105℃ until the mass change rate is less than 0.5% twice. Calculate its gel content by the mass difference between the potting material before and after the test.

[0018] Furthermore, the organic solvent is one of butyl acetate solvent, acetone solvent or xylene solvent.

[0019] Furthermore, 20 ml of the solvent after the gel content test is completed is taken and its pH value is tested.

[0020] Compared with the existing technology, the beneficial effect of the present invention is that it can evaluate the water absorption, electrical conductivity, gel content and pH value of the potting material, that is, the water absorption of the potting material, the content of impurity ions (such as halogen ions, alkali metal ions and other easily hydrolyzed substances) that migrate with water, the content of non-cured cross-linked components that may potentially migrate or precipitate, and the pH value of potential migrating or precipitating substances, and comprehensively evaluate the corrosiveness of the potting material. The evaluation cycle is short and the evaluation steps are simple. DETAILED DESCRIPTION

[0021] Below, in conjunction with specific embodiments, the present invention is further described:

[0022] In the description of the present invention, it should be noted that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating directions or positional relationships, are based on directions or positional relationships and are only used to facilitate the description of the present invention and simplify the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0024] A method for evaluating the corrosiveness of a potting material, comprising:

[0025] The water absorption test step is to take a certain mass of potting material sample S1 and test the water absorption rate of the potting material sample S1;

[0026] Conductivity test step: taking a certain mass of potting material sample S2 and testing the conductivity of the potting material sample S2;

[0027] Gel content testing step: taking a certain mass of potting material sample S3 and testing the gel content of the potting material sample S3;

[0028] pH value testing step: taking a certain mass of potting material sample S4 and testing the pH value of the potting material sample S4;

[0029] The potting material samples S1, S2, and S3 have the same quality, that is, the samples measured each time are the same and can be used for unified evaluation.

[0030] Since the potting compound is used to pot the metallized film inside the capacitor shell, and the coating of the metallized film is amphoteric metal aluminum and zinc with a thickness of nanometer level, it is very susceptible to water corrosion, resulting in capacitance attenuation. If the potting compound itself has a high water absorption rate, it will not play the due protective role in an environment with high humidity. Therefore, the water absorption rate of the potting compound is required to be as low as possible.

[0031] During the production and processing of resins, catalysts and fillers in the potting material, there will always be residual metal ions and halogen ions. When the content of these ions exceeds a certain level, they will migrate to the metallized film coating with water, forming corrosive substances under the action of the electric field, causing erosion of the coating. Therefore, the less impurity ions in the potting material, the better.

[0032] In order to reduce the viscosity of the potting material, some diluents are usually added to the potting material formula, and some are inactive diluents. Because this part does not participate in the curing reaction of the potting material, it may migrate during use, causing the metallized base film to swell and the coating to fall off. Therefore, the potting material is required to have as low unreacted substances or migratable substances as possible after curing.

[0033] Among the substances that can migrate, if they contain organic acids or organic amines, they will cause corrosion to the coating of the metallized film. Therefore, it is required that the acidic and alkaline substances in the migrants should be as little as possible.

[0034] Therefore, the water absorption, electrical conductivity, gel content and pH value of the potting material can be tested through the above steps, that is, the water absorption of the potting material, the content of impurity ions (such as halogen ions, alkali metal ions and other easily hydrolyzed substances) that migrate with water, the content of non-curing cross-linked components that may potentially migrate or precipitate, and the pH value of the potential migrating or precipitating substances can be evaluated, and the corrosiveness of the potting material can be comprehensively evaluated. The evaluation cycle is short and the evaluation steps are simple.

[0035] It should be noted that, in the prior art, after the cured block of potting material for capacitors is soaked in an organic solvent, a small amount of the substance will dissolve in the organic solvent, while most of the substance will not dissolve in the organic solvent. Therefore, in this application, the substance that can dissolve in the organic solvent is referred to as a migratable substance, and the substance that is mostly undissolved in the organic solvent can be referred to as a gel.

[0036] Furthermore, in the water absorption test step,

[0037] Take 10g of potting material sample S1 with a thickness of 1-2mm, first dry it in a 105℃ forced air oven for 2h, weigh it, soak it in boiling water for 2h, then place it in 23℃ distilled water to cool for 15min, wipe off the visible water droplets on the surface, and weigh it again. Calculate its water absorption rate based on the mass difference between the potting material before and after the test.

[0038] In this embodiment, the water absorption rate is ≤0.5%, which can be evaluated as qualified.

[0039] Furthermore, in the conductivity test step,

[0040] Take (10±0.1) g of potting material sample S2 with a particle size of less than 3 mm, add deionized water to 100 mL, then place it in 95°C water for 20 hours, and then cool it to room temperature. The conductivity of its water immersion liquid is calculated by the difference in the conductivity of the aqueous solution before and after the test.

[0041] The above-mentioned water immersion liquid conductivity is ≤100μs / cm and can be assessed as qualified.

[0042] Furthermore, in the gel content testing step,

[0043] Take (10±0.1) g of potting material sample S3 with a particle size of less than 3 mm, add 100 mL of organic solvent, seal, and place at room temperature for 48 hours. After pouring out the solvent, evaporate the solvent in an oven at room temperature and 105°C until the mass change rate is less than 0.5%. Calculate the gel content of the potting material based on the mass difference before and after the test.

[0044] The specific test shows that the gel content should be ≥70%, which can be evaluated as qualified.

[0045] Furthermore, the organic solvent is one of butyl acetate solvent, acetone solvent or xylene solvent.

[0046] Specifically, butyl acetate solvent can be selected for polyurethane potting material, acetone solvent can be selected for epoxy potting material, and xylene solvent can be selected for silicone potting material. The specific selection can be made according to actual needs.

[0047] Furthermore, 50 ml of the solvent after the gel content test is taken and its pH value is tested. Specifically, the pH value is tested by the acid-base titration method in the prior art. When the pH value is ≤ 0.5 mg / g, it can be evaluated as qualified.

[0048] Those skilled in the art can make various other corresponding changes and deformations based on the technical solutions and concepts described above, and all of these changes and deformations should fall within the scope of protection of the claims of the present invention.

Claims

1. A method for evaluating the corrosiveness of a potting material, characterized in that: include, The water absorption test step is to take a certain mass of potting material sample S1 and test the water absorption rate of the potting material sample S1; Conductivity test step: taking a certain mass of potting material sample S2 and testing the conductivity of the potting material sample S2; Gel content test step: taking a certain mass of potting material sample S3 and testing the gel content of the potting material sample S3; pH value testing step: taking a certain mass of potting material sample S4 and testing the pH value of the potting material sample S4; The potting material samples S1, S2, and S3 have the same quality; In the conductivity testing step, Take 10±0.1g of potting material sample S2 with a particle size of less than 3mm, add deionized water to 100mL, then place it in 95℃ water for 20h, then cool it to room temperature. Calculate the conductivity of its water immersion liquid by the difference in the conductivity of the aqueous solution before and after the test; The above steps are used to evaluate the water absorption of the potting material, the content of impurity ions that migrate with water, the content of non-cured cross-linked components that may migrate or precipitate, and the pH value of the potential migrating or precipitating substances, and comprehensively assess the corrosiveness of the potting material.

2. The method for evaluating the corrosiveness of a potting material according to claim 1, wherein: In the water absorption test step, Take 10g of potting material sample S1 with a thickness of 1-2mm, first dry it in a 105℃ forced air oven for 2h, weigh it, soak it in boiling water for 2h, then place it in 23℃ distilled water to cool for 15min, wipe off any visible water droplets on the surface, and weigh it again. The water absorption rate of the potting material is calculated based on the mass difference before and after the test.

3. The method for evaluating the corrosiveness of a potting material according to claim 1, wherein: In the gel content testing step, Take 10±0.1g of potting material sample S3 with a particle size of less than 3mm, add 100mL of organic solvent, seal it, and place it at room temperature for 48h. After pouring out the solvent, evaporate the solvent in an oven at room temperature and 105℃ until the mass change rate is less than 0.5% twice. Calculate its gel content based on the mass difference between the potting material before and after the test.

4. The method for evaluating the corrosiveness of a potting material according to claim 3, wherein: The organic solvent is one of butyl acetate solvent, acetone solvent and xylene solvent.

5. The method for evaluating the corrosiveness of a potting material according to claim 3, wherein: Take 50 ml of the solvent after the gel content test step and test its pH value.