Application Of Double Planetary Mixer in Photovoltaic Auxiliary Materials—Silver Paste

In the photovoltaic industry chain, photovoltaic silver paste, as the core electrode material of crystalline silicon solar cells, is hailed as the "nerve network" of the cell. It serves as a crucial bridge connecting photogenerated carriers to external circuits, and its dispersion uniformity, viscosity stability, and printing performance directly determine the photoelectric conversion efficiency, cycle stability, and lifespan of the photovoltaic cell. As the global photovoltaic industry upgrades towards higher efficiency and lower costs, and high-efficiency cell technologies such as N-type TOPCon and HJT are rapidly becoming widespread, more stringent requirements are being placed on the preparation process of photovoltaic silver paste. The dual planetary mixer, as the core mixing equipment in silver paste production, directly affects the quality of the silver paste and production efficiency.

一. Classification and Production Process of Photovoltaic Silver Paste

Photovoltaic silver paste production is a multi-stage, high-precision system engineering process. The core process revolves around "raw material pretreatment → mixing and homogenization → grinding → filtration and testing → curing and packaging." Among these, the mixing and homogenization stage is crucial in determining the dispersion effect and quality stability of the silver paste, directly affecting the smooth progress of subsequent processes. The specific process is as follows:

1. Raw Material Pretreatment and Precise Batching: First, raw materials such as silver powder and glass powder are pretreated to remove impurities and moisture, ensuring raw material purity. Then, according to the product formula, silver powder, glass powder, organic resin, solvent, and additives are precisely weighed, with the ratio error controlled within ±0.5%. This stage requires strict adherence to the feeding sequence to avoid premature agglomeration of silver powder and incompatibility between glass powder and the organic carrier.

2. Mixing and Homogenization (Core Stage): The pretreated raw materials are fed into a mixing device for initial dry premixing, allowing the silver powder and glass powder to be initially and uniformly mixed, establishing a basic dispersion system. Then, the organic carrier and solvent are gradually added, using strong shear force to break up silver powder agglomerates, achieving molecular-level uniform fusion of all components. This step requires precise control of stirring speed, time, and temperature to ensure the slurry is free of agglomeration and stratification, and that the viscosity reaches the preset standard (typically 5000-10000 mPa·s).

3. Grinding and Refining: The homogenized slurry is fed into a sand mill or similar equipment to further refine the particles, ensuring the glass powder particle size is controlled within a suitable range (typically D50 ≤ 25μm), while simultaneously ensuring uniform dispersion of the silver powder to prevent large particles from affecting subsequent printing performance.

4. Filtration and Inspection: Large particles and undispersed agglomerates are removed from the slurry using a 5-10μm precision filter. The filtration pressure must be controlled at ≤0.3MPa to avoid excessive compression that could deform the silver powder. Subsequently, the slurry's viscosity, thixotropy, solid content, and particle size distribution are tested to ensure compliance with production standards. Unqualified products must be returned for re-mixing and grinding.

5. Maturation and Packaging: The qualified slurry is matured at low temperature and low speed to balance internal stress and ensure stable viscosity. After maturation, it is filled and packaged in a clean environment to avoid contamination by impurities. The final product must be left to stand for 24 hours without separation before it can be shipped out.

二. Choose Yushun Intelligent Double Planetary Mixer: Precisely tailored to meet the requirements of silver paste, customized solutions enhance production capabilities

1. The planetary gearbox and high-speed dispersion bearing housing are made of stainless steel, fully enclosed, and operate under vacuum negative pressure and pressure holding conditions.

2. The probe revolves with the planetary gearbox; the temperature reading on the digital display is within 1°C of the actual slurry temperature (measuring the tank wall).

3. The agitator is precision-cast and then machined in a machining center, ensuring precision between paddles and between the paddle and the tank wall while maintaining a consistent helix.

4. The agitator has a hexagonal cross-section, which helps to knead the material during movement. The dispersion disc on the high-speed dispersion shaft rotates counterclockwise while revolving, rapidly dispersing and mixing the material.

5. Low-gap design: low gaps between paddles, between the paddle and the tank wall, and between the paddle and the tank bottom.

6. Suitable for high-viscosity, high-solids-content battery positive and negative electrode slurries, adaptable to different mixing processes.

7. Easy-to-clean surface with a polishing degree of not less than Ra0.32; the dispersion and mixing systems use a quick-release structure for easy cleaning.

8. High system integration: seamless quick-release connection between premixing, mixing, turnover, and filtration processes, fully automatic control.