NdFeB surface treatment: parylene

What is parylene?

Parylene is prepared by a unique vacuum vapor deposition process. A fully conformal polymer film coating is “grown” on the surface of the substrate from active small molecules, which has performance advantages that other coatings cannot match. It can be applied to surfaces of various shapes, including sharp edges, cracks and internal surfaces.

Parylene is a new type of conformal coating material developed and applied by UnionCarbide Co. in the mid-1960s. It is a polymer of para-xylene. According to the different molecular structure, Parylene can be divided into N type and C type. , D type, F type, HT type and many other types.
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Parylene is a protective polymer material, the Chinese name is parylene. Parylene can be vapor-deposited under vacuum. The good penetration of Parylene active molecules can form no pinholes inside, at the bottom and around the component. The uniform thickness of the transparent insulating coating provides a complete high-quality protective coating for the components to resist acid and alkali, salt spray, mold and various corrosive gas parts. Because Parylene is not a liquid, there will be no aggregation or bridging to form a meniscus during the coating process. There are performance advantages that other coatings cannot match. It can be applied to surfaces of various shapes, including sharp edges, cracks and internal surfaces.
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Why is NdFeB permanent magnet coated with Parylene?

NdFeB permanent magnet material is a kind of high performance and strong magnetic material, but this material is very unstable in the air. Larger size usually uses electroplating or epoxy electrophoretic paint as protective coating. Smaller size magnetic material, Especially for ring-shaped and cylindrical magnetic materials, it is difficult to meet the requirements of use for protection by the above-mentioned traditional methods. Parylene’s unique preparation process and excellent performance combine to enable it to fully coat small and ultra-small magnetic materials without weak points. The magnetic materials can be immersed in hydrochloric acid for more than 10 days without corrosion. At present, there are many small and ultra-small magnetic materials in the world. Parylene is used as insulation and protective coating.

Parylene film preparation polymerization process

The commonly used method for preparing parylene is chemical vapor deposition (CVD), which is a process in which reaction materials undergo a space vapor chemical reaction under gaseous conditions to directly generate solid materials on the surface of a solid substrate, and then form a coating on the surface of the substrate technology.
The preparation process of Parylene film is divided into three steps: vaporization and pyrolysis of monomer, and adhesion and deposition on the substrate surface.

  • 1. In a vacuum environment, the solid tetrachlorop-xylene ring dimer sublimates to a gaseous state at about 150°C;
  • 2. At about 650℃, the tetrachlorop-xylene ring dimer is broken into active 2,5-dichlorop-xylene benzene with free radicals;
  • 3. At room temperature (25°C), free 2,5-dichloro-p-dimethylene benzene is deposited and polymerized on the surface of the solid substrate to form a pinhole-free conformal film.

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The protective effect of parylene coating

  • 1. It is resistant to acid and alkali corrosion and can solve the problem of corrosion by acid or alkaline substances.
  • 2. Low water and gas permeability, with high barrier effect, can achieve the effects of moisture-proof, waterproof, anti-rust and slow down weathering.
  • 3. Resistance to organic solvents (insoluble in common solvents).
  • 4. The film is colorless, with high transparency, and does not affect the original appearance of the product.
  • 5. The membrane layer has dust-proof, moisture-proof, waterproof and air-permeable effects, which can make the product meet the international dust-proof and waterproof IP rating specifications.

Source: China Permanent Magnet Manufacturer – www.ymagnet.com

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