Disruptive application of magnesium hydroxide in ultra-thin cables by vapor deposition
With the rapid development of 5G communications, the Internet of Things and new energy vehicles, ultra-thin cables, as core components of signal transmission and power supply, have put forward higher requirements on material performance: they must have excellent insulation, high temperature resistance and mechanical strength, and must meet the requirements of lightweight and flexible design. However, traditional cable insulation materials (such as polyethylene and polyvinyl chloride) have obvious bottlenecks in high temperature stability, flame retardancy and thickness control. In recent years, magnesium hydroxide coating technology prepared by vapor deposition has brought revolutionary breakthroughs to the ultra-thin cable industry with its nano-level uniform film formation, ultra-thin thickness control and super strong adhesion.
1. Analysis of the technical advantages of vapor deposition (CVD)
Chemical Vapor Deposition (CVD) is an advanced process that forms a solid coating by chemical reaction of gaseous precursors on the surface of the substrate. Compared with traditional solution coating or physical vapor deposition (PVD), CVD technology has three core advantages in the preparation of ultra-thin cable insulation layers:
1. Nano-level thickness control: CVD can accurately control the coating thickness to sub-micron or even nano-level, meeting the stringent requirements of ultra-thin cables for "thin but not leaking" insulation layers. For example, the use of low-pressure CVD technology can control the thickness of magnesium hydroxide coating to 50-200 nanometers, which is more than 90% lower than traditional processes.
2. Three-dimensional uniform coverage: Gaseous reactants can penetrate into the microscopic pores on the cable surface, achieving full coverage of complex structure surfaces, avoiding coating cracks or voids, and significantly improving insulation reliability.
3. Enhanced high-temperature stability: The high temperature environment (usually 300-800℃) during the CVD process promotes the formation of chemical bonds between magnesium hydroxide and the substrate, and the coating adhesion reaches more than 50MPa, which remains stable under long-term thermal cycles.
2. Magnesium hydroxide: an underestimated high-performance insulating material
Magnesium hydroxide (Mg(OH)₂) is an ideal choice for cable insulation materials due to its unique layered crystal structure and thermal decomposition characteristics:
- Excellent flame retardant performance: When the temperature exceeds 340°C, magnesium hydroxide decomposes into magnesium oxide and water vapor. The endothermic reaction can reduce the ambient temperature, and the released water vapor dilutes the oxygen concentration, achieving a dual flame retardant mechanism. Experiments show that cables with 35% magnesium hydroxide can increase the limiting oxygen index (LOI) from 18% (ordinary PVC) to more than 32%.
- Outstanding dielectric strength: The dielectric constant of magnesium hydroxide (ε≈3.0) is much lower than that of traditional materials (such as aluminum oxide ε≈9.8), which can reduce signal transmission loss and is especially suitable for high-frequency communication cables.
- Environmental friendliness: Magnesium hydroxide is non-toxic and halogen-free, and the decomposition products will not release corrosive gases, which complies with RoHS and REACH environmental standards.
3. Disruptive process of preparing magnesium hydroxide coating by CVD
The traditional method is to add magnesium hydroxide powder to the polymer matrix by melt blending, but there are problems such as uneven dispersion, limited addition amount (usually ≤60%), and decreased mechanical properties. CVD technology achieves performance leap through the following innovative paths:
1. Precursor design and reaction optimization
Using magnesium organic compounds (such as magnesium acetylacetonate) as precursors, it decomposes in a hydrogen/argon atmosphere to generate high-purity Mg(OH)₂. By adjusting the reaction temperature, gas flow rate and pressure, the crystal orientation can be precisely controlled to form a sheet structure dominated by the (001) crystal plane, maximizing flame retardancy and insulation performance.
2. Low-temperature plasma-assisted technology
For heat-sensitive cable substrates (such as polyimide), plasma-enhanced CVD (PE-CVD) is introduced to reduce the deposition temperature to below 150°C, and plasma is used to activate the substrate surface to improve the coating adhesion.
3. Gradient coating structure design
Using a multi-layer deposition process, a Mg(OH)₂ flame retardant layer, a SiO₂ insulation layer and a hydrophobic protective layer are sequentially generated on the cable surface to achieve the integrated function of "flame retardant - insulation - weather resistant".
IV. Practical application cases in the ultra-thin cable industry
1. 5G high-speed backplane connection cable
A leading communication equipment manufacturer uses the CVD method to deposit a 1μm magnesium hydroxide coating on a 0.08mm thick copper wire, reducing the overall cable diameter by 40%, reducing transmission loss by 22%, and passing the UL94 V-0 flame retardant certification.
2. High-voltage wiring harness for new energy vehicles
A German car company applies CVD coating to 800V high-voltage cables. Under -40℃~200℃ working conditions, the insulation resistance is stable at more than 10¹⁴Ω·cm, and the arc resistance performance is improved by 3 times, which helps to upgrade lightweighting and safety.
3. Flexible wearable device cables
Japanese companies have developed a spiral ultra-thin cable with a thickness of only 0.15mm. After 5,000 bending tests, the CVD coating did not fall off, and the impedance change rate was <2%, which is perfectly suitable for scenarios such as smart watches and medical sensors.
V. Technical challenges and future development directions
Although the CVD-magnesium hydroxide technology has significant advantages, it still needs to break through the following bottlenecks:
- Cost control: High-purity precursors and vacuum equipment lead to high initial investment, and low-cost magnesium sources (such as magnesium chloride) and continuous deposition processes need to be developed.
- Large-scale production: Most of the existing equipment is batch production, and it is urgent to develop a roll-to-roll CVD system to adapt to the continuous coating of kilometer-level cables.
- Composite function expansion: Explore the co-deposition technology with materials such as graphene and boron nitride to give cables additional functions such as thermal conductivity and electromagnetic shielding.
According to MarketsandMarkets, by 2028, the global ultra-thin cable market will reach US$27 billion, of which the penetration rate of vapor deposition coating technology is expected to exceed 35%. With the localization of equipment and process optimization, this technology