Aluminum hydroxide (ATH), as the most widely used halogen-free flame retardant filler in epoxy resin, rubber, composite materials, and electronic sealing materials, has multiple advantages such as flame retardancy, smoke suppression, filling, insulation, and controllable cost. It is an indispensable functional component in the global high-end material system. However, in practical applications, unmodified aluminum hydroxide has poor compatibility with organic polymer matrices, weak interfacial bonding, easy agglomeration due to high filling, and significantly reduced mechanical properties of the system, which have long constrained product stability and international market competitiveness.
Surface treatment is the core technology path to solve the above pain points, and it is also the most effective means to improve the dispersibility, wettability, compatibility, mechanical strength, heat resistance, and long-term reliability of aluminum hydroxide in polymer systems such as epoxy resin.
The surface of unmodified aluminum hydroxide is rich in hydroxyl groups (- OH), exhibiting strong polarity and high surface energy characteristics. It has natural interface barriers with low polarity organic matrices such as epoxy resins and elastomers, mainly manifested as:
1. Poor interface compatibility, easy agglomeration of fillers, and difficulty in uniform dispersion;
2. The resin cannot fully wet the surface of the filler, forming interface voids and defects;
3. Under external force, interface debonding is prone to occur, leading to material cracking and brittle fracture;
4. The viscosity of the high filling system sharply increases, and the processing flowability significantly deteriorates;
5. The tensile strength, bending strength, and impact toughness decrease synchronously, which cannot meet the requirements of high-end applications.
These issues directly lead to the inability of products to pass international certifications such as UL, IEC, RoHS, etc., and are also the key reasons why ordinary aluminum hydroxide is difficult to enter the global high-end supply chain.
The essence of surface treatment of aluminum hydroxide is interface engineering, which achieves three core functions by constructing a molecular level organic coating layer on the surface of inorganic particles:
1. Reduce surface energy, minimize self aggregation between particles, and improve dispersion uniformity;
2. Polarity matching changes the hydrophilicity of the filler to oleophilicity, making it highly compatible with the organic matrix;
3. Interface bridging, forming chemical bonds between fillers and resins to transfer stress and enhance mechanical strength.
Simply put, surface treatment transforms aluminum hydroxide from "simple filling" to "effective synergy", and from "destructive performance" to "enhanced performance".
At present, high-end aluminum hydroxide products worldwide generally use specific or compound surface treatment agents. Different systems show significant differences in compatibility improvement, mechanical enhancement, and processing flowability. The following are the most mature and stable technical routes in the industry.
Silane coupling agent is the most effective and widely used treatment method to enhance the compatibility between aluminum hydroxide and epoxy resin, especially suitable for high-end fields such as electronic sealing, castables, and copper-clad laminates.
Mechanism of action:
-One end of the silane molecule forms a stable covalent bond with the hydroxyl group on the ATH surface;
-The other end contains functional groups such as epoxy, amino, and vinyl groups, which can directly participate in the curing reaction of epoxy resin;
-Form a strong 'molecular bridge' at the interface, greatly enhancing the interfacial adhesion.
Enhancement effect:
-Improve compatibility and dispersibility by more than 50%;
-Increase tensile strength and bending strength by 20% -40%;
-Significant improvement in impact toughness, without cracking or brittle fracture;
-Under high filling, the viscosity is lower and the flowability is more stable.
Titanium and aluminum ester treatment agents are suitable for composite material systems that require high addition amounts, low viscosity, and strong wettability, and can significantly improve interfacial lubricity and processing flowability.
Mechanism of action:
-Single molecular layer coating reduces inter particle friction;
-Long chain structure intertwines with resin matrix to enhance compatibility;
-Not forming a rigid interface, balancing toughness and processability.
Enhancement effect:
-The viscosity of the system has significantly decreased, allowing for higher filling levels to be achieved;
-Evenly dispersed, without aggregation or separation;
-The material surface is smoother, and the appearance and processability are significantly optimized.
Hyperbranched polymer composite treatment has become the new mainstream technology for the world's top materials that require high flame retardancy, high CTI, high insulation, and high reliability.
Mechanism of action:
-The multi branched structure provides spatial hindrance, completely preventing particle aggregation;
-High functional group density, stronger and more stable interface bonding;
-Low moisture absorption and low dielectric, suitable for high-end electronic devices.
Enhancement effect:
-The interface does not fail in long-term humid and hot environments;
-Significant improvement in insulation performance and voltage resistance;
-Achieve the optimal balance between mechanical properties and flame retardancy.
Surface treatment is not simply "mixing and stirring", only precise control of process conditions can maximize the modification effect.
1. Precise control of the amount of treatment agent added
Insufficient treatment agent → incomplete coating;
Excessive treatment agent → appearance of free layer at the interface, reducing curing strength and heat resistance.
Optimal addition amount: 0.5% -2.0% of the mass of aluminum hydroxide.
2. Activation temperature and time
Different treatment agents correspond to different activation temperatures to ensure complete formation of chemical bonds rather than physical adsorption.
-Silane coupling agent: 100 ℃ -150 ℃, 60-120 minutes;
-Titanate/Aluminate: 80 ℃ -120 ℃, 30-60 minutes.
3. High uniform dispersion
Adopting high-speed mixing, dry coating, and dynamic grinding processes to ensure that each aluminum hydroxide particle is uniformly coated and prevent local agglomeration.
4. Control of low moisture content
Strictly control the moisture content after processing to avoid issues such as curing, foaming, and insulation degradation of epoxy resin, in compliance with international electronic grade standards.
After professional surface treatment, aluminum hydroxide can achieve comprehensive performance upgrades by adding epoxy resin:
1. Significant improvement in compatibility: no delamination, no settlement, no agglomeration, high filling still maintains uniform stability;
2. Significant enhancement of mechanical properties: comprehensive improvement in tensile strength, bending strength, and impact toughness, making it less prone to cracking;
3. Stronger interface bonding: higher performance retention after wet heat aging and thermal shock;
4. Better processing fluidity: lower viscosity, suitable for automated sealing, pouring, and molding processes;
5. Insulation and reliability improvement: interface voids are reduced, voltage resistance, CTI value, and long-term stability meet international high-end requirements;
6. Higher flame retardant efficiency: Uniform dispersion makes ATH undergo more synchronous thermal decomposition, resulting in more stable flame retardant and smoke suppression effects.
The surface treatment of aluminum hydroxide is the core technology for improving the compatibility of fillers, interfacial bonding strength, mechanical properties of the system, processing flowability, and long-term reliability. Through scientific modifications such as silane, titanate, and hyperbranched polymers, the interface barrier between inorganic fillers and organic matrices can be fundamentally solved, making high filling, high-performance, halogen-free and environmentally friendly epoxy resin systems a reality.
In today's increasingly competitive global high-end materials market, aluminum hydroxide products with stable, efficient, and standardized surface treatment technologies are not only the key to formula upgrades, but also an important support for enterprises to open up international markets, achieve quality breakthroughs, and establish long-term competitiveness.
