Introduction to Three Common Types of Flame-Retardant Adhesives: Silicone, Epoxy, and PU Encapsulation Adhesives

Introduction to Three Common Types of Flame-Retardant Adhesives: Silicone, Epoxy, and PU Encapsulation Adhesives

As electronic components become increasingly sophisticated, stricter requirements are placed on safety performance and operational stability. To meet these requirements, encapsulation adhesives are commonly injected into electrical components and circuit boards to achieve the desired performance standards. Which type of encapsulation adhesive offers superior thermal conductivity: epoxy resin, polyurethane, or silicone thermal conductive encapsulation adhesive? The following is a comparison of the performance characteristics of encapsulation adhesives.

I. Silicone Thermal Encapsulation Adhesive

1. Advantages

Silicone encapsulation adhesives are a type of electronic encapsulation adhesive, divided into two major categories: silicone resins and silicone rubbers. Based on application, methods they are categorized into single-component silicone encapsulation adhesives and two-component silicone encapsulation adhesives. Silicone encapsulation adhesives are cost-effective and achieve deep curing after curing. There are many types of silicone encapsulation adhesives, and different types vary significantly in terms of temperature resistance, waterproofing, insulation, optical properties, adhesion to different materials, and hardness. Selection or development should be based on specific application requirements. From a functional perspective, silicone encapsulation adhesives can be used for shock absorption, insulation, waterproofing, sealing, high and low temperature resistance, and anti-aging. They are suitable for the encapsulation and protection of various electronic materials, components, instruments, and meters.

2. Disadvantages

They are prone to poisoning and exhibit a non-curing phenomenon. Silicone encapsulation adhesives are relatively environmentally friendly, but since platinum curing agents are highly reactive, they easily react with other impurities, leading to poisoning. Additionally, they have poor adhesion. When used as an encapsulation or coating material, to enhance the adhesion of the organic encapsulation adhesive, it is necessary to first apply a primer to the substrate or modify it with an adhesion enhancer, which can be cumbersome to use.

3. Product applications

Encapsulation, sealing, and thermal conductivity,  protecting electronic components from moisture and contamination, thermal conductivity encapsulation for power supplies, controllers, and high-power heat-generating components, insulation and waterproof encapsulation of sensors and small electrical devices, sealing, thermal conductivity, and noise reduction of coils,  vibration protection of precision electronic components, waterproof encapsulation of lighting fixtures and junction boxes, thermal conductivity encapsulation of lithium-ion battery packs and new energy vehicle control systems.

II. Epoxy Resin Encapsulation Adhesive

1. Advantages

The advantages of epoxy resin electronic encapsulation adhesives primarily lie in their hardness and insulation properties after curing. Although some modified products exhibit softness after curing, overall, epoxy resin encapsulation adhesives have relatively high hardness. Additionally, they exhibit excellent adhesion to substrates and superior resistance to acids and alkalis. Furthermore, these adhesives have good temperature resistance, typically up to 150°C. If transparent materials are used to manufacture epoxy resin electronic encapsulation adhesives, their light transmission properties are also outstanding.

2. Disadvantages

Epoxy resin has relatively limited temperature resistance and weak resistance to thermal shock. After exposure to thermal shock, it is prone to cracking, allowing moisture to penetrate into electronic components through the cracks, resulting in poor moisture resistance. Additionally, after curing, the adhesive has high hardness and brittleness, which can damage electronic components. Once encapsulated, it cannot be opened, and its reparability is poor. High-quality epoxy encapsulation adhesives may improve these issues.

3. Product applications

Encapsulation protection for automotive electronics and sensors, insulation encapsulation for transformers, capacitors, and current transformers, encapsulation for automotive ignition coils and explosion-proof power supplies, bonding and sealing of water treatment membrane assemblies, waterproof encapsulation for smart water meters, encapsulation of stator windings for various motors such as industrial linear motors, fan motors, and electric vehicle drive motors.

III. Polyurethane Encapsulation Adhesive

1. Advantages

Polyurethane encapsulation adhesive, also known as PU encapsulation adhesive, is soft and elastic after curing, allowing for repair, commonly referred to as a soft adhesive. Its adhesion properties fall between epoxy and silicone, with average temperature resistance, typically not exceeding 150°C. It tends to form bubbles after encapsulation, so encapsulation must be performed under vacuum conditions. It has excellent low-temperature resistance and superior vibration resistance among the three types. It features low hardness, moderate strength, good elasticity, water resistance, mold resistance, vibration resistance, and transparency. It also has excellent electrical insulation properties and flame resistance, is non-corrosive to electrical components, and has good adhesion to metals such as steel, aluminum, copper, and tin, as well as materials like rubber, plastic, and wood.

2. Disadvantages

The electrical insulation performance of polyurethane PU encapsulation adhesive is relatively weak and may not be suitable for applications with extremely high electrical performance requirements. Additionally, some shrinkage may occur during the curing process, so precise control of construction the process is necessary to prevent defects.

3. Product applications

Encapsulation protection for automotive electronic components, sensors, and electronic devices, providing effective protection and insulation for electrical and electronic components such as transformers, chokes, and capacitors to ensure uniform heat dissipation, thermal conductivity and waterproof encapsulation for industrial power supplies and controllers, waterproof encapsulation protection for electric vehicle charging guns, etc.

Epoxy encapsulation adhesives, silicone encapsulation adhesives, and polyurethane encapsulation adhesives each have their own advantages in application. For example, if the product requires good adhesion, epoxy-based encapsulation adhesives can be considered first. For products with high temperature resistance requirements, such as those requiring temperatures below -50°C and above 250°C, silicone potting compounds should be selected. For applications requiring vibration resistance, polyurethane potting compounds should be considered.

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