How does phenolic paper sheet perform in a humid environment?

Phenolic paper sheet is a common material in the field of electrical insulation. It is made by impregnating electrical insulation paper with phenolic resin and then pressing it. This material has good electrical insulation, mechanical strength and heat resistance, so it is often used as an insulating structure, support or gasket in motors, electrical appliances and electronic equipment. However, the performance of phenolic paper sheet is not constant and will be affected by environmental factors. Especially in a humid environment, the performance changes are particularly obvious.

What effects does a humid environment have on the performance of phenolic paper sheet?

Degradation of electrical insulation performance

In a dry state, phenolic paper sheet can effectively prevent current leakage. However, when it is in a humid environment, moisture in the air will penetrate into the inside of the paperboard. Since water is conductive, this will change the charge distribution inside the paperboard, which will cause a significant decrease in insulation resistance. After the insulation resistance decreases, the risk of electrical leakage in electrical equipment increases, and in severe cases, it may even cause faults such as short circuits.

Under the action of an alternating electric field, the moisture inside the wet phenolic paper sheet will form conductive channels. These conductive channels will convert more electrical energy into heat energy, resulting in increased dielectric loss. Increased dielectric loss will not only reduce the operating efficiency of the equipment, but also increase the temperature of the paper sheet, accelerating the decline of insulation performance. In addition, moisture will ionize under the action of the electric field to produce conductive ions, which will cause the electric field to be unevenly distributed and the local electric field strength to increase, thereby reducing the breakdown voltage of the phenolic paper sheet. Once the electric field strength exceeds the tolerance range of the paper sheet, insulation breakdown will occur, which affects the normal operation of the equipment.

Deterioration of mechanical properties

For phenolic paper sheet as a structural component, mechanical strength is crucial. In a humid environment, moisture enters the fiber structure of the paperboard, weakening the bonding force between the fibers. The weakened bonding force between the fibers reduces the tensile, compressive and bending strength of the paperboard, and it is easy to deform or break when subjected to external forces.

At the same time, the phenolic paper sheet will expand after absorbing moisture. Due to the different degrees of moisture absorption in different parts of the paperboard, stress will be generated inside, resulting in dimensional changes. In motor manufacturing, if the size of the insulating gasket made of phenolic paper sheet changes, it will affect the air gap between the stator and the rotor. The air gap is affected, which will cause the motor to vibrate more and reduce efficiency.

Appearance changes

A humid environment is conducive to the growth of mold. If there are impurities such as dust and oil on the surface of phenolic paper sheet, it is easier to breed mold. Mold grows on the surface of the paperboard, forming black, green or gray mold spots. These mold spots not only affect the appearance of the product, but the acidic substances secreted by the mold will also corrode the paperboard, accelerate the aging of the material, and further reduce the insulation and mechanical properties of the paperboard. In addition, moisture will chemically react with the components of the paperboard, making the paperboard darker. Darkening of paperboard often means that chemical degradation has occurred within the paperboard and its properties have been compromised.

How to improve the performance of phenolic paper sheet in a humid environment?

Material improvement

Phenolic resins with better water resistance and chemical corrosion resistance can be developed. During the research and development process, by adding modifiers such as silane coupling agents and nanomaterials, the bonding force between resin and fiber can be enhanced, thereby improving the overall performance of paperboard. Phenolic paper sheet can also be compounded with materials with good moisture resistance such as polyimide film and polytetrafluoroethylene film, combining the advantages of each material to improve the comprehensive performance of phenolic paper sheet in a humid environment.

Surface treatment

Surface waterproofing of phenolic paper sheet can effectively prevent moisture intrusion. Common surface waterproofing methods include coating with waterproof coating and coating. After coating with waterproof coating, a waterproof film can be formed on the surface of the paperboard to prevent moisture penetration; coating technology is to deposit a hydrophobic film on the surface of the paperboard to reduce moisture adhesion.

Environmental control

When using phenolic paperboard, it is very important to control the ambient temperature and humidity. Dehumidification equipment and air conditioning systems can be installed to control the relative humidity of the environment at an appropriate level. At the same time, the temperature should be adjusted reasonably to avoid extreme temperatures affecting the performance of the paperboard and create a stable use environment for it.

A humid environment will affect the performance of phenolic paper sheet in many aspects, including electrical insulation performance, mechanical performance and appearance. Through methods such as material improvement, surface treatment and environmental control, the performance of phenolic paper sheet in a humid environment can be effectively improved to ensure the stable and safe operation of electrical equipment.