Solvent-free composite films produce white spots for two main reasons:
"points" from physical reasons
1. Feature 1:
The number of areas with irregular distribution and often different thickness of ink layer is different. In severe cases, a "snowflake" phenomenon can be observed in the shallow ink.
Analysis of the cause: The amount of glue applied is too small, and the applied glue is insufficient to fill the voids of the ink layer in the composite film and the pits on the surface of the material. This "point" is actually a "void" formed without glue.
Solution: Increase the amount of glue applied.
2. Feature 2:
Some "points" are periodically concentrated and repeated in a fixed area of ​​the pattern.
Analysis of the cause: A certain part of the coated part is not clean or has mechanical defects, resulting in poor transfer of the amount of glue on a specific area, and the formation of "points".
Solution: According to the length of the periodic recurrence, compare the circumference of each roller, find the roller where the problem is located, and clean the foreign object or repair the defect
Reminder: By the following measures, it is usually avoided that the composite film has a "dot" caused by insufficient glue or uneven glue.
1. Reasonably set the amount of glue applied to various composite structures;
2. Pay attention to keep the rollers of the coating unit clean and clean up the foreign objects in time;
3. Always check the surface condition of each roller of the coating unit, and replace the defective roller on the surface in time;
4. Reasonably set the glue liquid level in the glue storage tank, observe the glue condition in the tank frequently, and timely deal with the abnormal phenomenon such as silt accumulation, viscous and agglomeration.
"points" from chemical reasons
Features: The distribution is irregular, but the distribution is wide. Although the size of the "point" is different, its shape tends to be a relatively regular circle... In the wet weather, the material structure with good barrier properties (such as aluminized film) It is easy to appear when compounding.
Analysis of the cause: The isocyanate (-NCO) component in the two-component solvent-free gel reacts with water in the air to form carbon dioxide gas, because these gases cannot be precipitated from the composite film with good barrier properties, and are deposited in the composite film. Form a "point" between them. Therefore, these points are actually carbon dioxide "bubbles".
Solution: The following measures can generally avoid the occurrence of "bubbles" in the composite membrane caused by the reaction of water in the air with the glue.
1. Control the humidity of the composite operation and curing environment, and the relative humidity is generally controlled below 70%;
2. Regularly change the desiccant of the rubber mixing barrel of the mixing machine to ensure the drying of the air in the storage barrel;
3. After the glue packaging drum (especially the curing agent component) is opened, if there is residual glue inside, it should be sealed tightly in time and the residual glue should be used as soon as possible.
Aluminum Nitride Ceramic
The AIN crystal is a covalently bonded compound with a [AIN4] tetrahedron as a structural unit, and has a wurtzite structure and is a hexagonal system. Chemical composition AI 65.81%, N 34.19%, specific gravity 3.261g / cm3, white or grayish white, single crystal colorless and transparent, sublimation decomposition temperature under normal pressure is 2450 °C. It is a high temperature heat resistant material. Thermal expansion coefficient (4.0-6.0) × 10 -6 / ° C. Polycrystalline AIN has a thermal conductivity of 260W/(MK), which is 5-8 times higher than alumina, so it has good thermal shock resistance and can withstand extreme heat of 2200 °C. In addition, aluminum nitride is not attacked by aluminum liquid and other molten metals and gallium arsenide, and particularly has excellent corrosion resistance to molten aluminum liquid.
Aluminum Nitride Ceramic,Aluminum Nitride Plate,Aluminum Nitride Shaft,Boron Nitride Ceramic Shaft
Dongguan Haikun New Material Co., Ltd. , https://www.nitrideceramic.com