There is floating fiber on the surface of nylon and glass fiber, and the product application is limited. What should we do?
TIME：2021-10-7
Adding glass fiber, toughening agent and other fillers to nylon can significantly increase the mechanical properties of the material. However, in the process of glass fiber reinforced nylon injection molding, "floating fiber" phenomenon often occurs. Floating fiber is also called exposed fiber, that is, glass fiber is exposed on the product surface, which is relatively rough. Due to the exposure of glass fiber, the application of such products is limited. The causes and solutions of "floating fiber" phenomenon will be analyzed below
Causes of "floating fiber" phenomenon
01
Density difference between glass fiber and base material
In the process of plastic melt flow, due to the difference in fluidity and density between glass fiber and resin, they have the trend of separation. Glass fiber floats to the surface and resin sinks to the inside, so the phenomenon of glass fiber exposure is formed.
02
The compatibility between glass fiber and nylon is poor
Because the plastic melt is subjected to the friction and shear force of screw, nozzle, runner and gate in the flow process, it will not only cause the difference of local viscosity, but also destroy the interface layer on the surface of glass fiber. The smaller the melt viscosity, the more serious the damage of the interface layer, and the smaller the bonding force between glass fiber and resin. When the bonding force is small to a certain extent, glass fiber will get rid of the bondage of resin matrix, Gradually accumulate and expose to the surface area.
03
Fountain effect
When nylon melt is injected into the mold, it will form a "Fountain" effect, that is, the glass fiber will flow from the inside to the outside and contact with the surface of the mold cavity. Due to the low temperature of the mold surface, the glass fiber with light weight and fast condensation is instantly frozen. If it cannot be fully surrounded by the melt in time, it will be exposed and form a "floating fiber".
Therefore, the formation of "floating fiber" phenomenon is not only related to the composition and characteristics of plastic materials, but also related to the molding process, which has great complexity and uncertainty.
The solution of "floating fiber" appears
01
Mold aspect
The appearance of the product is deliberately made into a matte surface or an etched surface to reduce the visual response of glass fiber exposure.
02
Improving the compatibility between glass fiber and nylon
Add compatibilizers, dispersants, lubricants and other additives into the molding materials, including silane coupling agents, maleic anhydride graft compatibilizers, fatty acid lubricants and some domestic or imported anti glass fiber exposure agents. These additives can improve the compatibility between glass fiber and resin, improve the uniformity of dispersion, increase the interfacial bonding strength and reduce the separation between glass fiber and resin, So as to improve the exposure of glass fiber. The results show that the compatibility of modified glass fiber in the matrix is significantly higher than that of non added materials.
03
Improve molding process conditions
① Increase filling speed
After increasing the speed, although the flow rates of glass fiber and plastic are different, the proportion of this relative speed difference is smaller than that of high-speed glue injection.
② Raise die temperature
This effect is the greatest. Increasing the mold temperature is to reduce the contact resistance between glass fiber and mold and minimize the speed difference between glass fiber and plastic. And make the middle melting layer of plastic flow as thick as possible and the skin layer on both sides as thin as possible, just like the smooth river bank can't retain branches. RHCM high-speed high-temperature forming technology uses this principle to achieve no floating fiber in appearance.
③ Reduce the temperature of the screw metering section and reduce the amount of sol
This is to minimize the possibility of separation of plastic and glass fiber. Generally speaking, it has the least impact on floating fiber and has little effect in practical operation. However, this can solve the problem of burning. This is because after adding glass fiber, it is easy to block the exhaust channel, so it is difficult to exhaust in the end, and glass fiber is easy to burn in high-pressure and high oxygen gas environment.
