In the process of glass fiber reinforced nylon injection molding, the "floating fiber" phenomenon often appears. Floating fiber is also called exposed fiber, that is, glass fiber is rough on the surface of the product, and it is difficult to accept the appearance. Due to the exposure of glass fiber, the application of such products has been limited, and it is mainly used in some high-strength structural parts. As for the appearance parts made of fiber-reinforced materials, they are basically matte or etched surfaces (such as power tools), because ordinary fiber-reinforced materials are difficult to achieve a bright appearance.
There are three main reasons for the formation of floating fibers:
(1) Poor compatibility between glass fiber and nylon
As the plastic melt is subjected to the frictional shear force of the screw, nozzle, runner and gate during the flow process, it will cause the difference in local viscosity, and will also destroy the interface layer on the glass fiber surface. The smaller the melt viscosity, the interface The more the layer is damaged, the smaller the adhesive force between the glass fiber and the resin is. When the adhesive force is small to a certain extent, the glass fiber will get rid of the bondage of the resin matrix, gradually accumulate to the surface and be exposed.
The glass fiber will get rid of the bondage of the resin matrix and gradually accumulate to the surface and be exposed
(2) Difference in specific gravity between glass fiber and base material
During the flow of the plastic melt, due to the different fluidity of the glass fiber and the resin, and the different mass densities, the two have a tendency to separate. The glass fiber floats to the surface and the resin sinks inward, so the glass fiber is exposed. The phenomenon.
(3) Fountain effect
When the nylon melt is injected into the mold, a "fountain" effect is formed, that is, the glass fiber flows from the inside to the outside surface and contacts the cavity surface. Due to the lower mold surface temperature, the light-weight and fast-condensing glass fiber is instantly frozen. If it is not fully surrounded by the melt in time, it will be exposed and form "floating fibers".
Therefore, the formation of the "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.
How to solve the "floating fiber" in glass fiber reinforced nylon
(1) Improve the compatibility between glass fiber and nylon
?我公司研发出的第四代新型高分子材料-树枝状聚合物（ CYD-701 ）可提高玻璃纤维在尼龙体系中的分散程度，有效解决表面浮纤问题，提高制品表面的光泽度。 Adding additives such as compatibility, dispersant and lubricant into the molding material, ?? The fourth generation of new polymer material developed by our company-dendrimer ( CYD-701 ) can improve the fiberglass in nylon system. The degree of dispersion effectively solves the problem of floating fiber on the surface and improves the gloss of the product surface. Can double the melt index of nylon, and avoid the degradation of mechanical properties to the greatest extent. ?通过我公司的尼龙润滑剂来改进玻纤与树脂间的相容性，提高分散相的均匀性，增加界面粘结强度，减少玻纤与树脂的分离，从而改善玻纤外露现象。 ? Through our company's nylon lubricant to improve the compatibility between glass fiber and resin, improve the uniformity of the dispersed phase, increase the interfacial bonding strength, reduce the separation of glass fiber and resin, thereby improving the exposure of glass fiber. As the experiment shows, with the addition of nylon lubricant (CYD-701) in the matrix, the compatibility of the modified glass fiber (left in the figure below) in the matrix is significantly improved compared with the non-added material (right in the figure below).
The compatibility of the modified glass fiber in the matrix is significantly higher than that of the non-added material
(2) Improve the molding process conditions
a. Increase filling speed
After increasing the speed, although the flow velocity of glass fiber and plastic is different, the ratio of this relative speed difference is small compared to high-speed injection glue.
b. Increase mold temperature
This effect is the greatest. Increasing the temperature of the mold is to reduce the contact resistance between the glass fiber and the mold, and to make the speed difference between the glass fiber and the plastic as small as possible. And make the middle molten layer as thick as possible when the plastic is flowing, and make the skin layers on both sides as thin as possible, so that it is as if the smooth river bank cannot retain the branches. RHCM uses this principle to achieve no floating fiber appearance.
c. Reduce the temperature of the screw metering section and reduce the amount of sol
This is to reduce the possibility of separating plastic from glass fiber as much as possible. Generally speaking, it has the least impact on floating fiber and has little effect in actual operation. However, this can be a good solution to scorch. This is because after the glass fiber is added, it is easy to block the exhaust passage, so it is difficult to exhaust the gas at the end, and the glass fiber is easy to burn in the high pressure and high oxygen gas environment.
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