How to improve the degree of bonding of secondary injection molding ?

- Jul 05, 2019-

How to improve the degree of bonding of secondary injection molding ?

  The secondary injection molding process mainly refers to an injection molding process in which thermoplastic elastomers (TPE, TPR, TPU) are bonded to engineering plastics (PP, PC, ABS, PA, PS, PE, POM) by melt adhesion. There are currently two main methods of achieving bonding: overmolding and coextrusion.


   In the case of secondary molding, the surface softening of the soft and hard segments, the molecular diffusion of the outer elastic body, and the engineering plastics must be compatible with each other, that is, they cannot reject each other's molecules. As the molecular mobility increases, the molecules of the two materials diffuse into each other, producing a melt adhesion. Eventually a cohesive weld layer is formed in the surface layer network.


The TPE secondary molding materials developed by Dongguan Plastics Co., Ltd. have good adhesion to general plastics and engineering plastics, including: polypropylene PP, ABS, polycarbonate PC, polyester nylon PA and so on. Of course, the adhesion will vary slightly depending on the engineering plastics provided by the manufacturer.


   The best way to ensure good adhesion during the secondary molding process is to allow the injection molding machine (pictured, two-color injection molding machine for secondary molding) to be automatically carried out throughout the process, that is, the engineering plastic is injected first, then the mold is opened. The thermoplastic elastomer alloy is injected into the mold. Of course, it is also possible to inject the thermoplastic elastomer alloy TPE and then the engineering plastic. Another method is to first process the engineering plastic part and then manually move it to another set of molds to inject the thermoplastic elastomer TPE onto the surface of the engineering plastic part. The latter method is labor intensive and requires an external connection to the engineering plastic when moving between the molds.


   In order to improve the adhesion between thermoplastic elastomer TPE and engineering plastics, the following points should be noted during molding:


1, high mixing temperature


2, high injection speed


3. The mold temperature of the thermoplastic elastomer section should be between 20 ° C and 60 ° C.


4, to avoid excessive holding pressure


5, avoid wrinkles / shrinkage


6, as high as possible injection pressure


7, matrix type - additives (plus glass fiber, mineral filling, heat stabilized, added lubricant)


8, color masterbatch carrier type


9. Moisture content in the secondary injection layer and matrix


10. Quality and proportion of recycled materials


11. Cleanliness, preparation and preheating of the substrate


12, the design of the workpiece and mold

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