Eight Points to Pay Attention to in Injection Molding of TPE Encapsulated Rubber
Source：德创化工Time：2019-12-24Hits：2650
1. For different substrates, TPE and TPR coating materials with different raw materials shall be selected. For example, the data including PP cannot include ABS, and the data including ABS cannot include PA, etc. At present, the coated TPE in the market can be divided into the following categories: PP coated, ABS coated, PETG coated, PC coated, PA coated, etc.
2. Thickness of TPE and TPR coating. In most application of encapsulation molding, a wall thickness of 1.5-3.0mm will ensure good adhesion. If TPE glue is too thin, injection molding is difficult, adhesion strength is low, and hand feeling is poor. If TPE glue is too thick, on the one hand the cost is relatively high, on the other hand it is prone to shrinkage, bubbles and other shortcomings. The wall thickness of TPE glue should be as uniform as possible to reach the best forming period. The transition between different wall thicknesses should be gradual to reduce problems arising from fluid activities, such as air streaks and bubbles.
3. Radius (minimum radius is 0.5mm) should be selected at sharp corners to reduce partial stress. Deep closed air chambers or arched parts that cannot be exhausted should be prevented. If necessary, sufficient exhaust grooves (0.015-0.025mm) can be added at the end of TPE glue position. Lack of exhaust may lead to bad phenomena such as trapped air, burning glue and lack of adhesive relay.
4. It is very helpful to improve the bonding effect of TPE by adding buckling positions or making some properly designed deeper concave and convex parts on the substrate.
5. Treatment of mold appearance:
1) The mold shall be polished to obtain a smooth or clear appearance.
2) In order to produce the lusterless appearance of thermosetting rubber, a rougher mold appearance is required. Generally speaking, the rough appearance of the mold cavity after electrical discharge machining (EDM) will produce excellent workpiece appearance and make demolding comparison simple. Grinding methods such as steam eruption, sandblasting or shot peening, and chemical etching can also be used to produce appearance with different luster and appearance.
3) In order to facilitate mold release, a mold release coating can be applied to the mold cavity or core, for example, a layer of PTFE (polytetrafluoroethylene)-impregnated nickel can be applied after the mold cavity or core is subjected to sandblasting treatment or electric discharge machining (EDM).
6. The base material should prevent the application of release agent. The surface of the substrate should be cleaned to prevent touching dust as much as possible.
7. The processing temperature of TPE and TPR rubber coating shall be based on the measured melting temperature of rubber, rather than the apparent temperature of injection molding machine.
8. If TPE is requested, TPR is coated on metal parts and can be assisted by appropriate adhesive.
