If the surface quality of TPE injection molded parts is critical, they must be dried before molding. This is typically done in a hopper at 70-80°C for 2 hours or on a tray at 80-100°C for 1 hour. For tray drying, the ideal layer thickness should not exceed 50mm. Tray drying is recommended. If the molded strips exhibit blistering, or if hollows are found when the strips are cut, or if scattered silver streaks are observed on the surface of the product, this indicates excessive moisture in the TPE/TPR raw material.
1, Flow marks
appear as streaks with different gloss on the surface of the molded product. Generally speaking, there are three types of flow marks in resin injection molding:
(1) narrow-spaced streaks;
(2) relatively wide-spaced streaks that appear in the same phase on the upper and lower surfaces of the molded product;
(3) relatively narrow-spaced streaks that appear in different phases on the upper and lower surfaces of the molded product.
Solution: These can be solved by adding pure monomer resin, increasing the injection speed, mold temperature, increasing the injection port, increasing the resin temperature and injection rate, increasing the molding temperature, mold temperature, or reducing the injection speed. Increasing the injection speed and mold temperature are both effective.
2, Poor demolding
Poor demolding refers to a molded part that is difficult to remove from the mold or completely deforms during removal. Adhesive materials are particularly prone to this problem, but it can be improved by adding a release agent to the material or applying it to the mold before molding. Insufficient cooling (undercuring) of the molded part can also lead to this problem, so sufficient cooling of the molded part is essential.
In addition, unreasonable mold design can also make demolding difficult, especially in areas prone to mold sticking, such as the injection port and the glue inlet channel. Increasing the extraction angle of the injection port and widening the glue inlet channel are very effective.
3, Aging
The mechanical properties of the product significantly deteriorate, and the appearance quality deteriorates.
Cause: Compared with inorganic and metal materials, polymer materials have poorer heat and UV resistance, which leads to product aging. Most products experience a significant decrease in mechanical properties and a deterioration in appearance due to aging.
Solution: Aging can be suppressed to a certain extent by adding stabilizers such as heat and weathering agents, as well as UV absorbers and light stabilizers.
4, Uneven color
When using a masterbatch of thermoplastic elastomer particles and dry blend as pigment for coloring, uneven color of the molded product is likely to occur. As a countermeasure, increasing the screw back pressure and strengthening the mixing of fillers are effective.
5, Albinism
It refers to the phenomenon that the stabilizer and other compounding agents migrate to the surface of the molded product, and the surface appears white as if it were sprayed with powder.
Cause: This is primarily due to an overdose of stabilizer or incompatibility with the polymer.
Solution: For this type of problem, choose a stabilizer that is highly compatible with the polymer or control the stabilizer dosage within the optimal range.
Alternatively, switching to a stabilizer with a higher molecular weight can be very effective. Alternatively, some stabilizers work by migrating to the surface of the molded part.
For example, antistatic agents and lubricants. For these stabilizers, it’s crucial to choose one that’s less likely to whiten even if it migrates. Whitening rarely occurs in normal environments, but in high-temperature, humid, or long-term outdoor use, adding heat-resistant and weather-resistant stabilizers is essential to improve durability. High temperatures are particularly prone to migration, so the choice of stabilizer is crucial.
