One of the reasons for the surface problems of TPE injection molded parts is the poor quality of the raw materials, which is also related to uneven dispersion of the formulation, and secondly to some parameter settings of the injection molding process.
1, whitening phenomenon:
Refers to the stabilizer and other complex agents migrate to the surface of the molded product, the surface as sprayed with powder showed a white phenomenon.
Reason: Mainly due to over-compatibility with the stabilizer or incompatibility with the polymer caused by the incompatibility can be added to the Nanjing-compatible plasticizer to solve. Should choose a good compatibility with the polymer stabilizer or The amount of stabilizer control in the best range.
Second, it is also very effective to change to a stabilizer with a relatively high molecular weight, and also stabilizers that function by migrating to the surface of molded products, for example, antistatic agents, lubricants, etc. For such stabilizers, It is necessary to choose a stabilizer which is hard to whiten even if it is migrated.
Thermoplastic elastomers rarely cause whitening when they are used under normal conditions. However, when they are used at high temperatures and humidity for long-term outdoor use, thermal stabilizers (antioxidants), weather stabilizers Is very necessary.Especially under high temperature, because of its very easy to cause migration, so the choice of stabilizer is also very important.
2, sticky phenomenon:
Compared with the resin, soft thermoplastic elastomer surface more prone to sticky phenomenon.
Reasons: mainly due to aging generated low molecular weight polymers and plasticizers, stabilizers migrate to the surface caused by However, no matter what kind of situation, the use of infrared spectroscopy (IR) and other analytical tools, by analyzing the sticky Components will be able to more easily identify the relevant substances.
The tackiness is mainly due to the molding temperature being too high and the polymer being thermally decomposed to form low molecular weight substances.Although the set temperature of the molding machine itself does not reach the thermal decomposition temperature, the shearing heat generation in the molding process is sometimes Will make it temporarily reach high temperatures.
Solution: As a countermeasure to reduce molding temperature, low shear, purify the interior of cylinder body with nitrogen gas is very effective.In addition, in the molding machine is suspended, the plastic material to stay in the molten state for a long time in the molding Machine mold cavity, sometimes due to thermal aging and sticky In addition, the products used at high temperatures prone to sticky phenomenon.Therefore, the choice of stabilizer, softener type and dosage is very important .
3, aging phenomenon:
Mechanical properties of products significantly reduced, the appearance of poor quality.
Reasons: Compared with inorganic materials and metal materials, polymer materials, heat resistance, poor UV resistance caused by aging products.Most products due to aging make it significantly reduced mechanical properties, the appearance of poor quality.
Solution: By adding heat stabilizer, weatherability and other stabilizers, by adding UV absorbers, light stabilizers, to a certain extent, can inhibit the generation of aging phenomenon. Problems with injection molding and countermeasures.
4, stomata:
In the molded product appears concave hole phenomenon, mainly due to the shrinkage of the molded product during the cooling process in the mold .In addition to the material must be filled cavity, rapid cooling is also very necessary .In particular, is to enhance the protection Pressure (secondary pressure), reduce the resin and mold set temperature.
In addition, there is a great dependency on the shape of the molded product, and since the blisters are likely to occur in the thick area, a model design such as a plastic injection port or a glue gate should be used for such a product .
5, burrs:
This is caused by resin spillage from the cavity, which is normal for injection molding of rubber but is not normal for resin or thermoplastic elastomer.
The reason is:
Compared with the rubber compound, the molten resin or thermoplastic elastomer has higher fluidity and lower injection pressure.
Contact with the mold, cooling, in an instant can be cured to stop the flow.Therefore, the resin or thermoplastic elastomer is usually not prone to flash phenomenon.
As a countermeasure, firstly, it is necessary to reduce the filling amount, reduce the packing pressure and shorten the packing time, and in the case of a mold having a poor dimensional accuracy and a parting surface gap, it is necessary to repair the molded product in a large projected area When the mold force is relatively lower than the injection pressure, flash sometimes occurs, so a larger molding machine must be used.
6, the flow marks:
In the molding surface appear different fringe phenomenon.
In general, in the resin injection molding are:
Striped recording stripes;
The formation of the upper and lower surface of the molding phase with a relatively wide interval stripe;
There are three types of narrower interval stripes that appear above and below the molding surface.
Solve this problem can be solved by these methods, such as adding pure monomer resin, increase injection speed, mold temperature, increase the plastic injection port, increase the resin temperature and injection rate, increase the molding temperature, mold temperature or reduce the injection speed. By increasing the injection speed and mold temperature are valid.
7, poor mold release:
Poor mold releasability means that the molded product is difficult to remove from the mold or is completely deformed during the removal process. Adhesive materials are extremely susceptible to this problem, but mold release is applied to the mold or mold release is applied prior to molding The method of the agent can be improved.
In addition, it is necessary to sufficiently cool the molded product, because the under-cooling of the molded product is insufficient (under-curing), and it is also very difficult to mold the molded product. In particular, Into the glue and other parts easy to stick model, increase the pull-out angle injection port, widening into the rubber are very effective.
8, silver stripes:
The phenomenon of radial streaks centered on the plastic injection port is caused by the gasification of moisture or volatile components in the material, of which the air trapped in the mold or in the mold can also cause this phenomenon. , It is necessary to fully dry the moisture-absorbing material before molding and to reduce the molding temperature of the decomposable gas material.
9, the lack of plastic:
Not full of cavity end of the phenomenon known as the lack of plastic.This is mainly due to lack of plastic filling conditions caused by discomfort, but the molding exhaust is not sufficient or flow imbalance (multi-cavity mold) will Lead to this phenomenon.
10, burned:
Means not unfilled to the end and the cavity is not filled with the part of the phenomenon of burning like burning.This is mainly due to inadequate exhaust, air or gas generated by thermal insulation compression, instantaneous temperature caused by a significant increase The result (ie, heat aging on the surface of the molded product).
To improve the exhaust is a better solution, the case of light, reduce the injection speed can be solved.
11, color is not uniform:
In the coloration of the mother mixture using the thermoplastic elastomer particles and the dry blend as a pigment, the color unevenness of the molded product is liable to occur, which results in uneven mixing or poor bonding.
As a countermeasure, use a suitable coupling agent, compatibilizer, and improve the screw back pressure, strengthening the filler mixing are effective.