For most injection factory，TPE is a little difficult to adjust the surface. One of the reasons for the surface problems of TPE，is the poor quality of the raw materials. which is also related to the uneven dispersion of the formula. Secondly, it is also relatenjection molding process.
1.White patches on surface :
Refers to stabilizers and other compounding agents migrate to the surface of the molded product, and the surface appears a white phenomenon like spraying powder.
Reason: The excessive compounding of the stabilizer or incompatibility with the polymer caused this problem. Incompatibilities can be solved by adding related compatibilizers of Nanjing Sutai. We should select stabilizers with good compatibility with polymers or control the amount of stabilizers should be led in the optimal range.
In addition, there are stabilizers that exert their functions by migrating to the surface of the molded product. For example, antistatic agents, additives, etc. For this stabilizer component, it is necessary to select a stabilizer that hardly causes whitening even if it migrates.
Thermoplastic elastomers rarely bleach when used in general environments, but in high temperature, vertical, outdoor long-term use, in order to improve and improve the addition of heat stabilizers (anti-aging agents), weather stabilizers are Very necessary. Especially at high temperatures, because it is very easy to cause migration, the choice of stabilizer is also very important.
2. Sticky after injection
Compared with resin, the surface of soft thermoplastic elastomer is more prone to stickiness.
Reason: Mainly caused by the migration of low molecular weight polymers and plasticizers and stabilizers to the surface due to aging. However, no matter what kind of situation, using infrared spectroscopy (IR) and other analytical methods, by analyzing the sticky components, it is relatively easy to identify the relevant substances.
Tackiness is mainly due to the excessively high molding temperature, and the polymer is 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 shear heat generation in the molding process sometimes makes it temporarily reach a high temperature.
Solution: As its countermeasure, reducing the molding temperature and lowering the shear, purifying the inside of the hydraulic cylinder of the molding machine with nitrogen is very effective. In addition, when the molding machine is suspended, the rubber material is left in the molten state of the molding machine cavity for a long time, and sometimes it may become sticky due to thermal aging. In addition, products used at high temperatures are prone to stickiness. Therefore, the selection of stabilizers and softeners and the determination of dosage are very important.
The mechanical properties of the products are obviously reduced, and the appearance quality is deteriorated.
Reason: Compared with inorganic materials and metal materials, polymer materials are poor in heat resistance and ultraviolet resistance, causing product aging. The mechanical properties of most products are significantly reduced due to aging, and the appearance quality is deteriorated.
Solution: By adding stabilizers such as heat resistance and weather resistance, by adding ultraviolet absorbers and light stabilizers, the occurrence of aging can be suppressed to a certain extent. Problems and countermeasures related to injection molding.00nbnb
The phenomenon of concave holes in the molded product is mainly caused by the shrinkage of the molded product during the cooling process in the mold. In addition to requiring the material to fill the mold cavity, rapid cooling is also necessary. Specifically, it is to increase the holding pressure (secondary pressure) and lower the set temperature of the resin and mold.
In addition, there is a great dependence on the shape of the molded product. Because air holes are prone to appear in thick parts, for such products, a model design such as a plastic injection port or a plastic flow channel should be used around it.
This is caused by resin overflowing from the cavity. For rubber injection molding, burrs are normal, but they are not normal for resins or thermoplastic elastomers.
The reasons are:
Compared with rubber compounds, molten resin or thermoplastic elastomer has higher fluidity and lower injection pressure;
Contacting with the mold and cooling, it can solidify and stop the flow in an instant. Therefore, resins or thermoplastic elastomers are generally less prone to burrs.
As a countermeasure, first of all, it is necessary to reduce the filling amount, lower the holding pressure and shorten the holding time. In addition, for molds with poor dimensional accuracy and gaps on the parting surface, repairs are necessary. When the projected area of the molded product is large and the mold clamping force is relatively lower than the injection pressure, burrs may sometimes appear, so a larger molding machine must be used.
6. Flow Mark
Streaks of different gloss appear on the surface of the molded produt.
Generally speaking, in the injection molding of resin are:
Recording stripes with narrow intervals;
A relatively wide stripe pattern of the same phase appears on the surface of the molded product;
Three types of relatively narrow spaced stripes appearing on the upper and lower surfaces of the molded product.
Many methods can solve this problem, such as 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. It is effective by increasing the injection speed and mold temperature.
7. Demolding fault
Demolding fault means that the molded product is difficult to remove from the mold or completely deformed during the removal process. Adhesive materials can easily cause this problem, but the method of adding a release agent to the material or applying relese agent to the mold before molding can be improved.
Insufficient cooling of the molded product (inadequate solidification) is also prone to such problems, so it is necessary to sufficiently cool the molded product. In addition, the unreasonable mold design will also be the reason for the difficulty of demoulding, especially in the parts of the glue injection port, the glue inlet, etc. that are easy to stick the mold.
8. Silver streak
The phenomenon of radial streaks centering on the injection port is caused by the vaporization of moisture or volatile components in the material. Among them, the air trapped in the plasticizing process or remaining in the mold can also cause this phenomenon. Therefore, it is necessary to sufficiently dry the moisture-absorbing material before molding and to reduce the molding temperature of the material that easily generates decomposable gas.
The lack of glue,we call it short shot. The insufficient molding conditions such as insufficient filling amount, but insufficient exhaust during molding or uneven flow path (multi-cavity mold) can also cause this phenomenon.
It means that the part don’t filled up to the end and the mold cavity filled with aging phenomenon like burning. This is mainly due to insufficient exhaust, air or generated gas to cause thermal insulation compression, and instantaneously increase the temperature significantly (the result of thermal aging on the surface of the molded product).
Improving the exhaust method is a better solution. In the case of a light degree, reducing the injection speed can also be solved.
11.Off color & Uneven color
When the thermoplastic material and the dry blend are as the pigment for the coloring of the mother mixture, the phenomenon of uneven color of the molded product is easy to occur, and the mixing is uneven or the combination is not good;
Longterm Manufacturing Solutions Limited have many experience for TPE injection molding.