What are the common types of plastic over molding for TPE/TPR/TPU?
In recent years, metal over molding has become a new application or potential application field of TPE/TPR and TPU. A layer of soft rubber material is coated on the metal surface to prevent slip, shock absorption, corrosion resistance, etc. TPE/ TPR and TPU are used in rubber-coated metals, and there are several types of coating methods.
1. True over molding: TPE and plastic, metal and other materials, formed by chemical interactions, such as molecular layer penetration, reactive group linkage of polar groups or similar hydrogen bonds (van der Waals force), formed at the bonding interface of the two materials Strong welding or bonding without any mechanical and physical effects. Without the aid of adhesive, it can be directly combined with metal by injection molding.
This type of processing is usually TPE and metal parts are integrally encapsulated, and the hardness of TPE is as high as possible (70~80A and above), so as to achieve a certain encapsulation effect, because TPE and metal encapsulation do not exist. The bonding on the meaning (chemical and molecular level) is completely wrapped by the strength of the TPE. In addition, the surface of the metal part has grooves, and the hole position (such as nut and shank) will be more conducive to TPE and metal parts. Form a relatively strong bond.
2. Fake over molding: TPE and hard materials (plastic, metal or other materials) are physically and mechanically bonded by means of holes, grooves and the like, rather than simply chemically bonding the two materials. There is no molecular level of infiltration at the binding plane of the two materials, the reaction of the polar groups is linked or similar to the action of hydrogen bonds (Van der Waals forces). Bonded by adhesive.
Sometimes some special products, the rubber material only partially covers the corresponding position of the metal parts, thus, it is not conducive to the formation of a relatively strong bond between the TPE and the metal parts. By applying a layer of adhesive on the metal surface where the rubber is required to be coated. , is a common idea. But in fact, due to the different molding process of TPE and rubber, it has an important influence on the bonding strength of rubber parts and metal parts. The choice of adhesive type for this kind of metal products Glue is very important. In addition, the structure of the metal to be coated and the hardness of the TPE are also factors to be considered and evaluated.
3. Overall over molding
The whole encapsulation is equivalent to injection of a TPE/TPR and TPU rubber parts. The hardware is wrapped in it. There is no chemically bonded, and the package is still feasible. Generally, the higher hardness TPE/TPR and TPU are used, and the hardness is 80A or more, and the rubber can be encapsulated, but the rubberized hardware is coated as a whole, and if only a part is packaged, it is difficult to achieve.
4. Partial over molding
Partial encapsulation, hardness is soft, strength is not enough, it is difficult to adhere, through the hole processing of the hardware, the physical and mechanical combination of TPE and hardware can be strengthened, thereby improving the firmness of the encapsulation. This kind of rubber is a case of vulcanized rubber parts, but the rubber is vulcanized. If injection molding is used, it is very difficult to partially coat TPE/TPR, TPU and hardware. If the hardware is punched, TPE/TPR and TPU glue can be injected into the hardware to improve the tightness of the rubber. Another customer tried to pre-apply the glue to the hardware, and then injection molding, but the effect is not good.
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