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Analysis of elastomeric TPE and nylon PA coated rubber from the secondary injection molding process

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    With the deepening of TPE R&D and innovation and the expansion of TPE applications, TPE coated nylon is increasingly used. It has mature applications in auto parts, kitchen tools, sports equipment and other industries. In the TPE industry, the adhesive bonding effect of TPE and nylon PA is not as good as TPE plastic PP, ABS, PC.
 
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    TPE and PA nylon covered rubber, the bonding effect is not so good. This aspect is related to the performance of the TPE compound itself, and the other is the processing technology when the TPE is overmolded with the PA nylon. This paper focuses on the effect of TPE secondary injection molding process on the bonding effect of PA nylon. The double injection molding of the two-color injection molding machine almost completely overcomes the unfavorable factors of the process of PA nylon encapsulation due to its high-efficiency processing performance, and the adhesive bonding effect is very good. The encapsulation effect is not good. It usually occurs in the traditional molding method of using an ordinary injection molding machine and using two sets of molds to embed the nylon rubber parts into the rubberized mold.
 
    Injection molding temperature is one of the most important processing factors affecting the bonding effect of TPE and PA nylon. Nylon is a high melting point crystalline or semi-crystalline engineering plastic. If the temperature is not enough, it will affect the sintering of TPE and PA on the rubber-bonding surface, which will obviously affect the bonding effect of the two. When embedding an injection molded TPE in a double injection, the following three aspects should be noted:
 
1. Baking pretreatment of nylon PA plastic parts
    To do the baking process, one can remove the moisture in the rubber (the nylon material is easy to absorb water). The adhesive contains more moisture, which is not conducive to the bonding of TPE and PA;
    The second is to make the PA adhesive parts have higher temperature and energy when they are bonded to the TPE by baking. From the physicochemical point of view, It is advantageous for the TPE and the PA to be welded to each other to form a bonding layer.
 
2. Use a temperature close to the melting point of PA nylon
    TPE injection temperature should be as high as possible during overmolding. Using injection temperature close to the melting point of PA will be more conducive to the bonding of TPE and PA. How much injection temperature is used depends on the specific type of nylon (PA6, PA66 and others), whether it is modified (added fiber, toughened, Flame retardant, enhanced). It is not convenient to give a more accurate value here. It is recommended to set it according to the material characteristics and make appropriate adjustment according to the actual production situation.
 
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3. Design of the mold gate
    Some products, the rubberized area is large, it is easy to appear in the vicinity of the rubber mouth, the bonding effect is good, and the location far from the gate is not well bonded. Happening. This is because, at a position farther from the gate, the rubber material flows for a relatively longer period of time, and the temperature of the rubber material decreases during the flow in the cavity splitting passage, thereby affecting the adhesive bonding with the PA nylon. The solution is to open the rubber inlet properly, or if possible, set a few rubber inlets to allow the rubber to spread on the surface of the nylon rubber material more quickly, which is beneficial to the rubber coating.
 
    Some cases of nylon encapsulation, by grinding the surface of nylon parts, or punching, grooving, also facilitate the encapsulation of nylon, but this The kind of rubber is based on physical mechanics, which is different from the gelling mechanism discussed by the author.
 
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    Everything has two major factors: internal and external. Although the secondary injection molding process has a greater impact on the bonding of TPE nylon PA, TPE The performance of the rubber compound is the key. Only the TPE compound with the adhesion to the PA can provide the material basis for the effective bonding of the TPE and the PA.

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