TPE material overmolding according to different substrates should be analyzed from the following aspects

　　1. Non-polar substrate TPE-S, TPV.

　　-> The package of non-polar or weakly polar hard plastic materials naturally, without further ado; -> The difficulty is that the package of polar materials, heat-resistant plastics are thieves.

　　-> The difficulty is that it is very difficult to cover polar materials and high temperature resistant plastics; -> The hardness range is very wide.

　　-> Wide range of hardness, not comparable to TPU, TPEE, TPE-A and most other TPE substrates.

　　-> Good handfeel, not sticky, not slippery, so the people like it very much.

　　So TPE-S/ TPV and polar hard plastic material overmolding, adjust the formula focus on: ->TPE-S, improve the resistance of TPE-A, and improve the adhesion of TPE-A and other TPE base materials.

　　->TPE-S, improve temperature resistance, use more SEBS and less SBS (poor temperature resistance);

　　->TPE-S, substrate with high polarity substrate (this, suppliers such as Kraton, Kuraray have their own secrets), or MAH graft-type substrate, with polar substrates such as TPU + solubilizer for co-mingling and change the polarity of the method can only be used as an auxiliary means, otherwise, the overmolding may not necessarily be good, but is prone to add polar substrates and solubilizers to migrate or precipitation! Phenomenon!

　　-> TPV and polar hard plastic material overmolding, TPV is actually dynamic crosslinked EPDM rubber micro-particles distributed in the PP matrix, in the TPV overmolded hard plastic material to achieve the melt mixing process, has been crosslinked EPDM rubber micro-particles can not be with the polar hard plastic material to occur penetration, infiltration, etc., so the main point of the formula design is to increase the polarity of the PP matrix phase as much as possible (eg, by using MAH graft PP such as Chemtura Polybond series graft PP), and to maximize the content of graft-modified PP in the formula, and reduce the filler, plasticizer (such as paraffin oil) content in the formula. Simply put, it means that there should be more resin in the formula and more graft-modified PP in the dispersed phase of the resin!

　　2. TPEE, ETPV, medium polar substrate

　　-> TPEE is a polyester elastomer, ETPV is ACM (AEM) / TPEE through the dynamic vulcanization technology to produce rubber / plastic hybrid elastomers (technology similar to EPDM / PP-based TPV), -> TPEE is the main substrate of polyester elastomers, ETPV is ACM (AEM) / TPEE through the dynamic vulcanization technology to produce rubber / plastic hybrid elastomers (technology similar to EPDM / PP-based TPV).

　　-> Nylon 6, nylon 66, there is still a certain difference in polarity, resulting in unsatisfactory compatibility, unless the polarity of the substrate is improved.

　　-> TPEE, ETPV has good temperature resistance, allowing high melt temperature during injection molding, so that the high temperature melt can melt an ultra-thin layer on the surface of the hard plastic to achieve cohesion; -> TPEE, ETPV has good temperature resistance, allowing high melt temperature during injection molding, so that the high temperature melt can melt an ultra-thin layer on the surface of the hard plastic to realize cohesion.

　　The problems and shortcomings are:

　　-> The hardness of TPEE is very high due to its chemical structure, at least from Shore A 90 /Shore D 35, corresponding to the pursuit of soft feel of the overmolding application, can not achieve the desired results.

　　->ETPV is actually a dynamic vulcanization process of ACM (AEM) rubber particles dispersed into the TPEE continuous phase substrate to achieve the purpose of reducing the hardness, and to maintain the original TPEE's high temperature, fatigue, chemical resistance, and a series of advantages, the hardness can only be achieved at a minimum of Shore A 60, and can not be compared with the low hardness of the TPE-S, TPV, ultra-soft.

　　-> The most critical point, TPEE or ETPV materials are expensive!

　　3. TPE-U(TPU), TPE-A(Nylon Elastomer), PEBA(Long Carbon Chain Copolymerized Nylon Elastomer) with strong polarity base material.

　　-> Undoubtedly, these strong polarity TPEs have similar polarity with strong polarity hard plastics such as PA6, PA66, which is good for intermiscibility in overmolding; -> The polarity of these TPEs is similar to that of hard plastics, which is good for intermiscibility in overmolding.

　　-> The short-term temperature resistance of these TPEs is very high, so it is easy to use high melt temperature in injection molding to shoot out to the surface of the strong polarity nylon hard plastic to form a molten thin layer, and then the two materials through the molecular chain segment penetration, infiltration to form a joint (cohesion) level of overmolding effect;.

　　Problems and shortcomings are.

　　-> TPU hardness from Shore A 50 or so is not easy to realize the soft feel, and because it is a polar material feel sticky; -> TPU melt is not easy to realize the soft feel, and because it is a polar material feel sticky.

　　->TPU melt viscosity is very sensitive to the temperature, sensitive temperature range of 180C ~ 200C or so, higher than this temperature range, TPU melt fluidity will be suddenly too high, resulting in injection molding to the hard plastic surface of the phenomenon of flying edge; ->TPE-A and PPE-A can be used in the production of hard plastics, but not in the production of hard plastics.

　　->TPE-A and PEBA theoretically with strong polarity PA6, PA66 intermiscibility is very ideal, and injection molding temperature resistance is also high enough, but the hardness are generally high starting from Shore A90, in addition to the material price is not expensive is also a constraint.

　　All of the above, resulting in TPE-S/TPV to realize the ideal overmolding in the joint (cohesion) effect, the most soft and dry hand.

　　Become the most soft and dry feel, the economy of the most economical direction.

　　So that is why TPE-S/TPV overmolded nylon is so difficult.

　　But TPE manufacturers have been persistent to develop the background of this technology.

　　Of course, these discussions are still only based on a variety of TPE substrate properties to explore the difficulties or requirements of the formulation.

　　There is no consideration of the differences in the molecular structure design of the various substrates, the additives in the TPE formulation components and other factors.

　　Even so, it is a very wide topic.

　　Has not included the hard plastic formulation factors, process factors in the processing.