Over molding overmolding process.
The process has been applied to engineering plastics for a long time. For  example, the package of the electronic charger coil skeleton (PET GF  FR) and the package of the micro motor (internal PA66 or PET skeleton,  coated with PBT GF).
The encapsulation in the market segment of elastomer applications is only a special overmolding. The  speciality is that the soft TPE material is used as the second material  component, and is coated on the surface or part or inside of various  hard ordinary plastics to realize the effect of a single component and  multiple materials. Simply  speaking, the overmolding can be plastic overmolding, soft plastic  coating, or soft plastic soft rubber. We often say that it is a specific  overmolding process of soft plastic hard plastic.
There are many advantages of TPE plastic glue sticking. Here, we mainly popularize it with customers.
TPE encapsulated sticking mechanism.
Simply put, the TPE encapsulated glue has a distinction between true rubber and fake rubber. True rubber is made of soft rubber
And  the compatibility of the hard rubber in softening and melting, forming a  layer of adhesive layer on the contact surface of the hard rubber and  the soft rubber to realize the adhesiveness of the TPE hard plastic. Fake  rubber is almost unrelated to the compatibility of the two materials.  The rubber encapsulation of the material is made by mechanical force,  through the design of the mold and the product and the surface  treatment, so that the soft rubber and the hard rubber can be joined  together.
We mainly talk about the real encapsulation (chemical method)
The  chemical method relies on the molecular affinity between the two  materials and the bonding force of the chemical bond to bond the two  materials together to form a single component, two or more components,  and materials, so that there is strong adhesion between the contact  interfaces. a process. It is more secure and more flexible in design.
(2) The concept of adhesion and cohesion in the encapsulation is clearly
In  PE elastomer/hard plastic encapsulation applications, chemical bonding  of TPE to hard plastic is the preferred method of bonding between two  materials. It is impossible to understand two words: adhesion and  cohesion.
Mainly talk about bonding and bonding
The  material bonding method is because of the chemical bonding method. The  difference is that the bonding relies on the molecular polarity  attraction or hydrogen bonding force between the two materials to  realize the bonding between the second material TPE and the hard  plastic; It  is a mutual dissolution and polar attraction between two materials to  achieve bonding of at least a molecular segment level on the contact  interface between the two materials.
The  theoretical level is very complicated, but from the practical point of  view, there is a very simple method of judging whether it is bonding or  bonding.
The  bonding effect is strong adhesion on the double material interface, but  as long as there is enough tearing force to tear the TPE from the hard  plastic surface, the hard plastic surface is smooth and flat, without  the residue of TPE material.
The  bonding effect is to strongly tear the TPE from the hard plastic  surface. There are many TPE residues on the hard plastic surface, which  means that the TPE/hard plastic is actually mutually soluble at the  interface, just like the two metals are welded together, even if the TPE  itself is The  tearing is broken and the bonding on the interface is also very tight,  resulting in residual TPE on the hard plastic surface. That  is to say, the adhesion is by the strong adsorption force between the  TPE/hard plastic, and the bonding is the mutual dissolution and chemical  bonding of the molecular section between the TPE/hard plastic.
Undoubtedly, the joint is the most ideal chemical bonding method in TPE/hard plastic coated design.
(3)  The principle of interface chemical reaction in the encapsulation  process has been discussed above. To achieve the special overmolding  effect of encapsulation, the most ideal one is to form the molecular  segment surface between TPE soft rubber/hard plastic. Bonding. This powerful chemical form involves a miscible, penetrating, penetrating welding process of molecular or molecular segments. One  metal is used as the substrate, and the other metal is applied to the  surface in the form of a high-temperature melt, and an ultra-thin layer  of one or several molecular layer thicknesses is formed at the interface  of the two metals by high temperature, and the two metal molecules are The  high-temperature ultra-thin contact interface layer is in a liquid or  molten state, penetrates each other and penetrates to the other  interface through the free diffusion movement of liquid molecules, and  after cooling, forms a thin layer of mutual solubility and penetration  interface.
According  to the above-mentioned metallization theory of the metal-like welding  mechanism, the key points of the TPE/hard plastic molecular segment are  achieved, and the key is to do the following three points.
a.  The material of TPE is similar to the polarity of hard plastic  (otherwise it cannot dissolve, penetrate, penetrate in the melt state)
b.  The surface tension of the TPE material is less than the surface  tension of the hard plastic (otherwise the TPE melt will not spread on  the surface of the hard plastic insert).
With  regard to the surface tension, it is easy to understand that mercury is  condensed on the surface of the glass and the water droplets can spread  on the surface of the glass.
c.  When the TPE melt flows along the hard plastic surface in the mold  cavity, the cooling process releases heat, which can quickly and  effectively melt the hard plastic surface layer to form a thin layer  that can penetrate each other.
The  formula design of the rubber-coated grade TPE, the molding process of  the rubber-clad, and even some of the seemingly irregular and  difficult-to-coat problems in the rubber-filled rubber, it is not  difficult to grasp and understand after knowing the three basic points  of the above basic theoretical model.
(4)  Technical points and difficulties of chemical bonding and hard plastic  bonding Since TPE/hard plastic overmolding is a branch of the relatively  mature overmolding process, it does not seem very much from the  mechanism of TPE/hard plastic coating. Complex,  why do major TPE manufacturers still use TPE rubber, especially nylon  TPE rubber as a major technical selling point or as a technical  challenge? This seemingly simple mechanism to achieve true chemical  bonding properties of TPE / hard plastic The joint effect, the technical point is also difficult, lies in the following four points
a.  First of all, it must be ensured that the TPE has sufficient  temperature resistance. It will not degrade in the barrel of the  injection molding machine when it is shot at high temperature, and it  must ensure that the temperature of the TPE is much higher than the  melting/softening temperature of the hard plastic. A thin layer of plastic surface is melted.
That  is to say, the two requirements are combined, in fact, the TPE is  required to have a high temperature resistance, and the higher the  melting point/softening point temperature of the hard plastic, the  greater the technical difficulty.
b.  When the high temperature TPE melt flows at high speed along the  surface of the hard plastic part in the mold cavity, the heat released  during the cooling process is sufficient to melt the surface of the hard  plastic substrate.
That  is to say, the higher the melt temperature at the time of TPE injection  molding, the higher the melting/softening temperature of the hard  plastic, or the higher the crystallinity and the larger the melting  enthalpy of the crystal, the more difficult the joining.
c  Even if the TPE has sufficient temperature resistance, the injected  melt is enough to melt the thin layer of the hard plastic surface. It  also requires that the polarity of the TPE and the engineering plastic  are similar in polarity, and the thermodynamic mutual dissolution and  cooling fusion of the chain segment level are achieved. During  the melt contact time of the short TPE hard plastic substrate, it  diffuses due to the movement of the molecular segment and penetrates  into the interface of the other side. Otherwise, once the TPE melt  cools, only the polar adsorption force between the molecules is formed. The bonding force of TPE/hard plastic is the type of bonding.
d.  The surface tension of the TPE melt must be as far as possible as much  as the surface tension of the hard plastic substrate. Otherwise, the TPE  melt cannot be unfolded as soon as possible and the hard plastic  surface is melted. After the TPE is cooled, only the adhesive type  package can be formed. glue.