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TPE is a new generation of polymer material with both elastomer characteristics and thermoplastic forming ability. It is easy to process and can be recycled many times. In recent years, the market demand of TPE has increased greatly. There are more and more kinds of TPE, and its processing technology and processing machinery have also developed accordingly. However, due to the high molecular weight of TPE, TPE is a thermoplastic elastomer. With high viscosity, product processing technology is an important challenge. For example, even though the extrusion process is very simple, there are still some problems in the use of thermoplastic elasticity in extrusion process.
1. Scaling
Scaling is the deposit accumulated at the edge of the die during extrusion moulding. Some of its components are from extrusion moulding materials, and some are from special additives. As a countermeasure, the properties of materials can be effectively improved by reducing the amount of lubricant, because when excessive lubricant is added, lubricant itself is one of the factors causing scaling. The application of Teflon can also reduce scaling. In addition, damp materials should be avoided.
2. Extrusion volume is unstable
The fluctuation of extrusion volume is an unstable phenomenon. The fluctuation of melting point in screw feeding or compression part is the main cause of instability, and the magnitude and period of extrusion fluctuation are irregular. These phenomena can be attributed to the unsuitability of screw shape and extrusion conditions for materials, so it is necessary to adjust extrusion conditions and replace screw with different shapes.
In the case of large fluctuation of extruder temperature, the instability of material flow in the extruder is also one of the reasons for this problem. In addition, the slippage of screw and granular material at the feeding position can also lead to unstable extrusion. While preheating granular material with Douglas dryer, it can be improved by increasing the temperature of the lower barrel of the hopper.
3. Rough surface of moulded products
The surface of the moulded product is not smooth and rough (hemp surface), which is usually caused by poor plasticization. As a countermeasure, of course, it is not necessary to choose the suitable forming machine, but it is also very important to optimize the forming conditions such as setting temperature, type of screw speed filter, etc. In addition, the plasticizing efficiency can also be improved by using high temperature and fine mesh (filter).
In thermoplastic elastomer TPE, some grades themselves contain a lot of moisture absorption components or fillers, so it is necessary to dry them before forming. When forming without drying, problems such as foaming and rough surface will occur.
4. Deformation
TPE is usually extruded from the die and cooled through the water tank. At this time, if the product can not be uniformly cooled, it is very easy to produce deformation. Especially for the complex shape and high dimensional precision products, it is necessary to use cooling calibration or detection device. In addition, in the process of multi-layer extrusion, it is easy to produce deformation because of the different shrinkage of composite materials.
5. Stripes
Extrusion products sometimes have stripe scars or marks on the same part. At this time, it is necessary to check or confirm whether there are any signs of damage, dirt and scaling on the mouth. Secondly, cleaning or eliminating dirty materials is one of the reasons for this problem. In addition, poor melting of materials at the mouth junction can easily lead to stripe phenomenon. The abnormalities of production and processing usually occur, which can be eliminated by adjusting process parameters. Some abnormalities can also be solved from the perspective of TPE raw materials.
Common applications of TPE extrusion:
All kinds of wire and cable, sealing strip (special-shaped door and window sealing strip, automobile door and window sealing strip), furniture sealing strip, all kinds of rubber hose (medical, garden, daily use), all kinds of shock-absorbing and collision-proof tape, process weaving strip and so on.
