Table of Contents
What is TPV？
TPV has excellent characteristics such as good elasticity, compression deformation resistance, ageing resistance, wide operating temperature range (-60-150℃), adjustable hardness (25A-54D), etc. Green environmental protection, recyclable and other processing characteristics. Widely used in automobiles, construction, rail transit, home appliances, electronic appliances, shoe materials, medical equipment, cables, photovoltaics and other fields. At present, TPV is most widely used in the automotive field, followed by the construction industry, and thirdly in the home appliance field.
How is TPV produced?
There are usually three preparation methods for TPV: melt blending, solution blending, and latex blending. There are two main types of equipment, a mixing mill or a twin-screw extruder. In industry, the twin-screw extruder has become the most common dynamic vulcanization equipment due to the continuous production of the twin-screw extruder.
The most common process for TPV twin screw extruder production of TPV materials is dynamic vulcanization.
Dynamic vulcanization refers to the vulcanization of rubber during the melt blending of rubber and thermoplastics. TPV exhibits remarkable non-Newtonian fluid properties, so it has good processability in moulding or calendering and extrusion.
Since the rubber in the vulcanization process needs to be mixed with thermoplastics, in order to make TPV materials, the surfaces of the two materials need to be matched. At present, the most commonly used materials are EPDM and PP. Such functional materials not only have the characteristics of rubber but also have the characteristics of elastomers.
Recommended TPV twin-screw extruders
Project Details
- Factory Location: China
- Equipment: CHT65 Twin Screw Extruder Underwater Pelletizing Line
- Application: TPV processing
- Output: 300 kg/h
- Date: 2018.05
Introduction to TPV processing technology
Basic raw materials: EPDM (particle or block) + PP + oil + vulcanizing agent (initiator crosslinking agent) + calcium powder
Multi-step process:
The most mature technology used by domestic manufacturers;
Advantage:
- Simple equipment requirements, low screw torque requirements,L / D = 48 ~ 52 is enough
- Multi-step processing can be completed on the same equipment(screw combination does not need to be changed)
- The same equipment can also meet the production of TPE / TPR and other elastomers
Required equipment:
Horizontal mixer; twin-screw extruder; liquid injection system; underwater pelletizing line (water-cooling strand pelletizing line; water ring pelletizing line for a few customers); high-speed mixer (used by some manufacturers), etc.
Process steps:
Step 1: Preliminary plasticization and oil filling
Mixing EPDM (particle) + PP + oil + calcium powder with horizontal mixer, mixing and granulating with twin-screw;
Step 2: Filling the particles produced in the first step with oil in the horizontal mixer again, and then granulate with twin-screw;
The second step can be repeated or not repeated as needed;
Step 3: Add oil and mix the particles in the first step again with a horizontal mixer, and add vulcanizing agent (initiator crosslinking agent). Some customers also use the high-speed mixer to mix materials in this step; Then use twin-screw granulation again.
One-step process:
The earliest process adopted in Europe and America must be realized by multiple gravity dosing systems.
The L / D is very long, generally about 56 ~ 68.
The screw torque must be very large, it should be used a D-type gearbox;
Advantages: energy saving and low processing cost; Suitable for batch continuous production with mature formula and technology;
Disadvantages: the investment is large, and the equipment investment is several times more expensive than the ordinary multi-step method;
The universality of the equipment is very poor, It means no advantage in processing other elastomers;
For customers who have just started to produce TPV, the material waste in the production process is serious.
Required equipment:
various loss-in-weight feeder (particle, powder and liquid scales), high torsion twin-screw extruder, single-stage high-speed forced side feeder, melt pump and underwater pelletizer;
Principle: Making use of the advantages of high torque and large aspect ratio to feed point by point in the twin-screw extruder according to the process needs;
Processing once is enough.
Feeding sequence in the screw:
(EPDM (particle) + PP + calcium powder) + liquid filling + side feeder of vulcanizing agent (initiator crosslinking agent) + liquid filling.
TPV Twin Screw Extruder Guide
Filling and reinforcing of TPV
The polymer and the additive Premix are continuously fed into the first barrel section of the twin-screw compounder (CHT) by suitable metering devices. If low bulk density powders have to be fed, the gravimetric feeder should be installed as close to the extruder intake as possible in order to prevent the entrapment of air in the feed stream.
The first extruder barrel is typically cooled continually with water, the other barrels are cooled or heated electrically during production depending on process requirements and the temperature regulation of the different zones. The counter-rotating, closely intermeshing twin screws of the TPV twin-screw extruder pick up the product, transport and compact it. Finally, the product is melted in the plastification area (barrel sections 2, 3) by the kneading elements.
During the melting process, the additives and stabilizers are worked into the polymer melt homogeneously. A variable speed drive allows choosing the appropriate range of screw speeds (maximum up to 600 rpm) for the process.
Via side feeder additives or mineral fillers can be fed to the extruder. This side feeder has to be fed by one or several gravimetric feeders.
Via liquid injection bores, liquid additives can be fed to the TPV twin screw extruder.
Openings for atmospheric venting in open barrels allow evacuating air and moisture from the melt.
Volatiles can be evacuated from the machine in the degassing zone barrel. For this purpose, a vacuum pump may be connected to the vacuum vent installed on the top opening of the barrel. In the last barrel, the machine builds up the pressure that is needed to extrude the via die head.
