Key Elements for Creating High-quality TPE

With the rapid development of the economy, human awareness of environmental protection and product requirements have been continuously improved. TPE (Thermoplastic Elastomer) is a material with high elasticity, high strength, high resilience of rubber, and can be injection molded. It is non-toxic and environmentally friendly, has excellent colorability, weather resistance and temperature resistance, and has excellent processing performance. It can be recycled and coated and bonded with base materials such as PP, PC, PS, ABS, etc., or it can be molded alone. TPE has both the processing performance of thermoplastics and the physical properties of vulcanized rubber. It is an advantageous combination of the advantages of plastics and rubber. Providing customers with a TPE material formula with low price, high yield rate, and excellent performance has always been the core pursuit of TPE granulation manufacturers.

As we all know, the basic formula of TPE materials includes ingredients: SEBS, white oil, filler, and lubricant. The basic molding process of TPE materials is generally: put SEBS into a mixer, fill it with white oil and stir it, add PP, lubricant and filler into the mixer after sufficient oil absorption, stir evenly, and then add the mixture to the twin-screw extruder for extrusion and granulation.

Therefore, in order to obtain TPE materials that meet the performance requirements of customers, the focus is on the formula of the TPE material itself and the influence of the granulation process.

Influence of material formula

1. Raw material SEBS

SEBS is a linear triblock copolymer with polystyrene as the terminal segment and ethylene-butene copolymer obtained by hydrogenation of polybutadiene as the middle elastic block. It does not contain unsaturated double bonds and has good stability and aging resistance. The molecular weight and styrene content of different SEBS grades directly affect the mechanical properties of TPE materials. Choosing a suitable SEBS grade is the key to the performance of TPE materials.

2. Raw material PP

PP polypropylene plastic has high impact resistance, mechanical properties and toughness, and is resistant to corrosion by a variety of organic solvents and acids and alkalis. It can control the hardness, mechanical properties and processing properties of TPE materials. The important indicator for selecting PP is the PP melt index. If the melt index is too low, it will significantly affect the plasticization of the material, and the surface of the product will be uneven and have bumps.

In general, the price of powder PP is lower than that of granular PP, and it has better dispersibility. However, the mixing of PP and SEBS generally reduces the original transparency of SEBS, except for some special grades; it is often used in the formulation system of PP and extrusion materials with low transparency requirements. If the transparency requirements are high, random copolymer transparent PP should be selected, but the amount of addition should not be too much.

3. Filler oil

White oil is a petroleum refining product, which is colorless, odorless and non-toxic. Generally, TPE materials use paraffin-based white oil, which has better compatibility with SEBS. While reducing the cost of TPE materials, it can also adjust the processing performance and hardness of the material. The filler oil needs to strictly control the aromatic (CA) value, and the filling amount can be appropriately selected according to the different SEBS grades. As the filling amount of oil increases, the mechanical strength of the material will decrease, and the filling amount should be based on no oil spitting as the basic standard; oil with high viscosity has lower loss of mechanical properties, but the surface smoothness of the product is also reduced.

4. Filler and lubricant components

Common fillers include calcium carbonate, talcum powder, etc., which can not only reduce the cost of TPE materials, but also affect the processing and mechanical properties of TPE materials. Generally, heavy calcium powder with a mesh size of 1000 or above is selected. The amount of calcium powder added greatly affects the specific gravity of the material. The greater the amount added, the higher the specific gravity.

Lubricants generally include zinc stearate, calcium stearate, etc., which have good material processing lubrication effects and can also adjust the surface gloss of TPE materials. It is mainly used to reduce the friction between molecules in the molten state of macromolecules. The general addition amount is 1-3 parts, which can be adjusted specifically.

Influence of processing technology

The mixing method of some TPE material formulas mentioned above usually requires strict requirements on the mixing order and mixing temperature to ensure the uniformity of the mixed ingredients. At present, TPE materials generally need to go through the granulation process, mainly for the following reasons:

① Granules are more convenient to feed than powders, and no forced feeder is required;

② Granules are denser than powders, and the product quality is better;

③ The volatile matter and air content are less, and the product is not easy to produce bubbles;

④ It is easier to disperse using functional masterbatch than directly adding functional additives.

Therefore, different granulation processes have an important influence on the performance of TPE materials, mainly including the following aspects:

1. Temperature

Temperature has a significant effect on the extrusion and parison performance of TPE: it can reduce the melt viscosity, improve the fluidity of the melt, reduce the power consumption of the extruder, and appropriately increase the screw speed without affecting the mixing and plasticizing effect of the material, which is beneficial to improve the strength and brightness of the final product, and is beneficial to improve the transparency of the final product. However, if the melt temperature is too high, the extruded parison will easily sag due to its own weight, causing uneven longitudinal wall thickness of the parison. Therefore, the heating temperature of the extruder should be set in accordance with the following principle, that is, under the premise of being able to extrude a smooth and uniform parison without overloading the transmission system, in order to ensure that the parison has a higher melt strength, a lower heating temperature should be used as much as possible.

2. Melt pressure

The melt entering the die should have uniform pressure. Appropriately increasing the pressure of the melt in the extruder can make the material mixing uniform and stabilize the performance of the parison and the final product. In order to control the extrusion pressure of the melt, a melt pressure measuring instrument can be installed in the discharge section of the extruder.

3. Melt conveying speed

The higher the melt conveying speed, the larger the extruder's extrusion volume. Increasing the melt conveying speed can improve the phenomenon of the deadweight sagging of the preform and increase the wall thickness of the preform.

In addition to the extrusion process, the pelletizing process also has a relatively large impact on the product. At present, it is mainly divided into cold cutting and hot cutting.

Cold cutting method

1. Pull-sheet cold cutting

The material that has passed through the kneading machine or internal mixer is plasticized into sheets by the open mixer and then pelletized.

2. Extrusion sheet cold cutting

The kneaded material is plasticized by the extruder, extruded into sheets, and then air-cooled or naturally cooled before entering the flat pelletizer for pelletizing.

3. Extrusion cold cutting

Extrusion cold cutting is the most common granulation method for thermoplastic TPE, and the equipment and process are relatively simple. The material is plasticized by the extruder into round strips for extrusion. After the round strips are air-cooled or water-cooled, they are cut into cylindrical pellets by the pelletizer.

Hot cutting method

1. Dry hot cutting

The rotating cutter is placed close to the die template to directly cut the extruded hot round strip material into pellets.

2. Underwater hot cutting

It is a new technology for polyolefin TPE granulation. The die and cutter work in circulating warm water.

3. Air hot cutting

Aerial hot cutting is similar to dry hot cutting. In order to prevent the pellets from sticking, the pellets are cooled by blowing cold air or spraying warm water in the pelletizing hood.

In summary, from TPE material formula to TPE granulation process, I believe that everyone has a deeper understanding of TPE materials and can better meet your needs.

NANJING HAISI is professional manufacturer of TPE extruder, we supply Twin Screw Extruder, Single Screw Extruder, Plastic Recycling Extruder, Two Stage Extruder, Lab Scale Machinery, Mixing and Feeding Machine, Cooling and Pelletizing Machine, Crushing Machine and so on.