Thermoplastic Elastomer

The thermoplastic Elastomer is abbreviated as TPE. The most common TPE material is SBS/SEBS modified material. 

TPE extruder is used for a rubber with high elasticity. It also has the characteristics of injection molding. It has a wide range of hardness, superior processing performance, no need for vulcanization, and can be recycled to reduce costs. It is mainly used in various types of seals, automotive interiors, rubberized materials, various pipe fittings, wire and cable etc.

SBS or SEBS compounding modification can be adjusted according to the ratio between SBS/SEBS, PP, filler and filling oil to meet different hardness requirements. PP provides rigidity, and increasing of SBS/SEBS and filling oil improves flexibility

Compounding and Water Ring Hot Face Pelletizing Line for Thermoplastic Elastomers

1. high-speed mixer  2. main feeder  3. side feeder  4.twin screw extruder  5. water-ring granulator  6. centrifugal dewatering  7. vibrating sieve  8. silo

Features of SBS / SEBS Blending Line

1. Longer L/D design. L/D 48: 1 ~ 52: 1 provides a longer residence time, which is benefits the completion of the resin and elastomer melting, homogenization and mixing process of the filling oil and the polymer.

2. High precision screw and barrel design. The gap between the screw and the barrel is small, the dimensional accuracy is high, and the screw structure is optimized to effectively complete the mixing process of resin melting, filler dispersion and homogenization of filling oil.

3. The pelletizing method is selected according to the characteristics of the melt. With different raw material ratios in the formula, the melt characteristics vary greatly. High hardness uses water ring pelletizing. Materials easy to stick with low viscosity uses underwater pelletizing.

TPU is named as thermoplastic polyurethane elastomer rubber, which is formed by the reaction and polymerization of diisocyanate molecules, macromolecular polyols and low-molecular polyols. It has thermoplasticity. It is a kind of polymer materials between rubber and plastics.

TPU material has gradually developed into an important part of many industries. It is an ideal material to replace PVC (polyvinyl chloride) to meet environmental protection requirements in many fields. It is called a new environmentally friendly polymer material internationally. Its main end markets cover the fields of building materials decoration, auto parts, clothing and shoe materials, cables and wires, medicine and health, pipelines and pipes, and aerospace etc. At present, the design of the twin screw TPU granulation line in my country generally adopts a flat streamlined design scheme. The advantages of this scheme are simple design, convenient construction, concentrated production equipment, and low plant investment.

1.      TPU reaction process

TPU is a polymer compound produced by the co-polymerization of cyanate resin and polyol. TPU is a block copolymer consisting of alternating sequences of hard and soft segments or domains formed by the reaction of (1) diisocyanates with short-chain diols (so-called chain extenders) and (2) diisocyanates with long-chain diols.

1.1   Production materials

1.1.1      Polyol polymer

There are two major types of polyol polymers used in TPU production line: polyester polyols and polyether polyols. Common polyester polyols include polyethylene adipate, polybutylene adipate, polyethylene dipropylene glycol adipate, etc. Polyether polyols include polypropylene oxide glycol and polytetrahydrofuran glycol. The main indicators for evaluating its quality are: hydroxyl value, acid value, viscosity, moisture, molecular weight distribution range, degree of unsaturation, etc.

1.1.2  Isocyanates

The isocyanate commonly used in the production of TPU extruder is diphenylmethane diisocyanate (MDI), the molecular formula is C₁₅H₁₀N₂O₂, and the relative molecular weight is 250. It is an aromatic compound. Pure MDI is a white or slightly yellow solid at room temperature. Sometimes it has an irritating odor, which is less irritating to the respiratory organs. Melting point ≥ 38 ℃. Boiling point: 194 ~ 199 ℃. Density: 1.19.

1.1.3 Chain extender

The chain extenders are mainly low-molecular diols and small-molecular diamines, with a molecular weight of 80-350. It mainly has 1, 4-butanediol (BDO), 1, 4-cyclohexane dimethanol, 1, 4 bis 2-hydroxyethoxy benzene and so on. Among them, I, 4-butanediol is commonly used. Molecular formula: C₄H₁₀O₂. Relative molecular weight: 90.12. It belongs to fatty open-chain diol, which is a colorless and thick oily liquid, easily absorbs water, can be miscible with water. Density: 1.02. Melting point: 20.2 ℃. Boiling point: 229.5 ℃.

1.2   The ratio of raw materials

Taking polyester polyol as 1 mol, the isocyanate (MDI) is about 2 to 8 mol, and the chain extender (BDO) is 1 to 7 mol. The isocyanate index R = (NCO/OH )=0.97-1.03. When R ≤1.0, it is a fully thermoplastic TPU. The polymer molecule is a terminal hydroxyl group, a completely linear structure, and it is easily soluble in organic solvents. When R is slightly greater than 1, and less than 1.1, it is semi-thermoplastic TPU, which is used to produce various products.

1.3   Introduction to TPU production process

Heat and melt the polymer polyester polyol and add it to tank A. After heating to 100~120℃, vacuum dehydrate under low-speed stirring for 2~3 h to make the water content<0.05%, release the vacuum and pass nitrogen for protection before use.

Melt the isocyanate and add it to the B tank, heat it to 60~70℃, and dehydrate it under low-speed stirring under vacuum for 0.5~1h, release the vacuum and pass nitrogen protection for use.

Add the chain extender to the C tank, heat it to 80~90 ℃, and dehydrate it in vacuum for 0.5~1h under low-speed stirring. After the water content reaches the required level, release the vacuum and pass nitrogen for protection.

The three raw materials are mixed by the TPU casting machine, and then enter the twin screw compounding extruder at about 100℃. After reacting for a certain period of time in different segmented strength zones (120~220℃), the melted strands are extruded from the die and pulled down by water cooling, then pelletized, classified via vibrator, dried and other operations are finished after passing the inspection.

2.      Brief introduction of TPU granulation line

The process equipment for producing TPU by twin screw extruder machine generally includes the following parts, and the names and functions of each part are as follows:

2.1   Raw material storage system

Keep the raw material polyol, isocyanate, chain extender at a certain temperature, dehydrate, stir and mix the catalyst.

2.2   Metering and pouring system (pouring machine)

Control raw materials to the best response degree, accurately adjust the ratio of raw materials according to production formula, and feed by metering.

2.3   Double screw reaction extruder

The main reactive extrusion for TPU production. The raw materials undergo polymerization under a certain intensity and pressure to produce TPU products.

2.4   Underwater pelletizer

Water cooling and product pelletizing are performed on the TPU product produced by the reaction of the twin screw extruder.

2.5   Screening machine

Classify and screen TPU product particles.

2.6   Drying and removal system

Remove the moisture in the TPU product to achieve the corresponding dryness required by different specifications of products.

2.7   Automated packaging system

Product packaging.

The TPU granulation production line is shown as follows:

Thermoplastic Vulcanizate is abbreviated as TPV. TPV extrusion is called dynamic vulcanization process in the industry. The current composition is PP, EPDM, filler, filling oil, crosslinking agent and processing additives. The so-called dynamic vulcanization means that the vulcanization (crosslinking) of the rubber and the melt dispersion are simultaneously performed, and the vulcanized rubber phase uniformly disperses the continuous phase of the resin to form rubber particles having a particle size of 1 to 2 μm under severe shearing action. TPV products are mainly used in various types of seals, soles, various pipe fittings, wire and cable, etc.

Equipment Characteristics:

1. Adopt high speed and high torque twin screw extruder. The high torque can withstand higher loads and adapt to the high melt strength of the vulcanized rubber. The high screw speed provides a higher shear rate, disperses the vulcanized rubber into small-sized rubber particles and uniformly disperses in the resin.

2. Long L/D screw barrel and multi-way dosing feeding. Long L/D 48:1~52:1 provides longer residence time, which is beneficial to complete complex mixing process of melt homogenization, vulcanization and dispersion. At the same time, it is equipped with multiple sets of dosing feeders to feed the resin, rubber, filler, filling oil and the crosslinking agent into the barrel step by step.

3. High precision screw and barrel design. The screw and barrel have small gap and high dimensional accuracy, and the screw structure is optimized to effectively complete the homogenization process of resin melting and filling oil, and complete the dynamic vulcanization process by shearing and dispersing elements.

4. The pelletizing method is selected according to the melt characteristics. Different raw materials and ratios in the formulation have large differences in melt characteristics. The higher hardness products can select water cooling strand pelletizer, and the low-viscosity and easy-adhesive products can adopt under water pelletizer.

The above description is a one-step dynamic vulcanization process, which is suitable for products with stable formulation ratios. In actual production, due to different product performance requirements, the proportion of each component in the formulation varies greatly, and the proportion and degree of vulcanized rubber are also quite different. The two-steps dynamic vulcanization process will have stronger applicability. That is, two sets of twin screw extruder production lines:

1.The first twin screw extruder is to uniformly mix PP, EPDM, filler and a small amount of filling oil and then pelletizing.

2.The second twin screw plastic extruder is for compounding the polymer, most of the filling oil and crosslinking agent to complete the crosslinking of the EPDM and uniformly disperse it.