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Processing of TPU by Extrusion and Special Processes Contents Processing of TPU by Extrusion and Special Processes Contents 1. Product description . .4 2. General remarks. 6 2.1 Form supplied. 6 2.2 Storage. .6 2.3 Pretreatment of the granules. 6 2.4 Post-treatment of the finished articles . .8 2.5 Coloring. .8 2.5.1 Color masterbatches. 8 2.5.2 Color pastes, liquid colors and pigments. 9 2.6 Additives . .9 2.7 Occupational hygiene and environmental information . .9 2.7.1 Air extraction . .9 2.7.2 Waste disposal. 9 2.7.3 Energy efficiency . 9 3. Processing by extrusion. 10 3.1 General . .10 3.2 Screw design . .12 3.3 Processing parameters. 14 3.3.1 Temperature setting for the barrel and die . 14 3.3.2 Screw speed . .14 3.4 Adapters and extrusion dies . .15 3.4.1 Adapters . 15 3.4.2 Melt pump. 15 3.4.3 Extrusion dies. 16 3.5 Cooling and calibrating the extrudate . .18 3.6 Extruded articles. 19 3.6.1 Tubing. .19 3.6.2 Sheathing of electric cables, ropes and connecting hoses. 20 3.6.3 Profiles . .21 3.6.4 Flat film . 21 3.6.5 Blown film . .21 3.6.6 Extrusion coating . .22 3.6.7 Coextrusion. 22 3.6.8 Extrusion blow molding . .23 2 4. Special processes . .24 4.1 Calendering . .24 4.2 Powder coating. 24 4.3 Slush molding. 25 5. Machining and fabrication. 26 5.1 Bonding. .26 5.2 Bonding to metals . 26 5.3 Printing . .26 5.3.1 Hot embossing / Hot stamping . .26 5.3.2 Ink jet printing. 26 5.3.3 Pad printing . 26 5.3.4 Laser printing. 26 5.4 Coating . .26 5.5 Metallizing . .26 5.6 Welding. .27 5.6.1 Hot air and nitrogen welding . .27 5.6.2 Hot plate welding. 27 5.6.3 Heated tool and heat impulse welding. 27 5.6.4 High-frequency welding . 27 5.6.5 Friction welding. 27 5.6.6 Vibration welding. 28 5.6.7 Ultrasonic welding. 28 5.7 Machining . .28 5.7.1 Sawing . .29 5.7.2 Drilling. .29 5.7.3 Turning . .29 5.7.4 Milling and planing. 29 5.7.5 Punching. 29 5.7.6 Thread cutting . .29 5.7.7 Grinding. 29 6. Index . 30 3 1. Product description Covestro’s TPU ... Covestro’s TPU, are thermoplastic polyure- the link between rubber and plastic thanes. Their properties qualify them as high-grade thermo- Elasticity modules plastic elastomers (TPEs) that 100 101 102 103 104 MPa bridge the gap between rubber and traditional thermoplastic 70A 75D Shore hardness materials. Rubber PC Covestro’s TPU POM Polyamide 6 and 66 PA-GF; PC-GF ABS 4 Product description The main advantages • High abrasion resistance • Good resistance to weathering • High elasticity over the entire and high-energy radiation hardness range • Pleasant tactile properties • Excellent low-temperature • Weldable and bondable impact strength • Easy coloring • Flexibility over a wide • Easy recycling temp erature range • Excellent rot resistance • Freedom from plasticizers (special grades) • Excellent resistance to oils, greases and many solvents 5 2. General remarks Covestro’s TPU can be processed on the 2.2 Storage equipment normally used for processing Covestro’s TPU should be stored in cool, dry thermoplastics. The most important pro- conditions. Temperatures above 40°C should cessing techniques are: be avoided. Optimum processing is ensured within approximately 6 months after delivery. Injection molding Extrusion Blow molding 2.3 Pretreatment of the granules TPU absorbs moisture from the air. The extent and rate at which this happens depends on the 2.1 Form supplied raw mate rial type, hardness and climate (Figs. 1 and 2). Covestro’s TPU are supplied as natural-colored cylindrical or lentil-shaped granules. Depend- ing on the particular grade, the color ranges from transparent / clear and whitish opaque to white. Moisture absorption of Covestro‘s TPU granules (at 23°C/50% r. h.) The product can be supplied in quantities of between 20kg and 1,000kg, depending on 0.6 the grade. For sampling purposes, 20kg or Ether-based 25kg sacks or plastic drums with a content of % 20kg can be supplied. 0.4 Ester-based 0.3 0.2 Moisture content 0.1 0 0 1 2 3 4 5 Days 7 Storage period 0.10 Fig. 1 % Ether-based TPU Ester-based TPU 0.06 Threshold value for optimum processing 0.05 0.04 0.02 Moisture content 0 0 2 4 6 8 10 12 min 16 Storage period Fig. 2 6 General remarks To ensure trouble-free processing and avoid Operation of a dry-air drier any loss of quality, we recommend drying to a moisture content of ≤ 0.05%. If the granules are too moist, blisters or streaks can occur on the surface of the finished com- ponents. The extrudate is no longer smooth and glossy but foamy and gassy. A frequent cause of defects is also the use of undried functional concentrates. These batch- es should be separately pre-dried and have a moisture content of ≤ 0.05%. Such levels can be reliably reached in conventional dry-air and circulating air dryers (Fig. 3). A = Dry air B = Return air Depending on the hardness, the recommend- C = Fresh air ed drying temperatures are between 80 and D = Waste air 110°C, with drying times of 1 to 3 hours. Better drying can be achieved in a shorter time with Fig. 3 dry-air dryers (Fig. 4). Dried, hot granules should not be left to cool down in the open air. They must be stored in dry containers that can be re-sealed. The machine hopper must be kept covered. Drying kinetics for Covestro‘s TPU granules 0.20 % 0.16 Circulating air 110°C 0.14 Dry air 110°C Threshold value for 0.12 optimum processing 0.10 0.08 0.06 Moisture content 0.05 0.04 0.02 0 0 15 30 45 60 75 90 105 120 min 150 Drying time Fig. 4 7 2. General remarks 2.4 Post-treatment of the Standard commercial equipment can be used to add the colorants and mix them in with the finished articles Covestro’s TPU. For occasional coloring, use TPU products attain their optimum physical rolling-drum mixers, tumble mixers or similar. It property level only after they have spent some is important to ensure that the colorants and time at room temperature. This process can be other additives do not contain any moisture. A speeded up by an annealing process in a circu- static mixer in the adapter will significantly im- lating air heating oven, reducing it to 15 to 20 prove color dispersion and also reduce the hours. amount of colorant needed. For articles with a hardness of ≤ 92 Shore A, 2.5.1 Color masterbatches we recommend annealing at 80-90°C, and for Color masterbatches provide the simplest, a hardness of ≥ 93 Shore A, 100-110°C. The cleanest and most reliable means of coloring optimum compression set can only be Covestro’s TPU, particularly when Covestro’s TPU achieved by annealing! are also the carrier materials. SAN-resin-based color granules are also suitable to a limited The physical data given in our data sheets are extent. Color granules based on polyolefins always measured on annealed, conditioned and PVC are not suitable. Suppliers normally test specimens. recommend employing metering quantities of between 1.0 and 4.0% depending on the wall 2.5 Coloring thickness of the articles and the color density Covestro’s TPU are supplied in their natural of the pigments. color and can easily be pigmented, most com- monly using color granules (masterbatches), but also using coloring pastes, liquid colors or pure pigments. 8 General remarks 2.5.2 Color pastes, liquid colors and 2.7.2 Waste disposal pigments Provided that they are not contaminated with It is less common to use color pastes, liquid other substances, Covestro’s TPU can essen- colors and pigments to color Covestro’s TPU tially be disposed of in municipal landfill sites. because of the more complicated procedure involved. However, there may be bene fits in the They do not constitute a hazard to water. If the form of fast color changes and transparent materials can no longer be recycled, they pigmentation. The standard quantities general- should be incinerated in a waste incineration ly range from 0.2 to 1.0%. plant on account of their high calorific value. 2.6 Additives 2.7.3 Energy efficiency Thermoplastic polyurethanes are demanding To improve the processing characteristics high-performance materials that can reach or specific properties, we recommend the their full potential only by a precise and opti- addition of conventional functional concen- mum processing. trates such as: • antiblocking agents, All process steps in the extrusion of TPU • release aids, and (pre-drying, extrusion, post-treatment such • UV stabilizers, as calibration, cooling, etc.) are associated with which must also be pre-dried. a high consumption of energy. Following the recommended processing parameters is very 2.7 Occupational hygiene and important. The energy efficiency of the pro- cessing equipment is of great importance for environmental information economic and environmentally friendly pro- cessing. 2.7.1 Air extraction Covestro’s TPU can be machined and pro- Therefore, we recommend paying attention cessed over a wide temperature range but, as to modern, precise controlling and energy- with all natural and synthetic organic materials, efficient machinery. they decompose above a certain temperature. Smoke generation signifies that decomposition is taking place. Slow decomposition commences at approximately 240°C, depending on the grade of Covestro’s TPU involved.
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