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TPR and TPE are the same system Definition of thermoplastic elastomer (TPE) Thermoplastic elastomer (short: TPE) refers to polymer materials that have the properties of vulcanized rubber at room temperature (that is, the properties of elastomers) and can be plasticized and deformed at high temperatures. It can use plastic processing machines such as injection molding, extrusion molding, blow molding, calendering, T-Die casting molding and other faster processing methods than traditional vulcanized rubber to manufacture finished products, and has the advantages of light weight (low density), environmental protection (recyclable, non-toxic combustion), long service life (can be more than 5~10 times more than traditional rubber), large degree of processing change, low total cost of products and so on. In various industries, it is gradually widely used. TPEs are sometimes referred to as thermoplastic rubber (TPR), but by definition, it is more appropriate to call them TPEs. TPEs are elastomers that have the properties of vulcanized rubber, but do not require vulcanization.
Advantages of TPEs
The biggest feature of TPE is that it has a multi-phase structure, and its soft and hard segments produce high elasticity and cross-linking points respectively, so it is used to process rubber products with the following advantages:
(1) It can be processed by general thermoplastic molding machines, such as injection molding, extrusion molding, blow molding, compression molding, forward molding, etc.; (2) It can be vulcanized with rubber injection molding machine, and the time can be shortened from about 20min to less than 1min; (3) It can be formed and vulcanized by press-out machine, with fast speed and short vulcanization time; (4) The waste generated in the production process (escaping burrs, extruded waste glue) and the final waste products can be directly returned for reuse; (5) Used TPE products can be simply recycled and reused, reducing environmental pollution and expanding the source of resource regeneration; (6) No need for vulcanization, taking the production energy consumption of high-pressure hoses as an example: rubber is 188MJ/kg, TPE is 144MJ/kg, which can save more than 25%; (7) The self-reinforcement is large, and the formula is greatly simplified, so that the influence of the compound on the polymer is greatly reduced, and the quality performance is easier to grasp. Thermoplastic rubber breaks through the traditional process of rubber processing, opens up new ways for the rubber industry, and expands the application field of rubber products. Notable examples are hollow molding, injection molding and extrusion.
Classification of TPEs
Type Structure Composition Method Purpose Hard segment Soft segment ----------------------------------------------------------------- Styrene TPE (TPS) SBS Polystyrene (PS) BR Chemical Polymerization Universal SIS polystyrene (PS) IR chemical polymerization is universal SEBS Polystyrene (PS) Hydrogenated BR Chemical Polymerization General, Engineering SEPS Polystyrene (PS) Hydrogenated IR Chemical Polymerization General, Engineering ------------------------------------------------------------------- Olefin-like TPEs TPO polypropylene (PP) EPDM mechanical blending is universal TPV-PP/EPDM polypropylene (PP) EPDM+ vulcanizing agent mechanical blending universal TPV-PP/NBR Polypropylene (PP) NBR+ Vulcanizing Agent Mechanical Blending Universal Purpose TPV-PP/NR Polypropylene (PP) NR+ Vulcanizing Agent Mechanical Blending Universal Purpose TPV-PP/IIR Polypropylene (PP) IIR+ Vulcanizing Agent Mechanical Blending Universal Purpose ------------------------------------------------------------------- Diene TPEs TPB(1,2-IR) poly1,2-butadiene chemical polymerization universal TPI (trans-1,4-IR) Polytrans-1,4-isoprene Chemical polymerization General T-NR (trans-1,4-NR) Polytrans-1,4-isoprene Natural polymer Universal TP-NR (modified cis-1,4-NR) polycis 1,4 isoprene modification grafted polymerization universal ------------------------------------------------------------------- Vinyl chloride TPE TPVC (HPVC) crystalline polyvinyl chloride (PVC) amorphous PVC polymerization or blending is universal TPVC (PVC, NBR) polyvinyl chloride (PVC) NBR mechanical blending universal TCPE crystalline chlorinated polyethylene (CPE) amorphous CPE polymerization or blending universal ------------------------------------------------------------------- Aminoester TPE (TPU) Aminoester structure Polyester or polyester Polyaddition General, engineering ------------------------------------------------------------------- Ester TPE (TPEE) ester structure polyether or polyester polycondensation engineering -------------------------------------------------------------------- Amide TPE (TPAE) amide structure polyether or polyester polycondensation engineering -------------------------------------------------------------------- Organofluorine TPE (TPF) Fluororesin F Rubber Chemical polymerization General, engineering --------------------------------------------------------------------
Injection molding of TPE
Screw speed (rpm), back pressure and screw delay time
The speed of the screw should be set so that the screw can be fully retracted in time, usually 2-3 seconds before the mold is opened, so that the next injection can be made. Typical screw speeds range from 50 to 150 revolutions per minute.
If the screw retracts too quickly and the machine is equipped with a screw delay timer, the delay time should be set so that the delay time after the screw is fully retracted and the mold is opened is minimized. This will shorten the residence time of the material at this temperature and the rest time in the chamber.
Increasing the back pressure will increase the shear heating phenomenon of the material. The normal setting range for back pressure is 50- 150 psi. When mixing color masterbatches, a higher back pressure should be used to achieve optimal dispersion.
Injection speed
If possible, the injection speed control program should be set up in such a way that the runner system is filled rapidly and then reduced after the material has passed through the gate and started flowing into the mold cavity. This speed is maintained until 90% of the workpiece is filled, and then the speed is further reduced to completely fill the cavity without spillage of the workpiece. Injection and transition pressure
If the machine cannot be controlled by the filling speed, the injection pressure should be set so that it is sufficient to fill the runner system and mold cavity in about 1 to 5 seconds. The initial transition pressure is adjusted to approximately 50% of the injection pressure required to fill the workpiece cavity. This will help to reduce pressure during the filling and packing stages during injection molding to a minimum. When setting the injection volume, the buffer volume should be monitored to ensure that it is maintained during the filling and packing phases.
The transition from pressurization to filling to packing Newer molding equipment offers additional options for the transition from injection pressurization (the first stage of injection) to filling and packing. The most precise way to transition from the pressurization to the filling stage is to control it according to the position of the screw. Depending on the position of the screw, the processor can consistently inject a certain volume of material into the cavity. It also provides precise control of the filling and densification of the workpiece, helping to prevent the collapse and cavitation of the workpiece. Time is another way to control the transition, but it is not recommended. Using cavity pressure to control transitions is expensive because it involves installing a pressure sensor inside the workpiece cavity. This process is only used when high precision molding tolerances are required. Reducing the transition pressure from the boost pressure to the filling and packing stages will help control dripping at the top of the bushing. If the injection equipment has a pressure control program during the filling and packing stages, it can be used to reduce the speed and pressure to the runner.
Injection time
The optimal time to fill the runner system is about 0.5-1.5 seconds. It should take another 1-5 seconds to fill the cavity. If possible, it is best to control the filling time by controlling the injection speed. Holding time The holding time before the gate solidifies should be set. In general, the size of the gate is a decisive factor in the holding time. The larger the gate, the longer the holding time before the gate solidifies. Cooldown time The cooling time mainly depends on the melt temperature, the wall thickness of the workpiece and the cooling efficiency. In addition, the hardness of the material is also a factor. Compared to very soft varieties (Shore hardness < 20 A), harder varieties (Shore hardness > 50 A) will solidify faster in the mold. For a typical workpiece of a medium hardness SEBS composite, if cooled from both sides, the cooling time required per 0.100" wall thickness will be approximately 15 to 20 seconds. Overmolded workpieces will require longer cooling times as they can be cooled efficiently with a smaller surface area. The cooldown time required per 0.100" wall thickness will be approximately 35 to 40 seconds. |
Sep 20, 2023Leave a message
Advantages, classification and injection molding process of TPE
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