Processing of TROGAMID compounds

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1 Processing of TROGAMID compounds TROGAMID compounds are processed mainly in the form of granules. For processing we recommend that you follow the information in this flyer. Evonik offers extensive technical service that is dedicated to finding technically sophisticated system solutions together with our customers. This includes support with simulation calculations for developing tools and molds. Drying TROGAMID compounds are supplied in moisture-proof packaging predried to a water content less than 0.1 %. Further drying is not imperative if the packaging is not damaged. Before the packaging is opened, its contents should be allowed to reach ambient temperature, in order to avoid moisture condensing on the cold granules. Under certain conditions if, for example, the retention time in the feed hopper is exceedingly high or the material for processing is from packages that have already been opened the granules should be pre-dried in a dry-air dryer at a temperature of C over a period of 8 to 12 hours. Drying cabinets with a fresh air supply are not suitable. In certain cases, such as the extrusion of thickwalled profiles, and injection molding of thickwalled and optical components or of components of high surface quality, the granules should be pre-dried at any rate to prevent moisture streaks or uneven surfaces from forming. Incompatibility with other thermoplastics TROGAMID compounds are not compatible with most other plastics. Even small quantities of other plastics contaminating TROGAMID resins lead to clouding of the melt and the finished parts. Before work is started, therefore, the plastification units of the processing machine and all other melt channels should be very carefully cleaned with the usual cleaning agents or with prepared TROGAMID sprue or start-up waste. Use of regrind Due to the hygroscopic properties immediate reprocessing of TROGAMID scrap is recommended. The regrind material must be free from foreign matter and dirt particles, the moisture content should be below 0.1 wt.-%. Small quantities of other polymers, even other polyamides except of the same TROGAMID grade will cause clouding of the corresponding molded parts. If an immediate reprocessing of the scrap is not possible, sprues or defective parts should be grinded and stored in moisture-proof bags straightaway. A careful drying before reuse is necessary. 1

2 The quantity of regrind added to virgin material is generally dependent on the required part properties and must therefore be determined by tests on the ready molded part. If the use of regrind is allowed by the requirements and specifications of the enduser, additions of up to 25 wt.-% regrind are possible. Coloring of TROGAMID TROGAMID is best colored with color concentrates based on identical TROGAMID resins. Dry coloring by tumbling with finely powdered pigments is another possibility but it is inconvenient, as pneumatic conveying is impossible. The use of color pastes or color concentrates having a "neutral" (e.g. PE) base can lead to incompatibility with TROGAMID and hence to poor part properties (poor weld line strength or low transparency due to clouding). Therefore, prior testing of compatibility is absolutely necessary. Viscosity number, thermal stability, flowability TROGAMID T compounds but not TROGAMID CX, mycx oder Care compounds - have a wide processing window due to their amorphous structure and high level of thermal stability. Generally, any changes in flow resistance in the mold can therefore be adjusted by appropriate temperature settings. Nevertheless, compounds with internal flow promoter are also available. In terms of quality control and to verify your processing conditions we recommend determining the viscosity number acc. to ISO 307 of any molded part. The viscosity number is related to the molecular weight of a polymer and allows therefore to draw conclusions of the impact of processing and the mechanical properties of a molded part indirectly. Owing to the high level of melt viscosity TROGAMID shear stress should be kept as low as possible. High screw speeds or mixing and shear elements with a wrong layout affect the viscosity number of molded parts adversely. Furthermore moisture (>0.1 % by weight) or processing temperatures exceeding 310 C are disadvantageous for the viscosity number too. Internal stress, chemical resistance The inherent good chemical resistance of molded parts made out of TROGAMID can be reduced through the so-called internal stress. To a greater or lesser extent, internal stress is always build-up during the processing of articles 2 through the cooling and shrinkage of the polymer melt, even when the mold temperature is controlled carefully. Furthermore, a process called displacement of cold fronts causes internal stress as well. Because of its low tendency to creep a property highly regarded for engineering plastics TROGAMID belongs to the group of polymers with a low ability to relax, which is why the internal stress level caused by processing or part geometry is maintained. Such stresses that are frozen into the material, if combined with functional stresses (pressure, impact, etc.), can cause weak spots that crack on contact with aggressive media (stress corrosion cracking). It is noted here that the good chemical resistance of the TROGAMID T series has been further enhanced in the more recently developed TROGAMID CX. Some of the factors influencing the internal stresses caused by processing are listed below. Mold temperature Recommended mold temperature of TROGAMID is in the range of 60 C - 80 C. The mold temperature should be adjusted to the later operating temperature. If the operating temperature is higher than the mold temperature the internal stress will be released by warpage of the molded part later on. Temperature differences at the surface of the molded parts should be avoided. Melt temperature The optimal melt temperature of TROGAMID is between 280 C to 310 C. Short injection molding cycles and a short dwell time allow even higher temperatures, but then the thermal stability of any additives or colorants have to be considered as well as the inherent color of the molded part. Holding pressure After filling the mold cavity, the holding pressure compensates for the volume contraction of the polymer melt. The time, in which additional polymer melt can flow into the cavity, is directly proportional to the level of holding pressure, the sealing of the gate and the wall thickness. Molding temperature and melt temperature have a negligible influence. After optimising the part geometry and the gate the holding pressure should be chosen just high enough to avoid sink marks. Part geometry and gate Big changes of wall thickness, rips on one side only, and/or sharp edges should be avoided in

3 the course of part s design. Generally, symmetrically designed molding articles show less warpage than asymmetric parts. A direct feed is preferred to pinpoint gating. Stress relaxation / annealing By annealing molded parts the internal stress level can be reduced significantly and therefore the chemical resistance increases. The influence of annealing is naturally strongly depending on time, temperature and part geometry. Usually the internal stress level of a molded part decreases during storage. This effect is of course depending on time and temperature also. Stress peaks at sharp edges or in transition zones are not compensated completely, only their level is lowered. By after-shrinkage additional stress can arise in notched regions (for example, screw threads under tensile stress load). Processing of TROGAMID compounds Generally, the working areas of all thermoplastics processing should be well ventilated especially during the production. It is recommended that an exhaust system should be located over the machine nozzles. Under the circumstances of unfavorable conditions, for example given in the processing of excessively elevated temperatures, or during cleaning of the screws by burning off remaining polymer residues, it is possible that small amounts of noxious fumes would be produced. Therefore, the cleaning of screws by burning off should always be done under an exhaust hood. Further details are notable from the relevant safety data sheet. Injection molding Plasticizing unit Screw and cylinder Three zone screw with a length between 18 and 22 D Depth flight ratio shall be > 2 Minimum flight depth: 2 mm in the metering zone, and 4 mm in the feeding zone Screw and barrel diameter should be in the magnitude that a metering stroke between 1 D and 3 D is realizable For more information see Figure Three-zonescrew Design of a three-zone screw Typical figures for injection molding of TROGAMID Nozzle In general free-flow nozzles should be used. If shut-off nozzles are applied, keep friction as low as possible. Bore of nozzle larger than 4 mm. Back flow valve Clearance between back flow valve and cylinder shall be 0.02 mm Cleaning Light contamination (e.g. cleaning due to changing of resin) 1) Provide a high viscosity PP. 2) Increase the temperature settings of heating zones by 30 to 40 K but not above 310 C. 3) Plasticate PP with a long metering stroke and high dynamic pressure and discharge at high speed ("air shot"). 4) Flush the plasticating unit with the new resin until no purging mixture is contained in the melt. Persistent contamination Persistent contamination can be mostly removed only by mechanical cleaning of screw, cylinder, back-flow valve etc. Sometimes a cleaning of the cylinder can be avoided by using special purging material. Clamping Unit Clamping force Guideline number for maximum cavity pressure with TROGAMID resins is bar. Mold Gate All common types of sprues, runners and gates possible. Diameter or thickness of pin, submarine and film gates depending on viscosity of resin between 1 and 2 mm 3

4 Hot runner Externally heated hot runners with open sprue nozzle recommended, nozzle diameter 1 mm Venting Venting slots in mold parting surface: 0.03 to 0.05 mm deep, 4 to 5 mm wide Cooling In case of processing TROGAMID CX, mycx und Care resins consider intensive cooling of the mold to avoid forming of clouding of parts with a wall thickness of more than 8 mm. Steel Suitable steels are (X45NiCrMo4), (X155CrVMo121), (40CrMnMo58), and (X38CrMo V51). Pressure sensor Use of a pressure sensor for the cavity pressure is recommended to facilitate the carefully setting of change-over point. Demolding Mold release agent normally is not necessary. Some resins are available containing a demolding agent. More information can be obtained from the TROGAMID brochures or please contact us. Decrease of mold temperature very often eases demolding. Suitable coatings of mold surface are Ni-P- PTFE, and TiAlOx. Processing conditions Temperatures Refer to the following table for general settings on melt temperatures Decreasing temperature profile in the heating zones towards hopper in steps of 10 K is recommended. If the melt temperature exceeds 310 C the ready molded part should be checked for degradation, e.g. by determining its viscosity number. Note: Controlling of the melt color is not sufficient to determine possible degradation. Cooling of feeding zone should be C. Peripheral screw speed In the range of 3-12 m/min optimum, 10 m/min preferred Higher speeds (i.d. > 18 m/min) can be applied, but might lead to problems in processing. Decompression After the metering is completed, a decompression could negatively affect the surface of the parts and hence should be not applied. Pressures Dynamic pressure: bar Injection pressure: bar Pressure in holding phase: up to 1400 bar Shrinkage of various TROGAMID compounds TROGAMID Shrinkage acc. to ISO in flow in transverse direction [%] direction [%) T T-GF CX

5 Interruption of production For short production breaks (e.g. up to 1 hour): discharge of the plasticizing unit, moving of screw to ultimate front position and decreasing temperature setting at heating zones down to 150 C. For long production breaks: flushing of the plasticizing unit with high viscous PP or PMMA, discharge of the plasticizing unit, moving of screw in ultimate front position, switch off of cylinder heating. Remove resin left in the hopper and store in moisture proof packaging. General temperature settings for injection molding TROGAMID TROGAMID Lower temperature limit [ C] Upper temperature limit [ C] Melt temperature [ C] Mold temperature [ C] T grades CX grades Extrusion General information Srew and extruder design Conventional three zone screw with a length 24 D Flight depth ratio ranging from 2.5 to 3.5 : 1 Suitable ratios between feeding / compression / metering zone: 2:1:3, 2:2:2, 1:1:1 Radial clearance between screw and barrel: mm Mixing and shear elements may be useful to increase the melt homogeneity (e.g. processing resins colored with pigment concentrates). For more information see Figure Three-zonescrew Note: Other screw designs (e.g. barrier screws) may lead to proper processing conditions as well. Design of a three-zone-screw Breaker plate Not necessary for the processing of virgin material, recommended only as support for screen packs, e.g., when processing regrind Mold and calibration Coated or very highly polished mold and calibration surfaces for tube or profile production reduce striation and lead to smooth and even extrudate surfaces. Temperature setting Cooling of the feeding section is mostly required. Melt temperature in the range of C with decreasing temperature profile from hopper to die. The general temperature setting is very much dependent on the resin and type of extrudate (film, profile, tube) to be processed. Thus, a general recommendation cannot be given. Optimising temperature setting by monitoring the temperatures of the heating zones, the melt temperature and the consistency of the melt leaving the die: high pressure build-up and a dull surface of the melt leaving the die: increase temperature profile melt with a low stability: decrease temperature profile In case of large discrepancies between temperature setting and measured temperature the screw design might not be suitable for processing TROGAMID. 5

6 Cleaning 1) Raise temperature of all heater bands for about 20 C and purge by using polypropylene (PP with MFI 230/5 kg 12 g/10 min) 2) Disassemble die, remove plastic residues and polish. 3) Continue to purge extruder with PP and reduce temperature to about 170 C 4) At this temperature replace PP by a purging mixture comprising heat stabilised PVC/ cleaning fluid/glass fibres (ratio 98:1:1). If the PVC grade is not sufficiently heat stabilized, degradation may easily occur. 5) Pull out screw and remove plastic residues from screw and barrel Trouble shooting Pulsation of melt caused by the extruder Insufficient cooling of feeding section Insufficient lubrication of pellets Shape of pellets inhomogeneous (e.g., when processing regrind) Pressure build-up at die too low Improper design of feeding section (grooved/smooth) Improper screw design - Variation of die temperature due to improper setting of control parameters for die heater band Problems with motor/gear box Note: Pulsation of melt can be caused by the downstream equipment as well. Inconsistencies in temperature measurement Dirt in bore of thermocouple Tip of thermocouple not in contact with metal surface Problems with thermocouple and/or recording device (e.g. thermocouple damaged) Fabricating and finishing of molded parts and semi-finished products Bonding Adherent surfaces should be kept clean. Avoid use of mold release agents when manufacturing parts to be bonded. Adhesives Commercially available adhesives based on Polyurethanes: One- or two-pack and (reactive) hot melt adhesives (gap filling, flexible adhesives mostly with longer pot life and clamping time) suitable for larger adherent surfaces. Cyanoacrylates: One-pack adhesives (short setting time) suitable for small gluelines and adherent surfaces Formic acid: Diffusion bonding at room or elevated temperature 6 Epoxies: One- or two pack adhesives (gap filling), better results at elevated temperatures Pretreatment Improvement of bonding strength by a pretreatment of the surface to be bonded, e.g. by use of primers, roughening, electrical discharge, chemical treatment or flame treatment. Follow safety instructions at all times especially when using primers and chemical treatment. Machining Sawing, turning, milling, drilling, and planing of TROGAMID parts is possible. We recommend to cool by fluids or compressed air to reduce heating up of the parts and hence to avoid problems with sticking. Printing and painting Laser marking Laser-markable TROGAMID compounds are available. Inks and paints For sublimation colors most types of inks are possible. Screen printing colors must be modified for application on TROGAMID parts. Pre- and post-treatment Surface treatment, e.g., by electrical discharge, flame treatment or bristling very often lead to an improvement of the adhesion of the ink. After printing the adhesion of the ink can be improved, e.g., by heating or flame treatment. Welding All established types of welding technologies can be applied on TROGAMID ; typical technologies used are: Hot plate welding: Apply PTFE coated hot plate welding tools to avoid/reduce sticking of the resin at temperatures up to 270 C. Ultrasonic welding: Joint design like a triangular projection (called an energy director) or like a shear joint. Friction welding by rotation (spin welding) or vibration High frequency welding

7 Processing of TROGAMID TCR film TROGAMID TCR films have been developed specifically for the film lamination technique. The excellent chemical resistance requires the use of special printing inks. The films can be excellently formed even to high forming depths. Mold surface structures are very accurately reproduced. Preparation It is recommended that the film will be climatized under the conditions of the subsequent printing process so as to prevent changes in length. The surface can be printed directly with the recommended inks and needs no further pretreatment. Printing and forming NoriAmid screen printing inks from Pröll KG are particularly suitable for printing. These inks have been specially designed for the film lamination technique with TROGAMID TCR films. The film thermoforms very well using standard technology. Especially, the high pressure forming process developed by equipment manufacturer Niebling yields very good results. Detailed information on the printing process and on forming is available in the provisional technical communication 9/2010 from Pröll. In-mold lamination by injection TROGAMID TCR films can be in-mold laminated by injection with the usual injection molding compounds if appropriate adhesion promoters are used. Particularly low-stress components can be produced by combining TROGAMID TCR films with TROGAMID CX molding compounds. We recommend the optical grade TROGAMID mycx for overmolding. 7

8 Contacts Dr. Karl Kuhmann Jochen Fritz (Injection molding) Rainer Göring (Extrusion) = registered trademark September 2011 This information and all technical and other advice are based on Evonik s present knowledge and experience. However, Evonik assumes no liability for such information or advice, including the extent to which such information or advice may relate to third party intellectual property rights. Evonik reserves the right to make any changes to information or advice at any time, without prior or subsequent notice. Evonik disclaims all representations and warranties, whether express or implied, and shall have no liability for, merchantability of the product or its fitness for a particular purpose (even if Evonik is aware of such purpose), or otherwise. Evonik shall not be responsible for consequential, indirect or incidental damages (including loss of profits) of any kind. It is the customer s sole responsibility to arrange for inspection and testing of all products by qualified experts. Reference to trade names used by other companies is neither a recommenddation nor an endorsement of the corresponding product, and does not imply that similar products could not be used. Evonik Industries AG High Performance Polymers Marl Germany 8 PHONE evonik-hp@evonik.com