Vistamaxx™ Propylene-based Propylene-based Elastomers Processing Processing Guidelines for Meltblown Fabrics
Introduction Vistamaxx propylene-based elastomers are a amily o polyolen resins exhibiting a wide range o elastic properties along with the capability o processing on equipment designed or polypropylene. These specialty elastomers are produced rom ExxonMobil Chemical’s Chemical’s proprietary metallocene catalyst technology that allows them to be molecularly designed or specic end-use applications such as meltblown abrics. Meltblown products can be either monolithic webs or multilayer composite abrics. The elasticity o the bers can be tailored or specic applications by choosing the appropriate grade, processing conditions and optionally, an additive package.
Resin characteristics Vistamaxx propylene-based elastomers are ree-fowing pellets designed or use in conventional resin conveying systems. The elastomers are non-hygroscopic and, thereore, do not require require drying beore extrusion. Resins designed or meltblown applications typically have melt fow rates in excess o 20 MFR (230°C/2.16 kg). Vistamaxx propylene-based elastomers or meltblown systems have a very narrow molecular weight distribution and, thereore, are very easy to draw down and achieve
ne ber diameter. They are designed to process at relatively low melt temperatures and are capable o producing rom coarse to very ne bers. These specialty elastomers have a broad melting range, are chemically compatible with other polyolens and can be thermally bonded at relatively low temperatures to other polyolen substrates such as polypropylene and polyethylene.
Processing conditions/extruder Vistamaxx can be processed at similar conditions t o polypropylene resins. A temperature range o 230° to 290°C is typical, but the actual temperature is dependent on the grade selected and the properties desired. Vistamaxx has a slower rate rat e o crystallization compared to polypropylene. Consequently, an auxiliary quenching system has been ound benecial to accelerate ber crystallization ater t he ber has been attenuated. Typical systems used in the industry include an auxiliary quench air or a water mist located between the die ace and the orming belt. For a given resin grade, the web’s properties can be optimized by adjusting the melt temperature, output rate, primary airfow rate, die-to-collector distance, and auxiliary quenching rate. The elasticity o the abric is controlled partially by the molecular orientation o the bers. A highly oriented ber will have lower elongation and elasticity compared to a ber that is less oriented. For example, to produce a barrier abric with relatively good elasticity, a high MFR grade (300 MFR) processed at lower output rate, high process airfow rate and low DCD is recommended. For abric that does not require high barrier properties, a lower MFR grade (rom 200 MFR to 20/MFR) processed at a relatively lower process airfow rate is better because the ber will be less oriented and will have a higher elasticity. For example, or a grade having a 300 MFR: • Barrel temperature: 195° (zone 1), 220°, 240°, 240°C (and all down stream zones) • Adequate cooling at the extruder throat • Die temperature: 245°C • True melt temperature: 240° – 255°C • Process air temperature: 250°C
Meltblown die system Vistamaxx™ propylene-based elastomers can be processed in typical meltblown systems designed or polypropylene and having an extrusion system capable o delivering a homogeneous melt to the meltblown die over a wide range o output rates. In general, a long L/D single-screw extruder (e.g., 30:1 L/D) with a screw having mixing sections is recommended. The meltblown system can be a stand-alone meltblown line or part o a SMS (spunbond-meltblown-spunbond) system. The meltblown die system can be either a single- or multiple-row system. The die capillary size and air gap are very similar to those used or polypropylene. For example: • Die capillary hole density: 800 – 1200 holes/meter, (25 – 35 hole/inch) • Capillary hole diameter: 0.35 – 0.5 mm (0.014 – 0.020”) • Air gap: 0.8 – 1.2 mm • Set back: 0.8 – 1.2 mm
the ber ormation, Vistamaxx propylene-based elastomers crystallize slower than polypropylene bers and require additional quenching. The ber size and web ormation adjustments are very similar to that or polypropylene resin.
Web ormation/die-to-collector distance (DCD) The DCD has a strong impact on web uniormity. A short DCD produces a more uniorm web structure, better barrier properties and better aesthetics. However, a shorter DCD shortens the ber quenching distance and, thereore, web release rom the orming belt may be more dicult unless the bers are adequately quenched (e.g., auxiliary quenching, lower output rate). This is particularly signicant for low basis weight fabrics (e.g., 35 gsm). For monolithic meltblown web, 250 mm (10”) or greater is a good starting position. A higher DCD may be required to improve web release rom the orming belt, but web uniormity will be impacted due to a tendency or ber roping. To acilitate abric release, a slip additive should also be considered and can be added in-line with the Vistamaxx. The suction underneath the belt can also be lowered.
Spinneret/fber ormation The diameter o bers made with Vistamaxx is controlled by the melt viscosity at the die, the specic output rate (i.e., output per capillary, or gram/hole/min), and the process airfow rate and velocity. Output rates o 0.4 to 0.6 gram/hole/min are typical with lower output rates or ner bers and better barrier properties. Following
A shorter DCD, less than 250 mm, is recommended for producing composite abrics made rom Vistamaxx and polypropylene webs. A polypropylene web is placed on the orming belt rst (or o the line) and the Vistamaxx-based web is then ormed over the polypropylene web.
Meltblown bers emerging rom die and orming nonwoven web on moving orming belt Resin
Additives Melt Pump
Extruder Compressed Polymer Compressed Hot Air Hot Air
Filter
Meltblown Die System Meltblown Fibers
Meltblown Web
Detail of the Die Tip
Contact your ExxonMobil Chemical representative or more inormation.
exxonmobilchemical.com vistamaxxelastomers.com
©2010 Exxon Mobil Corporation. To the extent the user is entitled to disclose and distribute this document, the user may orward, distribute, and/or photocopy this copyrighted document only i unaltered and complete, including all o its headers, ooters, disclaimers, and other inormation. You may not copy this document to a Web site. ExxonMobil does not guarantee the typical (or other) values. Analysis may be perormed on representative samples and not the actual product shipped. The inormation in this document relates only to the named product or materials when not in combination with any other product or materials. We based the inormation on data believed to be reliable on the date compiled, but we do not represent, warrant, or otherwise guarantee, expressly or impliedly, the merchantability, ftness or a particular purpose, suitability, accuracy, reliability, or completeness o this inormation or the products, materials, or processes described. The user is solely responsible or all determinations regarding any use o material or product and any process in its territories o interest. We expressly disclaim liability or any loss, damage, or injury directly or indirectly suered or incurred as a result o or related to anyone using or relying on any o the inormation in this document. There is no endorsement o any product or process, and we expressly disclaim any contrary implication. The terms, “we”, “our”, “ExxonMobil Chemical”, or “ExxonMobil” are used or convenience, and may include any one or more o ExxonMobil Chemical Company, Exxon Mobil Corporation, or any afliates they directly or indirectly steward. ExxonMobil, the ExxonMobil Logo, the interlocking “X” Device, and all other product names used herein are trademarks o ExxonMobil unless indicated otherwise.
2 4 E 1 6 1 1 0 1 4 0 S • A S U n i d e t n i r P
