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Halobutyl Inner Liner Is Key to Tire Reliability

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Halobutyl Inner Liner Is Key to Tire Reliability P016_RPN_20160321.qxp 3/16/2016 4:24 PM Page 1 16 Rubber & Plastics News ● March 21, 2016 www.rubbernews.com Technical Halobutyl inner liner is key to tire reliability By Jeffrey Valentage ExxonMobil Chemical Co. Executive summary The author Butyl rubber is a copolymer of isobuty- Jeffrey Valentage has been in- lene and about 2 percent isoprene, and it When it comes to tires, consumers want longer tread life, a smooth and quiet ride, volved in the automotive industry for has a significantly lower vapor transmis- fuel economy and consistent performance. All of these traits are hallmarks of a tire more than 25 years. sion to small molecule diffusants than that maintains optimal air pressure, or simply stated—keeps the air in the tires. He began his career as a process/ other elastomers. Today’s tires are a complex piece of construction, and regardless of the tire mod- project engineer and manufacturing Butyl rubber was first used to produce el, it’s the job of the inner liner to contain the air in the tire. There is a wide varia- manager at a major plastics molder tire tubes because of its excellent flexibili- tion in air retention performance among tires, but in all types of tires, it is con- that supplies a wide variety of interi- ty, fatigue resistance and improved air re- cluded that the key parameters driving air retention properties in the inner liner or and exterior automotive compo- tention in comparison to natural rubber. are halobutyl content, gauge and tire operating temperature. As regulations continue to change and progress, the goal of any new standard or nents. TECHNICAL NOTEBOOK regulation should be to drive consistent and reliable performance and efficiency im- Valentage joined ExxonMobil Chem- ical in 1997 and has served as an appli- Edited by Harold Herzlich provements over the life of a tire. However, without including an inflation pressure loss rate specification maximum, the performance characteristics shown on any label cations engineer, OEM account Halogenation by either bromine or or minimal standard guideline is unlikely to reflect a consumer’s real world results. manager, global chlorine greatly extended the usefulness A simple and effective solution to maintaining consistent tire performance effi- automotive busi- of butyl rubbers by significantly increas- ciency is by improving air retention of the tire, and there is proven and readily ness develop- ing curing rates. This enabled co-vulcan- available technology with which to accomplish this critical trait of a tire. By in- ment manager ization with other general purpose rub- creasing halobutyl content and optimizing the inner liner gauge, air retention can and global auto- bers used in the tire carcass without be improved significantly without sacrificing any other tire performance attribute. motive market affecting the desirable impermeability planner, cover- and fatigue properties, a significant con- ing the broad tribution to the development of a reli- sure loss seven to nine times higher. The combination provides manufac- spectrum of poly- able tubeless tire. ExxonMobil also has extended its glob- turers the tools to balance air retention, mers ExxonMo- al tire studies to include truck and bus weight and total cost of the inner liner. Valentage Inner liner—The tire foundation radials (TBR) 11R22.5 (Fig 4). Based on Based on our global tire studies, best- bil Chemical sup- plies to the automotive industry. Today’s tires are not just a simple 22 commercially available TBR tires, in-class passenger car radials have an In his current role as global tire commodity but a highly complex lami- values ranged from 0.6 percent to 1.9 inflation pressure loss rate of less than market development manager, butyl, nate construction of multiple compo- percent inflation pressure loss rate. 1.5 percent per month, with an inner Valentage focuses on advancing nents and chemically different materials Regardless of the tire type, by analyz- liner composition of 100 phr halobutyl halobutyl inner liner developments that allow manufacturers to address the ing the construction and composition content and a gauge of ~ 1mm. to improve tire air retention. balance between performance, durabili- along with testing inflation pressure loss Comparing the regional average infla- Maintaining proper inflation pres- ty and efficiency for each specific tire rate, we can conclude that key parame- tion pressure loss rates for passenger sure helps retain consistent and reli- model and application. ters are driving air retention properties car radials, the Americas had the lowest able performance and efficiency over Regardless of the specific tire model, it in the inner liner: halobutyl content, at 2.2 percent, Europe at 2.4 percent, the life of the tire, he said, improves is the job of the inner liner to contain the gauge and tire operating temperature. Asia-Pacific region as a whole at 2.6 per- tire durability and reduces mainte- air once the tire has been mounted prop- The passenger car radial examples in cent, and China had the highest average nance requirements. erly and inflated on the wheel. If the tire Fig. 5 show that composition is the at 2.8 percent. Valentage holds a bachelor’s de- is unable to maintain optimal air infla- main driver, as halobutyl content is in- For truck and bus radials, best-in- gree from the University of Phoenix. tion pressure reliably between service creased, air loss per month is signifi- class tires tested had an inflation pres- He has presented several times at intervals, benefits from any performance cantly reduced. Gauge or inner liner sure loss rate of less than 0.7 percent the Society of Plastics Engineers; So- improvements made can be reduced sig- thickness also can affect air retention per month, with an inner liner composi- ciety of Automotive Engineers; and nificantly and serviceability suffers. but to a lesser extent. tion of 100 phr halobutyl content and a other technical conferences on a vari- Testing air retention ety of topics. He also has served as an SPE chairman. To test how well a tire holds air, the Fig. 1. Example cutaway showing the multiple components of a typical tire. ASTM F1112 IPLR or inflation pressure loss rate test method is utilized, which measures the percentage of air loss per Fig. 2. Tire being tested at ExxonMo- month. bil’s facility in Baytown, Texas. This static test is conducted at 21°C (70°F) in a temperature-controlled room, with the tire inflated to 2.4 Bar or 35 psi, and can be completed in as few as 42 days. Great care has to be taken when mounting the tire and installing the valve stem to ensure a good seal to the rim, eliminating any possibility of air leaks. ExxonMobil Chemical is a global butyl industry leader in testing IPLR and oth- er tire related analytical capabilities. Even though the industry has an estab- lished and recognized testing standard for IPLR, only General Motors1 and more recently Fiat Chrysler Automo- biles have adopted and implemented a specification of 2.5 percent or less for all Fig. 3. Commercially available PCR tires tested for IPLR Fig. 4. Commercially available TBR tires tested for IPLR. tires purchased. Not all tires hold air the same— Importance of understanding the variation in air retention Contrary to popular belief that “all tires hold air the same,” there is a wide variation in air retention performance in tires. Based on more than 300 commercially available passenger car radials (PCR) tested and analyzed by ExxonMobil since 1985, the amount of air loss per month varied from as low as 0.9 percent to more than 4 percent (Fig. 3). In-service pressure loss can be two to three times higher than static, while tires tested at typical operating temper- atures of 60°C (140°F) can have air pres- P017_RPN_20160321.qxp 3/17/2016 3:59 PM Page 1 www.rubbernews.com Rubber & Plastics News ● March 21, 2016 17 Technical gauge of ~ 2mm. under-inflated (Fig 9). in tire life because of uneven treadwear very difficult to tell visually whether a Comparing truck and bus radials pur- In the examples shown, durability de- can be from 10-50 percent2 depending on tire is under-inflated, and with today’s chased in the U.S. and China, all tires creased more than 45 percent and belt the inflation pressure conditions over stiffer sidewalls, kicking the tire is sim- manufactured in the Americas and Thai- area cracking increased ~ 40 times from a the life of the tire. ply not very affective. land had </= 0.9 percent inflation pressure best-in-class to an industry average infla- With OEMs continuing to extend time be- loss rates, while tires manufactured in tion pressure loss rate. Reducing the per- TPMS and extended vehicle tween vehicle service intervals to improve China had the widest range and inflation meability of the inner liner by increasing service intervals customer experience and satisfaction, tires pressure loss, rates as high as 1.9 percent. the halobutyl content is the most effective With the addition of TPMS, or tire will need to maintain optimal air inflation If we take into account the significant way to minimize oxygen migration and pressure monitoring systems, and ex- pressure for longer periods of time. amount of tires that have higher infla- pressure build-up in the tire carcass. tended service intervals, maintaining tion pressure loss rates than best-in- optimal air inflation pressure has be- Higher pressure tires and class tires tested (Figs. 3 and 4), the in- Air retention and wear come even more critical. TPMS, which secondary maintenance systems dustry as a whole has significant room As previously discussed, if optimal air in the U.S.
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