50 Years of Keeping the Rubber Industry in the Black

ASTM Committee D24 on Carbon Black

This article is based on an article by William C. Jones, published in the August 1992 issue of SN.

Today’s high performance automobiles are so much part of our lives that they are often taken for granted. We need only to look back one or two generations to see the birth of the automobile industry and to understand its impact on the rubber and carbon black industries and to see the critical role that ASTM Committees D11 on Rubber and D24 on Carbon Black have played in their success.

A Black Diamond in the Rough

In 1845 Robert W. Thompson obtained the first patent on a rubber pneumatic tire, but it wasn’t until 1888 that the first commercial tire was developed by John Boyd Dunlop for use on bicycles. The Michelin brothers of France are credited with the introduction of the pneumatic tire to the “horseless carriage” in 1895 and the modern rubber industry was born. In 1900, about 4,200 cars and 300,000 tires were made in the United States. Today there are over 260 million registered vehicles on U.S. highways (passenger cars, light trucks, trucks and miscellaneous vehicles), over 250 million tires produced annually in the United States and over 450 million produced worldwide. Today those numbers are decreasing in North America due to economic and industrial developments in China and India, where production costs are significantly lower.

In 1912, when ASTM Committee D11 was organized, carbon black was only beginning to emerge as a rubber compounding material. While both Hancock and Goodyear had prescribed mixing lampblack into rubber in their patents dating from 1830, their application was mainly for coloring. It was S.C. Mote, chief chemist of the India Rubber, Gutta Percha and Telegraph Works in Silverton, England, who discovered in 1904 that the carbon black used as a pigment by ink makers had some reinforcement capabilities in rubber. It wasn’t until 1912, however, that this secret ingredient was used in tires by the Diamond Rubber Co. of Akron, Ohio, which acquired the rights to the use of the material from Mote’s company. Carbon black soon completely replaced zinc oxide as the primary reinforcing agent in rubber. The carbon black industry experienced immediate and constant growth from the approximate 11 million kilograms manufactured in 1912 to today’s 20 million kilograms. Of that production, approximately 90 percent will be shipped to the rubber industry (about 70 percent to the tire industry and approximately 20 percent to the mechanical rubber goods sector).

ASTM International Helps the Black Market

With the 1940s and 1950s came a number of factors that led to the proliferation of carbon black grades. Among those factors was the development of the oil furnace process for making carbon black with very high surface area and structure, the development of the electron microscope and its contribution to understanding carbon black morphology, the development of the synthetic rubber industry and its requirement for increased reinforcement, and the boom in highway construction coupled with the development of heavier automobiles with increased horsepower and motorists’ expectations for greater tire wear and durability.

In 1952, in this period of rapid change, members of the eight U.S. carbon black producers formed the Carbon Black Industry Committee and began to hold meetings in Amarillo, Texas, to rationalize and develop uniform chemical and physio-chemical testing procedures. This committee was able to agree upon a single procedure for the 13 primary tests being specified by carbon black users at the time. This committee was represented by Godfrey L. Cabot Inc., Columbian Carbon Co., Continental Carbon Co., Sid Richardson Carbon Co., Thermatomic Carbon Co., and United Carbon Co., Inc.

Until this time, each carbon black producer and each rubber goods or tire manufacturer had its own specifications and test methods for the carbon black it sold or purchased. The story is told by Frank Svetlik, a founding father of D24, that once a lot of carbon black was produced, it was tested to determine if it met the specifications of any customers from whom orders had been received. If it failed to meet requirements of Company A, then it would be tested by the methods of Company B, Company C, etc., until it qualified for a particular customer. This duplication of testing was, of course, costly and time-consuming, and it created a chaotic situation that grew progressively worse as the types of blacks increased in number. Once the producers were somewhat in agreement on their methods of test, the next step was to get the rubber manufacturers on board.

In early 1955, members of the major carbon black producers and the big tire companies met in Akron to discuss the testing of carbon black in rubber. Each rubber producer considered his test recipe to be confidential and none were willing to consider the use of any other’s. Since the carbon black people knew all of the recipes, it was possible to show each without identification of ownership and to discuss the similarities.

It was found that all were very similar except for the accelerator used by one company. The opportunity for a compromise “industry” recipe seemed possible and it was decided to ask ASTM Committee D11 on Rubber to provide the forum for gaining the needed consensus. The executive subcommittee of D11 considered the request and concluded that the testing of carbon black had so many ramifications outside the normal realm of rubber technologists that it recommended to the ASTM board of directors that a separate committee be established for carbon black.

The formation of ASTM Committee D24 on Carbon Black was approved at the Sept. 20, 1955, meeting of the ASTM board. R.C. Alden, an ASTM director and employee of Phillips Petroleum Co., was appointed chairman of the organizational steering committee. The organizational meeting was held in Buffalo, N.Y., on Feb. 29, 1956, and the first official meeting of Committee D24 was held on June 22, 1956, in Atlantic City, N.J. The first main committee officers elected were S.R. Doner of Rybestos-Manhattan, Inc., as chairman, C.A. Carlton of J.M. Huber Corp. as vice-chairman, and A.B. Cobbe of Godfrey L. Cabot, Inc., as secretary.

The charter membership included 11 producer members, 24 consumer members, and six general members. From that initial meeting to the present time, Committees D11 and D24 have continued to hold their meetings together because of their shared interests and shared membership. In July 1956, an ASTM Bulletin was issued that contained the first publication of carbon black test methods by ASTM. This original publication included tentative test methods for pellet size distribution, solvent-extractable material, sieve residue, attrition, benzene discoloration, iodine adsorption, fines, heating loss, pour density, volatile content, pH value, ash content, and mass strength. In 1962, the International Organization for Standardization (ISO) Technical Committee 45 expressed interest in undertaking the international standardization of carbon black. ASTM Committee D24 sent a representative to the annual meeting and the D24 test methods were adopted nearly verbatim by TC 45.

D24 Makes the Black List

The committee abandoned early the notion of developing carbon black specifications and committed its efforts to the development of test methods that were useful in characterizing carbon blacks for the purposes of assuring standardization and the interchangeability of grades between producers with regard to their reinforcement, processing and handling. Research has been encouraged by communicating the needs of the market and the inadequacy of certain test methods and by providing a classification system for carbon black grades that is based primarily on particle size and permits input into the classification number by the petitioning party.

D24 encourages the development of new carbon black grades with unique performance properties by encouraging exclusive producer/user evaluations of non-classified carbons in order to establish the commercial value of the new grade. The classification of a new grade is encouraged when multiple producers or multiple users of a new grade exist and there is commercial value to the standardization of the properties of the carbon. The 2006 revision of D 1765, Classification System for Carbon Blacks Used in Rubber Products, lists 43 commercial grades. The most recent addition to the D 1765 list was N120, which was added in 1997 by Continental Carbon Co.

Today, new grades are rarely submitted due to the development of advanced reactor technology. Thus all new carbon blacks developed are considered specialty blacks and are proprietary. Many of the new carbon blacks are developed in conjunction with one of the major tire manufacturers and neither is willing to give up potential market to their respective competitors. Also, it is generally accepted that, once a carbon black is listed in D 1765, it is considered a commodity black, therefore reducing its overall market value versus a single sourced specialty black.

The D 1765 classification and nomenclature system and “Black List” were under the joint jurisdiction of D11 and D24 from 1961 to 1971 when it became the sole responsibility of D24. In 1967, the nomenclature system was revised from the use of names such as HAF (high abrasion furnace), to an alphanumeric system with codes such as N330, in order to provide a better technical description of the properties of each grade.

Committee D24 is unique in its organization in that every main committee member is also a member of every subcommittee. The executive subcommittee is composed of each subcommittee chairman and secretary along with the main committee officers. This organization has provided exceptional teamwork in the development of standards and has permitted more expedient standards development by the resulting open communications and by the use of concurrent subcommittee and main committee letter ballots. Through a change in the bylaws in 1990, the committee adopted the preferred use of the international system of units (SI) which further united the international community with D24.

Black References and Quality Taken Seriously

In 1959, D24 first developed the idea of an industry reference black for use in standardizing various test methods and in conducting comparisons with other carbon blacks. These IRBs have been replaced as supplies have been consumed. The current generation is IRB#7. Additionally, other standard reference blacks have been developed to permit calibration of the various instruments and verification of test methods. Currently, the seventh series of SRBs (A7 – G7) are in use. In 2005, iodine standards (HT-1, HT-2, and HT-3) were approved as reference materials for D 1510, Test Method for Carbon Black – Iodine Adsorption Number. These partially graphitized carbon black standards are extremely stable and are used as controls in labs conducting iodine testing. Other reference materials maintained by the committee include an industry tint reference black and an industry tint zinc oxide used in ASTM D 3265, Test Method for Carbon Black – Tint Strength.

Committee D24 responded to the quality revolution of the early 1980s by facilitating an agreement among all carbon black producers of common target properties for each grade of carbon black. This significant accomplishment permits the use of statistical process control on a grade of carbon black independent of its producer and has advanced the standardization of grades on an international basis. Those target properties for each grade have been listed in D 1765 since 1985.

Committee D24 has been effective in providing a forum for the evaluation of various proposed test methods for predicting those carbon black properties believed to correlate best with rubber reinforcement, for example, structure and surface area or particle size. Currently, the property of structure is estimated by ASTM standards D 2414, Test Method for Carbon Black-Oil Absorption Number (OAN), and D 3493, Test Method for Carbon Black-Oil Absorption Number of Compressed Sample (COAN). The property of surface area is measured by D 6556, Test Method for Carbon Black-Total and External Surface Area by Nitrogen Adsorption, and D 1510, Test Method for Carbon Black-Iodine Adsorption Number. The older CTAB method, D 3765, Test Method for Carbon Black—CTAB (Cetyltrimethylammonium Bromide) Surface Area, is being replaced by statistical thickness surface area as defined in D 6556.

Laboratory Proficiency Rating System Established1

Committee D24 faces challenges when it comes to improving test method proficiency and preparing mandatory precision and bias statements. It is important for producers, consumers, and instrument manufacturers to know how well their laboratories perform compared to other laboratories in conducting tests. The time and effort to organize and participate in an interlaboratory testing program, or ITP, commonly referred to as a round robin, discouraged many potential participants. Most saw the ITP as a lot of work with little tangible benefit to the participants. Usually, fewer than 10 laboratories would agree to participate in an ITP.

At the June 1995 D24 meeting in Denver, Colo., a proposal was presented by John Bailey of Continental Carbon Company, chairman of Subcommittee D24.61 on Statistics, showing how D24 could organize a standing ITP to address the challenges of improving testing proficiency, preparing precision and bias statements, validating SRB and IRB materials, and benefit the participating laboratories by giving them feedback on their testing proficiency. The program would become known as the Laboratory Proficiency Rating System.

The first ITP was conducted in September 1995 using an N234 carbon black with 45 labs participating. The results of this first program were so well received that the second one in March 1996 added seven tests and expanded the number of labs to 75. Today the standard LPRS consists of 12 tests and approximately 75 labs. Due to the large number of laboratories participating and the international representation of those laboratories, it is generally accepted that the precision and bias numbers more accurately reflect the state of testing proficiency in the carbon black industry.

In addition to preparing precision and bias statements, LPRS data have been used to validate the uniformity of SRB and IRB materials, publish new target and acceptable range values for the SRBs, and investigate SRB candidate materials.

The longevity of the LPRS program and the various uses of the data demonstrate its value and show that it has met or exceeded the expectations of that original proposal. The fact that it is conducted entirely within the technical committee makes it a unique program and a source of pride and satisfaction for the D24 members.

D24 Reaches Out

Committee D24 held its first meeting outside the United States when it met in Stresa, Italy, in April 2004. This meeting marked a new chapter for D24 by reflecting the committee’s international membership and a desire to internationally promote the knowledge of carbon black properties through the development of superior technical standards. The event was attended by 33 members and visitors from most regions of the world. ASTM International staff provided an overview of ASTM International; the chairman discussed D24’s scope and function; and members of the D24 committee provided technical presentations representing the latest developments in subcommittee activities, reference materials, and the LPRS program.

The Future Is Still Black for D24

Competition in the tire industry today is driving the expected mileage for a set of tires to the 100,000 mile (160,000 km) level while simultaneously requiring reduced rolling resistance (for improved fuel consumption) and also improving both wet and dry traction. To obtain these advances, silica has been introduced to the mix. This newcomer has forced the carbon black industry to gain a greater understanding of the mechanisms of reinforcement, hysteresis and modulus.

While the concept of carbon black surface activity or surface energy has been under study for at least 50 years, there currently is no ASTM method for its measurement. Research continues around the world on this property in an effort to establish whether it can augment carbon black reinforcement theory with respect to the observed effects in different polymers. The application of fractal geometry to carbon black morphology by Gerspacher and others has focused attention on the role of the carbon-carbon network in rubber reinforcement.

The requirements for rubber reinforcement continue to increase and the carbon black industry continues to respond with new and novel products. Advances have been made in void volume with instrument manufacturers developing next-generation structure measurement equipment, in tint testing with the introduction of the Speed Mixer® over the standard muller, in nitrogen surface area with the improvement in equipment designed specifically for carbon black, in structure testing with the approval of paraffinic oil replacing n-dibutyl phthalate for current structure testing. The world relies on ASTM Committee D24 to continue its leadership in methods development, instrument improvements and the standardization of both. D24 expects to see continued progress in the future and especially within the next 10 years. //

1 John Bailey and Jeffery Melsom, Laboratory Proficiency Rating System for Carbon Black, Standardization News, October 2005.

Jeffery Melsom is lab and quality guarantee manager at Michelin’s Sandy Springs, S.C., plant. He is a past chairman of D24 and actively participates on ASTM Committees D11 on Rubber, D24 on Carbon Black, and serves on ASTM’s board of directors. He has held officer positions in various D11 and D24 subcommittees and is the editor of D24’s biannual newsletter, The Carbon Aggregate.
Copyright 2006, ASTM International