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New blacks address compounding challenges.

In the face of ever-increasing competition, end-user demands, environmental concerns and cost pressures, industrial rubber product manufacturers are seeking fresh approaches to a process that has traditionally required trade-offs and compromises among a myriad of competing interests.

The introduction of new, advanced carbon black technology by Cabot is assisting rubber compounders in their balancing act by allowing them to compound for specific properties and performance while maintaining firm control of the bottom line.

Global and regional competition, encroachment by thermoplastic elastomers and relatively slow market growth for rubber parts are driving profits down at all levels of the industrial rubber products market. Therefore, rubber compounders must find ways to cut production costs while continuing to meet customer needs.

However, the performance needs of industrial rubber product end users are expanding just as compounders' profit margins are shrinking. In their drive for higher quality, end users such is automotive OEMS are demanding improved product performance from their suppliers. Their increasingly stringent specifications for rubber parts focus on:

* Maintaining desired physical properties over a wider range of operating conditions;

* extending part life; and

* improving appearance factors such as surface gloss and smoothness,

Rubber compounders must also respond to end-user requests for a wider range of product choices to meet the needs of new or specialty markets. And they must comply with environmental and health regulations by adjusting their formulating and processing methods.

To satisfy these demands, compounders may consider new or modified processing methods, new part designs or changes to compound formulations. However, any one of these approaches carries the potential for significant capital and material expenditures at a time when overall cost reduction is imperative.

The new custom carbon black products that are being developed and commercially produced by Cabot under the Sterling trade name offer solutions to many of these challenges confronting rubber compounders.

Each new black is designed to meet precise performance specifications for a range of industrial rubber product applications, giving compounders more control in meeting existing end-use performance requirements. Moreover, these custom carbon blacks - through their unique design and properties can facilitate compounders' efforts to improve, rather than simply meet, product performance standards.

In many cases, the new blacks provide compounders with improved processing characteristics not previously available under a given set of product performance and cost requirements. In others, the improved processing translates into direct cost savings to compounders.

The performance advantages offered by these carbon blacks also provide flexibility to the rubber manufacturer in designing new parts or improving existing designs. Attributes such as improved compression set, tear strength, durability and tensile strength allow greater design latitude. These and other performance features, such as improved surface appearance, also allow rubber parts manufacturers to improve the quality of their existing products independent of any design changes.

Additionally, the use of Sterling carbon black products can in many cases reduce overall compounding costs while maintaining or improving quality and performance. In some cases, higher carbon black loadings are possible at equal durometer. Some of the new carbon blacks allow for higher oil-loading levels that can further reduce costs. And, because of their improved performance characteristics, the new grades may enable compounders to select alternative elastomers that cost less or permit more design options.

Product performance

One example of how these custom carbon blacks favorably affect cost, processing and performance is S 1120 carbon black - a new product designed for molded rubber applications that require superior flex add fatigue properties.

S 1120 carbon black is a unique grade that builds hardness and strength while retaining flexibility, an important combination of properties for many automotive and industrial rubber products. The novel characteristics of this new carbon black give it the ability to achieve added value over both SRF and N990 grades in many applications.

Compared to conventional grades, S 1120 carbon black builds similar hardness yet exhibits a substantially lower crack growth rate in flex and fatigue testing. For example, a natural rubber compound with a 70 phr loading of the new product displays a crack growth rate of 1.4 cm/million cycles, compared to 1.9 cm/million cycles for N990 carbon black and 3.7 cm/million cycles for N762 carbon black (figure 1).

These properties lend themselves to such applications as motor mounts and body mounts. S 1120 carbon black's contribution to low heat build-up and improved tensile retention after heat aging also makes this unique product an excellent choice for use in dynamic applications that require good flex life. This new carbon black also exhibits lower damping than the SRF grades, allowing it to be used with high-damping polymers. This property gives S 1120 the ability to achieve more optimum dynamic properties than either SRF or N990 in many applications:

S 1120 also delivers several processing and cost advantages. To help lower costs, rubber compounders can use higher loadings of this new black at equal durometer. For ease of processing, S 1120 enables engineers to compound for high bardness levels at relatively low viscosities by using high carbon black loadings. This; can be done without the sacrifice of tensile strength that often accompanies high loadings of conventional grades (figure, 2).

Another new black is S 4620 - a product that provides superior performance and ease of processing in extruded, hose and molded rubber applications.

Compared with conventional grades used in extruded industrial product applications such as weather stripping for automotive and architectural use, S 4620 offers a much smoother, high-gloss surface appearance. For example, surface analysis of EPDM compounds containing various carbon blacks shows that the compound using S 4620 has significantly fewer surface blemishes and a smoother background than compounds using N550, N6510 or N762 grades.

The new product's excellent dispersion in one-pass mixes contributes to ease of processing in extruded applications - an important factor in reducing overall compounding costs. The good green strength and dimensional stability achieved with this new carbon black also help reduce scrap and lower costs.

In molded industrial rubber applications, the new product contributes to improved compression set and lower mold shrinkage compared to conventional grades. For example, a 60-durometer polyacrylate compound containing S 4620 shows a compression set of 27.3% over 70 hours at 150[degrees]C, compared to 30.3% for a compound using N550 carbon black (figure 3). Additionally, the new product delivers this improved performance at a higher loading level. In the same polyacrylate compound at 60 durometer, a loading of 63 phr S 4620 can be accommodated, compared to only 53 phr of the N550 grade (figure 4). This new carbon black is also well-suited to industrial rubber applications where very high electrical resistivity is required.

Also demonstrating the new line's value-added attributes is S 6740 carbon black - designed to deliver processing and performance advantages such as excellent compression set, good tear strength and high receptivity to microwave curing in molded and extruded industrial rubber applications.

In molded applications, this new carbon black offers improved compression set over standard reinforcing carbon blacks. For example, an EPDM compound containing S 6740 shows a compression set of 12% over 22 hours at 100[degrees]C, compared to 15% in a compound containing an N330 grade. In a polyacrylate compound over 70 hours at 150[degrees]C, this new carbon black shows a compression set of 21%, compared to 27% with N:330 (figure 5).

S 6740 carbon black also contributes to improved tear strength and low damping compared to standard reinforcing grades, making this carbon black an excellent choice for general-purpose molding compounds, belts and belt components, and other demanding applications. This carbon black's processing advantages include low mold shrinkage, enhanced green strength for extrusion profiles and excellent dispersion in multipass mixes.

In extrusion applications, S 6740 contributes to improved extrusion stability, which can significantly improve productivity and thus reduce overall costs. it also contributes to a high-gloss surface appearance and superior jet black color.

S 6740 carbon black's receptivity to microwave curing is another important advantage, as several factors drive the trend toward use of microwave curing for rubber products (figure 6).

Two other new products that are now commercially available - Sterling C and XC-72 carbon blacks - offer similar processing and performance advantages, with special emphasis on improved electrical conductivity in rubber compounds (figure 7)


As a key ingredient in rubber formulations, carbon black can affect compounding options, processing and end-product performance. By eliminating many of the traditional trade-offs between cost and performance that have hampered compounders, the new Sterling carbon blacks can provide added flexibility in meeting existing market demands needs as well as design solutions for future industrial rubber product applications.
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Title Annotation:carbon black products
Author:Podobnik, John
Publication:Rubber World
Date:Jun 1, 1994
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