Cabot's Industrial Rubber Products is an industry sector covering essentially all rubber-related manufacturing, with the exception of tire products. It's a very diversified sector of the rubber industry, with such rubber products as extruded profiles, hoses, belts, sheeting and roofing, geomembranes, films, roll coverings, vibration isolation devices, fuel cells, diaphragms, gaskets, o-rings, tubes, footwear, foamed insulation tubes and sheets, among others.

Due to the diversity of industrial rubber products applications, the sector has a spectrum of performance requirements, ranging from common strength properties to fluid resistance, permeation, conductivity, friction coefficient, and dynamic properties, and more. Many different rubber polymers are used in this sector, ranging from commodities such as SBR, NR, BR, IR, to semi-specialized ones such as NBR, EPDM, CR, IIR, to highly specialized ones as HNBR, PPO, ACM, FKM, etc.

Here, we briefly review a few important industrial rubber products and their key requirements and how carbon black may affect their performance.

EXTRUDED PRODUCTS

Simply put, extruded products are those rubber products processed through an extruder, through which uncured rubber is formed into certain shapes. These shapes are then cured to keep their forms. Major extruded products include automotive weatherstrips, hood and trunk seals, building seals, ship container seals, tubes, appliance seals, wiper blades and gaskets.

Key requirements for extruded products are shape consistency and blemish-free surfaces. Consistent shape provides proper sealing capability. Blemish-free surfaces are required by automotive manufacturers who seek perfect appearance. Other important performance requirements include low compression set, aging resistance, and tear/wear resistance.

Only semi-reinforcing blacks, such as Sterling 6630, 5630,  SO, VH, V, NS, NS1, and Spheron 5000 and 6000, are widely used for extruded products because they are easier to disperse in mixing, have good extrudability (rubber stocks are not "nervy" with these blacks) and they provide high loading capability, which—in turn—reduces the cost of extrusion compounds.

EXTRUSION PROCESS

Rubber is fed into an extruder, homogenized, and shaped through a die. It is then cured continuously in a curing oven (hot air, UHF, etc.), and finally cut into required length. Important carbon black properties for extrusion are explained in the following:

OAN/COAN: High structure (high OAN) blacks deliver improved dispersion and lower die swell in extrusion. Most popular extrusion blacks have OAN higher than 100 ml/100 gram.

Grit: Contaminants, cokes and highly compacted blacks are not dispersible in the rubber mixing process and will show up as blemishes on extruded surfaces. This can result in a high scrap rate that can be extremely costly. Scrap costs one customer $60MM/year, which is almost 6% of their sales! Although not all the scrap is grit-related, surface imperfections are generally considered to be one of the most important causes for scrap.

Pellet Quality: We all know that pellet quality affects dispersion, and perfect dispersion is a must for extruded products that require perfect surfaces and consistent extruded dimension. Poor mixing can lead to variability in extrusion, especially for sponge, where any variation is greatly amplified by the sensitive blowing process. Furthermore, most extrusion customers use bulk black handling systems. Poor pellet quality can provide a lot of fines, causing blockage in the handling systems. In one case, due to the change in pellet quality, a customer has to use six times more time to inject black into the mixing chamber.

Overall Consistency: Although this may sound ill-defined to many, it is a very critical and practical issue with this segment of our market. Consistency may not be measured simply with carbon black analytical properties as not everything is tested analytically. Consistently is grossly measured by compound performances. Many of our process changes may not show any effect on carbon black analytical properties. However, these changes can often be clearly seen in compound scorch, compatibility, viscosity, dispersibility and extruded surface finish. When automotive companies are seeking extended enterprise concepts, they get increasingly involved with our processes to ensure that we provide them with materials of consistent performances.

HOSES
Two major types of rubber hose are hydraulic and non-hydraulic. In addition, hoses can be classified as reinforced or non-reinforced hoses. In our Industrial Products business, non-reinforced hoses are called tubes, which we discuss above. Almost exclusively, hoses are make via extrusion process. In general, hoses are used to convey materials such as air and fuel, or hydraulic forces. This conveying function sets the key requirements for the rubber in hoses. Here are a few important products:

Fuel Hose:  Regulations to lower hydrocarbon emissions require fuel hoses to have extremely low permeability to fuel. An ultra-thin veneer of FKM is used in many fuel hoses to reduce the permeability. Mixed fuels (methanol, ethanol, etc.) require hoses with super resistance to these polar solvents. Adding carbon blacks to hose rubbers generally reduces both permeability of gasoline and swelling of solvents.

Radiator Hose:  It is critical that these types of hoses are resistant to coolants at elevated temperatures. In addition, because of the heat a hose can experience while in use, the aging properties of rubber is also very important. Another challenge is electric static cracking, which can be reduced by the use of lower conductivity blacks.

Hydraulic Hose: Almost all hydraulic hoses are reinforced. Strength and resistance to hydraulic liquids are key requirements for the hose rubbers.

Industrial Hose:  There are many different types of applications for this segment of the industry, including water and steam hoses, air hoses, oil and petroleum hoses, refrigerant hoses, food quality hoses and chemical hoses. Again, strength and resistance to solvents and chemicals are key requirements.

Hose Process:  Inner layers of hoses are extruded. Yarn is then knitted onto the inner layer, after which a rubber cover is extruded onto the knitted yarn. Finally, the extruded hoses are cut into length and mandrel cured into shapes.

BELTS

The main function of a belt is to move power or energy from one point to another. This power is then used to either drive an application or carry material from one point to another. Even though all belts are similar in their basic attributes, each is used for a different, specific task. Therefore, belts are divided into three types: timing, power drive and conveyor belts.

Timing Belts: Timing belts are designed to work with a specific set of gears so that the "teeth" of the belt fit snugly into the groove of a gear. The belt turns the gear in a very precise manner and keeps the resulting engine or system in correct timing.

Power Transmission Belts:There are many different types of power transmission belts available, including those used in automotive applications, industrial applications and mining applications. These belts take power from a drive shaft and transfer the energy to one or more additional drive shafts, so that several applications can run by the same motor. Sometimes power drive belts are used to energize applications that are significant distances away from the initiating source.

Conveyor Belts: Conveyor belts are used to carry all types of materials efficiently over long distances. These belts are usually manufactured in long ribbons, the ends of which are connected when installed.

Belt Process: Belts are usually made by two processes. Timing and power drive belts are made in a similar process to tires. First, a liner-like layer is built onto a drum. Next, layers of reinforcement and rubber are added until the correct thickness is reached. Timing belts usually have "teeth" molded onto one of the surfaces to facilitate their ability to be matched to a timing gear. Finally, the belt is cured in a small autoclave and cut to the right width. Conveyor belts are usually made in long ribbons. Rubber and fabric layers are skimmed, or calendered, onto a base until the correct thickness is reached. Then, the belt is cured (either a section at a time in a press or in line) with one of several curing techniques, such as hot air or microwave. Finally, the belt is cut to length for the specific application.

MOLDED PRODUCTS

Molded products refer to a diverse group of vulcanized rubber products that are manufactured in a mold used to obtain the desired size and shape. Products made this way include diaphragms, vibration isolation devices, bushings, air springs, chassis bumpers, all kinds of pads, boots, wiper blades, fascia, conveyor wheels, grommets, and more.

Molding Process: Compounded rubber is injected, transferred, or simply put into a heated molds, and cured under pressure to obtain required size and shape.

The following are a few examples of molded products:

Motor Mounts: These mounts are used to isolate vibration of a motor from the chassis. Key requirements are consistent static and dynamic rates (spring rates); good fatigue life, resistance to hot tear, and resistance to heat aging.

Molded Seals: These include oil seals, air seals, water seals and thermal insulation. Critical performances range from oil resistance, temperature resistance, to compression set.

Pads: Many products in this category include sheets of rubber with certain patterns on them. Cost is key to this sub-segment of the industry. Certain pads have requirements of resistance to corrosion, solvent, or temperature.

EFFECTS OF CARBON BLACK ON RUBBER PROPERTIES

As a reinforcing material, and one of the major ingredients in rubber compound, carbon black has a significant effect on any properties of rubber. The following table is a partial list of these effects.

Table I: Impact of Carbon Black on Rubber Properties

Property	High Impact	Medium Impact	Low Impact
Viscosity	√
Cure Rate	√
Extrudability	√
Density		√
Hardness	√
Strength (tensile, tear, etc.)	√
Modulus	√
Resilience		√
Compression Set		√
Aging		√
Dynamic Properties		√
Abrasion Resistance	√
Fatige	√
Low Temperature Properties	√
Solvent Resistance		√
Corrosion Resistance			√
Conductivity	√
UV Resistance	√
UHF Receptivity	√
Other Properties	√	√	√
Cost		√