Consumers may not realize that creating a safer, more durable tire can be an extremely complex process. The constant evolution of materials, compounds and processes must be taken into consideration when designing a future tire.

One aspect of this process involves rubber casting for tire manufacture, whereby manufacturers cast tire plies — the layers comprised of rubber compounds and a variety of other materials — onto plastic film substrates. The reinforced tire layers are made of rubber compounds, steel cables or other strong materials that enable tires to maintain their shape, durability and safety. The tire plies provide form, rolling resistance, tread life and sidewall construction.

The rubber used is compounded and blended with a variety of ingredients and can be cast onto one of three types of silicone-coated liners: monolayer, composite or scrim reinforced. Once the rubber is cast onto a silicone liner, the result is a large roll of single-layer rubber that is typically used for the innermost part of the tire or incorporated into other layers such as the steel reinforcement layer.

A Look at Casting Liners and Coatings Evolution

Casting tires from a single casting model enables the manufacture of more complex features in the sidewall shells, better alignment, and advantages in size, shape and appearance.

During the past three decades, there has been a steady evolution of casting film products designed specifically to increase lifespan, including:

• Monolayer construction is a heavy-gauge colored high-density polyethylene (HDPE) film that has a release coating applied on both sides. Its downside is a short product lifespan (around four to six months), and it is also easy to nick and tear.
• Composite lamination is a second-generation product, typically polyethylene terephthalate (PET)/PET or PET/HDPE, that has a release coating applied on both sides and incorporates a clear or tinted adhesive. This product features a longer lifespan (six to 12 months), with less propensity to nick and tear.
• Scrim reinforced lamination is a third-generation solution. It is a PET/PET lamination utilizing a scrim layer and also features release coatings on both sides and a clear or tinted adhesive, similar to composite construction. Product lifespan with a reinforced layer is greater than one year.

A closer look at Saint-Gobain's casting film products is below:

Monolayer

VERSIV^™ Films monolayer construction is a 375 to 575 microns (µ) thick HDPE (high-density polyethylene) film. This film is coated on two sides with a silicone release coating. These films are available in whatever color is required for an application, including green, red or blue. This was a first-generation product that is still in use today at many sites.

Composite Lamination

This is a lamination of two polyester films and adhesive, measuring around 250 microns in thickness and coated on two sides with a silicone release coating. The adhesive in the laminate could be clear, red, white, or any other required color. This lamination delivers a more durable product with good scuff resistance and longer shelf life as compared to a monolayer construction.

Scrim Reinforced Lamination

The laminate incorporates an open mesh fiberglass scrim that is laminated between two polyester films. The laminate uses an adhesive, applied in clear, red, orange, and other colors, which bonds the film and fiberglass scrim together. The outer polyester layers are coated with a silicone release on each side for a total 325 µ thickness.

The scrim-reinforced lamination is the most recent evolution in rubber casting and features a much more durable product. Due to product construction with a scrim layer, this has lead to increased product shelf life, going from months to years.

The scrim acts as a reinforcement for the film, preventing the propagation of tears that can occur while handling the product. Currently, tears in the film are the leading reason for the film needing to be replaced. By adding the scrim, end users see that the composite construction is much less likely to tear, thus increasing the useful life of the composite construction significantly.

Why Saint-Gobain?

Saint-Gobain Composite Solutions has more than 40 years of coating experience and an extensive line of release-coated liners, used in a variety of casting applications in industries such as automotive, medical, consumer electronics, graphics, and digital printing, tapes, labels, decals, and general industrial. In addition to supplying release and non-stick coated plastic films for the tire manufacturing industry, Saint-Gobain is also a leader in such applications as:

• Ceramic casting (green tape)
• Polyurethane casting
• Polyvinyl chloride casting (vinyl)
• Rubber casting
• Ink decal transfer
• Photoresist
• Medical transdermal patches

Along with its casting liners, which come in clear and matte versions and function as carrier films for a variety of coatings, Saint-Gobain’s experience in modifying chemistries to fit specific casting end uses results in market leadership. Coatings include silicone and non-silicone formulations and clear and matte versions.

Saint-Gobain’s vast experience with coating chemistries and substrates allows it to process smooth and thin films with precision and ease. Capabilities include the equipment and ingenuity to customize and process differential and two-sided release coatings, as well as a multitude of other surface coatings, including anti-graffiti and tints. Saint-Gobain chemists and application engineers define and customize products that work for its customers globally.

Saint-Gobain’s VERSIV^™ technology delivers several advantages, including:

• Multiple formulas available
• Excellent clarity and optics
• Smooth uniform surface profile
• Clear and matte versions
• Multiple film gauges
• Excellent adhesion to base film
• Excellent solvent resistance
• Wide web or narrow roll availability
• Polyethylene terephthalate and polyethylene base films
• Customized solutions

This article was produced by IEEE GlobalSpec. Visit the Saint-Gobain Composite Solutions' Engineering360 page on IEEE GlobalSpec.