Tire paints: a challenge of the 90s.

Almost from the inception of the tire industry, paints have played a quiet, but significant role in the manufacture of tires. Paint has been used both to improve product appearance and to assist in curing of the tires. But as the industry has matured, the paint technology it uses has not changed, until recently. This article discusses these recent developments.

Originally the inside and outside tire paints were made by tire companies in their cement houses and these products typically were solvent based paints of low sophistication. In those days, the paints' sole requirements were to provide lubricity and air bleed to the tire during the curing process. The appearance of the inside of the tire was of no concern and consequently large amounts of mica, talc and clay were always present. Outside appearance of the tire was then and is still today of major concern; however, in the past the effect of the paint on the rubber stock itself and specifically splice integrity was unknown.

Over the past 30 years, the tire industry has significantly altered its product mix to produce radial rather than bias ply tires. This change brought with it critical concerns over tire uniformity, splice integrity on both the inner and outer surfaces, and appearance of the inside of the tire. But, with all these changes taking effect, did the inside and outside paints change? In most cases, no! Instead, procedures surrounding the curing process were, generally, tailored to make the old familiar paints work. A dubious technique, at best.

Recently, several major tire manufacturers have begun to explore updating paint formulations to match more nearly the progress made in tire design. These explorations have -- in turn -- highlighted new concerns for product design and production in this decade. These concerns are (ranked in order of importance as judged by the author): Tire quality; tire appearance; tire uniformity; splice integrity; cured tire defects; curing bag life; and tire mold fouling.

To address these concerns a well designed, effective inside tire lubricant of the 90s and beyond 2000 should have the following characteristics:

* High lubricity -- to allow tubber to flow over the rubber curing bag during the shaping cycle, thus eliminating cocked tires; and to produce a more uniform tire, i.e., conicity and 1st harmonic.

* Release -- to allow the tire to separate from the curing bag completely, cleanly and easily during extraction.

* Air bleed -- to allow air caught between the curing bag and the tire innerliner to escape reducing the chance of tire defects.

* Non-transference -- to reduce the buildup of fillers in the curing bag which causes outside tire defects.

* Extension of curing bag life -- to retard increase in Shore A hardness.

* Clean post cure appearance -- to help in magnifying buyer appeal.

* Low or no silicone content -- to afford-easy cleaning and transfer to unpainted surfaces minimizes paint defects at automotive assembly plants.

* No volatile organic compounds -- to reduce drastically any negative environmental effect.

* Stability -- fillers should stay in suspension; oils should not float to the surface; and bacterial growth should be retarded.

Similarly, an outside tire paint of the 90s should have the following characteristics:

* High adhesion -- to allow rubber to rubber bonding in the splice areas; and to allow tensile strength at the splice to equal or exceed the strength of the base stocks.

* Air bleed -- to allow air caught between the tire sidewall and the aluminum mold to escape, reducing a source of defects.

* Lubricity -- to allow rubber to flow over the mold surface and faithfully replicate the mold design.

* Appearance -- to provide the desired blackness and loss.

* Prevents mold fouling -- to avoid accelerated buildup of material on the mold surface.

* No volatile organic compounds -- to reduce drastically any negative environmental effect.

* Environmentally safe.

* Stable -- fillers should stay in suspension; oils should not float to the surface; bacterial growth should be retarded.

While coatings meeting all of the desired characteristics outlined above have been developed, there are limitations on how widespread any individual formulation's usefulness is. These limitations are due to variables in each individual tire plant. These variables include:

* Tire mix -- does the plant manufacture all radial passenger or a mix, i.e., passenger and truck?

* Spray booths -- are booths dedicated to one tire type or a mix?

* Curing bag -- what type of plasticizer is used? What is the bag's surface topography (pebble surface, vent line spacing, micro architecture)? Is the bag dedicated to one tire line or multiple fit?

* Post cure appearance -- there is no consensus within the tire industry on what the ideal tire should look like.

Nor does knowing the answers to the foregoing questions guarantee success.

Case study A: What you want isn't necessarily what you can use

Kalcor was approached by a domestic tire company and asked to develop a high lubricity inside tire lubricant having a clean non-greasy post-cure appearance. The plants use a curing bladder with a normal pebble surface and have many years' history with a high filler loaded inside tire lubricant. We developed a lubricant meeting all of the design parameters. The lubricant was tested in production and did what it was designed to do. Success? An excess of air bleed related defects developed immediately. The problem: Being a clean post cure lubricant the filler was at a low level and did not allow trapped air to migrate to the vent lines. The solution: Change all the curing bags to a new design which would allow the curing bag to provide air bleed, i.e., micro architecture. This option was not exercised due to the high cost of retooling all of their bladder molds. The plant remains today, on the high filler lubricant.

Case study B: How to limit your options

Another domestic tire company requested that Kalcor develop a high lubricity clean post-cure inside tire lubricant which was silicone free. As before, we were successful in developing the requested lubricant. In addition to fillers the formulation contained two dispersions and two emulsions. In order to offer long term stability the viscosity was set at 3,000 cps (LVT #3 @ 30rpm). A sample was sent to one of their production plants and was evaluated by the plant chemist. Surprisingly, they reported that the lubricant could not be sprayed! How is this possible? Tiffs location had removed all of its spray booths, some years ago, and now sprays every fourth tire, by hand, at the curing press with a hand held pressure pot. The viscosity of the emulsion they use is water thin. The viscosity of the sample sent was, as noted by the plant, much too high. Incidentally this technique of spraying every fourth tire accentuates uniformity differences. To solve this location's problems requires a reinvestment in equipment and manpower. The options: Install spray booths or live with the problem! Every production man's nightmare.

Case study C: How to hide your problem

At another tire company's plant a stranger tale unfolds. This location wanted an inside tire lubricant offering a cleaner post-cure appearance while minimizing foreign material defects on the sidewalls of their tires. Kalcor provided such a product and successfully ran it on the production line. The desired results were obtained and the future for this product looked encouraging. Did they switch to this superior product? Nope! It seems the cleaner look allowed their final finish inspectors to see, for the first time, what the innerliner looked like. Defects related to fire building, calendering, etc., were suddenly apparent. Rather then correcting the obvious problems their production manager decided to remain with the inside tire lubricant that hid the surface. Is quality its own reward? You'd get an argument here!

Obviously, adapting to changes in production techniques during the second half of this decade and beyond requires courage. Change can be risky, but we believe those who take well calculated risks will succeed and so benefit by improving their production techniques and products. These companies will become the leaders of tomorrow's industry.

Example: One of our domestic tire plants expressed an interest in reducing the level of inside tire lubricant related defects, specifically cocked tires and foreign material on the outside of the tire. After careful study over many months the plant decided to convert from the inside tire lubricant they had used for over ten years to a new inside tire lubricant. The results were as expected, very good. Cocked tire defects dropped, foreign material defects dropped and, as an extra benefit, the appearance of the inside of the tire improved. This plant took the challenge to improve their procedures and is benefitting from the change.

Example 2: Kalcor was approached with the concept of developing a high adhesion outside tire paint with all the characteristics noted earlier in this article. The main problem to be solved related to the integrity of the sidewall to tread base splice area. Traditional water based outside tire paints act to block the bonding of these two stocks. The traditional solvent based paints do allow these stocks to bond. Yet, in the American market place producers are under heavy regulatory pressure to eliminate use of solvent based paints. This seemingly impossible request for a water based high adhesion paint was the focus of a three year research program. After many failures a candidate paint was finally developed which did allow the two stocks to bond at increased levels of strength.

The formulation is considered confidential by Kalcor, but in general terms has these components:

* Air bleed factor;

* Lubricity factor;

* Esoteric additive factor;

* Generic surfactant factor;

* Water

As formulated, the product has the following characteristics:

* Bond strength equal to the tensile strength of the base stocks;

* A color match equivalent to solvent based paints;

* Superior air bleed;

* Sprays and wets the rubber stocks extremely well;

* Very stable dispersion;

* No effect on mold fouling.

The above formulation is now in production use at several major American tire plants. No problems are being reported and the future commercial success of this product appears bright.

As noted in the previous examples there are changes being made in the perception of how tires should appear and in what defect rate is considered to be acceptable. The challenge of the 90s and beyond will be to continue to explore new manufacturing methods and new chemistries developed to minimize production problems and to assure the highest possible level of quality.

George Ross is Business Development Manager for the Rubber Products Group of Kalcor Coatings, Willoughby, Ohio. He joined Kalcor in 1987 after having spent eight years with Wacker Chemical.