Inside Tire Paints

The life of tire curing bladders can be increased through the application of a curing bladder treatment, which helps to protect the bladder against chemical and abrasion attack throughout its service life. This type of attack is prevalent at the surface of the curing bladders that contacts with the beads of the tires being cured. Coatings can significantly help increase average bladder life. The choice of inside tire paint can also have a positive impact on the service life of curing bladders.

Most products for the tire industry are developed for application to green tires using any of the following systems:

• Spray gun, either automated, e.g. Ilmberger or Plummer units etc., or hand-held spray guns.
• Paint brush.
• Sponge or swab.

The actual application technique(s) chosen by any given tire plant depends primarily on the equipment available and the logistics of the particular plant. Experienced release agent suppliers should be able to provide recommendations to improve and optimize application techniques where desired.

Generally speaking the optimum coating of inside paint is one that is evenly spread across the entire inner face of the of tire reaching across the tire from bead to bead. For outside paint the coverage should be a thin even film applied to the areas of the tire that benefit most from the use of an outside paint, typically this would be the tire sidewall areas and perhaps an area around the external shoulders. The tread area is often not coated with an outside paint.

Once the optimum coverage is obtained, using the visual guidelines mentioned above then the actual coat weight maybe determined. This may be achieved by either measuring the shot weight or using pre-weighed patches adhered to the inside or outside of the tire, the so called “patch-test”. The shot weight may be determined by using pre-weighed polythene bags placed over the spray gun heads to capture the amount emerging from the spray gun head when it is activated. The “patch-test” involves applying pre-weighed patches applied to the inner-liner or outer face of the tire, depending whether one is measuring the volume of inside or outside paint being applied. In the case of the plastic bag technique it is usually best to measure an average of five to six activations of the spray gun to simulate the spraying of five to six tires, and then calculating the average amount in order to obtain better accuracy. In the case of the “patch test” it is better to apply three patches spread around the inside or outside of the tire to help determine the distribution of the film around the tire. In both cases the measured coat weight is obtained from calculating the differences between the pre-weighed empty bags or pre-weighed clean patch, and the weight after the tire is sprayed or the spray cycles simulated, depending on which technique is being used. An experienced release agent supplier should be able to provide support in this process.

Inside tire paints are applied to the inner-liner of uncured tires to provide the necessary slip required to allow the curing bladder (membrane) to locate easily inside the uncured tire during the shaping process of the curing cycle. High slip at this point of the process aids the bladder to conform to the contour of the inside of the tire, thus ensuring a well-centered tire. These paints also assist in the elimination of trapped air. Their use is important in ensuring minimal curing defect levels and optimum tire uniformity. At the end of the curing cycle inside tire paints provide the effective release needed to remove the tire from the bladder.

This is a difficult question to answer to provide a definitive answer to because it depends on the type of tires being cured, the equipment they are being cured on and the application equipment available. The best product can only be determined by a thorough assessment and is best answered in consultation with an experienced release agent supplier.

A filled inside tire paint contains specially selected fillers. An unfilled inside paint does not contain any fillers.

A single release inside tire paint is applied to the inside of each tire prior to it being cured. A durable inside tire paint is applied to the inside of one tire prior to it being cured; the film is designed to transfer from the treated tire to the surface of the curing bladder during its curing cycle. The transferred film forms a layer on the bladder that has sufficient slip and release to permit the curing of several tires before the film requires replenishment via the curing of another coated tire.

A single release inside tire paint is particularly useful when curing tires with complicated contours like ultra-high performance tires, where the low profile and square shoulders create the likelihood of trapped air. In these cases a specialist filled inside tire paint applied to each tire is required. Durable inside tire paints are preferred with tires having less complex contours and in regions where labor costs are high.

A filled inside tire paint contains specially selected fillers, like mica, to help provide the air-bleed necessary to allow any air that becomes trapped between the tire and the curing bladder to escape. An unfilled inside paint does not contain any filler and is used to obtain optimum finished tire appearance, air-bleed comes solely from the venting pattern on the curing bladder when using an unfilled inside tire paint.