Tire Curing Envelopes and Bladders


Curing bladders are a key component in the building of radial tires.  An unvulcanized tire is placed in a mold with the curing bladder located on the inside of the mold cavity.  Pressurized steam is used to inflate the bladder stimulating the curing process and giving the tire its final shape.  The demands of this application require careful selection of the polymer type to ensure the curing bladder is long lasting as it undergoes numerous cure cycles.   Regular X_Butyl® RB301 is the polymer of choice for this application. In addition, a blend of a butyl polymer with high unsaturation (X_Butyl® RB 301) with a butyl polymer lower unsaturation (X_Butyl® RB 100) has been shown to provide improved aging properties.



Curing envelopes are a key component in the retreading of tires. During this process the tire composed of uncured cushion gum and a pre-cured tread is encased in a flexible rubber envelope which conforms to the shape of the tire. A ring is then applied to the inside of the tire creating a tight seal.  The tire is then placed in a curing chamber  which applies heat and pressure to cure the unvulcanized cushion gum bonding the pre-cured tread to the tire casing. As these envelopes undergo numerous cycles, the choice of polymer is very important. While the use of Regular X_Butyl® provides long lasting envelopes, Chlorinated X_Butyl® may also be used in order to improve the production throughput of the curing envelopes although product lifetime will suffer.



When curing bladder / envelope compounds based on X_Butyl® are  correctly  formulated  and  processed,   they possess:


     ▪ very low permeability  to gases  and steam


     ▪ high resistance to heat


     ▪ excellent hot tear and  crack growth resistance


     ▪ low compression and permanent  set