Tire-curing bladders

Quinone dioximes, alkylphenol disulfides, and phenol—formaldehyde reaction products are used to cross-link halobutyl mbbers. In some cases, nonhalogenated butyl mbber can be cross-linked by these materials if there is some other source of halogen in the formulation. Alkylphenol disulfides are used in halobutyl innerliners for tires. Methylol phenol—formaldehyde resins are used for heat resistance in tire curing bladders. Bisphenols, accelerated by phosphonium salts, are used to cross-link fluorocarbon mbbers. 

Resin Cure. Resin cure systems yield carbon—carbon cross-links and, consequendy, thermally stable materials. Butyl mbber vulcanised with resins are used as tire-curing bladders, and have a life of 300—700 curing cycles at steam temperature of 175°C at about 20 m/cycle. 

The compounded rubber stock will be further processed for use. The process could be injection or transfer molding into a hot mold where it is cured. Tire curing bladders are made in this fashion. Extrusion of the rubber stock is used to make hose or tire treads and sidewalls. Another common process is calendaring, in which a fabric is passed through rolls where rubber is squeezed into the fabric to make fabric-reinforced rubber sheets for roofing membranes or body plies for tires. The actual construction of the final product can be quite complex. For example, a tire contains many different rubber components some of which are cord or fabric reinforced. All of... 

The most important characteristics of butyl rubber are its low permeability to air and its thermal stability. These properties account for its major uses in inner tubes, tire inner liners, and tire curing bladders. Because of the poor compatibility of butyl with other rubbers (with respect to both solubility and cure), the halobutyls are preferred. The brominated p-methylstyrene-containing butyl rubbers are used in a number of grafting reactions for tire applications and adhesives. Other uses for butyl rubber are automotive mechanical parts (due to the high damping characteristics of butyl), mastics, and sealants.55... 

Acetylene carbon black is derived from the pyrolysis (thermal decomposition) of acetylene gas. The production volumes of acetylene black are extremely low compared to the billions of pounds of furnace blacks produced annually. Acetylene blacks are basically used where special compounding applications are needed, such as improved thermal conductivity. One of the larger areas of use is in the production of tire-curing bladders (because of the need for better thermal conductivity). 

TYPICAL FORMULATIONS Tire curing bladder lubricant ... 

Butyl and Halobutyl Rubber. Butyl mbber is made by the polymerization of isobutylene a small amount of isoprene is added to provide sites for curing. It is designated HR because of these monomers. Halogenation of butyl mbber with bromine or chlorine increases the reaction rate for vulcanization and laminates or blends of halobutyl are feasible for production of mbber goods. It is estimated that of the - 100 million kg of butyl (UR) and halobutyl (HIIR) mbber in North America, over 90% is used in tire apphcations. The halogenated polymer is used in the innerliner of tubeless tires. Butyl mbber is used to make innertubes and curing bladders. The two major suppHers of butyl and halobutyl polymers in North America are Exxon and Bayer (see ELASTOLffiRS,SYNTHETIC-BUTYLrubber). 

Building on technologies first developed in Germany in the early 1930s, Robert M. Thomas and William J. Sparks, both employees of Standard Oil (now ExxonMobil Chemical), patented a new synthetic rubber in 1937. Butyl rubber is characterized by a very saturated linear polymer chain, leaving little space between molecules for transmission of air, vapors, moisture, or water. As such, butyl rubber was successfully used during World War II as a substitute for natural rubber in the manufacture of tire inner tubes and curing bladders. 

Uses Rubber for use in tire inner tubes/liners/curing bladders, pharmaceutical closures, mech. goods, conveyor belts/hosing antivibration mounts food/drug seals adhesives in closure-sealing gaskets for food containers in food-contact articles for repeated use... 

Applications conveyor belts, curing bladders, hoses, membranes, pharmaceutical stoppers, seals, tank liners, tire innerlines, tire non-staining sidewalls ... 

Generally, the remaining 10% of ruhher compounds have cure systems based mostly on peroxide curatives. However, a small number of compounds based on halogen-ated elastomers (such as polychloroprene) have cure systems based on metal oxides. Also, resin cures are used in special cases to cure some compounds such as curing bladders for tires. 

PF curing resin is used with hutyl compounds to impart excellent heat resistance. Thus butyl-ruhher-based compounds with these curing resins can be used to make curing bladders that can withstand many repeated heats in curing tires. 

A very small amount of the total formaldehyde is used to make methylol-terminated phenol formaldehyde curing resins, usually used in rubber bladders for tire curing. 

The imique properties of butyl rubber are used to advantage in tire inner tubes and air cushions (air impermeability), sheet roofing and cable insulation (ozone and weather resistanee), tire-euring bladders, hoses for high temperature service, and conveyor belts for hot materials (thermal stability with resin cure). 

Sulfur cross-links have limited stability at elevated temperatures and can rearrange to form new cross-links. These results in poor permanent set and creep for vulcanizates when exposed for long periods of time at high temperatures. Resin cure systems provide C-C cross-links and heat stability. Alkyl phenol-formaldehyde derivatives are usually employed for tire bladder application. Typical vulcanization system is shown in Table 14.24. The properties are summarized in Tables 14.25 and 14.26. 

Uses of Butyl Ruhher. Butyl rubber is used in the manufacture of inner liners of tubeless tires, inner tubes, cable insulation, pharmaceutical stoppers, curing bags, and bladders for tire manufacture. When tires are in the molds for vulcanization, the inside of the tire is filled with a butyl rubber bag or bladder of steam under enough pressure to obtain the vulcanization temperature. This is possible only because of the good resistance of butyl rubber to heat and water. 

Methylol-terminated para-alkyl-substituted phenol formaldehyde resin is used as the vulcanizing agent for compounds based on butyl and EPDM rubber. The alkyl group is usually octyl. It is commonly used to cure butyl rubber where superior heat resistance is needed. Therefore, this vulcanizing agent is commonly used as the curative to make butyl bladders for repetitive curing of tires. It is also sometimes used in dynamic vulcanization with a tin chloride activator to make thermoplastic vulcanizates (TPVs). 

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