Tire repair patch including bis-imide compound

Details Tire repair patch including bis-imide compound Tire repair patch including bis-imide compound

1999-07-30

2002-05-14

Maki, Steven D. (Department: 1733)

Resilient tires and wheels

Tires, resilient

Patches

C152S370000, C156S097000

Reexamination Certificate

active

06386255

ABSTRACT:

FIELD OF INVENTION
Tire patches for off-the-road (OTR) tires use multiple plies of fabric, generally embedded in gum rubber cushion layer. These patches are installed in the inner cavity of the tire. A plug of rubber is used to patch the injury from the outside of the tire. The patch is either cured in place or partially cured before installation and then adhered to the inner cavity with gum rubber or an adhesive. Due to the slower rotation speeds and higher tire costs of OTR tires, these patches are designed to repair even substantial holes in a tire. These tires are used on a variety of commercial, construction, and excavation equipment.
BACKGROUND OF THE INVENTION
Only very small holes are patched in tires used on vehicles operated at high speed due to the multiplicity of problems caused by tire failure or deflation when traveling at high rates of speed. Due to the decreased hazards associated with failure at lower speeds of operation and increased costs associated with replacing specialized off-the-road (OTR) tires, they are routinely patched when the holes therein are substantial. Off-the-road tires with larger holes can be patched or repaired by applying fabric reinforced patch on the inside of the tire and a plug on the exterior portion of the tire.
Various configurations of multiple fabric reinforcements, in combination with layers of gum rubber, have been used to patch tires. U.S. Pat. No. 4,399,854 provides details on one such patch with a partially-vulcanized ply or plies. These patches are intended to bridge over the injury to the tire transferring stresses to the non-injured portion of the tire.
Problems encountered with this technique include 1) overcuring and/or undercuring the patch components due to problems associated with uniformly heating and crosslinking thick patches and 2) crack initiation at the interface between the tire and the patch. Patches without fabric reinforcement are generally too low in modulus to be effective repairs.
SUMMARY OF THE INVENTION
Tire patches are disclosed that utilize bis-imide compounds as part of the gum rubber composition of the patch. This compound 1) helps prevent reversion of the rubber during the curing (crosslinking) process for the tire patch and 2) minimizes heat buildup and reversion of the gum rubber components of the tire patch during tire use (revolution), which may cause failure of the rubber components at the high stress locations near the interface of the tire and the patch.
The patches generally comprise at least two overlapping plies of reinforcing cords coated or embedded in a gum rubber composition which form a ply package, an unvulcanized base cushion gum layer at the underside of said patch for engagement with a surface of a tire, an unvulcanized top cushion gum layer at the opposite side of the patch from said underside, said base and top cushion gum layers enclosing and surrounding said ply package and usually being joined at a location beyond the edges of said ply package. The gum rubber composition of the top and/or base cushion gum layer desirably includes from about 0.1 to about 5 phr of a bis-imide compound to stabilized the gum rubber against reversion and heat buildup. The gum rubber composition of the plies may also include the bis-imide compound. Preferred bis-imide compounds include Perkalink® 900 and HVA-2® from Flexsys in Akron, Ohio and DuPont in Wilmington, Del., respectively. In a tire patch gum rubber composition, these bis-imides will decrease the tendency to undergo reversion and will increase the time to blowout in the Goodrich blow-out test.
DETAILED DESCRIPTION OF THE INVENTION
The repair of off-the-road (OTR) tires typically uses a patch comprising at least a first and optionally a second gum rubber composition, a ply package which includes at least two overlapping plies of reinforcing cords coated with rubber or partially or fully embedded in said first or second gum rubber composition, an unvulcanized base cushion gum layer at the underside of said patch for engagement with a surface of said tire, an unvulcanized top cushion gum layer (protective layer) at the opposite side of the patch from said underside, said base and top cushion gum layers surrounding and enclosing said ply package and usually being joined at a location beyond the edges of said ply package. In the current embodiment at least the top cushion gum rubber composition, optionally said base gum rubber composition, and optionally said second gum rubber composition comprises an effective amount of a bis-imide compound to reduce reversion and/or heat buildup in the Goodrich blow-out test. Said bis-imide compound desirably having the structure:
where R
1
, R
2
, R
3
, and R
4
are independently hydrogen, an alkyl group of 1 to 5 carbon atoms, an alkylphenyl group having 7 to 10 carbon atoms or a halogen substituted alkyl group having from 1 to 5 carbon atoms, a halogen substituted phenyl group, or a halogen substituted alkylphenylene group having a total of from 7 to 10 carbon atoms, and where X is an alkylene group having from 1 to 5 carbon atoms, a phenylene group, an alkylphenylene or alkylenephenyl group having 7 to 10 carbon atoms, an oligomer of alkylene and phenylene groups having from 11 to 30 carbon atoms, or a halogen substituted alkylene group having from 1 to 5 carbon atoms, a halogen substituted phenylene group, or a halogen substituted alkylphenylene or alkylenephenyl group having a total of from 7 to 10 carbons atoms.
Preferred bis-imides are Perkalink®900 from Flexsys having the chemical structure N,N′-m-xylylene bis-citronic imide and HVA-2® from DuPont having the chemical structure N,N′-m-phenylene bismaleimide. These compounds are desirably used in an effective amount to reduce reversion and/or heat buildup in the Goodrich blowout test. Effective amounts are generally from about 0.1, 0.2 or 0.3 to about 5 or 10 phr (parts by weight per 100 parts by weight of rubber in the composition), and are more desirably from about 0.3 or 0.5 to about 2 or 3 phr.
The gum rubber compositions of the base and top cushion layers and optionally of the ply layers generally comprises a hydrocarbon sulfur curable rubber, fillers, and curatives. For example, a curative agent such as phenol formaldehyde can be added to the gum rubber compositions in amounts from about 1 to about 10 parts by weight per 100 parts by weight of rubber in the composition. It may optionally include oils, antioxidants, antiozonants, stearic acid, etc. in conventional amounts. It generally will not include fibrous reinforcements such as fibers or cords unless converted to a ply layer. The gum rubber composition may include tackifiers in an effective amount to promote adhesion of the gum rubber composition to itself, fibers or cords, and to the cured tire carcass. U.S. Pat. No. 5,503,940 is hereby incorporated by reference for its general teachings on bis-imides and its specific teachings on tackifiers. Desirably the tackifier is present in an amount from about 2 to about 25 phr. Carbon black is desirably present from about 20 to about 70 phr and more desirably from about 30 to about 55 phr. Desirably the carbon black has a mean ultimate particle diameter of less than 285 and preferably less than 60 nm per ASTM D-3849. The gum rubber compositions can be mixed in any rubber mixing equipment such as a Banbury, multiple roll mill, etc. It is desirable to perform the mixing so the heat sensitive curatives are added in a late mixing step at a rubber temperature below the activation temperature for the curative. Generally the gum rubber compositions are formed into sheets (e.g. by calendering) having a thickness from about 0.01 5 to about 0.500 inches.
The rubber in the gum rubber compositions can be any conventional hydrocarbon rubber used in tire manufacturing such as those derived from polymerizing conjugated dienes of 4 to 10 carbon atoms, optionally, copolymerized with vinyl substituted aromatic monomers having from 8 to 12 carbon atoms. Such rubbers include natural rubber, styrene-butadiene rubber (SBR), polybutadiene, polyisoprene. E

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