Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2002-07-29
2004-07-20
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S213000, C525S232000, C525S238000, C525S241000
Reexamination Certificate
active
06765063
ABSTRACT:
The present invention relates to a pneumatic rubber tire having an integral innerliner of a rubber composition comprised of butyl rubber and/or halogenated butyl rubber and low molecular weight trans 1,4-polybutadiene rubber, wherein said rubber composition may also contain a minor amount of at least one additional, sulfur curable, elastomer.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 6,024,146 relates to a tire having an integral innerliner comprised of bromobutyl rubber, trans 1,4-polybutadiene rubber and, optionally, a minor amount of sulfur curable rubber.
Although the trans 1,4-polybutadiene rubber in U.S. Pat. No. 6,024,146 is broadly referred to, the specification specifically describes a high molecular weight trans 1,4-polybutadiene rubber having a preferable number average molecular weight value (Mn) measured by GPC (gel permeation chromatograph analysis) of greater than 130,000, although its first claim does not contain a molecular weight restriction. The specification observes that use of the high molecular weight trans 1,4-polybutadiene rubber in the tire innerliner rubber composition beneficially increases the green strength of the innerliner composition. Preparation of the trans 1,4-polybutadiene is recited as being prepared by batch polymerizing 1,3-butadiene in an organic solvent in the presence of cobalt octoate and triethyl aluminum as a catalyst system with a para alkyl substituted phenol as a catalyst modifier.
For this invention, a low molecular weight trans 1,4-polybutadiene rubber is prescribed having a number average molecular weight value (Mn) measured by GPC in a range of from 10,000 to 50,000 which is spaced apart from said high molecular weight trans 1,4-polybutadiene described in U.S. Pat. No. 6,024,146 by at least 80,000 molecular weight units and is thereby a significant and substantial departure from use of the aforesaid high molecular weight trans 1,4-polybutadiene rubber.
The low molecular weight trans 1,4-polybutadiene rubber for this invention may be prepared by polymerizing 1,3-butadiene monomer in an organic solvent (e.g. hexane) with a combination of triethylaluminum, barium thymolate and n-butyllithium (n-BuLi) as a catalyst complex system instead of the cobalt octoate and triethylaluminum based catalyst system utilized in said U.S. Pat. No. 6,024,146.
Historically, the inner surface of a pneumatic tire is typically comprised of a layer of a rubber composition designed to prevent or retard the permeation of air and moisture into the carcass from the tire's inner air chamber. It is often referred to as an innerliner. Innerliners have also been used for many years in tubeless pneumatic vehicle tires to retard or prevent the escape of air used to inflate the tire, thereby maintaining tire pressure. Rubbers, such as butyl rubber and halogenated butyl rubber, often referred to as halobutyl rubber, as well as blends thereof, are often used for such tire innerliners which are relatively impermeable to air.
Historically, the tire innerliner itself is normally prepared by conventional calendering or milling techniques to form a strip of uncured rubber composition of appropriate width which is sometimes referred to as a gum strip. Typically, the gum strip is the first element of the tire applied to a tire building drum, over and around which the remainder of the tire is built. When the tire is cured, the innerliner becomes an integral, co-cured, part of the tire. Tire innerliners and their methods of preparation are well known to those having skill in such art.
The use of the prescribed low molecular weight trans 1,4-polybutadiene rubber for this invention is considered herein to be significant to reduce cost of an associated rubber composition for a tire innerliner where a portion of halobutyl rubber content is replaced, while significantly maintaining a low strain stiffness property and providing a desirable low air permeability. This is considered herein to be significant because, in contrast, while a relatively high molecular weight cis 1,4-polybutadiene rubber would be expected to similarly reduce rubber innerliner rubber composition cost, such higher molecular weight polybutadiene would be more difficult to process because of its higher Mooney viscosity and would have a much higher air permeability property.
In the description of this invention, the term “phr” means parts by weight of an ingredient per 100 parts by weight of elastomer in a rubber composition unless otherwise indicated. The terms “rubber” and “elastomer” are used interchangeably unless otherwise indicated. The terms “cure” and “vulcanize” are used interchangeably unless otherwise indicated. The terms “rubber composition” and “rubber compound” are used interchangeably unless otherwise indicated.
SUMMARY AND PRACTICE OF THE INVENTION
In accordance with this invention a tire is provided having an innerliner rubber composition comprised of, based upon 100 parts of rubber (phr);
(A) from about 70 to about 98 phr of rubber selected from the group consisting of butyl rubber, chlorobutyl rubber, bromobutyl rubber and mixtures thereof;
(B) about 2 to 30 phr of a trans 1,4-polybutadiene rubber having a number average molecular weight (Mn) (as measured by GPC, or gel permeation chromatograph) of not greater than 50,000 and desirably in a range of from about 10,000 to about 50,000, a trans 1,4-content in a range of about 80 to about 85 percent, and a vinyl content of less than 5 percent;
(C) from zero to 30, alternatively from about 5 to about 15, phr of at least one elastomer selected from acrylonitrile/butadiene copolymer, styrene/butadiene copolymer, cis 1,4-polyisoprene natural and/or synthetic rubber and mixtures thereof.
A significant aspect of utilization of a low molecular weight trans 1,4-polybutadiene for the tire innerliner of this invention is improved processing with a substantially maintained low strain stiffness with a relatively small increase in air permeability.
While the trans 1,4-polybutadiene of aforesaid U.S. Pat. No. 6,024,146 is of a relatively high crystallinity, a significant aspect of this invention is the use of a low molecular weight trans 1,4-polybutadiene also of relatively high crystallinity to obtain the aforesaid rubber composition processing, physical property(ies) and suitable air permeability.
This is in contrast with using a low molecular weight trans 1,4-polybutadiene of relatively low or no crystallinity which would have much higher air permeability.
Thus a significant aspect of this invention is the combination of both low molecular weight and high crystallinity for the trans 1,4-polybutadiene for the tire innerliner rubber composition
A significance of relatively high crystallinity of the low molecular weight trans 1,4-polybutadiene is considered herein as being advantageous for maintaining low air permeability and low strain cured stiffness while providing improved processing.
The relatively high crystallinity aspect of the low molecular weight trans 1,4-polybutadiene, as measured by differential scanning calorimeter (DSC) at a heating rate of 10° C. per minute, is evidenced by two relatively sharp melting point peaks, namely a first peak at about 36° C. (about 30° C. to about 40° C.) and a second peak at about 44° C. (about 40° C. to about 50° C.). It also has a Tg (glass transition temperature determined at a temperature rise of about 10° C.) of about −91° C. In contrast, the high molecular weight trans 1,4-polybutadiene has two melting point peaks with a first peak in a the range of 35° C. to about 45° C. and a second peak in a range of about 55° C. to about 65° C.
In general, the low molecular weight trans 1,4-polybutadiene polymer has a microstructure composed of a trans 1,4-content in a range of about 80 to about 85 percent, a vinyl 1,2-content in a range of about 2 to about 5 percent with the remainder being primarily of a cis 1,4-content in contrast to a vinyl content value of from 5 to 20 weight percent and a cis 1,4-content of from 2 to 15 weight percent of the high molecular weigh trans 1,4-polybutadiene polymer prescribed
Beers Roger Neil
Halasa Adel Farhan
Hsu Wen-Liane
Sandstrom Paul Harry
Nutter Nathan M.
The Goodyear Tire & Rubber Company
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