Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2002-12-23
2004-07-27
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S247000, C524S575500
Reexamination Certificate
active
06767945
ABSTRACT:
FIELD OF THE INVENTION
A green tire reinforced with carbon black is provided with a sidewall composition which upon being cured presents a glossy or shiny black surface. The terms “glossy” and “shiny” are equivalent terms used interchangeably herein, each being measured by reflectivity in a meter designed for the purpose, such as an Erichsen Pico Glossmeter Model 500. Known sidewall compositions comprising an unsaturated rubber, whether predominantly synthetic or natural (1,4-cis polyisoprene) rubber, suffer from weathering due to exposure to atmospheric conditions, including exposure to UV (ultraviolet) light, ozone and high humidity. Such exposure results in fatigue cracking due to continual flexing of the tire sidewall under operating conditions. It is desirable to maintain a cosmetically pleasing appearance of the sidewall without sacrificing the performance characteristics of the sidewall compound.
BACKGROUND OF THE INVENTION
Tire appearance is a major factor in influencing a customer's perception of tire quality and results in purchase of the tire by the customer. Pneumatic rubber tires mounted on wheel rims of a vehicle are visually appraised, typically, only in an elevational view which presents the tires' sidewalls. In the competition for visual attention, the wheel rim easily wins. However, granted the arresting design of a state-of-the-art wheel rim, the drab, dull grey-black appearance of the sidewall denigrates the visual impact of the wheel; it becomes a detrimental distraction and a problem to be coped with, first, when the tire is sold in a salesroom, and then, by the customer who purchased the tire.
A typical mold which is used to cure tires continuously to produce approximately 100 tires during a 24 hr period, is refurbished, that is cleaned and refinished to remove fouling, after about 1500 cures. The period over which tires are produced without having to clean the mold's sidewall surfaces is referred to as a “clean run”. The “polish” or “finish” at the beginning of a clean run, and the ability of the mold's surface to combat fouling determines, to a large extent, the length of a clean run. To at least the same, if not a greater extent, the length of a clean run is determined by the chemical interaction of ingredients in the sidewall compound. An extension of the clean run of only 10% is economically significant and a greater extension is of major significance.
An uncured sidewall surface of a typical green passenger tire has a gloss no higher than 10; a typical truck tire has an even lower gloss. Over a typical number of curing cycles (“cures”) in a mold, sidewalls have an average gloss lower than 10, typically in the range from about 1 to 6. If refurbished to minimize fouling, a hard smooth chromed surface on a sidewall mold produces a gloss in the range from about 5-15, with a polished surface giving a higher gloss up to about 50 with a 8-microfinish, but upon exposure outdoors over a period of one month, the gloss falls to 5 or less.
To date, one generally copes with the problem by coating the sidewall with a thin protective film, whether liquid or solid, of a glossy compound, e.g. a silicone-containing fluid sprayed or wiped onto a dry and clean sidewall; or a film of polymer such as a waterborne polyurethane or polyepoxide as disclosed in U.S. Pat. No. 6,093,271 to Majumdar, and in WO 01/94453 A1 to Cottin et al.; or by coating with a polyepoxide. Because all sidewalls are subjected to sunlight and oxidation, exposure to ultraviolet light, ozone and high humidity robs black sidewalls of such gloss as they may have had when freshly cured. Continuous distortion under normal operating conditions (of tires), causes high stress and results in fatigue cracking. Abrasion against curbs on paved roads and gravel and stones in unpaved roads, greatly shortens the period of its effectiveness of any coating. Moreover, sidewalls of tires operated on dry pavement quickly acquire a coating of road grime; when run on wet roads, as they are expected to be, they are also coated with mud, in either case requiring repetitive cleaning. Such cleaning damages any thin protective film. Hard experience teaches that the gloss attributable to coatings, to date, is short-lived, lasting less than a month in an outdoor environment. Nevertheless, assuming a coating is highly effective for the purpose, applying the coating is an additional step which the invention disclosed herein now makes unnecessary.
Still another approach to providing a cosmetically enhanced sidewall is to dress up a black sidewall with a band of decorative white rubber, its color due to being heavily reinforced with a light-colored inorganic pigment such as titanium dioxide or calcium carbonate. In addition, or as an alternative, white or palc rubber appliques, whether logos or trade names, are applied to the sidewall to advertise a car owner's choice of a manufacturer. However, despite the additional expense, the impact of such cosmetic improvements is also relatively short-lived because colored rubber sidewalls and appliques, whether light-colored or dark, are difficult to keep clean, particularly if white, not only because of road grime and mud unavoidably applied exteriorly from the environment, but also because of well-known staining due to conventionally used ingredients of a black sidewall compound, which ingredients include processing oils, antiozonants, antioxidants, zinc oxide and other ingredients in a typical recipe.
Numerous prior art references are directed to sidewall compositions which improve the performance of the sidewall with little or no regard as to what the reflectivity of the sidewall might be, and no suggestion that the glossy or shiny visual appearance of the sidewall, one way or another, might be affected in any way. For example, U.S. Pat. No. 5,066,721 to Hamada et al discloses a silane compound-modified rubbery polymer (“silanated rubber”) which may be blended in an amount not less than 10% by weight, with a conventional rubber compound to allow the blend to incorporate from 5 to 90 parts of silica per 100 parts of reinforcement, the remaining reinforcement being carbon black. The effectiveness of the silica is attributed to a silane coupling agent and the silanated rubber in the blend. In a typical recipe (see col 11, lines 33-45) 100 parts by weight of a silane compound-modified rubber (see col 11, line 20) contains 40 phr of silica and 1.5 phr of trioethanolamine. Though the function of the triethanolamine is unstated, it appears to be as a condensation catalyst or an accelerator for the silane coupling agent, and as such it is unclear whether the triethanolamine survives in the cured compound. Such a high level of a tertiary alkanolamine (“t-alkanolamine”) such as triethanolamine deleteriously affects the physical properties, particularly the tear strength, of a typical black sidewall compound which contains at least 30 phr of carbon black. A conventional black sidewall compound blended with at least 10 phr of silanated rubber is distinct from a typical black sidewall compound in which, when cured, the t-alkanolamine is reacted with one or more of the ingredients in the sidewall recipe leaving no evidence of the t-alkanolamine originally present. Moreover, a preferred black sidewall compound contains less than 10 parts of silanated rubber per 100 parts, preferably, essentially no silanated rubber.
Several other references refer to shiny sidewalls on cured tires but fail to state what criterion was used to determine that the sidewall was “shiny” or whether the shine lasts for any substantial length of time after the tire is removed from the mold, or whether the shine, whatever its original level, can be maintained after exposure to sunlight, and/or to multiple washings with soap and water.
A shiny sidewall is most readily provided by using a highly polished mold surface in contact with the sidewall. To produce a significant number of tires in such a mold, its polished surface must resist fouling. Efforts to do this have produced fouling-resistant coatings
Hahn Bruce Raymond
Majumdar Ramendra Nath
Hendricks Bruce J.
Lobo Alfred D.
The Goodyear Tire & Rubber Company
Young, Jr. Henry C.
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