Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-05-30
2004-03-02
Mulcahy, Peter D. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S432000
Reexamination Certificate
active
06699924
ABSTRACT:
BACKGROUND OF INVENTION
The present invention relates to rubber compositions intended for use in the manufacture of tires.
More particularly, the invention provides colored rubber compositions intended to form at least part of the outer surface of tires. The term “colored” is understood here to exclude the color black, but to include all colors, including white.
The compositions of the invention are intended to cover the surfaces of tires at least partially, whatever the nature and the composition of the rubber mixes on which they are deposited. Since the compositions form a surface covering, they are more particularly intended to cover what are called “non-wearing” surfaces of tires, that is to say those which are not in contact with the road under normal conditions of use. Thus, such colored compositions according to the invention, which are in particular for decorative and marking purposes, may constitute, at least in part, the outer surface of a tire sidewall or the bottoms of tread patterns of the tread.
It is known that, vulcanized rubber compositions of essentially unsaturated natural and synthetic diene rubbers, because of the presence of double bonds in their molecular chains, are likely to deteriorate more or less rapidly after prolonged exposure to the atmosphere, if they are not protected, as a result of known oxidation mechanisms. These complex mechanisms have been described, for example, in the following documents: ref. [1
]: “Antidegradants for tire applications
” in “
Tire compounding
”, Education Symposium No. 37 (ACS), Cleveland, Communication I, October 1995; and [2
]: “Antioxidants
” in Encycl. Polym. Sci. and Eng., 2d Edition, Vol. 2, 73-91.
It has been gradually possible to inhibit these oxidation phenomena as a result of the development and sale of various antioxidants, the most effective of which are, known derivatives of quinoline (“TMQ”), or derivatives of p-phenylenediamine (“PPD” or “PPDA”), which are even more active than the former, such as, for example, N-1,3-dimethylbutyl-N′-phenyl-p-phenylenediamine (6-PPD). These TMQ and PPD-type antidegradants, singly or in combination with each other, have found widespread systematically use (see, e.g., refs. [1] and [2] above) in conventional tire rubber compositions, filled at least in part with carbon black, which imparts thereto their characteristic black color.
However, the above-mentioned antioxidants, particularly the TMQ or PPD derivatives, are not light-fast. Under the action of UV radiation, they produce colored chemical types which cause an adverse color change of the rubber compositions, staining them dark brown. It is clear that this characteristic rules out the use of such agents within white, clear or colored compositions. Moreover, such characteristics of these antioxidants also cause problems when used in compositions that come into contact with white, clear or colored compositions. If nothing is done to prevent it, the antioxidants will naturally migrate into and onto the surface of the white, clear or colored compositions and stain them.
This is why it is extremely complicated to develop colored compositions intended to cover part of the outer surface of tires and to resist the staining due to the antioxidants present in the other compositions used in tires.
The majority of the solutions that have been considered are based on the use of constituents, that have impereability properties, which may be introduced into rubber compositions. In the tire field, it is known to make use of the impermeability properties of butyl rubber. However, using butyl rubber also creates a number of problems.
In order to make it possible to produce white or colored sidewalls, it has been envisaged to modify the structure of the tires by providing “screen” compositions containing a large amount of butyl rubber in order to prevent the migration of the staining antioxidants. Such screen compositions are intended to separate the white compositions from the other compositions making up said tires. It will readily be understood that such embodiments are liable to adversely affect the properties and performance of the tires concerned, to the extent that significant modifications are made to their structure. Furthermore, it is known that large proportions of butyl rubber in compositions create problems of adhesion of the latter to the other compositions present in the tire.
Other solutions have consisted of directly introducing butyl rubber into the colored compositions. Thus publication CA-2 228 692 describes a composition for white sidewalls which uses an elastomeric base containing a majority of butyl rubbers in order to constitute a barrier to the staining antioxidants. These solutions make it possible to avoid certain modifications of the structure of the tire, but do not rectify the problems linked to adhesion. This is why, since the interface obtained between white sidewalls and the other mixes present in the tire is fragile, such compositions for white sidewalls can only be deposited on very limited non-stressed parts of the sidewall, in order to avoid detachment at interfaces of the compositions.
Additional solutions involve producing compositions intended to be used within the mass and not just at the surface, which abandon the use of the antioxidants based on PPD or TMQ derivatives within these compositions. However, because such antioxidants are very effective, replacing them requires providing complex protective systems, such as those described in the publication WO 99/02590. It should furthermore be noted that it is not generally possible, in all the compositions present in the tire, to replace the antioxidants based on PPD or TMQ derivatives, which are very high-performance. Thus, because of their migration, it is necessary to provide a solution, such as that using butyl rubber, the drawbacks of which have already been mentioned.
SUMMARY OF THE INVENTION
The invention is directed to colored compositions capable of forming part of the outer surface of tires, which overcome the disadvantages of prior compositions.
The Inventor has surprisingly discovered that sulphur-vulcanizable, colored rubber compositions having a very high content of titanium dioxide or zinc monoxide, in an amount of more than 100 parts per 100 parts by weight of elastomer (phr) make it possible to produce colored surface compositions for tires which are capable of being deposited directly on compositions containing staining antioxidants without requiring the use of barrier agents typical of antioxidants, and preserve their surface color.
Although the photocatalytic activity of titanium dioxide which causes degradation of organic or biorganic molecules is known, this compound is generally used in colored rubber compositions to impart a white coloration thereto, when present in an amount of 10 to 55 parts to one hundred parts by weight of elastomer (phr), as set forth in publication CA-2 228 692.
It was thus surprising that such large quantities of titanium dioxide could be used in rubber compositions without adverse effect, since (1) its ability to degrade double bonds is contrary to desired protective characteristics provided for in the tire in order to avoid this degradation by oxidation, and (2) the fact of having a composition with a very low ratio between the amount of elastomeric base and the amount of mineral filler would lead one skilled in the art to doubt much that such a composition in the form of a mix could be produced, rather than the composition remaining in the form of a powder, and to know that such a composition would not become detached from the other compositions of the tire over time.
Zinc monoxide also has advantageous photocatalytic properties, although it is not as well used as titanium dioxide. While zinc monoxide is often used in very small amounts, of the order of several parts by weight per one hundred parts of elastomer in tire rubber compositions, for its participation in the vulcanization system of the rubber polymers, it has not been used at all for its colo
Baker & Botts L.L.P.
Michelin & Recherche et Technique S.A.
Mulcahy Peter D.
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