Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making named article
Reexamination Certificate
2001-07-19
2004-02-10
McPherson, John A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making named article
C430S009000, C430S017000, C430S018000, C430S346000, C156S272800, C152S151000, C264S400000, C264S446000, C264S482000
Reexamination Certificate
active
06689542
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a process for marking a pattern formed by at least two contrasting colors on a black or dark surface of a rubber article, in particular a tire, the said process using a laser in pulsed operation. This invention also relates to articles based on rubber and having a colored marking created using a process for marking using a laser in pulsed operation.
To create a marking on a tire surface with a predetermined pattern in a color different from the initial color of the black surface of the said tire and which contrasts therewith, it is known, for example from U.S. Pat. No. 5,478,426, during manufacture of the black tire to position a layer of rubber of a color other than black in the vicinity of the said surface in order to cover it with a layer of black rubber and then to carry out molding and vulcanization of the said tire in a mold. In order to reveal a pattern having the color of the subjacent rubber layer, the covering layer is removed over its entire thickness and in accordance with the said pattern. Removal of the outer layer is performed by means of a laser beam.
The process of creating a colored pattern on the surface of this tire by means of a laser is regulated to eliminate a fixed and pre-selected thickness of the covering rubber. For example, in the patent U.S. Pat. No. 5,478,426 it is proposed to use as the covering rubber a formulation which is a rubber mix having a greater sensitivity to the laser radiation than the subjacent rubber mix.
However, molding of the tire is accompanied by various movements in the rubber mixes under the action of molding forces and an increase in temperature of the said mixes, which causes them to soften; these movements are moreover enhanced by molding patterns formed in relief on the outer surface of the said tire. The result of these movements, which are due to the molding operation, is that the position of the common interface between the mixes of different colors, as measured with respect to the outer surface of the tire, can vary to a greater or lesser extent. It follows that to obtain a satisfactory colored pattern, it is frequently necessary to make a plurality of passages with the laser beam: if colored zones are not visible after the first passage, a second or even a third passage is indispensable.
On the other hand, this process has an adverse effect on the surface of the tire, since part of the thickness of the surface mix is removed to a greater or lesser depth, which over time may be the source of a relatively severe local fatigue of the rubber mix.
It should be noted that this process is expensive, since it requires a plurality of rubber mixes of different colors to be positioned, and moreover it is highly energy-intensive, since there is a necessity for a greater or lesser thickness of the rubber mix to be removed. It is also apparent that creating patterns formed by at least two parts of different colors is virtually impossible to do using this process, unless the colored mixes are disposed very precisely with respect to one another.
EP patent application 0 327 508 describes a process for inscribing organic materials using a laser, which consists in incorporating into the formulation of the said materials at least one adjuvant which removes color and is photo-sensitive to laser radiation, and a compound which does not remove color and is less photo-sensitive, which fulfils the role of pigment and whereof the color is revealed in a desired pattern after exposure to the laser. The action of the laser on the photo-sensitive adjuvant which removes color brings about a fading of the color of the said adjuvant, which then reveals the color of the compound which is not sensitive to the laser.
This process, while it does not disturb the surface of the object to be marked by comparison with the previous process described, does however require the presence of at least two photo-sensitive adjuvants which remove color, such as an azo or indanthrene pigment, to create a pattern formed by at least two distinct colors. It is known that these adjuvants are very expensive: to give an order of magnitude, at the time of filing the present application these products were almost one hundred times as expensive as the fillers commonly used in the tire industry, such as carbon black.
SUMMARY OF THE INVENTION
The object of the invention is to provide a process for marking with a laser a colored pattern formed by at least two distinct colors on the surface of a rubber article which does not have the disadvantages associated with the processes which have just been mentioned and which, among other things, does not cause apparent degradation to the condition of the surface of the marked article.
The process according to the invention enables marking to be created, in particular on a surface of a tire or any article having at its surface at least one rubber composition, this marking comprising a pattern formed by at least two different colors, the said colors contrasting with the dark or black color of the initial surface of the said tire or article, without removing material visible to the naked eye (and thus without having an adverse effect on the condition of the surface). The process according to the invention does not require recourse to the use of photo-sensitive pigments which remove color.
To this end, the process for marking a pattern formed by at least two parts of different colors on a rubber article having a dark or black surface for marking comprises the following steps:
preparing a light-colored rubber composition which can be used to manufacture the article in such a way as to form at least part of the surface intended to be marked, the said composition having at least one elastomer and at least two coloring agents of different light colors giving the said composition its initial color after mixing;
incorporating into the previously obtained composition a masking agent in a quantity of less than 15 ppc (that is, 15 parts by weight per hundred parts of elastomer) to darken and/or mask the initial color of the rubber composition;
building up or molding the article having at its surface at least the dark or black rubber composition;
creating the first part of the pattern on the said surface by means of a laser supplying a pulsed beam of appropriate characteristics for interaction with the masking agent, the said pattern obtained having a light color and contrasting with the dark or black color of the adjacent surface of the article (this color substantially corresponds to the color resulting from the blend of coloring agents);
on the first part of the pattern, creating the second part of the pattern in a different color from the color of the part of the pattern obtained in the preceding step, by means of a laser supplying a pulsed beam of appropriate characteristics for interaction with one of the coloring agents present in the material after the first step.
This last operation of the process may of course be repeated to reveal other pattern parts of different colors from the first two colors obtained; all that is necessary for this is to introduce an appropriate number of coloring agents of distinct colors into the initial composition.
By a pulsed beam of appropriate characteristics for interaction either with the masking agent or with a coloring agent, there is understood here a beam obtained for example by means of a laser of the YAG type having a frequency multiplier and capable of supplying a series of pulses of pulse durations appropriate for interaction with the said masking or coloring agent in order to eliminate it selectively; these pulse durations are preferably selected to be between 300 nanoseconds and a few tens of nanoseconds.
By a coloring agent of light color, there is understood a coloring agent having a color which is essentially different from black and capable of interacting with a laser beam supplying pulses having specific characteristics as regards frequency/pulse duration/wavelength which are appropriate to extract the said agent.
By a light-colored rubber comp
Baker & Botts L.L.P.
McPherson John A.
Michelin & Recherche et Technique S.A.
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