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...
Patent
1998-04-01
1999-06-29
Hoke, Veronica P.
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...
430200, 522 2, C08K 507, H01M 604, C08F 246
Patent
active
059169435
DESCRIPTION:
BRIEF SUMMARY
This invention relates to articles that can be marked and to marking of articles, and especially, although not exclusively, to laser marking of articles.
Laser marking methods have become widespread in recent years for applying visible marks such as alphanumerics indicia to various articles, for example to electrical wires and cable. Laser writing on plastics, polymers, thin films (such as cellophane), paints, and varnishes can be achieved by burning, melting or ablation of the surface. These types of laser writing can lead to surface damage and reduce the durability of the material (e.g. the insulating coating on fine wires). Other processes, for example, foaming of the material or partial carbonisation of the material to provide a visible mark, can lead to damage if the energy of the laser pulse is too high or lead to a mark which lacks wear resistance if the energy of the laser pulse is too low.
Alternative processes comprise the application of lacquer to the surface of the plastic so that as the lacquer is ablated by the laser energy, exposing the plastic to produce a contrasting mark (this process involves risk of surface damage and the additional coating process adds substantially to the cost) or irradiating a material that will change colour when subjected to a pulse of laser energy. In the latter process, an ultraviolet laser, such as an excimer laser, is normally employed and the article contains a material that will change colour when subjected to the laser radiation.
Typically, titanium dioxide is employed in a concentration of 5-10% by weight but such systems, containing the titanium dioxide as a suspension, can suffer from the disadvantage that the concentgration of titanium oxide can adversely affect the physical properties of the article.
A recent patent describes yellow and red dyes incorporated into plastic to give an orange lacquer which is bleached by lasers to generate a yellow mark on a red background (Ciba Geigy EP 0327508). This process lacks the required contrast for laser writing in many instances. In addition, EP-A-0 572 178 describes resin compositions for laser marking which comprise a thermoplastic resin, one or more compounds selected from tetrazole compounds, sulfonylhydrazide compounds, nitroso compounds and azo compounds, carbon black and optionally a flame-retarding agent.
It is an object of the present invention to provide a system in which the material that will change colour can be incorporated into a range of highly visible mark after irradiation. Since the material may have to be incorporated into the whole product it is preferably of relatively low cost, i.e. it is preferably capable of being prepared in high yield and purity from inexpensive reactants in a simple one-step process.
According to one aspect, the invention provides an article of manufacture which has a surface formed from a polymer composition, the polymer composition incorporating a quantity of a compound of the general formula I ##STR1## wherein
R.sub.1 and R.sub.4 which may be the same or different, each is a straight-chain, branched-chain or cyclic alkyl group or an aryl group, which groups may be unsubstituted or substituted and may include one or more hetero atoms;
R.sub.2 is a straight-chain, branched-chain or cyclic alkyl group or an aryl group which may be unsubstituted or substituted and may include one or more hetero atoms, but which does not include any eliminatable .alpha.-hydrogen atoms; and
R.sub.3, which may be fused with or separate from R.sub.2 or which may be fused with or separate from R.sub.4, is straight-chain, branched-chain or cyclic alkyl group or an aryl group which may be unsubstituted and many include one or more hetero atoms;
provided that, whenever water is eliminated from the compound of the general formula I to form a cyclopentadienone, the groups R.sub.1 and R.sub.4 together have sufficient conjugated unsaturation to produce an absorption band in the visible spectrum.
According to another aspect, the invention provides a method of marking an article which has a surface f
REFERENCES:
patent: 4371711 (1983-02-01), Saito
patent: 5373039 (1994-12-01), Sakai et al.
Heller Harry George
Vincent Mark John
BICC Public Limited Company
Hoke Veronica P.
Nath Gary M.
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