Coating processes – Direct application of electrical – magnetic – wave – or... – Pretreatment of substrate or post-treatment of coated substrate
Reexamination Certificate
2000-11-08
2003-07-15
Beck, Shrive P. (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Pretreatment of substrate or post-treatment of coated substrate
C427S256000, C427S282000, C427S286000, C427S487000, C427S492000, C427S508000, C427S510000, C427S511000, C427S514000, C427S554000, C427S555000, C427S558000, C427S596000, C427S400000, C427S346000, C427S372200, C427S375000, C427S384000, C427S385500, C427S393500, C427S553000
Reexamination Certificate
active
06592949
ABSTRACT:
The invention relates to a method of marking plastics surfaces, especially with plastics-based compositions.
It is known to mark metal, glass and ceramic surfaces using mixtures comprising a temperature-resistant chromophore and finely ground glass. This mixture is first applied to the surface in question. The surface is then heated locally, i.e., at every point where marking is to take place and the mixture has been applied beforehand, using a laser of appropriate wavelength, in a very short time, until the melting point of the ground glass is reached. The chromophores, usually solid inorganic pigment particles having a diameter of approximately 10 &mgr;m, absorb the incident radiation without themselves melting, the surrounding glass mass melting as a result of the absorption of energy by the pigments themselves. The resulting melt then bonds locally with the surface in question and forms a continuous, abrasion-resistant covering. The unfixed portions, i.e., those where marking has not taken place, can be washed off again thereafter.
This method is very rapid and reliable and produces a stable, clear mark on the respective surfaces.
To date, an analogous method for the marking of plastics surfaces has not existed.
It is an object of the present invention to provide an analogous or at least similar method for the marking of plastics surfaces and a corresponding composition which may be used for marking. A hurdle in the way of the present invention relative to the methods described in the prior art is that the temperature window within which plastics are in the melted state without undergoing decomposition is narrow.
We have found that this object is achieved by the method of the invention as claimed in claim
1
of the present invention and by the corresponding composition as claimed in claim
11
of the present invention. Further advantageous embodiments are specified in the subclaims.
Accordingly, the invention provides a method of marking a plastics surface, said method comprising at least the following steps:
a) applying a composition comprising at least one coloring component to a plastics surface,
b) irradiating the plastics surface with light from a light source.
In one preferred embodiment, the light source is a laser, preferably a laser with a variably adjustable wavelength. In addition to a laser, however, all other suitable light sources are conceivable.
When a laser is used as the light source, its output, wavelength and write speed are determined as a function of the composition of the plastics surface and of the makeup of the composition. Owing to the narrow temperature window to be observed, it is necessary to operate with relatively low (local) energy, since otherwise there is a risk of decomposition of the plastics constituents. For this purpose, during the marking operation it is preferred not to pass over the target area once, as is conventional, but rather two or more times, possibly by moving the light source and/or the target surface backward and forward.
The primary aim of the above method is to fix the composition locally by means of radiation. For this purpose, at least part of the composition and/or part of the plastics surface must be fully or partly melted, after which a firm bond is formed between the locally fixed composition and the plastics surface.
The best bonds—i.e., the mechanically most solid bonds—between plastics surface and the composition are formed when during irradiation both components are liquefied and in this liquid state mix together at the molecular level at the interface, so that the phase boundaries virtually disappear. For this, however, the plastic of the plastics surface must be meltable and the temperature must be maintained until the phase boundary between composition and plastics surface has disappeared. Furthermore, the plastics fractions of the composition, where present, and the plastic of the substrate must be at least partly miscible with one another.
Accordingly, the composition comprising at least one coloring component preferably also comprises at least one plastics component. This component preferably comprises fine plastics particles. The plastics component may be selected arbitrarily from all meltable plastics which in the fully or partly melted state are highly mobile and possess film-forming properties. Depending on the surface which is to be provided with a marking, these plastics are selected freely from thermoplastics and thermosets. Particular plastics that may be mentioned include polyether urethanes and polyester urethanes, polyvinyl chloride, alkyd resins, phenolic resins, polyolefins, especially polyethylene homopolymers and copolymers, epoxy resins, polyesters, polystyrenes, styrene-acrylonitrile copolymers, polybutylene terephthalates, polyamides, and acrylic resins.
Also very suitable for use are the known powder coating or powder slurry systems, which comprise appropriate plastics and pigments in particle form, together if appropriate with a solvent.
Good adhesion is also produced when only the composition forms a film which adheres well to the unmelted plastics surface. Here too, the plastics fraction of the composition should be compatible with the plastics surface, should be able to wet this surface well in the melted state, and should subsequently adhere adequately.
It is also possible, however, to use a composition merely comprising as coloring component an organic or inorganic pigment and an appropriate solvent, such as THF, aliphatic or aromatic hydrocarbons, such as hexane, cyclohexane, toluene, etc.
The at least one coloring component of the composition is preferably temperature stable. For the purposes of the present invention, “temperature stable” means that its melting point is higher than the temperatures to which it is or may be exposed during implementation of the method of the invention. Coloring components which may be used include both organic and inorganic, temperature-stable pigments. Specific pigments that may be mentioned include naturally occurring inorganic pigments, such as chalk, ocher, umber, green earth, graphite, for example; synthetic inorganic pigments, such as white pigments, e.g., titanium dioxide, lead white, zinc white, lithopones, and antimony white, for example; black pigments, e.g., carbon blacks, black iron oxide, manganese black, and cobalt black, for example; color pigments, e.g., lead chromate, red lead oxide, zinc yellow, zinc green, cadmium red, cobalt blue, Prussian blue, ultramarine, manganese violet, cadmium yellow, Schweinfurt green, molybdate red and molybdate orange, chrome orange and chrome red, red iron oxide, chromium oxide green, and strontium yellow; and luster pigments, such as zinc powders or lead powders and pearluster pigments, for example, naturally occurring organic pigments, such as sepia brown, gamboge, bone charcoal, cassel brown, indigo, and chloropyl, for example; synthetic organic pigments, such as azo dyes, indigoids, phthalocyanines, those of the Heliogen type, isoindolinone pigments, perylene pigments and perinone pigments, for example; and also colored plastics, such as those, for example, composed of monomers which themselves in turn have a chromophoric group, and also mixtures of polymers with coloring substances. It is also possible to use what are known as composite pigments, i.e., SiO
2
particles with a colorant coating, for example. Further pigments suitable for use, and details on pigments in general, may be found in Ullmann, “Enzyklopädie der technischen Chemie”, 4th edition, vol. 18, VCH-Verlag, Weinheim, and also Römpp's Chemielexikon, CD version 1.5, Georg Thieme Verlag 1998, in each case under the entry on Pigments, whose content in this respect is incorporated in its entirety by reference into the present specification.
Preferably, the at least one coloring component is dispersed uniformly in the at least one plastics component, it being possible for the latter in turn to be uncolored or colored itself.
Furthermore, the actual plastics component or the actual individual fine plastics particles may be chromo
Polke Reinhard
Reimann Manfred
Schäfer Michael
Welz Martin
BASF - Aktiengesellschaft
Beck Shrive P.
Keil & Weinkauf
Kolb Michener Jennifer
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