Coating processes – Direct application of electrical – magnetic – wave – or... – Polymerization of coating utilizing direct application of...
Reexamination Certificate
2000-10-02
2003-03-04
Padgett, Marianne (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Polymerization of coating utilizing direct application of...
C427S492000, C427S508000, C427S514000, C427S521000
Reexamination Certificate
active
06528126
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a process for the multi-coat lacquering of substrates using radiation-curing coating compounds. The process can advantageously be applied in vehicle and industrial lacquering, preferably in vehicle refinishing lacquering.
In the wood coating industry in particular, UV technology has been the state of the art in coating and curing for some time. In other areas of application too, however, including vehicle lacquering, the use of coating compounds which can be cured by high-energy radiation has become known. The advantages of radiation-curing coating compounds, such as e.g. the very short cure times, the low solvent emission of the coating compounds and the very good hardness of the resulting coatings, are also exploited here.
In addition to suitable radiation-curing binders and photoinitiators, various types of radiation sources and possible processes for curing by means of high-energy radiation have also become known.
Thus, for example, in the UV coating of industrial goods in a continuous conveyor plant using radiation-curing binders or coating compounds, the UV radiation can be combined with a thermal treatment. This means that the actual curing process by means of UV radiation can, for example, be followed by a heating phase. The heating or thermal treatment can be applied, for example, by means of hot air, a hot plate or infrared radiation (IR radiation). The inventors of the present application have found, and described in the German patent application by the same applicants on the same date of application with the title “Verfahren zur Mehrschichtlackierung” [A process for multi-coat lacquering], that, for example, drying of the coating with IR radiation can take place before the UV irradiation and in this way various properties, such as e.g. inter-layer adhesion, weathering resistance and appearance, can be improved. Solvent evaporation times necessary after the application of the radiation-curing lacquer can also be reduced in this way. When using radiation-curing water-based lacquers in particular, a considerable shortening of the solvent evaporation phase is achieved in this way. Subsequent IR irradiation is advantageous when, for example, apart from the radiation-curing binders, other binders are contained in the lacquer which cross-link via an additional mechanism. In this case, complete curing can be achieved rapidly with subsequent IR irradiation.
A combination of UV and IR irradiation during the curing process in the broader sense can be achieved, for example, by continuously passing the UV source and IR source and/or the object to be irradiated in front of one another, or by discontinuously placing the UV source and IR source alternately in front of the object to be irradiated. Disadvantages of the processes described are that, on the one hand, in the continuous process, there have to be at least two zones for drying and curing (UV zone and IR zone) to be passed through and the UV and IR zones have to be separated from one another, e.g. by a glare shield, and that, on the other hand, in the discontinuous process, UV and IR sources have to be exchanged with one another in front of the object to be irradiated as a function of the number of irradiation intervals desired, the UV radiator generally not being operated during the IR drying phase. The latter discontinuous method, and the burn-in times necessary for each of the radiation sources, especially the UV radiators, generally have a delaying effect on the entire lacquering operation. Especially when the discontinuous method is used, e.g. in lacquering workshops, the vehicle throughput and thus, ultimately, the profitability of the workshop can be impaired in this way.
SUMMARY OF THE INVENTION
The object of the invention was therefore to provide a process for multi-coat lacquering using coating compounds that are at least partially radiation-curing, which enables UV irradiation and IR irradiation to be combined in a simple, economical and time-saving manner when curing radiation-curing coatings, without having to use an undesirably large amount of apparatus and therefore to operate cost-intensively.
The object is achieved by the process for multi-coat lacquering provided by the invention, by applying one or more fillers and/or other coats of coating compound on to an optionally pre-coated substrate and then a top coat consisting of a base coat/clear lacquer construction or of a pigmented one-coat finish, at least one of the coats in the multi-coat construction being prepared from a coating compound which is at least partially curable by high-energy radiation, and irradiating this (these) coat(s) with UV radiation and IR radiation, which is characterized in that a UV source having a proportion of IR radiation in its emission spectrum is used for the irradiation with UV and IR radiation and that, by alternately adding a UV filter and an IR filter and/or alternately adding and removing a UV filter or an IR filter in front of the UV source, at least two irradiation intervals are formed, during which irradiation is variously carried out with UV radiation, IR radiation or UV radiation and IR radiation simultaneously.
With the method according to the invention it is possible to use UV filters and IR filters alternately. It is also possible to work either with a UV filter or with an IR filter and to remove this alternately so that irradiation is performed with UV and IR radiation simultaneously. The two methods can be combined with one another so that irradiation intervals with UV radiation, IR radiation or UV and IR radiation together are formed alternately.
DETAILED DESCRIPTION OF THE INVENTION
The UV sources modified with an removable filter which can be used in the process according to the invention can thus be used quickly and easily as pure IR radiators.
Conventional UV sources can be used as a UV source in the process according to the invention, provided that they have a proportion of IR radiation in their emission spectrum. Such UV sources are known to the person skilled in the art and are generally accessible. The proportion of IR radiation necessary in the emission spectrum of the UV source is preferably a proportion of radiation in the short-wave range of IR radiation. This involves the wavelength range of about 700 to about 2500 nm. This range substantially corresponds to the emission spectra of conventional IR radiators that can be used in lacquer drying, which are in the range of 500 to 2500 mn, preferably 800 to 2000 nm. UV sources that can be used according to the invention thus have, for example, an emission spectrum, including the UV and IR emission proportions, in the range of 180 to 2500 nn, preferably 200 to 2500 nm, particularly preferably 200 to 2000 nm.
The UV sources common in practice and known to the person skilled in the art generally have a proportion of UV radiation in the emission spectrum of about 25%. In addition, there is a considerable proportion of IR radiation in the emission spectrum in each case. For example, the proportion of IR radiation can be up to about 60%.
Suitable UV sources for the process according to the invention are, for example, high-pressure, medium-pressure and low-pressure mercury vapor radiators. Of these, lamps with a lamp length of between 5 and 200 cm are common. Depending on the particular application and the radiation energy required, lamp and reflector geometry are coordinated in the conventional manner. The lamp output in each case can vary, for example between 20 and 250 W/cm (watts per cm lamp length). Lamps with outputs of between 80 and 120 W/cm are preferably used. The mercury vapor lamps can also optionally be doped by introducing metal halides. Examples of doped radiators are iron or gallium mercury vapor lamps.
Other examples of UV sources are gas-filled tubes, such as e.g. low-pressure xenon lamps. In addition to these continuously operating UV sources, however, discontinuous UV sources can also be used. These are preferably so-called high-energy flash devices (UV flashlights for short)
Feyrer Wolfgang
Kimpel Christine
Löffler Helmut
Maag Karin
Zeyen Jens
Benjamin Steven C.
E. I. du Pont de Nemours and Company
Padgett Marianne
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