Optics: measuring and testing – Of light reflection
Reexamination Certificate
2000-10-05
2001-09-18
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Of light reflection
Reexamination Certificate
active
06292264
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for the contactless measurement of optical parameters on coating layers applied from liquid coating agents and also to a device for performing the method.
In the lacquer industry it is necessary, for example, in the production, standardization and development of lacquers to perform optical measurements, in particular colorimetric measurements, on the lacquers, for example to obtain information about whether the lacquers meet the required optical parameters, for example the required colour intensity. This may then be followed by necessary correction steps. For example, in the production of pigmented coating agents, shading steps are necessary to establish the required shade precisely. After every shading step, the lacquer has to be lacquered onto a metal test sheet and dried or cured. The “actual-state metal sheet” obtained in this way can then be compared with a “required-state metal sheet”. In the case of plain colouring, it may be necessary, in addition, to produce initially a white-lacquer mixture of every shade. In the standardization of pigment pastes, this is additionally supplemented, furthermore, by lacquering with suitable binders prior to the application as an additional working step. The work, time and cost expenditure is appreciable.
In principle, optical measurements may be made not only on applied and dried or cured lacquer layers, but also on wet lacquers if the correlation between optical measurement results on wet lacquer and on the applied and dried or cured lacquer layer is known. Whenever possible, there is therefore the desire to perform optical measurements on wet lacquers and colorimetric methods have been developed for wet lacquers. For example, measuring cells are known for wet-lacquer measurement. These are, for example, glass measuring cuvettes that can be placed in front of the measurement aperture of a colorimeter. The disadvantage of these simple measuring cells is that the accuracy of the measurement results achieved with them is unsatisfactory, for example due to rapid sedimentation of the lacquer in the cuvette or to the influence of the glass as an intervening medium, for example as a result of physical interactions. The method is completely unsuitable for colorimetric measurements on special effect lacquers.
DE-A-25 25 701 describes a method of colorimetric measurements on liquid lacquers. In this method, a continuous film of the lacquer to be investigated is formed and a portion of said film is measured colorimetrically. In this method, the lacquer film may be a film that moves with a substrate or a film moving past over a substrate with laminar flow. In the first case, the substrate is a measuring disc that can be rotated around a horizontal axis and, in the second case, it is a plate-like body having an approximately perpendicular surface which the lacquer runs down and drips off at the bottom. In both cases, the lacquer is applied by means of a casting tank having an outlet slit to the particular substrate. A disadvantage of said method if a rotatable measuring disc is used is that it is only possible to work with an acceptable disc size if colorimeters are used that have a measurement aperture disposed laterally on the housing. In the case of colorimeters having centrally disposed measurement apertures, extremely large discs have to be employed. A disadvantage of colorimetric measurements is that the measurement result, in particular in the case of special effect lacquers, vary for one and the same wet-lacquer sample depending on the point of measurement on the rotating disc. If the plate-type body having an approximately vertical surface is used, it is only possible to work with wet-lacquer sheet thicknesses above the sagging limit. In particular, colorimetric measurement can consequently not be meaningfully performed on special effect lacquers.
DE 36 38 932 C2 describes an on-line method of continuously determining the coating amount of silicones on a continuous paper or plastic web to be coated. In this case, the gloss before and after the coating is determined with two separate measuring units and the amount applied is determined therefrom.
SUMMARY OF INVENTION
The object of the invention is to provide an improved method for the contactless measurement of optical parameters on coating layers applied from liquid coating compounds. The method is intended to make it possible to deal with a wide variety of technical problems and is therefore intended to have as many degrees of freedom as possible in regard to its practical execution, i.e. it is intended to be as universally applicable as possible. The method is intended, in particular, also to enable the reproducibility defects described above to be avoided.
The object can be achieved if a coating, layer composed of a liquid coating compound is produced on a carrier strip stretched over a drive roller and one or more tensioning rollers and closed upon itself and a contactless optical measurement is performed on said coating layer.
The object of the invention is therefore a method for the contactless measurement of optical parameters on a plane coating layer applied from a liquid coating compound or a liquid component of a coating compound using one or more optical measuring instruments, which is characterized in that the coating layer is applied to the outer surface of a circulating carrier strip that is stretched across a drive roller and one or more tensioning rollers and is closed upon itself and then the contactless optical measurement is performed on the coating layer at a plane point in the carrier strip, wherein the carrier strip may be circulating during the measurement.
In the method according to the invention, a coating layer composed of a liquid coating compound is first applied to a circulating carrier strip (closed upon itself) that is stretched over a drive roller and one or more tensioning rollers, for example up to 3 tensioning rollers. The description below explains the method according to the invention on the basis of an embodiment of a carrier strip stretched over a drive roller and only one tensioning roller. It is clear to the person skilled in the art that the principle of the present invention is in no way limited to this embodiment.
The carrier strip has a flat outer surface and may be composed of standard materials, for example of plastic, rubber or metal. For example, this may involve a plastic film or a seamlessly welded stainless-steel strip. The outside of the carrier strip to be coated with coating compound may be formed as unprecoated and, optionally, as reflecting, for example as a specular surface, for example it may be metallized or, if the carrier strip is composed of metal, it may be polished. It is also possible that the outside of the carrier strip has a one-layer or multilayer preliminary coating, for example a cured primer or filler layer, such as those encountered, for example, in decorative multilayer lacquerings underneath colouring and/or effect producing base lacquer layers. The finish of the outside of the carrier strip expediently depends on the particular technical problem to be dealt with by means of the method according to the invention. Depending on expediency, the carrier strip may be discarded after completion of an optical measurement or measurement series, for example if it is composed of an inexpensive plastic film or it is cleaned, for example by means of a skimmer and/or with the aid of cleaning agents, for example organic solvents.
The carrier strip is stretched across a drive roller and a tensioning roller spaced apart from it so that the outside of the carrier strip forms a plane, uncurved surface between the two rollers. It is advantageous that the surface of the outside of the carrier strip stretched between the two rollers can assume a horizontal or vertical position or a position in between for the purpose of the method according to the invention. This increases the degrees of freedom for performing the method according to the invention and application a
Cramm Joachim
Rupieper Paul
Voyé Christian
E. I. Du Pont de Nemours and Company
Font Frank G.
Stafira Michael P.
Tessari Joseph A.
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