Optics: measuring and testing – By shade or color
Reexamination Certificate
2000-12-11
2003-06-24
Evans, F. L. (Department: 2877)
Optics: measuring and testing
By shade or color
C356S244000
Reexamination Certificate
active
06583878
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a process for measuring optical, especially colorimetric, parameters on liquid, coloured media, especially on wet lacquers, and to an apparatus for carrying out the process.
In the lacquers industry it is necessary in the various production, standardisation and development stages of lacquer manufacture and lacquer development to carry out optical measurements on the lacquers for the purposes of quality control. In that manner, information is obtained as to whether the lacquers meet the required optical parameters, for example the required colour strength, and any corrective steps that are required can be taken. Measurement may in principle be carried out on wet lacquers or on applied and dried, or hardened, lacquers. In the standardisation of lacquers, for example in the manufacture of standardised mixed lacquers or pigment pastes for automotive repair, measurement on applied and hardened lacquers, for example on coated metal sheets, is essential because that method, in comparison with measurement on wet lacquers, is concerned with the appearance of the film of lacquer finished by drying or hardening, and ultimately it is the perceived colour of the applied lacquer which is important and not that of the wet lacquer.
However, measurement on applied lacquers is relatively complicated because, before measurement can be carried out, coated metal sheets, so-called test or sample plates, must first be produced. To that end, for example in the case of plain colours, a mixture of each colour with white lacquer must first be prepared and then applied and dried or hardened. In the standardisation of pigment pastes, there is the additional step of lacquering-up with appropriate binders before the application.
In particular applications, however, such as, for example, in the first test steps in the standardisation or manufacture of lacquers, and also for delivery monitoring, it is sufficient, in order to determine intermediate results, to carry out the calorimetric measurements initially on the wet lacquer, which can be effected substantially more rapidly and less expensively than measurements on the applied hardened lacquer. Colour-measuring devices that can be used are known and commercially available. Corresponding measuring cells for wet-lacquer measurement are likewise known. Such cells are, for example, cylindrical or cuboidal glass measuring vessels, which are placed in front of the measuring aperture of the colour-measuring device. A disadvantage of such simple measuring cells is that the accuracy of the measuring results obtained therewith is unsatisfactory, for example caused by rapid deposition of the lacquer in the vessel or by the influence of the intermediate medium glass, for example owing to physical interactions.
Furthermore, a method of colorimetry on liquid lacquers is described in DE-A-2531459, in which method the lacquer is removed from the mixing container by means of an overflow vessel, which is arranged in a raisable manner in a mixing container containing lacquer, and fresh lacquer from the mixing container is introduced into the lacquer in the overflow vessel by way of a pipe, and the surface of the lacquer in the overflow vessel is measured by colorimetry.
DE-A-2525701 describes a further method of colorimetry on liquid lacquers. In that method, a continuous thin film is formed from the lacquer to be tested, and a portion of the film is measured by colorimetry. In that method, the film of lacquer may be a film that moves with a support or a film that moves with a laminar flow over a support. In the first case, the support is a measuring disk that is rotatable about a horizontal axis, and in the second case it is a plate-like body having an approximately vertical surface. In both cases, the lacquer is applied to the respective support by means of a pouring tank having an outlet opening. A disadvantage of that method in the case of the use of a rotatable measuring disk is that a disk of an acceptable size can only be used when colour-measuring devices having a measuring aperture arranged more to the side of the housing are employed. With colour-measuring devices having measuring apertures arranged centrally, extremely large disks must be used. In the case of the use of a vertical plate-like body, flocculation effects may occur owing to the absence of shear. The effect of gravity and the disadvantages associated therewith must also be taken into account. For example, it is only possible to work with layer thicknesses of the wet lacquer that are above the run-off limit.
Accordingly, the object of the invention was to provide a process for measuring optical, especially colorimetric, parameters on liquid, coloured media, especially on wet lacquers, which process permits rapid and effective measurement of the optical parameters and at the same time ensures the accuracy of measurement required, for example, for quality control purposes. The process is to be such that measuring devices having any desired arrangement of the measuring aperture can be used in the optimum manner.
SUMMARY OF THE INVENTION
The object is achieved by a process for measuring optical, especially calorimetric, parameters on liquid, coloured media, especially on wet lacquers, which process is characterised in that the liquid, coloured medium is applied to a continuously moving cylindrical support, a film of the liquid, coloured medium forms on the continuously moving cylindrical support, and optical, especially calorimetric, parameters are measured on the film of the liquid, coloured medium.
Optical parameters to be measured are, for example, brightness and calorimetric parameters, such as colour strength or colour difference.
The liquid, coloured media are especially liquid lacquers. Accordingly, for the purposes of simplicity, the term lacquer will always be used hereinbelow, but that term is to be understood as including in principle also other liquid media.
Application of the lacquer to the cylindrical support, hereinafter called the roller for short, may be effected by various methods, for example by pouring, spraying, roller application, knife application or brush application. It is preferably carried out by pouring or knife application. That may be effected by means of a suitable device, for example by means of a vessel or a box knife.
When the lacquer has been applied to the roller, the measurement may be carried out. In order to protect the measuring device from contamination by the lacquer, the roller is preferably not positioned directly in front of the measuring aperture of a corresponding measuring device until shortly before the measurement. However, it is also possible to connect the roller and the measuring device together at the required distance for the measurement and to apply the lacquer in that position.
The process according to the invention will be described in greater detail below.
DETAILED DESCRIPTION OF THE INVENTION
In a first process step, the lacquer is applied by a suitable method to the roller, which is already rotating. The roller is preferably arranged horizontally or vertically with respect to the measuring aperture of the measuring device. A horizontal arrangement may be used, for example, in the case of very high viscosity lacquer materials. In general, however, a vertical arrangement is preferred. The roller is made to rotate by a set of gears which can be driven by a drive device.
The roller to be used in the process according to the invention as the support for the lacquer may be in various forms. For example, the roller may be a hollow cylinder of variable wall thickness, or a solid cylinder, it being possible for a solid cylinder to be hollowed out on the inside for weight reasons. The roller is preferably made of metal, especially of high-grade steel. The dimensions of the roller may be varied within certain limits. The width of the roller cylinder is dependent, for example, on the type and size of the measuring device, especially colour-measuring device and measuring aperture. The roller with the applied
E. I. du Pont de Nemours and Company
Evans F. L.
Geisel Kara
Lerman Bart E.
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