Measuring and testing – Liquid analysis or analysis of the suspension of solids in a... – Viscosity
Patent
1990-08-31
1993-05-25
Goldstein, Herbert
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
Viscosity
73 5423, G01N 1102
Patent
active
052129810
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method of measuring the effective viscosity and the elastic properties of coatings and to an apparatus for carrying out this method.
Very high demands are placed on the corrosion protection and the optical properties of industrial paints. The paints must flow well, and may not have any surface imperfections, such as solvent poppings and craters, nor any formation of runs. The edge coverage by the coating must be as good as possible. Essentially, these required properties depend on the temporal variation of the flow behavior of the applied coating during drying. The flow behavior and its temporal variation are determined by the qualitative and quantitative composition of the recipe of the coating material, and by the conditions during the drying process (duration of the flash-off phase, stoving time, stoving temperature, etc).
The measurement of the flow behavior of coatings using the "rolling sphere method" stems from work done in 1936. Since then, this measurement method has frequently been employed. A computer-controlled measuring apparatus, which is described in DE 3,420,341 C2, allows the apparent viscosity to be measured quantitatively during the flash-off and stoving process. In this connection, a coated plate is inclined at a defined angle (e.g. 30.degree.) to the horizontal, and the rolling motion of a steel sphere in the paint film is compensated by rotating the plate with the aid of a motor drive about an axis which is perpendicular to its plane and passes through its center. In conjunction with an electrical unit, a punctiform light source and an associated light detector serve to control the motor drive, the motor rotating the coated plate against the direction of motion of the sphere, in order to keep the latter at approximately the same location in the vertical direction. The speed of rotation of the coated plate is inversely proportional to the viscosity of the coating. In this way, the film viscosity can be measured as a function of the time or temperature of the film.
This measurement method has the disadvantage that the inclination of the coated plate causes both the formation of runs, and also the settling of the relatively heavy solvent vapors during the process of physical drying. Thus, it can happen that the steel spheres employed for measurement come into regions of different layer thickness, which manifests itself unfavorably in the measurement accuracy.
Known from the teachings of EP-A1-0 144 437 is a device for measuring the viscoelasticity of low viscose imide, whereby a ball within the liquid is moved by magnetic forces in an oscillating manner with high frequency. The liquid and the ball are located in a sealed container. The liquid must be transparent. The device is not suitable for measuring the effective viscosity and the elastic properties of coatings during the exhaust and annealing phase.
It is the object of the invention to create a measurement method and a measurement apparatus, with which the disturbing formation of runs, and also the settling of solvent vapors are avoided, and with which the magnitude of the force acting on the sphere can be adjusted over a wide range, so that an expansion of the viscosity measuring range can be achieved.
This object, on which the invention is based, is achieved by means of the proposal according to the invention that the coated substrate can be arranged horizontally, and that thus both the disturbing formation of runs and also the settling of solvent vapors are avoided. The magnitude of the magnetic force acting on the sphere composed of ferromagnetic material can be adjusted over a wide range, which signifies a substantial expansion of the viscosity measuring range from approximately 10 mPas to approximately 1000 Pas or more. As compared with the previous measuring apparatuses, it is therefore technically possible, during the stoving process of the coating, to encompass a larger, previously unknown range of viscosity.
The measurement of the speed of the sphere in the viscous paint film can take place on-li
REFERENCES:
patent: 4627272 (1986-12-01), Wright
patent: 4781808 (1988-11-01), Geist et al.
patent: 5040410 (1991-08-01), Chu et al.
Revue de Physique Appliquee, Band 19, Nr. 3, Marz 1984, (Orsay, FR).
M. Adams et al.: "Magnetorheometre a bille": Seiten 253-264.
Farbe and Lack, 83. Jahrgang, Nr. 4, 1977, (Hannover, DE) W. Goring et al.: "Zur Messung der Viskositat von Lackfilmen wahrend des Abulft-und Einbrennvorganges", pp. 270-277.
Dirking Theodora
Goring Wolfgang
Laun Martin
Streitberger Hans-Joachim
BASF Lacke & Farben AG
Goldstein Herbert
Mah Raymond Y.
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