AU622124B2 - Process and device for measuring the viscosity of materials - Google Patents

Description

-7 OPI DATE 01/08/89 APPLN. IJD 21151 88

PCT

INTERNATIONALE AN AOJP DATE 31/08/89 -PCT NUMBER PCT/EP88/01070 INTERNATIONALE ZUW fA FITUF bM G EB IET DES PATENTWES ENS (PCT) (51) Internationale Patent klassif ikati It1) jernat le Ver61ffentlichungsnummer: W'O 89/ 06352 GOIN 11/10 Al 4 (21) Internationales Aktenzeichen: PCT/E P8 8/0 1070 (22) Internationales Anmeldedatum: 24. November 1988 (24.11.88) (31) Prioritatsaktenzeichen: (32) Priori titsdatumr: (33) Prioritatsland: P 38 00 474.7 (74) Anwalt: LEIFERT, Elmar; BASF Lacke Farben AG, Postfrch 61 23, D-4400 M~nster (DE).

(81) Bestinimungsstaaten: AT (europtiisches Patent), AU, BE (europaisches Patent), BR, CR (europaiisches Patent), DE (europaisches Patent), DK, FR (europilisches Patent), GB (europaisches Patent), IT (europisches Patent), JP, KR, LU (europdisches Patent), NL: (europ~isches Patent), NO, SE (europ~iisches Patent),

US.

Veroiffentlicht Mit internationalein Recherchenbericht.

11. Januar 1988 (11.01.88)

DE

(71) Anmnelder (fuir alle Bestimmungssicaren ausser US): BASF LACKE FARBEN AKTIENGESELL- SCHAFT [DE/DE]: Max-Winkelmann-Strale 80, D- 4400 Mijnster (DE).

(72) Erfinder;und Erfinder/Anmelder (nurfijr US) LAUN, Martin [DE/ DE]; Dilrerstr. 22, D-6700 Ludwigshafen GO- RING, Wolfgang [DE/DE]; Zum Roten Berge 34, D- 4400 M~nster DIRKING, Theodora [DE/DE]; S~dstrage 22, D-4400 MOnster STREITBER- GER, Hans-Joachim [DE/DE]; Linckenstra~e 21, D- 4400 Mijnster (DE).

I

(54) Title: PROCESS AND DEVICE FOR MEASURING THE VISCOSITY OF MATERIALS (54) Bezeichnung: VERFARREN UND VORRICHTUNG ZUM MESSEN DER VISKOSITAT VON STOFFEN (57) Abstract

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R 1 Process and device for measuring the effective viscosity and the elastic properties of coatings. Known measuring processes and measuring devices based on the "rolling, ball method" suffer from drawbacks, namely run formation and sinking of the relatively heavy solvent vapours, due to the inclination of the coated sheet metal. To overcome these drawbacks, rolling movements are imparted to a magnetizable ball displaced from its rest position in a magnetic field, during movement of the horizontally disposed substrate, under the influence of the Field gradient of a permanent magnet or electromagnet located below the substrate. The rolling movements are used as the basis for the measurement-,.

F-6r q efRV K sin a 2 4 K-32KHgrad

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V-R 2 sin H grad H qI f (57) Zusammenfassung Verfahren und Vorrichtung zur Messung der effektiven Viskositdt und der elastischen Eigenschaften von Beschichtungen. Bei den bisher bekannten Messverfahren und M~essvorrichtungen, die mit der "Rollende Kugel Methode" arbeiten, besteht der Nachteil, dlass die Schragstellung des beschichteten Bleches die Bildung von LUufern als auch das Herabfallen der relativ schweren Lbsemitteldgm pfe bexvtrkt. Um diesen Nachteil der bekannten Verfahren auszuschalten, wvird das beschichtete Substrat horizontal ausgerichtet, eine magnetisierbare Kugel nach Auslenkung aus der Ruhelage eines Magnetfeldes bei Bewegung des horizon- Ital angeordneten Substrates unter Einfluss des Feldgradienten eines unterhalb descSubstrates angeordneten Permanent- 1 oder Elektromagneten zu Rollbewegungen angeregt wird, wobei diese Bewegungen als Messgrundlage dienen.

/1 7 71 :4 4 p p'f-.

V's 6 @6 0 0 PAT a8 170 BASF Lacke Farben Aktiengesellschaft Max-Winkelmann-Str. 80, 4400 MUnster-Hiltrup "Method of and apparatus for measuring the viscosity of materials" The invention relates to a method of measuring the effective viscosity and the elastic properties of coatings according to the preamble of the main claim, 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 15 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-

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0 0 7'*Cli Zii~j~; i: I 2 off and stoving process. In this connection, a coated plate is inclined at a defined angle (eg. 300) 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 func- 15 tion 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.

20 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.

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 w A

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3range can be achieved.

According to the present invention there is provided a method of measuring the effective viscosity and elastic properties of a coating during flash-off and stoving phases of the coating after the coating has been applied to a substrate, comprising moving the substrate in order to excite a magnetisable element into a moving condition in the coating on the substrate, said substrate being arranged horizontally in a non-uniform magnetic field applied to the substrate by a magnetising means located underneath the substrate, and adjusting the speed of movement of the substrate so that the magnetisable element is maintained in the moving condition at a desired position on the substrate located at a constant separation from a prearranged fixed position of rest wherein the position of the magnetisable element maintained at the constant preselected position is detected by a sensor means which does not physically contact the magnetisable element whereby the effective viscosity and elastic properties of the coating are obtained in accordance with the value of the 20 speed of the substrate required to maintain the magnetisable oooe0 element in the desired position as detected by the sensor

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means.

According to the present invention there is provided an apparatus suitable for carrying out the method :2I. according to the present invention in which the substrate comprises a plate of non-ferro magnetic material, the sphere comprises a ferro-magnetic material and has a sphere diameter of from 1 to 10 millimeters, a servomotor drive being provided for moving the substrate.

*In other words, it 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 vapours 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 mPas to approximately 1000 Pas or more. As compared with a T 0)> 3A 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-line, and the measurement method can therefore be fully automated.

An illustrative embodiment of the invention is explained below with reference to the drawings, in which Figure 1 shows a sketch of the magnetic measurement arrangement, and Figure 2 shows a curve obtained with the measurement apparatus according to the invention.

The essential parts of the measurement apparatus are represented in Figure 1. A magnetisable sphere 1 is-7 a a AQ"'2.

T 0< -4 excited to a rolling motion in a coating 2 in conjunction with the movement of a horizontally arranged substrate 3 consisting of non-ferromagnetic material, eg. glass, under the influence of the field gradient of a permanent magnet or electromagnet 4 arranged underneath the substrate 3.

Given fixed magnets 4, the speed v of the substrate 3 is regulated in such a way that the sphere 1 is held rolling at a constant separation A x from the position of rest.

In this connection, the position of the sphere is detected by a non-contacting sensor. This corresponds to a test with constant magnetic driving force on the sphere 1, 4 there being established a rolling speed which is propor- I tional to the reciprocal of the effective coating viscosity. The motion of the substrate 3 caused by a servo- 15 motor drive can either be a purely linear motion or a rotation (circular path). However, it can also be a combination of the two (eg. spiral path).

The generation of the field by an electromagnet 4 Shas the advantage that the force acting on the sphere 1 20 can be varied and regulated over a wide range via the coil current. This signifies a substantial advantage over the previous measuring apparatuses, in which a constant force, namely gravity, acts on the rolling sphere. According to the invention, there is therefore an extension of the viscosity measuring range to values between 10 mPas and 1000 Pas or more.

However, the measurement method according to the invention includes still further possibilities for adjusting the driving force or rolling speed of the sphere 1 to 5 the variable coating viscosity: a) selection of a different displacement A x b) selection of a different substrate thickness c) selection of a different pole shoe geometry d) selection of a different sphere diameter e) selection of a sphere material having a different magnetic permeability.

Thus, the following advantages arise by comparison with the mode of procedure which belongs to the prior art and operates with an inclined plate: 1. No formation of runs in the coating, eg. a paint film.

2. No settling of the relatively heavy solvent vapors, or or no formation of s iovent traps.

3. On-line measurement of the effective viscosity.

15 4. The magnitude of the magnetic force acting on the sphere 1 can be adjusted over a wide range.

Viscosity range 10 mPas to 1000 Pas or more.

6. Lateral focussing of the sphere 1 by the magnetic field.

7. The measurement method can be fully automated.

20 8. The measurement method can be extended to oscillatory 0 rolling motions in order to measure the viscoelasticity.

Figure 2 shows a graph obtained with the magnetic measuring apparatus described. The sphere rolling time is given as a function of the magnetic field *for oil films (film thickness 250 um) of different viscosity, a permanent magnet having been employed. Spheres 1 of soft iron were used, which had a diameter of 2.5 mm. Five calibration oils of different viscosity in the range from y A to 1200 mPas were selected for the measurements. The oil 6 films were produced with a drawing straight-edge on glass plates 3 of thickness 1 mm. The measuring temperature amounted to 20.0 C, and the length of the measuring distance A x to 3 cm.

The physico-mathematical relationship which is given in Figure 1 signifies that the rolling speed of the sphere 1 is inversely proportional to the effective viscosity of the coating 2. This theoretically derivable Linear relationship between the measuring time t (or rolling speed v of the sphere), together with the viscosity of the coating 2, eg. the o4l films, is experimentally confirmed e« by the measurement results according to Figure 2. The up-

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shot is that the magnetic measurement method can be used for the required application, namely the determination of the viscosity of coatings.

In the stoving phase of the coating in the temperature range from 200 0 C (or also up to 300 0 C) account must be taken of the decrease of the magnetization of the ferromagnetic iron spheres. This dependency of the magne- S 20 tic susceptibility on temperature is known, and is taken into account via the software by means of the computer during calculation of the effective viscosity.

e a The measuring apparatus can be extended in such a way that the sphere 1 executes oscillatory rolling motions under the additional influence of a lateral alternating magnetic field of an electromagnet 4, the elastic properties of coatings 2 can be determined in this way. The real and imaginary parts of the complex modulus of rigidity (storage modulus and loss modulus, respectively) can 0 be determined as a function of the frequency.

Claims (15)

1. A method of measuring the effective viscosity and elastic properties of a coating during flash-off and stoving phases of the coating after the coating has been applied to a substrate, comprising moving the substrate in order to excite a magnetisable element into a moving condition in the coating on the substrate, said substrate being arranged horizontally in a non-uniform magnetic field applied to the substrate by a magnetising means located underneath the substrate, and adjusting the speed of movement of the substrate so that the magnetisable element is maintained in the moving condition at a desired position on the substrate located at a constant separation from a prearranged fixed position of rest wherein the position of the magnetisable element maintained at the constant preselected position is detected by a sensor means which does not physically contact the magnetisable element whereby the effective viscosity and elastic properties of the coating are obtained in accordance with the value of the speed of the substrate required to maintain the magnetisable element in the desired position as detected by the sensor ooooo S means. *o

2. A method according to claim 1 in which the magnetising means comprises a permanent magnet or an electro- S magnet.

3. A method according to claim 1 or 2 in which the magnetising means is located at a fixed location underneath S the substrate. ooeoo oooo

4. A method according to any preceding claim in which oo ~the nmagnetisable element is a sphere. o o•

5. A method according to any preceding claim in which the moving condition is a rolling motion.

6. A method according to any preceding claim in which w ~\the magnetisable sphere executes lateral oscillatory rolling 8 motions under the influence of a further alternating magnetic field applied to the substrate by an electro-magnet.

7. An apparatus suitable for carrying out the method according to any preceding claim in which the substrate is a plate of non-ferro magnetic material, the magnetisable element is a sphere made from a ferro-magnetic material and has a diameter of from 1 to 10 millimetres, and further comprising a servomotor for driving the substrate.

8. An apparatus according to claim 7 in which the sphere diameter is from 1.5 to 4 mm. o

9. An apparatus according to claims 7 or 8 in which the sphere is made from steel and has a sphere diameter of 2.5 mm. *:0

10. An apparatus according to any one of claims 7 to 9 in which the substrate executes a linear motion.

11. An apparatus according to any one of claims 7 to 9 in which the substrate executes a combination of a linear motion and a rotational motion.

12. Apparatus according to any one of claims 7 to 11 S2. further comprising a regulable electromagnet with which the force acting on the sphere due to the magnetic field can be varied and regulated over a wide range by means of a variable current applied to the coil of the electromagnet.

13. Apparatus according to any one of claims 7 to 12 in which different magnetisable spheres made of ferro-magnetic materials having different magnetic susceptibilities are used.

14. Apparatus according to any one of claims 7 to 13 in which the substrate is made from glass. 9 A method of measuring the effect of viscosity and elastic properties substantially as hereinbefore described with reference to any one of the accompanying drawings.

16. An apparatus suitable for carrying out the method of measuring the effect of viscosity and elastic properties substantially as hereinbefore described with reference to any one of the accompanying drawings. Dated this 20th day of November, 1991 BASF LACKE FARBEN AG By its Patent Attorneys: GRIFFITH HACK CO. Fellows Institute of Patent Attorneys of Australia.