Rotary viscometer / Rotary rheometer and Capillary viscometer

Rheometer RHEOTEST^® RN and Capillary Viscometer RHEOTEST^® LK - Paints, Varnishes and other Coating Materials - application paints, laquers and other coating materials

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Measuring tasks in research and development departments

Rheological parameters should be defined and measured with the help of a rheometer with good reproducibility to optimize products properties. In addition, one influences on rheological properties of paints and varnishes in such a way that listed below quality criteria are achieved and they could be determined with the help of measurement technique.

	Optimal stability in processes of storage and transportation *Yield point* and / or *zero-viscosity* are set in such a way that processes of sedimentation and separation into layers do not take place
	Good flow properities during processing They are defined by means of flow curves taking for shear rates range that is typical for processing conditions, e.g., for:

•	Simple spread on a flat surface	between	0,001	and	1 s^-1
•	Pumping and mixing processes	between	1	and	1 000 s^-1
•	Processes of painting and spraying as well as applying with roller	between	1 000	and	100 000 s^-1

	Good adhesion with wall or surface To this effect *yield point* and *zero-vicosity* have to be set and controlled using the measurement instruments
	Optimal spread, dry and hardening during obtaining necessary surface *Yield point* and *zero-viscosity* have to be defined and controlled with the help of measurement instruments taking into account thixotropic effects and viscoelastic properties

Measuring task in the area of quality control

First of all, quality control serves for reproducible and metrologically correct data acquisition on flow properties. Flow characteristics determined with the help of rheometer must have good comparability in production range of a producer, as well as be methrologically significant for suppliers and quality control authorities. To characterize flow properties of pharmaceutics and cosmetics products it is necessary, on the one hand, to take flow curves in typical for processing range of shear rates and, on the other hand, to measure exactly the yield point of end product. Approximate determination of yield point by means of deformation measurements and rotational measurements with consequent extrapolation could lead to great distortions and to quality defects and could be recommended only in sound, exceptional cases.
The most important parameters for product characterization are yield point, zero-viscosity, shear rate-dependent viscosity and viscosity at infinity rate of shear. Measurement methods for their determination are described and some measurement results are presented in graphical form. The standard methods of measurements and assessment algorithms must find application to assure good reproducibility and comparability.

It is necessary to control viscosity directly before and during processes of coating application in order to check quality of printing inks and varnishes for coatings. It must be carried out by production personnel quickly, simply and exactly. New capillary viscometer series RHEOTEST^® LK was designed by us for this measuring task. This viscometer allows obtain even in heavy production conditions less than in a minute exact measurement results in viscosity range from 1 to 10,000 mPas owing to rigid design and measuring system made of high quality steel. One could calibrate RHEOTEST^® LK very simple and quickly using controlled value of viscosity set for internal standards of quality control even if this value have been set for use with other viscosity measurement method.

•	Measurement procedure to determine yield point and zero-viscosity
	Controlled stress tests - CS-tests

a	Linear ramps with controlled stress to measure yield point or zero-viscosity
	Example: Figure 4

•	Measurement procedure to determine shear rate-dependent viscosity
	Controlled rate tests - CR-tests

	Equilibrium flow curve in the shear rate range of 0.04 ... 20,000 s^-1for investigation of shear rate-dependent flow properties
	Example: Figure 1

	Linear ramps with controlled shear rate in forward and backward direction to research shear rate-dependent and time-dependent flow properties (thixotropy).
	Example: Figure 2

•	Measurement procedure to determine kinetics of structure destruction or formation processes
	Controlled rate tests - CR-tests

	Step-change tests with controlled shear rate to determine structure formation or destruction
	Example: Figure 3

Controlled stress tests - CS-tests)

	Step-change tests with controlled stress to determine structure formation or destruction
	Example: Figure 5

•	Measurement procedure to determine viscoelastic properties
	Controlled stress tests - CS-tests)

	Creep tests and creep-recovery test with controlled stress to determine material's viscoelastic properties
	Example: Figure 6

•	Exact viscosity measurement of printing inks and varnishes for coatings with low viscosity (e.g., for textile printing inks and varnishes for coatings of PC and TV-sets screens)
	One-point measurement with the help of patented capillary viscometer RHEOTEST^® LK. 25 ml of investigated material is automatically sucked in capillary made of high quality steel and returns back into measuring cup after viscosity determination. Result of measurement is presented on display and to the interface RS 232 already in 25 s. Integrated electronic temperature compensation of viscosity assures smoothing of ambient temperature deviations approximately up to 5 K without loosing precision of measurements.
	Example: Figure 7

Measuring task (Figure 1)

Influence determination of receipt components on viscosity change with the help of equilibrium flow curve in very wide range of shear rates. Influence determination of receipt components on flow stability that has influence on processing.
(Measuring task for research and development)

Control and assessment of equilibrium flow curves by comparison of set curves. Control and assessment of equilibrium flow curve by algorithms related to the product, e.g., according to Casson or Herschel-Bulkley and measurement results processing using basis values.
(Measuring task for quality control)

Notes

	Viscosity decrease should correspond to conditions of use or processing
	Irregularities of flow curve indicate on unstable flow properties and result in quality imperfections
	Small viscosities at high shear gradients are signs of good properties during pumping and processing

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Measuring tasks (Figure 2)

Influence determination of receipt components on product stability and viscosity fall under load (shear) with the help of ramps in forward and backward direction.
(Measuring task for research and development)

Hysteresis area determination. (Measuring task for quality control)

Notes

In connection with facilitation of end products processing, one aims at relatively considerable decrease of viscosity under load; of coarse, the load must not exceed the limit value as it leads to irreversible destruction of structure.

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Measuring tasks (Figure 3)

Receipt components influence characterization on formation and destruction of internal structure with the help of step-change tests with controlled shear rate (CR-step-change-tests)
(Measuring task for research and development)

Notes

	Shear rate-dependent destruction of structure allows to obtain important forecasts concerning the necessary viscosity fall in connection with further processing of the end products
	Structure formation in rest conditions (zero viscosity) at small shear gradients is typical for stability during storage and for properties in process
	In contrast to carrying out of measurements with controlled stress, it is possible to obtain also measurement results with good reproducibility using CR-tests. However, there is not direct correlation between these data and product stability.

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Measuring tasks (Figure 4)

Influence determination of receipt components on the yield point of end product and its viscosity at very small shear rates with the help of controlled stress tests.
(Measuring task for research and development)

Yield point measurements (Measuring task for quality control)

Notes

	Yield point has corresponding influence upon optimal film thickness of the coating
	Zero-viscosity is typical for properties in process

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Measuring tasks (Figure 5)

Receipt components influence characterization on formation and destruction of internal structure of the product with the help of step-change tests with controlled stress (CS-step-change-tests)
(Measuring task for research and development)

Purposeful regulation of structure destruction (decrease of the yield point) and structure formation (increase of the yield point).

Notes

	Shear rate-dependent destruction of structure allows to obtain important forecasts concerning the necessary viscosity fall in connection with further processing of the end product. In contrast to carrying out of measurements with controlled shear rate, product stability correlates directly with the stress.
	Structure formation in rest conditions (zero-viscosity) at small stresses is typical for stability during storage and for properties in process. Influence on the yield point is measured directly in contrast to measurements carrying out with controlled shear rate.

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Measuring tasks (Figure 6)

Viscoelastic flow properties characterization as well as study of structure changes in conditions of shear without destruction is done by means of creep measurements with controlled stress (creep tests) and creep-recovery-tests.
(Measuring task for research and development)

Notes

	Measurement results of function of deformation and stress against duration of load are the basis for calculation of structure elasticity through the function of elastic deformation or modulus or of special parameters of viscoelastic models.
	Inter-particular forces and Brownian motion are the reason of viscoelastic properties. One obtains important data via results of measurements for forecasting of interactions in connection with pigments and their influence through processes of additives addition and dispersion.

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Measuring tasks (Figure 7)

Quality control of printing inks and coatings varnishes with the help of capillary viscometer RHEOTEST^® LK

Advantages of RHEOTEST^® LK for quality maintenance laboratories:

•	The measuring values of viscosity, temperature and the temperature compensated viscosity are output to display, printer or PC after 25 seconds only
•	Very simple control using 4 keys or through PC
•	Electronic viscosity-temperature-compensation: that means the viscosity result at measured temperature is calculated and displayed automatically at your wished standard temperature (e.g. 20 �C). One only have to insert in software menue a calculated temperature coefficient.
•	Measuring system of high quality steel could not be damaged at normal conditions
•	Very simple control using 4 keys or through PC
•	Simple maintenance, calibration and cleaning
•	RHEOTEST^® LK could be purchased as automatic, PC-controlled working place for viscosity measurement with sampler for 20 samples
•	Commercial offer includes two versions of viscometer: - Main instrument without jacket for temperature control (for measurement conditions at ambient temperature) - Main instrument with jacket for temperature control (for measurement conditions beyond the ambient temperature)

Some examples of viscosity:

	Coatings of cathode-ray tubes:	about	5	to	50 mPas at 20�C
	Printing inks	about	100	to	500 mPas at 20�C

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