RU2314514C1 - Method and device for measuring viscosity - Google Patents

Abstract

FIELD: measuring technique.

SUBSTANCE: method comprises determining the dependence of the refractive index and viscosity of the paint on the paint dry residual, measuring the critical angle of the total internal reflection of the paint by means of a refractometer, determining refraction index of the paint from the value of the critical angle of the total internal reflection, and determining the concentration of the dry residual and violate component of the paint from the dependence of the refraction index on the dry residual. The device comprises circuits of pressurization, discharging, viscosimetry and solvent supply, and control unit.

EFFECT: enhanced reliability.

3 cl, 6 dwg

Description

The invention relates to measuring equipment and can be used in electro-inkjet marking printers.

To ensure high-quality printing and reliable operation of the electro-ink jet technology, it is necessary to constantly measure the viscosity of the working fluid (inks, ink) and control this parameter, for example, stabilize it by dosing topping up the solvent.

There are two main methods for measuring the viscosity of a liquid both in laboratory conditions during the study or preparation of paints, and directly in electro-ink jet printers during their operation to control the parameters of the liquid.

The first method for determining the viscosity of a liquid is based on the Stokes law

Ftr = 6πηrυ,

where Ftr is the friction force in the fluid, υ is the ball’s rate of fall relative to the fluid, r is the radius of the ball, and η is the dynamic viscosity.

The determination of viscosity based on a Happler viscometer is based on this law. At the same time, a ball is lowered into a tube of a certain diameter filled with the test liquid and its fall rate or the time of flight of certain marks on the tube are measured, which are a measure of the viscosity of the liquid. It is taken into account that during laminar flow around a falling ball the friction force is balanced by the weight of the ball minus the static lifting force / (1) - p. 129; (2) - p. 202 /.

The disadvantages of this method of measuring viscosity include the significant dimensions of the measurement setup and the difficulty of miniaturizing it, the difficulty and complexity in automating the measurement process, and the significant time required for the measurement process.

The second method for measuring viscosity is based on Newton's hypothesis, later substantiated by prof. N.P. Petrov, which characterizes the friction force between the fluid layers / (3) - p. 11; (1) - p. 126; (2) - p. 188 /.

Ftr = ηFdυ / dy,

where Ftr is the friction force between the fluid layers, F is the area of the contacting layers, dυ / dy is the velocity gradient in the boundary layer, or if the plate is moved parallel to a flat wall in the fluid, at a distance between the plates “a” less than the boundary layer, then

Ftr = ηFυ / a.

This method is based on the so-called rotary or drum viscometers, in which, for example, the glass rotates at a given speed in a fixed glass, between the walls of which a test fluid is located in a thin layer. In this case, the force of action on one of the glasses is dynamically recorded. The configuration of bodies immersed in a liquid can be different, as well as the method of measuring the friction force or directly viscosity, such as in / 4 /.

This method has all of the aforementioned disadvantages: cumbersomeness, automation complexity, long measurement duration.

There is also a method of measuring the viscosity of a liquid and a device for measuring the viscosity of a liquid by this method, while the known method is based on the Poiseuille formula / (2) - p. 201; (1) - p. 128 /, which describes the process of laminar flow of liquid through a thin tube (capillary):

where V is the volume of fluid flowing through the tube over time t, R is the radius of the tube, Δp is the pressure difference at the ends of the tube, l is the length of the tube, η is the dynamic viscosity. In particular, this method of measuring viscosity is implemented in industrial viscometers of capillary glass type VPZH / (5); (6) /.

The method involves filling (pumping) a test liquid into a tank of a certain volume, and then the time of expiration of a specified volume of liquid under the influence of hydrostatic (gravitational) pressure is measured, i.e. by gravity through a calibrated capillary glass channel with defined dimensions.

The dynamic viscosity of a liquid is determined by the ratio

η = κρt,

where η is the dynamic viscosity, κ is the constant of a particular viscometer, ρ is the density of the liquid, t is the time of fluid outflow.

The disadvantages of this method and device for measuring the viscosity of a liquid are cumbersome, the complexity of embedding in a printer and the complexity of automating the measurement process, as well as the significant measurement time.

The so-called exponential method for measuring the viscosity of a liquid / 8 /.

Its essence lies in the fact that in the process of measuring the viscosity of a liquid, including pumping liquid into a battery (receiver), its subsequent outflow through a capillary channel and measurement of flow parameters, which determine the viscosity of a liquid, the liquid is pumped into the battery by means of a pulse pressure source, and the process of fluid flow through the capillary channel measures the pressure drop between two pressure levels, which determine the instantaneous (current) viscosity of the fluid.

The pressure decay time is measured periodically with the frequency of the pressure pulses when the liquid is injected into the battery.

The device for measuring the viscosity of a liquid in the hydraulic system of an electro-inkjet printer according to this method consists of a pulse pressure source and a battery connected in series, and a capillary channel and a pressure decay time measuring device connected to the battery are additionally introduced, for example, a piezoresistive pressure sensor.

The liquid under pressure from a pulsed source of overpressure, for example, is supplied periodically or once to several atmospheres to a battery (receiver), for example, of a spring type, which can be considered as a process of charging a hydraulic tank, and then the tank spontaneously discharges through the capillary channel, i.e. . hydraulic resistance. In this case, the time of a short-term pressure drop is measured, i.e. part time of the transition process between two pressure levels. The measurement is automatically carried out, for example, using a piezoelectric pressure sensor in the measuring unit, and the measured part of the transient is one or tens of milliseconds.

In this case, the battery discharge transient is described by the relation

where p (t) is the current pressure value, Pmax is the maximum pressure, e = 2.718, τ _per is the transient time constant, which is proposed to be measured.

Moreover

τ _per = CgRg = kη,

where Cr, Rg are the hydraulic capacity of the accumulator and the hydraulic resistance of the capillary channel, k is the constant of the measuring circuit, η is the dynamic viscosity of the liquid.

Known hydraulic systems for electro-ink jet markers / (7) - p. 149; (10) /, which include an injection circuit (ink tank, filter, pump, battery, pressure sensor, valve, droplet generator in the print head), a suction circuit (print head trap, filter, vacuum pump, ink tank), a chain viscometry (including a measuring receiver, a bypass channel, a pressure sensor), a chain of dosed topping up the solvent from the solvent tank to the paint tank, for example, using a pump. All processes in the hydraulic system of the electro-ink jet marker are controlled from the control unit.

The disadvantages of the known hydraulic systems with viscometry and dosed topping up the solvent are insufficient accuracy, speed and reliability of devices that measure the viscosity and significant dimensions of these devices.

A refractometric method for determining the concentration of a substance / 11 / is known in the art.

Refractometry is one of the most widely used analytical methods to determine a substance in a liquid state, or the concentration of two-component solutions. Refractometry is based on the phenomenon of light refraction during the transition from one medium to another, called refraction.

The objective of the present invention is to improve the accuracy of determining the viscosity of paints in electro-ink jet markers and to create a device for its implementation, which provides automation and speed of the viscosity determination process.

The essence of the proposed invention is as follows.

The method for determining the viscosity of an ink in an electro-ink jet marker includes preliminary determination for each type of ink experimentally the dependences of the optical refractive index n of the ink and viscosity η of the ink on the dry residue of Co, n = n (Co) and η = η (Co), measuring the critical angle total internal reflection of the paint by means of a refractometer according to the position of the chiaroscuro boundary containing a source of a beam of diverging light rays, a prism and a receiver of the type of a CCD array of reflected light from the boundary p the boundary between the prism and the ink, determining the refractive index of the ink from the critical angle of total internal reflection of the ink, based on which the concentration of solids and volatiles in the ink is determined using the dependence of the refractive index n on the solids Co experimentally obtained for each ink, and the concentration of solids determine the viscosity of the paint using the experimentally obtained for each type of paint, the dependence of viscosity η on the dry residue.

When determining the viscosity of the ink for each type of ink, experimentally measured dependences of the optical refractive index n of the ink and viscosity η of the ink on the temperature n = n (t ° C) and η = η (t ° C) are used.

The essence of the proposed invention is also as follows.

The hydraulic system of the electro-ink jet marker contains a device for determining the viscosity of the paint, which is made in the form of a refractometer, which measures the viscosity of the dry residue in the paint.

The hydraulic system of the electro-inkjet marking machine includes a chain of injection, suction, viscometry and topping up the solvent, as well as a control unit, while the refractometer is included in one of the circuits of the hydraulic system as a viscosity sensor and is connected to the control unit and the device for dosed topping up of the solvent.

In the simplest version, the refractometer is connected only with an indication device (with manual topping up of the solvent).

Figure 1 shows a diagram of the construction of a refractometer; in Fig.2 shows the dependence of the refractive index n on the dry residue Co for sucrose; figure 3 shows the experimentally measured dependence of the refractive index n on the dry residue Co for serial paint EXT-220; figure 4, a) shows the experimentally measured dependence of the dry residue Co and viscosity η for one of the typical imported paints 16-8200; figure 4, b) is the dependence of the viscosity η on temperature for the purpose of temperature compensation during measurements; figure 5 shows a generalized structural diagram of the hydraulic system of an electro-ink jet marker; figure 6 presents one of the embodiments of the proposed hydraulic system with a refractometer for measuring viscosity.

Presented in figure 1, the construction scheme of the refractometer includes a light source 1, an optical prism 2, a photodetector 3, for example, of the type of a CCD line, the test solution 4.

Refractometry is based on the effect of refraction (light refraction during the transition from one medium to another) and the dependence of the refractive index of the solution on the concentration. With an increase in the angle of incidence on the interface between two media, the light is partially refracted into another medium, and partially reflected. This angle is called the angle of total internal reflection and its value can be used to determine the refractive index.

The light from the source 1 is introduced into the optical prism 2 and falls on its inner surface in contact with the test solution 4. A part of the rays, the incidence angle of which is more than critical, is completely reflected from the inner surface of the prism and forms the bright part of the image on the photodetector. The coordinate of the interface between the light and dark parts of the image determines the refractive index of the test solution, which is a function of its concentration.

The refractometer under consideration is built on the basis of a compact and reliable optical design with a high-quality, for example, sapphire prism. The optical scheme is constructed in such a way that the light forming the border of light and shadow on the photodetector does not pass through the solution. Due to this, neither the transparency and light of the solution, nor the presence of insoluble inclusions and gas bubbles in it affect the measurement results. Which also expands the scope of its application.

To compensate for the influence of the temperature of the controlled solution on the value of the refractive index, a heat sensor is used in the refractometer.

The exact position of the border of light and shadow on a coordinate-sensitive photodetector is determined by the built-in microcontroller as a result of processing data on the distribution of radiation intensity using a noise-tolerant algorithm.

Due to the rigid and reliable design of the optical circuit and the fully digital path for receiving and processing optical information, the device does not have signal drift and does not require regular maintenance.

This refractometer can work with completely opaque solutions, provides data on concentration in real time, does not need samplers. His testimony does not depend on possible errors when taking and analyzing samples in laboratory conditions. The refractometer allows you to quickly respond to changes during the process and can be used as a feedback sensor for automation of production.

Figure 2 shows the dependence of the refractive index on the dry residue for sucrose, i.e. for a solution of sugar in water. In most industrial refractometers, this curve is used to calibrate instruments not in absolute values of the refractive index, but in% of the solids concentration (Br - brixes).

The operating range of a refractometer measuring a refractive index can be from 1.333 to 1.520, and the working range of a concentration measurement in this case will correspond to from 0 to 90%. Since the CCD line has 1024 or 2048 sensitive elements, the measurement error by the refractive index is ± 0.0002%, and the measurement error of the concentration (dry residue) is ± 0.1%. Thus, the accuracy of the measurement with a refractometer is very high.

Figure 3 shows the experimentally measured dependence of the refractive index n on the dry residue Co for serial paint EKST-220 for an electro-ink-jet ink-jet marker based on a methyl ethyl ketone solvent with a composition of a non-volatile part (dye, binder, additives, etc.). The concentration of solids was varied by measuring the dilution of the original paint with a known proportion of solids (mass concentration). The refractive index for each point was found on the sucrose curve (Fig. 2) using a PAL-1 type refractometer calibrated in Br (brix).

Figure 4, a) shows the experimentally measured dependence of the dry residue Co and viscosity η for one of the typical imported paints 16-8200 for electro-ink jet ink, and figure 4, b) the temperature dependence of viscosity η for temperature compensation during measurements .

The table shows the results of an experimental study of some typical paints.

Results of an experimental study of the dependence of viscosity on solids and temperature for some paints IEC purple IEC blue IEC black Alcohol Black η, s C _about % η, s C _about % η, s C _about % t °, C η, s 1.31 23,2 2,4 28.5 3.8 22.54 5.25 4.89 1,58 26.7 2.42 30,0 5.32 24.85 10.3 4.18 2.15 32.1 3.81 36.0 8.91 31.75 14.0 3.8 2.49 33.5 4,54 38,0 13.22 37.1 16.5 3,54 2.71 35.1 10.71 46.0 16.5 38.88 20.9 3.18 4.09 39.8 11.3 47.6 23.9 2.98 6.95 47.1 13.06 50,0 25.8 2.81 15.44 56.4

Based on the foregoing, for each ink for a marking printer, one can obtain a set of dependencies n = n (Co), η = η (Co), η = η (t) and implement the proposed technical solution for determining the viscosity of ink in real time.

Figure 5 shows a generalized structural diagram of the hydraulic system of an electro-ink jet marker, including a paint reservoir 5, a solvent reservoir 6, a discharge circuit 7, a suction circuit 8, a viscometry circuit 9, a solvent dosage addition circuit 10, a print head 11, a control unit 12.

Figure 6 presents one of the embodiments of the proposed hydraulic system with a refractometer for measuring viscosity. The refractometer is included in a typical hydraulic system instead of the measuring receiver / 7, p. 149 /, and there is no need for an expensive liquid pressure sensor. The refractometer as a viscosity sensor can be included in any other circuit or placed in hydraulic reservoirs.

The hydraulic system of the electro-ink jet marker (Fig.6) includes the following chains.

Pressure (high pressure) circuit: filter 13 in the paint tank 14, valve 15, charge pump (cylinder) 16, receiver 17, pressure sensor 18, filter 19, valve 20 of the print head 21, nozzle element 22 of the drop generator 23.

The suction (vacuum) circuit includes a trap 24, a filter 25, a suction cylinder 26, and a paint reservoir 14.

The viscometry circuit is organized using a tee, in one embodiment structurally combined with a refractometer 27, then a bypass channel 28 and a paint reservoir 14. In this case, the viscometry circuit is combined with the bypass circuit.

The circuit of the metered solvent topping consists of a filter 29 in the reservoir of the solvent 30, a valve 31, associated with the discharge cylinder 16.

An additional discharge circuit has been introduced into the hydraulic system: from valve 20 using valve 32 to paint tank 14.

The diagram also shows the elements of level sensors 33, 34 in the tanks 14 and 30, respectively, as well as the sensor-charging electrode 35 and the deflecting electrodes 36. The hydraulic system and marking processes are controlled by a control unit (not shown in the diagram).

In real continuous electro-inkjet printers using high-pressure droplet emission with ultrasonic crushing / 7 /, in the case of using fast-volatile paints based on alcohol, methyl ethyl ketone, etc. it is necessary to constantly monitor the viscosity of the paint in the system and in the case of critical thickening of the paint, i.e. reaching the threshold viscosity, it is required to automatically carry out a metered addition of solvent into the paint.

The proposed method for determining the viscosity and the device that implements it, allow with great accuracy (error not more than a fraction of a percent), promptly, with the frequency of the pulse pump (5-10 Hz), i.e. for each period and more often to control, measure and adjust (stabilize) the most important printing parameter - viscosity.

Thus, the proposed technical solution, in contrast to the known solutions, provides the following: increases accuracy, speed, frequency of viscosity measurements, allows to optimize this process, reduce the dimensions of structures, which allows you to integrate this viscometer into electro-ink jet markers, in this case, the print quality and reliability of printers .

Sources of information taken into account:

1. Kuhling X. Handbook of physics. M., World, 1982.

2. Paul R.V. Mechanics, acoustics and the theory of heat. M., Science, 1971.

3. V.G. Geyer, V.S. Dulin, A.G. Borumensky, A.N. Dawn. Hydraulics and hydrodynamics. M., Nedra, 1981.

4. The brochure of the rotary viscometer Rheomat 108 Swiss company DONAU (copy attached).

5. GOST 10028-81. Glass capillary viscometers, specifications. M., USSR State Committee for Standardization.

6. Viscometer capillary glass VPZh-3. Passport, M., Ministry of Instrumentation of the USSR, 1982 (copy attached).

7. Bezrukov V.I. Basics of electro-jet technology. SPb., Shipbuilding, 2001.

8. RF patent No. 2196317.

9. Advertising brochure. Industrial refractometer PR-3. LLC Engineering Center Technocon (copy attached).

10. RF patent No. 2212633.

11. Polytechnical dictionary. M., 1980, p. 451.

Claims (3)

1. A method for determining the viscosity of a paint in an electro-ink jet marker, including preliminary determination for each type of paint experimentally the dependences of the optical refractive index n of the paint and viscosity η of the paint on the dry residue of Co paint, respectively n = n (Co) and η = η (Co), measuring the critical angle of the total internal reflection of the paint by means of a refractometer according to the position of the chiaroscuro boundary containing a source of a beam of diverging light rays, a prism and a receiver of the type of a CCD line of reflected light from the boundaries s are the sections of the face of the prism and ink, the determination of the refractive index of the ink from the critical angle of the total internal reflection of the ink, based on which the concentration of solids and volatiles in the ink is determined using the dependence of the refractive index n on the solids Co experimentally obtained for each ink, and the concentration of the dry residue determines the viscosity of the paint using experimentally obtained for each type of paint, the dependence of viscosity η on the dry residue. 2. The method according to claim 1, characterized in that when determining the viscosity of the ink for each type of ink, experimentally measured dependences of the optical refractive index n of the ink and viscosity η of the ink on the temperature n = n (t ° C) and η = η (t ° C) 3. The hydraulic system of the electro-ink-jet marker, containing a paint tank, a solvent tank, a discharge circuit, a suction, and topping up a solvent, a device for determining the viscosity of ink, included in one of the hydraulic circuits, a print head and a control unit, characterized in that the device for determining the viscosity of the ink made in the form of a refractometer, which measures the viscosity of the dry residue in the paint.

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