DE102011050957A1 - Method for determining the mass concentration of particles in a particle and liquid dispersion - Google Patents

Abstract

The dispersion is exposed to an alternating field of variable frequency in a measuring cell, e.g. an alternating electrical field. The alternating field causes the particles in the dispersion to vibrate, the particles in the dispersion generating sound pressure waves. The amplitudes (ESA) of the sound pressure waves are measured as a function of the frequency (f), the maximum amplitude of the sound pressure waves being determined and the frequency associated with this amplitude being determined as the resonance frequency of the sound pressure wave. The mass concentration (TC) of the particles in the dispersion is determined from the resonance frequency. The dependence of the resonance frequencies on the mass concentrations of the particles was determined in a calibration process with a known mass concentration and e.g. stored in a table.

Description

As an example of such a dispersion may be considered a liquid developer used in electrophoretic printing. This has as particles on toner particles which are dispersed in a carrier liquid as a liquid. In the following, the invention is explained essentially with reference to a liquid developer, without thereby restricting the invention to liquid developers.

For single or multi-color printing of a printing material, e.g. a single sheet or a tape-shaped recording medium, it is known on a charge image carrier, e.g. To produce a photoconductor, image-dependent charge images corresponding to the images to be printed, consisting of areas to be inked and non-inked. The areas to be inked of the charge images are visualized with a developer station on the charge image carrier by toner particles as toner images. The toner image produced in this way is transported to the substrate via a transfer station and transferred to the substrate in a transfer printing station. On this, the toner images are fixed in a fuser.

For coloring the charge images, a liquid developer having at least charged toner particles and carrier liquid may be used. A method for such electrophoretic printing in digital printing systems is, for example US 2006/0150836 A1 or US 2008/279597 A1 known. After the charge images of the images to be printed have been formed on the charge image carrier, they are colored by a developer station with toner particles into toner images. Here, as the liquid developer, a silicone oil-containing carrier liquid having dispersed therein color particles (toner particles) is used. The supply of the liquid developer to the charge image carrier can be effected by a developer roller, which is supplied to the liquid developer from a reservoir with liquid developer. The image film formed during development on the charge image carrier from toner images embedded in carrier liquid is subsequently transferred by a transfer unit from the charge image carrier and transferred to the printing material in a transfer printing zone.

Thus, in these printing processes using liquid developers, the process of electrophoresis is used to transfer toner particles in the carrier liquid to the substrate. The solid electrically charged toner particles migrate through the carrier liquid as a transport to the substrate, the transport can be controlled by an electric field between the transfer roller and the substrate. The prerequisite for this is, in addition to the toner particle charge and the electric field, the provision of a sufficiently thick carrier liquid layer through which the toner particles can migrate and a sufficient concentration of the toner particles in the carrier liquid.

The liquid developer used in the printing apparatus may be stored in the developer station e.g. in a mixing unit of a toner and carrier liquid having toner concentrate and carrier liquid are mixed together. For a flawless print image, it is necessary that sufficient toner particles be contained in the liquid developer so that the toner mass concentration in the liquid developer is at the intended value. It must be taken into account that liquid developer is removed from the mixing unit during printing and is partially applied to the printing material.

For a successful and undisturbed development of the charge images, a defined toner mass concentration and electrophoretic mobility of the toner particles in the carrier liquid is thus required.

The adjustment of the toner mass concentration and mobility of the toner particles in the carrier liquid requires that the toner mass concentration and the mobility of the toner particles in the developer station can be determined. At a relevant toner mass concentration, e.g. in the range of 2% to 40% of the liquid developer electroacoustic methods for the determination of the electrophoretic mobility of toner particles are known, but require an accurate knowledge of the toner mass concentration.

Out US 2011/58838 A1 For example, a method is known according to which the toner mass concentration in a liquid developer can be determined. For this purpose, the liquid developer is subjected to at least one ultrasonic wave. It is assumed here that the speed of sound of the sound propagating in the liquid developer within predetermined temperature limits and constant carrier liquid essentially depends on the proportion of the toner particles in the carrier liquid. Accordingly, the transit time of an ultrasonic wave in the liquid developer is measured along a predetermined measurement path and the sound velocity is determined therefrom, which is a measure of the toner mass concentration in the liquid developer. Thus, the toner mass concentration can be determined by measuring the transit time of the sound wave in the liquid developer. About Einmessvorgänge the relationship between the transit time of an ultrasonic wave and the toner mass concentration, taking into account the temperature of the liquid developer at a plurality of Liquid developers are determined with known toner mass concentrations and the values determined in terms of time and toner mass concentration, for example, stored in a table. This table can then be used to determine its toner mass concentration by measuring the transit time of a sound wave through a liquid developer. If necessary, you must interpolate between the values in the table. Comparable methods for determining the mass concentration in dispersions are for example US Pat. No. 6,817,229 B2 . US 5 121 629 A or US Pat. No. 7,764,891 B2 known.

Out US 5 245 290 A is a measuring device for determining the electrophoretic mobility of electrically charged particles in a liquid known. A measuring cell contains a dispersion to be tested which contains electrically charged particles whose mobility is to be determined. An alternating electric field is applied to the measuring cell, which excites the particles in the liquid to vibrate. The oscillating particles generate sound waves whose velocity can be evaluated. From the electric field and the average velocity of the particles in the liquid can be concluded that the electrophoretic mobility of the particles. A formula for calculating the dynamic mobility of particles in a dispersion can RW O'Brien et. al./Colloids and Surfaces A: Physiochem. Closely. Aspects 218 (2003) p.89-101 be removed.

In the known measuring methods, either the mass concentration or the electrophoretic mobility of particles in different measuring cells and with different sample volumes is measured, whereby concentration and temperature differences lead to a reduced accuracy of measurement.

The problem to be solved by the invention is to specify a method with which the mass concentration of particles in a dispersion and also their electrophoretic mobility in the dispersion can be determined in one measuring operation. The dispersion has liquid in which particles are dispersed.

This problem is solved by a method according to the features of claim 1.

The dispersion is exposed in a measuring cell to an alternating field of variable frequency, e.g. an alternating electric field. The alternating field causes the particles in the dispersion to vibrate, with the particles generating sound pressure waves in the dispersion. The amplitudes (ESA signal) of the sound pressure waves are measured as a function of the frequencies, wherein the maximum amplitude of the sound pressure waves is detected and the amplitude associated with this frequency is determined as the resonance frequency of the sound pressure wave. The resonance frequency is used to determine the mass concentration of the particles in the dispersion. The dependence of the resonance frequencies on the mass concentrations of the particles in dispersions was previously determined in a calibration procedure at known mass concentrations of the particles in the dispersion, and e.g. stored in a table.

Further developments of the invention will become apparent from the dependent claims.

The simultaneous determination of the electrophoretic mobility of the particles in the dispersion is also possible with the measuring arrangement, since from the ESA signal and the strength of the electric field it is possible to conclude the electrophoretic mobility ( RW O'Brien et. al./Colloids and Surfaces A: Physiochem. Closely. Aspects 218 (2003) p.89-101 ).

The advantage of the method according to the invention is the fact that the mass concentration of particles in a dispersion and their mobility in the dispersion can be determined in one measuring operation. The result is an improvement in the measurement accuracy for the measured mass concentration of the particles and electrophoretic mobility of the particles in the dispersion. Applied to liquid developers, this means that the toner mass concentration and the mobility of the toner particles can be more accurately measured. However, this is crucial for the control of these parameters in the fluid management of pressure systems that liquid developers use to develop the charge images.

With reference to an embodiment, which is shown in schematic figures, the invention will be further explained.

Show it

1 a measuring arrangement for determining the mass concentration and the dynamic mobility of particles in a dispersion,

2 an example of a measuring cell used in the measuring arrangement;

3 in a diagram, the dependence of the sound pressure amplitude ESA a sound pressure wave of the frequency in the measuring cell and

4 a diagram showing the dependence of the mass concentration of the particles on the resonance frequency of the sound pressure wave in the measuring cell.

The starting point in the invention is a known measuring arrangement with which the electroacoustic pressure amplitude (ESA = Electroacoustic Sonic Amplitude) of a sound pressure wave in a dispersion can be measured ( US 5 245 290 A ).

In the explanation of the invention, the following is spoken of a dispersion having particles in a liquid, wherein the mass concentration and mobility of the particles to be determined in the dispersion. As an example of a dispersion, a liquid developer can be used at an electrographic pressure comprising as particles toner particles and as liquid e.g. Mineral oil or silicone oil, wherein the liquid carrier liquid or carrier is called.

1 shows an example of a measuring arrangement MA in the block diagram, with the simultaneous mass concentration TK and the dynamic mobility μ _d of electrically charged particles can be determined in a dispersion. The dispersion is introduced into a measuring cell MZ, whose more detailed structure is made 2 can be removed. The dispersion in the measuring cell MZ is exposed to an alternating electric field U (f), where U indicates the voltage and f the frequency of the alternating field. The alternating electric field causes the particles to vibrate, thereby generating a sound pressure wave in the dispersion. At the output of the measuring cell MZ, the amplitude of this sound pressure wave is output as output signal ESA (f), in addition the temperature T in the measuring cell MZ. This sequence is controlled by a control unit ST, which supplies the measuring cell MZ with the AC voltage U (f) and receives from it the ESA signal ESA (f). The control unit ST transmits the ESA signal to a processor unit PR which determines from the ESA signal the mass concentration TK of the particles in the dispersion. The mass concentration TK can be stored in a memory unit SP; the storage unit SP can contain, as further known quantities of the dispersion, the speed of sound c of the liquid of the dispersion, the viscosity η of the liquid and the density difference Δρ between the particles and the liquid. These variables are supplied to the control unit ST, which determines the dynamic mobility μ _{d of} the particles from the variables ESA, TK, c, η and Δρ according to the formula (2) given below in the dispersion. The process is carried out at a defined temperature T in the measuring cell MZ, which is therefore measured in the measuring cell MZ. A change in the temperature T in the measuring cell MZ would lead to changes in the mobility μ _{d of} the particles and the amplitude ESA of the sound pressure wave.

2 shows an example of a structure of a measuring cell MZ. This has a sample chamber 2 in which a dispersion 1 is filled. The sample chamber 2 consists for example of a cylindrical acoustic resonator, which is connected to parallel surfaces on the top and bottom with electrodes 3 is provided, between which an alternating electric field 4 is created. Through the electric alternating field 4 between the electrodes 3 For example, the electrically charged particles in the dispersion are excited to a periodic motion whose amplitude is tuned by tuning the frequency of the electric field 4 to the resonant frequency in the sample chamber 2 is maximized. The oscillating particles generate sound pressure waves in the sample chamber 2 , which can be amplified by an acoustic resonator and depending on the frequency of the alternating field 4 have different sound pressure amplitudes. The through the alternating field 4 generated sound pressure wave in the dispersion 1 is over a sound conductor 5 a sound pressure transducer 6 supplied, which converts the sound pressure wave into an electrical signal. The amplitude of this signal is called the ESA signal as a function of the frequencies f of the alternating field 4 determined. In addition, by a temperature sensor 7 the temperature of the sample chamber 2 measured. For example, the sample chamber 2 have an electrode spacing of ≈3mm and to the electrodes 3 An alternating voltage of 80V with changeable frequencies, eg in the range of ≈1MHz, can be applied.

The sound pressure amplitudes (ESA signal) are thus measured as a function of the set frequencies f, with the curve being shown as an example 3 (the sound pressure amplitudes are plotted against the frequencies f) gives. From this curve, the resonance frequency can be determined by a frequency-resolved evaluation. This resonance frequency is determined by the geometry of the sample chamber 2 and the acoustic properties of the dispersion. In 3 For example, the maximum of the sound pressure amplitude ESA is at a resonance frequency of 891 kHz. In 3 For example, the sound pressure amplitude as a function of the frequency for a liquid developer with toner particles is shown.

At different mass concentrations TK of the particles in the dispersion, different resonance frequencies result. Thus, from the resonance frequency of a dispersion determined by measurement, the mass concentration TK of the particles in the dispersion can be deduced. If the dependence of the resonance frequencies on the mass concentrations of the particles in dispersions with known mass concentrations TK is determined in a preceding calibration process, the mass concentration TK can be determined from a measured resonance frequency. 4 shows as an example such a diagram for liquid developer in which the resonance frequencies as a function of the toner mass concentrations TK at five known Toner mass concentrations TK has been measured, the temperature and the carrier liquid remain the same. If at an unknown toner mass concentration of a liquid developer whose resonance frequency with the measuring arrangement according to 1 can be measured over the graph of 4 the toner concentration TK be read. The curve after 4 may be stored as a table in the processor unit PR. Thus it can be concluded directly from the resonance frequency to the toner concentration TK, in contrast to a method in which the speed of sound is first determined and then closed over a determined by a Einmessvorgang table from the speed of sound on the toner concentration. However, the measurement of the speed of sound over the duration of the sound wave in a sample chamber is less accurate compared to the determination of the resonance frequency.

In addition, with the measuring arrangement of 1 from the evaluation of the ESA signal and the mass concentration TK obtained via the resonance frequency at a given temperature T, the mobility in a sample volume RW O'Brien et. al./Colloids and Surfaces A be determined. The prerequisite is according to the formula (2) that the quantities ESA (sound pressure amplitude), TK (mass concentration), c (sound velocity of the liquid) and η (viscosity of the liquid) and Δρ (density difference between particle and liquid) are known. The sound pressure amplitude ESA is measured by the measuring cell MZ. The mass concentration TK is determined from the resonance frequency in the processor unit. The further variables c (sound velocity of the liquid) and Δρ (density difference between particle and liquid) are known for the dispersions to be investigated, for example liquid developers. In a liquid developer, the liquid is the carrier liquid or the carrier.

The influencing variables on the amplitude (ESA) of the sound pressure wave are (after RW O'Brien et. al./Colloids and Surfaces A ): ESA = c · Δp · TK · μ _d · G (1)

c:

Schallgeschwindigkeit der Flüssigkeit in der Dispersion

Δp:

Dichtedifferenz zwischen Partikel und Flüssigkeit

TK:

Partikelmassenkonzentration

µ_d:

dynamische Mobilität der Partikel

G:

Kalibierfaktor, der z.B. die Eigenschaften der Messzelle MZ enthält.

Here are:

c:

Speed of sound of the liquid in the dispersion

Ap:

Density difference between particle and liquid

TK:

Particle mass concentration

μ _d :

dynamic mobility of the particles

G:

Calibration factor, which contains eg the properties of the measuring cell MZ.

From the ESA values, the value of the dynamic mobility μ _{d of} the particles can be calculated as: μ _d = ESA / c × Δp × TK × G (2)

G is determined by the calibration of the mobility measurement.

If only the mass concentration TK of the particles is to be determined, the excitation of the acoustic wave in the measuring cell MZ can also take place photoacoustically, e.g. with optical radiation (e.g., by a laser) at appropriate wavelengths in which the dispersion absorbs the radiation sufficiently.

LIST OF REFERENCE NUMBERS

MA

measuring arrangement

MZ

cell

ST

control unit

PR

processor unit

SP

storage unit

1

dispersion

2

sample chamber

3

electrodes

4

AC voltage source

5

Schallleitstab

6

Sound pressure transducer

7

temperature sensor

ESA

 Sound pressure level

c

Speed of sound of the liquid in the dispersion

Ap

Density difference between particle and liquid

TK

Particle mass concentration

μ _d

dynamic mobility

G

calibration

U (f)

 Excitation voltage with the frequency f

f

frequency

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2006/0150836 A1 [0003]
• US 2008/279597 A1 [0003]
• US 2011/58838 A1 [0008]
• US 6817229 B2 [0008]
• US 5121629 A [0008]
• US 7764891 B2 [0008]
• US 5245290 A [0009, 0023]

Cited non-patent literature

• RW O'Brien et. al./Colloids and Surfaces A: Physiochem. Closely. Aspects 218 (2003) p.89-101 [0009]
• RW O'Brien et. al./Colloids and Surfaces A: Physiochem. Closely. Aspects 218 (2003) p.89-101 [0015]
• RW O'Brien et. al./Colloids and Surfaces A [0029]
• RW O'Brien et. al./Colloids and Surfaces A [0030]

Claims (9)

Method for determining the particle mass concentration in a particle and liquid dispersion, - In which the dispersion in a measuring cell (MZ) is exposed to an alternating field of variable frequency, by which the particles are vibrated in the dispersion, whereby the particles in the dispersion generate sound pressure waves, - In which the amplitudes (ESA) of the sound pressure waves are measured in dependence of the frequencies, wherein the maximum amplitude of the sound pressure waves is determined and the frequency associated with this amplitude is determined as the resonance frequency of the sound pressure wave, and - In which from the resonance frequency, the mass concentration (TK) of the particles in the dispersion is determined. Method according to Claim 1, in which the alternating field is generated by an electrical alternating voltage of adjustable frequency. The method of claim 1, wherein the alternating field is generated photoacoustically. The method of claim 1 or 2, wherein the dependence of the resonance frequency of the mass concentration (TK) is determined in a Einmessvorgang in which at a given temperature (T) in the measuring cell (MZ) dispersions with known mass concentrations (TK) are filled and their Resonant frequencies are detected and the dependence of the resonance frequencies of the mass concentrations (TK) is entered in a table, so that from a measured resonance frequency of a dispersion from the table, the mass concentration (TK) of the particles in the dispersion can be read. A method according to any one of the preceding claims, wherein the dispersion is a liquid developer comprising toner particles and carrier liquid used to develop charge images in an electrographic printing apparatus. Method according to one of the preceding claims, in which the amplitudes (ESA) of the sound pressure waves are measured as a function of the frequencies in the measuring cell (MZ) and the measured values are fed to a control unit (ST), in which the control unit (ST) supplies the measured values to a processor unit (PR) which determines the resonance frequency from the measured values and determines the mass concentration (TK) as a function of the resonance frequency and outputs it at the output. Method according to Claim 6, in which the control unit (ST) is composed of the mass concentration (TK), the sound pressure amplitude (ESA) and the known dispersion variables of the speed of sound (c) of the liquid in the dispersion, the density difference (Δp) between the particle and the liquid in the Dispersion determines the dynamic electrophoretic mobility (μ _d ) of the particles in the dispersion. The method of claim 7, wherein the dynamic electrophoretic mobility μ _{d of} the particles in the dispersion of the formula μ _d = ESA / c × Δp × TK × G where c = sound velocity Δp = density difference between particles and liquid TK = mass concentration and G = a calibration factor which is dependent on the frequency. The method of claim 8, wherein the determination of the mass concentration (TK) and the electrophoretic mobility (μ _d ) takes place simultaneously in a measuring operation.

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