JP5713349B2 - Zeta potential measurement method and zeta potential measurement system - Google Patents

Description

  The present invention relates to a zeta potential measurement method and a zeta potential measurement system.

  An important indicator of particles is the zeta potential. The zeta potential is usually calculated by directly observing the mobility of the electrophoresed particles. As such a zeta potential measuring device, for example, Zeta Sizer 2000 manufactured by Malvern Instruments Ltd. is known.

  On the other hand, methods for classifying fine particles using the difference in zeta potential on the surface of fine particles have been actively studied in recent years (see Patent Documents 1 to 3).

JP 2005-230712 A JP 2005-334865 A JP 2011-125801 A

  In a method of classifying fine particles using a difference in zeta potential on the surface of the fine particles, a precise numerical value of zeta potential for each particle size is required.

  However, since the zeta potential measuring apparatus as described above directly observes the mobility of particles in the suspension, it cannot simply measure the zeta potential for each particle size of the particles in the suspension. Therefore, the present inventors have searched for a new method that can easily measure the zeta potential for each particle size.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a zeta potential measurement method and a zeta potential measurement system in which a zeta potential for each particle size of particles can be easily obtained.

  In order to solve the above-described problem, a zeta potential measurement method according to one aspect of the present invention is a method in which a parameter related to pressure at a position in a suspension is changed over time while an electric field is applied to the suspension including particles. And a step of calculating a zeta potential for each particle size of the particles using a change with time of the parameter and a particle size distribution of the particles.

  In the above zeta potential measurement method, the density of the columnar portion of the suspension existing above the position in the suspension changes with time as the particles move. For this reason, the parameter related to the pressure at the position in the suspension changes with time. Here, since the zeta potential is different for each particle size, the moving speed of the particles due to the electric field is also different for each particle size. Therefore, the zeta potential for each particle size is reflected in the change with time of the parameter related to the pressure at the position in the suspension. Therefore, the zeta potential for each particle diameter can be easily obtained by using the change with time of the parameter and the particle size distribution of the particles.

  The zeta potential measurement method may further include a step of imparting a charge to the particles in the suspension before measuring the time-dependent change of the parameter.

  When employing a method of classifying fine particles by utilizing the difference in zeta potential on the surface of the fine particles, it is preferable to perform tribocharging in advance by a bead mill or the like. In the bead mill, apart from fine particles to be classified, beads having a uniform particle size having a large particle diameter are charged into the suspension, and the fine particles to be classified are charged by stirring. According to the classic concept of zeta potential, the zeta potential is equal for particles of the same composition. However, when tribocharging is performed in advance with a bead mill or the like, a phenomenon occurs in which the zeta potential varies depending on the particle size. This is considered to be because the contact property between the fine particles to be classified and the large-diameter bead having a uniform diameter varies depending on the particle diameter of the fine particles.

  It is preferable that the beads having a large diameter and uniform diameter are positively or negatively charged. The more uniform the particle size of the beads, the better results. Specifically, a bead having a coefficient of variation (CV) of the bead particle size of less than 3% may be used. After applying a charge to the particles by such a method, the accuracy of classification can be expected by measuring the zeta potential for each particle size using the above-described zeta potential measurement method.

  The parameter may be the weight of an object placed at a position in the suspension. In this case, as the pressure at the position in the suspension changes with time, the buoyancy received by the object changes with time. For example, if the pressure at the position in the suspension decreases with time, the buoyancy received by the object also decreases with time. In this case, the weight of the object increases with time. Therefore, if the weight of the object arranged at the position in the suspension is measured, the zeta potential for each particle diameter can be obtained more easily. The weight of the object can be measured using, for example, a scale that measures the weight of the object placed at a position in the suspension. In this case, the weight of the object is measured by placing the scale above the suspension and suspending the object from the scale.

  The parameter may be a pressure at a position in the suspension. The pressure can be measured using, for example, a pressure sensor that measures the pressure at a position in the suspension.

  The parameter may be the turbidity or refractive index of the suspension at a position in the suspension, or the particle density of the suspension at a position in the suspension. The particle density in the suspension can be measured, for example, by counting the number of particles in the image of the suspension in a certain range.

  A zeta potential measurement system according to one aspect of the present invention includes an electrode for applying an electric field to a suspension containing particles, and a measurement device that measures a change over time in a parameter related to pressure at a position in the suspension. And an arithmetic unit that calculates a zeta potential for each particle size of the particles using the change with time of the parameters and the particle size distribution of the particles.

  In this system, as described above, the zeta potential for each particle size of the particles can be easily obtained by using the parameter change with time and the particle size distribution of the particles.

  The zeta potential measurement system may further include a charge imparting device that imparts a charge to the particles in the suspension.

  The measuring device may be a scale that measures the weight of an object placed at a position in the suspension. In this case, as described above, the zeta potential for each particle size of the particles can be obtained more easily.

  The measurement device may be a pressure sensor that measures a change in pressure over time at a position in the suspension.

  The measuring device may be a device that measures a change over time in turbidity or refractive index of the suspension at a position in the suspension, or the particle density of the suspension at a position in the suspension. An apparatus for measuring a change with time may be used. The apparatus for measuring the change in the particle density with time may include an apparatus for taking an image of the suspension in a certain range and an apparatus for counting the number of particles in the image.

  ADVANTAGE OF THE INVENTION According to this invention, the zeta potential measuring method and zeta potential measuring system which can obtain the zeta potential for every particle diameter of particle | grains simply are provided.

It is a figure showing typically the zeta potential measurement system concerning a 1st embodiment. It is the figure which expanded a part of FIG. It is a flowchart which shows the zeta potential measurement method which concerns on 1st Embodiment. It is a graph which shows an example of a particle size distribution. It is a graph which shows an example of a time-dependent change of the weight of a detection container. It is a graph which shows an example of the relationship between a particle size and zeta potential. It is a graph which shows another example of the time-dependent change of the weight of a detection container. It is a graph which shows another example of the relationship between a particle size and zeta potential. It is a figure which shows typically the zeta potential measurement system which concerns on 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same reference numerals are used for the same or equivalent elements, and duplicate descriptions are omitted.

(First embodiment)
FIG. 1 is a diagram schematically illustrating a zeta potential measurement system according to the first embodiment. FIG. 2 is an enlarged view of a part of FIG. In the zeta potential measurement system 10 shown in FIG. 1, a sedimentation balance method is used. The zeta potential measurement system 10 includes electrodes 44 and 46, a measurement device 36, and a calculation device 38. The zeta potential measurement system 10 may include a charge applying device 12 as necessary.

  The charge imparting device 12 imparts electric charge to particles (powder) in the suspension and stirs the particles in the suspension by, for example, stirring the suspension (slurry) accommodated in the stirring tank 14. It can be uniformly dispersed. The particles are usually given a negative charge, but may be given a positive charge. The charge applying device 12 is a stirrer such as a bead mill. The charge applying device 12 is connected to the controller 16, for example. The controller 16 can control, for example, the stirring speed (peripheral speed of the stirring blade), the stirring time, and the like of the charge applying device 12. The charge imparting device 12 may impart a charge to the particles in the suspension by a method other than stirring.

The suspension includes particles and a liquid (dispersion). The particles in the suspension may be organic particles or inorganic particles. Such particles can be used as a core of conductive particles contained in an anisotropic conductive film or anisotropic conductive paste. Examples of the organic particle material include acrylic resin and styrene resin. Examples of the material of the inorganic particles include silica (SiO ₂ ). The average particle diameter of the particles in the suspension is, for example, 100 μm or less, 3 μm or less, or 50 μm or more. Examples of the liquid in the suspension include water.

  When the charge imparting device 12 is a bead mill, the beads used are made of an inorganic material such as silica. The particle size of the beads is not particularly limited, but is preferably 100 μm or more and 1000 μm or less in consideration of ease of separation by filtration. As the beads are monodispersed, a charge corresponding to the particle diameter can be imparted to the particles. Regarding the variation in the particle size of the beads, it is preferable that CV <3%, where the coefficient of variation of the particle size is CV.

  An ultrasonic vibrator 20 may be attached to the stirring tank 14. The ultrasonic transducer 20 is driven by the ultrasonic transmitter 22 and irradiates the suspension in the stirring tank 14 with ultrasonic waves. Thereby, aggregation of the particles in the suspension is suppressed, and the particles can be more uniformly dispersed in the suspension.

  For example, a valve 18 is provided in the agitation tank 14. The opening and closing of the valve 18 is controlled by the controller 16. When the valve 18 is opened, the suspension is supplied to the sedimentation tank 30 through the supply pipe 26 and the bypass pipe 28 after passing through the pipe 24. When the charge imparting device 12 is a bead mill, the particle size of the beads used is preferably larger than the particle size of the particles in the suspension. Thereby, it can suppress that a bead passes the valve | bulb 18. FIG.

  An electric field is applied to the suspension containing particles between the electrodes 44 and 46. The electric field is applied along the direction of gravity, for example. The electrodes 44 and 46 are made of a conductive material such as a metal or a conductive polymer. The electrode 44 is, for example, a metal plate disposed on the bottom surface of the settling tank 30. The electrode 46 is, for example, a metal mesh disposed on the liquid level of the suspension accommodated in the settling tank 30. The electrodes 44 and 46 are connected to a DC power source 48 via, for example, electrical wiring. As a result, a voltage ΔV is applied between the electrodes 44 and 46. The voltage ΔV between the electrodes 44 and 46 is preferably 1 to 200V. For example, the electrode 44 can be a positive potential and the electrode 46 can be a negative potential.

  The measuring device 36 measures a change with time of a parameter related to pressure at a depth h (position in the suspension) from the liquid surface of the suspension. The depth h is about 8 cm, for example. In the present embodiment, the measuring device 36 is a scale that measures the weight of the detection container 32 (object) disposed at the depth h. An example of the scale is a precision electronic balance with high measurement accuracy. The weight of the detection container 32 is an example of a parameter related to the pressure at the depth h. By measuring the weight of the detection container 32, the pressure at the depth h can be indirectly detected. The measuring device 36 is connected to the arithmetic device 38. Thereby, the weight data of the detection container 32 measured by the measuring device 36 is sent to the arithmetic device 38.

  The detection container 32 is suspended from the measuring device 36 by a support wire 34, for example. The detection container 32 is disposed between the opposing electrodes 44 and 46. The bottom surface of the detection container 32 is located at a depth h. The detection container 32 is filled with a suspension. By supplying the suspension from the bypass pipe 28 into the sedimentation tank 30, it is possible to suppress the detection container 32 from vibrating due to the supply of the suspension.

  The computing device 38 calculates the zeta potential for each particle size of the particle using the change with time of the parameter and the particle size distribution of the particle. In the present embodiment, the arithmetic unit 38 calculates the zeta potential for each particle size of the particle using the change over time of the weight of the detection container 32 and the particle size distribution of the particle. The arithmetic device 38 is a computer, for example. The arithmetic device 38 may include a storage device such as a hard disk. An output device 40 such as a display and an input device 42 such as a keyboard are connected to the arithmetic device 38. The particle size distribution of the particles is measured in advance by, for example, a particle size distribution measuring device using a dynamic light scattering method, and is recorded in the storage device of the arithmetic device 38.

  FIG. 3 is a flowchart showing the zeta potential measurement method according to the first embodiment. The zeta potential measurement method according to the present embodiment is performed by, for example, the zeta potential measurement system 10 shown in FIG.

  First, a charge is applied to the particles in the suspension (step S1). In the present embodiment, charges are imparted to particles in the suspension in the stirring tank 14 using the charge imparting device 12. After charge is applied to the particles, the suspension in the stirring tank 14 is supplied to the settling tank 30. However, step S1 for imparting electric charge to the particles may not be performed.

  Next, a parameter change with time is measured while applying an electric field to the suspension containing particles (step S2). In the present embodiment, an electric field is applied to the suspension in the settling tank 30 using the electrodes 44 and 46. While the electric field is continuously applied, the change over time of the weight of the detection container 32 is measured using the measuring device 36. The change over time in the measured weight of the detection container 32 is recorded in the storage device of the arithmetic device 38.

  Next, the zeta potential for each particle size is calculated using the parameter change with time and the particle size distribution (step S3). In the present embodiment, using the time-dependent change in the weight of the detection container 32 and the particle size distribution of the particles, the calculation device 38 calculates the zeta potential for each particle size as follows.

Regarding the change over time of the measured weight of the detection container 32, the following expression (1) is established at an arbitrary time t.

G _t represents the amount of weight change at time t. G _te indicates the amount of weight change at the measurement end time. W _t indicates the weight of the detection container 32 measured at time t. W _te indicates the weight of the detection container 32 measured at the measurement end time. W ₀ indicates the weight of the detection container 32 measured in the initial stage (time t = 0). f (D _p ) represents the particle size distribution of the particles. D _p represents the particle size. _De indicates a predetermined particle size. h represents the depth from the liquid surface of the suspension. ν represents the moving speed of the particles. t indicates time. Therefore, νt corresponds to the moving distance of the particles.

G _t / G _{te on the} left side indicates the ratio of the total mass of particles that have passed the depth h at time t to the total mass of particles that have passed the depth h at the measurement end time. First half of the right side shows that the particles having a particle size larger than a predetermined particle size D _e has passed through the depth h at the time t. Second part of the right side, of the particles having a particle size not greater than a predetermined particle diameter D _e, only particles located within a range of a distance νt on the depth h will pass through the depth h at the time t Indicates that

The moving speed ν (D _p ) of the particles is expressed by the following formula (2). The moving speed ν (D _p ) of the particles is the same as the moving speed ν of the particles in the formula (1).

[rho _p represents the density of the particles. ρ _f represents the density of the dispersion. g represents gravitational acceleration. μ indicates the viscosity of the dispersion. e indicates the base of natural logarithm (about 2.7). ε represents the dielectric constant of the dispersion. ΔV represents the voltage applied to the suspension. l represents the distance between the opposing electrodes. ζ represents the zeta potential.

  The first half of the right side corresponds to the particle settling velocity due to gravity (Stokes equation). The latter half of the right side corresponds to the speed of particle movement by the electric field.

Since the zeta potential depends on the particle size, the zeta potential ζ is a function H (D _p ) of the particle size D _p . For example, when a quadratic expression is used as an approximate expression of the zeta potential, the following expression (3) is established. As an approximate expression of the zeta potential, for example, a higher order expression such as a cubic expression or a quartic expression may be used.
ζ = aD _p ² + bD _p + c (3)

On the other hand, the particle size distribution f (D _p ) of the particles is measured in advance by, for example, a particle size distribution measuring apparatus using a dynamic light scattering method. Further, G _t / G _te which is the left side of the expression (1) is calculated from a plurality of (for example, 40) time t from the experimental data of the change over time of the weight of the detection container 32. These values are applied to Equation (1), and using Equations (1) to (3), a, b, and c are matched to experimental values (G _t / G _te calculated at a plurality of times t). Determine the optimal value of. When the approximate expression of the zeta potential is an n-order expression, n + 1 optimum values are determined.

  The above procedure may be executed by a computer program. The computer program may be stored in a storage device of the arithmetic device 38, a computer-readable recording medium, or other storage device.

  It is preferable to start step S2 within 4 hours, more preferably within 1 hour after step S1. In this case, the differential value (gradient) of the zeta potential with respect to the particle size increases.

  In the zeta potential measurement system 10 and the zeta potential measurement method according to the present embodiment, the density of the columnar portion of the suspension that exists above the depth h from the liquid surface of the suspension is changed over time as the particles move. Change. For this reason, when the pressure at the depth h changes with time, the buoyancy received by the detection container 32 changes with time. For example, when the pressure at the depth h decreases with time, the buoyancy received by the detection container 32 also decreases with time. As a result, the weight of the detection container 32 increases with time. Here, since the zeta potential is different for each particle size, the moving speed of the particles due to the electric field is also different for each particle size. Therefore, the change in the weight of the detection container 32 with time reflects the zeta potential for each particle size. Therefore, the zeta potential for each particle diameter can be easily obtained by using the change over time of the weight of the detection container 32 and the particle size distribution of the particles. Further, it can be measured even with a zeta potential of large particles having an average particle size of 10 μm or more, which is usually difficult.

  Using the fact that the zeta potential is different for each particle size, the particles can be classified. When the differential value (gradient) of the zeta potential with respect to the particle size is large, the coefficient of variation (CV) of the particle size in the particles obtained by classification can be reduced.

  Next, experimental examples in the case where the particles in the suspension are silica particles will be described with reference to FIGS.

FIG. 4 is a graph showing an example of the particle size distribution. The horizontal axis indicates the particle size D _p (μm). The vertical axis represents frequency (%).

  FIG. 5 is a graph showing an example of the change over time (sedimentation curve) of the weight of the detection container. The horizontal axis indicates time t (seconds). The vertical axis represents the weight (gram) of the detection container 32. When the voltage applied between the electrodes 44 and 46 is 0 V, the weight of the detection container 32 does not change with time. When the voltage applied between the electrodes 44 and 46 is 70 V, the weight of the detection container 32 increases with time. As shown in FIG. 5, by applying an electric field, the sedimentation rate can be increased even for fine particles.

FIG. 6 is a graph showing an example of the relationship between the particle size and the zeta potential. The horizontal axis indicates the particle size D _p (μm). The vertical axis represents the zeta potential (mV). The density ρ _{p of the} silica particles was 2.24 g / cm ³ . The number of revolutions of the bead mill was 2300 rpm. As shown in FIG. 6, the absolute value of the zeta potential gradually decreases as the particle size increases. The value of the zeta potential varies depending on the number of rotations of the bead mill.

Next, an experimental example in which the particles in the suspension are acrylic resin particles (median diameter 2.59 μm, specific gravity 1.18 g / cm ³ ) will be described with reference to FIGS.

FIG. 7 is a graph showing another example of the change over time of the weight of the detection container. The horizontal axis indicates time t (seconds). The vertical axis represents the weight (gram) of the detection container 32. The voltage ΔV applied between the electrodes 44 and 46 was 30V. The concentration _{C 0} of the acrylic resin particles was 0.75 wt%. Using silica particles with a particle diameter of 100 μm, beads were milled for 30 minutes at a peripheral speed (u _θ ) of 6.65 m / s, thereby imparting charges to the acrylic resin particles.

FIG. 8 is a graph showing another example of the relationship between the particle size and the zeta potential. The horizontal axis indicates the particle size D _p (μm). The vertical axis represents the zeta potential (mV). The density ρ _pe of the acrylic resin particles was 1.18 g / cm ³ . As shown in FIG. 8, the absolute value of the zeta potential gradually increases as the particle size increases. The gradient of the zeta potential of the resin particles (FIG. 8) is opposite to the gradient of the zeta potential of the inorganic particles (FIG. 6). The number average of the zeta potential was -37.1 mV. On the other hand, the zeta potential measured with a zeta sizer was -42 mV. The zeta potential measured in the present embodiment was a value close to the zeta potential measured by the zeta sizer.

(Second Embodiment)
FIG. 9 is a diagram schematically showing a zeta potential measurement system according to the second embodiment. The zeta potential measurement system 10A shown in FIG. 9 includes the pressure detector 54, the support member 52, and the measurement device 50 in place of the detection container 32, the support wire 34, and the measurement device 36, and the zeta potential shown in FIG. The same configuration as that of the potential measurement system 10 is provided. Therefore, the zeta potential measurement system 10A exhibits at least the same effects as those based on the configuration of the zeta potential measurement system 10 excluding the detection container 32, the support wire 34, and the measurement device 36.

The pressure detector 54 is disposed at a depth h from the liquid level of the suspension. The pressure detection unit 54 is connected to the measurement device 50 via the support member 52. In the present embodiment, the measuring device 50 is a pressure sensor that measures a change in pressure over time at a depth h. The measuring device 50 is connected to the arithmetic device 38. Thereby, the pressure data measured in the measuring device 50 is sent to the arithmetic device 38. The computing device 38 can calculate the zeta potential using the change with time of the pressure at the depth h and the particle size distribution of the particles, as in the first embodiment. In this case, the left side of Equation (1) is P _t / P _te . P _t indicates the amount of pressure change at time t. _Pte indicates the amount of pressure change at the measurement end time. In addition, another pressure detection part may be arrange | positioned also at the liquid level of a suspension, a pressure may be measured, and the pressure difference between the liquid level and the depth h of a suspension may be measured.

  In the present embodiment, the pressure at the depth h is measured as an example of a parameter related to the pressure at the depth h. In this case, as the particles move, the pressure at the depth h decreases with time. In the present embodiment, similarly to the first embodiment, the zeta potential for each particle diameter of the particles can be easily obtained by using the change with time of the pressure at the depth h and the particle size distribution of the particles.

  As mentioned above, although preferred embodiment of this invention was described in detail, this invention is not limited to the said embodiment.

  For example, the parameter related to the pressure at the depth h from the liquid level of the suspension may be a parameter obtained by converting the pressure using an arbitrary physical quantity, or may be a parameter capable of indirectly detecting the pressure.

  DESCRIPTION OF SYMBOLS 10,10 ... A zeta potential measurement system, 12 ... Charge application apparatus, 32 ... Detection container (object), 36, 50 ... Measurement apparatus, 38 ... Calculation apparatus, 44, 46 ... Electrode.

Claims (8)

Measuring an aging of a parameter related to pressure at a position in the suspension while applying an electric field to the suspension containing particles;
Calculating the zeta potential for each particle size of the particles using the time course of the parameters and the particle size distribution of the particles;
A zeta potential measurement method comprising:   The zeta potential measurement method according to claim 1, further comprising a step of applying a charge to the particles in the suspension before measuring a change in the parameter with time.   The zeta potential measurement method according to claim 1 or 2, wherein the parameter is a weight of an object placed at a position in the suspension.   The zeta potential measurement method according to claim 1 or 2, wherein the parameter is a pressure at a position in the suspension. An electrode for applying an electric field to a suspension containing particles;
A measuring device for measuring a time-dependent change of a parameter related to pressure at a position in the suspension;
An arithmetic unit that calculates a zeta potential for each particle size of the particles, using the change over time of the parameters and the particle size distribution of the particles;
A zeta potential measurement system comprising:   The zeta potential measurement system according to claim 5, further comprising a charge imparting device that imparts a charge to the particles in the suspension.   The zeta potential measurement system according to claim 5 or 6, wherein the measurement device is a scale that measures the weight of an object disposed at a position in the suspension.   The zeta potential measurement system according to claim 5 or 6, wherein the measurement device is a pressure sensor that measures a change in pressure over time at a position in the suspension.

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