JP2910596B2 - Particle size distribution analyzer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser diffraction / scattering type particle size distribution measuring apparatus, and more particularly to a method suitable for measuring the particle size distribution of a sample in which particles are dispersed in a medium at a high concentration. The present invention relates to a particle size distribution measuring device.

[0002]

2. Description of the Related Art In a laser diffraction / scattering type particle size distribution measuring apparatus, a spatial intensity distribution of diffraction / scattered light generated by irradiating a particle group in a dispersed state with laser light is measured, and the measurement result is measured. It is converted into the particle size distribution of the sample particle group based on the Fraunhofer diffraction theory or Mie scattering theory.

That is, when a particle is irradiated with a laser beam,
The laser light is diffracted or scattered by the particles. The intensity distribution pattern of the diffraction / scattered light changes depending on the size of the particles. The laser diffraction / scattering type particle size distribution measuring device utilizes such a principle, and by measuring the spatial intensity distribution of the diffracted / scattered light obtained by irradiating the dispersed particles with laser light, Calculate the particle size distribution of the particle group. In an actual particle group, particles having different sizes are mixed, so that the intensity distribution pattern of the diffraction / scattered light by the particle group is a superposition of the diffraction / scattered light from each particle.

In an actual apparatus, as shown schematically in FIG. 7, an example of a basic configuration thereof is shown. As shown in FIG. Of the diffraction / scattered light by the group,
The forward diffracted / scattered light is condensed by the lens 73 to form a ring-shaped diffracted / scattered image at a position of the focal length, and at the position, a ring-shaped or semi-ring-shaped having a radius different from each other. A ring detector 74, which is an aggregate of optical sensors having a plurality of light receiving surfaces, is arranged to measure the light intensity at each diffraction / scattering angle in a predetermined forward angle range. Further, the scattered light to the side and the back is separated from the side scattered light sensor 75 and the back scattered light sensor 7 respectively.
6 to detect.

[0005] The spatial intensity distribution of the diffracted / scattered light obtained in this manner is obtained by superimposing the diffracted / scattered light from a large number of particles having different sizes as described above. Expressed as a matrix,

[0006]

(Equation 1)

[0007] Each element s _i of the light intensity distribution vector
(I = 1, 2,..., M) is the amount of incident light on each of the optical sensor elements for detecting the intensity of the diffracted / scattered light placed forward, side, rear, and the like. Also, each element q _j (j =
1, 2,... N) make the particle size distribution measurement range finite, divide this range into n, set the maximum value to d ₁ and the minimum value to d _{n + 1,} and set each divided section [d _j, d _{j + 1]} of the one particle size _{x j (j = 1,2, ····} n) when a representative in corresponding to the respective particle diameter x _j

[0008]

(Equation 2)

Is a relative particle amount (%) normalized (normalized) so that The coefficient matrix A (matrix) is a coefficient matrix for converting the particle size distribution q (vector) into the light intensity distribution s (vector), and each element a _{i, j}
The physical meaning of (i = 1, 2,..., M = 1, 2,..., N) is that the light diffracted / scattered by a particle group having a unit particle amount of particle diameter x _j is a light intensity. It is the light intensity detected by the i-th element from the sensor located at the smallest angle side in the sensor group for measuring the distribution. This numerical value of a _{i, j} can be theoretically calculated. For this, the Fraunhofer diffraction theory is used when the particle diameter is sufficiently large compared to the wavelength of the laser light serving as the light source. However, in the submicron region where the particle size is equal to or smaller than the laser wavelength,
Mie scattering theory must be used. The Fraunhofer diffraction theory can be considered to be an excellent approximation of the Mie scattering theory that is effective when the particle diameter is sufficiently larger than the wavelength in forward small angle scattering.

However, a coefficient matrix A using Mie scattering theory
In order to calculate the elements of (matrix), it is necessary to set the refractive index of the particles and the medium in which the particles are dispersed.
By deriving an equation for obtaining a least square solution of the particle size distribution vector q based on the equation (1),

[0011]

(Equation 3)

Is obtained. The coefficient matrix A (matrix) can be calculated in advance based on the Fraunhofer diffraction theory or the Mie scattering theory as described above, and each element of the light intensity distribution s (vector) on the right side of the equation (5) is It is clear that the particle size distribution q (vector) can be obtained using these since the light amounts are actually measured by the sensor.

The principle of particle size distribution measurement by the laser diffraction / scattering method has been described above. However, this is an example of the calculation method, and there are various other variations.
Also, there are various variations in types and arrangements of sensors and detectors.

In this type of measuring apparatus, the sample particles are usually dispersed in an appropriate medium to form a suspension, and the suspension is irradiated with laser light. If the sample itself is already in the form of a suspension, it is general to irradiate the sample directly or appropriately diluted with laser light. The irradiation of the suspension with the laser beam is performed in a state where the suspension is flowed in the flow cell or in a state where the suspension is accommodated in a container-shaped batch cell.

[0015]

By the way, in this type of measuring apparatus, the concentration of the particle group in the suspension needs to be lower than a certain concentration in order not to cause multiple scattering. Multiple scattering, as schematically shown in FIG. 8, is a phenomenon in which light diffracted or scattered by one particle is scattered again by another particle, and occurs when the suspension concentration is too high. When such multiple scattering occurs, the particle size distribution calculated based on the obtained spatial intensity distribution of the diffracted / scattered light naturally does not accurately represent the true particle size distribution of the sample particle group. I can't get it.

In order to avoid the occurrence of such multiple scattering, the concentration of the suspension to be irradiated with the laser beam is set to a certain concentration or less. In this case, if the sample itself is already in the form of a suspension, It is necessary to irradiate a laser beam in a state diluted with an appropriate medium. However, depending on the type of sample, the particle size distribution may change due to dilution, for example, as with ink. For such a sample, a conventional laser diffraction / scattering type particle size distribution measuring apparatus may be used. It has been considered difficult to measure an accurate particle size distribution.

The present invention has been made in view of such circumstances, and enables accurate measurement of particle size distribution without diluting a high-concentration sample suspension and without causing multiple scattering. It is intended to provide equipment.

[0018]

Means for Solving the Problems To achieve the above object, a particle size distribution measuring apparatus according to the present invention uses a diffraction / observation method obtained by irradiating a group of particles to be measured in a dispersed state with a laser beam.
In a device that measures the spatial intensity distribution of scattered light and calculates the particle size distribution of the group of particles to be measured from the measurement result, the sample cell that contains the group of particles to be measured to irradiate laser light has two glass plates and And a support member for detachably supporting these in a state of intersecting with the optical axis of the irradiation laser light, and a suspension formed by dispersing the particles to be measured in the medium between the two glass plates. The method is characterized in that the suspension is held in a sandwiched state and the sample cell is arranged to be inclined with respect to the optical axis of the irradiation laser light.

[0019]

As described above, multiple scattering is a phenomenon in which diffraction / scattered light by one particle is again scattered by another particle, and is greatly affected by the suspension concentration. The shorter the optical path length in the liquid, the lower the probability that multiple scattering will occur even at the same suspension concentration. The present invention utilizes this point.

That is, if the sample suspension is sandwiched between the two glass plates 31 and 32 and is arranged so as to intersect with the optical axis of the irradiation laser beam, as shown in FIG. The laser light will pass through a very thin suspension layer,
There is no danger of multiple scattering even in a highly concentrated suspension.

[0021]

FIG. 1 is a schematic diagram showing the configuration of a measuring optical system according to an embodiment of the present invention. The output light from the laser light source 1 is applied to a sample suspension S in a sample cell 3 having a structure described later in a state where the output light is converted into a parallel light beam by a collimator 2. Sample cell 3
A condensing lens 4 is provided on the optical axis of the laser light on the opposite side of the laser light source 1 with respect to the laser light source 1. A conventional ring detector 5 for measurement is provided. Further, a side scattered light sensor 6 and a back scattered light sensor 7 for measuring side scattered light and back scattered light, respectively, are arranged on the side and rear side (on the side of the laser light source 1) of the sample cell 3. .

The outputs of the ring detector 5 and the side scattered light sensor 6 and the back scattered light sensor 7 are amplified by an amplifier and digitized by an A / D converter. And is converted into the particle size distribution of the group of particles to be measured by a known algorithm.

FIG. 2 is an exploded perspective view of the sample cell 3 which is a feature of the embodiment of the present invention. The sample cell 3 includes two thin glass plates 31 and 32 and a support member 33 that supports the thin glass plates 31 and 32 in a state of intersecting the optical axis of the laser beam passing through the collimator 2. Then, the sample suspension S
Is statically held on the optical axis of the laser beam while being sandwiched between the two glass plates 31 and 32, and is used for measuring the diffraction / scattered light intensity distribution.

In this example, the method of setting the sample suspension S at the measurement location as described above is as follows. First, the sample cell 3 is disassembled and one glass plate 31 is placed substantially horizontally.
After a small amount of the sample suspension S is dropped on the surface, the other glass plate 32 is overlaid thereon. At this time, the two glass plates 31 and 32 are attached to each other due to the surface tension of the liquid medium in the sample suspension S. The two glass plates 31 and 32 are attached to the support member 33 and are attached as shown in FIG. Are arranged so as to intersect the optical axis of the laser light. At this time, even if the concentration of the sample suspension S is considerably high, it is not diluted and the glass plate 3 is not diluted.
1 and 32.

Thus, the two thin glass plates 31, 32
When the laser beam is irradiated with the sample suspension S interposed therebetween, the optical path length of the laser beam in the sample suspension becomes extremely short because the sample suspension S has an extremely thin layer. . Therefore, even if the high-concentration sample suspension S is used as it is, multiple scattering does not occur as schematically shown in FIG.

Here, for example, when the particle diameter of the particles to be measured is relatively large, or when the concentration of the sample suspension S is not so high and it is desired to obtain a sufficient intensity of diffraction / scattered light, two sheets An appropriate spacer may be interposed between the glass plates 31 and 32. 4A and 4B are explanatory views of a structure example of a sample cell with a spacer interposed therebetween. FIG. 4A is a cross-sectional view, and FIGS. 4B and 4C are front views showing the spacer 34 extracted and its CC cross-sectional view. It is. In this example, a through hole 34a is formed in a central portion of a thin spacer 34 having a thickness of about 0.1 to 1 mm, and the spacer 34 is attached to the glass plates 31 and 3.
2 and the through holes 3 of the spacer 34
The sample suspension S is sandwiched between two glass plates 31 and 32 in 4a.

In order to fix the glass plates 31, 32 and the spacer 34 to each other, for example, the surfaces on both sides of the spacer 34 may be provided with adhesiveness, or as shown in a sectional view in FIG. Alternatively, the upper and lower ends of the glass plates 31 and 32 may be sandwiched from both sides with screws 36 via the fixing plate 35 so as not to overlap with the through hole 34a and not to block the laser beam.

In each of the above examples, it is desirable that the angle formed between the sample cell 3 and the laser optical axis be slightly inclined as illustrated in a plan sectional view in FIG. 6 rather than perpendicular. That is, when the sample cell 3 is arranged perpendicular to the laser optical axis, accurate detection of side scattered light (scattered light in a direction perpendicular to the laser optical axis) is performed particularly when the spacer 34 is interposed. Although it is difficult, by giving an inclination as shown in FIG. 6, accurate detection of side scattered light becomes possible, which makes it possible to measure the particle size distribution of a considerably small particle group in the submicron region with higher accuracy. That can be done.

Further, the support member 33 in each of the above examples is used.
In addition to supporting the two glass plates 31 and 32, or a spacer 34 and a fixing plate 35 in addition to the two glass plates 31 and 32, the glass plates 31 and 32 or the fixing plate 35 Needless to say, the method of pressing with a set screw or the like can be modified.

[0030]

As described above, according to the present invention,
The sample cell in the laser diffraction / scattering type particle size distribution measuring device is constituted by two glass plates and a supporting member which detachably supports these glass plates in a state of intersecting with the optical axis of the irradiation laser beam. Laser light is emitted while the sample suspension is sandwiched between glass plates of high concentration, and high-concentration suspensions that could not be measured due to the occurrence of multiple scattering with the conventional particle size distribution analyzer using a flow cell or batch cell It has become possible to measure the diffraction / scattered light intensity distribution accurately without causing multiple scattering while maintaining the liquid sample at a high concentration without any dilution. As a result, accurate particle size distribution can be obtained even for highly concentrated sample suspensions, such as inks, in which the dispersoids disperse, disintegrate, or agglomerate due to dilution, and multiple scattering occurs as it is. It is now possible to make measurements. Moreover, in the present invention, the sample cell is arranged at an angle with respect to the optical axis of the irradiation laser light, so that it is possible to accurately detect side scattered light, and thereby, a particle group of a considerably small submicron region can be detected. The particle size distribution can be measured with higher accuracy.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an embodiment of the present invention, showing a schematic diagram of a measurement optical system.

FIG. 2 is an exploded perspective view of the sample cell 3.

FIG. 3 is a diagram illustrating the operation of the embodiment of the present invention.

FIG. 4 is a structural explanatory view of a sample cell according to another embodiment of the present invention.

FIG. 5 is a structural explanatory view of a sample cell according to still another embodiment of the present invention.

FIG. 6 is an explanatory diagram of an example of the arrangement of the sample cell 3 with respect to the laser optical axis in each embodiment of the present invention.

FIG. 7 is a schematic diagram showing a basic configuration of a laser diffraction / scattering type particle size distribution analyzer.

FIG. 8 is an explanatory diagram of multiple scattering generated when a high-concentration suspension is irradiated with laser light.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser light source 2 Collimator 3 Sample cell 31, 32 Glass plate 33 Support member 34 Spacer 34a Through-hole 4 Condensing lens 5 Ring detector 6 Side scattered light sensor 7 Back scattered light sensor

Claims (1)

(57) [Claims] An apparatus for measuring a spatial intensity distribution of diffracted / scattered light obtained by irradiating a laser beam onto a group of particles to be measured in a dispersed state and calculating a particle size distribution of the group of particles to be measured from the measurement result. A sample cell containing a group of particles to be measured for irradiating a laser beam is composed of two glass plates and a supporting member for detachably supporting the two glass plates in a state of crossing the optical axis of the irradiating laser beam. Between the two glass plates, holding the suspension in which the particles to be measured are dispersed in the medium , and irradiating the sample cell.
A particle size distribution measuring device, which is arranged to be inclined with respect to the optical axis of a laser beam .