JP3391152B2 - Laser diffraction / scattering particle size distribution analyzer - Google Patents

Description

Description: 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, for example, an actual particle size distribution of a coating element of a paint being sprayed. The present invention relates to a laser diffraction / scattering type particle size distribution measuring apparatus suitable for accurately measuring the particle size distribution. 2. Description of the Related Art In a laser diffraction / scattering type particle size distribution measuring apparatus, generally, a spatial intensity distribution of diffraction / scattered light obtained by irradiating a group of particles to be measured in a dispersed and flying state with laser light is measured. Then, the measurement result is converted into a particle size distribution of the particle group to be measured based on the Fraunhofer diffraction theory or the Mie scattering theory. That is, when a particle is irradiated with a parallel laser beam, the laser beam is diffracted or scattered by the particle.
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 measures the spatial intensity distribution of the diffracted / scattered light obtained by irradiating a group of dispersed flying particles with laser light. , The particle size distribution of the particle group is calculated. 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. [0004] In an actual apparatus, as schematically shown in FIG. 4, an example of a basic configuration thereof is shown. Of the diffracted / scattered light by the particle group P, the forward diffracted / scattered light is condensed by the lens 43 to form a ring-shaped diffracted / scattered image at the position of the focal length, and the positions are mutually separated. A ring detector 44, which is an aggregate of optical sensors having a plurality of concentric ring-shaped or semi-ring-shaped light-receiving surfaces having different radii, is arranged to measure the light intensity at each diffraction / scattering angle in a predetermined forward angle range. . The side scattered light and the back scattered light are detected by independent side scattered light sensors 45 and back scattered light sensors 46, respectively. [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. When expressed by a matrix, [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, sideways, and the like. Also, each element q _j (j = 1,
2,... N) has a finite particle size distribution range, divides the range into n, and sets the maximum value to d ₁ and the minimum value to d _{n + 1.}
And each divided section [d _j, d _{j + 1} ] is represented by one particle diameter x _j (j = 1, 2,... J), and corresponds to each particle diameter x _j. [0008] 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, j = 1, 2,... N) is that light diffracted / scattered by a particle group having a unit particle amount of a particle diameter x _j is represented by This 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 light intensity 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 sub-micron region where the particle diameter is equal to or smaller than the laser wavelength, it is necessary to use Mie scattering theory. 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 large compared to the wavelength in forward small angle scattering. However, in order to calculate the elements of the coefficient matrix A (matrix) using the Mie scattering theory, it is necessary to set the refractive indexes of the particles and the medium in which the particles are dispersed. By deriving an equation for obtaining the least square solution of the particle size distribution vector q based on the equation (1), the following equation is obtained. 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 particles to be measured are dispersed in an appropriate medium to form a suspension (wet method) in order to make the particles to be measured dispersed. Aerosol (dry method) and irradiate a laser beam. [0015] By the way, using the laser diffraction / scattering type particle size distribution measuring apparatus as described above, particles such as paints, that is, particles serving as coating film elements contained in a solvent, When measuring the particle size distribution of the paint, if the coating material itself is irradiated with laser light, the particle concentration is too high, causing multiple scattering, making it impossible to measure the particle size distribution accurately. Multiple scattering, as schematically shown in FIG. 5, is a phenomenon in which light diffracted or scattered by one particle is scattered again by another particle, and occurs when the concentration of the sample suspension is too high. In order to avoid such multiple scattering, it is conceivable to irradiate a laser beam not in the paint itself but in a state diluted with a solvent, but in this case, the state of the coating element may be changed. It is not preferable. It is also conceivable to spray the coating material to form an aerosol and irradiate the laser beam in that state. In this case, as shown schematically in FIG.
Since the droplets L themselves become particles in the air as an aerosol in a dissolved state, the particle size distribution of the particles p of the coating film element cannot be measured. The present invention has been made in view of such circumstances, and in a sample of a paint or the like in which a solid particle group is dispersed at a predetermined concentration in a solvent, fixed particles such as coating film element particles are prepared. It is an object of the present invention to provide a laser diffraction / scattering particle size distribution measuring device capable of accurately and easily measuring the particle size distribution of a group. In order to achieve the above object, a laser diffraction / scattering type particle size distribution measuring apparatus according to the present invention is provided.
As shown in FIGS. 1 and 2, which are drawings of the embodiment, a laser light irradiation optical system 1 for irradiating a laser beam to a group of particles to be measured in a dispersed state, and diffraction / scattered light of the laser beam by the group of particles to be measured. In an apparatus including a measuring optical system 3 for measuring a spatial intensity distribution and an arithmetic unit 6 for measuring a particle size distribution of a group of particles to be measured from the obtained diffraction / scattered light intensity distribution, the particles to be measured are irradiated with laser light. A means 2 for holding the group in a dispersed state comprises a transparent plate 2a and a support member 2b for detachably supporting the transparent plate 2a in a state of crossing the optical axis of the irradiation laser beam.
The transparent plate 2a is formed by spraying a group of particles to be measured dispersed in a solvent and evaporating the solvent.
In the state where the particles to be measured are attached to the surface of a, diffraction /
It is characterized by being subjected to measurement of scattered light. When a sample of a paint or the like containing solid particles such as particles of a coating element in a solvent is sprayed on the surface of the transparent plate 2a and left or appropriately heated, the solvent evaporates. As shown schematically in FIG. 3, only the solid particles p such as coating film element particles adhere to the surface of the transparent plate 2a. In this state, when the transparent plate 2a is mounted on the support member 2b and irradiated with laser light from the laser light irradiation optical system 1, the laser light is diffracted by solid particles p attached to the surface of the transparent plate 2a. Since the particles are scattered, the particle size distribution of the solid particles p in the solvent itself can be obtained by measuring the diffraction / scattered light with the measuring optical system 3. FIG. 1 is a schematic diagram showing the overall configuration of an embodiment of the present invention. The laser light irradiation optical system 1 includes a laser light source 1a such as a semiconductor laser and a collimator 1b that converts output light from the laser light source 1a into a parallel light beam, and can irradiate a parallel laser light to a sample holder 2 described later. A measuring optical system 3 is provided on the opposite side of the laser irradiation optical system 1 with the sample holder 3 interposed therebetween. The measuring optical system 3 includes a condenser lens 3a disposed on the optical axis of the irradiation laser beam, and a group of particles to be measured held at the focal position of the condenser lens 3a and held by the sample holder 2. A ring detector 3b equivalent to the conventional one for measuring the intensity distribution of the diffracted / scattered light to the front due to the above, and also measures the scattered light to the side and to the rear of the particle group to be measured held on the sample holder 2, respectively. Scattered light sensor 3c and back scattered light sensor 3d. Each sensor element of the ring detector 3b and each output of the side and back scattered light sensors 3c and 3d are individually amplified by an amplifier 4 and then converted by an A / D converter 5
And digitized by the computer 6. The computer 6 converts the diffraction / scattered light intensity distribution data from each sensor into a particle size distribution of the particle group to be measured by a known calculation based on the above equation (5), and displays the result on the CRT 7. FIG. 2 is an exploded perspective view of the sample holder 2 which is a feature of the embodiment of the present invention. The sample holder 2 includes a transparent plate 2a such as a glass plate and a support member 2b that supports the transparent plate 2a in a state of intersecting the optical axis of the laser light irradiation optical system 1.
The transparent plate 2a is detachable from the support member 2b. Using the above examples of the present invention, for a sample in which solid particles are dispersed at a high concentration in a solvent, including particles of a coating element in a paint, the solid particles are The procedure for measuring the particle size distribution will be described. First, the transparent plate 2a is detached from the support member 2b, and a liquid to be measured such as paint is sprayed on one surface thereof by a spray or the like. Thereby, the droplet of the solvent in which the solid particles are dispersed adheres to one surface of the transparent plate 2a. In this state, if air drying or drying with appropriate heating is performed, only the solvent evaporates, and one surface of the transparent plate 2a, as schematically shown in FIG. Only the adhered state. In this state, the transparent plate 2a is mounted on the support member 2b and arranged so as to intersect the optical axis of the irradiation laser light,
The diffraction / scattered light intensity distribution is measured. Since the measurement result of the diffraction / scattered light intensity distribution obtained in this way is a diffraction / scattered light intensity distribution by a solid particle group which is not affected by the solvent, the particle size distribution calculated using the measurement result is In other words, an accurate particle size distribution of the solid particles is represented. It is needless to say that any transparent material can be used for the transparent plate 2a in addition to the glass plate. As described above, according to the present invention, a sample in which solid particles are dispersed at a high concentration in a solvent, such as a paint, is sprayed onto the surface of a transparent plate to evaporate the solvent. In this state, only the solid particles are adhered to the surface of the transparent plate, and the transparent plate is supported by crossing the optical axis of the laser light irradiation optical system so that the solid particles are dispersed. Since the configuration is such that the particles are retained, the particle size distribution of the particle group of the coating film element in the paint which could not be measured conventionally can be accurately measured without being affected by the solvent.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view showing the overall configuration of an embodiment of the present invention. FIG. 2 is an exploded perspective view of the sample holder 2. FIG. FIG. 4 is a schematic diagram showing a state after evaporating. FIG. 4 is a schematic diagram showing a basic configuration of a laser diffraction / scattering type particle size distribution analyzer. FIG. 5 is generated when a high-concentration suspension is irradiated with laser light. Illustration of multiple scattering [Fig. 6] Schematic diagram showing the state when paint is sprayed [Explanation of reference numerals] 1 Laser beam irradiation optical system 2 Sample holder 2a Transparent plate 2b Support member 3 Measurement optical system 6 Computer p Solid state Particles (coating element particles, etc.)

Claims (1)

(57) Claims 1. A laser light irradiation optical system for irradiating a laser beam to a group of particles to be measured in a dispersed state, and the spatial intensity of the diffraction / scattered light of the laser beam by the group of particles to be measured. In a device equipped with a measuring optical system for measuring the distribution and an arithmetic means for measuring the particle size distribution of the particles to be measured from the obtained diffraction / scattered light intensity distribution, the particles to be measured are dispersed in order to irradiate laser light. Means for holding the transparent plate, and a supporting member for detachably supporting the transparent plate in a state of intersecting with the optical axis of the irradiation laser beam, wherein the transparent plate is a substrate dispersed in a solvent. By spraying the measurement particle group and evaporating the solvent, diffraction /
Laser diffraction characterized by being used for measuring scattered light /
Scattering type particle size distribution analyzer.