CS226874B1 - Method of spectrophotometric monitoring of pigment dispersion state - Google Patents

Description

(54) Spectrophotometric method for monitoring the dispersion of color pigments

The invention relates to a method for spectrophotometric monitoring of the dispersion of color pigments in aqueous dispersions. The treatment of most pigments is carried out in various grinding processes, where it is important to assess the degree of fineness that must match the intended use of the pigment »Determining the particle size and milling is very important. The microscopic methods used require measurement of the size and addition of large numbers of particles, are demanding on equipment (electron microscope) and very laborious. Methods based on the conductivity of particles passing through the capillary (Coulter Counter) require a special apparatus and are also quite lengthy. Commonly used centrifugal methods are apparatus-intensive, determination of very fine fractions requires long time and accuracy and accuracy is influenced by final determination of pigment in fractions. Methods based on light scattering do not allow direct determination of absolute dispersion parameters, but they can be used to compare samples with the type or to observe the grinding process. The disadvantage of a number of methods based on light scattering is the necessity of special apparatus equipment, a rather large time nationality and a limitation mainly to monodisperse, non-color systems. New techniques based on the analysis of scattered laser radiation (QLS-quasielastic scattering) allow particle size determination and distribution also for color pigments, but are highly equipment-intensive.

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Light scattering in polydisperse color pigment dispersions can be used to evaluate the fineness of pigments by spectrophotometric measurement of the absorbances at two different cell-to-detector distances, the coarser the dispersion, the greater the difference between the amount of light incident on the detector in both configurations. The absorbance in the cell closer to the detector is always lower. For true solutions, the difference in absorbance at both cell positions is practically zero.

The above-mentioned disadvantages are eliminated by the method of spectrophotometric monitoring of the dispersion of color pigments in the aqueous dispersion of the present invention, which consists in dispersing the color pigment in water or in a dilute surfactant solution.

a non-ionic, then one absorbance A or a series of absorbances A ^ to A _Q in the visible region of the spectrum is measured on the spectrophotometer at a distance d takto of cells from the detector and at a distance dg of the cells from the detector where d ^ is greater than dg, whereupon a ratio or A A ^ / AA ^ independent of the dispersion concentration is calculated from the absorbances A or the sums of the absorbances at the corresponding distances d ^, dg.

Its value increases with increasing fineness of the pigment and allows comparison with the same absorbance ratios of the type dispersion or monitoring of dispersion changes during adjustments of pigment dispersion. The proposed procedure is very fast, especially when measuring absorbances at one wavelength. Measuring the same dispersion at two specific rocking positions does not require accurate concentration to be maintained, which is otherwise quite difficult, especially for pigment pastes. At the same time, the effect of the possible presence of different crystal modifications of the pigment is compensated because their ratio to each other is constant.

The main advantage of the procedure is its speed and low demands on apparatus equipment - it will satisfy any spectrophotometer, allowing measurement at two different distances of the cuvette from the detector. The present invention is described in the following Examples 1-3, but is not exhaustive or limited.

Example 1

Dispersions of two ground samples (A, B) of the red pigment (1-amino-2-phenoxy-4-hydroxy-anthraquinone) in water were prepared. The ratios (A. / A.) were calculated from the absorbances A measured at 530 nm in a 1 cm cuvette at position 1 (distance d ^ of the cuvette to the detector) and at position 2 (distance dg of the cuvette to the detector). Sample B is significantly finer.

1

Sample c (g / l)

A. / ^A ad ₂ dj.

And about 0.020 0.311 0.233 0.7492

B about 0.015 0.430 0.401 0.9326 which was confirmed by calculating the log-normal particle distribution parameters from the centrifugation assay data

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Sample equivalency dispersion most likely 3 ^ ^ m /

A 1.880 0.5633

B 0.222 0.5464

Example 2

The ground copper phthalocyanine beta-modification paste was sampled after the first and second pass through the mill. Dispersions with a pigment concentration of about 0.02 g / l in a 1% aqueous solution of non-ionic dispersants were prepared and their absorbance A at 400-450 nm measured at 10 mn intervals at positions 1 and 2 (see Example 1). sum and calculated ratios of sums.

Grinding - Sample A ^ A ^ é ^ d ^^

first 1 2,103 1,606 0.7637 first 2 2,071 1,569 0.7576 0 0.7606 second 3 1,799 1,432 0.7960 second 4 2,568 2,031 0.7909

0.7934

By repeated grinding, the dispersity improved but not too significantly. This was also confirmed by electron microscope size measurement and particle distribution

Particle size grinding 2 / Pi knows / 1 maximal 0.511 0.350 minimal 0.020 0,021 phtharithmetic 0,083 0,072 the most numerous 0,056 0,045

Example 3

From the ground copper phthalocyanine alpha-modification paste (sample C) a dispersion was prepared as in Example 2 and a type pigment dispersion was prepared as well. The absorbances of both dispersions at position 1 (A _d ^) and at position 2 (A _d ) in the screed 390 - 740 nm at 10 nm were measured, the absorbances added for each position were summed and the ratios of these sums (--A _d / é-) were calculated. A ^)

1

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Sample A _di A ^ ^ A ^

C 16.9215 16.5895 0.9804 type 11.2670 10.5770 0.9387

Sample C is finer than type by spectrophotometric evaluation, which is also confirmed by centrifugal particle fraction determination above a certain limit

Sample fraction above 2 / µm fraction above 0.25 / µm (%) (%)

G 2,5 6,5 type 1,9 12,5

Colouristically, sample C was evaluated against type: silo = 90/100, 1 greener, 1 brighter.

Claims (1)

SUBJECT OF THE INVENTION A method of spectrophotometric monitoring of the dispersion of color pigments in an aqueous dispersion, characterized in that the color solution of the surfactants, in particular of the nonionic, prepared dispersion of one absorbance A or of the spectral region at a distance of d-cuvettes from detector where d ^ is greater than dg. se And at appropriate distances d, d, independent of the dispersion concentration. pigment is dispersed in water or zreděpoté measured with a spectrophotometer at a series absorbancl steps A to A 'in the visible and in the detector at a distance dg from the cuvettes from absorbancl A or the combined absorbancl calculated ratio A. _& ^ / ^ or Z / EA ^ Printed by Moravian Printing Works, plant 12, Leninova 21, Olomouc Price: 2,40 Kčs