CS264477B1 - Method for monitoring changes in mean particle size of diazopigments - Google Patents

Abstract

A method of monitoring changes in the mean particle size of disazo pigments of the general formula I, where B is phenyl and A is phenylene, the essence of which is the measurement of the absorbance of suitably undiluted pigment dispersions in the region of the absorption maximum between 22,000 and 26,000 cm"i and at the long-wave edge of the 1st absorption band, whereby the measure of particle size is the parameter p calculated as the ratio of both measured absorbances.

Description

The subject of the invention is a rapid analytical method for monitoring changes in the mean particle size of disazopigments. The method finds application mainly as a control method in production processes where the crystal particle size changes during the heating of pigments in organic solvents.

The particle size of organic pigments is an important parameter that largely affects the application properties of the produced pigment. Along with the particle size distribution, it affects pigment yield, shade and shade brilliance, opacity, but also stability, especially migration stability in softened PVC and lightfastness. The particle size also affects the processability of pigments in some binders, especially during pigmentation of paints. The particle size also plays an important role in the actual production of the pigment, where it mainly affects the filtration properties of the suspension from which the pigment is isolated. The choice of the optimum particle size is in some cases determined by both the coloristic properties of the pigment and its manufacturing behavior.

For this reason, particle size monitoring and evaluation has been given great attention in the production of organic pigments. There are several indirect or direct methods that allow quantitative evaluation of particle size and shape distribution. These include electron microscopy and sedimentation analysis. However, these methods are instrumental and time consuming and thus only suitable for dispersing the pigment after its production. Existing methods for determining the average particle size are either instrument-intensive (Coulter N4) or are directed to the process of dispersing pigment powders in the binder (developing pigment color strength or measuring gloss).

From the standpoint of laboratory equipment in laboratories, the most accessible is the evaluation of particle size from turbidity of diluted pigment dispersions in a given environment.

However, the use of this measurement method makes it difficult to apply a complex mathematical procedure with a number of limiting assumptions in the calculation of mean particle sizes. The method requires knowledge of the pigment concentration in the measured dispersion.

A rapid and instrumentally available method for particle size monitoring of disazopigments of formula 1 has now been found

COCH, COCH, ³ and ³

BN = N-CH-CO-NH-A-NH-CO-CH-N = "NB (I) wherein B is phenyl and A is phenylene, which are optionally further substituted by groups which are not solubilizing in nature. The principle of the method is to measure the absorbance of suitably diluted pigment dispersions in the region of the absorption maximum between 22,000 to 26,000 cm ^-1 and at the longitudinal edge of the 1st absorbent belt, the particle size measurement being the P parameter calculated as the ratio of the two absorbances measured. The new method is based on the observation that monotonous changes in the absorption spectrum occur in the range of mean particle sizes of 0.01 to 0.5 µm in a series of similar pigment samples, which are usually available for continuous control of their recrystallization. These changes are best registered by measuring the absorbance at the maximum absorption of these substances, which is between 22,000 to 26,000 cm ^-1 and the absorbance at the longwave edge of the 1st absorbent sheet. By dividing the absorbance measured at the longwave edge of the 1st absorbent sheet and at the maximum eosorption, a dimensionless parameter P is obtained which is used to characterize the mean particle size. The conversion function of the P parameter to the mean particle size is obtained empirically by comparing the P parameter in several control samples with the results of measurements performed on a suitable particle size direct meter, preferably using a quasielastic light scattering device. In most cases, however, the conversion of the P parameter to the mean particle size is not necessary, but it is sufficient to use predetermined dependencies of the observed properties of the pigment (spreading, shade) on the value of the P parameter.

The described method for monitoring the changes in the mean particle sizes is fast enough to be able to control the process of recrystallization of the pigments of the formula I so that the process can be interrupted in an optimal state. Knowing the dependence of the filtration rate of the solvent suspension of the pigment on the P parameter, it is possible at the same time to interrupt the recrystallization in a state which is also satisfactory from the technological point of view. In addition to the above-mentioned impact on pigment quality, this method of control results in energy savings and production time.

Particle size control is mainly used in the laboratory development of pigment technology and in the transfer of technology from the laboratory to pilot scale and operational scale, where the change of the apparatus also affects the rate of recrystallization. Advantageously, this method can be used for all other changes in the established production process, for example, by changing the quality of raw materials, solvents, etc., the growth rate of pigment particles during recrystallization can also be influenced.

Recrystallization, which is monitored analytically, occurs by heating the disazopigments of formula I or mixtures of these pigments to temperatures above 80 ° C in solvents such as toluene, xylenes, chlorobenzene, o-dichlorobenzene, nitrobenzene, p-chlorotoluene, o-nitrotoluene, tetralin, dimethylformamide, aniline, N-methylpyrrolidone, pyridine, quinoline, cyclohexanone, ethylene glycol ethers, amyl alcohol or dioxane, optionally under pressure in water or in an ethanol-water mixture and the like.

The following examples illustrate the use of the method.

Example 1 g of a pigment prepared by coupling 2 mol of aminodimethyl terephthalate with 1 mol of 1,4-bisacetoacetylaminobenzene in an aqueous medium is heated with stirring in 600 ml of dimethylformamide to 115 ° C. During heating, 5 ml samples of the suspension are taken, from which the pigment is filtered off and the filter cake is washed with water. Approximately 50 mg of the aqueous paste is mixed in about 20 ml of a 4% aqueous Slovasol solution 0 and dispersed in a Tesla UC 405 BJ 1 ultrasonic bath for 3 min. Dilute the aqueous 4% Slovasol 0 solution to analytical concentration and measure the absorbance at 18,000 cm. ^- ^ (556 nm) absorbance at 24000 cm ^- '(417 nm) and the calculated ratio of the absorbance at 556 nm and 417 nm. This ratio is sufficient to characterize the mean particle size. If it is desired to express the mean particle size in absolute terms, this value shall be subtracted from a pre-constructed calibration curve of the ratio given to the mean particle size detected by another method, eg on a Coulter N4.

For this example, the following values were found, along with the dependence of color strength and pigment shade.

Warm-up time (clock) P Stř. particle size Qim) Coverage Hue (against type) 0.5 0,098 0.187 87.0 0,27č 1 0.130 0.207 88.1 0,22č 2 0.134 0.232 91.8 0,62No 4 0.238 0.249 96.8 0,93No 8 0.279 0.257 100.00 l, 19č

No ..... redder

P ..... absorbance ratio at 556 nm and 417 nm redder

P ..... absorbance ratio at 556 nm and 417 nm

Example 2

An aqueous paste containing 165 g of disazopigments, prepared by coupling 2 mol of 2-nitro-4-chloroaniline with 1 mol of 1,4-bisacetoacetylaminobenzene, is heated with stirring in 3000 ml of dimethylformamide for 4 h at 110 ° C. From the samples taken from the reaction slurry during heating, the pigment is isolated by filtration and the filter cake is washed with water. Approximately 50 mg of the aqueous paste is mixed in about 20 ml of a 1% aqueous Slovasol EL solution and dispersed for 1 min on a Fritseh Laborette 19, Grade 7 ultrasonic disintegrator. Dilute to an analytical concentration with an aqueous 1% Siovasol E solution. cm ^-1 (600 nm), absorbance at 22 620 cm ¹ (442 nm) and the extinction ratio at 600 nm and 442 nm is calculated (parameter P).

The following table shows the wavelengths at which the absorbance of aqueous dispersions of other disazopigments can be measured and the ratio of the two measured values can be used to monitor the recrystallization of amorphous forms of these pigments from organic solvents.

Example Active component Passive component Solvent E ₂ cm ^-1 cm ^-1

3 2-Methoxy-5-methyl- aniline 1,4-bisacetoacetylaminobenzene o-dichloro- benzene 13 000 24 200 4 2,3-dimethylaniline 1,4-bisacetoacetylaminobenzene cyclohexanone 13 000 23 000 5 aminodimethy lter e f talát 1,4-bisacetoacetylamino-2,5-dimethylbenzene dimethylformamide 18 000 24 000 6 aminodimethylterephthalate 1,4-bisacetoacetyl- amino-2-chloro-5- -methylbenzene dimethylforma- mid 19 Dec 500 24 600 7 aminodietylterefta- lath 1,4-bisacetoacetylaminobenzene chlorobenzene 18 000 24 000 8 aminodimethylterefta- lath 1,4-bisacetoacetylaminobenzene ethanol-water 1 - 1 18 000 24 000

I will invent the object

Claims (1)

Method for monitoring the mean particle size changes of disazopigments of the general formula I COCH2 COCH3 BN = N - CH - CO - NH - A - NH - CO - CH - N = NB (I) wherein B is phenyl and A phenylene optionally further substituted by groups having no solubilizing character, characterized in that absorbance measurements of appropriately diluted dispersions are performed % of the pigments in the region of the absorption maximum between 22,000 to 26,000 cm ^-1 and at the longitudinal edge of the absorbent web, the particle size measure being the parameter P calculated as the ratio of the two absorbances measured.