PROCESS FOR PREPARING ORGANIC PIGMENTS OF HIGH TINCTORIAL STRENGTH AND GRAIN SOFTNESS

MODE DE PREPARATION DE PIGMENTS ORGANIQUES AU GRAIN UNIFORME ET A FORT POUVOIR TINCTORIAL

English Abstract

PROCESS FOR PREPARING ORGANIC PIGMENTS OF HIGH TINCTORIAL
STRENGTH AND GRAIN SOFTNESS
Abstract of the disclosure:
An improved process for preparing an organic pigment
having a high tinctorial strength by heating a crude organic
pigment as an aqueous suspension having a consistency suitable
for being pumped, to a temperature of from 80 to 300°C and for
a period of from 10 seconds to 20 minutes in a continuously
operating flow apparatus which is shaped as a heat exchanger
provided with moving internal elements.

Claims

We claim:
In a process for preparing an organic pigment having a
high tinctorial strength by heating a crude organic pigment
as an aqueous suspension having a consistency suitable for
being pumped in a continuously operating flow apparatus to
a temperature of from 80 to 300°C and for a period of from
10 seconds to 20 minutes, the improvement which comprises
heating the suspension of the crude pigment in a flow apparatus
shaped as a heat exchanger which is provided with moving
internal elements.
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Description

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The present invention relates to a process for preparing
organic pigments which have a high tinctorial strength and grain
softness.
Copending Canadia~ Pat~t Appli~ation ~rial ~o. 166.881
relates to a process for preparing color-intense organic
pigments by heating an aqueous suspension of an organic crude
pigment having a consistency suitable for being pumped in a
continuously operating flow apparatus to a temperature of from
80 to 300C for a period of from 10 seconds to 20 minutes,
In modification to this process, it has now been found
that, instead of using a flow apparatus, the continuous pressure
finlsh of the aqueous pigment suspension can also be carried
out using a continuously operating heat exchanger provided with
moving internal elements. Such a heat exchanger provided with
moving internal elements also allows pigment suspensions or
pigment pastes having a substantially higher pigment concentra-
tion to be processed than those according to the process dis-
closed in the above-said patént application.
The prvcess of the invention can be carried out with
particular advantage using any pressure-tight, cylindrical heat
exchanger which is provided with one or more shafts or screws
rotating or vibrating in its interior and which may also have
stirring elements fixed on the moving parts or on its walls
(~or exa~ple scrapers, wipers, fins, bars, rods, and so on),
thus assuring a thorough mixing of the highly concentrated -
pigment pastes and, due to this and to a simultaneous self-
cleaning effect of the heat exchanger surfaces, a good heat
transfer. Further advantages are the low pressure loss in the
29 apparatus and the possibility of increasing the heat exchange
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surface in a rational manner by internally heating the
moving parts and thus raising the throughput of product.
The concentration of the pigment pastes ranges from about 10
to ~0 percent by weight.
A precise control of the finishing process, which is
possible by purposefully varying the temperature of the
pigment suspension and its residence time in the apparatus,
is the necessary condition for a rationalized pressure finish
process of pigments. The compact arrangement of the heat
exchanger of the invention offers not only an easy maintenance1
but also the advantage of reduced cost compared to conventional
pressure finishing apparatus (large-volume stirrer containers,
coils of pipe, pipe assembly exchangers) as well as increased
operational safety of the apparatus, due to an only small
volume under pressure. ~~
Owing to a very uniform dwe:Lling time of the material
particles, the thermal treatment of aqueous pigment pastes in
the heat exchangers of the inven-tion yields products having
~aluable technological properties.
The percentages given in the following Examples are by
weight, the temperatures are given in centigrades. The
- dwelling times are calculated from the product throughput and
the volume of the heat exchanger used, in which the heating
and cooling zones are advantageously arranged in one apparatus,
~5 one immediately behind the other, according to a variable
mechanical assembly technique~ The pressures required depend
on the temperature chosen and should always ~e above the
saturation vapor pressure.

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In a ring-gap heat exchanger formed by two slim concentric
cylinders, of which the inner one rotated and carried mobile
wipers on its circumference to shear the product without con-
veying it, a 20 % aqueous paste of the crude pigment obtained
by coupling anthranilic acid n butyl ester with 5-(2'-hydroxy-
3'-naphthoylamino)-benzimidazolone was heated under pressure to
170C for 6 minutes. A pigment powder was obtained which had
the same qualities as those obtained by conventional methods
only after a several-hour heating to 150C with the addition of
o-dichlorobenzene (cf. German Patent Specification No.
1,217,008).
E X A M P L E 2:
In this case, a cylindrical finishing apparatus was used
which was provided with two screws adequately arranged in such
a manner that they necessarily cleaned themselves and simul-
taneously the in-ternal wall o~ the cylinder. The active con-
~eying effect on the product and thus the dwelling time of the
pigment suspension could be varied via the rotational speed of
the screws. In this apparatus, a 25 ~ paste of the crude
pigment obtained by diazotization of anthranilic acid and
coupling with 5-acetoacetylamino--benzimidazolone (according to
German Offenlegungsschrfit No. 1,939,466) was heated under
. pressure to 160C for 8 minutes. A well-dispersible pigment
powder was obtained which differed from a product obtained
hitherto by 2.5-hour heating to 150C in an increased tinctorial
strength and a higher gloss of the lacquered articles produced
therewith.
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