Process for preparing dyes and/or brightener formulations

Details Process for preparing dyes and/or brightener formulations Process for preparing dyes and/or brightener formulations

1999-09-20

2001-06-05

Einsmann, Margaret (Department: 1751)

Bleaching and dyeing; fluid treatment and chemical modification

Dye concentrate composition wherein an additional amount of...

C008S648000, C008S680000, C008S673000

Reexamination Certificate

active

06241786

ABSTRACT:

The invention relates to processes for preparing dyes and/or brightener formulations.
EP-A-835 906 describes dispersions of optical brighteners having SO
3
H groups for whitening paper. Since the synthesis salts obtained when the brightener is prepared are very detrimental to the subsequent dissolution with sodium hydroxide, in terms of the maximum brightener concentration possible, the salt content must be kept as low as possible even in aqueous dispersions of optical brighteners having SO
3
H groups.
In EP-A-835 906 desalination takes place, for example, by washing the brightener presscake with demineralized water. Disadvantages of this procedure are on the one hand that a high product loss is suffered when the presscake is handled and on the other hand that only moderate and non-reproducible desalination conditions are present owing to the formation of channels in the presscake, as a result of which effective desalination is locally restricted.
A process has now been found by means of which it is possible to overcome the above-described disadvantages of the prior art.
The invention therefore provides a process for preparing formulations comprising dyes and/or brighteners which possess at least one free SO
3
H and/or COOH group, characterized in that an aqueous suspension comprising
a) dyes and/or brighteners which possess at least one free SO
3
H and/or COOH group and
b) inorganic synthesis salts is desalinated using a microfiltration membrane having pore diameters of from 0.05 to 40 &mgr;m.
The dyes and/or brighteners having at least one free SO
3
H and/or COOH group can of course also be present together with their salt forms (for example alkali metal, alkaline earth metal or ammonium salts). It is preferred, however, if at least one dye and/or brightener is present in the form of its free acid to the extent of at least 90 mol-%.
The microfiltration membrane employed can be operated, for example, in the cross-flow mode.
For cross-flow membrane filtration it is preferred to employ microporous membranes as capillaries, tubes and in spiral-wound modular form. The membranes are produced, for example, from inorganic (e.g. TiO
2
, ZrO
2
, Al
2
O
3
) or organic materials (e.g. propylene or partly fluorinated or perfluorinated polymers, polysulphone, polyether sulphone), the pore diameters preferably being from 0.05 to 3.0 &mgr;m. A feature of the cross-flow mode is that the membranes are traversed tangentially by the product solution/suspension. In this context it is preferred to apply transmembrane pressures of from 1 to 10 bar. It is likewise preferred to conduct a periodic backwash from the permeate side in order to maintain high permeate performances.
The process of the invention operates with particular advantage if the pH of the suspension to be desalinated is from 1 to 6, in particular from 2 to 5.
It is likewise advantageous if the acid form (SO
3
H and/or COOH) of the dye or brightener has a water solubility of less than 5 g/l, preferably less than 1 g/l under the respective process conditions.
The process of the invention is preferably used to desalinate SO
3
H-containing dyes and/or brighteners, especially brighteners.
The preferred amount of dye and/or brightener in the aqueous suspension to be desalinated is from 100 to 500 g/l, in particular from 150 to 400 g/l of aqueous suspension to be desalinated. At the same time the inorganic salt content in the suspension prior to desalination is generally from 1 to 25, preferably from 2 to 8% by weight, based on the suspension. The inorganic salt content to be established preferably, by means of the process of the invention, is <1% by weight, in particular less than 0.5% by weight. The inorganic synthesis salt preferably comprises alkali metal halides, sulphates or hydrogen sulphates.
The desalination of the invention takes place preferably at a temperature from 25 to 70° C., in particular at from 30 to 50° C.
The desalination can be operated with concentration or as diafiltration. In the case of diafiltration, the permeate formed is replaced continuously by demineralized water.
Optical brighteners employed in connection with the process of the invention are with particular preference those of the formulae (I), (II) and/or (III):
in which
M represents H,
R
1
and R
2
independently of one another denote —NH
2
, —NHCH
3
, —NHC
2
H
5
, —N(CH
3
)
2
, —N(C
2
H
5
)
2
, —NHCH
2
CH
2
OH, —NHCH
2
CH
2
CH
2
OH, —N(CH
2
CH
2
OH)
2
, —N(CH
2
CH
2
CH
2
OH)
2
, —N(CH
3
)(CH
2
CH
2
OH), —NHCH
2
CH
2
OCH
2
CH
2
OH, —NHCH
2
CH
2
CH
2
SO
3
M, —OH, —OCH
3
, —OCH(CH
3
)
2
, —OCH
2
CH
2
OCH
3
,
 in which
M is as defined;
or of the formula
 in which
R
3
is hydrogen, alkyl of 1 to 4 carbon atoms, alkoxy of 1 to 4 carbon atoms, halogen or SO
3
M, and
R
4
is hydrogen or alkyl having 1 to 4 carbon atoms and
M is as defined;
and also the formula
 in which
M is as defined and
R
5
and R
6
independently of one another denote hydrogen, CH
3
,
or
R
5
and R
6
together complete a benzene ring.
Very particular preference is given to such brighteners of the formula (I), especially those of the formula (Ia)
It is likewise advantageous to append to the process of the invention a concentration by means, for example, of membrane dewatering.
Prior to, during or after the process of the invention it is possible if desired to adjust the particle size of the dye dispersion or brightener dispersion by means of a wet comminution technique, such as, for example, Cavitron milling, jet disperser technology, beadmilling, etc.
The dye dispersions and/or brightener dispersions obtained in accordance with the process of the invention can be mixed and/or homogenized, for example following the addition of further additives such as polyvinylpyrrolidone, commercially customary anionic dispersants, for example formaldehyde-naphthalenesulphonic acid condensates or other condensation products of aromatic sulphonic acids and formaldehydes, or starch degradation products, such as anionic polyhydroxy compounds, for example, preferably xanthan, and can then be used for dyeing or whitening paper pulps in papermaking and for whitening or dyeing the coating slips which are commonly used in the paper industry, the latter being unpigmented or, preferably, pigmented pulps and slips.
Reducing agents and preservatives may also be mentioned as further additives, however.
Brighteners are preferably applied by three methods in papermaking:
Pulp: This is the cellulose suspension before the paper is made. Here it is preferred to employ the brighteners having 2 sulpho groups.
Coating slip, coating: Here, a coating is applied to the finished paper after the drying section. In addition to optical brighteners, preferably those having 6 sulpho groups, the coating slip comprises, inter alia, pigments (chalk, clay), latex binders, cobinders and dispersants.
Size press: After the drying section, paper which is almost finished runs through the size press, which may consist, for example, of counterrotating rolls, which in turn run through a sump containing starch and optical brightener. Alternatively, the application can be made via a padder or by spraying, preferably followed by a drying section.
For the application of the dye dispersions and/or brightener dispersions prepared in accordance with the process of the invention, an alkaline pH is advantageous for unhindered dissolution. In the case of coating slips, this pH should in particular lie within the range from 8 to 11, and in the pulp should in particular be from 7.5 to 9. The desired pH can be established, for example, by adding NaOH, in which case this pH is preferably established in the fibre dispersion or in the coating slip prior to the addition of the brightener dispersion. When using alkaline fillers, such as precipitated or natural calcium carbonate, it is possible to dispense with the addition of alkali.
It is possible to improve not only the preparation of SO
3
H— and/or COOH-containing dyes and brightener formulations but also the preparation of their salts, especially their aqueous solutions.
At the end of th

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