Synthetic thickeners, obtained by water-in-oil emulsion polymerization, having improved characteristics for the use in textile printing

The preparation and use of water-soluble or water-swellable copolymers by polymerization in water-in-oil emulsions of an olephinically unsaturated acid, a salt thereof, a multifunctional monomer, acrylonitrile and optionally a monomer with hydrophilic functional groups.

Natural and, more recently, synthetic thickeners, are widely used in 
textile printing. The synthetic thickners are obtained by copolymerizing, 
according to different methods, unsaturated olephinic acids with a 
multifunctional unsaturated monomer as a curing agent. 
These copolymers, dispersed in water, give rise to microgels. The microgels 
swell remarkably after neutralization with an organic or inorganic base 
and are therefore suited for use as a thickener in aqueous medium or in 
polar solvents. 
They may be obtained in form of very fine powder requiring, for their use 
in the industrial practice, a further work-up in order to make their use 
more easy (said work-up consisting in the dispersion in an organic vehicle 
so as to obtain a suspension) or they may directly be obtained in form of 
oil-suspension by polymerizing according to the method of the 
"water-in-oil" polymerization, also known as reverse phase polymerization, 
as disclosed in EP-A-161038. 
Whichever preparation method is used, said copolymers alone are not able to 
impart to the printing paste all the necessary characteristics, 
particularly when textiles mainly consisting of hydrophilic synthetic 
fibers are to be printed, such as polyester-cotton textiles with high 
polyester content, where the problem of the contour sharpness, known as 
"flushing" or "bleeding" is particularly important. 
Although the problem of contour sharpness is less pronounced for the 
polymers obtained by reverse phase polymerization (EP-A-161038), 
nevertheless they also ask for additives to avoid flushing, as it is 
reported in EP-A-190002. 
Another common feature of said polymer is that of a considerable loss of 
their thickening activity in the presence of electrolytes. In order to 
overcome the problem of the contour sharpness, the printing pastes are 
formulated with additives which are generally hydrosoluble polymers of 
different kind having low or relatively low molecular weight. 
Said additions however have a more or less negative influence on other 
printing characteristics and particular brightness, resistance to washings 
and softness of the printed textile in the pigment printing. 
It is therefore evident that a thickener able to impart alone to the 
printing pastes a good contour sharpness involves a considerable 
improvement for the thickeners used in the textile printing. 
It has now been found that by carrying out a reverse phase polymerization 
with an olephinically unsaturated acid and a salt thereof, a 
multifunctional unsaturated monomer, an unsaturated monomer (preferably 
acrylonitrile) and optionally a monomer having hydrophylic functional 
groups, it is possible to obtain a copolymer meeting the contour sharpness 
requirement in printing pastes wherein it is used and exhibits moreover a 
remarkably improved resistance to electrolytes. 
In the preparation of said copolymer, the presence of the unsaturated 
nitrile (preferably acrylonitrile) is essential in order to obtain 
resistance to bleeding without prejudicating the other printing 
characteristics. 
Olephinically unsaturated acids, which may be used, are all the organic 
compounds containing a double bond and at least a carboxy group. Examples 
of said compounds are acrylic, metacrylic, crotonic, itaconic, maleic 
acids and mixtures thereof. 
The definition of olephinically unsaturated acid should be understood to 
comprise also the anhydrides of the above acids, with the proviso that 
said anhydrides derive from a dicarboxylic acid after elimination of a 
water molecule between two carboxy groups of the same molecule. 
The salts of said acids may derive from organic or inorganic bases. 
As multifunctional unsaturated monomers all the compounds having at least 
two double bonds and which are soluble in water in the used amount or 
which are soluble in the monomeric mixture may be used. Suitable examples 
are allyl(met)acrylate, glycoldi(met)acrylate, methylenebisacrylamide. The 
used amount is generally lower than 1% in respect to the total monomers. 
Monomers with hydrophilic groups which may be used are for instance 
acrylamide, metacrylamide, hydroxyethylacrylate, hydroxyethylmetacrylate, 
hydroxypropylacrylate, hydroxypropylmetacrylate and mixtures thereof. 
The water-in-oil emulsion polymerization consists in dispersing in an 
organic medium, suitably added with an oleosoluble surfactant and 
optionally added with a polymeric stabilizer such as that disclosed in US 
3691124, the monomers mixture dissolved in water. 
The dispersion is carried out by an homogenizer which emulsifies the 
aqueous mixture in the organic vehicle, generally consisting of an high 
boiling hydrocarbon. 
A water-in-oil emulsion is obtained, which, after removal of oxygen by 
nitrogen stream, is catalyzed with an hydrosoluble polymerization primer 
able to yield free radicals. 
Polimerization primers may be peracids, persalts, hydroperoxides, used 
alone or in other systems. The polymerization occurs within a few hours. 
Once the polymerization is complete, the water is azeotropically 
eliminated and a final product as a suspension of the finely dispersed 
polymer in high-boiling hydrocarbon is obtained. 
The polymerization is carried out in an inert medium at reduced pressure, 
normal pressure or under pressure.

The following non-limitative examples further illustrate the invention. 
EXAMPLE 1 
127 g of water, 83 g of acrylic acid, 12 g of acrylamide and 5 g of 
acrylonitrile are mixed in a three-neck flask with condenser and stirrer. 
An ammonia solution is dropped up to pH=6.5, taking care that temperature 
does not exceed 25.degree. C. The final weight of the resulting solution 
is 297 g. 2.8 g of a 1% methylenebisacrylamide solution, 0.07 g of 40% 
pentasodium salt of diethylenetriammino pentaacetic acid and 0.03 g of 
2,2'-azobis(2-amidinopropane)hydrochloride are added thereto. 
Separately the oily phase is prepared which consisted of 47 g of paraffin 
oil, 10.5 g of sorbitan-monooleate, 145 g of n-octane and 9 g of polymer 
stabilizer. The aqueous solution is emulsionated with a suitable apparatus 
in the organic phase, whereafter the mixture is transferred into a reactor 
having a stirrer and condenser and the oxygen is removed by a nitrogen 
stream. 
3.5 g of a 1% t-butyl-hydroperoxide water solution are added thereto and 
3.5 g of a 1% sodium bisulfite water solution, so as to keep the 
temperature from 40.degree. to 50.degree. C. 
The polymerization is complete within 3 hours, whereafter water and then 
n-octane are azeotropically removed. 178.55 g are obtained which are added 
with 3% nonylphenol ethoxylated with 7 mols of ethylene oxide. 
The following solution is prepared: 98.2 g of tap water, 1.5 g of the above 
suspension, 0.3 g of 26% ammonia. The viscosity, measured with Brookfield 
apparatus at 20 rpm at 20.degree. C., is 25.000 cps. 0.1% of sodium 
sulfate is added to the solution and the viscosity is measured again, 
which is 15.000 cps. 
EXAMPLE 2 
A polymerization is carried out as in Example 1, but using 84.5 g of 
acrylic acid, 12 g of acrylamide, 2.75 g of acrylonitrile, with the same 
amounts of curing agent of the Example 1. 
The viscosity is measured as in Example 1. It was 26.250 cps; after 
addition of 0.1% sodium sulfate, it was 13.400 cps. 
EXAMPLE 3 
A polymerization is carried out as in Example 1, but using 87.5 g of 
acrylic acid and 12.5 of acrylamide and with the same amount of curing 
agent. The yield is practically equivalent to that of Example 1. The 
viscosity is measured as in Example 1. It was 38.000 cps; after addition 
of 0.1% of sodium sulfate, it was 9.000 cps. 
EXAMPLE 4 
A polymerization is carried out as in Example 1, but using 100 g of acrylic 
acid and with the same amount of curing agent of the Example 1. The 
viscosity was 29.000; after addition of 0.1% of sodium sulfate, it was 
8.200 cps. 
EXAMPLE 5 
A series of printing pastes containing 12% of curing acrylic latex, 1% of 
melanine resin, 0.2% of antifoam agent, 3% of Halizarin Blau RT.sup.R 
(BASF) was formulated with different amounts of thickeners of Examples 1-4 
so as to have an apparent viscosity of 16.000 cps (Brookfield Viscosimeter 
RVT 20 rpm, 20.degree. C.); the remaining part being tap water. 
These printing pastes were used to print a 65/35 polyester-cotton textile 
by means of a laboratory printing machine. After the printing, the textile 
was left in the air for 120" and then dried at 150.degree. C. for 150". 
Only the pastes formulated according to examples 1 and 2 are able to give 
prints endowed with very good contour sharpness and colour appearance.