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

Abstract: The preparation and use of water-soluble or water-swellable copolymers by copolymerization 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.

Description: In textile printing, natural and, more recently, synthetic thickeners, the latter obtained by copolymerizing by different methods unsaturated olefinic acids with a multifunctional unsaturated monomer as a curing agent, are widely used. These copolymers, dispersed in water give rise to microgels remarkably swelling after neutralization with an organic or inorganic base and they are therefore suited for the use as 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 polymerising 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 hydrophobic 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. DE 3641700 discloses a process for the preparation of water-in-oil emulsions of polymers to be used as thickeners in textile printing pastes. The critical aspect of said process is represented by the use of an emulsifying agent having HLB > 10 in order to render the water-in-oil emulsion stable. 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 water-in-oil polymerization with an olefinically unsaturated acid and a salt thereof a multifunctional unsaturated monomer, an olefinically unsaturated monomer having a nitrile group (preferably acrylonitrile) and optionally an olefinically unsaturated monomer having hydrophilic functional groups, it is possible to obtain a synthetic thickener 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 in amount of 0.2-20% by weight ratio in comparison to the total amount of monomers) is essential in order to obtain resistance to bleeding without prejudicating the other printing characteristics. Olefinically 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, methacrylic, crotonic, itaconic, maleic acids and mixtures thereof. The definition of olefinically 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(meth)acrylate, glycoldi(meth)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, methacrylamide, hydroxyethylacrylate, hydroxyethylmethacrylate, hydroxypropylacrylate, hydroxypropylmethacrylate and mixtures thereof. A preferred combination of monomers is described in claim 5. 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 can be 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 a hydrosoluble polymerization initiator able to yield free radicals. Polimerization initiators 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°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 emulsified 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 to 50°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°C, is 25.000 mPa·s (cps). 0.1% of sodium sulfate is added to the solution and the viscosity is measured again, which is 15.000 mPa·s (cps). EXAMPLE 2 A polymerization is carried out as in Example 1, but using 84.5 g of acrylic acid, 12 g of acrylamide, 3.75 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 mPa·s (cps); after addition of 0.1% sodium sulfate, it was 13.400 mPa·s (cps). EXAMPLE 3 (COMPARATIVE) A polymerization is carried out as in Example 1, but using 87.5 g of acrylic acid and 12.5 g 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 mPa·s (cps); after addition of 0.1% of sodium sulfate, it was 9.000 mPa·s (cps). EXAMPLE 4 (COMPARATIVE) 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 mPa·s (cps); after addition of 0.1% of sodium sulfate, it was 8.200 mPa·s (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 R (BASF) was formulated with different amounts of thickeners of Examples 1-4 so as to have an apparent viscosity of 16.000 mPa·s (cps) (Brookfield Viscosimeter RVT 20 rpm, 20°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°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.

Claims: Synthetic thickeners obtainable by water-in-oil polymerisation of a) an olefinically unsaturated acid, b) a salt thereof, c) a multifunctional unsaturated monomer, d) an olefinically unsaturated monomer having a nitrile group and optionally e) an olefinically unsaturated monomer having hydrophilic functional groups. Synthetic thickeners according to claim 1, characterized in that the olefinically unsaturated monomer having a nitrile group is acrylonitrile. Synthetic thickeners according to claim 2, characterized in that the used acrylonitrile is used in 0.2-20% by weight ratio in comparison to the total amount of monomers. Synthetic thickeners according to claims 1-3, characterized in that the olefinically unsaturated acid is acrylic acid. Synthetic thickeners according to claims 1, obtained by copolymerization of acrylic acid, ammonium acrylate, methylenebisacrylamide, acrylonitrile and acrylamide. Thickener aqueous compositions comprising the synthetic thickeners of claims 1-5. Printing pastes obtained from the synthetic thickener of claims 1-5. A water-in-oil polymerization process consisting in: i) dispersing in an organic medium, suitably added with an oleosoluble surfactant and optionally added with a polymeric stabilizer, a monomer mixture dissolved in water, said mixture comprising a) an olefinically unsaturated acid, b) a salt thereof, c) a multifunctional unsaturated monomer, d) an olefinically unsaturated monomer having a nitrile group and optionally, e) an olefinically unsaturated monomer having hydrophilic functional groups; ii) removing oxygen from the obtained water-in-oil emulsion by nitrogen stream; iii) catalyzing the reverse-phase polymerization with a hydrosoluble polymerization initiator, which is selected from the group consisting of peracids, persalts, hydroperoxides; iv) carrying out the reverse-phase polymerization; v) azeotropically eliminating water. A process according to claim 8, wherein the monomer having a nitrile group is acrylonitrile. A process according to claim 8, wherein the olefinically unsaturated acid is acrylic acid.

Inventors: BRESCIANI ANGELO, BRESCIANI, ANGELO
Applicants: SIGMA PROD CHIM, SIGMA PRODOTTI CHIMICI S.P.A.
Application year: 1990
Main classification: C08F220
IPC codes: C09J133, D06P5, C08F2, D06P1, C08F220