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  • Indian Journal of Fibre & Textile Research Vol. 19, March 1994, pp. 22-29

    Pigment printing o!fcotton with methacrylic acid-based synthetic thickeners

    R B Chavan, P Bajaja & Meenakshi Goyal Department of Textile Technology, Indian Institute of Technology, New Delhi 110016, India

    Received 11 June 1993; revised received 13 September 1993; accepted 28 October 1993

    Methacrylic acid (MAA) - ethyl acrylate (EA) - ethylene glycol dimethacrylate (EGDM)/N~'- methylene bisacrylamide (MBAM) polymers of different compositions were used as synthetic thickeners in pigment printing of cotton. Crosslinked polymers with different feed ratios were synthesized and their printing behaviour was compared with the conventional kerosene emulsion thickener and a commer- cial synthetic thickener Alcoprint PTF in terms of colour value, back penetration, wash, rub (dry and wet) and scrub fastness, and handle of the fabric. Methacrylic acid-based thickeners (solid con- tent 4%), when used as a substitute of kerosene emulsion, produced prints with harsh feel. There- fore, partial substitution of kerosene emulsion (60-80%) was tried and a significant improvement in the handle of fabric was observed.

    Keywords: Bending length, Colour value, Kerosene emulsion, Pigment printing, Synthetic thickener

    1 Introduction Pigment prints on cotton using kerosene emul-

    sion thickener are characterized by good fastness properties and high degree of brilliance with no adverse effect on the handle of the fabric. How- ever, there is an increasing tendency towards the substitution of kerosene emulsion by synthetic thickeners due to disadvantages like risk of explo- sion in the drier, air pollution, loss of valuable kerosene during drying and curing processes, and inadequate availability of kerosene for domestic use":'.

    Successful use of aqueous system for pigment printing and its beneficial effect on safety, envi- ronmental pollution and economy of operation has given added impetus to the use of synthetic thickenersv". Synthetic thickeners are high molec- ular weight polymers (M, 3,00,000-5,00,000) containing an acidic monomer such as. acrylic, methacrylic or maleic acid as an essential compo- nent. Acid comonomer appears to be the major constituent of such synthetic thickeners as it is re- sponsible for the building up of viscosity on neu- tralization with a base which is necessary for thickening action. Neutralization converts the acid groups into carboxylate anions which repel each other, resulting into uncoiling of the polymer chains, thereby developing the viscosity.

    "To whom all the correspondence should be addressed.

    Copolymers of acrylic or methacrylic acid with their esters":" or acrylamide':', and ethylene and maleic anhydride!", and their crosslinked polym- ers using ethylene glycol dimethacrylate, N,N'- methylene bisacrylamide, divinyl benzene, methy- 101 acrylamide, etc. as crosslinking agents have been primarily used as thickeners for textile print- ing. Different systems for replacing kerosene, par- tially or completely, based on these chemical compositions have been evaluated. Information regarding the chemical compositions and synthe- sis of such thickeners, available in patented litera- ture, has been documented recently".

    In the present paper, the performance of me- thacrylic acid-based synthetic thickeners, as sub- stitutes of kerosene emulsion thickener, in pig- ment printing of cotton fabric is reported. Four organic pigments were used. Performance was evaluated on comparison with the prints obtained from a commercial synthetic thickener (Alcoprint PTF) and conventional kerosene emulsion thick- ener.

    2 Materials and Methods

    2.1 Polymer Preparation Emulsion polymerization of methacrylic acid-

    ethyl acrylate-ethylene glycol dimethacrylatel N,N'-methylene bisacrylamide was carried out at 50°C using potassium persulphate (0.125 wt % of

  • CHAVAN et al: PIGMENT PRINTING OF COTTON 23

    monomers)-sodium metabisulphite (0.25 wt % of monomers) as redox initiator and a mixed emulsi- fier containing non-ionic and ionic emulsifying agents. Methacrylic acid-ethyl acrylate ratio was kept at 65:35 and the amount of crosslinking agents was varied to get the desired viscosity for printing.

    Details of synthesis and rheological behaviour of methacrylic acid-based synthetic thickeners has been reported elsewhere",

    2.2 Fabric

    Cotton fabric used for printing was scoured and bleached. It had the following specifications: warp count, 62; weft count, 74; and weight, 96g1io2•

    2.3 Printing Auxiliaries

    Acramine Binder SLN of Colour Chern Ltd (In- dia), Pidifix 361-a melamine-formaldehyde based fixer of Pidilite Ind (India), Golden Yellow TRM, Black TBR, Blue TFB pigments of Good- lass Nerolac Paints Ltd (India), and Acramine Red FGR of Colour Chern Ltd (India) were used for printing. Carboxymethyl cellulose (completely water soluble) of Loba Chemie Indoaustranal Co. (India) and urea of BDH Chemicals (India) were used for the preparation of kerosene emulsion. Diammonium hydrogen phosphate (DAP) of Merck Ltd (Germany) was used as a catalyst.

    2.4 Print Paste and Stock Paste Formulations

    2.4.1 Stock Paste

    2.4.1.1 Kerosene Emulsion Thickener

    Ingredient

    Acramine Binder SLN Urea Carboxymethyl Cellulose (6%) Water Kerosene

    Parts

    10 2 1

    10 77

    2.4.1.2 Synthetic Thickener Paste

    The polymer content of the emulsion of me- thacrylic acid-based terpolymers varied between 16 and 18%. To prepare the stock paste from these emulsions, desired amount of water was added to the emulsion so as to bring down the polymer content to 4%, and then 28% ammonium hydroxide solution was added to adjust the pH to

    7.5. In case of Alcoprint PTF, 2% solution was prepared and the pH was adjusted to 7.5.

    2.4.2 Printing Paste

    Ingredient Kerosene emulsion Synthetic thickener (Parts) (Parts)

    Other Black Other Black colours colour colour colour

    4 6 4 6 2 2 2 2

    Pigment Pidifix 363 (fixer) DAP (catalyst) Acramine SLN (binder) Stock paste

    1.5 1.5

    5 10 15

    92.5 85.5 84 77

    100 100 100 100

    With Alcoprint thickener, the viscosity of the ~ printing paste increased significantly on addition of black pigment, which was brought back to nor- mal by the addition of 2 parts ammonium sulph- ate as suggested by the manufacturer.

    2.5 Printing

    Samples were screen printed with two squeegee strokes followed by drying of the printed samples at 90°C for 4 min and curing at 150°C for 5 min. In the case of methacrylic acid-based thickeners, fixation was carried out at 170°C for 5 min.

    2.5.1 Partial Substitution of Kerosene Emulsion

    Blends 'of synthetic thickeners (laboratory syn- thesized products and Alcoprint) and kerosene emulsion were prepared in the ratio of 80:20 and 60:40 (w/w) and used for printing.

    2.6 Evaluation of Printed Samples

    The prints obtained were evaluated in terms of colour value, wash, rob and scrub fastness, and stiffness.

    Colour value from front and back to determine the back penetration -was expressed in terms of KI S and was determined by using ACS Spectro-Sen- sor II (Applied Color Systems Inc. Spectro- photometer). The wash fastness (ISO 3) was de- termined using Atlas launderometer and dry and wet rub fastness was determined using Shirley crockmeter. Scrub fastness was measured by

  • 24 INDIAN J. FIBRE TEXT. RES., MARCH 1994

    scrubbing the sample, dipped in soap solution, 100 times with a nylon brush. Stiffness of the samples was measured in terms of bending length by using Eureka bending length tester.

    2.7 Viscosity Measurement The viscosity of the various pastes was mea-

    sured using Brookfield Viscometer (Model RV, Spindle No. 29).

    3 Results and Discussion The composition of various synthetic thickeners

    investigated in the present study are given in Table 1. Also included in this table is the code of each, which will be used hereafter.

    3.1 Viscosity of Stock and Print Pastes Brookfield viscosity of all the stock pastes and

    printing pastes were measured (at 5 rpm) and the values are reported in Table 2. Stock pastes of all the three methacrylic acid-based thickeners were prepared at a concentration of 4% for achieving printable viscosity. Among the three synthetic thickeners, P2M3, P2E4 and P2Es, Brookfield vis- cosity of P2M3 was the highest (70,400 cp). The viscosity of PZE4 and P2Es was 32,000 and 26,000 cp respectively. This behaviour can be ex- plained on the basis of the gel content of these polymers, which gives an idea of the degree of crosslinking. According to Kanter", crosslinked polymers do not undergo dissolution on the addi- tion of bases but they swell. Therefore, higher the degree of crosslinking, higher will be the viscosity. P2M3, showing the highest viscosity value, had a gel content of 90.7% as compared to 83.0 and 80.6% for P2E4 and P2Es respectively. Kerosene emulsion had a viscosity of 63,000 cp and Alco- print PTF (2% solution) had a Brookfield viscos- ity of 1,11,000 cpo When the printing auxiliaries like binder, pigment and fixer (and catalyst in the case of kerosene emulsion only) were added to the stock paste, a drop in the viscosity in all the cases was observed, maximum drop being in the case of Alcoprint PTF. The drop in viscosity was more prominent in cases where the initial viscos- ity was higher. The extent of reduction in viscos- ity varied with different pigments. With black pig- ment, v.iscosity was lowest because 5% extra bin- der and 2% extra pigment were added to this paste.

    3.2 Printing Performance of Synthetic Thickeners

    3.2.1 Colour Value (KIS) T