Effect of Padder Roller Speed and Pressure During Pre-treatment on Color Characteristics of Digitally Printed Cotton Knit Fabric Grace Wasike Namwamba, Ph.D. and Devona L. Dixon, M.S. Textile Technology Southern University Agricultural Research and Extension Center Baton Rouge, LA 70813

Background Purpose of roller speed (RPM) Importance of roller pressure (PSI) Importance of color

Purpose of the Study The purpose of this study was to determine the effect of padder roller speed (RPM) and pressure (PSI) on the color of digitally printed cotton fabrics. The padder for applying pre-treatment and fabric preparation is critical to the overall appearance of color of the final product. The padder parameters, which include roller speed and pressure, contribute to the final overall print quality/appearance.

Procedure Procedure: 1-yd of 100% Double –knit cotton fabric was padded with a pre- treatment fabric solution made in lab: aliginate (.008%), soda ash (.04%), urea (.1%), and distilled water (.852%). A smooth padding pretreatment mixture was poured into the padder reservoir for fabric padding pre-treatment.

Procedure (Continued) Padding Speeds: 20, 40, & 60 rpm Padding Pressures: 5, 15, 40, 60, & 70 psi Backing with warm iron and freezer paper Printing: Reactive inks on a Mimaki TX Digital Textile Printer Colors: Individual one inch stripes of cyan, yellow, magenta, black (CYMK) and measurable areas of red, pink, violet and green.

Procedure Continued Steaming: Low pressure bullet steamer for 30 minutes at 245°F the reactive ink dyes were “fixed” to the fabric with steam. Post treatment (Wash/rinse): a commercial washing machine used. No chemical or detergent was added to the wash water. The wash/rinse post-treatment cycles consisted of two cold washes (20-30C° or 68-86F°) for 6 minutes and two cold rinse cycles, immediately followed by two hot washes (60C° or 140 F°) for 6 minutes and two cold rinse cycles. One additional cold rinse was added after the final wash/rinse cycle.

Procedure Continued Color Readings: Color readings were taken from each of the samples using the Colorguide 45/0 spectrophotometer. Ten (10) readings were taken from each solid color represented in the print in each condition (post-print, steamed, post wash/rinse).

Statistical Analysis Statistical Analysis: Data obtained by instrumental color measurement were analyzed using SPSS to determine if there was significant differences in L, a, b and  E after the treatments. Descriptive statistics were also computed. The General Linear Model (GLM); p<.05 The statistical model used was as follows: Y i,j =  i +  i + e j(i) y ij is the value of the dependent variable for sample j receiving treatment i,  i is the overall mean for the dependent variable,  i is the effect of treatment i on the dependent variable, and e j(i) is the effect of jth sample receiving treatment i.

Results and Discussion Effect of Roller Speed on Color Depth: The general trend of L* was consistent among the eight colors. Fabrics padded at 40rpm produced the darkest shades (see Chart). Multiple comparisons using LSD indicated that there was no significant difference in L* values for fabrics padded at 20 rpm and those padded at 60 rpm. Padding at a lower speed of 20 rpm did not produce the darkest fabrics as expected.

Results and Discussion The explanation of the lightness of fabrics padded at 20 rpm lies in the dye chemistry of the fiber reactive dyes used to print the fabric. Fiber reactive dyes react with cellulose in the presence of alkali (NaOH) and electrolyte (NaCl) to form cross-linked compounds that are insoluble in water. The slow padding speed means greater uptake of the padding liquid into the fiber. This in turn would result in deeper dye penetration into the fiber and less dye on the surface of the fabric. Less dye on the surface of the fiber results in lighter colors.

Results and Discussion