Studies On The Digital Ink-jet Printing Of Wool Fabric

Woolen products are high-grade textiles. However, there are few printed wool textiles on the market due to the following reasons: the restricted diffusion of dyes caused by the compact scale layer of wool fiber, the poor pattern fineness caused by the rough fabric surface, the long product process and high cost of traditional printing, the great difficulty in printing, etc. Digital ink-jet printing technology offers many benefits such as short production cycle, smart creativity, flexibility of processing, wide adaptability, etc., and can adapt to the current market of wool printing which requires personalization, small batch production, and fast delivery. In the light of the structures of wool fiber and the progress in the printing technology of woolen textiles, the key technologies of the digital ink-jet printing of wool fabric with reactive dyes were investigated in this paper. The influences of additives in the sizing liquid used for pretreatment on the results of ink-jet printing and the damage of wool fiber as well as steaming characteristics of wool ink-jet printing were discussed. Three fiber modification methods, namely hydrogen peroxide oxidation, potassium permanganate oxidation and oxygen plasma treatment were used to enhance the ink-jet printing performance of wool fabric, and the reasons for the improved printing properties were given by means of instrument analyses. The main results obtained were as follows:Ammonium sulfate and sodium bicarbonate was able to adjust the acidity and alkalinity of sizing liquid and exhibit almost the same color depth of printings at their proper dosages. Ammonium sulfate gave the printing process a better stability, and the application of sodium bicarbonate required the strict control on its dosage and the steaming time. The application of sodium carbonate easily caused the degradation and yellowing of wool fiber, and the decrease in the color brilliance of printings. The fixation rate of reactive dyes during steaming was decisively affected by the speed of dye migration from size layer to fiber surface. The migration and fixation rates of reactive dyes were faster on the printed fabric which was padded the sizing liquid containing ammonium sulfate. The color depth of printings depended greatly on the dosages of sodium alginate, ammonium sulfate, urea and sodium sulfite as well as steaming time. The printings obtained under the optimizational condition exhibited dark color, good color fastness and good sharpness.After wool fabric modified using hydrogen peroxide and potassium permanganate oxidation, its printing properties were greatly enhanced. The modified and printed fabric displayed higher color depth than the unmodified and printed fabric, and the time required for the steaming of the printed fabric was obviously shortened. The analyses by scanning electron microscope, infrared spectroscopy and X–ray photoelectron spectroscopy revealed that the scale of wool fiber surface was partially peeled off, the disulfide linkage was broken, and the quantity of lipid compounds covered on wool fiber surface became fewer. These changes originated from oxidation modification led to the enhanced ability of the diffusion of reactive dyes into fiber interior, and accordingly the increased color depth of printings. However the increased color depth gave rise to the slight decrease in the wash and rub color fastness of printings. Additionally, the strong oxidation of potassium permanganate caused the degradation of wool fiber and the complete elimination of wool scale, and accordingly resulted in the obvious reduction in the tensile strength of printings.The oxygen plasma treatment prior to printing was also able to improve the printing properties of wool fabric, and increase the color depth of printings because it loosened the scale structure of wool fiber, increased the oxygen content of fiber surface and decreased the carbon content, and activated the surface of wool fiber. The color fastness of the modified and printed fabric was slight lower than that of the unmodified and printed fabric. Compared with the oxidative modification, the oxygen plasma treatment increased the tensile strength of printings.