| In the field of ink-jet printing of textiles, plasma treatment of fabrics which has advantages of low energy consumption, high reliability, and environmentally-friendly, etc. rapidly developed in recent years. The etching and chemically modifying on the fiber surface which is caused by active particles is the microscopic reason for the changing of the property of fabrics, and also enhanced the color expression and pattern definition of the printing on the fabric. This research can provide the basic theoretical guidance for the practical application.In this research, the polyester plain fabric was firstly surface modified with pulsed atmospheric-pressure plasma, and then ink-jet printed with pigment ink. The influence of discharging time, gap distance and atmosphere on the plasma treatment was firstly researched. The color performance, bleeding and color fastness was analyzed to evaluate the effect of the plasma on the property of ink-jet printing fabrics. The surface wettability, surface free energy, the fiber surface morphology and surface chemical composition of the fabric were characterized by the drop shape analyzer, SEM, AFM and XPS. That revealed the causation and mechanism of the property enhancement of the printing fabric treated with plasma.Plasma treatment of a stack of polyester fabrics and storing of the treated samples were carried to analyze the effect of penetration depth and aging of plasma surface modification on the ink-jet printing performance. The results are listed as follows:(1) The much higher K/S value of polyester fabric treated by atmospheric-pressure plasma represented better property ink-jet printing. That can be summarized that the most befitting gap distance in this experiment was 3mm by which the highest K/S value was obtained. On the other hand, the K/S value would decrease with the increase of gap distance which could also weaken the effect of plasma discharging. While the atmosphere and gap distance was certain, the K/S values increased with the increasing of plasma exposure time and got its max when 180s. Then the electron number may not change any more. When the fabric was treated for more time, the K/S value began to decrease. It is generally agreed that a large number of active particles will be generated during plasma treatment, such as electrons, ions, free radicals, photons, and excited atom/molecules. Thereinto, the high-speed electron was really contributing to the surface modification of samples. The effects of air+20%Ar plasma treatment were better than air plasma at the same treatment time. This phenomenon can be explained as that argon is much easier to discharge due to its much lower breakdown potential energy than air. The mixture of argon reinforced the discharge of plasma and made the treatment more sufficient(2) The CMYK color measurement results of treated and untreated polyester fabrics show that K/S and C values increased after plasma treatment. That means the sample got deeper chroma and saturation. The surface roughness of the fabric which enhanced the diffuse reflection of light was increased by the etching effect of plasma. The decreasing of the lightness (L value) was corresponding to the more soft color.(3) It can be found via video zoom microscope observation that he anti-bleeding performance of the four-color ink-jet printing polyester fabrics dramatically improved with excellent sharpness after the plasma treatment. The linewidth along the weft and warp edge of inkjet-printed fabrics decreased 38%~46% compared with untreated sample. The dry and wet rubbing fastnesses indicated that plasma treatment has no effect on the color fastness of inkjet printed polyester fabrics.(4) The SEM and AFM images show that the fiber treated with plasma had an evident change with the presence of grooves in the fiber surface morphology compared with the smooth surface of the untreated polyester fiber. The convex-shaped surface sediments formed when the gaseous substance generated by the etching of the plasma returned to the surface of the substrate and the active particles played an important role in that process. The grooves and sediments dramatically enhanced the roughness of the fiber surface.(5) The XPS analysis shows that the content of C1s which is 81.05% for controlled sample decreased to 73.90% and 66.89% respectively assign to air plasma and air/Ar plasma. The content of O1s increased to 22.85% and 29.51%, compared with 16.68% for untreated sample. The O/C ratio on the surface of treated fabric increased 0.1 and 0.23. the deconvolution analysis of C1s peaks indicates that the oxygen containing polar groups such as C-O(and/or C-OH), O=C-O(and/or COOH) and C=O which has stronger polarity increased on the surface of treated polyester fibers while the C-C component significantly decreased.(6) It was difficult for the droplet to spread during the first 140s on untreated polyester substrate which has poor wettability. Nevertheless, fabrics treated with plasma got obvious improvement in hydrophilicity. The drop shape analyzer shows that the droplet fully spread on the substrate within 500ms after being dropped on it. By Fowkes theory and Young's equation, contact angles of two kinds of liquids on solid surfaces are measured and calculated. The surface free energy of fabrics treated with air and air/Ar plasma increased to 72.55mN/m and 78.83mN/m compared with 25.59mN/m for untreated sample. The part of polar groups was particularly significant among the changes.(7) In order to compare the etching effect with the role of polar groups, different atmospheres were selected to bring different effects of plasma treatment. Although more remarkable and symmetrical grooves were generated on the surfaces of polyester fiber treated by air plasma as revealed by AFM images, XPS indicated that air+50%Ar plasma introduced more oxygen-containing groups which led to rather better wettability of polyester fabric than air plasma treated which led to rather better wettability of polyester fabric than air plasma treated.(8) Penetration of multiple layers of inkjet printing polyester fabric surface modified with atmospheric pressure plasma was possible. The plasma treatment effect on the fabric was gradually reduced as the fabric layer got deeper. The research of anti-bleeding property and color strength revealed that the atmospheric pressure plasma could substantially penetrate two layers of polyester fabrics to observably improve their inkjet printing effect. This effect also contributes to the deeper and more vivid color and better anti-bleeding performance.(9) The experiment of wetting time and XPS analysis indicates that the wettability and polar groups of the treated fiber surface gradually weakened as long as the fabric been stored. Although SEM images showed that the etching effect hadn't changed during the storing process, the printing K/S value and the anti-bleeding property of the fabric was influenced by the aging of the plasma. Therefore, the perfect printing time should within 24 hours after the plasma treatment.The main contribution of the paper is in investigation on mechanism of the effect on the property of pigment ink-jet printing polyester fabric treated with atmospheric-pressure plasma. By changing the atmosphere of the plasma treatment on the multiple layers polyester fabric and the aging of the plasma, this paper further illustrates the application foreground of the plasma in the pretreatment of ink-jet printing. |
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