| Digital inkjet printing technology has the characteristics of low pollution,low energy consumption,simple process,fast speed and flexible production,which developed rapidly in recent years and is regarded as the most promising new textile printing technology in the future.The pattern of the discharge printed fabric is fine,rich in level and full of background color.The advantages of discharge printing can not be replaced by direct printing,and it can increase the added value of the fabric.However,the operation process of the traditional screen printing is complex and it has high technical requirements,which is the reason why the discharge printing has no a good development.In this work,digital inkjet printing was creatively combined with discharge printing,and a kind of white digital printing ink was developed.It was hoped that the complex discharge printing process could be realized by a simple digital printing method.Firstly,the reduction performance of thiourea dioxide,a new formaldehyde-free reducing white discharging agent,was discussed.The effects of concentration of thiourea dioxide,p H and temperature on the reduction potential of thiourea dioxide were studied.And the potential changes of thiourea dioxide about it mixed with different mass fraction of anhydrous sodium sulfite and sodium pyrosulfite,respectively.The reducibility of thiourea dioxide was compared with those of common white discharge agents includingsodium hydrosulfite,sodium rongalite,and Decrolin,The results show that thiourea dioxide had a high reduction potential in a solution with a concentration of 2.3% and p H of 8-9 and a temperature of about 80 ?,so it could be used as a white discharging agent for white discharge printing.Secondly,in view of the water-based ink,thiourea dioxide was chosen as main reducing white discharging agent.Taking the physical properties of ink,such as viscosity,surface tension and conductivity as test indexes,the amount of ink components was optimized: thiourea dioxide 2.3%,anhydrous sodium sulfite 0.8%,ethylene glycol 8%-10%,diethylene glycol 8%-10%,propanetriol 4%-5%,isopropyl alcohol 1%-2%,polyethylene glycol200 3%-5%,polyethylene glycol10000 3.5%-4.5%,OP-10 emulsifier 0.12%,silicone defoamer 0.22%.The effect of temperature on the prepared white digital printing ink was investigated,and it was concluded that the temperature change had no effect on the surface tension of ink.The viscosity of ink decreased slightly with the increase of temperature,however,it could still meet the requirements of ink-jet printing.It was also found that the physical and chemical properties and reductive properties of the ink could be kept stable for three months under the condition of p H 3-4 and low temperature of 0?-3?.But the ink-jet printer required the p H of ink was 7-9 when printed,so the p H of white digital printing ink need to be adjusted when in use.In addition,the printing fluency of ink,the shape and status of ink droplets,and the whitening effect of ink showed that the white digital printing ink had good printing performance.Finally,based on the white digital printing ink,the processing technology before and after white ink-jet printing of silk fabric was studied.The results showed that,the whitening effect,the outline sharpness and line uniformity of pattern was good for the silk fabric that treated in the condition of the pretreatment process was CMC 2.8%,sodium bicarbonate 2%,hygroscopic agent mixed of glycerol and triethylene glycol 5%,the ratio of glycerol to triethylene glycol was 3/1 and the steaming condition was saturated steaming mode,steaming temperature was 100 ?,steaming time was 6 min.Compared with the traditional white screen printing process,and the mass fraction of thiourea dioxide in white pulp of white screen printing was the same as that of white digital printing ink.It was found that to reach the same whiteness requirement as screen printing,ink-jet printing used less white discharging agent and other additives.In order to illustrate the performance of white digital printing ink,several azo reactive dyes were selected as ground color dye and printed with white ink-jet printing,which all could obtain good whitening effect. |
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