Digital inkjet printing, also known as color inkjet printing, is to input the required graphics to the computer through an input device such as a scanner or digital camera, edited by the electronic color separation system, and then directly controlled by the computer Dyes or pigments are sprayed onto fabrics for printing. Inkjet printing can be divided into two types: continuous inkjet and on-demand inkjet based on the principle of inkjet.
1. Continuous jet CIJ (Continuous lnk Jet)
The principle of continuous jetting is to apply a high-frequency oscillating pressure to the ink, so that the ink is ejected from the nozzle to form a uniform and continuous stream of droplets. An electric field that changes synchronously with the pattern photoelectric conversion signal is provided at the nozzle. The ejected droplets are selectively charged in the charging electric field. When the flow of droplets continues to pass through the deflection electric field, the charged droplets are deflected under the action of the electric field, and the uncharged droplets continue to fly in a straight line. The droplets flying in a straight line cannot reach the substrate and are recovered by the liquid collector. The charged droplets are ejected onto the substrate to complete the printing.
2. On-demand jet DOD (Drop On Demand)
The working principle of the on-demand jet printing system is that when printing is required, the system applies high-frequency mechanical force and electromagnetic thermal shock to the ink in the nozzle to form tiny droplets that are ejected from the nozzle. Set the pattern. The most widely used on-demand jet is thermal inkjet technology, which relies on thermal pulsation to generate ink droplets, and a computer controls a heating resistance wire to a specified temperature, causing ink gas (fog) to be ejected from the nozzle after being atomized. Another type of DOD technology is a voltage-type ejection system, that is, a computer controls to impose a potential on the conductive material to cause the conductive material to compress in the direction of the electric field and expand in the vertical direction to eject the ink.
Inkjet printing not only requires high-precision nozzle technology and high-precision control technology, but also requires ink (ink) with high purity, high concentration, high fastness, and high stability to match it before it has use value.
3. The process of digital inkjet printing
The process of inkjet printing depends on the ink used. Generally, acid dyes are mainly used for carpet printing, disperse dyes are mainly used in polyester fabrics, and reactive dyes are mainly used in cotton fabrics. The following is an example of the inkjet printing process of reactive dye ink used in cotton fabrics.
Fabric pretreatment → drying before printing → inkjet printing → drying after printing → steaming (100 ~ 102 ℃, 8min) → washing → drying.
The pretreatment of the fabric is mainly due to the wettability of the fabric and the capillary effect between the fibers. In conventional fabric printing pastes, appropriate printing fillers must be used to prevent seepage. The general inkjet printer can only use low-viscosity water-based ink. If it is directly printed on the fabric, the dyeing solution will permeate in all directions, so the printed fabric must be properly pretreated. When spray printing, special software is used to print lines and patterns at an appropriate resolution. The post-processing of printed fabrics is mainly to improve their color fastness.
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