Digital ink-jet printing is to convert the pattern into digital form and input it to the computer through the scanner, edit and process it through the computer printing color separation tracing system, and then the computer controls the micro piezoelectric ink-jet nozzle to directly spray the special dye (collectively referred to as ink) onto the textile, and the color is mixed and restored to the original scanning image. Compared with the traditional printing method, it has the advantages of flexible design, fast speed, low energy consumption, no pollution, material saving, and high product quality. It not only reduces the burden on enterprises, but also meets the requirements of environmental protection, and makes up for the technical defects and gaps of traditional printing. According to different inkjet methods, there are two types of digital inkjet printing machines, namely, continuous inkjet (CIJ) and drop-on-demand (DoD) printing machines.
Ink jet printing ink is one of the key factors affecting the quality of printing products. Ink jet printing inks for fabrics not only have specific requirements for pigment purity, insoluble solid particle size, ink viscosity, surface tension, stability, pH, and foaming but also require good color fastness to washing and rubbing after the ink is sprayed on the fabric to form a pattern. At present, there is no ink-jet printing ink that is generally applicable to fabrics. Most of the inkjet printing inks are formulated according to specific requirements, and there are some problems, such as high price, unstable quality, poor universality of inks from various ink manufacturers, and color difference. Therefore, with the development of digital ink-jet printing technology, it is imperative to study high-performance ink.
Types and performance requirements of digital ink jet printing inks
- Type
Ink jet printing inks are generally composed of pigments, water, organic solvents, and additives (such as antibacterial agents, dispersants, pH regulators, humectants, defoamers, etc.). Textile inkjet printing inks can be divided into two categories: water-based ink and solvent ink. The former is called ink for short, and the latter is called ink or non-aqueous ink. Water-based ink is the main variety used in ink-jet printing at present. The use of pigment can be divided into dye ink and pigment ink.
Theoretically, all the dyes used in traditional textile printing can be formulated into ink-jet printing inks, but at present, the commonly used dye inks are mainly reactive dyes, acid dyes, metal complex dyes, and disperse dyes. According to the state of dyes in aqueous solution, they can be divided into real solution ink and water dispersion ink.
The pigment is insoluble, so the preparation of pigment ink for inkjet printing is special. Firstly, the pigments need to be ground into small particles and stably dispersed in the corresponding aqueous system; Secondly, the pigment should be modified or the pigment fixative should be added to the ink so that it can be fixed on the fiber after ink-jet printing so that the printing pattern can obtain sufficient color fastness.
- Performance requirements
Inkjet printing ink determines the ink type according to the characteristics of digital inkjet printing technology and product requirements. The following performance requirements are required for any type of ink:
Safety: nontoxic, odorless, carcinogenic, and ignitable.
Viscosity: the viscosity of inkjet printing ink is lower than that of traditional printing. If the viscosity is high, the sprayed droplets will be in wiredrawing shape and affect the spraying speed. Generally, the viscosity required by CIJ technology is 2 ~ 10 mpa s. The viscosity required by DoD technology is 10 ~ 30 mpa s。
Surface tension: the surface tension of the ink is high. Different printing methods have different requirements on the surface tension of the ink. The recommended surface tension of ink for the CIJ printing machine is 40-60 mn/m, and that for the DOD printing machine is usually 40-50 Mn / m.
Conductivity: CIJ printing machine requires more than 750 s/m, while the DOD printing machine does not.
Particle size: it is generally required to be controlled below 1ym, and the nozzle cannot be blocked.
PH: it is required to be controlled at 4 ~ 8.
Others: high ink purity, good stability, and wide adaptability are required; It can produce high-quality patterns on the substrate, with high coloring rate, good light fastness, and the dry rubbing fastness can reach grade 4 or above, and the wet rubbing fastness can reach grade 3.5 or above.