Ink selection and control in inkjet printing process (2)

3. Selection of dye inks and pigment inks

From a chemical point of view, the dyes are present in a single molecular state in the ink, while the pigments are composed of a floc that has numerous pigment molecules aggregated.

In general, the color performance or color gamut of a dye ink is superior to that of a pigment ink. When printing on a relatively good substrate, the use of a dye ink can achieve an effect comparable to that of a silver salt photograph. However, dyestuff inks have poor stability, especially lightfastness, dark storage stability, moisture resistance, and water resistance. The reason is that individual dye molecules have very unstable chemical properties under light, moisture, and oxidation conditions. Chemical reactions are very likely to occur, causing prints to fade. Unlike dyes, pigments in pigment inks exist in a state of flocculation in which numerous pigment molecules aggregate, and therefore their stability to the environment is better.

Dye inks are also very picky on print media and often require specialized media support to achieve this. When printing on ordinary copy paper, because the copy paper is composed of criss-crossing paper fibers, the glue material is filled between them, and the proportion of hydrophilic factors in the general dye ink accounts for a large proportion due to these hydrophilic factors. The role of dye ink is very easy to infiltrate into the paper fibers, resulting in the production of smudge on ordinary copy paper, seriously affecting the final printing effect. In contrast, pigment inks are the opposite. Instead of the hydrophilic factors, a large number of water-repelling factors are used so that the ink does not penetrate into the deep layers along the fibers, but rather adheres to the surface of the paper.

According to the above advantages and disadvantages, we can know that the dye ink has strong performance, colorful, uniform, high brightness levels, easy to express color, so it is particularly suitable for indoor use; pigment ink stability and durability, suitable for outdoor use .

Third, ink-jet printing ink control

In inkjet printing, in order to ensure the results, we must do a more appropriate control of the parameters of the printing ink, water-based ink, for example, the conditions for printing control are the following:

1. In order to not block the inkjet head, it must pass 0.2μm filter.

2. Sodium chloride content must be less than 100ppm. Sodium chloride causes the dye to settle, and sodium chloride is corrosive, especially in bubble jet systems. Although the nozzles are all made of titanium, they are still corroded by sodium chloride at high temperatures. .

3. With buffer solution effect. The pH of the ink is stable and some dyes will precipitate due to changes in pH.

4. Viscosity control (1 to 5 cp). Micro Piezo Inkjet systems have a higher viscosity requirement and bubble jet systems have lower viscosity requirements.

5. Surface tension (30 to 60 dyne/cm). Micro Piezo Inkjet systems require lower surface tension, and bubble jet systems require higher surface tension.

6. Drying speed is just right. Too fast and easy to plug the inkjet head or break the ink, too slow to spread, so that the dot overlap is serious.

7. Shelf life. It takes up to three months, usually one year, for the ink to be manufactured from the factory to the end of the consumer's use. Generally, the ink must be able to pass through a 0.2μm filter for one year.

8. Thermal stability. The thermal stability of the dye for the bubble jet system is better because the ink of the bubble jet system is heated to a high temperature of 400[deg.] C., and if the dye does not withstand high temperatures, it will decompose or discolor. While controlling the property parameters of the ink well, the desired printing product must be obtained when using the ink. The method used must be correct. The performance of the ink should be monitored before, during and after printing. The printing environment should be monitored. And storage conditions such as temperature, humidity, cleanliness, and air flow can all affect the performance of inkjet inks.

In addition, after printing, inkjet inks may also be exposed to undesirable environments such as UV rays, ozone, adhesives, and corrosive environments. All of these factors may degrade the quality of the printed product. The type of ink may be selected as needed to ensure that both the prepress and postpress can meet the needs of the printing environment. Inkjet ink is a chemical product and it should be properly handled to ensure safety. The MSDS Material Safety Data Sheet is a guide to operations that ensures that ink storage, use, transportation, and disposal are all performed under the specification. The best equipment does not necessarily get the best prints. For ink-jet printing, choose the right ink, deeply understand the applicable range of various types of ink, adjust the ink parameters, monitor the ink change in the inkjet printing process, and control the environment of the workshop. Only in this way can the stability of production be maintained. And the quality of the product.