Water-based ink refers to a volatile ink that uses a part of alcohol as a solvent. The ink is dried as the water evaporates. The printing process has no pollution to the environment. The water-based ink is not toxic to the human body, and it is not easy to burn. The water-based ink is environmentally safe. The advantage is that when many paper products are printed, they can be designed to emit low VOCs or zero VOOs. With the world's attention to environmental protection, Jinjia Group launched the printing of environmental protection cigarettes at the beginning of this century. Water-based inks developed jointly with ink suppliers have been successfully put into production, which has opened up a new era of environmental protection for domestic cigarette printing.
In the use of gravure solvent inks, alcohol inks, and water-based inks, Jing Jia Group directly challenged water-based inks, led the development of water-based ink cigarette markings in China, completely changed the performance of inks, and used water and alcohol as diluents. The cost of solvent is saved, the environmental protection level is improved, and the customer's needs are met. First of all, Jingjia Group provided the “New Pride Seven Wolfs” for Fujian Longyan Cigarette Factory and became the leader of domestic water-based inks in cigarette label printing. Solvent-based inks also use a volatile dry method, but there is a large amount of volatile organics.
As international crude oil prices have remained high, the price of downstream chemical products has been rising all the way. In the past, solvent-based inks lost their price advantage. The amount of solvent used is based on 100% of the ink quantity. The solvent cost for solvent-based ink increases to RMB 4,000/ton to RMB 5,000/ton. Considering that the drying requirement of water-based ink is higher than that of solvent-based ink, the coating amount of water-based ink is higher than that of water-based ink. The solvent-based ink is 15% to 20% less. The three are combined on average. Even though the surface price of the water-based ink is 5,000 yuan/ton higher than that of the solvent ink, the actual use cost is still lower than that of the solvent-based ink.
First, the relationship between water-based ink PH value and viscosity
Viscosity is closely related to the fluidity of aqueous inks. The decrease of the PH value of the water-based ink directly affects the decrease of the ink activity and the solubility of the resin. As a result, the viscosity of the ink may increase, which may cause the printing plate to dry up, thereby causing problems such as failure of the printing plate and dropping of dots. Conversely, if the PH value of water-based ink is high, the alkalinity is strong, and the resin dissolves too much, the pigment and the binder may separate, the ink flowability will increase, leading to unclear printing dots, agglomeration, etc., and the ink will not dry easily (rotary printing The machine easily sticks to the paper roll).
In actual printing, when the PH value is between 6.0 and 7.0, the ink will have a delamination phenomenon, and the printing phenomenon will occur when printing. When the pH is between 7.0 and 8.5, the ink system becomes unstable and the viscosity of the ink rises, resulting in poor transfer, dry printing, and dropping, and the color intensity of the printed matter decreases (black ink is most noticeable). When the PH value is between 8.5 and 9.1, the water-based ink has good fluidity, the ink viscosity is suitable for printing needs, has good wettability and spreadability to the substrate, and the ink layer also has good drying properties. PH value of 9.1 to 11.5, a large number of foam in the ink tank, the ink viscosity has a significant decrease, resulting in slower drying speed, water resistance becomes worse, the dot gain rate increases, the print is not clear, caking, trademark The standard barcode bar increases. At the same time, due to the strong alkaline ink, the properties of the pigment may be damaged, and the ammonia odor remaining in the mature aqueous ink print after the end of the process is used. Therefore, the pH of water-based inks should generally be controlled between 8.5 and 9.1.
Second, the relationship between aqueous ink hue and PH value
The pigment is the main factor that determines the color of the ink. It should be an inert substance. Its chemical stability determines the color rendering effect of the pigment. The chemicals that the ink is usually exposed to are nothing more than acids, alkalis, salts, water, corrosive gases, organic solvents (the ink tank is not clean), and these factors can affect the hue of the ink. Although the pigments used in water-based inks have good alkali resistance, generally speaking, regardless of the pigment used, if the pH value of the ink is too high and the alkalinity is too strong, it will have more or less influence on the pigment and thus affect the pigment. The hue of the ink, so try to avoid the ink PH value is too high. If the PH value is too high, the color will become lighter and poor transfer will occur. Conversely, the solubility of the alkali-soluble resin will decrease, the viscosity of the ink will increase, the printing ink film will be thicker, and the color density of the ink layer will also be high. . Of course, if the pH value of the ink is properly controlled (between 8.5 and 9.1), the pigment is well dissolved, disperses well, and the hue remains normal.
Third, the relationship between aqueous ink gloss and PH value
The glossiness of water-based ink is mainly related to the thickness of the ink film, the glossiness of the linking material, the transparency and fluidity of the ink, the particle size of the pigment, the resin content, and the drying speed of the ink. Since the change of the ink PH value will have an effect on the ink layer thickness, fluidity, and drying speed, the gloss of the ink will be affected. In addition, the solubility of the alkali-soluble and dispersion-type resin in the aqueous ink, the size of the pigment particles, and the degree of polymerization are also related to the PH value of the ink. In the conversion of solvent-based inks and aqueous inks, a glossy varnish was directly selected. Only one varnish can reach the brightness of the solvent-based ink twice, greatly reducing production costs.
Fourth, water-based ink printing environment and solutions
In actual production, the working environment of the printing shop requires relatively strict temperature and humidity. When the temperature is higher than 26.5°C, the volatilization of ammonia in the ink is accelerated, and the pH value decreases. A suitable amount of pH adjustment solution may be added in advance to the aqueous solvent: during the printing process, the printing ink is extracted at regular intervals or when the hue of the printed product is changed. If the PH value is lower than 8.5, an appropriate amount of the PH value adjustment liquid may be added. When the pH value is lower than 8.5, hot air and hot water may be used to heat the ink, so that the alkaline substance in the ink is volatilized, thereby lowering the PH value of the ink. Do not reduce the pH by adding acidic substances. Doing so may cause deterioration of the ink. It is generally believed that the ambient temperature of the workshop is maintained at 19°C to 25°C and the relative humidity is controlled at 55% to 65%.
The current research focuses on the stability of water-based inks with pH values. Ink manufacturers must develop water-based inks with stable PH values during the printing process. That is, there is no need to detect and adjust PH values during printing; re-dissolvability is another key area of research. In the process of ammonia volatilization, the resin tends to solidify and even adhere to the printing plate. To this end, we appeal to water-based ink suppliers and do their utmost to research and develop high-quality water-based inks that are convenient for printing companies.
Source: China Packaging News
