Ink in printing is mainly divided into four categories according to the printing type: relief ink, lithographic ink, gravure ink and mesh
Printing Ink, and can be divided into two categories according to its own characteristics:
Water Based Ink and oily ink.
In many market applications, water based ink printing has become an increasingly popular choice. When the chemistry and performance of inks are optimized, they are expected to become safer and more sustainable substitutes for solvent inks in printing workshops, especially for packagers.
1. water based ink and oily ink
1.1 water based ink
Water based ink is a kind of water-soluble ink, and flexographic water based ink is also called liquid ink, which is mainly made of water-soluble resin, organic pigment, solvent and related additives through compound grinding.
Water based ink is a uniform paste-like substance composed of binders, pigments, additives and other substances. Binder provides the necessary transfer performance of ink, and pigment gives color to ink. The binders of water-based inks are mainly divided into two types: water dilution type and water dispersion type. There are many types of resins that can be used in the former, such as maleic acid resin, lac, maleic acid resin modified shellac, urethane, water-soluble acrylic resin and water-based amino resin. The water-dispersible binder is obtained by emulsion monomer polymerization in water, and it is a two-phase system, in which the oil phase is dispersed in the water phase in granular form, which can be diluted by water although it cannot be dissolved by water, so it can also be considered as an oil-in-water emulsion.
Water based ink is characterized by low price, good adhesion after printing, quick drying and strong water resistance. In addition, it does not need organic solvents, and it is especially favored by industries with hygienic requirements, such as cigarettes, wine, food, beverages, medicines, children's toys and other packaging and printing products with strict hygienic conditions.
1.2 oily ink
Oil-type Ink, also known as oil-based ink or oily printing ink, is an ink in which pigment particles are dispersed in nonpolar binders and nonpolar solvents. It is mainly composed of pigment particles, nonpolar binders and nonpolar solvents.
Oily ink is characterized by its high viscosity, quick drying, water resistance, softness and good light resistance. When used, the ink is more economical and the cost is effectively saved. In addition, there are also environmentally friendly products, so they are widely used, such as the printing of paper substrates such as books and periodicals, picture books, and other materials, such as metal, plastic, wood, aluminum foil, cartons and building materials.
1.3 Difference
The biggest difference between water based ink and oily ink is that the former can be dissolved in water, while the latter can only be dissolved in specific organic solvents. Therefore, water based ink can be diluted with water, which has the advantages of no need for organic solvent, reducing solvent volatilization, preventing air pollution, not affecting human health, and not easy to burn, and belongs to environmental protection ink.
Oily ink can be diluted with organic solvent, and can be spray-printed on absorption surface and non-absorption surface, which is not easy to fade after spray-printing, and the ink is more economical when used, effectively saving costs. In addition, oily ink also has environmental protection oily ink, which can be coded without machine solvent.
2.Four technical indexes of water based ink 2.1. Viscosity Viscosity is a property that prevents fluid flow, and it is a measure of the ability of fluid molecules to interact with each other to hinder their relative motion, that is, the resistance of fluid flow.
Viscosity is the most important control index in ink application, which directly affects the transfer performance of ink and the quality of flexographic printed matter. The viscosity is not only related to the viscosity and density of the resin in the binder, but also related to the type and granularity of the pigment. In printing, ink with low viscosity will transfer quickly, which will cause disadvantages such as light color, large dot expansion, high-gloss dot deformation and uneven ink transfer. High viscosity and slow ink transfer will affect the transfer performance of the anilox roller, resulting in uneven ink color, sometimes poor color printing, dirty version and paste version.
Low viscosity, which can be adjusted by mixing with new ink; When the viscosity is high, it can be diluted with water or water and ethanol (50% each), and can also be adjusted with ink stabilizer. In addition, in the printing process, temperature also has a great influence on the viscosity of ink, usually the viscosity decreases with the increase of temperature, and vice versa. Therefore, in the printing process, in order to keep the density of printed products consistent, the temperature of the printing workshop should be kept constant.
2. 2 PH value The binder used in ink painting is mainly alkali-soluble acid resin, so the control of PH value is very important. Usually, the PH value should be controlled at 8.5-9.5, when the printing performance of ink is the best and the quality of printed products is the most stable.
Because amine is constantly volatilized in the printing process, operators have to add new ink and various additives from time to time, so the PH value of ink is changing at any time. When the PH value of ink is higher than 9.5, the alkalinity is too strong, and the viscosity of ink will decrease, resulting in slower drying speed and worse water resistance. When the PH value is lower than 8.5, the alkalinity is too weak, and the viscosity of ink will increase, resulting in faster drying speed, easy to block printing plates and anilox rollers, causing dirty pages and bubbles.
Because the influence of PH value is directly related to viscosity, it is suggested that the two should be controlled in practical printing, especially in color printing. Usually, in addition to the viscosity cup, a simple PH indicator should be prepared for testing at any time. When the PH value of ink is low, PH stabilizer or a small amount of alkaline substances can be added; When the PH value is high, solvent or diluent can be added for dilution.
2.3 Thickness The so-called ink thickness refers to the degree to which solid powdery substances such as pigments and fillers mixed in the joint branch are dispersed.
The thickness of ink is also a very important quality index, because it is not only related to the application performance of ink (including coloring power, hue, stability, etc.), but also related to the rheological properties and economic benefits of ink. If the ink is too thick, it will cause problems such as piling up ink and pasting, and the coloring power and hue of ink will also become worse; If the ink is too fine, it will flow greatly, and it will flow after printing, which will lead to the expansion of dot and affect the quality of printed products. In addition, the thickness of ink will also affect its dispersibility. When the dispersion of ink is not ideal, its printing performance will not be satisfactory, which shows that the surface of printed matter is not smooth, smooth and soft, and it will produce a "block" feeling, thus greatly reducing the printing effect.
In actual printing, we can choose ink with different thickness according to specific requirements. When printing printed matter with thin screen lines and high precision, the fineness of ink and wash should be higher; When printing printed products or field printed products that do not require high accuracy, the thickness of ink can be appropriately reduced, which is also to reduce costs and improve economic benefits.
2.4 dryness The drying speed of ink is not only related to the performance of ink itself, but also related to the printing speed, the drying capacity of drying equipment and the performance of printing materials. This paper only considers the factors of ink itself. The principle of selecting ink dryness is usually: the ink should be fully dried before the next printing and before rewinding or stacking under the existing conditions of the printing press, but not on the printing plate.
Ink and wash uses water as solvent and alkali-soluble acid resin as binder, which is mostly used for printing corrugated boxes and paper bags, so the drying forms are mainly osmotic drying and a small amount of volatile drying. Because water is used as solvent, its volatilization speed is not as fast as other solvents, so the drying of ink is slower than
Solvent Based Ink. Therefore, it is usually necessary to add a small amount of alcohol to the solvent to improve the drying speed of ink. In addition, under the condition of determining the solvent, choosing different kinds of resins also has an impact on the drying of ink. Because different resins have different curing speeds on the substrate and different release characteristics of solvents, the drying property of ink is different.
In practical application, the dryness of ink is also related to its viscosity and PH value. The ink is dry, but the viscosity may be too high, which can be solved by further dilution; Ink dries quickly, which may be that the PH value is lower than 8.5. Stabilizers can be added to adjust it. In addition, a quick-drying agent or a slow-drying agent can be added to the ink according to the actual printing speed, and the drying speed of the ink can be appropriately changed to obtain a stable printing effect. The dosage of quick-drying agent or slow-drying agent is generally 1%-2% of the total ink amount.
There are many quality indicators that need to be controlled in the application of ink painting, including color, luster, adhesion and stability. In actual printing, in order to improve the printing quality in an all-round way, all indicators should be considered comprehensively.
3.Water based ink, an increasingly popular choice. According to the exclusive data of smithers Report, by 2022, the total consumption of water based ink will be 493,000 tons, with a value of 5.1 billion US dollars. Demand growth will expand the market with a stable compound annual growth rate (CAGR) of 3.1%, reaching 576,000 tons by 2027.
In contrast, the usage of solvent based ink will increase from 1.02 million tons (worth $8.09 billion) in 2022 to 1.13 million tons in 2027. During the forecast period, the compound annual growth rate by volume slowed down significantly to 2.1%. This shows that in many markets, the enthusiasm for investing in alternative ink types is greater, and the price of water based ink sets can get a higher premium.
Water-based printing is still limited to a few areas in the market-packaging, labels, commercial printing and publications. Even in these areas, there are obvious subtle differences due to a series of technical and market factors.
Water based ink is widely used in gravure, flexography and inkjet printing. These are also the main platforms for solvent based ink, and some screen printing using them. In the past three years, the printing market has undergone profound changes, which makes packaging and labels more and more the core of the future strategy of printing equipment manufacturers.
Several latest printing machine models in the field of packaging are based on water-based inkjet or flexographic systems. In the next five years, these will become more and more important, as suppliers seek to transition to more paper packaging substrates. Solvent ink systems will have a wider range of applications, but concerns about the release of volatile organic compounds mean that water-based systems will be preferred when drying technology allows these systems to run at acceptable printing speeds. Waterborne inkjet is particularly attractive in food packaging, because people are still worried about the safety of radiation curing system, especially the existence of unreacted ink components.
For water-based inkjet, with the installation of new printing machines and the shift of printing purchase to on-demand printing mode, the growth of all packaging types will reach double digits. Similar factors will make water-based printing more and more important in book printing. In the next five years, this will become the most profitable market for water-based inkjet ink.
For flexography, with the support of the recovery of commercial printing demand, most major packaging types-folding cartons, corrugated boxes and flexible substrates-will have a gradual but unobtrusive change. Solvent-based printing is still very common in flexographic printing, which is mainly used for long-term flexible packaging that is not used for food or other sensitive goods. This will also be the case with gravure printing, although publishing is still an important application of this process, although it is decreasing. At the same time, solvent based ink will have some additional applications in packaging inkjet printers, but the biggest application will still be in advertising.
