Waterless offset printing plates are composed of an oleophilic resin layer and an oil repellent silicone layer. For waterless offset inks, the most important properties are anti-dirt resistance, ink transferability, and ink/ink properties.
1. Development points of waterless offset inks
(1) Development towards low viscosity and high mobility
Due to the improvement of paperless paper and recycled paper, and the increase in the amount of paper, in order to increase production efficiency, the printing speed has been continuously improved, and the occurrence of paper picking and printing plate stacking has subsequently occurred. Waterless offset printing Because the fountain solution is not used, the viscosity of the ink on the paper surface is higher than that of the offset printing with water and is more prone to pick-up and stack failure. Therefore, the low viscosity and high fluidity of the ink is an innovation of the ink technology. The essential.
The use of a polymer and a highly soluble new resin is effective for obtaining a low-viscosity, high-fluidity ink, and can be used to cross-link low-viscosity resins without impairing fluidity. In the cross-linking process of the resin, a network structure is formed between the macromolecules, the internal cohesive force is increased, and the viscosity is increased. If the aluminum chelate compound gelator, the fluidity of the ink may be lost. Thus, a heat-polymerized resin composed of a rosin-modified phenolic resin and a molecular chain-length oligomer was proposed to make the resin quantified with high plasticity, thereby obtaining a low-viscosity resin binder.
(2) Improve anti-dirt
Resistance to scumming is expressed in terms of cT, which is related to ink viscosity, viscosity, and fluidity, and is proportional to viscosity and viscosity, and inversely proportional to fluidity. Therefore, it is not easy to design high cT inks with ink technology with low viscosity, low viscosity, and good flowability (high speed printing). Waterless offset printing should have anti-dirt resistance while achieving low viscosity. Therefore, the key issue in formula design of waterless offset inks is how to suppress the dirtiness of the printing plate. In general, there is a close relationship between the resistance to dinging and the viscosity of the ink, the solvent used and the density of the printing field, the structure of the printing press, and the printing speed.
(3) improve ink receptivity
Soybean oil ink is an environmentally friendly ink that replaces organic solvent inks. Compared with high-curing inks or waterless offset inks, the curing speed is slower. However, from the perspective of practical results, the transferability of the ink is good, and the ink repellency in the field is good.
After the ordinary offset printing ink reaches the paper, the solvent penetrates quickly. In the part near the paper surface, the ink film will break off, while the soy ink is slow to penetrate, and the ink break surface is closer to the side of the blanket, which is equal to The thicker ink film is transferred to the paper surface, so the ink transfer amount increases.
(4) Improve ink transferability
There is a certain relationship between ink characteristics and color development, that is, the higher the ink viscosity and viscosity, the lower the color development; the smaller the fluidity, the lower the color development. In order to obtain high color developability, it is necessary to improve the transferability of the ink, and thus it is required that the ink must have low viscosity, low viscosity, and high flowability.
Both the offset resistance and the ink transferability cannot be taken into consideration. How to balance it is the key to the design of the waterless offset ink.
2. New products and features that have been developed
In response to these problems, ink manufacturers have conducted research based on actual printing conditions and have developed a series of products.
(1) Since the ambient temperature of waterless offset printing is to be as low as possible, it should be kept at a constant temperature. Therefore, ink manufacturers are fully committed to the development of low-viscosity and non-stick version of the ink series.
(2) Due to the business features of waterless offset printing, many types of inks are required. Therefore, spot inks, specialty inks, synthetic paper inks, and special inks have been developed.
Sheet-fed waterless offset inks have the characteristics of good fluidity, low viscosity, soft body, etc., while maintaining the same anti-dirt properties as the original products. They have passed trials by many companies and Heidelberg is also on the Quickmaster D146. The printing was carried out to prove that it has greatly improved in terms of ink repellency, fluidity, stain resistance, glossiness and abrasion resistance of the ink film.
3. Web printing anhydrous ink
In the past, the popularity of waterless offset printing on webs has been slow due to the poor printing durability of printing plates and the poor hiding power of printing inks. However, recently, due to the increase in the strength of the non-image portion of the silicone layer, in Japan, more than 20 web offset presses have been converted to waterless offset presses.
In order to cope with the high-speed production of web-free offset printing presses, inks need to have high viscosity and high fluidity that are resistant to high-speed printing, so as to obtain good ink transferability, ink repellency, and dryness, and to prevent ink from becoming dirty. One of the most notable technologies is the self-adhesive resin technology led by Japan.
Since the self-adhesive resin has a large molecular weight and a large number of cross-linking points between molecules, it is not necessary to use a metal chelate gelator to obtain a binder having a strong gelling elasticity. The ink using such a binder has lower viscosity than the ink using a resin binder, and thus can maintain high speed while avoiding paper fluffing. In addition, its viscoelasticity is less affected by the temperature, which can reduce the problem of dirt caused by the rise in the temperature of the printing press during the long live printing, and shows the superiority of high-speed printing. The aromatic-free inks using these resins have been used in production and will undoubtedly promote the development of web-free offset printing.
4. UV waterless offset ink develops to low viscosity
UV waterless offset inks are characterized by a fast drying and strong dry ink film. Similarly, UV-curing inks have also been improved from high-viscosity type to low-viscosity type, and they are expanding into the field of film printing (PP, PC, PVC, PS, synthetic paper, telephone cards, etc.) after satisfying paper printing.