Water-based inks can solve the problems of emissions and pollution in the current packaging and printing industry due to their excellent environmental performance. They have received more and more attention and become the main target of future research. At the same time, its use will also be replaced. Traditional solvent based inks. China has clearly listed water-based inks and related raw materials as the focus of future development research and the main direction of the development of the ink industry. Water-based ink is a new "green" printing material in the 21st century. It has two remarkable characteristics: one is low viscosity and good fluidity; the other is that it does not use organic solvents and is beneficial to environmental protection. Water-based inks are water-based, with extremely low VOC content, which greatly improves the working environment of ink manufacturers and print operators compared to solvent-based inks, thereby reducing the harmful effects of harmful substances on their bodies. In addition, it also reduces the risk of fire and toxicity caused by static electricity and flammable solvents, and provides favorable conditions for the greening and environmental protection of the packaging and printing industry in the future. Although water-based inks have great advantages in the packaging and printing industry due to their environmental friendliness, they still cannot achieve zero emissions. They still contain small amounts of alcohols, ethers and even organic amines. These are little environmental pollution, but The air pollution to the workshop is serious. Titanium dioxide and Petroleum Resin C9 are one of the important raw materials for the production of inks.
1 Development of water-based inks
1.1 Development of foreign water-based inks
Foreign research on water-based inks began in the 1960s and has mainly gone through three stages: the first stage is the first generation of ink products with rosin and maleic acid modified resin as the binder, and the second stage is solvent. The styrene-acrylic copolymer resin is the second generation ink product of the binder, and the third stage is the third generation ink product with the polymerized emulsion resin as the binder. In the first phase of the study, the design and development of resins for aqueous binders was the key to the development of waterborne inks. As a polymerized emulsion resin having a core-shell structure and a network structure prepared by polymerizing an acrylic monomer and styrene is used in an aqueous ink, not only the gloss and dryness of the ink are greatly improved, but also promoted. The development of water-based inks has broadened the competition with solvent-based inks, and the development of water-based inks has entered a new stage of development. Currently, green and environmentally friendly inks have been used in the United States and some European countries, and solvent-based inks containing benzene have been banned. In the US market, 40% of plastic printing uses water-based inks, and sales of inks are rising. It can be seen that ink has become the main ink for printing. In other developed countries, ink and wash will gradually become the main ink used in plastic film printing. It is reported that the United Kingdom has legislation prohibiting the use of solvent-based inks to print films for packaged foods. Petroleum Resin C9
1.2 Development of domestic water-based inks
Compared with foreign countries, domestic research on water-based inks started late, which can be roughly divided into four stages: the first generation of ink products was introduced from Singapore, and the second generation of ink products was developed on the basis of the first generation of ink. The third generation of ink products were imported directly from abroad. The fourth generation of ink products is the high-grade ink currently used. The high-end products currently used are produced by self-developed resins or directly using imported resins, and were first developed and put into production by Tianjin Ink Factory. After joining the WTO, faced with severe challenges, the development of environmentally-friendly and energy-saving inks to replace traditional solvent-based inks has gradually been put on the agenda, so water-based inks with good environmental performance are increasingly favored by researchers and toward The development of "high speed, multi-color, fast drying, pollution-free, low energy consumption, standardization". At the end of 2003, Wuhan Modern Industrial Technology Research Institute developed a series of water-based inks with non-toxic, non-irritating odor, non-corrosive, non-flammable, non-explosive and safe to use , widely used in gold. Printing in coated paper, whiteboard, corrugated paper, self-adhesive paper, books and magazines. At the beginning of 2004, Shanghai Meide Fine Chemical Co., Ltd. recently launched the odorless high-quality environmentally-friendly full-water low-temperature thermosetting ink MD-1002 . The formaldehyde content of this product is below 15pp, which meets the requirements of Japanese and German textile printing and dyeing environmental protection. The utility model has the advantages of strong hiding power, fine texture, and the ability to pass through a screen of 250 mesh or more, convenient operation, and the ink color can be arbitrarily adjusted. In 2005, there were reports in the literature on the use of styrene-acrylic resin as a raw material for the synthesis of water-based inks. Compared with foreign inks, the fineness is better than that of foreign similar products. The gloss of the ink is comparable, and the viscosity is slightly higher than that of foreign ink. In the same year, it was reported in the literature that a polyurethane-polyacrylate composite emulsion was used as a binder and a plastic gravure aqueous ink was prepared by using phthalocyanine blue as a pigment. The product has good adhesion fastness to PET film and OPP film and good water resistance. In 2011, it was reported in the literature that the cross-linked modified styrene-acrylic emulsion was used to prepare aqueous ink, and the prepared product had relatively good rubbing fastness, stability, water resistance, gloss and tinting strength. Compared with before, China's water-based inks have made great progress in research and development and technology. The four-color ink, dot, overprint and high-speed printing carton water-based inks produced by the company have basically met the requirements of most carton factories. In addition to its low cost, its quality is not inferior to imported ink, and it is trusted by customers. In recent years, with the continuous improvement of packaging aesthetic awareness and environmental awareness, the number of imported flexographic printing production lines in China has been increasing every year. Many of them are imported high-grade three-color and four-color water-based printing for corrugated paper. Ink printing slot machine, etc.
2 Research status of water-based inks
2.1 Research Status of Bonding Materials
As the base material of water-based ink, the binder plays a decisive role in the performance and printing effect of the ink. The innovation in the technical research of the binder has promoted the rapid development of ink technology. The water-based resin known as the 21st century green resin has received more and more attention and research because of its low toxicity, non-flammability, no organic solvent, no pollution and other excellent characteristics. At present, there are many researches on binders at home and abroad, mainly modified rosin water-soluble resin, polyacrylic acid water-soluble resin and emulsion water-soluble resin.
2.1.1 Modified rosin water-soluble resin
The resin is used for formulating water-based inks in an amount of about 70%, and has the advantages of low price, simple manufacturing process, high gloss of ink, etc. The disadvantage is that the water resistance is poor after printing, the printing process is unstable, and the medium and high-grade are not achieved. The gloss and water resistance requirements required for packaging printing. Chen Xueheng and other modified natural rosin with fumaric acid and pentaerythritol to prepare fumaric acid modified pine perfume resin with low cost, high softening temperature, good solubility and excellent comprehensive performance. Feng Lianxiang and others use acrylic acid to modify rosin, and then the aqueous ink binder prepared by copolymerization with polyvinyl butyral (PVB) has excellent adhesion and water solubility, and is suitable for tobacco tipping paper.
2.1.2 Polyacrylic acid water soluble resin
It is mainly used in the preparation of high-grade water-based inks, and has excellent moldability, light resistance, adhesion, corrosion resistance and weather resistance. After years of research, great progress has been made in modification. However, the main shortcomings are poor water resistance and stain resistance, low adhesion on non-absorbent materials, and slow drying speed. Therefore, it is still the main research to modify it to improve its adhesion and water resistance. direction. In EP1059341, a silicon-containing organic substance is added to an acrylic resin and a styrene copolymer to synthesize a water-soluble acrylic resin which can be used for preparing an aqueous ink for inkjet, and the ink prepared therefrom has good abrasion resistance and light resistance. And water resistance, but the cost of the ink is high, can only be used as a high-grade trademark printing ink. Therefore, research and development with low cost and extensive use of ink is still the future research direction.
Peng Xuejun et al. used azobisisobutyronitrile as initiator N, N-dimethylethanolamine as a neutralizing agent to copolymerize methyl methacrylate, methyl acrylate, acrylic acid and N-methylol acrylamide quaternary monomers. A dispersion resin and a film-forming resin suitable for a flexographic four-color overprinting aqueous ink were prepared, and a set of three-color and black four-color overprint aqueous inks was developed as a connecting material. The process is simple and low in cost, and the content of organic volatiles is far lower than that of domestic similar products, and has a good application prospect with the currently imported ink products. Liu Xu et al. modified the acrylic resin by introducing epoxy resin to improve its adhesion and composite fastness. The index of water-based ink prepared by it has reached or exceeded the national standard and meets the requirements of practical application. The gravure composite plastic ink field has great application value and market prospect.
2.1.3 Emulsion type water soluble resin
In recent years, the development of emulsion type binders has been very rapid, especially the development of composite emulsions. In US 4,973,617, a polyamide is added to a system in which maleic anhydride is reacted with rosin, and the obtained product is used for modifying an emulsion acrylic resin, and then adding a small amount of propanol to form a binder, which is used in ink to make ink. The printability and water resistance have been improved. Cai Dongyu et al. combined the advantages of waterborne polyurethane and acrylic resin, and prepared an aqueous ink binder-urethane with good water resistance and excellent adhesion fastness and good stability to PET and OPP films by emulsion polymerization. Polyacrylate (PUA) composite emulsion, the aqueous ink prepared therefrom is mainly used in gravure printing of plastics. Hu Mingjin et al. used methyl acrylate as a hard monomer, butyl acrylate as a soft monomer, and acrylic acid as a functional monomer. These raw materials were synthesized into a emulsion binder by a pre-emulsification process, and gloss and water resistance were prepared therefrom. Ultra-fine water-based inks with excellent specifications such as fineness. Jiang Chen et al. synthesized a cross-linked polyacrylate emulsion by core-shell emulsion polymerization, and discussed the adhesion, water resistance and resistance of the film-forming materials of this emulsion to common food packaging materials at room temperature and heat curing. The influence of properties such as solvent and hardness. The research results show that the core shell design, soft and hard monomer ratio and the selection and dosage of functional monomers of different synthetic processes have a great influence on the performance of ink-based binders.
Zhang Lin designed a hard monomer with a high Tg as the core, a soft monomer with a low Tg as a shell, a crosslinking monomer M in the core, a slight crosslinking, and a functional group such as a carboxyl group or an amide group in the shell layer. A core-shell acrylic emulsion synthesized by crosslinking reaction during drying. It was found that when the amount of cross-linking monomer M is 0.5% of the mass of the core monomer, and the total amount of MAA and MAM is 1% of the mass of the shell monomer and MAA/MAM=1, the obtained product is water-resistant to the coating film. The sex is the best. Wang Haiqiao et al. copolymerized silane A-174 containing a double bond of a coupling agent with an acrylic monomer to synthesize an aqueous emulsion for acrylic inks on a plastic film substrate. The emulsion can be passed through the silicon during film formation. The hydroxyl group is rapidly crosslinked, thereby improving the water resistance of the coating film and the like. Studies have shown that the use of A-174 silane coupling agent can improve the water resistance of the polymer and greatly improve the scrub resistance of the formulated aqueous ink. It can be seen that the use of silicon-containing organic compounds to improve the water resistance of the emulsion and the preparation of a mass controllable emulsion polymer to solve the disadvantage of poor resolubility will be the main research direction in the future. In recent years, the research on emulsion type water-soluble resin is relatively hot, but there are still characteristics of poor resolubility and poor water resistance. Therefore, the optimum dosage for compounding with polyacrylic resin and the development of new composite emulsion type water solubility are determined. Resin to improve the above shortcomings is still the direction of future efforts.
2.2 Research Status of Additives
As an important raw material for changing the performance of water-based inks, auxiliaries have gradually flourished in recent years. At present, commonly used additives are: pH stabilizer, quick-drying agent, antifoaming agent, dilution agent, slow drying agent, wetting and dispersing agent, leveling agent, bactericide and the like. The scientific use of these auxiliaries can improve the performance of aqueous inks and improve the stability of aqueous inks. It has been reported in the literature that for high-grade carton inks, the use of wax additives is key to achieving wear and slip properties. Three types of waxes were selected: ultrafine wax (with the narrowest particle size distribution), wax emulsion (with fine particle size) and wax dispersion. The results show that wax can improve the wear resistance and anti-blocking of the stamp. Sex, in addition to the different processing methods of the wax will affect the performance of the wax in the ink. Therefore, when selecting wax additives, it is necessary to comprehensively consider the influence of the particle size and dispersion system of the wax on the performance of the ink.
Water-based inks generally have the problem of insufficient gloss, which seriously hinders the wide application of water-based inks in the field of packaging and printing. According to the gloss analysis, the gloss of the aqueous ink becomes smaller as the mass fraction of the added antifoaming agent increases, which indicates that when the defoaming agent is added to the ink, the dispersibility of the aqueous ink is adversely affected. Therefore, the gloss of the ink is deteriorated; the thickener can increase the gloss of the ink within a certain amount range, but after a certain amount, the gloss is decreased; in addition, since the gloss of the bright paste type is very glossy Well, so it is used to blend water-based inks, and the obtained products have a light and transparent color, and at the same time, the effect and gloss of the ink film are also improved. In the use of auxiliaries, it has been reported in the ink system that the extremely low-volatility and odorless water-based polymer type multifunctional auxiliaries can quickly and effectively control the pH of the system. In order to achieve good dispersion and stabilizing effect, polymers such as polyurethane, polyacrylic acid and carboxylic acid can be selected as dispersing agents for aqueous inks; in order to avoid the occurrence of undesirable phenomena such as shrinkage, fish eyes and orange peel, it is necessary to follow The principle of using defoamer with the lowest dosage and the best defoaming effect; polyurethane is often used as the most commonly used leveling agent in aqueous ink systems. In addition, it has been reported in the literature that when the suds suppressor is mixed with the inner and outer surface plasticizing antifoaming agents and the amount of the antifoaming agent is 2%, the problem of foaming of the ink can be well solved.
2.3 Research Status of Pigments
When pigments are selected, hue is the primary consideration, followed by factors such as ease of dispersibility, resistance to alcohol and alkalinity, and compatibility with other ingredients. Water-based inks generally use water-based pigments that are compatible with aqueous resins to achieve a good dispersion. Aqueous inks are generally prepared from lake-based pigments because the lake-based pigments cause poor stability of the ink in the storage process and the viscosity increases in the alkaline medium to thicken the ink film. For organic pigments, azo or disazo, indigo and other high-grade pigments are generally used as pigments for ink to meet the design requirements of ink formulations. In the printing process, domestic high-grade pigments with bright colors, low viscosity and stable system are selected as the pigments for ink. With the continuous development of water-based inks, the development of pigments suitable for inks with good performance is still a hot topic in the future. At present, foreign patents on water-based inks mainly focus on the development of binders, such as the addition of rosin and the introduction of water-soluble organic compounds, emulsions, alkyl polyoxyethylene ether sulfonate and other monomers, so that the clarity of the image is obvious. The improvement is that the obtained product has uniform pigment, good particle flowability, optical density greater than 0.9 and water-based ink product which can be quickly dried.
3 Research direction
At present, both imported and domestic inks have the disadvantages of not being resistant to alkali, not resistant to ethanol and water, slow drying, poor gloss, and easily causing paper shrinkage. It has been reported in the literature that the use of UV inks can solve the above drawbacks, but this not only increases the printing process but also increases the printing cost, and does not achieve a good economic benefit. However, water-based UV inks will become a hot spot in future research because of their good development and application prospects. In addition, with the further development of nanomaterials and nanotechnology, the research and development of nano inks will gradually flourish. As an important technical index of ink, viscosity is very important for its control. Some experimental studies have found that amination reagent plays a vital role in the viscosity change of the ink system and the stability of its viscosity. This finding is high and low in the future. The design of the viscous ink formulation system and the ideal viscosity of the ink application provide an important theoretical basis.
Drying time, blistering and color dullness and unevenness after drying are still the most important problems in ink application, which directly affects the speed of replacement of solvent-based inks by aqueous inks, and limits the wide application of water-based inks. Therefore, the development of new ink additives and pigments to improve ink performance and reduce costs is still the direction of our future research.
In summary, water-based inks are environmentally friendly inks that are solvent-free and solvent-free. They are especially suitable for packaging and printing products with strict hygienic conditions. Therefore, the development of water-based inks meets market requirements and can be adapted. Market demand. Although water-based inks are environmentally friendly and have good printing adaptability, there are still some shortcomings in its development. For example, ink drying speed is slow, drying energy is high, production efficiency is low, and cost is high. Study the issues that need to be addressed. Researchers need to further research and develop new ink materials to improve the performance of ink and reduce prices, so as to better adapt to market demand.