In the past, most people paid attention to ink in terms of color, rheological properties, etc. The current environmental protection calls have become increasingly high. Printers must strictly implement environmental protection standards in their production. Therefore, all links in the supply chain of printing raw materials are also Generated a chain reaction. In order to eliminate the VOCs released by the ink solvent system, printers began to search for new ink products. Water-based inks are a new type of environmentally friendly printing material, especially suitable for tobacco, wine, food, beverages, pharmaceuticals, children's toys and other health Conditions require strict packaging products, have a significant growth potential in the specific packaging market, is the development of the ink industry in a new direction.
The characteristics of water-based plastic printing inks are non-toxic and odorless. They are suitable for various types of gravure and rotary flexographic printing processes, with good transfer and attachment fastness; water-based inks are easy to use, thinners are aqueous solutions of water and alcohol, printing inks High gloss, good transparency, water resistance and weather resistance. To test the printability of water-based plastic composite printing inks, PET, PE and BOPP films were used in this experiment.
Experiment introduction
1. Raw materials and reagents
Solvents: water, isopropanol;
Resin: 315 resin, 310 resin, M04 resin, 317 resin, 54 resin, Z604 resin, 36 resin, 81 resin, 73 resin, 14 resin;
Pigments: brilliant red, Lisol red, benzidine yellow, indigo blue, carbon black, titanium dioxide;
In addition, there are dispersants and defoamers.
2. Experimental equipment and testing instruments
SGM-1.4L sand mill, US 5400 Red Devil blender, scraper, acidity meter, American exhibition color wheel, gloss meter, QXD type scraper fineness meter (0-50μm), 3# Zahn cup, Tongji Rotary viscometer, British RK printing tester.
3. Water-based ink preparation
According to the formula, each raw material is weighed accurately, and evenly dispersed into the sand mill until it is finely distributed. After grinding, the water is gradually grinded until the fineness reaches the target, and the emulsion can be discharged.
Experimental results and discussion
1. Selection of water-based resin binder
The main ingredient of the binder is the resin, which is the heart of aqueous ink. Ink viscosity, gloss, water resistance, drying, fluidity, transferability, and fixing properties are mainly determined by the binder. The ink's acid resistance, alkali resistance and solvent resistance are also related to the binder. Therefore, the development of ink painting focuses on the development of ink binders.
The important indicators for the selection of water-soluble resins are molecular weight (Mw) and acid value (AV), among which molecular weight is the most important. With a high solids content of low molecular weight resin, the ink can have a higher gloss, reduce water evaporation, and speed up drying. The high acidity resin has a high re-solubility in the ink and can improve the wettability of the pigment, but it lowers the wet abrasion resistance. The low acid resin has good alkali resistance and detergent resistance, but the pigment has poor dispersibility and resolubility.
Acrylic resin is used as a binder for water-based inks. The inks have significant advantages in terms of gloss, weatherability, heat resistance, water resistance, chemical resistance, and stain resistance, and are used to directly disperse dissolved or synthetic polymer emulsions. , also has excellent performance. Therefore, at present, most of the foreign countries use acrylic alkali-soluble resin and modified acrylic resin such as maleic anhydride as the ink film-forming resin.
The reason why the polymer is soluble is that the resin contains hydrophilic functional groups (-O-, -COOH, -NH2, -OH), and the carboxyl group on the side chain in the amine neutralizes the water-soluble salt. The salt-forming amination method is a method commonly used for polymer water-based polymerization. A polymer containing a certain amount of acidic functional groups (carboxyl groups, sulfonic acid groups, and acid anhydrides) can be neutralized with an amine when the acid value is 30 to 150. Forms a polymer aqueous system. The properties of water-based blue inks formulated with several water-soluble resins are shown in Table 1, as can be seen from Table 1 and Figure 1:
1 The adhesion of each resin to the PET film was good, while the adhesion on the BOPP film was successively decreased, ie, M04>315+SGY>315>Z604>54 resin solution>315+polyethylene glycol 4000.
2 Considering the adhesion of the ink film and the viscosity of the ink comprehensively, it is better to select the acrylic resin as the linking material of the grinding disperse pigment.
2. The choice of aminating agent
The amount and type of amine have a great influence on the hydration and hydration of the resin, and it is required that the aminating agent be volatile, with good stability and low odor. The higher the degree of hydration, the greater the viscosity of the ink, after the requirements for water solubility and storage stability, there is no need for further hydration to 100%, generally the pH is controlled at 7.5 to 8.5. The results of the comparative tests of the same type of water-soluble acrylic resin aminating agent are shown in Table 2.
Among several amines used for the hydration of resins, ammonia is best used as an aminating agent, but ammonia is easily volatilized, resulting in poor stability of the resin liquid. Considering viscosity and glossiness, dimethylaminoethanol is the most suitable, but considering the combination of cost and performance, dimethylaminoethanol is relatively expensive, and ammonia can be added with a small amount of AMP to make up for the unstable and volatile nature of ammonia. Also improves the color rendering of the ink.
3. Selection of emulsion resin
Emulsion-based resins are the main film-forming resins & the final properties of the ink can be maintained by controlling the rheology of the emulsion. For example, a high Tg (glass transition temperature) emulsion can increase the hardness, gloss, and heat resistance of the ink film and accelerate the drying speed of the ink film. Low Tg emulsions have excellent film formation and can increase the water resistance, grease resistance and flexibility of the ink film, as well as adhesion to non-porous substrates such as polyethylene, polypropylene, polyester film and aluminum foil.
Through the compounding research and orthogonal test of a variety of film-forming resins, the appropriate emulsion resin and ink formulation are determined. The prepared ink is gravure-printed and compounded on a BOPP film. It can be dried by infrared heating or high-frequency heating during printing. The printing speed is 20 to 80 m/min and the peel strength is 2.8 N/cm or more.