text: Water-based ink plastic products, optimistic future prospects!-广东顺德科展环保材料有限公司
  Water-based ink with green environmental protection, non-toxic and harmless advantages, plastic products in the packaging and other fields. The experience accumulated in polymer synthesis and modification and the preparation of water-based ink, the composition of water-based composite ink, the performance requirements and testing analysis of water-based ink and the development trend of water-based ink are good.
  1. Water-based ink joint material
  As the water-based ink "heart" of the linker determines the water-based ink printing performance. From the perspective of polymer materials, water-based ink commonly used water-based resin joint material is water-soluble resin and water-dilute resin.
  The performance parameters of water-soluble resin and water-dilutive resin are shown in table 1. It can be seen that the two have certain complementarity in various properties. Based on the experience of the author preparation of ink, water dilute resin as the main resin, as resin, water soluble resin in the preparation of black ink, for example, water soluble resin content increased from 1% to 5%, water table printing ink after soluble and flow property are improved, and at the same time, the early/dry time increasing, when the water soluble resin content of 5%, dry relative value > 1. Therefore, after comprehensive consideration of the resolubility, drying, water resistance and flow equality properties of ink, the highest addition amount of water-soluble resin was 5%.
  2. Ink pigments
  Pigment is the coloring matter of ink, blue/product/yellow generally use organic pigment, white ink with titanium dioxide, black ink with carbon black. The grinding fineness of pigments is generally controlled within 10 m. The pigments with low fineness can ensure good stability and color spreadability. Organic pigments or inorganic pigments are generally treated with anions or non-ions. The reason is: (1) water surface tension and polarity are larger, color dispersion is more difficult, such as untreated, color distribution is not uniform, not conducive to printing; (2) due to flexo printing water-based ink linker is mostly alkaline, if the pigment molecules containing sulfonic acid/carboxylic acid group reaction with alkaline substances and other groups, will occur condensation reaction, so the pigment generally through anionic or non-ionic treatment.
  3. Ink additives
  Water-based ink according to the different properties, but also need to add additives, such as dispersant, wetting agent, defoaming agent, adhesion promoter. Usually choose non - ionic or anionic additives (ink for anionic). In addition, the cosolvent will also be included in the auxiliary, because although the amount of cosolvent, but for flexographic water-based ink performance has a very important role. The function and screening principle of cosolvent are discussed here.
  The main role of the cosolvent: (1) water soluble resin connection material; (2) adjust ink viscosity; (3) adjust flexo printing water-based ink drying speed.
  Cosolvent selection of 3 rules: (1) the principle of similar polarity, the polarity of similar substances can be dissolved; (2) the principle of solvation, solvation refers to the solvent molecules to solute molecules produced by the interaction, as force is greater than the cohesion of solute molecules, so that solute molecules are separated from each other and dissolved in the solvent; (3) the solubility principle, that is, if the solvent solubility and polymer solubility is close or equal, can make the polymer solution. According to the above three rules for the selection of cosolvent, can effectively improve flexo printing water-based ink viscosity, drying, stability, dispersibility, fluidity and other properties.
  The commonly used waterborne resins are polyacrylic resins or polyurethane resins. According to the above principles, some solvents are selected to improve the solubility and dryness of water ink.
  Plastic table printing ink
  Performance requirements and test analysis of ink
  1. Ink adhesion
  As a result of the film resin polarity is different, both polar polyester PET, nylon PA, PVC, but also non-polar polypropylene PP and polyethylene PE, so the adhesion of water-based ink in various plastic products has become the primary problem.
  Adhesion shall be tested in accordance with GB/T 13217.7-2009 test method for adhesion fastness of liquid inks. Two necessary conditions for good adhesion shall be obtained: close contact (clean surface, wetting and diffusion) with sufficient area, attraction between molecules and even chemical bond formation. In order to meet the above two conditions, under the condition of ensuring good wettability of ink on the substrate, the adhesion is improved by mechanical bonding theory, diffusion theory and adsorption theory.
  2. Ink surface tension
  The proper control of the surface tension of ink will directly affect the printing effect, first of all, the biggest impact is flexographic water-based ink on the substrate leveling, low surface tension of the material is easy to high surface tension of the material surface spread, and high surface tension of the material is not low surface tension of the surface spread; Secondly, flexo printing water ink on the substrate adhesion, flexo printing water ink surface tension is higher, the wetting degree of the substrate is worse, resin and substrate between the bond point is reduced, and then affect the adhesion. In addition, when the surface tension of plastic products is low or the surface tension of ink is high, it will lead to shrinkage and other phenomena of certain printing samples.
  In general, water-based ink in water-based resin joint material surface tension is greater than the surface tension of the printing substrate (water surface tension of 72mN/m). Usually choose a small surface tension solvent to reduce the flexo printing ink system surface tension, such as isopropanol (surface tension of 21.7mN/m), isopropyl acetate (surface tension of 21.2mN/m), etc. (as shown in table 2). In addition, it can also reduce the surface tension by selecting the appropriate additives, such as leveling agent, wetting agent, defoaming agent, etc., can reduce the surface tension of ink.
  Plastic compound ink
  3. Ink viscosity
  Water - based ink viscosity is mainly determined by water - based resin joint material. In order to ensure high speed printing, it is necessary to use high solid and low viscosity water-based resin joint. For water-based resin joint material, many people think that high solid content, low viscosity is difficult to obtain at the same time. After years of research, the author has developed a resin with high solidity (50%) and low viscosity (<250mPa · s), which is suitable for flexographic ink printing of plastic products, and has proved the feasibility of flexographic ink with high solidity and low viscosity.
  4. Ink drying speed
  According to the printing requirements, water-based paper ink in a certain range to meet the "initial dry slow, dry fast" is the best state. In order to solve the flexo printing water-based ink drying problems, in addition to the usual increase in temperature, reduce humidity, increase wind speed and other solutions, mainly from the water-based ink to improve. On the one hand, it is to improve the solid content of ink, that is, the use of high solid low viscosity resin joint material mentioned above, the ink viscosity control in flexo printing required range, as far as possible to increase the solid content of flexo printing ink, reduce the total amount of evaporation water; On the other hand as far as possible to choose a lower boiling point of the true solvent to speed up the drying time.
  5. Ink resolubility
  At present, there is no specific quantitative index for the resolubility, and most of the time it is based on experience to judge the resolubility of ink. The resolubility is too strong, in the process of printing and glue coating is prone to "color bite" phenomenon (that is, the back color will dissolve part of the front color), and then affect the printing quality, composite strength and so on. The resolubility is weak, and the residual ink at the bottom of the mesh hole is difficult to be dissolved again by the ink in the ink tank, so it is easy to block the plate, and the reproduction of the shallow mesh is poor. Therefore, the resolubility of ink is an important factor affecting the quality of composite products. In practical application, can be improved by two methods of resolubility of ink: (2) choose the appropriate water-soluble resin and adjust the proportion. Both aspects are explained above and will not be repeated here.
  6. Water resistance of ink
  Usually choose ammonia or organic amine as pH value regulator. Ammonia volatilization faster, can quickly get water-resistant ink film, but in the process of printing ink may be unstable, and the smell is larger; Organic amine volatilization is slow, the printing process does not need to adjust the pH value frequently, but the boiling point of organic amine is high, they will stay in the ink film for a long time, after the film resistance is poor. Therefore, ammonia and organic amine mixed use, flexo printing ink can improve the overall performance.
  1. Ink high solid low viscosity
  High solid and low viscosity ink can not only shorten the drying time of ink, but also improve the adhesion, fluidity and glossiness of ink. Although high solid content and low viscosity are a pair of contradictions, the balance can be found within a certain range. With the development of waterborne resin synthesis technology, solid content 50% can be achieved.
  2. Ink high color density
  The water-based ink for plastic products, an important aspect is to show the quality of fine image printing, this requires the use of high-line plate to show the pattern rich layers, at the same time match the number of high-line anilox roller, the higher the number of anilox roller line, the lower the ink, will inevitably lead to the printing out of the ink layer is thinner, low color density. Therefore, to improve the flexo ink color concentration, that is, to increase the pigment content. Through the experimental test, flexo ink pigment can be increased to more than 20%, so that the color density of C1.7 ~ 2.0, M1.7 ~ 2.0, Y1.2 ~ 1.5, K1.8 ~ 2.1 (wet film thickness 9 m). The key point is that the future use of flexo ink printing sample density value can meet the requirements, the level of performance is not less than gravure.