The characteristics of metallic inks will be described below from three aspects: optical characteristics, mechanical characteristics and chemical characteristics.
1. Optical properties
(1) Differences from ordinary ink optical properties
Since the optical properties of metallic pigments are different from those of ordinary pigments, the optical properties of the produced metallic inks are also very different from ordinary inks. The color of ordinary ink does not change with the change of viewing angle, but for metallic ink, the change of viewing angle will change the hue and brightness of metallic ink.
(2) Factors affecting the optical properties of metal inks
The shiny effect of metallic ink is the result of the combination of specular reflection and diffuse reflection of metallic pigments. In order to achieve a better metallic effect, the specular reflection of the metallic pigment should be increased and the diffuse reflection reduced. The main factors affecting the optical properties of ink are as follows.
① The larger the particle size of the metallic pigment, the better the specular reflection effect of a single pigment particle, and the higher the metallic gloss of the metallic ink, but its hiding power and dot reproducibility will become worse. The smaller the particle size of the metallic pigment, the better the hiding power and dot reproducibility of the metallic ink, but due to excessive edge diffuse reflection, the metallic gloss of the metallic ink will decrease. Users can choose the appropriate particle size according to their own requirements, but the selection should be combined with the specific printing method. Different printing methods require the use of metal inks with different particle sizes of metallic pigments. Otherwise, the ink cannot be transferred smoothly during the printing process because the particle size is too large, or the printing effect is not good if the particle size is too small.
② The particle size distribution of metallic pigments is also a factor affecting the optical properties of metallic inks. The particle size of the metal ink we usually refer to generally refers to the average particle size D50 of the metal pigment in the ink. For example, for a metal ink of 10 μm, it means that 50% of the pigment particle size is less than 10 μm during detection. In fact, this indicator is not very accurate. It can clearly explain the performance of metal ink.
Many users will find that when you use metallic inks from different manufacturers, although the particle sizes shown in their technical data are the same, the hiding power and metallic gloss of metallic inks after printing sometimes vary greatly. This is because The particle size distribution of metallic pigments in metallic inks from different manufacturers varies from wide to narrow. The same average particle size, the narrower the particle size distribution, the more orderly the overall arrangement of the pigments, the better the gloss and hiding power of the produced metallic ink, therefore, analyzing the particle size distribution is important for the characterization and quality control of metallic pigments It is very important, and it is also an important reflection of the technical level of different metallic pigment manufacturers.
③The shape of metallic pigment particles in traditional metallic inks is irregular, called cornflakes (corn grains, see Figure 1). Since the shape of each metallic pigment particle is irregular and the edges are not smooth, the specular reflection effect of the particles is poor , The diffuse reflection at the edge is serious, so the metallic luster and hiding power of the metallic ink are correspondingly poor. Aika has produced a new type of silverdollars (silver dollar type, see Figure 2) metallic pigments using a new condensation and grinding technology. Each particle of this metal pigment is approximately circular in structure, uniform in size, and has good specular reflection effect. The ink produced with it has very good metallic effect and hiding power. Therefore, this new type of metallic pigment has been widely used as soon as it was introduced.
2. Mechanical properties
Since the metal raw materials used to produce metal inks are relatively soft and thin metal sheets, they are very sensitive to shear force. Excessive shear force will cause the metal pigment particles to deform or form many fine particles, which will make the final product optical Performance drops, Figure 3 shows the effect of shear force on metallic pigment particles. So use some smoother materials to stir, and avoid high-speed stirring. It should be emphasized that many printing factories are used to stirring ink with metal tools with relatively hard edges, which is very undesirable.
3. chemical properties
Since the substances used to make metal inks are active metal materials, the chemical properties of metal inks are also very unstable. When using and storing, they should be strictly sealed to avoid absorbing too much water and direct light for a long time. Recycled metal inks are also not suitable for storage for too long.
Advantages of Metallic Inks
In order to achieve a good metallic luster, the content of metallic pigments in metallic inks is generally 2 to 4 times that of ordinary inks, so the price of metallic inks is higher than that of ordinary inks. Nevertheless, metal ink printing is still welcomed by the packaging and printing industry because of its unique expressiveness that can enhance product competitiveness and attract more consumers' attention. Compared with processes such as hot stamping and aluminized film printing, which can also achieve metallic effects, metallic ink printing has many advantages.
(1) It is easy to apply, does not need to modify equipment, and does not require more investment.
(2) It can be printed like ordinary ink, which improves production efficiency.
(3) Cost saving.
Also note:
(1) Due to the high density of metallic pigments, compared with ordinary inks, the pigment particles of metallic inks are very easy to precipitate, and must be fully stirred before use. Before printing on the machine, check whether there is sediment at the bottom of the ink tank. Even, the hue and gloss of the printed matter are quite different.
(2) During the printing process, as the solvent continues to volatilize, the viscosity of the metal ink will gradually increase. In order to ensure the stability and good fluidity and transferability of the metal ink, it is necessary to measure the viscosity of the ink regularly and add solvent appropriately to make the ink Viscosity remains within a stable range.
(3) Many printing factories often achieve colored metallic effects by adding color paste or toner to metallic inks. NBCHAO reminds you: due to the particularity of metallic pigments, some colorants or toners may thicken the ink or change its performance, so you must do a test before use. Generally, metal ink manufacturers have their own colorants for customers to choose. .
(4) Metallic inks are easy to generate gas, especially silver inks. During transportation or storage, a lot of gas may have accumulated in the ink barrels, so special care should be taken when opening the packaging barrels to avoid injury due to the popping of the lids when the ink barrels are opened vigorously. people.
(5) Since the price of metal ink is much higher than that of ordinary ink, the glossiness of the recycled metal ink will decrease significantly. Therefore, under the premise of satisfying continuous operation, metal ink should be added as little as possible during the printing process. Special ink tanks can be remade when needed.
Conclusion Ito Ink Coating Chemical Technology Co., Ltd. provides comprehensive technical guidance, high-quality and precise products to the world.
As a new type of printing ink, metallic ink expands the creative space of packaging designers and opens up new ideas for the packaging industry. It is applied in cigarette packs, wine labels, industrial packaging, daily chemical product labels, flexible packaging, etc. very broad. But we also need to see that there are still many imperfections in metallic inks, especially the quality of mirror silver ink series products is not very stable. In addition, many users do not understand the performance of metallic inks, and the production process is not properly controlled, which also compromises the printing effect of metallic inks.
