Brief Discussion on the Influence of Ink Resin on Ink Performance
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First. Overview
The liquid portion of the ink composition is referred to as a binder; the solid component is a colorant (pigment or dye) and various auxiliaries. The resin for ink is first used as a carrier for the pigment, and solid particles such as powdery pigment are mixed and mixed, and the color material is uniformly dispersed therein, and it is more easily processed and ground to a certain fineness on the grinding machine by virtue of its wetting action. Secondly, as a binder, the pigment is evenly wrapped by the resin and finally can be fixed on the surface of the substrate to achieve the purpose of displaying the pattern; at the same time, relying on its connection, the ink can be transferred and transferred to the base on the printing machine. On the film or paper; finally, on the printed product, the binder also acts as a protective film and exhibits the necessary luster, and even has the effect of protecting the substrate.
It can be seen that the resin for ink is the carrier of the pigment in the ink, which is the core material of the ink. The quality of the ink will directly affect the performance of the ink, because the binder determines the viscosity and viscosity of the ink to a large extent. Dryness, fluidity and other properties. In order to obtain high-quality inks, it is necessary to use high-quality inks for resins.
Second, the effect of resin on ink properties
1, ink adhesion fastness
The adhesion between the ink and the substrate mainly includes the chemical bond force (ie, the force between atoms), the interaction between the molecules (hydrogen bond force and van der Waals force), the interface electrostatic attraction force and the mechanical force. The main source of these forces is the interaction between the resin binder and the substrate. For different substrates, the selection of suitable resin binders has become the key. Generally speaking, for non-polar substrates such as PE and PP, even with corona surface treatment, the surface tension can only reach 38 dyne. A non-polar resin such as a chlorinated polypropylene resin binder should be used; and for a surface polar substrate such as PET or PA, a polyurethane resin binder can be used. Nowadays, the polyurethane ink binder system can solve the problem of adhesion on non-polar substrates by adding a small amount of adhesion promoter for PP and PE, or by using a small amount of chlorinated polypropylene resin in combination with polyurethane resin. It has been able to solve the problem of the versatility of a resin binder, and at the same time solve the problem that the residue of toluene solvent which is prone to occur with chlorinated polypropylene resin as a binder is excessive. In today's green environmental protection, this breakthrough is particularly important.
It can be seen that the resin binder as a dispersing and wetting medium in the ink also provides the most basic and important adhesion fastness between the ink and the substrate, and is one of the most basic indicators of the ink.
2, the tinting strength of the ink
Organic pigments are the most basic materials for coloring inks, but as the inks adhere to the surface of the substrate, the color that is exhibited to the consumer tends to be more or less different from the color of the pigment itself. The reason is attributed to the fact that in the ink, the pigment particles are not present separately but are dispersed in the binder medium. Microscopically, the best wetting and dispersing state of a pigment particle is completely encapsulated in the resin binder and adhered to the surface of the substrate. The color manifestation is that light is incident on the surface of the wrapped pigment through the resin film layer and is transmitted to the consumer's eye by reflection. The transparency of the resin is good or bad, and the size of the color number directly affects the color expression of different color materials. At the same time, the sufficientness of the resin to wet and disperse the pigment directly affects the uniform encapsulation of the resin on the pigment, and also affects the hue of the ink itself.
3, anti-adhesion
Anti-stickiness is an important physical indicator of printing inks. Gravure printing is a printing method with high ink supply, good tone reproducibility, and fast printing speed. Most of the inks used are solvent-type volatile drying inks. After the ink is transferred to the printing substrate through the printing plate, the ink is passed through the drying tunnel, and the organic solvent is quickly evaporated and dried. It is well known that when the film is wound by a high-temperature drying tunnel, the surface temperature of the printing film is generally between 40 ° C and 60 ° C. At the same time, if the anti-adhesion of the ink itself is not good due to the winding pressure, serious winding is caused. Adhesive quality accidents cause irreparable economic losses to ink customers.
The anti-reverse viscosity of the ink is good and poor, and it is directly related to the film formation of the resin binder and the molecular properties of the resin, in addition to the thoroughness after evaporation of the solvent gradient during printing. The resinous binder having good film forming property can impart good dryness to the ink, and after the solvent is volatilized and thoroughly dried, the film formation is thorough, and the anti-blocking property is excellent after winding.
4, resolubility
In gravure printing, ink resolubility is also a key indicator for detecting ink performance. Especially in the color ink printing, the moderate resolubility can not only make the color display sufficient, but also solve the problem of the blocking plate and the overprinting color of the printing plate.
In the process of color ink printing, according to the requirements of the color tone, the depth of the ink cell of the printing plate is different, the amount of ink transferred to the surface of the substrate is also different, the volume of the ink hole is large, and the amount of ink filled in the printing process is large. The thickness of the film layer transferred to the substrate is small; the volume of the ink orifice is small, the amount of ink filled is small, and the film layer transferred to the substrate is thin. Thus, a thick, colorful, and colorful picture is formed on the substrate. In the ink with poor resolubility, the residual ink is not easily re-dissolved by the ink in the ink tank due to the high-speed rotation of the drum in the ink tank, and the ink is more and more shallow, which eventually causes a jamming accident. For re-solubility inks, the printed ink is easily dissolved by the ink solvent in the printing plate during the overprinting process, resulting in ink cross-color problems.
5, storage stability
After the ink is stored for a period of time, the upper part of the container is thin, the viscosity is small, and the color and concentration are relatively poor; the lower part is thick, the viscosity is large, and the color and concentration are relatively good. Gravure printing inks are thin and viscous fluids due to poor dispersion of pigments in the binder; the density of pigments or fillers is too large; precipitation is prone to precipitation in long-term storage. All of these problems can affect the performance of the ink. Even after fully shaking, the state of the ink will not give a bad impression to the customer, and at the same time increase the burden on the worker, without affecting the conditions of use.