Ink is the most important material in screen printing. It occupies an extremely important position in the entire printing process because the objects of screen printing are quite extensive. The substrates include paper, wood, metal, plastic, glass, ceramics, and textiles. Therefore, the correct understanding of the ink's performance is an indispensable prerequisite for smooth screen printing.
The screen printing ink is made up of pigments, binders, fillers and auxiliary materials according to the suitability requirements of the screen printing process and the printing substrates, so that the pigments and the like are uniformly dispersed in the binder composed of the macromolecular compound and formed. A stable, suspended colloidal material. Whether the screen printing ink is in a stable state depends to a certain extent on the dispersion of the pigment and the viscosity of the binder, and more importantly, it depends on whether the pigment particles are surrounded by the surface active material in the binder. .
The role of pigments in inks is to impart color to the ink and determine the concentration of the ink according to the amount; to give the ink a certain thickness and other physical properties; to maximize the durability of the ink; in a certain degree To a certain extent, the ink dryness is affected, and the oxidative conjunctiva drying is the most significant.
The printing material for screen printing ink is a kind of fluid medium with a certain viscosity which acts as a dispersing pigment in the ink. Its role in the ink is to give the ink a certain viscosity, viscosity, flow properties, thixotropy; Drying type and drying speed of ink; determining ink glossiness, abrasion resistance, firmness, etc.
One of the most prominent problems in screen printing is the fastness of the ink on the substrate after printing. If there is not a good adhesion fastness, it means no printing, and it will also cause great waste. The problem of fastness involves many factors such as the adhesion mechanism of inks and substrates, the formulation of ink components, and the quality of chemical raw materials. There are several factors that affect the adhesion fastness of screen printing inks.
First, the effect of resin in screen printing ink
Various resins constitute an important component of the screen printing ink connection material, and the adhesion fastness of the ink is good and bad, and how the effect is closely related to the performance of the resin.
Resins are divided into natural resins and synthetic resins, which are polymers or condensates of some organic compounds. Natural resins include rosin, peach gum, and gum arabic, and are amorphous or crystalline structures. The characteristics of the resin are gradual softening upon heating and the formation of a viscous, stable melt. Another distinctive feature is the ability to dissolve or melt in organic solvents. The commonly used resins in the ink binders are phenolic resins, alkyd resins, maleic anhydride resins, polyamide resins, and the like, and their effects are:
1 to improve the glossiness of the blot, the yellowing is not easy after the conjunctiva, and the lightfastness is better;
2 enhance the imprinted fastness, fluidity, thixotropy, such as alkyd resin ink fixed faster on the paper, after drying is better;
3 The vegetable oil modified alkyd resin is a good wetting agent, adding more pigments to the ink containing alkyd resin, and the viscosity does not change much, and the fluidity is good;
4 After the resin is added into the ink connecting material, the ink layer has strong adhesion, soft quality, good drying performance, bright conjunctiva, and good printing performance.
Resin composition: The functional groups and the branched structure of the resin molecules directly affect the adhesion of the ink on the substrate. Therefore, screen printing inks are more and more specific to different substrates, and a single resin can not satisfy the special screen printing. The need for ink. In fact, the use of two-way or three-way copolymer resins, mixed resins, or modification of resins can produce inks with excellent textures, and the selection of suitable resin components is very favorable to the ink's firmness.
The molecular weight of the resin: If the molecular weight of the resin is too close to the molecular weight of the substrate, the ink solvent is not easily selectable. The molecular weight of the resin is too large. In order for the ink to reach the viscosity required for screen printing, the content of the solid resin in the ink is too small, resulting in waste of the solvent. On the other hand, if the molecular weight of the resin is too small, the cohesive force and compatibility are too poor, and the adhesion effect will be poor. Therefore, it is very important to choose the appropriate molecular weight resin and it must be adapted accordingly.
Glass transition temperature: The polymer segment movement only has a significant diffusion rate above the glass transition temperature. The whole chain movement can only be carried out at a higher temperature, and the glass transition temperature of the resin for the room-temperature curing ink should be very low, which is obviously advantageous for the attachment effect. For heat-curing inks, the heating temperature should be higher than the glass transition temperature and lower than the thermal deformation temperature of the substrate. Therefore, the ink adhesion effect is related to the glass transition temperature.
Elemental content of the resin monomer: The change in the content of a certain element of the synthetic resin monomer also changes the performance of the resin. When designing an ink process recipe, the synthesis of some special resins will greatly improve the performance of the ink. Changes in the content of a certain element of the resin monomer will lead to a prominent change in a certain characteristic of the resin.
Source: Dongguan Printing Network
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