In the packaging and printing industry, screen printing ink should meet the requirements of storage, printing, durability, economy and safety, but in terms of technical performance, it is mainly printability and application applicability.Performance Introduction Of Screen Ink Printability
Printability is also called operating characteristics. Generally speaking, the ink should be able to leak smoothly from the printing plate to the substrate without blocking the silk screen, dry quickly on the substrate, and have good embossing reproducibility. The influencing factors of Printability are very complex, with about 60 variables. Here are some main attributes.Performance Introduction Of Screen Ink Printability.
One of the characteristics of ink is that it hinders its relative flow viscosity. The unit is Pascal second (PA · s). The viscosity of screen printing ink is in the middle or high among various inks. The viscosity has a great impact on the printing effect. If the viscosity is too large, it will make it difficult for the ink to transfer and affect the integrity of the ink. Performance Introduction Of Screen Ink Printability.
The adhesion and gloss of embossing will become poor, and even there will be wire drawing, lack of ink at the screen opening Mesh blockage and other problems; If the viscosity is too small, the embossing will expand, the definition is poor, and the printing plate and printed matter are easy to get dirty.Performance Introduction Of Screen Ink Printability.
Generally speaking, the preparation viscosity of ink is greater than 4pa · s. The use viscosity needs to be properly adjusted according to the mesh number, graphic size, printing speed, substrate performance and printing temperature, and is allowed to change in the range of 1-100pa · s
The viscosity of some screen printing inks may change during the printing process. For example, the volatilization of solvent will thicken the ink and increase the viscosity. The viscosity of some inks varies with shear speed. There are three cases, such as adhesive and liquid ink with low viscosity (less than 10Pa · s), whose viscosity is constant and is not affected by shear speed; Performance Introduction Of Screen Ink Printability
The viscosity of pseudoplastic fluid decreases with the increase of shear rate, also known as shear thinning fluid, such as cellulose solution, emulsion and most screen printing inks. This kind of ink has good leveling, that is, the viscosity increases with the increase of shear rate, also known as shear thickener. Some inks with high solid content (pigments and fillers) are prone to shear expansion. The viscosity of some inks decreases with the increase of shear speed or shear time or both. This phenomenon is called thixotropy.Performance Introduction Of Screen Ink Printability
The relationship between viscosity change and printability is that the more stable the viscosity of the ink on the printing plate, the better. However, after being transferred to the print, the greater the viscosity and the faster the thixotropy, the better. It is unfavorable to the former and beneficial to the latter. Therefore, appropriate thixotropy is desirable, and shear thickening is harmful to printing.Performance Introduction Of Screen Ink Printability
Viscosity adjustment and shearing, adding solvent, diluent or plasticizer can reduce viscosity, and adding filler, pigment, silicide and viscous transparent substrate can improve viscosity.Performance Introduction Of Screen Ink Printability
The minimum shear stress required to start the ink flow is called yield value. The yield value is too large, the ink is hard and difficult to open, the ink conveying is inconvenient, and the leveling is poor; The yield value is too small, and the reproducibility of printing fine line or dot is poor. The ink layer of screen printing is thick, so the yield value cannot be too small, usually between 10-2-10-3n / cm2. When printing thin lines, the yield value should be high.Performance Introduction Of Screen Ink Printability.Performance Introduction Of Screen Ink Printability
In lithographic printing, the concept of fluidity is usually used to describe the flow development of ink. It means that when the parallel plate is pressurized, a certain amount of ink diameter is measured within the specified time as the fluidity value of screen printing. The concept of fluidity is more convenient. Performan.ce Introduction Of Screen Ink Printability
Fluidity is the result of the comprehensive reaction of ink viscosity, yield value and thixotropy, indicating that there is no external force on the fluidity of ink, the fluidity of screen printing ink is too large, and the transfer of ink is difficult to control, There will be self leakage (refers to the ink on the screen, which will leak without pressure).
reply (refers to the ink on the screen overflowing to the printing surface – the back of the printing plate), and the ink fluidity along the scraping direction is too small, the fine line printing is difficult, the embossing gloss is poor, and even the silk screen is short of ink. The appropriate fluidity should be: the ink will not leak on the screen due to its own weight, The screen knots should not be exposed on the embossed surface.Performance Introduction Of Screen Ink Printability
The empirical judgment method of fluidity is to pick up the ink with an ink mixing knife and let it flow downward. If the ink wire is long, the fluidity is good, otherwise the fluidity is poor.Performance Introduction Of Screen Ink Printability