Abstract: This paper tests the performance of screen printing inks and other printing inks. The results show that the screen printing inks have higher viscosity, ink thickness, and higher ink transfer rate than other inks.
Keywords: screen printing ink/ink performance/ink thickness
Stencil printing and letterpress printing, gravure printing, and lithographic printing are called four major printing techniques. Screen printing is a major printing method in stencil printing. Printing methods that are similar to screen printing include stencil printing, typing wax printing, stencil printing, and spray printing. Screen printing is an ancient printing method, also known as silk lacquer printing, silk leakage printing, affixing printing. Flat, convex, concave three kinds of printing methods are to transfer the ink to the surface of the substrate, to achieve the reproduction of the graphic; and screen printing is to pass the ink through the screen of the plate, so that the ink leaks to the substrate Printing on the surface. Therefore, there are more and more kinds of inks available for screen printing, and substrates are not limited to paper, and metal, plastic, wood, etc. can be screen-printed. With the continuous expansion of screen printing inks and their applications, it is important to study the properties of screen printing inks. This article is a method that uses screen printing inks and other inks for printing experiments and compares ink performances, and specifically analyzes the characteristics of screen printing inks.
theoretical analysis
According to Newton's law of viscosity, we know formula 1
τ=ηD 1
among them:
Ï„ - shear stress applied to the ink;
η - constant independent of shear rate, known as the viscosity coefficient;
D—Rheological rate gradient, D=dv/dr.
When the fluid is subjected to an external force, it does not immediately begin to flow and must begin to flow after the applied external force reaches a certain level. Such a fluid is defined as a plastic fluid whose mathematical expression is Formula 2:
τ=τ0+ηD 2
Τ0 is the minimum shear stress value that the external force must overcome in order to overcome the internal molecular structure of the fluid and make the fluid flow.
Screen transfer ink transfer process is through the mesh under the action of the external force to reach the surface of the substrate, ink (fluid) through the mesh to meet the formula 3.
Q=πr4Δp/8ηl 3
among them:
Q—ink transfer volume;
Δp - pressure difference between the two sides of the screen, in fact, squeegee pressure;
R—screen aperture;
l - screen thickness;
η - screen ink viscosity.
From Equation 3, it can be seen that the screen transfer ink amount is inversely proportional to the viscosity of the ink and inversely proportional to the thickness of the screen. The thickness of the screen is generally not changed after plate making, and this article takes it as a constant value. Therefore, the key factor affecting the ink transfer amount is the viscosity of the ink.
Due to different colors of screen printing inks, the proportions of color materials and linking materials are not the same, so the viscosity is naturally different; while the amount of ink is proportional to the pressure, so the pressure when the viscosity is large should also be correspondingly large; and the size of the pressure The angle between the squeegee and the screen is directly related.
The experimental screens used Japanese-made 350 mesh nylon and stainless steel mesh.
The screen printing inks used were 45 yellow, 14 magenta, 58 cyan, and 85 black inks produced by Sumiyoshi Ink Co., Ltd., and SS1-000 series yellow, magenta, cyan, black ink, and BASF manufactured by Toyo Ink Manufacturing Co., Ltd., Japan. SS8000 series screen printing ink. Other printing inks are domestic inks.
The measuring instruments were Macbeth TR524 reflective densitometer, NXS-11 rotary viscometer, and SPM100 spectrophotometer.
Experimental substrates include newsprint, letterpress, offset and coated paper.
The biggest feature of screen printing is the thick printing ink layer and high ink transfer rate. Moreover, its viscosity range is wider, and the viscosity of the ink can be determined according to the printing material, so that a high ink transfer rate can be achieved and a sufficient ink layer thickness can be obtained. By controlling the amount of ink transferred, the concentration range of the color can be increased, and a rich print can be reproduced. Screen printing inks have good drying adaptability, so screen printing can be applied to various substrates of different texture materials, can exhibit a certain three-dimensional effect, and the picture quality is obviously improved. However, due to the short silk screen printing ink and the limitations of the screen itself, screen printing cannot print very fine print products.
in conclusion
Compared with other printing methods, screen printing has the following features:
Screen printing inks have a wide range of viscosities, and the viscosity of the ink can be determined according to the printing substrate material, a high ink transfer rate can be achieved, and a sufficient ink layer thickness can be obtained. Large amount of ink transfer, strong hiding power, colorful print, rich texture.
Compared with other printing methods, the screen printing has the characteristics of simple plate making and printing, and the required equipment and operating costs are less; the layout is flexible, the surface requirements of the printing materials are low, and almost all surfaces can be used silk Web printing, get beautiful printing effect. Therefore, other printing methods (press, gravure, lithographic), printing materials that are difficult to print, and various industrial products can be surface-printed by screen printing.
Reprinted from: Guangdong Printing Network