Technical defects and remedies for printing inks (3)
When the process of packaging and varnish coating of inks is performed on a vertical surface, the ink or coating oil tends to flow down due to the force of gravity during film formation (A. When the ink or oil contacts the substrate Spreading; B. When a certain amount of gravities is reached at the last minute; C. Exposure to substrates is gradually spread.) This flow is maintained after film formation, resulting in uneven surface flow (spreading), uneven film thickness across the top and bottom, and increased bottom edge. In the above three situations, we hope to see the status of C. Because from the observed fluidity, the spreading task was completed within the prescribed time, but A often produces water marks, and B often produces cracks. In this way, according to the shape of the above-mentioned flow marks, we can be divided into the following types: (1) Sagging: The ink and coating oil cannot flow upward (front) and gradually thicken. Or stay on the bottom edge, after drying and curing are often retained as they are; (2) Flowing: When ink or varnish is mechanically printed on the surface of the substrate, large areas hang, often called water lines; (3) flow drop : This is the B condition mentioned in this article, that is, the local sagging occurs during printing, painting, or temperature-increasing drying to form waves (water lines), semicircles (stripes), or stripe-like secondary waste products.
In essence, ink or varnish sag is associated with the fluidity or rheological characteristics of the ink or varnish during printing and coating. Sometimes it is related to the processing of the substrate. If the pressure on the poorly adhered surface is printed or applied, the sagging condition is likely to occur. When we adjusted the rheological properties of packaging printing inks or coating oils, it greatly promoted the low viscosity of inks or coating oils at high shearing speeds, which in turn favored the inks or coating oils. Leveling. At the same time, we have high viscosity at low shear rate (ink or varnish film) to prevent sagging, which is a very difficult task. Most manufacturers use suitable low viscosity, high content resin binders, The inks or varnish made from pigments, fillers, and additives with a moderate pH have thixotropy for general printing. It pursues the unifying purpose of preventing conflicts between sag and leveling.
The viscosity of packaging printing inks and coating oils has a great relationship with the solvent volatilization rate and volatilization gradient in the printing and coating processes. The solvent evaporates quickly and the ink has a faster viscosity. This helps prevent sagging, but it is not easy to level out. The drying and curing speed of thermosetting or light-curing packaging printing inks or coating oils is directly related to viscosity changes. Slow response, low viscosity, and easy sagging are tasks that we should take seriously.
We know that temperature and light intensity have a great influence on viscosity. In packaging printing inks or varnish systems that are volatile, dry, osmotic, photocurable, and thermosetting, the viscosity of the wet film of the amino ink is high-temperature baking. The phenomenon of sagging caused by falling is one of the most troublesome headaches. Printing is usually solved using "wet-to-wet" printing.
This is what we often say that Newtonian fluids flow under gravity in the vertical plane. If the viscosity of the ink film or film is not taken into account, the speed of the outflow (spreading) of the packaged printing ink or coating and the spreading of ink or ink from the ink, or the density of the ink or varnish, and the gravitational acceleration The viscosity of the ink and the varnish film is related to the thickness of the film.
In fact, the viscosity of packaging printing inks or coating oils is a non-Newtonian fluid in the process of equilibrating proton acceptors (acids) and electron donors (bases) and film formation and drying processes. As can be seen from the above two forms, it is not suitable for applying inks or coating oils. However, it can be seen that it is proportional to the square of the film thickness n and the third power of D and n. Therefore, in order to prevent sagging, it is crucial to strictly control the thickness of the ink film or film.
On the other hand, the yield value of the ink or varnish can be increased to increase the sag limit, which is a direct relationship between them. There are also new technologies such as â€œwet-to-wetâ€ printing or ultra-high-speed cup-type electrostatic printers.
Sagging and leveling is one of the most common failures in the development of ink packaging printing and gloss coating development. The development of inks to meet the printing operation, Varnish coating requires a certain thixotropic ink or coating oil is the basis for the prevention of sag.
First, it is an effective way to select the appropriate components of anti-sagging additives and leveling agents for different inks and varnish. If the two are harmonized together, additives are the direction of development. If ink is added to the VIII-2OOS solvent ink, add VIII-2 7 coupling agent to increase the viscosity and improve the gloss. Gel and gelled ink can immediately flow when added to TH-3 to prevent stack printing. Ink. Second, the correct choice of solvents and thinners controls the viscosity of the ink or coating and changes in viscosity during the drying process. Thirdly, it is also possible to use the above-mentioned methods for the presence of light thermosetting inks or varnish, photocurable UV inks or varnish. Ink film, film reprint, recoating or pre-polished. Fourth, packaging and printing or coating and finishing, strict ink film, oil film thickness management, operator skills assessment when printing glazing, print quality control of various substrates, and air pressure, printing speed , Drying time, blowing angle, overprint spacing, etc. should be mastered. Fifth, strictly control the environmental management in the printing and finishing process, including time, temperature, humidity, ventilation, and ventilation control.
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