In order to obtain consistent high quality of printed products and reduce waste, it is a good way to control the ink color density, which often does not attract people's attention. Nowadays most people like the old traditional control method-often measuring the viscosity of ink (measured by the well-known flow cup). In fact, ink viscosity measurement is not a standard, and there are still problems. Whether it is solvent ink or water-based ink, varnish or paint, will be affected by many variables, and these variables will make the viscosity measurement inconsistent. The variable factors that affect the viscosity control when using a flow cup to measure viscosity are: temperature changes, changes in fluidity measurement technology and sensitivity, changes in flow cup conditions, changes in operators, changes in the amount of newly added solvent or dilution, and in New inks with different temperatures and different viscosities are added during the production process. Although there are many types of flow cups on the market, some of which are better or more accurate, but because of the many variables mentioned above, it is difficult to obtain satisfactory results if the viscosity of the ink is continuously measured with the flow cup on the printing machine. Influencing the viscosity is an internal resistance to the flow of liquid. We try to achieve the consistency and balance of colors in the printing process by measuring the viscosity of the ink.
If the viscosity of the ink changes, it will affect the following aspects: 1, the drying time of the ink 2, the intensity and consistency of the color; 3. The retention and coverage thickness of the print; 4. The transfer ability of the ink; 5. The ink and solvent Consumption; 6. Waste of materials; 7. Production speed As the ink flows through the pumping system, it undergoes many changes. In fact, in addition to being limited by the additives and fluidity of the ink, the viscosity of the ink is also affected by the drying device, ink pump, ink roller friction, temperature and evaporation in the plant. But the main influence often comes from temperature changes. The ideal viscosity of the ink varies depending on the type of printing and the type of printing machine, but it must have a stable ink concentration to maintain a uniform color density, to reduce waste and increase production. Please note that maintaining the same viscosity at different temperatures will cause changes in color density. This approach is extremely inappropriate! Factors that affect viscosity are included in the measurement. If human factors are also taken into account, then the possibility of error increases. For example, if the No. 2 Zahn cup is used to measure the viscosity within three shifts, the error is ± 2 seconds. This is equivalent to a ± 10% change in the 20-second measurement, which directly results in a defective print. In the late 1970s, Dr. K Schlacpfer mentioned in his UGRA report that a 1 degree Celsius temperature fluctuation is approximately equal to a 3% viscosity change. This means that the temperature at startup is 70 degrees Fahrenheit. After about three quarters of an hour, the temperature rises to 79-90 ° Fahrenheit. An increase in temperature of 9-10 ° will change the viscosity of the solvent ink by 15%. The viscosity of the ink changes by 5-7%.
This change was confirmed by William Chorvat of Sun Chemical at the Louisville GTA workshop in 1986. He said that a 10 degree Fahrenheit temperature fluctuation caused a 15% viscosity change, and this change in viscosity would cost you more. At the GRI meeting, Mr. Paul Stefko of Flint Ink Company pointed out in his report entitled "The Effect of Temperature on the Viscosity of Inks", "What we often forget is that viscosity is also extremely sensitive to changes in liquid temperature, And the heat generated by the friction of the printing machinery will also greatly increase the ink temperature. In the above figure, we can see that the ink temperature change affects the results of viscosity and color density. Therefore, we must use a concentration control device to maintain the ink constantly The color density. Because we have seen that using a flow cup or ordinary viscometer to control the viscosity without some temperature compensation is incorrect and not feasible. It is not enough to measure the viscosity without considering the temperature. Therefore, we must rely on And use our technology to achieve the purpose of precise control of color density. In order to achieve complete viscosity adjustment, temperature fluctuations must be continuously monitored by a system. This system will convert temperature fluctuations into viscosity adjustments. The color depth control device checks and adjusts the density of the ink while taking into account changes in the ink temperature This can ensure the correct balance of ink components. The color density control device keeps the color depth constant at a correct value.
However, there is currently a debate about temperature control. If you consider all the piping systems and energy losses on each ink tank, the cost of this control method is obviously not cheap, and it is not very practical for the packaging and printing industry. At the Corrugated Paperboard Printing Exhibition held in Paris in June 1994, viscosity control and color depth control were also regarded as one of the most important factors related to the production of high-quality prints. Other factors were also considered, such as:
â— Before printing, use anti-static roll paper vacuum suction system to clean roll paper or sheet paper.
â— In addition to color density control, pH value must be controlled.
â— Preparation of ink in the ink workshop, through the effective use of time, labor and materials, can greatly save costs. In flexographic printing and gravure printing, the ink color density control device can be effectively used for solvent inks, water-based inks, varnishes and wax grams. Using the ink concentration automatic control device can save a lot of time, labor and materials, because the increase of one second time or temperature change with the flow cup measurement will increase the loss of ink pigment. If the automatic viscosity control device is used with temperature compensation or temperature control devices, it can reduce the consumption of ink, solvents and other materials, while maintaining stable product quality. Which kind of automatic control device should we use to consider the following factors: [next]
◠Monitor the temperature change and adjust the viscosity accordingly. In this way, the viscosity control device becomes the color depth control device. The control device can be a combination of ink cooler / heater in order to maintain the same temperature precisely, especially under very hot environment (such as above 95 ° F)
â— Can accurately measure the viscosity;
â— The operation has nothing to do with the amount of ink on the ink fountain;
â— Use a sealed circuit to prevent solvent evaporation;
â— Ink can be changed quickly and conveniently on the printing unit;
â— No ink accumulates on the control device;
â— Safe operating environment;
â— Requires little to no maintenance;
â— The device itself will be cleaned automatically at the end of printing;
â— Easy to operate, not easy to malfunction;
â— Can be used with pH control device. At present, there are more advanced systems on the market that are controlled by electronic computers, which can not only control the color density of the ink, but also control the PH value (for water-based inks), and at the same time provide ink on the screen or printing paper. Subtle changes and the system's various steps to maintain ink color density at optimal levels. Using automatic ink color density control and temperature compensated viscosity control, you can obtain consistent print quality, save ink, reduce waste, save time and improve production. Therefore, in order to achieve the above purpose, the printing factory should implement ink color density control. The best way is to install an appropriate automatic ink color density control system, or a viscosity control device combined with an ink temperature adjustment system.
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