Key points for controlling the concentration of th

Key points of ink concentration control

in order to obtain consistent high quality of prints and reduce waste, controlling ink color concentration is a good method, which often does not attract people's attention. Nowadays, most people are happy with the old traditional control method - often measuring the viscosity of ink (with the help of the well-known flow cup measurement). In fact, the measurement of ink viscosity is not a standard, and there are still problems. Whether solvent inks or water-based inks, varnishes or coatings, will be affected by many variable factors, which will make the viscosity measurement inconsistent. When using the flow cup to measure viscosity, the variable factors that affect viscosity control 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 dose, and the addition of new inks with different temperatures and viscosities in the production process. Although there are many kinds of flow cups on the market, some of which are better or more accurate, due to the existence of many variable factors mentioned above, If the ink viscosity is continuously measured with a flow cup on the printer "It is difficult to achieve satisfactory results. The influence of viscosity on ink viscosity is an internal resistance to the flow of liquid. We try to achieve the consistency and balance of color in the printing process by measuring the viscosity of ink. If the viscosity of ink changes, it will affect the following aspects: 1. The drying time of ink. Malaysia fully supports and is willing to seize the opportunity. 2. The strength and consistency of color; 3. The maintenance and coverage thickness of imprint; 4. The thickness of ink Transfer capability; 5. Consumption of ink and solvent; 6. Waste of materials; 7. Production speed when 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, etc. But the main influence often comes from the change of temperature. The ideal viscosity of ink depends on the type of printing piece and the type of printing machine, but there must be a stable ink concentration to maintain a uniform color density, reduce waste and improve output. Please note that maintaining the same viscosity at different temperatures will cause changes in color concentration. This is extremely inappropriate! If human factors are also taken into account in the measurement of factors affecting viscosity, the possibility of error will be increased. For example, if Zahn 2 such as PC shaped product annealing cup is used to measure the viscosity in the third shift, the error is ± 2 seconds. This is equivalent to a change of ± 10% in the measurement of 20 seconds, which directly leads to the generation of unqualified prints. In the late 1970s, Dr. K schlacpfer mentioned in his UGRA report that a temperature fluctuation of 1 ° C was approximately equal to a 3% viscosity change. This means that when the machine is turned on, the temperature is 70 degrees Fahrenheit. After about three quarters of an hour, the temperature rises to degrees Fahrenheit. An increase in the temperature of degrees will change the viscosity of solvent ink by 15% and the viscosity of water-based ink by%. This change was confirmed by William chorvat of Sun Chemical Company at the Louisville GTA printing workshop seminar in 1986. He said that the temperature fluctuation of 10 degrees Fahrenheit causes a 15% viscosity change, which will cost you more. At the GRI meeting, Paul stanfko of flint ink company pointed out in his report entitled "the effect of temperature on ink viscosity", "We often forget that viscosity is also very sensitive to the change of liquid temperature, and the heat generated by the friction of printing machinery will also greatly increase the ink temperature. In the above figure, we can see that the change of ink temperature affects the result of viscosity and color concentration. Therefore, we need to use a concentration control device to constantly maintain the color concentration of ink. Because we have seen the use of flow cups or ordinary viscometers to control Viscosity without some temperature compensation is incorrect and infeasible. It is not enough to measure viscosity without considering temperature. Therefore, we must rely on and use our technology to accurately control the color concentration. Color concentration control in order to completely adjust viscosity, temperature fluctuations must be continuously monitored by a system. This system converts temperature fluctuations into viscosity regulation. Using the force value of color depth control and displacement control device to check and adjust the ink concentration, while considering the change of 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. But at present, people also argue about temperature control. If you consider all the piping systems and energy losses on each ink reservoir, 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 board printing exhibition held in Paris in June, 1994, people also regarded viscosity control and color depth control as one of the most important factors related to the production of high-quality prints. At the same time, other factors were also considered to ensure the normal operation of the experiment, such as:

● before printing, use the anti-static web vacuum suction system to clean the web or sheet

● in addition to the color concentration control, the pH value should also be controlled

● preparing ink in the ink workshop can greatly save costs by effectively using time, labor and materials. In flexographic printing and gravure printing, the ink color concentration control device can be effectively used for solvent inks, water-based inks, varnishes and waxes. Using the automatic ink concentration control device can save a lot of time, labor and materials, because the loss of ink and pigment will be increased by adding one second of time or temperature change to the measurement with the flow cup. If the automatic viscosity control device is used together with temperature compensation or temperature control device, the consumption of ink, solvent and other materials can be reduced, while maintaining the stability of product quality. We should consider which kind of automatic control device to use in combination with the following factors:

● monitor the temperature change and adjust the viscosity accordingly. In this way, in fact, the viscosity control device becomes the color depth control device. The control device can be a combination of ink cooler/heater to accurately maintain the same temperature, especially in a very hot environment (such as above 95 ° f)

● viscosity can be accurately measured

● it has nothing to do with the amount of ink on the ink bucket during operation

● use a sealed circuit to prevent solvent evaporation

● ink can be exchanged quickly and conveniently on the printing unit

● no ink accumulation on the control device

● safe operating environment

● requires little or no maintenance

● the device itself will be automatically cleaned at the end of printing

● easy to operate and not prone to failure

● can be used with pH control device. At present, there are more advanced systems on the market that are controlled by computers, which can not only control the color concentration of ink, but also control the pH value (for water-based ink). At the same time, they can provide subtle changes of ink on the screen or print paper, as well as all steps of the system to maintain the color concentration of ink at the best level. Using automatic ink color concentration control and viscosity control with temperature compensation, we 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 the control of ink color concentration. The best way is to install an appropriate automatic ink color concentration control system, or a viscosity control device combined with the ink temperature regulation system

translated from flexo 1994.2