Ink concentration control points (1)

In order to obtain consistent high quality and reduce waste of printed products, it is a good idea to control the ink color density, which often does not attract people's attention. Most people today rejoice on old, traditional methods of control—often measuring the viscosity of the ink (by means of the well-known flow cup measurement). In fact, ink viscosity measurement is not a standard and there are still problems. Whether it is solvent inks or water-based inks, coating oils or paints are affected by many variables that make the viscosity measurement inconsistent. The use of flow cups to measure viscosity, variable factors affecting viscosity control are: temperature changes, changes in flow measurement techniques and sensitivities, changes in flow cup conditions, changes in operator, changes in the amount of new solvent or diluent, and In the production process, new inks with different temperatures and different viscosities are added. Although there are many types of flow cups on the market, some are better or more accurate, but because of the many variables mentioned above, it is difficult to obtain satisfactory results if the ink viscosity is continuously measured on a printer using a flow cup. Viscosity vs. Ink Influencing the viscosity is an internal resistance to the flow of liquid. We managed to achieve the consistency and balance of color during the printing process by measuring the viscosity of the ink.

If the ink viscosity changes, it will affect the following aspects: 1, the ink drying time 2, the strength and consistency of the color; 3. The retention of the imprinting and coverage thickness; 4. The ink transfer ability; 5. The ink and solvent Consumption; 6. Waste of material; 7. Production speed When the ink flows through the pumping system, it undergoes many changes. In fact, in addition to the restrictions imposed by ink additions and fluidity, the viscosity of the ink is also affected by the drying device, ink pump, ink roller friction, temperature and evaporation inside the building, and the like. But the main influence often comes from changes in temperature. The ideal viscosity of the ink varies depending on the type of print and the type of press, but there must be a stable ink concentration to maintain a uniform color density in order to reduce waste and increase throughput. Please note that maintaining the same viscosity at different temperatures will cause a change in the color concentration. This is extremely inappropriate! Factors that affect viscosity In the measurement, human factors are also taken into account, then increase the possibility of error. For example, if the viscosity is measured using a Zahn cup No. 2 in three shifts, the error is ±2 seconds. This corresponds to a ±10% change in the 20-second measurement, which directly results in the generation of a defective print. In the late 1970s, Dr. K Schlacpfer mentioned in his UGRA report that a temperature fluctuation of 1 degree Celsius is approximately equal to 3% viscosity change. This means that the temperature is 70 degrees Fahrenheit when it is turned on. After about three quarters of an hour, the temperature rises to 79-90 degrees Fahrenheit. When the temperature increases by 9-10 degrees, the viscosity of the solvent ink will change by 15%. The viscosity of the ink varies by 5-7%.

This change was confirmed by William Chorvat of the Sun Chemical Company at the Louisville GTA Printing Workshop in 1986. He said that a temperature fluctuation of 10 degrees Fahrenheit causes a 15% change in viscosity, and this change in viscosity will cost you more. At the GRI conference, Mr. Paul Stangke of Flint Ink pointed out in his report entitled “The Effect of Temperature on the Viscosity of Inks” that “we often forget that viscosity is also extremely sensitive to changes in liquid temperature. And the heat generated by the friction of the printing machine will also make the ink temperature greatly increase.In the above picture, we can see the change of the ink temperature affects the result of viscosity and color concentration.So we must use a concentration control device to maintain the ink constantly Because we have seen that using flow cups or common viscometers to control viscosity without some temperature compensation is not correct and feasible, it is not sufficient to measure viscosity without considering temperature, and therefore it is necessary to rely on And with our technology, precise color density control is achieved.Color Density Control In order to fully adjust the viscosity, temperature fluctuations must be continuously monitored by a system that will convert temperature fluctuations into viscosity adjustments. The color depth control device checks and adjusts the density of the ink while taking into account the change of the ink temperature This ensures that the ink composition is properly balanced, and the color density control means maintains the color depth at a constant and constant value.

However, there are also disputes over temperature control. If you consider all the plumbing 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 in Paris in June 1994, people also considered viscosity control and color depth control as one of the most important factors related to the production of high-quality prints. Other factors such as:

● Before printing, use a static web vacuum suction system to clean the web or sheet.

● In addition to the color concentration control, it is also necessary to control the pH value.

● Prepare the ink in the ink shop. By effectively using time, labor and materials, you can save money. In flexo printing and gravure printing, the ink color density control device can be effectively used for solvent inks, water-based inks, coating oils, waxes, and the like. 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 pigments. If the automatic viscosity control device is used together with a temperature compensation or temperature control device, the consumption of ink, solvent and other materials can be reduced while maintaining the stability of the product quality. Which automatic control device to use, we should consider the following factors: