by clicking the arrows at the side of the page, or by using the toolbar.
by clicking anywhere on the page.
by dragging the page around when zoomed in.
by clicking anywhere on the page when zoomed in.
web sites or send emails by clicking on hyperlinks.
Email this page to a friend
Search this issue
Index - jump to page or section
Archive - view past issues
Panpa Bulletin : February 2006
Offset technology requires precise demands from the fountain solution. Incorrect fount, inaccurate dosing and/or unchecked raw water can lead to a series of problems such as lack of contrast, ink and water imbalance, toning as well as lack of consistent colour through the run of the job. There are certain areas in fountain solution and various parameters that the printer can verify him or herself and focus attention upon. To prevent ink emulsification, it is said that dampening levels need to be kept as low as possible. Un- coated stocks absorb a high volume of fountain solution. Unwanted ex- cess water opens the paper surface, leading to release of fibres. When printing a single or two-colour job, general practice is to keep the dampening levels high to prevent the toning, scumming on the plate, which leads to emulsification and loss of ink density. Understanding the different pa- rameters pHGum Arabic was used many years ago as a major desensitizer. A desensitizer keeps the non-image areas free from ink. When the gum is acidified it has an attraction for metal areas, which we call etching. We are all aware of the pH range for printing, that is in the range 4 to 6. If it is outside that range, the gum is not effective and toning and scum- ming etc would occur. Thus it was important for the printers to check pH. Today, most of the fountains are buffered to keep pH in control, making pH is less of a problem. Conductivity Conductivity is the ability or power to transmit or conduct an electrical charge. In water or any solution, the degree of conductiv- ity is determined by the number of ions present as a result of minerals or other compounds in the water. Basically, the higher the concentra- tion of ions, the higher the degree of conductivity. Alcohol does not conduct electrical charge, so has a conductivity reading of zero. Dur- ing printing there is a contamina- tion of fountain solution by things such as ink in water, emulsification, paper fibres, loose fluff and paper coating. As a result, a number of ions per unit volume of solution in- creases and conductivity increases. Typical conductivity of pure water is 0.055 microsiemens per centime- tre; deionised water is 1 microsie- mens per centimetre and tap water (drinking) is 500 microsiemens per centimetre. It is important to ob- serve conductivity at a steady tem- perature, as there is a striking rela- tion between the temperature and conductivity of the solution. . Quality of raw water It is important to define exact criteria for every consumable in a pressroom including water and fount concentrate. As around 98 per cent of fountain solution is water, being aware of water conditions is of vital importance. To begin with, it is important to establish that there are no serious variations in water hardness. Water quality can vary seasonally, monthly, weekly and even daily. If you decide to change the source of supply of water, it can have important consequences for print quality and the choice of addi- tive often depends on the nature of raw water. To correctly select your water, you should take a sample of the water, establish the dosage curve of the fount calculating dos- age of the additive corresponding to lowest surface tension and then use a conductivity meter to workout the concentration of the additive. Viscosity of Fountain Solution Viscosity is a measure of a fluid's resistance to flow. Adding IPA to dampening solution significantly increases its viscosity. As the viscos- ity increases, the water film at the rubber roller surface will be dragged through the nip more effectively. Surface Tension Surface tension determines wet- ting property and ability of solution to form thin films. The surface ten- sion of water is 72 dyne per cen- timetre. You can measure surface tension with apparatus called a stalagnometer. Lower surface ten- sion means rapid wetting will oc- cur, which is important at faster press speeds. The fountain solution should travel from the water pan through the dampening train and finally to the plate easily. Using al- cohol or substitutes, which are also called as surfactants, reduces sur- face tension of fountain solution. The surfactants of the fountain so- lution help in splitting water films. Increased wettability of the foun- tain solution results in low water settings, reducing consumption of water and ink giving an enhanced print quality. Water without any surfactants gives inconsistent den- sity values in press run as against using a fountain solution with alco- hol or alcohol substitutes. Recirculation Systems Through my study of many presses in India, I have made a number of observations of small and medium sized presses regarding the dampening circula- tion system. 1.There may or may not be an auto dosing system or recirculation systems 2.The fountain pan of each unit is connected to a central tank, through pipelines and fountain so- lution is recirculated by pump. 3.A simple sponge is used for filtration purpose, which removes only solid contamination. 4.There is no monitoring system to maintain correct concentration of fount solution Present day auto replenishment systems consist of a central water tank when the storage of fountain in this tank comes to an end, then the central tank is refilled auto- matically with water and fount (additive). Recirculation systems have to be cleaned at frequent time intervals as the dampening hoses can get choked with fluff, dirt or deposition. They have to be flushed with warm water every week to remove dirt. Effect of Refrigeration on fountain solution Tap water has a conductivity of 500 microsiemens per centimetre at a temperature of 25 Degrees Celsius. There is a virtually linear associa- tion between the temperature and conductivity of fountain solution. Also, during long runs, heating of inking systems can take place that makes the process unstable, hence Fountains: not so difficult as we may think Get the fountain solution wrong, and an entire job can end up in the rubbish. Research from Professor Madhura Mahajan has shown how to get the fountain solution right. The Essentials > Offset technology requires precise demands from the fountain solution, otherwise problems such as lack of contrast, ink and water imbalance, toning and lack of consistent colour can exist throughout the run of the job > There are certain parameters that the printer can verify himself. These include pH, conductivity, quality of raw water, viscosity, surface tension, recirculation systems and the effect of refrigeration > Tests results show how these parameters can affect the quality of printing 38 | PANPA BULLETIN February 2006 PRODUCTION