The property tested was tackiness of ink in difference printing conditions. Both variable speeds and temperatures were recorded and analysed. This test helped determine and understand the relationship of ink in press running conditions (speed and temperature) and the tack property. Further research helped identify possible tack related problems and solutions. The results showed up as expected in conjunction with the research found and previous tests on the tack property.
The speed of the press greatly increased the tack while the temperature lowered it. Initially when recording early readings, the tack was much lower on the higher temperature setting (100 degrees Fahrenheit), but over the course of 10 minutes all results with the same speed setting showed a very similar value. The speed variable showed a much higher tack value both in the beginning and end of the 10 minute testing timeframe indicating that speed might have a greater overall effect on tack than temperature.
Some suggestions to solve picking, which is induced from high tack, are to decrease the press speed, decrease pressure on the impression cylinder and reduce the tack. Some interesting findings have also given evidence that there are more modern methods, such as regulating the cylinders to help maintain the desired tack on a press. Introduction This test is just one characteristic on the many properties of ink. Tack is in close relations to ink film thickness, speed of the press, temperature of the press, and viscosity of the ink.
Tack is an important characteristic of ink in that it helps determine the sharpness and clarity of an image. The objective of this test is to determine what the best recommended tack values are for sheet-fed and other means of printing as well as problems and solutions to tack related scenarios. Understanding some of the possible future or modern technologies or finding for ink tack is beneficial and crucial for this paper. Definitions “Tack – Resistance of a liquid to splitting. It is measured by determining the force required to split an ink film between two surfaces. (Pg 433, Wilson: 2005) Viscosity is a measure of internal friction in a liquid; tack is a measure of internal cohesion. ” (Pg 284, Apps: 1958) Equations •Slope = Rise/Run Materials Used •O/S Pro Cyan – Colmar Inks Co. Equipment Used •Electronics Inkometer – Model No. 101-A Thwing – Albert Instrument Company •Pipette •Ink knives Test Principle The purpose of a tack test is to measure the resistance the ink has against splitting. In this particular test, the difference in tack at varying temperatures and at varying speeds is observed and compared.
As the temperature is increased, more heat is transferred into the inks through the rollers. (Idminstruments) This creates various degrees of ink tack measurable on the machine. Since different forms of printing have different production speeds the tester can also be calibrated to simulate high or low speeds depending on the type of press it is used for. The equipment and procedures work similarly to press conditions, first the roller is run for one minute to warm up then when heat transfer and speed of the rollers are all reproduced on the tester, one can expect the same and accurate results to be found on a press.
The procedures of reapplying ink on the rollers can be found to be similar to that of make-ready in production. Procedure 1. Prepare a clean and organized work area with the necessary materials and equipment. 2. Obtain a preferable ink to use. 3. Adjust the Inkometer’s temperature settings to 90°F. 4. Set the speed to 800 RPM. 5. Set the ink tack value to zero by turning left on the knob while the machine is running. 6. Turn the Inkometer off. 7. Calibrate the pipette to 1. 2CC. Fill in the pipette with the selected ink. 8. Apply the ink onto the rollers. 9.
Turn on the Inkometer and allow one minute for the ink to ____ onto the rollers. 10. Record results of the tack value after 1 minute and then every 30 seconds for 10 minutes. 11. Once results are recorded, stop the machine and clean the rollers. 12. Perform steps 4 – 11 while increasing the speed to 1200 RPM. 13. Obtain data and record. 14. Change the speed back to 800 RPM but increase the temperature to 100°F and perform steps 5 – 11. 15. Increase RPM value to 1200, repeat steps 5 – 11. 16. Collect all recorded data and place into four tables.
In accordance to our results, tack is affected marginally by both speed and temperature at which the press operates at. However, when the results were compared, tack values were affected more by the temperature than by speed (friction) itself. In the results portrayed above, when the Inkometer was set at 90 degrees Fahrenheit, 800 RPM, the initial tack value measured at 1 minute was 8. 2, as opposed to 10. 4 when the speed increased to 1200 RPM. Furthermore, when the same results were compared to that of 100 degrees Fahrenheit, both 800 RPM and 1200 RPM, tack values taken at 1 minute had marginal differences, 7. and 8. 2, respectively. This shows that as the temperature increases, the tack of an ink in a press decreases. The heat liquefies the ink, which makes the ink less viscous (thick), allowing it to become less tacky when placed on top of paper through the rollers. The ending results between the similar rpm tests were similar in values. After 10 minutes the higher rpm’s tack value was closer to what research suggests should be standard. Research indicates that a tack value for web offset printing should be around 10 and for this instance, sheet-fed lithographic printing, around 15 (Podhajny: 2002).
This indicates that the higher rpm helped the ink reach the desired tack value faster. In accordance to our results, tack is affected marginally by both speed and temperature at which the press operates at. However, when the results were compared, tack values were affected more by the temperature than by speed (friction) itself. In the results portrayed above, when the Inkometer was set at 90 degrees Fahrenheit, 800 RPM, the initial tack value measured at 1 minute was 8. 2, as opposed to 10. when the speed increased to 1200 RPM. Furthermore, when the same results were compared to that of 100 degrees Fahrenheit, both 800 RPM and 1200 RPM, tack values taken at 1 minute had marginal differences, 7. 0 and 8. 2, respectively. This shows that as the temperature increases, the tack of an ink in a press decreases. The heat liquefies the ink, which makes the ink less viscous (thick), allowing it to become less tacky when placed on top of paper through the rollers. RECOMMENDATIONS Ink tack can’t be too high or low.
If the ink is too high then it will cause picking on the paper surface, but if the tack is too low then the image can be blurred. Therefore the tack needs to be somewhere in between where the paper does not pick and the image will remain sharp (Kipphan p. 132: 2001). Not all printing types have the same recommended ink tackiness either and therefore it is necessary to know the capabilities of the individual press to insure that its maximum potential is reached; i. e. newspapers recommended tack is 3. 5 – 5 where as waterless offset printing is much higher (Schneider: 2006).
In the event of tack related picking there are some remedies that Wilson suggests (Wilson p. 56: 1998): •Reduce ink tack •Change to an easier releasing blanket •Lower press speed •Decrease the pressure of the impression cylinder These are good recommendations, but sometimes not a great means to an end in industry. All of the above solutions either sacrifice time or quality; neither of which is affordable in today’s market. One of the more costly, but efficient ways for controlling tack is to using a temperature regulating device within the press.
They are particularly effective for cooling the cylinders in order to maintain a proper temperature in opposition to the fiction caused from the cylinders themselves (Schneider: 2006). In Schneider’s cylinder temperature regulating invention, he only regulates the inking form roller and not the transfer roller to test the results of tackiness, but suggests that it is possible to regulate the transfer cylinder to help regulate the tackiness of extremely high press-speeds (Schneider: 2006). Problems that occur from high tackiness, namely picking, can occur due to the substrate being printed on.
It is suggested that paper with a coating of 20g/m2 or less (also known as “light weight coated paper”) should take precautions from picking due to the substrate’s make-up (Schneider: 2006) With today’s technology quality of a job is not the only issue; the speeds of press technology are getting faster. Apps states that “as the machine warms up and attains maximum speed, the tack becomes worse, as it is proportional to the rate at which the ink film is split (Apps, p. 284: 1958). ” A common practice would be to add more wax additive or extender in the ink, or to reduce the viscosity of the vehicle (Apps p. 84, 1958). However, doing so can affect the color strength of the image and thereby decreasing the quality of the job or having to increase the ink film thickness to counter the chemical change in the ink. In the case of waterless lithography, it is even more crucial to maintain a steady temperature on the press. Roller cooling systems are employed to reduce heat applied to the ink from the vibration of rollers. Typically, waterless inks have 2 or 3 times the viscosity of conventional inks and will cause picking and piling. These inks are carefully manufactured to have high viscosity while also having low tack.
Waterless printing results in the elimnation of the fountain solution thus causing the press to heat up even more, different inks are required for different parts of the year contrary to conventional printer stocking practises such as stocking up on fewer inks. This also means the press must have large chillers and thermostatic controls in place in order to function efficiently. It is also very common to see chilled plates and chilled rollers to moderate the press temperature between 26 C and 31 C to keep the press from being too cold producing poor ink transfer and prevent being too hot producing background toning effects. Krishnan, Ramasamy) Ink tack testers today are more and more common. Ink tack control is a necessity in the pressroom and used as a form of quality control. Rather than using such a large device as the Model No. 101-A, much more portable tack testers are available on the market today.