Effect of Ink Temperature on Solvent Volatilization and Printing Quality (Part 2)

(THE EFFECT OF INK TEMPERATURE ON SOLVENT LOSSES AND PRINT QUALITY)

Two nitrification inks (type C) commonly used in the packaging and printing industry were used in the experiment. They were run through a 42-inch, 300-feet/minute 4-color gravure printer and were run for 3 hours. In the experiment, the ink was a common organic ester or organic ketone C type ink, and the ink solvent was made of an equal volume (50% each) of ethyl acetate and propanol. During the experiment, the two C-type colored inks were sampled at 66, 79, and 92 degrees Fahrenheit respectively. The experimental low temperature conditions (66 kWh) are achieved through the ice water circulation tube at the bottom of the ink tank; high temperature (92 degrees) conditions are achieved through hot water circulation; and at room temperature conditions of 79 degrees Fahrenheit, no water circulation treatment is taken. After 3 hours of operation, the temperature of the ink may be 3 to 5 degrees higher than room temperature.

During the experiment, the ink temperature was measured every 5 minutes, and the viscosity of the ink was tested and adjusted. A printing quality record was also recorded every 20 minutes, and many relevant data about the printing effect were measured (see the experimental parameters in related materials). .

Studies have shown that at low temperatures, the ink requires more solvent to reach the necessary viscosity; and as the temperature rises, the solvent evaporates faster and the ink also requires more solvent to maintain the necessary viscosity. (See Sosa, 1999 Research Report)

As the temperature rises, the total solvent consumption of the magenta ink (sum of the amount of solvent added before the press is ready and during the printing process) also increases (see Figure 1);
The solvent consumption of cyan ink is slightly higher at 66 degrees Fahrenheit than at 79 degrees Fahrenheit. This is due to the fact that at the low temperature, when the machine is ready, the ink needs to add some solvent in order to reach a certain viscosity. When the temperature rises from 79 to 92 degrees, the ink solvent consumption also increases.
The total amount of ink (ink plus solvent) increases with temperature. At 66 degrees to 79 degrees, an increase of 9% to 28%, 79 degrees to 92 degrees increased by 37% to 56%.

When the temperature rises, the consumption of pure ink (excluding the solvent added before and during operation of the printer) also increases (see Figure 2). This may be the result of an increase in the "pigment/solvent ratio" of the ink at a high temperature and the thickening of the print layer.

The University of Western Michigan University research report also shows that when the ink temperature increases, the quality of the print will be affected. This is mainly reflected in the printing field and color.

* Reflectance density: 79 degrees Fahrenheit to 92 degrees Fahrenheit, and the reflection density drops by 0.055% for every 5 degrees increase in temperature. Theoretically, when the temperature is high, the color of the printed matter should be deeper, but the reflection density tends to decrease at high temperatures. This phenomenon has also been reported elsewhere. (See Celio, 1998 report)

When the temperature is higher, the volatilization speed of the ink becomes faster, which may cause the ink wetness to decrease and the printed cable phenomenon occurs. This phenomenon is due to the poor flow of ink molecules caused by printing defects (see GAA, 1991 study report). According to a study by the University of Western Michigan, when the temperature rises to 92 degrees Fahrenheit, the ink is not fully spread on the printing materials and it will dry out, which will cause a decrease in the reflection density and a reduction in the printed area. In this case, the most affected is the printing color, and many fine points cannot be printed at all.

* Printing gloss: When the temperature rose from 66 degrees to 79 degrees, the gloss decreased by 20%; from 79 degrees to 92 degrees, it increased by 3% (see Figure 4). In general, when the temperature is low, the ink needs more solvent to reach a certain viscosity; and low viscosity, it will cause thinning of the printing layer. According to a study by the University of Western Michigan, the gloss of printing at low temperatures is mainly derived from polyethylene substrates. Because the printing layer is thinner, the gloss of the printing material can be directly transmitted through the printing layer to make the surface of the printing material appear glossy. When the temperature rises from 79 degrees to 92 degrees, the gloss of the polyethylene printing material is also transmitted due to the decrease of the wetness of the ink under high temperature and the appearance of the printed wire, so the gloss is increased.

* Dot structure (see Fig. 5, Fig. 6): Due to the "vortex effect", the ink dot temperature will cause deformation of the dot. When the ink is injected into the cavity of the printing cylinder, the ink forms a concave surface due to the influence of the surface tension of the liquid, so that during printing, air is trapped between the ink and the printing material, and air bubbles are generated. This air bubble prevents the ink from penetrating the center of the ink dot body and spreads it to the periphery, forming a so-called "vortex phenomenon." The higher the temperature and the lower the viscosity, the larger the bubbles formed by the ink and the more pronounced the “vortex phenomenon”. As the "vortex" becomes more and more pronounced with the rise of the ink temperature, the printed image will become more and more light, and the dot enlargement will become more and more obvious.

The dot distortion caused by the vortex phenomenon will cause the increase of the diameter of the ink dot, and the increase of the ink dot diameter will cause the dot enlargement and the color unevenness, which will affect the printing quality. When the temperature of the ink finally becomes higher, the ink wetness decreases, and the printed area becomes more and more.

* Fog - This phenomenon is difficult to quantify, but it does occur at low temperatures. By reducing the ink flow rate or squeegee pressure will help reduce the occurrence of fog.

* Abrasion resistance of ink: At different temperatures, the wear resistance of the ink does not change much. The abrasion resistance test was performed on a Sutherland Ink Abrasion Tester by placing the printed film on a white surface for a period of time before measuring the light reflection density to determine how much ink was rubbed off the film. The results show that when the temperature is the lowest and the highest, the ink reflection density is not much different and it is within the error range of the optoelectronic densitometer.

Conclusions Western Michigan University's research is based on experiments to understand the effects of type C inks on print quality and solvent consumption at different temperatures (66, 79, and 92 degrees Fahrenheit). This experiment aims to make a preliminary assessment of the relationship between temperature and gravure printing and its economic benefits (see the scope of research in the relevant data). The results are encouraging.

Through the temperature control, small and medium-sized printing companies can achieve the purpose of reducing ink solvent consumption, improving printing quality, and reducing costs.
Reducing the amount of solvent used also helps to reduce the danger of solvent evaporation to the human body.
When the ink is near normal room temperature, the best printing effect can be achieved. The farther the people estimate the lower the temperature, the better. From this, we can know that the best job performance can be achieved only by slightly lowering the ink temperature.
By controlling the ink temperature, the consumption of ink can be reduced (up to 20%---30%) without affecting the printing effect. However, this research result needs further demonstration of different printing materials and actual operations.
The temperature control of the ink can also reduce solvent consumption (up to 50%). Especially in summer when the ambient temperature is high, the control effect is even more pronounced.

In order to assess its potential economic benefits, ink and solvent consumption, the team at West Michigan University assumed that the two scenarios were simulated (see related data). The two conditions are as follows: 1) Assume that a small printing plant runs at 92 degrees Fahrenheit every year for 3 months and the other 9 months at 79 degrees Fahrenheit; 2) Assume that the factory is temperature controlled and it runs at Fahrenheit 79 throughout the year. Degree of condition.

Of course, different manufacturers will have different production conditions, and many other factors will also have a certain impact on the assessment results. But in any case, for each company, the results of this assessment will at least provide them with a reference. Although the cost of temperature control, temperature control methods, and their energy requirements were not considered in the assessment program, significant investment savings in ink and solvent allowed the investment costs in this area to be recovered within one year.

Relevant information

1. area of ​​research:
Research experiments at Western Michigan University only evaluated the effect of temperature control on the environment, print quality, and printing costs in gravure printing, and given the exact relationship between temperature, print quality, and solvent evaporation.
This test only evaluated C inks. Other inks may not be the same as this test.
Fahrenheit 66 to 92 degrees represents the extreme conditions that may be encountered in the printing industry. Small print manufacturers may reach the upper limit of the temperature range during the summer, but this does not always happen within a year.

Many inks and solvents are affected by the humidity in the printing shop. Especially at low temperatures, the relative humidity of the shop will increase, which will affect the printing effect. The effect of humidity was not evaluated in this test, but no special effect on the printing effect was seen in the experiment.

2. Potential economic benefits

Parameter Option 1 Option 2 Savings

Solvent consumption (lb/year) 113,400 86,400 27,000
Ink consumption (lbs/year) 97,200 86,400 10,800
Annual solvent cost $56,700 $43,200 $13,500
Annual ink cost $388,800 $345,600 $43,200
Total cost $445,500 $388,800 $56,700


Printing Facilities Press Type: 23-inch wide printing components: 3
Year of operation: 7200 hours/year Printing speed: 300 feet/minute Solvent use speed: 9 lbs/hour (92 degrees Fahrenheit)
(per color): 4 lbs/hour (79 degrees Fahrenheit)
Ink usage speed: 6 lbs/hr (92 degrees Fahrenheit)
(per color): 4 lbs/hour (79 degrees Fahrenheit)
Solvent cost: $0.50/lb ink cost: $4.00/lb