A Better Resin for Heatset Gel Varnishes
Environmental Resin ER-125 is a hydrocarbon-based resin created by ATMD Gilsonite Company for use in offset inks, particularly heatset inks. ER-125 Resin is soluble in aliphatic mineral distillates and vegetable oils. It creates varnishes with low and stable viscosities and is an almost totally pure aliphatic hydrocarbon with less than 0.05% impurity content.
The raw material for ER-125 manufacture is Gilsonite® resin, a naturally occurring hydrocarbon material, well known in ink making for its excellent carbon black dispersing abilities. Gilsonite resin itself is a wide variety of different types of hydrocarbon molecules which may be characterized into two major types: straight chained aliphatics and ring-structured aromatics. Gilsonite also contains a small amount of impurity content, about 0.5%, and a small amount of light oils.
American Gilsonite Co. has isolated and separated out the aliphatic hydrocarbon molecules in Gilsonite via a solvent extraction process to make ER-125. ER's manufacturing process also removes the impurities found in Gilsonite, removes the light oils and their smell, and flakes out this new resin (removing Gilsonite's dust). ER-125 resin has been proven by major printing ink companies in Europe, the U .S. and Asia to replace the hydrocarbon resin (C5 - C9's), phenolic resin and even alkyd resin from offset ink formulations.
Research has shown that Environmental Resin ER-125 provides the ink maker (especially heatset) many different advantages, including:
- reduced tack;
- increased tack stability;
- increased gloss;
- reduced misting;
- increased density; and
- Increased flow.
In addition to these advantages, American Gilsonite and its German ink consultants have shown that ER-125 resin has some extraordinary ink making properties, considering that it is a hydrocarbon-based resin. One major advantage is that ER-125 resin is reactive with gellation agents such that it can provide "rheological structure" to ink systems. Rheological structure is a combination of viscosity and yield value. Viscosity is a measure of a system's resistance to flow. Yield value is a measure of a system's thixotropy. It can be thought of as a "gellification index" that tells how far away the system is from being a Newtonian liquid, like water. For example, the yield value of water is 0, whereas the yield value of whipped cream is very high, meaning the whipped cream has structure, or can be gelled.
The ER-125 resin can be used to create gelled varnishes that have increased structure at a low initial tack level, a great benefit for fast running heatset inks. Also, these varnishes provide high gloss levels to the ink film and resist the ink degrading or breaking down when it is used on fast-running printing presses.
Why do ink makers want varnishes with rheological structure? Ink varnishes with increased structure give the final heatset inks the necessary body to flow between the many rollers of a printing press without breaking down. Usually, the high shear forces of the many rollers of a printing press break down an ink and cause it to fall apart, making it become less of a paste and more like a liquid. Therefore, the ink maker wants a certain high structure to increase the ink's ability to resist degradation caused by the high shearing rollers. Normally, in order to achieve this high structure, ink makers often use less soluble hard resins, which change the performance of the ink.
Usually, higher structured inks lead to lower tack levels which, in turn, lead to the disadvantage of lower gloss. Ink makers prefer inks with lower tack levels because they give faster setting (ink drying), which make faster printing speeds possible. However, low tack levels imply low solubility of raw materials in the ink system, which gives lower gloss levels two big disadvantages.
Therefore, an ink maker is forced to counter-balance between desired structure and low tack. Ink makers would like to create an ink that has both the necessary structure for printability and the low tack for faster printing speeds without the concurrent loss of gloss. This may be achieved using ER-125 resin.
Normally, the relationship between structure, tack level and gloss level is:
Higher structure yields lower tack, which yields lower gloss.
This results in two advantages and one disadvantage. The advantages are that the high structure gives good printability and the low tack gives fast printing speeds. The disadvantage is that the lower tack level also leads to lower gloss. By replacing the traditional resins in the varnish (hydrocarbons, phenolics and alkyds) with ER-125 resin, the ink maker can achieve three advantages and no disadvantage--high structure, low tack and high gloss, all at the same time.
Table 1 presents two different varnish formulations, one using an unmodified hydrocarbon resin and the other using ER-125 resin. Table 2 summarizes the performance results of these varnish formulations from our German consultant's laboratory experiments. Please note that these are varnish formulations, not finished heatset inks. The intent here is to prove ER-125 resin can be gelled, increasing both viscosity and yield value (effectively increasing structure) without increasing the tack.
The first step was to make a varnish using an unmodified hydrocarbon resin. We chose SK-150 from Taiwan with a 150°C softening point. It required a 45 percent solids solution in an aliphatic solvent, Haltermann PKWF-28/31 (280°C to 310°C boiling point range, 20% aromatic content, 82°C aniline point), to yield a varnish viscosity of 7.7 Pa.s. (Pascal seconds, Rotovisco at 20°C). By comparison, a second varnish with similar viscosity, 22 Pa.s., was made using ER-125 resin with only a 35 percent solids solution, rather than the 45 percent. This means that ER resin is cost effective because it yields a higher initial viscosity using 35 percent resin instead of 45 percent resin.
In Table 2, the columns labeled "standard" compare with the performance results of the standard SK-150 and ER-125 varnishes, without gelling agents. Neither of these varnishes have any structure, demonstrated by low viscosities and low yield values. However, the ER-125 based standard varnish shows lower initial tack (68) and much better flow (1390) than the SK-150 standard varnish.
Our next step was to add 1 percent and 2 percent of Manalox 205 gelling agent to each of these standard varnishes and examine the resulting gellification. Looking first at the initial viscosities, the SK-150 varnish did not gel at all. Its viscosity only increased from 8 to 12 to 13 Pa.s. On the other hand, the ER-125 varnish did build structure. Its viscosity increased considerably, from 22 to 72 to 95 Pa.s. This demonstrates the ability of the ER-125 resin varnish to build structure without increasing tack, which only went from 68 to 76 to 85.
The difference between the unmodified hydrocarbon, SK-150, and ER-125 resin is even more dramatic when the yield value of the varnishes is examined. Table 2 shows that the yield value of the SK-150 varnish only increases from 14 to 36 to 175 dyn when 1 percent and 2 percent of the Manalox 205 is added, respectively. However, the yield value of the ER-125 resin varnish increases from 5 to 90 to 1100 dyn when 1 percent and 2 percent of the Manalox 205 is added, indicating a significant amount of structure.
Equally important are the results in tack level. The standard SK-150 varnish's tack starts higher than ER-125's and it increases 66 points over time (10 minutes total). When 1 percent and 2 percent Manalox 205 is added, the SK-150's initial tack increases considerably (from 110 to 144 to 160, respectively) and the size of the increase over time increases too (from 66 to 90 to 80). By comparison, the standard ER-125 resin varnish's initial tack (68) is lower and it does not increase at all over time. After the 1 percent and 2 percent Manalox 205 is added, the initial tack increases only slightly (from 68 to 76 to 85, respectively) and these tack levels are essentially constant over time.
Therefore, these experiments prove a major advantage of ER-125 resin over unmodified hydrocarbon resins. Compared to the unmodified hydrocarbons, the ink maker can increase the structure of an ER-125 based varnish, or ink, by gellation and not increase the tack. This cannot be done with hydrocarbons unless other costly raw materials like rosin modified phenolic resins are added.