Inks Technical News inks

Environmental Resin's Performance in Low Rub Black Offset Inks

(to download the pdf file of this data, please right click here and select "Save Target As..."

INTRODUCTION

The development work covered in this article compares the use of American Gilsonite Company's product, Environmental Resin ER-125, in rub- resistant web offset blacks, versus the Asian and European use of rosin modified phenolics. While phenolic systems are not common in the U.S., they can produce inks of ultimate rub resistance. With the use of suitable gelling agents, phenolic systems can be made to lithograph extremely well at very high speeds on all types of presses.

Secondly, the work looks at using combinations of ER-125 and Gilsonite to alter flow and rheology to produce inks that are suited to all common ducts systems including overshot, undershot, and rail system without the need for flow agents such as treated clay.

MODIFIED PHENOLIC SYSTEMS

The introduction of high-speed web offset presses for the printing of high quality newspapers in Europe, Australia, and parts of Asia over the last decade has seen the development of inks that truly have almost no scuff in time frames as low as four hours after printing. This unique performance has in some cases been achieved by the use of high viscosity rosin modified phenolic resins that retain good solubility in low aromatic distillates and compatibility in vegetable oils such as Soy and Canola oils. These inks, because of the binding capacity of the resin, are able to use low-cost carbons normally only associated with the rubber industry . The final balance of ingredients produces an ink of superb transfer, good strength, easy water balance, and above all, fast set and the ultimate in scuff resistance.

These systems employ Gilsonite to aid in pigment wetting and, because of the predominance of overshot ink ducts, generally prefer the lower viscosity grades such as American Gilsonite Company's Selects 300 Grade.

One such system is described as follows:

Modified Phenolic Varnish:

	Scuff Percent
	4 Hours	24 Hours	Lithomat	Duke	Print Density 100 mm³
Product			Lithomat	Duke	Print Density 100 mm³
Product

Phenolic System	1.9%	1.1%	75/100	45%/10m	1.12
ER-125	2.2%	1.8%	85/100	39%/10m	1.12

SCUFF TEST PROCEDURE

Each ink was printed on the Prufbau at 100 mm³ on Fletcher Challenge 43 gsm newsprint and the density measured using a Techkon Colorsens Densitometer model R412 fitted with Status E filters. After four hours, each print was subject to 20 rubs with clean newsprint using the Holmes Empirical Scuff Tester. The density of the ink transferred to the clean panel was then measured for density using the Techkon Densitometer and the ratio of the two readings expressed as a percentage. This procedure was repeated with separate prints after 24 hours.

It should be noted here that conventional web offset blacks yield a scuff percentage according to this procedure at four hours of 16-20 percent. So called low rub inks yield 6-8 percent while the phenolic system as illustrated can yield results as low as 1-2 percent. At this level the ink transfer to the hands or clothes of a newspaper reader is below the background level and hence not discernible. Thus, the difference between the phenolic and ER-125 systems is so small as to be insignificant.

PRUFBAU LITHOMAT EMULSION STABILITY

The inks were tested for resistance to pile in accordance with a well documented procedure(6) where the performance of each ink is scored out of 100 points. Fifty points are allotted if the ink shows no sign of pile on any roller in a given period with the balance being allotted to tack retention, resistance to bleed or contamination of the fountain solution and resistance to stripping. Any ink achieving better than 60 points is considered commercially acceptable, while those scoring above 85 points are considered excellent products with robust lithographic tolerance and a wide window of press performance.

The test is conducted over 10 minutes at high speed at 20-22°C using distilled water. Table I indicates that the ER-125 system achieved a top end result and additionally, did so without the use of hydrophobic additives of any kind.

DUKE WATER TAKE UP

Both inks were tested for water take up over 10 minutes using distilled water as a control. Graph 1 illustrates clearly the difference in the two systems. The ER-125 produces a near perfect "C" curve with rapid initial water take up and a definite end point at around 10 minutes. Again, this balance was achieved without the use of additives.

The result of this laboratory work indicates that American Gilsonite's ER-125 is indeed an excellent replacement for the modified phenolic system. The ER-125 produces an ink of lower viscositybut with similar flow to the alternative and with better lithographic water balance and resistance to pile, all without the need for the use of hydrophobic additives so common with modified phenolic products.

The fast set characteristics of ER-125 are comparable, if not better, than the competitive system. While the scuff resistance is quite marginally inferior, the difference in the commercial sense is so small as to be indiscernible.

The first part of this development program has been involved in the replacement of modified phenolics in very rub-resistant inks with American Gilsonite's Environmental Resin ER-l25. The rheology of both inks was designed to be long flowing and suited to overshot duct systems, as this has been the predominant feed system adopted by machine manufacturers in Europe in recent years. Part two of this study looks at the influence of Gilsonite (or ER-125 Resin) choice on the rheology of web offset coldset blacks and how ink may be formulated to suit other duct systems such as undershot and rails, without the need for common expensive additives such as Tixogel(4) and fumed silicas.

What are the differences in the various feed systems and why do they require different ink rheology?

OVERSHOT SYSTEM

In the Overshot System the ink is picked up by the pan roller and lifted into contact with a metering roller which allows a small amount of ink to pass through the nip for distribution to the plate. The excess ink is forced to return to the ink duct or pan by the force of gravity subject to the ink's rheology. Short, paste-like inks become partly suspended, causing ink pan sensors to refill the pan and overflow problems can occur when the press stops and the suspended ink finally returns to the pan. These inks can also aerate, increasing the volume of product and ultimately causing starvation of the system.

Inks suited to overshot systems need to be long flowing so that the transition time from the point of being picked up by the duct roller and cascading back to the pan is short. These inks also aerate, but because of their long flow, the air bubbles are able to leave the ink easily and dissipate.

UNDERSHOT SYSTEM

In the Undershot System, the ink is pulled from the duct by the duct roller as it rotates. The amount of ink removed is largely determined by the gap between the duct blade and the roller, but partly by the body or viscosity of the ink. Long flowing inks are not suited to this system as they tend to drip through the gap, particularly when the press stops.

RAIL SYSTEM

In the Rail System the ink is pumped into a chamber called the rail, which has small holes evenly spaced along its length facing the distribution roller. The ink is forced through the holes and, because of the close proximity of the rail to the distribution roller, onto the roller itself. This ink must be soft enough or sufficiently low in viscosity to enable the pump to force the ink through the rail, but also short enough to prevent dripping when the press is stationary.

Thus, in these three systems, three different ink rheologies are required for the press feed to function correctly. While ink formulations can be altered in body and flow by the choice of the carbon and additives such as clay and fumed silica, the choice of resin is also vital and, in this regard, the Gilsonite range offers a low-cost solution.

In order to explain the significance of the different properties of Gilsonite Selects 300, Selects 325, and ER-125, three varnishes were developed:

C:
Gilsonite Selects 325 Grade
Alkali Refined Soy Oil

Equals

35.00%
65.00%

100.00%

Varnish A was lightly chelated in order to increase the viscosity of the system and, because of the low reactivity of ER-125 to chelate, a little fatty acid was added.

The three varnishes were formulated into inks and adjusted to a common tack of 4.5 units measured at 800 rpm and 32°C and from this standard rheology of each ink was compared. (See Table 3)

Thus, it can be seen that while the three resins produce inks of the same tack and similar high shear vis-cosities, the low shear viscosity of each is very different, and hence the shortness factors vary widely. This data clearly indicates that there is a significant difference in each resin and shows how the body and flow of inks can be adjusted by the right selection of Gilsonite Grade or ER-125 Resin. Since the system used for this evaluation was almost entirely Soy based, further work was undertaken to test the Soy compatibility of the Gilsonite resins and the temperature dependence of the systems. Three additional varnishes were cooked at constant resin loading and their rheological properties tested at 20°C, 30°C, and 40°C with three levels of dilution in Soy Oil.

Compatibility Test
Varnishes	G	H	I
ER-125	40%
Gilsonite Selects 300		40%
Gilsonite Selects 325			40%
Alkali Refined Soy Oil	60% 100%	60% 100%	60% 100%

Table 2 illustrates the results achieved, lists the Laray and Brookfield viscosities in poise and the shortness factor, as previously defined. Varnish G was tested on the Brookfield using spindle No. 5 at 2.5 rpm and varnish H and I with spindle No. 7, also 2.5 rpm.

It can be clearly seen that the shortness factors approach unity as the temperature increases, indicating that the systems are becoming more Newtonian. Conversely, as the temperature falls, only the ER-125 system maintains flow, while both the Selects 300 and 325 rapidly become shorter, indicating limited solubility in the vegetable oil.

Graph 2 is included to illustrate the change in shortness of the three resins as the temperature changes. Only three examples from Table 2 have been plotted, all of which have similar Laray or high shear viscosities, that is, Varnish G with no additional Soy Oil, Varnish H with 5 percent Soy Oil, and Varnish I with 10 percent Soy Oil.

If this information is now related back to press ink fed, it is obvious that ER-125 is most suited to overshot systems. It has natural long flow and maintains this even as the temperature is decreased. Both the Selects 300 and 325 are more suited to undershot and possibly rails systems where their natural body and shortness suit the design criteria of the press. The Selects 300 is possibly the preferred Gilsonite for large pumping installations while the Selects 325 might
find application in products packed in pails where the knifeability of the ink at the point of application to the press demands shortness.

Inks designed for rails systems might require a blend of these products, particularly the Selects 300 and ER-125 blended together in order to achieve a lower viscosity to aid pumping and feed but at the same time, a degree of shortness to prevent dripping.

In conclusion, the Gilsonite family of bituminous resins offers the ink formulator a unique opportunity to develop lithographic news inks with controlled rheology to suit all press designs. The resins wet carbon extremely well, aiding in the dispersion process and ultimately binding the pigments to the newsprint, producing a high degree of rub resistance.

In particular, Environmental Resin ER-125 can be used to replace modified phenolic resins and ink additives in both full vegetable oil systems or more traditional mineral oil products. Of great significance, these resins produce inks possessing a natural water balance, maintaining good transfer under the most
severe of high speed printing, all without the need for hydrophobic additives. Couple this with the unmistakable economic advantage of ER-125 over any modified phenolic product and it's easy to see why this resin demands exploitation.

By Joseph Baldassare
American Gilsonite Company, Salt Lake City, Utah
American Ink Maker, Volume 74, No. 4, April 1996

REFERENCES

1. Haltermann PKWF 30/33 is a narrow cut high boiling hydrocarbon manufactured by Haltermann GmbH of Hamburg, Germany. Its boiling point range is 300-330°C, 20 percent aromatic content, 83°C aniline point.
2. Chelate OAO is an aluminum chelate produced by Chattem Chemicals, USA.
3. Elftex Pellets 115 is a grade of carbon black made in pellet form by Cabot Corporation of the USA.
4. Tixogel VP is a quaternary ammonium compound of Montomorillomite clay manufactured by United Catalysts of the USA.
5. Pronap 280 is a grade of high viscosity, paraffinic-based lubricating oil produced by the Shell company.
6. The score system for the Prufbau Lithomat was developed by Independent Ink Technologies of Sydney, Australia. Phone number: 61-2-683-4400; facsimile number: 61-2-683-4152.

Back to Inks Technical Page