Authors Present Findings at European Coatings Conference.

Berlin, Germany was the venue for the European Coatings Conference addressing printing inks, which was held June 10-11 this year.

Maurice Bowtell is a freelance writer based in Knustsford U.K.

The organizers, Vincentz Verlag, Hanover, Germany, put together some 15 very good papers presented by eminent authors from Belgium, Germany, the Netherlands, U.K. and the U.S.

Forecast for Inks

The conference was opened by Dr. Frank Rothbarth of Vincentz Verlag, who gave an overview of the economic situation affecting printing inks. This detailed the shipment of printing inks in Europe, which was 737.1 thousand metric tons in 1993, forecast to rise to 1,039.6 by 2003. Revenues for printing inks in Europe were $3.27 billion in 1993, gauged to increase to $4.66 billion in 2003. The source for these figures was provided by a 1997 Frost & Sullivan report. Details were also presented on U.S. printing ink demand by type and market.

As to be expected, there was a major input from the host nation, both in terms of delegates and speakers.

Special Effects 

There were three papers addressing special effects. The first was a very well received presentation given by Dr. Frank Meyer of BASF AG, Ludwigshafen, Germany, on behalf of co-authors from BASF. Dr. Meyer discussed new non-pigmented printing inks having special effects.

A major emphasis was placed on interference colors. Dr. Meyer said that color could be realized by absorption of a colorant such as a dye or a pigment, or by interference of thin films with a thickness in the range of the wavelength of visible light. An example of the latter is a soap bubble or oil film on water. Dr. Meyer pointed out that it has been shown by optical spectroscopy that the reflection of interfering layers can be very narrow providing the possibility of creating brilliant colors. Efforts to use this effect are well known from inorganic effect pigments, where materials of different refractive indices are processed on top of each other. Depending on the thickness of the layers, constructive or destructive interference occurs.

Special effect pigments in printing inks formed the subject of a paper by Dr. Klaus Bohm on behalf of co-workers from Merck KgaA, Darmstedt, Germany. Dr. Bohm said that pearl luster pigments as one category of special effect pigments have become a standard tool for stylists and designers. They are used to achieve vivid interactions of color and luster, with the added dynamic of variation affected by the direction of illumination and observation.

These pigments are central to the generation of many new and unique effects when used in printing inks, plastics, cosmetic formulations and paints for automotive and industrial applications. The unique pearl luster effect is produced by light interference rather than by absorption. However, they complement and enhance the appearance created by conventional absorption and/or metal effect pigments. Special color effects, chemical stability and ease of use are their main advantages; also, they are said to be non-toxic.

Dr. Gunther Sommer of Eckard Werke, Velden, Germany, described metal effect pigments. He said that gold and silver inks give exquisite products a high appreciation value. To achieve these special decorative effects, metal pigments are also applied in printing inks. In addition, the possibilities of application that these decorative inks offer to the graphic art industries are many fold and have not yet been exhausted. He detailed the production and properties of metal effect pigments, as well as the disadvantages associated with these properties.

Dr. Sommer gave some interesting historical details. For example, the production of metal pigments has a long tradition, developed from the gold beaters' craft, which existed as long ago as 1000 B.C. The waste resulting from the gold leaf production was pulverized in a mortar, pasted with a binder and used as a paint. This process was also applied on other metal leaves. For historical reasons, metal effect pigments are therefore called silver and gold bronze, although from the metallurgical point of view they have nothing to do with gold, silver or bronze. In fact, they consist of aluminum, copper and brass pigments (copper-zinc alloy).

International Authors

The international flavor of the meeting was enhanced by presentations given by authors from The Netherlands, U.K. and the U.S.

Modern characterization methods relating to current offset resins were outlined in a paper by Doug Weisel of Akzo Nobel Resins, Bergen op Zoom, The Netherlands; the co-author was Phil Sieg, also of Akzo Nobel. They put forward that in lithographic printing, an ink maker relies heavily on the quality of varnish, primarily to provide a vehicle to transfer and direct the pigment to the substrate. A key factor is the ability to emulsify a sufficient quantity to transfer the ink flow and simply adhere to the image area on a printing plate.

After being mixed and squeezed at various shear rates, this varnish must be dry and be resistant to the elements. Also, it should be given optimum visual properties when supplied to the customer. According to Mr. Weisel, the essence of a good offset varnish consists of strategically selected hard resins chosen for their economical, structural and compatibility attributes that they will contribute to the final product. As the polymers are generally solid at ambient temperatures, final assessment of the resin s characteristics involves dispersion into a fluid medium.

Dr. Richard Chylla of SC Johnson Polymer, Heerenveen, The Netherlands, discussed on behalf of co-workers the chemistry of resin-stabilized pigment dispersions. Concentrated pigment dispersions are commonly used as precursors in the manufacture of aqueous inks and paints. The pigment dispersions are prepared by the reduction of particle size of the pigment through mechanical grinding, followed by the stabilization of the pigment particle in the aqueous media. This stabilization is frequently accomplished using low molecular weight acrylic resins.

The main objective of Dr. Chylla's study was to determine the connection between the macroscopic properties, such as rheology and color development which are important for the end application, with the controllable polymer properties like acid value, molecular weight and microstructure.

The U.K. papers included one by Dr. Robert B. McKay of Ciba Specialty Chemicals, Paisley, Scotland; co-author was M. McGarvey, also of Ciba. This described the optical and rheological properties of lithographic inks. It was put forward that the use of a computerized diffractometer and detailed knowledge of the crystal lattice structure have improved the ability to size crystals of CI Pigment Yellow 13-type pigments. This has apparently permitted confirmation and refinement of correlations observed in earlier work between crystal sizes, as well as the optical and rheological properties of commercially available pigments in lithographic inks. The correlations indicate that the dispersion procedures used produced inks in which the pigments exist substantially as individually dispersed crystals.

These correlations also show that the crystals of the commercially available pigments are effectively perfect. There is, however, an alternative explanation on the basis that the various pigments all have similar degrees of aggregation, and imperfection of crystals is also possible but improbable due to the widely different compositions and sources of the pigments. The authors raised the question of whether or not abietyl resin added to improve dispersibility of pigments remains on the crystal surfaces in inks; this has not been resolved.

The benefit of surface and interfacial analysis for the printing industry was the subject of a paper by Dr. Robin West of CSMA Ltd., Manchester, England; co-author was Andrew J. Swift, also of CSMA. The authors said that printing performance is controlled by chemical and physical processes, which occur at critical interfaces of a printing system. For example, the receptivity and stability of a surface for ink retention can be critically controlled by the state of its outermost atomic layers. Trace levels of contamination and the migration of additives to the bonding interfaces are all potential causes of print failure.

Furthermore, many problems in this industry are difficult to detect using conventional analysis techniques, where the sampling depth and chemical specificity are insufficient. Techniques such as ToF SIMS and XPS provide a route to understanding the chemical properties of this region but, the authors held, the application of these techniques in this sector is still relatively new with comparatively little work published in readily available literature. Their paper described a series of examples from different aspects of the printing industry, ranging from pigment formulation to consumer packaging.

An interesting paper from the U.S. was presented by Jack Baarends, Lawter International, Pleasant Prairie, WI. Mr. Baarends raised the question of what modern resins contribute to high-speed offset printing. Higher speeds are being utilized with aboutl5 m/sec for the heatset process and for sheetfed, 15,000 prints per hour. Mr. Baarends said that in the very near future, even higher rates will be achieved for both applications.

This means that the inks must give a better performance under these more severe circumstances, and an additional problem is the very high price pressure of inks and their raw materials. An offset ink, for example, is made up of pigments, mineral distillates, alkyd resin/vegetable oils, additives and resins. The resin is responsible for the quality of the printed matter, but equally important for the behavior of the press.

In his presentation, Mr. Baarends discussed the most recent developments in offset resins. Mr. Baarends said that it was well known that the influence of raw materials as well as the processing of resins are essential to the final properties of a resin, resulting in press performance and the final print. These severe conditions give a printer a very small window for printing.

From Belgium came a paper by Dr. Daniel Bien of Exxon Chemical Europe Inc., Machelen.

This outlined oil-based inks for ink jet technology with particular reference to the advantages and challenges. Dr. Bien held that hydrocarbon fluid-based inks provide significant advantages over water-based inks, particularly in piezo ink jet technology. Also, analysis of formulations had shown that water-based inks contain a significant solvent component, so that issues regarding health and the environment are more or less the same for both types.

Apparently, an examination of special hydrocarbons, in particular synthetic manufactured isoparaffins, shows that with the right choice of product and handling, there is an effective way to benefit from the advantages of hydrocarbon fluid-based inks without damage to health or the environment.