Gold

Printing inks with a metallic effect create interesting possibilities for designing a printing job. For example, they are very popular for printing high-quality labels, brochures and packaging materials. Gold effects are obtained by using pigments containing brass (an alloy of copper and zinc). (The popular term "bronze" – which is actually a copper/tin alloy – is misleading.) The various metallic shades result from different alloying proportions:

• Rich Gold is 70 parts copper/30 parts zinc.
• Rich Pale Gold is 85 parts copper/15 parts zinc.
• Pale Gold is 90 parts copper/10 parts zinc.
• Copper is 100 parts copper.

Alternatively, aluminum-based pigments can also be prepared in combination with suitable color pigments; in this case the color pigment is responsible for the tint (reddish, yellowish, etc.). The metallic character of this variant may be classified as very intense, although not comparable with the brass shades discussed above.

Printing instructions

The best metallic effect is obtained on coated stocks that have a uniform, smooth surface. Because these inks are highly pigmented and have outstanding opacity, it is not necessary or even recommended to try and enhance the effect by excessive inking.

As a rule, this simply leads to printing problems such as piling, poor stacking characteristics, long drying times, and insufficient rub resistance. One rule that has proven useful, especially on heavy subject areas, is never to print gold ink in the last unit. Smoothing the print with an additional rubber blanket helps to enhance the effect.

Metal pigments that contain copper are particularly susceptible to corrosion. The printer must also take this fact into consideration: for example, the pH of the damping solution should be above 5.5 to ensure the best metallic effect. We recommend using 4% COMBIFIX 8039 (see TI 5.03 E). Damping should also be kept as low as possible, especially when ink transfer is also low, to prevent excessive emulsification, poor ink lay, and drying problems.

Aluminum-based gold printing inks are easier to classify in terms of printing characteristics than inks containing powdered brass, since the proportion of relatively coarse-grained metal pigment, which is not wetted as readily, can be kept much lower.

Any surface finishing, for example in order to improve rub resistance, will always reduce the metallic effect. The best solution is still to coat the surface with a dispersion varnish.

Printing black on gold printing inks

When printing is to be applied on top of previously printed gold inks, the peculiarities of the surface must be taken into account by using inks with special drying and adhesion characteristics. Special Black 49 N 5135 (coatable) has proven successful. These combinations also create the most favorable conditions for wet-on-wet printing. Subsequent printing should be made quickly so as to prevent possible drying problems.

Two-component inks

In this case, gold printing inks are mixed by the printer himself immediately before use, using bronze paste and bronze varnish. If it is performed carefully, i.e. without using high-speed mixers that can result in detrimental heating of the mixed material, this procedure yields the best possible metallic effect. Our recommendations for sheet-fed offset are as follows:

Paste Varnish

Rich Gold 46 G 2975 10 G 0010

Rich Pale Gold 46 G 2985 10 G 0010

Pale Gold 46 G 2995 10 G 0010

Copper 46 G 2999 10 G 0009

A special binding medium formulation for web offset printing is also available on request. A mixing ratio of 1:1 is normally recommended, but it can also be varied:
• More paste gives a greater metallic effect, but with slightly lower rub resistance.
• More varnish improves mechanical strength, but diminishes the metallic effect.

To improve opacity, Varnish 10 G 0010 is tinted with yellow or orange pigments. "Clear" Varnish 10 G 0011 can also be used for mixing; this yields a slight improvement in metallic effect.

Gold printing inks for packaging materials

Certain applications, such as printing onto food packaging materials, require the use of organoleptically neutral inks. The suitability of gold printing inks for these applications is limited, since regardless of the binding medium system selected, the metallic pigment paste has an unavoidable negative effect on organoleptic properties. Aluminum-based gold printing inks may be considered slightly better in this regard since the proportion of paste in the finished ink is lower.

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