Special effects inks, varnishes and coatings

It should be noted that there are a wide range of inks and varnishes available that are able to perform dedicated brand protection tasks, adding layers of security to a product, protecting them against counterfeiting, theft or tampering.

The focus of this article will therefore be on inks and varnishes that have a decorative appeal, as well as perhaps a functional one. 

MATT AND GLOSS VARNISHES

Perhaps one of the simplest decorative effects that can be achieved is by printing gloss or matt varnishes onto the surface of a label.

A varnish is a clear ink containing no coloring pigments. When printed or coated over the top of a printed or unprinted substrate in-line, the varnish gives a protective matt or gloss finish that enhances appearance and increases durability.

Varnishes are suitable for water-based, solvent or UV applications.

There are a number of varnish types available;

• Matt

• Gloss

• Semi-matt

Where the entire surface of the label is covered with a varnish, this is known as a ‘flood coat’.

SPOT VARNISH

Spot varnishes are typically printed in register to the label design. A clear matt or gloss varnish can be applied to specific areas of a printed label to improve the visual appeal of the label surface and in some cases provide surface protection, or improve slip or grip. The contrast between a matt and gloss varnish printed over a label surface offer interesting light refractive effects that can provide visual appeal (see Figure 10.1).

LACQUERS

A lacquer is a clear resin/solvent coating, which may be glossy or matt, applied to a sheet or web of printed labels, to provide protection or resistance against scuffing, rubbing, chemicals, moisture, etc.

Carried out as an off-press operation, lacquering is performed on a machine equipped with a roller coater, after the inks have been dried. Since lacquering is a separate operation, using expensive materials, it significantly increases the unit cost of the labels.

High performance UV lacquers are available in both matt and gloss.

It should be noted that glue-applied cut single labels, when they are printed using the gravure process, tend to use water-based or solvent-based lacquers.

This process can however increase the tendency for the label to curl, which can result in problems during application to the container.

TACTILE VARNISHES AND RAISED IMAGES - APPEALING TO A WIDER RANGE OF SENSES

Inks and varnishes can also be used to enhance the visual and sensory appeal of the label or pack.

Textures are becoming an important aspect of packaging design. New materials and processes offer designers opportunities to add a tactile quality to their packaging thereby appealing to a consumer’s sense of touch.

Particularly popular are textured or raised surface effects. These are achieved by using special tactile inks that produce a relief effect similar to embossing (Figure 10.2).

The most popular way of achieving a texture finish is by using a special tactile ink delivered using the screen printing process. UV rotary screen is particularly effective as it can deliver up to 300 micron deposits in one pass (Figure 10.3).

BRAILLE

Textured or raised image varnishes can be used for printing Braille. Raised image tactile warning labels can be printed on a label surface to alert blind or partially sighted people to the potential dangers of the contents of drugs, medicines, hazardous chemicals, aerosols, etc. and distinguish them from harmless products.

Raised tactile labels for the blind have also been developed and used for wines and spirits (providing information on alcoholic strength), groceries and other consumer products.

Some countries have also introduced legislation (e.g. BS EN ISO 11683: 1997) that states that all labels sold to the public which are labeled ‘very toxic’, ‘corrosive’, ‘toxic, ‘harmful’ or ‘extremely flammable’ must by law have a tactile danger warning label included, to alert the blind or partially sighted that they are handling a dangerous product.

These warning labels consist of a raised equilateral warning triangle or three raised dots forming the points of an equilateral triangle. The labels may be either incorporated into an existing label design or applied as a separate label (See Figure 10.5).

For mass production of tactile warning labels on consumer products the label industry has developed a number of solutions, notably rotary screen printing units incorporated into a roll-label press can print deposits of up to 300 microns in thickness to provide the required tactile effects. Some converters are using a tactile varnish to print dots of precise dimensions (125 microns high and less than a millimeter in diameter).

OTHER VARNISH EFFECTS

There are other varnishes which are being used that can add a tactile quality to the label surface, thereby appealing to the consumer’s sense of touch.

‘Soft touch’ label varnishes (and materials) for example, are able to convey a warm velvety feel that can compliment a brand in certain markets. Soft touch varnishes are of low viscosity and therefore well suited for use on flexographic printing and coating units.

Grip varnishes have a ‘rubbery’ feel and actually increase their grip potential when wet and have therefore been used in the beauty care sector on products such as shower gels.

SCENTED PRINT - SCRATCH AND SNIFF

Appealing to the consumer’s sense of smell, scented print or ‘scratch and sniff’ applications (as they are often referred to), add a new dimension to product promotion. In the toiletries sector for example, scented inks allow the user to pre-sample perfumes prior to purchase by scratching or rubbing a printed panel on the label to release the fragrance.

The preservation of fragrances on printed matter uses a technique called micro-encapsulation.

Fragrance capsules are mixed with an overprint varnish or ink and applied with an additional print unit on the press, so offering an economical solution for printing scents in combination with high quality printing.

Being encapsulated, the scent will not evaporate until the capsules are rubbed.

PEARLESCENT DISPERSIONS

Inks or varnishes using pearlescent dispersions, based on the natural mineral mica, can create a unique lustrous effect on the surface of a label.

Mica particles or flakes are typically coated with a thin layer of metal oxide, such as titanium dioxide and/or iron oxide, to achieve a metallic sheen. The interplay of transparency, refraction and multiple reflections produces a spectrum of effects and colors - silver-white, gold and metal lustre (see Figure 10.6).

Pearlescent pigments produce their lustre through light being reflected, refracted and scattered when hitting the multiple surfaces of the pigment.

Due to particle size of the pigments, pearlescents are better suited to printing through a screen or flexographic unit. Pigments can be used alone or in combination with other colors.

GLITTER INKS

Glitter Inks are made of multi-color metallic flakes suspended in a clear varnish or ink which can be can be applied to all or just part of a label design.

Glitter inks are available in a wide range of colors.

IRIDESCENT INKS

Iridescent inks change color when viewed from different angles. The ink is colored with newly developed liquid-crystal polymers instead of conventional dies and pigments and is a mixture of two different liquid crystal components that can be cured with UV light.

The inks must be printed on top of another color for the effect to be obtained; the best results being achieved when printing on a black background.

Maximum effect is obtained when a heavy deposit of ink is used.

Applications are in the packaging of cosmetics, beverages and pharmaceuticals.

THERMOCHROMIC AND PHOTOCHROMIC INKS

For information on thermochromic temperature change inks and photochromic light reactive inks.

FLUORESCENT INKS

The printed effect of using fluorescent inks is to add brightness and luminescence to the image printed on the label (See Figure 10.7).

The pigments in fluorescent inks absorb ultraviolet energy invisible to the human eye and then transmit them back as longer waves in the visible spectrum.

Fluorescent inks can be printed in either visible or invisible forms, which change color when subjected to shortwave light or long-wave light.

Historically these inks have been used for fraud protection, but are now used for promotional and other applications. The availability of pigments (short wave) for fraud protection is strictly controlled to preserve the authenticity of such inks.

For some applications , Cyan, Magenta, and Yellow process inks can be replaced with their fluorescent equivalents to create high impact graphics.

Originally limited to screen printing, the pigments now have sufficient strength to permit colors to be printed in one impression by lithography, flexo and gravure.

INVISIBLE FLUORESCENT INKS

These inks are invisible under normal lighting conditions, but glow in a variety of colors when exposed to UV light (Figure 10.8).

PHOSPHORESCENT INKS

Commonly known as ‘glow in the dark’ inks, phosphorescence occurs when a compound, after excitation ceases, continues to glow for a finite amount of time. This period of continued light emission or ‘afterglow’ will range from a few milliseconds to some hours.

This phenomenon can be used to characterize phosphors, or as a trigger in a machine readable system. They can also be used for promotional or decorative purposes. Items printed with photo-luminescent pigments have to be first charged in ambient light to allow them to then glow in the dark. The ink is transparent and can be printed by the screen or flexographic process.

Phosphorescent Inks will emit a green or in some cases a pale blue glow.

OPTICALLY VARIABLE INKS

Optically variable inks (OVI) are inks which appear to change color when viewed from different angles. These inks go from a color to clear depending on the angle of the light.

Sometimes known as the ‘flip-flop’ type, OVI inks contain flakes of special film and are most effectively applied using a very heavy coating weight which can only be achieved using intaglio or screen printing.

There is a range of gravure and flexo printed optically variable inks which give reasonable effects.

OVI inks are expensive and are extremely difficult to replicate and are therefore used as an anti-reproduction device, for visual verification and protection against counterfeiting.

SCRATCH OFF/RUB AND REVEAL INKS

Scratch-off inks are often used in ‘scratch and reveal’ type promotions or competitions where a hidden message or symbol is revealed (Figure 10.9).

An opaque coating or ink is applied to a specific area on printed matter to hide the details underneath. The hidden details are revealed when the coating/ink area is removed by scratching or rubbing with a fingernail or coin.

Scratch-off inks are available in UV and water-based formats and are typically printed over a release barrier which helps the removal of the opaque scratch-off layer.

In security applications, related ink systems are often referred to as ‘Rub and Reveal’.

Patented ink security systems such as that on offer from Nocopi are impossible to replicate.

Any paper-based document, tag, ticket or receipt can be secured using this versatile ink, which can be printed using the flexo process.

With ‘Rub & Reveal’ ink there is no need for special equipment to authenticate a document. After the ink is rubbed or scratched it uniquely changes colors thereby offering both physical and chemical verification.

COIN REACTIVE INKS

With this type of reactive ink a coin is used to reveal a hidden image.

The pigment in the ink reacts with the metal of the coin to produce a grey color when scratched. A typical use would be for promotions where an invisible message is revealed when the consumer rubs an indicated panel with the edge of a coin (Figure 10.10).

SUMMARY

Find below a summary of the recommended processes for printing speciality inks. (Figure 10.11)