Reflex Blue is one of the most commonly used spot colours — especially for corporate colours — and it is one of the most problematic inks to use on press.
Singing the blues
Reflex Blue is a very deep blue-violet colour. It gets its rich colour from a family of pigments referred to as Alkali Blue pigments, which includes the mineral cobalt. These minerals are very strong in colour and gives Reflex Blue its deep blue hue. Unfortunately, it suffers from excessive marking, low scuff resistance, poor lightfastness and poor, very slow, drying qualities. It also has a bronzed look that causes it to shift colour, from Blue to Purple when viewed at different angles (see illustration on right).
And when mixed as part of another blue spot colour, Reflex Blue effectively contaminates that ink colour with its poor performance characteristics.
Reflex Blue blues – slow drying
Printing inks are made primarily with resins, varnish, linseed oil, soybean oil, or a heavy petroleum distillate as the solvent (called the vehicle) combined with organic pigments. The resins and varnish control the tack (ink tack refers to the stickiness of the ink or the force required to split an ink film from one surface to another) and gloss of the ink while the solvents control press stability and fluidity. Drying oils control surface strength, drying time, and set, while the pigment acts as the colouring agent.
Although each ink pigment is unique, most have fairly uniform shapes and surface areas. Reflex Blue pigment on the other hand has jagged, irregular surfaces and shapes. At the molecular level, the porous pigments act like little sponges. To blend Reflex Blue ink, ink manufacturers must add surface active agents to the mix that allow proper wetting of the pigment. As a result, the ink retains a higher level of moisture than other ink formulations and therefore takes longer to dry.
Offset inks are generally designed to dry by two methods: absorption into the paper and evaporation from the surface. As the ink dries, the small, uniform colour pigments settle close together and leave a flat ink film surface. However, when Reflex Blue pigments set, they have a rough ink film surface. Although the ink may feel dry to the touch, just a light rub will break the surface and expose the wet pigment underneath. This results in unsightly scuff marks and colour transfer (set-off) to surfaces that come into contact with it.
Reflex Blue blues — colour-shift/burn-out
Reflex blue colour-shift or “burn-out” can occur when the printed ink film is over-coated with aqueous, or UV coating. This effect results from a chemical reaction due to pH incompatibilities between the alkaline aqueous coating and certain alkaline sensitive ink pigments like Reflex Blue. The chemical reaction basically changes the way the colour pigments reflect light. Individual press sheets pulled during the press run or top sheets in the pile are rarely as affected as the sheets within in the press loads. This indicates that heat and oxygen deprivation are contributing factors in accentuating and accelerating, the colour-shift effect. Unfortunately the colour-shift may not be apparent immediately off press and may take 24 hours or longer to be noticeable.
Tips for subduing the Reflex Blue blues
1. Don’t use it.
If that’s too drastic then consider reformulating an “imitation” Reflex Blue ink substitute from the ink supplier. The most common is a Carbazole Violet & Phthalo Blue mix. Note that the imitation Reflex Blue may have a slightly different hue than the actual Reflex Blue.
Or select a Reflex Blue colour substitute with less Reflex Blue in its ink formulation from the Pantone Colour Formula Guide.
2. Use UV inks.
Print the job using UV inks since they dry immediately. UV inks cost more than conventional inks.
3. Stack small lifts.
Shorter stacks of paper at the press delivery facilitate faster drying by allowing more air to circulate between sheets enabling gasses to escape. Shorter stacks will add extra run time on press. The printed loads are winded as soon as possible to reduce unnecessary exposure to high heat builds captive in the pile.
4. Allow extra drying time.
We can schedule the job to print on Friday to allow the sheets to dry over the weekend before printing the second side or sending the presswork to the finishing/binding processes.
5. Reformulate the ink.
Check with us to decide whether reformulating the Reflex Blue ink by adding drying agents is an option. Note that doing so may increase cost and/or compromise the inks on press performance in other ways e.g. it may adversely affect the quality of screen tint areas.
6. Seal the ink.
Apply a varnish or aqueous coating to help seal the ink and eliminate scuffing, fingerprinting and bronzing of larger ink areas. We will make sure that the coating to be applied has been thoroughly tested before running the job.
Other alkali sensitive pigments that can have similar issues to Reflex Blue include:
• Rhodamine Red
• Warm Red
• 072 Blue
• Rubine Red
• Fluorescent inks
This article is a repost of a blog entry from The Print Guide.
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