Choose the way you want to print : spot color or CMYKOGV
Mixing the inks or mixing the dots
Achieving accurate, repeatable brand colours cost-effectively: Strategies for reaching perfect colour on waterless offset presses
By Pierre Panel, export sales manager, Codimag.
Article published in Labels & Labeling
Colour preparation is a stage of the label printing workflow where time and money are easily lost – irrespective of printing process used. Today, printers use different methods to achieve special brand colours. Some organisations have standardised process, using advanced software to create the colours of the PANTONE® Formula Guide (for example). Others might rely on the human eye, a formula guide, and a spectrophotometer to ‘mix and match’ until the colour target is finally achieved.
Both methods provide the basis for efficiency and repeatable quality, but in a supply chain when quality and the flexibility to supply labels or packaging on a ‘just in time’ basis are essential, an acknowedged, standardised process is needed for both customer assurance and cost-control.
Mixing the inks or mixing the dots, quite a question!
Color matching: the importance of standardising processes
Colour consistency is a basic requirement from brand owners who expect suppliers to meet targets of within 2 Delta E or sometimes tighter, to ensure a globally consistent look for their packaging. It is not uncommon for customers to demand a very precise brand colour to be supplied on a specific substrate, delivered at short notice, and have the printer produce the same result on repeat orders.
The PANTONE® Formula Guide is the most commonly accepted reference for colour precision. However, while the formula guide gives a target, using it alone is only part of the solution. First, the Guide is primarily suited for sheet-fed commercial offset applications with instructions aimed at printing on coated and uncoated papers only. Label and packaging printing, however, can involve different ink sets, plastic and paper substrates, and diffesring printing, drying and curing processes that all affect the resultant colour.
Furthermore, because everyone sees colours differently, a solution to achieving repeatable colour objectively involves dedicated software and spectral instruments used in strict adherence to press makeready procedures. Using these tools, operators are better placed to achieve the correct result on the press on the first attempt, minimising makeready time and material waste.
The two strategies for achieving colour are:
- “mixing the inks” – printing with direct PANTONE® (or other) colours using ‘InkFormulation’ software from X-Rite
- “mixing the dots” – using extended gamut printing with Esko Equinox or OpenColor from GMG
Mixing the inks : InkFormulation Software
InkFormulation software provides a fast, accurate and consistent ink formulation, storage, approval and retrieval solution, for offset, flexo, gravure and screen processes.
Designed for ink suppliers as well as printers, the software speeds up ink mixing and helping operators achieve accurate formulations for different substrates. The software can be used for flexo, gravure and screen as well as offset printing, and helps meet specifications, mix the right spot colours, and do it quickly and cost-effectively.
InkFormulation software performs calculations based on combinations of print surfaces and substrates using the profile supplied by the manufacturer for each base ink. This mathematical description of the behaviour of the ink on specific materials is made for each substrate and printing process.
The software then calculates a number of unique recipes for achieving the target colour, relying on base colours in specific quantities, differing by components or percentages. All recipes differ in their Delta E factors. The operator then formulates the ink according to the recipe provided and makes a draw-down, or physical proof, using a spectrophotometer.
The software compares the spectral curve generated by the measurement of the proof to the target. Slight corrections are usually needed, as the environment of the printing house will almost certainly differ from the ‘ideal’ of the ink manufacturer’s laboratory. Based on the curve generated, the software gives a final set of changes and the colour can be prepared for the press. Provided the press is correctly set up and materials conform to the quality standard, colour targets will be reached.
InkFormulation software automatically adapts recipes for different processes, so a printer can, for example, switch between flexo and offset and be assured of the same results, though the actual steps will vary. In offset, for example, ink film thickness is an important variable affecting colour results which can be limited by printing speed. The printer can use the software to analyse how colour results correlate with different ink thicknesses, rather than rely on ‘gut feeling’. With flexo, the formulation is fine-tuned by entering values for viscosity and anilox cell angles.
Results can also be adapted for specific illumination levels that affect how we perceive colour. Operators can also choose the criteria for measuring colour from the common Delta E based on L*a*b* 1976, Delta E 2000, LCH, and CMC, among others.
Mixing the dots: Expanded Gamut
The second strategy for achieving colour targets is by using three additional colours (orange, violet, green) plus CMYK for an “Expanded Gamut.” The software guides the user to choose the colours in specific proportions. Ultimately, Expanded Gamut is about variation of dot size and distribution. Common software tools for Expanded Gamut printing are Esko Equinox and OpenColor from GMG. It converts the colour into a maximum of three colours in a four to seven-colour printing process.
These software convert spot colours in the packaging artwork into standard colours, or adds one, two or three fixed colours to the colour palette. This combination covers the majority of PANTONE® Colours. It uses colour profiles and colour algorithms to calculate the colours. Thes softwares allow the operator to accurately see the colour builds with the expected Delta E result, so the best option can be chosen.
Depending on the substrate, one can achieve over 90 per cent of the PANTONE® Colour Book gamut with the same set of inks without specially formulated colours. Up to 60 per cent of colours can be built from CMYK alone to within a 2 Delta E tolerance.
Furthermore, with advanced editing functions, operators can choose the closest Delta E coordinate for direct tones, calculated from the colour profile. Colour separations are converted by assuring a colour coordinate without the risk of conflicting frame angles or problems relating to opacity. End results are enhanced with use of the correct high-definition plate and anilox roller.
As a result, using Expanded Gamut Printing, presses can use the same set of inks for every job, resulting in significant savings in operational costs. Most importantly, it eliminates the need to change inks and wash up after each printing run. This means substantially shorter make-ready time, and, because there are no leftover inks to deal with, ink waste is reduced and stock management is simplified. Savings can be increased when similar jobs, such as different variations of the same brand, can be run back-to-back without cleaning and adjustment.
Expanded Gamut Printing is available for offset, flexo, gravure, and digital (where spot colours can be very expensive to run), and can be built into Adobe® Photoshop®. Also, X-Rite has published the PANTONE® Extended Gamut Guide, giving a visual reference for printing a PANTONE® Colour in expanded gamut. This helps designers and brand owners decide when to select extended gamut, CMYK or spot colour for their packaging.
Printing with an increased number of colours does require careful press calibration to ensure tight registration.
Adhering to the procedure to restore efficiency and productivity
Whichever approach is used – and both provide the basis for efficiency and repeatable quality – the printer must standardise procedures throughout the workflow, with a method, and means of recording results and tolerance levels at each stage. It is important to have a calibrated colour testing system capable of simulating the printing of the label on the press to be used to ensure results correspond to the expectations of the client, and that the PDF file complies with these expectations.
It must be emphasised that the human eye is not a reliable way of judging colour: colour perception varies from person to person, because of physiological factors, tiredness, exposure to light, and lighting types and levels. Our colour memory can be unreliable, and optical illusions show that we see what our brain tells us to see, while Instruments provide accepted objective, measurable and recordable results.
Spectrophotometry provides the highest level of colour information, including colour curves, and the calculation of dot area, colorimetry and colour density. The spectrophotometer measures reflectance of each individual wavelength, giving the entire spectral curve. They are also used to check the quality and inks used for printing.
The imaging of plates also requires standardisation. Fortunately, recent advances in computer-to-plate imaging technology mean that offset and flexo printers can be assured of repeatable, high-definition quality.
Press makeready procedures must be strictly followed to ensure colour stability. For flexo printers, critical points are anilox and chamber cleaning, maintaining ink stability, and calibration of the plate and sleeve, secured with tape, in relation to the anilox, with the correct pressure setting. Traditional offset printers must take care to adjust the ink tank, blankets, capacity of the drivers, and ink key settings, which must be controlled with sensitivity.
Codimag’s Aniflo waterless offset: fewer variables, more stability
Aniflo printing technology is based on elements of both offset and flexo. It uses viscous, paste-like waterless offset inks and plates, but the ink is supplied in a manner similar to flexo. Ink is transferred from a chamber to the anilox roll, which then delivers a constant film of ink to a form rubber roller, which transfers it to the plate, then on to the blanket. There are only four inking cylinders, and thus a short inking path and a stable density along and across the web.
This creates consistent press conditions and, thus, colour quality. Thanks to a high level of automation, few moving parts, and a short web path, minimal manual intervention is needed. If needed, adjustments can be made to the anilox roll’s temperature – cooling it to thin the ink and reduce colour density, or heating it to thicken ink and increase colour density. Temperature is controlled at every point in the Aniflo process, so colour quality will not be affected by environmental changes, even in extreme climates.
There are no ink-water balance issues to address and no ink keys as used in conventional offset printing. Even when value-added processes are included inline, such as semi-rotary screen printing, or flat-bed embossing, Aniflo maintains a short web path. A dancer system compensates for speed differences that occur between the flat-bed or semi-rotary process and the rewinder.
The choice between Ink Formulation and Expanded Colour Gamut needs careful evaluation, as company culture, experience and available expertise will need to be taken into consideration. Choosing either colour strategy can give the label printer the confidence to expand into other market sectors with the knowledge that the most demanding targets can be reached quickly and on the first attempt.
Choosing one strategy and sticking with it will yield benefits in uptime, waste levels and the ability to assure the repeatable quality to ensure success. With the right procedures and equipment, Ink Formulation and Expanded Colour Gamut provide the structure and a rule book for measuring and explaining colour that can be agreed by the label printer, the label buyer, the packaging designer and the ink supplier, creating a framework for meeting expectations. Using the right tools, and a stable and predictable inking technology, such as Aniflo, would help converters to reach this goal.
About Aniflo Technology
Aniflo combines offset quality, flexo simplicity and digital flexibility. It features an offset unit, with offset plates and a simple anilox delivery system that brings a uniform ink amount across the web. With low operational costs, Aniflo is an economical choice for high-definition quality short and medium runs on any commonly used label substrate – filmic or paper. Plate costs and imaging times are very short: all plates for the press can be prepared within about 15 minutes. Because it is intermittent, fewer consumables are needed, making Aniflo suited for short and medium run work. The high definition capability and superior stability means Aniflo can print in extended gamut, offering over 90 percent of the PMS colours without any need for ink changes and consequential washing.
For 40 years, Codimag has designed, manufactured and sold printing presses with high added-value at its facilities in Bondoufle, France. Today, it is the world leader in intermittent waterless offset label printing. Codimag offers solutions tailored to label printers’ needs with a high level of innovation, both in terms in technology and application, making its presses productive and cost-effective for many different markets. With a worldwide network of agents, Codimag is able to take its technologies around the world, and support its customers in a profitable, long-term relationship.
For further information, please contact Pierre Panel, export sales manager, Codimag
Adrian Tippetts, Tippetts & Partners Ltd, Telephone: +44 (0)7799 14 18 42; Email: Adrian@adriantippetts.com
Read the full article published in Labels&Labelings.