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Automating ink logistics

Gaining operational efficiencies with automatic ink mixing

Ink accounts for about six percent of the operational costs of a typical label printing business. But that figure greatly underplays the value that controlled, integrated and automated ink logistics brings, not to mention the potential for lost value. 

Inks are either supplied pre-mixed to the converting plant, or are mixed on site.

Manual mixing of flexographic inks to match a particular pantone color is a long-established process in the label industry. Inks are weighed out according to ‘recipes’ then the color is tested, either by eye, or with a spectrophotometer and possibly a testing rig, involving a miniature flexo print station (see article on Testing, proofing and quality assurance).

Once at the press, the ink tray is filled manually. 

Narrow and mid web presses increasingly make use of chambered doctor blade systems where the ink is pumped directly from the bucket into a sealed chamber that inks the anilox cells directly rather than via an ink tray and meter roll.

After the job is printed, leftover (return) inks are labeled before being placed into a storage area.

There has been a major move to automate many stages of the ink logistics workflow from color matching and mixing, to recycling of ink returns. Integration with management information systems (MIS) for complying with traceability requirements for GMP or BRC is also a task well-suited to automation rather than manual form-filling and filing systems.

Automated ink logistics (see Figure 7.1) starts from the idea that inks are dispensed based upon recipes of base components. Leftover inks coming back from the press are weighed in before being returned to storage, and these ink returns can be recycled into new color formulations. To understand how this dramatically reduces waste, consider how value is lost with no system in place: it is not uncommon to see a converter’s ink store full of partly used ink containers that are eventually thrown away if that exact color is not used again on a customer job. 

Figure 7.1 In-house ink logistics

Another waste-saving benefit is eliminating overproduction.

Typically, in a manual ink mixing operation, the ink shop manager might buy 5kg from the ink supplier when only 3.8kg is needed for the print run, with the balance being wasted. Automated dispensing, from an ink stock inventory of base components, allows only the exact volume to be dispensed according to the job requirements.

Buying in base components instead of using ready-mixed inks is generally more economical and also saves on transport, warehousing and administration costs and avoids the need to check deliveries for defective batches (see Figure 7.2). 

Figure 7.2 Trend towards standardized ink formulation
THE INK DISPENSING PROCESS
 
The basis of automated ink dispensing is building recipes from base components, which might be base colors, extenders or a technical medium. This ties in to a trend towards standardization in the label ink industry.
 
The benefit is that the converter has instant availability of all colors, and in the precise quantity for the job. The converter does not have to keep buying ready-mixed colors. Also, the software helps in the management of the ink supply chain. Ordering of base components is handled by an MRP system based upon future manufacturing requirements, with the software automatically generating purchase orders once stocks of a base component fall below a certain level. Both new ink deliveries and ink returns can be scanned with a barcode into the system.
 
In some cases, the automated ink dispenser is closely integrated with MIS, bringing together the technologies, for example, of GSE and CERM.
 
Historically, narrow-web ink manufacturers used single-component ink systems, with pigment colors pre-mixed with the technical medium. Today the trend is to keep the (mono-pigmented) colors separate from the technical medium, giving the converter more flexibility. This means the same base colors can also be used for reverse printing, simply by adding another technical medium. This also gives a wide choice in color mixing. An example might be a recipe which uses one technical medium and two colors – yellow and red making an orange – which are mixed and dispensed automatically. 
 
The ink type adds certain requirements to an ink storage or dispensing system. Solvent-based equipment has to be explosion-proof, to ensure that solvents cannot explode during dispensing. 
 
For UV or LED-UV systems, equipment like pumps must be blacked out to prevent UV light entering the inks and starting the curing process before the inks have even been dispensed. Viscosity and rheological characteristics are important factors that determine valves and pump selection. In some cases, extra agitator should be fitted, to ensure base components comply with these material specifications. 
 
The batch size is another important consideration. In narrow web label printing, batches are usually from five to 10kg, while for larger format presses or chambered doctor blade systems, batches can be anywhere between 20kg and 200kg. 
 
Other factors will include production capacity and the number and type of base components. 
 
Usually, for label applications, at least 12 to 14 components are required. 
 
LEFTOVER INKS
 
Leftovers, or press return inks, can account for up to one third of the amount of dispensed ink. Ink management software allows these inks to be recycled into new recipes. As an example, press returns of Coca-Cola red could obviously be recycled into a new batch of that special color. But, since we know the recipe of the color – this Coca-Cola red consists of maybe warm red with some yellow and orange – we can use this to make a color like a Nestlé orange, with the same base ingredients. The software guides the operator through this process. 
 
Another way of working is to collect the returned inks in ‘Clusters’ of colors. Ink management software can for example help to collect all the blue return inks with the same base ingredients. The collected inks are dispensed to a large container, typically a 200 liter vessel, and color formulation software can determine the recipe of this blue ‘Cluster’ ink. This helps the converter recycle those return inks automatically, without retrieving every separate bucket from the returns storage. 
 
It is also possible to use substitutes – for example, a recipe with a high-quality varnish can be recycled into recipes with a lower quality varnish (but not vice versa). 
 
COLOR FORMULATION 
 
Automated ink logistics can be implemented in stages, starting with an ink dispensing and ink management system, then integrating with color formulation software.
 
Color formulation software can be used as a quality control tool for deliveries of base components.
 
Samples of new colors can be made either by using a theoretical formula, or by a process of component dispensing. For example, the system can dispense the warm red, yellow and varnish, and the resulting color is then measured either using the operator’s experience, or with a spectrophotometer and color formulation software. If the color is not correct after measurement, the operator can add ingredients until the recipe is correct. Then that particular recipe is stored in the database. Even these leftovers from sample buckets can be recycled into new ink jobs providing everything is properly registered.
 
An automated dispensing system can work in parallel with a desktop proofing system (see article on Testing, proofing and quality assurance) to make sure all inks are tested before they go on press together with the correct substrate and anilox roll.
 
This creates a parallel process to the primary process of printing as part of a lean workflow. This is important to increase press uptime by not correcting color on the press itself. 
 
If adjustments need to be made to the ink recipe – for example because of substrate variability they can be done either manually or with the help of color formulation software. Regardless of method used, it is critical to register those corrections. If the operator corrects the color without ‘telling’ the software, all traceability is lost – the color cannot be automatically reordered and those returns cannot be recycled because the recipe is no longer known. 
 
TRACEABILITY
 
Ink management software is a key tool for establishing traceability as a part of good manufacturing practice and to comply with industry accreditation schemes such as GMP, BRC/IOP and ISO. For pharmaceuticals, ink batch expiry dates now have to be registered, and any return ink use must be traceable. 
 
Traceability has two aspects: the final product that goes to the customer, and the ink batch coming from the ink supplier. Ink management software gives instant access to information about those batches during the print run and throughout the complete workflow. 
 
A traceability report will tell the converter which particular batch of blue, for example, has been used in a particular dispensed container or sales order, or which return inks contain the blue from this particular batch. 
 
If there is a problem with one particular batch, converters can also access information about the batches which have been connected to the dispenser previously and after this batch. This helps determine where the problem lies. 
 
Looking to the future, automated ink logistics will increasingly support Industry 4.0 or ‘smart industry’ systems. This involves, in addition to the described color formulation software interface, integrating with MIS/ERP systems. In the future this could also include communicating with mobile apps or the press itself to reorder inks or automatically determine ink returns using load cells integrated in the press.
 
Ink dispensing systems can reduce ink costs by up to 30 percent, and deliver improvements in process control, color consistency, waste reduction, increasing press uptime and traceability. They can also prevent rework and human errors by integrating ink logistics into the print shop workflow.

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