Effortlessly reusing press return inks for spot colour printing: a best-practice guide

A gravimetric ink dispenser and software makes it easy to reuse ‘return’ inks for spot colours in label and packaging printing – bringing big cost reductions. We explain how.

When you’re using flexo, gravure or screen processes, not all the ink that you prepare for a job will get printed on the substrate. After the job, some ink is left over in the press – inside the ink chamber and supply hoses, for example.

The ‘CMYK’ process colours can normally be left where they are for the next run, as they are permanent fixtures of the printing sequence. However, spot colours that are specially formulated for a particular brand must almost always be drained from the press.

These ‘returns’, as we call them, typically amount to 7kg per printing station on a wide-web press. Over time, they will accumulate fast, especially when shifts are loaded with short and medium runs – so it’s critical to reuse them as much as possible if you’re serious about protecting profit margins.

Using a gravimetric ink dispensing system with a weighing scale and dedicated software, you can reuse returns in new jobs, trace them, and keep the ink storage room in the kind of order a librarian would be proud of. Here’s a step-by-step guide, using the GSE Return Ink management software module.

Setting up: create a system for storage and ID of return inks

If you’re starting to re-use returns for the first time, it’s important to create the conditions for orderly, efficient processing – and a culture where it becomes a habit.

  • Designate space for storing return inks in an orderly fashion.
  • Design a storage system: this can be numbered shelves, or ‘indexes’ for multiple rows of containers on a single shelf. You will need to log the storage location for each returned container on the system for fast retrieval.
  • Install a barcode printer and reader, to print a label and swiftly identify a container of returned ink.

We advise appointing an ink room manager, responsible for creating and maintaining a policy of returning inks during production shifts.

The continuous press return cycle

Let’s imagine a printing run for a cola package. One of the colours for this job is a special red colour (“cola red”), of which 20 kg is required. This batch can consist of one or more containers, depending on the container size that you use. The ink management software gives each container a unique ID number, and the cola red batch is dispensed. For each container a label is printed with the container ID and job details, as well as exact weight and ink formula, for easy traceability.

Stage 1: booking in the return at the end of a run

The print run has finished, and the 7kg of the cola red remains in the press. You must book this in as follows:

  • Pump the remaining ink into a bucket.
  • Open the Return ink management software programme and scan the label, to retrieve details about the container.
  • The software specifies a storage location for the returned batch. Weigh the container on the dispensing system’s weighing scale. The software calculates the nett return weight (deducting container and lid weight from the total).
  • Print a new label providing content data including the formula code, container ID and return ink weight and apply to the bucket.
  • Store the container in the designated location.

Stage 2: choosing returns in a new spot colour job

Whenever a new spot colour blend is to be made, the software program prompts the user to choose from a list of usable returns already booked into storage. It lists the available returned inks that contain the ingredients needed to make the new spot colour. It also highlights stocks with the earliest expiry dates, to avoid obsolescence.

Let’s assume we receive an order to print a package for an orange soda brand. It requires 20kg of special orange colour ink (“soda orange”) and that we want to reuse returns.

Option A: REUSE – directly book out a return – no added ingredients

The simplest method of reusing inks is by using return stocks that have exactly the same formulation as the required spot colour, in our case “soda orange”. These are marked on the screen with an asterisk. There is no need to do any new dispensing: empty the contents of the return ink bucket into the press’s supply system.

Option B: RECYCLE – choose returns for mixing with other ingredients

However, if we can only choose returns whose formula is not an exact match of the required spot colour, then dispensing will be necessary.

As above, there is a list of return inks, each with different formula codes to choose from. We now choose the 7kg stock of the cola red that we have booked in at stage 1. Once selected, the system will automatically calculate the amount of fresh ink to be dispensed, in order to hit the soda orange colour target. It is possible to use more than one return container for a job, but this is not relevant to our example.

The mathematical method for formulating new spot colours with returns

Informally, printers talk about ‘recipes’ for making spot colours, but strictly speaking, it’s a formula. A formula is a fixed set of ingredients, represented by percentages of total weight. Making colour according to a formula assures consistency when we perform and repeat the job – regardless of scale.

To ensure consistency, therefore, we must use a mathematical method for making new spot colours with returned inks. Not only is this method the most reliable, it is the easiest and most time-efficient way to get precise colour results ‘first time right’ and ensure full traceability.

In our example we require 20kg of “soda orange” ink. We will use the same formula as described in our “basics ink dispensing” blog. The software suggests formulating this batch by using:

  • 7kg of cola red we have in our return stock
  • 13kg of a fresh ink formulation

20kg ink
7kg return ink
13kg fresh inks

Because we know the exact proportion of each ingredient in percentage terms, we can know the exact weight of each ingredient needed to make the target orange colour.

To determine the exact weights of the ingredients we need in the fresh ink formulation, we subtract the weight of each ingredient used in the return (column B) from the weight requirements of the target orange colour (column A).

For instance, the varnish requirement in the orange colour is 45%, and therefore 9kg of the 20kg batch. The cola red ink is also made with the same percentage of varnish, which equates to 3.15kg of the 7kg batch. Therefore the varnish requirement in the new 13kg formulation must be (9.00 – 3.15)kg = 5.85kg.

The return selected for a new spot colour must contain at least some of the ingredients of the target colour – but no unwanted ones. No matter, therefore, that yellow is missing in the red batch above – so long as we compensate for that in the fresh formulation.

The GSE Return ink management software performs these calculations in an instant, even when multiple return containers are recycled.

Stage 3: blend ingredients

With the cola red selected, it is time to blend the precise weights of ink together as prescribed, according to the soda orange formula. Follow instructions given by the software program:

  • Place the designated dispense container with return ink on the weighing scale.
  • Based upon the actual weight of the return ink, the system automatically calculates how much fresh inks need to be added to reach the requested formula and dispenses these fresh ingredients.
  • Print a label for the container.

The blended soda orange is now ready to be taken to the press. Once the job is complete, the remaining return ink is drained from the press, weighed, given a label and booked in to storage as explained in stage 1.

Following these steps, reusing press returns for spot colours becomes an orderly, effortless and continuous cycle, where big long-term savings can be made and ingredients are easily traced to each job – over and over again.

In a next blog we will look at how we can collect return inks into drums. These can be connected to the dispenser in order to automatically recycle the returns into new jobs (otherwise known as the “cluster” method).

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