What happens during the manufacture of inks? What issues must be considered when discussing inks for the narrow web market? The editorial team of NarrowWebTech investigates the often underestimated issue of inks and their manufacture by reporting from a visit at Siegwerk’s facility in Aarberg, Switzerland.
Written by Rosina Obermayer
The majority of printing inks are pigment-based, although soluble dyes are used, for example, to stain/colour textiles, leather or even foods.
Siegwerk Narrow-Web manufactures inks for this market in Bargen, Switzerland. Siegwerk has its headquarters in Siegwerk, Germany, with more than 1000 employees it is one of the biggest ink facilities in Europe. In their Swiss facility in Aarberg, Siegwerk Narrow Web produces about 2400 products and approximately 1400 different ones.
The manufacturing process and the specifically developed machines play an important role and are responsible for the final quality of an ink. The fineness, the wetting of the pigments and their stabilisation through the binders and the homogeneity of the composition are very important parameters in the ink manufacturing process.
Basically, the composition of an ink consists of pigments, binders and additives. The question is what is the perfect ink formulation? The company says that the choice of the right type and mixture ratio of each compound is based on past results in an optimum ink formulation.
UV ink manufacturing
Coming back to how inks are produced, it is remarkable how many different components are involved and how each one of them reacts to the other.
There are several different operations involved in the manufacturing of inks:
- Weighing
- Blending
- Milling
- Quality control
If low migration ink:
- Analysing before filling
- Filling, labelling and logistics
Pigments
It is also possible that inks can be dye-based but in contrast to dyes, which are soluble, pigments contain insoluble particles. Pigments are subdivided into organic and inorganic pigments. Therefore, pigment-based printing inks involve a suspension of solids in a liquid. If inks containing these pigment particles whether dry or set, the pigment particles are enveloped by the binding agent and kept in place. Because pigment particles are relatively large, they can’t move freely within the dried ink film environment, which generally prevents migration.
If inorganic pigments are concerned, the structure of the pigment does not contain any hydrocarbon compounds. They are usually mineral products, such as titanium dioxide, which is by far the most common white pigment. Inorganic pigments also include iridescent, mica- or silica-based pigments.
Organic pigments involve different chemical compounds, the basic structure of which is based on a hydrocarbon backbone. Pigment-fineness is another very relevant factor in the manufacture of pigment-based inks. To enable a pigment to release its colour intensity to the full, it first of all has to be enveloped and coated by the binding agent system (e.g. UV resin or acrylic resin). Second, it has to feature the required fineness (= particle size). Usually the particle size target is between 0.5 and 1 micron but in any case particles may not be larger than 10 μm. If the pigments are not sufficiently fine (> 10 micron), faults can occur during printing.
The pigment can be sufficiently coated by mixing the dry pigment with the binding agent to form a kind of “paste” and milling or grinding it using either a pearl mill or a three roller mill. In order to accelerate the process, a dispersant, which ensures quicker and better coating of the pigment, can be added.
Dyes
Dyes are chemical compounds, which have the characteristic of colouring other materials and which occur in a solute state in the application medium. This does not involve any kind of dispersion as with pigments, but instead a so-called true solution of the dye in the liquid application medium, which consists of a solvent, an aqueous solution or binding agent.
When talking to Siegwerk, they say that pigments are generally more resistant (permanent) than dyes. Resistance (permanence) can be tested using a range of different test media, such as acids, bases, fats, oils, solvent mixtures or hydrogen peroxide, always provided that the binding agent itself (UV binding agent, aqueous solution, solvent) can withstand the test medium.
Another question is: how does the manufacture of an ink continue currently? Prices for raw materials are increasing more and more, causing a price increase. What is becoming more relevant in this segment is the customer’s support. Which ink is the most suitable? If a customer wants to change the colour, e.g. to low migration inks, what must be considered?
Quality control is a relevant part if manufacturing inks, especially low migration inks (Source: Siegwerk)
Summary
Visiting Siegwerk Narrow Web in Switzerland showed up at least three things: 1) the manufacturing of inks is not easy. Different stations are involved in the production at each station a range of issues has to be considered.
2) Although inks are a basic part of printing labels and packaging, the market is changing all the time. Migration and UV are discussed more and more and that is just a small part of the market trends and developments within the recent years.
3) Eventually, never underestimate an ink manufacturer. The receipt, the quality control, the logistics having the ingredients and also in this niche, the service is becoming more relevant by having e.g. a good customer support.
This article was first published in NarrowWebTech issue 3-2018.