Ink Types used in Wide Format

There are several different types of ink  used today in wide format printing. All perform the same task - colour on a page - but each method has it's own strengths and weaknesses. Understanding those when discussing a job will ensure you get the most appropriate ink type for the work in hand.

1) Aqueous inks.

Aqueous refers to the liquid that carries the colourant. Water. Water based inks come in two varieties, dye and pigment, often referred to, confusingly, as Dye and UV.

Dye inks are best though of as cordials - the colour is dissolved in the water - and like spilt cordial the ink soaks in and stains the page as the water evaporates. The colourant size in dye inks is tiny, allowing a very small dot size which allows for detailed images with smooth tones. The smooth surface of the dried ink reflects light accurately - leading to bright punchy colours. The trade off for these bright punchy colours are two fold. 1) Dye inks will fade in UV light. (If you were to leave a dye print in the window of a shop it would show noticeable fading or colour shift within a few weeks.) 2) If you pour water onto a dye print the colourant dissolves in the water again, and washes away, or runs. So Dye inks are not waterproof. Dye inks - suitable for dry environments for either short term use in UV Light, or indoor lighting only. Primarily therefore, used for short run promotional work, and portable indoor displays such as roller and pop up stands. Use where image quality and striking colour are critical. Pros: Strong punchy colours, small dot size = high quality image. Cons: Not waterproof, fade in UV light.

Pigment (UV) inks - best thought of as chalk dust suspended in water. The colourant particles are bigger than those of dye inks, but not by a great deal. They remain small enough to give a small dot size, and a good high resolution image. However, when the ink is on the page the particles are left on the surface, like a miniature mountain range. When light hits this rough surface it is scattered, which leads to a slightly muted colour response.  

So why use Pigment inks over dye. You guessed it, once dry if you pour water over pigment inks the particles will largely remain behind on the surface, so the print is considered short term waterproof. But most importantly, the pigment inks are stable in UV light. That's the main time to switch from Dye to Pigment, where you want the image quality you associate with Dye inks, but you need the stability in UV light. Window displays, or longer term promotional work. Pigment inks - suitable for all the work you'd use dye inks for provided you don't mind very slightly muted colours. In addition, suited for work displayed in direct sunlight, and short term outdoor work. An important point to remember is that aqueous inks, dye or pigment, are only used on media manufactured with a special ink receptive coating. This adds cost to the process. So an additional trade off is the cost of ink and media.

2) Solvent Inks

The next category is Solvent inks - but this is where the categories get a little confused. Solvent inks are generally pigment inks. They contain pigments rather than dyes, but unlike the Aqueous version where the carrier is water - in solvent inks it's volotile organic compounds (VOCs) - solvent.The chief advantage of solvent inks is that they are comparatively inexpensive and enable printing on flexible, uncoated vinyl substrates, which are used to produce vehicle graphics, billboards, banners and adhesive decals. Unlike the aqueous inks, prints made using solvent-based inks are generally waterproof and UV safe (for outdoor use) without special over-coatings. Solvent can offer excellent punchy colours, albeit often not as strong a aqueous dye inks. The key pro though is the durability of the print, offering excellent outdoor life.Hard solvent ink offers the greatest durability without specialized over-coatings but require specialized ventilation of the printing area to avoid exposure to hazardous fumes. Mild or "Eco" solvent inks, while still not as safe as aqueous inks, are intended for use in enclosed spaces without specialized ventilation of the printing area. Mild solvent inks have rapidly gained popularity in recent years as their colour quality and durability have increased while ink cost has dropped significantly. Pros: Excellent durability, excellent stability in UV Light, low cost. Cons: Inks need careful handling/disposal/ventilation at the print stage. 

3) UV Cured Inks

UV-curable inks: After printing, the ink is cured by exposure to strong UV-light. The advantage of UV-curable inks is that they "dry" as soon as they are cured, they can be applied to a wide range of uncoated substrates, and they produce a very robust image. Disadvantages are that they are expensive, require expensive curing modules in the printer, and the cured ink has a significant volume and so gives a slight relief on the surface. Though improvements are being made in the technology, UV-curable inks, because of their volume, are somewhat susceptible to cracking if applied to a flexible substrate. As such, they are often used in large "flatbed" printers, which print directly to rigid substrates such as plastic, wood or aluminum where flexibility is not a concern. However, they are becoming increasingly used in "hybrid" printers to print onto vinyl and other flexible media traditionally associated with solvent printing. There are some pros here with regards to ink densities and speed of drying.The colourants in UV cured inks can be dye-based or pigment-based. However, usually they are pigment-based because of the greater light fastness and durability of pigments compared with dyes. Pigments used in outdoor advertising and display applications have similar requirements to those used in automotive paints.Pros: can print onto rigid substrates, instantly dry, heavy ink load. Cons: ink is on surface only, physical ink layer with 3D relief, structure to machine passes.

4) Latex Inks

Latex- the new kid on the block.  Latex Ink, currently only from HP, is said to offer equal or improved performance compared to solvent ink for printing on PVC (vinyl), as well as printing onto paper, fabrics, polyester and polyethylene – substrates that solvent technology struggles with. (early adopters aren't all backing up this claim, but all new technologies have teething issues.) The latex ink, which is water based with a polymer that is bonded to the substrate by heat, doesn't need air purification or solvent extraction. The output is also odourless, making it suitable for a range of indoor applications that solvent machines aren't suitable for. Output is promised to have an unlaminated exterior life of three years. Another advantage claimed over solvent is that the print is dry and can be finished and mounted straight from the printer without requiring the "out gassing" period of several hours.

Reports are mixed on the success of this ink. Unsurprisingly, those who have invested in the technology sell it based on "green" credentials, yet there is some suggestion that it is no greener than Eco Solvent, and there have been some reliability issues that can be put down to "teething" for now. 

5) Dye Sublimation Inks

Dye Sublimation: - There are two types of dye sublimation inks available in the market. The most popular one is aqueous dye sublimation ink for use in both desktop and large format printers. The other one is solvent dye sublimation ink that can be used in XAAR, Spectra and Konica  printhead wide format printers. Dye sublimation is almost best not thought of as inkjet, but as an entirely different process altogether - and as such will be written about elsewhere.