Different situations call for different ink formulations

Better Wraps Through Chemistry

Ken Kisner is the President/CEO of Molecule Digital, www.MoleculeDigital.com.

Chemistry is part of our everyday life, from the fabric on your couch to the cleaning products you use in your house. As you look around the office or home that you are in right now, nearly every product involves chemistry and formulation. Each one of these products—from the stain on your floor, to the paint on the wall, to the ink in this magazine, or the dye in the carpet—must be carefully formulated for the application while keeping in mind the manufacturing process of the individual products as well as the methods the product will be used in. The wrap industry is no exception as it indeed has challenging specifications for the application process as well as end use criteria.

The Substrate

The substrate for the wrap industry is dominated by self-adhesive vinyl (SAV). These products have seen incremental improvements in durability and vast improvements in ease of use. Whether you use films from Orafol, 3M, Avery Dennison, Arlon or another manufacturer for your vehicle wrap applications, they have been extremely well formulated for this purpose. Currently inks are general purpose and must be formulated to work on a variety of substrates including the substrates used for vehicle wraps. These same inks are also used for a huge assortment of sign and graphic applications.

The Ink

True solvent inks were the first industrial grade inkjet inks used for vehicle wraps. These products were launched in the mid ’90s by Raster Graphics for their first generation Arizona as well as VUTEk and Scitex soon after. These inks use copolymer vinyl as the resin with solvents such as EB Acetate and Cyclohexanone along with automotive grade pigments ground down to sub-micron particle size for optimal jetting performance. The beauty of this technology is that the ink, when jetted on to a vinyl substrate, melts into the surface creating a monolithic colored vinyl film. The copolymer vinyl ink becomes a single component with the substrate itself giving the system extremely consistent properties and making the application of the product consistent as if applying the SAV with no ink at all. True solvent inks also delivered excellent chemical resistance to fluids such as gasoline, window cleaner and soaps used in car washes. 

While true solvent inks had significant advantages they also became known for VOC concerns and their strong odor, which was difficult for nearly all shops to work with. Additionally it was critical that the strong solvents did not penetrate through the SAV causing the adhesive to act differently when applied. Certain true solvent ink formulations in combination with certain adhesive formulations either caused the product to be difficult to remove or prematurely delaminate from the vehicle.

The advent of eco-solvent inks which were launched in the wide-format industry by Mutoh, Mimaki and Roland around 2001 allowed smaller sign shops to enter the wrap market with a fairly low investment in these machines and avoid much of the issue of odor in the workplace. The early eco-solvent inks were predominately formulated with acrylic resin and diethylene glycol diethyl ether as the solvent system. The pigments used in eco-solvent inks are automotive grade pigments similar or the same as those used in the true solvent inks which, with the proper laminate, were usually warranted for three to seven years depending on the company. While the acrylic resin used in the formulations is not nearly as chemical resistant, these inks still perform extremely well with the substrate. 

In the last several years Epson has entered the market with an Epson-branded machine and ink system. While their original inks for the GS printer used pigment yellow 180 and suffered with exterior durability, their most recent release of SureColor ink now uses Pigment Yellow 155 which is performing well for outdoor durability. Eco-solvent inks continue to dominate the market and perform extremely well.

A few years ago HP entered the wide-format market with their Latex printer and ink series. Although the system requires additional electricity to run the heaters, this was the first water-based ink formulation to hit the wide format market with outdoor durability. The resin is a low molecular weight acrylic polymer emulsion, which creates a durable film similar to latex house paint. 

As the heat in the printer drives off the water in the formulation, the co-solvents cause the emulsified resins to coalesce and create a durable film. While the latex film has excellent characteristics, it differs from the true solvent and eco-solvent formulations, as it tends to create more of a lamination of two different products rather than a cohesive single monolithic film. 

This does create some drawbacks in areas that require extreme elongation such as bumpers where some wrap experts have noticed a slight reduction in density due to the ink stretching slightly less than the substrate. However this has not been a major drawback and Latex is continuing to gain market share in the industry.

It is important that the machine manufacturer, ink formulation, SAV formulation and laminate formulation all work in concert.

UV-curable ink systems have been entering grand-format and wide-format markets for the last decade and have had a massive impact on the graphic arts industry as a whole, allowing printing on a variety of non-porous substrates including glass, wood, ceramic tile, metal and a variety of plastic substrates. UV-curable inks can be formulated with all multifunction monomers which, when reacted create a very tight, brittle hard finish, which are very scratch resistant and chemical resistant, or they can be formulated with all mono-functional monomers which, when reacted, create a very stretchable (up to 400-plus percent in elongation) film. More often UV-curable formulations use some combination of the two to get optimal performance for a certain application. However in vehicle wraps it is extremely important to have significant elongation and for this reason mono-functional monomers are required. 

One major difference between ink technologies is that water-based and solvent inks have 80 percent or more of the formulation evaporate from the film, leaving a thin layer of color and polymer behind while UV curable ink crosslinks and 100 percent of the original ink is left on the substrate. This creates a thicker film, which in some applications is an advantage and in others may be a disadvantage. UV curable ink typically has excellent adhesion to vinyl substrates but creates a separate film on top of the SAV with separate properties. UV inks are constantly improving for vehicle wraps but do have a different feel during the application process.

Most recently we have seem Mimaki enter the market with SUV, which is a hybrid solvent and UV formulation. This ink does boast excellent scratch resistance and seems to bridge the gap between solvent formulations and UV. There is no doubt that more hybrid systems will hit the market in coming years, possibly seeing water-borne ink systems with higher solvent content or even water reducible UV ink systems as all the chemistry companies and machine companies continue to work to provide the best system to the wrap industry.

Whether you prefer true solvent, eco-solvent, water-based, or UV-curable inks you will find each may have slightly different advantages and disadvantages for your target market. While there is no doubt that applying a vehicle wrap is an art and those good in the craft seem to make the process look easy, it is important that the machine manufacturer, ink formulation, vinyl and laminate formulations all work in concert to make a robust product that meets the final end use demands.