by Olivia Cahoon
Direct printing to pre-manufactured objects like fabric, glass, metal, and plastic requires ink formulated to industrial strength printheads. However, challenges remain in ink formulation such as adhesion, drop placement, and clogging—deterring direct to object printing’s integration into manufacturing facilities.
As a result, ink chemists partner with printhead and hardware manufacturers in a verticalized effort to solve ink challenges for direct printing technology.
Above: Roland developed an on-board ECO-UV Primer Ink option that enables users to quickly increase adhesion to graphics on challenging materials such as smartphone cases.
Ink enhancements are designed to improve direct to object printing while avoiding challenges in adhesion, printhead compatibility, and ink droplet. For inkjet inks specifically, enhancements are application dependent.
“Inkjet technology is increasingly used in industrial printing applications where objects in a variety of shapes and materials are decorated inline with manufacturing,” reveals Phil Jackman, global product manager, digital, Sun Chemical. In each application, there is typically an existing specification the inks meet.
Jackman says some products need inks that resist detergents and other cleaning chemicals. Interior components for automotive use have extreme weather requirements due to UV exposure and temperature variations. As a result, in nearly every application there are established tests and specifications that existing pad or screen printing inks attain. “Thus, inkjet must achieve the same performance standards if the process is to transition successfully from analog to digital,” he continues.
Certain inkjet technologies offer the ability to print to nearly any object. While this benefits manufacturers, it also presents challenges in adhesion as each material features different chemical properties.
“With literally hundreds of substrates to choose from, including glass, metals, finished wood, or some plastic and acrylic, customers demand the ability to create durable products for clients regardless of what those items are made of,” shares Jay Roberts, product manager, UV printers, Roland DGA Corporation.
The most common challenge with adhesion is that end users need to predict finishes and adapt products accordingly. When adhesion is an issue, operators may select adhesion promoters to meet the customer’s expectations, according to Roberts.
For example, Roland developed an on-board ECO-UV Primer ink option that enables users to quickly increase adhesion to graphics on challenging materials such as highly polished glass. “It’s a colorless, transparent coating material that can be used as a base for ink to improve adhesion,” explains Roberts. With this primer, users prepare objects for customization to achieve an accurate, clean finish.
Higher pigments and thinner inks also help adhesion to challenging substrates. For example, Agfa Graphics’ chemical ink engineers and patented ink grinding methods allow vendors to pulverize raw color pigments beyond the minimum specifications that inkjet printhead manufacturing partners set. “This allows us to suspend more physical pigment particles within each ink droplet, resulting in what we refer to as ‘Thin Ink’ technology—less ink equals higher yield,” shares Matt Meany, senior application specialist, Agfa.
Adhesion is further complicated by applications that require specific standards, such as food and beverage safety or enhanced decoration for luxury brands. Max Winograd, global business director, Avery Dennison Digital Ink Solutions, says that as a result, many companies now issue a Restricted Substance List (RSL) for end use applications. The ink formulators use RSLs as a guide to properly formulate inks for adhesion and food safety characteristics.
In the beverage container market, many ink enhancements are dictated by legislation regarding low migration compliancy. However, Jackman shares that other containers for industrial purposes, such as paints or silicone and adhesive tubes, don’t require inks with food packaging compliance status and instead demand resistance property requirements due to the contents.
To serve these markets, ink manufacturers like Sun Chemical develop a variety of ink formulations. For example, Sun Chemical Amphora UCP UV inks for beverage container printing meet regulatory requirements for food packaging and deliver the adhesion and water resistance expected by these applications.
Ink challenges occur during direct to object printing that relate to printhead technology, such as nozzle dry out, drop placement, jetting conditions, and clogging.
New ink formulations are designed to solve nozzle dry out, which requires printhead purging and increases ink waste. Grant French, business development manager, Digital Ink Sciences, LLC, says new formulations permit printheads to remain off the capping station longer than traditional inks while also allowing for a longer fly time. “This means you don’t have to print those end of line full-color bars on wide prints, thus increasing print time.”
Digital Ink Sciences takes advantage of this technology with its DIS1000 and DIS3000 series sublimation ink sets, designed to solve nozzle dry out complications by the printheads remaining off the capping station for as long as possible.
In many direct to object printing applications, inks are applied in a single pass. “Droplet control during jetting and the subsequent control and spread of the drops on substrates is integral for color development and good image quality,” admits Jackman. These ink enhancements are typically required over those used in multi-pass applications for graphics.
Obtaining optimum jetting conditions is a common challenge in direct printing as many objects are irregular shapes. Thus, Jackman says the drop throw distance is further than many other digital applications because it is not possible to get the printheads any closer. Additionally, the print speed of some applications also induces turbulence, which exacerbates good jetting and drop placement accuracy. “Inks utilizing high-performance pigment dispersions are required in these demanding situations,” he adds.
To achieve better drop placement, today’s chemists are becoming proficient with aerodynamics. Jim Lambert, VP, digital division, INX International Ink Co., believes this is a result of desired speeds, part rates, and how air turbulence affects drop in the print zone. “It’s about how the drop flies and what happens when it hits the surface—as this greatly influences the print quality.”
Additional Ink Challenges
Aside from adhesion and printhead technology, other ink challenges focus on sustainability, color, and direct printing’s market adoption.
A potential area for great improvement in direct printing is an ink that enables greater sustainability. According to Winograd, no large food or beverage brands currently displace their label use with direct printing on plastic or glass containers. “Labels are inexpensive, but a huge hurdle when it comes to recyclability,” he explains.
However, if the technology can demonstrate to large brands the potential to eliminate labels at a competitive price point—while also enabling easier ways to recycle—Winograd believes it will take off at a faster pace.
From a color perspective, creating inks that maintain a high degree of opacity— but don’t require many ink layers to lay down on a substrate—is challenging, reveals Winograd. “Customers want inks in their specific brand colors and to pop on a substrate, but they also want the substrate and ink to feel smooth to the touch.”
Market adoption is a barrier as brand owners and filling companies often use direct printing technology rather than experienced printers. Matthieu Carni, director business unit inkjet, Siegwerk, believes widespread adoption challenges mainly concern educating non-print experts in how to use the technology. “Adhesion and print quality are largely influenced by the surface treatment of the object to be printed so that the OEM’s expertise in surface treatment as well as the partnership with the ink maker play key roles for a successful print.”
To help with adhesion, laminates and protective coatings are available that provide longer life to printed areas.
A number of cold, hot, and liquid laminates offer extended protection to UV printed applications. Much like clear coatings widely used in the automotive industry, Meany says these coatings and films are specifically designed for the purpose of protecting the underlying layer of color from wear, harsh environmental conditions, and chemicals.
Using films or jettable chemistries improves rub resistance while increasing light fastness and fade resistance, depending on the overvarnish’s components, shares Lambert. Laminates and protective coatings also improve the printed object’s overall appearance. “It tends to hide things like peaks or valleys in the process colors that have been printed. In most cases, it provides a gloss or sheen that is perceived as very desirable,” he adds.
Coatings and laminates are helpful in packaging applications where direct printing can be challenging. For example, tube formation or PE/PET caps and bottles need to meet recyclable regulations. According to Carni, the application of primers and protective varnishes improves inkjet print results by optimizing print quality and resilience to post-processing steps like increasing cap scratch resistance. Siegwerk offers optimized varnishes and primers to meet quality and resilience needs.
The ink creation process for direct to object printing evolved in recent years. Currently, the formulation process begins with printhead creation followed by machine and ink formulation—depending on the vendor.
“The printheads and machines are developed first, and then it is up to the ink chemist to formulate to the equipment,” reveals Winograd. Ink chemists typically create formulations with a printhead, application, and machine in mind as certain printheads provide greater flexibility in terms of which raw materials are included.
Being aware of which printheads and machines the ink is intended for helps prevent clogging. “When a printhead is clogged or a machine is down for repairs, it’s a huge pain point for our end customers, so this is an issue that we pay significant attention to,” admits Winograd.
According to Lambert, selecting the printhead first dictates many of the downstream development processes. With this underway, the client immediately knows what type of image quality they need and the object surface they intend to print on.
After the printhead is selected, the chemist creates a specific formula that meets the printhead’s specifications with regards to viscosity at a specific thermal or operating temperature range. Once complete, the application portion starts. “The ink is tested on the specific or intended substrate,” shares Lambert.
Today, printhead, hardware, and software manufacturers as well as ink chemists work together as a team to develop inks for specific applications—each using what they learn to improve what they specialize in, says French.
“Tight alliances are created,” offers Lambert. “There isn’t a week that goes by where you don’t hear about a joint venture or a partnership between machine and ink companies to solve specific direct to object printing challenges.”
Direct to Object Printing
Ink used to print directly to pre-manufactured objects must work with printheads to jet ink at the correct rate, without clogging or nozzle dry out. To avoid challenges, today’s ink manufacturers work with hardware partners to further advance the direct printing process.
Jun2019, Industrial Print Magazine