Q&A: Digital Inkjet for Plastics Decorating

Digital inkjet continues to be a popular choice for decorating 3D molded plastic parts. Although digital inkjet is not new technology or the best fit for all applications, it continues to make inroads into several industries, including cups and containers, medical products and automotive parts. Peter Baldwin, marketing manager with Engineered Printing Solutions, shared insight into current applications for digital inkjet, advantages and disadvantages of the process, and improvements over the last several years in digital inkjet technology.

What are some of the most common applications for digital inkjet? What areas are new or have continued to grow with digital inkjet printing?

Many of the common requests for digital inkjet applications are from injection molding companies or parts suppliers looking to decorate directly to the object instead of using labels, image-transfers or other analog printing devices. In recent years, there has been increased demand for integrating printers directly to the injection-molding presses manufacturing the parts. Many times, a robot will load the part directly from the mold. Additionally, robots often can be integrated into downstream processes, eliminating the need for labor between these stations, and reducing the total number of touches the part sees from start to finish. Pulling directly from the mold also can help reduce contaminants that may settle on the part during the transition between stations and further reducing waste. At times, this process also can eliminate the need for surface pretreatment as well.

Another area of growth has been with faux wood grains printed to composites or plastics in place of traditional wood. These customers are now able to custom-match specific wood colors or grain patterns at low cost with shorter delivery times. Usually, the end product is far more durable than ones made from traditional materials.

As for new opportunities, we’ve seen increased interest in printing on cylindrical objects that have industrial applications and have been traditionally screen printed, such as medical vats, propane tanks, oil filters, hole saws and so forth. Screen printing larger cylindrical objects is becoming more difficult to maintain as there are fewer suppliers for this space and less skilled labor available for the facilities doing the printing.

Advanced specialty applications have been growing as well. We have seen more requests for inkjetting on pharmaceutical fluids such as medicines, adhesives, radio frequency identification and dimensional embellishments.

What advantages does digital inkjet offer for plastics part decoration?

There are several notable advantages. Perhaps the most important advantage is the ability to produce short runs with minimal set-up times and changeover. With some older analog technologies, short runs can be too labor-intensive to justify the set-up and changeover costs. Hence the need for higher minimum order quantity. Digital inkjet can make a single-piece order more cost-effective for the customer while still allowing the print service provider to be profitable.

The ability to produce economical short runs becomes especially valuable with the addition of variable data. In manual/analog processes, it may be necessary to produce a physical plate or screen to customize decorations with names or alphanumeric variances, but with digital it can be as simple as attaching a .csv file to the print job. Each individual piece then can be decorated with a master image and a unique name on the fly with no need for specific plates/screens or changeover between each part.

There are additional advantages such as the ability to use CMYK process colors instead of mixing spot colors, high-resolution photographic artwork and digitized calculations of ink consumptions/costs.

What are the questions to ask when considering investing in digital inkjet technology?

First and foremost, it’s important to identify what the push/need is for a digital conversion. Is it for speed, photographic reproduction, variable data capability, minimizing setups/changeovers or just an advancement in technology to the customer? Once that is identified, consider what limitations or sacrifices will need to be made to convert the process.

For example, can the parts the operators are attempting to print be printed with digital? Not all parts are the right fit for digital, such as ones with highly undulated part topography or recessed areas within the object.

Digital is no-contact printing, and the drops can only travel a short distance before the quality of the print is compromised. On average, this is somewhere between 3-5mm. There are applications where extended jetting upwards of 10mm is achievable, but they are not common and come with many tradeoffs in print quality and reliability.

Secondly, what is the material to be printed? Not all substrates are compatible with digital ink and may require a significant investment in surface pretreatment that could be avoided with analog technologies. Some are simply not printable at all, like silicone.

Of course, digital inkjet isn’t the answer for all decorating applications. What are some of the limitations and when do other secondary printing technologies make more sense?

Not every application makes sense economically, even if digital is fully capable of doing the job. Simple one- or two-color prints can make far more sense by using pad or screen printing technology.

Long runs where the image does not change also can be significantly more efficient when utilizing analog technologies. For example, cylindrical printing with inkjet is not yet capable of achieving the speeds of most analog processes and simply does not make sense for longer production runs.

Other times, the part topography may be too challenging to print with digital as the drop placement is only accurate up to a certain offset. It varies by head technology and speed but, on average, once inkjet is applied from more than 5 mm away or so, users begin to see significant drop off in print quality.

What type of improvements have there been in recent years in digital inkjet that has made it a more feasible option for certain applications? Have there been improvements in inkjet heads, in digital inks, etc.?

The most notable advancement is with inks. Over the past 10 years or so, the inks have become far more flexible, durable and capable of brighter, more vibrant colors. While there are still some areas left to develop, such as fluorescents and metallic inks, the gap is closing between digital and analog inks each year. Inkjet inks today are capable of withstanding some of the toughest adhesion standards – autoclave, weatherization testing, dishwasher testing and solvent resistance.

Print heads have seen gains in recent years as well. High laydown technology and higher-viscosity heads have been a dramatic improvement in the amount of ink that can applied through digital inkjet at high speeds and the types of fluid used as well. Additionally, digital inkjet print heads have improved overall in recent years in print speeds and drop placement accuracy.

There also is new technology that is being used with digital inkjet to apply cold foil for applications that includes award ribbons, yearbooks, etc. that can replace hot foil stamping for certain applications.

Engineered Printing Solutions, East Dorset, Vermont, is a direct-to-object printing equipment manufacturer offering a complete line of pad printing equipment and industrial inkjet printers, from simple one-color pad print machines to highly automated bespoke single-pass equipment that integrates into existing production lines. For more information, visit www.epsvt.com.