Digital Textile PrintingShahid Pasha
By Cassandra Balentine
Textile printing is a hot and growing industry segment. Wide format digital print technologies evolve to better serve this market, especially for direct printing methods. Advancements in inks, and media—including pre-coatings—are essential. However, printheads specifically designed for textile printing help improve speed and quality as well as reduce challenges commonly associated with textile printing.
Water-based inks are popular for printing to textiles, and printheads designed for textile printing are advancing to better accommodate these inks. The number of nozzles per channel, droplet size, firing frequency, the area between the printhead and substrate, and ink circulation capabilities are all characteristics that may have an effect on fabric printing.
Above: The Ricoh MH5421MF printhead utilizes piezoelectric drop on demand technology featuring an ink recirculating structure.
Printheads for Textile Printing
Digital printing to textile materials continues to advance as the applications multiply, from signage to apparel and décor.
“Digital print in textile banners was the initial frontier, now there is demand for digital printing of apparel,” says John Harman, director of sales and strategy, Ricoh Printing Systems America. He explains that print technology has evolved from indirect transfer printing to direct printing to textile substrates and because of contact with the skin a shift to a predominance of aqueous inks.
It is important to note that generally, application of a primer is required prior to printing directly on fabric to enhance the image quality and image density. Harman says a larger drop printhead—15 to 27 picoliters (pL)—is ideal for this type of application, where high definition is not required. The use of white inks, which feature high pigment content, has led to the development of printheads with flow-through technology. This mitigates the settling of the pigments and nozzle blocking. “In summary, printhead technology has advanced to meet the challenges of printing aqueous textile inks including compatibility and performance robustness,” shares Harman.
Further, the adhesive technology and internal design of textile printheads are optimized to jet the lower viscous aqueous fluids. Harman points out that the larger drop size printheads enable efficient primer deposition. “The flow-through technology feature enables print robustness of heavy loaded pigment inks,” he explains.
Ricoh offers the seven pL MH5421 and MH5421MF flow-through printheads and most recently the five pL MH5320 printhead with enhanced aqueous ink performance, including enhanced aqueous ink compatibility. The 15 pL MH2620 and MH2820 27 pL apply primers and the 27 pL flow-through MH2810F printhead prints heavy pigmented white inks. In addition, Ricoh provides the lower cost GH2220 three to five pL printhead. In 2021, Ricoh plans to launch its 5.2-inch thin film technology flow-through five pL printhead TH64320F, which will offer value and performance advantages by enabling single-pass, high production volume textile printing.
Printhead productivity improvements are important for moving digital textile printing into true production speed capability. Bailey Smith, SVP sales, marketing, and business development, Fujifilm Dimatix, Inc., points out that advancements in printhead technology will make a significant difference in the adoption of digital printing in the textile marketplace. “Higher production speeds, more aggressive inks, and longer printhead life are some of the keys to faster adoption in our view.”
He says ink recirculation in ceramics provided a big improvement in process reliability. “Using ink recirculation at the nozzle also makes big improvements in textiles because of the open time management challenges with textile inks, priming, and reducing blocked jets in pigment applications. This feature improves the uptime performance of the printer and reduces maintenance.”
Further, a larger print gap between the printhead and the substrate provides a benefit in the reliability of printheads due to reduction of contact with the fabric. “The type of printhead technology used is directly related to the ability to print reliably with a large print gap,” adds Smith.
He explains that printhead reliability can also be a challenge with the typically more aggressive textile aqueous formulations compared to many other industrial printing applications. “The material selection and manufacturing process are key drivers to printhead life in textile inks.”
Additionally, Smith says higher nozzle count is becoming more common. This strategy provides more redundancy in the printing system allowing faster speeds and better printer uptime performance.
Fujifilm offers the StarFire SG1024 with ink recirculation at the nozzle range from seven up to 80 pL native drop sizes and can cover just about any application. The StarFire SG family is repairable, improving total cost of ownership in the event that a printhead is damaged, according to Smith.
Additionally, the StarFire SG600 is available in seven and 12 pL drop sizes. These printheads also include recirculation at the nozzle and repairable architecture.
The Fujifilm Samba G3L provides three pL native drop size with 1,200 dpi and recirculation at the nozzle. Smith says this product is intended for high-productivity applications where the finest quality prints are required.
Fujifilm plans to launch a new product family in 2020 incorporating many of the advantages of its other products into a package, which the company believes will be ideal for digital textile printing.
Traditional Versus Textile
There are several differences when comparing the requirements of printheads used specifically for textiles versus those used for more traditional media.
Smith notes that for graphics applications there are typically no seams, creases, dust, or fibers in the production process. This normally means the print gap can be small. As
previously mentioned, he says the print gap capability is highly related to the printhead design and is an important consideration.
Additionally, ink composed for textiles is different from inks used for graphic applications, so printhead construction and features—such as recirculation at the nozzle—are critical to address the needs of the textile market, admits Smith.
Harman sees an increasing demand for aqueous inks across multiple markets; therefore the broader performance requirements are common across these segments.
The relationship between the printhead and substrate is another critical factor.
Smith feels that many discussions with substrate manufacturers are managed by the ink manufacturer. “It is important to us that we understand these interactions to ensure our printhead will meet the needs of the final application. We work closely with ink companies to ensure we are producing the right product.”
He adds that features like productivity and printhead life directly relate to the total cost of ownership for the printer and should be considered when a print provider or manufacturer is researching digital textile printing solutions. Fujifilm is heavily focused on meeting these demands with its products.
It is also important to consider the ability of the printhead to meet the image quality of the applications of interest. “Will the native drop size and resolution of the printhead in combination with the printer architecture provide what you need for your customers?” asks Smith.
“Consideration of the printhead, jetting fluid, and substrate in addition to the drying mechanism are critical as these combined ultimately determine the image quality, and robustness of the print and productivity of process,” offers Harman. “Ricoh has expertise in all the above mentioned areas, thereby bringing this value to all of its digital print customers,” he adds.
For high-productivity textile printing the use of flow-through technology printheads should be considered for productivity robustness, shares Harman. “The use of printheads to apply the primer should also be considered as this will enable application of the primer to the specific areas where it is required, thereby saving on the cost of primer and delivering a more efficient print process.”
Textile Printhead Challenges
Printing to textiles can be challenging, but the right printheads can help address concerns like productivity, image quality, and printer reliability.
Harman says the biggest challenges are jetting heavier pigment loaded inks, which are addressed by utilizing printheads with flow-through capability and delivering the increasing production volume requirements for textile printing.
Smith points out that the right printheads enable textile producers to reliably print all types of patterns at high speed to improve productivity.
For image quality, Smith explains that each application has somewhat different requirements. “The selection of the printhead can have a significant bearing on the final output, but it is not the only factor,” cautions Smith.
Printer reliability is also improved with the right printheads. “From the morning startup to the number of print runs before maintenance to mean time between failures, the printhead can have an influence in the overall output. Again, the printer design, machine maintenance, and substrate type are also contributing factors,” shares Smith.
Textile printing is an attractive market segment, however it does present challenges. Advancements in inks and substrates as well as printheads continue to move this segment into new applications. Consider the droplet size, firing frequency, and flow-through of a printhead when investigating an investment in a digital textile printer.
Mar 2020, Digital Output