Technology

In previous blog posts, I focused on digital printing technology for roll to roll printing of fabric. Digital inkjet systems that support the ability to print on assembled product have also become available and are referred to as Direct-to-Garment or DTG printers. Although it’s possible to use the systems for printing of garment types such as hoodies or small accessory items such as tote bags, DTG technologies are primarily used for t-shirt printing. The last two to three years there has been considerable growth in this technology area and available systems are now being used for direct to consumer applications and by small shops and start-ups for printing of short runs and customized shirts.  

DTG Hardware

Currently available equipment falls into two general categories. The first category includes equipment derived from Epson desktop technologies that have been re-engineered with platens to transport the garment under the printing mechanism. There are numerous vendors for this variety of printer including Anajet, Azon, DTG, Groner, and MS Macchine. The second category includes equipment designed from the ground up. Some of the machines falling into this category make use of more industrial printhead systems to support greater print speed and ensure reliable jetting of the pigment based colorants. This second category of equipment is typically viewed as more robust and there is generally greater cost associated with the purchase of these printers. Vendors of this type of technology include Aeoon, Brother and Kornit Digital.

Both categories of equipment include single and multi-platen technologies. Multi-platen systems offer two or more positions for garment loading. For a dual platen system the machine operator is loading one platen while the second is printing, thus providing increased levels of throughput. To date, most available DTG technologies operate at relatively modest print rates. At the high end of the spectrum, Kornit’s Avalanche printer, a dual platen system, offers a maximum print area of 23.5 x 35 inches and is capable of imaging up to 300 light garments per hour. Brother’s GT-782 model is also a dual platen machine and can print up to 60 light shirts per hour. The larger platen for this device supports a maximum print area of 16 x 18 inches. Aeoon recently joined the ranks with the introduction of a higher speed DTG machine that can be engineered with printhead technology from Fujifilm Dimatix (Spectra) or Kyocera according to customer preference. The Kyocera version supports printing of up to 400 light shirts per hour, offering the highest print rates in the DTG area to date.

Printing of Dark Garments

Unlike their wide format counterparts, the majority of DTG systems in the market have been designed for printing with pigments on both light and dark colored garments. Almost all DTG systems are designed as 4 color devices and most offer the addition of pigment white to block out the foundation color when printing on dark garments. This pigment white is applied in advance of the color and although the method works quite well, it reduces print rates to roughly half that of printing on light shirts.  In most instances the dark shirts are pretreated prior to imaging to optimize results and some vendors suggest this operation for printing of light shirts as well. The pretreatment step can be accomplished off-line with a separate machine or spray gun technology or integrated into the printing operation as is the case for Kornit’s printers.

Early adopters of pigment white for Epson based systems found the chemistry inclined to settle out over time and cause clogging of the printhead nozzles. However, experts would suggest that regular cleaning and maintenance of these systems support more reliable performance. In some cases, vendors have also developed on-line ink mixing systems that prevent the settling of the pigment in the ink formulation. An alternate strategy for imaging on dark shirts is offered by Mimaki through the application of a discharge liquid for removing the base color from the shirt. While the use of pigment white produces a shirt with a slightly heavier hand, the discharge method maintains softness and offers a pleasing print effect on it’s own.

Color Fastness

Poor color fastness with respect to washing was among the early criticisms of the digital direct-to-garment printing method. Over time, this characteristic seems to have improved assuming correct processing methods have been followed. It has been stated that providing adequate dwell time during the curing procedure is key to achieving fastness properties and conveyer curing systems must be slowed as compared to practices in the screen print environment. In some instances, vendors also suggest drying the print area with a heat press in advance of the printing operation. 

To date, best print results have been achieved when printing on 100% cotton garments while printing on blends and synthetics have demonstrated limitations in terms of image quality and color fastness. Given tremendous interest in this application for markets such as team jerseys and athletic garments, shirt pretreatments and ink chemistries will likely evolve to meet needs in this area and some vendors are already advertising this capability for specific fiber types.

Trends in DTG Printing

As I’ve already stated, one of the most important trends in DTG printing is the development of more production oriented systems. The introduction of the Aeoon machine is of particular interest and one of the questions surrounding this device is how the Kyocera KJ4B printhead will perform in conjunction with the pigment based colorants used for DTG. Only time will tell. Additional trends include the introduction of supporting software solutions for enabling print customization, on-line ordering and automation and management of data flow to multiple print machines. These systems are integral to successful adoption of direct-to-consumer and small quantity print strategies that are primary targets for DTG printing.

Ultimately, the development of viable DTG systems will have tremendous impact on production flexibility and sustainability within the garment printing area.  Within the current screen print context there can be tremendous color waste associated with over mixing, ink storage and screen cleaning. There is also consumption of water associated with screen engraving and reclamation. The implementation of a digital DTG strategy at the production level will offer an alternative to this scenario and will support small quantity, print-on-demand and rapid replenishment capabilities among traditional volume providers.

For my next blog post I’ll be shifting focus and looking at the topic of product lifecycle management. In the mean time, we welcome your comments and questions regarding DTG and wide format digital textile printing.

In essence, the purpose of digital textile printing is to apply color and pattern onto fabric. Thus, the development of colorant chemistry is a primary area of focus within the scope of overall system design. For companies developing colorants for inkjet printing, a number of factors are taken into account. First and foremost, the colorants must be formulated for compatibility with the inkjet printhead to support reliable jetting. The resulting formulation must also be chemically stable for a period of shipping, storage and operation. Additionally, individual colorants within the set are selected for optimization of color space, ease of formulation, color fastness characteristics, and for compliance with standards and regulations governing chemical use for textile products. To date, some of the leading developers of colorants for inkjet textile printing include DuPont, DyStar, Huntsman Textile Effects, J-Teck, Lyson, Sawgrass, Sensient, SPG (Stork Prints), Xennia and Yuhan-Kimberly (now marketed through Expand Systems). Most of the vendors listed offer multiple colorant types to address compatibility with a selection of fiber types. These inks are formulated as process color sets for the textile inkjet environment.  

Process Color Printing

As described in Part I of this series, digital printing normally involves the creation of ink drops from a master color set. This strategy is referred to as process color printing and is fundamentally different than the spot color approach used within conventional textile printing methods. Cyan, magenta, yellow and black form the foundation of the process color set. For textile applications, developers have expanded the printable color space or gamut through the addition of hues such as orange, red, green, blue or violet. In some instances, vendors have also developed colorant sets that include dilutions such as light cyan, light magenta and/or light black (grey). These colors have been added to support smoother tones and lighter shades. However over recent years, the advent of variable drop size printing has reduced the need to include dilutions in the master color set. 

Dyes & Pigments

Colorants for digital textile printing applications have been derived from conventional textile printing chemistries and can be classified as either dyes or pigments. Within the inkjet environment, colorants are typically referred to as inks and within the dye category, fiber reactive and acid dyes were the first to enter the market. While acid dyes are used for printing on silk and polyamide fibers, fiber reactives are compatible with cellulosic fibers and are often the colorant type of choice for printing on cotton within the inkjet setting. These colorants are now well developed for the inkjet process and are normally offered as an 8 color arrangement. Dye based printing offers excellent fabric hand and good to excellent wash and crock fastness properties. Acid and reactive colorants typically support a broad and luminous color space which lends itself to both sampling and production applications. On the down side, the processing of these colorants continues to be somewhat complex and requires pretreatment or coating of the fabric prior to printing to support color fixation and maintain image clarity. Steaming and washing is also a requirement for reactive and acid dye printing and ensures color fastness and minimizes color mark-off during use and care of the printed textile product. 

Disperse dyes are also available for digital textile printing and are compatible with polyester.  For the inkjet environment, disperse dyes are typically offered as a 4 color set and are almost exclusively of the sublimation variety. These sublimation inks are applied via a transfer or direct printing method. Fabrics are typically pretreated and ink formulations may be tweaked to optimize print results for the direct printing approach. For both application methods, dry heat is used to sublime the chemistry and drive the colorants into the fiber during the fixation stage. As stated in Part II of the series, the adoption of direct sublimation printing within the soft signage sector has been a significant driver for hardware development. 

Pigments have been among the more difficult chemistry types to formulate for inkjet, but are now available for both wide format and direct-to-garment printing applications. Colorant sets for DTG printing are normally offered as a 4 color arrangement, whereas pigments for wide format applications often incorporate up to 8 colors for a broader printable color space (gamut). In terms of fabric preparation and finishing, pigments can be applied to standard prepared for print (PFP) goods and once applied the pigment is cured using dry heat. For wide format printing of pigments and disperse dyes, fixation can be accomplished through the use of heated drum or calendar type systems. Pigments can also be cured via non-contact technology such as a tenter frame or curing range. For DTG printing, fixation may involve the use of a small heat press or a conveyor system as used in a typical t-shirt printing operation.

Given the relative ease of processing for pigments, they have tremendous appeal to potential users.  Pigments for digital printing typically offer a soft fabric hand as compared to those used in conventional printing. However, digitally printed pigments may still fall short of industrial laundering requirements and specific hues within a set may exhibit some weakness with respect to crocking – wet crock in particular. Leading solution providers have invested in development and/or application of binder strategies that optimize fastness properties, but also support reliable operation within the inkjet setting. The best of today’s solutions offer good color fastness properties for typical wash and wear requirements assuming the printed fabric has been processed correctly.

Although dyes and pigments differ with respect to color gamut in the conventional printing environment, this issue is amplified within the digital context. Thus color is one of the primary limitations in terms of adoption of digital pigment printing and nanoparticle formulation strategies have been a key area of focus for advancing technology. The inability to obtain very saturated color or deep, rich blacks and related dark shades is of particular note within available pigment ranges. On the up side, I’ve observed that some of the best color results with pigment printing are obtained on cotton substrates.

In some cases, adopters are able to look past color limitations and offer print opportunities for customers and markets where precise color matching is not a primary requirement and there is greater flexibility in terms of color quality. It may also be fair to say that adopters coming from outside traditional textile circles are able to approach the use of pigments with more flexible expectations for the performance of this chemistry type. In a nut shell, these users focus on what can be done with this chemistry as opposed to what can not and they fashion designs and business ventures to exploit the best features the chemistry offers.     

Software for Inkjet Printing    

Before concluding my comments on color and ink chemistry for digital printing, I think it’s important to point out that software and auxiliary equipment for finishing also play an important role in the final color results obtained. From a software perspective, CAD solutions including off-the-shelf software support the development or creation of the artwork in digital format. Raster image processing or RIP software, interprets the image data for output on fabric and textile specific solutions support layout capabilities for printing of repeats and continuous fabric lengths. Color management solutions are used to create color profiles that describe the printable color space for a given fabric, ink and printer combination. These color profiles are referenced for accurate reproduction of color on the cloth.

Within this discussion of software it should be pointed out that some vendors select to bundle solutions for image processing and color management with the printer, while others provide more open platforms. It should also be stated that from a user perspective, workflows are developed based on the specifics of the software solution and the type of image being printed. Since inkjet technology can reproduce highly tonal or photographic imagery in addition to typical spot color textile images the strategies for optimizing and fine tuning color may vary based on image type. The workflow strategy also takes into account whether the digital process is being utilized for sampling or for final print production. For designs being funneled toward digital production and having tonal or photographic qualities, the general goal is to obtain a pleasing color effect that balances lights and darks and provides global accuracy of color and detail in reference to the original artwork. For spot color images – particularly those serving as samples for screen print production, the user will look to match individual hues in reference to a color standard.     

Auxilliary Equipment

With respect to auxiliary equipment, a number of companies have developed machines to support processing of dye based prints for the modest volumes typically associated with digital printing. Machines have been designed for fabric pretreatment, steaming and washing of reactive and acid dye prints. As mentioned previously, there is also technology for curing of pigments and development of sublimation chemistry. In some cases, vendors have developed multiple pieces of equipment to support a selection of processing steps. Some vendors have also taken a flexible approach, allowing the user to purchase the unit in modules based on throughput requirements. Some of the hardware vendors serving this area include Arioli, DigiFab, Gessner, Hollanders, MS Macchine, Rimslow and SETeMa and Transmatic.

Given the rapid growth and relevance of digital garment printing for the cotton industry, my next post will provide greater insight into this area and will expand on both hardware solutions and pigment chemistry for DTG. In the meantime, there are a number of links in the Resource Library pertaining to digital textile printing for readers to reference.

Over the last three to five years the launch of robust hardware solutions that are designed to withstand the rigors of a production operation has been the primary goal among a number of digital textile print technology providers. The adoption of digital sublimation printing for soft signage has been a significant driver for technology development. The broader textile industry is benefitting from this effort and today, equipment is specifically engineered for textile requirements. Machines for direct printing on fabric now incorporate the use of tacky belt or cylinder feed mechanisms to advance the fabric. Machines are also equipped with bulk ink capabilities to support greater throughput. Ink developers work closely with printer manufacturers to formulate colorants for a variety of fiber types that support reliable jetting as well as optimized color gamut and fastness characteristics.

Printhead technologies are also advancing and primary areas for development have included increasing the number of inkjet nozzles per printhead and in some cases, the density of the nozzles. Benefits include improvements in print speed, print resolution, and consistent quality output. It’s also becoming possible to bank printheads together to form arrays that traverse across the width of the fabric covering larger areas of the cloth in a single pass of the print carriage. The ultimate goal has been the creation of fixed array technology in which machines are engineered so that printheads span the width of the fabric, remaining stationary while the fabric is transported beneath. This method is sometimes referred to as single pass, continuous printing.

Machines with Epson printhead technologies have dominated the market to date and a number of vendors have used wide format print engines from Mimaki, Mutoh or Roland as the foundation for printer development. In this case vendors act as technology integrators, mounting the engines on fabric feed systems for the textile printing market. For printing of roll goods, Epson based solutions have been offered by vendors including ATPColor, Costruzione Macchine Speciali, La Meccanica, MS Macchine, Robustelli, SPG Prints (Stork Prints), and Yuhan-Kimberly (now through Expand Systems). Mimaki and Mutoh also offer their own textile printing equipment and within the garment printing area, modified desktop technologies from Epson are also used.

Recently, developers have looked to more industrial printhead technologies to pave the way for greater production capabilities. These technology solutions are available from a variety of vendors. Here is a list of printer vendors organized by printhead manufacturer. Direct-to-garment (DTG) systems have been noted:

- Brother (Brother DTG printer)

- Fujifilm Dimatix (Agfa, Durst and Kornit Digital DTG Printer)

- Konica Minolta (Konica Minolta’s Nassenger series)

- Kyocera (Aeoon DTG printer, MS Macchine, SPG Prints and Reggiani)

- Markem Imaje (Osiris)

- Ricoh (Mimaki)

- and Seiko Printek (d·gen, Hollanders, Zimmer)

Among the vendors listed, Kyocera has been gaining considerable attention of late in regard to the KJ4B printhead. According to the Kyocera website, this device is capable of pulsing at a very high rate. It contains 2, 656 ink nozzles per head and offers a 4.25 inch print width. MS Macchine, SPG Prints and Reggiani have adopted this technology and the related systems support print speeds over a hundred linear yards per hour. In the case of the MS-JPK and SPG’s Sphene printer, it’s possible to purchase multi-carriage configurations that support print speeds of several hundred yards per hour at the top end.

In addition to the JP6 and JPK models, MS Macchine recently introduced the LaRio printer. This machine makes use of a single pass, continuous strategy and is equipped with up to 8 stationary print bars. Kyocera printheads span the machine width and each print bar is dedicated to the delivery of a single color. In this arrangement the machine is capable of printing up to 70 meters per minute. It is also possible to install a second set of printheads on the back of each print bar for operation of a second ink set in support of multi-fiber printing. MS indicates that the first machine is currently being installed in Italy and should be running production by mid-July. A second machine is scheduled for installation at a Brazilian site during the month of September.

The Isis machine by Osiris Digital is another example of a single pass, continuous printing system. The Markem Imaje printheads used in this system are of the continuous inkjet variety, rather than the drop-on-demand systems that currently dominate technologies for textile applications. As the respective labels suggest, continuous inkjet systems are constantly pulsing and forming ink droplets, while drop-on-demand systems form drops as required by the image data. Continuous inkjet has generally been viewed as an approach that supports faster drop formation for higher speed printing. In the case of the Isis machine, print rates of up to 30 linear meters per minute are possible. The machine supports a modest print resolution, but thought to be comparable to the screen print method in terms of image detail possible.

In early June, Osiris announced that their assets had been acquired by Ten Cate with a plan to continue sales and support of the Isis machine under Ten Cate’s Xennia division. Ten Cate is also currently engaged with Reggiani with respect to a printer described as employing “diagonal, multi-pass” technology. Elimination of banding associated with nozzle failure is among the benefits described for this system. This development follows the completion of the Digitex project, which was coordinated by Ten Cate and executed in conjunction with a number of European companies and universities. The Digitex project involved research into digital application of functional finishing chemistry and culminated in a conference held in late 2010 that showcased the results of the 4 year development effort.

In addition to the hardware described thus far, a new printer is anticipated to be introduced by Konica Minolta and Durst recently announced the development of the Kappa 180 printer to support production level printing within the broader textile market. This equipment is scheduled to be shown at ITMA Barcelona. Currently available textile technology from Durst is designed for printing of soft signage materials using sublimation chemistry. Durst joins vendors including Agfa, ATPColor, d·gen and Hollanders in a growing list of technology providers offering superwide format technology for printing of very large scale graphics.

While this post has been focused on technology development for digital print hardware, I’ve only provided mention of systems for direct-to-garment printing. As I mentioned in the first post of this series, DTG printing is of great relevance to the cotton product industry. With that in mind, I will be providing greater detail on this application going forward. My next post will address color & ink chemistry for digital printing with a focus on advancements of relevance to the cotton industry.