Digital inks are specific to the fabric: Unlike the desktop ink-jet printer in your home or office, the substrate or 'medium' used for our technology requires a specific ink chemistry is used depending on the fabric. Generally speaking and ignoring the exceptions, they are: POLYESTERS use 'disperse' inks NYLON, SILK, WOOL use 'acid' inks (sometimes called acid dyes) COTTON, NATURAL FIBERS use 'reactive' inks
In addition to these inks or dyes, PIGMENT dyes can be applied to several different fabrics and do not require pre-treatment of the fabric. Pigment is the most popular for digital printing because of this and the ability to simply heat set or affect the pigments without much post-processing, as well. This limits saturation and color density or bloom, so the proper application must be determined before selecting pigment printing.
Digital direct ink-jet fabric printing is not a new technology. What's new is the application of high-speed printing as a service bureau and the evolution of the equipment used for printing. Unlike other digital printing mediums, in order to print on fabric, there are additional processes required.
The first stage is pre-coating of fabrics:
Each fabric using disperse, acid or reactive requires, for the most part, a pre-coating. A specific chemistry suitable for the fabric/ink is produced to obtain ideal color, saturation and 'bloom' (color pop and density). Pre-coatings also affect saturation from the surface through to the back, as with scarves where saturation is desired, or display, where it may not be desired. Pre-coatings are the first step in a successful formulation of chemistries for digital ink-jet printing.
Pigment inks do not require pre-coating, but 'sit' more on the surface of the fabric. While considered permanent, it is not as permanent as a fully processed fabric, such as silk.
The printing process:
Printing directly to fabric after it is coated now puts water based inks on the surface, sitting on top of the pre-coating material. The coating creates the level of penetration but after printing, the image may appear dull or 'dusty' before post-processing is completed. Ink drop sizes vary depending on the equipment, the smallest drop size is the slowest to print but creates incredibly fine detail in the image, mostly suitable for fine art or photographic printing, depending on application. The speed of the equipment varies depending on many factors, including number of print 'heads', ink drop size relative to speed of application, substrate entry system (flat bed so fabric sticks directly to a surface and is carried through the system) or via paper-backed fabrics for smaller printers when speed is not offered. Ink-jet printing does not touch the surface of the fabric, unlike silk screen or rotary printing. The ink is dropped at a set height above the fabric, depending on the fabric texture (flat silky surface versus velvet or a high pile textured fabric, for example).
The final sage is post-processing:
After printing, larger printing systems initially heat set the ink to dry it before rolling. From this stage, the final treatment to produce full color printing is either heat setting (high temp, longer duration or 'dwell time') or steaming then washing. These processes affect the pre-coat and ink interaction and the colors then 'bloom' to reach full potential and density. Heat setting burns off the unused pre-treatment to remove residual material. Washing after steaming serves this purpose. Fabric is then dried or set and can be rolled and is 'retail ready' for the end user.
Commonly asked questions:
What is a CAD print? This is a print that has not been post-processed, so cannot be handled like a retail ready fabric, especially not getting wet, which would streak or let the ink surface run or smudge.
What is a flat bed printer? This is simply a type of entry system, more commonly used in digital graphics printing but also now used in digital fabric printing at production level. A belt type system the width of the printing area carries the fabric from the entry point, through the printing area, into the drying area (if applicable) then allows it to be dismounted onto a roll. The bed area is coated with a special 'glue' type substance, thermal in nature. A roller at the entry point is heated and, in combination with pressure, allows the fabric to be pressed into the warmed surface so it is now stable. At the end of the process when the fabric is removed, the belt rolls underneath on its way around and a washing system removes any fiber or ink remnants.
Why is paper backing used for some fabrics? For smaller, slower printers not considered production level equipment, it is necessary to apply paper to the fabric because there is no flat bed to lay the fabric on to guide it into the printing area or handle it on the back end. If the fabric is stiff enough, it can sometimes be used without paper backing.
What type of fabrics can be printed on? Almost any fabric can be printed on, sometimes only limited by the surface texture and height (too much terry loop is an example of what doesn't work well). Each fabric requires a specific chemistry of ink or dye, reactive to the nature of the fabric. For example, the chemistry for printing polyester is different than cotton. The reaction of each determines the pre-coating and the ink formula applied. Nylon, silk and some other fibers all react to acid inks, so it's not just a matter of natural versus synthetic. Some fabric can cross over and work on other chemistries, all part of the testing process before making this determination. Pigment printing crosses most boundaries but works primarily on natural fibers compared to polyester, which works best with chemical assistance in processing.
Why has it been hard to get more than short cuts and sample yardage? Until the addition of Dream Digital to the fabric printing service industry, production printing has been very limited due to speed of processing. A typical printing system used is a Mimaki or Stork, operating at 5 -8 yards per hour on average. Recently, the DuPont (tm) Artistri(tm) system changed the benchmark by increasing speed to 18-40 yards per hour depending on settings and coverage of ink on the fabric. A versatile system, however, with a flatbed system and enough speed to be considered a production level machine. The next step us are the Reggiani Dream printing systems offered through Dream Digital. The flatbed printing system operates at speeds of 80-80 yards per hour, a considerable increase in speed from any other system. Using smaller, slower system, it is difficult to acquire even a reasonable volume of printing easily. Post processing equipment, when used by these small system printers, only accept smaller cuts of fabric, 5-15 yards on average as it stands now. The advent of new development will certainly change this situation and allow for all ranges of printing and processing.
Does digital printing look like rotary or screen printing? Yes and no. The quality of each is different in certain aspects, including what ink colors are used and how they are mixed. Digital can print with unlimited colors and photo images, graphic details and color combinations not possible with silkscreen or rotary, but cannot print with opaque white (over another color) or metallic colors. However, new software and file manipulation allows digital to "dummy down" and copy screen or rotary, important if a client is using digital to start the sample process but will ultimately go overseas to rotary or screen printing for production. It's not helpful to make samples that don't end up looking like the production. Screen and rotary use a limited amount of color, each being a layer and costing quite a bit of money per screen or engraving. Digital frees design from this restriction, but if you design a digital type image with complex attributes, you will have to stay digital to produce your fabric. Your end product should be known before starting the process to avoid ending up going down the wrong road. Re white, if the substrate (fabric) used is PFP (prepared for printing), required before precoating is applied, then white is created in the image by absence of color. It is not applied over a color and if the fabric is naturally tinted or colored, white is not possible.
Can fabric be dyed before printing digitally? The best preparation for fabric is that it is PFP (prepared for printing) or PFD (prepared for dying), indicating the fabric is scoured and has no additional coatings or treatments which may counteract the precoating necessary for printing. Most fabric manufactures sell their products in this condition and make them available to us.
Contact Dream Fabric Printing for more information about our printing and production services. Tel: 917-267-8920 orInfo@dreamfabricprinting.com