In the dye sublimation world, heat is king. In order to fixate the dyes to the fabric, they must first be heated at 400˚F for at least 30 seconds. For that you need a good quality heat press or calendar unit. Any variation in consistency of time, temperature and pressure can impact color, ruin the job and in the end, cost you more money. Thus understanding the equipment necessary to achieve effective dye sublimation and rich output is one of the most important steps you can take.
This is the third in our five-part series that explores the intricacies of dye sublimation with guest expert Michael Syverson, Director of Special Projects at Louisville, Colo.-based PrinterEvolution. Syverson has been in the printing industry more than 20 years, and was an applications specialist on the VUTEk project team when it unveiled its first grand-format dye sub printer in 2001. In this article, we will discuss the heat press and calendar equipment that is used in the signage and graphics industry and other applications. The final articles in the series will explore finishing, marketplace economics and workflow.
This beltless calendar is designed specifically for direct dye-sub printing and doesn’t require transfer paper. (Image courtesy of Global Imaging)
Q: What does a heat press/calendar machine do, and why is it important in the dye sublimation process?
A: The primary purpose of a heat press or calendar is to facilitate the sublimation of dyes into fabric. All of these devices have a heated element and some sort of feature to apply pressure to the transfer paper and fabric to convert the ink to gas (sublimate) and have it permeate the fibers of the polyester fabric (or polyester coating). This is a required step in the dye sublimation process as the dyes are not fixated until they have been heated at a certain temperature for a certain amount of time.
Q: The terms “heat press” and “calendar” are frequently interchanged. Can you explain the difference?
A: Although the function of a heat press and a calendar in dye sublimation are basically the same—fixate the colors into fabric—the fundamental difference is that a calendar is designed for roll-to-roll sublimating, typically for rolled textiles and more commonly used in the signage and graphics industry. A heat press is designed for one-off images. Heat presses come in many different sizes and designs depending on the specific application. There are flatbed-heat presses that can be used for one-off flat prints such as mouse pads, glass or ceramic tiles, or other specialty small graphics. There are also circular heat presses with a curved heating element for imaging on to a mug, for example.
Smaller clamshell-style heat presses, such as this hand-operated model are ideal for one-off production of smaller imprintable items. (Image courtesy of U.S Cutter)
The most common heat presses are clamshell and swing-away units. A clamshell opens from the rear and the platen opens up at an angle to allow access to your image area. This is good for small imprintable items and garments. The swing-away style raises and lowers the platen vertically and swings to one side and is usually used for rigid surfaces. Some of these presses are automatic in that they will close and open on a timer so you have precise control of your transfers. Many units are fully manual. These are much more popular as they require a lower initial investment. Finally, there are units designed for transferring onto t-shirts. These have a shuttle type system so you can stage a t-shirt on a jig while one is transferring. If you are doing short-run t-shirts, this is a good way to produce this type of product.
There are many choices for calendars as well. They are available in several different widths and can come with many options, such as a staging table for setting up flexible sheeted goods, multiple rolls, different diameter drums, auto shutdown timers, blanket or belt lengths and a variety of other enhancements. There are also beltless calendars specifically for direct printing that don’t require transfer paper. You may need protection paper however if you’re working with delicate fabrics. Although these are less expensive machines, the results cannot be compared. The transfer paper produces a higher quality image, with sharper, deeper color output.
Calendar equipment, like this Klieverik model GTC 81/3400, is designed to transfer sublimate onto rolled fabric substrates. Fabric must be heated at 400˚F for at least 30 seconds in order for dye-sub inks to fixate into the fabric. (Image courtesy of Global Imaging)
Q: What is a flatbed heat press, how does it work, and what applications is it best used for?
A: Flatbed heat presses are designed for sheeted applications only. The presses can range in size from small 11" x 14" presses to 4' x 8' presses with two full size beds. They usually have a bed where the substrates and transfer paper is laid out. Above the bed is a heated platen that is lowered on the substrate. This bed is heated to approximately 400˚F and is lowered on to the substrate with an amount of pressure sufficient enough to sublimate the inks into the donor substrates. The pressure and time can be changed based on the substrate. Some of these devices are manually actuated while some of the more sophisticated devices have electronic or pneumatic systems for raising or lowering the platen. Many of the smaller products, such as gifts, promotional items, and specialty graphics are imaged with the smaller units. Some larger shops use the bigger presses for higher volume products. A 4' x 8' press can be used to set up 32 12" tiles with one large sheet of transfer paper to create custom tiled mosaics, for example. The units with two 4' x 8' beds are designed so you are laying out one print while the other is sublimating, creating a more efficient workflow.
Q: What is a rotary calendar and how does it work? What applications is it best used for?
A: A rotary calendar is designed for output onto flexible substrates, such as rolled fabrics. Its operation is somewhat similar to a laminator. There is a continuous blanket (or belt) that wraps around a heated cylinder. Fabric and transfer paper are put together and set upon this blanket. The blanket carries the fabric and paper and presses it against the heated drum for a given time to sublimate the image to the fabric. The blanket also has pressure applied to it against the drum to help facilitate the process. The advantage of this device is that is can be used for high volume rolled goods (and some select sheet materials).
Because the material is wrapping around a heated cylinder, items such as coated tiles or other rigid materials cannot be sublimated with this process. For rigid materials, you must use a heat press. Calendars are ideal for the big production textile industry as well as large-format graphics such as exhibition signage, banners, exterior and interior design displays and upholstery.
These illustrations show a schematic of how fabric is threaded through a calendar fixation unit. (Image courtesy of Klieverik)
Q: What is “protection paper” and why is it used? Is it different than transfer paper?
A: Protection paper, or tissue paper, is used on a calendar or heat press to protect either the drum/platen or the blanket from ink sublimating on to it. It absorbs excess gasses that do not sublimate into your polyester fabric or coating. If, for example, you did not use tissue paper on the blanket of your calendar and ink sublimated through the fabric, there is a possibility the ink in the blanket would offset back into your fabric the next time that spot in the blanket wrapped around and came into contact with the fabric. This is a very important component to use on the calendar in order to extend the life of the blanket and prevent any unwanted offsetting of ink onto your printed graphics.
Q: What should a print shop owner look for when purchasing a calendar and/or heat press?
A: There are many things to consider when choosing a calendar or heat press.
For calendars you need to consider:
The width—The calendar should match up in terms of width with the output device being used. Calendars are available in sizes from 64" up to 10' wide. Many shops will purchase a calendar that is wider than their current output device in the event they decide down the road to purchase a wider printing device. Companies will purchase the calendar and keep it many more years than a printer so anticipated growth should be taken into account when purchasing.
This dual swing-away heat press is designed to sublimate onto larger polyester-coated rigid substrates. (Image courtesy of GraphicsOne)
Maximum capacity—Calendars have a cylindrical drum that is heated. The diameter of this drum determines the speed of the calendar, as fabric needs a certain amount of contact time with the drum to achieve proper fixation. The bigger the diameter, the faster it will produce graphics.
How the drum is heated—Most calendar units these days have a drum filled with oil that is heated to approximately 400˚F. You want a calendar that uses oil because it produces a very even heat across the width of the unit and the temperature will stay very stable. Calendars with electrically heated drums can cause hot spots in the fabric and some units cannot keep up with the transfer speed in terms of heat. Hot spots can cause color differences and a variance in temperature from the beginning to the end of a print.
The length of the printing blanket or belt—The longer the belt, the steadier it runs through the calendar. The belt will tend to wander and move which has to be corrected and different machines have different ways of handling that. Some machines use a pushing and pulling mechanism that tends to damage the belt over time. Others use an electrical steering arm that moves up and down which doesn’t damage the belt and extends its lifetime.
Understanding the function and applications of the heat press and/or calendar unit is crucial to achieving beautiful dye-sub output such as this. (Image courtesy of Mimaki)
For heat presses, the following areas need to be considered:
Size of press bed—How large do you need the press to be? It again depends on the application.
Heating element—Most heat presses use an aluminum upper heating element with a heat rod or heating wire attached or cast into it. Make sure the heating element heats evenly and can keep consistent heat. Where many heat presses are one-off type machines, it is easier to maintain heat as you can let the press heat back while you are staging your next print.
Warranties—You should expect at least a one-year warranty on your purchased piece of equipment in addition to training and installation.
Q: What is the Black Box equipment used in direct printing?
A: This type of device is usually associated with all-in-one units that print and sublimate in one pass. These units have infrared heaters (or similar) that heat the box and start the sublimation process. They have the advantage of not needing a separate device for sublimation, but do have limits. Some of these units cannot sublimate the ink completely and may require the finished graphics to be washed after printing/sublimating to prevent any of the un-sublimated ink running on the finished graphic. Also, due to the nature of these units, transfer printing is usually not possible due to the architecture of the printer/heating element. A calendar or heat press provides the best possible solution for sublimation as it has the ability to apply pressure to the graphics as it goes around the drum (or under a platen). Most of the black box units do not have this ability.
Q: How can a shop owner justify the cost of the calendar versus that of a heat press. What are the particular benefits?
A: The choice between a flatbed heat press versus a calendar unit is fairly simple. It really depends on the applications. If a shop owner is producing soft signage (banners, flags, etc.), then a rotary calendar is the way to go. If a shop is producing nothing but small garments, gift and promotional items, then a flatbed press is more appropriate. Several shops that have rotary calendars may also have a small heat press for proofing small files or testing different applications. The smaller heat presses are relatively inexpensive and cost much less to operate than a 10' rotary calendar.
To continue to Part 4, Click Here.