The Key Elements of Sublimation Heat Transfer Printing
Sublimation Heat Transfer Printing
The use of a heat transfer press for sublimation printing of polyester and other fabrics with “sublimation” dyes is a technology that has been in use for over 30 years. The process is environmentally clean and the vibrant colors and clear images give the process many advantages.
New textile technologies produce polyester fabrics that look and feel like cotton, rayon, and even silks. Also, new technology has produced polyester fabrics for athletic wear that are warmer/cooler than traditional cotton.
New digital technology has been introduced in recent years which allow a design to be created and printed onto a special sublimation paper, and then transferred onto the fabric using a heat press. The entire process can be completed within a matter of hours. Samples and short run production can now be printed, sewn and shipped within days instead of weeks.
Definition of "Sublimation" Printing
A process of printing synthetic fabrics and other substrates using special, “subliming” dies which turn from a solid into a gas at a specified time, temperature and pressure. Under pressure these dyes in gas form are absorbed and encapsulated with pinpoint accuracy into the substrate. The gas returns to solid form once encapsulated. The result is a permanent print which will not wear off and is washable and with withstand dry-cleaning.
The Key Elements of Heat Transfer Printing
There are three integral specifications necessary to achieve optimal heat transfer printing - time, temperature and pressure. All are interrelated to each other during the process, i.e. more time - less temperature; more pressure - less time and vice versa. The relationships are not proportional, but do have an effect on the quality of the print.
Time
The period in which the sublimation transfer paper and substrate is subjected to heat and pressure. On a continuous, rotary drum machine, this is a function of belt speed and the length of the heated area. On a platen style machine, it is the time that the heads are closed on the machine. Twenty to thirty seconds is a typical range for traditional off-set, screen printed and E-Stat printed paper.
The time variance is dependant on the dye formulation and the substrate to be printed. Forty to forty-five seconds is typical on inkjet printed sublimation paper. On press machines, the time is automatically set with a dial on the control panel.
Pressure
The process by which the sublimation paper and substrate is uniformly introduced to the heat source of the machine. Pressure requirements are relatively low (2 to 6 psi) but it is critical that the pressure is evenly distributed.
The Astex/AIT rotary drum heat transfer machines, including model 7300IJ, apply pressure in a conventional, time-proven method of belt tension applied to the contoured heated surface of a heated drum. This requires a special high temperature belt that has characteristics allowing it to conform evenly and firmly to a curved surface.
Astex/AIT platen style machines such as model 165CR use pneumatic, hydraulic or electro-magnetic (see model 1112) systems to apply the pressure. A common misconception is that 80 to 100 psi of pressure is needed for sublimation. This value only represents the amount of air pressure brought to the machine, and is displayed on the air gauge. The actual applied pressure (2 to 6 psi) is a calculation of the cylinder size and plate area.
Temperature
Traditional sublimation ink used in the apparel and textile industries for the past 30 years have required temperatures in the range of 400°F. These printed products have to perform well in wash and dry-cleaning tests.
The temperature must be maintained in the range of (+/-) 5° F, or there can be a shade differential in the print. The nature of the heat transfer printing process makes this a fairly complicated specification to control. Heat is constantly withdrawn from the heat source and must be replaced with a control standard of +/- 5° F. As a further complication, the heat is constantly moving toward the outside edges of the heat source with or without substrate withdrawal of heat. Astechnologies pioneered the multi-zone heat control system and was the first manufacturer to provide separate control of the heat across the width of the heated drum to achieve absolute security in temperature variance.
Always use AIT temperature test strips to verify actual temperatures and calibrate your machinery.
Added Value Elements
The heat press is the focal point of the heat transfer process. As the last step in the process, the printed product emerges from the heat transfer press. The heat transfer press must provide user friendly and precise control over the functions of time, temperature and pressure in order to produce the very best possible print on a wide variety of substrates.
These are some of the experiences I have summarized in the usual practice, and we can provide the best quality sublimation paper and services.If you have other questions, feel free to contact us.
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