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 method of printing synthetic materials like textiles and other substrates by employing specialized "subliming" dies that change state from solid to gas at a predetermined temperature, pressure, and time. These gaseous dyes are precisely absorbed and incorporated into the substrate when placed under pressure. Once enclosed, the gas transforms back into a solid state. The end product is a washable, dry-cleanable, and permanently imprinted design that will not fade.
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 such as the Astex/AIT 354CR, 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 substrate to be printed on and the dye composition affect the variance in time. Typically, sublimation paper produced with ink jet printing takes 45 to 50 seconds. Using a dial on the control panel, the time is automatically set on all Astex/AIT computers. For instance, the Astex 7960T rotary drum machine can produce 5.93 feet per minute at a dwell duration of 20 seconds because of a belt wrap that is about 24 feet long and placed on the heated drum.
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.
Pneumatic, hydraulic, or electro-magnetic (see model 1112) systems are used by Astex/AIT platen type machines, like the model 165CR, to provide pressure. A widespread misperception is that sublimation requires pressures between 80 and 100 psi. This figure, which is shown on the air gauge, solely indicates the amount of air pressure applied to the machine. The cylinder size and plate area are used to calculate the actual applied pressure, which ranges from 2 to 6 psi.
Temperature
Traditional sublimation inks 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.
There can be a difference in tone in the print if the temperature is not kept within the range of +/- 5° F. Because of the nature of the heat transfer printing process, controlling this parameter can be challenging. Heat must be replaced with a control standard of +/- 5° F since heat is continuously removed from the heat source. The fact that the heat is continuously traveling toward the heat source's outer borders, whether or not the substrate is removing heat, adds to the complexity. In order to ensure complete security in temperature variation, Astechnologies was the first manufacturer to offer independent control of the heat across the breadth of the heated drum. They also invented the multi-zone heat control system.
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.
The key elements of added value in the heat press are productivity, quality, after-the-sale service and price.
Productivity
The Astex/AIT range of heat transfer printing machines is purposely designed to provide a choice of models, so that our customers can buy no more or no less than what is required for their specific production needs. For example, the Astex 7960T is designed to run at a maximum production speed of 5 feet per minute. This is the model which would normally be preferred and be the best value to a purchaser of a digital printing system like E-Stat which prints four-color sublimation transfer paper at 1.5 to 2 feet per minute.
However, conventional, offset, or screen printing sublimation systems have had a need for a more productive machine, for example our Model 7460 (14 feet per minute) or our Model 7072 (21 feet per minute). In these cases, the best 'value' in productivity was a larger, more expensive model. The lowest cost option for rotary heat transfer printing is the AIT model 7240IJ featuring a printing width up to 40'.
Quality
For reliable and reproducible color transfer, precise control over the parameters of time, temperature, and pressure at the intended or ideal production speed is needed. The length of the belt that makes contact with the heated drum limits the production speed of all rotary drum heat transfer machines. AIT provides a number of models that can run at different output rates.
Astex/AIT machines have superior control over temperature with our multi-zone heat control system and a proven pressure control system assuring consistent quality.
Price
Astex/AIT machinery is competitive in the initial purchase price with several ranges of productivity. However, the true value of Astex/AIT machines is found in state-of-the-art technology and after-the-sale support. A lower cost machine that does not produce to a desired quality or production speed is not of value. The cost of a production machine sitting idle because of a lack of a part or service support will quickly equal any initial cost savings.
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