White Paper: The science of sublimation

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White Paper: The science of sublimation

Dye sublimation is somewhat limited in application. You usually need special transfer paper to accomplish this and it is best applied to ceramic surfaces

The science of sublimation

First, let us go back to our high school physics class so that we can understand sublimation dyes. The dyes are called sublimation dyes because when heated, they sublimate. This means they change from a solid to a gaseous state. There is no intermediate liquid state ( similar to dry ice.

Digitally printing with sublimation inks

There are four digital technologies used to transfer sublimation inks:

Dye Sublimation

Wax Thermal

Wax Thermal Hybrid

Ink Jet Hybrid

These "multi-level" dots blend together to create photorealism and continuous tones very effectively, but the process is much slower than wax thermal. The process is slow because the printer must generate tightly controlled and much higher temperatures than a wax thermal printer.

Re-sublimating to do a heat transfer poses problems as well. Due to the paper's absorption qualities, it is difficult to coax the dyes to absorb into the transfer surface. Also, because you must sublimate the dyes a second time to heat transfer the image, you will see a somewhat subdued colour.

Dye sublimation is somewhat limited in application. You typically need special transfer paper to accomplish this and it is best applied to ceramic surfaces. Wax thermal printers utilise low temperatures to melt wax from a print ribbon onto paper. The pigments in the wax create the colourful image. There are only three colours, although some printers print a fourth colour: black. Wax thermal printers generally print 200 to 300 equally sized dots per inch. Because they print only three or four colours, they must use a method called half-toning or dithering to create a wide spectrum of colours.

To accomplish this they use a concept called screening that divides the print area into cells, each cell containing a grid of dots. For example, each cell could consist of a 5x5 grid of printer dots. This resulting cell of 25 dots gets filled in with the appropriate number of cyan, magenta and yellow dots such that, when viewed at a distance, fool the eye and create the illusion of continuous colours. Screening does, however, reduce the effective resolution of the printer. In this case, the resolution is reduced to 60 cells per inch (300 dots per inch divided by five dots per cell). Even though the image is sharp, when viewed closely, the dots are evident. This is a disadvantage of wax thermal.

To heat transfer a wax thermal image, you will need to use a transfer paper. Transfer paper has a polymer coating that is transferred to a fabric such as a tee shirt or hat, sealing the wax pigments on the fabric. This coating adds weight to the fabric and makes it stiff. You can only print on white or light fabrics. And you cannot print on hard surfaces such as plaques and awards.

Wax Thermal Hybrid Sublimation is a merging of wax thermal and dye sublimation technology. That, in fact, is why we call it hybrid sublimation. You may also have heard it referred to as true sublimation or deferred sublimation.

Hybrid sublimation dyes are suspended in a wax carrier. The low temperatures of the wax thermal process serve only to transfer the sublimation dyes to the paper but not to sublimate them. When you heat the image in a press, the dyes sublimate and the wax stays on the paper, keeping the sublimation dyes from being absorbed into the paper. They are absorbed, instead, by the transfer surface. No specially treated paper is necessary. Sawgrass Systems holds patents on the hybrid sublimation process.

Because wax thermal hybrid sublimation is printed using wax thermal mode, you will see some of the dither patterns but you will also enjoy the speed of wax thermal printing and the ability to transfer powerful, vibrant colours onto many more surfaces than are available with the other methods. Any polymer-coated surface is a candidate for a hybrid sublimation heat transfer.

Compiled by Will Garside

( Sublimation 1999

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This was first published in October 1999

 

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