The Dye Sub Column
Choosing a heat press for sublimation
In this month’s article, Jimmy Lamb, Sawgrass’ education manager, outlines why it is so important to choose the right heat press for dye sublimation printing.
S
ublimation is a chemical process that depends on molecular bonding. It requires precise heat press settings on three levels – time/ temperature/ pressure. Even a small variance in one parameter can affect the quality of the image. It’s imperative to choose a high-quality heat press that can consistently deliver the required settings for each and every job.
Time All heat presses come with
programmable timers. Most automatically activate when the heat press is closed and sound a buzzer when the time runs out. Some also have an auto-open feature but the abrupt opening may cause the transfer paper to shift in regard to the substrate. This can cause ghosting of the image. If using such a heat press, consider turning off the auto-open feature.
Temperature
Most sublimation products require a constant temperature of 200°C for one minute. A variation of even a few degrees may affect the colours and details of the final image.
Heat presses consist of two platens – upper and lower. The upper platen contains the heating elements, whereas the lower is a stable surface for supporting the substrate during pressing. Good quality heat presses have reliable heating elements that deliver accurate temperature with minor fluctuations. They are positioned close together to ensure that the temperature of the upper platen is consistent across the entire surface, thereby preventing cold spots. Cold spots will create uneven colourisation in a sublimated image. Lower priced heat presses utilise lower quality elements spaced further apart in order to save cost, but quality can be compromised.
Pressure
The upper platen also produces pressure on the substrate, another key part of the sublimation process. It’s critical that the platen be constructed of quality materials such that the surface is flat and even and
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does not give during the pressing process. Inconsistent or uneven pressure will affect the quality of the sublimation, leading to imbalances in colour, imperfect details and possible ghosting.
Heat press characteristics When choosing a heat press focus on the products you plan to produce in terms of size, shape and thickness and take these physical factors into account: Platen configuration
The majority of all sublimation substrates are pressed using a flat heat press, which come in several sizes and three different configurations – clamshell, swing-away and drawer.
Clamshell presses are the most common. The upper and lower platens are connected by a hinge at one end. Thus, the press opens and closes in an angular
up and down. The lower platen pulls forward, providing easy access for setting up the substrate. This press works well for both thin and thick substrates. Platen size
fashion. These are fine for thin substrates, but may have uneven pressure when dealing with thicker items like plaques, ceramic tiles etc. as more pressure will be applied close to the hinge. The end result may be uneven imaging and unbalanced colours.
Swing-away units have the upper platen mounted on an arm so that it can be lifted straight up and down. It is therefore exerting equal pressure across the entire surface of the substrate, regardless of the thickness of the item. Additionally, the upper platen is opened to one side, making it easier to access the lower platen for placing substrates.
Drawer units also have the upper platen mounted on an arm, allowing it to be lifted
Platen size determines the maximum size of images that can be applied. Equal heating across the entire surface is important for producing high-quality sublimation. There is a tendency for temperature to decrease along the outer edges of a press, so only press images that are smaller than the size of the platen, with a one inch buffer zone on all sides. Manual or pneumatic Platen pressure is an important production parameter. The recommended pressure for sublimation on most substrates is 40psi. However, most presses do not have pressure indicators, so medium pressure is the given standard. On a manual press, the pressure is easily adjusted by controlling the spacing between the two platens via a jack-screw system. Some presses are pneumatically controlled, which utilises air pressure to close the platen and apply a selected amount of pressure to the substrate surface. Pnuematic systems offer two distinct advantages. Firstly, the operator does not have to apply physical exertion to operate the system, and secondly, the precise pressure can be dialled-in, making it quick and easy to setup different types of substrates for production.
Specialty presses
Curved and rounded products require special heat presses such as the mug press and the cap press which have curved surfaces. In summary, the heat press is a critical part of the sublimation production and the focus should be on purchasing a reliable unit that will deliver precise temperature and even pressure on each and every job. Inconsistent pressing will lead to inconsistent imaging. Select a unit from a reliable source that offers technical support, parts and service. Focus on the long-term investment rather than the short-term purchase price.
March 2021 |69 |
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