How to Choose The Best Sublimation Paper When We Need
Category : Blog
More issues need to be addressed too: How important is transfer yield? When do I need “high speed” sublimation paper? An entrepreneur who is considering his first investment in digital transfer printing is confronted with other dilemmas, too: Do I choose a water-based system, or should I consider oil-based or solvent-based inks? Which type of sublimation paper is preferable for transfers onto metal or tiles?
As a specialist supplier, Fei Yue carries a broad range of sublimation paper. As our customers are entitled to objective advice, we wanted to describe the right sublimationpaper choice in a simple diagram for us to use when advising them. When we showed the draft diagram to a number of dye sublimation experts, they encouraged us to provide more background information. Thus, this article evolved from a diagram into a manual for choosing the right sublimation transfer paper, based upon the professionals’ collective experience. Unfortunately, it is not the simple diagram that we thought of at the outset. Rather, it is more complex.
First, we shall discuss the fundamental choices for ink systems: water-based, oil-based or solvent-based.
Then we will provide a guide for water-based systems focusing on three aspects:
transfer onto textile fabric versus transfer onto a hard substrate
the “basis weight”- “high speed” versus “normal” transfer paper
Finally, we shall look at other aspects of the transfer printing operation because the right paper choice is by no means the only condition for successful transfer printing.
Water-based Systems versus Oil-based and Solvent-based Systems
For many reasons, water continues to be the ideal carrier for sublimation inks. However, water and paper are not ideally suited for each other. Paper fibers absorb water by swelling. This mechanism poses an inherent problem for printing processes with water-based inks. Small variations in the amount of water can cause the paper to expand or shrink by as much as 1 percent or more. Such moisture variations not only occur as a result of the water-based ink being applied to the paper surface, but also because of variations in the air’s moisture content in the print room, to the extent that the unpacked paper is exposed to them. The limited dimensional stability of paper as a function of variations in moisture content generally does not pose many problems with narrow printers and small sheet sizes. However, wide-format printing is an altogether different matter. A change of 1 percent in the web width amounts to as much as 2.5 cm (nearly 1 inch) or more across the full width!
Grand Format printers are used for sublimation transfer printing with oil-based inks at widths of more than 3 metres.
photo credit: SGIA
Compared with water-based inks, oil-based inks cause less swelling of the paper fibers and none of the resulting problems, such as linear extension and cockling. For widths greater than 250 cm (98 inches), we advise our customers to consider oil-based systems but to take into account the following limitations.
Limitations of Oil-based Systems
Printed transfer paper is made up of a highly unstable system. This is because the transfer paper delivers a maximum amount of dye to the substrate during the transfer process. Dye particles in the printed paper must sublimate freely when exposed to heat in the transfer press. They must not be bound chemically or by any other means. Yet, before the transfer, the dye is not supposed to “migrate.” These more or less conflicting demands make the system extremely vulnerable and susceptible to contaminants from the environment. Even certain components of the paper and the ink may cause problems. Unfortunately, the “oil” in the oil-based ink is such a component.
When an oil-based ink is drying, the oil does not evaporate from the paper. At most the volatile fractions will evaporate. The remaining fractions facilitate the paper dye’s migration, causing colors to shift and details to lose their sharpness. Therefore, transfer paper printed with oil-based inks must be run through a transfer calender immediately after printing.
Promise of Solvent-based Systems
Solvents hold the best promise of enabling wide-format printing systems without having the limitations associated with oil-based inks. Solvent-based systems would make a larger number of printing platforms available for dye sublimation transfer.
There is a very good reason why solvent inks have not played a bigger role in sublimation transfer printing. Solvents bring environmental and safety hazards, which printers thought they eliminated when they embraced water-based sublimation inks. Printers with a background in the textile industry are accustomed to water-based ink chemistry, which has its own environmental problems. To them, water-based transfer printing provides a clean and safe business model. The situation in the sign industry is quite different. Solvent ink is the preferred method for producing outdoor graphics on uncoated, non-absorbent media. Sign printers are fully familiar with health and safety requirements. To the sign industry, solvent-based dye sublimation is not equivalent with new health and safety hazards.
It is too early to make recommendations about solvent-based sublimation transfer printing because there are still technical hurdles. However, we will be following developments in this new technology closely.
Small objects – the most popular application of sublimation transfer printing on hard surfaces.
photo credit: SGIA
Guide for Water-based Systems
Open Substrate (textile fabric) versus Closed Substrate (metal, ceramics)
Transfer papers for textile fabrics are specially designed to deliver the maximum amount of dye to the substrate (maximum “transfer yield”) during the pressing process, thus meeting the highest coloristic demands and allowing for the least ink consumption. Maximum-dye release occurs when carrier liquid and dye particles are not strongly absorbed into the paper and the dye particles are not bound to the internal paper structure. To achieve this, manufacturers have developed a closed film coating, which forms a gel with water from the printing ink. The barrier character of these coatings makes the papers less suitable for transfer to hard (closed) substrates. The vapor, generated when the paper is heated during transfer, can only escape in a lateral direction. This can easily cause damage to the print, which is visible in the cloudy vapor patterns in full colors and blurred contours.
For transfer onto hard surfaces, we recommend a transfer paper that allows the vapor to escape through the paper. This type of paper is similar to photo-quality inkjet papers, which dry immediately after printing. But there is a tradeoff. The dry paper surface is made possible by a special silicate-based coating, which draws the ink faster and deeper into the paper compared with the paper for textile fabrics. This results in a noticeably lower transfer yield. A second disadvantage of the hard-surface papers is that they cockle more easily due to the quick water absorption.
It should be noted that the hard-surface paper is popular with textiles and rigid surfaces in North America. Elsewhere textile printers generally prefer papers specially designed for soft substrates.