Heat transfers might not be one of the most obvious uses of digital printing, but for years, innovative companies have succeeded in creating a market in a variety of ways.
Heat transfers might not be one of the most obvious uses of digital printing, but for years, innovative companies have succeeded in creating a market in a variety of ways. From bar codes to plastic decorations using digital presses, the uses of thermal transfer printing have continued to develop. Today thermal transfer can offer a choice of finished printed items, pre-printed transfers, or blank foil rolls that customers can apply themselves.
New advantages of thermal transfer techniques include: instant uptime without the need for plates or screens, short to medium runs with customization as needed, high resolution, wide color gamut and opaque white undercoats of the latest generation of digital presses, as well as a transfer application from foils and machines developed by avant-garde users.
Since the transfers are dry applied with instant set glue, the printed casts can be handled, assembled and packaged immediately afterwards. It is much simpler and much more flexible than using in-mold decorations.
Some users have gone so far as to use their own chemical researchers to develop their sheet materials. Lacquer and adhesive can be matched to different substrates: for example, alcohol resistant lacquer can be used successfully on cosmetic bottles.
The ability to print small quantities in color at high resolution, with white backing if necessary, allows attractive designs to be developed for smaller quantities and with more variation than with conventional processes.
The very fine transfer gives a “label-less” look, according to users. It appears to have been printed directly onto the surface. A paper or plastic tag is always separate from the item. Brands, especially cosmetics and pharmaceutical companies, are increasingly concerned about counterfeiting. They see a substantial advantage in “printed” transfers because of their permanence.
Before the development of the digital method, heat transfers had to be carried out either by screen printing of limited quality, or by gravure printing and solvent inks, which offer high quality but the cost of creating the printing cylinders means that only very long prints are achievable. Digital transfer printing allows variations within a series, so that branded items can be produced with the names of individual stores, bars or restaurants, or sporting events, for example.
How it works
Heat transfers are built on a roll of plastic film that is discarded after the image is transferred to the final article. The film is coated on one side with a heat activated release layer. Above this is a very thin layer of lacquer which forms the final upper protective surface of the image. Blank aluminum rolls are loaded into the press, which prints on the lacquer layer. Its thermal process fuses the toner particles together and they adhere to the lacquer.
After printing, the sheets are rolled up and transported to a coating station, where a heat activated adhesive is applied. Different adhesives are used, depending on the use of the transfers. Originally, sheets were only used with rigid plastics, but flexible plastics (such as polypropylene and polyethylene) are also an option.
A myriad of possible uses
Techniques such as heated roller heads and custom-designed application machines allow the thermal transfer process to be used for a wide variety of products. From large and small cylinders (ice buckets, beverage containers, cosmetic pens and applicators) to covers for phones and tablets, images may be completely transparent and look like direct print, but with much higher color quality than screen process.
Other transfer processes
Promotional heat transfers are just one of many “indirect printing” processes that can be handled by these presses. The others are textile transfers, decals for water slides and industrial transfers.
For textile transfers, color images are combined with a white undercoat and specialized glue and are applied by screen printing. Images are transferred to textiles using widely available heat presses.
Waterslide decals are used for tricky shapes such as sports helmets and ceramic plates and bowls. They are usually applied by hand. Here, a paper backing is coated with water soluble gum, and then the toner image is printed on it. A protective lacquer is then applied on top.
Although popular in uses around promotional products, a very similar process is also used for industrial work, such as labels for paint and chemical drums which must be tear-proof and resistant to chemicals.
Clearly, heat transfers hold tremendous potential, even beyond current use on plastics. Innovative users are working on sheets suitable for metals, glass, ceramics and other materials, and are working to automate more application systems. The future is certainly bright (and hot) for thermal transfer techniques using digital printing.