Q&A: Digital Heat Transfers
by Eric Steinwachs, sales and marketing director
Digital heat transfers are much like any other type of heat transfer – preprinted images on a carrier, supplied in a roll form and applied with heat, dwell (time) and pressure.
What are digital heat transfers?
The heat transfers are supplied in a roll form, on a polyester carrier, with an eye-mark to register the image to the part. The heat transfers are printed on a 12″-wide web for a max print area of about 12″, but usually slit down onto smaller width rolls. The final width is determined by the image size and machine requirements.
The difference in various types of transfers is in how the image is printed on the carrier. Digital printing uses toner-based 4-color CMYK process plus white (cyan, magenta, yellow, black and white) to produce the image. More traditional transfers use wet ink printing methods such as screen printing, flexography or gravure.
The customer-supplied image is pre-pressed for orientation and spacing on the web, and eye-marks are added for registration purposes in production. The image is sent by a computer to the print engine. After printing, the printed transfer film is flood-coated with a substrate-specific adhesive. If required, the roll is processed one more time to be slit down into rolls of the correct width.
What are the advantages of digital printed heat transfers over the other types of transfers?
Digital printing offers several unique advantages over other printing processes. Many of the same advantages with digital printing apply to digital heat transfers, including the following:
- No setup charges. The images are sent electronically to the print engine, which eliminates the need for screens, plates, cylinders or color-matching charges.
- Fast turnaround time. In most cases, digital heat transfers are shipped two to three days after receipt of artwork. This allows for quick samples, short lead times, lower inventory requirements and better response to customer requirements.
- Short runs. Eliminating the need for ancillary print items and having no setup charges make digitally printed heat transfers an ideal short-run solution. Customers can order several SKUs or different designs for the same product without needing any change to the printing process. Images can be provided in a requested order so the artwork changes in midstream without affecting production.
- Variable data or personalization. The image is sent to the print engine every time an image is printed, which allows the image to be unique or personalized. The variable data can be used for barcoding, serialization, lot codes or security numbering.
- 4-color process plus white. Digital transfer allows decorators to print as many colors as wanted in one pass for the same price as the one-color transfers. With the CMYK+W process and printing up to 1200dpi, photographic-quality prints can be created.
When wouldnt digital heat transfers be the best option?
Like all printing processes, digital heat transfers have limitations inherent to the method of manufacturing the images. When choosing the best printing process, consider the substrate, the part design, the required finished look and testing requirements to the finished product.
The part material will help determine the best process to use. I wouldnt recommend using digital heat transfers on parts or substrates that are flexible, such as stress balls, flexible PVC, soft rubber, balloons or soft touch material.
The part finish also will determine the best process with which to print. Heavily textured parts will not work well with digital heat transfers because the process is a dry printing method, so the image will not flow into the texture as it would with pad or screen printing.
If a project requires a finish like metallic silver, gold or holographic images, hot stamping would be the best option. If fluorescent or backlit options are needed, digital heat transfer may not be the correct solution.
I recommend sampling and testing before any process is chosen as the correct printing method.
Can I use my existing heat transfer equipment to apply digital heat transfers?
Yes, heat transfer equipment can be used to apply digital heat transfers, too. CDigital uses the standard 3″ core size, as well as black eye marks to register the image. The difference would be in some of the machine settings. Application requirements – such as temperature, strip delay, dwell and pressure – may require different settings than other types of heat transfers. Users also may require a softer rubber die or roller when using a digital heat transfer.
How has the technology changed with digital heat transfers?
Technology has changed in three areas: the print engine, chemistry and application equipment to apply the transfers have all improved.
At CDigital, Xeikon 3500 printing presses are used. This upgrade from previous equipment doubled the available print resolution from 600dpi to 1,200dpi. With the new print engines, these presses also print brighter whites and provide better color-to-color consistency between runs, compared to the previous equipment.
Several new film and adhesive systems have been developed for digital heat transfers. This increases the number of substrates upon which digital transfers will work. Most ridged plastics – as well as glass, wood, metals, hard rubber, paints, foil and lacquers – can be decorated. While most substrates dont require any post treatment, glass and ceramics require a post cure in a heat tunnel or oven for full adhesion.
The biggest change I have seen in the equipment is the pad transfer machine. This equipment was developed for low-pressure digital heat transfers. Traditional heat transfers require 500 lbs. per sq. inch of die contact area, and the pad material was too soft to apply a full image. The low-pressure digital heat transfers require a fraction of the force while applying the same size image. This opened the door for a hybrid machine using pad printing pads and a heated platen.
The pad transfer machine, used in combination with digital heat transfers, provides many of the benefits of both pad printing and heat transfer, including the flexibility of the pad conforming to various shaped parts while applying a preprinted multicolor image in one pass. This eliminates the need for custom countered dies and molds for various shaped parts. The flexible pad also will make up for greater part variation while still applying perfect images. In some cases, a heat transfer can be applied to assembled parts or in places where support behind the stamping area is impossible because of part design. A video of this style of equipment applying multicolor images in one hit can be seen at www.cdigital.com/video-gallery.php.
Will this process work for PMS colors?
I recommend getting a Pantone color bridge swatch book. This handy tool will show what a PMS color looks like next to its CMYK equivalent. Some colors are right on, others are close, some are off, and metallic colors – such as gold and silver – are not achievable. The guide will serve as a tool to avoid unnecessary preproduction expense.
Can digital heat transfers be used for any other applications?
Digital transfers also can be used for patterns including camouflage, diamond, woodgrain or herringbone. Digital transfers can print like wallpaper. The height max is 12 inches, but images also can be printed continuous length. If a solid color is printed, it can be used as short-run custom color foil. A light see-through color also can be printed to use as a tint. This process has applications in cosmetic packaging and on picture frames to create a patina effect.
The possibilities are endless. There is no limit on the number of colors and no need for long delays to prototype a printed part. Short runs and many SKUs are not an issue. Unique numbering, lot codes, barcodes, customization and security numbers all can be combined with multicolor artwork.