Q&A: Heat Transfer vs. Hot Stamping
by Eric Steinwachs
Question: What is the difference between heat transfer and hot stamping?
Answer: Hot stamping and heat transfer both require heat, pressure and dwell (time) to apply an image to a part. However, heat transfers are pre-printed images using silkscreened, gravure, flexography or digital printing methods on a release paper or film; whereas, hot stamp images are created by the art in the die. Heat transfers can be one-color or multi-colored images, while hot stamping is generally one color.
Question: Can existing hot stamp equipment be used to apply a heat transfer?
Answer: No. The equipment is similar, but applying a heat transfer requires an eye mark registration system. A "Webtrak" or heat transfer indexer uses a photo eye system to locate the image under the stamping head. After each image is applied to a part, the indexer advances the web to move a new image into place. This locates the image in the left-to-right position, while the front-to-back registration is controlled by the web tracking with guide rollers.
The tonnage required to apply a heat transfer is another equipment consideration. As a rule, 500lbs per square inch of die contact area is used to figure out the correct tonnage required to apply a heat transfer. For example, a 2x4" image area results in eight square inches of die contact or (8x500 = 4,000 / 2,000) a two-ton machine. However, a hot stamp image of the same size would require less than one-ton. Also, at some point the image area becomes too large to vertically transfer so a roll-on style machine would be required to avoid air entrapment.
Question: What are the advantages of heat transfers?
Answer: The major advantage of heat transfer decorating is that it is a dry process. There are no storage problems with flammable materials or strong odors, no ink mixing and no messy clean-up. The decorated part also is ready to be handled or packaged directly after printing. Printing and registration of the artwork is done on high-tech presses where multiple colors are printed in registration to each other. The image quality, along with the art registration, is inspected prior to the application process, thus minimizing scrap. In addition, all of the colors are transferred in one step, reducing the number of hits or passes required to apply a multi-color graphic. Changing the image on the same part only requires a roll change, resulting in a reduction in the set-up time between jobs.
In addition, heat transfers are engineered to meet precise customer requirements and specifications. Formulas specific to the individual product include chemical and abrasion resistance, UV stability, adhesion specifications and other requirements depending on the product being decorated. Finally, heat transfers are versatile and can be used on a wide range of plastics in production today, as well as glass, metal, wood, painted surfaces, paper and fabrics.
Question: In what industries are heat transfers being used to decorate plastics?
Answer: Because heat transfers work on most substrates, they are seen in all industries. For example, United Silicone has worked on applications in the appliance, automotive, personal care, industrial container, cosmetics, sporting goods, ad specialty, medical and apparel industries. With heat transfers, the possibilities are endless because of the wide range of spot colors and the use of process colors (CMYK+W), along with a variety of finishes. In addition to all of the color options, bold and fine graphics can be combined within the same print, along with the ability to print variable data. This is very attractive in many markets.
Question: What technology advancements have occurred in heat transfers?
Answer: I have seen advances in heat transfers regarding both the transfers and the application equipment. Heat transfer formulations improve continuously to keep up with ever-increasing substrate changes. Closer tolerances of color-to-color within the image and more accurate image placement on the part have met or exceeded customer demands. The application cycle and faster machinery have increased with better part handling and shorter dwell (time) required to apply the transfer. The capability of variable data (such as barcodes or lot numbers) has opened the door to applications that were not feasible in the past. The heat transfer web now can be laser or diecut, enabling raised or recessed areas on a part to be decorated. In the past, a part with a recessed or raised area would cause the web to wrinkle, creating a defect in the print. With the versatility in colors – including a new line of metallic inks, chrome-look inks and brushed-metal-appearance inks – and the ability to add decorations with a tactile sensation, I foresee a big marketing push to bring heat transfer decorating to a new level.