By Jeff Peterson, editor-in-chief, Plastics Decorating

The process of hot stamping a three-dimensional plastic part has been around for many years and is one of the oldest decorating processes. Although many decorating processes today have changed or evolved in different aspects, there is no other way to create a true metallic finish on a plastic part except through a hot stamping machine with a die and transfer hot stamping foil.

Actuating hot stamp press to apply gold metallic foil to blank disc mounted on fixture. Image provided by Hot Stamp Supply Company.

Plastics Decorating asked Jeff Wolford, technical coordinator/equipment sales at Hot Stamp Supply Company, to answer a few questions when working with plastic parts and hot stamping applications.

What questions should producers ask to determine the type of hot stamping equipment and correct tooling?
What type of plastic will the producer be stamping? The type of plastic will help determine the hot stamping foil and potentially the type of die that will be used for the application. Not all foil is made the same. There are different adhesives developed for different types of plastic. This is the first step when analyzing the application.

Are parts and drawings/prints available? This is important for setting up the tooling needed on the hot stamping machine to hold the part in place as it is hot stamped. If time is a factor in the job, it is important to have prints early to begin the process of making the nesting fixture and die before the part is molded.

Attaching 1/4″ magnesium die to dovetail using screws. Image provided by Hot Stamp Supply Company.

Is the area on the part to be hot stamped flat, contoured or concaved? This will determine the type of hot stamp machine and set-up for the part. This is important in producing the tooling and what type of die will be utilized for the job. If the area to hot stamp is flat, a metal die may be used to stamp the part. If it is contoured or concaved, a silicone rubber die may be used.

How large is the image? This is important for determining the type of die to use, but also the hot stamping foil. There are different hot stamping foils for fine lines versus a larger hot stamped image.

What is the end use of the part? It is important to know if the hot stamped part needs to have chemical, scratch or UV light resistance. As explained, there are a variety of different hot stamping foil formulations and certain foils that have resistant properties.

What type of dies are available for hot stamping, and what are the advantages
of each?
Silicone Rubber – a commonly used die choice for many hot stamping applications. The rubber can conform to slight surface sinks and irregularities in the plastic and reduce waste in the hot stamping process. Rubber dies have excellent thermal conductivity and heat conduction properties, which is extremely important – especially for large runs where the machine is running at high speeds. They are available in flat, multi-level and contoured configurations for diverse applications.

Magnesium – magnesium dies are photo-etched and less costly than silicone rubber or other metal engravings. They are a great choice for flat surfaces and short runs. Magnesium is a softer metal and not recommended for very fine detail or longer runs.

Copper – photo-etched and a stronger metal for flat hot
stamping applications. Excellent heat conductivity, so a good choice for high-speed and longer runs for plastic parts.

Brass – extremely durable choice for high-speed, longer runs. Brass allows for greater depth with the die if the application calls for the image to be pressed into the plastic part. Brass also is a great choice for hot stamping fine detail on plastic substrates.

Steel – hardened tool steel can be used for hot stamping for extremely long production runs but is not common for most applications.

One of the advantages of a metal die is it allows the image to be pressed into the plastic as the foil is applied. This can be important for outdoor applications where the hot stamping foil may wear off over time. The image or writing will still be readable if the foil is removed. Metal dies are best suited for softer plastics and for image areas that have a flat, non-contoured surface.

What advantages does hot foil stamping have over other secondary decorating processes?
Hot stamping is a flexible process that allows the user to mark a variety of different plastic materials and other materials such as rubber, leather, fabric and paper. One of the biggest advantages for the decorator is that hot stamping is a relatively clean, dry process and eliminates the use of any type of inks or chemicals. In addition, a hot-stamped image is a durable decorating process with excellent adhesion and abrasion resistance. As previously stated there are a variety of hot stamping foil formulations for different plastic materials and applications.

Hot stamping also provides flexibility with many choices of foil colors and types. Customers can choose standard metallic gold and silver as well as a variety of other metallic colors. There also are pigments and holographic patterns that can be used for plastics applications. A holographic foil can create a dazzling look to applications that include toys and advertising specialties.

What are disadvantages of hot stamping?
Although hot stamping can be accomplished on curved or contoured surfaces, it may not be the best choice for extremely uneven surfaces. This type of application is better suited for pad printing or possibly digital inkjet. In addition, if there are multiple colors to a specific image on a plastic part, hot stamping is most likely not the best choice. However, a multi-color heat transfer may be an alternative. It can still be applied by the hot stamp machine and a die and produce a multiple color image in one pass.

Another disadvantage to hot stamping is that once the image is applied, it is not going to be removed. With the application of pad printing, screen printing or digital inkjet ink, the print may be able to be wiped off and the part re-decorated for set-up and makeready. This is not a possibility with hot stamping. Lastly, the cost for the tooling for both the fixtures and dies can become quite costly depending on the application. This is more concerning with short runs and may be an obstacle for the feasibility of using hot stamping for certain applications.

Are different colors and types of foils available for hot stamping plastic parts?
As previously stated, hot stamping foils are available in an infinite variety of colors and designs including metallized, pigment, woodgrains and holographic foils. This provides the user and the final customer a variety of choices for the finished plastic part. Although the specific design is not easily changed in hot stamping a part, changing out the foil color or type of foil is an easy adjustment.

There are different series and formulations for specific plastics and foil coverage. What may work on a polypropylene part may not adhere to polyethylene. It is always recommended to test several foils for a particular job to choose the best foil for adhesion, resistance and color matching.

Any suggestions for alleviating common challenges and decreasing scrap rates when hot stamping a plastic part?
Precisely packing out parts is generally very important to consistently achieve a quality hot stamped image. This tends to alleviate wall thickness issues and decreases scrap rates. Moderate rough textures on the part can be overcome by using a silicone rubber die or hot stamping with a metal die with slightly higher heat and pressure. Precisely designed and manufactured fixtures also are important to accurately hold the part in place, which will ensure a quality stamp and decrease scrap.

Lastly, having the proper hot stamp machine tonnage and head/throat clearance is vital to eliminate challenges for a specific hot stamping job. A low-tonnage machine will struggle in its ability to achieve a complete hot stamped image if the surface area is too large or the material is too dense. This is another reason it is important to test the plastic material on the machine and with the correct hot stamping foils and dies.

Hot Stamp Supply Company’s commitment to the hot stamping industry – since its inception in 2000 – shines through its technical expertise and dedication to customer support. As a full-service distributor, Hot Stamp Supply Company provides a comprehensive range of premium quality stamping foils, hot stamping dies, graphics services, equipment and presses to meet all hot stamping needs. Its custom services, expert technical assistance and top-notch customer service ensure a seamless experience. Learn more by visiting www.hotstampsupply.com or calling 877.343.4321.