Question and Answer
Awareness of Potential Hot Stamping Foil Challenges
by Jeff Peterson
February-March, 2001What is happening to the hot stamping foil when silver (the metal coat) is showing through the color of the foil?
This problem is most commonly called splitting or silver splitting. It is very uncommon in lighter shades, including golds, but does occur occasionally with darker metallic colors. The reason that splitting sometimes occurs is because the lacquer coat, which contains the colorant that produces the desired shade, doesn't bond correctly to the aluminum layer of the foil. First, if the adhesive coat (sizing) is not consistently applied, certain areas of the foil roll may not release from the carrier properly, causing the lacquer/color coat to stay on the carrier while allowing the adhesive and metal coat to transfer. As a result, silver spots can appear on the foil stamped image where the lacquer did not transfer. The second reason splitting can occur is when there is too tight of a release between the lacquer and the polyester carrier. When there is a strong bond between the lacquer and the polyester and a good bond between the sizing (adhesive coat) and the substrate, you can get a splitting between the lacquer and metalization. This is caused by a lack of release agents when the release coat is applied to the foil roll.
One way to test the foil for potential splitting problems is to take a piece of scotch tape and secure it down on the adhesive side of the foil. Slowly pull the tape up and check to see that there is a clean transfer between the lacquer and the polyester carrier. If you still see some of the color coat remaining on the carrier, you may have a splitting problem with the foil on press.
What is Guage Band and how does it affect hot stamping foil?
Guage band is a problem that occurs in the manufacturing of the polyester film. Simply put, gauge band occurs because the thickness of the polyester film is not consistent throughout the roll. It is difficult to monitor on the film, but becomes more evident during the manufacturing process of the hot stamping foil. The biggest problem that gauge band causes is in the converting process where a foil roll is cut by the foil manufacturer or the final user.
You can detect guage band with a wavy appearance that occurs on one end of the roll. On a standard roll of foil, air acts as a lubricating layer that allows the lateral movement of the foil when it is cut with a single bevel blade. Guage banding creates an uneven surface that prevents lateral movement and causes friction between the cutting blade and roll. This friction can cuase the cutting edge of the foil roll to fuse or weld together. In turn, if the foil is used on press, it will tear and rip from the welded edge. Gauge band will usually not cause workability problems with hot stamping foil. However, the converting of the foil roll is where problems can occur.
What is occurring when small pin holes begin showing on the foil stamped image?
Pin holes or blisters in the stamped image are caused by air that is trapped between the foil and the substrate. Most foils are manufactured for graphic applications with what is referred to as "blush." This is a controlled amount of moisture that helps foil to adhere to porous surfaces. As heat and pressure is applied, this moisture content in the adhesive penetrates the surface of the substrate. If the substrate is not porous at all, the moisture and air will be trapped between the substrate and foil and the only place for it to release is through bubbles or pin holes in the foiled image. This is common with laminated sheets or certain types of coated stocks. In addition to air entrapment, pin holes can be caused by gasses that are activated when stamping over certain inks or coatings. The heat and pressure of the hot stamping process can create a gas that will usually try to escape though the foil stamped image.
Air entrapment or gassing problems can be dealt with by creating a domed makeready where the image is being stamped. Simply build up your makeready ever so slightly in a dome shape with makeready tissue using three to four layers. If you are utilizing a Kluge press, it is recommended to actually create the domed makeready on a seperate sheet and slip it between the 1/8" steel plate and the platen, making sure it is registered to the stamped image. This will push the air or gas out the side of the stamped image and help keep it from being trapped. In addition, it is always a good idea to have your engraver drill holes in the stamping die in non-image areas, especially for medium to large solid coverage. This, again, will allow the air to travel through the die versus being trapped between the foil and the paper.
What are plasticizers and how do they affect hot stamping foils?
Plasticizers are used to make PVC flexible, which is most commonly known as vinyl. The tricky part about plasticizers is that many times hot stamping foil can be applied without any problem. However, the plasticizers will begin to migrate up into the foil stamped area after the product is stamped and begin to deteriorate the color/lacquer coat. This can sometimes become evident in a matter of days or up to a year. Eventually, the plasticizers will compromise the metalization layer and completely erode the stamped image.
The best way to deal with plasticizer migration is to utilize a foil product specifically formulated for vinyl. However, even specially designed foil products may not be 100% effective due to the aggressive nature of plasticizers. A simple test is to stack a dozen or so stamped items and rubber band them together. Place the stack on the dashboard of a car and expose the stack to the heat of the sun for a week or so. Stacking them allows the foil stamped area to be exposed to the plasticizers from both the top and bottom. If it holds up under these types of conditions, you can feel fairly certain you are using the proper foil product.
There are an enormous amount of challenges that hot stamping foils can create. Many start from the manufacturing process (which is extremely difficult - just ask a foil manufacturer,) and many from on-press situations with the substrate or makeready. The best solution to most challenges is to make sure that you have explained your application to your foil supplier in detail before just simply throwing on whatever foil is available. Utilizing the correct foil product for specific applications is the best place to start, and can save an enormous amount of time and money.
InsideFinishing would like to thank Anthony Zerillo of Sanyo Corporation (877-565-1888,) and Brian Hill of Kurz Transfer Products (888-333-2306,) for their assistance with this article.