Thermographic Printing / Thermography is a form of raised printing that is created by applying a specific type of finely powdered resin, originally copal resin and currently polyester resin to wet ink and then melting it to form a smooth glossy three dimensional image.

This raised effect is also known as “poor Man’s Engraving”.

The principles of the thermographic printing process are extremely simple to explain.

Thermography-thermographic printing describes a post printing process that is done in today’s printing environment using traditional printing methods (ink on paper or other substrate) in conjunction with a thermograph also known as a thermography machine.

Thermographs consist of three separate components, that perform three different functions and that are connected by a through conveyor.

The first component of the modern day thermograph applies finely powdered polymer resin to the entire sheet. The areas selected for raised printing have been printed with inks that do not contain dryers or hardeners. These printed areas remain wet during the application of the powder. The powdered polymer resin adheres to these wet areas

The second component of the thermograph is a removal system that removes excess powdered resin from areas of the paper or other substrate that do not have printing that has been printed using inks not containing dryers or hardeners.

The surplus thermographic powder is then removed by suction, vibration or shaking, with the powder adhering only to the wet ink.

The third component of the thermograph conveys the printed product through a radiant oven where it is exposed to temperatures of that can range from 900 to 1300 degrees Fahrenheit (488 to 704 degrees Celsius) depending on the printed material being cured. The heating process generally takes approximately 2.5 to 3 seconds. The ink is dried or hardened during this heating (curing) process.

The substrate (usually paper) has a peak in IR absorption at the wavelength used in the curing oven (electric ovens only). Through conduction from the paper, the thermographic powder’s temperature rapidly increases and starts melting. When the thermographic process is correctly done, the center of the largest printed areas reaches the expected quality level as the printed product exits the curing oven.

The amount of heat applied to the printed material is determined by two variables, the speed of the conveyor belt and the heat settings of the oven. There are no simple rules to specify the conveyor speed control setting or the oven temperature setting which together gives the correct amount of heat for a particular job. This depends on several factors the most important the thickness of paper or other substrate used.

With thicker printed material more heat is required as well as a slower conveyor belt speed to allow the printed material more time in the curing oven.

Other variables include the grade of thermographic powder. Coarser thermographic powder or boldness of type will require more heat to process.

Atmospheric temperature, humidity of paper, reflectiveness of the paper’s surface, the metallic content of the thermographic powder and the voltage of the electric current to the thermographer can all be factors influencing heat control

The melted ink then solidifies as the product cools. The printed material is cooled as it follows the conveyor to a receiving tray where the material is delivered to.