| Direct Thermal Imaging is a common process used in | | | | the substrate before it passes under a powerful jet |
| many commercial applications. This process does not | | | | stream of air that "blows off" the excess material. |
| use ink; instead the paper is coated with a special | | | | Slot Die Coating: The coating squeezed through a |
| material that turns dark when heated. The image is | | | | narrow slot onto the substrate. The slot width and the |
| made when heat pulses applied by a direct thermal | | | | substrate speed along with the flow rate of the |
| print head are delivered to the coated surface. | | | | coating solution through the slot head determine the |
| Because the only consumable part of the print system | | | | coating thickness. |
| is the special paper or film, commercial direct thermal | | | | The final coated product must be able to consistently |
| imaging printers can be made lighter and smaller than | | | | enable quality printing in a number of different |
| inkjet type printers. Additionally these systems can be | | | | applications. Some of the characteristics to consider |
| refilled very rapidly and require very little maintenance. | | | | are: |
| This makes direct thermal imaging ideal for point of | | | | Image density: The denser image results in more |
| sale systems that print receipts and self service | | | | opaque printing. Less density results in "grayer" or |
| systems such as gas station pumps, kiosks information | | | | lighter black making it more difficult to read. |
| systems and ATMs. Direct thermal imaging is also | | | | Image clarity: The sharpness or clarity relates to the |
| used in many hand held devices used in inventory | | | | resolution. A sharper image is easier to read and |
| tracking and they are also used in many medical | | | | allows higher resolution which is critical in bar code and |
| monitoring devices. The applications for direct thermal | | | | QR code printing. |
| imaging are expanding as technology enables smaller | | | | Image stability: Image does not fade or lose color as it |
| and more portable equipment. | | | | ages. |
| Up until recently, paper and film converting companies | | | | Resistance to Environment: Many applications such as |
| had to rely on a select few suppliers with specialty | | | | gas pumps are subject to weather extremes in |
| equipment to obtain the coated material. However, | | | | addition to oils, grease, gasoline and solvents. |
| now there are liquid formulations available that can be | | | | Residue build- up: Residue building up on the print head |
| coated onto paper or film using common coating | | | | will result in maintenance issues or print quality issues. |
| technologies. This is good news for the converter | | | | Adhesion Properties: How well does the material |
| because they can use their existing coating equipment | | | | adhere to the paper or film that is being coated. |
| with no modifications. Using their own equipment should | | | | Cost effective coating requires a material that is |
| result in significant cost benefits, however one must | | | | "friendly" to the manufacturing process. A material that |
| insure that quality of product is not sacrificed. | | | | allows for quick set up and long trouble-free runs will |
| The following are some of the more common coating | | | | allow a manufacturer to efficiently utilize its coating |
| methods that are used by converting companies. | | | | equipment. |
| Gravure Coating: An engraved roller picks up the | | | | Some considerations relating to manufacturability are: |
| coating liquid and then deposits it onto the substrate | | | | Pot Life: A coating material that can maintain its |
| Reverse Roll Coating: A precise layer of material is | | | | properties for an extended time will result in consistent |
| applied to an application roller by a metered roller. The | | | | coating and more efficient production runs. |
| material thickness is controlled by the gap between | | | | Emissions: Volatiles and toxicity are important issues |
| these two rollers. The material is then "wiped off" the | | | | for environmental and employee safety. A "green" |
| application roller by the substrate. | | | | material is very desirable. |
| Knife Coating: Coating is applied onto a substrate | | | | Flow Properties: The viscosity of the material needs to |
| which then passes between a knife and a support | | | | be compatible with the coating process used. The |
| roller. The knife then doctors the excess material | | | | ability to "tune" the viscosity to the coating system will |
| away. The gap between the knife and roller | | | | result in a more efficient process. |
| determines the coating thickness. | | | | Clean Up/ Change Over: Ease of cleanup can |
| Mayer Rod Coating: The Mayer rod is a stainless steel | | | | dramatically impact change over costs. |
| rod that is wound tightly with stainless steel wire of | | | | Summary |
| varying diameter. The rod is used to doctor off the | | | | Applications for Direct Thermal imaging are increasing |
| excess coating solution and control the coating weight. | | | | as technology is expanding, any converter that has the |
| The coating thickness is controlled by the diameter of | | | | ability to coat with its own equipment while providing a |
| the wire wound around the rod. | | | | quality product should be able to increase its revenue |
| Air Knife Coating: Excess material is deposited onto | | | | and profits. |