Curl Control for Printed Paper Grades
NW DeCurler® System provides superior curl control for narrow web printing presses.
Features/Benefits
- Can be used with all printing processes
- Patented Coanda nozzle Steam Application
- Simple to install and operate
- Profilable CD control zones
- Auto On/Off Control
- Steam application method provides consistent and precise curl control
- Simple to install and operate
- Faster Sheeting speeds
- Better performing product to customers
- Typically pays for itself in six months or less
The Need for a New Solution
Traditional methods of controlling curl such as back wetting, drying restraint, and mechanical deformation are no longer considered acceptable given their limited effectiveness and the emergence of quality as a driving force in the marketplace. In today's competitive business world, there is increased importance in searching out new, more effective means of curl control.
What is Curl?
Curl can be defined as the tendency for a flat piece of paper to distort in a cylindrical fashion. Curl is caused by the uneven expansion and contraction of fibers and/or coating, which causes one side of the paper to appear to "grow" more than the other. Once the curl memory state is set, a change in the exhibited web curl can usually be attributed to a change in its moisture content. This is due to the fibers growing more in the cross-machine direction (CD) than the machine-direction (MD). Processing techniques which can cause curl include:
- Differential drying
- Coating applications
- Mechanical forces (e.g. roll set)
- Two-sidedness
- Laminations
- Solving the Problem
When steam is applied to paper it condenses, imparting both heat and moisture to the paper. This heat and moisture softens and re-moisturizes the fibers in addition to loosening the fiber bonds. Subsequent growing of the fibers and evaporation of surface moisture reset the curl memory state of the restrained paper. The objective of curl control is to reset the curl memory state of the paper so that lay-flat is achieved throughout the desired range of conditions.
The NW DeCurler Solution
Technological developments in nozzle and actuator design have led to the development of the NW DeCurler. Through its unique construction, the NW DeCurler can selectively and precisely control the amount of steam it applies across the width of the web, providing both cross-machine direction and machine-direction curl control. At the heart of the system is the Coanda nozzle which applies steam parallel and counterflow to the web. This steam flow pattern enhances the uniformity and efficiency of heat transfer by maximizing the time of steam engagement and minimizing entrained air traveling with the web. Steam flow is controlled by an auto-pilot pressure regulator and three steam-flow control nozzles spaced evenly across the shower. This gives the operator front, middle, and back cross-machine direction curl control. The outer surfaces of the NW DeCurler are heated to prevent moisture from collecting and dripping onto the web. This design feature allows the actuator to be mounted in any orientation, including above the web.
Application Considerations
When controlling the curl of printed paper, the NW DeCurler is typically located after the final print station. When used in conjunction with an on-machine laminator, the NW DeCurler is typically located before the laminator. The NW DeCurler has proven effective in con-trolling curl in a variety of applications, including printing processes:
- Rotogravure
- Flexographic
- Offset
- Intaglio
- Printed Paper:
- Metallized
- Embossed
- Laminations:
- Paper/Paper
- Film/Paper
- Foil/Paper