Screen roller technology with a chamber doctor blade has established itself in our field in fewer than ten years. Kroenert has been involved in the development of this technology since the beginning and March 2010 marked the commissioning of its 250th chamber doctor blade assembly. Kroenert is rated among the world’s leading specialists in this field.
Rotogravure coating, the primary coating technology up to about ten years ago, has lost significance since the introduction of water-based coating. To meet the new demand for environmentally friendly technology and high production speeds, screen roller technology combined with a chamber doctor blade was developed. Foam and air bubbles in aqueous dispersions and sedimentation of pigmented coating compounds could be eliminated by using this technology, even running at high production speeds.
The development of the T-Doctor Blade, MG 300/900 and the MPG 600 CI by Kroenert opened the adaption of the doctor blade system for different coating requirements.
The T-Doctor Blade is a closed, chamber system requiring very little compound volume. The chamber doctor blade has a negative blade setting and does not oscillate. This system is used especially for low coating weights; compound volume in the chamber is minimal. Depending on the cell volume of the roll, a consistent coating weight can be achieved; the system is accessible and suited for a self-cleaning process.
Similarly, the MPG 300/900 is a closed, chamber system with an oscillating metering blade for screen roll applications. The doctor blade has a positive setting, and the system combines the advantages of classical rotogravure coating with those of the T-Doctor Blade. Doctor blade settings are controlled pneumatically, and blade changes can be performed without flushing the chamber. There is reduced vapour loss due to minimised process distance from metering to transfer, and even at high speeds of up to 600m/min neither foam nor bubbling occurs.
The MPG 600 CI is a closed, pressurised chamber system. Oscillation of the chamber doctor blade is possible. A large number of coating and viscosity variances are achievable without changing screen roller. The system is based on a three-chamber design to ensure great accuracy in compound distribution, metering and flushing. The metering blade setting can be either positive or negative, and quick blade changes are possible without tools or adjustments.
All screen roller pressurised doctor blade systems are suitable for use in direct or indirect runs. In the case of the T-Doctor Blade and the MG 300/900 this can be achieved either by the adjustment from a three o’clock position to a nine o’clock position, or by turning the trolley. This adjustment can be made in less than 15 minutes.
In the case of the gravure roller with pressurised chamber doctor blade, the MPG 600 CI, only the patented inner part needs to be turned – taking less than two minutes.
The application volume during operation with the T-Doctor Blade and MG 300/900 is determined primarily by the cell volume of the screen roller. To change the application quantity different screen rollers are required. However, using screen roller quick-change technology – sleeve technology – this process requires only about 15 minutes. A Kroenert coating head in the trolley format allows a fast roller change; new trolley preparation offline, parallel to production run, is possible.
Using the MPG 600 CI system from Kroenert, screen roller changes to adjust the coating weight are not required. Stepless coating weight changes of 40% to 200% are made quickly and easily by adjusting the chamber pressure. Almost all applicable compounds can be coated using aqueous solutions, solvents or 100% systems (such as UV silicone). With more than 140 deliveries, Kroenert and BMB are experienced partners.
A comparison of the features of screen roller systems clearly shows the differences. Download the chart as a pdf from our website.
We would be happy to advise you regarding screen roller technology with the chamber doctor blade. Moreover, from the end of November 2009 more detailed information will be available as a download from our website.