Surface Modification of Coated Paper

To produce glossy coated paper, a calendering process is essential. Historically, the "supercalender"-featuring a combination of resilient rolls (made of cotton or wool) and chilled cast-iron rolls-was the standard equipment. More recently, the "soft calender"-which utilizes rolls covered with a polymer material-has gained popularity, originating in Europe and the US and now widely adopted in Japan.
Compared to standard machine calenders and supercalenders, soft calenders offer the following advantages:
They impart higher bulk, stiffness, opacity, and strength to the paper, while further improving two-sidedness (uniformity between the top and bottom sides).
After calendering, the paper web exhibits uniform density, excellent printability, and even ink penetration.
They tolerate slightly higher sheet moisture content, resulting in fewer web breaks and a reduced risk of black spots, thereby ensuring good runnability.
They allow for a moderate reduction in wood pulp content or a decrease in the basis weight of coated paper and newsprint without compromising print quality.
They are versatile, capable of being installed either on-machine or off-machine, and can also function as semi-wet calenders. All rolls feature independent drives and interchangeable positions, offering a wide range of applications.
Compared to supercalenders, they offer benefits such as lower investment costs, a smaller factory footprint, ease of operation and maintenance, fewer nips, and lower energy consumption.
However, soft calenders have limitations: the low number of nips makes them unsuitable for processing high-gloss art paper, whereas supercalenders suffer from slow operating speeds that constrain output. To address these issues, the "Janus Concept" calender-combining the strengths of both supercalenders and soft calenders-was introduced in 1995. Its key features include:
1. The number of nips can be selected according to requirements; an 8-nip Janus Concept calender achieves calendering results comparable to a traditional 12-nip supercalender.
2. It employs hot calendering and consumes less energy than standard soft calenders.