(219e) Validation of Calendering Models for Coated Papers Made From Blend of Agri-Residue and Softwood Pulp with Softnip Calendering Techniques

Sanjay Tyagi ^{a *} and A. K. Ray ^b

^a  Scientist C, Central Pulp and Paper Research Institute, Post box no. 174, Paper Mill Road, Saharanpur  – 247001 (U.P.), INDIA

^b Professor, Department of Paper Technology, IIT Roorkee (Saharanpur Campus), Saharanpur – 247001 (U.P.), INDIA

ABSTRACT

Calendering is the final operation in the manufacturing of papers with the purpose  for quality products by densification, and to  increase smoothness( or to decrease the surface roughness) and gloss.  In order to do so  it decreases the thickness and bulk of paper. It is especially important in case of coated papers  or paper boards where increase of gloss is essential. Paper is therefore, pigment coated to obtain a surface with improved optical and print performance additionally. However this is done under many modified operations such as supercalendering or softnip calendaring process. Generally, during calendering operation paper is subjected to compressive pressure pulse under the nip. After the nip, there is time dependent partial recovery of the initial thickness. The behaviour of the paper under calender nip  is therefore viscoelastic in nature.

In the present paper modelling of stress – strain behaviour of coated paper under soft nip calender and its viscoelastic properties are attempted. The base paper used in this study was collected from the paper mill in reel form and having the furnish composition of 75% agricultural residue (bagasse/wheat straw) and 25% of soft wood chemical pulp. The paper coating trials were conducted on DT pilot coater at the speed of 20- 30m/min. During the run only one top side of paper was coated with the coat weight ranging 10 - 12 g/m². The coating formulation consisted of 100 parts pigment (fine ground calcium carbonate and fine clay in ratio of 80:20), 12 parts SB latex, 1 part CMC , 0.12 part OBA and 0.5 part dispersant). Calendering was carried out using soft nip rolls under varying calendering conditions of temperature from 60ºC to 85¢ªC and nip load of 84 kN/m to 120 kN/m. The moisture content of paper varies from 4.1% to 5.7 % . For drying of paper two IRT- Monocassettes of infrared units were used to give a temperature of 60 – 70°C. The temperature of air drying unit was kept at 50 °C .The data obtained after softcalendering were subjected to  various  investigation.

   Available models for viscoelastic properties were critically examined and systematic estimation of the interrelated parameters of the viscoelastic models were made. The models were simulated with the data obtained from laboratory soft nip calender for coated paper. The flow chart is drawn to estimate the various parameters to the model simulation. The parametric effects were interpreted  through various graphs  and figures.