VALIDATION OF CALENDERING MODELS FOR COATED PAPERS MADE FROM BLEND OF AGRI-RESIDUE AND SOFTWOOD PULP WITH SOFTNIP CALENDERING TECHNIQUES

摘要

Calendering is the final operation in the manufacturing of papers with the purpose forquality products by densification, and to increase smoothness (or to decrease thesurface roughness) and gloss. In order to do so it decreases the thickness and bulk ofpaper. It is especially important in case of coated papers or paper boards whereincrease of gloss is essential. Paper is therefore, pigment coated to obtain a surfacewith improved optical and print performance additionally. However this is done undermany modified operations such as supercalendering or softnip calendaring process.Generally, during calendering operation paper is subjected to compressive pressurepulse under the nip. After the nip, there is time dependent partial recovery of the initialthickness. The behaviour of the paper under calender nip is therefore viscoelastic innature.In the present paper modelling of stress – strain behaviour of coated paper under softnip calender and its viscoelastic properties are attempted. The base paper used in thisstudy was collected from the paper mill in reel form and having the furnish compositionof 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/m~2. The coating formulation consisted of 100 parts pigment (fine ground calciumcarbonate and fine clay in ratio of 80:20), 12 parts SB latex, 1 part CMC, 0.12 part OBAand 0.5 part dispersant). Calendering was carried out using soft nip rolls under varyingcalendering conditions of temperature from 60°C to 85￠~aC and nip load of 84 kN/m to120 kN/m. The moisture content of paper varies from 4.1% to 5.7 %. For drying of papertwo 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 aftersoftcalendering were subjected to various investigation.Available models for viscoelastic properties were critically examined and systematicestimation of the interrelated parameters of the viscoelastic models were made. Themodels were simulated with the data obtained from laboratory soft nip calender forcoated paper. The flow chart is drawn to estimate the various parameters to the modelsimulation. The parametric effects were interpreted through various graphs and figures.