Fluting and kraft liner papers with GCC coatings and PVA binder

Background and objectives: Several studies have been conducted to improve the paper properties and this research is for coating process in the converting operations of papers. Improvement of paper properties can cause a variety of its applications. In general, the desirable properties are expressed by barrier, mechanical and optical properties. The aim of this study was to evaluate the effect of the GCC coatings on two types of base papers with two levels of binder.
Materials and methods: For this purpose, two different base papers (kraft liner and fluting from Mazandaran pulp and paper mill), immersion and bar coating methods as well as a binder (PVA) at two levels were used. Coating material had 20% solid content, including GCC (100 parts), dispersant (0.3 parts) and PVA (6 and 12 parts). Two suspensions with low and high binder were named no.1 and no.2 combination respectively. Dip coating was performed in the two suspensions for one minute, and the bar coating was carried out by the bench coater with the same combinations. Physical characteristics such as air resistance, thickness, mass, brightness and water absorption (Cobb60) for control and treated paper were determined. After the calculation, the coating weight and grammage was obtained, and then these data were entered to SPSS 16.0 software for analysis of variance.
Results: In comparison to the control group, all the treated fluting papers showed significant difference in grammage, thickness and coating weight. The significant effect was observed on air resistance of fluting and kraft liner papers at 5% level. However there were not any differences in bar coating method on air resistance at 1% level in fluting papers with low PVA and so in the kraft liner papers with high PVA. The amount of water absorption in the treated fluting samples with low and high PVA using bar coating method indicated a significant difference at 5% level compared with treated samples in immersion method and control group. However, the Cobb60 significant reduction at 1% level was seen in the low binder combination with rod coating method. In terms of lower water absorption, rod coating with high PVA was much better than the other treatments. Due to more coating weight in the immersion method, the value of brightness increased in the immersed samples. Except rod method with low PVA, other treatments created significant differences (5%) in brightness between the treated fluting papers and control group. Kraft paper samples showed significant differences in brightness at 1% with both suspensions in immersion method, but kraft samples of bar method with low PVA were significant at 5% level. Correlation coefficients between the coating weight and air resistance, thickness, brightness as well as grammage were 0.549, 0.734, 0.687 and 0.489 in the tested papers respectively.
Conclusion: According to information of this research, changes of water absorption in samples were low, but the rod method reduced water absorption and had positive influence on paper barrier properties. Brightness of studied kraft liner was pretty good and the brightness of this brown paper reached to 57. Even in cases such as water absorption and brightness, the first composition (low binder) was better than the other suspension. The air resistance improved in all treatments and increment of this measurement is more evident in the fluting papers and the immersion method. Due to the improvement of physical properties, barrier and brightness in treated paper, made value-added papers in these samples compared to the control groups.