Abstract
The objective of this laboratory-scale study was to find out how soy protein and three PVOHs functioned in comparison with CMC as co-binders in a 25:75 mixture of PCC and GCC, respectively, with 11% SB-latex as the main binder. Dosages of the co-binder varied at four dosage levels between 0.3-3% depending on the co-binder. Base paper was wood-free coating base paper. On the basis of the results obtained, CMC gave the highest low shear viscosity as well as water retention to the coating colors. Brightness measurements also included the effect of the co-binders as carriers of OBA. Here CMC and soy protein performed worst. Low DH PVOHs performed best. Behavior of high DH PVOH was not clear. As for opacity, CMC and soy preformed worst while low viscosity low DH PVOH performed best. As for the surface properties, again CMC and soy protein behaved quite similarly while PVOHs formed a group of their own. Gloss of PVOHs was higher and PPS roughness lower than that of CMC and soy protein. Also print gloss of CMC and soy protein was lower than that of PVOHs. IGT dry pick strength of CMC and soy protein was higher than that of PVOHs. No clear difference between the examined co-binder groups formed regarding K & N ink absorption. CMC gave the highest IGT ink transfer % while low viscosity high DH PVOH gave the lowest.