Abstract:

Objective: Aiming at the poor permeability of formaldehyde-free adhesive in the paper interlayers as well as the covering the original paper colour and texture to some extent, To reduce the influence of formaldehyde-free adhesive on surface patterns of decorative paper, and also to provide a suitable method for the preparation of formaldehyde-free decorative paper, originated from the performance of decorative raw paper, the combination of intra-pulp filler filling and surface pigmented coating to treat the decorative raw paper was adopted., which aimed to improve the printing suitability and covering power of the paper under the prerequisite of guaranteeing the paper's permeability and absorption of the adhesive solution. Method: In this experiment, high-quality hardwood pulp and softwood pulp were selected for papermaking. The content of filler (TiO₂) in the pulp was set to three gradients of 20%, 30% and 40%, then the mixture of silicon dioxide (SiO₂) and polyvinyl alcohol (PVA) to coat theses base paper were used. After calendaring, the coated decorative base paper was obtained. The decorative base paper was impregnated with aldehyde-free adhesive, after hot pressing and veneering to obtain the decorated wood-based panels. The surface state and dynamic permeability of the decorative base paper were characterized and tested using scanning electron microscopy (SEM) and dynamic penetration analyzer, respectively. Inkjet printer was used to print in order to analyze the printing performance of the decorative base paper by the Spectrophotometer combined with the calculation of the relative contrast. The physical properties such as tensile strength, smoothness, air permeability, water absorption and whiteness of decorative base paper and the surface wear resistance, surface hardness and surface bonding strength of decorated wood-based panels are tested and analyzed. Result: The more pores of the base paper were filled with the amount of filler increasing, which would affect the permeability of the adhesives inside the paper. On the other hand, the dense surface coating would also reduce the permeability of the adhesives inside the paper to a certain extent. The color density of uncoated base paper declined with the increase of pulp filling, the density of green, magenta, yellow and black of coated base paper increased by 69.0%, 96.2%, 45.6% and 86.5% compared with that uncoated base paper respectively. The relative contrast of magenta, yellow and black reached the standard requirements. Coating can play a positive role in the printing suitability of decorative base paper, but the change of filling amount has no significant effect on the printing suitability of decorative base paper coated; With the increase of filling amount, the tensile strength and water absorption of decorative base paper decreased, and the smoothness, apparent density and whiteness increased. The tensile strength and smoothness of coated decorative base paper increased by 52.8% and 97.56% compared with that of uncoated decorative base paper, but the whiteness did not significantly change and a slight increase in opacity. The surface wear resistance, hardness and surface bonding strength of the coated aldehyde-free impregnated paper after hot pressing meet the standard requirements. Conclusion: Reducing the filling amount of decorative base paper pulp with surface coating, can improve the physical properties of decorative base paper and printing suitability. The decorative base paper produced in this way is suitable for the impregnation of non-formaldehyde adhesive, which is conducive to the development of non-formaldehyde development of decorative paper.

Key words: formaldehyde-free adhesive, decorative base paper, pigment coating, printability, dynamic permeability