The Behavior Analysis And Fractal Modeling Of The Imbibitions For Paper Coating Materials

The imbibition of the coating determines the combination of the ink and the coating,which in turn affects the quality of the printing.If the coating has poor permeability,it will cause print quality problems such as offset printing and ink stains.Therefore,it is of great significance to study the wicking behavior of paper coating materials to improve the printing quality of coated paper.Paper coating material is a widely used porous medium with a large number of disordered pores,and it is difficult to characterize with traditional geometric methods,which brings some difficulties in studying behaviors of imbibition.The fractal theory provides an effective theoretical basis for characterizing the microstructure of porous media.Some studies had applied the fractal theory to the problem of fluid permeability in porous media.However,studies on the characterization of the self-imbibition of paper coating materials based on fractal theory were limited.Therefore,based on the paper coating material imbibition experiments,this paper explored the paper imbibition behaviors,and the network modeling software PoreXpert was used to simulate the imbibition of the samples.Moreover,based on the fractal theory,a imbibition model including the pore fractal structure was established by considering the pore structure of the paper coating material,and the validity of the model was verified by matching with the imbibition experimental data.The specific research work and some conclusions are as follows:(1)Aiming at the measurement of the coating material’s imbibition,an imbibition characteristic measurement device and a data acquisition system were established.The position control of the sample measurement was realized through the design of an automatic lifting fixture.Based on the communication mechanism between the Lab VIEW software platform and the RS-232 serial port of the balance,an acquisition module for imbibition data was developed,which realized automatic collection of imbibition data and provided data support for the later measurement of the imbibition characteristics of paper coating materials.(2)The mercury porosimeter was used to determine the basic parameters and distribution characteristics of the pore structure of three paper coating materials,i.e.cbGCC,fbGCC,and fnGCC,were obtained by mercury detector.Results showed that the equivalent capillary radius followed RfbGCC<RcbGCC<RfnGCC.The imbibition measurement system was used to measure the three coating materials,and the behaviors of imbibition were described under the time mechanism and the root time mechanism.The imbibition behaviors of the samples were analyzed through the classic inertial force mechanism,Lucas-Washburn mechanism and Bosanquet mechanism.It was found that in the initial stage of the imbibition,the behaviors of imbibition conformed to the inertial force model;the behaviors of imbibition followed the Lucas-Washburn mechanism and the Bosanquet mechanism over longer periods of time.The imbibition measurement system was used to measure the paper filled with fbGCC(90 w/w%<2μm finely ground calcium carbonate),at different filler levels of 0 w/w%,0.75 w/w%,1.25 w/w%,1.5 w/w%.Results showed that For papers with no filler or less filler,the y-direction imbibition followed either the inertial model or the Lucas-Washburn model.With continuous increase in calcium carbonate filling on paper,the pure inertial force model was followed at the initial stage,and then converted to the Lucas-Washburn model.In addition,the Matlab software was used to simulate the three classic imbibition models.It was found that there was a gap between the model prediction and the experimental data.Therefore,these three classic models were only suitable for qualitatively predicting the imbibition behaviors of paper coating materials,and cannot accurately quantify the imbibition results of samples.(3)Based on the pore characteristic data,the three-dimensional network models of the samples were established by a channel network modeling software-PoreXpert,and the sample models were simulated by imbibition.The results of the model simulation experiments were in accordance with the experimental results in Chapter 3.It was further verified that the initial phase of the samples in accordance with the inertial force model.With the progress of the experiments,the imbibition characteristics of the coating materials followed Lucas-Washburn equation.(4)The fractal geometry was used to describe the pore structure characteristics.And the fractal geometry theory was used to characterize the pore structure of the coating material.The fractal dimension of the pore structure of the samples were calculated by the mercury intrusion method.There was a corresponding relationship between the fractal dimension of coatings and the pore structure and imbibition characteristics,which further proved that the pore structure of coating materials has fractal characteristics.Based on the existing porous material permeation model,the imbibition expression including fractal structure parameters was derived and matched with the results of imbibition experiments.The results showed that the porous media imbibition model with fractal structure parameters does not agree well with the experimental results of paper coating materials.Therefore,a coefficient k and a constant B were introduced to modify the model which can accurately predict the imbibition weight of paper coating material.