Filter Cake Formation and the Development of Porous Structure during Drying of Latex-pigment Coatings
A new mechanism for the consolidation of the structure of latex-pigment coatings has been proposed,by assuming the formation of filter cake at the coating surface,and by introducing the concept of the Latex Coalescence Concentration (LCC).The new model combines Lepoutres classic consolidation mechanism for coatings and Crolls film formation model for latex paints.The proposed model considers that,since water is evaporated during dry at the coating-air interface,while the solids(including particles and soluble polymers)are filtered out to remain in the suspension,a filter cake is formed at the top surface at the FCC,the first critical concentration,at which the continuous water film on the coating surface disappeared.Drying after FCC causes free water within the coating under the cake layer to migrate to the surface by capillary flow,and the filter cake will become thicker,until the front the cake reaches the substrate and a loose,gelling,three-dimensional capillary network is formed within the whole coating (LCC).As the distances between particles(or capillary radius)remain relatively constant before LCC,the latex particles retain their original shapes.However,after LCC,all water within the coating is hold by the capillaries.Further evaporation will cause the coating capillary to become smaller and the capillary force to become greater.Increased capillary forces induce the latex particles to deform and to coalesce,causing latex to adhere to pigment particles,or the binder particles to adhere to each other,until the coating reaches SCC,the second critical concentration,where the coating structure becomes so rigid that both latex and pigments can no longer deform and move,resulting in a solidified coating layer.The new coating structure consolidation mechanism is consistent with Lepoutres classic observation that latex particles retained their original shapes well after the FCC,and the experimental results of Whalen-Shaw and el.That the solid content at the FCC increased with increasing initial solid content of the coating colors.It also explains a common industry practice that the drying intensity after FCC must be controlled,because boiling of free water within the coating may disturb the filter cake.
filter cake coating consolidation latex coalescence skin formation drying
YONGHUA ZANG ZHONG LIU HONGBIN LIU ZHENLEI CAO PATRICE MANGIN
Tianjin Key Lab of Pulp and Paper,Tianjin University of Science and Technology,Tianjin,300457,P.R.Ch China National Pulp and Paper Research Institute,Beijing,100020,P.R.China CIPP,University du Quebec A Trois Riveres,Trois Riveres,Quebec,Canada G9A 5H7
国际会议
第二届国际造纸与环境学术会议(The Second International Papermaking & Environment Conference)
天津
英文
833-838
2008-05-14（万方平台首次上网日期，不代表论文的发表时间）