Study On The Preparation And Stability Mechanism Of Clay-based Composite Pigments

Composite pigments present bright color,good dispersibility and hiding power,as well as good light stability and thermal stability compared with single component pigments.Maya blue is a special organic-inorganic composite pigment with excellent weather resistance and acid resistance.Studies have found that the stability of Maya blue comes from the encapsulation of indigo in the channel of palygorskite and complex bonding between indigo and palygorskite.Inspired by the stability of Maya blue,sepiolite and basic red 46 were used to prepare composite pigments by negative pressure method.The product was compared with the composite pigments prepared by normal methods,liquid method and solid method.The result shows that the filling rate of the basic red 46 in the sepiolite pores in the composite pigment prepared by the negative pressure method was increased by 31.38%and 15.28%,respectively,compared with the solid phase method and the liquid phase method.In the test of the chemical stability and color stability,the composite pigment prepared by negative pressure method is the best.Three common clay minerals,sepiolite,palygorskite and montmorillonite are used as inorganic substrates,the cationic dye methylene blue and the non-ionic dye indigo are used as organic components to prepare composite pigments.The results show that the composite pigment prepared by the montmorillonite with the open layer structure and the cationic dye has the best chemical stability and weather resistance.The weather resistance of composite pigments prepared from indigo and clay minerals is affected by the very strong-strength acid sites in the clay minerals.Palygorskite with appropriate amount of very strong-strength acid sites can make the redox reaction of indigo reversible,and the prepared composite pigments have the best weather resistance.Sepiolite less Al content was modified by metal cations through hydrothermal reaction.The effect of the type of modified cations on the substitution amounts was studied.Among the three cations,the Al³⁺has the largest substitution for Mg²⁺and Si⁴⁺,reaching 1.2257 mmol/g.Change the amount of Al³⁺to modify sepiolite.The result shows that as the amount of Al³⁺increases,the amount of Mg²⁺replaced in sepiolite increases.When the modified concentration of Al³⁺is 1.00mol/L,the amount of Mg²⁺replaced in sepiolite reaches 1.6756 mmol/g,Al³⁺substitution mainly occurs on the octahedron of the sepiolite.After Al³⁺modification,the specific surface area of sepiolite decreased from 364.02 m²/g to 301.34 m²/g,and the amount acid of the sepiolite increased from 1.258 mmol/g to 2.562 mmol/g.The Al-modified sepiolite was used as inorganic substrate to prepare composite pigments with cationic dye and non-ionic dye indigo respectively.Studies have found that cationic dyes form electrostatic attraction with Lewis base sites in sepiolite through N⁺,and from hydrogen bonds with hydroxyl groups in sepiolite through N-H bonds.Among them,the sepiolite modified with 0.05 mol/L Al Cl₃ solution can absorb cationic dyes close to 100%under the conditions of this paper,and the prepared composite pigments have better chemical stability and weather resistance than that prepared by unmodified sepiolite.The bonding strength of Al-modified sepiolite and indigo dye is related to the Al-OH-H in the sepiolite.The more Al-OH-H,the higher the bonding strength.The acid in sepiolite will reduce the weather resistance of indigo-sepiolite composite pigments.