1. Application mechanism:
(1) The difference between coupling agents and surfactants:
In the process of coating manufacturing, it is necessary to disperse hydrophilic polar substances such as pigments and fillers into hydrophobic non-polar organic binders. In order to increase the affinity between inorganic substances and organic polymers, coupling agents or other surfactants are generally used to treat the surface of inorganic substances, transforming them from hydrophilic to hydrophobic, thereby promoting interfacial bonding between inorganic and organic substances.
Coupling agents and surfactants have some similarities in molecular structure and application performance, but there are also differences. Both are composed of hydrophilic and hydrophobic functional groups. Surfactants selectively adsorb onto the surface of inorganic pigments and fillers through hydrophilic groups in their molecules, forming a monolayer. This is a physical adsorption phenomenon that improves the dispersibility and wettability of pigments and fillers in the base material. Therefore, only physical adsorption is required, and surfactants have migration phenomena that affect gloss, appearance, and adhesion. Coupling agents are used to couple and bind inorganic pigments and fillers on the surface through chemical reactions, and crosslink with polymer substrates to combine two substances with different properties, playing a bridging role. In terms of bonding strength, improving the dispersion program of pigments and fillers in the substrate, and reducing the amplitude of interfacial free energy, coupling agents greatly outperform surfactants.
(2) The coupling mechanism of coupling agents:
Regarding the mechanism of action of titanium ester coupling agents, it is generally believed that only one isopropoxide group in the monoalkoxytitanium ester coupling agent is a hydrolytic group that can couple with inorganic substances, thus forming a monolayer on the surface of inorganic pigments and fillers. In contrast, titanium ester coupling agents can more tightly connect inorganic pigments and fillers with organic polymer materials, fully utilizing the function of each titanium ester molecule. Therefore, the dosage is small and the effect is great. Due to the single-molecule encapsulation of titanium ester coupling agents on the surface of inorganic pigments and fillers to replace the originally adsorbed trace amounts of water and gas, and the hydrophobic non-aqueous intermediate group closure of long carbon chains in the molecules, the compatibility with organic polymer substrates is increased, and the free energy at the interface is reduced, which is conducive to the wetting and dispersion of powder aggregates by organic polymer substrates.
2. Practical research
Given that the application prospects of titanium ester coupling agents in the coating industry are very broad. Some domestic units are developing and producing titanium ester coupling agents, which have already been applied and developed in calcium and plastic materials. The variety and structure of coatings are shifting from low-end to mid to high-end products. The variety of coatings is gradually evolving from traditional solvent based coatings to water-based high solid molecular solvents, powders, and inorganic coatings. In addition to significantly improving the decorative and protective properties of coatings, it also requires coatings to develop towards high-performance, multifunctional, special effects, and specialized directions, requiring various new types of functional coatings. Due to the unique structure and diverse, multifunctional characteristics of titanium ester coupling agents. Although the dosage is small, it can meet the performance requirements of coatings in various aspects.
3. Application Function:
Due to the characteristics of the six different functional zones in the molecular structure of titanium ester coupling agents, different functional groups of titanium ester coupling agents can be designed according to the needs of the coating industry, making them specific or multifunctional coupling agents, endowing coatings/inks with the following functions.
(1) Good dispersibility and wetting function can significantly improve the dispersibility of most inorganic and organic pigments and fillers in organic base materials, and is particularly effective in dispersing carbon black, phthalocyanine blue, iron red, medium chromium yellow, etc.
(2) Good anti sinking performance and improved storage stability.
(3) Beneficial for grinding, it can shorten the number of grinding passes and time, and the same grinding time can make the particles grind finer.
(4) It can increase the adhesion of the paint film to the substrate, improve the adhesion of the paint film to various metals, glass, and inorganic materials, improve wear resistance, enhance impact strength, and increase flexibility.
(5) It can significantly increase the coloring strength and reflective ability of coatings, improve the gloss of paint films, and increase coverage.
(6) It can produce flame retardant effect in fireproof coatings.
(7) It can have anti rust effect in anti rust coatings.
(8) It can reduce the viscosity of the coating system and lower the curing temperature of the resin.
(9) Has good thixotropic properties and can improve the water repellency, wear resistance, and washing resistance of the coating film.
(10) Has good antioxidant properties and UV resistance.
(11) Significantly improve the mechanical properties, weather resistance, salt spray resistance, and yellowing resistance of the coating film.
4. Usage:
Titanium ester coupling agents can undergo chemical reactions on the surface of pigments and fillers, forming a single molecular layer to play a bridging role for each molecule, so the dosage is small and the effect is large. In order to evenly distribute a small amount of titanium ester coupling agent on the surface of the pigment and filler, effective usage methods should be adopted, and the following principles should be followed: do not add additional surfactants, as they will interfere with the reaction of titanium ester at the filler interface, in order to achieve their intended effect.
According to the structural type, water resistance, actual usage objects and occasions of coupling agents, different methods should be adopted. The following are several usage methods:
(1) Pre treatment method for pigments and fillers:
The method of pre coating titanium ester coupling agent onto the surface of pigments and fillers may be cumbersome, but it yields better results.
The method is to dissolve the coupling agent in a small amount of hydrocarbon solvents such as toluene and xylene, add it to the pigment and filler, and stir at high speed (about 1000 rpm) to a suitable temperature of about 90 ℃ for about half an hour, so that each pigment and filler particle can be coated with a layer of coupling agent. After the pigment filler is coated with a coupling agent, the coating can be prepared according to the usual method.
(2) Direct addition method:
The method of directly adding coupling agent before high-speed dispersion in the paint making process.
The method is to dissolve the coupling agent in solvents such as gasoline and xylene, disperse it into an organic base material, add pigments and fillers for high-speed dispersion, and then prepare the coating according to the usual method.
Water based coatings use water-soluble coupling agents, and the treatment method is the same as above. Simply replace the solvent with water.
5. The dosage of coupling agent
The theoretical dosage of coupling agent is to allow all hydrophilic reactive groups in the coupling agent to react with the hydroxyl or proton groups provided by the pigment and filler, and there is no need to be excessive. However, the actual dosage should be determined based on the particle size and surface functional groups of the filler to determine the most suitable dosage. The relationship between viscosity and the amount of coupling agent can be determined using viscosity measurement method.
The point where viscosity decreases the most is the most appropriate amount of titanium acid ester.
Based on experience, the dosage of coupling agent should be around 1-3% of the solid pigment and filler in the coating. The finer the particle size and larger the surface area of the pigment and filler, the more coupling agent should be used.
Titanate coupling agents are a novel class of chemical additives that have rapidly developed and widely used in many production fields in the past decade. There have been many reports on their synthesis and application abroad, and they are also receiving increasing attention domestically.
Titanium ester coupling agent is widely used in the coating industry and is a multifunctional additive, but it also needs to undergo practical application tests to achieve the best results. In order to achieve modernization of the coating industry, extensive research on the application of titanium esters in the coating industry is necessary.
