Technical Guidelines for Dispersant Selection in Epoxy Coatings and Ink Systems

Technical Guidelines for Dispersant Selection in Epoxy Coatings and Ink Systems

The epoxy system can be divided into two major categories: solvent-based epoxy and water-based epoxy, with water-based epoxy further subdivided into anionic/nonionic epoxy dispersions and two-component water-based epoxy. Due to the highly polar nature of epoxy anchoring groups, the core of dispersant selection lies in matching the surface characteristics of pigments with the compatibility of epoxy resins, thereby avoiding issues such as floating color, flocculation, interference with curing reactions, and reduced corrosion resistance.

I、 Firstly, clarify the core selection criteria for each of the two epoxy systems

1. Solvent based epoxy system (liquid epoxy resin combined with polyamide/polyamine curing agent)

Core issue: The overall polarity of the system is high, and dispersants must not interfere with the amine curing process to prevent problems such as slow curing rate and decreased water and salt spray resistance of the paint film; Priority should be given to selecting polymer hyperdispersants with polar anchoring groups, and dispersants containing a large number of acidic groups should be used with caution - high acid values can easily cause side reactions with amine curing agents.

2. Waterborne epoxy system covers two sub categories: one component epoxy lotion and two component reactive waterborne epoxy

Core issue: The system uses water as the continuous phase and exhibits pH sensitive characteristics as a whole; Dispersants need to balance their steric stability and not introduce excessive hydrophilic segments, otherwise it will significantly weaken the anti-corrosion and water resistance of the paint film. Small molecule polycarboxylate dispersants are usually not suitable for anti-corrosion water-based epoxy systems.

II、 Selection Scheme for Solvent based Epoxy Coatings/Ink Dispersants

(1) Inorganic pigments and functional fillers such as titanium dioxide, iron oxide red, zinc phosphate, aluminum tripolyphosphate, talc powder, barium sulfate, etc

-Priority should be given to two types of products: polyurethane super dispersants and medium acid value modified polyacrylic esters. The polyamine/amide anchoring groups on their molecular chains can form strong adsorption on inorganic powders

-Reference models: RK-4013A, RK-4013C;

-Addition amount: Based on the total mass of inorganic powder, control within the range of 2% to 6%; The use of high acid value dispersants needs to be strictly controlled. Excessive acid value can consume amine curing agents, ultimately leading to incomplete curing reactions.

(2) Organic pigments such as carbon black and phthalocyanine blue/green, suitable for epoxy colorants and epoxy ink systems

-Priority should be given to using high anchoring polyurethane hyperdispersants, while ordinary polyacrylic ester dispersants have insufficient adhesion force to carbon black and organic pigments, which can easily lead to system flocculation and coarsening problems.

-Reference models: RK-4031, RK-4036, RK-4036B;

-Addition amount: 15-35% carbon black; Organic pigments account for 12-30%.

Key points for avoiding pitfalls in solvent based epoxy systems: It is necessary to strictly control the amount of strongly acidic phosphate ester dispersants used. These additives are prone to acid-base neutralization reactions with amine curing agents, ultimately causing thickening of the materials in the tank and slowing down the curing rate.

III、 Selection guide for water-based epoxy coatings and ink dispersants, with a focus on distinguishing between single component and two-component systems

1) The most widely used two-component waterborne epoxy system is composed of epoxy lotion and waterborne amine curing agent

Selection core red line: Dispersants must not contain a large amount of free carboxylic acids, as carboxylic acid groups can interact with amine components, leading to problems such as thickening, flocculation, and deterioration of storage stability.

-For the dispersion selection of inorganic pigments and fillers, priority should be given to using high molecular weight non-ionic polyurethane dispersants and low acid value ammonium polyacrylate products, while avoiding high acid value ammonium acrylate dispersants.

Reference models: RK-4010, RK-4017E; Addition amount 3-7% (pigment mass)

-Carbon black/organic pigment: water-based polyurethane super dispersant;

Reference models: RK-4044, RK-4039AB; Add 15-35% carbon black.

2) One component self crosslinking waterborne epoxy lotion system

Compared to two-component systems, the tolerance is slightly higher. Intermediate acid value ammonium acrylate or polyurethane dispersants can be used, but the total content of hydrophilic groups still needs to be strictly controlled to avoid a significant decline in the water resistance of the paint film

Water based epoxy systems need to avoid: ordinary small molecule polycarboxylate dispersants, which have decent dispersion efficiency, but can significantly degrade the coating's water and salt spray resistance after film formation. Therefore, anti-corrosion water-based epoxy systems are not recommended.

IV、 Epoxy ink covers two categories: solvent based and water-based, and requires exclusive differentiation selection points to be added

Compared with conventional epoxy coatings, epoxy ink has a higher pigment filling concentration and stricter requirements for grinding fineness. At the same time, it is necessary to ensure that sedimentation and delamination problems are not easily encountered during long-term storage;

1. Polyurethane based hyperdispersants are preferred for solvent based epoxy inks, which can effectively reduce system viscosity at high pigment filling concentrations;

2. Non ionic polyurethane dispersants are preferred for water-based epoxy ink systems, which can minimize the risk of system flocculation caused by pH fluctuations;

3. Low molecular weight dispersants that are prone to migration should be avoided, otherwise they will have a negative impact on the adhesion and chemical resistance of the ink coating.

V、 General taboos for epoxy systems

1. The acid value of dispersants is the core reference for selecting epoxy systems: solvent based epoxy systems should avoid high acid value dispersants, and two-component water-based epoxides are also not recommended to use products with a high proportion of carboxylic acid groups.

2. Dispersants should not be added in excess, as excessive amounts can have a counterproductive effect similar to plasticizers in the epoxy system, directly reducing the hardness, solvent resistance, and anti-corrosion performance of the paint film.

3. Dispersants should be added during the grinding stage, don't wait until the later paint adjustment stage to add them.

4. Four core verifications must be conducted: storage stability, benchmarking of curing speed, water resistance, and salt spray resistance.

Quick selection summary table