1. Introduction

Solvent-borne universal color pastes represent one of the most widely used colorant intermediates in the industrial coatings industry. Their core value lies in delivering high pigment loading with a universal resin carrier, enabling cross-system tinting across multiple binder chemistries. Dongguan DENSON Functional Materials Co., Ltd. (DENSON) FLTY series solvent-borne universal color pastes are formulated with a universal resin carrier designed for excellent compatibility and let-down properties in two-component polyurethane (2K PU), one-component acrylic, thermosetting acrylic, alkyd, nitrocellulose, and various other solvent-borne coating systems. This article examines the technical principles, application performance, and selection parameters of FLTY universal color pastes, with reference to peer-reviewed research in polymer dispersion and coating science.

The technical challenge of solvent-borne universal color pastes is twofold: achieving nanoscale pigment dispersion and long-term stability in non-aqueous media, while maintaining compatibility across chemically diverse binder systems without flocculation, seeding, or floating/flooding. This balance requires synergistic optimization of dispersant molecular architecture, carrier resin solubility parameter matching, and pigment surface treatment technology.

2. Technical Features and Mechanism

Solvent-borne universal color paste is defined as a high-concentration pigment dispersion comprising organic solvent as the continuous phase, universal-type resin as the carrier, high-performance organic or inorganic pigments as the color phase, and hyperdispersants, processed through high-speed dispersion and bead milling. Typical pigment mass fraction ranges from 40% to 72%, fineness is ≤10 μm, and the product exhibits excellent let-down properties, broad compatibility, high tinting strength, and migration resistance.

2.1 Pigment Dispersion: Thermodynamics and Kinetics

Pigment dispersion in organic solvents follows the three-stage model of wetting, deagglomeration, and stabilization. The driving force for wetting depends on the matching between pigment surface energy and solvent surface tension; deagglomeration relies on shear and impact forces from dispersion equipment; stabilization is provided by the adsorbed dispersant layer through steric hindrance or electrostatic repulsion. Research published in the Journal of Applied Polymer Science (2025, DOI: 10.1002/app.56144) demonstrated that PEGylated partially hydrolyzed poly(N-vinylamide) dispersants form an adsorbed layer of 8–12 nm thickness on carbon black surfaces, effectively preventing van der Waals aggregation through steric stabilization in non-polar solvents.

In solvent-borne systems, the dielectric constant of organic solvents is typically low (2–10), rendering electrostatic double-layer repulsion weak. Steric stabilization therefore becomes the dominant mechanism. The solvated chains of hyperdispersants extend fully in good solvents, forming an adsorbed layer of 5–20 nm thickness. When two pigment particles approach within the overlap region, the conformational entropy of the chains decreases, generating repulsive force; the osmotic pressure difference in the mixed solvation layer also contributes to repulsion energy.

Figure 1. Industrial high-speed disperser for pigment pre-dispersion in solvent-borne color paste manufacturing.

2.2 Hyperdispersant Architecture: Anchoring Groups and Solvated Chains

Hyperdispersant molecules consist of anchoring groups and solvated chains. Anchoring groups adsorb onto pigment surfaces through ionic bonds, hydrogen bonds, van der Waals forces, or acid-base interactions; solvated chains extend into the continuous phase to provide steric stabilization. A study in ACS Applied Polymer Materials (2026, 8(6), 4573–4586, DOI: 10.1021/acsapm.6c00349) proposed a "soft-core hard-shell gradient copolymer" strategy for pigment encapsulation, where the gradient copolymer forms a continuous transition from anchoring segment to solvated segment at the pigment surface, significantly reducing interfacial tension and improving long-term dispersion stability.

The FLTY series employs a multi-anchoring-point hyperdispersant system. The anchoring groups include amine, carboxyl, and ester functionalities, adaptable to the diverse surface chemistries of organic pigments (azo, phthalocyanine, quinacridone) and inorganic pigments (titanium dioxide, carbon black, iron oxide). The solvated chains are selected from polyester or polyacrylate segments with solubility parameters close to those of multiple coating binders, ensuring full extension in polyurethane, acrylic, and alkyd systems.

2.3 Universal Resin Carrier: Compatibility Mechanism

The universal resin carrier is the key to cross-system compatibility. According to Hansen solubility parameter theory, two polymers are thermodynamically compatible when the difference in their dispersion (δd), polar (δp), and hydrogen-bonding (δh) components satisfies (Δδd)² + (Δδp)² + (Δδh)² ≤ R₀², where R₀ is the interaction radius.

The FLTY universal carrier resin is engineered with solubility parameters in the intersection region of polyurethane resins (δ ≈ 20–22 MPa^0.5), acrylic resins (δ ≈ 19–21 MPa^0.5), and alkyd resins (δ ≈ 18–20 MPa^0.5), thereby avoiding carrier precipitation and pigment flocculation caused by solubility parameter mismatch. The molecular weight is controlled at Mn = 3,000–8,000 g/mol, balancing adhesion contribution, film performance, and paste fluidity.

2.4 Migration Resistance and Bleed-Free Mechanism

Migration resistance and bleed-free performance are critical quality indicators for solvent-borne color pastes. Pigment migration is essentially the diffusion of pigment particles in the coating film driven by concentration gradients, temperature gradients, or solvent action. The FLTY series achieves migration resistance through: (1) selection of high-molecular-weight, solvent-resistant organic pigments (e.g., phthalocyanine blue PB15:3, quinacridone red PR122, azo yellow PY155) with extremely low solubility in organic solvents; (2) submicron particle size control (D50 ≤ 0.5 μm), providing large specific surface area and strong interfacial binding with the binder; (3) carrier resin anchoring, where the universal carrier forms strong interfacial bonds with pigment particles and interpenetrating networks with the binder resin after curing, physically locking pigment particles in the film network.

3. Application Case 1: 2K PU Automotive Topcoat

Background: An automotive parts manufacturer producing bumpers and mirror housings sought a domestic alternative to imported color pastes for their 2K PU topcoat line, targeting cost reduction without compromising performance.

Process parameters: PP+EPDM plastic substrate, waterborne adhesion primer, 2K PU topcoat (hydroxy acrylic resin + HDI trimer curing agent, NCO/OH = 1.05), dry film thickness 35–45 μm, spray viscosity 18–22 s (Ford Cup #4, 25°C), baking at 80°C for 30 min.

FLTY application: FLTY black (carbon black, 50% pigment loading) at 4.5% and tinting pastes at 2.0%, total color paste addition 6.5%. Pastes were pre-mixed with the hydroxy component under high-speed dispersion for 5 min before adding the curing agent; pot life controlled within 4 hours.

Performance results:

Outcome: FLTY pastes fully replaced the imported product, reducing综合 cost by approximately 35% while maintaining batch color stability at ΔE ≤ 0.4 over six months of continuous production.

4. Application Case 2: One-Component Acrylic Plastic Coating

Background: A home appliance parts manufacturer applied thermoplastic acrylic topcoats on ABS plastic housings, requiring high gloss, high hardness, and alcohol resistance across multiple solid and metallic colors.

Process parameters: ABS substrate with electrostatic dust removal and flame treatment, thermoplastic acrylic resin (Mn 80,000–120,000), toluene/butyl acetate/butanol solvent blend, film thickness 20–30 μm, air spray, viscosity 15–18 s (Ford Cup #4), baking at 60°C for 20 min.

FLTY application: Solid colors using FLTY red, yellow, blue, black, and white at 5%–10%; metallic colors using FLTY transparent pastes (40% pigment loading) at 3%–5% in combination with aluminum pigment paste. Pastes were added directly to the acrylic lacquer with low-speed stirring for 5 min.

Key performance: Gloss (60°) 91.5%, adhesion grade 1, pencil hardness H, alcohol resistance (500 g load, 50 wipes) pass, batch ΔE ≤ 0.3, QUV 500h ΔE = 1.4. The transparent pastes did not interfere with aluminum pigment orientation, maintaining strong metallic appearance.

Figure 2. Solvent-borne 2K PU topcoat spray application in automotive refinishing.

5. Application Case 3: Thermosetting Acrylic Amino Baking Enamel

Background: A home appliance manufacturer produced metal panels for microwave ovens and rice cookers using acrylic amino baking enamels, requiring high gloss, high hardness, stain resistance, and steam resistance.

Process parameters: Cold-rolled and galvanized steel substrates, phosphating pretreatment, epoxy primer (5–10 μm), topcoat of hydroxy acrylic + butylated melamine-formaldehyde resin (7:3 mass ratio) with 0.5% p-toluenesulfonic acid catalyst, dry film 20–25 μm, electrostatic bell spray, viscosity 16–20 s, curing at 150°C for 25 min (metal temperature).

FLTY application: White using FLTY titanium dioxide paste (rutile TiO2, 72% pigment loading) at 15%; black using FLTY carbon black paste (50% loading) at 3%; metallic colors using FLTY transparent pastes at 4% with non-leafing aluminum paste. Pastes were pre-mixed with acrylic resin for 8 min before adding melamine resin and catalyst.

Key performance: Gloss (60°) 94.5%, pencil hardness 2H, adhesion grade 0, flexibility (1 mm mandrel) pass, stain resistance (coffee/soy sauce, 24h) pass, steam resistance (100°C water, 30 min) pass, batch ΔE ≤ 0.25. No significant color shift or gloss loss after 150°C high-temperature curing.

6. Key Selection Parameters and Usage Recommendations

Usage recommendations: (1) Stir thoroughly before use; mild thixotropic settling during storage is normal and recoverable. (2) Conduct laboratory trials before production scale-up to verify compatibility and color. (3) In 2K PU systems, use within pot life after adding curing agent. (4) Compare color difference between batches before use to ensure consistency. (5) In 2K PU systems, always mix color paste with the hydroxy component first before adding the isocyanate curing agent.

7. Conclusion

DENSON FLTY series solvent-borne universal color pastes achieve high concentration, high hiding power, broad compatibility, and migration resistance across 2K PU, 1K acrylic, thermosetting acrylic, and other solvent-borne coating systems through multi-anchoring hyperdispersant adsorption, universal carrier resin solubility parameter matching, and submicron particle size control. The technical principles align with current research in polymer dispersion and pigment encapsulation as reported in leading polymer science journals. For more product information, visit the DENSON literature section or the company website.

8. Frequently Asked Questions (FAQ)

Q1: What is the main difference between universal color pastes and system-specific color pastes?

A: Universal color pastes use a general-purpose resin carrier compatible with multiple coating systems, suitable for multi-product small-batch tinting. System-specific pastes are optimized for a particular binder, offering superior compatibility and performance but limited versatility. The FLTY series balances universality and performance through solubility parameter engineering.

Q2: Why does floating or flooding occur after adding color paste to coatings?

A: Floating/flooding is primarily caused by Benard cell convection due to density differences among pigment particles, or by pigment flocculation from insufficient binder compatibility. Solutions include adjusting paste addition level, increasing dispersant dosage, raising binder viscosity, or selecting a more compatible paste series.

Q3: Will FLTY pastes affect the curing reaction in 2K PU systems?

A: The FLTY series uses alcohol-free solvents and low-hydroxyl carrier resins, so it does not consume NCO groups. At high addition levels (>10%), it is advisable to verify the NCO/OH ratio and adjust curing agent dosage accordingly to ensure adequate crosslink density.

Q4: Can color paste with mild settling after storage still be used?

A: High-pigment pastes may develop mild thixotropic settling during long-term storage, which is normal. High-speed stirring for 5–10 minutes restores fineness and tinting strength. If hard caking, severe flocculation, or significant solvent separation occurs, the paste may have exceeded shelf life or been stored improperly and should be tested before use.

Q5: How do I evaluate the compatibility of a solvent-borne color paste with a target binder?

A: Common methods include: finger rub test (light rubbing after surface dry to observe color change), thermal cycling (50°C/−10°C alternating for 7 days to observe flocculation), fineness recheck (measuring fineness 24h after mixing), and visual observation of film gloss and transparency. The FLTY series undergoes compatibility validation with mainstream binders before release.