HALLCOTE® HECA

HALLCOTE HECA enables formulators to create premium quality, ultra-low VOC latex paints and coatings. Odorless and with an 80% reduction in VOCs compared to TexanolTexanol, HECA not only meets but surpasses international no VOC regulations. Using HECA at half the level of Texanol leads to a greater reduction in MFFT (minimum film formation temperature). It offers superior scrub resistance and gloss, aligning with consumer demands, and is certified by both US and EU standards.

The information provided within this document is believed to be accurate and reliable. However, no warranty or guarantee, either expressed or implied, is made regarding the information or the performance of any product. Furthermore, nothing contained herein should be construed as an inducement or recommendation to use, manufacture, or sell that may infringe on patents or any proprietary rights. Additionally, compliance with any regulatory requirements is not implied.

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By Kyle Flack, Nicholas Foley, Tyrone Vaughn, Lisa Kicklighter, and John Mangano, BASF Corporation

Proper film formation is an essential factor in high-performance coatings, ensuring minimal porosity, enhanced corrosion resistance, and superior film surface features. For decades, waterborne coatings have used volatile coalescing aids (solvents) to help hydrophobic latex particles coalesce. If the latex’s glass transition temperature (Tg) is at or below the intended application temperature, coalescing aids are unnecessary, but this often results in softer final paint films. Thus, harder latexes have been created that require coalescing aids to soften the system enough to form a continuous film during water evaporation (See Figure 1). Coalescents play a crucial role in steps 3 to 4 of the drying process.

Historically, volatile solvents like dipropylene glycol n-butyl ether (DPnB) and 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (Eastman Texanol® Ester solvent, referred to as Texanol) were adjusted based on compatibility with the formulation and latex system to optimize film coalescence while remaining volatile during or after film formation. However, the industry faces challenges in adhering to regulations on volatile organic compound (VOC) levels, especially in interior architectural coatings. Permanent or nonvolatile coalescents have become crucial as they interact similarly to volatile counterparts while remaining in the final dry film. This permanence can have drawbacks, such as poorer block resistance and increased leaching.

Various options are now available for low- to zero-VOC coatings. This study aimed to find the optimal levels of coalescent required in a system to understand the impact of an ultra-low VOC coalescent structure on efficiency and performance properties and to investigate the interactions behind the preferred coalescents.

Experimental Design

This evaluation focused on three primary coalescing agents: Loxanol® CA 5330 and Efka® PL 5383 from BASF Corporation and Eastman Optifilm® Enhancer 400 (from Eastman Chemical Company, referred to as Optifilm 400). These materials differ significantly in structure, providing insights into their effects on primary coalescing and secondary performance properties in latexes. Optifilm 400 is an industry benchmark for ultra-low VOC coalescing agents, while Loxanol CA 5330 and Efka PL 5383 are also ultra-low VOC coalescing agents. Descriptors of the chemistries and Hansen solubility parameter predictions are shown in Table 1.

Hansen solubility parameters were estimated and may differ from literature values based on the Y-MB model within the HSPiP software tool (version 3.1.14). Although some assumptions are made within the model, the predictions aligned with literature values for Texanol and Optifilm 400, validating their relevance as comparative tools.

The efficiency of coalescing agents was assessed by evaluating the minimum film formation temperature (MFFT) upon adding coalescing agents to diluted latex systems. The latex systems evaluated are referred to as Latex A, B, and C throughout this text.

Latex A: All-acrylic latex designed for zero-VOC capable paints and enhanced cleanability.
Latex B: All-acrylic latex for interior/exterior paint and primer in one systems.
Latex C: Styrene/acrylic latex for primer applications.

The influence of latex parameters such as particle size was also evaluated. Latex A was synthesized via emulsion polymerization maintaining the surfactant level while modifying the number of particles accessible through polymer growth. This resulted in a particle size range from 99 nm to 135 nm by volume. Even small changes in particle size impacted the demand for coalescent.

Efficiency tests involved adding 90 g of latex to a container, adding the coalescent to be tested, and adjusting with water to total 100 g. Samples were mixed under low-shear paddle mixing for five minutes and then rested in a controlled temperature and humidity room (CTH, 50% relative humidity and 70°F) overnight.

Paint evaluation used an interior architectural formulation with Latex A, as shown in Table 2. Different coalescing aids were compared at equal loadings across the systems. Evaluations included key performance parameters like gloss, scrub cycles, stain resistance (cleanability), and hardness. Gloss was measured using a 7 mil Dow Film Caster drawdown bar on a sealed chart, allowed to dry for 24 hours under CTH conditions, and read in triplicate with a BYK-Gardner micro-TRI-gloss meter. Scrub and stain resistance were measured by drawing down the control and test paint side by side on a black vinyl chart, cured for seven days under CTH conditions, split in two, with half used for scrub resistance and half for stain resistance.

Scrub resistance was conducted using a calibrated Gardco® scrub machine fitted with brushes, using 10 mL aliquots of Leneta SC-2 abrasive medium, and 5 mL of water added after each set of 400 cycles. Samples showed failure when a line due to complete film erosion appeared, revealing the vinyl chart.

Stain resistance tests applied one-inch wide strips of various stains across control and test paints, which rested for one hour before removal via a simple rinse. The panels were placed on the Gardco scrub machine, the brush replaced with a sponge, and Fantastik® used as a cleaning agent for 25 cycles. Pendulum (Koenig) hardness tests involved drawing paints down at 10 mil thickness (250 microns) on glass plates, then drying under CTH conditions for three days prior to testing in duplicates.

*Gardco® is a registered trademark of the Paul N. Gardner Company, Inc.
†Fantastik® is a registered trademark of S.C Johnson & Son, Inc.

Results

The initial focus was on incorporating BASF’s Loxanol CA 5330 and Efka PL 5383 coalescents. Despite similar molecular weights, their polar and hydrogen bonding contributions varied significantly. Latex A showed good compatibility at all tested levels for both Loxanol CA 5330 and Efka PL 5383, with MFFT dropping more significantly with Efka PL 5383 (See Figure 2).

In Latex B, a comparison revealed that Loxanol CA 5330 was not manageable within the system. However, Efka PL 5383 provided clean, clear films at temperatures as low as 4°C, while immiscibility issues caused a separation layer with Loxanol CA 5330. The differential compatibility might be attributed to solubility parameters predicting higher hydrogen bonding and polar components for Loxanol CA 5330 than Efka PL 5383, but solubility in water limits the Latex B system’s effectiveness. This suggests that stabilizing surfactants in Latex B alter the interaction or miscibility of the coalescents with the latex.

Figure 3 demonstrates (a) highly water-soluble coalescing aid as ineffective due to reduced interaction with hydrophobic latex species, (b) latex-soluble but low water-solubility coalescing aid, and (c) surfactant-miscible coalescing aid stable at latex particle boundaries. Loxanol CA 5330’s poor migration through the water phase to interact with latex particles, due to its surfactant-like structure, might reduce efficiency by forming its own micelles. Figure 4 shows that MFFT couldn’t be recorded due to film issues with Loxanol CA 5330 in Latex B.

In Latex C, a styrene-acrylic, Optifilm 400 was introduced as an additional coalescing aid with distinct polar and hydrogen bonding contributions. The study showed Efka PL 5383 as most efficient, followed by Loxanol CA 5330, and Optifilm 400. All systems were stable and miscible, with Efka PL 5383 achieving an MFFT of 0°C at 7% based on latex solids.

Additionally, latex composition played a role in coalescent selection, with particle size calculations revealing significant surface area changes. Evaluating Efka PL 5383 and Optifilm 400 within the 99 nm to 135 nm range showed that increased particle size decreased solubvent efficiency. Lesser surface area allows more surfactant to exist in the water phase, possibly acting as a shuttle for the coalescent or as