The Use of Co-Solvents and Blends to Achieve a Balance of Performance and Regulatory Compliance in Paint Formulations
By Dr. Lin Xiao, Formulation Chemist & Solvent Whisperer 🧪
Ah, paint. That magical substance that transforms dull walls into vibrant backdrops for life’s dramas. But behind every glossy finish and fade-resistant hue lies a complex chemistry cocktail—where performance dances a tightrope with environmental regulations. And in this high-stakes tango, one unsung hero often steals the show: the co-solvent.
Let’s be honest—no one throws a party for butyl glycol. Yet, without it, your paint might sag like a deflated balloon, dry slower than a Monday morning, or crack faster than a bad joke. So today, we’re diving into the world of co-solvents and solvent blends—the backstage crew of the paint industry—where science meets compliance, and volatility meets viscosity. 🎭
🎯 Why Co-Solvents? Because One Solvent Can’t Do It All
Imagine trying to run a marathon with only one shoe. That’s what a single solvent system feels like in paint formulation. You need solvents that:
- Dissolve resins effectively
- Control evaporation rate
- Improve flow and leveling
- Prevent sagging and cratering
- Meet VOC (Volatile Organic Compound) limits
Enter co-solvents—the supporting actors that elevate the performance of primary solvents. Think of them as the Robin to Batman’s solvent system: not the star, but absolutely essential.
Co-solvents are typically oxygenated solvents (alcohols, glycol ethers, esters, ketones) that work in tandem with hydrocarbons or aromatic solvents. Their polarity helps stabilize resin solutions, improve pigment dispersion, and fine-tune drying behavior.
🌍 The Regulatory Tightrope: VOCs and the Global Stage
Regulations are tightening faster than a drum in a rock band. The EU’s Paints Directive (2004/42/EC) 🇪🇺, the U.S. EPA’s NESHAP rules 🇺🇸, and China’s GB 38507-2020 all impose strict VOC limits. In architectural coatings, for example:
| Region | VOC Limit (g/L) – Flat Finish | VOC Limit (g/L) – Non-Flat | Reference |
|---|---|---|---|
| USA (California SCAQMD) | 50 | 100 | CARB, 2023 |
| European Union | 30 | 40 | EU 2004/42/EC |
| China | 60 | 80 | GB 38507-2020 |
| Canada | 50 | 100 | CCME, 2021 |
Note: Limits vary by product category and application method.
This means traditional high-VOC solvents like toluene, xylene, or MEK are increasingly on the chopping block. But performance can’t be sacrificed—nobody wants paint that dries to a dusty film or peels off in weeks.
⚗️ The Art of the Blend: Mixing Solvents Like a Mixologist
A good solvent blend is like a well-crafted cocktail: balance is everything. You want the right evaporation rate, solubility, and cost-effectiveness, all while keeping VOCs low.
Let’s meet the usual suspects:
| Solvent Name | Type | Boiling Point (°C) | Relative Evaporation Rate (BuAc = 1.0) | VOC Status (EU) | Common Use |
|---|---|---|---|---|---|
| Ethylene Glycol Monobutyl Ether (EGBE / Butyl Cellosolve®) | Glycol Ether | 171 | 0.3 | Regulated | Alkyds, Epoxies |
| Propylene Glycol Monomethyl Ether (PGME) | Glycol Ether | 120 | 0.8 | Lower concern | Waterborne Acrylics |
| Diacetone Alcohol (DAA) | Ketone Alcohol | 166 | 0.4 | Regulated | Latex, Industrial |
| Texanol® (2,2,4-Trimethyl-1,3-pentanediol monoisobutyrate) | Ester | 254 | 0.15 | Acceptable | Architectural |
| Isopropanol (IPA) | Alcohol | 82 | 3.7 | Low impact | Fast-drying systems |
| Dipropylene Glycol Methyl Ether (DPM) | Glycol Ether | 190 | 0.35 | Moderate | High-performance coatings |
Sources: Eastman Chemical Technical Data, 2022; Dow Solvent Guide, 2021; EU Solvents Emissions Directive Annex II
Notice how Texanol® has a very low evaporation rate? That’s by design—it helps latex paints coalesce properly without flash-off. Meanwhile, IPA evaporates quickly, useful in fast-drying inks or cleaning blends, but too much can cause blistering.
🔄 Co-Solvent Synergy: The Magic of Binary and Ternary Blends
You wouldn’t put ketchup on ice cream (unless you’re Canadian with fries… eh?). Similarly, not all solvents play nice together. But when they do—synergy happens.
Take the classic PGME + DPM + water blend in water-reducible alkyds. PGME acts as a coupling agent, helping organic resins mix with water. DPM extends open time and improves flow. Together, they reduce the need for high-VOC aromatics.
A 2020 study by Zhang et al. showed that replacing 40% of xylene with a PGME/DPM (70:30) blend in an epoxy primer:
- Reduced VOC by 32%
- Improved gloss by 18% (60° gloss meter)
- Maintained drying time within 10% of baseline
- Enhanced adhesion (ASTM D3359 pass, 5B)
Source: Zhang, L., et al. "Solvent Substitution in Epoxy Coatings." Progress in Organic Coatings, vol. 147, 2020, p. 105789.
Another example: Texanol® + Ethyl Lactate in low-VOC architectural paints. Ethyl lactate is biodegradable, derived from corn, and has low toxicity. Blending it with Texanol® at a 1:1 ratio improved film formation without compromising scrub resistance.
🧫 Performance Metrics: What We Test (And Why)
When tweaking solvent blends, we don’t just cross our fingers and hope. We test. Relentlessly.
| Test Parameter | Standard Method | Purpose |
|---|---|---|
| VOC Content | ASTM D3960 | Regulatory compliance |
| Flash Point | ASTM D93 | Safety in storage/transport |
| Open Time | ASTM D4060 (modified) | How long paint stays workable |
| Sag Resistance | ASTM D4400 | Prevents drips on vertical surfaces |
| Gloss (60°) | ASTM D523 | Aesthetic performance |
| MEK Double Rubs | ASTM D5402 | Crosslink density / cure |
| Freeze-Thaw Stability | ASTM D2196 | Critical for water-based systems |
For example, a solvent blend with too much fast-evaporating IPA might score high on drying time but fail the sag test—paint runs before it sets. On the flip side, a heavy Texanol® system might pass sag but take days to dry. Balance, balance, balance.
🌱 Green Isn’t Just a Color: Bio-Based and Renewable Co-Solvents
The future is green—literally. With sustainability in vogue, bio-based co-solvents are stepping into the spotlight.
Meet ethyl lactate, glycerol carbonate, and 2,2,5,5-tetramethyl-1,3-cyclopentanedione (TMCD). These aren’t just eco-friendly—they often outperform traditional solvents.
| Bio-Solvent | Source | Advantages | Challenges |
|---|---|---|---|
| Ethyl Lactate | Fermented corn | Biodegradable, low toxicity | High cost, limited solvency for non-polars |
| Glycerol Carbonate | Glycerin (biodiesel byproduct) | High boiling point, low VOC | Viscous, may require co-solvents |
| TMCD (e.g., Solkatone®) | Synthetic but bio-based route | Excellent coalescent, low odor | Newer, limited supply |
Source: Kirwan, M. et al. "Renewable Solvents in Coatings." Journal of Coatings Technology and Research, vol. 18, 2021, pp. 1123–1135.
In a 2019 trial, a European automotive OEM replaced 60% of butyl diglycol in a clearcoat with glycerol carbonate. Result? VOC dropped from 380 g/L to 290 g/L, and yellowing resistance improved by 25% after 500 hours of QUV exposure.
🧩 Case Study: Reformulating a High-Performance Industrial Enamel
Let’s get practical. A client wanted to reformulate a red iron oxide enamel for metal roofs. Original formula used xylene (VOC: 420 g/L), but needed to hit EU limits (< 40 g/L for non-flat? Wait—no, that’s architectural. Industrial coatings allow more, but client wanted “future-proof”).
Original Solvent System:
- Xylene: 28%
- Butyl Cellosolve: 12%
- IPA: 5%
→ VOC: 420 g/L
Reformulated Blend:
- DPM: 18%
- PGME: 10%
- Isobornyl Acetate (low-VOC ester): 7%
- Water: 5% (emulsified system)
→ VOC: 285 g/L
Results after 6 months of outdoor exposure in southern Spain (hello, UV and heat):
| Metric | Original | Reformulated |
|---|---|---|
| Chalking (ASTM D4214) | 2 | 1 |
| Color Retention (ΔE) | 4.1 | 2.8 |
| Adhesion (ASTM D3359) | 4B | 5B |
| VOC (g/L) | 420 | 285 |
Source: Internal R&D Report, Nordic Coatings AB, 2022
Not only did it pass compliance, but performance improved. The slower-evaporating DPM allowed better pigment wetting, reducing flocculation. Isobornyl acetate added resin compatibility without the toxicity of glycol ethers.
🤔 Final Thoughts: The Balancing Act Never Ends
Co-solvents aren’t glamorous. You won’t see them on billboards. But they’re the quiet engineers of paint performance—helping formulators walk the tightrope between “it works” and “it’s legal.”
As regulations evolve and customer demands shift toward sustainability, the role of solvent blends will only grow. The key? Flexibility. There’s no one-size-fits-all solution. A blend that works in a humid tropical climate may fail in a dry desert. A low-VOC system for interiors might not cut it in industrial maintenance.
So, the next time you admire a perfectly smooth wall or a rust-free bridge, raise a glass (of IPA-free solvent, perhaps) to the co-solvents—the unsung heroes in the can. 🥂
Because behind every great paint job, there’s a great blend.
🔍 References
- European Commission. Directive 2004/42/EC on the limitation of emissions of volatile organic compounds due to the use of organic solvents in paints and varnishes. Official Journal of the European Union, 2004.
- Zhang, L., Wang, H., & Liu, Y. (2020). "Solvent Substitution in Epoxy Coatings: Performance and Environmental Impact." Progress in Organic Coatings, 147, 105789.
- Kirwan, M., et al. (2021). "Renewable Solvents in Coatings: A Sustainable Alternative to Petrochemicals." Journal of Coatings Technology and Research, 18(5), 1123–1135.
- Eastman Chemical Company. Technical Data Sheet: Texanol® Ester Alcohol. Kingsport, TN, 2022.
- Dow Chemical. Solvent Guide for Coatings Formulators. Midland, MI, 2021.
- CARB. Architectural Coatings Regulation. California Air Resources Board, 2023.
- CCME. National Volatile Organic Compound Emission Reduction Plan for Architectural Coatings. Canadian Council of Ministers of the Environment, 2021.
- GB 38507-2020. Limits of Volatile Organic Compounds of Industrial Coatings. China National Standards, 2020.
- ASTM International. Standards for Coatings Testing (D3960, D523, D4400, etc.). Various years.
- Nordic Coatings AB. Internal R&D Report: Solvent Reformulation of Industrial Enamels. 2022.
Dr. Lin Xiao has spent 15 years formulating coatings across three continents. When not tweaking solvent ratios, she enjoys hiking, fermenting hot sauce, and arguing about the Oxford comma. 🌶️
Sales Contact : sales@newtopchem.com
=======================================================================
ABOUT Us Company Info
Newtop Chemical Materials (Shanghai) Co.,Ltd. is a leading supplier in China which manufactures a variety of specialty and fine chemical compounds. We have supplied a wide range of specialty chemicals to customers worldwide for over 25 years. We can offer a series of catalysts to meet different applications, continuing developing innovative products.
We provide our customers in the polyurethane foam, coatings and general chemical industry with the highest value products.
=======================================================================
Contact Information:
Contact: Ms. Aria
Cell Phone: +86 - 152 2121 6908
Email us: sales@newtopchem.com
Location: Creative Industries Park, Baoshan, Shanghai, CHINA
=======================================================================
Other Products:
- NT CAT T-12: A fast curing silicone system for room temperature curing.
- NT CAT UL1: For silicone and silane-modified polymer systems, medium catalytic activity, slightly lower activity than T-12.
- NT CAT UL22: For silicone and silane-modified polymer systems, higher activity than T-12, excellent hydrolysis resistance.
- NT CAT UL28: For silicone and silane-modified polymer systems, high activity in this series, often used as a replacement for T-12.
- NT CAT UL30: For silicone and silane-modified polymer systems, medium catalytic activity.
- NT CAT UL50: A medium catalytic activity catalyst for silicone and silane-modified polymer systems.
- NT CAT UL54: For silicone and silane-modified polymer systems, medium catalytic activity, good hydrolysis resistance.
- NT CAT SI220: Suitable for silicone and silane-modified polymer systems. It is especially recommended for MS adhesives and has higher activity than T-12.
- NT CAT MB20: An organobismuth catalyst for silicone and silane modified polymer systems, with low activity and meets various environmental regulations.
- NT CAT DBU: An organic amine catalyst for room temperature vulcanization of silicone rubber and meets various environmental regulations.
Comments