Automotive Coatings

Advantages of EEP (Ethyl 3-Ethoxypropionate) in Automotive Coatings

The solvent Ethyl 3-Ethoxypropionate (EEP), as a type of high-performance eco-friendly solvent, possesses the characteristics of effective solvency, high boiling point, low evaporation rate, low toxicity, environmental friendliness, and strong application adaptability. Its unique physical and chemical properties enable it to play a key role in improving film quality, optimizing the application window, and meeting environmental regulations, which highly aligns with the core requirements of original equipment manufacturer (OEM) automotive coatings and refinish paints. The following systematically elaborates on its application value based on the key demands of automotive coatings:

I. High Boiling Point and Slow Evaporation Enhance Film Leveling

EEP has a high boiling point (169°C, at atmospheric pressure) and a moderate evaporation rate (approximately 12.94, based on n-butyl acetate as 100). This effectively extends the wet film open time, allowing the wet film more sufficient time to flow and spread, thereby avoiding leveling issues caused by excessively fast surface drying. This effectively eliminates surface defects such as brush marks, orange peel, pinholes, etc., generated during the spraying process, ultimately forming a smooth, flat, and high-gloss (≥90° GU) perfect paint film, meeting the stringent requirements of automotive coatings for top-tier appearance.

This characteristic is particularly suitable for robotic automatic spraying processes. The evaporation rate of EEP can match the spraying rhythm, significantly suppressing defects like “orange peel,” “sagging,” and “edge thinning” during large-area continuous spraying. This ensures the paint film meets first-class decorative standards, satisfying the OEM’s stringent requirements for vehicle body appearance. Additionally, it prevents spray gun clogging due to overly rapid solvent evaporation, ensuring continuous production line operation.

In experimental tests, the paint film prepared with a basecoat formulation containing 8% EEP achieved a gloss of 90-95° GU, about 2-5° higher than the formulation without EEP. Orange peel testing showed Long Wave (LW) < 3.2 and Short Wave (SW) < 12.5, compared to approximately LW < 11 and SW < 26 for the formulation without EEP (general standards are typically LW < 10 and SW < 25). The film containing EEP showed significant improvements in distinctness of image (DOI), gloss, and leveling effect.

II. Excellent Solvency Reduces Viscosity and Enhance Dispersion & Wettability

The molecular structure of EEP contains both ester and ether groups, giving it excellent solvency power and low selectivity. It exhibits excellent solvency and compatibility with mainstream film-forming resins commonly used in automotive coatings, such as acrylic resins, polyurethanes, epoxy resins, and amino resins. Simultaneously, it can form low-viscosity polymer solutions, which is beneficial not only for spray application (reducing energy consumption, improving atomization) but also for achieving higher pigment loading, perfectly adapting to the complex systems of automotive coatings.

In experimental tests, compared to PMA (Propylene Glycol Monomethyl Ether Acetate), EEP efficiently dissolved the acrylate resins in basecoats. The resulting coating had lower viscosity and exhibited smaller changes over a certain period when exposed to air, indicating a longer pot life and higher application tolerance. The viscosity of the resin solution after dissolution remained stable.

EEP has a low surface tension (28 mN/m), which effectively reduces the agglomeration force between pigment particles, avoiding pigment flocculation due to insufficient solvent power. This enhances the film’s flop index, side-door clarity, and flop effect, ensuring a spray-finished body free of color difference spots, and guaranteeing color consistency and high decorativeness. Its low surface tension also helps the coating wet and spread better on substrates, especially on damp or complex-shaped substrates, effectively preventing “blushing” and improving application tolerance.

During the pigment grinding stage, EEP can quickly wet pigment particles (such as titanium dioxide, carbon black, and organic pigments), reduce the viscosity of the grinding system, improve dispersion efficiency, and extend the storage stability of color pastes. It is particularly suitable for handling difficult-to-disperse pigments like high-pigment carbon black.

III. Strong Chemical Stability Enhances Performance of Functional Coatings

The high boiling point of EEP causes it to evaporate relatively slowly during the film drying process, contributing to the formation of a denser and more uniform film structure. This dense film can effectively slow down the penetration rate of water molecules, improving the film’s water resistance. It also reduces the attachment and deposition of salt spray on the film surface, lowering the probability of corrosion occurrence.

Ultraviolet (UV) light is a major factor causing paint film aging. The addition of EEP enhances the dissolution of resins and the wettability of pigments, reducing pinholes caused by poor wetting, which is crucial for durability tests. During application, the linear structural characteristics of the EEP solvent facilitate the coordinated, linear release with other solvents, effectively reducing micro-bubbles. This can improve the film’s integrity, flexibility, and chemical corrosion resistance, making it less prone to cracking, chalking, etc., under UV exposure, thereby slowing the aging process. The excellent solvency and stability of EEP also help maintain the uniform distribution of various components within the film, avoiding component separation or precipitation due to environmental factors, and ensuring the long-term stability of the film’s performance.

In experimental tests, a red automotive coating composite layer containing EEP solvent showed no chalking, blistering, delamination, or cracking after 1000 hours of artificial weathering aging. Color change was < Grade 1 and gloss loss was < Grade 1, demonstrating excellent performance. In contrast, the red automotive coating composite layer without EEP solvent showed slight blistering, color change < Grade 2, and gloss loss < Grade 2, failing to meet standard requirements.

IV. Low VOC Meets Low Toxicity and Environmental Requirements

EEP has very low acute toxicity (rat oral LD50 > 5000 mg/kg) and a relatively mild odor. It can significantly improve the working environment in coating workshops, reduce health risks for operators, and enhance work comfort.

The evaporation rate of EEP is much lower than that of traditional solvents (e.g., n-butyl acetate). It is a solvent with low photochemical reactivity (OH reaction rate constant). In some regions (e.g., the European Union), it is classified as a “low contributor VOC” and may be excluded from total VOC calculations. In tests, the VOC content of solvent-based coatings using EEP + MAK (Methyl Amyl Ketone) could be reduced to 469.09 g/L, complying with the VOC limit for automotive refinish clearcoats (≤480 g/L). It can meet domestic and international environmental standards, avoiding production bans or market access risks due to VOC non-compliance. Furthermore, EEP exhibits good biodegradability, is environmentally friendly, and aligns with the trends of green chemistry and sustainable development.

V. Moderate Solvency Adapts to Multi-Material Body Structures

Modern vehicle bodies commonly adopt mixed structures of steel/aluminum/engineering plastics (such as non-metal parts made of PP, TPO, ABS, etc.). On plastic components of the vehicle body, strong solvents might cause issues like cracking or deformation. EEP, however, ensures good dissolution of coating resins without adversely affecting the plastic substrate, ensuring good adhesion and compatibility between the coating and the plastic substrate. For metal substrates, EEP does not cause corrosion or oxidation like some acidic or alkaline solvents might. For rubber components, EEP does not cause swelling or aging of the rubber. This allows EEP to be safely applied in coatings for multi-material body structures without negatively impacting substrate performance and lifespan, being compatible with various substrate materials. Its moderate solvency ensures good intercoat adhesion between electrophoretic primer, primer surfacer, basecoat, and clearcoat, meeting the process compatibility requirements of OEM multi-layer coating systems.

Summary

EEP, as a functional solvent combining high solvency, controllable volatility, good substrate adaptability, and environmental compliance, comprehensively enhances the application performance of automotive coatings and the quality of the final paint film. Its environmental characteristics of low VOC, low toxicity, and non-HAP status make it an ideal choice for replacing traditional high-VOC, high-toxicity solvents. This dual advantage of “performance and environmental protection” renders it an irreplaceable position in automotive OEM painting, refinish repairs, and special functional coatings.

For more information about functional solvents, please visit: PREC EEP Solvent