Liquid EPDM Waterborne Coating Formulations with Trilene®

Liquid ethylene propylene diene (EPDM) is one of the top elastomers used in ambient cure paints and coatings, especially for roofing and ambient maintenance coatings. Liquid EPDM resins are formulated into water-based liquid coatings that may be cured with peroxides, metal driers, or UV radiation. Liquid EPDM resins are also blended with other standard coating resins to improve various properties, such as surface wetting, adhesion, impact strength, resistance, and more.
L-EPDM resins are blended with elastomeric acrylics, alkyds, and polyurethanes without the use of compatibilizers.

 
Liquid EPDM Applications:

EPDM rubbers have been used extensively in various industrial applications, including automotive, wire and cable, roof membranes, and thermoplastic vulcanite (TPC) applications. It is an ideal material for exterior coatings due to the following:
 
  • EPDM's unique polymer structure
  • Ease of processing
  • Low-temperature flexibility
  • Superior ozone and UV resistance
  • Hydrophobicity or low moisture permeability
  • Excellent high- and low-temperature properties
  • Improved mechanical strength
  • Enhanced adhesion to polar substrates
     
Coating formulations utilizing EPDM meet the industrial standards and requirements in protective coatings. This includes solid content, rheology, curing speed, shelf life, and pot life. Liquid EPDM coatings can can be produced at a comparable cost to commercial elastomeric acrylic coatings.

EPDM coatings are also used as liquid roofing membranes outperforming solid EPDM sheets and elastomeric acrylic coatings in terms of ease of installation, solar reflectance, water, and weathering resistance.
 
Trilene® 65D is one of the top-quality liquid EPDM dispersions in the market. Trilene® 65D is a low molecular weight EPDM polymer consisting of 45% ethylene, 45% propylene, and 10% dicyclopentadiene monomers by weight. It can be blended with surfactants and dispersed in water at 50-55% solids concentration, especially for formulating low-VOC coatings. 

Typical Properties of Trilene® 65D:

Blending L-EPDM Dispersion (Trilene® 65D) with Other Binders:

T65D was added into a 100g SpeedMixer cup to test the compatibility with other co-binders without compatibilizers or surfactants. Next, 10% co-binder was added to the mixer cup and mixed at 2,000 rpm with a FlackTek highspeed mixer until a homogenous dispersion was formed. Then, about 10–15 g of the blend was transferred to a glass vial for stability testing, and an additional amount of co-binder was added to the remaining blend to prepare a 20 wt % blend.
 
The process was repeated for blends of Trilene® 65D with different co-binders and the samples were left undisturbed at ambient conditions for three months to watch for separation or destabilization. All the co-binders that passed the stability test are listed in the table below:
The co-binders/polymers listed above can be blended successfully with Trilene® 65D and liquid EPDM dispersions: acrylic, acrylonitrile-acrylic, styrene-acrylic latexes, alkyd latex, water-reducible alkyd, melamine-formaldehyde resins, polyurethane dispersions, carboxylated styrene-butadiene, chloroprene rubber latexes, and wax dispersions.

Trilene® 65D Coating Formulations:

Trilene® 65D was tested in several coating formulations which were conducted on the final coatings against ASTM standard lab equipment. Each coating formulation was applied to desired substrates, including cold-rolled steel (CRS), Lineta charts, and release paper, using a Gardco® wet-film applicator to 0.2–0.5 mm thickness.

1. Trilene® 65D Clear Coating Formulation:
  • The Properties of Trilene® 65D Clear Coating Formulation:
While the solids in this formulation are 50 wt %, the viscosity is somewhat high at low shear rates. However, this formulation is shear thinning, which allows for easy application and the dry time is sufficient for complete flow and leveling. This low-VOC coating is completely dry after overnight drying at ambient conditions (~22 °C, 55% RH). This elastomeric coating is understandably soft but has great impact and excellent adhesion and flexibility over a steel substrate.

Liquid EPDM Pigmented Formulations:

For pigmented formulations, dispersant was dissolved in water before the pigment addition then mixed at 2,000 rpm with a FlackTek high-speed mixer until the formation of a homogenous dispersion. Next, catalysts or peroxides were added to the dispersion and mixed for 2 minutes. Crosslinkers and coalescing solvents were mixed in a scintillation vial until fully dissolved and were then added to the Trilene and co-binder blend and mixed at 2,000 rpm with a high-speed mixer until achieving a uniform mixture.
 
The pigment and the polymer mixture were sufficiently mixed at 1,000 rpm to form a final smooth paint which was allowed to equilibrate for one week at room temperature before testing.
 
2. Trilene® 65D Pigmented Modified Acrylic Formulation:
Dry times for the clear coating and pigmented acrylic formulations were measured following ASTM D1640 using a Gardco Ultracycle dry-time recorder and then allowed to cure indoors at ambient conditions for seven days to achieve final properties before testing.
 
  • The Properties of Trilene® 65D Pigmented Modified Acrylic Formulation:
The pigmented modified acrylic coating has a higher solids content than the previous formulation due to the high pigment concentration (PVC), but the viscosity was much lower. The VOC is also lower as the acrylic does not require a coalescing solvent like L-EPDM.

The dry time of this modified acrylic/Trilene® coating is much shorter than the pure liquid EPDM coating, greatly reducing the time to recoat or use. While still soft, the coating does not lose any of its adhesion or flexibility and is slightly improved in its reverse impact resistance.

Compared to the 100% acrylic formulation, the L-EPDM modified acrylic coating provides better adhesion to cold-rolled steel. In addition, L-EPDM improves the wetting properties and increases the tensile strength of elastomeric acrylic roof coatings.

3. Trilene® 65D Pigmented Alkyd Coating Formulation:
The Trilene® pigmented alkyd coating formulation samples were placed in an 80°C oven for 5 minutes to flash off the water and then placed in a 170°C oven for 15–30 minutes. The 50:50 formulation from Table 4 was also cured at 60°C and 80°C for 1 hour with a dry timer.
 
  • Properties of Trilene® 65D Modified-Alkyd Coating:
 
In the L-EDPM/Alkyd formulation, while the solids content stays consistent across all formulations, the viscosity increases with Trilene® 65D loading but begins to plateau at approximately 50% concentration of Trilene® by weight.
 
The drying time in ambient conditions also increases as more Trilene® 65D is added to the formulation. However, in all blends, the dry times are significantly shorter than coatings prepared with Trilene® 65D alone. This is due to the increased unsaturation in the system from the alkyd resin and its higher mobility compared to the L-EPDM polymer, which allows reactive groups to come in contact more often.
 
The impact strength of the coatings reaches its maximum at a Trilene® concentration of 50%. This is likely due to the formation of an interpenetrating polymer network in the coating at this loading which fully reinforces the alkyd system. The gloss and color of the coating also decreased with increasing Trilene® loading rate, but like viscosity, it reaches an inflection point at 50% weight.
 
 
  • Properties of Trilene® Heat-cured Modified-Alkyd Coating:

As with the acrylic blends, the alkyd blends have improved wetting over low surface energy substrates as the Trilene® 65D loading increases. This is partly due to the low polarity of the Trilene® 65D resin, but it is also related to viscosity. All the formulations are sheer thinning and viscosity increases slightly with Trilene® 65D content.
 
At the lowest sheer, which a coating might experience while leveling and drying, the high-alkyd sample has a much lower viscosity. This allows the coating to crawl and bead on the low-surface energy substrate. By increasing the loading by 15%, the low-sheer viscosity increases by nearly an order of magnitude. An additional 25% increase in Trilene® 65D increases the low-sheer viscosity by another order of magnitude and eliminates the low-sheer viscosity drop. This, in addition to the decreased polarity, leads to improved wetting over low-energy substrates.
 
The effect of heat on the cure and properties of the 50:50 T65: alkyd dispersion was tested. The coatings showed a rapid cure rate and were tack free in under 5 minutes. It cured twice as fast at 80 °C and at 60 °C. Each coating did require 15 minutes of cooling to achieve a mar-free hard surface. This shows that this improved alkyd coating can be used in a heat-cured industrial coating process.

4. Trilene® 65D Heat-Cured Industrial Coating Formulation:
The Heat-cured industrial coating formulation in the above table was coated in triplicate and placed in an 80°C oven for 5 minutes to flash off the water and then placed in three ovens at 160°C, 180°C, or 200°C for 5–30 minutes. A sample was removed from each oven every 5 minutes to check the degree of cure. After drying, the coating film was used to measure physical properties, including pencil hardness, crosshatch adhesion, impact strength, and flexural strength.
 
  • Properties of Trilene® 65D Heat-Cured Industrial Coating Formulation:
The table above shows the properties of pigmented and clear coatings of T65D formulated with VUL-CUP 40KE as the crosslinking initiator. A peroxide was used instead of the metal driers for its efficient radical generation at the tested temperatures. As this peroxide is stable at room temperature, this is a 1K system. 10 mil WFT samples were cured with a 20-minute water flash at 80 °C followed by a 30-minute cure at 170 °C.
 
A second set of tests looked at a thinner 5 mil WFT film with a 5-minute water flash and 15-minute cure at the same temperatures. Pigmented coatings took slightly longer to fully dry due to the absorption of water into the pigment. While the pigment loadings, film thickness, and cure times varied between each of these samples, the final properties of each of these films were the same. This demonstrates a flexibility in film thickness and cure profile of industrial coatings made with Trilene® 65D.
 
5. Trilene® 65D Low-PVC Heat-Cured Industrial Coating Formulation:
In this formulation, we investigated the effect of various cure temperatures on the coating’s properties. In the above formulation, dicumyl peroxide was used as the crosslinking initiator. As this peroxide is stable at room temperature, this is a 1K system. As the cure temperature was increased, the curing time was shortened by 5 minutes for each 20 °C increase.
 
The additional 5 minutes for dry-to-touch was the time it took for the film to come to room temperature and lose enough molecular motion to become non-tacky. An additional 10 minutes was needed for the substrate to cool enough to avoid deformation in the coating by thumb twist. In each case the physical properties of the coating were the same, showing that the required process time can be controlled by increasing the temperature.
 
  • Properties of Trilene® 65D Low-PVC Heat-Cured Industrial Coating Formulation:

Summary and Results:

Trilene® 65D is a new waterborne resin for coatings applications with unique properties and added benefits to common coating resins.
 
Trilene® 65D is exceptionally compatible with a wide range of waterborne binders. An example of a good blend and a partially destabilized blend are shown below:
 

The results of blending waterborne resins with Trilene® 65D are shown in the table below with loading rate limits by the co-binder type without the use of surfactants or compatibilizers:



Conclusion:

 
Blends of Trilene® 65D with these other resins form highly flexible and impact resistant coatings with improved wetting over low-energy surfaces. With excellent blending at all loadings, Trilene® 65D or L-EPDM could be used as a modifier, co-binder, or as the primary resin, along with the other binder for performance enhancement or for cost reduction.

This makes Trilene® 65D an excellent choice for waterborne coating formulation, especially roof coatings, elastomeric coatings, and industrial coating formulations.
 

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