ADVANCED CONCRETE COATINGS

ADVANCEMENTS IN REACTIVE LIQUID POLYMER CHEMISTRY

NEW TOUGHENERS FOR COATING ADHESIVES

 

Cycloaliphatic resins are a unique class of materials that are characterized by non-aromatic saturated rings in their molecular structures. There are two general commercial types of cycloaliphatic resins. Among their most notable features are inherently low viscosity, coupled with excellent weathering and electrical performance. Both commercial cycloaliphatic resins are ideally suited for applications in severe environments such as near seacoasts and in areas of high industrial pollution as in low desert valleys.

Cycloaliphatic resins show distinct advantages over the glycidyl-ether coating materials due to their ability to produce tenacious bond strength on even poorly-cleaned and oily surfaces. BulletProof Brand Concrete Coatings makes commercially available these adhesive coating formulations.

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Improved chemical resistance, thermal performance, modulus, cure speed and UV stability are significant performance advantages with BulletProof Brand cycloaliphatic resin over other standard resins. This makes the critical difference to achieving a high performance-rated coating.

COMMERCIAL CYCLOALIPHATIC EPOXIDES

An important and widely-used cycloaliphatic resin is the diglycidyl ester of hexahydrophthalic acid.

Another pervasive cycloaliphatic resin that has been readily available until recent supply issues has the chemical name of 3,4 epoxycyclohexylmethyl -3,4 epoxy-cyclohexane carboxylate.

The most common curing agents for the diglycidyl ester cycloaliphatic resin include the carboxylic acid anhydrides and acid catalytic types. For outdoor applications, it is recommended to use fully saturated curing agents in order to retain both optimum UV light resistance and electrical arc-tracking resistance. The most common acid anhydrides of this type include both hexahydrophthalic anhydride and methylhexahydrophthalic anhydride. At room ambient temperature, HHPA is a solid but melts to a low very viscosity liquid at 35°-37°C. The MHHPA is a very low viscosity liquid at room temperature having a melting point of less than -15°C. Lewis acid catalysts including both BF3 and BCl3 amine complexes are used to formulate single component systems with this resin. Such formulations exhibit excellent latency at room temperatures with rapid cure at elevated temperatures.

Two-component casting formulations utilizing resin that employs saturated acid anhydride curatives commonly contain inorganic mineral fillers. These fillers are used to increase thermal conductivity and modulus while reducing thermal expansion, reaction exotherm during gelation and cost. The recommended fillers for outdoor electrical applications are silica and hydrated alumina. Silane pre-treatment of these fillers has been shown to significantly improve retention of mechanical and electrical properties on long term exposure in outdoor conditions and in hostile environments. Such silane coupling agents provide a stronger bond between the resin matrix and filler surfaces.

Thermal endurance testing is used to predict the long-term stability of an insulating material. Property changes such as tensile or flexural strength are measured after exposure to heat. The test times may vary between 5,000 and 20,000 hours.

The 3,4 epoxycyclohexylmethyl-3,4 epoxycyclohexane carboxylate resin has exceptionally low viscosity as well as very low color. Similar to the diglycidyl ester cycloaliphatic type, the most common curing agents used with this resin are the acid anhydrides and certain acid catalytic types. This resin type is manufactured by epoxidizing a diolefin with peracetic acid. Since chlorine is not present in these raw materials they are free of hydrolysable chlorine. This characteristic is of great importance in formulating high purity encapsulants.

For high Tg applications, this resin can either be used alone or in combination with other resins for the best balance of physical properties. Certain Lewis acid-type catalysts such as BF3- amine complex types can be used with this resin to yield systems with moderate latency at room temperature coupled with a very rapid elevated temperature cure.

In applications that require superior electrical properties in outdoor environments, either of the cycloaliphatic resins discussed can be used if cured with fully saturated acid anhydrides.

For use in temperatures in excess of 125°C, flexibilizing additives, such as polyether or polyester polyols, may be utilized.

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