In U.S. Patent 7,648,653 BASF SE (Ludwigshafen, DE) divulges formulations for corrosion resistant conductive polyoxymethylene compositions with carbon nanotube and carbon nanofiber conductive fillers. Carbon nanomaterials are believed to be slightly acidic and cause a deterioration of polyoxymethylene compositions which have not been stabilized.
An boron oxyacid or a boron oxyacid salt is used in a first polyamide oligomer to stabilize the composition such that articles formed from it exhibit reduced or eliminated deterioration. Further, when exposed to higher temperature, pressure, and high-fuel content environments, the articles maintain the desired physical properties.
An boron oxyacid or a boron oxyacid salt is used in a first polyamide oligomer to stabilize the composition such that articles formed from it exhibit reduced or eliminated deterioration. Further, when exposed to higher temperature, pressure, and high-fuel content environments, the articles maintain the desired physical properties.
Inventors David C. Krueger Majiid Khalatbri Wolfgang Heim and Theodore Zavadil concocted a conductive polyoxymethylene composition comprised of a first polyoxymethylene component, a conductive filler, at least one boron oxyacid or salt thereof, and at least one first polyamide oligomer.
The first polyoxymethylene component is comprised of a copolymer of oxymethylene, a homopolymer of oxymethylene, and mixtures thereof. The polyoxymethylene component is present in an amount of from about 50 to about 99.5 weight percent based on the total weight of the composition. The conductive filler is present in an amount of from about 0.1 to about 40 percent by weight based on the total weight of the composition.
Electrically conductive polymeric materials are desirable for many applications including the dissipation of electrostatic charge from parts, electrostatic spray painting, and the shielding of electrical components to prevent transmission of electromagnetic waves. The primary method of increasing the electrical conductivity of polymers is to fill the polymers with conductive additives such as metallic powders, metallic fibers, ionic conductive polymers, intrinsically conductive polymeric powder, e.g., polypyrrole, carbon fibers or carbon black. However, these approaches have shortcomings. For example, metallic fibers and polymeric powders have poor corrosion resistance and insufficient mechanical strength. Further, their density makes high weight loadings necessary; therefore, their use is frequently impractical.
Carbon nanotubes have been used in place of carbon black in a number of applications. For example, it has been recognized that the addition of carbon nanotubes to polymers in quantities less than that of carbon black, can be used to produce conductive end products. It has also been recognized that the addition of carbon nanotubes to polymers can be used to enhance the tensile and flexural characteristics of end products.
The BASF conductive polymer compositions include nanocarbon conductive fillers. Without intending to be bound to theory, the invetors believed that the conductive filler is at least slightly acidic which increases the deterioration of the polyoxymethylene component. One example of the conductive filler is carbon nanotubes. It is to be appreciated that the conductive filler may include a mixture of other conductive fillers, such as carbon black, conductive wollastonite, conductive carbon powders, and the like; however, it is preferred that the conductive filler are conductive fibers.
Carbon nanotubes typically have the form of tubes formed from graphite layers. The graphite layers are concentrically arranged around the cylinder axis. The carbon nanotubes may be single walled or multi-walled. The boron oxyacid or salt stabilizes the polymer and resists deterioration caused by the conductive carbon fillers.
