Transparent static dissipative coating compostitions

Abstract

A method of preparing an electrostatic dissipative composition that includes combining a conductive polymer; a crosslinkable polymer, and a crosslinking agent to form a fluidized dispersion, and providing the fluidized dispersion with a pH of about 7 to 9 to form the electrostatic discharge composition.

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)[0001]Provisional Application Ser. No. 60 / 107,401 that was filed on Nov. 6, 1998BACKGROUND OF THE INVENTION[0002]The present invention generally relates to an electrostatic dissipative (ESD) composition for preparing films and / or coating substrates. More particularly, the present invention relates to a method of forming a transparent, water-based, electrostatic dissipative composition, to a method of using the composition to form an electrostatic dissipative film on a substrate, and to a method of using the composition to form an electrostatic dissipative article.[0003]Many plastics are prized for their insulating ability that is derived from the relatively high electrical surface resistance of these plastics. Unfortunately, high electrical surface resistance is an undesirable property in some applications since the high electrical surface resistance will typically allow build-up or accumulation of static electricity charge on outer surfaces ...

AI Technical Summary

Benefits of technology

The solution results in a highly transparent, cost-effective ESD coating with stable surface resistivity, minimal ion contamination, and resistance to temperature and humidity changes, preventing static charge accumulation and dust buildup while maintaining mechanical properties suitable for thermoforming.

Problems solved by technology

Unfortunately, high electrical surface resistance is an undesirable property in some applications since the high electrical surface resistance will typically allow build-up or accumulation of static electricity charge on outer surfaces of the plastic.

This static electricity charge accumulation is problematic in and of itself because the accumulated charge may attract migrant dust particles and cause the surface of the plastic to collect dust.

However, this method of packaging electronic components and articles has not realized its full potential because of the damage and / or destruction that discharges of static electricity may cause to packaged electronic components and articles.

However, despite advancing the knowledge base with regard to static dissipative materials, these efforts have not been entirely satisfactory for a variety of different reasons.

However, these types of internal anti-static compounds require a relative humidity of at least about 15% in the surrounding environment to perform effectively.

Thus, the practical applications of these types of internal anti-static materials are limited, since packaged electronic components and products are frequently shipped from, through, or to arid parts of the world with relative humidities of less than 15%.

Furthermore, conductive surface moisture layers that are created by these internal anti-static compounds quickly lose their effectiveness when conditions change that cause evaporation of the moisture and under conditions when the package is jostled or otherwise subject to surface contact with other articles being shipped, with conveying equipment, or with the shipping equipment itself.

Traditional conductive fillers, such as carbon black, metallic powder, and metallic fibers are problematic, because each of these materials reduces the transparency of the plastic packaging material.

Inherently dissipative polymers (IDP), such as the polypyrroles and polyanilines, may also create transparency problems when incorporated at the relatively high concentrations needed to effect adequate static discharge properties in the plastic packaging materials.

Additionally, IDP polymers are relatively high cost, which limits use of IDP polymers to packaging only the most valuable and costly electronic components and products.

Furthermore, since IDP polymers typically are thermally stable only up to relatively low temperatures of about 200° C., or so, the physical ability to internally incorporate IDP polymers into plastic packaging materials is severely limited.

For example, at the hot temperatures typically required during conventional polymer processing, such as extrusion and injection molding, many anti-static IDP polymers are incapable of withstanding the high temperatures and are damaged or destroyed, thereby rendering the IDP polymers that are incorporated useless for purposes of providing electrostatic discharge properties to the plastic packaging materials.

Though these various approaches have advanced the knowledge base with respect to electrostatic dissipative packaging materials, none of these approaches have optimally addressed and achieved a satisfactory balance of the various properties that such electrostatic dissipative packaging should have.

Aside from sometimes being difficult to achieve individually, achieving an optimal combination of these different properties is a very difficult challenge, since several of these properties are based upon variables that conflict with each other.

Tramp ions, such as chloride, sulfate, phosphate, fluoride, nitrite, bromide, nitrate, and silicon, that escape from the ESD coating or film of the ESD packaging material are often highly corrosive and detrimental to electronic components that are encapsulated in the ESD packaging material.

This is a difficult proposition, since the ESD substances in the ESD composition should also remain uniformly dispersed within the composition over relatively long periods of time, such as 30 to 60 days or more.

However, the steric and electrostatic effects pose significant barriers to uniform film formation once the ESD composition is spread on the substrate and the suspending water and / or solvents of the composition are evaporated.

Thus, what is needed to maintain a uniform dispersion and suspension of the ESD substance in the ESD composition is deleterious for uniform film formation due to impedance of uniform intermixing of the ESD substance in the coating during and after removal of water and hydrophillic solvents.

Thus, these competing variables of uniform dispersability and suspendability in the ESD composition along with achievement of uniform coating or film thickness are inherently inconsistent with each other and present complex competing variable problems.

None of the presently known or existing ESD coating compositions support optimal achievement of these various properties.