Coating processes – Electrical product produced
Reexamination Certificate
2000-05-02
2003-07-01
Egwim, Kelechi (Department: 1713)
Coating processes
Electrical product produced
C427S385500, C427S393500, C427S340000, C524S501000
Reexamination Certificate
active
06586041
ABSTRACT:
BACKGROUND OF THE INVENTION
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.
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 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.
Furthermore, under certain circumstances which commonly occur, the accumulated static electricity charge may discharge to adjacent articles. Electrical components, such as computer chips, and electronic products, such as computers, televisions, and other industrial or consumer goods are frequently wrapped in plastic, such as by shrink wrapping, due to the relatively low cost of such packaging methods. 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.
There have been numerous attempts to develop acceptable coatings and compositions for plastics that are capable of minimizing the amount of static electricity charge development on the surface of plastic packaging materials. 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. One approach involves incorporation of anti-static material into the polymer matrix of the plastic packaging materials. Quaternary ammonium compounds and amine-type compounds are known internal anti-static materials that function by attracting moisture from the surrounding environment to create a conductive layer of surface moisture on the plastic packaging material. 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.
Other traditional types of internal anti-static materials include conductive fillers, such as carbon black, metallic powder, fibers, and inherently dissipative polymers (IDP), such as polypyrroles and polyanilines. 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. For aesthetic reasons, as well as practical reasons, it is desirable that packaging materials be highly transparent. For example, a high level of transparency is needed to permit inspection of the goods in the package through the packaging material using a variety of different methods, including, but not limited to, automated bar code inspection, without the need to physically open the package.
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.
As an alternative to internally mixing or filling a plastic packaging material with an electrostatic dissipative substance, a film of an electrostatic dissipative material may be applied onto one or both sides of the plastic packaging material. A number of attempts have been made to create such a packaging material that incorporates a film of electrostatic dissipative material onto a plastic substrate. 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. First, both the electrostatic dissipative film or coating and the electrostatic dissipative packaging material should desirably be economical to produce. Thus, the electrostatic dissipative substance that is incorporated preferably should be a low cost substance, incorporated at a relatively low concentration, or be both low in cost and incorporated at a relatively low concentration. Additionally, the ESD coating should preferably be highly transparent and without color. These properties are desirable to allow for quick visual inspection of the packaged contents and machine-based inspection of the contents, such as automated bar code inspection, without the need to open the package.
Also, the completed electrostatic dissipative film or coating should preferably have a relatively high surface resistivity that minimizes or prevents charge accumulation in the ESD coating or film and in the ESD packaging product. The surface resistivity of the ESD coating should preferably be adequate to minimize or prevent dust buildup on the packaging material and should also preferably be adequate to prevent a level of current discharge that either damages the packaged goods or that causes discomfort or fear in persons touching the packaged product.
Furthermore, the ESD coating or film should preferably have a very low level of ion contamination and a relatively neutral pH ranging from about 6 to about 9 standard pH units, especially when used for packaging electronic components and articles. 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. The relatively neutral pH of the ESD composition will further help prevent corrosive damage to products encapsulated in the ESD packaging material. This eliminates ESD substances, such
Egwim Kelechi
Goex Corporation
Kinney & Lange , P.A.
LandOfFree
Transparent static dissipative coating compositions does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Transparent static dissipative coating compositions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Transparent static dissipative coating compositions will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3007607