Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
2002-04-10
2003-12-16
Powell, William A. (Department: 1765)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C428S331000, C428S409000
Reexamination Certificate
active
06663956
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a method for creating a static resistant or conductive product, typically a polymer film, by means of coating the product with a polythiophene and surfactant-based antistatic coating. The antistatic or conductive coating is also disclosed.
2. Description of Related Art
Antistatic coatings are desirable for many applications, such as photographic films, electronics packaging and other types of packaging. Polymeric films, for example, have the tendency to develop built up static charge when subjected to frictional forces in manufacture, processing, conversion, use and the like. An effective antistatic coating can minimize or eliminate any detrimental buildup and discharge of static electricity on the film or other surface. For other applications (including capacitors and the like), the conductivity of the antistatic coating can be employed for other purposes. For many end uses, it is important that an antistatic coating be substantially transparent. However, prior art antistatic coatings have suffered from numerous limitations, including high cost, inadequate transparency, incorporation of organic solvents, need for polymeric binders to provide sufficient adhesion to the substrate and limited antistatic properties. There is a need for antistatic coatings that address one or more of these problems. A need also exists for antistatic coatings that are adapted for application to polymer film substrates. Coatings adapted for in-line application are also desirable.
Polythiophene-based conductive coatings are known in the art. These polymeric conductors have been found to provide good antistatic properties. Their application to polymer films has been explored, alone and in conjunction with certain surface active agents. However, as is conventional in the use of surfactants, typically relatively low levels of surfactants were contemplated or tested in combination with the polythiophene polymers. Moreover, binders, organic solvents or both were used in conjunction with the polythiophene-surfactant combination to create an acceptable coating. Compositions substantially free of binders and organic solvents through the use of high levels of surfactants were not found.
BRIEF SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an antistatic coating suitable for application to a base polymer film.
It is a further object of the present invention to provide a base polymer film with an antistatic coating on one or both sides.
It is another object of the present invention to provide an antistatic coating that is substantially free of streaks and smears, particularly when applied to a base polymer film.
It is yet another object of the present invention to provide an antistatic coating that is substantially transparent.
It is yet another object of the present invention to provide a cost-effective antistatic coating with positive performance and antistatic properties.
It is yet another object of the present invention to provide an antistatic coating that is substantially free of organic solvents, and can be applied without the use of significant amounts of organic solvents.
It is a further object of the present invention to provide an antistatic coating containing polythiophenes that does not require a separate polymeric binder to achieve satisfactory adhesion to the film substrate.
The present invention has accomplished these objectives by providing in a preferred embodiment a coated polymer film having a coated surface that resists the formation of static, the film including a polymer film layer, and an antistatic coating on the film layer, where the antistatic coating includes a polythiophene and a surfactant, where said surfactant is present in an amount by weight at least about equal to an amount by weight in which said polythiophene is present.
DETAILED DESCRIPTION OF THE INVENTION
The present inventors have surprisingly found that excellent antistatic properties are provided by a coating that includes a polythiophene polymer and a high level of surfactant. While smaller amounts of surfactant have been considered in the past for use in conjunction with polythiophene polymers, the present inventors have unexpectedly found that by increasing the surfactant content beyond conventional levels, not only is adequate wet-out of the coating on film achieved, but in fact the conductivity and related antistatic performance of the coated film are improved. Furthermore, binders and organic solvents can be avoided or minimized by such use of high surfactant levels.
The antistatic coating of the present invention includes a polythiophene polymer to give antistatic and/or conductive properties to the coating and base polymer film. Polythiophenes are typically dark blue in color. However, due to the extreme thinness of the preferred coating of the present invention, the blue color is not perceptible in a single layer of film. Thus, as discussed later, coatings applied thinly by an in-line process are preferred to thicker, off-line coated layers where the blue color is noticeable, and usually undesirable. One preferred polythiophene is a 3,4-polyethylene dioxythiophene. Other preferred polythiophenes are disclosed in U.S. Pat. No. 5,766,515 to Jonas et al., the disclosure of which is incorporated herein by reference. This polythiophene is commercially available in a dispersion with polystyrene sulfonate from Bayer under the trade name Baytron PH, which contains no organic solvent or polymeric binder. Baytron PH is disclosed to contain 0.8% polystyrene sulfonic acid and 0.5% polythiophene, homogenized in a water base. Alternatively, a two component system of polythiophene and polystyrene sulfonic acid (available from Bayer as Baytron C and Baytron M) can be polymerized to achieve a similar product. Thus, in a preferred embodiment the polythiophene is used in conjunction with a dispersing agent, preferably a polymeric dispersing agent, more preferably a water-dispersible dispersing agent. Polystyrene sulfonic acid is preferred for use as such a dispersing agent.
The polythiophene is preferably present at about 0.08 to about 0.5 percent by weight of the coating solution, and in an alternate preferred embodiment, it is present at about 0.2 to about 0.4 percent by weight of the coating solution. About 0.2 to about 0.3 percent by weight is also preferred. Typically, the amount of polythiophene is minimized to increase cost effectiveness.
When a dispersing agent such as polystyrene sulfonic acid is used, it is preferably present at about 0.1 to about 2 percent by weight of the coating solution, and in an alternate preferred embodiment, it is present at about 0.15 to about 1 percent by weight of the coating solution. As discussed above, the preferred ratio of polystyrene sulfonic acid to polythiophene is 1.6 to 1.
The antistatic coatings of the present invention also include a surfactant or mixture of surfactants. In one preferred embodiment, the antistatic coating contains an anionic surfactant. The anionic surfactant results in a high wetting tension on the surface of the dried coating, and the high wetting tension enables an even application of the polythiophene to the coated surface. The anionic surfactant further enhances the wet-out of the water to maintain a clear, non-charged surface.
Various surfactants have been evaluated for use in conjunction with the polythiophene of the present invention and have been found to be effective. Anionic and nonionic surfactants are preferred. In an alternate preferred embodiment, a fluorosurfactant is included in the antistatic coating of the present invention. Preferably, this fluorosurfactant contains fluoroaliphatic oxyethylenes of carbon chain lengths of about 4 to about 8, and it can also include polyethylene glycol. Such a flurosurfactant is commercially available from 3M as Fluorad FC-170C surfactant, which is nonionic. The fluorosurfactant works beneficially because it minimizes or eliminates the coating streaks that can be caused by c
Donald Robin M.
Heberger John M.
Mitsubishi Polyerster Film, LLC
Powell William A.
LandOfFree
Antistatic coating and coated film does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Antistatic coating and coated film, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Antistatic coating and coated film will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3146006