Coating processes – Base supplied constituent
Reexamination Certificate
2002-02-20
2003-04-29
Cameron, Erma (Department: 1762)
Coating processes
Base supplied constituent
C427S393500, C427S399000
Reexamination Certificate
active
06555175
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process for treating polymeric materials and, more particularly, to a process for modifying the surface of a polymeric substrate using a solution of an aromatic diazonium salt.
2. Discussion of the Related Art
The many surface-modified polymers that have been reported in the literature reflect the continuing need to provide materials having a unique combination of properties. A surface modified polymer may retain inherent, bulk properties of the polymer, such as tensile strength, elongation, chemical stability, optical properties, impact strength, dielectric, conductive, thermal, and acoustic attributes, inertness to specific environments, porosity and the like, while obtaining different surface properties, such as wettability, adhesion, solvent interaction, herbicidal or pharmaceutical activity, chemical reactivity, rheology, and reactive groups. In many instances, the modification of polymers which exhibit enhanced properties at their surface is cumbersome, diminishes bulk polymer properties, or requires costly synthesis.
Numerous types of polymer surface modifications and methods for preparing such modifications are known. Such existing surface modification methods on polymers include gas plasma, radiation grafting, photoinduced grafting, sol-gel process, surface etching, and adsorption. Although these existing surface modification techniques may be adequate for their purposes, they each have their drawbacks. For instance, the gas plasma technique tends to yield non-uniform surface modification. Ionizing radiation may weaken and discolor the polymer material, which is a significant drawback, since the bulk polymer properties are diminished due to an uncontrollable chemical reaction. In photoinduced grafting, a coupling agent reacts directly with the polymer substrate surface, and is sensitive to the particular reactive groups located on the surface of the polymer substrate and the energy level, duration, and distribution of illumination on the surface of the polymer. The sol-gel process creates a modified surface that lacks long-term stability, due to adhesion constraints. Surface etching cleaves the polymer backbone, which weakens the surface structure of the polymer.
Other methods of modifying surfaces of preformed polymer articles are well known and include dissolution and resolubilization, surface degradation, swelling with solvents as well as the reactions between polymers and inorganic groups, e.g., sulftric, nitric, and hydrochloric acids. Each of these means of modifying the surface of a polymer article is cumbersome in controlling the surface reaction without destroying polymer, or is limited to a very small range of polymer substrates and modifying reactants.
Bulk interpenetrating polymer networking is a combination of two polymers in the network form, at least one of which is polymerized in the presence of, and throughout, the other. European Pat. No. 643,083 and U.S. Pat. No. 5,426,158 disclose examples of bulk interpenetrating polymer networks. Drawbacks of interpenetrating polymer networks include a random distribution of polymers, and changes in the bulk properties of the initial polymers. For example, a clear polymer may be modified by the incorporating a transparent polymer, causing the resultant polymer to become hazy.
Methods of reacting aromatic groups with diazo compounds are well known and are the foundation of many azo dye and lithographic applications. However, these technologies involve the coupling of an aromatic group with a diazo compound through an azo complex containing the N═N bond, and typically forming a colored complex. The coupling of aromatic groups, without an azo bridging complex, may be obtained using the Gomberg-Bachmann reaction. The reaction has been performed on several types of aromatic rings and quinones. However, conditions for the reaction require the initial formation of a diazonium salt in an acid solution followed by a reaction in alkali media. Olefins may also be arylated by treatment with a diazonium salt in the presence of a cupric chloride catalyst. However, conditions require an abundance of chloride ions in addition to the cupric chloride catalyst. Additionally, an intramolecular reaction can occur in aromatic compounds by the alkaline solution or the copper-ion procedure resulting in a ring closure, termed the Pschorr reaction. All of these common methods of reacting aromatic groups and diazo compounds involve specific reaction conditions, but are limited to non-polymers.
A variety of techniques for the chemical modification of surfaces, including those of polymeric materials, are known in the art. U.S. Pat. No. 3,376,278, for example, the disclosure of which is incorporated herein by reference, describes a process for chemically modifying a polymer surface by contacting it with a compound containing a diazo radical attached to a nonaromatic carbon atom. Exposure of the surface to actinic radiation causes decomposition of the diazo compound to a divalent carbon species that reacts with the surface.
U.S. Pat. No. 5,075,427, the disclosure of which is incorporated by reference, describes storage stable diazo compositions that consist essentially of an aqueous solution of a compound in which the diazo group is attached to an aliphatic carbon that is also substituted with an electron-withdrawing group.
U.S. Pat. No. 5,277,772, the disclosure of which is incorporated herein by reference, relates to the chemical modification of various surfaces, including glass, aluminum, and organic polymers, by photoactivation of a heterocyclic azido compound in the presence of the surface and in the substantial absence of air and water.
U.S. Pat. No. 4,309,453, the disclosure of which is incorporated herein by reference, describes a process for surface modification of natural or synthetic macromolecular substrates in which a solution of a diazo or an azido compound in an organic solvent is applied as a thin layer on the substrate surface, which is irradiated to produce, respectively, a carbene or a nitrene that reacts with the surface.
U.S. Pat. No. 5,922,118, the disclosure of which is incorporated herein by reference, describes ink jet compositions containing colored pigments such as carbon black that have been modified by treatment with a solution of an aryl or an alkyl diazonium salt.
Despite the technology discussed above, there remains a need to modify the surface chemistry of polymers and impart desired properties while retaining other inherent properties. The numerous methods of continued surface modification of polymers reflect the need for improved properties. In many cases, the modification of polymers is cumbersome or impractical, diminishes polymer properties, requires costly synthesis, or does not achieve the expected results.
It will be appreciated from the foregoing that there is a definite need for a process whereby the surface of a polymer can be modified to have certain desired surface properties, while at the same time maintaining the desirable bulk physical properties of the polymer. Desired surface properties resulting from the surface modification of the polymer include the ability to control wettability, adhesion, solvent interactions, herbicidal or pharmaceutical activity, dielectric, thermal, and acoustic activity, chemical reactivity, rheology, and porosity. These properties may be controlled by varying the amount and type of hydrophilic and hydrophobic groups on the surface of the polymer. Chemical reactivity is defined as the ability of surface groups of the modified polymer to interact with chemicals, including further chemical reactions. Chemical compatibility is the ability of the surface groups of the modified polymer to enhance the interactions with liquids, gases, solids, and mixtures of these. Further, the surface modification process should be controlled so as to yield a defined type, amount and distribution of modifying groups on the polymer. Also, the process should not weaken or discolor the polymer mater
Cameron Erma
Johnson Joseph E.
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