Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2002-10-17
2004-07-27
Niland, Patrick D. (Department: 1714)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S255120, C427S255130, C427S255140, C427S255230, C427S255250, C427S255600, C427S295000, C427S296000, C427S407100
Reexamination Certificate
active
06767587
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to compositions for coating surfaces, surfaces coated with compositions, and methods of forming coated surfaces. More particularly, the present invention relates to hydrophobic coatings for laboratory vessels and other articles. The present invention also relates to processes for forming a hydrophobic coating on a surface of an article
BACKGROUND OF THE INVENTION
Hydrophobic coatings are useful for many applications, for example, to prevent rain from wetting-out or collecting on a windshield. Another application of hydrophobic coatings is in the field of laboratory vessels. Laboratory vessels including chambers, microtiter plates, vials, flasks, test tubes, syringes, microcentrifuge tubes, pipette tips, selectively coated microscope slides, coverslips, films, porous substrates and assemblies comprising such devices are often used to handle, measure, react, incubate, contain, store, restrain, isolate and/or transport very precise and sometimes minute volumes of liquid, often biological samples. When samples are quantitatively analyzed, it can be of critical importance that precise and representative amounts of sample are transferred, or else inaccurate results are obtained. Due to the different affinities of some materials to adhere to the walls of a laboratory vessel, qualitative analyses such as concentrations of materials may also be adversely affected if certain materials in a sample selectively adhere to operational surfaces of the vessel walls.
Unfortunately, materials typically used in the manufacture of laboratory vessels do not sufficiently repel many biological sample fluids nor do they sufficiently resist the adherence of molecular constituents of such a sample fluid. The sample fluids often wet the surface of the vessel causing residual quantities of liquid sample to cling to an operational surface of the vessel when the sample is removed. In some cases, significant quantitative and/or qualitative errors result. It is therefore desirable to provide extremely hydrophobic coatings for laboratory vessels which will reduce the wetting of the operational surfaces of the vessels and reduce clinging by even the most adherent samples so that virtually no sample remains in the vessel when poured, ejected or vacuumed therefrom.
In some laboratory techniques, it is important to restrain, isolate or limit the position of liquid samples to prescribed locations within or on a laboratory vessel, while keeping adjacent surfaces of the vessel substantially free of liquid sample. Such techniques can be used to facilitate chemical and biological reactions, as well as improving sample recovery. The prescribed locations may (1) have surfaces that are reactive, (2) have a surface that exhibits a specific affinity, (3) optimize the sample volume to area ratio, (4) restrict sample movement during at least some vessel motion, and (5) have porous surfaces.
Vessels for handling, measuring, storing and transporting liquids have previously been rendered less wettable and less adherent to fluids by application of silicone compounds to the vessel surfaces which come in contact with the fluid. For example, silane monomers and polymers have been added to polyolefins prior to injection molding, resulting in laboratory vessels with an improved repellency to many sample fluids and their constituents. These materials produce surfaces with surface energies potentially as low as 22 ergs per square centimeter. In practice, however, silane treated vessels exhibit surface energies that measure 25 to 30 dynes/cm.
Drawbacks associated with silane treatments include a continued wetting of the vessel, adherence to the vessel walls by many samples, chemical reactivity with many reagents, and a tendency for the vessel to become wettable following the common practice of autoclaving for sterilization. Silicones are known to freely migrate, leading to worries over sample integrity. Many pipette tips are plugged with porous filters to prevent sample contamination from the pipettor barrel, yet these free silicones make the pipette tips slippery and cause the filters to become loose or dislodged. Additionally, silicones must typically be added at a level of 2 percent by weight to be effective, making the cost prohibitive for many price sensitive applications.
Fluorination processes have been used to treat laboratory vessels and have resulted in vessels having interior surfaces with surface energies approaching 22 dynes/cm. These processes generally involve the full or partial replacement of superficial hydrogen by fluorine using chemical processes or the plasma polymerization of fluorine containing gases. U.S. Pat. No. 4,902,529 to Rebhan et al. discloses a plasma torch process using CF
4
or SiF
6
to fluorinate the interior of resin articles and containers in an attempt to eliminate the use of dangerous mixtures of fluorine and inert gases. This method is impractical, however, for treating the vast quantities of small vessels consumed by industrial, clinical and research establishments. Furthermore, improvements in performance over silicone processes are only marginal.
The plasma polymerization of perfluorobutene onto the exterior surface of various articles has been reported to produce exterior surfaces with up to 24 percent —CF
3
groups, and a high percentage of —CF
2
— groups. Resultant surface energies of 22 to 24 dynes/cm are obtained due to the presence of cross-linkages and numerous monofluorinated carbons. Time-consuming, carefully controlled RF plasmas employing fluorine-containing monomers have also been used to reduce the wettability and adhesion of laboratory vessels, producing exterior surface energies of 12 to 15 dynes/cm and surface populations of up to about 25% by area CF
3
groups on exterior non-operational surfaces. Interior operational surfaces, however, are still not reduced to below 22 dynes/cm. While these methods offer improvements over silicon-based treatments, the time, expense and equipment required are not appropriate for high commercial volume articles that are often for one-time use and require very low inherent cost.
Perfluoroalkyl polymers and carefully prepared monolayer films of perfluoroalkyl surfactants are widely recognized as having surface energies below 20 dynes/cm. FEP and PFA Teflons®, available from DuPont's Polymer Products Department, Wilmington, Del., have surface energies of 15 to 16 dynes/cm with —CF
3
populations as high as 25 percent. Extruded and fused Teflon® vessels are currently manufactured for special applications involving exceptionally harsh reagents but are expected to have a long service life because of their high material cost when compared to the cost of glass or polypropylene vessels.
Fluoroalkyl polymers have been used to produce oleophobic, hydrophobic membrane surfaces that are not wetted by common organic solvents. Membranes coated with such polymers are disclosed in U.S. Pat. No. 4,954,256 to Degen et al. These membranes have surface energies ranging from about 6 to about 15 dynes/cm but require a manufacturing procedure which involves soaking a membrane with a solution containing polymerizable monomers, exposing the solution-wetted membrane to high doses of ionizing radiation, and then washing the ionized membrane with organic solvent to remove unreacted monomer. While no attempts are known to coat laboratory vessels by such a procedure, it is expected that difficulties would arise as well as high cost in coating such vessels because of the shear bulk of the polymerizable solution to be irradiated and problems with fully washing the coated vessel.
Methods of making disposable, one-time use laboratory vessels such as pipette tips can involve a substantial loss of costly solvent when a coating solution is used to form a hydrophobic coating. A need exists for a process of coating laboratory vessels at a cost of a few cents per thousand with an insignificant loss of solvent.
Recent patents may suggest the practice of solvent recovery in the application of certain branched fluoropolymers, such
Cytonix Corporation
Kilyk & Bowersox P.L.L.C.
Niland Patrick D.
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