Laboratory Vessel Having Hydrophobic Coating and Process for Manufacturing Same

The present invention relates to laboratory vessels for handling, measuring, reacting, incubating, containing, storing, restraining, isolating and transporting liquids, and operational surfaces for such vessels. More particularly, the present invention relates to a pipette tip and method for its production. The invention also relates to processes for manufacturing laboratory vessels and coatings for such 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 transport very precise and sometimes minute volumes of liquid, particularly 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 repel many biological sample fluids, or do not resist the adherence of their molecular constituents. 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) may 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.sub.4 or SiF.sub.6 to fluorinate the interior of resin articles and containers, proposing to replace 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.sub.3 groups, and a high percentage of --CF.sub.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.sub.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.RTM., available from DuPont's Polymer Products Department, Wilmington, Del., have surface energies of 15 to 16 dynes/cm with --CF.sub.3 populations as high as 25 percent. Extruded and fused Teflon.RTM. 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.

Materials have been co-injected to form parts with surface properties that are distinguishable from interior non-surface properties. U.S. Pat. No. 5,464,585 discloses a process for the pre-injection of a first material followed by the injection of a second material under laminar flow conditions to develop surface layers or concentration gradients of colorants, hardeners, fire retardants and combinations thereof. However, the present inventor knows of no co-injection process used to make very thin (e.g. less than 100 .mu.m) hydrophobic coatings for laboratory vessels.

Described by Dettre and Johnson in 1964 are phenomena related to rough hydrophobic surfaces. Dettre and Johnson developed a theoretical model based on experiments with glass beads coated with paraffin or TFE telomer. For even moderately hydrophobic surfaces (e.g. about 40 dynes/cm or less) with high levels of microscopic roughness, where the average height of bumps is close to or exceeds their average width, an aqueous liquid, especially one without surfactant activity, in contact with the surface only wets the top of the bumps, forming what is known as a "composite" air-liquid-solid interface. For example, water at rest on a surface of this kind may exhibit contact angles greater than 160 degrees. This unusual property has been practiced and is the basis for a variety of proprietary microscope slide, plate and membrane products using coatings sold by Cytonix Corporation, in Beltsville, Md. However, such products are based on Teflon.RTM. and the hydrophobic properties of difluoromethylene (--CF.sub.2 --) groups, which exhibit surface energies of from about 18 to about 20 dynes/cm.

A widely recognized need exists for providing liquid handling, measuring, reacting, incubating, containing, storing, restraining, isolating and transporting vessels which exhibit, on all or part of their operational surfaces, interfacial contact angles to liquid samples of 120.degree. and above, and surface energies well below 20 dynes/cm. A need also exists for vessels having surface energies of below 10 dynes/cm for some applications. This need is especially acute but difficult to achieve for one-time-use vessels costing only a few dollars per thousand.

A need more generally exists for liquid handling, measuring, storing, isolating, restraining and transporting vessels which have low retention of liquid samples and sample constituents.

The present invention is based on the discovery that laboratory vessel surfaces coated with a polymerization product of a fluorinated monomer containing from about 3 to about 20 carbon atoms and at least one terminal trifluoromethyl group are extremely hydrophobic and highly resistant to removal by solvents. Herein, the term "fluorinated" includes both perfluorinated and non-perfluorinated monomers and/or polymers. The present invention relates to such laboratory vessels, and processes of forming such coatings. The processes include applying a solution, suspension or other liquid containing a coating monomer and/or polymer and allowing the solution, suspension or other liquid to dry on a laboratory vessel operational surface. The present invention also provides a method wherein a solution or suspension of such polymer is partially, selectively or conformally coated onto at least a portion of an operational surface of a laboratory vessel, and then subsequently dried to remove solvent or suspension medium. The coatings provide surfaces exhibiting extremely low surface energies and high resistance to solvent removal.

According to some embodiments of the invention, the coating may be formed from a coating monomer and/or polymer applied or co-injected as a resin, powder, particle or mixture which is dried, melted, sintered, fused cured or otherwise formed on an operational surface of a laboratory vessel.

Moreover, the present invention is based on the discovery that laboratory vessel surfaces of low surface energy can be provided by coating a solution, suspension, other liquid, resin, powder, particle or mixture of a fluorinated polymerization product or fluorinated monomer according to the invention, admixed with microscopic particles. Upon subsequent drying, melting, solidifying, sintering, fusing or curing of the coating formulation, a laboratory vessel is produced exhibiting extraordinarily high contact angles to aqueous liquids.

The present invention is also based on the discovery that coatings of the polymerization product of a monomer containing 3 to 20 carbon atoms and at least one terminal trifluoromethyl group are extremely hydrophobic and can provide populations of 30% by area or greater of trifluoromethyl groups on exposed coating surfaces. According to the present invention, a polymerization product of such a monomer may be coated from a formulation onto at least a portion of an operational surface of a laboratory vessel, for example, a vessel surface which contacts or restrains a liquid sample. The coatings have tightly packed, exposed trifluoromethyl groups.

According to some embodiments, at least about 30% of the area of the exposed coating surface is covered by trifluoromethyl groups. According to more preferred methods of the invention, the exposed coating surface is covered with a population of trifluoromethyl groups of from about 50% to 100% by area of the surface.

According to the present invention, the coating material comprises a fluorinated polymer made from a monomer of fluorocarbons, hydrofluorocarbons, epoxies, urethanes, silicones, acrylics or other materials that have terminal trifluoromethyl groups and contain from about 3 to about 20 carbon atoms. Preferably, coatings made from such materials exhibit tightly packed trifluoromethyl groups on the exposed coating surface. According to some embodiments of the invention, coating polymers made from substantially non-branched fluorinated monomers having carbon chains of from about 3 to about 20 carbon atoms in length, and more particularly from about 6 to about 12 carbon atoms in length, enable a dense packing of the terminal trifluoromethyl groups and thus can form hydrophobic surfaces of very low surface energy, having critical surface tensions of about 10 dynes/cm or lower at 20.degree. C., and having high resistance to solvent removal and low retention of biological samples.

According to yet other embodiments of the invention, laboratory vessels are coated with hydrophobic coating formulations containing terminal trifluoromethyl groups and optionally further containing polymers, polymerizable monomers or other additives which also become incorporated in the hydrophobic coatings.

According to embodiments of the present invention, laboratory vessels for handling, measuring, reacting, incubating, containing, storing, restraining, isolating and transporting liquids are coated with a hydrophobic polymer or polymerizable coating formulation comprising, or consisting essentially of, the polymerization product of a monomer containing a terminal trifluoromethyl group. Particular "vessels" which can be coated according to the present invention and which are preferred for fluid manipulation applications include vials, flasks, test tubes, pipette tips, microcentrifuge tubes, syringes, microscope slides, microscope slide assemblies, sample chambers for analytical devices, tapes, laminates, plates, arrays, tubing, and devices and apparatus with operational surfaces comprising plastic, sintered materials, semiconductors, glass, ceramic, metal and primed or pre-coated surfaces. The invention may also be used on operational surfaces which are porous, smooth, rough, pitted, grooved, cross-hatched, striated, or having patterned physical features.

Laboratory vessels according to the present invention have at least one operational surface. Many vessels according to the invention have at least one interior wall which defines a reservoir portion for containing a volume of liquid, and at least one opening in communication with the reservoir portion. According to some embodiments of the invention, a laboratory vessel having an interior wall and an opening is coated on the interior wall and on the area surrounding and forming the opening, with a polymer coating according to the invention.

Plastic or glass is often used to manufacture low-cost laboratory vessels. Some preferred materials used to manufacture laboratory vessels include polypropylene, polyethylene, polyethyleneterephthalate, polystyrene, polycarbonate and cellulosics. More expensive plastics such as polytetra-fluoroethylene and other fluorinated polymers have been used. Some vessels made from these plastics are hydrophobic without any additional coating. Herein, the term "hydrophobic" refers to a surface exhibiting an average surface energy of about 40 dynes/cm or less. Because polypropylene is inexpensive and quite hydrophobic itself, it is a particularly preferred material for laboratory vessels, including pipette tips, used for handling and transporting minute and precise amounts of biological sample.

In addition to the materials mentioned above, examples of other suitable materials for the laboratory vessels of the present invention include polyolefins, polyamides, polyesters, silicones, polyurethanes, epoxies, acrylics, polyacrylates, polyesters, polysulfones, polymethacrylates, polycarbonate, PEEK, polyimide, polystyrene, and fluoropolymers such as PTFE Teflon.RTM., FEP Teflon.RTM., Tefzel.RTM., poly(vinylidene fluoride), PVDF, and perfluoroalkoxy resins. Glass products including silica glass are also used to manufacture laboratory vessels. One exemplary glass product is PYREX.RTM. (available from Corning Glass, Corning, N.Y.). Ceramic or oxide surfaces can be coated according to embodiments of the invention. Cellulosic products such as paper and reinforced paper containers can be coated to form coated laboratory vessels according to the invention. Metal surfaces can be coated according to the invention, as can surfaces of glass, silicon, silicon compounds or ceramics that have or have not been primed with silane containing materials or other adhesion promoting materials. Primed metal, primed glass, primed ceramic and primed oxide surfaces can be coated according to embodiments of the invention. Vessel surfaces that have been pre-coated with epoxies, silicones, urethanes, acrylics, or other materials can also be coated according to embodiments of the invention.

Although some wash-off of polymerized coating material or coating monomer might be expected after repeated usage, the coatings of the present invention do not measurably wash off most laboratory vessel surfaces. It is believed that little if any wash-off occurs because the coating solution causes softening and swelling of the vessel material in uncross-linked plastics and enables entanglement of coating and vessel substrate molecules allowing strong Van der Waals and other bonding forces which hold the prepolymerized product where applied to an operational surface of the vessel. The linear swelling of many polymers and elastomers, including some fluoroelastomers and some silicones, is reported in Table 8 of the 1996 Technical Information sheet for Vertrel.TM. XF, available from DuPont's Polymer Products Division, Wilmington, Del. Little if any wash-off occurs from other vessel materials because of the extremely low solubility of the coatings of the present invention in most solvents and limited solubility in fluorinated solvents.

According to some embodiments of the present invention, hydrophobic polymers having terminal trifluoromethyl groups are coated from a fluoropolymer/fluorosolvent solution or suspension onto linear, hydrophobic, essentially uncrosslinked polymers such as polyolefins and TEFLON.RTM., and show particular resistance to removal even by fluorinated solvents. According to the present invention, swelling of the polyolefin surface during application of the fluoropolymer solution or suspension and subsequent entanglement of the polymers at the interface, result in strong hydrophobic bonds between the coating and the polyolefin surface. Surprisingly, the coatings according to embodiments of the invention are not measurably removed, even with chloroform or chloroethene.

According to some embodiments of the invention, the laboratory vessel comprises a microscope slide or other substantially flat device having an operational surface at least partially coated with a coating formulation according to the invention. According to some embodiments of the invention, a delineated area of a laboratory vessel surface, for example, a portion of the surface of a microscope slide, is not coated with the coating formulation, but is instead surrounded by the coating. The coating thus forms a boundary to restrain, contain or isolate a fluid sample on the non-coated area of the surface, while adjacent surfaces remain free of liquid sample, thus isolating and facilitating chemical and biological reactions as well as improving sample recovery. The uncoated locations may have surfaces that are reactive or have specific affinities, may optimize the sample volume to area ratio, or may restrict sample movement during some vessel motion. The uncoated region may be surrounded with a hydrophobic coating material according to the invention which comprises microparticles and the polymerization product of trifluoromethyl containing monomers.

According to some embodiments of the invention, the operational surface of a vessel such as a microscope slide is partially coated with a hydrophobic coating formulation according to the invention and partially coated with nonfluorinated material in delineated regions to isolate or constrain the position of a liquid sample to prescribed locations that do not contain the hydrophobic coating formulation.

According to embodiments of the invention, an operational surface comprises a sample retaining barrier of a rough surface composite coating according to the invention, which isolates and restrains an aqueous sample. Surrounding the composite coating is a smooth coating material which does not contain a sufficient amount of microparticles and does not exhibit surface roughness. The surrounding smooth coating permits the run-off of non-aqueous liquids therefrom, such as organic solvents, for example, acetone or xylene. For example, according to some embodiments, a laboratory vessel is provided with a low surface energy coating of the present invention and further comprises a second coating. The second coating comprises the polymerization product of a second fluorinated monomer. The second fluorinated monomer has from about 3 to about 20 carbon atoms, at least one terminal trifluoromethyl group, and a micropowder which provides the second coating with a rough surface. The second coating has an exposed surface area populated with 30% by area or more trifluoromethyl groups and a surface energy of about 22 dynes/cm or less at 20.degree. C. The second coating forms a continuous sample retaining barrier for retaining an aqueous sample within the barrier, and the low surface energy coating is substantially free of surface roughness and surrounds the second coating.

According to embodiments of the invention, regions on a surface of a laboratory vessel such as a microscope slide are used to isolate or constrain aqueous sample, and the regions are defined by a coating comprising microscopic particles and the polymerization product of trifluoromethyl containing monomers, surrounding a portion of the surface coated with the polymerization product of trifluoromethyl containing monomer. The microparticle-containing coating provides a greater hydrophobicity to aqueous liquids and thus a greater water repelling nature than the region coated with the polymerization product coating that does not contain the microparticles.

According to embodiments of the invention, regions on a surface of a laboratory vessel such as a microscope slide are used to isolate or constrain an organic solvent-based liquid sample, and the regions are defined by a coating comprising the polymerization product of trifluoromethyl containing monomers, surrounding a portion of the surface coated with a formulation comprising microparticles and the polymerization product of trifluoromethyl containing monomer. The microparticle-containing coating provides a greater affinity to organic solvent-based liquids than the region coated with the polymerization product coating not containing the microparticles.

The terminal trifluoromethyl groups of the coating polymer or monomer preferably constitutes the entire operational surface of the coating. According to preferred embodiments of the invention, the polymer coating is applied in a manner such that the exposed coating surface comprises from about 30% by area to about 100% by area trifluoromethyl (--CF.sub.3) groups. In other words, of the molecules and substituent groups making up the exposed operational surface of the coating, from about 30% by area to 100% by area of the exposed surface area of the coating is made up of --CF.sub.3 groups. The exposed surface of the coating exhibits an extremely low surface energy which can approach about six dynes/cm, depending upon the percentage or "population" of --CF.sub.3 groups making up the exposed surface of the coating and the vessel material coated according to the invention. In more preferred embodiments of the invention, from about 50% by area to 100% by area of the exposed surface is populated with trifluoromethyl groups, and even more preferably, at least about 75% by area is populated with trifluoromethyl groups.

According to some preferred embodiments of the invention, laboratory vessels are provided having an operational surface coated with a polymer comprising the polymerization product of trifluoromethyl-terminated, substantially unbranched and fluorinated monomers containing from 6 to 12 carbon atoms. Coatings made from such products are extremely hydrophobic, oleophobic, and highly resistant to solvent removal and biological sample retention.

A particularly preferred coating solution for forming coatings according to the invention comprises the polymerization product of a trifluoromethyl terminated, substantially unbranched perfluorooctyl monomer. Coating solutions containing at least about 50% by weight of a product of such a perfluorooctyl monomer are particularly preferred for printing applications.

The hydrophobicity and solvent resistance of the operational surface coating of the invention depends on a number of factors including the material of the laboratory vessel which is coated and the amount or population of terminal trifluoromethyl groups present on the exposed surface of the coating. For example, it has been determined according to the invention that when an operational surface of a polypropylene vessel is coated with a hydrophobic polymer solution to form a coating comprising 30% by area or more trifluoromethyl-terminated, substantially unbranched perfluorinated monomer having from 6 to 12 carbon atoms, the coating exhibits a surface energy of below 20 dynes/cm with high resistance to solvent removal and low retention of biological samples.

It has also been determined according to the invention that when an operational surface of a polypropylene vessel is coated with a hydrophobic polymer solution to form a coating comprising 50% by area or more trifluoromethyl-terminated, substantially unbranched perfluorinated monomer having from 6 to 12 carbon atoms, the coating exhibits a surface energy of below 15 dynes/cm with high resistance to solvent removal and low retention of biological samples.

It has also been determined according to the invention that when an operational surface of a polypropylene vessel is coated with a hydrophobic polymer solution to form a coating comprising 80% by area or more trifluoromethyl-terminated, substantially unbranched perfluorinated monomer having from 6 to 12 carbon atoms, the coating exhibits a surface energy of below 10 dynes/cm with high resistance to solvent removal and low retention of biological samples.

It has also been determined according to the invention that when an operational surface of a polypropylene vessel is coated with a hydrophobic polymer solution to form a coating comprising 100% by area or more trifluoromethyl-terminated, substantially unbranched perfluorinated monomer having from 6 to 12 carbon atoms, the coating exhibits a surface energy of about 10 dynes/cm or lower with high resistance to solvent removal and low retention of biological samples.

The most hydrophobic properties are achieved when the coating has an exposed surface consisting entirely of trifluoromethyl (--CF.sub.3) groups, that is, 100% by area, with no other substituent groups exposed at the surface.

According to some embodiments of the invention, branched fluoroalkyl monomers containing terminal trifluoromethyl groups may also be used as reactive monomers or polymerized product in the coating solutions used according to the present invention. An example of a suitable branched monomer for such purposes is a perfluorinated iso-octyl monomer having two terminal trifluoromethyl groups.

According to embodiments of the invention, the carbon chain length of the trifluoromethyl containing monomers used to form the polymer coatings of the invention, and any functional groups used to form linkages between the fluoropolymer and the laboratory vessel, should be selected to provide an exposed surface of the coating which mainly comprises --CF.sub.3 groups. The --CF.sub.3 groups, which provide extremely hydrophobic properties, prevent liquids and samples contained in the vessel from infiltrating the exposed coating and reacting with the intermediate carbon groups and linkage groups of the polymerized monomer. Such infiltration is particularly prevented when the coating consists of monomers of substantially uniform length of greater than 6 carbon atoms, rather than a mixture of monomers of substantially different lengths.

According to embodiments of the invention, a polymer coating formed from a fluoroalkyl methacrylate monomer which has the chemical formula C.sub.7 F.sub.15 CH.sub.2 OCOC(CH.sub.3).dbd.CH.sub.2 is provided. Coatings made with the polymerized product of this monomer or similar fluoroalkyl monomers having a tri-fluoro methyl group, have exposed coating surfaces comprising tightly packed terminal --CF.sub.3 groups. The resultant coating has a low surface energy, or critical surface tension, which can be as low as about 6 dynes/cm at 20.degree. C. depending upon the population of trifluoromethyl groups on the exposed surface and depending upon the material of the vessel which is coated. However, when a surface population of 100% by area trifluoromethyl groups is achieved, the vessel material is irrelevant to the hydrophobicity of the surface.

As the packing of terminal trifluoromethyl groups increases, the surface energy of the packed surface decreases, such that coatings having the lowest critical surface tension have the closest packed --CF.sub.3 groups. The replacement of a single fluorine atom by a hydrogen atom in each terminal trifluoromethyl group of such a surface would more than double the critical surface tension of the surface. Critical surface tensions of teflon vessels and teflon coated vessels are only as low as about 18 dynes/cm at 20.degree. C. because such surfaces mainly comprise --CF.sub.2 -- groups. Although it is difficult to obtain an exposed surface entirely composed of tightly packed --CF.sub.3 groups, extremely low surface tensions can be achieved by the formation of exposed coating surfaces which contain 30% or more, by surface area, --CF.sub.3 groups. Preferably, an exposed surface having 50% or more --CF.sub.3 groups can be achieved according to the processes of the present invention. These processes tend to result in coatings having critical surface tensions ranging from about 6 dynes/cm to about 22 dynes/cm when formed on hydrophobic vessel materials.

Critical surface tensions, also referred to as surface energies, of as low as about 6 dynes/cm can be obtained according to the processes of the present invention, depending upon which terminal trifluoromethyl group-containing polymer or mixture of polymers is used to form the hydrophobic coating, the population of trifluoromethyl groups on the exposed surface, and the material of the vessel to be coated. According to embodiments of the invention wherein the exposed surface area of the hydrophobic coating material is populated with from about 50% by area to about 100% by area trifluoromethyl groups, surface energies of about 10 dynes/cm or less can be provided, particularly if the coating is formed on a polypropylene or other substantially hydrophobic laboratory vessel material, for example, a vessel material which exhibits a surface energy of 40 dynes/cm or less. Such surface energies are even lower than those of Teflon.RTM. which generally provides a surface energy of from about 18.5 to about 20 dynes/cm. Although Teflone.RTM. is formed from polymerized fully fluorinated monomers, most of the surface structure of a Teflon.RTM. coating consists of --CF.sub.2 -- groups as opposed to closely packed terminal tri-fluoro methyl(--CF.sub.3) groups. Even the most hydrophobic forms of Teflon.RTM., FEP Teflon.RTM. and PFA Teflon.RTM., which comprise mixtures of fully fluorinated polypropylene and polyethylene polymerized monomers, only provide surface energies of about 16.5 dynes/cm. As with other forms of Teflon.RTM., the exposed surface of an FEP Teflon.RTM. coating consists mainly of --CF.sub.2 -- groups as opposed to closely packed terminal tri-fluoro methyl (--CF.sub.3) groups. Teflon.RTM. and FEP Teflon.RTM., are available from DuPont Polymer Products Department, Wilmington, Del.

According to the present invention, lower surface tensions are obtained when the coating polymer comprises the polymerization product of a perfluoroalkyl monomer, when compared to coatings comprising the product of a partially non-fluorinated monomer. Substantially non-branched fluoroalkyl and perfluoroalkyl ethylenically unsaturated monomers are preferred for producing the coating polymers of the invention. According to other embodiments, a methacrylate group is used as a preferred ethylenically unsaturated monomer for making the polymeric coating material of the invention. Other monomers which can be used include silicones, epoxies and polyurethanes. Polymers made from mixtures of acrylates and epoxies or of acrylates and silicones are particularly preferred according to some embodiments of the invention.

According to embodiments of the present invention, laboratory vessels are provided having a coating thereon comprised of a prepolymerized fluoroalkyl, or preferably perfluoroalkyl, ethylenically unsaturated monomer having a terminal trifluoromethyl group. More particularly, the present invention relates to such a coating which consists essentially of a polymerization product of a fluoroalkyl or perfluoroalkyl ethylenically unsaturated monomer having a terminal tri-fluoro methyl group and an average carbon atom chain length of from 3 to about 20 atoms, more preferably from about 6 to about 14 atoms.

According to a preferred embodiment of the present invention, prepolymerized terminal trifluoromethyl containing monomers having a uniform pendant group length of from 8 to 10 carbon atoms and substantially free of branching can be deposited on laboratory vessels to form coatings with low surface energies and critical surface tensions of about 10 dynes/cm or less. The coatings also exhibit exceptional resistance to many solvents with the exception of substantially fluorinated solvents. Coating solutions containing polymers of such monomers produce a highly ordered, densely packed polymer with a predominantly trifluoromethyl surface.

Solutions of polymers made from monomers having terminal trifluoromethyl groups are commercially available. One solution which can be used to form polymeric hydrophobic coatings according to the invention is available from The 3M Company as FC-722. Other trifluoromethyl group-containing polymer solutions in fluorosolvents are available from Cytonix Corporation of Beltsville, Md. as the PerFluoroCoat and FluoroPel products lines. The coating solutions used according to embodiments of the present invention comprise fluoropolymers having terminal trifluoromethyl groups. The solutions can be used full strength but may be diluted with a fluorosolvent to form low concentrations of coating polymer. The polymer solution used to make the coatings of the invention preferably have a coating polymer content of from about 0.01% by weight to about 2% by weight.

Methods of making fluoropolymer coating solutions or suspensions for use with the invention comprise prepolymerizing a fluoroalkyl ethylenically unsaturated monomer having a terminal tri-fluoro methyl group to form a polyfluoroalkyl polymer, and dissolving or suspending the polymer in a fluorinated solvent. When making such solutions, the fluoroalkyl ethylenically unsaturated monomer preferably has a carbon chain length of from about 3 to about to 20 carbon atoms, with carbon chain lengths of from about 6 to about 12 atoms being more preferred. Carbon chain lengths of from 8 to 10 atoms are particularly preferred. Mixtures of different fluoroalkyl ethylenically unsaturated monomers having different carbon chain lengths may be employed, however, when the polymerized monomers have essentially uniform carbon chain lengths, hydrophobic coatings of extremely low and repeatable surface tension can be provided.

According to embodiments of the invention, hydrophobic coatings are provided which may preferably comprise, and more preferably consist essentially of, a polymerization product of a substantially non-branched perfluoroalkyl unsaturated monomer. Coatings according to the invention may comprise polymerized products of monomers having terminal trifluoromethyl groups, including fluorinated or perfluorinated monomers such as hexyl ethylenically unsaturated monomers, heptyl ethylenically unsaturated monomers, octyl ethylenically unsaturated monomers, nonyl ethylenically unsaturated monomers, decyl ethylenically unsaturated monomers, undecyl ethylenically unsaturated monomers, and dodecyl ethylenically unsaturated monomers. Mixtures of two or more different monomers may also be used and are preferred when it is desired to adjust surface energy properties to precise values.

The coatings of the present invention may comprise or consist essentially of a polymerization product of a fluoroalkyl ethylenically unsaturated monomer having a terminal trifluoromethyl group and a carbon chain length of from 3 to 20 atoms, preferably from 6 to 12 carbon atoms in length, and more preferably from 8 to 10 carbon atoms in length. In particular, polymerization products of fluoroalkyl methacrylates are preferred. According to some embodiments of the invention, polymerization products of perfluorohexyl methacrylate, perfluoroheptyl methacrylate, perfluorooctyl methacrylate, perfluorononyl perfluorodecyl methacrylate, perfluoroundecyl methacrylate or perfluorododecyl methacrylate, and mixtures thereof, are preferred. Acrylates of such perfluoroalkyls are also preferred. According to one particularly preferred embodiment, the polymer coating consists essentially of a polymerization product of perfluorooctyl methacrylate.

Exemplary materials for making the coatings of the present invention include PerFluoroCoat and FluoroPel, both available from Cytonix Corporation, the fluorinated materials FC-722, FX-13, FX-14, FX-189, L-9187, L-9186, Fluorel.TM. FC 2174 and Fluorel.TM. FC 2181, all available from Commercial Chemicals Division/3M, St. Paul, Minn., silastic fluorosilicone rubbers from Dow Corning STI identified as LS-2249U, LS-2332U, LS-2840 and LS-2860, and fluorinated materials from DuPont including materials traded under the name ZONYL.

The solvent for the coating solutions used according to the invention may comprise a fully fluorinated non-branched fluorocarbon having a carbon chain length of 7 or 8 carbon atoms. Such a solvent exhibits a boiling point of about 80.degree. C. Perfluorinated fluorocarbon solvents are preferred according to some embodiments of the invention.

According to embodiments of the invention, preferred fluorinated solvents include the Fluorinert.RTM. line of fluorinated solvents, FC-71, FC-77 and FC-84, all from the 3M Company. Other fluorinated solvents which may be used include Vertrel.RTM. XF (C.sub.5 H.sub.2 F.sub.10) or Freon TF from DuPont, Wilmington, Del., the fluorinated polyethers HT70, HT85, HT90, HT100, HT110, HT135, HT200, HT230, HT250 and HT270, and the perfluorinated polyethers sold as GALDEN, all from Ausimont USA, Inc. The Ausimont USA, Inc. solvent designations indicate the boiling point of each solvent. Higher boiling solvents, for example, HT270 and HT250, would form coatings requiring more heat to dry than coatings made with the lower boiling solvents, for example, HT70. The lower boiling Ausimont USA, Inc. solvents more rapidly evaporate when compared to the higher boiling solvents.

Other fluorocarbon solvents may be used and typically have boiling ranges of from about 30.degree. C. to about 250.degree. C., depending upon a number of factors including the length of the carbon chain. At least partially fluorinated solvents are preferred, particularly those fluorocarbon solvents having at least about 20% by weight fluorine atoms per molecule. Solvents exhibiting surface energies of 18 dynes/cm or lower are preferred, with solvents having surface energies of 13 dynes/cm or lower being more preferred and those having 9 dynes/cm being even more preferred. In preferred embodiments of the methods of the present invention, the solvent is substantially recovered after a coating procedure. Volatile fluorinated surfactants may be included in the coating formulations of the present invention.

Additives may be incorporated into or polymerized with the coating polymers and monomers used to provide coatings according to the invention having improved toughness, chemical resistance, hardness, softness, processability, elasticity, adhesion, color, texture, thickness and/or uv-resistance. Hydrophobic additives are preferred. Chemically resistant additives are preferred. Additives including non-trifluoromethyl containing monomers may be added in amounts ranging from 1 to about 95% by weight and are described in more detail below.

According to some embodiments of the invention, hydrophobic coatings are made of a polymerization product of a fluorinated monomer having a terminal trifluoromethyl group, and further containing small amounts of co-monomers, for example, silanes, that serve to promote adhesion to metal, glass or ceramic vessels without compromising the extremely low surface energy of the coating. Coupling agents may also be used as adhesion promoting monomers and include those listed in Table 1 under the heading "Coupling Agents" in the Polymer Encyclopedia. Exemplary coupling agents include vinyltrimethoxysilane, chloropropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, and 3-methacryloxypropyl-trimethoxysilane. Such-silanes and coupling agents, if present, can be present in amounts of from 1% by weight to 10% by weight, more preferably from about 2% by weight to about 5% by weight. If co-monomer is added, the amount added is not so much as to cause the surface population of trifluoromethyl groups to be less than 30% by area.

Other adhesion promoting monomers can be added to the coating formulations of the invention. If used, adhesion promoting monomers other than silanes are preferably added in amounts of from about 1% by weight to about 40% by weight, more preferably from about 5% by weight to about 20% by weight, based on the weight of the polymerization product making up the coating material. Adhesion promoting monomers which may be used include alkoxy terminated monomers and methacrylate esters and acrylate esters listed as adhesion promoting monomers on page 16 of the 1994 Sartomer Product Catalog, including mono-, di- and tri-functional acrylate or methacrylate ester monomers.

Other additives which may be incorporated or polymerized with the terminal trifluoromethyl-containing monomers or products of the inventive coatings include high glass transition temperature (high T.sub.g) perfluorinated or non-perfluorinated monomers, and low T.sub.g perfluorinated or non-perfluorinated monomers. High T.sub.g monomers can be included to form hard hydrophobic coatings for laboratory vessels, which are highly resistant to solvent removal and retention of biological sample. The hard coatings are harder than similar coatings which differ only in that they do not incorporate the high T.sub.g component. High T.sub.g monomers which may be employed include those fluorochemical acrylate or methacrylate monomers which form homopolymers exhibiting T.sub.g 's of 50.degree. C. or higher. Exemplary additives of this category are available from the 3M Company as FX-14 (homopolymer T.sub.g =60.degree. C.), L-9187 (homopolymer T.sub.g =60.degree. C.), and L-11913 (homopolymer T.sub.g =116.degree. C.). Of the exemplary monomers denoted above, L-11913 is a preferred monomer, and has the formula: cyclo-C.sub.6 F.sub.11 CH.sub.2 OCOC(CH.sub.3).dbd.CH.sub.2. If L-11913 is incorporated, it is preferably employed in an amount of from about 1% by weight to about 60% by weight, based on the weight of the coating.

Low T.sub.g monomers can be included to form soft, hydrophobic coatings for laboratory vessels, which are highly resistant to solvent removal and retention of biological sample. The soft coatings are softer than similar coatings which differ only in that they do not incorporate the low T.sub.g component. Low T.sub.g additive monomers can be used to form hydrophobic pressure sensitive adhesive coatings, which find many uses including the ability to adhere to covering materials such as Teflon tape or high T.sub.g coatings of the present invention, even underwater. Low T.sub.g monomers which may be employed include fluorochemical acrylate or methacrylate monomers which form homopolymers having T.sub.g 's of about 5.degree. C. or lower, preferably about 0.degree. C. or lower. More preferred low T.sub.g monomers have terminal trifluoromethyl groups. Exemplary additives of this category are available from the 3M Company as FX-189 (homopolymer T.sub.g =3.degree. C.), L-9186 (homopolymer T.sub.g =0.degree. C.), L-9911 (homopolymer T.sub.g =-53.degree. C.), L-12044 (homopolymer T.sub.g =-23.degree. C.), L-12043 (homopolymer T.sub.g =-5.degree. C.), and L-9367 (homopolymer T.sub.g =-120.degree. C.). Of the foregoing monomers, L-9186 is a preferred monomer and has the formula: C.sub.7 F.sub.15 CH.sub.2 OCOCH.dbd.CH.sub.2. Combinations of different low T.sub.g and high T.sub.g monomers may be added to the coating formulations of the present invention to provide the coating with a specific hardness or pressure sensitive adhesiveness.

Other additives which may be added to the coating solutions of the invention include perfluorinated and non-perfluorinated plasticizers. Plasticizers can be added in amounts of from about 1% by weight to about 30% by weight, more preferably 5% by weight to about 10% by weight, based on the weight of the coating. Exemplary plasticizers include high boiling point Fluorinert solvents from the 3M Company including FC-71, and high boiling point perfluorinated polyethers available from Ausimont USA, Inc., including HT 270.

Cross-linkable monomers may be incorporated into the coating solutions, suspensions and formulations according to embodiments of the present invention. Cross-linkable monomers may preferably be used for some applications in amounts ranging from about 1% by weight to about 95% by weight, preferably from about 5% by weight to about 70% by weight, and even more preferably from about 10% by weight to about 20% by weight. Cross-linkable monomers which may be incorporated include epoxies such as novolac epoxies, bisphenol A epoxies, acrylates, silicones, urethanes, anhydrides, and silicates.

Reactive non-fluorinated monomers and resins can also be added to the coating formulations of the invention to provide different properties to the coatings. According to embodiments of the invention, reactive monomers and resins such as methacrylate monomers, silicone monomers, epoxy monomers, urethane monomers and oximes can be included in the coating formulations.

According to embodiments of the invention, coating formulations are provided comprising epoxy monomer or resin in amounts of from about 20% by weight to about 95% by weight, based on the total weight of the coating formulation. Preferably, from about 30% by weight to about 70% by weight epoxy monomer may be included in a curable coating formulation. Epoxy resins may be used including the EPON Resins from Shell Chemical Company, Houston, Tex., for example, EPON Resins 1001F, 1002F, 1007F and 1009F, as well as the 2000 series powdered EPON Resins, for example, EPON Resins 2002, 2003, 2004 and 2005. Preferably, the epoxy monomer or resin has a high crosslink density, a functionality of about 3 or greater, and an epoxy equivalent weight of less than 250. Exemplary epoxies which may be employed according to embodiments of the invention include The Dow Chemical Company (Midland, Mich.) epoxy novolac resins D.E.N. 431, D.E.N. 438 and D.E.N. 439.

If an epoxy is included in the coating formulation, a curing agent for the epoxy may be added in amounts of from about 1% by weight to about 10% by weight of the epoxy component. The curing agent may be a catalyst or a reactant, for example, the reactant dicyandiamide. From about 1% by weight to about 50% by weight epoxy solvent, based on the weight of the coating formulation, may also be included in the coating formulations. Epoxy solvents can be added to liquify the epoxy monomer or resin or adjust the viscosity thereof. Preferred epoxy solvents are triethylphosphate and ethylene glycol. A separate epoxy solvent may not be needed according to some embodiments of the invention wherein the epoxy is liquid at room temperature or wherein a fluorinated monomer or surfactant component of the coating formulation acts as a solvent for the epoxy.

Even when a large amount of non-fluorinated epoxy is included in a coating formulation according to the invention, surface populations of trifluoromethyl groups of about 30% by area or more can nonetheless be achieved on the coating. Prepolymerized trifluoromethyl-containing monomers and/or reactive trifluoromethyl-containing monomers in the coating formulation tend to migrate to the surface of the coating during heat curing of the epoxy. The trifluoromethyl-containing components are mobile during epoxy curing due to thermal forces, convective forces, evaporative forces and diffusion forces. If included in a formulation, volatile trifluoromethyl-containing monomer is mostly driven off during heat curing of the epoxy, but can be polymerized into the coating in the presence of peroxide or azo compound catalysts, initiators or promoters.

According to some embodiments of the invention, the coating formulation comprises an aqueous suspension of the trifluoromethyl containing component such as ZONYL NWA, from DuPont. Suspension formulations according to the invention, may further include additives as discussed above, including epoxy resins. Exemplary waterborne epoxy resins which may be used in aqueous suspension coating formulations according to the invention include the EPI-REZ Resins from Shell Chemical Company, for example, the EPI-REZ Resins WD-510, WD-511, WD-512, 3510-W-60, 3515-W-60, 3519-W-50, 3520-WY-55 and 3522-W-60.

According to some embodiments of the invention, a coating solution or suspension is provided which comprises prepolymerized fluorinated monomer, reactive non-polymerized fluorinated monomer, and an additional additive, for example, at least one of the additives discussed above. The additional additive may be added in substantial amounts, for example, up to 95% by weight, provided the resultant coating has a surface population of trifluoromethyl groups which is about 30% by area or more. Preferably, coating techniques which involve application of a solution containing unreacted monomer further include a step of recovering unreacted monomer after coating.

According to some embodiments of the invention, an operational surface of a laboratory vessel is at least partially coated with trifluoromethyl containing monomers and non-trifluoromethyl containing monomers followed by polymerization of the monomers and removal and recovery of unreacted monomers. According to some embodiments, the monomers are applied from a coating solution which further includes a fluorinated solvent. Preferably, when reactive fluorinated monomers are used to coat an operational surface, and subsequently polymerized, unreacted monomer is removed and substantially recovered after coating and curing.

According to some embodiments of the invention, the coating solution comprises the polymerization product of substantially terminal trifluoromethyl containing monomers, and unreacted terminal trifluoromethyl containing monomers. After coating an operational surface, the coating is then subsequently polymerized to form polymer from the unreacted monomer in the coating solution. Such a procedure results in extremely hydrophobic coatings. When partially unreacted coating solutions are used, they may also include from about 15% by weight to about 95% by weight, based on the weight of the coating, of non-perfluorinated functional monomer, such as an epoxy.

Linkage mechanisms for binding the trifluoromethyl containing monomer or polymer of the present coating formulations to an operational surface of a vessel include functional linkage groups such as peroxide catalyzed linkages, azo catalyzed linkages, free radical induced linkages, cationically induced linkages, radiation induced linkages, vinyl linkages, methacrylate linkages, urethane linkages, epoxy linkages, silane linkages, and siloxane linkages.

According to embodiments of the invention, prepolymerized hydrophobic coatings according to the invention comprise a polymerization product of a substantially trifluoromethyl containing monomer, that is, having at least about 30% of the terminal groups of the reactant monomer or monomers comprising trifluoromethyl groups, and from about 1% by weight to about 10% by weight of comonomers having additional functionality that is polymerizable by a second, different mechanism than the mechanism used to polymerize the substantially trifluoromethyl containing monomer. The second polymerization mechanism may be activated during or following application of the hydrophobic coating to an operational surface, allowing the hydrophobic coating to become crosslinked with itself or with the vessel walls. For example, the initial polymerization may be carried out as an addition reaction of acrylates or methacrylates using a free radical catalyst, whereas the second polymerization may be carried out as a cationic reaction of epoxides using a cationic or acid catalyst. An exemplary material having epoxy functionality and acrylate functionality is glycidyl-methacrylate. Peroxides will attach hydrocarbon groups to hydrocarbons on the surface of the vessel.

According to some embodiments of the invention, low surface energies can be obtained when a terminal trifluoromethyl containing monomer is coated onto the operational surface of a vessel and subsequently polymerized after coating. Substantially non-branched fluoroalkyl and perfluoroalkyl ethylenically unsaturated monomers are preferred according to embodiments of the invention. According to some embodiments, a methacrylate group is used as the preferred ethylenically unsaturated monomer. Other monomers which can be used include fluorinated or perfluorinated silicones, epoxies, urethanes and oximes. Polymers made from mixtures of acrylates and epoxies are particularly preferred. According to some embodiments, both prepolymerized fluorinated monomer and reactive non-polymerized fluorinated monomer are used in the coating formulation, and after application to an operational surface, the reactive monomer is then polymerized or volatilized. Preferably, the reactive monomer is polymerized.

Another method of forming a coating according to embodiments of the invention is by using monomers capable of free radical linkages. Such monomers can be attached to vessel surfaces if the vessel surfaces are first treated by ionizing radiation or other means to generate free radicals across the surface. A monomer capable of free radical linkages can be formed by mixing a fluoroalkyl ethylenically unsaturated monomer dissolved in a suitable fluorocarbon solvent with an effective amount of a free radical initiator. Vessels coated with the mixture are then heated to the temperature at which the free radical initiator initiates free radical generation. Many conventional azo compounds have an appropriate activation temperature, particularly within the range of 30.degree.-200.degree. C.

According to some embodiments of the invention, when working with liquids which only slightly wet fluorinated surfaces, for example, when the contact angle between the liquid and the surface is greater than 90.degree., it may be desirable to provide a rough surface coating on a laboratory vessel to more effectively prevent runoff of the liquid as might occur from a smooth hydrophobic coating. Such would be the objective when it is desired to maintain a drop of liquid sample on a microscope slide. A microscopically roughened or porous hydrophobic surface which will not be wetted can be made according to the present invention by adding microscopic particles, for example, a micropowder, to the hydrophobic coating material or to the surface to which the coating polymer is to be applied. According to embodiments of the invention, microscopic particles can be added to coating formulations of the present invention which comprise (1) a polymerization product of a trifluoromethyl containing monomer, (2) an unreacted trifluoromethyl containing monomer, or both (1) and (2). Microscopic particles can also be added to coating formulations which further include a fluorinated solvent.

Micropowders are defined herein as those powders or particles having average diameters of from submicron sizes up to 100 microns. A preferred micropowder average diameter is about 10 microns or less. Hydrophobic materials are particularly preferred for the micropowders. Suitable micropowders include silicon glass particles with and without silane coatings, pigments, Teflon.RTM. powders, flour, cornstarch, siliconized glass and micronized cellulosics. According to embodiments of the invention, a composite surface is formed by adding a substantially uniformly sized micropowder to a fluoropolymer or a fluoromonomer which is to be subsequently coated and then polymerized. The use of micropowders exhibiting wide particle size distributions also provides preferred coatings according to some embodiments of the present invention.

Inert micropowders are preferred, particularly for applications where the resultant coating is exposed to liquids which are other than aqueous in nature. One particularly preferred micropowder is a siliconized glass particulate material having a 0.3 micron average particle size diameter available as TULLANOX HM 250 or TULLANOX HM 250D, from Tulco, Inc., Ayer, Mass. Another preferred micropowder is Teflon.RTM. MP 1200, available from DuPont Polymer Products Department, Wilmington, Del., and having an average particle diameter of about 4 .mu.m.

The methods of the present invention may comprise diluting a trifluoromethyl containing coating polymer solution or suspension prior to applying the solution or suspension to an operational surface of a laboratory vessel. The coating solution or suspension is preferably diluted to between about 0.01 and 2 percent by weight coating polymer. Higher weight percentages of the polymer may be used although higher concentrations tend to clog small orifices such as the opening at the end of a pipette tip for a volumetric pipettor.

One preferred method for applying a coating polymer solution or suspension comprises dip-coating the vessel into a polymer solution or suspension. Other coating methods may also be used, including spray coating, tumbling the vessel in the solution, brush coating, padding, spraying, fogging, transferring, painting, printing, stenciling, screen printing, pad printing, ink jet printing, injection molding, laminating and doctoring. For vessels having interior walls defining a reservoir portion, the area of the vessel around and defining an opening to the reservoir is preferably also coated. For simultaneously coating a large number of small vessels, each having a reservoir portion, a tumbling method of coating is preferred.

Dip coating may be used according to some embodiments of the invention to apply the coating polymer from a solution of the polymer dissolved in a fluorosolvent or from a suspension of the polymer. After coating the polymer solution, the coating is allowed to dry and solvent or carrier is driven off.

After forming a first coating of polymer according to the invention, the methods of the invention may also comprise applying at least one other coating formulation comprising a polymer having terminal trifluoromethyl groups. According to some embodiments of the invention, one or more coatings of the same or different terminal trifluoromethyl containing polymers may be applied, depending upon the desired surface energy of an operational surface being coated.

According to some embodiments of the invention, the coating formulation is not a polymer solution or suspension but instead comprises a fluidized micropowder of the polymerization product of entirely or substantially trifluoromethyl-containing monomers. The micropowder formulation can be applied to at least a portion of an operational surface of a laboratory vessel and melted to form a hydrophobic coating having an extremely low surface energy, a high resistance to solvent removal, and a low retention of biological samples. According to some embodiments, the coating formulation comprises a fluidized micropowder of the polymerization product of entirely or substantially trifluoromethyl-containing monomers, and at least one substantially non-perfluorinated resin. The micropowder and resin are applied to an operational surface of a laboratory vessel and heated to melt the fluidized micropowder.

According to embodiments of the invention, the coating polymer or coating monomer formulation of the invention is applied as a micropowder along with at least one of a curable resin and a non-curable resin. Preferably, the at least one resin is substantially non-perfluorinated. Curable resins which can be used in formulations of micropowder coating material include epoxy resins, urethane resins, acrylate resins, methacrylate resins. Highly cross-linked resins provide excellent solvent resistance according to embodiments of the invention. An exemplary resin having a high crosslink density is the epoxy novolac resin D.E.N. 439, available from Dow Chemical Co., Midland, Mich.

According to other embodiments, resins with low cross-link densities may be employed for coatings subsequently used with aqueous mediums. An exemplary low crosslink density resin is the fusion solid EPON Resin 1004F available from Shell Chemical Company, Houston, Tex. EPON Resin 1004F is a bisphenol A epoxy resin having a melting point of about 100.degree. C. Other EPON Resins from Shell Chemical Company may also be used, including 1001F, 1002F, 1007F and 1009F, as well as the 2000 series powdered EPON Resins, for example, EPON Resins 2002, 2003, 2004 and 2005.

Non-curable resins which may be employed include powdered ethyl cellulose, powdered polyethylene, powdered polypropylene and powdered polyvinylidenedifluoride. Cellulose acetate butyrate pellets also be jet milled and applied as a powder. Cellulose acetate butyrate is typically non-curable but can be cross-linked with peroxides.

The substantially non-perfluorinated resin is preferably non-fluorinated according to some embodiments of the invention.

The micropowders and resins used according to embodiments of the invention can be formed, for example, by jet milling. The micropowders and resins are preferably particles having an average diameter of about 50 microns or less, with average diameters of 10 microns or less being more preferred. The powders can be electrostatically sprayed onto a surface with or without a curing agent.

In another embodiment of the invention, the coating is formed from a fluidized micropowder product of trifluoromethyl-containing monomer and substantially non-perfluorinated resin, wherein the micropowder is applied and melted on an operational surface.

In another embodiment of the invention, a fluidized micropowder of a non-perfluorinated resin is coated with the polymerization product of a substantially trifluoromethyl-containing monomer. The powder is subsequently melted to form a hydrophobic coating.

In another embodiment of the invention, an operational surface is coated with a coating formulation comprising a fluidized micropowder of a polymerization product of substantially trifluoromethyl-containing monomer, and a hydrophobic non-melting micropowder that does not melt at temperatures required for formation of the coating. The formulation is then heated or sintered to melt the fluidized polymerization product micropowder without melting the non-melting micropowder. The non-melting micropowder is preferably selected from the group consisting of Teflon micropowders, Tefzel.TM. micropowders, Kynar.TM. micropowders, polyvinylidene difluoride micropowders, and polypropylene micropowders.

According to embodiments of the invention which involve forming coatings by melting micropowders, the coating formulations may be applied as a suspension to the operational surface and subsequently dried prior to melting.

Another method of forming laboratory vessels having hydrophobic coatings according to the present invention involves preinjecting or coinjecting a coating formulation prior to or during the laminar flow of molten materials injected into a mold or through an orifice to form laboratory vessels. The coating formulation comprises the prepolymerization product of a trifluoromethyl containing monomer, preferably a product which has from about 50% to 100% of exposed terminal groups being trifluoromethyl groups. The preinjected or coinjected coating formulation may also comprise a thermoplastic resin and/or a thermosetting resin. The injectable coating formulation may comprise mixtures of trifluoromethyl containing monomer, catalyst, and resin. The injectable coating formulation may comprise mixtures of molten prepolymerized trifluoromethyl containing monomer and microparticles, to form coatings exhibiting extraordinarily high contact angles of 160.degree. or more to aqueous liquids. The injectable coating formulations may comprise mixtures of molten prepolymerized entirely or essentially trifluoromethyl containing monomers, other resins, and microparticles, which are preinjected or coinjected to or during the laminar flow of molten materials injected into a mold or through an orifice to form coatings on the resultant vessels having extraordinarily high contact angles to aqueous liquids, high resistance to solvent removal, and low retention of biological samples.

According to yet other embodiments of the invention, a tubular laboratory vessel such as a microcentrifuge tube or test tube is provided and comprises a tubular body having an interior sidewall and a closed lower end having an interior surface. A hydrophobic coating according to the invention is applied to the interior sidewall but not to the interior surface of the closed lower end, or the interior closed end is substantially free of the coating. An aqueous sample placed in the tubular body tends to be retained at the closed lower end of the vessel and tends not to creep or advance onto the coated interior sidewall, even during movement of the vessel.

The present invention is exemplified with reference to the following Example.

A plurality of polypropylene pipette tips were enclosed in a monofilament polyester mesh bag and the bag was placed in a tumbling or agitating device. The mesh bag permitted treatment of the pipette tips by allowing coating solution to pass through the bag and substantially wet the surfaces of the pipette tip, including surfaces at and around the tip openings. The tumbling device was fitted with special gaskets to render the machine interior air-tight and fluid-tight. To the machine interior was also added a sufficient amount of coating solution to at least partially immerse the bag of pipette tips. The coating solution comprised a diluted solution of a fluorocarbon polymer having terminal tri-fluoro methyl groups. The fluorocarbon polymer solution is available as FluoroPel from Cytonix Corporation. The FluoroPel solution provides the polymer completely dissolved in a fully fluorinated solvent of perfluorinated fluorocarbons having an average carbon chain length of from about 7 to about 8 carbon atoms. The solvent exhibited a boiling point of from about 90.degree. C. to about 100.degree. C. Additional perfluorinated solvent or similar perfluorinated fluorocarbon solvent was added as a diluent to the FluoroPel solution to provide a coating solution having a solids content of coating polymer of about 0.5% by weight.

The tumbling device was equipped with a blower for removing volatile solvent from the coating and interior airspace, and with a heater for heating air to be blown by the blower. The tumbling device was run to agitate and tumble the pipette tips and the coating solution, thus evenly distributing the coating solution on the surfaces of the tips and sufficiently wetting the surfaces of the tips, including surfaces at or around the tip openings. The interior of the device was maintained at or below room temperature during solution coating of the tips. After a few minutes of tumbling, a drain in the interior of the device was opened to allow excess coating solution to drain out from the tumbling device interior during further tumbling. After a few minutes of draining with continued tumbling, the blower and heater were turned on and air having a temperature of about 80.degree. C. was blown through the device interior, and exhausted. The heated air evaporated solvent from the coated solution and from the interior airspace of the tumbling device. The bag of pipette tips continued to tumble during the drying process. The drained and evaporated solution and solvent was collected, reconcentrated and recycled. The coating polymer was not volatile under exposure to the 80.degree. C. air.

The coated and dried pipette tips were removed from the device interior and mesh bag. Both exterior and interior surfaces of the tips were coated by the process. The coated surfaces had a resultant surface energy of less than about 10 dynes/cm and an estimated surface population of tri-fluoro methyl groups of about 50% by area or more.

A highly chemically and solvent resistant hydrophobic coating for a microscope slide was prepared. The coating was provided from a coating formulation having the following ingredients:

50 parts by weight high functionality novolac epoxy resin, available as D.E.N. 439 from The Dow Chemical Company, Midland, Mich., having an epoxy functionality of 3.9, an epoxy equivalent weight of about 220, and a high cross-link density;

8% by weight dicyandiamide as a reactant agent for curing the epoxy, based on the weight of the epoxy;

50 parts by weight calcinated pigment;

10 parts by weight epoxy solvent triethylphosphate to liquify and reduce the viscosity of the epoxy;

10 parts by weight trifluoromethyl-containing polymer, comprising PerFluoroCoat (PFC) 468MP (a solution of polymerized and non-polymerized perfluoroalkyl monomers) available from Cytonix Corporation; and

1 part by weight 3-glycidoxypropyltrimethoxysilane.

The coating formulation was mixed, screen printed on a microscope slide, heat cured and allowed to dry. The resultant cured and dried coating exhibited a contact angle to water of 120.degree., was very hard, could not be scratched with a #8H pencil, and was chemically resistant to removal in a plurality of common lab solvents including acetone, water, chloroform, trichloroethane and trifluoroethane, at 20.degree. C. The coating exhibited a very low surface energy, and the population of trifluoromethyl groups on the exposed surface of the coating exceeded 80% by area as determined by surface energy analysis.

A composite hydrophobic coating was prepared and provides a rough surface upon curing. The coating can exhibit extremely high contact angles to water. The coating was prepared as follows:

50 parts by weight D.E.N. 438 epoxy, 70 parts by weight triethylphosphate, 4 parts by weight dicyandiamide, and 1 part by weight 3-glycidoxypropyltrimethoxysilane were thoroughly mixed together. Then, 50 parts by weight TiO.sub.2 having an average particle size diameter of about 1 .mu.m was added and the mixture was again mixed thoroughly. Then, 100 parts by weight Teflon.RTM. MP 1200 powder was added and the mixture was again mixed thoroughly. Then, 100 parts by weight Teflon.RTM. MP 1200 powder was added and the mixture was again mixed thoroughly. Then, 10 parts by weight PFC 468MP was added and the mixture was again mixed thoroughly. The resulting formulation was applied to an operational surface of a laboratory vessel and allowed to cure for 3 minutes at 200.degree. C.

A composite hydrophobic coating was prepared and provides a rough surface upon curing. The coating can exhibit extremely high contact angles to water. The coating was prepared as follows:

90 parts by weight Shell 1004-QX-55 (bis-A epoxy in xylene and propylene glycol monomethyl ether acetate), 1 part by weight imidizol (optional), 40 parts by weight ethylene glycol, and 10 parts by weight organic pigment were thoroughly mixed together. Then, 10 parts by weight Tullanox glass micropowder was added and the mixture was again mixed thoroughly. Then, 10 parts by weight PFC 468TF (solution of perfluoroalkyl polymer in Freon TF), available from Cytonix Corporation, was added and the mixture was again mixed thoroughly. The resulting formulation was applied to an operational surface of a laboratory vessel and allowed to dry at room temperature for 24 hours.

Although the present invention has been described in connection with preferred embodiments, it will be appreciated by those skilled in the art that additions, modifications, substitutions and deletions not specifically described may be made without departing from the spirit and scope of the invention defined in the appended claims.