Methods for Manufacturing Selectively Hydrophilic Thermoplastic Elastomer Surfaces and Articles Manufactured Thereby TECHNICAL FIELD

This invention relates to elastomer materials whose surface is made controllably and/or selectively hydrophilic. It relates particularly to hydrophilic thermoplastic elastomer compositions, to processes for preparing hydrophilic thermoplastic elastomer molding compositions, to methods of manufacturing articles having a selectively hydrophilic elastomer surface, and to articles such as hair rollers made with a selectively hydrophilic surface having predetermined moisture capacities.

BACKGROUND OF THE INVENTION

There are many diverse applications for a controllably and/or selectively hydrophilic elastomer surface. Selectively hydrophilic surfaces are used in offset printing and in medical test apparatus, for example. A controllably hydrophilic elastomer surface is generally useful for articles that are intended to be used in contact with skin, mucous membrane, hair, or other body tissue. Transparent hydrophilic polymer surfaces are useful in contact lenses and the like. Hydrophilic polymer surfaces are useful in medical dosage units such as transdermal delivery systems, and in absorbent devices such as diapers. Elastomer surfaces with controlled hydrophilicity are useful in the handling and packaging of static sensitive devices, such as electronic integrated circuits and circuit boards. Controlled hydrophilicity may be used to provide elastomer surfaces with a desired coefficient of friction when in contact with wet surfaces of other materials. There are applications in the field of sporting goods, as for example in the handle grips of sporting equipment. A particular useful application is in the field of personal hair care products, such as hair curlers or rollers.

NOTATIONS AND NOMENCLATURE

As used in this specification and in the appended claims, "hydrophilicity" is the property characterizing a surface with respect to its tendency to be wet by liquid water. It will be understood that any aqueous fluid may be substituted for water in the descriptions contained herein, in the uses of the invention described herein, and in those other uses of the invention that will be apparent to those skilled in the art. Hydrophilic or hydrophobic characteristics of solid surfaces are commonly characterized by a water wetting angle, such that wetting angles greater than 90° characterize a hydrophobic surface. The Greek letter θ (theta) will be used herein to denote wetting angles. "Moisture capacity" is used throughout

this specification to mean the amount of water that adheres to a surface, expressed in milligrams of water per square centimeter of surface area or equivalent units. Hydrophilicity or moisture capacity may vary locally across a macroscopic surface and thus be functions of position. "Overall moisture capacity" will be used herein to denote the total amount of water that adheres to a particular defined macroscopic surface area, in the same units of milligrams per square centimeter or equivalent.

Throughout this specification and the appended claims, the term "TPE" is used to mean a thermoplastic elastomer, and the term "HTPE" is used to mean a hydrophilic thermoplastic elastomer. The terms "curler" and "roller" are used interchangeably except in referring to any related-art patents which may distinguish between the two terms.

DESCRIPTION OF THE RELATED ART

The related arts provide many examples of materials made more hydrophilic by chemical methods which have the effect of attaching or substituting hydrophilic moieties to molecules otherwise hydrophobic (or conversely made more hydrophobic by similar methods). Other chemical methods provide means of chemically altering part of a molecule to render it more or less hydrophilic. These molecular-level chemical methods are not directly relevant to the methods of the present invention, although they may be used to make precursor materials that may then be used in the methods of the present invention.

A hydrophilic polymer composite and a product containing it are described in U.S. Pat. No. 5,374,671 (Corvasce et al., 1994). In one embodiment of that polymer composite, the hydrophilic polymer forms fibers in a resulting elastomeric matrix. The elastomeric matrix interspersed with hydrophilic polymer can be used in reinforced elastomeric products such as tires.

In the field of hair care products of special interest in this specification, there are a number of references in the related arts that use hydrophilic foam or sponge-like materials to maximize moisture capacity of hair care products. In U.S. Pat. No. 4,605,021, (1986) Hodson et al. disclose a self-tensioning hair-waving rod which includes a cylindrical sponge body and retainer means for holding a strand of hair wrapped around the sponge body. The sponge body is formed of a hydrophilic polymer which expands from a dry condition upon application of water to increase its volume by at least 50%. Examples of the expandable synthetic sponge material used include water-activated polyisocyanate terminated polyethers. The prepolymers contain sufficient polyoxyethylene groups to provide hydrophilicity. U.S. Pat. No. 5,261,426 and U.S. Pat. No. 5,002,075 (Kellett et al., 1993) disclose a hydrophilic foam pad for hair styling, comprising a shaped body of a resilient, open-celled hydrophilic polyurethane foam matrix, integrally incorporating an aqueous phase incorporating water, hair conditioning agent, and non-ionic surfactant. The pad is preferably attached to the tines of a

styling brush or comb. These patents of Kellett et al. also mention commonly assigned patent U.S. Pat. No. 4,856,541 (Kellett et al., 1989), disclosing other hair cleaning and conditioning foam pads.

U.S. Pat. No. 3,910,290 (Litman, 1975) discloses a disposable hair setting roller formed of at least two layers of sheet material, including an inner paperboard layer and an outer hair-contacting layer consisting of an embossed metal foil. The embossed foil provides an irregular or textured, non-absorbent outer surface. A dry film coating of a water-soluble hair treating agent is distributed over the embossed outer surface, preferably being sufficiently thin that the coated surface remains rough to the touch. The indentations in the foil provide reservoirs of the treating agent, which permit the rollers to be reused a number of times. U.S. Pat. No. 3,888,266 (Weldon et al., 1975) discloses a hair curling roller comprising on its outer surface a myriad of upstanding short non-hygroscopic filaments or fibers capable of retaining moisture or lotions by capillary attraction. U.S. Pat. No. 3,858,588 (Walter et al., 1975) discloses a hair roller having a tubular body with a substantially smooth outer surface. The body is molded from a "thermoplastic material, either filled or unfilled, the plastic being etched to make it polar and hydrophilic, as is known in the art." The mandrel surface is described as "having a pattern of small depressions thereon to increase moisture retention." U.S. Pat. No. 3,762,424 (Chen, 1973) discloses an improvement in heatable and moistenable hair rollers. The roller has an outer surface provided with means, such as a plurality of flexible resilient protrusions, for increasing the outer surface area, and thus increasing the moisture retaining capacity of the roller. In addition, a groove located adjacent to the end edges prevents excess water on the rollers from overflowing the end edges and scalding the user's fingers. U.S. Design Pat. No. Des 226,738 (Chen, 1973) shows an ornamental design for a hair roller with a plurality of outward extending protrusions on the exterior surface and a plurality of inwardly projecting flutes on the interior surface. Bagrodia et al., U.S. Pat. No. 5,346,422 (1994) disclose an article of manufacture consisting of a toy having a plurality of synthetic fibers capable of spontaneously transporting water on their surface.

U.S. Pat. No. 4,957,949 by Kamada et al. discloses a thermochromic color master batch for use in a thermoplastic resin comprising a wax having dispersed in it a thermochromic granular material which is coated with a hydrophilic high-molecular- weight substance. U.S. Pat, No. 4,826,550 by Shimizu et al. discloses a process for preparing molded products of thermochromic polyvinyl chloride. U.S. Pat. No. 4,666,949 by Shimizu et al. discloses a thermochromic polyurethane foam and a thermochromic composition comprising an electron- donating chromogenic material, an acidic substance, and a solvent. Kito et al. (U.S. Pat. No. 4,421,560) disclose a reversible thermochromic material which may be contained within micro-capsules and undergoes reversible metachromatism at a temperature within the range from - 50° C to + 60° C. Nakasuji et al.(U.S. Pat. No. 4,028,118) disclose a reversibly thermochromic material which exhibits metachromatism within a range from - 40°C to + 80°C,

and which may be occluded in fine micro-capsules. The basic thermochromic material or microencapsulated thermochromic material of Nakasuji et al. can be incorporated into a polymer to obtain a thermochromic polymer composition.

PROBLEMS SOLVED BY THE INVENTION As mentioned hereinabove under "Background of the Invention, " there are many diverse applications for a controllably and/or selectively hydrophilic elastomer surface. In these diverse application areas, it is often difficult to find a material that has a needed amount of moisture capacity per unit area. Thus available materials often hold too little or too much water on their surface (or in the case of open-cell foams, within their pores) for the particular problem at hand. These problems will be illustrated by an example from the field of hair care, specifically hair rollers.

If a hair roller is hydrophobic, as are many types of hair roller which are molded of polyolefins and the like, the hair is curled without the beneficial effects of moisture, or else depends on moisture provided by steam in the atmosphere around the curled hair. If a hair roller is of the type made with open-cell foam, an excess of water may be available when the hair is curled, because excess water may be held in the open pores of the foam body curler, as in a sponge. This can result in longer time needed for curling at a given initial temperature of the roller and hair. Between these two extremes there is an optimal range of available moisture capacity of the hair roller, such that hair curled with moisture capacity within that range has improved curl retention. Furthermore, commonly available hair rollers hold moisture if any with a substantially uniform density per unit area of roller surface or mandrel surface, where the hair is wound during curling. Such a uniform distribution of water does not take into account the fact that the bundle of hair wound on a roller is typically thicker in the center than at the ends of the roller, nor of the fact that hair near the ends of the roller tends to dry faster than hair near the center.

PURPOSES, OBJECTS, AND ADVANTAGES OF THE INVENTION

A major object of the invention is a process for manufacturing a controllably and/or selectively hydrophilic elastomer surface. A related object of the invention is a controllably and/or selectively hydrophilic elastomer surface. A more particular object is a hydrophilic elastomer surface that has a predetermined moisture capacity. Another more particular object is an elastomer surface whose moisture capacity may be varied as a function of position on its surface. An even more particular object is an elastomer surface whose moisture capacity may be either a discrete function or a continuous function of position, or both in various portions of its surface. A particular object is an elastomer surface which has one or more hydrophobic portions and one or more hydrophilic portions such that each hydrophilic portion has

predetermined moisture capacity. Processes for manufacturing elastomer surfaces having these diverse properties are essential objects of the invention.

From another point of view, an object of the invention is a controllably hydrophilic thermoplastic elastomer molding composition. A related object is a process for preparing a controllably hydrophilic thermoplastic molding composition. Another related object is a process for manufacturing articles having at least a portion of their surface comprising an elastomer that is selectively and/or controllably hydrophilic. A more particular object is a process for manufacturing articles having at least a portion of their elastomer surface hydrophilic with a predetermined moisture capacity. Even more particular objects of the invention are articles having at least a portion of their surface hydrophilic with a predetermined moisture capacity.

Specific objects of the invention are articles for care of hair that have at least a portion of their surface comprising a hydrophilic thermoplastic elastomer with predetermined moisture capacity. Another specific object is a hair roller or curler having at least a mandrel portion whose outer surface comprises a hydrophilic thermoplastic elastomer layer with predetermined moisture capacity. A more specific object of the invention is such a hair roller whose hydrophilicity varies with position along its surface, with a predetermined functional dependence on position. An even more specific object of the invention is a hair roller whose hydrophilicity varies axially in a predetermined manner.

SUMMARY OF THE INVENTION

This invention includes elastomer processes and materials which provide controllably and selectively hydrophilic elastomer surfaces. Hydrophilic thermoplastic elastomer compositions and processes for preparing hydrophilic thermoplastic elastomer molding compositions are used in preliminary operations of a manufacturing process. The manufacturing process is completed by using further methods to manufacture articles having a controllably and or selectively hydrophilic elastomer surface. A particular useful application is described to the manufacture of articles such as hair rollers made with a controllably and/or selectively hydrophilic surface having predetermined moisture capacities and optionally having predetermined variation of moisture capacity per unit area with position on the roller's surface. The controlled hydrophilicity hair roller surface may also be made reversibly thermochromic. Hair rollers made by the methods disclosed have improved curl retention.

The invention uses molded artificial pore shapes, sizes, and density per unit area to produce a predetermined moisture retention (not simply to maximize moisture retention). The artificial pore shape is adapted to fit a given wetting angle of water on a hydrophilic surface. The possibility of varying pore shape, size and number per unit area with position gives the

method a capability of non-uniform moisture retention — i.e. more moisture on some portions of an elastomeric surface than on others. Other variations of the basic process allow production of a selectively hydrophilic surface of elastomer (i.e. some portions of the surface area being hydrophilic, while some portions of the surface area are hydrophobic).

The invention includes a new hydrophilic elastomer material, a method for making the material, and articles (such as hair rollers) made with the material. The hydrophilic and partially porous surface is produced by making an artificial texture using shaped pores or grooves to customize the surface to hold a specified amount of water per unit area of the surface. The amount of water per unit area may be measured in milligrams per square centimeter of the surface, for example. The improvement in the amount of water held is a factor of about 10 times or more. The sizes and shapes of the artificial pores or grooves are customized to match the contact angle for water on the hydrophilic surface.

For retaining a predetermined amount of water on a hair roller, two things are needed: (1) a modification of the (otherwise hydrophobic) elastomer surface to make it hydrophilic to a predetermined hydrophilicity, and (2) a customizing of the surface topography. Part (1) is achieved by adding a particulate hydrophilic agent as an additive in the elastomer formulation. Part (2) is achieved by molding the surface of the resultant elastomer material. With a certain given amount of the hydrophilic additive, water on a flat surface of the modified elastomer exhibits a corresponding specific wetting angle. Recesses are molded in a size and shape suitable to that wetting angle to make the water just fill the artificial pore or groove recesses flush and hold the predetermined desired water amount in mg/c rr of the cylindrical surface of the curler. For attaining the desired amount of about 9 mg ^O/crn^ (58 mg ^O/in. ), using a particular preferred elastomer and hydrophilic additive, a non-re-entrant pore or groove shape is preferred. A hair curler's surface is made hydrophilic, attracting a desired limited predetermined amount of moisture, as contrasted with conventional non-foam curlers (which are hydrophobic) and the common open-cell foam curler, which are hydrophilic but can retain too much water in the foam cells.

Each curler has a controllably hydrophilic thermoplastic elastomer surface layer (around which hair is to be curled) which covers a mandrel portion of a thermoplastic body. The thermoplastic body has ends of larger diameter than the mandrel portion of the body and the mandrel may be hollow. A hollow mandrel may contain a double-walled metal core, which may contain a heat-retaining material. The elastomeric surface layer is preferably molded from an thermoplastic elastomer material containing particulate hydrophilic material, which preferably comprises a dye encapsulated in hydrophilic micro-capsules.

In a preferred process for manufacturing the curlers, an HTPE composition is prepared containing thermoplastic elastomer polymer, plasticizer, lubricant, fillers, heat- and UV- stabilizers, and a predetermined proportion of particulate hydrophilic material. A curler body form with a hollow mandrel portion and integral end flanges is made from a thermoplastic resin. A metal core may be prepared, containing a heat-retaining material, and inserted into the hollow mandrel portion of the curler body. The above-mentioned HTPE composition may be insert-molded or extrusion-molded around the molded thermoplastic curler body.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a cross-section view of drops of an aqueous fluid on a surface, illustrating the definitions of wetting angle used to describe the invention.

Fig. 2 shows a cross section view of a portion of a surface layer, illustrating various pore shapes and a pore side wall angle used to describe the invention.

Figs. 3 A and 3B show perspective views of two stages in the manufacture of a preferred embodiment of a hair roller with a surface layer made in accordance with the invention.

Fig. 4 shows a partial cross-section of a preferred embodiment of a hair roller.

Fig. 5 shows a perspective view of a particular preferred embodiment of a hair roller with a surface layer made in accordance with the invention.

Fig. 6 shows a graph illustrating the axial dependence of moisture capacity for particular preferred embodiment of a hair curler.

DETAH.ED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fig. 1 shows a cross-section view of drops of an aqueous fluid on a surface, illustrating the definitions of angles used to describe the invention. The Greek letter θ (theta) is be used in Fig. 1 to denote the wetting angle, measured from the solid surface on which a drop rests to a tangent to the drop contour where it meets the solid surface. As mentioned herein above, wetting angles greater than 90° conventionally characterize a hydrophobic surface. Wetting angles less than 90° conventionally characterize a hydrophilic surface, such that smaller wetting angles correspond to more wetting, or higher hydrophilicity.

Fig. 2 shows a cross section view of a portion of an elastomer surface 10 made in accordance with the invention, illustrating various shapes of reservoir recesses and a side wall angle 0 (phi). The first three recess shapes shown are non-reentrant; the recess shape at the right end of Fig. 2 is a reentrant shape. Artificial reservoir recesses 20 are molded into elastomer surface 10 with predetermined shapes, sizes, and density per unit area. The shapes, sizes and density parameters of reservoir recesses 20 are not necessarily uniform over the

elastomer surface, but may be varied intentionally over the useful surface area of the elastomer, depending upon the application. Reservoir recesses 20 may be shaped as pores, grooves, or other cavity shapes, according to the needs of the application, but their side wall angles 0 (phi) with respect to the major elastomer surface are made to be the supplement of wetting angle θ (theta) so that aqueous fluids held in reservoir recesses 20 fill the recesses flush. The amount of aqueous fluid held in all of the reservoir recesses over the whole elastomer surface 10 is thus a predetermined amount. The amount held in any sub-portion of the surface area is predetermined by the shapes, sizes, and areal density of the artificial reservoir recesses 20 in that sub-portion. Thus selective and optionally non-uniform moisture capacity is provided.

Figures 3 A and 3B respectively show perspective views of two stages in the manufacture of a hair curler 30 in accordance with this invention. Fig. 3 A illustrates the first of these two stages: a molded curler body 40, before addition of a hydrophilic thermoplastic elastomer (HTPE) layer 10 over mandrel portion 50 of curler body 40. Fig. 3B illustrates the second of these two stages, having HTPE surface layer 10 in place on mandrel portion 50. While Fig. 3B shows an elastomer surface layer 10 with substantially uniform sizes and areal density of grooves, it will be understood that they need not be uniform. Each curler has two integrally molded end flanges 60 having diameters larger than mandrel portions 50.

Fig. 4 shows a partial cross-section of hair curler 30. As shown in Fig. 4, hair curler 30 may have inserted into it a double-walled metal core element 70, having an inner wall 80 and an outer wall 90. In the annular space between inner wall 80 and outer wall 90, there may be a heat-retaining substance 100, such as a wax or the like. Heat-retaining substance 100 may be selected to have a phase change at the desired curler use temperature (i.e. the temperature at which the user's hair is curled). Inner and outer walls 80 and 90 may be joined and sealed by a rolled edge 110 after filling, as shown in the cross-section view of Fig. 4 Inner wall 80 surrounds a cavity 120, which may be adapted to fit over heating posts of a personal hair care appliance. Each curler may have a cap insert 130 shaped to snap into and be retained by curler body 30 or be retained by a portion of core element 70.

In a preferred process for manufacturing the curler 30, a substantially homogeneous HTPE composition is prepared having predetermined proportions of a TPE, plasticizer, lubricant, fillers, heat- and UV-stabilizers, and a predetermined proportion of particulate hydrophilic material. The particulate hydrophilic material preferably comprises micro- capsules.

The TPE is preferably a saturated block copolymer having a polystyrene phase and a hydrogenated polyisoprene phase, or may be for example a block copolymer having a polystyrene phase and a butadiene phase, a block copolymer having a polystyrene phase and an ethylene propylene phase, or mixtures of these various copolymers. A preferred composition has 5% to 20% by weight of the particulate hydrophilic material, and even more preferred is a mixture of 10% particulate hydrophilic material by weight. The particulate hydrophilic material preferably comprises a hydrophilic concentrate material, encapsulated in micro-capsules. The micro-capsules should have diameters of 3 millimeters or less (preferably 100 micrometers or less), for effective mixing, for uniform physical characteristics, and for uniform appearance of the product. For the hair curler application, preferred micro-capsules contain a liquid or low-melting hydrophilic concentrate, encapsulated with a hydrophilic high-molecular-weight polymer compound. An example of such micro-capsule material is Xantrix™ ADS 7000 Series (manufactured by Himont U.S.A. Inc. of Wilmington, DE). Any dye materials used are preferably used in a micro-capsule form in the preferred size range, with the encapsulant being a high-molecular- weight hydrophilic polymer substantially inert to the TPE composition. Examples of suitable high-molecular- weight hydrophilic polymer encapsulants are polypropylene, polyvinyl alcohol, polyacrylic acid, gelatin, methyl cellulose or alginic acid. Experiments have shown that a preferred amount of moisture capacity for hair curlers is between 50 and 70 mg ^O/in. and more preferably about 58 mg ^O/in. (equivalent to about 9.0 mg ^O/cm^).

An especially preferred HTPE composition comprises 100 parts of a saturated block copolymer having a polystyrene phase and a hydrogenated polyisoprene phase, 50 to 200 parts of a plasticizer oil, 0 to 200 parts of an inert particulate filler, 1 to 5 parts of an anti-oxidant and UV stabilizer, 0 (zero) to 10 parts of a lubricant, 10 to 100 parts of a hydrophilic particulate material, and (optionally) 0 (zero) to 100 parts of conventional dyes and pigments. A suitable block copolymer component is "Kraton 1651" available from the Shell Chemical Company, for example. A suitable plasticizer oil is a paraffinic or naphthalenic plasticizer oil, such as "Shellflex 371N," available from the Shell Chemical Company. Many suitable inert particulate fillers are well-known in the art. The anti-oxidants and UV-stabilizers may be "Irganox 1010" and "Tinuvin 328" available from the Ciba Geigy Corporation, for example. Examples of suitable lubricants are calcium stearate, stearic acid, palmitic acid, saturated fatty acids or their esters, or waxes. The hydrophilic particulate material may be, for example, "Xantrix™ ADS 7015H" available from Himont U.S.A. Inc. of Wilmington, DE.

Continuing the manufacturing process, a metal core element 70 is prepared, containing a heat-retaining material 100. A curler body 40 with integral end flanges 60 is molded from a thermoplastic resin, such as polypropylene or polycarbonate. Core element 70 is inserted into curler body 40. The above-mentioned HTPE composition is insert-molded around mandrel

portion 50 of the molded thermoplastic curler body 40 to a preferred thickness of between 0.5 mm and 3 mm, with a predetermined number of artificial pores, cavities, or grooves 20 per unit area, completing manufacture of curler 30. The artificial cavities, pores, or grooves are used as reservoir recesses for aqueous fluids on the elastomer surface layer 10. In an alternative embodiment, the HTPE may be insert-molded or otherwise applied to one end of curler body 40. An alternative manufacturing method would use a mandrel portion subassembly and would extrusion-mold the HTPE layer onto the mandrel portion subassembly, and then fasten flange portions to the mandrel portion, for example.

The invention will be further clarified by considering the following examples, which are intended to be purely exemplary of the use of the invention.

Fig. 5 shows a perspective view of a particular preferred embodiment of a hair roller 30 with a surface layer 10 made in accordance with the invention. Fig. 6 shows a graph in which curve 210 illustrates the axial dependence of moisture capacity for the particular preferred embodiment of Fig. 5. The peak value of hydrophilicity 220 near the center of the hair roller axially provides for more moisture at the portion of the hair roller where the hair is typically rolled to greater thickness. The lower sub-peak values 230 of hydrophilicity near the hair roller ends compensate for the faster drying that occurs near the ends.

In another embodiment, a tailored hydrophilic surface as described above is insert molded in a predetermined pattern with a similar elastomer not treated to be hydrophilic and not having reservoir recesses, i.e. an elastomer surface is made selectively hydrophilic with the predetermined H2O capacity. The basic method also has the capability of effectively varying hydrophilicity locally (in other words, creating a patterned elastomer surface having some portions of the surface holding more moisture per unit surface area than other portions). One type of use for such a patterned elastomer surface is that a water-based material like ink or paint can be transferred from an ink source using that patterned elastomer, to print the pattern on another surface, such as paper or fabric.

INDUSTRIAL APPLICABB ITY

The methods and materials of the invention may be used to manufacture articles having a controllably and/or selectively hydrophilic elastomer surface. A particular useful application is the manufacture of articles such as hair rollers made with a mandrel portion having a controllably and/or selectively hydrophilic surface, which has a predetermined moisture capacity and which optionally has predetermined variation of moisture capacity per unit area with position on the roller's mandrel surface. Hair rollers made by the methods have improved curl retention. Among many other industrial applications of the patterned selectively

hydrophilic thermoplastic elastomer surface described above, is its use to transfer ink or paint from a source, to print the pattern on another surface, such as paper or fabric.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various alterations and modifications of the invention to adapt it to various usages and conditions. Other embodiments of the invention will be apparent to those skilled in the art from a consideration of this specification or from practice of the invention disclosed herein. It will be apparent that there are many applications of an elastomer surface having a predetermined desired amount of water per unit surface area other than the particular applications described herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the invention being defined by the following claims.

Having described my invention, I claim: