WO1999005986A1 - Improved dental floss - Google Patents

Abstract

Loaded, homopolymer and multipolymer, multifilament, high-tenacity dental flosses with improved: elongation, gentleness and resistance to shredding, that are capable of releasing at least some of said load during flossing, while exhibiting improved gentleness on gums, resistance to shredding and a tendency to 'give' rather than cut.

Description

IMPROVED DENTAL FLOSS

FIELD OF THE INVENTION

The present invention relates to improved dental flosses. Specifically, the improved dental flosses of the present invention are loaded, homopolymer and multipolymer, multifilament, high-tenacity dental flosses with improved elongation, gentleness and resistance to shredding. The flosses of this invention are capable of releasing at least some of the "load" during flossing, while exhibiting improved gentleness on gums, resistance to shredding and a tendency to "give" rather than cut the user.

BACKGROUND OF THE INVENTION

The purpose of dental floss is (1) to dislodge and remove any decomposing food material that has accumulated at the interproximal and subgingival surfaces that cannot be removed by brushing, and (2) to dislodge and remove as much as possible the growth of bacterial material (plaque) upon the teeth or the superimposed calculus that has accumulated interproximally since the previous cleaning.

The concept of the use of dental floss for cleansing interproximal spaces appears to have been introduced by Parmly in 1819. Parmly suggested the use of waxed silk to clean teeth of persons subject to gingival inflammation.

Numerous types of floss were developed and used for cleaning, until finally in 1948 Bass established the optimum characteristics of dental floss. (Dental Items of Interest, 1948:70 921-34). Surprisingly, floss marketers have generally ignored the teachings of Bass for the past 40 years. Bass warned that dental floss treated with sizing, binders and/or wax produces a "cord" effect which reduces flossing efficiency dramatically by reducing the floss' ability to spread, i.e. splay. Almost all floss sold today including unwaxed floss contains binders and/ or sizing substances. These "sticky" substances are used to keep the floss twists from unwinding during use and to keep the floss turns from falling off a spool during dispensing by holding the floss together. Additionally, most floss sold at retail today is also "waxed" supposedly to assist penetration of interproximal regions. In reality, the "cord" effect described by Bass resists splaying, which in turn makes the floss bundle difficult to work between closely spaced teeth, and it generally results in a perception of ungentleness, while also failing to remove dislodged material from interproximal spaces.

The optimum characteristics of dental floss as described by Bass in 1948 are ignored by today's multifilament flosses except for REACH® Gentle Gum Care Dental Floss. Specifically, Bass suggests that these waxed and sized flosses produce the "cord" effect discussed above as distinguished from the "spread effect" of unwaxed, unsized floss which flattens out and widens, with the filaments spread out (splaying). The potential for separate mechanical action of spread out filaments is nullified by this "cord" effect, which essentially eliminates the spaces between the filaments, which according to Bass are necessary to receive, hold and remove the microscopic material dislodged during flossing. Thus, the mechanical cleaning attributed to spread filaments, as well as the evacuation of microscopic materials from the interproximal spaces by entrapment in the spread-out filaments is impaired or sacrificed with waxed and/or sized flosses, because of this "cord" effect.

As an alternative to sizing, binders, wax etc. Bass suggested "steamset" to set the twist in dental floss so that the floss will not untwist during use.

Commercial floss twisters and floss spoolers, opted to use various binders and sizing materials instead. These "sticky" substances facilitate floss handling, keep the floss from untwisting during use, and keep the floss from falling off the spool. Although steamset floss does not untwist during use, absent sticky substances, steamset floss does unravel off the spool during dispensing and during spooling. Thus, the optimum floss described by Bass could not be manufactured commercially in 1948. Accordingly, water insoluble binders, sizing and wax coatings were adopted early on and continue up to the present with their "cord" effect.

From 1960 thru 1982, numerous clinical studies reported that there is no clinical difference as to plaque removal and gingivitis scores between waxed and unwaxed dental floss. Note, both are "cord" flosses and contain sizing, binders etc. These studies also confirmed that waxed and unwaxed floss are approximately 50% effective with respect to plaque removal and gingivitis scores. Thus the "cord" effect severely restricts efficiency of flossing.

O'Leary in 1970, and Hill et al in 1973, found no difference in the interproximal cleansing properties of waxed or unwaxed dental floss. This was reconfirmed in 1982 by Lobene et al who showed no significant clinical difference on plaque and gingivitis scores. Similar results, i.e. no clinical difference between waxed and unwaxed floss with respect to reduced gingival inflammation were shown by Finkelstein in 1979. No differences in gingival health were shown by Wunderlich in 1981. No differences in plaque removal were reported by Schmidt et al in 1981 with flosses of various types. Stevens, 1980, studied floss with variable diameters and showed no difference in plaque and gingival health. Carter et al 1975, studied professional and self administered waxed and unwaxed floss, both significantly reduced gingival bleeding of interproximal and gingival sulci. Unwaxed floss appeared slightly, but not significantly, more effective. Hill, U.S. 5, 165,913 reported a modest improvement in plaque reduction for a "compression" loaded floss over a placebo of commercial waxed dental floss. In view of this clinical work, it is not surprising that most of the dental floss sold today is bonded and/or waxed. Clearly, the "bonding" in the yarn industry today is used more to facilitate processing and production during floss manufacture and packaging than for "flossing" reasons. Since clinical tests show no difference between waxed and unwaxed floss (both unfortunately are "bonded") the floss industry has been comfortable with the yarn industry's propensity to use bonding agents in floss.

Today there are three basic nylon strand constructions approved by the FDA for flossing. These are 140 denier (68 filament), 100 denier (34 filament), and 70 denier (34 filament). Analysis of the commercial flosses sold worldwide show that almost all flosses available are twisted in generally the same manner, contain bonding agents, and are constructed by twisting several (6- 10) strands selected from one of these three strand types.

Almost 100% of the multifilament floss sold today is manufactured by "yarn" manufacturers with little consideration given to the influence of twisting or of floss construction on interproximal cleaning, etc.

The simple removal of binders, to allow the floss strands to spread out, introduces a "user-unfriendly" effect which reduces compliance. These commercial flosses with little or no binders are notorious for frustrating flossers with their tendency to fray, break, etc. The removal of binders requires adjuncts (lubricants, etc) to reduce snagging, fraying, etc.

Since the introduction of nylon dental floss in 1945, most synthetic fibers purchased for use in manufacturing various dental flosses have been purchased from textile fiber manufacturers servicing the carpet, upholstery, tire and related industrial markets.

To date, essentially little research has been devoted to improving those synthetic polymeric filaments traditionally used to produce dental floss. Thus, essentially all of the types of dental floss marketed today are comprised of textile-type fibers including the polytetrafluoroethylene monofilament commercial dental flosses marketed under the trademarks Glide®, Easy Slide®, Precision®, etc.

The net of this failure of floss manufacturers to develop "other" fibers has been the marginal performance of all "twisted" multifilament dental flosses with respect to consumer complaints regarding shredding, breaking, tearing, gentleness on gums, etc. Similarly, the shred resistant "monofilament" flosses have been met with consumer complaints relating to "hand", stretching, "snapping", i.e., not gentle on the gums when drawn through tight spaces, failure to remove dislodged material, etc.

The object of the present invention is to provide improved dental flosses based on innovative polymer and multipolymer, multifilament construction not used heretofore in the dental floss category.

Another object of this invention is to provide dental flosses with improvements in resistance to shredding, including improved tensile and tear strength, along with improved elongation.

A further object of this invention is to provide dental flosses with improvements in gentleness based on intrinsic self-activation (self-crimping) properties, improved elongation and filament construction, in combination with improved release of lubricating substances.

Still another object of this invention is to provide improved loaded dental floss that is shred resistant and capable of releasing at least a portion of said load during flossing into interproximal and subgingival areas with little or no shredding.

Other features and advantages of this invention will hereinafter appear. BRIEF DESCRIPTION OF THE DRAWINGS

Figures 1-23 show greatly magnified cross sections, i.e., sections perpendicular to the filament axis of typical multipolymer filaments of this invention.

In these drawings one component is either shaded or cross-hatched to illustrate separation between components.

Figures 24A and 24B illustrate a test method using an Instron for helping to establish resistance to fraying.

Figure 25 is a schematic representation of equipment useful in practicing the spin-stretch process embodiment of the present invention.

SUMMARY OF THE INVENTION

The present invention is directed to improved dental flosses. Specifically the present invention includes loadable polymer and multipolymer, multifilament, high-tenacity dental flosses having improved elongation, gentleness and resistance to shredding along with the capacity to release at least a portion of said load interproximally and subgingivally during flossing, where the floss tends to "give" rather than cut when encountering abrasive, sharp and /or tight spaces.

As discussed above, for the purposes of the present invention, the term dental floss includes a broad array of filament type interdental devices, used to clean and remove plaque and tartar, material alba, food debris, etc. from interproximal and subgingival areas of the gums and/or to treat these areas with substances released during flossing. Typical dental flosses for the purposes of the present invention, include: (a) traditional waxed dental flosses such as described in U.S. Patent Nos. 2,667,443; 2,700,636; 3,771 ,536; 3,800,812; 3,830,246; 3,897,795; 3,943,949; 4,029, 1 13; 4,033,365; 4,215,478; 4,414,990; 4,548,219 and 4,638,823 (as well as the references cited in these references).

(b) "loaded dental flosses" which can contain therapeutic substances such as described in U.S. Patent Nos. 4,91 1 ,927; 5,098,71 1 and 5, 165,913;

(c) textured dental flosses such as described in U.S. Patent Nos. 3,837,351 ; 3,896,824; 4,008,727; 4, 142,538 and 5,353,820;

(d) dental tapes such as described in U.S. Patent Nos. 3,800,812 and 4,646,766;

(e) loaded, texturized dental flosses such as described in U.S. pending patent application, Serial No. 08/240, 149, filed 10 May 1994.

(f) monofilament dental flosses such as described in U.S. Patent Nos. 3,664,915; 3,953,566; 3,962, 153; 4, 187,390; 4,256,806; 4,385,093; 4,478,665; 5,033,488; 5,209,251 and 5,220,932; and

(g) other constructions such as disclosed in U.S. Patent No. 4,817,643 which provides for a specially weaved dental floss with reduced susceptibility to fraying with a thickness that is variable and controlled by the longitudinal tension applied to the floss during use. The special weave is described as a Chinese fingercuff weave. As this floss is stretched, it reinforces itself against fraying and breaking.

All of the foregoing references are hereby incorporated by reference into the disclosure of this invention. By definition the strength or tenacity of the polymer filaments and multipolymer multifilaments useful in the dental flosses of this invention can be defined in terms of tensile strength, i.e. the maximum tensile stress, expressed in force per unit cross sectional area of the multifilament, which the multifilament will withstand without breaking. See for example The American Society for Testing and Materials 1970 Annual Book of ASTM Standards, Part 24 at p. 41.

The strength of the polymer filaments and multipolymer multifilaments useful in the dental flosses of the present invention is dependent upon the strength of the extruded polymer and πrultipolymer, the degree of crystallinity of the multipolymers, the rate and temperature of the draw and the rate and temperature of self-activation of the multipolymer filaments.

Surprisingly^ it has been observed that the strength of homopolymer filaments, which are useful in the improved dental flosses of the invention exhibit high-tenacity to elongation ratios, i.e. ratios from between 0.5:6 an 0.8:8. Typically, the high-tenacity polypropylene filaments exhibit tensile strengths of 6g/ denier and above with elongations of about 40% or greater.

Preferred polypropylene filaments useful in the shred resistant dental flosses of this invention are spun from low melt flow index (MFI) resins which are generally considered non-spinning grade resins. .Spun at suitable temperatures using spin plates with low L/D (length/ diameter) ratios to reduce shear, these high molecular weight, low melt flow viscosity, generally narrow molecular weight range polypropylene polymers unexpectedly produce high tenacity yarns with high elongation properties.

It has been observed that in order to maintain the elongation properties of these preferred polypropylene filaments, the spinning is carried out under low shear conditions to reduce the tendency of polymer chains to break. Accordingly, spin plates are typically constructed with low L/D ratios in an attempt to minimize shear and optimize polymer molecular weight during spinning.

Low denier/filament dental flosses are preferred for ease of floss fit between teeth and improved gentleness. This requires drawing the spun filaments under carefully controlled conditions with long residence time in heat controlled zones in order to promote polymer molecule orientation with corresponding high tenacity.

The high-tenacity polypropylene filaments of the present invention exhibit a distinct elongation advantage which allows the filaments to "give" rather than be cut when encountering abrasive, sharp or narrow spaces. This combination of high tenacity and high elongation results in multifilament dental flosses with improved resistance to shredding which is further optimized by loading the floss with lubricants and the like such as MICRODENT®.

The improved elongation properties of the filaments of the present invention contributes to a perception of "gentleness" when these stretchable filaments are constructed into loaded dental flosses. Additionally, such improved elongation properties allow these filaments to be texturized with minimum loss of tenacity thereby allowing further improvements in gentleness of such high-tenacity loaded dental flosses. These improvements in elongation are particularly relevant to non round flosses of the present invention such as trilobal filament flosses.

The high-elongation/high-tenacity filaments of the present invention are particularly useful in the multicomponent flosses of the invention to impart improved strength, resistance to shredding and elongation.

In general, the tensile strength of the finished loaded dental floss should be from about 5 to 25 lbs., although higher tensile strengths are acceptable. The tensile strength of the floss is preferably from about 7 to 15 lbs. If a dental floss with a tensile strength of less than about 5 lbs. is prepared, it will break and /or fray easily and not be satisfactory for use as a floss. Dental floss with tensile strengths greater than 25 lbs. are satisfactory but offer few additional advantages and are less economical to produce. The thickness of the dental floss should be from about 300 to 2,000 denier, preferably from about 500 to 1,500 denier.

A preferred embodiment of the present invention comprises a loaded dental floss formed of polymer multifilament or multipolymer multifilaments suitable for use as a dental floss. The plurality of individual filaments are formed together to give a larger thread of a sufficiently small diameter to permit working into the interproximal areas between the teeth. If desired, the filaments of yarn can be colored utilizing any compatible and accepted color dye such as FD&C Blue No. 1 , FD&C Yellow No. 5, FD&C Red No. 40, mixtures thereof and the like.

It is preferred to twist the individual filaments to form the floss in order to give the product additional integrity, that is, additional strength to prevent shredding and filament separation. Dental floss can be made without twisting the individual filaments. Dental tape is usually made with little or no filament twist. The twist of the filaments can be from about 0.5 to 3.0 turns per inch, with a preferred twist of about 1.5 to 2.0 turns per inch.

As discussed above, historically, dental flosses have contained wax and/or flavor with various "active ingredients" such as fluoride as described in several of the traditional waxed flosses cited above. U.S. Patent Nos. 4,91 1 ,927; 5,098,711 ; 5, 165,913 and pending patent application 08/240, 149 described various substances being loaded throughout these flosses at levels from a few milligrams to over 100 milligrams yd., with the release of a substantial quantity of this load occurring during flossing. For purposes of the present invention the "load" described in the foregoing references is incorporated in this disclosure by reference.

In addition to wax, flavors, baking soda, abrasives, toothpaste and mouthrinse ingredients the load of the present invention can include various chemotherapeutic agents, antiplaque, anticalculus, antigingivitis ingredients including stannous fluoride, chlorhexidene, cetylpyridinium chloride and triclosan. Therapeutics such as tetracycline, metronidazole, antibiotics, coagulants such as described in U.S. Patent No. 5,033,488, as well as anti- plaque substances such as MICRODENT® and ULTRAMULSION®, are suitable and useful in the present invention. Each of these substances can be released from the flosses of the present invention into interproximal and subgingival areas during flossing as described in the U.S. Patent Nos. cited above and in U.S. Patent Nos. 4,950,479; 5,032,387 and 5,538,667. Anticalculus agents described in U.S. Patent No. 4,627,977 can also be used.

Coagulants suitable for inclusion in the load in the flosses of the present invention include: K vitamins ( 1-4), calcium ions in the form of a soluble (water) calcium salt and blood factors that initiate the coagulation cascade. Additional coagulants useful in the flosses of the present invention include: aminocaproic acid, tranexamic acid, adrenaline, alum, noradrenaline, iron salts, zinc salts, and calcium alginate. See also Martindale (The Extra Pharmacopeia), the Pharmaceutical Press, London Ed. 5. EF Reynolds.

Other actives which may be loaded or otherwise incorporated into the flosses of this invention which promote oral hygiene, include fluoride, quaternary salts, hexachlorophene, soluble pyrophosphate salts with hydrolysis inhibiting agent(s), as well as compounds that assist in wound healing such as allantoin, zinc sulphate and similar astringents.

The load of this invention can optionally contain at least one humectant selected from the group consisting of glycerine, xylitol, sorbitol, hydrogenated glucose syrup and propylene glycol. Generally, such humectants are utilized in the proportion of about 0.1 percent to about 25 percent by weight based upon the total weight of the composition. Preferably, the humectant is utilized in an amount of about 3 to 15 percent by weight, see Examples below.

Flavors, colorants, sweeteners, non-cariogenic sugars and humectants are also used to impart optimum cosmetic characteristics to the compositions of the present invention. Generally, the flavoring component is present as an oil, emulsified into the composition by the surfactant component.

The conventional flavoring components are exemplified by the following materials, menthol, anise oil, benzaldehyde, bitter almond oil, camphor, cedar leaf oil, cinnamic aldehyde, cinnamon oil, citronella oil, clove oil, eucalyptol, heliotropin, lavender oil, mustard oil, peppermint oil, phenyl salicylate, pine oil, pine needle oil, rosemary oil, sassafras oil, spearmint oil, thyme oil, thymol, wintergreen oil, lemon and orange oils, vanillin, spice extracts and other flavoring oils generally regarded as safe (GRAS) by health authorities.

Additional adjuvants can be added to provide color, flavor, or sweetening effects, as desired. Examples of suitable sweetening agents include sorbitol, sodium cyclamate, saccharine, commercial materials such as NutraSweet brand of aspartame and xylitol. Citric acid or acetic acid is often utilized as a flavor additive. All types of flavoring materials are generally used in amounts of about 1.0 to about 20 percent by weight, preferably about 2.0 percent to about 15 percent by weight.

A buffering ingredient may also be added to the load of this invention in order to prevent natural degradation of the flavoring components or therapeutically active ingredients. Generally, the pH of these compositions is adjusted from about 3.5 to about 8, depending on the chemistry of the active ingredient most requiring protection. The buffering ingredients such as alkali metal salt of a weak organic acid, for instance, sodium benzoate, sodium citrate, sodium phosphate, sodium bicarbonate or potassium tartrate is generally added in an amount of about 0.1 to about 1.0 percent by weight. Other buffering agents such as weak organic acids or salts of weak bases and strong acids such as boric acid, citric acid, ammonium chloride, etc. can also be used in similar concentrations.

Stabilizers are often added to the compositions for additional control, such as:

a. sodium benzoate, sodium or potassium sorbate, methyl paraben, propylparaben and others approved for ingestion; and

b. chemical oxidative control substances, such as ethylene- diaminetetraacetic acid, BHA, BHT, propyl gallate and similar substances approved for ingestion. Concentration levels of these stabilizers comply with industry and regulatory standards.

Successful loading of the compositions of this invention into the multi- strand interdental device requires unique manufacturing processes other than those presently used to "wax" or "flavor" commercial flosses. For example, processes used for the addition of microencapsulated flavor substances, "flavor oils" or wax to floss do not provide for the quantity of load required for the present invention nor the "controlled release" of this loaded material interproximally during flossing. Those processes used for waxing, for example, primarily coat the outer surfaces of the bundle of floss strands.

In contrast, the compositions of this invention are loaded throughout the floss in concentrations ranging from about 10% to over 100% by weight of the floss. This translates to from between about 10 mg and about 100+ mg per yard of floss. These loaded substances are then controflably released into the oral cavity during flossing at from between about 10 and about 80% of the load. For example, a floss containing 40 mg/yd of load will generally release between about 20 and about 32 mg of load during flossing. Note, the rate of release of these loaded actives is easily controlled by varying the floss construction, the process of loading, and the composition of the loaded material, providing additional novelty and utility to the present invention.

It is critical for the "release" function of the flosses of the present invention that most of this "loading" be accomplished in the interstitial spaces of the floss as distinguished from simply "coating" the outer surfaces of the bundle of floss strands.

The expression "homopolymers" means one polymer, such as polypropylene, preferably made from low MFI resins.

The expression "multipolymers" means two or more synthetic polymers made from relatively low molecular weight compounds (monomers) generally by addition or condensation, polymerization, methods. Preferred multipolymers include various nylon polymers with high RV values.

In one embodiment of this invention, suitable, preferred multipolymers include: polyamides, polyesters, polyethers, polycaprolactones, polyolefins, polyester amides, etc. such as described in U.S. Patent Nos. 2,071 ,250; 2,071 ,253; 2, 130,523; 2, 130,948; 2, 190,770; 2,465,319; 3,399, 108; 3,418, 1 19; 3,526,802; 3,803,453; 4,019,31 1 ; 4,202,854; 4,244,907 and 4,271 ,233, wherein each of these polymers includes two or more polymers of the same type or different types with different molecular weights and/ or different melt viscosities, wherein at least one of said polymers is fully oriented and said polymers exhibit differential linear behavior when spun into filaments.

Homologous polymers, for example, a combination of the same kind of polyesters having different intrinsic viscosities, a combination of the same kind of polyolefins having different melt indexes; a combination of different kinds of homopolyamides, such as, polycapramide/polyhexamethylene adipamide, polycapramide/polyhexamethylene sebacamide, polyhexamethylene/adipamide polyamino-undecanoic acid; a combination of homopolyester and homopolyester ether, such as polyethylene terephthalate/polyethylene- paraoxybenzoate; a combination of homopolyolefins, such as polyethylene having a high density/ polyethylene having a low density, polyethylene having a high density/ isocactic polypropylene; a combination of homologous homopolymer and copolymer, such as polycapramide/polycapramide- polyhexamethylene isophthalamide copolymer, polyhexamethylene- adipamide/polyhexamethylene adipamide-polyhexamethylene terephthalamide copolymer, polyethylene terephthalate/polyethylene terephthalate- polyethyleneisophthalate copolymer; a combination of different kinds of polymers, such as polyamide/ polyester, polyester/ polyolefin, polyamide/polyolefin, polysulfonamide/polyurea, polyvinyl chloride/ polyvinylidene chloride. Furthermore, thermoplastic synthetic linear polymers, such as polyurethane, polyoxymethylene, polypivalolactone and polychlorotrifluoroethylene can be used properly by combining with the above mentioned various kinds of polymers. Further, besides the copolymers, graft polymers and mixtures thereof or the above described polymers added with viscosity stabilizer, dye-stuff, pigment, plasticizer and other organic or inorganic additives can, of course, be used.

Multipolymers suitable for the purposes of the present invention in addition to hexamethylene adipamide include other polyamides, including copolymers, whether prepared by the reaction of diamines and dibasic acids, and their derivatives, amino acids, or other compounds (e.g., caprolactam, which yields a polyamide under proper reaction conditions). This invention is applicable similarly to other fiber-forming polymers that may contain amine groups, including polyureas derived, for example, from a diisocyanate and a diamine, as shown by Rinke et al. in U.S. Patent No. 2,51 1 ,544; polyurethanes; polythioureas; polythioamides; polysulfonamides, as taught by Jones et al. in U.S. Patent No. 2,667,468; polyimides; and poly-4-amino- l-2-4-triazoles as taught by Fisher et al. in U.S. Patent No. 2,512,629. Copolyesteramides also can be used. The amine content of the core polymer may arise from a blend of a polymer containing amine groups and another polymer with few or no amine groups as, for example, a blend of a polyamide and a polyester, such as polyethyleneterephthalate.

Although this invention has application to polymers containing primary amine groups, it is of value with polymers containing secondary and tertiary amine groups. Thus, an N-amino-alkyl morpholine can be used as a viscosity stabilizer in the preparation of polyamides, as taught by Watson in U.S. Patent No. 2,585, 199, in order to obtain polymers with tertiary amine end-groups, having increased dyability with acid dyes. Other means of forming amine end- groups by polymerization or after-treatment of a polymer will be obvious to those skilled in the art.

Polyamides having an intrinsic viscosity of at least about 0.4 can be converted into self-supporting filaments by extrusion of the molten polymer through fine orifices ("melt-spinning"). Tenacity and other properties of the product being enhanced subsequently by cold-drawing it to increased length. Sometimes an excess of one or the other of the polymerizing reactants is employed in the polymerization of diamines and dicarboxylic acids or their amide-forming derivatives, or some other "viscosity stabilizer" is used with these reactants or in the polymerization of aminocarboxylic acids, with the objective of terminating growth of the polymer molecules. Residual unreacted amine and carboxyl end-groups are determinable by microtitration methods, as described by Waltz and Taylor in Analytical Chemistry, 19, 448 ( 1947); neutral (e.g., alkyl) and end-group content can be calculated from the amount of stabilizer (e.g., acetic acid) reacted with the polymer or its polymerizable components. According to G. B. Taylor, who discusses relationships of end- groups, relative viscosity, intrinsic viscosity, and number- average molecular weight of polyhexamethylene adipamide in J. Am. Chem. Soc, 69, 635 ( 1947), use of equal amounts of diamine and dicarboxylic acid (as their salt) and an acidic viscosity stabilizer always produces polymer with a finite quantity of amine end-groups (e.g., from 14 to 40 equivalents, per 10" grams for polymer having relative viscosity of from 12 to 46).

For the present purpose, polymers having fewer than 50 amine equivalents per 10" grams of polymer is considered essentially free of amine end-groups because at that content melt-spinning of the polymer is commercially feasible, despite degradation (attributal to amine content) that occurs upon exposure of the polymer to the atmosphere. Spinning of polymer containing more than this amount has not been commercial, and a content of 10^ equivalents of amine end-groups per 10" grams of polymer is termed high in degradable amine. Although the usual terminal amine group is primary, secondary and tertiary amine groups are included also. Filaments of high average amine end-group content are dyable to deep fast colors with acid dyes.

Polyhexamethylene adipamide (nylon 66) and polycaprolactam (nylon 6) are preferred polyamides for use in this invention. However, the other suitable polyamides include those formed by the polycondensation of one or more diamines of the formula NH2"(-CH2-)-_nNH with one or more diacids of the formula HOOC-(-CH₂-)- COOH and/or HOOC-Ar -COOH, where n is an integer from 4 to 12 and Ar is:

Commercial examples of such polyamides include nylon 6TA/6IA, nylon 66/6TA, nylon 66/6TA/6IA and the like. The polyamides from which the multifilaments are produced may contain additives or modifiers such as those commonly employed in textile and carpet yarns.

When the multipolymer is comprised of distinct homopolyamides, orientation of the homopolyamides' filaments should take place to a substantial degree by the end of the filament drawing step in order to avoid substantial shrinkage in the subsequent self crimping step. The addition of another polymer as a melt blend is acceptable including other homopolyamides such as: polyheptanamide, polyundecanamide, polyoctamethylene oxamide, polytetramethylene suberamide, polyhexamethylene suberamide, polyxylylene azelamide and poly-2-methyl-hexamethylene terephthalamide. Crystallizable isomorphic copolymers such as the copolymer of polyhexamethylene adipamide and polyhexamethylene terephthalamide may be used in place of the homopolyamide component.

Acrylonitrile multipolymers are also viable for the dental flosses of the present invention such as those described in U.S. Patent Nos. 2,837,500; 2,988,420; 3,038,236; 3,038,240; 3,039,237; 3,039,524; 3,092,892; 3,864,447; 4,284,598 and 4,309,475.

Suitable comonomers useful in preparing the desired acrylonitrile polymers may be selected from, but are not limited to, for example, methyl acrylate; ethyl acrylate; butyl acrylate; methoxymethylacrylate; beta-chloro- ethyl acrylate and the corresponding esters of methacrylic and chloracrylic acids; vinyl chloride; vinyl fluoride; vinyl bromide; vinylidene chloride; vinylidene bromide; allyl chloride; 1 -chloro- 1 -bromo-ethylene; methacrylonitrile; methyl vinyl ketone; vinyl formate; vinyl acetate; vinyl propionate; vinyl stearate; vinyl benzoate; N-vinyl phthalimide; N-vinyl succinimide; methylene malonic esters; itaconic esters; diethyl citraconate; diethyl mesaconate; styrene; dibromostyrene; vinyl naphthalene; 2-methyl- l- vinyl imidazole; 4-methyl- l -vinyl imidazole; 5-methyl- 1 -vinyl imidazole; acrylic acid; methacrylic acid; alpha-chloroacrylic acid; itaconic acid; vinyl sulfonic acid; styrene sulfonic acid; methallyl sulfonic acid; p-methoxyallyl benzene sulfonic acid; acrylamidomethylpropane sulfonic acid; ethylene-alphabeta- dicarboxylic acids and their salts; acrylamide; methacrylamide; isopropylamide; allyl alcohol; 2-vinylpyridine; 4-vinylpyridine, 2-methyl-5-vinylpyridine; vinylpyrrolidone; hydroxyethyl methacrylate; vinylpiperidone; 1 ,2- hydroxypropyl methancrylate; and the like.

Synthetic addition polymers and linear polyesters suitable for the multipolymers of the present invention include, in addition to polyethyleneterephthalate, the corresponding copolymers containing sebacic acid, adipic acid, isophthalic acid as well as the polyesters containing recurring units derived from glycols with more than two carbons in the chain, e.g., diethylene glycol, butylene glycol, decamethylene glycol and trans-bis- 1 ,4- (hydroxymethyl)-cyclohexane. Polymers derived from acrylonitrile and particularly those containing 80% or more of acrylonitrile combined in the polymer molecule are particularly useful in the practice of this invention. Polymers containing 80% or more of acrylonitrile combined in the polymer molecule, i.e., both the homopolymers and copolymers, are especially preferred in the practice of this invention because of the chemical inertness, general water insensitivity, high modulus, high tensile strength and especially the pleasing handle, etc. that are characteristics of filament formed from these polymers. In general, both components will be preferably made of similar polymers (e.g., both acrylonitrile polymers) in order that optimum adhesion be obtained between the two components. The necessary differential reversible length change between the components is readily obtained by altering the content of ionizable groups in the two polymers.

Such ionizable groups are readily obtained by copolymerizing acrylonitrile, for example, with monomers containing acid groups such as carboxylic, sulfonic or phosphonic in either the salt or free-acid form.

Among the carboxylic monomers suitable for use in this invention are: acrylic acid, alpha-chloroacrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid, citraconic acid, crotonic acid, vinyl benzoic acid and the like.

The use of stronger (i.e., more highly ionized) acid groups as sulfonic or phosphonic acids as, for example, l-propene-2-phosphonic (see U.S. Patent No. 2,439,214) or phenylethene-2-phosphonic acids are preferred in this invention since they are, in general, more effective than carboxylic acids in causing a reversible length change and also because their copolymers are substantially more stable to heat discoloration.

In addition to p-styrene sulfonic acid, methallyl sulfonic acid, allyl sulfonic acid and ethylene sulfonic acid disclosed above in this application, the following sulfonated polymerizable monomers and their salts are eminently suited for use in this invention: o- and m-styrene sulfonic acid, allyloxyethylsulfonic acid, methallyloxyethylsulfonic acid, allyloxypropanolsulfonic acid, allylthioethylsulfonic acid, allylthiopropanolsulfonic acid, isopropenylbenzenesulfonic acid, vinylbromobenzenesulfonic acid, vinylfluorobenzenesulfonic acid, vinylmethylbenzenesulfonic acid, vinylethylbenzenesulfonic acid, isopropenylisopropylbenzenesulfonic acid, vinylhydroxybenzenesulfonic acid, vinyldichlorobenzenesulfonic acid, vinyldihydroxybenzenesulfonic acid, vinyltrihydroxybenzenesulfonic acid, vinylhydroxynaphthalenesulfonic acid, isopropenylnaphthalenesulfonic acid, sulfodichlorovinylnaphthalene, allylbenzenesulfonic acid, methallylbenzenesulfonic acid, isopropenylphenyl-n- butanesulfonic acid, vinylchlorophenylethanesulfonic acid, vinylhydroxyphenylmethanesulfonic acid, vinyltrihydroxyphenylethanesulfonic acid, 1-isopropylethylene- l -sulfonic acid, 1-acetylethylene- l -sulfonic acid, naphthylethylenesulfonic acid, biphenyloxyethylenesulfonic acid, propenesulfonic acid, butenesulfonic acid, hexenesulfonic acid, etc. Salts of diacids such as of disulfonic acids may also be used, for example, salts of 3,4- disulfobutene(l), vinylbenzenedisulfonic acid, vmylsulfophenylmethanesulfonic acid, allylidinesulfonic acid, etc.

Sulfonic acid groups can be introduced as end groups in polyesters by using metallic salts of sulfomonocarboxylic esters such as sodium p- carbomethoxy benzene sulfonate and dipotassium 5-carbomethoxy benzene- 1,3-disulfonate and sulfomonohydric alcohols, such as sodium-3-hydroxy propane- 1 -sulfonate as chain terminators.

Sulfonate acid groups can be placed in mid-chain units of a polyester by using as a monomer, a dicarboxylic acid compound or its derivative containing a metallic salt of a sulfonate, such as sodium l ,8-di(carbomethoxy)naphthalene 3-sulfonate, potassium 2,5-di(carbomethoxy) benzene sulfonate, and sodium 4,4-dicarbomethoxy butane- 1 -sulfonate.

Carboxy groups and their salts in a polyester are also useful in this invention although sulfonic acid is preferred. They can be introduced as end groups by using an excess of a dibasic acid or by degrading a polymer by various means. Chain terminators such as potassium monomethyl terephthalate, potassium hydroxybutyrate, or potassium monomethyl sebacate can be used in ester exchange polymerizations.

Carboxy groups can also be introduced to midchain units of a polyester. Metallic salts of carboxylic acids do not enter into an ester exchange polymerization, so that compounds such as potassium dimethyltrimesate, or the potassium salt of desoxycholic acid

(HO)₂C₂₃H₃₇COOK

can be copolymerized with, for example, dimethyl terephthalate. Mid-chain carboxy groups can also be introduced by melt blending a polyester having predominately hydroxyl end-groups with a dianhydride such as pyromellitic anhydride followed by extrusion of the modified polyester into shaped articles, the holding time at the high temperature of melt-blending and extrusion being of short duration.

The required ionizable groups can also be obtained by the use of basic comonomers, such as 2-vinyl pyridine, 2-methyl-5-vinyl pyridine and others of that type as disclosed in U.S. Patent No. 2,491,471 , issued to Arnold, p- dimethylaminomethyl styrene (see U.S. Patent No. 2,691 ,640), vinyl ethers of amino alcohols such as betadiethyl aminoethyl vinyl ether, esters of acrylic and methacrylic acid with amino alcohols such as N,N-diethylaminoethyl acrylate, and polymerizable quaternary ammonium compounds, such as allyltriethylammionium chloride, vinyl pyridinium chloride, allylpyridinium bromide, methallylpyridinium chloride, and others as disclosed in Price, U.S. Patent No. 2,723,238 issued November 8, 1955, beta-vinyloxyethyl dicarbomethoxyethyl methylammonium chloride and others as disclosed in Albisetti and Barney, U.S. Patent No. 2,729,622 issued January 3, 1956, and others. The use of polymerizable quaternary ammonium compounds as sources of basic ionizable groups in the polymers of the filaments of this invention are preferred over other basic modified polymers due to their higher basic strength.

Although the polymers containing basic groups are preferably made by copolymerization, it will be obvious to those skilled in the art that such basic groups can arise from the after- treatment of the polymer or of the fiber, as for example, the reduction-amination of polymers containing ketone groups made from such monomers as methyl vinyl ketone, isopropenyl methyl ketone and the like as disclosed in Ham, U.S. Patent No. 2,740,763 issued April 3, 1956, or by the quaternization of a nitrogen group in a solution of a copolymer such as a copolymer of acrylonitrile and 2-vinyl pyridine as shown in Ham, U.S. Patent No. 2,676,952 issued April 27, 1954, or by exposure of a copolymer containing a methallyl haloacetate to quaternization conditions in a spinning solution as disclosed in Ham, U.S. Patent No. 2,656,326 issued October 20, 1953.

It will be clear to those skilled in the art that the required ionizable groups can be incorporated into a polymeric component by the blending of 2 or more polymers. The polymers should preferably be compatible.

The use of acidic modifiers in a copolymer are preferred since in general they afford better polymerizations, such as less tendency to form insoluble gels than basic modifiers. Polymers, their spinning solutions and spun fibers containing acid groups (especially sulfonic), are more resistant to discoloration by heat than are the basic modified polymers.

Among the more desirable monomers from the point of view of enhancing the effect of ionizable group content are methyl acrylate, methyl methacrylate, methyl vinyl ketone, acrylamide, N-tertiary butyl acrylamide, vinyl methoxyethyl ether, methoxyethyl acrylate, and vinyl acetate bis-(2- chloroethyl) vinyl phosphonate, N-vinyl pyrrolidone, N-vinyl methylformamide and N,N-dimethyl acrylamide.

Suitable monomers may be found among ethyl methacrylate, butyl methacrylate, octyl methacrylate, methoxyethyl methacrylate, phenyl methacrylate, cyclohexyl methacrylate, dimethyl amidoethyl methacrylate, and the corresponding esters of acrylic acid; acrylamides and methacrylamides or alkyl substitution products thereof; unsattirated ketones such as phenyl vinyl ketone, methyl isopropenyl ketone and the like; vinyl carboxylates such as vinyl formate, vinyl propionate, vinyl butyrate, vinyl thiolacetate, vinyl benzoate, esters of ethylene alpha, betacarboxylic acids such as maleic, fumaric, citraconic, mesaconic, aconic acids, N-vinyl succinimide, vinyl ethers.

The multifilament dental flosses of the present invention include:

1. unitary filaments comprised of high-tenacity homopolymers spun from low MFI resins, which filaments exhibit high-elongation properties.

2. unitary filaments comprised of multipolymers having different melt viscosities and different physical properties, wherein the filament is comprised of at least two of such polymers while having a uniform multipolymer composition throughout, and 3. composite filaments wherein each of the multipolymers comprises a distinct component in the filament construction. See Figures 1 to 23. These latter are referred to as:

(a) bicomponent fibers, see Vol. 1 Chemical Processing of Fibers and

Fabrics, FUNDAMENTALS AND PREPARATION, Part A, pp. 1 -33 and U.S. Patent Nos. 3,038,237; 3,039,524; 3,092,892; 4,309,475; 4,547,420; 5,059,482 and 5, 130, 195. See also INDA Journal, 4 no. 4, 22-26 ( 1992);

(b) "conjugate filaments", see U.S. Patent No. 4,601 ,949;

(c) composite filaments, see U.S. Patent Nos. 3,038,237; 3,038,239;

3,399, 108; 3,536,802; 4,414,276 and 5,059,482;

(d) plural-compound fibers, see U.S. Patent No. 5, 162,074; and/or

(e) multicomponent fibers, see Encyclopedia of Textiles, Fibers and Non- woven Fabrics, pp. 152- 172, 1984.

For the purposes of the present invention, all of the foregoing composite filaments are included within the term "multifilament" self- activating dental floss.

The multipolymers suitable for the dental flosses of the present invention may differ from one another with respect to, for example, their chemical structure. See U.S. Patent Nos. 3,399, 108; 3,418, 1 19 and 4,019,31 1. Or, the polymers may have the same structure and be different because of a difference in relative viscosity. See U.S. Patent No. 3,536,802. Or, because one polymer contains an additive that changes its morphology and the other polymer does not undergo such change. See U.S. Patent No. 4,271 ,233. Or, instead of co-extruding two different polymers, a single polymer of two distinct molecular weights is extruded to form a multipolymer filament comprised of this two molecular weight polymer mixture. This latter is not considered a composite filament, rather a "unitary filament" construction for the purposes of the present invention.

Composite molecularly-oriented multipolymer filaments suitable for this invention are described in Chemical Processing of Fibers and Fabrics, Fundamentals and Preparation, Part A, Handbook of Fiber Science and Technology, Vol. 1 , pp. 1-33, Marcel Dekker Inc. , New York, NY and the references cited therein at pp. 30-33, all of which is incorporated herein by reference.

Particularly preferred multipolymer filaments contain at least two polymers wherein the polymer components have different linear behavior properties suitable for supporting self-crimping such as described in U.S. Patent No. 5, 162,074 and the 86 patents cited therein which are included herein by reference. See also U.S. Patent Nos. 2,439,814; 3,038,237; 3,039,524; 3,092,892; 3,094, 174; 3,399, 108; 3,536,802; 4,019,31 1 ; 4,244,907; 4,309,475; 4,601,949 and 5, 130, 195.

In another embodiment of this invention the multipolymer composition is continuous along the entire fiber length and with at least two of the polymer components permanently joined at an interface form, a side-by-side arrangement such as described in U.S. Patent Nos. 3,038,237; 3,038,239; 4,019,31 1 ; 4,309,475 and 4,601 ,949. See also Figures 1 to 23 of the drawings.

The self-activating, multipolymer, multifilaments suitable for use in the dental flosses of the present invention are generally referred to as self- crimping, since their "bi-metallic" type of behavior causes them to curl when exposed to heat and/or moisture, resulting in a more fibrous mass. Sheath- core composites will behave similar to side-by-side composites although their curling forces are not as great. According to U.S. Patent No. 2,439,814, the differential linear behavior of the multipolymer filaments of the dental flosses of the present invention is attributed to the differential polymer orientation obtained by stretching a bicomponent filament comprised of two different polymers to beyond the classic limit of one of the components.

The self-activating, self-crimping, multipolymer, multifilament dental flosses of the present invention can be produced by spinning two or more polymers differing from one another in their linear behavior in the form of individual filaments and combining them to form a yarn or spinning them in the form of bicomponent or so-called composite filaments or fibers. Since, in both cases, the combined components form a homogeneous length of filament, the "longer" component is forced by the different linear behavior of the components to wrap itself in turns around the "shorter" component. This provides the resulting yarn with crimp, bulkiness and voluminosity.

It is known that the differential linear behavior is caused by the type of polymers used (for example Austrian Patent No. 228,919, French Patent No. 1 ,416,022 or U.S. Patent No. 3,099, 174), by the viscosity of the spinning melts (British Patent No. 969, 1 10), by additives (British Patent No. 1 , 128,536) and various other treatments (for example British Patent No. 1 ,087,823 or British Patent No. 1,028,873). The differential linear behavior can be produced simply by stretching the yarn or the bicomponent filament (for example as disclosed by Austrian Patent No. 228,919) or by subsequent shrinkage treatment carried out in the absence of tension (British Patent No. 950,429) or by a swelling treatment (French Patent No. 1,205, 162). It is also known that linear behavior is influenced by a differential orientation in identical or different polymers. Thus, according to U.S. Patent No. 2,439,814, differential linear behavior is obtained through differential orientation by stretching a bicomponent filament of different polymers to beyond the elastic limit of one of the two components. According to German Patent No. (DOS) 2,052,729, differential orientation (double refraction) is obtained in filaments of the same kind which have been spun together by applying a different conveying force to certain portions of the filament bundle or tow.

To develop adequate crimp in the composite filaments, the shrinkability of one component should be at least 1% greater than the shrinkability of the other component, that is, said component has at least 1% greater loss of the original length upon shrinkage than the other component. The shrinkability of a component is determined by measuring the shrinkage, upon immersion in boiling water under no tension, of a monocomponent filament made from the component polymer (spun and otherwise processed under substantially the same conditions as the composite filament). If a component cannot be spun into a monocomponent filament, e.g., because its molecular weight is too low, its shrinkability is determined by extrapolation from a graph of the shrinkage characteristics of monocomponent filaments of the same polymer (in different, spinnable molecular weights).

In considering the extent of drawing, one should take into consideration the amount of draw which may be effected during the spinning of the filaments, and, in fact, the desired amount of drawing may be effected during spinning rather than as a separate drawing step following the windup of the filaments from the spinning operation.

As used herein: the term "spontaneous crimp" means crimp observed upon release at ambient temperatures of the tension applied to the filaments during the drawing thereof; the term "latent crimp" means crimp which is not observed even upon release of the drawing tension until the filaments are subjected to heat while relaxed; the term "crimp" means crimp res ilting from the additive effect of both spontaneous and latent crimps.

U.S. Patent No. 3,832,435 describes a melt spinning process for producing partially drawn polyester filaments having latent crimp. Latent crimp is imparted to the filaments after they leave the spinneret by cooling the freshly spun filaments on one side before they completely solidify. The cooling is accomplished by passing the individual filaments over a cooled roll (quench roll) driven at a given peripheral speed. The yarn is passed from the quench roll over a second cooled roll of smaller diameter which is normally stationary or substantially stationary when compared to the speed of the first roll. The filaments are pulled from the second roll at a speed such that they are partially drawn as they leave the second roll. The partially drawn filaments prepared by this process must be further drawn in a separate operation and then heated to develop the latent crimp.

In a preferred embodiment of this invention, the bicomponent dental floss contains bilaminar (or side-by-side) and multilaminar filaments. The expression bilaminar filament is to be understood as meaning a continuous filament comprising two different components which have a surface of contact with one another and with the outside over substantially the whole length of the filaments. The expression multilaminar filament is to be understood as meaning a filament in which at least one of the components is present more than once in its cross-section of over substantially the whole of its length.

In addition to the term bicomponent, preferred multipolymer multifilaments for the dental flosses of the present invention can be described as "conjugate filaments". This means a filament combining a first longitudinal polymeric segment and a second longitudinal polymeric segment arranged in an eccentric configuration along the length of the filament and differing from each other in longitudinal dimensional change characteristics. The term "eccentric" as used herein includes both side-by-side and asymmetrical sheath- core structures. By differing in "longitudinal dimensional change characteristics" is meant that when the filament is structurally relaxed, as evidenced by the filament assuming a helical configuration. The formation of helical crimp in the foregoing test, of course, confirms the presence of at least two eccentrically arranged segments as well as their differing dimensional change characteristics. Conjugate filaments having segments differing from each other in longitudinal dimensional change characteristics can be produced by methods well known in the art, such as, by using polymers having different relative viscosities (e.g., see U.S. Patent No. 3,536,802). There may be a distinct line of demarcation between the segments at their interface or, in some instances, merely a gradient change in composition of the filament across its cross-section.

Conjugate filaments and their preparation are well known in the art. Typically, their preparation comprises two completely separate and discontinuous operations; a melt spinning operation in which two different polymers are co-extruded to form as-spun filaments which are wound onto a bobbin to form a package, and a stretching operation in which the as- spun filaments are withdrawn from the bobbin, stretched and then wound onto a second bobbin to once again form a package.

Composite filaments prepared for use in accordance with the present invention may be subjected to a drawing (permanent stretching) operation in order to impart to the filaments the desired physical properties as tenacity, elongation and initial modulus. Although drawing may affect shrinkability and the reversible length change of a filament, crimped filaments with a reversible crimp have been made from dry-spun filaments withovit a drawing treatment. The conditions applied to drawing the spun multi-component filaments may vary in wide limits. The drawing characteristics of the components can readily be determined from those of mono-component filaments of each of the component polymers of the composite filaments. The drawing can be accomplished in accordance with known principles applicable to the particular polymers of the composite filaments and, in general, the composite filaments are drawn at least 50% (i.e., to 150% of original undrawn length) and preferably about 2-8 times the original lengths. The extent of drawing will, of course, also depend somewhat upon the nature of the particular polymers used in the composite filaments and upon the type of eccentric relationship between those polymers in the composite filament. In considering the extent of drawing, one should take into consideration the amount of draw which may be effected during the spinning of the filaments, and, in fact, the desired amount of drawing may be effected during spinning rather than as a separate drawing step following the windup of the filaments from the spinning operation.

The shrinkage of the composite filaments in order to affect crimping, may be carried out by the use of any suitable known shrinking agent. Shrinking will ordinarily be carried out by the use of hot aqueous media such as hot or boiling water, steam, or hot highly humid atmosphere, or by the use of hot air or other hot gaseous or liquid media chemically inert to the polymers of the composite filaments. The shrinking temperature is generally in the neighborhood of 100°C, but may be higher or lower, e.g. , 50°C up to about 150°C or even up to a temperature not exceeding the melting point of the lowest melting polymeric component of the fiber.

This invention is particularly directed to filaments and yarns (i.e., bundles of filaments) having deniers of the magnitude used in textiles. It is preferred that the filaments of this invention have a denier of 1 to 10 (inclusive) and that the yarns of this invention have a denier of 30 to 8,000 (inclusive) .

Distinguishing features of the polymer and multipolymer filament flosses of the present invention include:

(a) The polymers are substantially fully oriented.

(b) The polymers used in the spinning of these filaments have higher viscosities (low MFI) and correspondingly higher molecular weights than those polymers generally used heretofore in dental floss.

(c) The physical strength properties of the resultant dental flosses' tenacity are substantially improved over traditional filament flosses. (d) The dental floss filaments of the invention exhibit exceptional elongation properties.

(e) ._ The polymers of the multipolymer flosses exhibit differential linear behavior which intrinsically provides the basis for "self-activation" and release during flossing of "loaded" substances from the gentler flosses of this invention.

Of the multipolymer filament loaded dental flosses of the present invention, those comprised of bicomponent fibers are preferred. The major types of bi-component fibers are:

( 1) concentric sheath/ core fibers (see Figures 1 1- 14 and 22-23),

(2) side-by-side (see Figures 1- 10 and 15-21),

(3) sheath fibers with an eccentric core (see Figure 14),

(4) islands-in-the-sea, and

(5) citrus.

The foregoing are generally illustrated by the cross-sections of these fibers as set forth in Figures 1 through 5.

Some of the basic methods for spinning these bicomponent fibers include: ( 1) pipe-in-pipe mixer, (2) circular steam plate mixer, and (3) parallel- steam plate mixer as described and illustrated by Fitzgerald and Knudson, Textile Res. J., 37; 447-453 ( 1967) and expanded upon by Chemical Processing of Fibers and Fabrics Fundamentals and Preparation, Volume 1 , pp. 4- 14. See also U.S. Patent Nos. 4,414,276; 4,861 ,661 ; 4,941 ,812; 5,059,482 and

5, 162,074, Encyclopedia of Textiles, Fibers and Non-woven Fabrics, pp. 152- 172, Wiley and Sons, New York, NY, 1984, Bicomponent Fibres, Merrow Publishing, Watford Herts, England, 1971.

Side-by-side bicomponent fibers of different cross-sections which are particularly suitable for use in the dental flosses of this invention are illustrated in Figures 9, 20, 12; 15 to 21 and 23 of the drawings. These fibers are obtained by changing the shape of the spinning orifice as described in U.S. Patent No. 5, 162,074. As discussed below, it has been observed that trilobal cross-section filaments and other non-round filaments, quadralobal, pentalobal, hexalobal, etc., contribute substantially to the gentleness of the dental flosses of this invention. This feature is discussed in more detail below.

Side-by-side bicomponent fibers are produced as the name implies by spinning two fiber components together so that they are joined longitudinally. The main reason for manufacturing these fibers is to provide helical crimp caused by differences in the expansion or shrinkage of the two components of the fibers. The two fiber components may differ in chemical composition or differ in some property such as molecular weight or degree of crystallization which provides differential expansion or shrinkage. Sometimes the polymer components may differ in degree of hydrophilicity; for example, both polymers may be copolymers of polyacrylonitrile but contain different amounts of sulfonic acid groups. Some bicomponent fibers develop crimp when they are heated in a relaxed state. Crimp can also be produced in bicomponent side-by- side fibers by a water-quenching or a hot knife-edge treatment.

There are two types of crimp that can be produced in side-by-side bicomponent fibers, non-water reversible and water reversible. The non-water reversible crimp fibers are visually composed of two nonionic polymers which have different shrinkage properties. The crimp produced in these bicomponent fibers is usually not affected by subsequent wetting. Usually one of the polymers used in the bicomponent fibers with water-reversible crimp in side- by-side fibers contains water-ionizable groups, which allow that polymer component to swell in water. The second polymer may contain no water- ionizable groups or fewer groups so that differential shrinkage can occur. Crimp in this fiber develops when the fiber is dried after hot-wet treatment. This crimp decreases when the fiber is wet; it exhibits "squirming" and the crimp increases upon drying.

The spinning equipment used to produce bicomponent fibers can be summarized as follows: Side-by-side bicomponent fibers can be spun by vising a bilateral spinneret. Sheath/core fibers can be prepared with a pipe-in-pipe spinneret. Islands-in-the-sea fibers can be produced by pipe-in-pipe spinnerets with several small pipes in a large pipe or small pipes can be used to inject several core polymer streams into one sheath stream pipe. Islands-in-the-sea fibers can also be made with merged streams spinning vising static or similar mixers. The cross sections of commercial islands-in-the-sea fibers show great variation in the number, shape, size and distribution of the islands. Citrvis type bicomponent fibers can be made by spinneret modifications to allow the bicomponent fibers to be produced in various configurations. The cross sections of commercial citrvis type bicomponent fibers vary considerably. Additional spinning methods for bicomponent fibers can be found in the patents cited previously.

The physical properties of the spinning solution (dope) are very important in producing suitable bicomponent fibers. Much that is known abovit the rheological properties of dopes for spinning the standard fibers of single polymers is applicable to bicomponent fibers. However, bicomponent dope compatibility is a very important factor in satisfactorily spinning bicomponent fibers. Individual viscosities, under the conditions of spinning, must be (1) high enough to prevent turbulence after the spinneret and (2) not too dissimilar. If the viscosities are not similar, the flow patterns designed to give the required fiber cross section may not be stable. Also, unstable extrusion may occur leading to flickering filaments and interfilament coalescence in the molten thread line. Difficulties may occur in frictional properties, flow behavior and polymer-to-spinneret adhesion. Viscosities of the individual dopes can be changed by modifying the polymer concentration or molecular weight, although these changes may affect the resulting fiber properties. See Encyclopedia of Textiles, Fibers and Non-woven Fabrics, pp. 152- 172, 1984.

Another compatibility problem is adhesion of the individual polymers in the bicomponent fiber. Usually adhesion of the components is satisfactory if similar classes of polymers such as (1) polypropylene (PP) and polyethylene (PE), (2) nylon 6 and nylon 66 and (3) polyethylene terephthalate (PET) and copolymers of polyethylene terephthalate (coPET) are vised together.

A preferred embodiment of this invention comprises stretching a fresh filament at a stretch ratio greater than 1.0 and less than that which would cause the filament to break, said filament being melt spun at a spinning speed of at least 1829 mpm (meters per minute) and comprising a first longitudinal polyamide segment and a second longitudinal polyamide segment arranged in an eccentric configuration along the length of the filament and differing from each other in dimensional change characteristics, said difference and said stretch ratio being selected to provide a filament having a high-load crimp test value.

By "fresh" filament is meant a filament which has not been allowed to age under conditions such that when stretched, no substantial improvement is obtained as compared to characteristics obtained when a filament spun under the same conditions is aged for four (4) hours at 70% relative humidity and at a temperature of 25°C prior to stretching to the same stretch ratio. Fresh filament characteristics can, in some instances, be preserved at least temporarily by collecting and maintaining the filament under anhydrous conditions until it is drawn. Although applicant does not wish to be limited by theory, the use of a fresh filament is believed to provide desirable results due to crystalline characteristics at the time of stretching. According to a preferred embodiment of this invention, the process is a spin-stretch process wherein the stretching of the filament is accomplished inline during melt spinning after the filament is formed and before it is collected.

According to the preferred embodiment of this invention, the process is a spin-stretch process comprising co-extruding two molten fiber-forming polyamides having different terminal velocity distances to form a molten stream in which the polyamides are arranged in an eccentric configuration along the length thereof, cooling and solidifying said molten stream in a quenching zone to form a filament (solidified molten stream), attenviating and accelerating said molten stream by withdrawing the filament from the qvienching zone at a speed (i.e., spinning speed) of at least 1829 mpm and then stretching the filament at a stretch ratio greater than 1.0 in-line before it is collected and, preferably, as soon as possible after the molten stream has solidified, the processing conditions and polyamides being selected to provide a filament having a high- load crimp test value. As used herein, the term "solidified" means the molten stream has cooled sufficiently so that it no longer sticks (i.e. fuses) to other filaments or to yarn guide surfaces. Polyamides having "different terminal velocity distances" are characterized in that under the particular spin-stretch conditions employed to form the molten stream the polyamides solidify at different distances from their point of extrvision (i.e. at different distances from the spinneret). The measurement of terminal velocity distances is hereinafter described.

In general, the highest high-load crimp test values are attained by selecting highly crystalline homopolyamides, svich as nylon 66 and nylon 6. Preferably, both homopolyamides are of the same chemical structure, that is, consist of recurring structural units of the same chemical formula. Most preferably each polyamide is Nylon 66.

The polyamide conjugate filaments of the present invention have little or not torque (i.e., are substantially torque-free) and, therefore, offer certain advantages over false-twist textured filaments which contain substantial torque (i.e., are torque-lively).

The polyamide conjugate filaments of the present invention have a high- load crimp test value. In general, the higher the high-load crimp test value the more suitable the filament is for "activation". Conjugate filaments of the present invention, when subjected to mild conditions, develop adequate crimp having characteristics of the type required for "activation".

In a preferred embodiment of this invention, the process is carried out using the equipment arrangement shown in FIG 25. Referring to FIG 25, polyamides A and B of different terminal velocity distances are coextruded at about the same melt temperature at a given speed (extrusion speed) in molten form through circular capillaries 2 and 3, respectively, of spinneret 1. The molten polymers converge below the spinneret face to form molten stream 4 in which polyamides A and B are arranged, as segments, in a side-by-side configuration. For purposes of illustration the formation of only one filament is shown in FIG 25. It will be understood, however, in actual practice of this invention the spinneret will normally have provisions for forming a plurality of molten streams; that is, the spinneret will have a plurality of capillary pairs 2 and 3. Molten stream 4 is then qvienched by conventional means to form a filament (i.e., solidified molten stream). The filament is then passed into contact with finish applicator means 5 which applies a liquid finish to the filament. Where there is a plurality of filaments, the filaments are conveniently converged on applicator means 5. The filament is then passed around feed roll 6 with a partial wrap, around stretch roll 7 with a partial wrap, heated by heating means 8 (e.g., a heated tube through which the filament passes) and finally collected by collecting means 9 (e.g., a bobbin on which the filament is wound). Roll 6 is rotated at a peripheral speed of at least 1829 mpm. Roll 7 is rotated at a peripheral speed greater than that of roll 6 but usually no greater than twice that of roll 6. The partial wraps are of an angle sufficient to prevent slippage of the filament on the rolls. When the filament is collected on a bobbin, it should be collected at a speed less than the peripheral speed of roll 7, thereby permitting the filament to relax (retract) before it is collected: otherwise, difficulty is encountered in removing the bobbin from the chuck on which it is rotated, particularly, where the filament or yarn makes a large number of wraps on the bobbin to form the package. In instances where the filament makes only a small number of wraps on the bobbin, heating of the filament by means 8 may be omitted. The filament collected on the bobbin normally has both original crimp (visible crimp) which manifests itself when the spinning tension is released and latent crimp which can be developed by subsequent treatment of the yarn.

In accordance with the preferred embodiment of this invention, the spin- stretch process is carried out under processing conditions and using polyamides so as to provide a filament having a high-load crimp test value. The following discussion considers the effect of changing the indicated processing variable while leaving all other variables constant.

One segment of the conjugate filament is preferably formed from a rapidly crystallizable fiber-forming polyamide and the other from a less rapidly crystallizable fiber-forming polyamide. This difference in crystallizability may be achieved by selecting polyamides having different terminal velocity distances. In general as the difference between their terminal velocity distances increases, the high-load crimp test value increases to or approaches a maximum value and thereafter remains substantially the same. In general, polymers become less crystallizable as the ratio of homopolymeric segments to copolymeric segments increases, for example, the crystallizability of nylon 66>nylon 66-6 (95:5)>nylon 66-6 (90: 10)>nylon 66-6 (85: 15). Therefore, highly crystalline homopolyamides such as nylon 66 and nylon 6 are preferred, with nylon 66 giving the highest high-load crimp test values and, therefore, being the preferred polyamide for use in practicing this invention. Nylon copolymers are designated herein in a conventional manner, for example, "nylon 66-6" means the copolymer consisting of randomly occurring 66 units, -NH(CH₂)6NHCO(CH2)₄CO-, and 6 units, -NH(CH₂)₅CO-, formed, for example, by copolymerizing hexamethylene diammonium adipate and caprolactam. Mole ratios when given are given in parenthesis following the copolymer designation, for example, (95:5) means a mole ratio of 95:5, respectively.

When the polyamide used to form one of the segments of the conjugate filament is composed of strvictural repeating units of the same chemical formula as the polyamide used to form the other segment, selection of polyamides differing from each other in relative viscosity values will provide the desired result in this process. When nylon 66 polyamides of different relative viscosities (RV) are used to form the segments, the difference in RV between the two nylon 66's should be at least 5, preferably at least 15 and most preferably at least 30 with the RV of the low RV nylon 66 being at least 20 and, preferably, at least 50 and most preferably at least 65.

While nylon 66 is the preferred polyamide, other polyamides may be used in practicing this invention. Examples of other suitable homopolyamides include nylon 6 and nylon 610. Examples of suitable copolyamides include, but are not limited to, those described in U.S. Patent Nos. 3,399, 108; 3,418, 199; 3,558,760 and 3,667,207. Examples of such copolyamides are: nylon 6-66, nylon 66-610: nylon 66-610 61 1-612; nylon 66-612; nylon 66-61, where 61 is:

units; nylon 66-6T, where 6T is:

units; nylon 66-6-612; nylon 6-66-610 and nylon 6-612.

The spinneret may be designed so that in forming a molten stream each of the molten polymers may be extruded through a separate capillary in such a manner that the molten polymers converge at the spinneret face to form the molten stream or the polymers may be combined and then extruded through a common spinneret capillary to form the molten stream. However, it is preferred that each of the molten polymers be extruded though a separate capillary and converge below the spinneret face to form the molten stream as shown in FIG 25. Unless the molten polymers converge at or below the face of the spinneret, the one segment (e.g., the low RV segment) tends to wrap around the other segment (e.g., high RV segment), which in tvirn tends to reduce the ultimate crimp of the filament.

The filament may be of any desired cross-section, e.g., circular, trilobal, etc. Filaments having a cross-section resulting from the use of various capillaries are shown in FIGS 1-23.

The volume ratio of the polyamide segments can vary over a wide range.

As a practical matter, the segment system normally will be within the range of 3: 1 to 1 :3. In the case where both segments are nylon 66, a ratio of 1 : 1 to 1 :3 (high to low relative viscosity) is preferred with the greatest amount of crimp being obtained with a ratio of about 30:70 (high to low relative viscosity).

Cooling of the molten streams normally occurs in a quench chamber, commonly referred to as a chimney. The term "quench" as used herein means the cooling of the molten streams sufficiently to provide solidified streams (i.e., filaments). Although cooling of the streams may be assisted by a transverse (or concurrent) stream of flowing air, such a stream is not required in order to provide filaments having high levels of high-load crimp. In conventional processes, the filaments are passed from the quenching chamber through what is called a "steam conditioning" tube. Steam is circulated through the tube and comes into intimate contact with the filaments. The purpose of the steam is to facilitate subsequent processing of the filament. It has been found, however, that the use of conditioning steam with the spin-stretch process of this invention significantly reduces high-load crimp. Accordingly, conditioning steam should not be used with the process when high-load crimp is desired or, if it is used, it should be used very sparingly.

The molten streams are attenviated and accelerated from the spinneret (or, when formed below the spinneret, from their point of formation) by a feed roll which withdraws the quenched streams (filaments) from the quenching zone at a spinning speed greater than the extrusion speed. The extrusion speed is the linear speed at which the molten polyamide is theoretically traveling through the spinneret capillary or capillaries and is calculated from the dimensions of the capillary, the extrusion rate and the density of the polyamide. When more than one capillary is used to form the filament, the linear speeds are averaged and the average speed is used as the extrusion speed.

In accordance with a preferred embodiment of the present invention, the filaments are stretched in-line before being collected, for example, before being wound onto a bobbin. Normally, if the filaments are collected and then subsequently stretched in a separate operation, the filaments will not possess a significant level of high-load crimp even thovigh they may possess a moderate level of low-load crimp. It has been discovered, however, that if the filaments are spun and collected under anhydrous conditions and kept under anhydrous conditions for a limited period of time until subsequently stretched, it is possible to obtain filaments having a high-load crimp level in excess of 8% even though the stretching of the filaments is accomplished in an operation subsequent to and separate from the spinning operation. However, such conditions are usually not practical from the standpoint of commercial operations.

The stretching is preferably accomplished using a roll arrangement as shown in FIG 25 wherein roll 6 is a feed roll and roll 7 is a stretch roll. The stretch roll is operated at a peripheral speed higher than the peripheral speed of the feed roll. With the roll arrangement shown in FIG 25 the filaments are stretched as they leave feed roll 6. In general, as the stretch ratio is increased from 1 , the level of high-load crimp imparted to the filaments increases through a maximum level and thereafter decreases slightly. Normally, maximum high- load crimp test values are attained when the filaments are stretched at a ratio greater than 1.0. In many instances, use of a stretch ratio greater than 2.0 can not be used without breaking filaments. It is contemplated that, if desired, the stretching of the filaments may occur downstream of the feel roll; for example, between two pairs of rolls where the first pair is rotating at the same peripheral speed as that of the feed roll and the second pair at a higher peripheral speed. Preferably, the filaments are stretched as soon as possible after being quenched.

Side-by-side bicomponent fibers can be prepared with many polymer combinations including those shown in Table I below.

TABLE I

Bicomponent Fiber Combinations (side-by-side)

PE (HDPE, LDPE AND LLDPE) */PP PP/PET

PE/PET PP/ rayon

PE/nylon PP/ethylene-vinyl acetate copolymer

PE/polyoxyalkylene methacrylate PP/butene polymer

PP/nylon 66

PET/polyoxyalkylene methacrylate Nylon 6 or nylon 66 /PET

Copolymer Nylon 6/CoPET CoPET/PET Nylon /rayon PET/ polycarbonate Nylon polyurethane PET/ low melting metal alloy Nylon 6/nylon 66 PET/ poly alkylene naphthalate PET/ethylene vinyl alcohol copolymer PET/cyclohexane dimethanol polyester

* HDPE - high density polyethylene LDPE - high density polyethylene LLDPE - linear, low density polyethylene

The multipolymer, multifilament dental flosses of the present invention can be loaded with various substances, described above, generally according to the teachings of U.S. Patent Nos. 4,91 1,927; 5,033,488; 5,098,71 1; 5, 165,913 and U.S. Patent Application Serial No. 08/240, 149 filed 10 May 1994. Preferred loadable substances include MICRODENT® and ULTRAMULSION® as described in U.S. Patent Nos. 5,032,387 and 5,538,667, respectively.

Prior to flossing, the loaded, self-active dental flosses of this invention can be "activated" as follows:

The floss is wound around middle fingers leaving about 4 inches of floss between them. See FIG 1. The floss is then stretched. When pressure on this 4 inch section is relaxed, the floss expands and is thereby activated. The load is prepared for release. (See FIG 2.) See "Tips on using R_χ MICROSTAN™ Gentle Dental Floss" ©1997, IDS.

The differential linear behavior of the respective polymers in the multipolymer, multifilament dental floss of this invention is responsible for the floss filament expansion and the release (and/or breaking up) of the load prior to flossing. See also Pending Application Serial No. 08/240, 149.

In addition to releasing/ breaking up the "load" the "activation step" also expands the dental floss dramatically as shown in FIG 2. This expansion feature allows the floss to be stretched during flossing and to fit into tighter spaces without "snapping" onto gum surfaces, while also covering substantially larger tooth surface areas while it is being worked between the teeth and below the gum line.

Apparently, this activation feature of the flosses of the present invention is attributable to the multipolymer construction of the floss. Activation is accomplished when one of these polymers is stretched beyond their limit. See U.S. Patent No. 2,439,814. The gentleness features of the dental flosses of the present invention are influenced by:

(a) "activation" of the loaded multipolymer, multifilament,

(b) release of at least some of the "load" from the activated floss during flossing,

(c) the gum lubricating properties of the released "load", and

(d) The number of gum contact points in the activated multipolymer, multifilaments as determined by the cross-section configurations of those multifilaments in contact with the gum.

It is suggested that the gentleness of the dental flosses of the present invention which is far superior to that of traditional dental flosses, may be dvie to a more effective distribution of the flossing pressvire across the multipolymer, multifilament, with their multiple gum contact points as illustrated in FIGS 1 1 to 23 in the drawings.

Rather than essentially round cross-section configurations, the dental floss multifilaments of the present invention have irregular shaped cross- sections featuring ribs and channels and/ or lobes rather than the smooth round surfaces of commercial flosses.

Probably the most gentle commercial dental floss on the market today is REACH® Gentle Gum Care Dental Floss, which is described and claimed in pending U.S. Patent Application Serial No. 08/240, 149 filed 10 May 1994. Each of the filaments in this floss has potentially a single contact point with the gum surface. The maximum contact points available for the disclosed preferred gentle flosses in this pending patent application would be approximately 272. In practice, approximately only one-fifth of these filaments actually touch the surface of the gums during flossing. Hence, the pressure applied to the floss during flossing is transmitted to the gums through approximately 50 to 70 contact points.

The improved gentleness featv re of preferred dental flosses of the present invention is attributed in part to the non-round cross-section construction of the multipolymer multifilament flosses of the present invention. These gentle filaments are characterized by multiple gum surface contact points/filament. These filaments include multilobal filaments with cross- sections such as shown in FIGS 9, 10, 12, 19, 22 and 23. Pentalobal and hexalobal cross-sections may in fact offer the optimum number of contact points/filament.

The gentleness property of the flosses of the present invention is also attributed in part to the lower coefficient of friction characteristic of the self- activated flosses of the present invention with the release of various "lubricantlike" compositions contained in the load. The coefficient of friction of standard commercial flosses, i.e. about 0.2 and about 0.08 for PTFE flosses (see U.S. Patent No. 5,033,488) and 0.15 for wax coated PTFE flosses. This lower coefficient of friction of the flosses of the present invention results in less force being reqv ired during flossing to pull these flosses between "contact points", thereby generally avoiding snapping the floss into the gums after the floss passes through the contact point.

According to U.S. Patent No. 5,033,488, a technique whereby the coefficient of friction is measured is described by Scott and Robbins J. Soc. Cosmet. Chem. 31, pp. 179-200, July/ August 1980. In the technique described for measuring friction of reference surfaces by passing hair fibers through an immersed combing device and measuring coefficient of friction with an Instron Tensile Tester, interstitial dental surfaces replace the combing device, without immersing. The improved coefficient of friction characteristic of the flosses of the present invention gives these flosses the significantly enhanced ability to glide easily between tight interproximal contact points and these flosses are gentler on gingival tissue, enamel, dentin and cementum.

It is desirable to utilize a melt or solution spinning system to extrude the various preferred "non-round" filaments such as the particularly preferred trilobal shaped composite fibers wherein the three tips of the fiber lobes are of a different polymer from the central core of the fiber, and /or the three tips are each of different polymers. This can be accomplished by modifying spinnerets such as described in U.S. Patent No. 4,406,850 according to the teachings of U.S. Patent No. 5, 162,074. Finer fiber version of these trilobal filaments can be extruded following the teachings of U.S. Patent Nos. 4,381 ,274 and 4,445,833. The use of static mixing devices in this extruding process is described in U.S. Patent Nos. 3,286,992; 4,307,054; 4,414,276 and European Patent Application No. 0104081 to Kato. See also U.S. Patent Nos. 3,787, 162 and 4,052, 146. All of the foregoing references as well as the 86 references cited in U.S. Patent No. 5, 162,074 are incorporated in this disclosure by reference.

Many multipolymer, multifilaments exhibit excellent strength, abrasion resistance, chemical resistance, tear resistance, etc. However, there appears to be only slight correlation between these "strength properties" and resistance to shredding during flossing.

Favorable tensile strength and knot tensile strength values certainly are positive indications of potential resistance to shredding. However, standard abrasion resistance as used in the carpet and textile fields is not an accurate predictor of the filaments' performance when encountering a sharp surface.

In order to assess the shredding resistance of various filament/floss construction, a shredding value (SV) was established for various multipolymer, multifilament constructions by pulling the filaments across a machined knife edge with an Instron, in a motion comparable to the pull used in a tensile strength/ elongation test. See FIGS 24A and 24B.

Results of this shredding resistance test run with various commercial dental flosses and various multipolymer, multifilament combinations are summarized in Table 2 below.

In Table 2, the results of 10 Instron pulls were averaged. "Knife Deflected" means that a machined knife edge was placed perpendicular to filament/floss line at mid-point so as to create about 1 /8 inch deflection of the straight line path (see FIG 24B). As elongation occurs, the yarn is "dragged" across the knife edge. In some examples, fraying, filament-by-filament, was observed before breaking.

TABLE 2

Polymer Sample Normal Knife Deflected

Tensile Elonj Tensile Elongation

J&J virgin green Nylon 6 for tape (1200 d) 4.22 62.5 2.13 34.4

REACH® Gentle Gum Care

"Off the shelf 3.75 34.0 2.30 25.3

RANIR white, unwaxed

840 d from DuPont 5.57 25.1 2.8 14.1

PET/PBT trilobal, self-textured 1.93 59.1 1 .38 35.9

PP/PP (18/25)

Trilobal, self-texturized 2.29 28.6 2.29 23.3

It is evident that, the composite dental flosses of the presented invention with their multipolymer, multifilaments such as the polypropylene 18/25 (PP/PP 18/25) with its gentle "trilobal self-activation" construction resist fraying under the Knife Deflection test much more effectively than do the commercial dental flosses with their single polymer construction. It is interesting to note that the Tensile Value under Knife Deflection for commercial flosses such as J&J Nylon 6 ( 1200 d) and Ranir nylon 840 d both were approximately 50% of the Tensile Values Normal, despite the differences in denier, i.e. 1200 vs. 840.

As discussed previously under gentleness, the release of some of the load during flossing, the lubricity of said load combined with "activation" which expands the flosses of this invention and presents distinct multipolymer, multifilament elements to the fraying surface. This can be distinguished from presenting the complete 800+ denier dental floss to said fraying surface. The net is the loaded activatable multipolymer, multifilament dental flosses of the present invention tend to resist fraying more effectively than commercial flosses, particularly when polyethylene or polypropylene polymers are included in the multipolymer, multifilament construction of the flosses of the present invention. Preferred dental flosses of the present invention with high resistance to fraying are the composite multifilament flosses, particularly those of sheath and core construction as shown in FIGS 1-3, 5, 1 1-20, 22 and 23 and side-by- side construction as illustrated in drawing FIGS 2, 6- 10 and 21.

A series of multipolymer, self- activatable, composite, multifilament fibers were spun from various polymer chips including: polyamides, polyesters, polyolefins and mixtures thereof. The resulting filaments were generally drawn to dental floss deniers, i.e. from between about 3 and about 6 dpf.

A synthetic fiber spinning operation similar to that illustrated and described in FIG 25 of the drawings was used. Certain features of the dental flosses constructed from these filaments were established including: dpf, self- activation, gentleness, loadability, approximate load release level for each floss sample. Various irregular cross-section filaments including trilobal were spun and evaluated as well.

These are noted under "Comments /Observations" in Table 3 below.

Table 4 below illustrates various high-tenacity, high-elongation, polypropylene, loaded dental flosses of the invention.

TABLE 3

TABLE 4

The present invention has been described in detail, including the preferred embodiments thereof. However, it will be appreciated that those skilled in the art, upon consideration of the present disclosure, may make modifications and /or improvements on this invention and still be within the scope and spirit of this invention as set forth in the following claims.

Claims

CLAIMS:

1. A loaded dental floss comprised of multifilaments, wherein said multifilaments are selected from the group consisting of high-tenacity, low MFI, high-elongation homopolymers and multipolymers, wherein during flossing said floss releases a portion of said load while exhibiting improved tenacity and resistance to shredding.

2. A dental floss according to Claim 1 , wherein said homopolymer is polypropylene.

3. A dental floss according to Claim 1 , wherein said load is selected from the group consisting of toothpaste and mouthrinse ingredients, chemotherapeutic ingredients, anti-plaque, anti-tartar and anti-gingivitis ingredients, coagulants, antimicrobials, antibiotics, healants and mixtures thereof.

4. A dental floss according to Claim 3, wherein said load is distributed substantially throughout the dental floss.

5. A dental floss according to Claim 3, wherein said load comprises from between about 10% by weight and about 100% by weight of the dental floss.

6. A dental floss according to Claim 4, wherein said load comprises from between about 10 mg/yd and about 100 mg/yd of the dental floss.

7. A dental floss according to Claim 1 , wherein said multipolymer is a synthetic polymer made from monomers by addition or condensation polymerization and is selected from the group consisting of high RV polyamides, polyesters, polyolefins, polyesteramides, polycaprolactones, polyureas, polyurethanes, polythioureas, polythioamides, polysulfonamides, polyimides, poly-4-amino- 1-2-4- triazoles, copolyesteramides, acrylonitrile s and mixtures thereof.

8. A dental floss according to Claim 7, wherein said multipolymer comprises a mixture of homologous polymers having different intrinsic viscosities.

9. A dental floss according to Claim 8, wherein said multipolymer comprises a combination of homologous polyolefins having different melt indices.

10. A dental floss according to Claim 8, wherein said multipolymer comprises a combination of different homopolyamides having high RV values.

11. A dental floss according to Claim 7, wherein said multipolymer comprises a combination of homopolyesters and homopolyester ethers.

12. A dental floss according to Claim 7, wherein said multipolymer is a combination of a homologous homopolymers and copolymers.

13. A dental floss according to Claim 7, wherein said multipolymer is a combination of different polymers.

14. A dental floss according to Claim 1 , wherein said multifilament dental floss is comprised of unitary filaments comprised of multipolymers having different melt viscosities and different physical properties, wherein said filament has uniform multipolymer composition substantially throughout.

15. A dental floss according to Claim 1 , wherein said multifilament dental floss is comprised of composite filaments, wherein each said multipolymer comprises a distinct component in the composite filament construction selected from the group consisting of bicomponent fibers, conjugate filaments, composite filaments, multicomponent fibers and combinations thereof.

16. A dental floss according to Claim 15, wherein said multipolymer filaments contain at least two polymers having different linear behavior properties suitable for self-supporting or self-crimping.

17. A dental floss according to Claim 1 , wherein said floss is self- activatable due to the differential linear behavior of said multipolymers.

18. A dental floss according to Claim 15, wherein said floss contains multifilaments selected from the group consisting of bilaminar and multilaminar filaments.

19. A dental floss according to Claim 1, wherein said multipolymer, multifilaments are comprised of bicomponent fibers selected from the group consisting of concentric sheath/core, side-by-side, sheath fibers with an eccentric core, islands-in-the-sea, cirrus and combinations thereof.

20. A dental floss according to Claim 1, wherein said dental floss filaments have a non-round cross-sectional configuration selected from the group of multi-gum surface contact constructions, consisting of ribbed, grooved, trilobal, quadralobal, pentalobal, hexalobal, heptalobal, octalobal, and combinations thereof.

21. A loaded multifilament dental floss with improved tenacity, resistance to shredding and gentleness, wherein said filaments are constructed to distribute the "flossing pressure" through multiple gum surface contact sites.

22. A multifilament dental floss according to Claim 21, wherein said filaments have a non-round cross-sectional configuration, selected from the group consisting of trilobal, quatralobal, pentalobal, hexalobal, heptalobal, octalobal, and combinations thereof.

23. A method of cleaning the interproximal and subgingival areas in the oral cavity comprising flossing said areas with a loaded dental floss comprised of multifilaments, said multifilaments being selected from the group consisting of high-tenacity, low MFI, high-elongation homopolymers or multipolymers, wherein during flossing said floss releases a portion of said load while exhibiting improved tenacity and resistance to shredding.

24. A method of manufacturing a loaded, shred resistant, gentle dental floss comprised of multifilaments, wherein said multifilaments are selected from the group consisting of high tenacity, low MFI, high elongation homopolymers and multipolymers, wherein said multifilaments are subjected to compression loading with various oral care substances suitable for release into the oral cavity.