AU749645B2 - Monofil for and for producing bristles or interdental cleaning elements, bristle products with bristles of this type and interdental cleaning elements - Google Patents

Description

17256.5 PCT/EP98/06954 Translation of Application as amended on December 31, 1999 MONOFILAMENT AND METHOD FOR PRODUCING BRISTLES AND INTERDENTAL CLEANERS AND BRISTLES AND INTERDENTAL CLEANERS MADE FROM SUCH MONOFILAMENTS The invention relates to a monofilament with reduced secondary binding forces of at least two polymers commonly extruded in regular geometric relationship with substantially axially extending border surfaces for producing bristles or interdental cleaners, which are substantially axially slittable by the action of mechanical forces. The invention also relates to a method for producing bristles or interdental cleaners from such monofilaments as well as to brush-ware with such bristles and to interdental cleaners.

Bristles for brushware of random types, e.g. personal hygiene and tooth-brushes, household brushes, industrial brushes, paint brushes, etc., are nowadays mainly produced from polymers, in that the polymer melt is extruded to continuous monofilaments, the monofilaments are stretched and optionally stabilized. The bristles are then produced from such monofilaments by cutting to the desired length. As a rule, the monofilaments, like the bristles, have a circular cylindrical cross-section. For special applications bristles tUh a different cross-section are known, e.g. an oval or ~iffiP~d~~"~i~Eisn~i~;V~L~ 2 polygonal cross-section. The monofilaments is then extruded with a corresponding profile.

In many cases it is desirable to use bristles in a fibrous, particularly fine fibrous structure at the use end. This e.g.

applies for brushware intended for the application of media to surfaces or the like, e.g. paint brushes. Even if a fleecy structure is sought, the bristle must be of a fine fibrous nature. Of late in the dental sector it has been found that conventional bristles of toothbrushes have an inadequate cleaning action, because they do not penetrate the fine cracks of the tooth surface and instead slide over the same.

Much the same applies for the cleaning action in the interdental space.

In order to obtain a highly fibrous structure, proposals have already been made for extruding the monofilament from polymer blends. During the extrusion and subsequent stretching of the monofilament, the polymer molecules are oriented in the longitudinal direction of the monofilament. The primary binding forces acting in the longitudinal direction ensure a high tensile strength. The longitudinal orientation of the molecules also effects the desired flexural elasticity. In monofilaments made from a single polymer, the so-called secondary binding forces, namely the forces transversely to the molecular extension, are adequate in order to prevent a unraveling or cleaving of the monofilament or bristle. In the case of monofilaments from two different, blended polymers, 6Teen the molecular chains of the polymers during w stretching sliding zones occur, in which the secondary binding forces are reduced. Such a monofilament or a bristle produced therefrom can be unraveled by the action of mechanical forces using knife-like tools. The resulting flags have a very irregular shape, irregular cross-sections and frayed circumferential surfaces. In a larger bundle of such bristles admittedly a fleecy and good absorbing structure is obtained, but the flags have uncontrolled strength characteristics. They tear out, break off or wrap round. Such unraveled bristles are consequently unsatisfactory and are even unusable for many applications. For hygienic reasons their use in toothbrushes is risky.

The same disadvantages are encountered in a known bristle structure (W097/14830) which has a core and an envelope, which are produced by the coextrusion of two different polymers. The core material is mechanically or chemically removed at the use-side end of the bristle in order to form a deep pocket, which is intended to receive a dentifrice or 0 paint. In addition, a discription is given of flags which are obtained by the unraveling of the envelope material to the extent that it projects over the core. This unraveling takes place in conventional manner by cutting with knives. The bristles obtained show the same irregular structure.

Particularly for toothbrushes, bristles have already been proposed which comprise a plurality of this fibers, similar textile fibers, and an envelope enveloping the fibers (DE 08 268 Ul). The envelope and fibers can be coextruded as a filament. After cutting to the bristle length, the envelope is removed at the use-side end of the bristle by mechanical working or cutting, so that the fibers are free over a short length. Quite apart from the complicated production of such bristles, they can only be used to a limited extent. It is particularly disadvantageous that there is a sudden change in the bending behavior at transition from the fibers to the envelope. If such bristles are used in applicators, there can be damage to the surface due to the hard transition. The same applies when such bristles are used in toothbrushes in connection with the action on the teeth and gums. In addition, the fibers are bending-limp, so that they do not or do not adequately penetrate deeper cavities, intendental spaces etc. In the case of permanent stressing, the fibers also easily break off at the edge of the envelope.

W096/39117 discloses an intendental cleaner made from monofilaments which are co-extruded in defined geometric relationship. Each monofilament comprises at least two polymer components leading to reduced secondary binding forces at the borders between neighboring monofilaments. The secondary forces are reduced through the action of axial tensile forces to produce a multi-fibered fleecy structure similar to that of dental floss.

Conventional textile fibers (US-A-3117362) are produced having glossy, sharp-cornered structures by co-extruding various polymers, each of which has a suitable cross ectional shape, which bond to each other at their bordering '~7L ~L7 surfaces and which are separated through introduction of a solvent which dissolves one of the polymers.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed in Australia before the priority date of each claim of this application.

The problem of the invention is to propose a monofilament of at least two commonly extruded polymers, which is suitable for producing slitted bristles or interdental cleaners with reproducible strength characteristics and flags or slits which are definable according to number, shape and dimensioning. The invention is also directed at a method for the production of bristles or interdental cleaners from such monofilaments.

The present invention provides monofilament with reduced secondary binding forces, the monofilament being for the production of bristles or interdental cleaners and comprising at least two polymers commonly extruded in regular geometric configuration having bordering surfaces extending :substantially in an axial direction, the monofilament being capable of being 20 substantially axially slit by the action of mechanical forces, characterised in that oo° the monofilament comprises at least one polymer in the form of a matrix capable of determining the physical and chemical characteristics of a bristle or interdental cleaner respectively and at least one other polymer in the form of at °o least one layer incorporated in the matrix, the at least one layer having reduced secondary binding forces relative to the secondary binding forces of the polymer matrix.

Preferably, the layer or layers formed are thin relative to the polymer S"matrix.

Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

As a result of the geometry of the polymer configuration it is possible to forecast in what way the monofilament for example for an interdental cleaner or the bristle produced from the monofilament by cutting to length will be p~ r r nM disintegrated or split by the action of mechanical forces. The slits or flags occur precisely with the predetermined contour given by the extrudate geometry. As the bordering surfaces extend in the longitudinal direction of the monofilament, over their entire length a single flag has the same shape and same crosssection. Thus, all the flags have the same strength characteristics, in particular an identical bending behaviour and identical tensile strength. However, it is possible by appropriately defining the geometry to produce flags with different cross-sections. As the monofilament or bristle, under the action of mechanical forces, exclusively and precisely splits at the polymer layer having reduced secondary binding forces, the flags form edges on the facing surfaces depending on the cross-section which assist the cleaning action. A bristle split in this way is consequently more effective at its circumferential surface than conventional spreading of the bristle flags. The congruent shapes prevent excessive spreading of the bristles. Each bristle acquires in a densely packed bundle a monofilament-like shape again and the full effect of the flags only results from the axial or radial pressure. Thus, media can be well absorbed ~.and delivered on application by pressure action.

This makes it possible to produce bristles, whose flags have the desired :characteristics of conventional bristles. During splitting no or few fine parts are formed, so that there is no need for an extensive cleaning of the bristle.

Definitely flagged and definitely slit monofilaments for interdental cleaners are obtained, with which the proceeding of splitting or slitting can be avoided.

rftrft~tftfryf~rfftftr..tftft .ftf~fl ft. f The polymer of the matrix as well as of the thin layers can also be a copolymer or a polymer blend. These aforementioned advantages are achieved in a particularly optimum form if the thin layers comprise at least partly the polymer of the matrix. In this case the polymer or the bristle tears at the weakest point when force is exerted, namely roughly in the center of the thin layers, but the adhesiveness of the part of the matrix polymer in the thin layer at the resulting, neighboring flags is adequate to avoid the formation of fine parts.

Preferably the thin layers have a thickness of a few pm.

Practical extrusion tests have revealed that such thin layers can be coextruded with the polymer of the matrix.

The two polymers can be present in roughly equal parts in the thin layers.

The specific definition of the geometry is determined by the desired characteristics of the bristle and interdental cleaner. Thus, the thin layers in the matrix can extend to the circumference of the monofilament, so that the monofilament can be split or slit with a relatively limited force action.

It is possible instead of this for the thin layers to terminate in the matrix at the distance from the monofilament circumference. In this case a somewhat greater force action is required, but it is advantageous that the resulting flags, also in the edge region, comprise the matrix material, i.e.

have the same wear characteristics as the envelope of the bristle or the flags.

Optionally the monofilament matrix can have a third polymer incorporated into said matrix and which is mainly used for influencing the strength characteristics of the resulting flags.

As is normally the case with bristles, the monofilament can be circular, but can also have a non-circular cross-section.

Particular mention is made of polygonal cross-sections, which are more effective in their cleaning action than circular cross-sections.

In this case the thin layers can run out to the corners of the polygonal cross-section, so as to give relatively sharp edges with an edge angle smaller than 900 Instead the thin layers can also run out to the surfaces of the polygonal cross-section and it is then possible to obtain edges with an angle of approximately 90 0 According to a preferred development the matrix comprises a polyamide and the thin layers a polyolefine, particularly polypropylene or polyethylene. This material pairing has at the interfaces adequately high secondary binding forces in der to prevent an untimely tearing or unraveling during the processing and use of the bristles. However, the polymer union tears in the case of a strong, planned force action.

The method according to the invention for producing bristles from the aforementioned monofilament comprises the following steps: coextruding the at least two polymers to a monofilament, stretching and optionally stabilizing the monofilament, cutting the monofilament to bristles of the desired length, splitting the bristles at their use ends along the boundary layers on a limited length by the action of mechanical forces transversely to the axis of the bristle.

Another method suitable for producing bristles as well as interdental cleaners from the aforementioned monofilament comprises the following steps: coextruding the at least two polymers to a monofilament, slitting, following extrusion, stretching and optically stabilizing, the monofilament along the boundary layers on a locally limited length for forming short slits by the action of mechanical forces transversely to the axis of the monofilament. With the method in accordance with the invention, crack-like slits can be formed in the monofilament envelope and these can be used for receiving media. In the case of toothbrushes or interdental cleaners these are more particularly dentifrices or dental or antibacterial preparations. As a result of the slitting action, the monofilaments envelope has an increased roughness.

Interdental cleaners of arbitrary length can be manufactured from the monofilament described above. The same measure can r -,~n-nrrr;ixrrrii~r,~,.~-rr. I- I~L~IIV W~II~YUF~i3~s~ naturally be carried out on the bristle cut to length from the monofilament. The location of slitting and the extension of the slits can be matched to the bristle length, in order to either prevent or encourage in planned manner a split ting of the bristle end. For example, only the bristle end may be split. The slits made on the envelope can be used for the further splitting of the bristle following the wearing away of the flags. As a function of the nature and number of incorporated layers, a corresponding number of flags is formed at the use end of the bristle.

For processing monofilaments into interdental cleaners of arbitrary length, a variation of the method provides for compressing the monofilament in its axial direction during or after the action of the mechanical forces. Thereby the lengthwise slitted areas and the strips limiting the slits respectively are rendered bulged.

The mechanical forces are preferably applied to a greater part of the circumference of the monofilament or bristle to ensure that an action takes place on all the boundary layers of the polymers.

The slitting of the monofilament or the splitting of the bristles preferably takes place by impact forces. Instead of this, it is also possible to use squeezing or torsional forces. These forces can be applied to the cut to length bristle or also simultaneously to groups of bristles, e.g.

bristle bundles, before or after the fixing thereof to the bristle carrier of the brush.

Preferably the bristles are rounded at their use-side ends.

This can take place before and/or after splitting. In accordance with a further preferred embodiment of the method, the several ends obtained after splitting are provided with a marking optically indicating the usable length. This indicates to the user that the bristle has become worn up to the marking, i.e. following the wearing of the split ends the use characteristics suddenly change, because then the much more bending-stiff cross-section of the complete bristle comes into action. The split ends also become ever shorter and consequently mechanically more aggressive. Such an indication is particularly appropriate in the case of toothbrushes, personal hygiene brushes, etc.

The invention is described in greater detail hereinafter relative to embodiments and the attached drawings, wherein show: Figs. 1 to 5 Different cross-sections of a monofilament.

Fig. 6 A view of a bristle with a split, use-side end.

Fig. 7 A bristle or interdental cleaner with a slit envelope.

Fig. 8 A further form of the cross-section of a monofilament.

Fig. 9 A view of an interdental cleaner in an alternative form.

The monofilament 1 according to fig. 1 has a circular crosssection and is produced by coextrusion of at least two polymers. It comprises a matrix 2 of a polymer determining the characteristics of the bristle and thin layers 3 incorporated in a geometrical shape, in this case in the shape of a cross and which comprise a different polymer or a blend thereof with the polymer of matrix 2. The secondary binding forces, i.e. binding forces at right angles to the longitudinal extension of the monofilament, are reduced in the regions of the thin layers 3 or the borders of the matrix 2. In the represented embodiment the thin layers 3 run out at the circumferential surface 4 of the monofilament, but can also terminate at a short distance therefrom.

The polymer for matrix 2 can in particular be polyamide (PA), whereas the thin layers 3 e. g. comprise a PA/PP of PA/PE polymer blend.

In the embodiment according to fig. 2 the thin layers 3 are incorporated in the form of a three-armed star into the matrix 2, whilst fig. 3 shows a monofilament 1 with a polygonal, namely triangular cross-section. In this odiment the incorporating thin layers, which extend outwards from the center here, run out in the corners of the polygon. They can a naturally also terminate on the surfaces between the corners.

In the embodiment according to fig. 4 with matrix 2 of the monofilament 1 is extruded a further polymer from among the several possible polymers in such a way that it is fully incorporated into the matrix. For example, these can be thread-like structures 5, which following the production of the bristle or the splitting or slitting thereof influence the bending behavior or strength of the resulting flags.

Fig. 5 shows a flat, rectangular monofilament 1, in which the thin layers 3 are applied in grid or raster-like manner, so that from the monofilament can be produced a plurality of substantially rectangular flags. Finally, figure 8 illustrates a cross section through a monofilament with which the matrix 2 comprises four equal outer portions having circular segment cross sections and a central core which are bordered by correspondingly disposed thin layers 3.

Fig. 6 diagrammatically shows a bristle 6, produced by cutting a monofilament e.g. of fig. 2 to length, which is split on its use-side end by the action of mechanical forces, so that individual flags 7 are obtained, whose shape corresponds to that of the monofilament areas forming the matrix 2. The same number of flags are formed as the matrix 2 &s divided up by thin layers 3. The usable length of the flags can be optically marked by a transverse line shown in Fig. 6.

In the embodiment of fig. 7, the mechanical forces are applied to the circumferential surface of a monofilament with identical spacings or to a bristles at a distance from the use-side end. Through the thickness of the layers and the magnitude of the force and/or the frequency of its application, it is possible to ensure that the envelope of the monofilament or the bristle 6 only tears over a locally limited length and that slits 8, 9 and 10 are formed. These slits are roughly in a row, namely in the areas formed by the thin layers 3. In this variant the slits tear at the bristle end, accompanied by the formation of flags. The flags constantly re-form as the bristle wear increases.

The monofilament according to fig. 7 can be used with a random length as interdental cleaner (dental floss). The slits can receive dentifrice, antiseptics or antibacterizides. In the case of a interdental cleaner it is recommendable to axially upset the monofilament as shown in fig. 9 so that the matrix strips 10 delimiting the slits 9 are bulged outwardly.

With all the embodiments specified the matrix polymer can be dyed with different colors in the various cross-section parts 2 delimited by the thin layers 3.

Claims (29)

1. Monofilament with reduced secondary binding forces, the monofilament being for the production of bristles or interdental cleaners and comprising at least two polymers commonly extruded in regular geometric configuration having bordering surfaces extending substantially in an axial direction, the monofilament being capable of being substantially axially slit by the action of mechanical forces, characterised in that the monofilament comprises at least one polymer in the form of a matrix capable of determining the physical and chemical characteristics of a bristle or interdental cleaner respectively and at least one other polymer in the form of at least one layer incorporated in the matrix, the at least one layer having reduced secondary binding forces relative to the secondary binding forces of the polymer matrix.

2. Monofilament according to claim 1, characterised in that the matrix comprises a copolymer or a polymer blend.

3. Monofilament according to claim 1 or 2, characterised in that the layer(s) incorporated in the matrix comprise(s) a copolymer or a polymer blend.

4. Monofilament according to claim 1 or 2, characterised in that the polymer of the layer(s) comprise(s) a portion of the polymer in the matrix.

5. Monofilament according to claim 4, characterised in that the two 20 polymers are present in roughly equal parts in the layer(s). i

6. Monofilament according to claim 1 or 3, characterised in that the layer(s) have a thickness of a few pm.

7. Monofilament according to claim 1 or 3, characterised in that the layer(s) in the matrix extend up to the circumference of the monofilament.

8. Monofilament according to claim 1 or 3, characterised in that the layer(s) in the matrix terminate at a distance from the monofilament circumference.

9. Monofilament according to claim 1, characterised in that the monofilament matrix has a third polymer incorporated into said matrix.

10. Monofilament according to claim 1 or 3, characterised in that the polymer of the matrix and that of the layer(s) have different colours.

11. Monofilament according to claim 1, characterised in that the monofilament has a cross-section diverging from the circular shape.

12. Monofilament according to claim 11, characterised in that the monofilament has a polygonal cross-section.

13. Monofilament according to claim 12, characterised in that the layers run ,,out to the corners of the polygonal cross-section. A0Z

14. Monofilament according to claim 12, characterised in that the layers run out to the surfaces of the polygonal cross-section.

Monofilament according to claim 1 or 3, characterised in that the matrix comprises a polyamide and the layers a polyolefine.

16. Method for producing bristles from monofilaments according to any one of the claims 1 to 15, characterised in that the at least two polymers are coextruded into the monofilament, the monofilament is stretched, optionally stabilised and is cut to bristles of a desired length, the bristles are split at their use ends along the layer(s) through a limited length by the action of mechanical forces transverse to the axis of the bristle.

17. Method for producing bristles or interdental cleaners from monofilaments according to any one of the claims 1 to 15, characterised in that the at least two polymers are coextruded to a monofilament, said monofilament is stretched and optionally stabilised and is slit along the layer(s) through a locally limited length for forming short slits, under the action of mechanical forces transverse to the axis of the monfilament.

:18. Method according to claim 17, characterised in that the monofilament is compressed in its axial direction during or after the action of the mechanical forces. 20

19. Method according to claim 16 or 17, characterised in that the mechanical forces act on a greater part of the circumference of the monofilament or bristle.

Method according to claim 16 or 17, characterised in that the monofilament or bristle is split or slit by impact forces.

21. Method according to claim 16 or 17, characterised in that the 25 monofilament or bristle is split or slit by squeezing forces.

22. Method according to claim 16 or 17, characterised in that the monofilament or bristle is split or slit by torsional forces.

23. Method according to claim 16 or 17, characterised in that, prior to splitting, the use-side end of the bristle is rounded.

24. Method according to claim 16 or 17, characterised in that, after splitting, the use-side end of the bristle is rounded.

Method according to claim 16 or 17, characterised in that the several flags of the bristle resulting from splitting are provided at a distance from their ends with a marking optically indicating the useable length.

26. Brushware, comprising a bristle carrier and bristles fixed thereto, wherein at least a part of the bristles are produced from a monofilament according to M Y- Q 17 any one of the claims 1 to 15 by a method according to any one of the claims 16 to

27. Brushware according to claim 26, characterised in that the several ends of the split bristles have a marking indicating their useable length.

28. Brushware in the form of a interdental cleaner, produced from a monofilament according to any one of the claims 1 to 17 by a method according to claim 19 or 20, characterised in that the interdental cleaner is slit at equal distances about its circumference.

29. Brushware according to claim 28, characterised in that the interdental cleaner is bulged in the area of the slits. Monofilament according to claim 1 as hereinbefore defined with reference to the drawings. Dated this tenth day of April 2002 Pedex Co. GmbH Patent Attorneys for the Applicant: F B RICE CO r.Nw~v~