Process of making monofilaments

Details Process of making monofilaments Process of making monofilaments

2001-11-29

2003-01-14

Tentoni, Leo B. (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

With severing, removing material from preform mechanically,...

Forming continuous work followed by cutting

C264S148000, C264S162000, C264S172120, C264S172130, C264S172140, C264S172150, C264S172170, C264S172180

Reexamination Certificate

active

06506327

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a monofilament with reduced secondary binding forces having 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 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 all types, e.g. personal hygiene and tooth-brushes, household brushes, industrial brushes, paint brushes, etc., are mainly produced from polymers, in that the polymer melt is extruded into 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 with a different cross-section are known, e.g. an oval or polygonal cross-section. The monofilaments are then extruded with a corresponding profile.
In many cases it is desirable to use bristles having a fibrous and preferably 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 inadequate cleaning action, because they do not penetrate into the fine cracks of the tooth surface and instead slide over 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 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 transverse 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, sliding zones, in which the secondary binding forces are reduced, occur between the molecular chains of the polymers during stretching. 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 peripheral surfaces. Although a larger bundle of such bristles is fleecy and of good absorbing structure, 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 (WO97/14830) 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 paint. In addition, flags can be obtained by unraveling the envelope material to the extent that it projects over the core. This unraveling takes place in a conventional manner by cutting with knives. The bristles obtained show the same irregular structure mentioned above.
Particularly for toothbrushes, bristles have already been proposed which comprise a plurality of such fibers, similar to textile fibers, and an envelope jacketing the fibers (DE 94 08 268 U1). The envelope and fibers can be coextruded as a filament. After cutting the bristle to 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 the transition between the fibers and 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 into deeper cavities, intendental spaces etc. In case of permanent stressing, the fibers also easily break off at the edge of the envelope.
WO96/39117 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 (U.S. Pat. No. 3,117,362) are produced having glossy, sharp-cornered structures by co-extruding various polymers, each of which has a suitable cross sectional shape, which bond to each other at their bordering surfaces and which are separated through introduction of a solvent which dissolves one of the polymers.
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 dimension. The invention is directed to a method for the production of bristles or interdental cleaners from such monofilaments.
SUMMARY OF THE INVENTION
A monofilament solving this problem is characterized in accordance with the invention in that the border surfaces are border layers having reduced secondary binding forces, wherein the monofilament comprises a matrix of polymers whose physical and chemical properties define the properties of the bristle or interdental cleaner. A second polymer is imbedded as a thin layer into the matrix.
As a result of the geometry of the boundary layers 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 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 boundary layers extend in the longitudinal direction of the monofilament, each flag has a constant shape and cross-section along its entire length. Thus, the flags have the same strength characteristics, in particular, identical bending behavior and identical tensile strength. By appropriately defining the geometry, flags can also be produced with different cross-sections. Since the monofilament or bristle, under the action of mechanical forces, splits exclusively and precisely at the boundary layers, the flags can have edges at their facing surfaces in dependence on the thin layer array to assist the cleaning action. A bristle split in this way is consequently more effective at its peripheral surface than conventional spreading of the bristle flags. The congruent shapes prevent excessive spreading of the bristles. In a densely packed bundle, each bristle once more acquires a monofilament-like shape and the full effect of the flags only results from the axial or radial pressure. Media can thereby be well absorbed and delivered on application by pressure action.
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