HK1078525A - Method and device of the production of brushes - Google Patents

Description

Method and device for producing bristles

Technical Field

The invention relates to a method for producing bristles from thermoplastic polymers by means of injection molding, wherein a polymer solution is injected under pressure into bristle-forming channels having a defined length and a defined cross-sectional shape over said length, the channels being vented during the injection molding process. The invention also relates to a device for carrying out said method.

Background

Animal hair or natural fibers previously used as bristle material in the production of brushes, etc. are largely replaced by artificial bristles, wherein the production of bristle material goes back completely to the production of synthetic textile fibers which have been practiced previously, i.e. to the extrusion or spinning process. However, bristles are subject to requirements that are quite different from the infinite fibers in the composite fibers. It stands freely, is fixed only at one end, and can be regarded as a single-end clamped bending beam in terms of strength theory. In use, are subjected to compressive or upsetting forces and sometimes also tensile forces. This results in different processing requirements in the direction of bending strength, alternating bending strength, flexural strength and ability to re-erect (bend-recovery) compared to infinite fibers.

The filaments for the bristles are thus extruded with a large diameter of up to a few millimeters. The shaping by means of the extrusion or spinning nozzle achieves a certain longitudinal orientation of the molecules in the polymer melt, which is, however, not sufficient to impart the desired properties to the individual fibers, so that the individual fibers are drawn, i.e., stretched under the action of a corresponding tensile force. A pre-stretching, a subsequent stretching and subsequent, in some cases repeated, heat-setting is usually required here. The endless filament is then wound up and in some cases the wound-up article is set again.

If the endless filaments are not directly handled by the reel in the brush manufacture-which has been the exception so far-a large number of filaments are combined, tied up into strands and cut to an operable length of between 60 and 120cm in staple length. The strip material is cut into short sections, the length of which is slightly longer than that of the final bristles. About 30% of the raw material becomes waste. In the case of valuable plastic bristles, such as polyamides (nylons), which are necessary for example for high-quality brushes, such as toothbrushes, sanitary brushes, etc., the price of the raw material is the largest cost factor for the bristle price. The price of the extruded bristles is heavily loaded by the high waste.

The bristles are then fixed to the bristle carrier after the bristles have been manufactured in the brush manufacture. This can be done mechanically or thermally. Because of the large fluctuations in the overhanging length of the bristles in this intermediate stage, trimming is then carried out, and in most cases trimming of the bristles, in particular of the bristle tips, is carried out in order to remove sharp cutting edges. If the effective brush surface constituted by the free ends has to meet special requirements, for example for a toothbrush, the flat brush surface has to be given a concave-convex profile at the time of fixation or after it. About 10% of the waste material is also formed.

In view of the fact that about 90% of the worldwide bristle requirements are limited to bristle lengths of less than 10cm, the production of infinitely long single fibers by spinning together with all subsequent processes up to the finished bristles is also uneconomical only due to the very large degree of raw material waste. Other limitations arise from the fact that single fibers can generally only be manufactured in a cylindrical shape, even if a concave-convex profile is formed in the cross-section, and thus the structural shape of the bristles is limited. In some cases, a complicated finishing process is required.

On the other hand, in the brush and brush industry, injection molding has long been used for the production of brush bodies, brush holders, etc. from plastic, in order to utilize the various shaping possibilities of the injection molding process. As a result, it was possible to avoid the test of integrating the brush body and the brush bristles by injection molding. These methods are only used practically for brushes with low quality and firmness requirements, in particular such brushes that are used only once, or only a few times. The injection molded bristles have non-uniform poor bending strength, alternating bending strength and flexural strength, defective re-erectability and small abrasion resistance. Injection moulded brushes have bristles with a high taper due to the process, and a larger cross-section at the base of the bristle and are therefore better suited to be referred to as pins or rods rather than bristles. Some known methods in the art of brush manufacture are described below.

Industrial rotary brushes for grinding and polishing surfaces are built up from a combination of disc-shaped segment brushes, each of which can be manufactured by injection moulding (US 5,903,951). Each segment has a central base disk from which bristles extend radially or at an angle inclined outwardly relative to the radial counter-rotational direction. The brush block is composed of a thermoplastic or thermoelastic polymer (TP or TPE) filled with abrasive particles. These bristles should in particular have a length of between 1cm and 5cm and a diameter of between 0.25mm and 10mm, in particular between 1mm and 2mm, in a particular embodiment the conical bristles have a length of 75mm and a diameter of 2mm at the root and 1.5mm at the tip. The two-part injection mold consists of two plates which have cavities for the base plate and the bristles on the sides facing each other and simultaneously forming the parting plane. The polymer melt with the incorporated abrasive particles is injected from the center of the matrix disc with an injection pressure of 690 to 6900kPa (0.59 to 69 bar). A preferred pressure range is 2070 to 4830 kPa. The necessary forced venting of the cavity takes place at the parting plane, i.e. parallel to the bristles. This entails the creation of two parting lines on the bristle envelope surface, which extend from the root to the tip and beyond the tip. Since the abrasive particles narrow the small cross-section of the bristle cavity and the polymer melt hardens rapidly in this region without filling the bristle cavity, a two-stage injection molding method is proposed in which a large amount of the abrasive particle-filled polymer melt is first injected into the bristle cavity, and subsequently a smaller or no abrasive particle-filled polymer melt is injected. The person skilled in the art knows that virtually no molecular orientation within the polymer occurs during the injection molding process (US2001/0007161, a1, see paragraph 6, line 1). This results in a very insufficient bending performance for the bristles, which becomes worse due to the incorporation of abrasive particles. The specified maximum injection pressure of 6900kPa (69bar) decays sharply due to the flow resistance in the narrow cavity used to form the base plate and in the connected bristle channel, so that there is an educated set for the practitioner on the practical feasibility of this approach.

US3,618,154 describes the manufacture of a toothbrush in a single injection moulding process in which the bristles on the head are injection moulded in a tuft-like configuration. For this purpose, the two-part injection mold, whose parting plane is in the plane of the toothbrush head, has substantially cylindrical bores which start from the profile which forms the bristle side of the toothbrush head. A substantially cylindrical core is inserted into the holes from the opposite side, the end face of the core forming part of the profile for the bristle carrier side of the toothbrush head and having groove-shaped grooves running from this face and distributed along a generatrix. The groove-shaped recesses taper uniformly from the profile on the end face side to the other end and end in hemispherical ball segments on the core shell face, the recesses being arranged uniformly distributed on the core. Each groove forms, together with the wall of the hole in a part of the injection mould, a channel forming the bristle, so that it tapers from the cavity of the toothbrush head to the other end. The venting of the channel takes place over its entire length at the interface between the core and the bore, i.e. essentially parallel to the bristles. For this reason US3,618,154 requires a high precision of the co-acting surfaces. Here too, each bristle has to have two partial molding slits which run along the generatrices of the bristles. Circular cross-section bristles cannot be produced here either because the groove-shaped recess in the core has a much larger radius of curvature than the bore. This results in a cross section with discontinuities, which at the interruption points simultaneously form the die lines and which cannot be removed later. Furthermore, the bristles have different bending properties in different directions perpendicular to their axes. It also results in bristle tufts which are not solid, in particular hollow in their center, and therefore cannot bear against one another, as are conventional bristle tufts. The important drawing problem of individual bristles should on the one hand be solved by the corresponding conicity of the grooves forming the bristles. This is clearly insufficient, since the core simultaneously also serves as an ejector pin, which pushes the bristle tips through the segment-shaped ends of the groove-shaped recesses during demolding. The taper may provide a softer bristle end when the toothbrush is in use. This document also does not describe measures which, beyond the usual injection molding techniques, lead to an improvement in the flexural properties of the molded bristles, so that the polymer molecules are present here in a random form which is customary in injection molding and which is advantageous for energy saving but disadvantageous for robustness (US2001/0007161a 1).

Furthermore, it is known (US 5,158,342) to subsequently injection mold bristle groups in a prepared recess in a toothbrush head on a prefabricated brush body consisting of a handle and a toothbrush head during the manufacture of toothbrushes. Since the usual injection molding process has an injection pressure of 30 to 60bar (3000 to 6000kPa), this results in bristles having very insufficient bending properties.

GB 2151971 also describes a two-stage method of making bristle sets and bristle carriers. In this document, in particular, the problem of the bristles being released from the channel in which they are formed can be seen. In addition to the large taper of the bristles, which facilitates demolding, a considerable delay and a controlled delay for demolding are additionally planned, which reduces the power of the injection molding device. No technological measures are described to improve the firmness of the bristles.

Much better results are achieved according to an old, unpublished patent application by the inventor (PCT/EP01/07439) in which bristle carriers are provided with holes which have a cross-sectional profile in the form of a nozzle. The molten polymer for the bristles is injected through nozzle-shaped openings into shaping channels of an injection mold, which are connected to the openings, in such a way that a semi-finished product consisting of the bristle carrier and the bristles is produced, or-when the bristle carrier is appropriately shaped-a finished brush is produced, in which the bristles exhibit values in terms of their flexural properties which are as good as those of extruded bristles, but the shaping of the bristles does not meet the mandatory requirements for the production of extruded endless filaments.

It is also known (US 4,712,936) to produce, for example, small applicator brushes for decorations, which are immersed in a container and fixed to the closure cap of this container, as one-piece injection-molded parts consisting of a cap, a handle centrally mounted on the inside thereof and brush bristles arranged at the ends thereof. The cavities for the cover, the central shank and the associated channels forming the bristles are made axially aligned in two part-moulds of the injection mould, the openings of the cover being located in the part-mould planes. The handle and bristles are produced by a core inserted concentrically. The injection surface is located on the cover. The polymer melt must therefore traverse long flow paths with a large number of cross-sectional changes and large material requirements before it reaches the thin bristle channel. The entire degassing of the handle and bristle field takes place at the end of the bristle channel by means of a cylindrical closure plug with a knurled structure, which is intended to form a filter with a high flow resistance. It can be seen in this prior art that bristles which can be produced by injection moulding are particularly unsuitable for use as brushes. They are therefore reheated after demolding outside the injection mold and subsequently drawn. This involves, in particular, a reduction in the cross-section, which has to lead to an increase in the distance between the bristles. However, with this type of application brush, the bristles should be arranged as closely spaced as possible in order to create a capillary action between the bristles for storing and retaining the application medium.

Furthermore, attempts have been made (DE2155888C3) to produce brushes with bristles produced thereon by injection molding, in which the injection mold consists of a first part mold for the bristle support and a second part mold which completely covers the open cavity and in which a short channel is formed which widens at its other end and closes there. During injection, the polymer solution is forced out of the carrier cavity into the short channel and into the enlarged region, so that a stub with a head is formed. When the mold is opened, the head is lifted and the columnar bristle blank is stretched. Thus, as in the production of endless filaments, a certain molecular orientation is carried out, which leads to increased stability.

Tests in which bristles are produced from extruded endless filaments and are fixed on separately manufactured brush bodies instead of injection-moulding complete brushes with bristles have to be regarded as rational (US2001/0007161A 1).

This also applies to the known proposals, only the bristles being produced by injection molding (US3,256,545). The starting point of this newly developed prior art is that the finishing of the extruded bristles by the bristle ends is very good, although at the same time the taper of the bristles obtained by injection molding of the integral brush, which is necessary because of the injection molding process, is very goodA flexible tip. But this comes at the expense of wear resistance. The wear resistance, which is increasingly lower towards the ends in the proposed method, can be increased by the fact that the cross section of the injection-molded bristles becomes increasingly thicker from the fixed side ends (bristle roots) forming the injection end towards the free end. The cross-sectional profile may be continuous or discontinuous, with the result that the bristles present a greater amount of plastic in the region of the working end than at the fixed end. I.e. the insufficient performance of known tapered bristles is compensated by the greater amount of plastic gathering in the region of the bristle ends. However, it was determined that, with increasing amounts of plastic or cross-section, the structural components of the bristle structure which are advantageous for energy saving are also increased, i.e. the bristle loses its bending elasticity to a greater extent due to the increased cross-section. The injection pressures recommended in this injection molding process are between 800 and 1200bar (approximately 0.8-10 bar)⁵To 1.2.10⁵kPa) and therefore this is necessary in order to enable the polymer melt to pass through the initially narrow channel of the injection end until the enlarged channel is filled. Unoriented molecular structure is sought despite the higher pressure ratios at the newly recommended bristle diameters in the finer range between 1.6 and 2.2mm and in the coarser cross-sectional range between 11 and 12mm (column 5, lines 43 to 48 and column 6, lines 32 to 42). In order to fasten the molded bristles to the bristle carrier, a support structure consisting of the same polymer melt is formed at the injection end of the bristles, which in some cases connect a plurality of bristles to one another.

Finally, it is known from the technical literature (Ehrenstein: the inherent strengthening of thermoplastics during melt shaping, journal of Germany, applied Polymer chemistry 175 (1990), pages 187 to 203), the modulus of elasticity [ N/mm ] by extrusion and injection moulding processes²]And tensile strength [ N/mm ]²]The theoretical mechanical values of (A) are only 3% or 6% for polyamides and 33% or 5.5% for polyethylene, wherein the stress-free state (disordered structure of molecules) is preferred in injection-molded parts.

Disclosure of Invention

The object of the invention is to produce bristles by injection molding, which have flexural properties and a repeated erection capability which exceed those of extruded bristles, and which can be used to extract the theoretical values of modulus of elasticity and tensile strength as far as possible, and which can produce high-quality bristles having a relatively small cross-section over a large length range, in order to be able to produce bristle geometries and bristle arrangements in a simple manner and in a manner which is adapted to the requirements of the finished product, such as a brush or a hairbrush. It is an object of the invention to propose a device suitable for carrying out the method.

Starting from a known injection molding method in which a molten polymer is injected under pressure into a bristle-forming channel of a predetermined length and having a predetermined cross-sectional profile over this length, the channel is vented during the injection molding process, the object being achieved by adjusting the injection pressure as a function of the cross-sectional profile of the bristle-forming channel in such a way that, due to wall friction of the molten polymer, shear flows having a high core velocity in the center of the flowing molten polymer and large shear effects are generated at least in the region of the wall of the molten polymer and are maintained over the channel length in the case of a pronounced longitudinal orientation of the polymer molecules, wherein the channel is simultaneously vented over its length in such a way that the maintenance of the shear flows is supported.

The invention proceeds from the recognition that the bending behavior of the individual fibers can be improved above all by producing and maintaining the molecular orientation, which has not been achieved hitherto in the injection molding of bristles, brushes and brushes. It is clear that the molecular structure in a flowing polymer melt can be controlled only in a sufficiently narrow cross section and only by forcing the melt flow to generate a velocity profile with a high shearing effect in order to modify and stretch the energy-saving, stress-free scattering structure. The injection pressure is therefore selected according to the invention to be so high that a steep flow profile is formed in the bristle-forming channel, which is characterized by a high core speed in the center of the flow due to the frictional action of the polymer melt on the channel walls and a high shearing effect in the edge regions of the flow, the greater the difference in speed due to the wall friction against the adjacent flow layers, the greater the shearing force. Secondly, such a flow profile with a high core velocity ensures an indiscriminate filling of the bristle-forming channel even at the narrowest channel cross-section (small bristle diameter) and at large channel lengths (bristle length).

The velocity profile can be adjusted by a relatively high, in some cases variable, injection pressure, according to a defined cross-sectional profile over the bristle-forming channel length. This achieves a longitudinal orientation of the polymer molecules in the vicinity of the channel walls and a gradual weakening within the entire melt flow, wherein, moreover, the high core speed prevents premature hardening of the melt at small cross-sections and large lengths. But only high pressures are still not sufficient to quickly fill narrow forming channels. The channel is thus evacuated over its length in such a way that a shear flow with a high flow velocity is supported up to the end of the channel, so that the desired molecular longitudinal orientation up to the bristle tips is achieved.

Practical tests have shown that the injection pressure, depending on the cross-sectional profile of the bristle forming channel, should be at least 500bar (0.5X 10)⁵kPa). For the advanced bristles described here, with an average bristle diameter of, for example, 0.3 (measured at half the length), i.e. a bristle-forming channel with a corresponding cross-section and a length of 10.5mm, more than 500bar (0.5X 10)⁵kPa) to produce a desired velocity profile. The injection pressure is usually about 2/3, which can be converted to a unit pressure in the bristle-forming channel, so that the polymer melt in the channel should have a pressure of more than 300bar (0.3-10 bar)⁵kPa) pressure.

Thermoplastics form crystals when they harden below the crystal melting temperature, and they influence the modulus of elasticity (E modulus) and the tensile strength (crack resistance) depending on the shape and arrangement. The advantageous effect in the sense of increased rigidity by increasing the E-modulus and the strengthening in the sense of increased tensile strength can be achieved by the formation of needle-like crystals, provided that stretched chain nuclei are first formed in the molecular cross section running parallel. This nucleation structure can be increased by a number of times by stress induction, such as occurs during flow, relative to adiabatic crystallization. The high injection pressures and the resulting high flow speeds of the polymer solution in the bristle-forming channel, which are envisaged according to the invention, therefore cause not only the longitudinal orientation of the molecules but also the formation of crystals, the high pressures simultaneously increasing the density of the crystals, in addition to further stress induction. The relaxation time is also increased by partial crystallization of the molecular-oriented melt, i.e. the molecular orientation is retained longer.

The aforementioned effects are also supported in the improved structure of the present invention by cooling the bristle-forming channels.

The narrower the cross-section, the longer the bristle-forming channel, and the greater the previous consideration of insulating the channel walls to obtain the viscosity of the polymer melt and to achieve complete filling of the mold. However, when the process parameters are adjusted according to the invention, the mold filling is ensured even when the bristle forming channels are cooled. The stable outer layer of the bristles formed on the channel walls makes it possible to increase the pressure prevailing during injection molding, by the cooling of the channel and the stress induction associated therewith additionally promoting the formation of crystals and increasing the relaxation time. The higher the pressurization, the more sharply the formation of crystal nuclei in the core of the bristle, which is still in a molten flowing state, is promoted. By increasing the melting temperature simultaneously with the pressurization, the melt is supercooled sharply at the specified shell temperature, which also has a favorable effect on the crystal growth rate and makes the relaxation of the molecules more difficult.

High injection pressures and high flow rates require special or additional measures for rapid and effective venting in order to ensure complete filling of the mold cavity and to avoid cavitation on the forming channel or the ingress of air into the melt. In the injection molding method according to the prior art, the air discharge of the bristle forming channel takes place via the channel ends in the case of a fully closed cavity, and in the case of injection molds with longitudinally separated channels in two planes parallel to the bristles. In the former case, in order to form a non-sharp, in particular rounded bristle end, the degassing has to be throttled very strongly in order to avoid polymer melt overflow into the degassing cross section. When the mold surface is vented parallel to the bristles, it runs in the direction of flow, with the result that the polymer melt penetrates even the narrowest venting seam and leads to the formation of a parting seam along the outer surface of the bristles.

It is therefore envisaged according to the invention that the bristle-forming channels are vented perpendicularly to the flow direction of the polymer melt, wherein the venting preferably takes place in a plurality of planes perpendicular to the flow direction of the polymer. The longer the bristle-forming channel, the greater the number of venting planes selected so that venting over a given channel length appears to proceed in a controlled manner in accordance with the flow velocity of the polymer front. Since the air can escape in such a plane over the entire circumference of the bristle channel, a considerable gap length is provided, which in many planes perpendicular to the flow direction can be greater than in a parting plane parallel to the bristles.

The air discharge planes can be arranged at equal distances along the length of the bristle forming channel, and can be arranged at increasing or decreasing intervals in the direction of the polymer flow, depending on the requirements. So that at the same time a sufficiently large counter pressure can be maintained in the channel in order to achieve a uniform filling of the mould cavity.

The bristle-forming channel can be vented merely by the extrusion of air by means of the flow pressure of the polymer melt, but can also be backed up by an external underpressure.

The method according to the invention offers the possibility of injecting the polymer solution into a bristle-forming channel having a cross section which remains substantially constant from the injection end, so that substantially cylindrical bristles are obtained, which has not been produced hitherto in the injection molding technology for bristles and brushes.

However, it is also possible to provide a substantially continuously decreasing cross-section from the injection end, so that bristles with a particularly small taper are obtained, which bristles are desirable in many applications for increasing the bending flexibility from the base of the bristle to the end of the bristle. This taper also promotes the maintenance or even intensification of a steep velocity profile with a high core velocity and a shear effect which becomes greater over the entire length in the edge region, so that the orientation of the molecules and the formation of crystals up to the bristle ends are promoted despite an increased flow resistance.

Dimensionally stable bristles with a cross-sectional area and length tolerance of + -3% can be produced by injection molding, while extruded bristles with the same construction parameters have a tolerance of + -10%. Furthermore, for extruded bristles, a process-dependent ovalization of the initially round cross section is present, which can be avoided for bristles produced according to the invention.

In injection molding technology, draft angles of a few degrees (> 1.00 ℃) are generally considered necessary in order to be able to release the injection molded parts without any problems. Demolding must often be assisted by ejector pins. The draft angle must be selected to be much greater when the bristles are injection molded according to the prior art described at the outset in order to prevent the bristles from being pulled apart during demolding (US 3256545). In particular, for this reason the prior art injection molds with a parting plane parallel to the bristles have to tolerate these disadvantages. The method according to the invention makes it possible to reduce the draft to 0 ° with the same filling. That is, if the advantageous properties of tapered bristles having increasingly greater bend angles up to the bristle ends are desired, it is also possible to manufacture long lengths of elongated bristles having a relatively small taper in the range of 0.2 to 0.5 °. It can also be released very well due to the crystal formation by longitudinal orientation and strengthening and the resulting increase in the tensile strength (tensile strength) of the bristles, in particular in the region near the wall, which is important for the release. Other means for facilitating demolding will be described in connection with the apparatus.

In a further variant of the method according to the invention, the molten polymer is injected into an inlet region which narrows in a nozzle-like manner towards the bristle-forming channel, in order to generate an expanding flow, in order to obtain a bristle with a thickened base region having in some cases a continuously tapering profile towards the bristle itself.

The narrowing produces an expanding flow which to a significant extent leads to an orientation of the molecules and, for reasons of flow technology, to a corresponding increase in the flow profile in the region adjoining the narrowing, which makes it worthwhile to arrange the narrowing member in the vicinity of the injection end. However, it is also possible to provide narrowing elements over the length of the bristle-forming channel in order to obtain a stepped bristle, wherein the narrowing also has a favorable effect on the molecular structure and crystal formation.

The cross-section of the bristle-forming channel, which in some cases is arranged behind the front inlet region, is preferably selected to have a maximum width of not more than 3mm, so that the molded bristles have a corresponding diameter, in some cases with a thickened root region. Such bristles with thickened root regions of cross section cannot be produced by extrusion or weaving. The term "maximum width" here means that the bristles can also have a cross-section other than circular, for example elliptical, wherein the maximum width corresponds to the length of the major axis of the ellipse.

Secondly, the ratio of the maximum width to the length of the channels in the application of the process according to the invention can be selected from the range from ≦ 1: 5 to 1: 1000, in particular to ≦ 1: 250. For example, bristles having a length of between 15mm and 750mm at a maximum diameter of 3mm in or near the root region may be manufactured. The smaller the maximum width, the shorter the length is chosen. For high requirements, for example in toothbrushes, application brushes, etc., it is proposed to use diameters of 0.5mm or less above the root region, which allow bristle lengths of more than 60mm when using the method according to the invention.

The method according to the invention can also be advantageously modified in that the polymer melt is injected simultaneously into a plurality of adjacently arranged bristle forming channels to form a corresponding number of bristles, so that a set of bristles can be produced in one injection molding process. By minimizing the distance between the bristle-forming channels, a tuft-state (disk) bristle structure can be produced by slight compression of the demoulded bristles.

The number and arrangement of the bristle-forming channels can also be determined such that a single injection molding process produces an entire bristle pack of a brush or brush, wherein the distances between the bristles and their geometric arrangement can be varied according to the desired arrangement within the bristle pack.

In a further embodiment, it is provided that the polymer melt is injected into the bristle-forming channels arranged adjacent to one another with simultaneous formation of a connection between at least two bristles, wherein this connection can be used both for further processing in conjunction with the bristles and as an aid for the connection to the brush body, the brush shaft or the like. Furthermore, after the bristles have been injection-molded from one polymer, a polymer melt consisting of another polymer can be subsequently injected in order to establish the connection between the bristles. The connection may be in the form of a rib, a grid connecting a plurality of bristles, or the like. A sufficiently reliable connection is ensured when different polymers with a binding factor of ≥ 20% are used.

The connection can be designed such that it forms a bristle carrier, which can simultaneously be a brush body or a part thereof, or can be completed by injection of at least one further polymer melt to a brush body or a bristle holder. Here another thermoplastic or thermoelastic polymer.

In a further aspect of the invention, a plurality of bristles of different lengths can be injection molded, so that in combination with the bristle carrier connecting them, it is possible to produce a complete bristle set or a partial bristle set for a brush or brush, in which the bristle ends are located at different heights in a planar or non-planar envelope, in order to optimally take into account the curved profile with the bristle ends with the finished brush.

It is also possible to mould a plurality of bristles with different cross-sections so that different effects can be produced in defined areas with a single finished brush.

It is also possible to injection mold a plurality of bristles having different cross-sectional profiles over their length. Finally, a plurality of bristles can be injection molded that are not parallel to each other to create bristle groupings having different bristle orientations.

According to another version of the method, bristles of the same geometry, but different flexural elasticity (stiffness) can be produced by injecting different polymer solutions into the same shaping channel. In the case of extruded bristles for brushes having different hardness classes (constructions), for example for toothbrushes having three hardness classes, soft, medium and hard, the desired hardness class can only be controlled by the bristle diameter, i.e. up to three different bristle diameters are prepared and processed for toothbrushes of the same construction. These hardness classes can be achieved with the method according to the invention only by polymer selection and in some cases by adaptation of the injection pressure to the same bristle diameter.

Furthermore, bristles can be injection-molded from a polymer or polymer mixture, which in the hardened state have a reduced secondary binding force. Such bristles can be split after manufacture, in some cases by mechanical force after subsequent processing into brushes or bristled brushes, and in this way tassels (flags) are formed.

Finally, bristles consisting of polymers with additives which are effective in use can be injection-molded. These can be organic, for example abrasive, or, for example, in the case of bristles for toothbrushes, additives having a care, therapeutic or conditioning action are involved. A wide variety of such additives are known.

The invention further relates to a device for injection molding bristles from thermoplastic polymers, comprising a device for generating an injection pressure and an injection mold having at least one supply channel for the molten polymer and at least one cavity shaped as a shaping channel having a shape profile corresponding to the length and cross-sectional profile of the bristles to be produced, wherein the shaping channel is assigned a venting structure for venting air that is compressed during injection. Devices of this type are known from the prior art mentioned at the outset.

The device according to the invention is characterized in that the device is designed to produce, in particular, at least 500bar (0.5.10)⁵kPa) and the venting structure has a venting cross-section distributed over the entire length of the forming channel, which together with the injection pressure are designed to form a shear flow with a high core velocity in the center of the polymer melt and a large shearing effect on the walls of the forming channel.

With this device, bristles which have already been described in connection with the method can be manufactured by injection moulding. In contrast to known injection molding devices for producing bristles or integral brushes with bristles, the device according to the invention is designed in such a way that the flow dynamics sought are achieved in the channels forming the bristles.

The device for generating the injection pressure is preferably designed in such a way that the injection pressure can be distributed between 500 and 4000bar (0.5.10) depending on the length and cross section of the shaping channel⁵To 4.10⁵kPa) the smaller the cross-section of the bristle to be manufactured, the greater its length, the higher the pressure is selected.

The device for generating the injection pressure and the venting cross section of the forming channel are designed in terms of design and control technology such that the polymer melt in the forming channel has at least 300bar (0.3.10)⁵kPa) to 1300bar (1.3.10)⁵kPa) per unit pressure. This design is adapted to the solid flow and the flow resistance to be overcome up to the forming channel.

The injection pressure can preferably be controlled as a function of the length and cross-sectional profile of the shaping channel when a defined, sufficiently high injection pressure is generated at the generating device, in order to be able to inject injection molds of different geometries with one injection molding machine.

For this purpose, a further measure is taken that the venting structure has a venting cross section that can be controlled as a function of the specific pressure.

In the device according to the invention, the injection mold with the shaping channel is advantageously provided with a cooling structure, which can be external cooling after each injection or demolding. However, it is also possible to provide the shaping channel with a cooling structure inside the injection mold, with which the shaping channel is kept at a low temperature.

In a particularly preferred embodiment of the invention, it is provided that the injection mold consists of a plurality of mold plates which are layered perpendicular to the longitudinal direction of the shaping channel, wherein each mold plate has a length of the shaping channel.

Unlike the prior art with more or less block-shaped injection molds, the present invention contemplates a layered structure consisting of mold plates. This structure makes it possible to manufacture the smallest hole cross section with high accuracy in each template having a small thickness. But such any other process is ineffective at larger hole depths. This is also the reason why injection molds have hitherto been resorted to for longitudinal split molding in the production of narrow cross sections. The disadvantages of which have already been explained in connection with the prior art. By the inventive division of the injection mold into a plurality of plates, a long shaping channel can be realized with high and reproducible precision over the entire length. The mold plates with replicated bristle tips forming the channel ends can have cavities with only a small depth due to the small thickness of the mold plates, they do not require additional venting measures to replicate the bristle tips in a sharp contour and without any parting seams. The oxidation of the polymer, which is observed in narrow mold cross sections and which occurs by the so-called Diesel effect, does not occur when the cavity depth is small.

Furthermore, the layered structure of the injection mold offers the possibility of forming the venting structure on the mold plate, i.e. with a frequency corresponding to the number of mold plates. The venting structure is preferably designed between the mutually facing joint surfaces of the formwork, for example by narrow slits or channels. Due to the high flow velocity of the polymer solution perpendicular to such narrow gaps or channels, the melt is prevented from penetrating into the venting cross section despite the high pressure. The venting cross section can thus be larger than in the case of the two mold halves, the parting plane of which lies in the melt flow direction. The exhaust channel cross section can be made to have a maximum width of only a few μm to 300 μm. In particular, the venting structure is formed entirely or partially by the surface roughness of the mold plates facing each other.

In a further advantageous embodiment, the venting structure has venting cross sections which, starting from the contour of the shaping channel, expand outward, so that the air can flow out without hindrance after passing through the narrowest point of the venting cross section.

The air displacement, which is effected exclusively by the unit pressure in the shaping channel, can also be supported in that the venting structure is connected to an external underpressure source.

The device may be designed such that the shaping channel has a cross-section which remains substantially constant over its length or which decreases substantially uniformly towards its ends, so as to obtain cylindrical or slightly conical bristles.

Actual injection molding tests under the specified process conditions have shown that the forming channel can be uniformly narrowed at an angle of less than 1 ° at the straight centerline to obtain a draft angle sufficient for demolding of a micro-tapered bristle having outstanding bending properties.

The shaping channel can furthermore have a cross section which decreases discontinuously towards the ends in order to obtain a specially designed bristle end which is adapted to the intended use of the finished bristled article.

The maximum width of the cross section of the forming channel is preferably less than or equal to 3 mm. With which it is possible to cover the desired bristle cross-section for quality brushes and hairbrushes.

In front of the die plate with the shaping channel having the maximum width mentioned above, on its side facing the feed channel, an injection end die plate can be connected which has a flare that tapers toward the shaping channel, in order to produce, on the one hand, a thickened cross section at the base of the bristles and, on the other hand, to support the formation of the desired flow dynamics, since this flare results in a tensile flow in the inlet region of the shaping channel. The flaring can be narrowed in a trumpet-like manner towards the shaped channel in order to create a transition-free step on the bristle-connecting carrier, brush body or the like, which is of particular importance for various types of sanitary brushes.

The ratio of the maximum width of the cross-section of the shaping channel to its length is preferably between 1: 5 and 1: 250, but may also be up to 1: 1000, where the narrower the cross-section of the shaping channel, the closer this ratio is to the maximum, and conversely the narrower the cross-section, the closer it is to the minimum.

In a further configuration of the invention, it is provided that the number and thickness of the die plates are adapted to the length of the shaping channel, wherein the number of die plates is inversely proportional to the ratio of the maximum clear width of the cross-section to the length of the shaping channel. Furthermore, the number of plates belonging to an injection mold can be varied, so that bristles of different lengths can be produced with the same mold.

The die plate preferably has a thickness of about 3 to 15 times the average diameter of the forming channels. For bristles having an average diameter of 0.3mm and a length of 10.5mm, the template has a thickness of 1.5mm to 2.00mm, for example. The 1.5mm to 2.0mm shaped channel length sections present in the die plate can be drilled very precisely.

The templates can be moved individually or in groups perpendicular to their plate planes. In this way, the bristles can be released from the mold by, for example, starting from a mold plate with a shaping contour at the end of the shaping channel and proceeding to the mold plate facing the feed channel, the mold plates being withdrawn one after the other in time, individually or in groups, in particular in a manner known from the prior art.

The mold plates are reliably held together under the high clamping pressure of the injection molding machine, which is determined by the process, and are not subjected to deformation forces during injection despite their small thickness. The outer corner cross section is sealed by the clamping pressure. In particular, no additional blocking devices are required, as is the case with channels for longitudinal venting.

Practical tests have shown that, given a narrow cross-section and channel length, considerable drawing forces are required for the demolding of the bristles, if, for example, only two modules are present. The bristles are typically snapped apart. By increasing the number of die plates and their mutual gradual movement, the bristles can be demolded without damage, in particular if the die plates facing the feed channel are finally retracted. The edge of the aperture of each die plate acts like a die during demolding, and the "polymer skin" that may be present and formed in the parting plane is pulled smooth without adversely affecting the bristle envelope surface. The bristle ends are rounded in a nonsinguishable manner.

Furthermore, the individual plates can be moved parallel to the adjacent plates in order to subject the bristles to a transverse load after the injection molding process, thereby optimizing the molecular structure.

In another preferred construction, the injection mold has shaped channels of different lengths and/or different cross-sectional profiles to achieve the desired geometry and group shape of the bristle pack in one injection stroke.

According to another embodiment, the injection mold has a shaping channel with a center line which is inclined at an angle to the direction of movement of the mold plates, wherein each mold plate has a length of the shaping channel, the length of which is selected such that the mold can be removed by a progressive displacement of the individual mold plates despite angular errors.

The division of the injection mold into a plurality of mold blocks running perpendicularly to the shaping channel offers the possibility of dividing the shaping channel into lengths such that even if the bristle axes are inclined with respect to the direction of movement of the mold plates (demolding direction), individual lengths can still be demolded without the bristles being excessively stressed and deformed, in such a way that bristle packs can be produced in a single injection mold, in which bristle packs the bristles are parallel to one another but are arranged at an angle to the bristle carrier joining them, or have different angular positions with respect to one another.

According to another embodiment, the injection mold has a shaping channel with a center line which is curved relative to the direction of movement of the mold plates, wherein each mold plate has a length of the shaping channel, so that depending on the curvature, the mold can be removed by gradually lifting the mold plates.

In this way, for example, wave-shaped bristles can be produced, which can likewise be released without difficulty. It is also possible to produce straight, wavy and curved bristles simultaneously in a single injection mold.

In a further embodiment, the injection mold has at least one mold plate which is movable in its plane relative to the adjacent mold plate and, together with the adjacent mold plate, forms a clamping device for the entire bristle active over a corresponding partial length of the shaping channel after the injection molding of the bristle.

The invention therefore creates the possibility of using parts of the injection mould as fixing means for the injection moulded bristles, so that the bristles are fixed in the injection mould only over a part of their length, for example in order to remove the mould plates near the ends in the demoulding direction from the remaining mould plates and to clamp the bristle injection moulded part so that the bristles are suspended in the middle part of the length, i.e. between the mould plate and the remaining mould plates. The end of the template is then extended beyond the injection end of the bristles by movement of the clamping template and retraction of the template near the end toward the injection end of the bristles. By transfer through an injection mold. In some cases, the injection mold can be connected to another injection mold having cavities that replicate the bristle carrier or brush body, with the clamping effect of the fastening device continuing. In a further injection molding process, the projecting end is cast around with a further polymer melt which fills the mold cavity.

The clamping device can furthermore be used as a transport gripper for the clamped bristles, after being released from the other mould plates, to be transferred to another station for connection to the brush body. This is particularly desirable if the bristles have been interconnected by means such as ribs, grids or bristle holders. The clamping die plate is thus located in the vicinity of the transition from the bristles to the bristle carrier, the clamping tool is moved in the stripping direction while the connecting region is stripped, and the clamping die plate is then transferred and replaced by a set of identical clamping die plates in order to obtain a complete injection mold again. The holders may be formed as moving holders on an endless track and reused to replenish the injection mold after the bristles have been completely removed from the holders. If the attachment point is not directly required for the next shaping step, for example, drawing, gluing, welding, casting around, etc., it can also be cut off and the bristles can be attached to the bristle carrier or brush body only by known joining processes.

In a further embodiment of the invention, it is provided that the injection mold comprises at least two sets of mold plates with clamping devices, wherein the first set comprises a part of the shaping channel with its end and the remaining sets comprise the remaining part of the shaping channel, wherein the first set can be moved away from the second set and thereafter moved away from each other in time sequence. The injection process is divided into injection strokes corresponding to the number of groups, so that in the closed outlet position of the injection mold the molten polymer is injected into the complete shaping channel in a first injection stroke, then the first group of mold plates can be moved away from the other group with the injection blank being carried along by means of the clamping device, wherein the movement distance is shorter than the length of the injection blank, then in a second injection stroke the remaining molten polymer is injected into the free length of the shaping channel of the other group, and the injection/lifting process is repeated until the penultimate group is moved away from the last group, in order to produce bristles longer than the length of the shaping channel. That is, the bristles are manufactured segment by segment, so that bristles of a large length can be manufactured.

In a device of this type, different polymer melts can also be injected in each injection stroke, so that multicomponent bristles can be produced over the length of the bristles, the polymer used in each section being adapted to the desired profile of the bristles and their connection to the bristle carrier. In this way, a multi-region bristle is obtained. The displacement movement of the individual mold plate groups can take place at short intervals in the injection stroke, during which the injection mold cools to such an extent that it is released from the remaining mold plates during the displacement movement. The connection between the individual zones is preferably effected by material fusion, but can also be effected positively or non-positively by correspondingly forming a concave-convex profile at the end of the partial length which is finally injection-molded.

In particular the bristle tips and the templates with the model profiles at the ends of the shaped channels are exchanged for templates with other model profiles to produce bristles with differently shaped tips. Such a template should only comprise a planar contour in order to allow the bristle ends, which are decisive for the purpose of use, to be demoulded without any problems.

In this way, the end contour of the bristle can be changed while the geometry of the rest of the bristle remains unchanged, for example, to produce bristles which are pointed or more or less rounded, or have bifurcated ends (two points, etc.). Such a template may also have shaped channels of lengths of different depths to form a patterned envelope for the bristle tips in a set of bristles.

It is advantageous to provide a cavity between the inlet channel and the shaping channel of the injection mould, which connects two or more shaping channels, in order to form a connection between the bristles, which in some cases may also connect all the bristles. It can be used both as an aid for the subsequent treatment of the entire bristle group and as an aid for the alignment of the bristle group with the brush body.

Furthermore, the cavity can also be designed to produce a brush body or a part thereof.

In particular, the cavity can be designed here to produce a brush body or a part thereof of a multicomponent structure composed of different polymers.

Drawings

The invention is explained below with the aid of schematic illustrations and embodiments shown in the drawings. In the drawings:

FIG. 1 is a schematic representation of velocity profiles within forming channels of different diameters;

FIGS. 2 to 4 each show a schematic representation of an embodiment of a forming channel with a corresponding velocity profile;

FIG. 5 is a schematic illustration of bristles injection molded in a forming channel according to FIG. 2, together with velocity profiles that are determinative of longitudinal orientation;

FIG. 6 is a schematic illustration of the constriction of a forming channel with a stretch flow;

FIG. 7 is a schematic view of a tapered bristle having a specified size, shown in a 2: 1 ratio;

FIG. 8 is a schematic view of a tapered bristle having a specified size, shown in a ratio of 1: 5;

FIG. 9 is a comparative schematic of velocity profiles within an extrusion nozzle and a forming channel;

FIGS. 10 to 13 each show a schematic longitudinal section through an embodiment of an injection mold in different operating phases;

FIG. 14 is a schematic longitudinal section of another embodiment of the injection mold;

FIG. 15 is a detail view of the injection mold according to FIG. 14 in the region of the outer shaping channel;

fig. 16 to 20 each show a schematic longitudinal section through a modified embodiment of the injection mold in different movement phases;

FIGS. 21 to 23 each show a schematic longitudinal section through a further embodiment of an injection mold in different operating phases;

fig. 24 is a longitudinal section of the injection mold together with a mold which has been supplemented with it, corresponding to fig. 21 to 23;

FIGS. 25 and 26 are longitudinal sectional views of an injection mold of a further variant of the design in two operating phases;

FIGS. 27 and 28 show longitudinal sections of an injection mold with a formed movable platen, corresponding to FIGS. 25 and 26, respectively;

FIGS. 29, 30 show longitudinal sections of injection molds of injection molded blanks having another shape, respectively, corresponding to FIGS. 25, 26;

FIG. 31 is a schematic longitudinal section of an injection mold for making bristles of different longitudinal lengths;

FIG. 32 is a schematic cross-sectional view of an injection mold for making bristles having bifurcated bristle tips;

FIG. 33 is a greatly enlarged schematic view of a bristle;

FIG. 34 is a greatly enlarged schematic illustration of a two bristle arrangement;

FIG. 35 is a greatly enlarged schematic view of another embodiment of a bristle;

fig. 36 is a top view of the free end of the bristle according to fig. 35.

Detailed Description

Figure 1 shows schematically the flow diagram (velocity profile) in bristle-forming channels of different diameters. The channel walls are shown in vertical dashed lines and the associated diameters (in mm) are shown below the graph. The smallest bristle-forming channel has a diameter of 0.3mm and the largest channel has a diameter of 6 mm. When the channel centers have the same flow velocity, referred to below as the core velocity, the various flow profiles shown, which can be regarded roughly approximately as parabolas, are formed as a function of the channel diameters. The flow profile does not change its shape or at most only very little over its length while the diameter of the shaping channel remains constant.

When the microtube forms a channel, as is schematically shown in fig. 2 to 4, the core speed can also be increased at equally high pressures and a strong shearing effect is produced in the region near the wall due to wall friction. If such a shaping channel is injected into the polymer melt during the injection molding process, a pronounced longitudinal orientation of the molecules in the wall region is produced due to the shearing effect, while in the melt without stress induction the molecules have a random structure which is advantageous for energy saving. Transfer to the polymer melt injected in the shaping channel under relatively high pressure means that the bristles produced in the region near the wall are strengthened, reaching the bristle ends at relatively high core speeds and becoming less and less oriented towards the central molecule. Furthermore, the molecular orientation due to the shear flow with a strong shear effect in the region near the wall is superimposed on the stress-induced crystal formation, which promotes the formation of long needle-like crystals by the strong shear effect in the edge region. Furthermore, the nucleation and the crystal density are advantageously influenced by the high injection pressures used. The unit pressure in the forming channel is more than 300bar (0.3.10)⁵kPa), in particular > 1300bar (1.3.10)⁵kPa), the modulus of elasticity, and thus also the bend, can be concluded in advance considering the forming tunnel is sufficiently ventedA significant increase in bending elasticity with an increase in breaking strength (tensile strength). The unit pressure is more than 500bar (0.5-10) according to the injection pressure of the pressure generating device⁵kPa) is a precondition.

The bristle according to fig. 5 produced in the shaping channel according to fig. 2 has a root region with comparatively good flexural rigidityaAnd at high tensile strength in its overhanging length1Having a bending elasticity gradually increasing toward the bristle tips. The root region a is intended primarily for attachment to or in a bristle carrier or body, and the bristles are in their cantilevered length1A base part of the rod is arranged onbRod andcthe stem region (dry part) itself. In a regionbAndcthe reduction in cross section which is decisive for the amount of bending deflection is compensated by the increased bending elasticity due to the previously described effect. In the region of the shankb、 cUpper working zone d connected to itself, i.e. the zone decisive for the brushing action, and the top zonetTogether forming a region that determines the flexibility of the bristles. The top region and its configuration determine the direct surface action of the bristles, the depth of intrusion into surface irregularities, and the like. Unlike in fig. 2, the bristles may be at a flare that is connected before the inherent shaping channel. As shown in fig. 3 and 4, there is a flared root region which appears more or less clearly.

If a discontinuous constriction is provided upstream of the transition from the entry end of the polymer melt to the actual bristle-forming channel, as shown in fig. 6, the reinforcing effect can also be improved thereby, in particular at short bristle lengths. At the constriction, a tensile flow is formed which, over a short path, leads to the formation of high core velocities with a large shearing effect in the region near the wall.

With the injection pressure operating parameters according to the invention and the high core speeds which can be achieved thereby with a large shearing effect by wall friction, it is possible to produce thin bristles with variable length by injection molding, whereas it has hitherto been impossible to produce such thin, infinitely long filaments by extrusion, wherein the microtaperturing of the bristles consisting of such infinitely long filaments can only be achieved with very great production expenditure (gap drawing). Two examples are shown in figures 7 and 8, figure 7 showing a bristle having a diameter of 0.77mm in the root region and a diameter of 0.2mm at the bristle ends in a 2: 1 ratio, which has an average diameter of 0.49 at half the length. Bristles of 60mm length or more can be produced by injection molding with a particularly small taper corresponding to an angle of 0.27 ° of the draft angle of the bristle-forming channel, as is required, for example, for expensive brushes and the like. They have an average diameter of about 0.5mm at half the bristle length. Figure 8 shows a bristle having a diameter of 0.35mm at the base and a diameter of 0.25mm at the bristle end for the same taper angle (draft) length of 10.5mm at a ratio of 5: 1. The average diameter was 0.3 mm. Bristles of this type are suitable, for example, for toothbrushes. Due to the elongated geometry of such bristles they can be arranged very densely, unlike conventional injection molded bristles, where the distance in the end region of the bristles is too great.

The technical and practical advantages of the bristles produced according to the invention compared with bristles produced by extrusion are shown with the aid of fig. 9.

The spinning nozzle had an outlet diameter of 0.9mm when extrusion spinning was used to produce filaments having bristles with an average diameter of 0.3mm, as indicated by the outer vertical lines in fig. 9. The polymer melt has a maximum flow velocity (core velocity) inside the nozzle, which is typically about 300 mm/s. It is determined by the extrusion pressure and the drawing speed of the filaments. The filaments leaving the nozzle are drawn in a short path by means of a drawing force to a diameter of between 0.9mm and 0.3mm and then immediately cooled in order to set the molecular structure. The single fibers, when subsequently drawn, gave a final diameter of 0.3mm with an error of about. + -. 10%. In FIG. 9 for velocity profilee(extrusion) is shown.

The bristle-forming channels have an average diameter of 0.3mm during injection molding according to the invention. It uses two internal verticals in FIG. 9The boundary line indicates. At an injection pressure of 2000bar (2.10)⁵kPa) to produce a core velocity in the channel of about 1000 mm/s. For velocity profileiIndicated (injected). The shear effect in the flow, in particular in the region near the wall, which is decisive for the inherent strengthening of the thermoplastic polymer, is indicated by the shear rate (shear moment) γ. The shear rate at the radius r of the flow channel is calculated from the derivative of the velocity profile with respect to the radius r.

It is therefore inversely proportional to the square of the effective diameter of the flow channel. The shear rate is proportional to the first power of the maximum flow velocity (core velocity). Thus, for the example shown above, a shear rate is obtained for the injection molded bristles that exceeds the shear rate in a given extrusion flow by at least a factor of 10.

Shear rates are shown in FIG. 9 without scale by dashed lines for extrusion e₁For injection molding with i₁And (4) showing. They have their maximum values at the nozzle wall and bristle-forming channel wall, respectively.

Fig. 10 to 13 show schematically an embodiment of an injection mold in various operating phases. It is particularly suitable for injection molding bristles produced by the method of the invention. The scale is greatly exaggerated to better illustrate the details.

The injection mould 1 has a plurality of parallel, long shaping channels 2 which are connected to an injection moulding device via a feed channel 3. The injection molding apparatus is designed in such a way that a pressure of 500bar (0.5.10) can be produced⁵kPa) range, in particular ≥ 2000bar(2.10⁵kPa) injection pressure in the range. The exact magnitude of the injection pressure is adjusted as a function of the cross-sectional distribution of the shaping channel 2 over its length and the length of the shaping channel in such a way that > 300bar (0.3.10) is provided in the shaping channel⁵kPa) per unit pressure.

The injection mold consists of a number of layered mold plates 4 of essentially the same thickness, as well as a mold plate 5 for the injection end and a mold plate 6 for forming the bristle tips. The die plates 4, 5, 6 each have one length of the forming channel 2. They are produced in particular by drilling.

The injection-end die plate 5 has a flare 7 which tapers in the direction of the shaping channel 2, for example, in order to generate the drawing flow according to fig. 6 and to form the base region of the bristlesa(FIG. 5). The subsequent length of the shaping channel in the die plate 4 has a cylindrical or slightly conical cross-sectional profile over its length, while the die plate 6 forming the bristle tips has blind holes 8, which in the embodiment shown are made hemispherical.

During injection molding, the polymer melt enters through the supply channel 3 into the narrowing flare 7 of the mold plate 5 and fills the entire forming channel, due to the high core speed, until the end mold plate 6 is formed. The polymer melt in the supply channel 3 also has only completely disordered, random molecular structures which are transformed into longitudinally oriented molecular structures in the flaring 7 of the injection end and the subsequent shaping channel 2 by means of a pronounced shear flow.

The mold plates 4, 5 and 6 can be moved perpendicular to the plate plane in order to demould the injected bristles after sufficient form stability has been achieved. The injection mold 1 is preferably cooled in such a way that the walls of the forming channel 2 remain relatively cool, thereby supporting the formation of crystals in the polymer melt.

The stencil 6 is first withdrawn for stripping the bristles (fig. 11). In this case, only a small adhesion force has to be overcome, which ensures that the bristle tips, which are particularly important for the later use of the brush or bristle, maintain a uniform contour. The templates 4 are then moved individually or in groups (fig. 12) until the bristles 9 with their ends 10 are demoulded over most of their length. During this demolding step, the bristles are retained by the mold plate 5 at the injection end, and the mold plate 5 is then moved such that the entire bristle 9 is ejected together with its slightly thickened root region 11 (fig. 13). The polymer melt in the feed channel at the injection end simultaneously forms a connection point for all the bristles 9. The entire injection-molded part can be removed and completed as a brush, brush or the like, wherein the connection points are unified in the structure or merely serve as auxiliary tools for the handling of the bristles and are cut off before the bristles are combined with the brush body or the like.

Providing optimal venting of the forming channels during injection molding that enables the desired high core velocities. Fig. 14 shows an embodiment for this. The evacuation takes place through narrow gaps between the die plates 4, 5 and 6, so that the air is evacuated over the entire length of the forming channel 2 in accordance with the advance of the melt front. Instead of narrow slits 13, the surfaces of the mold plates 4, 5, 6 facing one another can also be roughened so that, in total, a sufficiently large exhaust cross section is produced. In order to allow the air flowing out to escape quickly, the exhaust cross section has an outward flare 14.

The shaping channel 2 can be reduced over its entire length by a draft angle of < 1.0 °, wherein the reduction is not primarily a demolding problem but rather a desired bristle shape and its bending flexibility. The cross-sectional profile of the shaping channel 2 can also differ from a continuous taper, as is shown in fig. 15 on an enlarged scale in conjunction with a defined venting. In the figure, a cylindrical length 15 of the forming channel 2 is shown in the upper die plate 4 and a cylindrical length 16 is shown in the lower die plate 4. The cross-sectional area between the two die plates 4 decreases by a few μm from the length 15 to the length 16 of the forming channel 2, so that an insignificant step is formed in this region. In this region, the gas is also discharged through a gap 13 between the two die plates, which opens out at a flare 14. These imperceptible steps are not visible in appearance upon demolding. But causes a slight taper over the entire length of the bristles. The lengths 15, 16 on each module 4 can be produced in this way by simple holes. Instead, the lengths on the individual plates can also have the same diameter, so that cylindrical bristles are obtained. Stepped bristles can also be produced in the case of a sharp diameter jump.

The bristles of conical design have the advantage of an injection molding process and demolding, i.e. the smallest cross section at the bristle ends cools off more rapidly than in the subsequent region of the bristles up to the root region. That is, the step-wise release from the bristle tips to the bristle roots follows the temperature gradient within the bristles.

The thickness of the template 4 is a few millimeters. It may correspond to about 3 to 15 times the diameter of the forming channel 2, so that the length in each module can be drilled very precisely. Because they are brought into contact with one another under the clamping pressure of the injection molding machine, these thin mold plates themselves retain their dimensions and shape despite the high injection pressures. Good heat dissipation is also ensured due to the small thickness, since the formworks are approximately thermally insulated from one another by the venting gap. For the same reason, they can also be cooled without problems, for example by an external coolant, which cools them particularly effectively during the closing process but also during the time between opening and reclosing. Due to the separation of the mold plate and its small thickness, effective cooling is already possible by ambient air alone. But in addition the coolant may also be built into the mould plates or between them. Finally, the low stresses under the injection pressure offer the possibility of producing the mold plate from a material with a good heat conductivity with lower strength values than steel or the like.

The effect of effective cooling on the molecular structure of the bristles has been demonstrated.

Fig. 16 also shows schematically an injection mold 1, which consists of a layered mold plate 4, wherein the mold plate at the injection end does not have an enlarged cross section, in contrast to the previously described embodiments, the mold plate 4 being divided into two groups 17, 18 (see fig. 17), wherein each group has at least one mold plate that can be moved laterally, as indicated in fig. 17 to 20 by double arrows 19, 20.

These laterally movable templates, together with the adjacent templates, act as a clamping device for the injection molded blank 21, which in the present embodiment constitutes only one area (length) of the final bristles. The injection molded blank 21 is injection molded from a thermoplastic polymer having a performance profile consistent with the finished bristle over this length. At least one movable platen (fig. 17) in the set 18 of platens 4 is moved to a clamping position after the injection stroke, and the injection preforms 21 are carried along as the set 18 is withdrawn, and are partially ejected from the platens 4 of the injection end set 17, leaving a defined length 22 of the forming tunnel in the platens 4 of the set 17 free. In some cases, a concave-convex profile may be generated on the end of the injection molded preform 21, as shown in the drawing. The movable die plates in the set 17 move to the clamping position after the die plates 4 of the set 18 are removed. And then injected into the open length 22 with a polymer melt consisting of another polymer or a polymer with other additives. The bristle length 23 formed in this case is connected to the injection-molded blank 21 by material fusion and/or form-fitting. The movable platen in the group 17 is then retracted into its starting position, and the injection molded blank 21 with the resulting length 23 is again partially pulled out of the shaping channel of the group 17 with the clamping devices in the group 18 closed, so that the length 24 is free in the shaping channel. In a further injection stroke, the length 24 is injected with a further melt of a polymer, which in some cases also has different properties, so that a multi-segment bristle 27 is finally obtained. It consists of three regions (sections 21, 23 and 25) which have different strength values over the length of the bristle and/or different performance properties. Wherein in particular the area 21 comprising the bristle tips can be used as a display of the degree of wear of the bristles. Final demolding of the bristles is carried out as described above.

Fig. 21 to 24 again show an injection mold 1 (fig. 21) which is composed of two groups 17, 18 of mold blocks 4, each of which has at least one mold plate which can be moved transversely to form a clamping device. The mold plates 5 of the injection end, which differ from the above-described construction, have a flaring, which tapers in the direction of the forming channel. The template 6, which reproduces the bristle tips, has blind holes 28, 29 and 30 with hemispherical bottoms of different depths, so that a large number of bristles of different lengths can be manufactured, the ends of which lie on a curved envelope surface.

In the exemplary embodiment according to fig. 21 to 24, two different regions 31, 32 of the bristles are injection-molded one after the other, wherein region 31 has a thickened bristle base 33. Multiple regions of bristles 34 (fig. 22) injection molded in this manner are then de-molded by withdrawing (fig. 22) the templates 6 forming the bristle tips and a set 18 of templates 4, in some cases with a time delay. At least one laterally movable template of the set 18 is then moved into the clamping position and the entire set 18, in some cases together with the template 6 at the end, is moved in the opposite direction, so that the bristles 34 project with a part of their area 31 with the root area 33 beyond the template 5 of the injection end. The injection mold 1 (fig. 23) is then connected to a further injection mold 35 with a cavity 36, into which a polymer melt is injected, and the root region 23 and the length of the region 31 extending into the cavity 36 are cast around with this polymer melt. The cavity 36 can be designed such that it forms an intermediate carrier or a complete brush body for the bristles, the bristle ends being embedded in a tensile manner and without gaps.

In this variant embodiment, the molding channel 2 of the injection mold 1 can also be completely filled with only one polymer melt according to fig. 21 and its root region together with the adjoining lengths can be suspended in the manner shown in fig. 22 and 23 in order to be cast around with the polymer melt forming the carrier according to fig. 24.

In a further variant, the bristles, which are injection-molded in accordance with fig. 21 to 23 and which are suspended at the ends of their fixed ends, are completely removed by the withdrawal of the end-forming die plate 6 and the following most die plate 4, while the bristles are held by a few, i.e. at least three, die plates, for example the injection-end die plate 5 and the following two die plates, one of which can be moved transversely to form the clamping device. These mold plates, which serve as transport fixtures, can then be moved together with the bristles to another injection molding station, where they are connected to the injection mold 35, while a new set of mold plates is combined with the injection-end mold plate 5 in order to complete the injection mold 1. The transport gripper can be used not only to transport the bristles to the second injection-molding station, but also to continue to other processing stations.

Fig. 25 and 26 show a part of the injection mould 1 with the mould plates 4 and 5 after bristle making and at least (not shown) withdrawal of the mould plate 6 for the ends. In front of the overhanging ends of the bristles 38, a planar pusher plate 39 is also moved in. By means of which the bristles 38 are pushed into the shaping channel of the remaining mold plate until they project with their base region 37 and the length connected thereto in some cases out of the mold plate 5 of the injection end or into the cavity 36 of a further injection mold 35 and are cast around with the polymer melt forming the bristle carrier or brush body.

Fig. 27 and 28 show an embodiment in which, after the manufacture of the bristles 38, in front of the ends of the overhanging bristles, a pusher plate 40 is moved in front of the flat pusher plate 39 by the method described with reference to fig. 25 and 26, the pusher plate 40 being provided with lug-shaped protrusions 41 and 42 of different heights. After the pusher plate 40 has hit the mold block 4, the bristles are pushed into the shaping channel over different pushing paths, so that the bristles with their root regions 37 project into the cavity 36 of the injection mold 35 over different depths, the bristle ends lying on a curved envelope surface after the casting and pusher plate 40 and the mold plates 4 and 5 have been retracted.

Fig. 29 and 30 show an embodiment which differs from fig. 25 and 26 only in that the bristles 38 are connected to one another in the region of the injection-end mold plate 5 by connecting points 43 in the form of ribs, grids or the like and, after displacement by means of the thrust plate 39, project with the connecting points 43 and the connected lengths of bristles 38 into the cavity 36 of the injection mold 35.

A small set of mold plates 4, in particular mold plates 5 comprising an injection end and at least one laterally movable mold plate 4 acting as a clamping device, can also be used as a transport jig for transferring bristles to other injection molding stations, processing stations, etc.

The layered structure of the injection mold, which consists of a plurality of mold plates, and the section-by-section demolding made possible thereby, as well as the increase in the modulus of elasticity and tensile strength achieved by the process parameters of the injection pressure and the flow velocity in the shaping channel according to the invention, also allow bristles to be produced whose center lines are not oriented in the demolding direction. Examples of which are shown in fig. 31 and 32. Fig. 31 shows a part of an injection mould with inclined shaping channels 44, 45, in this embodiment the shaping channels 44, 45 are inclined to each other. In addition or as an alternative, the injection mold 1 can have a corrugated shaping channel 46 or a multiply bent shaping channel 47, so that correspondingly shaped bristles are obtained, which can be injection-molded into a bundle via a connecting point 48. During demolding, the mold plates 4 and 6 are withdrawn from the latter, so that the bristles are demolded section by section, without the bristles being subjected to deformation due to their high flexural elasticity and small demolding length.

The bristles after cutting off the connection points can be shaped into a brush, individually or in groups or together with the connection points 48, by their circumferential casting, or by other known types of thermal or mechanical connection methods.

In the exemplary embodiment according to fig. 32, the injection mold 1 likewise has a layered template 4 and two end templates 49, 50, which are used to form the strongly diverging bristle ends. The molded bristles 51 each have finger-shaped bristle ends 52, which can be easily removed due to the thinness of the mold plate and the increased bristle firmness.

The template 6 or 49, 50 forming the bristle ends, in particular in the case of strongly diverging bristle ends, may in some cases consist of sintered metal, which also allows for additional venting in this region to effectively avoid air inclusions. Of course the template 4 may also consist of such sintered metal to support the venting of the shaped channels. The microscopic roughness, which is present, for example, in sintered metal or can also be produced by surface treatment of the shaping channel, causes a corresponding microscopic-scale roughness on the surface of the finished bristle, which leads to a "Lotus" effect which rejects humidity when the bristle is in use.

Fig. 33 shows a single bristle 53 which can be used in particular for sanitary brushes, such as toothbrushes, washing brushes in the medical and hospital sectors, or as a washing or smearing brush in the food industry. The bending properties of bristles having an average diameter of 0.3 to 3mm over their length can be optimally matched to the purpose of use by appropriately adjusting the injection pressure and the flow velocity (core velocity) in the bristle-forming channel. Secondly, it can flare out in the root region 54 to give a relatively strong bend boss which simultaneously forms a well rounded intersection with the brush body surface, indicated at 55. Such completely seamless regions, such as the shaft base and the shaft portion of the bristles 53 themselves and in this case the uniformly rounded bristle tips 56, can be produced by injection molding techniques in such a way that the roughness is smooth or has a roughness such that it is not contaminated, since a brush with bristles of this type can be cleaned and/or sterilized without problems even after use, since there are no recesses, gaps or the like. Bristles having such a shape and properties compatible with the use thereof cannot be produced by the hitherto known extrusion or injection molding processes.

Fig. 34 shows two adjacent bristles 57 which are joined together at their flared root regions 58 by a connecting point denoted by 59. The bristles 57 with the connecting points 59 can be arranged at a small distance from one another by the method according to the invention, and moreover can be optimally adapted to the particular application. In particular, the bristles 57 can be arranged very tightly without becoming contaminated with moisture, dirt or bacteria in any part or remaining after rinsing.

Fig. 35 shows a front view and fig. 36 shows a top view of a bristle 60 produced according to the method of the invention, which likewise has a flared transition at the base region 61 to the bristle carrier surface 62 and has a shaft 63 with a comparatively high flexural rigidity and a working region 64 which is shaped in a concave-convex profile. In this embodiment the working area 64 has a cross-shaped cross-section, which transitions into the shaft region by a smooth junction 65. The working area 64 forms brush ribs with its cruciform cross-section, which act when the brushes are strongly pressed and when the working area is curved. This effect occurs at the rounded bristle tips 66 with the cross-shaped contour present there when the pressure is low. In addition, the bristle tips 60 can enter corners, crevices and grooves to clean those areas. The same effect can be achieved with other polygonal cross-sectional shapes.

Claims (77)

1. A process for the injection-moulding of bristles from thermoplastic polymers, in which a polymer melt is injected under pressure into a bristle-forming channel of defined length and defined cross-sectional profile over this length, the channel being vented during the injection-moulding process, characterized in that: the magnitude of the injection pressure is adjusted in dependence on the cross-sectional profile of the bristle-forming channel in such a way that a shear flow is generated which has a high core velocity in the center of the flowing polymer melt and a high shear effect at least in the region of the wall of the polymer melt due to the wall friction of the polymer melt, the polymer molecules are oriented in a pronounced longitudinal direction and such a shear flow is maintained over the length of the channel, while the channel is vented over its length in such a way that it is advantageous to maintain the shear flow.

2. A method according to claim 1, characterized by: the injection pressure acting on the molten polymer is adjusted to, in particular, at least 500bar (0.5-10) depending on the cross-sectional profile of the bristle-forming channel⁵kPa)。

3. A method according to claim 1 or 2, characterized by: the injection pressure is adjusted to 2000 to 5000bar (2.10)⁵kPa to 5.10⁵kPa)。

4. A method according to any one of claims 1 to 3, characterized by: the injection pressure is adjusted in such a way that the polymer solution in the bristle forming channel has a value of more than 300bar (0.3.10)⁵kPa) per unit pressure.

5. A method according to any one of claims 1 to 4, characterized by: the injection pressure is adjusted for a given cross-sectional distribution and length of the bristle-forming channel in such a way that nucleation between adjacent longitudinally oriented molecular regions is supported.

6. A method according to any one of claims 1 to 5, characterized by: the bristle-forming channels are cooled.

7. A method according to any one of claims 1 to 6, characterized by: the bristle-forming channels are vented perpendicularly to the direction of flow of the molten polymer.

8. The method of claim 7, wherein: the bristle-forming channels are vented in a plurality of planes that lie perpendicular to the direction of flow of the molten polymer.

9. A method according to claim 8, characterized by: the bristle-forming channels are vented through generally equidistantly disposed planes along their lengths.

10. A method according to any one of claims 1 to 9, characterized by: the bristle-forming channel is vented by the extrusion of air by means of the flow pressure of the polymer melt.

11. A method according to any one of claims 1 to 10, characterized by: the channel is vented by means of the support of an external underpressure.

12. A method according to any one of claims 1 to 11, characterized by: the polymer melt is injected into a bristle-forming channel having a cross-section that remains substantially constant from the injection end.

13. A method according to any one of claims 1 to 12, characterized by: the polymer melt is injected into a bristle-forming channel having a substantially continuously decreasing cross-section from the injection end.

14. A method according to any one of claims 1 to 13, characterized by: the polymer melt is injected into an inlet region which tapers toward the bristle-forming channel nozzle to produce a drawing flow.

15. A method according to any one of claims 1 to 14, characterized by: the molten polymer is injected into the bristle-forming channel and has a cross-sectional profile with at least one discontinuity which decreases in the direction of the polymer flow.

16. A method according to any one of claims 1 to 15, characterized by: a bristle-forming channel cross-section having a maximum width of 3mm was selected.

17. A method as claimed in claim 16, wherein: the ratio of the maximum width to the length of the channel is selected to be less than or equal to 1: 5.

18. A method as claimed in claim 17, wherein: the ratio of the maximum width to the length of the channel is selected to be less than or equal to 1: 10.

19. A method as claimed in claim 17, wherein: the ratio of the maximum width to the length of the channel is selected to be less than or equal to 1: 250.

20. A method according to any one of claims 1 to 19, characterized by: the polymer melt is simultaneously injected into a plurality of adjacently disposed bristle forming channels to form a corresponding number of bristles.

21. A method as claimed in claim 20, wherein: the polymer melt is injected into the adjacently arranged bristle forming channels while simultaneously forming a connecting portion between at least two bristles.

22. A method as claimed in claim 20, wherein: after the bristles are injected, a polymer melt consisting of another polymer is injected, forming a connection between at least two bristles.

23. A method according to any one of claims 20 to 22, characterized by: the polymer melt is injected in the case of forming at least one bristle carrier connecting two or more bristles.

24. A method according to any one of claims 21 to 23, characterized by: the polymer melt is injected while forming a bristle carrier that connects the bristles and forms a brush body.

25. A method according to claim 23, wherein: at least one other polymer melt consisting of other polymers is injected onto the bristle carrier.

26. A method according to any one of claims 20 to 25, characterized by: a number of bristles of different lengths were injected.

27. A method according to any one of claims 20 to 26, characterized by: a number of bristles with different cross-sections were injected.

28. A method according to any one of claims 20 to 27, wherein: a number of bristles are injected having different cross-sectional profiles over their length.

29. A method according to any one of claims 20 to 28, wherein: a plurality of bristles are injected in a parallel orientation to each other.

30. A method according to any one of claims 20 to 28, wherein: at least a portion of the bristles that are not parallel to each other are injected.

31. A method according to any one of claims 20 to 30, characterized by: bristles of the same geometry but differing flexural elasticity (stiffness) are produced by injecting different polymer melts into the same shaping channel.

32. A method according to any one of claims 1 to 31, characterized by: bristles consisting of a polymer or polymer mixture are injection-molded, which in the hardened state have a reduced secondary binding force.

33. A method according to any one of claims 1 to 32, characterized by: bristles consisting of a polymer with additives that become effective in use are injection molded.

34. Device for injection molding bristles from thermoplastic polymers, comprising a device for generating an injection pressure and an injection mold, which has at least one supply channel for the molten polymer and at least one cavity shaped as a shaping channel with a profile corresponding to the length and cross-sectional profile of the bristles to be produced, wherein the shaping channel is assigned a venting structure for venting air that is compressed during injection molding, characterized in that: the device is designed to produce at least 500bar (0.5-10)⁵kPa) and the venting structure has a venting cross-section that is distributed over the length of the forming channel and that is designed to cooperate with the injection pressure to form a shear flow having a high core velocity in the center of the polymer melt and a large shearing effect at the walls of the forming channel.

35. The apparatus of claim 34, wherein: the device for generating the injection pressure is designed in such a way that a distribution of 2000 and 5000 (2.10) is possible depending on the length and cross section of the shaping channel⁵To 5.10⁵kPa) was adjusted.

36. An apparatus as claimed in claim 34 or 35, wherein: device for generating injection pressure and venting cross section at forming channelIs designed in such a way that the polymer melt in the forming channel has at least 300bar (0.3.10 bar)⁵kPa) per unit pressure.

37. Apparatus according to any one of claims 34 to 36, wherein: the injection pressure can be controlled according to the length and cross-sectional profile of the shaping channel.

38. Apparatus according to any one of claims 34 to 37, wherein: the venting structure has a venting cross section that can be controlled in accordance with the specific pressure.

39. Apparatus according to any one of claims 34 to 38, wherein: the injection mould with the forming channel is provided with a cooling structure.

40. The apparatus of claim 39, wherein: a cooling structure is provided for a forming passage in an injection mold.

41. Apparatus according to any one of claims 34 to 40, wherein: the injection mold is comprised of a plurality of layered die plates perpendicular to the longitudinal direction of the shaping channel, wherein each die plate has a length of the shaping channel.

42. The apparatus of claim 41, wherein: the exhaust structure is formed on the mold plate.

43. An apparatus as claimed in claim 42, wherein: the exhaust structure is arranged between the joint surfaces of the templates which face each other.

44. An apparatus as claimed in claim 43, wherein: the exhaust structure is formed by a gap between mutually facing surfaces of the templates.

45. An apparatus as claimed in claim 43, wherein: the exhaust structure is constituted by roughness on the surface of the template.

46. Apparatus according to any one of claims 34 to 45, wherein: the venting structure has a venting cross-section with a width of 5 to 300 μm over the shaped channel-shaped profile.

47. Apparatus according to any one of claims 34 to 46, wherein: the venting structure has a venting cross section which expands outward from the profile of the shaped channel shape.

48. Apparatus as claimed in any one of claims 34 to 47, wherein: the exhaust structure is connected to an external negative pressure source.

49. Apparatus according to any one of claims 34 to 48, wherein: the shaping channel has a cross-section that remains substantially constant over its length.

50. Apparatus according to any one of claims 34 to 48, wherein: the shaping channel has a substantially uniformly decreasing cross-section towards its end.

51. An apparatus as recited in claim 50, wherein: the shaping channel tapers at an angle (draft) of less than 1.0 ° on the straight centerline.

52. Apparatus as claimed in any one of claims 34 to 51, wherein: the shaping channel has a cross-section that decreases discontinuously towards the end.

53. Apparatus as claimed in any one of claims 34 to 52, wherein: the maximum width of the cross section of the forming channel is less than or equal to 3 mm.

54. Apparatus according to any one of claims 34 to 53, wherein: at least one injection end die plate with a flare tapering toward the shaping channel is connected in front of the die plate with the shaping channel on its end facing the inlet channel.

55. Apparatus as claimed in any one of claims 34 to 54, wherein: the ratio of the maximum width of the cross-section of the shaping channel to its length is between 1: 5 and 1: 1000.

56. Apparatus according to any one of claims 34 to 55, wherein: the number and thickness of the die plates match the length of the forming channel.

57. Apparatus according to any one of claims 34 to 56, wherein: the number of die plates is inversely proportional to the ratio of the cross-sectional maximum clear width to the shaping channel length.

58. Apparatus as claimed in any one of claims 34 to 57, wherein: the die plate has a thickness of about 3 to 15 times the average diameter of the forming channel.

59. Apparatus as claimed in any one of claims 34 to 58, wherein: the templates are movable individually or in groups perpendicular to the plane of the plates.

60. Apparatus as claimed in any one of claims 34 to 59, wherein: at least some of the templates may be movable parallel to adjacent templates.

61. An apparatus as claimed in claim 59 or 60, wherein: for demolding the bristles, the templates can be withdrawn individually or in groups in time.

62. Apparatus according to any one of claims 59 to 61, wherein: the die plate facing the feed channel can be finally retracted during demolding.

63. Apparatus according to any one of claims 34 to 62, wherein: the injection mould has shaped channels of different lengths and/or different cross-sectional profiles.

64. Apparatus according to any one of claims 34 to 63, wherein: injection molds of standard design for producing bristles of a predetermined length have a number of templates which is adapted to the length thereof and can be removed or fitted in a number adapted thereto in order to vary the bristle length.

65. Apparatus according to any one of claims 34 to 64, wherein: the injection mould has a shaping channel with a centre line which is inclined at an angle to the direction of movement of the mould plates, and each mould plate has a length of the shaping channel, the dimensions of which are selected such that the mould can be removed by a stepwise displacement of each mould plate despite the angular deviation.

66. Apparatus according to any one of claims 34 to 65, wherein: the injection mould has a shaping channel with a centre line which is curved relative to the direction of movement of the mould plates, each mould plate having a length of the shaping channel, the dimensions of which are selected such that demoulding is possible by gradual lifting of the respective mould plate according to the curvature.

67. Apparatus according to any one of claims 34 to 66, wherein: the injection mould has at least one such mould block which is movable in its plane relative to the adjacent mould plate and which together with it forms a clamping device for the entire bristle active over the corresponding length of the shaping channel after injection moulding of the bristle.

68. An apparatus as set forth in claim 67, wherein: the die plates forming the clamping device are movable in or against the direction of stripping.

69. An apparatus as claimed in claim 67 or 68, wherein: the mold plates forming the clamping device together with the clamped bristles can be removed from the injection mold after demolding and serve as handles for the bristle displacement position.

70. An apparatus as claimed in any one of claims 67 to 69, wherein: the mold plates forming the clamping device are replaced after removal by a set of identical mold plates in order to replenish the injection mold completely for the next injection stroke.

71. Apparatus according to any one of claims 34 to 70, wherein: the injection mould is composed of at least two groups of mould plates with a clamping device, wherein the first group comprises a part of the forming channel with the end, the other group comprises the rest part of the forming channel, the first group can be withdrawn from the second group and the second group in sequence, the injection process is divided into injection stroke numbers corresponding to the group number, so that the polymer melt is injected into the complete forming channel in the first injection stroke at the initial position of the injection mould closing, then the first group is withdrawn from the other groups under the condition that the injection blank is moved together by the clamping device, the withdrawal stroke is smaller than the length of the injection blank, then the other polymer melt is injected into the empty length of the forming channel of the other group in the second injection stroke, the injection/withdrawal steps are repeated until the last group is withdrawn, to produce bristles that in some cases are composed of different polymers that are longer than the length of the shaping channel.

72. Apparatus as claimed in any one of claims 34 to 71, wherein: at least the template having the shape profile at the end of the shaping channel can be exchanged for a template having other shape profiles for creating bristles with differently shaped ends.

73. Apparatus according to any one of claims 34 to 72, wherein: at least the die plate having the shape profile at the end of the shaping channel can be exchanged for a die plate having a different shaping channel length section.

74. Apparatus as claimed in any one of claims 34 to 73, wherein: a cavity for connecting two or more shaping channels is arranged between the input channel and the shaping channel of the injection mould so as to form the mutual connection part of the bristles.

75. An apparatus as recited in claim 74, wherein: a cavity is formed for creating a bristle carrier that connects all of the bristles.

76. An apparatus as claimed in claim 74 or 75, wherein: forming a cavity for creating a brush body or a part thereof.

77. Apparatus according to any one of claims 74 to 76, wherein: the mould cavity used to produce the brush body or a part thereof is made as a multicomponent structure consisting of different polymers.