CZ293029B6 - Process for forming a two-component, resiliently flexible joint in a personal grooming implement and the personal grooming implement formed in such a manner - Google Patents

Abstract

The present invention relates to a process for forming a two-component, resiliently flexible joint in a personal grooming implement, whereby elastomer (7) is injected into a void space in a plastic handle (5) or head (2) at a temperature of at least 245 degC, thereby fusing the elastomer (7) to the plastic and forming the resiliently flexible joint. The invention further relates to a personal grooming implement including a resiliently flexible joint between a plastic material having a Vicat softening point of less than 245 degC, and an elastomer (7), wherein the elastomer is fused to the plastic material such that the elastomer (7) can be stretched to at least 120 percent of its unstressed length without separation of the elastomer (7) from the plastic. The invention provides improved adhesion between the elastomer (7) and the plastic, from which segments (6) are made, so that flexible joints are better able to withstand repeated flexing.

Description

A method of making a flexible joint for a personal cleaning tool and a personal cleaning tool produced in this way

Technical field

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a process for the manufacture of a flexible flexible joint for a personal cleansing tool and a personal cleansing tool produced therewith, and more particularly to a process for manufacturing two-component injection molded personal cleansing tools, particularly toothbrushes. so that the elastic joints between the neck or tool head materials can withstand repeated bending without losing the adhesion of the joints, and further provides two-component injection molded personal cleansing tools having a high level of adhesion between components.

BACKGROUND OF THE INVENTION

The arrangement and shaping of human teeth requires that the ideal shape of the toothbrush bristles for cleaning the tooth surfaces on the mouth side or the outer surfaces of the teeth be concave and that the ideal shape of the toothbrush bristles for cleaning the tooth surfaces on the tongue side or the inner surfaces of the teeth is convex. Toothbrush or similar tool bodies are typically made of polypropylene or a similar thermoplastic material.

In a number of brushes, a second elastomeric component, such as a thermoplastic elastomer, is employed for better gripping of the handle or for a distinctive appearance. A typical two-component brush is now manufactured by injection molding, as described in the publication "Zahoransky's fully automatic two-color molding", published by Brossa Press (1989). This manufacturing process typically comprises a first molding step during which a thermoplastic body is formed in which cavities for the elastomer inlet are formed. During the second step, the elastomer is injected into these cavities in which it is anchored partly mechanically by cooling and settling and partly by bonding to the thermoplastic body. Typically, in the case of a handle, high demands are not placed between the thermoplastic body and the elastomer.

However, there are brushes that have a cell that allows the head to bend relative to the handle, as described in EP 0 371 293 or in EP 0 613 636, for example. In the case of said brushes, these elastic members comprise an elastomer that aids elasticity or it adjusts the elasticity so that the joints between the elastomer and the body are subjected to greater strain.

WO 92/17 092, WO 92/17 093 and WO 96/02 165 disclose toothbrushes having resiliently flexible, bristle-bearing heads, wherein in certain embodiments these heads are in the form of two or more than two segments that flexibly and resiliently attach together. The gaps between the segments may be wholly or partially filled with an elastomer. In the case of brushes of this type, the joint between the elastomer and the body may be subjected to repeated stress associated with partial use. However, neither document describes how a durable bond can be formed between the two materials to withstand repeated use.

Also known is the toothbrush described in EP 0 577 656, whose structure is arranged to contain gaps filled with elastomer, but the brush head does not rest on the elastomer that holds the individual segments of the brush together. The rigid connection is mediated by thin layers of polypropylene. The elastomer, as a highly extensible material, is not directly used to bond the segments itself.

-1 CZ 293029 B6

It has now been found that the bond strength between the elastomer and the brush body can be substantially improved by increasing the temperature of the injected elastomer to the commonly used temperature range of 190 ° C to 210 ° C without deteriorating the elastomer properties by heat.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a method for producing 10 two-component injection molded personal cleansing tools that can be flexibly bent and exhibit long-term durability.

It is a further object of the present invention to provide a method for producing two-component, injection molded, personal cleansing tools having improved bond strength between the body and the elastomer.

Said objects are achieved by a method of making a flexible joint for a personal cleaning tool according to the invention, said tool comprising a handle having two ends and a cleaning agent head at one end, the invention comprising forming a tool blank having at least one an area of plastic material defining an empty space in the head or handle; and injecting the elastomer into the void at a temperature of at least 245 ° C, 25, thereby causing the elastomer to bond to the plastic material to form a resiliently flexible joint.

A preferred embodiment of the method is that the resiliently flexible joint is formed in the head.

It is further preferred that the plastic material is polypropylene.

Further, it is preferred to carry out the process by injecting the elastomer at a temperature in the range of from 245 ° C to 270 °, more preferably in the range of from 250 ° C to 260 ° C.

According to the method of the present invention, a personal cleansing tool having a resilient flexible joint is produced having a 35 elongated handle and a head disposed at one end of the handle, and cleaners are located on the head, the handle or head comprising a resiliently flexible joint between the first area made of plastic material. A Vicat softening temperature of less than 245 ° C and a second region made of elastomer, wherein the present invention is that the elastomer is bonded to a plastics material such that the elastomer 40 can be stretched to at least 120% of its unstressed length without separating the elastomer from the plastic material.

The personal cleansing tool can also be designed such that the plastic material is polypropylene.

The personal cleansing tool may also be preferably made of an elastomer that is stretchable up to 150%, more preferably up to 200% of its stressed length without separating the elastomer from the plastic material.

The invention provides improved adhesion between the elastomer and the plastic components, so that the elastic joints in which the two components are joined together have a better ability to withstand repeated bending without degrading the joint properties. This improves tool life.

The personal cleaning tool may be any tool of the type having a sufficiently elongated handle which is held by the user, and positioned at one end of the handle.

-2GB 293029 B6 Cleaning agent head. Such a tool may be, for example, a toothbrush, a hair comb or a massage tool. More specifically, it is a toothbrush whose head comprises cleaning agents. Such cleaning compositions may take the form of bristles, brushing teeth, polishing materials, rubber massage cushions and the like. In preferred embodiments of the present invention, it is a toothbrush wherein the cleaning compositions are in the form of a plurality of bristles protruding from the head.

The head may attach to the handle, for example, to allow the head to be replaced after the bristles have worn, in which case the head has a point for attaching the handle. The head may comprise a number of segments to be joined. The first head segment may adjoin the handle. AND

In a preferred embodiment, the handle and the first head segment form a single injection molded part. It is preferred that all head segments are made in a single mold by injection molding. In either case, the handle has a longitudinal axis that extends between both ends thereof. This axis also defines a longitudinal axis of the head that is adjacent to the handle axis. Advantageously, the head has a generally flattened structure with a pair of opposing faces, and the head also has a transverse axis that is perpendicular to the longitudinal axis and substantially parallel to the opposite faces. Unless explicitly stated otherwise, references to transverse or longitudinal directions refer to directions that are substantially parallel to these transverse or longitudinal axes.

An essential feature of the tool according to the invention and the method for manufacturing such a tool is that the tool thus produced has a resiliently flexible connection in the handle or head, the connection comprising a plastic material and an elastomer. "Flexible joint" here means an area containing both a plastic material and an elastomer, which has the ability to react flexibly to the effect of the force exerted under normal conditions of use of the tool and which in addition has the ability to return to virtually its initial form after 60 seconds, preferably after 30 seconds. seconds, from the end of the force that previously applied to the tool. Preferably, the head comprises such a resiliently flexible connection.

The head and handle are generally made of relatively incompressible materials having preferably a modulus of elasticity of at least 500 MPa, more preferably at least 1000 MPa, which is common in plastic toothbrush manufacturing conditions. In particular, the plastic materials have a Vicat softening point of less than 245 ° C, more preferably less than 220 ° C and particularly preferably less than 200 ° C. Suitable plastic materials include, for example, polyamides and polypropylenes. Polypropylene is preferred. Suitable polypropylenes include "Polypropylene PM 1600" (sold by Shell) having a modulus of elasticity (ISO 178) of 1500 MPa and "Apryl 3400 MAI" from "Elf Atochem". It is preferred that the foaming agent such as " Hydrocerol HP20DP " from Boehringer-Manheim is mixed with polypropylene at a level of from 1% to 3%, preferably from 1.5% to 2.5%, of the total weight of the polypropylene. The foaming agent aids in the flow of polypropylene during molding, and in particular assists in ensuring uniform hinge formation when used. The handle itself is generally rigid and may have a shape that is conventional in the toothbrush industry. Alternatively, such a handle may have a neck portion that is more flexible than the rest of the handle and which may be formed, for example, by incorporating the aforementioned, flexible joint.

During the execution of the first step of the present invention, a tool blank is formed which comprises at least one region of plastic material defining an empty space in the head or handle. The tool blank is essentially a tool prior to the injection of elastomers and optionally prior to further finishing procedures such as the attachment of cleaning agents. All or a smaller portion of the tool blank may take the form of at least one area of plastic material. Suitable plastic materials have been mentioned above. The void may be in the form of a single groove in the head or may have a more complex shape. The void should be sized to weaken the head or handle or otherwise create the existence of resilient conditions at the designated location. In the preferred embodiments described herein, the tool blank comprises one or more empty space in the form of grooves or gaps that divide the head into segments. Preferably, two, three or four such segments are employed, with four segments being preferred. Larger quantities above the indicated number

This would increase the complexity of production, and in the case of a toothbrush in which tufts of bristles are placed on the head segments, it would be difficult to achieve the necessary tuft density on the brush cleaning head. Said segments are positioned in a longitudinal sequence on the head such that a longitudinal line extending from the end of the handle to the free end of the head extends through the first head segment before the second head segment and so on. More specifically, there is a first head segment that attaches to or adjoins the handle and one or more additional head segments that are aligned in a longitudinal sequence toward the free end of the head. It is preferred that the head segments are single-layered so that any straight line perpendicular to the opposite faces will generally pass through a single type of material. In general, each head segment will be made of the same material, which will preferably be the same material from which the handle is made, so that all segments will be made in a single injection molding step.

In the finished tool, all head segments are connected by means of fasteners. These connection means may take any form that is suitable for the intended purpose of the tool, and in practice this will result in at least one resiliently flexible connection in which the elastomer attaches to the plastic region. Such connection means may be, for example, glue, plastic joints which are integral with or separate from the head segments, metal joints or an elastomer which is fused to said plastic segments. In the preferred embodiments described herein, at least one of the segments is attached to an adjacent segment or handle by connecting means comprising mainly an elastomer having an elastic modulus of less than 500 MPa. As used herein, "containing mainly elastomer" means that the elastomer is the only mechanical joint between one segment and an adjacent segment or handle. The only mechanical connection means that there are no adjacent non-elastomeric connections, such as bridges or springs connecting the segments together. However, the elastomers may contain other buoyant materials, such as metal granules or pigments to provide a distinctive appearance. These filler materials can generally contribute neutrally to the mechanical bonding of the segments and / or the segment and the handle and their removal, if any, does not alter the bond strength of the materials. In preferred embodiments, there are one or more segments that do not bond until the elastomer injection molding is performed, and the tool blank may include several unbonded segments held in place only by the mold in which the tool blank is prepared and formed. The gaps between the segments are voids which, when filled with the elastomer, can take the form of resiliently flexible joints so that one segment can form a link relative to the other segment.

In the highly preferred embodiments described herein, the head has an upper face and a lower face, and the fasteners are in the form of strips of elastomer that extend transversely across the head and from the lower and from the upper face to the lower face. For example, in a head comprising four segments that are spaced longitudinally on the head when the first segment is immediately adjacent the handle, there are three such connecting means. The elastomer strips may have different thicknesses, which may vary from one strip to the next, or even the width or depth of the strip. A suitable thickness of these strips, which is measured on the longitudinal axis, is in the range of 0.1 mm to 10 mm, preferably 0.3 mm to 5 mm, and most preferably 0.5 mm to 3 mm.

In alternative embodiments, the segments are additionally connected by hinges of the same material as the segments, the hinges being thinner or narrower than the segments to be joined, and the entire tool blank forms a single interconnected part. It goes without saying that in the same tool there may be some fasteners which form the hinges and other means which mainly comprise the elastomer. The free spaces between the segments that are joined by the hinges will be referred to in this patent specification as grooves.

The grooves may have different width and depth, and the distances between the grooves may also be different. In this way, the elasticity of the head can be adjusted along the length and / or on the head surface. It is advantageous

That only the transverse grooves are changed in this way. Changing the groove depth affects the placement and thickness of the hinges that connect the segments. In preferred suspension designs, the head has a pair of opposing faces on which grooves are located which are located in pairs so that there is a residual hinge between the two faces. In the case of a toothbrush head having a thickness of from 4 mm to 6 mm, typically 5 mm, groove depths in the range of 1.4 mm to 3 mm, more preferably 1.5 to 2.8 mm, are suitable. Suitable hinge thicknesses range from 0.4 mm to 2.0 mm, more preferably from 0.5 to 1.5 mm. When using transverse grooves, some of the hinges that are or will be near the handle are less flexible than those hinges that are or will be farther away from the handle. In this way, more uniform bending of the head can be achieved. Variations in elasticity can also be achieved by varying the thickness of the hinges. In a preferred embodiment, the hinge closest to the handle is three times, preferably more than twice, thicker than the hinge furthest from ^the handle. By way of example, a toothbrush thickness assembly having 3 transverse grooves with respective thicknesses of 1.2 mm, 0.6 mm and 0.6 mm respectively from the end of the handle. When the same hinges are used on the entire brush head, there is a tendency to predominate bending the head on the hinge closest to the handle. The groove depth on one face may be different than the groove depth on the opposite face.

Increasing the width of the grooves increases the gap between the segments and hence the length of the hinges, which increases their flexibility. However, since in the case of cleaning agents such as bristles, it is preferable to be placed on the segments rather than on the elastomer injected between the segments, the increased groove length also leaves less space for placing the cleaning agents in proportion to a given head size. Suitable groove widths range from 0.3 mm to 3.0 mm, more preferably from 1.2 mm to 2.0 mm. The grooves are preferably slightly sloped inwardly to the bottom of the groove, and are water-approached at an angle of from 3 ° to 10 ° for ease of injection molding. When bending the tool, the groove width changes more rapidly at the top of the groove than at the bottom of the groove, this relative change being a function of the groove width and depth. Since this groove change results in the compression or tensioning of the elastomer in such groove, the geometry of the groove containing a particular elastomer can be used to control the flexibility of the tool.

The hinges may have the entire length of the grooves or preferably may take the form of one or more gaps in the hinges or on the side of the hinges of the grooves in these regions having the same depth as the head depth. In injection molding, such a gap allows the elastomer to flow from one face to the other. In a preferred embodiment, the hinges are intermittent and two or more than two hinges are used, but preferably just two, which connect each segment to an adjacent segment or handle. In this embodiment, there are gaps between the hinges and each side. In the case of rectilinear grooves, the widths of the hinges are not so severe as such limits can still be formed, but wide hinges may be subject to structural deterioration when used with a non-rectilinear groove. Suitable hinge widths range from 0.5 mm to 4.0 mm, preferably from 1.0 mm to 3.0 mm.

Preferably, each hinge is positioned between two faces and at a distance of at least 10%, more preferably at least 20% and most preferably at least 30% of the depth of the head from each face. The distance of the hinge from the face is measured by a perpendicular from the top of the face to the nearest boundary surface of the hinge means. Placing the hinges away from the tool head faces means that the hinges are subjected to less tension or compression when bending the head, thereby extending their durability. In a particularly preferred embodiment, the tool head has transverse grooves which are arranged in pairs such that one member of one pair is on one face in direct opposite relationship to the other member of the pair, with one or more hinges located between the segments so connected, so that each hinge is located between two faces and at a distance of at least 10%, more preferably at least 20% and most preferably at least 30% of the depth of the head from each face.

During the second, essential step of the process of the present invention, the elastomer is injected into the free space (s) at a temperature of at least 245 ° C, wherein:

-5GB 293029 B6

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The elastomer fuses into the plastic material to form a flexible joint. It is preferred that the elastomer be injected at a temperature in the range of from 245 ° C to 270 ° C, more preferably in the range of from 250 ° C to 260 ° C. Injection temperature is understood to be the temperature at which the elastomer enters the mold.

In a typical injection molding assembly using a screw extrusion cylinder, this temperature need not be the same as the temperature of the elastomer in the cylinder. Typically, the cylinder is maintained at a lower temperature in the range of 210 ° C to 220 ° C to limit the possibility of combustion or thermal degradation of the elastomer, wherein heating to the final injection temperature is accomplished by a hot channel assembly incorporated between the cylinder nozzle and final injection outlet.

Other preferred conditions of the injection molding step include:

An injection pressure in the range of from 30 MPa to 80 MPa, more preferably from 40 MPa to 70 MPa, and most preferably from 50 MPa to 60 MPa, and an elastomer injection time period of less than one second, more preferably less than 0.8 seconds. The shorter injection time ensures that the elastomer reaches all regions of the elastic joint at the desired temperature.

The holding pressure upon completion of the injection of the elastomer in the range from 5 MPa to 15 MPa, more preferably from 8 MPa to 12 MPa, for a period of from 2 seconds to 5 seconds.

Elastomers are well known in the art of injection molding. As used herein, the term "elastomer" refers to a material that is both elastically compressible and elastically stretchable. For the purposes of the present invention, suitable elastomers have a modulus of elasticity of less than 500 MPa. Preferred elastomers for use in the context of the present invention have a modulus of elasticity of less than 300 MPa, with thermoplastic elastomers having a Shore hardness of 30 Shore A to 74 Shore D being particularly preferred, polyolefin types such as styrene-ethylene-butylene-styrene (SEBS) being preferred. ), such as "Kraton® G", but other classes of elastomer such as polyurethanes and polyamides may be used. An example of an elastomer is "PTS Thermoflex 75" (marketed by "Plastic Technology Service", Germany) having a modulus of elasticity (ISO 178) of 100 MPa and a Shore hardness (ISO 868) of 80 Shore A. Elastomers of "PL 12 292 and PL 12 293 '(marketed by' Multibase, Saint Laurent DuPont 'France) are also applicable for the purposes described here. In general, an elastomer is chosen which is based on the same chemical class of polymers as that applied to the head segment material, as this helps to seal the elastomer into the head segments. For example, when the head segments are made of polypropylene, a polyolefin-based elastomer is selected. Optionally, the elastomers may be mixed with a suitable plasticizer or foaming agent, giving them greater compressibility. The color of the elastomeric material may be the same as the color of the head segments or may be different to achieve a different strip appearance or other distinctive pattern. More than one type of elastomer may be used in the tool as a whole. This can be applied, for example, when there is a requirement to gradually vary the head elasticity over its entire length. One way of accomplishing this is to use a soft elastomer as a tie between the pair of segments nearest the free end of the head and a hard elastomer as a tie between the pair of segments nearest the handle end of the head.

The elastomer is bonded to adjacent segments and / or handle so that the elastomer can stretch at least up to 120%, more preferably up to 150% and most preferably up to 200% of its unstressed length without separating the elastomer from the head segments. This gives the present invention particular utility in the design of flexible toothbrush toothbrushes, which will be further developed hereinafter. The degree and extent of bonding is sufficient when the elastomer can stretch up to 120% of its unstressed length without separating the elastomer from the head and / or handle segments. In this way, preferably at least 50%, more preferably at least 75% and extremely 100% of the bonding area between the elastomer and the head or handle segment are bonded to each bonding area of one elastomer / segment.

-6GB 293029 B6

By "without separating the elastomer from the head and / or handle segments" is meant that the elastomer does not completely separate from the head and / or handle segments. Since even a partial loss of attachment of the elastomer to the head segment or handle can compromise the functionality and / or integrity of the tool, it is advantageous to avoid even partial separation. In preferred embodiments, the elastomer begins to separate to less than 30%, more preferably less than 15%, and most preferably to less than 5% of the bonding area between the elastomer and the head or handle segment when the elastomer extends to at least 120%, more preferably to 150% and most preferably up to 200% of its unstressed length. These results should reflect the fact whether the elastomer is stretched by the linear bending, folding or twisting of one segment relative to the adjacent segment or handle. Due to some geometric differences of the individual joints between the two segments or segment and the handle or to the folding and twisting of one segment relative to the other segment, as the stretching ranges of the elastomer on the joint face vary, special attention is required when measuring partial separation. In cases of such different stretching, each point of any bonding surface to be measured should be measured on a line guided by an elastomer that is perpendicular to the bonding surface at the location of the detected separation, in the idle, non-tensioned state of the tool. In cases of folding or twisting, this line could deviate from the perpendicular as one segment moves relative to the other.

During its useful life, a tool having the elastically flexible head described herein may be subjected to the stretching of the elastomer by, for example, bending the head many times, in the order of thousands of bends. Advantageously, the elastomer-segment joint is able to withstand repeated stretching of the elastomer in the above range and thereafter and release back to at least 10,000, more preferably at least 25,000, and most preferably at least 75,000 stretching-release cycles.

In highly preferred embodiments of the present invention, the head comprises at least one longitudinal groove that interconnects the transversely arranged elastomeric strips and allows the elastomer to flow from one strip to the other during injection molding. In the case of a tool whose grip is made by injection molding together with the head, this longitudinal groove may extend along the length of the grip so that the same injection point in the mold usually used to inject the gripping material may be used for injection into voids in head. Normally, this longitudinal groove will not pass through the full depth of the handle or head at all points, although this is possible, for example, when forming opposite grips at the upper and lower surfaces of the handle.

The present invention is particularly applicable in the manufacture of tools having a resiliently flexible head. The term "resiliently flexible head" here means that the force under Newton's law acts at one end of the head and the other end is held motionless, the end exerted by the force bending at an angle of at least 2 °, and after termination under the influence of Newton's third law, the head returns to its original position without external force. The rigidly maintained end of the head is defined by a straight line perpendicular to the bending axis and which touches the first point of placement of the cleaning compositions in the form of a row of toothbrush bristles. The end of the head on which the force is applied is located at the opposite end of the head at a point farther from the bending axis. The range of angle at which the head bends due to a force of 3 N is referred to herein as "bending angle". The bending angle can be readily determined by measuring the extent of the vertical displacement of the free end of the head due to a force of 3 N according to a distance x between the fixed point and the point at which the force F is applied. / x. In preferred embodiments, the bending angle is at least 3 °, more preferably at least 5 °, and can be up to 15 ° or more.

In preferred embodiments of the present invention, the tool comprises cleaning means which are located only at one end of the head face, the face having a concave shape. Advantageously, in these embodiments, the head has a bending angle to which the concave shape of the face can be changed to

-7GB 293029 B6 Convex. The head face containing the cleaning means may be concave at rest in relation to both the longitudinal and transverse axes. In a situation where this face is concave relative to the longitudinal axis, the radius of curvature may be different along the length of the head. The radius of curvature is from 10 mm to 500 mm, more preferably from 15 mm to 250 mm and especially from 25 mm to 150 mm.

In practice, the toothbrush of the present invention can be used for brushing teeth by an entirely conventional hand brushing method, preferably according to the recommendations of dental specialists. This tool can also be used in combination with an electric motor as an electrically powered toothbrush.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 is a perspective view of a toothbrush according to the present invention. Some bristles are omitted for clarity and clarity;

Fig. 2 is a partial side view of a toothbrush head according to the present invention;

Fig. 3 is a plan view of a lower face of a toothbrush head according to the present invention;

Fig. 4 is a perspective view of a hanging toothbrush according to the present invention wherein the elastomer is not shown for a clearer transfer of the hinges and grooves; and Fig. 5 is a schematic illustration showing the measurement of the bending angle.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Fig. 1, the toothbrush 1 has a resiliently flexible, flattened head 2 having an upper face 3 and a lower face 4 that is substantially parallel to the upper face 3, and an elongated polypropylene handle 5. The head 2 comprises four polypropylene segments 6, the first of which is part of the handle 5. These segments 6 are joined only by strips of SEBS type elastomer 7 having a hardness of 60 Shore A. The segments 6 are aligned one after the other on the longitudinal axis A - A. according to the transverse axis B - B of the head 2 and from the top face 3 to the bottom face 4. Tufts 19 of the bristles 8 protrude from the top face 3. In fact, these bristles 8 protrude from all four segments of the toothbrush 1. A - A axis slightly concave and has a radius of curvature of 75 mm. The strips of elastomer 7 allow the head 2 of the brush 1 to have sufficient elasticity to effect bending in relation to the longitudinal axis A-A until the upper face 3 has a convex shape. During this change in shape, the elastomer 7 is tensioned at the upper face 3. The elastomer 7 can be stretched over more than 200% of its unstressed length without any noticeable loss of attachment of the elastomer 7 to the segments 6. The head 2 is capable of repetitive bending to said position and back to a rest position in approximately 75,000 cycles without any separation of the elastomer 7 The handle 5 comprises another area of the same elastomer 7 and forms a functional and aesthetically attractive gripping portion.

Toothbrush 1 is produced by sequential injection molding, first by injecting polypropylene forming handle 5 and segments 6 and in a second step injecting elastomer 7 at 25 ° C, which begins to melt together with polypropylene. After the brush 1 has cooled, tufts 19 of the bristles 8 are placed in the pre-formed holes using a stapling procedure.

Referring to Fig. 2, the head 2 having the free end 10 and the end 11 of the handle 5 forms part of the toothbrush assembly. The head 2 has five segments 6 which are aligned longitudinally along the length of the head 2. The segments 6 are resiliently connected through strips

293029 B6 of elastomer 7 and the segment 6 closest to the end 11 of the handle 5 is attached to the handle 5 only by a strip of elastomer 7. The strips of elastomer 7 extend completely transversely along the transverse axis B-B of head 2 and taper from the top face 3 In the upper face 3, these strips of elastomer 7 have a width of 1.2 mm and at the lower face 4, these strips of elastomer 7 have a width of 0.8 mm. The tufts 19 of the bristles 8 protrude from the upper face 3 of the head 2.

This toothbrush 1 is produced by sequential injection molding followed by fastening of the bristles 8 as described in connection with the embodiment shown in Fig. 1.

Referring to FIG. 3, the toothbrush head 2 is attached at one end 11 to the handle 5 so that a complete tool is formed. The head 2 comprises four segments 6, one of which is part of the handle 5. These segments 6 are connected only by strips of SEBS type elastomer 7 having a hardness of 60 Shore A and have waveguides extending obliquely to the transverse axis B - B of head 2. Longitudinal groove 12 it passes over the lower face 4 of the head 2 and the handle 2 so that they can be manufactured using a single injection point.

Referring to Fig. 4, the toothbrush 1 has a head 2 which is made by injection molding together with the handle 5, which head 2 is concave on its upper face 3 with respect to the longitudinal axis A-A. in the handle 5, it is filled with elastomer 7 and forms a handle. These spaces 13 are interconnected by a longitudinal groove 12 which is formed on the underside of the handle 5 and extends further into the head 2 where it connects the transverse grooves 14 between the segments 6. The segments 6 are connected together by thin hinges 15. The elastomer 7 can be injected into the voids 13 from a single injection point 16 and has a color that differs from that of the head 2 material to achieve a distinctive appearance. The head 2 has holes 17 that are disposed on its upper surface to accommodate tufts 19 of the bristles 8.

Giant. 5 shows a measurement of the bending angle. The head 2 has a clamping 18 in the immediate vicinity of the first row of bristles 8 at that end 11 which is adjacent to the handle 5, and a force F = 3 N acts on the opposite end 10. The broken lines show the original position of the head 2 of the brush 1 before applying force F. the vertical displacement y of the free end 10 of the force head F 2 is measured and the bending angle is derived from the displacement y and the distance x between the clamping point and the force applying point F based on the relation tg (bending angle) = y / x.

Industrial applicability

The invention is useful in the manufacture of toothbrushes.

PATENT CLAIMS

Claims (3)

A method of making a flexible joint for a personal cleaning tool, the tool comprising a handle (5) having two ends and a cleaning agent head (2) at one of the ends, comprising: providing a tool blank having at least one region of plastic material defining an empty space in the head (2) or handle (5); and injection molding the elastomer (7) into the void at a temperature of at least 245 ° C, thereby causing the elastomer (7) to bond to the plastic material to form a resiliently flexible joint. Method according to claim 1, characterized in that the resiliently flexible joint is formed in the head (2). -9EN 293029 B6 Method according to claim 2 or 3, characterized in that the plastic material is polypropylene. Method according to any one of the preceding claims 1 to 3, characterized in that the elastomer (7) is injected at a temperature in the range from 245 ° C to 270 ° C, more preferably in the range from 250 ° C to 260 ° C. A personal cleansing tool having a flexible connection made by the method of claim 1, having an elongated handle (5) and a head (2) disposed at one end (10, 11) of said handle (5) and located on said head (2) cleaning means, wherein the handle (5) or head (2) comprises a resiliently flexible joint between a first region made of plastic material having a Vicat softening temperature of less than 245 ° C and a second region made of elastomer (7), characterized in that the elastomer (7) is bonded to the plastic material such that the elastomer (7) can be stretched to at least 120% of its unstressed length without separating the elastomer (7) from the plastic material. Personal cleaning tool according to claim 5, characterized in that the plastic material is polypropylene forming tool segments (6). Personal cleaning tool according to claim 5 or 6, characterized in that the elastomer (7) is stretchable up to 150%, more preferably up to 200% of its unstressed length without separating the elastomer (7) from the plastic material. 3 drawings -10GB 293029 B6 <ε \ <t I