Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – To produce composite – plural part or multilayered article
Reexamination Certificate
1999-06-24
2003-02-04
Silbaugh, Jan H. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
To produce composite, plural part or multilayered article
C264S247000, C264S267000, C264S273000
Reexamination Certificate
active
06514445
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for making two component, injection moulded personal grooming implements, especially toothbrushes. In particular it relates to a process for improving the adhesion between thermoplastics and thermoplastic elastomers so that flexible joints between the materials in the neck or head of the implement can withstand repeated flexing without loss of adhesion at the joint. The invention further relates to two component, injection moulded personal grooming implements having high levels of adhesion between the components.
BACKGROUND OF THE INVENTION
The configuration of human teeth requires that the ideal bristle contour for toothbrushes for brushing the buccal or outside surfaces of teeth be concave and that the ideal bristle contour for brushing the lingual or inside surfaces of teeth be convex. Yet, most brushes are still of relatively rigid, single piece construction and of fixed configuration. The bodies of toothbrushes and similar implements are typically made from polypropylene or similar thermoplastic materials.
In many brushes a second, elastomeric component, such as a thermoplastic elastomer, is employed in the handle to aid grip or to provide a distinctive appearance. The two component brush is typically now made by injection moulding, such as described in “Zahoransky's fully automatic two-colour mould”. Brossa Press (1989). The process typically involves a first moulding step in which a thermoplastic body is made, incorporating voids to accept the elastomer. In a second step, the elastomer is injected into the voids where it will typically become partially mechanically anchored, on cooling and setting, and also fused to the thermoplastic body. In the handle, the demands on the joint between the thermoplastic body and the elastomer are, typically, not high.
Brushes have, however, been described that incorporate a link for allowing the head to flex relative to the handle, as described for example in EP-A-371,293 to EP-A-613,636. In the brushes described therein the flexible linking employs an elastomer to aid or modify flexibility and the joint between the elastomer and the body will be subject to greater stress.
WO 92/17092, WO 92/17093 and WO 96/02165 disclose toothbrushes having resiliently flexible, bristle-bearing heads, the heads, in certain embodiments being in the form of two or more segments which are flexibly and resiliently linked to each. Gaps between the segments can be wholly or partially filled with an elastomer. In brushes of the type of construction the bond between the elastomer and the body can be subject to great stress, repeatedly applied through frequent use. However, none of the aforementioned documents describes how to achieve a robust joint between the two materials which will stand up to repeated use.
It has now surprisingly been found that the strength of fusion between the elastomer and the brush body can be substantially improved by raising the elastomer injection temperature above the range from 190° C.-210° C. customarily employed, without thermal degradation of the elastomer.
It is accordingly an object of this invention to provide a process for making two component, injection moulded personal grooming implements which can flex resiliently and which had good long-term durability.
It is a further object of this invention to provide a two component, injection moulded personal grooming implement having increased strength of fusion between a plastic body and an elastomer.
SUMMARY OF THE INVENTION
According to one aspect of the present invention there is provided a process for forming a resiliently flexible joint in the handle or head of a personal grooming implement; the implement comprising a handle having two ends, and at one end thereof, a head comprising a grooming means; the process comprising the steps of:
i) providing an implement blank including at least one region of plastic material defining a void space in the head or the handle; and
ii) injecting an elastomer into the void space at a temperature of at least 245° C. thereby fusing the elastomer to the plastic material and forming the resiliently flexible joint.
According to a second aspect of the invention there is provided a personal grooming implement having an elongated handle and a head disposed at one end thereof, the head comprising a grooming means; the handle or head including a resiliently flexible joint between a first region made from a plastic material with a Vicat softening point of less than 245° C., and a second region made from an elastomer, wherein the elastomer is fused to the plastic material such that the elastomer can be stretched to 120% of its unstressed length without separation of the elastomer from the plastic material.
The process of this invention provides improved adhesion between the elastomer and the plastic components so that flexible joints where the two components are bonded together by fusion are better able to withstand repeated flexing without degradation of the bond. The durability of the implement is thereby improved.
DETAILED DESCRIPTION OF THE INVENTION
The personal grooming implement of this invention can be any implement of the type that has a sufficiently elongated handle for the user to grip and, disposed at one end of the handle, a head comprising a grooming means. The implement can, for example be a toothbrush, hairbrush or a massaging implement. More especially, it is a toothbrush.
The head comprises a grooming means. The grooming means can take the form of bristles, combing teeth, polishing materials, rubber massage pads and the like. In preferred embodiments herein the implement is a toothbrush wherein the grooming means comprises a plurality of bristles extending from the head.
The head can be detachably connected to the handle, for example to permit replacement of the head when bristles become worn, in which case the head has a point of attachment for the handle. The head can comprise a multiplicity of connected segments. A first head segment can be continuous with the handle. In a preferred embodiment the handle and first head segment is a single piece formed by injection moulding. Preferably, the handle and all of the head segments are formed within a single mould by injection moulding. In any case the handle has a longitudinal axis extending between its two ends. This axis also defines the longitudinal axis of the head which is co-extensive with the axis of the handle. Preferably the head is of generally flattened construction having a pair of opposing faces and the head also has a transverse axis lying orthogonal to the longitudinal axis and generally parallel to the opposed faces. References to transverse or longitudinal herein refer to directions which are respectively parallel to these transverse and longitudinal axes, unless indicated otherwise.
An essential feature of the implement of this invention, and of the process for forming an implement is that the implement, or the implement thereby formed, includes a resiliently flexible joint in the handle or the head, the joint comprising a plastic material and an elastomer. By “resiliently flexible joint” herein is meant a region comprising both plastic material and elastomer which is able to articulate on the application of a force experienced under normal usage conditions for the implement, and further, that when the force is removed the implement will return to essentially the same starting configuration within 60 seconds, preferably within 30 seconds. Preferably the head includes such a resiliently flexible joint.
The head and handle are generally made of relatively non-compressible materials, preferably with a modulus of elasticity of at least about 500 MPa, more preferably at least about 1000 MPa, which are conventional in the manufacture of toothbrushes, especially plastic materials. Especially the plastic material has a Vicat softening point of less than 245° C., more preferably less than 220° C. and especially less than 200° C. Suitable plastic materials include, for example, polyamides and polypropylen
Cann David Victor
O'Neill Kilian John
Stark Roland
Lee Edmund H.
Silbaugh Jan H.
The Procter & Gamble & Company
Vago James C.
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