GB2249739A

GB2249739A - Methods for the manufacture of sealing elements

Info

Publication number: GB2249739A
Application number: GB9122410A
Authority: GB
Inventors: Alistair Hill; Hans-Juergen Warnecke
Original assignee: Meteor Gummiwerke KH Badje GmbH and Co
Current assignee: Meteor Gummiwerke KH Badje GmbH and Co
Priority date: 1990-11-09
Filing date: 1991-10-22
Publication date: 1992-05-20
Anticipated expiration: 2011-10-22
Also published as: GB9122410D0; ITTO910836A0; ITTO910836A1; GB2249739B; IT1250039B; DE4035657A1

Abstract

The method comprises applying to a rubber-like substrate a friction-reducing layer of an ethylene-chlortrifluoroethylene copolymer or a mixed polymerisate of this material with other thermoplasts.

Description

2 ""+ 0 7 3'? METHODS FOR THE MANUFACTURE OF SEALING ELEMENTS This

invention relates to methods for the manufacture of sealing elements having a substrate comprising an elastomer, a thermoplastic elastomer or a thermoplast, wherein at least one surface part of the surface of the substrate is overlaid with a polymeric layer which has a greater capacity f or slip than the material of the substrate.

Sealing elements having at least one sealing surface which cooperates with an opposing surface movable relative to the sealing surface and which are overlaid with a friction-reducing layer for this purpose are basically known. one particular application for such seals is for example for motor vehicle windows in which on the one hand a reliable sealing between frame and glass is required, but where it is necessary however that the opening and closing movement of the window should be hindered as little as possible in spite of the seal.

One problem of such sealing structures lies in the reliable connection of the friction-reducing layer with the material of the substrate. From EP 0154121 Al, one such sealing element is known where the substrate is of rubber and wherein a prefabricated overlay strip which constitutes the friction-reducing layer is united with the substrate in an extrusion process, is forced through an extrusion nozzle and finally is subjected to a vulcanisation process.

Polymeric coatings which have a low coefficient of sliding friction are basically known. These can consist for example of polytetrafluoroethylene. The construction of a compound profile, consisting for example of rubber and an anti-friction layer of this material, poses 1 1 difficulties however because of the different elastic properties of these two materials, so that with small bending radii one can expect peeling effects, the appearance of wrinkles in the region of the antifriction layer, and the like.

From DE 3741251 Al there is known a process for the manufacture of a polymer-coated foamed material in which the material forming the foiltype coating is applied in a liquid state to a layer of foamed material and wherein the compound material produced in this way is used as a moisture-resistant foam and insulating foam, for example in the form of double-sided adhesive tape.

The application of friction-reducing. layers to seal bodies is also known in the form of flocculation or varnishing.

From DE-OLS 1450364 it is known to dissolve in a solvent a prepolymer consisting of polyurethane resin and at least one anti-friction means, such as for example chlortrifluoroethylene or polytetrafluoroethylene, as a filler. The solution is applied directly to the sealing surfaces of the substrate 7, 12, 16, is dried and is hardened by exposure to atmospheric moisture, so that a first layer 5, 10, 13 having thickness of 0.025 mm, to 0.075 mm is created. As a rule, larger overall seal thicknesses are necessary. If so. as a subsequent step, at least one further layer 9, 11, 14 is applied in the same way to the initially prepared layer. The application in the form of a solution is expensive, time-consuming and complicated. This is particularly so if on the one hand a slip agent has to be used to reduce the frictional resistance of the polyurethane resin, and if on the other hand several layers have to be superimposed one upon another, which takes considerable -4 4 j i i j i time.

From the US Reissue patent 24478 it is known to provide a sheathing 13, 23 on the surface of the body 14, 24 of silicone rubber O-rings 10, 20, that surface being ridged in the transverse direction, in order to make the O-rings more resistant to chemicals and solvents and to enable them to maintain their elasticity even after lengthy exposure to extreme temperatures. The sheathing should preferably be of polytrifluorochlorethylene, possibly also of for example polytetrafluoroethylene, polyvinylchloride, polyethylene or polyamide. The application of the sheathing should be effected by immersion in a solution or dispersion and possibly with subsequent heating and melting of the sheathing particles in several cycles.

From EP 329048 Al it is known to manufacture a seal profile 10 for a vehicle window aperture by coextrusion of types of rubber of different hardness 22, 23. At the outlet of the extrusion nozzle 21 is provided a guide ring 24 with radial channels 25 and axial channels 25a for strips 14. The strips 14 consist for example of 0.08 to 0.6 mm thickness polytetrafluoroethylene and are sprayed 27 with adhesive on their rear side 14a before their application to sealing lips 11 of the seal profile.

This is expensive to manufacture correctly. The strips 14 are not coextruded together with the rubber profile 10, but are secured by adhesive subsequently.

DE 3036025 Al shows it to be known to provide a seal ring whose substrate 1 is provided on its sealing edge 2 with a chemically bonded, fluoro-organic antifriction overlay of 0.01 to 1.0 pm thickness.

From US 2597976A it is known to overlay a sealing ring of vulcanised rubber-like material with a layer of film-forming material which is resistant to is solvents and swelling as a result of diffusion of liquid hydrocarbons through the film. If a particularly strong bonding between the sealing ring and the layer is desired, then the surface which is to be provided with the layer should be treated with an adhesive.

It is an object of the invention to provide a method of the type first referred to above in which one achieves a sealing element of high elasticity and sealing effect with sealing surfaces having reduced coefficients of sliding friction in the region where they are movable relative to one another, and which simultaneously has a high capacity for flexing without the bond between the friction-reducing slip layer and the substance of the substrate being adversely affected and also avoiding a reduction in the sealing properties and sliding properties.

This object is achieved in a method of the type first referred to above by applying to the parting surface part a layer comprising an ethylenechlortrifluoroethylene copolymer or a mixed polymerisate of this material with other thermoplasts. Such thermoplasts may include polyvinylchloride, polyamide, polyethylene, polypropylene and the like.

It is important to the invention according to this that specific thermoplastic materials are used for the covering, particularly an ethylenechlortrifluoroethylene copolymer. One such material is known for example from the prospectus "HALAR, Der vielseitige thermoplastische Fluorkunststoff" of Allied Corporation Engineered Plastics, PO Box 2332 R, Morristown, New Jersey 07960, USA. The layer can consist solely of this material, which is applied to the substrate in a suitable layer thickness. An essential advantage of this material lies in the fact 1 t 1 1 j i i i t i i is that it gives a good adhesive power relative to rubber and rubber-like materials, and that this material, in the sense of the subject matter of the invention, has favourable sliding properties. By the use of this layer, the rigidity and stiffness of the material of the substrate is in general not affected and the substrate can be flexed to adapt it to very small bending radii without adversely affecting the bonding between the substrate and the layer. Also, the hardness of the material of the substrate is generally not affected, so that a sealing structure formed in this way has a high elastic adaptability to unevenness of a sealing surface. If in individual cases the mechanical properties of this basic material are to be modified, one can do this by using a mixed polymerisate with other thermoplasts, and in this connection reference is made for example to polyvinylchloride, polyamide, polyethylene, polypropylene and the like.

Preferably, the layer is applied in powder form to the parting surface and is heated to a molten state so that after cooling one has a bonding with the material of the substrate. The application of the friction- reducing layer within the framework of a sintering process such as this leads to a particularly reliable bonding to the substrate. For the application of a powder layer one can make use of conventional known devices, in which a heating of the aforesaid materials up to temperatures of about 3000C takes place. At these temperatures the applied powder is transformed into a molten state and forms a uniform layer which, after cooling, forms a reliable bond with the rubber-like material of the substrate. Reference to the application of powder is intended also to include a mixture of materials of the type first referred to above which are treated in the same way but J is possibly with modifications to the temperature of the process.

Alternatively, the layer can be applied by extrusion or injection moulding onto the surface part.

The substrate may have a strip-like shape or alternatively an annular shape. Sealing structures having these shapes find application for various shape seals, particularly for essentially static seals, such as window surrounds, door seals or vehicle seals, for sliding roofs and the like, in which two sealing surfaces which face one another are moved only from time to time and then are moved relatively slowly relative to one another. The sealing structure can however also find use in rotary seals, in which the surfaces to be sealed undergo comparatively rapid movements and over longer periods of time.

Preferably, the coefficient of sliding friction of the layer relative to glass is equal to or less than 0.03, and preferably is equal to or less than 0.02. By the use of the materials referred to above, coefficients of sliding friction having these values are achievable, so that an optimum efficiency of the sealing surfaces which oppose one another is achieved, and indeed with a uniform and enduring sealing effect.

The thickness of the layer can be varied within wide limits. Preferably, the thickness of the layer is between 1 pm and 150 pm, preferably between 10 Mm and 100 pm. After the substrate and the layer have been formed into a unitary body, in the case of flexing of the material of the substrate and of that of the layer one has approximately the same deformation conditions for both, so that with different elasticities one has stress conditions which differ from one another. The thickness of the layer can be adapted within the given limits to the maximum 1 q i i i i j permissible deformation or to the expected deformation. Simultaneously, by means of the thickness of the layer, the friction coefficient can be influenced within certain limits.

Preferably, the parting surface part which is to be covered is mechanically, electrically or chemically roughened before the application of the layer. The surface part may be provided with an adhesive layer which forms the bonding agent between the substrate and the frictionreducing layer. These represent different ways of bonding the layer to the material of the substrate. This can apply both to the roughening of the surface and also to the intermediate provision of an adhesive layer. Reference to the use of an adhesive layer can include the us-e of conventional substances. Because the surface part of the substrate which is to be covered is prepared in this sense for an application of the layer, the reliability of the bond between substrate and layer can be even further improved in this way.

In one embodiment, the substrate and the layer are produced in a coextrusion process in which they are connected one with the other. The manufacture of the sealing structure by such a method represents a particularly economical process.

The substrate can consist basically of a solid, i.e. unfoamed material. It can however alternatively be made of a foamed material, for example cellular or sponge rubber or the like.

In order that the invention may be fully understood, embodiments in accordance with the invention will now be described by way of example and with reference to the accompanying schematic drawings, in which:

Fig. 1 is a sectional view through the 9 is sequence of layers of a sealing element in accordance with the invention; and, Fig. 2 is a sectional view through the sequence of layers of a second embodiment of sealing element in accordance with the invention.

In Fig. 1 the reference numeral 1 indicates the substrate of a strandlike or strip-like sealing element which is manufactured for example by extrusion and consists of an elastomer, for example a soft rubber. The cross-sectional profile of the substrate 1 is relatively unimportant - it is only necessary that it should be characterised by at least a surface part 2 which is to be overlaid with a friction-reducing layer 3. One is aiming for a value for the coefficient of sliding friction of the layer 3 of between 0.02 and 0.03, but preferably equal to or less than 0.02.

The layer 3 has a layer thickness 4 which is chosen to be between 10 pm and 100 pm. It consists of I a high-elasticity material and is securely, immovably bonded to the material of the substrate 1. Because of its small layer thickness it has no adverse effect either on the rigidity or on the stiffness or hardness of the substrate 1.

The layer 3 consists preferably of an ethylene-chlortrifluoroethylene copolymer. The following procedure is proposed in accordance with the invention for the application of the layer 3.

The material of the layer 3 is first applied in powder form to the surface part 2, for which purpose conventional powder coating systems may be used. A sintering process is then.carried out in which this layer is transformed by heating up to temperatures up to 3001C into a molten state, as a result of which a uniform layer thickness results and, after cooling, the layer 3 is securely bonded to the material of the 1 i j 1 1 -4 9_ substrate 1.

The aforesaid powder can, if need be, in order to modify its mechanical properties, f or example the flexibility, be mixed with other thermoplastic plastics materials in powder form, for example polyolefins such as polyethylene or polypropylene and polyamide or polyvinylchloride.

The layer 3 can be applied directly to the surface part 2. However, in order further to improve the adhesion properties of the layer 3, a preparatory surface treatment of the surface part 2 is desirable. This can be effected for example by mechanical roughening, by corona treatment, , by chemical roughening, for example etching with oxidising acids, halogenisation, for example bonding by chlorine, bromine, iodine or fluorine in the surface, or by plasma treatment.

In addition to a surface treatment in the manner aforesaid, an intermediate adhesive layer 5 can be applied to the roughened surface (Fig. 2), which for its part forms the bonding agent for the frictionreducing layer 3. Conventional substances can be used for this intermediate adhesive layer 5, and it is therefore not necessary to describe these in more detail.

A sealing element overlaid on its surface part 2 in this manner canbe used in a multiplicity of ways for static seals, for example for door seals or vehicle seals, wherein the layer 3 forms the actual surface against which an opposing sealing surface, for example of a motor vehicle window, is arranged to be movable, and wherein this movement is hindered as little as possible by virtue of the small coefficient of sliding friction of the layer 3. of particular advantage in this connection is the fact that the 1 sealing element is flexible without problems, which thus makes it particularly suitable f or the reliable covering or lining even of the smallest bending radii. Such a sealing element is also usable however f or dynamic sealing elements, for example rotating sealing elements.

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Claims

CLAIMS:

1. A method for the manufacture of a sealing element having a substrate comprising an elastomer, a thermoplastic elastomer or a thermoplast, wherein at least one surface part of the surface of the substrate is overlaid with a polymeric layer which has a greater capacity for slip than the material of the substrate, which comprises applying to the surface part a layer comprising an ethylene-chlortrifluoroethylene copolymer or a mixed polymerisate of this material with other thermoplasts.

2. A method as claimed in claim 1, in which said other thermoplasts are taken from the group consisting of polyvinylchloride, polyamide, polyethylene and polypropylene.

3. A method as claimed in claim 1 or 2, in which the layer is applied to the surface part in powder form and is heated to a molten state so that, after cooling, the layer is bonded to the material of the substrate.

4. A method as claimed in claim 1 or 2, in which the layer is applied to the surface part by injection moulding or extrusion.

5. A method as claimed in any preceding claim, in which the substrate has a strip-like shape.

6. A method as claimed in any of claims 1 to 4, in which the substrate has an annular shape.

7. A method as claimed in any preceding claim, in which the coefficient of sliding friction of the layer relative to glass is equal to or less than 0.03.

8. A method as claimed in claim 7, in which the said coefficient of sliding friction is equal to or less than 0.02.

9. A method as claimed in any preceding claim, in which the thickness of the layer is within the range of 1 pm to 150 pm.

10. A method as claimed in claim 9, in which the thickness of the layer is from 10 pm to 100 pm.

11. A method as claimed in any preceding claim, in which the surface part to be overlaid is mechanically, electrically or chemically roughened before the application of the layer.

12. A method as claimed in any preceding claim, in which an adhesive intermediate layer is applied to the surface part to act as a bonding means between the substrate and the friction-reducing layer.

13. A method as claimed in any one of claims 1,2 or 4 to 12, in which the substrate and the layer are produced and connected to each other in a coextrusion process.

14. A method of manufacturing a sealing element substantially as hereinbefore described with I reference to Fig. 1 or Fig. 2 of the accompanying drawing.

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