WO1997046817A1

WO1997046817A1 - Tubular sealing article

Info

Publication number: WO1997046817A1
Application number: PCT/GB1997/001545
Authority: WO
Inventors: Michael John Carpenter; Stéphane KLEIN; Frank James Lowe; Alan Roger Gay; Alistair Alfred Preston Sutherland
Original assignee: Raychem Limited
Priority date: 1996-06-07
Filing date: 1997-06-06
Publication date: 1997-12-11
Also published as: AU3040597A; GB9612298D0; CA2253843A1; EP0901587A1; JP2000511619A

Abstract

An article for use as an environmental sealing gasket comprising an elongate body of gel sealant (30, Fig. 3), a solid, porous, or tubular elongate carrier (31), and an elongate tubular casing (32), wherein the casing has interstices and either (a) the casing (32) encloses the gel (30) on the carrier (31) and the gel is selected to be capable of protrusion through the casing interstices when the article is under compression and of retraction from such protrusion when the compression is removed; or (b) the casing is on the carrier and the body of gel at least partly encloses the casing on the carrier and is selected to be capable of deformation to expose enclosed portions of the casing when the article is under compression and of recovering to re-enclose the exposed portions when the compression is removed.

Description

TUBULAR SEALING ARTICLE

This invention relates to tubular sealing articles which may be useful, for example as gaskets for environmental and/or electrical sealing, as hereinafter described.

The invention provides an article comprising an elongate body of gel sealant, a solid, porous, or tubular elongate carrier, and an elongate tubular casing, wherein the casing has interstices and either (a) the casing encloses the gel on the carrier and the gel is selected to be capable of protrusion through the casing interstices when the article is under compression and of retraction from such protrusion when the compression is removed; or (b) the casing is on the carrier and the body of gel at least partly encloses the casing on the carrier and is selected to be capable of deformation to expose enclosed portions of the casing when the article is under compression and of recovery to re-enclose the exposed portions when the compression is removed.

Articles according to this invention are convenient to handle in any desired orientation, being substantially "dry" to the touch on all sides when the gel is not compressed to protrude through the casing interstices. Such articles have the further advantage that the tubular casing protects the gel from contamination on all sides (and even at its ends if the tubular casing ends are closed) thus eliminating the contaminatable exposed edges of a flat gel sheet in a "sandwich" construction between two open-cell layers described in WO-A-9416884 (MP1469).

The casing could, for example, be formed of open-cell polymeric foam, possibly a hollow tube whose wall is formed of such foam which has been stretched to receive a pre¬ formed body of the gel sealant about which the tube contracts when the stretching force is released. However, preferred casings for the present purposes are formed of fabric.

Preferred articles according to the invention are those wherein the casing is a tubular fabric, preferably a woven, braided or knitted tubular fabric. Non- woven fabrics could be used if desired, but it is generally preferred to use woven, braided or knitted tubular fabric, in which the size of the interstices can be more readily controlled. Preferred articles according to the invention include those wherein the tubular fabric casing has been formed in situ, preferably by tubular weaving, braiding, or knitting around the elongate body of gel. Contrary to the natural expectation that the fabric-forming yarns or filaments would tend to cut the relatively soft gel materials and/or that the gels would be too flexible and soft for adequate control in the fabric-forming operations, it has been found according to the present invention that the fabric can be acceptably formed around the elongate body of gel, provided that the said carrier is present to support the gel and control its elongation, the carrier preferably being flexible and substantially unspringy to provide substantially "dead" bending of the articles to assume and retain the shapes required for use as gaskets in practice.

Suitable equipment, methods and parameters for the weaving, braiding, or knitting operation may be determined by those skilled in such technology, bearing in mind the need to avoid damaging or unacceptably deforming the gel. For example, a small-diameter (37.5mm) weft knitting machine may be mounted horizontally, downstream from an extruder of known design capable of extruding the gel in question. A simple single jersey plain weft knitted tube may then be formed around an elongate profile of a gel as hereinafter described, as it is being extruded. Knitting is the preferred method, since open fabric structures can be formed readily from relatively rigid monofilaments of polymer or single- or multi-stranded wire, which are relatively stable, and suitable equipment is already available, for example in rubber extrusion companies for reinforcing automotive hoses with weft-knitted Kevlar (Trade Mark) fabrics.

Alternatively, the elongate body of gel may be inserted into or formed within the pre-existing tubular fabric casing. In this alternative, an extruded profile of the gel having the desired cross sectional shape with, or in this case possibly without, the aforementioned carrier, could simply be inserted into a pre-existing length of the tubular fabric casing, preferably after expanding the casing somewhat, for example by lengthways compression of a braid. Possibly, the gel profile, with or without the carrier, could be directly extruded or moulded into the pre-existing casing. The preferred fabric casings may, for example, comprise flexible filaments, of any appropriate cross-sectional shape, not excluding tapes, spun yarns, monofilaments, and multi-filament yarns, which may be chosen from polymeric materials, preferably those which are relatively impervious to the extender fluids used in the preferred gels. For example, fabrics consisting of or including filaments of high-density polyethylene may be advantageous, and other materials such as medium-density polyethylene, polyesters, polyamides, or polypropylene may also be useful. For many purposes, the fabric casing will preferably comprise substantially all polymeric filaments, but a proportion of glass, carbon fibre, or other filaments may be included for specific purposes if desired. Filaments which have significant resistance to abrasion or other mechanical damage could be advantageous in providing tough and durable gaskets.

In one particularly preferred form of the articles according to the present invention, the fabric casing comprises electrically conductive filaments, preferably metal filaments, or metal-coated polymeric filaments (e.g. silver-coated or nickel-coated polyamide filaments, known examples of which comprise 18% by weight of silver metal), or hybrid yarns of metal and polymer fibres. Such use of some, or preferably all, conductive (preferably metal) filaments produces an article which may be especially useful as an EMI shielding gasket, wherein the electrically conductive filaments provide the desired shielding effect and the gel protrudes through the interstices of the metallic fabric when under pressure to provide environmental sealing. Suitable alloys of metals such as nickel, copper, beryllium, or aluminium are known, alloys of beryllium and copper being especially preferred to provide highly resilient EMI gaskets in which the metal filaments resist compression set. Other metals, for example Monel alloys of nickel and copper, tin- plated phosphor bronze, or Ferex (Trade Mark of Chomerics) tin-plated copper-clad steel, may also be useful and may benefit from the protective presence of the gel reducing their interaction with certain corrosive environments, e.g. salt spray.

The casing and hence the article as a whole, will preferably be flexible to provide advantageous versatility of positioning in use, although articles which are relatively or substantially rigid longitudinally may be useful for some purposes, provided that the tubular fabric is adequately compressible in the lateral sense to bring about the desired protrusion of the gels through the interstices of the fabric.

The elongate body of gel may be in any desired cross-sectional shape, regardless of whether the gel or the casing forms the outermost layer of the article. Gel profiles having gas-containing, preferably hollow tubular, carriers which may be suitable for enclosing in the fabric casing according to the present invention are described in WO-A-9609483 (RK508) and other forms of gel profile having, for example, rod-like, sheet-like, or V- shaped carriers are described in our WO-A-9709391 (RK532), WO-A-9707350 (RK533), and PCT/GB97/00773 (RK537), and especially preferred are the gel profiles having low- moisture-content multi-filament synthetic polymeric yarn carriers described in our PCT/GB97/00775 (RK567), the disclosures of all of which are incorporated herein by reference. Although the cross-sectional shape of the body of gel is not critical, generally rod-like or tubular profiles will usually be preferred, and generally rounded, especially oval or round, cross-sectional shapes may be preferable for many purposes, although square, triangular or other cross-sectional shapes, e.g. tapes of rectangular cross-section, are not excluded.

The gel sealant material forming the said elongate body preferably comprises a silicone, polyurethane, or EPDM gel, or more preferably a thermoplastic oil-extended styrene-alkylene-styrene block co-polymer gel or an oil-extended methacrylate-alkylene- methacrylate block co-polymer gel.

The aforementioned methacrylate block co-polymer gels are new materials described in our WO-A-9700292 (RK 509), the disclosure of which is incorporated herein by reference. The other gels mentioned above are known per se, for example from US-A- 4600261 and US-A-5140476 (polyurethane gels), US-A^,634207, US-A-4680233, US-A- 4777063, and US-A-5079300 (silicone gels), US-A-5177143 (EPDM gels), and preferably from EP-A-0426658 (RK308 tri-block co-polymer gels with added PPO), WO-A-9305113 (RK451 tri-block co-polymer gels with added di-block), WO-A-9323472 (RK469 styrene- ethylene/propylene-styrene tri-block co-polymer gels), and WO-A-9418273 (RK472 styrene-ethylene/propylene-styrene triblock copolymer gels with added poly-alpha-olefins), the disclosures of all of which are incorporated herein by reference. The thermoplastic block copolymer gels, especially the styrene-alkylene-styrene block copolymer gels, are preferred for the present purposes in view of their relatively low cost and ease of manufacture and shaping to form the present articles.

The gel forming the said elongate body will preferably have an ultimate elongation of at least 100%, preferably at least 150%, more preferably at least 200% , preferably with substantially elastic recovery up to at least 100% elongation. These elongation criteria are tested at room temperature by known methods, for example as described in the above- mentioned patent specifications. The gel will usually have a Voland hardness within the range from 5 - 200 grammes, preferably 7 - 150 grammes, more preferably 10-100 grammes. Softer gels are generally preferred for use with fabrics having smaller apertures, Voland hardness in the range from 10 - 50 grammes being suitable for some purposes using the aforementioned triblock gels of less than 10% triblock content, whereas firmer gels of 20 - 24% triblock content having Voland hardness in the range 150 - 200 may be more suitable for other purposes with relatively large fabric apertures. The Voland hardness criteria are determined using a Voland/Stevens Texture Analyser, preferably as described in US-A-4852646 (MP1203), the disclosure of which is incorporated herein by reference. The preferred thermoplastic gels may be selected from visco-elastic materials of relatively high cohesive strength with elongation to break of at least 500%, preferably at least 750% , more preferably at least 1000%; elastic recovery to at least 100%, preferably at least 200%, elongation; and preferably zero slump at temperatures up to 100 , preferably up to 120°, more preferably up to 135°, and especially up to 150 Celsius. These preferred thermoplastic gels are thus distinguished from commonly known viscous sealants such as tackified elastomer mastics and pressure- sensitive adhesives. It is an advantage in terms of simplicity that the thermoplastic gel layer may preferably be self-supporting in the sense that it does not require an internal porous support of the kind used with known cross-linked polysiloxane gels, although the use of such a porous layer carrying the thermoplastic gel therewithin is not necessarily excluded. The preferred gels may also have tensile strength, dynamic and/or storage moduli, and other characteristics which meet the criteria described in any or all of the aforementioned EP-A-0426658, WO-A-9305113, WO-A-9323472, and WO-A-9418273.

The present invention includes a method of making an article as hereinbefore described, comprising the steps of (a) providing an assembly of the said elongate body of gel or the said casing on the carrier and (b) forming the said casing (preferably by weaving, braiding, or knitting) or the said body of gel accordingly around the said assembly; or comprising the steps of (i) providing the said tubular casing and (ii) inserting the said elongate body of gel, with or without the said carrier, into, or forming it within, the said casing. Also included is the use of an article according to, or formed by a method according to, the present invention as an environmental sealing gasket; and the use of such articles including electrically conductive filaments in the casing as an EMI shielding gasket. The articles are not limited to these specific uses, and may be used in any appropriate way. Means for attaching the articles to the objects which they are to be in contact with in use may be provided, for example hooks or tie-wraps attached to or provided together with the elongate sealing articles of this invention. Alternatively, the sealing articles may be fixed in place by means of adhesive, or may be located in a retaining groove from which part of the article may project, or into which part of the surface to be sealed against may be inserted, for example in a re-openable tongue-and- groove sealing arrangement. Because the gel tends to retract and therefore be protected by the casing whenever the compression is removed from the article, the articles according to this invention may be especially advantageous in circumstances where repeated opening and closing of a gasket seal may be desired.

Specific embodiments of this invention will now be described by way of example with reference to the accompanying drawings wherein: -

- Figure.1 illustrates schematically a generally D-shaped extruded profile of oil- extended tri-block copolymer gel 10 with a woven tubular fabric casing 11 of the aforementioned silver-coated filaments; Figure 2 shows schematically a substantially circular gel profile 20, which may have a solid internal support string or rod 21 as indicated by broken lines, with a braided fabric casing 22 of organic polymeric filaments such as nylon;

Figure 3 shows schematically a hollow tubular gel profile 30 having a hollow tubular internal carrier 31 of ethylene/vinyl acetate with a knitted metallic filament casing 32;

Figure 4 shows on the left a substantially round gel profile 40 enclosed by metallic fabric casing 41, indicated by crosses, in position to act as an environmental and EMI seal between two parts 42 and 43 of an electrically-shielding housing for electrical apparatus, the same arrangement being shown in closed position on the right of Figure 4, with the gel 40 under compression so that it projects through the interstices of the metallic fabric casing 41 to make the desired environmental seal against the housing parts 42, 43, in addition to the electrical contact between those parts and the metallic fabric casing 41.

Specific examples of materials, equipment and operating conditions for forming the articles according to this invention include the following :

Example 1.

A 37.5mm diameter Harry Lucas Textilmaschinen Model RHU knitting machine was set up as aforementioned downstream of an extruder producing an extrudate of a known gel of 12% styrene-ethylene/propylene-styrene triblock copolymer in FIN A A360B extender oil on a multi-filament low-moisture-content synthetic-polymer carrier of the kind described in the aforementioned PCT/GB97/00775, the extrudate being of sufficient diameter substantially to fill the fabric tube to be knitted by the knitting machine. A single jersey plain weft-knitted fabric tube was then progressively knitted around the solidified extrudate using a 5-gauge machine (5 needles per 25.4mm) to knit 0.35mm diameter polyethylene terephthalate monofilaments at 10 courses per 25.4mm using a machine speed of 600 revolutions per minute. The tension in the monofilaments was kept low at about 0.3 Newtons per Tex (Tex being the ISO standard for linear density of textile strands, calculated as the weight in grams of 1000 metres length), to avoid unacceptable cutting of the gel by the filaments during knitting. Example 2.

A pre-existing hollow tube of gel on a tubular carrier, as described in the aforementioned WO-A-9609483, was enclosed in a knitted fabric tube of 5-strand 38AWG tinned copper wire, produced on the same machine as Example 1, at 8 courses per 25.4mm, the resulting fabric having an optical coverage of about 50% . The machine was run at a slower speed of 300 rpm to accommodate lower tensions so that the wire did not cut the gel.

Example 3.

The knitting machine of Examples 1 and 2 was replaced with a 48-spool, vertical- track-plate, horizontal braiding machine, and yarns of 2-fold, 94 Tex Nylon 6,6 multi- filament with three ends per spool were braided around a gel extrudate similar to that of Example 1 using a tension of about 0.5 Newtons per Tex. In the relaxed state, the resulting braid gave an optical coverage of about 70% .

Example 4.

A circular weaving machine of the kind used to produce fire hoses may be used to weave a fabric tube around a vertically-fed gel profile similar to that of Example 1.

Example 5.

A weft-insertion weaving machine was set up in known manner to produce a 50mm- diameter fabric tube with knitted edge closure and locking thread, using 4-fold 110 Tex polyethylene terephthalate in the warp at 24 ends per 25.4mm and 3-fold 110 Tex polyethylene terephthalate in the weft at 18 picks (insertions) per 25.4mm. The warp tension was about 0.8 Newtons per Tex and the weft tension on leaving the insertion needle was about 0.25 Newtons per Tex. A gel profile similar to that of Example 1 and of appropriate diameter was inserted (or alternatively could be extruded or moulded) into this fabric tube, which gave an optical coverage of about 85% around the gel.

Example 6 A tubular carrier similar to that carrying the gel in Example 2 was first enclosed in a braided fabric of metal filaments using braiding methods and equipment known per se, and a layer of gel was applied thereover in a manner similar to that described in the aforementioned WO-A-9609483 to produce an article according to alternative (b) of the present invention.

Claims

CLAIMS :

1. An article comprising an elongate body of gel sealant, a solid, porous, or tubular elongate carrier, and an elongate tubular casing, wherein the casing has interstices and either (a) the casing encloses the gel on the carrier and the gel is selected to be capable of protrusion through the casing interstices when the article is under compression and of retraction from such protrusion when the compression is removed; or (b) the casing is on the carrier and the body of gel at least partly encloses the casing on the carrier and is selected to be capable of deformation to expose enclosed portions of the casing when the article is under compression and of recovering to re-enclose the exposed portions when the compression is removed.

2. An article according to claim 1, wherein the casing is a tubular fabric, preferably a woven, braided or knitted tubular fabric.

3. An article according to claim 2, wherein the tubular fabric casing has been formed in situ, preferably by weaving, braiding or knitting around the elongate body of gel.

4. An article according to claim 2, wherein the elongate body of gel has been inserted into, or formed within, the pre-existing tubular fabric casing.

5. An article according to any of claims 2 to 4, wherein the fabric casing comprises flexible polymeric filaments.

6. An article according to any of claims 2 to 5, wherein the fabric casing comprises electrically conductive, preferably metal or metal-coated, fibres or filaments.

7- An article according to any preceding claim, wherein the said carrier is (i) flexible and substantially non-springy to provide the article with "dead" bending characteristics and/or (ii) is a low-moisture-content multi-filament synthetic polymer yarn.

8. An article according to any preceding claim, wherein the gel forming the said elongate body comprises a silicone, polyurethane, or EPDM gel, or preferably a thermoplastic oil-extended styrene-alkylene-styrene block copolymer gel or an oil-extended methacrylate-alkylene-methacrylate block copolymer gel.

9. An article according to any preceding claim, wherein the gel forming the said elongate body has an ultimate elongation of at least 100%, preferably at least 150%, more preferably at least 200%, preferably with substantially elastic recovery up to at least 100% elongation.

10. An article according to any preceding claim, wherein the gel forming the said elongate body has a Voland hardness within the range from 5 to 200 grammes, preferably 7 to 150 grammes, more preferably 10 to 100 grammes.

11. A method of making an article according to any preceding claim, comprising the steps of (a) providing an assembly of the said elongate body of gel or the said casing on the said carrier and (b) forming the said casing or the said body of gel accordingly around the said assembly; or comprising the steps of (i) providing the said tubular casing and (ii) inserting the said elongate body of gel, with or without the said carrier, into, or forming it within, the said casing.

12. Use of an article according to any of claims 1 to 10, or made by a method according to claim 11, as an environmental sealing gasket.

13. Use of an article according to claim 6 or any claim depending thereon as an EMI shielding gasket.

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