DISSIPATION OF STATIC ELECTRICITY IN WORKWEAR

Abstract: An article of workwear comprises a plurality of components (17, 18) incorporating electrically conductive fibres (21), and an electrically conductive member (20) bridging the junction between adjacent components. The electrically conductive member comprises a strip or tape (20) incorporating a plurality of electrically conductive filaments or yarns (22), each filament or yarn being incorporated in the strip or tape in such a manner as to have alternate portions of the filament or yarn exposed at opposite faces of the strip or tape. The strip or tape may be secured to each of the adjacent components by stitching (19).

Description: - 1 - DISSIPATION OF STATIC ELECTRICITY IN WORKWEAR Field of the Invention This invention relates to dissipating static electricity in specialised workwear. Background to the invention As electronic components become smaller and more sensitive they may be easily damaged by static electrical charges. It is therefore important that operatives engaged in the manufacture of such components are at earth potential, that is they do not carry a static electrical charge. For this purpose specialised garments for use in the micro electronics industry have been developed which are made from tightly woven fabric incorporating a grid or stripe of electrically conductive yarn. This is designed to dissipate static electrical charges which would otherwise build-up as the garment is worn. In particularly sensitive situations static dissipation is improved by earthing the operator, the garment or both. As well as in the microelectronics industry, the control of static build-up in clothing is also important in the pharmaceutical and microbiological industries, for three main reasons. Firstly, the build up of an electrostatic charge may cause attraction or repulsion of bacteria or microscopic particles of active pharmaceutical agents, thereby changing the performance of the protective clothing, which may not only serve to protect the product from contamination but also protect the wearer from contact with the materials being handled. The performance of the clothing is therefore closely specified, and the effects of electrostatic attraction or repulsion of materials may be that the performance standard is not achieved in practice. By reducing the electrostatic charge to zero or a very low voltage consistently, the performance of the clothing can be guaranteed. Secondly, the build-up of electrostatic charge can involve a risk of discharge to neighbouring earthed surfaces, giving rise to sparks which can ignite flammable vapours used in processing, for example. The third reason is allied to the second, in that the discharge of high electrostatic voltages through sensitive electronic measuring or monitoring equipment can lead to false readings or to damage. In the context of medical work, false readings or disruption to monitoring equipment could have very serious conse- quences for patients, for example. - 2 - Difficulties can arise in relation to such garments due to the fact that the conductive filaments are woven into the fabric and as such come to the surface of the fabric relatively infrequently and in an erratic manner. As a result if one piece of fabric is placed on top of another, as occurs, for example in the case of a seam between adjacent parts of a garment, the electrically conductive filaments in each piece of fabric are unlikely to make contact or satisfactory contact with one another with the result that it is unlikely a satisfactory electrical connection will be made across the seam. A similar problem arises in the case of articles of workwear consisting of more than one garment, for example where a hood or an item of footwear are used in association with a main garment. As a result it is difficult to satisfactorily earth an entire garment from a single earthing point. In US-A-5 71 5 536 there is disclosed a static electricity dissipating garment in which a continuous conducting ribbon extends through all the seams and is connected to a grounding wire. Similarly, in US-A-4 546 497 there is disclosed antistatic clothing incorporating electroconductive tape in the seams. A problem which arises with antistatic clothing is that the antistatic properties tends to degrade with repeated cleaning of the articles. For example, garments may be washed, chemically treated (so-called "dry cleaning") and/or radiation treated to ensure that it is clean and sterile. It has been found that the residual static voltage on the clothing tends to rise with repeated cleaning cycles until it reaches an unacceptable level. For conventional clothing of the types described, it has been found that this state is reached long before the clothing has otherwise come to the end of its working life. Summary of the Invention According to the present invention there is provided an article of workwear comprising a plurality of components incorporating electrically conductive fibres, and an electrically conductive member bridging the junction between adjacent components, characterised in that the electrically conductive member comprises a strip or tape incorporating a plurality of electrically conductive filaments or yarns, each filament or yarn being incorporated in the strip or tape in such a manner as to have alternate por- tions of the filament or yarn exposed at opposite faces of the strip or tape. - 3 - The strip or tape is preferably secured to each of the adjacent components by stitching, but it will be understood that other methods of attachment may also be used, for example welding using heat, ultrasonics or high frequency electromagnetic radiation, or adhesives. Preferably, each component is of woven construction. The term "component" is used herein to refer both to adjacent components of a single article of workwear and adjacent garments or other items which together form a complete article of workwear. A single article may, for example, be formed from a number of panels connected together by seams, each of the panels comprising a com- ponent of the complete article. Alternatively an item of workwear may consist of a number of separate articles which are worn together such as a body garment, a hood and articles of footwear, each of which comprises a component of the overall article. Where the article of workwear comprises a single garment, the components may comprise adjacent panels from which the garment is constructed and which are connected to one another by seams. In such cases said electrically conductive member may extend across each of the seams of the article so as to bridge the seam and interconnect electrically conductive members incorporated in the respective panels. Alternatively the electrically conductive member may be incorporated in the seam in surface contact with each of the panels connected together at the seam. Where the components comprise a plurality of separate garments employed together to form a complete article of workwear, said electrically conductive member may incorporate fastening means adapted for engagement with complimentary fastening means on an adjacent article, the respective fastening means being associated with respective electrically conducting members bridging a plurality of conductive fibres in- corporated in each of the articles. The articles may comprise an upper body or jacket portion of a garment and a lower body or trouser portion. Alternatively, or in addition, the articles may comprise a hood together with an upper body portion or a unitary upper and lower body portion of a garment. In either case the lower body portion of the garment may incorporate integral or separate articles of footwear. Alternatively, the articles may comprise a complete body garment or a lower body garment and associated articles of footwear, said electrically conductive member - 4 - extending across the junction of one article to the other and being connected to or juxtaposed with one or both of the articles. Alternatively, an electrically conductive member may be associated with each article, the electrically conductive members incorporating complementary fastening mem- bers adapted for engagement with one another to secure the articles together and form an electrically conducting path between them. The complementary fastening members may comprise components of a press or stud fastener. In an alternative arrangement said electrically conductive member may comprise a stirrup, opposite ends of which are secured to lower edge regions of leg portions of a garment, the stirrup being adapted to extend beneath the wearer's foot in contact with an article of footwear having a conductive sole. The stirrup member may be located around the wearer's foot internally of the article of footwear whereby to be compressed in use between the wearer's foot and the inner surface of the conductive sole of the article of footwear. Alternatively, the stirrup member may be arranged to extend around the outer surface of an article of footwear whereby to be compressed in use between the outer surface of the conductive sole of the article of footwear and the floor. The electrically conductive member may consist entirely of electrically conductive material but preferably comprises a strip or tape incorporating a plurality of fila- ments formed from or coated with electrically conductive material. The member may advantageously be formed from woven polyester fabric incorporating electrically conductive yarns. In a typical construction the electrically conducting fibres in the fabric from which the articles are constructed are arranged to form a 5mm grid pattern, the electrically conducting fibres in the electrically conducting member being arranged in parallel lines approximately 2mm apart. It is believed that the arrangement of the tape with conductive elements woven into it in such a way as to protrude from the surface of the tape helps bond the fabric electrically in two ways: 1. The protrusions are forced into the fabric of the seam by virtue of the stitching, to ensure physical contact between the conductive elements in the tape and those in the fabric; and - 5 - 2. The protrusions formed by the sharply bent conductor yarns may promote corona discharge at voltages above about 500, so increasing the rapid conduction of charge across the seams. It is thought that this corona discharge is responsible for the extremely rapid and successful discharge from the made up garment. In addition, garments in accordance with the invention have been found to retain their ability to dissipate electrostatic charge after repeated cleaning and sterilisation treatment. For example, garments subjected to 60 typical wash and wear cycles have shown no significant change in the ability to dissipate charge, and equally garments subjected to 60 gamma radiation sterilisation cycles also displayed no loss of electrical bonding in the seams. Garments in accordance with the invention are therefore considerably more economical in use, lasting many more cycles of use and cleaning/sterilisation than conventional antistatic garments. Brief Description of the Drawings Embodiments of the invention will now be described, by way of example only, with reference to the drawings, which are diagrammatic and in which:- Figure 1 is an illustration of an article of workwear incorporating one embodiment of the invention; Figure 2 is a perspective view showing the manner of interconnection of adjacent panels of the garment shown in Figure 1 ; Figure 3 is an enlarged cross-section through the seam formed between the adjacent panels shown in Figures I and 2; Figure 4 is an illustration of fabric and tape constructions incorporated in the embodiment of Figures 1 to 3; Figures 5 and 6 show alternative means of interconnecting the components of a garment similar to that shown in Figure 1 ; Figure 7 shows a means of electrically interconnecting a sleeve and cuff of a similar garment; Figure 8 illustrates a method of interconnecting a garment and articles of footwear according to a further embodiment of the invention; Figure 9 is an enlarged fragmentary side view of part of the embodiment shown in Figure 8; - 6 - Figure 10 shows a further method of interconnecting a garment with a hood and with articles of footwear; Figure 1 1 is an enlarged cross-section showing the manner of interconnection in the arrangement of Figure 10; Figure 2 is a side view of the arrangement shown in Figure 10; and Figure 1 3 is an enlarged cross-sectional view of a section of the tape in contact with a piece of the conductive fabric. Detailed Description of the Illustrated Embodiments Referring to Figures 1-3, an article of workwear in the form of an overall com- prises four components, namely a main body component 10, first and second arm components 1 1 and a trouser or lower body component 12 comprising two leg portions 13. Each of the components is constructed from a woven cleanroom fabric such as continuous filament polyester and incorporates a grid of electrically conductive fibres generally constructed from polyester and carbon and typically spaced apart by intervals of 5mm or more. This electrically conductive grid forms a path for localised electrical static charge to be dissipated across the conductive grid. The body panel 10 is connected to the arm panels 1 1 by seams 15 and to the lower body or leg portion 12 by a seam 16. In order to ensure electrical continuity between the panels across the seams 5 and 16, each of the seams incorporates a strip or tape of electrically conductive material as best seen in Figures 2 and 3. For this purpose the edge regions of each panel are folded into generally hook or U-shaped configuration and engaged with one another as shown in Figure 2 and 3 so that two layers 17A.17B of one panel and two layers 18A,1 8B of the adjacent panel overlie one another. A strip or tape 20 of electrically conductive material is located between adjacent portions 17A and 18B of the overlapping panels and the assembly secured together by lines of stitching indicated diagrammatically at 19A and 1 B. The strip or tape 20 of electrically conducting material is thus clamped between the overlapping portions of the two panels and extends longitudinally for the full length of the associated seam 1 5 or 16. The strip 20 is formed from polyester fabric incorporating a plurality of electri- cally conductive yarns 22 formed, for example, from carbon coated nylon or conductive polyester yarns. The conductive yarns are woven through the strip and come frequently - 7 - to the surface where they are bent around the yarns forming the strip or tape itself and thus project from the surface of the tape, typically by 0.5-1.Omm. In this way the projecting yarns are pressed into contact with the conductive yarns of the grid 21 , thereby enhancing the electrical contact between them. In addition, the relatively sharp bends in the conductive yarns promote corona discharge within the fabric at voltages above about 500V, ensuring transfer of charge even where there is no direct contact between the conductive yarns of the fabric and the conductive yarns in the strip 20. Figure 4 shows a typical garment fabric 10 and tape 20 to scale, the electrically conductive yarns 21 in the fabric forming a grid of 5mm mesh size compared with a 2mm spacing of the electrically conductive yarns 22 of the tape 20. The yarns 22 are exposed at the surface of the tape at the zones 22A indicated by heavy lines in Figure 4. The yarns 22 are also of larger diameter than the yarns 21 , generally being of the order of 0.5-1.0mm in diameter compared with 0.01 -0.05mm diameter for the yarns 21. By virtue of the dose spacing of the yarns 22 compared with the grid size of the yarns 21 and the relatively high degree of exposure of the yarns 22 at the surface of the tape 20, the yarns 22 make contact with a high proportion of the fibres 21 in the overlapping portions 17A 8B of the adjacent panels of the garment and provide an effective electrical connection between them. This enables the garment to be earthed from a single point since the electrical continuity which exists in the individual panels by virtue of the electrically conducting fibres 21 woven into the material, is continued across the seams 1 5 and 16 by virtue of the electrically conductive tape incorporated in the seams. Figure 5 of the drawing shows an alternative arrangement in which electrical continuity between body panels 10,1 1 and 12 of a garment is maintained across interconnecting seams 1 5 and 16 by short lengths of electrically conductive tape similar to the tape 20 described with reference to Figures 1 to 4. In this embodiment short sections of tape 20 are arranged to bridge the seams 15 and 1 6, each section being connected at its opposite ends by sewing or other suitable means to the respective panels 10,1 1 or 10,12. In this way the loss of electrical continuity across the seams is compensated by the electrical "bridges" formed by the sections 20 of tape. The number of sec- tions of tape employed may be varied dependent on the spacing of the electrically con- - 8 - ducting grid in the fabric, the length of the seams and the measured electrical conductivity across the seams. Figure 6 of the drawings shows an alternative means of improving electrical conductivity across seams of a unitary garment in which electrically conductive tape 20 of similar construction to that described with reference to Figures 1 to 4 is sewn to the surface of the garment and extends across the panels from which the garment is constructed. In the embodiment shown in Figure 6 a first length of tape 20A extends from one arm portion 1 1 across the main body panel 10 to the other arm portion 1 1 , thereby bridging the seams 1 5 formed between the body portion 10 and the two arm portions. A second length of electrically conductive tape 20B extends across the body portion 10 and down one leg 1 3 of the lower body portion 12. The strip 20B intersects and is secured to the strip 20A adjacent the upper region of the body portion 10 and thereby provides electrical continuity between the arm components 1 1 , the body portion 10 and the leg portion 12 of the garment. Figure 6 also shows an extension 20C of the strip 20B connected to an integral hood portion 23 of the garment connected to the body portion 10 by a seam 24. In this way electrical continuity is maintained between all the panels making up the garment thereby enabling it to be earthed from a single point. Figure 7 shows an embodiment of the invention employed to establish electrical connection between a sleeve 1 1 constructed from fabric incorporating electrically conducting fibres 21 as previously described, and a cuff 1 1 A. Generally such cuffs are formed from electrically conductive knitted yarns and serve to ensure close contact between the garment and the wearer's skin. In the arrangement shown in Figure 7 electrically conductive tape 20 similar to that described above is sewn onto the sleeve 1 1 and projects beyond the end of the sleeve over the cuff 1 1 A. The tape 20 is connected to a component 25 of a metallic stud-type fastener secured to the cuff 1 1 A and adapted to form a terminal by means of which the garment can be connected to earth. The tape 20 bridges the seam 26 between the sleeve 1 1 and the cuff 1 1 A thereby maintaining electrical conductivity from the sleeve to the cuff in the manner previously described. The electrical connection between the stud 25, tape 20 and cuff 1 1 A may be enhanced, if desired, by attachment of a section 27 of the fabric from which the arm and remainder - 9 - of the garment is constructed around the area of the stud 25. The tape 20 may be relatively short in length as illustrated in Figure 7 serving simply to bridge the seam 26. Alternatively the tape 20 may comprise a terminal portion of a tape which extends to other parts of the garment in the manner illustrated, for example, in Figure 6. Figures 8 and 9 of the drawings show an alternative arrangement in which electrical continuity is maintained between a one piece garment indicated at 30 and a separate article of footwear (not shown). As shown in the drawing the garment 30 is of integral one piece construction comprising a hood 31 and a body portion 32 incorporating integral arm portions 33 and integral leg portions 34. The garment is constructed from a cleanroom fabric incorporating electrically conductive fibres in the manner previously described and electrical continuity is therefore maintained throughout the garment by virtue of the conductive fibres incorporated in its construction. A stirrup 35 is fitted to the lower end of each leg of the garment and is formed from similar electrically conductive cleanroom fabric incorporating a grid of conductive fibres. The stirrup is connected at each of its ends to the lower edge of the associated leg portion 34 of the garment and is adapted in use to extend under the user's foot 36 and inside a separate article of footwear (not shown). In order to enhance electrical conductivity between the garment and the stirrup, a strip 37 of electrically conductive material similar to that described with reference to the previous embodiments is sewn into the stirrup 35 and projects at opposite ends where it is sewn to the lower region of the leg portion 34. In this way the electrically conductive tape bridges the seams between the stirrup and the associated leg portion and maintains electrical continuity between the conductive grids incorporated in the fabrics from which both components are formed. A stud 38 may be provided on the stir- rup 35 for connection of an ankle earth if required. The articles of footwear worn by operatives are conventionally provided with electrically conductive soles whereby the operative is earthed to the floor. By virtue of the arrangement described with reference to Figures 8 and 9, the operative's garment is earthed through the conductive sole by virtue of the electrically conductive tape 37 which connects with the main body of the garment and the stirrup and thereby enables - 10 - th e entire garment to be earthed from the stirrups fitted to each of the leg portions of the garment. While in the arrangement shown in Figures 8 and 9 the garment is illustrated as being of integral construction, in practice it will normally comprise separate components interconnected by seams in the manner described with reference to Figures 1 to 6. In that event the panels from which the garment is constructed are preferably interconnected by electrically conductive strip or tape material in the manner described with reference to these figures, thereby ensuring electrical continuity is maintained across the seams. Alternatively the workwear may comprise separate hood, body and leg compo- nents in which event these are preferably interconnected using electrically conductive tape and suitable fasteners in the manner to be described with reference to Figures 10 to 12 of the drawings to maintain electrical continuity between the separate garments or components making up the overall article of workwear. Referring now to Figures 10 to 12, there is shown a means of maintaining elec- trical continuity between separate garments which together form a complete article of workwear. In the embodiment shown in Figures 10 to 12 the complete article of workwear comprises an integral body portion 40 incorporating arm and leg portions 41 and 42, a separate hood portion 43 and separate shoes or boots 44 adapted to be fitted over the lower portions of the legs 42. The hood portion 43 is adapted to overlie the upper region of the body portion 40. At the area where the two components overlap, short sections of electrically conductive tape 20 similar to that described with reference to Figures 1 to 4 are sewn into the lower edge region of the hood 43 and the neck region of the body portion 40 respectively. Each section of tape is fitted with a respective component of a stud or other suitable fastener 45 which engages the conduc- tive tape which in turn is in contact with the grid of electrically conductive fibres woven into the fabric from which the articles are made. Each component of the stud fastener is therefore electrically connected to the associated garment and when the garments are fitted and the stud fasteners interconnected, electrical continuity is effected between the separate garments. The boots 44 are connected to the leg portions 42 of the garment in a similar fashion. As shown in Figures 1 1 and 12, a strip 46 of electrically conductive tape similar - 1 1 - to that described with reference to Figures 1 to 4 is sewn into an upper region of each boot 44 and a similar strip 47 of tape is sewn on to the adjacent lower region of each leg portion 42. Each section of tape bridges a number of the fibres forming the conductive grid in the fabric from which the boot and body portion are formed and respective components 48A.48B of a stud fastener are fitted to the tape connected to each article. When the boot is fitted over the lower end of the leg, the respective components of the stud fastener are engaged thereby forming electrical continuity between the shoe or boot and the garment as a whole. Although not shown in Figure 10, the arm, body and leg portions of the gar- ment are preferably electrically interconnected across the seams between them by any of the means shown in Figures 1 , 5 or 6 of the drawings. By virtue of the arrangements described electrical continuity may be maintained across seams of a single article or between separate components forming a complete article of workwear. This enables the workwear to be earthed from a single point, such as from a cuff or ankle or through an article of footwear in the manner described with reference to Figures 7 to 12 of the drawings. The arrangements described are also of simple construction yet provide an effective means of maintaining electrical continuity throughout workwear consisting of multiple interconnected panels and/or multiple separate garments, thereby enabling static electrical charges to be dissipated without requiring complex multiple earthing arrangements. The construction of the tape is also such that it will withstand repeated exposure to commercial laundering cycles without loss of electrical conductivity. Figure 1 3 shows in exaggerated form the relationship between the conductive elements in the tape and those in the fabric in a seam. The tape 1 30 has conductive threads 131 woven into it in a relatively tight stitch or weave so that the threads or yarns 1 31 protrude from each face in sharp bends 1 31 A. The fabric of the garment is represented by smaller fibres 1 32 and larger conductive fibres 1 33 spaced therein. It will be appreciated, however, that the relative sizes of the fibres 1 32 and 1 33 are not intended to be accurate representations of the relative sizes in reality. The conductive threads 1 31 , while perhaps being pressed into contact with some of the fibres 1 33, exhibit sharp bends 1 31 A which pass close to others of the conductive fibres 1 33, and the - 12 - corona discharge effect at the sharp bends ensures that charge is transferred effectively between the fibres 1 33 of one part of the garment to the tape 1 30, and from there to the fibres in another part of the garment, ensuring that any static charge is quickly dissipated through the garment to the earthing point, for example the floor, through con- ductive shoe soles, for example. Various modifications may be made without departing from the invention. For example the invention may be applied to a wide range of workwear garments consisting of multiple separate articles or incorporating seams in a variety of different locations. The fabric from which the garments is constructed may vary as regards its material and the nature and extent of the electrically conductive fibres incorporated in it. For example while such fibres are normally incorporated in a grid formation, they may alternatively be incorporated in the form of stripes. The electrically conducting strip or tape employed in the embodiments may be constructed in a wide variety of alternative forms provided it has a substantial electrically conductive surface area adapted to bridge a plu- rality of the conductive fibres incorporated in the fabric from which the components of the garment are constructed to thereby maintain electrical continuity throughout the workwear article. The tape may also be secured to the inside or outside surfaces of the components by sewing or other suitable means. Moreover while reference has been made herein primarily to effecting electrical continuity between components of articles of workwear, the invention may also be applied to other situations where it is necessary to maintain electrical continuity across seams, joins or other areas where a break in electrical continuity would otherwise occur.

Claims: - 1 3 - CLAIMS 1. An article of workwear comprising a plurality of components incorporating electrically conductive fibres, and an electrically conductive member bridging the junction between adjacent components, characterised in that the electrically conductive member comprises a strip or tape incorporating a plurality of electrically conductive filaments or yarns, each filament or yarn being incorporated in the strip or tape in such a manner as to have alternate portions of the filament or yarn exposed at opposite faces of the strip or tape. 2. An article according to Claim 1 , wherein the strip or tape is secured to each of the adjacent components by stitching. 3. An article according to Claim 1 or 2, wherein the conductive filaments or yarns are repeatedly looped through the strip or tape so as to be raised above the surface of the strip or tape on each side thereof. 4. An article according to Claim 3, wherein the conductive filaments or yarns project from the surface of the strip or tape by a distance of 0.5 to 1 mm. 5. An article according to any preceding claim, wherein the conductive yarns are formed of carbon coated polyamide or conductive polyester. 6. An article according to any preceding claim, wherein the strip or tape is incorporated longitudinally into a seam formed between adjacent fabric panels in the article. 7. An article according to any of Claims 1 to 5, wherein the strip or tape extends transversely of the seam so as to bridge the seam. 8. An article according to Claim 7, wherein the or each seam has a plurality of strips or tapes bridging the seam.

Inventors: BARKER MICHELLE SHARON, HURST NORMAN JOHN ALFRED, BARKER, MICHELLE, SHARON, HURST, NORMAN, JOHN, ALFRED
Applicants: BARKER MICHELLE SHARON, FENLAND LAUNDRIES LIMITED, HURST NORMAN JOHN ALFRED, BARKER, MICHELLE, SHARON, HURST, NORMAN, JOHN, ALFRED
Application year: 1999
Main classification: A41D13
IPC codes: A41D13, A41D31