US3898538A

US3898538A - Anti-static footwear

Info

Publication number: US3898538A
Application number: US423991A
Authority: US
Inventors: John Arthur Dalton
Original assignee: STAT E CON Pty Ltd
Current assignee: STAT E CON Pty Ltd
Priority date: 1972-12-12
Filing date: 1973-12-12
Publication date: 1975-08-05
Anticipated expiration: 1992-08-05
Also published as: ZA739064B; AU7070774A; JPS4995746A

Abstract

Anti-static footwear, having a member of substantially constant resistance conductively connecting the lower surface of the insole with an exposed face of the outer sole, wherein the resistance of the path between the foot of a wearer and ground remains substantially between a required upper limit and a required lower limit even if the insole should in use become a perfect conductor.

Description

United States Patent Dalton 1 1 Aug. 5, 1975 [54] ANTI-STATIC FOOTWEAR 2,818,534 12/1957 Horne 317/2 B 7 v 5] In e John A hur a on, A ma ale, 3,293,494 l../1966 Fischer 317/2 B Australia [73] Assignee: Stat-E-Con Pty. Limited, Prmwry Emmmer Hix v Melbourne Australia Attorney, Agent, or Fzrm-Depao1i & O Brien [22] Filed: Dec. 12, 1973 12 1 pp 423,991 57 ABSTRACT [30] Foreign Application Priority Anti-static footwear, having a member of substantially D 12 1977 NW 2e, nd 169 311 constant resistance conductively connectmg the lower surface of the insole with an exposed face of the outer sole, wherein the resistance of the path between the 2? 3 1 47 foot of a wearer and ground remains substantially be- 1 B tween a required upper limit and a required lower 1 0 earc limit even if the insole should in use become a perfect [56] References Cited conductor' UNITED STATES PATENTS 5 Claims, 2 Drawing Figures 2,712.099 6/1955 Legge 317/2 B ANTI-STATIC FOOTWEAR This invention relates to footwear (referred to generically herein as shoes) including shoes having outer soles of rubber, polyvinyl chloride or other thermally and/or electrically insulating material.

In the past it has been found that some shoes became uncomfortable to wear after a certain time during which they are in continuous or substantially continuous use by the wearer without him resting or removing the shoes. This discomfort has been ascribed to various causes including increase in temperature of the feet and/or an accumulation of static electricity in his body. Such a thermal or electrical charge cannot under normal walking conditions readily escape unless it be through his feet to the ground, and it will be evident that insulating soles such as of plastics tend to block any flow of electrical or thermal current from the body of the wearer.

It has been proposed to alleviate these shortcomings by rendering the outersole conductive such as by forming it of graphite. However graphite has not found favour because of its propensity to leave unsightly marks on the floor or other surface upon which the wearer walks. In an attempt to overcome this problem it has been proposed to impregnate an otherwise insulating sole e.g. of rubber or plastics with metal or other conductive particles or threads; but in the former case it is difficult to ensure sufficient interparticle contact to increase the conductivity of the sole to any significant extent. In the case of threads, the conductivity is liable to become excessive, because it needs but one thread to extend throughout the full breadth of the insulating material to render the sole virtually a perfect conductor, especially if that thread happens to be in the heel or ball portion of the foot where the contact pressure with the ground is relatively high.

To have an excessively conductive path between the wearers body and the ground can under some circumstances be undesirable because it exposes him to the danger of electric shock should he happen to touch a source of high voltage.

I have found that one of the main sources of difficulty stems from the insole. Most insoles are of leather or of a fibrous material which under normal conditions is a reasonably good insulator. After a period of use, however, it tends to absorb perspiration from the foot whereupon its resistance drops markedly e.g. from about 2 X 10 ohm to about 1 X 10 ohm. Should the outersole have been rendered conductive (by means known per se) i.e. usually having a resistance less than 2 X ohm, it will be evident that after a period of wearing, especially in warm weather, there will be a highly conductive path between the wearers body and the ground. This could be dangerous if the wearer were exposed to high voltage equipment.

It is an object of my invention to provide for controlling the resistance of this path between an upper limit of effectiveness or comfort and a lower limit of safety, in a manner that is simple, relatively inexpensive and readily adaptable, to existing methods of making footwear in general and soles in particular.

According to one aspect, the present invention provides footwear comprising an outer sole or electrically insulating material and an insole the resistance of which is liable to drop substantially upon absorption of moisture from the wearers foot, characterized by the provision between the insole and outer sole of a member of substantially constant'resistance which conductively corrects the lower surface of the insole with an exposed face of the outer sole such that when the wearer stands upon the ground, the resistance of the total electrical path between his foot within the shoe and the ground contacted by said exposed outer sole face, remains substantially between a required upper limit and a required lower limit as hereinafter defined even if the insole should in use become a perfect conductor.

The invention according to another aspect provides a method of making anti-static footwear which comprises placing pre-manufactured conductive members into a mould for outer soles and then moulding the outer sole around the conductive members, but in order that the invention may be better understood reference will now be made to the accompanying drawings which are to be considered as part of thisspecification and read therewith. v I

In the drawings:

FIG. 1 is a section through part of a shoe according to one embodiment of this invention, and

FIG. 2 shows the lower exposed face of the of the shoe illustrated in FIG. 1.

Referring to the drawings in more detail, a shoe 3 has an electrically insulating outer sole 4 of rubber, polyvinychloride or other electrically insulating material and an insole 5 of fibrous or other material and preferably cellulosic material rather than leather which deteriorates rapidly in such conditions because of heat, moisture, perspiration, etc. of which the electrical resistance is liable to drop substantially upon absorption of moisture from the wearers foot.

Between the insole 5 and outer sole 4 if a panel 6 of graphite rubber or other material of known resistance or at least of a resistance that remains substantially constant under such conditions of use as will be experienced by the shoe. Panel 6 is associated with the lower face of the insole i.e. the face which is lowermost in use, and is thinner than the outer sole so that no part of the panel extends to or beyond exposed face 7 of outer sole 4. Conductive means are provided so as electrically to connect panel 6 with both the insole and exposed face 7 of outer sole 4, so that when the wearer stands upon the ground, the resistance of the total electrical path between his foot within the shoe, and the ground contacted by face 7, remains substantially within required limits, even if the insole 5 should in use become a perfect conductor of electricity.

The conductive means between the panel and insole may include a connection e.g. by means of graphite glue between these integers.

As shown in FIGS. 1 and 2 the conductive means between the panel and ground may consist of a piece of fine wire mesh 8 fastened e.g. by stitching to the panel. Outer sole 4 may be moulded over the assembly of insole 5, panel 6 and mesh 8, but before doing so the ends of one series of wires making up the mesh are preferably interwoven into mutual contact to ensure that at least some of the wires have ends 9 exposed in the outer face 7 of the completed outer sole 4, as shownin FIG. 2.

Panel 6 and mesh 8 are advantageously attached to insole 5 in the region of the ball of the foot, where the contact pressure with the ground is relatively high. The electrical path may be considered to consist of the outer sole thickness of insole 5, that of panel 6 and finally that provided by metallic mesh 8. Since the resistance of the last mentioned is practically zero, the effective resistance of the electrical path must be regarded as that produced by the series arrangement of insole and panel 6. As stated above, the resistance of the insole can vary widely depending inter alia upon the amount of moisture it may have absorbed. However as the resistance of the panel remains substantially constant irrespective of resistance changes of the insole, the total effective resistance of the shoe can be predicted fairly accurately by virtue of the insertion of the panel.

An advantage of this shoe resides in the fact that as the outsole wears, the thin metallic fibres the ends of which are exposed in the outer surface thereof wear at the same or substantially the same rate thereby reducing any tendency to scratch the floor or any other surface upon which the wearer walks. Those fibres may be of any suitable material such as aluminum or copper, however the former is preferred as it does not tend to colour the outersole through chemical reaction.

The resistance panel may be attached to the insole by a surface" attachment which desirably may be conductive in nature e.g. a conductive glue such as graphite glue which can be regarded as a conventional glue incorporating a suspension of graphite particles. Alternatively or additionally, the attachment may be by means of tacks or spikes of plastics or other material of low conductivity.

It will be evident from the foregoing that this shoe provides for controlling the conductivity of footwear between close limits, irrespective of substantial resistance changes in the insole, in a manner that is simple, inexpensive and readily amenable to conventional methods used in the boot trade.

This shoe also finds advantageous application in operating theatres where it is highly desirable that staff should wear shoes that are sufficiently conductive to avoid build up of body static electricity which might lead to sparking, but of sufficient resistance to minimise the likelihood of fatal shock in the event of the wearer coming in contact with high voltage e.g. X-ray apparatus or electromedical equipment.

For similar reasons this shoe can be worn to advantage in chemical laboratories and plants or installations where explosive substances are manufactured or volatile substances handled.

It is pointed out that most conductors of electricity are also conductors of heat and therefore the anti-static footwear according to the present invention can also be used such that they are not only being used to dissipate heat.

Some applications of this use are those of sporting shoes, such as golf shoes, bowling shoes and the like.

Thus the present invention provides novel anti-static footwear that fulfills all requirements yet has the additional features that it is safe to use near high voltage equipment, easily manufactured, relatively inexpensive, will not mark floors and can be made in many varying styles.

What I claim is:

1. Anti-static footwear having an electrically insulating outer sole and an insole the resistance of which is liable to drop substantially upon absorption of moisture from the wearers foot, comprising a member of substantially constant resistance which conductively connects the lower surface of said insole with an exposed face of said outer sole such that when a wearer of said anti-static footwear stands upon the ground, the resistance of the total electrical path, between his foot within said footwear and said ground contacted by said exposed face of said outer sole, remains substantially between a required upper limit and a required lower limit, even if said insole should in use become a perfect conductor, said member comprising:

A. a panel which contacts said lower surface of said insole and is thinner than said outer sole so that no part of said panel extends to or beyond said exposed face of said outer sole, and

B. a conductive means which electrically connects said panel with said exposed face of said outer sole.

2. The footwear of claim 1 wherein said panel extends over a smaller area than the area of said insole and said outer sole.

3. The footwear of claim 2 wherein said panel is located in the vicinity of the ball of said foot.

4. The footwear of claim 1 wherein said conductive means comprises metal threads in electrical communication with said panel and having at least one end extending to said exposed face of said outer sole.

5. The footwear of claim 4 wherein said metal threads are at least part of a piece of fine wire mesh.

Claims

1. Anti-static footwear having an electrically insulating outer sole and an insole the resistance of which is liable to drop substantially upon absorption of moisture from the wearer''s foot, comprising a member of substantially constant resistance which conductively connects the lower surface of said insole with an exposed face of said outer sole such that when a wearer of said anti-static footwear stands upon the ground, the resistance of the total electrical path, between his foot within said footwear and said ground contacted by said exposed face of said outer sole, remains substantially between a required upper limit and a required lower limit, even if said insole should in use become a perfect conductor, said member comprising: A. a panel which contacts said lower surface of said insole and is thinner than said outer sole so that no part of said panel extends to or beyond said exposed face of said outer sole, and B. a conductive means which electrically connects said panel with said exposed face of said outer sole.