US3839135A

US3839135A - Antistatic laminate filament and fabric prepared therefrom

Info

Publication number: US3839135A
Authority: US
Inventors: C Lowry; W Gilbertson; J Gusack
Original assignee: Dow Badische Co
Current assignee: Badische Corp; BASF Corp
Priority date: 1970-11-27
Filing date: 1971-08-25
Publication date: 1974-10-01
Anticipated expiration: 1991-10-01

Abstract

Disclosed is a fabric which avoids the accumulation of high concentrations of static electricity while presenting no appreciable electrocution hazard. The fabric comprises novel continuous laminate filaments each of which has (A) at least one polymeric ply bonded to (B) a ply made of electrically conductive material and having at least one discontinuity along its length.

Description

United States Patent 1191 Lowry et al.

1 1 Oct.1, 1974 1 ANTISTATIC LAMINATE FILAMENT AND FABRIC PREPARED THEREFROM [75] Inventors: Charles Everett Lowry; William J.

Gilbertson; James A. Gusack, all of Williamsburg, Va.

[73] Assignee: Dow Badische Company,

Williamsburg, Va.

[22] Filed: Aug. 25, 1971 21 Appl.No.:174,743

Related US. Application Data [63] Continuation-in-partof Ser. No. 93,194, Nov. 27,

1970, abandoned.

52 us. c1 .,161/65,161/67,161/146, 161/172, 161/214, 161/403 51 1111. C1 D03d 27/00 [58] Field Of Search 161/65, 67, 146, 172, 175, 161/178, 214

[56] References Cited UNITED STATES PATENTS 3,069,746 12/1962 Scharf 161/220 3,361,616 l/1968 Scharf 161/214 3,379,000 4/1968 Wcbber et a1. 161/172 3,582,444 6/1971 Ngo ct a1. 161/175 3,582,445 6/1971 Okushaski.... 3,678,675 7/1972 Klein 3,690,057 9/1972 Norris 57/157 AS Primary Examiner-William J. Van Balen Attorney, Agent, or Firm-George F. Helfrich [57] v 7 ABSTRACT Disclosed is a fabric which avoids the accumulation of high concentrations of static electricity while presenting no appreciable electrocution hazard. The fabric comprises novel continuous laminate filaments each of which has (A) at least one polymeric ply bonded to (B) a ply made of electrically conductive material and having at least one discontinuity along its length.

7 Claims, 4 Drawing Figures S R O T N E V W WIL LIAM J. GI LBE RTSON JAMES A. GUSACK THEIR ATTORNEY PATENTED 0m 1 974 Y m L T T E R E. V E S E L R A H C O O W CROSS REFERENCE TO OTHER APPLICATION This application is a Continuation-in-Part of our copending application Ser. No. 93,194 filed Nov. 27, 1970 now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to textiles in general, and more specifically to fabrics'having excellent antit of static electricity, while presenting no appreciable static characteristics, which fabrics contain laminate filaments.

2. Prior Art The accumulation of static electricity as a result of the utilization of fabrics is a phenomenon which has commanded the attention of the textile industry for some time. The presence of static is a cause not only of annoyance (e.g., items' of apparel cling to the body and are attracted to other garments; fine particles of lint and dust are attracted to upholstery fabrics, increasing the frequency of required cleaning; one experiences a jolt or shock upon touching a metal doorknob after walking across a carpet), but also of danger (e.g., the discharge of static electricity can result in sparks capable of igniting flammable mixtures such as ether/air, which are commonly found in hospitals, especially in operating rooms). All of these effects are accentuated in atmospheres of low relative humidity.

f the many proposals for preventing the undesirable buildup of static electricity, the most satisfactory, with respect to their efficiency and permanence. appear to be those which comprehend the utilization of fibers possessing electrical conductivity (e.g., metal fibers, fibers coated with electrically conductive material, or metallic laminate filaments) in combination with common natural and man-made fibers to produce a woven, knitted, netted, tufted, or otherwise fabricated structure, which readily dissipates the static charges as they are generated. Some of the more noteworthy of these methods and structures may be found in US. Pat. Nos. 2,129,504; 2,714,569; 3,069,746; 3,288,175; 3,582,444; and 3,582,445; and in Webber, Metal Fibers. Modern Textiles Magazine, May, I966, pp. 72-75.

Notwithstanding the efficacy of these expedients in the dissipation of static, they are found lacking in one most important aspect; viz., there is no comprehension of, and therefore no specified provision to eliminate, the electrocution hazard which could result from the employment of such electrically conductive material. Specifically, the continuum of electrically conductive material, which affords the conductivity necessary for dissipation of any static charges which may have been generated in the fabrics, could also result in harm to those touching these fabrics in the event of accidental contact of such fabrics with a source of essentially unlimited electrical current, as is available from an ordinary electrical outlet, or an electrical appliance shortcircuited by insulation failure.

SUMMARY OF THE INVENTION Accordingly, it is a primary object of this invention to provide a fabric which efficiently and permanently avoids the accumulation of undesirable concentrations electrocution hazard. It is another primary object of this invention to provide novel laminate filaments which find utility in the preparation of these novel fabrics.

In accordance with this invention, these advantages are achieved, and the problems inherent in prior structures are eliminated, by providing a fabric composed either entirely or in part of continuous laminate filaments (advantageously between about 0.5 and percent of the laminate filaments with any remainder being any commonly employed natural or man-made fiber), each laminate filament having (A) at least one polymeric ply bonded to (B) a ply made of electrically conductive material and having at least one discontinuity along its length. The structure is fabricated using standard weaving, knitting, netting, tufting, or braiding techniques.

Although it is necessary to produce only one discontinuity along the length of the electrically conductive ply of each laminate filament to be utilized in fabricating the structure of the present invention, more than one such discontinuity may be employed-if desired for any reason, or if naturally resulting fromthe process used to effect discontinuity--without any substantial vitlation of the antistatic properties of the fabric, and without any substantial further enhancement in the disposition of the electrocution hazard. Indeed, when many discontinuities are present in the otherwise electrically conductive ply of the laminate filament, e.g., when the average interval between discontinuities is as small as approximately one inch, the antistatic properties of the fabric have been found to be satisfactory. No technical advantage is presently envisioned, however, in the production of such or larger numbers of discontinuities.

In fine, the instant invention comprehends in essence the interruption of the continuum of conducting surface which would have been established under the prior art for the purpose of dissipation of static electricity generated in the fabric, one interruption along the length of the electrically conductive ply of each laminate filament employed in the structure being necessary to dispose of the electrocution hazard otherwise presented, more than one such interruption (and even very many) being acceptable, although not especially advantageous. That any such interruption would not cause an enormous diminution in the dissipation of static electricity generated in the structure is totally unexpected.

- invention, including its objects and benefits, reference is made to the detailed description set forth below, which should be read together with the accompanying drawing, wherein:

FIG. 1 is a plan view of one preferred fabric in accordance with the invention;

FIG. 2 is a warpwise section of another ric embodying the invention;

FIG. 3 is a perspective view of one preferred form of novel, continuous laminate filament employed in the fabrics of FIGS. 1 and 2; and

FIG. 4 is a sectional view of the laminate filament of FIG. 3.

preferred fab- DESCRIPTION OF THE PREFERRED EMBODIMENTS With particular reference to the drawing, FIG. 1 shows a woven fabric according to the invention, produced by interweaving laminate filaments (30) with ordinary threads (11) which are made from natural fibers such as cotton or wool, and/or man-made fibers such as nylon, rayon, acrylic, or polyester. The laminate filaments (30) are present in an amount equal to about 0.5-100 percent by weight of the woven fabric (10).

Referring now to FIG. 2, there is shown a pile fabric according to the invention, which fabric comprises a backing material (21) having pile loops (22) anchored to the backing material (21). In the pictured embodiment, the backing material (21) comprises chain yarns (23) interwoven with filler yarns (24), as is well known in the art. The backing material may possess any other structure heretofore employed in the production of pile fabrics. The backing material (21) may be constructed from any of the materials commonly employed in the art, such as jute or hemp, among many others. The pile loops (22) comprise a yarn (25), which is made of one or more strands, three such strands being pictured here. The yarn (25) contains a laminate filament which is present in an amount equal to about 0.5-100 and preferably 2-l5 percent by weight of the yarn (25). The balance, if any, of the yarn (25) comprises any commonly employed natural or man-made fibers (26).

Laminate filaments according to the present invention may be prepared from any of the well-known film or fiber forming polymers, such as cellulosics, polyamides, polyolefins or polyesters coated with a layer or laminated to a ply made of an electrically conductive material. This electrically conductive material is preferably a metal or mixture of metals and most preferably, for laminate filaments prepared by the slitting of laminated films, consists of a metal foil. Equally satisfactory conductive plies can be prepared by plating films or filaments with metal, for example, electrolytically or by high vacuum deposition methods so long as such metal deposits are thick enough to provide adequate electrical conductivity. Vapor deposited aluminum coatings must, for example, be about 0.5 microns in thickness to obtain adequate electrical conductivity. such conductive plies must, of course, be adequately adherent to withstand textile processing and use requirements. This is readily accomplished by lamination ofa second polymeric ply over the electrically conductive ply. Satisfactory results can also be obtained by coating the metallic ply with polymers or adhesives, which in some cases may require curing. Moreover, such coatings can contain finely divided metal particles and/or other electrically conductive materials, thus directly providing the required electrically conductive ply.

Turning now to FIGS. 3 and 4, there is shown a preferred laminate filament (30) which is used in the construction of the fabrics (10 and (20) pictured in FIGS. 1 and 2. This laminate filament (30) is a modification of those already known in the art, as, for example, those shown in Scharf, US. Pat. No. 3,069,746. The laminate filament (30) comprises a metal ply (33) bonded on each side thereof to polymeric plies (31) and (32) by suitable means, such as layers of adhesive (34) and 35). The metal ply (33) may be composed of copper, silver, nickel, chromium, lead, tin, or aluminum, or' alloys of these metals. Aluminum is preferred because of its properties of high ductility, electrical conductivity, and resistance to oxidative changes. The polymeric plies (31) and (32), which may be composed of the same or different materials, are prepared from any of many well-known polymeric materials. Preferred polymeric materials are the fiber-forming polymers having a high tensile strength, such as the cellulosics, e.g., cellulose butyrate; the polyamides, e.g., nylon; the polyolefins, e.g., crystalline polypropylene; and most preferably, the polyesters, e.g., polyethylene terephthalate.

The laminate filament (30) is further characterized by the presence of at least one interruption or discontinuity (36) along the length of the metal ply (33). The mean distance between segments of continuous metal ply, i.e., the mean length of the discontinuity (36), is at least about 0.003 inches, such being ordinarily sufficient to eliminate corona discharge at potentials readily available from convenience outlets. More than one discontinuity (36) may be present along the length of the metal ply (33) of the laminate filament (30), although such in neither required nor particularly advantageous. Pictured in FIGS. 3 and 4 are two such discontinuities (36), which are schematically depicted here, solely for the purposes of simplicity, as regular voids resulting from sharp, even breaks in the metal ply. That these voids are oftentimes irregular will be apparent to one skilled in the art, upon perusing the remaining portions of the disclosure.

In the incorporation of the laminate filaments of the present invention into pile fabrics, especially carpets, it has been found advantageous to recognize a relationship existing between the average distance between successive discontinuities in the metal ply of a particular laminate filament--hereinafter designated L--and the average length of the individual discontinuities therein--hereinafter designated G. Specifically, it has been found that loop pile carpets exhibiting highly satisfactory static dissipation characteristics and presenting no appreciable electrocution hazard will result from the employment of metallic laminate filaments according to the present invention, which filaments have an L/G ratio equal to or greater than about I00.

As will be understood by one of skill in the art upon a careful reading of the foregoing portions of this detailed description, it is not necessary that every end of yarn in the pile contain a strand of the metallic laminate filament. Moreover, more than one strand of metallic laminate filament per end of yarn in the pile may be advantageous, especially under conditions of very low relative humidity.

The laminate filament (30) according to the present invention can have a width of from less than 0.001 inches to over 0.25 inches, although widths within this range are generally preferred, and a width of 0.01 inches has been found suitable for a number of applications. Depending upon such factors as the width of the filament (30), the thickness of the plies (31 (32), and (33), and the amount of adhesive (34) and 35), a laminate filament (30) useful in the present invention has a wide range of acceptable deniers.

Laminate filaments (30) employed in preparing the fabric of this invention are conveniently prepared by modifications of standard processes known in the art for the production of ordinary laminate filaments, such, for example, as is shown in Scharf US. Pat. No. 3,069,746. By way of example, to produce laminate filaments (30), used in this invention, a discontinuous adhesive layer is applied to one or both of the opposed surfaces of webs of the selected polymeric film and metal foil, which materials are then laminated into a 3-ply structure by means of heat and pressure, for example, in a continuous manner, utilizing pairs of pressure rollers adapted to bring the webs into intimate contact. The resulting laminate is then stretched to a degree sufficient to break the metallic layer at the point(s) at which no adhesive is present, but insufficient to break the metallic layer in the relatively greater areas where adhesive, film, and foil are in intimate contact. After being so stretched, the laminate is then slit into narrow strands of the desired width. Alternatively, the laminate may be first slit into narrow strands, which strands are then stretched to the desired degree.

The present invention may be better understood by a reference to the following illustrative examples, wherein all parts and percentages are by weight unless otherwise indicated.

EXAMPLE I This example specifies detail concerning the structure and characteristics of certain of the laminate filaments embodying the present invention.

A 3-ply laminate was prepared from two sheets of polyethylene terephthalate, each of which was about 0.0005 inches in thickness, and a sheet of aluminum 0.00045 inches in thickness, employing a commercially available polyester adhesive to bond the polyethylene terephthalate sheets to each side of the aluminum sheet. Before the lamination was effected, however, a wedge-shaped area had been removed from the aluminum sheet, with the result that when the laminate was subsequently slit into specimens 0.01 inches in width, a series of laminate filaments was obtained, each having a single discontinuity in the metal ply thereof, the length of this discontinuity or gap" varying from 0 to about 0.100 inches.

A. Employing a current measuring cell equippedwith salt water contacts and utilizing a source of essentially unlimited electrical current, each filament of the series prepared as described above was individually tested to determine whether it would conduct an electrical cur rent at a potential of 440 volts rms (60 HZ). Those filaments having a length of discontinuity or gap in the metal ply of 0.003 inches or more conducted no measurable current under these circumstances.

B. ln a second set of tests performed upon the series of filaments described above, the minimum potential necessary for each filament to conduct an electrical direct current was determined. The results of this series of tests are summarized in the accompanying Table I.

TABLE I Length of discon- Minimum potential necessary TABLE l-Continued Length of discon- Minimum potential necessary Illustrated in this example is a useful method of construction of a laminate filament according to the present invention. A sheet of aluminum 0.00045 inches thick was laminated to two sheets of polyethylene terephthalate, each of which was 0.0005 inches thick, employing a commercially available polyester adhesive on each side of the aluminum. Instead of the two continuous layers of adhesive, as is generally employed in the art--see, e.g., US. Pat. No. 3,069,746 a discontinuous adhesive layer was applied to one side of the aluminum, each of the discontinuities in the adhesive layer being approximately 1/16 inch in length, and the average interval between the discontinuities being approximately 32 inches, these distances being measured along the linear direction of the laminate. After the adhesive had been cured, the laminate was slit into filaments about 1/ inch wide, which filaments were then stretched to about 40 percent of their original length. Under such conditions, it was observed that the metallic foil component of the laminate was broken into discontinuities of approximately l/l 6 inch in length, the average length between discontinuities being about 32 inches, both measurements being taken along the length of the filament. It was also observed that the polymeric components of the laminate remained intact, no discontinuities being observable therein. This filament, which is designated Filament A, had a denier of about I50.

EXAMPLE 3 Illustrated in this example are structures of other laminate filaments according to the present invention. Employing a procedure equivalent to that outlined in Example 2 above, metallic laminate filaments, otherwise identical to those in Example 2 above, were prepared having the following characteristics:

For comparative purposes, a metallic laminate filament otherwise identical to those of Examples 2 and 3 above, but having no discontinuities in the metal ply thereof, was prepared using standard techniques, as, for example, according to US. Pat. No. 3,069,746. This filament, which is not useful in the practice of the present invention. is designated Filament I, being prepared for comparative purposes only.

EXAMPLE This example illustrates the production of a composite yarn useful in the practice of the present invention. A single strand of the metallic laminate Filament A of Example 2 above was twisted with two ends of 2/ l cotton count yarn of polymerized acrylonitrile.

The resulting yarn contained 3 weight percent of the metallic laminate filament, based upon the weight of the yarn. This yarn is designated Yarn A.

EXAMPLE 6 Using the procedure of Example 5, Filaments B, C, D, E, F, G, and H were individually employed in the preparation of seven other composite yarns useful in the preparation of a fabric in accordance with this invention, which yarns are designated as follows:

Filament Yarn B B C C D D E E F F G G H H EXAMPLE 7 This example, which is not illustrative of the present invention, is set forth for comparative purposes only. Using the procedure of Example 5, Filament l of Example 4 was employed in the preparation of a composite yarn which is not useful in the preparation of a fabric in accordance with this invention, such yarn being designated Yarn l.

EXAMPLE 8 This example, which is also not illustrative of the present invention, is set forth for comparative purposes only. Two ends of 2/ l cotton count yarn of polymerized acrylonitrile and containing no metallic laminate filament were twisted together. The resulting yarn is designated Yarn J.

EXAMPLE 9 STATIC ELECTRICITY TEST The fabric to be tested is first cut into sample squares 36 inches on a side. These samples are conditioned for 7 days by being hung from racks in a test room equipped with a rubber floor mat and having an area of at least 100 square feet, wherein the temperature is controlled at 70i 2F. and the relative humidity is controlled at percent i 1 percent. Free circulation of air over all sample surfaces is effected, but the samples are not allowed to contact each other. A pair of leathersole test shoes is also conditioned for the same period, under the same conditions.

Residual static change on the rubber floor mat is then neutralized by passing twice over its entire surface a polonium wand, which consists of 6 polonium 210 alloy strips mounted end-to-end on a head attached to a handie. A fabric sample is then placed upon the rubber floor mat, and its residual static charge is neutralized in the same manner. The leather soles of the test shoes are then cleaned by sanding their entire surface with fine sandpaper, followed by a wiping with cheesecloth to remove dust particles.

Wearing the test shoes and holding a hand probe which is connected to an electrostatic detection head, a human operator steps upon the carpet sample and grounds the probe. Then while holding the hand probe, the operator walks normally on the sample at a rate of 2 steps a second for a 30-second period, being careful not to scuff or rub the shoes over the fabric. if at the end of the 30-second period the voltage has not reached a steady maximum, the walk is continued for an additional 30 seconds. The maximum voltage recorded during the walk is the static level of the sample, the average for two operators being recorded in Table II as static electricity in volts. Other standard tests are used for determining the static level of fabrics having utility as garments, etc.

CONDUCTIVITY TEST The test for electrical conductivity was performed in accordance with Number 56 of the National Fire Protection Association Standards, revision of June 1968, entitled Code for the Use of Flammable Anesthetics 1968, available from the National Fire protection Association, 6O Batterymarch Street, Boston, Mass. 021 10. To meet the requirements of this Code, a conductive fabric used as a floor covering shall have a resistance of greater than 25,000 ohms, as measured between a ground connection and an electrode placed at any point on the floor covering, and also as measured between 2 electrodes placed 3 feet apart at any points on the floor covering.

The fabric to be tested is first cleaned and dried, and the test room freed of any flammable gas mixtures. Provided are 2 electrodes, each weighing 5 pounds and having a dry, flat, circular contact area 2 /2 inches in diameter, which comprises a surface of aluminum foil about 0.001 inch thick, backed by a layer of rubber inch thick and measuring between 40 and 60 durometer hardness as determined with a Shore Type A durometer. (See American Society for Testing and Materials Method designated D-2240-64T, obtainable from the Society at 1916 Race Street, Philadelphia, Pa. 19103.) Provided also are two lead wires and a calibrated ohmmeter which operates on a nominal open circuit output voltage of 500 volts DC. and a shortcircuit current of 2.5 to 10 milliamperes, the scale of the ohmmeter showing units of resistance.

Measurements of the resistance of the fabric are made at five or more locations on the floor covering,

and the results are averaged. If the resistance changes appreciably with time during a measurement, the value observed after the voltage has been applied for about 5 seconds is considered the measured value. Where resistance to ground is measured, two measurements are appended claims.

What is claimed is: l. A continuous laminate filament which comprises:

A. A polymeric ply bonded to V g B. A ply made of electrically conductive material and havinga discontinuity along its length. 2. A laminate filament according to claim 1, wherein the electrically conductive material is a metal.

3. A fabric comprising a continuous laminate fila- TABLE II Mean length in inches of Mean distance in inches Designation of Weight percent discontinuities in between discontinuities Static Fabric the yarn in the of metallic laminate I the metal ply of the in the metal ply of L/G Electricity Resistance pile fabric filament in the yarn metallic laminate the metallic laminate volts ohms Filament employed (G) filament employed (L) THIS INVENTION 3 0.06 32 533 1400 13 3 0.003 I 333 3250 10 C 3 0.003 10 3333 2750 10 D 3 0.003 100 33333 2250 10 E 3 0.02 10 500 2900 10 F 3 0.02 100 5000 2250 10 G 3 0.1 10 100 3400 10 H 3 0| 100 1000 2400 10 FOR COMPARISON s i I (no discontinuities) (no discontinuities) w 2000 10 J 0 I 2000 107 From Table I it can be seen that although the passage of current from an ordinary electrical outlet is effectively blocked by discontinuities of at least 0.003 inches in the metal ply of a laminate filament according to the present invention as evidenced by the resistance being much greater than 25,000 ohms, such discontinuities are not capable of preventing the dissipation of the charges of much greater magnitude which might result. for example, from repeated rubbing and separation of shoes and carpet pile.

From Table II it can be seen that pile fabrics according to the present invention. when employed as carpets in anatmosphere the'relative humidity of which is percent, will not generate a static charge above about 3,500 volts, which is in proximity to the threshold level of human sensitivity. From Table ll it can also be seen that the same fabrics do not present an electrocution hazard, as evidenced by the resistance data. Furthermore, it can be seen from Table II that a pile fabric according to the present invention possesses this highly desirable combination of properties when the laminate filaments comprising it have an L/G ratio, as hereinbefore explained, of at least about 100.

Fabrics having this combination of properties find special utility not only as carpets, rugs, and other floor coverings, but also as bed coverings, especially in hospitals', as curtains, especially in hospitals for separation of cubicles; and in the production of articles of clothmg.

Although the present invention has been described in detail with respect to certain preferred embodiments thereof, it is apparent to those of skill in the art that variations and modifications in this detail may be effected without any departure from the spirit and scope of the present invention, as defined in the heretoment, which comprisesf A. A polymeric ply bonded to B. A ply made of electrically conductive material and having a discontinuity along its length.

4. A fabric according to claim 3, wherein the electrically conductive material is a metal.

5. A pile fabric comprising:

A. A backing material; and

B. Pile anchored in the backing material, the pile comprising a continuous laminate filament, which comprises: i

l. A metal ply having at least one discontinuity of at least about 0.003 inches along the length thereof, and

2. A polymeric ply bonded to the metal ply; the

ratio of the mean distance between discontinuities in the metal ply to the mean length of the discontinuities being at least about 100.

6. A pile fabric according to claim 5, wherein the metal ply is aluminum and the polymeric ply is polyeth

Claims

1. A CONTINUOUS LAMINATE FILAMENT WHICH COMPRISES: A. A POLYMERIC PLY BONDED TO B. A PLY MADE OF ELECTRICALLY CONDUCTIVE MATERIAL AND HAVING A DISCONTINUITY ALONG ITS LENGTH.

2. A laminate filament according to claim 1, wherein the electrically conductive material is a metal.

2. A polymeric ply bonded to the metal ply; the ratio of the mean distance between discontinuities in the metal ply to the mean length of the discontinuities being at least about 100.

2. Two polyethylene terephthalate plies, the polyethylene terephthalate plies being bonded to opposite sides of the aluminum ply; the ratio of the mean distance between discontinuities in the aluminum ply to the mean length of the discontinuities being at least about 100.

3. A fabric comprising a continuous laminate filament, which comprises: A. A polymeric ply bonded to B. A ply made of electrically conductive material and having a discontinuity along its length.

5. A pile fabric comprising: A. A backing material; and B. Pile anchored in the backing material, the pile comprising a continuous laminate filament, which comprises:

6. A pile fabric according to claim 5, wherein the metal ply is aluminum and the polymeric ply is polyethylene terephthalate.

7. An antistatic carpet comprising: A. A backing material; B. Pile anchored in the backing material, the pile comprising a continuous laminate filament, which comprises: