JPS62257474A - Antistatic carpet tile and its production - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to antistatic carpet tiles and a method for producing carpet tiles of this type.

[Prior Art] Floor covering materials, such as carpet tiles, accumulate a large amount of static electricity when people walk on them or when objects such as furniture are moved while coming into contact with the floor covering. When this accumulated static electricity is suddenly discharged onto the floor covering material, it causes discomfort to humans and inhibits the functionality of computers and electronic devices.

Static electricity buildup and discharge can be prevented by providing a conductive path from the carpet surface to electrical ground and by providing resistance to the floor surface material (
i.e., bulk resistance and surface resistance) within predetermined standards, such as those required by computer and electronic component manufacturers to protect sensitive computers, electronic components, and equipment with microchips. can be minimized. Typically this type of standard is a minimum of 5X105Ω in surface and bulk resistance.
and requires a maximum of 2×1010Ω. Furthermore, for safety reasons, there is often a desired minimum resistance value of 10 3 to 10 4 Ω.

Carpet tiles have been developed as carpet materials that prevent the generation or build-up of static electricity and can rapidly dissipate static electricity without danger to people or equipment. To date, however, floor coverings of this type have not been completely satisfactory.

An antistatic floor surface material can be produced by applying an antistatic top coat material to the surface of the floor material. however,
Typically, this type of antistatic treatment is not permanent, results in staining of the floor covering, and is generally not very effective under conditions of low humidity and relative humidity. Permanent or static conductivity in fibrous flooring can be created by incorporating conductive fibers or yarn members into the flooring (eg, carpet tiles).

Conductive male elements of this type may consist, for example, of fine thin metal wires or metal-coated wires as yarn elements, or they may consist of, for example, carbon-filled carbon-containing core yarns or non-conductive surface fibers or fibers mixed into the yarns. can do. This type of permanent protection often provides both low static electricity generated by interaction between the carpet surface and people and items, and electrical conductivity in the carpet surface. However, the conductive w4M surface does not by itself provide effective electrical conductivity through the surface of the carpet. That is, it does not provide acceptable conductivity or bulk resistance (so-called capacitive resistance).

6. Carpet tiles which are incorporated into the fiber side of the carpet to fix the i-male side of the carpet and which are fixed by the use of a conductive pre-coat or backing layer to very quickly dissipate the static electricity generated. has been done. Typically, this type of conductive precoat is made of a styrene-butadiene latex that has been incorporated with a conductive material (such as metal particles, especially dispersed fine carbon black particles) to increase its conductivity. Made of polymer material. This type of carpet tile or other carpet material must also have a relatively thick backing layer to ensure dimensional stability of the carpet tile during use and a flat surface on which to place the carpet tile. Although a wide variety of polymeric materials may be used, the most prevalent materials currently used as backings for commercial carpet tiles are atactic polypropylene, bitumen, and polyvinyl chloride. This type of material must be non-conductive,
Therefore, the charge cannot be easily grounded or conducted to the back side of the carpet tile.

Generally, the use of antistatic or conductive chemicals in relatively thick backing layers and the use of particulate materials, such as carbon black particles, with polymeric backing materials have not been found to be sufficient. This is because the amount of carbon black required to obtain the desired conductive or antistatic effect results in a significant viscosity increase or often affects the actual chemistry. Furthermore, the use and incorporation of other antistatic additives into the lining material, such as metal fatty acid soaps, glycols, etc., often alters the chemical and mechanical properties of the lining material, resulting in unsatisfactory quality and properties. bring. For example, the use of stearic acid compounds in the solid bitumen backing in the manufacture of carpet tiles often affects the adhesion of the bitumen and also affects the mechanical properties of the bitumen or bituminous fillers (e.g. lime, backing material). weaken. Carpet tiles and methods for their manufacture are described in British Patent No. 20573536, published March 28, 1984, which is hereby incorporated by reference.

[Problems to be Solved by the Invention] Accordingly, a conductive 1JIi fiber surface having improved conductivity and more effective and improved antistatic properties which avoids the drawbacks associated with the above-mentioned conventional surface materials. It would be desirable to provide a surface covering and a method of making the same.

SUMMARY OF THE INVENTION The present invention relates to a fibrous surface covering material having antistatic properties or improved conductivity, and methods of making and using the same. More particularly, the present invention relates to antistatic carpet tiles and methods of construction and use thereof for use, for example, in computer and electronic industry and office environments to prevent damage to sensitive computer and electronic equipment.

The antistatic conductive carpet or surface covering of the present invention has a fibrous surface and a backing layer, with a plurality of columns of conductive material extending from the back of the carpet through the backing layer to the bottom of the carpet. Then, an electrical path is formed through this island-shaped conductive material column from the back surface of the carpet to the back surface of the carpet.

In particular, the invention provides that the Carpella 1 to tile is a primary backing sheet (typically non-woven polypropylene, polyester, hemp,
An antistatic carpet tile having a fibrous surface fixed to a sheet material such as glass fiber as a primary backing sheet, and a Frecote layer that acts to secure the fibrous surface to the reverse side of the primary backing sheet. I will provide a. The carpet has a backing layer of relatively thick solids or foam or polymers thereof, which can be formed in one layer or in several layers, and which further contains a dimensionally stable sheet material such as a fiberglass sheet. be able to. If desired, a secondary backing layer of sheet material, such as polyester, can also be secured to the back side of the backing layer.

The carpet tile has a plurality of spaced apart columns of conductive material formed in the backing layer and extending from the back side of the carpet tile approximately to the back side of the precoat layer and the primary backing sheet, from the back side of the facing carpeller 1 to Forms an electrical path to the back side, increasing conductivity and
X1010 ohms or less, typically 106 ohms per square
or less, providing improved conductivity or bulk resistance.

If desired, the antistatic carpet tile may optionally be further provided with one or more layers of conductive material, such as thin coating layers or strips, on the back side to form conductive columns on the back side of the carpet tile. Conductive strips can also be formed that connect the columns and extend substantially across the bottom surface of the carpet tile to connect spaced apart column ends on the back surface of the carpet tile. Furthermore, the conductive layer or strip can also consist of a conductive adhesive layer that secures the carpet to the floor.

In a particularly preferred embodiment, the antistatic carpet of the present invention has a fibrous surface comprising conductive fibers or yarns and the precoat is a conductive precoat, i.e. antistatic carpets such as carbon particles or metal particles. J containing an additive and further having one end of the conductive column projecting into the precoat and the other end extending approximately perpendicular to the backside of the carpet to the conductive strip or backside of the carpet.
: Made of una carpet tiles. In fact, conductive or antistatic additives can be applied as a top coat to the surface of the carpet, or incorporated into the backing layer, or incorporated into any of the sheet materials used in the carpet. Typically, the backing layer is non-conductive or poorly conductive, and a plurality of islands of conductive material, such as islands approximately uniformly spaced in one dimension of the carpet tile, provide effective grounding. Form an electrical path.

Antistatic and effective conductive carpets suitable for use in the computer and electronics industry and having a bulk resistance of less than about 108 ohms per square include carpet tiles having a fibrous surface of synthetic fibers such as polyester, nylon, etc. formed using needle-punched, fused or tufted fibers, the fiber side of which includes several fine stainless steel yarns or carbon-core synthetic yarns to form the carpet surface. imparts conductivity to This type of fine stainless steel yarn can be coated to increase its conductivity and can also be composed of carbon-filled polymeric fibers, e.g. 6 water vs. 12 conductive fibers vs. non-conductive fibers. The ratio of approximately 1 conductive yarn per 1 conductive yarn is used. Additionally, this type of carpet tile also includes a primary backing sheet, such as nonwoven polypropylene, and uses a conductive precoat (eg, a styrene-butadiene latex layer) to secure the fibers to the primary backing sheet. The latex precoat is applied in an amount that imparts conductivity to the thin precoat layer, e.g.
An amount of carbon particles of 40 ounces can be included to provide a conductivity of generally less than 1×10 8 ohms per square.

This carpet tile furthermore has a relatively thick layer of dense polymeric backing, e.g. of bitumen or a bitumen-filler mixture of e.g. finely divided lime and bitumen, e.g. 150 ounces, specifically 630 per square yard.
Use in amounts of ~120 oz. If desired, the backing layer can also contain a texture or scrim of glass fibers or synthetic fibers, such as polyester, to impart dimensional stability to the carpet tile. The polymeric backing, such as bitumen or lime-filled bitumen, must be electrically non-conductive. In addition, carpet tiles typically also have a secondary backing layer, such as a woven polyester layer, on the back side of the carpet tile to facilitate securing the carpet tile to the ground or resting on the surface during installation.

The carpet tiles of the present invention typically have a series of dense columns of conductive material, typically comprised of a conductive ink-type polymeric material, such as a water-based or volatile organic solvent-based ink containing fine carbon particles. Carpets generally have columns of conductive ink extending from the conductive precoat layer or from the back side of the primary layer or optionally to the back side of the secondary backing sheet. These columns are spaced and aligned, but can vary, and run approximately the entire length of the carpet tile from one end to the other, e.g., 1 to 6 inches, more typically 1/2 to 2 inches. They can be spaced uniformly with a certain degree. The linearly spaced edges of the electrically conductive material, which preferably extend across the back side of the secondary backing sheet, are optionally coated with a thin coated strip of material containing carbon black particles (e.g. SBR latex or electrically conductive ink). Connections can also be made with thin strips of conductive material such as. This conductive coating layer or strip generally extends over the entire surface of the carpet tile and connects the ends of the columns to form islands on the backside of the carpet tile and extends to the edges of the carpet tile. do. Instead of a covering strip, an electrical path to earth can also be constructed using a conductive adhesive to secure the back side of the carpet to the base floor. The carpet tile of the present invention can be used in a computer room or a room with electronic equipment.
A conductive strip or coating on the conductive column and the back side of the column in a conductive precoat layer and a thick non-conductive backing layer, providing an improved electrical bulk resistance of less than 1 x 1 on ohms per square, typically less than 1 x 106 ohms per square. Through this, static electricity is rapidly discharged from the conductive fiber surface to the ground. If desired, the carpet tile can have columns that are linear, zigzag, or substantially inconstant or evenly distributed over the entire backside of the carpet. If highly antistatic carpet tiles are desired, there may be one or more conductive strips or even a grid thereof connecting these columns.

The polymeric materials used in the backing layer can consist of a wide variety of hot melt or thermoplastic type polymeric materials, including but not limited to: bitumen, vinyl chloride resin, atactic polypropylene, urethane, and Ethylene vinyl acetate resin.

These polymers include various additives such as plasticizers, flame retardants, hardeners, viscosity index improvers, and talc,
It may also contain fillers such as lime and diatomaceous earth. The bitumen used shall consist of petroleum-based bitumen or asphalt material, and shall be suitable for use as a hot-melt carpet backing material, with soot derived from or containing carcinogenic coal tar derivatives.

The present invention further provides a method for making an antistatic or conductive surface covering, such as a carpet tile having a fibrous surface, which method comprises a plurality of conductive carbon-containing polymeric ink materials. forming narrow columns of spaced conductive material extending from the back side of the backing layer to the precoat layer or to the back side of the primary backing of the carpet material to form a conductive path from the side of the face covering to the back side; At the same time, it provides an improved bulk resistance value. The narrow column of conductive material is curved by penetrating the backing layer with one or more spikes or needles containing the conductive material to be deposited to form a narrow column in the backing layer. Easily formed.

For example, a narrow column may be applied by coating the surface of one or more spike-like members mounted on a rotating wheel or reciprocating member with a conductive drying liquid, such as a conductive carbon-containing ink, and then coating the back surface of a carpet backing layer. It can be formed by inserting a predetermined length of spike-like or needle-like members into the precoat layer or onto the back side of the primary sheet of the carpet tile. The conductive column is formed when the needle-like or spike-like member is removed, and the conductive material is deposited as a column within the entry hole. Generally, after the needles or spikes are removed, they are recoated with conductive material and used to penetrate the back side of the backing layer again. Generally, by using a rotating wheel having a plurality of spikes or needles, the column is formed as a generally discontinuous, but predetermined straight path over substantially the entire back surface of the carpet tile.

Furthermore, the method consists of coating the back side of the carpet tile with an electrically conductive coating layer, strip or adhesive to connect the ends of the narrow columns on the back side. In general, the covering may consist only of strips connecting the column ends on the back side of the carpet tights C, but if desired, of course a conductive material covering all or part of the back side of the carpet before or after applying the secondary backing layer. It can also be used as a covering layer. In one method of operation, a carpet tile is supported with the fiber side down or up, and then a rotating wheel having a needle-like member of a predetermined length that reaches into the pre-layers is placed next to the carpet tile on the support layer. Rotation by directional movement causes the needle-like member to penetrate the back side of the backing layer in a predetermined pattern, and after this penetration, it is extracted and the surface of the needle-like member is recoated with conductive ink, and said pattern is repeat. Since conductive inks generally exhibit a dark color due to carbon black particles, the needle must not penetrate to the surface of the carpet to prevent discoloration of the surface fibers.

[Effects of the Invention] The antistatic conductive surface covering material, particularly the carpet tile, and the method for manufacturing the same of the present invention overcome many of the drawbacks associated with the prior art, and provide a compact material with improved electrical resistance. Provides an excellent surface covering, especially carpet tiles, with a non-conductive backing layer.

[Example] The production of an antistatic carpet tile according to the present invention will be described below with reference to the accompanying drawings, but is not limited thereto.
The present invention is equally applicable to the production of many types of antistatic surface covering materials, and many modifications, improvements, additions, etc. may be made without departing from the spirit and scope of the present invention. will be understood by those skilled in the art.

The drawings show a carpet tile having a tufted fibrous surface woven with conductive yarns 14 made of a synthetic polymer, such as nylon, with the fibrous surface positioned on a support belt 12. 1lil 14 is secured to a single layer backing sheet of polyester and held in place using a conductive pre-coated SBR latex layer 18 containing conductive carbon black particles. Gochumen lime lining 2
0 to the precoat layer 18, while a secondary backing sheet 22, for example made of polyester Fa fibers, is secured to the back side of the bituminous backing layer 20.

As explained in more detail in FIG.
The wheel 28 is positioned above the carpet tile 10 on the moving support layer 12 and has a plurality of evenly spaced spikes or needles 26 around its outer periphery. Foam roll coater made of open-cell foaming agent
28 is arranged to rotate in a bath containing conductive liquid ink material 32.

The forward movement of the carpet 10 on the belt 12 causes the rotating wheel 24 to move freely with the spikes 26 about its axis. As wheel 24 rotates, the spikes penetrate into open cell foam layer 28 and conductive liquid 32 from bath 30.
and coats the outer surface of the spike 26.

When the carpeters 1 to 10 move on the support layer, the spikes come into contact with the back surface of the carpet tile 10. The spikes 26 end-coated with conductive liquid penetrate the secondary backing layer 22 and the bitumen 20 into the conductive precoat layer 18 and, upon withdrawal, penetrate the penetration hole 36.
A conductive ink is deposited therein to form conductive columns 32 that form an electrical path from the conductive precoat layer 18 to the backside of the secondary actual layer 22 .

Rotation of the wheel forms a plurality of columns of conductive material 32 in a predetermined spaced linear arrangement over the entire back surface of the carpet tile 10 to a predetermined depth relative to the precoat layer, which may vary depending on, for example, the thickness of the backing coating and precoat. 30~
150 mils, especially 60-120 mils. As shown in more detail in FIG. 2, a conductive layer, e.g., a conductive ink, is applied to the back side of the carpet 10 to form a dry conductive strip 34 over the entire back side of the carpet, and a secondary backing layer 22. Connect the ends of columns 32 at.

Next, the carpet made as shown in Figures 1 and 2 is used by placing it on the ground, but if desired, it can be electrically connected with a wire grounded in the ground or with a conductive adhesive. An electrical connection can be made, or more conveniently, it can simply be placed on the ground, and in operation, static electricity that builds up on the surface of the carpet 14 passes through the conductive fibers on the surface 14 and connects the conductive precoat layer and the Column 3 of
2 to the strip 34, which is further grounded.

The improved carpet of the present invention and its manufacturing method have been explained above using specific examples, but it is necessary to make the fiber surface of the carpet conductive or the precoat conductive depending on the desired type of conductivity. Not. This is because forming narrow columns of conductive material extending through the backing layer to a precoat or single ply sheet is often desirable to create an electrical path across the face of a carpet tile, especially when using a thick backing layer. It is advantageous when constructed from electrically non-conductive materials, as it actually acts as an electrical insulator for surface coverings such as porcelain or lime-filled bitumen.

[Brief explanation of drawings]

FIG. 1 is a schematic partial cross-sectional view of the method for manufacturing a conductive carpet tile according to the invention, and FIG. 2 is a rear view of the carpet tile according to FIG. 10...Carpet tile 12...Belt 14
... Yarn 18 ... Latex layer 2
0... Lining layer 22... Lining sheet 2
4... Rotating wheel 26... Needle-like member.

Claims (37)

[Claims] (1) comprising a layer of fibrous surface fixed to a primary backing sheet;
In manufacturing an antistatic or conductive surface covering having a non-conductive backing layer further having a back surface, a plurality of spaced apart thin columns of conductive material extending from about the back side of the backing layer to about the primary sheet. to form a conductive path for static charge from the fibrous surface of the surface covering material to the back surface of the backing layer, and to form a surface covering material with improved low electrical resistance. A method for producing a conductive or conductive surface covering material. (2) A thin spike-like member containing a conductive material is inserted into the backing layer, and the thin spike-like member is extracted from the backing layer to form a column of conductive material in the backing layer. Method. 3. The method of claim 1, wherein the thin spike-like member has a coating of a liquid conductive ink material, said ink material containing conductive carbon black or metal particles. (4) The method according to claim 1, wherein the fiber surface comprises an electrically conductive fiber surface + A material. (5) Claim 1, wherein the surface covering material has an electrically conductive precoat layer on the back side of the primary backing sheet, forming thin spike-like columns that protrude from the back side of the backing layer into the conductive precoat layer. the method of. (6) The method according to claim 1, wherein a plurality of ends of the conductive material on the back surface of the backing layer are connected to the conductive layer. (7) A patent for covering a conductive strip to connect the conductive material extending on the back side of the backing layer, forming electrical paths for a plurality of conductive materials to the strip, and grounding when attaching the surface covering material. The method according to claim 6. (8) A method according to claim 1, wherein the backing layer is selected from the group of polymeric materials consisting of vinyl chloride resin, bitumen, atactic polypropylene, ethylene vinyl acetate resin and polyurethane. (9) The method according to claim 1, wherein the conductive surface covering material is fixed to the support using a conductive adhesive. (10) An antistatic surface covering material produced by the method according to claim 1. (11) a relatively thick non-conductive insulating layer having a fibrous surface layer affixed to the face of the primary backing sheet, a conductive precoat layer on the back side of said primary backing sheet, and a back side affixed to said precoach layer; A conductive carpet tile having a backing layer is manufactured by forming a plurality of spaced apart columns of conductive material that protrude from the back side of the backing layer into the conductive precoat layer to form a plurality of spaced apart columns of conductive material that protrude from the back side of the backing layer into the conductive precoat layer. A method of manufacturing a conductive carpet tile comprising forming an electrical path to a carpet tile and forming a carpet tile of improved conductivity. 12. The method of claim 11, wherein a spike-like member having a liquid conductive material is penetrated into the backing layer, and the conductive material forms columns. (13) Coating the surface of one or more spike-like members with a liquid conductive material, and penetrating the coated spike-like member into the back side of the backing layer of the carpet so that the conductive liquid adheres to these penetration holes, and 12. The method of claim 11, wherein the columns are formed and the spike-like members are extracted from the backing layer. (14) moving a plurality of spaced apart spike-like members on the surface of a rotating wheel in an interstitial relationship with respect to the back side of the carpet tile, coating the outer surface of the spike-like members with a conductive liquid ink material; A liquid coating spike is inserted into the underside of the backing layer of the carpet to form a plurality of spaced apart entry holes in the surface of the backing layer extending to the precoat layer and to deposit the liquid into the entry holes. 12. A method as claimed in claim 11, in which further coating and penetration are carried out by depositing and removing uncoated spikes during rotation of said wheel. (15) The method according to claim 11, wherein the column is formed in a straight path over substantially the entire back surface of the carpet tile. 16. The method of claim 11, wherein the columns extend in a straight line over substantially the entire back surface of the carpet and are spaced apart on the order of about 1/2 to 4 inches. (17) The method according to claim 11, wherein the fibrous surface of the carpet contains conductive yarns to form a conductive fibrous surface. (18) The method of claim 11, wherein the fibrous surface of the carpet tile is top-treated with an antistatic additive to form a conductive fibrous surface. (19) The method according to claim 11, wherein a conductive layer is provided on the back side of the carpet tile to connect the ends of the columns on the back side of the backing layer. (20) arranging a plurality of columns substantially in a straight line at a predetermined spacing over the entire back surface or substantially the entire back surface of the carpet tile, and applying a thin strip layer of conductive coating to each edge of the carpet tile along the lines of said columns; 12. The method according to claim 11, wherein the method extends along the . (21) The method according to claim 11, wherein the conductive coating layer comprises a carbon black-containing polymer layer. (22) The method of claim 11, wherein a secondary backing sheet is fixed to the surface of the backing layer. (23) The method of claim 11, wherein the backing layer is selected from the group of polymeric materials consisting of vinyl chloride resin, bitumen, atactic polypropylene, ethylene vinyl acetate resin and polyurethane. (24) supporting the fiber side of the carpet tile on a movable support sheet material and moving the support carpet under a wheel having a plurality of spaced apart spike-like members;
The spike-like member projects outwardly from the outer periphery of the wheel, positions the wheel to rotate about an axis together with the spike-like member during movement thereof, and penetrates the back side of the backing layer into the precoat layer to a predetermined depth; The spike-like members are sequentially coated with a conductive liquid ink material, and as the carpet is moved, the spike-like member penetrates the back side of the backing layer to form a plurality of discontinuous spaced columns, and as the carpet moves, the liquid conductive material is applied. 12. The method of claim 11, wherein the spike-like member is extracted from the backing layer of the carpet tile after being deposited, and the surface of the extracted spike-like member is coated with a conductive material to further penetrate the backing layer during movement of the wheel. (25) A conductive carpet tile manufactured by the method according to claim 11. (26) A conductive carpet tile manufactured by the method according to claim 7. (27) (a) a fibrous facing material; (b) a primary backing sheet securing the fibrous facing material; (c) a relatively thick backing layer comprising an electrically insulating backing material and having a backing surface; d) a plurality of narrow columns of electrically conductive material extending from substantially the back side of the backing layer to substantially the area of the primary backing sheet to form a conductive path from the back side of the fibrous side of the floor covering to the back side of the backing layer; A fibrous floor covering having improved electrical conductivity, wherein the columns are spaced apart and extend substantially perpendicular to the surface of the fibrous surface layer. (28) The material of claim 27 consisting of a carpet tile having a bituminous backing layer. (29) The material of claim 27, wherein the fibrous surface material comprises electrically conductive yarns. 30. The material of claim 27, wherein the primary backing sheet has an electrically conductive precoat layer which acts to fix the fiber surface to the backing sheet, with the columns projecting into the electrically conductive precoat layer. 31. The material of claim 27, wherein the columns are spaced about 1/2 to 4 inches apart over substantially the entire length of the back surface of the floor covering. (32) The material of claim 27 having a secondary backing sheet secured to the back side of the backing layer. (33) The material according to claim 27, wherein a conductive adhesive layer is provided on the back side of the backing layer to form an electrical path connecting the ends of the columns to earth on the back side. 34. The material of claim 27, comprising a conductive cover layer strip to electrically connect a plurality of conductive columns on the back side of the backing layer. (35) The material of claim 27, wherein the backing layer is selected from the group of polymeric materials consisting of vinyl chloride resin, bitumen, atactic polypropylene, ethylene vinyl acetate resin and polyurethane. (36) The material of claim 27 having a bulk electrical resistance of less than about 1 x 10^8 ohms per square. (37) (a) an electrically conductive fibrous facing material; (b) a primary backing sheet securing the fibrous facing material; (c) a conductive precoat layer secured to the primary backing sheet; and (d) a backing surface. (e) extending substantially perpendicular to the plane of the carpet tile surface from the back side of the backing layer through the backing layer to the precoat layer and from the precoat layer to the surface of the backing layer; (f) a secondary backing sheet secured to the back side of the backing layer; (g) overlying the secondary backing sheet and on the back side; 1 per square, comprising a conductive precoat layer connected to a plurality of column ends in the conductive fiber surface and a conductive coating layer forming an electrical path to ground through the column. ×10^
Antistatic carpet tiles with an electrical resistance of 8 ohms or less.