Patent Description:
In critical environments the control of static electrical discharges can be imperative. These environments can include large areas as sensitive electronics manufacturing, aerospace and defense, medical equipment manufacturing, data centers etc. Static charges rising in such areas may degrade delicate components and/or cause product failures or loss of data in other situations. By convention, electrostatically dissipative (ESD) flooring systems are deployed in order to dissipate, or conduct away static charges generated in buildings or manufacturing environments that may otherwise be detrimental to the purposeful process of the area.

A variety of electrostatically dissipative (ESD) floor covering solutions are commercially available. Such solutions include carpet tiles, vinyl or rubber sheet and tile products and liquid applied, two-part thermosetting resin products, for example epoxy resin or polyurethane-based compositions. All such covering solutions commercially available are reliant on permanent adhesive bonding to the sub-floor.

<CIT> discloses a carpet tile system which is conductive and antistatic. Such a carpet tile comprises several layers which are all conductive in order to be able to transfer electric charges from the top to the bottom of the tile. It is provided, that these carpet tiles are fixed to the ground by means of the conductive adhesive.

<CIT> discloses conductive laminate floorings which reverently dissipates static electricity. Such a flooring comprises several layers, in particular one overlay layer and, under this, a decorative layer. At the bottom of the decorative layer some core-layers some of which comprised carbon-pigments a provided. interlocking vinyl tile systems are also commercially available.

<CIT> discloses a magnetically ahead floor covering, which comprises a plurality of magnetic floor tiles, which are held in place on a magnetically receptive floor surface by magnetic interaction between the tiles and the magnetically receptive surface. For this purpose, the floor tiles comprise a planner magnetic layer, which allows the magnetic interaction between the floor tiles and the magnetically receptive surface.

Portability becomes an important feature when considering that these manufacturing areas may regularly need to be re-configured, remodeled, expanded or moved around the facility based upon changing manufacturing processes or equipment. Moving heavy equipment over standard ESD tile flooring or over loose-lay / interlocking systems is frequently problematic. Standard adhesive bonded tiles, or resin flooring, can be damaged or loosened up from the floor under heavy point loads. Repairing these systems is time consuming and expensive, usually requiring specialist contractors to complete the work. Loose-lay / interlocking tiles often shift under these weight loads and then will not re-align correctly, resulting in impaired connectivity of the conductive system and rendering the floor ineffective. Thus, an industry need exists for a moveable ESD flooring product that does not exhibit the inherent functional drawbacks associated with conventional loose-lay interlocking systems.

It is an objective of the present invention to provide a method of creating a flooring system available without the disadvantages mentioned above.

This objective is realized by a method of creating a magnetically adhered, static dissipative floor covering which comprises the steps of:.

The invention is based on the consideration that a magnetic interaction between the tiles and the magnetically receptive surface guarantees on one side a good and reliable fixation to the underground and allows on the other side an easy removal of the tiles from the floor surface as only magnetic forces must be counteracted because no firmly bonded or interlocking connection exists.

In one embodiment of the present invention the floor surface is intrinsically magnetically receptive. Such an intrinsically magnetically receptive floor surface may be given for example in the case of steel raised access floors. Such floors comprise elements made of ferromagnetic steel which allows a direct interaction with magnetic floor tiles placed thereon.

In another embodiment of the invention the floor surface is provided with a magnetically receptive underlayment. Concretely such a magnetically receptive underlayment may be formed by the application of a liquid coating composition comprising a polymeric binder and magnetic or magnetisable particles. Such coatings are well-known and commercially available.

For example, the polymeric binder of the coating composition may comprise an air-drying resin, in particular an acrylic, alkyd, epoxy-ester or vinyl resin.

Alternatively, the polymeric binder may comprise a two-part, thermosetting resin in particular an epoxy, polyurethane or polyurea resin. Preferably, the two-part, thermosetting resin comprises at least one aliphatic poly-isocyanate component and at least one poly-aspartic acid ester component.

The magnetic and/or magnetisable particles may be selected from paramagnetic, superparamagnetic and/or ferromagnetic substances, in particular selected from the group comprising iron, iron oxides, preferably mixed iron oxides with other metal oxides from the transition elements group like iron-nickel oxides, ferro-silicones or combinations thereof. Such magnetic or magnetisable particles allow an interaction with tiles placed on the magnetically receptive surface.

According to the invention, the floor tiles are of composite construction comprising.

In other words the floor tiles comprise three basic elements, namely a resilient, electrostatically dissipative vinyl wearing layer, which forms the top surface being visible and being in contact with the environment. At the bottom of this surface an electrically conductive ground plane is provided which allows static charges draining down from the surface to be drained off in a lateral direction. On the underside of the conductive ground plane a planar magnetic layer is arranged which allows the magnetic interaction between the tiles and the magnetically receptive surface. The magnetic interaction between the floor coating and the tiles keeps the tiles fixed at their position. At the same time however, the tiles can easily be exchanged, for example if the wear surface is worn out or if the floor color shall simply be changed.

In a preferred embodiment of the invention the static dissipative vinyl wearing layer has a resistivity from <NUM><NUM> ohm. cm to <NUM><NUM> ohm. cm according to the ASTM D257 standard. The ASTM D257 discloses a standard test for the measuring of the resistivity or the conductivity of insulating materials provided by the American Society for Testing and Materials. Furthermore the static dissipative vinyl wearing layer may have a static decay time (<NUM>,<NUM> volts - <NUM> volts) of less than <NUM> seconds according to the Federal TM 101B, Method <NUM> standard.

Alternatively the static dissipative vinyl wearing layer may have a resistivity from <NUM>×<NUM><NUM> ohm. cm to <NUM>×<NUM><NUM> ohm. cm according to the ASTM D257 standard. In such a case the static dissipative vinyl wearing layer preferably has a static decay time (<NUM>,<NUM> volts - <NUM> volts) of less than <NUM> seconds according to the Federal TM 101B, Method <NUM> standard. Such vinyl tiles are commercially available, for example from Desco Industries Inc. sold under the name <NUM> Statguard ESD. The tiles available have preferably a thickness from <NUM>, in particular from <NUM>, to <NUM>, in particular to <NUM>. A thickness of tiles in such a range corresponds to standard thicknesses of commercially available tiles.

The conductive ground plane may comprise a non-woven synthetic fabric with a nickel-copper coating and a conductive adhesive backing. A nickel-copper coating on a non-woven synthetic fabric allows an efficient draining off of static charges. The nickel-copper coated fabric preferably has a thickness from <NUM>, in particular from <NUM>, to <NUM>, in particular to <NUM>. Such a thickness has been proven to be advantageous to achieve an efficient transmission of electrical charges.

The conductive ground plane can be bonded to the static dissipative vinyl wear layer by means of the conductive adhesive backing. Such a fabric which is pre-coated with a conductive adhesive facilitates the bonding of the conductive ground plane to the underside of the electrostatically dissipative vinyl wearing surface. Preferably the conductive adhesive is a pressure sensitive adhesive, which means that the bonding can be realized only by application of pressure forces.

In another embodiment of the invention the conductive ground plane comprises a conductive adhesive or coating composition containing graphene powder. Preferably the conductive adhesive or coating composition comprises a two-part, thermosetting polyurethane composition blended with graphene powder. The polyurethane composition preferably has a thickness from <NUM>, particularly preferred from <NUM>, to <NUM>, particularly preferred to <NUM>. The conductivity is realized by blending graphene powder which is in particular added from <NUM>%, preferably from <NUM>%, to <NUM>%, preferably to <NUM>% by weight.

Preferably the conductive ground plane has a sheet resistivity from <NUM> ohm/sq. to <NUM> ohm/sq. according to the ASTM F390 standard. The ASTM F390 is a standard test method for the sheet resistivity of thin metallic films with a collinear four-probe array provided by the American Society for Testing and Materials. Preferably the resistivity is in the range from <NUM> ohm/sq. to <NUM> ohm/sq. It has to be noted that the unit ohm/sq. is generally equivalent to the unit ohm. The addition /sq. indicates that not a classic volume resistivity is meant, but a sheet resistivity. A sheet resistivity in the range given allows an efficient draining off of a static charge.

The planar magnetic layer may comprise a flexible, polymeric magnetic sheet which is bonded to the conductive ground plane by means of an adhesive. Such a planar magnetic layer formed as a flexible, polymeric magnetic sheet being bonded to the underside of the conductive ground plane allows the magnetic interaction between the magnetic floor tiles and the magnetically receptive floor surface. A connection between the planar magnetic layer and the conductive ground plane by means of an adhesive presents an easy and simple way to manufacture static dissipative, magnetic floor tiles.

Preferably the adhesive is a pressure sensitive adhesive. Such a pressure sensitive adhesive allows a simple application of the magnetic layer to the conductive ground plane as only pressure forces have to be applied to achieve a bonding.

In a further elaboration of the invention the magnetic layer has a magnetic remanence from <NUM> Tesla, in particular from <NUM> Tesla, to <NUM> Tesla, in particular to <NUM> Tesla. Tesla is the standard unit for the magnetic flux density as it was previously Gauss which means that the magnetic layer may have a corresponding magnetic remanence from <NUM> Gauss, in particular from <NUM> Gauss, to <NUM> Gauss, in particular to <NUM> Gauss. The magnetic layer may have a coercivity from <NUM> A/m, in particular from <NUM> A/m, to <NUM> A/m, in particular to <NUM> A/m. These values correspond approximately to a magnetic coercivity from <NUM> Oersted, in particular from <NUM> Oersted, to <NUM> Oersted, in particular to <NUM> Oersted. Preferably, the magnetic layer has a thickness from <NUM>, in particular preferred from <NUM>, to <NUM>, in particular preferred to <NUM>. Such a thickness in combination with the magnetic properties given by the values of the magnetic remanence and the coercivity allow on one side a magnetic interaction between the floor coating and the tiles which keeps the tiles fixed at their position, and allow on the other side an easy removal of the tiles when they have to be changed.

According to a further aspect of the invention the magnetically adhered, static dissipative floor covering system has a resistivity from <NUM><NUM> ohm. cm to <NUM><NUM> ohm. cm according to the ASTM D257 standard.

Furthermore, the magnetically adhered, static dissipative floor covering system may have a static decay time (<NUM>,<NUM> volts - <NUM> volts) of less than <NUM> seconds according to the Federal TM 101B, Method <NUM> standard.

Alternatively the magnetically adhered, static dissipative floor covering system can have a resistivity from <NUM> × <NUM><NUM> ohm. cm to <NUM> × <NUM><NUM> ohm. cm according to the ASTM D257 standard and/or a static decay time (<NUM>,<NUM> volts - <NUM> volts) of less than <NUM> seconds according to the Federal TM 101B, Method <NUM> standard.

Such values for the resistivity and the static decay time allow an efficient draining off of static charges so that the risk of destruction or damages of delicate components is eliminated or at least reduced.

Further characteristics and advantages of the present invention become clear by the following description of magnetically adhered, static dissipative floor coverings with reference to the enclosed drawing.

<FIG> and <FIG> show a magnetically adhered, static dissipative floor covering <NUM> which was created by a method according to the present invention and is applied to a substrate floor <NUM> which has a magnetically receptive surface <NUM>.

The floor covering <NUM> is composed of static dissipative, magnetic floor tiles <NUM> which can be placed on the magnetically receptive surface <NUM>. Concretely the floor tiles <NUM> are of composite construction comprising a static dissipative vinyl wearing layer <NUM>, an integral, conductive ground plane <NUM> and an integral, planar magnetic layer <NUM>.

The conductive ground plane <NUM> is formed by a non-woven synthetic fabric <NUM> with a nickel-copper coating and a conductive adhesive backing. Presently a conductive adhesive <NUM> is applied onto the copper-nickel coated fabric <NUM> which allows an efficient bonding to the static dissipative vinyl wearing layer <NUM> on top. Alternatively, the conductive ground plane <NUM> could also be formed by a conductive adhesive composition comprising in particular a two-part, thermosetting polyurethane composition blended with graphene powder.

On the underside of the nickel-copper-fabric <NUM> the magnetic layer <NUM> is bonded by means of an adhesive layer <NUM>. The magnetic layer <NUM> ensures that the tiles deposited on the substrate floor, respectively the magnetically receptive surface <NUM> are fixed at their position due to the magnetic interaction. At the same time the tiles <NUM> can easily be exchanged.

In <FIG> it is visible how a static charge applied by a person <NUM> walking on the floor covering <NUM> is drained off. As the arrows show the static charge is transmitted via the vinyl wearing layer <NUM> and the adhesive <NUM> on top of the nickel-copper-fabric <NUM> to the latter, drained to the sides before a connection of the conductive ground plane <NUM> to the substrate floor <NUM> ensures that the charge is drained to the building.

To create such a magnetically adhered, static dissipative floor covering <NUM>, at first a magnetically receptive floor surface <NUM> has to be provided. After that a floor covering <NUM> has to be provided which comprises a plurality of static dissipative, magnetic floor tiles <NUM>, wherein the tiles <NUM> are held in place by magnetic interaction between the tiles <NUM> and the magnetically receptive surface <NUM>.

<FIG> shows a test arrangement for a floor covering according to the present invention to allow measurements of surface resistivity in a two-dimensional array, as per the ASTM D257 standard. The resistivity is measured on tiles 4b, 4c, 4d with respect to tile 4a by means of a test electrode <NUM> in respect to a reference electrode <NUM>.

The following examples are given for illustrative purposes only and are not meant to be a limitation of the scope of protection defined by the claims.

Four Statguard® <NUM> ESD Vinyl Floor Tiles (<NUM> × <NUM> × <NUM>) commercially sold by Desco Industries Inc. were coated on the underside with a conductive adhesive composition formed by blending <NUM> parts by weight of GS030P graphene powder available from Graphene Star Ltd. with <NUM> parts by weight of Magna Tak polyurethane adhesive from Thortex America Inc. The conductive adhesive composition was applied using a serrated edge comb and then lightly rolled with a short nap roller to provide a thickness of approximately <NUM> microns. After allowing to gel for <NUM> hours, KM <NUM> magnetic sheet received from Kingfine Magnetics Ltd. was applied to the conductive layer. The composite tiles were allowed to cure overnight and then affixed to marine ply boards which had previously been treated with MS <NUM> Magnetised Floor System from IOBAC Ltd. The tiles were butted against each other in a two-dimensional array and surface resistivity measurements, as per the ASTM D257 standard, undertaken on tiles 4b, 4c, 4d in turn with respect to tile 4a, as per <FIG> below.

Four Statguard® <NUM> ESD Vinyl Floor Tiles (<NUM> × <NUM> × <NUM>) were coated on the underside with a conductive adhesive composition formed by blending <NUM> parts by weight of GS030P graphene powder commercially sold by Graphene Star Ltd. with <NUM> parts by weight of Magna Tak polyurethane adhesive. The conductive adhesive composition was applied using a serrated edge comb and then lightly rolled with a short nap roller to provide a thickness of approximately <NUM> microns. After allowing to gel for <NUM> hours, KM <NUM> magnetic sheet from Kingfine Magnetics Ltd. was applied to the conductive layer. The composite tiles were allowed to cure overnight and affixed to marine ply boards which had previously been treated with MS <NUM> Magnetised Floor System. The tiles were butted against each other in a two-dimensional array and surface resistivity measurements, as per the ASTM D257 standard, undertaken on tiles 4b, 4c, 4d in turn with respect to tile 4a, as per example <NUM>.

EMF RF Shielding Nickel Copper Fabric commercially sold by Faraday Defense was applied to the underside of four Statguard® <NUM> ESD Vinyl Floor Tiles (<NUM> × <NUM> × <NUM>). KMG <NUM> self-adhesive magnetic sheet was then affixed to the Nickel Copper fabric. The composite tiles were affixed to marine ply boards which had previously been treated with MS <NUM> Magnetised Floor System. The tiles were butted against each other in a two-dimensional array and surface resistivity measurements, as per the ASTM D257 standard, undertaken on tiles 4b, 4c, 4d in turn with respect to tile 4a, as per example <NUM>.

EMF RF Shielding Nickel Copper Fabric was applied to the underside of four Statguard® <NUM> ESD Vinyl Floor Tiles (<NUM> × <NUM> × <NUM>) commercially available from Desco Industries Ltd. KMG <NUM> self-adhesive magnetic sheet was then affixed to the Nickel Copper fabric. The composite tiles were affixed to marine ply boards which had previously been treated with MS <NUM> Magnetised Floor System. The tiles were butted against each other in a two-dimensional array and surface resistivity measurements, as per the ASTM D257 standard, undertaken on tiles 4b, 4c, 4d in turn with respect to tile 4a, as per example <NUM>.

EMF RF Shielding Nickel Copper Fabric was applied to the underside of four Statguard® <NUM> ESD Vinyl Floor Tiles (<NUM> × <NUM> × <NUM>). KMG <NUM> self-adhesive magnetic sheet was then affixed to the Nickel Copper fabric. The composite tiles were affixed to marine ply boards which had previously been treated with MS <NUM> Magnetised Floor System. The tiles were butted against each other in a two-dimensional array and surface resistivity measurements, as per the ASTM D257 standard, undertaken on tiles 4b, 4c, 4d in turn with respect to tile 4a, as per example <NUM>.

The individual resistivity measurements recorded for Examples <NUM> - <NUM>, as per the ASTM D257 standard, are detailed in Table <NUM> below.

Claim 1:
A method of creating a magnetically adhered, static dissipative floor covering (<NUM>), the method comprising the steps of:
providing a magnetically receptive floor surface (<NUM>);
providing a floor covering comprising a plurality of static dissipative, magnetic floor tiles (<NUM>), wherein the tiles (<NUM>) are held in place by magnetic interaction between the tiles (<NUM>) and the magnetically receptive surface (<NUM>),
wherein the floor tiles (<NUM>) are of composite construction comprising
- a static dissipative vinyl wearing layer (<NUM>), which forms a surface being visible and being in contact with the environment,
- an integral, conductive ground plane (<NUM>), which is provided at the bottom of the surface and allows static charges draining down from the surface to be drained off in a lateral direction, and
- an integral, planar magnetic layer (<NUM>), which is arranged on the underside of the conductive ground plane (<NUM>) and allows the magnetic interaction between the floor tiles (<NUM>) and the magnetically receptive surface (<NUM>).