WO1990005632A1

WO1990005632A1 - Controlled electrical surface resistance epoxy-based flooring and coating compositions

Info

Publication number: WO1990005632A1
Application number: PCT/US1989/004862
Authority: WO
Inventors: Frederick A. Pfaff; Perry C. Springsted; Timothy J. Stover
Original assignee: Stonhard, Inc
Priority date: 1988-11-01
Filing date: 1989-10-30
Publication date: 1990-05-31
Also published as: ES2017196A6; AU4629589A

Abstract

A non-black or colorable, anti-static, epoxy-based flooring composition exhibiting a low electrical surface resistance and a seamless surface after curing, including a hardener component, an epoxy resin component, and a carbon fiber component comprising milled unsized carbon fiber and chopped carbon fiber, or chopped carbon fiber.

Description

CONTROLLED ELECTRICAL SURFACE RESISTANCE EPOXY-BASED FLOORING AND COATING COMPOSITIONS

Field of the Invention

As used herein "flooring" denotes a composition foi covering a substantially horizontal substrate which (1) when applied to the substrate has a thickness of at least about one-tenth of an inch, (2) in nearly all cases includes an aggregate component of relatively large particle size (about 0.001 to about 0.10 inch diameter) which may constitute a relatively high percent by weight of the composition, (3) when in liquid-rich form has a viscosity not greater than about 5000 centipoise and when in aggregate-rich form is so thick that it is no longer free-flowing liquid, (4) is preferably spread on the substrate using a trowel, a rake, a screed box or like mechanical device and (5) has a relatively high, mechanical durability, with mechanical durability increasing with the degree to which the flooring is rich in the aggregate component to a point at which the composition can withstand heavy duty industrial use, including heavy vehicular traffic.

As used herein, "coating" denotes a composition foi covering a substantially horizontal substrate which (1) when applied to the substrate has a maximum thickness oi about twenty thousandths (0.020) of an inch, (2) may—but does not necessarily—include an aggregate component which, if present, has a relatively small particle size and constitutes only a relatively low percent by weight of the composition, (3) has viscosity no greater than about 2000 centipoise (at a shear rate of at least 10C sec"¹), (4) is preferably applied to the substrate usinc a roller, squeegee, brush or by spraying and (5) has moderate mechanical durability, withstanding light to moderate traffic conditions, including pedestrian and indoor vehicular traffic.

As used herein, "high-build coating" denotes a coating composition for covering a substantially horizontal substrate which (1) when applied to the substrate has a maximum thickness of about eighty thousandths (0.080) of an inch, (2) may—but does not necessarily—include an aggregate component which, if present, may constitute from a relatively low percent by weight to a relatively high percent by weight of the composition, (3) has viscosity no greater than about 4000 centipoise (at a shear rate of at least 100 sec"¹), (4) is preferably applied to the substrate using a notched squeegee, a notched trowel or some similar mechanical device and (5) has moderate mechanical durability, withstanding light to moderate traffic conditions, including pedestrian and indoor vehicular traffic.

Coatings and floorings, especially coatings, are to be distinguished from paints. Paint is typically applied ass a layer from about one thousandth to about two thousandths (0.001-0.002) of an inch thick, to provide.* pleasing appearance for the surface. Coatings and floorings are formulated to provide durability and substrate protection, as well as other desired properties.

Coatings and high build coatings are retrofitable over floors.

Description of the Prior Art

Many known coatings purporting to have controllable electrical surface resistance contain carbon black and/or metal powders or flakes. These known coatings, seeking to provide good (i.e. low) electrical surface resistance, have generally been formulated to be as electrically conductive as possible. These coatings are sprayed on electronic components to control electro-magnetic interference and undesired current arcing and discharge, which may otherwise occur during component operation. These known coatings generally contain volatile solvents or water. Upon evaporation of the volatile solvent(s) or the water, these known coatings contract and compact, resulting in a change in their electrical surface resistance.

Lander, U.S. patent 4,795,592, relates to filled polymer compositions and discloses electrically conductive filled polymer compositions having carbon black as a major constituent component. Lander provides a composition including a particulate filler of electrically conductive material dispersed in an insulating polymeric base in which at least 0.5% by weight of the conductive filler is char carbon made by carbonizing non-woody plant material (column 2, lines 40 through 44 and lines 53 and 54). Lander utilizes such char carbon in polymeric materials to produce polymeric materials having electrical surface resistance values of 100,000 ohms and higher. Use of carbon black, as taught by Lander, results in a black, non-colorable polymeric product. Additionally, the examples set forth in Lander all utilize volatile solvents, giving rise to the disadvantages noted above which are inherent with use of such volatile solvents.

Among the known coatings is a solvent-based epoxy product containing two nickel powders and a copper-nickel powder. This solvent-based epoxy product is noxious, expensive and upon solvent evaporation exhibits uncontrolled and unstable electrical properties. To applicants' knowledge there has been no disclosure of epoxy-based coatings having predetermined desired electrical surface resistance, which are also colorable and which provide a smooth coating surface for coating thicknesses down to 0.005 inches or even less.

Some known epoxy-based floorings have used carbon fiber in attempts to impart electrical conductivity to inherently non-electrically conductive epoxy-based flooring. It is known to mix both (i) "sized" coarsely milled carbon fiber and (ii) "sized" one-quarter inch length chopped carbon fiber, together with epoxy resin and hardener components, and to blend these materials with an aggregate at a job site to produce a controlled electrical surface resistance flooring, having electrical surface resistance from about one to about fifty megohms. ("Sized" denotes that an organic coating is applied to the fiber during fiber manufacture.) Workers applying the flooring combine the milled sized carbon fiber and chopped sized carbon fiber, as a dry mix, with the resin and the hardener at the job site. While this product, sold heretofore in the United States under the trademark Stonlux AT by Stonhard, Inc., the assignee of this patent application, has been generally satisfactory in producing floorings having resistance in the one to fifty megohm range, the one-quarter inch carbon fibers present some proble —they tend to cling together and to forai unacceptable lumps as the flooring product is applied. These lumps sometimes result in unacceptable variations in electrical surface resistance over the flooring surface. Additionally, this product has not been successful in repeatedly and consistently providing an electrical surface resistance lower than one megohm. Epoxy resin-based flooring and coating compositions, while having good durability and wear resistance, havii high intrinsic electrical surface resistance. This high electrical surface resistance can lead to build-up of static charge on the flooring or coating and on people and equipment on such flooring or coating—the high electrical surface resistance does not allow charge to dissipate or move away from or along the surface of the flooring or coating.

While Lander, U.S. patent 4,795,592, noted above, discloses using chopped carbon fiber in a coating composition, he only uses chopped carbon fiber together with char carbon—char carbon is always present in Lander's compositions. Lander's compositions preferably contain char carbon in an amount between 5% and 80% of the conductive filler by weight, commonly between 20% and 50% by weight.

Lander speculates as to possible addition of fillerfs for "colouring" his compositions. However, known prior art coloring of carbon black-containing compositions typically results in compositions which are tho uncolorable, black color of carbon black.

Lander uses a high percentage of carbon black and other carbon constituents relative to the polymeric base material thereby insuring an essentially non-colorable., black product.

Background of the Invention

This invention recognizes and fills the need for colorable (i.e. non-black) controlled electrical surface resistance, chemically resistant epoxy-based floorings and coatings for application to substantially horizontal substrates, to protect the substrate and to provide desired surface properties, including the presentation of a smooth exposed surface. In many industrial environments, especially those in which microprocessor and computer-controlled equipment operates, there is a need to dissipate static charges which build up on such equipment. Because microprocessors and computer circuitry operate at very low voltages and currents, even a small build-up of static can adversely affect their operation. Thus, there is a need for electrically conductive floorings and floor coatings in such industrial environments.

However, if a floor in an industrial environment is too electrically conductive (the critical electrical surface resistance is generally recognized to be about 25,000 ohms) , there is an inherent electrical shock hazard for workers on the work floor. Below the 25,000 ohm value, electrical surface resistance is sufficiently -low that a worker standing on such a floor and accidentally touching a "live" electrical wire becomes a series-connected element in a conductive path leading directly to ground potential. Hence, a danger of electrocution exists in such facilities.

As a result of these two conflicting factors, there is a need for controlled electrical surface resistance floorings and coatings, which have electrical surface resistance high enough to effectively minimize the risk of electrocution to workers yet low enough to reduce the instantaneous discharge current associated with static build-up in microprocessors and other electronic circuits.

The difference in thickness and the presence (o:c absence) of aggregate of different size, as between coatings and floorings presents two different problems in trying to develop coatings and floorings having desired properties, especially (1) electrical surface resistance of a preselected, repeatable .value or being repeatedly within a preselected range, (2) colorability and (3) a smooth, aesthetically pleasing surface which may be essentially devoid of texture. For a coating, the maximum size of particulate materials (used to influence or adjust electrical surface resistance) is limited by coating thickness if the coating surface is to be smooth. For a flooring, presence of relatively large aggregate, which may be necessary to obtain the requisite wear- resistance, may dictate minimum size and, perhaps, the shape of particulate material used to influence or adjust electrical surface resistance. Volume (within the flooring composition) occupied by the aggregate and/or aggregate internal electrical resistance may create an effective upper bound on the electrical conductivity of the flooring. Hence, an approach that works to produce a coating having the desired, or at least an acceptable, electrical surface resistance might not work with floorings and may produce a flooring having a totally unacceptable electrical surface resistance.

Colorability is an important characteristic for coatings and floorings. Many industrial applications require a non-black surface. Non-black, colored surfaces provide improved light reflection and visibility in work environments. Non-black, colored surfaces also facilitate detection and removal of dirt and spills occurring in work environments. Additionally, non- black, colored surfaces greatly improve the ambience and aesthetic appearance of indoor environments as compared to very dark or black surfaces. Improved ambience and aesthetic appearance often result in improved worker morale and productivity.

Heretofore, it has not been known to provide controlled electrical surface resistance epoxy-based compositions, having electrical surface resistance in the range frcm about 25,000 to about 100,000,000 ohms, which can be colored to a wide range of hues, including pastel shades. let alone such compositions with smooth exterior surfaces after cure.

. Carbon fiber is expensive, costing upward of $16.00 a pound. One important advantage provided by the instant invention is the provision of a controlled electrical surface resistance coatings and floorings, utilizing small, amounts of chopped carbon fiber to control electrical surface resistance.

Lexicography

As used hereinbelow, the following terms shall have the meaning stated:

"Colorable" refers to the property of a composition whereby the color of the cured composition can be altered by the addition, prior to curing, of coloring agents such as pigments to produce colors much lighter than carbon black, with such colors (in some cases, depending on the composition) running all the way through pastels to white.

"Carbon fiber" includes graphite fibers as well at. other types of carbon fiber.

"Non-black" means a color other than the color o carbon black.

All percentages are given in weight percent.

Summary of the Invention

The invention provides anti-static, colorable, spreadable, epoxy-based flooring compositions and coating compositions exhibiting a controlled and predictable surface electrical resistance after curing and presenting a smooth surface upon cure. The anti-static flooring compositions and the anti-static coating compositions each contain three basic components: a hardener component, an epoxy resin component, and a carbon fiber component. The carbon fiber component for the flooring compositions preferably comprises both milled carbon fiber and chopped carbon fiber.

The carbon fiber component for the coating compositions may be milled carbon fiber, chopped carbon fiber or both milled and chopped carbon fiber; in the coating compositions, the carbon fiber component preferably comprises both milled and chopped carbon fiber.

The chopped carbon fiber may be all the same length or may be of two or more different lengths.

In another aspect, the invention provides colorable coating compositions providing predetermined electrical surface resistance, a desired non-black color and a smooth cured exterior surface at coating thicknesses as low as 5 mils. The coating compositions, in their simplest form, contain epoxy resin with a suitable hardener and a carbon fiber component. The carbon fiber length may preferably range from 3/8" down to finely milled carbon fiber. More preferably, the fiber ranges from 5/16" to finely milled carbon fiber and most preferably from about 1/4" to finely milled carbon fiber. The coating composition may also contain pigment to yield a desired coating color. The coating thickness is preferably 5 - 40 mils and more preferably 5 - 10 mils per application.

In another aspect, this invention provides a spreadable epoxy-based composition which exhibits a preselected substantially uniform electrical surface resistance, contains hardener, resin, milled carbon fiber and aggregate components, and is manufactured according to the steps of (a) introducing the milled carbon fiber into the epoxy resin sufficiently prior to combining the milled carbon fiber-epoxy resin mixture with the hardener component that the milled carbon fiber is thoroughly wetted with the epoxy resin when the combining step is performed, (b) combining the epoxy resin-milled carbon fiber mixture with the hardener and (c) adding the aggregate to the epoxy resin-milled carbon-hardener combination.

In another, optional, aspect of the invention, use of milled unsized carbon fiber as an additive to the resin at the factory results in improved and readily controllable anti-static properties in the floorings and coatings and eliminates the need to add milled carbon fiber at the job site. The new floorings and coatings have superior chemical resistance compared to aluminum containing resins and superior colorability compared to carbon black-containing resins.

The invention, whether embodied in a flooring composition or a coating composition, can provide a pastel or even a white controlled electrical resistance surface. Among the colors which have been attained using compositions according to the invention are camel, silver gray, sky blue, sandstone, mauve and sea foam. These colors have been attained while providing very smooth, non-textured surfaces in the flooring and coating compositions according to the invention. This colorability, the range of attainable colors and the resulting smooth exterior surface after cure all contribute to the cleanability of the floors and coated surfaces having the flooring and coating compositions of the invention applied thereto. This colorability allows the floor or coating to be color-coordinated with the remainder of the room or work area. The smooth exterior surface combined with the range of colors in which the flooring and coating materials of the invention can be made results in surfaces which are very easy to clean and on which dust, dirt, soil, debris and the like may be easily seen, thereby assisting in maintenance of "clean room" conditions, which may be necessary. The flooring and coating compositions of the invention preferably also comprise a filler component of fine particle size filler material and, optionally, a coarse particulate material such as sand.

In another aspect, the anti-static epoxy-based flooring and coating compositions may also include known additives such as rheological modifiers, anti-settling agents, air release additives, pigment dispersing agents and diluents.

The invention provides a flooring or coating composition having a separate resin component and a separate hardener component wherein a carbon fiber component comprising milled carbon fiber is combined and thoroughly wetted with the resin component before blending with the hardener component. This aspect of the invention eliminates the need to add milled carbon fiber at the job site in order to obtain controlled and predictable anti-static properties over a broader range of electrical surface resistance values than known heretofore. The known additives discussed above are also usable in conjunction with this aspect of the invention.

Because coatings are retrofitable over existing floors, coatings according to this invention in many situations provide low cost ways of achieving surfaces of desired electrical resistivity and color on all or part of existing floors without the necessity of removing or extensively modifying the existing floors.

Description of the Drawing

Figure 1 is a plot demonstrating the relationship between electrical surface resistance and amount cf chopped carbon fiber in a coating composition according to the invention. Detailed Description of the Invention

The anti-static epoxy-based flooring and coating compositions of the invention comprise three essential components: a hardener component, an epoxy resin component and a carbon fiber component. For the flooring compositions, the carbon fiber component comprises milled carbon fiber and chopped carbon fiber or chopped carbon fiber alone. For the coating compositions, the carbon fiber component comprises milled carbon fiber or chopped carbon fiber or both milled carbon fiber and chopped carbon fiber.

The hardener component preferably is about five (5) to about fifty percent (50%) of the total flooring or coating composition. The hardener component preferably comprises a modified aliphatic amine, but other conventional hardeners for epoxy resins may be used. Preferred modified aliphatic amines are sold as Ancamine 2074 and Ancamine TC-925 by Pacific Anchor Chemical Company in Cumberland, Rhode Island.

The epoxy resin component preferably forms from about thirty percent (30) to about eighty-five percent (85%) of the total flooring or coating composition. Preferred epoxy resins are bisphenol formaldehyde epoxy and bisphenol acetone epoxy. These preferred epoxies are sold by Shell Chemical Company and others.

The carbon fiber component for the flooring comprises milled carbon fiber and chopped carbon fiber or only chopped carbon fiber. The carbon fiber component for the coating may be milled and/or chopped carbon fiber. Preferably, the amount of carbon fiber component is about 0.25 percent to about five percent (5%) of the total flooring or coating composition. The milled carbon fiber has a length ranging from about 0.02 millimeters to about 2.0 millimeters-; The milled carbon fiber is preferably finely or triply milled unsized carbon fiber. This type of fiber is available under the name Fortafil Finely Milled Carbon Fiber and is sold by Akzo Chemie. The chopped carbon fiber has a length preferably about 1/8 inch to about 1/4 inch. Akzo Chemie also markets this chopped carbon fiber under the name Fortafil.

The type and amount of carbon fiber and the length(s) of the fiber used affect the electrical surface resistance of the resulting flooring or coating. . In general, surface resistance decreases with increasing carbon fiber content. Also, generally, the greater the proportion of lengthy fibers, the greater the effect in lowering electrical surface resistance per unit weight of fibers added. The flooring and coating compositions of the invention preferably have electrical surface resistance of about 25,000 ohms to about 100 megohms as measured by the method described in NFPA 99 and the corresponding ASTM standard.

In two preferred flooring composition embodiments, the electrical surface resistance is controlled by varying the relative proportions of 1/8 inch and 1/4 inch chopped carbon fiber in the composition. When the chopped carbon fiber comprises sixty percent (60%) 1/8 inch fiber and forty percent (40%) 1/4 inch length fiber, the electrical surface resistance is between about twenty-five thousand (25,000) ohms and one million ohms (1,000,000) when measured using the NFPA 99 test method. When the chopped carbon fiber comprises ninety percent (90%) 1/8 inch length fiber and ten percent (10%) 1/4 inch length fiber, the electrical surface resistance is between about one million (1,000,000) ohms and one hundred million (100,000,000) ohms when measured using the NFPA 99 test method.

When milled carbon fiber is used, it is preferably incorporated into the flooring composition in fixed amounts at the factory. This eliminates the necessity of adding milled carbon fiber to the flooring composition mixture at the job site and also broadens the achievable range of electrical surface resistance for such floorings.

Another specification used in the electrical industry calls for surface resistance of 1 megohm to 100 megohms. The testing method for this specification is NFPA 99, noted above. The carbon fiber content of the flooring or ^"coating composition can be varied to meet these or other specifications for electrical surface resistance.

As noted above, additional materials conventional to epoxy resin flooring or coating systems may be used in the flooring and coating compositions of the invention. These materials include pigments, fillers, air release agents, rheological modifiers, pigment dispersing agents and diluents.

Pigment preferably forms about 2.5% to about twenty- five percent (25%) of the total flooring or coating composition. Examples of pigments typically used include titanium dioxide, iron oxides, zinc oxide, phthalo green, carbon black, phthalo blue and lead chromate; preferably, titanium dioxide is the principal pigment. Any combination of compatible, non-reactive pigments may be used to achieve the color desired in the cured flooring or coating.

Filler is an optional component, which may be added to reduce the amount of resin required in the flooring or coating and/or to inexpensively modify the composition flow characteristics. The filler preferably forms zero (0) i:o about fifty percent (50%) of the total flooring or coating composition. Preferred fillers include fine silica such as silica flour, marketed by U.S. Silica under the tradename Sil-Co-Sil 125, and silica sand. Other compatible fillers may also be used.

Air release agents facilitate escape of gas from the flooring or coating during and prior to cure. Air release agents preferably form zero (0) to about five percent (5%) of the total flooring or coating composition. Preferred air release agents are polyether modified dialkylpolysiloxane copolymer solutions sold by Byk Chemie under the names Byk A500 and Byk 320.

Rheological modifiers retard settling and impart certain flow characteristics to the flooring or coating. Rheological modifiers preferably form zero (0) to about ten percent (10%) of the total flooring or coating composition. Preferred rheological modifiers include anti-settling agents and rheological clays. Two preferred rheological clays are sold by NL Chemicals under the trademarks Bentone 27 and Bentone SD2.

Pigment dispersing agents facilitate coloration of the flooring or coating. These pigment dispersants preferably form zero (0) to about 2.5% of the total flooring or coating composition. A preferred pigment dispersant is a polyamide solution such as a solution of polyamine amides of unsaturated polycarboxylic acids sold by Byk Chemie under the name Disperbyk 130.

Diluents preferably form zero (0) to about twenty-five percent (25%) of the total flooring or coating composition. Preferred diluents include mineral oil, such as Benol, benzyl alcohol and monoepoxide such as alkylglycidyl ether, Epodil 748 sold by Pacific Anchor Chemical Company.

The example and resulting coating and flooring compositions detailed below are embodiments of the invention, however, they should not be construed as limiting the invention.

Example 1

A number of batches of compositions according to the invention corresponding to coating composition 2 were prepared. Specifically, a first portion of coating composition 2 was prepared including the epoxy resin ingredient, the monoepoxide diluent, the silica filler, the pigment, the pigment dispersant, anti-settling additive, rheological additive, mineral oil, air release additives and finely milled carbon fiber, all as shown under the table entitled "Coating Composition 2" below. Additionally, an amine hardener was used as a second portion. These two portions were mixed by hand for at least 90 seconds before being applied onto a floor and later rolled.

Prior to mixing the two portions, preselected amounts of chopped carbon fiber were added to identical batches of the first portion. Different amounts of chopped carbon fiber were added to the various batches of the first portion. The ratio of 1/4 inch chopped carbon fiber to 1/8 inch chopped carbon fiber was kept constant for each batch at the ratio illustrated in the "Coating Composition 2" table. Specifically, that ratio was about 9 parts 1/8 chopped carbon fiber to one part 1/4 inch chopped carbon fiber. The selected amounts of combined 1/8 inch and 1/4 inch chopped carbon fiber had a maximum of 32 grams and a minimum of 4; the selected amounts were separated from each other in four (4) gram increments. After the combination of chopped carbon with the batches of first portion, the resultant mixture was combined with second portion (i.e. hardener). Each batch contained identical proportions of first and second portions (the combination of said first and second portions totaling 22 lbs. for each batch.) Thus, eight batches of test composition differing only in chopped carbon fiber content were made.

The resulting eight batches were then applied in 15 square foot test patches on a concrete floor which had been coated with primer. The electrical surface resistance values for the respective patches were then measured according to NFPA 99. The resulting resistance values as a function of the amount of chopped carbon fiber in each patch are shown on Figure 1, depicting the natural logarithm of the measured electrical surface resistance in megohms versus the amount of chopped carbon fiber in each batch where the amount of chopped carbon fiber is on a linear scale. Hence, the relationship between electrical surface resistance and the amount of chopped carbon fiber in a coating composition according to the invention is logarithmic, not linear.

Flooring Composition 1 Ingredient Parts B Wei ht

Epoxy Resin Monoepoxide Diluent Silica Filler Pigment

Pigment Dispersant Rheological Additive Mineral Oil Air Release Additives Finely Milled Carbon Fiber 1/8" Chopped Carbon Fiber 1/4" Chopped Carbon Fiber Amine Hardener Silica Aggregate

This flooring composition 1 when applied at a thickness of about one-eighth inch consistently exhibits an electrical surface resistance of from 25,000 to 1,000,000 ohms when measured as described in NFPA 99. Flooring Composition 2 Ingredient Parts B Weight

Epoxy Resin Monoepoxide Diluent Silica Filler Pigment

This flooring composition 2 when applied at a thickness of about one-eighth inch consistently exhibits an electrical surface resistance of from 1,000,000 to 100,000,000 ohms when measured as described in NFPA 99.

Coating Composition 1

Ingredient Parts By Weight

Epoxy Resin 35.873

Monoepoxide Diluent 4.730

Benzyl Alcohol 2.259

Silica Filler 29.050

Pigment 4.903

Pigment Dispersant 0.157

Anti-Settling Additive 0.472

Rheological Additive 0.787

Air Release Additives 0.472

Finely Milled Carbon Fiber 0.669

1/8" Chopped Carbon Fiber 0.173

Amine Hardener 20.455

This coating^"composition 1 when applied at a thickness of about 0.030 to about 0.035 inches consistently exhibits an electrical surface resistance of from 25,000 to 1,000,000 ohms when measured as described in NFPA 99.

Coating Composition 2 Ingredient Parts by Weight (Rounded Off)

Epoxy Resin 35.69

Monoepoxide Diluent 7.02

Silica Filler 27.45

Pigment 4.89

Pigment Dispersant 0.02

Anti-Settling Additive 0.47

Rheological Additive 0.15

Mineral Oil 2.14

Air Release Additives 0.47

Finely Milled Carbon Fiber 0.67

1/8" Chopped Carbon Fiber 0.16

1/4" Chopped Carbon Fiber 0.02

Amine Hardener 20.94

This coating composition 2 when applied at a thickness of from about 0.006 to about 0.012 inches consistently exhibits an electrical surface resistance of from 100,000 to 100,000,000 ohms when measured as described in NFPA 99.

Coating Composition 3 Ingredient Parts By Weight (Rounded Off)

Epoxy Resin 29.41

Monoepoxide Diluent 5.79

Silica Filler 22.62

Pigment 4.03

Pigment Dispersant 0.13

Anti-Settling Additive 0.04

Rheological Additive 0.13

Mineral Oil 1.76

Air Release Additives 0.39

Finely Milled Carbon Fiber 0.55

1/8" Chopped Carbon Fiber 0.13

1/4" Chopped Carbon Fiber 0.02

Amine Hardener 13.168

Silica Aggregate 23.58

This coating composition 3 when applied at a thickness of from about 0.006 inches to about 0.012 inches consistently exhibits an electrical surface resistance of from 100,000 to 100,000,000 ohms when measured as described in NFPA 99. Coating composition 3 also provides slip resistance.

Application techniques are important whether applying a flooring or coating composition of the invention. When applying coating compositions according to the invention, a notched tool (such as a notched trowel or notched squeegee) or similar mechanical device is preferred. This is for at least two reasons. First, use of the notched tool serves to evenly distribute the coating composition on the floor. Second, the notched tool distributes the carbon fibers evenly throughout the coating composition, avoiding clumps of carbon fibers in the coating composition. A suitable notched trowel is of the type used conventionally for applying mastic cement prior to laying ceramic tile. In addition to using the notched tool, the installer should preferably exercise a proper technique. While using this technique is not critical to invention, good results are attained when the following technique is utilized. This technique involves several steps. The first step is to trowel the coating composition in place using the notched tool. Next, the notched tool is lightly run in a direction transverse to the direction of the original troweling. This orients some of the fibers at right angles to other fibers remaining in the original troweling direction. Optionally, the notched tool may then be run across the coating composition at a diagonal to the two first directions of troweling to enhance tha characteristic of the coating whereby the same electrical surface resistance is obtained in every direction. After finishing with the notched tool, it is desirable to roll the troweled coating with either a conventional paint roller or a plastic textured roller.

Depending on the porosity of the surface to which the coating is applied, it may be necessary to initially apply a sealer or primer to the surface to prevent the coating from soaking into the porous surface. Any conventional, preferably epoxy-based, primer may be used.

It is also desirable to employ a proper technique when installing flooring compositions according to the invention. One proper technique is as follows: When installing flooring compositions, initially the flooring composition is troweled or rake to a uniform thickness about 1/8 inch or slightly less. In contrast to the coating compositions, it is not necessary to trowel the flooring composition at a direction transverse to ths direction of initial troweling. Next, a spiked roller, having plastic radially extending spikes or spines, is rolled over the flooring surface. One suitable roller is made by Bonness & Partner G.m.b.h. and sold under tha tradename "Porcupine Roller. "

Such rolling of the flooring composition promotes air release at the surface of the flooring composition, provides greater uniformity of appearance over the surface of the composition and promotes migration of the fiber ends to the surface of the flooring composition, resulting in more uniform electrical surface resistance over the surface of the flooring composition.

Although the hardener and resin components should be in stoichiometric amounts respecting one another, the proportion of hardener and resin relative to the overall material composition may vary according to the amount of pigment and filler used. For example, a red coating may require a larger proportion of pigment than a blue coating and therefore the overall proportions of hardener and resin would be less for the red coating than for the blue. Such variations are be within the scope of the invention.

Claims

ClaimsWe claim the following:

1. A colorable antistatic coating composition, capable of producing a cured seamless, smooth antistatic coating about 5 - 40 mils thick, comprising: a.. an epoxy resin; b. a hardener; and c. carbon fiber.

2. The composition of claim 1 comprising a pigment.

3. The composition of claim 1 wherein the carbon fiber comprises milled or chopped carbon fiber or both milled carbon fiber and chopped carbon fiber.

4. The composition of claim 3 wherein the carbon fiber consists essentially of milled or chopped carbon fiber or both.

5. The composition of claim 4 wherein the carbon fibers have lengths of about 0.02 millimeters to about 3/8 inch.

6. The composition of claim 5 wherein the carbon fibers have lengths of about 0.02 millimeters to about 5/16 inch.

7. The composition of claim 6 wherein the carbon fibers have lengths of about 0.02 millimeters to 1/4 inch.

8. A cured, non-black, antistatic coating having a thickness of about 5 to about 40 mils, said coating comprising: a. epoxy resin; b. hardener; and c. carbon fiber.

9. The cured coating of claim 8 further comprising a pigment.

10. The coating of claim 8 having a thickness of about 5 to about 10 mils.

11. The coating of claim 8 having a electrical surface resistance of about 25 kilohms to about 1 megohm.

12. The coating of claim 8 having a electrical surface resistance of about 1 megohm to about 100 megohms.

13. The coating of claim 8 wherein the carbon fibers have lengths in the range of about 0.02 mm to about 3/8 inch (9.525 mm).

14. The coating of claim 13 wherein the carbon fibers have lengths in the range of about 0.02 mm to about 5/16 inch (7.9375 mm).

15. The coating of claim 14 wherein the carbon fibers have lengths in the range of about 0.02 mm to about 1/4 inch (6.35 mm).

16. A non-black or colorable, anti-static, epoxy-based flooring composition exhibiting a low electrical surface resistance and a seamless surface after curing, comprising: a. a hardener component, b. an epoxy resin component, and c. a carbon fiber component comprising i. milled unsized carbon fiber and chopped carbon fiber, or ii. chopped carbon fiber.

17. The flooring composition of claim 16 wherein the chopped carbon fiber has a length of about 1/8 to about 1/4 inch.

18. The flooring composition of claim 16 comprising about five (5) wt. % to about forty (40) wt. % hardener component, about thirty (30) wt. % to about eighty-five (85) wt. % epoxy resin component, and about 0.25 wt. % to about five (5) wt. % carbon fiber component based on the weight of the flooring composition.

19. The flooring composition of claim 16 further comprising a pigment.

20. The flooring composition of claim 19 further comprising an aggregate.

21. A method of forming a non-black, smooth, seamless., antistatic curved epoxy-based coating on a surface, comprising: a) forming a mixture comprising i) epoxy resin, ii) hardener, iii) carbon fibers, and iv) pigment, b) applying said mixture to said surface, c) to distribute the mixture evenly passing a notched tool over the mixture on the surface, d) passing the notched tool over the distributed mixture to orient the fibers in a first direction using a notched tool, e) further passing said tool over the mixture transverse to an original direction of fibe:: orientation to reorient some of the fibers transverse to said original direction, f) allowing said mixture to cure.