WO2001051238A1

WO2001051238A1 - Esd protective flooring system and method

Info

Publication number: WO2001051238A1
Application number: PCT/US2000/034544
Authority: WO
Inventors: John R. Copp
Original assignee: United Technical Products, Inc.
Priority date: 2000-01-13
Filing date: 2000-12-19
Publication date: 2001-07-19
Also published as: AU2001224407A1

Abstract

An ESD protective flooring system with an undercoat layer, (28) including an epoxy with plurality of conductive particles distributed therethrough; a base coat layer, (30), over the primer coat layer, the base coat, (30), having a conductive medium therein; a non-mineral aggregate, (29), on and in the base coat layer, the non-mineral aggregate, (29), including a number of conductive pieces; and at least one sealer coat layer, (32), over the aggregate.

Description

ESD PROTECTIVE FLOORING SYSTEM AND METHOD

FIELD OF THE INVENTION

This invention relates to an ESD protective flooring system and method employed to protect and seal concrete and other floors, typically in the electronic industry, and other industries, against solvent, solder flux and other chemical spills, and machinery traffic, and mechanical abuse and to protect against electrostatic discharge (ESD)..

BACKGROUND OF THE INVENTION

Protective flooring systems or toppings or coatings are used in various industries to protect and seal concrete and other floors. In the electronic and other industries, such floors protect against solvent, solder flux, and other chemical spills, and heavy machinery, traffic, and mechanical abuse. Such protective floorings may be used for example, in surface mount technology fabrication facilities, other electronic manufacturing, assembly, or testing facilities, and in munitions facilities, pharmaceutical plants, and hospitals. In many of these facilities, electro-static discharge (ESD) is a concern.

Rust-Oleum Concrete Protection System, Inc. (Tulsa, Oklahoma), for example, offers a "Brite Cast HD" concrete topping product which includes (from top to bottom) one or more sealer coats, a color quartz aggregate, a base coat, and, usually, a primer coat on the existing concrete floor. Harris Corporation (Melbome, FL) and Stonehard, Inc. (Maple Shade, NJ) make similar products. Also, a "TerraChip" system which provides the look of an epoxy terrazzo floor is available from American Industrial, 1218 W. 41^st Street, Suite B, Tulsa, OK 74107.

In Rust-Oleum's "Brite Cast HD" product, the sealer and base coats include conductive fibers and conductive silicon carbide particles were added to the color quartz aggregate in an attempt to make the protective topping system conductive through its thickness to counteract the effects of electro-static discharge (ESD).

When subjected to electrical resistance tests, however, this product was found to be less than satisfactory and did not meet ESD 7.1 specification parameters for static dissipative or conductive flooring.

Moreover, the conductive fibers in the base coat caused numerous problems. They tend to conglomerate leaving whole areas in the ground plane which are not conductive. Also, the cost of conductive fibers added significantly to the cost of the product because many conductive fibers are required in order to form an interlaced conductive network of fibers. Second, the conductive fibers tend to all lie in the same direction in the wet epoxy base coat when it is applied. Workers used rollers to get the fibers to "stand up" - again, a process which added significantly to the cost of a given application. Thus, the fibers failed to provide a consistent ground plane: the fibers each clumped together in some areas forming conductive regions but insulative regions were formed proximate the areas where the fibers clumped together. And, the fibers generally fail to provide a truly conductive (10,000 ohms) ground plane.

One advantage of the "TerraChip" system which includes paint chips for decoration instead of quartz is that is less expensive and has a higher gloss shine and is available in light reflective colors when compared to quartz patterns. On the other hand, the current "TerraChip" system does not provide adequate ESD control.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide an ESD protective flooring system that is useful, for example, in the electronics industry proximate surface mount equipment and solder reflow and solder oven equipment and useful in other electronic manufacturing, assembly, or testing facilities and in munitions facilities, pharmaceutical plants, hospitals, and the like.

It is a further object of this invention to provide a method of protecting flooring against chemical spills, heavy machinery traffic, mechanical abuse, and electrostatic discharge.

It is a further object of this invention to provide such a system and such a method which is less expensive and less labor intensive than prior art systems and methods.

This invention results from the realization that an aesthetically pleasing, more conductive, better ground plane, and yet heavy duty industrial paint chip based floor topping system can be effected by adding carbon black instead of fibers to an under coat, by the addition of a white or off-white epoxy base coat with a conductive medium therein, by making a number of the paint chips conductive, by making the sealer coat as thin as practical, and by adding conductive fibers to the sealer coat. In this way, any electrical charges which accumulate on the floor dissipate through the floor via 1) the conductive fibers in the sealer coat, 2) the conductive paint chips, 3) the conductive medium (e.g., doped titanium dioxide) in the base coat, and 4) the primary ground plane which includes the carbon black in the under coat, all four of which are preferably in electrical and physical contact with each other through the thickness of the floor topping or coatings. Thus, the four level construction offers a serious advantage over prior art floor toppings and coatings.

An ESD protective flooring system and method. An undercoat layer including an epoxy with plurality of conductive particles distributed therethrough is applied to an existing floor. A base coat layer is applied over the under coat layer, the base coat having a conductive medium therein. A non-mineral aggregate is broadcast onto the base coat layer and the non-mineral aggregate includes a number of conductive pieces. At least one sealer coat layer is applied over the aggregate and the sealer coat typically includes a plurality of conductive fibers therein.

The conductive particles in the undercoat layer are typically carbon black added to an epoxy composition in an amount between 5 to 15% by weight. The conductive medium in the base coat layer is typically a mineral such as doped titanium dioxide ranging from 5 to 20% by weight of the base coat. The non- mineral aggregate is typically colored paint flakes and the conductive pieces are paint flakes including carbon black. The conductive pieces may comprise between 3 and 10% the paint chips by volume. The conductive fibers in the sealer coat are preferably carbon fibers comprising 1/2 to 6% by weight of the sealer coat. The sealer coat is typically between 5 to 30 mils thick. This invention also features a method of protecting a floor, the method comprising preparing and applying to the floor an undercoat layer including an epoxy composition with a plurality of conductive particles distributed therethrough; preparing and applying to the undercoat a base coat layer, the base coat having a conductive medium therein; preparing and broadcasting over the base coat a non-mineral aggregate including a number of conductive pieces; and preparing and applying over the non-mineral aggregate a sealer coat including a plurality of conductive fibers therein.

Preparing the undercoat layer typically includes mixing carbon black powder with an epoxy composition. Mixing includes adding 5 to 15% carbon black by weight to the epoxy composition. Preparing the base coat layer includes mixing doped titanium dioxide with a resin composition. Mixing includes adding 5-20% by weight titanium dioxide.

Preparing the non-mineral aggregate may include adding carbon black paste to a liquid paint formulation, drying the mixture, fragmenting the dry paint into a number of conductive flakes, and adding the conductive flakes to other colored paint chips. Between 3 and 10% conductive flakes are added to the other colored paint chips. Preparing the sealer coat typically includes adding conductive fibers to a resin compound. 1/2 to 6% fibers are typically added to the resin compound.

Applying the undercoat layer may include spreading the undercoat over the floor to a thickness of between 4 and 12 mils. Applying the base coat layer includes spreading the base coat over the undercoat to a thickness of between 4 and 12 mils. Broadcasting the non-mineral aggregate includes casting the aggregate over the base coat while the base coat is still wet until rejection and then sweeping off any remaimng aggregate. Applying the at least one sealer coat includes spreading the sealer coat over the broadcast aggregate to a thickness of between 5 and 30 mils.

The novel method of protecting a floor in accordance with this invention includes applying to the floor an undercoat layer including an epoxy with a plurality of conductive particles distributed therethrough; applying over the undercoat layer a base coat layer, the base coat having a conductive medium therein; broadcasting onto the base coat a non-mineral aggregate including a number of conductive pieces; and applying over the non-mineral aggregate a sealer coat including a plurality of conductive fibers therein. The ESD protective flooring system of this invention includes a non-mineral aggregate including a number of conductive pieces; and at least one conductive sealer coat over the aggregate. Preferable but not necessary additional components of this system include a base coat layer under the aggregate, the base coat having a conductive medium therein and an under coat layer under the base coat layer, the under coat layer including a plurality of conductive particles distributed therethrough.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiment and the accompanying drawings, in which: Figs. 1 and 2 are schematic views of an ESD protective flooring system in accordance with the subject invention;

Fig. 3 is a cross-sectional illustrative view of the flooring system shown in Fig. 1 ; and

Fig. 4 is a block diagram showing the conductive path provided by the flooring system of this invention.

DISCLOSURE OF THE PREFERRED EMBODIMENT Concrete protective flooring system, topping or coating 10, Figs. 1 and 2 is used to both protect and seal an original or existing concrete floor in the electronic and other industries against solder flux, solvent, and other chemical spills, heavy machinery traffic, and mechanical abuse, and, in this invention, electrostatic discharge. Such flooring systems or toppings are useful in areas where surface mount equipment 12, Fig. is used, and where fork lifts 13, Fig. 1, and other mechanical devices regularly operate. Topping or coating 10 can be employed in electronic manufacturing, assembly, or testing facilities, munitions facilities, pharmaceutical plants, hospitals, and other facilities.

Flooring 10 is typically disposed on an existing concrete floor 20, Fig. 3 although the system and method of this invention can be employed with other flooring materials. Optionally applied over a concrete floor 20 is a pre-coat or primer (not shown), if necessary, typically a 100% solids epoxy composition (e.g., the "TerraRich" product available from American Industrial). On this optional coat or even directly on a concrete floor 20 may be one or more conductive foil strip 24 as shown (one strip every 1000 sq. ft.). This conductive foil strip is electrically connected to ground via a metal column or some other ground source in the facility. Over these conductive foil strips is under coat 28, typically an epoxy or urethane composition impregnated with a plurality of conductive particles, for example, carbon black. The under coat is typically between 4-12 mils thick when wet and typically includes between 5% and 15% carbon black added to it by weight. The thickness of undercoat 28 when dry is typically 1.5-4 mils.

The carbon black is added to the epoxy in a high speed industrial mixer with agitation capabilities. The Hegman gauge quality should be about 6. 10% carbon black is preferred. Carbon black is not desirable in many applications because it turns whatever substance it is added to black. In the subject invention, however, under coat 28 is not seen due to the existence of base coat 30, Fig. 3. Base coat 30 is preferably a white or off-white epoxy coat including a conductive mineral therein such as Rutile type acicular titanium dioxide doped with stannic oxide and antimony pentoxide.

As made clear in the Background of the Invention section above, prior art systems included conductive fibers in base coat 28. Conductive fibers, however, especially metallic salt fibers, have been found to degrade and oxidize in some applications thus lose conductivity, and in any case, in order to provide the required conductive network of interlaced conductive fibers, many, many conductive fibers are required which causes mixing and dispensing problems. Also, during the application of base coat 28, the workers were required to roll the base coat 28 with rollers to get the conductive fibers to "stand up" ~ another problem with the prior art system since these rolling procedures added to the cost of the installation of the protective flooring. And, even still, the resulting flooring was not conductive enough to adequately dissipate electrical charges which came in to contact with the flooring thereby presenting possible ESD problems for sensitive electronic components. In particular, it was found that the conductive fibers conglomerate in some areas but there was almost a complete absence of fibers in other areas forming a very poor ground plane.

In the subject invention, it is preferred that carbon black is added to under coat 28, Fig. 3, by mixing before under coat 28 is applied to the floor.

Non-mineral aggregate "layer" 29 is preferably a plurality of colored paint flakes broadcast over base coat 30 until rejection. After curing for about eight hours, any excess paint flakes are swept off the floor. The floor may then be sanded, buffed, and vacuumed. A number (e.g. 3-10%) of these paint flakes, preferably black colored paint flakes, are made conductive by adding a carbon black paste to the liquid paint formulation, drying that mixture, and fragmenting the dried paint into a number of conductive flakes. These black conductive flakes are then added to the other colored paint chips available from suppliers such as Pleko Southwest, Inc., 182 East 6^th Street, Tempe, AZ 85281. "Non-mineral aggregate" as used herein means non-quartz and typically means paint chips (also called flakes) some of which are conductive even though the paint itself includes minerals. Note, however, that other types of chips may be employed so long as they are not quartz. Plastic is one example.

Then, a first sealer coat 32 (and an optional second sealer coat) are applied. Sealer coat 32 includes a plurality of conductive fibers disposed therein, preferably less than 1% by weight. The fiber quantity, however, may range from 1/2% up to 6%. The sealer coat or coats are preferably very thin (e.g. 5-30 mils) and in this instance the conductive fibers provide adequate conductivity in the sealer coat because it is thin. The conductive fibers may be nylon or acrylic coated with carbon or metal. In the preferred embodiment, they are 1/8 to 1/4" in length and have Denier value of between 2 and 9. The fibers are mixed in with the epoxy of the sealer coat using a high speed industrial mixer with agitation capabilities. Typically, 1/3 of the fibers are added and mixed well, then another 1/3 of the fibers are added and mixed well, and then the final 1/3 of the fibers are added and mixed well. Preferably a light stabilizer compound such as a hindered Amine is added to the resin to counter any dulling which may occur due to exposure to light. Sealer coat materials include the "TC Sealer LS" (American Industrial) and other sealer coats available from other manufacturers.

Carbon black is not desirable in the sealer coats because the carbon black would cover and detract from the decorative appearance of the paint chips 29 on and extending into base coat 30. Sealer coat 32 is typically not so thin that the paint chips can be felt through the sealer coats. In the electronic manufacturing and assembly industry , a fairly smooth top surface is preferred because it is easier to clean and shiny in appearance. Therefore, in this case, the thickness of sealer coat 32 is about 12.8 mils.

There is, in general, a tradeoff between the amount of carbon black which can be present in under coat 28 and the amount of conductive fibers which can be present in sealer coat 32. Too much carbon black in under coat 28 could adversely affect the viscosity and even the chemical properties of the epoxy in under coat 28. Too little carbon black in under coat 28 fails to provide a proper conductive path through the thickness of protective flooring or topping 10. There is also a trade off between the thickness of the sealer coat and also the amount of fibers in the sealer coat. Too many conductive fibers in sealer coat 32 tend to hide the decorative appearance of paint chips and too little conductive fibers in sealer coat 32 does not provide a sufficient conductive path through the thickness of topping 10. A too thick sealer coat(s) layer is aesthetically pleasing because it is smooth but decreases the conductivity of the system because there is an upper limit to the amount of fibers which can be added to the sealer coats before they detract from the appearance of the system.

This conductive path, illustrated in Fig. 4, enables a charge 50 which builds up on the surface of floor 10, Fig. 1, to bleed to a ground wire, a foil strip, or otherwise to ground 60 via the conductive fibers 52 in the sealer coat, the conductive paint chips 54 in the aggregate "layer", the conductive medium 56 in the base coat, and the carbon black 58 in base coat.

In one embodiment, the following composition may be employed.

Layer Composition Thickness Amount Application Method

Undercoat 28 34% volume solids 4-12 mils (8 200 sq Spreading by Fig. 3 Conductive carbon black 10% mils preferred) ft/gal. squeegee and Modified bisphenol A based backroll allowed to epoxy resin (18%) dry Polyethylene polyamine adduct

Conductive path: Carbon black particles, 15-15% by weight, 10% preferred

Conductive pat : Doped titanium dioxide conductive medium, 5-20% by weight, 15% preferred.

Note, the remaining paint chips do not have any carbon black. The paint chips or flakes are typically 10-20% polyvinyl acetate, 60-80% barium sulfate, 2-10% talc, and less than .2% potassium tripolyphosphate.

Conductive path: carbon fibers .5 to 6% by weight

To apply the ESD protective flooring system of this invention to concrete, the concrete substrate was prepared in accordance with ASTM D-4259 (sec. 6, Mechanical Abrading, sec. 8, Abrasive Blast) and/or ASTM D-4260 (Chemical Preparation). A portable steel shot blasting machine and/or hand abrasive grinder may be used. All dust, debris, oil and other contaminants are removed. If necessary, a primer coat may be applied. Under coat 28 is then applied, to a thickness of between 4-12 mils. Grounding strips 24, 26 at columns or grounding points are also applied. Base coat 30 is then applied to a thickness of 8 mils and backrolled to distribute uniformly . Non-mineral aggregate 29 is then broadcast to rejection onto the still wet base coat. After drying, sanding and buffing operations are performed followed by vacuuming.

Sealer coat 32 is then applied by a squeegee and backrolling operations and allowed to dry.

The electrical resistance based on ESD 7.1 Test Methodology of such a system is expected to be between 1.0 x 10⁸ and lx 10⁴ ohms at 100 vdc. Body voltage generation is preferably less than 100 volts with conductive footwear. Static decay is preferably 5000 volts to 50 volts in less than .5 seconds. The following tables list the chemical resistance and performance properties of the subject invention:

CHEMICAL RESISTANCE

PERFORMANCE PROPERTIES

System 10, Fig. 1 thus provides a method of protecting flooring against solvent, flux and other chemical spills, heavy machinery traffic, mechanical abuse, and electrostatic discharge. It is more aesthetically pleasing, and less expensive and less labor intensive than prior art systems and methods. It is also more conductive and yet still includes the features of an industrial aggregate based floor topping system. The conductive paint chips or flakes, the carbon black instead of fibers in the conductive under coat, the conductive medium in the base coat, the thin sealer coat, and the conductive fibers in the sealer coat dissipate any electrical charges which accumulate on the floor.

Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as each feature may be combined with any or all of the other features in accordance with the invention. For example, in some installations, the under coat or the base coat may be eliminated. Other embodiments will occur to those skilled in the art and are within the following claims:

Claims

1. An ESD protective flooring system comprising: an undercoat layer including a plurality of conductive particles distributed therethrough; a base coat layer over the under coat layer, the base coat having a conductive medium therein; a non-mineral aggregate on and in the base coat layer, the non-mineral aggregate including a number of conductive pieces; and at least one sealer coat layer over the aggregate.

2. The system of claim 1 in which the under coat layer includes an epoxy and the conductive particles are carbon black.

3. The system of claim 2 in which carbon black is added to the epoxy in an amount between 5 to 15% by weight.

4. The system of claim 1 in which conductive medium in the base coat layer is a mineral.

5. The system of claim 4 in which said mineral is doped titanium dioxide.

6. The system of claim 1 in which the conductive medium ranges from 5 to 20% by weight of the base coat.

7. The system of claim 1 in which the non-mineral aggregate is colored paint flakes and the conductive pieces are paint flakes including carbon black.

8. The system of claim 7 in which the conductive pieces comprise between 3 and 10% the paint chips by volume.

9. The system of claim 1 in which the sealer includes conductive fibers therein.

10. The system of claim 9 in which the conductive fibers comprise 1/2 to 6% by weight of the sealer coat.

11. The system of claim 1 in which the sealer coat is between 5 to 30 mils thick.

12. A method of protecting a floor, the method comprising: preparing and applying to the floor an undercoat layer including a plurality of conductive particles distributed therethrough; preparing and applying to the undercoat a base coat layer, the base coat having a conductive medium therein; preparing and broadcasting over the base coat a non- mineral aggregate including a number of conductive pieces; and preparing and applying over the non-mineral aggregate a sealer coat.

13. The method of claim 12 in which preparing the undercoat layer includes mixing carbon black powder with an epoxy composition.

14. The method of claim 13 in which mixing includes adding 5 to 15% carbon black by weight to the epoxy composition.

15. The method of claim 12 in which preparing the base coat layer includes mixing doped titanium dioxide with a resin composition.

16. The method of claim 15 in which mixing includes adding 5-20% by weight doped titanium dioxide.

17. The method of claim 12 in which preparing the non- mineral aggregate includes adding carbon black paste to a liquid paint formulation, drying the mixture, fragmenting the dry paint into a number of conductive flakes, and adding the conductive flakes to other colored paint chips.

18. The method of claim 17 in which between 3 and 10% conductive flakes are added to the other colored paint chips.

19. The method of claim 12 in which preparing the sealer coat includes adding conductive fibers to a resin compound.

20. The method of claim 19 in which 1/2 to 6% fibers are added to the resin compound.

21. The method of claim 12 in which applying the undercoat layer includes spreading the undercoat over the floor to a thickness of between 4 and 12 mils.

22. The method of claim 12 in which applying the base coat layer includes spreading the base coat over the undercoat to a thickness of between 4 and 12 mils.

23. The method of claim 12 in which broadcasting the non- mineral aggregate includes casting the aggregate over the base coat while the base coat is still wet until rejection and then sweeping off any remaimng aggregate.

24. The method of claim 12 in which applying the at least one sealer coat includes spreading the sealer coat over the broadcast aggregate to a thickness of between 5 and 30 mils.

25. A method of protecting a floor, the method comprising: applying to the floor an undercoat layer including a plurality of conductive particles distributed therethrough; applying over the undercoat layer a base coat layer, the base coat having a conductive medium therein; broadcasting onto the base coat a non-mineral aggregate including a number of conductive pieces; and applying over the non-mineral aggregate a sealer coat.

26. The method of claim 25 in which applying the undercoat includes spreading the undercoat over the floor to a thickness of between 4 and 12 mils.

27. The method of claim 25 in which applying the base coat includes spreading the base coat over the undercoat layer to a thickness between 4 and 12 mils.

28. The method of claim 25 in which broadcasting the non- mineral aggregate includes casting the aggregate onto the base coat while the base coat is still wet until rejection and then sweeping off any remaining

aggregate.

29. The method of claim 25 in which applying the sealer coat includes spreading the sealer coat over the broadcast aggregate to a thickness of between 5 and 20 mils.

30. An ESD protective flooring system comprising: a non-mineral aggregate including a number of conductive pieces; and at least one conductive sealer coat over the aggregate.

31. The system of claim 30 further including a base coat layer under the aggregate, the base coat having a conductive medium therein and the system further including an under coat layer under the base coat layer, the under coat layer including a plurality of conductive particles distributed therethrough.