CA2128089A1 - A coated abrasive article containing an electrically conductive backing - Google Patents

Abstract

A coated abrasive article having a backing comprising a sufficient amount of an electrically conductive material therein to reduce the buildup of static electricity during the use of the article.
In another aspect, a method of making the same is taught.

Description

Wo 93/15879 2 1 2 8 0 8 9 Pcr/uss3/0l2s2 A COATED ABR~SIVE ARTICLE CONTAINING AN ELECTRICALLY
CONDUCTIVE BACK~G

Back~round of the Invention 5 Field of the Inventi~n This invention pertains to a coated abrasive artide having an electrieally conductive material incoIporated into the backing thereof; and a method of making the same. The abrasive article is useful in reducing the accumulation Qf the static electnc charge in the abrasive article during abrading of a workpiece.
Description of th~ Related Art Coa~ed a~rasi~es, conside~ed the premier tool for abrading and finishing wood and wood-like materials, unfortunately suffer from the generation of staticelec~icity dunng their use. Static electricity is generated by the constant 15 separation of ~e abrasive product from the work~iece, the machinery drive rolls~
idler rolls, and support pad for the abrasive pr~duct. This static charge is typically on ~e order of 50 to l00 ldlovolts.
Static electnci~,r is re~onsible f~r numerous problems. For example, a sudden discharge of ~e accumula~ed sta~dc charge can eause injury to an operator20 in the forrn of an elect~ic shock or it can cause the ignition of wood dust par~cles, which poses a serious threat of fire or explosion. The static charge also causes the sawdust to cling to v~rious surfaees, including that of ~he coated abrasive, theabrading machine and the elect~ically insulating wood workpiece, thereby making it difficult to remove by use of a conventional exhaust system. If the static 25 electrical charge is reduced or eliminated, ~e coated abrasive article can have a sigmfi~y long~ u~l li~e and the potential for the above-mentioned hazards can be elimina~ed or reducad.
Many attempts, with v~ng degree of success, have been made to solve the static el~ctricity problem. One common ap~roach has been to incorp~ate an 30 electrically conductive or antista~c material into the coated abrasive cons~uc~on to eliminate the accumulation of electrical sharge. Por example,~ U.S. Pat. No~
3,l63,968 (Nafus) discloses a coated abrasive ar~cle having a coating compAsing g~aphite in the binder on the surface opposite the ab~asive material. U.S. Pat. No.

2l2~n~
wo 93/15879 PCr/US93/0125 3,l68,387 (Adams) discloses a coated abrasive having a metal leaf pigment over the abrasive grains. U.S. Pat. No. 3,377,264 (Duke) discloses an electrically conductive layer, such as a metal foil, overlying the front surface of a coated abrasive.
U.S. Pat. No. 3,942,959 (Markoo et al.) teaches a coated abrasive construction having an electrically conductive resin layer sandwiched between two electrically nonconductive resin layers to prevent the accumulation of electrostatic charge during grinding. In the latter construction, the resin layer is made electrically conductive by incorporating into the resin an electrically conductive 10 filler which may be a metal alloy, metal pigment, metal salt, or metal complex.
U.S. Pat. No. 3,992,178 (Markoo et al.) discloses a coated abrasive anicle having an outer layer comprised of graphite particles in a bonding resin which reduces ~e elecbnstatic charges generated during grinding.
U.S. Pat. No. 4,826,508 (Schwartz et al.) discloses a flexible abrasive 15 member comprising a length of flexiUe fabric that has been treated to render it dec~ically conductive, an electricalb non-conductive mesh layer ap~lied to one surface of the fabric, said non-conductive mesh layer having a multitude of discrete openings therein, and electrodeposited metal adhering to the electrically conductive fabric in each of the openings, the electrodeposited metal having 20 particulate abrasive material embedded thereim U.S. Patent No. 5,06l~294 (Hanner et al.) teaches a co~ted abrasive that is rendered conductive by the addition of a doped conjugated polymer.

Sumnl~y~hç Invçntion The present invention provides a coated abrasive article having a sufficient amount of an electrîcally conductive matenal inco~porated into the backing the~eof to reduce the static electrical problems associated with conventional coated ab~asives during the abrading of worl~pieces. The static electric problems tend to be more pronounced when abrading electrically insulating or semi-insuladng 30 workpieces, for eJcample, wood (e.g., pine, oak, che~y, etc.), plastic, mineral ~e.g., miuble), ~e like (e.g., pu~cle board pressed board), or workpieces ~oa~d with an insulating material (e.g., lacquer). In another aspect, the present invention provides a method of making the same.

212~0~!~
wo 93/l5879 PC~`/U~93/01252 A first coated abrasive ar~icle in accordance with the present invention compnses:
(a) a nonwoven, fibrous backing comprising at least one ply, wherein said ply comprises electIically non-conductive fibers and electIically conductive matenal; and (b) an abrasive layer bonded to one major surfaee of the bacldng, wherein the electrically conductive material is at least one of electrically conduc~ve fibers selected from the group consisting of graphite fibers, carbon fibers, metal fibers, electrically conduc~ve polymer fibers, graphite coated ISbers, 10 carbon coated fibers, metal coated fibers, elect~ically conductive polymer coated fibers~ and combinationsthereof; and electrically conductivepartiele,~ selected from the group consisting of graphite particles, carbon particles, metal particles, electrically conductive polymer par~cles~ graphite coated par~cles, carbon coated particles, metal coated par~cles, electrically conductive polymer coated ~cles, 15 and combinations thereof; and wherein the electrically conductiYe material ispresent in an amount sufficient to reduce the accumulation of static electric charge in the coated abrasive ar~cle during the abrading of a wo~lcpieee.
The term "electrically non-conductive fiber" refers to a fiber which has ~
elecmcal resistivi~ of at least 10" ohms/square. The electrically non-conduc~ve 20 fibers t~ically have a l~llg~h in the range ~rom about 0.5 to about 7 mm, a diameter in the range from about 15 to about 50 micrometers, and an aspect ra~ioin the range from about 40 to about 160.
The present inventinn provides a second coa~ed abrasive article which comprises:
~a) a backing comprising at least two plies and an innerlayer interposed between at least ~wo of the plies, the innerlayer comprising an electrically eonductive material; and (b) an abrasive layer bonded to one major surface of the backing, 30 wherein the electrically conductivs material is present in an amount sufficient to reduoe a~umuladon of static electric charge in the coated ab~asive ar8de duIing ~e abrading of a worl~piece.
The electrically conductive material can be in any of a variety of shapes 212SO~
Wo 93/15879 Pcr/us93/0125 including, for example, spheres, flakes, squares, pyramids, fibers, etc' ~ and with regard to the second embodiment described above, can be in the shape of a sheet.
The term "electrically conductive material" or "electroconductive material"
5 refers to materials having sufficient electrical conductivity such that when incorporated into a coated abrasive article as herein described the buildup of static electricity during the use of the coated abrasive article is significantly reduced as compared to a coated abrasive which has a backing which does not contain such electrically conductive material. Pseferably, the electrically conductive material 10 has an electrical resistivity of less than 2,000 kilo-ohms per square. More preferably, the electrically conducdve material has an electrical resisdvity of less than 500 kilo-ohms per square. Most preferably, the electrical resistivity of the electridly conduc~ve material is less~an lO0 kilo-ohrns per square.
Por electrically conductive materials having suitable dimensions, the 15 electrical resistivity can be measured by placing ~e probes of an ohmméter l .4 cm apart on the electrically conductive material. Suitable ohmmeters are commercially available and include, for e~ample, those available under the tradedesignations "Bechnan Indust~ial Digit~l Multimeter," Model 44lO from Beckman Industrial Co~p. of Brea, CA; and "Industrial Development Bangor Surface ~0 Resistivity Meter," Model 482 from Industrial Development Ltd. of Bangor Gwynned, Wales).
Preferably, the ~lec~ically conductive material forms a continuous network.
A method for maldng the first ~ated abrasive article compIises the steps of:
(a) providing a nonwov~n, fibrous baclcing comprising at least one ply, wherein the ply comprises elec~rically non-conductive fibers and electrically conductive material; and (b~ ap~lying an abrasive layer to a major surface of said backing, wherein the electrically conductive material is at least one of electrically 30 conductive fibers sd~ted from the group consisting of graphite fibers, carbon- ; fibus, ~metal fibers, dect~ ly cond:w~vc polymer fibers, graphite coated fibe¢s, cubon c~ated fibers, metal co~ted fibers, electrically conduc~ve polymer coated fibs, and ~s thereof; and elec~ically conductiveparticles selected from ~12S~9 WO 93J1S879 PCI`/US93/01252 the group consisting of graphite particles, carbon particles, metal particles, elec~ically conductive polymer par~cles, graphite coated particles, carbon coated parti~les, metal coated particles, electrically conductive polymer coated particles, and combinations thereof; and wherein the electrically conductive material is S present in an amount sufficient to provide a coat~d abrasive article having a reduced tendency to accumulate static electric charge during the abrading of a workpiece.
A method for making the second coated abrasive article comprises the steps of:
10(a) providing a backing comprising at least two plies and an innerlayer interposed between at least two of ~e plies, the innerlayer comprising an electrically conduclive materiaI; and (b) applying an~ abrasive layer to a major surface of the backing, wherein the electrically conductive material is present in an amount sufficient to 15 provide a coated abrasive article having a reduced tendency to accumulate static dechic charge ~dudng ~e abrading of a worl~iece.
In regard to the second coated abrasive article, the outer major surfaces (i.e., the front side and the back side) of the bacldng used to pre~are the c~ated abrasiw article according to the present imention is not a~ffected by the presence 20 of the conductive layer such that there is no ~equirement to select particular adhesive formulations or inks for manufacturing the abrasiYe since the conventional compositions may be employed. In addi~on, the abili~ to print information, such as ~e t~ and grade of abrasive mineral~ on the backside (i.e., non-ab~asive side) of the backing is not impaired by the presence of the elec~ically conductive 25 ma~erial wi~in the backing. Further the disadvantages inherent with ~e use ofdarlc col~red electridly conductive layers based on carbon black on the backsideof ~e backing, whic}i may limit use of coated abrasive belts on machines having infra-red sensors for ~acking puIposes, is avoided by a coated ab~sive ar~cle according to the present invention. Furthermore, the electrically conductive 30 material doa not significantly interfere with the structural integrity of the abrasive ~, ~g- :
; ~Thc c~led ab~ive ar~cle may be in any conventional form including ~-~ose having an abrasive layer compnsing a make layer, abrasive grains, a size 2~R~ 6- PCr/USs3/0 layer, etc., and other functional layers (e.g., a supersize layer), and those having a monolayer as an abrasive layer comprising a slurry layer comprising a bond system and abrasive grain, and other functional layers. The backing of the coated abrasive optionally has a presize coating, a backsize coating, a saturant~ or 5 combinations thereof.
The inventive coated abrasive article provides a solution to the serious static - electricity build-up problem associated with abrading a work~iece with a coated abrasive article.

10 B~ief Descri~tion of the Drawing PIG. 1 is an enlarged cross-sectional view of an embodiment of a coated abrasive article made in accordance~with the present invention.
PMS. 2-3 are enlarged closs-sectional views of various backings in accordance with the p~nt invention.
PIG. 4 is an~ enlar~ed cross-sectional view of another embodiment of a coa~ e article made in a~dance with the present invention.

Detailed Descnption of Prefened Bmbodiment This invention pertains to a coated abrasive ar~icle which is made 20 el:rically conductive by inc~pora~ng electrically conductive material therein.
The coated abrasive article of the present inven~on may take a~y of the variety of embodiments, as will be explained belsw.

First Çoat~ Abrasive Arti~le l~eIernng to FIG. 1, coated ab~asive 8 comprises nonwoven, fibrous backing 9 having plu~ality of abrasive granules 12 bonded to backing 9 by means of bond system 10 which typically consists of ffrst bond coat 1 l (generally refer~ed ' .to as a "~ake" coat or "make" layer) and second bond coat 13 (generally ~eferred to as a "size" coat or "size" hyer). Make coat ll secures abrasive g~anules 12 to bac1~ng 9 and size coat 13 fr~erruDforca ab~as~ve g~ains 12. Altemat~vely, bond~ slem 10 cons~s s of ~a~ single ~ coat ~e.g., a slurry coat).
Nonwoven, fibrous bacl~ng Q includes dec~ically non~onductive fibers 17 and at least onc~ of electrically conduc~ve fibers 15 and electrically conductive ~::
"
,, - ~ ,.

h. ~ r~ ~J V V v W O 93/15879 PC~r/US93/01252 particles 16~
Coated abrasive 8 may also contain supersize coat 18. The purpose of the supersize coat is to reduce the amount of loading. "Loading" is the term used todescribe the filling of spaces between abrasive grains with swarf (the material 5 removed from the workpiece) and the subsequent build-up of that material. For example, during wood sanding, swarf comprised of wood particles becomes lodged -in the spaces bet~,veen abrasive grains, dramatically reducing the cutting ability of the grains.
Examples of alternative electrically conductive backing embodiments useful 10 in the coated abrasive article of the present invention are depicted in FIGS. 2 and 3.
Referring to FIG. 2, electrically conductive nonwoven, fibrous bacl~ng 19 compnses first ply 20 and second ply 21. Plies 20 and 21 each include electrically non conductivo fibers 24 and 25 and collectively include at least one of electrically 15 conductive fibers 22 and 51 and electrically conductive particles 23 and 52. A
coated abtasive hyer can be applied to exposed surface 26 or 27.
Refer~ing to FIG. 3, electrically conductive nonwoven9 fibrous backing 29 compnses first ply 30, second ply 31, and third ply 32. Plies 30, 31, and 32 each include electrically non-conductive fibers 35, 38, and 41 and collectively include 20 at least one of elect~ically conductive fibers 33, 36, and 39 and electrically conductive par~cles 34, 37, and 40. A coated abrasive layer can be applied to exposed surface 42 or 43.
The preferred electrically conductive mat~rials are carbon par~cles, carbon fibers, graphite particles, graphite fibers, metallic particles, metallic fibers, 25 electrically conductivepolymenc par~cles, electrically conduc~vepolymeric ~e.g., polypy~role, polyacetylene, and polyaniline) fibers, and combina~ons the~eof.
Prefe~ably, at least one ply compnsing the nonwoven, fibrous backing !_ compnses electrically conductive material in the ~ange from about 0.75 to about ; 15 pe~cent by volume, based on the total volume of ~e ply and thc electrically 30 conduc~ve materi~l compdsing the ply. More preferably, at least one ply cr~es declria~lly u~ material in the range from about 4 to about 12 pe~ent by volume, and most pref~ably, at least one ply compnses electrically conductive matedal in the range of about 5 to about 8 percent by volume.

~' ,:

21280~'3 wo g3/15~79 PCr/USs3/0125 Preferably, the shape of the elec~ically conductive material is at least one of fibers and particles, wherein "electrically conductive fiber" refers to an electrically conductive filament, preferably having a diameter in the range fromabout 2 to about 20 micrometers and a length of up to about 2 cm. More 5 preferably, the electrically conductive fibers have a length in the range from about 0.1 to about 1 cm. The electrically conductive fibers preferably have a high aspect ratio. The higher the aspect ratio of the fibers, gene~ally the lower the amount of such fibers needed to render the article sufficiently electrically conductive toreduce the static electric problems associated with conventional coated abrasives 10 during the abrading of electrically insulating wor~pieces. Preferably, the electrically conduclive particles can ~pass through a 200 mesh sieve (i.e., having 75 micrometer ~penings). More p~eferably, ~e largest dimension of the particles is in the ~ange from ~about 45 to about 75 micrometers. Although particlc sizes outside of the p~ed ranges are useful, p~articles that cannot pass through the 15 200 mesh sieve tend to be more difficult to incorporate into the backing in acon~rolled manner. Such particl, for; example, tend to settle in the wood pulp disper~on used to make the bacl~ng, there~oy reducing the control in distributing the particles as desired.
The most preferred electrically conductive material is carbon fibers.
20 Preferably, the bacldng comprises ca~ fibers in the range from about S to about ~- ~ 25 weight percent, based on the total weight of ~he backing and the caioon fibers comprising the bacl~ng. More preferably, carbon fibers comprise in the range from about S to about 15 weight percent, and most preferably in the range from about 7 to about 12 weight percent~
For a backing comprising el~trically conductive ~bon matenal, it is preferable that the c~rbon con~int of the carbon material is at least 80 peircent by weight. More preferably, the carbon content of the el~trically conductive carbon 1,, : ~ j mateIial is at least 90 percent by weight.
Useiful electrically conductive metals include, for example, stainless steel, 30 nicbel,ailuminumtsilvertal~d s~f. Usefillelectricallyconductive ls~ude,fore11ample,polpniline,p~1ypy~rol~s~polyaceqlene, and _ s ~eo ~- ~ The prefclled size o~ the dec~ ly conductive material is based on 212S0~3 WO 93/1587g ` PCr/US93/0~252 compatibility with the method of making the paper.
Methods for mal~ng carbon fibers are h~own in the art. For example, U.S. Pat. No. 3,011,981 (Soltes) teaches carbon fibers made by heating cellulosic materials in the absence of oxygen and moisture at a temperature between 120 and5 815C until substantial carbonization has occurred. The carbonized material isthen subjected to a temperature above 815C for a time sufficient to render the - carboniæd material electrically conductive.
Carbon fibers are commercially availaUe, for example, ~rom Amoco Chemicals Corp. of Chicago, IL, and Concordia Mfg. Co. of West Warwick, Rl.
Methods known in the art for making graphite fibers include that disclosed in U.S. Pat. No. 3,635,675 (Ezekiel).
Graphite fibers are also commercial]y available, for e~ample, from Fibre-Glast Developments Corp. of Dayton, OH, and Hercules Aerospace Co. of Magna, ~lT.
Commercially available carbon particles include ~ose from Cabot Corp.
of Waltham, MA.
Commercially available graphite particles include those from Lonza of Fairlawn, NJ.
Metallic particles commercially available include, for example~ nickel 20 particles from Novamet of Wyckoff, NJ. Commercially available metallic fibersinclude, for example, s~nless steel fibers marketed under ~e ~ade designa~on "B~SHELD" from Bekaert Fiber Technology of Marietea, GA; and nickel fibers marketed under the ~ade designadon "FIBREXU from NaJdonal Standard Co.
of Niles, MI.
Electrically conduc~ve polymenc par~cles or powde~s are commercially available (e.g., polyaniline powder is ~vaila~le from Uniax of Santa Barbara, CA)~
Electrically conductive polymeric fibers are commercially available, for example, , . i .
from Mi~iken & Co. of Spartanburg, SC, under the ~ade designation "CONT~Xn (natural and syn~etic fibers ~eated, for example, w~th polypyrrole). Methods for 30 doposi~g ~b~ aphie, metsllic, and electrically conduc~dvepobme~ic coa~ng onto pai~les and fibers a~e lcnown in ~e art (see, e.g., U.S. Pat No. 4,696,835,~uS et al-)-Metal coated fibers and par~cles are commercially available and include, :,,'' ' ~, 2 ~
wO 93/15879 PCr/US93/012' for example, silvered fibers from Pofleis Industries of Harsbrouck He~ghts, NJ;
and nickel coated mica from Suzorite Mica Corp. of Boucherville, Quebec, Canada.
The electrically conductive material can be incoIpora~d into conven~onal S nonwoven, fibrous coated abrasive bacl~ing materials which comprise electrically non-conductive fibers (e.g., paper backings, fiber backings, etc.). The preferred - backing is paper.
Preferred electrically non-conductive fibers include, for example, cellulosic fibers (i.e., fibers derived from hardwood pulp or softwood pulp), cotton fibers, 10 or combinations thereof. The non-woven, fibrous backing may further comprise other electrically non~onductive fibers such as synthetic fibers (e.g., polyester fibers,~polypropylene fibers, ghss fibers, polyvinyl alcohol fibers, polyimide .
fibers, rayon fibers, nylon fibers, and polyethylene fibers), natural fibers (e.g., fibers of hemp, kapok, flax, sisa~, jute, manila, and combinations theleof), and15 combina~ons thereof.
PrefeIably, the electrically conductive material forms a continuous network.
Such a network can be formed, for e~wnple, by having the fibers or particles of electrically conductive material touching at least one adjacent fi~er or particle, or by having the fiber or particle in close proximity to each other. The anti-static 20 properties of a coated abrasive article comprising a backing having such a network generally demonstrate supenor antistatic properties as compared to a coated abrasive artide comprising a bacl~ng which does not have such a network.
The elec~rically conductive b2cl~ng may fur~er comprise a binder which serves to reinf~rce the backing and to hold vaIious components of the backing 25 together. Such binders are known in the art and include, for example, polymeric la~ces (e.g., polyac~yla~es ~ e~ylene/vinyl acetate copolymers), rubber (e.g~, styrene/butadiene, neoprene, and butadiene/nitrile), and combinations thereof.
Methods known for incoIporating electrically conduc~ve fibe~s in paper or paper-type sheet material include, for e~tample, ~ose described in U.S. Pat. Nos.
30 3,367,8Sl (Fillds), 4,347,104 (Dr~sler), and 4,909,901 (McAllister et at.).
Tho dectri~lly ~u~ve bacldng may further comprise at least one of a presize (i.e., a barier coat overlying the major surface of the backing onto which thc abrasive laycr is applied), a backsize (i.e., a barrier coat overlying the major - W O 93/15879 2 ~ 2 8 ~ 8 9 PC~r/US93/01252 surface of the backing opposite the major surface onto which the abrasive layer is applied), and a saturant (i.e., a barrier coat that is coated on all exposed surfaces of the backing). Preferably, the electrically conductive backing comprises a presize. Suitable presize, backsize, or saturant materials are ~own in the art.
5 Such materials include, for example, resin or polymer latices, neoprene rubber, butylacrylate, styrol, starch, hide glue, and combinations thereof.
Preferably, the surface resistivity of the backing comprises electrically conductive matedal is less than 2,000 kilo-ohms/square. More preferably, the surface resisdvity of the backing is less than 1,000 kilo-ohms/square, and, most10 preferably, it is less than about 500 ldlo-ohms/square. The surface resistivity is measured by placing the probes of an ohmmeter 1.4 cm apart on a major surface of the backing.
- Some dec~lly conductive backings may have the electrically conductive matedal inanpo~ed therein such that the surface resistivity of a major surface of 15 the backing does not have an electrical resistivity less th~n 2,000 l~lo-ohms per sguare (see, e.g., the backings shown in FIGS. 2 and 3). However, when an abmsive article in accordance with the present invention having such a backing is used, one sldlled in the art will readily realize that ~he backing is sufficiently - electrical~y conduc~ve because the static electricity will be dissipated.
Second ~oated A~rasive Ar~icle Refening to FIG. 4, coated abrasive 49 comprises backing 50 having plu~ality of ab~asive granules 52 bollded to backing 50 by means of bond system 54 which typically consists of first bond coat 56 (generally r~ferred to as a "makeH
25 coat or "make" layer) and second bond coated 58 (gene~ally ~efe~ed to as a "sizeH
coat or nsize" layer). Alte~natively, bond system 54 consists of a single bond coat (e.g., a sluny coat).
Bacldng 50 includes plies 66 and 68, and innerlayer 70. Innerlayer 70 comprises elec~ically conductive material 72 and optional binder 74.
Coaled ab~:asive 49 may also cont~in supersize coat 82. The innerlayer can bc essitially frec of each of cdlulosic fibers and cotlon fibers.
Thc plia of ~c backing may be formed ~om any suitable material known in ~c art, including 91l0ng py~ers, polymeric films, fab~s or cloth, e.g., cotton, : , ~.-) o ~
wo 93/15879 Pcr/uss3/0l25- 12 -and woven and non-woven webs of both natural and synthetic polymeric fibers.
The ply material preferably has a significantly lower electroconductivity than the innerlayer, i.e., it is at least semi-insulating. More preferably, the ply material is a non-conductor (i.e., has an electrical resistivity of at least 10" ohms/square).
S A preferred ply material îs paper having a weight in the range from about 70 to 300 g/m2. Preferably, a paper ply has a weight in the range from about 120 to about 200 g/m2.
The optional innerlayer binder desirably has adhesive properties to bond the innerlayer to the plies. Examples of suitable innerlayer binders include glues 10 obtained from bones (animal glue), gelatin, starch and polymeric resins including phenolic resins, urea-formaldehyde resins, melamine-formaldehyde resins, epoxy resins, acrylate and modified acrylate resins, e.g., homopolymers and copolymersof esters of acrylic acid and methacrylic acid, other latex resins, and combinations thereof.
15Suitabb electroccnduc~ve materials include graphite, carbon black, metals and alloys thereof, elec~oconducdve polymers, and combinations ~ereof. The most preferTed electroconductive material is carbon Uack.
Commercially available graphite useful in the present invention include powdered or colloidal graphite (including a suspension of powdered graphite and 20 oil). Powdered or colloidal graphite is available, for example, under the trade designations "DAG,n "AQUADAG," and "OILDAG" from Acheson Colloids Company of Plymouth, lX.
Useful commercially available metals and alloys thereof include aluminum, silver, gold, copper, iron, lead, tin, zinc, and combinations thereof. The metal25 may be a foil (e.g., ~n foil or aluminum foil). A pref~red metal aUoy is bronze (e.g., a copper-based alloy s~eng~ened with 1 percent by weight cadmium and 0.06 percent by weight ~in).
Useful electncally conduc~ve polymers include p~ly(vinylbenzyl trimethyl ammonium chl~ride), which is commerciaUy availaUe from Polysciences Inc. of 30 ~amngton, PA, and those disclosed in U.S. Patent No. 5,061,294 (P~rmer et al.).
--Other useful dec~ lly conductive material may be hygroscopic salts (e.g., - ~ ~a quaternary salt, including that o~mmerciaUy available unde~ the ~ade designa~on ,~
, :~
,; .

212~0~3 wo 93/15879 - 13 - Pcr/uss3/01252 "EMERSTAT 6660A" from Emery Chemicals of Cincinnati, OH), N,N-bis (2-hydroxyethyl)-N-(3'-dodecyloxy-2'-hydroxy-pro~yl) methylammonium methosulfate (commercially available as a solution, for example, from the American Cyanamid Company of Wayne, NJ, under the trade designation "CYSTAT 609n), 5 stearamidopropyldimethyl-hydroxyethylammonium-dihydrogen phosphate (commercially available as a solution, for example, from the American Cyanamid Company under the trade designation "CYSTAT SP"), stearamidopropyldimethyl-~hydroxyethylammonium nitrate (commercially available as a solution, for example, from the American Cyanamid Company under the trade designation 10 "CYSTAT SNn), (3-lauramidopropyl) trimethylammonium methylsulfate (commercially available, for example, under the trade designation "CYSTAT LS"
from the AmeriG~n Cyanamid Company), and n-alkyl-dimethylbenzyl ammonium chloride (commercially available, for example, from Ony~ Chemical of Jersey City, NJ, und the trade designation "BTC-SOUSP")). For further details 15 regarding hygroscopic salts, see U.S. Pat. No. 4,973,338 (Gaeta et al.).
Preferably, a humectant (e.g., glycerol, polyglycols, polyethylene glycols, polyethers, and polymers of alkylene oxides) is used with a hydroscopic salt.
The carbon black useful in the present invention is an amo~phous modification of carbon, typically formed by the partial combustion of 20 hydrocarbons, which has an outermost oxidized atomic layer due to the exposure to air. The carbon black which is typically aggregated, can be directly incorporated between two plies. Alternatively, the carbon blaek aggregates can be inco~rated between two plies as a dispersion, preferably an aqueous dispersion.
The lat~er is preferred as a dispersion of carbon black aggregates is usually easier 25 to ap~ly onto a mayor surface of a ply when ~e car~on black aggregates are di~persed in a liquid media. Furdler, if the caIbon black aggregates are dis~ersed in a liquid media, prior to their addidon to a binder precursor, a greater percentage of carbon black aggregates usually may be present in she innerlayer binder procur~or while maintaining the proper coating viscosity for the precursor. If the aggDples are not dispersed prior to their sddition to ~c bir~l, ~c viscosi~ of thc ag~s/bi~er precursor is higher, which may lcad to processing difficultia.
Suitable aqueous dispersions of carbon black aggregates are commercially ,~, 2123~
wo 93/15879 PCr/US93/012 available from sources such as FDI Dispersions of Newark, NJ.
Preferably, the carbon black dispersion ~urther comprises one or more dispersing aids. Typically exarnples of commercially available dispersion aids include those marketed under the ~ade designations "DAXAD llG" from W.R.
S Grace of Lexington, MA; "LOMAR PWA" and HNOPCOSPERSE A-23" from Henkel Corporation of Ambler, PA; and "MARASPERSE CBOS~" from Daishowa Chemieals Inc. of Rothschild, WI.
The weight rado of carbon black aggregates to dispersing aid preferably is in the range from about 2:1 to about 30:1. More preferably, the weight ratio is 10 in the ~ange from about 4:1 and about 12:1. If the amount of ~he dispersing aid is too low, the viscosity of the pre~i~persion may be excessive. ~Dn the other hand~ if the amount of dispersing aid is too high unwanted recoagulation of the carbon black aggregates may occur. P~eferably the dispersion compnses in the ~nge from about 1 to about 25 percent by weight carbon black aggregat~s, based 15 on the total weight of the dispersion.
The liquid media for the ~on black aggregate dispersion may be an aqueous, nonaqu~ous (e.g., an orga~c liquid), or a eompatible combination thereof. The liquid media and dispersing aid chosen should be compatible with each other. To avoid the environmental concerns associated with organic liquids,20 the liquid media is preferably water.
As will be recognized by those skilled in the art, it is important to match the proper dispersing aid with the innerlayer binder. If the dispersing aid and the innerlayer binder are not compatible~ the resulting aggregate/innerlayer binder preeursor eomposition may be t~o viscous for easy applica~don to a ma~or su~face25 of a ply. For e~ample, an anionic dispersing aid is pre~e~red with phenolic adhesive systems. (~e s~lled in the binder art should be able to make such an assessment.
. - The aggregate/binder precursor is typically prepared by dis~ng carbon blacl~ aggregates in a liquid medium (e.g., water) containing a di~persing aid, and 30 then mixing the ingredients un~l a homogeneous dispersion is formed. The resul~ng di~on is ~en added to the innerlayer binder precursor. If ~e li~uid medium is water, ~e di~persing aid can be an anionic or non-ionic surfacta~at.
Suitable dispersing aids include, for example, those commercially available under 2~ 2S089 Wo 93/15879 Pcr/us93/01252 the trade designation "LOMAR PWA" and "NOPCOSPERSE A-23" from Henkel Corp. of Ambler, PA and "DAXAD llG" from W. R. Grace & Co. of Lexington, MA.
Preferably, the electrically conductive material forms a continuous network.
S Such a network can be forrned, for example, by having particles of the electrically conductive material touching or by having particles of the electrically conductive material in dose proximity to each other. The anti-static properties of a coatedabrasive article comprising a backing having such a network generally demonstrate superior antistatic properties as compared to a coated abrasive article comprising 10 a backing which does not have such a network.
PreferaUy, the concentration of carbon black in the innerlayer is high enough to provide a conbnuous electroconductive pathway throughout the coating.
Since the electrical conductivity of caioon black is isotropic; that is, it does not rely on the juxtaposition of the carbon along a particular plane to yield an 15 d~ path through the coating, the threshold concerltration of car'oonblack required to provide a continuous electroconductive pathway throughout the coating is generally lower than the threshold conoentration required for other electroconductive matenals, such as graphite, in which the electrical conduc~on is anisotropic. Below the threshold concentration of carbon black there are only20 intermittent electroconductive pathways, formed by short chains of the amorphous carbon Uack aggregates, which is believed to explain the poor and/or erratic electrical conductivity of coated abrasives a~ticles containing low loadings of carbon black. Preferably, carbon black is present in the innerlayer in an amountsufficient to provide an innerlayer with an electrical surface resisdvity of a major 2S surface of the bacldng of less than about 2000 kilo ohms-cm, and most pre~erably, less than about 200 Idlo ohms-cm.
Carbon black aggregates useful in the invention include those formed of a multitude of smaller carbon black particles that are permanently fused together during the manufactunng process. Generalb, these carbon black par~cles are 30 nearly sphencal with diam~s ~gin~ from about 10 nm to about 90 nm. The amount of cubon black in ~e innerlayer neoded to lower the electrical surface resis~vity of the bac~ing to the ange ~pccified above depends on factors including the structure of the aggregate, ~e surface area of the aggregate, the surface ~3~1~8~99 Pcr/Us93/012 chemistry of the aggregate and the size of the carbon black particles comprisingthe aggregate. For equal loadings of carbon black aggregates, reducing the size of the individual carbon black particles comprising the aggregates, while maintaining the other parameters constant, results in a reduction in the electrical 5 surface resistivity of the abrasive article.
Preferably, the size of the carbon black aggregates is less than about 300 micrometers. More preferably, the size of the carbon black aggregates is in the range from about 125 to about 275 micrometers. A mixture of carbon black aggregates having two or more sizes of carbon black aggregates (e.g., a mixture 10 of relativdy large aggregates and rdatively small aggregates) may also be used.
Such mixtures tend to provide a more efficient distribution of carbon black aggregates in the binder.
The structure of carbon black aggregates refers to ~e siæ and configuration of the aggregate. High structure carbon blacks are composed of 15 relativdy highly branched aggregates while low structure car'oon blacks are composed of Idatively small compact aggregates. The structure of carbon black - aggregates is charac~ized by the aggregate's void volume. High structure carbon black contains more void space than low structure carbon black because the former has a highly branched shape that prevents close packing. One common way of 20 quantifying structure is the Dibutyl Phthalate Absorption Test. This test measures the volume of dibutyl phthalate (in ml~ absorbed by 100 grams of carbon black, which is a measure of the amount of fluid required to fill the voids be~ween aggregates. The dibu~l phthalate absoIption can be used as a guide to structure level because, for a given surfa~e are~, the higher ~e structure, the higber the25 dibutyl phthalate abso~ption will be. For equal loadings of carbon black aggregates, increasing the structure of the carbon black aggregates used, while maintaining the other parameters constant, results in a reduc~on in the electrical surface resis~vity of an innerlayer compri~ing a cured inne~layer binder and carbon black agg~egates. Preferably, the carbon black aggregates have a dibutyl phthalate 30 abso~ption in the ~ange f~om ~t 50 to about 400 ml/l00 g. More preferably, - thc dibulyl phtbable ab~ n is in the~ range from about l00 to about 400 : ' ml/100 g.
:
In the manu~actu~ing of carbon black, chemisorbed oxygen complexes, such 21~ 08 ~
WO 93/1~i879 PCI`/US93/01252 as carboxylic, quinonic, lactonic and hydroxylic groups, typically form on the surface of the aggregates. These adsorbed molecules act as an electrically insulating layer. Decreasing the volatile content of the carbon black aggregateswhile maintaining the other parameters constant, result~ in a reduction of the 5 electrical surface resistivity of an innerlayer comprising a cured innerlayer binder - and carbon black aggregates. At volatile contents greater than about 4 percent by weight, based on the weight of the carbon black present, the carbon black aggregates are electrically non-conductive. Preferably, the volatile content of the carbon black aggregates is less than about 3 percent by weight, more preferably,10 less than about 2 percent by weight.
The reduction in the electrical surface resistivity of an innerlayer comprising binder and carbon black aggregates is also a function of the surface area of the carbon black aggregates. Por equal loadings of carbon black aggregates, increasing the surface area of the car'oon black aggregates, while 15 maintaining the other parame~s constant, results in a reducdon in the electrical ~; surf~ce resistiviq of the cured binder. Preferably, the sutface area of the ca bon black aggregates is in the range from about 100 to about lOQ0 m21g. More prefaably, the surface area of the carbon black aggregates in the range from about 130 to about 1000 m2/g.
Preferably, the total solid content of an uncured innerlayer binder according to the present invention is in the range from about 20 to about 75 percent by w~ight. More preferably, the t~tal solids con~ent is in the range from about 35 to about 65 percent by weight.
In another as~ect, the viscosi~ at 25C of an uncured innerlayer binder according to the present invention is p~eferably in the range from about 25 to 2000 cps. The viscosi~ is preferably measured using a Brooh'ield viscometer ~e.g., a Brookfield Model DV-II digital viscometer from Brool~leld Engineering I~boratofies, Inc. of Stoughton, MA) with a number 2 spindle at 20 Ipm. More preferably, the viscosity at 25C of ~e uncured innerlayer binder is in ~e rangefrom about 100 to about 1000 ~ps, and most preferably, in the ~ange from about 100 eo about 750 cps.
The innlayer bind can be cured by conventional means including heat.
The innerlayer of elec~ically conductive material can be incorporated into ' ~

.

212~0~9 wo93/1~879 - l8- PCr/USs3/012 the backing of the coated abrasive article during the fabrication of the backing or during any convenient or desired time thereafter. If incorporated into the backing after fabrication of the backing, one or more plies comprising the backing can be removed. The electrically conductive material can then be applied to the newly 5 exposed surface of the backing, for example, by coating a dispersion of the electrically conductive material, or by coating a dispersion/binder composition.The ply(s) that is removed can then be reattached to the backing, for example, by using an adhesive such as glue, or if the innerlayer comprises a binder, the binder may serve as the adhesive.
Coated Abrasive Construction With ~e exception of the electrically conductive backing, ~e inventive coated abrasiw articles can be prepared using materials and techniques known in the art for constructing coated abrasive ar~cles.
15The preferred bond system is a resinous or glutinous adhesive. Examples -~ of ~ res~nous adhesiv include phenolic resinsS urea-formaldehyde resins,~an~i_~a~ resin, epoxy resins, acrylate resins, urethane resins, and s thereof. The bond system may contain other additives which are well lalown in the art, such as, for example, grinding aids, plasticizers, fillers, 20 coupling agents, wetting agents, dyes, and pigments.
PreferaUy, the abrasive grains are selected from such known grains as fused aluminum oxide, heat-~eated aluminum oxide, ceramic aluminum oxide, co-fused alumina-zirconia, garnet, silicon carbide, diamond, cubic boron nitride, and combinations thereof.
25Examples of useful materials which may be used in the supersize coat include the metal salts of fatty acids, urea-formaldehyde, novolak phenolic ~ns,waxes, n~ine~al oils, and fluo~ochemicals. The preferred supersize is a metal salt o a fatty acid such as, for example, zinc stearate.
In the first prefe~red convendonal method for prep~ing a coated abrasive - 30 ar~cle, a make coat is appDed to a major swfilce of the electrically conducdve `~ ~ backing followèd by pr~jecting a plu~ality of abrasive gr.uns into the make ooat.
~ ~ It is pref~bb in plepa~,ne the coated ~b~asive that *e abrasive grains be ~ ~ ~b coated. The make coating is cured in a manner sufficient to at ~ :
~, wo 93/1s879 2 1 2 ~ ~ 8 9 Pcr/us93/01252 least partially solidify it such that a size coat can be applied over the abrasive grains. Next, the size coat is applied over the abrasive grains and the make coat.
Finally, the make and size coats are fully cured. Optionally, a supersize coat can be applied over the size coat and cured.
SIn the second preferred conventional method for preparing a coated abrasive - article, a slurry containing abrasive grains dispersed in a bond material is applied - to a major surface of the backing. The bond material is then cured. Optionally, a supersize coat can be applied over the slurry coat and cured.
The coated abrasive article according to the present invention can be in the 10 shape of c~nventional coated abrasive articles, for example, belts, discs, sheets, and strips. The most preferred shape is a belt.
In the above methods, the make coat and size coat or slurry coat can be solidified or cured by means known in the art, including, for example, heat or radiation energy.
15The co;~d abrasive article according to the present invention can be in the shape of ~ coated abrasive articles, for example, belts, discs, sheets, and strips. The most preferred shape is a belt.
The incoIporation of the electrically conductive backing into the coated abrasive construction provides cenain desirable antistatic proper~es. Although not 20 wanting to be bound by theory, it is believed that the electrically conducdve coated ~- abrasive according to the present invention rapidly dissipates static electricity generated during the abrading of electrically insulating workpieces. When the static electricity is dissipated, the worl~piece dust pardcles gene~ated in the abrading ope~ation are removed by the normal exhaust systems. If the static 25 electricity is not dissipated, ~e worl~piece dust particles ca~ry a charge, and may not be removed as readily by the no~nal exhaust system.
The present invention pro~ides a coated abrasive a~cle which provides a solution toi the serious sta~c electricity build-up problem associated with abrading a workpiece with a coated abrasive article.
30Obiects and advan_ of this invention are further illustrated by the foD~ing ;o~ es, but~e par~cular n~rials and amounts ~eroof recited in ~esc e~unple5, as wdl as other~ cooAitions and details, should not be construed ~-;to undub limit thîs imention. All parts and percentages are by weight unless ~ : ' 21280~9 otherwise indicated.

Procedure for Makin~ a o~t~rasive Article An unfilled phenol resorcinol formaldehyde resin make coat (64% solids) S was applied to a major surface of the backing specifi~d in the example or control to provide an add-on wet weight of about 45 +5 grams/square meter.
- Immediately thereafter, grade P150 fused aluminum oxide abrasive was electrostatically projected into the make coat to provide an add-on weight of 132 +8 grams/square meter. The make coat was precured for 90 minutes at 88C in 10 a forced air oven. Ne~t, a calcium carbonate filled resole phenolic resin size coat (76* solids) was coated over the make coat and abrasive granules to provide a wet add-on weight of 59 _8 grams/squa~e meter. The make and siæ coat were then final cured for 10 hours at 100C. The resulting coated abrasive was then conventionally flexed and rehumidified to prevent the paper from becoming brittle.

Pro~ures f~or_Teffl~he (~oated Abrasiye Test Procedure I
The coated abrasive was then converted into 16 cm by 762 cm endless 20 co~ted abrasive belts and installed on an Oaldey Model D Single Belt Stroke Sander. The coated abrasive belt abraded three red oak workpieces for seven minutes each. The pressure at the interface was approximately 0.20 Newton/square cen~meter. The belt speed co~sponded to about 1670 surfa~e meters per minute. I~e ~ount of red oak removed (cut) was measured and the 25 amount of dust (swar~ llected on metal plate immediately past thie workpiece holder was detern~ined. Ibe amiount of red oak ~em~ved was divided by the amount of dust collected to gene~ate a dimensionless "Dust Ef~lciency Factor"
(l~EF). High values of the DE~; indicate that the production of du~t uncollectedby the exhaust system was low.
30 Test;Procedures II
Test P~e II is ~e same as Test Procedure I except six rod oak , ~
- wor~pieces we~e abr~ded fo¢ about S minutes each.

WO93/15879 2~2~n~9 P~/US93/01252 Example 1 cl~ng P~p A 3-ply, 0.32 mm thick backing having a basic weight of about 280 g/m2 was prepared as described in U.S. Pat. No. 4,909,901 ~IcAllister et al.). The S two outer plies were formed from a cellulose blend containing montmorillonite clay in an amount sufficient to eliminate the capacitor effect between the outer ply and the inner plies. The outer plies had a surface electrically conductivity of about 101 ohms/square. The inner ply was formed from a carbon fiber/cellulose blend containing about 10 percent of 1.25 cm (0.5 inch) long carbon fibers 10 (commercially available under the trade designation "CARBO~LEX" of Ashland Oil Company of Ashland, KY.
;Specifically the backing was prepared using a conventional wet paper m~ng machine using ~ree vats. The vats supplying ~e feed for ~e two outer piies contained a 3 pera nt solids aqueous dispersion wherein the solids comprised 15 bleached nor~rn so~wood Kraft wood pulp (commercially available under the ~-trade desi~gnation "HARMAC R" from MacMillian Bloedel of Nanaimo, Bri~sh Columbia). The vat supplying the feed for the inner ply contained a 3 percent solids aqueous dispersion wberein the solids comprised about 90 percent bleach northern softwood Kraft wood pulp ("HARMAC R") and about 10 percent of the 20 carbon fi~ers.
-The external surfaces of the outer plies were coated with an aqueous disI>ersion comprising about 10 percent montmorillonite clay (commercially available under the trade designa~on "VAN GEL B" from R. T. Vande~bilt Company of Norwalk, CT3 using a conventional ver~cal size press. The coated 25 backing was then ste~un dried using a heated drier can. The dried coated bacldng had a surface elec~ical resistivity of about l0~ ohmslsquare at 50% rela~ve humidity.
A coated abrasive article was prepared using this backing acc~rding to ~e method entitled "Procedure for Making a Coated Abrasive Article," above. The 30 abrasive hyer was coated on the fdt side.
Tl# coated ab~Ye ar~cle was tested according to ~Test Procedure I,"
above. The results are shown in Table I b~low.
' ~ -;~ ~
,;

212SO~
WO 93/15879 - 22 - P~r/US93/Ol Table 1 Amount of Amount Workpiece of Dust S Removed, Collected Example Grams Grams DEF
811 11 73.7 Con~ol A 596 221 2.7 Control A
A control coated abrasive ar~cle was pr~parcd and tested in the same manner as Example 1 except ~e bacl~ng was an E weight cylinder paper (basis weight of about 240 g/m23.
It can be seen from the above data that the use of the electrically conductive backing significantly increased the cut (i.e., the amount of workpiece removed) and dramatically reduced the amount of dust ~i.e., swarf~ accumul~ted.
Example 2 A backing was prepared as descr~ed in E~ample 1 except the backing had 20 four plies, and the carbon fibers were in outer ply on the "~e side. ~ The other thr~e plies did not contain electncally conductive material.
A coated ab~ive ar~cle was pre~ared using ~s backing according to the method entitled "Procedure for Maldng a Coated Abrasive Article" above. The abrasive layer was coated on the rfelt side."
The coated abIasive article was tested according to "Test Procedure II"
aboYe. The results are shown in Table 2 below.
Table 2 Amount of Amount Wo~l~iece of Dust R~m~ved, Collected F~mple G~m~. Qr~ns Dl~F
. .
2 596 0.6 993.3 3$ Conbol B S10 80 6.4 It can be seen from the above d~ta that ~e use of the electriG~ly conductive bacl~ng significantly incr~ the cut (i.e., ehe amount of worl~iece removed) 2~ 2~0~
- wo g3/.5879 Pcr/us93/01252 - ~3 -and dramatically reduced the amount of dust (i.e., swarf~ accumulated.
Control_B
The Control B coated abrasive was a PlS0 closed coat, resin bond coated abrasive belt (commercially available under the trade designation "Pl50 3M 363I

BELT" from the 3M Co. of St. Paul, MN).
It can be seen from the above data that the use of the electrically conductive backing significantly increased the cut (i.e., the amount of workpiece removed) and dramatically reduced the amount of dust (i.e., swarfl accumulated.
l0 ~xamples 3-6 The stabc electric decay of several coated abrasive backings with or without an abrasive layer coated thereon were measured using a commercial static decay meter ~Mode1406 C STATIC DECAY METER; Electro-Tech Systems, Inc., of Glenside, PA), wherdn each backing`was charged to +5000 volts, and wherein lS the cutoff levd of the static decay meter was set at 0% .
Example 3 was a 90 lb., 4 ply cylinderpaper with l0 percent carbon black in all 4 plies, commercially available under from Specialty Coatings Group, Inc.of Richmond, VA, under the trade desig~ion "CARBON BLACK SHIELDING
MEDIA, GRADE 99l26."
Example 4 was a ll0 lb., 4 p~y cylinder paper with 2.5 percent carbon ~ ~ black in all 4 plies, commercially available under from ~pecialty Coa~ngs Group, - ~- ~c. under ~e trade designation "CARBON BLACK SHIELDING MEDIA, 9l22 Example 5, a 1 ply b~cking with nickel coated mica particles (cor;.~nercially 25 available from Suzorite Mica Corp. of Boucherville, Quebec, Canada), was plepaTcd as follows. An indus~ial size blender (commercially available under thetrade designation "WARING BLENDOR" from Waring P~oducts Div., Dynamic Corp. of America of New Hartford, CT) was charged with waeer, bleached nor~ern softwood Kraft wood pulp ("HARMAC R"), and nickel coated mica in 30 amounts sufficient to provide a 3 percent solids dispersion having a 4:1 weight of wood~lp to r~l ~aled mica. The ingredients were thoroughly mi~ced in ~e bl~r. Tlie Dsul~ng dispsion was transferred to a Noble and Wood shest macllne (commercially available from Noble and Woods Machine Co. of ; :

~lzsn~
W 0 93/15879 - 24 - PC~r/US93/0125 Hoosick Falls, NY). The dispersion was then diluted with water to pravide a 0.5 percent solids aqueous dispersion. A sheet was made using the sheet machine.
The sheet was lightly pressed between two felt pads to remove some of the water,and then dried on a heated drier can.
S Example 6, a 1 ply, E wt. backing with about 50 percent stainless steelflake (particles) (commercially availaUe from Novamet Co~. of Wyckoff, NJ), was prepared as described for Example 5 except the solids portion of the dispersion comprised about 40 percent ' bleached northern ~aft wood pulp (nHARMAC Rn), about 10 percent of the stainless steel flake, and about 10 10 percent acrylic latex (commercially available under the trade designation "HYCAR
2671" from B. P. Goodrich of Cleveland, OH).
Prior to maldng the static decay measurements, each sample was conditioned for about 12 days by placing it in a chamber having a relative humidity of about 35 percent. The condidoned samples were cut into pieces about 7.6 cm (3 inches) by about 12.7 cm (5 inches). The average of four static decay measu~s for each sample are given in Table 3, below. The measurements were made on the backside (i.e., the felt side) of the sample (i.e., the side opposite that which the abrasive layer was or would be coated on)~
Control C was an E wt. cylinder paper commercially available under the trade designation "130 # CYLINDER SAND (P0502-0)" from Specialty Coatings Group, Inc.
Control D was an F wt. cylinder paper commercially available under the trade designation "165 # CYLINDER SAND (P0502-0)" from Special~ Coa~ngs G~oup, Inc.
Comparative I, an E wt., 1 ply backing with about 50.3 percent (12.8 volume percent) iron powder ~commercially available unde~ the trade designation "CARBONYL IRON~ from G.A.F. Chemical of Wayne, NJ) was pre~ared as described in Example S except the 3 percent solids aqueous dispersion comprised 39.7 percent northern softwood Kraft wood pulp (nHARMAC R"), 10 percent acrylic la~ (-HYCAR 2671"), and 50.3 percent of the iron powder.

212~08~
wo 93/15879 Pcr/us93/ol2s2 Table 3 Time to discharge +5000 v~lts, Example Description s~c.
lA-2A Coated abras*e bac~ng O.Ol used to prepare Examples or less 1 and 2 Example l 0.02 Con~ol A 0.08 2 Ex~nple 2 0.02 Con~ol B 0.12 20- Control C E wt. sylinder paper 0.06 Control D P wt. cylinder paper 0.06 3 90 lb. cylinder, 1 ply O.Ol paper with lO wt% car~n or less black 4 llO lb. cylinder ply paper O.Ol with 2.5 wt% carbon black S E wt. cylinder paper with O.Ol 20 wt!~ nickel coated mica or less par~icles 6 E wt. cylinderpaper with 0.û2 50 wt% stainless s~eel flake (par~cles) Compara- E wt. cylinder paper with 0.40 ~ive I 50.3 wt. % (12.8 volume %) iron powder The above stadc elec~ic decay measurements illus~ate the reduction of 45 static eJec~ic build-up in pa~er suitable for use a~ coated abrasive bacl~ngs or a coated abrasive ar~cle having a paper backing wherein a sufficient amolmt of elec~ically conduc~ve material has been incorporated therein. The "dme to 212~089 wo 93/15879 PCr/uss3to discharge +5000 volts" value for Comparative I was surprising. It was expected that the Comparative I construction would have a "time to discharge +5000 volts"value similar or the same as that recorded for Examples lA-2A and 1-6. A
backing having the Comparative I construction was not made into a coated abrasive S article. Based on a comparison of the grinding data and static decay measurements above, it appears that a coated abrasive article having a backing with the Comparative I construction would not exhibit a reduction in the accumulation of static electric charge in the coated abrasive article during the abrading of a workpiece. The reason why the Comparative I construction provided such a high 10 "time to discharge +5000 volts" value is unhlown. One possible explanation isthat the iron par~cles, or a portion thereof), oxidized during preparadon of theComparative I construction, providing an electrically insulating material rather than an electrically conducting material.
ample 7 E~ample 7 was prepared as follows. A P150 coated abrasive belt (for woodworking) having a cylinder paper backing (2740mm x lOOmm; 300 g/m2), a phenolic resin make and size, and semi-friable alun~ina abrasive partides was prepared using conventional techniques. The surface ply of the pnntside of the abrasive belt was delaminated. This ply was coated with a dispersion of carbon 20 black having the following formulation:
60 per~ent water;
8 percent of a sodium naphthalene sulphonate-formaldehyde copolymer dispersing agent (commercially available under the trade designation "DAXAD llG~ from W.R. (irace & Co. of Lexington, MA)/water mixture (23 parts dispersing agent:77 parts water);
16 percent carbon black (commercially available under the trade designation "VULCAN XC-72R" from Cabot CoIporation of Boston, MA~; and 16 percent e~ylene glycol monoethyl ether The coa~al di~persion was ~en dried for about 15 minutes at about ~0C.
The ply was then reattached to the coated abrasive using an acrylic copolymer 212gO8~
W O 93/15879 PC~r/US93/01252 - 27 -pressure sensitive adhesive (commercially available under the trade designation "VANTAC 343" from Bevaloid Ltd. of Beverley, North Humberside, United Kingdom) to create a carbon black innerlayer within the paper backing.
The abrading performance of the resulting coated abrasive belt was then 5 tested by abrading 10 pine workpieces for a period of 30 seconds each using a backstand belt machine (trade designation "MEGGAMASTER") from Meggit Engineering Ltd. of Bournemouth, UK. A constant load was applied using a handheld force gauge. The contact area was about 6.5 cm2 (1 in.2). The speed of the abrasive belt was about 20 meters/second (4000 feet/minute).
10The Control E coated abrasive belt prepared and tested as described for E~ample 7, except t~he belt was not d:elaminated, nor was electrically conductive material i~c p:~ated therein. ~ ~
~ ~ Contlol E produced a significant accumulation of wood dust on the metal - claddir~5 parts of the belt machine;afte~ only five minutes of abrading. After an 15 oquival= peliod of abrading with the E~ample 7 belt, the~machine remained clean strating~thatgooddustc~ontrolwasbeingachieved. ~

A commelcially avail!e woodworxing paper belt P180 (available under the trade designation "3M 250 UZ" firom the 3M Company), which includes on 20 the pnntside of the belt a arbon black-based electrically conductive ink (commercially available under the trade designation "LORRILEAUX 62120 ANTI-STATIC INK" from Lorrileaux International of Prance), was treated as follows.
The ink-coated ply of dle printside of the belt was delaminated. Using an adhesive (commercially available under the trade designation "3M DISC PAD
25 ADHESIVE OB054" ~om ~e 3M Company), the ply was reattached to the coated ablasive such that the coated ink was sandwiched within the bacl~ng.
The resulting coated abrasive belt was ~en tested on pinewood as descri~
in Exampb 7. Thmll hout the test pedod the machine remained clean, demonstradng the ef~ctiveness of ~e presence of the electrically conducdve ink 30 within~the b~mg at rcducmg the buildup of static dectricity dudng ~e abrading of - w~pi~. ~

. .
r ~f '~
", ,, ,~"~
~ .

.",:, , , 2 ~ 2 ~ '3 wo 93/15879 PCr/US93/012 Various modifications and alterations of this invention will becolhe apparent to those skilled in the art without departing from the scope and spirit of this invention, and it should be understood that this invention is not to be unduly limited to the illustrative embodiments set forth herein.
s

Claims (43)

What is Claimed is:

1. A coated abrasive article comprising (a) a nonwoven, fibrous backing comprising at least one ply, wherein said ply comprises electrically non-conductive fibers and electrically conductive material; and (b) an abrasive layer bonded to one major surface of said backing;
wherein said electrically conductive material is at least one of electrically conductive fibers selected from the group consisting of graphite fibers, carbon fibers, metal fibers, electrically conductive polymer fibers, and combinations thereof; and electrically conductive particles selected from the group consisting of graphite particles, carbon particles, metal particles, electrically conductive polymer particles, and combinations thereof; and wherein said electrically conductive material is present in an amount sufficient to reduce accumulation of static electric charge in said coated abrasive article during abrading of a workpiece.

2. The coated abrasive article according to claim 1 wherein said ply comprises in the range from 0.75 to about 15 percent by volume of said electrically conductive material, based on the total volume of said ply and saidelectrically conductive material comprising said ply.

3. The coated abrasive article according to claim 1 wherein said ply comprises in the range from about 4 to about 12 percent by volume of said electrically conductive material, based on the total volume of said ply and saidelectrically conductive material comprising said ply.

4. The coated abrasive article according to claim 1 wherein said ply comprises in the range from about 5 to about 8 percent by volume of said electrically conductive material, based on the total volume of said ply and saidelectrically conductive material comprising said ply.

5. The coated abrasive article according to claim 1 wherein the largest dimension of said electrically conductive particles is less than about 75 micrometers.

6. The coated abrasive article according to claim 1 wherein said electrically conductive fibers have a length in the range from about 0.1 to about 2 centimeters.

7. The coated abrasive article according to claim 1 wherein said electrically conductive fibers have a length in the range from about 0.1 to about 1 centimeter.

8. The coated abrasive article according to claim 1 wherein said electrically conductive fibers have a diameter in the range from about 2 to about 20 micrometers.

9. The coated abrasive article according to claim 1 wherein said electrically conductive material is at least one of electrically conductive fibers selected from the group consisting of graphite fibers, carbon fibers, metal fibers, electrically conductive polymer fibers, and combinations thereof; and electrically conductive particles selected from the group consisting of graphite particles, carbon particles, metal particles, electrically conductive polymer particles, and combinations thereof.

10. The coated abrasive article according to claim 1 wherein said electrically conductive material is carbon fibers.

11. The coated abrasive article according to claim 10 wherein said carbon fibers contain at least 80 percent by weight carbon.

12. The coated abrasive article according to claim 10 wherein said backing comprises in the range from about 4 to about 25 percent by weight of said carbon fibers, based on the total weight of said backing and said carbon fibers comprising said backing.

13. The coated abrasive article according to claim 1 wherein said backing comprises in the range from about 5 to about 25 percent by weight of said electrically conductive material, based on the total weight of said backing and said electrically conductive material comprising said backing, and wherein said electrically conductive material is carbon fibers.

14. The coated abrasive article according to claim 1 wherein said electrically non-conductive fibers are selected from the group consisting of cellulose fibers, cotton fibers, and combinations thereof.

15. The coated abrasive article according to claim 1 wherein said backing comprises at least two plies, said electrically conductive material being located essentially in at least one of said plies.

16. The coated abrasive article according to claim 1 wherein said backing comprises an inner ply interposed between two outer plies, said electrically conductive material being located essentially in at least one of said plies.

17. A coated abrasive comprising:
(a) a backing comprising at least two plies and an innerlayer interposed between at least two of said plies, said innerlayer comprising an electrically conductive material; and (b) an abrasive layer bonded to one major surface of said backing, wherein said electrically conductive material is present in an amount sufficient to reduce accumulation of static electrical charge in said coated abrasive article during the abrading of a workpiece.

18. The coated abrasive article according to claim 17 wherein said plies are independently selected from the group consisting of paper, polymeric film, and cloth.

19. The coated abrasive article according to the claim 18 wherein said plies are independently one of a woven ply and a nonwoven ply.

20. The coated abrasive article according to claim 17 wherein said innerlayer further comprises a binder.

21. The coated abrasive article according to claim 20 wherein said binder is selected from the group consisting of phenolic resin, urea-formaldehyde resin, melamine-formaldehyde resin, epoxy resin, urethane resin, acrylate resin,latex resin, and combinations thereof.

22. The coated abrasive article according to claim 17 wherein said electrically conductive material is a material selected from the group consisting of graphite, carbon black, an electroconductive polymer, a metal, and combinations thereof.

23. The coated abrasive article according to claim 22 wherein said metal is selected from the group consisting of aluminum, iron, tin, nickel, copper, zinc, silver, gold, lead, and combinations thereof.

24. The coated abrasive article according to claim 17 wherein said electrically conductive material comprises powdered or colloidal graphite.

25. The coated abrasive article according to claim 17 wherein said innerlayer has an electrical conductivity of less than about 2,000 kilo-ohms-cm.

26. A method of making a coated abrasive article having a reduced tendency to accumulate static electric charge during the abrading of a workpiece, said method comprising the steps of (a) providing a nonwoven, fibrous backing comprising at least one ply, wherein said ply comprises electrically non-conductive fibers and electrically conductive material; and (b) applying an abrasive layer to a major surface of said backing, wherein said electrically conductive material is at least one of electrically conductive fibers selected from the group consisting of graphite fibers, carbon fibers, metal fibers, electrically conductive polymer fibers, and combinations thereof; and electrically conductive particles selected from the group consisting of graphite particles, carbon particles, metal particles, electrically conductive polymer particles, and combinations thereof; and wherein said electrically conductive material is present in an amount sufficient to provide a coated abrasive articlehaving a reduced tendency to accumulate static electric charge during the abrading of a workpiece.

27. The method according to claim 26 wherein said ply comprises in the range from about 0.75 to about 15 percent by volume of said electrically conductive material, based on the total volume of said ply and said electricallyconductive material comprising said ply.

28. The method according to claim 26 wherein said ply comprises in the range from about 4 to about 12 percent by volume of said electrically conductivematerial, based on the total volume of said ply and said electrically conductivematerial comprising said ply.

29. The method according to claim 26 wherein the largest dimension of said electrically conductive particles is less than about 75 micrometers.

30. The method according to claim 26 wherein said electrically conductive fibers have a length in the range from about 0.1 to about 2 centimeters.

31. The method according to claim 26 wherein said electrically conductive fibers have a diameter in the range from about 2 to about 20 micrometers.

32. The method according to claim 26 wherein said wherein said electrically conductive material is at least one of electrically conductive fibers selected from the group consisting of graphite fibers, carbon fibers, metal fibers, electrically conductive polymer fibers, and combinations thereof; and electrically conductive particles selected from the group consisting of graphite particles, carbon particles, metal particles, electrically conductive polymer particles, and combinations thereof.

33. The method according to claim 26 wherein said electrically conductive material is carbon fibers.

34. The method according to claim 33 wherein said carbon fiber contains at least 80 percent by weight carbon.

35. The method according to claim 26 wherein said electrically non-conductive fibers are selected from the group consisting of cellulose fibers, cotton fibers, and combinations thereof.

36. The method according to claim 26 wherein said backing comprises at least two plies, said electrically conductive material being located essentially in at least one of said plies.

37. The method according to claim 26 wherein said backing comprises an inner ply interposed between two outer plies, said electrically conductive material being located essentially in at least one of said plies.

38. A method of making a coated abrasive article having a reduced tendency to accumulate static electric charge during the abrading of a workpiece, said method comprising the steps of:
(a) providing a backing comprising at least two plies and an innerlayer interposed between at least two of said plies, said innerlayer comprising an electrically conductive material; and (b) applying an abrasive layer to a major surface of said backing, wherein said electrically conductive material is present in an amount sufficient to provide a coated abrasive article having a reduced tendency to accumulate static electric charge during the abrading of a workpiece.

39. The method according to claim 38 wherein said plies are independently selected from the group consisting of paper, polymeric film, and cloth.

40. The method according to claim 38 wherein said innerlayer further comprises a binder.

41. The method according to claim 38 wherein said electrically conductive material is a material selected from the group consisting of graphite, carbon black, an electroconductive polymer, a metal, and combinations thereof.

42. The method according to claim 41 wherein said metal is selected from the group consisting of aluminum, iron, tin, nickel, copper, zinc, silver, gold, lead, and combinations thereof.

43. The coated abrasive article according to claim 41 wherein said electrically conductive material comprises powdered or colloidal graphite.