CA2015720C - Patterned coated abrasive for fine surface finishing - Google Patents

Abstract

Coated abrasive material for fine finishing applications including second fining ophthalmic application, having patterned surface coating of abrasive grains dispersed in radiation-cured adhesive binder. The patterned surface coating is defined by a plurality of formations of such abrasive/binder each having an inner bottom edge defining an area devoid of coated abrasive, a top edge defining a somewhat larger area devoid of coated abrasive and an inner wall connecting the top and bottom edges.

Description

- ~- 2 ~ 7 2 ~

PArTERNED COATED ABRASIVE FOR
FINE SURFACE FINISHING

BACKGROUND OF ~HE INVENTION
(a.) Field of the Invention This invention relates to specific, radiation-cured, coated abrasive products having novel patterned surface coatings useful in the ophthalmic, crankshaf' and other fine finishing operations such as the sanding of automotive parts requiring a combination of controllable fine surface finishin~ and high cut rate.
(b.) Description of the Prior Art The so-called conventional manufacture of coated abrasive material requires, in general, the coating of a ~maker~ coat, i.e., a solvent or water-based adhesive composition, ~nto a backing member, followed by the application of grain thereto by electrostatic deposition. The curing of the maker coat, i.e., the adhesive or binder layer, to adhere the grain to that layer and the maker coat layer to the backing member is by thermal curing 2~ and, generally, requires a relatively long time, e.g., up to several hours in some cases. This is accomplished while passing the coated abrasive material through a loop dryer. While a loop dryer allows for long drying and curing times, the use of such is attendant with certain disadvantages such as the formation of defects where the material is suspended, sagging of the maker coat before it becomes sufficiently hardened and changing of the grain position due to the material being vertically suspended, variations in temperature and the resulting inconsistent cross-linking of the binder compricing the maker coat due to the necessarily slow air circulation.
In addition to the maker coat, a size coat is also generally applied over the abrasive grains, in the manufacture of conventional coated abrasive material, sometimes before the maker ~1 201~720 coat is completely cured. This coat also necessitates curing and passing of the coated abrasive material through a loop dryer due to the relatively long curing times required. Also, in some cases, the backing member, particularly if of cloth, need be provided with a so-called ~back~ coat and a pre-size coat, prior to the application of the maker coat. Thus, the conventional manufacture of coated abrasive material requires not only a considerable time for thermal curing of various coatings involved in its manufacture, but also, as earlier pointed out, is accompanied with certain necessary defects resulting from the manner of manufacture involved.
In somewhat more recent times, it has been suggested that a reduction in the manufacturing time for coated abrasive material could be achieved through curing of the various coating materials involved by electron beam radiation. Thus, in U.S. 4,047,903, which issued on September 13, 1977 to Hesse et al, there is disclosed coated abrasive material which is manufactured by coating a backing member with at least one base layer of a binder resin hardenable by irradiation, at least one intermediate layer of abrasive grains, and at least one top layer of binding resin hardenable by irradiation. The binder resin comprises, in general, the reaction product of a polycarboxylic acid with an esterified epoxy resin, prepared by the reaction of an epoxy resin with a member selected from the group consisting of acrylic acid and methacrylic acid and the reaction product of such an epoxy resin first reacted with diketenes and then reacted with a chelate forming compound. Although the binder system is different than found in the conventional coated abrasive materials, the construction is much the same. Neither is there any suggestion ~y Hesse et al that patterned surface coatings can be obtained.
Subsequently, in United States Pat. No. 4,457,766, which issued July 3, 1984, on an application filed October 8, 1980, and which is now assigned to Norton Company, the Assignee of the l ~1 instant application, there was disclosed another binder system for use in the manufacture of coated abrasive material. Such a binder system comprises, in general, an oligomer, a d luent, fillers an minor amounts of other additives, the various components being selected in each case to give the desired physical properties to , the coated abrasive material manufactured. The oligomer selected, as disclosed by the patentee, can be any reactive polymer which gives the desired properties to the backing member and the coated abrasive material. Suitable electron beam curable materials lo disclosed are urethane-acrylates and epoxy-acrylates.
Particularly preferred are the diacrylate esters such as the diacrylate esters of bisphenol-A epoxy resin. Among the diluents . disclosed, which are disclosed by the patentee to be utilized to adjust the viscosity of the binder so as to be suitable for the various coating methods to be used, are the vinyl pyrrolidones and ` the multifunctional and monofunctional acrylates. The compounds that are disclosed to be preferred by the patentee are N-vinyl-2-pyrrolidone (NVP): 1,6 hexanediol diacrylate (HDODA);
tetraethylene glycol diacrylate (TTEGDA); and trimethylopropane triacrylate (TMPTA). Such materials have been found by the , patentee not only successfully used in adjusting viscosity and controlling flexibility, but also in reducing the radiation required for curing. The coated abrasive materials disclosed, nevertheless, are of the conventional type long manufactured except that an electron beam curable binder is used. Thus, a cloth backing member may be provided with a back and face fill of the binder, as conventionally done, and partially cured prior to a?plication of a maker coat, all of which may comprise the same components but in somewhat different formulation. Following application of the maker coat, abrasive grain is app!ied to t~.e maker coat and the maker coat is then cured by electron beam through the backing member. The size coat of similar formulation 201~720 as the maker coat is then applied and cured. Patte~ned surface coatings are not disclosed or even ruqgested.
~ he manufacture of coated abras$ve material characterized by various patterned curface coatings of abrasive material has long been disclosed by those ~n the art. Examplary of prior art patents showing euch abrasive coatings are United States Patents Nos. 1,657,784; 2,108,645; 3,60S,349; and 3,991,527. In U.S.
1,657,784, there is disclosed a coated abrasive material in which various adhesive patterns can be provided on a backing me~ber by means of a roll coater, followed by application of grain to the adhesive coating before it hardens. ~he desired pattern can be provided in relief on the roll or cylinder used in the adhesive coating. In general, the pattern consists of regular and uniforr alterations of abrasive ~nd non-abrading portions with definite channels for the exit from the abrading surface of t~e dust or particles produced by the abrasion operation.
U.S. 2,108,645 discloses coated abrasive material in whic~. a backing me~ber is provided with an intermittent or discontinuous coating of adhesive. This is accomplished by passing the backing member between two rollers, one of which is smooth and rotates in an adhesive bath. The other roller has a pattern of depresse~
portions thereon each surrounded by a raised portion. The portior of the backing member which comes opposite the depressions receives adhesive from the smooth roller while that coming under the raised portions receives relatively little. Thus, there results, when abrasive grain i5 applied, essentially a pattern of islands of abrasive grain ~urrounded by areas or c~annels ~it~.
little or no ~rain ~tuck to the backing member.

B

201~720 In U.S. 3,60S,349, there is disclosed an abrasive finishing article compri~inq, in general, a backing member, on the ~urface of which is provided a pattern of islands of abrasive, resulting in channels for circulation of slurry. The abrasive articles can be manufactured by various means one of which involves the use of a roller on the periphery of which are provided raised ~islands~
or lands, e.g., in diamond shape. The abrasive mixture i5 first transferred to the roller having the diSmond-shaped pattern provided thereon by a smooth roller which rotates in an adhesiva bath and which peripherally contacts the patterned roller. The patterned roller then transfers the pattern of abrasive material onto the backing member. Thus, in effect, the diamond-shaped pattern is printed onto the backing member.
The pattern on the coated abr~sive material disclosed in V.S.

3,991,527 results from transferring geometrical-shaped patterns of ad~esive binder onto a backing me~ber, followed by application of abrasive grain to the adhesive. The adhesive, in one manner of manufacture, is transferred by a smooth roller, rotating in an adhesive bath, to the patterns provided on the patterned roller which, in turn, transfers adhesive in the shape of the pattern to the backing member. As disclosed by the drawings in this patent, the pattern produced comprises what one ~ight call islands of abrasive. And, the islands are ~urrounded by rightangularly intersecting channels which open onto the outer or peripheral edge of the abrasive discs provided from the abrasive material.
The use of intaglio or rotogravure rolls in various coating processes, including the manufacture of coated abrasive material is well known. Such rolls are provided with various patterns of cells, or well~ as they are 60metimes called, cut into the surfa~e of the perimeter of the roll, the cell pattern provided and the capacity thereof depending ~omewhat upon the particular coating application. In general, when cuch a roll is used in a coating application, it rotates in a pan of the coating material and, as lt rotates through ~he coating ~aterial, the cells are loaded up with the coating material much like a bueket conveyer. After the gravure roll rotates out of the pan and before it eontacts the backing ~ember o~to vhich the coating m~terial is to be transferred, its ~urface is wiped with a knife or doctor blade.
Thus, only the material contained in the cells is available f~r coating of the backing member. ~he amount transferred depends, in general, upon the total theoretical volume of the cells and the particular material that is being coated. As a result, gravu.e ro~ls are commonly used when it ~ 6 desired to apply a controlled amount of coating material to a backing ~ember. Also, such rolls are com~only used when it is desired to provide a particular pattern of coating material onto a ~ubstrate. In such a case, cells the shape of the pattern desired in the coating to be provided will be provided in the peripheral ~urface of the gravure roll. Thus, if it is desired to coat a design having a hexagonal shape onto a substrate, a gravure roll having such a design cut in its surface will be used. Nevertheless, such a roll is not expected to transfer merely an outline of ~uch a design.
~rior to the $nvention disclosed ~n this application, others have disclosed the manufacture of coated abrasive material in which a slurry of a radiation curable binder and abrasive grain is applied to a backing me~ber using a gravure roll. ~hus, in United States Pat. No. 4,644,703, which issued February 24, 1987 to Norton Company, the Assignee of this patent application, there is disclosed coated abrasive ~aterial suitable for one step fining c' plastic ophthalmic lenses. Suc~ a product is ~anufactured by coating two distinct layers of an adhesive/abrasive grain slurry onto a backing me~ber, to provide a coar6e outer layer and a finer inner layer of abrasive grains. The ~lurry coatings in that patent are deposited by a gravure roll havinq a trihelical pattern cut therein which, ~n turn, ~mparts a pattern of parallel lines o~
adhesiveJabrasive grain slurry to ehe backing member and, in turn, .

to the first deposited coating. Subsequent to ~pplication of the first coating, the backing ~ember with the wet slurry thereon passes through a texturing bar ~ssembly whe-eat the-continuity of the deposited coating ~aterial, i.e., the lines of wet ~lurry, is broken up to provide a somewhat discontinuous pattern.
Afterwards, the wet slurry coating ic ~ubjected to ultraviolet light to cure the adhesive binder and to adhere the abrasive grains to the backing ~e~ber. After curing of this first coating, a second adhesive/abrasive grain slurry is coated onto the first coated backing ~e~ber, to provide the outer grain layer in the coated abrasive product. This processing is the same except that a gravure roll havinq a different helical pattern is used, and there is no texturing of the second applied wet slurry. The abrasive grains are adhered to the bac~ing re~ber, which ~ay be a ~lyester film, ~ith binders compounded pri~arily of acrylates in omewhat different formulations for the respective first and aecond coats. The radiation curable binders, in general, comprise mix of triacrylated monomers, e.g., trimethylolpropane triacrylate (TMPTA), diacrylated ~ono~ers, e.g., he~anediol diacrylate (HDODA) ~nd acrylated oligomers, the preferred being the diacrylates of epoxy resins of the bisphenol-A type.
Importantly, also, the patentees disclose including in the adhesive fornulations unsaturated organic amines, e.g. ~-vinyl pyrrolidone (~NVP~), in a controlled amount to promote adhesicn.
Although a gravure roll is used in the ~anufacture of the coated abrasive material disclosed, such roll functions as usual. It deposits a slurry coating of parallel lines as refle~ted ~y the pattern cut in the roll surface.
United States Pat. No. 4,773,920, ~hich issued to Chasman et al on September 27, 1988, discloses a coated abrasive ~aterial suitable for lapping operations ~ncl~dinq second fining applications for ophthal~ic lenses. She coated abrasive ~aterial is ~anufactured by coating a suspension of abrasive grain in a 201572~
radiation-curable ~inder onto a backing member 6uch as polyester film. The binder can co~prise radiation-curable ~onomers, as believed disclosed earlier by others above-mentioned, and, optionally, reactive diluents. ~f the monomers that are disclosed S to be useful, the patentee discloses that such hould contain two ethylenically unsaturated moities therein, e.g., hexane diol diacrylate. The preferred radiation curable 'monomers~, as disclosed, include oligomers selected from urethane acrylates, isocyanurate acrylates, polyester-urethane acrylates and epoxy acrylates. As reactive diluents, the patentees disclose trimeth-ylolpropane triacrylate (IMP~A) and also hexane diol diacrylate.
It is preferred, according to the patentees, that a coupling agent, e.g., gamma methacryloxypropyl trimethoxy silane, be included with the ~onomer to promote adhesion between the abrasive grains and the cured binder. Nevertheless, the patentees disclose that it is al~o preferred that such ~ilane be coated on the abrasive grain prior to dispersion of the grains in the binder.
Rotogravure coating is disclosed to be preferred by the patentees for the reason that the rotogravure coater can impart a uniform pattern of ridges and valleys to the binder composition, which, after the composition is cured, can ~erve as channels for flow of lubricants and for removal of abraded material. Nevertheless, the patentees fail to disclose any particular gravure roll or the pattern provided therein. fforeover, none of the examples in the patent disclose the use of a gravure roll, even though such is is disclosed as preferred. Thus, it is believed that the patentees merely speculate that use of a gravure roll would impart a patterr of ridges and ~alleys to the binder composition, i.e., a reflection of the design cut in the roll surface, much like the islands of abrasives and channels obtained by those earlier in the prior art.
The expression 'ophthalmic lens fining~, when it is perfor~e~
wi'h coated ~brasive material on a Coburn-505 fining machine, can B-refer to a ~imple ~one-step~ process or lt can denote a more complex 'two-ctep~ operation. In one--tep fining, a cingle daisy vheel or film backed fining pad ('Snowflake~) ~c employed before the final clurry-polishing. Such a pad i- capable of removing relatively large amounts (0.4-0.6mm) of excess tock and, at the same time, generate a eufficiently fine, scratch-free surface. In the more common tw~-~tep operation, a silicon carbide coate~l abrasive product (a first fining pad) is used first which removes most of the 6urplus stock. This is followed then by use of a cecond-fining pad, a ~uch finer grain, ~luminum oxide based, coated abrasive product. This cecond pad removes little stock (0.03-0.05mm) but bas fine ~inishing capab$1ities. ~reference for the one-step or the two-step process depends on a nu~er of factor6 ~hich include the lens type used (glass, CR-39 plastic and polycarbonate are the three most common lens types), the lense curvature (diopter), shape (cylindrical and cpherical), and lens cize. One-step lens fining is most com~on with plastic lenses of relatively low diopter and of medium (~.g. 65mm) size.
~n either case, the main objective of lens fining is to prepare the lens for the final or slurry polishing ~tep which is usually performed with slurries of various small particle size alu~inum oxide (0.5-1.0 micron range). As a consequence of such low particle ~ize, the slurries cannot remove deep scratches (~t values qreater than, say, 50-70 microns) from lenses obtained during the fining process. Therefore, there is always a need fcr products that improve the results of the fining or prefinishing process thus reducing the burden, both time and in fine polishing requirements, placed on the clurry-polishing ~tep.
A description of the fining process and of suitable machiner~
for accomplishing it are disclosed in United States Patents No.
3,~32,647 tto Stith) and 4,320,599 (to ~ill et al). Stith discloses in Fig. 2 of the patent, a lapping tool such as envisioned by one aspect of the instant invention. The lapping surface 78 of the tool provided in stith may be a coated abrasive material consisting of abrasive grains adhered to ~ flexible bac~ing which, in turn, is supported by the ~tructure disclosed in Stith.
Recently there has become available commercially a second fining pad which is characterized by ~paced-apart spherical-shaped aggregates of aluminum oxide abrasive qrain (3-4 ~icrons) on a backing member. Tl~e abrasive grains are held together in the aggregate and the aggregates to the film backi~g member by a phenolic binder system. During the fining operation, the aggregates are ~upposed to break down and the fine abrasive particles are then li~erated. ~hese liberated abrasive particles are believed responsible for the fine finish obtained.
Although this most recently introduced second fining pad is characterized by its good cut rate and finishing qualities, its use nevertheless is attendant with certain disadvantages. The ~brasive aggregates have to be manu~actured in a separate process ~dding cost and quality control problems to the manufacture of the final product. Moreover,-although the aggregates are supposed to break down uniformly during the fining process, yielding a quantity of fine grain particles and, ultimately, a more finely finished lens, ~niform aggregate breakdown does not always appear to be accomplished in use. Oftentimes, we have discovered, whole aggregates are torn out of the coating under the prevailing pressure (20 psi) in the lapping tool used, leaving holes in the coating which then can cause uneven finishing. Moreover, the binder system is solvent-based, leadinq to certain problems, as above-disclosed, in addition to pollutinq ~he atmosphere.
SUMMARY OF ~HE INVENTIO~
A primary object of the instant invention is to provide coated abrasive material havinq a unique ~urface coating pa~ern of coated abras$ve.

B

20157~0 A further object i6 to provide coated abrasive material not attendent with the problems and disadvantages of so-called ~con~entional~ coated abrasive material and with its manufacture.
A still further object of the ~nvention is to provide a coated abrasive product useful in providing h$9h quality finishes in various lapping or fine finishing operations, in particular, ophthalmic applications.
Another object of the invention is to provide a coated abrasive product suitable for second fining ophthalmic and other applications requiring a combination of controllable fine surface finishing and relatively high cut rate.
Still another object of the invention is to provide a coated abrasive product which provides a combination of surface finish and cut that is equivalent to t~at provided by the now commer-cially available coated abrasive material having aggregates of abrasive material coated on the turface of its backing member.
A further object is to provide a coated abrasive product having improved adhesion between the abrasive grain and binder.
A ~till further object is to provide an improved process for the manufacture of coated abrasive material.
~n even further object of t~is invention is to provide a coated abrasive product euitable for second fining ophthalmic applications wherein its use results in improved pre-finish, resulting in less time required in the slurry polishing step an~
an overall reduction in the total ophthalmic processing time needed heretofor.
An additional object i5 to provide coated abrasive produets suitable for use in ophthalmic applications resulting in a fewer number of rejects than heretofor.
Quite advantageously, the coated abrasive material according to this invention offers economies in manufacture through the savings of using less coated abrasive grain, in that less t~n t~.e total surface area of the backing member is coated.

201~720 A further advantage i6 that the coated abrasive material of this invention is manufactured from olventless, non-polluting dispersions which can be cured rapidly within a ma-tter of seconds by ultraviolet light The objects and advantages offered by this invention are provided in coated abrasive material comprising (a) a backing member having a top and bottom surface; and (b) an abrasive coating adhered to the top ~urface of said backing member, said abrasive coating comprising a cured radiation curable binder and abrasive grains dispersed therein and being characterized by a relatively uniform three-dimensional pattern defined by a plurality of coated abrasive formations each of which is contiguous to other of said coated abrasive formations, each said abrasive formation being defined by a bottom inner edge adhered to said top surface and defining an area on the backing me~ber devoid of the said abrasive coating and a top edge defining a somewhat larger area devoid of said abrasive coating, and an inner ~ide wall of the said abrasive coating connecting the said top and bottom edges of the said abrasive coating formation BRIEF ~ESCRIPTION OF THE DRAwINGS
The invention will be more clearly understood by reference to the drawing in conjunction with reading of the following spe~ifi-cation, in which FIG 1 is a view $n cross-section of coated abrasive material in accordance with the invention FIG 2 is a photomicrograph at 40x magnification of a plan view of the coated abrasive material shown in FIG 1 showing the unigue pattern of coated abrasive formations provided on the coated abrasive material 20157~0 ~IG 3 ~s a photomicrograph at 200x magnlfication of a plan view of the coated abra~ive material shown ln ~IG 2 showing one of the abrasive formations in the pattern of contiguous abrasive formations;
FIG 4 is a photomicrograph at 50x magnification of coated abrasive material according to the invention taken at a 60~ tilt from the horizontal FIG 5 is a photomicrograph of the coated abrasive material shown in FIG 4, and at the same angle of tilt, but at lOOx magnification FIG 6 $s a schematic ~iew of the manufacturing process used to manufacture the coated abrasive material of the invention;
FIG 7 i8 a greatly enlarged view, in perspective, of a portion of the most preferred rotogravure roll used in the manufacture of coated abrasive material $n accordance with the invention, showing the hexagonal-chaped cells provided in the roll surface and FIG 8 shows a plan view of a 60-called ~Snowflake~ abrasive pad cut from the coated abrasive material of the invention used in the finishing process for ophthal~ic lens D~TAILED DESCRIP~ION OF THE INVENT10~ AND
~H PRE~ERRED EMBODIME~TS T~EREOF
Referring now to the drawing there is ~hown in FlG
thereof, in cross-section, coated abrasive material 10 according to this invention which comprises, in general, a backing me-ber 12 and an abrasive layer 14 adhered to the top surface 16 thereof Abrasive layer 14 i~ provided on the backing member 12 b~
coating a dispersion 18 of abrasive grain 20 in a radiation curable binder 22 onto the bottom surface (top surface 16 in t~e finished coated abrasive material) of the backing member 12, as hereinafter ~ore fully described After~ards, the radiation curable binder 22 $~ cured through a free radical mechanism B

201572~
induced by exposure to actinic (ultraviolet) radiation or eleetron beam co as to harden the binder and to cecure the coated abrasive layer 14 to the backing member. Quite advantageously, the dispersions of this invention lend themselves to cure by ultraviolet light (UV lig~t), as well as by electron beam.
The abrasive layer 14, as is chown more clearly in FIGS. 2 and 3 of the drawing, i8 characterized by a relatively uniform, grid-like pattern of a plurality of parallel rows 24 disposed at an angle of ninety degrees to a plurality of other parallel rows 26, each of caid rows having therein a plurality of abrasive formations 28. The abrasive formations in next adjacent rows are set off from one another, to the right and left, as ceen in FIG.
2. As will be ;urther appreciated from FIGS. 2, 4, S, each~
abrasive formation 28 is contiguous to others in the pattern of coated abrasive provided. By the term ~contiguous~, it is meant that the abrasive formations are in close proximity to one another. As well be ceen by reference to FIG. S, however, a photomicrograph of a portion of coated abrasive material 10 taken at lOOx magnification, come of the abrasive for~ations 28 appear to abut with and join to next adjacent formations and others see-to be ~omewhat spaced-apart therefrom.
The coated abrasive formations 28 (~IGS. 1 and 3) are defin~
by an inner bottom edge 30 of coated abrasive which, in turn, defines an area 32 on the top surface 16 of the backing member 1' t~at is devoid of coated abrasive. The abrasive formations-28 are each further defined at their top by a top edge 34 (FIG. 3) ~hie~., in turn, defines a somewhat larger area 36 devoid of coated abrasive material. Connecting the top and bottom edges of each of the abrasive formations, as ~est ceen by reference to ~IGS. 1 an~
3, is an inner wall 38 of abrasive ~aterial which tends to slope in graduated manner inwardly in comewhat concave fashion from the top edge 34 to the bottom inner edge 30 of the formation.
B

It will be appreciated by reference to the drawing, in particular FIG. 6, that with respect to those coated abrasive formations 28 contiguous to one another in the pattern, the top edges 34 are sometimes connected or integral one wlth the other, whereby to provide a unitary or combined top edge. Other abrasive formations 28 are defined, however, by a distinct outer wall 39 which surrounds that particular abrasive formation and sets it apart from those formations contiguous to it. ~s will be appreciated further by reference to FIGS. 4, 5, those particular o abrasive formations 28 thouqh more or less isolated from one another appear to be interconnected by a matrix 40 (FIG. 5) which surrounds that particular coated abrasive for~ation and such matrix is shared with other contiguous coated abrasive formations.
The matrix 40, as seen ln the drawing, ~oins together outer walls 39 of the contiguous abrasive formations ~nd provides a continuous layer of abrasive material on the top surface 16. ~evertheless, i~portantly, this layer or matrlx 40 (except where the top edges of contiguous formations are connected) ic at a level lower than that of the top edges 34 of the abrasive formatlons 28 (FIG. 1).
Thus, there results in what-amount6 to a discontinuous layer of abrasive material having the unigue surface pattern of the invention.
~he particular shape that the top edge 34 of an abrasive formation takes will depend somewhat upon the particular pattern carried in the surface of the qravure roll used in the manufacture of the coated abrasive material. The more preferred shape define~
by the top edges of the coated abrasive formations, as shown in FIG. 2 is, in general, a hexagonal-shape. ~he important thing is, however, that a top edge ls formed which defines an area on the backing member 12 and ln the abrasive coating provided thereon that is devoid of abrasive coating. Thus, the patterned surface coating provided has a unique surface topography that provides a discontinuous surface of coated abrasive. It wae quite D

surprising, and quite unexpected, that, contrary to past experience, such a patterned coating as cet forth herein could be obtained by gravure roll coating of the adhesive/abrasive grain slurry onto the backing member. Such ~anner of coating generally transfers a pattern reflected by the design cut in the gravure roll, not merely an outline of cuch pattern. Nevertheless, it was discovered that as the coating dispersion viscosity increased poorer and poorer coatings were obtained until suddenly a discontinuous pattern resulted cuch as disclosed in the drawin~s.
It was, ~oreover, quite surprising to find that such a patterned coating showed excellent performance $n ophthalmic fining.
The adhesives or binders used in the patterned coated abrasive layer of the invention comprlce essentially a unique combination of radiation curable ~onomers having mono-, di, and tri- acrylate functionality. Importantly, the monofunctional monomer is N-vinyl-2 pyrrolidone, a cylic'amide derivative of a tertiary amine. Such monomer has been discovered not only to be unique in that it provides i~proved adhesion between the adhesive binder and abrasive grain but ~lso because it results in good dispersions of the abrasive ~rains ln the adhesive/abrasive grain slurries used in the practice of the invention. This apparently results from the fact that such monomer is hydrophilic as is the aluminum oxide grain used: however, we do not wish to be limited to this theory. Importantly also is the fact that the vinyl pyrrolidone monomer functions in the adhesive formulation as a reactive diluent whereby the desired viscosity and other rheological properties of the binder/adhesive grain dispersion can be adjusted as desired.
~t is of criti~al importance, however, that only a limited amount of the vinyl pyrrolidone be used ~n the adhesive binder formulations. Such ~onomer wants to copolymerize only ~ith curing of the adhesive formulation by uitraviolet exposure, as later more fully disclosed. ~hus, the amount of vinyl pyrrolidone in the binder composition chould be less than about 20% by weight, generally less than about 15% by weight. The ~ore preferred formulations will comprifie from about 10-15% by weight~vinyl pyrrolidone. With regard to the ~onomers having diacrylate functionality, it is preferred that a combination of such be used in the binder formulations, namely, diacrylated epoxy oliqomers and diacrylate ~onomers. The preferred acrylated epoxy oligomers are the diacrylates of epoxy resins of the bisphenol-A type. Such acrylated oligomers are readily available commercialiy under such tradenames as Celrad from Celanese Corporation and Novacure from Interez, Inc. The preferred ~uch oliqomers are amine rodified acrylated epoxy monomers. Moreover, the preferred such diacrylate oligomers have average molecular weights per acrylate unit of about 250 to 90G, with a range of 270-400 ~ost preferred.
Small amounts of hiqher and lower oligomers, characteristi-cally present in all practical products of t~is type, have no known harmful effect. Oligomer6 termlnating with unsubstituted acrylate groups are preferred, but ~ethacrylates or other eubstituted acrylate groups could alco be used.
~he preferred diacrylated monomer ~6 hexanediol diacrylate (~HDODA~) but, in some cases, tetraethylene glycol diacrylate and tripropylene qlycol diacrylate can al~o be used. In order to achieve ~atisfactory coated abrasive products accordinq to this invention, it is necessary to use ~ubstantial amounts of the triacrylated monomers. Trimethylolpropane triacrylate (~TMPTA~) is usually preferred in the practice of this invention, primarily because it is reported to be least likely of all the commercially ovailable triacrylated monomers to cau~e allergic ~kin reactions.
Minor amounts of acrylated monomers with four or ~ore acrylate groups per ~olecule can be used, however, ~n lieu of part of the triacrylates.
~he relative amounts of diacrylated ~onomers and triacrylate~
mooomers i~ adjusted alonq with variations ln the other components 201~720 of the adhesive DiXture e.g., the vinyl pyrrolidone and the acrylated epoxy otigomer, to give uitable rheological properties, in particular Yisco~it~ for coat~ng, as well as effective grinding and~or finishing characteristics to the coated abrasive material ultimately ~ade with the adhesive. A mixture of HDODA
and IMPTA in a weight ratio of about 0.45 is preferred.
For all types of acrylated monomers used in this invention, unsubstituted acrylates are preferred but substituted ones such as methacrylates could be used. The average ~olecular weight per acrylate unit of suitable monomer6 varies from 95 to 160, with 95-llS ~eing preferred.
The preferred binder compositions of this ~nvention should comprise from about 25t to about 40% by weight of the triacrylated monomer tTMPTA), from ~0% to about 20% by weight of the diacrylated ~onomer (HDODA), and from about 20% to about 50~ by weight of the acrylated epoxy oligo~er. ~mportantly also, the ~inder composition will include from about 10 to 20% of vinyl pyrrolidone.
The binder composition, to cure the above-disclosed radiation cur~ble components, should also include a photoinitiator whic~
will adequately absorb and transfer to the acrylate components the energy from the W lamps used to initiate cure. Methods for determining the amounts and types of photoinitiator used are eonventional in the art of W light cured surface coatings, and the same rethods were found effective for purposes of the present invention. The amount of photoinitiator is generally from about 0.5 to 7.0% by weight of the amount of adhesive used.
The photoinitiator preferred for use in the practice of the invention for fining product embodiments of this invention is 2.2-dimethoxy-2-phenyl acetophenone (hereinafter DMPA). However, 2-chlorothioxanthone, benzophenone, and l-hydroxycyclohexyl p~enyl ketone, may al~o ~e used, along wit~ ~any others known in the art.
Ot~er components ~ay also be found useful to be included in 201~720 the binder com~osition, e.g., coupling agents and adhesion promoters, and colorants to give a particular color to-the abrasive products. Examples of adhesion promoters are the organosilanes and organotitanates containing at least one organic group with from 10-20 carbon atoms. An often preferred material, especially for products to be used for lens fining, is tetrakis t(2.2-diallyloxvmethyl) l-butoxy] titanium di(tridecyl) monoacid phosphite. ~n the case of colorants, as with other components, care must be taken to select those which will not unduly absorb the W light and thus interfere with curing of the radiation-curable components of the binder. As usual, in coating compositions, the binder co Fositions disclosed herein can also include ~uitable surfactants and foam ~uppressants.
The abrasive grains, which will be found most 6uitable for use in the practice of the $nvention, will depend somewhat upon the particular application and the manner of curing the binder.
Curinq of the binder is most desirably accomplished by electron beam or actinic radiation, $.e., 6uch as by exposure to ultraviolet (W) light. Nevertheless, electron beam curing, while effective, requires 6ignificantly greater capital investment than curing by W light. Moreover, 6uch manner of curing presents a more serious potential hazard to manufacturing personnel. In an~
event, the binder composition useful in the practice of this invention have been found quite advantageously, to be curable by W light. Thus, white aluminum oxide abrasive grains are usually preferred, as such are not a strong absorber of W light.
Moreover, ruch ~ineral scatters light and is advantageous to t~e UV curing in this invention. For tecond fining applications, moreover, we have discovered that the ~ost preferred ~brasive grains found suitable are high purity aluminum oxide abrasive grain. Nevertheless, whatever the abrasive grain used, it must have adequate transmission for W light so as not to interfere with curing of the binder.

A representat$ve bras$ve graln meeting these requirements is a precision graded aluminum oxide, a product of the Norton Company. Such abrasive grain, as deslred, can, moreover, be termed a ~virqin~ grain which means that it conta~ns no additives which are customarily added to abrasive grain to improve wettability, ease of dispersion or to reduce flocculation. Such additives have been discovered to be detrimental to the proper functioning of abras$ve qrain in radiation curable formulations.
They tend to $ncrease the hydrophil$c nature of the surface of aluminum oxide particles which ~- undesirable when the grain is to be dispersed in a radiation curable, mostly hydrophobic coating liquid. The abrasive grain used ln the ~nvention is, moreover, air classified, l.e., during the grading process of the starting aluminum oxide gra$n mix, no water or dispersant is used.
lS The particle size of the abrasive grains used can vary somewhat depending upon the particular fin$shing or lapping operation for which the coated abrasive ~aterial $s intended. In general, however, the abrasive grain ~ize used ~hould be from about 0.2 to 35 microns. For a product for econd fining in opht~almic finishing operations, the preferred grain ize is fro~
about 0.5 to 12.0 microns, even more preferably from about 2 to 4 microns. Where the coated abrasive material is intended for first fining applications, the grain ize can range from about 12-20 microns. Coated abrasive material for camshaft finishing can have abrasive grains ranging from about 9-30 microns.
The precision alumina grain is sorted into the appropriate fractions of average (nominal) particle size by air-classification methods according to techniques well known to those in the abrasive art. ~n the present lnvent$on for second flning applications, the nominal particle size that has been found to be ~ost useful $s ~n the range of O.S to 12.0 microns, ~ore preferably 2-4 m$crons, ~6 above-disclosed. T~e air classified abrasive grains most preferred for ~econd fining applications chould be about 3 microns and dry ground. Air classified (precision graded) grains are most preferred for use in th~
practice of the lnvention because ln wet classification dispersions aids such as sodium cilir:ate or various organics such as eodium polyacrylate are necessary to achieve good aqueous dispersion. The dispersion aids tend to remain on the surface of the grain particles rendering them hydrophlic. The term ~precision graded~ means that for any particular ~ize, the deviation from the average cannot be greater than four times the ~tated grade, ~n either direction. For the more preferred second fining product of the invention, it is preferred, ~oreover, that the mass ratio of abrasive grains to binder in the dispersion to be coated be from about 1.0 to about 3.0, more preferably from about 1.5 to 3.5.
lt has been discovered that it is of critical importance, in particular, in products useful for second fini~g applications, that the abrasive grain particles be pretreated with a coupling agent prior to being dispersed in the liquid binder components.
~he preferred coupling agent i~ gamma-methacryloxypropyl trimethoxy cilane co~ercially available from Dow Corning Corp.
under the trade designation 2 6030 and Union Carbide Corp. under the trade designation A-174. Preferably, the amount of silane to be bound to the grain surface is in the range of from about 0.1%-5%, even more preferably from about 0.2% to about 1.0%, based upon the weight of the alu~inum oxide or other abrasive grains. Other cilane coupling agents can, instead, be used, if desired. For cxample, ~inyl, ~inyl-~lkyl, cyclohcxl o~ acryloxy, meth~cryl, etc. cilanes ~ay be found euitable for use in the practice of the ~nvention. Amino silanes may also be found useful ln the practice of the invention. The cilane is first dissolved in water or in a colution of water:methanol (e.g., a 9:1 colution) prior to application to the abrasive grains. Preferably, however, the A-174 silane will be ~ydrolyzed, preferably in deionized water prior to application. After treatlng t~e abrasive graln wlth such coupling agent, moreover, it is preferred that such pretreated grains go throuqh a conditioning or ripen~ng period, prior to being subjected to drying. Such a ripening period should last for several hours, e.g., from overnight to 15-18 hours. Next, the pretreated abrasive grains are dried at a temperature above 100^C
for several hours, e.g., 110C for 4 hrs, after which they are screened to break up any agglomerates.
The backing members for use in this invention will depend to come extent upon the particular application involved. For ophthalmic lens fining applications, it is necessary that the backing member ehould be waterproof, since the product is normally used wet; that the strength of the backing should be sufficient to resist tearing or other damage in use; that the t~ickness and smoothness of the backing ehould allow the achievement of the product thickness and smoothness ranges noted further below; and that the adhesion of the adhesive to the bac~ing should be sufficient to prevent significant shedding of the abrasive/adhesive coating during normal use of the product. These requirements are most readily met by the use of flexible and dimensionally stable plastic fil~s or waterproof paper as the backing. ~he most preferred film backing member is polyethylene terephthalate film. Nevertheless, for some applications, other polymeric films, e.g., polycarbonate films, will be found 2~ suitable. Such backing members chould, in general, be primed or pretreated to promote adhesion between the surface pattern of coated abrasive and the polyester backing member. Various of such primed or pretreated polyster films will be found suitable in the practice of t~e invention, ~.g. Melinex 505 polyester film fro~
ICI Americas Inc., Hostaphon 4500 from American Hoechst Corporation, and Mylar 300XM, available commercially from E.I.
DuPont de Nemours Co. Such a film is disclosed in United States Patent No. 4,476,189, which issued on October 9,1984 and entitle~

,cOpolyester ~rimed Polyester ~ilm~ and in ~Polyester ~ilm for printins~ an article published in 'Screen Printing~, May, 1982, ~uthored by Dr. B. Lee Kindberg.

The thickness of the backing member will depend to ~ome extent upon the particular application for the coated abrasive material of the invention. It should be cf ~ufficient thickness to provide the strength desired to bear the patterned coating and for the application intended. Nevertheless, it should not be so thick as to adversely affect the desired flexibility in the coated abrasive product. Typically, the baeking ~ember should have a thickness less than about 10 mils, preferably ln the range of from about 2 to 5 ~ils.
In the continous manufacture of the coated abraslve material 10 accordinq to the invention, as disclosed by ~IG. 6, the backing member 12 i5 withdrawn in conventional fashion frcm a roll 42 thereof provided on a conventional unwind stand (not ~hown). The unwind stand is fitted with a brake, according to usual practice, to give the desired resistance to unwinding of the backing member.
~he backinq member 12, as shown in the drawing travels from the unwind area around one or ~orc suitable rolls designated by reference numerals 44, 46, 48 and 50, and thence to the coating area denoted generally by reference numeral 52 whereat it is passed between the nip formed by roll 54 and gravure roll 56, rotating in the directions indicated by the arrows. ~hence the backing ~ember 12 with the abrasive coating 14 coated thereon is passed around one or more rolls 58, 60 to a ~ource 62 of actinic light, i.e., ultraviolet(W) light, which provides the ~eans for curing of the binder composition to the desired hardness. ~olls 64, 66 provide that the coated abrasive material 10 travels in horizontal disposition through the curing zone. ~rom the curing zone, the coated abrasive material 10 travels over roll 68 to a conventional takedown ~ssembly denoted generally by reference numeral 70 and which comprises roll 72, a rubber-covered roll 74, and compressed air driven takedown roll 76 which functions according to usual technique to provide a wrinkle-free, tig~tly wound roll of coated abrasive material.
The radiant power of the source of actinic light can be provided by any conventional W souce. For example, in the practice of the invention, the W light producing components were cuccessive Model F440 10 lamp holders, fitted with one Type D
followed by one Type H lamp. A total energy output of 300 watts per inch of width is provided. ~he power supply for each lamp was designated Type P 140A.
~n some cases, additional heat input can be provided, if desired, by conventional thermal means. The main consideration, however, is that the radiant power of the W light source 62, together with any optional ther~al heat input from other sources (not shown) located between W light source 62 and the takedown rubber-covered idler contact roll 72 ~ust be sufficient to cause the desired curing, i.e., hardening, of the binder before the coated abrasive material reaches the roll 72.
~he intensity and time of exposure of the coated abrasive material to the W light and to any auxiliary thermal heating use~
are deter~ined by methods well known in the art of coating with adhesives cured by exposure to W light, supplemented if necessar~
by testing of the grinding or other surface finishing performance of the coated abrasive materials produced.
For lens fining applications, the thickness of coating in itself is not inherently critical, but a combined thickness of the backing me~ber and the ~urface coating has become esta~lished as ~tandard in the industry and is relied upon to give the proper lens cur~ature when used with the backup lapping tool supports which are conventional. ~he thickness range, 1~5-23~ microns, established in the art can readily be produced according to this invention. ~he uniformity of thickness is inherently critical, because ~f the thickness of coating varies excessively from one part of the ~brasive to another, it is possible for one part of t~e lens to escape proper polishing, as a result of a low spoe on the abrasive, or to be excessively thinned, by a high ~pot on the abrasive. The combined thickness of the backing ~ember ;~nd t~.e patterned adhesive/abrasive layer over the surface of tht portion of coated abrasive material used for a s.ngle lens chould not vary by more than 25 microns, when ~easured with an instrument, s~ch as a conventional ~icrometer, which measures the thickness of local high spots on the coating over an area of at least 0.05 square centimeters.
Of critical importance, however, in obtaining the patterned curface coating of abrasive grain diF,persed in the binder, as shown in FlGS. 1-5, i6 the use of a particular rotogravure roll and a binder/grain dispersion having non-Newtonian flow characteristics. In the practice of the invention, ~n 80-Hex, R-ll gravure cylinder, availa~le coDercially fro~ Consolidated Engravers, Corp., was used. It is well known in the art of gravure printing that in such designation 80 refers to the number of cells, in this case hexagonal-shaped, per linear inch and R-'l denotes the particular tool that was used to generate the cells.
This latter number is related to cell depth and thus the combination 80 ffex and R-ll defines a particular cell shape as well as cell volume. The total theoretical cell volume of t~is particular roll is 22.1 x 109 cubic billion microns/in.2. Each cell has a depth of 0.0049 inc~es. Other ~anufacturers, however, produ~e rolls having the same or a similar pattern, and such ma~
also be found useful provided they ~eet t~e other requirements set forth herein.
~he dispersion coating ~ust be of high viscosity and possess non-Newtonian l$quid flow characteri-tics, we have discovered, for the patterned curface coating to be produced. Otherwise a continuous surface coating will result when the dispersion coating B ~ -25-is transferred to the backing ~ember. ~he particular viscosity of any dispersion coating formulation, as will be readily appreciate~
by those in the art, will, of course, ~epend upon a number of factors in combination with one another, e.g., the particular components used, the relative ~eights thereof in the dispersion, the relative amount of abrasive grains and other solids t~at might be present. As an example of a suitable dispersion viscosity for production of the patterned ~urface coating disclosed herein, the viscosity should be about 1750 cps (Erookfield visoometer, spindle ~2, at 6 rpm) at 76~ and 3400 cps ~spindle ~2, at 30 rpm), indicating that the dispersion possesses non-~ewtonian liquid flob characteristics. ~mportantly, no heat is applied to the coating dispersion that could possibly change its viscosity and provide greater ease in coating.
Wit~out being bound by the explanation offered here, it is felt that the unique combination of relatively high dispersion viscosity, non-~ewtonian liguid flow characteristics, and the gravure cells are resFonsible for the particular pattern generate~
on the coating surface. It is thus possible that individual gravure cells are only incompletely filled with the dispersion coating material and thus it becomes impossible to generate a continuous coating. Fractional transfer of liquid from t~e perimeter only of completely filled gravure cells might provide ar alternative explanation. In either event, we have discovered tha~
with particular, radiation-curable coating formulations, as disclosed in this application, it is possible to generate patterned eoatings repeatedly and reprodu~ibly, while non-patterned coatinqs are obtained from relatively low viscosity coating liquids or dispersions with a low grain to resin ratio.
~his ratio is defined as the quotient obtained from dividing the weight of grain used by the combined weight of cligomers and ~onomers present in the formulation. In general, such a ratio ~hould be preferably in a range of from ~bout 1.5 to about 2.~.

Other gravure rolls having different cell patterns, e.g., quadratic, pyramidal, may also be found suitable $n producing a surface coating d~fining useful qeometrical patterns of coated a~rasive other than the hexagonal-shaped pattern resulting in this invention, provided the dispersion being coated meets the other requirements set forth herein.
~he preferred embodiments of the present invention may be further appreciated from the following examples. All preparations set forth herein are to be understood as being based upon mass or weight, unless otherwise stated.

Example No. 1 Coated Abrasive Product Suitable for Second Fining Ophthalmic Operations ~he components listed below, except for the coloring agent and abrasive grain were readily mixed together without special care to for~ a ~clear liquid~. About three-fifths of this clear coat was then separately mixed with the coloring agent for at least 15 minutes to assure thorough mixing; the remainder of the clear coat was then added and mixed until uniform color was achieved.
A dispersion of the mixed ingredients and the abrasive grain was then prepared on a standard Ross type double planetary mixer, according to usual techniques, at a medium speed for 30 minutes.
B

Incredients Parts bY Weioht Acrylate ester of epoxy resin 100 (Celrad 3600)~
~rimethylol propane triacrylate tTMPTA) 2 132 1,6 hexane diol diacrylate ~onomer (HDODA)~ 60 N-Vinyl-2 pyrrolidone (V-Pyrrol)~ 60 Reactive Acrylic Pigment (Penn Color 9R-75)s 10 Titanate coupling agent (XR-55)~ 1 Fluoro chemical surfactant (FC-171) 7 2 Dimethoxy phenyl acetophenone (Irgacure 651)~ 18 Defoamer (Byk-A-510)9 2 Silane treated aluminum oxide abrasive grain t3 micron) 870 1. Celrad 3600, like Novacure 3600 (Exa~ple 5), is an amine ~odified diacrylated epoxy oligomer of the bisphencl-A
type.
2. IMPTA was supplied by Interez, Inc.
3. HDODA was supplied by Celanese Plastics and Specialties.

4. V-Pyrrol was supplied by GA~ Corporation.

5. Penn Color 9R-75, available from PennColor gives the product a purple color. Other colors could also be used, if desired.

6. KR-55, available from Kenrich Petro Chemicals, Inc., is tetra (2.2 diallyloxymethyl-l-butoxy) titanium di ~ditridecyl phosphite).

7. FC-171, available from 3M Company, is a fluorocarbon surfactant.

8. Irgacure 651, available from Ciba Ceigy Co. is a photoinitiator.

9. Byk-A-S10, ava1lable from ~YK MallinKrodt Company is a solvent containing bubble breaker (foam suppressant).

The viscocity of the mix at ~6F vas deter~ined to be 1750 cps (Brookfield viscometer, ~pindle 2 at 6 rpm) and 3400 cps (spindle 2 at 30 rpm) indicating that the dispersion was non-Newtonian.
The above coated abrasive dispersion was coated on 3 mil.
Melinex 505~polyester film, a biaxially oriented, high clarity film pretreated to promote adhesion, ce -rcially available from ~CI America~ ~nc., using a conventional 80 Hex, R-ll gravure cylinder at 30 feet per ~inute web speed. The coated abrasive layer was cured with two Fusion Company medium p-essure mercury vapor lamps. A coating weight of 0.8 pounds per ream was provided on the polyester film backing me~ber. A ream is equivalent to 33 J
~quare feet of coating area.
The cpeed of the gravure roll 56 was maintained so that the periphery of the roll matched the backing ~e~ber 12 in linear speed. Before contacting the backing, the wetted curface of the gravure roll ' 6 wiped with a trailing doctor blade 78. A Benton type A blade constructed of Type 304 stainless cteel, 203 microns thick and 5 cm wide, with a blade angle of 97 was found satisfactory when used at an angle of 46 to the web at the point of contact. The blade ued was cupplied by Input Graphics, Inc.
~he backing member was supported in the coating nip by a non-driven, freely rotating, rubber-coated backup roll 54. The rubber on this roll had a hardness of Shore A-75. For convenience in maintaining cleanliness of the coating, the backup roll was generally undercut ~o that a zone about cix mm in width on each edge o~ the bac)~ing me~er ~as not ~ j ected to pressure in the nip and thus was not coated.
The adhesive/abrasive grain slurry was supplied to the gravure roll 56 from a coating pan 80 which was kept filled to a constant level via a recirculation loop not ~hown. A pump in ~he recirculation loop maintained constant agitation of the slurry, s~
that settlin~ of the denser abrasive component did not occur to B

any si~nificant extent. No heat was applied to this pan, the dispersion being coated at room temperat~lre, $.e., about 72-80~F.
The film backing member 12 was passed between felt wipers 82, according to usual technique, to remove any foreign particles therefrom which would endanger the uniformity of the coat, or its adhesion to the backing ~ember. As usual, lengths 84 of loosely ~uspended copper tinsel connected to a suitable ground are provided on the coating line to eliminate any dangerous build-up of electrostatic charge.
Gravure roll 56, as earlier disclosed, has 80 hexagonal-shaped cells 86 per inch provided in itc ~urface (FIG. 5). ~he cells, as shown, are provided in rows of cells that extend lengthwise of the gravure roll 56. Those cells 86 in next adjacent rows are staggered to the right and left of the cells in the row next to it. ~hus, any particular cell 86 in the coating roll is in contact with other cells and those cells inwardly of the edge of the cell pattern are surrounded by ~ plurality of other cells, in this case six.
~he dispersion coated backing me~ber was exposed for about two seconds at a web ~peed of about 20-40 ft./min. to the output of the mercury vapor W lamp with radiant power of about 300 watts per inch of width.
A uniq~e, three dimensional, ùniformly thick pattern of coated abrasive was provided, as chown in F~GS. 1-5. The coated abrasive pattern is seen to be defined by a plurality of coa~ed abrasive formations 28 each of which is contiguous to and some are interconnected with other ruch coated abrasi~e formations. Each of the coated abrasi~e formations 28 is defined by a bottom ed~e 30 which defines an ~rea 32 on the backing member which is approximately of a circular-~hape and which ~c devoid of an~
coated abrasive. The top of ~ach coated abrasive formation 28 is further defined by a top edge 34 which, in turn, defines a somewhat larger area devoid of coated abrasive. ~hese two edges ,~B -`' 201~72~

are connected together by a sloping ~nner wall 38 of abrasive coating which, as best seen from FIG. 3, curves inwardly 60mewhat from top to bottom in a somewhat concave fashion. As will be appreciated from the white areas hown in FIG. 2 of the drawing, such areas indicating the presence of abrasive grain, the abrasive grain particles in the patterned coating are somewhat concentrated at the top edges of the coated abrasive formations. Nevertheless, as the white areas in the photographs indicate, the abrasive grain particles 20 are dispersed throughout the coated abrasive formation from top edge 34 to bottom edge 30, decreasing somewhat in concentration fro~ top to bottom. In general, the coated abrasive pattern provided ~s defined by a plurality of void areas, i.e., by a plurality of abrasive for~ations each defining an area with no coated abrasive. ~he pattern has the appearance of a surface having a plural~ty of rather uniform craters like found in volcanos. The craters are alined $n parallel rows and are offset from one another in a right and left manner in next adjacent rows whereby a grid like pattern results of what might be termed vertical and horizontal rows of craters and coated abrasive formations.
Snowflake fining pads, i.e., pads 88, having the shape sho~n in FIG. 8, were cut from this coated abrasive material, according to usual techniques. Afterwards, the fining pads were tested on a conventional Coburn Model-505 ophthalmic finishing machine using the standard two-step fining procedure to complete the fining of a cylindrical, 6.25 diopter, lO cm. diameter plastic lens. ~he pads were mounted in usual ~anncr by pressure-sensitive ad~esive to the lapping tool backup structure described in the stith patent cited earlier. ~he initial thickness of the lens blank was measured and the lens clamped in position. ~he pressure urging the coated abrasive lapping tool against the lens blank was adjusted to 20 psi force. ~he machine was then operated for three minutes.

B:

During that time the lens and lapping tool were flooded with water.
The criteria prescribed for a nuccessful result of this test for second fining application are: (1) removal of from 0.03 to 0.06mm from the center of the lens; ~2) a lens surface finish of not more than 6-8 microns AA ~nd not more than about 60 microns Rt (depth for the deepest ~ingle ccratch within a ~tandard traversal range of the ~urface measuring instrument); (3) general uniformity of the lens surface, and ~4) lack of appreciable chedding of the coating of the coat abrasive lapping tool. The lens was removed and final t~ickness measured. Finish was determined with a Surtronic 3 instrument, according to conventional techniques.
Snowflake fining pads, cut from commercially available coated abrasive material, as earlier disclosed, ~aving aggregates of abrasive provided thereon were used as a control. These pads were tested on the Coburn Model-505 ophthalmic finishing machine in the came manner as the product according to this invention and above-described.
The results of the two tests, comparing Snowflake second fining pads from the two different coated abrasive materials, are shown in Table I below:
TAB~E ~
Comparison Between Snowfla~e Pads of Aggregate Containinq and Pattern Coated Abrasive ~ining Pad Location of Finish Lens Quality Material Heasurement Ra Rt Cut Erosion Control Abrasive Right 8 85 - -~Aggregate Center 4 30 O. OSmm none Containing) Left 4 34 Pattern Coating Right 4 42 (Silane Treated Center 4 36 0.06mm none Abrasive) Left 5 44 Non-Pattern Rig~t 7 48 - ~ome at 20 (Continuous Center 6 56 O.Olmm excessive a~
Coat.ng) Left 6 32 - 32 psi B ~ -32-As indicated in Table I, the Snowflake pad obtained from the coated abrasive material accordinq to the $nvention, and that manufactured from the aqqregate abrasive material are equivalent in performance. Accordingly, eatisfactory cut rate and fine lens finis~es can be obtained from non-aggregate abrasive qrair.
containing coatinqs of the present invention leading to substantial reduction in manufacturing cost of abrasive material for production of Snowflake pads.
By further comparision, a coated abrasive material having a continuous coating on the backing member was ~ade from the same dispersion as that used for the patterned coating. A Consler wire-wound coating bar was used instead of the gravure cylinder havinq the hexagonal cell structure, to obtain coating weights compara~le to that of the patterned coating. Although acceptable fining quality, as indicated $n Table I, was obtained from the continuous coating material, the cut value is seen to be unsatisfactory because it is well below the reguired 0.03-0.06rr, value. Furthermore, there is evidence of erosion or shedding of tne coated abrasive on the Snowfla~e fining pad having the continuous i.e., the non-patterned, coatlng after the fining process. Such characteristic also indicates unsatisfactory performance.
~he abrasive grain used in this example is a precision graded, virgin aluminum oxide (~orton Co~pany-Type 7920). These 2~ abrasive grain particles were air-classified, instead of being classified by the more co~mon and cheaper sedimertation-or slurr~-classific~tion ~ethod. ~his latter ~et~od tends to introduce large amounts of ~urface-bound water on the in-:v~dual grain particles. Such bound water, $n turn, tends t render the grain hydrophilic and ineffective $n the radiation curable binder s~ste used which contains ~ostly hydrophobic ingredients, as will be better appreciated hereinafter.

B~

201572û
" ~
~he abracive grain, after class$fication into the desired cize range, vas treated by cpraying a dilute ~olution of gamma meth~cryloxypropyl trimethoxysilane (~rade designation ~A-174~, available co~mercially from Union Carbide Corp.) dissolved in a 50:50 mix of deionized ~ater:A-174 onto the abrasive grain particles by mixin~ in a conventional Hobart mixer for 15 ~inutes.
~he 50:50 mix was ctirred, prior to mixinq with the abrasive qrains, until ~uch was ~ clear ~olution, indicatinq that the A-17;
had hydrolyzed. The hydrolyzed A-174 ~as then mixed with abrasive grains in an amount of 30 gms hydroly2ed A-174:1500 grams grains, after which the ~ilane pretreated abrasive grains were allo~ed to ~ripen~ for eighteen hours prior to being cubjected to drying.
She ~ripened~ cilane treated abrasive grain particles were then dried at 110C for four hours, and the coated grain particles were then pulverized according to usual techniques to the desired size range, and ccreened through a 78 cs wire. The pick up by the grain particles of the cilane was determined to be about 1%, based on the the weight of the abrasive grain.
The performance of a candidate material for ophthalmic lens fining is usually defined in terms of the guality of ~inish generated consistently together with the presence or absence of signs of erosion of the coated abrasive on the used fining pad.
Erosion or removal of the coating from cmall areas, especially a~
the edges of a fining pad, ic usually taken as a cign cf non-reliable product performance. Coatings that chow erosion are normally rejected. Lens finish guality is co~monly measured ~
the Ra and Rt values taken ~rom traces at various spots (e . g . at the center and at the left, right edges) along the finished lens.
~he meaning of these ~tatictical parameters ~s well known to thcse ckilled in the art. Such are clearly defined in a publicaeion entitled ~An ~ntroduction to Surface Sexture and Part Geometr~ b~
~ Industrial Metal Products Incorporated (IMPC0). In B

general, Ra is a measure of average surface roughness.- Since many surfaces of differing topography might yield timilar Ra values, this number is usually supplemented by other parameters generated from the same surface. In the ophthalmic finishing art, Rt is often employed to supplement the Ra measurement. ~he value of R~
is a ~easure of the depth of qouqes or scratches that might remain on the lens surface after fining. These scratches must be removed from the lens surface in the slurry-polishing process.

Example No. 2 Comparision of Coated Abrasive Products Using Precision Graded Abrasive Grain Which ~as ~een Slurry Classified Aqainst Air Classified Grain P~tterned coated abrasive material was manufactured as set forth in Example 1; however the aluminum oxide abrasive grain used was a different precision graded aluminum oxide grain (Norton-Type 7995). With this type grain, however, the abrasive grain particles are slurry classified, rather than being air classified.
Such was accomplished according to usual techniques with a slurry containing eilicates as a dispersion aid. Snowflake pads were cut from this coated abrasive material and tested as set forth earlier. The used pads showed evidence of excessive erosion, indicating the product was totally unsuitable for this application.

Example ~o. 3 Comparison Between Abrasive Coatings With Silane Treated and Untreated Abrasive Grain ~his example compares the performance of a ~econd fining product when untreated high purity aluminum oxide abrasive grain t3 micron), as in Example 1, is substituted in the dispersion for the silane treated abrasive grain. Snowflake fining pads were produced and the coated abra~ive product incorporating untreated ~rain was tested, ~ before, on the Coburn Model-505 ophthalmic finishing machine. The results ~re cet forth in ~able Il belo~.

TABLE II
~ining Pad Location of Finish Lens Quality Material Measurement Ra Rt Cut Erosion Control(Abrasive Right 4 34 - -Coating Containing Left 4 30 0.06mm none Aggregates) Center 4 26 Pattern Coating Right 5 36 With Silane Left 4 35 0.05mm none ~reated Abrasive Center 4 27 Grain Pattern Coating, Rig~ S 39 - unaccepeable With Untreated Left 6 55 O.OOmm at ~tandard Abrasive Grain Center S 45 - 20 psi o As can be seen from the test results in ~able II, the use of a fine particle ~ize abrasive grain in both pattern coatings results in low Ra and Rt values; however, no reasurable stock removal (cut rate) resulted fro~ the use of the abrasive product in which the abrasive grain was not pretreated with silane. Hore-over, the untreated abrasive grain product resulted in excessive erosion of the coating, even at the tandard 20 psi operating pressure.

Example No. 4 Comparison of Patterned Coated Abrasive Material ~avinq Silane MerelY IncorPorated In ~he Dis~ersion A further coated abrasive product was produced as disclosed in Example 1 having a patterned coating thereon. The abrasive grain, however, was not pretreated with silane. Instead, the silane was merely added to the coating mix (dispersion) in comparable amount. In testing of the Snowflake pads as before, sirilar results to those obtained from the patterned coating with untreated abrasive grain (Example 3) were obtained. The cut values were low and erosion was excessive. As a result, such a coated abrasive product ~s not cuitable for lens ~econd fining applications. ~hus, for good results, it is seen to be critical to the invention disclosed not to just rerely provide silane in the binder for~ulation. It ~ust be provided on the a~rasive qrains s ~ pretreatment prior to the grains being dispersed in the binder formulation.

Example No. S
Comparision of Patterned Coatinq Of Invention With Product Havinq A Dot Pattern ~ his example illustrates the unigue performance obtained fro coated abrasive material having the patterned surface coating resulting from use of t~e gravure roll having hexagonal-shaped cells provided in its surface.
A formulation was prepared as in Example 1 of the following ingredients:
Inqredients Parts by Weight Novacure 3600 1000 ~MP~A 1320 H~ODA 600 V-Pyrol 600 Penn Violet 9R-75 100 Irgacure 651 180 Zonyl A~ 50 Kr-55 10.0 Cab-O-Sil ,y52 SO
Silane Treated Aluminum 9760 Oxide Abrasive Grain (3 micron) 1. Zonyl A, commercially available from duPont, is a surfactant which aids in wetting the abrasive grains and thereby reduces t~e viscosity.

2. Cab-O-Sil is a fumed silica thixotropic agent commercially available from the Cabot Corpora~ion.
~he viscosity of the above abrasive grain/binder dispersioa measured on a Brookfield, Model LV viscometer at room temperature, vas determined to be 19,000 cps at 12rpm (Spindle No. 3) and 3~,oo0 cps at 30rpm using the came ~pindle, giving a t~ixotropic index of 1.95.
~he dispersion was coated, according to conventional tec~-nique, onto a Melinex~ 3mil polyester film backing member using a 12-inch pilot size Stork rotary creen printer ~nit to provide a coated abrasive dot pattern on the backing member. ~wo cylinders were tested, one (60 HD) with 120 microns diameter openings and open area, and the other (70 HD) with 80 micron dots and 14% open area. ~ot patterns were reproduced ~harply on the film substrate without significant distortion. The cc .rsition was cured with two ~usion System medium pressure mercury vapor lamps as before described.
Snow flake fining pads were cut, according to ~sual techniques, from each of the dot patterned coated abrasive raterials and these pads were then tested in conventional manner on the Coburn-505 ophthalmic fining machine. In each case, the measured cut rate was either zero or near zero. Although the Ra and Rt values were nearly acceptable for both such patterned products, zero or near zero (0.01-0.02mm) cut values eliminated these coated abrasive materials from possible consideration in ophthalmic ~econd-fining applications.
With the pattern of coated abrasive dots provided on the backing member, the coated abrasive dots are like islands of abrasive material on the backing member surrounded by channels os areas on the backing member devoid of any coated abrasive. On t~.e other hand, when considering the pattern provided on the coated abrasive material of this invention, the pattern compriees void areas, i.e., areas on the backin~ member each having no coated abrasi~e thereon surrounded by formations of coated abrasive material.

~, Example Showing Criticality of Rheology of Abrasive Grain~Binder Dis~ersion The criticality of the rheology of the abrasive grain/binder mix in providing the patterned coated abrasive product of the invention is shown by this example.
A dispersion was prepared as before by mixing the abrasive grain with the other ingredients already ~ixed together, on a Ross double planetary mixer for 30 minutes at the ~edium ~peed ~etting:
In~redientsParts bv Weiqht Novacure 3702' 1,100 TMPTA 1,320 lS Y-Pyrol 600 Penn Voilet 9R-75 100 Irgecure 651 180 Zonyl ~ 5.0 XR-55 10.0 BYX A-510 10.0 3 Micron, Silane-Treated Precision Aluminum Oxide Grain 870 1. Novacure 3702 is available commercially from Interez, Inc. and is the diacrylate ester of the basic bisphenol-A epoxy resin and also contains some fatty acid ester groups.

~he viscosity of this binder/grain ~ix, measured as before, on a Brookfield Model LV Viscometer at room te~perature, was determined to be 1,000 cps. (Spindle No. 2, 12 rpm) and 960 cps.
~Spindle No. 2, 30 rpm) lndicating a dispersion having Newtonian flow-characteristics.

When a coatlng was made with this dispersion, usinq the same gravure roll used in Example 1, a non-patterned ~oating was obtained.
In a further adhesive binder/grain mix, the Novacure 3702 was replaced with Novacure 3700, the other ingredients remaining the same. This oligomer has the same backbone as the Novacure 3702 but is without the fatty acid ester groups. Similar unsatisfactory results, as with the Novacure 3702, were obtained.
A further binder/grain mix W2S obtained by replacing Novacure 3702, with Urethane 783, an acrylated urethane oligomer, commercially available from Thiokol Corporation. A pattern coating as in Example l was obtained; however, on testing Snowflake pads made therefrom, erosion was found to be excessive.
Erosion was also found to be extensive in fining pads made from abrasive material made from dispersions not containing the V-Pyrol, or alternately ~hen other diluent monomers such as Sipomer-BCEU are substituted therefor. Sipomer-8CEU, available commercially from Alcolac Corp., is a dimerized form of acrylic acid.

~ .

Claims (33)

1. A coated abrasive material suitable for use in lapping operations comprising:
a. a flexible and dimensionally stable backing member:
b. an abrasive grain containing material adhered to one surface of the backing member, said material being configured in a plurality of discrete raised three-dimensional formations having widths which diminish in the direction away from said backing member.

2. The coated abrasive as recited in claim 1 wherein at least two of said formations are adjacent to one another to define an intermediate area devoid of abrasive material.

3. The coated abrasive as recited in claim 2 wherein at least some of said formations have widths which are substantially uniform along their lengths.

4. The coated abrasive as recited in claim 1 wherein said abrasive material comprises abrasive grains disposed in a radiation curable binder.

5. The coated abrasive as recited in claim 1 wherein said abrasive material comprises a dispersion of abrasive grains in a curable binder having non-Newtonian properties.

6. The coated abrasive as recited in claim 1 wherein a plurality of said formations form a hexagon.

7. Coated abrasive material according to claim 1 wherein the abrasive grains in the abrasive material are in the size range of from about 0.2 microns to about 35 microns.

8. Coated abrasive material according to claim 7 wherein the abrasive grains are of aluminum oxide.

9. Coated abrasive material according to claim 8 wherein the size range of the abrasive grains is from about from 0.5-5 microns.

10. Coated abrasive material according to claim 9 wherein the aluminum oxide grain is a virgin grain.

11. Coated abrasive material according to claim 10 wherein the abrasive grain has been air classified.

12. Coated abrasive material according to claim 8 wherein the abrasive grain has been treated with a coupling agent.

13. Coated abrasive material according to claim 12 wherein the coupling agent is a silane.

14. Coated abrasive material according to claim 13 wherein the silane is gamma-methacryloxypropyl trimethoxy silane.

15. Coated abrasive material according to claim 4 wherein the said radiation curable binder comprises an acrylated epoxy resin oligomer.

16. Coated abrasive material according to claim 15 wherein the acrylated epoxy resin oligomer is a diacrylated epoxy oligomer.

17. Coated abrasive material according to claim 4 wherein the said radiation curable binder further comprise an acrylated monomer as a reactive diluent.

18. Coated abrasive material according to claim 17 wherein the reactive diluent is selected from the group consisting of trimethylolpropane triacrylate and hexanediol diacrylate.

19. Coated abrasive material according to claim 1 wherein the backing member is a plastic film.

20. Coated abrasive material according to claim 19 wherein the plastic film is polyethylene terephthalate.

21. Coated abrasive material according to claim 19 wherein the said polyester film has been pretreated with an adhesion promoter.

22. Coated abrasive material according to claim 1 wherein the said formations are provided on the said backing member by coating said abrasive grain containing material on the backing member using a rotogravure roll.

23. Coated abrasive material according to claim 22 wherein the said rotogravure roll has a hexagonal-shaped pattern provided in its surface.

24. Coated abrasive material according to claim 23 wherein the hexagonal-shaped pattern is characterized by 80 hexagonal-shaped cells per inch.

25. A process for the manufacture of a coated abrasive material suitable for use in lapping operations comprising:
a. providing a dispersion of abrasive grain in a curable binder, said dispersion having non-Newtonian properties;
b. depositing said dispersion on one side of a dimensionally stable backing member in a three-dimensional pattern defined by a plurality of coated abrasive formations; and c. curing said binder to freeze said dispersion in said three-dimensional pattern.

26. The process as recited in claim 25 wherein said binder is a radiation curable binder and said step of curing said binder includes exposing said binder to actinic radiation.

27. The process as recited in claim 25 wherein said depositing step is performed by a gravure roll by rotating said gravure roll in a coating pan containing said non-Newtonian dispersion, and by bringing said gravure roll into contact with the backing member for transferring said dispersion from the gravure roll to the backing member, the gravure roll being wiped with a doctor blade prior to contact with the backing member.

28. Process for the manufacture of coated abrasive material according to claim 25 wherein the gravure roll used is characterized by a pattern of hexagonal-shaped cells provided in its peripheral surface, said pattern being defined by a multiplicity of rows extending lengthwise of the said gravure roll, each said row comprising a plurality of said hexagonal-shaped cells which are in alignment linear fashion with respect to one another.

29. Process for the manufacture of coated abrasive material according to claim 25 wherein the abrasive grain comprises aluminum oxide in the size range of from about 0.2 microns to 35 microns.

30. Process for the manufacture of coated abrasive material according to claim 26 wherein the radiation-curable binder comprises a mixture of an acrylated epoxy oligomer and a member selected from the group consisting of multifunctional acrylic monomers and a mono-functional radiation-curable monomer.

31. Process for the manufacture of coated abrasive material according to claim 26 wherein the abrasive grain is precision graded, virgin aluminum oxide in the size range of from about 0.5 to 5.0 microns, and the radiation-curable binder comprises a mixture of an oligomer of a diacrylated ester of epoxy resin of the bisphenol-A type, trimethylopropane triacrylate monomer, a hexanediol diacrylate monomer, and N-vinyl-2 pyrrolidone, and the viscosity of the said binder mixture is about 1750 cps when measured with a #2 spindle at 6 rpm, at 76°F and about 3400 cps (spindle #2, at 30 rpm), indicating that the dispersion is characterized by non-Newtonian liquid flow characteristics.

32. Process for the manufacture of coated abrasive material according to claim 25 wherein the abrasive grain is pretreated with a solution comprising a silane coupling agent prior to being dispersed in the radiation-curable binder.

33. Process for the manufacture of coated abrasive material according to claim 27 wherein 80 hexagonal-shaped cells per inch are provided in the rotogravure roll, each having a depth of 0.0049 inches whereby the theoretical cell volume inch in cubic billion microns is 22.1 x 109.