CA1283783C - Plural layered coated abrasive - Google Patents
Plural layered coated abrasiveInfo
- Publication number
- CA1283783C CA1283783C CA000529154A CA529154A CA1283783C CA 1283783 C CA1283783 C CA 1283783C CA 000529154 A CA000529154 A CA 000529154A CA 529154 A CA529154 A CA 529154A CA 1283783 C CA1283783 C CA 1283783C
- Authority
- CA
- Canada
- Prior art keywords
- grits
- adhesive
- abrasive
- weight
- coated abrasive
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24D—TOOLS FOR GRINDING, BUFFING OR SHARPENING
- B24D11/00—Constructional features of flexible abrasive materials; Special features in the manufacture of such materials
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24D—TOOLS FOR GRINDING, BUFFING OR SHARPENING
- B24D11/00—Constructional features of flexible abrasive materials; Special features in the manufacture of such materials
- B24D11/001—Manufacture of flexible abrasive materials
- B24D11/005—Making abrasive webs
Abstract
ABSTRACT OF THE DISCLOSURE
A coated abrasive which is advantageous for cer-tain applications has at least two distinct layers of abrasive grits: a coarse outer layer and a finer in-ner layer. The median particle size of the grits in the outer layer is at least 150% of that of the inner layer grits. The grits may be adhered to the backing with adhesives compounded primarily of acrylates and cured by exposure to UV light. A product made in this way is effective for one step fining of plastic oph-thalmic lenses.
A coated abrasive which is advantageous for cer-tain applications has at least two distinct layers of abrasive grits: a coarse outer layer and a finer in-ner layer. The median particle size of the grits in the outer layer is at least 150% of that of the inner layer grits. The grits may be adhered to the backing with adhesives compounded primarily of acrylates and cured by exposure to UV light. A product made in this way is effective for one step fining of plastic oph-thalmic lenses.
Description
lZ~3~7~33 Docket D-2093 PLURAL LAYERED COATED ABRASIVE
BACKGROUND OF THE INVENTION
Field of the Invention This invention is an example of the general field of coated abrasives, which consist of a plurali-ty of abrasive grit particles distributed over atleast one major surface of and adhered to a flexible backing material.
In one specific embodiment, this invention relates to the provisio~l of coated abrasives which can accomplish lens finis~g in a single step. The term "fining" is an established term of ophthalmic art.
Originally, lens fining with coated abrasives was divided into two steps requiring different coated abrasives for each step. Much commercial use is still made of this two step process, but in recent years at least one type of commercial product capable of accomplishing in a single step what had previously required two steps has been introduced. The prior art product of this type known to the applicants is believed to have only a single grits containing layer with one type of abrasive grits therein.
This invention in its preferred embodiments also relates to the field of adhesives curable by exposure to ultraviolet (hereinafter UV) light.
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Technical Background Further descriptions of the fining process and of suitable machinery for accomplishing it are readily available in prior patents, e.g., U.S. Patents 4,320,599 to Hill et al and 3,732,647 to Stith.
A properly designed coated abrasive can be an advantageous type of lapping tool such as is shown as lapping surface 78 of Figure 2 of the Stith patent, as has been known in general terms heretofore.
In prior art coated abrasives known to the ap-plicants, the abrasive grit particles are normally size graded, which means that grits with sizes greater or lesser than the average or median size for the particular abrasive article by more than a selected ratio are excluded as thoroughly as is practical from the collection of grits making up the article. Nor-mally, all the grits in a single size graded coated abrasive article are part of a single population, so that samples of grits from different areas of the art-icle or from different layers within the depth of the grits coating on the article will have the same dis-tribution of grit siæes as the entire article, within the normal level of statistical variation or random samples of different sizes from the same population.
The use of adhesives capable of rapid cure under the influence of actinic radiation, particularly W
light, has provided attractive combinations of man-ufacturing speed and adhesive quality in many coatingoperations, including a wide variety of decorative surface coating, in which relatively thin and trans-parent adhesive coatings are adequate. ~evertheless, the use of W cured coating materials for coated abrasives has been very limited. It appears to have been generally believed that the relatively thick layers of adhesives typically required for coated j: ., ~ 2 ~, ...
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abrasives would be very difficult or impossible to cure with W light, because of the limited depth of penetration of such light into most appropriate adhe-sive formulations. Therefore, most of the workers in the field are believed to have concentrated instead on electron beam curing, as exemplified by U. S. Patent 4,547,204 of Oct. 15, 1985 to Caul. Electron beam curing, while effective, requires significantly great-er capital investment than curing with W light and presents a more serious potential hazard to personnel.
German Offenlegungsschrift 1956810 published July 21, 1971 purports to describe processes for mak-ing coated abrasives with adhesives cured by UV light, but appears to be purely speculative and non-enabling.
No working examples are given, and the exposure times suggested are so impractically long--30-300 seconds--that the probable result of trying the suggested pro-cess would be the thermal destruction of the backing.
The only published enabling example of a coated abrasive prepared by UV curing known to the applicants is in Japanese Laid-Open Application No. 119491/1978, dated 18 October 1978. This document indicates that the presence of an isocyanate compound in the adhesive is important for success with UV light initiated cure of adhesives for coated abxasiv~s. Furthermore, al-though it was generally asserted in this Japanese pub-lication that all the formulations disclosed therein are suitable for cure by UV light as well as electron beam curing, only one of the sixteen specific examples actually used UV light, and the adhesive used for this example contained no triacrylated monomers and only a little diacrylated monomer, with the bulk of the ad-hesive being non-acrylic types of polymerizable unsat-urated esters and styrene. The main goal of the art described in this publication appeared to be the use of electron beams with lower than normal energy and of relatively inexpensive adhesives.
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A waterproof paper coated abrasive with fast curing adhesives was disclosed in U. S. Patent 4,047,-903 to Hesse et al., but this product was cured by electron beam radiation only.
SUMMARY OF THE INVENTION
It has been discovered that an especially advan-tageous coated abrasive for certain processes can be made by using at least two distinctly different popu-lations of size graded abrasive ~rits and coating the larger sized grits in a distinct outer layer on top of the inner layer of finer sized grits. When the thick-ness of the outer layer is properly adapted to the work to be performed, such a design results in a rela-tively fast initial stock removal and/or surface fin-ish refinement at the beginning of use of the coatedabrasive according to this invention, followed by eventual generation of a finer finish on the surface worked by the abrasive than would be achieved if the same size grits were used throughout the depth of the grits coating.
Such a plural layered coated abrasive is espe-cially advantageous for the fining of ophthalmic lens-es. Thus, one of the preferred embodiments of this invention is a coated abrasive article suited to one step lens fining.
For convenience of manufacture, adhesives cur-able by exposure to UV light have been preferably ut-ilized in making the embodiment of this invention for one step lens fining. Styrene and most non-acrylic unsaturated polyesters, as used in Japanese Laid-Open Application No. 119491/1978, have not been found de-sirable as components of adhesives for this purpose, because their presence in the adhesives usually has led to inferior coated abrasive performance. Instead, adhesives consisting primarily of particular acrylated monomers, vinyl amines, and acrylated oligomers have been found to give superior results. Specific details 121~337133 are given below. High purity aluminum oxide abrasive grits having adequate transmission for UV light are preferred as the abrasive grits. The mass ratio of grits to adhesive is preferably between 1.5 and 2.5 and more preferably between 1.6 and 2.1.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 illustrates a typical process line for continuous production of coated abrasives according to this invention. Figure 2 shcwn the shape of a repre-sentative product of the invention, ready for actualuse on a machine as described in the Stith patent.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Adhesive ComPonents Acrvlated Monomers: For most coated abrasive products except the most flexible ones, the most im-portant polymerizable components of the adhesive used for the products according to this invention are the materials generally known commercially as acrylate monomers. We refer to these materials, which are di-, tri-, or higher poly-alcohols that have usually been acrylated to the maximum extent practical, as acryl-ated monomers for consistency with our other termi-nolo~y. (It may be noted that both our term and the more common commercial one are chemically correct, be-cause these materials are acxylates and are produced by acrylating alcohols.) Typical commercial products of this class are trimethylolpropane triacrylate (hereinaftcr TMPTA) and hexanediol diacrylate (herein-after HDODA).
In order to achieve satisfactory coated abrasive products according to this invention, it is necessary to use substantial amounts of triacrylated monomers.
TMPTA is usually preferred as a triacrylated monomer for the practice of this invention, primarily because it is reported to be least likely of all the commer-cially available triacrylated monomers to cause aller-gic skin reactions. For certain applications, ~2~337~33 however, particularly for the adhesive preferred for the outer coating of the products according to this invention, glycidyl propoxy triacrylate (hereinafter GPTA) is preferred. Minor amounts of acrylated monomers with four or more acrylate groups per mole-cule can be used in lieu of part of the triacrylates.
Adhesives in which all the acrylated monomers have three or more acrylate groups often produce very brittle cured products. It has been found desirable for the adhesive used for the inner grits layer of a one step lens fining product according to this inven-tion to use some diacrylated monomers in the adhesive.
The preferred diacrylated monomer is HDODA, but tetra-ethylene glycol diacrylate and tripropylene glycol di-acrylate could also be used. The relative amounts ofdiacrylated monomers and triacrylated monomers is ad-justed along with variations in other components of the adhesive mixture to give suitable viscosity for coating as well as effective grinding and/or finishing characteristics to the coated abrasive ultimately made with the adhesive~ A mixture o HDODA and TMPTA in a weight ratio of rom 0 to 0.83 i5 preferred, with ra-tios from 0.50 to .83 most pr~Eerr~d.
Sisniicant amounts o monoacrylated monomers such as ethyl acrylate and methyl methacrylate or of vinyl substituted aromatics such as styrene are not normally desirable in the adhesives because they can retard cure rates and yield cured products which are more brittle than is desirable for fast-cutting coated abrasives.
For all types of acrylated monomers, unsubsti-tuted acrylates are preferred but substituted ones such as methacrylates could be used. The average mo-lecular weight per acrylate unit of suitable monomers 35 varies from 95 to 160, with 95-115 preferred.
Acrylated Oligomers: For adjustment of the ~Z83~133 rheology of the adhesive before cure and of the tough-ness and cutting characteristics of the cured coated abrasive products, it is often advantageous to use ac-rylated oligomers in addition to the acrylated mono-mers noted above. The "oligomer" part of the term"acrylated oligomer" refers not to oligomers of acrylates, but rather oligomers oE other monomers which yield oligomers bearing hydroxyl or other func-tional groups suitable for reaction with acrylic acid or anhydride. The preferred acrylated oligomers ~or a one step lens fining product are (1) the diacrylates of epoxy resins of the bisphenol-A type, for use in the inner grits layer, and (2) tetra- to hexa-acryl-ates made by reacting oligomers of aromatic diure-thanes, with an average oligomer molecular weight ofabout 750 before reaction, with monomers, such as pen-taerythritol triacrylate, that contain at least one hydroxyl group and at least two, preferably three, acrylate groups. Acrylated oligomers are readily available commercially under such tradenames as Celrad from Celanese, Ebecryl from Radcure Specialties, Inc., Uvithane from Thiokol Corporation, Uvime~ from Poly-chrome, Inc., Purelast from Polymer Systems Corpora-tion, etc. Preferred diacrylate oligomers have aver-25 age molecular weights per acrylate unit of 250 to 900, with a range of 270-400 most preferred.
The tetra- to hexa-acrylated oligomers are pre-ferred when slightly harder cured adhesives are desired, as in the outer layer of the one step lens fining product. Obtaining hardness with an oligomer capped with more than one acrylate on each end is be-lieved to yield cured films with less brittleness than if the same hardness were obtained by increasing the proportion of tri- and higher acrylated monomers in-stead.
Small amounts of higher and lower oligomers,characteristically present in all practical products ~ ~ T~ADEMARK
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~Z~33~7~33 of this type, have no known harmful effect. Oligomers terminating with unsubstituted acrylate groups are preferred, but methacrylates or other substituted acrylate groups could also be used.
Amines: In the prior art, tertiary organic amines have often been added to acrylate adhesive for-mulations to promote adhesion to particular surfaces.
Some of these amines, if unsaturated, are also suit-able to serve as vlscosity reducers. N-vinyl pyrrolidone (hereinafter NVP) is a suitable unsaturat-ed tertiary amine and is often preferred for the products of our invention.
Preferred Acrylate/Amine Combinations: The ad-hesive component f~r the inner layer of a one step lens fining product as described herein preferably comprises from 100% to 36 ~ by weight of triacrylated monomers, from 0-46% by weight of diacrylated monomers, and from 0-33% by weight of acrylated oligomers. More preferably, the percentage of triacrylaked monomer should lie between 70 and 38%.
The adhesive component for the outer layer of a one step lens fining product as described herein prefer-ably comprises from 20-30 ~ by weight of triacrylated monomers, from 15-30% by weight of diacrylated mono-mers, from 15-30~ by weight of acrylated oligomers, and from 10-20~ of monovinyl tertiary amines.
Photoinitiators: If cure of the adhesives is to be initiated by UV light as is normally preferred, the adhesive composition must contain a photoinitiator which will adequately absorb and transfer to the ac-rylate components the energy from the lamps used to initiate cure. Methods for determining the amounts and types of photoinitiator used are conventional in the art of UV cured surface coatings, and the same methods were found effective for purposes of the pres-ent invention. The amount of photoinitiator is gen-erally from 0.5 to 7.0 % by weight of the amount of - lzs3~7a3 adhesive used.
The photoinitiator preferred for the one step lens fining product embodiments of this invention was 2,2-dimethoxy-2-phenyl acetophenone (hereinafter DMPA). However, 2-chlorothioxanthone, benzophenone, and 1-hydroxycyclohexyl phenyl ketone, may also be used, along with many others.
Adhesion Promoters: A normally preferred compo-nent in the adhesive formulations is a material which improves the bonding between the adhesive and the abrasive grits. Most organosilanes and organoti-tanates containing at least one organic group with from 10-20 carbon atoms have this property. An often preferred material, especially for products to be used for lens fining, was tetrakis[(2,2-diallyloxymethyl)-l-butoxy] titanium di(tridecyl) monoacid phosphite (hereinafter OTI).
Colorants: Dyes or pigments may be used if desired to color the products. However, if UV light is to be used for cure, care must be taken to select colorants which will not unduly absorb the light and thus interfere with the cure.
Fillers: As with conventional coated abrasives, in many cases it is both economical and advantageous to the product performance to use a finely ground sol-id filler in the adhesive composition. For purposes of this invention, the UV light absorption of the filler must be considered along with other charac-teristics considered for normal coated abrasive prod-ucts. Silica or calcium sulfate filler is preferred,but other fillers with adequate UV transmission could also be used.
Other Product Components Abrasive Grits: In general, abrasive grits sim-ilar to those used on conventional types of conven-. tional coated abrasives are preferred for coated abra-sives made according to this invention for the same ~2~ 7~3 applications. However, in the embodiments of this in-vention featuring adhesive cure by exposure to UV
light, white aluminum oxide abras:ive grits are usually preferred even though brown aluminum oxide or some other abrasive such as silicon carbide might be pre-ferred for coated abrasives made with normal adhe-sives. This is true because brown aluminum oxide, zirconia-alumina abrasive, silicon carbide, and most other conventional chemical types of abrasive grits, except for white aluminum oxide and the softer and thus generally less effective silica, are strong absorbers of W light. Typical satisfactory commer-cial white aluminum oxide abrasive grits products are Types 38 or 1690 Alundum available from Norton Compa-ny, Worcester, Massachusetts, and Alodur WSK fromTreibacher USA, Inc., New York City.
Various methods of measuring the size of abra-sive grits are known in the art. All of them are sub-ject to some uncertainties and disadvantages, but are generally adequate for the purposes to which they are applied. Any of the standard methods such as sieving, elutriation, sedimentation, a Coulter counter, or the like could be used to measure the grits for products according to this invention.
For grits in the size ran~e suitable for a one step lens fining product, a technique based on the diffraction of laser light has given the most satis-factory results. A commercially manufactured instru-ment, the MICROTRAC~Model 7991-3 Particle Size Analyz-er, available from Leeds & Northrup Instruments, St.
Petersburg, FL 33702, was used. This instrument mea-sures the diffraction of light by a sample of the grits and converts the results into a histogram of the particle sizes.
The values of the least upper bounds on the sizes of the smallest grit particles sufficient in to-tal to comprise 10, 50, and 90 percent by volume of - TRAD~ARX
~Z~3~l33 the whole sample are the form of output data from the MICROTRAC which was found most useful for controlling the grit sizes needed for this invention. The size for the 50% volume point is designated herein as the median grit size for the sample of grits.
Abrasive grits according to this invention should be size graded so that the 10~ size is at least 45 % of the median size and the 90% size is no more than 185 % of the median. For the inner layer of a product for one step lens fining, the grits used pref-erably have a median size between 9 and 11 microns, while for the outer layer the grits should have a me-dian size between 14 and 18 microns. A range of 9.5-10.2 microns for the inner layer and 14.0-15.0 for the outer layer is more preferred. It is additionally preferred that the outer layer of coated abrasives made according to this invention should have grits with a median size which is at least 150 % of the me-dian size of the grits in the inner layer.
For a product for one step lens fining according to this invention, it i8 pref0rred that the mass ratio of grits to adhesive in the inner layer should be from 1.5 to 2.5, more preferabl~ from 1.6 to 2.1. For the outer layer of the same product, the mass ratio of grits to adhesive is preferably 1.6 to 2.1, more pref-erably 1.6-1.8.
Backings: A very wide variety of backing mate-rials may be used for products according to the pre-sent invention. This includes backinss which are con-ventional for coated abrasives generally, such as suitably finished cloth, paper, and vulcanized fiber, along with other less conventional backings such as films of polyethylene terephthalate, polyvinyl chlor-ide, aluminum, etc.
For the particular embodiments cf this invention especially suited for one step lens fining, it is nec-essary that the backing should be waterproof, since ~Z83~7~33 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 thickness and smoothness of the backing should allow the achievement of the product thickness and smoothness ranges noted further below; and that the adhesion of the adhesive to the backing 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 plastic films or water-proof paper as the backing. The most preferred back-ing is polyethylene terephthalate film.
General Processina Characteristics The adhesive may be applied to the backing by any of the variety of ways generally well known in the coated abrasive art. For example, direct roll coat-ing, transfer roll coating, knife coating, and combi-nations of these could all be used. The final thick-ness of separate maker and size layers of adhesive used for manufacturing most ~eneral purpose types of coated abrasive should be appro~imately the same with these adhesives as with conventional ones, 50 that the thickness of the wet adhesives as applied during man-ufacture should take appropriate account of the lesser tendency o these adhesives to shrink upon cure than that of conventional adhesives.
The intensity and time of exposure of the prod-ucts to UV light and to any auxiliary heating used are determined by methods well known in the art of coating with adhesives cured by exposure to UV light, supple-mented if necessary by testing of the grinding or oth-er surface finishing performance of the coated abra-sives produced. Abrasive grits may be applied to the wet adhesive in any conventional manner, usually by electrocoating. For the embodiments of this invention especially adapted to one step lens fining, however, the grits are slurried with the adhesive, and no size 128~7~3~
coat is required or desirable.
For lens fining, the thickness of coating in it-self is not inherently critical, but a combined thick-ness of the backing and the product has become estab-lished as standard in the industry and is relied uponto give the proper lens curvature when used with the backup lapping tool supports which are conventional.
Two thickness ranges, 175-230 microns, and 430-485 mi-crons, are established in the art; both can readily be produced according to this invention and should normally be used unless there is a special reason to deviate from them. The uniformity of thickness is in-herently critical, because if the thickness of coating varies excessively from one part of the abrasive to another, it is possible for one part of the lens to escape proper polishing, as a result of a low spot on the abrasive, or to be excessively thinned, by a high spot on the abrasive. The combined thickness of back-ing and adhesive/abrasive over the surface of the por-tion of coatéd abrasive used for a single lens shouldnot vary by more than 25 microns, when measured with an inst~ument, such as a conventional micrometer, which measures the thickness of local high spots on the coating over an area of at least 0.05 square cen-timeters.
A method of coating which has been found suit-able to achieve the required thickness uniformity oth-er product characteristics in continuous processing is shown schematically in Figure 1. The backing to be coated is placed on an unwind stand 1 fitted with a brake which can be adjusted to give a resistance to unwinding corresponding to 90 gms force per centimeter of width of the backing. Lengths 2 of loosely sus-pended copper tinsel connected to an efficient ground are provided on the coating line to eliminate any dan-gerous build-up of electrostatic charge. Before en-tering the coating area, the backing is passed between ~-~83~7a3 felt wipers 3 to remove any foreign particles which would endanger the uniformity of the coat.
The coating that is to form the inner layer of the final product according to this invention is ap-plied by a direct gravure roll 6 which has a trihel-ical pattern with sixty-two lines per inch cut with a number eighty-one tool by Consolidated Engravers. The speed of rotation of this roll is maintained so that the periphery of the roll matches the backing in lin-ear speed. ~efore contacting the backing, the wettedsurface of the gravure roll is wiped with a trailing doctor blade 5. A Benton type A blade constructed of Type 304 stainless steel, 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 used was supplied by Input Graphics, Inc. The backing web was supported in the coating nip by a non-driven, freely rotating, rub-ber-coated backup roll 4. The rubber on this roll had a hardness of Shore A-75. For convenience in main-tainin~ cleanliness of the coating, the backup roll was generally undercut so that a zone about six mm in width on each edge o the backin~ was not subjected to pressure in the nip and thus was not coated.
~dhesive/abrasive slurry was supplied to the gravure roll from a coating pan 7 which was kept filled to a constant level via a recirculation loop not shown. A pump in the recirculation loop main-tained constant agitation of the slurry, so that settling of the denser abrasive component did not oc-cur to any significant extent.
After receiving the wet slurry coating on its lower side, the web passes through a texturing bar as-sembly 8. The texturing bar proper 81 is a case hardened steel bar about 25 mm in diameter. ~he bar 81 is driven to rotate opposite to the direction of passage of the backing web at a speed about one-third ~Z~33~33 higher than that of the web. The texturing bar is mounted so as to cause a displacement of the web of about 19 mm from the "natural" path it would otherwise assume; this natural path is defined by the lower sur-face of the two idler rolls 82 ~nd 83, which contactthe uncoated back of the web.
After texturing, the wet backing web is passed under a source 9 of UV light. ~he radiant power of the source 9, together with the heat input of any ad-lo ditional heat source not shown in the Figure but op-tionally introduced between the outlet from the W
light source and the takedown rubber covered idler contact roll 10 must be sufficient to cause hardening of the adhesive be~ore the web reaches roll 10. An effectiv0 UV light source for the formulations de-scribed below in preparation of products for lens fin-ing was provided by two successive Model F440-10 lamp holders fitted with one Type D followed by one Type H
lamp bulbs, each of the bulbs having a light output of 46 watts per square centimeter. The power supply for each lamp was Type P 140A. ~11 these UV light produc-ing components were supplied by Fusion Systems, Inc.
of Rockville, Maryland.
Roll 10, a rubber covered drive roll 11, and compressed air driven takedown 12 together constitute a conventional takedown assembly, which functions to product a wrinkle-free, tightly wound roll of coated abrasive product.
After the first c~ating is completed and cured as described above, the once coated roll can be placed on unwind stand 1 for application of the second coat-ing, with a different abrasive-adhesive slurry formu-lation as specified below. In applying the second coating, which forms the outer layer of the eventual product, the processing is the same except that a gravure roll had 85 lines per inch cut with a #35 tool is substituted in position 6 of the Figure, and texturing bar 81 is ~283~783 removed, allowing the web to pass under rolls 82 and 83 without being distorted from its natural straight path.
It will be appreciated by those skilled in the art that many variations of all these coating con-ditions are possible and are included within the scope of the instant invention.
While the description above has concerned pri-marily coated abrasives with two distinct layers, it is evident that one or more intermediate adhesive lay-ers, either with or without abrasive grits, could be used between the inner and outer layers described.
In such a product, the grits in the outer layer are still adhered to the inner layer, via the intermediate adhesives.
The practice of the instant invention may be further appreciated from the following examples. In these examples, all proportions stated are to be un-derstood as proportions by mass or weight, unless oth-erwise noted.
Example 1 This example illustrates the preparation of anembodiment of the invention suitable for one step lens fining. Biaxially stretched polyethylene terephthal-ate film with a thickness of 75 microns was used asthe backing material. The composition of the first coating layer was:
Celrad 3600 890 parts TMPTA 1120 parts HDODA 927 parts NVP 743 parts DMPA 180 parts Zonyl A 3.7 parts OTI 6.7 parts Yellow L-0962 40 parts Bon Red Y/S 40 parts 3'~33 Abrasive grits, 12 micron 7,267 parts In this formulation, Celrad 3600 is a diacrylated epoxy oligomer of the bisphenol-A type, Zonyl A, supplied by duPont, is a surfactant which aids in wetting the abrasive grits and thereby reduces the viscosity which would otherwise prevail, and Yello~
L-0962 and Bon Red Y/S are colorants available from BASF and Penn Color respectively. The abrasive grits was type 1690 from ~orton Co. The grading analysis of the abrasive grits was performed on the MICROTRAC
apparatus already described above, using a sample of grits with a mass of about 0.05-0.2 gms. (The amount of sample must be adjusted according to instructions supplied with the MICROTRAC instrument, but this mass range was usually satisfactory.) The grits were slurried in water and dispersed before measuring their size distribution with the aid of a*Sonicator Model W
370 ultrasonic probe instrument, available from Heat Systems-Ultrasonics, Inc., Plainview, New York. The result o~ the analysis showed a 10~ size of 5-1 microns, a median size of 9.9 microns, and a 90~ size of 17.8 microns. The other ingredients have already been identified.
All but the last three ingredients listed above were readily mixed together without special care to form a "clear coat". About three-fifths of this clear coat was then separately mixed with the two coloring agents 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. These mixed liquid ingredients are then added to a Ross mixer already containing the abrasive grits, and the slurry thus formed was mixed for one hour to disperse the grits as uniformly as practicable.
A coating of the slurry of adhesive and abrasive grits was spread to a uniform thickness of about 0.9 mil (= 0.022 mm) over the surface of the backing, ; *TRADEMAR~
-; 17 . .
lZ837~3~
using the coating apparatus shown schematically in Figure 1. The coated backing was then exposed for 2 seconds to to the output of a mercury vapor W lamp with radiant power of about 80 watts per centimeter of width.
The backing coated and cured as above was then overcoated with a second slurry of abrasive grits and adhesives. The composition of the second coating was:
Ebecryl 6220 650 parts TMPTA 300 parts GPTA 500 parts HDODA 750 parts NVP 550 parts DMPA 150 parts Zonyl A 8.5 parts OTI 5 parts Yellow L-0962 30 parts Bon Red Y/S 30 parts Abrasive grits, 18-S grade4,675 parts In this formulation, Ebecryl i9 primarily a hexa-acrylated oligomer o an aromatic diurethane, with an average oligomer molecular weight of about 750. The abrasive grits are the same chemical type as for the first coating above, but the grading analysis showed a 10% size of 6.8 microns, a median size of 14.4 mi-crons, and a 90% size of 26.6 microns. The mixing was the same as for the first coating, except that the first eight rather than the first seven ingredients constituted the clear coating for this formula. This slurry was applied in a thickness of 26 microns and cured by exposure to UV lights for two seconds as for the first coating.
From the coated abrasive web thereby produced, sections were die cut in the "snowflake" shape shown in Figure 2. One of these sections was attached with pressure sensitive adhesive to a lapping tool backup ~'2f3~7B:3 structure properly sized and curved to generate lens surfaces of the curvature required for 6~ diopter lenses of 10 cm diameter, said lapping tool backup structure being mounted in a lens polishing machine essentially as described in the Stith patent cited above. An acrylic plastic, 6~ diopter lens blank, with surface as generated by a conventional grit 40 diamond grinding wheel used to shape the proper curvature, was mounted in each of the appropriate positions on the polishing machine, and the pressure urging the coated abrasive lapping tool against the lens blank was adjusted to 9 kg force. The machine was then operated for three minutes.
The criteria prescribed for a successful result of this test are (1) removal of between 0.30 and 0.40 mm from the center of the lens, (2) a lens surface finish of not more than 0.25 microns AA and not more than 2.5 micron depth for the deepest single scratch within a standard traversal range of the surface measuring instrument, (3) general uniformity of the lens surface, and (4) lack of appreciable shedding of the coating of the abrasive lapping tool.
The product made according to this example was highly successful in this test. Product samples were additionally tested in actual use by comparing them to an established commercial product for one step fining of lenses: Fifteen~Micron CSF Imperial Lapping Film, supplied by Minnesota Mining and Manufacturing Co.
The products of this example were judged at least equal in performance to the commercial product in fining low curvature lenses made of polycarbonate plastic.
Example 2 This was the same as Example 1, except that the abrasive grits used in the second coating had a 10%
particle size of 8.5 microns, a median particle size of 17.3 microns, and a 90% particle size of 31.4.
'P TRADEMARK
BACKGROUND OF THE INVENTION
Field of the Invention This invention is an example of the general field of coated abrasives, which consist of a plurali-ty of abrasive grit particles distributed over atleast one major surface of and adhered to a flexible backing material.
In one specific embodiment, this invention relates to the provisio~l of coated abrasives which can accomplish lens finis~g in a single step. The term "fining" is an established term of ophthalmic art.
Originally, lens fining with coated abrasives was divided into two steps requiring different coated abrasives for each step. Much commercial use is still made of this two step process, but in recent years at least one type of commercial product capable of accomplishing in a single step what had previously required two steps has been introduced. The prior art product of this type known to the applicants is believed to have only a single grits containing layer with one type of abrasive grits therein.
This invention in its preferred embodiments also relates to the field of adhesives curable by exposure to ultraviolet (hereinafter UV) light.
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Technical Background Further descriptions of the fining process and of suitable machinery for accomplishing it are readily available in prior patents, e.g., U.S. Patents 4,320,599 to Hill et al and 3,732,647 to Stith.
A properly designed coated abrasive can be an advantageous type of lapping tool such as is shown as lapping surface 78 of Figure 2 of the Stith patent, as has been known in general terms heretofore.
In prior art coated abrasives known to the ap-plicants, the abrasive grit particles are normally size graded, which means that grits with sizes greater or lesser than the average or median size for the particular abrasive article by more than a selected ratio are excluded as thoroughly as is practical from the collection of grits making up the article. Nor-mally, all the grits in a single size graded coated abrasive article are part of a single population, so that samples of grits from different areas of the art-icle or from different layers within the depth of the grits coating on the article will have the same dis-tribution of grit siæes as the entire article, within the normal level of statistical variation or random samples of different sizes from the same population.
The use of adhesives capable of rapid cure under the influence of actinic radiation, particularly W
light, has provided attractive combinations of man-ufacturing speed and adhesive quality in many coatingoperations, including a wide variety of decorative surface coating, in which relatively thin and trans-parent adhesive coatings are adequate. ~evertheless, the use of W cured coating materials for coated abrasives has been very limited. It appears to have been generally believed that the relatively thick layers of adhesives typically required for coated j: ., ~ 2 ~, ...
~83~713~
abrasives would be very difficult or impossible to cure with W light, because of the limited depth of penetration of such light into most appropriate adhe-sive formulations. Therefore, most of the workers in the field are believed to have concentrated instead on electron beam curing, as exemplified by U. S. Patent 4,547,204 of Oct. 15, 1985 to Caul. Electron beam curing, while effective, requires significantly great-er capital investment than curing with W light and presents a more serious potential hazard to personnel.
German Offenlegungsschrift 1956810 published July 21, 1971 purports to describe processes for mak-ing coated abrasives with adhesives cured by UV light, but appears to be purely speculative and non-enabling.
No working examples are given, and the exposure times suggested are so impractically long--30-300 seconds--that the probable result of trying the suggested pro-cess would be the thermal destruction of the backing.
The only published enabling example of a coated abrasive prepared by UV curing known to the applicants is in Japanese Laid-Open Application No. 119491/1978, dated 18 October 1978. This document indicates that the presence of an isocyanate compound in the adhesive is important for success with UV light initiated cure of adhesives for coated abxasiv~s. Furthermore, al-though it was generally asserted in this Japanese pub-lication that all the formulations disclosed therein are suitable for cure by UV light as well as electron beam curing, only one of the sixteen specific examples actually used UV light, and the adhesive used for this example contained no triacrylated monomers and only a little diacrylated monomer, with the bulk of the ad-hesive being non-acrylic types of polymerizable unsat-urated esters and styrene. The main goal of the art described in this publication appeared to be the use of electron beams with lower than normal energy and of relatively inexpensive adhesives.
1283 7~3~
A waterproof paper coated abrasive with fast curing adhesives was disclosed in U. S. Patent 4,047,-903 to Hesse et al., but this product was cured by electron beam radiation only.
SUMMARY OF THE INVENTION
It has been discovered that an especially advan-tageous coated abrasive for certain processes can be made by using at least two distinctly different popu-lations of size graded abrasive ~rits and coating the larger sized grits in a distinct outer layer on top of the inner layer of finer sized grits. When the thick-ness of the outer layer is properly adapted to the work to be performed, such a design results in a rela-tively fast initial stock removal and/or surface fin-ish refinement at the beginning of use of the coatedabrasive according to this invention, followed by eventual generation of a finer finish on the surface worked by the abrasive than would be achieved if the same size grits were used throughout the depth of the grits coating.
Such a plural layered coated abrasive is espe-cially advantageous for the fining of ophthalmic lens-es. Thus, one of the preferred embodiments of this invention is a coated abrasive article suited to one step lens fining.
For convenience of manufacture, adhesives cur-able by exposure to UV light have been preferably ut-ilized in making the embodiment of this invention for one step lens fining. Styrene and most non-acrylic unsaturated polyesters, as used in Japanese Laid-Open Application No. 119491/1978, have not been found de-sirable as components of adhesives for this purpose, because their presence in the adhesives usually has led to inferior coated abrasive performance. Instead, adhesives consisting primarily of particular acrylated monomers, vinyl amines, and acrylated oligomers have been found to give superior results. Specific details 121~337133 are given below. High purity aluminum oxide abrasive grits having adequate transmission for UV light are preferred as the abrasive grits. The mass ratio of grits to adhesive is preferably between 1.5 and 2.5 and more preferably between 1.6 and 2.1.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 illustrates a typical process line for continuous production of coated abrasives according to this invention. Figure 2 shcwn the shape of a repre-sentative product of the invention, ready for actualuse on a machine as described in the Stith patent.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Adhesive ComPonents Acrvlated Monomers: For most coated abrasive products except the most flexible ones, the most im-portant polymerizable components of the adhesive used for the products according to this invention are the materials generally known commercially as acrylate monomers. We refer to these materials, which are di-, tri-, or higher poly-alcohols that have usually been acrylated to the maximum extent practical, as acryl-ated monomers for consistency with our other termi-nolo~y. (It may be noted that both our term and the more common commercial one are chemically correct, be-cause these materials are acxylates and are produced by acrylating alcohols.) Typical commercial products of this class are trimethylolpropane triacrylate (hereinaftcr TMPTA) and hexanediol diacrylate (herein-after HDODA).
In order to achieve satisfactory coated abrasive products according to this invention, it is necessary to use substantial amounts of triacrylated monomers.
TMPTA is usually preferred as a triacrylated monomer for the practice of this invention, primarily because it is reported to be least likely of all the commer-cially available triacrylated monomers to cause aller-gic skin reactions. For certain applications, ~2~337~33 however, particularly for the adhesive preferred for the outer coating of the products according to this invention, glycidyl propoxy triacrylate (hereinafter GPTA) is preferred. Minor amounts of acrylated monomers with four or more acrylate groups per mole-cule can be used in lieu of part of the triacrylates.
Adhesives in which all the acrylated monomers have three or more acrylate groups often produce very brittle cured products. It has been found desirable for the adhesive used for the inner grits layer of a one step lens fining product according to this inven-tion to use some diacrylated monomers in the adhesive.
The preferred diacrylated monomer is HDODA, but tetra-ethylene glycol diacrylate and tripropylene glycol di-acrylate could also be used. The relative amounts ofdiacrylated monomers and triacrylated monomers is ad-justed along with variations in other components of the adhesive mixture to give suitable viscosity for coating as well as effective grinding and/or finishing characteristics to the coated abrasive ultimately made with the adhesive~ A mixture o HDODA and TMPTA in a weight ratio of rom 0 to 0.83 i5 preferred, with ra-tios from 0.50 to .83 most pr~Eerr~d.
Sisniicant amounts o monoacrylated monomers such as ethyl acrylate and methyl methacrylate or of vinyl substituted aromatics such as styrene are not normally desirable in the adhesives because they can retard cure rates and yield cured products which are more brittle than is desirable for fast-cutting coated abrasives.
For all types of acrylated monomers, unsubsti-tuted acrylates are preferred but substituted ones such as methacrylates could be used. The average mo-lecular weight per acrylate unit of suitable monomers 35 varies from 95 to 160, with 95-115 preferred.
Acrylated Oligomers: For adjustment of the ~Z83~133 rheology of the adhesive before cure and of the tough-ness and cutting characteristics of the cured coated abrasive products, it is often advantageous to use ac-rylated oligomers in addition to the acrylated mono-mers noted above. The "oligomer" part of the term"acrylated oligomer" refers not to oligomers of acrylates, but rather oligomers oE other monomers which yield oligomers bearing hydroxyl or other func-tional groups suitable for reaction with acrylic acid or anhydride. The preferred acrylated oligomers ~or a one step lens fining product are (1) the diacrylates of epoxy resins of the bisphenol-A type, for use in the inner grits layer, and (2) tetra- to hexa-acryl-ates made by reacting oligomers of aromatic diure-thanes, with an average oligomer molecular weight ofabout 750 before reaction, with monomers, such as pen-taerythritol triacrylate, that contain at least one hydroxyl group and at least two, preferably three, acrylate groups. Acrylated oligomers are readily available commercially under such tradenames as Celrad from Celanese, Ebecryl from Radcure Specialties, Inc., Uvithane from Thiokol Corporation, Uvime~ from Poly-chrome, Inc., Purelast from Polymer Systems Corpora-tion, etc. Preferred diacrylate oligomers have aver-25 age molecular weights per acrylate unit of 250 to 900, with a range of 270-400 most preferred.
The tetra- to hexa-acrylated oligomers are pre-ferred when slightly harder cured adhesives are desired, as in the outer layer of the one step lens fining product. Obtaining hardness with an oligomer capped with more than one acrylate on each end is be-lieved to yield cured films with less brittleness than if the same hardness were obtained by increasing the proportion of tri- and higher acrylated monomers in-stead.
Small amounts of higher and lower oligomers,characteristically present in all practical products ~ ~ T~ADEMARK
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~Z~33~7~33 of this type, have no known harmful effect. Oligomers terminating with unsubstituted acrylate groups are preferred, but methacrylates or other substituted acrylate groups could also be used.
Amines: In the prior art, tertiary organic amines have often been added to acrylate adhesive for-mulations to promote adhesion to particular surfaces.
Some of these amines, if unsaturated, are also suit-able to serve as vlscosity reducers. N-vinyl pyrrolidone (hereinafter NVP) is a suitable unsaturat-ed tertiary amine and is often preferred for the products of our invention.
Preferred Acrylate/Amine Combinations: The ad-hesive component f~r the inner layer of a one step lens fining product as described herein preferably comprises from 100% to 36 ~ by weight of triacrylated monomers, from 0-46% by weight of diacrylated monomers, and from 0-33% by weight of acrylated oligomers. More preferably, the percentage of triacrylaked monomer should lie between 70 and 38%.
The adhesive component for the outer layer of a one step lens fining product as described herein prefer-ably comprises from 20-30 ~ by weight of triacrylated monomers, from 15-30% by weight of diacrylated mono-mers, from 15-30~ by weight of acrylated oligomers, and from 10-20~ of monovinyl tertiary amines.
Photoinitiators: If cure of the adhesives is to be initiated by UV light as is normally preferred, the adhesive composition must contain a photoinitiator which will adequately absorb and transfer to the ac-rylate components the energy from the lamps used to initiate cure. Methods for determining the amounts and types of photoinitiator used are conventional in the art of UV cured surface coatings, and the same methods were found effective for purposes of the pres-ent invention. The amount of photoinitiator is gen-erally from 0.5 to 7.0 % by weight of the amount of - lzs3~7a3 adhesive used.
The photoinitiator preferred for the one step lens fining product embodiments of this invention was 2,2-dimethoxy-2-phenyl acetophenone (hereinafter DMPA). However, 2-chlorothioxanthone, benzophenone, and 1-hydroxycyclohexyl phenyl ketone, may also be used, along with many others.
Adhesion Promoters: A normally preferred compo-nent in the adhesive formulations is a material which improves the bonding between the adhesive and the abrasive grits. Most organosilanes and organoti-tanates containing at least one organic group with from 10-20 carbon atoms have this property. An often preferred material, especially for products to be used for lens fining, was tetrakis[(2,2-diallyloxymethyl)-l-butoxy] titanium di(tridecyl) monoacid phosphite (hereinafter OTI).
Colorants: Dyes or pigments may be used if desired to color the products. However, if UV light is to be used for cure, care must be taken to select colorants which will not unduly absorb the light and thus interfere with the cure.
Fillers: As with conventional coated abrasives, in many cases it is both economical and advantageous to the product performance to use a finely ground sol-id filler in the adhesive composition. For purposes of this invention, the UV light absorption of the filler must be considered along with other charac-teristics considered for normal coated abrasive prod-ucts. Silica or calcium sulfate filler is preferred,but other fillers with adequate UV transmission could also be used.
Other Product Components Abrasive Grits: In general, abrasive grits sim-ilar to those used on conventional types of conven-. tional coated abrasives are preferred for coated abra-sives made according to this invention for the same ~2~ 7~3 applications. However, in the embodiments of this in-vention featuring adhesive cure by exposure to UV
light, white aluminum oxide abras:ive grits are usually preferred even though brown aluminum oxide or some other abrasive such as silicon carbide might be pre-ferred for coated abrasives made with normal adhe-sives. This is true because brown aluminum oxide, zirconia-alumina abrasive, silicon carbide, and most other conventional chemical types of abrasive grits, except for white aluminum oxide and the softer and thus generally less effective silica, are strong absorbers of W light. Typical satisfactory commer-cial white aluminum oxide abrasive grits products are Types 38 or 1690 Alundum available from Norton Compa-ny, Worcester, Massachusetts, and Alodur WSK fromTreibacher USA, Inc., New York City.
Various methods of measuring the size of abra-sive grits are known in the art. All of them are sub-ject to some uncertainties and disadvantages, but are generally adequate for the purposes to which they are applied. Any of the standard methods such as sieving, elutriation, sedimentation, a Coulter counter, or the like could be used to measure the grits for products according to this invention.
For grits in the size ran~e suitable for a one step lens fining product, a technique based on the diffraction of laser light has given the most satis-factory results. A commercially manufactured instru-ment, the MICROTRAC~Model 7991-3 Particle Size Analyz-er, available from Leeds & Northrup Instruments, St.
Petersburg, FL 33702, was used. This instrument mea-sures the diffraction of light by a sample of the grits and converts the results into a histogram of the particle sizes.
The values of the least upper bounds on the sizes of the smallest grit particles sufficient in to-tal to comprise 10, 50, and 90 percent by volume of - TRAD~ARX
~Z~3~l33 the whole sample are the form of output data from the MICROTRAC which was found most useful for controlling the grit sizes needed for this invention. The size for the 50% volume point is designated herein as the median grit size for the sample of grits.
Abrasive grits according to this invention should be size graded so that the 10~ size is at least 45 % of the median size and the 90% size is no more than 185 % of the median. For the inner layer of a product for one step lens fining, the grits used pref-erably have a median size between 9 and 11 microns, while for the outer layer the grits should have a me-dian size between 14 and 18 microns. A range of 9.5-10.2 microns for the inner layer and 14.0-15.0 for the outer layer is more preferred. It is additionally preferred that the outer layer of coated abrasives made according to this invention should have grits with a median size which is at least 150 % of the me-dian size of the grits in the inner layer.
For a product for one step lens fining according to this invention, it i8 pref0rred that the mass ratio of grits to adhesive in the inner layer should be from 1.5 to 2.5, more preferabl~ from 1.6 to 2.1. For the outer layer of the same product, the mass ratio of grits to adhesive is preferably 1.6 to 2.1, more pref-erably 1.6-1.8.
Backings: A very wide variety of backing mate-rials may be used for products according to the pre-sent invention. This includes backinss which are con-ventional for coated abrasives generally, such as suitably finished cloth, paper, and vulcanized fiber, along with other less conventional backings such as films of polyethylene terephthalate, polyvinyl chlor-ide, aluminum, etc.
For the particular embodiments cf this invention especially suited for one step lens fining, it is nec-essary that the backing should be waterproof, since ~Z83~7~33 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 thickness and smoothness of the backing should allow the achievement of the product thickness and smoothness ranges noted further below; and that the adhesion of the adhesive to the backing 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 plastic films or water-proof paper as the backing. The most preferred back-ing is polyethylene terephthalate film.
General Processina Characteristics The adhesive may be applied to the backing by any of the variety of ways generally well known in the coated abrasive art. For example, direct roll coat-ing, transfer roll coating, knife coating, and combi-nations of these could all be used. The final thick-ness of separate maker and size layers of adhesive used for manufacturing most ~eneral purpose types of coated abrasive should be appro~imately the same with these adhesives as with conventional ones, 50 that the thickness of the wet adhesives as applied during man-ufacture should take appropriate account of the lesser tendency o these adhesives to shrink upon cure than that of conventional adhesives.
The intensity and time of exposure of the prod-ucts to UV light and to any auxiliary heating used are determined by methods well known in the art of coating with adhesives cured by exposure to UV light, supple-mented if necessary by testing of the grinding or oth-er surface finishing performance of the coated abra-sives produced. Abrasive grits may be applied to the wet adhesive in any conventional manner, usually by electrocoating. For the embodiments of this invention especially adapted to one step lens fining, however, the grits are slurried with the adhesive, and no size 128~7~3~
coat is required or desirable.
For lens fining, the thickness of coating in it-self is not inherently critical, but a combined thick-ness of the backing and the product has become estab-lished as standard in the industry and is relied uponto give the proper lens curvature when used with the backup lapping tool supports which are conventional.
Two thickness ranges, 175-230 microns, and 430-485 mi-crons, are established in the art; both can readily be produced according to this invention and should normally be used unless there is a special reason to deviate from them. The uniformity of thickness is in-herently critical, because if the thickness of coating varies excessively from one part of the abrasive to another, it is possible for one part of the lens to escape proper polishing, as a result of a low spot on the abrasive, or to be excessively thinned, by a high spot on the abrasive. The combined thickness of back-ing and adhesive/abrasive over the surface of the por-tion of coatéd abrasive used for a single lens shouldnot vary by more than 25 microns, when measured with an inst~ument, such as a conventional micrometer, which measures the thickness of local high spots on the coating over an area of at least 0.05 square cen-timeters.
A method of coating which has been found suit-able to achieve the required thickness uniformity oth-er product characteristics in continuous processing is shown schematically in Figure 1. The backing to be coated is placed on an unwind stand 1 fitted with a brake which can be adjusted to give a resistance to unwinding corresponding to 90 gms force per centimeter of width of the backing. Lengths 2 of loosely sus-pended copper tinsel connected to an efficient ground are provided on the coating line to eliminate any dan-gerous build-up of electrostatic charge. Before en-tering the coating area, the backing is passed between ~-~83~7a3 felt wipers 3 to remove any foreign particles which would endanger the uniformity of the coat.
The coating that is to form the inner layer of the final product according to this invention is ap-plied by a direct gravure roll 6 which has a trihel-ical pattern with sixty-two lines per inch cut with a number eighty-one tool by Consolidated Engravers. The speed of rotation of this roll is maintained so that the periphery of the roll matches the backing in lin-ear speed. ~efore contacting the backing, the wettedsurface of the gravure roll is wiped with a trailing doctor blade 5. A Benton type A blade constructed of Type 304 stainless steel, 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 used was supplied by Input Graphics, Inc. The backing web was supported in the coating nip by a non-driven, freely rotating, rub-ber-coated backup roll 4. The rubber on this roll had a hardness of Shore A-75. For convenience in main-tainin~ cleanliness of the coating, the backup roll was generally undercut so that a zone about six mm in width on each edge o the backin~ was not subjected to pressure in the nip and thus was not coated.
~dhesive/abrasive slurry was supplied to the gravure roll from a coating pan 7 which was kept filled to a constant level via a recirculation loop not shown. A pump in the recirculation loop main-tained constant agitation of the slurry, so that settling of the denser abrasive component did not oc-cur to any significant extent.
After receiving the wet slurry coating on its lower side, the web passes through a texturing bar as-sembly 8. The texturing bar proper 81 is a case hardened steel bar about 25 mm in diameter. ~he bar 81 is driven to rotate opposite to the direction of passage of the backing web at a speed about one-third ~Z~33~33 higher than that of the web. The texturing bar is mounted so as to cause a displacement of the web of about 19 mm from the "natural" path it would otherwise assume; this natural path is defined by the lower sur-face of the two idler rolls 82 ~nd 83, which contactthe uncoated back of the web.
After texturing, the wet backing web is passed under a source 9 of UV light. ~he radiant power of the source 9, together with the heat input of any ad-lo ditional heat source not shown in the Figure but op-tionally introduced between the outlet from the W
light source and the takedown rubber covered idler contact roll 10 must be sufficient to cause hardening of the adhesive be~ore the web reaches roll 10. An effectiv0 UV light source for the formulations de-scribed below in preparation of products for lens fin-ing was provided by two successive Model F440-10 lamp holders fitted with one Type D followed by one Type H
lamp bulbs, each of the bulbs having a light output of 46 watts per square centimeter. The power supply for each lamp was Type P 140A. ~11 these UV light produc-ing components were supplied by Fusion Systems, Inc.
of Rockville, Maryland.
Roll 10, a rubber covered drive roll 11, and compressed air driven takedown 12 together constitute a conventional takedown assembly, which functions to product a wrinkle-free, tightly wound roll of coated abrasive product.
After the first c~ating is completed and cured as described above, the once coated roll can be placed on unwind stand 1 for application of the second coat-ing, with a different abrasive-adhesive slurry formu-lation as specified below. In applying the second coating, which forms the outer layer of the eventual product, the processing is the same except that a gravure roll had 85 lines per inch cut with a #35 tool is substituted in position 6 of the Figure, and texturing bar 81 is ~283~783 removed, allowing the web to pass under rolls 82 and 83 without being distorted from its natural straight path.
It will be appreciated by those skilled in the art that many variations of all these coating con-ditions are possible and are included within the scope of the instant invention.
While the description above has concerned pri-marily coated abrasives with two distinct layers, it is evident that one or more intermediate adhesive lay-ers, either with or without abrasive grits, could be used between the inner and outer layers described.
In such a product, the grits in the outer layer are still adhered to the inner layer, via the intermediate adhesives.
The practice of the instant invention may be further appreciated from the following examples. In these examples, all proportions stated are to be un-derstood as proportions by mass or weight, unless oth-erwise noted.
Example 1 This example illustrates the preparation of anembodiment of the invention suitable for one step lens fining. Biaxially stretched polyethylene terephthal-ate film with a thickness of 75 microns was used asthe backing material. The composition of the first coating layer was:
Celrad 3600 890 parts TMPTA 1120 parts HDODA 927 parts NVP 743 parts DMPA 180 parts Zonyl A 3.7 parts OTI 6.7 parts Yellow L-0962 40 parts Bon Red Y/S 40 parts 3'~33 Abrasive grits, 12 micron 7,267 parts In this formulation, Celrad 3600 is a diacrylated epoxy oligomer of the bisphenol-A type, Zonyl A, supplied by duPont, is a surfactant which aids in wetting the abrasive grits and thereby reduces the viscosity which would otherwise prevail, and Yello~
L-0962 and Bon Red Y/S are colorants available from BASF and Penn Color respectively. The abrasive grits was type 1690 from ~orton Co. The grading analysis of the abrasive grits was performed on the MICROTRAC
apparatus already described above, using a sample of grits with a mass of about 0.05-0.2 gms. (The amount of sample must be adjusted according to instructions supplied with the MICROTRAC instrument, but this mass range was usually satisfactory.) The grits were slurried in water and dispersed before measuring their size distribution with the aid of a*Sonicator Model W
370 ultrasonic probe instrument, available from Heat Systems-Ultrasonics, Inc., Plainview, New York. The result o~ the analysis showed a 10~ size of 5-1 microns, a median size of 9.9 microns, and a 90~ size of 17.8 microns. The other ingredients have already been identified.
All but the last three ingredients listed above were readily mixed together without special care to form a "clear coat". About three-fifths of this clear coat was then separately mixed with the two coloring agents 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. These mixed liquid ingredients are then added to a Ross mixer already containing the abrasive grits, and the slurry thus formed was mixed for one hour to disperse the grits as uniformly as practicable.
A coating of the slurry of adhesive and abrasive grits was spread to a uniform thickness of about 0.9 mil (= 0.022 mm) over the surface of the backing, ; *TRADEMAR~
-; 17 . .
lZ837~3~
using the coating apparatus shown schematically in Figure 1. The coated backing was then exposed for 2 seconds to to the output of a mercury vapor W lamp with radiant power of about 80 watts per centimeter of width.
The backing coated and cured as above was then overcoated with a second slurry of abrasive grits and adhesives. The composition of the second coating was:
Ebecryl 6220 650 parts TMPTA 300 parts GPTA 500 parts HDODA 750 parts NVP 550 parts DMPA 150 parts Zonyl A 8.5 parts OTI 5 parts Yellow L-0962 30 parts Bon Red Y/S 30 parts Abrasive grits, 18-S grade4,675 parts In this formulation, Ebecryl i9 primarily a hexa-acrylated oligomer o an aromatic diurethane, with an average oligomer molecular weight of about 750. The abrasive grits are the same chemical type as for the first coating above, but the grading analysis showed a 10% size of 6.8 microns, a median size of 14.4 mi-crons, and a 90% size of 26.6 microns. The mixing was the same as for the first coating, except that the first eight rather than the first seven ingredients constituted the clear coating for this formula. This slurry was applied in a thickness of 26 microns and cured by exposure to UV lights for two seconds as for the first coating.
From the coated abrasive web thereby produced, sections were die cut in the "snowflake" shape shown in Figure 2. One of these sections was attached with pressure sensitive adhesive to a lapping tool backup ~'2f3~7B:3 structure properly sized and curved to generate lens surfaces of the curvature required for 6~ diopter lenses of 10 cm diameter, said lapping tool backup structure being mounted in a lens polishing machine essentially as described in the Stith patent cited above. An acrylic plastic, 6~ diopter lens blank, with surface as generated by a conventional grit 40 diamond grinding wheel used to shape the proper curvature, was mounted in each of the appropriate positions on the polishing machine, and the pressure urging the coated abrasive lapping tool against the lens blank was adjusted to 9 kg force. The machine was then operated for three minutes.
The criteria prescribed for a successful result of this test are (1) removal of between 0.30 and 0.40 mm from the center of the lens, (2) a lens surface finish of not more than 0.25 microns AA and not more than 2.5 micron depth for the deepest single scratch within a standard traversal range of the surface measuring instrument, (3) general uniformity of the lens surface, and (4) lack of appreciable shedding of the coating of the abrasive lapping tool.
The product made according to this example was highly successful in this test. Product samples were additionally tested in actual use by comparing them to an established commercial product for one step fining of lenses: Fifteen~Micron CSF Imperial Lapping Film, supplied by Minnesota Mining and Manufacturing Co.
The products of this example were judged at least equal in performance to the commercial product in fining low curvature lenses made of polycarbonate plastic.
Example 2 This was the same as Example 1, except that the abrasive grits used in the second coating had a 10%
particle size of 8.5 microns, a median particle size of 17.3 microns, and a 90% particle size of 31.4.
'P TRADEMARK
4 , . .
~.Z837f~3 Performance of this product with larger abrasive grits in the outer layer was adequate according to the criteria stated in Example 1, but the product was not as effective in actual usage tests as the product of Example 1.
~.Z837f~3 Performance of this product with larger abrasive grits in the outer layer was adequate according to the criteria stated in Example 1, but the product was not as effective in actual usage tests as the product of Example 1.
Claims (32)
1. A plural layer coated abrasive, comprising:
(a) a flexible backing;
(b) an inner layer of first size graded abrasive grits distributed over at least one major surface of and adhered to said flexible backing; and (c) an outer layer of second size graded abrasive grits distributed over and adhered to the side of said inner layer opposite from said backing, wherein said second size graded abrasive grits have a median size which is at least 150 % of the median size of said first size graded abrasive grits.
(a) a flexible backing;
(b) an inner layer of first size graded abrasive grits distributed over at least one major surface of and adhered to said flexible backing; and (c) an outer layer of second size graded abrasive grits distributed over and adhered to the side of said inner layer opposite from said backing, wherein said second size graded abrasive grits have a median size which is at least 150 % of the median size of said first size graded abrasive grits.
2. A coated abrasive according to Claim 1 which is suitable for use as a one step lens fining product on ophthalmic lenses generated by a grit 40 diamond grinding wheel.
3. A coated abrasive according to Claim 2, wherein said size graded abrasive grits are adhered by means of adhesives which are the cured product of a liquid mixture containing a photoinitiator and suscep-tible to cure by exposure to UV light.
4. A coated abrasive according to Claim 3, wherein said inner layer is a substantially uniform mixture of abrasive grits and adhesive comprising:
(a) an adhesive component comprising (i) from 100% to 36 % by weight of triacrylated monomers, (ii) from 0-46% by weight of diacryl-ated monomers, and (iii) from 0-33% by weight of acrylated oligomers; and (b) white aluminum oxide abrasive grits having a median particle size between 9 and 11 microns, said abrasive grits being present in the mixture in a mass ratio to the adhesive component of from 1.5 to 2.5.
(a) an adhesive component comprising (i) from 100% to 36 % by weight of triacrylated monomers, (ii) from 0-46% by weight of diacryl-ated monomers, and (iii) from 0-33% by weight of acrylated oligomers; and (b) white aluminum oxide abrasive grits having a median particle size between 9 and 11 microns, said abrasive grits being present in the mixture in a mass ratio to the adhesive component of from 1.5 to 2.5.
5. A coated abrasive according to Claim 4, wherein said percentage of triacrylated monomer is from 70% to 38% and said abrasive grits have a median particle size between 9.5 and 10.2 and are present in a mass ratio to the adhesive component of from 1.6 to 2.1.
6. A coated abrasive according to Claim 5, wherein said outer layer is a substantially uniform mixture of abrasive grits and adhesive comprising:
(a) an adhesive component comprising (i) from 20-30 % by weight of triacrylated monomers, (ii) from 15-30% by weight of diacrylated monomers, (iii) from 15-30% by weight of acryl-ated oligomers, and (iv) from 10-20% of mono-vinyl tertiary amines; and (b) white aluminum oxide abrasive grits having a median size from 14-18 microns, said abrasive grits being present in the mixture in a weight ratio to the adhesive component of from 1.6 to 2.1.
(a) an adhesive component comprising (i) from 20-30 % by weight of triacrylated monomers, (ii) from 15-30% by weight of diacrylated monomers, (iii) from 15-30% by weight of acryl-ated oligomers, and (iv) from 10-20% of mono-vinyl tertiary amines; and (b) white aluminum oxide abrasive grits having a median size from 14-18 microns, said abrasive grits being present in the mixture in a weight ratio to the adhesive component of from 1.6 to 2.1.
7. A coated abrasive according to Claim 6, wherein said abrasive grits have a median particle size from 14.0-15.0 microns and axe present in a mass ratio to said adhesive of from 1.6-1.8.
8. A coated abrasive according to Claim 4, wherein said outer layer is a substantially uniform mixture of abrasive grits and adhesive comprising:
(a) an adhesive component comprising (i) from 20-30 % by weight of triacrylated monomers, (ii) from 15-30% by weight of diacrylated monomers, (iii) from 15-30% by weight of acryl-ated oligomers, and (iv) from 10-20% of mono-vinyl tertiary amines; and (b) white aluminum oxide abrasive grits having a median size from 14-18 microns, said abrasive grits being present in the mixture in a weight ratio to the adhesive component of from 1.6 to 2.1.
(a) an adhesive component comprising (i) from 20-30 % by weight of triacrylated monomers, (ii) from 15-30% by weight of diacrylated monomers, (iii) from 15-30% by weight of acryl-ated oligomers, and (iv) from 10-20% of mono-vinyl tertiary amines; and (b) white aluminum oxide abrasive grits having a median size from 14-18 microns, said abrasive grits being present in the mixture in a weight ratio to the adhesive component of from 1.6 to 2.1.
9. A coated abrasive according to Claim 8, wherein said abrasive grits have a median particle size from 14.0-15.0 microns and are present in a mass ratio to said adhesive of from 1.6-1.8.
10. A coated abrasive according to Claim 3, wherein said outer layer is a substantially uniform mixture of abrasive grits and adhesive comprising:
(a) an adhesive component comprising (i) from 20-30 % by weight of triacrylated monomers, (ii) from 15-30 % by weight of diacrylated monomers, (iii) from 15-30% by weight of acryl-ated oligomers, and (iv) from 10-20% of mono-vinyl tertiary amines; and (b) white aluminum oxide abrasive grits having a median size from 14-18 microns, said abrasive grits being present in the mixture in a weight ratio to the adhesive component of from 1.6 to 2.1.
(a) an adhesive component comprising (i) from 20-30 % by weight of triacrylated monomers, (ii) from 15-30 % by weight of diacrylated monomers, (iii) from 15-30% by weight of acryl-ated oligomers, and (iv) from 10-20% of mono-vinyl tertiary amines; and (b) white aluminum oxide abrasive grits having a median size from 14-18 microns, said abrasive grits being present in the mixture in a weight ratio to the adhesive component of from 1.6 to 2.1.
11. A coated abrasive according to Claim 10, wherein said abrasive grits have a median particle size from 14.0-15.0 microns and are present in a mass ratio to said adhesive of from 1.6-1.8.
12. A coated abrasive according to Claim 2, wherein said outer layer is a substantially uniform mixture of abrasive grits and adhesive comprising:
(a) an adhesive component comprising (i) from 20-30 % by weight of triacrylated monomers, (ii) from 15-30 % by weight of diacrylated monomers, (iii) from 15-30% by weight of acryl-ated oligomers, and (iv) from 10-20% of mono-vinyl tertiary amines; and (b) white aluminum oxide abrasive grits having a median size from 14-18 microns, said abrasive grits being present in the mixture in a weight ratio to the adhesive component of from 1.6 to 2.1.
(a) an adhesive component comprising (i) from 20-30 % by weight of triacrylated monomers, (ii) from 15-30 % by weight of diacrylated monomers, (iii) from 15-30% by weight of acryl-ated oligomers, and (iv) from 10-20% of mono-vinyl tertiary amines; and (b) white aluminum oxide abrasive grits having a median size from 14-18 microns, said abrasive grits being present in the mixture in a weight ratio to the adhesive component of from 1.6 to 2.1.
13. A coated abrasive according to Claim 12, wherein said abrasive grits have a median particle size from 14.0-15.0 microns and are present in a mass ratio to said adhesive of from 1.6-1.8.
14. A coated abrasive according to Claim 13, wherein at least half of said acrylated oligomers in the adhesive of said outer layer have at least four acrylate groups per molecule.
15. A coated abrasive according to Claim 12, wherein at least half of said acrylated oligomers in the adhesive of said outer layer have at least four acrylate groups per molecule.
16. A coated abrasive according to Claim 11, wherein at least half of said acrylated oligomers in the adhesive of said outer layer have at least four acrylate groups per molecule.
17. A coated abrasive according to Claim 10, wherein at least half of said acrylated oligomers in the adhesive of said outer layer have at least four acrylate groups per molecule.
18. A coated abrasive according to Claim 9, wherein at least half of said acrylated oligomers in the adhesive of said outer layer have at least four acrylate groups per molecule.
19. A coated abrasive according to Claim 8, wherein at least half of said acrylated oligomers in the adhesive of said outer layer have at least four acrylate groups per molecule.
20. A coated abrasive according to Claim 7, wherein at least half of said acrylated oligomers in the adhesive of said outer layer have at least four acrylate groups per molecule.
21. A coated abrasive comprising a flexible backing and a plurality of abrasive grits distributed over and adhered to at least one major surface of said backing by a dried or cured adhesive, characterized in that (1) said abrasive grits are divided into two size graded groups, an inner layer nearer the backing and an outer layer disposed over the inner layer on the side opposite the backing, and (2) the abrasive grits in said outer layer have an average particle size at least 1.5 times the average size of the grits in said inner layer.
22. A coated abrasive according to claim 21, further characterized in that at least part of said dried or cured adhesive consists of the cured product of a liquid mixture containing a photoinitiator and susceptible to cure by exposure to W light.
23. A coated abrasive according to claim 22, wherein (1) said inner layer of abrasive grits consists essentially of white aluminum oxide having a median particle size between 9 and 11 microns; and (2) the adhesive immediately surrounding said inner layer of abrasive grits is the product of cure of a mixture comprising:
(a) from 100-36 weight percent of triacrylated monomers;
(b) up to 46 weight percent of diacrylated monomers;
and (c) up to 33 weight percent of acrylated oligomers.
(a) from 100-36 weight percent of triacrylated monomers;
(b) up to 46 weight percent of diacrylated monomers;
and (c) up to 33 weight percent of acrylated oligomers.
24. A coated abrasive according to claim 23, wherein said triacrylated monomers are present in an amount from 70-36 weight percent and said abrasive grits in the inner layer have a median particle size between 9.5 and 10.2 microns.
25. A coated abrasive according to claim 21, wherein (1) the abrasive grits in said outer layer have a median particle size between 14 and 18 microns; and (2) the adhesive immediately surrounding the grits in said outer layer is the product of cure of mixture comprising;
(a) from 20-30 weight percent of triacrylated monomers;
(b) from 15-30 weight percent of diacrylated monomers;
(c) from 15-30 weight percent of acrylated oligomers;
and (d) from 10-20 weight percent of monovinyl tertiary amines.
(a) from 20-30 weight percent of triacrylated monomers;
(b) from 15-30 weight percent of diacrylated monomers;
(c) from 15-30 weight percent of acrylated oligomers;
and (d) from 10-20 weight percent of monovinyl tertiary amines.
26. A coated abrasive according to claim 25, wherein said outer layer abrasive grits have a median particle size between 14.0-15.0 microns.
27. A coated abrasive according to any one of claims 23, 24 or 25, further characterized in that at least half of the acrylated oligomers in the liquid from which the adhesive surrounding the abrasive grits of the outer layer was derived had four acrylate groups per molecule.
28. A process for fining ophthalmic lenses, characterized in that lenses having a surface finish produced by a conventional grit 40 diamond grinding wheel are completely fined by use of a single patch of a coated abrasive according to any one of claims 21, 23 or 25.
29. A process for the manufacture of a plural layer coated abrasive said abrasive being defined by claim 23, characterized in that the inner layer of abrasive grits is applied to the backing as a slurry in the adhesive liquid and that the ratio of masses of grits to adhesive in said slurry is between 1.5 and 2.5.
30. A process according to claim 29, wherein the ratio of masses of grits to adhesive in said slurry is between 1.6 and 2.1.
31. A process for the manufacture of a plural layer coated abrasive said abrasive being defined by claim 25, characterized in that the outer layer of abrasive grits is applied as a slurry in the adhesive liquid and that the ratio of masses of grits to adhesive in said slurry is between 1.6 and 2.1.
32. A process according to claim 31, wherein the ratio of masses of grits to adhesive in said slurry is between 1.6 and 1.8.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US839,243 | 1986-03-13 | ||
| US06/839,243 US4644703A (en) | 1986-03-13 | 1986-03-13 | Plural layered coated abrasive |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1283783C true CA1283783C (en) | 1991-05-07 |
Family
ID=25279224
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000529154A Expired - Fee Related CA1283783C (en) | 1986-03-13 | 1987-02-06 | Plural layered coated abrasive |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US4644703A (en) |
| JP (1) | JPS62218072A (en) |
| CA (1) | CA1283783C (en) |
| DE (2) | DE3708164A1 (en) |
| FR (1) | FR2595606A1 (en) |
| GB (1) | GB2188332B (en) |
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| US3899050A (en) * | 1971-07-06 | 1975-08-12 | Textar Gmbh | Lining for brake shoes |
| US3732647A (en) * | 1971-08-05 | 1973-05-15 | Coburn Manuf Co Inc | Polisher-finer machine |
| DE2342869A1 (en) * | 1973-08-24 | 1975-03-06 | Wilhelm Fleissner | Polishing or grinding wheel or block - corundum particles are supported by foam plastics material |
| JPS5377612A (en) * | 1976-12-21 | 1978-07-10 | Fuji Photo Film Co Ltd | Cleaning tape for magnetic recorder |
| JPS53119491A (en) * | 1977-03-28 | 1978-10-18 | Kansai Paint Co Ltd | Method of manufacturing abraisives |
| US4135007A (en) * | 1977-12-29 | 1979-01-16 | Gaf Corporation | Radiation curable coating composition comprising an acryl urethane oligomer, and an ultra-violet absorber |
| US4320599A (en) * | 1980-06-24 | 1982-03-23 | Coburn Optical Industries, Inc. | Polisher-finer apparatus |
| US4547204A (en) * | 1980-10-08 | 1985-10-15 | Carborundum Abrasives Company | Resin systems for high energy electron curable resin coated webs |
| US4565034A (en) * | 1984-01-03 | 1986-01-21 | Disco Abrasive Systems, Ltd. | Grinding and/or cutting endless belt |
-
1986
- 1986-03-13 US US06/839,243 patent/US4644703A/en not_active Expired - Fee Related
-
1987
- 1987-02-06 CA CA000529154A patent/CA1283783C/en not_active Expired - Fee Related
- 1987-03-09 GB GB8705515A patent/GB2188332B/en not_active Expired - Fee Related
- 1987-03-09 FR FR8703165A patent/FR2595606A1/en not_active Withdrawn
- 1987-03-12 JP JP62055492A patent/JPS62218072A/en active Pending
- 1987-03-13 DE DE19873708164 patent/DE3708164A1/en not_active Withdrawn
- 1987-03-13 DE DE8703821U patent/DE8703821U1/de not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE8703821U1 (en) | 1987-09-24 |
| DE3708164A1 (en) | 1987-09-17 |
| US4644703A (en) | 1987-02-24 |
| GB2188332B (en) | 1990-01-17 |
| JPS62218072A (en) | 1987-09-25 |
| GB8705515D0 (en) | 1987-04-15 |
| FR2595606A1 (en) | 1987-09-18 |
| GB2188332A (en) | 1987-09-30 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |