US3710517A

US3710517A - Process for finish polishing of glass lenses

Info

Publication number: US3710517A
Application number: US00117780A
Authority: US
Inventors: P Valerio; R Werner
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1971-02-22
Filing date: 1971-02-22
Publication date: 1973-01-16
Anticipated expiration: 1990-01-16

Abstract

The use of tiny diamonds for finish polishing of glass lenses has been made possible by incorporating them into a lap material comprising very small diamonds in a special polymeric matrix of the reaction product of an organic epoxide with an appropriate ''''hardener,'''' such as a polyamine.

Description

United States Patent 1 1 Valerio et a1.

1451 Jan. 16,1973

[54] PROCESS FOR FINISH POLISHING OF GLASS LENSES [75] Inventors: Paul F. Valerio; Robert M; Werner,

both of Rochester, NY.

[73] Assignee: Eastman Kodak Rochester, NY.

[22] Filed: Feb. 22, 1971 [211 Appl. No.: 117,780

Related US. Application Data [62] Division Of Ser. No 788,655, Jan. 2, 1969.

Company,

[52] US. Cl ..51/284 [51] Int. Cl ..B24b 1/00, B24d 17/00 [58] Field of Search....51/283, 284, 298, 308, 209 R,

51/209 DL," 206 R [56] References Cited UNITED STATES PATENTS 3,177,624 4/1965 l-lighberg ..s1 2s3x Primary Examiner-Donald G. Kelly Attorney-William T. French, Robert F. Crocker and John T. Lewis [57] ABSTRACT 11 Claims, N0 Drawings PROCESS FOR FINISH POLISHING F GLASS LENSES This application is a division of our copending application, Ser. No. 788,655, filed Jan. 2, 1969.

This invention relates to optical polishing materials and methods for use and manufacture thereof.

Lenses and other optical elements are commonly manufactured by grinding such elements to the approximate shape desired and then polishing to remove scratches created in grinding. A small amount of shaping can also be done in polishing. One type of grinding process is carried out in one or more steps using a material made of finely crushed and carefully graded diamonds embedded in sintered or friable metal. The grinding effect can be made either coarse or fine not only by the size of the diamonds used, but also by the character of the sintered metal bonding the diamonds. For example, if the bond is made quite close, the friable part of the metal does not break away as readily and tends to give a finger-grind thandoes a more open sinter. In the grinding operation, a coolant is necessary.

After one or more grinding steps have been performed on a lens, the scratches in grinding give the surface of the lens a frosted appearance. This frosted appearance is removed by polishing. A common method of polishing involves use of a nonabrasive wax lap combined with a coolant containing an abrasive such as rouge or ceric oxide. It is believed that friction created with the polishing composition and rubbing pressure from the wax heats the surface, thereby giving it a tendency to flow. .The material from the ridges of a scratch flow into the depressions of the scratch, thereby eliminating the scratch and making the surface optically usable. It is also believed that some abrasion of the ridge occurs simultaneously.

In the course of the polishing operation, the wax itself has a tendency to flow,thereby filling up indentations which have been cut in the wax for application of polishing composition and coolant. As these indentations are filled up. the operator must recut them or there will be no room for the coolant. Similarly, as the wax flows, it tends to change its shape which in turn has a tendency to change the shape of the lens surface being polished resulting in an inaccurate test-glass fit. Additional polishing steps with a more accurate lap are often used to obtain a good test-glass fit.

in any polishing operation, the polishing compound in the coolant creates a substantial cleaning problem.

Occasionally, with certain materials, a slurry charged with diamond particles of submicron size has been used as the abrasive-coolant in the polishing operation. In general, this has not been successful for high quality glass lens production.

It is an object of this invention to provide an optical polishing lap material having greatly increased life.

It is another object of this invention to sharply reduce or eliminate the need for polishing compositions in the coolant in an optical glass polishing operation.

It is another object of this invention to provide a lens polishing method which requires reduced operator attention.

It is another object of this invention to provide a lap material for optical polishing in which the tendency to flow is reduced or sharply eliminated.

It is another object of this invention to provide a lens polisher which has a tendency to give a superior testglass fit.

It is another object of this invention to provide polished glass lenses having improved sub-surfaces or substrates (just under the surfaces).

These and other objects are accomplished by manufacture and use of a new lap material for lens polishing. This lap material contains crushed diamonds in a plastic bond thereby supplying the polishing abrasive in the lap material rather than in the coolant. The finely crushed diamonds, surprisingly, operate as polishing abrasives. When bonded in a proper matrix according to the invention the use of diamonds does not result in a scratched optical surface, but instead, results in a highly polished surface.

It is thus a feature and object of this invention to provide amatrix or bond containing tiny diamonds. With this diamond-matrix lap material, glass can be finish polished without being scratched. Such a bond constructed according to the invention includes an epoxide which has been polymerized with an appropriate epoxide hardener while the diamond particles are distributed therein. Throughout a long life, this bond or matrix somehow holds the diamond particles in such a manner as to prevent grinding or scratching, and to aid the diamonds in polishing the glass.

With the use of this lap material, the following remarkable results can be obtained:

diamonds which can be crushed and graded to the same size as grinding" diamonds do not scratch or grind the glass, but polish it;

. the polisher (lap material) can be made to provide an order of magnitude more wear than conventional polishers; and

the polishing compound in the coolant can be eliminated or sharply reduced, thereby reducing operator attention in cleaning.

The valuable lap materials of this invention can be manufactured by (a) blending together (1) an appropriate organic epoxide compound having an epoxide equivalent of from about to about 450, wherein the epoxide contains an average of at least about 1.5 (preferably about 2) epoxide units or groups per molecule, (2) an appropriate hardener, and (3) from about 5 to about 50 weight percent of diamonds having diameters of from about 1 to about 50 microns, and (b) thereafter permitting a reaction between the epoxide and the hardener" to occur (preferably by warming the blend in an oven at elevated temperatures up to 250 F or more) to thereby produce the valuable lap materials of this invention. It can readily be appreciated that these lap materials can be shaped in any desired manner by permitting the epoxidation reaction to occur while the materials arecontained in a mold, for example. In this manner pellets of shaped polishing blocks of practically any desired size and configuration can be obtained.

Preferred organic epoxide materials are those having epoxide equivalents between about and about 300, and having the basic bisphenol structure:

HGH

wherein R contains from zero to eight carbon atoms and X can result from reaction with another bisphenol or bisphenol epoxide. Such bisphenol epoxides and modified bisphenol epoxides are well known in the art and need not be described in great detail herein.

Preferred hardeners (for reaction with the epoxide compounds that are useful in the practice of this inven-.

that at least about 50 weight percent of the final lap material must be represented by product(s) of the;

- hardener reaction. Materials other than;

epoxide diamonds and epoxide-hardener matrix material can also be present in the lap materials of this invention (in minor amounts up to about 20 weight percent). For example, it is believed that the inclusion of up to about weight percent of a phenyl glycidyl ether (a monofunctional epoxide), when included into the original blend of materials, functions as a beneficial plasticizer and/or extender in the final, hardened lap material of this invention. Similarly, dyes and pigments and polyvinyl acetate can be present in the lap materials of this invention, if desired, without detracting substantially from the valuable benefits that can be obtained by practicing it.

Also, it has been discovered that the presence, in the lap materials of this invention, of up to as much as about 50 volume percent of fairly uniformly dispersed gas bubbles (which appear as holes in the final, hardened lap material) actually significantly improves the efficiency of the hardened lap material. Such bubbles can be forced into the lap material by simply beating (or stirring intensively) the fluid blend of epoxide plus hardener plus diamonds to thereby disperse air through the blend, and thereafter hardening" the matrix while the air bubbles remain entrapped in the matrix. There should generally be at least about 5 volume percent of such gas bubbles (as compared with the unaerated volume of the blend), whereas the preferred volume of gas is from about to about 35 percent.

The final solidified lap materials of this invention should preferably contain from about l0 to about weight percent of diamonds having diameters of from about 1 to about 50 microns, and substantially no diamonds having diameters as great as 60 microns. The diamonds in the preferred compositions of this invention have average diameters of from about 5 to about 20 microns, while still further preferred are those diamonds having diameters ranging from about 8 to about 16 microns, with their number average diameter being about 12 microns.

diethylenediamine;

One of the most surprising aspects of this invention relates to the fact that the use of diamonds in accordance herewith results in polishing, rather than grinding. Heretofore, it is believed that there was no way known to accomplish this. Diamonds were believed to scratch too much to be useful in the finish polishing operations of glass lens manufacture. Apparently it is the peculiar combination of ingredients (small diamonds in the epoxy-hardener matrix) that makes this valuable effect possible, because it is apparently only in this way that acceptable polishing with diamonds can be accomplished.

Still another surprising aspect of the present invention relates to the fact that glass finish polishing can be accomplished using the lap materials of this invention in the essential absence of other polishing compositions. This is particularly advantageous in most instances in that it makes possible the elimination of not only expensive recovery (for reuse) of polishing compositions, as well as elimination of the fairly expensive polishing composition itself, but also, it can significantly simplify the final cleaning step, as compared with that of processes that involve the use ofconventional polishing compositions.

One of the most valuable contributions of the present invention to the art of glass polishing can readily be appreciated from the fact that the lap materials of this ingiven are by weight unless otherwise stated.

EXAMPLE 1 Into a conventional stainless steel mixer are poured 763 parts of a modified bisphenol A epoxide having an epoxide equivalent of 200 (sold by Ciba Corporation under the trade name Araldite 502 Epoxy"), 57 parts of diethylene triamine hardener, and 164 parts of diamond powder (US. 8.8. No. 12), with particles having an average diameter of about 12 microns and a range of diameter from 8 to l6 microns. The mixture is stirred vigorously to whip about 20 volume percent of air into it. Then it is poured into molds to form round pellets or discs Va inch high and 1: inch in diameter. The molds are cured at 210 F for 12 hours. The resulting solid pellets or laps are mounted on a conventional curved block (wherein the radius of curvature around the top surfaces of the pellets equals the desired radius of curvature of the final polished glass elements). Lenses to be polished are mounted on a block (with their top surfaces exposed) having the opposite shape. During the polishing operation, the block holding the lenses is rotated at high speed about the vertical axis. In addition the block holding the lap is oscillated backward and forward and allowed to turn freely on a spinner being separated from the other block only by a EXAMPLE 2 Laps are prepared as in Example 1, except that 16 parts of silica aerogel (thickening material sold by Cabot Labs under the trade name Cab-O-Sil) are blended into the material to aid in the entrapment of air thereinto. Also, curing of the laps is accomplished this time at 160 F for l2 hours. Excellent lens polishing results, similar to those of Example 1, are obtained using the resulting laps.

EXAMPLE 3 Example 1 is repeated, except that the diamond powder is replaced with Cerox (a conventional cerium oxide polishing compound). Lenses polished with the resulting solid laps are scratched excessively and not really polished acceptably.

Example 4 EXAMPLE 5 Example 1 is repeated, except that half of the diamond powder is replaced with -500-mesh ground glass. Unsatisfactory results similar to those from Example 4 are obtained.

EXAMPLE 6 Example 1 is repeated, except that Shell 828 Epoxy" is used as the epoxide material and 80 parts of triethylene tetramine hardener is used (in place of the diethylene triamine). In addition, 24 parts of the silica aerogel thickener is mixed into the blend. The resulting blend is cured first for 12 hours at room temperature and then for 5 hours at 160 F; The resulting laps show wear rates five times as long as those of conventional wax laps. The use of these laps in lens polishing operations results in excellent polished surfaces on the lenses.

EXAMPLE 7 Example 6 is repeated using 80 parts additional of monoepoxidized alkyl glycidyl ether in the initial blend. The resulting solid lap material finish polishes glass lenses in a manner fully comparable to that of the laps of Example 6.

EXAMPLE 8 Example 1 is repeated, except that 9 micron diame ter emery (aluminum oxide) is substituted for the diamond powder. Unacceptably scratched lenses result from attempts to use the resulting laps to finish polish glass lenses.

EXAMPLE 9 Example 1 isrepeated without the diamond powder. The resulting laps wear out quickly, and polish glass lenses very slowly.

EXAMPLE 10' EXAMPLE 1 is repeated, except that the epoxide and hardener are replaced with sintered nylon powder (sold by the Polymer Corp. under the trade name Nylasint No. 66"). The blend is pressed in a mold under a pressure of 3.5 tons, and then sintered for one hour at 450 F. Wear rates for the resulting laps are found to be excessively high. 1

Other epoxide materials having the above-described requisite activity, as well as other well known hardeners for such epoxides can be substituted accordingly into Example 1, above to yield useful lap materials for lens polishing, in accordance with this invention.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

- What is claimed is:

l. A process which comprises finish polishing the ground surface of a ground glass object to remove scratches created therein in grinding the object by rubbing said ground surface in the presence of a coolant with a lap supplying polishing; abrasive in the lap material, said lap material containing (a) from about 1 to about 50 weight percent of diamonds having diameters of from I to about 50 microns dispersed through (b) a porous matrix; said matrix consisting essentially of porous epoxide resin product of the reaction of (i) an organic epoxide compound having an epoxide equivalent of from about to about 450 with (ii) an organic amine hardener; said organic amine hardener having a molecular weight of at most about 200; substantially all of said diamonds having diameters below 60 microns and said epoxide resin product being present in said lap material in an amount equal to at least about 50 weight, percent of said lap material.

2. A process as in claim 1, wherein said lap material also contains gas bubbles dispersed through said matrix; the total volume of the gas in said gas bubbles being from about 5 to about 50 weight percent of the unaerated volume of said lap material.

3. A process as in claim 2, therein said organic epoxide compound has an epoxide equivalent of from about to about 300, and said organic amine is polyamine.

4. A process as in claim 3, wherein said organic polyamine is a polyalkyl polyamine.

5. A process as in claim 4, wherein said organic epoxide material is a modified bisphenol epoxide, containing an average of at least about l.5 epoxide units per molecule.

6. A process as in claim 5, wherein the average particle size of said diamonds is about 12 microns; said lap material being substantially free of diamonds having diameters greater than 60 microns; the amount of said diamonds in said lap material being from about 10 to about 25 weight percent and the amount of said gas in said lap material being from about 15 to about 35 volume percent.

epoxide units per molecule and has an epoxide equivalent of from about to about 450, and the amount of said organic polyamine is equal to from about 0.5 to about 1.5 amine groups per epoxide group.

10. A process as in claim 9, wherein said polyamine is a polyalkyl polyamine.

1 1. A process as in claim 5, wherein said glass object is a glass lens.

Claims

2. A process as in claim 1, wherein said lap material also contains gas bubbles dispersed through said matrix; the total volume of the gas in said gas bubbles being from about 5 to about 50 weight percent of the unaerated volume of said lap material.
3. A process as in claim 2, therein said organic epoxide compound has an epoxide equivalent of from about 175 to about 300, and said organic amine is a polyamine.
4. A process as in claim 3, wherein said organic polyamine is a polyalkyl polyamine.
5. A process as in claim 4, wherein said organic epoxide material is a modified bisphenol epoxide, containing an average of at least about 1.5 epoxide units per molecUle.
6. A process as in claim 5, wherein the average particle size of said diamonds is about 12 microns; said lap material being substantially free of diamonds having diameters greater than 60 microns; the amount of said diamonds in said lap material being from about 10 to about 25 weight percent and the amount of said gas in said lap material being from about 15 to about 35 volume percent.
7. A process as in claim 2, wherein said lap material also contains from about 0.15 to about 5 weight percent of a silica thickening agent.
8. A process as in claim 3, wherein said lap material contains from about 10 to about 25 weight percent of diamonds having diameters of from about 8 to about 16 microns.
9. A process as in claim 8, wherein said organic epoxide material contains an average of at least about 1.5 epoxide units per molecule and has an epoxide equivalent of from about 150 to about 450, and the amount of said organic polyamine is equal to from about 0.5 to about 1.5 amine groups per epoxide group.
10. A process as in claim 9, wherein said polyamine is a polyalkyl polyamine.
11. A process as in claim 5, wherein said glass object is a glass lens.