US2701191A - Polishing pads - Google Patents

Description

Feb. 1, 1955 A. J. LALIBERTE POLISHING PADS 2 Sheets-Sheet 1 Filed Feb. 2, 1949 INVENTOR ALBERT .1. LAUBERTE.

ATTORNEY Feb. 1, 1955 A. J. LALIBERTE 2,701,191

POLISHING PADS Filed Feb. 2. 1949 2 Sheets-Sheet 2 INVENT ALBERT J. LAUBE a BY 5 2: i 6 u ATTORNEY United States Patent POLISHING PADS Albert J. Laliberte, West Brookfield, Mass., assignor to American Optical Company, Southbridge, Mass, a voluntary association of Massachusetts Application February 2, 1949, Serial No. 74,066

8 Claims. (Cl. 51298) This invention relates to polishing pads and has particular reference to polishing pads of the type used in polishing the surfaces of glass articles such as optical elements, lenses or other desired articles and the method of making same.

One of the principal objects of the invention is to provide a long-life high speed, substantially abrasive-free polishing pad of the above character and method of making same controlled, during the fabrication thereof, so as to obtain maximum and substantially balanced efficiency as to the ability of the pad to conform to the shape of surface or surfaces being polished, to obtain maximum elficiency as to rate of removal and further to obtain maximum efiiciency as to quality of the resultant polished surface, said pad being varied according to the article or articles to be polished and according to conditions of polishing so as to have maximum wear resistance.

Another important object is to provide a long-life, high speed, inherently substantially abrasive-free, resilient substantially non-elastic, solid polishing pad formed of a vulcanized and plasticized elastomeric material having incorporated therewith a compatible thermoplastic material and filler in an amount in accordance with the resiliency and polishing characteristics desired and method of making same.

Another important object is to provide a polishing pad of the above character having incorporated therein as a filler an amount of cellulose material and/or cerium oxide for obtaining desired resiliency and improved polishing characteristics.

Another important object is to provide an improved polishing pad embodying a relatively thick backing layerof resilient material having a relatively thin layer of polishing material secured to a side surface thereof, the inherent resiliency of the backing layer enabling the polishing layer to conform to the surface shapes of the articles or lenses being polished, and the method of making same.

Another important object is to provide a polishing pad of the above character embodying a backing layer formed of material having an inherently resilient nature with a polishing surface inseparably bonded to the backing layer through direct surface vulcanization or by the use of a suitably compounded vulcanizing cement, the polishing surface comprising essentially a relatively thin, inherently substantially abrasive-free flexible or resilient, substantially non-elastic solid layer composed of a vulcanized and plasticized elastomeric material in which is intimately dispersed or dissolved a compatible thermoplastic material, the resultant pad being characterized by its ability to conform under operating pressures to the shape of the surface being polished, and the method of making same.

Another object is the provision of a polishing pad of the above character embodying a backing layer formed of material of an inherently resilient nature and of substantially uniform thickness such as sheeted felt, rubber, or the like, the backing layer having secured to a side surface thereof a relatively thin layer of polishing material of substantially uniform thickness, the polishing layer being formed of suitable polishing material such as a composition formed basically of natural or synthetic rubber mixed with a compatible thermoplastic material and extended with a suitable ligno-cellulosic fibrous filler such as corn cob, wood flour, or other like woody cellulosic material and/or cerium oxide.

Another object is to provide a polishing pad of the above character embodying a backing layer of felt hav- 2,701,191 Patented Feb. 1, 1955 ing an inherently resilient nature with a substantially thin layer of polishing material of relatively uniform thickness attached to a side surface thereof through the use of a heat vulcanizable solvent-type bonding cement which penetrates the felt surface when applied and when dried and vulcanized to the thin polishing layer under heat and pressure, provides a bond which extends in depth between the fibers of the felt whereby the polishing layer will be securely and inseparably aifixed to the felt to form a durable heat resistant laminated pad capable of withstanding the torque and twisting action incurred during actual usage.

Another object is to provide a polishing pad of the above character embodying a backing layer of an inherently resilient napped fabric material having a substantially thin layer of polishing material of relatively uniform thickness cemented to a side surface thereof through the use of a bonding cement compounded from suitable ingredients whereby upon vulcanization the cement and layer of polishing material will be vulcanized to form an integral bond therebetween and the cement will impregnate the backing layer sufiiciently to form an integral mechanical bond therebetween, thus forming a durable heat resistant laminated polishing pad.

Another object is to provide a device for use in polishing articles such as ophthalmic lenses embodying a movable lap having a surface curvature shaped substantially to the shape of the surfaces of the articles to be polished, the lap having a resilient substantially non-elastic, solid polishing pad of substantially uniform thickness attached thereto by an adhesive such as pitch or the like, the inherent resiliency of the pad enabling it to conform to the surface shape of the articles being polished upon eccentric movement of the lap during the polishing operatron.

Other objects and advantages of the invention will become apparent from the following description taken in connection with the accompanying drawing, in which:

Fig. 1 is a front elevational view of a lens polishing mechanism employing a polishing pad embodying the invention;

Fig. 2 is a sectional view of an embodiment of the invention; and

Fig. 3 is an enlarged exaggerated fragmentary sectional view illustrating the conforming characteristics of the resilient pad during a polishing operation.

The present method of forming articles such as ophthalmic lenses involves first the providing of the lens blanks with ground surfaces of substantially the surface shapes desired and the subsequent polishing of said surfaces to a continuous high lustre finish.

There are several different factors which must be carefully considered and controlled in producing such highly polished surfaces,

(1) The surface texture of the finally polished surface must be of highest quality.

(2) The time required in producing such polished surfaces must be maintained to the lowest cycle.

(3) The cost of the polishing compound and the wear and tear on the equipment must be maintained to a minimum.

In many instances, in order to further reduce cost, several lens blanks are mounted on a single block and simultaneously polished to a given controlled shape. The pads used in such polishing operations must, therefore, not only produce the above results but must further have the inherent ability to conform to the surface shapes of all of the blanks during the polishing operation in order to obtain uniform results.

One of the main difiiculties with prior art pads possessing all of the above characteristics is their tendency to wear quite quickly and due to the inherent high costs of such pads and costly and time consuming methods which must be employed in securing and removing them from their supporting laps so as to have the surface shapes desired the resultant cost per surface produced by such pads made them very expensive to use.

One of the prime objects, therefore, of the present invention is to provide a polishing pad which not only produces highest quality of polished surface but which also gives maximum polishing rate and, in instances where a plurality of blanks are polished simultaneously, has the ability to conform to the surface shapes of the various. blanks during the polishing operation whereby a uniform high quality polish is obtained and more particularly to provide a pad of the above nature which is extremely resistant to wear and which may be used with any of the known polishing compounds. The polishing pads embodying the present invention, as proven by actual tests, have greatly exceeded all expectations as to durability and efficiency as compared with known prior art pads.

Referring more particularly to the drawing wherein like characters of reference designate like parts throughout the views, the invention is directed particularly to the provision of a laminated polishing pad 3 embodying a backing layer 4 formed of a material of a resilient nature and having a layer 5 of polishing material attached to a side surface thereof, the assembled pad 3 being suitably attached by an adhesive 6 to an article such as a lap 7 used in the ophthalmic profession for polishing the surfaces of articles such as lenses 8 which are conventionally retained as by pitch or other suitable adhesive 9 upon the surface of a supporting block 10. The surfaces of the lenses 8 which are to be polished by the pad 3 embodying the invention, are preferably shaped substantially to the final shape desired by fine grinding with emery or the like after first being formed by commonly known rough grinding methods employed in the ophthalmic art, as through the use of a diamond abrading tool or other suitable means.

The block 10 is carried by means such as a spindle 12 rotatably mounted within a bearing 13 and driven by any suitable source of power through means such as pulley 14 and belt 15. The lap 7 is provided with a socket 16 in which is extended a pin member 17 carried by a supporting member 18, which member is carried by a shaft 19 rotatably mounted in a suitable bearing 20. The shaft 19 may be rotated by any suitable means such as a pulley 21 and belt 22, which means may be operated by any suitable source of power.

The polishing operation is performed by applying to the exposed surface of the pad 3 a suitable polishing compound such as rouge and water, clay and water, or any other of the well known glass polishing compounds, and by causing the pad 3 to be rotated through rotation of the shaft 19, and finally causing the block 10 to be moved so as to move the lenses 8 over the surface of the pad 3, with the movement of the pad 3 being controlled by the eccentric relationship of the pin 17 and shaft 19 which is in turn rotated. The lap 7 and block 10, during the polishing operation, are rotated with respect to one another with sufficient pressure being provided to maintain the pad 3 in constant engagement with the surfaces of the lenses 8.

It has been found that in the past some polishing compounds, although extremely efficient as glass polishing agents, have caused considerable wear of polishing pads particularly when such pads were made of felt as now commonly used in the art. The pad 3 as described herein has been found to be much more resistant to wear during polishing operations and has a life which greatly exceeds that of the above mentioned commonly used polishing materials.

Certain trade names are. used in the following description and, therefore, the following tabulation is included to define in each instance the chemical composition of material denoted by the trade names so that the nomenclature used throughout. the description will be clearly understood:

Trade Name Composition Hycar 0R A butadicne-acrylonitrile copolymer. Geon 500-503 An elastomeric material consisting of 55% poly- GMF Polyvinyl Chloride Mixture containing 90% polyvinyl chloride and VYHH 10% polyvinyl acetate. Solka Floc A highly water absorbing cellulose.

The backing layer 4 of the polishing pad 3 is formed of a material having an inherently resilient nature such as felt, rubber, certain plastics, or the like, of such nature that it possesses expandable and compressible characteristics whereby it may be initially formed relatively fiat and shaped to conform substantially uniformly to the curved shapes of the surfaces of the lenses 8 being polished with the ability to retain that shape. The layer when made of felt is preferably comprised of a wool cloth woven from good quality wool fabric of relatively long fibers and felted or filled with short wool fibers, combed or napped to provide a fuzz on its surfaces, and subsequently trimmed to a substantially uniform thickness.

A laminated pad using felt as the material of the backing layer 4 may be formed with a substantially thin layer 5 of polishing material secured to a side surface thereof, the layer 5 being of substantially uniform thickness throughout its area and compounded of suitable ingredients in desired proportions for producing the polished surfaces on the lenses 8. Such polishing layers 5 may be made of various ingredients, with elastomeric materials such as rubber, either natural or synthetic being used as the base material, and may be extended with aligno-cellulosic fibrous vegetable filler such as corn cob particles, wood flour, walnut shell flour, or the like, or with cerium oxide particles.

One suitable base material for the polishing layer is. compounded as follows:

Table A Ingredients: Parts by weight Hycar OR 300 Thiokol 240 Geon 500-503 280 Sulphur 40 Zinc oxide 24 Laurex l6 Monex 1.6 Captax 24 Piccol0 40 In producing a polishing layer from the above ingredicuts, the Hycar OR, Thiokol and Geon 500-503 are milled and mixed thoroughly with the Picco-ll) being slowly added during the mixing. Then after cooling the preparation the sulphur, zinc oxide, Laurex, Monex and Captax are added and thoroughly milled in and the preparation thereafter formed in sheets of the desired thickness, preferably about A" thick. The corn cob particles are then added and milled slowly on cool rolls. It is preferable, although not necessary, to divide the batch into two portions and add proportionate amounts of the cob to insure thorough dispersion of the cob particles throughout the mixture. The preparation is then calendered into sheets of the desired thickness, preferably about .060 and cut into discs of the required diameter.

The uncured discs or layers are then attached to the felt discs or backing layers 4 by the use of a specially compounded cement. This cement is a heat vulcanizable solvent-type cement which penetrates the felt when applied to the surface thereof and when dried and vulcanized to the polishing layer under heat and pressure provides an inseparable bond between the polishing layer and felt backing layer capable of withstanding severe usage during polishing operations. The cement may be made as The Hycar OR is broken down by milling and the Picco-lO (plasticizer) is then added slowly. Then, after cooling, the Captax, Monex and sulphur are added and the preparation mixed thoroughly, then sheeted out as thin as possible and cut into small pieces. Then, to every 500 guns. of the above mixture is added 830 gms. of 2- nitropropane followed by 830 girls. of benzene. After standing for the desired period of time a very heavy cement is formed which is diluted with 1170 gms. of benzene and after thoroughly mixing the cement is usable.

The felt, which has been previously shaped into discs of the proper diameter and thickness, the thickness being preferably about .0190", is provided on'o'n'e' side with a coating of the cement and dried in an oven maintained at about 180 F. for approximately 10 minutes. This short period of time will not cure the cement compound but will permit the solvent to be driven off. Then the polishing layer is positioned against the cemented surface of fhe felt and the assembled parts vulcanized under heat and pressure for about 10 minutes, which operation results in the formation of a laminated polishing pad ready for attachment to a lap. It is to be noted here that the Thiokol present in the polishing layer is not compounded with materials which will make it vulcanize and, therefore, acts as a softener or plasticizer and tends to give better flexiblity to the pad surface.

It is to be understood that other base materials may be used for the backing layers4 such as various types of uncured natural or synthetic rubbers. Where rubber is used it is not necessary to use'a cement for attaching the polishing layer 5 to the layer 4 since upon vulcanizing under heat and pressure the layer 5 will be integrally bonded to the polishing layer 4. Any suitable high gum type of either synthetic or natural rubber may be used since they may be compounded to possess the required resiliency for conformation properties. An example another suitable backing layer is as follows: a

Table C Specifiic amounts in Ingredients: parts by weight Hycar OR 300 Thiokol 240 Geon 500-503 280 Sulphur 40 Zinc oxide 24 Laurex 16 Monex 1.6 Captax 24 Picco-lO I 40 Another example:

Table D Ingredients: 7 Parts by weight Natural smoked sheet rubber 700 Sulphur 8.4 Zinc oxi 31 Laurex 1 l Captax 10.5

Tuex 3.5 BXA 14 The above compositions, when compounded and formed into discs by milling and mixing in a manner similar to that described in forming the polishing layer, will result in satisfactory backing layers possessing the desired characteristics.

It is also to be understood that other cements other than the foregoing may be used to secure the polishing layer to the backing layer 4. Many penetrating, heat vulcanizable, solvent types of rubber cements work satisfactorily and can be used to secure the polishing layer to a backing layer or felt or, if desired, to a rubber base Z-nitropropane 150 In forming the polishing layers 5 it is important that they comprise an unvulcanized base material and specific amounts of polyvinyl chloride or other compatible thermoplastic materials in increasing amounts up to a certain limit. The inclusion of a vinyl chloride as a constitutent in a polishing layer results in the production of improved pads possessing desirable polishing characteristics while retaining the physical properties required for conformation, with the amount of vinyl chloride being varied in accordance with the amount of corn cob or other filler used.

It will be understood that the resiliency characteristics of the pad should be controlled since with various polishing operations it is possible and sometimes desirable to use pads of varying resiliencies. As an example, to produce a satisfactory pad able to conform to the surfaces of lenses which are of varying curvatures and which may require considerable surface removal it is desirable to use a pad with specific resiliency enabling it to conform to the various surfaces. However, in cases Where lenses have been previously ground close to the final tolerances, which are substantially uniformly surfaced and blocked, and which consequently require removal of only a slight amount of their surfaces, it is possible to use a relatively hard polishing pad.

The composition from which the polishing layer is made should contain the polyvinyl chloride ingredient in controlled amounts since the resiliency characteristics can be controlled by this ingredient, and also it is significant to note that the polishing characteristics improve with increasing amounts of thermoplastic up to a certain point (about 50% concentration), beyond which point the pad progressively loses its flexibility and becomes harder.

In evaluating thermoplastics other than polyvinyl chloride the ones that are most satisfactory are those which exhibit excellent compatability or solution characteristics in the base elastomer mixture. Polyvinyl acetate, polyethylene, Lucite (polymethyl methacrylate), polyvinyl formal, and rubber chloride are some of the materials which mill and disperse readily in the base elastomer mixture and impart very rapid polishing characteristics to the resultant pad.

Improved polishing characteristics are noted in the range between 10 to 70% of thermoplastic, preferably a vinyl resin, with the most desirable concentration giving maximum polishing performance and most satisfactory conformation characteristics in the range between 30 and 40%. The following Table G illustrates three compositions using the various amounts of thermoplastic in the base composition from which the polishing layer is formed without the inclusion'of corn cob particles or other filler.

Table G Approximate Parts by Weight Ingredients- Bateh 1 Batch 2 Batch 3 Hycar OR 63.0 63.0 63.0 Thiokol 35. 5 35. 5 35. 5 Polyvinyl Chloride VYHH 30. 4 80.0 280.0 Sulphur 5. 9 5. 9 5. 9 3. 6 3. 6 3. 6 2. 4 2. 4 2. 4

.24 24 24 3. 6 3.6 3. 6 Piece-l0 5. 9 5. 9 5. 9

Batch 1 above indicates the formula when using 20% polyvinyl chloride, batch 2 using 40% polyvinyl chloride and batch 3 70% polyvinyl chloride.

The evaluation was obtained by polishing duplicate lenses with a 30% fresh polishing clay suspension in a bowl feed machine carrying the pad mounted on a lap and revolving at a speed of 250 R. P. M. at 28 lbs. pressure for six minutes, after which the lenses were examined for weight removal and surface texture.

Batch 1 results in a polishing layer which produces a satisfactory surface texture on a lens polished thereby with weight removal of 51.5 mg. Batch 2, which is within the preferred range of 30%-40% polyvinyl chloride content, results in a pad having very excellent polishing characteristics respecting surface texture and weight removal of 55.8 mg. A pad produced from-batch 3 tends to be harder, more diflicult to form and shape, but when properly dressed will produce excellent results with respect to surface texture and weight removal of 29.5 mg. Since it is noted that with increasing amounts of polyvinyl chloride there is an increase in the hardness of the resultant polishing layer, where the polyvinyl chloride content is substantially large the polishing layer can be made sufficiently thin so that when secured to a resilient backing layer it will continue to have excellent resilience and general operating characteristics,

It is also possible, however, where the polyvinyl chloride content is small enough, preferably within the 3040% range, to produce a matrix 4 in accordance with the desired formula and attach the matrix 4 directly to a lap 7 for use without a backing layer. Such a pad can be produced in accordance with the following formula:

Table H Approximate par-ts Ingredients: by weight Hycar-OR 200 'Thiokol 180 Geon 500-503 440 Sulphur 27 Zinc oxide 16 'Laurex 11 Monex 1.1 Captax 16 Piece-10 27 Table H will produce a pad having a weight removal of approximately 50.1 mg. to provide a lens with a good surface texture.

Certain fillers, particularly of aligno-cellulose fibrous woody type, have been found to impart improved polishing characteristics to the resultant pad, with classified Wood sawdust or flour being the most satisfactory. .Such types as mahogany, pine and maple sawdust and ground corn cobs are very good. The effect of such a filler is marked when using a base composition containing a substantially low concentration of thermoplastic. Ground felt, wool batting, felt sanding, and the like are also partly efiect-ive, while the inclusion in the mixture .of cerium oxide as a filler is extremely effective in imparting very rapid polishing characteristics to the pad.

Particle size of the woody fillers also effects the .quality of polish although this varies from filler to filler. In the case of corn cob particles the fine material (finer than 50 mesh) .gives a better polished surface per given time than the coarser particles.

Change in concentration of woody filler produces vari able results depending upon the hardness of the pad in accordance with the amount of thermoplastic present in the mixture. For instance, a high concentration of corn cob present in a low polyvinyl chloride mixture (soft) will produce more rapid polishing than a low concentration of cob, and a lower concentration of .corn cob is desirable in a mixture having .a higher concentration of thermoplastic.

The following compositions all contain a 30% concentration of fine corn cob particles and various amounts of thermoplastic, all producing satisfactory polishing layers:

Table I Approximate Parts by'Weight Ingredients Batch 4 Batch 5 Batch 6 Batch 7 Batch 8 Hycar OR 63. 63. 0 63:0 63. 0 63.0 Thiokol 35. 35. 5 35. 5 35. 5 35. 5 Polyvinyl Chloride VYHH. 13. 6 30. 4 51.3 80.0 120. 1 Sulphur -5. 9 5.9 1 5. 9 5. 9 5. 9 3.6 3.6 3.6 3.6 3.6 2.4 2. 4 2. 4 2. 4 2.4

Weight removals were: Batch 4, 51.6 mg; batch 5, 59.2 mg.; batch 6, 53.6 mg.; batch '7, 61.2 mg.; and batch 8, 53.2 mg. All produced excellent surface texture.

Batch 4 results in a pad having improved polishing characteristics. Pads resulting from batches 5, 6 and 7 have still better polishing characteristics, while batch 8 results in a pad comparable to the Pad produced from batch 4..

It willbe noted that in the above formulas all ingredients in each batch have been retained in like proportions with 8 onlythepolyvinyl chloride content varying, with the corn cob-content being maintained at 30%. At a content of approximately 30% of corn cob to obtain the best cone formation characteristics the thermoplastic content should, preferably be from approximately 2 040% Thus, from a comparison of polishing layers produced from formulae given in :the foregoing Tables G and I, we find that at lower cont fintrations of thermoplastic the filler accelerates the polishing action of the pad. However, at higher concentrations the cob hardens the surface to a point where it prevents the proper conformance characteristics from being obtained.

It has been found that when using, for example, an efficient polishing medium vinyl concentration, various, amounts of fine corn cob particles of other filler can be added to produce satisfactory results. It was found preferable to add approx-irnatelyy30%-.-40% cob concentration but the cob can be added in amounts ranging from approximately 0100% based on the total amount of material already in the mixture, Lar er amounts, of course, tend to render the resultant pad harder and less conformable. Although ground corn cob has been described as being the principal filler, it is to be understood that many other ground :lignoscellulose fibrous woody fillers are equivalents and in some cases are superior to corn cob. Such mat rials as ground mahogany, pine and maple sawdust and other fillers have proved to be exceptionally beneficial and may be substituted one for the other in like proportions or mixtures thereof mav be used.

Other organic or inorganic fillers such as clay, rouge, carbon black, polishing silica, wool batting, and 'Solka Floc, can be added to the composition in varying amounts with minor beneficial results, the addition of cerium oxide, however, particularly benefiting the composition and aiding considerably in the production of a greatly improved polishing pad.

Tables G and J include a base compound with the thermoplastic separately milled into the mix. However, the thermoplastic may be added in the form of Geon 500-503 rubber which contains approximately 55% of the thermoplastic intimately mixed with a butadiene-acr-ylonitr-ile polymer. Table K whichfollows illustrates three formulae using Geon 500-503 which produce very eflicient pads:

A pad produced from batch 9 has a weight removal of 49.1 mg., from batch 1 0, 44.3 mg., and from batch 11, 40.9 mg., all having good polishing characteristics and producing good surface texture on lenses.

Batches containing approximately 63 parts by weight of Hycar OR, approximately 35.5 parts by weight of Thiokol, approximately 5.9 parts .by'weight of sulphur, approximately 3.6 parts by weight of zinc oxide, approximately 2.4 parts by weight of Laurex, approximately .24 parts by weight of Monex, approximately 3.6 parts by weight of Captax, approximately 5.9 parts by weight of Piece-10, and approximately 190 parts by wei ht of fine cob, have all produced pads having satisfactory polishing characteristics when approximately parts by weight of polyvinyl chloride, polyvinyl acetate, polyethylene, rubber chloride, Lucite, polyvinyl formal or other compatible thermoplastic material is included in the batch mix. Operational use of pads made from compositions including these thermoplastic materials indicate that materials of this nature definitely impart the desirable polishing characteristics to the pads. V

When forming a sol-id one-piece polishing pad using corn cob as a filler it is necessary to be exceptionally careful in controlling the amount of cob to be added. However, a satisfactory pad can be produced by add- Q ing to a mixture such as given in the formula'in Table H approximately 233 parts or enough cob to comprise from 15-25% of the total composition. This will produce a pad having good conformation characteristics and having a weight removal of 62.8 mg. to produce a good surface texture on a lens polished thereby. A combination of cerium oxide and a ligno-cellulosic filler can be used such as by adding to the mixture in Table H amounts of cerium oxide and cob in accordance with the resiliency desired of the pad.

When forming a polishing layer to be attached to a resilient backing layer, the formula in Table H can have added thereto preferably about 50% (or from 10% to 65%), based on the total composition, of cerium oxide particles which preferable addition will produce a pad having a weight removal of approximately 67.9 mg. with good surface texture resulting. A combination of about 390 parts by weight (about 21% of the total composition) of cerium oxide and about 565 parts by weight of cob (about 30% of the total composition) can be added to the same formula to produce a pad having exceptional conformation and polishing characteristics.

The foregoing description refers particularly to polishing layer compositions using Hycar-OR and/or Geon 500-503 as the base elastomer ingredient. Other alternative base ingredients, however, can be used to produce satisfactory polishers such as indicated in the following Table L:

Table L Approximate Parts by Weight Ingredients Batch Batch Batch Batch Batch Med. Mahogany Med. P1119 130. 0 5 Carbon Black 60. 0 Tuex 7 The above Table L illustrates that Thiokol or natural rubber can be used in place of or in combination with Hycar OR or Geon 500-503 and the pads produced therefrom will possess all the desirable conformation characteristics. Any of the compositions using Hycar OR, Thiokol, natural rubber or Geon 500-503 or combinations thereof as the base ingredient may have added thereto the thermoplastic material in controlled amounts in accordance with the amount of filler used so as to produce a polishing pad having not only the desired conformation characteristics but also efficient polishing characteristics.

In producing a complete laminated polishing pad using felt as a backing layer in accordance with the foregoing description, the desired compositions are selected and the felt layer, polishing layer, and cement are made in accordance with the procedures described. After the parts have been formed and shaped substantially as de sired the polishing layer 5 is fixedly secured to the felt layer 4 by a layer of bonding cement 11 which is interposed between the polishing layer 5 and matrix 4. The cement may be applied as a layer of substantially uniform thickness, and upon vulcanizing under heat and pressure will form an integral bond between the felt layer and polishing layer.

It will be understood, however, that if a rubber base backing layer is used, the polishing layer may be attached directly to the backing layer by vulcanizing under heat and pressure without the use of any layer of cement.

The assembled pad 3 may then be attached to a lap 7 by conventional means, as through the use of a layer of pitch 6 or other suitable adhesive, which layer 6 is of substantially uniform thickness. Since the pad 3 is also of substantially uniform thickness throughout, it will be seen that the polishing surface thereof will possess the same general curvature of the lap 7.

During the polishing operation the polishing surface of the pad 3 will be in constant engagement with the surfaces of the articles or lenses 8 being polished, regardless of irregularities of their surface contours, since, as illustrated in Fig. 2, the resilient backing layer 4 will compress and expand so that the polishing layer 5 will conform to the shape of the surfaces being polished, the resilient backing being essential to insure intimate contact between the polishing layer 5 and the curved surface areas of the lenses 8. It will be understood here that it is very desirable to use a substantially non-elastic material for the polishing layer since under friction during operating conditions an elastic layer will after stretching snap back and sometimes produces valleys or waves on the lens surfaces. However, with the resiliency and elasticity controlled so as to insure a dead flow of the material on the lens surface this objection is overcome. I

In accordance with the foregoing, it will be understood that an improved long-life high speed polishing pad embodying an inherently substantially abrasive-free, resilient substantially non-elastic solid member can be produced by first selecting a desired amount of base elastomeric material, i. e., an elastic diolefin polymer such as natural rubber or butadiene-acrylonitrile copolymer (Hycar OR). To this base elastomer a compatible vinyl resin or thermoplastic material such as polyvinyl chloride, polyvinyl acetate, polyethylene, Lucite (polymethyl methacrylate), polyvinyl formal or rubber chloride or mixtures thereof can be added in amounts ranging from 10% to 70% based on the amount of elastomeric material used, the actual amount added being in accordance with the polishing characteristics and resiliency desired of the resultant pad. To the mixture of elastomer and thermoplastic can be added particles of ligno-cellulosic materials, to further control the clasticity and polishing characteristics of the resultant pad, such as classified wood flour, corn cob, or other fillers such as ground felt or ground felt or cerium oxide, either alone or in different combinations. However, the filler must be added in controlled amounts since as the amount of filler is increased the resultant pad tends to become increasingly harder with respect to resiliency. It is preferable to use about 20% of filler based on the total amount of other material in the mixture. However, filler can be used in amounts ranging from 0 to as much as 70% depending upon the resultant characteristics de sired. It might be desirable to use as a base elastomer an amount of material known commercially as Geon 500-503 which is an elastomeric material consisting of 55% polyvinyl chloride and 45% butadiene-acrylonitrile copolymer. In such instances the amount of thermoplastic material added to the base elastomer must be computed to allow for the thermoplastic material already in the base elastomer. Another satisfactory synthetic base elastomer is the commercially known product Thiokol which is a polysulphide type synthetic rubber polymer.

In forming a pad in accordance with the foregoing description the base elastomer can be selected and the thermoplastic material added thereto in an amount in accordance with the resiliency desired of the resultant pad. From this mixture the pad can be formed in accordance with the methods described hereinbefore, it being understood that the necessary vulcanizing agents and plasticizers are also included in the mixture, a few of which are sulphur, zinc oxide, Laurex, Monex, Captax, Tuex, BXA, Picco-lO, CA-lO and GMF. While I have described the use of one or more of these vulcanizing agents and plasticizers as being used with one or more of the formulas given hereinbefore, I do not wish to be restricted to the use of these particular ingredients since others well known in the art may be substituted therefor.

If it is desired to produce a relatively soft pad having excellent polishing and conformation characteristics it is desirable to add to the base elastomer an amount of thermoplastic material ranging from 10 to 30% based on the amount of elastomer in the mixture. This will produce a pad of a substantially soft nature which will conform readily to the variously shaped surfaces of a plurality of articles such as ophthalmic lenses being simultaneously polished. The preferred amount for best results as to both conformation and polishing characteristics, however, would be within the range of from to of thermoplastic material since this amount produces slightly better polishing characteristics. The addition of 40 to 70% of thermoplastic material will produce pads which will be of a substantially harder nature and which have a tendency to become harder and less conforming as the amount of thermoplastic .is increased. However, such pads are .practical for use in polishing fiat surfaces or in polishing a single element such as a special ophthalmic or other lens and in such instances special care must be exercised in controlling the shape of the effective surface of the pad.

To further control the physical characteristics of the resultant polishing pad one or more of the fillers listed above can be added to the elastomer-thermoplastic mixture, it .being understood, however, .that as the amount of filler is increased the pad will tend to become .correspondinglv less yielding. The preferred pad having the best polishing and conformation characteristics would contain polyvinyl chloride in the amount of from 30 to 4.0% based on the amount of base material used and filler in an amount to comprise about 20% of the total composition. The filler when added in smaller amounts does not materially affect the pad but may, however, be increased to comprise over half of the total mixture, this producing a pad having little or no conformation characteristics when made as a one-piece pad which would preferably be approximately onequarter of an inch thick. It is to be .understood, however, that such pads containing a substantially large amount of thermoplastic and filler can be made in the form of substantially thin sheets, preferably about 60 thousandths of an inch thick, which sheet can be affixed .to a resilient backing of felt or elastomericmaterial. Such a pad will then possess excellent conformation properties .as well as very excellent polishing characteristics, with said properties being variable by varying the thickness .of the sheets according to the related proportions of the thermoplastic and filler used.

When producing a laminated pad, the backing layer will be formed of any suitable resilient material, such as felt or various types of rubber. The thin sheet or polishing layer will be attached to the backing layer either directly by vulcanization under heat and pressure, as in the case of a rubber backing layer, or by use .of a heat vulcanizable solvent-type cement, as in the use of a felt backing layer, the cement penetrating the felt when applied to the surface thereof and when dried and vuleanized to the polishing layer under heat and pressure providing an inseparable bond between the felt and polishing layer. The cement would be a suitable compounded rubber base, either natural or synthetic, having conventional vul'canizing agents, plasticizers and solvents added thereto and mixed as previously described. I

From the foregoing it will be seen that I have produced means and methods of a simple and efficient nature for producing all of the objects and advantages of the present invention.

Reference also may be had to the Edward W. Maass copending patent application, Serial No. 74,180, filed on even date with this patent and owned by the same assignee wherein there is described and claimed other polishing pads embodying corn cob or wood flours bonded in rubber-like matrices.

While the novel features of the invention have been shown and described and are pointed out in the annexed claims, it will be understood that various omissions, substitutions and changes in and widely different embodiments of the invention can be made without departing from the scope thereof, and it is intended that all matters contained in the above description and shown in the accompanying drawing be interpreted as illustrative and not in a limiting sense.

I claim:

1. A long-life high speed polishing pad for use in polishing glass articles such as lenses comprising an inherently substantially abrasive-free, resilient substantially non-elastic solid member consisting essentially of vulcanized and plasticized base material from the group consisting of elastic diolefin polymer, polysulphide synthetic rubber polymer and mixtures thereof, and which material contains a compatible thermoplastic vinyl resin that is substantially uniformly dispersed therethrough, the proportion of resin being in the range of from about herently l2 10 to 7.0% by weight -.of the vulcanized and plasticized base material and resin, and said member further containing particles of material from the group consisting of corn cob, Wood flours, cerium oxide and mixtures thereof substantially uniformly distributed .therethrough in an amount up to but not substantially exceeding about by weight of the whole.

2. A long-life high speed polishing pad for :use in polishing glass articles such as lenses comprising a backing member of resilient material having affixed thereto an inherently substantially abrasive-free, resilient .substantially non-elastic .solid polishing member consisting essentially of vulcanized and plasticized base material from the groupconsisting of'elasticidiolefin polymenpolysulphide synthetic rubber polymer and mixtures thereof, said material containing substantially uniformly dispersed therethrough a compatible thermoplastic vinyl resin, the proportion vof resin being in the range of from about 10 to 70% by weight of the said vulcanized and plasticized base material and resin, and said polishing member further containing particles of material from the group consisting of corn cob, Wood flours, cerium oxide and mixtures thereof substantially uniformly .distributed therethrough in an amount up to but not substantially exceeding about 70% by weight of the polishing member.

3. A long-life high speed polishing pad for use in polishing glass articles such as lenses comprising an inherently substantially abrasive-free, resilient substantially non-elastic solid member consisting essentially of vulcanized and plasticized base material from the group consisting of elastic diolefin polymer, polysulphide synthetic rubber polymer and mixtures thereof, and a compatible thermoplastic resin substantially uniformly dispersed through said material, the resin being selected from the group consisting of polyvinyl chloride, polyvinyl acetate, polyethylene, polymethyl methacrylate, polyvinyl formal, rubber chloride and mixtures thereof, and the proportion of said resin being in the range of from about 10 to 70% by weight of the vulcanized and plasticized base material and resin, and said member further containing particles of material from the group consisting of corn cob, wood flours, cerium oxide and mixtures thereof in an amount up to and not substantially exceeding about 70% by weight of the Whole.

4. A long-life high speed polishing pad for use in polishing glass articles such as lenses comprising an inherently substantially abrasive-free, resilient substantially non-elastic solid member consisting essentially of vulcanized and plasticized base material from the group consisting of elastic diolefin polymer, polysulphide synthetic rubber polymer and mixtures thereof, and said base material containing a compatible thermoplastic vinyl resin substantially uniformly dispersed therethrough, the proportion of resin being in the range of from about 10 to 70% by weight of the vulcanized and plasticized base material and resin, and said member further containing corn cob particles substantially uniformly distributed therethroough in an amount up to and not substantially exceeding about 70% by weight of the whole.

5. A long-life high speed polishing pad for use in polishing glass articles such as lenses comprising an inherently substantially abrasive-free, resilient substantially non-elastic solid member consisting essentially of vulcanized and plasticized base embodying butadieneacrylonitrile copolymer rubber, mixed with polysulphide synthetic rubber polymer and polyvinyl chloride, the proportion of polyvinyl chloride being in the range of from about 10 to 70% by weight of the said mixture, and

7 said member further containing particles of corn cob in an amount up to but not substantially exceeding about 70% by weight of the whole.

6. A long-life high speed polishing pad for use in polishing glass articles such as lenses comprising an insubstantially abrasive-free, resilient substantially non-elastic solid member consisting essentially of a vulcanized and plasticized base material from the group consisting of elastic diolefin polymer, polysulphide synthetic rubber polymer and mixtures thereof, said base material containing a .compatible thermoplastic vinyl resin substantially uniformly dispersed therethrough, the proportion of resin being in the range of from about 10 to 70% by weight of the vulcanized and plasticized base material and resin, and said member further con-. taining particles of cellulosic material distributed therethrough in an amount up to and not substantially exceeding about 70% by weight of the whole.

7. A long-life high speed polishing pad for use in polishing glass articles such as lenses comprising an inherently substantially abrasive-free, resilient substantially non-elastic solid member consisting essentially of a vulcanized and plasticized base material from the group consisting of elastic diolefin polymer, polysulphide synthetic rubber polymer and mixtures thereof, said base material containing substantially uniformly dispersed therethrough a compatible thermoplastic vinyl-resin, the proportion of resin being in the range of from about 30 to 40% by weight of the mixture of the base material and resin, said member further containing cellulosic particles substantially uniformly distributed therethrough as filler in an amount up to but not substantially exceeding about 70% by weight of the whole. I

8. A long-life high speed polishing pad for use in polishing glass articles such as lenses comprising an inherently substantially abrasive-free, resilient substantially non-elastic solid member consisting essentially of a vulcanized and plasticized mixture of elastic diolefin polymer, polysulphide synthetic rubber polymer and a compatible thermoplastic vinyl resin substantially uniformly dispersed through said mixture, the proportion of resin being in the range of from about 10 to 70% by weight of the vulcanized and plasticized mixture, and

said member further containing particles of cellulosic material distributed therethrough in an amount up to and not 1substantially exceeding about 70% by weight of the w o e.

References Cited in the file of this patent UNITED STATES PATENTS 1,355,888 Burlew Oct. 19, 1920 1,706,402 Hawn Mar. 26, 1929 1,822,856 Dirkes Sept. 8, 1931 1,953,983 Benner Apr. 10, 1934 2,167,037 Benner et al. July 25, 1939 2,232,389 Jurkat Feb. 18, 1941 2,318,578 Bolz et a1. May 11, 1943 2,378,630 Hill June 19, 1945 2,388,568 Penning Nov. 6, 1945 2,450,433 Leeman Oct. 5, 1948 2,534,482 Lapo Dec. 19, 1950 2,582,741 Ayers Ian. 15, 1952 OTHER REFERENCES Characteristic Properties and Applications of Geon Poly-Blend, Pittenger and Cohan, Rubber Age, August 1947, pages 563-566.

Modern Plastics, No. 2, vol. 25; October 1947; pages 91 and 96.

Claims (1)

1. A LONG-LIFE HIGH SPEED POLISHING PAD FOR USE IN POLISHING GLASS ARTICLES SUCH AS LENSES COMPRISING AN INHERENTLY SUBSTANTIALLY ABRASIVE-FREE, RESILIENT SUBSTANTIALLY NON-ELASTIC SOLID MEMBER CONSISTING ESSENTIALLY OF VULCANIZED AND PLASTICIZED BASE MATERIAL FROM THE GROUP CONSISTING OF ELASTIC DIOLEFIN POLYMER, POLYSULPHIDE SYNTHETIC RUBBER POLYMER AND MIXTURES THEREOF, AND WHICH MATERIAL CONTAINS A COMPATIBLE THERMOPLASTIC VINYL RESIN THAT IS SUBSTANTIALLY UNIFORMLY DISPERSED THERETHROUGH, THE PROPORTION OF RESIN BEING IN THE RANGE OF FROM ABOUT 10 TO 70% BY WEIGHT OF THE VULCANIZED AND PLASTICIZED BASE MATERIAL AND RESIN, AND SAID MEMBER FURTHER CONTAINING PARTICLES OF MATERIAL FROM THE GROUP CONSISTING OF CORN COB, WOOD FLOURS, CERIUM OXIDE AND MIXTURES THEREOF SUBSTANTIALLY UNIFORMLY DISTRIBUTED THERETHROUGH IN AN AMOUNT UP TO BUT NOT SUBSTANTIALLY EXCEEDING ABOUT 70% BY WEIGHT OF THE WHOLE.

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