US2544940A - Polishing pad - Google Patents

Description

March 13, 1 51 H. F. RITTERBUSCH ET AL 2,544,940

POLISHING PAD Filed Aug. 15, 1948 INVENTOR. HARRY F. RITTEKBUSCH HOMER L- LANGEVN BY ATTORNEY Patented Mar. 13, 1951 POLISHING PAD Harry F. Ritt erbusch, Southbridge, Mass., and Homer L. Langevin, Hartford, Conn assignors to American Optical Company, Southbridge, Mass., a voluntary association of Massachusetts Application August 1a, 1948, Serial No. 44,046

This invention relates to new and useful im- V provements in polishers and has particular reference to a polishing pad adapted especially for use in polishing ophthalmic lenses or the like and method of making the same.

One of the principal objectsof the invention is to provide a polisher of the above nature comprising a sheet-like pad of a napped fabric having a pressure-sensitive adhesive coating of a tacky elastic nature on one side thereof and having a protective covering over said adhesive coating which may be removed quickly and easily to permit the pad to be readily attached to laps such as are employed in polishing lenses or other similar glass articles, and without requiring the use of heat. I

Another object is to provide a pad of the above nature formed of a relatively thin initially flat fabric of substantially uniform thickness and possessing characteristics whereby it may be readily and uniformly shaped to conform to the differently curved surfaces of laps and method of making the same.

Another object is to provide a pad of the above nature with an adhesive coating on one side thereof which is of a relatively thin controlled substantially uniform thickness throughout its area with the adhesive being of such nature that, under the action of the heat generated during polishing, it will not creep or penetrate the material of the pad.

Another object is to provide a pad of the above nature having a removable backing or covering formed of cloth impregnated with a material which will readily permit its removal fromrthe adhesive coating with substantially no loss of the adhesive through adhesion therewith during said removal.

Another object is to provide a pad of the above nature which may be readily attached to supporting laps having surfaces of differently controlled curvatures which may be selected according to the shape of curvature of surface to be polished and which is of such thickness as to introduce substantially no change in said curved shape and which may be readily attached to the lap or removed therefrom for transfer to another lap of a different curvature whereby the pad may be employed in successive polishing operations.

Another object is to provide a pad of the above nature with which a desired cleanliness of lap may be maintained during theattaching or removal of the pad from the lap.

Another object is to provide a pad of the above nature embodying means which will prolong the 4 Claims. (01. 51-185) life and usefulness of such pads and more particularly the tackiness of the adhesive coating thereon whereby pads of this nature may be retained in stock for a considerable length'of time without deterioration.

Other objects and advantages of the invention will become apparent from the following description taken in connection with the accompanying drawings and it will be apparent that many changes may be made in the details of construction, arrangement of parts and method shown and described without departing from the spirit of the invention as expressed in the accompany: ing claims. It, therefore, is desired that the invention not be limited to the exact details of construction, arrangement of parts and method shown and described as the preferred form only has been given by way of illustration.

Referring to the drawings:

Fig. 1 is a top plan view of a polisher constructed in accordance with the invention;

Fig. 2 is a slightly enlarged sectional view taken as on line 2-'2 of Fig. 1 and looking in the direction indicated by the arrows; and

Fig. 3 is a sectional view showing the relation of the pad attached to the lap in accordance with the invention.

Polishing pads formed of felt or felted fabric have been used in the art of polishing glass articles such as lenses for several years. Such pads, however, have, in most instances in the past and up to the present time, been attached to the supporting lap through the use of a heat softenable adhesive such as pitch or the like which was first flowed onto the surface of the lap and which subsequently required heat in securing the pad to the lap.

This method of attaching polishing pads to laps requires great skill in obtaining the required accuracy as to curvature of polishing surface and at best is considerable messy and in general an undesirable procedure.

This has been a problem for quite some years and some attempts have been made in the past to produce a pad having a coating of adhesive on one side thereof for attachment to laps but this also required the use of heat, could not be readily distorted to conform to the differently curved surfaces of laps and never came into practical commercial use.

One of the major difficulties is that of obtaining a pad having an adhesive coating thereon which can be readily distorted as to conform uniformly to the shape of the curved surface of the lap desired.

Removable protective coverings on adhesively coated articles also are known but such articles were not in the art of lens polishing and in no way taught the present invention. Several different factors had to be taken into consideration and it was only after very lengthy research and effort that a pad suitable for use in the art of lens polishing was obtained. One of the main distinctions of the present invention over the major art is that of providing a polishing pad formed of a material which, in itself, is readily distortable and conformable to .the different curved surfaces of laps and of providing an adhesive which is elastic in nature and suitable for coating a surface of such pads, particularly an adhesive which can be appliedwith a substan-v tially uniform thickness, which will retain its tacky nature for a considerable length of time, which will permit the pad to readily conform to and which may be attached to the lap without the requirement of heat, which will permit the use of a protective covering which may be readily removed without loss of adhesive, which will permit the pad to be readily attached to the surface of a lap and be removed therefrom for transferring to another lap without loss of adhesive, and which will retain a substantially uniform thickness when in secured relation with the surface of the lap whereby the true curve desired to be polished can be retained.

Referring more particularly to the drawings wherein like characters of reference designate like parts throughout the several views, the device embodying the invention comprises a main pad portion 4 preferably of a wool cloth woven from good quality wool fabric of relatively long fibers, which may thereafter be felted or filled with short wool fibers, combed or napped to raise a fuzz on its surfaces and which may subsequently be sheared to a uniform thickness. The resultant fabric is of such nature that it possesses expandable and compressible characteristics whereby it may be initially formed relatively flat and thereafter be shaped to conform substantially uniformly to the curved shape of a supporting lap such as shown at 5 in Fig. 3. These laps are formed with a curved surface 6 selected according to the shape of the surface to be polished on a glass article or lens following the conventional method of impregnating the surface of the pad with a suitable polishing compound such as rouge, clay, ceria. silica or other known polishing compounds and by moving the article or lens in a controlled path over the surface of the pad.

In forming the pad 4 embodying the invention, the wool fabric is provided with a coating 1 of an adhesive having a pressure-sensitive and elastic nature. The coating I may be formed of natural, synthetic or chlorinated rubber to act as a base and to give strength to adhesive, compounded with polyisobutylene and/or polyvinyl isopropyl ether to introduce permanent tack and adhesiveness and/or plasticized with material such as dioctyl phthalate, dibutyl phthalate, dibutyl sebacate or the like and filled or extended with clay, silene, barytes, zinc oxide, titanium oxide or other known fillers which will provide ease of spreading and aid in obtaining a uniform thickness of coating.

The coating 1 formed as specified above has an elastic tacky nature which will maintain its adhesive characteristics for a considerable length of time thereby enabling reasonably large stocks of such pads to be stored for use as required.

Iii forming the adhesive coating, great care is exercised in obtaining a relatively thin uniform layer of adhesive of from approximately 0.015 to 0.020 inch in thickness.

The coating 1, while possessing and maintaining exceedingly desirable tacky and adhesive characteristics is of such nature that a removable protective covering 8 may be placed thereon. This covering -8 is preferably formed of Holland cloth or the like, which cloth is a highly sized, glazed, light weight cotton cloth of high thread count with the sizing and glazing being of a, gum arabic or starch or other suitable material to which the adhesive coating will adhere but will permit the ready removal thereof without pulling the adhesive loose from or in any way removing the adhesive from the pad material.

An adhesive which is one of several which may be formed through the use of the previously mentioned ingredients and which has proven very satisfactory comprises:

Approximate Ingredient Parts By Weight Butyl rubber (isobutyleiie-isoprcne copolymer) Polyvinyl isopropyl ether l. 120 Low molecular weight polyisobutylene.-- 120 Zinc oxide 35 The adhesive is compounded by thoroughly milling all four of the above ingredients in any suitable manner, preferably by using a suitable conventional type of mixer. The thoroughly mixed material may then be applied to the felt by a calendering or other known process.

Other adhesives which may be formed and embodying materials such as previously mentioned above and which have produced satisfactory re sults are as follows:

should be compounded utilizing suitable conventional mixers and should be applied to the felt by calendering or other known processes.

The pad 4 which is out to the size and shape desired from the assembled fabric, adhesive and protective covering, when in use is of a controlled thickness preferably ranging from 0.040 to 0.050 thousandths of an inch. This is to enable the pad to be attached to the lap 5 without intro- 7 ducing any material change in the curvature generated by the polishing operation. This enables a lap 5 to be directly selected according to the shape of surface to be generated on the glass article or lens and avoids the necessity of initially having to alter the curvature 6 to compensate for the thickness of pad. The thickness of the adhesive coating is also preferably maintained within the above given limits for this purpose. It has also been found preferable to employ an adhesive coating of the thickness specified above so as to avoid creeping of the pad on the surface 5 when adhered thereto and during the polishing operation. The tackiness of the adhesive can be controlled by varying the zinc oxide content and Vistanex. It has been found that by including less than 120 parts by weight of zinc oxide will increase the tackiness while decreasing the amount of low mol c lar weight polyisopropylene will decrease t tackin s.

It is also pointed out that adhe ives of the tvpe set forth above are particularly desirable in that they have no tendency to penetrate the material of the polishing pad during the polishing o eration, that is, they are of such a nature that heat generated during the polish ng operation has no tendency to cause the adhesive to penetrate the material of the pad.

Another feature of the pre ent invention is that the pads 4 having the adhesive coatings I thereon, due to the read ly distortable nature of the pad and coatings, can be removed from one lap and transferred to another of a different curvatu e if desired, that is, the ads may be used for a plura ity of successive ol shing operations.

Although it has been specified above that the thickne s of adhesive coating and the thickness of pad is definitely contro led so as to be within tolerab e limits which may be employed without any r aterial change in the sha e of curvature to be polished, it, however, is possible to adhesively secure pads of con iderably greater thickness to la s by following the above-mentioned teach ngs. If the ad thickne s is increa ed beyond the limits spec fied above, it will, however, be necessary to init ally alter the curvature of the surface of the la to com ensate for such increased thickness of ad. A though this latter procedure is not particularly desirable, it may, in some isolated instances, be employed.

From the foregoing description, it will be seen that simple, efiic ent and economical means and method have been provided for accomplishing all of the objects and advantages of the invention.

Having described our invention, we claim:

1, A polishing pad of the character described compr sing a thin fiat sheet of relatively long wool fibres woven together and filled with shorter wool fibres so as to have expansible and compressib e characteristics such as to permit it to be readilv cupped to different curved shapes, and a coating of pressure-sensitive adhesive on one surface thereof embodying a rubbery synthetic resinous base containing filler, said coating of adhesive being of a sufficiently permanent tacky nature as to permit the pad to be detachably secured to a lap without the application of heat, and of a sufficiently elastic nature as to be enabled to follow the expansion and compression characteristics of the sheet and sufficiently firm as to prevent creeping of the pad on the lap during use.

2. A polishing pad of the character described comprising a thin flat sheet of relatively long wool fibres woven together and filled with shorter wool fibres so as to have expansible and compressible characteristics such as to permit it to be readily cupped to different curved shapes, and a coating of pressure-sensitive adhesive on one surface thereof formed to a uniform thickness of between .015 and .020 inch, said adhesive embodying a rubbery synthetic resinous base containing filler, said coating of adhesive being of a sufficiently permanent tacky nature as to permt the pad to be detachably secured to a lap without the application of heat, of a sufficiently elastic nature as to be enabled to follow the expansion and compression characteristics of the sheet, and sufiiciently firm as to prevent creeping of the pad on the lap during use, said pad having an overall uniform thickness ranging from .040 to .050 inch.

3. A polishing pad of the character described comprising a thin flat sheet of relatively long wool fibres woven together and filled with shorter wool fibres so as to have expansible and compressible characteristics such as to permit it to be readily cupped to different curved shapes, a coating of pressure-sensitive adhesive on one surface thereof embodying a rubbery synthetic resinous base containing filler, said coating of adhesive being of a sufllcently permanent tacky nature as to permit the pad to be detachablysecured to a lap without the application of heat, of a sufficiently elastic nature as to be enabled to fol ow the expansion and compression characteristics of the sheet and sufilc ently firm as to prevent creeping of the pad on the lap during use, said coating of adhesive having a protective covering removably positioned thereon.

4. A polishing pad of the character described comprising a thin flat sheet of relatively long wool fibres woven together and filled with shorter wool fibres so as to have expansible and compressible characteristics such as to permit it to be readily cupped to different curved shapes, and a coat ng of pressure-sensitive adhesive on one surface thereof embodying essentially a rubber-like synthetic resinous base including low molecular weight polyisobutylene and further containing filler, said adhesive being of a sufficiently permanent tacky nature as to permit the pad to be detachably secured to a lap without the application of heat, of a sufiiciently elastic nature as to be enabled to follow the expansion and compression characteristics of the sheet and sufliciently firm as to prevent creeping of the pad on the lap during use.

HARRY F. RITTERBUSCH. HOMER L. LANGEVIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,166,639 Hill Jan. 4, 1916 1,383,863 Scheuerle July 5, 1921 2,059,583 Jackson et a1 Nov. 3, 1936 ,28 ,208 Kirchner June 16, 1942

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