CA2033360C - Injection moldable plastic laps - Google Patents
Injection moldable plastic laps Download PDFInfo
- Publication number
- CA2033360C CA2033360C CA002033360A CA2033360A CA2033360C CA 2033360 C CA2033360 C CA 2033360C CA 002033360 A CA002033360 A CA 002033360A CA 2033360 A CA2033360 A CA 2033360A CA 2033360 C CA2033360 C CA 2033360C
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- Canada
- Prior art keywords
- lap
- lap according
- ribs
- polymer
- rim
- 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 - Lifetime
Links
- 239000004033 plastic Substances 0.000 title abstract description 21
- 229920003023 plastic Polymers 0.000 title abstract description 21
- 238000002347 injection Methods 0.000 title description 10
- 239000007924 injection Substances 0.000 title description 10
- 229920000642 polymer Polymers 0.000 claims abstract description 27
- 239000011521 glass Substances 0.000 claims abstract description 13
- 229920001577 copolymer Polymers 0.000 claims abstract description 4
- 239000000945 filler Substances 0.000 claims description 13
- -1 polybutylene terephthalate Polymers 0.000 claims description 12
- 229910052500 inorganic mineral Inorganic materials 0.000 claims description 9
- 239000011707 mineral Substances 0.000 claims description 9
- 229920001707 polybutylene terephthalate Polymers 0.000 claims description 6
- 229920006324 polyoxymethylene Polymers 0.000 claims description 6
- 239000004952 Polyamide Substances 0.000 claims description 5
- 239000004642 Polyimide Substances 0.000 claims description 5
- 239000000463 material Substances 0.000 claims description 5
- 229920002647 polyamide Polymers 0.000 claims description 5
- 229920001721 polyimide Polymers 0.000 claims description 5
- VTYYLEPIZMXCLO-UHFFFAOYSA-L Calcium carbonate Chemical compound [Ca+2].[O-]C([O-])=O VTYYLEPIZMXCLO-UHFFFAOYSA-L 0.000 claims description 4
- 238000010276 construction Methods 0.000 claims description 4
- 239000011152 fibreglass Substances 0.000 claims description 4
- 229920000728 polyester Polymers 0.000 claims description 4
- 229930040373 Paraformaldehyde Natural products 0.000 claims description 3
- 230000002093 peripheral effect Effects 0.000 claims description 3
- 239000004734 Polyphenylene sulfide Substances 0.000 claims description 2
- 229910000019 calcium carbonate Inorganic materials 0.000 claims description 2
- 239000010445 mica Substances 0.000 claims description 2
- 229910052618 mica group Inorganic materials 0.000 claims description 2
- 229920000139 polyethylene terephthalate Polymers 0.000 claims description 2
- 239000005020 polyethylene terephthalate Substances 0.000 claims description 2
- 229920000069 polyphenylene sulfide Polymers 0.000 claims description 2
- 229930182556 Polyacetal Natural products 0.000 claims 2
- 239000002245 particle Substances 0.000 claims 2
- 238000004519 manufacturing process Methods 0.000 claims 1
- 239000000126 substance Substances 0.000 abstract description 8
- 238000005498 polishing Methods 0.000 abstract description 6
- 239000007787 solid Substances 0.000 description 11
- 238000000465 moulding Methods 0.000 description 8
- 238000001746 injection moulding Methods 0.000 description 6
- SYJPAKDNFZLSMV-HYXAFXHYSA-N (Z)-2-methylpropanal oxime Chemical compound CC(C)\C=N/O SYJPAKDNFZLSMV-HYXAFXHYSA-N 0.000 description 5
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 4
- 229910001018 Cast iron Inorganic materials 0.000 description 4
- 238000000034 method Methods 0.000 description 4
- 230000003287 optical effect Effects 0.000 description 4
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 3
- 229910052782 aluminium Inorganic materials 0.000 description 3
- 229920001778 nylon Polymers 0.000 description 3
- 239000005077 polysulfide Substances 0.000 description 3
- 229920001021 polysulfide Polymers 0.000 description 3
- 150000008117 polysulfides Polymers 0.000 description 3
- 229920000049 Carbon (fiber) Polymers 0.000 description 2
- 239000003082 abrasive agent Substances 0.000 description 2
- 239000004917 carbon fiber Substances 0.000 description 2
- 150000002576 ketones Chemical class 0.000 description 2
- 239000012764 mineral filler Substances 0.000 description 2
- 239000002904 solvent Substances 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- DHKHKXVYLBGOIT-UHFFFAOYSA-N 1,1-Diethoxyethane Chemical compound CCOC(C)OCC DHKHKXVYLBGOIT-UHFFFAOYSA-N 0.000 description 1
- 101150034533 ATIC gene Proteins 0.000 description 1
- 241000905957 Channa melasoma Species 0.000 description 1
- 241000490229 Eucephalus Species 0.000 description 1
- 241001508691 Martes zibellina Species 0.000 description 1
- 239000004727 Noryl Substances 0.000 description 1
- 229920001207 Noryl Polymers 0.000 description 1
- 239000004677 Nylon Substances 0.000 description 1
- 239000004721 Polyphenylene oxide Substances 0.000 description 1
- 239000004793 Polystyrene Substances 0.000 description 1
- 239000004957 Zytel Substances 0.000 description 1
- 229920006102 Zytel® Polymers 0.000 description 1
- 239000004411 aluminium Substances 0.000 description 1
- 239000004568 cement Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 230000000295 complement effect Effects 0.000 description 1
- 229920006351 engineering plastic Polymers 0.000 description 1
- 150000002148 esters Chemical class 0.000 description 1
- 230000001747 exhibiting effect Effects 0.000 description 1
- 239000000835 fiber Substances 0.000 description 1
- 239000010419 fine particle Substances 0.000 description 1
- 239000003365 glass fiber Substances 0.000 description 1
- 239000003041 laboratory chemical Substances 0.000 description 1
- 230000013011 mating Effects 0.000 description 1
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 230000003534 oscillatory effect Effects 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 229920001748 polybutylene Polymers 0.000 description 1
- 229920002959 polymer blend Polymers 0.000 description 1
- 229920006380 polyphenylene oxide Polymers 0.000 description 1
- 229920002223 polystyrene Polymers 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 230000002787 reinforcement Effects 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
- B24B13/00—Machines or devices designed for grinding or polishing optical surfaces on lenses or surfaces of similar shape on other work; Accessories therefor
- B24B13/01—Specific tools, e.g. bowl-like; Production, dressing or fastening of these tools
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Polishing Bodies And Polishing Tools (AREA)
- Grinding And Polishing Of Tertiary Curved Surfaces And Surfaces With Complex Shapes (AREA)
- Finish Polishing, Edge Sharpening, And Grinding By Specific Grinding Devices (AREA)
Abstract
A lap used for the grinding, fining and polishing of glass and plastic lenses is constructed of a one-piece injection-molded reinforced polymer body. The front surface of the lap is curved and adapted to receive an abrasive pad.
The rear of the lap has a skeletal rib structure of projecting interconnected ribs. Polymers suitable for forming the lap include various crystalline polymers and copolymers having adequate chemical resistance, strength, rigidity and thermal resistance.
The rear of the lap has a skeletal rib structure of projecting interconnected ribs. Polymers suitable for forming the lap include various crystalline polymers and copolymers having adequate chemical resistance, strength, rigidity and thermal resistance.
Description
2C3~~~0 INJECTION MOLDABLE PLASTIC LAPS
The present invention relates to a lapping article used for the grinding, fining, and polishing of glass and plastic ophthalmic lenses and, in particular, to laps made of plastic.
The lapping of glass ophthalmic lenses was original-1y performed by cast iron laps whic:~ were rototed and/or cscillated against a glass lens blank with l::~se abrasives l0 disposed therebetween to perform grinding, fining and polishing operations on the blank. Eventually, grinding mac~:lines were developed to perforn the grinding step, but the fining and poliszing operations continued to be performed by cast-iron laps. ?among their shortcomings, i:, loos tended to wear rapidly, necessitating that they be fre:~uently recur and retrued. Also, the considerable weight of the cast iron laps induced a rapid wearing of the bearings and imposed limitations on both the maximum oscillatory speed which could be attained and the energy 20 efficiency of the lap-driving mechanism.
Eventually, the practice of using loose abrasives was phased out in favor of mounting replaceable abrasive tads on the face of the lab. Because the lab itself c,Tould then be subjected to less wear, the laps could be formed of 25 materials exhibiting less toughness and weight than cast iron, such as aluminum and plastic for example.
2C.333~~
Attention is directed, for example, to German OS 36 40 678 and OS-37 12 148 which describe plastic laps used in conjunction with replaceable pads. The laps described therein are of solid construction and the bottom faces thereof are provided with customary side notches and central rectangular aperture for proper mating with a face of a receiver to which the laps are to be mounted.
Due to the reduced weight of the plastic laps, the rate of bearing wear is reduced and the effic_ency of the lap-driving mechanism is increased. However, room for i~;,provement remains if further reductions in lap weight could be attained.
urthe~-more, the techniques presently available for manuyacturing plastic laps are limited, due to the need for 1~ achieving and maintaining a precision curvature of the pad-receiving front face of the lap. In that regard, the primary function performed by such a lap is to provide a proper shape to the abrasive pads; the pads are flexible and will assume the shape of the front face of the late.
.hat face must thus exhibit the true optical curvature being imparted to the lens. It is, therefore, necessary that the techniques for making the plastic laps ensure that the proper curvature of the front face will be maintained.
One way of manu=acturing solid plastic laps is to extrude a solid plastic cylinder and then cut the cylinder into disks. A curved face would then be machined into one 2C."~.~3~~
_ :3 _ side of the disc to define a pad-supporting surface, and the earlier-mentioned side notches and central rectangular aperture would be cut into the other side of the disc. Due to its solid construction, the lap exhibits sufficient strength to maintain the shape of the abrasive pad applied to the front surface. However, laps made by that technique are very expensive. The laps cannot be made by aster and less expensive techniques, such as high-speed injection molding, because such a large piece of solid plastic would cool much too slowly in the mold and would tend, as it cools, to shrink excessively, as well as to shrink at different rates in different directions, whereby the resulting lap would be warned and the molding cycle excessively long.
Therefore, it would be desirable to not only provide a lighter weight lap but also to provide a lap which can be made by a faster, less costly, end more accurate techniaue.
Such a semi-finished plastic lap would also desirably be easily machinable to exact front-surface curvature on standard lap-cutting machines as has hereinbefore been done ~~:ith solid plastic and aluminum laps to match the exact curvature desired on the lens surface.
~C'33~3~~
The present invention relates to a lapping article used for the grinding, fining and polishing of glass and plastic ophthalmic lenses and, in particular, to laps made of plastic. The lap comprises a one-piece injection-molded polymer body with a curved front surface adapted to receive an abrasive pad for grinding, fining, or polishing a glass or plastic ophthalmic lens. Projecting ~_c:~ the rear side of the lap is a skeletal rib structure co~:,~r=sing a plurality of interconnected ribs. The polymer has fiber and/or mineral reinforcement.
'n a preferred embodiment, the rear side of the lap comprises an annular outer peripheral rim extending along at least a portion of the outer circumference of the rear side, and a recessed surface disposed radially inwardly of the =im and recessed relative to the rim in a direction toward the front surface ~ said skeletal rib structure projecting rearwardly from said recessed surface.
The present invention relates to a lapping article used for the grinding, fining, and polishing of glass and plastic ophthalmic lenses and, in particular, to laps made of plastic.
The lapping of glass ophthalmic lenses was original-1y performed by cast iron laps whic:~ were rototed and/or cscillated against a glass lens blank with l::~se abrasives l0 disposed therebetween to perform grinding, fining and polishing operations on the blank. Eventually, grinding mac~:lines were developed to perforn the grinding step, but the fining and poliszing operations continued to be performed by cast-iron laps. ?among their shortcomings, i:, loos tended to wear rapidly, necessitating that they be fre:~uently recur and retrued. Also, the considerable weight of the cast iron laps induced a rapid wearing of the bearings and imposed limitations on both the maximum oscillatory speed which could be attained and the energy 20 efficiency of the lap-driving mechanism.
Eventually, the practice of using loose abrasives was phased out in favor of mounting replaceable abrasive tads on the face of the lab. Because the lab itself c,Tould then be subjected to less wear, the laps could be formed of 25 materials exhibiting less toughness and weight than cast iron, such as aluminum and plastic for example.
2C.333~~
Attention is directed, for example, to German OS 36 40 678 and OS-37 12 148 which describe plastic laps used in conjunction with replaceable pads. The laps described therein are of solid construction and the bottom faces thereof are provided with customary side notches and central rectangular aperture for proper mating with a face of a receiver to which the laps are to be mounted.
Due to the reduced weight of the plastic laps, the rate of bearing wear is reduced and the effic_ency of the lap-driving mechanism is increased. However, room for i~;,provement remains if further reductions in lap weight could be attained.
urthe~-more, the techniques presently available for manuyacturing plastic laps are limited, due to the need for 1~ achieving and maintaining a precision curvature of the pad-receiving front face of the lap. In that regard, the primary function performed by such a lap is to provide a proper shape to the abrasive pads; the pads are flexible and will assume the shape of the front face of the late.
.hat face must thus exhibit the true optical curvature being imparted to the lens. It is, therefore, necessary that the techniques for making the plastic laps ensure that the proper curvature of the front face will be maintained.
One way of manu=acturing solid plastic laps is to extrude a solid plastic cylinder and then cut the cylinder into disks. A curved face would then be machined into one 2C."~.~3~~
_ :3 _ side of the disc to define a pad-supporting surface, and the earlier-mentioned side notches and central rectangular aperture would be cut into the other side of the disc. Due to its solid construction, the lap exhibits sufficient strength to maintain the shape of the abrasive pad applied to the front surface. However, laps made by that technique are very expensive. The laps cannot be made by aster and less expensive techniques, such as high-speed injection molding, because such a large piece of solid plastic would cool much too slowly in the mold and would tend, as it cools, to shrink excessively, as well as to shrink at different rates in different directions, whereby the resulting lap would be warned and the molding cycle excessively long.
Therefore, it would be desirable to not only provide a lighter weight lap but also to provide a lap which can be made by a faster, less costly, end more accurate techniaue.
Such a semi-finished plastic lap would also desirably be easily machinable to exact front-surface curvature on standard lap-cutting machines as has hereinbefore been done ~~:ith solid plastic and aluminum laps to match the exact curvature desired on the lens surface.
~C'33~3~~
The present invention relates to a lapping article used for the grinding, fining and polishing of glass and plastic ophthalmic lenses and, in particular, to laps made of plastic. The lap comprises a one-piece injection-molded polymer body with a curved front surface adapted to receive an abrasive pad for grinding, fining, or polishing a glass or plastic ophthalmic lens. Projecting ~_c:~ the rear side of the lap is a skeletal rib structure co~:,~r=sing a plurality of interconnected ribs. The polymer has fiber and/or mineral reinforcement.
'n a preferred embodiment, the rear side of the lap comprises an annular outer peripheral rim extending along at least a portion of the outer circumference of the rear side, and a recessed surface disposed radially inwardly of the =im and recessed relative to the rim in a direction toward the front surface ~ said skeletal rib structure projecting rearwardly from said recessed surface.
2 0 Preferred polymers suitable for forming the lap include the various homo- and copolymers of polyesters, polyacetals, polyamides, polysulfides and polyimides.
The objects and advantages of the invention will become apparent from the following detailed description of the preferred embodiment thereof in connection with the ~~333~~
accompanying drawings, in which like numerals designate like elements, and in which:
FIGURE 1 is a perspective view of the rear side of a lap according to the present invention;
FIGURE 2 is an end view of the rear side of the lap;
FIGURE 3 is a side view of the lap as viewed in the direction of arrow A of FIG. 2;
FTGL'R~ 4 is a side view of the lap as viewed in the direction of arrow B cf FIG. 2;
0 FIGURE 5 is a doss-sectional view taken along 5 of FIG. 2; and FIGURE 6 is a cross-sectional view taken alcng line 6 of FIG. 2.
1~
A lap 10 according to the present invention com-prises a one-piece injection-molded body 12 having a cu~.red 20 front surface 14 adapted to receive an abrasive pad for grinding, fining, or polishing a glass or plastic ophthal-mic lens. Accordingly, the curvature of the front surface corresponds to the shape of the lens surface being made.
While the molded front curvature of the semi-finished 25 plastic lap is close to the desired lens surface curvature, the final enact curvature is cut on a standard lap cutting machine as is done for solid aluminium and plastic laps.
A rear side of the body 12 comprises an annular outer peripheral rim 15 extending along at least a portion of the outer peiphery of the body 12. The rim 15 includes annular ridges 16 which have rearwardly facing annular surfaces 17.
Disposed radially within the confines of the rim 15 is a recessed surface 18 which is recessed relative to the rim in a direction toward the front surface 14. The recessed surface 18 is preferably curved generally complementary to the f rout surf ace 14 .
Projecting rearward from the recessed surface 18 is a skeletal rib structure 19. The rib structure 19 includes a pair of parallel main ribs 20 recessed radially inwardly of portions of the rim 15 to form side notches 21 (see FIG. 3).
Interconnecting the main ribs 20 are a plurality of parallel, shorter secondary ribs 22. Two of the secondary ribs 22 are spaced apart to define a central rectangular aperture 23. A
plurality of intermediate ribs 24 interconnect the secondary ribs 22 and are disposed parallel to the main ribs 20. A
pair of end ribs 26 extend parallel to the secondary ribs 22 and interconnect respective main ribs 20 with a ridge 16.
Ends of the main ribs 20 are interconnected by curved walls 28 which define tall extensions of the ridges 16.
- 7 - ~C'~33'fi~J
Preferably, the cross-sectional thickness t of the ribs and the cross-sectional thickness t' between the surfaces 14, 18 does not exceed 1.27cm (0.5 in.). Most preferably, those thicknesses are in the range of 0.25 to 0.89 cm (0.1 to 0.35 in.). As a result, the lap will cool rapidly enough to be produced by high speed injection molding.
As a result of such a structure, the lap can be economically formed by high speed injection molding operations. That is, since the maximum cross-sectional thickness of the ribs and front portion is 1.27 cm (0.5 in.), the injection molded lap will cool at a sufficiently rapid rate to adapt to high speed injection molding. Furthermore, the rib structure imparts sufficient strength and rigidity to the front portion to ensue that the front surface will hold its shape during contact with a lens being made. Hence, the lens will be shaped with a proper curvature.
The polymers used in construction of the lap must, in addition to being moldable, have adequate rigidity, strength, thermal resistance, and stability to chemical attack e.g.
chemical resistance to organic solvents for repeated use as a lapping tool. Suitable materials include crystalline engineering plastics. The crystallinity provides the requisite chemical resistance, and crystallinity, together with the particular molecular structure of the polymer, provides engineering characteristics such as strength and rigidity.
Chemical resistance is important because typical prescription laboratories use chemicals such as acetone or _ 8 _ ~C'.~'.33u0 other ketones, and esters which will readily dissolve most non-crystalline polymers.
It will be understood, however, that the invention is not limited to the use of crystalline polymers but encompasses any type of polymeric material suitable for injection molding and having the reauisite engineering characteristics and chemical resistance.
The specific strength and rigidity characteristics and/or other characteristics of the pol ~~er are dictated by the particular use intended, for example, expected life of the lap, lap size and lap curva~ure. One skilled in the art can readily select a specific polymer having the reauisite characteristics based on the polymer's known physical properties, e.g. strength and modulus values.
'-5 examples of pol~~ners useful in the invention include homo- and co-polymers of polyesters and poiyacetals, polyamides, polysulfides, and polyimides. Of the poly-amides, various nylons have good properties, but some absorb significant amounts of water and result in variation in dimensions in actual use. Other polyamides absorb less water but are more expensive. Polysulfides and polyimides, while both have good properties, are significantly more expensive.
Specific examples of suitable polymers include polybutylene terethalate, polyethylene terephthalate, 9 - ~~.~'.~3~~
polyoxymethylene, the various nylons, polyphenylene sulfide, and polyimide.
The polymer is preferably filled. While the unfilled polymer is both strong and chemically resistant, it oftentimes cannot be processed easily by injection molding because as it cools, it shrinks excessively and differently in the flow and transverse directions. In addition, unfilled polymer can warn as it cools and thus c,nnot be made to hold simple tolerances. T_ncorporation of mineral fillers, and possibly glass or carbon fibers, or combinations thereof, allows for much less and more unifor~.;~
shrinkage. Warpage will be generally eliminated, and the molded part will hold the reauired tolerances.
Typical short fiber glass useful as a filler consists of fine particles having a length of from about 0.015 cm to about 0.036 cm (about 0.006 to about 0.014 in.3, while suitable longer fiber glass has a length of from about 0.25 cm to about 0.76 cm (about 0.1 to about 0.3 in.), with about 0.51 cm (about 0.200 in.) being typical.
The typical mineral filler is finely divided and 2 0 blended calcium carbonate or mica. Filler content can range from about 10 to about 50 weight percent of the polymer composi-Lion, while the polymer itself constitutes from about ~0 to about 50 weight percent. Preferred levels of filler are from about 20 to about 45 weight percent with the remainder being the polymer. The ratio of mineral to glass filler can range from 100% mineral to 25% mineral and 75% glass.
Similar ratios apply to the use of carbon fiber fillers.
The following non-limiting Examples and Comparative Examples illustrate the invention.
A thick (3.66 cm) (1.44 in.), solid lap machined from a molded block of an unfilled polymer blend of polystyrene end polyphenylene oxide designated Noryl N-190 from General Electric Company resulted in a useful but heavy lap. The lap had no chemical resistance as it can be attacked by acetone and other common laboratory chemicals such as Pad Cement Solvent, a solution of ketone and arc:~atic solvents defined as Coburn Optical Part Number 9839-70.
A thick (3.10 cm) (1.22 in.), solid lap injection molded from unfilled polybutylene terephthalate designated Valox 325 =rom General Electric company resulted in long molding cycles (3 minutes or more). Excessive shrinkage and ' warpage was observed. The lap was not usable.
COMPA~tATIVE EXAMPLE 3 A hollow, cored lap (maximum cross-section thickness D,g38 cm (0.330 in.); height 3.51 cm (1.38 in.)), injection molded from unfilled polyoxymethylene designated Delrin 500 from E. I.
* Trade-mark Dupont deNemours Company resulted in a short molding cycle (less than one minute), but showed unacceptable and non-uniform shrinkage and poor dimensional reproducibility.
The lap was not usable because of the warpage.
A less thick (2.46 cm) (0.97 in.), solid lap injection molded from polybutylene terephthalate filled with 20% mineral end 20% glass designated Valox 735 from General Electric company resulted in long molding cycles. The lap had more controllable and uniform shrinkage and was usable over a limited range of curves.
A less thick (2.46 cm) (0.97 in.), solid lap injection molded from polybutylene terephthalate filled with 25% mineral designated Valox 745 from General Electric Company resulted in long molding cycles. The lap had more controllable and uniform shrinkage and was usable over a limited range of curves.
A hollow, c..~.red lap (maximum cross-section thickness 0.838 em (0.330 in.); height 3.51 cm (1.38 in.)), injection molded from polybutylene terephthalate filled with 20% mineral and 20%
glass designated*Valox 735 from General Electric Company * Trade-mark resulted in a short molding cycle (less than one minute).
The lap had minimum and uniform shrinkage and good dimen-sional reproducibility. The lap was usable and the optical surface could be machined over a full range of curves.
A hollow, cored lap (maximum cross-section thickness 0.838 cm (0.330 in.); height 3.51 cm (1.38 in.)), injection molded from polybutylene terephthalate filled with 25% mineral desig-nated Valox 745 from General Electric~Company resulted in a short molding cycle (less than one minute), minimum and uniform shrinkage and good dimensional reproducibility.
The lap was ~~sable end the optical surface could be machined over a full range of curves.
A hollow cored lap (maximum cross-section thickness 0.838 cm (0.330 in.); height 3.51 cm (1.38 in.)), injection molded from a polyamide filled with 33% glass designated Zytel Nylon 70G-33L from E. I. DuPont deNemours Company resulted in a short molding cycle (less than one minute). The lap had minimum and uniform shrinkage and good dimensional reproducibility.
The lap was usable over a full range of curves.
* Trade-mark
The objects and advantages of the invention will become apparent from the following detailed description of the preferred embodiment thereof in connection with the ~~333~~
accompanying drawings, in which like numerals designate like elements, and in which:
FIGURE 1 is a perspective view of the rear side of a lap according to the present invention;
FIGURE 2 is an end view of the rear side of the lap;
FIGURE 3 is a side view of the lap as viewed in the direction of arrow A of FIG. 2;
FTGL'R~ 4 is a side view of the lap as viewed in the direction of arrow B cf FIG. 2;
0 FIGURE 5 is a doss-sectional view taken along 5 of FIG. 2; and FIGURE 6 is a cross-sectional view taken alcng line 6 of FIG. 2.
1~
A lap 10 according to the present invention com-prises a one-piece injection-molded body 12 having a cu~.red 20 front surface 14 adapted to receive an abrasive pad for grinding, fining, or polishing a glass or plastic ophthal-mic lens. Accordingly, the curvature of the front surface corresponds to the shape of the lens surface being made.
While the molded front curvature of the semi-finished 25 plastic lap is close to the desired lens surface curvature, the final enact curvature is cut on a standard lap cutting machine as is done for solid aluminium and plastic laps.
A rear side of the body 12 comprises an annular outer peripheral rim 15 extending along at least a portion of the outer peiphery of the body 12. The rim 15 includes annular ridges 16 which have rearwardly facing annular surfaces 17.
Disposed radially within the confines of the rim 15 is a recessed surface 18 which is recessed relative to the rim in a direction toward the front surface 14. The recessed surface 18 is preferably curved generally complementary to the f rout surf ace 14 .
Projecting rearward from the recessed surface 18 is a skeletal rib structure 19. The rib structure 19 includes a pair of parallel main ribs 20 recessed radially inwardly of portions of the rim 15 to form side notches 21 (see FIG. 3).
Interconnecting the main ribs 20 are a plurality of parallel, shorter secondary ribs 22. Two of the secondary ribs 22 are spaced apart to define a central rectangular aperture 23. A
plurality of intermediate ribs 24 interconnect the secondary ribs 22 and are disposed parallel to the main ribs 20. A
pair of end ribs 26 extend parallel to the secondary ribs 22 and interconnect respective main ribs 20 with a ridge 16.
Ends of the main ribs 20 are interconnected by curved walls 28 which define tall extensions of the ridges 16.
- 7 - ~C'~33'fi~J
Preferably, the cross-sectional thickness t of the ribs and the cross-sectional thickness t' between the surfaces 14, 18 does not exceed 1.27cm (0.5 in.). Most preferably, those thicknesses are in the range of 0.25 to 0.89 cm (0.1 to 0.35 in.). As a result, the lap will cool rapidly enough to be produced by high speed injection molding.
As a result of such a structure, the lap can be economically formed by high speed injection molding operations. That is, since the maximum cross-sectional thickness of the ribs and front portion is 1.27 cm (0.5 in.), the injection molded lap will cool at a sufficiently rapid rate to adapt to high speed injection molding. Furthermore, the rib structure imparts sufficient strength and rigidity to the front portion to ensue that the front surface will hold its shape during contact with a lens being made. Hence, the lens will be shaped with a proper curvature.
The polymers used in construction of the lap must, in addition to being moldable, have adequate rigidity, strength, thermal resistance, and stability to chemical attack e.g.
chemical resistance to organic solvents for repeated use as a lapping tool. Suitable materials include crystalline engineering plastics. The crystallinity provides the requisite chemical resistance, and crystallinity, together with the particular molecular structure of the polymer, provides engineering characteristics such as strength and rigidity.
Chemical resistance is important because typical prescription laboratories use chemicals such as acetone or _ 8 _ ~C'.~'.33u0 other ketones, and esters which will readily dissolve most non-crystalline polymers.
It will be understood, however, that the invention is not limited to the use of crystalline polymers but encompasses any type of polymeric material suitable for injection molding and having the reauisite engineering characteristics and chemical resistance.
The specific strength and rigidity characteristics and/or other characteristics of the pol ~~er are dictated by the particular use intended, for example, expected life of the lap, lap size and lap curva~ure. One skilled in the art can readily select a specific polymer having the reauisite characteristics based on the polymer's known physical properties, e.g. strength and modulus values.
'-5 examples of pol~~ners useful in the invention include homo- and co-polymers of polyesters and poiyacetals, polyamides, polysulfides, and polyimides. Of the poly-amides, various nylons have good properties, but some absorb significant amounts of water and result in variation in dimensions in actual use. Other polyamides absorb less water but are more expensive. Polysulfides and polyimides, while both have good properties, are significantly more expensive.
Specific examples of suitable polymers include polybutylene terethalate, polyethylene terephthalate, 9 - ~~.~'.~3~~
polyoxymethylene, the various nylons, polyphenylene sulfide, and polyimide.
The polymer is preferably filled. While the unfilled polymer is both strong and chemically resistant, it oftentimes cannot be processed easily by injection molding because as it cools, it shrinks excessively and differently in the flow and transverse directions. In addition, unfilled polymer can warn as it cools and thus c,nnot be made to hold simple tolerances. T_ncorporation of mineral fillers, and possibly glass or carbon fibers, or combinations thereof, allows for much less and more unifor~.;~
shrinkage. Warpage will be generally eliminated, and the molded part will hold the reauired tolerances.
Typical short fiber glass useful as a filler consists of fine particles having a length of from about 0.015 cm to about 0.036 cm (about 0.006 to about 0.014 in.3, while suitable longer fiber glass has a length of from about 0.25 cm to about 0.76 cm (about 0.1 to about 0.3 in.), with about 0.51 cm (about 0.200 in.) being typical.
The typical mineral filler is finely divided and 2 0 blended calcium carbonate or mica. Filler content can range from about 10 to about 50 weight percent of the polymer composi-Lion, while the polymer itself constitutes from about ~0 to about 50 weight percent. Preferred levels of filler are from about 20 to about 45 weight percent with the remainder being the polymer. The ratio of mineral to glass filler can range from 100% mineral to 25% mineral and 75% glass.
Similar ratios apply to the use of carbon fiber fillers.
The following non-limiting Examples and Comparative Examples illustrate the invention.
A thick (3.66 cm) (1.44 in.), solid lap machined from a molded block of an unfilled polymer blend of polystyrene end polyphenylene oxide designated Noryl N-190 from General Electric Company resulted in a useful but heavy lap. The lap had no chemical resistance as it can be attacked by acetone and other common laboratory chemicals such as Pad Cement Solvent, a solution of ketone and arc:~atic solvents defined as Coburn Optical Part Number 9839-70.
A thick (3.10 cm) (1.22 in.), solid lap injection molded from unfilled polybutylene terephthalate designated Valox 325 =rom General Electric company resulted in long molding cycles (3 minutes or more). Excessive shrinkage and ' warpage was observed. The lap was not usable.
COMPA~tATIVE EXAMPLE 3 A hollow, cored lap (maximum cross-section thickness D,g38 cm (0.330 in.); height 3.51 cm (1.38 in.)), injection molded from unfilled polyoxymethylene designated Delrin 500 from E. I.
* Trade-mark Dupont deNemours Company resulted in a short molding cycle (less than one minute), but showed unacceptable and non-uniform shrinkage and poor dimensional reproducibility.
The lap was not usable because of the warpage.
A less thick (2.46 cm) (0.97 in.), solid lap injection molded from polybutylene terephthalate filled with 20% mineral end 20% glass designated Valox 735 from General Electric company resulted in long molding cycles. The lap had more controllable and uniform shrinkage and was usable over a limited range of curves.
A less thick (2.46 cm) (0.97 in.), solid lap injection molded from polybutylene terephthalate filled with 25% mineral designated Valox 745 from General Electric Company resulted in long molding cycles. The lap had more controllable and uniform shrinkage and was usable over a limited range of curves.
A hollow, c..~.red lap (maximum cross-section thickness 0.838 em (0.330 in.); height 3.51 cm (1.38 in.)), injection molded from polybutylene terephthalate filled with 20% mineral and 20%
glass designated*Valox 735 from General Electric Company * Trade-mark resulted in a short molding cycle (less than one minute).
The lap had minimum and uniform shrinkage and good dimen-sional reproducibility. The lap was usable and the optical surface could be machined over a full range of curves.
A hollow, cored lap (maximum cross-section thickness 0.838 cm (0.330 in.); height 3.51 cm (1.38 in.)), injection molded from polybutylene terephthalate filled with 25% mineral desig-nated Valox 745 from General Electric~Company resulted in a short molding cycle (less than one minute), minimum and uniform shrinkage and good dimensional reproducibility.
The lap was ~~sable end the optical surface could be machined over a full range of curves.
A hollow cored lap (maximum cross-section thickness 0.838 cm (0.330 in.); height 3.51 cm (1.38 in.)), injection molded from a polyamide filled with 33% glass designated Zytel Nylon 70G-33L from E. I. DuPont deNemours Company resulted in a short molding cycle (less than one minute). The lap had minimum and uniform shrinkage and good dimensional reproducibility.
The lap was usable over a full range of curves.
* Trade-mark
Claims (22)
1. A lap for holding an abrasive paid in the manufacture of ophthalmic lens surfaces comprising a body having front and rear sides, a curved front surface formed on said front side and a skeletal rib structure comprising a plurality of interconnected ribs projecting from said rear side, said body being of one-piece injection-molded construction of a reinforced polymer.
2. A lap according to claim 1, wherein said rear side comprises an annular outer peripheral rim extending along at least a portion of an outer circumference of said rear side, and a recessed surface disposed radially inwardly of said rim and recessed relative to said rim in a direction toward said front surface, said skeletal rib structure projecting rearwardly from said recessed surface.
3. A lap according to claim 2, wherein said rim comprises an annular ridge having a rearwardly facing annular surface.
4. A lap according to claim 2, wherein said skeletal rib structure includes two parallel first ribs recessed radially inwardly relative to portions of said rim to define two side notches, said rib structure including additional ribs extending between said first ribs.
5. A lap according to claim 4, wherein said additional ribs include parallel second ribs defining a central generally rectangular aperture.
6. A lap according to claim 5, wherein said additional ribs include at least two third ribs extending between said first ribs and said rim.
7. A lap according to any foregoing claim, wherein each of said ribs has a cross-sectional thickness of not greater than 1.27 cm or 0.50 in.
8. A lap according to claim 7, wherein each of said ribs has a cross-sectional thickness of not greater than 0.89 cm or 0.35 in.
9. A lap according to claim 8 wherein each rib has a cross-sectional thickness in the range of 0.25 to 0.89 cm or 0.10 to 0.35 in.
10. A lap according to any one of claims 2 to 6, wherein a maximum thickness between said front surface and said recessed surface is 1.27 cm or 0.50 in.
11. A lap according to claim 10, wherein said maximum thickness is 0.89 cm or 0.35 in.
12. A lap according to any one of claims 2 to 6, wherein the reinforced polymer comprises a filler material and a polymer.
13. A lap according to claim 12 wherein the polymer and filler material are in the combination of from 20 to 45 wt.%
filler and from 80 to 55 wt.% polymer.
filler and from 80 to 55 wt.% polymer.
14. A lap according to claim 12, wherein the filler is a combination of from 100 to 25 wt.% mineral and from 0. to 75 wt.% glass.
15. A lap according to claim 12, wherein the polymer is a crystalline polymer.
16. A lap according to claim 15, wherein the polymer is selected from a polyester, a polyacetal, a polyamide, a polyimide, or a polyphenylene sulfide.
17. A lap according to claim 16, where the polyester is polybutylene terephthalate or polyethylene terephthalate.
18. A lap according to claim 16, where the polyacetal is polyoxymethylene homo- or co-polymer.
19. A lap according to claim 12, wherein the filler includes short fibre glass having a particle size of from about 0.015 to about 0.036 cm or about 0.006 to about 0.014 inch in length.
20. A lap according to claim 12, wherein the filler includes long fibre glass having a particle size of from about 0.25 to about 0.76 cm or about 0.1 to about 0.3 inch in length.
21. A lap according to claim 12, wherein the filler includes calcium carbonate.
22. A lap according to claim 12, wherein the filler includes mica.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US46037890A | 1990-01-03 | 1990-01-03 | |
| US460,378 | 1990-01-03 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2033360A1 CA2033360A1 (en) | 1991-07-04 |
| CA2033360C true CA2033360C (en) | 2001-10-30 |
Family
ID=23828473
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002033360A Expired - Lifetime CA2033360C (en) | 1990-01-03 | 1990-12-28 | Injection moldable plastic laps |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP0436315A3 (en) |
| JP (1) | JPH04135153A (en) |
| AU (1) | AU641962B2 (en) |
| BR (1) | BR9006670A (en) |
| CA (1) | CA2033360C (en) |
| ZA (1) | ZA918B (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5140782A (en) * | 1990-10-29 | 1992-08-25 | Honore Mecteau | Tool and method for forming a lens |
| US5779529A (en) * | 1996-11-25 | 1998-07-14 | Bizer Industries | Thermoplastic optical lap with reinforced webbing |
| CN112207877B (en) * | 2020-09-07 | 2022-04-26 | 中国工程物理研究院激光聚变研究中心 | Method for generating spiral groove on surface of asphalt polishing disc in annular polishing |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4098028A (en) * | 1977-04-21 | 1978-07-04 | American Optical Corporation | Adaptor for lens surfacing tool |
| US4148160A (en) * | 1977-12-05 | 1979-04-10 | American Optical Corporation | Lens surfacing tool and tool holder |
| US4377057A (en) * | 1978-06-14 | 1983-03-22 | Lortone, Inc. | Hand cabbing apparatus |
| US4382803A (en) * | 1980-07-31 | 1983-05-10 | Rowland, Incorporated | Tools for optical lenses |
| DE3712148A1 (en) * | 1986-11-28 | 1988-06-09 | Klaus Kassner | Bearing body |
| FR2612823B1 (en) * | 1987-03-27 | 1994-02-25 | Essilor Internal Cie Gle Optique | TOOL WITH SELF-CONFORMING PRESSURE ON THE SURFACE OF AN OPHTHALMIC LENS AND USABLE IN PARTICULAR AS AN APPLICATOR OR POLISHING PAD |
-
1990
- 1990-12-07 EP EP19900313344 patent/EP0436315A3/en not_active Withdrawn
- 1990-12-13 AU AU68014/90A patent/AU641962B2/en not_active Expired
- 1990-12-28 BR BR909006670A patent/BR9006670A/en unknown
- 1990-12-28 CA CA002033360A patent/CA2033360C/en not_active Expired - Lifetime
- 1990-12-28 JP JP2418100A patent/JPH04135153A/en active Pending
-
1991
- 1991-01-02 ZA ZA918A patent/ZA918B/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| EP0436315A3 (en) | 1991-12-11 |
| EP0436315A2 (en) | 1991-07-10 |
| AU641962B2 (en) | 1993-10-07 |
| AU6801490A (en) | 1991-07-04 |
| CA2033360A1 (en) | 1991-07-04 |
| JPH04135153A (en) | 1992-05-08 |
| BR9006670A (en) | 1991-10-01 |
| ZA918B (en) | 1992-08-26 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| MKEX | Expiry | ||
| MKEX | Expiry |
Effective date: 20101228 |