IL27883A - Light transmitting elements and method of forming the same - Google Patents

Description

niiui ]T\3 -nmrn n PATENT ATTORNEYS · □ ' D ] 0 □ 'mil) OR. REINHOLD COHN Π 3 ΙΙΙΠΙ'Ί n DR. MICHAEL COHN |Π 3 1K3 The ability to transmit light, the clarity, the relativ ly high abrasion resistance, the ease of processing, and its low cost, have all contributed to the widespread acceptance of glass for an almost infinite variety of uses. Windows for homes, offic buildings and vehicles; heat insulating glass for windows and shields; optical elements, such as lenses, for cameras and telescopes; and ophthalmic lenses, for spectacles are among the most common uses for glass.

Among the principal shortcomings of glass, however, is that it is a brittle material of low impact resistance. Furthermore, for some applications, such as ophthalmic lenses of deep prescription, glass iaarrelatively heavy material.

. Attempts to improve the properties of glass itself, or find substitutes for glass, or combine glass with other materials ) f to overcome its shortcomings have not been fully satisfactory.

For example, the substitution of plastic for glass is well known. Like glass, plastic structures have high light transmittance and are even lighter and generally have greater impact resistance than glass. However, the poor resistance to abrasion commonly makes a plastic structure unacceptable. In addition, plastic lenses have been generally found to be an unsatisfactory substitute for glass because their low index of refraction necessitates difficult compensations in grinding curv in the lenses, and because they cannot be ground and polished on standard equipment.

In trying to overcome the deficiencies of glass, laminat comprising, opposing layers of glass cemented together by an inter mediate layer of thin thermoplastic material have also been used for some applications. Inasmuch as laminates principally contai glass in both mass and. volume, however, they are considerably thicker and naturally heavier than single layers of glass or plastic structures. Moreover, it has been found that such laminates are subject to deterioration and subsequent separation with age and use.. Also, the costs of such laminates are far greater than most other presently available light transmitting structures. This is particularly true for laminated optical elements, such as safety spectacles, wherein the major cost of production is in the grinding and polishing of the optical surfaces. For in such elements, both the internal and outer surfaces of each opposing glass layer must be ground and polished,, With respect to optical elements, another factor adding to the cost is that a more expensive optical glass must be presently used for such purpose. To meet present demands, moreover, the blanks that form the optical elements must be available in a variety of curvatures which, in turn, necessitates a large inventory0 The structure of British Patent No. 907, 5t>k discloses materials that are thermoplastic and/or are not rigid and infusible.

British Patent No, 975, 779 discloses inner and outer skins between which is interposed a deformable resin layer that is thinner than the skins. This structure is used principally in forming the canopy of an aircraft.

United States Patent 2, 678 ,586 teaches the bonding of lens material by a particular adhesive.

The present invention thus arose from the problem of providing a light transmitting structure with the versatility of glass but without the drawbacks of glass and its substitutes In accordance with this invention, there is provided a light-transmitting element, comprising a main body of rigid and infusible thermosetting resin material having chemically bonded to an outer surface a layer of glass or plastics material which is relatively thin as compared to said main body and which is more abrasion-resistant than is the thermosetting resin material.

The invention also provides a method of forming a light-transmitting element, comprising a main body of rigid and infusible thermosetting resin material having chemically bonded to an outer surface an outer layer of glass or plastics material which is relatively thin as compared to said main body and which is more abrasion-resistant than is the thermosetting resin material, comprising forming a mold chamber corresponding to the desired shape of the main body of the element, wherein a wall of the chamber is formed by said outer layer of the element, filling the chamber with a thermosetting resin material which interacts chemically with the inner surface of the layer of glass or plastics material and curing the thermosetting resin material, to thereby form a rigid and infusible solid which is chemically bonded to the relatively thin sheet of greater abrasion-resistance.

Preferably, the main portion vis composed of light transmitting thermosetting material and is plaoed between a pair of ou^er layers before curing or polymerization thereof so that said main portion will become chemically linked or bonded to at least one of the outer layers when it is cured. The bond thusly formed is surprisingly and unexpectedly stronger than the material of each bonded outer layer itself so that a unitary structure results. In other words, the strength of the bond * between the outer layer and the thermosetting material is higher than cohesive strength of the material of the outer layer itself. In addition, it is preferred that each outer layer be considerabl •thinner than the main portion to provide a relatively lightweight structure. · "' ' . " ' By providing a unitary structure of a light transmittin abrasion resistant, outer layer and a lightweight, light transmitting thermosetting main portion, the versatility of glass is obtained without being beset by the drawbacks of glass or its substitutes. The structures of the invention are clear, thermally stable, and are more resistant to impact and abrasion than glass, plastic or laminates of equivalent thickness. Also, the structure are lighter than glass or glass laminates of the equivalent thickness.

Furthermore, by chemically bonding glass to the thermo- setting materials of the invention, it is no longer necessary to commercial transparent glass, such as plate or window glass, can be used even though the commercial glass contains the usual striations and other imperfections on its inner surface. The desired optical element is obtained by curving the window or plat glass to the desired curvature and then chemically bonding the main infusible solid portion to the inner surface of said curved glass as previously described. Surprisingly and unexpectedly the striations and other inner surface imperfections are eliminated. This is believed due to the interaction between the reactive groups at the inner surface of each glass layer and corresponding surface of the thermosetting material. Each outer glass surface may be ground and polished in the standard manner to provide an optically clear element. ( In. another embodiment of the invention there is provided an element that transmits light having a plurality of foci, such as a vari-focal or multi-focal ophthalmic lens, comprising a main portion including a segment of thermosetting material having one index of refraction and a second segment, preferably of a different thermoset ing material, with a second index of refraction, and a pair of outer layers chemically bonded to said main portion desirably of glass or other material having a greater resistance to abrasion than said inner portion.

Thermosetting materials of the present invention are desirably flowable substances that can be poured into a space IRK-1 defined by two outer layers, such as glass, and cured or polymer ized in situ, to form infusible solids that are chemically linke or bonded to at least one of said layers. Preferably the thermosetting materials are liquid casting. For most applications, the thermosetting materials are also transparent but may be colored s as for forming tinted windows and colored lenses. Illustrative liquid thermosetting materials include epoxies, flexibilized epoxies, poiybutadiene and copolymers of butadine and styrene, ' unfilled silicones containing additives to promote chemical linkage, such as epoxies and polyesters, polyurethanes, and unsaturated polyesters. Other flowable thermosetting materials of the invention include urethane elastomers and formaldehyde- urea polymers. "Si The main portion of the light transmitting structure ca -.15 also contain an insert that pan be specifically treated or colore so as to filter or otherwise modify the transmission of light or increase the impact resistance of the light transmitting structur Moreover, the main portion of the structure can include materials which are hot capable of being chemically bonded to an outer laye of the structure but which will chemically bond to thermosetting materials which, in turn, will chemically bond to said outer layer. In such .embodiment, the outer layer can be first bonded to the desired thermosetting material and thereafter the other material-can be linked to said thermosetting material.

Each outer layer of the light transmitting structure is more resistant to abrasion than the main portion of said structu Again, for most applications each outer layer is transparent but may be colored to form the described tinted window or lens.

Preferably 'the outer layer exposed to the surrounding environment is glass. Almost all of the many varieties of readily available glass contain silica (Sii^) as the principal ingredient. It has been found that in such glass, the silica has one of its oxygen atoms always available for combination. with appropriate reactive groups, such as the ether groups present in described epoxies, that will react with. the oxygen at the surface of the outer glass laye■■r as it i'.s b·e■■ing cured, to thereby form an infusible solid chemically linked to the inner portion. The strength of such bon between the outer glass layer and the main thermosetting portion is surprisingly and unexpectedly greater than the cohesive streng of the glass itself.

In still another embodiment of the invention the light transmitting structure comprises a main.portion composed of a thermosetting material and a pair of outer layers chemically bonded to the main portion wherein said outer layers have a great resistance to abrasion than said main portion; and wherein at leas one. of said layers is made of glass. Preferably the outer layer o glass is exposed to the surrounding environment. The other outer layers can also be composed of glass, or can be of a plastic material, such as an allyl resin, having greater resistance to abrasion than said main portion.

Where only one surface of the light transmitting structu is to be exposed to the surrounding environment, such as in a telescopic lens and heat insulating windows having ah interme< air space, the structure of the invention can include only one outer glass layer wherein said layer is exposed to the surroundin environment. ■ ■ . ' ■ Additional objects and advantages will be set forth in part hereinafter and in part will be obvious herefrom or may be learned by practice with the invention, the same being realized and attained by means of the steps, combinations and improvements pointed out in the appended claims.

Figure 1 is a front elevation of an optical element of the invention; Figure 2 is a cross-sectional view of Figure 1 taken alon the lines 2-2 thereof; Figure 3 'is a side elevational view, partly in section of one method of forming the light transmitting elements of the invention; ··,,* Figure 4 is a front. elevation of another optical element KIRK-l Figure 5 is a cross-sectional view of Figure 4 taken along the lines 5-5 thereof, which shows the plastic insert withi the main portion of the element;' Figure 6 is a front elevation of still another optical element of the invention; Figure 7 is a cross-sectional view of Figure 6 taken al the lines 7-7 thereof, which shows a main portion containing a major segment which is not chemically bondable,to the outer layer Figures 8a and 8b are side elevational views in section schematically illustrating one method for forming the light trans mitting structure shown in Figures 6 and 7; Figure 9 is a front elevation of a vari-focal optical c element of the invention showing the multiplicity of foci from edge to edge; Figure 10 is a cross-sectional view of Figure 9 taken along the lines lQ-10 thereof; Figures lla-^lld are side elevational views in section schematically illustrating one method of forming a vari-focal optical element; r Figure 12 is a' front elevational view of a multi-focal optical element of the invention indicating the various foci of this element; v.

Figure 13 is a cross-sectional view of Figure 12 taken along the lines 10-10 thereof; · ,·', Figure 14 is a front elevational view of another embodim of the invention which may be used as a window; Figure 15 is a crossrsectional view of Figure 14 taken along the lines 15-15 thereof; Figure 16 is a perspective view illustrating a portion o one embodiment of a heat insulating light transmitting structure of the invention; Figure 17 is a front elevational view of still another embodiment of the invention which may be used as a curved panoramic windshield for an automobile; and Figure 18, is a cross-sectional view of Figure 16 taken along the lines 18-18 thereof.

Referring in detail to the drawings, Figures 1 and 2 illustrate one embodiment of the invention: a lens 10 comprising a transparent main lens portion 12 of the thermosetting material of the present invention, chemically bonded to outer layers 14 and 16 desirably of glass or other lens medium of higher abrasion resistance than the inner portion 10. Both the main portion 12 and outer layers 14 and 16 have indices of refraction that are about equal. For providing a lens 10 of particularly light weight, each outer layer 14 and 16 is substantially less thick than the main portion 12.

The lens 10 may be formed by firs curving the layers 14 and 16 to the desired curvature by standard techniques. As illustrated in Figure 3 the opposing curved layers 14 and 16 are then spaced the desired distance apart by a rubber or silicone gasket 18 positioned about the layers 14 and 16 to form a chambe therebetween. A polyester tape 20 is used to keep the assembly together. The thermosetting resin is gradually fed through an opening 21 in the gasket 18 and tape 20 into the chamber until t space between the outer layers 14 and 16 is completely filled. Thereafter the thermosetting resin is cured or polymerized to form the inner portion 12 of an infusible solid chemically linke to the outer layers as will presently be described. After the unitary lens 10 is formed the gasket 18 and tape 20 are removed. If desired, any one of a variety of means may be used to help ho the assembly in place, during the formation of the lens 10, such a spring clamp. . * r Referring now in more detail to the outer layer, such as layers 14 and 16 of lens 10, they are of light transmitting material that is more abrasive resistant than the main portion o a thermosetting material and are capable of chemical interaction therewith. Commercial glass has been found to be a particularly suitable material for at least one of the layers 14 and 16. For, while commercial glass may contain any number of dissimilar compounds, its principal constituent is almost always silica (Si02) which, in turn, invariably has one of its oxygen atoms available for combination with appropriate reactive groups at t glass surface. In many glass compositions, moreover, active hydrogen atoms are also available to aid in the chemical inter- action.

Illustrative of the types of commercial glass which cont silica and which may be used in the present invention are ordina glass sheets that belong to the soda lime silica glass family, t principal constituents of which are: silica (Si02), soda ( a20) and lime (CaO) ; and optical glass including crown glass that contains silica, sodium, lime and alumina (A^O^) ,, flint glass that contains calcium oxide, borium silicate glass, zinco silica glass and boro silicate glass.

In addition to glass, light transmitting plastic materia that have a greater resistance to abrasion than the main portion of the lens and which are chemically bondable thereto can also b used in forming an outer layer. Allyl resins, such as allyl diglycol carbonate,, have been found to be particularly useful fo this purpose. Thus, a lens 10 can be formed as previously described, wherein the outer layer 16 is made of glass and the outer layer 14 is made of allyl diglycol carbonate. Safety glasses containing a pair of lenses of such construction with th plastic outer layer 14 positioned adjacent the eyes has safety features presently unknown in any lens where glass is employed KI -1 because the possibility of glass entering the eye of the wearer when the lenses are impacted has been removed. Also, with the outer layer 16 of glass exposed to the surrounding environment, the scratch resistance of each lens is also substantially greater than in so-called safety lenses made of plastic alone.

Furthermore, where only one surface of the light transmitting structure is to be exposed to the surrounding environment, such as i microscopic or telescopic lenses, only one layer of glass can be used. In such instance, the structure can be formed by spacing the glass outer layer 16 and a conventional glass mold (not shown) coated with a release agent the desired distance apart and filling the space with a thermosetting material as previously described. After the thermosetting material has been cured and bonded to the outer layer 16, the glass mold is removed to thereby 1* provide a lens of the invention with only outer layers of glass.

Surprisingly and unexpectedly, lenses of the present invention, such as lens 10, no longer have to be made from the more expensive optical glass but can now be made from ordinary plate or window glass despite surface imperfections such as striations. Moreover, the inner surfaces of the outer layers 14 and 16 no longer have to be polished and ground irrespective of whether window or optical glass is used.

KI K-1 Thus, the lens 10 may be formed from commerical soda-lim silica flat glass by curving two pieces of such glass to form the curved layers 14 and 16. Thereafter a liquid thermosetting material can then be poured between the two layers as previously described and cured to form an infusible solid inner portion 12 that is chemically linked to the outer layers 14 and 16. The interaction between the inner portion 12 and the outer layers 14 and 16 eliminate their inner surface imperfections. This inter- action also eliminates the need, to polish and ground the inner surfaces of the layers 14 and 16 before they are used. The outer surfaces of the layers 14 and 16 may be ground and polished to provide a lens 10 of the desired power by standard techniques.

The resultant light transmitting lens 10 is optically clear.

Such lens 10 is also of light weight, is heat stable, has the IS necessary surface hardness and resistance to abrasion, as well as having the desired property of being more resistan to impact than an equivalent thickness of glass.

To make the lens of the present invention as light as possible each layer can be reduced to a minimum by grinding each outer glass surface until it is parallel to the inner surface.

Furthermore, optical prescriptions are presently measured in quarter diopter units. Accordingly, a wide variety of optical curved blanks must be presently kept on hand. The present invention greatly reduces this practice because the final grinding - operation of any glass layer of the lens can vary the final curvature of the surface over a range of several diopters without materially changing the overall volume of the glass in each lens.

. For a given application, however, it may be desirable to utilize finished optical glass rather than the less expensive plat window glass. A lens of the invention having outer layers of optical glass would not require a final grinding and polishing operation, but would be complete and ready for use once the .. thermosetting material had been cured. If desired, of course, the outer surfaces of the optical glass may be polished after > the lens is formed.

The thermosetting materials for forming the main portion contain reactive groups that will interact with groups in the outer, layers as the thermosetting material is cured to thereby form a permanent bond therebetween. To facilitate the.bonding of the two materials the thermosetting material is preferably liquid. What is believed to occur is. that as the thermosetting material is curing it will concurrently interact with the groups in the outer layer as well as form a network of cross-linked thermosetting molecules within itself. The movement of any . molecule in said cross-linked network is thereafter hindered in all directions so, that once the thermosetting material is cured it will retain its dimensional stability and maintai the bond with the groups in the outer layer. For most applications the thermosetting materials are also transparent but may be ^colored for special applications, such as forming colored lenses.

Exemplary thermosetting materials are liquid epoxies having reactive ether groups that provide a point of permanent chemical linkage or bonding during polymerization or curing of the resin, because once formed the linking groups undergo no further change. To provide void-free castings of thermosetting material between the outer layers the viscosity of the epoxy materials is" preferably greater than about 9000 centipoises.

For applications that require elements of high transparency, moreover, epoxies which tend to have a yellowish straw color, such as those derived from certain organic sources, i.e. soy beans, and 'which cannot be corrected by additives should not be used. Howeve where a deeply colored element is desired, such epoxies can be use Specific illustrations of useful epoxy materials include: An epoxy resin of the aromatic type wherein diepoxide 0 is the principal constituent, and wherein the resin has an epoxide equivalent range Of 173 to 179 e.g. Dow Chemical Co. DE 332; A cycloalliphatic epoxy resin having epoxide equivalent range of 140 e.g. Ciba Chemical Company Ardelite CY 179; A modified epoxy resin including aromatic diepoxides and diluants, such as butyl glycidyl ether or phenyl glycidyl ethe! and wherein the epoxide equivalent range is 179 to 194, e.g. Union Carbide Plastics Corporation ERL 2795; A modified epoxy that may be copolyraerized with styrene solution having an epoxide equivalent of about 200 that may be varied depending upon the amount of styrene solution in said resin, e.g. Shell Oil Company EPON 11; and An epoxilated'novolac resin having an epoxide equivalen range of 175 to 182.

Other useful thermosetting materials for the present invention include flexibilized polysulfide epoxy copolymers; polybutadiene, and especially polybutadiene that has been flexibilized. by appropriate additives, such Both flexible and rigid liquid ' urethanes are also usefu for joining the light transmitting elements of this invention.

For urethanes all contain hydroxyl groups that facilitate chemical bonding between the outer layers and the inner portion.

While liquid thermosetting materials are preferred because of the ease of handling in casting and their ability to form chemical bonds, selected other thermosetting materials or systems which have a tendency to flow may also be used to form thej light transmitting elements of this invention. Illustrative of these materials are urethare elastomers and formaldehyde-urea polymers. Many of these polymers can be co-polymerized with each other or with still other materials to formulate a thermosetting system which is sufficiently liquid to be used in forming an infusible solid chemicllybonded to the outer layers of a light transmitting element of this invention.

In another embodiment of the invention, the infusible main portion includes light transmitting inserts to give the structures of the invention specific additional properties. Thi embodiment, is illustrated in Figures 4 and 5 and includes an optical lens 22 having a thin light' transmitting sheet 24, such as a sheet composed of a cellulose acetate, centrally positioned within a main lens portion 26 of a thermosetting material. As in Figures 1 and 2, the outer layers 28 and 30 are chemically bonded to the main portion and are composed of glass. The sheet 24 may be specially treated or colored so as to filter or otherwise modify the transmission of light or it may be added to increase the impact resistance of the lens 22. This type of lens is formed by centrally positioning the sheet 24 between t outer glass layers 28 and 30, pouring the selected thermosetting material into the remaining space between the layers until it has completely filled the space, and thereafter curing the thermosetting material to form the inner lens portion 26.

The colored lens so formed, moreover, is completely uniform in density despite the substantial variation in lens thickness.. This ability to produce a lens of "uniform color density" is very advantageous. If an attempt were made to make such a lens of a regular colored glass, which substantially varie in thickness, it would equally vary in density and color, and be in may cases undesirable. In another embodiment of the invention colored lenses of uniform density are obtained without employing an insert, and irrespective of the differences in the thickness of the main portion, by utilizing colored glass wherein the surfaces thereof are almost parallel. Furthermore, the clear plastic insert materially increases the safety properties of the lens because the impact required to break the outer surface is so cushioned that it fails to penetrate to the inner plastic sheet. o For protection against extreme industrial hazards, lenses of this construction are highly desirable since they would afford maximum safety with minimum weight.

The main portion of the light transmitting structure can also include inserts added thereto in the fluid state rather than as a solid sheet, such as insert 24. Furthermore, the main part of the light transmitting structure can contain, in major proportions, substances that are not capable of being chemically bonded to a glass' outer layer, but which will otherwise provide the desired properties. This embodiment of the invention is illustrated in Figures 6 and 7, and the method for forming such structure is illustrated in Figures 8a and 8b.

. Referring first to Figures 6 and 7 there is shown a lens 32 including a main portion 34 having a major segment 36 of a light transmitting .material that is not capable of being chemically bonded to glass but which is chemically bonded to outer layers 38 composed of a thermosetting material of the invention. The layers 38 are, in turn, chemically bonded to outer glass layers 40 and 42.

The lens 32 can be formed by first bonding the thermo- setting outer layers 38 of the main portion 34 to the glass layers 40 and 42, and thereafter bonding the^ major segment 36 · •o to said thermosetting outer layers 38. In so doing, the curved glass layer 40 is spaced from a glass mold or another glass layer 44 coated with a release agent a distance equal to the thickness of the layer 38, and an annular gasket 46 and polyester tape 48 are used to hold the layer 40 and layer 44 in spaced relationship as. shown in Figure 8a. As previously described the space is filled with the thermosetting material and cured. Thereafter, the tape 48, gasket 46 and mold 44 are removed. Tte process is again repeated to form the glass outer layer 42 and its chemicall bonded thermosetting layer 38 employing a mold 44^, gasket 46 and tape 48 as shown in Figure' 8b« The two layers 40 and 42 are the^ spaced the desired distance apart with the thermosetting layers 38 opposing each other, and thereafter the space is filled with a substance to form the major segment 36 that cannot be directly bonded to the glass layers AO and 42 but which will chemically bond to the thermosetting layers 38 to form a main portion 34 composed of a light transmitting infusible material. For example the major segment 36 can be composed of an unmodified and unfille silicone.

In the embodiment of. the invention, there is provided a us , lens having more than one foci, . such as a multi-focal or vari- focal lens, shewn in Figures 9-13. This embodiment preferably .. utilizes thermosetting resins of different indices of refraction to produce multi-focal and vari-focal lenses therein both of the external curves of each lens are either spherical or toric, but wherein the lens has an orderly and controlled variation in its power. Such lenses may be formed by leaving voids or creating voids in the process of producing the finished lens, and then filling the voids with, a formulation to suit the specific need.

Consequently, the shapes and sizes of the voids can be varied at. ill.

In Figures 9 and 10 there is provided a vari-focal lens 50 including outer layers of curved glass 52 and 54 chemicall bonded to a main portion 56. The main portion 56 includes a pair of wedge shaped segments 58 and 60 of thermosetting materials extending the diameter of the lens and each having a different index of refraction. The thermosetting wedge 58 is chemically bonded to the outer glass layer 52 and the wedge 60 is chemicall bonded to the outer glass layer 54. Furthermore, the wedges 58 and 60. are chemically bonded to one another along their contiguo length. When the lens 50 is optically neutralized it has a multiplicity of foci running in ascending order from edge to edge One method of forming the lens 50 is illustrated in Figures lla-lld and includes combining the curved glass layer 52 with a glass mold 62 having its inner surface coated with a release agent. A wedge shaped neoprene or silicone die 64 is employed for the separation of the layers 52 and mold 62 and is tapered so as to vary in thickness as from about 0.01mm to 3.0mm. As previously described, a tape 66 and gasket 68 are then used to secure the assembly together. A thermosetting material of the invention having one index of refraction is then poured into the resulting cavity through the opening 69 in the gasket and tape and cured to form segmet 58. The securing tape 66, the gasket 68, the die 64 and the mold 62 are removed. This leaves one layer 52 of glass chemically linked with a. cured wedge segment 58. After removing all .traces of the release agent from the wedge surface, the other layer 54 is used to again form an assembly. In this instance the die is placed between the layer 54 and the wedge surface, positioned so that its thinnest part is now adjacent the thickest part of the segment 58 and the opening 69 is placed at the bottom of the assembly. After securing this assembly the d i e 64 is removed and the as.sembly is inverted and a second thermosetting material of the invention of a different refractive index is introduced into the cavity through the opening 69. When the wedge 60 is cured, the tape 66 and gasket 68 are removed and the lens 50 is inverted to the position shown in Figure 10. The resulting lens 50 when optically neutralized proved to have a , multiplicity of foci running in an ascending order from edge to edge along the contiguous line formed, between the wedges 58 and Ό 60 as shown in Figure X. This constitutes a vari-focal lens.

In Figures 12 and 13 there is shown a multi-focal, lens;■ comprising a main lens portion 72 of a thermosetting material of the invention having a wedged shaped segment 74 centrally positioned in its lower half that is filled by a thermosetting material having a different index of refraction. As in the other embodiments of the invention, chemically bonded to the opposed surfaces of the main lens portion, 72 are a pair of outer layers 76 and 78 desirably composed of glass or other lens , medium of higher 'abrasion resistance than the main portion 72.

Because the lens 70 contains a main portion 72 and wedge 74 of different indices of refraction, the lens 70 possesses two distinct foci.

The lens 70 can be formed as previously described except that a polished steel insert which is made to conform with the shape and power of the wedge 74 is placed within, the spa between spaced outer layers 76 and 78. This steel insert is coated with a release agent. After the selected thermosett ng material is poured into the chamber between the layers 76 and 78 •and cured, the steel insert is removed. All traces of the release agent are also removed from the main portion that defines the wedge shaped void. The assembly is again taped, recreating a leak-proof chamber. Using -a thermosetting material of a different refractive index, the void is filled and the assembly cured. The lens 70 thus formed when examined optically,, has - two distinct foci.

As previously described the outer layers of the light transmitting structures of the invention are preferably relatively thinner than the main portion. For instance, satisfactory optical elements have been formed wherein the main portion was 2 to 4 time the thickness of each outer layer. Furthermore, the structure is thermally stable, inasmuch as it will maintain its integrity over a wide range of temperatures. In addition, the structures are optically clear; have a greater resistance to. abrasion than plastic optical elements and are more resistant to impact than an optical element of equivalent thickness of glass, plastic or a laminated structure. The light transmitting structures of the invention are also lighter than a structure of equivalent thicknesfe of glass or laminated structures containing glass.

Typical examples of optical elements made in accordance with this invention are as follows : Example 1 •An ophthalmic lens for spectacles having a power of minus 12 diopters was formed from flat window glass having a thickness of 2mm and an index of refraction of 1.53. Two pieces of glass both 52mm in diameter were cut from the flat glass. One piece was thermally curved to measure about 13,00 diopters on both its concave and convex surfaces, and the other piece was thermally curved to measure about 1.00 diopters on both surfaces. This resulted in distorted lens surfaces normally unusable for ophthalmic purposes in that they deviate from spherocity in small but uncontrolled amounts. Moreover, the lenses had the usual surface striations found in commercial window glass which also normally makes these, lenses unsuitable, but no attempt was made to eliminate the striations. Both curved pieces of glass were chemically clean in order to remove any grease from their faces, and assembled together as previously described with a silicone rubber gasket of sufficient thickness to ensure that the centers of the two lenses were approximately 1.00 mm from each other. At this time it is _^ important to note that the assembly had no optical powe whatever, and the glass of different curvature merely represented the preselected desired curvatures for the finished lens.

An epoxy resin of the aromatic type wherein diepoxide 0 is the principal ingredient and having an index of refraction of 1.53 and an epoxide equivalent range of 173 to 179, e.g. Dow Chemical Co. DER 332, was mixed with 3 per cent by weight of benzyl amine and the blend was poured into the chamber between the outer layers of glass and cured at 185°F to form a transparen infusible solid chemically bonded to the outer glass layers.

Using standard grinding and polishing methods the glass was reduced in thickness on each surface by 1.5mm at the same time giving optical curvatures of minus 13 diopters and plus 1.00 diopters to each surface.

The finished lens was a unitary element because the strength of the bond between the glass outer layers and the inner lens portion was greater than the cohesive strength of the glass itself. The light transmitting finished lens also did not contain any of the imperfections found in the initially curved glass layer but was optically clear. The lens was also thermally stable, resistant to abrasion, and was more resistant to impact than a lens of equivalent thickness of glass, plastic or laminated lenses Example 2 An ophthalmic lens was formed as described in Example 1, except that the main portion of the lens was formed from an epoxilated novolac resin with an epoxide equivalent range of 175 to 182 and an index of refraction of 1.53, and the resin was blended with 12% by weight of, diethylene triamine. The blend wa poured between the glass layers and cured at the ambient tempera ture of 77°F.

Again the lens was a unitary structure and possessed the required optical and physical properties for lenses.

I ' ' 1 . Example 3 *. · « An ophthalmic lens described in Example 1, having two thermally curved pieces of glass, one having curvatures of plus 13 and minus 13, and the other having curvatures of plus 1 and minus 1 was ground and polished to form a lens having a power of minus 13 diopters instead of minus 12 diopters. To make a minus 13 diopter lens only required the changing of curvatures in the final grinding and polishing step. Considering the thickness of available glass, the combination of selected curves was a convex curve of 0.50 combined with a concave curve 13.50, resultin in a total lens power of minus 13 diopters.

From this example it is apparent that many combinations of both spherical and cylindrical prescriptions are possible.

This results in a substantial reduction of the number of blanks that have to be prepared for lens production, with obvious corresponding savings in cost. A lens as described in Example 1 can be ground and polished to have a power from 11.25 diopters to 13 diopters.

KIRK-1 Example 4- An ophthalmic lens for spectacles having a power of plu 6 diopters was formed as described in Example 1 except that the convex side of the lens was formed from a glass layer that had a curvature of 9.00 diopters and the concave side of the lens was formed from a glass layer that had a curvature of 3.00 diopters; and the distance between the edge of the glass layers was 0.5mm.

Once again a unitary ophthalmic lens having the required physical and optical properties was formed.

Exam le 5 An ophthalmic lens was formed as described in Example 4 except that the main portion of the lens was formed from an epoxilated novolac resin with an epoxide equivalent range of 175 to 182 and an index of refraction of 1.53; and the resin was blended with 12% by weight of resin of diethylene triaraine. The blend was poured between the glass layers and cured at the ambient temperature of 77°F, Again the lens was of unitary structure and possessed the required optical and physical properties.

Example 6 An ophthalmic lens for spectacles having a power of minus 12 diopters was formed from a layer of optical glass and a plastic layer of allyl diglycol carbonate. The finished uncut glass layer had its concave and convex surfaces ground and polish to a 1 diopter curve. The plastic outer layer had a power of 13.00 diopters on both its concave and convex surfaces. Both outer layers were chemically cleaned in order to remove any greas from their surfaces and assembled together as previously describe with a silicone rubber gasket of sufficient thickness to ensure that- the centers of the two layers were approximately 0.5mm apart from each other. At this time the assembly had no optical power whatever and the different curvatures of the layers merely represented the preselected desired curvatures for the finished lens. A thermosetting resin essentially consisting of 75% by weight of resin of unsaturated polyester resin and 25% by weight of resin o styrene monomer was mixed with 1/27» by weight of methyl ethyl ketone peroxide in 607» solution used as a catalyst and 1/10th of 1% cobalt naphthgn&te (67. of which is metal) used as an accelerato This mixture of resin, catalyst and accelerator was blended and poured into the chamber between the outer layers of glass and plastic and cured at 77°F for five hours.

The finished lens was a unitary element because the strength of the bond between the glass and plastic outer layers and the main lens portion was greater than the cohesive strength of the glass itself. The finished lens had all the desired properties including the desired optical properties, such as light transmission and clarity, and the physical properties, such as thermostability and resistance to abrasion. Moreover, the impact resistance of the lens was greater than a lens of equivalent ated lenses.

.Example 7 An ophthalmic lens for spectacles having a power of minus 12 diopters and containing thermosetting material which is not chemically bondable to glass was formed as follows. Four pieces of glass each 52mm in diameter were first cut from flat glass. Two pieces were thermally curved to measure about 13 diopters on each concave and convex surface, the other pieces wer thermally curved to measure about l'.OO diopters on the concave and convex surfaces. These lenses were distorted and normally not usable for optical purposes in that they deviate from spherocity in small uncontrolled amounts. Moreover, the lenses h the usual surface striations found in window glass. One lens of the 13.00 diopter plus and minus curvature, and one lens of the 1.00 diopter plus and minus curvature were chemically cleaned to remove any grease from their surfaces. The other two lenses were coated on their surfaces with a release agent. The lenses were then assembled together in matching pairs · (the two 13.00 together, and the two 1.00 together) with a silicone gasket between them as previously described so that the lenses were about 0.5mm apar from each other. The chamber of each assembly was then filled with a blended solution of epoxilated novolac resin having an epoxide equivalent range of 175 to 182 and 12% by weight of resin of diethylene triamine. The blend was poured between the glass layers and cured at the ambient temperature of 77°F. After curing the glass layers containing the release agent were removed from the assemblies and all traces of the release agent chemically removed from the elements of. glass and resin combined in a unitar structure.

Each of these two combined elements were then spaced apart with. the thermosetting layers opposing one another and assembled as previously described so that the centers of the. two lenses were approximately 0.5mm from each other. A polysiloxane resin blended with 3% by weight ditertiarybutylperoxide as a curing agent was poured into the space and cured.at 90°F for 4 hours. In so doing, the polysiloxane resin interacted with the epoxy layers to form a unitary lens wherein the bond between the epoxy and polysiloxane had a strength greater than the cohesive strength of the glass itself.

, As in the previous examples, the finished lens also had all the desired optical properties and a greater resistance to impact than an equivalent lens formed from either glass, plastic, o laminated .construction.

• - - Example 8 An optical lens having a power of plus 12 diopters was formed which had only one outer glass layer. Optical glass approximately 1mm in thickness was ground and polished to plus 6 diopters on its concave and convex surfaces and was chemically cleaned in order . to remove any traces of grease. A mold of glass While the invention has been illustrated by describing in detail optical elements, it is to be understood that the present invention is not limited thereto.

In the embodiment shown in Figures 14 and 15 there is provided a flat light transmitting element 80 including a main portion 82 composed of a thermosetting material chemically bonded to outer layers 84 and 86 which are desirably made of glass or other medium that has greater abrasion resistance than the inner portion 82.

For forming an element 80 of relatively light weight, the thickness of the main portion 82 is preferably substantially greater than the thickness of each outer layer 84 and 86, as from 2 to 8 times the thickness of each outer. layerj and for high light transmission the indices of refraction of the main portion 82 and the layers 84 and 86 are about equal. As previously described, the thermosetting material chemically interacts with reactive groups in the inner surface of layers 84 and 86, and striations or other surface imperfections contained in the glass are not present in the final element 80. In addition, the strength of th« chemical bond is greater than the cohesive strength of the glass ' itself. If desired the outer surfaces may be polished.

More commonly the element 80 is clear transparent, however, it may be colored by adding any well known coloring additives to the batch which forms the glass layers 84 and 86.

As in the previous embodiments, the main portion 82 of the element 80 can contain inserts to give specific additional KIRK-1 properties, such as wire mesh to form wire glass and specially treated or colored inserts to filter or otherwise modify the transmission of light. The element 80 can also include an outer layer made of a selected plastic material, or the element can include only one outer layer, particularly where only one surface is exposed to the . surrounding environment.

The flat element 80 can be used in a variety of ways.

It can be used for windows, wire panels, bullet proof panels, X-ray plates, instrument dials, display cases, shelving and desk tops. It also may be used where laminated glass is presently used, such as in office partitions and room dividers.

The light transmitting structure of the invention is particularly useful for thermal insulating purposes, such as for windows and refrigerator cases. A single structure, or spaced structures with a sealed air space between each pair of structures can be used for such purpose. Furthermore, presen thermal insula ting windows include two pieces of glass panes sealed so as to for an air space therebetween. These all glass thermal insulating windows must be factory produced to a particular window size and cannot be subsequently altered, and extreme care must be taken in installing such windows to avoid uneven pressure or insufficien expansion room. In addition, the ordinary glass panes do not have any safety value.

However, thermal insulating windows of the present . invention have high impac resistance, and can be formed- to overcome the problems- hich beset all glass thermal insulating 'windows. As illustrated in Figure 16, two elements 80 of the invention are spaced the desired distance apart and a rectangular or square frame 88 of somewhat less length 'and height than the elements 80 is placed, in the air space between the elements 80. Thereafter, the trough defined by the frame 88 and elements 80 is filled in excess of the height thereof to form a rim 90 which extends from the thermal insulating window about its perimeter. The window with its rim 90 can now be fitted to a window frame without any special precautions, and if necessary, the height of the rim 90 can be reduced to ensure proper fit.

In forming such a thermal insulating window the frame 88 is preferably a thermosetting material of the invention that is bonded to the elements 80 to form a sealed' air space. Moreover] the rim 90 is preferably formed of the same material as the frame 88, and a pair of rubber gaskets (not shown) may be placed about the perimeter of the elements 80, defining along with the trough, the gap which is thereafter filled by the rim 90.

. · The substantially improved thermal insulating property of the structures' of the invention is demonstrated in the followin examples. '.■· .' .

Example 9 A thermal insulating window pane of the present invent was formed from two glass sheets each having a thickness of 1mm were separated by the previously described rubber gasket a dista of 8mm. The chamber thereby formed between the glass layers was filled with a thermosetting resin essentially consisting of 80% by weight of resin of polybutadejine and 207» by weight of resin of styrene monomer that had been blended with 3% by weight of dimethyldihexine used as a catalytic agent. The blend was cured at 170°F.

Thereafter, the thermal conductivity of said thermal insulating pane was compared with that of ordinary plate glass having a thickness of 10mm. The thermal insulating pane of the invention had a thermal conductivity of 0.0008 calories per secon per square centimeter whereas the pane made solely of plate glass had a conductivity of 0.0024 calories per second per sqare centimeter. In other words, the thermal insulating pane of the inven-tion had three times better insulating properties than the plate glass pane.

Example 10 .·., · ' ' ' A further comparison was made between the thermal insulating window pane of the invention and an ordinary plate glass window .pane as follows: KIRK-1 A thermal insulating pane of the invention was formed from four sheets of flat window glass each 12 inches square and inch in thickness. Two glass sheets were chemically cleaned, th other two covered with a release agent. Two assemblies were prepared, each consisting of one cleaned sheet and one with the release agent placed together with a silicone gasket between them the gasket being 1/8 inch in thickness. The two chambers were then filled with epoxilated novolac resin as described in Example and then cured. After cure the two sheets of glass having the release agent on their surfaces were removed. The two remaining assemblies were then chemically cleaned to remove traces of release agent, and then assembled together with a silicone rubber gasket 1/2 inch in thickness between them. This chamber was then filled with silicone resin as described in Example 7 and cured.

The finished element 1 inch in thickness was compared to a 1. inch sheet of plate glass.

The thermal insulating pane of the invention had a thermal conductivity of 2.725 BTU/sq. ft/hr/inch thickness Degree F, whereas the plate glass pane had a thermal conductivity of 6.674 BTU/sq. ft/hr/inch thickness/Degree F. Thus, once again the thermal insulating pane of the invention had substantially improved insulating properties over that of the ordinary plate glass pane. ' \ ■ KIRK-1 In the embodiment shown in Figures 17 and 18 there is provided a panoramic windshield 92 that includes curved glass layers 96 and 98, and a main portion 94 of the thermosetting material that fills the space between such layers 96 and 9S„ Generally, the layers 96 and 98 are curved first and then the thermosetting material is placed therebetween and thereafter cured to form an infusible solid bonded to the outer glass layers, If desired the glass layers 96 and 98 may be tinted by standard techniques to form a tinted windshield.

With respect to the main portion of the light transmitting structures of the invention, it has been found that the epoxy resins of the invention are especially suited for the embodiments of the invention where high compression strength is desired, such as optical and ophthalmic lenses, prisms and windows Furthermore, the flexibilized epoxies and polybutadi,ne are well suited for bullet-proof glass, protective shields for vehicles, ophthalmic safety lenses and industrial safety protective lenses, and shield; and the unfilled, modified silicones are admirably suited for safety and particularly high heat stability, such as heat shields for furnaces, protective, windows for ovens and pressure chambers. The less expensive unsaturated polyesters lend themselves to embodiments of the invention where larger products are desired, such as automobile windshields and windows.

KIRK-1 The invention in its broader aspects is not limited to the specific embodiments, steps, methods, compositions described, but departures can be made therefrom within the scope of the accompanying claims without departing from the principles of the invention and without sacrificing its chief advantages. v

Claims (10)

1. U.S. 518.1l8 CLAIMS. le A light-transmitting element, comprising a main body of rigid and infusible thermosetting resin material having chemically bonded to an outer surface a layer of glass or plastics material which is relatively thin as compared to said main body and which is more abrasion-resistant than is the thermosetting resin material;

2. A light-transmitting element according to claim 1, wherein the bond between said outer layer of glass and said thermosetting material of said main portion is greater than the cohesive strength of glass itself.

3. A light-transmitting element according to claim 1, wherein said main portion is composed of a thermosetting material which in the un-cured condition is flowable and which in the cured condition forms an infusible solid that is chemically bonded to the; glass in said outer layer.

4. '. A light-transmitting element according to claim 1, wherein said thermosetting material is a member selected from the group consisting of epoxy resins, polysulfide and epoxy copolymers, flexibilized polybuta-diene, polybutadiene and styrene copolymers, unfilled silicones containing chemical groups that interact with groups in said glass outer layer, liquid and flowable polyurethanes, unsaturated polyesters, and flowable formaldehydeurea polymers.

5. >o A light-transmitting element according to claim 1, wherein said main portion contains an infusible segment that is chemically bonded to said thermosetting material and that is not chemically bondable to said outer layer.

6. A light-transmitting element according to claim 1, wherein said element is curved.

7. A light- ransmitting element according to claim 6, wherein said element is an optical lens .

8. A light-transmitting element acc ording to claim 7, wherein said outer layer is formed from ordinary window or plate glass.

9. A light- transmitting element according to any one of the preceding claims, wherein the outer layer comprises an allyl resin.

10. A method of forming a light-transmitting element comprising a main body of rigid and infusible thermosetting resin material having chemically bonded to an outer surface an outer layer of glass or plastics material which is relatively thin as compared to said main body and which is more abrasion-resistant than is the thermosetting resin material, comprising forming a mold chamber corresponding to the desired shape of the main body of the element, wherein a wall of the chamber is formed by said outer layer of the element, filling the chamber with a thermosetting resin materi^L which interacts chemically with the inner surface of the layer of glass or plastics material and curing the thermosetting resin material, to thereby form a rigid and infusible solid which is chemically bonded to the relatively thin sheet of greater abrasion-resistance.