OPHTHALMIC SEGMENT GLASS WITH HIGH nD

Abstract: The present invention relates to very high refractive index glasses (1.78 < n < 1.83), having the following composition of oxides, expressed in percentages by weight :SiO220- < 27B2O35-11Li2O2-8Na2O0-5K2O0-5BaO7-15CaO0-11La2O37-12PbO7-20TiO27-14ZrO20-5Nb2O5 > 8-16with: Li2O+Na2O+K2O > 6BaO+CaO+La2O3 > 27TiO2+Nb2O5+PbO > 29,to their use for the production of segments for multifocal corrective lenses and to multifocal corrective lenses incorporating at least one such segment in their structure.

Description: OPHTHALMIC SEGMENT GLASS WITH HIGH nD FIELD OF THE INVENTION The present invention relates to very high refractive index inorganic glasses; said index being more specifically greater than 1.78 and lower than or equal to 1.83. Said glasses notably have interesting uses as optical or ophthalmic glasses and are more particularly appropriate for manufacturing segments which enter into the making of multifocal corrective lenses. Said multifocal corrective lenses which incorporate at least one segment in a glass of the invention make up an integral part of the present invention. BACKGROUND OF THE INVENTION A multifocal lens is constituted of a principal lens in glass and of one or more segments in glass which are fused onto it. These segments have a higher refractive index than that of the principal lens; this enables obtaining areas of higher corrective power. Said segment(s) is (are) normally soldered onto the principal lens during a heat treatment bringing the whole of the glasses to a temperature close to the softening point of the glass constituting the principal lens. Consequently, the segment glasses must have characteristics of viscosity close to those of the glass of the principal lens. They must also have close thermal dilation characteristics, so that the resulting soldering has a very low strain level. The objective of the present invention was to obtain glasses of refractive index between 1.78 and 1.83 (1.78 < n < 1.83), fusible particularly to an ophthalmic glass manufactured by Corning S.A., of index 1.6, of Abbe number 41 and which has the following physical characteristics: -thermal dilation coefficient : 100 x 10 "7 K "1 (between 25 and 300°C) ; -softening point : 610°C; -strain point : 460°C; -annealing point : 490°C. Said glass bears the code-name 8008. It was described in US patent US- A-4,540,672. It has been determined experimentally that, in order to be fusible to said glass code-named 8008, the glasses must at least have a thermal dilation coefficient between about 90 and 110 x 10 "7 K "1 and a softening point between about 570 and 620°C . The technical problem to be solved within the context of the present invention was in fact that of providing glasses having the following specifications : - very high refractive index : 1.78 < n < 1.83 ; - Abbe number greater than 30 ; - thermal dilation coefficient : between 90 and 110 x 10 "7 K "1 (between 25 and 300°C) ; - softening point : between 570 and 620°C ; - fusible with glass of code 8008 ; - good chemical durability (i.e. good resistance to acids ; it being thus possible for the glasses and therefore the lenses in said glasses to be subjected to various surface treatments). PRIOR ART According to the prior art, some glasses, having a refractive index greater than 1.79 and being able to be used as segment glasses, are already known. However, none are known to exist which have the specifications indicated above. Glasses which are used for the same application, but which have a lower refractive index : 1.70 < n < 1.78, are described in the two patent applications : FR-A-2,762,837 and FR-A-2,769,618. Said glasses have the respective compositions by weight below. FR-A-2,762,837 FR-A-2,769,618 SiO 2 27 - 36 SiO 2 29 35 B 2 O 3 0 9 B 2 O 3 0.5 5 Li 2 O 1 5 Li 2 O 0.5 3 Na 2 O 1 7 Na 2 O 4 - 8 K 2 O 0 7 K 2 O 0 2 CaO 0 7 CaO 0 5 BaO 4 13 BaO 4 14 ZnO 0 8 ZnO 0 - 8 La 2 O 3 4 15 La 2 O 3 4 12 PbO 4 27 PbO 28 40 TiO 2 7 18 TiO 2 3 8 ZrO 2 0 9 ZrO 2 0 4 Nb 2 O 5 0 8 Nb 2 O 5 0 5 with with Li 2 O+Na 2 O+K 2 O 6 15 Li 2 O+Na 2 O+K 2 O ! 5.5 - 9 SiO 2 +TiO 2 +ZrO 2 42 - 55 PbO+TiO 2 +ZrO 2 +Nb 2 29 - 40. O 5 These glasses meet the present specifications from the point of view of the thermal dilation, the softening point, the chemical durability and the compatibility with the glass code-named 8008, but they do not permit the required index to be obtained. These glasses of the prior art have, respectively, a higher silica and lower niobium content than those of the glasses of the invention. Furthermore, the glasses according to FR-A-2,769,618 have a higher lead content than that of the glasses of the invention. In the US patent US-A- 4,351 ,906, optical glasses are described which have refractive indices between 1.745 and 1.771. Said glasses have the composition by weight below : SiO 2 28 - 32.5 Li 2 O 0 - 1 Na 2 O 2 - 9 K 2 O 0 - 4 PbO 28.5 - 34 BaO 0 - 22 ZnO 0 - 4 La 2 O 3 0 - 20 TiO 2 0 - 9 ZrO 2 2 - 6.5 Nb 2 O 5 0 - 10 WIIΠ Li 2 O+Na 2 O+K 2 O 4 - 10.5 BaO+La 2 O 3 14 - 22 TiO 2 +Nb 2 O 5 4.5 - 12 TiO 2 +ZrO 2 +Nb 2 O 5 6 - 17. With reference to the specifications set forth above, said glasses have, respectively, refractive indices which are too low (1.745 and 1.771) and softening points which are too high (640°C-700°C). Said glasses are not fusible with the glass code-named 8008. Hence, in order to meet the specifications as set forth above, an original solution (original glass compositions) is proposed. The glasses of the invention - novel - are remarkable in that they exhibit a very high index (1.78 < n < 1.83) associated with a good, even excellent, chemical durability. To develop glasses which combine these two types of property was not obvious. SUMMARY OF THE INVENTION Thus, novel glasses, which have the following composition of oxides, expressed in percentages by weight, are proposed: SiO 2 20 < 27 B 2 O 3 5 11 Li 2 O 2 8 Na 2 O 0 5 K 2 O 0 5 BaO 7 15 CaO 0 11 La 2 O 3 7 12 PbO 7 20 TiO 2 7 14 ZrO 2 0 5 Nb 2 O 5 > 8 16 with : Li 2 O+Na 2 O+ K 2 O 6 BaO+CaO+La 2 O 3 27 TiO 2 +Nb 2 O 5 +PbO 29. DESCRIPTION OF THE INVENTION The glasses of the invention are obtained essentially from the oxides identified above, taken in the amount specified above. It is certainly not excluded that other oxides intervene (vide infra) but, in any case, said other oxides do not intervene in significant amounts (always < 5 % by weight) and do not have a significant influence upon the properties sought after. They only intervene for adjustments. As regards the optional components (Na 2 O, K 2 O, CaO, ZrO 2 ), it is specified here, to all useful ends, that the minimal intervening amount from which they exert a significant effect is generally in the order of 0.5%. Thus, the glasses of the invention cannot contain said constituents or, if they do contain them, it is generally in a minimal amount of 0.5% (% by weight). Within the context of the present invention, glasses are preferred which have the composition of oxides below, expressed in percentages by weight : SiO 2 20 - 23 B 2 O 3 5 - 9 Li 2 O 3 - 7 Na 2 O 0 - 5 BaO 9 - 12 CaO 5 - 11 La 2 O 3 7 - 11 PbO 8 - 13 TiO 2 8 - 12 ZrO 2 2 - 5 Nb 2 O 5 9 - 15 WILΠ . Li 2 O+Na 2 O > 6 BaO+CaO+La 2 O 3 > 27 TiO 2 +Nb 2 O 5 +PbO > 29) These preferred glasses of the invention possess a very good chemical durability, which is very interesting, notably for ophthalmic glasses possessing such a high refractive index. All the glasses belonging to this composition range have a loss of weight, in a normalised test « A.O. test » (familiar to the person skilled in the art, recalled in the Example part of the present text) of less than 0.2 mg/cm 2 . Glasses of the invention having the composition of oxides expressed in percentages by weight below : SiO 2 21 - 23 B 2 O 3 6.8 - 7.8 Li 2 O 5.1 - 6.1 Na 2 O 0.2 - 2.2 CaO 8.7 - 9.7 BaO 10.2 - 11.2 PbO 8.7 - 10.7 ZrO 2 3.6 - 4.6 TiO 2 8 - 10 Nb 2 O 5 12.4 - 13.4 La 2 O 3 7.8 - 8.8 (with : Li 2 O+ Na 2 O > 6 BaO+CaO+l _a 2 O 3 > 27 TiO 2 +Nb 2 O 5 +PbO > 29) are more particularly preferred. The glass of Example 3 below is one of these particularly preferred glasses. Its composition by weight appears in Table 1. The high refractive index (1 .78 < n < 1.83) of the glasses of the invention is obtained in the main by virtue of their high contents of TiO 2 , Nb 2 O 5 and PbO. It is for this reason that the sum of these three oxides in the composition must be greater than 29%. TiO 2 , which is used in the proportions indicated, further enables a good chemical durability to be obtained. PbO enables the softening point of the glass to be lowered. As for Nb 2 O 5 , this is used in large amounts in order to obtain good transmission and devitrification properties. The oxides BaO, CaO and La 2 O 3 are used to adjust the refractive index and the viscosity without giving rise to a loss on the Abbe number. This is the reason why the sum of these three oxides in the composition must be greater than 27%. The alkali metal oxides (Li 2 O, optionally Na 2 O and optionally K 2 O) and B 2 O 3 , used in the proportions indicated above, enable obtaining the dilation and the characteristics of viscosity sought after. Li 2 O, in particular, decreases the softening point very strongly. It has been observed that the chemical durability of the glasses of the invention depended essentially upon their SiO 2 content. This is why the content of this element is at least 20%. At more than 24% of SiO 2 it is relatively difficult to keep the refractive index. ZrO 2 contributes advantageously to obtaining a high index, but contents of this element which are too high very rapidly cause the devitrification of said glasses. In order to adjust the properties of the glasses of the invention, as indicated above, other oxides such as AI 2 O 3 , ZnO, MgO, and SrO can also be added. Their total content must not go over 5% (by weight). If desired, bleaching agents can be added. It is also possible to colour the glass by adding conventional colouring elements, e.g. transition metal oxides or rare earth oxides. It is also possible to add conventional finishing agents such as As 2 O 3 or Sb 2 O 3 , fluorides, bromides or chlorides with the proviso that their total content does not exceed 1 % (by weight). The manufacture of the glasses of the invention does not bring about any particular difficulty; it does not necessitate any unusual condition or measure. It is within the reach of the person skilled in the art. The conventional starting materials, such as oxides, carbonates and nitrates, can be used for the preparation of the fillers to be melted. The usual precautions, as to the purity of said intervening starting materials, for obtaining optical glasses suffice (obviously if it is desired to obtain glasses of optical quality). According to another of its objects, the present invention relates to the use of the glasses having the original compositions specified above for the production of segments, of very high refractive index, of multifocal corrective lenses. In other words, another objective of the present invention is multifocal corrective lenses which comprise, in a manner known perse, a principal lens in a glass of refractive index ni and at least one segment, soldered to said lens, in a glass of higher refractive index n 2 (n 2 > ni) ; said segment(s) being characteristically in an original glass of the invention. Said multifocal corrective lenses of the invention generally comprise one sole segment of this type in their structure. The intervention of several of said segments is however in no way excluded. As indicated in the introduction of the present text, the glasses of the invention have been most particularly developed to be fused with a glass (code 8008) having the characteristics below: - thermal dilation coefficient : 100 x 10 "7 K "1 (between 25 and 300°C) ; - softening point : 610°C. The two characteristics recalled here are the main characteristics which render the fusion possible and efficient. Thus the invention, more particularly within the context of its second objective, relates to multifocal corrective lenses whose principal lens is in said glass (having the characteristics above) and whose segment(s) is (are) in a glass of the invention. SPECIFIC EMBODIMENTS The invention is illustrated in a totally non-limiting manner by Examples 1, 2 and 3 below. The glass of Example 3 is a glass of the invention which is more particularly preferred. According to an operating method specified below, glasses of the invention have been prepared whose compositions are given in the Table 1 below. Said compositions are expressed in percentages by weight. In each case, 4,000 g of starting materials were melted for 1 hour at 1 ,250°C in a platinum, crucible. The glass was then made into bars of 2 cm thickness. The annealing was carried out with a cooling rate of 60°C/hour. This operating method was carried out on a laboratory scale. It is obvious that the glasses of the invention may be manufactured industrially by using conventional methods of melting and forming. In said Table 1 below, the physical characteristics of the glasses obtained are specified. The measurements of these characteristics was carried out by conventional methods. The index measured is given by the spectral ray « d ». The dilation coefficients were measured between 25 and 300°C. They are expressed in multiples of 10 "7 K "1 . The softening point or Littleton point is the temperature at which the viscosity of the glass is 10 6'5 Pa.s. (10 7'5 poises). The durability was estimated by a test commonly used for ophthalmic applications, namely the A.O. test which consists of immersing a sample, whose surface has been polished, for 10 minutes in a solution of 10% by weight of hydrochloric acid kept at 25°C, by recovering said sample, and by measuring the loss of weight thereof. This loss of weight is then referred to the surface unit. The glasses of the preferred field of the invention have a loss of weight lower than 0.2 mg/cm 2 . TABLE 1

Claims: CLAIMS . Ophthalmic glasses having a refractive index of at least 1.78, and having a composition consisting essentially of, as expressed in weight percent on an oxide basis: SiO 2 20 - < 27 B 2 O 3 5 - 11 Li 2 O 2 - 8 Na 2 O 0 - 5 K 2 O 0 - 5 BaO 7 - 15 CaO 0 - 11 La 2 O 3 7 - 12 PbO 7 - 20 TiO 2 7 - 14 ZrO 2 0 - 5 Nb 2 O 5 > 8 - 16 with : Li 2 O+Na 2 O+K 2 O > 6 BaO+CaO+La 2 O 3 > 27 TiO 2 +Nb 2 O 5 +PbO > 29. 2. The glasses according to claim 1 , having the following composition of oxides, expressed in percentages by weight : SiO 2 20 - 23 B 2 O 3 5 - 9 Li 2 O 3 - 7 Na 2 O 0 - 5 BaO 9 - 12 CaO 5 - 11 La 2 O 3 7 - 11 PbO 8 - 13 TiO 2 8 - 12 ZrO 2 2 - 5 Nb 2 O 5 9 - 15 3. The glasses according to one of claims 1 or 2, having the following composition of oxides, expressed in percentages by weight : SiO 2 21 - 23 B 2 O 3 6.8 - 7.8 Li 2 O 5.1 - 6.1 Na 2 O 0.2 - 2.2 CaO 8.7 - 9.7 BaO 10.2 - 11.2 PbO 8.7 - 10.7 ZrO 2 3.6 - 4.6 TiO 2 8 - 10 Nb 2 O 5 12.4 - 13.4 La 2 O 3 7.8 - 8.8 4. An ophthalmic glass according to claim 3 consisting of, as expressed in weight percent on an oxide basis: SiO 2 22.0 B 2 O 3 7.3 Li 2 O 5.6 Na 2 O 1.2 CaO 9.2 BaO 10.7 PbO 9.7 ZrO 2 4.1 TiO 2 9.0 Nb 2 O 5 12.9 La 2 O 3 8.3 5. A segment for a multifocal, ophthalmic lens, the segment having a thermal dilation coefficient between 90x10 "7 /°K. and 110x10 "7 /°K., a softening point between 570-620° C, a refractive index of 1.78-1.83 and a composition, as expressed in weight percent on an oxide basis, and as recited in claim 1. 6. A segment according to claim 5 having a composition as follows: SiO 2 20 - 23 B 2 O 3 5 - 9 Li 2 O 3 - 7 Na 2 O 0 - 5 BaO 9 - 12 CaO 5 - 11 La 2 O 3 7 - 11 PbO 8 - 13 TiO 2 8 - 12 ZrO 2 2 - 5 Nb 2 O 5 9 - 15 7. A segment according to claim 5 having a composition as follows: SiO 2 21 - 23 B 2 O 3 6.8 - 7.8 Li 2 O 5.1 - 6.1 Na 2 O 0.2 - 2.2 CaO 8.7 - 9.7 BaO 10.2 - 11.2 PbO 8.7 - 10.7 ZrO 2 3.6 - 4.6 TiO 2 8 - 10 Nb 2 O 5 12.4 - 13.4 La 2 O 3 7.8 - 8.8. 8. A segment according to claim 5 having the composition as follows: SiO 2 22.0 B 2 O 3 7.3 Li 2 O 5.6 Na 2 O 1.2 CaO 9.2 BaO 10.7 PbO 9.7 ZrO 2 4.1 TiO 2 9.0 Nb 2 O 5 12.9 La 2 O 3 8.3 9. A multifocal lens comprising a principal lens and a segment, as recited in claim 5, sealed thereto. 10. A multifocal lens according to claim 9 in which the segment has a composition as follows: SiO 2 20 - 23 B 2 O 3 5 - 9 Li 2 O 3 - 7 Na 2 O 0 - 5 BaO 9 - 12 CaO 5 - 11 La 2 O 3 7 - 11 PbO 8 - 13 TiO 2 8 - 12 ZrO 2 2 - 5 Nb 2 O 5 9 - 15 11. A multifocal lens according to claim 9 in which the segment has a composition as follows: SiO 2 21 - 23 B 2 O 3 6.8 - 7.8 Li 2 O 5.1 - 6.1 Na 2 O 0.2 - 2.2 CaO 8.7 - 9.7 BaO 10.2 - 11.2 PbO 8.7 - 10.7 ZrO 2 3.6 - 4.6 TiO 2 8 - 10 Nb 2 O 5 12.4 - 13.4 La 2 O 3 7.8 - 8.8 12. A multifocal lens according to claim 9 in which the segment has the composition as follows: SiO 2 22.0 B 2 O 3 7.3 Li 2 O 5.6 Na 2 O 1.2 CaO 9.2 BaO 10.7 PbO 9.7 ZrO 2 4.1 TiO 2 9.0 Nb 2 O 5 12.9 La 2 O 3 8.3 13. A multifocal lens according to claim 9 wherein the pricipal lens has a thermal dilation coefficient of about 100 and a softening point of about 610° C.

Inventors: COMTE MARIE, MARQUES PAULO, COMTE, MARIE, MARQUES, PAULO
Applicants: COMTE MARIE, CORNING INC, MARQUES PAULO, COMTE, MARIE, CORNING INCORPORATED, MARQUES, PAULO
Application year: 2001
Main classification: C03C3
IPC codes: C03C3, G02C7