FR2740130A1 - Ultraviolet absorbing high-index glass - Google Patents

Abstract

Transparent, non photochromic glasses of refractive index more than 1.58, with abrupt cutoff at 400 nm, of composition in wt.%: 30-52 SiO2, 12-22 B2O3, 5-14 ZrO2, 0-12 Al2O3, 1.5-3.5 Li2O, 0-6 Na2O, 2-9 K2O, 0-5 MgO, 0-5 CaO, 0-9 SrO, 0-14 BaO, 0-4 Sb2O3, 0-4 As2O3, 0.15-1 CuO, 0-3 Cl, 0-2 I, 0-8 ZnO, 0-2 PbO, 0-15 Y2O3, 5-25 La2O3, 0-2 TiO2, 0-2 HfO2, 0-2 Nb2O5, 0-2 Ta2O5, 0-2 MoO3, 0-2 WO3, 0-4 SnO, 0-4 SnO2, 0-1 CdO, 0-2 F, 0-3 Br; with the conditions: Li2O+Na2O+K2O(X2O) range 7-14; MgO+CaO+SrO+BaO(XO) 12-20; ZrO2-Al2O3 less than 15; F+Cl+Br+I 0.2-4.0; TiO2+PbO+Nb2O5 less than or equal 2; As2O3+Sb2O3+SnO2+SnO 0.05-4.0; and ratio R=(M2O+2MO-Al2O3-ZrO2)/B2O3, where M2O and MO are alkali metal oxide and alkaline earth metal oxides in total, in mol% is 0.5-1.00.

Description

Field of the invention
The present invention relates to ophthalmic lenses having a refractive index of at least 1.58, which, in addition to their high visible-domain transmittance and low intrinsic staining, have a high (or even complete) absorption in the range. ultra-violet radiation, while being non-photochromic.

Context of the invention
In recent years, great attention has been paid to the harmful effects of ultraviolet (W) radiation on humans. Among the parts of the body requiring effective protection against biological damage caused by the sun or radiation W in general, the eye is often cited because of its relative fragility.

This fragility is at the base of the development of many colored glasses intended to filter the sun.

 Moreover, it is well known that the effects of W radiation are not limited to an interaction with living matter but can also lead to the degradation of organic matter (paints, plastics, etc.). Similarly, the sun is not the only source that can emit UV radiation that could be the cause of this degradation. Several types of artificial sources, such as halogen or Xenon lamps, can also emit significant ultraviolet radiation.

 Thus, it would be of interest to have a transparent glass in the visible but providing good protection or total protection vis-à-vis ultraviolet radiation. The applications of such glasses may relate inter alia to the fields of lighting, flasks, radiation protection and the design of ophthalmic lenses.

 In this field, it is known that photochromic lenses including halide crystals are activated by absorption of UV radiation. This absorption obviously results in a variation in the visible transmission of the glass, thus a certain protection of the eye is offered because such glasses strongly absorb radiation with wavelengths lower than 320 nm and weakly those between 320 and 400 nm. Although this range of radiation is less dangerous than that of shorter wavelengths, it is necessary to eliminate it in some cases.

 However, for other applications, it is not necessary that a change of transmission occurs during exposure to W rays or the sun. Therefore, it is essential to be able to obtain a clear cut of the radiation W, without photochromism being developed.

 On the other hand, the trend in the eyewear market is the use of high index materials. Indeed, the surfaced lenses, with high negative powers, result in very high edge thicknesses if a glass of conventional index of 1.523 is used. Compared with the lenses produced in such glasses, the use of higher index glasses makes it possible, for the same correction, to increase the radius of curvature of the lens and consequently to reduce the thickness.

 Until now, glasses combining the benefit of a high refractive index and a clear cutoff between ultraviolet and visible radiation, while being nonphotochromic and not colored, were not known.

Summary of the invention
The object of the present invention is to provide essentially transparent non-photochromic glasses of refractive index at least equal to 1.58, having an abrupt cut at 400 nm with respect to ultraviolet radiation, characterized by the following composition, expressed in percentages by weight on the basis of the oxides
SiO2 30 - 52 ZnO 0 - 8
B203 12 - 18 PbO 0 - 2 ZrO2 6 - 14 Y203 0 - 15
A1203 0 - 12 La2O3 5 - 25
Li2O 1.5 - 3.5 TiO2 0 - 2
Na2O 0 - 3 HfO2 0 - 2
K2O 2 - 9 Nb205 0 - 2
MgO 0 - 5 Ta2O5 0 - 2
CaO 0 - 5 MoO3 0 - 2
SrO 0 - 9 W03 0 - 2
BaO 0 - 14 SnO 0 - 4
Sb203 0 - 4 SnO2 0 - 4
As2O3 0 - 4 Cdo 0 - 1
CuO 0.15 - 1 F 0 - 2
Cl 0 - 3 Br 0 - 3
I 0-2 with the following conditions:
Li2O + Na2O + K2O (X2O) 7 - 14
MgO + CaO + SrO + BaO (XO) 12 - 20
ZrO2 + A1203 <15
F + Cl + Br + I 0.2 - 4.0
TiO2 + PbO + Nb2O5 s 2 and a ratio R = (M2O + 2M0-A1203-ZrO2) / B2O3 where M2O and MO represent the total content of alkali metal oxide and the total content of alkaline earth metal oxides, respectively, expressed in mole-percent, ranging from 0.50 to 1.00.

 The ratio R is related to the basicity of the glass. In general, the value of the ratio R allowing the best precipitation of the crystals is about 0.60 to 0.90, in particular about 0.70. The lowest values in the range indicated for R are given by the combination of high levels of ZrO 2 and Al 2 O 3, which makes the glass difficult to melt without a particular benefit being derived. At the other extreme, the highest values of the ratio R are obtained for glasses whose alkali metal and / or alkaline earth oxide contents are important. Under these conditions, the precipitation of copper colloids is favored and it is necessary to exercise a strict control of the elements necessary for the constitution of the crystals (copper and halogens), as well as a reduction of the quantity of reducing agents necessary for the reduction of the copper.

 In case of precipitation of colloids, the resulting glass can take various colors (green-blue, red, brown, orange ...), according to the redox state of copper and the amount of reductants it contains. An adjustment of its transmission in the visible range and of its final coloration is then possible by the addition of small amounts of dyes such as transition metal ions or rare earths, without any damage to the performance of the properties of the dyes. absorption of the ultraviolet cut is not detectable. Thus, although obtaining colorless glasses is the main objective of the invention, the latter also includes colored glasses. Colored glasses can be produced by the use of relatively high levels (for example 3 to 4W). reducing agents, such as SnO, or by incorporating conventional coloring agents into the glass composition. Such colored glasses may be useful especially for the manufacture of lenses for sunglasses.

 The presence of at least one halogen is necessary to combine with copper and form copper halide crystals, responsible for the UV cutoff. Chlorine and bromine are the most commonly used halogens. Fluoride and iodine may be beneficial but are not usually used in the absence of chlorine and bromine.

 The use of cadmium oxide is not required to achieve UV absorption. The benefits that can be obtained from the absorption complement that it brings to copper is low in view of its high toxicity. In addition, in some cases, it may promote photochromism, an undesired phenomenon in the present invention. Also, it is preferable that its content is less than 1% and preferably zero.

In order to raise the refractive index, significant amounts of one or more oxides such as TiO 2, Nb 2 O 5,
ZrO 2, ZnO, PbO, with optional additions of alkaline earth metal oxides, are generally employed.

The inclusion of TiO2 or Nb205 offers the advantage of rapidly increasing the refractive index without significantly affecting the density of the glasses considered. Thus, currently sold glasses having refractive indices of about 1.6 contain large amounts of such oxides. Unfortunately, the use of TiO2, PbO or Nib205, in the presence of the copper necessary to obtain the ultraviolet cut at 400 nm, leads to a strong yellow color of the glasses. This coloration can be used for the development of glasses for solar application is not acceptable for glasses "crowns". Thus, the glasses of the invention are preferably substantially free of TiO 2, PbO and Nb 2 O 5, although very small amounts, i.e. less than 2 W in total, can be tolerated.

Also, to obtain a high refractive index, we will rather use oxides such as ZrO2, Al2O3, La2O3, Y2O3, ZnO and alkaline earth metal oxides while the total content of other heavy metals such as MoO3,
WO3, PbO, TiO2 and Nb2O5 will preferably be maintained below 4%, especially below 2%. Of course, for applications where the coloring is less important, for example for colored sun protection glasses, this total content can be considerably higher.

 Other reasons are at the origin of the limitation of the use of the heavy oxides such as the increase of the density, and, for MoO3 and WO3, the fact that they favor the appearance of a photochromism to avoid .

Preferred glass compositions are as follows, in W by weight
SiO2 35 - 47 CaO O - 3 B203 12 - 16 SrO O - 7
ZrO2 9 - 12 BaO 2 - 7 Au203 O - 6 ZnO O - 3
Li2O 1.5 - 3 Y203 O - 12
Na2O 2 - 3 La2O3 8 - 20
K2O 2 - 7 SnO 0.2 - 2.5
CuO 0.25 - 0.75 Br 0.1 - 2
Cl 0,1 - 2
The glasses of the invention have the following properties:
a refractive index of between 1.58 and 1.65
- an Abbe number between 40 and 60
- density less than 3.5 g / cm3
- an optical transmission in the visible range of more than 85%.

 a total absorption of the radiation W defined by an average transmission between the wavelengths of 315 and 380 nm of less than 0.5 W.

 - no photochromism.

Prior art
US Patent No. 5,023,209 (Grateau et al.) Is representative of commercial glasses having a refractive index close to 1.6. This patent provides base glass compositions comprising large amounts of TiO 2 and leading to the development of a marked photochromism after heat treatment.

FR-A-2717915 discloses photochromic glasses of high refractive index having a low color at the origin. This improvement is obtained through the use of quantities of less than 2% of TiO2 and greater than 6% of
Nb2O5. The compositions of the present invention, however, differ from these glasses in the absence of silver and substantially lower levels of Nib205.

U.S. Patent No. 5,145,805 (Tarumi et al.) Covers two families of glasses containing up to more than 15% copper chloride. The non-phosphate family includes the percentages by weight of the following components: SiO2 20-85%, B203 2-75%, 15% Al2O3 or less, about 30 W or less of at least one alkali metal oxide , 10% or less of at least one divalent metal oxide, at least about 10% of one of the following oxides ZrO 2, La 2 O 3, Y 2 O 3,
Ta2O3, Gd2O3. No range of refractive index is claimed and, in the working examples, the concentrations of oxides such as ZrO 2, La 2 O 3, Y 2 O 3 are less than 1 s. Therefore, although there is an overlap between the Tarumi wide intervals and the compositional ranges of the present invention, none of the working examples provided in this patent have a base composition entering the intervals of the glasses of the present invention. present invention.

 U.S. Patent No. 5,281,562 (Araujo et al.) Discloses transparent non-photochromic borosilicate glass compositions containing a crystalline phase of copper or copper / cadmium chloride and having a sharp cutoff W at about 400 nm. The authors claim a composition range related to a ratio R expressed in molar percentage of between 0.15 and 0.45 with an optimum for the value of approximately 0.25. Thus, the amount of alkali and alkaline earth metal oxides must be strictly controlled to achieve this condition. They also mention that the oxides generally used to raise the refractive index such as those of titanium, zirconium, niobium, lead must be used in small quantities. Consequently, the compositions described in the patent have a refractive index. in the range close to the standard value (1,523). The present invention discloses glass compositions of much higher refractive index and for which the ratio R expressed in mole% is outside the claimed range.

 EP-A-0 586 948 (Sugimoto et al.) Discloses ultraviolet radiation absorbing alumino-borosilicate glasses. The use of heavy oxides such as La2O3 and Y203 is not mentioned and no value of the refractive index is given.

Description of Preferred Embodiments
Table I summarizes glass compositions, expressed in parts by weight based on the oxides, illustrating the products of the invention. Since the sum of the individual components is equal to or close to 100, the values mentioned in the table can be considered for all practical purposes as representing weight percentages. In addition, since the cation (s) with which the halogens are combined are not known and the proportions of the latter are small, Cl, Br, I and F are expressed in elemental form. The values indicated for Cl, Br, I and F are the stored values. Experience has shown that the percentage actually remaining in the vitreous matrix is significantly lower and that the retention rate for halogens is typically around 50 to 75%.

 The feedstock ingredients may be any material, whether oxides or other compounds, which, when melted together, are converted to the desired oxides in the desired proportions . Cl, Br, I and F are generally incorporated into the feed as alkali or alkaline earth metal halides.

The ingredients of the filler were combined, intimately mixed together to promote homogeneous melting, and placed in a Joule heated platinum crucible between 1250 OC and 1300 OC depending on the composition of the filler. When the charge reached complete melting, the temperature of the melt was raised to about 1350
OC at 1450 OC to ensure good homogeneity and good ripening. The melt was then cooled and simultaneously shaped into a glass article of a desired configuration which was immediately transferred to a baking oven operating at about 450 ° C.

 It should be noted that the above description reflects only fusion and forming work in the laboratory and that the glasses of the invention can be melted in large-scale melters and shaped into desired configuration articles using classical techniques in glass technology. Thus, according to the usual practice of melting and forming glass, it is only necessary to intimately mix the filler, melt the filler at temperatures and for sufficient time to obtain a homogeneous cast iron, cool the cast iron and shape it simultaneously in a glass body having a desired configuration, and normally annealing this glass body.

 Samples were cut from the annealed glass articles. These samples were introduced into an electrically heated oven and exposed for the times in minutes and OC temperatures shown in Table II to develop the crystalline phase of copper halides responsible for absorption in the field of ultra-violet radiation. -violettes.

 To obtain this precipitation, the glass must contain at least 0.15% copper oxide CuO. This amount can rise up to about 1%, however when this is done, cupric and / or cuprous ions tend to be reduced to neutral form. Thus, the use of about 0.25-0.75% CuO is preferred.

 The absorption of the red part of the spectrum leading to the development of a green-blue color is related to the "d" transitions of cupric ions (Cu2 +). These orbital d are totally occupied if the copper is in cuprous form (Cu +). These ions do not contribute to give the glass a visible color. Since only this form of copper is needed to obtain the cutoff W, a colorless glass is obtained by suitably adjusting the oxidation-reduction state of the copper.

The oxidation-reduction state of the copper obtained in the glass is influenced by several parameters, the main ones being the basicity of the glass, estimated by the ratio R, and the concentrations of reducing agents such as As2O3, Sb203, SnO2 and
SnO. These polyvalent ions are very powerful for moving the cupric ion / cuprous ion balance and therefore have a significant effect on the color of the glass. Among the reducing agents mentioned, the SnO 2 stannous oxide is preferred because of its high reducing power. Its concentration must, however, be carefully controlled to avoid the reduction of Cu0 metal copper responsible for the appearance of a strong red color of the glass. High concentrations of reducing agents, up to 4%, can be used without colloidal copper precipitation being observed.

Table II indicates for each example of given glass
the value of the ratio R defined above,
the temperature, in OC, and the time, in minutes, used to develop the crystalline phase responsible for the absorption W,
the refractive index (IR),
- the number of Abbe (Abbe),
- the density in g / cm3 measured by the immersion method,
- the transmission factor in the visible range (T) measured on samples with a thickness of 2 mm,
the color determined by the trichromatic coordinates (x and y),
- the ultraviolet cut (W cut) defined as the wavelength given in nanometer (nm) for which the transmission is equal to 1%.

 the mean transmission in percent in the ultraviolet range defined as the mean of the transmissions measured every 5 nm between 315 and 380 nm.

 Example 1 is representative of a transparent glass having an index equal to about 1.6 in which no element necessary for the development of a crystalline phase absorbing ultraviolet radiation is introduced. This glass, which can be considered as an illustration of the optical performance of high-index glasses on the market, provides no protection vis-à-vis the ultraviolet radiation. In particular, the ultraviolet cut of such glasses occurs only at around 315 nanometers, which causes an average transmission in the range of W A of the order of 45%.

 Examples 2 to 6 show the perfect protection vis-à-vis radiation W obtained through the precipitation of copper halides in glasses whose refractive index is close to 1.6 and therefore R ratio greater than 0.5.

 Example 2 establishes a comparison between the performance of the glasses of the invention and the standard glasses represented by Example 1. The glasses of the present invention have, for transmission factors in the visible range equivalent and without great penalties on color, a total absorption of ultraviolet radiation. This results in a UV cutoff for a wavelength well above 380 nm, the upper limit of the W radiation. These optical properties are achieved with a basic composition identical to that used in Example 1, to which halides, copper and a reducing agent such as SnO have been added.

 Example 3 is representative of the use of high levels of lanthanum oxide to achieve the desired properties.

 Example 4 is representative of the use of high levels of lanthanum and yttrium oxide; which has the advantage of lowering the density of the glass obtained.

 Examples 5 and 6 illustrate the possibility of introducing additional quantities of alkaline and alkaline-earth oxides without penalties on the optical performance of the product. In these examples, the ratio R is 0.80 and the absorption W is excellent. Example 6 shows the influence of the heat treatment on the absorption properties. This example illustrates the possibilities of adapting the final performance of the product by means of an appropriate heat treatment.

 Examples 7 to 9 are compositions which, for one reason or another, do not fall within the scope of the patent.

 Example 7 is representative of compositions using high levels of alkaline earth metal oxides without particular precautions taken on the adjustment of either the ratio R or the constituent elements of the crystalline phase, that is to say copper, halogens. and / or reducing agents. As a result, the barium oxide content is outside the claimed range and the ratio R is at the upper limit. This example illustrates the phenomenon of precipitation that is observed in some cases. Despite a significant reduction in its transmittance and the loss of transparency, the glass retains its radiation absorption properties. Such a glass, without falling within the scope of the claims, can be used in applications where the properties of transparency are less important such as solar glasses for example.

 Example 8 shows a glass in which the zinc oxide content is outside the claimed range. In this case, the glass remains transparent but on the other hand loses its ultraviolet radiation absorption properties.

 Example 9 shows a glass in which the niobium oxide content is higher than the claimed limit value. The described glass is yellowish in color without any particular benefit to W absorption.

TABLE I

1 <SEP> 2 <SEP> 3 <SEP> 4 <SEP> 5 <SEP> 6 <SEP> 7 <SEP> 8 <SEP> 9
<tb> SiO2 <SEP> 45.2 <SEP> 45.2 <SEP> 38.6 <SEP> 37.3 <SEP> 48.8 <SEP> 48.8 <SEP> 38.8 <SEP> 36 , 2 <SEP> 46.1
<tb> B2O3 <SEP> 14.3 <SEP> 14.3 <SEP> 13.4 <SEP> 13.6 <SEP> 15.4 <SEP> 15.4 <SEP> 13.4 <SEP> 13 , 9 <SEP> 14.5
<tb> ZrO2 <SEP> 11.3 <SEP> 11.3 <SEP> 10.6 <SEP> 10.7 <SEP> 12.2 <SEP> 12.2 <SEP> 10.6 <SEP> 11 , 0 <SEP> 11.5
<tb> Li2O <SEP> 1.9 <SEP> 1.9 <SEP> 1.8 <SEP> 1.8 <SEP> 2.8 <SEP> 2.8 <SEP> 1.8 <SEP> 1 , 8 <SEP> 1.9
<tb> Na2O <SEP> 2.6 <SEP> 2.6 <SEP> 2.4 <SEP> 2.5 <SEP> 2.8 <SEP> 2.8 <SEP> 2.4 <SEP> 2 , 5 <SEP> 1,1
<tb> K2O <SEP> 2.7 <SEP> 2.7 <SEP> 2.6 <SEP> 2.6 <SEP> 3.0 <SEP> 3.0 <SEP> 2.6 <SEP> 2 , 7 <SEP> 5.2
<tb> SrO <SEP> 1.7 <SEP> 1.7 <SEP> 1.6 <SEP> 1.6 <SEP> 1.9 <SEP> 1.9 <SEP> 1.6 <SEP> 1 , 7 <SEP> 1,8
<tb> BaO <SEP> 5.4 <SEP> 5.4 <SEP> 5.0 <SEP> 5.1 <SEP> 5.8 <SEP> 5.8 <SEP> 14.7 <SEP> 5 , 2 <SEP> 5.5
<tb> ZnO <SEP> - <SEP> - <SEP> - <SEP> - <SEP> - <SEP> - <SEP> - <SEP> 10.5 <SEP>
Nb2O5 <SEP> - <SEP> - <SEP> - <SEP> - <SEP> - <SEP> - <SEP> - <SEP> - <SEP> 12.4
<tb> La2O3 <SEP> 14.9 <SEP> 14.9 <SEP> 24.1 <SEP> 14.2 <SEP> 7.3 <SEP> 7.3 <SEP> 14.0 <SEP> 14 , 5 <SEP>
Y2O3 <SEP> - <SEP> - <SEP> - <SEP> 10.7 <SEP> - <SEP> - <SEP> - <SEP> - <SEP>
CuO <SEP> - <SEP> 0.5 <SEP> 0.5 <SEP> 0.5 <SEP> 0.5 <SEP> 0.5 <SEP> 0.5 <SEP> 0.5 <SEP> 0.5
<tb> Cl <SEP> - <SEP> 1 <SEP> 1 <SEP> 1 <SEP> 1 <SEP> 1 <SEP> 1 <SEP> 1 <SEP> 0
####
<tb> SnO <SEP> - <SEP> 2 <SEP> 2 <SEP> 2 <SEP> 2 <SEP> 2 <SEP> 2 <SEP> 2 <SEP> 1
<tb> TABLE II

1 <SEP> 2 <SEP> 3 <SEP> 4 <SEP> 5 <SEP> 6 <SEP> 7 <SEP> 8 <SEP> 9
<tb> Ratio <SEP> R <SEP> 0.68 <SEP> 0.68 <SEP> 0.68 <SEP> 0.68 <SEP> 0.8 <SEP> 0.8 <SEP> 1.01 <SEP> 0.68 <SEP> 0.68
<tb> Treatment <SEP> thermal
<tb> Temperature <SEP> 680 <SEP> 680 <SEP> 680 <SEP> 680 <SEP> 680 <SEP> 600 <SEP> 680 <SEP> 680 <SEP> 680
<tb> Time <SEP> 15 <SEP> 15 <SEP> 15 <SEP> 15 <SEP> 15 <SEP> 15 <SEP> 15 <SEP> 15 <SEP> 15
<tb> Physical <SEP> Properties
<tb> IR <SEP> 1.598 <SEP> 1.598 <SEP> 1.632 <SEP> 1.634 <SEP> 1.582 <SEP> 1.582 <SEP> 1.624 <SEP> 1.626 <SEP> 1.600
<tb> Nb.Abbe <SEP> 52.5 <SEP> 52.5 <SEP> 52.1 <SEP> 51.2 <SEP> 54.9 <SEP> 54.9 <SEP> 52.5 <SEP > 51.3 <SEP> 45.2
<tb> Mass <SEP> 3.01 <SEP> 3.01 <SEP> 3.28 <SEP> 3.25 <SEP> 2.85 <SEP> 2.85 <SEP> 3.26 <SEP> 3 , 24 <SEP> 2,81
<tb> volumic
<tb> Optical <SEP> Properties
<tb> T <SEP> 89.4 <SEP> 89.6 <SEP> 88.7 <SEP> 88.8 <SEP> 88.2 <SEP> 89.6 <SE> 51.1 <SEP> 88 , 1 <SEP> 85.6
<tb> x <SEP> 0.3118 <SEP> 0.3133 <SEP> 0.3126 <SEP> 0.3120 <SEP> 0.3172 <SEP> 0.3112 <SEP> 0.3660 <SEP> 0 , 3111 <SEP> 0.3265
<tb> y <SEP> 0.3188 <SEP> 0.3228 <SEP> 0.3214 <SEP> 0.3202 <SEP> 0.3293 <SEP> 0.3184 <SEP> 0.3341 <SEP> 0 , 3175 <SEP> 0.3392
<tb> Aspect <SEP> Incol. <SEP> Incol. <SEP> Incol. <SEP> Incol. <SEP> Incol. <SEP> Incol. <SEP> Red <SEP> Incol. <SEP> Yellow
<tb> Cleavage <SEP> UV, <SEP> 315 <SEP> 404 <SEP> 408 <SEP> 405 <SEP> 413 <SEP> 389 <SEP> 412 <SEP> 320 <SEP> 344
<tb> nm
<tb> Transmission
<tb> average <SEP> in
<tb> 46.8 <SEP> 0 <SEP> 0 <SEP> 0 <SEP> 0 <SEP> 0 <SEP> 0 <SEP> 38.9 <SEP> 6.5
<tb> UV
<Tb>

Claims (5)

 1. Non-photochromic glasses essentially transparent, having a refractive index of at least 1.58, having an abrupt cut towards 400 nm with respect to ultraviolet radiation, characterized by the following composition, expressed as percentages of weight on the basis of oxides SiO2 30 - 52 ZnO 0 - 8 B2O3 12 - 18 PbO 0 - 2 ZrO2 6 - 14 Y2O3 0 - 15 A1203 0 - 12 La2O3 5 - 25 Li2O 1.5 - 3.5 TiO2 0 - 2 Na2O 0 - 3 HfO2 O - 2 K2O 2 - 9 Nb2O5 0 - 2 MgO 0 - 5 Ta2O5 0 - 2 CaO 0 - 5 MoO3 0 - 2 SrO 0 - 9 WO3 0 - 2 BaO 0 - 14 SnO 0 - 4 Sb2O3 0 - 4 SnO2 0 - 4 As2O3 0 - 4 CdO 0 - 1 CuO 0.15 - 1 F 0 - 2 Cl 0 - 3 Br 0 - 3 I 0-2 with the following conditions: Li2O + Na2O + K2O (X2O) 7 - 14 MgO + CaO + SrO + BaO (XO) 12 - 20 ZrO2 + Al2O3 <15 F + Cl + Br + I 0.2 - 4.0 TiO2 + PbO + Nb205 s2 and a ratio R = (M2O + 2M0 - Al2O3 - ZrO2) / B2O3 where M2O and MO represent the total content of alkali metal oxide and the total content of alkaline earth metal oxides, respectively expressed as mole-percent, ranging from 0.50 to 1.00.  2. Glasses according to claim 1, characterized in that they are substantially free of CdO.  3. Glasses according to claim 1 or 2, characterized in that they have the following composition SiO2 35 - 47 CaO 0 - 3 B2O3 12 - 16 SrO 0 - 7 ZrO2 9 - 12 BaO 2 - 7 A1203 0 - 6 ZnO 0 - 3 Li2O 1.5 - 3 Y203 0 - 12 Na2O 2 - 3 La203 8 - 20 K2O 2 - 7 SnO 0.2 - 2.5 CuO 0.25 - 0.75 Br 0.1 - 2 Cl 0,1 - 2  4. Glasses according to claim 1, characterized in that they are colored by adding coloring oxides and / or by a precipitate of copper colloids.  5. Lentil characterized in that it consists of a glass as defined in any one of claims 1 to 4.