FR2744114A1 - LIGHT GLASS OF OPTICAL QUALITY FREE OF LEAD AND ARSENIC - Google Patents

Abstract

The present invention relates to a light optical glass free of lead and arsenic having a density rho of between 2.92 and 3.06 g / cm ** 3, a refractive index nd of between 1.68 and 1 , 74 and an Abbe nud number between 28 and 32, and exhibiting very good chemical resistance and excellent crystallization stability, and having the following composition (in% by weight): SiO2 35.1 - 44 ; GeO2 0 - 2; B2 O3 2 - 3.5; Na2 O9 - 14; K2 O6 - 9; Li2 O 0 - 1; Cs2 O 0 - 2; SIGMAM2 O 16 - 21; CaO 0.5 - 3; BaO 3 - 8; ZnO 0-1; SrO 0.02 - 1; SIGMAMO 5.5 - 9; TiO2 22 - 30; ZrO 2 0.2 - 1.99; Nb 2 O 5 4-10; Al2 O3 0-1; WO3 0-2; SnO2 0 - 0.5.

Description

Lightweight optical quality glass free of lead and arsenic During

  in recent years the components of glass PbO and As203 have been the subject of a certain number of debates because it is supposed that these two components of glass are harmful for the environment. Some manufacturers of optical instruments and consumer optical products will no longer produce only lenses free of

lead and arsenic.

  The state of the art is revealed in particular by the documents

  DE3216451C2, DE2259183C3, EP 0 645348A1, EP 0 645349 A1, FR

  23,902 (utility certificate, publication no.2,320,031), JP 6,107,425 A,

  JP 53/16718 (7816,718) and documents JP 52/25812 (77 25 812).

  According to this state of the art, it is possible to manufacture lead-free glasses and in part also light glasses, but these glasses

  have significant drawbacks.

  The glasses described in German patent DE 32 16 451 C2 require, for a low SiO2 content not exceeding 35% by weight, the presence of alkaline earth metal oxides in an amount ranging up to 15% by weight, in particular from 7 to 13% by weight of BaO, in order to

  maintain sufficient crystallization stability. Obtaining ver-

  res having a refractive index nd> 1.70 requires not only a TiO2 content of 20 to 30% by weight but also the presence of 7 to

  19% by weight of Nb205, a very expensive raw material.

  German patent DE 22 59 183 C3 describes glasses which reach

  achieve the desired refractive index by adding zir dioxide

  conium, an expensive raw material, in relatively large quantities

  aunts compared to those used in the present invention. This German patent also provides only for optional use of CaO, BaO and K20, while their use is essential and compulsory in the

  present invention for obtaining the desired optical properties.

  The glasses described in the unexamined European patent application

  mined EP 0 645 348 Ai are part of the SiO2-M20-TiO2 system, but do not contain A1203, B203 and ZrO2, and consequently exhibit poor resistance to chemicals. Mention should be made in this context in particular of alkali resistance. For a high

  SiO2 content, between 46 - 65%, the melting of these glasses is difficult

  due to the absence of B203, or else they require a high content of alkali oxides (up to 25% Na2O, up to 30% K20) this

  which, in turn, decreases the stability to crystallization and the chemical resistance

  mique and makes it difficult to obtain high refractive indices.

  In the unexamined European patent application EP 0 645 349 A1, it is a glass system very similar to that of the application EP 0 645 348 Ai, and similar remarks are therefore necessary. The main difference lies in the fact that smaller amounts of TiO2 and BaO are used, which does not make it possible to obtain the optical quality required by the present invention without using the ZrO2 components

Num205.

  The French utility model FR 75 23 902 describes glasses free of A1203 and B203 and which contain up to 47% by weight of SiO2. To facilitate the melting of these glasses, it is necessary to introduce therein up to 31% by weight of alkali metal oxides, in particular up to 17% by weight of K20. This decreases the chemical resistance. The manufacture of glasses with a higher refractive index (nd = 1.75) requires, for

  relatively low Nb205 contents of only 3.5% by weight, the pre-

  sence of up to 35.5% by weight of TiO2 (see Example III of the document

in question).

  Japanese document JP 6-107 425 A describes glasses of the system

  teme SiO2-B203-BaO. These are glasses with a low refractive index. In particular the high content of B203 of 5 to 20% by weight gives glasses to

  high Abbe number, i.e. vd> 40, for a low refractive index

  nd ble> 1.54. As these glasses still have significant contents in

  M20 (up to 30%) and BaO (up to 45%), their tendency to crystallize -

  tion and their chemical resistance do not meet the requirements for

  optical lenses under normal operating conditions.

  The glasses described in document JP 53/16718 are part of the

  SiO2-MO-TiO2-Nb205 system. To obtain refractive index glasses

  important, we use very expensive raw materials here that

  are Nb205 (up to 40% by weight) and Ta205 (up to 10% by weight).

  These glasses also require the presence of 15 to 50% by weight of alkaline earth metal oxides. This makes these glasses not only

  not very profitable but also have a low stability to crystallization

station.

  Document JP 52/25812 describes glasses forming part of the system.

  teme SiO2-TiO2-Nb205. These glasses necessarily contain a total of 5 to 50% of alkali metal oxides. The glass of the present invention necessarily requires the presence of the oxides B203, Na2O, K20, CaO, BaO and ZrO2. The Japanese patent does not indicate lower limits for these oxides (for example CaO: 0 - 30%, BaO: 0 - 30% and ZrO2: 0 - 20%). Therefore, in this Japanese patent, these oxides are only optional,

  that is, they can optionally be omitted.

  The glass presented in the present invention is distinguished by

  in addition by a content of SrO which improves the stability to crystallization.

  It should also be noted that such broad limiting ranges (for example from 0 - 30% of alkaline earth metal oxides) encompass several families of glasses between which there are no continuous transitions. For a more precise limitation of these, it is necessary

  to consider the examples. In 7 out of 8 examples, the ver-

  res contain 0% BaO, i.e. they belong to a family of glasses which does not require the presence of BaO and, in one of the 8 examples, they

  contain 30% BaO. This value is not included in the four-

  chette claimed by the present invention which is 3 - 8% and the glasses also have a refractive index outside the claimed range. The same goes for ZrO2 (in 7 examples: 0%, in 1 example 5%, range claimed by the present invention: 0.2 to 1.99%; all glasses have Abbe numbers outside the range fork

  claimed) and for CaO (in 6 examples 0%, in 2 examples> 5%).

  As far as the Na2O content is concerned, the examples for which this content is 0% do not give refractive indices and Abbe numbers included in the corresponding claimed ranges. All

  the examples for which this is the case have higher Na2O contents

less than 14%.

  If, conversely, we consider the two examples (2 and 5) for which the refractive index and the Abbe number are included in the ranges claimed by the present invention, it will be seen that these examples do not correspond to compositions claimed for the glasses of the present invention: Example 2 of the Japanese document: 0% of ZrO2; 40% Nb2O5, 20% SiO2; 0% BaO or Example 5: 0% ZrO2; 20% Na2O; 3% K20, 2% Li2O, 0%

CaO and BaO; 35% SiO2.

  The object of the present invention is therefore to define composition ranges for optical glasses which, without the use of As203 and PbO, give glasses having a refractive index nd

  between 1.68 and 1.74 and an Abbe vd number between 28 and 32.

  These glasses must have optical properties equivalent to those of

  usual heavy flints but must be characterized by a specific gravity

  reduced mique, excellent chemical resistance and very good stability

lity to crystallization.

  Another objective is to develop low density heavy flints free of PbO and As203 having a density lower than 3.06 g / cm3, which are easy to melt and transform. They must also have a very good stability to crystallization and thus allow the

  manufacturing in a tank for optical glasses. Good resistance chi-

  The high hardness of these glasses is essential for their transformation.

  subsequent mation (abrasion, polishing).

  To make a glass that meets all the requirements

  It was necessary to find new ranges of composites.

  tion. These composition ranges are as follows (in% by weight) glass-forming oxides: SiO2 35.1 - 44; GeO2 0 - 2; B203 2 - 3.5; A1203 0 - 1; oxides serving as flux: Li2O 0 - 1; Na2O 9-14; K20 6 - 9; Cs20 0 - 2;

  the sum of the alkali metal oxides being between 16 and 21%.

  CaO 0.5 - 3; BaO 3 - 8; SrO 0.02 - 1; ZnO 0 - 1 and the sum of the alkaline earth metal oxides being between

, 5 - 9%;

  and other TiO2 components 22-30; ZrO2 0.2 - 1.99; Num 205 4-10; WO3 0 - 2, SnO2 0 - 0.5;

  the SiO2 / 1 TiO2 + ZrO2 ratio must be between 1.24 and 1.75.

  The glasses of the present invention do not only have the low

  density required (p <3.06 g / cm3), associated with refractive indices

  tion nd between 1.68 and 1.74 and Abbe vd numbers between

  28 and 32, but also exhibit very good crystallinity stability.

  sation and excellent chemical resistance in the absence of PbO and As203. The high crystallization stability of these glasses is obtained in the present invention thanks to the contents of B203, Nb205 and the sum

  MO (BaO + SrO + CaO) as well as thanks to a balanced SiO2 content

  brée. The good chemical resistance of the glasses of the present invention is due to the particular SiO2 / ZTiO2 + ZrO2 ratio of between 1.24 and 1.75. For a ratio lower than 1.24, the chemical resistance decreases, in

  especially resistance to alkalis. For a value of this higher ratio

  lower than 1.75, the fusibility is considerably reduced. This could certainly be compensated by an increase in the oxide concentration

  of alkali metals or in B203 but this increase would have repercussions

  negative effects on stability to crystallization and chemical resistance

  mique. Furthermore, the high refractive index could not be preserved, which would require the addition of larger quantities of Nb205, an expensive raw material. This would question profitability

  glasses having such a composition.

  The balance between the sum of the oxides forming the glass and the

  sum of the fondants gives the glasses of the present invention a viscous

  sity allowing the manufacture of these glasses in large melting devices, for example a tank for optical glasses. This fact is

  essential for the profitability of the glasses of the present invention.

  The good "internal" quality of the glasses of the present invention, that is to say the absence of air bubbles or streaks, is obtained by the addition of refining agents such as Sb203, of ions chloride (for example in the form of NaCl), of fluoride ions (for example in the form of KF), of ions S042- (for example in the form of BaSO4) in a proportion of at most 1% by weight, preferably 0 , 5% by weight. According to a particular aspect of the invention, light optical glasses can be characterized by an SiO2 composition 35.1 - 38

B203 2.1 - 2.8

Na2O 12- 13

K20 6- 8

Li20 0- 1 Cs2O 0 - 0.6

XM2O 18.5 - 20.5

  CaO 0.5 - 2.2 BaO 5, 3 - 7.5 SrO 0.02 - 0.5

__MO 6.3 - 8.2

  TiO2 23 - 28 ZrO2 0.2- 1.99 Nb2O5 4.5 - 9.5

A1203 0 - 0.8

W03 0.3 - 0.8

  SnO2 0.05 - 0.3 the refractive index nd being between 1.71 and 1.73 and the

  number of Abbe vd being between 28.5 and 30.0.

  According to another particular aspect of the invention, the optical glasses

  which may have a SiO2 composition 41 - 44

B203 2.5 - 3

Na2O 9.3-11

K20 6.5-7

Li20 0- 1 Cs2O 0 - 2

YM2O 16-19

  CaO 1.5 - 2 BaO 3.5 - 5 SrO 0.02 - 0.5

IMO 5.7 - 6.5

  TiO2 22.5 - 24 ZrO2 1.7 - 1.99 Nb205 4.5 - 6

A1203 0.5 - 0.8

WO3 0 - 0.5

  SnO2 0 - 0.2 the refractive index nd being between 1.68 and 1.70 and the number

  d'Abbe vd being between 30 and 32.

  It is understood that the description, in particular of the aspects

  particulars of the foregoing invention has been given only purely

  illustrative and not limiting and that variations or modifications may

  wind be made in the context of the present invention.

  Table 1 shows with a few examples the properties

  glasses of the present invention in comparison with custom glasses

  tuels. The glasses used for the comparison, i.e. the glasses SF 1, SF 8, SF 10 and SF 15, are glasses with a high lead content containing

between 52 and 62% by weight of PbO.

Table 1

  SF1 Ex. 1 SF10 Ex. 4 SF8 Ex. 6 SF15 Ex. 7 nd 1, 7173 1.7177 1.7282 1.7255 1.6889 1.6874 1.6989 1.6981 vd 29, 51 29.54 28.41 28 , 67 31.18 31.33 30.07 30.24 vol.4.46 3.03 4.28 3.044 4.22 2.92 4.06 2.93 Rac *) 3.2 1, 0 1, 0 1.0 2.3 1.0 1.0 1.0 Ralc **) 2.3 1.0 1.2 1.0 2.3 1.0 1.2 1.0 *) Rac = acid resistance according to ISO 8424 Rac 1 Rac 2 Rac 3 Rac 4 Rac 5 time (h)> 100 100 - 10 10 - 1 1 -, 01 <0.1 time (in hours) for elimination with HNO3 0.5 N a layer of 0.1 prm from a polished surface **) Ralc = alkali resistance according to ISO / DIS 10629 Ralc 1 Ralc 2 time (h)> 120 120 - 30 time (in hours) for removal with NaOH pH = 10 of a 0.1 grm layer from a polished surface coding 0 no visible changes 1 grainy surface, no visible layer formation 2 interference colors 3 white spot Table 2 contains 7 corresponding implementation examples

  to the preferred composition ranges. The glasses of the present invention

  tion are prepared as follows:

  We weigh the raw materials giving the oxides, preferably

  carbonates, possibly nitrates, up to 1% of one or more refining agents, such as Sb203 and / or chlorides such as for example NaCl, and / or sulfates such as for example Na2SO4 or BaSO4 are added thereto, then mix well. The mixture is brought to fusion at a temperature of approximately 1200 - 1250 C in a continuous melting device, it is then refined and homogenized. The glass is given the desired shape and dimensions at a casting temperature of about 950 to

1050 C.

  Example of fusion calculated to give 100 kg of glass oxide% c by weight raw material weight (kg)

A1203 0.80 A1O (OH) 1.03

B203 2.75 H3BO3 4.88

  BaO 3.86 BaCO3 5.04 CaO 2.00 CaCO3 3.54 SrO 0.04 SrCO3 0.05 Cs2O 1.40 Cs2CO3 1.56

K20 6.90 K2CO3 10.13

  Na2O 10.20 Na2CO3 17.48 Nb2O5 5.00 Nb2O5 5.00 SiO2 42.55 SiO2 42.59 TiO2 22.50 TiO2 22.62 ZrO2 1.90 ZrO2 1.93 Sb20O 0.1 10 Sb2O3 0.1 sum 100 115.95 kg The properties of the glass thus obtained are indicated in the

Table 2, Example 6.

  Table 2 Examples of fusion (in% by weight)

A1203 2 3 4 5 6 7

A1203 - 0.12I 70 10.65 0.80 0.50

  SiO2 37.4 36.00 36.15 35.15 42.00 42.55 43.70

  B203 2.7 2.10 2.47 2.50 2.80 2.75 2.50

  BaO 5.94 6.22 5.27 7.32 3.86 3.86 4.95 CaO 2.0 1.39 1.02 0. 80 2.00 2.00 1.50 SrO 0.06 0.06 0.05 0.08 0.04 0.04 0.05

  E MO 8.00 7.67 6.34 8.20 5.90 5.90 6.50

  Na2O 12.0 12.33 12.21 12.60 10.20 10.20 9.30

  K20 6.0 6.13 8.00 6.50 6.90 6.90 6.70

Cs20 0.5 0.45 1.60 1.40 -

  E M20 18.5 18.91 20.21 19.10 18.70 18.50 16.00

  TiO2 23.1 24.26 27.70 26.60 22.70 22.50 24.00 ZrO2 0.2 1.97 1.41 0. 50 1.70 1.90 1.90 Nb2O5 9.2 8.53 4.57 6.50 5.40 5.00 4.50

WO3 0.5 0.32 0.76 0.30

  SnO2 0.2 0.05 0.20 0.30 AT - 0.20 Sb203 0.2 0.19 0.19 0. 15 0.15 0.10 0.20 Si02 / ETiO2 + ZrO2 1.6 1.37 1.24 1.29 1.72 1.74 1.68 nd 1.7177 1.7266 1.7219 1.7255 1.6906 1.6874 1.6981 Vm 29.54 28.96 28.72 28.64 31.0.33 . 3.03 3.06 3.003 3.044 2.92 2.92 2.93

  P.F 0.6033 0.6046 0.6061 0.6063 0.6001 0.5995 0.6034

  A PF 0.0093 0.0095 0.0104 0.0106 0.0086 0.0084 0.0105

  0C2o.300 (106K ') 10.42 10.48 10.86 10.81 9.80 9.70 9.19 Rac 1.0 1.0 1.0 1.0 1.3 1.0 1.0 Ralc 1.0 1. 0 1.0 1.0 1.2 1.0 1.0

Claims (6)

  1. Lightweight lead-arsenic-free optical glass with a   density p between 2.92 and 3.06 g / cm3, a refractive index   tion nd between 1.68 and 1.74 and an Abbe vd number between 28 and 32, and having very good resistance to chemicals and excellent stability to crystallization, characterized in that it has the com - next position (in% by weight) SiO2 35.1 - 44 GeO2 0- 2 B203 2 - 3.5 Na2O 9-14 K20 6 -9   Li20 0- 1 Cs2O 0- 2 yM20 16 - 21 CaO 0.5 - 3 BaO 3 - 8 ZnO 0- 1 SrO 0.021 YMO 5.5 - 9   TiO2 22 - 30 ZrO2 0.2- 1.99 Nb205 4 - A1203 0- 1   SnO2 0 - 0.5 2. Glass according to claim 1, characterized in that it has the following composition (in% by weight): SiO2 35.1 - 44 GeO2 0- 2 B203 2 - 3.5 Na2O 9-14 K20 6-9 Li20 0- 1 Cs2O 0- 2 DM20 16 - 21   CaO 0.5 - 3 BaO 3 - 8 ZnO 0 - 1 SrO 0.02 - 1 MO 5.5 - 9   TiO2 22 - 30 ZrO2 0.2- 1.99 Nb205 4- A1203 0- 1 SnO2 0.05 - 0.5   3. Glass according to claims 1 or 2, characterized in that   that it has the following composition (in% by weight): SiO2 35.1 - 38 B203 2.1 - 2.8 Na2O 12- 13 K20 6- 8 Li20 0- 1 Cs2O 0 - 0.6 ZM20 18.5 - 20.5   CaO 0.5 - 2.2 BaO 5.3 - 7.5 SrO 0.02 - 0.5 YMO 6.3 - 8.2   TiO2 23 - 28 ZrO2 0.2- 1.99 Nb205 4.5 - 9.5 A1203 0- 0.8   SnO2 0.05 - 0.3 the refractive index nd being between 1.71 and 1.73 and the number   d'Abbe vd being between 28.5 and 30.0.   4. Glass according to claim 1, characterized in that it has the following composition (in% by weight): SiO2 41 - 44 B203 2.5 - 3 Na2O 9.3 - 11 K20 6.5-7 Li20 0- 1 Cs2O 0- 2 YEM20 16-19   CaO 1.5 - 2 BaO 3.5 - 5 SrO 0.02 - 0.5 YMO 5.7 - 6.5   TiO2 22.5 - 24 ZrO2 1.7 - 1.99 Nb205 4.5 - 6 A1203 0.5 - 0.8   SnO2 0 - 0.2 the refractive index nd being between 1.68 and 1.70 and the number   d'Abbe vd being between 30 and 32.   5. Glass according to claims 1 to 4, characterized in that   the ratio of SiO2 to 1 (TiO2 + ZrO2) is between 1.24 and 1.75.   6. Glass according to claims 1 to 5, characterized in that   that it contains, as a refining agent, from 0 - 1% by weight, in particular   from 0 - 0.5% by weight of the components Sb203 and / or C- and / or F- and / or S042.