FR2755125A1 - OPTICAL QUALITY LIGHT OR ULTRA-LIGHT FLINTS, LEAD FREE - Google Patents

Abstract

Light or ultralight flints of optical quality are described, free of lead having a refractive index nd of 1.52 to 1.57 and an Abbe number vd of 43 to 52, and having the following composition (in% by weight relative to oxides): SiO2 48 - 55; B2 O3 7 - 9; K2 O 18-20; A12 O3 7 - 9; La2 O3 0.1 - 2; ZrO2 0 - 1; SIGMALa2 O3 + ZrO2 0.5 - 2; TiO2 5.5-12; F ** - 1.5 - 6; (A12 O3 + La2 O3) / (TiO2 + ZrO2) = 0.73 - 1.15. The glasses have excellent crystallization resistance and very good chemical resistance.

Description

Light or ultra-light optical quality flints, lead-free La

  The present invention relates to light and ultra-light flints of optical quality lead-free which have refractive indices nd

  between 1.52 and 1.57 and Abbe vd numbers between 43 and 52.

  As in recent years, PbO and As203 glass components have acquired a reputation for being harmful to the environment, some manufacturers of consumer products and optical instruments will increasingly tend to use more than glasses free of PbO and As203. Such glasses having optical properties

  therefore should be available on the market.

  The absence of PbO is also interesting when we want to

  manufacture low-weight glass parts, i.e. low-cost glasses

ble density.

  The simple replacement of lead oxide by one or more

  components generally do not reproduce the physical properties

  interesting sicochemicals and optics that PbO brings. It is necessary

  be able to develop new formulas or to modify considerably

  the compositions of the glasses.

  There are documents in the patent literature describing

  for glasses having the indicated optical characteristics. These

  glasses, however, have significant drawbacks.

  Thus, the document JP 1-133956 A describes fibrous glasses belonging to the SiO2 - A1203 - M20 - F 'system and in which lead oxide is an optional component. These glasses require a content

  important in A1203, essential for obtaining sufficient resistance

  health to crystallization, which translates into a decrease in the fusibi-

  lity. To improve this, these glasses can contain up to 25% in

  moles of Li2O. Such high contents of Li2O are nevertheless reflected

  less in turn by poorer resistance to crystallization.

  The glasses described in document JP 6-107425 A, the optical characteristics of which vary within very wide intervals, contain BaO. In view of the partly significant contents in

  B203, and also in M20, we would obtain chemically insta-

  but not resistant to crystallization, defects which can however be

  Dant remedy by using up to 25% by weight of Nb205. This com-

  costly posing however considerably increases the price of the mixture

  vitrifiable and therefore also the cost price of the product.

  The glasses described in patent EP 0 645 349 B 1 also contain NB205. They are free of B203. To improve the fusibility of the glasses, they contain up to 40% by weight of alkali metal oxides, which, for F 'content up to 8% by weight,

  will result in low crystallization resistance and chemical resistance

insufficient mique.

  The glasses disclosed in the German patent DE 973 350 are part of the SiO2 - M20 - F system. They contain neither La203 nor ZrO2. Lead oxide is an optional component. These glasses too

  have optical characteristics which can vary widely.

  For the values indicated above, the glasses contain a significant fraction of F-. The chemical composition of these glasses means that they will have

  poor chemical resistance, in particular insufficient resistance

  health with acids and alkalis. They will also have a tendency to

  demixing (cloudiness) and, at the upper devitrification limit, present

  will have an unfavorable viscosity profile.

  In document JP 6-92674 A, optical glasses are described

  being part of the glassy system SiO2 - M20 - P205. These glasses contain-

  obligatorily Na2O as alkali metal oxide (at least 12.5% by weight). Due to their high content of M20 and the presence of

  P205 (up to 15% by weight), these glasses will not have a resistance

  sufficient crystallization strength and will have poor resistance

chemical tance.

  The aim of the present invention is to provide light or ultralight lead-free flints having a refractive index nd of 1.52 and 1.57 and an Abbe number between 43 and 52, which flints have a low mass. volume (p <2.60 g / cm3) and good melting and processing properties as well as very good resistance to crystallization and a viscosity which allows their preparation in melting devices of

  large size, for example in tanks for optical glasses, i.e.

  say a viscosity at the upper devitrification limit which is higher than

  greater than or equal to 1000 dPa.s. The glass must also have a good

  chemical resistance, very important property for subsequent treatments

  such as sanding and polishing, and it must be possible to manufacture it

at low cost.

  This objective is achieved thanks to light or ultra-light flints of optical quality, free of lead having a refractive index nd of 1.52 to 1.57 and an Abbe vd number of 43 to 52, characterized by the following composition (in% by weight relative to the oxides) SiO2 48 -

B203 7 - 9

K20 18 - 20

A1203 7- 9

  La2O3 0.1 - 2 ZrO2 0- 1 y La203 + ZrO2 0.5 - 2 TiO2 5.5- 12

F 1.5 - 6

  (A1203 + La203) / (TiO2 + ZrO2) 0.73 - 1.15

  and possibly containing refining agents in usual quantities

  tuelles. The glass contains 48 to 55% by weight of the vitrifiable material SiO2. For too low silica contents, the tendency to crystallize

  increases and the chemical resistance decreases, for higher contents

  Aunts, the glasses are difficult to melt. We prefer a content included

between 50 and 52% by weight.

  B203, another vitrifiable material, is present at a rate of 7 to 9% by weight. This minimum content is necessary to improve fusibility

  glasses and to limit the evaporation of fluoride. Said maximum content

  male should not be exceeded because this would decrease the resistance to hydro-

  lysis. A maximum content of 8% by weight is preferred.

  The glass contains 7 to 9% by weight of A1203. The minimum content of this component improves resistance to crystallization and chemical resistance. For higher contents the viscosity of the glass increases too strongly. It is preferred to limit the maximum content to 8.5% by weight. To improve behavior during fusion and to obtain

  good transmission, the glass contains 18 - 20% by weight, preferably

  rence of 19 - 20% by weight, of K20.

  To obtain the desired optical characteristics and a high chemical resistance, the glass contains 0.1 to 2% by weight of La203. For higher contents, the desired optical position is impossible to obtain and the price of the batch is unnecessarily

increases.

  The presence of ZrO2 also has a considerable influence on the optical characteristics. This oxide may be present at a rate of at least

  plus 1% by weight, because for higher contents, the refractive index

tion increases too strongly.

  The sum of La203 and ZrO2 must be between 0.5 and 2% by weight because for contents higher or lower than these we

  notes the drawbacks discussed with regard to each of these oxides.

  In a particularly recommended embodiment, the sum of the

  two oxides is in the range of 0.6 to 1.4% by weight.

  The fact that these glasses have, despite a relatively high K20 content, a very good resistance to crystallization is due to the

  balanced ratio (A1203 + La203) / B203. In a pre-

  fere of the present invention, the weight ratio (A1203 + La203) / B203 must be greater than 1. It has been found that the SiO2 content must be at

  less than 49% so that there are enough vitrifiable oxides.

  To obtain the indicated optical characteristics, the glass

  contains, as another component, TiO2 in an amount of 5.5 to 12% by weight.

  Lower contents translate into a decrease in chemical resistance and higher contents decrease the transmission. We

  recommend a content between 8 and 11% by weight.

  The excellent chemical resistance of the glasses of the present invention does not only depend on the absolute amounts of A1203, La203 of TiO2 and ZrO2 but also on the particular ratio (A1203 +

  La203) / (TiO2 + ZrO2). This ratio must be between 0.73 and 1.15.

  For a weight ratio of less than 0.73, the chemical resistance, in particular the resistance to acids and alkalis decreases. For a value

  greater than 1.15, the fusibility deteriorates. We can overcome these inconveniences.

  by increasing the contents of K20 and B203, but this would result in a deterioration of the resistance to crystallization. Furthermore, obtaining the desired optical characteristics, in particular the number of Abbe, would become very difficult, that is to say would not be possible

  than at the cost of other disadvantages. In a particular embodiment

  Interestingly, the weight ratio (A1203 + La203) / (TiO2 + ZrO2) is

between 0.77 and 1.10.

  The glass also contains fluoride ions in an amount of 1.5 to 6% by weight, preferably in an amount of 2 and 5.5% by weight. A very good "internal" quality of the glass is thus obtained (absence of air bubbles and streaks) as well as excellent light transmission, that is to say t25 mm (for a sample thickness of 25 mm) in the wavelength range 400 nm - 1600 nm is at least 80%. Beyond a maximum content of 6% by weight of F, demixing phenomena occur

and therefore a disorder.

  Glasses in which all the components are present in

  amounts within the preferred composition ranges indicated

  are ultra-light flints with a refractive index ranging from

  1.52 to 1.55 and an Abbe number from 45 to 50.

  To further improve the quality of the glass, we can add

  one or more known refining agents in known amounts.

  If we use for this, instead of As203, Sb203, which is

  possible without reducing the quality of the glass, the lead-free glasses of the pre-

  sente invention will also be free of arsenic.

  In another preferred embodiment of the invention, the glass contains the following refining agents: Y; Sb203 + CI- = 0.1 to 0.5% in

  weight of which 0 - 0.5% by weight of Sb203 and 0 - 0.5% by weight of CI-.

  The field of glass composition of the present invention therefore provides another group of light or ultra-light flints free of

  lead having the indicated optical characteristics. These glasses stand out

  against the usual light and ultra-light flints by a lower mass

  volume (p <2.6 g / cm3) as well as by the following properties:

  res have very good chemical resistance, excellent resistance to crystallization, very good "internal" quality of the glass,

  high processing temperature, as well as very good transmission

  light in the wavelength range from 400 to 1600 nm. Furthermore, their manufacture is relatively inexpensive, among other things because it is possible to omit the expensive component that is Nb205. Another advantage is that these glasses are not only lead-free but, in a preferred embodiment, also

free of As203.

Examples

  For example, 7 glasses were manufactured in accordance with the present

  invention by fusion of mixtures of usual raw materials

  taken from the preferred composition domain. Table 2 gives the com-

  positions (in% by weight with respect to the oxides), as well as by way of example

  ple, essential characteristics of glasses.

  The glasses of the present invention were manufactured in the following way: The raw materials for the oxides and fluorides are weighed,

  preferences of carbonates, nitrates and fluorides. We add one or more

  several refining agents, for example Sb203, then carefully mix

  sement. The batch is melted at around 1250 - 1300 C

  in a continuous melting device, refining and homogenization are carried out

  generation. The glass is poured at 1200 ° C. and introduced at 550 ° C. into a cooling oven where it is cooled to room temperature, this

  which gives a glass free of constraints.

Table 1

  Example of oxide melting% by weight of raw material (kg) SiO2 15.60 SiO2 51.61

A1203 8.10 A1O (OH) 10.33

B203 7.79 H3BO3 13.83

K20 19.60 KNO3 36.79

F- 2.00 KHF2 4.14

  La203 0.10 La2O3 0.10 TiO2 10.12 TiO2 10.17 ZrO2 0.51 ZrO2 0.52 Sb203 0.18 Sb2O3 0.20 sum 100 _127, 69 The characteristics of the glass thus obtained are gathered in

Table 2, Example 7.

Table 2

  Composition (in% by weight relative to the oxides) and characteristics

essential glasses

  _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ __ _ _7_

1 2 3 4 5 6 7

  SiO2 51.08 51.08 51.59 50.98 50.85 51.35 51.60

  B203 7.37 7.37 7.44 7.35 7.68 7.75 7.79

  K20 19.06 19.06 19.25 19.02 19.34 19.54 19.60

  A1203 7.56 7.56 7.64 7.55 7.90 8.00 8.10

  La203 0.79 1.18 1.19 1.37 0.15 0.17 0.10 TiO2 8.55 8.15 8.23 8.14 9.97 10.08 10.12 ZrO2 - - - - 0 .50 0.51 0.51

  F 5.40 5.40 4.46 5.39 3.48 2.50 2.00

  Sb203 0.20 0.20 0.20 0.20 0.13 0.10 0.18 La203 + ZrO2 0.79 1.18 1.19 1.37 0.65 0.68 0.61 A1203 + La2O_ TiO2 + ZrO2 0.98 1.07 1.07 1.10 0.77 0.77 0.77 A1203 + La2O3 1.13 1.19 1.19 1.21 1.05 1.05 1.05 B203 nd 1, 5315 1.5285 1.5304 1.5287 1.5425 1.5448 1.5460 Vd 48.19 48.94 49.12 49.04 45.94 46.03 46.06 P [g / cm3] 2.500 2.498 2.502 2,501 2,493 2,504 2,496 Tg [C] 488 500 500 523 531 Pg. F 0.5670 0.5658 0.5659 0.5656 0.5712 0.5705 0.5700 A Pg.F 0.0043 0.0043 0.0042 0.0042 0.0047 0.0041 0.0036 Rac 1.0 1.0 1. 0 Ra; c 1.0 1.0 1.0 T 400 nm25 mm 0.84 0.85 0.86 0.86 0.82 0.83 0.84 viscosity at 1550 1600 1700 1500 3000 14000 3200 upper devitrification limit [dPa.s] Tg transformation temperature Ralc alkali resistance according to ISO draft 10629 Rac acid resistance according to ISO 8424 Pg, F relative partial diffusion for the wavelengths indicated At Pg: deviation of the relative partial diffusion of the "normal line" 400nn / 25mm 'spectral transmission rate for a wavelength X = 400 nm and a sample thickness d = 25 mmn

  It is understood that the above description has not been given

  for illustrative purposes only and not limiting, and that variants or

  modifications may be made to it as part of this invention

tion.

Claims (7)

  1. Light or ultra-light flints of optical quality, lead-free, with a refractive index nd of 1.52 to 1.57 and an Abbe Vd number of 43 to 52, characterized by the following composition (in% by weight compared to oxides): SiO2 48- B203 7- 9 K20 18 - 20 A1203 7- 9   La203 0.1 - 2 ZrO2 0- 1 z La2O3 + ZrO2 0.5 - 2 TiO2 5.5- 12 F '1.5 - 6   (A1203 + La203) / (TiO2 + ZrO2) 0.73 - 1.15   and possibly containing refining agents in usual quantities   tuelles. 2. Light or ultra-light flints of optical quality, lead-free according to claim 1, characterized in that the weight ratio (A1203 + La203) / B203 is greater than 1 and in that the content of SiO2   is at least equal to 49% by weight.   3. Light or ultra-light flints of optical quality, lead-free according to claim 1 or 2 having a refractive index nd   from 1.52 to 1.55 and an Abbe vd number from 45 to 50, characterized by the com-   next position (in% by weight relative to the oxides) SiO2 50 - 52 B203 7- 8 K20 19-20 A1203 7 - 8.5   La203 0.1 - 2 Zro2 0- 1 Y La203 + ZrO2 0.5 - 2 TiO2 8- 11 F '2- 5.5   (A1203 + La2O3) / (TiO2 + ZrO2) 0.73 - 1.15   and possibly containing priming agents in regular quantities   tuelles. 4. Light or ultra-light optical quality flints, free of   lead according to at least one of claims 1 to 3, characterized in   that the sum of La203 and ZrO2 is between 0.6 and 1.4% by weight. 5. Light or ultra-light optical quality flints, free of   lead according to at least one of claims 1 to 4, characterized in   that the weight ratio (A1203 + La203) / (TiO2 + ZrO2) is between 0.77 and 1.10.   6. Light or ultra-light optical quality flints, free of   lead according to at least one of claims 1 to 5, characterized in   what they contain as fluxing agents (in% by weight) Sb203 0 - 0.5 CI- 0- 0.5 E Sb203 + CI- 0.1 - 0.5.   7. Light or ultra-light optical quality flints, free of   lead according to at least one of claims 1 to 6, characterized in   that they are free of arsenic oxide, apart from that due to impurities inevitable.