Lead-free optical light flint glass materials

Details Lead-free optical light flint glass materials Lead-free optical light flint glass materials

2000-11-29

2003-04-22

Sample, David (Department: 1755)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

C501S057000, C501S903000

Reexamination Certificate

active

06551952

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to lead-free optical glass materials which have refractive indices n
d
of between 1.54 and 1.61 and Abbe numbers &ngr;
d
of between 38 and 45. Glass materials of this type belong to the optical glass family of the light flint glass materials.
2. Prior Art
Because the glass ingredients PbO and As
2
O
3
have become the subject of public discussions regarding environmental pollution which they cause, the manufacturers of optical equipment need PbO-free and preferably also As
2
O
3
-free glass materials having the appropriate optical properties.
Simply exchanging the lead oxide for one or more ingredients does not generally allow the PbO-influenced, desired optical and glass technology properties to be reproduced. Instead, new developments or far-reaching changes in the glass composition are required.
Lead-free glass materials with similar optical characteristics and a similar composition are already known.
The closest prior art glass materials are described in JP 56-59640 A. However, the glass materials for spectacles described in that document contain only 11 to 18% by weight alkali metal oxides, which may be composed of Na
2
O, K
2
O and Li
2
O. Furthermore, they optionally contain the ingredients Nb
2
O
5
, La
2
O
3
and also ZrO
2
, which in this case inhibit crystallization but are expensive, as partial replacements for TiO
2
.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a lead-free optical glass material with a refractive index n
d
of between 1.54 and 1.61 and an Abbe number &ngr;
d
of between 38 and 45 which can be produced at low cost and have good melting and processing properties. This also includes the requirement for sufficient crystallization stability.
According to the invention the lead-free optical glass material with a refractive index n
d
of between 1.54 and 1.61 and an Abbe number &ngr;
d
of between 38 and 45 has a composition, based on oxide content, of:
SiO
2
from 52 to 62% by weight,
Al
2
O
3
from 3 to 8% by weight,
Na
2
O
from 7 to 14% by weight,
K
2
O
from 8 to 14% by weight,
TiO
2
from 13 to 18% by weight,
ZrO
2
from 0 to 5% by weight,
and at least one refining agent, if needed, in an amount suitable for the purposes of refining; with the proviso that a sum total of Na
2
O and K
2
O present is greater than 18% by weight.
The glass materials according to the invention contain the glass formers SiO
2
and Al
2
O
3
, in balanced proportions of 52 to 62% by weight SiO
2
and 3 to 8% by weight Al
2
O
3
. In this way, both the meltability of the glass materials, which deteriorates as the Al
2
O
3
content rises, and their chemical durability, which would deteriorate if the Al
2
O
3
content were too low, are satisfactory. Moreover, if the above-mentioned minimum Al
2
O
3
content were to be increased, the risk of devitrification would rise excessively. There is no B
2
O
3
, which is a common third glass former, used, which is of benefit to the chemical durability of the glass materials. An SiO
2
content of between 53 and 59% by weight is preferred, but an SiO
2
content of between 55 and 59% is particularly preferred. The Al
2
O
3
content is preferably between 4 and 7% by weight, particularly preferably between 5 and 7% by weight.
To obtain the desired high refractive index combined, at the same time, with a low Abbe number, the glass materials contain relatively large amounts of TiO
2
, at 13 to 18% by weight. The TiO
2
content is preferably between 14 and 17% by weight, particularly preferably between 15 and 17% by weight. In addition to TiO
2
, the glass materials according to the invention may also contain up to 5% by weight ZrO
2
. The presence of the two ingredients improves the chemical durability, in particular the alkali resistance. If the levels were to be higher, the crystallization stability would be considerably reduced. Preferably, the sum of the TiO
2
and ZrO
2
is less than 18% by weight. In preferred embodiments, there is no ZrO
2
.
To improve the meltability, that is to reduce the melting temperatures, with the given high level of glass formers, the glass materials contain from 7 to 14% by weight Na
2
O and 8 to 14% by weight K
2
O as fluxing agents. If the levels were to be higher, in particular in relation to the high TiO
2
content, the tendency towards crystallization would rise excessively. Therefore, the sum of R
2
O and TiO
2
is preferably less than or equal to 42% by weight. For the same reason, LiO
2
is dispensed with altogether. Increasing the alkali metal content further would also mean that the desired range of refractive indices would not be reached. The sum of Na
2
O and K
2
O is at least greater than 18% by weight. An Na
2
O content of 8 to 13% by weight and a K
2
O content of 10 to 14% by weight are preferred. An Na
2
O content of 8 to 11% by weight and a K
2
O content 10 to 12% by weight are particular preferred.
To improve the quality of the glass, one or more refining agents, which are known per se, may be added in the customary amounts to the batch in order to refine the glass material. This provides the glass material with a particularly good internal glass quality with regard to the freedom from bubbles and cords.
If the refining agent used is not As
2
O
3
, but rather, instead, Sb
2
O
3
, for example, which is possible without any loss in glass quality, the lead-free glass materials according to the invention are additionally free of arsenic.
The Sb
2
O
3
content is preferably between 0.1 and 0.5% by weight. It is also preferable for the glass materials, if appropriate in addition to Sb
2
O
3
, to contain up to 0.5% by weight fluoride, which likewise has a refining action. Fluoride is added, for example, as NaF.
In addition to a refractive index n
d
of between 1.54 and 1.61, and an Abbe number of between 38 and 45, and a positive anomalous partial dispersion in the blue region of the spectrum, the glass materials according to the invention have the benefits as described in the following paragraphs.
The glass materials are PbO-free and, in a preferred embodiment are also As
2
O
3
-free. The glass materials exhibit good crystallization stability. This allows production in a continuously operating melting unit. A measure of the crystallization stability being sufficient for production of this nature is the viscosity at the liquidus temperature. For continuous production, it should be ≧1000 dPas. This condition is satisfied with the glass materials according to the invention. Since the glass materials exhibit a crystallization stability of this nature, further thermal treatment of the glass materials, such as pressing or repressing, also becomes possible. It is advantageous that it is possible to dispense with the expensive ingredients Nb
2
O
5
and La
2
O
3
while the glass materials, despite the high TiO
2
content, still exhibit a sufficient crystallization stability, this fact also being contributed to by the fact that alkaline-earth metal oxides are eliminated altogether. Therefore, apart from inevitable impurities, the glass materials are free of alkaline-earth metal oxides, Nb
2
O
5
and La
2
O
5
.
In addition, the “length of the glass materials” (viscosity curve which falls slowly with temperature) ensures good processability despite the relatively high melting temperatures of approximately 1400° C.
The glass materials have an exceptional alkali resistance, as attested to by the fact that they belong to the alkali resistance class AR=1, while also retaining a chemical durability which is adequate in other respects. The chemical durability of the glass materials is of importance for their further processing, such as grinding and polishing.
Glass materials within a compositional range (in % by weight based on oxides) SiO
2
from 52 to 62, preferably from 53 to 59, % by weight; Al
2
O
3
from 3 to 8, preferably from 4 to 7, % by weight; Na
2
O, from 7 to 14% by weight, K
2
O from 8 to 14% by weight, with a sum of Na
2
O and K
2
O greater than 18% by weight; preferably Na
2
O from

Affiliated with

Also associated with

Rating

Lead-free optical light flint glass materials does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Lead-free optical light flint glass materials, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Lead-free optical light flint glass materials will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3055867