JP3157458B2 - Optical glass for mold press - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical glass which has good devitrification resistance and chemical durability, contains no harmful substances, and has improved mold pressability.

[0002]

2. Description of the Related Art At the same time as miniaturization and high performance of optical devices have been remarkably progressing, light weight, small size and high performance are also required for optical lenses. There is an aspheric lens as a method for solving this problem. As a result, the number of lenses can be reduced, and is becoming mainstream in optical design. In the method of manufacturing an aspherical lens, a preform material obtained by cutting and polishing a gob or a glass block is heated and softened, and is subjected to pressure molding with a mold having a highly accurate surface. The feature of this method is that since the grinding and polishing steps can be omitted after molding, low cost and mass production can be realized.

[0003] By the way, low cost of this aspherical lens
In order to achieve the major goal of mass production, it is necessary to thoroughly consider the following conditions. First, if the mold used for the mold press cannot be used repeatedly,
It cannot meet the purpose of low cost and mass production. For that purpose, it is necessary to set the temperature at the time of mold pressing as low as possible in order to minimize the surface oxidation of the mold. Currently, the upper limit temperature of the mold press is 650-700 ° C, and the upper limit of the glass transition temperature is 550-600 ° C.
However, as the temperature is lower, the progress of surface oxidation of the mold is suppressed, which is preferable from the viewpoint of life. However, glasses with low glass transition temperatures generally have poor chemical durability. Therefore, the key is how to obtain a glass having good chemical durability while having a low glass transition temperature. Further, it is necessary to sufficiently consider the cost of manufacturing a preform material, which is a stage before molding.

At present, there is a method of manufacturing a preform by dropping a glass melt and cooling it. This method has high mass productivity of the preform material itself, is currently the cheapest in terms of manufacturing cost, and since the preform obtained by this method is close to a spherical or biconvex lens shape,
The amount of shape change during mold pressing can be reduced, and the mass productivity of the lens itself can be significantly improved.

On the other hand, there is a method of obtaining a preform material by cutting from a glass block material. However, in this method, a process of cutting the block material into a ball is required. When molding into a shape, the amount of change during molding is large and it takes time to mold.From the viewpoint of cost and mass productivity, it is better to use a preform material obtained by dropping and cooling a glass melt. It is much better. A representative example of obtaining a preform by this method is described in JP-A-6-122526.

[0006] When a preform material is produced by dropping a glass melt, it is necessary to mutually optimize the manufacturing conditions and the properties of the glass itself.
In other words, when molding a preform material by this molding method,
If the viscosity is low, it is difficult to obtain a shape close to a spherical or biconvex lens with a smooth and uniform curved surface. On the other hand, if the viscosity is high, the glass melt cannot be separated from the tip of the outflow pipe, and a preform having a uniform and smooth curved surface cannot be obtained. Therefore, the viscosity of the glass melt at the time of preform molding must be sufficiently studied.

Further, the devitrification temperature must be lower than that of the preform, that is, the glass must not devitrify when dropped. In other words, if the viscosity of the glass melt is low, the temperature of the glass melt must be lowered in order to increase the viscosity of the glass melt, but if it does so, it will fall below the devitrification temperature, that is, the preform material will be devitrified. Will happen. In particular, the tendency becomes remarkable in glass having low viscosity. On the other hand,
If the temperature of the glass is raised to lower the viscosity because the viscosity is high, the problem of devitrification will be resolved, but this time it may be a problem such as seizure of the glass to the mold or premature wear due to surface oxidation of the mold. appear. In particular, the tendency is remarkable in highly viscous glass. According to the experiment, there is no problem if the preform is formed at 1,000 ° C. or lower.

As described above, the composition of the optical glass for mold press has not only a desired optical constant and a low glass transition temperature, but also sufficient chemical durability.
It is necessary to mutually optimize each property, that is, to have high devitrification resistance so that a preform can be formed by dropping.

Conventionally, as a glass having a low glass transition temperature, glass containing PbO or TeO ₂ is known, but these components are environmentally unfavorable and have a small Abbe number (νd). You can only get things.

[0010] In the glass achieves low glass transition temperature without containing PbO, for example, P ₂ O ₅ -RO-R ₂ is O systems are known, R ₂ to the system to obtain a low glass transition temperature Since the O component is increased, the chemical durability is not good.

In order to improve this point, P ₂ O ₅ -B ₂ O ₃ -Al ₂ O ₃ containing La ₂ O ₃ and having improved chemical durability is used.
-La ₂ O ₃ -RO-R ₂ O based glass is disclosed in
Although it is described in JP-A-71244, from the viewpoint of mold pressability, numerical values are not sufficiently limited, and no examples of compositions satisfying the above-mentioned conditions are disclosed. Can not match.

JP-A-3-40934 discloses a P ₂ O ₅ -RE ₂ Ox-Zn which also contains a rare earth element.
O-R ₂ O-based glass (RE ₂ Ox is selected from Y ₂ O ₃ and / or lanthanide group, one or more rare earth metal oxides) have been described to improve the devitrification resistance component since B ₂ O ₃ is not contained is, devitrification resistance is not good. Moreover, the examples disclose only those in which the total content of rare earth elements exceeds 2% by weight, and in such a case, the devitrification resistance is further deteriorated. In such a glass, it is impossible to form a good preform because the viscosity of the glass melt already causes devitrification at a temperature suitable for obtaining the preform by the dropping method. This is because this composition is premised on manufacturing a preform by cutting a block material into an appropriate size, and is not suitable as a mold press glass for obtaining a preform by dropping a glass melt. . As described above, in the production of a preform by the dropping method, no clear solution has been found for optimizing the viscosity and the devitrification temperature of the glass melt during the production.

[0013]

DISCLOSURE OF THE INVENTION The present invention has a low glass transition temperature, excellent chemical durability, does not contain environmentally undesirable substances, and has good mold pressability, that is, a smooth curved surface. To obtain a uniform preform,
An object of the present invention is to provide a zinc phosphate optical glass.

[0014]

The inventor of the present invention has conducted intensive studies to solve the above-mentioned problems, and as a result, the refractive index (nd) was 1.5 to 1.6 and the Abbe number (νd) was 55 to 65. The glass transition temperature (T
g) By obtaining the viscosity and devitrification temperature of the glass melt at 1,000 ° C., obtaining a zinc phosphate optical glass having good preform productivity, preform characteristics, and mold pressability. In addition, a very limited specific component in the composition range described in the claims of JP-A-60-171244 (however, there is a part outside the range for the R ₂ O component). Only for the range, it has the above-mentioned desired optical constant, low glass transition temperature, good devitrification resistance and chemical durability, and does not contain environmentally unfavorable substances, and has extremely good mold pressability. It has been found that an optical glass having excellent overall properties can be obtained, which has led to the present invention.

In order to achieve the above object, the present invention provides an optical constant having a refractive index (nd) of 1.5 to 1.6 and an Abbe number (νd) of 55 to 65, and a glass transition temperature ( Tg)
Is 300 to 400 ° C., and the viscosity η (Poise) of the glass melt at 1,000 ° C. is Logη ≦ 2.0, and the viscosity η of the glass melt is Logη = 0.
The fact that the optical glass for zinc phosphate based, which is not more than the temperature at the time of 6 , is suitable for mold press ,
The composition of the optical glass for mold press capable of satisfying all the conditions is SiO ₂ 0 to 2%, B ₂ O ₃ 1 to 3%, Al ₂ O ₃ 1 to 5%, P ₂ O ₅ by weight%. _{45 ~55%, Y 2 O 3} 0 ~ 1.3%, La 2 O 3 0.2~ 1.5%, Gd 2 O 3 0 ~ 1.3%, _{however, Y 2 O 3 + La 2} O 3 + Gd ₂ O ₃ = 0.2 to 1.5
_{%, TiO 2 0 ~ 5%} , Nb 2 O 5 0 ~ 5%, Ta 2 O 5 0 ~ 5%, ZnO 20 ~40%, MgO 0 ~ 5%, CaO 0 ~ 5%, SrO 0 ~ 5% BaO 0 to 5%, Li ₂ O 1 to 5%, Na ₂ O 0 to 10%, K ₂ O 0 to 20%, provided that Li ₂ O + Na ₂ O + K ₂ O = 6 to 25%, Sb ₂ O ₃ The feature of the present invention is that each component is in the range of 0 to 0.5% and F ₂ 0 to 5%. The reasons for limiting the composition range of each component as described above are as follows.

[0016] SiO ₂ is added to adjust the optical constant, but if its amount exceeds 2%, a desired glass transition temperature cannot be obtained. Therefore, it is limited to the range of 0 to 2%.

B ₂ O ₃ is an essential component added to improve the devitrification resistance. If its amount is less than 1%, its effect is not exhibited. If it exceeds 3%, the desired glass transition temperature is obtained. Can not be obtained. Therefore, it is limited to the range of 1 to 3%.

Al ₂ O ₃ is an essential component effective for improving the chemical durability, but its effect is not exhibited if its amount is less than 1%, and if it exceeds 5%, the desired glass transition temperature is lowered. I can't get it. Therefore, it is limited to the range of 1 to 5%.

P ₂ O ₅ is an essential component for forming glass, but if it is less than 45%, the devitrification resistance is poor, and if it exceeds 55%, the chemical durability is reduced. Therefore, 45-5
It is limited to the range of 5%.

La ₂ O ₃ is a relatively small amount and is an essential component for improving the chemical durability, and if less than 0.2%, its effect is not sufficient. However, La ₂ O ₃ is also a component that rapidly deteriorates the devitrification resistance in P ₂ O ₅ -based glass. According to experiments performed by the present inventors, B ₂ O ₃ = 1.5%, Al ₂ O ₃ = 3%,
P ₂ O ₅ = 50%, La ₂ O ₃ = 0 → 1.5%, ZnO =
30 → 28.5%, Li ₂ O = 3%, Na ₂ O = 5%, K
FIG. 1 shows the change of the devitrification temperature in the composition of ₂ O = 7.5%. As shown in FIG. 1, the devitrification temperature Tc is 945 ° C. when the content of La ₂ O ₃ is 1.5% by weight, and when the content exceeds 1.5%, the devitrification temperature rapidly increases. FIG. 2 shows La in the above composition.
₃ shows a viscosity curve of a glass melt when ₂ O ₃ = 1.5%. As shown in FIG. 2, viscosity η of glass melt at 950 ° C.
(Poise) is the upper limit of the La ₂ O ₃ range of the present invention.
At 5%, it was approximately 0.6. That is, if the La ₂ O ₃ component exceeds 1.5% by weight, devitrification occurs at a lower limit viscosity Logη = 0.6 during preform molding, and a good preform cannot be obtained. Therefore, it is limited to the range of 0.2 to 1.5%.

Although lanthanide-based oxides other than La ₂ O ₃ also have various components having an effect of improving the chemical stability, in view of the emission / absorption characteristics in the visible light region and the cost of raw materials, optical glass is not suitable for optical glass. Gd ₂ O ₃ is most suitable.

In addition to Gd ₂ O ₃ , Y ₂ O ₃ also has an effect of adjusting optical constants and improving chemical durability. However, La ₂ O ₃ is more effective than Gd ₂ O ₃ and Y ₂ O _{3 in} terms of improving chemical durability, and is effective with a small amount.
Therefore, it is preferable to use La ₂ O ₃ with priority.

For the above three components, La ₂ O ₃ + Y ₂ O ₃ +
If the total amount of Gd ₂ O ₃ is less than 0.2%, the effect is not sufficient, and if it exceeds 1.5%, the devitrification temperature sharply rises as in the case of using La ₂ O ₃ alone. For this reason, a good preform cannot be obtained. Therefore,
It is limited to the range of 0.2 to 1.5%. Further, by limiting the total amount of these components, each component of Y ₂ O ₃ and Gd ₂ O ₃ is limited to the range of 0 to 1.3%.

ZnO is a necessary component to form glass and obtain a low glass transition temperature. However, if it is less than 20%, a predetermined transition temperature cannot be obtained while maintaining durability. If it exceeds, the desired glass transition temperature cannot be obtained while maintaining the devitrification resistance. Therefore,
It is limited to the range of 20 to 40%.

TiO ₂ , Nb ₂ O ₃ , Ta ₂ O ₅ , MgO,
Each component of CaO, SrO, and BaO can be added to adjust optical constants. However, if each exceeds 5%, a desired glass transition temperature cannot be obtained while maintaining durability. Therefore, each of these components is limited to the range of 0 to 5%.

Li ₂ O is an essential component having an effect of lowering the glass transition temperature. However, if it is less than 1%, the effect cannot be obtained, and if it exceeds 5%, the devitrification resistance sharply decreases. Therefore, it is limited to the range of 1 to 5%.

[0027] As with Na ₂ O, K ₂ O is Li ₂ O, has the effect of lowering the glass transition temperature, it is an essential component for use with Li ₂ O, the total amount of _{Li 2 O + Na 2 O +} K 2 O is If it is less than 6%, a desired glass transition temperature cannot be obtained and 2
If it exceeds 5%, the chemical durability sharply decreases. Also N
If a ₂ O exceeds 10% and K ₂ O exceeds 20%, the devitrification resistance sharply decreases. Therefore, Na ₂ O is 0 to
10%, K ₂ O is limited to the range of 0 to 20%, and L
The total amount of _{i 2 O + Na 2 O +} K 2 O is limited to the range 6 to 25%.

Sb ₂ O ₃ can be added for defoaming, but amounts up to 0.5% are sufficient. Therefore, Sb ₂
O ₃ is limited to the range 0 to 0.5%.

F ₂ has the effect of adjusting the optical constants and lowering the glass transition temperature, but if it exceeds 5%, it volatilizes from the surface layer of the glass melt at the time of preform molding, and the molded preform becomes Causes fogging. Therefore, 0
It is limited to the range of ５5%.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION Table 1 shows preferred working compositions (Nos. 1 to 1) of an optical glass for a mold press according to the present invention.
0) and conventional optical glass composition examples (Comparative Examples A and B) as comparative examples and the refractive indexes (nd), Abbe number (νd), glass transition temperature (Tg), devitrification test results, and chemical Shows durability (RW, RA). Comparative Example A
Example N described in JP-A-60-171244
o. Comparative Example B is Example No. 3 described in JP-A-3-40934. 3.

[0031]

[Table 1]

[0032]

[Table 1]

[0033]

[Table 1]

Each of the glasses described above was prepared and mixed using ordinary glass raw materials, and then mixed with a platinum crucible for about 1,10.
Heat and melt at 0 to 1,300 ° C for about 2 to 5 hours to remove bubbles.
After homogenization by stirring or the like, it is cast into a block shape and obtained through a slow cooling step.

The devitrification test was performed by placing 80 g of a glass sample in a 50 CC pot made of platinum and heating at about 1,100 to 1,300 ° C. for 2 hours.
After heating and melting for 2 hours, the material kept at 950 ° C for 2 hours was cooled, and the presence or absence of devitrification was confirmed by a microscope. Glasses which did not show devitrification in this test were marked with ○, and devitrification was found. The obtained glass was marked with x. As for chemical durability, JOGIS06 in Japanese Optical Glass Industry Association Standard
Based on -1975 “Method for measuring chemical durability of optical glass (powder method)”, water resistance (RW) indicates a weight loss rate after immersing glass powder in boiling water at 100 ° C. for 1 hour, The acid resistance (RA) is set at 100 ° C.
The graph shows the weight loss after immersion in 1N nitric acid for 1 hour. In both RW and RA, the smaller the weight loss rate, the better the chemical durability.
If A is 2.0% or less, it can be sufficiently used for practical use.

As can be seen from Table 1, the glasses of Examples 1 to 10 have a refractive index (nd) of 1.5 to 1.6 and an Abbe number (ν).
d) has an optical constant in the range of 55 to 65, and has a glass transition temperature (Tg) in the range of 300 to 400 ° C., which is excellent in mold pressability. Further, no devitrification occurs even in a devitrification test at 950 ° C., and the chemical durability is good, and it is optimal as an optical glass for forming a preform by dropping a glass melt. In contrast, Comparative Example A
Has a glass transition temperature (Tg) higher than that of the present invention,
In addition, devitrification occurs due to the large content of La ₂ O ₃ component. Comparative Example B also has a low glass transition temperature and good chemical durability because it contains a large amount of the La ₂ O ₃ component, but has devitrification. Cannot be formed by dropping the preform.

[0037]

As described above, according to the present invention, when manufacturing a preform material for a mold press, the viscosity η of a glass melt is controlled to be constant within a range of Log η = 0.6 to 2.0. By this, the curved surface of the surface is smoother and more uniform than before,
At the same time that a shape suitable for a mold press can be obtained, the optical glass itself is also an overall improvement of the disadvantages of the conventional mold press glass.
That is, the refractive index (nd) is 1.5 to 1.6, and the Abbe number (ν
Although d) has an optical constant of 55 to 65, it has a low glass transition temperature of 300 to 400 ° C., is excellent in devitrification resistance and chemical durability, and contains environmentally unfavorable substances. The present invention provides an optical glass which does not have good melt preform molding and mold press properties. Using this glass, a preform is obtained by a melt dropping method, and the preform is subjected to mold press molding to produce a lens, thereby obtaining a desired optical constant, chemical durability, devitrification resistance, and preform moldability. In addition, since molding can be performed at a lower temperature than in the past while obtaining moldability and moldability, wear due to surface oxidation of a mold is reduced, and as a result, manufacturing costs can be significantly reduced.

[0038]

[Brief description of the drawings]

FIG. 1 shows an example of the relationship between the La ₂ O ₃ content% of a glass according to the present invention and the devitrification temperature.

FIG. 2 shows an example of a temperature-viscosity curve of a glass according to the present invention, a devitrification temperature of the glass, and a viscosity range when a preform is formed by dripping a glass melt.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C03C 3/068 C03C 3/16 C03C 3/247 C03C 4/00

Claims (1)

(57) [Claims] 1. An optical constant having a refractive index (nd) of 1.5 to 1.6 and an Abbe number (νd) of 55 to 65, a glass transition temperature (Tg) of 300 to 400 ° C., 1,0
The viscosity η (Poise) of the glass melt at 00 ° C is Logη
≦ 2.0, and yet the devitrification temperature Ri der temperature below when the viscosity η is log [eta = 0.6 in the glass melt, in _{weight%, SiO 2 0 ~ 2%} , B 2 O 3 1 _{~ 3%, Al 2 O 3} 1 ~ 5%, P 2 O 5 45 ~55%, Y 2 O 3 0 ~ 1.3%, La 2 O 3 0.2~ 1.5%, Gd 2 O 3 0 to 1.3%, provided that Y ₂ O ₃ + La ₂ O ₃ + Gd ₂ O ₃ = 0.2 to 1.5
_{%, TiO 2 0 ~ 5%} , Nb 2 O 5 0 ~ 5%, Ta 2 O 5 0 ~ 5%, ZnO 20 ~40%, MgO 0 ~ 5%, CaO 0 ~ 5%, SrO 0 ~ 5% , BaO 0 ~ 5%, Li 2 O 1 ~ 5%, Na 2 O 0 ~10%, K 2 O 0 ~20%, _{however, Li 2 O + Na 2 O} + K 2 O = 6~25%, Sb 2 O 3 0 to 0.5%, zinc phosphate system characterized in that it consists of the components of F ₂ 0 ~ 5% range
Optical glass for mold press.