JP2021119106A - Optical transmission fiber glass and optical transmission fiber - Google Patents

Abstract

To provide an optical transmission fiber glass, free of PbO, suitable for a core of an optical transmission fiber, having excellent optical transmittivity, chemical durability, and thermal stability, while having a high refractive index and low degree of coloration.SOLUTION: Provided is an optical transmission fiber glass characterized in that the fiber glass substantially does not contain Pb, As, or Ti; has a refractive index nd in the range from 1.60 to 1.70; and contains as glass components at least SiO2, B2O3, BaO, La2O3, ZrO2, and ZnO, wherein, expressed in mass%, the total content of the SiO2 and B2O3 is 25% to 50%, the content of BaO is 10% to 50%, and the content of La2O3 is 6% to 30%.SELECTED DRAWING: None

Description

The present invention relates to a glass for a photoconducting fiber used at the time of image transfer and a photoconducting fiber using this glass as a core. The photoconducting fiber of the present invention is particularly preferably used for a photoconducting fiber bundle for an endoscope or the like.

As a medium for light transmission, glass fiber is used in a wide range of fields such as medical and biotechnology, including the semiconductor industry. The fiber consists of a core glass in the center and a clad glass surrounding the core glass. Generally, a photoconducting fiber is composed of a core glass having a high refractive index and a clad glass having a slightly lower refractive index. With this configuration, the light incident on the core can be repeatedly totally reflected and conducted in the glass fiber without loss due to light leakage. Further, the higher the refractive index of the core glass is, the higher the aperture ratio (also referred to as numerical aperture) of the optical element is, which is preferable.

The method for producing the photoconducting fiber includes a double crucible method and a rod-in-tube method. The former is a method in which glass melted in a double-structured crucible is adjusted to an appropriate viscosity and spin-molded with a core / clad structure, and the latter is a method in which a cylindrically processed core glass and a tubular processed clad glass are laminated. This is a method of stretching and spinning while heating.

Conventionally, glass containing PbO in its composition has been widely used for fibers because it is easy to adjust the refractive index, has high transmittance, is hard to devitrify, and is easy to spin. However, in recent years, a glass fiber containing no PbO has been demanded in consideration of the environmental load. Therefore, the present inventor has previously developed a PbO-free glass containing no PbO (Patent Document 1).

JP-A-2004-010365

However, the conventional glass for photoconducting fibers has a problem that the chemical durability is lowered when trying to increase the refractive index. In particular, the conventional PbO-free photoconducting fiber has a problem that the glass is easily eroded by commercially available cleaning chemicals and the photoconducting performance is easily deteriorated.

Therefore, the present invention provides a glass for a photoconductive fiber which is excellent in photoconductivity, chemical durability, and thermal stability while having a high refractive index and a low degree of coloring, and which is substantially free of PbO. It is an object of the core glass to provide a light conductive fiber made of the glass.

The present invention that solves the above problems includes the following.
[1] Pb, As and Ti are substantially not contained, the refractive index nd is in the range of 1.60 to 1.70, and at least SiO ₂ , B ₂ O ₃ , BaO, La ₂ O _{3 are used as glass components.} , ZrO ₂ , and ZnO, in% by mass,
The total content of SiO ₂ and B ₂ O _{3 is 25-50%,}
BaO content is 10-50%,
La ₂ O ₃ content is 6-30%,
A glass for photoconducting fibers, which is characterized by being.
[2] As a glass component,
Na ₂ O 0.1% to 15%,
K ₂ O 0-15%,
Li ₂ O 0-5%,
The total content of Li ₂ O, Na ₂ O and K ₂ O is 5 to 15%.
[1] The glass for a light conductive fiber according to [1].
[3] The glass for light conductive fibers according to [1] or [2], wherein the content of _{B 2} O _{3 is 0.1 to 10%.}
[4] The photoconducting fiber according to any one of [1] to [3], wherein the average linear expansion coefficient at 100 ° C. to 300 ° C. is in ^{the range of 80 × 10 -7 to} 110 × 10 ^{-7 / ° C.} Glass for.
[5] The glass for a light conductive fiber according to any one of [1] to [4], which is a glass for a core of a light conductive fiber.
[6] A light conductive fiber comprising a core glass and a clad glass, wherein the core glass is the glass for a light conductive fiber according to any one of [1] to [5].
[7] The clad glass is substantially free of Pb, As and Ti, has a refractive index nd in the range of 1.50 to 1.60, has a liquid phase temperature of 1000 ° C. or lower, and is mass%.
SiO ₂ 40-75%,
B ₂ O ₃ 0.1 to 20%,
Na ₂ O 0.1 to 20%,
The light conductive fiber according to [6], which comprises.
[8] The clad glass is a group of Li ₂ O, K ₂ O, Al ₂ O ₃ , MgO, CaO, SrO, BaO, ZnO, Cs ₂ O, Sb ₂ O ₃ , and SnO _{2 as components other than the above.} [7] The photoconducting fiber according to [7], which contains at least one component selected from the above.

According to the present invention, there is provided a glass for a Pb-free photoconducting fiber having a high refractive index, a low degree of coloring, and excellent chemical durability, and having high thermal stability during spinning molding. The photoconducting fiber using the glass for photoconducting fiber of the present invention can be molded by, for example, the double crucible method, and a high-performance fiber bundle can be produced.

[Glass for photoconducting fiber]
The composition of the glass for photoconducting fibers will be described. Unless otherwise specified in the present specification, "%" used when displaying the glass composition means "mass%". Further, in the present specification, "~" used when specifying a numerical range shall be included in both the upper limit and the lower limit. For example, when "10 to 20%" is displayed as the content of the glass constituent component, it means that it is 10% by mass or more and 20% by mass or less.
Further, the content of the glass constituents can be quantified by a known method, for example, an inductively coupled plasma emission spectroscopic analysis method (ICP-AES), an inductively coupled plasma mass spectrometry method (ICP-MS), or the like. In the present invention, the content of the glass constituent component is 0%, which means that the constituent component is substantially not contained, and the component is allowed to be contained at an unavoidable impurity level.

In the glass for photoconductive fibers of the present invention, SiO ₂ is a basic component and an important component that determines thermal properties and chemical durability. B ₂ O _{3 is} also a basic component of glass, and is a component that improves meltability and spinning characteristics. In the glass for photoconductive fibers of the present invention, if the total content of _{SiO 2} and B ₂ O _{3 (SiO 2} + B ₂ O ₃ ) is less than 25%, the average linear expansion coefficient of the glass becomes too large and 50%. If it exceeds, the refractive index becomes too low. Therefore, _{the total content of SiO 2} and B ₂ O ₃ is set to 25 to 50%. The preferable lower limit of the total content of SiO ₂ and B ₂ O ₃ is 30%, and the more preferable lower limit is 35%. The preferred upper limit of the total content of SiO ₂ and B ₂ O _{3 is 45%.}

The SiO ₂ content, as long as the total content of SiO ₂ and _B 2 _{O 3} satisfies 25-50%, is not particularly limited, as long as SiO ₂ of 20% or more, predetermined average beam The coefficient of expansion can be obtained, and the thermal stability and viscosity of the glass do not become too low, which facilitates spin molding. Furthermore, the chemical durability is also improved. When _{the content of SiO 2} is 45% or less, melting is easy and the refractive index is high. Therefore, in the glass for photoconductive fibers of the present invention, _{the content of SiO 2} is preferably 20% to 45%. The more preferable lower limit of the content of SiO ₂ is 30%, the further preferable lower limit is 32%, _{the more preferable upper limit of the content of SiO 2} is 40%, and the further preferable upper limit is 38%.

The content of B ₂ O _3, as long as the total content of SiO ₂ and _B 2 _{O 3} satisfies 25-50%, is not particularly limited, the melting property as long as it is 0.1% or more, spinning The properties can be improved, and if it is 10% or less, the chemical durability can be improved. Therefore, _{the content of B 2} O ₃ is preferably in the range of 0.1 to 10%. The more preferable lower limit of the content of B ₂ O ₃ is 1%, and the more preferable lower limit is 3%. A more preferred upper limit of the B ₂ O ₃ content is 8%, and a more preferred upper limit is 6%.

Al ₂ O ₃ is not an essential component, but it is a component that affects devitrification resistance, flexibility, and chemical durability. When _{the content of Al 2} O ₃ is 3% or less, the devitrification resistance, flexibility, and transmittance are good. Therefore, _{the content of Al 2} O ₃ is preferably 0 to 3%. The content of Al ₂ O ₃ is more preferably in the range of 0 to 2%.

Na ₂ O is not an essential component, but it is a component that improves meltability. When _{the content of Na 2} O is 0.1% or more, the effect is observed, and when it is 15% or less, the viscosity of the glass does not decrease too much, which is suitable for double crucible molding. Therefore, the Na ₂ O content is preferably in the range of 0.1 to 15%. The more preferable lower limit of the Na ₂ O content is 3%, the more preferable lower limit is 4%, and the more preferable lower limit is 5%. A more preferred upper limit of the Na ₂ O content is 10%, and a more preferred upper limit is 8%.

K ₂ O is not an essential component, but it is a component that improves the meltability of glass. If it is 15% or less, the viscosity of the glass does not decrease too much, and double crucible molding can be performed. The content of _{K 2} O is preferably in the range 0-15%. A more preferable lower limit of the K ₂ O content is 1%, and a further preferable lower limit is 2%. More preferable upper limit of K 2 _O content is 10%, still more preferred upper limit is 5%.

The total amount of alkali metal oxides (Li ₂ O + Na ₂ O + K ₂ O) is preferably 5 to 15%. As one of the preferred embodiments of the glass of the present invention, the total amount of alkali metal oxides is 5% _{by setting the content of Al 2} O ₃ to 3% or less and _{the content of SiO 2 to 30% or more.} Even if the above is included, the chemical durability of the glass can be maintained. The total content of the alkali metal oxides (Li ₂ O + Na ₂ O + K ₂ O) is more preferably 5 to 15%, and even more preferably 5% or more and less than 15%. A more preferable lower limit of the total content of alkali metal oxides (Li ₂ O + Na ₂ O + K ₂ O) is 7%. A more preferable upper limit of the total content of alkali metal oxides (Li ₂ O + Na ₂ O + K ₂ O) is 12%.
In the glass for photoconductive fibers of the present invention, Li ₂ O is not an essential component, but is added for the purpose of improving meltability, adjusting the coefficient of linear expansion, adjusting the constant number, adjusting the glass transition point, and the like. It is an ingredient that can be.

CaO is not an essential component, but it is a component that improves meltability and refractive index. Further, by combining with BaO, it becomes easy to adjust the refractive index, the viscosity of the glass, and the devitrification resistance. When the CaO content is 20% or less, deterioration of chemical durability due to too much CaO can be suppressed, and deterioration of devitrification resistance can also be suppressed. Therefore, the CaO content is preferably in the range of 0 to 20%. The more preferred upper limit of the CaO content is 15%, the more preferred upper limit is 10%, and the more preferred upper limit is 5%.

BaO is a component having a great effect of improving the refractive index, and is an essential component of the present invention. Further, by combining with ZnO, it becomes easy to adjust the refractive index, the viscosity of the glass, and the devitrification resistance. When the BaO content is 10% or more, the refractive index is high and the devitrification resistance is also good. When the content of BaO is 50% or less, the viscosity of the glass does not decrease too much, and it is possible to suppress the deterioration of the devitrification resistance. Therefore, the content of BaO is set in the range of 10 to 50%. The preferable lower limit of the BaO content is 15%, and the more preferable lower limit is 20%. The preferred upper limit of the BaO content is 45%, the more preferred upper limit is 40%, and the more preferred upper limit is 35%.

ZnO is an essential component and is a component that improves meltability, refractive index, and chemical durability. By using ZnO as an essential component, the meltability, refractive index, and chemical durability of glass can be improved. If the content of ZnO is 0.1% or more, the effect is remarkable, and if it is 20% or less, deterioration of devitrification resistance due to too much ZnO can be suppressed. Therefore, the preferred lower limit of the ZnO content is 0.1%, the more preferred lower limit is 1%, the more preferred lower limit is 5%, and the more preferred lower limit is 10%. The preferred upper limit of the ZnO content is 20%, the more preferred upper limit is 18%, and the still more preferred upper limit is 15%.

La ₂ O ₃ is an essential component, and is a component that greatly improves the refractive index without deteriorating the transmittance and chemical durability. When the La ₂ O ₃ content is 6% or more, the effect can be seen, and the acid resistance is particularly good. If it is 30% or less, deterioration of devitrification resistance can be suppressed. Therefore, _{the content of La 2} O ₃ is in the range of 6 to 30%. The preferable lower limit of the content of La ₂ O ₃ is 7%, and the more preferable lower limit is 8%. The preferred upper limit of the La ₂ O ₃ content is 20%, the more preferred upper limit is 15%, and even more preferably 12%.

ZrO ₂ is an essential component, which greatly improves the refractive index without deteriorating the transmittance and improves the chemical durability. By using ZrO ₂ as an essential component, the refractive index can be greatly improved without deteriorating the transmittance of the glass, and the chemical durability can be improved. If the ZrO ₂ content is 0.1% or more, the effect can be seen, and if it is 10% or less, deterioration of devitrification resistance can be suppressed. Therefore, _{the preferable lower limit of the content of ZrO 2} is 0.1%, the more preferable lower limit is 1%, and the further preferable lower limit is 3%. The preferred upper limit of the ZrO ₂ content is 10%, the more preferred upper limit is 6%, and the further preferred upper limit is 5%.

SrO, Nb ₂ O ₅ , Cs ₂ O, Gd ₂ O ₃ , Sb ₂ O ₃ , and SnO ₂ are not essential components. However, although the purpose (function, effect) differs depending on the component, it is added for any one or more purposes such as improvement of meltability, adjustment of average coefficient of linear expansion, adjustment of constant number, clarification, and improvement of chemical durability. can do.

The glass for photoconducting fibers of the present invention is substantially free of _{Pb (PbO), As (As 2} O ₃ ) and Ti (TiO _2). Pb and As are not included because they have a large impact on the environment. Since Ti has a large absorption at short wavelengths, the glass for photoconducting fibers of the present invention does not substantially contain Ti because it significantly deteriorates the transmittance.
In addition, "substantially free" means that the _{content of Pb, As, and Ti converted to PbO, As 2} O ₃ , and TiO ₂ , respectively, is less than 0.1%, preferably 0.05%. Means less than. It may be 0%.
In addition, it is desirable that Er, Eu, Nd, Tb, Ni, V, Pr, and Cu, which can cause coloring of glass, are not substantially contained.
Further, like Pb and As, it is desirable that Tl, Te, U and Th are not substantially contained from the viewpoint of reducing the load on the environment.

Fe and Cr are impurities that deteriorate the transmittance of glass, and Fe mainly lowers the transmittance of short wavelengths near the ultraviolet region. If the Fe content exceeds 10 ppm, the transmittance of the light-conducting fiber glass in the short visible wavelength range may be significantly reduced. Therefore, the Fe content is preferably less than 10 ppm. It is more preferably less than 5 ppm, still more preferably less than 2 ppm. Cr is an impurity that causes absorption peculiar to the visible region, and if it exceeds 2 ppm, absorption occurs in the vicinity of 450 nm and 650 nm, which may deteriorate the color reproducibility of the fiber. Therefore, the Cr content is preferably less than 2 ppm. It is more preferably less than 0.5 ppm, still more preferably less than 0.2 ppm.

The glass for photoconducting fibers of the present invention can be used as a core glass or clad glass of a photoconducting fiber, but it is preferably used as a core glass. Further, the glass for photoconductive fibers of the present invention has a refractive index of 1.60 to 1.70. The liquidus temperature of the glass is preferably 1000 ° C. or lower. The refractive index is in the range of 1.60 to 1.70 in order to increase the aperture ratio of the fiber and transmit a bright image. Further, having a refractive index of 1.60 to 1.70 has an advantage that the thermal stability and viscosity of the glass can be easily adjusted, and when used as a core glass, it can be easily combined with a clad glass. .. The refractive index is preferably in the range of 1.61 to 1.69. More preferably, it is 1.62 to 1.65. Of the above glass compositions, mainly BaO, ZnO and La ₂ O ₃ are components that increase the refractive index. Therefore, by adjusting the content of these components within the above range, the above 1.60 to 1 It can be adjusted to the range of .70.

Further, by setting the liquidus temperature to 1000 ° C. or lower, spinning molding of photoconducting fibers becomes easy, and especially when glass is melted and molded by the double crucible method, it does not crystallize and defects or disconnections do not occur. Can be done. The liquidus temperature is more preferably 950 ° C. or lower. Of the above glass compositions, ZnO and optional components Li ₂ O, Na ₂ O, K ₂ O, and Ca O are components that improve the meltability, so the content of these components is within the above range. The liquidus temperature can be adjusted to 1000 ° C. or lower by adjusting with.

The glass for photoconducting fibers of the present invention preferably has a coloration degree λ80 of 35 or less. The reason why the degree of coloring λ80 is 35 or less is to prevent the transmittance of the photoconductive fiber from deteriorating. The degree of coloration λ80 is expressed in units of 10 nm by rounding off the first integer of the wavelength indicating a transmittance of 80% in a glass having a thickness of 10 mm. The thickness of the glass and the length of the photoconducting fiber when measuring the degree of coloration λ80 are not necessarily the same, but when a photoconducting fiber is produced using a glass having a λ80 of 35 or less as a core glass, the photoconducting fiber Was found to be almost transparent to visible light. When the degree of coloring λ80 is 35 or less, it is possible to suppress a decrease in the transmittance of the photoconductive fiber due to light absorption of the core glass and transmit a bright and high-contrast image. The degree of coloring λ80 is more preferably 33 or less, still more preferably 32 or less. Of the above glass compositions, SiO ₂ is a component that has a positive effect on the degree of coloration λ80 and TiO ₂ is a component that has an adverse effect. Therefore, by adjusting the content of these components within the above range, the above It can be adjusted to 35 or less.

The glass for photoconducting fibers of the present invention is preferably a glass having a characteristic of an ^{average linear expansion coefficient of 80 × 10-7 to} 110 × ^{10-7 / ° C at 100 to 300 ° C.} By setting the average coefficient of linear expansion at 100 to 300 ° C. in the above range, it becomes easy to adjust various properties required for photoconducting fibers as a high-refractive index multi-component glass, and when used as a core glass, a clad glass. It becomes easier to match with the coefficient of linear expansion of. The average coefficient of linear expansion of 100 to 300 ° C. is more preferably in the range of ^{90 × 10 -7 to} 100 × 10 ^{-7 / ° C.} The average coefficient of linear expansion is a component of the above glass composition in which SiO ₂ has a large influence on the average coefficient of linear expansion. Therefore, by adjusting the content of this component within the above range, the above Can be adjusted to a range. By satisfying these characteristics, the glass for photoconducting fibers of the present invention can be used as a glass for spinning molding.

[Photoconducting fiber]
The light conductive fiber of the present invention is composed of a core glass and a clad glass, and the glass for the light conductive fiber of the present invention is used for this core glass. At this time, the clad glass is preferably formed by using the following clad glass.

The clad glass used for the photoconductive fiber of the present invention contains, for example, Pb, As and Ti substantially free, the refractive index nd is in the range of 1.50 to 1.60, and the liquidus temperature is 1000. Clad glass having a temperature of ° C. or lower and containing 40 to 75% SiO ₂ , 0.1 to 20% B ₂ O ₃ , and 0.1 to 20% Na _{2 O in mass%.}

In the clad glass used in the present invention, SiO ₂ is a basic component of glass and an important component that determines thermal properties. When _{the content of SiO 2} is 40% or more, the stability and viscosity of the glass are good, and spinning molding becomes easy. If it is 75% or less, the melting is good. Therefore, the clad glass suitable for the present invention has a SiO ₂ content of preferably 40 to 75%, more preferably 45 to 70%, and even more preferably 50 to 70%.

In the clad glass used in the present invention, B ₂ O ₃ is also a basic component of glass and at the same time improves meltability and spinning characteristics. If _{the content of B 2} O ₃ is 0.1% or more, the effect can be seen, and if it is 20% or less, spinning molding becomes easy. Therefore, _{the content of B 2} O ₃ is preferably 0.1 to 20%, more preferably 1 to 15%, and even more preferably 5 to 15%.

In the clad glass used in the present invention, Na ₂ O is a component that improves meltability. If the Na ₂ O content is 0.1% or more, the effect is seen, and if it is 20% or less, the viscosity of the glass does not decrease too much, and the double crucible molding with the glass for photoconducting fibers of the present invention can be performed. It can be carried out. Therefore, the Na ₂ O content is preferably in the range of 0.1 to 20%, more preferably 1 to 15%, and even more preferably 5 to 15%.

In the clad glass used in the present invention, Li ₂ O is an effective component for improving the meltability, spinning characteristics, and average linear expansion characteristics of the glass. In particular, it may be an important component for adjusting to a glass having a low melting point and low expansion. If it is 5% or less, the devitrification resistance is suppressed from deterioration, and crystals are formed during spinning, so that problems such as disconnection are less likely to occur. The content of Li ₂ O is preferably 0 to 3%, more preferably 0 to 1.5%.

In the cladding glass used in the present invention, K 2 _O is a component for improving the meltability. If the K ₂ O content is 0.1% or more, the effect can be seen, and if it is 20% or less, the viscosity of the glass does not decrease too much, and double crucible molding with the core glass becomes easy. Therefore, the content of _{K 2} O is preferably from 0.1 to 20%, more preferably 1 to 15%, more preferably 5 to 15%.

In the clad glass used in the present invention, Al ₂ O ₃ is a component that improves the stability of the glass, and the devitrification resistance of the clad glass is improved by adding a small amount. Further, if it is 5% or less, the viscosity of the glass does not become too high, and spinning by the double crucible method can be performed. A more preferable content is 0 to 3%.

In the clad glass used in the present invention, MgO, CaO, SrO, BaO, and ZnO are optional components that improve the meltability and spinning properties, average linear expansion properties, and chemical durability of the glass. It can be appropriately contained in the clad glass depending on the purpose, and if it is contained in an amount of 1% or more, the effect of the added component may be observed, and if it is 15% or less, good devitrification resistance and spinning characteristics are obtained. You may be able to.

In the clad glass used in the present invention, Cs ₂ O, Sb ₂ O ₃ , and SnO ₂ are not essential components. However, although the purpose (function, effect) differs depending on the component, it is added for any one or more purposes such as improvement of meltability, adjustment of average coefficient of linear expansion, adjustment of constant number, clarification, and improvement of chemical durability. can do.

The clad glass is also substantially free of Pb (PbO), As (As ₂ O ₃ ) and Ti (TIO _2). Note that "substantially free", Pb, As, respectively Ti converted _PbO, the _As 2 O 3, TiO _2, PbO, AsO, each content of TiO ₂ is less than 0.1%, It means that it is preferably less than 0.05%. It may be 0%.
Pb and As are not included because they have a large impact on the environment. Clad glass is substantially free of Ti because Ti increases the index of refraction too much.
Further, like Pb and As, it is desirable that Tl, Te, U and Th are not substantially contained from the viewpoint of reducing the load on the environment.

Due to its characteristics, the clad glass preferably has a refractive index slightly lower than that of the core glass. For example, it is appropriate that the clad glass has a refractive index in the range of 1.50 to 1.70. From the viewpoint of being used in combination with the glass for photoconductive fibers of the present invention, the refractive index of the clad glass is 1.50 to 1.60. Of the above glass compositions, the refractive index is mainly composed of SiO ₂ and B ₂ O ₃ which lower the refractive index. Therefore, by adjusting the content of these components within the above range, the above 1. It can be adjusted in the range of 50 to 1.60. The refractive index of the core glass and the refractive index of the clad glass may be set in the above ranges according to the specifications of the photoconductive fiber.

Further, in the clad glass used in the present invention, by setting the liquidus temperature to 1000 ° C. or lower, defects or disconnection due to crystallization of the glass during spinning molding, particularly melting and molding by the double crucible method. Can be prevented. The liquidus temperature of the clad glass is preferably 950 ° C. or lower. Regarding the liquidus temperature, since B ₂ O ₃ , Na ₂ O, and in some cases K ₂ O are components of the above glass composition that improve the meltability, the content of these components is described above. By adjusting within the range, the temperature can be adjusted to 1000 ° C. or lower.

Further, the photoconducting fiber of the present invention can be produced by spinning molding using the double crucible method. Therefore, the average linear expansion coefficient of the clad glass at 100 to 300 ° C. is preferably in the range of ^{80 to 110 × 10 -7 / ° C., which is an average linear expansion coefficient substantially equal to that of the core glass described above.} The average coefficient of linear expansion is a component of the above glass composition in which SiO ₂ has a large influence on the average coefficient of linear expansion. Therefore, by adjusting the content of this component within the above range, the above Can be adjusted to a range.

The glass for photoconducting fibers and the clad glass of the present invention can be produced by a general manufacturing process of optical glass. For example, a process of appropriately using oxides, hydroxides, carbonates, nitrates, chlorides, sulfides, etc. as glass raw materials, weighing them to obtain a desired composition, and mixing them to prepare a blending raw material, and a blending raw material are prepared in advance. A step of heating and vitrifying, a step of heating the molten glass in a heat-resistant container having a platinum content of 95% or more, and stirring the molten glass with a blade thruster having a platinum content of at least 95% or more on the surface to make it homogeneous. It is manufactured through a process of making it into a glass and a process of defoaming and clarifying air bubbles in the molten glass. The molten glass homogenized in this way is poured into a frame and molded, and then placed in a heated furnace near the slow cooling point of the glass and slowly cooled to room temperature. In the present invention, it is preferable that all the glass manufacturing steps are performed at 1500 ° C. or lower.

The production of the photoconducting fiber is preferably spun-molded using the double crucible method. The conditions of the double crucible method used for producing the photoconducting fiber are not particularly limited and may be known conditions.

Examples The present invention will be further described below with reference to Examples.

(Examples 1 to 7)
Using raw materials such as optical glass grade high-purity oxides, hydroxides, carbonates, nitrates, chlorides, and sulfates, so that glasses having the respective compositions of Examples 1 to 7 in Table 1 can be obtained. The raw materials were weighed and mixed to prepare a mixed raw material. Next, each of the compounded raw materials was placed in a platinum crucible, heated to 1500 to 1500 ° C., melted, stirred and homogenized, allowed to stand for clarification, and then poured into a mold. After the glass solidified, it was then transferred to an electric furnace heated near the slow cooling point of the glass and slowly cooled to room temperature. In this way, blocks made of 7 types of glass of Examples 1 to 7 shown in Table 1 were prepared. A test piece necessary for measurement was cut out from each of the obtained glass blocks, polished, and evaluated for characteristics.

The method for measuring each physical property of glass is as follows.
Refractive index: Measured according to the Japan Optical Glass Industry Association standard JOGIS-01.
Color degree (color degree λ80): Measured according to the Japan Optical Glass Industry Association standard JOBIS-02 2003 “Method for measuring color degree of optical glass”.
Glass transition temperature (Tg) and average linear expansion coefficient of 100 ° C to 300 ° C: Measured according to the Japan Optical Glass Industry Association standard JOGIS-08 2003 "Measurement method of thermal expansion of optical glass".
Water resistance by powder method: Measured according to the Japan Optical Glass Industry Association standard JOGIS-06 2009 "Measuring method of chemical durability of optical glass (powder method)". Table 1 shows the grades of water resistance by the powder method.
Powder method Acid resistance: Measured according to the Japan Optical Glass Industry Association standard JOGIS-06 2009 "Measuring method of chemical durability of optical glass (powder method)". Table 1 shows the grades of acid resistance of the powder method.
Liquid phase temperature: Glass was placed in a platinum crucible, heated and held at 950 ° C. for 2 hours, cooled to room temperature, and the presence or absence of crystals in the glass was magnified and observed using an optical microscope. When no crystals were observed, the liquidus temperature was set to 950 ° C. or lower.
Table 1 shows the physical characteristics of the seven types of glass of Examples 1 to 7. The liquidus temperature of each of the seven types of glass of Examples 1 to 7 was 950 ° C. or lower.

Next, the glass of Example 1 shown in Table 1 was used as the core glass, and the clad glass 1 shown in Table 2 was used as the clad glass and spun under known conditions by the double crucible method to obtain a photoconducting fiber. In spinning the photoconducting fiber, there were no problems such as crystallization of glass or disconnection due to crystallization.
Similarly, using each of the glasses of Examples 2 to 7 shown in Table 1 as the core glass, a light conductive fiber was produced by a double crucible method. In spinning each photoconducting fiber, problems such as glass crystallization and disconnection due to crystallization did not occur.

Each photoconducting fiber produced in this way was used to prepare a photoconducting fiber bundle. Each photoconducting fiber bundle is excellent in conducting visible light and is suitable as a photoconducting fiber bundle for an endoscope.

(Comparative Examples 1 and 2)
Glasses having the compositions shown in Comparative Examples 1 and 2 in Table 1 were prepared.
Comparative Example 1 does not contain _{ZrO 2} as a glass component _{and contains La 2} O ₃ , but the content thereof is as low as 4.6%. Therefore, the acid resistance of the powder method was inferior to that of the fourth grade and the glasses of Examples 1 to 7.
Since Comparative Example 2 did _{not contain La 2} O ₃ , the acid resistance of the powder method was 4th grade, which was inferior to that of the glasses of Examples 1 to 7.

The present invention is useful in the technical field of optical fibers.

Claims (8)

It is substantially free of Pb, As and Ti, has a refractive index nd in the range of 1.60 to 1.70, and has at least SiO ₂ , B ₂ O ₃ , BaO, La ₂ O ₃ , and ZrO _{2 as glass components.} , And ZnO, in% by mass,
The total content of SiO ₂ and B ₂ O _{3 is 25-50%,}
BaO content is 10-50%,
La ₂ O ₃ content is 6-30%,
A glass for photoconducting fibers, which is characterized by being. As a glass component,
Na ₂ O 0.1% to 15%,
K ₂ O 0-15%,
Li ₂ O 0-5%,
The total content of Li ₂ O, Na ₂ O and K ₂ O is 5 to 15%.
The glass for a light conductive fiber according to claim 1. The glass for a light conductive fiber according to claim 1 or 2, wherein the content of _{B 2} O _{3 is 0.1 to 10%.} The glass for photoconducting fibers according to any one of claims 1 to 3, wherein the average linear expansion coefficient of 100 ° C. to 300 ° ^{C. is in the range of 80 × 10 -7 to} 110 × 10 ^{-7 / ° C.} The glass for a light conductive fiber according to any one of claims 1 to 4, which is a glass for a core of a light conductive fiber. A light conductive fiber comprising a core glass and a clad glass, wherein the core glass is the glass for a light conductive fiber according to any one of claims 1 to 5. The clad glass is substantially free of Pb, As and Ti, has a refractive index nd in the range of 1.50 to 1.60, a liquidus temperature of 1000 ° C. or lower, and by mass%.
SiO ₂ 40-75%,
B ₂ O ₃ 0.1 to 20%,
Na ₂ O 0.1 to 20%,
The light conductive fiber according to claim 6, wherein the light conductive fiber comprises. The clad glass is selected from the group _{of Li 2} O, K ₂ O, Al ₂ O ₃ , MgO, CaO, SrO, BaO, ZnO, Cs ₂ O, Sb ₂ O ₃ , and SnO ₂ as components other than the above. The photoconducting fiber according to claim 7, wherein the photoconducting fiber contains at least one component.