JP2008013386A - Glass tube for fluorescent lamp - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass tube for a fluorescent lamp, which can sufficiently shield ultraviolet rays having wavelengths of 254 nm and 313 nm and reduce coloration in the visible light region. <P>SOLUTION: The glass tube for a fluorescent lamp is formed of borosilicate glass containing GeO<SB>2</SB>and CeO<SB>2</SB>. The borosilicate glass comprises essentially, by mass based on following oxides, 60-80% SiO<SB>2</SB>, 10-25% B<SB>2</SB>O<SB>3</SB>, 1-7% Al<SB>2</SB>O<SB>3</SB>, 3-15% of Li<SB>2</SB>O+Na<SB>2</SB>O+K<SB>2</SB>O, 0-5% ZnO, 0.1-5% GeO<SB>2</SB>, 0.1-5% CeO<SB>2</SB>, 0-3% ZrO<SB>2</SB>and 0.01-0.1% Fe<SB>2</SB>O<SB>3</SB>. In the borosilicate glass, the ratio of Ce<SP>3+</SP>ion to the total Ce ion is ≥90%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a glass tube suitable for a fluorescent lamp used for a backlight or a front light of a display device such as a liquid crystal display (hereinafter referred to as LCD), such as an envelope of a light source accompanied by ultraviolet radiation.

LCDs are widely used as key devices for multimedia-related equipment, and in recent years, there have been demands for weight reduction, thinning, low power consumption, high brightness, low cost, and the like. In particular, high-quality display screens are required for personal computer displays, in-vehicle display devices, TV monitors, and the like.
Since the liquid crystal display element itself used in LCDs does not emit light, a transmissive liquid crystal display element using a fluorescent lamp as a backlight is used when a high-quality display screen is required. Some devices using a liquid crystal display element use a front light as an irradiation light source from the front.

With the trend toward lighter, thinner, higher brightness and lower power consumption of LCDs, backlight fluorescent lamps are also becoming thinner and thinner.
However, thinning and thinning of fluorescent lamps leads to a decrease in mechanical strength, and the amount of heat generated by the lamp tends to increase due to the improvement of luminous efficiency, so a glass with higher mechanical strength and heat resistance is required. It has been said that.

The light emission principle of the fluorescent lamp for the backlight is the same as that for general lighting. Mercury vapor excited by the discharge between the electrodes emits ultraviolet rays, and the fluorescent material applied to the inner wall of the tube receives ultraviolet rays to emit visible light. It occurs. Ultraviolet rays are generated in the lamp, and most of the light is converted into visible light. However, some of the light is a phosphor and does not convert into visible light, and sometimes reaches the glass.
In such a case, when ultraviolet rays are transmitted without being shielded by glass, the resin light guide plate, the reflection plate and the like constituting the backlight are discolored or deteriorated. Therefore, there is a need for a glass with ultraviolet shielding properties.
As a glass tube for a fluorescent lamp that meets these requirements, a tube made of a borosilicate hard glass containing TiO ₂ and CeO ₂ is known (see, for example, Patent Document 1).

JP 2002-293571 A

  As described above, ultraviolet rays are generated in the fluorescent lamp. The main one of them is ultraviolet light of 253.7 nm, but other ultraviolet light of 297 nm, 313 nm, 334 nm, and 366 nm exists.

In the backlight for a liquid crystal TV, the number of fluorescent lamps used is from several to 10 or more per unit, so that the total amount of emitted ultraviolet rays inevitably increases.
As an improvement for improving the luminance required for backlight units, mainly for LCD TVs, the characteristics of the lamp itself are natural. . Resins such as polyester, polystyrene, polypropylene, polycarbonate film and cycloolefin polymer used in such light guide plates and reflectors cannot have sufficient UV resistance, and particularly have a degradation wavelength in the vicinity of 300 to 330 nm. When exposed to ultraviolet rays of a wavelength, it causes deterioration in display quality as a backlight unit, product life and reliability. For this reason, it has been necessary to take measures to absorb ultraviolet rays in the above-mentioned wavelength range with glass and prevent the emission to the outside of the lamp.

As a countermeasure, Al ₂ O ₃ , TiO ₂ , ZnO or the like, which is a component that reflects or absorbs ultraviolet rays, is coated on the inner surface of the glass tube, and a phosphor is applied thereon to form a multilayer film. The method is to reduce the intensity of the ultraviolet rays that reach it. However, such a method has a problem that the difficulty in coating and the increase in coating process are unavoidable due to the reduction in the diameter and length of the glass tube.

The borosilicate hard glass containing TiO ₂ and CeO ₂ may be able to shield not only ultraviolet rays of 253.7 nm but also ultraviolet rays of 313 nm that cause deterioration of the resin used in the backlight unit to some extent.
However, if both TiO ₂ and CeO ₂ are contained, there is a possibility that remarkably coloring occurs in the visible region, which may not be suitable for a liquid crystal TV that requires sufficient brightness and color reproducibility.
An object of this invention is to provide the glass tube for fluorescent lamps which can solve such a problem.

The present invention provides a glass tube for a fluorescent lamp made of borosilicate glass containing GeO ₂ and CeO ₂ .

Since the glass tube for a fluorescent lamp of the present invention has an excellent ultraviolet cut characteristic, even if it is used for a fluorescent lamp for a backlight of a display device such as an LCD, the material such as resin parts inside the display device is not easily deteriorated. Reliability is improved.
In addition, sufficient brightness and color reproducibility can be realized when used in a backlight for a liquid crystal TV.

  The fluorescent lamp glass tube of the present invention typically has an outer diameter of 0.7 to 6 mm and a wall thickness of 0.07 to 0.7 mm.

The borosilicate glass constituting the glass tube for a fluorescent lamp of the present invention (hereinafter, this glass is referred to as the glass of the present invention) has transmittances T ₂₅₄ and T ₃₁₃ at a thickness of 0.3 mm for light of wavelengths 254 nm and 313 nm. The transmittance T ₄₀₀ at a thickness of 1 mm for light of 1% or less, 10% or less, and a wavelength of 400 nm is preferably 85% or more. If T ₂₅₄ exceeds 1% or T ₃₁₃ exceeds 10%, the material deterioration of the resin component or the like may not be sufficiently suppressed. If _T400 is less than 85%, the transmittance of visible light is lowered, and sufficient brightness or color reproducibility cannot be obtained in an LCD backlight, which may make it difficult to use for a liquid crystal TV.

In the glass of the present invention, CeO ₂ is a component that makes Ce ³⁺ present in the glass and makes T ₃₁₃ smaller, and is essential. The typical mass percentage content of CeO ₂ is 0.1-5%. If it exceeds 5%, devitrification tends to occur. In addition, below, content of each component in glass is displayed by the mass percentage.
CeO ₂ has a strong oxidizing power, so it itself is reduced and tends to be in a trivalent state. Usually, it coexists in a state of Ce ³⁺ and Ce ^{4+ in} glass, Ce ³⁺ is 316 nm and Ce ⁴⁺ is 243 nm, respectively. Has an absorption band. For example, when the glass of the present invention contains CeO ₂ , this only means that Ce is contained, and it means that all of the contained Ce is contained in the form of Ce ⁴⁺ . is not.

Ce ³⁺ shows sharp absorption, whereas Ce ⁴⁺ shows broad absorption in the visible range. Therefore, the ratio (R) of Ce ³⁺ ions to all Ce ions is preferably 90% or more. If it is less than 90%, the glass tends to be colored. More preferably, it is 95% or more, and particularly preferably 98% or more.
As a method for increasing the R, a C-based reducing agent such as carbon or sucrose is added to the raw material, an ammonium-based reducing agent such as ammonium citrate is added to the raw material, and the metal is used as a raw material for the metal oxide component of glass. Methods such as adding a suboxide or its metal itself as a reducing agent and controlling the melting atmosphere are conceivable.

Further, when it is desired to increase R, when the glass is melted so that R is 98% or more and T ₂₅₄ is desired to be reduced without decreasing T ₄₀₀ , the glass of the present invention contains SnO. It is preferable. In that case, the typical content of SnO is 0.1-5%. If it exceeds 5%, devitrification tends to occur.

In the glass of the present invention, GeO ₂ is a component that reduces T ₂₅₄ without lowering T ₄₀₀ even when the glass is melted so that R is 98% or more, and is essential.
The typical content of GeO ₂ in terms of mass percentage is 0.1-5%. If it exceeds 5%, devitrification tends to occur.

It is preferable that the glass of the present invention does not contain PbO, and typically, SiO ₂ 60 to 80%, B ₂ O ₃ 10 to 25%, Al ₂ O ₃ 1 to 7%, Li ₂ O + Na ₂ O + K ₂ O 3-15%, ZnO 0-5%, GeO ₂ 0.1-5%, CeO ₂ 0.1-5%, ZrO ₂ 0-3%, Fe ₂ O ₃ 0.01-0.1 %, Consisting essentially of. Hereinafter, the glass of this typical embodiment will be described.

SiO ₂ is a glass network forming component and is essential. If it is less than 60%, the chemical durability of the glass is lowered, weathering, burning, etc. are likely to occur, the luminance of the fluorescent lamp is lowered, or uneven color tends to occur. Preferably it is 62% or more. If it exceeds 80%, the meltability and moldability of the glass deteriorate, and a decrease in chemical durability causes weathering, burns, etc., causing a decrease in luminance of the fluorescent lamp and occurrence of uneven color. Preferably it is 78% or less.

B ₂ O ₃ is a component that improves the meltability or adjusts the viscosity, and is essential. If it is less than 10%, the meltability deteriorates. Preferably it is 12% or more. If it exceeds 25%, volatilization becomes remarkable, and the homogeneity of the glass decreases. Preferably it is 20% or less.

Al ₂ O ₃ is a component that improves the devitrification or chemical durability of glass and is essential. If it is less than 1%, phase separation or devitrification tends to occur, or the chemical durability of the glass decreases. Preferably it is 2% or more. If it exceeds 7%, the meltability deteriorates and striae occur. Preferably it is 5% or less.

Li ₂ O, Na ₂ O and K ₂ O are fluxes, components that improve the meltability of the glass and adjust the viscosity and thermal expansion coefficient, and contain any one or more of these three components Must. If the total content of these three components exceeds 15%, the thermal expansion coefficient becomes too large, or the chemical durability deteriorates.
It is preferable to contain all of these three components or two of them because an effect such as an improvement in insulation by mixed alkali can be expected.
Preferably, Li ₂ O is 0~3%, Na ₂ O is 0~8%, _{K 2} O is from 2 to 12%. If Li ₂ O exceeds 3%, Na ₂ O exceeds 8%, or K ₂ O exceeds 12%, the thermal expansion coefficient may be excessively increased or the chemical durability may be deteriorated.

It is known that Na ₂ O reacts with mercury to form amalgam during the operation of the fluorescent lamp, and excessive Na ₂ O in the glass results in a reduction in the amount of mercury that works effectively in the fluorescent lamp. Therefore, from the viewpoint of reducing the amount of mercury used, the content of Na ₂ O exceeding the upper limit is not preferable, and Na ₂ O is more preferably 0 to 4%.
When sealing with Kovar metal, Na ₂ O is preferably 8 to 15%, and when sealing with tungsten, Na ₂ O is preferably 3 to 10%. If it is less than each lower limit value, the coefficient of thermal expansion is significantly reduced, and there is a possibility that good sealing with Kovar alloy or tungsten cannot be achieved due to a significant increase in viscosity.

  ZnO is not essential, but is a component that increases the resistance to ultraviolet solarization, and may be contained up to 5%. If it exceeds 5%, devitrification tends to occur.

GeO ₂ is essential as described above. If it is less than 0.1%, T ₂₅₄ increases. Preferably it is 0.3% or more. If it exceeds 5%, devitrification tends to occur. Preferably it is 1.5% or less.

CeO ₂ is essential as described above. If it exceeds 5%, devitrification tends to occur. Preferably it is 1-2%.

ZrO ₂ is not essential, but may be contained up to 3% in order to increase the ultraviolet solarization resistance or to reduce the brick erosion resistance. If it exceeds 3%, devitrification tends to occur.

Fe ₂ O ₃ is not essential, but is preferably contained in order to reduce T ₂₅₄ and T ₃₁₃ . Usually, it contains 0.01% or more of the raw material derived from impurity components. If it exceeds 0.1%, T ₄₀₀ tends to be small, or the ultraviolet solarization resistance may be reduced. Typically, it is 0.05% or less.

The glass of the typical embodiment of the present invention consists essentially of the above components, but may contain other components within a range not impairing the object of the present invention. In that case, the total content of such components is preferably 10% or less, more preferably 5% or less.
Examples of such components include CaO, MgO, BaO, and SrO, which have the effect of reducing the viscosity of glass at a high temperature and improving the meltability. When these components are contained, the total content is preferably 5% or less. If it exceeds 5%, the glass state becomes unstable and devitrification tends to occur.

The fining agent used when melting the glass of the present invention is preferably a reducing fining agent. The use of an oxidizing fining agent is not preferred because it is intended to obtain good ultraviolet absorption characteristics by controlling CeO ₂ to a state of Ce ³⁺ ions. For the same reason, it is preferable not to use a raw material that acts as an oxidizing agent.
As the clarifier, the combined use of Na ₂ SO ₄ and C or the use of NaCl is preferable, and the use of Sb ₂ O ₅ or As ₂ O ₅ is not preferable. Also, the use of alkali metal nitrates is not preferred.

The raw materials are prepared and mixed so as to have a composition expressed by mass percentage in the columns from SiO ₂ to Fe ₂ O _{3 in the} table, mixed and put into an alumina crucible, which is held at 1500 ° C. for 1 hour to dissolve, and then sufficiently The mixture was stirred and clarified to obtain a homogeneous molten glass. Next, this molten glass was poured into a rectangular frame and slowly cooled to obtain the glasses of Examples 1 to 4. Examples 1 and 2 are examples, and examples 3 and 4 are comparative examples.
As raw materials, silica sand, powders of carbonates, nitrates, hydroxides, and the like of each metal were used. The obtained glass was 100 g, 0.25 g of NaCl for each example as a refining agent, and Example 1 as a reducing agent. 2 and 4, 5 g of ammonium citrate was used as a raw material.

About the obtained glass, R (unit:%), _T254 (unit:%), _T313 (unit:%), and _T400 (unit:%) were measured as follows. The results are shown in the table.
R: The glass was crushed, and the content of total Ce ions was determined by the fluorescent X-ray method using a wavelength dispersion type fully automatic fluorescent X-ray analyzer RIX3000 manufactured by Rigaku Corporation. On the other hand, the content of Ce ⁴⁺ ions was determined by a redox titration method. Specifically, 300 mg of crushed glass was precisely weighed in a polypropylene container with a lid, 15 mL of 0.73 [N] H ₂ SO ₄ and 2 mL of HF were added thereto, the lid was capped, and the mixture was stirred and decomposed at room temperature for 10 minutes. . Next, 25 mL of 4% H ₃ BO ₃ was added and stirred gently, then washed into a beaker with 0.73 [N] H ₂ SO ₄ to about 100 mL. About 100 mL of this solution was titrated for Ce ⁴⁺ in the solution with a 0.001 mol / L Fe ²⁺ standard solution using an automatic titrator. A 0.02 mol / L KMnO ₄ standard solution was used for standardization of the standard solution.
The content obtained by subtracting the content of Ce ⁴⁺ ions from the content of all Ce ions was used as the content of Ce ³⁺ ions, and this was divided by the content of all Ce ions to obtain R.

T ₂₅₄ , T ₃₁₃ : The transmittance of the sample subjected to double-sided optical polishing so as to have a thickness of 0.3 mm was measured using a U3500 self-recording spectrophotometer manufactured by Hitachi, Ltd.
T ₄₀₀ : The transmittance of the sample subjected to double-sided optical polishing so as to have a thickness of 1.0 mm was measured using the self-recording spectrophotometer.

The present invention can be used for manufacturing a fluorescent tube such as a backlight.

Claims (5)

A glass tube for a fluorescent lamp made of borosilicate glass containing GeO ₂ and CeO ₂ . The borosilicate glass by mass percentage based on the following _{oxides, SiO 2 60~80%, B 2} O 3 10~25%, Al 2 O 3 1~7%, Li 2 O + Na 2 O + K 2 O 3~15 %, ZnO 0-5%, GeO ₂ 0.1-5%, CeO ₂ 0.1-5%, ZrO ₂ 0-3%, Fe ₂ O ₃ 0.01-0.1%, essentially from The glass tube for a fluorescent lamp according to claim 1. The glass tube for a fluorescent lamp according to claim 1 or 2, wherein a ratio of Ce ³⁺ ions to total Ce ions in the borosilicate glass is 90% or more.   The transmittance of the borosilicate glass at a thickness of 0.3 mm for light having a wavelength of 254 nm and 313 nm is 1% or less, 10% or less, respectively, and the transmittance at a thickness of 1 mm for light having a wavelength of 400 nm is 85% or more. The glass tube for fluorescent lamps according to 2 or 3. The glass tube for a fluorescent lamp according to any one of claims 1 to 4, which has an outer diameter of 0.7 to 6 mm and a thickness of 0.07 to 0.7 mm.