JP2007277016A - Lead-free glass for coating fluorescent flat lamp electrode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lead-free glass for coating a fluorescent flat lamp electrode. <P>SOLUTION: The lead-free glass for coating the fluorescent flat lamp electrode essentially comprises, in mol%, 20-50% B<SB>2</SB>O<SB>3</SB>, 5-35% SiO<SB>2</SB>, 10-30% ZnO, 0-10% Al<SB>2</SB>O<SB>3</SB>, 0-10% SrO, 6-16% BaO, 2-16% Li<SB>2</SB>O, 0-10% Na<SB>2</SB>O+K<SB>2</SB>O, 0-9% Bi<SB>2</SB>O<SB>3</SB>, 0-2% CuO+CeO<SB>2</SB>, provided that the molar ratio of (B<SB>2</SB>O<SB>3</SB>+SiO<SB>2</SB>+Al<SB>2</SB>O<SB>3</SB>)/(Bi<SB>2</SB>O<SB>3</SB>+BaO) is ≥3.25 and the total amount of MgO and CaO is ≤8 mol%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a lead-free glass suitable for insulatingly coating an electrode of a flat fluorescent lamp (sometimes abbreviated as FFL).

  In recent years, thin flat panel color display devices have attracted attention. In such a display device, an electrode is formed in each pixel in order to control a display state in the pixel forming the image. As such an electrode, a transparent electrode such as an ITO or tin oxide thin film formed on a glass substrate is used in order to prevent deterioration in image quality.

The transparent electrode formed on the surface of the glass substrate used as the display surface of the display device is processed into a thin line shape in order to realize a fine image. And in order to control each pixel independently, it is necessary to ensure the insulation between such finely processed transparent electrodes. However, when moisture is present on the surface of the glass substrate or when an alkali component is present in the glass substrate, a slight current may flow through the surface of the glass substrate. In order to prevent such a current, it is effective to form an insulating layer between the transparent electrodes. The insulating layer is preferably transparent in order to prevent deterioration in image quality due to the insulating layer formed between the transparent electrodes.
Various insulating materials for forming such an insulating layer are known. Among them, glass materials that are transparent and highly reliable insulating materials are widely used.

  In a plasma display panel (PDP), which has recently been expected as a large flat color display device, cells are partitioned by a front substrate, a rear substrate and barrier ribs used as display surfaces, and plasma discharge is generated in the cells. By doing so, an image is formed. A transparent electrode is formed on the surface of the front substrate. In order to protect the transparent electrode from plasma, it is essential to cover the transparent electrode with glass having excellent plasma durability.

  The glass used for such electrode coating is usually used as a glass powder. For example, a method of adding a filler or the like to the glass powder as needed and mixing it with a resin, a solvent or the like to form a glass paste on a glass substrate on which a transparent electrode is formed and baking it, The transparent electrode is formed by a method such as a method of forming a slurry obtained by mixing a resin and, if necessary, a filler or the like into a green sheet, laminating the slurry on a glass substrate on which the transparent electrode is formed, and firing. Cover.

In addition to the electrical insulation as described above, the electrode coating glass has, for example, a softening point (Ts) of 450 to 650 ° C. and an average linear expansion coefficient (α) at 50 to 350 ° C. of 60. There are demands that the electrode-coated glass layer obtained by firing has a high transparency, a low dielectric constant, and the like, and that various glasses have been conventionally used, such as × 10 ^{−7 to} 90 × 10 ⁻⁷ / ° C. Proposed.
Furthermore, recently, glass containing no lead has been desired. For example, in terms of mass percentage, B ₂ O ₃ 34.0%, SiO ₂ 4.4%, ZnO 49.9%, BaO 3.9%, K ₂ O 7.8%, glass for covering electrodes is disclosed consisting of (refer to Patent Document 1.).

JP 2002-249343 A (Table 1)

The glass containing no lead is such that the visible light transmittance of the ITO film-coated glass coated thereby is 74% (see Patent Document 1).
In recent years, there has been a demand for lead-free glass that can increase the visible light transmittance and lower the dielectric constant.
An object of the present invention is to provide a lead-free glass for solving such problems, which can be used for covering a flat fluorescent lamp electrode.

The present invention is expressed in terms of mol% based on the following oxides: B ₂ O ₃ 20 to 50%, SiO ₂ 5 to 35%, ZnO 10 to 30%, Al ₂ O ₃ 0 to 10%, SrO 0 to 10% BaO 6-16%, Li ₂ O 2-16%, Na ₂ O + K ₂ O 0-10%, Bi ₂ O ₃ 0-9%, CuO + CeO ₂ 0-2%, (B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ ) / (Bi ₂ O ₃ + BaO) is 3.25 or more, and when MgO or CaO is contained, it is made of lead-free glass (glass 1 of the present invention) in which MgO + CaO is 8 mol% or less. A flat fluorescent lamp electrode coating glass is provided.

In the same display, B ₂ O ₃ 20-50%, SiO ₂ 5-35%, ZnO 10-30%, Al ₂ O ₃ 0-10%, SrO 0-10%, BaO 6-16%, Li _A flat fluorescent lamp made of lead-free glass (glass 2 of the present invention) consisting essentially of ₂ O 2-16%, Na ₂ O + K ₂ O 0-10%, CuO + CeO ₂ 0-2% and not containing Bi ₂ O ₃ An electrode coating glass is provided.

  According to the present invention, lead-free glass for flat fluorescent lamp electrode coating is obtained.

  The lead-free glass of the present invention (hereinafter referred to as the glass of the present invention) is usually powdered.

  For example, the glass powder of the present invention is made into a glass paste using an organic vehicle or the like for imparting printability, and the glass paste is applied onto the electrode formed on the glass substrate and fired to coat the electrode. . The organic vehicle is obtained by dissolving a binder such as ethyl cellulose in an organic solvent such as α-terpineol. Further, the electrode may be coated using the green sheet method as described above.

What added the heat resistant pigment and the ceramic filler to the glass powder of this invention as needed may be used as an electrode coating material.
Examples of heat-resistant pigments include black pigments such as composite oxide powders mainly composed of chromium and copper, composite oxide powders mainly composed of chromium and iron, white pigments such as rutile type titanium oxide powders and anatase type titanium oxide powders, etc. Is exemplified.
Examples of the ceramic filler include silica powder and alumina powder capable of adjusting dielectric constant and sinterability.

  The glass of the present invention is particularly suitable for coating transparent electrodes and silver electrodes.

It is preferable that Ts of the glass of this invention is 450-650 degreeC. If it exceeds 650 ° C., a commonly used glass substrate (glass transition point: 550 to 620 ° C.) may be deformed during firing.
In the case of using a glass substrate having a glass transition point of 610 to 630 ° C., Ts is preferably 630 ° C. or less, and more preferably 580 to 600 ° C.
In the case of using a glass substrate having a glass transition point of 550 to 560 ° C., Ts is preferably less than 580 ° C., and preferably 530 ° C. or more.
Further, when used for an electrode-coated glass layer having a single layer structure, Ts is preferably 520 ° C. or higher, more preferably 550 ° C. or higher, and a glass substrate having a glass transition point of 610 to 630 ° C. is used. In particular, the temperature is preferably 580 ° C. or higher.

As the glass substrate, those having α of 80 × 10 ^{−7 to} 90 × 10 ⁻⁷ / ° C. are usually used. Therefore, in order to match the expansion characteristics with such a glass substrate and prevent warpage of the glass substrate and a decrease in strength, α of the glass of the present invention is preferably 60 × 10 ^{−7 to} 90 × 10 ⁻⁷ / ° C. More preferably, it is 70 * 10 < ^-7 > -85 * 10 < ^-7 > / degreeC.
The glass of the present invention preferably has a Ts of 450 to 650 ° C. and α of 60 × 10 ^{−7 to} 90 × 10 ⁻⁷ / ° C.

The relative dielectric constant (ε) at 1 MHz of the glass of the present invention is preferably 9.5 or less. If it exceeds 9.5, the capacitance of the PDP cell becomes too large, and the power consumption of the PDP may increase. More preferably, it is 9 or less, Especially preferably, it is 8.5 or less.
The specific resistance (ρ) at 250 ° C. of the glass of the present invention is preferably 10 ⁹ Ωcm or more. If it is less than 10 ⁹ Ωcm, electrical insulation failure may occur.

  It is preferable that the glass of the present invention does not exhibit a silver coloring phenomenon when it is used for coating a silver electrode on a substrate, or is not noticeable even if it exhibits a silver coloring phenomenon. The silver coloring phenomenon is a phenomenon in which, for example, when a silver-containing bus electrode formed on a transparent electrode on a glass substrate is covered with glass, silver diffuses into the glass and the glass is colored brown or yellow. .

Next, the composition of the glass of the present invention will be described using a mole percentage display.
B ₂ O ₃ is a component that stabilizes the glass and is essential. If it is less than 20%, the glass becomes unstable. It is preferably 22% or more, and more preferably 25% or more when it is desired to increase Ts or decrease ε. If it exceeds 50%, Ts becomes high. Preferably it is 45% or less, typically 40% or less.

SiO ₂ is a component that stabilizes the glass and is essential. In addition, it has the effect of suppressing the silver coloring phenomenon. If it is less than 5%, the glass becomes unstable and the weather resistance deteriorates. Want to increase the Ts or T _550, preferably in the case of such desirable to reduce the epsilon 7% or more, more preferably 10% or more, particularly preferably 13% or more. If it exceeds 35%, Ts becomes high. It is preferably 29% or less, more preferably 25% or less, and typically 24% or less.

ZnO is a component that lowers Ts and is essential. If it is less than 10%, Ts becomes high. Preferably it is 15% or more, More preferably, it is 17% or more. If it exceeds 30%, crystals tend to precipitate during firing and _T550 may be lowered. It is preferably 29% or less, more preferably 28% or less, and typically 25% or less.

Al ₂ O ₃ is not essential, but may be contained up to 10% in order to stabilize the glass. If it exceeds 10%, devitrification tends to occur. Preferably it is 8% or less, More preferably, it is 7% or less. When Al ₂ O ₃ is contained, the content is preferably 2% or more.
The total B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ content of B ₂ O ₃ , SiO ₂ and Al ₂ O ₃ is preferably 46% or more in the glass of the present invention, particularly in the glass 1. If it is less than 46%, the ε may increase. More preferably, it is 48% or more, and particularly preferably 49% or more.

SrO is not essential, but may be contained up to 10% in order to improve water resistance, suppress phase separation, or increase α. If it exceeds 10%, Ts tends to be high, or T ₅₅₀ may be low. Preferably it is 7% or less, More preferably, it is 5% or less, Most preferably, it is 4% or less. When it is desired to increase _T550 , it is preferably 3% or less or 2% or less.

BaO suppresses phase separation has the effect of increasing the α be increased, or _{T 550,} is essential. If it is less than 6%, the effect is small. Preferably it is 7% or more, typically 8% or more. If it exceeds 16%, α will be too large. Preferably it is 14% or less.

Li ₂ O has an effect of decreasing Ts, increasing α, or increasing T ₅₅₀ and is essential. If it is less than 2%, the effect is small. Preferably it is 2.5% or more, More preferably, it is 4% or more, Most preferably, it is 5% or more. If it exceeds 16%, α becomes too large.
Typically, Li ₂ O is 4 to 16%, and BaO is 5 to 14%.
Both Na ₂ O and K ₂ O are not essential, but either one or both may be contained within a total range of up to 10% in order to decrease Ts or increase α. If it exceeds 10%, α will be too large.

When Na ₂ O is contained, the content is preferably 9% or less. If it exceeds 9%, T _{550 tends to} be low. Content of Na ₂ O in the case of such is desired to further increase the T ₅₅₀ is preferably at most 6%.
When K ₂ O is contained, its content is preferably 9% or less. If K ₂ O exceeds 9%, it is difficult to match the expansion characteristics with the glass substrate, or the T ₅₅₀ may be lowered when applied to the front substrate of the PDP. The content of K ₂ O is more preferably 6% or less, particularly preferably 4% or less, and most preferably 3% or less.
The total Li ₂ O + Na ₂ O + K ₂ O content of Li ₂ O, Na ₂ O and K ₂ O is preferably 16% or less. _{Further, Li 2 O + Na 2 O} + K 2 O is preferably 4% or more. Typically, it is 6% or more or 7% or more.

In the glass 1, Bi ₂ O ₃ is not essential, but may be contained up to 9% in order to reduce Ts. If it exceeds 9%, ε may be high. Preferably it is 5% or less, More preferably, it is 4% or less. It is preferable not to contain Bi ₂ O ₃ or to contain Bi ₂ O ₃ in a range of less than 1 mol%. The glass 2 contains no _Bi 2 _{O 3.}
The molar ratio (B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ ) / (Bi ₂ O ₃ + BaO) is preferably 3.25 or more for glass 1 and 3.25 or more for glass 2. If it is less than 3.25, ε becomes large or there is a risk of it. More preferably, it is 3.8 or more.

Both CuO and CeO ₂ are not essential, but may be contained up to 2% in total when it is desired to suppress the silver coloring phenomenon. In this case, any one of them may be contained, but CuO is preferably contained, more preferably both. If CuO + CeO ₂ exceeds 2%, the electrode-coated glass layer is markedly colored and _T550 is lowered. Preferably it is 1.6% or less. When CuO and / or CeO ₂ is contained, CuO + CeO ₂ is preferably 0.2% or more, more preferably 0.4% or more. When both CuO and CeO ₂ are contained, each content is preferably 0.1 to 0.8%.

  When CuO is contained, the content is preferably 0.1% or more, more preferably 0.2% or more, and particularly preferably 0.3% or more.

When CeO ₂ is contained, its content is preferably at least 0.1%, more preferably at least 0.2%, particularly preferably at least 0.4%.

When it is desired to further suppress the silver coloring phenomenon in the glass 1, it is preferable that Bi ₂ O ₃ is 1% or more and CuO + CeO ₂ is 0.2% or more, Bi ₂ O ₃ is 1.5% or more and It is more preferable that CuO + CeO ₂ is 0.5% or more.
In this case, when CuO is contained by 0.2% or more, for example, the total ZnO + Na ₂ O + K ₂ O content of ZnO, Na ₂ O and K ₂ O is preferably 30% or less. If it exceeds 30%, T _{550 tends to} be low. More preferably, it is 26% or less.

The glass of the present invention consists essentially of the above components, but may contain other components as long as the object of the present invention is not impaired. When such components are contained, the total content thereof is preferably 10% or less, more preferably 5% or less.
Examples of the other components include TiO ₂ , ZrO ₂ , La ₂ O ₃ for adjusting Ts or α, stabilization of glass, improvement of chemical durability, etc., halogen components such as F for lowering Ts, Etc. are exemplified.
The glass of the present invention does not contain PbO.

When the glass of the present invention contains MgO or CaO, the total content thereof is 8% or less in the glass 1 and preferably 8% or less in the glass 2. If it exceeds 8%, T ₅₅₀ may be decreased, or there is a possibility of this. When it is desired to make T ₅₅₀ higher, MgO + CaO is preferably 3% or less, more preferably MgO and CaO are each 2% or less, and particularly preferably no MgO is contained.

When it is desired to suppress the silver coloring phenomenon in the glass 1, SiO ₂ is 7% or more, Al ₂ O ₃ is 0 to 8%, SrO is 0 to 5%, Li ₂ O is 2.5% or more, ZnO + Na _{When 2} O + K ₂ O is 30% or less, CuO is 0.2% or more, and MgO or CaO is contained, MgO + CaO is preferably 3% or less. More preferably, Al ₂ O ₃ is 0 to 7%, Li ₂ O is 4% or more, and ZnO + Na ₂ O + K ₂ O is 26% or less. Further, BaO is more preferably 7% or more.

When Ts is desired to be 530 ° C. or higher and lower than 580 ° C. in the glass of the present invention, typically, B ₂ O ₃ is 23 to 38%, SiO ₂ is 6 to 23%, ZnO is 21 to 28%, Al ₂ O ₃ is 4 to 6%, BaO is 8 to 11%, Li ₂ O is 10 to 15% and Na ₂ O + K ₂ O is 0.5 to 6%, or Li ₂ O is 8 to 8%. 15% and _Na 2 O + _{K 2} O is 2-6%.

When Ts is set to 580 ° C. or more and 630 ° C. or less and silver color development is desired to be suppressed, typically, B ₂ O ₃ is 29 to 39%, SiO ₂ is 12 to 23%, ZnO is 20 to 28%, Al ₂ O ₃ is 2 to 8%, BaO 14% or less, Li ₂ O is 13 percent or _less, Na ₂ O + _K 2 O 0 to 6%, is CuO + CeO ₂ is more than 0.2 mol%.

For Examples 1 to 75, the raw materials were mixed and mixed so as to have a composition expressed in mole percentages in the columns from B ₂ O ₃ to CeO ₂ in the table, and a platinum crucible was placed in an electric furnace at 1200 to 1350 ° C. It was melted for 1 hour, formed into a sheet glass, and then pulverized with a ball mill to obtain a glass powder. Incidentally, the molar percentage display content of _{B 2 O 3 + SiO 2 +} Al 2 O 3 in the column of the table of B + Si + Al, the molar ratio in the column of _{BSiAl / BiBa (B 2 O 3} + SiO 2 + Al 2 O 3) / (Bi 2 O ₃ + BaO) respectively.
Examples 1 to 23 and 31 to 75 are examples, and examples 24 to 30 are comparative examples.

For these glass powders, the softening point Ts (unit: ° C.), the crystallization peak temperature Tc (unit: ° C.), the average linear expansion coefficient α (unit: 10 ⁻⁷ / ° C.), the relative dielectric constant ε, and the specific resistance. ρ (unit: Ωcm) was measured as described below. The results are shown in the table, but the blank indicates that no measurement was performed.
Ts, Tc: Measured with a differential thermal analyzer in the range up to 800 ° C. “−” In the column of Tc indicates that no crystallization peak was observed up to 800 ° C. In the case where a crystallization peak is observed up to 800 ° C., crystals may precipitate during firing, and the transmittance may not be increased.
α: After the glass powder is pressure-molded, a fired body obtained by firing at a temperature 30 ° C. higher than Ts for 10 minutes is processed into a cylindrical shape having a diameter of 5 mm and a length of 2 cm, and an average of 50 to 350 ° C. with a thermal dilatometer. The linear expansion coefficient was measured.

ε: The glass powder was remelted, formed into a plate shape, and then processed to obtain a measurement sample of 50 mm × 50 mm × thickness 3 mm. Aluminum electrodes were formed on both surfaces of the measurement sample by vapor deposition, and the relative dielectric constant at a frequency of 1 MHz was measured using an LCR meter.
The specific resistance was measured in an electric furnace at 250 ° C. using the same sample as the measurement sample of ρ: ε. The table shows the common logarithm of ρ expressed in units.

Further, 100 g of the glass powder was kneaded with 25 g of an organic vehicle to prepare a glass paste. The organic vehicle was prepared by dissolving 12% of ethyl cellulose in α-terpineol in terms of mass percentage.
Next, a glass substrate having a size of 50 mm × 75 mm and a thickness of 2.8 mm was prepared, and a silver paste for screen printing was printed and fired on the surface of the glass substrate having a surface of 48 mm × 73 mm to form a silver layer. The glass substrate has a mass percentage display composition of SiO ₂ 58%, Al ₂ O ₃ 7%, Na ₂ O 4%, K ₂ O 6.5%, MgO 2%, CaO 5%, SrO 7%. BaO 7.5%, ZrO ₂ 3%, and a glass transition point of 626 ° C. and α of 83 × 10 ⁻⁷ / ° C.

A glass substrate on which a silver layer is thus formed and a glass substrate on which no silver layer is formed are prepared, and the glass paste is uniformly screen-printed on each 50 mm × 50 mm portion, and then at 120 ° C. for 10 minutes. Dried. These glass substrates were heated at a heating rate of 10 ° C./min until the temperature reached Ts, and the temperature was maintained at Ts for 30 minutes, followed by firing. Thus, the thickness of the glass layer formed on the glass substrate was 30-35 micrometers.
For a sample in which the glass layer was formed on a glass substrate on which no silver layer was formed, the light transmittance (unit:%) and turbidity (unit:%) at a wavelength of 550 nm were measured as described below. . Moreover, the presence or absence of silver coloring was investigated about the sample in which the said glass layer was formed on the glass substrate in which the silver layer was formed. The results are shown in the table.

  Transmittance: The transmittance of light having a wavelength of 550 nm was measured using a self-recording spectrophotometer U-3500 (integrating sphere type) manufactured by Hitachi, Ltd. (the state where no sample was taken was defined as 100%). This transmittance is preferably 78% or more, more preferably 81% or more. In addition, what added 1% to this transmittance | permeability is equivalent to the transmittance | permeability of the light of wavelength 550nm with respect to a PDP front substrate at the time of forming the said glass layer for coating | cover on a transparent electrode.

Turbidity: A haze meter (C light source using a halogen bulb) manufactured by Suga Test Instruments Co., Ltd. was used. The light from the halogen sphere was made incident on the sample as a parallel light beam through a lens, and the total light transmittance Tt and the diffuse transmittance Td were measured with an integrating sphere.
Turbidity (%) = (Td / Tt) × 100.
This turbidity is preferably 25% or less, more preferably 20% or less. In addition, what added 1% to this turbidity is equivalent to the turbidity with respect to the PDP front substrate at the time of forming the said glass layer for coating | cover on a transparent electrode.

Silver color development: The glass layer color was colorless, blue or blue-green when the silver color development was suppressed, and the glass layer color yellow when the silver color development was marked as x. The results are shown in the column of silver coloring A in the table.
In order to make the silver coloring phenomenon more prominent, the temperature is lower than Ts, that is, 590 ° C. for Ts of 600 ° C. or higher, and 570 ° C. for Ts of 580 ° C. or higher and lower than 600 ° C. The glass layers obtained by firing at 550 ° C. for Ts of 560 ° C. or more and less than 580 ° C. were evaluated. The results are shown in the column of silver coloring B in the table. In the same column, ○ is the same as ○ of silver color A, but Δ is silver color due to the fact that the color of the glass layer is light yellow, yellowish green, etc. X indicates that the color of the glass layer is markedly yellow and silver coloration is significant.

  About Examples 76-101, Ts, (alpha), and (epsilon) were calculated | required by calculation from the composition. The results are shown in the table.

Claims (12)

In mole% based on the following _{oxides, B 2 O 3 20~50%,} SiO 2 5~35%, 10~30% ZnO, Al 2 O 3 0~10%, SrO 0~10%, BaO 6~ 16%, Li ₂ O 2-16%, Na ₂ O + K ₂ O 0-10%, Bi ₂ O ₃ 0-9%, CuO + CeO ₂ 0-2%, consisting essentially of (B ₂ O ₃ + SiO ₂ A lead-free glass for covering a flat fluorescent lamp electrode in which + Al ₂ O ₃ ) / (Bi ₂ O ₃ + BaO) is 3.25 or more and MgO or CaO is contained, and MgO + CaO is 8 mol% or less. The lead-free glass for covering a flat fluorescent lamp electrode according to claim 1, wherein B ₂ O ₃ + SiO ₂ + Al ₂ O ₃ is 46 mol% or more. In terms of mol%, SiO ₂ is 7% or more, Al ₂ O ₃ is 0 to 8%, SrO is 0 to 5%, Li ₂ O is 2.5% or more, ZnO + Na ₂ O + K ₂ O is 30% or less, CuO The lead-free glass for covering a flat fluorescent lamp electrode according to claim 1 or 2, wherein MgO + CaO is 3% or less when MgO or CaO is contained. The lead-free glass for covering a flat fluorescent lamp electrode according to claim 1, wherein Li ₂ O + Na ₂ O + K ₂ O is 16 mol% or less. Bi ₂ O ₃ does not contain, or _Bi 2 _{O 3} the flat fluorescent lamp for covering electrodes lead-free glass according to claim 1 containing in the range of less than 1 mole%. Bi ₂ O ₃ is 1 mol% or more, CuO + flat fluorescent lamp for covering electrodes lead-free glass according to any one of claims 1 to 4 CeO ₂ is not less than 0.2 mol%. In mole% based on the following _{oxides, B 2 O 3 20~50%,} SiO 2 5~35%, 10~30% ZnO, Al 2 O 3 0~10%, SrO 0~10%, BaO 6~ Lead-free glass for covering a flat fluorescent lamp electrode, which is essentially composed of 16%, Li ₂ O 2-16%, Na ₂ O + K ₂ O 0-10%, CuO + CeO ₂ 0-2%, and does not contain Bi ₂ O ₃ . The lead-free glass for covering a flat fluorescent lamp electrode according to claim 7, wherein CuO + CeO ₂ is 0.2 mol% or more. In terms of mol%, B ₂ O ₃ is 23 to 38%, SiO ₂ is 6 to 23%, ZnO is 21 to 28%, Al ₂ O ₃ is 4 to 6%, BaO is 8 to 11%, 9. Li ₂ O is 10 to 15% and Na ₂ O + K ₂ O is 0.5 to 6%, or Li ₂ O is 8 to 15% and Na ₂ O + K ₂ O is 2 to 6%. Lead-free glass for covering flat fluorescent lamp electrodes according to any one of the above. In terms of mol%, B ₂ O ₃ is 29 to 39%, SiO ₂ is 12 to 23%, ZnO is 20 to 28%, Al ₂ O ₃ is 2 to 8%, BaO is 14% or less, Li ₂ O is 13% or _less, Na ₂ O + _K 2 O 0 to 6%, the plane fluorescent lamp for covering electrodes lead-free glass according to any one of claims 1 to 7 CuO + CeO ₂ is not less than 0.2 mol%. The softening point is 450 to 650 ° C, and the average linear expansion coefficient at 50 to 350 ° C is 60 x 10 ^{-7 to} 90 x 10 ^-7 / ° C. The flat fluorescent lamp electrode coating according to any one of claims 1 to 10 Lead-free glass. The lead-free glass for covering a flat fluorescent lamp electrode according to any one of claims 1 to 11, wherein a relative dielectric constant at 1 MHz is 9.5 or less.