KR100685112B1 - Dielectric composition useful for light transparent layer in pdp - Google Patents

Abstract

The dielectric composition for use in forming the light transparent dielectric layer in the plasma display panel of the present invention comprises 90 to 100 wt% glass powder and 0 to 10 wt% ceramic powder. The glass powder is essentially composed of 15 to 45 weight percent BaO, 20 to 45 weight percent ZnO, 15 to 35 weight percent B ₂ O ₃ , 3 to 15 weight percent SiO ₂ and 0 to 24.5 weight percent PbO. Glass powder.

Description

Dielectric composition useful for light transmitting layer of plasma display panel {DIELECTRIC COMPOSITION USEFUL FOR LIGHT TRANSPARENT LAYER IN PDP}

FIELD OF THE INVENTION The present invention relates to dielectric forming materials useful in plasma display panels (PDPs), and more particularly to dielectric compositions used to form light transmissive dielectric layers on front glass plates of high strain points of PDPs.

In general, a PDP has a front glass plate in which a plurality of electrodes are arranged to act with electrodes located on the rear glass plate facing the front glass plate with a gap therebetween to generate a plasma discharge. A transparent dielectric layer is formed on the glass plate to cover the electrodes to maintain the generated plasma discharge.

Typically, the front glass plate is made of soda lime glass or other high strain glass, while the light transmissive dielectric layer is formed from a dielectric material comprising low melting glass powder, such as excess Pb containing glass powder. When forming the light transmissive dielectric layer, the dielectric material is ignited or baked at the softening point of the low melting glass powder to prevent the electrode from reacting with the metal.

As is known in the art, a dielectric material produces a dielectric layer having (1) a thermal expansion coefficient compatible with a glass plate, (2) an ignition temperature of 500 to 600 ° C., (3) high light transmittance and a high withstand voltage with reduced bubble amount. It is important to have various properties such as excellent defoamability during ignition.

JP-A 11-21148 describes a dielectric material using glass powder of PbO-B ₂ O ₃ -SiO ₂ -BaO glass having a coefficient of thermal expansion compatible with that of a high strain point glass plate. PbO-B ₂ O ₃ -SiO ₂ -BaO glass has a rapid change in viscosity over the softening point, thus facilitating defoaming.

The excellent defoaming properties allow dielectric materials using PbO-B ₂ O ₃ -SiO ₂ -BaO glass powders to provide dielectric layers with high light transmittance, but the resulting dielectric layers have residual large bubbles having diameters of 30 μm or more. There is a problem of having.

SUMMARY OF THE INVENTION An object of the present invention is to provide a dielectric material that is compatible with a glass plate having a high strain point in thermal expansion coefficient, is capable of defoaming at ignition at a temperature near the softening point, and can provide a transparent dielectric layer without leaving large bubbles. It is.

In certain glasses, such as the PbO-B ₂ O ₃ -SiO ₂ -BaO glasses described above, where the viscosity change is very rapid over the softening point, we find that almost all bubbles are released from the glass at relatively low temperatures during the initiation of the firing process, It was found that bubbles remained in the glass as residual bubbles, and then the remaining bubbles expanded to large bubbles due to the rise of the glass temperature in the subsequent ignition process.

In order to improve the PbO-B ₂ O ₃ -SiO ₂ -BaO glasses described above, the inventors, on the one hand, have made the PbO in PbO-B ₂ O ₃ -SiO ₂ -BaO glasses to adjust the viscosity change relatively slightly over the softening point. Attempts were made to reduce the content to 24.5% by weight or less. On the other hand, attempts were made to increase the content of BaO to compensate for the lower coefficient of thermal expansion due to a decrease in PbO content.

According to the present invention there is provided a dielectric composition for use in forming a light transmissive dielectric layer in a plasma display panel, the composition comprising 90 to 100% by weight of glass powder and 0 to 10% by weight of ceramic powder, The powder contains as essential components 15 to 45 wt% BaO, 20 to 45 wt% ZnO, 15 to 35 wt% B ₂ O ₃ , 3 to 15 wt% SiO ₂ and 0 to 24.5 wt% PbO It is glass powder.

BaO is a component for adjusting the viscosity at a high temperature that affects the anti-foaming property of the glass and increasing the thermal expansion coefficient of the glass. The content of BaO is 15 to 45% by weight, preferably 20.5 to 40% by weight. A BaO content of less than 15% by weight lowers the defoaming and also lowers the coefficient of thermal expansion of the glass formed to extremely low levels incompatible with high strain glass plates. If the BaO content exceeds 45% by weight, the glass formed has an excessively high coefficient of thermal expansion which is incompatible with the coefficient of thermal expansion of high strain point glass.

ZnO is a component for lowering the softening point and adjusting the thermal expansion coefficient of the glass. The content of ZnO is 20 to 45% by weight, preferably 22 to 42% by weight. If the content is selected below 20% by weight, the function of ZnO described above is not achieved. If the content is selected to exceed 45% by weight, the coefficient of thermal expansion becomes too low.

B ₂ O ₃ is a glass forming component for broadening the vitrification range of the composition and should be contained at 15 to 40% by weight, preferably 16 to 33% by weight. Less than 15% by weight of B ₂ O ₃ is likely to cause devitrification of the glass during ignition. If the content exceeds 40% by weight, the softening point becomes too high, making it difficult to ignite at a temperature of 600 ° C or lower.

SiO ₂ is also a glass forming component, the content of which should be selected from 3 to 15% by weight, preferably 4 to 13% by weight. If SiO ₂ is less than 3% by weight, the glass formed is easily devitrified during ignition. On the other hand, in the case of using the SiO ₂ in 15 weight% has to too high a softening point of glass formed over the change in viscosity over the softening point is slow and difficult to degas.

PbO is a component for lowering the softening point of the glass, the content of which should be selected from 0 to 24.5% by weight, preferably 0 to 24% by weight. If the content of PbO is chosen to be higher than 24.5% by weight, the viscosity change of the glass formed is too fast over the softening point to promote the growth of bubbles, thus leaving the remaining large bubbles in the ignited layer.

The weight-based content of PbO, B ₂ O ₃ and SiO ₂ expressed by weight should be less than 1, preferably less than 0.9, by the ratio of (PbO ₂ / (B ₂ O ₃ + SiO ₂ )). When the ratio is selected to be one or more, the glass formed has an excessively rapid change in viscosity over the softening point to promote bubble growth. Residual bubbles in the fired layer may be at least 30 μm in diameter.

In addition, the content of PbO and BaO expressed by weight is 1.5 by the ratio of (PbO / BaO) so that the glass formed can easily have a coefficient of thermal expansion compatible with that of the high strain point glass plate. Or less, preferably 1.3 or less.

For certain purposes, other components may be added to the glass, for example CaO and MgO not more than 10% of the total amount, and the Ag electrode and the transparent dielectric layer discolor to yellow to increase the coefficient of thermal expansion. CuO can be added up to 2% to prevent the electrode from becoming blue.

According to another aspect of the invention, the glass powder preferably has an average particle size (D50) of 3.0 μm or less and a maximum particle size (D _max ) of 20 μm or less. When the average particle size and the maximum particle size exceed the upper limit, large gaps exist between adjacent glass particles, thereby facilitating the generation of large bubbles remaining in the fired dielectric layer.

The dielectric composition according to the present invention may comprise ceramic powders such as alumina, zircon, zirconia and / or titania (titanium oxide) in addition to the glass powder to enhance the strength of the fired layer and to adjust its appearance. The maximum particle size (D _max ) of the ceramic powder is preferably 15 μm or less.

In terms of content, the glass powder and the ceramic powder are 90 to 100% by weight and 0 to 10% by weight, respectively. When the content of the ceramic powder exceeds 10% by weight, the formed ignition dielectric layer scatters visible light and becomes opaque.

Examples of the present invention will be described below.

Tables 1 and 2 describe examples (sample numbers 1 to 8) and comparative examples (sample numbers 9) of the present invention.

Table 1

Table 2

Each example was prepared by the following steps.

The amount of raw material was mixed for each of the samples listed in Tables 1 and 2 and melted in a platinum crucible at 1300 ° C. for 2 hours. Thereafter, the molten glass was formed into a thin plate shape, pulverized and classified to obtain a glass powder having an average particle size (D50) of 3.0 µm or less and a maximum particle size (D _max ) of 20 µm or less. The transition point and softening point of the glass powder were measured and recorded. Sample number 8 glass powder was mixed with aluminum powder to obtain a mixed powder thereof.

Average particle size (D50) and maximum particle size (D _max ) were confirmed using a particle size distribution meter of the laser diffraction type "Microtrack SPA" manufactured by Nikkiso Ltd.

For each sample, the coefficient of thermal expansion, the flash point, the thickness of the fired layer and the spectral transmittance at 550 nm were measured. In addition, bubbles having a diameter of 30 µm or more present in the fired layer were counted. The measured data is shown in Tables 1 and 2.

From Tables 1 and 2, the glass transition points of Sample Nos. 1 to 8 of Examples of the present invention were 485 to 915 ° C, the softening point was 580 to 620 ° C, the temperature difference between the transition point and the softening point was 95 to 105 ° C, and the coefficient of thermal expansion was 74. It can be seen that it is from 82 x 10 ^-7 / ℃, the ignition temperature is 570 to 600 ℃. The fired layer had a thickness of 28 to 34 mu m, a transmittance of 79% or more at a wavelength of 550 nm, and only three or less large bubbles existed therein. Compared with such a sample, the sample number 9 of the comparative example had a glass transition temperature of 480 ° C, a softening point of 570 ° C, and a temperature difference between the transition point and the softening point of 90 ° C. Therefore, the viscosity change was too fast in the firing temperature range to promote bubble growth. Accordingly, the fired layer had very many large bubbles as fifteen bubbles.

In measuring the glass transition point and softening point, a macroscopic differential thermal analyzer was used, and the values of the first and fourth inflection points were selected as the glass transition temperature and the softening point, respectively.

The coefficient of thermal expansion was measured according to JIS R 3102 at a temperature of 30 to 300 ° C for the sample pieces formed by the following steps. Each sample powder was press-molded, ignited and ground to form sample pieces of cylindrical rods 4 mm in diameter and 40 mm in length.

The thickness of the fired layer, the transmittance and the number of large bubbles were obtained in the following manner. Each sample powder was mixed in a 5% terpineol solution of ethyl cellulose, kneaded using a 3-roll mill to form a paste, and then subjected to screen printing to obtain a 30 μm thick glass plate on a high strain point glass plate. A fired layer (coefficient of thermal expansion is 83 × 10 ⁻⁷ / ° C.) was obtained and fired in an electric furnace for 10 minutes at the fire temperature. The thickness of the fired layer was checked using a digital micrometer.

By setting a high strain point glass plate with a ignited layer on the sample setting side of the spectrophotometer, the transmittance for a wavelength of 550 nm was specified using an integrating sphere of a spectrophotometer.

A stereoscopic mirror (grade 30) was used to count large bubbles with a diameter of 30 μm or more observed within the 3 cm × 4 cm area of the surface of the fired layer.

As described above, the dielectric composition of the present invention is useful for forming a light transmissive dielectric layer onto a front glass plate that has a high strain point and covers an electrode formed on the front glass plate.

Claims (4)

A dielectric composition for use in forming a light transmissive dielectric layer in a plasma display panel, comprising 90 to 100 weight percent glass powder and 0 to 10 weight percent ceramic powder, wherein the glass powder comprises 15 to 45 weight percent BaO, A dielectric composition that is a glass powder comprising 20 to 45 weight percent ZnO, 15 to 35 weight percent B ₂ O ₃ , 3 to 15 weight percent SiO ₂ and 0 to 24.5 weight percent PbO as essential components. The dielectric composition according to claim 1, wherein the contents of PbO, B ₂ O ₃ and SiO ₂ expressed by weight are measured to be less than 1 by a ratio of (PbO / (B ₂ O ₃ + SiO ₂ )). The dielectric composition according to claim 1, wherein the content of PbO and BaO expressed by weight is determined to be 1.5 or less by the ratio of (PbO / BaO). The dielectric composition of claim 1, wherein the average particle size (D50) of the glass powder is 3.0 µm or less and the maximum particle size (D _max ) is 20 µm or less.