KR100597149B1 - Lead-free Transparent Dielectric Composition for Preparing Green Sheet - Google Patents

Abstract

The present invention relates to a lead-free transparent dielectric composition for manufacturing a green sheet for forming a transparent dielectric material into a plasma display panel (hereinafter referred to as "PDP") plate, the lead-free transparent dielectric composition according to the present invention is Bi _2- O ₃ -B ₂ O ₃ -BaO-based lead-free transparent dielectric powder 64-70% by weight, azeotrope mixed solvent of methyl ethyl ketone and ethanol 21-24% by weight, fish oil 0.6-0.7% by weight as dispersant 5-12 wt% polyethyl methacrylate (PEMA) as binder and 0.5-6.0 wt% of a mixture of polyethylene glycol (PEG) and dibutylphthalate (DBP) in a 1: 1 weight ratio as plasticizer. The present invention also relates to a PDP member comprising a green sheet manufactured using the lead-free transparent dielectric composition and a transparent dielectric prepared using the green sheet.

Plasma Display Panel, Pb-Free Transparent Dielectric Composition, Green Sheet, Doctor Blade, Degreasing Temperature

Description

Lead-free transparent dielectric composition for preparing green sheet

BRIEF DESCRIPTION OF THE DRAWINGS The schematic diagram which shows an example of the surface discharge type plasma display panel of an AC drive system.

Figure 2 is a manufacturing process of the green sheet according to the present invention.

Figure 3 is a graph showing the thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) result data of the green sheet according to the present invention.

4 is a graph showing the transmittance of the transparent dielectric material according to the present invention.

5 is an electron scanning micrograph of a transparent dielectric cross section according to the present invention.

The present invention relates to a lead-free transparent dielectric composition for producing a green sheet for a plasma display panel (hereinafter referred to as "PDP"). More specifically, the present invention relates to a lead-free transparent dielectric composition for producing a green sheet for use in a dry film method of forming a transparent dielectric into a PDP top plate, a green sheet manufactured using the composition and this green The present invention relates to a member for a PDP comprising a transparent dielectric fabricated using a sheet.

A PDP is a device in which a plasma excites a phosphor from vacuum ultraviolet rays generated in a gas discharge and displays characters or graphics using visible light generated therefrom.

Referring to FIG. 1, the front substrate of the PDP is composed of an ITO electrode, a bus electrode, a transparent dielectric, and a dielectric protective film, and the back substrate is composed of an address electrode, a white dielectric, a partition, and a phosphor. Transparent dielectrics entering the PDP front substrate provide a charge memory function to the panel as a current limiting capacitor, and as the panel becomes larger, various researches on such transparent dielectrics are being conducted.

Currently, PbO-B ₂ O ₃ -SiO ₂ -based compositions are mainly used for the PDP transparent dielectric. However, PbO is a material that is generally stable in itself or frit, but when disposed, there is a problem of causing a chemical reaction with an acid or alkaline solution in the waste water to cause environmental pollution by soil and water pollution. Therefore, in accordance with regulations on future environmental pollution, a transparent dielectric composed of a lead-free transparent dielectric composition is required.

As a method of forming a transparent dielectric, there is a screen printing method commonly used. The thick film firing technique of the transparent dielectric material which depends on this method is likely to be bubble-prone and uneven surface due to several processes. Therefore, the film thickness is uneven, so the dielectric properties appear differently at different parts, resulting in poor brightness characteristics. In addition, since the mesh shape of the screen plate remains on the film forming material layer, the surface smoothness tends to be lowered. In addition, this method is accompanied with the problem that the larger the area, the more uneven the thickness as the panel is enlarged.

Dry film, a new method to replace the screen printing method, forms a film forming material layer (green sheet) on a support film, compresses the surface of a glass substrate on which electrodes are fixed, and forms a compressed film. It is a method of forming a transparent dielectric by heat-processing a material layer.

An object of the present invention is to provide a PDP member comprising a lead-free transparent dielectric composition for producing a green sheet used in the dry film method, a green sheet manufactured using the composition, and a transparent dielectric prepared using the green sheet. To provide.

Hereinafter, the present invention will be described in detail.

A first embodiment of the present invention relates to a lead-free transparent dielectric composition for producing a green sheet for forming a transparent dielectric layer of PDP.

The lead-free transparent dielectric composition of the present invention is Bi ₂ O ₃ -B ₂ O ₃ -BaO-based lead-free transparent dielectric powder 64-70% by weight, azeotrope mixed solvent of methyl ethyl ketone and ethanol 21-24% by weight, fish oil as a dispersant (fish oil) 0.6-0.7% by weight, mixture of polyethylene glycol (PEG) and dibutylphthalate (DBP) in a weight ratio of polyethyl methacrylate (PEMA) 5-12% by weight and 1: 1 by weight as plasticizer 0.5-6.0 By weight percent.

Bi ₂ O ₃ -B ₂ O ₃ -BaO-based transparent dielectric powder used as a lead-free transparent dielectric powder in the composition of the present invention is 50-60% by weight Bi ₂ O ₃ , 25-35% by weight B ₂ O ₃ , BaO 5 -10 wt%, SiO ₂ 0-5 wt%, Al ₂ O ₃ 0-5 wt%, ZnO 0-5 wt% and SrO 0-1 wt%, followed by melting and quenching to form glass flakes. It is prepared by grinding after making. As described above, the composition of the present invention does not include PbO, that is, it includes a lead-free transparent dielectric powder, so that there is no problem such as environmental pollution caused by using the transparent dielectric powder containing PbO.

The lead-free transparent dielectric composition of the present invention is characterized by using polyethyl methacrylate as a binder in an amount of 5 to 12% by weight based on the total weight of the composition in order to impart tackiness to a glass substrate. When using less than 5% by weight of polyethyl methacrylate, not only is it difficult to form a green sheet, it is not separated from the supporting film, and when it is used more than 12% by weight, it takes a long time to burn out and a high shrinkage rate when firing. Problems such as cracking or warping may occur.

Polyethyl methacrylate used as the binder in the present invention is 400 ℃ or less Since it is completely decomposed at temperature, it does not act as an impurity in the transparent dielectric powder entering the PDP whose glass transition temperature (T _g ) is around 450 ° C. That is, the polyethyl methacrylate does not affect the transparent dielectric powder itself because the transparent dielectric powder is completely decomposed at a temperature much lower than the temperature at which viscous flow occurs.

In addition, the composition of the present invention contains fish oil as a dispersant 0.6-0.7% by weight relative to the total weight of the composition in order to improve the dispersibility of the transparent dielectric powder. If the amount of fish oil is less than 0.6% by weight, the solvent is present between the pores of the agglomerate, so that the solvent shortage occurs, so that uniform mixing is difficult.If the content is more than 0.7% by weight, the dispersion effect is due to the crosslinking between the dispersants. Falls.

In addition, in the composition of the present invention, the solvent serves to impart proper fluidity or plasticity, and good film formability to the composition, and the azeotropic mixed solvent of methyl ethyl ketone and ethanol is in an amount of 21 to 24% by weight based on the total weight of the composition. It is preferably used in the present invention. If the azeotrope mixed solvent is included in the composition of the present invention in less than 21% by weight, the viscosity of the composition becomes high, and the tape can not be prepared when the tape is cached, and when included in more than 24% by weight, the solvent is degassed to deflate the composition to the desired viscosity. There is a problem that takes a lot of time because it must evaporate.

The composition of the present invention comprises, as a plasticizer, a mixture of polyethylene glycol (PEG) and dibutylphthalate (DBP) in a 1: 1 weight ratio, based on the total weight of the composition, from 0.5 to 6.0% by weight. If the plasticizer content is less than 0.5% by weight, green sheet handling is poor due to the lack of flexibility, and if it exceeds 6.0% by weight, cracking may occur during degreasing.

A second embodiment of the present invention relates to a green sheet used for forming a transparent dielectric of PDP. The green sheet of the present invention is characterized by using the entire lead-free transparent oil composition according to the present invention.

The overall manufacturing process for producing the green sheet according to the present invention is shown in FIG.

Referring to FIG. 2, the Bi ₂ O ₃ -B ₂ O ₃ -BaO-based lead-free transparent dielectric powder 64 to 70 wt%, the solvent 21 to 24 wt%, and the dispersant 0.6 to 0.7 wt% based on the total weight of the composition. After mixing and grinding with a ball mill for about 24 hours, 5 to 12% by weight of the binder and 0.5 to 6.0% by weight of the plasticizer are added to the total weight of the composition and mixed and ground for about 24 hours with the ball mill again. Thereafter, a small amount of antifoaming agent is added to undergo a defoaming process, tape casting onto a support film with a doctor blade, and drying to prepare a green sheet according to the present invention.

The green sheet according to the present invention manufactured as described above can efficiently form a transparent dielectric required for a large panel while maintaining uniformity of the film thickness.

A third embodiment of the present invention relates to a member for PDP comprising a lead-free transparent dielectric prepared using the green sheet described above. The lead-free transparent dielectric material has a transmittance of 78% or more (wavelength: 550 nm), a breakdown voltage of 4.5 kV or more, and no pinholes or cracks in the membrane.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the present invention is not limited by the following examples.

<Example>

The raw material of the composition used in each Example is as follows.

Lead-free transparent dielectric powder: Bi ₂ O ₃ (56.79 wt%), B ₂ O ₃ (31.08 wt%), BaO (7.29 wt%) SiO ₂ (1.63 wt%), Al ₂ O ₃ (1.62 wt%), ZnO (1.12 wt.%) and SrO (0.47 wt%) were mixed sufficiently, and then after using the alumina crucible made of the queen-etched glass plate on top of the molten steel at a high temperature and a Bi ₂ O ₃ -B ₂ O ₃ -BaO ground to System powder (average particle diameter: 2.196 µm, dielectric constant 9.39 MHz, linear expansion coefficient 75.7 x 10 ^-7 / K, Tg 481 ° C).

Dispersant: Fish oil (Aldrich, USA).

Binder: Polyethyl methacrylate (Aldrich, USA).

Plasticizer: A 1: 1 (weight ratio) mixture of polyethylene glycol and dibutyl phthalate.

Solvent: A 6: 4 (volume ratio) mixed solvent of methyl ethyl ketone and ethanol.

In addition, the mechanical properties of the green sheet produced in each example were measured as follows.

How to measure mechanical properties of green sheets

Mechanical properties such as tensile strength and strain of the green sheet were measured after fabricating the specimen according to ASTM D 638IV using a universal testing machine (Universal Testing Machine (Instron, UK)).

<Example 1>

Lead-free transparent dielectric powder of Bi ₂ O ₃ -B ₂ O ₃ -BaO-based 64.59 wt%, 21.53 wt% solvent, and 0.65 wt% dispersant were mixed and pulverized in a ball mill for about 24 hours, followed by 9.93 wt% binder and plasticizer 3.30 Weight percent was added and again mixed and ground with a ball mill for about 24 hours. Subsequently, a small amount (about 1 cc) of antifoaming agent, SN-8024L (San Nopco Korea, Ltd.) was added, followed by a defoaming process, followed by a support film (SiO ₂ coated polyethylene film, thickness of 100 μm). The tape was cast on and dried to produce a green sheet.

The tensile strength and strain of the green sheet thus prepared were measured as described above, and the results are shown in Table 1 below.

<Example 2>

Example 1 except that 65.80 wt% of lead-free transparent dielectric powder of Bi ₂ O ₃ -B ₂ O ₃ -BaO system, 8.71 wt% of binder, 2.91 wt% of plasticizer, 0.66 wt% of dispersant, and 21.92 wt% of solvent were used. In the same manner as the green sheet was prepared. The tensile strength and strain of the green sheet thus prepared were measured as described above, and the results are shown in Table 1 below.

<Example 3>

Example 1 except that 66.99% by weight of lead-free transparent dielectric powder of Bi ₂ O ₃ -B ₂ O ₃ -BaO system, 7.51% by weight binder, 2.50% by weight plasticizer, 0.67% by weight dispersant and 22.33% by weight solvent were used. In the same manner as the green sheet was prepared. The tensile strength and strain of the green sheet thus prepared were measured as described above, and the results are shown in Table 1 below.

<Example 4>

Example 1, except that 68.17% by weight of Bi ₂ O ₃ -B ₂ O ₃ -BaO-based lead-free transparent dielectric powder, 6.33% by weight binder, 2.10% by weight plasticizer, 0.68% by weight dispersant and 22.72% by weight solvent were used. In the same manner as the green sheet was prepared. The tensile strength and strain of the green sheet thus prepared were measured as described above, and the results are shown in Table 1 below.

Example 5

Example 1 Except for using 69.34% by weight of lead-free transparent dielectric powder of Bi ₂ O ₃ -B ₂ O ₃ -BaO, 5.14% by weight of binder, 1.71% by weight of plasticizer, 0.69% by weight of dispersant and 23.11% by weight of solvent. In the same manner as the green sheet was prepared. The tensile strength and strain of the green sheet thus prepared were measured as described above, and the results are shown in Table 1 below.

<Example 6>

Example 1 except that 65.80 wt% of lead-free transparent dielectric powder of Bi ₂ O ₃ -B ₂ O ₃ -BaO system, 7.55 wt% of binder, 4.06 wt% of plasticizer, 0.66 wt% of dispersant, and 21.93 wt% of solvent were used. In the same manner as the green sheet was prepared. The tensile strength and strain of the green sheet thus prepared were measured as described above, and the results are shown in Table 1 below.

<Example 7>

Example 1 except that 65.80 wt% of lead-free transparent dielectric powder of Bi ₂ O ₃ -B ₂ O ₃ -BaO system, 8.71 wt% of binder, 2.90 wt% of plasticizer, 0.66 wt% of dispersant, and 21.93 wt% of solvent were used. In the same manner as the green sheet was prepared. The tensile strength and strain of the green sheet thus prepared were measured as described above, and the results are shown in Table 1 below.

<Example 8>

Example 1 except that 65.80 wt% of lead-free transparent dielectric powder of Bi ₂ O ₃ -B ₂ O ₃ -BaO system, 9.87 wt% of binder, 1.74 wt% of plasticizer, 0.66 wt% of dispersant, and 21.93 wt% of solvent were used. In the same manner as the green sheet was prepared. The tensile strength and strain of the green sheet thus prepared were measured as described above, and the results are shown in Table 1 below.

Example Characteristics of Green Sheet Tensile strength (MPa) Strain rate (%) One 0.6627 120.62 2 0.3619 105.3 3 0.1273 91.1 4 0.4877 45.57 5 0.4709 34.69 6 0.1165 255.07 7 0.4469 120.83 8 1.8063 10.83

Example 9

Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were performed on the green sheet prepared in Example 2 to determine the degreasing temperature of the green sheet. Figure 3 is a graph showing the TGA and DSC results data, the organic additives began to volatilize at 70 ℃, a strong endothermic peak at 382 ℃ with the organic material completely burned out (burn-out) almost at the temperature change almost Not observed. Therefore, when baking a green sheet, the degreasing temperature was determined to be 400 degreeC.

The green sheet prepared in Example 2 was thermally pressed onto the surface of a glass substrate (PD200, Asahi Glass Co., Ltd., Japan) preheated to 80 ° C. using a laminator. At this time, the laminator surface temperature was 80 ° C. and a pressure of 5 kg / cm ² was applied for 5 minutes. After the thermocompression bonding, the support film was peeled off from the green sheet bonded to the surface of the glass substrate to transfer the green sheet.

The glass substrate on which the green sheet is transferred is placed in a firing furnace, and the temperature of the firing furnace is raised to 400 ° C at a degreasing temperature determined by the TGA and DSC analysis results at a heating rate of 5 ° C / min at room temperature, and at 400 ° C. After degreasing for an hour, the temperature was raised to 580 ° C. at a temperature increase rate of 5 ° C./min, and maintained at this temperature for 15 minutes to form a transparent dielectric.

The thickness of the formed transparent dielectric material was in the range of 25 µm ± 1 µm, which was excellent in uniformity of the film thickness.

The transmittance in the visible region (wavelength: 400-800 nm) was measured using an ultraviolet / visible spectrometer (LAMBDA19 UV / VIS / NIR, Perkin-elmer Co., Germany) for the transparent dielectric material thus formed. The results are shown in FIG.

In addition, when the cross section of the transparent dielectric material was observed with a scanning electron microscope (SEM), there was no binding such as internal pores or cracks of 0.25 μm or more (see FIG. 5).

In addition, after making a Pt electrode having a diameter of 2 mm in the lead-free transparent dielectric, applying a DC between both electrodes and raising the voltage, the withstand voltage was measured by measuring the voltage immediately before the dielectric breakdown occurred, and the minimum value was 4.5 kV. An average value of about 5 kV was found, indicating a good withstand voltage.

According to this invention, the outstanding green sheet for applying the dry film method can be formed. The green sheet according to the present invention can efficiently form the transparent dielectric required for a large panel while maintaining the uniformity of the film thickness. According to the present invention, it is possible to form a transparent dielectric having improved transmittance and no defects such as pinholes or cracks in the film. The lead-free transparent dielectric prepared according to the present invention has an excellent withstand voltage of 5 kV on average.

Claims (5)

Bi ₂ O ₃ -B ₂ O ₃ -BaO-SrO-based transparent dielectric powder 64-70% by weight, azeotrope mixed solvent of methyl ethyl ketone and ethanol 21-24% by weight, fish oil as dispersant 0.6-0.7 Wt%, 5-12 wt% polyethyl methacrylate (PEMA) as binder, 0.5-6.0 wt% of a mixture of polyethylene glycol (PEG) and dibutylphthalate (DBP) in a 1: 1 weight ratio as plasticizer A lead-free transparent dielectric composition for producing a green sheet for forming a transparent dielectric for a panel. According to claim 1, wherein the Bi ₂ O ₃ -B ₂ O ₃ -BaO-SrO-based transparent dielectric powder is Bi ₂ O ₃ 50-60% by weight, B ₂ O ₃ 25-35% by weight, BaO 5-10 weight Prepared by mixing, melting and quenching%, SiO ₂ 0-5 wt%, Al ₂ O ₃ 0-5 wt%, ZnO 0-5 wt% and SrO 0.3-1 wt% to form a glass plate Lead free transparent dielectric composition. The green sheet manufactured using the lead-free transparent dielectric composition of Claim 1 or 2. A member for plasma display comprising a lead-free transparent dielectric produced using the green sheet described in claim 3. The member for plasma display according to claim 4, wherein the lead-free transparent dielectric has a transmittance of 78% or more and a withstand voltage of 4.5 kPa or more in the visible light region.

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