METHOD FOR PREPARING PHOTOSENSITIVE BARRIER RIB PASTE COMPOSITION FOR FABRICATING PLASMA DISPLAY PANNEL Technical Field The present invention relates to a method for fabricating a plasma display panel (PDP); and, more particularly, to a method for preparing a photosensitive barrier rib paste composition containing barrier rib powder whose surface is treated with nano-size fumed silica particles, and a method for fabricating PDP barrier ribs using the method.

Description of the Prior Art A plasma display panel (PDP) is a flat panel display device using the effect of vacuum ultraviolet rays (mostly in the wavelength of 147nm) changing into red, green, and blue rays in the range of visible rays, after colliding with a corresponding phosphor. The vacuum ultraviolet rays are emitted from plasma generated during the discharge of gas, such as Ne or Xe, filled in a space between a front plate and a rear plate.

PDP is divided into a DC type and an AC type. In a DC-type PDP, an electrode used to apply voltage from outside to form plasma is exposed directly to the plasma and the conduction current flows directly through the electrode.

It has an advantage that the structure is very simple, but has a shortcoming that it should equip external resistance to limit the current because the electrode is exposed in the discharge space. In an AC-type PDP, an electrode is not exposed directly but covered with a dielectric substance, so displacement current flows. Since the electrode is covered with a dielectric substance, electric current can be limited naturally. Also, because the electrode can be protected from ion impact during the discharge, the lifetime of the AC-type PDP is longer than

that of the DC-type PDP.

Meanwhile, among various flat board display devices, PDP is drawing public attention as a next-generation display along with high-definition television (HDTV), because PDP can embody full-color display and a large display device over 40 inches, and has quick response time and wide-angle vision.

Fig. 1 is a cross-sectional view showing a surface- discharging AC-type PDP. Referring to Fig. 1, a surface- discharging AC-type PDP comprises a rear plate and a front plate. The rear plate is formed of a rear substrate 10, an address electrode 11, a white dielectric substance 12 and barrier ribs 13. The front plate is formed of a front substrate 14, a transparent electrode 15, a bus electrode 16, a transparent dielectric 17, a dielectric protection film 18 and black stripes (not shown). The phosphors (red, green, and blue) 19 for embodying colors in the PDP are placed between the barrier ribs 13 of the rear plate in the surface discharging AC-type PDP.

In PDP, the barrier ribs is a structure formed on the rear substrate of the PDP for obtaining discharge space and preventing electric and optical cross talk between neighboring cells. Detailed structure of barrier ribs is different according to the design of a PDP. In case of a stripe-shaped barrier rib, the barrier ribs has an upper width of 60-80pm, a lower width of 80~110, um, a height of 100~120, um, and each barrier rib pattern is placed at an interval of 200-300pm. The structure of PDP is a significant factor affecting the image quality of display.

Formation of barrier ribs for PDP consisted of two steps. The first step is obtaining a fine pattern of barrier ribs with predetermined geometrical structure by using a barrier rib paste. The barrier rib paste is composed of two parts. One part is inorganic barrier rib powder including low melting glass frit and ceramic material such as alumina (A1203) and titanium oxide (Tio2).

Here the ceramic material has function of increasing the mechanical property of the barrier rib after sintering

while glass frit forms the amorphous matrix of barrier rib by melting at low temperature ranging of from about 530 C to about 550 C. The other part is organic material which has the function of making paste with the inorganic barrier rib powder and enabling a fine patterning of barrier ribs on the rear panel of PDP. In the second step the organic part of patterned barrier ribs is completely burnt off through the sintering process leaving only the inorganic materials forming the barrier ribs.

The barrier ribs of a PDP device can be patterned by various methods, such as screen printing, sandblasting, and photolithography. The screen printing is a method for obtaining barrier ribs by printing a barrier rib paste on a glass substrate using a screen mask patterned with a predetermined barrier rib structure and drying to remove the solvent. This printing and drying process are repeated 8-10 times to get a dry barrier rib height of 200 um to 250 gm. This method takes long time and has a problem of low throughput. It is also hard to form uniform barrier rib pattern due to mis-alignment of screen mask by repeated process.

In the sandblasting method, barrier ribs are formed by coating and drying a barrier rib paste in a thickness of 150 250pm, laminating an anti-sanding dry film resist (DFR), forming patterns with the DFR by performing light exposure and development, and removing barrier rib particles by applying impact thereto with fine abrasive particles along with high-pressure air. This method has problems that the process is complicated and has high material loss. In addition, it is difficult to separate out the powder mixture generated from the sandblasting, and it is not environment-friendly.

The photolithographic method is performed by coating and drying a photosensitive barrier rib paste, exposing the paste to ultraviolet (UV) light through a photo mask, and removing the paste in the unexposed area by selectively dissolving it in developing solution. The photolithography

method has an advantage that it can form fine and clean barrier ribs. However, it has a problem that barrier ribs over 100 J. m-high can hardly be formed, because the intensity of UV light is greatly reduced at the lower portion of the photosensitive barrier rib layer due to absorption, reflection and scattering of the light.

Therefore, there is a problem that the process of coating-drying-exposing to UV light should be performed two or three times prior to the development of the photosensitive barrier rib layer.

The complete penetration of UV light is especially difficult when the glass frit, the major component of the barrier rib powder, is composed of PbO-SiO2-B203-group glass.

This is because the metal oxide, especially PbO, has high refractive index compared to the organic materials which constitute another part of the photosensitive barrier rib paste, thus increasing the dispersion of UV light at the interface between the inorganic barrier rib powder and organic material.

To solve this problem related to the light penetration, U. S. Patent No. 6,197, 480 discloses a method that can reduce the reflection and scattering of UV light in the interface by reducing the difference in the mean refractive index of the inorganic barrier rib material and the organic material that form the photosensitive barrier rib paste. The inorganic barrier rib materials used for this purpose include P205, BiO, Na2O, Li20 or K20 in place of PbO in the conventional glass frit consisted of PbO-B203-SiO2.

This technology, however, has a problem that the composition of the organic part of photosensitive barrier rib paste which has the function of inducing photocrosslinking reaction has to be changed according to the composition of the inorganic barrier rib materials with reduced refractive indices.

When photosensitive barrier rib paste in which PbO is replaced with P205, BiO, or K2O is used in the photolithographic process of obtaining barrier rib pattern, the color of the barrier ribs after sintering (or firing)

process is usually darker than the one employing PbO in the glass frit. The dark barrier ribs reduce the luminance intensity of the PDP due to increased absorption of red (R), green (G) or blue (B) light emitted from the phosphor layer.

When photosensitive barrier rib pastes in which PbO is replaced with other inorganic oxides are used in the formation of barrier ribs for PDP, usually higher sintering temperature is required than the one with PbO in the glass frit. The high sintering temperature is detrimental to the PDP manufacturing process because it induces cracking or warp of the PDP panel, resulting low yield in the production of PDP.

Summary of the Invention It is, therefore, an object of the present invention to provide a photosensitive barrier rib paste that can enhance the efficiency of UV light exposure regardless of the various composition of glass frits when the barrier ribs of a plasma display panel (PDP) are formed with a photolithography method.

It is another object of the present invention to provide a photosensitive barrier rib paste which could reduce the sintering temperature and increase the whiteness of the barrier ribs after sintering.

In accordance with an aspect of the present invention, there is provided a method for preparing a photosensitive barrier rib paste, comprising the steps of: mixing barrier rib powder including glass frit and ceramic material with nano-size (5nm-200nm) silica particles, heat treating the mixture powder in an oven, pulverizing the mixture powder in a ball mill thus providing a barrier rib powder on which surface nano-size silica particles are adsorbed; and forming the photosensitive barrier rib paste by mixing the barrier rib powder of which surface is treated with the nano-size silica particles with the photosensitive vehicle.

In accordance with another aspect of the present invention, there is provided a method for preparing a

photosensitive vehicle including binder polymer, a first material selected from a group consisting of multifunctional monomer and multifunctional oligomer, photoinitiator and additives such as dispersing agent, polymerization inhibitor, photosensitizer, and leveling agent.

In accordance with another aspect of the present invention, there is provided a method for forming barrier ribs of a plasma display panel, comprising the steps of: providing a substrate: coating a photosensitive barrier rib paste including barrier rib powder of which surface is treated with fumed silica; drying the photosensitive barrier rib paste; and forming barrier pattern by exposing and developing the photosensitive barrier rib layer.

According to the present invention, the surface of the inorganic barrier rib powder of the photosensitive barrier rib paste is treated with nano-size (the average diameter is 5-200nm) silica particles. As nano-size silica particles, fumed silica is useful since fumed silica can be prepared easily with diameter in narrow distribution under specified nano-size. Since fumed silica particles are amorphous and have high purity, fumed silica particles are transparent and have small light propagation loss. Inorganic barrier rib powder whose surface is treated with nano-size fumed silica can be obtained by mixing nano-size fumed silica with inorganic barrier rib powder, the average size of which is 2-5 pm, using a ball mill, baking the powder mixture at a temperature of 50~150 C, and then re- pulverizing the baked powder mixture. Since the size of the fumed silica is nanometer scale, the silica particles are firmly adsorbed on the porous surface of the barrier rib powder whose size is in micrometer range. When the photosensitive barrier rib paste is prepared using the barrier rib powder whose surface is treated with nano-size silica particles, and the barrier rib pattern is formed with a photolithography method, the light-exposure efficiency of the photosensitive barrier rib paste is

enhanced because the nano-size silica particles on the surface of the barrier rib powder can form a kind of light guide channels between the barrier rib powders for ultraviolet ray to penetrate into the dry photosensitive barrier rib layer.

Brief Description of the Drawings The above and other objects and features of the present invention will become apparent from the following description of the preferred embodiments given in conjunction with the accompanying drawings, in which: Fig. 1 is a cross-sectional view showing a surface- discharging AC-type plasma display panel (PDP); Fig. 2 is a flow chart illustrating a method for surface treating barrier rib powder in accordance with an embodiment of the present invention; Fig. 3 is a scanning electron microscope (SEM) photograph of barrier rib powder of which surface is treated with the nano-size silica particles; and Fig. 4 is a flow chart describing a method for preparing a photosensitive barrier rib paste in accordance with an embodiment of the present invention.

Detailed Description of the Preferred Embodiments Other objects and aspects of the invention will become apparent from the following description of the embodiments with reference to the accompanying drawings, which is set forth hereinafter.

Fig. 2 is a flow chart illustrating a method for preparing barrier rib powder which is a mixture of glass frit and ceramic material in accordance with an embodiment of the present invention. Referring to Fig. 2, at step 100, barrier rib powder and nano-size fumed silica are mixed together and pulverized with a ball mill. Here, the barrier rib powder could be mixture of glass frit of a PbO- SiO2-B203-group or other glass frit in which PbO is replaced

with P205, BiO or alkalimetal oxide such as K20, Na2O or Li20 and ceramic powder which could be alumina (Al203) or titanium oxide (Ti02). The ball milling process is performed at a room temperature for 10-60 minutes, desirably.

After the ball milling, at step 102, the barrier rib powder of which is surface treated with nano-size fumed silica is baked in an oven at a temperature of 50~150 C for 10-30 minutes.

Subsequently, at step 104, the baked barrier rib powder, which includes the fumed silica, is re-pulverized using a ball mill. The pulverization is performed at a room temperature for 10-30 minutes, desirably.

In the barrier rib powder prepared from the above processes, the nano-size silica particles (the average diameter of which is 5-200nm) are firmly adsorbed on the barrier rib particles composed of glass frit and ceramic powder as shown in Fig. 3.

Fig. 4 is a flow chart describing a method for preparing photosensitive barrier rib paste in accordance with an embodiment of the present invention.

Referring to Fig. 4, at step 200, binder polymers are dissolved in solvents to have an appropriate viscosity.

At step 202, a photosensitive vehicle is prepared by mixing multifunctional monomer/oligomer having two or more double bonds, photoinitiator, and additives into the binder polymer solution. The additives include dispersing agent, polymerization inhibitor, photosensitizer, and leveling agent.

Subsequently, at step 204, the photosensitive vehicle and the barrier rib powder whose surface is treated with nano-size silica particles, which has been prepared through the process illustrated in Fig. 2, are mixed.

At step 206, the above mixture is dispersed homogeneously, and the viscosity is controlled finally.

Here, it is desirable to use a ceramic 3-roller mill.

The photosensitive barrier rib paste composition of the present invention which has been prepared through the

above process includes 5-20 wt% binder polymer, 8-20 wt% multifunctional monomer/oligomer, 1-2 wt% photoinitiator, 0. 1-1 wt% nano-size fumed silica, 40-60 wt% glass frit, 10-25 wt% ceramic powder, 1-5 wt% additives and 10-23 wt% solvent.

The additives include dispersing agent (0. 1-1 wt%), polymerization inhibitor (0. 1-1 wt%), photosensitizer (0. 2-2 wt%), and leveling agent (0. 1-1 wt%).

The above prepared photosensitive barrier rib paste has a viscosity of 10, 000-100, 000 cps, desirably. If the viscosity of the photosensitive barrier rib paste is not more than 10, 000cps, it runs on the glass substrate too easily to coat the glass substrate. On the other hand, if the viscosity is more than 100,000 cps, the paste does not penetrate the screen meshes but blocks them up.

In the photosensitive barrier rib paste having the composition described above, the binder polymer combines barrier rib powder that forms the barrier ribs and controls the viscosity of the paste. As for the binder polymer, a polymer having good miscibility with other components of the barrier rib paste and preventing the generation of foams can be used. Desirably, the binder polymer includes materials of cellulose group and acrylate group. The binder polymer of cellulose group includes cellulose derivatives, such as, hydroxyethyl cellulose, hydroxypropyl cellulose, and hydroxyethyl-hydroxypropyl cellulose. The cellulose derivative has excellent miscibility with the inorganic barrier rib powder and has good wetting property to the glass substrate. Therefore foaming is greatly reduced when cellulose derivative, for example, hydroxypropyl cellulose is used as a binder polymer in combination with a acrylic copolymer. Moreover, the cellulose derivative make it possible to perform sintering, which is the last process for forming barrier ribs, at a low temperature around 480°C-550°C.

As for the binder polymers of acrylate group, a copolymer synthesized from a comonomer selected from methylmethacrylate, isobutylmethacrylate,

benzylmethacrylate and another comonomer methacrylic acid can be used. The molecular weight of copolymer is 5, 000-20, OOOg/mole.

The mole percent of methacrylic acid should be 10-30 mole % in the copolymer, which facilitates the development with aqueous alkali solution ofter exposure to UV light. It is also important to use the cellulose derivative and acrylate copolymer in combination as binder polymer because the former has effect on screen printing process such as good wetting and less foaming and the latter helps rheological property and development with aqueous alkaline solution. Multifunctional monomer includes ethyleneglycol diacrylate, ethyleneglycol dimethacrylate, diethyleneglycol diacrylate, propyleneglycol diacrylate, 1,2, 4-butanetriol triacrylate, 1,4-benzenediol diacrylate, Trimethylolpropane triacrylate, pentaerythritol tetraacrylate, pentaerythritol tetramethacrylate, dipentaerythritol hexaacrylate, and dipentaerythritol hexamethacrylate. Multifunctional oligomer includes epoxy acrylate, urethane acrylate, and polyester acrylate, whose molecular weight is 200-800. One of the multifunctional monomer and multifunctional oligomer can be selected and used. However, if both multifunctional monomer and oligomer are used together, the adhesion of the barrier ribs to rear panel of PDP on which dielectric layer (so called white back) is formed can be enhanced.

The UV oligomer of urethane acrylate type is especially good for this purpose, because it increases the so called time to clear (TTC) which is the time reguired for the complete development of the photosensitive barrier rib layer after UV-exposure.

Also, for ceramic powder that forms barrier ribs along with glass frit ofter sintering, one selected from a group consisting of Al203, CaO, Cr203, CuO, Fe203, K20, MnO, Na20, NiO, PbO, Si02, Sn02, ZnO, ZrOz, B203, and Ti02 can be used.

The photoinitiator is a chemical whis is decomposed <BR> <BR> when exposed to light source, i. e. , ultraviolet ray and forms free radicals to initiate photopolymerization. Any photoinitiator that shows excellent photoreaction in the

ultraviolet ray wavelength (200-400nm) can be used as a photoinitiator. For example, 2, 2-dimethoxy-2-phenyl acetophenone (DMPA) can be used as a photoinitiator, alone or mixed with other photoinitiators.

To enhance the photoreaction to the bottom of the photosensitive barrier rib layer in one exposure to UV irradiation, a photosensitizer such as isopropyl-9H- thioxanthen-9-one is used in the photosensitive barrier rib paste formulation. It is also needed to use a polymerization inhibitor such as hydroquinone to control the width of barrier rib within certain limit, i. e. 30pm in case of standard definition PDP. Besides, various additives, such as silicone antifoaming agent and leveling agent can be used to improve the screen printing or other coating characteristic of the photosensitive barrier rib paste.

Hereinafter, a method for forming barrier ribs of a PDP using the photosensitive barrier rib paste in which barrier rib powder is surface treated with nano-size silica particles is described in accordance with an embodiment of the present invention.

First of all, the photosensitive barrier rib paste is coated on a rear glass panel where address electrode and dielectric layer (not shown) have been formed using a screen printer or other coater to a thickness of 150-250jm, and dried at a temperature of 50 ~ 130 C for 5-30 minutes.

Subsequently, the dry photosensitive barrier rib layer is exposed to UV light through a photomask, wherein a desired barrier rib pattern is formed. Here, it is desirable to use ultraviolet ray generated by a high- pressure mercury lamp, and the amount of the light energy exposed thereto is 200-1, OOOmJ/cm Subsequently, the un-exposed photosensitive barrier rib layer is removed in the developing process. Here, 0.3 - 2 wt% Na2CO3 aqueous solution is used as developing solution. The developing solution is sprayed for 1-3 minutes and then the panel is dried. Subsequently, the sintering process is performed at 350-450°C for 20-30

minutes isothermally, after that the temperature is increased up to 480-550°C at a speed of 10 C/min for the complete combustion of organic materials. Through the sintering process, all the organic materials such as photopolymerized multifunctional monomer and oligomer, binder polymer and other additives are thermally decomposed and removed, and an inorganic barrier ribs composed of glass frit and ceramic powder can be obtained.

If the photosensitive barrier rib paste of the present invention is used, the dry barrier rib layer can be exposed to UV light to a thickness of over 200ßm in one time.

Therefore, the process time for forming barrier ribs can be reduced. Meanwhile, since the enhanced photosensitivity of barrier rib paste of the present invention is due to the surface treatment of barrier rib powder with nano-size fumed silica, it is another merit of this invention that either barrier rib powder based on conventional PbO-SiO2- B203 glass frit or other so called"non-Pb barrier rib powder"can be used in the photosensitive barrier rib paste with minimal change in composition of the organic component of the paste which has the function of patterning the barrier ribs by the photolithographic process.

The composition of the photosensitive barrier rib paste presented in the present invention is optimized values after many experiments. Some important experimental data are introduced as follows.

Table 1 shows the composition of the photosensitive barrier rib paste designated as Experiment 1 and 2.

In the Experiment 1 and 2, the photosensitive vehicle was prepared as following. First, poly (methylmethacrylate- co-methacrylic acid) abbreviated as poly (MMA-co-MAA) was dissolved in butyl carbitol acetate solvent and hydroxypropyl cellulose was dissolved in 3-methoxy-3- methylbutanol solvent, and then the two binder polymer [Table 1] Photosensitive barrier rib pastes for Experiment land 2. Components Experiment 1 Experiment 2 (materials) (Unit: g) (Unit: g) Part (A): photosensitive vehicle Binder polymer of acrylate group 3. 000 3, 000 (Poly (MMA-co-MAA) ) Solvent for acrylate polymer 4.500 4.500 (Butyl carbitol acetate) Binder polymer of cellulose group 0. 750 0. 750 (Hydroxypropyl cellulose) Solvent for cellulose 3.000 3.000 polymer (3-methoxy-3-methyl butanol) Multifunctional monomer 3.000 3.000 (pentaerythriol tetracrylate) Multifunctional oligomer 3. 000 3. 000 (Urethane acrylate, SKucb E- 204) Photoinitiator 2. 280 2. 280 (2,2-dimethoxy-2-phenyl acetophenone) Photosensitizer 1.254 1.254 (Isopropyl-9H-thioxanthen-9- one) Polymerization inhibitor 0.024 0.024 (Hydroquinone) Leveling agent (BYK-354) 0.062 0.062 Dispersing Agent (BYK-180) 0.156 0.156 Part (B): Barrier rib powder Glass Frit 26. 500 26. 500 (PbO-Si02-B203-group glass) Ceramic powder (Al203) 6.114 6.114 Nano-size fumed silica-0. 326 (12nm) Total weight 53. 640 53.966 (Part A + part B)

solutions were mixed. Second, to the binder polymer mixture solution were added multifunctional monomer, multifunctional oligomer, photoinitiator, and additives such as polymerization inhibitor, photosensitizer, dispersing agent, and leveling agent to make a photosensitive vehicle. In the Experiment 1, the glass frit and ceramic powder were mixed to the photosensitive vehicle prepared and then the mixture was dispersed in the 3-roller mill to obtain a photosensitive barrier rib paste according to the well known method in the industry. In the Experiment 2, nano-size fumed silica was added in addition to the glass frit and ceramic powder as in Experiment 1. Here fumed silica was just added as powder without surface treatment to the barrier rib powder composed of glass frit and ceramic powder.

The results of the photolithographic patterning of barrier ribs are shown in Table 2 utilizing the photosensitive barrier rib paste of Experiment 1 and 2 of Table 1. The barrier ribs were fallen during the development with 1.0 wt% Na2CO3 aqueous solution in the case of photosensitive barrier rib paste prepared according to the Experiment 1. This is due to incomplete penetration of UV light to the bottom of dry photosensitive barrier rib layer (thickness: 220pm) by scattering and absorption of UV light during the passage. In this case the bottom part of the barrier could be cut or dissolved by the developing solution since this part was not cross-linked enough due to insufficient intensity of UV light even with large dose of UV exposure up to 1300mJ/cm2.

It is noted that this barrier rib paste is a negative type photosensitive paste in which the multifunctional monomers are cross-linked by the free radicals generated

from the photoinitiator by UV light. The development of the unexposed area of barrier rib layer is, however, dependant on the binder polymer which is soluble to the aqueous alkali solution.

In the case of Experiment 2, the barrier ribs fell off when UV exposure was less then 700mJ/cm2.

[Table 2] Photolithography patterning of binder ribs using Experiment 1 and Experiment 2 photosensitive barrier rib paste UV exposure Width of Results of photolithographic (Unit: mJ/cm2) rib patterning (Unit: (Paste: Experiment (Paste : Experiment m) 1) 2) 300-No pattern No pattern 500 78 Ribs fall off Ribs fall off during during development development Ribs fall off Part of ribs 700 80 during fall off. development Some unexposed areas were not developed Ribs fall off Part of ribs 900 83 during fall off. development Some unexposed areas were not developed Ribs fall off Part of ribs 1100 85 during fall off. development Some unexposed areas were not developed Ribs fall off A large parts 1300 89 during of unexposed development areas could not be developed

As the dose of UV irradiation was increased above 700mJ/cm2, some unexposed areas could not be developed with the aqueous alkali developing solution. This phenomenon should be caused by the presence of the small amount of nano-size silica particles, because this is the only difference between barrier rib pastes of Exp. 1 and 2. The reason for the inability of development of unexposed areas of barrier rib layer using the paste of Exp. 2 is exceptionally large surface area of the nano-size silica particles which were not adsorbed firmly on the surface of barrier rib powder consisted of glass frit and ceramic powder but distributed randomly in the barrier rib paste by just simple mixing. An excess amount multifunctional monomer and oligomer could be adsorbed on the nano-size silica particles due to the large surface area of the silica particles and this cause easy photocrosslinking of barrier rib layer even with weak intensity of UV light scattered from the UV exposed areas of the barrier rib layer. The average width of barrier ribs also increased slightly as the dose of UV exposure was increased although this width was determined in the partly developed area of barrier rib layer. These results suggested that nano-size silica particles are effective in increasing the photosensitivity of the barrier rib paste.

In order to use the nano-size silica particles in the photolithographic patterning of barrier ribs we tried surface treatment of barrier rib powder composed of glass frit and ceramic powder with the nano-size fumed silica as shown in Table 3.

In experiments from Exp3 to Exp8, barrier rib powder containing connectional glass frit of PbO-B203-SiO2 group and ceramic powder (Al203 : TiO2=3 : 1) was mixed with nano-size silica particles with different average diameter for the surface treatment. The mixture powder was then kept in the

oven at 100 C for 20min and then pulverized in the ball mill. In Exp9, only Al203 ceramic powder was used in stead of mixture of Al203 and Ti02 as ceramic powder. The rest of the operation was same as Exp. 3-8. In Expll, Expl2, barrier rib powder containing so call non-Pb type glass frit such as BiO-B203-SiO2, P205-B203-SiO2, and Li2O-B203- si02 group respectively and ceramic powder (Al203 : Ti02=3 : 1) was surface treated with nano-size silica particles, and then used in the photolithographic patterning of barrier ribs for PDP.

[Table 3] Composition of photosensitive barrier rib powder surface treated with nano-size silica particles.

components Exp3 Exp4 Exp5 Exp6 Exp7 Exp8 Exp9 (1) Glass frit 26. 500 26.500 26.500 26.500 26. 500 26.500 26.500 (PbO-B203-Sio2) (2) Glass frit------- (BiO-Bz03-SiO2) (3) Glass frit (P205-B203-SiO2) (4) Glass frit------- (Li2O-B203-SiO2) (5) Ceramic powder------6. 114 (Al203) (6) Ceramic powder 6. 114 6. 114 6. 114 6. 114 6. 114 6. 114- (Al203 : Ti02=3 : 1) (7) Nano-size silica 0. 326------ (5nm) (8) Nano-size silica-0. 326----0. 326 (12nm) (9) Nano-size silica--0. 326---- (50nm) (10) Nano-size silica---0. 326-- (lOOnm) (11) Nano-size silica----0. 326-- (200nm) (12) Nano-size silica-----0. 326- (250nm) Total weight 32. 940 32. 940 32. 940 32. 940 32. 940 32. 940 32. 940 (g) [Table 31 Continued components ExplO Expll Expl2 Expl3 Expl4 Expl5 Expl6 (1) Glass frit---26. 500 26.500 26.500 26.500 (PbO-B203-SiO2) (2) Glass frit 26. 500------ (BiO-B203-SiO2) (3) Glass frit-26. 500- (P205-B203-SiO2) (4) Glass frit--26. 500---- (Li20-B2O3-SiO2) (5) Ceramic powder--- (Al203) (6) Ceramic powder 6. 114 6. 114 6. 114 6. 114 6. 114 6. 114 6. 114 (Al2O3 : Ti02=3 : 1) (7) Nano-size silica------- (5nm) (8) Nano-size silica 0. 326 0. 326 0. 326 0. 060 0. 170 0. 500 0. 700 (12nm) (9) Nano-size silica------- (50nm) (10) Nano-size silica------- (lOOnm) (11) Nano-size silica------- (200nm) (12) Nano-size silica------- (250nm) Total weight 32. 940 32. 940 32. 940 32. 664 32. 840 33. 140 33. 240 (g)

In Expl3~Expl6, the amount of fumed silica was varied in the range of 0. 2-2. Owt% based on total amount of barrier rib powder including glass frit and ceramic powder which using the same size fumed silica (12nm) particles. Here again same procedure was followed as in Exp3-Exp8 for the surface treatment of barrier rib powder with nano-size silica particles. After surface treatment with nano-size silica particles the barrier rib powder samples were incorporated in the photosensitive vehicle of which composition and procedure of preparation were same as in Part (A) of Table 1. The results of the photolithographic patterning of barrier ribs are shown in Table 4. In Exp3-Exp8, it is noted that optimum size of fumed silica for surface treatment of barrier rib is 5-200nm. As the size of fumed silica used in the surface treatment of barrier rib powder was over 200nm, the barrier ribs fall

off in the development step of the photolithographic patterning of barrier ribs. Exp9 suggests that the change of ceramic powder from Al203 and Ti02 mixture to A1203 alone does not affect the photolithographic process. The results of ExplO-Expl2 indicate that the surface treatment of barrier rib powder with nano-size silica particles of this invention is working regardless of the type of glass frit i. e. , connectional PbO-B203-SiO2 group frit glass or so- called non-Pb type glass frit in which PbO is replaced with BiO, P205, or alkali metal oxide such as Li2O, Na20 or K20.

The tests using Expl3 to Expl6 show that the optimum amount of nano-size silica particles for surface treatment is in the range of 0. 5~1. 5wt% based on the total weight of barrier rib powder. When the amount of nano-size fumed silica was above 2wt% of barrier rib powder as in Exl6, some residual fumed silica was observed after the surface treatment process. This residual silica particles caused absorption of excess amount of multifunctional monomer thus resulting in some undeveloped areas in the development stage.

[Table 4] Photolithographic results of barrier ribs using Exp3-Expl6 photosensitive barrier rib pastes uv Width of Results of barrier rib patterning * exposure rib (mJ/cm2) (jjm) Ex3 Ex4 Ex5 Ex6 Ex7 Ex8 Ex9 200-600 78-82 S S S S M F S ExlO Exll Exl2 Exl3 Exl4 Exl5 Exl6 S S S F S S F * S : Succesful, M : Marginal, F : Fail Table 5 shows the effect of each components of photosensitive vehicle on the photolithographic patterning of barrier ribs. In these tests, the barrier rib powder was surfaced treated one as in Exp4 of Table 3. The

photosensitive barrier rib pastes prepared with the composition of photosensitive vehicles in Table 5 gave different results in the photolithographic patterning of barrier ribs.

Comparision of Expl7-Exp20 showed that the use of mixture of binder polymers was important. Good patterns of barrier ribs were obtained with Expl7'-Expl9 pastes, but Exp20 paste gave uneven barrier rib height after photolithographic process. This was caused by the poor screen printing property of the paste Exp20 without hydroxypropyl cellulose as the component of binder polymer.

Exp21 paste without photosensitizer could not give barrier rib pattern due to reduced photosensitivity of the barrier rib layer near the bottom.

Exp22 paste gave wide (about 100pm) barrier rib although the photomask had slit of 80pm for UV light irradiation.

This result suggests that the effect of polymerization inhibitor is to stop polymerization in the unexposed area thus controlling the width of barrier rib in the photolithographic process. Exp23 paste resulted in uneven barrier ribs after photolithographic patterning of barrier ribs. This phenomenon could be explained by poor dispersion of barrier rib paste when dispersing agent was not employed in the paste formulation [Table 5l Effect of composition of photosensitive vehicle on the photolithographic patterning of barrier rib Photosensitive Exl7 Exl8 Exl9 Ex20 Ex21 Ex22 Ex23 vehicle * (1) Binder polymer + solvent Poly (MMA-co-MAA) 3. 000 3. 000 3. 000 3. 000 Poly (IBMA-co-MAA)-3. 000----- Poly (BZMA-co-MAA)--3. 000 3. 750--- Solvent (BCA) 4.000 4.000 4.000 4.000 4.000 4.000 4.000 Hydroxypropyl 0.750 0.750 0. 750-0. 750 0.750 0.750 cellulose 3.000 3.000 3. 000-3. 000 3.000 3.000 Solvent (3MMB) (2) Multifunctional Monomer+Oligomer PETA 3.000 3.000 3.000 3.000 3.000 3.000 3.000 EB204 3.000 3.000 3.000 3.000 3.000 3.000 3.000 (3) Photoinitiator (Benzophenone 2.280 2.280 2.280 2.280 2.280 2.280 2.280 mixture) (4) Photosensitizer 1. 254 1. 254 1. 254 1. 254 1. 254 1. 254 (IPT) (5) Polymerization inhibitor 0.024 0.024 0.024 0.024 0.024 0 0.024 (Hydroquinone) (6) Leveling agent (BYK-354) 0.062 0. 062 0.062 0.062 0.062 0.062 0.062 (7) Dispersing agent (BYK-180) 0.156 0.156 0.156 0.156 0.156 0.156 0 Total Weight (g) 20.526 20. 526 20. 526 21. 276 19.272 20. 502 20.526

*Poly (MMA-co-MAA) : Poly (Methylmethacrylate-co- Methacrylic acid) Poly (IBMA-co-MAA) : Poly (Isobutylmethacrylate-co- Methacrylic acid) Poly (BZMA-co-MAA) : Poly (Benzylmethacrylate-co- Methacrylic acid) BCA : Butyl carbitol acetate, 3MMB : 3-methoxy-3-methyl butanol PETA : pentaerythriol tetracrylate, EB204 : Urethane acrylate IPT : Isopropyl-9H-thioxanthen-9-one Although the preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.