Description

DISPLAY PANEL, ELECTRODE COMPOSITION AND A METHOD OF MANUFACTURING THEREOF

Technical Field

[1] This document relates to a display panel, an electrode composition and a method of manufacturing a display panel Background Art

[2] A display panel displays an image on a screen. The display panel comprises a liquid crystal display (LCD), a field emission display (FED), an organic light emitting device, and a plasma display panel (PDP). Disclosure of Invention Brief Description of the Drawings

[3] FlG. 1 is a view for illustrating a display panel according to an exemplary embodiment of the present invention;

[4] FIGS. 2 to 5 are views for illustrating a method of manufacturing an electrode according to an exemplary embodiment of the present invention;

[5] FIGS. 6 to 8 is a detailed view for illustrating an electrode manufactured by an offset printing method; and

[6] FlG. 9 is a view for illustrating a change in width of a section of an electrode depending on the amount of a solvent. Mode for the Invention

[7] Ffereinafter, it is described that an exemplary embodiment of the present invention employs a plasma display panel as a display panel The present invention, however, is not limited thereto, and may use a liquid crystal display, a field emission display, and an organic light emitting display as a display panel

[8] FlG. 1 is a view for illustrating a display panel according to an exemplary embodiment of the present invention.

[9] Referring to FlG. 1, a plasma display panel comprises a front substrate 101 and a rear substrate 111 facing the front substrate 101. Scan electrodes 102 and sustain electrodes 103 are arranged in parallel on the front substrate 101. Address electrodes 113 crossing the scan electrodes 102 and sustain electrodes 103 are arranged on the rear substrate 111.

[10] An upper dielectric layer 104 may be arranged on the front substrate 101 to cover the

scan electrodes 102 and sustain electrodes 103.

[11] The upper dielectric layer 104 may limit a discharge current of the scan electrodes

102 and sustain electrodes 103 and insulate the scan electrodes 102 and sustain electrodes 103 from each other.

[12] A protection layer 105 may be arranged on the upper dielectric layer 104 to easily cause discharge. The protection layer 105 may comprise a material that has a high emission coefficient, such as MgO.

[13] The address electrodes 113 are arranged on the rear substrate 111, and a dielectric layer, e.g. lower dielectric layer 115, may be arranged on the rear substrate 111 to cover the address electrodes 113 and insulate the address electrodes 113 from each other.

[14] Barrier ribs 112, which comprise a stripe type, a wel type, a delta type, and the like, may be arranged between the front substrate 101 and rear substrate 111 to define discharge spaces, i.e. discharge eels. Red, green, and blue discharge eels may be defined by the barrier ribs 112 between the front substrate 101 and rear substrate 111.

[15] The closed-type barrier ribs shown in HG. 1 may comprise a first barrier rib 112b and a second barrier rib 112a crossing the first barrier rib 112b.

[16] Various barrier ribs other than the barrier ribs 112 shown in HG. 1 may be employed as an exemplary embodiment of the present invention. For example, the height of the first barrier rib 112b may be different from that of the second barrier rib 112a.

[17] The discharge eels defined by the barrier ribs 112 are filled with a discharge gas. A phosphor layer 114 may be arranged in the discharge eels to emit a visible ray for displaying an image during address discharge. For example, red, green, and blue phosphor layers may be arranged in the discharge eels.

[18] Although a display panel has been described according to an exemplary embodiment of the present invention, the present invention is not limited thereto. For example, although the scan electrodes 102 and sustain electrodes 103 are arranged on the front substrate 101, at least one functional layer, for example another dielectric layer, may be further arranged between the front substrate 101 and scan electrodes 102 and sustain electrodes 103.

[19] HGS. 2 to 5 are views for illustrating a method of manufacturing an electrode according to an exemplary embodiment of the present invention.

[20] HG. 2 illustrates an offset printing method as an example of direct patterning methods.

[21] Referring to HG. 2, an electrode material 210, which is in the form of a paste or

slurry, is applied on the surface of the mold 200 (Step (a)). [22] Next, a roler 220 moves on the surface of the mold 200 applied with the electrode material 210 (Step (b)), and the electrode material 210 may be printed on the surface of the roler 220. [23] Then, the electrode material 210 printed on the surface of the roler 220 is printed on a substrate 230 for manufacturing a display panel while the roler 220 moves on the substrate 230 (Step (c)). [24] Next, a backing process or a drying process may be done, and then an electrode 240 may be formed on the substrate 230 (Step (d)). [25] As described above, the electrode material 210 that is in the form of a paste or slurry may be directly printed on the substrate 230. Therefore, the surface tension may make a contact angle (θ) between the substrate 230 and electrode 240, which is formed after a baking process or drying process, relatively smat [26] The contact angle (θ) may be a maximum angle between a tangent line, which is formed when the substrate 230 is connected to the surface of the electrode 240 with a line, and the substrate 230. [27] The electrode 240 that is formed in the method of HG. 2a may be at least one of the scan electrode 102, sustain electrode 103, and address electrode 113. [28] HG. 3 illustrates an example of an electrode formed in the method of HG. 2.

[29] Referring to HG. 3, the electrode is formed in a convex shape as in (a), and the contact angle is about 45°

[30] The contact angle between the substrate and electrode may be about 26°as in (b).

[31] The contact angle between the substrate and electrode may be about 10°as in (c).

[32] The contact angle between the substrate and electrode may be about 7°as in (d).

[33] HG. 4 illustrates an example of a method of forming an electrode in a photosensitive method. [34] Referring to HG. 4, firstly, an electrode material 260 is applied on a substrate 250 for manufacturing a display panel (Step (a)). [35] For example, an electrode material that is in the form of a paste or slurry and formed by mixing a metallic material with other materials such as a solvent, a binder, and the like, is applied on a screen mask, and pressurized. Then, the electrode material may be applied on a substrate 250 through a hole of the screen mask. [36] Then, a photo mask 270 that has a prescribed pattern is placed on the substrate 250 applied with the electrode material 260, and a part of the electrode material 260 may be cured by illuminating the electrode material 260 with light, such as ultraviolet rays,

through the pattern of the mask 270. This process may be called an exposing process.

[37] Next, the electrode material 260 that has teen illustrated with the light is developed with a developer. This process may be called a developing process.

[38] If a baking or drying process is performed after the developing process, then an electrode 280 that has a constant pattern may be formed on the substrate 230 as in (c).

[39] The contact angle between the electrode 280 and substrate 230 is relatively large because the electrode is formed through exposing and developing processes in the method of HG. 4.

[40] The photosensitive method as in HG. 4 requires a screen printing process, an exposing process, and a developing process for the electrode material unlike the offset printing method as in HG. 2. In the offset printing method, an electrode may be formed only by moving a roller on a substrate. Accordingly, the offset printing method as in HG. 2 may reduce the number of processes and time required to form an electrode, thus making it possible to manufacturing costs.

[41] Furthermore, assuming that a functional layer, e.g. another dielectric layer, is further formed on the substrate 230 to cover the electrode 280 in HG. 4, a dielectric material that constitutes the dielectric layer may be not sufficiently filled in a space near an end portion of the electrode 280 since the contact angle between the substrate 230 and electrode 280 is relatively large.

[42] Then, gases or moisture may gather in space between the substrate 230 and electrode

280, and therefore, gas bubbles 290 may be created. The gas bubbles(290) may increase the resistance of the electrode 280, reduce the driving efficiency of a display panel, and even, cause the break of insulation during driving.

[43] On the contrary, in a case where the contact angle between the substrate 230 and electrode 240 is sufficiently small as in HG. 2, a dielectric material that constitutes the dielectric layer may be more easily filled in a space near end portion of the electrode 240. Therefore, the method of HG. 2 may prevent gas bubbles from rising unlike the method of HG. 4.

[44] HG. 5 illustrates an example of an electrode formed in the method of HG. 4.

[45] Referring to HG. 5, an electrode formed in the photosensitive method has a relatively large contact angle. For example, the contact angle between the electrode and substrate is about 71°.

[46] HGS. 6 to 8 illustrate an electrode formed in an offset printing method in more detail

[47] Referring to HG. 6, firstly, a section of an electrode 310 arranged on the substrate

300 may be formed to be convex in the opposite direction to the direction of arranging the substrate 300. ffere, the section of the electrode 310 is a section taken in the longitudinal direction.

[48] As described in HG. 2, an electrode material that is in the form of a paste or slurry is directly printed on the substrate 230, and therefore, the surface tension is created, which may, in turn, make the shape of electrode 310 become convex as in HG. 6.

[49] If the resistance of the electrode 310 is excessive large, the driving efficiency may be lowered during driving the display panel Accordingly, the resistance of the electrode 310 needs to be sufficiently reduced in order to prevent the lowering of the driving efficiency.

[30] The resistance of the electrode 310 according to the exemplary embodiment of the present invention is not limited, and may be more than about 30 ω and less than 70 ω so as to acquire a sufficiently large driving efficiency during driving.

[51] On the other hand, if the width of a section of the electrode 310 is excessively small, the area of the section is excessively reduced, and therefore, the resistance of the electrode 310 may be excessively high. Otherwise, if the width L of the electrode 310 is excessively large, a short circuit may occur between two adjacent lines due to fluidity of the electrode material when the electrode material is printed on the substrate 300 by an offset printing device.

[52] Considering above, the width of the electrode 310 may be more than 60/M and less than 90/M.

[53] If the section of the electrode 310 is excessively high, the width of electrode material line may be excessively large due to fluidity of the electrode material when the electrode material is printed on the substrate 300 by the offset printing device, and therefore, the possibility of a short circuit between two adjacent lines may be increased. Otherwise, if the section of the electrode 310 is excessively low, the area of the section is excessively reduced, and therefore, the resistance of the electrode 310 may be excessively increased.

[54] Considering above, the height of the section of the electrode 310 may be more than

3/M and less than 10/M.

[55] Referring to HG. 7, a height hi of the section of the electrode 320 arranged on the substrate 300 may gradually increase at a region Wl, be maintained constantly at a region Wl, and decrease at a region W3.

[56] Referring to HG. 8, a height h2 of the section of the electrode 330 arranged on the substrate 300 may gradually increase at a region WlO, decrease at a region W20,

increase at a region W30, and decrease at a region W40.

[57] Tables 1 and 2 show the electrode compositions used in the offset printing method as described above. [58] Table 1 [Table 1] [Table ]

[59] Referring to Table 1, the electrode composition used in the offset printing method may comprise more than 60 and less than 95 parts by weight of metal powder, more than 5 and less than 40 parts by weight of a binder, more than 1 and less than 30 parts by weight of an organic solvent, and more than 1 and less than 20 parts by weight of glass frit. On the other hand, the electrode composition may be applicable to other methods, such as a spin coating method, as wel as the offset printing method.

[60] The metal powder, which endows the electrode with conductivity, is not particularly limited only if it has conductivity. Considering the easiness of working during an offset printing process and high conductivity, the metal powder may be at least one of Ag, Cu, Al, and Au.

[61] If the content of metal powder is excessively high, the fluidity of the electrode material used in the offset printing method may be excessively lowered. Then, the width of the electrode that is formed after a baking or drying process may be excessively short compared with its height. In contrast, if the content of the metal powder is excessively low, the resistance of the electrode that is formed after a baking or drying process may be excessively increased. Accordingly, the content of the metal powder may be more than 60 and less than 95 parts by weight.

[62] The binder is not particularly limited, and may comprise either an acrylic -based binder or methacrylic-based binder, or a mixture of an acrylic-based binder and methacrylic-based binder, considering manufacturing costs.

[63] If the content of the binder is excessively high, the fluidity of the electrode material used in the offset printing method may be excessively lowered, and if the content of the binder is excessively low, the fluidity of the electrode material is too high, so that two adjacent electrode lines may be mixed, and therefore, the electrode may be difficult to form during an offset printing process.

[64] Accordingly, the content of the binder may be more than 5 and less than 40 parts by weight. [65] The organic solvent is not particularly limited, but may comprise toluene or texanol considering solubility or manufacturing costs. [66] If the content of the organic solvent is excessively high, the fluidity of the electrode material used in the offset printing method may be excessively increased, and if the content of the organic solvent is excessively low, the fluidity of the electrode material is excessively lowered

[67] Accordingly, the content of the organic solvent may be more than 1 and less than 30 parts by weight. [68] The glass frit, which is glass powder, melts during a baking process, and allows the shape of the electrode to be maintained, so that the electrode has a sufficient strength. In the glass frit including an electrode composition according to an exemplary embodiment of the present invention, Tg may be about 46O ⁰ C, and Ts may be about 495 ⁰ C.

[69] If the content of the glass frit is excessively high, the dielectric constant and resistance of the electrode is excessively increased, and therefore, the driving efficiency of the display panel may be lowered. Otherwise, if the content of the glass frit is excessively low, it is difficult for the electrode to have such a shape as in HGS. 6 to 8, and the strength of the electrode may be excessively weakened. Accordingly, the content of the glass frit may be more than 1 and less than 20 parts by weight.

[70] Table 2 [Table 2] [Table ]

[71] Referring to Table 2, the electrode composition used in the offset printing method may further comprise more than 0.5 and less than 15 of a dispersion stabilizer as an additive besides the metal powder, binder, organic solvent, and glass frit.

[72] The dispersion stabilizer allows the metal powder and glass frit to be uniformly dispersed in the electrode material that is in the state of a paste or slurry. [73] The dispersion stabilizer is not particularly limited, and may comprise any one of xylene, butylacetate, and methoxypropylacetate.

[74] The electrode material that is in the shape of a paste or slurry is formed by mixing the components of Tables 1 and 2, the electrode is formed in the offset printing method using the electrode material Then, the conditions detailed in HGS. 2 and 3, and HGS. 6 to 8. may be satisfied.

[75] More detailed description of the glass frit wil be given with reference to Tables 3 and 4. [76] Table 3 [Table 3] [Table ]

[77] Referring to Table 3, the glass frit may comprise more than 33 and less than 69 parts by weight of Bi ₂ O ₃ , more than 9 and less than 36 parts by weight of B ₂ O ₃ , more than 1 and less than 19 parts by weight of SiO ₂ , and more than 1 and less than 18 parts by weight of Al ₂ O ₃ , based on the total weight of the glass frit.

[78] Bi ₂ O ₃ that is a main component of the glass frit improves the reactivity, and facilitates the formation of electrode while the electrode is made in the offset printing method. If the content of Bi ₂ O ₃ is excessively high, the strength of the electrode may be weakened while the electrode is formed, and if the content of Bi ₂ O ₃ is lower, the electrode may be difficult to form. Accordingly, the content of Bi ₂ O ₃ may be more than 33 and less than 69 parts by weight.

[79] B ₂ O ₃ may improve melting characteristics of the glass frit. If the content of B ₂ O ₃ is excessively high, the thermal expansion coefficient of the glass frit may be excessively lowered, and if the content of B ₂ O ₃ is excessively low, the melting characteristics of the glass frit may be excessively lowered. Accordingly, the content of Bi ₂ O ₃ may be more than 9 and less than 36 parts by weight.

[80] SiO ₂ may improve the strength of the electrode when the electrode is formed. If the content of SiO ₂ is excessively high, the thermal expansion coefficient of the glass frit may be excessively lowered, and if the content of SiO ₂ is excessively low, the thermal resistance of the glass frit may be excessively lowered. Accordingly, the content of SiO ₂ may be more than 1 and less than 19 parts by weight.

[81] Al ₂ O ₃ may raise the transition temperature of the glass frit and improve the thermal resistance of the glass frit. If the content of Al ₂ O ₃ is excessively high, the melting characteristics of the glass frit may be excessively lowered, and if the content of Al ₂ O ₃ is

excessively low, the thermal resistance of the glass frit may be excessively lowered.

[82] Accordingly, the content of Al ₂ O ₃ may be more than 1 and less than 18 parts by weight. [83] Table 4 [Table 4] [Table ]

[84] Referring to Table 4, the glass frit may further comprise more than 0.5 and less than 20 parts by weight of BaO, more than 0.5 and less than 9 parts by weight of CaO, and more than 0.5 and less than 14 parts by weight of ZnO.

[85] BaO is not an essential component, but may lower the viscosity of the glass frit while melting the glass frit and accelerate the melting of the glass frit. If the content BaO is excessively high, the strength of the electrode may be excessively weakened. Accordingly, the content of BaO may be more than 0.5 and less than 20 parts by weight.

[86] CaO is not an essential component, but may lower the viscosity of the glass frit while melting the glass frit and accelerate the melting of the glass frit. If the content CaO is excessively high, the strength of the electrode may be excessively weakened. Accordingly, the content of CaO may be more than 0.5 and less than 9 parts by weight.

[87] ZnO is not an essential component, but may further be comprised in the glass frit in the range of more than 0.5 and less than 14 parts by weight. [88] tfereinafter, exemplary embodiments wil be compared with each other with reference to Table 5 and HG. 9. [89] HG. 9 is a view for illustrating a change in width of a section of an electrode depending on the amount of a solvent. [90] Referring to Table 5 and HG. 9, the electrode paste is formed by mixing the components, and the electrode is formed by printing the electrode paste in the offset printing method.

[91] The metal powder may be Ag powder. The characteristics of Ag powder used are as follows. [92] The Ag powder comprises DlO with granularity of more than 0.05 μm and less than 0.5/M, D50 with granularity of more than 0.2/M and less than 0.9/M, D90 with granularity of more than 0.5/M and less than 2.0/M, and DlOO with granularity of less

than 5/M.

[93] The tap density of the Ag powder is more than 2.0g/cm ³ and less than 5.5g/cm ³ , and the surface area of the Ag powder is more than 0.5m ² /g and less than 4.5m ² /g.

[94] The binder used is an acrylic -based binder, and its characteristics are as follows.

[95] The acid value of the binder is more than lQngKOH/g and less than 18QngKOH/g, and the viscosity of the binder is more than 5000 and less than 45000 at the temperature of more than 24 ⁰ C and less than 25 ⁰ C. The content of solids is more than 20 and less than 89 parts by weight, and the molecular weight (Mw) is more than 1000 and less than 170000.

[96] The organic solvent used is toluene, and the characteristics of the organic solvent are as follows.

[97] The density of the organic solvent is more than 0.8g/ml and less than 0.99g/ml, the boiling point of the organic solvent is more than 18O ⁰ C and less than 29O ⁰ C, and the molecular weight of the organic solvent is more than 100 and less than 200. And, the organic solvent is a C-HO type.

[98] The dispersion stabilizer used as an additive is buthylacetate, and its characteristics are as follows.

[99] The acid value is more than 7mgKOH/g and less than 22 mgKOH/g, the density is more than 0.8g/ml and less than 1. lg/ml at the temperature of 2O ⁰ C, and the content of solids is more than 25 and less than 66 parts by weight.

[100] The glass frit comprises 52 parts by weight of Bi ₂ O ₃ , 20 parts by weight of B ₂ O ₃ , 11 parts by weight of SiO ₂ , 8 parts by weight of Al ₂ O ₃ , 4 parts by weight of BaO, 2 parts by weight of CaO, and 2 parts by weight of ZnO.

[101] Table 5

[Table 5] [Table ]

[102] [103] Referring to Table 5, in an exemplary embodiment 1, the electrode material that is in the shape of a paste is formed by mixing 70 parts by weight of the metal powder, 18 parts by weight of the binder, 4 parts by weight of the organic solvent, 6 parts by weight of the glass frit, and 2 parts by weight of the additive, the electrode material is printed on the substrate using a roler, and then the electrode is formed by baking the printed electrode material

[104] The section of the electrode formed in the exemplary embodiment 1 has a width of 82.3/M and maximum height of 5.6/M. [105] In an exemplary embodiment 2, the electrode material that is in the shape of a paste is formed by mixing 80 parts by weight of the metal powder, 8 parts by weight of the binder, 5 parts by weight of the organic solvent, 5 parts by weight of the glass frit, and 2 parts by weight of the additive, the electrode material is printed on the substrate

using a roler, and then the electrode is formed by baking the printed electrode material

[106] The section of the electrode formed in the exemplary embodiment 3 has a width of 80. lμm and a maximum height of 5.4/M.

[107] In an exemplary embodiment 3, the electrode material that is in the shape of a paste is formed by mixing 85 parts by weight of the metal powder, 5 parts by weight of the binder, 5 parts by weight of the organic solvent, 3 parts by weight of the glass frit, and 2 parts by weight of the additive, the electrode material is printed on the substrate using a roler, and then the electrode is formed by baking the printed electrode material

[108] The section of the electrode formed in the exemplary embodiment 3 has a width of 79.7 'μm and maximum height of 5.9/M.

[109] The exemplary embodiments 1, 2 and 3 show that if the electrode is formed in the offset printing method under the conditions for the electrode composition of the present invention, the width and maximum height of the section of the electrode may be improved.

[110] On the other hand, in a comparative example 1, the electrode material that is in the shape of a paste is formed by mixing 50 parts by weight of the metal powder, 10 parts by weight of the binder, 32 parts by weight of the organic solvent, 6 parts by weight of the glass frit, and 2 parts by weight of the additive, the electrode material is printed on the substrate using a roler, and then the electrode is formed by baking the printed electrode material

[111] The section of the electrode formed in the comparative example 1 has a width of 92/M and maximum height of 2.9/M.

[112] In a comparative example 2, the electrode material that is in the shape of a paste is formed by mixing 90 parts by weight of the metal powder, 5 parts by weight of the binder, 0.5 parts by weight of the organic solvent, 3 parts by weight of the glass frit, and 1.5 parts by weight of the additive, the electrode material is printed on the substrate using a roler, and then the electrode is formed by baking the printed electrode material

[113] The section of the electrode formed in the comparative example 2 has a width of 59/M and maximum height of 8.4/M.

[114] The comparative examples 1 and 2 show that if the content of the organic solvent is excessive high or low, the width and maximum height of the section of the electrode is not improved wel

[115] The correlation of the content of the organic solvent and the width of the section of the electrode wil be described with reference to HG. 9.

[116] Referring to HG. 9, the width of section of the electrode formed after a baking process is measured while the content of the organic solvent is varied from 0.5 parts by weight to 35 parts by weight.

[117] In this experiment, the same offset printing device is used, the additive is fixed to have 2 parts by weight, and if the content of the organic solvent is increased, the content of at least one of the binder or glass frit is decreased in the range of satisfying the conditions for the electrode composition of the present invention.

[118] If the content of the organic solvent is 0.5 parts by weight, the width of section of the electrode is about 59/M. In this case, the content of the organic solvent is excessively low, and therefore, the fluidity of the electrode paste is excessively lowered, thereby excessively shortening the width of section of the electrode.

[119] If the content of the organic solvent is more than 1 and less than 30 parts by weight, the width of section of the electrode is more than about 76/M and less than about 85/M. In this case, the content of the organic solvent is very appropriate, and therefore, the characteristics of the width of section may be improved.

[120] If the content of the organic solvent is in excess of 30 parts by weight, the width of section of the electrode is in excess of 90/M and sharply increased. In this case, the content of the organic solvent is excessively high, and therefore, the width of section of the electrode is too long.

[121] As mentioned above, the resistance and shaping characteristics of the electrode may be improved if an electrode material is formed by mixing more than 60 and less than 95 parts by weight of the metal powder, more than 5 and less than 40 parts by weight of the binder, more than 1 and less than 30 parts by weight of the organic solvent, more than 1 and less than 20 parts by weight of the glass frit, and the electrode is formed by printing the electrode material on a substrate in an offset printing method.

[122] The foregoing embodiments and advantages are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. The description of the foregoing embodiments is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations wil be apparent to those skilled in the art.