Patent Grant
8004171
I. Field of the Invention
The present invention relates to a plasma display panel. In particular, the present invention relates to a plasma display panel characterized by a carbon concentration of a dielectric layer thereof. The present invention also relates to a method for producing such a plasma display panel.
II. Description of Related Art
The market for large screen flat-panel displays has been recently growing. In these circumstances, a plasma display panel suited to high-definition pictures and a large screen has been further developed.
The plasma display panel comprises a front panel and a rear panel opposed to each other. The front panel and the rear panel are sealed along their peripheries. Between the front panel and the rear panel, there is formed a discharge space filled with a discharge gas (helium, neon or the like).
The front panel is generally provided with a glass substrate, display electrodes (each of which comprises a scan electrode and a sustain electrode), a dielectric layer and a protective layer. Specifically, (i) on one of principal surfaces of the glass substrate, the display electrodes are formed in a form of stripes; (ii) the dielectric layer is formed on the principal surface of the glass substrate so as to cover the display electrodes; and (iii) the protective layer is formed on the dielectric layer so as to protect the dielectric layer.
The rear panel is generally provided with a glass substrate, address electrodes, a dielectric layer, partition walls and phosphor layers (i.e. red, green and blue fluorescent layers). Specifically, (i) on one of principal surfaces of the glass substrate, the address electrodes are formed in a form of stripes; (ii) the dielectric layer is formed on the principal surface of the glass substrate so as to cover the address electrodes; (iii) a plurality of partition walls are formed on the dielectric layer at equal intervals; and (iv) the phosphor layers are formed on the dielectric layer such that each of them is located between the adjacent partition walls.
In operation of the plasma display panel, ultraviolet rays are generated in the discharge space upon applying a voltage, and thereby the phosphor layers capable of emitting different visible lights are excited. As a result, the excited phosphor layers respectively emit lights in red, green and blue colors, which will lead to an achievement of a full-color display.
The dielectric layers can serve as a capacitor. Especially as for the dielectric layer of the front panel, not only a high performance of capacitor is required for achieving a high efficiency of the discharge, but also a resistance to a dielectric breakdown phenomenon is required (such breakdown phenomenon may occur when the voltage is applied on the dielectric layer). See Japanese Patent Kohyo Publication No. 2003-518318 and Japanese Patent Kokai Publication No. 11-195382, for example.
Especially in recent years, there has been an increasing demand for a higher definition and a lower power consumption of the plasma display panels. Thus, some research has been done in order to increase not only the energy effectiveness of the discharge gas but also the number of scanning lines. The realization of a higher definition leads to a smaller pitch between the electrodes, and thereby the dielectric breakdown may occur between the electrode and the dielectric layer upon applying the voltage. For this reason, it is required that the dielectric layer has a lesser physical defect, such as peeling or cracking therein or on its surface.
Moreover, the smaller the panel opening area becomes, the lower the panel brightness becomes. Thus, the dielectric layer is required to have a high purity and a low dielectric constant (or low permittivity). To this end, it is necessary to prevent the dielectric layer from turning yellow. This yellow discoloration of the dielectric layer is known as “yellowing” or “yellowing phenomenon” wherein the dielectric layer is deteriorated to turn yellowish due to a secondary reaction with the electrodes upon calcining the dielectric layer.
Therefore, an object of the present invention is to provide a plasma display panel characterized by a dielectric layer substantially free from the cracking, the yellowing and the like.
In order to achieve the object described above, the present invention provides a plasma display panel comprising:
a front panel comprising a first substrate, a first electrode, a first dielectric layer and a protective layer wherein the first electrode is formed on the first substrate, the first dielectric layer is formed over the first substrate so as to cover the first electrode, and the protective layer is formed on the first dielectric layer; and
a rear panel comprising a second substrate, a second electrode, a second dielectric layer and a phosphor layer wherein the second electrode is formed on the second substrate, the second dielectric layer is formed over the second substrate so as to cover the second electrode, the phosphor layer is formed on the second dielectric layer, wherein
the front panel and the rear panel are disposed such that the protective layer and the phosphor layer are opposed to each other, and thereby a discharge space is formed between the front panel and the rear panel; and
at least the first dielectric layer has a carbon concentration (or carbon component concentration) of from about 1.0×103 ppm to about 1.0×105 ppm.
As used in this specification and claims, “carbon concentration” substantially means a carbon (C) content of the dielectric layer, the carbon (C) content being measured by a secondary ion mass spectrometry (SIMS)(“SIMS” will be described later in Example). The carbon is preferably derived from an alkyl group or an alkylene group bonded to a siloxane backbone (i.e. “siloxane linkage” or “siloxane bond”) contained in the dielectric layer.
As used in this specification and claims, the phrase “at least the first dielectric layer has a carbon concentration” substantially means “the first dielectric layer has a carbon concentration” or “each of the first and second dielectric layers has a carbon concentration”.
The present invention is characterized in that the concentration of carbon remaining in the first dielectric layer or in each of the first and the second dielectric layers is in the range of from 1.0×103 ppm to 1.0×105 ppm. In other words, the carbon concentration (or carbon content) of the first dielectric layer or of each of the first and the second dielectric layers is “1.0×103 ppm or higher” and “1.0×105 ppm or lower”. Due to this carbon concentration, there is substantially no cracking and peeling-off in the dielectric layer, and also the yellowing phenomenon is substantially prevented from occurring in the dielectric layer.
In one preferred embodiment, the carbon concentration of the first dielectric layer or of each of the first and the second dielectric layers is in the range of from about 1.0×104 ppm to about 1.0×105 ppm. In another preferred embodiment, the first dielectric layer has a two-layered structure composed of a lower layer (i.e. layer being in contact with the electrode) and an upper layer (i.e. layer being in contact with the protective layer) wherein the lower layer has the carbon concentration of from 1.0×103 ppm to 1.0×104 ppm, and the upper layer has the carbon concentration of from 1.0×103 ppm to 1.0×105 ppm. In this embodiment, the carbon concentration of the lower layer which is in contact with the first electrodes is characterized in that it serves to prevent the yellowing phenomenon. The meaning of the phrase “two-layered structure” used in this specification and claims includes not only an embodiment wherein the upper layer is clearly distinguished from the lower layer, but also an embodiment the upper layer is not clearly distinguished from the lower layer (for example, an interface or boundary between the upper layer and the lower layer is not clearly formed).
In another preferred embodiment, the plasma display panel comprises another dielectric layer provided between the first dielectric layer and the first electrodes wherein the another dielectric layer has the carbon concentration of 104 ppm or lower (i.e. carbon concentration ranging from 0 to 1.0×104 ppm). In this case, an occurrence of the yellowing phenomenon is more effectively prevented. It should be noted that this embodiment may be regarded as being equivalent to an embodiment wherein the first dielectric layer has the two-layered structure and the lower layer thereof (i.e. layer being in contact with the electrode) has the carbon concentration of 104 ppm or lower.
The present invention also provides a method for producing a plasma display panel as described above, wherein a dielectric layer of a front panel and a dielectric layer of a rear panel are formed. According to the method of the present invention, the formation of at least one of the front-sided and rear-sided dielectric layers comprises the steps of:
(1) supplying a dielectric material onto a substrate (the substrate being provided with an electrode thereon), the dielectric material comprising an organic solvent and a glass component (the glass component comprising an alkyl or alkylene group bonded to a siloxane backbone thereof); and
(2) heating the supplied dielectric material; wherein a dielectric layer produced from the dielectric material due to the heating has a carbon concentration of from 1.0×103 ppm to 1.0×105 ppm.
The method of the present invention is characterized by the use of the dielectric material comprising the glass component in which the alkyl group or the alkylene group is bonded to the siloxane backbone (i.e. “siloxane bond” or “siloxane linkage”). With respect to the glass component, the molar ratio of the alkyl group to Si atom of the siloxane backbone is preferably 1 or more, and more preferably in the range from 1 to 3. It is preferred that the alkyl group has 1 to 6 carbon atoms.
As described above, the dielectric material used in the method of the present invention comprises the glass component and the organic solvent. However, if needed, the dielectric material additionally may comprise a binder resin.
Due to the carbon concentration, the dielectric layer of the plasma display panel substantially does not have physical defects such as peeling or cracking. This results in a high resistance to the dielectric breakdown phenomenon, and thereby a higher definition of the plasma display panels can be achieved. In other words, even when a high voltage is applied, there is occurred no “dielectric breakdown phenomenon” in the dielectric layer, which will lead to an achievement of high definition of the plasma display panel. Moreover, due to the carbon concentration of the dielectric layer, the yellowing of the dielectric layer is substantially prevented, which makes it possible to compensate for the decrease of the panel brightness attributable to the smaller panel opening area.
Accordingly, the present invention can achieve a higher definition, a lower power consumption and a higher efficiency of the plasma display panels.
Hereinafter, the plasma display panel and the method for producing the same of the present invention will be described in detail.
(Construction of Plasma Display Panel of Present Invention)
The plasma display panel (hereinafter referred to also as PDP) of the present invention will be described.
Turning now to
the front panel 10 comprising a first substrate 11, first electrodes 12, a first dielectric layer 13 and a protective layer 14 wherein the first electrodes 12, the first dielectric layer 13 and the protective layer 14 are provided on the first substrate 11; and
the rear panel 20 comprising a second substrate 21, second electrodes 22, a second dielectric layer 23 and phosphor layers (26R, 26G, 26B) wherein the second electrodes 22, a second dielectric layer 23 and the phosphor layers (26R, 26G, 26B) are provided on the second substrate 21.
In the front panel 10, the first electrodes 12 are formed on the first substrate 11; the first dielectric layer 13 is formed on the first substrate 11 so that the first electrodes 12 are covered with the first dielectric layer 13; and the protective layer 14 is formed on the first dielectric layer 13.
In the rear panel 20, the second electrodes 22 are formed on the second substrate 21; the second dielectric layer 23 is formed on the second substrate 21 so that the second electrodes 22 are covered with the second dielectric layer 23; and the phosphor layers (26R, 26G, 26B) are formed on the second dielectric layer 23.
The front panel 10 and the rear panel 20 are disposed so that the protective layer 14 and the phosphor layers (26R, 26G, 26B) are opposed to each other.
There is formed a discharge space 30 (or discharge cells 31) between the front panel 10 and the rear panel 20.
The construction of the PDP and the method for producing the PDP according to the present invention will be described in much more detail. The front panel 10 of the PDP of the present invention comprises the first substrate 11, the first electrodes 12, the first dielectric layer 13 and the protective layer 14. The first substrate 11 is a transparent substrate having an electrical insulating property. The thickness of the first substrate 11 may be in the range of from about 1.0 mm to about 3 mm. The first substrate 11 may be a float glass substrate produced by a floating process. The first substrate 11 may also be a soda lime glass substrate, a lead alkali silicate glass substrate or a borosilicate glass substrate. A plurality of the first electrodes 12 are formed in a pattern of parallel stripes on the first substrate 11. It is preferred that the first electrode 12 is a display electrode (whose thickness is for example about 1 μm to about 50 μm) which is composed of a scan electrode and a sustain electrode. Each of the scan electrode and the sustain electrode is composed of a transparent electrode and a bus electrode. The transparent electrode may be an electrically conductive transparent film made of indium oxide (ITO) or tin oxide (SnO2) in which case the visible light generated from the phosphor layer can go through the film. The bus electrode is formed on the transparent electrode, and serves to reduce a resistance of the display electrode and give an electrical conductivity in the longitudinal direction for the transparent electrode.
The first dielectric layer 13 is provided to cover the first electrodes 12 formed on the surface of the first substrate 11. The first dielectric layer 13 may be an oxide film (e.g. silicon oxide film). Such oxide film can be formed by applying a dielectric material paste consisting mainly of a glass component and an organic solvent, followed by heating the dielectric material paste. As described above or as will be described later in detail, the first dielectric layer 13 of the PDP 40 is characterized in that the carbon concentration is in the range of from 103 ppm to 105 ppm. It is preferred that the thickness of the first dielectric layer 13 is in the range of from about 5 μm to about 50 μm. On the first dielectric layer 13, there is formed the protective layer 14 whose thickness is for example from about 0.5 μm to about 1.5 μm. The protective layer 14 serves to protect the first dielectric layer 13 from a discharge impact (more specifically, from the impact of ion bombardment attributable to the plasma). For example, the protective layer 14 is made of magnesium oxide (MgO). The protective layer 14 can be formed by electron-beam vapor deposition process, CVD process, sputtering process or the like.
The rear panel 20 of the PDP of the present invention comprises the second substrate 21, the second electrodes 22, the second dielectric layer 23 and the phosphor layers (26R, 26G, 26B). The second substrate 21 is a transparent substrate having an electrical insulating property. The thickness of the second substrate 21 may be in the range of from about 1.0 mm to about 3 mm. The second substrate 21 may be a float glass substrate produced by a floating process. The second substrate 21 may also be a soda lime glass substrate, a lead alkali silicate glass substrate or a borosilicate glass substrate. Furthermore, the second substrate 21 may also be a substrate made of various ceramic materials. A plurality of the second electrodes 22 are formed in a pattern of parallel stripes on the second substrate 21. For example, the second electrode 22 is an address electrode or a data electrode (whose thickness is for example about 1 μm to about 4 μm). The address electrodes serve to cause the discharge to occur selectively in particular discharge cells. The address electrodes can be formed from an electrically conductive paste including silver as a main component. The application of the electrically conductive paste is performed by a screen printing process, followed by a drying. Alternatively, the address electrodes can also be formed by a photolithography process wherein a photosensitive paste including silver as a main component is applied by die coating method or printing method, followed by drying the applied paste at a temperature condition of from about 100° C. to about 200° C., followed by exposing to light and developing to form an electrode pattern. After that, the calcination is performed at a temperature condition of from about 400° C. to about 700° C. so as to form the address electrodes.
The second dielectric layer 23 is provided to cover the second electrodes 22 formed on the surface of the second substrate 21. The second dielectric layer 23 is an oxide film (e.g. silicon oxide film). Such oxide film can be formed by applying a dielectric material paste consisting mainly of a glass component and an organic solvent, followed by heating the dielectric material paste. As described above or as will be described later in detail, the second dielectric layer 23 of the PDP 40 is characterized in that the carbon concentration is in the range of from 103 ppm to 105 ppm. It is preferred that the thickness of the second dielectric layer 23 is in the range of from about 5 μm to about 50 μm. On the second dielectric layer 23, there is formed the phosphor layers (26R, 26G, 26B) whose thickness is for example from about 5 μm to about 50 μm. The phosphor layers (26R, 26G, 26B) serve to convert the ultraviolet ray emitted due to the discharge into visual light ray. The three-kinds of the phosphor layer (26R, 26G, 26B) constitute a basic unit wherein three kind of fluorescent material layers, each of which is separated from each other by the partition walls 25, are respectively capable of emitting red, green and blue lights. The partition walls 25 serve to divide the discharge space into cells each of which is allocated to one of the address electrodes 22. The phosphor layers (26R, 26G, 26B) can be made from a paste consisting of a fluorescent material powder, a binder resin (for example, polyvinyl alcohol, polyvinyl butyral, a methacrylate ester polymer, an acrylate ester polymer) and an organic solvent (for example, ketones such as methyl ethyl ketone; aromatic hydrocarbons such as toluene; glycol ether such as propylene glycol monomethyl ether). The paste is applied by a die coating process, a printing process, a dispensing process, an ink jet process or the like, followed by drying the applied paste at about 100° C. to form the phosphor layers therefrom. The fluorescent material powder may be such as Y2O3:Eu, YVO4:Eu or Y2O3S:Eu for the red fluorescent material powder, Zn2GeO2:M, BaAl12O19:Mn or LaPO4:Tb for the green fluorescent material powder, and Sr5(PO4)3Cl:Eu, BaMg2Al14O24:Eu for the blue fluorescent material powder. The partition walls 25 are provided in a form of stripes or in two pairs of perpendicularly intersecting parallel lines on the second dielectric layer 23. The partition walls 25 can be made from a paste consisting of a glass power having a low melting point (for example, glass powder based on lead oxide-boron oxide-silicon oxide or lead oxide-boron oxide-silicon oxide-zinc oxide etc.), a filler (for example, oxide ceramics or the like), a binder resin (for example, polyvinyl alcohol, polyvinyl butyral, methacrylate ester polymer, acrylate ester polymer, etc.) and an organic solvent (for example, ketones such as methyl ethyl ketone; aromatic hydrocarbons such as toluene; glycol ether such as propylene glycol monomethyl ether). Such paste is applied by a die coating process or a printing process, followed by drying the applied paste at a temperature from about 100 to 200° C., followed by performing a photolithography process to form a partition pattern through the exposure and development. After the photolithography process, the calcination is performed at a temperature from about 400° C. to 700° C. to form the partition walls 25 from the paste. Alternatively, the partition walls 25 may also be formed through a sand blasting process, an etching process or a molding process.
The front panel 10 and the rear panel 20 are disposed so that the protective layer 14 and the phosphor layers (26R, 26G, 26B) are opposed to each other. The discharge space 30 is formed between the front panel 10 and the rear panel 20. More specifically, the front panel 10 and the rear panel 20 are disposed via the discharge space in such an arrangement as the scan electrodes and the sustain electrodes of the front panel 10 cross the address electrodes 22 of the rear panel 20 at right angles. The opposed front panel 10 and the rear panel 20 are heated while being secured in place, and thereby there is formed an airtight seal between the front panel 10 and the rear panel 20. Subsequently, the front panel 10 and the rear panel 20 are subjected to an evacuation baking step to remove the gas from the discharge space 30 while heating. After that, the discharge space 30 is filled with the discharge gas, which makes it possible to complete the manufacturing process of the PDP 40. As the discharge gas, a noble gas or rare gas (e.g. helium, neon, argon or xenon gas) may be used. Such noble gas is injected into the discharge space 30 so that the pressure of the space 30 becomes in the range of from 400 to 600 Torr.
In the PDP 40, the discharge space 30 is divided by the partition walls 25 into the discharge cells 31. In each of the discharge cells 31, there is provided a intersection portion of the address electrodes 22 and the display electrodes 12. As a result, the discharge cells arranged in a form of matrix serve to constitute the display region. The discharge gas is caused to discharge by applying a picture signal voltage selectively to the display electrodes from an external drive circuit. The ultraviolet ray generated due to the discharge of the discharge gas can excite the phosphor layers so as to emit visible lights of red, green and blue colors therefrom, which will lead to an achievement of a display of color images or pictures.
Hereinafter, according to the present invention, the carbon concentration of the PDP dielectric layer will be described in more detail.
(Correlation between Carbon Concentration and Dielectric Layer Thickness)
With reference to “point a” shown in the graph, a more detailed explanation will be given below:
In a case where the dielectric layer has the carbon concentration of point a (i.e. the carbon concentration of about 1.0×105 ppm), the physical defects such as peeling or cracking tend to occur when the dielectric layer thickness is larger than about 2 μm. While on the other hand, such physical defects are less likely to occur when the dielectric layer thickness is smaller than about 2 μm. These explanations will lead to better understanding of the meaning of the
As described above, the dielectric layer is provided so that the electrodes are covered with the dielectric layer. In this regard, the actual electrodes may have a protrusion (i.e. so-called “edge curl”) as shown in
Lately, for the purpose of improving the contrast of a screen, there has been provided a bus electrode which has a two-layered structure composed of a black layer (i.e. a layer being in contact with a transparent layer) formed on the display side and a white layer formed on the black layer. The black layer is formed by applying a black electrode paste, and the white layer is formed by applying a conductive electrode paste on the black layer. In this regard, as the black electrode paste, a resin composition comprising a black composite oxide of copper-iron (Cu—Fe), copper-chromium (Cu—Cr) or the like is used. In concrete, the bus electrode can be formed from these electrode pastes by applying each of the electrode pastes for each layer, and pattering each of the resulting layers (through exposure and development), followed by calcining each of the resulting layers. Upon the collective exposure of the black layer and the white layer, it may be insufficient for light to reach the lower layer, and thereby the curing of the lower layer becomes insufficient. Consequently, the amount of the insufficiently cured lower layer to be removed during development becomes larger than that of the upper layer. As a result, after the development, the width of the lower layer becomes smaller than the width of the upper layer. The schematic sectional view of such a bus electrode is shown in
In order to cover the electrode having such protrusions with the dielectric layer, thickness of the dielectric layer must be about 0.5 μm or more, preferably about 1.0 μm or more. In other words, the dielectric layer thickness must be about 0.5 μm or more, preferably about 1.0 μm or more so as to cover the edge-curled electrodes. Considering this requirement of the dielectric layer thickness, it can be understood, based on the graph of
(Correlation between Carbon Concentration and Heat-resistant Temperature of Dielectric Layer)
With reference to “point b” shown in the graph, a more detailed explanation will be given below:
In a case where the dielectric layer has the carbon concentration of point b (i.e. the carbon concentration of about 1.0×103 ppm), the physical defects such as peeling or cracking tend to occur when the temperature of the dielectric layer is higher than about 540° C. While on the other hand, such physical defects are less likely to occur when the temperature of the dielectric layer is lower than about 540° C. These explanations will lead to better understanding of the meaning of the
It should be noted that, the calcining temperature for the phosphor layers upon producing the PDP is about 470° C., and also the temperature for the sealing process in which the front panel and the rear panel are sealed together airtight is about 470° C. In view of this, it is required that the dielectric layer has a heat-resistance at a temperature of approximately 450° C. or higher. It can be therefore seen from
With respect to the PDP of the present invention, it should be noted that the carbon concentration of the first dielectric layer or of each of the first and the second dielectric layers is in the range of from about 1.0 ×103 ppm to about 1.0×105 ppm, preferably from about 1.0 ×103 ppm to about 1.0×104 ppm. Therefore, the physical defects such as peeling or cracking are suppressed from occurring in the dielectric layer, which leads to a better resistance to dielectric breakdown phenomenon. As a result, a high-definition display is achieved in the PDP of the present invention.
(Correlation between Carbon Concentration and Yellowing Phenomenon)
It can be seen from the graph of
When this requirement (i.e. carbon concentration of 1.0×104 ppm or lower) determined in term of “yellowing phenomenon” is combined with the above requirement of the carbon concentration of from 1.0×103 ppm to 1.0×105 ppm determined in terms of the suppression of the physical defects, it is concluded that the carbon concentration is required to be in the range of from 1.0×103 ppm to 1.0×104 ppm so as to prevent not only the physical defects (i.e. peeling or cracking) but also the yellowing phenomenon.
It is preferred that the first dielectric layer of. the front panel has a two-layered structure composed of a lower layer 13a (i.e. layer being in contact with the electrode) and an upper layer 13b (i.e. layer being in contact with the protective layer) as shown in
The carbon concentration of the lower layer 13a may be 1.0×103 ppm or lower, in which case the yellowing phenomenon can be more effectively prevented.
It is preferred that the carbon contained in the first dielectric layer or in each of the first and the second dielectric layers is derived from an alkyl group bonded to a siloxane backbone (e.g. linear siloxane backbone, cyclic siloxane backbone or three-dimensional network siloxane backbone) as shown below:
In such case, it is preferred that the alkyl group has 1 to 6 carbon atoms. For example, the alkyl group may be a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group or the like. The siloxane backbone may contain one or more kinds of these alkyl groups. A functional group bonded to the siloxane backbone of the glass component is not limited to the alkyl group as long as it contains a carbon atom. For example, the carbon contained in the first dielectric layer or in each of the first and the second dielectric layers may be derived from an alkylene group (e.g. a methylene group, an ethylene group, a propylene group or a butylene group).
Hereinafter, the method for producing PDP of the present invention will be described. The method of the present invention substantially relates to a formation of the dielectric layers wherein the dielectric layer of the front panel and the dielectric layer of the rear panel are formed. According to the method of the present invention, the formation of at least one of the front and rear-sided dielectric layers comprises the steps of:
(1) supplying a dielectric material onto a substrate (the substrate being provided with an electrode thereon), the dielectric material comprising an organic solvent and a glass component (the glass component comprising an alkyl or alkylene group and a siloxane backbone in which they bond with each other); and
(2) heating the supplied dielectric material. This method of the present invention is characterized in that the dielectric material of the step (1) comprises a glass component wherein the alkyl group is bonded to the siloxane backbone, as shown below:
Because of this characteristic, the dielectric layer obtained from the dielectric material by the heat treatment of step (2) can have the carbon concentration of from 1.0×103 ppm to 1.0×105 ppm.
The siloxane backbone of the glass component of the dielectric material used in the step (1) may be a linear, cyclic or three-dimensional network siloxane backbone. In the glass component, the molar ratio of the alkyl group to Si atom of the siloxane backbone is preferably 1 or more, and more preferably in the range of from 1 to 3. It is preferred that the alkyl group has 1 to 6 carbon atoms (in other words, the number of the carbon atom contained in the alkyl group is in the range of from 1 to 6). The alkyl group may be a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group or the like. In this case, the siloxane backbone may contain one or more kinds of these alkyl groups. It should be noted that a functional group bonded to the siloxane backbone of the glass component is not limited to the alkyl group as long as it contains a carbon atom. For example, the glass component may comprise an alkylene group (e.g. a methylene group, an ethylene group, a propylene group or a butylene group) bonded to the siloxane backbone.
In addition to the glass component and the organic solvent, the dielectric material used in the step (1) may further comprise a binder resin if necessary.
It is preferred that the glass component comprises, in addition to the siloxane backbone material (e.g. polyalkylsiloxane), a glass material (e.g. glass frit). Such glass material may be a silicon dioxide (SiO2). In this case, in order to decrease Tg (glass transition temperature) of the silicon dioxide, the glass component preferably contains at least one kind of oxide of a typical element (representative element), selected from the group consisting of sodium oxide (Na2O), potassium oxide (K2O), magnesium oxide (MgO), barium oxide (BaO), lead oxide (PbO) and boron oxide (B2O3). Examples of the organic solvent include alcohols such as methanol, ethanol, propanol, isopropyl alcohol, isobutyl alcohol, ethylene glycol, propylene glycol and terpineol; ketones such as methyl ethyl ketone and cyclohexane; aromatic hydrocarbons such as toluene, xylene and tetramethylbenzene; glycolethers such as cellosolve, methyl cellosolve, carbitol, methylcarbitol, butylcarbitol, propylene glycol monomethyl ether, dipropylene glycol monomethyl ether and triethylene glycol monomethyl ether; acetate esters such as ethyl acetate, butyl acetate, cellosolve acetate, butyl cellosolve acetate, carbitol acetate, butyl carbitol acetate, propylene glycol monomethyl ether acetate; aliphatic hydrocarbons such as octane and decane; and petroleum-based solvents such as petroleum ether, petroleum naphtha and solvent naphtha. Although each of these organic solvents can be used alone, two or more kinds of them may be used in combination. Examples of the binder resin include a polyvinyl alcohol, a polyvinyl butyral, a methacrylate ester polymer, an acrylate ester polymer, an acrylate ester-methacrylate ester copolymer, an α-methylstyrene polymer and a butyl methacrylate resin. Although each of these binder resins can be used alone, two or more kinds of them may be used in combination.
There is no limitation on the proportions of the components contained in the dielectric material. Such proportions may be those employed in common practice of producing the dielectric layer of typical PDPs. For example, in a case where the dielectric material consists of a glass component and an organic solvent, the proportion of the glass component may be in the range of from 40% by weight to 60% by weight and the proportion of the organic solvent may be in the range of from 60% by weight to 40% by weight. In a case where the dielectric material consists of a glass component, an organic solvent and a binder resin, the proportion of the glass component may be about 55% by weight, the proportion of the organic solvent may be about 40% by weight and the proportion of the binder resin may be about 5% by weight.
“A substrate with an electrode formed thereon” onto which the dielectric material is supplied in the step (1) means “the first substrate whereon the first electrodes are formed” with regard to the process of forming the dielectric layer of the front panel. Specifically, for example, a glass substrate whereon the display electrodes are formed is intended. Similarly, “a substrate with an electrode formed thereon” means “the second substrate whereon the second electrodes are formed” with regard to the process of forming the dielectric layer of the rear panel. Specifically, for example, a glass substrate whereon the address electrodes are formed is intended.
The supply of the dielectric material onto “a substrate with an electrode formed thereon” in the step (1) can be carried out by a dip-coating process (to be described in detail in Example). Alternatively, such supply can be carried out by various methods, for example by means of an apparatus shown in
In the step (2), the supplied dielectric material is subjected to heat treatment. “Heating” or “heat treatment” used in this specification and claims substantially means drying and/or calcining. There is no limitation on heating condition as long as it is an ordinary condition suited to the formation of the PDP dielectric layer. For example, the drying may be carried out for from 1 hour to 2 hours under the drying temperature condition of from about 100° C. to about 300° C. The calcination may be carried out for from 1 hour to 2 hours under the calcining temperature condition of from about 400° C. to about 500° C.
Although a few embodiments of the present invention have been hereinbefore described, the present invention is not limited to these embodiments. It will be readily appreciated by those skilled in the art that various modifications are possible without departing from the scope of the present invention.
For example, the heating treatment is not limited to the drying or the calcining, and sputtering, CVD, PVD, EB vapor deposition, plasma gun vapor deposition or sol-gel method may be used to form the dielectric layer. Even in this case, there is occurred no physical defects and yellowing in the dielectric layer as long as it has a carbon concentration of from 103 ppm to 105 ppm.
Test to Obtain Correlation between Carbon Concentration and Dielectric Layer Thickness
The test was conducted to obtain the correlation between “carbon concentration (ppm) of dielectric layer” and “critical thickness (μm) of dielectric layer”. To this end, firstly, a dielectric material paste was applied on a glass substrate (L×W×H:12.5 cm×12.5 cm×1.8 cm, Nippon Electric Glass Co., Ltd.) to form a thin film consisting of the dielectric material. Subsequently, the thin film was dried at 150° C. for 10 minutes, and then was calcined at 500° C. for 1 hour. As a result, a dielectric layer was obtained on the glass substrate.
Specifically, the dielectric layers were formed from the following four kinds of the dielectric material pastes while changing the thickness of the thin film formed on the glass substrate, so as to determine the problem-free thickness above which there is occurred no peeling and no cracking in the dielectric layer (namely, so as to determine the critical thickness of the dielectric layer). In this regard, the carbon concentrations (C concentration) of each dielectric layer were measured to obtain the correlation between the critical film thickness and the carbon concentration.
The thickness of the thin film formed on the glass substrate was controlled by a dip-coating method using an apparatus 50 shown in
The carbon concentration of the dielectric layer was determined by a secondary ion mass spectroscopy (SIMS) wherein a secondary ion was C− of an atomic weight m/e=12. For a quantitative analysis, an oxide sample with a predetermined amount of C ion injected therein was prepared as a standard sample. The quantitative analysis was conducted by using a sensitivity coefficient of C wherein the sensitivity coefficient of C was calculated from C profile determined by using the intensity of the matrix element (oxygen) of the sample as reference. In a case where the intensity of the C profile of the C ion-injected sample prepared for the measurement was too low, a standard sample with a predetermined amount of Si injected therein was prepared wherein the ratio of sensitivity coefficients of C and Si had been preliminarily determined. In this case, the sensitivity coefficient of Si was calculated from the Si profile, and then the sensitivity coefficient of C was extrapolated by a proportional calculation based on the above ratio, and thereby the concentration of C was finally determined. The analysis was conducted by using SIMS 4500 produced by ATOMIKA under the following conditions
The following four kinds of dielectric materials (referred to as “sample A”, “sample B” and “sample C” in the ascending order of contents of alkyl group and alkoxyl group) were used in the test.
Solid Component Content of Sample A:Solid Component Content of Sample B:Solid Component Content of Sample C =20:50:60
The obtained correlation between the carbon concentration (ppm) of the dielectric layer and the critical thickness (μm) of the dielectric layer is shown as a graph in
Test to Obtain Correlation between Carbon Concentration and Heat-Resistant Temperature of Dielectric Layer
The test was conducted to obtain the correlation between “carbon concentration (ppm) of dielectric layer”and “heat-resistant temperature (° C.) of dielectric layer”. To this end, firstly, a dielectric material paste was applied on a glass substrate to form a thin film consisting of the dielectric material. Subsequently, the thin film was dried and calcined. As a result, the dielectric layer was obtained on the glass substrate.
Specifically, the dielectric layers were formed from the above raw material pastes while changing the calcining temperature condition, so as to determine the critical temperature below which there is occurred no peeling and no cracking in the dielectric layer (namely, so as to determine the critical heat-resistant temperature of the dielectric layer). In this regard, the carbon concentration of the dielectric layer was measured. The carbon concentration of the dielectric layer was measured by the secondary ion mass spectrometry (SIMS), similarly to the above “Test to Obtain Correlation between Carbon Concentration and Dielectric Layer Thickness”.
The obtained correlation between the carbon concentration (ppm) of the dielectric layer and the critical heat-resistant temperature (° C.) of the dielectric layer is shown as a graph in
Test to Obtain Correlation between Carbon Concentration and Yellowing
The test was conducted to obtain the correlation between “carbon concentration (ppm) of the dielectric layer” and “yellowing phenomenon occurred in the dielectric layer”. To this end, a plurality of substrates made of soda lime glass was used, and then the display electrodes and the dielectric layer were successively formed on each of the substrates through the calcining process. As the dielectric material paste, the TEOS sample and the sample A described above were used. In this test, sample D (see
“Yellowing” of the obtained dielectric layer was evaluated by determining the value of parameter b (index of the degree of yellowish discoloration) by means of a color meter (NF999, Nippon Denshoku Industries Co., Ltd.).
The obtained correlation between the carbon concentration (ppm) of the dielectric layer and the value of parameter b is shown as a graph in
Now, the mechanism of the above correlation (i.e. mechanism why the value of b increases in proportion to the increase of the carbon concentration) will be described. In general, the yellowing phenomenon of the panel is supposed to be caused due to the reaction between silver of the electrodes and the dielectric layer during the time course of the calcining process. It is known that the colloidal aggregation of the silver causes the yellowing phenomenon. In a case where the dielectric layer contains a large amount of the carbon-containing groups (e.g. alkyl group), voids could be formed in the dielectric layer by the evaporation or dissipation of such groups due to the breaking of the bonding during the calcining process. As a result, the active silver ions can diffuse into the voids. In this case, as the calcining temperature becomes lower, the movement of the silver ions decreases, and thereby the diffused and isolated silver particles tend to aggregate, thus resulting in the occurrence of the yellowing phenomenon. Accordingly, it can be assumed that the carbon concentration of 104 ppm or lower served to prevent the formation of more voids in the dielectric layer during the calcining process, and thereby the silver ion diffusion could be prevented, which resulted in the prevention of the yellowing phenomenon.
In this test, it was additionally confirmed that the similar results could be obtained even by employing the CVD process using TEOS gas for forming SiO film. In this regard, this SiO film was prepared by supplying O2 at a flow rate of 700 sccm, He at a flow rate of 150 sccm and TEOS at a flow rate of 0.25 liters per minute and setting the pressure to 5.9 Pa, followed by carrying out a discharge step with RF output power of 700 W and BIAS=100 W.
The dielectric layer of the PDP of the present invention is substantially free from not only the physical defects such as peeling-off or cracking, but also the yellowing. Therefore, the present invention can contribute to an achievement of a higher definition, a lower power consumption and a higher efficiency of the plasma display panels.
| Number | Date | Country | Kind |
|---|---|---|---|
| P2007-126384 | May 2007 | JP | national |
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