US20050104532A1 - Method for restoring function of plasma display panel and plasma display panel - Google Patents

Abstract

A method for restoring the function of a plasma display panel according to the present invention restores a function of a plasma display panel by raising the temperature of the plasma display panel to 400° C. to 800° C.

Description

BACKGROUND OF THE INVENTION
• (1) Field of the Invention
• The present invention relates to a plasma display panel (PDP) and a method for restoring the function of a PDP, when it becomes deteriorated, the PDP being capable of being used as the display of wall-hanging color televisions and variety of other information display devices for the reason that PDP is inexpensive to produce and is thin with a large, high-resolution screen.
• (2) Description of the Related Art
• Plasma display panels (hereinafter referred to also as PDP(s)) are roughly categorized into AC type and DC type in terms of their drive methods, whereas they are roughly divided into surface discharge type and counter discharge type in terms of their discharge methods. Nowadays, AC surface discharge PDPs are in the mainstream because PDPs of this type can have a high-definition screen and allow for easy and simple production. An attempt has been made to improve viewability and color reproducibility of the PDPs by increasing the luminance of display that utilizes phosphors.
• For example, conventional PDPs include a technology in which phosphor layers are composed of a large number of granular phosphors, each being coated with a thin film made of translucent material whose refractive index is smaller than that of the phosphors (see Japanese Laid-Open Patent publication No. 7-320645). This conventional PDP is capable of producing the following effects: the display luminance is increased thanks to the improvement in the excitation efficiency, which is attributable to the fact that the reflection at the surface layer of the phosphors is reduced and that the transmittance of ultraviolet (UV) light into the phosphors is increased; and the decay of the phosphors can be prevented because the thin-films protect the phosphors from ions at the time of plasma discharge.
• Meanwhile, as AC-driven PDP, which uses a magnesium oxide film as a dielectric protective film, a PDP is known that prevents the degradation of electric characteristics by forming, on the magnesium oxide film, an anti-gas-absorbing film having insulating property and visible-light transmission property so as to prevent the magnesium oxide film from absorbing gas at the fabrication stage (see Japanese Laid-Open Patent publication No. 2000-348626). Since this PDP is capable of reducing the gas absorption of magnesium oxide as well as reducing the breakdown voltage by successively forming an anti-gas-absorbing film on the magnesium oxide film, it is possible to achieve the enhanced stability and improved performance of discharge.
• Furthermore, there has been proposed a PDP fabrication method that includes a process in which: electrodes, which are formed on at least one of a pair of glass substrates, are covered with a dielectric layer; a protective layer for protecting such dielectric layer from discharge and a temporary protective film for temporarily protecting the surface of such protective film up until the panel assembling process, are formed on the surface of such dielectric layer; after said one glass substrate and the other substrate are assembled into a panel, the temporary protective film is removed by generating plasma in the panel (see Japanese Patent No. 3073451). In this fabrication method, since the temporary protective film is successively formed on the protective film after such protective film is formed, no affected layer is formed on the surface of the protective film. Accordingly, it becomes possible for the plasma display panel to have a protective film with excellent discharge properties.
• Meanwhile, it is known that wavelength shift and luminance degradation of phosphors occur when a PDP is sealed in the fabrication and assembling processes or after being used for a long period of time as a product. Such wavelength shift and luminance degradation are especially notable in blue phosphors out of the three color phosphors. In the case of wavelength shift, discoloration of luminescent colors occurs, whereas in the case of luminance degradation, luminescence intensity is reduced, both of which lead to the deterioration in display function.
• Such deterioration in the display function of PDPs is assumed to occur because of one of the following factors: wavelength shift that occurs due to the OH group being bound to BAM (blue phosphor: an abbreviation of BaMgAl₁₀O₁₇) as a result of oxygen defect and luminance degradation due to the oxidization of EU²⁺; and destruction of BAM structure due to (UV) light, i.e., due to lowered crystallinity. However, no proposal has been made about means for restoring a deteriorated display function of PDPs attributable to the above wavelength shift and luminance degradation.
• The present invention has been conceived in view of the above conventional problem, and it is an object of the present invention to provide a method for restoring the function of a plasma display panel that can efficiently restore the display function of a plasma display panel when its display function is deteriorated due to wavelength shift and luminance degradation of phosphors, as well as to provide a plasma display panel that is equipped with means for efficiently restoring its deteriorated display function.
SUMMARY OF THE INVENTION
• In order to achieve the above object, the method for restoring the function of a plasma display panel of the invention according toclaim1 is characterized in that it comprises restoring a function of a PDP by raising a temperature of at least a phosphor layer in the PDP to 400° C. to 800° C.
• The invention according toclaim2 is characterized in that, in the method for restoring the function of a PDP according toclaim1, the PDP is equipped with a heating element, and the temperature of at least the phosphor layer in the PDP is raised to 400° C. to 800° C. by energizing the heating element.
• The method for restoring the function of a plasma display panel of the invention according toclaim3 is characterized in that it comprises restoring a function of a PDP by raising a temperature of a phosphor layer in the PDP to 400° C. to 800° C. through irradiation of light to the PDP.
• The invention according toclaim4 is characterized in that, in the method for restoring the function of a PDP according toclaim3, the light is irradiated to the phosphor layer from outside the PDP through a glass substrate and a dielectric layer in the PDP.
• The method for restoring the function of a plasma display panel of the invention according toclaim5 is characterized in that it comprises restoring a PDP by raising a temperature of a phosphor layer in the PDP to 400° C. to 800° C. by inductively heating conductive particles through application of a high-frequency electric field to the PDP, said conductive particles being mixed, at a predetermined ratio, with phosphor particles that make up the phosphor layer.
• The method for restoring the function of a plasma display panel of the invention according toclaim6 is characterized in that it comprises restoring a PDP by raising a temperature of a phosphor layer in the PDP to 400° C. to 800° C. by inductively heating dielectric particles through application of a high-frequency electric field to the PDP, said dielectric particles being mixed, at a predetermined ratio, with phosphor particles that make up the phosphor layer.
• The plasma display panel of the invention according toclaim7 is characterized in that it comprises: a first substrate on which discharge electrodes and a first dielectric layer are formed, each of said discharge electrodes generating a display discharge and said first dielectric layer covering the discharge electrodes; and a second substrate on which the following are formed: address electrodes that are located orthogonally to the discharge electrodes; a second dielectric layer that covers the address electrodes; barrier ribs that are formed on the second dielectric layer; phosphor layers, each being formed in a concave portion between each two neighboring barrier ribs; and heating elements that are located close to the respective phosphor layers.
• The invention according toclaim8 is characterized in that the heating elements according toclaim7 have a linear shape and are formed on the second substrate, each of the heating elements being located between each two neighboring address electrodes in parallel with said address electrodes and being embedded in the second dielectric layer.
• The invention according toclaim9 is characterized in that the heating elements according toclaim7 have a linear shape and are located above the respective address electrodes in parallel with said address electrodes, the heating elements being embedded in the second dielectric layer.
• The invention according toclaim10 is characterized in that, in the PDP according toclaim7, each of the heating elements is formed at least as part of each of the barrier ribs.
• The invention according toclaim11 is characterized in that the PDP according toclaim7 further comprises: a control drive circuit that controls drive of the discharge electrodes and the address electrodes; and a heating element energization circuit that controls energization of the heating elements so that said heating elements heat the phosphor layers at a predetermined temperature for a predetermined time.
• The invention according toclaim12 is characterized in that the PDP according toclaim7 further comprises: a timer circuit that measures a panel drive time during which the PDP has been driven; a memory that stores a total drive time that is obtained by accumulating each panel drive time measured by the timer circuit, said total drive time being updated and stored into the memory every time the timer circuit newly measures a panel drive time; a function restoration key by which an instruction for energizing the heating element is inputted, said key being operated manually; a heating element energization circuit that energizes the heating elements when the function restoration key is operated; and a control unit operable to indicate that an operation of the function restoration key should be performed, when judging that the total drive time stored in the memory reaches a set time.
• The invention according toclaim13 is characterized in that the PDP according toclaim7 further comprises: a timer circuit that measures a panel drive time during which the PDP has been driven; a memory that stores a total drive time that is obtained by accumulating each panel drive time measured by the timer circuit, said total drive time being updated and stored into the memory every time the timer circuit newly measures a panel drive time; a heating element energization circuit that energizes the heating elements; and a control unit operable to direct the heating element energization circuit to energize the heating elements when judging that the total drive time stored in the memory reaches a set time.
• The invention according toclaim14 is characterized in that the PDP according toclaim13 further comprises a clock circuit that provides time information, wherein when a pre-set time is reached, the control unit directs the heating element energization circuit to energize the heating elements, based on the time information provided by the clock circuit.
• The invention according to claim15 is characterized in that in the PDP according toclaim11, the heating element energization circuit controls the energization of the heating element so that the phosphor layers are heated at 400° C. to 800° C., preferably 500° C. to 600° C., for 10 to 120 minutes, preferably 20 to 60 minutes.
• The disclosure of Japanese Patent Application No. 2003-388616 filed on Nov. 19, 2003 and the disclosure of Japanese Patent Application No. 2004-161925 filed on May 31, 2004 including specification, drawings and claims are incorporated herein by reference in its entirety.
BRIEF DESCRIPTION OF THE DRAWINGS
• These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings that illustrate a specific embodiment of the invention. In the Drawings:
• FIG. 1 is a cutaway perspective view showing a plasma display panel (PDP) according to a first embodiment of the present invention;
• FIG. 2 is a cross-sectional diagram of the PDP along the line A-A shown inFIG. 1;
• FIG. 3 is a cross-sectional diagram of the PDP along the line B-B shown inFIG. 1;
• FIG. 4 is a block diagram showing an electric system of the PDP;
• FIG. 5 is a flowchart showing control processing for restoring display function of the PDP;
• FIG. 6A is a flowchart showing a process of fabricating a front structure;
• FIG. 6B is a flowchart showing a process of fabricating a rear structure;
• FIG. 6C is a flowchart showing a process of assembling the front structure and the rear structure;
• FIGS. 7A, 7B, and7C are diagrams, each showing a different pattern of forming heating elements on the PDP;
• FIG. 8 is a cross-sectional diagram showing a PDP according to a second embodiment of the present invention;
• FIG. 9 is a cross-sectional diagram showing a PDP according to a third embodiment of the present invention;
• FIG. 10 is a flowchart showing processing of fabricating the rear structure of the PDP according to the second embodiment;
• FIG. 11 is a flowchart showing another control processing for function restoration according to each of the aforementioned embodiments;
• FIG. 12 is a flowchart showing a first method for restoring the function of a PDP according to the present invention;
• FIG. 13 is a schematic diagram showing a second method for restoring the function of a PDP according to the present invention;
• FIG. 14 is a schematic diagram showing a variation of the second method for restoring the function of a PDP;
• FIG. 15 is a schematic diagram showing a third method for restoring the function of a PDP according to the present invention; and
• FIG. 16 is a schematic diagram showing a fourth method for restoring the function of a PDP according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
• The following describes the preferred embodiments of the present invention with reference to the drawings.
First Embodiment
• FIG. 1 is a cutaway perspective view showing a plasma display panel (PDP)100 according to the first embodiment of the present invention,FIG. 2 is a cross-sectional diagram of thePDP100 along the line A-A shown inFIG. 1, andFIG. 3 is a cross-sectional diagram of thePDP100 along the line B-B shown inFIG. 1.
• In FIGS.1 to3, afront glass substrate1 is made of a heat-resistant glass for PDP such as soda glass substrate and high-distortion point glass substrate. On one of the surfaces of the front glass substrate1 (the undersurface inFIG. 1/FIG. 3), a plurality ofdischarge electrodes4, each being comprised of a pair of ascan electrode2 and a sustainelectrode3 which are made of silver or Cr—Cu—Cr and which are placed in parallel and opposite each other. Between each two neighboringdischarge electrodes4, a light-shielding layer5 is formed. Eachscan electrode2 and each sustainelectrode3 are respectively made of atransparent electrode2aand atransparent electrode3a, as well as of abus electrode2band abus electrode3bsuch as silver that are electrically connected to thetransparent electrodes2aand3a, respectively.
• Furthermore, the above plurality ofdischarge electrodes4 are covered with adielectric layer6 that is formed on one surface of thefront glass substrate1. Moreover, aprotective film7 made of MgO is formed on one surface of thedielectric layer6. Thisprotective film7 serves also as a secondary electron emission film.
• Meanwhile, arear glass substrate8, which is also made of a heat-resistant glass for PDP such as soda glass substrate and high-distortion point glass substrate as in the case of thefront glass substrate1, is placed in parallel and facing one surface of thefront glass substrate1. On the surface of thisrear glass substrate8 that faces thefront glass substrate1, addresselectrodes10 are formed orthogonally to thedischarge electrodes4, each being comprised of ascan electrode2 and a sustainelectrode3. Between each two neighboringaddress electrodes10, aheating element11 is placed in parallel with theaddress electrodes10. Eachheating element11, which is made of a high-resistivity material such as stainless, nichrome, tungsten, and molybdenum, is formed in a linear form. When power is applied, eachheating element11 generates heat so as to restore the deteriorated display function. Detailed descriptions ofheating elements11 are given later.
• The above-describedaddress electrodes10 andheating elements11 are covered with adielectric layer9 that is on therear glass substrate8. On thisdielectric layer9, a plurality ofstriped barrier ribs12 are formed above therespective heating elements11 in parallel withsuch heating elements11 and theaddress electrodes10. Aphosphor layer13 is formed on the outer surface of eachbarrier rib12 as well as on the surface of thedielectric layer9. Each of the abovedielectric layers6 and9 is an electrical insulating material that serves as a capacitor storing electric charge.
• Thefront glass substrate1 andrear glass substrate8, which are placed facing each other with a predetermined gap between them, are sealed around them, as a result of which a small discharge space is created inside such sealed two substrates. Thus, thescan electrodes2 and sustainelectrodes3, and theaddress electrodes10 are placed orthogonally to each other across such small discharge space. This discharge space is filled, as discharge gas, with one of helium, neon, argon, and xenon, or a mixture of two or more of such gases. Furthermore, asFIG. 2 shows, the discharge space is divided by thebarrier ribs12 into a plurality of display spaces, and an intersection part of eachdischarge electrode4 and addresselectrode10 facing each other across each display space, forms adischarge cell14. In eachdischarge cell14, red, blue, and green phosphor layers13 are successively deposited on a color-by-color basis. A gap between each of thedischarge cells14 is covered with a light-shielding layer5, so that no discharges outside the discharge cells can be visible from outside.
• Aheat insulation material17 is provided on a surface of therear glass substrate8 that is in the opposite direction to thefront glass substrate1. Inside thisheat insulation material17, as shown inFIG. 2, a plurality ofbeams17acreate a plurality ofvacuum insulation spaces17b. Thisheat insulation material17 prevents heat generated by theheating elements11 from emitting to outside from the surface of therear glass substrate8 that is in the opposite direction to thefront glass substrate1.
• FIG. 4 is a block diagram showing the electric system of thePDP100. A plurality of methods are available as a method for driving thePDP100, but since the present invention is applicable to any of such methods, only a typical drive method is described in the present embodiment.
• When thePDP100 is driven, adisplay control circuit18 supplies common sustain voltage to all thedischarge cells14 via a sustainvoltage supply circuit19. When thecontrol unit20 specifies, to thedisplay control circuit18, eachdischarge cell14 to be driven, thedisplay control circuit18 selects, via anX address circuit21 and aY address circuit22, anaddress electrode10 and adischarge electrode4 corresponding to eachdischarge cell14 specified by thecontrol unit20 from among a plurality ofdischarge cells14, and energizes such selectedaddress electrode10 and dischargeelectrode4. Accordingly, in each selecteddischarge cell14, a small writing discharge first occurs between thescan electrode2 and the sustainelectrode3, as a result of which a wall charge is formed. Using this wall charge, a main discharge occurs between two neighboringdischarge electrodes4, and UV light that is generated by such main discharge is then emitted to the phosphor layers13. Accordingly, a color image is displayed on thePDP100.
• When a total drive time of thePDP100 reaches 2000 to 3000 hours, for example, its display function becomes slightly deteriorated in the form of wavelength shift and luminance degradation especially in the blue phosphors out of the phosphor layers13 of each color. In view of this, the present embodiment is equipped with a function of restoring the deteriorated display function, when the above total drive time is reached, by presenting a screen display that prompts a user to carry out an operation for restoring the display function and then by energizing theheating elements11 if such user has carried out the restoration operation as prompted by the screen display. Here, screen display is only an example, and therefore other means such as lamp and alarm may be used to notify the user that an operation for restoring the display function should be performed.
• As the constituent elements for restoring the display function, thePDP10 is equipped with: a heatingelement energization circuit23 that energizes theheating elements11 by supplying power to them in response to an instruction from thecontrol unit20; atimer circuit24 that measures a total drive time; amemory27 that stores the total drive time measured by thetimer circuit24; apower detection circuit28 that detects whether or not thePDP100 is powered on; afunction restoration key30 that gives an instruction, when it is operated, that processing for restoring the display function should be performed; and aninterlock circuit29 that locks thefunction restoration key30 so that thefunction restoration key30 cannot be operated, when thepower detection circuit28 detects that thePDP100 is powered on.
• Next, referring to a flowchart ofFIG. 5, a description is given of control processing for restoring the display function. Thecontrol unit20 continuously monitors whether the power of thePDP100 is on or not, i.e., whether thePDP100 is in the driven state or not, based on the presence/absence of a power-on signal inputted from the power detection circuit28 (Step S1). Every time there is an input of power-on signal, thecontrol unit20 causes thetimer circuit24 to start a time measuring operation (Step S2). Then, thecontrol unit20 monitors if a power-on signal will stop being inputted as a result of terminating the drive of the PDP100 (Step S3). When judging that thePDP100 has been powered off and no power-on signal is inputted any more, thecontrol unit20 obtains a new total drive time by adding the total drive time read from thememory27 to the drive time measured by the timer circuit24 (Step S4), and judges whether such obtained total drive time exceeds a predetermined time or not (Step S5). Here, as the predetermined time, 2000 to 3000 hours is set after which processing for restoring the display function is required to be performed.
• When judging that the predetermined time is not exceeded, thecontrol unit20 updates thememory27 by storing a newly obtained total drive time (Step S6), after which thecontrol unit20 returns to Step S1 to repeat the above control processing. Meanwhile, when judging that the predetermined time is exceeded (Step S5), thecontrol unit20 directs thedisplay control circuit18 to present a screen display that prompts the user to operate the function restoration key30 (Step S7). Accordingly, the display screen shows a message saying, for example, as follows: “Display function restoration processing is required now. Press function restoration key after turning off the power.”
• Then, thecontrol unit20 first monitors whether or not the user has powered off thePDP100 as promoted by the screen display, on the basis of the presence/absence of a power-on signal from the power detection circuit28 (Step S8), and when judging that thePDP100 has been powered off, directs theinterlock circuit29 to unlock the function restoration key30 (Step S9). Stated another way, thefunction restoration key30 is usually locked by theinterlock circuit29 so that the key30 cannot be operated. This aims at preventing the occurrence of inconveniences to be caused by the fact that function restoration processing is initiated by the user who has operated thefunction restoration key30 by mistake although function restoration is not required.
• Next, thecontrol unit20 judges whether the power has been turned on or not (Step10), and when thePDP100 is not powered on, thecontrol unit20 then judges whether thefunction restoration key30 has been operated by the user or not (Step S11). Here, when the user performs an operation to power on thePDP100 before operating thefunction restoration key30, the control unit directs theinterlock circuit29 to lock thefunction restoration key30 so that it cannot be operated (Step S12). This process aims at preventing the occurrence of inconveniences caused by the execution of function restoration processing while thePDP100 is in the power on state. Possible inconveniences are described later. After this, thecontrol unit20 returns to Step57, and repeatedly performs the control processes of Steps S7 to S12, after causing thedisplay control circuit18 to present a screen display that prompts the user to operate thefunction restoration key30.
• Meanwhile, when judging that thefunction restoration key30 has been operated while thePDP100 is in the power off state (Step S1), thecontrol unit20, after a certain lapse of time, directs the heatingelement energization circuit23 to energize each of theheating elements11 and causes thetimer circuit24 to start a time measuring operation (Step S13). Accordingly, the energizedheating elements11 generate heat, which is transferred to the phosphor layers13 through thedielectric layer9 and thebarrier ribs12. Accordingly, the phosphor layers13 are heated. By heating the phosphor layers13, it becomes possible to improve crystallinity that has been lowered after the exposure to UV light for a certain accumulated time, and therefore to restore its wavelength and luminance to the original state. A mechanism for restoring the wavelength and luminance of the phosphor layers13 by heating them in the above manner is the same as a process of restoring crystallinity by means of annealing that is often used for other materials too.
• Here, by heating the phosphor layers13 at a temperature in the range of 400° C. to 800° C., preferably 500° C. to 600° C. as a predetermined heating temperature, it is possible to achieve a favorable effect of wavelength and luminance restoration. Therefore, the heatingelement energization circuit23 energizes theheating elements11 so that the phosphor layers13 are heated at a temperature within the above range. However, there occurs a temperature gradient between the temperature of heat generated by theheating elements11 and the temperature at which the phosphor layers13 are heated because there exist thedielectric layer9 and thebarrier ribs12 therebetween. Therefore, the temperature of heat generated by theheating elements11 needs to be set in consideration of such temperature gradient. For example, when the heating temperature of the phosphor layers13 is set to 500° C., the temperature of theheating elements11 should be set to 600° C. In this case, since theheat insulation material17 is provided on the other surface of therear glass substrate8, the temperature of the outer surface of theheat insulation material17 is reduced to 100° C. or lower. Thus, there is no fear that the user burns his/her hands or that electric components attached near thePDP100 are degraded because of the heat.
• Furthermore, it is preferable to set the heating time of the phosphor layers13 at the above heating temperature to be in the range between 10 and 120 minutes inclusive, and more preferably in the range between 20 and 60 minutes inclusive. This is because heating of less than 10 minutes is not sufficient to restore the wavelength and luminance of the phosphor layers13, whereas heating of over 60 minutes needlessly consumes electric power. Note that “heating time” here refers to a length of time during which the temperature of the phosphor layers13 remains at the above target heating temperature after the temperature of the phosphor layers13 reaches such target heating temperature, rather than the time from when the heating of thephosphor13 starts to when the temperature of the phosphor layers13 returns to ordinary temperature. In Step S13, therefore, theheating elements11 starts being energized after a certain lapse of time that is required by the respective constituent elements of thePDP100 to go back to ordinary temperature after the power is turned off.
• Moreover, after directing the heatingelement energization circuit23 to energize the heating elements11 (Step S13), thecontrol unit20 monitors whether the above predetermined heating time has elapsed or not on the basis of the time measured by the timer circuit24 (Step S14), while continuously monitoring if the user will not perform an operation to turn on the power by mistake (Step S15). If the user turns the power on while function restoration processing of the phosphor layers13 is carried out, thePDP100 moves to driven state, making it impossible for the function restoration processing of the phosphor layers13 to be performed correctly. For the same reason, theinterlock circuit29 locks thefunction restoration key30 when the power is on so that the key30 will not be operated.
• Upon judging that the power of thePDP100 has been turned on while the function restoration processing of the phosphor layers13 is taking place (Step S15), thecontrol unit20 directs the heatingelement energization circuit23 to suspend the energization of theheating elements11 and directs theinterlock circuit29 to lock thefunction restoration key30 so that it will not be operated (Step S16). Furthermore, after resetting the time measuring operation of the timer circuit24 (Step S17), thecontrol unit20 returns to Step S7 to repeatedly perform the control processes of the above Steps S7 to S15.
• Meanwhile, when judging that a predetermined heating time has elapsed after the start of the function restoration processing of the phosphor layers13 (Step S14), thecontrol unit20 directs the heatingelement energization circuit23 to stop energizing theheating elements11 and directs theinterlock circuit29 to lock thefunction restoration key30 so that it will not be operated (Step S18), as well as deleting the contents stored in the memory27 (Step S19) to complete the function restoration processing of the phosphor layers13.
• Note that in the present embodiment, an example case has been illustrated where theheating elements11 are provided for the respective phosphor layers13 of red, blue, and green colors, but it is also possible to achieve an effect equivalent to the above described effect ifheating elements11 are provided only near the blue phosphor layers13. This is because wavelength shift and luminance degradation are especially notable in blue phosphor layers13, while wavelength shift and luminance degradation of red and green phosphor layers13 are small.
• Next, referring toFIGS. 6A, 6B, and6C, a description is given of a method for fabricating thePDP100 according to the present embodiment. First, referring toFIG. 6A, a description is given of processing of fabricating a front structure. After forming an Indium Tin Oxide (ITO) film on the cleansedfront glass substrate1 by a sputtering method,transparent electrodes2aand3aare formed by removing unnecessary parts using a known photo-etching method (Step20). Then,bus electrodes2band3bare formed on thesetransparent electrodes2aand3bby means of a printing method that uses screen or by a photo-etching method, for example (Step S21).
• Next, after forming a light-shielding layer5 between each of thedischarge electrodes4 formed on thefront glass substrate1, eachdischarge electrode4 being comprised oftransparent electrodes2aand3aandbus electrodes2band3b, paste made from glass powder is applied all over thefront glass substrate1 by means of printing, for example. Then, thefront glass substrate1 is heated at around 600° C. to allow the glass powder layer to melt, as a result of which atransparent dielectric layer6 is formed (Step S22). Finally, aprotective film7 made of magnesium oxide is formed on thedielectric layer6 by a vacuum evaporation method (Step S23), and the fabrication of the front structure is completed.
• Next, referring toFIG. 6B, a description is given of processing of fabricating the rear structure. First, addresselectrodes10 are formed on the cleansedrear glass substrate8 into a predetermined pattern by using a thick-film printing method utilizing silver paste (Step S24). Subsequently, processes of fabricatingheating elements11 of Steps S25 to S28 are performed. More specifically, using a dispenser or the like, paste, which is obtained by mixing glass powder with a powdery high-resistivity material (e.g. stainless, nichrome, tungsten, molybdenum) and then by mixing the resulting powder with a solvent, is applied between each of theaddress electrodes10 on the rear glass substrate8 (Step S25). After this, such applied paste is patterned into lines, each with a width of 50 μm to 100 μm (Step S26), dried (Step S27), and then burnt (Step S28). Accordingly, the glass components included in the paste melt to serve as glue with which glasses are coupled onto therear glass substrate8, and the high-resistivity material is fixed onto the outer surface of therear glass substrate8, allowing a predetermined pattern ofheating elements11 to be formed.
• Next, after applying, by means of printing or the like, paste made from glass powder all over therear glass substrate8 on which theaddress electrodes10 andheating elements11 have been formed, therear glass substrate8 is heated at around 600° C. to allow the glass power layer to melt and atransparent dielectric layer9 to be formed (Step S29). Then, by performing overlay printing by repeating thick-film printing that uses low melting glasses and drying, glass powder ribs are formed, which are then burnt to form barrier ribs12 (Step S30). Furthermore, on thedielectric layer9 and thebarrier ribs12, phosphor layers13 that are colored into red, green, and blue are formed in therespective discharge cells14 by means of thick-film printing (Step S31). Finally, a sealing layer serving as a vacuum sealer is formed around therear glass substrate8 by a printing method, and the fabrication of the rear structure is completed.
• Next, referring toFIG. 6C, a description is given of processing of assembling the front structure and the rear structure. The front structure as thefront glass substrate1 and the rear structure as therear glass substrate8 fabricated through the above-described processes are assembled at mutually opposing positions and tentatively fixed in such position (Step S32).
• Then, a sealing/evacuation/gas filling process (Step S33) is performed. In this process, a chip tube for taking discharge gas to inside is formed on an air exist of therear glass substrate8, and then the two substrates are burnt in a calcining furnace for sealing. Accordingly, the seal glass in the low-melting sealing layer formed in the final process of fabricating the rear structure and the seal glass of the chip tube melt and weld the twoglass substrates1 and8 and the exhaust tube together. As a result, one panel is formed. As gas filling, the exhaust tube gets connected to a vacuum device so as to exhaust the gas inside the panel in a high-temperature atmosphere that is set at around 400° C. in the high-temperature calcining furnace. Then, by filling the panel with discharge gas (e.g. a mixture of neon and xenon), the fabrication of a requiredPDP100 completes. Finally, an aging process is performed in which voltage that is higher than the breakdown voltage is applied to all thedischarge electrodes4 of the completedpanel100 to perform long-time discharge (Step S34). This process aims at further stabilizing discharge characteristics.
• This fabrication method is realized by adding the processes of fabricating heating elements11 (Steps S25 to S28) to the existing processes, and thus such processes of fabricating theheating elements11 may be performed prior to the process of fabricating address electrodes10 (Step S24). In other words, sinceheating elements11 can be successively formed in the same fabrication process as that ofaddress electrodes10, it is possible to formheating elements11 through simple fabrication processes. As a result, the present method does not require high fabrication cost compared with the existing fabrication methods.
• FIGS. 7A, 7B, and7C are diagrams showing preferable forming patterns ofheating elements11.FIG. 7A shows thatheating elements11 are formed like a ladder by arranginglinear heating elements11 in parallel with each other and commonly connecting the both ends of eachheating element11 to lead them to joiningterminals01 and02.FIG. 7B shows thatheating elements11 are formed in a zigzag pattern by arranginglinear heating elements11 in parallel with each other, serially connecting theheating elements11, and leading the both ends of such serial connection to joiningterminals01 and02, respectively. Theheating elements11 that are formed according to the patterns shown inFIGS. 7A and 7B can be supplied with power from the heatingelement energization circuit23 shown inFIG. 4 to be energized.FIG. 7C shows thatheating elements11 are formed independently of each other by simply arranging them in parallel with each other without leading them to joiningterminals01 and02. Each of theseheating elements11 is one to which radio frequencies and microwaves are radiated from outside, by providing a high-frequency field generation unit or the like instead of the heatingelement energization circuit23 shown inFIG. 4, in order to make theheating elements11 generate heat by themselves by means of induction heating. Note that it is preferable that top seven and bottom seven connection points illustrated inFIG. 7A serve as low-voltage resistors that prevent voltage effects in a lateral direction in the drawing.
• FIG. 8 is a cross-sectional diagram showing aplasma display panel101 according to the second embodiment of the present invention. This cross-sectional diagram shows thePDP101 that is cut at a position corresponding to the A-A line shown inFIG. 1. In this drawing, consistent elements that are the same as or equivalent to those shown inFIG. 2 are assigned the same reference numbers, and descriptions thereof are omitted. Whileheating elements11 are provided between each two neighboringaddress electrodes10 in the first embodiment,heating elements11 of thePDP101 of the present embodiment are embedded in thedielectric layer9, facing therespective address electrodes10 across the dielectric layer. The other constituent elements are the same as those presented in the first embodiment.
• As is obvious from a comparison betweenFIG. 2 andFIG. 8, since theheating elements11 in thePDP101 are placed closer to the phosphor layers13 than those of thePDP100 of the first embodiment, it is possible to transfer the heat generated by theheating elements11 efficiently to the phosphor layers13, which are then heated efficiently as a result. This makes it possible to achieve the effect that the phosphor layers13 are heated at a predetermined temperature, while setting the heat temperature of theheating elements11 to lower compared with the first embodiment. Note that theheating elements11 are energized by thecontrol unit20 executing the control processing based on the flowchart shown inFIG. 5.
• FIG. 9 is a cross-sectional diagram showing aplasma display panel102 according to the third embodiment of the present invention. This cross-sectional diagram shows thePDP102 that is cut at a position corresponding to the A-A line shown inFIG. 1. In this drawing, consistent elements that are the same as or equivalent to those shown inFIG. 2 are assigned the same reference numbers, and descriptions thereof are omitted. Whileheating elements11 are provided between each of theaddress electrodes10 in the first embodiment, plural steps (three steps in the present embodiment) ofheating elements11, which are placed with a gap between each of them and which are embedded in thebarrier ribs12, are in thePDP102 of the present embodiment. The other construction is the same as that of the first embodiment.
• In thisPDP102, since plural steps ofheating elements11 are placed closer to the phosphor layers13 than those of thePDPs100 and101 of the first and second embodiments, it is possible to transfer the heat generated by theheating elements11 in an extremely efficient manner and therefore to heat the phosphor layers13 efficiently. This makes it possible to achieve the effect that the phosphor layers13 are heated at a predetermined temperature, while setting the heat temperature of theheating elements11 to further lower than in the case of the second embodiment. Here, theheating elements11 are energized by thecontrol unit20 executing the control processing on the basis of the flowchart shown inFIG. 5. Note that a part or the whole of therespective barrier ribs12 may be made of high-resistivity material so that power is applied to each portion made of high-resistivity material, rather than embedding theheating elements11 in thebarrier ribs12. With this construction, thebarrier ribs12 serve also as heating elements. In this case, it is possible to heat the phosphor layers13 in a more efficient manner.
• FIG. 10 is a flowchart showing processing of fabricating the rear structure of thePDP101 illustrated inFIG. 8 according to the second embodiment. First, addresselectrodes10 are formed on the cleansedrear glass substrate8 into a predetermined pattern by using a thick-film printing method that utilizes silver paste (Step S35). Subsequently, by means of printing or the like, paste made from glass powder is applied all over therear glass substrate8 on which theaddress electrodes10 have been formed. Then, thefront glass substrate8 is heated at around 600° C. to allow the glass powder layer to melt, as a result of which a transparent reardielectric layer9athat is thick enough to cover theaddress electrodes10 is formed (Step S36).
• Next, photosensitive paste including a high-resistivity material is formed to be applied over an upper surface of eachaddress electrode10 on therear dielectric layer9a(Step S37). Then, by forming such applied photosensitive paste into a predetermined pattern through exposure and development processes (Step S38),heating elements11 are formed. Then, a transparent front dielectric layer9bis formed through a process equivalent to Step S36 described above in a manner that the first and seconddielectric layer9aand9bcan form adielectric layer9 having a predetermined thickness as a whole (Step S39).
• Then, by performing overlay printing by repeating thick-film printing that uses low melting glasses and drying, glass power ribs are formed, which are then burnt to form barrier ribs12 (Step S40). Furthermore, on thedielectric layer9 and thebarrier ribs12, phosphor layers13 that are colored into red, green, and blue are formed in therespective discharge cells14 by means of thick-film printing (Step S41). Finally, a sealing layer serving as a vacuum sealer is formed around therear glass substrate8 by a printing method, and the processing of fabricating the rear structure is completed. Note that the processing of fabricating the front structure and the processing of assembling the front structure and the rear structure are the same as those shown inFIGS. 6A and 6C.
• While the present fabrication method involves two processes for forming thedielectric layer9 compared with the processing shown inFIG. 6 of the first embodiment, there is an advantage that theheating elements11 can be placed closer to the phosphor layers13 than in the case of thePDP100 of the first embodiment. Note that theheating elements11 may be formed through each of the processes of Steps S25 to S28 shown inFIG. 6B of the first embodiment, rather than through each of the processes of Steps S37 and S38 shown inFIG. 10. Furthermore, theheating elements11 may also be formed through the known fabrication processes that are the same as those for fabricating rear glasses of automobiles.
• Moreover, while no diagrammatic illustration is given for processing of fabricating the rear structure of thePDP102 shown inFIG. 9 according to the third embodiment, it is possible to form, through the following procedure, a construction in which plural steps ofheating elements11 with a gap between them are embedded in the barrier ribs12: formingaddress electrodes10 and adielectric layer9 on therear glass substrate8 through processes equivalent to Steps S24 and S29 shown inFIG. 6B; and then repeatedly and alternately performing the process of Step S30 shown inFIG. 6B for forming thebarrier ribs12 and the processes of Steps S25 to S28 shown inFIG. 6B or the processes of Steps S37 and S38 for forming theheating elements11.
• In the first or third embodiment, by thecontrol unit20 shown inFIG. 1 executing the control processing based on the flowchart ofFIG. 5, a screen display is presented to prompt the user to perform the function restoration operation and the user then initiates processing of function restoration by manually operating thefunction restoration key30 based on such display screen. In addition to this construction, thecontrol unit20 may also perform function restoration processing automatically upon judging that the PDP is in need of function restoration.FIG. 11 is a flowchart showing control processing performed by thecontrol unit20 when it automatically performs function restoration processing. The following describes such control processing shown inFIG. 11. Note that reference numbers of the constituent elements shown inFIG. 4 are referred to when explainingFIG. 11. However, in the control processing shown inFIG. 11, the function restoration key shown inFIG. 4 is not required, and theinterlock circuit29 locks the power key instead so that it will not be operated. Furthermore, a clock circuit is additionally required for this control processing.
• Thecontrol unit20 continuously monitors whether the power of the PDP is on or not based on the presence/absence of a power-on signal inputted from the power detection circuit28 (Step S42). Every time there is an input of power-on signal from thepower detection circuit28, thecontrol unit20 causes thetimer circuit24 to start its operation (Step S43). Then, thecontrol unit20 monitors if a power-on signal will stop being inputted from thepower detection circuit28 as a result of terminating the drive of the PDP (Step S44). When judging that the PDP is powered off and no power-on signal is inputted any more, thecontrol unit20 obtains a new total drive time by adding the total drive time read from thememory27 to the drive time measured by the timer circuit24 (Step S45), and judges whether such obtained total drive time exceeds a predetermined time or not (Step S46). Here, as the predetermined time, 2000 to 3000 hours is set after which processing for restoring the display function is required to be performed.
• When judging that the predetermined time is not exceeded, thecontrol unit20 updates thememory27 by storing a newly obtained total drive time (Step S47), after which thecontrol unit20 returns to Step S42 and repeats the above control processing. Meanwhile, when judging tht the predetermined time is exceeded (Step S46), thecontrol unit20 directs thedisplay control circuit18 to present a screen display indicating that function restoration processing is to be performed (Step S48). Accordingly, the display screen shows a message saying, for example, as follows: “Display function restoration processing starts after the power is turned off. Note that you cannot turn on the power until five next morning”.
• Then, thecontrol unit20 monitors if a predetermined processing start time is reached, with reference to a time signal from the clock circuit (Step S49). Here, the processing start time is set in advance within the time period during which the user has the least possibility to turn the power on (e.g. from two to four in the morning) or in the time period during which the PDP is not used, the time period being detected by thecontrol unit20 from a certain length of time starting from when the PDP use starts.
• When judging that the processing start time is reached (Step S49), thecontrol unit20 judges whether the power is turned off or not based on the presence/absence of a power-on signal from the power detection circuit28 (Step S50). If the power is turned on, thecontrol unit20 causes thedisplay control circuit18 to present a screen display that prompts the user to turn the power off, such as “When the power gets turned off, display function restoration processing is initiated” (Step S51) and then waits for the user to turn the power off.
• When judging that the power has been turned off, thecontrol unit20 directs theinterlock circuit29 to lock the power key so that it cannot be turned on (Step S52), as well as directing the heatingelement energization circuit23 to energize each of theheating elements11 and causes thetimer circuit24 to start time measuring operation (Step S53). Accordingly, the energizedheating elements11 generate heat, which is transferred to the phosphor layers13 to heat them. Then, thecontrol unit20 monitors whether a predetermined heating time has elapsed or not on the basis of the time measured by the timer circuit24 (Step S54). Here, a heating temperature and a heating time of theheating elements11 are set equivalently to those of the first embodiment.
• When judging that a predetermined heating time has elapsed since the function restoration processing of the phosphor layers13 started, thecontrol unit20 directs the heatingelement energization circuit23 to stop energizing theheating elements11 as well as directing theinterlock circuit29 to unlock the power key (Step S55), and deletes the contents stored in the memory27 (Step S56) to complete the function restoration processing of the phosphor layers13. Accordingly, the crystallinity of the phosphor layers13 is improved and their wavelength and luminance are restored to the original state.
• The first and third embodiments have a configuration in which theheating elements11 are provided, and display function restoration processing is performed by energizing theheating elements11 when a total drive time reaches a predetermined time so as to heat the phosphor layers13. However, it is also possible to cause a conventional PDP to perform display function restoration processing if such conventional PDP does not have a mechanism for restoring display function. Next, referring to a flowchart shown inFIG. 12, a description is given of a first method for restoring the function of a PDP according to the present invention.
• Before explainingFIG. 12, a description is given of a PDP. In addition to the conventional constituent elements, the PDP is equipped with thepower detection circuit28, thetimer circuit24, thememory27, and thecontrol unit20 that are shown inFIG. 4. As in the case of the first or third embodiment, the control unit20 (i) causes thetimer circuit24 to time a length of time during which a power-on signal is inputted from thepower detection circuit28, (ii) performs a calculation for adding the length of time measured by thetimer circuit24 so as to obtain a total drive time, (iii) causes thememory27 to store a total drive time every time a total drive time is updated, and (iv) continuously monitors whether the total drive time has reached a predetermined time or not. Furthermore, upon judging that the above predetermined time has been reached, thecontrol unit20 gives a direction that a screen display should be presented to prompt the user to request the manufacturer of the PDP to perform function restoration processing. For example, the screen display says as follows: “Display function restoration processing is required now. Contact the store where you purchased it”.
• The manufacturer, after receiving a notification from the user who has contacted it as prompted by the above screen display, collects the PDP and removes the discharge gas (e.g. a mixture of neon and xenon) from such collected PDP (Step S57). Then, the manufacturer puts the PDP into the heating furnace to heat it at a predetermined heating temperature for a predetermined period of time, while exhausting air from the internal spaces from which the discharge gas has been removed (Step S58). The heating temperature and heating time are as described in the first or third embodiment. Through this heating processing, the crystallinity of the phosphor layers13 that has become lowered after the exposure to UV radiation for a certain accumulated time is improved and their wavelength and luminance are restored to the original state. After this heating processing for restoring display function, the manufacturer fills the PDP with discharge gas to return it to the original state (Step S59). Finally, the manufacturer performs an aging process in which voltage that is higher than the breakdown voltage is applied to all thedischarge electrodes4 of the completed panel to perform long-time discharge (Step S60).
• This method for restoring the function of a PDP is capable of draining, to outside, impurities that are generated inside the internal spaces at the time of heating, since discharge gas is removed from the PDP prior to heating, and air is exhausted, while the PDP is heated, from the internal spaces from which discharge gas has been drained. Accordingly, since it is possible to prevent the occurrence of adverse effects caused by the fact that the impurities vaporized by heating react with the phosphor layers13, it becomes possible to restore the display function in a further efficient manner. What is more, since the PDP is heated in a heating furnace according to the present restoration method, no temperature gradient occurs across the area from the vicinity of the heating elements to the phosphor layers13, in the case where theheating elements11 are provided as described above. Accordingly, it is possible to heat the phosphor layers13 correctly at a heating temperature that is set to the heating furnace and therefore to perform a desirable function restoration processing. Note that the same function restoration effect can be achieved if the collected PDP is inserted directly into the heating furnace for heating, without performing the above gas exchange.
• FIG. 13 is a schematic diagram showing a second method for restoring the function of a PDP according to the present invention. As in the case of the PDP presented for the explanation of the first restoration method shown inFIG. 12, aPDP110 according to this embodiment is equipped with thepower detection circuit28, thetimer circuit24, thememory27, and thecontrol unit20 shown inFIG. 4, without including any heating elements and energization units. In other words, in the present restoration method, as in the case of the first restoration method shown inFIG. 12, the manufacturer collects thePDP110 when receiving a notification from the user who has contacted it as prompted by the above screen display, but it restores the function of the phosphor layers by heating them by use of a photoirradiation unit, rather than through heating processing utilizing the heating units as in the case of the first restoration method.
• Referring toFIG. 13, the present embodiment uses, as a photoirradiation unit, aphotoirradiation apparatus31 that is comprised of a plurality ofxenon flash lamps32 that are placed in parallel with each other. By flashing each of suchxenon flash lamps32 in synchronization with alamp drive circuit33, lights L are irradiated to thePDP110. Then, by irradiating such lights L to the outer surface of the phosphor layers13 via theglass substrate1,dielectric layer6, andprotective film7 shown inFIG. 1, the surface of the phosphor layers13 are heated at 400° C. to 800° C.
• In the present embodiment, an example case is presented in which the lights L are directly irradiated to thePDP110 without disassembling it. In this case, in order to heat the phosphor layers13 at the above-described temperature, a condition needs to be set as follows: as axenon flash lamp32, a lamp that emits a light L with wavelengths in the range between 200 nm and 4.5 μm inclusive should be selected. This is because the use of a light L with a wavelength of 4.5 μm or less makes it possible for the light L to reliably reach the phosphor layers13 via theglass substrate1,dielectric layer6, andprotective film7, whereas the reason for using a light L with a wavelength of 200 nm or more is because a light L with a wavelength of 200 nm or less might destroy the phosphor crystallinity of the phosphor layers13. Note that it is more preferable to use an infrared radiation with a wavelength of 800 nm or more since it is conceivable that a visible light's high reflectivity and transmittance from and to the phosphor layers13 hinders the heating from being performed in an efficient manner.
• Meanwhile, thedrive control unit34 controls the power supply from thelamp drive circuit33 to thexenon flash lamps32 so that each of thexenon flash lamps32 emits a light L with energy densities in the range between 100J/cm²and 5000J/cm²inclusive. This is because the energy density of 100J/cm²or less is not enough for heating, whereas the energy density of 5000J/cm²or more is too high since luminance restoration of the phosphor layers13 becomes saturated, resulting in a waste of energy.
• Furthermore, thedrive control unit34 controls a length of time for which thephotoirradiation apparatus31 comprised of a plurality ofxenon flash lights32 remains driven to irradiate lights L, to an extremely short time such as in the range between 1 nsec and 10 msec inclusive. This is because it is technically difficult to drive eachxenon flash lamp32 to make it flash for an extremely short time of 1 nsec or less and it is costly even if it is possible. Meanwhile, if eachxenon flash lamp32 is driven for 10 msec or more, heat is transferred further than the outer surface of the phosphor layers13, and restoration processing is performed also for phosphor particles that are not suffering from serious degradation, resulting in a waste of processing energy and processing time. Furthermore, there also occurs the possibility that constituent elements of thePDP110 become cracked by thermal shock because thermal expansion coefficients are different on an element-by-element basis, and that defects such as the coming off of films and quality degradation occur due to the fact that the constituent elements other than the phosphor layers13 are adversely affected because thermal expansion coefficients are different for each constituent element.
• Note that in the case where the collectedPDP110 is disassembled and lights L are directly irradiated to the phosphor layers13, there is no need to set the above conditions concerning the wavelength and energy density of each light L and concerning a length of time during which lights L should be irradiated. In this case, however, processes of disassembling and reassembling thePDP110 are required.
• In such case where the lights L are directly irradiated to the phosphor layers13, there is an advantage that only a least possible processing energy as well as a shorter processing time is required since only the outermost surface of eachphosphor layer13 suffering from the most serious degradation is heated. Furthermore, since a processing time is extremely short, there is no thermal shock on thePDP110, which causes no possibility that the constituent elements other than the phosphor layers13 become subject to the coming off of films and quality degradation.
• Note that phosphor particles, which can be restored by the irradiation of lights L, emit lights according to the following mechanism: their parent body or parent crystal such as BAM absorb energy from outside; the absorbed energy is then transferred to luminescent ions; the ions in the ground state move to the excited state; the excited ions reach the luminescence level that is a more stable excited state, while losing energy due to thermal/lattice vibration; and the excited ions return to the ground state, emitting lights.
• FIG. 14 is a schematic diagram showing another example of the second method for restoring the function of a PDP according to the present invention. In this example, laser beams are used as lights L to be irradiated. More specifically, laser beams emitted from anexcimer laser apparatus37 are irradiated to thePDP110, with their linear beam shape maintained using an optical system. Astage39, on which thePDP110 is fixedly mounted, moves in directions indicated by arrows so that laser beams L are irradiated all over thePDP110. The same effect as described inFIG. 13 is achieved through the use of the laser beams L.
• FIG. 15 is a schematic diagram showing a third method for restoring the function of a PDP according to the present invention. The present embodiment requires a condition that phosphor layers of aPDP111 should be composed of phosphor particles to which conductive particles whose electric resistivity is in the range between 8 μΩcm and 200 μΩcm inclusive are mixed at a predetermined ratio. Here, conductive particles are mixed in a ratio of 0.1 (wt %) to 10 (wt %) with regard to the whole phosphor layers. Moreover, it is preferable to use iron, nickel, or chromium as conductivity particles. Furthermore, thePDP111 is equipped with thepower detection circuit28, thetimer circuit24, thememory27, and thecontrol unit20 shown inFIG. 4, as in the case of thePDP110 used in the second restoration method.
• In this restoration method, as in the case of the above-described second restoration method, a manufacturer collects thePDP111, when receiving a notification from its user who has contacted such manufacturer as prompted by the screen display, and inductively heats the conductive particles mixed in the phosphor layers by applying a high-frequency electric field to thePDP111. Accordingly, the phosphor layers are heated and their functions are restored. More specifically, asFIG. 15 shows, the collectedPDP111 is placed onto atubular base frame40. Then, by applying high-frequency power from a high-frequency power supplier42 to spiral heating coils41 such as IH coils that are placed below thebase frame40, the heating coils41 generate electromagnetic waves by which a high-frequency electric field is applied to the phosphor layers of the PDP. Accordingly, the conductive particles included in such phosphor layers are inductively heated and generate eddy currents. The phosphor particles included in the phosphor layers are heated by Joule heat caused by such eddy currents, as a result of which the function of the phosphor layers is improved.
• Conductive particles are mixed to the phosphor layers with a mixing ratio of 0.1 (wt %) to 10 (wt %), as described above. This is because a mixing ratio of 0.1 (wt %) or less is not enough to inductively heat thePDP111 and therefore a function restoration of the phosphor layers cannot be performed as desired, whereas a mixing ratio of 10 (wt %) or over leads to a reduction in the number of phosphor particles included in the phosphor layers and therefore the phosphor layers cannot achieve desired luminance.
• Furthermore, as conductive particles to be mixed into the phosphor layers, it is preferable to use ones whose electric resistivity is in the range between 8 μΩcm and 200 μΩcm inclusive, as described above. This is because an electric resistivity of 8 μΩcm or less is too low and only a small amount of Joule heat is generated, whereas an electric resistivity of 200 μΩcm or over causes too small induced currents and only a small amount of Joule heat is generated. In other words, the phosphor layers cannot be heated sufficiently in either case.
• Furthermore, the high-frequency power supplier42 supplies, under the control of acontroller43, the heating coils41 with high-frequency power with which it is possible to apply, to the conductive particles included in the phosphor layers, a high-frequency electric field that is in the range between 10V/cm and 300V/cm inclusive. This is because the application of a high-frequency electric field of 10V/cm or less results in too small induced current and only a small amount of Joule heat is generated, as a result of which the phosphor layers cannot be heated sufficiently. Meanwhile, the application of a high-frequency electric field of 300V/cm or over is too high and there is a possibility that other constituent elements mounted on thePDP111 will be damaged.
• As the high-frequency power supplier42, a high-frequency power supplier is selected that applies a high-frequency electric field in the frequency range between 1 KHz and 3 GHz inclusive to the conductive particles included in the phosphor layers. This is because sufficient induction heating cannot be carried out if the frequency of a high-frequency electric field is 1 KHz or lower, whereas a high-frequency power supplier that generates a high-frequency electric field in the frequency range of 3 GHz or higher is costly.
• In the above-described function restoration method in which the phosphor layers are heated by inductively heating the conductive particles mixed into the phosphor layers through the application of a high-frequency electric field to the phosphor layers, there is an advantage that only a least possible processing energy as well as a shorter processing time is required since only the phosphor layers are heated locally, as in the case of the second restoration method in which lights are irradiated. Furthermore, since a processing time is extremely short, there is no thermal shock on thePDP111, which causes no possibility that the constituent elements other than the phosphor layers become subject to defects such as the coming off of films and quality degradation. What is more, in addition to this effect, this third restoration method requires only an inexpensive electromagnetic field generation apparatus, while the second restoration method, in which lights are irradiated, requires expensive apparatuses such as thexenon flash lamps32 andexcimer laser apparatus37. Therefore, the third restoration method is applicable, for example, to IH cooking equipments for household use or larger IH cooking equipments for industrial use, which produces the effect that there is no cost overrunFIG. 16 is a schematic diagram showing a fourth method for restoring the function of a PDP according to the present invention. The fourth restoration method, which is a variation of the third restoration method, is different from the third restoration method only in that, instead of conductive particles that are mixed to the phosphor layers in the third restoration method, phosphor layers of aPDP112 are composed of phosphor particles to which dielectric particles are mixed in a predetermined ratio, the dielectric particles being made of dielectric materials whose dielectric loss factor fall within the range between 0.01 and 0.6 inclusive when the frequency of a high-frequency electric field to be applied is in the range between 1 KHz to 3 GHz.
• The dielectric particles are mixed in a ratio of 0.1 (wt %) to 10 (wt %) with regard to the whole phosphor layers, as in the case of the conductive particles in the third restoration method. As dielectric particles, it is preferable to use dielectric particles whose dielectric loss factor is high and which are highly heat-resistant. For example, lead zirconate titanate is a highly preferable dielectric particle to be mixed to phosphor particles since its dielectric loss factor is 0.04 and it has heat resistance up to 500° C. or over.
• Furthermore, thePDP112 is equipped with thepower detection circuit28, thetimer circuit24, thememory27, and thecontrol unit20 shown inFIG. 4, as in the case of thePDPs100,110, and111 used in the first or third restoration method.
• In the fourth restoration method, as in the case of the above-described third restoration method, a manufacturer collects thePDP112, when receiving a notification from its user who has contacted such manufacturer as promoted by the screen display, and asFIG. 16 shows, places the collectedPDP112 onto a support table44 made of dielectric material. Then, by applying high-frequency power from the high-frequency power supplier42 to spiral heating coils41 that are located under such support table 44, the heating coils41 generate electromagnetic waves by which a high-frequency electric field is applied to the phosphor layers of thePDP112 via the support table44. Accordingly, the dielectric particles included in such phosphor layers are inductively heated and generate eddy currents. The phosphor particles included in the phosphor layers are heated by Joule heat caused by such eddy currents, as a result of which the function of the phosphor layers is improved.
• Dielectric particles are mixed to the phosphor layers with a mixing ratio of 0.1 (wt %) to 10 (wt %), as described above. This is because a mixing ratio of 0.1 (wt %) or lower is not enough to inductively heat thePDP112 and therefore a function restoration of the phosphor layers cannot be performed as desired, whereas a mixing ratio of 10 (wt %) or over leads to a reduction in the number of phosphor particles included in the phosphor layers and therefore the phosphor layers cannot achieve desired luminance.
• Moreover, the dielectric loss factor of dielectric particles to be mixed into the phosphor layers in relation to the frequency of a high-frequency electric field to be applied is in the range between 0.01 and 0.6. This is because dielectric loss (heating value) W can be represented as W=ω×Co×Vo²×ε×tan δ, where “ω” denotes each frequency of high-frequency power, “Co” denotes the capacitance of dielectric particles, “Vo” denotes voltage to be applied to the dielectric particles, “ε” denotes the dielectric constant of the dielectric particles, and “tan δ” denotes the dielectric loss factor of the dielectric particles.
• Thus, when the dielectric loss factor is 0.01 or smaller, heating cannot be performed sufficiently since tan δ in the above expression is too small and the amount of heat to be generated becomes small, whereas when the dielectric loss factor is 0.6 or larger, accumulated charge of address discharge becomes likely to be dissipated and therefore there arises the possibility that memory effect achieved by address discharge is lost.
• Furthermore, the high-frequency power supplier42 supplies, under the control of acontroller43, the heating coils41 with high-frequency power with which it is possible to apply, to the dielectric particles included in the phosphor layers, a high-frequency electric field that is in the range between 10V/cm and 300V/cm inclusive. This is because the application of a high-frequency electric field of 10V/cm or less results in too small induced current and only a small amount of Joule heat is generated, as a result of which the phosphor layers cannot be heated sufficiently. Meanwhile, the application of a high-frequency electric field of 300V/cm or over is too high and there is a possibility that other constituent elements mounted on thePDP112 will be damaged.
• As the high-frequency power supplier42, a high-frequency power supplier is selected that applies a high-frequency electric field in the frequency range between 1 KHz and 3 GHz inclusive to the dielectric particles included in the phosphor layers. This is because sufficient induction heating cannot be carried out if the frequency of a high-frequency electric field is 1 KHz or lower, whereas a high-frequency power supplier that generates a high-frequency electric field in the frequency range of 3 GHz or higher is costly.
• In the above-described function restoration method in which the phosphor layers are heated by inductively heating the dielectric particles mixed into the phosphor layers through the application of a high-frequency electric field to the phosphor layers, there is an advantage that only a least possible processing energy as well as a shorter processing time is required since only the phosphor layers are heated locally, as in the case of the second restoration method in which lights are irradiated. Furthermore, since a processing time is extremely short, there is no thermal shock on thePDP112, which causes no possibility that the constituent elements other than the phosphor layers become subject to defects such as the coming off of films and quality degradation. What is more, in addition to this effect, this fourth restoration method requires only an inexpensive electromagnetic field generation apparatus, while the second restoration method, in which lights are irradiated, requires expensive apparatuses such as thexenon flash lamps32 andexcimer laser apparatus37. Therefore, the fourth restoration method is applicable, for example, to IH cooking equipments for household use or larger IH cooking equipments for industrial use, which produces the effect that there is no cost overrun.
• Although only some exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention.

Claims (15)

1. A method for restoring a function of a plasma display panel (PDP), comprising

restoring a function of a PDP by raising a temperature of at least a phosphor layer in the PDP to 400° C. to 800° C.

2. The method for restoring a function of a PDP according toclaim 1,

wherein the PDP is equipped with a heating element, and

the temperature of at least the phosphor layer in the PDP is raised to 400° C. to 800° C. by energizing the heating element.

3. A method for restoring a function of a plasma display panel (PDP), comprising

restoring a function of a PDP by raising a temperature of a phosphor layer in the PDP to 400° C. to 800° C. through irradiation of light to the PDP.

4. The method for restoring a function of a PDP according toclaim 3,

wherein the light is irradiated to the phosphor layer from outside the PDP through a glass substrate and a dielectric layer in the PDP.

5. A method for restoring a function of a plasma display panel (PDP), comprising

restoring a PDP by raising a temperature of a phosphor layer in the PDP to 400° C. to 800° C. by inductively heating conductive particles through application of a high-frequency electric field to the PDP, said conductive particles being mixed, at a predetermined ratio, with phosphor particles that make up the phosphor layer.

6. A method for restoring a function of a plasma display panel (PDP), comprising

restoring a PDP by raising a temperature of a phosphor layer in the PDP to 400° C. to 800° C. by inductively heating dielectric particles through application of a high-frequency electric field to the PDP, said dielectric particles being mixed, at a predetermined ratio, with phosphor particles that make up the phosphor layer.

7. A plasma display panel (PDP), comprising

a first substrate on which discharge electrodes and a first dielectric layer are formed, each of said discharge electrodes generating a display discharge and said first dielectric layer covering the discharge electrodes; and

a second substrate on which the following are formed: address electrodes that are located orthogonally to the discharge electrodes; a second dielectric layer that covers the address electrodes; barrier ribs that are formed on the second dielectric layer; phosphor layers, each being formed in a concave portion between each two neighboring barrier ribs; and heating elements that are located close to the respective phosphor layers.

8. The PDP according toclaim 7,

wherein the heating elements have a linear shape and are formed on the second substrate, each of the heating elements being located between each two neighboring address electrodes in parallel with said address electrodes and being embedded in the second dielectric layer.

9. The PDP according toclaim 7,

wherein the heating elements have a linear shape and are located above the respective address electrodes in parallel with said address electrodes, the heating elements being embedded in the second dielectric layer.

10. The PDP according toclaim 7,

wherein each of the heating elements is formed at least as part of each of the barrier ribs.

11. The PDP according toclaim 7, further comprising:

a control drive circuit that controls drive of the discharge electrodes and the address electrodes; and

a heating element energization circuit that controls energization of the heating elements so that said heating elements heat the phosphor layers at a predetermined temperature for a predetermined time.

12. The PDP according toclaim 7, further comprising:

a timer circuit that measures a panel drive time during which the PDP has been driven;

a memory that stores a total drive time that is obtained by accumulating each panel drive time measured by the timer circuit, said total drive time being updated and stored into the memory every time the timer circuit newly measures a panel drive time;

a function restoration key by which an instruction for energizing the heating element is inputted, said key being operated manually;

a heating element energization circuit that energizes the heating elements when the function restoration key is operated; and

a control unit operable to indicate that an operation of the function restoration key should be performed, when judging that the total drive time stored in the memory reaches a set time.

13. The PDP according toclaim 7, further comprising:

a timer circuit that measures a panel drive time during which the PDP has been driven;

a memory that stores a total drive time that is obtained by accumulating each panel drive time measured by the timer circuit, said total drive time being updated and stored into the memory every time the timer circuit newly measures a panel drive time;

a heating element energization circuit that energizes the heating elements; and

a control unit operable to direct the heating element energization circuit to energize the heating elements when judging that the total drive time stored in the memory reaches a set time.

14. The PDP according toclaim 13, further comprising

a clock circuit that provides time information,

wherein when a pre-set time is reached, the control unit directs the heating element energization circuit to energize the heating elements, based on the time information provided by the clock circuit.

15. The PDP according toclaim 11,

wherein the heating element energization circuit controls the energization of the heating element so that the phosphor layers are heated at 400° C. to 800° C., preferably 500° C. to 600° C., for 10 to 120 minutes, preferably 20 to 60 minutes.

Images