Patent Application
20060208201
1. Field of the Invention
This invention relates to a method and an apparatus for neutralizing an insulative substrate, and a method and an apparatus for preventing the charging of the insulative substrate,
2. Description of the Related Art
In the conventional process of producing a glass substrate used for a liquid crystal display, electrons are trapped in the incompletely combined parts of atoms due to the friction with the conveyor belt surface during transportation or at the time of separation by a vacuum chuck. Also, the insulative substrate may be charged to positive or negative polarity by ionization of atoms.
Once the glass substrate is charged, the surrounding particles are adsorbed to or deposited on the substrate often causing the problem of dielectric breakdown of various thin films. Also, in the case where a liquid crystal display is fabricated using a charged glass substrate, the starting voltage of the liquid crystal display is changed by the charge on the glass substrate, thereby posing the problem that the brightness of the liquid crystal screen changes.
Conventionally, in view of these problems, the glass substrate or the like insulating member is neutralized by a method using the corona discharge or the soft X-ray. In the neutralizing method using the corona discharge, positive and negative ions are generated from a discharge electrode and applied to the glass substrate to neutralize the charge. In the neutralizing method using the soft X-ray (wavelength of not less than 1 Å), on the other hand, the air in the neighborhood of the insulating member is ionized by the soft X-ray and the charge of the insulating member is neutralized by the ionized air. Japanese Patent Application Laid-Open Nos. 11-214191, 2000-267106, 2002-257702 and 2004-299814 and Japanese Patent Publication No. 2749202 disclose a method of neutralizing an insulating member using the soft X-ray.
The neutralizing method using the corona discharge, however, raises dust when ions are applied and therefore finds no suitable application in an environment required to be kept clean. This method also poses the problem that the ionized air is recombined for a low neutralization performance.
As shown in
The soft X-ray, though high in air ionization efficiency, is easily absorbed into the air, and therefore a sufficient distance cannot be secured from the insulating member to the soft X-ray source, resulting in a narrow neutralization area.
Also, the reverse surface of the glass substrate is charged by separation or friction when the glass substrate is lifted from the stage or transported, respectively, and the potential increases instantaneously at the time of separation. The neutralization, therefore, requires a space between the glass substrate and the stage into which the ionized air is sent or the soft X-ray is radiated.
In the case where the soft X-ray is radiated to the reverse surface of the glass substrate horizontally or specifically from the soft X-ray generating device 5#A on the right side and the soft X-ray generating device 5#B on the left side as shown in
An attempt to eliminate the neutralization variations and neutralize a wide area of the glass substrate, therefore, requires a multiplicity of soft X-ray generating devices 5# as shown in
Embodiments of the invention solve the problems described above, and an object of the invention is to provide a neutralizing method and a neutralizing apparatus capable of neutralizing an object such as an insulating member effectively in a simple and efficient way.
Another object of this invention is to provide a charging prevention method and a charging prevention apparatus for preventing object or insulating member from being charged when lifted up from the stage or transported.
According to one aspect of this invention, there is provided a neutralizing method in which the hard X-ray having the wavelength of not less than 0.05 Å but less than 1 Å is radiated directly on a charged object to be neutralized (hereinafter sometimes referred to simply as “the object”).
According to another aspect of the invention, there is provided a neutralizing method in which a hard X-ray generating device for generating a hard X-ray having the wavelength of not less than 0.05 Å but less than 1 Å is arranged at a position from which the hard X-ray can be radiated directly on the object, and the hard X-ray is so radiated.
In some preferred embodiments of the invention, the object is a glass substrate.
Specifically, the hard X-ray is radiated on the charged glass substrate directly from the direction perpendicular to an obverse surface thereof (or surface facing an observer,) and the reverse surface of the glass substrate is neutralized by the hard X-ray transmitted through the glass substrate.
According to still another aspect of the invention, there is provided a neutralizing method in which a glass substrate placed on or adjacent to a stage or platform is neutralized by being irradiated directly with the hard X-ray having the wavelength of not less than 0.05 Å but less than 1 Å from the direction perpendicular to the upper surface of the stage.
According to yet another aspect of the invention, there is provided a method of preventing the charging of a glass substrate, wherein a hard X-ray having the wavelength of not less than 0.05 Å but less than 1 Å is radiated directly on the upper surface of the stage from the direction perpendicular thereto while the glass substrate is lifted up from the upper surface of the stage.
According to a further aspect of the invention, there is provided a neutralizing apparatus comprising a stage on which a glass substrate is placed and a radiation mechanism for radiating a hard X-ray having the wavelength of not less than 0.05 Å but less than 1 Å directly on the insulating member or glass substrate. The insulating member or glass substrate may be placed on a support extending from the upper surface of the stage. The radiation may originate from the direction perpendicular to the upper surface of the stage.
According to a still further aspect of the invention, there is provided a charge prevention apparatus for a glass substrate or insulating member comprising a stage on which the glass substrate is placed and a radiation mechanism for radiating a hard X-ray having the wavelength of not less than 0.05 Å but less than 1 Å directly on the glass substrate placed above the upper surface of the stage. The radiation may originate from the direction perpendicular to the upper surface of the stage while the glass substrate is supported above the stage.
In the neutralizing method and apparatus according to this invention, a hard X-ray having the wavelength of not less than 0.05 Å but less than 1 Å is radiated on the object. The hard X-ray can ionize the gas in the neighborhood of the object from a position distant from the object, and therefore a wide neutralization area can be secured, and the neutralization can be effectively carried out in a simple and efficient way.
In the charge prevention method and apparatus according to this invention, a hard X-ray having the wavelength of not less than 0.05 Å but less than 1 Å is radiated directly on a glass substrate or insulating member when lifted up or separated by a distance from the upper surface of the stage. The hard X-ray, as compared with the soft X-ray, has a higher transmittance through the glass substrate, and therefore the reverse surface, in addition to the obverse surface, of the glass substrate can be neutralized by the transmitted X-ray, thereby preventing the charging by separation and friction.
Embodiments of this invention are described in detail below with reference to the drawings. In the drawings, the same or equivalent component elements are designated by the same reference numerals, respectively, and not explained repeatedly.
Referring to
The hard X-ray generating device 5 and the insulating member 10 are arranged in spaced relation to each other with a distance Z therebetween. In this position, the hard X-ray is radiated directly from the direction perpendicular to the upper or obverse surface of the insulating member 10. The insulating member 10 is assumed to be in a charged state. In this embodiment, a glass substrate for a liquid crystal display (hereinafter referred to also as the LCD glass substrate) or a glass substrate for a plasma display (hereinafter referred to also as the PDP glass substrate) is used as an example of the insulating member 10.
In the neutralizing method according to this embodiment of the invention, the insulating member 10 is neutralized by the hard X-ray directly radiated thereon.
Referring to
The protective case is formed with an aperture, from which the X-ray is radiated outside. Also, 99% of the kinetic energy of the thermal electrons emanating from the filament 54 is converted to heat, which can be cooled by the X-ray tube cooling unit 52 pneumatically or hydraulically.
In the neutralizing method according to this embodiment of the invention shown in
The hard X-ray radiated from the hard X-ray generating device 5 is absorbed into the air and generates ions. At the same time, the ions generated in the neighborhood of the insulating member 10 are neutralized by reacting with the charge of the insulating member 10.
Unlike the soft X-ray, the hard X-ray is directly radiated on the insulating member 10 and generates the secondary electrons, the secondary X-ray and the scattered X-ray in accordance with the atomic number of the insulating member 10 thereby to ionize the air in the neighborhood of the insulating member 10. Specifically, the radiation of the hard X-ray generates the secondary X-ray, the scattered X-ray and the secondary electrons from the transition elements, the light elements and the heavy elements contained in the insulating member 10. These X-rays and electrons also contribute to the generation of ions by reacting with the air. The ions thus generated neutralize the charge of the insulating member 10 by reaction therewith. In this way, the neutralization effect is further enhanced by the secondary X-ray, the scattered X-ray and the secondary electrons in addition to the hard X-ray.
Also, the electric dissociation of the solid insulating member 10 neutralizes the charge of the insulating member 10 by solid ionization. Specifically, the hard X-ray passed through the glass substrate ionizes and shorts the glass or other insulating material. As a result, the residual charge in the substrate can be removed.
X-ray According to an embodiment of the invention, the hard X-ray has a higher energy than the soft X-ray, and therefore is not easily absorbed into the air. Thus, a longer distance can be secured from the insulating member 10 to the hard X-ray generating device 5 than the corresponding distance from the insulating member 10 to the soft X-ray generating device. Accordingly, assuming the radiation angle from the X-ray tube is equal in both scenarios, a wider radiation area (neutralization area) can be secured through the hard X-ray than by the soft X-ray.
As shown in
As shown in
Further, the hard X-ray radiated from the hard X-ray generating device 5 is transmitted through the insulating member 10. Therefore, the hard X-ray that has been transmitted through the obverse surface of the insulating member 10 reacts with the air on the reverse surface to generate ions. The air in the neighborhood of the reverse surface of the insulating member 10 is ionized by the transmitted hard X-ray, and therefore, the charge on the reverse surface of the insulating member 10, which may be a glass substrate or the like, is neutralized.
Specifically, by radiating the hard X-ray only from one side of the insulating member 10 such as a glass substrate, the reverse surface and the obverse surface of the insulating member can be neutralized at the same time.
The secondary X-ray, the scattered X-ray and the secondary electrons are generated also from the hard X-ray radiated on the reverse surface, and as in the aforementioned case, react with the air to generate ions. These ions generated are neutralized by reaction with the charge on the reverse surface of the insulating member 10.
The transmittance of the glass substrate is explained with reference to the radiation of the soft X-ray and the hard X-ray.
The soft X-ray is low in energy and therefore the transmittance thereof through the LCD glass is very low.
Also in this case, the soft X-ray is low in energy and therefore the transmittance thereof through the PDP glass is so low that only the hard X-ray is measurable,
The hard X-ray is transmitted through the LCD glass (0.7 mm) or the PDP glass (2.8 mm), and therefore the reverse surface of the glass substrate can be neutralized by the hard X-ray transmitted through the insulating member.
In the case where a secondary excitation plate is provided to facilitate the generation of the secondary electrons, the secondary X-ray and the scattered X-ray are arranged to face the reverse surface of the insulating member. The X-ray transmitted through the insulating member impinges on the secondary excitation plate, and the air around the reverse surface of the object is ionized by the secondary X-ray, the scattered X-ray and the secondary electrons thus generated, thereby making a more effective neutralization possible.
In the case where the obverse surface of the insulating member is charged, such as when the glass substrate is wetted with water after the cleaning step, the radiation of the soft X-ray reduces the surface potential of the obverse surface of the insulating member to substantially 0 V. Due to the presence of static inductance on the reverse surface of the glass substrate, however, a reverse surface potential of several tens to several hundreds of volts may be generated or a potential may be generated on the obverse surface thus far at 0 V by the radiation of the soft X-ray. In such a case, the charge on the obverse surface of the glass substrate may not be completely neutralized by the soft X-ray due to the wet condition.
As shown in
Furthermore, in the case where the hard X-ray is used, the obverse and reverse surfaces of the glass can be neutralized regardless of the wet condition of the glass.
In the case where the glass substrate is lifted up from the stage or transported, the charging is caused by separation or friction, as the case may be, on the reverse surface of the glass substrate, and the potential may instantaneously increase at the time of separation. Especially in the case where the soft X-ray is used, the residual charge and the closely attached state of the glass substrate on the stage makes it difficult to secure a spatial interval for sending ionized air or radiating the soft X-ray. In the case where the hard X-ray is used, in contrast, the transmitted X-ray, the secondary electrons, the secondary X-ray and the scattered X-ray are generated under the reverse surface of the insulating member. Therefore, the charging by separation and friction which otherwise might be caused at the time of separation is prevented thereby to suppress the instantaneous potential rise of the glass substrate.
As a result, the charging of the glass substrate by separation and friction can be prevented by radiating the hard X-ray on the glass substrate when lifted up or transported.
By radiating the hard X-ray having the wavelength of less than about 1 Å (with the energy of not less than 12.4 eV), the secondary electrons, the secondary X-ray and the scattered X-ray are generated for all of the listed metals including those which cannot be excited by the soft X-ray. Accordingly, a higher neutralization effect than with the soft X-ray is expected. The higher energy of the X-ray and the shorter wavelength thereof, require a larger scale of the shield structure. Taking these facts and the necessity of the X-ray to reach the reverse surface of the PDP glass substrate with the minimum X-ray transmittance into consideration, the proper wavelength of the X-ray is considered to be not less than 0.05 Å.
In the neutralizing method according to an embodiment of the invention using a hard X-ray high in energy, as compared with a case using the soft X-ray low in energy, the neutralization can be carried out sufficiently even in the case where the radiation distance is long or the radiation angle is widened for a larger radiation range. As a result, the number of the hard X-ray generating devices required to neutralize the insulating member of a large size such as a glass substrate can be reduced, thereby facilitating the maintenance and installation while at the same time decreasing the total cost.
Also, generally, the X-ray tube for generating the soft X-ray has a beryllium window as an X-ray window member high in soft X-ray transmission efficiency. However, beryllium, which is a harmful material and therefore essentially requires management including recovery to ensure safety and protect the environment, is required to be handled with care.
The X-ray tube for generating the hard X-ray, on the other hand, uses no harmful material and therefore can be handled and recovered advantageously from the viewpoint of safety and environmental protection.
In the embodiments described above, an experiment is conducted by applying a high voltage of 40 kV as a tube voltage 53 with a filament current of 0.6 mA in order to radiate the hard X-ray. Nevertheless, the invention is not limited to these figures and a similar effect can be secured by adjusting the numerical values in accordance with the thickness of the insulating member, etc.
Also, in the foregoing description of the embodiments, the hard X-ray is radiated from the direction perpendicular to the obverse surface of the glass substrate to neutralize also the charge on the reverse surface by the transmitted X-ray. This invention, however, is not limited to this configuration, and the hard X-ray can be radiated on the reverse surface from the hard X-ray generating devices located on the right and left sides, respectively, as shown in
In the description above, the LCD glass and the PDP glass are cited as an example. This invention is not limited to the use of these types of glass and is applicable also to the neutralization of SED (surface-conduction electron-emitter display), an organic EL (organic electroluminescence display), FPD (flat panel display) and various other insulative solid or liquid materials including copy paper and packaging and packing materials.
Further, the case of enlarging the radiation range by lengthening the radiation distance and widening the radiation angle is explained above. As an alternative, the radiation range is narrowed by a bundle of thin hard X-ray beams using the collimator, slit or the capillary, and by thus limiting the neutralization area of a solid, liquid or gas, the neutralizing method described above can be used only for the desired area. Further, a great variety of charge prevention and neutralizing methods can be implemented in keeping with the user needs by spatially and temporally controlling the beams.
The embodiments disclosed above should be considered illustrative in all respects but not limiting. The scope of this invention is defined not by the foregoing description but by the appended claims, and intended to include all the changes within the meaning and scope equivalent to the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP2005-073571 | Mar 2005 | JP | national |
