Electric lamp and discharge devices – With getter
Reexamination Certificate
2000-02-24
2003-05-06
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With getter
C313S495000, C313S558000
Reexamination Certificate
active
06559596
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a getter which can physically and chemically absorb gas and a method of manufacturing the getter, and particularly to a getter which can maintain its performance for a long time even under an atmosphere in which getter performance is easily deteriorated and to a method of manufacturing the getter.
The present invention also relates to an airtight chamber which maintains a pressure that is equal to or less than an atmospheric pressure and to an image forming apparatus having the getter. Particularly, the image forming apparatus of the present invention is preferably used in the image forming apparatus which comprises: a vacuum chamber, an electron source; and an image-forming member for forming an image by irradiation of an electron beam emitted from the electron source.
2. Related Background Art
A substance which can physically and chemically absorb residual gases present in vacuo or in the atmosphere of inert gases or the like is usually referred to as the getter.
Preferable material used as the getter is a material having a high residual gas absorption rate, and being able to keep the absorption rate slow in order to keep the vacuum as long as possible in a system in which the material is disposed and to eliminate the influence of the residual gases in the atmosphere of inert gases or the like.
As the getter material, metal simple bodies of Ba, Li, Al, Zr, Ti, Hf, Nb, Ta, Th, Mo, V, and the like or alloys formed of the metal simple bodies are heretofore known.
Moreover, the getter for heating and evaporating the metal simple bodies or the alloy of the metal simple bodies in vacuo or in the atmosphere of inert gases or the like, and exposing a clean metal surface to chemically absorb a residual gases component in vacuo is called an evaporating getter, while a getter for the heating in vacuo or in the atmosphere of inert gases or the like to diffuse inwardly an oxide coat present on the surface, and exposing the metal surface to the top surface at every heating to absorb the residual gases in vacuo is called a non-evaporable getter.
The non-evaporable getter is formed of the metal simple body mainly containing zirconium (Zr), or titanium (Ti), or the alloy containing these metals, and a getter ability is usually obtained and used by forming a film of the metal or the alloy on a substrate of stainless, nichrome, or the like, and heating the substrate by energization heating and other means. For example, the manufacture method comprises: placing about 100 &mgr;m of a material powder to the substrate of stainless, nichrome, and the like by a rolling process, and the like; and calcining the substrate at a temperature of about 1000° C. in vacuo. This is performed in order to take a large reactive surface area by using the powder and effectively perform physical and chemical absorption.
In order to obtain the getter performance of the non-evaporable getter manufactured as described above, the vacuum, inert gases, and other atmospheres are used as the atmosphere in which the getter is disposed, and an active surface is formed and prepared for gas absorption by applying the heating operation (activation operation) to decompose and diffuse the surface oxide.
However, when the thin film of the metal simple body of Zr, Ti, and the like is formed on the substrate of stainless, nichrome, and the like by generally known means such as a vacuum evaporation process, a very stable oxide is formed on the surface of the formed film simultaneously with atmospheric exposure, and the heating to a high temperature of 800 to 900° C. in vacuo is necessary for removing the oxide film by diffusion to form the active surface (Japan J. Appl. Phys. Suppl. 2, Pt. 1, 49, 1974). Additionally, since after the activation operation the reaction of the simple body metal thin film and the residual gases in vacuo occurs usually at 200° C. or a higher temperature, the getter performance is hardly fulfilled around the room temperature.
Therefore, the non-evaporable getter can perform the activation operation at a lower temperature, and the getter material enables the getter function to be obtained at or near room temperature after the activation operation has been developed.
For example, the getter material of an alloy of 84 wt % of Zr-16 wt % of Al, disclosed in Japanese Patent Publication No. 46-39811, is a powder of a crushed alloy block obtained by melting Zr and Al (tradename: St-101, SAES Co. in Italy). When the Zr—Al alloy powder is used instead of the simple-body Zr powder, the surface oxide film can be diffused/removed at a low temperature, the particles can therefore be prevented from being sintered with one another, and a surface structure in which the surface area is relatively maintained is constructed. Moreover, the Zr—Al alloy is higher in safety than Zr which is highly reactive in the room-temperature atmosphere. It is disclosed that the weight ratio having a highest absorptivity is set to be Zr 84%-Al 16{circumflex over ( )} in SAES Co. by changing the weight ratio of Zr—Al in a range of Al 6 to 37% to prepare the alloy on trial and by comparing the getter characteristics (Proc. 4
th
Int. Symp. on Residual Gases in Electron Tubes 221, 1972). However, the alloy does not have a high residual gases absorption rate, and has a problem that it takes much time to exhaust a large amount of gas at room temperature. To obtain a sufficient absorption rate from this alloy, the residual gases has to be absorbed by heating the activated alloy to 300° C. or a higher temperature.
Moreover, from the standpoint of prevention of reduction of the surface area by sintering the mixture of different types of powders, as disclosed in Japanese Patent Publication No. 53-1141, the getter material is obtained by mixing the simple-body metal powder of Zr, Ta, Hf, Nb, Ti, Th, U, and the like with the Zr—Al alloy powder, but the material has a disadvantage that a sufficient exhaust ability cannot be recognized in the room temperature.
Furthermore, U.S. Pat. No. 3,584,253 discloses a getter obtained by mixing Zr simple-body powder and graphite powder.
In this example, the alloy powder mixed with Zr powder has no getter ability or insufficient ability if any, and the main point is to sinter the powders with each other not to reduce the surface area. Therefore, since the alloy powder is added, the getter ability is deteriorated. If the alloy powder to mix is provided with the getter ability, the reduction of the surface area can be prevented, so that the deterioration of the getter ability can be avoided.
As the non-evaporable getter, as disclosed in U.S. Pat. No. 4,312,669, the non-evaporable getter material consisting of a three-element alloy of Zr, V, Fe, or Zr, Ni, Fe has been developed. The non-evaporable getter is obtained by mixing the Zr powder with the Zr—V—Fe alloy powder having the getter ability, or the Zr—Ni—Fe alloy powder so as to prevent the sintering of the powders. Additionally, the getter function is obtained even when activation occurs at a temperature lower than a conventional temperature because of the high reactivity (absorptivity) of the Zr—V—Fe alloy, or the Zr—Ni—Fe alloy.
However, in view of the material cost, it is unfavorable to use the alloy powder which causes many synthesis problems and which is difficult to form into powder. Moreover, it is troublesome and unfavorable to fix the mixed powder onto the base material by the rolling process or the like, sinter the materials in vacuo and further bond the materials. Moreover, since the getter function is obtained in the low temperature around the room temperature after the activation, the getter easily reacts, that is, the getter is quickly deteriorated. There is a disadvantage that desired characteristics cannot be maintained for a long time dependent on a use environment. For example, the member with the getter disposed thereon is subjected to a process in which a high temperature has to be obtained in a low vacuum atmosphere containing oxygen, moisture, and the like,
Arai Yutaka
Hasegawa Mitsutoshi
Shigeoka Kazuya
Berck Ken A
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Patel Vip
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