JP3023338B2 - Evaporative getter with reduced activation time - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an evaporable getter device having a reduced activation time. The present invention also relates to an evaporable getter device having a reduced activation time and being frit sealable.

[0002]

2. Description of the Related Art As is known, evaporable getter materials are mainly used to maintain a vacuum inside a picture tube (CRT) or a computer screen of television equipment. The use of evaporable getter materials inside flat (flat) displays is also currently in research and development and is expected to be explored in the future.

A commonly used getter material in picture tubes is metal barium, which is deposited in a thin film on the inner wall of the picture tube. To obtain this thin film, a device known in the art as an evaporable getter device incorporated therein during the manufacture of the picture tube is used. These devices consist of a powder of BaAl ₄ , a compound of barium and aluminum having a particle size of generally less than about 250 μm, and typically a powder of
It comprises an open metal container containing nickel (Ni) powder having a particle size of less than μm in a weight ratio of about 1: 1. This device is well known in the art, see for example, U.S. Pat. No. 5,118,988 to the present applicant. Barium is vaporized in an activation process, also referred to as a "flash", by inductively heating the getter device with a coil located outside the picture tube itself. When the temperature of the powder reaches a temperature in the range of about 800-850 ° C., the following reaction takes place:

[0004]

Embedded image BaAl ₄ + 4Ni → Ba + 4NiAl (I)

The reaction is highly exothermic and raises the temperature of the powder to about 1200 ° C., at which point the barium evaporates and the barium vapor deposits on the tube walls to form a metal film.

The time required to evaporate all of the barium stored in the device by starting the measurement from the point at which power is supplied to the device by the coil is referred to as “total time (Total Time: TT). ) "
It is defined in the art. For example, to obtain the barium coating of approximately 300 mg required by large size color picture tubes, the T required using current getter equipment is required.
T ranges from 40 to 45 seconds. However, this time corresponds to a low speed stage in current electron tube manufacturing lines, which requires the manufacturer to develop a device that can release barium with a much shorter TT value. ing.

In order to obtain such a result, in principle,
The power supplied to the coils can be increased, and the increased reactivity of the powders can be obtained by reducing their grain size.

However, it is not possible to increase the coil power with the currently available getter devices. In effect, by doing so, the powder container raises its temperature very quickly, so that there is not enough time for a uniform diffusion of heat inside the powder filling and melting of the container occurs.

Reduction of the particle size of the powder is also not possible. The reason for this is that this leads to an excessive and local increase in the rate of reaction between BaAl ₄ and Ni, resulting in the expansion of the powder filling and even the risk of debris jumping out of the powder filling. .

[0010]

It is an object of the present invention to provide an evaporable getter device with a reduced activation time, which does not exhibit the disadvantages of the prior art.

[0011]

Means for Solving the Problems The above object is achieved by BaAl4
Compound powder, Ni powder, and powder of the third component selected from the group consisting of iron, titanium, and alloys thereof .
The resulting mixture is achieved by a getter device having a metal container containing the mixture in which the third component is present in an amount ranging from about 0.3 to 5% of the total weight of the mixture.
It is also an object of the invention to provide a powder mixture in said container, in the form of a metal container having an open top and a filling and having a radial recess in the upper surface, wherein BaAl ₄ , nickel, aluminum, iron A powder mixture with a third component selected from the group consisting of titanium and alloys thereof, wherein the third component is present in an amount ranging from about 0.3 to 5% of the total weight of the mixture; A discontinuous metal element having a substantially flat shape and substantially parallel to the bottom surface of the container and embedded in the powder filling such that it does not emerge from the free surface of the filling itself at a location spaced from the bottom surface of the container. This is achieved by an evaporable getter device which has a reduced activation time and which is frit sealable.

[0012]

DETAILED DESCRIPTION OF THE INVENTION The amount of powder of the third component in the powder mixture depends on the type of component actually used and is generally in the range of about 0.3-5%. In particular, the weight percentage of the third component is in the range of about 0.8-2% for aluminum, about 0.3-1.2% for iron, and about 0.5-1.2% for titanium. It is in the range of 5%. If the amount of the third component is lower than these specified values, the desired effect of shortening the barium evaporation time cannot be obtained. On the other hand, when the getter device is operated with the amount of the third component higher than these specified values, the barium flash becomes intense and almost uncontrollable.

The weight ratio between nickel and BaAl ₄ is similar to that in prior art devices, generally about 1:
1, especially in this field, getter devices having a ratio of 5.3: 4.7 between nickel and BaAl ₄ are widely used.

For the purposes of the present invention, the third component does not need to be particularly pure, but can be made from commercially available metal and alloy powders, which generally have a purity of about 98-99%. The particle size of the powdered third component useful for the purposes of the present invention is about 80
It is less than μm, preferably less than about 55 μm.

The nickel powder and compound BaAl ₄ powder used in the getter device of the present invention are similar to those used in prior art devices. Generally, powders having a particle size of less than about 60 μm are used for nickel, while powders having a particle size of less than about 250 μm are generally used for the compound BaAl ₄ .

The metal container can be made from a variety of materials such as nickel-plated iron and constantan, and exhibits good resistance to oxidation and heat treatment and good cold workability.
The use of ISI 304 and AISI 305 stainless steel is preferred. The metal container can take any shape, in particular U.S. Patent Nos. 4,127,361, 4,323,81.
8, 4,486,686, 4,504,765, 4,6
42,516, 4,961,040 and 5,118,9
Any of those known and used in the art, such as the container of a device according to No. 88.

It would be advantageous if the activation time could be reduced and a fritable evaporable getter device could be obtained. The term fritable evaporable getter device is about 4
It means that it can withstand an oxidizing atmosphere at a temperature of 50 ° C. for a period of up to 2 hours. These are the conditions that the getter device must undergo in some processes for the manufacture of picture tubes. During the evaporation of barium from a fritable getter device, more heat is generated than in a typical getter device, resulting in greater difficulty maintaining the powder filling in the container.
Fritable getter devices having an evaporable barium content of up to about 200 mg have already been manufactured and sold by the applicant for several years. However, a fritable getter device capable of evaporating larger amounts of barium, especially about 300 mg of barium, has to adopt special solutions due to its greater reactivity.
The applicant's co-pending patent application entitled "Fritable Getter Apparatus with High Barium Yield" is based on the addition of an element that suppresses heat distribution in the circumferential direction in the powder filling, and the addition of substantially an element in the powder filling. A fritable getter device having a high barium yield obtained through the addition of a flat discontinuous metal element is disclosed. Third-generation getter devices, either conventional or high-yield
By adding the components, it is possible to obtain fritable getter devices with comparable barium emission characteristics with reduced evaporation times.

To supplement the content of the same application, the process of making a picture tube involves the step of welding two glass parts together, ie, a melting point of about 450 ° C. between the two glass parts in the presence of air. This is performed in a so-called “frit sealing” operation by melting or softening a glass paste having In traditional picture tubes, after the frit sealing step, the getter device can be introduced through a neck provided to house the electron gun.
However, in this case, the size of the getter device is limited by the diameter of the neck, and accurate positioning of the getter device within the picture tube is difficult. As a result, picture tube manufacturers have a greater tendency to insert getter devices before frit sealing. During the frit sealing phase, the getter device is
Exposure to the atmosphere at a temperature of 50 ° C. and the vapor is released by the low melting glass paste. The main result is surface oxidation of nickel. During the barium flash, the nickel oxide, together with the aluminum, exhibits a strong, uncontrollable, exothermic reaction. This can lead to bulging of the powder filling, spattering of debris therefrom or partial melting of the container, and thus overall is detrimental to the proper operation of the getter device and picture tube.

An evaporable getter device that can withstand frit sealing without the disadvantages described above is defined as "fritable." As mentioned above, fritable getter devices have already been manufactured and sold by the Applicant. These getter devices can be made using traditional techniques as long as some critical values are not exceeded. In particular, it is not possible to exceed a certain predetermined thickness of the powder filling. This means that, if the thickness is too large, the heat generated in the body of the powder filling is released only very slowly, thus presenting the problem described above. Thus, the maximum amount of barium that can be evaporated from a fritable getter device made using traditional techniques is 200 mg. However, large size picture tubes require at least 300 mg of evaporating barium and such requirements cannot be met by fritable devices according to the prior art. A fritable getter device capable of evaporating more than 200 mg of barium is defined as being "high yielding".

In order to obtain a high-yield type fritable getter device, it is necessary that the metal part is embedded in the powder filling at a position spaced from the bottom surface and not emerging from the surface. . In practice, the induction heating of the getter device occurs primarily in the container and in the metal member embedded in the powder, and then transfers heat to the getter material powder. It was observed that heat transfer to the powder in the contact area between the metal member and the bottom of the vessel was almost inefficient and local overheating occurred. If these contact areas extend too much or too much, the non-dissipating heat can cause the powder filling to rise and in some cases also cause the equipment parts to melt. Conversely, if the metal members appear on the free surface of the padding, the surfaces themselves are subdivided into zones that bond poorly to one another and thus fly inside the picture tube during flash.

The metal member can be made from various metals, such as an iron alloy, a nickel alloy or an aluminum alloy. Stainless steel AI for ease of cold working
The use of SI 304 is preferred. The metal member can take a variety of different shapes if it is discontinuous and substantially planar. The discontinuity is necessary so that the metal member does not interfere with the release of barium vapor generated in the powder portion between the member itself and the container bottom. This condition can be obtained through many different sizes and shapes. As a possible embodiment, the metal member can be formed as a metal cutting material having a radial shape with a central hole to aid in the release of barium from the underlying powder, and in either a random or ordered pattern. Can be formed as a cutting material having a large number of holes distributed on the surface. Alternatively, the metal member can be a wire net as described in U.S. Pat. No. 3,558,962.

The metal part must also be substantially flat so that it can be embedded inside a powder filling, typically having a thickness of a few mm, without coming into contact with the bottom of the container and emerging from the free surface of the powder. The condition that the metal member must not contact the bottom of the container can be realized in various ways. For example, it is obtained by pouring a first part of the powder on the bottom of the container, laying a flat metal member on its upper surface and covering the metal member with the rest of the powder. Finally, the powder is compressed in a container using a forming punch such that a radial recess is formed in the upper surface. In yet another embodiment, the metal member is locally deformed so as to obtain some legs therein and is placed on the bottom inside the container. A deformed portion can be formed on the side wall of the container, and the metal member can be placed thereon. A raised portion is formed on the bottom surface of the container, thereby forming a support on which the metal member is placed.

Further, it is necessary to form a radial recess on the upper surface of the powder filling to suppress heat dispersion in the circumferential direction. On the upper surface of the powder filling, several recesses are formed in the radial direction, in numbers of 2 to 8.

[0024]

The present invention will be described in more detail with reference to the following examples. These examples are not intended to limit the invention but to teach one of ordinary skill in the art how to practice the invention and to illustrate embodiments deemed optimal for practicing the invention. is there.

(Example 1: Example) Stainless steel AISI3
04, having a diameter of 20 mm and a height of 4 mm, and having a bottom surface shaped like a ridge as described in US Pat. No. 5,118,988. A number of getter devices were manufactured, all of which were equivalent. For each sample, 767 mg of powdered BaAl ₄ with a particle size of less than 250 μm, 60 μm
866 mg of powdered nickel having a particle size of less than 8.6 mg and 1 having a purity of 99% and a particle size of less than 80 μm
A homogeneous mixture consisting of 8 mg of powdered iron was poured into the container. Thereafter, the powder mixture was compressed inside the container with a suitable punch. Place the sample one at a time in a glass measuring chamber connected to the pump system, evacuate the measuring chamber,
A barium evaporation test was performed according to the method described in standard ASTM F111-72. Each device is
Heating was performed by radio frequency using electric power such that evaporation of barium occurred 12 seconds after the start of heating. The tests were different from each other with various changes in the total heating time (TT) in the range of 35 to 45 seconds. At the end of each test, the amount of barium evaporated was detected. 300mg
TT required to evaporate the amount of barium from the apparatus
Are shown in Table 1.

Example 2: Example A number of equivalent getter devices were made using a steel container as described in Example 1. AIS with 1.5 mm width mesh in container
An I304 steel net was placed on the bottom ridge. For each sample, 767 mg of powdered BaAl ₄ with a particle size of less than 250 μm, 866 with a particle size of less than 60 μm
mg of powdered nickel, and having 99% purity and 5
A homogeneous mixture consisting of 18 mg of powdered aluminum having a particle size of less than 0 μm was poured into the container. afterwards,
The powder mixture was compressed inside the container using a punch shaped to form four radial recesses on the powder filling. The sample thus obtained was treated at 450 ° C. for one hour in the atmosphere to simulate frit sealing conditions. According to Example 1, each sample was similarly subjected to a barium evaporation test. Again, each device was heated by radio frequency using power such that barium evaporation occurred 12 seconds after the start of heating. The test was performed differently, varying the total heating time (TT) in the range of 35-45 seconds, and then measuring the TT required to evaporate 300 mg of barium from the apparatus. Table 1 shows the results.

Example 3: Comparative Example Same as Example 1, but using a series of samples without the addition of iron powder, using a power level such that barium evaporation occurs 12 seconds after the start of heating. The test of Example 1 was repeated by heating with radio frequency. The test is the total heating time (TT)
Were variously changed in the range of 35 to 45 seconds to be different from each other. Table 1 shows the test results.

Example 4 Comparative Example A series of tests was repeated using the same materials as in Example 1 except that no powdered aluminum was used and using the same getter device as in Example 2. Table 1 shows the TT required to evaporate 30 mg of barium from these samples.

[0029]

[Table 1]

[0030]

As can be seen from the results in Table 1, using the apparatus according to the invention at a TT of 35 seconds 300
mg barium yields can be obtained and the TT can be reduced by 5 to 10 seconds compared to the prior art. Forming radial recesses on the top surface of the powder filling to suppress heat spread in the circumferential direction, having a reduced activation time through the addition of substantially flat discontinuous metal elements within the powder filling and having a frit seal A wearable getter device is obtained.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Stefano Triverato Ballese, Gerenzano, Via Issonzo, Italy, 6 / D Nobembure, 94 (56) References JP-A-59-117038 (JP, A) JP-A-7-176278 (JP, A) JP-A-49-49571 (JP, A) JP-B-51-36037 (JP) , B1) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01J 29/94 H01J 7/18

Claims (2)

(57) [Claims] A powder of claim 1] BaAl ₄ compound, a powder of nickel, iron, and titanium and the powder more comprising a mixture of a third component selected from the group consisting of alloys thereof, said third component is a mixture An evaporable getter device having a metal container containing a mixture present in an amount ranging from about 0.3 to 5% of the total weight. 2. A powder mixture in said container, said metal container having an open top and a filling in said container and having a radial recess formed in said upper surface, comprising: BaAl ₄ , nickel,
A powder comprising a third component selected from the group consisting of aluminum, iron, titanium and alloys thereof, wherein the third component is present in an amount ranging from about 0.3 to 5% of the total weight of the mixture. With the mixture, having a substantially flat shape and substantially parallel to the bottom surface of the container, and being embedded in the powder filling such that it does not emerge from the free surface of the filling itself at a location spaced from the bottom surface of the container. An evaporable getter device having a reduced activation time and a frit sealable including a continuous metal element.