A method for preparing a carbon nanotube cold cathode, an x-ray tube electron gun assembly

Abstract

The application provides a preparation method of a carbon nanotube cold cathode and an X-ray tube electron gun assembly. The preparation method of the carbon nanotube cold cathode comprises the following steps: providing a positioning plate, wherein at least one positioning hole is arranged on the positioning plate; providing a cold cathode substrate; embedding the cold cathode substrate in the positioning hole; and adhering a screen printing screen plate to the positioning plate, printing carbon nanotube paste on the surface of the cold cathode substrate by using a screen printing method, so as to obtain the carbon nanotube cold cathode. The preparation method of the carbon nanotube cold cathode utilizes a positioning method of a positioning plate with a larger area, is accurate and reliable, is simple to operate, has low requirements on the shape of the cold cathode substrate, is highly applicable, and is positioned by relying on the positioning plate, so that the accuracy of the carbon nanotube cold cathode array pattern is improved, the quality of the array pattern is improved, and the reusability of the screen printing screen plate is increased.

Description

Technical Field

[0001] This invention relates to the field of field emission technology, and in particular to a method for preparing a carbon nanotube cold cathode and an X-ray tube electron gun assembly. Background Technology

[0002] In computed tomography (CT) imaging, traditional X-ray emission sources typically employ thermionic cathodes, usually made of tungsten wire. The cathode is heated to extremely high temperatures, allowing electrons within it to gain sufficient energy to escape from the cathode surface and generate an electron beam. This thermionic electron beam is accelerated by a high-voltage electric field, and the high-speed electron beam bombards an anode metal target, producing X-rays through bremsstrahlung. Traditional thermionic cathodes suffer from high operating temperatures, long heating times to the required temperatures, high power consumption, and the wires are prone to damage during heating and cooling, resulting in short lifespans and difficulties in integration. Furthermore, CT imaging systems using traditional light sources exhibit motion artifacts due to the rotation of the light source during imaging. Carbon nanotube-based cold cathode X-ray sources generate electron beams through field emission. The most basic structure is a transistor: cathode, grid, and anode. Under the influence of an applied electric field, the potential barrier height and width of the cathode surface decrease, allowing electrons to tunnel through the vacuum, achieving high-speed, high-density electron emission. This offers advantages such as room-temperature operation, small size, high temporal resolution, and programmability. Furthermore, it can be fabricated into multi-focal-spot X-ray arrays for static X-ray CT imaging. However, compared to hot cathode X-ray tubes, to reduce the required start-up voltage and achieve rapid startup, a grid is typically added at the cathode distance (0.1-0.5 mm), applying a voltage of 0-3000V to control the activation of field emission electrons from the carbon nanotube cold cathode. Existing cold cathode field emission X-ray sources face a problem: field emission requires an electric field to be applied to the cathode through the grid, and cathode electrons must pass through the grid to reach the anode. This results in high electron capture by the grid, typically around 20-50%. Electrons intercepted by the grid not only generate heat and deform the grid, affecting its operational reliability and shortening the X-ray tube's lifespan, but also consume significant current, leading to reduced anode current, degraded imaging performance, and ultimately, a shorter X-ray tube lifespan. Furthermore, the high electric field beneath the grid promotes localized arcing between the cathode and the grid, further reducing equipment reliability. To address these issues, it is necessary to minimize the grid's electron interception rate. Therefore, aligning the carbon nanotube cathode array substrate with the grid openings improves the grid's electron throughput, thereby enhancing the X-ray tube's performance parameters.

[0003] Achieving alignment between the cold cathode array and the gate aperture presents several challenges. Firstly, fabricating precise arrays using methods like PECVD requires complex and costly processes. Secondly, screen printing for field emission cold cathode substrates offers a simpler, easier-to-operate, and lower-cost process, suitable for mass production of carbon nanotube cold cathode substrates. After printing, the screen detaches from the substrate, and the paste forms a pattern on the substrate. The paste spreads and covers the entire patterned area, but most of the cathode film surface is continuous, with carbon nanotubes and metals mixed and distributed throughout the area. The grid exhibits a high interception rate for electrons emitted from the continuous cathode plane. While screen printing can also be used to fabricate array patterns, it's difficult to guarantee the precision of the carbon nanotube cold cathode array position relative to the substrate. This further increases the difficulty of aligning the subsequent gate aperture with the cathode array pattern, making it challenging to achieve a low interception rate of electrons emitted from the cathode. To improve electron throughput at the gate, finer patterns need to be printed and aligned with the gate aperture. This requires matching and aligning the carbon nanotube film array with the gate aperture to reduce electron interception and improve the overall performance of the cold cathode X-ray tube.

[0004] The fabrication process of carbon nanotube cold cathodes is complex, currently involving methods such as PECVD, electrophoresis, and screen printing. This involves a wide range of processes and is quite intricate. Screen printing is an ancient technique that utilizes the principle that ink passes through the mesh openings of the screen in the image areas, while ink does not pass through the openings in the non-image areas. However, with technological advancements, to improve precision and accuracy, precise alignment is required before printing. Currently, there are two main methods for printing positioning in the industry. One is to use positioning blocks, which, after determining the printing range, are aligned and printed within a fixed range. However, this method is cumbersome, requires a long preparation time, wastes a lot of time and effort, and has low positioning accuracy. The other method is to use CCD alignment for printing. CCD alignment offers high precision, high speed (less than 1 second), and precise alignment (less than 5 μm accuracy). It also has a compensation function to effectively compensate for mechanical errors and is easy to debug. However, CCD alignment systems are expensive, and the marking points required for alignment need to be precise and pollution-free, which inevitably causes contamination during cold cathode fabrication. Currently, the carbon nanotube cold cathode substrates prepared by screen printing require miniaturization of X-ray tube equipment, typically with a cold cathode substrate diameter in the millimeter range. The small size of the cold cathode substrate makes it difficult to achieve precise positioning of the carbon nanotube cold cathode array on the substrate, hindering accurate array printing. Furthermore, due to the small substrate size, pressure cannot be applied evenly during array pattern printing, leading to uneven printing pressure and significant differences in the quality of the printed carbon nanotube array films.

[0005] Given the current shortcomings in the fabrication of carbon nanotube cold cathodes using screen printing, it is necessary to improve upon this method. Summary of the Invention

[0006] In view of this, the present invention proposes a method for preparing a carbon nanotube cold cathode and an X-ray tube electron gun assembly to solve the technical problems existing in the prior art.

[0007] In a first aspect, the present invention provides a method for preparing a carbon nanotube cold cathode, comprising the following steps:

[0008] A positioning plate is provided, wherein the positioning plate is provided with at least one positioning hole;

[0009] A cold cathode substrate is provided, the cold cathode substrate being adapted to the positioning hole;

[0010] The cold cathode substrate is embedded in the positioning hole;

[0011] A screen printing stencil is attached to the positioning plate, and carbon nanotube paste is printed on the surface of the cold cathode substrate using a screen printing method to prepare a carbon nanotube cold cathode.

[0012] Preferably, in the method for preparing the carbon nanotube cold cathode, the area of ​​the positioning plate is n times the area of ​​the cold cathode substrate, where n ≥ 8.

[0013] Preferably, in the method for preparing the carbon nanotube cold cathode, the cold cathode substrate has protrusions on both sides, and the positioning hole has a groove corresponding to the protrusion, the protrusion and the groove are adapted to each other, and the protrusion is embedded in the groove.

[0014] Preferably, in the method for preparing the carbon nanotube cold cathode, the positioning plate is provided with a first positioning part, and the screen printing plate is provided with a first positioning groove corresponding to the first positioning part. The first positioning groove is adapted to the first positioning part, and the first positioning part is engaged in the first positioning groove.

[0015] Preferably, in the method for preparing the carbon nanotube cold cathode, a second positioning part is provided on the positioning plate around the positioning hole, and a second positioning groove is provided on the screen printing plate corresponding to the second positioning part. The second positioning groove is adapted to the second positioning part, and the second positioning part is engaged in the second positioning groove.

[0016] Preferably, in the method for preparing the carbon nanotube cold cathode, the carbon nanotube slurry includes carbon nanotubes, terpineol, ethyl cellulose, titanium carbide powder, and titanium powder.

[0017] The mass ratio of carbon nanotubes, terpineol, ethyl cellulose, titanium carbide powder, and titanium powder is (0.5-2):(15-25):(0.5-1.5):(1-5):(0.5-2).

[0018] Preferably, the method for preparing the carbon nanotube cold cathode involves printing carbon nanotube paste onto the surface of a cold cathode substrate using a screen printing method to obtain the carbon nanotube cold cathode, specifically including:

[0019] Carbon nanotube paste is printed onto the surface of a cold cathode substrate using a screen printing method.

[0020] The cold cathode substrate is then heated to 200-300℃ at a rate of 4-6℃ / min and held for 2-4 hours. Then, it is heated to 750-850℃ at a rate of 4-6℃ / min and held for 1-3 hours. After cooling, carbon nanotube cold cathode is obtained.

[0021] And / or, the material of the cold cathode substrate includes any one of Kovar alloy, TC4 titanium alloy, stainless steel, and copper;

[0022] And / or, the mesh count of the screen printing stencil is 350 to 450 mesh.

[0023] Secondly, the present invention also provides an X-ray tube electron gun assembly, including a gate and a carbon nanotube cold cathode, wherein the carbon nanotube cold cathode is a carbon nanotube cold cathode prepared by the method described above.

[0024] Preferably, the X-ray tube electron gun assembly further includes:

[0025] A cathode mounting base is provided with a cathode mounting groove, and the carbon nanotube cold cathode is clamped in the cathode mounting groove;

[0026] A gate mounting base is provided with a gate mounting groove, and the gate is snapped into the gate mounting groove;

[0027] An insulating pad, one side of which is attached to the carbon nanotube cold cathode and the other side of which is attached to the gate;

[0028] The gate hole on the gate corresponds to the carbon nanotube on the carbon nanotube cold cathode;

[0029] The insulating pad has a through hole corresponding to the gate hole region to allow electrons to pass through.

[0030] Preferably, in the X-ray tube electron gun assembly, the carbon nanotube cold cathode has first lugs on both sides, and the cathode mounting groove has a first slot corresponding to the first lugs, with the first lugs being engaged in the first slots.

[0031] The gate is provided with second lugs on both sides, and the gate mounting groove is provided with a second slot corresponding to the second lugs, and the second lugs are engaged in the second slots;

[0032] A circular cathode insulating ring is fitted around the cathode mounting groove on the cathode fixing base, and an insulating sleeve is provided between the cathode insulating ring and the cathode mounting groove on the cathode fixing base.

[0033] A screw connector passes through the cathode mounting base and the insulating sleeve in sequence and is screwed to the gate mounting base.

[0034] The present invention provides a method for preparing a carbon nanotube cold cathode and an X-ray tube electron gun assembly, which have the following advantages over the prior art:

[0035] 1. The method for preparing carbon nanotube cold cathodes of the present invention uses a positioning plate with an area larger than that of the cold cathode substrate. During screen printing, the screen printing plate and the positioning plate are simply positioned to fit together. The positioning method using the larger positioning plate ensures accurate and reliable positioning, is simple to operate, has low requirements for the shape of the cold cathode substrate, and is highly applicable. Relying on the positioning plate not only improves the accuracy of the carbon nanotube cold cathode array pattern but also improves the quality of the array pattern and increases the reusability of the screen printing plate. It can meet the needs of preparing single or multiple cold cathode substrates. The carbon nanotube cold cathode prepared by the method of the present invention has a significantly higher printing quality than that of direct printing using a cold cathode substrate. Its alignment accuracy is high, with an error within 5μm. Through physical assembly, the alignment of the carbon nanotube cold cathode array pattern and the gate mesh is achieved, and the actual gate throughput can reach more than 90%, with a long-term stable operation rate of more than 80%.

[0036] 2. The X-ray tube electron gun assembly of the present invention includes a carbon nanotube cold cathode and a grid. The carbon nanotube cold cathode has first lugs on both sides, and a corresponding first slot is provided on the cathode mounting groove, with the first lugs being engaged in the first slots. The grid has second lugs on both sides, and a corresponding second slot is provided on the grid mounting groove, with the second lugs being engaged in the second slots. Due to the arrangement of the first lugs and the second lugs, after the grid is installed in the cathode mounting groove and the grid is installed in the grid mounting groove, the carbon nanotubes arrayed on the carbon nanotube cold cathode and the grid holes arrayed on the grid are exactly in one-to-one correspondence, so as to ensure the positional accuracy of the carbon nanotube cold cathode and the grid in the electron gun assembly, thereby improving the transmittance of the cold cathode X-ray tube field emission electron grid. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This is a schematic diagram of the positioning plate in one embodiment of the present invention;

[0039] Figure 2 This is a schematic diagram of the positioning plate in another embodiment of the present invention;

[0040] Figure 3 This is a schematic diagram of the positioning plate in another embodiment of the present invention;

[0041] Figure 4 This is a schematic diagram of the positioning plate in another embodiment of the present invention;

[0042] Figure 5 This is a schematic diagram of the structure of a screen printing stencil in one embodiment of the present invention;

[0043] Figure 6 This is a schematic diagram of the structure of the cold cathode substrate in one embodiment of the present invention;

[0044] Figure 7 This is a schematic diagram of the positioning plate in another embodiment of the present invention;

[0045] Figure 8 This is a schematic diagram of the positioning plate in another embodiment of the present invention;

[0046] Figure 9 This is a schematic diagram illustrating the use of a screen printing stencil in one embodiment of the present invention.

[0047] Figure 10 This is a schematic diagram illustrating the use of a screen printing stencil in another embodiment of the present invention;

[0048] Figure 11 This is a schematic diagram of the X-ray tube electron gun assembly structure in one embodiment of the present invention;

[0049] Figure 12 This is a schematic diagram of the connection structure between the cathode holder and the carbon nanotube cold cathode in one embodiment of the present invention;

[0050] Figure 13 This is a schematic diagram of the structure of the cathode holder in one embodiment of the present invention;

[0051] Figure 14 This is a schematic diagram of the structure of a carbon nanotube cold cathode in one embodiment of the present invention;

[0052] Figure 15 This is a schematic diagram of the connection structure between the carbon nanotube cold cathode and the gate holder in one embodiment of the present invention;

[0053] Figure 16This is a schematic diagram of the connection structure of the carbon nanotube cold cathode, insulating pad, and gate in one embodiment of the present invention;

[0054] Figure 17 This is a schematic diagram of the connection structure of the insulating pad and the gate fixing seat in one embodiment of the present invention;

[0055] Figure 18 This is a schematic diagram of the connection structure between the gate and the gate holder in one embodiment of the present invention;

[0056] Figure 19 This is a schematic diagram of the connection structure of the gate holder in one embodiment of the present invention;

[0057] Figure 20 This is a schematic diagram of the gate connection structure in one embodiment of the present invention;

[0058] Figure 21 This is a schematic diagram of the connection structure of the cathode fixing seat and the cathode insulating ring in one embodiment of the present invention.

[0059] Figure 22 The pattern of the carbon nanotube array finally printed according to the methods in Example 1 and Comparative Example 1 above;

[0060] Figure 23 A photograph of the carbon nanotube cold cathode prepared according to the method in Example 1;

[0061] Figures 24-25 This shows the alignment of the carbon nanotubes arrayed on the carbon nanotube cold cathode and the gate holes arrayed on the gate in Example 2.

[0062] Figure 26 This is a schematic diagram of the substrate field emission test and stability test of the X-ray tube electron gun assembly in Example 2;

[0063] Figure 27 The substrate field emission (IV) curve of the X-ray tube electron gun assembly in Example 2;

[0064] Figure 28 The stability test curve of the X-ray tube electron gun assembly in Example 2 after 2 hours of continuous operation is shown. Detailed Implementation

[0065] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0066] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0067] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0068] In the description of this invention, it should be understood that the orientation or positional relationship indicated by terms such as "above" is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed when in use, or the orientation or positional relationship in which those skilled in the art are usually understood. It is only for the convenience of describing this invention and simplifying the description, and is not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0069] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this application’s specification means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. It should be understood that when we say an element is “connected” to another element, it can be directly connected to the other element, or there may be an intermediate element. Furthermore, the term “connected” as used herein can include wireless connections. The term “and / or” as used herein includes all or any unit and all combinations of one or more associated listed items. Furthermore, the terms “first,” “second,” etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0070] This invention provides a method for preparing a carbon nanotube cold cathode, comprising the following steps:

[0071] S1. Provide a positioning plate, which has at least one positioning hole;

[0072] S2. Provide a cold cathode substrate that is compatible with the positioning hole;

[0073] S3. Embed the cold cathode substrate into the positioning hole;

[0074] S4. The screen printing plate is attached to the positioning plate, and carbon nanotube paste is printed on the surface of the cold cathode substrate using the screen printing method to prepare a carbon nanotube cold cathode.

[0075] It should be noted that the preparation method of the carbon nanotube cold cathode of the present invention is based on... Figures 1-10 As shown, the positioning plate 1 is provided with at least one positioning hole 11. Specifically, the number of positioning holes 11 can be 1, 2, 3, or 4 (e.g., Figures 3-4 (As shown) ... n, the number of positioning holes 11 is determined according to the carbon nanotube cold cathode to be prepared. Multiple positioning holes 11 can be set to prepare multiple carbon nanotube cold cathodes at once. The positioning holes 11 are adapted to the cold cathode substrate 2, and the size of the positioning holes 11 is basically the same as the size of the cold cathode substrate 2. The cold cathode substrate 2 is embedded in the positioning holes 11, and then the screen printing plate 3 is attached to the positioning plate. The screen printing plate 3 has mesh holes 31 arranged in an array corresponding to the cold cathode substrate 2. Carbon nanotube paste is printed on the surface of the cold cathode substrate using screen printing to prepare the carbon nanotube cold cathode. The area of ​​the positioning plate of this invention is larger than the area of ​​the cold cathode substrate. During screen printing, it is only necessary to position the screen printing plate and the positioning plate so that the screen printing mesh... The plate and positioning plate are bonded together, and the positioning method using the larger positioning plate ensures accurate and reliable positioning, simple operation, low requirements for the shape of the cold cathode substrate, and strong applicability. Relying on the positioning plate for positioning not only improves the accuracy of the carbon nanotube cold cathode array pattern, but also improves the array pattern quality and increases the reusability of the screen printing plate. It can meet the needs of preparing single or multiple cold cathode substrates. The carbon nanotube cold cathode prepared by the method of this invention has a significantly higher printing quality than that of direct printing using a cold cathode substrate. Its alignment accuracy is high, with an error within 5μm. Through physical assembly, the alignment of the carbon nanotube cold cathode array pattern and the gate mesh is achieved, and the actual gate throughput can reach more than 90%, with a long-term stable operation rate of more than 80%.

[0076] In some embodiments, the area of ​​the positioning plate 1 is n times the area of ​​the cold cathode substrate 2, where n ≥ 8. Obviously, the larger the area of ​​the positioning plate 1, the simpler and more accurate the positioning between the screen printing stencil 3 and the positioning plate 1.

[0077] In some embodiments, the shape of the positioning plate 1 is not limited in this invention; for example, the cross-sectional shape of the positioning plate 1 may be rectangular. Figure 1 (as shown), square, circle, oval ( Figure 2 (as shown) or other irregular shapes; the cross-sectional shape of the positioning hole 11 can be rectangular, square, circular, elliptical or other irregular shapes.

[0078] In some embodiments, the cross-sectional shape of the positioning plate 1 is a square, specifically the size of the square is 25mm × 25mm, that is, the side length of the square is 25mm. The size of the square can also be 20mm × 20mm.

[0079] In some embodiments, the cold cathode substrate 2 has a circular cross-section with a diameter of 10 mm.

[0080] In some embodiments, the thickness of the positioning plate 1 is the same as the thickness of the cold cathode substrate 2. When the positioning plate 1 is manufactured, its thickness is equal to the thickness of the cold cathode substrate 2, with an error within ±0.01mm. A positioning hole 11 that is consistent with the cold cathode substrate 2 is cut out in its center by laser cutting or other high-precision processing methods, with a processing accuracy within ±0.01mm. Its shape is consistent with the cold cathode substrate 2.

[0081] In some embodiments, the thickness of the positioning plate 1 is not limited. For example, the thickness of the positioning plate 1 is 0.5 to 2 mm, and preferably, the thickness is 1 mm.

[0082] In some embodiments, such as Figure 6 As shown, the cold cathode substrate 2 has protrusions 21 on both sides, and the positioning hole 11 has a groove 12 corresponding to the protrusion 21. The protrusion 21 and the groove 21 are adapted to each other, and the protrusion 21 is embedded in the groove 12.

[0083] In the above embodiment, the protrusions 21 provided on both sides of the cold cathode substrate 2 are embedded in the groove 12, and the protrusions 21 also serve a positioning function.

[0084] In some embodiments, to facilitate the adhesion of the screen printing stencil 3 to the positioning plate 1, a positioning reference line can be set on the positioning plate 1. The positioning reference line is adapted to the contour of the positioning plate 1, that is, the contour of the positioning plate 1 is the positioning reference line of the positioning plate 1. At the same time, the screen printing stencil 3 is also provided with a positioning reference line. The positioning reference line of the screen printing stencil is aligned with the positioning reference line of the positioning plate (that is, aligned with the contour of the positioning plate) by visual inspection or magnification, thereby realizing the positioning and adhesion of the screen printing stencil and the positioning plate, and then the subsequent printing of carbon nanotube paste is carried out.

[0085] In some embodiments, the screen printing stencil 3 is provided with a positioning groove that is compatible with the positioning plate 1. The positioning plate 1 can be locked in the positioning groove. By locking the positioning plate 1 in the positioning groove, the positioning plate 1 and the screen printing stencil 3 can be positioned and attached.

[0086] In some embodiments, such as Figure 7As shown, the positioning plate 1 is provided with a first positioning part 13, and the screen printing plate 3 is provided with a first positioning groove corresponding to the first positioning part 13. The first positioning groove is adapted to the first positioning part 13, and the first positioning part 13 is engaged in the first positioning groove.

[0087] In the above embodiment, the first positioning groove provided on the screen printing stencil 3 is the positioning reference line of the screen printing stencil. The positioning plate 1 is provided with a first positioning part 13. Specifically, the first positioning part 13 is provided circumferentially along the edge of the positioning plate 1. The first positioning part 13 is the positioning reference line of the positioning plate. In use, the first positioning part 13 is engaged in the first positioning groove, so that the positioning reference line of the screen printing stencil is aligned with the positioning reference line of the positioning plate, thereby positioning the screen printing stencil 3 and the positioning plate 1.

[0088] In some embodiments, such as Figure 8 As shown, a second positioning part 14 is provided on the positioning plate 1 around the positioning hole 11, and a second positioning groove is provided on the screen printing plate 3 corresponding to the second positioning part 14. The second positioning groove is adapted to the second positioning part 14, and the second positioning part 14 is engaged in the second positioning groove.

[0089] In the above embodiment, the second positioning groove provided on the screen printing stencil 3 is the positioning reference line of the screen printing stencil 3. The second positioning part 14 is arranged circumferentially along the positioning hole 11. The second positioning part 13 is the positioning reference line of the positioning plate. In use, the second positioning part 14 is engaged in the second positioning groove, so that the positioning reference line of the screen printing stencil 3 is aligned with the positioning reference line of the positioning plate, thereby positioning the screen printing stencil 3 and the positioning plate 1.

[0090] This invention utilizes a positioning plate for positioning. Firstly, it overcomes the difficulty of positioning and marking on a small cold cathode substrate. Secondly, the small substrate size results in a small force-bearing area for the squeegee during screen printing, leading to uneven force distribution. Using a positioning plate for positioning and alignment improves the accuracy of the cold cathode array's positioning relative to the entire cold cathode substrate. At the same time, it increases the force-bearing area of ​​the screen printing squeegee, thereby improving the printing quality and the precision of the array pattern.

[0091] In some embodiments, the positioning plate 1 is made of stainless steel, copper, titanium alloy, etc.

[0092] In some embodiments, the carbon nanotube slurry includes carbon nanotubes, terpineol, ethyl cellulose, titanium carbide powder, and titanium powder;

[0093] The mass ratio of carbon nanotubes, terpineol, ethyl cellulose, titanium carbide powder, and titanium powder is (0.5-2):(15-25):(0.5-1.5):(1-5):(0.5-2).

[0094] Specifically, the carbon nanotubes are single-walled carbon nanotubes (SWCNTs).

[0095] Preferably, the mass ratio of carbon nanotubes, terpineol, ethyl cellulose, titanium carbide powder, and titanium powder is 1:19:1:3:1.

[0096] In some embodiments, the carbon nanotube slurry is prepared by mixing carbon nanotubes, terpineol, ethyl cellulose, titanium carbide, and titanium, and then ball milling them in a planetary ball mill to obtain the carbon nanotube slurry; wherein the ball milling speed is 300-400 r / min.

[0097] In some embodiments, carbon nanotube paste is printed on the surface of a cold cathode substrate using a screen printing method to prepare a carbon nanotube cold cathode, specifically including:

[0098] Carbon nanotube paste is printed onto the surface of a cold cathode substrate using a screen printing method.

[0099] The cold cathode substrate is then heated to 200-300℃ at a rate of 4-6℃ / min and held for 2-4 hours. Then, it is heated to 750-850℃ at a rate of 4-6℃ / min and held for 1-3 hours. After cooling, carbon nanotube cold cathode is obtained.

[0100] In the above embodiments, carbon nanotube slurry is printed on the surface of a cold cathode substrate and then annealed to form an array of carbon nanotubes on the surface of the cold cathode substrate, thus finally preparing a carbon nanotube cold cathode.

[0101] In some embodiments, carbon nanotube paste is printed onto the surface of a cold cathode substrate by screen printing, and then annealed to obtain a carbon nanotube cold cathode. Then, 3M tape is used to treat the surface of the cold cathode substrate, the tape is adhered to the substrate, and the tape is used to remove carbon nanotubes that are not in firm contact with the substrate.

[0102] In some embodiments, the material of the cold cathode substrate 2 includes any one of Kovar alloy, TC4 titanium alloy, stainless steel, and copper.

[0103] In some embodiments, such as Figure 5 As shown, the screen printing stencil 3 has multiple mesh openings 31 arranged in an array, with a mesh count of 350 to 450 meshes.

[0104] This invention innovatively employs a positioning plate for accurate positioning. Compared to traditional positioning blocks and CCD camera alignment, it is lower in cost, simpler to operate, and more applicable. Compared to direct positioning using the outline pattern of the cold cathode substrate, the positioning plate increases the marking baseline, making the alignment marks more obvious. Due to the increased size of the positioning plate, alignment is easier during carbon nanotube cold cathode screen printing compared to using the cold cathode substrate for positioning marks. Furthermore, directly using the outline of the cold cathode substrate as positioning marks is easily contaminated by the paste after a few uses, making them difficult to clean and causing the positioning baseline to become blurred, increasing the difficulty of positioning. This invention, using a positioning plate, increases the size of the positioning baseline and absorbs errors from the small substrate processing and positioning outline marking, increasing positioning reliability. It solves the problems of unreliability and inaccuracy of direct positioning with the cold cathode substrate. Simultaneously, the positioning plate increases the force-bearing area of ​​the squeegee during printing, improving printing quality and enhancing the accuracy of the carbon nanotube cold cathode array position relative to the substrate, achieving micron-level precision. For cold cathode X-ray tubes of different sizes and shapes, when different cold cathode substrates are required, secondary positioning only requires replacing the positioning plate. The positioning plate and positioning holes are re-processed according to the size and shape of the cold cathode substrate. Secondary positioning does not require the processing of new screen printing stencils, which improves the versatility of screen printing stencil positioning and reduces costs and product development cycles.

[0105] Based on the same inventive concept, the present invention also provides an X-ray tube electron gun assembly, including a grid 4 and a carbon nanotube cold cathode 5, wherein the carbon nanotube cold cathode 5 is a carbon nanotube cold cathode prepared by the above method.

[0106] In some embodiments, the X-ray tube electron gun assembly further includes:

[0107] A cathode mounting base 6 is provided with a cathode mounting groove 61, and a carbon nanotube cold cathode 5 is fitted into the cathode mounting groove 61.

[0108] A gate mounting base 7 is provided with a gate mounting groove 71, and the gate 4 is engaged in the gate mounting groove 71.

[0109] An insulating pad 8 has a carbon nanotube cold cathode 5 attached to one side and a grid 4 attached to the other side.

[0110] The gate hole 41 on the gate 4 corresponds to the carbon nanotube 51 on the carbon nanotube cold cathode 5;

[0111] An insulating pad 8 has a through hole 81 in the area corresponding to the gate hole to allow electrons to pass through.

[0112] The X-ray tube electron gun assembly of the present invention comprises a carbon nanotube cold cathode 5 with an array of carbon nanotubes 51 arranged on it, and a grid hole 41 arranged on it. The grid hole 41 corresponds one-to-one with the carbon nanotube 51. Specifically, the diameter of the carbon nanotube 51 is slightly smaller than the diameter of the grid hole 41 to ensure the field emission electron throughput. The carbon nanotube cold cathode 5 is mounted on a cathode mounting base 6. Specifically, the carbon nanotube cold cathode 5 is snapped into a cathode mounting groove 61. The grid 4 is mounted on a grid mounting base 7. Specifically, the grid 4 is snapped into a grid mounting groove 71. At the same time, an insulating gasket 8 is provided between the carbon nanotube cold cathode 5 and the grid 4. The two sides of the insulating gasket 8 are respectively attached to the carbon nanotube cold cathode 5 and the grid 4. Through holes 81 are opened on the insulating gasket 8 corresponding to the grid hole area to allow field emission electrons to pass through.

[0113] In some embodiments, the carbon nanotube cold cathode 5 is provided with first lugs 52 on both sides, and the cathode mounting groove 61 is provided with a first slot 62 corresponding to the first lugs 52, and the first lugs 52 are engaged in the first slot 62.

[0114] The gate 4 has a second lug 42 on both sides, and the gate mounting groove 71 has a second slot 72 corresponding to the second lug 42. The second lug 42 is engaged in the second slot 72.

[0115] In the above embodiment, the carbon nanotube cold cathode 5 is provided with first lugs 52 on both sides, and a corresponding first slot 62 is provided on the cathode mounting groove 61. The first lugs 52 are engaged in the first slot 62, and the first lugs 52 serve a positioning function to facilitate the installation of the carbon nanotube cold cathode 5 in the cathode mounting groove 61. The gate 4 is provided with second lugs 42 on both sides, and a corresponding second slot 72 is provided on the gate mounting groove 71. The second lugs 42 are engaged in the second slot 72, and the second lugs 42 serve a positioning function to facilitate the installation of the gate 4 in the gate mounting groove 71. At the same time, due to the arrangement of the first lugs 52 and the second lugs 42, after the gate 4 is installed in the cathode mounting groove 61 and the gate 4 is installed in the gate mounting groove 71, the carbon nanotubes arrayed on the carbon nanotube cold cathode 5 and the gate holes arrayed on the gate 4 correspond one-to-one, so as to ensure the positional accuracy of the carbon nanotube cold cathode 5 and the gate 4 in the electron gun component, thereby improving the transmittance of the cold cathode X-ray tube field emission electron gate.

[0116] It is understandable that the carbon nanotube cold cathode 5 with first lugs 52 on both sides is prepared by the above method. Specifically, by setting first lugs (i.e., corresponding to the protrusions mentioned above) on both sides of the cold cathode substrate, an array of carbon nanotubes is prepared on the cold cathode substrate by screen printing, thus finally obtaining the carbon nanotube cold cathode 5 with first lugs 52 on both sides.

[0117] In some embodiments, an annular cathode insulating ring 9 is sleeved on the cathode mounting groove 61 on the cathode fixing seat 6, and an insulating sleeve 91 is provided on the cathode fixing seat 6 between the cathode insulating ring 9 and the cathode mounting groove 61.

[0118] A screw connector 92 passes through the cathode fixing seat 6 and the insulating sleeve 91 in sequence and is screwed to the gate fixing seat 7.

[0119] In the above embodiment, the insulating sleeve 91 is located between the cathode insulating ring 9 and the cathode mounting groove 61, that is, the insulating sleeve 91 is located inside the cathode insulating ring 9, and the screw connector 92 passes through the cathode fixing seat 6 and the insulating sleeve 91 in sequence and is screwed to the gate fixing seat 7.

[0120] Specifically, in some embodiments, the upper and lower end faces of the cathode insulating ring 9 and the upper and lower end faces of the insulating sleeve 91 are respectively attached to the surfaces of the gate fixing seat 7 and the cathode fixing seat 6; the screw connection 92 can be a bolt, screw, etc.

[0121] In some embodiments, a cathode through-hole 63 is provided on the cathode mounting groove 61 corresponding to the carbon nanotube 51 area arrayed on the carbon nanotube cold cathode 5.

[0122] In some embodiments, a gate through-hole 73 is provided on the gate mounting groove 71 corresponding to the gate hole 41 region of the gate 4.

[0123] The following detailed embodiments further illustrate the preparation method of the carbon nanotube cold cathode and the X-ray tube electron gun assembly of the present invention. This section further describes the content of the present invention in conjunction with specific embodiments, but should not be construed as limiting the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the methods and equipment used in the present invention are conventional methods and equipment in the art.

[0124] Example 1

[0125] This application provides a method for preparing a carbon nanotube cold cathode, comprising the following steps:

[0126] S1. A positioning plate is provided, which has a positioning hole; the positioning plate is a cuboid with a thickness (i.e., height) of 1mm, a length of 25mm, and a width of 25mm;

[0127] S2. Provide a cold cathode substrate that is compatible with the positioning hole; the cold cathode substrate has a circular cross-section with a diameter of 10mm, and protrusions are provided on both sides of the cold cathode substrate; the material of the cold cathode substrate is stainless steel.

[0128] S3. Embed the cold cathode substrate into the positioning hole;

[0129] S4. The outline of the positioning plate is the positioning reference line of the positioning plate. The screen printing screen also has a positioning reference line corresponding to the outline of the positioning plate. Align the positioning reference line on the screen printing screen with the outline of the positioning plate and make the positioning plate adhere to the screen printing screen. Use screen printing method to print carbon nanotube paste on the surface of the cold cathode substrate to prepare carbon nanotube cold cathode.

[0130] Carbon nanotube cold cathodes are prepared by printing carbon nanotube paste onto the surface of a cold cathode substrate using screen printing. Specifically, this includes:

[0131] Carbon nanotube paste is printed onto the surface of a cold cathode substrate using a screen printing method.

[0132] The cold cathode substrate is then placed in a vacuum annealing furnace and heated to 250°C at 5°C / min, held for 3 hours, then heated to 800°C at 5°C / min, held for 2 hours, and then cooled. The surface of the cold cathode substrate is then treated with 3M tape. The tape is adhered to the substrate, and the carbon nanotubes that are not in firm contact with the substrate are removed with the tape to obtain the carbon nanotube cold cathode.

[0133] The preparation method of carbon nanotube slurry includes: mixing 0.2g single-walled carbon nanotubes, 3.8g terpineol, 0.2g ethyl cellulose, 0.36g titanium carbide powder, and 0.2g titanium powder, and then placing them in a planetary ball mill and ball milling at a speed of 350r / min to obtain carbon nanotube slurry;

[0134] The mesh size of the screen printing stencil is 400 mesh.

[0135] Comparative Example 1

[0136] The method for preparing the carbon nanotube cold cathode provided in this comparative example is the same as that in Example 1, except that a positioning plate is not used for positioning. Instead, carbon nanotube paste is directly printed on the surface of the cold cathode substrate using a screen printing method to prepare the carbon nanotube cold cathode. The specific method for preparing the carbon nanotube cold cathode by printing carbon nanotube paste on the surface of the cold cathode substrate using a screen printing method is the same as that in Example 1.

[0137] like Figure 22 The images show the patterns of carbon nanotube arrays finally printed according to the methods in Example 1 and Comparative Example 1, respectively. Figure 22 (a) shows the pattern of the carbon nanotube array obtained according to the method in Example 1. Figure 22 (b) shows the pattern of the carbon nanotube array obtained according to the method in Comparative Example 1.

[0138] from Figure 22 As can be seen from the example, using a positioning plate for positioning in Example 1 results in a carbon nanotube array with higher pattern quality and greater accuracy.

[0139] Figure 23 This is a photograph of the carbon nanotube cold cathode prepared according to the method in Example 1.

[0140] Example 2

[0141] This application provides an X-ray tube electron gun assembly, including the carbon nanotube cold cathode and grid prepared in Example 1, the structure of which is as follows: Figures 11-21 As shown, the second lugs on both sides of the gate are engaged in the second slot, so that the gate is installed in the gate mounting slot of the gate fixing seat; the first lugs on both sides of the carbon nanotube cold cathode (since the cold cathode substrate used in Example 1 has protrusions on both sides, the carbon nanotube cold cathode finally prepared has first lugs on both sides) are engaged in the first slot, so that the gate is installed in the cathode mounting slot of the cathode fixing seat, so that the carbon nanotubes arrayed on the carbon nanotube cold cathode correspond one-to-one with the gate holes arrayed on the gate.

[0142] like Figures 24-25 As shown, this illustrates the alignment of the carbon nanotubes arrayed on the carbon nanotube cold cathode and the gate holes arrayed on the gate in Example 2.

[0143] Figure 27 The image shows the base field emission (IV) curve of the X-ray tube electron gun assembly in Example 2.

[0144] Figure 28 This is a stability test of the X-ray tube electron gun assembly in Example 2 under 2 hours of continuous operation.

[0145] Specifically, the X-ray tube electron gun assembly in Example 2 was subjected to field emission testing under the following conditions: the test was conducted in a vacuum chamber at room temperature; the carbon nanotube cold cathode of the X-ray tube electron gun assembly was grounded, the grid was connected to a high-voltage power supply, and stainless steel was used as the anode, which was connected to a high-voltage power supply; all field emission tests were conducted under high vacuum conditions (5.0 × 10⁻⁶). -5 The continuous drive mode was measured using a LabVIEW program with a Keithley 248 power supply. During the field emission test, a high-voltage power supply was applied to the gate, forming a cathode-gate diode structure (the gate being the diode anode). The DC voltage range was 100 to 1500V. The computer automatically recorded the relationship between the emission current and the applied voltage, thus obtaining the field emission IV curve. The stability test under 2 hours of continuous operation involved fixing the gate high-voltage power supply at a certain voltage for two hours and recording the current stability.

[0146] Specific test diagrams are shown below. Figure 26 As shown, Figure 26In this diagram, Cathode (CNT) is the carbon nanotube cold cathode, Gate is the gate electrode, and Anode is the stainless steel anode; V1 is the high-voltage power supply connected to the anode, and V2 is the high-voltage power supply connected to the gate electrode.

[0147] from Figures 27-28 As can be seen from the data, the fabricated electron gun component can generate an anode current of 5mA at 1300V. Figure 28 This indicates good field emission current stability within 2 hours and a gate electron throughput of 80% over a long period. Figure 28 In the diagram, when the anode current is increased to V1 > V2, the current on the vertical axis is 1mA. Electrons are attracted by the anode voltage and pass through the gate hole to reach the anode.

[0148] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a carbon nanotube cold cathode, characterized in that, Includes the following steps: A positioning plate is provided, wherein the positioning plate is provided with at least one positioning hole; A cold cathode substrate is provided, the cold cathode substrate being adapted to the positioning hole; The cold cathode substrate is embedded in the positioning hole; A screen printing stencil is attached to the positioning plate, and carbon nanotube paste is printed on the surface of the cold cathode substrate using a screen printing method to prepare a carbon nanotube cold cathode. The cold cathode substrate has protrusions on both sides, and the positioning hole has a groove corresponding to the protrusion. The protrusion and the groove are adapted to each other and the protrusion is embedded in the groove. The positioning plate is provided with a second positioning part on the outer periphery of the positioning hole, and the screen printing plate is provided with a second positioning groove corresponding to the second positioning part. The second positioning groove is adapted to the second positioning part, and the second positioning part is engaged in the second positioning groove. The carbon nanotube slurry includes carbon nanotubes, terpineol, ethyl cellulose, titanium carbide powder, and titanium powder. The mass ratio of carbon nanotubes, terpineol, ethyl cellulose, titanium carbide powder, and titanium powder is (0.5~2):(15~25):(0.5~1.5):(1~5):(0.5~2). Carbon nanotube cold cathodes are prepared by printing carbon nanotube paste onto the surface of a cold cathode substrate using a screen printing method, specifically including: Carbon nanotube paste is printed onto the surface of a cold cathode substrate using a screen printing method. The cold cathode substrate is then heated to 200-300℃ at a rate of 4-6℃ / min and held for 2-4 hours. Then, it is heated to 750-850℃ at a rate of 4-6℃ / min and held for 1-3 hours. After cooling, carbon nanotube cold cathode is obtained. And / or, the material of the cold cathode substrate includes any one of Kovar alloy, TC4 titanium alloy, stainless steel, and copper; And / or, the mesh count of the screen printing stencil is 350~450 mesh.

2. The method for preparing a carbon nanotube cold cathode as described in claim 1, characterized in that, The area of ​​the positioning plate is n times the area of ​​the cold cathode substrate, where n ≥ 8.

3. The method for preparing a carbon nanotube cold cathode as described in claim 1, characterized in that, The positioning plate is provided with a first positioning part, and the screen printing plate is provided with a first positioning groove corresponding to the first positioning part. The first positioning groove is adapted to the first positioning part, and the first positioning part is engaged in the first positioning groove.

4. An X-ray tube electron gun assembly, characterized in that, It includes a gate and a carbon nanotube cold cathode, wherein the carbon nanotube cold cathode is a carbon nanotube cold cathode prepared by any one of the methods described in claims 1 to 3.

5. The X-ray tube electron gun assembly as described in claim 4, characterized in that, Also includes: A cathode mounting base is provided with a cathode mounting groove, and the carbon nanotube cold cathode is clamped in the cathode mounting groove; A gate mounting base is provided with a gate mounting groove, and the gate is snapped into the gate mounting groove; An insulating pad, one side of which is attached to the carbon nanotube cold cathode and the other side of which is attached to the gate; The gate hole on the gate corresponds to the carbon nanotube on the carbon nanotube cold cathode; The insulating pad has a through hole corresponding to the gate hole region to allow electrons to pass through.

6. The X-ray tube electron gun assembly as described in claim 5, characterized in that, The carbon nanotube cold cathode is provided with first lugs on both sides, and the cathode mounting groove is provided with a first slot corresponding to the first lugs, with the first lugs being engaged in the first slot. The gate is provided with second lugs on both sides, and the gate mounting groove is provided with a second slot corresponding to the second lugs, and the second lugs are engaged in the second slots; A circular cathode insulating ring is fitted around the cathode mounting groove on the cathode fixing base, and an insulating sleeve is provided between the cathode insulating ring and the cathode mounting groove on the cathode fixing base. A screw connector passes through the cathode mounting base and the insulating sleeve in sequence and is screwed to the gate mounting base.

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