Manufacturing method for carbon-nanotube cold cathode, and x-ray tube electron gun assembly

Abstract

A manufacturing method for a carbon-nanotube cold cathode (5), comprising the following steps: providing a positioning plate (1), the positioning plate (1) being provided with at least one positioning hole (11); providing a cold cathode substrate (2); embedding the cold cathode substrate (2) in the positioning hole (11); and fitting a screen printing mesh plate (3) onto the positioning plate (1), and using a screen printing method to print a carbon-nanotube slurry on the surface of the cold cathode substrate (2), so as to prepare a carbon-nanotube cold cathode (5). An X-ray tube electron gun assembly comprises the carbon-nanotube cold cathode (5). The manufacturing method for the carbon-nanotube cold cathode (5) uses the positioning plate (1) having a larger area for positioning, achieving accurate and reliable positioning and simple operation, and having low requirement for the appearance of the cold cathode substrate (2), thus achieving high applicability; using the positioning plate (1) for positioning not only increases the accuracy of an array pattern of the carbon-nanotube cold cathode (5), but also improves the array pattern quality and increases the reuse rate of the screen printing mesh plate (3).

Description

A method for preparing a carbon nanotube cold cathode and an X-ray tube electron gun assembly Technical Field

[0001] The present 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 Art

[0002] In computed tomography (CT), traditional X-ray emission sources typically use a hot cathode, typically a tungsten wire. The cathode is heated to an extremely high temperature, allowing electrons in the cathode to gain sufficient energy to overflow from the cathode surface, generating an electron beam. A high-voltage electric field is then applied to accelerate the electron beam generated by thermal emission. This high-speed electron beam then strikes a metal target anode, generating X-rays via bremsstrahlung radiation. Traditional hot metal wire cathodes operate at high temperatures, require a long time to heat to the required temperature, consume high power, and are susceptible to damage during heating and cooling, resulting in a short lifespan and difficulty in integration. CT imaging systems built with traditional light sources often experience motion artifacts due to the rotating imaging of the light source. Carbon nanotube-based cold cathode X-ray sources generate electron beams through field emission. The most basic structure is a triode, consisting of a cathode, a gate, and an anode. The gate lowers the potential barrier height and narrows the width of the cathode surface under the influence of an external electric field, allowing electrons at the cathode to escape into the vacuum via the tunneling effect, achieving high-speed, high-density electron emission. These sources offer advantages such as room-temperature operation, compact size, high temporal resolution, and programmability. They can also be fabricated into multi-focal spot X-ray sources, enabling static X-ray CT imaging. However, compared to hot cathode X-ray tubes, to reduce the applied turn-on voltage and achieve rapid startup, a gate is typically added at a distance of 0.1-0.5 mm from the cathode. A voltage of 0-3000 V is applied to the gate to control the field emission of electrons from the carbon nanotube cold cathode. Existing cold cathode field emission X-ray sources also face a problem: field emission requires the application of an electric field to the cathode through the gate, and cathode electrons must pass through the gate to reach the anode. This results in high electron interception by the gate, typically around 20-50%. When electrons intercepted by the gate hit the gate, they not only generate heat and cause deformation of the gate, which affects the reliability of the gate and shortens the service life of the X-ray tube, but also consume a large amount of current, resulting in a decrease in the anode current and poor imaging performance, thereby shortening the service life of the X-ray tube. In addition, due to the high electric field under the gate, this droop promotes local arc discharge between the cathode and the gate, further reducing the reliability of the equipment. To solve the above problems, it is necessary to reduce the interception rate of electrons by the gate as much as possible. To this end, the carbon nanotube cathode array substrate is aligned with the grid mesh to improve the gate electron pass rate, thereby improving the performance parameters of the X-ray tube.

[0003] Achieving alignment of the cold cathode array with the gate apertures presents many challenges. Precise array fabrication through methods like PECVD requires complex and tedious processes, leading to increased costs. Screen printing, however, allows for a simple, easy-to-use, and low-cost process suitable for mass-producing carbon nanotube cold cathode substrates. After printing, the screen is removed from the substrate, and the slurry forms a pattern on the substrate. The slurry spreads over the entire patterned area, but the cathode film surface is mostly continuous, with the carbon nanotubes and metal mixed throughout the entire area. The grid has a high interception rate for electrons emitted from the continuous cathode plane. Screen printing can also be used to create the array pattern, but ensuring the precise positioning of the carbon nanotube cold cathode array relative to the substrate poses challenges, further complicating the subsequent alignment of the gate apertures with the cathode array pattern. This makes it difficult to achieve a low interception rate of cathode field-emission electrons. To improve the gate's pass rate, a finer pattern must be printed and aligned with the gate apertures. This requires matching alignment of the carbon nanotube film array with the gate apertures to reduce electron interception and improve the overall performance of the cold cathode X-ray tube. Technical issues

[0004] The preparation process for carbon nanotube cold cathodes is complex. Currently, the main methods include PECVD, electrophoresis, and screen printing. These involve a wide range of processes and are complex. Screen printing is an ancient process that uses the principle that the mesh holes in the image area of ​​the screen printing plate are permeable to ink, while the mesh holes in the non-image area are impermeable to ink. With the development of technology, in order to improve precision and accuracy, the position alignment before printing is required. Currently, there are two methods of printing positioning in the industry. One is to use limit blocks. After determining the printing range, the limit blocks are adapted to perform alignment printing within a fixed range. However, the limit block positioning method is relatively cumbersome and takes a long time to prepare, which wastes a lot of time and energy, and has low positioning accuracy. The second is to use CCD alignment for printing. CCD alignment has high precision and fast speed, with an alignment speed of less than 1s, precise alignment, and an alignment accuracy of less than 5μm. It also has a compensation function, which can effectively compensate for mechanical errors and facilitate debugging. However, the CCD alignment system is expensive, and the marking points required for alignment need to be precise and pollution-free, which will inevitably cause contamination when preparing the cold cathode. The carbon nanotube cold cathode substrate currently prepared by screen printing requires miniaturization of X-ray tube equipment, and the diameter of the cold cathode substrate is usually in the millimeter level. The cold cathode substrate is small, and it is difficult to achieve the accuracy of the position of the carbon nanotube cold cathode array on the substrate, making it difficult to achieve accurate array printing. At the same time, due to the small substrate, pressure cannot be applied evenly when printing the array pattern, resulting in uneven printing force and large differences in the quality of the printed carbon nanotube array film.

[0005] Based on the defects of the current screen printing method for preparing carbon nanotube cold cathodes, it is necessary to improve it. Technical Solutions

[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] Providing a positioning plate, wherein the positioning plate is provided with at least one positioning hole;

[0009] Providing a cold cathode substrate, wherein the cold cathode substrate is adapted to the positioning hole;

[0010] embedding the cold cathode substrate in the positioning hole;

[0011] The screen printing plate is attached to the positioning plate, and the carbon nanotube slurry is printed on the surface of the cold cathode substrate by 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, protrusions are provided on both sides of the cold cathode substrate, grooves are provided at the positioning holes corresponding to the protrusions, the protrusions are adapted to the grooves, and the protrusions are embedded in the grooves.

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

[0015] Preferably, in the method for preparing the carbon nanotube cold cathode, a second positioning portion is provided on the positioning plate at the periphery of the positioning hole, a second positioning groove is provided on the screen printing screen corresponding to the second positioning portion, the second positioning groove is adapted to the second positioning portion, and the second positioning portion is clamped in the second positioning groove.

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

[0017] The mass ratio of the 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 comprises printing carbon nanotube slurry on the surface of the cold cathode substrate by screen printing to prepare the carbon nanotube cold cathode, which specifically comprises:

[0019] Printing carbon nanotube paste on the surface of the cold cathode substrate by screen printing;

[0020] The cold cathode substrate is then heated to 200-300°C at a rate of 4-6°C / min, kept at this temperature for 2-4 hours, then heated to 750-850°C at a rate of 4-6°C / min, kept at this temperature for 1-3 hours, and then cooled to obtain a carbon nanotube cold cathode.

[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 size of the screen printing screen is 350-450 meshes.

[0023] In a second aspect, the present invention further provides an X-ray tube electron gun assembly, comprising a grid and a carbon nanotube cold cathode, wherein the carbon nanotube cold cathode is the carbon nanotube cold cathode prepared by the method.

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

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

[0026] A grid fixing seat, on which a grid mounting groove is provided, and the grid is clamped in the grid mounting groove;

[0027] an insulating spacer, one side of which is attached to the carbon nanotube cold cathode and the other side of which is attached to the grid;

[0028] The gate holes on the gate correspond to the carbon nanotubes on the carbon nanotube cold cathode;

[0029] The insulating spacer is provided with a through hole corresponding to the gate hole area to allow electrons to pass through.

[0030] Preferably, in the X-ray tube electron gun assembly, first lugs are provided on both sides of the carbon nanotube cold cathode, and first clamping slots are provided at locations of the cathode mounting slot corresponding to the first lugs, wherein the first lugs are clamped in the first clamping slots;

[0031] Second lugs are provided on both sides of the gate, and second clamping grooves are provided at the gate mounting grooves corresponding to the second lugs, and the second lugs are clamped in the second clamping grooves;

[0032] The cathode fixing seat is provided with an annular cathode insulating ring on the outer periphery of the cathode mounting groove, and an insulating sleeve is provided on the cathode fixing seat between the cathode insulating ring and the cathode mounting groove;

[0033] A screw connection piece passes through the cathode fixing seat and the insulating sleeve in sequence and is screwed to the grid fixing seat. Beneficial effects

[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. In the preparation method of the carbon nanotube cold cathode of the present invention, the area of ​​the positioning plate is larger than the area of ​​the cold cathode substrate. During screen printing, it is only necessary to position the screen printing screen and the positioning plate so that the screen printing screen and the positioning plate are attached. The positioning method uses the positioning plate with a larger area. The positioning is accurate and reliable, and the operation is simple. The requirements for the shape of the cold cathode substrate are low, and the applicability is strong. Relying on the positioning plate for positioning not only improves the accuracy of the carbon nanotube cold cathode array pattern, but also improves the quality of the array pattern, increases the reuse rate of the screen printing screen, and can meet the needs of single or multiple preparations of different cold cathode substrates. The carbon nanotube cold cathode prepared by the method of the present invention has a printing quality significantly higher than that of direct printing using the cold cathode substrate. The positioning accuracy is high, with an error within 5 μm. The alignment of the carbon nanotube cold cathode array pattern and the grid mesh is achieved through physical assembly. The actual grid pass rate can reach more than 90%, and long-term stable operation can achieve 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. First lugs are provided on both sides of the carbon nanotube cold cathode, and a first clamping groove is correspondingly provided on the cathode mounting groove, and the first lugs are clamped in the first clamping groove; second lugs are provided on both sides of the grid, and a second clamping groove is correspondingly provided on the grid mounting groove, and the second lugs are clamped in the second clamping groove; 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 arranged in an array on the carbon nanotube cold cathode and the grid holes arranged in an array on the grid are exactly corresponding to each other, so as to ensure the position accuracy of the carbon nanotube cold cathode and the grid in the electron gun component, thereby improving the pass rate of the field emission electron grid of the cold cathode X-ray tube. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0038] FIG1 is a schematic structural diagram of a positioning plate in one embodiment of the present invention;

[0039] FIG2 is a schematic structural diagram of a positioning plate in another embodiment of the present invention;

[0040] FIG3 is a schematic structural diagram of a positioning plate in another embodiment of the present invention;

[0041] FIG4 is a schematic structural diagram of a positioning plate in another embodiment of the present invention;

[0042] FIG5 is a schematic structural diagram of a screen printing plate in one embodiment of the present invention;

[0043] FIG6 is a schematic structural diagram of a cold cathode substrate in one embodiment of the present invention;

[0044] FIG7 is a schematic structural diagram of a positioning plate in another embodiment of the present invention;

[0045] FIG8 is a schematic structural diagram of a positioning plate in another embodiment of the present invention;

[0046] FIG9 is a schematic diagram of screen printing using a screen printing plate in one embodiment of the present invention;

[0047] FIG10 is a schematic diagram of another embodiment of the present invention when using a screen printing plate for printing;

[0048] FIG11 is a schematic structural diagram of an electron gun assembly of an X-ray tube in one embodiment of the present invention;

[0049] FIG12 is a schematic diagram of the connection structure of a cathode fixing base and a carbon nanotube cold cathode in one embodiment of the present invention;

[0050] FIG13 is a schematic structural diagram of a cathode fixing seat in one embodiment of the present invention;

[0051] FIG14 is a schematic diagram of the structure of a carbon nanotube cold cathode in one embodiment of the present invention;

[0052] FIG15 is a schematic diagram of the connection structure of a carbon nanotube cold cathode and a gate fixing base in one embodiment of the present invention;

[0053] FIG16 is a schematic diagram of the connection structure of a carbon nanotube cold cathode, an insulating spacer, and a gate in one embodiment of the present invention;

[0054] FIG17 is a schematic diagram of the connection structure of the insulating gasket and the gate fixing seat in one embodiment of the present invention;

[0055] FIG18 is a schematic diagram of the connection structure of the gate and the gate fixing seat in one embodiment of the present invention;

[0056] FIG19 is a schematic diagram of the connection structure of a gate fixing base in one embodiment of the present invention;

[0057] FIG20 is a schematic diagram of the connection structure of the gate in one embodiment of the present invention;

[0058] FIG21 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] FIG22 shows the pattern of the carbon nanotube array finally printed according to the methods in Example 1 and Comparative Example 1;

[0060] FIG23 is a physical picture of a carbon nanotube cold cathode prepared according to the method of Example 1;

[0061] 24-25 illustrate 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] FIG26 is a schematic diagram of a substrate field emission test and a stability test of an X-ray tube electron gun assembly in Example 2;

[0063] FIG27 is a field emission IV curve of the substrate of the X-ray tube electron gun assembly in Example 2;

[0064] FIG28 is a stability test curve of the X-ray tube electron gun assembly in Example 2 under 2 h continuous operation. Best Mode for Carrying Out the Invention

[0065] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings of the embodiments of the present invention. It should be understood that the described embodiments are only a portion of the embodiments of the present invention, not all of them. Generally, the components of the embodiments of the present invention described and illustrated in the drawings herein may be arranged and designed in a variety of different configurations.

[0066] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0067] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0068] In the description of the present invention, it should be understood that the directions or positions indicated by “upper” and the like are based on the directions or positions shown in the accompanying drawings, or are the directions or positions in which the product of the invention is usually placed when in use, or are the directions or positions commonly understood by those skilled in the art. These directions or positions are only for the convenience of describing the present invention and simplifying the description, and are not intended to indicate or imply that the device or component referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0069] Those skilled in the art will understand that, unless expressly stated otherwise, the singular forms "a", "an", "said" and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of this application refers to the presence of the 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 refer to an element as being "connected" to another element, it can be directly connected to the other element, or there may be intermediate elements. In addition, the "connection" used here may include wireless connections. The term "and / or" used here includes all or any unit and all combinations of one or more associated listed items. In addition, the terms "first", "second", etc. are only used to distinguish descriptions and are not to be understood as indicating or implying relative importance.

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

[0071] S1. Provide a positioning plate, wherein the positioning plate is provided with at least one positioning hole;

[0072] S2. Providing a cold cathode substrate, wherein the cold cathode substrate is adapted to the positioning hole;

[0073] S3, embedding the cold cathode substrate into the positioning hole;

[0074] S4. Laminating the screen printing plate on the positioning plate, and printing the carbon nanotube slurry on the surface of the cold cathode substrate by screen printing to prepare a carbon nanotube cold cathode.

[0075] It should be noted that, in the preparation method of the carbon nanotube cold cathode of the present invention, as shown in reference figures 1 to 10, at least one positioning hole 11 is provided on the positioning plate 1. Specifically, the number of positioning holes 11 can be 1, 2, 3, 4 (as shown in figures 3 to 4) ... n. The number of positioning holes 11 is determined according to the carbon nanotube cold cathode to be prepared. By providing a plurality of positioning holes 11, a plurality of carbon nanotube cold cathodes can be prepared at one time; the positioning hole 11 is adapted to the cold cathode substrate 2, and the size of the positioning hole 11 is substantially the same as the size of the cold cathode substrate 2. The cold cathode substrate 2 is embedded in the positioning hole 11, and then the screen printing screen 3 is attached to the positioning plate. The screen printing screen 3 is provided with mesh holes 31 corresponding to the array of the cold cathode substrate 2, and the screen printing method is used to print the mesh holes 31 on the surface of the cold cathode substrate. The invention discloses a method for preparing a carbon nanotube cold cathode by surface printing carbon nanotube slurry; the area of ​​the positioning plate of the invention is larger than the area of ​​the cold cathode substrate; during screen printing, it is only necessary to position the screen printing screen and the positioning plate so that the screen printing screen and the positioning plate are fitted together, and the positioning method is performed using a positioning plate with a larger area. The positioning method has the advantages of accurate and reliable positioning, simple operation, low requirements on the shape of the cold cathode substrate, strong applicability, and relying on the positioning plate for positioning, which not only improves the accuracy of the carbon nanotube cold cathode array pattern, but also improves the array pattern quality, increases the reuse rate of the screen printing screen, and can meet the needs of single or multiple preparations of different cold cathode substrates; the carbon nanotube cold cathode is prepared by the method of the invention, and the printing quality is significantly higher than that of direct printing using the cold cathode substrate, and the alignment accuracy is high, with an error within 5 μm. Through physical assembly, the carbon nanotube cold cathode array pattern and the grid mesh are aligned, and the actual grid pass rate can reach more than 90%, and long-term stable operation can obtain 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 plate 3 and the positioning plate 1 .

[0077] In some embodiments, the present invention does not limit the shape of the positioning plate 1. For example, the cross-sectional shape of the positioning plate 1 may be rectangular (as shown in FIG1 ), square, circular, elliptical (as shown in FIG2 ), or other irregular shapes; the cross-sectional shape of the positioning hole 11 may 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 25 mm×25 mm, that is, the side length of the square is 25 mm. The size of the square can also be 20 mm×20 mm.

[0079] In some embodiments, the cross section of the cold cathode substrate 2 is circular, and the diameter of the circle is 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 manufacturing the positioning plate 1, its thickness is equal to the thickness of the cold cathode substrate 2, with an error within ±0.01 mm. Laser cutting or other high-precision processing methods are used to cut a positioning hole 11 in its center that is consistent with the cold cathode substrate 2. The processing accuracy is within ±0.01 mm, and 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 0.5-2 mm, and preferably, the thickness is 1 mm.

[0082] In some embodiments, as shown in FIG6 , protrusions 21 are provided on both sides of the cold cathode substrate 2 , and grooves 12 are provided at the positioning holes 11 corresponding to the protrusions 21 . The protrusions 21 match the grooves 21 and are embedded in the grooves 12 .

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

[0084] In some embodiments, in order to facilitate the fitting of the screen printing screen 3 on the positioning plate 1, a positioning reference line can be set on the positioning plate 1, and the positioning reference line is adapted to the outline of the positioning plate 1, that is, the outline of the positioning plate 1 is the positioning reference line of the positioning plate 1; at the same time, a positioning reference line is also provided on the screen printing screen 3, and the positioning reference line of the screen printing screen is aligned with the positioning reference line of the positioning plate by visual inspection or a magnifying glass (that is, aligned with the outline of the positioning plate), thereby realizing the positioning and fitting of the screen printing screen and the positioning plate, and then performing subsequent printing of the carbon nanotube slurry.

[0085] In some embodiments, a positioning groove adapted to the positioning plate 1 is provided on the screen printing mesh 3, and the positioning plate 1 can be clamped in the positioning groove. By clamping the positioning plate 1 in the positioning groove, the positioning plate 1 and the screen printing mesh 3 can be positioned and fitted.

[0086] In some embodiments, as shown in FIG7 , a first positioning portion 13 is provided on the positioning plate 1 , and a first positioning groove is provided on the screen printing screen 3 corresponding to the first positioning portion 13 . The first positioning groove is adapted to the first positioning portion 13 , and the first positioning portion 13 is clamped in the first positioning groove.

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

[0088] In some embodiments, as shown in Figure 8, a second positioning portion 14 is provided on the positioning plate 1 at the periphery of the positioning hole 11, and a second positioning groove is provided on the screen printing screen 3 corresponding to the second positioning portion 14. The second positioning groove is adapted to the second positioning portion 14, and the second positioning portion 14 is clamped in the second positioning groove.

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

[0090] The present invention utilizes a positioning plate for positioning, which can overcome the problem that the cold cathode substrate is small and it is difficult to position marks on the small substrate. At the same time, the small substrate leads to a small force area of ​​the scraper during the screen printing process, resulting in uneven force. The use of a positioning plate for positioning and alignment improves the accuracy of the positioning of the cold cathode array relative to the entire cold cathode substrate, and at the same time increases the force area of ​​the screen printing scraper, thereby improving the printing quality and the accuracy 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 the mixture 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, a carbon nanotube slurry is printed on a surface of a cold cathode substrate using a screen printing method to prepare a carbon nanotube cold cathode, specifically comprising:

[0098] Printing carbon nanotube paste on the surface of the cold cathode substrate by screen printing;

[0099] The cold cathode substrate is then heated to 200-300°C at a rate of 4-6°C / min, kept warm for 2-4 hours, then heated to 750-850°C at a rate of 4-6°C / min, kept warm for 1-3 hours, and then cooled to obtain a carbon nanotube cold cathode.

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

[0101] In some embodiments, carbon nanotube slurry is printed on the surface of a cold cathode substrate by screen printing, and then annealed to obtain a carbon nanotube cold cathode. The surface of the cold cathode substrate is then treated with 3M tape, and the tape is adhered to the substrate. The carbon nanotubes that are not in firm contact with the substrate are removed with the tape.

[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, as shown in FIG5 , a plurality of meshes 31 are arranged in an array on the screen printing screen 3 , and the mesh size is 350-450 meshes.

[0104] The present invention innovatively uses a positioning plate to achieve accurate positioning. Compared with traditional limit blocks and CCD camera alignment, it has low cost, simple operation and strong applicability. Compared with direct positioning using the cold cathode substrate outline pattern, the positioning plate increases the marking reference line, making the alignment mark more obvious. Due to the increase in the size of the positioning plate, during the carbon nanotube cold cathode screen printing process, it is more convenient to align than making a positioning mark on the cold cathode substrate. At the same time, directly using the cold cathode substrate outline as a positioning mark, the positioning mark is easily contaminated by slurry after several uses and is difficult to clean, resulting in blurred positioning mark reference lines and increasing positioning difficulty. The present invention uses a positioning plate for positioning, which increases the size of the positioning reference line and absorbs the errors in the cold cathode small substrate processing and positioning outline marking, thereby increasing positioning reliability. On the one hand, it solves the problem of unreliable and inaccurate direct positioning of the cold cathode substrate. At the same time, the positioning plate increases the force-bearing area of ​​the scraper during printing, thereby improving printing quality. At the same time, it improves the accuracy of the carbon nanotube cold cathode array position relative to the substrate, achieving micron-level accuracy. For cold cathode X-ray tubes of different sizes and shapes, when cold cathode substrates of different structures are required, secondary positioning only requires replacing the positioning plate and reprocessing the positioning plate and positioning holes according to the size and shape of the cold cathode substrate. Secondary positioning does not require processing a new silk screen, which improves the versatility of silk 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, comprising 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 comprises:

[0107] The cathode fixing base 6 is provided with a cathode mounting groove 61, and the carbon nanotube cold cathode 5 is clamped in the cathode mounting groove 61;

[0108] The gate fixing seat 7 is provided with a gate mounting groove 71, and the gate 4 is clamped in the gate mounting groove 71;

[0109] An insulating spacer 8, one side of which is attached to the carbon nanotube cold cathode 5 and the other side of which is attached to the gate 4;

[0110] The gate holes 41 on the gate 4 correspond to the carbon nanotubes 51 on the carbon nanotube cold cathode 5;

[0111] A through hole 81 is formed on the insulating spacer 8 in a region corresponding to the gate hole to allow electrons to pass through.

[0112] In the X-ray tube electron gun assembly of the present invention, carbon nanotubes 51 are arranged in an array on the carbon nanotube cold cathode 5, and grid holes 41 are arranged in an array on the grid 4. The grid holes 41 correspond to the carbon nanotubes 51 one by one. Specifically, the diameter of the carbon nanotubes 51 is slightly smaller than the diameter of the grid holes 41 to ensure the pass rate of field emission electrons; the carbon nanotube cold cathode 5 is installed on the cathode fixing seat 6, specifically, the carbon nanotube cold cathode 5 is clamped in the cathode mounting groove 61; the grid 4 is installed on the grid fixing seat 7, specifically, the grid 4 is clamped in the 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, and the two side surfaces of the insulating gasket 8 are respectively in contact with the carbon nanotube cold cathode 5 and the grid 4, and a through hole 81 is opened on the insulating gasket 8 corresponding to the grid hole area to allow field emission electrons to pass through.

[0113] In some embodiments, first lugs 52 are provided on both sides of the carbon nanotube cold cathode 5, and first clamping grooves 62 are provided at the cathode mounting groove 61 corresponding to the first lugs 52, and the first lugs 52 are clamped in the first clamping grooves 62;

[0114] Second lugs 42 are provided on both sides of the grid 4 . Second locking grooves 72 are formed in the grid mounting groove 71 corresponding to the second lugs 42 . The second lugs 42 are locked in the second locking grooves 72 .

[0115] In the above embodiment, first lugs 52 are provided on both sides of the carbon nanotube cold cathode 5, and first clamping grooves 62 are correspondingly provided on the cathode mounting groove 61. The first lugs 52 are clamped in the first clamping grooves 62, and the first lugs 52 play a positioning role, so that the carbon nanotube cold cathode 5 is easily installed in the cathode mounting groove 61; second lugs 42 are provided on both sides of the grid 4, and second clamping grooves 72 are correspondingly provided on the grid mounting groove 71. The second lugs 42 are clamped in the second clamping grooves 72, and the second lugs 42 play a positioning role, so that the grid 4 is easily installed in the grid mounting groove 71; at the same time, due to the provision of the first lugs 52 and the second lugs 42, after the grid 4 is installed in the cathode mounting groove 61 and the grid mounting groove 71, the carbon nanotubes arrayed on the carbon nanotube cold cathode 5 and the grid holes 41 arrayed on the grid 4 exactly correspond to each other, so as to ensure the position accuracy of the carbon nanotube cold cathode 5 and the grid 4 in the electron gun component, thereby improving the pass rate of the field emission electron grid of the cold cathode X-ray tube.

[0116] It can be understood that the carbon nanotube cold cathode 5 with the first protrusions 52 on both sides is prepared by the above method. Specifically, by setting the first protrusions (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, and finally a carbon nanotube cold cathode 5 with the first protrusions 52 on both sides is obtained.

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

[0118] A screw connection piece 92 passes through the cathode fixing base 6 and the insulating sleeve 91 in sequence and is screwed to the grid fixing base 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 on the inner side of the cathode insulating ring 9, and the screw member 92 passes through the cathode fixing base 6 and the insulating sleeve 91 in sequence and is screwed to the grid fixing base 7;

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

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

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

[0123] The following further illustrates the present invention's method for preparing a carbon nanotube cold cathode and an X-ray tube electron gun assembly using specific examples. This section further illustrates the present invention with reference to specific examples, but should not be construed as limiting the present invention. Unless otherwise specified, the techniques employed in the examples are conventional techniques well known to those skilled in the art. Unless otherwise specified, the methods and equipment employed in the present invention are conventional in the art. Modes for Carrying Out the Invention

[0124] Example 1

[0125] The present invention provides a method for preparing a carbon nanotube cold cathode, comprising the following steps:

[0126] S1. Provide a positioning plate with a positioning hole. The positioning plate is a rectangular parallelepiped with a thickness (i.e., height) of 1 mm, a length of 25 mm, and a width of 25 mm.

[0127] S2. Providing a cold cathode substrate, which is adapted to the positioning hole; the cross-section of the cold cathode substrate is circular, the diameter of the circle is 10 mm, and protrusions are provided on both sides of the cold cathode substrate. The cold cathode substrate is made of stainless steel;

[0128] S3, embedding the cold cathode substrate into the positioning hole;

[0129] S4. The outline of the positioning plate is used as the positioning reference line of the positioning plate. The screen printing stencil is also provided with a positioning reference line corresponding to the outline of the positioning plate. The positioning reference line on the screen printing stencil is aligned with the outline of the positioning plate, and the positioning plate is attached to the screen printing stencil. A carbon nanotube slurry is printed on the surface of the cold cathode substrate using a screen printing method to prepare a carbon nanotube cold cathode.

[0130] The carbon nanotube cold cathode is prepared by printing a carbon nanotube slurry on the surface of a cold cathode substrate using a screen printing method, specifically comprising:

[0131] Printing carbon nanotube paste on the surface of the cold cathode substrate by screen printing;

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

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

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

[0135] Comparative Example 1

[0136] The preparation method of the carbon nanotube cold cathode provided in this comparative example is the same as that in Example 1, except that no positioning plate is used for positioning, and the carbon nanotube slurry is directly printed on the surface of the cold cathode substrate by screen printing to prepare the carbon nanotube cold cathode; the specific method of printing the carbon nanotube slurry on the surface of the cold cathode substrate by screen printing to prepare the carbon nanotube cold cathode is the same as that in Example 1.

[0137] As shown in FIG22 , the patterns of the carbon nanotube arrays finally printed according to the methods in Example 1 and Comparative Example 1 are respectively shown; FIG22 (a) is the pattern of the carbon nanotube array obtained according to the method in Example 1, and FIG22 (b) is the pattern of the carbon nanotube array obtained according to the method in Comparative Example 1.

[0138] As can be seen from FIG. 22 , by using the positioning plate for positioning in Example 1, the obtained carbon nanotube array has higher pattern quality and higher precision.

[0139] FIG23 is a physical picture of the carbon nanotube cold cathode prepared according to the method in Example 1.

[0140] Example 2

[0141] An embodiment of the present application provides an X-ray tube electron gun assembly, comprising the carbon nanotube cold cathode and gate prepared in Example 1, the structure of which is shown in Figures 11 to 21. The second lugs on both sides of the gate are clamped in the second clamping groove, so that the gate is installed in the gate mounting groove of the gate fixing base; the first lugs on both sides of the carbon nanotube cold cathode (because 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 clamped in the first clamping groove, so that the gate is installed in the cathode mounting groove of the cathode fixing base, so that the carbon nanotubes arranged in an array on the carbon nanotube cold cathode and the gate holes arranged in an array on the gate are exactly corresponding to each other.

[0142] As shown in FIG. 24 and FIG. 25 , the carbon nanotubes arrayed on the carbon nanotube cold cathode and the gate holes arrayed on the gate in Example 2 are aligned.

[0143] FIG27 is a field emission IV curve of the base of the X-ray tube electron gun assembly in Example 2.

[0144] FIG28 is a stability test of the X-ray tube electron gun assembly in Example 2 under 2 h continuous operation.

[0145] Specifically, the X-ray tube electron gun assembly in Example 2 was subjected to a field emission test under the following test conditions: the test was carried out 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; the field emission test was carried out under high vacuum conditions (at 5.0×10 -5 Pa), using a LabVIEW program with a Keithley 248 power supply to measure continuous drive mode. During field emission testing, the gate is connected to a high-voltage power supply, forming a cathode-gate diode structure (the gate serves as the diode's anode). The DC voltage range is 100 to 1500V. The computer automatically records the relationship between the emission current and the applied voltage, thus generating the field emission IV curve. The stability test under 2 hours of continuous operation involves holding the gate high-voltage power supply at a fixed voltage for two hours and recording the current stability.

[0146] The specific test schematic diagram is shown in Figure 26. In Figure 26, Cathode (CNT) is the carbon nanotube cold cathode, Gate is the gate, 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.

[0147] Figures 27 and 28 show that the prepared electron gun component can generate an anode current of 5 mA at 1300 V. Figure 28 demonstrates good field emission current stability over a 2-hour period, with a long-term gate electron pass rate of 80%. (In Figure 28, when the anode current is increased to V1 > V2, the vertical axis represents 1 mA. Electrons, attracted by the anode voltage, pass through the gate aperture and 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 in the scope of protection of the present invention.

Claims

1. A method for preparing a carbon nanotube cold cathode, characterized in that: The following steps are involved: Providing a positioning plate, wherein at least one positioning hole is provided on the positioning plate; Providing a cold cathode substrate, wherein the cold cathode substrate is adapted to the positioning hole; Embedding the cold cathode substrate in the positioning hole; The screen printing screen is attached to the positioning plate, and the carbon nanotube slurry is printed on the surface of the cold cathode substrate by screen printing to prepare a carbon nanotube cold cathode.

2. The method for preparing a carbon nanotube cold cathode according to 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 according to claim 1, characterized in that: The cold cathode substrate is provided with protrusions on both sides, the positioning holes are provided with grooves corresponding to the protrusions, the protrusions are matched with the grooves, and the protrusions are embedded in the grooves.

4. The method for preparing a carbon nanotube cold cathode according to claim 1, characterized in that: The positioning plate is provided with a first positioning portion, and the screen printing plate is provided with a first positioning groove corresponding to the first positioning portion, the first positioning groove is adapted to the first positioning portion, and the first positioning portion is clamped in the first positioning groove.

5. The method for preparing a carbon nanotube cold cathode according to claim 1, characterized in that: A second positioning portion is provided on the positioning plate at the periphery of the positioning hole, and a second positioning groove is provided on the screen printing plate corresponding to the second positioning portion. The second positioning groove is matched with the second positioning portion, and the second positioning portion is clamped in the second positioning groove.

6. The method for preparing a carbon nanotube cold cathode according to any one of claims 1 to 5, characterized in that: The carbon nanotube slurry comprises carbon nanotubes, terpineol, ethyl cellulose, titanium carbide powder and titanium powder; Among them, the mass ratio of the carbon nanotubes, pineol, ethyl cellulose, titanium carbide powder and titanium powder is (0.5~2):(15~25):(0.5~1.5):(1~5):(0.5~2).

7. The method for preparing a carbon nanotube cold cathode according to any one of claims 1 to 5, characterized in that: The carbon nanotube slurry is printed on the surface of the cold cathode substrate by screen printing to prepare the carbon nanotube cold cathode, which specifically includes: Printing carbon nanotube slurry on the surface of cold cathode substrate by screen printing method; The cold cathode substrate is then heated to 200-300°C at 4-6°C / min, kept at this temperature for 2-4 hours, and then heated to 750-850°C at 4-6°C / min, kept at this temperature for 1-3 hours, and then cooled to obtain a carbon nanotube cold cathode; 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 size of the screen printing screen is 350-450 meshes.

8. An X-ray tube electron gun assembly, characterized in that: It comprises a grid and a carbon nanotube cold cathode, wherein the carbon nanotube cold cathode is a carbon nanotube cold cathode prepared by the method according to any one of claims 1 to 7.

9. The X-ray tube electron gun assembly according to claim 8, characterized in that: Also includes: A cathode fixing seat, on which a cathode mounting groove is provided, and the carbon nanotube cold cathode is clamped in the cathode mounting groove; A grid fixing seat, on which a grid installation groove is provided, and the grid is clamped in the grid installation groove; An insulating gasket, one side of which is attached to the carbon nanotube cold cathode and the other side of which is attached to the grid; The gate holes on the gate correspond to the carbon nanotubes on the carbon nanotube cold cathode; The insulating gasket is provided with through holes corresponding to the gate hole area to allow electrons to pass through.

10. The X-ray tube electron gun assembly according to claim 9, characterized in that: The carbon nanotube cold cathode is provided with first lugs on both sides, the cathode mounting slot is provided with first clamping slots corresponding to the first lugs, and the first lugs are clamped in the first clamping slots; The grid is provided with second lugs on both sides, the grid installation slot is provided with second clamping grooves corresponding to the second lugs, and the second lugs are clamped in the second clamping grooves; The cathode fixing seat is provided with an annular cathode insulating ring on the outer periphery of the cathode mounting groove, and the cathode fixing seat is provided with an insulating sleeve between the cathode insulating ring and the cathode mounting groove; A screw connection piece passes through the cathode fixing seat and the insulating sleeve in sequence and is screwed to the grid fixing seat.

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