CN103911678B - A kind of coaxial nozzle for electrofluid spray printing - Google Patents

Abstract

The invention discloses a coaxial nozzle for electrofluid jet printing, which comprises an outer nozzle and an inner nozzle. The bottom of the outer nozzle is provided with a shaft hole, the shaft hole is sleeved with a connecting seat, and the connecting seat is provided with an axial stepped hole. The inner nozzle base is sleeved in the step hole, and the inner cylinder on the side of the outer nozzle close to the nozzle is also sleeved with a centering bracket. One end of the inner spray needle is fixed on the inner nozzle base, and the other end passes through the positioning through hole of the centering bracket fixed, the outer wall of the connecting seat is also sleeved with a piezoelectric ceramic driver, and the piezoelectric ceramic driver is fixedly connected with the outer spray barrel. In the coaxial nozzle for electrofluid jet printing provided by the present invention, the relative heights of the inner and outer nozzles can be precisely adjusted by the piezoelectric ceramic driving device, so as to realize the precise control of the relative flow rates of different solutions in the inner and outer layers, and the control of each layer of coaxial spinning. More precise control of the thickness of the "shell" structure, and improve the coaxial alignment accuracy of the inner and outer nozzles through the setting of the centering bracket.

Description

A coaxial nozzle for electrofluid jet printing

technical field

The invention relates to a coaxial nozzle device, in particular to a coaxial nozzle used for preparing multi-layer nanofibers and multi-layer composite droplets by electrofluid jet printing.

Background technique

Electrofluidic jet printing is an important method for preparing multilayer nanofibers and multilayer composite droplets. The electrofluid jet printing method adopts the coaxial nozzle device of the sleeve type needle, sprays two or more different polymer solutions through the coaxial nozzle, and obtains a uniform, long-sized multilayer with a "shell-core" structure. coaxial nanofibers, or to obtain multilayer composite droplets with a "shell-core" structure. Multilayer composite droplets and/or "hollow powder" structured fibers have great potential in the fields of microfluidics, optoelectronics, and energy storage, and a large number of devices are yet to be developed.

Coaxial nanofibers prepared by current jet printing include nanowires, nanowires, nanorods, nanotubes, nanoribbons and nanocables. Due to their large specific surface area, large surface energy and activity, they have small size effects, surface or interface effects. , quantum size effect, macroscopic quantum tunneling effect, etc., and then show specificity in chemical and physical (thermal, optical, electromagnetic, etc.) properties, and are widely used in filtration, sensing, catalysis, tissue engineering, protective clothing, advanced optoelectronic components , MEMS inductive components and drug delivery and other technical fields. Specifically, in lithium-ion batteries, electrodes with coaxial fiber structures can not only improve the energy conversion rate, but also improve the stability of cycle use; coaxial fibers can also be used to prepare electrodes for solar cells and light-emitting elements (LEDs). In addition, in the field of electrochemistry, coaxial fibers can be fabricated into fiber transistors after certain post-processing, which greatly reduces the production cost and difficulty while ensuring its electrical properties. In addition, the structure of high specific area allows coaxial fibers with certain performance to form supercapacitors, which have great energy density and power density, and materials with high catalytic activity can be used in the field of photocatalysis. At the same time, the film assembled by a large number of fibers can also achieve the filtering effect through high porosity, and even complete the environmental remediation.

The multi-layer composite droplets with a "shell-core" structure prepared by electrofluid jet printing are mainly used in the field of microencapsulation, especially in drug sustained release packaging, that is, the outer layer of the microsphere is covered with a protective material with a certain effect. Drugs, drugs diffuse into the body at a certain rate through the nano-sized gaps in the permeation or coating layer, which greatly weakens the phenomenon of excessive initial drug release speed and can artificially control the release time, and can more effectively play the role of drugs. Various complex structures and electronic devices can be prepared in one step by designing various special nozzles. The electrofluid printing method can encapsulate functional components in the "hollow powder" structure, which greatly saves space, or directly make electronic devices with a "shell-core" structure, and control the dissolution of the structure through the thickness of the "shell" time, providing an efficient fabrication method for the fabrication of transient electronics.

However, the coaxial nozzles used in the electrofluid jet printing method of the prior art also have obvious defects:

First, most of the nozzles are of non-replaceable structure, and the size of the nozzle nozzle is fixed. The flow rate and flow of the solution cannot be adjusted through the nozzle. It meets the needs of preparing various complex and changeable multi-layer composite fibers and composite droplets, and the device has poor versatility.

The 2nd, even if some nozzles in the prior art adopt replaceable nozzles, the replaceable nozzles are all sleeved on the periphery of the nozzles. Because the size of the nozzles is very small, generally in the order of microns, the diameter of the nozzles sleeved inside is smaller. The small size makes the processing of the nozzle difficult and the processing precision low, which seriously affects the structural precision of the prepared multi-layer composite fibers and droplets.

The third is that the relative height of the inner and outer nozzles of the coaxial nozzle is fixed and cannot be adjusted. Therefore, the relative flow of different solutions in each layer cannot be controlled more precisely by adjusting the relative height of the inner and outer nozzles to compensate for the control accuracy of the precision flow pump. Insufficient defects, so that the precise control of the thickness of the "shell" structure of each layer of multi-layer composite fibers and droplets cannot be achieved through more precise adjustment and control of relative flow, so it is impossible to meet the requirements of preparing multi-layer nanofibers with various complex structures. and the need for composite droplets.

Invention patent "An Electrohydrodynamic Coaxial Printing Head and Its Application", authorized announcement number: CN102275386B, authorized announcement date: 2013.05.22, discloses an electrohydrodynamic coaxial printing head, including a probe placement platform , nozzle, support seat, metal probe and lip cover, the nozzle is fixed on the probe placement platform, the support seat is installed on the upper end of the nozzle, the lip cover is set on the nozzle at the lower end of the nozzle, the metal probe The needle end of the upper part of the needle is set in the threaded hole in the center of the support seat, the needle body is placed in the inner cavity of the nozzle, the axis of the needle body is coaxial with the central axis of the nozzle, and the needle tip of the lower part of the metal probe passes through the through hole in the lip sleeve and extends out of the nozzle. The coaxial spray head has the advantages of improving the control accuracy of ink supply, and can form a series of spray heads by replacing the lip sleeve.

However, the coaxial nozzle disclosed in the above-mentioned invention patent uses a metal probe instead of a needle. The metal probe is only used to change the electric field distribution and improve spinning stability. Therefore, the coaxial nozzle cannot Realizing coaxial spinning, it is impossible to prepare fibers with "shell-core" structure or "hollow powder" structure or composite droplets and multi-layer fiber structures. On the other hand, although the lip cover is also a replaceable structure, its purpose is only to facilitate the replacement of metal probes, but it cannot adjust the flow of the solution, realize the control and control of the "shell" thickness of the multi-layer composite fiber structure or composite droplets. Adjustment function.

Contents of the invention

The purpose of the present invention is to overcome the relative heights of the inner and outer nozzles in the coaxial nozzles of the electrofluid jet printing in the prior art, the non-replaceable nozzle structure cannot realize the adjustment of the solution flow rate, and the replaceable nozzle structure is difficult to process. For defects and deficiencies such as low precision, a new type of coaxial nozzle for electrofluid jet printing is provided. The relative height of the inner and outer nozzles can be precisely adjusted through the piezoelectric ceramic drive device to achieve precise control of the relative flow of different solutions in the inner and outer layers. And through the setting of the centering bracket structure, the coaxial centering accuracy of the inner and outer nozzles is improved, and the fixing effect of the inner spray needle is strengthened.

The technical scheme that the present invention adopts for realizing above-mentioned technical purpose is:

A coaxial nozzle for electrofluid jet printing, comprising an outer nozzle and an inner nozzle, the outer nozzle includes an outer spray barrel and an outer spray head sleeved on the nozzle end of the outer spray barrel, and the end of the outer spray barrel is far away from the nozzle A shaft hole with a diameter greater than that of the inner cylinder of the outer spray cylinder is provided, and a hollow cylindrical connection seat is sleeved in the shaft hole, and the connection seat is transitionally fitted with the outer spray cylinder, and the middle part of the connection seat is provided with a shaft The diameter of the stepped hole on the outside is greater than that of the inside. The inner nozzle includes an inner nozzle base and an inner spray needle. The inner nozzle base is sleeved on the large diameter end of the stepped hole of the connecting seat and connected to the The step hole of the seat is transitionally fitted, and the side of the inner cylinder of the outer spray tube close to the nozzle is also sleeved with a centering bracket. The centering bracket is a ring structure, and a positioning through hole is provided in the center. One end of the needle is fixed on the base of the inner nozzle, and the other end is inserted into the outer spray barrel and fixed through the positioning through hole of the centering bracket. The outer wall of the connecting seat is also sleeved with a piezoelectric ceramic driver, and the piezoelectric ceramic driver It is fixedly connected with the outer spray barrel.

A coaxial nozzle for electrofluid jet printing, one end of the outer spray head is provided with an external thread, and the nozzle end of the external spray barrel is provided with an internal thread, and the external thread of the external spray head is connected with the inner thread of the outer spray barrel. When the threads are screwed together, when the outer spray head is screwed into the outer spray barrel, the centering bracket is in contact with the surface of the outer spray head, and the middle part of the outer spray head is provided with a tapered through hole, and the tapered through hole of the outer spray head One side of the outer spray barrel has a larger diameter than the other side.

A coaxial nozzle for electrofluid jet printing, the outer wall of the outer spray cylinder away from the nozzle is also fixed with a ring-shaped fixed shoulder, and the fixed shoulder of the outer spray cylinder is fixedly connected with the nozzle fixed platform .

A coaxial nozzle for electrofluidic printing, the inner needle comprising a set of replaceable needles having different diameters.

A coaxial nozzle for electrofluid jet printing, the outer nozzle includes a group of replaceable nozzles with different taper diameters and taper angles.

A coaxial nozzle for electrofluid jet printing, the inner nozzle base is made of metal or non-conductive material.

A coaxial nozzle for electrofluid jet printing, the outer spray cylinder and the connecting seat are made of non-conductive material, and the outer spray head is made of metal or non-conductive material.

A coaxial nozzle for electrofluid jet printing, the outer wall of the outer nozzle is also provided with an annular limiting shoulder.

A coaxial nozzle for electrofluid jet printing, the outer spray cylinder is a combination of a cylinder and a cone, and the one near the nozzle end is a cone.

The utility model relates to a coaxial nozzle for electrofluid jet printing, and an outer nozzle liquid inlet is arranged on the outer wall of the outer spray cylinder.

Compared with the electrofluid jet printing coaxial nozzles of the prior art, the present invention has the following significant advantages:

1. There is a micro-displacement structure between the inner and outer nozzles, and the piezoelectric ceramic driver is used to change the relative height of the inner nozzles, so as to realize the precise control of the relative flow of different solutions in the inner and outer layers, and to make up for the defect of insufficient control accuracy of the precision flow pump. The more precise control of the thickness of the outer "shell" structure during the shaft spinning process meets the structural needs of various complex nanofibers and composite droplets.

2. A replaceable outer spray head is set on the top of the outer nozzle, and the outer spray head is sleeved inside the spray barrel of the outer nozzle, so that the size of the spray barrel of the outer nozzle can be processed larger, thereby reducing the processing difficulty of the outer nozzle and improving the accuracy. It also facilitates the installation and positioning of the inner nozzle in the inner cylinder of the outer nozzle, and is beneficial to improving the coaxial precision of the inner and outer nozzles.

3. Increase the centering support structure installed in the inner cylinder of the outer nozzle, so that both ends of the inner spray needle can be fixed, and the coaxial alignment accuracy of the inner nozzle relative to the outer nozzle can be improved. The size of the middle bracket is also increased accordingly, thereby reducing the processing difficulty of the centering bracket and further improving the coaxial alignment accuracy of the inner and outer nozzles.

4. The coaxial nozzle has replaceable outer nozzles and inner nozzles of a series of sizes. Through the combination of outer nozzles and inner nozzles with different inner diameters, coaxial nozzles with outer nozzles and inner nozzles with different fluid channel sizes are obtained to realize The supply amount of the solution, the diameter of micro-nano fibers, and the thickness of the coaxial fiber "shell" structure are regulated, and it is suitable for solutions with different wettability and rheology.

5. There is a micro-displacement structure between the inner and outer nozzles, and the inner nozzle can protrude from the outer nozzle. Its surface adsorption can promote the formation of the Taylor cone at the outer nozzle, effectively reducing the critical voltage value of the applied voltage required by the process.

6. The material of the outer nozzle and the inner nozzle of the outer nozzle can be metal or non-conductive material. Through different combinations, three power-on modes can be realized: inner nozzle power supply alone, outer nozzle power supply alone, and inner nozzle power supply at the same time. The electrical method can change the spinning parameters, and then play a role in controlling the spinning process.

Description of drawings

FIG. 1 is a schematic structural view of a coaxial nozzle for electrofluid jet printing according to the present invention.

FIG. 2 is a schematic diagram of adjusting the relative heights of the inner and outer nozzles of the coaxial nozzle for electrofluid jet printing according to the present invention.

3 is a schematic diagram of a group of outer nozzles with different taper hole sizes of the coaxial nozzle for electrofluid jet printing of the present invention.

Fig. 4 is a working schematic diagram of the coaxial nozzle for electrofluid jet printing of the present invention.

Fig. 5 is a schematic diagram of coaxial nanofibers prepared by using the coaxial nozzle for electrofluid jet printing of the present invention.

FIG. 6 is a schematic diagram of composite droplets prepared by using the coaxial nozzle for electrofluid jet printing of the present invention.

In the figure: outer nozzle 1, outer spray barrel 11, outer nozzle 12, outer nozzle fixed shoulder 13, inner nozzle 2, inner nozzle base 21, inner spray needle 22, connecting seat 3, centering bracket 4, piezoelectric ceramic driver 5. Outer nozzle liquid inlet 6, nozzle fixing platform 7.

detailed description

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.

Referring to FIG. 1 , the coaxial nozzle for electrofluid jet printing provided by the present invention includes an outer nozzle 1 and an inner nozzle 2 . Wherein, the outer nozzle 1 includes an outer spray barrel 11 and an outer spray head 12 sleeved on the nozzle end of the outer spray barrel 11 , and the outer spray head 12 communicates with the outer spray barrel 11 . The end of the outer spray tube 11 away from the nozzle is provided with a shaft hole with a diameter larger than the diameter of the inner tube of the outer spray tube 11, and a hollow cylindrical connecting seat 3 is sleeved in the shaft hole, and the connecting seat 3 and the outer spray tube 11 are transitionally fitted. The middle part of the connecting seat 3 is provided with an axial stepped hole, and the diameter of the stepped hole located on the outer side is larger than that on the inner side. The inner nozzle 2 includes an inner nozzle base 21 and an inner spray needle 22 , the inner nozzle base 21 is sleeved on the large-diameter end of the stepped hole of the connecting seat 3 and transition-fitted with the stepped hole of the connecting seat 3 . The side of the inner cylinder of the outer spray cylinder 11 close to the spout is also sleeved with a centering bracket 4, which is an annular structure with a positioning through hole in the center. One end of the inner spray needle 22 is fixed on the inner nozzle base 21 , and the other end is inserted into the outer spray barrel 11 and fixed through the positioning through hole of the centering bracket 4 . A piezoelectric ceramic driver 5 is also sleeved on the outer wall of the connection base 3 , and the piezoelectric ceramic driver 5 is fixedly connected with the outer spray tube 11 . The piezoelectric ceramic driver is an existing product (cylindrical package), and the fixed connection form with the outer spray barrel 11 depends on the structural form of the piezoelectric ceramic driver itself.

The coaxial nozzle for electrofluid jet printing provided by the present invention, when in use, the piezoelectric ceramic driver 5 is controlled by the computer to move up and down, driving the connected connecting seat 3, and further driving the inner nozzle 2 to move up and down, thereby accurately adjusting the inner and outer nozzles relative height. The inner spray needle 22 is about 20 mm long, and the inner diameter is in the order of micron, and the adjustable range of the inner spray needle is 0-100 micron. Referring to Fig. 3, the schematic diagram of the relative height adjustment of the inner and outer nozzles of the coaxial nozzle of the electrofluid jet printing of the present invention, (a) the inner nozzle in the figure is flush with the spout of the outer nozzle, (b) the spout of the inner nozzle in the figure Shrink in the outer nozzle inner cylinder, the spout of the inner nozzle in (c) figure stretches out a certain distance from the outer nozzle.

In the coaxial nozzle for electrofluid jet printing provided by the present invention, one end of the outer nozzle 12 is provided with an external thread, and the nozzle end of the outer spray cylinder 11 is provided with an internal thread, and the external thread of the external nozzle 12 and the internal thread of the external spray cylinder 11 When the outer nozzle 12 is screwed into the outer nozzle 11, the centering bracket 4 is in contact with the outer nozzle 12, and the middle of the outer nozzle 12 is provided with a tapered through hole, which is close to the side of the outer nozzle diameter is larger than the other side. The outer spray head 12 is threadedly connected with the outer spray barrel 11, which is convenient for installing and replacing the outer spray head 12. The outer spray head 12 is socketed in the barrel of the outer spray barrel 11, so that the size of the outer spray barrel 11 is increased, which not only reduces the processing difficulty of the outer spray barrel 11, but also facilitates the installation and fixing of the inner nozzle 2 inside the outer spray barrel 11. At the same time, the size of the centering bracket 4 is increased, the processing difficulty of the centering bracket 4 is reduced, and the fixing of the inner spray needle 22 on the centering bracket 4 is also facilitated, thereby improving the centering accuracy of the inner and outer nozzles. When the outer spray head 12 is screwed into the outer spray barrel 11, the outer spray head 12 also plays the role of supporting the centering bracket 4.

In the coaxial nozzle for electrofluid jet printing provided by the present invention, the inner nozzle 22 includes a group of replaceable nozzles with different diameters, and the outer nozzle 12 includes a group of replaceable nozzles with cone holes with different taper diameters and tapers. Fig. 3 is the schematic diagram of the outer nozzle with different taper hole sizes of the electrofluid jet printing coaxial nozzle of the present invention, wherein the taper of the taper hole of the outer nozzle is 10 to 30 degrees, and the inner diameter of the small diameter end of the taper hole is several Ten microns to hundreds of microns, and can be serialized, such as 20 microns, 50 microns, 100 microns, 200 microns, etc., to meet the need for precise adjustment of the inner diameter of the nozzle. The inner spray needle is about 20mm long, and the inner diameter is in the order of microns, and the inner diameter can range from tens of microns to hundreds of microns. Through the combination of outer nozzles and inner nozzles with different inner diameters, coaxial nozzles with outer nozzles and inner nozzles with different fluid channel sizes are obtained to realize the supply volume of the solution, the diameter of micro-nano fibers, and the thickness of the coaxial fiber "shell" structure Adjustable and suitable for solutions with different wettability and rheology.

In the coaxial nozzle used for electrofluid jet printing provided by the present invention, the outer nozzle 12 can also be provided with an annular limiting shoulder on the outer wall. to the limiting effect. In order to facilitate the fitting of the limiting shoulder to the outer spray barrel 11 , preferably the diameter of the limiting shoulder is set to be the same as the nozzle diameter of the outer spray barrel 11 . The limiting shoulder divides the outer spray head 12 into two parts, and the diameter of the part of the outer spray head 12 outside the outer spray tube 11 may be smaller than the part inside the outer spray tube 11 .

For the coaxial nozzle used for electrofluid jet printing provided by the present invention, in order to facilitate the fixing of the coaxial nozzle and the nozzle fixing platform 7, it is preferable to fix an annular fixed shoulder on the outer wall of the outer spray cylinder 11 away from the nozzle. , the fixed shoulder of the outer spray tube 12 is fixedly connected with the nozzle fixed platform 7, and the connection method is preferably bolt connection. The shape of the outer spray barrel 11 is preferably set as a combination of a cylinder and a cone, and the one near the nozzle end is a cone. An outer nozzle liquid inlet 6 for supplying solution is also arranged on the outer wall of the outer spray cylinder 11 .

In the coaxial nozzle for electrofluid jet printing provided by the present invention, the outer spray barrel and the connecting seat are made of non-conductive material, the outer nozzle 12 is made of metal or non-conductive material, and the inner nozzle base 21 is made of metal or non-conductive material. Through the selection and matching of the material of the outer nozzle and the inner nozzle base, three power supply modes can be realized: inner nozzle power supply alone, outer nozzle power supply alone, and inner and outer nozzle power supply at the same time. The spinning parameters can be changed through different power supply methods, and then the spinning can be controlled. The role of silk process.

The coaxial nozzle for electrofluid jet printing provided by the present invention, when in use, firstly connect the fixed shoulder of the outer nozzle 1 with the nozzle fixing platform 7 with bolts, and then fix the nozzle fixing platform 7 on the workbench with a clamp. Put on the carrier substrate, and fix it on the X‐Y working platform through a certain connection method, and then ground the substrate. Then screw in the outer spray head 12, and make the centering bracket 4 contact with the surface of the outer spray head 12. Then connect the connecting seat 3 to the opening of the outer spray barrel 11, then set the inner nozzle base 21 in the step hole of the connecting seat 3 and fix it, insert the inner spray needle 22 into the outer spray barrel 11, and pass through the centering bracket 4 and fixed to ensure that the central axes of the inner and outer nozzles are coaxial. Before the preparation, it is also necessary to carry out surface treatment on the outer nozzle and the inner nozzle to enhance the wettability of the solution, so that the solution is not easy to naturally drip and block the nozzle. During the preparation, by adjusting the concentration, viscosity, surface tension and conductivity of the inner and outer solutions, the relative distance between the inner nozzle and the outer nozzle, the liquid supply rate of the inner and outer solutions, the applied electric field, the distance between electrodes and the movement of the X-Y working platform The process parameters such as the speed, ambient temperature and humidity and other environmental parameters can control the structural size of the coaxial micro-nano fiber or composite droplet, especially the adjustment of the thickness of the "shell" structure.

Claims (10)

1. A coaxial nozzle for electrofluid jet printing, comprising an outer nozzle (1) and an inner nozzle (2), characterized in that: the outer nozzle (1) includes an outer spray cylinder (11) and is sleeved on The outer nozzle (12) of the spout end of the outer spray tube (11), the end of the outer spray tube (11) away from the spout is provided with a shaft hole with a diameter greater than the diameter of the inner tube of the outer spray tube (11), and the shaft hole A hollow cylindrical connection seat (3) is sleeved, and the connection seat (3) is transitionally fitted with the outer spray tube (11). The middle part of the connection seat (3) is provided with an axial step hole, and the step The diameter of the hole located on the outer side is larger than the inner side, the inner nozzle (2) includes an inner nozzle base (21) and an inner spray needle (22), and the inner nozzle base (21) is sleeved on the stepped hole of the connecting seat (3) The large-diameter end of the connecting seat (3) transition fits with the step hole of the connecting seat (3), and the side of the inner cylinder of the outer spray tube (11) near the spout is also sleeved with a centering bracket (4), and the centering bracket ( 4) It is a ring structure with a positioning through hole in the center, one end of the inner spray needle (22) is fixed on the inner nozzle base (21), the other end is inserted into the outer spray barrel (11) and passes through the centering The positioning through hole of the bracket (4) is fixed, and the outer wall of the connecting seat (3) is also sleeved with a piezoelectric ceramic driver (5), and the piezoelectric ceramic driver (5) is fixedly connected with the outer spray tube (11). 2. A coaxial nozzle for electrofluid jet printing according to claim 1, characterized in that: one end of the outer spray head (12) is provided with an external thread, and the nozzle of the outer spray barrel (11) The end is provided with an internal thread, and the external thread of the external spray head (12) is screwed together with the internal thread of the external spray cylinder (11). When the external spray head (12) is screwed into the external spray cylinder (11), the The centering bracket (4) is in surface contact with the outer spray head (12), and the middle part of the outer spray head (12) is provided with a tapered through hole, and the tapered through hole of the outer spray head (12) is close to the outer spray barrel (11) One side has a larger diameter than the other. 3. A coaxial nozzle for electrofluid jet printing according to claim 1 or 2, characterized in that: the outer wall of the outer spray cylinder (11) on the side away from the nozzle is also fixed with an annular fixed Shoulder, the fixed shoulder of the outer spray barrel (12) is fixedly connected with the nozzle fixed platform (7). 4. A coaxial nozzle for electrofluid jet printing according to claim 1, characterized in that the inner needle (22) comprises a group of replaceable needles with different diameters. 5 . A coaxial nozzle for electrofluid jet printing according to claim 2 , characterized in that: the outer nozzle ( 12 ) includes a group of replaceable nozzles with tapered holes having different taper diameters and taper degrees. 6 . 6. A coaxial nozzle for electrofluid jet printing according to claim 1, characterized in that the inner nozzle base (21) is made of metal or non-conductive material. 7. A coaxial nozzle for electrofluid jet printing according to claim 2, characterized in that: the outer spray barrel (11) and the connecting seat (3) are non-conductive materials, and the outer spray head ( 12) It is metal or non-conductive material. 8. A coaxial nozzle for electrofluid jet printing according to claim 2, characterized in that: the outer wall of the outer nozzle (12) is also provided with an annular limiting shoulder. 9. A coaxial nozzle for electrofluid jet printing according to claim 1, characterized in that: the outer spray barrel (11) is a combination of a cylinder and a cone, and the one near the nozzle end is a cone. 10. A coaxial nozzle for electrofluid jet printing according to claim 1 or 2, characterized in that: the outer wall of the outer spray cylinder (11) is provided with an outer nozzle liquid inlet (6) .