阅读说明：本技术 一种金属化聚酰亚胺纤维及其制备方法 (Metallized polyimide fiber and preparation method thereof ) 是由 王彬 刘大亮 于 2020-12-24 设计创作，主要内容包括：本发明公开了一种金属化聚酰亚胺纤维及其制备方法。该金属化聚酰亚胺纤维包括基材纤维和包覆于基材纤维表面的复合金属层,所述基材纤维为纤度为200D-2000D、断裂强度≥3.5Gpa的聚酰亚胺纤维；所述复合金属层包括内层金属层、中间层金属层和外层金属层,所述内层金属层的金属选自银、镍、铜或锡中的一种；所述中间层金属层的金属选自银、镍、铜或锡中的一种；所述外层金属层的金属选自银、镍、铜或锡中的一种,且内层金属层、中间层金属层和外层金属层的金属互不相同。该金属化聚酰亚胺纤维性能优异,具有强度高、导电性能优、耐高温、柔韧性好、金属层结合牢固等特性。(The invention discloses a metallized polyimide fiber and a preparation method thereof. The metallized polyimide fiber comprises a base material fiber and a composite metal layer coated on the surface of the base material fiber, wherein the base material fiber is a polyimide fiber with the fineness of 200D-2000D and the breaking strength of more than or equal to 3.5 Gpa; the composite metal layer comprises an inner metal layer, a middle metal layer and an outer metal layer, wherein the metal of the inner metal layer is selected from one of silver, nickel, copper or tin; the metal of the intermediate metal layer is selected from one of silver, nickel, copper or tin; the metal of the outer metal layer is selected from one of silver, nickel, copper or tin, and the metals of the inner metal layer, the middle metal layer and the outer metal layer are different from each other. The metallized polyimide fiber has excellent performance, and has the characteristics of high strength, excellent conductivity, high temperature resistance, good flexibility, firm combination of metal layers and the like.)

1. The metallized polyimide fiber is characterized by comprising a base material fiber and a composite metal layer coated on the surface of the base material fiber, wherein the base material fiber is a polyimide fiber with the fineness of 200D-2000D and the breaking strength of more than or equal to 3.5 Gpa; the composite metal layer comprises an inner metal layer, a middle metal layer and an outer metal layer, wherein the metal of the inner metal layer is selected from one of silver, nickel, copper or tin; the metal of the intermediate metal layer is selected from one of silver, nickel, copper or tin; the metal of the outer metal layer is selected from one of silver, nickel, copper or tin, and the metals of the inner metal layer, the middle metal layer and the outer metal layer are different from each other.

2. The metallized polyimide fiber of claim 1, wherein the thickness of said inner metal layer is 1 to 3 μm.

3. The metallized polyimide fiber of claim 1, wherein the thickness of the middle layer metal layer is 2 to 6 μm.

4. The metallized polyimide fiber of claim 1, wherein the thickness of said outer metal layer is 1 to 3 μm.

5. A process for the preparation of metallized polyimide fibers according to any one of claims 1 to 4, comprising the steps of:

(1) oil and glue removal: carrying out oil and glue removing treatment on the base material fiber, washing the base material fiber to be neutral by deionized water after the treatment is finished, and then drying the base material fiber;

(2) surface modification: performing low-temperature plasma treatment on the polyimide fiber treated in the step (1), wherein the treatment power is 500-2500W, the treatment time is 2-20min, and the treated polyimide fiber is washed to be neutral by deionized water and then dried;

(3) surface conditioning: carrying out surface conditioning treatment on the polyimide fibers treated in the step (2) by adopting an enamine cationic surfactant solution, washing the polyimide fibers to be neutral by using deionized water after the treatment is finished, and then drying the polyimide fibers;

(4) metallization: carrying out metallization treatment on the surface of the polyimide fiber treated in the step (3), washing the surface of the polyimide fiber with deionized water to be neutral after the treatment is finished, and then drying the surface of the polyimide fiber;

(5) post-protection: and (4) performing post-protection treatment on the polyimide fiber surface treated in the step (4), washing the treated polyimide fiber surface to be neutral by using deionized water, and then drying the polyimide fiber surface to obtain a metallized polyimide fiber finished product.

6. The method for preparing metallized polyimide fiber according to claim 5, wherein in step (1), the method for degreasing and degumming is selected from one or more of organic solvent method, high-temperature chemical method, high-temperature alkaline solution method and electrochemical method, and the time for degreasing and degumming is 1-10 min.

7. The method for preparing metallized polyimide fibers according to claim 5, wherein the surface conditioning treatment in step (3) is carried out by a specific process comprising:

activating the polyimide fiber treated in the step (2) by adopting an enamine cationic surfactant solution, wherein the concentration of the enamine cationic surfactant in the enamine cationic surfactant solution is 40-60mL/L, the treatment temperature is 50-60 ℃, the treatment time is 2-7min, and mechanical stirring, air stirring, ultrasonic oscillation or mechanical vibration is assisted in the activation process to ensure that each monofilament in the polyimide fiber is treated in place.

8. The method for producing metallized polyimide fibers according to claim 7, wherein the metallization treatment in step (4) specifically comprises the steps of:

(4.1) prepreg: performing pre-dipping treatment on the polyimide fibers treated in the step (3), wherein the treatment time is 1-10min, and mechanical stirring, air stirring, ultrasonic oscillation or mechanical vibration is assisted in the pre-dipping process to ensure that each monofilament in the polyimide fibers is treated in place;

(4.2) activation: activating the polyimide fibers treated in the step (4.1) for 1-10min, wherein mechanical stirring, air stirring, ultrasonic oscillation or mechanical vibration is assisted in the activation process to ensure that each monofilament in the polyimide fibers is treated in place;

(4.3) dispergation: and (3) performing degumming treatment on the polyimide fiber treated in the step (4.2), wherein the treatment time is 1-10min, and mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the degumming process to ensure that each monofilament in the polyimide fiber is treated in place.

(4.4) electroless plating: putting the polyimide fibers treated in the step (4.4) into a chemical plating solution, wherein the chemical plating solution is chemical silver plating, chemical nickel plating, chemical copper plating or chemical tin plating, and mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the chemical plating process to keep the polyimide fibers in a good dispersion state in the solution and ensure that each monofilament in the fiber bundle is uniformly and continuously deposited with metal to obtain an inner metal layer, wherein the chemical plating temperature is 20-100 ℃, and the reaction time is 1-60 min;

(4.5) repeating the steps (4.1-4.4) to respectively obtain an intermediate metal layer and an outer metal layer.

Technical Field

The invention relates to the technical field of high-performance fibers, in particular to a metallized polyimide fiber and a preparation method thereof.

Background

With the rapid development of modern high and new technologies such as high-frequency communication, microelectronics, artificial intelligence, aerospace and the like, the requirements on the comprehensive performance of materials are higher and higher, and the development is continuously towards high performance, multiple functions, light weight and the like. The polyimide fiber has the advantages of low density, high strength, corrosion resistance, radiation resistance, low expansion, good thermal stability and the like, and is an ideal matrix material for preparing the conductive functional fiber material. The conductive functional fiber material has the characteristics of light weight, softness, bending resistance and the like, not only has the functions of eliminating static electricity, electromagnetic shielding, detecting and transmitting electric signals and the like, but also is easy to process, shows excellent comprehensive performance, and has wide application prospect in the fields of aerospace, national defense and military industry, weapon equipment, high-frequency communication, microelectronics, artificial intelligence, medical treatment, protection and the like.

CN101446037B discloses a preparation method of conductive polyimide fiber, and the technical route disclosed by the invention is as follows: pretreatment and washing → chemical coarsening → sensitization → activation → dispergation → chemical copper plating → deionized water washing → sensitization → activation → dispergation → chemical nickel plating → water washing → drying → finished product, the process flow is very complicated, the time consumption is very long, and the method is not suitable for industrial production. CN106637934A discloses a polyimide fiber surface metallization treatment method, which comprises the following process flows: acetone ultrasonic cleaning → chemical coarsening → activation → reduction → chemical copper plating, which belongs to the traditional chemical plating process, in particular to 600D-2000D crude fiber bundles, each fiber filament can not be uniformly covered with a metal coating, and the plating leakage phenomenon exists on the crude fiber bundles. CN109989263A discloses a preparation method of a high-performance silver-plated conductive fiber, which comprises the following process flows: the phenomenon of plating leakage can also occur when the crude fiber bundle is plated with a metal layer.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide the metallized polyimide fiber which has the characteristics of excellent performance, high strength, excellent conductivity, high temperature resistance, good flexibility, firm combination of metal layers and the like.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

the metallized polyimide fiber comprises a base material fiber and a composite metal layer coated on the surface of the base material fiber, wherein the base material fiber is a polyimide fiber with the fineness of 200D-2000D and the breaking strength of more than or equal to 3.5 Gpa; the composite metal layer comprises an inner metal layer, a middle metal layer and an outer metal layer, wherein the metal of the inner metal layer is selected from one of silver, nickel, copper or tin; the metal of the intermediate metal layer is selected from one of silver, nickel, copper or tin; the metal of the outer metal layer is selected from one of silver, nickel, copper or tin, and the metals of the inner metal layer, the middle metal layer and the outer metal layer are different from each other.

The metallized polyimide fiber prepared by using the polyimide fiber with the fineness of 200D-2000D and the breaking strength of more than or equal to 3.5Gpa as the base fiber and coating the composite metal layer on the surface of the fiber has the advantages of excellent performance, high strength (the breaking strength of more than or equal to 3.0GPa), excellent conductivity (the surface resistance of the length of less than or equal to 2.0 omega/m), high temperature resistance, good flexibility, firm bonding of the metal layer and the like.

Preferably, the metal of the inner metal layer is copper, the metal of the middle metal layer is nickel, and the metal of the outer metal layer is silver, so that the conductivity of the fiber can be improved.

Preferably, the thickness of the inner metal layer is 1-3 μm, which is beneficial to improving the conductivity of the fiber.

Preferably, the thickness of the middle layer metal layer is 2-6 μm, which is beneficial to improving the conductivity of the fiber.

Preferably, the thickness of the outer metal layer is 1-3 μm, which is beneficial to improving the conductivity of the fiber.

The invention also provides a preparation method of the metallized polyimide fiber, which comprises the following steps:

(1) oil and glue removal: carrying out oil and glue removing treatment on the base material fiber, washing the base material fiber to be neutral by deionized water after the treatment is finished, and then drying the base material fiber;

(2) surface modification: performing low-temperature plasma treatment on the polyimide fiber treated in the step (1), wherein the treatment power is 500-2500W, the treatment time is 2-20min, and the treated polyimide fiber is washed to be neutral by deionized water and then dried;

(3) surface conditioning: carrying out surface conditioning treatment on the polyimide fibers treated in the step (2) by adopting an enamine cationic surfactant solution, washing the polyimide fibers to be neutral by using deionized water after the treatment is finished, and then drying the polyimide fibers;

(4) metallization: carrying out metallization treatment on the surface of the polyimide fiber treated in the step (3), washing the surface of the polyimide fiber with deionized water to be neutral after the treatment is finished, and then drying the surface of the polyimide fiber;

(5) post-protection: and (4) performing post-protection treatment on the polyimide fiber surface treated in the step (4), washing the treated polyimide fiber surface to be neutral by using deionized water, and then drying the polyimide fiber surface to obtain a metallized polyimide fiber finished product.

In the preparation process flow, firstly, the surface of the base material fiber is subjected to oil and glue removing treatment to obtain a clean surface; then, modifying the fiber through low-temperature plasma treatment to obtain a surface with certain defects and roughness so as to facilitate the subsequent adhesion of conductive metal substances; then, surface adjustment is carried out on the modified fiber by adopting an enamine cationic surfactant, so that the surface of the fiber is positively charged, the hydrophilicity of the surface of the fiber is favorably improved, and the deposition effect of a conductive metal substance on the surface of a material is improved; and finally, carrying out metallization processing on the modified polyimide fiber to obtain the metallized polyimide fiber. Compared with the traditional chemical plating process, the preparation process disclosed by the invention can ensure that each fiber wire of the 600D-2000D coarse fiber bundle is uniformly covered with the metal coating, so that the occurrence of the phenomenon of plating leakage is reduced, and the comprehensive performance of the fiber is further improved.

The preparation method has the advantages of simple preparation process, short time consumption, low cost, energy conservation, safety, environmental protection and easy realization of batch production.

Tests show that compared with surface modification methods such as a chemical method, an electrochemical method, a coupling agent method, ultraviolet irradiation and the like, the method disclosed by the invention has the advantages that the low-temperature plasma treatment is used for modifying the fibers, so that the roughness of the surfaces of the fibers is favorably improved, and the subsequent adhesion of conductive metal substances is favorably realized.

Compared with other surfactants, the invention adopts enamine cationic surfactant solution for surface adjustment treatment, which is more beneficial to subsequently improving the deposition effect of conductive metal substances on the fiber surface.

Preferably, in the step (1), the method for oil and glue removing treatment is one or more selected from an organic solvent method, a high-temperature chemical method, a high-temperature alkaline solution method and an electrochemical method, and the time for oil and glue removing treatment is 1-10 min.

Preferably, the specific process of the surface conditioning treatment in step (3) is: activating the polyimide fiber treated in the step (2) by adopting an enamine cationic surfactant solution, wherein the concentration of the enamine cationic surfactant in the enamine cationic surfactant solution is 40-60mL/L, the treatment temperature is 50-60 ℃, the treatment time is 2-7min, and mechanical stirring, air stirring, ultrasonic oscillation or mechanical vibration is assisted in the activation process to ensure that each monofilament in the polyimide fiber is treated in place.

The invention is beneficial to subsequently improving the deposition effect of the conductive substance on the surface of the fiber by increasing and optimizing the process steps of surface adjustment treatment and related process parameters.

Preferably, the metallization treatment in step (4) specifically includes the following steps:

(4.1) prepreg: performing pre-dipping treatment on the polyimide fibers treated in the step (3), wherein the treatment time is 1-10min, and mechanical stirring, air stirring, ultrasonic oscillation or mechanical vibration is assisted in the pre-dipping process to ensure that each monofilament in the polyimide fibers is treated in place;

(4.2) activation: activating the polyimide fibers treated in the step (4.1) for 1-10min, wherein mechanical stirring, air stirring, ultrasonic oscillation or mechanical vibration is assisted in the activation process to ensure that each monofilament in the polyimide fibers is treated in place;

(4.3) dispergation: and (3) performing degumming treatment on the polyimide fiber treated in the step (4.2), wherein the treatment time is 1-10min, and mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the degumming process to ensure that each monofilament in the polyimide fiber is treated in place.

(4.4) electroless plating: putting the polyimide fibers treated in the step (4.4) into a chemical plating solution, wherein the chemical plating solution is chemical silver plating, chemical nickel plating, chemical copper plating or chemical tin plating, and mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the chemical plating process to keep the polyimide fibers in a good dispersion state in the solution and ensure that each monofilament in the fiber bundle is uniformly and continuously deposited with metal to obtain an inner metal layer, wherein the chemical plating temperature is 20-100 ℃, and the reaction time is 1-60 min;

(4.5) repeating the steps (4.1-4.4) to respectively obtain an intermediate metal layer and an outer metal layer.

Compared with the prior art, the invention has the beneficial effects that:

1. the metallized polyimide fiber prepared by the invention has excellent performance, particularly, the 600D-2000D crude fiber bundle can enable each fiber yarn to be uniformly covered with a metal coating, and the phenomenon of plating leakage in the actual production process of the crude fiber bundle is avoided.

2. The metallized polyimide fiber provided by the invention has the advantages of simple preparation process, short time consumption, low cost, energy conservation, safety, environmental friendliness, no need of strong oxidant and easiness in realization of batch production.

Drawings

Fig. 1 shows a copper-plated polyimide fiber (a) obtained by the method of example 1 and a copper-plated polyimide fiber (B) obtained by the method of comparative example 4, and it should be noted that the original drawing of the drawing is a color drawing, and the fiber bundle plating layer of fig. 1(a) is uniform, whereas the fiber bundle of fig. 1(B) has a plating missing phenomenon.

FIG. 2 is a metallographic photograph of a cross-section of the metallized polyimide fibers prepared in example 1, wherein the fibers were uniformly coated with a metal coating;

FIG. 3 is a metallographic photograph of a cross-section of a metallized polyimide fiber prepared in example 2, wherein the fiber was uniformly coated with a metal coating;

FIG. 4 is a metallographic photograph of a cross-section of a metallized polyimide fiber prepared in example 3, wherein the fiber was uniformly coated with a metal coating;

FIG. 5 is a metallographic photograph of a cross-section of the metallized polyimide fibers prepared in example 4, wherein the fibers were uniformly coated with a metal coating.

Detailed Description

To better illustrate the objects, aspects and advantages of the present invention, the present invention will be further described with reference to specific examples. It will be understood by those skilled in the art that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

In the examples, the experimental methods used were all conventional methods unless otherwise specified, and the materials, reagents and the like used were commercially available without otherwise specified.

Example 1

A method of making a metallized polyimide fiber comprising the steps of:

(1) oil and glue removal: selecting polyimide fibers with the fineness of 1000D and the breaking strength of 3.5Gpa as base material fibers, carrying out oil and glue removing treatment on the base material fibers, washing the base material fibers to be neutral by deionized water after the treatment is finished, and then drying the base material fibers;

(2) surface modification: performing low-temperature plasma treatment on the polyimide fiber treated in the step (1), wherein the treatment power is 1000W, the treatment time is 10min, and the polyimide fiber is washed to be neutral by deionized water after the treatment is finished and then dried;

(3) surface conditioning: activating the polyimide fibers treated in the step (2) by adopting an enamine cationic surfactant solution, wherein the concentration of the enamine cationic surfactant in the enamine cationic surfactant solution is 50mL/L, the treatment temperature is 60 ℃, the treatment time is 5min, and mechanical stirring, air stirring, ultrasonic oscillation or mechanical vibration is assisted in the activation process to ensure that each monofilament in the polyimide fibers is treated in place;

(4) metallization:

(4.1) prepreg: performing pre-dipping treatment on the polyimide fibers treated in the step (3), wherein the treatment time is 5min, and mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the pre-dipping process to ensure that each monofilament in the polyimide fibers is treated in place;

(4.2) activation: activating the polyimide fibers treated in the step (4.1) for 5min, wherein mechanical stirring, air stirring, ultrasonic oscillation or mechanical vibration is assisted in the activation process to ensure that each monofilament in the polyimide fibers is treated in place;

(4.3) dispergation: performing degumming treatment on the polyimide fibers treated in the step (4.2), wherein the treatment time is 5min, mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the degumming process to ensure that each monofilament in the polyimide fibers is treated in place, and deionized water is used for washing the polyimide fibers to be neutral after the treatment is finished, and then the polyimide fibers are dried;

(4.4) electroless plating: putting the polyimide fiber treated in the step (4.3) into a chemical plating solution, wherein the chemical plating solution is electroless copper plating, and mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration are assisted in the chemical plating process to keep the polyimide fiber in a good dispersion state in the solution, so as to ensure that each monofilament in a fiber bundle is uniformly and continuously deposited with metal to obtain an inner metal layer with the thickness of 2 microns, wherein the chemical plating temperature is 50 ℃, the reaction time is 10min, and the prepared copper-plated polyimide fiber is uniform and consistent in plating layer on the fiber and free of plating leakage as shown in figure 1 (A);

(4.5) repeating the step (4.1-4.4) to obtain an intermediate metal layer with the thickness of 2 microns, wherein the chemical plating solution is chemical nickel plating, the chemical plating temperature is 80 ℃, and the reaction time is 2 min;

(4.6) repeating the steps (4.1-4.4) to obtain an outer metal layer with the thickness of 1 mu m, wherein the chemical plating solution is chemical silvering, the chemical plating temperature is 80 ℃, the reaction time is 2min, and the outer metal layer is washed to be neutral by deionized water after the treatment is finished and then dried;

(5) post-protection: and (4) performing post-protection treatment on the polyimide fiber surface treated in the step (4), washing the treated polyimide fiber surface to be neutral by using deionized water, and then drying the polyimide fiber surface to obtain a metallized polyimide fiber finished product.

Example 2

A method of making a metallized polyimide fiber comprising the steps of:

(1) oil and glue removal: selecting polyimide fibers with the fineness of 1000D and the breaking strength of 3.5Gpa as base material fibers, carrying out oil and glue removing treatment on the base material fibers, washing the base material fibers to be neutral by deionized water after the treatment is finished, and then drying the base material fibers;

(2) surface modification: performing low-temperature plasma treatment on the polyimide fiber treated in the step (1), wherein the treatment power is 1000W, the treatment time is 10min, and the polyimide fiber is washed to be neutral by deionized water after the treatment is finished and then dried;

(3) surface conditioning: activating the polyimide fibers treated in the step (2) by adopting an enamine cationic surfactant solution, wherein the concentration of the enamine cationic surfactant in the enamine cationic surfactant solution is 50mL/L, the treatment temperature is 60 ℃, the treatment time is 5min, and mechanical stirring, air stirring, ultrasonic oscillation or mechanical vibration is assisted in the activation process to ensure that each monofilament in the polyimide fibers is treated in place; each monofilament in the imine fiber is treated in place, washed to be neutral by deionized water after treatment, and then dried;

(4) metallization:

(4.1) prepreg: performing pre-dipping treatment on the polyimide fibers treated in the step (3), wherein the treatment time is 5min, and mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the pre-dipping process to ensure that each monofilament in the polyimide fibers is treated in place;

(4.2) activation: activating the polyimide fibers treated in the step (4.1) for 5min, wherein mechanical stirring, air stirring, ultrasonic oscillation or mechanical vibration is assisted in the activation process to ensure that each monofilament in the polyimide fibers is treated in place;

(4.3) dispergation: performing degumming treatment on the polyimide fibers treated in the step (4.2), wherein the treatment time is 5min, mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the degumming process to ensure that each monofilament in the polyimide fibers is treated in place, and deionized water is used for washing the polyimide fibers to be neutral after the treatment is finished, and then the polyimide fibers are dried;

(4.1) electroless plating: putting the polyimide fibers treated in the step (4.3) into a chemical plating solution, wherein the chemical plating solution is electroless copper plating, and mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the chemical plating process so that the polyimide fibers are kept in a good dispersion state in the solution, each monofilament in a fiber bundle is ensured to be uniformly and continuously deposited with metal, an inner metal layer with the thickness of 1 mu m is obtained, the chemical plating temperature is 50 ℃, and the reaction time is 3 min;

(4.5) repeating the step (4.1-4.4) to obtain an intermediate metal layer with the thickness of 2 microns, wherein the chemical plating solution is selected from chemical nickel plating, the chemical plating temperature is 60 ℃, and the reaction time is 5 min;

(4.6) repeating the steps (4.1-4.4) to obtain an outer metal layer with the thickness of 1 mu m, wherein the chemical plating solution is selected from chemical silver plating, the chemical plating temperature is 100 ℃, and the reaction time is 1 min; washing the treated product with deionized water to be neutral, and then drying the product;

(5) post-protection: and (4) performing post-protection treatment on the polyimide fiber surface treated in the step (4), washing the treated polyimide fiber surface to be neutral by using deionized water, and then drying the polyimide fiber surface to obtain a metallized polyimide fiber finished product.

Example 3

A method of making a metallized polyimide fiber comprising the steps of:

(1) oil and glue removal: selecting polyimide fibers with the fineness of 1000D and the breaking strength of 3.5Gpa as base material fibers, carrying out oil and glue removing treatment on the base material fibers, washing the base material fibers to be neutral by deionized water after the treatment is finished, and then drying the base material fibers;

(2) surface modification: performing low-temperature plasma treatment on the polyimide fiber treated in the step (1), wherein the treatment power is 1000W, the treatment time is 10min, and the polyimide fiber is washed to be neutral by deionized water after the treatment is finished and then dried;

(3) surface conditioning: activating the polyimide fibers treated in the step (2), wherein the concentration of the enamine cationic surfactant in the enamine cationic surfactant solution is 50mL/L, the treatment temperature is 60 ℃, the treatment time is 5min, and mechanical stirring, air stirring, ultrasonic oscillation or mechanical vibration is assisted in the activation process to ensure that each monofilament in the polyimide fibers is treated in place;

(4) metallization:

(4.1) prepreg: performing pre-dipping treatment on the polyimide fibers treated in the step (3), wherein the treatment time is 5min, and mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the pre-dipping process to ensure that each monofilament in the polyimide fibers is treated in place;

(4.2) activation: activating the polyimide fibers treated in the step (4.1) for 5min, wherein mechanical stirring, air stirring, ultrasonic oscillation or mechanical vibration is assisted in the activation process to ensure that each monofilament in the polyimide fibers is treated in place;

(4.3) dispergation: performing degumming treatment on the polyimide fibers treated in the step (4.2), wherein the treatment time is 5min, mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the degumming process to ensure that each monofilament in the polyimide fibers is treated in place, and deionized water is used for washing the polyimide fibers to be neutral after the treatment is finished, and then the polyimide fibers are dried;

(4.4) electroless plating: putting the polyimide fibers treated in the step (4.3) into a chemical plating solution, wherein the chemical plating solution is electroless copper plating, and mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the chemical plating process so that the polyimide fibers are kept in a good dispersion state in the solution, each monofilament in a fiber bundle is ensured to be uniformly and continuously deposited with metal, an inner metal layer with the thickness of 3 microns is obtained, the chemical plating temperature is 100 ℃, and the reaction time is 5 min;

(4.5) repeating the step (4.1-4.4) to obtain an intermediate metal layer with the thickness of 6 microns, wherein the chemical plating solution is chemical nickel plating, the chemical plating temperature is 70 ℃, and the reaction time is 40 min;

(4.6) repeating the steps (4.1-4.4) to obtain an outer metal layer with the thickness of 3 microns, wherein the chemical plating solution is chemical silvering, the chemical plating temperature is 60 ℃, the reaction time is 15min, and the outer metal layer is washed to be neutral by deionized water after the treatment is finished and then dried;

(5) post-protection: and (4) performing post-protection treatment on the polyimide fiber surface treated in the step (4), washing the treated polyimide fiber surface to be neutral by using deionized water, and then drying the polyimide fiber surface to obtain a metallized polyimide fiber finished product.

Example 4

A method of making a metallized polyimide fiber comprising the steps of:

(1) the oil and glue removing method comprises the following steps of selecting polyimide fibers with the fineness of 1000D and the breaking strength of 3.5Gpa as base material fibers, carrying out oil and glue removing treatment on the base material fibers, washing the base material fibers to be neutral by deionized water after the treatment is finished, and then drying the base material fibers;

(2) surface modification: performing low-temperature plasma treatment on the polyimide fiber treated in the step (1), wherein the treatment power is 1000W, the treatment time is 10min, and the polyimide fiber is washed to be neutral by deionized water after the treatment is finished and then dried;

(3) surface conditioning: activating the polyimide fibers treated in the step (2) by adopting an enamine cationic surfactant solution, wherein the concentration of the enamine cationic surfactant in the enamine cationic surfactant solution is 50mL/L, the treatment temperature is 60 ℃, the treatment time is 5min, and mechanical stirring, air stirring, ultrasonic oscillation or mechanical vibration is assisted in the activation process to ensure that each monofilament in the polyimide fibers is treated in place; (4) metallization:

(4.1) prepreg: performing pre-dipping treatment on the polyimide fibers treated in the step (3), wherein the treatment time is 5min, and mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the pre-dipping process to ensure that each monofilament in the polyimide fibers is treated in place;

(4.2) activation: activating the polyimide fiber treated in the step (4.1), wherein the concentration of the enamine cationic surfactant in the enamine cationic surfactant solution is 50mL/L, the treatment temperature is 60 ℃, the treatment time is 5min, and mechanical stirring, air stirring, ultrasonic oscillation or mechanical vibration is assisted in the activation process to ensure that each monofilament in the polyimide fiber is treated in place;

(4.3) dispergation: performing degumming treatment on the polyimide fibers treated in the step (4.2), wherein the treatment time is 5min, mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the degumming process to ensure that each monofilament in the polyimide fibers is treated in place, and deionized water is used for washing the polyimide fibers to be neutral after the treatment is finished, and then the polyimide fibers are dried;

(4.4) electroless plating: putting the polyimide fibers treated in the step (4.3) into a chemical plating solution, wherein the chemical plating solution is electroless copper plating, and mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the chemical plating process so that the polyimide fibers are kept in a good dispersion state in the solution, each monofilament in a fiber bundle is ensured to be uniformly and continuously deposited with metal, an inner metal layer with the thickness of 1 mu m is obtained, the chemical plating temperature is 50 ℃, and the reaction time is 1 min;

(4.5) repeating the step (4.1-4.4) to obtain an intermediate metal layer with the thickness of 6 microns, wherein the chemical plating solution is chemical nickel plating, the chemical plating temperature is 30 ℃, and the reaction time is 60 min;

(4.6) repeating the steps (4.1-4.4) to obtain an outer metal layer with the thickness of 2 microns, wherein the chemical plating solution is chemical silvering, the chemical plating temperature is 50 ℃, the reaction time is 10min, and the outer metal layer is washed to be neutral by deionized water after the treatment is finished and then dried;

(5) post-protection: and (4) performing post-protection treatment on the polyimide fiber surface treated in the step (4), washing the treated polyimide fiber surface to be neutral by using deionized water, and then drying the polyimide fiber surface to obtain a metallized polyimide fiber finished product.

Example 5

A method of making a metallized polyimide fiber comprising the steps of:

(1) oil and glue removal: selecting polyimide fibers with the fineness of 2000D and the breaking strength of 3.5Gpa as base material fibers, carrying out oil and glue removing treatment on the base material fibers, washing the base material fibers to be neutral by deionized water after the treatment is finished, and then drying the base material fibers;

(2) surface modification: performing low-temperature plasma treatment on the polyimide fiber treated in the step (1), wherein the treatment power is 500W, the treatment time is 20min, and the polyimide fiber is washed to be neutral by deionized water after the treatment is finished and then dried;

(3) surface conditioning: activating the polyimide fibers treated in the step (2) by adopting an enamine cationic surfactant solution, wherein the concentration of the enamine cationic surfactant in the enamine cationic surfactant solution is 40mL/L, the treatment temperature is 50 ℃, the treatment time is 7min, and mechanical stirring, air stirring, ultrasonic oscillation or mechanical vibration is assisted in the activation process to ensure that each monofilament in the polyimide fibers is treated in place; each monofilament in the amine fiber is treated in place, washed to be neutral by deionized water after treatment, and then dried;

(4) metallization:

(4.1) prepreg: performing pre-dipping treatment on the polyimide fibers treated in the step (3), wherein the treatment time is 1min, and mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the pre-dipping process to ensure that each monofilament in the polyimide fibers is treated in place;

(4.2) activation: activating the polyimide fibers treated in the step (4.1) for 7min, wherein mechanical stirring, air stirring, ultrasonic oscillation or mechanical vibration is assisted in the activation process to ensure that each monofilament in the polyimide fibers is treated in place;

(4.3) dispergation: performing degumming treatment on the polyimide fibers treated in the step (4.2), wherein the treatment time is 1-10min, mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the degumming process to ensure that each monofilament in the polyimide fibers is treated in place, and deionized water is used for washing the polyimide fibers to be neutral after the treatment is finished, and then the polyimide fibers are dried;

(4.4) electroless plating: putting the polyimide fibers treated in the step (4.3) into a chemical plating solution, wherein the chemical plating solution is electroless copper plating, and mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the chemical plating process so that the polyimide fibers are kept in a good dispersion state in the solution, each monofilament in a fiber bundle is ensured to be uniformly and continuously deposited with metal, an inner metal layer with the thickness of 3 microns is obtained, the chemical plating temperature is 50 ℃, and the reaction time is 15 min;

(4.5) repeating the step (4.1-4.4) to obtain an intermediate metal layer with the thickness of 4 microns, wherein the chemical plating solution is chemical tinning, the chemical plating temperature is 80 ℃, and the reaction time is 20 min;

(4.6) repeating the steps (4.1-4.4) to obtain an outer metal layer with the thickness of 1 mu m, wherein the chemical plating solution is chemical silvering, the chemical plating temperature is 55 ℃, the reaction time is 2min, and the outer metal layer is washed to be neutral by deionized water after the treatment is finished and then dried;

(5) post-protection: and (4) performing post-protection treatment on the polyimide fiber surface treated in the step (4), washing the treated polyimide fiber surface to be neutral by using deionized water, and then drying the polyimide fiber surface to obtain a metallized polyimide fiber finished product.

Example 6

A method of making a metallized polyimide fiber comprising the steps of:

(1) oil and glue removal: selecting polyimide fibers with the fineness of 600D and the breaking strength of 3.5Gpa as base material fibers, carrying out oil and glue removing treatment on the base material fibers, washing the base material fibers to be neutral by deionized water after the treatment is finished, and then drying the base material fibers;

(2) surface modification: performing low-temperature plasma treatment on the polyimide fiber treated in the step (1), wherein the treatment power is 2500W, the treatment time is 2min, and the polyimide fiber is washed to be neutral by deionized water after the treatment is finished and then dried;

(3) surface conditioning: activating the polyimide fibers treated in the step (2) by adopting an enamine cationic surfactant solution, wherein the concentration of the enamine cationic surfactant in the enamine cationic surfactant solution is 60mL/L, the treatment temperature is 60 ℃, the treatment time is 2min, and mechanical stirring, air stirring, ultrasonic oscillation or mechanical vibration is assisted in the activation process to ensure that each monofilament in the polyimide fibers is treated in place; (4) metallization:

(4.1) prepreg: performing pre-dipping treatment on the polyimide fibers treated in the step (3), wherein the treatment time is 10min, and mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the pre-dipping process to ensure that each monofilament in the polyimide fibers is treated in place;

(4.2) activation: activating the polyimide fibers treated in the step (4.1) for 2min, wherein mechanical stirring, air stirring, ultrasonic oscillation or mechanical vibration is assisted in the activation process to ensure that each monofilament in the polyimide fibers is treated in place;

(4.3) dispergation: performing degumming treatment on the polyimide fibers treated in the step (4.2), wherein the treatment time is 1-10min, mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the degumming process to ensure that each monofilament in the polyimide fibers is treated in place, and deionized water is used for washing the polyimide fibers to be neutral after the treatment is finished, and then the polyimide fibers are dried;

(4.4) electroless plating: putting the polyimide fibers treated in the step (4.3) into a chemical plating solution, wherein the chemical plating solution is electroless copper plating, and mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the chemical plating process so that the polyimide fibers are kept in a good dispersion state in the solution, each monofilament in a fiber bundle is ensured to be uniformly and continuously deposited with metal, an inner metal layer with the thickness of 2 microns is obtained, the chemical plating temperature is 60 ℃, and the reaction time is 8 min;

(4.5) repeating the step (4.1-4.4) to obtain an intermediate metal layer with the thickness of 6 microns, wherein the chemical plating solution is chemical nickel plating, the chemical plating temperature is 85 ℃, and the reaction time is 30 min;

(4.6) repeating the steps (4.1-4.4) to obtain an outer metal layer with the thickness of 2 microns, wherein the chemical plating solution is chemical silvering, the chemical plating temperature is 70 ℃, the reaction time is 5min, and the outer metal layer is washed to be neutral by deionized water after the treatment is finished and then dried;

(5) post-protection: and (4) performing post-protection treatment on the polyimide fiber surface treated in the step (4), washing the treated polyimide fiber surface to be neutral by using deionized water, and then drying the polyimide fiber surface to obtain a metallized polyimide fiber finished product.

Comparative example 1

A method of making a metallized polyimide fiber comprising the steps of:

(1) oil and glue removal: selecting polyimide fibers with the fineness of 1000D and the breaking strength of 3.5Gpa as base material fibers, carrying out oil and glue removing treatment on the base material fibers, washing the base material fibers to be neutral by deionized water after the treatment is finished, and then drying the base material fibers;

(2) surface modification: performing low-temperature plasma treatment on the polyimide fiber treated in the step (1), wherein the treatment power is 1000W, the treatment time is 10min, and the polyimide fiber is washed to be neutral by deionized water after the treatment is finished and then dried;

(3) surface conditioning: activating the polyimide fibers treated in the step (2) by adopting an enamine cationic surfactant solution, wherein the concentration of the enamine cationic surfactant in the enamine cationic surfactant solution is 50mL/L, the treatment temperature is 60 ℃, the treatment time is 5min, and mechanical stirring, air stirring, ultrasonic oscillation or mechanical vibration is assisted in the activation process to ensure that each monofilament in the polyimide fibers is treated in place;

(4) metallization:

(4.1) electroless plating:

(4.1) prepreg: performing pre-dipping treatment on the polyimide fibers treated in the step (3), wherein the treatment time is 5min, and mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the pre-dipping process to ensure that each monofilament in the polyimide fibers is treated in place;

(4.2) activation: activating the polyimide fibers treated in the step (4.1) for 5min, wherein mechanical stirring, air stirring, ultrasonic oscillation or mechanical vibration is assisted in the activation process to ensure that each monofilament in the polyimide fibers is treated in place;

(4.3) dispergation: performing degumming treatment on the polyimide fibers treated in the step (4.2), wherein the treatment time is 5min, mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the degumming process to ensure that each monofilament in the polyimide fibers is treated in place, and deionized water is used for washing the polyimide fibers to be neutral after the treatment is finished, and then the polyimide fibers are dried;

(4.4) putting the polyimide fibers treated in the step (4.3) into a chemical plating solution, wherein the chemical plating solution is chemical silver plating, mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is used as an auxiliary in the chemical plating process to keep the polyimide fibers in a good dispersion state in the solution, so that each monofilament in a fiber bundle is uniformly and continuously deposited with metal to obtain a metal layer with the thickness of 1 mu m, the chemical plating temperature is 80 ℃, the reaction time is 2min, and after the treatment is finished, washing the polyimide fibers to be neutral by using deionized water and then drying the polyimide fibers;

(5) post-protection: and (4) performing post-protection treatment on the polyimide fiber surface treated in the step (4), washing the treated polyimide fiber surface to be neutral by using deionized water, and then drying the polyimide fiber surface to obtain a metallized polyimide fiber finished product.

Comparative example 2

A method of making a metallized polyimide fiber comprising the steps of:

(1) oil and glue removal: selecting polyimide fibers with the fineness of 1000D and the breaking strength of 3.5Gpa as base material fibers, carrying out oil and glue removing treatment on the base material fibers, washing the base material fibers to be neutral by deionized water after the treatment is finished, and then drying the base material fibers;

(2) surface modification: modifying the polyimide fiber treated in the step (1) by adopting a silane coupling agent for 10min, washing the polyimide fiber with deionized water to be neutral after the treatment is finished, and then drying the polyimide fiber;

(3) surface conditioning: activating the polyimide fibers treated in the step (2) by adopting an enamine cationic surfactant solution, wherein the concentration of the enamine cationic surfactant in the enamine cationic surfactant solution is 50mL/L, the treatment temperature is 60 ℃, the treatment time is 5min, and mechanical stirring, air stirring, ultrasonic oscillation or mechanical vibration is assisted in the activation process to ensure that each monofilament in the polyimide fibers is treated in place;

(4) metallization:

(4.1) prepreg: performing pre-dipping treatment on the polyimide fibers treated in the step (3), wherein the treatment time is 5min, and mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the pre-dipping process to ensure that each monofilament in the polyimide fibers is treated in place;

(4.2) activation: activating the polyimide fibers treated in the step (4.1) for 5min, wherein mechanical stirring, air stirring, ultrasonic oscillation or mechanical vibration is assisted in the activation process to ensure that each monofilament in the polyimide fibers is treated in place;

(4.3) dispergation: performing degumming treatment on the polyimide fibers treated in the step (4.2), wherein the treatment time is 5min, mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the degumming process to ensure that each monofilament in the polyimide fibers is treated in place, and deionized water is used for washing the polyimide fibers to be neutral after the treatment is finished, and then the polyimide fibers are dried;

(4.4) electroless plating: putting the polyimide fibers treated in the step (4.3) into a chemical plating solution, wherein the chemical plating solution is electroless copper plating, and mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the chemical plating process so that the polyimide fibers are kept in a good dispersion state in the solution, each monofilament in a fiber bundle is ensured to be uniformly and continuously deposited with metal, an inner metal layer with the thickness of 2 microns is obtained, the chemical plating temperature is 50 ℃, and the reaction time is 10 min;

(4.5) repeating the step (4.1-4.4) to obtain an intermediate metal layer with the thickness of 2 microns, wherein the chemical plating solution is chemical nickel plating, the chemical plating temperature is 80 ℃, and the reaction time is 2 min;

(4.6) repeating the steps (4.1-4.4) to obtain an outer metal layer with the thickness of 1 mu m, wherein the chemical plating solution is chemical silvering, the chemical plating temperature is 80 ℃, the reaction time is 2min, and the outer metal layer is washed to be neutral by deionized water after the treatment is finished and then dried;

(5) post-protection: and (4) performing post-protection treatment on the polyimide fiber surface treated in the step (4), washing the treated polyimide fiber surface to be neutral by using deionized water, and then drying the polyimide fiber surface to obtain a metallized polyimide fiber finished product.

Comparative example 3

A method of making a metallized polyimide fiber comprising the steps of:

(1) oil and glue removal: selecting polyimide fibers with the fineness of 100D and the breaking strength of 2.5Gpa as base material fibers, carrying out oil and glue removing treatment on the base material fibers, washing the base material fibers to be neutral by deionized water after the treatment is finished, and then drying the base material fibers;

(2) surface modification: performing low-temperature plasma treatment on the polyimide fiber treated in the step (1), wherein the treatment power is 1000W, the treatment time is 10min, and the polyimide fiber is washed to be neutral by deionized water after the treatment is finished and then dried;

(3) surface conditioning: activating the polyimide fibers treated in the step (2) by adopting an enamine cationic surfactant solution, wherein the concentration of the enamine cationic surfactant in the enamine cationic surfactant solution is 50mL/L, the treatment temperature is 60 ℃, the treatment time is 5min, and mechanical stirring, air stirring, ultrasonic oscillation or mechanical vibration is assisted in the activation process to ensure that each monofilament in the polyimide fibers is treated in place; (4) metallization:

(4.1) prepreg: performing pre-dipping treatment on the polyimide fibers treated in the step (3), wherein the treatment time is 5min, and mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the pre-dipping process to ensure that each monofilament in the polyimide fibers is treated in place;

(4.2) activation: activating the polyimide fibers treated in the step (4.1) for 5min, wherein mechanical stirring, air stirring, ultrasonic oscillation or mechanical vibration is assisted in the activation process to ensure that each monofilament in the polyimide fibers is treated in place;

(4.3) dispergation: performing degumming treatment on the polyimide fibers treated in the step (4.2), wherein the treatment time is 5min, mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the degumming process to ensure that each monofilament in the polyimide fibers is treated in place, and deionized water is used for washing the polyimide fibers to be neutral after the treatment is finished, and then the polyimide fibers are dried;

(4.4) electroless plating: putting the polyimide fibers treated in the step (4.3) into a chemical plating solution, wherein the chemical plating solution is electroless copper plating, and mechanical stirring, air stirring, ultrasonic vibration or mechanical vibration is assisted in the chemical plating process so that the polyimide fibers are kept in a good dispersion state in the solution, each monofilament in a fiber bundle is ensured to be uniformly and continuously deposited with metal, an inner metal layer with the thickness of 2 microns is obtained, the chemical plating temperature is 50 ℃, and the reaction time is 10 min;

(4.5) repeating the step (4.1-4.4) to obtain an intermediate metal layer with the thickness of 2 microns, wherein the chemical plating solution is chemical nickel plating, the chemical plating temperature is 80 ℃, and the reaction time is 2 min;

(4.6) repeating the steps (4.1-4.4) to obtain an outer metal layer with the thickness of 1 mu m, wherein the chemical plating solution is chemical silvering, the chemical plating temperature is 80 ℃, the reaction time is 2min, and the outer metal layer is washed to be neutral by deionized water after the treatment is finished and then dried;

(5) post-protection: and (4) performing post-protection treatment on the polyimide fiber surface treated in the step (4), washing the treated polyimide fiber surface to be neutral by using deionized water, and then drying the polyimide fiber surface to obtain a metallized polyimide fiber finished product.

Comparative example 4

A method of making a metallized polyimide fiber comprising the steps of:

(1) selecting polyimide fibers with the fineness of 1000D and the breaking strength of 3.5Gpa as base material fibers, and ultrasonically cleaning and drying the polyimide fibers in acetone;

(2) coarsening the polyimide fiber in a mixed solution of potassium permanganate and sodium hydroxide at 80 ℃ for 10min, wherein the concentration of potassium permanganate in the mixed solution of potassium permanganate and sodium hydroxide is 80g/L, and the concentration of sodium hydroxide is 100 g/L;

(3) activating the polyimide fiber in an ionic palladium complex solution with the concentration of palladium ions of 250mg/L for 10min at 50 ℃;

(4) reducing the polyimide fibers in a dimethyl ammonia borane solution with the concentration of 5g/L for 10min at 30 ℃ to reduce ionic palladium adsorbed on the surfaces of the fibers into metal palladium;

(5) and (2) placing the polyimide fiber in a chemical copper solution, and depositing chemical copper on the surface of the polyimide fiber for 20min at 40 ℃ by using a chemical copper plating method to prepare the copper-plated polyimide fiber, wherein the chemical copper solution consists of 60g/L potassium sodium tartrate, 10g/L copper sulfate, 15g/L sodium hydroxide, 15mL/L formaldehyde and 10g/L nickel chloride.

As shown in FIG. 1B, the copper-plated polyimide fiber prepared by the comparative example has a plating leakage phenomenon in a coarse fiber bundle, and each fiber filament cannot be uniformly coated with a metal plating layer.

The metallized polyimide fibers prepared in the above examples and comparative examples were subjected to conductivity and breaking strength tests, and the results are shown in table 1.

TABLE 1

Group of	Length surface resistance (omega/m)	Breaking strength (GPa)
			Example 1	1.92	3.3
Example 2	2.00	3.2
			Example 3	1.58	3.2
Example 4	1.74	3.3
			Example 5	1.78	3.4
Example 6	1.60	3.2
			Comparative example 1	3.94	3.2
Comparative example 2	2.38	3.2
			Comparative example 3	1.93	2.2

From the above results, it is clear that the metallized polyimide fibers obtained in examples 1 to 6 have both higher conductivity and breaking strength as compared with the comparative examples.

Fig. 2 to 5 are metallography photographs of the cross section of the metallized polyimide fiber prepared in example 1, example 2, example 3 and example 4, respectively, and it can be known that each fiber filament can be uniformly coated with a metal coating layer without plating leakage, thereby effectively solving the plating leakage phenomenon existing in the actual production process of 600D to 2000D thick fiber bundles in the conventional chemical plating process.

Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the protection scope of the present invention, and although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.