阅读说明：本技术 一种勃姆石改性电纺膜及其制备方法和应用 (Boehmite modified electrospun membrane and preparation method and application thereof ) 是由 张秀芳 马洪洋 赵炯心 于 2020-12-24 设计创作，主要内容包括：本发明提供了一种勃姆石改性电纺膜及其制备方法和应用,所述勃姆石改性电纺膜为：将含有勃姆石和第一高分子聚合物的纺丝液,通过静电纺丝附着在第二高分子聚合物表面,得到勃姆石改性电纺膜；本发明通过将掺杂勃姆石和高分子聚合物的纺丝液进行静电纺丝,沉积在高分子聚合物的表面,提高了单独使用纤维膜的机械性能、热稳定性和孔隙尺寸稳定性,形成了耐热、耐高温的多孔电纺膜,相比于现有的聚烯烃类多孔膜,具有更好的热稳定性,兼具70％～80％的高孔隙度且孔径可调,轻薄且耐用,具有较高的熔断温度,使原本的多孔材料孔径闭合进而达到保护电池的作用,可以满足对高安全性与高能量密度的电池的需求。(The invention provides a boehmite modified electrospun membrane as well as a preparation method and an application thereof, wherein the boehmite modified electrospun membrane comprises the following components in parts by weight: attaching spinning solution containing boehmite and a first high polymer to the surface of a second high polymer through electrostatic spinning to obtain a boehmite modified electrospun membrane; according to the invention, the spinning solution doped with boehmite and a high molecular polymer is subjected to electrostatic spinning and deposited on the surface of the high molecular polymer, so that the mechanical property, the thermal stability and the pore size stability of a fiber membrane used alone are improved, and a heat-resistant and high-temperature-resistant porous electrospun membrane is formed.)

1. A boehmite-modified electrospun membrane characterized in that said boehmite-modified electrospun membrane is: and (3) attaching the spinning solution containing boehmite and the first high polymer to the surface of the second high polymer through electrostatic spinning to obtain the boehmite modified electrospun membrane.

2. The boehmite-modified electrospun membrane according to claim 1 characterized in that said first high molecular polymer comprises any one or a combination of at least two of polyethersulfone, polysulfone or polyimide;

preferably, the concentration of the first high molecular polymer in the spinning solution is 5-50%; preferably 28%.

3. The boehmite-modified electrospun membrane according to claim 1 or 2, characterized in that the concentration of boehmite in the spinning solution is 1% to 90%; preferably 10% to 50%.

4. The boehmite-modified electrospun membrane according to any one of claims 1-3 characterized in that the spinning solution comprises any one of or a combination of at least two of dimethylacetamide, dimethylformamide, dimethylsulfoxide, acetone or chloroform.

5. The boehmite-modified electrospun membrane according to any one of claims 1-4 characterized in that the second high molecular polymer comprises any one of polyethylene, polyvinyl chloride, polypropylene, polystyrene or ABS plastic or a combination of at least two thereof;

preferably, the second high molecular polymer is polyethylene.

6. The boehmite-modified electrospun membrane according to any one of claims 1-5 characterized in that the second high molecular polymer is treated with potassium dichromate;

preferably, the method of using potassium dichromate treatment is: and immersing the second high molecular polymer into a mixed solution of potassium dichromate, water and sulfuric acid with the mass ratio of 7:12:150, and taking out and drying to obtain the second high molecular polymer.

7. The boehmite-modified electrospun membrane according to any one of claims 1-6, wherein said electrospun membrane obtained after said electrospun membrane has been attached to the surface of a second high molecular polymer further comprises the step of immersing the electrospun membrane in a boehmite suspension and drying it, resulting in said boehmite-modified electrospun membrane;

preferably, the concentration of the boehmite suspension is 0.5% to 10%;

preferably, the immersion time is 2-5 min;

preferably, the drying temperature is 50-80 ℃.

8. The method of preparing a boehmite-modified electrospun membrane according to any one of claims 1-7, characterized in that it comprises the steps of:

(1) dissolving boehmite and a first high molecular polymer in a solvent, heating and stirring to prepare a spinning solution;

(2) dipping a second high molecular polymer by using a mixed solution of potassium dichromate, water and sulfuric acid with a mass ratio of 7:12:150, then drying in vacuum, wrapping on a roller aluminum foil, setting electrostatic spinning parameters, attaching the spinning solution obtained in the step (1) to the surface of the second high molecular polymer through electrostatic spinning, and optionally immersing the obtained electro-spinning membrane into a boehmite suspension for drying to obtain the boehmite modified electro-spinning membrane.

9. The method according to claim 8, wherein the heating temperature in the step (1) is 80 to 95 ℃;

preferably, the stirring time in the step (1) is 1-3 days;

preferably, the parameters of the electrostatic spinning in the step (2) are as follows: the distance from the spinneret plate to the collector is set to be 10.5cm, the applied voltage is 12kV, the ambient temperature is 25-27 ℃, and the relative humidity of the environment is 38% -42%;

preferably, the flow rate of the spinning solution in the step (2) is 20-80 mL/min.

10. Use of the boehmite-modified electrospun membrane according to any one of claims 1-7 in a battery.

Technical Field

The invention belongs to the field of composite materials, and relates to a boehmite modified electrospun membrane as well as a preparation method and application thereof.

Background

With the global energy shortage and the improvement of environmental protection standards, lithium ion batteries are widely applied to the fields of electronic products, vehicles, aerospace and the like. Among them, the battery separator is a key inner layer component affecting the performance of the lithium ion battery, and needs to have excellent electronic insulation, excellent chemical stability, excellent thermal stability and excellent mechanical strength. Generally, as a material of a battery diaphragm, the heat resistance and the wettability to an electrolyte are poor, the porosity is low, and functional modification is needed to improve the energy density and the safety of the battery. Common modification methods include: surface grafting, surface coating, radiation crosslinking, polymer blending, and the like.

CN111129396A discloses a method for modifying a lithium battery diaphragm by temperature-resistant high molecules and a corresponding lithium battery diaphragm. The technical scheme is as follows: mechanically stirring the required temperature-resistant high polymer material and an organic solvent for 1-10 hours at the normal temperature of 120 ℃; and then carrying out ultrasonic treatment for 0.1-2 h to prepare a precursor solution, wherein the concentration of the precursor solution is 5-30%. And cutting the lithium battery diaphragm to be modified, fixing the lithium battery diaphragm on an electrostatic spinning spraying device, carrying out electrostatic spraying or spinning on the precursor solution onto the lithium battery diaphragm, and finally flattening and vacuum drying the lithium battery diaphragm to obtain the modified lithium battery diaphragm. The modified diaphragm greatly improves the electrochemical performance and safety performance of the lithium ion battery. However, the separator provided by this method may have a problem of poor adhesion of the spun yarn to the film.

CN111640902A discloses a preparation process of a lithium battery diaphragm. The technical scheme is as follows: dissolving modified polyimide in N-methyl pyrrolidone to prepare a modified polyimide spinning solution with the mass fraction of 20-25%, and storing at 2-3 ℃; spinning under the conditions that the spinning voltage is-4-22 kV, the solution propelling speed is 10mL/h, and the room temperature and the humidity are lower than 50% to obtain a prefabricated fiber membrane; placing the nanofiber membrane in a high-temperature oven, heating to 300 ℃ at the speed of 3.5 ℃/min, keeping for 8-10min, stopping heating after the reaction is finished, and taking out the nanofiber membrane after the temperature is reduced to room temperature to obtain the fiber membrane; and (3) placing the fiber membrane on a coating machine, coating boehmite ceramic slurry on the surface of the fiber membrane by using a 4-micron concave roller, baking for 3-4min at 100 ℃, coating boehmite ceramic slurry on the back of the fiber membrane by adopting the same method, and baking to obtain the lithium battery diaphragm.

Under the current trend, the diaphragm should tend to be light and thin on the premise of keeping good safety performance and bearing high-rate and high-function charging and discharging, and the diaphragm is thicker through a coating method, and the diaphragm of a general battery has small specific surface area, small porosity, low liquid absorption and retention rate, difficult thickness control and the like, so that a series of problems to be improved exist. Therefore, how to develop a thin and excellent film has important value for improving the performance of the lithium battery.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a boehmite modified electrospun membrane as well as a preparation method and application thereof, which are used for solving the problems of thicker membrane thickness, small specific surface area and low fusing temperature of the existing separator and preventing the problem of thermal runaway in a battery under the condition of overcharge or abuse of the battery.

In order to achieve the purpose, the invention adopts the following technical scheme:

in a first aspect, the present invention provides a boehmite-modified electrospun membrane, said boehmite-modified electrospun membrane being: and (3) attaching the spinning solution containing boehmite and the first high polymer to the surface of the second high polymer through electrostatic spinning to obtain the boehmite modified electrospun membrane.

According to the boehmite modified electrospun membrane provided by the invention, the spinning solution doped with boehmite and a high molecular polymer is subjected to electrostatic spinning and is deposited on the surface of the high molecular polymer, so that the mechanical property, the thermal stability and the pore size stability of a fiber membrane used alone are improved, and a heat-resistant and high-temperature-resistant porous electrospun membrane is formed.

The attachment mode of the invention can be deposition direct attachment, crosslinking by using a crosslinking agent, or other methods such as physical action, chemical action and the like, so that the spinning solution is formed into a film to be attached to the surface of the high molecular polymer.

The attachment may be single-sided or double-sided.

Preferably, the first high molecular polymer comprises any one or a combination of at least two of polyethersulfone, polysulfone or polyimide. The first polymer used in the present invention is not limited to the above, and may be a heat-resistant polymer generally used for spinning.

Preferably, the concentration of the first high molecular polymer in the spinning solution is 5% to 50%, for example, 5%, 10%, 15%, 20%, 23%, 28%, 30%, 35%, 36%, 41%, 43%, 45%, 5%, or the like, preferably 28%.

Preferably, the concentration of boehmite in the spinning solution is 1% to 90%, for example, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or 90%, and preferably 10% to 50%.

Preferably, the spinning dope comprises any one of or a combination of at least two of dimethylacetamide (DMAc), Dimethylformamide (DMF), Dimethylsulfoxide (DMSO), acetone, or chloroform. In the present invention, dimethylformamide is preferably used as a solvent for the spinning solution.

Preferably, the second high molecular polymer comprises any one of polyethylene, polyvinyl chloride, polypropylene, polystyrene or ABS plastic or a combination of at least two of the above.

Preferably, the second high molecular polymer is polyethylene.

In the present invention, the second high molecular polymer preferably uses polyethylene; further, the polyethylene may be a polyethylene lithium ion separator membrane.

Preferably, the second high molecular polymer is treated with potassium dichromate.

In the present invention, generally speaking, electrostatic spinning has poor adhesion to the polymer surface, and etching the polymer surface with potassium dichromate can increase the surface roughness thereof to enhance the bonding force with electrostatic spinning.

Preferably, the method of using potassium dichromate treatment is: and immersing the second high molecular polymer into a mixed solution of potassium dichromate, water and sulfuric acid with the mass ratio of 7:12:150, and taking out and drying to obtain the second high molecular polymer.

Preferably, the electrospun membrane obtained after the electrostatic spinning is attached to the surface of the second high molecular polymer further comprises a step of immersing the electrospun membrane into a boehmite suspension and drying the immersed electrospun membrane, so as to obtain the boehmite-modified electrospun membrane.

In the invention, boehmite is doped in the spinning solution for spinning, and then the spinning solution is compounded with boehmite again through surface impregnation, so that the heat resistance of the electrospun membrane can be further improved.

Preferably, the boehmite suspension has a concentration of 1% to 10%, and may be, for example, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or the like.

Preferably, the immersion time is 2-5 min, for example, 2min, 3min, 4min, 5min, etc.

Preferably, the drying temperature is 50-80 ℃, for example, 50 ℃, 55 ℃, 60 ℃, 65 ℃, 70 ℃, 75 ℃, 80 ℃ and the like.

In a second aspect, the present invention provides a method for preparing a boehmite-modified electrospun membrane according to the first aspect, comprising the steps of:

(1) dissolving boehmite and a first high molecular polymer in a solvent, heating and stirring to prepare a spinning solution;

(2) dipping a second high molecular polymer by using a mixed solution of potassium dichromate, water and sulfuric acid with a mass ratio of 7:12:150, then drying in vacuum, wrapping on a roller aluminum foil, setting electrostatic spinning parameters, attaching the spinning solution obtained in the step (1) to the surface of the second high molecular polymer through electrostatic spinning, and optionally immersing the obtained electro-spinning membrane into a boehmite suspension for drying to obtain the boehmite modified electro-spinning membrane.

In the present invention, boehmite is prepared by the following method: dissolving aluminum isopropoxide into isopropanol to obtain a solution A; dissolving ammonia water or glacial acetic acid in quantitative deionized water to obtain a solution B, and slowly dripping the solution B into the solution A; continuously stirring after the dropwise adding is finished, heating for reaction, and adding the balance of deionized water into the reaction solution; adding the reaction liquid into a reaction kettle, crystallizing for a period of time, and cooling to room temperature; washing the obtained product with deionized water and ethanol, and drying to obtain boehmite powder.

In the present invention, the second high molecular polymer is impregnated with potassium dichromate and then wrapped on a rotating drum, the diameter of which is generally 10cm, and the rotating speed is set to 300 revolutions per minute.

Preferably, the heating temperature in step (1) is 80 to 95 ℃, for example, 80 ℃, 85 ℃, 90 ℃, 95 ℃ and the like.

Preferably, the stirring time in step (1) is 1 to 3 days, for example, 1 day, 2 days, 3 days, etc.

Preferably, the parameters of the electrostatic spinning in the step (2) are as follows: the distance from the spinneret plate to the collector is set to be 10.5cm, the applied voltage is 12kV, the ambient temperature is 25-27 ℃, and the relative humidity of the environment is 38% -42%.

Preferably, the flow rate of the dope in the step (2) is 20 to 80mL/min, and may be, for example, 20mL/min, 30mL/min, 40mL/min, 50mL/min, 60mL/min, 70mL/min, or 80 mL/min.

In a third aspect, the present invention provides a boehmite-modified electrospun membrane according to the first aspect for use in a battery.

In the invention, the boehmite modified electrospun membrane can be applied to batteries, and also can be applied to the fields of electronic products, vehicles, aerospace and the like, and the application scene is wide.

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

according to the boehmite modified electrospun membrane provided by the invention, the spinning solution doped with boehmite and a high molecular polymer is subjected to electrostatic spinning and is deposited on the surface of the high molecular polymer, so that the mechanical property, the thermal stability and the pore size stability of a fiber membrane used alone are improved, and the heat-resistant and high-temperature-resistant porous electrospun membrane is formed.

Drawings

Figure 1 is a particle size distribution plot of boehmite suspensions prepared according to the invention.

Detailed Description

In order to better illustrate the present invention and facilitate the understanding of the technical solutions, the present invention is further described in detail below.

In the following examples of the invention, boehmite was prepared by the following method: dissolving aluminum isopropoxide into isopropanol to obtain a solution A; dissolving ammonia water or glacial acetic acid in quantitative deionized water to obtain a solution B, and slowly dripping the solution B into the solution A; continuously stirring after the dropwise adding is finished, heating for reaction, and adding the balance of deionized water into the reaction solution; adding the reaction liquid into a reaction kettle, crystallizing for a period of time, and cooling to room temperature; washing the obtained product with deionized water and ethanol, and drying to obtain boehmite powder. Formulation of boehmite suspension: the commercially available 11% boehmite suspension was directly diluted to the desired concentration. The boehmite suspension was subjected to particle size distribution testing and the results are shown in figure 1: the results show that the boehmite has a predominant Z-average dimension (length) of 113.7 nanometers; the peak is 116.2 + -24.5 nm, which can be considered as the length of boehmite, and a small amount of boehmite is 30.7 + -3.7 nm in size.

Example 1

This example prepared a boehmite-modified electrospun membrane by the following procedure

(1) Dissolving polyether sulfone in DMF, doping boehmite particles, and stirring at 90 ℃ for 2 days to prepare a spinning solution with the concentration of 28%;

(2) immersing a polyethylene base material into ethanol, washing by using deionized water to remove surface pollutants, adding the polyethylene base material into a mixed solution of potassium dichromate, water and sulfuric acid with a mass ratio of 7:12:150, soaking, then vacuum-drying, wrapping on a roller aluminum foil with the diameter of 10cm, setting electrostatic spinning parameters at the roller rotating speed of 300 r/min, setting the distance from a spinneret plate to a collector electrode to be 10.5cm, applying an external voltage of 12kV, the environmental temperature of 26 ℃, the environmental relative humidity of 40% and the spinning flow of 40mL/min, attaching the spinning solution to the surface of polyethylene through electrostatic spinning to obtain an electrostatic spinning film, immersing the electrostatic spinning film into 5% boehmite suspension for 3min, and then placing the electrostatic spinning film in a 60 ℃ oven to dry for 10min to obtain the electrostatic spinning film.

Example 2

This example prepared a boehmite-modified electrospun membrane by the following procedure

(1) Dissolving polysulfone in DMF, doping boehmite particles, and stirring at 90 ℃ for 2 days to prepare spinning solution with the concentration of 45%;

(2) soaking a polyvinyl chloride base material in ethanol, washing with deionized water to remove surface pollutants, adding the polyvinyl chloride base material into a mixed solution of potassium dichromate, water and sulfuric acid with a mass ratio of 7:12:150, soaking, then carrying out vacuum drying, wrapping the polyvinyl chloride base material on a roller aluminum foil with the diameter of 10cm at the rotating speed of 300 rpm, setting electrostatic spinning parameters, setting the distance from a spinneret plate to a collector electrode to be 10.5cm, applying an external voltage of 12kV, keeping the environment temperature at 26 ℃, keeping the environment relative humidity at 41%, enabling the spinning flow to be 40mL/min, attaching a spinning solution to the surface of polyvinyl chloride through electrostatic spinning to obtain an electro-spinning film, soaking the electro-spinning film into a 10% boehmite suspension for 1min, and then placing the electro-spinning film in a 70 ℃ oven to dry for 8min to obtain the electro-spinning film.

Example 3

This example prepared a boehmite-modified electrospun membrane by the following procedure

(1) Dissolving polyimide in DMF, doping boehmite particles, and stirring at 90 ℃ for 2 days to prepare a spinning solution with the concentration of 20%;

(2) immersing a polypropylene substrate into ethanol, washing by using deionized water to remove surface pollutants, adding the solution into a mixed solution of potassium dichromate, water and sulfuric acid with a mass ratio of 7:12:150, soaking, then vacuum-drying, wrapping on a roller aluminum foil with the diameter of 10cm, setting electrostatic spinning parameters with the rotating speed of 300 r/min, setting the distance from a spinneret plate to a collector electrode to be 10.5cm, applying an external voltage of 12kV, the ambient temperature of 26 ℃, the relative humidity of the environment of 38% and the spinning flow of 40mL/min, attaching the spinning solution to the surface of polypropylene through electrostatic spinning to obtain an electro-spinning film, immersing the electro-spinning film into 0.5% boehmite suspension for 5min, and then placing the electro-spinning film in a 50 ℃ oven to dry for 10min to obtain the electro-spinning film.

Example 4

This example prepared a boehmite-modified electrospun membrane by the following procedure

(1) Dissolving polyether sulfone in DMF, doping boehmite particles, and stirring at 90 ℃ for 2 days to prepare a spinning solution with the concentration of 28%;

(2) immersing a polyethylene substrate into ethanol, washing with deionized water to remove surface pollutants, then drying in vacuum, wrapping on a roller aluminum foil with the diameter of 10cm, setting the rotation speed of a roller at 300 revolutions per minute, setting electrostatic spinning parameters, setting the distance from a spinneret plate to a collector electrode at 10.5cm, applying voltage at 12kV, the ambient temperature at 26 ℃, the ambient relative humidity at 41%, and the spinning flow at 40mL/min, attaching a spinning solution to the surface of polyethylene through electrostatic spinning to obtain an electro-spinning film, immersing the electro-spinning film into 5% boehmite suspension for 3min, and then drying the electro-spinning film in a 60 ℃ oven for 10min to obtain the boehmite modified electro-spinning film.

Example 5

This example prepared a boehmite-modified electrospun membrane by the following procedure

(1) Dissolving polyether sulfone in DMF, doping boehmite particles, and stirring at 90 ℃ for 2 days to prepare a spinning solution with the concentration of 28%;

(2) soaking a polyethylene base material in ethanol, washing with deionized water to remove surface pollutants, adding the polyethylene base material into a mixed solution of potassium dichromate, water and sulfuric acid with a mass ratio of 7:12:150, soaking, then drying in vacuum, wrapping on a roller aluminum foil with the diameter of 10cm, setting electrostatic spinning parameters at the roller rotating speed of 300 r/min, setting the distance from a spinneret plate to a collector electrode to be 10.5cm, applying voltage to be 12kV, keeping the environment temperature at 26 ℃, keeping the environment relative humidity at 40%, setting the spinning flow at 40mL/min, and attaching a spinning solution to the polyethylene surface through electrostatic spinning to obtain the boehmite modified electrospun membrane.

Example 6

This example differs from example 1 in that the boehmite suspension concentration in this example was 8%.

Example 7

This example differs from example 1 in that the boehmite suspension concentration in this example was 2%.

Comparative example 1

This example prepared a boehmite-modified electrospun membrane by the following procedure

(1) Dissolving polyether sulfone in DMF, and stirring at 90 deg.C for 2 days to obtain 28% spinning solution;

(2) immersing a polyethylene base material into ethanol, washing by using deionized water to remove surface pollutants, adding the polyethylene base material into a mixed solution of potassium dichromate, water and sulfuric acid with a mass ratio of 7:12:150, soaking, then vacuum-drying, wrapping on a roller aluminum foil with the diameter of 10cm, setting electrostatic spinning parameters at the roller rotating speed of 300 r/min, setting the distance from a spinneret plate to a collector electrode to be 10.5cm, applying an external voltage of 12kV, the environmental temperature of 26 ℃, the environmental relative humidity of 40% and the spinning flow of 40mL/min, attaching the spinning solution to the surface of polyethylene through electrostatic spinning to obtain an electrostatic spinning film, immersing the electrostatic spinning film into 5% boehmite suspension for 3min, and then placing the electrostatic spinning film in a 60 ℃ oven to dry for 10min to obtain the electrostatic spinning film.

Comparative example 2

This example produced an electrospun membrane by the following procedure

(1) Dissolving polyether sulfone in DMF, and stirring at 90 deg.C for 2 days to obtain 28% spinning solution;

(2) soaking a polyethylene base material in ethanol, washing with deionized water to remove surface pollutants, adding the polyethylene base material into a mixed solution of potassium dichromate, water and sulfuric acid with a mass ratio of 7:12:150, soaking, then drying in vacuum, wrapping on a roller aluminum foil with the diameter of 10cm, setting electrostatic spinning parameters at the roller rotating speed of 300 r/min, setting the distance from a spinneret plate to a collector electrode to be 10.5cm, applying voltage to be 12kV, keeping the environment temperature at 26 ℃, keeping the environment relative humidity at 40%, setting the spinning flow at 40mL/min, and attaching a spinning solution to the polyethylene surface through electrostatic spinning to obtain an electro-spinning film.

The fusing temperature tests of the electrospun membranes prepared in the examples 1-7 and the comparative examples 1-2 show that the fusing temperature of the examples 1-3 is high, the fusing temperature of the examples 4-7 is low, and the bonding force between the electrostatic spinning and the base material is poor and the stability is reduced because the potassium dichromate leaching is lacked in the example 4; in example 5, a subsequent boehmite impregnation step is omitted, so that the heat resistance of the prepared boehmite modified electrospun membrane is reduced; the boehmite modified electrospun films of examples 6-7 had higher and lower concentrations, respectively, and the fusing temperature was also reduced. In comparative example 1, boehmite is absent from the spinning solution and the electrospun membrane has poor performance, so the fusing temperature is low, while in comparative example 2, boehmite is completely absent for modification, and the fusing temperature is lowest.

From the above results, it can be seen that the fusing temperature of the electrospun membrane prepared by electrospinning is increased by modifying boehmite.

The boehmite modified electrospun membrane and the preparation method and application thereof are illustrated by the examples, but the invention is not limited to the detailed process equipment and process flow, i.e. the invention is not limited to the detailed process equipment and process flow. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.